Design, fabrication, and testing of a hybrid vacuum-electric actuated robotic arm

Abstract

his thesis presents the design, fabrication, and testing of a robotic arm that is inherently safe, lightweight and affordable. The arm’s three joints are driven by novel hybrid vacuum-electric actuators that each combine origami-inspired soft pneumatic actuators (OSPAs) with a DC motor. The arm is a type of collaborative robot, or cobot, that is suitable for low payload, low speed applications. The OSPA was redesigned in the first stage of the research. In particular, the new endcaps are 59% shorter than the previous design. This made the actuators more compact and increased their stroke-to-length ratio. Next, the OSPA fabrication process was significantly changed. The heating of the heat shrink tubing was changed from immersion in boiling water to heating with a heat gun, and a motorized stand with several assisting parts was developed. These changes improved the consistency of the fabrication, reduced the skills required, and improved the safety. The joints of the arm and its structural components were designed next. The rotation of each joint is achieved by connecting multiple OSPAs to custom-made pulleys using cables and connecting a DC motor in parallel using a timing belt. Joint 2, the shoulder joint, had to produce the largest torque. This was accomplished by applying optimization methods to design a variable-radius pulley. The prototype arm utilized laser-cut acrylic and 3D printed components to keep its cost and weight low. Finally, after a simple pressure control system was developed, the prototype arm’s performance was extensively tested. The joints’ ranges of motion, velocities, accelerations, and blocked torques are tested at multiple pressures and motor currents, and the results discussed. The thesis concludes with a summary of the research’s achievements and limitations, and recommendations for future improvements to the robotic arm’s design.