Adjusting and improving the backlash between the screw and the nut of the corresponding coordinate axis drive chain, the backlash of the gear drive, etc. are not allowed in the servo feed system. In order to ensure flexible transmission between the screw and the nut, between the driving gear and the driven gear, a certain gap must be left during mechanical installation. However, the gap is too large but is not allowed. Because the excessive clearance will seriously affect the machining accuracy of the machine tool, the ball screw nut pair and gear pair used in the CNC machine feed system must have a reliable clearance adjustment mechanism to ensure that the backlash and the flank clearance are controlled. The software can be reasonably compensated within the scope. Therefore, in the case that changing the coordinate vector momentum compensation value can not be effective, adjusting the mechanical axial clearance, improving the corresponding coordinate axis transmission chain, shortening the transmission route becomes an effective method to finally improve the misalignment error of the two semicircles.
The error analysis and debugging method of the workpiece profile is oblique ellipse. The contour of the test piece shown in (b) is 45° oblique ellipse with the coordinate axis, that is, the diameter of the test piece in the direction of the coordinate axis 45° is not equal, which is mainly determined by the machine parameters. The position loop proportional gain value is improperly set. The actual system error in the two coordinate axes is inconsistent, causing the coordinate axis motion to follow the error on the 45° oblique line, so the precision of the machine tool is relatively poor when machining the circle. Of course, it is easy to set the two-axis position loop proportional gain to exactly the same in the control system. However, due to different external factors such as mechanical part structure, assembly quality and load condition, the actual system gain difference will also be caused, so that the motion quality of the two coordinate axes is different. At this time, the position loop proportional gain parameter should be re-adjusted so that the following errors of the two axes are equal when the machine axis is interpolated at 45°. Generally, in the X-Y plane, a 45° slash interpolation procedure should be programmed and reciprocated. Observe the output waveform of the X-axis and Y-axis rotary encoder (or tachogenerator) with an oscilloscope, and modify the position loop proportional gain parameter value while checking the waveform. There should be no overshoot phenomenon (in case of overshoot, the gain should be reduced). Parameter value), after the gain value is adjusted, the above error phenomenon should be significantly improved.
The setting of the position loop proportional gain parameter is selected according to the magnitude of the mechanical inertia and the servo stiffness required for the coordinate axis. The larger the setting value, the higher the gain and the higher the rigidity. At the same speed, the dynamic response is higher. Well, the position dynamic error is smaller. However, the system's rapid response and stability are a pair of contradictions. When the system adjusts to a certain fast response (critical point) and then increases the gain, it will cause unstable oscillation of position control. Therefore, the gain value should be based on the inherent performance of the machine tool. First, consider the position accuracy and system stability. Under the premise of not causing position overshoot, select a larger gain value and improve the fast response. It is worth noting that when using an oscilloscope to measure the output waveform of the encoder, an isolation transformer should be used to power the oscilloscope. Try to avoid the interference of the external electric field on the numerical control system and the voltage drop on the electrical components of the system. The cause of the error on the contoured surface with zigzag stripes and the method of debugging (c) have zigzag stripes on the contour surface of the test piece. The cause of this phenomenon is generally due to the feed rate control of one of the axes when the two axes are linked. The loop and position control loops are not adjusted, resulting in uneven feed rate or uneven mechanical load, low speed creep, and uneven transmission of position feedback components.
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