Inspired by the octopus and snakes, we designed and built a wire-driven serpentine robot arm. The robot arm is made of a number of rigid nodes connected by two sets of wires. The rigid nodes act as the backbone while the wires work as the muscle, which enables the 2 DOF bending. The forward kinematics is derived using D-H method, while the inverse kinematics and its workspace can be solved by geometric analysis. To validate the design, a prototype is built. It is found that the positioning error of the robot arm is generally less than 2%. The advantage of this robot arm is that with several nodes fixed the rest nodes are still controllable. The positioning error is smaller when the fixed node is closer to the end effector.
Surface roughness plays an important role in product quality and has received serious attention for many years. It has formulated an important design feature in many situations such as parts subject to fatigue loads、precision fits、fastener holes and aesthetic requirements. In addition to tolerances, surface roughness imposes one of the most critical constraints for the selection of machines and cutting parameters in process planning. This paper focuses on developing a geometric model of turn-milling process in order to predict the surface roughness effectively so that we can offer reference or consulting in the practical machining process. The surface roughness model takes into account both cutting parameters and movement parameters such as cutter radius feed per tooth 、 cutting speed 、number of teeth 、cutters' eccentricity、 depth of cutting、spindle rotating speed and so on. Through this model, we discussed the influencing effects of various cutting parameters on the surface roughness and analyze which one has the most important impact.
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