Friction Rendering : A New Computational Model of Friction Applied to Haptic Rendering

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Friction Rendering A New Computational Model of
Friction Applied to Haptic Rendering

• Han, Gabjong
• hkj84_at_postech.ac.kr
• POSTECH VR Lab
• 2006. 5. 29.

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Outline

• Introduction
• Previous Models
• An Online Discrete Scalar Model
• A Discrete Vectorial Model
• Experimental Results
• Conclusion

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Introduction - Motivation

• Friction occurs when two objects are in contacts
• Previous approach
• Add dynamic friction effects depending on time or
  on state
• Proposed method
• Make autonomous friction model whose computation
  is based on displacements

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Introduction - Contributions

• It is autonomous
• It neither drifts, nor relaxes
• It is robust to noise
• It is computationally efficient
• It accounts for vector motions and forces
• It has four regimes
• Its parameters have physical meaning
• It has continuous counterpart

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Previous Models Basic Model

• Use mass-spring behavior
• Add damping term
• Add viscosity
• z w-x, v dx/dt

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Previous Models Bristle Model

• Compute bristles deflection effect
• Bristles deflection model
• v is relative velocity
• g(v) depends on material property
• Steady state condition

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Previous Models Seven Parameter Model

• Seven parameters
• s0, s1, s2, Fc, Fs, vs and v
• Simulate Stribeck effect
• Fc is Coulomb friction force
• Fs is Stribeck friction force
• vs is Stribeck velocity

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Previous Models Integrated Model

• Steady state situation
• Basic Bristle Stribeck model
• Integrated model

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Previous Models Dahls Model

• Use a differential equation
• Account for Coulomb friction
• Basic Bristle model

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Previous Models General Dahls Model

• Change the converging rate of F
• Take i 1, s0 1 and a F / Fc for simple
  computation

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An Online Discrete Scalar Model Autonomous Form
of Dahls Model

• Eliminating time
• In drifting situation

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An Online Discrete Scalar Model Drift Problem

• Drift occurs when a small cycle exists
• Drift-free friction model
• Have no minor paths
• Make a depend on z

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An Online Discrete Scalar Model Simple Model

• Integrating Dahls model

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An Online Discrete Scalar Model Simple Model

• Stick-slide
• No integration to Stick-slide
• Two regimes stuck and sliding
• a(z) 0 for z lt zmax
• a(z) 1 elsewhere

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An Online Discrete Scalar Model General Model

• Integration to displacements
• Stick-slip-slide
• Three regimes stuck, sliding and oscillating
• a(z) 0 for z lt zstick
• a(z) 1 elsewhere

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An Online Discrete Scalar Model General Model

• Stick-creep-slip-slide
• Four regimes stuck, sliding and oscillating and
  creeping
• Function of a(z)
• Stick-gtcreeping-gtsliping-gtoscillrating-gtreversal-
  gtfast-moving

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A Discrete Vectorial Model- Simple Model

• Point is vector model
• Z X-W
• Straightforward

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A Discrete Vectorial Model- General Model

• Direction must be updated before W

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Experimental Results - Setup

• Using PenCat haptic device
• 400 Hz update rate
• Haptic Technologies Inc.
• 3D vector test

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Experimental Results - First Experiment

• Using HIP as virtual pointer
• Z values represented by the set of lines

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Experimental Results - Second Experiment

• Actual test for general model
• X-Z plot

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Conclusion

• No drifts
• Autonomous
• Robust to noise
• Suitable for event-based interfaces
• Directly implementable
• Extension for 2D and 3D
• Showing four physical behaviors

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Reference

• Hayward, V. Armstrong, B. "A New Computational
  Model of Friction Applied to Haptic Rendering."
  Experimental Robotics VI, PP. Corke and J.
  Trevelyan (Eds.), Springer, New York, 2000,
  pp.404-412.
• C. Canudas, H. Olsson, K.J. Astr om, and P.
  Lischinsky. A new-model for control of systems
  with friction. IEEE Transactions on Automatic
  Control, 40(3)419--425, 1995.

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QnA