IMPROVEMENTS IN OR RELATING TO ELECTRIC SWITCH CONTROLS FOR ELECTRIC MOTOR-DRIVEN ACTUATORS

摘要

1,207,967. Valves. ROTORK CONTROLS Ltd. 2 Nov., 1966 [15 Dec., 1966], No. 56137/66. Heading F2V. [Also in Division H1] In a limit switch arrangement for controlling the electric motor drive of an actuator shaft 28, Fig. 1, and substantially the same as that of Specification 1,003,761 in which the limit switches 13b, 14b, 15b are actuated through pivoted striker plate 55, in response to actuator overload and through striker plate assembly 87, 98 in response to actuator end-stop movement, means is provided for initially latching the striker plate 55 against movement so that it is not responsive to overload until the actuator has moved a predetermined distance. The arrangement is particularly applied to the actuation of a fluid valve as in Specification 939,353 in which an initially large torque may be required to start the opening movements of the valve and would otherwise cause immediate operation of the limit switch 13b and prevent any opening movement. The latch device comprises leaf spring 110, Fig. 6, attached at 111 to the striker plate part 98 associated with the nut 76 of the threaded end-stop shaft 66 and riding over a cammed lower surface 113 of a slot 112 in a fixed plate 20, the spring 110 has a slot 116 so arranged that in a switch operated position (valve closed) the spring 110 drops to engage the slot 116 over one or other of projections 117 of the overload striker plate 55. On reopening the valve the spring 110 and slot 116 holds the overload striker plate 55 against rotation until the end-stop striker plate 98 has moved the spring 110. Adjustable lost-motion connection 103, 104 provided between the striker plates 55, 98 and at 56, 60 between an overload indicator dial 51 and the overload striker plate 55 are described in the Specification 1,207,969. Adjustable end-stop lock-nuts 88, 89 are described in the Specification 1,207,968. Reference has been directed by the Comptroller to Specifications 1,003,761, 1,003,764, 1,003,765, 1,003,766, 1,011,989 and 1,027,526.