3. Tooth difference gap structure
The outer ends of the two nuts are made into cylindrical external gears with a difference in the number of teeth. The two ring gears are fixed to the nut seat with screws and pins. When pre-tightening, first remove the inner ring gear so that the two nuts rotate one or several teeth in the same direction respectively. At this time, the two nuts have corresponding displacements in the axial direction, and the anti-backlash displacement distance s can be calculated by the following formula:
n----number of teeth turned, t----screw lead. Z 1 , Z 2 ---- number of teeth.
(3) Pre-stretching of the lead screw
The ball screw will heat up when it is working. The heat causes the screw to thermally expand, thereby increasing the lead and affecting the transmission and positioning accuracy. For screw screws that require very precise transmission, thermal expansion needs to be compensated. The pre-stretching of the lead screw makes the usual compensation method.
At the time of manufacture, the length of the threaded portion of the lead screw is made less than the nominal length (lead by the number of turns) a pre-stretching amount. The amount of pre-stretching is slightly larger than the amount of thermal expansion. During assembly, the lead screw is stretched by a pre-stretching amount by a certain tensile structure, so that the threaded portion of the lead screw reaches the nominal length. During operation, the amount of thermal expansion counteracts part of the pre-stretching amount, and the tensile stress of the lead screw decreases, but the length does not change. This ensures that the pitch accuracy is not affected by thermal expansion.
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