csit.selu.educsit.selu.edu/~csit/seniorprojects/SeniorProjects2016/... · Web viewRather than making the lead attachment near the sensor, the Piezo polymer tail extends from the active

“Assessment of Applications of Force Sensing Materials in Robotics”

ET-493_01Senior Design I

Cris Koutsougeras / Junkun MaAdvisor: Mohammad Saadeh

Spring 2016

Andrew AllemondW0511221

Mechanical Engineering TechnologyBlake Dufour

W0442892Mechanical Engineering Technology

ET-493_01 Andrew AllemondSenior Design I W0511221Spring 2016 Blake DufourCris Koutsougeras / Junkun Ma W0442892

Table Of ContentsAbstract…………………………………………………………………………………………....3

Introduction………………………………………………………………………………………..4

Background………………………………………………………………………………………..5

Piezoelectricity………………………………………………………………………………….6-7

Piezoelectric FDT Sensor ……………………………………………………………………....8-9

Sensor Sampling Materials…………………………………………………………………...10-13

Timeline………………………………………………………………………………………….14

References………………………………………………………………………………....……..15

Southeastern Louisiana University500 Western Ave. Hammond, LA 70402

College of Computer Science and Industrial Technology Department of Engineering Technology


Abstract:

Create a tactile sensor system into two realistic-looking artificial skin gloves. These

artificial skin tactile sensors will use suitable technologies (Research is needed in order to

determine the best suitable technology needed) to measure applied force at multiple points on

each glove. The sensors will have to be placed in certain areas of the glove in order to receive a

full reading of the force on the entire hand. The use of an Open Source Program will be needed

in this step (Arduino or Raspberry Pi). The gloves will be created using silicone rubber to

simulate both the texture and look of human skin, while maintaining both flexibility and

durability (research will be needed in order to determine a suitable silicone rubber product with

molding capabilities). Sensor data will first be sent via USB to a computer, where a graphical

user display will be created to show the tactile information in real time. The use of an Open

Source Program will be used in this step (Research still needed on a suitable program for this

step). Once the gloves are completed, research will be needed in order to wirelessly record the

data (XBee’s or Raspberry Pi’s equivalent wireless communication).




Introduction:

With technology making ever more advanced mechanical manipulators possible. The

field of robotics now has a need for tactile sensors that are more advanced than those already in

society. Current tactile sensors consist mainly of rigid or semi-rigid flat sheets that must be

conformed to flat grippers. Recent studies have found that greater handling can be achieved by

using deformable grippers in order to maintain more contact area and contact friction with the

object, much as human skin is able to deform around a hard object. To create a tactile sensor

system out of materials not used in robotics today, while sustaining the ability for precise

measurement would be beneficial to many different fields of science and engineering.




Background:

Often times sensors are used to quantify information about the environment, such as telling

temperature or force. Sensors are sometimes used to relay information from an inaccessible location, such

as beyond a wall or inside a chamber. Many times they provide information beyond the capability of

human senses, such as extremely high speeds. In other cases, the sensor can provide a range of data about

the measurement, such as the magnitude of a force value relative to a known measurement. Perhaps the

most basic sense, but also the most useful type of sensor is one that provides input about pressure or

force. Sensing the magnitude of the force via touch is crucial when dealing with fragile objects, such as

picking up an egg or screwing in a light bulb. If too great a force is exerted on a fragile object, the object

is likely to break. Today’s society has relied on resistive force sensing modules in robotics, which has

limited the advancements of sensing. The use of a new sensing ability will bring light to the advancement

in this field of study.




Piezoelectricity:

Piezoelectricity was first discovered by Pierre and Jacques Curie in 1880 when they found

electric surface charges appearing on specially prepared crystals (tourmaline, quartz, topaz, cane sugar,

and Rochelle salt among them) when subjected to a mechanical stress. Scientifically, the relationship

between applied forces and the resultant responses in piezoelectric materials is caused by the atomic

lattice structures of the material. In piezoelectric materials, this lattice structure has an essential unit or

“cell” of a cubic or rhomboid cage made of atoms. Inside this cell is a single semi-mobile ion which has

several stable quantum states. This post-ion state of the ion can be caused to shift by either deforming the

cage through applied strain or by applying an electric field.

The relationship between applied force and the resultant response depends on the piezoelectric

properties of the ceramic, the size and shape of the piece, and the direction of the electrical or mechanical

load/stress. In order to characterize a piezo, a number of property coefficients are defined, many of which

feature single or double subscripts that link electrical and mechanical quantities. The first of these

subscripts indicates the direction (as defined in the Figure above) of the electrical field associated with the

voltage applied, or charge produced. The second subscript gives the direction of the mechanical stress or

strain. The most important property constant to discuss is the voltage coefficient, “G,” which is used to




relate the electric field produced by the mechanical stress, having units of volts/meter per Newton/square

meter. The expected output voltage can be calculated by multiplying the electric field by the thickness of

the ceramic between electrodes.

Piezoelectric FDT Sensor:




The “F” in FDT Series stands for “‘Flexible Leads”. These are rectangle elements of Piezo film with silver

ink screen printed electrodes. Rather than making the lead attachment near the sensor, the Piezo polymer tail extends

from the active sensor area as flex circuit material with offset traces. This gives a very flat, flexible lead with a

connector at the end. The FDT elements are available in a variety of different sizes and thicknesses. They are

available without a laminate (FDT), with a laminated (0.005” mylar) on one side (FLDT) or with tape release layer

adhesive (FDT with adh) in the sensor area.

The connector pins on the FDT sensors can be directly soldered to a PCB with a reasonable level of care.

This component cannot withstand high temperatures (>80°C) and therefore soldering of the pins to a PCB must be

done quickly. A heat sink clamped to the interface area between the film and the crimps will take the heat away

from the film. Pre-tin the pins and then quickly solder them to the board. Do not allow the soldering iron to touch

the film and do not use a dwell time of more than 5 seconds on the pins. Low temperature solder can also be

used.

The idea of using piezoelectricity as a force sensor is to use the electrical charge generated when

polyvinylidene fluoride (PVDF) film is deformed on impact, i.e. pressed, bent, etc. The measured voltage is

proportional to the applied force in an area of the film. These come in different sizes and thicknesses to fit the

application at hand. The physical dimensions and properties of the films available to us are listed in reference to

each individual sensor. Piezoelectric materials are anisotropic, meaning that the response to pressure will be

dependent on the axis on which the pressure is applied. As we will be applying pressure on the thickness of the film,

i.e. the third axis the voltage will be directly proportional to the force applied.

The lower-right inset shows that the time

sequential electrical output was 11 mV at less than 30 kPa pressure. We applied the pressure for 2 s and Southeastern Louisiana University

500 Western Ave. Hammond, LA 70402 College of Computer Science and Industrial Technology

Department of Engineering Technology


measured the electrical output under six different pressure conditions. The pressure range converted from

the applied force was calculated as a range from 3 kPa to 30 kPa. A gentle touch, reportedly, refers to a

pressure below 10 kPa [2], which is included in the pressure range we measured. For the discrete run, we

acquired a linear sensor response from 3 kPa to 30 kPa pressure ranges and the output voltage was

linearly proportional to the applied pressures from 1.8 mV to 11 mV. The upper-left inset shows the P-E

hysteresis of PZT films, showing good ferroelectric properties.

Sensor Sampling Materials:




A multiplexer, or mux, is another common component of many circuit designs. A multiplexer is

an electronic device capable of selecting one out of a number of analog or digital input signals and

forwarding that signal along its output line. As a general rule, multiplexers come with 2n input lines,

requiring n select lines which are used to choose which input line to forward to the output. A multiplexer

thus makes it possible to send several signals worth of data over a single communication line, rather than

having one line per device. A multiplexer will be used in this project in order to read multiple

Piezoelectric sensors simultaneously throughout the many different data analysis components of the

project.

Operational amplifiers are high-gain electronic amplifiers feature a differential input and usually

a single-ended output, capable of amplifying some voltage hundreds to thousands of times larger than the

voltage difference between the inputs. Ideally, an op-amp has an input offset voltage of zero, as well as

infinite input resistance. While ideal op-amps do not exist in real life, present day op-amps have come so

close to ideal that they can usually be assumed as ideal for analysis purposes. A multitude of circuits can

be created using op-amps, including noninverting amplifiers, inverting amplifiers, differential amplifiers,

adding circuits, and many others, each serving a different purpose. When operating at unity gain (no

amplification), the noninverting amplifier reduces to a voltage follower, where the output voltage is

identical to the input voltage. By using an op-amp to create a voltage follower circuit, a high impedance

input source can be buffered to a low impedance output. When used with a piezoelectric sensor, it allows

for measuring of the voltage difference, while greatly reducing charge leakage.




Invented in 1833 by Samuel Hunter Christie and later improved upon by Charles Wheatstone in

1843, the Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by

balancing two legs of a bridge circuit where one leg includes the unknown component. The main benefit

of the Wheatstone bridge is that it can provide extremely accurate measurements unlike a simple voltage

divider. A Wheatstone bridge’s ability to measure is similar to an original potentiometer; however, its

initial purpose was for soils analysis and comparison.

An example of the Wheatstone bridge is featured in the example above. Rx symbolizes the

unknown resistance to be measured with R1, R2, and R3 are the resistors with a known value of

resistance and R2 is the resistance that is adjustable. The theory states that if the ratio of the two

resistances in the known leg (R2, R1) is equal to the ratio of the two in the unknown leg (Rx,R3), then the

voltage between the two midpoints (Band D) will be zero and no current will flow through the

galvanometer Vg. Therefore, when the bridge is unbalanced, the direction of the current indicates whether




R2 is too low or too high. Since R2 is variable, the galvanometer reads zero once there is no current

passing through. A galvanometer is highly accurate. Thus, if R1, R2, and R3 are known to be highly

accurate, then Rx can be found to the same level of accuracy. Any small changes in Rx are easily and

quickly detected.

At the point where balance is achieved, the ratio of R2/R1=Rx/R3 or it can be done as Rx=R2/R1

x R3. In other words, if R1, R2, R3 are known and R2 is not adjustable, the difference of voltage across

or current flow through the meter can be used to calculate the value of Rx, using Kirchhoff’s circuit laws.

This is used frequently in resistance thermometer and strain gauge measures, since it is faster to read a

voltage level off a meter than to adjust a resistance to zero voltage.

What all of this means is that the Wheatstone bridge demonstrates the concept of a difference

measurement, which can be extremely accurate. Variances on the Wheatstone bridge can be used to

measure capacitance, inductance, impedance and other quantities. The Wheatstone bridge was specially

adapted and the Kelvin bridge was developed from the Wheatstone bridge to measure very low resistance.

This is important because measuring the unknown resistance is related to measuring the impact of a

certain physical event such as temperature, pressure, or force and this allows the use of the Wheatstone

bridge in measuring these elements indirectly. Later developments upon the Wheatstone bridge was

conducted to measure alternating current measurements by James Clark Maxwell in 1865 and again by

Alan Blumlein in 1926.

Processing is an open source programming language and environment meant to create images,

animations, and interactions. Because the Arduino programming environment is based on the Processing

programming environment, Processing was chosen to create a graphical user display. This graphical user

display would enable viewing the data from each sensor in real-time using a computer screen. Several

sample programs included in the Arduino programming environment provided instruction for how to read




data from the serial port using Processing, and a multitude of tutorials on the Processing website provided

instruction for drawing simple shapes for a graphical display.

Timeline:

February 10th – 24th:




Research piezoelectric sensors. Research method for sampling multiple sensors. Research data acquisition method.

March 3rd – 16th:

Order Materials for testing purposes. Research piezoelectric equations.

March 16th – 23rd:

Code microcontroller for sampling sensors. Receiving materials.

March 23rd – April 6th:

Sample sensors for quality assurance. Perform data analysis of sensors. Create graphical display of sensor data analysis.

April 6th – 20th:

Infiltrate sensors into silicone medium. * Perform data analysis of sensors in silicone medium. * Create graphical display of data analysis. *

April 20th – May 4th:

Research live-feed software for graphical display. Code software for live-feed display. Prepare/critique end of semester final presentation.

(* Items are Subject to change)

References:

Analog/Digital MUX Breakout. (2010). Retrieved February 16, 2016, from SparkFun Electronics:




http:// www.sparkfun.com/commerce/product_info.php?products_id=9056

FingerTipMulti-Touch Screen Controller with Ultra-Low Power. (n.d.). Retrieved March 02, 2016, from

http://www.st.com/web/catalog/sense_power/FM89/SC1717/SS990/PF251157

Operational Amplifier Basics - Op-amp tutorial. (2013). Retrieved February 27, 2016, from

http://www.electronics-tutorials.ws/opamp/opamp_1.html

Mancini, R. (2002, August). Op Amps For Everyone. Retrieved January 20, 2016, from Texas

Instruments: http:// focus.ti.com/lit/an/slod006b/slod006b.pdf

Piezo Systems, I. (2008). Introduction of Piezo Transducers. Retrieved January 9, 2016, from Piezo.com:

http:// www.piezo.com/catalog7C.pdf%20files/Cat7C.20,21,22,23,60,61&62.pdf

Stutz, M. (2001). Multiplexers. Retrieved February 16, 2016, from

http ://www.allaboutcircuits.com/textbook/digital/chpt-9/multiplexers /



http://www.allaboutcircuits.com/textbook/digital/chpt-9/multiplexers/



http://www.piezo.com/catalog7C.pdf%20files/Cat7C.20,21,22,23,60,61&62.pdf

http://www.piezo.com/catalog7C.pdf%20files/Cat7C.20,21,22,23,60,61&62.pdf

http://focus.ti.com/lit/an/slod006b/slod006b.pdf

http://focus.ti.com/lit/an/slod006b/slod006b.pdf

http://www.sparkfun.com/commerce/product_info.php?products_id=9056

http://www.sparkfun.com/commerce/product_info.php?products_id=9056

Documents

csit.selu.educsit.selu.edu/~csit/seniorprojects/SeniorProjects2016/... · Web viewRather than making the lead attachment near the sensor, the Piezo polymer tail extends from the active