Impedance And Admittance Control Of Serial Flexible Joint And Its Application In Rehabilitation Robot

Compared to the traditional industrial robots, the main characteristic of rehabilitation robot is to interactive with human, and in the process of physical human-robot interaction(PHRI), high stability and safety is required. So it is still a research focus and difficulty in how to improve the safety of robot in the process of physical human-robot interaction. In this paper, a new type of series elastic joint, which can realize both passive and active compliant control, is provided to improve effectively the safety in the process of physical human-robot interaction. On the other hand, the complexity of the whole control system is increased because of the extra elastic element. In this paper, the dynamical model of the series elastic joint is built and reliable control algorithms are designed for the rehabilitation robot. The research contributions of this paper are as followings:1. Design the compact integration series elastic joint and its hardware and software platform. The joint consists of the Frameless-brushless DC motor, harmonic gearbox, elastic element, position and torque sensor and circuit board and reasonable assembly is achieved in joint space. And based on FPGA, the PWM, current detection, position and torque encoder and other customized IP cores are completed so as to the SOPC system is available. The control system is built by using the embedded NIOS softcore in FPGA, such as, the PD type controller, classical PID controller, impedance and admittance controller, etc.2. Analysis and simulation of the series elastic joint: Modeling is divided into two kinds of categories, one is that the brushless dc motor is not taken into account and the other considers brushless dc motor model. The transfer function is obtained through the modeling, and then the stability conditions of the control system are acquired by using lawes criterion. On the other hand, the impedance characteristics of the system is analyzed. As a result, the steady-state response and the stiffness of the system are obtained. At last, a simulation is carried out to verify the effectiveness of the proposed method by using Matlab/Simulink.3. Impedance and admittance control for series elastic joint are implemented. Based on the position controller, impedance and admittance controller are closed by using the inherent torque sensing. And it can improve the stability for the series elastic joint, which enhances the safety in the process of physical human-robot interaction.4. Gravity compensation is added to accomplish the “zero gravity” impedance and admittance control, which can be used to realize the robot teaching and the active and passive rehabilitation modes.