In order to guarantee the reverse transmission precision and axial rigidity of the ball screw assembly, the axial clearance must be eliminated. In addition to the individual with a single nut to eliminate the gap, the ball screw nut assembly usually use double nuts preload to eliminate clearance. The principle is: the use of two nuts relative axial displacement, so that the balls in the two ball nuts are in close contact with two opposite sides of spiral track, when using this method to eliminate the gap, should pay attention to the preload force can not be too large, too large preload will make the unloading torque increases, thereby reducing the transmission efficiency, and shorten life. Thus, generally require several adjustments to ensure both can eliminate the gap and flexible operation. In addition to nut preload in adjustment, it should also pay special attention to make the gap between screw mounting portion and driving portion as small as possible, and has sufficient rigidity.
Adjust the clearance of the ball screw, is to guarantee the reverse transmission accuracy and axial rigidity. When using preload method to eliminate axial clearance, should pay attention to the preload should not be too large, too large preload will make the unloading torque increases, reducing transmission efficiency, increase transmission assembly wear and shorten life. The methods commonly used in double-nut screw eliminate clearance are:
1, Double nut gasket gap adjustment type, changing the thickness of the gasket to make both internal and external nuts generate axial relative displacement.
Double nut gasket gap adjustment structure advantages and disadvantages: this kind of adjustment method can accurately adjust the preload, the structure is simple, high rigidity, reliable, but the adjustment is not convenient, raceway wear can not be adjusted at any time.
2, Spring automatic gap adjustment type: with the spring to produce the axial displacement between the two nuts. Its characteristic is in the use process can automatic compensate the gap due to the wear or elastic deformation, but its structure is complex, the axial rigidity is low, suitable for light loads application.
3, Tooth difference gap adjustment type, through the adjustment of the nut on the end of the external tooth relative to the internal tooth of the meshing angle to eliminate the gap.
Double nut tooth difference gap adjustment of the structure advantages and disadvantages: this kind of adjustment method can accurately fine adjust the preload, reliable, easy to adjust when the raceway wear. But the structure is complex, suitable for the precise positioning system needed to obtain the accurate preload.
4, Thread gap adjustment type, rotate adjusting nut 1, so that the axial displacement of the nut 2.
Double nut thread gap adjustment structure advantages and disadvantages: this kind of adjustment method structure is simple, easy adjustment, raceway wear can be adjusted at any time, but the preload is not very accurate.
Source: http://www.machineballscrew.com Ball Screw Nut Assembly Manufacturer.
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