Patent GB-486281-A (GB)
Title: Means for correcting for backlash in screw and nut drive mechanism
IPC: B23Q5/56
Filed: 1937-10-06
Abstract: 486,281. Feed motions for milling- machines &c. WANDERER-WERKE VORM. WINKLHOFER & JAENICKE AKT.- GES. Oct. 6, 1937, No. 27102. Convention date, Oct. 8, 1936. [Class 83 (iii)] [Also in Group XXIV] In a backlash-eliminating device for a screw- and-nut drive for operating a machine-tool slide, such as a milling-machine table, the screw carries a non-rotatable auxiliary nut which is urged axially of the screw from a neutral position towards or away from the main nut by an adjustable force determined by the working conditions. A milling-machine table carrying work 45 is traversed by means of a rotary screw 3 slidably keyed to a bearing sleeve 6 integral with the driven gear 5. The screw runs in a fixed nut 10 and moves axially therethrough to impart movement to the table. In modifications, the nut may be rotative and the screw fixed or the screw may be on the stationary part and the nut on the moving part. The screw also carries an auxiliary nut 12 which is coupled at 11 to the fixed nut but is movable axially relative thereto. The auxiliary nut is displaceable axially by power in either direction, such direction being selected so that the main and auxiliary nuts are firmly engaged with opposite sides of the thread of the screw as shown in Fig. 5. For feeding the work to the left against the direction of the cutter as in Fig. 5, the auxiliary nut must be moved to the right by a moderate force, but if in similar conditions the feed is in the same direction as the cutter, Fig. 2, the screw will be urged so that its left-hand Hanks engage the nut and to avoid backlash the auxiliary nut must be thrust to the left so as to maintain the engagement of the left-hand flanks with the nut in all conditions. Similarly, if the feed is to the right the auxiliary nut must be urged weakly to the left or strongly to the right according to the direction of cutter rotation. In one form, the nut 12 is urged by a pivoted lever 16 coacting with a pair of springs 20, 21, either of which may be compressed to exert the required force on the lever by the longitudinal displacement over a scale 27 of a rod 24 carrying the spring abutments. The springs 20, 21 may be released and the lever returned to neutral by another spring. In place of springs, electromagnetic or electro-mechanical means may be employed. In another modification, Fig. 6, the lever 16 is operated by two hydraulic cylinders 29, 30 supplied from a pump 33 through a pressure control 34 and a valve 35. The valve may direct pressure fluid to either of the cylinders 29, 30 or may short-circuit the pump supply. The valve is controlled by the member 39 which also controls the direction and speed of the table movement. The positions I and II of the handle give respectively the fast approach and slow feed table movements to the left and the positions IV and V the slow and fast movements respectively to the right. III is a neutral position. A cam 40 operates a lever 44 to move the valve to positions where force is applied to the auxiliary nut only at the positions II and IV corresponding to slow table feed movements. The fast movements are then unimpeded by the friction in the nut 12. In a modification, the cam 40 may have three sections of which one gives no movement of the nut 12, the second and third giving opposite movements to the nut for the same direction of table feed so that the device may be adapted for cutting either with or against the table feed. In another modification, the valve is provided with two axially-spaced control sections for adjusting the machine for cutting with or against the work.