Patent GB-874908-A (GB)
Title: Improvements in or relating to electrical control systems
Inventor: BRAMLEY LIONEL NAPIER
IPC: B30B15/16
Filed: 1956-10-31
Abstract: 874,908. Switching systems. BRITISH IRON & STEEL RESEARCH ASSOCIATION. Oct. 28, 1957 [Oct. 31, 1956; Sept. 10, 1957], Nos. 33230/56 and 28514/57. Class 38 (4). [Also in Groups XXII, XXIX, XXXVII and XXXVIII] The upper and lower limits of movement of a press-member for forging are determined by the settings of potentiometers 16, 17, from which voltages are selectively derived for comparison with a voltage obtained from a potentiometer 13 having a slider 12. The position of the slider corresponds with that of the press member, the error voltage being applied to a polarized relay PR having contacts PR1 in circuit with relays U, D for controlling the upward and downward movement of the press member. To initiate automatic repetitive motion of the press, a push-button PS1 is actuated to operate relay B, relays A, A<SP>1</SP> remaining de-energized until the push-button is released. These relays are of the two-coil type and are operated only when a single coil is energized. Contacts A2 change over to connect potentiometer 17 to relay PR, so operating contacts PR1 and energizing relay D for downward movement until the signal applied to relay PR becomes zero upon approaching the lower limit. A tachometer generator T provides a voltage proportional to the speed of the press member for opposing the voltage derived from the potentiometer 13 and preventing over-shooting of the limiting positions. The de-energization of relay PR causes the relay D to become non-operative and contacts A2 are changed over to connect potentiometer 16 to relay PR. The press member is then moved upwardly due to energization of relay U. As determined by the signal derived from tachometer generator T, the voltage applied to relay PR becomes zero shortly before the press member reaches its upper limit, but the change-over of the contacts A2 is delayed by the discharge of capacitor CD into the coil of relay UX. The member continues to reciprocate between the upper and lower limits, a delay being provided between the completion of an upward movement and the initiation of a successive downward movement. A single reciprocation only for each operationof the push-button PS1 is effected by adjust ment of switches 26, 27. Manual control of the drive for the press by push-buttons or from a separate control panel may be provided when switches AM1, AM3 are adjusted to alternative positions. Lamps 42, 43 indicate automatic and manual operation respectively, and lamps 44, 45 indicate the bottom and top limits of the press member. The relay PR is protected from overloads by a relay L. Contacts A1 and voltage divider 22 are arranged so that a greater velocity feedback signal is provided during upward movement of the press member. The servomotors which drive the press member and which are controlled by the relays U and D may be of the electric or hydraulic types. In one arrangement, these relays control the windings of valves for regulating the flow of liquid under pressure to the press, the slider 12 and the tachometer generator T being coupled to the movable press member so that the voltages derived therefrom are dependent upon the position and velocity of the member. A piston working in a cylinder is coupled to the press member and liquid under pressure can be supplied above or below the piston under the control of a valve which is connected to a pump and a discharge passage. The control valve is in turn controlled by a pilot valve having a pilot pump and windings which are controlled by the relays U and D, Fig. 5 (not shown). In a modification, the change-over relay for connecting the potentiometers 16, 17 selectively to the relay PR is controlled by switches operated by a cam-shaft which is driven by an electric pilot motor. For single reciprocations of the press member, the pilot motor is started by a push-button and is stopped after one revolution by means of one of the cam-operated switches. The pilot motor may also be operated continuously for continuous reciprocation of the press member, which may be stopped at its upper or lower limits for periods determined by the adjustment of the positions of cams on the camshaft. Changes in the overall cycle time are effected by adjusting the speed of the pilot motor, Figs. 6-8 (not shown). For a single quick reciprocation of the press member the change-over relay may be controlled manually.