Patent Application
20090066449
Relays are electromechanical switches operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A typical relay comprises basically an electromagnet with a soft iron bar, called an armature, held close to it. A movable contact is connected to the armature in such a way that the contact is held in its normal position by a spring. When the electromagnet is energized, it exerts a force on the armature that overcomes the pull of the spring and moves the contact so as to either complete or break a circuit. When the electromagnet is de-energized, the contact returns to its original position. Variations on this mechanism are possible: some relays have multiple contacts; some are encapsulated; some have built-in circuits that delay contact closure after actuation; some, as in early telephone circuits, advance through a series of positions step by step as they are energized and de-energized, and some relays are of latching type.
Latching relays are the types of relays which can maintain closed and open contact positions without energizing an electromagnet. Short current pulses are used to temporally energize the electromagnet and switch the relay from one contact position to the other. An important advantage of latching relays is that they do not consume power (actually they do not need a power supply) in the quiescent state. Conventional electromechanical relays have traditionally been fabricated one at a time, by either manual or automated processes. The individual relays produced by such an “assembly-line” type process generally have relatively complicated structures and exhibit high unit-to-unit variability and high unit cost. Conventional electromechanical relays are also relatively large when compared to other electronic components. Size becomes an increasing concern as the packaging density of electronic devices continues to increase.
Many designs and configurations have been used to make latching electromechanical relays. Two forms of conventional latching relays are described in the Engineers' Relay Handbook (Page 3-24, Ref. [1]). A permanent magnet supplies flux to either of two permeable paths that can be completed by an armature. To transfer the armature and its associated contacts from one position to the other requires energizing current through the electromagnetic coil using the correct polarity. One drawback of these traditional latching relay designs is that they require the coil to generate a relatively large reversing magnetic field in order to transfer the armature from one position to the other. This requirement mandates a large number of wire windings for the coil, making the coil size large and impossible or very difficult to fabricate other than using conventional winding methods.
A non-volatile programmable switch is described in U.S. Pat. No. 5,818,316 issued to Shen et al. on Oct. 6, 1998, the entirety of which is incorporated herein by reference. The switch disclosed in this reference includes first and second magnetizable conductors having first and second ends, respectively, each of which is a north or south pole. The ends are mounted for relative movement between a first position in which they are in contact and a second position in which they are insulated from each other. The first conductor is permanently magnetized and the second conductor is switchable in response to a magnetic field applied thereto. Programming means are associated with the second conductor for switchably magnetizing the second conductor so that the second end is alternatively a north or south pole. The first and second ends are held in the first position by magnetic attraction and in the second position by magnetic repulsion.
Another latching relay is described in U.S. Pat. No. 6,469,602 B2 issued to Ruan et al. on Oct. 22, 2002 (claiming priority established by the Provisional Application No. 60/155,757, filed on Sep. 23,1999), the entirety of which is incorporated herein by reference. The relay disclosed in this reference is operated by providing a cantilever sensitive to magnetic fields such that the cantilever exhibits a first state corresponding to the open state of the relay and a second state corresponding to the closed state of the relay. A first magnetic field may be provided to induce a magnetic torque in the cantilever, and the cantilever may be switched between the first state and the second state with a second magnetic field that may be generated by, for example, a conductor formed on a substrate with the relay.
Yet another non-volatile micro relay is described in U.S. Pat. No. 6,124,650 issued to Bishop et al. on Sep. 26, 2000, the entirety of which is incorporated herein by reference. The device disclosed in this reference employs square-loop latchable magnetic material having a magnetization direction capable of being changed in response to exposure to an external magnetic field. The magnetic field is created by a conductor assembly. The attractive or repulsive force between the magnetic poles keeps the switch in the closed or open state.
Each of the prior arts, though providing a unique approach to make latching electomechanical relays and possessing some advantages, has some drawbacks and limitations. Some of them may require large current for switching, and some may require precise relative placement of individual components. These drawbacks and limitations can make manufacturing difficult and costly, and hinder their value in practical applications.
Accordingly, it would be highly desirable to provide an easily switchable latching relay which is also simple and easy to manufacture and use.
It is a purpose of the present invention to provide a new and improved latching electromechanical relay.
It is another purpose of the present invention to provide a new and improved latching electromechanical relay which is easy to switch and simple and easy to manufacture and use.
The above problems and others are at least partially solved and the above purposes and others are realized in a relay including a first magnet mounted on a movable cantilever and a second magnet placed near the first magnet. The first magnet is permanently magnetized along its long (horizontal) axis. The cantilever has a first end associated to the first pole (e.g., north pole) of the first magnet, and a second end associated to the second pole (e.g., south pole) of the first magnet. When the first end of the cantilever approaches the second magnet, the first pole of the first magnet induces a local opposite pole (e.g., south pole) in the second magnet and causes the first end of the cantilever to be attracted to the local opposite pole of the second magnet, closing an electrical conduction path (closed state). An open state on the first end of the cantilever can be maintained either by the second pole of first magnet being attracted to a local opposite pole in the second magnet or by a mechanical restoring force of the flexure spring which supports the cantilever. A third electromagnet (e.g., a coil or solenoid), when energized, provides a third perpendicular magnetic field about the first magnet and produces a magnetic torque on the associated cantilever to force the cantilever to switch between closed and open states. A few alternate embodiments of the relay is also disclosed which include a case where the latching feature is disabled, and another case where an external magnet is used to switch the cantilever.
The above and other features and advantages of the present invention are hereinafter described in the following detailed description of illustrative embodiments to be read in conjunction with the accompanying figures, wherein like reference numerals are used to identify the same or similar parts in the similar views, and:
It should be appreciated that the particular implementations shown and described herein are examples of the invention and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional electronics, manufacturing, and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail herein. Furthermore, for purposes of brevity, the invention is frequently described herein as pertaining to an electromagnetic relay for use in electrical or electronic systems. It should be appreciated that many other manufacturing techniques could be used to create the relays described herein, and that the techniques described herein could be used in mechanical relays, optical switches, fluidic control systems, or any other switching devices. Further, the techniques would be suitable for application in electrical systems, optical systems, consumer electronics, industrial electronics, wireless systems, space applications, fluidic control systems, medical systems, or any other application. Moreover, it should be understood that the spatial descriptions made herein are for purposes of illustration only, and that practical latching relays may be spatially arranged in any orientation or manner. Arrays of these relays can also be formed by connecting them in appropriate ways and with appropriate devices.
Movable cantilever 10 comprises a permanent (hard) magnetic layer 11 (first magnet), flexure spring and support 12, and electrical contacts 13 and 14. Magnetic layer 11 is permanently magnetized (with a magnetic moment m) along the long axis of the cantilever (e.g., predominantly along the positive x-axis as shown). Cantilever 10 has a first (right) end associated to the first (north) pole of first magnet 11 and contact 13, and has a second (left) end associated to the second (south) pole of first magnet 11 and contact 14. Magnetic layer 11 can be any type of hard magnetic material that can retain a remnant magnetization in the absence of an external magnetic field and its remnant magnetization can not be easily demagnetized. In an exemplary embodiment, magnetic layer 11 is a thin SmCo permanent magnet with an approximate remnant magnetization (Br=μ0M) of about 1 T along its long axis (predominantly along the x-axis). Other possible hard magnetic materials are, for example, NdFeB, AlNiCo, Ceramic magnets (made of Barium and Strontium Ferrite), CoPtP alloy, and others, that can maintain a remnant magnetization (Br=μ0M) from about 0.001 T (10 Gauss) to above 1 (104 Gauss), with coercivity (Hc) from about 7.96×102 A/m (10 Oe) to above 7.96×105 A/m (104 Oe). Flexure spring and support 12 can be any flexible material that on one hand supports cantilever 10 and on the other allows cantilever 10 to be able to move and rotate. Flexure spring and support can be made of metal layers (such as Beryllium Copper, Ni, stainless steel, etc.), or non-metal layers (such as polyimide, Si, Si3Ni4, etc.). The flexibility of the flexure spring can be adjusted by its thickness, width, length, and shape, etc. Similarly, other structures (e.g., a raised bar, a hinge, etc.) can be used to support cantilever 10 for its seesaw motion. Electrical contacts 13 and 14 can be any electrically conducting layer such as Au, Ag, Rh, Ru, Pd, AgCdO, Tungsten, etc., or suitable alloys. Electrical contacts 13 and 14 can be formed onto the tips (ends) of the cantilever by electroplating, deposition, welding, lamination, or any other suitable means. Flexure spring and support 12 and electrical contacts 13 and 14 can be formed by either using one process and the same material, or by using multiple processes, multiple layers, and different materials. When the cantilever rotates and its two ends moves up or down, electrical contact 13 or 14 either makes or breaks the electrical connection with the bottom contact 41 or 42. Optional insulating layers (not shown) can be placed between the conducting layers to isolate electrical signals in some cases.
Coil 20 (the third electromagnet) is formed by having multiple windings of conducting wires around the cantilever. The conducting wires can be any conducting materials such as Cu, Al, Au, or others. The windings can be formed by either winding the conducting wires around a bobbin, or by electroplating, deposition, etching, laser forming, or other means used in electronics industry (e.g., semiconductor integrated circuits, printed circuit boards, etc.). One purpose of coil 20 in relay 100, when energized, is to provide a third perpendicular (y-axis) magnetic field (Hs) so that a magnetic torque (τs=μm×Hs) can be created on cantilever 10. Because magnetic moment m is fixed, the direction and magnitude of the torque depends on the direction and magnitude of the current in coil 20. This arrangement provides a means for external electronic control of the relay switching between different states, as to be explained in detail below.
Soft magnetic layers 31 (second magnet) and 32 can be any magnetic material which has high permeability (e.g., from about 100 to above 105) and can easily be magnetized by the influence of an external magnetic field. Examples of these soft magnetic materials include permalloy (NiFe alloys), Iron, Silicon Steels, FeCo alloys, soft ferrites, etc. One purpose of soft magnetic layers 31 and 32 is to cause an attractive force between the pole of hard magnetic layer 11 and the induced local opposite magnetic pole of the soft magnetic layer so that a stable contact force can be maintained between electrical contact 13 (or 14) and electrical contact 41 (or 42). Another purpose of soft magnetic layers 31 and 32 is to form a closed magnetic circuit and enhance the coil-induced magnetic flux density (third perpendicular magnetic field) in the cantilever region. Yet another purpose of soft magnetic layers 31 and 32 is to confine the magnetic field inside the cavity enclosed by soft magnetic layers 31 and 32 so that the magnetic interference between adjacent devices can be eliminated or reduced.
Electrical contacts 41 and 42 can be any electrically conducting layer such as Au, Ag, Rh, Ru, Pd, AgCdO, Tungsten, etc., or suitable alloys. Electrical contacts 41 and 42 can be formed on the surface of soft magnetic layer 31 by electroplating, deposition, welding, lamination, or any other suitable means. Alternatively, electrical contacts 41 and/or 42 can be formed on the surface of soft magnetic layer 32 by similar means. Optional insulating layers (not shown) can be placed between the conducting layers to isolate electrical signals in some cases. Transmission-line types of contacts and metal traces can also be suitably designed and formed for high performance radio-frequency applications.
In a broad aspect of the invention, the first pole (e.g., north pole) of first magnet 11 induces a local (e.g., near contact 41 ) opposite (e.g., south) pole in the soft magnetic layer 31 (second magnet) to produce an attractive force between the poles which forces electrical contact 13 toward electrical contact 41 and maintains good electrical conduction between the two contacts. To break the electrical contact and switch cantilever 10 to another state, coil 20 is energized with a short current pulse which produces a third predominantly perpendicular magnetic field (Hs). A clockwise or counter-clockwise torque can be produced on cantilever 10 through the interaction between the magnetic moment (m) of magnet 11 and the coil-induced magnetic field (Hs), depending on the direction of the coil current. The torque rotates cantilever 10 from one state to another for switching purposes.
With continued reference to
Switching between the stable states is accomplished by passing a short current pulse (I) through coil 20 to create a third predominantly perpendicular (along y-axis) magnetic field (Hs) in the cantilever region. An additional magnetic torque (τs=μ0m×Hs) is produced on cantilever 10 which can cause the cantilever to rotate either clockwise or counterclockwise (front view 1B) depending on the direction of the coil current (which determines Hs).
Switching can also be accomplished by using another external movable magnet (not shown). The interaction between the first magnet 11 and the external movable magnet can produce torques and forces on cantilever 10 for switching and electrical contacting purposes.
Some of the aforementioned advantages of the disclosed invention can be evidenced by the following exemplary analysis.
Assuming the first magnet having the following characteristics: length=4 mm (along long axis), width=4 mm, thickness=0.2 mm, volume V=length×width×thickness, remnant magnetization Br=μ0M=1 T, the magnetic moment μ0m=μ0M×V=3.2×10−9 T·m3. For a coil-induced magnetic field μ0Hs=0.05 T (Hs=500 Oe), the induced magnetic torque about the length center is τs=μ0m×Hs=1.27×10−4 m·N (assuming m is perpendicular to Hs) which corresponds to a force of Fm=τs/(length/2)=6.4×10−2 N at the end of the first magnet. This force, combining with the flexure restoring force, needs to be larger than the pole attraction for cantilever switching. The above exemplary parameters show that for a relatively small coil-induced magnetic field (Hs=500 Oe), a significantly large torque and force can be generated. The torque and force can continue to increase with larger Hs (correspondingly larger coil current). Another point worth noting is that when the angle between m and Hs changes from perfectly perpendicular (90°) to 80°, the change in the magnitude of the torque (and force) is only 1.5%=1-98.5%=1-sin(80°), which gives a larger tolerance in production variations, simplifies the production process, and reduces costs.
Assuming all the dimensions of the first magnet are reduced by an order of magnitude: length=0.4 mm (along long axis), width=0.4 mm, thickness=0.02 mm, remnant magnetization Br=μ0M=1 T, the magnetic moment μ0m=μ0M×V=3.2×10−12 T·m3. For a coil-induced magnetic field μ0Hs=0.05 T (Hs=500 Oe), the induced magnetic torque about the length center is τs=μ0m×Hs=1.27×10−7 m·N (assuming m is perpendicular to Hs) which corresponds to a force of Fm=Ts/(length/2)=6.4×10−4 N at the end of the first magnet. The force is still quite large in such micro dimensions.
Fabricating a Latching Relay
It is understood that a variety of methods can be used to fabricate the latching relay. These methods include, but not limited to, semiconductor integrated circuit fabrication methods, printed circuit board fabrication methods, micro-machining methods, and so on. The methods include processes such as photo lithography for pattern definition, deposition, plating, screen printing, etching, lamination, molding, welding, adhering, bonding, and so on. The detailed descriptions of various possible fabrication methods are omitted here for brevity.
The operation of device 300 is first described for the case where substrate 331 is made of soft magnetic material, such as the type specified for soft magnetic layer 31 in
The operation of device 300 is now described for the case where substrate 331 is made of non-magnetic material such as the type specified for substrate 231 in
It will be understood that many other embodiments and combinations of difference choices of materials and arrangements could be formulated without departing from the scope of the invention. Similarly, various topographies and geometries of relay 100 could be formulated by varying the layout of the various components.
The corresponding structures, materials, acts and equivalents of all elements in the claims below are intended to include any structure, material or acts for performing the functions in combination with other claimed elements as specifically claimed. Moreover, the steps recited in any method claims may be executed in any order. The scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given above.
This is a divisional application Ser. No. 11/534,655, filed on Sep. 24, 2006, now U.S. Pat. No. ______, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/725,335, filed on Oct. 2, 2005, which is hereby incorporated by reference. The present invention relates to relays. More specifically, the present invention relates to latching electromechanical relays and to methods of operating and formulating electromechanical relays.
| Number | Date | Country | |
|---|---|---|---|
| 60725335 | Oct 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11534655 | Sep 2006 | US |
| Child | 12268936 | US |
