Commercially available robotic prosthetic arms currently use independent joint control. An alternative controller involving only control of the hand in a Cartesian frame rather than controlling each joint independently is proposed and tested. A training tool that was previously developed for amputee patients was used as the platform for testing the proposed control approach. As opposed to joint control, Cartesian control requires the solution to the inverse kinematics problem. The inverse kinematics solution was developed for the robotic arm component of the training tool using the extended Jacobian method. The two control methodologies, joint control and Cartesian control, were tested on five able-bodied human subjects. Improvement of one control methodology over the other was measured by the time it took for the subjects to complete a simple motor task. In order to more systematically evaluate the perceived benefits of Cartesian control, two versions of Cartesian control were tested. Version 1 implemented the Cartesian control methodology but only allowed for motion in one direction at a time. Version 2 allowed for the combination of two directions, therefore, allowing straight-line motion. Each subject completed five timed trials with each control methodology. The initial timed trial results were, on average, faster for both versions of Cartesian control, indicating that Cartesian control was more intuitive, and thus, easier to learn. Once, the ability for straight-line motion was incorporated in version 2 of the Cartesian controller, the average timed trial results for all trials improved significantly over joint control. These results indicate a clear superiority of Cartesian control over joint control in the control of a robotic prosthetic arm. Additionally, comparisons were made to previous trials performed with the training tool. The previous trials only tested joint control but implemented myoelectric control, a feature not available for the Cartesian control testing discussed here. Myoelectric control involves measuring signals from a user's muscle activity in a particular site. These comparisons helped to validate the trends seen in the testing discussed here as well as suggest that further improvement of the Cartesian control methodology could be obtained by implementing myoelectric control.
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