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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.