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Gianni Campion, Andrew H. Gosline, and Vincent Hayward

Initial Results using Eddy Current Brakes as Fast Turn-on, Programmable, Physical Dampers for Haptic Rendering. Gianni Campion, Andrew H. Gosline, and Vincent Hayward Haptics Laboratory, Center for Intelligent Machines McGill University Montréal, Québec, Canada

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Gianni Campion, Andrew H. Gosline, and Vincent Hayward

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  1. Initial Results using Eddy Current Brakes as Fast Turn-on, Programmable, Physical Dampers for Haptic Rendering Gianni Campion, Andrew H. Gosline, and Vincent Hayward Haptics Laboratory, Center for Intelligent Machines McGill University Montréal, Québec, Canada {champ,andrewg,hayward}@cim.mcgill.ca Haptics Laboratory

  2. Motivation • Physical damping is required for passivity [Colgate and Schenkel, 1994] • Sources of physical damping: • Dry Friction • Viscosity • Electromagnetic • Dissipation is accidental byproduct of design. • Difficult to model and not controllable. Haptics Laboratory

  3. Prior Work • Shunting a DC motor creates electrical damping.[Mehling and Colgate, 2005] • Frequency dependent, but not programmable, and limited to back EMF of DC motor. • Magnetorheological (MR) particle brakes are programmable • Nonlinear, slow to actuate, and suffer from hysteresis [An and Kwon, 2004], [Gogola and Goldfarb, 1999], [Arcy, 1996] Haptics Laboratory

  4. Proposal • Eddy current brakes are: • Controllable • Fast turn-on • Linear • Friction free • Inexpensive • Add eddy current brake to each driven joint • Create multi DOF hybrid device Haptics Laboratory

  5. Eddy Current Brakes • Move a conductor through a magnetic field, get dissipative resistance. • Currents generated according to the Lorentz Force Law. • Energy is dissipated by the Joule Effect. • Do not use contact. • Inductance/Vcc determines max update rate. Haptics Laboratory

  6. Eddy Current Brake Physics Induced current density: |J| = R|B| Power dissipated: Pd = 0.25D2dB2R22 Resistive torque: d= 0.25D2dB2R2 [Lee and Park, 1999] d D R Haptics Laboratory

  7. Prototype Haptic Device • Concentric aluminum blade added to each base joint of Pantograph. • Toroidal electromagnet cores machined from iron and wrapped with 24g enamel coated magnet wire. • Magnets driven in current mode by AMC 20A20 PWM servoamplifiers can achieve approx 500Hz on/off freq. Haptics Laboratory

  8. Rendering Results - Wall • Manipulandum thrust and held against virtual wall by elastic band . • Dampers on during wall penetration. • Limit cycles quenched or reduced. Haptics Laboratory

  9. Rendering Results - Friction • Friction model by Hayward and Armstrong, 2000, is prone to limit cycles in elastic stuck region. • Dampers used in stuck state. • Limit cycles quenched Haptics Laboratory

  10. Limitations • Damper blades add considerable inertia to the device. • Considerable power is required to generate damping torque. • Large ‘C’ shaped magnets flex and release under electromagnetic force, generating vibrations that are both audible and palpable. • Damping is not homogeneous through the workspace. Haptics Laboratory

  11. Conclusions • Physical damping from eddy current brakes can stabilize renderings of virtual walls and friction that were unstable without it. Future Work • Optimize design for both electromagnetic and dynamic performance • Verify linearity of damping • Further explore programmable damping in future control/passivity experiments Haptics Laboratory

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