Conclusion / Lessons / Future Work

In this project, we strove to build an upper body exoskeleton that would teach users the correct form of shooting a basketball. Initially, the exoskeleton was a simple six-bar Watt mechanism; however, further iterations incorporated a crank-rocker and a geneva mechanism. The final prototype was able to move the user's arm in the motion of shooting a basketball; however, due to the limitations of the motor, the user had to help move the exoskeleton along the upward shooting motion. During the downward returning motion, the motor was capable of moving the user's arm with no complications. For improvements, a larger motor that can provide more torque can be used to move the exoskeleton with little effort from the user. Another issue that restricted the exoskeleton's motion was the alignment of the linkages. In future work, machining will be done with more precision to ensure that axes are straight and linkages line up correctly. This will reduce bending moments and stresses on the joints. Another complication was the fixing of bearings to the linkages. Initially, we designed the joints to have press-fitted bearings but due to the ductility of the Delrin, the bearings holes expanded after use. Axial and bending forces were able to pull the bearings out of their sockets. To fix that problem, we used loctite to fix the bearings. Although this design ensures minimal obstructions with the bearings and shafts, it places large stresses on the loctite bond site which rapidly overcome the strength of the adhesive. Also, more room is required between the holes and bearings to allow the glue to cure. Future work will involve redesigning the placement and fixing of the bearings to prevent this problem. A major flaw in our design was our approximation of the basketball shooting motion as two dimensional rather than three dimensional. This, in actuality, was not the case so the excess axial and bending forces were applied on the system in order to confine the user's motion to a 2D plane. In order to fix this problem in the future, we will need to redesign the exoskeleton to account for the extra degree of freedom due to the shoulder rotation involved in shooting a basketball.  

Figure 1. Final Prototype                                                                                 

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