A STUDY ON STABLE HAPTIC RENDERING METHODS USING FPGA

Student: Trung Hieu Do Advisor: Jee-Hwan RyuBioRobotics Lab. School of ME - Korea University of Technology and Education

Contents Haptic Interfaces and Stability Analysis Review of the Time Domain Passivity

Approach Proposed Methods

Memory-based Method Multi-rate TDPA Method

Experimental Setup Conclusions & Future works References

Haptic Interfaces & Stability Analysis

Overview of Haptic Interfaces

Human Operat

or

Computer-based

VESlow

update rate

EmbeddedHaptic

ControllerFast

update rate

hx

hf vef

vex

10-100 Hz1-10kHz

MasterDevice

mx

mf

Assumption: Virtual Objects are Static & Passive

MasterDevice

Human Operat

or

Computer-based

VESlow

update rate

hx

hf

vex

vef

N. Diolaiti, G. Niemeyer, F. Barbagli, J. Kenneth Salisbury, Jr, ”Stability of Haptic Rendering: Discreatization, Quantization, Time-Delay and Coulomb Effects,”  IEEE Transactions on Robotics, 22(2): pp. 256-268, April 2006.

Zero Order Hold & The Effect of Discretization

Analog

t

f

Unstable Behavior of Haptic Interface

102.425 /

ve

ve

T msk kN m

Review of the Time Domain Passivity Approach

Time Domain Passivity Approach

Passivity Observer (PO):

Passivity Controller (PC):

Human Operator

MasterDevice

Computer-based

VEPC PO

pcf

mx

mf vef

vex

10-100 Hz

TDPA

Ideal Behavior of TPDA Method

Block Diagram Conventional TDPA

method

POUpdate PO

PC

Clock signal

Reset PO

Conv. TDPA Stability Controller

Update PC

Noisy Behavior of Conventional TDPAJ-H. Ryu, B. Hannaford, D-S. Kwon, and J-H. Kim, “A Simulation/Experimental Study of the Noisy Behavior of the Time Domain Passivity Controller,” IEEE Trans. on Robotics, Vol. 21, No. 4, pp. 733-741.

Noisy Behavior of Conv. TDPA

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ve

ve

T msk kN m

Block Diagram FPGA-based TDPA

PO

Update PO

PC

Reset PO

FPGA-based TDPA Stability ControllerMotion Detector

Update PC

Reset PO

1. Irregular activating method2. Increase activating speed of PC3. Reduce generated energy

B. Han, J-H. Ryu “An Injecting Method of Physical Damping to Haptic Interfaces Based on FPGA,” Proceedings of the International Conference on Control, Automation and Systems (ICCAS 2008), Seoul, Korea, pp. 1835-1840.

Stable Behavior FPGA-based TDPA 102.425 /

ve

ve

T msk kN m

Noisy Behavior in Stiffer VE104.85 /

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T msk kN m

Memory-based method

Proposed methods

Idea of Memory-based Method

Pressin

g

Releasi

ng

Position

• Memorize the pressing forces• Use pressing forces as boundaries for releasing forces• VE characteristics changes when releasing.• However Pressing period is more important for human feeling.

Block Diagram Memory-based Method

Select

Switch

Data

Address

R/W

Memory

Direction Detector

Memory-based method Stability Controller

Stable Behavior Memory-based Method

104.85 /

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ve

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Slow Interaction Behavior Memory-based

method102.425 /

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ve

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Proposed MethodsMulti-rate TDPA method

Multi-rate Haptic

Computer-based VE0.1kHz

Multi-rate Haptic

Controller10kHz

10kHz sample rate

Master device

FPGA

Analog

t

f f

0.1kHz sample rate

f

t t

Human Operato

r

tx

tf

Multi-rate Haptic Interpolation Method

M. C. Cavusoglu and F. Tendick, "Multirate Simulation for High Fidelity Haptic Interaction with Deformable Objects in Virtual Environments," in Proceedings of the IEEE International Conference on Robotics and Automation, 2000, pp. 2458-2465.

F(t)

Behavior of Multi-rate Haptic

Fm[N]

Activity of Multi-rate Haptic Interface

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ve

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Active period

Passive period

Activity of Multi-rate Haptic

Multi-rate haptic can’t guarantee Stability

TDPA method

Generated energy:

Multi-rate TDPA

Computer-based VE

0.1kHz

Multi-rateForce

estimator10kHz

Time Domain Passivity Controlle

r10kHz

Human Operator

FPGA

Masterdevice

tf

tx

Block Diagram of Multi-rate TDPA

FPGA-based Haptic Controller

Force interpolator

PC-based VE

Down sample

Encoder reader

Multi-rate TDPA Stability Controller

Conv.TDPAor

event-based TDPA

tF

Dissipitation of Generated Energy

PC activated

Stability of Multi-rate TDPA104.85 /

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ve

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Slow Interaction of Multi-rate TDPA

104.85 /

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Experimental Setup

Haptic System

Human operator Motor driverMechanical

interface

Master Device

FPGA-BasedHaptic ControllerPC-based VE

Physical interaction

Virtual Interaction

Software Architecture

Stability Controller

PC-basedVE

0.1kHz

PI Current Controller

50kHz

Position counter

Elapsed timer

Directiondetector

Encoder reader

A phase

B phase

Position

PWM output

Measured force (current)

FPGA-based haptic controller

PWMgenerator

FIFO data acquisition

5 kHz

TCP/IP

Parrallel, complicated, flexible, high-speed and simultaneous tasksThe necessity of FPGA technology.A DSP/MCU-based system is possible but difficult to realize.

Conclusions & Future Works

Maximum VE Stiffness

VE

Conclusions MethodsFeatures

FPGA-based TDPA Memory-based Multi-rate TDPA

Performance Worst performance Better performance Best performance

Range of impedance Lowest max. stiffness Higher max.stiffness Highest max.stiffness

Noise behavior Noise behavior Less noise behavior Least noise behavior

Distortion (VE) When activity detected

When releasing force higher than pressing force

Interpolation&When activity detected

Conservativeness No No Assumption of slowly change VE

Update method Irregular updatefast interupt

Irregular updatefast interupt

Regular update

Algorithm comlexity Simple Simplest Complicated

Others Need high-speed RAM (Random access memory)

Future Works Apply proposed methods to moving and

time varying VE. Improve performance of methods: less

noise, wider range of impedace, more general cases.

Implement to Teleoperation. Implement methods in lower cost

devices: MCUs or DSPs.

References M. C. Cavusoglu and F. Tendick, "Multirate Simulation for High Fidelity

Haptic Interaction with Deformable Objects in Virtual Environments," in Proceedings of the IEEE International Conference on Robotics and Automation, 2000, pp. 2458-2465.

B. Han, J-H. Ryu “An Injecting Method of Physical Damping to Haptic Interfaces Based on FPGA,” Proceedings of the International Conference on Control, Automation and Systems (ICCAS 2008), Seoul, Korea, pp. 1835-1840.

J-H. Ryu, B. Hannaford, D-S. Kwon, and J-H. Kim, “A Simulation/Experimental Study of the Noisy Behavior of the Time Domain Passivity Controller,” IEEE Trans. on Robotics, Vol. 21, No. 4, pp. 733-741.

N. Diolaiti, G. Niemeyer, F. Barbagli, J. Kenneth Salisbury, Jr, ”Stability of Haptic Rendering: Discreatization, Quantization, Time-Delay and Coulomb Effects,” IEEE Transactions on Robotics, 22(2): pp. 256-268, April 2006.

J-H. Ryu, B. Hannaford, D-S. Kwon, and J-H. Kim, “A Simulation/Experimental Study of the Noisy Behavior of the Time Domain Passivity Controller,” IEEE Trans. on Robotics, Vol. 21, No. 4, pp. 733-741.

Implementation on High-Stiffness Moving Objects

, 00, 0eF k e e

F e

F F

Master 1 Master 2

Passivate Object

Virtual object

THANK YOU