AC 2012-4628: FABRICATION AND TESTING OF A SIMPLE "BIONIC ARM" DEMONSTRATOR WITH AN ARTIFICIAL TENDON

This paper reports on a research experience for a teacher in the fabrication of “Bionic” or human-like arms. These have inspired many movies and science fiction books, but have many possible purposes, including active prosthetics, robotic arms, and exoskeletons to aid the movement of heavy objects. Previously, students and faculty at Texas A&M UniversityKingsville fabricated two simple Bionic Arms that used Rubber Muscle Actuators (RMA). The current work develops an improved RMA that replicates human like range of movement through the use of integrated artificial “tendons.” The tendons made of a flexible elastomer and braided carbon fiber do not stretch but bend relative to their attached “bone structure.” Previous “Kingsville Arms One & Two” utilized actuators that transferred loads through rigid attachments to “bones.” The rigid attach points allowed good load transfer but restricted range of movement. The current Kingsville Arm 3 (KA3) utilizes a 3D printed mold of rigid and flexible elastomeric composites to make artificial “tendons” that are placed between the rigid closure of a RMA and rigid attach points to the “bone.” Two KA3 actuators were completed. The first used a fiberfilled brittle resin for the rigid components on each side of the tendon. The tendon performed well, but an adjoining rigid section failed under load. A second KA3 actuator used a carbonfiber filled semi-rigid polyurethane for the rigid sections, and performed well in flexure and load transfer. A learning module based on a legacy cycle is developed that challenges the students to position the actuators to allow for maximum range of movement and to find the relationship on how the output force varies with the configurations. The learning modules will be introduced in basic algebra classes in schools with majority Hispanic students in the fall semester. Assessment of the students’ performance will be carried out and reported. Overview of Research Experience During the summer of 2011, a high school Algebra teacher was granted the opportunity to participate in the Research Experience for Teachers program at Texas A&M UniversityKingsville (TAMUK). The teacher spent six weeks working on a mechanical engineering project with a mechanical engineering professor and a graduate student. The research focused on fabricating and testing part of a simple “bionic” or human-like arm similar to those in Figure 1. The objectives of the summer research were to: 1) Fabricate an actuator that could produce high forces while utilizing the new flexible tendons, 2) Improve the range of motion (rotation) for the third generation bionic arm, and 3) Have a more human like muscle placement. Previously, students and faculty 1 at TAMUK fabricated two simple bionic arms that used Rubber Muscle Actuators (RMAs), as shown in Figure 1. KA1, the left-hand arm was completed in only 2 weeks, and proved quite powerful, but the RMAs used in it were attached to the “bones” by bonded carbon fibers. This allowed the muscles to rotate relative to the bone, but they frayed and “tore a ligament” quickly. The second or KA2 arm had RMAs that were also very powerful, and that lasted much longer, but their rigid molded ends did not allow rotation between the muscle and bone. A better RMA end attachment was desired. A unique feature of the current research is that the new design incorporated artificial tendons at the rigid attach points where the RMAs connect to the artificial bone structure. Figure 1: Kingsville Arm 1 and Kingsville Arm 2 1 . As seen in Figure 1, previous “Kingsville Arms One & Two” utilized actuators that transferred loads through rigid attachments to “bones.” The rigid attach points allowed good load transfer but restricted range of movement. A new attach method, involving ligaments, was developed, based on suggestions from a previous work 1 . Figure 2 shows previous RMA attach methods, and a suggestion for a new attachment. Figure 2: KA1 and KA2 ends, and suggested KA3 RMA end attachment. The summer Research Experience for Teacher (RET) work focused primarily on the design, fabrication of molds for the RMA ends/tendons and the complete RMA assembly. New Rubber Muscle Actuators with integrated tendons were fabricated using molds made with a 3D printer as shown in Figure 3. The new RMAs as shown in Figure 3 were tested for range of rotation and tensile force. The new integrated tendons allowed the RMAs and thus the KA3 Bionic Arm to have a much greater range of rotation, however the new tendons were too thick, and the polyurethane used for the rigid parts of the actuators were too brittle and failed prematurely. More tests using tougher (more compliant) polyurethane for the end attachments and a thinner tendon are needed to make a working bionic arm, however. Through this experience the teacher was introduced to both the demands and frustrations associated with designing, fabricating, and testing RMAs. Figure 3: 3D printed molds, KA3 RMA being tested, new RMA showing bending.