GB1428021A - Shaft drive mechanism incorporating a clearance take-up device - Google Patents

Abstract

1428021 One-way friction brakes GITAC 28 March 1973 [29 March 1972] 14939/73 Heading F2E A shaft drive mechanism which includes a driven shaft and a device for taking up the clearance between two contacting elements of the mechanism makes use of resilient retardation of the driven shaft and comprises a spiral spring having at least one convolution prestressed between the driven shaft and an abutment and tending to apply to the shaft a torque in the opposite direction to the normal direction of rotation imparted to the shaft. As shown in Fig. 1, meshing teeth on pinions 3 and 2 on driving shaft 4 and driven shaft 1 respectively have clearance, compensated for by placing around shaft 1 a spiral spring 5 having one end secured to a stationary abutment 6 and the other end bearing frictionally against shaft 1. The spring is pre-tensioned so that its convolutions have a tendency to tighten, so that with the shaft 1 being driven in the counter-clockwise direction f 2 , the spring applies a torque in the clockwise direction. In Fig. 2, the inner end 5b of the spring is located between two friction shoes 7, 7a, disposed on shaft 1 and pressed into contact therewith by the innermost convolution of the spring. The shoes may be interconnected by a flexible strip or hinge, or they may be replaced by a split sleeve. In Fig. 4 (not shown) a pre-tensioned spiral spring has its inner end in frictional engagement with a shaft and its outer end in frictional engagement with the inner surface of a drum. When either the shaft or the drum is driven in the direction to wind up the spring further, the required frictional torque is applied. Either or both ends of the spring may have a friction shoe attached (Fig. 5, not shown). Shaft 1 may be the hand-setting shaft of a timepiece or the needle shaft of an indicating instrument.