Patent GB-826484-A (GB)
Title: Improvements in or relating to means for controlling the arresting of a rotary shaft or the like
IPC: H03J1/22
Filed: 1956-06-19
Abstract: 826,484. Stopping shafts in predetermined positions; toothed gearing. COLE Ltd., E. K., and COPPIN, K. J. Sept. 19, 1957 [June 19, 1956], No. 18891/56. Classes 80 (1) and 80 (2). [Also in Group XXXVII] In means for stopping a shaft in a predetermined position, a device driven step-by-step by the shaft controls a flexible arm co-operating with contacts associated with drive energizing means for the shaft, the flexible arm has three positions corresponding to two directions of rotation and rest of the shaft and the arrangement is such that over-shooting of the shaft results in it being driven back to the rest position. A flexible contact arm A is movable from a central position where it contacts a contact A1 to positions where, by flexing, it contacts A2 and opens A1, and where it opens both A1 and A2. The movement is produced by a lever L engaging a rocker R pivoted at P and having a tip T dimensioned to enter a notch N of a cam C during a small part of the rotation of the latter. The cam C is driven by a ratchet wheel W engaged by a striker pin SP attached to a disc O on the shaft, the wheel W being held by a detent D. If the shaft is displaced slightly from its rest position in an anti-clockwise direction, the arm A will contact neither A1 nor A2 and a forward relay FR is operated through a lamp LP1 so that contacts FR1 connect terminal a of the driving motor M to the - ve and the released contacts RR 1 connect terminal b to the + ve supply. This causes the motor to drive in a clockwise direction until the striker and cam mechanism flex the arm A into contact with A1. This shorts the relay FR to release FR 1 to contact the - ve supply and stops the motor under regenerative braking and allows full voltage to light the lamp LP1 to indicate completion. If the motor runs-on due to inertia, the arm A flexes to contact A2 which energizes the reverse relay RR to connect the contacts FR1 to the + ve supply to run the motor in the reverse direction until the contacts A2 again open. If the contacts A1 open the system reverts to the original condition and a fresh approach is made from the original direction. In a modification to ensure that backlash is always taken in the same direction, a contact controlled by relay RR is inserted between A1 and A2, such that the final approach to rest is always in the same direction. By the use of a selector switch and a plurality of pairs of contacts A1, A2 the device may be used to position the shaft in a number of positions. In an embodiment, which may be used for radio apparatus, two adjacent control systems have the devices grouped in pairs on a circle centred round the controlled shaft, the devices being arranged alternately to the front and rear of a central insulating plate. To enable rapid setting of the embodiment the operating devices are held to their shafts, geared to the controlled shaft, by lock nuts, and setting is performed with the lock nuts released and the use of the indicator lamps to indicate the moment of rest. To indicate the position of the output shaft OS (Figs. 10 and 11) a knob K and dial D1 are fixed thereto and carry a spring- loaded ball BB. A second revolution counting dial D2 is located behind the dial D1 and observed through an aperture therein, and rotates with slight frictional drag about a boss B attached to the front plate. The boss B extends through the dial D2 and carries a spring strip S having semi-circular cut-out with the same spacing as the holes in D2. As the shaft OS rotates it carries the dials D1 and D2 round by virtue of the ball BB, until the ball meets the strip S, whereupon it releases dial D2 and reengages the next hole, thus moving D2 one division per revolution relatively to D1. To reduce the speed of approach to the rest position a worm drive in which the worm W1 (Fig. 12) of coarse pitch is in fine threaded connection with its shaft IS is employed in the drive from the motor to the controlled shaft. The worm W1 is driven from the shaft IS through a driving pin DP engaging a driving disc DD free on the shaft IS but having an axial projection engageable by the tab of one of a number of tabwashers TW, the tab-washer at the remote end being engaged by an axial projection on a collar C fixed to the shaft IS. On removal of drive from the shaft IS the tab-washer assembly allows a rotational back-lash during which the worm screws along the fine thread to provide a slow speed drive to the worm wheel W2. A groove G in the worm W1 engaging a switch SS may be used to provide motor speed limitation during slow speed movement. In a modification (Fig. 2) to provide greater accuracy, the rocker R is operated jointly by identical concentric cams C and C1 which are driven respectively by the striker SP and gears G, G1 from the shaft. Since the striker SP and gear G are rigidly held together and the ratios of G, G1 and SP, W differ, the rocker R can only be moved into its operating position when the notches in the cams C and C1 coincide, which occurs less frequently than one revolution of the cam C.