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The rack and pinion eliminates backlash and improves the accuracy of your machine tool!

There are backlashes in every link of the CNC machine tool's feed drive chain, such as between the rack and pinion, the roller screw and the nut pair. This gap value can be large or small, unavoidable, and small enough to be ignored We will not consider it for the time being, the relatively large backlash value has a great impact on the accuracy of the machine tool.

The rack and pinion transmission system is widely used in large machine tools with large strokes due to its advantages such as large transmission ratio, high speed, high efficiency, and high rigidity. However, in addition to the rack and pinion of the CNC feed system, in addition to requiring high motion accuracy, it is necessary to eliminate the transmission gap between the paired racks and racks, otherwise the machine tool feed system will generate a backlash each time it is reversed , Has a great impact on processing accuracy.


How to eliminate the gap in the transmission? Find ways to eliminate or compensate to improve machining accuracy.

The traditional anti-backlash method is basically a rigid or flexible mechanical anti-backlash method. The mechanical anti-backlash method will increase the complexity of the mechanical structure, and the mechanical anti-backlash reliability is poor.

Backlash compensation needs to be measured first, especially for NC machine tools with semi-closed-loop control. It is necessary to pay attention to the factors that cause backlash in normal times and use the backlash compensation function to compensate the machine's feed drive chain. At the same time, the roller screw has a pitch error, and the backlash at each position is different.

First, the position of the gear should not be fixed. It must be adjustable, such as eccentric bearing seat structure or long hole, fine adjustment of the meshing gap of the gear rack. Adjust the number of servo motor pulses based on the actual gap value.


An automatic message device for rack and pinion transmission, a brain wide machine tool base and a driving beam, the driving beam slides along a linear guide provided on the machine tool base, and a servo motor and a driving gear connected to the servo motor are arranged at the end of the driving beam. The rack on the base of the machine tool meshes with a mounting plate at the end of the driving beam. A shaft bracket and a bracket are provided on the mounting plate. The shaft bracket and the reducer mounting bracket are connected together by a shaft and installed on the reducer. The opposite side of the frame is provided with protruding ear plates, a bolt passes through the through hole of the ear plate and is threadedly connected with the bracket, and a disc spring group is set between the bolt head and the ear plate.

When the transmission load is small, a two-piece thin-gear staggered tooth adjustment method can be adopted, which is in close contact with the tooth groove surfaces on the left and right sides of the rack, thereby eliminating tooth-side clearance. When the transmission load is large, the structure of double thick gear transmission can be adopted.

Adopting a dual-drive feed system, that is, using servo control to achieve backlash elimination. Although the dual-drive system overcomes the shortcomings of mechanical backlash elimination, in a high-precision, high-speed gear transmission system, manufacturing and assembly errors have a great impact on transmission accuracy.

Detection of correct rack and pinion engagement


That is, the reverse clearance of the rack and pinion is detected. The detection method is to use two dial gauges, one of which is fixed on the base surface of the bed, and the meter head measures the side of the motor base; the other dial indicator fixes the base surface of the bed On the meter side, the pinion diameter position of the meter side. Move the gear in one direction, and after the dial indicator is adjusted to zero, rotate the gear in the opposite direction. The difference between the changes of the two dial indicators is the backlash, which is less than 0.125 mm in the example.

For high-speed and high-precision large-stroke CNC machine tools, it is best to use the coloring method to check the rack and pinion contact to ensure the correct meshing of the rack and pinion.

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Record number: Shanghai ICP No. 2021025802


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