WO2000070634A1

WO2000070634A1 - Switch

Info

Publication number: WO2000070634A1
Application number: PCT/GB2000/001742
Authority: WO
Inventors: Norman Harold George Palmer; Nigel Bedggood
Original assignee: Danor Electronics Ltd.; Albright International Ltd.
Priority date: 1999-05-14
Filing date: 2000-05-12
Publication date: 2000-11-23
Also published as: GB9911162D0; AU4592500A

Abstract

A switch includes an armature, selectively movable between a first position and a second position, a coil for effecting movement of the armature between said first and second positions, a magnet for holding the armature in one of said positions and control means for controlling operation of said coil. The control means is operable to permit a current to be passed temporarily through the coil in a first direction, thereby to cause the armature to move from the first position into the second position and the magnet is operable to hold said armature in said second position after said current has ceased. The control means is also operable to permit a current to be passed temporarily through the coil in a second direction, thereby to cause the armature to move from the second position into the first position.

Description

Switch

The present invention relates to a switch and particularly, but not exclusively, to a switch in the form of an electrical contactor and to control circuitry for controlling the switching of such a contactor to make or break an electrical connection. More particularly, the invention relates to control circuitry for controlling the switching of a contactor having an armature moveable back and forth between a first, contact-breaking position and a second, contact- making position, and a coil for effecting movement of the armature.

Conventional contactors are operated by passing a current through a coil and the resulting magnetic field generated around the coil forces an armature within the field from a first position to a second position. In the first position, the armature causes contacts of the contactor to be broken. In the second position, the armature causes contacts to be made. The armature is often biassed towards one of the positions (usually the first position) and so must be held in the other position (the second position) by maintaining the current through the coil. However, the need to maintain the current results in the dissipation of a considerable amount of energy in the coil.

The present invention aims to provide an improved switch or contactor.

Accordingly, the present invention provides a switch for making or breaking an electrical connection, the switch comprising armature means, selectively movable between a first position and a second position, actuation means for effecting movement of the armature between said first and second positions, holding means for holding the armature means in one of said positions and control means for controlling operation of said actuation means, wherein said control means is operable to permit a current to be passed temporarily through said actuation means in a first direction, thereby to cause said armature means to move from said first position into said second position and said holding means is operative to hold said armature means in said second position after said current has ceased. The switch may be in the form of a contactor having an armature moveable between a first, contact-breaking position and a second contact-making position, a coil for effecting movement of the armature and magnet means for holding the armature in the second position. The magnet means may comprise a permanent magnet which holds the armature in the second position even when the coil is no longer acting upon the armature.

The armature may be moved from the first position to the second position by passing a current through the coil in a first direction and from the second position to the first position by passing a current through the coil in a second direction, opposite to the first. Preferably, the current is passed for not substantially longer than the time it takes for the armature to move from one position to the other. Thus, the coil only consumes power for sufficient time to enable the armature to move. This results in considerable energy savings, particularly in applications where the contacts need to be made for long periods. Temperature rises in the coil are minimal, enabling more powerful coils to be used, which gives increased reliability at low supply voltages.

Further preferably, the switch may include circuit means including timer circuitry and a switch, such as a transistor, controlled by the timer circuitry. The switch may control the flow of current through the coil and the timer circuitry may control the timing of the operation of the switch. The timer circuitry may comprise an integrated circuit 555 timer or other IC appropriately configured with RC networks.

Additionally preferably, the circuit means includes latching means in the form of a latching relay, for controlling the direction in which the current is passed through the coil. The latching relay may contain two changeover contacts, each connected to one terminal of the contactor coil and each arranged to selectively connect that one terminal either to a supply voltage or to ground via the switch. The latching relay may be controlled by an inductive voltage generated across the contactor coil. Hence, the operating power for the latching relay may be derived from the magnetic energy stored in the contactor coil. The inductive voltage may be generated as a result of the current passing through the coil subsiding. The inductive voltage may be used to charge a capacitor. The value of the capacitor may be selected such that it will charge up to a value sufficient to operate the latching relay only after the current passing through the switch has completely subsided. Thus, the changeover contacts may operate under no load conditions.

The switch may be controlled by at least one push button switch which may be depressed to initiate either or both movements of the armature.

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

Figure 1 is a schematic circuit diagram of a preferred form of switching mechanism according to the invention;

Figure 2 is a schematic circuit diagram of a variant of the switching mechanism of figure 1;

Figure 3 is a schematic circuit diagram of an alternative form of switching mechanism according to the invention; and

Figure 4 is a schematic circuit diagram of a variant of the switching mechanism of figure 3.

With reference to figure 1 , a preferred form of switch according to the invention is shown generally at 10. The switch comprises a contactor of the type described above having a coil CC for effecting movement of an armature 12 which is movable between two positions. In a first, contact breaking position, the contacts of the contactor (not shown) are held apart by the armature 12. In a second, contact making position, the contacts of the contactor are forced by the armature 12 to close thereby completing the circuit (not shown) in which the contactor is used. The movement of the armature 12 is achieved by passing a current through the coil CC so as to generate a magnetic field which acts upon the armature. The direction in which the current is passed dictates the direction of the magnetic field and thus the direction of action upon the armature 12. Thus, passing a current in a first direction through the coil CC forces the armature from the first position to the second position. The armature 12 is then held in the second position by a permanent magnet 14 so as to avoid the need to maintain the current through the coil CC and incur excessive energy dissipation. The armature 12 is returned to the first position, to which it is normally biased by a spring, by passing a current through the coil CC in the opposite direction in order to generate a magnetic field which opposes the attraction of the magnet 14.

The switch 10 includes control circuitry for controlling the operation of the contactor. The control circuitry includes latching means 18 for controlling the direction of current in the coil CC. The latching means 18 comprises a double-pole, latching relay LR, having two single- pole, double-throw changeover contacts LRl , LR2. Each changeover contact has a normally closed (N/C) fixed contact and a normally open (N/O) fixed contact. The two changeover contacts LRl, LR2 are connected together antagonistically with the N/C contact of LRl being connected to the N/O contact of LR2 and vice versa. The common terminal 20 of the first contact LRl is connected to one terminal of the coil CC whilst the common terminal 22 of the second contact LR2 is connected to the other terminal of the coil CC. A varistor VARl is connected in parallel with the coil CC, as is a series capacitor-resistor arrangement comprising capacitor C4 and resistor R6. The coil of the latching relay LR is connected in parallel with the capacitor C4.

The N/C contact of LRl and the N/O contact of LR2 are connected to the positive rail 16 of an electrical power supply via a push-button switch PB 1. The common terminals 20, 22 of LRl and LR2, respectively, are connected to a timing circuit 30 via diodes D2, Dl respectively and a resistor Rl. The N/O contact of LRl and the N/C contact of LR2 form a terminal 26 which is connected to a switching circuit 50. The timing circuit 30 comprises an integrated circuit 555 timer IC1 connected between resistor Rl and the earth rail of the power supply. The timer IC1 is provided with a stable 12 volt power supply and reverse polarity protection by the diodes Dl, D2, resistor Rl and a Zener diode ZD1 through which, when the switch PB1 is depressed, current will flow.

A resistor R2 and a capacitor Cl are connected in series between the junction of resistor Rl/ Zener diode ZD1 and the earth rail of the power supply and the junction between them is connected to the trigger input (pin 2) of the 555 timer IC1. In addition, a resistor R3 in series with a capacitor C2 are connected in parallel with resistor Rl and capacitor Cl and the junction between R3 and C2 is connected to pins 6 and 7 of the timer IC1.

The output of the timer IC1 is connected to the switching circuit 50.

The switching circuitry 50 includes a pair of transistors arranged to form a Darlington pair Ql . The base of the Darlington pair Ql is connected to the output of the 555 timer IC1 through a resistor R4 and to the earth line of the power supply through a resistor R5. The resistor pair R4, R5 thus form a potential divider whose output is connected to the base terminal of the Darlington pair Ql. The collector terminal of the Darlington pair Ql is connected to the terminal 26 from the latching circuit 18 and its emitter is connected directly to the earth line.

Operation of the switch of figure 1 will now be described. Prior to depression of the push button switch PB1, all capacitors are discharged. When the switch PB1 is depressed, current flows through PB 1 , LRl , D2 and Rl and a 12 volt supply is established over IC 1. When the supply first appears across IC1, pin 2 will be held momentarily low by Cl which will trigger the timer IC1 and cause its output on pin 3 to go high. The capacitor Cl begins to charge through R2 on a 0.1 millisecond time constant and is then ineffectual until the switch PB1 is again depressed. As soon as the output of IC1 goes high, current flows to the base of Darlington pair Ql which switches on. Current thus flows through the N/C contacts of LRl and LR2 and thereby through the coil from left to right. The resulting magnetic field causes the armature 12 of the contactor to move from the first position to the second position.

On depression of the switch PB1, the capacitor C2 begins to charge via the resistor R3 and after approximately 220 milliseconds the voltage across the capacitor C2 becomes sufficient to cause the output of IC1 to drop low thus causing Ql to turn off. The timer IC1 then remains dormant until the switch PB1 is released and depressed again.

With the Darlington pair Ql turned off, current can no longer flow through the coil CC from positive to negative. The reducing coil current causes the magnetic field acting on the armature 12 to collapse and generates an inductive voltage across the coil CC with the terminal connected to the common contact of LR2 becoming positive with respect to the terminal connected to the common of the contact LRl. This enables the coil current to flow into capacitor C4 via resistor R6. If the coil inductive voltage exceeds the voltage rating of the varistor VARl , current will flow into VARl until the inductive voltage drops below the voltage rating of VARl. The inclusion of VARl is optional but provides the advantage that large contactors with high magnetic energy may be controlled since the varistor VARl dissipates the excess magnetic energy and thus avoids overloading the latching relay coil circuit.

When the voltage across C4 reaches the operating voltage of the latching relay LR, the relay operates and the changeover contacts LRl and LR2 are switched over. At this point, current will not flow through the coil in the opposite direction since the Darlington pair Ql is not switched on. In fact, current will continue to flow in the same direction as previously until all of the magnetic energy has been dissipated. The contactor will remain closed since the armature 12 is held in the second position by a permanent magnet 14. When the changeover contacts LRl, LR2 switch over, the current through the N/C contact of LRl and diode D2 will cease but will be replaced by current through the N/O contact of LR2 and diode Dl within approximately 1ms. The capacitors Cl and C2 are unable to discharge much within this time and so IC1 is not re-triggered.

The circuit is thus placed in its initial state with the exception that the changeover contacts LRl, LR2 are in their opposite positions. If the switch PB1 is depressed again, the same sequence of events occurs except that this time the coil current flows through the coil CC in the opposite direction. The electro-magnetic flux generated opposes the magnetic flux of the permanent magnet, thus forcing the armature to return to the first position. The capacitor C4 is a bi-polar type and thus the latching relay circuit is symmetrical and able to cause the latching relay to "set" and "reset". The Darlington pair Ql and the associated circuitry is common to both the back and forth movements of the armature.

An additional capacitor (not shown) may be connected between the base and emitter terminals of the Darlington pair Ql in order to slow the turn-off of the transistor pair. The slow turn off of the transistor Ql enables the coil current to reduce and hence lower the amount of energy stored in the coil magnetic field to a level which is suitable for operating the latching relay LR without developing excessively high voltages.

The value of the capacitor C4 may be selected to ensure that the transistor Ql is fully off before the latching relay LR operates. If the capacitance of the capacitor C4 is too large, the voltage across it, when being charged by the coil inductive voltage, will not rise to a sufficient magnitude to operate the latching relay LR.

With reference to figure 2, in an alternative embodiment to that described with reference to figure 1, the control circuitry of the switch 10 includes two separate push button switches PBO and PBC for initiating the two separate movements of the contactor armature. The N/C contact of LRl is connected to the positive rail 16 of the electrical power supply only via the close push button switch PBC and the N/O contact of LR2 is connected to the positive rail only via the open push button switch PBO. Otherwise, the circuitry illustrated in Figure 2 is identical to that of the single push button embodiment described with reference to Figure 1.

In operation, actuation of the close push button switch PBC causes current to flow through LRl, D2, Rl, ZD1 and D3 to earth. The circuit thus operates in the same manner as the previously described embodiment. However, when the changeover contacts LRl, LR2 switch over, the current through D2 will be terminated but will not be replaced by a current through Dl since the open push button switch PBO will still be open. If push button switch PBO is actuated, a similar sequence of events occurs and causes the armature of the contactor to return to its original position.

It will be appreciated that the operation of the circuitry by actuation of either push button switch is independent of the status of the other push button switch.

Referring to figure 3, an alternative form of switch according to the invention is shown generally at 100. The switch 100 includes a contactor similar to that described in relation to the previous embodiment. However, the control circuitry for controlling the operation for the contactor is somewhat different. In particular, it will be seen that the embodiment of figure 3 is "negatively-switched" with the push button switch PB1 connected to the negative rail 116 of the electrical power supply. The arrangement of the circuit elements is similar to that of figure 1 but with appropriate changes to accommodate negative switching.

In addition, in the embodiment of Figure 3, the 555 timer of IC1 is replaced by an op-amp IC2 together with its appropriate connections.

In operation, when the push button switch is actuated, current flows through the reverse polarity protection diode Dl, Zener diode ZD1, resistor Rl, diode D3 and the N/C contact of LR2 to negative. The voltage over ZD1 is applied to the potential divider consisting of resistors R2 and R3 causing approximately 2/3 of the voltage across ZD1 to occur across R3 which is applied to the inverting input pin of IC2. The junction of resistor R4 and capacitor C2 is connected to the non-inverting input pin of IC2 and, since C2 is initially discharged, the output of IC2 will be low. As C2 charges via R4, the voltage applied to the non-inverting input will exceed that applied to the inverting input and the output of IC2 will go high.

When the output of IC2 is low, current flows from the base of the Darlington pair Ql and its collector current flows through the N/C contact of LRl , through the coil CC from left to right in the drawing and through the N/C contact of LR2 to negative. Once C2 is charged, the output of IC2 will go high and Ql will be turned off.

It can be seen that operation of the switch of figure 3 is substantially identical to that of figure 1. Similarly, the operation of the switch of figure 4 is substantially identical to that of figure 2.

Claims

Claims:

1. A switch for making or breaking an electrical connection, the switch comprising:

armature means, selectively movable between a first position and a second position;

actuation means for effecting movement of the armature between said first and second positions;

holding means for holding the armature means in one of said positions; and

control means for controlling operation of said actuation means;

wherein said control means is operable to permit a current to be passed temporarily through said actuation means in a first direction, thereby to cause said armature means to move from said first position into said second position and said holding means is operable to hold said armature means in said second position after said current has ceased.

2. A switch according to claim 1 wherein said control means is operable to permit a current to be passed temporarily through said actuation means in a second direction thereby to cause said armature means to move from said second position into said first position.

3. A switch according to claim 1 or claim 2 wherein said control means is operable to pass said current for not substantially longer than the time it takes for said armature means to move between said first and second positions.

4. A switch according to any preceding claim wherein said actuation means comprises an inductive coil.

5. A switch according to any preceding claim wherein said holding means comprises a magnet.

6. A switch according to claim 5 wherein said magnet is a permanent magnet.

7. A switch according to any preceding claim wherein said control means comprises timing means and switching means, said switching means being arranged to control the flow of current through the coil and said timing means being arranged to control the operation of said switching means.

8. A switch according to claim 7 wherein said timing means includes an integrated circuit timer whose timing function is controlled by an R-C network.

9. A switch according to claim 4 further comprising latching means for controlling the direction of said current through said coil, said latching means being operable to change the direction of current flow through said coil means in response to an inductive voltage generated in said coil following cessation of said current.

10. A switch according to claim 9 wherein said latching means comprises a latching relay having two single-pole, double-throw changeover contacts, each changeover contact being operable to connect one terminal of said coil means either to a supply voltage or to ground via said switching means in response to said inductive voltage.

11. A switch according to any preceding claim further comprising connecting means for selectively connecting said switch to a power supply.