Haptic interfaces (HI-s)

Daniela ConstantinescuMechanical Engineering

Objective

Introduce haptics terminology.Overview interface designs. Clarify performance specifications.

Lecture overview

Introduction to haptics.Haptic interfaces (HIs):

Mechanisms.Actuation.Sensing.

Performance measures.Design challenges.

Introduction to haptics

What is haptics?What are HIs?Applications.Terminology.Human haptics.Computer haptics.

What is haptics?Touch & manipulation of virtual environments (VEs).

User Haptic interface or device (HI or HD)

haptesthai = to touch

Virtual Environment (VE)

What are HIs?

Robotic computer interfaces:Mechanism.Actuators.Sensors.Control algorithms.

Mechatronic systems.Purpose: realistic feel & touch of virtual objects.Means: exchange of energy

-> stability very important.

Applications

Prof. Grigore Burdea, Computer Engineering, Rutgers Universityhttp://www.caip.rutgers.edu/vrlab/demos/ball_demo.html

Terminology

Human haptics Machine haptics(hardware)

Computer haptics(software)

psychology mechatronic design control, real-time simulation,

computer graphicsmechatronic design

Human haptics

Why care? To know:How good the HIs need to be.How good the simulations need to be.How to build useful simulations.How to use VEs for psychophysical/perceptual tests.

Human sensing (I)

Kinesthetic/proprioception/force:Sensors in muscles, tendons & joints.Manipulation.Forces.

Cutaneous/tactile:Sensors in the skin.Surface texture.Vibrations. Prof. Susan Lederman, Psychology, Queen’s University

http://psyc.queensu.ca/~cheryl/labpage.html

Human sensing (II)

Vibrations up to 400Hz.Force resolution: 0.06N.Grasping force: 400N.Just Noticeable Differences (JND): vary for each joint 0.8o – 6.8o.

Movement & position – threshold depends on velocity & whether the muscle is contracted.

Computer haptics (I)

From: Salisbury, Conti, Barbagli. “Haptic Rendering: Introductory Concepts”, IEEE Computer Society Magazine, pp. 24-32, 2004.

Computer haptics (II)

Control:Stability.Presence (transparency).Speed (> 500-1000 Hz).

VE simulation:Speed.Accuracy.

Haptic interfaces

Types of HIsKinesthetic HIs:

Mechanisms.Actuators.Sensors.

Tactile HIs:Principles.Actuators.

Types of HIs

Kinesthetic.Force, position.Manipulation.

Tactile.Vibration.Touch.

Prof. Vincent Hayward, CIM, McGill Universityhttp://www.cim.mcgill.ca/~haptic/devices.html

SensAble’s Omni

Mechanisms

Degrees of Freedom (DOFs).Grounded mechanisms:

Linkage topology.Wire-based mechanisms.Arm-based mechanisms.Body-based mechanisms.

Ungrounded mechanisms.

DOFs (I)

Planar HIs

Prof. Vincent Hayward, CIM, McGill Universityhttp://www.cim.mcgill.ca/~haptic/devices.html

Prof. Tim Salcudean, UBChttp://www.ece.ubc.ca/~tims/projects.htm

2 DOFs – point interaction 3DOF – body interaction

DOFs (II)

Spatial HIs

Quanser ForceDimension MPB Technologies

5 DOFs 6 DOFs 7 DOFs

Linkage topology

Serial linkage.Lower force.Larger workspace.

Parallel linkage. Higher force.Smaller workspace.Higher precision.

SensAble’s 1.5 Phantom

Rutgers Ankle

Wire-based mechanisms

More complex control.Enables grasping.

Tokyo Institute of Technology

Arm-based mechanisms

Sarcos Arm, Prof. John Hollerbach, University of Utah

Prof. Jacob Rosen, University of Washington

L-EXOS, Prof. Massimo Bergamaso, Scuola Superiore Sant’Anna, Italy

Body-based mechanisms

Sarcos treadport - slope, inertia, unilateral constraints.

Sarcos treadport, Prof. John Hollerbach, University of Utah

Ungrounded mechanisms

Rutger’s RMII Haptic Interface, Prof. Grigore Burdea

Immersion’s Cybergrasp

Actuators (I)

Electric:Friction, damping.Cogging (torque ripple).Stall torque.

Pneumatic:Friction.Bandwidth.

Magnetic levitation:Workspace.

Rutgers RMII Haptic Interface

UBC’s Magic Mouse

Actuators (II)

DOF of actuation:Sensing/actuation asymmetry?

3DOF – point interaction 6DOF – body interaction

ForceDimension’s 6DOF Haptic InterfaceForceDimension’s 3DOF Haptic Interface

Sensors

Need to measure:Position.Velocity.Force.

Magnetic: Hall effect.Optical: phase quadrature.Inertial – gyroscopic.Mechanical – most common in typical His.

Tactile actuation

Cutaneous stimulation:Pneumatic.Vibrotactile.Electrocutaneous.

Surface slip.

Skin stimulation (I)

Pneumatic.Air jets: non-invasive, non-painful, heavy.Air rings (cuffs): circular, inflatable device.Air pockets: inside a glove.

Localized geometry not easy to display.

Skin stimulation (II)

Vibrotactile:density?, high power, pain?

Solenoid + voice coil. Shape memory alloy (SMM)

Prof. Robert Howe, Harvard UniversityProf. Robert Howe, Harvard University

Skin stimulation (III)

Electrotactile:small currents through electrodes on skin.

Dr. Kurt Kaczmarek, University of Wisconsin, Madison

Surface slip

Prof. Vincent Hayward, McGill UniversityProf. Allison Okamura, Johns Hopkins University

HI performance measures (I)

Mechanical design Workspace:

Accessibility – can reach.Dexterity – can move in

all directions.Isotropy – equal force/velocity capability in all directions.

Prof. Grigore Gogu, IFMA, Blaise Pascal University, France

HI performance measures (II)

Mechanical design:Inertia - low.Backdrivability – high.

May be different for each DOF.

Friction & damping - low.Damping necessary for stable interaction.

Backlash – low.

HI performance measures (III)

Motors:Maximum exertable force – high.Continuous force – high.Minimum displayed force – low.Dynamic force range – high.

Sensors:Precision & repeatability - high. Position resolution – high.

HI performance measures (IV)

Control-related:Stiffness – high.Bandwidth – high.

Latency – low.Slow VE (computational delay).Remote VE, multiple users (communication delay).

BKTb +>2

Design Challenges

Workspace.Kinesthetic + tactile feedback combined.Cost.

Summary

HIs = robotic computer interfaces.Enable users to feel & touch VEs.Good feel:

HI design.Control design.VE design.

Many existing HI designs.Significant challenges ahead.