Active Handrest: A large workspace tool for precision manipulation

Abstract

To address the limited dexterous workspace of the human hand, we have developed the Active Handrest. This device assists in precision manipulation tasks by extending a user’s dexterous workspace while providing ergonomic support for reduced fatigue. People use handrests to complete dexterous activities as routine as providing a signature. However, the dexterous workspace of the statically supported hand is somewhat limited. By providing consistent support over large workspaces the Active Handrest could be useful for performing precision tasks, such as surgery, upper limb rehabilitation, and machining. Our prototype Active Handrest is a planar, human–machine interface that provides support for the user’s wrist and arm while allowing the user to retain complete control over a grasped tool or manipulated device. The Active Handrest uses force input from the user’s hand, position input from a grasped tool, or a combination of these inputs. The device’s controller then converts the input(s) into handrest motions. In this paper we describe our novel device prototype and establish a baseline for its performance. Preliminary experiments were conducted to investigate the effects of control input, velocity limits, and user experience. Subsequent experiments compared the Active Handrest to various other support conditions. Use of the Active Handrest was found to significantly reduce task error and provided better speed-accuracy performance than the other tested support methods.

Evaluation of Active Handrest performance using labyrinths with adaptive admittance control and virtual fixtures

“…In our previous works [7,8,9] we demonstrated that the Active Handrest is able to provide increased task accuracy over freehand, fixed supports, and passive supports. In this paper we discuss two experiments investigating factors that aid in accurate labyrinth navigation and to determine the effectiveness of adaptive admittance and virtual fixtures for the Active Handrest.…”

“…The focus of the experiments discussed herein is to explore the effectiveness of various adaptive admittance control and virtual fixture methods, and to quantify the performance differences between the Active Handrest and freehand, over a variety of conditions. In these experiments, static and passive handrests were not examined as our previous works [7,9] already showed the relative benefit of the Active Handrest compared to these support methods. The motivation of our experiments is to show the potential for the use of these methods on the Active Handrest to improve accuracy while maintaining or improving task completion times.…”

“…To date the majority of our research involving the Active Handrest [7,8,9] focused on the utility of the device under the fixed linear admittance law of:…”

“…To expand upon the capabilities of the Active Handrest here we examined various adaptive admittance strategies, as a method to improve accuracy and timing data. The first strategy, which we briefly explored in [9], was to adjust the admittance gain, Ka, based on the input force provided by the user such that:…”

“…Previous experiments conducted with Active Handrest showed that it was capable of increasing task accuracy while controlled by force, position, and force-position hybrid inputs [8]. Additional experiments showed an improvement in task accuracy compared to freehand, fixed support, and passive support conditions over a range of completion times [9]. These results were recorded with the Active Handrest used to conduct continuous/uniform tasks (i. e. , tracing circles) with fixed admittance gains and without virtual fixtures.…”