Embodiment of the present disclosure relates to a bi-stable magnetic actuator. More particularly, embodiments of the disclosure relate to an electro magnet for the transition phase and permanent magnet for holding phase in a bi-stable magnetic actuator.

BACKGROUND

Presently, known in the arts use pyro operated pin puller and shape memory alloy wire actuated devices. The pyro based systems are one shot operation and shape memory alloys has been emerged as replacement for pyro systems in some applications, because of their reusability and ground testing with reliability. The other advantages using shape memory devices are the ability to meet low outgassing requirements and absence of high levels of pyro shock which can be detrimental to spacecraft avionics. However, it is to be noted, that shape memory devices, hitherto, known from literature are only manually re-settable. Towards overcoming these shortcomings there is a need to devise a device that is electrically re-settable and at the same time generate reasonably good force and mechanical stroke requirements based on the current state of the art in electromagnetics. Known in art is electro-permanent magnet, which is a device that can have its external magnetic field switched ON and OFF by an electrical pulse, and retains its magnetic state with zero power. The electro-permanent magnets are strong, low-power devices at small scales, because their switching energy scales with volume, while their holding force scales with area. In conventional electro-magnet systems like solenoid valves, heat from I ² R (Ohmic losses) losses in the electromagnets has been a major limit on performance, manifesting itself either as destructive temperature rise, high power requirements, or low force capability. This can be by overcome by using pulse-driven electro-permanent magnets.

In general an electro-permanent magnet's external magnetic field can be modulated by an electrical pulse. Thereafter, no electrical power is required to maintain the field. Power is required only during mechanical working or changing the device's state. The electro permanent magnets as shown in Figure 1, comprises two magnetic materials, a magnetically hard (NIB) and a semi-hard (Alnico) material, capped at both ends with a magnetically soft material (Iron) and wrapped with a coil. A method in which a current pulse of one polarity is passed that magnetizes the materials together, increasing the external flow of magnetic flux. A current pulse of the opposite polarity reverses the magnetization of the semi-hard material, while leaving the hard material unchanged. The passing of current pulse diverts some part of flux or entire flux to circulate inside the device, thereby reducing the external magnetic flux. The method of passing the pulse of current through the coil in one direction magnetizes the material in the same direction. In this state, the flux exits the device and exerts a holding force. The passing of a pulse of current through the device in the opposite direction reverses the magnetization of the lower coercivity magnet but leaves the high coercivity magnet unchanged. In this state, the two magnets are oppositely magnetized and so the magnetic flux only circulates inside the device and there is no holding force.

Known in the art are the types of electro-permanent magnet (EPM) monostable EPM, series EPM and parallel EPM. The monostable EPM are made by temporarily reversible permanent magnets based on flux cancellation or flux switching principle. In flux cancellation principle, the EPM is constructed by wrapping a permanent magnet with a coil. When the coil is switched off, the permanent magnet holds a load. The switching ON of the magnets, releases the load and when the coil is switched OFF, the field returns. In flux switching principle, it is constructed by placing a permanent magnet and a coil in parallel between two Ferro magnetic pole pieces. When the coil is OFF, the permanent magnet exerts a holding force on nearby object. When the coil is turned on, the flux from the permanent magnet is shunted through the coil and the holding force switches OFF. When the coil is turned OFF, the holding force resumes.

In series EPM arrangement, a row of permanent magnets alternatively made from high coercivity materials and low coercivity materials are used. Initially, all the magnets are magnetized together and their flux passes through the bottom member. Coils surround the low coercivity magnet. Passing a momentary pulse of current through the coils reverses their magnetization. Now the net field across the bottom is zero so that no flux flows through it. Rather, the flux from each magnet exits the plate separately through the top, holding down the work piece. The parallel EPMs comprise two types of permanent magnetic materials, a high coercivity (NIB) and a lower coercivity (AINiCo). The two materials are place in parallel and surrounded by a coil.

Also, known in the art are bi-stable actuators similar to parallel EPM with two stable positions, one being held by spring and the other with permanent magnet. The switching is performed with a solenoid coil. In another prior art, a bi-stable actuator uses mutual magnetic repulsion for actuation. The bi-stable actuator comprises two permanent magnets members, which act in master, slave roles to achieve the two stable states. In another prior art, a mono- stable actuator by magnetic means uses an additional kinematic motion assembly to make it bi-stable actuator. In yet another prior art, an electro-magnetic actuator consists of two permanent magnets arranged along polar axis with proximal poles with same polarity. The electro magnet when energized over rides the repulsion the proximal poles and moves one permanent magnet towards the other fixed magnet. Further, known in the art is an EPM based actuator of coaxial plunger type with single coil and single permanent magnet. The direction is reversed by reversing the DC polarity. An EPM based armature displaces by EPM from rest position and restoring to the original position is by rebound energy from the wire getting deformed in previous state. Hence, there is a need of a solution to provide an improved, simple, safe, efficient, economical and effective bi-stable actuator which needs power only during the transition stage and needs no energy for holding force in either stable state without any additional restoring mechanisms like springs. References:

1. Ara Nerses Knaian" Electro permanent Magnetic Connectors and Actuators: Devices and Their Application in Programmable Matter", Ph.D Thesis, Department of Electrical Engineering and Computer science, MIT Jun, 2010.

2. Michael Salvinn, Charles Martus,"Bi stable Solenoid actuator", US Patent No 4758811 A, July 19, 1988.

3. John Petro, "Permanent magnet actuator Mechanism", US Patent No WO 2001069613 Al, Sep 20, 2001.

4. Costanzo Gadini, Daniele Cerruti, "Bi Stable Actuation Device", US Patent No US 6255934 B l, July, 3, 2001.

5. Jack E Fisher, "Fail Safe Actuator with Two Permanent Magnets", US Patent No 6040752 A March 21, 2001.

6. Frederik T. van Namen, "Bi Stable Electro Magnetic Mechanical Actuator", US Patent No 6512435 B2, Jan 28, 2003.

7. James J. McGonigal "Electromagnetic reciprocating linear actuator with permanent magnet armature" US Patent No 4259653 A, Mar 31, 1981. SUMMARY

The shortcomings of the prior art are overcome and additional advantages are provided through the provision of method of the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. In one embodiment, the present disclosure provides a bistable actuator comprising at least two magnets (7) interconnected through a central rod (5), said central rod (5) acts as a plunger connecting the at least two magnets and moves the at least two magnets as a single body, wherein surfaces of the two magnets facing each other are configured to have same polarity. The bistable actuator also comprises at least one soft magnet (6) configured around the central rod (5) between the two magnets (7), wherein the at least one soft magnet (6) is of bobbin shape. Further, the bistable actuator comprises a copper coil (11), wound around the at least one bobbin shaped soft magnet, the copper coil magnetizes the at least one soft magnet to a polarity based on an applied electric pulse. The at least one soft magnet (6) is attracted to one of the two magnets (7) based on the applied electric pulse, which is instantaneous.

It is to be understood that the aspects and embodiments of the invention described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the invention.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features and characteristic of the disclosure are set forth in the appended claims. The embodiments of the disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings.

Figure 1 shows an electro permanent magnet, in accordance with a prior art;

Figure 2 shows a cross sectional view of a bistable actuator in accordance with an embodiment of the present system.

Figures 3a and 3b illustrate principle of operation in initial position of the magnets and change in position of the magnets on application of electrical pulse in accordance with an embodiment of the present disclosure;

Figure 4 shows a perspective view of a bistable actuator, in accordance with an embodiment of the present disclosure; and

Figure 5 shows force generation in the bistable actuator, in accordance with an embodiment of the present disclosure The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein. DETAILED DESCRIPTION

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

An exemplary embodiment of the present disclosure provides a bistable actuator comprising two magnets (7) interconnected through a central rod (5), which acts as a plunger connecting the at least two magnets and moves the at least two magnets as a single body. The surfaces of the two magnets facing each other have same polarity. Also, the bistable actuator comprises at least one soft magnet (6) configured around the central rod (5) between the two magnets (7). The at least one soft magnet (6) is of bobbin shape. Further, the bistable actuator comprises a copper coil (11), wound around the at least one bobbin shaped soft magnet, the copper coil magnetizes the at least one soft magnet to a polarity based on an applied electric pulse. The at least one soft magnet (6) is attracted to one of the two magnets (7) based on the applied electric pulse, which is instantaneous.

One embodiment of the present disclosure is a device capable of operating in two states, referred as bi-stable, with respect to its last known position by changing the direction of the coil current in the field windings. The holding in both states is without any electrical power, i.e. by permanent magnets only. The device has at least one of the additional features such as, but not limited to, compact, simple, light weight, low shock, faster response, safe to use and maintain with minimum number of components. The peak power current may be required only during transition state and holding in state with no power.

In one embodiment, a secondary aerospace actuation mechanisms uses pyro based systems, solenoids and shape memory alloy based systems. The pyro systems have limitations in terms of single shot operation, not testable, can't be reset on-board, high pyro shock etc. The shape memory alloy based systems also have limitations like costly, sluggish, not resettable on-board etc. The solenoid systems are very popular but have limitations like bulky, needs large amount of copper, continuous power during operation, sluggish and can cater for only smaller strokes. The present disclosure aims at compact, high bandwidth, low power, and high speed bi-stable actuator with larger strokes. The present invention addresses all the above issues. The bi-stable actuators claimed in invention are based on Electro permanent magnets. They require instantaneous power for a few milliseconds. They are compact, low weight, less copper windings, low cost, cater for larger strokes, less shock, faster operation and high bandwidth systems which replaces the conventional aerospace actuation systems.

Figure 2 shows an exemplary cross sectional view of a bistable actuator in accordance with an embodiment of the present system. As shown in the figure 4, the bistable actuator comprises two permanent magnets or hard magnets (7), which are inter connected to each other using a central rod/ shaft arrangement or central rod/ shaft (5). The central rod (5) facilitates the motion of the two permanent magnets (7) as a single unit. In one embodiment, these permanent magnets are referred as hard magnets. The two hard magnets (7) are high energy product axially magnetized and assembled on to plunger with proper polarity to ensure the synergy for stage transition to take place with minimum force degrading during the stroke enabling larger strokes (air gaps) which are very critical as the magnet forces reduce drastically with air gap (f=k/d ² ). The central rod/ shaft (5), configured in the bistable actuator, to which both the hard magnets are fastened at the ends, functions as a plunger connecting the two hard magnets (7) and making them to move as a single body.

The bistable actuator also comprises a soft magnetic material or magnet (6), which is in the form of a bobbin and with a provision to wind a copper coil (11) around the bobbin. The soft magnetic (6) hereinafter is referred as a bobbin. The copper coil (11) enclosing the bobbin acts as magnetizer during the small duration of electric pulse and magnetizes the bobbin with proper polarity to switch between the two stable states. The bobbin acts as a core of electro magnet during transition stage, and acts as an iron for the permanent magnet during holding stage in both extreme stable states. The soft magnet (6) is configured to be held in a middle position of an assembly by fixing it to the body (2) of the bistable actuator, using a spacer arrangement. The bobbin (6) comprises a central hole through which a shaft or a rod, here it is the central rod (5) connecting the two permanent magnets, moves. The bobbin is fixed to the body (2) of the bistable actuator. The movement of central rod (5) makes the permanent magnets to contact the bobbin surface, which is based on the movement of the central rod (5). The permanent magnets are arranged to have same polarity on their surfaces facing each other.

In one embodiment of the present disclosure, a bistable actuator comprises of coaxial armature, which requires a single electrical coil with minimum copper, two high power permanent magnets, which can provide large holding force at both stable positions and during the transition both the permanent magnets provide the required motion with synergy, minimum degradation of force during the transition phase, resulting in a very compact, low weight and high speed secondary actuation system for aerospace systems.

In one embodiment, the bistable actuator system does not require any springs or other arrangements for bistable actuation. This results in low friction during the actuation of the bistable actuation system. The system response time is of the order of milli seconds and requires very less power consumption compared to the conventional available solenoids or any other conventionally known bistable actuators. In one embodiment, the assembly of the bistable actuator system is easier to fabricate and build a prototype. The bistable actuator of the present disclosure uses a combination of soft and hard magnetic materials to create a bistable actuation system. In one embodiment of the present disclosure, the bistable actuator based on electro permanent magnet operation uses only a short duration electric pulse of very high instantaneous power. The overall energy of almost zero is required for changing the state of the bistable actuator system. The holding force required for the two extreme stable states is achieved by the permanent magnets. The bistable actuation assembly consists of soft magnetic material based central bobbin.

Figures 3a and 3b illustrate principle of operation in initial position of the magnets and change in position of the magnets on application of electrical pulse in accordance with an embodiment of the present disclosure. As shown in figure 3a, initially the bobbin (6) is in contact with a permanent magnet on the left side with polarities North (N), on left side and South (S), on right side of the permanent magnet. The permanent magnet pole south (S) attracts the bobbin pole surface north (N). In one embodiment, when an electrical pulse is passed through the coil (11) to the bobbin (6), the bobbin surface poles are reversed. With the reversal of the poles, bobbin's north (N) pole changes to south (S) pole and it gets repelled from the left side permanent magnet, which was in touch with it. Simultaneously, the bobbin (6) gets attracted to the other permanent magnet on the other end (right side). In one embodiment, a reverse pulse through the coil wounded around the bobbin will result in bobbin being attracted to the former permanent magnet, i.e. the left side permanent magnet. Figure 4 shows a perspective view of a bistable actuator, in accordance with an embodiment of the present disclosure.

In one embodiment, the bistable actuator system comprises an extended rod to the central shaft at one end to ascertain the motion of the central shaft. The bistable actuator system is tested with a pre-requisite power supply and the time of response is measured i.e. the movement of the central shaft is achieved within a time frame of 20 milli seconds. The bistable actuator system draws the peak power (peak current) for 20 milli seconds during the operation of the actuation system.

Figure 5 shows force generation in the bistable actuator, in accordance with an embodiment of the present disclosure. As shown in the figure 5, it shows three different cases/ examples. In first case or case 1, a 10 mm thick hard or permanent magnet with one side soft magnet is used in the bistable actuator. In second case or case 2, a 6 mm thick hard or permanent magnet with one side soft magnet is used in the bistable actuator, and in third case or case 3, a 6 mm thick hard or permanent magnet with soft magnet on both sides. In one embodiment, the overall dimensions of all the magnets are 36 mm outer diameter, 10 mm internal diameter and 10 mm thickness. The magnet for the case 2 and case 3 has a thickness of 6 mm. In one embodiment, in order that a hard/permanent magnet with thickness 10 mm is to be separated from single soft magnet, then a plate required is of 25 kgf. The same hard magnet material of 6 mm thickness needed is 14 kg, whereas the same magnet of 6mm thick, when to be separated from two parallel steel plates required is 46 kgf for separation. This helps in obtaining greater force from less magnetic material. The separation force depends on may parameters of both soft and hard magnets in terms of shape, size, material, saturation, Maximum flux density, temperature and thickness. As shown in Figure 5, the central core is a soft magnetic material which may be supra

45. The thickness is maintained so that the soft magnet is not saturated when in contact with hard permanent magnet. In one embodiment, the hard magnet may be NdFeB rings with a proper polarity. The coil (not shown in Figure 5) is wound around the soft magnet, which is of bobbin shape. The coil is configured to alter the polarity of the soft magnet by altering the current direction. Based on standard calculation, the force generated by the permanent magnet is given as

Fg = B ^A 2 * A 12 μ ₀ ; and

the force distance relation of a permanent magnet is given as

F = K/d ^A 2;

The force distance relation is used to obtain force acting at air gap intervals of 1mm. In one embodiment, pull load tests are conducted to obtain the actual pull force generated by the hard magnets with the soft magnet, these values are as shown in the figure 5.

One embodiment of the present disclosure provides the advantages of the bistable actuator such as faster operation compared to the conventional actuators or solenoid systems of similar type; the bistable actuator requires only instantaneous power for transition which lasts for a few mill seconds and no need of any power during the operation of the bistable actuator. Also, the amount of copper requirement for the actuator is very minimal compared to a solenoid of similar force generating actuator. The coil heating problems does not exists in the of the bistable actuator of the present disclosure as compared to the conventional actuators and the overall energy consumption is minimal compared to similar solenoid based systems. The polarity reversal is simple and sufficient to switch the states of the actuator. The soft magnetic material works as electro magnet during transition phase and, as iron during long holding state. The total system is simple to operate easy to make, can generate more force compared to conventional or similar sized actuators and the system is able to stay in any of the stable states permanently.

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.