Design, control, and evaluation of a spatial active handrest for providing ergonomic support and gravity compensation over a large workspace

Most humans have difficulty performing precision tasks, such as writing and painting, without additional physical support(s) to help steady or offload their arm's weight. To alleviate this problem, various passive and active devices have been developed. However, such devices often have a small workspace and lack scalable gravity compensation throughout the workspace and/or diversity in their applications.;This dissertation describes the development of a Spatial Active Handrest (SAHR), a large-workspace manipulation aid, to offload the weight of the user's arm and increase user's accuracy over a large three-dimensional workspace. This device has four degrees-of-freedom and allows the user to perform dexterous tasks within a large workspace that matches the workspace of a human arm when performing daily tasks. Users can move this device to a desired position and orientation using force or position inputs, or a combination of both. The SAHR converts the given input(s) to desired velocities and commands corresponding motors using an admittance controller. This work builds on research of a previous two-degree-of-freedom robotic handrest.;To achieve this goal, the Vertical Active Handrest (VAHR), a one degree of freedom (DOF) handrest, was designed and constructed to investigate the benefit of providing support in only the vertical direction. Providing support in the vertical axis is more challenging than the horizontal plane since one must account for the effect of gravity. A series of experiments were conducted to develop various control strategies and evaluated the user's performance with these controllers versus other unassisted support conditions. The Vertical Active Handrest was found to reduce participants mean absolute tracing error and improve their skill level.;Next, the Enhanced Planar Active handrest (E-PAHR) was developed, which extended the workspace of the prior two-degree-of-freedom planar Cartesian handrest (PAHR) and better matched the kinematics of the human arm. This was achieved by adding a rotational DOF to allow for forearm rotation within the horizontal plane. Various control strategies were examined through a series of human-subject experiments and found multiple controllers that provided more natural interaction with the device than the PAHR while matching the PAHR's skill level.;Finally, the Spatial Active Handrest (SAHR) was developed by adding an elevation axis to the E-PAHR to extend its workspace to the third dimension. The effect of various control strategies and virtual fixtures were investigated and a controller that permits natural user interaction, high accuracy, and low muscle fatigue was identified. The SAHR was shown to improve a user's accuracy beyond unassisted support conditions while preventing fatigue compared to the unassisted support conditions.