Haptic Device Design: Theory CPSC 599.86 / 601.86 Sonny Chan - - PowerPoint PPT Presentation

Haptic Device Design: Theory

CPSC 599.86 / 601.86 Sonny Chan University of Calgary

Course Project Presentations

• I am working out logistical

details for equipment, etc.

• Hopefully I will have specific

instructions for you by Wednesday’s class

• Does anyone need me to

provide a computer for you?

Electro-Mechanical Devices

• A haptic device is an electro-mechanical, or mechatronic, assembly

A ROBOT!

The Haptic Device

• We’ve treated this component

as a black box through this course until now…

• position in,
• force out,
• rest was “magic”
• Let’s take a look inside!

Device Controller

position +

• rientation

force + torque

Force Output

Computer DAC Amplifier Motor

Digital-Analog Converter

Interfaces directly with computer

DAC

(Sensoray 826) 10110…

Current Amplifier

Supplies desired current to motor

Amplifier

DC Motor

Converts current to torque

τ = kT I

Motor

Mechanical Assembly

[From J. Forsslund et al., Proc. Tangible & Embedded Interfaces 2015.]

Position Input

Computer Counter Encoder Motor

Optical Quadrature Encoder

Counts rotational ticks in either direction

Encoder

Quadrature Counter

Communicates rotation back to computer

Counter

(Sensoray 826) 10110…

Components of an Impedance Haptic Device

Computer Counter Encoder Motor DAC Amplifier

… plus a few mechanical links

Position / Orientation

• Encoders and counters tell us

the rotational angles of our motors and joints

• Great! But how do I know where my

manipulandum (end-effector) is?

• Determine spatial position using

forward kinematics

Device Controller

position +

• rientation

force + torque

Kinematics of a Serial Manipulator

Known: Determine: `1, `2, ✓1, ✓2 x = (x, y) x = (`1 + `2 cos ✓2) cos ✓1 − `2 sin ✓2 sin ✓1 (`1 + `2 cos ✓2) sin ✓1 − `2 sin ✓2 cos ✓1

Kinematics of a Parallel Manipulator

`0 r1 r2 θ1 θ2 x = ??? (0, 0)

Force / Torque

• Recall that we can command

each of the motors to exert a desired torque

• How do we translate motor

torques into an output force vector?

Device Controller

position +

• rientation

force + torque

The Kinematic Jacobian Matrix

• Relates derivates of generalized coordinates to cartesian coordinates:

x = (`1 + `2 cos ✓2) cos ✓1 − `2 sin ✓2 sin ✓1 (`1 + `2 cos ✓2) sin ✓1 − `2 sin ✓2 cos ✓1

• J = dx

dθ = "

∂x ∂θ1 ∂x ∂θ2 ∂y ∂θ1 ∂y ∂θ2

# =  −(`1 + `2c✓2)s✓1 − `2s✓2c✓1 ... (`1 + `2c✓2)c✓1 + `2s✓2s✓1 ...

• τ =

τ1 τ2

• = JT F

principle of virtual work

Summary

• Haptic devices are made of motors, encoders, data input/output electronics,

and mechanical linkages

• Forward kinematic analysis allows us to determine the end-effector position

(and orientation) from measured joint angles

• The kinematic Jacobian, along with the force/torque relationship equation,

allows us to command a force (and torque) vector at the end-effector

Which one is a haptic device?

Human Factors

What makes a good haptic device?

Tenets of Haptic Interfaces

• Free motion should feel free
• Rigid objects should feel stiff, and not soft
• The user should not be able to go through rigid objects
• The user should not feel unintended vibrations
• The interface should be comfortable and ergonomic to use

[From M. Srinivasan and C. Basdogan, Computers & Graphics 21(4), 1997.]

• friction, back-drivability
• force output
• rendering
• stability
• design

Motors & Gearing

• Larger motors can exert more

force, but have more inertia

• affects back-drivability
• Gearing a motor can provide

significantly more force

• creates friction, backlash
• often lose back-drivability

5 10 15

Encoders

• High-resolution encoders can be

extremely expensive

• Insufficient encoder resolution

can be detrimental to stability

• Why?

Bearings & Linkages

• High quality bearings on joints

will reduce friction

• Very rigid link materials can

improve stability, but may add unwanted inertia

• Long links may reduce force
• utput capacity
• mechanical lever-arm

10-3 10-2 10-1 100 101 10-1 100 101 102 103

Human Dynamic Range

[Figure adapted from original by Lynette Jones, MIT]

Force (N) Displacement (m)

driving a car timed dexterity tests micro- assembly / surgery typing

Motor Dynamic Range

• Measured as Fmax : Fmin
• Human:
• Good motor:
• Maxon, $150
• Motor:
• Mabuchi, $3.99
• Major design challenge!

>1000 : 1 80 : 1 10 : 1

Consequence: no single haptic interface can suit all tasks and needs

And remember:

Be mindful of ergonomics!

Haptic Workstation - CyberGlove Systems