Backlash compensation of semi-closed CNC machine based on acceleration and deceleration control
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(61 Fund Project i South China University of Science and Technology Natural Science Fund-funded Housing (18House.Allrights for the semi-closed CNC machine tools commonly used in manufacturing, the main factors affecting the positioning accuracy of machine tools are machine geometry accuracy, servo control accuracy, measurement system Accuracy and fluctuations in ambient temperature, etc. Among them, the machine tool positioning error caused by the backlash and elastic deformation of the transmission mechanism accounts for 50% of the total machining error of 60%. 112. To reduce this error, in mechanical terms, by using high precision The ball screw and the method of adding the pre-tightening force when installing the screw can reduce the influence of the backlash to a certain extent. However, the lead screw always has manufacturing errors, and the wear is caused by long-term use. Therefore, the backlash is used. The semi-closed CNC machine tool with compensation function is an effective method to improve machining accuracy and reduce cost.
In the specific application of backlash compensation, how to shorten the backlash compensation time of the moving parts and how to control the dynamic process of the backlash compensation of the machine tool to prevent the limitation of the motor itself from being exceeded, resulting in a large following error and Oscillation, etc., these are still important issues to be considered in the implementation of the backlash compensation algorithm. Therefore, based on the basic principle of backlash compensation, this paper proposes a direction gap compensation algorithm that accords with the acceleration and deceleration control of the machine tool. Finally, a specific typical digital servo system of the algorithm is given to realize the backlash compensation. When it is necessary to ensure the smoothness of the servo system and avoid impact and oscillation, it is necessary to consider the limitation of the servo motor drive capability when adding backlash compensation. For example, the backlash compensation value cannot be added once in one sampling period. Otherwise, the actuator output will be saturated, resulting in a large following error. At the same time, the motor acceleration and deceleration caused by adding backlash compensation should meet the limitation of starting and stopping acceleration and deceleration defined by the servo motor driving torque. On the other hand, for fast moving systems with frequent commutation, the backlash compensation can be completed in the shortest time to ensure the positioning accuracy of the system. In order to meet the above constraints, this section introduces the acceleration and deceleration control method into the backlash compensation to realize a step backlash compensation algorithm based on acceleration and deceleration control. The goal of the algorithm is to make the system meet. Under the premise of the acceleration and deceleration control of the transition process, the backlash compensation is completed in the shortest time.
The relationship between speed and time in the acceleration and deceleration control is v=/(t). It should satisfy the following constraints/4々(1) The acceleration of the acceleration process should be as large as possible under the premise that the small linear acceleration/deceleration curve is accelerated by the servo motor driving torque. In order to ensure that the startup does not lose step, there is a faster response speed. (2) The speed change rate of the deceleration process should be reduced to zero before it is in place to ensure no overtravel when stopping. (3) At the end of the acceleration and deceleration process, the actual position should be consistent with the command position to ensure the position accuracy. As shown by the linear acceleration/deceleration curve, the acceleration a is less than or equal to the starting acceleration defined by the servo motor driving torque. V. is the average feed rate of the shaft. t is the acceleration time. S is the acceleration, constant speed and deceleration 3 for the author to achieve the anti-A-direction clearance acceleration and deceleration curve. The whole compensation process consists of two 1/°\ processes of acceleration section and deceleration section. The area of ​​5 57 surrounded by the two phases is the backlash compensation distance D. The acceleration a in the backlash compensation diagram is not only less than the acceleration/deceleration curve. The starting acceleration defined by the servo motor driving torque must also satisfy the difference between a maximum acceleration equal to or less than the motor and the acceleration set during normal acceleration. Since the medium constant speed motion time is designed to be zero, the shortest backlash compensation time is achieved while satisfying the acceleration and deceleration control. The following backlash compensation algorithm based on acceleration and deceleration control is derived.
The compensated position is satisfied: the gap value is 32Um. (b) The machine tool x-axis positioning error distribution curve obtained after adding the backlash compensation algorithm based on the acceleration/deceleration control proposed in this paper. The backlash has been reduced to 2Um. Within this, it can be seen that the backlash of the x-axis has been successfully compensated.
Backlash compensation is one of the main methods to improve the positioning accuracy of semi-closed CNC machine tool servo system. In the process of backlash compensation algorithm, how to shorten the backlash compensation time of moving parts and how to backlash of machine tool The problem of compensating the dynamic process for reasonable control is studied. Based on the traditional step backlash compensation method, a backlash compensation algorithm for acceleration and deceleration control is proposed. Finally, it is proved by experiments: The algorithm proposed in this paper can effectively reduce the influence of the backlash of the servo axis of the machine tool.