Implementation of a pulse widthmodulated driving unit for the artificial ear

Item Type text; Thesis-Reproduction (electronic)

Authors Magner, Arthur Leon, 1934-

Publisher The University of Arizona.

Rights Copyright © is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.

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Link to Item http://hdl.handle.net/10150/347757

IMPLEMENTATION OF A PULSE WIDTH MODULATED DRIVING UNIT FOR THE

ARTIFICIAL EAR

byArthur Leon Magner

A Thesis Submitted to the.Faculty of theDEPARTMENT OF ELECTRICAL ENGINEERING

In Partial Fulfillment of the Requirements For the Degree ofMASTER OF SCIENCE

- In the Graduate CollegeTHE UNIVERSITY OF ARIZONA

1971

STATEMENT BY AUTHOR

This thesis has been submitted in. partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University. Library to be made available to borrowers under rules of the Library,

Brief quotations from this thesis are allowable without special permission, provided that accurate acknow­ledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when-in his judgment the proposed use of the material is in the interests of scholarship,. In all other instances, however, permission must be obtained from the' author.

SIGNED

■ APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below;

. . . - - , 0*1FREDRICK m t L .' ' '"//DateAssociate Professor of (/Electrical Engineering

ACKNOWLEDGMENT It is a pleasure to acknowledge the outstanding

guidance which Dr 0 Fredrick J „ Hill provided during the preparation of this paper, I am especially indebted to himfor his inquisitive nature and presentation of new ideasduring ,the course of investigation,, The author would also like to express his appreciation to his wife, Judy, for herpersonal sacrifice, .

j

lii

TABLE-OF CONTENTS

o o o o o oo o o o o o

LIST OF ILLUSTRATIONS , . 0 . ". . . . • . . = . ,LIST OF TABLES O O O O O O O G O O O O O O O O O O

ABSTRACT o © © o o o © © © ' & © © © o o © o © o o ©INTRODUCT ION o o o o o o . o o o o oo o o o o o o o

3. T 1C X3-I ES-I* o o 0 6 O O O O 0 0 0 0 0 O 0 0Major Components © © © © o © © © © © © © ©

; Series Filter Network■ Driving Units © © © ©

Tactile Stimulators © © © © ©,© © © © ©■ 0 peration © © © © © © © © © © © © © © © © ©

' ; New Driving Unit © © © © © © © © © © © © © © ©INTERFACE TESTING © © © © © © © © © © © © © © © © ©

Int e r f ac e l © © © © © © © © © © ©„ © © © ©Interface II © © © © © © © © © © © © © ©

Optimum Operating Region © © © © © ©Test. Number 1 © © © ©Test Number 2 ©Test Number 3Test* Number 4Conclusions for Optimum Operating

Region Testing Tactile Stimulator Operation

Test Number 1 © © © © © © © © © © © © ©- Test Number 2 © © © © © © © © © © © © ©

Test Number 3 g © © © © © © © © © © © ©Test Number 4 © © © © © © © © © © © © ©Conclusions for Stimulator Operation© ©

Driving Unit Input/Output DesignFarameters © © © © © © © © © © © © © © ©

Input Parameters - Interface I © © © ©Output Parameters - Interface II © © ©Design Parameter Summary © © © © © © ©

0 0 0 0 0 0 0 0 0

O 0

o o

o o

o oO O 0 < 0 o

o o o o o o o o o o o o

0 0 0 0 0 0 0 0

DRIVER DESIGN, CONSTRUCTION AND TESTFull Wave Rectifier . © , © © © , Low Pass Filter © © © © © © © © ,

iv

Pageviix

12446910

14141717202223273333

I37383940414243-4446

!

V

■ TABLE OF CONTENTS— -Continued.

. • PageSiumner-Gomparator 0 <> o 0 e o o o => » » o « o. o 5,2Nonlinear Function Generator 0 0 0 o o » o o o 57

Design Criteria o e o o o o o o o o o o o o 57Design-' o e O G o o o o o o o o o o o o o o 5 9Construction and Test o o o o o o o o o o o 6l

Design Summary o o o o o o o o o o o o o o o o 6 2ARTIFICIAL EAR SCOPE . , . » . « , » „ . . . . . 65

Other Tactile Stimulation Devices 6 0 . 0 o','. 65Read m g A id . . . . . . . . . . . . . . . . 65Seeing-Eye Backpack , . „ . . « . « . . 0 66

Future Artificial Ear Operation o . „ b . - . . .-6?Equipment Hook Up . „ ■ „ > 0 . 0 . . . 68

, Testing . o o o o o e o o o o b, o o o o o o 68, Poor Recognition Capability „ „ „ 0 0 68

; Training Program' . . , . . » . . « . . 72Recommended Improvements ^ , , ., . . . « « 73

v V; Automatic Gain Control „ , „ „ . > , , 73Arm Rest . . . . . ». ■ . • . * . .. . 73N o F eel . . . . . . . . . . . . . . . . 7

Conclusion . . . . . . . . . .. . . . . . . . . 7 *APPENDIX A: MATHEMATICAL ANALYSIS OF STIMULATOR

OPERATION . o o . = . o o 0 . o A o 75Spring Constant . . , • . . i , . . , « • . 75Force on the Magnet « . . .' « = » . . . o . . o 75Analysis of Vibratory Downward Motion . . o '. . ?6

Vibratory Motion (Force.Applied) . . . . . v 77Vibratory Differential Equation 0 ■ » = « 77Solve for Resonant Frequency 0 o . , . 78Solve for (F/k) . o o o o o o o o o o o 7 9Solve for Plunger Displacement . . o o 79

Vibratory Motion (Force Removed) o = » . o 81Vibratory Differential Equation 0 o o 0 81Plunger Velocity o o o o o o o o o o o 82

, Total Plunger Displacement „ 0 o . . . 83' Vibratory Downward Motion Summary » » » « » 85

Analysis of Vibratory Upward Movement . « . o o 85COnClUSlOnS O O O O O O O O O O O O O O O O O O 88

LIST OF REFERENCES - o o . . o . . 91

LIST OF ILLUSTRATIONS

F igure Pagelo Artificial Ear Block Diagram „ 0 » . 0 0 o o o 0 32 0 Series Filter Network and Associated

Frequencxes o o o e o o o o 0 0 0 0 0 0 0 0 0 5.3« Tactile Stimulators 0 0 o' * » 0 0 0 . 0 0 0 0 0 » 7A 0 Magnetic Stimulator Height Adjustment 0 0 0 0 0 8

5» Driving Unit Interfaces 0 » 0 0 0 0 0 0 = 0. 0 o 1560 Series Filter Output Voltage versus Input

Frequency for 2, A, 6 , 8 and 10 Volt Inputs„ „ 167o Stimulator Test Circuit with Pulse

Generator (G) 0 0 o 0 0 0 0 0 0 0 o o o o 0 0 1980 Stimulator Test Circuit with Pulse

Generator (G) and DC Bias (V) 0 0 o 0 0 0 0 0 1990 Maximum Feel Curves for Finger 0 0 0 0 0 0 0 0 o 21

100 Test Number 2 Maximum and Minimum Feel Curvesfor the Arm with Fixed POD-AOHz„ 0V Bias and Stimulator Height 1/16 Inch 0 0 0 0 0 0 0 0 0 23

11 o Family of Maximum Feel Curves for the Arm withVarious Bias Voltages„ POD-AOHz» and Stimulator Height 1/16 Inch 0 0 0 0 0. » » 0 0 25

120 Family of Minimum Feel Curves for the Arm withVarious Bias Voltages, POD-AOHz, and Stimulator Height 1 /1 6 Inch 0 « « = = o .0 » o 26

13o Stimulation Control Curve 0 0 e » 0 0 0 0 0 0 e 30lA„ Just Noticeable Difference Test Circuit 0 . » » 3A15o Stimulation Recognition Errors for Linear Input

Just Noticeable Difference Pulse Increments* • 37* ■ .

vi

viiLIST OF ILLUSTRATIONS--Continued

Figure Page.160 Six Just Noticeable Differences , , , , 0 0 3917. Transfer of Feel Nonlinearity , , , , , 0 0 401 8 , Driving Unit Design Block Diagram , , , 0 0 0 0 4519. Full Wave Rectifier Circuit Diagram , , 0 0 0 0 .462 0 , Low Pass Filter Circuit Diagram , , 0 0 0 0 4?2 1 , Actual Filter Output for 5 Volt Input , 0 0 0 0 492 2 , Triangle Wave Generator Circuit Diagram 0 0 5123 = Summer-Comparator Circuit Diagram , , , 0 0 0 5224, Summer-Comparator Design Characteristics 0 0 0 0 5325 = Summer-Comparator Inputs and Their Summation

for an Adjusted Modulating Signal of Zero Volts 0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 54

2 6 . Summer-Comparator Input Summation for a Negative Adjusted Modulating Signal (E^) 0 0 0 55

27 = Output Voltage versus Input Voltage for the Nonlinear Function Generator , 0 0 0 0 0 0 0 0 58

28, Function Generator Circuit Diagram , , , 0 0 5929 = Pulse Modulated Driving Unit Circuit Diagram 0 0 6330 0 Photograph of the Prototype Driving Unit 0 0 0 » 64310 Artificial Ear Equipment Hook Up , , , , 0 0 * 0 6932, Driving Unit Layout Diagram , , , 0 = = 0 0 0 0 70A~10 Solenoid Current for the Optimum Operating .

Region , 0 0 = 0 0 0 ,,■ 0 0, 0 0 0 0 , 0 0 , 0 0 77A—2 , Free Body Diagram with Force Applied , , 0 0 0 0 78A—3 0 Free Body Diagram with Force Removed , , 0 0 d 0 81

Figure A“^ o

A-5oA-6 0

viiiLIST OF ILLUSTMT IONS--Continued

PageNonlinear Plunger Displacement Approximated, by

Two Line Segments o e o p e o o o o o o . o o o 86

Diagram of Plunger Position « o o s . . 0 0 0 0 0 0 87

Energy Transferred to the Arm versus PlungerDxsplacement © 0 © © © © © © © © © © © © © © © 89

LIST OF TABLES

Table1o Maximum Stimulator Control and Pulse Amplitude

for Various Bias Voltages when Stimulatingthe Arm o © o o » o o o e e o o o o o o o o o

20 Test Number k Data O O Q O Q Q Q O . C O O O O O Q

.3© Test Number 4 Recognition Errors betweenAdjacent Just Noticeable Differences for 100 Samples © © © © © © © © © © © © © © © © © © ©

4© Just Noticeable Difference Driving Unit.Input/Output Design Parameters © © © © © © © ©

5© Rectifier Input 400Hz and Filter OutputVoltages, for Connected System © © © © © © © ©

6© Summer-Comparator Computed Just NoticeableDifference Design Input/Outputs © © © © © © ©

A-l„ Computation of Forced Displacement (y^)A-2© Computation of Velocity (vQ) © © © © © © © © © ,A-3© Plunger Kinetic Energy and Maximum Displacements

. for Just Noticeable Differences © © © © © © ©A-4© Just Noticeable Difference Pulse Widths and

Maximum Displacements for Equal Energy .. Increments © o © © © © © © © © © © © © © © © ©

ix

Page

2729

38

42

50

*8082

88

90

ABSTRACT

The Artificial Ear is an electromechanical device designed to transfer audio information to a deaf person via tactile sensationso The device contains three major com­ponents as followsi • series filter network, driving unit, and the tactile stimulator, ' . . ,

This paper reports on the design and prototype con­struction of a pulse width modulated driving unit. The unit is interfaced at the input by the series filter network and at the output by the tactile stimulators.

The design of the driving unit was made only> after thorough testing of the interfaces„ Design input parameters were found by testing the filter outputs and the output parameters by testing the stimulator inputs. All testing was routine with one exception, A nonlinearity was deter­mined between the output pulse width and the stimulator, transfer of feel. This nonlinearity was investigated and taken into account in the design,

The design, construction and test of the driving. . unit was conducted using a modular operational amplifier approach. The composite modules are as follows: full waverectifier, low pass filter, triangle wave generator, function

x

generator and summer-cqmparator„ All modules were investi­gated and tested at the conclusion "of the driving unit implementation.

CHAPTER 1 INTRODUCTION

In the quiet world of the deaf, the only communi­cating link with the auditory world has been through lip reading or sign language, However, since the turn of the century, scientists and engineers have shown more interest in the possibility of a substitute auditory process for the deafo

One of these substitute processes is presently be­ing investigated in prototype form by the University ofZ -

Arizona Electrical Engineering Department, The project is under the direction of Dr, Fredrick J, Hill, Professor of Electrical Engineering.

• Artificial EarDr. Hill's substitute hearing device is coined the

"ARTEAR", an acronym for artificial ear, The theory that normal hearing can be replaced by another sense function, namely the sense of touch, was the guiding light in the development of the ARTEAR, The design assumes that the individual is totally deaf and therefore completely dis­regards any attempt at improving the use of any normal hearing sense organs„

1

2The ARTEAR operation can initially be explained by

giving a general description of the device0 The ARTEAR is an electro-mechanical unit, which receives audio inputs via a microphoneo The unit transforms these signals into elec­tronic audio information which is converted to mechanical energy and transmitted to the nervous system by vibratory tactile stimulation of the skin.

Major ComponentsFurther explanation of the ARTEAR operation requires

that the device be broken down into three major components which arei (1) The series filter network, (2) the driving units and (3) the tactile stimulators (Fig* 1 ) 0

The series filter network receives the microphone input and outputs the received audio as eight separate frequency bandso Each of these eight bands is then individually fed into its own driving unit which rectifies and filters the band of frequencies to a d 6 C o level. Each of the eight driving units then outputs a fixed frequency pulse whose width is dependent upon the filtered d 0c0 level for its respective band of frequencies0 The audio information, or variable pulse width for each driving unit is now individu­ally fed to one of eight tactile stimulators connected to the human skin. The stimulator then transmits the informa­tion to the nervous system by using the variable pulse width to control the vibratory amplitude of tactile stimulation.

The received tactile audio, in the form of eight individual stimulations, is then sent through the nervous system to the brain for analysis. A brief description of each major component will aid in understanding the ARTEAR operation.

MICROPHONEAUDIO INPUT

SERIES FILTER NETWORKBAND BAND BAND BAND BAND BAND BAND BAND#1 #2 #3 #4 #5 #6 #7 #8

Di

UV r ' r >w \/ V >

DKu

R N R NI I I IV T ADDITIONAL DRIVING UNITS V TI IN # • N #G 1 G 8

> / #1

---V- ...#2

___V#3 #4

N £___#5 #6 #7

\/#8

EIGHT TACTILE STIMULATORS

Fig. 1 Artificial Ear Block Diagram

4Series Filter Network, The series filter network

was designed by Raymond E. Wilsey under the direction of Lorin P, McRae„ An unpublished description of the design by Wilsey (196?)„ is titled “Series Active Filter for an Artificial Ear,"

The filter network consists of a series set of eight band pass filters which separate the input audio into compo­nent bands of frequencies, The series filter network (Pig. 2) shows the low (f^), center (fc) and high (f^) frequencies for the eight filtered bands. The frequencies above 4200 Hz and below 100 Hz are not passed by the filters since they contain information unneccessary for tactile recognition of audio.

Driving Units. The ARTEAR has eight identical driving units. Each driving unit takes that part of the audio signal within a particular band and uses it to con­trol a single stimulator. To provide stimulator control, the driving unit first accepts the filtered frequencies from its respective band pass as its input. The band of frequencies is then half wave rectified and filtered with a low pass filter to provide a d.c. reference level which follows the amplitude of the input frequencies. This ref­erence level is then used to control the pulse width of a constant 80 Hz pulse output. The output pulse width is

SERIES FILTER NETWORK

AUDIOBAND "band BAND BAND

#4BAND#5

BAND#6

BAND#7

BAND#8INPUT ' n #2 #3

!BAND

1

iPASS

1

iOUTPUT

1

IFREQUENCIES

I(Hz)I

\/ 1 1 i I I I >/LOW (f1) 2640 1650 1040 650 40? 255 160 100CENTER (fc) 3330 2090 1310 820 513 322 202 126

HIGH (fh) 4200 2640 1650 1040 650 407 255 160

Fig. 2 Series Filter Network and Associated Frequencies

designed to increase as the respective d„c„ level is in­creased, The tactile driving units were designed "by R, McClellan with no supporting documentation available.

Tactile Stimulators, The tactile stimulators (Figo 3) were built by Mr, Del Jackson at the University of Arizona Electrical Engineering shop. Each individual stimulator consists of a coil, of wire wound around a plastic cylinder with a magnetic plunger that is free to move inside the cylinder. The magnetic plunger rests on a spring and will vibrate when excited by the driving unit. This elec­tromechanical device provides tactile stimulation of the skin via a dulled nail affixed to the top of the plunger.The height of the plunger above the plastic reference plane can be adjusted (Fig, 4), The plunger height is determined by the position of a plastic rod inserted into the bottom of the plastic cylinder and held by a lock screw.

The tactile stimulators were designed to be placed on a table with the human test subject seated in a chair next to the table, The subject then rests his forearm on the plastic reference plane so that all eight stimulators have contact with the arm. The tactile stimulation or amplitude of feel transfered to the nervous system by the stimulators is then dependent upon the pulse width of the constant 80 Hz pulse driving unit output„

MAGNETICSTIMULATOR

PLASTICREFERENCEPLANE

APPROX

PULSE WIDTH MODULATED

SOLENOIDi

INPUTSFig. 3 Tactile Stimulators

B

PLASTICREFERENCEPLANE

MAGNETIC STIMULATOR

SPRING

o ADJUSTABLEPLASTICROD

LOCKSCREW

IIUTTT

Fig. 4 Magnetic Stimulator Height Adjustment

During the time period the pulse is being applied to the solenoid, the magnetic plunger is drawn into the cylin­der and compressed against the spring. When the pulse is removed, the plunger moves up the cylinder, forced by the compressed spring, and strikes the subject's arm. The amplitude of tactile stimulation transfered by the plunger is dependent upon how much the spring is compressed by the applied driving unit pulse. Since the pulse of the driving

’ 9unit has a constant amplitude, the amount of spring compres­sion, or tactile stimulation,.is totally dependent upon the pulse width.

OperationThe ARTEAR can now be described as a device which

continuously transmits received audio to an individual by varying the amplitude of eight simultanious tactile stimu­lations o The amplitude of each stimulation being dependent upon the continually varying filtered dc level of the re­spective frequency band sensed, .

When the ARTEAR is operating, the tactile stimula­tion relating to the audio input will form a continuous series of sensory patterns which the individual must, recog­nize, The ability to recognize these sensory patterns requires a proficiency which only a highly motivated, well trained individual can obtain. The necessary proficiency level is difficult to obtain during ARTEAR testing. However operationally, one can appreciate the fact that a deaf person would gladly consider the proficiency achievement as a lifetime project,

' i -Preliminary investigation of tactile recognition of speech utilizing the ARTEAR was conducted by F, Taylor Scanlon at the University of Arizona in early 1969= .The. investigation consisted of experiments and tests of the ARTEAR with two types of inputs, The first was artificial

10sounds synthesized in the PDP-9 digital computer and the second was true speech fed in by a microphone 6.

One set of criticisms emanating from the ARTEAR testing was directed toward the driving unit,component of the existing hardware.. The deficiencies determined, were as followss

(1) Audio information was lost when input voltages were low due to the diode offset voltage during rectifica­tion o

(2) The driving unit frequency output of 80 Hz was questionable0

(3) The amplitude of the individual driving unit output pulses could not be manually controlled to offset variable skin sensitivity for different regions of the arm0

Upon analyzing the driving unit deficiencies re-.- ported by Mr. Scanlon, Dr. Hill determined that further

ARTEAR testing should not be continued with the present driving unit hardware. Therefore, he requested that the author, for a thesis project, design and construct a new driving unit for the ARTEAR.

New Driving UnitDr. Hill's request for a new driving unit for the

ARTEAR was accepted. The initial research into designing the driving unit involved a look at the different ways of driving a vibrating solenoid plunger.

11Mechanical vibrations of the plunger may be con­

trolled by driving the solenoid with a sinusoidal input or a pulse inputo Compared to sinusoidal input vibrations, clicks or pulses affect a smaller skin area and provide a more intense stimulation magnitude (Lawrence 19685 p 0 3^)° Therefore, the pulse input for driving the stimulators was accepted for the new design.

Once the pulse input was accepted, the research was . then directed toward investigating different ways of con­trolling the stimulation with a pulse. The methods available to the designer were to vary the pulse frequency, vary the pulse amplitude, vary the pulse width, or any combination of the three, ;

In determining the best method for controlling stimulation, a problem was encountered due to the lack of information relating human skin tactile recognition response to pulsating forces. Generally speaking, the literature on vibrotactile sensing does not speak of the advantages or disadvantages of the different driving methods. Therefore, the method selected for the ARTEAR driving unit will be agreed upon logically rather than statistically.

The. variable frequency method was eliminated for one major reason. Future ARTEAR stimulation appears to be directed toward a piezoelectric bimorph stimulator, and the bimorph invariably responds at or near its natural fre­quency, Therefore, it would be advantagous to design the

12present prototype ARTEAR to operate at a constant frequency„ Then the type of stimulation would be closely related to the piezoelectric bimorph stimulator and the transition training period for the user would be minimized0

The two methods of stimulation control remaining for analysis, pulse amplitude and pulse width, both provide the same type of stimulation intensity. The hardware ad­vantage of one versus the other was not significant, so the decision was made to use the pulse width to control the stimulation. The decision was made based upon the prior success of the present ARTEAR driving unit.

The use of a combination of the various methods was eliminated because it is virtually impossible to recognize the different methods through tactile recognition. It is the author's opinion that for a tactile communications system to be practical, the apparatus must be designed as simply as possible, avoiding any complex coding which would only confuse and"handicap the user, •

The basic operation of the new driving unit will then be very similar to the present driving unit. The differences between the present and proposed.driving unit will be determined by a thorough test of series filter out­puts and tactile stimulator inputs necessary to provide optimum stimulation of the skin. The results of the compo­nent testing will then be used in the design and construction of a single prototype driving unit. Once the prototype

■ ' . ■ v ■ 13driving unit is constructed, it will be connected with the other major components for user testing0 However, the test­ing of the connected ARTEAR will not be a portion of this thesis.

An extensive analysis of the series filter and tac­tile stimulator components has not been accomplished to date; therefore, there is no available data relating to their operation. The present set of stimulator driving units were designed intentionally overlooking this extensive analysis because of time element involved. However, to further test the ARTEAR operation, it is now necessary to perform this analysis and design a driving unit which will provide the best possible interface between the series filter network and the tactile stimulators.

The remaining chapters of this thesis are directed toward reporting s

(1) The analysis of the series filter network and tactile stimulators.

(2) The design and construction of the new ARTEAR pulse width modulated driving unit.

CHAPTER 2

INTERFACE TESTING

To efficiently design the driving unit for the ARTEAR, the designer must be totally familiar with the in­put/output (I/O) requirements at the interfaces„ For the ARTEAR driving unit there exist two interfaces which must be investigated (Fig. 5)° Interface I input requirements for the driving unit were determined by testing the output of the existing series filter network. Interface II output requirements for the driving unit were determined.by testing for the tactile stimulator inputs during optimum stimulator operation. Neither interface had previously been investi­gated. Therefore, no data was available to the designer at the outset of interface testing.

Interface IThe output of the series filter network was tested

to aid in the determination of inputs for the driving unit design. In order to conduct the test, the network was calibrated in accordance with Wilsey (1 9 6 7). Upon comple­tion of the calibration, the network was tested by recording the output voltages for constant input voltages while vary­ing the input frequency between 100 and 4200 Hz. Results

14

15

INTERFACE INTERFACEI II

INOUTINOUT

Fig. 5 Driving Unit Interfaces

of the test are shown graphically (Fig. 6) for constant input voltages of 2, 4, 6, 8 and 10 volts. Input voltages greater than 10 volts caused extreme output distortion.

The average output voltages for the entire frequency spectrum was 1.6, 3.2, 4.8, 6.4, and 8.2 volts respectively for input voltages of 2, 4, 6, 8, and 10 volts. The aver­age filter output voltages will ultimately be used as input design criteria for the driving unit.

VOLTS

(rms)

16

BAND#8

BAND#7

BAND#6

BAND#5

BAND#4

BAND#3

BAND#2

BAND#1

8.2 V, 8.2v (Ave) for 1 0 .Ov,

3.2vn (Ave) /.Ovj.

1 .6v,

FREQUENCY (Hz)

Fig. 6 Series Filter Output Voltage versus Input Frequency for 2, 4, 6 , 8 and 10 Volt Inputs

Interface IIAll efforts were directed toward Interface II once

Interface I testing was completed. Here,, the testing was more extensive because of the many variables characteristic of the tactile stimulator.

The decision was made in Chapter 1 to drive the stimulator with a pulse width modulated signal. Therefore„ an analysis of the stimulator reaction to a periodic pulse was of prime importance.

The pulse inputs which provide optimum stimulation recognition were determined by a two part investigation. First, the stimulator variables were individually, tested to determine their optimum value for tactile stimulation. The variables for investigation were (1 ) the voltage pulse am­plitude, (2 ) the pulse width (PW), (3 ) the pulse frequency„(4) the d,c, bias voltage and (5 ) the height, of the stimu­lators above the plastic reference plane. Secondly, the stimulator was tested for stimulation recognition while, operating with the variables set at their optimum values.

Optimum Operating Region 'Interface II testing was initiated by determining

the stimulator optimum operating region (00R), The 00R is defined as the region for which:

(1) The individual can receive both maximum and . minimum feeling from the tactile stimulator.

18(2) The driving unit can provide maximum control

- ■ ’ ■ ■ z

for the tactile stimulator while changing the feel from maximum to minimum„

(3) The tactile stimulator variables are fixed and the requirements (1) and (2 ) previously defined are provided.

The maximum and minimum feel terms used in the defi­nition of the 00B are difficult to define, but can be easily explained. Maximum feel is obtained for a fixed PW for which an increase in PW will not increase the. amplitude of feel. Minimum feel is obtained for a minimum PW for which any decrease in PW will terminate the sense of feel.

The term maximum control used in the.definition of the OOB is obtained when the maximum PW, for maximum feel, minus the minimum PW, for minimum feel, is a maximum. The greatest possible variance of the PW will allow the designer to drive the stimulator with maximum control.

The testing for the OGB involved investigating each of four Variables individually while, varying the PW, or fifth variable, between maximum and minimum feel. The variable PW was supplied by a pulse generator (Pig. 7, 8 ) and the dc voltage (Big. 8 ) controlled a fixed bias. All tests were conducted with the author as the stimulator user. Upon completion of the testing, all stimulator variables were fixed and the OOB was determined.

1 - STIMULATOR

PULSEGENERATOR

— ^ ---------------

Fig. ? Stimulator Test Circuit with Pulse Generator (G)

1 - STIMULATOR

DC PULSEBIAS GENERATOR

^ — <I>Fig. 8 Stimulator Test Circuit with Pulse Generator (G) and DC Bias (V)

20Test Number 1 * When testing a complete unknown sys­

tem such as the stimulator®s response to a pulse of energy» the test designer must determine a point of departure (POD)for the testing* Test number 1 determined this point in

' 'terms of frequency* The test simply found the frequency- which provided maximum control with the following stimulator variables fixed throughout the tests pulse amplitude - 50V # height of. stimulator above the reference plane - 1 / 1 6 inch, and the dc. bias voltage - zero volts *

The test was then run in eight steps testing fre­quencies from 30 to 100 Hz in 10 Hz .increments * For each step of the test, the PW was recorded for minimum and maximum feel on the pad of the forefinger for (1) a heavy touch on the stimulator and (2 ) a light touch on the stimulator0

The heavy touch was achieved by placing the finger firmly on the reference plane, while the light touch was achieved by holding the finger approximately 1/1.6 inch above the reference plane„ Test data for maximum feel is shown graph­ically (Fig* 9)o The figure does not show a plot of minimum feel as the stimulation was always felt at near zero PW* Therefore, in the determination of maximum control, the minimum feel PW was considered as zero * The data for 30 Hz was hot plotted due to mechanical stimulator distortion which was. transmitted as sporadic feel* . .

21

HEAVY TOUCH

MAXCONTROLtoa

w

MAXCONTROL

LIGHT TOUCH

6040 80 1000 20FREQUENCY - HZ

Fig. 9 Maximum Feel Curves for Finger

The result of the test for the POD was 40 Hz asthis frequency demonstrated the maximum control (approxi­mately 2*5 ms) between minimum and maximum feel for a light touch. The POD was chosen for a light touch since thetactile stimulator is designed to stimulate the forearm,and the forearm is basically an area of light touch on the stimulator. The forearm was not used in this test since

22the sense of feel in the fingertip is greater than the arm and at this point the tester was a layman to the sense of feel.

Test Number 2e Test number 2 was conducted to make an initial investigation into stimulator control and feel at the POD (40 Hz)„ The test was made by measuring maximum and minimum feel PW's for various pulse amplitudes with the following stimulator variables set: dc bias - zero volts, frequency - 4-0 Hz and height of the stimulators - 1/16 inch. The variable pulse width was provided during testing by the circuit shown (Fig. 7)o

Data for the forearm and the pad of the fingertip were recorded even though the investigation was directed toward the arm. The reason for the dual data was two fold. First, testing of the finger aided the tester in objectively determining maximum and minimum feel for the arm. Secondly, the data will aid Dr. Hill in his over-all ARTEAR analysis.

Maximum and minimum feel curves for. the arm are shown graphically (Fig. 10). Data relating to the finger will not be reported in this thesis. The threshold of pain (Fig. 10) is a zone which caused redness of the arm and dis­comfort to the user; and the no stimulator.control zone was attributed to lack of energy to drive the stimulator.

The results of the test indicated that the 6 volt pulse provided maximum stimulator control for the stated

23

co3g

Ia

tyg

16 - ^ THRESHOLD OF PAIN ZONE

MINIMUMFEELARM

14 -

12 - MAXIMUMFEELARM

10 -

MAXIMUM CONTROL______x|ARM (9ms) |

NO STIMULATOR CONTROL ZONE

60 2 8 10 12PULSE WIDTH (ms)

Fig. 10 Test Number 2 Maximum and Minimum Feel Curves for the Arm with Fixed POD - 40. Hz, OV

Bias and Stimulator Height 1/16 Inch

test configuration. However, three of the unknown variables were fixed during testing and need further investigation.

Test Number 3. The objectives of test number 3 were: (1 ) to investigate the effect of dc bias on stimulator feel and control, and (2 ) to select the optimum dc bias for

, \ 24the OORo The test was conducted in a manner similar to testnumber 20 The only difference between the tests was the value assigned to the dc bias voltage„

In order to satisfy the objectives„ the test was conducted five times» each time using a different bias volt­age „ The bias voltages used during testing were 5» 7«5p 10# 12o5 and 15 volts0 The frequency of 40 Hz and height of the stimulator of 1/16 inch were set as in test number 20 Dual data for the finger and arm were again recorded as an aid to the testero , .

The data from test number 3 Is shown graphically asa family of maximum (Pig. 11) and a family of minimum(Fig. 12) feel curves. The curves relating to the data for a bias of zero volts from test number 2 is included in the figures for analysis.

The effects of do.: bias on stimulator feel (Fig. 11. 1 2) will be left for analysis by the reader, since there . Were no noticeable improvements in transfer of feel over the zero volt bias from test number 1. In analyzing the feel curves to select the optimum bias for the OCR. a table of maximum control data is important (Table 1). The maximum control of 11 ms for the 15V bias was considered as a pos­sible solution? however, it was eliminated because the current in the .stimulator coil was extremely high and pro­hibitive . The do bias of zero volts was then selected as

PULSE

AMPLITUDE

(V)

25

1 2 -

- 12.5V1 ERRATIC STIMULATION

7.5V11 -

10 -

ov 10V

NO STIMULATOR CONTROL ZONE

10 12PULSE WIDTH (ms)

Fig. 11 Family of Maximum Feel Curves for the Arm with Various Bias Voltages, POD - 40 Hz

and Stimulator Height 1/16 Inch

PULSE

AMPLITUDE

(V)26

12 _10 and 12.5V

11 -

OV

NO STIMULATOR CONTROL

620 1 3 8PULSE WIDTH (ms)

Fig. 12 Family of Minimum Feel Curves for the Arm with Various Bias Voltages, POD - 40Hz

and Stimulator Height - 1/16 Inch

2?Table 1 Maximum Stimulator Control and Pulse

Amplitude for Various Bias Voltages when- Stimulating the Arm

BIAS ' VOLTAGE

(V)MAXIMUM' CONTROL

1 (ms)PULSE

AMPLITUDE(V)

0 9 65 4.5 67o5 9.5 6

109o5

8

12o5 9.5 6 ,15 | 11,0 6

optimum as all other voltages were rejected since they did not improve the control enough to offset the additional hardware necessary to provide the bias 0

Test Number 4 . When test number k was designed, the optimum dc bias of zero volts had been determined0 The POD of 40 Hz had been selected, but was not definite for the OORo Therefore, four unknown stimulator variables remained to be investigated,, They were the height of the stimulator, the PW, the pulse amplitude and the frequency0

Test number 4 investigated these remaining parame­ters for the arm only0 The departure from the testing of the finger was due primarily to the large difference, finger versus arm, for the remaining stimulation variables0

28However» the testing for the finger was also terminated be­cause the author was totally familiar with the sense of feel. Thereforep the finger was no longer needed for comparison in testing.

The test was organized to determine the variables in three parts as follows s Part 1 determined the optimum fre­quency » Part 2 the optimum height of the stimulator and Part 3 determined both the optimum pulse amplitude and the opti­mum, maximum and minimum PW" s „ . -

. , Part 1 determined the optimum frequency for stimula­tor operation by utilizing the test circuit shown (Fig. 7)» The test was conducted by first fixings the height of the stimulator - 1 / 1 6 inch, dc bias - zero volts, frequency 30 Hz and the PW at maximum (half duty cycle). The pulse amplitude was then adjusted until maximum feeling was., achieved. Upon finding^maximum feel, the pulse amplitude and PW were recorded. The PW was then decreased to the minimum feel position and the PW recorded.

The frequency was then varied in 5 Hz increments up to 55 Hz repeating the foregoing procedure at each increment. All data for Part 1 is recorded (Table 2). "

During the test, stimulator vibrations were monitor-■ -

ed by viewing the stimulator with a stroboscope to insure synchronized vibrations. An oscilloscope was used to moni­tor voltage distortion caused by erratic stimulation.

Table 2 Test Number k Data29

FREQUENCY(Hz)

11.0

10.0

UNGERPLITUDE PLUNGER I MAX PW (V) |VIBRATION ■ (ms)

(cpm)

18?00208002370026.6002990032500

MIN PW (ms)

11.1

MAX • CONTROL

11.76.88.5 8.17.56.1J

Once the test was completed, maximum control of the stimulator was found by subtracting the minimum PW from the maximum PW. Maximum control of the stimulator Is shown graphically (Fig. 13).

The plot of maximum control versus frequency indi­cates that maybe" 3 0 Hz gives the maximum control. This is not the case however, since the mechanical vibrations were erratic when the PW was maximum. This was determined through feel and was also apparent from distortion por­trayed by both oscilloscope and stroboscope. ,

The frequencies above 45 Hz were rejected primarily because of less stimulator control. However, skin irrita­tion (red welts) caused by more frequent plunger strikes,

30

AREA OF OPTIMUM CONTROL

AREA OF PAIN

AREA OF _ STIMULATOR MECHANICAL DISTORTION12 -

to0

ogou

00RFREQUENCY10 -

HI40 50 5535

FREQUENCY (Hz)

Fig. 13 Stimulation Control Curve

as well as a difficulty in determining minimum feel attrib­uted to the decision.

The frequency of 40 Hz was selected as the optimum frequency as it was in the center of the area of optimum control. At this point in testing, the frequency and bias voltage had been determined for the 00R.

• - 31Part 2 determined the optimum height of the stimu­

lator above the plastic reference plane. The following variables were fixed $ frequency - 40 Hz, do bias - zero volts and amplitude - 11,0 volts. Up to now the stimulators had been positioned 1/16 inch above the plane. Now the stimulator was adjusted in 1 / 1 6 inch increments from level to 3/16 inch above the plane. The optimum position was de­termined by the tester's sense of feel. The sense.of feel

tmay seem inadequate as a measuring device, however, the author feels that this is reliable as he had logged approxi­mately 75 hours of training on the stimulator during previous testing, ■

The position of 1/8.inch was chosen for the QOR, It was at this point that the stimulator transfered the optimum feel while varying the PW from minimum to maximum. It ; should be pointed out that this point was determined for the fleshy portion of the forearm flexor muscle and is not. ne­cessarily reliable for all available positions of stimulation The position of level was unusable as it allows the plunger to leave the spring and cause uncontrollable stimulation.The position of 1/16 inch and 3/16 inch were tested and found to be adequate for stimulation, but were not optimum.

Two optimum stimulation variables now remain to be determined. They are the pulse amplitude and PW,

32Part 3 determined the two remaining stimulator

variableso The optimum pulse amplitude was the first of these variables and was found by test* The second variable, maximum and minimum PW's was a direct result from the test once the optimum pulse amplitude was found0

The pulse amplitude was found by first fixing theheight of the stimulator, the frequency and the bias voltageto their optimum values of 1/8 inch, 40 Hz and zero volts,respectivelyo The pulse was then varied in 1 volt stepsfrom 5 to 10 volts while maintaining the PW at maximum (§

■ • - - - duty cycle) for maximum stimulation,,The skin reaction (irritation) was then evaluated

after five minutes of maximum stimulation for each voltage incremento Voltages greater than 7 volts caused a redness about the point of stimulation* This reaction therefore rejected these voltages, as optimum*

The voltages 5 volts and below were rejected because of weak stimulation* Therefore, the optimum pulse amplitude was narrowed down to the range of voltages between 5 and 7

volts * - "■ ■ . ' • ■ 'The optimum pulse amplitude was then determined by

trial and error using the tester's sense of feel for evalu­ation* A pulse amplitude of 6*8 volts was selected as optimum*

Once the pulse amplitude was selected, only the maximum and minimum PW's remained to be found * With four

33of the five optimum variables fixed, the remaining PW determ­ination was a direct result of the fixed variables„

The optimum minimum and maximum PW's were measured• as 5 o5 and 1 1 05 ms respectively for maximum and minimum feel* This was the last variable to be determined in the OOR0

Conclusions for Optimum Operating Region Testing0

The stimulator variables as determined by Interface II test­ing for the OCR are as follows s -

• Voltage Pulse. Amplitude - 6 „ 8VMaximum Pulse Width - 11o5 msMinimum Pulse Width . - 5«5 msFrequency — 40 HzHeight of Stimulator - 1/8 inchDC Bias Voltage - OV

Tactile Stimulator OperationTactile stimulator operation was next to be investi­

gated now that the 00R had been determined0 In order to have some measure of the transfer of feel from the stimula­tor in relation to the input pulses, a series of Just Noticeable Difference (JND) tests were conducted* The JND0s are defined, as the number of different feel levels which can be recognized, including no feel as a level*

The objectives for the tactile stimulator JND tests were as followss (1) to determine the maximum number of JND * s between no feel and maximum feel and (2 ) to determine the

stimulator input PW's for each JND level. The tests to de­termine objectives 1 and 2 were performed on the author utilizing the test circuit (Fig. 14), Another testee could not be used for JND determination since the layman was unable to give valid results due to lack of training in tactile recognition.

PULSE ... z ONEGENERATOR SWITCH STIMULATOR

Fig, 14 Just Noticeable Difference Test Circuit

The JND tests were designed for the 00R while vary­ing the pulse width between 5 . 5 ms and 1 1 . 5 ms on the pulse generator. The determination of feel differences was then made by placing the arm on the stimulator, and stimulating the fleshy portion of the forearm flexor muscle.

Just Noticeable Difference testing was designed by first assuming that only four JND's exist for the stimula­tor. The available PW variation (5.5 ms - 11.5 ms) was then divided into equal increments to determine the four JND PW's. These PW's were then used to drive the stimulator to determine the testee's ability to recognize adjacent JND levels.

During the testing, the stimulation recognition ac­curacy for adjacent JND's was accomplished by having the testee recognize, by feel, an unknown high or low input PW.

' - ' 35.The high or low PW for the adjacent JND6s was set "by a test assistant adjusting the PW on the pulse generator0 Once the amplitude was set, the testee would sample the stimulation by closing the switch (Pig* 14). Then the stimulation would be related vocally as high or low and the test assistant would record the accuracy, r

The criteria followed during JND testing is as follows! (1) Twenty-five samples of high and low stimulator inputs were used for each pair of adjacent JND"s (2) The samples were randomly broken down into 13 highs and 12 lows and (3 ) % training period of one minute (high and low in­puts) was allowed between each test of adjacent JND”s,

The JND testing allowed for evaluation of the recog­nition accuracy at the completion of the test. If the accuracy was evaluated as adequate, the test was then re­peated, after adding one more JND level. This procedure was then continued until the maximum number of JND’s was found.

Test Number 1, Test number 1 was conducted assuming ,the four JND”s, The JND's were for 0, 5o5» 8,5» and 11,5 msvpw ” s, :

The test results were rather surprising as the cap­ability to determine stimulation amplitude differences between adjacent JND's was extremely simple. One hundred percent recognition was achieved on this test. Therefore, no data will be presented.

36Test Number 2 , Test number 2 was conducted assuming

five JND1 s„ The JND's were for 0„ 5«5? 7».5»' 9«5 and 11.5 ms PW's.

Recognition of the stimulation amplitude was more difficult than in test number 1 However, one hundred per­cent recognition was still accomplished. No data is presented for this test.

Test Number 3. Test number 3 was conducted assuming six JND’s. The JND's were for 0, 5»5» 7=0, 8.5, 10.0 and11.5 ms PW's.

Testing was conducted on the testee by using the 25 samples of high and low stimulation inputs for each pair of adjacent JND's as previously described. However, the test was repeated three times, after completion of the first run, to provide a total of 100 samples for test evaluation. To eliminate the possibility of any pattern recognition during the repeat testing, the test was started at random points by the test assistant. The test data, (Fig. 15) does not include the 0 versus 5=5 ms JND increment as their recogni­tion accuracy was one hundred percent.

The data from test number 3 indicated a nonlinearity between the input JND pulse increments and the output stimu­lation recognition. The nonlinearity can be seen by analyzing the data (Fig. 15). The number of recognition errors for each linear PW increment shows that the transfer

37

30CO

3

<CO

oo 20 -

a 1510

5

28 28

5.5 7.0 8.5 1 0 . 0vs vs vs vs7.0 8.5 1 0 . 0 11.5

Fig. 15 Stimulation Recognition Errors for Linear Input Just Noticeable Difference Pulse Increments

of feel decreases as the driving PW increases. Because of this obvious nonlinearity, a mathematical investigation into the operation of the stimulator was made (Appendix A). The results of the mathematical analysis for the nonlinearity were then used as a departure point for determining the PW1s necessary to provide equal feel increments between the six JND's.

Test Number 4 . Test number 4 was designed to adjust the PW1s for the six JND's taking into consideration the

38nonlinearity discovered in test number 3» The test used the data (Table A-4) for its departure, but in the final analy­sis, the JND pulse widths necessary to provide equal feel increments were determined by trial and error.

The PW's selected for the JND1s were 0, 5.5> 6.7,7.9, 9.4, and 11.5 ms. These nonlinear PW increments pro­vided linear increments of feel between adjacent JND*s.

In order to substantiate the PW's determined by test number 4, test number 3, with 100 samples was repeated using the new PW's. The success of the test is recorded in (Table 3)• The one hundred percent success between 0 and5 . 5 ms is a carryover from test number 3 .

Conclusions for Stimulator Operation. The stimula­tor was found to posses six JND's when operating in the 00R (Fig. 16). The findings are obviously dependent on the author's sense of feel. However, the data must be accepted since any data obtained from testees unskilled in stimula­tion recognition would be valueless.

Table 3 Test Number 4 Recognition Errors between Adjacent Just Noticeable Differences for 100 Samples

0 ms vs

5 . 5 ms5.5 ms

vs 6 . 7 ms

6.7 ms vs

7 . 9 ms7.9 ms vs

9.4 ms4,4 ms

vs 1 1 . 6 ms

0 4 5 6 5

39The nonlinearity between the stimulator input PW and

the amount of feel transfered (Fig, 1?) is approximated by two straight lines. The driver design will make the neces­sary adjustments to allow for this nonlinearity.

Driving Unit Input/Output Design ParametersAfter testing Interfaces I and II, the I/O design

parameters for the ARTEAR driving unit were approached. During ARTEAR operation, the driving unit will provide con­tinuous PW variations (5.5 - 11.5 ms) to the stimulator generated by continuous voltage input variations to the

aII

AMAX --

MIN 4-

NO i

SIXTHjJND FIFTH_JND _ FOURTH^ JND_ THIRD_JND SECOND JNDi FIRST JND

PULSE WIDTH Fig. 16 Six Just Noticeable Differences

40

ewg

g g

12

11 -

10 -

9-

\ g

MINIMUM MAXIMUMFEEL FEEL

EQUAL FEEL LEVELS FOR JND'S Fig. 1? Transfer of Feel Nonlinearity

series filter (0 - lOv). However, to aid in designing for the nonlinearity previously discussed, the driver design parameters will be determined using the six JND's.

Input Parameters - Interface I. The JND driver design input parameters can be determined utilizing the family of series filter output curves (Fig. 6 ). To use the curves, the series filter input for the six JND's had to be determined.

41The filter inputs were selected in the following

manner? • First6 zero volts was selected for no feel (first JND)o Then the minimum feel level, or second JND, was di­rected by Dro Hill as a 05 volt input„ Next, the maximum feel level, or sixth JND, was determined as 10 volts by the maximum allowable input to the series filter (Fig, 6 )„ The remaining three JND input voltages for the series filter were then selected in equal voltage increments between the second and sixth JND6sa Therefore, the series filter input voltages determined for JND0s one through six are 0, o5s2 ,9 , 5 ,3 , 7 ,7 , and 1 0 , 0 volts respectively.

The series filter family of output voltage curves (Fig, 6 ) determine the input voltages for the driving unit. In analyzing the curves, it can be seen that for series filter input voltages up to 8 volts, the output can be com­puted as oSv^o Therefore, the driving unit input voltages for JND's one through five can be computed as 0, ,4, 2,32, 4,24 and 6 ,l6 volts respectively. The input voltage for the sixth JND can be taken directly (Fig, 6 ) as 8,2.volts.

Output Parameters - Interface II, The output pulsei .parameters were determined directly from Interface II test­

ing, The PW for JND6s two through six in the 00R were 5®5i> 6,7, 7=9, 9,4 and 11,5 respectively. The PW for no feel or the first JND can be any pulse width less than 5=5 ms.

42Design Parameter Summary0 The JND driving unit de­

sign parameters are summarized (Table 4)„ The PW for the first JND, no feel, is not recorded since it may•take on any value less than 5«5 ms„

Table 4 Just Noticeable Difference Driving Unit Input/Output Design Parameters

INPUT PULSE OUTPUTVOLTS (rms)

PW(ms)

AMPLITUDE(VOLTS)

'FIRSTSECONDTHIRD

6.8. FOURTHFIFTH

8.20 11.5SIXTH

. CHAPTER 3

' . DRIVER DESIGNp CONSTRUCTION AM)'TEST

The design of the pulse width modulated driving unit for the ARTEAR was initiated at the conclusion of Interface Testing, The Operational Amplifier approach to the driver design was selected by the author for the following reasons: (1) it provides for flexibility in design, (2) it provides ARTEAR design continuity with the series filter network, and(3) * the Burr-Brown Research Corporation is conveniently located to the University for possible microminaturization and manufacturing of the ARTEAR, \ . ■ „

The research material (Burr-Brown, 1966) and (Burr- Brown, 1 9 6 9) obtained from the Burr-Brown Research Corpora­tion was used extensively during the design. The driving unit was constructed as a prototype model capable of driving only one stimulator.

The design and construction allows for close moni­toring of the driver operation during future testing of tactile stimulation recognition. If the future testing proves the design satisfactory, a complete .driving unit composed of eight individual driving; units will be construct­ed, Five basic modules compose the prototype design and are discussed next as a connected system,

■ '■ ■ . v , "3

44The block diagram (Fig. 18) shows the basic driving

unit design and operation. The input rms voltage from the series filter network can vary from 0 to 8.2 volts. This audio is then rectified and passed to the low pass filter which outputs a modulating voltage. The modulating voltage, which controls the driver output PW, is then adjusted by the function generator to compensate for the nonlinear transfer of feel by the stimulators. Modulation'of the driving unit output pulse is then accomplished by summing and comparing (summer-comparator) the adjusted modulating signal with a 40 Hz triangular waveform. The summer-comparator then pro­vides a 40 Hz, constantly varying PW which satisfies the pulse requirements for the stimulator0s 00R. The driver design and construction, using the JMD design parameters (Table 4), will now be presented by individually discussing the five modules (Pig, 18).

Full Wave RectifierThe full wave rectifier circuit (Fig, 19) was se­

lected for the design. Circuit construction was initiated by matching R^, Rg, and R^ from a batch of 10K, 1 % resistors. The variable resistors R4 and R^ were then trimmed to give the desired output. The amplitude of the rectified pulses were matched by trimming R4 , The overall gain of the recti­fier was adjusted by trimming R^ until the output peak voltage was equal to the input peak voltage.

SERIESFILTER-INPUT

ADJUSTEDMODULATING

SIGNALRECTIFIED ' OUTPUT

MODULATINGSIGNAL

-QJ1E0 REF 0 REF

SQUAREWAVEINPUT

TRIANGLEWAVE

OUTPUTPW MODULATEDDPTVKR OUTPU T

REFERENCE (+V) »

NONLINEAR

FUNCTIONGENERATOR

SUMMERCOMPAR­ATOR

FULL WAVE

RECTIFIERLOW PASS FILTER f = 30Hz

TRIANGLEWAVE

GENERATOR

Fig. 18 Driving Unit Design Block Diagram

The diode offset voltage is a major problem in the present ARTEAR driver design. However, in this design, the trimming of resistor R^ eliminates this problem.

Low Pass Filter The low pass filter module was designed for a cutoff

frequency (fc) of 30 Hz. This frequency is accepted by con­vention from McRae (1 9 6 8, p. 40). The 30 Hz cutoff frequency allows for a time constant long enough to filter the audio to a modulating signal which follows the audio vocal tract.

1 0 , 0 6 0

■A/V1 0 , 0 6 0 4 , 8 6 01 0 , 0 6 0

w A/V

Fig. 19 Full Wave Rectifier Circuit Diagram

4?However, the time constant is not too long and allows the modulating signal to follow rapid fading of the audio.

A multiple feedback low pass filter design (Fig. 20) was accepted for the driving unit. The filter circuit allows for a maximally flat response, with a 40 db/decade rolloff.

In the design of a multiple feedback circuit, it is desired to obtain a frequency normalized voltage transfer function of the form:

^ o ______ -HEi s2 + s + 1

For this circuit, the voltage transfer function is:f o ______________ ~G 1G3_________________K ~~ Pi s + SC2 (G 2 "t Gg + G- ) + G G/

224KRo

228K — R 1

- £ A r -

134k *RoT

A/V— f •01if

BB 1552/15

Fig. 20 Low Pass Filter Circuit Diagram

48Since the solution to this equation leads to a set of non­linear simultaneous equations, the initial values for the circuit components were evaluated from a Burr-Brown (1 9 6 6, p 0 74) set of equations.

The calculations are as follows;Choose a value for Cg = .Ol^fThen Cg = (k/2i7f0) or k = 1088 x 1 0"^Now = (4/©,2) (H + 1) (k/2nf0)

where ©t = J? and H (Gain) = 1

C 1 _ e04/ff Then ^ = (ef/2Hk) = 3?6K^.

R3 =^/2(H + 1) k = 188K^. . R2 = HR! = 376k^

These computed values were then used as a departure point for determining the actual components. To determine the actual values, three components were chosen as fixed and the other two determined hy trial and error in a test environment 0

The fixed components were C^ = .04?^, Cg = .Ol^f and R^ = 130K>v @10^. (134K^v Actual) . The values of R^ and Rg were then varied using R^ and Rg as 220K^%, plus 0-20K-fv trim pot each. The final actual values selected for R^ and Rg were 228K^% and 224K-^- respectively.

The circuit design was tested "by varying the fre­quency of a 5 volt rms input from an audio oscillator while

49measuring the output voltages, The graphical representation (Fig. 21) shows the actual filter response which is the same as the desired response.

pleted, the filter was then connected with the full wave rectifier and retested. For the test, a local oscillator set at 400 Hz was applied to the input of the rectifier.The input voltage was then set to the design JND voltages and the output voltages from the filter measured. The com­puted output for the filter with full wave rectificiation is .9 x v^ (rms). The results are tabulated for the actual and computed filter outputs (Table 5)•

Once the testing of the filter as a unit was com-

5

> 3.53V. 3-

o1 _

11-----1--- 1— |— r-i-r-rT2 3 4 5 10 20 30 40

1 T P-T-n — >100

FREQUENCY - Hz

Fig. 21 Actual Filter Output for 5 Volt Input

50Table 5 Rectifier Input 400 Hz and Filter

Output Voltages for Connected System

Rectifier JND Input Voltages

(rms) CALCULATED MEASURED

FILTER OUTPUT VOLTAGE (rms)

o362.093.o 825o5^ 7.35

342.324.246.16

2.13.95 = 6

8.2

Triangle Wave Generator The triangle wave generator was designed using a

simple integrator (Fig. 22) in conjunction with the opera­tional amplifier. The input frequency of the square wave generator determines the output frequency for the driving unit. This frequency of 40 Hz was taken from the data for the stimulator OOR. The design peak voltages for the in­tegrator input and output are 10 and 5 volts respectively (Fig, 2 2 ) The calculation of the component values is as follows 8

t(3.D

Now?i . (slope-triangle wave)

10V

0 REF 0 REF

Fig. 22 Triangle Wave Generator Circuit Diagram

And:T _ JL or Period (T) = 25 ms

fTherefore:

R1C1 = 12.5 ms from Equation 3.1 (3.2)Now assume that C^ - l^f, then using Equation 3.1

R 1 = 12.5K^_Since R^ R^ * ^2 ~ IN-a-These computed values were then used as a departure

point for the component testing. The resistor R^ was se­lected as a 0-20K.A. variable resistor. The resistor R^ was then trimmed to give E0 __ 5V. Actual component values are indicated on the circuit diagram (Fig. 22).

Summer-Comparator The summer-comparator was the next module to be de­

signed. The design allows the adjusted modulating input voltage to determine the pulse width at the output. To provide this design, a modification of the comparator design from Burr-Brown (19&9, p. 39) was selected. The circuit diagram (Fig. 23) provides the desired stimulator 00R variable pulse width (5.5 - 11.5 ms) with an amplitude of 6.8V. To aid in determining component values, the summer- comparator design characteristics (Fig. 24) were used.

NEGATIVEADJUSTEDMODULATINGSIGNAL

t 51K-/X.I RPOSITIVE 5.2V DC REFERENCETRIANGLE WAVE (+ 10V PEAK)

R4 0-20K

BB I5 5 5 / 2 5

PW MODULATED DRIVER OUTPUT

Fig. 23 Summer-Comparator Circuit Diagram

53

oSLOPE = tR^ + R(D1)/R1 R(D1) IS DIODE RESISTANCE

SLOPE = Open Loop Gain

. Fig. 24 Summer-Comparator Design Characteristics

The rise time of the pulse (Fig. 24) was no problem to the design since the open loop gain falls in the range of 10^ to 10^ Burr-Brown (1969, p. 28). However, the slope for the amplitude was adjusted to make it acceptable by se­lecting R^ _ IKw and R^ _ R2 _ R^ = 5 1 K w . To complete thedesign, component R^ was chosen as a 0-20Kw. trim pot toallow for amplitude change at the output and the negative voltage (-V) was taken from the -15V amplifier power supply.

A high current Burr-Brown operational amplifier (1555/25) was selected to drive the stimulator. The ampli­fier has a rated output of + 100 ma current.

Germanium diodes D^ and D2 were selected for thedesign. However, any diode can be used as the negativevoltage V (D2), can be offset by varying the input positive dc reference voltage.

54

The negative adjusted modulating signal input neces­sary to provide the JND design output pulse widths were determined next. The JND design pulse widths are: 5.5, 6.7, 7.9, 9.4 and 11.5 ms (Table 4).

The operation of the summer-comparator allows the output voltages to be 6.8 volts when the summation of the input voltages is less than zero and zero when the summation is greater than zero. The input voltages to the summer- comparator and their summation, assuming an adjusted modu­lating input of OV, is shown (Fig. 25) to aid in explaining the design,

TRIANGLE WAVE

0 REF —

POSITIVE DC REFERENCE0 REF

+5V

-5V

+5V

SUMMATION

0 REF

+ 10V

Fig. 25 Summer-Comparator Inputs and Their Summation for an Adjusted Modulating Signal of Zero Volts

55The adjusted modulating input voltage to the summer

comparator is directly proportional to the output pulse width. This direct proportion can be determined by summing the inputs (Fig, 26) and analyzing their summation. The direct proportion is as follows:

The summer-comparator input voltages respective to the JND design pulse width outputs (Table 6) were computed and uti­lized in testing the module.

Next, the summer-comparator was constructed and tested. The unit was tested by inputing the triangle wave at R^, the positive dc reference at and simulating the inputs from the negative adjusted modulating signal at R^ by using a dc power supply.

FUNCTION GENERATOR

or E _ .4 x 103 x PW PW ~ T i

INPUT (E1)

SUMMEROUTPUT

E TEg = 10V— A

COMPARATOROUTPUT PW

Fig. 26 Summer-Comparator Input Summation for a Negative Adjusted Modulating Signal (E^)

56Table 6 Summer-Gomparator Computed Just Noticeable Difference Design Input/Outputs

OUTPUTPL(ms) AMPLITUDE

(y ) .

11 = 5

The simulated Input was first set at 0 volts and the value of the positive reference voltage was found for zero PW at the outputo The value of +5o2V was determined* This value is »2V higher than the computed design voltage of 5oOV= The 0 * 2V" difference offsets the diode voltage drop for Dgo • - - -

The amplitude of the output was then adjusted to 6„8V by trimming R^o Now, simulated inputs were set at the JND design input voltages and the output PW’s measured0 Data from the test matched the computed values (Table 6) . exactly, thus completing the summer-comparator design, con­struction and testo ' _

■ 57, Nonlinear Function Generator

The nonlinear function generator was the last module to be designed* It was designed to take the inputs from the low pass filter and produce output voltages proportional to the desired driver pulse widths. The function generator JND design inputs are the computed outputs of the filter (Table5)o The function generator JND design output voltages are the computed input voltages of the summer-comparator (Fig.6). The desired nonlinear relation between design input voltages .(E ) and output voltages (EQ) is approximated by- two straight lines (Fig. 27).

Design Criteria : v :Using the data (Fig. 27), the equation for line seg­

ment number 1 and line segment number 2 were determined algebraically.

The computed equations are;Line, segment number 1 ■

Eo = ,281 E 1 + 2,1 (3.3)Line segment number 2

E0 = .457 + 1.21 (3.4)Equations 3.3 and 3.4 were then solved simultane­

ously to determine the break point voltage, EQ _ 5.07V (Fig. 27)o

OUTPUT

(V)

JND - 4 (3.82,3.17)

3JND - 2 (.36,2.2) SLOPE (m2) = 4.57

2 SLOPE (m,) = .281

1LINE SEGMENT #1 LINE SEGMENT #2 ^

6 75 E3210INPUT (V)

Fig. 27 Output Voltage versus Input Voltage for the Nonlinear Function Generator

59DesIgn

The circuit diagram (Fig. 28) is the design selectedto provide the following function (Eo).

E0 = .281 E i + 2.1Line segment number 1

06%i6 5.07V Line segment number 2

E0 = .457 %i + 1.21 5.07VThe slope of line segment number 1 is determined by

component values and R^. The values of these components can be computed from:

•Ri,ml = Ji: = .281RNow choose Rr _ 10K Then R1 = 35.7Kw

(3.5)

El -

35. ?K A.

- £ A r —

32. 8KHo

24.IK.Ro

+ V

- N t f -

R5 19K JV

d2.3V

10K^-R4

A A y -

=6>BB 1557/15

Fig, 28 Function Generator Circuit Diagram

Now the slope of the line segment number 2 is deter­mined by component values » Eg? and R^0 The values for these components can be calculated from:

m2

Substitute in values for mg, R^ and Rg and solve for (Rg + R- ) o

Then, R2 + R- = 56a 9K wNow, let R2 = 32«8K^Then R^ = 2^alK^_ .... .The breakpoint voltage, V-y equals 5-0?V (Fig0 2?) ,

is determined by the voltage on the diode (V^)0 Assuming no voltage drop across the diode when forward biased, we can compute from:

va ^ ‘ ■b , " a2 + r 3 (3.7)Now substituting in values for V^, R£ and R^Vd = 2 ,15VThe intersection of line segment number 1 with the

Eo axis is the only remaining item of the function to be computed. The intersection of line segment number 1 with the Eq axis can be computed from:

61Therefore, the Intersection falls at E0 = 089V0

This is not the design point however«, The design.point for the intersection is at 2„1V (Figo 2?)« Therefore, the whole function must be shifted in the positive E0 direction a value of le21 volts or the difference between the computed intersection and the design intersection* .

The function generator design will correct the off­set a value I*21 by selecting the proper value for R^0 The value of resistor can be initially calculated, assuming V (Di) = 0, to.provide the 1.21V offset from:

5i.vd = 1.21V ' ■ (3-9). h5 . ;Therefore Re = 1708K^. (V(Dj_) assumed 0V)

Construction and TestThe function generator was constructed using the

computed design values. The value of R^ wias a fixed 10K resistor. All other resistive components were constructed with fixed resistors plus 20K trimmers to allow for future design change if necessary.

The function generator was tested by inputing the JND design voltages (E^) (Fig. 2?) from a dc power supply and reading the output voltage (E )■. Before the testing was started, the input voltage was set to 0 volts and the value of V^ adjusted to allow for the voltage drop across .The measured diode voltage V^ was 2.3V. This allowed for the .15 diode voltage drop. The value of R^ was then

62recomputed (Equation 3 = 9) for the measured V^o The value computed was = 1 9 K w „ The test was then continued and all measured output voltages EQ for the JND design.input voltages matched the calculated values (Fig. 2?).

Design Summary Upon completion of the individual module design and

test, all modules were connected and system testing of the driving unit was conducted. The circuit diagram for the driving unit is shown (Fig. 29). The prototype of the driv­ing unit is shown (Fig. 30).

The prototype driving unit was system tested by in­put ing the JND design voltages and measuring the desired output pulse widths. The outputs were identical to the desired pulses for the stimulator 00R.

T

FUNCTION GENERATORFULL WAVE RECTIFIER LOW PASS FILTER

A/VA/VA A ? — r— v £a / vVv

_ C

+ 2.3V

Component Values are listed as follows: -15VNOTE: TRIANGLE WAVE GENERATOR SUMMER-COMPARATORFULL WAVE RECTIFIER FigureLOW PASS FILTER Figure 20

+5.2VWTRIANGLE WAVE GENERATOR Figure 22

WSUMMER-COMPARATOR FigureFUNCTION GENERATOR Figure

OUTPUT10VSQUARE WAVE INPUT

LFig. 29 Pulse Modulated Driving Unit Circuit Diagran

BOV P/P INPUT

NOT USEDp e i 8 . t v

mm m mm

O U T P U T>

tii ' : / -'IS. , z .; OR'H - «’ -

■ , . D R I V I N G. S U M M E R . .

T R I A N G L E

NON LINEAR

» ' U N I TGENERATOR " FUNCTION «GO HZ COMPARATOR

Fig. 30 Photograph of the Prototype Driving Unit ^

CHAPTER 4

ARTIFICIAL EAR SCOPE

The future for the ARTEAR appears very promising»Its feasibility has been greatly enhanced with the advent of space-age technology. At the.present, .integrated cir­cuits are providing low costs and small electronic component size. This electronic sophistication can now be used to achieve a small portable ARTEAR,

Other Tactile Stimulation DevicesThe advantages of microminiturized electric compo­

nents for tactile stimulation has also been recognized by other researchers, Two applications of tactile stimulation are being investigated as aids for the blind,

Reading AidBrugler and Young (1 9 6 9) describe a "Reading Aid for

the Blind" first conceived by Professor J , G„ Linvill at Stanford. University, The system, developed by the Depart­ment of Electrical Engineering at Stanford, permits the blind to feel ordinary printed matter and read it using the sense of touch,

; The reading aid is a system composed of photo- electric devices, arranged in a planar array, which receive

66an optical image of the reading material. The electronic system then transmits the image via, a planar array of piezo­electric reeds to generate the tactile image. For instance, the letter "A" is presented to the user as a vibrating tactile facsimile.

The present system allows the reader to read $ 0

words per minute» a letter-at-a-time„ after 180 hours of practice. Tests are now under way to increase the field of view to enable the user,to read a word-at-a-time.

Seeing-Eye BackpackBach-y-Rita and Collins (1 9 6 9) report the develop­

ment of a seeing-eye backpack. The device will be used as a tactile vision substitution system. The system is being developed at the University of the Pacific in San Francisco with the aid of graduate researchers.

The backpack, still in the laboratory experimenta­tion stage, operates with a small television camera, which transmits images to the back via tactile stimulation, A unit within the system provides electrical impulses which in turn go to 400 plastic tipped vibrators mounted in a 10 by 10 inch, metal square on the back of a wheelchair. The user sits in the chair and presses back against the square of vibrators and receives stimulation corresponding to the images transmitted by the camera.

The operation of the backpack indicates that the user can determine objects after about ten hours of practice,,

. However, with extensive training, one can also discriminate between shades of hair color«

Future Artificial Ear Operation The success of the Reading Aid and the Backpack in­

dicate that the future success of the ARTEAR is indeed feasible. This success depends largely upon the dedication of the researchers and the equipment designed. The proposed driving unit is a step in this direction. The operation of the ARTEAR with the prototype driving unit connected will provide a tactile stimulation from which, the researcher can make a valid investigation. The validity, of the data can

, now be based upon the known.stimulator QOR and JHD’s, and the known driver output accuracy, .

In testing the ARTEAR operation, data from stimula­tion tests of the Reading Aid and the Backpack would be of great value, However, the data at the present appears to be a closely guarded secret. In light of this situation, a complete investigation for tactile recognition of audio inputs must be accomplished. The remaining,.text will there­fore contain information on ARTEAR hook up, testing and recommended improvements,

Equipment Hook UpThe power supplies necessary for ARTEAR operation

(Pig, 31) requires only one additional comment» The posi­tive 15V supply must have a current rating greater than 50 ma0

The hookup of the driving unit is indicated direct­ly on the constructed prototype, but is repeated in the layout diagram (Fig, 32)„ Each individual module has a red output jack to allow for unit analysis during testing. The input hook up jacks are black for ground, green for negative and red for all others.

Testing -Future testing of the ARTEAR with the prototype

driving unit, will require an extensive lead in training program in tactile recognition6 The reason for the training program follows from the fact that the 00R does not provide a shocking stimulation of the arm. As a matter of fact, the stimulation is almost undetectable to the untrained re-• cipient.

Poor Recognition Capability. The poor recognition capability of the untrained was brought to the attention of the author during JND testing. Five different test assist­ants were tested on their tactile recognition capability.The results were unbelievably poor as they could not achieve even partial success in distinguishing maximum feel from

s \

AUDIO • INPUT

+2.3Vdc

SQUAREWAVEGENERATOR 20V P-P

+5.2Vdc

TACTILE STIMULATORS

PROTOTYPEDRIVING

UNITSERIESFILTERNETWORK

Fig. 31 Artificial Ear Equipment Hook Up

opos 15V

©INPUT

oMEG 15V

SERIESOFILTER

©NETWORK

20V P-P INPUTo ©SQUARE WAVE

INPUTo ©POS 23V

FULL WAVE RECTIFIER OUTPUT o

LP FILTER (30 Hz) OUTPUT

INPUTO ©POS 5.2V

TRIANGLEWAVEGENERATOROUTPUT

NONLINEARFUNCTIONGENERATOROUTPUT

o ©NOT USED

SUMMER- COMPARATOR OUTPUT o

DRIVINGoUNIT

©OUTPUT

Fig. 32 Driving Unit Layout Diagram

71minimum feel (11.5 ms versus 5.5 ms). To put it bluntly„they were undecided even to the point as to whether theyV ■ ... ■ ' ' . . ' ' v •felt any stimulation.

This tactile recognition in comparison with the author's proficiency was completely unacceptable. Since from.JND testing the analysis of tactile recognition pro­vided approximately accuracy in determination of the following adjacent JND'ss 5.5 versus 6,7 ms, 6,7 versus 7.9 ms, 7 „ 9 versus 9.4 ms and 9A versus 1 1 . 5 ms.

This unsatisfactory recognition capability of the layman„ when compared to the author's, should be very dis­turbing to the reader. However, the questioning mind can be relieved by analyzing Interface II, test number 1, (first tactile recognition test)„ Here the objective was to find a point of departure for determining the stimulator optimum

j " ,

operating region. In this test, the pulse amplitude was set at 50 volts and the finger was used for determining the feel. These two unrealistic stimulation parameters were selected because of the author's initial inability to recog­nize tactile stimulation.

The 50 volt amplitude, used initially by the author, is about 43 volts higher than the 6,8 volts finally selected for the optimum pulse, and the finger tip, used during test­ing, is the body's most sensitive area to tactual stimuli, with exception of the tongue (Lawrence 1968). This initial poor recognition capability substantiates the fact that for

72any valid data in future testing of the ARTEAR, a willing sacrifice must be made.by the testee. A sacrifice of the time necessary to complete a program designed to increase proficiency in recognition of tactile stimuli.

Training Program. A training program for tactile recognition must be designed before- conducting future tests, The initial part of a training program should be designed to have the stimulator driven by a pulse generator. By using the pulse generator, the amplitude of the pulse can be ad­justed high enough to provide adequate stimulation for the untrained user. Then, as the training progresses, the pulse amplitude can be decreased in increments as the testee’s proficiency increases. Once the amplitude reaches 10V, the ARTEAR, with the proposed driving unit, can be used for con­tinued training since the pulse amplitude can be varied to a maximum of 10 volts by adjusting the value of R^ on the summer-comparator (Fig. 29).

Then, when the testee1s proficiency fails to in­crease, with decrease in pulse amplitude, the optimum volt­age amplitude has been reached. The proficiency of the user can now be evaluated by comparing the JND recognition accuracy of the testee versus that of the author.

Another approach to the testing might be a computer * oriented program following the same approach. But no

73matter how the training is conducted„ the user can expect to forfeit approximately 35 hours before gaining the necessary proficiency to use the ARTEAR effectively*

This 35 hour conservative„ educated and recommended guess for gaining proficiency should be achieved in as short a time span (days) as possible„ The author achieved the proficiency for determining the six JND's after approximate­ly seven hours of training a day for five continuous days (Interface II testing)e . .

Recommended ImprovementsThe following is a recommended list of future ARTEAR

improvements * A brief explanation for each improvement is included*

Automatic Gain Control* Automatic gain control for the ARTEAR audio input should be designed. The control would be placed at the series filter input and maintain the ARTEAR with a constant maximum input, voltage of 10V rms>This control would then allow full range of tactile stimu­lation at all times (5-5 - 11.5 ms) as per driver unit design.

Arm Rest. Future testing of the ARTEAR must provide an arm rest designed to position the arm accurately and con- ' sistently in the same position. The positioning of the stimulator on the arm is all important to tactile

recognition. Once the arm rest is designed, a test should be performed on each o'f the eight stimulators to determine the transfer of feel for each position. Then the data for all' future audio input testing will be more valid.

No Feel. The proposed ARTEAR driving unit provides stimulation of the arm below 5°5 ms (minimum feel) even though the stimulation is undetectable (no feel)„ This stimulation appears to have no use at the present, and could be eliminated, if desireable, with a device which provides zero stimulation when the driver pulse width is less than 5.5 ms. The decision to make this change should only be made after a complete analysis of each of the eight indivi­dual stimulator's transfer of feel.

ConelusionIn light of the recent developments, it appears rela­

tively certain that an artificial hearing device will be operational in the near future. It is hoped that the University of Arizona, using the ARTEAR, will be the recog­nized developer of the little used tactile nervous system as a major replacement for the auditory system.

APPENDIX. A

MATHEMATICAL ANALYSIS OF STIMULATOR OPERATION

The mathematical approximation of the stimulator’s operation was necessary to aid in the evaluation of the nonlinear relationship between the input pulse width and stimulation recognition of the arm discovered in Chapter 2a An understanding of the nonlinear relationship will be bene­ficial in determining the JND input pulse widths necessary to provide equal feel increments between adjacent JND°se

Spring ConstantThe spring constant was determined by placing the

spring into a glass tube along with 15 ounces of weight and measuring the displacement. The calculation of the spring constant (k) is as follows $

k = I = i^tth = 15 oz/InForce on the Magnet-

The force acting on the permanent magnet in the solenoid is a direct result of the current in the coil. How­ever, the force is also a function of the magnet position in the coil.

In order to simplify the mathematical analysis of the stimulator’s operation, an assumption was made that the

' 75 ' - : ' ■■■■■■

force acting on the permanent magnet is a constant„ This approximation can be made since the: movement of the magnet in the solenoid (1/8 inch) is small in comparison to the length of the solenoid (3 inches)0 This assumption was sup­ported "by a paper by Mr, Donald Duff in a University of Arizona Honors Course, The paper was titled "Force on a Permanent Magnet in a Solenoid,"

The actual current in the solenoid, when operating in the OCR is plotted (Fig, A-l) for analysis. However, for ease of calculation, a constant current of 85 ma was assumed in the determination of the stimulator6s response,

- : 9 / ' ' ' "

The force on the magnet for a dc current of 85 ma was determined by applying the current to the coil and measuring the plunger deflection. The deflection of the magnet was ,11? inch. Therefore, using the measured deflec­tion and the spring constant, the force was calculated as:

F = ky= 1 5 (oil?) = 1,75 oz

Analysis of Vibratory Downward Motion The operation of the stimulator can now be broken

down into a simple spring problem The problem will be ana­lyzed in two parts. The motion of the plunger with the force applied will be analyzed first, and the motion with the force removed second.

77

80-

g-p 60- c(DU

% ~o40-

oc<D —i—Iow 20-

00R 11.5 ms

10 12

PULSE WIDTH (ms)Fig. A-l Solenoid Current for the Optimum Operating Region

Vibratory Motion (Force Applied)The vibratory motion with the force applied is

shown as a free body diagram (Fig. A-2).

Vibratory Differential Equation. F = ma-ky - Ak + W + F = W d y

5 dt2but W = Ak:

+ kSv - Z£dt2 W W

(Fig. A-2)

(A. 1)

78

FORCE

MAGNETICPLUNGER

SPRING

k (y + A)

Pos y

W + F

rrrtmFig. A-2 Free Body Diagram with Force Applied

Assuming the homogeneous and particular solutions, the complete solution (Yc) for Equation A .1 is:

Yc = A sin t + B cos jkg t + C (A.2)

After solving for the constants, Equation A.2 be­comes :

y = -F cos [kg t +F k NW k

(A.3)

Solve for Resonant Frequency. The solution for the resonant frequency (fr) is as follows;

6J = fkg or fy _ 1 kgJw 2 Wk = 15 oz/in, g = 386 in/sec2 W = .143 oz (Weight for one plunger)

W = llig = . 201 radians

fr = 3 2 . 1 cps

79Solve for (F/k)o Determine constant (F/k) where

the constant force is 1e 75 oz and k Is 15 oz/in for a sole­noid current of, 85 ma*

5 = = -117 l n .

Now equation A,3 with the numerical constants is: y = -.117-Cos 201t + .117 (A,4)

Solve for Plunger Displacement. At this point inthe analysis of stimulator operation, one must consider that-the magnetic plunger will initially be at rest for each pulse of energy. This is true since all energy imparted by the spring will be dissipated (resistive dampening) when the plunger strikes the arm. Therefore, in the analysis of the stimulator operation, only one cycle of the mechanical sys­tem will be investigated. -

If a force is applied on the magnet indefinitely, it will compress the spring a distance c. However, if the force is suddenly imposed, the spring, if allowed, will compress a distance 2c before reversing its direction of travel. For the stimulator which has a force of 1.75 oz suddenly imposed, the maximum distance that the spring can compress will be twice y = F/k. Therefore, the maximum displacement (d x)is d = .234 in. max

Now, to investigate the JND nonlinearity encountered in Chapter 2, the mechanical reaction to pulse widths of 5 ,5 , 7 <>0 , 8.5, 1 0 . 0 and 11.5 ms must be determined. Computations

- 80 for the displacements (y^) were made using Equation A .4 for the time intervals associated with the JND pulse widths. Equation A.4 computations and solutions (Table A-l) are shown for clarity0

By solving Equation A.4 for the various pulse widths, the distance the plunger travels» (y^) before the driving force is removed, was found„

Table A-l Computation of Forced Displacement (y1)

t(ms)

201tDEGREES

cos 20It - -oil?cos 201t (INCHES)

?!(INCHES)

5 = 5 - 63 o 5 .445 -o052 .0657.0 81 o0 .156 -.018 .0998.5 98.0 -.139 . 0 1 6 .133

O O 116

001 .051 016811.5 133 -.682 .080 .197

Vibratory Motion (Force Removed)Now the plunger with the force removed has a new

free body diagram (Fig. A-3)•

aOi

MAGNETICPLUNGER

SPRING Pos y

k(y h-A)

v

z W 7Fig. A-3 Free Body Diagram with Force Removed

Vibratory Differential Equation. From Figure A-3and £ F = ma it follows that:

W - k ( y + A ) = W d2yS dt2

but W = A kTherefore:

dt w(A.5)

Now assume honogeneous linear differential equation solution for equation A.5 to be;

y = A sin 201t = B cos 201t (A.6)The associated differential equation is:dZ - 201 A cos 201t - 201 B sin 201t d t (A.7)

82Plunger Velocity, In order to solve Equations A.6

and A.7, the velocity of the magnetic plunger (v^) must be determined for each individual pulse width at the time the- force is removed„ This is accomplished by differentiating Equation A„4 and solving for the velocity vQ for each JND interval of time.

In differentiating Equation A-4svo = dy = 23o5 sin 201t (A.8)

dtThe computations and solutions for vQ (Table A-2) are shown for the JND intervals of time (t)„

Table A-2 Computation of Velocity (vQ)

201tDEGREES

sin 201t(in/sec)(ms)

7.08.510.011.5

83Total Plunger Displacement0 The analysis of the

stimulator operation now turns to finding the total plunger displacement (yg). This will occur when the plunger veloc­ity (v) is equal to 0e The maximum displacement for the JND pulse widths must be solved individually since each pulse width is associated with a different initial velocity (v).

In order to solve for y^, the sinusoidal position of the plunger at v = 0 must be determined0 This can be accomplished by solving Equation A«7 for 201t in terms of degrees0 Once.the sinusoidal position is knownp the maximum displacement (y^) can be found by substituting 201t (degrees) into Equation A 06 and solving. The maximum displacements will now be found.

• - The maximum displacement for the 5»5 ms PW will be computed first. Solve for Sinusoidal Position:

Known quantitiess t = 0, v0 = 21.0 and y^ = .065Substitute into Equation A.7 and solve for As.A =s . 104-Substitute into Equation A.6 and solve for B $B = .065Substitute constants A and B into Equation A.7s

|| = 20=9 cos 201t - 13.0 sin 201t

Find sinusoidal position (201t) for v = 0sTan 201t „ 20.9 _ i Ai

13.0 °

201t = 58.1° -

84Now solve for yg at v = 0 using Equation A,7 ; yg = .104 sin 5 8 .1° = . 0 6 5 cos 5 8 .1° . y^ = . 1 2 2 In (maximum displacement)

This completes the solution for 5°5 ms. Now the. maximum displacements for the remaining pulse widths will be de­termined.

The method for computing the remaining displacements for 7.0 j , 8 .5 o 1 0 . 0 and 1 1 , 5 ms PW's is identical to that of the 5 ms PW. The difference in the maximum displacement (y2)> depends only on the different "known quantities" used in the solution for sinusoidal position. Therefore, only the "known quantities" and the solution for maximum dis­placement (y2) will be reported for each remaining pulse width. They ares

For the 7 o 0 ms PW sKnown quantitiess t = 0, v0 = 23.2 and y^ = .099 y2 = .1 5 1 in.

. For the 8.5 ms PW s Known quantitiess t = 0, v0 = 23 = 2 and y^ = .133 y2 = 0-177 in -For the 10.0 ms,PWsKnown quantities s t = 0, y0 = 21.1, and y^ = .168

. .... _ — - o .ILlfl .. «...—— - -* v “ - * — -- — — "

For the 11,5 ms PW sKnown quantities s t = 0, v 0 ~ 17=2 and y^ = ,197 y2 = .214 in

Vibratory Downward Motion SummaryThe .maximum displacement (y^) is the total downward

distance traveled by the plunger in the stimulator. The plunger then starts its uninterrupted travel back up to stimulate the arm.

The displacements (yg) and their respective PW's are plotted (Fig, A-4) and approximated by. two straight lines. This plot shows the nonlinearity of the stimulator displacements for linear pulse increments.

Analysis of Vibratory Upward Movement The analysis of the upward movement of the magnetic

plunger can best be analyzed by using kinetics, The plunger will travel from the maximum displacement position (y^) upward until it strikes the arm. The plunger will then transfer its kinetic energy into stimulation of the arm and having completed a full cycle„ start a downward movement.

It is now of interest to determine the kinetic ener­gy (T) transferred to the arm. for the following JND pulse widthss 5 .5 , ?,0, 8,5s> 10,0 and 11,5° 7The position of the plunger (Fig, A-5) initially is at a displacement (yg). The spring is compressed and the plunger velocity is 0, When the plunger starts its travel upward, the force doing the work is the spring force, (F = kx), The work done during the plunger travel to the arm is 5

PULSE

WIDTH

(ms)

11.5-11.0-

10.0-

9 .0 -

8.0 -

7.0 -

6.0 -

5.5 -

T -if-.12 .14 . 1 6 .18 2.0PLUNGER POSITION - y2 (inches)

2 ! 2

Fig. A-4 Nonlinear Plunger Displacement Approximated by Two Line Segments 00

ON

87

DISPLACEMENT (y)L.

PLUNGERCAVITY

SPRINGioZ4-1

/ v mw

POSIT ION OF ARM

PLUNGER

Fig. A-5 Diagram of Plunger Position

y2ky dy = ik(y2)2 0

This work is then equal to the gain in kinetic energy of the plunger which is transferred to the arm. The computed kin­etic energies with their respective JND pulse widths (Table A-3) are plotted graphically (Fig. A-6).

The energy transferred to the arm is nonlinear (Fig. A-6). The maximum energy transferred is 1.79 x 10"^ ft-lb for the 11.5 ms pulse and the minimum is .585 x 10""

ft-lb for the 5*5 ms pulse. To design for equal increments of energy between JND's, the energy between maximum and

88

Table A-3 Plunger Kinetic Energy arid Maximum Displacements for Just Noticeable Differences

JND PW (ms)

* 2(in)

TORQUE (FT-LB x 1CTJ)

5.5 ,122 00

7,0 ,151 oON00

8,5 • ,177 1 , 2 3 0

O o ,198 i , 54011,5 ,214 1,790

minimum pulse was divided to provide equal increments be­tween energy levels as followss <,585e a886» lo!9s 1 = 49and 1,79 (ft-lbs, x 10“3).

These energy levels were then used to compute the respective displacement (yg) and pulse width associated . with each level (Table A-4)e The data is plotted as addi­tional information (Fig, A-6)„

.ConclusionsThe data (Table A-4) was used as a departure point

for determining the JND's in Chapter 3» The analysis does not take into consideration any losses due to damping and the assumption of a constant current induces other errors

KINETIC

ENERGY

- FT-LB

x 10

“ENERGY LEVEL 1.791.9 —

ENERGY LEVEL 1.49

ENERGY LEVEL 1.19

ENERGY LEVEL .886 175

ENERGY LEVEL.585 ^.155

122

1614 18 2.2.12 2.0.1PLUNGER DISPLACEMENT - (in)

Fig. A-6 Energy Transferred to the Arm versus Plunger Displacement CDNO

90Table A~^ Just Noticeable Difference Pulse Widths and

Maximum Displacements for Equal Energy Increments

JND PW (ms)

yp(in)

TORQUE „ (FT-LB x 10~^)

5o5 = 122 00XT\7o0 = 152. = 8868„3 .175 1 = 1909.7 .195 1=490

11.5 .214- 1 = 790

into the calculations0 However„ the analysis does provide the designer an understanding of the nonlinear operation of the stimulatoro

LIST OF REFERENCES

Bach-y-Rita, P., and C. C. Collins, Seeing-Eye Backpack, Newsweek, 108, November 19&9.

Brugler, J . S., and W . T . Young, Reading Aid for the Blind, Electronics World, 48-50, 91 * November 1969.

Burr-Brown Research Corporation, Handbook of Operational Amplifier Active RC Networks, 1966.

Burr-Brown Research Corporation, Handbook and Catalog of Operational Amplifiers, 1 9 6 9.

Lawrence, L. G ., Communications via Touch, Electronics World, 33-34, 80, May 1968.

McRae, L. P. Tactile Perception of ElectronicallyTransformed Auditory Spectra, University of Arizona Dissertation, 1 9 6 8.

Wilsey, R. E. Series Active Filter for an Artificial Ear, Self Organizing Systems Lab, Report Number 0001,2? April 1 9 6 7.

91