Research On The Technology Of Zero Moment Control And Collision Detection Of Collaborative Robot

The safety of traditional industrial robots is poor,many restrictions such as guardrails are needed,and the decision-making and intelligent control of traditional industrial robots are far from reaching the intended effect.The emergence of collaborative robots will speed up the popularization of robots,and at the same time provide us with the possibility of allowing robots to enter the life,realizing real human-robot collaboration.This paper takes collaborative robot as the research object and explores the new driving principle.The frameless direct-drive motor and the harmonic reducer with certain flexibility were integrated in high density.The high power density ratio mechatronics joints were developed and serialized and modularized.Based on the theory of kinematics and dynamics,the technical difficulties of zero moment control and collision detection technology were researched in depth to realize the function of direct-teaching and collision detection for collaborative robot.A nonlinear dynamic model with static friction,coulomb friction,and viscous friction was established for zero moment control algorithm.It aims to improve the precision of the robot zero moment control algorithm and meet the requirement of easy direct-teaching under the external forces.Two collision detection methods without torque sensor were proposed for collision detection.The main research contents and innovation points of this paper are as follows:1.High power density ratio modular joint and robot system design:The new configuration design method of collaborative robot was explored to optimize the overall configuration of the robot and the configuration of six degrees of freedom.The multi-objective light-weight design method based on numerical optimization and finite element simulation was adopted to carry out light-weight design on the structure and design the high-strength light and thin shell.According to the requirement of maximum load and speed of the robot,the torque of the motor and harmonic reducer of the two modular joints of the robot were verified.The new driving principle were researched,the frameless direct-drive motor and the harmonic reducer with certain flexibility were integrated in high density.The high power density ratio mechatronics joint was developed and serialized and modularized.The new flexible brake mechanism was designed to simplify the joint structure,which is more conducive to heat dissipation.It provides a new idea for braking design of collaborative robot.2?Kinematics analytic method of new configuration collaborative robot:The forward and inverse kinematics of the robot is the connection of mechanical system and control system.In order to obtain the closed solution of inverse kinematics of the light-weight collaborative robot with six degrees of freedom,analytical method was used to get 8 solutions of the robot.It ensures the most important characteristics of real-time and accuracy.Finally,the accuracy and validity of the analytical method were verified by Matlab simulation.According to the forward kinematics,the workspace of the robot was obtained by using Monte Carlo method.According to the configuration and inverse kinematics,the singularity of the robot was analyzed,which provided a strong theoretical support for avoiding the singularity in motion control.3?Zero moment control technology based on the torque compensation:By overcoming the gravity and friction of the robot,the robot can adapt to the external force to move.The parameters of torque sensitivity and friction of the robot were identified by the method of least square method when the robot joint was rotating at a low speed.The identification of viscous friction and coulomb friction was achieved by controlling different velocities at the same position and different positions at the same speed respectively.By adding the compensation value of viscous friction and coulomb friction on the basis of the gravitational torque and static friction,more accurate torque compensation control can be realized,which makes the zero moment direct-teaching of the robot more precise and more smooth.4?Collision detection algorithm under sensorless control:A collision algorithm based on the generalized momentum observer was proposed for collision detection under sensorless control.On the basis of dynamic model,the generalized momentum observer was introduced to avoid the impact of acceleration instability in collision detection.At the same time,the classic friction model was introduced into the dynamic model,which improved the precision of the whole dynamic model.The appropriate threshold rth was set according to the collision requirements.When the residual value exceeds the threshold,the collision between the robot and the outside world occurs.The collision detection algorithm can be tested in real time without any external sensor or acceleration sensor and only the position information of the robot joint need to be measured.5?Double encoder collision detection method:Based on the special joint design of the robot,another collision detection method based on double encoder was proposed.Using the equivalent flexible characteristics of the harmonic reducer,the low-cost detection of external force collision was realized through the position error detection of the two encoders,which enables the robot to realize real-time collision detection.At the same time,three kinds of post-collision response strategies were proposed.Oscillating mode,zero moment response mode and forced stop mode can be selected according to actual needs.