CURSO-20061.1 Topics about of design and construction of experimental parallel robots in DISAM (based on examples) Roque Saltaren Universidad Politécnica

CURSO-2006 1.1

Topics about of design and Topics about of design and construction of experimental construction of experimental parallel robots in DISAM parallel robots in DISAM (based on examples)(based on examples)

Roque Saltaren Universidad Politécnica de Madrid, SPAIN

[email protected]

1.2Universidad Politécnica de Madrid

ContentsContents

1. Relevant characteristics of some parallel robots develops for biomechanics applications

2. Kinematics modeling and design considerations3. Dynamics modeling and design considerations4. Mechanical design and construction5. Hardware and control

Hardware architecture based on PC-104/PowerPC + LAN

Hardware architecture based on multiaxis card Hardware architecture based on dSPACE

6. User interfaces7. Real time operative systems (RTOS).8. Integration9. Conclusions: Real prototypes or scale prototypes:

The best techniques.


……Relevant characteristicsRelevant characteristics

Spherical pivot parallel platforms for robots (3RPS, 3PRS and 3RRS)

Applications: Prosthesis, endoscopies, humanoid necks, shoulders and eyes

Three types of kinematics configurations: End effectors articulate by

spherical joints

Short radius of turn

Reduce work space

Robustness

Easy of assembly and

machining



…..Spherical pivot platforms for robots

Mechanical parts can impose limitations:

Standard spherical joints works with: +/- 30º

Special spherical joints can allows +/- 90º

Actuators (better options)

Powering by cable

High technology cables: FORTATECH

(very good option!)

Powering by ball screws and servomotors

SKF (low cost) + Maxonmotor;

SteinMeyer (high cost) + Maxonmotor

(micro ball screws : 3 mm. aprox 350 eur.)

Powering by servomotors (aprox.



…..The 3 RRR configuration The Agile Eye

topics Easy of machining Servomotor + gear

reductor + arm = high torque

Very fast


…….Relevant characteristics.Relevant characteristics

…3UPU platforms Based on linear actuators With special universal joints =

high work space Singular configurations Very simple, except by the

rings, that need take account de P point (the P point is allow machining the rings with inclined planes to aligning the axis of the universal joints

Estimated costs, for example: Maxonmotor 20 W + Gear

Reductor Maxon + SKF ball screw + machining = 1000 eur.Rings: less of 150 eurosAmplifiers Maxon : 170 eur.


…….Relevant characteristics.Relevant characteristics

2UPS-1RU Chen platform

The more robust Eccentric rotation point! Two UPU limbs One RU limb (required a

special universal joint) Extreme orientations What is a special universal

joint?



Example-1.Performance evaluation of spherical parallel platforms for humanoid robots



Example-1.…Performance evaluation

Goals: Allows the work space of the neck or shoulder !












Example-1.…What is the better option ?



…..Stewart-Gough parallel robots

Mechanical parts can impose limitations:

Standard spherical joints works with: +/- 30º

Special spherical joints can allows +/- 90º

Actuators (better options!)

Powering by ball screws and servomotors

SKF + Control Techniques

Low cost: Ball screws (medium precision)

High cost: Ruler screws: very good

precision (aprox. 350 eur.)

Control Techniques servomotors

Examp. UNIMOTOR + Amplifier (800-

2000 eur.

An experimental medium size S-G platform can

to have a cost of: 10.500 eur.

An experimental small size S-G platfor can to

have a cost of: 6.000 eur.



…..Stewart-Gough parallel robots

How allows the maximum work space ?

Changing the spherical and universal joints by special joints!!



….How allows the maximum work space ?


..Kinematics modeling and design consideration..Kinematics modeling and design consideration

Two problematic aspects: Singularities (restrictions

over the work space!!) Don’t forget the theory!

(Hunt, Fletcher, Di-Gregory, etc.)

Modeling with screw based jacobian

Path planning control in base to the Conditioning Index CI, and Global Conditioning Index GCI

Direct kinematics solution: Numerical methods

based on multibody mechanics and Newton-Raphson methods!!

Design considerations: GCI index very useful to

know and understand the machine


……Dynamics modeling and design considerationsDynamics modeling and design considerations

For a Stewart-Gough platform: Dynamics modeling:

Multibody dynamics: we are use two ways:1. Programming with ADAMS

(after of know how program with ADAMS, very fast develops!) the problem is that the ADAMS language is not easy!!

2. Programming with Matlab: Is better, but is necessary to have a very good acknowledges on multibody dynamics!! and to have some experts in the group!

3. For real time RT, we works in multibody dynamics for RT: we used OOD, C++ + UML + RTLinux.


Mechanical design and constructionMechanical design and construction

The first prototype: Is necessary to have a PERFECT first experimental prototype??. Usually not!!

In many occasion we need first demonstrate some hypothesis!

In many occasion we need allows that the control and software run!

Really we need a prototype in real scale?? Not, we are sure that in many occasions to

demonstrate the hypothesis and develop computational algorithms is sufficiently to work with scaleable prototypes!!.


……Mechanical design and constructionMechanical design and construction

A case. We are developing an underwater parallel

robot We should optimized the useful internal space to

assembly the control and power hardware, because this:

The geometrical form of the robot hull is very complicated

The length of the hull is diffuse because we will need aggregate more hardware in the future

The machining costs can be high if we used an adjusted geometry to the hardware dimensions


……Mechanical design and constructionMechanical design and construction

The solution adopted. We decide use an engineering

plastic with non-hygroscopic performance, soldering and adhesive good properties (many plastics can not solder!!)

The plastic selected is appropriate to machining (for example, we can use joints with mechanical screws)

We use Delrin Acetal plastic (Du Pont)

The plastic weight 1/8 part of the steel!!

The design limit the machining to 2 ½ D

The design is modular We can use adhesives Machining with water jet cutting Assembly with mechanical

screws + GORE Tex seals and adhesives


Hardware and controlHardware and control

In many applications is sufficiently with the next hardware architecture: Based on PC-104 + RS 485

LAN + Ethernet Multiaxis control base on

multipoint RS-485 Duplex Network to 115200 Bps.

Capacity to control many axis (256)

Develop below QNX real time system or RT Linux

Flash SD memory (2 G) And the better!!: less of 1000

eur We used this card to control a S-G

parallel robot with 12 Step servomotors.

We used Stepper motors to avoid used encoder and its electric cables

The servomotors power and control hardware are prepared to connect in Network (Duplex RS-485) !!!

PC compatible Single Board Computer with 133 MHz AMD 586 processor.32-64 MB SDRAM 10/100 Ethernet PCMCIA socket Compact Flash socket Optional A/D & DAC 2 COM ports 23 DIO PC/104 expansion bus 2 MB Flash drive Technologic Systems, Incorporated16610 East Laser Drive, Suite 10Fountain Hills, AZ 85268480-837-5200FAX [email protected]://www.embeddedx86.com/

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CURSO-20061.1 Topics about of design and construction of experimental parallel robots in DISAM (based on examples) Roque Saltaren Universidad Politécnica