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.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18205 |
| Date | 11 1900 |
| Creators | Ashby, Graham |
| Contributors | Bone, Gary M., Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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