Research And Application Of A Cable-driven Manipulator With Series Mechanism

With the development of the technology of servo motor, motor drive gradually becomesrobot’s main driving way in recent years. Manipulators, which are directly driven by motors,are installed motors in the joints. So in order to overcome the weight of the drivingmechanism, we have to increase the power of motors, and have greatly increased the weightof each joint of the manipulator and inertia, limiting their capacity and the ability ofhigh-speed motion and rapid response. However, manipulators, which adopt the technology ofcable-driven, are put all driving mechanism onto the base. Use the cable to transfer the powerof motors at the bottom to each joint. In this way, the weight of manipulator is greatly reducedand the load-to-self weight ratio is improved, and the dynamic performance is enhanced.Among the researches on manipulators driven by cable in present, most of them direct atparallel mechanism. Although parallel mechanism contributes to improve the stiffness andcarrying capacity of manipulators, in generally it has complicated coupling, the analysis to thestructure and control becoming complex. What’s more, their structure is larger and morecomplex, and the weight of additional device is close to that of motors. The number of motorsis increased, so parallel mechanism consumes more energy. In view of these, this paper putforward a cable-driven manipulator with series mechanism. It realized the completelydecoupling of all the joints of manipulators; also solved the problem that cables can’t bearpressure in the cable operation.First, this paper came up with the structure and the cable-driven scheme of thecable-driven manipulator with series mechanism. It had five degrees of freedom and had thefixed initial condition to save space. The manipulator adopted special cables, which hassimilar structure with brake cables of bicycles. By this means, the completely decoupling ofeach joint was realized. Use one motor and two cables to fulfill each joint’s motion in bothdirections. Give appropriate pretightening force to cables in order to make them tensioned.Hence, make the driving mechanism, cables, actuator form force closed to make sure all thecables are tensioned all the operation time. Second, this paper analyzed the manipulator’scontrol performance, and established a model of cable-driven, and then put forward thecable-driven control diagram. Simulate and analyze the cable-driven joint’s motion by C language programming. We discussed the main factors influencing cable-driven controlperformance, including the friction and cable stiffness, and got the scope of the friction andcable stiffness which made the manipulator run smoothly. Results of simulation proved thatjoints driven by cable could smoothly move to the target position with high precision. Then,on basis of numerical control method used in multi-axis driven, we studied the manipulator’scontrol strategy. The paper established the numerical model of the manipulator, deducing itsforward kinematics equations, calculating its jacobian, analyzing its inverse kinematics andmanipulability. Finally, put the manipulator into the specific researches both in plane and inspace, and evaluated the simulation results. And analyzed the error and realized the errorcompensation, further improving the motion precision of the manipulator.At the end of this paper, conclusions and prospects of the research are given. From theresults of simulation, it verifies the effectiveness of the proposed cable-driven manipulatorwith series mechanism. At the same time, it has great theoretical signification to researches ofcable-driven manipulators. The further research is worth of studying.