Research On Joint Servo System Based On FPGA

Robotic arms can perform some complex and difficult tasks instead of humans,they are increasingly used in robotics fields such as industrial robots and medical robots.Light-weight manipulators have the characteristics of small size,light weight,and flexible operation.They are generally composed of 6 to 7 rotating joints in series to achieve multiple degrees of freedom movement.Therefore,the key to improving the control performance of the manipulator is to improve the control performance of each joint of the manipulator.A set of joint servo control algorithm including current loop and speed loop is designed for the self-developed 7-DOF Light-weight manipulator in the paper,and the algorithm is implemented with Verilog hardware description language.The algorithm runs in the main control chip FPGA of the joint controller,so that the manipulator has better load capacity and movement accuracy.Firstly,current loop optimization algorithm is proposed in this paper.When the vector control is adopted,the dynamic coupling effect between the excitation current and the torque current of impact the dynamic response performance of PMSM.The voltage feedforward decoupling algorithm is used for current dynamic decoupling,and the back-EMF compensation algorithm is also used to reduce the dynamic interference with torque current caused by back-EMF.In order to extend the current loop bandwidth,a new strategy of current sampling and duty cycle update is proposed which can reduce the delay time of the current loop.Then,the speed loop algorithm based on PI controller is completed,and a variable gain coefficient integral negative feedback strategy is proposed to solve the problem of regulator saturation during the speed dynamic response,which can improve the speed dynamic response performance of PMSM.On this basis,in order to make the speed loop response fast and the overshoot is small,the PDFF controller is designed to improve the speed loop.In order to improve the robustness of the speed loop,an on-line inertia identification algorithm based on recursive least square(RLS)method is proposed to identify the load inertia.The identified load inertia is used for the adjustment of the speed loop parameters and the observation of the load torque.A load torque observer based on the Gopinath principle is designed to observe the load torque online.The identified load torque is used for the feedforward compensation to the speed loop,which can improve the anti-load disturbance capability of the robotic arm.Finally,a control strategy based on notch filters and improved adaptive notch filters is proposed in the paper to solve the problem of torque/speed ripple of PMSM.In order to realize the filter parameter self-tuning function,an online speed harmonic identification strategy based on fast fourier transform(FFT)method is proposed,which can sample and analyze the speed information when the motor is running and obtain the frequency and amplitude of the speed harmonics.