Robots designed for human rehabilitation present a unique set of requirements. This dissertation addresses how to design a machine with properties suited to interface with human subjects, specifically, the design of a pneumatically actuated robot with high torque potential, which is also back-drivable. Machine design is a special mix of art and science. An elegant design is difficult to quantify, but reliability and efficiency often follow elegance as a design goal. The SUE robot described in this dissertation had to be designed with an appeal to subjects and therapists, as well as researchers and engineers. The designer of a robot with a human interface must consider that apparently mechanically useless features such as color, indeed matter. The mechanical requirements of a strong robot had to be balanced with the necessity of safety.
The robot SUE (SUpinator-Extender) was designed to be attached to the distal link of the UCI BONES exoskeleton robot and to the ArmeoSpring rehabilitation device. It adds forearm/wrist rehabilitation capability to both robots. SUE is a 2 degree-of-freedom (DOF) serial chain that can measure and assist forearm supination-pronation and wrist flexion-extension. The large power to weight ratio of pneumatic actuators allows SUE to achieve the forces needed for rehabilitation therapy while remaining lightweight enough to be carried by BONES and ArmeoSpring. Each degree of freedom has a range of 90 degrees, and a nominal torque of 2 ft-lbs. Positioning the two pneumatic cylinders used for actuation was the most challenging aspect of the design. The cylinders are mounted away from the patient's body, on the lateral aspect of the arm. This is to prevent the danger of a collision and maximize the workspace of the arm. The rotation axis used for supination-pronation is a small bearing just below the subject's wrist. The flexion-extension motion is actuated by a cantilevered pneumatic cylinder, which allows the palm of the hand to remain open.
This research found that the nonlinear forces due to cylinder seal friction can be minimized by sizing the pneumatic cylinder appropriately. This is a useful general result for the design of pneumatic exoskeletons. Data are presented demonstrating the ability of SUE to measure and cancel forearm/wrist passive tone, thereby extending the active range of motion for people with stroke.
Aside from designing an elegant machine, this research required the solution to a challenging pneumatic control problem. Our first attempt at flow control for pneumatic systems was to design a fast rotary servo valve. The valve project was successful, but demonstrated that the drawbacks of leakage, weight, and cost precluded the use of servo valves for the human scale project being undertaken. A variable deadband sliding mode force controller was then designed to gain improved performance from lightweight solenoid valves. Other related research conducted during the course of this dissertation and presented here is the design of a force sensitive gripper, and the creation of a new motor learning experiment in which human subjects use the BONES exoskeleton and SUE to toss balls to a novel target.
|Commitee:||Cramer, Steve C., Reinkensmeyer, David J.|
|School:||University of California, Irvine|
|Department:||Mechanical and Aerospace Engineering - Ph.D.|
|School Location:||United States -- California|
|Source:||DAI-B 74/03(E), Dissertation Abstracts International|
|Subjects:||Biomedical engineering, Mechanical engineering, Robotics|
|Keywords:||Actuated orthoses, Control, Design, Manufacturing, Motor learning, Optimization, Pnuematic, Stiction|
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