Haptic devices require physical contact between operator and machine, using force feedback and creating a coupled system. Human contact reduces stability due to the response of human operators to stiffen the arm to stabilize the system, leading to a less stable system. Controllers cannot account for this, as operator stiffness is not measurable. This research examined the decreased stability due to increased operator arm stiffness and designed a system to compensate by providing the controller with additional information about the environment. Operator arm stiffness was estimated by measuring muscle activity using EMGs, then the dynamic characteristics of an impedance controller were adjusted according. The design is discussed and experimentally validating, showing increased stability and higher performance. Based on the results, an advanced probabilistic model of operator actions is explored for its applicability to enhance the system. Such a system could be used in many applications, including force assisting devices in industrial facilities.

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