Analysis of Effect of Model Mismatch on Stability of Model-Mediated Teleoperation

Model-mediated teleoperation (MMT) is intended to improve system stability and transparency in the presence of time delay between the haptic device and the robot. Previous experimental researches, however, report that systems mediated using linear models become unstable when contacting nonlinear objects. This paper analytically shows the effect of model mismatch on the stability of the system. The analysis shows that the mismatch can generate surplus energy in the haptic system when the stiffness coefficient of the environment increases with the deformed depth. The analysis is verified experimentally in virtual environment with second-order polynomial stiffness object, a linear object with varying stiffness, and a nonlinear viscoelastic object described by Hunt-Crossley model. Results of experiments show that the additionally generated energy destabilizes the system when there is time delay. It is observed that MMT mediated by a linear model becomes unstable even when the object also has linear stiffness if the stiffness changes even once. The experiments with Hunt-Crossley model shows that the damping element may not prevent the instability due to model mismatch.