Anti-collision Device Based On Stewart Platform Mechanism For Robot Polishing

When an industrial robot is used for grinding operations,it is generally necessary to establish a three-dimensional model of the workpiece according to the outline parameters of the workpiece,and use this as a basis to generate the running trajectory of the grinding tool.However,in practical applications,due to the machining error of the workpiece and the installation error of the workpiece on the grinding station,etc.,the trajectory of the grinding tool may interfere with the workpiece,thereby causing a collision.This paper designs a robot polishing anti-collision device based on the Stewart platform mechanism,which monitors the contact force during the polishing process and judges whether the contact force reaches the set threshold.When the contact force is too large,the anticollision device responds quickly,performs an avoidance action,and adjusts the position and posture of the grinding tool installed at the end of the device to avoid a serious collision.First,the Stewart platform mechanism is used as the main structure to design an anticollision device.A one-dimensional force sensor is installed on each branch chain of the device to collect the force data on the branch chain during the polishing process,and then calculate the six-dimensional force on the device.Each branch chain has an air cylinder as a driving component,and when it is necessary to perform an adjustment action,the movement of the air cylinder can be controlled by a solenoid valve to realize the action.The mathematical model of the device is established,and the relationship between the Jacobian matrix of the device and the structural parameters is deduced,which lays the foundation for the subsequent optimization of the structural parameters for the optimization of the force detection performance.The configuration and structural parameters of the device were preliminarily determined,and the force range of each branch chain was calculated.Based on this,the models of key components such as cylinders and force sensors were selected.Then,the isotropy and decoupling performance of the force sensor of the anticollision device is studied.The Jacobian matrix of the anti-collision device describes the mapping relationship between the force on the branch chain and the end force.Therefore,the performance index of the device force sensor is essentially the nature of the Jacobian matrix,and the Jacobian matrix of the anti-collision device is based on its structure.Parameter determined,therefore,the performance of the device force sensor also depends on the choice of structural parameters.The relationship between the performance indicators and structural parameters of the device force sensor was discussed,and the configuration and structural parameters of the device were optimized.At the same time,the static parameters needed for gravity compensation were calibrated using parameter identification algorithm.On the one hand,the gravity and gravitational moment of the anti-collision device and the grinding tool installed on it will be mixed with the data detected by the anti-collision device force sensor;on the other hand,due to the existence of parts processing and assembly errors,the sensor will display when it is empty.The number is not zero,and there is a zero error.In order to obtain the true value of the contact force between the device and the outside world,the two parts of the system error need to be compensated.Before the force compensation calculation,static parameters such as the weight of the anti-collision device,the position of the center of gravity and the zero point error need to be obtained.The parameter identification algorithm of six-dimensional force sensor based on least square method is studied,and the algorithm is verified by CoppeliaSim simulation software.Finally,the control system of the anti-collision device was designed and built,including the sensor data acquisition system,the cylinder control loop,the upper and lower computer system for data transmission and processing,etc.The principle prototype of the anti-collision device was processed and assembled,and the experimental system was built.The designed parameter identification algorithm is used to calibrate the sensor parameters of the device.A simulated collision experiment was carried out on the anticollision device to verify the feasibility of the scheme.