Research On EtherCAT Communication System And Impedance Control For Anthropomorphic Dexterous Hand

Dexterous robot hand is a system which is composed of a single finger serial robot and parallel robots between fingers. Meanwhile, it is complex cross-technology fields, including mechanical design, circuit design, sensor design, combined with algorithm programming, etc. The purpose for this paper is to develop a control platform for HIT/DLR dexterous hand II with high-speed communication and good real-time performance, which is based on China national high technology research and development program 863 "Research on structure design and grasping manipulation of new five-fingered dexterous hand". At the same time, the features of complex algorithms of the HIT/DLR dexterous hand II are easy to be realized by this platform. Then, the strategies of impedance control algorithm based on this real-time control platform which can be applied in actual grasp and operation is proposed for special tasks.The development status of dexterous hand communication is firstly analyzed in this paper. For the problems of the dexterous hand communication combined with the features of the HIT/DLR dexterous hand II, we draw a conclusion that Ether CAT bus is the most suitable for designing HIT/DLR dexterous hand II communication. Furthermore, a platform of Ether CAT control system has been developed, which includes the development of the Ether CAT slave hardware circuit system, microcontroller FPGA Ether CAT slave software system, PLC control function layer in Ether CAT master and Matlab/Simulink algorithm modules in Twin CAT 3.1. The real-time and reliability for the HIT/DLR dexterous hand II dynamics modeling and control algorithm realization have been guaranteed by the Ether CAT platform.The accuracy of distinguishing five fingers dexterous hand dynamics model contributes to the precise position control, fingertip force control, force and position hybrid control and active compliance control. In Cartesian space, fingers reference coordinates has been discussed and the relationship of the fingertip position, velocity, angular velocity, acceleration and angular acceleration has been described. Referring to the dynamics of a single finger, the two fingers dynamics of the HIT/DLR dexterous hand II has been established by discussing two fingers constraints, and the multi-fingers dexterous hand dynamics model has been deducted. Finally, the multi-fingers dynamics model relied on multiplier has been applied to the Ether CAT platform, which is based on Ether CAT slave three interruption(IRQ) PDI communication. Thus, the proposed multi-fingers dynamics model applicability can be ensured.For the HIT/DLR dexterous hand II under the equality constraints, the existence of solutions, necessary and sufficient conditions, convergence and convergence rate of the dexterous hand finger in the free space with unconstrained condition are analyzed firstly in theory. Furthermore, the necessary and sufficient condition and sensitivity of the outside loop impedance controller are analyzed theoretically for the dexterous hand fingertips in the free space with constrained condition. According to the level of sensitivity function, we get a conclusion that the Lagrange multipliers*λ will decrease with the growth rate of the sensitivity function. Compared with the exact penalty function approach and the barrier method, the controller based on Lagrange multiplier algorithm has better real-time performance, faster fingertip force nonlinear programming and stronger robustness. Therefore, the double loops impedance controller of the HIT/DLR dexterous hand II are designed based on Lagrange multiplier theory. The fingertip force optimization strategy with double loops impedance controller has been provided by constructing augmented Lagrange function(,)k kkCL θ λ. Finally, an impedance controller with equality constraints based on Lagrange multiplier has been developed.The equality constraints when HIT/DLR dexterous hand II operates the actual object is only a special case, because the actual situation of the most situations are to complete specific tasks. So, inequality constraints between fingertips will be more practical. Thus, an inequality constraints strategy has been finally provided for inequality constraints grasp problems, which include single finger force optimization unconstrained inside loop based on Broyden Fletcher Goldfarb Shanno(BFGS) method and constrained outside loop based on Karush Kuhn Tucker(KKT) method. The experimental results show Ether CAT-based HIT/DLR dexterous hand II platform has high-speed, real-time and stability performance. Meanwhile, the double loop impedance control algorithm provided by this paper with the purpose of operating the specific tasks, can be well realized by Ether CAT platform. Finally, the strategies in this paper can be implemented and verified effectively through HIT/DLR dexterous hand II grasp and operation experiments.