Patent GB-1083591-A (GB)
Title: Safety systems for power operated machines
Inventor: FLATHER JOHN
IPC: F16P3/14
Filed: 1964-02-26
Abstract: 1,083,591. Angular bending; metal working presses; shearing. HENRY HOPE & SONS Ltd. Feb. 18, 1965 [Feb. 26, 1964], No. 7929/64. Headings B3E, B3H and B3W. [Also in Division F2] In a press-brake, press or guillotine wherein a crank-shaft actuated movable tool-carrying part is cyclically movable towards and away from a fixed tool-carrying part, and wherein the interruption, by the operator, of beams from light sources to photo-electric cells 24, mounted on or adjacent the machine, declutches and brakes the crank-shaft, switches 19, 20 are actuated by cams on the crank-shaft respectively to render the photo-electric cells incapable of control during the period when said movable part is close to and moving towards said fixed part and to arrest said movable part at approximately that position at which the cells become incapable of control so that the operator may manipulate the workpiece during the last part of the downstroke of said movable part. It is stated that the press-brake, press or guillotine may be hydraulically operated. A crank-shaft clutch/brake is resiliently loaded for clutch disengagement and brake engagement and is controlled by a pedal acting through a link which includes an air cylinder. When a solenoid-operated valve 15 is de-energized the air cylinder is opened to atmosphere and pedal depression is ineffective, and when the valve 15 is energized the link is virtually solid so that pedal depression engages the clutch and disengages the brake. Pedal depression also acts on a switch 16 to open contacts 16a and close contacts 16b. The photo-electric cells 24 bias the grid of the first stage triode of an amplifying circuit 23 the current from which energizes a relay R to close normally open holding contacts R 1  and contacts R 2  and open normally closed contacts R 3 . The grid bias relative to the cathode is reduced on light beam interruption. Actuation of the switch 19 reduces cathode potential thereby increasing grid bias to such a level that cell variation is insufficient to prevent current supply to the relay R. The switch 19 is cam actuated from a crank-shaft position approaching bottom dead centre, i.e. when said movable part approaches said fixed part, to crank-shaft top dead centre. The switch 20 is cam actuated twice per crank-shaft revolution: once when the switch 19 is actuated, this position for switch 20 being variable by adjustment of a cam lobe, and again at crank-shaft top dead centre. Actuation of the switch 20 disconnects a contact 20a from a contact 20c, through which a capacitor 28 is charged, and connects it to a contact 20b. The control circuit also comprises positive and negative lines 21, 22; a relay S the energization of which closes normally open contacts S 1 , S 2 ; a normally open reset switch 27; and a relay T the energization of which actuates a two-way switch T 1  normally in the position shown. In operation, with the crank-shaft at rest and at top dead centre, the switch 19 opens to render the photo-electric cells operative, and, since relay T at this position is not energized and with the reset switch 27 closed, the relay S is energized. Provided there is no light beam interruption, relay R is energized so that when the pedal is depressed the valve 15 closes and the engaged clutch rotates the crank-shaft. If the light beam is interrupted, relay R is deenergized and the clutch is disengaged. To reenergize the relay R the pedal has to be lifted to close the contacts 16a. If the beam is not interrupted, or after re-setting the machine in motion, the crank-shaft reaches the position in which the switch 20 is actuated for the relay T to be briefly energized by discharge of the capacitor 28, and since the contacts R 3  are open, the relay S is de-energized, the valve 15 is opened, and the clutch and brake are disengaged and engaged respectively. The relay S is not reenergized until the reset switch 27 is closed again. The crank-shaft comes to rest at a position in which the switch 19 is actuated, thus when the crank-shaft is again set in motion the light cells are ineffective. Crank-shaft rotation continues and the capacitor 28 is recharged. At crank-shaft top dead centre the switch 20 is again actuated to arrest the crank-shaft and the switch 19 returns control to the light cells.