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TECHNICAL PAPERS

Haptic Manipulation of Serial-Chain Virtual Mechanisms

[+] Author and Article Information
Daniela Constantinescu1

Department of Mechanical Engineering, University of Victoria, Victoria, BC V8W 3P6 Canadadanielac@me.uvic.ca

Septimiu E. Salcudean

Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC V6T 1Z4 Canada

Elizabeth A. Croft

Department of Mechanical Engineering, University of British Columbia, Vancouver, BC V6T 1Z4 Canada

The virtual proxy is a simulated small sphere connected to the user’s finger through a simulated spring and a damper when constrained by other objects in the virtual environment and collocated with the user’s finger otherwise.

The virtual proxy can be used only for pushing because it behaves similar to a contact constraint by definition.

The virtual coupler is a controller that acts as a generalized (translational and rotational) spring and damper connection between the user and the end effector of the VM.

Haptic manipulation of a crank has been used for tracing a virtual circle in (22) and haptic manipulation of a two-link Cartesian mechanism has been used for tracing NURBS surfaces in (23-24).

After premultiplication of τ=JhTFenv by JhD1 and substitution from Eq. 6.

Attempting to compute the SVD of the hand Jacobian on the haptics processor renders the local model too slow for the force feedback loop when implemented on the haptic planar interaction system described in Sec. 8.

These values represent the maximum impedance of the virtual coupler for which the interaction is stable, i.e., for which chattering does not occur.

For the impedance-type haptic interface employed in these experiments, a constant wrench represents a worst case scenario for stability (28).

Note also that the trajectories plotted in Figs.  1314 do not represent the same interaction as the one depicted in Figs.  1212 and, therefore, the device trajectory errors are different in the two sets of experiments.

1

Corresponding author.

J. Dyn. Sys., Meas., Control 128(1), 65-74 (Nov 10, 2005) (10 pages) doi:10.1115/1.2168479 History: Received March 30, 2005; Revised November 10, 2005

This paper presents an approach for providing realistic force feedback to users manipulating serial-chain virtual mechanisms. In the proposed approach, a haptic device controller is designed that penalizes users’ motion along the directions resisted by the virtual joints. The resisted directions span the nullspace the Jacobian of the virtual mechanism computed at the users’ hand, and are derived via a singular value decomposition-based algorithm. Haptic numerical performance is achieved by computing the resisted directions on the graphics processor, and by using them on the haptics processor to derive the control signal that restricts users’ motion as required by the virtual joints. The performance of the proposed approach is validated through experimental manipulations of links with unrestricted and with restricted motion within a planar virtual world.

FIGURES IN THIS ARTICLE
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Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

Grahic Jump Location
Figure 1

Mechanical representation (excluding the communication delay and force scaling) of one-dimensional haptic interaction within a virtual environment via the four channel teleoperation controller

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Figure 2

Example manipulations of a planar VM where the virtual joints restrict the instantaneous body motion at the user-selected operational point

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Figure 3

Penalty wrench constraining users to the configuration manifold of the VM that they manipulate

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Figure 4

Simulated manipulations of a three-links planar VM. The initial VM position is shown in black. VM positions during manipulation are shown in gray.

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Figure 5

Simulink diagram of the haptic manipulation of a three-links planar VM with motion unrestricted by other virtual objects

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Figure 6

Simulated planar manipulation of a three-links planar VM held from the COM of the middle link

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Figure 7

Simulated planar manipulation of a three-links planar VM held from the COM of the distal link

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Figure 8

Decoupling of the force control loop from the virtual environment (VE) simulation through a local model of rigid body interaction

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Figure 9

Testbed virtual environment used to illustrate haptic manipulation of VMs from arbitrary user-selected links

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Figure 10

Testbed virtual environment used to illustrate haptic manipulation of VMs within a dynamic virtual environment

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Figure 11

Manipulation from the middle link of the planar VM shown in Fig. 9

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Figure 12

Manipulation from the distal link of the planar VM shown in Fig. 9

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Figure 13

Manipulation from the distal link of the planar VM shown in Fig. 1 rendered via the proposed approach

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Figure 14

Manipulation from the distal link of the planar VM shown in Fig. 1 rendered via virtual coupling

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