The measurement and compensation of CNC machine reverse clearance ( CNC bending machine)
the introduction with the continuous development of machinery manufacturing technology, machine tool industry has been from the past traditional machine to CNC machine this transition and upgrading of products and get rapid development. The prevalence rate of nc machine tools, year after year rises, the main reason is that the superiority of numerical control technology. Numerical control technology is applied aviation, shipbuilding, NingZhou flight and weapons production, development and production of defense industry, it is especially suitable for processing of high precision and complex geometry, size is various, and frequent modification of the mechanical parts of small and medium-sized batch production. Starting from the late 40 s research abroad, with the development of the transistor integrated circuits and computing technology, in the late '50 s early 60 s used in the production, and more and more to get promotion and application. Is China's current manufacturing technology level and economic development, economical nc machine tool is more suitable for China's enterprises and related industries, the current share of such a machine tool is higher, most belong to the open loop or closed loop control system, its machining precision is largely influenced by the mechanical precision of the machine tool, and thus solve the problem of good machining error caused by the mechanical clearance, is an important link to ensure the quality of machining. Error analysis nc machine tool space error of nc machine tool mechanical clearance error refers to the head end from machine kinematic chain to perform a comprehensive error caused by mechanical clearance and all the way, as shown in figure 1. Machine tool feed chain, its error is derived from the motor shaft and the gear shaft caused by the bonding gap, gears, the gear clearance and caused by the key connection clearance between screw, coupling of linkage, lead screw nut gap spacing, etc. Machine tool error reverse clearance refers to because of mechanical clearance in the machine tool transmission chain, machine tools to perform in the process of movement, from the forward movement into reverse movement, the implementation of a workout with the theoretical value ( Programming values) There is error, finally reflect to overlay to the error of the workpiece machining accuracy on. When CNC machine workbench reversing on the direction of movement, as a result of the existence of reverse clearance will lead to servo motor idling and workbench has no actual movement, this is called a loss. Such as g01 cutting movement, reverse bias will affect the precision of interpolation motion, if the deviation is too large will cause & other; Circle is not round, not party & throughout; The situation; And in the goo rapid positioning, the reverse bias affect the positioning accuracy of machine tools, drilling, boring holes, such as processing between each hole location accuracy is lower. Such a backlash if the value is small, had a little effects on machining precision is not required to take any measures; If the value is bigger, the stability of the system decreases obviously, significantly lower machining accuracy, especially curve processing, will affect the size tolerance and the consistency of the curve at this time must be the reverse clearance measurement and compensation. Especially the half closed loop control of nc machine tools, reverse gap will affect the positioning accuracy and repeat positioning accuracy, this needs us at ordinary times when using CNC machine, attention and the study of the production of the reverse clearance as well as the influence factors and compensation function, etc. , in the study and practice seriously review found some regularity in the process of reverse clearance self-compensation error, take appropriate processing measures, improve the processing precision of parts. Figure 1 the forming principle of the reverse clearance figure 2 reverse clearance interface clearance error of the measurement for the sake of good study the influence of the backlash error for the processing, we use a small 3 d coordinate teaching and training platform. The platform integrated with multi-axis motion controller, motor and its drive, electric cabinet, motion platform etc. Is a mechanical device adopts the ball screw transmission modular cross platform, and is used to implement the target trajectory and action. Execute device adopts the stepper motor, control device by PC, the closed-loop motion control card based on DSP, and the corresponding drive, etc. Movement control CARDS accepted position and trajectory commands from the PC, the planning process, into servo drive can accept instruction format, sent to the servo drives, servo drives for processing and amplification, output to the device. Select one of the x axis, open the about measuring reverse clearance control software ( As shown in figure 2) And start measuring the axis platform in the reverse clearance error in the process of movement. ( 1) By manual adjustment put platform in the right position, general deputy section near the platform, and is set to the workpiece origin. ( 2) Input needs to be tested in the input box movement distance of movement distance, enter 0 in the reverse clearance input box again, don't compensate the gap. ( 3) Positive point move button, let the screw in the direction of the positive sports a short distance ( About 10 mm) , and then point to stop movement. ( 4) Test button, the system will automatically according to the input test distance test, finally according to the test results. ( 5) Repeat the above action, multiple backlash. Get the x axis direction is reverse clearance value. ( 6) With the above method, reverse inching button, test the x axis direction reverse clearance, measurement results are shown in table 1. ( 7) Calculate the average of two groups of data are: the x axis is direction of backlash - 0. 482, the x axis direction reverse clearance of 0. 480.