When a CNC machine tool reverse error and high positioning accuracy, unstable quadrant marks, the first to detect screw system there is no gap. Detection methods: indicator with the ball on the end of the center hole of screw, screw axial measurement, another piece of dialgauge measuring worktable. The rotation of the screw, observe the two block on the dial indicator shows, according to the change of different values confirm the fault location.
1）Inspection and repair of clearance of screw bearing
If the dial indicator measuring screw in the screw forward and reverse rotation of the pointer no swing, that no screw movement. If the indicator pointer swing, indicating screw channeling phenomenon. The dial indicator measuring the maximum and minimum value difference is the screw axial distance. At this point, we will check whether the back bearing of the support bearing is locked, whether the bearing is worn out or not, whether the preload bearing washer is suitable or not. If the bearings are all right, just re - load the pre - loaded gasket. If the bearings are damaged, the bearings need to be replaced, re - loaded with pre - load washers, and then backed back. The axial movement of the lead screw mainly depends on the precision of the preload bearing gasket. The most ideal condition of the installation accuracy of the screw rod is that there is no positive and negative clearance, and the support bearing must have about 0.02mm interference.
2）Detection and maintenance of gap between two nut pairs of ball screw
By inspection, if the fault is confirmed, it is not caused by the movement of the lead screw. It is necessary to consider whether the screw nut, the gap between the two, the detection of this situation basically with the detection of lead screw moving the same. Working table is connected with the dial indicator and the nut, forward and reverse rotation screw, detect the maximum clearance between a screw and a nut, and then adjusted. As shown in Fig. 2, the thickness of the shim 4 is adjusted so as to cause axial displacement of the left and the right two nuts 1 and 2 so as to eliminate the gap between the ball screw nut and the pretightening force. The structure of lead bar nut is different, so the adjustment methods are different, not to enumerate here.
3）Inspection and maintenance of single nut pair
For single nut ball screws, the gap between the screw and nut pairs cannot be adjusted. If the lead screw nut is detected, there is a gap. First check the lead screw and nut thread arc whether worn, such as serious wear, must replace the whole set of lead screw nut. If minor wear is detected, a larger diameter ball can be replaced to repair it. First of all, the maximum clearance of the screw nut pair is detected, converted to the increase of the ball diameter, and then fitted with the appropriate ball to reassemble. This kind of maintenance is complex and takes a long time and requires a high level of technology.
4）The gap between the flange and the table and is not fixed
This problem can easily be neglected for a long time, reciprocating machine, screw Fala disc loose gap, check the gap in the top screw failure factors to exclude, in order to avoid detours in repair.
5）The maintenance of the ball screw nut is not smooth and noise is too large.
Ball screw nut movement is not smooth and noise is too large, mostly due to poor lubrication, but sometimes may be due to servo motor drive parameters are not adjusted properly caused.
a) The bearing, lead screw and nut are badly lubricated
Machine tools such as noise and vibration in the work, in the detection of the mechanical transmission part is no problem, we must first consider the problem of bad lubrication, many machine after years of operation, the screw nut automatic lubrication system often blocked, not automatic lubrication. It is possible to solve the problem by adding high temperature and high speed grease to the bearings and nuts. Grease ensures the normal operation of bearings and nuts for several years.
b) Servo motor drive problem
Some machine tools produce vibration and crawl in the movement, and often detect the mechanical parts without any problems. No matter how to adjust, vibration and crawl can not be eliminated. After careful examination, it is found that the servo motor drive gain parameter is not suitable for actual operation. After adjusting the gain parameters, vibration and creep can be eliminated.
