The design and fabrication of a passive and continuously repositionable joint

Abstract

A cam based locking mechanism was designed and fabricated to secure the joints of a continuously repositionable table capable of supporting a 11 IN load. Additionally, a frame was designed and built to test the feasibility of this joint concept as an assembly. Conventional toothed mechanisms were found to not provide a desirable smoothness of motion or resolution for implementation as an adjustable table. They also require more geometrically complex components than the proposed solution. The proposed mechanism relies on the binding of an eccentric cam and pulley, and is of interest because these key components are geometrically simple in comparison to toothed mechanisms. The reduced complexity of this solution is expected to lower the manufacturing cost of this type of joint and increase the resolution of its angular position, when compared to similar mechanisms. A model of the jamming interaction was evaluated using Matlab. This model was used to select the optimal material, eccentricity and diameter of the components. The elements were then fabricated with an Omax 2626 Precision JetMachining Center, and mechanically tested using calibrated weights. The fabricated joint is capable of holding a 56.5N*m load with a stiffness of 7.8N*m/degree.