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Zero Backlash Screw Nut Drive

IP.com Disclosure Number: IPCOM000077542D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Graner, FL: AUTHOR

Abstract

Screw and nut drives utilized in moving carriages or tables in machine tools encounter problems of movement accuracies due to backlash, which prevents positive positioning of the table by the drive.

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Zero Backlash Screw Nut Drive

Screw and nut drives utilized in moving carriages or tables in machine tools encounter problems of movement accuracies due to backlash, which prevents positive positioning of the table by the drive.

Preloading the nut, by use of a split nut wherein the two halves are either forced apart or together, has been utilized to minimize backlash. The preloading method requires a preloading force exceeding the maximum driving force expected and doubles the friction force in a given drive.

Since inertia forces of a moving carriage reverse in direction between acceleration and deceleration, including reversal, backlash can be prevented by having the nut threads engaging both sides of the screw threads. This type of mechanism is provided above in Fig. 1 where screw 10 has two nuts 12 and 14 engaging thread 16. Nut 12 is connected to carriage 18 through a hydraulic cylinder 20, having a port 22 through which hydraulic pressure is applied. Nut 14 is connected to carriage 18 through a strain gauge link 24. Normally, a minimum force is maintained by hydraulic cylinder 20 to hold nuts 12 and 14 in close contact with its respective side of thread 16. As the inertia force of the carriage 18 tends to cause separation of one or the other nuts 12 or 14, the strain gauge on link 24 indicates a force less than normal and automatically causes an increase in hydraulic pressure to cylinder 20, to maintain both nuts 12 and 14 in contact with thread 16.

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