| Description |
Traditionally, hand rests are used to reduce muscle fatigue and to improve precision in small-workspace dexterous tasks. Dynamic hand rests have been shown to be beneficial for large-workspace planar tasks. However, providing high-bandwidth support in the vertical direction proves to be more challenging than in the horizontal plane. One must decouple the gravitational support of the arm from the intended vertical motion of the user. A vertically moving device, called the Vertical Active Handrest (VAHR), is presented in this thesis. This device dynamically supports the weight of the user's arm over a large workspace to add stability for precision dexterous tasks while providing gravitational support to the arm to reduce fatigue. The goal in developing the VAHR is to integrate its capabilities with the current Active Handrest, which provides dynamic support in the horizontal plane, thus creating a three degree-of-freedom active support device. The VAHR takes control inputs from a force sensor embedded in its armrest and from the tracked position of a tool. Studies were conducted with a variety of controllers and user input strategies to evaluate the VAHR's effectiveness at assisting participants in a single-axis tracking task. An initial pilot test with the VAHR shows no statistical improvements in tracking performance using force input control modes over conditions in which the arm is unsupported, or is supported by a static rest surface. The main experiment presented in this thesis focuses on either pure stylus position input or a combination of position and force inputs. Tracking accuracy significantly improves compared to the unsupported condition while using stylus position input control. Poor performance under pure force control is attributed to the required activation of large muscle groups in the arm to provide force input to the VAHR's instrumented armrest. These large muscle groups are poorly suited for the agile tracking task used for experimentation. It is theorized that the better performance when using the stylus position control modes is because inputs from smaller, more dexterous muscle groups in the hand are utilized, allowing the position of the arm to be controlled by muscles that are already adept at precision control. |
