FULLY AUTOMATED FABRICATION OF TWISTED COILED POLYMER ACTUATORS WITH PARAMETER CONTROL

摘要

Robotics undergoes constant evolution thanks to the steady emergence of new and better technologies. The common conception of robotics is that of the large, rigid mechatronic systems implemented in modern manufacturing, humanoid robotics and remote exploration systems. However, robotics also applies to advanced prosthetics that will allow us to replace lost or damaged limbs. The main limitation is the availability of small, discrete devices that can provide mobility to these robotic limbs. Most people are familiar with servos, DC motors, pneumatic and hydraulic systems. Applying these devices to prosthetics is not as easy as one would think, especially when large hydraulic pumps are required for their operation.Research has been done on soft bio-mimetic robotic systems that offer more of the benefits of biological systems regarding efficiency, durability, and combinability with existing biological substrates. Some examples of such bio-mimetic actuator systems are Electro-Active Polymers (EAP), Dielectric Elastomer Actuators (DEA) and Pneumatic Artificial Muscles (PAM). The Ionic-EAP depends on the movement of ions by an electric field to produce a large bending motion under a very low voltage (Jain et al. 2014; Tang et al. 2016). A significant problem with these devices is their relatively low force output, which limits their usefulness in loaded applications like an arm or leg. The DEA, on the other hand is another type of EAP actuator that gets very close to the requirements of ideal biomechatronic systems. This device is placed between electrodes and actuated by an electric field. By combining multiples of these devices in a rolled bundle, it is possible to achieve virtually any desired motion (Pei et al. 2004; Kovacs et al. 2009). However, these systems require substantial electrical input and currently do not scale well to large assemblies, not to mention the relative fragility of their active electrodes.Research on artificial muscle actuators driven by air pressure were shown to have a wide variety of output forces and motion (Martinez et al. 2012; Luo et al. 2015). From the results of the published work, it is evident that these PAMs are ideal actuators for bettering prosthetic systems in terms of actuation force, flexibility, and scalability. However, these pneumatic systems rely on bulky, loud and energy demanding hardware making them impractical for portable prostheses.A research group from the University of Texas at Dallas (Haines et al. 2014) demonstrated that by using inexpensive polymer fibers such as store-bought monofilament fishing line, and sewing thread it is possible to build artificial muscles that are fast, strong, and reliable. These actuators are constructed by applying extreme twisting to the filament until a helix is formed. According to Haines et al. (2014) these coiled muscles can contract up to 49% of their original length and lift loads 100 times heavier than human muscle of the same length and weight. These results have sparked much interest in researching the characteristics and behavior of these novel, simple, and affordable devices. Aziz et al. (2015) analyzed and characterized twisted yarns and fibers and presented different test methods for these coiled polymer actuators, and the theoretical results were compared against the experimental results. Arjun et al. (2016) presented the design and fabrication of 3D printed hand prosthesis actuated using twisted nylon 6–6. Their results show that it is possible to implement twisted artificial muscles to develop strong, flexible, and affordable prosthetics. However, more research is required to reduce their operating temperatures to make them viable for practical applications.In order to achieve reliable results from the analysis it is necessary to consistently fabricate these devices. For that reason, a machine that will aid in the fabrication of Twisted Coiled Polymer Actuators (TCPAs) was designed and constructed. By implementing a PID control sys