Design Of Time Grating CNC Rotary Table Control System Based On Position Prediction

The numerical control system is a key functional component of the CNC machine tool and is an important component to ensure the machining accuracy of the machine tool.The accuracy of the displacement sensor in the numerical control system determines the machining level of the numerical control system.The existing numerical control system mostly uses the grating as the position feedback unit.The time grating sensor is a new type of sensor developed by the group.Based on the theory of space-time conversion,it accurately measures the space by precise division of time.It has strong anti-interference ability and high measurement accuracy.There are obvious advantages in cost.Applying the time grid as an angle measuring component to a full-closed CNC system not only reduces costs,but also improves the ability to adapt to the environment.However,since the time grating is isochronous sampling,and the grating uses more fringes for spatial position measurement,the two work systems are different.For example,if the time grating is directly applied to the grating-based numerical control system,the sampling period is not synchronized and the sampling space is not synchronized.The problem cannot be directly matched to the incremental CNC system.In order to solve the above problems,the research based on the "Time Grating Displacement Sensor NC Turntable" project of Chongqing Institute of Metrology and Quality Inspection,developed a control system based on position prediction method for time grating CNC turntable.The main research contents are as follows:1.According to the principle of time grating sensor,the dynamic characteristics and static characteristics of time-grating are analyzed.The position feedback error of time-grating in grating numerical control system is studied.A research scheme for solving dynamic position feedback error is proposed.2.According to the feedback error solution mentioned above,the BP neural network based position prediction method is studied.By modeling the current value and the past angle value,the measured value of the next period is predicted,and the predicted value is feed back to the numerical control system.The system sends a pulse to drive the turntable to rotate the corresponding angle value,thus solving the dynamic position feedback error problem.A scheme for correcting the prediction error is proposed to eliminate the feedback error in the prediction measurement,so that the static measurement time grid sensor can be applied to the continuous feedback of the dynamic position.3.In order to verify the correctness of the prediction method,a turntable control system based on time grating sensor is designed.The system includes a TTL incremental interface compatible with the time grid.The synchronous acquisition card can simultaneously collect the feedback information of the grid and the grating.The system uses HEIDENHAIN circular grating.The collected angle value is truevalue,the time grating angle value is the measured value,and the experimental research of the time-gate numerical control turntable control system based on position prediction method is carried out.4.The experimental platform with the time-measured value and the measured value of the raster value is built.The experimental results show that under the static measurement condition,the TTL incremental interface of the compatible time grating is designed to measure the time-gate.There is no effect;under the dynamic measurement condition,the measurement accuracy of the gate sensor based on the position prediction method fluctuates within the range of the measurement accuracy error of the grating,and the result conforms to the accuracy requirement of the experiment.