As collaborative robotics become more prevalent, it is desirable to improve the inherent robot safety, on a mechanical level, while maintaining good position tracking. One method is to replace the electric motor+gearing currently used with an alternate actuator which introduces less inertia, friction, and stiffness. A promising approach is the use of hybrid pneumatic-electric actuators (HPEAs). A first generation (GEN1), proof-of-concept, HPEA with low payload capacity and poor mechanical reliability was improved upon to produce the next generation of HPEA. The 2nd generation (GEN2) actuator developed in this work was designed to increase payload capacity and improve mechanical reliability while maintaining low inertia, low friction and low stiffness. The torque capacity was improved by 511% while increasing inertia by only 292%. The majority of the system was modeled via relevant physical laws. The solenoid valves’ inverse model was provided by a black box artificial neural network (ANN), and the electric motor’s was empirical. The models were used to develop a position controller with an inner loop pressure controller based upon the ANN. An alternate (non-model-based) pressure controller was also developed to compare to the ANN based controllers. The system could operate as a purely pneumatic actuator, or as a HPEA. Experimentally it was found that the position control based upon the two pressure controllers led to similar performance, but the ANN based were superior more often. The hybrid mode reduced the purely pneumatic mode position error for vertical cycloidal position tracking by approximately 55%. The GEN2 achieved lower position tracking errors as compared to prior works of other HPEAs as well as purely pneumatic actuator control publications. Compared to the GEN1, the GEN2 achieved better position tracking errors in both pneumatic and hybrid operation. The GEN2 will serve as a superior testbed for future HPEA control and collaborative robotics research. / Thesis / Master of Applied Science (MASc) / Robots which work directly with people are becoming increasingly numerous in industry as their costs decrease. As robots and humans work more and more closely there is a desire for the robot to be more inherently safe, by merit of the underlying mechanical design. Previous research resulted in a prototype hybrid pneumatic-electric actuator (HPEA) designed to improve inherent safety by merit of its low inertia, low friction, and low stiffness. This prototype proved successful, but was of low payload capacity and unreliable mechanical design. The goal of the research was to design, build, model, control, and validate a second generation HPEA, with a larger payload capacity and of more reliable mechanical design while maintaining low friction, inertia and stiffness. Furthermore the improved actuator should maintain or improve upon the good position trajectory tracking of the prior actuator. These goals were successfully achieved with the improved prototype developed in this work.

Today the selection of drive technology for realizing of moving tasks is made by comparing of investment and energy costs in general. Pneumatic drives are characterized by their low purchase price, but at the same time they show high energy consumption in a comparison with electric drives. This general evaluation leads to the point, that in many cases the optimum drive structure for a certain handling task can’t be found regarding functionality and efficiency. To reach that goal, the dynamic, energy and costs characteristics of the actuator have to be observed and summarized. In this paper the EXonomy analysis is presented as a base for the inter-domain comparison of electric and pneumatic drives. Developed EXonomy approach enables the objective analysis and comparison of electric and pneumatic systems within 3 steps.

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. / Thesis / Master of Applied Science (MASc) / This 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 actuators that each combine soft pneumatic actuators (powered by vacuum pressure) with a DC motor. The arm is suitable for low payload, low speed applications. First, the pneumatic actuators were redesigned to make them more compact. Next, their fabrication process was changed to improve the consistency of the results, reduce the skills required, and improve the safety. The joints of the arm and its structural components were then designed. To produce the torque required for the shoulder joint, optimization methods were used to create 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.

Robot arms require actuators that are powerful, precise and safe. The safety concern is amplified when these robots work closely with people in collaborative applications. This thesis investigates the design and implementation of hybrid pneumatic-electric actuators (HPEA) for use in robot arms, particularly those intended for collaborative applications. The initial focus was on improving the control of an existing single HPEA-driven rotary joint. The torque is produced by four pneumatic cylinders connected in parallel with a small DC motor. The DC motor is directly connected to the output shaft. A cascaded control system is designed that consists of an outer position control loop and an inner pressure control loop. The pressure controller is based on a novel inverse valve model. High precision position tracking control is achieved due to the combination of the model-based pressure controller, model-based position controller, adaptive friction compensator and offline payload estimator. Experiments are performed with the actuator prototype rotating a link and payload with a rotational inertia equivalent to a linear actuator moving a 573 kg mass. Averaged over five tests, a root-mean-square error of 0.024° and a steady-state error (SSE) of 0.0045° are achieved for a fast multi-cycloidal trajectory. This SSE is almost ten times smaller than the best value reported for previous HPEAs. An offline payload estimation algorithm is used to improve the control system’s robustness. The superior safety of the HPEA is shown by modeling and simulating a constrained robot-head impact, and comparing the result with equivalent electric and pneumatic actuators. This research produced two journal papers. Since HPEAs are redundant actuators that combine the large force, low bandwidth characteristics of pneumatic actuators with the large bandwidth, small force characteristics of electric actuators, the effect of using optimization-based input allocation for HPEAs was studied. The goal was to improve the HPEA’s performance by distributing the required input (force or torque) between the redundant actuators in accordance with each actuator’s advantages and limitations. Three novel model-predictive control (MPC) approaches are designed to solve the position tracking and input allocation problems using convex optimization. The approaches are simulated on a HPEA-driven system and compared to a conventional linear controller without active input allocation. The first MPC approach uses a model that includes the dynamics of the payload and pneumatics; and performs the motion control using a single loop. The latter methods simplify the MPC law by separating the position and pressure controllers. Although the linear controller is the most computationally efficient, it is inferior to the MPC-based controllers in position tracking and force allocation performance. The third MPC-based controller design demonstrated the best position tracking with root mean square errors of 46%, 20%, and 55% smaller than the other three approaches. It also demonstrated sufficient speed for real-time operation. This research produced one journal paper. The research continued with the design and implementation of a two degree-of-freedom HPEA-driven arm. A HPEA-driven “elbow” joint is designed and added to the existing “shoulder” joint. The force from a single pneumatic cylinder is converted into torque using a 4-bar linkage. To eliminate backlash and keep the weight of the arm low, a 2nd smaller DC motor is directly connected to the joint. The kinematic and kinetic models of the new arm, as well as the geometry of the new elbow joint are studied. The resulting joint design is implemented, tested and controlled. This joint could achieve a SSE of 0.0045° in spite of its nonlinear joint geometry. The arm is experimentally tested for simultaneous tracking control of the two joints, and for end-effector position tracking in Cartesian space. The end-effector is able to follow a circular trajectory in pneumatic mode with position errors below 0.005 m. / Thesis / Doctor of Philosophy (PhD) / Robots that work with, or near, humans require greater safety considerations than other robots. A significant concern is collisions between the robot and humans that may happen when sensors or software fails. An actuator for robots that combines the inherent safety of pneumatic actuators with the accuracy of electric actuators, termed a “hybrid pneumatic electric actuator” (HPEA), is investigated. The design, instrumentation, modelling, and control of HPEAs are studied theoretically and experimentally. The proposed actuator could achieve high position control accuracy in a variety of experiments, with steady state error of less than 0.0045 degrees. Simulated impacts with a human head also showed that a HPEA-driven robot arm can achieve a 52% lower impact force, compared to an arm driven by conventional electric actuators. The HPEA design and control experiments are performed on a single HPEA-driven joint and extended to an arm consisting of two HPEA-driven revolute joints.