GB1604266A - Safety circuit for closure member - Google Patents

Description

(54) SAFETY CIRCUIT FOR CLOSURE MEMBER (71) 1, ANTONIUS FRANCISCUS HU1TEK, a subject of the Queen of the Netherlands, of 200 Mozartlaan, Enschede, The Netherlands. do hereby declare the invention, for which Spray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a safety circuit for controlling the supply of current to an electric motor. It is particularly useful for a motor which drives a closing member such as a garage door.

Opening or closing such a member often involves the problem that in the event of a contact between the moving door and an obstacle damage of both may result from the heavy force exerted. If a person is standing in the space required for the displacement of the door, the situation may even become hazardous. There are known mechanical movement limiters, for example, in the form of two fric tion-coupled plates. Devices of this kind have to be designed for specific uses, they are adjustable only with difficulty and have insufficiently stable operational characteristics for certain applications.

The invention obviates these disadvantages by providing a safety circuit for oontroliing the supply of current to an electric motor, comprising: current-sensing means, connected in series in a current path from a supply to the motor, which provides a signal indicative of the current flow; a comparator for comparing the currentindicating signal with a threshold value defined by a reference signal to provide an overload signal when the sensed current exceeds the threshold value; switching means responsive to the overload signal to interrupt the current supply to the motor; means for adjusting the threshold value; a bistable element which stores the direction of movement of the motor and a switch coupled with the bistable element and with the switching means responsive to the overload signal, the switch being responsive to the operation of the switching means to block the direction of motor movement chosen prior to the operation of the switching means and allowing the said direction of motor movement again only upon selection of that direction of motor movement after the other direction of motor movement has been chosen.

As soon as a moving member driven by the motor of such a circuit encounters an obstacle, as a result of which the speed of the motor is reduced, the current across the driving motor increases, as is known. When the selected threshold value of the current is exceeded, the switching means responds so that the motor current is interrupted.

When the moving member is movable in two opposite directions, for example a closure member, a different threshold value may be set for each direction of movement. In order to avoid damage by undesirable movements of the member with respect to the obstacle, motion in the same direction is precluded, subsequent to the interruption of the supply current, until there has been movement in the opposite direction.

An example of apparatus embodying the invention will be described more filly with reference to the accompanying drawing, which shows a safety circuit employed on a threephase motor for controlling a garage door rotatable about a horizontal shaft.

In the circuit diagram four relays are indicated by A, B, C and D and their contacts are designated by the corresponding lower-case letters and a numerical index, for example, b2.

In explaining the operation of the circuit it is first assumed that the relay contacts occupy the positions shown, and that the user wants to displace the door upwards. For this purpose he depresses the push-button Si, shown with an upwardly-directed arrow. As a result the following current circuit is conpleted: negative terminal of the supply unit, "stop" switch S3, contact d1, switch Si, relay A, contact C1, positive terminal of the supply unit 1. Thus relay A is energised and closes a1, which takes over the function of Si so that A remains in the energised state. The contacts a2, a3, a4 close.

Thus the three current paths of the connecting terminals U to R, V through the resistor R1 to S and W and through the resistor R2 to T are completed. The terminals R, S and T are connected to a three-phase mains and the terminals U, V and W to a driving motor. By closing. the three current paths the motor is caused to rotate in the direction chosen.

The function of the resistors R1 and R2 will be discussed hereinafter.

After the depression of the stop switch S3 the supply voltage across the relay A disappears so that the relay is deenergized. The contacts al, a2, a3 and a4 open and the motor stops.

If the user wants to lower the door, he depresses the push button S2 shown with a downwardly pointing arrow. Thus the following current circuit is completed: negative terminal of supply unit 1, stop switch S3, contact d2, switch S2, diode D2, relay C, contact d3, positive terminal of the supply unit 1. The relay C, a relay of the type comprising two active windings, "changes over" so that the position of the contacts cl to C4 changes. Thus the following current circuit is completed: negative terminal of the supply unit 1, contact d2, switch S2, relay B, contact cl,positive terminal of the supply unit 1. As a result relay B is energised and contact b1 closes, which takes over the function of S2 so that relay B remains in its energized state. The contacts b2 to b4 close.

Thus the three current paths from the connect ing terminals U to R, V via Rl to T and W via R2 to S are completed. With this polarity of the supply voltage the motor rotates in a sense such that the door moves downwards.

The motor can again be halted by actuating the stop switch S3 so that relay B is de-energized and the contacts b1 to b4 open.

When the motor is operating, the resistors R1 and R2 are each traversed by an alternating current, the amplitude of which increases with an increase in torque supplied by the motor. It is known that the motor current increases with the torque supplied. The alternating voltages across the resistors R1 and R2 are applied to peak-value rectifiers/limiters 2 and 3, the output signal of which is applied through a separation and buffer circuit 4, a network of resistors R3, R4 and R5 and the contact C4 to a comparison and delay circuit 5.To each of the two directions of movement corresponds an adjustable voltage divider R3, R5 and R4, R5 respectively, one of which is each time chosen by the contact c4. In this way the attenuated output voltage of the circuit 4 is applied to the circuit 5, which energizes relay E after a predetermined delay time, if its input voltage exceeds a reference voltage originating from the supply unit.

It will now be obvious that at a transgression of a predetermined threshold value of the torque supplied by the motor the contact e closes.

It will be apparent that relay D is thus energized and changes over so that the contacts dl to d4 change their positions. When this occurs during an upward movement of the door, hence when relay A is in the energized state, relay A is deenergized by contact d1 opening so that the motor stops in the manner described above. The relay D is of the bistable type and maintains its position last occupied. Since the current paths to the motor are interrupted, contact e again opens. Since contacts c2, dl are then in the right-hand position as shown in the drawing, relay A can no longer be energized through Sl so that the "upward" direction of rotation is blocked.

Subsequently, only "downwards" can be chosen. When the push button S2 is depressed, th following current circuit is completed: negative terminal of the supply unit 1, switch S3, contact c2, switch S2, diode D4, relay D, resistor Rg and capacitor C1, positive terminal of the supply unit 1. Relay D changes over so contacts dl, d2, d3, d4 return to their positions shown. Thus is completed the current circuit: negative terminal of the supply unit 1, switch S3, contact c2, switch S2, diode D2, relay C, contact d3, positive terminal of the supply unit 1, as a result of which relay C changes over.

Thus the position of contacts cl to c4 changes so that relay B is energized through cl and the driven door moves downwards.

If the predetermined torque is exceeded, contact e closes. Thus relay D changes over, contacts dl to d4 change their positions and relay B is deenergized. The "downward" direction of movement is then blocked, since relay B can no longer be energized through c2 or d2.

Subsequently, only "upwards" can be chosen. When the push-button S, is depressed, the following current circuit is completed: negative terminal of the supply unit 1, switch S3, contact c2, switch Si, diode D3, relay D, capacitor C1 and resistor R6, positive terminal of the supply unit 1. Relay D changes over so that contacts dl to d4 change their positions. The following circuit is thus completed: negative terminal of the supply unit 1, diode D1 relay C, contact d3, positive terminal of the supply unit 1. Relay C changes over and contacts cl to c3 return to the positions shown. Relay A is energized through contact cl and rises so that contacts al to a4 close and the motor causes the door to move upwards.

The voltage dividers R3, Rs, or R4, Rs chosen by contact c4 may be adjusted differently for the two directions of rotation interalia because gravity has to be overcome for moving the door upwards.

When the safety device described is employed, the door need not be provided with the conventional end switches (for example, microswitches), since at the arrival at a stop the safety device becomes operative so that the driving motor stops.

The delay function of circuit 5 ensures that the torque limiter does not become operative at th start of the motor.

In the embodiment shown two phases of the polyphase induction motor are guarded. Therefore, the safety circuit remains capable of operating when one phase becomes defective.

Three signaling lamps 6, 7 and 8 are provided to indicate "upwards", "stop" and "downwards". After the actuation of the safety device at a given direction of movement, the corresponding direction indicating lamp remains illuminated, whilst the "stop" lamp ignites. The user thus knows that the direction of movement concerned is blocked.

The diodes D5 and D6 serve for the separation between the current circuits of the signalling lamps 6,7 and 8 and the current circuit of relay D.

The contact d4 may serve for an external, optical and/or acoustic alarm.

The input of the circuit 5 is provided with two measuring terminals 9, 10, which may serve for determining the motor current in dependence upon the door displacement. This is in particular important for the adjustment of the desired safety threshold.

In the drawing are not shown conventional safety elements such as fuses, excess-voltage diodes and inhibiting resistors.

It will be obvious that the circuit arrangement described has a broad range of applications. It may be adapted to substantially any type of electric motor and may be externally included in the supply leads of the motor.

Different, functionally associated units may be accommodated in an individual housing. The signalling lamps and the control buttons, for example, may be disposed in a control box.

As an example of use reference is finally made to pressure limitation with the aid of a valve in a gas or liquid flow.

WHAT I CLAIM IS:- 1. A safety circuit for controlling the supply of current to an electric motor, comprising: current-sensing means, connected in series in a current path from a supply to the motor, which provides a signal indicative of the current flow; a comparator for comprising the current-indicating signal with a threshold value defined by a reference signal to provide an overload signal when the sensed current exceeds the threshold value; switching means responsive to the overload signal to interrupt the current supply to the motor; means for adjusting the threshold value; a bistable element which stores the direction of movement of the motor and a switch coupled with the bistable element and with the switching means responsive to the overload signal, the switch being responsive to the operation of the switching means to block the direction of motor movement chosen prior to the operation of the switching means and allowing the said direction of motor movement again only upon selection of that direction of motor movement after the other direction of motor movement has been chosen.

2. A safety circuit in accordance with Claim 1, for controlling the supply of current along two or more paths to an electric motor, wherein the current-sensing means, connected in series in at least one of the current paths to the motor, provides at least one signal indicative of the current flow, the comparator is res ponsive to the current-indicating signal or sig nals and to the reference signal to procude an overload signal when the current in any of the sensed current paths exceeds one of two thresholds, and the circuit is such that a first threshold is effective for one direction of movement of the motor and a second threshold for the other direction of motor movement, the circuit further comprising first and second adjusting means for independently adjusting the first and second thresholds respectively, directioncontrol means in the current paths between the supply and the motor, and switching means responsive to the overload signal to switch off the motor.

3. A safety circuit according to Claim 1 or 2, in which the threshold, or each threshold, is adjusted by varying the degree of attenuation of the current-indicating signal, the reference signal being fixed.

4. A safety circuit according to Claim 2 or 3, in which the adjustment of the two threshold values is effected by varying the values of respective adjustable resistors to which the current-indicating signal is applied, the circuit further comprising a switch for selectively connecting one or other of the adjustable resistors to the comparator.

5. A safety circuit according to Claim 1, 2, 3 or 4, in which the switching means is a relay.

6. A safety circuit according to any preceding claim, wherein the switch coupled with the bistable element is a bipolar relay.

7. A safety circuit according to any preceding claim, wherein the motor is a three-phase motor and the current-sensing means is connected in series in the current paths of at least two of the phases.

8. A safety circuit according to any preceding claim, wherein the current-sensing means in the or each current path is a resistor coupled with a peak-value rectifier or limiter which provides the current signal.

9. Closure apparatus including a closure member and a safety circuit according to any one of Claims 3 to 8, the closure member being driven by the motor.

10. Closure apparatus according to Claim 9, in which the safety circuit functions to stop the motor at the limit of travel of the closure member, the apparatus being without separate limit switches operative at the ends of travel of the closure member.

11. A safety circuit substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. corresponding direction indicating lamp remains illuminated, whilst the "stop" lamp ignites. The user thus knows that the direction of movement concerned is blocked. The diodes D5 and D6 serve for the separation between the current circuits of the signalling lamps 6,7 and 8 and the current circuit of relay D. The contact d4 may serve for an external, optical and/or acoustic alarm. The input of the circuit 5 is provided with two measuring terminals 9, 10, which may serve for determining the motor current in dependence upon the door displacement. This is in particular important for the adjustment of the desired safety threshold. In the drawing are not shown conventional safety elements such as fuses, excess-voltage diodes and inhibiting resistors. It will be obvious that the circuit arrangement described has a broad range of applications. It may be adapted to substantially any type of electric motor and may be externally included in the supply leads of the motor. Different, functionally associated units may be accommodated in an individual housing. The signalling lamps and the control buttons, for example, may be disposed in a control box. As an example of use reference is finally made to pressure limitation with the aid of a valve in a gas or liquid flow. WHAT I CLAIM IS:-

1. A safety circuit for controlling the supply of current to an electric motor, comprising: current-sensing means, connected in series in a current path from a supply to the motor, which provides a signal indicative of the current flow; a comparator for comprising the current-indicating signal with a threshold value defined by a reference signal to provide an overload signal when the sensed current exceeds the threshold value; switching means responsive to the overload signal to interrupt the current supply to the motor; means for adjusting the threshold value; a bistable element which stores the direction of movement of the motor and a switch coupled with the bistable element and with the switching means responsive to the overload signal, the switch being responsive to the operation of the switching means to block the direction of motor movement chosen prior to the operation of the switching means and allowing the said direction of motor movement again only upon selection of that direction of motor movement after the other direction of motor movement has been chosen.

2. A safety circuit in accordance with Claim 1, for controlling the supply of current along two or more paths to an electric motor, wherein the current-sensing means, connected in series in at least one of the current paths to the motor, provides at least one signal indicative of the current flow, the comparator is res ponsive to the current-indicating signal or sig nals and to the reference signal to procude an overload signal when the current in any of the sensed current paths exceeds one of two thresholds, and the circuit is such that a first threshold is effective for one direction of movement of the motor and a second threshold for the other direction of motor movement, the circuit further comprising first and second adjusting means for independently adjusting the first and second thresholds respectively, directioncontrol means in the current paths between the supply and the motor, and switching means responsive to the overload signal to switch off the motor.

3. A safety circuit according to Claim 1 or 2, in which the threshold, or each threshold, is adjusted by varying the degree of attenuation of the current-indicating signal, the reference signal being fixed.

4. A safety circuit according to Claim 2 or 3, in which the adjustment of the two threshold values is effected by varying the values of respective adjustable resistors to which the current-indicating signal is applied, the circuit further comprising a switch for selectively connecting one or other of the adjustable resistors to the comparator.

5. A safety circuit according to Claim 1, 2, 3 or 4, in which the switching means is a relay.

6. A safety circuit according to any preceding claim, wherein the switch coupled with the bistable element is a bipolar relay.

7. A safety circuit according to any preceding claim, wherein the motor is a three-phase motor and the current-sensing means is connected in series in the current paths of at least two of the phases.

8. A safety circuit according to any preceding claim, wherein the current-sensing means in the or each current path is a resistor coupled with a peak-value rectifier or limiter which provides the current signal.

9. Closure apparatus including a closure member and a safety circuit according to any one of Claims 3 to 8, the closure member being driven by the motor.

10. Closure apparatus according to Claim 9, in which the safety circuit functions to stop the motor at the limit of travel of the closure member, the apparatus being without separate limit switches operative at the ends of travel of the closure member.

11. A safety circuit substantially as herein described with reference to the accompanying drawing.