2. Introduction to Computer Haptics

Transcription

1 2. Introduction to Computer Haptics Seungmoon Choi, Ph.D. Assistant Professor Dept. of Computer Science and Engineering POSTECH Outline Basics of Force-Feedback Haptic Interfaces Introduction to Computer Haptics Reading List Wed EECE 700. Advanced Computer Haptics 2 1

2 Two Primary Types of Haptic Interfaces Force-feedback (Force-reflecting) device Mostly resembles a small robot arm Provide a point (or multiple point) interaction between a user and a virtual environment Can provide kinesthetic and temporal tactile information Tactile pin array An array of closely located actuating pins Can provide spatial and temporal tactile information Wed EECE 700. Advanced Computer Haptics 3 Examples of Haptic Interfaces Force-feedback device Tactile pin array Harvard BioRobotics Lab Omega Device Wed (ForceDimension) EECE 700. Advanced Computer Haptics 4 2

3 Research Issues Computer Haptics Force-feedback device Tactile pin array Device design Computational algorithms for rendering Perception issues O O O O X O Wed EECE 700. Advanced Computer Haptics 5 Classifications of Force-Feedback Devices (1) Degrees of Freedom (DoF) Number of independent directions of a motion Sensing DoF (input DoF) vs Actuation DoF (output DoF) Common force-feedback haptic interfaces has: 2 DoF = 2D force feedback 3 DoF = 3D force feedback 6 DoF = 3D force feedback + 3D torque feedback Wed EECE 700. Advanced Computer Haptics 6 3

4 Examples of Force-Feedback Devices 2 DoFs: Pantograph (McGill Haptics Lab) 6 DoFs: Delta (ForceDimension) Wed EECE 700. Advanced Computer Haptics 7 Classifications of Force-Feedback Devices (2) Mechanical Ground Grounded force-feedback device Desktop devices: PHANToM and Omega Exoskeletons Ungrounded force-feedback device Exoskeletons Wearable haptic interface We will focus on this type of devices. Exoskeleton (PERCRO) HapticGEAR (Hirose et.al) Wed EECE 700. Advanced Computer Haptics 8 4

5 Impedance and Admittance One-Port System Effort (e) Flow (i) Electrical System Voltage Current Mechanical System Force Velocity + e i Impedance: Z(s) E(s) = Z(s) I(s) Admittance: Y(s) I(s) = Y(s) E(s) Wed EECE 700. Advanced Computer Haptics 9 Classifications of Force-Feedback Devices (3) Impedance type Measure velocity We will focus on this type of devices. Command force after multiplying the velocity with desired impedance The device displays impedance. Most desktop force feedback devices are of impedance type. Admittance type Measure force Command velocity after multiplying the force with desired admittance The device displays admittance. A few large force feedback devices are of admittance type (e.g., HapticMaster, FCS System) Wed EECE 700. Advanced Computer Haptics 10 5

6 Outline Basics of Force-Feedback Haptic Interfaces Introduction to Computer Haptics Reading List Wed EECE 700. Advanced Computer Haptics 11 Research Steps in Computer Haptics What haptic effects (preferably specified in the perceptual domain) do you want to create? What force-feedback device are you using? How are you going to devise a computational algorithm that achieves the desired haptic effects with the force-feedback device? Wed EECE 700. Advanced Computer Haptics 12 6

7 Haptic Attributes Haptic attributes of objects and surfaces Geometrical properties Size Shape Material properties Stiffness Hardness Texture Roughness Friction Stickiness Weight Curvature Computer haptics is usually interested in these topics. Haptic perception in space Position Length And more Wed EECE 700. Advanced Computer Haptics 13 Performance of Force-Feedback Device Unfortunately, a force-feedback device is a mechanical system with its own dynamics, and thus an imperfect force generator. Usually, Force command that a haptic rendering algorithm sends to the force-feedback device Force output that the forcefeedback device produces and in Example: PHANToM Force Command And Output for Texture Rendering Force (N) Force Output Force Command turn a user feels Time (sec) Wed EECE 700. Advanced Computer Haptics 14 7

8 Control of a Force-Feedback Device Control of a force-feedback device Minimize errors between force command and output = Maximize the transparency of a force-feedback device Maximize the stability of device control The two goals often impede each other. Lessons You need to be aware of the fact that the force-feedback device you are using may not be happy with your force commands determined in your haptic rendering program and can produce unintended force outputs. Be always careful when you want to make abrupt force command changes, i.e., large and fast force command changes Wed EECE 700. Advanced Computer Haptics 15 Common Procedures in Haptic Rendering (1) Periodic Update Interaction Tool Position Sensing Collision Detection Response Force Computation Virtual Object Database Force Feedback Wed EECE 700. Advanced Computer Haptics 16 8

9 Common Procedures in Haptic Rendering (2) Interaction Tool Position Sensing Actuators (e.g., motors) in a force-feedback device usually have position sensors (e.g., optical encoders). The local position coordinates are transformed to the world position coordinates using kinematics. Collision detection The measured position of the interaction tool is compared to the model of virtual objects. If any contacts occur, information necessary for computing appropriate force commands is calculated in this step Wed EECE 700. Advanced Computer Haptics 17 Common Procedures in Haptic Rendering (3) Response Force Computation If no contacts occur between the interaction tool and virtual objects, zero force is commanded. If contacts occur, a response force is calculated using a haptic rendering algorithm designed to achieve desired haptic effects. Force Feedback The force command is converted to actuation command to drive the actuators in the device. Virtual Object Database Update The state of virtual objects are updated according to the modeled rules. Important for dynamic and deformable virtual objects Wed EECE 700. Advanced Computer Haptics 18 9

10 Outline Basics of Force-Feedback Haptic Interfaces Introduction to Computer Haptics Reading List Wed EECE 700. Advanced Computer Haptics 19 Reading List Introductory Articles Salisbury et. al, Haptic Rendering: Introductory Concepts, IEEE Computer Graphics & Applications, 2004 Srivasan et. al, Haptics in Virtual Environments: Taxonomy, Research Status, and Challenges, Computer & Graphics, 1997 Hayward et. al, Haptic Interfaces and Devices, Sensor Review, 2004 Haptic Perception Lecture slides on Haptic Perception, in POSTECH EECE 700B Introduction to Haptics, R. L. Klatzky and S. J. Lederman, "Touch," in Handbook of Psychology, vol. 4, I. B. Weiner, Ed. New York, USA: Wiley, 2002, pp Haptic Control Lecture slides on Stability of Haptic Interaction, in POSTECH EECE 700B Introduction to Haptics, D. A. Lawrence, "Stability and Transparency in Bilateral Teleoperation," IEEE Transactions on Robotics and Automation, vol. 9, pp , Wed EECE 700. Advanced Computer Haptics 20 10