Page 46 of catalogue Drive Units with Ball Screw Drives of Bosch Rexroth AG

46

Bosch Rexroth AG

Drive Units with Ball Screw Drives

R310EN 3304 (2007.05)

Drive Units with Driven Screw, AGK Series

Product Overview
Patented screw support
The patented screw support elegantly solves the problem of the critical speed in horizontal ball screw applications. If the screw is not supported, a longer stroke normally means a reduction in the critical speed and hence the permissible linear speed, corresponding to the square of the added length. Ball Screws therefore come up against their physical limitations, which is particularly inconvenient in applications where high speeds could help to achieve shorter machine cycle times. These limits can be very effectively extended with suitable supports for the rotating screw. Up to now, however, there were no readily available practical solutions, and it was the responsibility of the customer to implement such designs. With this product, Rexroth offers a solution that truly deserves the name “drive unit” because all of the design details of this system have been engineered and implemented as elements in a modular structure. Operating principle of the screw support (SPU) in horizontal operation: The screw support motion is triggered by the movement of the ball nut along the screw. Screw supports are used in pairs. Depending on the application, one, two or three pairs may be necessary. When the ball nut moves out of the central position, the screw supports are pushed together in the direction of movement, while those behind the nut are positioned at predetermined locations along the travel range. Even when the nut is at the end of its stroke, the screw will be supported radially at several points along its length. Since the unsupported length between two screw supports is relatively short, the critical speed can be very effectively increased. As a result, real restrictions of the maximum possible linear speed are practically eliminated. In vertical operation, a further benet is offered by the pillow blocks. The oating bearings in the pillow blocks contain two deep-groove Ball bearings which, in terms of the critical speed, act almost like a xed bearing, but without exerting any substantial stretching forces on the screw or the machine.