Patent GB-611061-A (GB)
Title: Multi-revolution electrical control apparatus
IPC: G05D3/12
Filed: 1945-11-09
Abstract: 611,061. Electric control systems. YARDENY, M. N. Nov. 9, 1945, No. 29965. [Class 40 (i)] In a system for controlling the movement of a shaft 13 to any one of a number of predetermined positions spread over more than one revolution, the positions are determined by the initial settings of the primary elements of followup switches such as I, II and I<SP>1</SP>, II<SP>1</SP> which are geared together with a ratio differing only slightly from unity. One switch of each pair has a primary member in the form of a gapped ring 5 and a secondary member 12 which makes contact with both halves of the ring when it is in the gap. The primary and secondary members of the other switch make contact in only one relative position of the two members. The primary and secondary members may be transposed. The switches of a pair may be adjusted separately or together. First system, Fig. 1. A particular setting is selected by operating one of a number of latching push-buttons 86, 88, whereupon the shaft driving motor 17 is energized through the lower of its two field windings 70, 81 and back contacts of both control relays 18, 19. The first time the switch II or II<SP>1</SP> makes its contact, relay 18 or 19, according to the condition of the other switch, pulls up and locks. If 18 is energized, the motor runs as before, but if 19 the upper field winding is substituted for the lower and the motor reverses. When the selected position is reached, the unoperated relay pulls up in addition to that already energized and the motor circuit is broken. To minimize hunting, breaking means (not shown) may be provided and the contacts of the switch I, II<SP>1</SP> may be as shown in Fig. 6. In addition, the motor circuit includes a switch 93 which is open when the motor speed exceeds a given value, but is normally short-circuited by one or other of two switches 103, 105 which are controlled by a finger coupled frictionally to a shaft driven directly or through gearing by the motor. If, after both relays 18, 19 have been operated, the switches continue to move, one of the relays will fall back and the motor will reverse and during the reverse movement the short-circuit on the switch 93 is removed to ensure that the motor shall not pick up enough speed to cause overshooting on the other side. Second system, Fig. 2. In this arrangement, the relays 18, 19 are replaced by a pair of coils which act on a common flexible armature pivoted at 122. A temporary operation of coil 18 when the armature is in the position shown, tilts the beam to the dotted position where it remains. Similarly, a temporary energizaton of coil 19 restores the armature to the full line position. By this means, the locking circuits of the previously described arrangement are eliminated. When, in the position of correspondence, both coils are energized, the armature bends, interrupting the motor circuit and short-circuiting the motor armature. To ensure that the armature, when both coils are de-energized, assumes the full line position, coil 18 may be designed to release its end more slowly than coil 19. A similar effect can be produced by suitably arranging the order of operation of contacts 22, 23 of the selecting switches. Hunting in this system may be prevented by the provision of a frictional coupling 140 between the motor and the driven shaft. Another anti-hunting expedient is to retard the movements of the armature by dashpots, Fig. 3 (not shown), and to cause it to make the motor circuit in two stages, the first stage including a resistance. By this means the motor runs slowly for a short time after it has been reversed. A similar effect can be brought about, Fig. 4 (not shown), by causing the armature to control sluggish relays which short-circuit a resistance initially included in the motor circuit shortly after each reversal.