Patent GB-1323542-A (GB)
Title: Electric combination lock
IPC: G07C9/00
Filed: 1971-01-13
Abstract: 1323542 Combination locks SHORROCK DEVELOPMENTS Ltd 4 Jan 1972 [13 Jan 1971] 1578/71 Heading E2A An electric combination lock comprises a set of code terminals, a code selecting switch S or set of push buttons connected to said terminals, a chain of thyristors S1, S2, S3 each associated with a respective one of the said terminals, connections from said respective terminals to the triggers of said thyristors, interconnections between said thyristors to ensure they are fired in a predetermined order during an unlocking operation, and unlocking means operated by the firing of the last thyristor in the chain. As shown, the switch S is a single pole ten way switch of which the contacts 1, 7 and 9 are connected to the thyristors S1, S2, S3 respectively the remaining contacts being connected to the negative line of the power supply; to release the locking means the switch S is placed on the contact 1 and a press button switch B, which is in series with the moving contact of the switch S, is depressed to apply a positive potential to the trigger of the thyristor S1 which therefore fires and causes a voltage drop across a resistor R1 which lowers the potential on the lefthand electrode of a capacitor Cl and hence the potential of a trigger of thyristor S2 is also lowered; since the thyristor requires a positive trigger potential to fire thyristor S2 remains non-conducting. However, when the switch S is moved to position 7 and button B pressed a positive potential is applied via capacitor C1 to thyristor S2 which is then switched on and current flows through resistor R2 and thyristor S2 thereby lowering the potential of the lefthand electrode of capacitor C3; when the switch S is moved to position 9 and the button B pressed for a third time, positive trigger potential is applied to the trigger of thyristor S3 which conducts and operates relay R3 to move a bolt to releasing position. If during the movement of the switch, an incorrect switch contact is selected and button B is depressed, the thyristors which are turned on are short circuited and hence switched off although resistor RA prevents the power supply itself from being short circuited. Users of the system are provided with an identity tab which acts as an on-and-off device for the lock and the tab has links L1, L2, L3 and L4 and when plugged into a socket provided by the lock this completes various parts of the circuit to enable the lock to be operated; an incorrect tab would not complete the circuit so that the lock could not be operated. To indicate who uses the lock a separate print-out unit is provided to print-out the code and the identity tab being used; when one of the identity tabs is: inserted into the socket in the lock one or more solenoids R15-R19 are energised and when a command to print is given the code is printed; the command can be given when the thyristor S2 is fired; a reset signal is given to the printout unit when the last thyristor is fired. The relay R can operate a clock printout mechanism to show the times at which the lock is operated. The opening of the door locked by the lock opens a contact U in series with the power supply thus extinguishing all the thyristors and restoring the lock to locking condition. An external alarm system E can be energised if terminals 13 and 14 are bridged by the tab incorrectly. In a modification, a circuit, Fig. 3, is added to detect misoperation by monitoring the junction of link L1 and resistor R1; if an incorrect switch position is selected and button B is depressed the junction point of L1 and R1 becomes temporarily connected to negative potential; this causes a transistor TR1 to stop conducting and hence produces a positive going pulse at its collector; a diode pulse counter consisting of diode, D10 and D11 charges up capacitor C11 and when a predetermined number of pulses are generated the potential across C11 rises to a point where a unijunction transistor TR2 starts to operate which generates a pulse across R21 which switches on a thyristor S10 to energise a relay RA; the contacts of the relay RA either operate an alarm to indicate tampering or inhibit further operation of the lock for a predetermined period by closing a circuit between the terminals 13 and 14 of Fig. 1.