Redundant multi-degree-of-freedom (MDOF) bilateral system in workspace is expected to be a key technology for the development of next generation robots because of the variety of feasible tasks. Nowadays, four channel bilateral structures based on acceleration control have been introduced to realize both position and force tracking in a bilateral control system. Additionally, torque observers have been implemented to facilitate force feedback without the use of torque/force sensors. However, differences in controller composition between the joint space and workspace are still unclear. In particular, observer designs in both spaces are important for a realization of torque/force sensorless bilateral control. This paper presents a performance evaluation of an MDOF force sensorless bilateral system performed by considering the design space of observers by numerical and experimental analyses.
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