Haptic Physical Human Assistance

This dissertation covers three aspects of upper-extremity exoskeleton design: 1) Kinematics & motion: How to support the full range of motion of the human shoulder? We present a 2D visualization method that can show coupling between the range of motion (ROM) of rotations of the glenohumeral joint. This visualization helps in communication, comparison, design and analysis of human and assistive device ROM. We furthermore provide a conceptual design and differential inverse kinematics method for a redundant 4 degree of freedom (DOF) shoulder-exoskeleton. The extra DOF allows for movement redundancy to steer away from body collisions and kinematic singularity. 2) Haptics & Control: How to get devices such robots or exoskeletons to behave as some defined impedance in a stable manner when interacting with human users; how to implement stable admittance control with inertia reduction? We analyze the energetic behavior of the control method ‘admittance control’. During admittance control an interaction force with a human user is measured, which is used in a dynamical mechanical model that prescribes a motion for the exoskeleton to follow. Such a method is inherently active (i.e. it generates energy that can result in coupled instability) when it is used to reduce the apparent inertia of the exoskeleton. We provide insight into why this energetically active behavior occurs, and provide guidelines to design a controller that is (close to) passive and is therefore (almost) always stable when in contact with a human limb. 3) Human Factors: How do humans respond to dissipative shared control forces? Passive and active exoskeletons can apply forces to the human user to steer or help the person and share control authority. A passive force that only dissipates energy is a damping force. We investigate how position dependent damping forces around reaching targets influence human reaching time and kinematics. Results show that humans increase their accelerations and decrease their reaching time when assisted in this manner. We pose the hypothesis that damping forces attenuate neural activation dependent motor noise. Without the damping, this higher noise for higher accelerations would have had too much of a negative effect on the required task accuracy.