Maglatch mechanism for use in lighting control pod

Abstract

An electrical contact assembly includes a magnetic latch solenoid for actuating a moveable contact of a contact pair. The magnetic latch solenoid includes a magnet that latches the contact assembly in an open position, and a coil that moves an armature to the latched position under current in one polarity, and disrupts the permanent magnet field to release the armature from the latched position under current in a reverse polarity. A spring biases the contacts to the closed position. The spring is separate from the magnetic latch solenoid. The contact assembly may also include a printed circuit board for providing pulses to the coil to operate the assembly. The contact assembly is part of a remote operated circuit breaker assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views of a magnetic latch solenoid in extended and retracted positions, respectively, in accordance with the invention.

FIG. 2 is a diagrammatic cross sectional view of a magnetic latch solenoid in accordance with the invention.

FIG. 3 is a perspective view of a partial electrical contact assembly in accordance with an embodiment of the invention.

FIGS. 4A-4D are simplified force diagrams showing a contact arm and moveable contact in accordance with the invention.

FIG. 5 is a perspective view of an electrical contact assembly including a printed circuit board and several associated components, in accordance with an embodiment of the invention.

FIGS. 6A and 6B are perspective views of an electrical contact assembly in open and closed positions, in accordance with an embodiment of the invention.

DESCRIPTION OF THE INVENTION

The present invention is a method and apparatus for opening and closing a pair of contacts in a circuit control pod such as a lighting control pod. A magnetic latch solenoid mechanism, or “maglatch,” is employed with a spring that is not located in close proximity to the contacts or to the maglatch in order to provide bi-stable operation.

A maglatch is a variation of a solenoid in which a permanent magnet is added to a solenoid. This component allows for translation of electrical signals to a mechanical motion. A maglatch used in a preferred embodiment of the present invention is shown in FIGS. 1A and 1B. The maglatch includes a maglatch housing 110 and a plunger 160. The plunger 160 may have a wrist pin hole 130 for accepting a wrist pin as described in more detail below.

A schematic cross sectional view of a maglatch 210 in accordance with the invention is shown in FIG. 2. A plunger 260 extends from the maglatch 210 and corresponds to the plunger 160 of FIG. 1A. Other element numbers incremented by multiples of 100 in other figures represent similar elements. A stationary magnetic core 250 surrounds the plunger. The magnetic core may be made of a soft ferrous material that responds to magnetic fields. The plunger 260 is mounted for reciprocating movement in the maglatch, using bushings or other means (not shown) as known in the art.

The maglatch 210 further comprises electromagnetic coil 230 connected to a housing of the maglatch (housing 111 of FIG. 1A). The coil 230 induces a magnetic field in the core 250 when current is passed through the coil. The magnetic field exerts a force on the armature 250 in an axial direction; i.e., along an axis 270 of the maglatch 210. When an electrical potential is placed across the coil in first polarity, magnetic force on the armature urges the armature in an upward direction as oriented in FIG. 2, retracting the plunger into the maglatch.

The maglatch 210 further comprises a permanent magnet 215 and may include a flux guide 216. When the plunger 260 is in a retracted position and therefore proximate the permanent magnet 215 and flux plate 216, a strong magnetic circuit is formed through those members, exerting an attractive force on the plunger 260 and “latching” it in the retracted position.

The effect of the permanent magnet 215 depends upon the position of the plunger 260. When the plunger is extended, the magnet provides no function because the air gap 280 in the magnetic circuit is sufficiently large to greatly weaken the field. When the solenoid is pulsed with current in the first polarity, electromagnetic forces on the plunger 260 pull it inward. Once the plunger is retracted, the permanent magnet 215 of the maglatch holds the plunger in place. That holding force creates one of the two stable positions of the switching mechanism of the invention. The holding force is directly dependant upon the strength of the maglatch permanent magnet. The solenoid portion of the maglatch creates the force that allows the plunger to move from the extended position to the retracted position.

In order to provide motion in the other direction, i.e., to extend the plunger, the switching mechanism also requires a spring 390, shown in FIG. 3. The spring 390 is mounted externally to the maglatch mechanism 310, and acts on an L-shaped contact arm 383, pivotably mounted to a base by a pivot pin 380. A moveable contact 382 is mounted on the contact arm 383 by welding or another method. In the closed position shown in FIG. 3, the moveable contact 382 is in contact with a fixed contact 381. The spring 390 is preferably a compression spring that places a continuous force on the contact arm 383 to extend the plunger 360. When the plunger is retracted, the spring force on the plunger 360 is lower than the force on the plunger of the permanent magnet, maintaining the plunger in the stable retracted position.

Returning to FIG. 2, when a brief DC pulse is provided to the maglatch 210 by applying a potential to the coil 230 in a second polarity, the electromagnetic field of the coil temporarily disables the permanent magnet 215 by interfering with the magnetic circuit containing the plunger 260. That allows the spring to move the plunger 260 outward until the plunger is fully extended. In the extended position, the spring holds the plunger in its second stable position, with the contacts 381, 382 in contact.

The contact assembly of the present invention has two stable equilibrium positions: contacts closed and contacts open. Those positions will now be described with reference to FIGS. 4A-4D. In the “contacts closed” position shown in FIG. 4A, the force of the spring (F_s) on the contact arm 483 creates a torque about the pivot pin 480, biasing the moveable contact 482 against the fixed contact (not shown), which acts as a mechanical stop. The spring force therefore holds the contacts closed. A reaction force (F_r) on the moveable contact 482 creates a corresponding torque on the contact arm 483, maintaining equilibrium. The maglatch does not affect the mechanism.

FIG. 4B shows the contact arm in the stable “contacts opened” position of the contact assembly. The permanent magnet in the maglatch applies a continuous force F_L to the device. The force F_L is greater than the force F_s exerted by the spring. A mechanical stop (not shown) applies a reaction force and prevents further counterclockwise rotation of the arm.

The force diagram of FIG. 4C shows the contact arm in a non-equilibrium state, resulting in motion from the “contacts closed” position to the “contacts open” position. To start that motion, a force F_sol is generated by the solenoid acting on the armature of the maglatch, placing a torque on the contact arm that exceeds the torque from the spring force F_s. The contacts are thereby moved apart as the plunger retracts into the maglatch, until the permanent magnet in the maglatch latches the plunger in the retracted position.

The force diagram of FIG. 4D illustrates motion of the contact assembly of the invention from the “contacts open” position to the “contacts closed” position. A DC pulse applied across the maglatch solenoid temporarily disables F_L by interfering with the magnetic field of the permanent magnet. As a result, the spring force F_s rotates the contact arm clockwise until the contacts are closed, providing a mechanical stop.

A preferred embodiment of the circuit control pod 500 of the invention, including its major components, is described below with reference to FIG. 5.

The spring 590 is a compression spring located away from the contacts 581, 582 to reduce the spring's exposure to heat generated by opening and closing the contacts. The spring is captured directly by the base and cover (not shown) of the circuit control pod 500, and acts on the L-shaped contact arm 583.

The contact arm 583 serves several functions. The arm provides a conductor for current flow to the moveable contact 582. Line current flows from a line side terminal 570 through a braided wire conductor (not shown) that is welded to the contact arm in the region near the pivot pin 580. The line current then flows from the braid weld site through the arm to the moveable contact 582. The moveable contact is also welded to the contact arm. Other connection techniques, such as soldering and brazing, may alternatively be used to attach the braid and the moveable contact to the contact arm.

The contact arm 583 pivots about the pivot pin 580 to provide the motion to open and close the electrical contacts 581, 582. The arm 583 further provides a mechanical interface 591 with spring 590. The arm provides mechanical support for both the pivot pin 580 and the wrist pin 530.

In one embodiment of the invention, the contact arm 583 provides mechanical support for an armature 571 used in a “blow closed” mechanism that also includes a magnetic yoke 572 mounted in proximity to the line side conductor 570 and the contact arm 583. The “blow closed” mechanism operates when excess current flows through the contact arm 583 and the line side conductor 570, inducing a magnetic field in the yoke 572, which exerts an attractive force on the armature 571. That attractive force holds the contacts closed and resists forces at the contacts that otherwise tend to blow the contacts apart under high current loads.

The contact arm 583 serves as one of a pair of parallel conductors that additionally holds the contacts 581, 582 together under over-current conditions. Current flowing in parallel paths in opposing surfaces of the contact arm 583 and the line side conductor 570 exert attractive forces between those two components. Those attractive forces, in addition to the force of the spring 590 and the above-described “blow-closed” mechanism, hold the contacts closed during an overcurrent condition. The parallel conductors and the “blow-closed” mechanism are described in more detail in the commonly assigned patent application entitled “Design and Method for Keeping Electrical Contacts Closed During Short Circuits,” filed concurrently with the present application, the contents of which are hereby incorporated by reference herein in their entirety.

The contact arm 583 may also serve as part of a visual flag indicator (not shown) and as part of an auxiliary contact mechanism (not shown). Further, if the angle of the spring is changed, and the contact arm 583 is slotted to permit translation relative to the pivot pin 580, the contact arm may be adapted to allow sliding motion between contacts to break tack welds that may result from arcing.

The pivot pin 580 provides for smooth rotation of the contact arm 583. The pin is captured in the base 675 (FIG. 6) and cover (not shown) of the lighting control pod. The pin may be made of hardened steel for additional endurance of the pivot joint. The pivot pin connection provides long life to the joint as compared to known contact arm joints.

The contact pair includes a moveable contact 582 and a fixed contact 581. The contacts make and break the electrical load. The moveable contact 582 is welded directly to the contact arm 583. The fixed contact 581 is welded to the load terminal 584.

The load terminal 584 provides an electrical connection from the contact 581 to the outside of the circuit control pod. The other end of the load terminal interfaces with a lug 585 for the securing of an external conductor (wire, electrical bus, etc.) to the circuit control pod. Features of the load terminal allow for a robust mechanical and electrical connection.

A wrist pin 530 is provided to allow for differences between the linear motion of the maglatch plunger 560 and the rotational motion of the contact arm 583. For the limited rotational motion of the preferred design relative to the length of the arm, a small amount of clearance is provided in the hole diameter where the wrist pin 530 engages the contact arm 583.

The printed circuit board 573 provides internal control of the circuit control pod. The printed circuit board receives power through an external connector 574. The printed circuit board 573 switches the polarity and duration of energy supplied to the maglatch 510 so that no additional devices (diode bridge, etc.) are required to operate the maglatch.

In a preferred embodiment, the circuit control pod is part of a larger system called an Integrated Lighting Control System. In the Integrated Lighting Control System, a set of many circuit control pods is connected to a computer via a communications bus. Signals to open or close the circuit control pod contacts are sent by the computer down the communication bus. When the signal reaches a circuit control pod, the circuit control pod electronics identify that the signal is intended for a particular circuit control pod. One technique for identifying a particular circuit control pod on a communications bus is disclosed in U.S. Patent Publication No. 20070064360, published Mar. 22, 2007 and entitled “Selection Line and Serial Control of Remote Operated Devices in an Integrated Power Distribution System,” the contents of which are incorporated by reference herein in their entirety.

Once the signal is decoded, the circuit control pod printed circuit board 573 issues a positive DC, pulse-width-controlled signal of 18-50 milliseconds in duration to the maglatch 510. The printed circuit board 573 must properly regulate the pulse width and polarity in order to retract the maglatch plunger 560. When the opposite motion is desired, the circuit control pod electronics board 573 delivers a negative DC pulse for 2-6 milliseconds. That second pulse temporarily disrupts the field of the permanent magnet within the maglatch 510, allowing the plunger 560 to extend.

A maglatch circuit control pod 600 of the present invention is shown in FIGS. 6A and 6B as mounted in a base 675. The base may be made from a heat-tolerant insulating material such as a high-temperature thermoplastic or a thermoset resin. The pod 600 is shown in an open position in FIG. 6A, with the maglatch 610 retracted. The pod 600 is shown in a closed position in FIG. 6B with the maglatch 610 extended and the contacts 682, 681 closed.

The maglatch circuit control pod of the present invention has numerous advantages over existing switching devices. As compared to a worm-gear motor design, the device is quiet; the only noise produced being the sound of contacts striking. The device furthermore runs on very low power. For example, a preferred embodiment of the invention requires only about 1.7 A at 24 VDC for 2-25 milliseconds.

Operation of maglatch circuit control pod of the present invention is rapid. The inventors have measured response times for a device according to the invention at less than 4.5 milliseconds to break continuity.

The device of the invention is compact in part because it does not require a large armature for mechanical advantage. Because the device does not also manage or conflict with circuit breaker functions, it is simplified electrically and mechanically, and does not require compromises on contact design.

Due in part to the pivot pin and wrist pin designs, the system has a longer machanical life. The expected life of a contact assembly according to one embodiment of the invention is in excess of 450,000 cycles.

The foregoing detailed description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the description of the invention, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. For example, while the contact arm is described herein as having a particular L-shaped configuration, other contact arm designs may be substituted. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.

Claims

1. A contact assembly for reciprocating between a stable closed position to allow current flow through the contact assembly and a stable open position to prevent current flow through the contact assembly, the assembly comprising: a base;a fixed contact mounted to the base;a contact arm;a pivot pin for pivotably mounting the contact arm to the base;a moveable contact mounted on the contact arm for movement between the stable closed position wherein the moveable contact is in contact with the fixed contact, and the stable open position wherein the moveable contact is spaced apart from the fixed contact;a spring exerting a spring force on the contact arm to bias the moveable contact toward the stable closed position of the contact assembly;a magnetic latch solenoid comprising: a magnetic armature;a permanent magnet in proximity to the armature when the armature is in a retracted position, the permanent magnet having a magnetic field exerting a latching force on the armature to maintain the armature in the retracted position; anda coil in proximity with the armature, the coil being adapted to exert a retracting force on the armature in excess of the spring force in a direction of the retracted position of the armature when electrical energy is applied to the coil in a first polarity, and to disrupt the magnetic field when electrical energy is applied to the coil in a second polarity to release the armature from the retracted position; anda wrist pin connecting the contact arm and the armature, the wrist pin being disposed in a clearance hole in at least one of the contact arm and the armature, permitting relative movement thereof;the retracted position of the armature resulting in the stable open position of the contact assembly.

2. The contact assembly of claim 1, wherein the spring is separate from the magnetic latch solenoid.

3. The contact assembly of claim 1, further comprising: a line terminal for connection with an electrical source of the current flow; anda braided wire connector electrically connecting the line terminal and the contact arm.

4. The contact assembly of claim 1, wherein the contact arm further comprises: a mechanical spring interface, the spring exerting the spring force between the mechanical spring interface and a base of the contact assembly.

5. The contact assembly of claim 4, wherein the mechanical spring interface is remote from the moveable contact on the contact arm.

6. The contact assembly of claim 1, further comprising: a load terminal electrically connected to the fixed contact for connecting a current load to the contact assembly.

7. The contact assembly of claim 1, further comprising: a printed circuit board connected to the coil for applying a pulse of electrical energy to the coil in the first polarity to open the contacts and for applying a pulse of electrical energy to the coil in the second polarity to close the contacts.

8. The contact assembly of claim 7, wherein the pulses of electrical energy are pulse-width-controlled DC signals.

9. A method for remotely operating a contact assembly between a stable closed position to allow current flow from a line to a load through the contact assembly and a stable open position to prevent current flow through the contact assembly, the method comprising the steps of: providing a fixed contact connected to a load side of a circuit breaker, the breaker being set to open the circuit between the line and the load at or above a predetermined current load;providing a moveable contact adapted for movement between the stable closed position wherein the moveable contact is in contact with the fixed contact and the stable open position wherein the moveable contact is spaced apart from the fixed contact;providing a spring exerting a spring force on the moveable contact toward the stable closed position;providing a magnetic latch solenoid including a magnetic armature connected to the moveable contact for movement therewith; a permanent magnet in proximity to the armature when the moveable contact is in the stable open position, the permanent magnet having a magnetic field exerting a latching force on the armature to maintain the armature and moveable contact in the stable open position; and a coil in proximity with the armature;applying electrical energy to the coil in a first polarity to exert an opening force on the armature in excess of the spring force to move the armature and moveable contact to be held in the stable open position by the latching force of the magnetic field; andapplying electrical energy to the coil in a second polarity to disrupt the magnetic field and release the armature and moveable contact from the stable open position to be displaced by the spring to the stable closed position.

10. The method of claim 9, wherein the steps of applying electrical energy to the coil further comprise applying electrical pulses to the coil.

11. The method of claim 10, wherein the pulses of electrical energy are pulse-width-controlled DC signals.

12. The method of claim 10, wherein the electrical energy is approximately 1.7 amps at 24 volts DC.

13. The method of claim 10, wherein the steps of applying electrical energy to the coil comprise applying at least one pulse having a duration of less than 50 milliseconds.

14. The method of claim 10, wherein the step of applying electrical energy to the coil in the second polarity comprises applying a pulse having a duration of less than 10 milliseconds.

15. A circuit breaker assembly positionable in a circuit between a line and a load, the assembly comprising: a circuit breaker set to open the circuit between the line and the load at or above a predetermined current load; anda contact assembly adapted for reciprocating between a stable closed position to allow current flow through the contact assembly and a stable open position to prevent current flow through the contact assembly, the assembly comprisinga fixed contact connected to the load side of the circuit breaker;a moveable contact electrically connected to a load side conductor for connection to a load, the moveable contact being moveable between the stable closed position wherein the moveable contact is in contact with the fixed contact and the stable open position wherein the moveable contact is spaced apart from the fixed contact;a spring exerting a spring force on the moveable contact and biasing the moveable contact toward the stable closed position; anda magnetic latch solenoid comprising: a magnetic armature connected to the moveable contact for movement therewith;a permanent magnet in proximity to the armature when the moveable contact is in the stable open position, the permanent magnet having a magnetic field exerting a latching force on the armature to maintain the armature and moveable contact in the stable open position; anda coil in proximity with the armature, the coil being adapted to exert an opening force on the armature in excess of the spring force in a direction of the stable open position when electrical energy is applied to the coil in a first polarity, and to disrupt the magnetic field when electrical energy is applied to the coil in a second polarity to release the armature and moveable contact from the stable open position.

16. The contact assembly of claim 15, wherein the spring is separate from the magnetic latch solenoid.

17. The contact assembly of claim 15, further comprising: a contact arm having a first end pivotably mounted to a base of the contact assembly, the moveable contact being mounted on a second end of the contact arm.

18. The contact assembly of claim 17, further comprising: a wrist pin connecting the armature and the contact arm, the wrist pin being disposed in at least one clearance hole permitting relative movement of the armature and the contact arm.

19. The contact assembly of claim 17, further comprising: a braided wire connector electrically connecting the load side conductor and the contact arm.

20. The contact assembly of claim 17, wherein the contact arm further comprises: a mechanical spring interface, the spring exerting the spring force between the mechanical spring interface and a base of the contact assembly.

21. The contact assembly of claim 20, wherein the mechanical spring interface is remote from the moveable contact on the contact arm.

22. The contact assembly of claim 15, further comprising: a printed circuit board connected to the coil for applying a pulse of electrical energy to the coil in the first polarity to open the contacts and for applying a pulse of electrical energy to the coil in the second polarity to close the contacts.

23. The contact assembly of claim 22, wherein the pulses of electrical energy are pulse-width-controlled DC signals.