Patent GB-738596-A (GB)
Title: Electric system governed by the movements of a movable member
IPC: G08C19/00
Filed: 1952-12-12
Abstract: 738,596. Electric follow-up control systems. LEBAR, M. LEVY-. Dec. 12, 1952 [Dec. 12 1951], No. 31602/52. Class 40 (1). In a two-way switch of the follow-up or null type (i.e. where the displaced control member is restored to its original position), the switch is actuated through a member pivoted to the feeler or follower about an axis perpendicular to the instantaneous paths of the switch elements. The switch is normally open and the follower may be moved manually or motor driven. An auxiliary switch may be provided for effecting high- and low-speed control of the motor according to the deviation of the follower from correspondence. Follow-up switch construction, Fig. 1. The control shaft 1, of a meter e.g., carries a hand 2, movement of which in either direction causes it to contact one of two contact pins 5, 6, carried by respective arms 3, 4 pivoted to the follower spindle 17, and urged by springs 11, 12 towards stop pins 7, 9 carried by the spindle. Closure of the contact 2-5 or 2-6, as the case may be, energizes, in the appropriate sense, a motor (not shown) which through worm gearing 18, 19 drives the spindle 17 to follow-up the movement of the hand 2. Should the deviation of the hand and follow-up spindle exceed a predetermined amount, switch contacts, formed by a pin 16 on arm 3, and a spring 14 controlled by a stop 15 mounted on a pin 13 on arm 4, are opened, whereby the follow-up motor is driven at high speed, this speed being reduced as coincidence is approached by closure of the switch 14-16 and so preventing hunting. Alternatively, the follow-up spindle may be rotated manually, the required direction of rotation and the speed (fast or slow) being indicated by relays or luminous signals controlled by the switches 2-5, 2-6, 14-16. The pins 5, 6 may be arranged at different radii from the spindle 17 so that the sensitivity and accuracy of the follower is greater for one direction of rotation. Modifications of the Fig. 1 construction. The hand 2 may have a diametrally opposite extension 2a rigid therewith, the hand elements 2-2a co-operating with the respective pins 6, 5, the supporting arms of which are, in this case, diametrally opposite when in the neutral or rest position. The meter pointer and the followup spindle need not be coaxial, Fig. 2 (not shown). The movements of the control member 2-2a and the follower may be rectilinear instead of rotary, a nut and screw mechanism being used to drive the follower, Fig. 4 (not shown).  Follow-up switch construction, Fig. 6. The control member m, movable lengthwise, carries a spindle 1 having arms 2b, 2c, individually pivoted thereto, and normally held diametrally opposite each other by springs 27, 28 which urge projections P, Q rigid with the respective arms 2b, 2c against stops 25, 26 rigid with arms 23, 24 projecting from the spindle 1. Movement of the control member m lengthwise, in either sense, causes a corresponding one of the contact arms 2b, 2c to be rocked anticlockwise by the associated contact pin 5d, 6d rigid with the follower member, whereby the latter is driven in the follow-up direction, e.g. through a screw and nut mechanism (not shown) as above described. The control member m also carries a spring-biased arm 29 and co-operating stop 33. A further contact 31 on the arm 29 is resiliently engaged by the contact arm 2b when the latter is deflected a predetermined amount to increase the speed of the follow-up drive, for large deviations and reduce the speed as coincidence is approached. This, one-way, speed control is used where overshooting is required in one direction so that ultimate coincidence is always approached from the other direction. A similar contact arrangement may, however, be provided for the contact arm 2c if the speed control is required for both directions of movement of the control and follow-up members. Linear dimension gauging, Fig. 7. The work 42 to be gauged is held between the stop 43 and feeler 41 by springs 45 acting on the slide m carrying the feeler. Movements of the slide m are followed by member 40 controlled through the follow-up switches 2b, 2c, 5d, 6d as above described. A crank 46 is used for manually driving the follower 40. If a motor is used it drives the screw 47 directly and moves the follower 40 along guide rails 48 through the nut 40a. Lamps or relays b, c, d controlled by the follow-up switches 2b-5d, 2c-6d, and the speed-control switch 2b-31 indicate the operations required for manual operation or directly control the motor for automatic control. Alternatively three keys G, R, D may be used for manually controlling the motor. The measurement indicator is operated from the screw 47. Modifications of Fig. 7. Weight, pressure or liquid level, e.g. may be measured by applying displacements corresponding to these variables to the movable member. Mechanical magnification may be provided, Fig. 8 (not shown), between the movement of the movable member and that of the movable arms actuating the contacts on the follower to enhance sensitivity. Weighing apparatus, Fig. 9. The scale-pan 101 is carried by an armature 102 floating and constrained by a parallel motion linkage 104, 105 to move vertically within a coil 103 the current in which is adjusted in the appropriate sense to balance the weight electromagnetically. In the balance position, an arm .110 pivoted at 100 and also pivoted to the scale carrying rod 101a is horizontal, with the follow-up switch 111-112-114, constructed as above described in Fig. 6, in its neutral position. Any variation of the weight then upsets the balance to energize through a relay 113 or 113a a motor 108 in the appropriate sense. The motor adjusts a rheostat 106 to vary the current in the coil to restore the lever 110 to the balance position. The coil current indicated on a meter 117 is a measure of the weight. Alternatively, the rheostat slider position may be used to indicate the weight. A resistor 119 in the armature circuit is short-circuited as above described to speed up the motor when the out-of-balance exceeds a predetermined value. The range of the weight measured may be varied by modifying the rheostat 106 and sorting according to weight may be effected by the motor or by a current proportional to that in the meter 117. Modifications of Fig. 9. The upward thrust balancing the weight may alternatively be produced by gaseous fluid pressure, Fig. 10 (not shown), controlled by the motor instead of the coil current, the fluid pressure then being a measure of the weight. In another embodiment, Fig. 11 (not shown), the scale is carried by a float resting on liquid in a tank, balance being achieved by adjusting the liquid level by pumping under control of the follow-up switch and the motor. The liquid level or the motor shaft position may then be used to indicate the weight. The liquid level may alternatively be adjusted by raising or lowering the tank, Figs. 12, 13 (not shown). These arrangements could be used conversely to measure pressure, viscosity, fluid speed or specific weight of the fluid as a function of weight.