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Volume 26 Issue 3 - Publication Date: 1 March 2007
 
The Low-Stiffness Teleoperator Slave – a Trade-off between Stability and Performance
 
G. A. V. Christiansson and F. C. T. van der Helm Delft Haptics Laboratory, Delft University of Technology, The Netherlands
 
Stability is essential for teleoperation and a prerequisite for performance. This paper analyzes the the stability/performance trade-off of a teleoperator where the slave device has a built-in passive intrinsic stiffness. Stability is quantified as time delay robustness and performance is expressed using teleoperator damping and teleoperator stiffness, the boundaries of the Colgate Z-width.
Two classic control schemes, position error and Lawrence 4-channel, are used along with a novel 5-channel scheme where the slave stiffness deflection is measured, and compensated for, to improve the performance.
The teleoperator system was analyzed theoretically using a linear model and the findings were experimentally validated on a one degree of freedom teleoperation setup.
It was found that:
  •  A lower slave stiffness improves stability for all three teleoperator architectures.
  •  The stability boundary of the three controllers is similar.
  •  The performance of the controllers increases from: (poor) position error, 4-Channel to (excellent) 5-channel.
  •  A classical linear analysis method can accurately predict the stability characteristics of the teleoperator system.
Therefore it can be concluded that a compliant slave device offers a stability advantage for a range of teleoperation situations and that the loss of performance can be partly compensated.
 
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