United States Patent: 3662227

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United States Patent	3,662,227
Morrison , et al.	May 9, 1972

CONTROL SYSTEMS

Abstract

An electrically operated machine has a bi-manual or double button control system which requires an operator to depress both buttons to institute operation, provision being made that both buttons have to be operated within a delay period thus preventing one or other button being wedged-on. If operation of both buttons does not occur within the delay period the circuit is disabled and can only be re-enabled by releasing both buttons.

Inventors:	Morrison; John J. (Disley, EN), Morton; John (Hazel Grove, EN)
Assignee:	Cableform Limited (Cheshire, EN)
Appl. No.:	05/010,198
Filed:	February 10, 1970

Foreign Application Priority Data


Feb 13, 1969 [GB]			7,815/69

Current U.S. Class: 361/189 ; 327/25; 361/197

Current International Class: F16P 3/00 (20060101); F16P 3/18 (20060101); F16P 3/20 (20060101); H01h 047/00 ()

Field of Search: 317/135,141,151,148.5 307/208,232,218

References Cited [Referenced By]

U.S. Patent Documents


2962633	November 1960	Raymond
3097307	July 1963	Bonn
3560800	February 1971	Weidenfeld
2882456	April 1959	Koch
3089985	May 1963	Camfield et al.
3312875	April 1967	Mayer

Primary Examiner: Miller; J. D.
Assistant Examiner: Moose, Jr.; Harry E.

Claims

What is claimed is:

1. A control system for an electrically controlled machine comprising a plurality of separate actuators connected to a first OR gate having a corresponding number of inputs, and connected to an AND gate having an input additional to the corresponding number of actuators, which additional input is connected to the output of a second OR gate having as its input the output of the AND gate and the output of a time delay device, the input of which receives the output of the first OR gate to initiate a time delay period, the output of the AND gate controlling switching means controlling the supply of power to the machine when all the actuators are operated within the delay period.

2. A control system for an electrically controlled machine comprising a transformer having two primary windings each of which is energized from an AC supply by operation of a corresponding actuator having contacts, said transformer having a secondary winding arrangement supplying a rectifier arrangement to energize a relay device in series with a capacitor thereby causing operation of the relay device for a predetermined delay time, said relay device having contacts in series with the contacts of the actuators and a contactor device thereby enabling initiation of operation of the contactor device during the delay time by operation of both actuators.

Description

This invention relates to a control system for use with electrically controlled machines.

It is known to provide for an electrically controlled machine a bi-manual or double-button control system which requires an operator to depress both buttons to institute operation of the machine. The purpose of this system is to ensure that both hands of the operator are clear from the operative parts of the machine so that it can be said that the control system acts as a safety guard. However, it has been found that this control system is not foolproof since if either button becomes short circuited or wedged in the "on" position then the machine can be controlled with one hand thus defeating the safety characteristic of the control system.

It is an object of the present invention to provide a control system of the bi-manual or double button type which obviates or mitigates the possibility of one hand operation.

It is a more specific object of the present invention to provide a control system which ensures that an electrically controlled machine or other device cannot be actuated while the operator or operators or any part of them are in the danger zone, or to provide a means whereby substantially coincident action by two or more people is required to initiate a functioning of the machine or device.

According to the present invention there is provided a control system for an electrically controlled machine, comprising a plurality of separate actuators and a time delay device, the operation of either of the actuators causing the delay period of the time delay device to commence, at the end of which period the system is disabled unless all of the, or a predetermined additional number of the actuators are operated within the delay period, the disabled system being re-enabled by simultaneous non-operation of all of the actuators.

Conveniently the control system may provide that the actuators are connected to a first OR gate having a corresponding number of inputs, and connected to an AND gate having an input additional to the corresponding number of actuators, which additional input is connected to the output of a second OR gate having as its input the output of the AND gate and the output of a time delay device, the input of which receives the output of the first OR gate.

Alternatively, the control system may provide that the actuators are connected to a first AND gate and a second AND gate, the first AND gate having a corresponding number of inputs, and the second AND having an input additional to the corresponding number of actuators, which additional input is connected to the output of an OR gate having as its input the output of the second AND gate and the output of a time delay device, the input of which receives the output of the first AND gate.

It will be seen that the control system in accordance with the present invention is rendered foolproof or substantially so by introducing a time limit within which both actuators must be operated to start the machine. The circuitry is a coincidence gate with a time boundary. This time boundary can be any predetermined interval but, it has been found on test that approximately 0.75 seconds is an optimum figure for typical machines and average human reactions.

If one actuator is held or wedged in the `on` position for longer than this time interval the machine cannot be set in motion by using the second button. In addition, full fail-safe protection is assured for any open or short circuit condition in the actuator circuit.

By suitable arrangement of the switching circuitry, the control system can also be used to secure coincident attendance by two or more people even out of sight of each other.

On single operation machines such, for example, as presses or guillotines, the control system can be connected so that both actuators must be operated during the whole time the machine is in motion. If either actuator is released even momentarily the machine will stop.

On continuous running machines the control system prevents the operator from starting the machine if either hand is in danger and minimizes the risk of accidental starting, which is the cause of many injuries particularly with hand fed machines, such for example, as saws or mixers, which cannot be effectively guarded. In this application, the control system is connected so that both actuators must be used to start the machine the actuators may then be released and the machine will continue to run until stopped in the normal manner.

The control system in no way interferes with existing stop switches, limit switches, overload protection devices, guard interlock switches or the like and, in fact, these can be interconnected with the control system to achieve maximum security.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a logic diagram of an arrangement in accordance with the invention, for producing a single shot operation of a machine,

FIG. 2 is an alternative logic diagram to that of FIG. 1,

FIG. 3 is a logic diagram of an arrangement in accordance with the invention, for providing continuous operation of a machine,

FIGS. 4 to 7 are circuit diagrams of a plurality of alternative control arrangements in accordance with the invention.

In FIG. 1, when pushbuttons A or B are operated the two input `OR` gate 1 operates and its output initiates in timer 2 a time sequence to the input of the two input `OR` gate 3. The times signal into the input of `OR` gate 3 gives an output to the three input `AND` gate 4. Provided both pushbuttons A and B are operated within the time delay the three inputs will be complete and an output from the `AND` gate 4 will control a relay. This output is also fed back to the input of `OR` gate 3 as a `hold in` circuit taking over from the timed signal when it goes negative. The output will, therefore, remain until one or both of the pushbuttons are released, cutting off either input A or B.

Referring to FIG. 2, with the two pushbuttons A and B unoperated the inputs to the two input `AND` gate 5 are negative, therefore, its output is positive providing, via timer 8, a signal input to the two input `OR` gate 6. The output of this gate provides one of the inputs to the three input `AND` gate 7. When the pushbuttons A and B are operated the other two inputs to the `AND` gate 7 are made thus giving an output to operate a relay, provided that both the pushbuttons are operated within the time delay of timer 8 which is operated due to the inputs to the `AND` gate 5 having gone positive.

The `AND` gate 7 output is also fed back as a `hold in` circuit to the `OR` gate 6 replacing the original input which goes negative after the time delay. The relay will remain energized so long as the pushbuttons remain operated.

The operation of the logic circuit of FIG. 3 is identical to that of FIG. 2 except that the relay is self-holding and remains energized even after the pushbuttons A and B have been released and until such times as the stop pushbutton 9 is operated.

FIG. 4 operates in accordance with the logic diagram of FIG. 1 in that so part of the circuit is energized until either or both of a pair of pushbuttons PBA and PBB are operated. When either of the pushbuttons is operated a supply from AC supply rails 11 and 12 is completed to the corresponding primary of transformer 10 so that a DC voltage is provided across capacitor C1 via rectifier 13. Transistor VT1 and its associated circuit of resistors R1, R2 and R3 and Zener diode Z1 is energized so that a relay RLC is energized until such times as a capacitor C2 in series therewith is charged. At the same time contactor L1 is energized provided both pushbuttons are operated before relay RLC and consequently contacts rlc1 drop out due to the time delay caused by capacitor C2. Contactor L1 is provided with self holding contacts l1(1) in parallel with contacts rlc1 and the contactor remains energized until one or both of the pushbuttons is released. Resistor R2 discharges capacitor C2 after each operation. Unless both pushbuttons are operated within the time delay provided by the charging of capacitor C2, contactor L1 cannot be energized because of the open circuit condition of contacts rlc1.

FIG. 5 shows an arrangement which operates according to the logic diagram of FIG. 2 and when modified as shown in broken line then according to the logic diagram of FIG. 3.

AC from rails 11 and 12 is supplied via a transformer 50 and rectifier 53 to provide DC voltage across capacitor C1. With the pushbuttons PBA and PBB unoperated transistors VT2 and VT3 are conducting so that relay RLD is energized closing contacts rld1. When the pushbuttons are operated the transistors are cut off but relay RLD remains operated for a delay time determined by a capacitor C3 in parallel with the operating coil. Also relay RLB is operated via contacts rld1 which are then bridged by self holding contacts rlb1. Contactor L1 is energized through contacts rlb2 and rlb3 of relay RLB. Unless the pushbuttons are operated within the delay time of relay RLD no energization of relay RLB is obtained.

Contactor L1 remains energized so long as the pushbuttons remain operated for the single shot condition. If continuous operation is required contactor L1 is provided with self-holding contacts l1(1) through a stop button SB (see broken line). When the continuous operation is to be stopped button SB opens the hold circuit so that contactor L1 drops out.

In FIG. 6 two change over switches SW1 and SW2 (which may be pushbuttons) are provided in the primary circuit of a transformer 60 which feeds a rectifier 63 to produce a DC current for relay RLA which is shunted by capacitor 1. When switch SW1 and SW2 are changed over the circuit through the contactor coil L1 will be completed through contacts rla1 provided that the change over of the switches takes place within the delay time provided by capacitor C1 across the coil of relay rla. The operation of contactor coil L1 closes contacts L1.1 which are self-holding contacts. If both of the changeover switches are not operated within the delays de-energization time of relay RLA then the contactor L1 will not be energized.

In FIG. 7, the normally closed contacts of pushbuttons PBA and PBB complete a circuit from the AC rails 11 and 12 through diode D1 and a resistor to the coil of relay RLE which is shunted by a capacitor C6 to provide a time delay for the drop-out of relay RLE. If either pushbutton is pressed the circuit to relay RLE is opened thus starting the time delay. If the other button is pressed within the time delay the normally open contacts of the pushbuttons complete the circuit to contactor L1 through contacts rle1 of relay RLE. Contactor L1 is held by self-holding contacts l1(1). If both pushbuttons are not pressed within the delay time then relay RLE drops-out and contacts rle1 open preventing the contactor L1 from being energized.

It will be seen that many variations of the arrangement of the present invention may be derived, the essential requirement being that a time delay is provided during which both of the pushbuttons must be operated if the contactor is to be energized. The pressing of one pushbutton followed by the pressing of the other pushbutton after an elapse of time greater than the delay time results in non operation of the contactor.

* * * * *

Current U.S. Class:	361/189 ; 327/25; 361/197
Current International Class:	F16P 3/00 (20060101); F16P 3/18 (20060101); F16P 3/20 (20060101); H01h 047/00 ()
Field of Search:	317/135,141,151,148.5 307/208,232,218