FR2458934A1 - LINEAR MOTOR - Google Patents

Abstract

LINEAR MOTOR. THIS MOTOR USES THE MAGNETIC ATTRACTION BETWEEN A WASHER 62, 64 CONSTITUTED OF A FERROUS MATERIAL, FOR EXAMPLE STEEL, AND A MAGNETIC POLE OF A REINFORCEMENT 26 TO AUTOMATICALLY RETURN THE REINFORCEMENT TO ITS INITIAL POSITION ON DE-EXCITATION OF ' A FIELD WINDING 54, 56. THE WASHER IS INITIALLY PLACED IN ALIGNMENT WITH AND SURROUNDED BY ONE OF THE EFFICIENT POLES OF THE FRAME. THE STROKE OF THE REINFORCEMENT IS LIMITED TO A DISTANCE WHICH ENSURES THAT AT ONE END OF THE STROKE OF THE EFFICIENT POLE IS CLOSER TO THE WASHER THAN ANY OTHER EFFICIENT POLE. WHEN DEEXCITATION OF THE FIELD WINDING, THE ATTRACTION OF THE MAGNET BETWEEN THE EFFECTIVE POLE AND THE WASHER CAUSES THE ARMATURE TO RETURN TO ITS INITIAL POSITION.

Description

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  The present invention relates to a linear motor.

  Dynamoelectric motors are well known and include

  generally a coil around which are wrapped one or more field windings. Mounted within the coil is an armature which may be a core formed from a piece of soft iron as shown in U.S. Patent No. 3,728. 654; or it may be comprised of a plurality of permanent magnets, as shown in U.S. Patent Nos. 3,022,400, 3,202,886 and 3,495. 147, or the frame may be a combination of a core and a permanent magnet. The application of a direct current in one direction to the field winding creates a magnetic field

  which produces a force to drive the armature into a first direction

  until it is physically stopped and the reverse application of the direct current to the field winding causes the armature to be driven in an opposite direction until it again hits a physical stop. A disadvantage of the motors described and represented by the patents indicated above is that each output shaft produces only one stroke, for each excitation and de-excitation of its field winding. In other words, the armature does not return to its initial position when de-energizing its field winding. One of the problems raised by returning an armature to its initial position is the precise positioning of the armature relative to the field winding, which ensures that the length of each stroke is substantially the same. One solution is provided by U.S. Patent No. 3,549,917 wherein the opposing springs are used to center or return an armature to its initial position upon de-excitation of its field winding. See also U.S. Patent No. 3,755,699 wherein flexible diaphragms are used to return a coil to its central position. However the adjustment of opposite springs or diaphragms to ensure that they will always provide equal and opposite forces leaves much to

  desire both from a practical and an economic point of view.

  U.S. Patent No. 3,860,300 discloses a control system comprising a plurality of permanent magnets made of cobalt-samarium and a pair of electromagnets for repositioning a tree.

  rotary. The output of each electromagnet is controlled by a cir-

  cooked containing a differential amplifier. See also U.S. Patent No. 3,874,750 wherein a permanent magnet thrust bearing system is used to position a rotating shaft relative to a stationary member. However, none of these systems relate to circumstances in which a field winding is excited to move an armature axially for the purpose of providing an output for driving an organ, and when de-energized automatically returns it to its initial position.

  The present invention relates to a dynamoelectric engine

  and more particularly to a linear motor. In a preferred embodiment of the invention, the linear motor comprises a coil of substantially cylindrical shape supporting between its cheeks

  electrically conductive means in the form of a pair of

  field bearings. The coil comprises an axial passage of form

  cylindrical to receive back and forth an armature form cor-

  sponding. The frame preferably comprises a core formed from a magnetically permeable material, such as steel. Fittings

  complemented by a pair of permanent magnets, preferably

  stored in a material containing a rare earth, such as cobalt-samarium.

  The magnets are fixedly attached to each axial end of the core so that common poles of the magnets are in contact with the ends of the core and the other common poles define opposite ends of the armature. Means in the form of a pair of end caps are secured to opposite ends

  of the spool to limit the length of the armature stroke.

  Each end cap has a central opening that is dimensioned to allow passage therethrough of a portion of an outlet bar that extends axially outwardly from each end of the frame. The end of each outlet bar which is secured to the frame is of a diameter greater than the diameter of the opening and that of the rest of the bar, whereby each end cap has the effect of limiting the movement. of

the frame along the passage.

  A pair of field windings are wound on the coil in juxtaposed relationship such that when they are not in excited condition they are placed symmetrically with respect to the steel core. A pair of washers (or discs) are fixedly attached to each end of the coil by the end caps so that they enclose and align with the poles at opposite ends of the armature when the windings are not not excited. Each washer is preferably formed of a material

  magnetically permeable such as steel.

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  The common poles of permanent magnets are fixed to the

  axial trenches of the steel core to provide a zone of maximum magnetic flux density which extends radially outwardly from the central portion of the steel core, thereby creating an armature which in fact has three poles, and that is to say two common poles, one to

  each end of the armature and a pole of opposite polarity equi-

  remote from the ends of the nucleus. These poles will be designated hereinafter by effective poles of the armature. The first of the two field windings when excited by a direct current is designed to produce a magnetic field whose force displaces the armature of a first position, wherein the steel washers are placed in alignment with the poles. effective joint end of the armature to a second position at which the movement of the armature is stopped by the enlarged portion of one of the output bars moving in contact with one of the end caps. This movement or stroke of the armature has a length that is less than half the distance between the north and south poles of the magnet which is placed on the end of the armature closest to the second position, this which ensures that the end pole of the magnet placed closest to the second position is still placed closer to its initially aligned steel washer than is the opposite pole of the magnet. When the flow of current to the first field winding is stopped, the magnetic attraction between the end pole placed closest to the second position and its respective steel washer is strong enough to return the armature to the first position in which the effective end plates are again in alignment with their respective steel washers. The second field winding, when excited by a DC current, is designed to move

  armature from the first position to a third position, sensi-

  opposed to the second position, in which the other effective end pole of the armature and its respective steel washer cooperate in a manner similar to that described with reference to the movement of the armature in the second position to automatically return the frame to the first position when de-energizing

the second field winding.

  In a variant of the invention the two steel washers are replaced by a single steel washer placed substantially

  in the plane of maximum density of the magnetic flux. In this combination

  naison, when the armature has been moved either in the second or in the third positions, the non-common effective pole of the armature -4- is placed closer to the steel washer than either of the two effective common poles of the magnet, which allows the attraction

  greater magnetic distance between them to return the frame to its first

  first position when de-energizing the field winding.

  In another embodiment, the linear motor comprises a coil supporting a single field winding, a single

  washer mounted on one end of the frame, an end cap

  mity, an armature comprising a single permanent magnet having opposite effective poles, and an output bar having one end

  - 10 is attached to one of the effective poles of the permanent magnet. The long

  Steel delle is placed in alignment with one of the effective poles

  armature when the armature (magnet) is in the first posi-

  tion. The armature is moved to the second position in response to the excitation of the field winding. Thus positioned the effective pole of the frame which was previously placed in alignment with the steel washer is still placed closer to the steel washer than the other effective pole. Therefore, when the field winding is de-energized, the greater magnetic attraction between the previously aligned washer and the effective pole is strong enough to

  return the frame to the first position.

  The object of the present invention is to provide a linear motor having improved means for returning an armature to its initial position when de-energizing a field winding.

  Another object of the present invention is to center magnetic

  tically an armature when de-energizing its field winding.

  Another object of the invention is to use the magnetic attraction

  between a magnetically permeable material and a magnet

  manent to return an armature to its original position during the

  disconnection of a field winding from a DC source.

  The present invention will now be explained by

  1 is an enlarged elevational view, partly in section, of a preferred embodiment of a linear motor in a non-energized condition, FIG. 2 is a view of the motor. FIGS. FIG. 1 showing the position of its armature when one of its field windings is excited, FIG. 3 is an enlarged elevational view, partly

  in section of a variant of a linear motor represented in its

  FIG. 4 is an elevational view of the linear motor of FIG. 3 in an excited condition, FIG. 5 is an enlarged elevational view, partly in section, of another embodiment of the present invention, and

  Figure 6 is a diagram of the relationships between an arma-

  of the present invention and a curve which represents the density

magnetic flux of the frame.

  Referring now to FIGS. 1 and 2 of the drawing, in which a preferred embodiment of a linear motor 10 is

  shown, the outer casing of the motor being omitted for clarity.

  The motor 10 comprises a substantially cylindrical coil 12 which is preferably made of a non-conductive material such as Delrin, a thermoplastic resin sold by E.I. Dupont de Nemours et al. The coil 12 comprises a plurality of annular cheeks 14, 16 and 18, end portions 20 and 22 and a longitudinal cylindrical passage 24. An armature 26 is mounted inside the passage 24 for

  a displacement back and forth in the passage 24. The frame 26 com

  takes a core 28, preferably formed of steel, and two permanent magnets 30 and 32, preferably made of a material containing

  a rare earth such as cobalt-samarium. Each of the permanent magnets

  30 and 32 has a common pole such that its north pole N

  ti fixedly to an end face of the steel core 28 so that the south poles S of the magnets define the opposite ends of

the frame 26.

  A pair of outlet bars 34 and 36, consisting of

  in Delrin, are fixed in the opposite extremes

  26. The outlet bar 34 comprises a cylindrical arm

  and an end portion 40 having a diameter greater than that of the arm 38. The outlet bar 36 comprises a similar arm and a head portion 42 and 44 respectively. The arm 38 is designed to pass through an opening 46 of an end cap 48 while the arm 42 is designed to pass through an opening

  in an end cap 52. Each of these end caps

  Mite 48 and 52 is preferably formed of a thermoplastic material

such as Delrin.

  Two field windings 54 and 56 are mounted side-by-side on the coil 12 so that the field winding 54 is placed between the cheeks 14 and 16 and the field winding 56 is placed between the cheeks 16 and 18. Each of the windings 54 and 56 is provided with an electrical cable 58 and 60 respectively for a connection of its associated field winding with a direct current source. Each of the cables includes a pair of wires to close a circuit to

through the winding.

  Two washers 62 and 64, preferably formed of a material

  magnetically permeable material such as mild steel, are provided to automatically move the armature 26 from the position shown in Figure 2 to the position shown in Figure 1 during the de-excitation of the field winding 54. The washer 62 is mounted

  on the end portion 20 so as to encompass and be aligned with

  with the left effective south pole of the frame 26 and is secured thereto by the end cap 48. The washer 64 is similarly mounted on the end portion 22 so as to encompass and align with the effective south pole right armature and

  is fixed on it by the end cap 52.

  As mentioned above, the north poles of the magnets 30 and 32 are fixedly attached to the axial end faces 66 and 68 of the steel core 28 to provide a zone of maximum magnetic flux density that extends radially to the outside of the central portion of the steel core 28, which creates an armature which in fact has three poles, that is to say two south poles designated by S in the drawing and a single north pole represented by the This is graphically represented in FIG. 6 by the curve 72 which represents the density of the radial flux of the armature 26, measured along its axis. Note that the maximum flux density is in alignment with the effective north pole 70 while the flux density of the magnets 30 and 32 is reversed at an equidistant point

  south and north poles of each magnet.

  In an example of a linear motor constructed according to

  In this invention, each of the magnets 30 and 32 has a length and a diameter of 3.175 mm, the steel core has a length of 1.905 mm and a diameter of 3.175 mm, the passage 24 has a diameter of 3.2512 mm and a diameter of 3.175 mm. length of 12.192 mm and the coil 12 has a maximum diameter of 9.525 mm and a minimum diameter of 3.5052 mm at the location where the field windings 54 and 56 are wound around the coil 12. This combination provides a maximum of about 800 Gauss at the north effective pole of armature 26, as represented by -7-

the line in broken lines 70.

  In its de-energized state, the armature 26 of the linear motor 10 assumes the position shown in FIG. 1. The armature 26 is

  moved from the position shown in Figure 1, hereinafter referred to

  Fig. 2 shows the first position, to a second position, shown in Fig. 2, by connecting the field winding 54 to a DC power source. Thus the armature moves through a distance Y before its left effective south pole comes into contact with the

  inner surface of the end cap 48. In the example of

  described above, this distance Y is equal to approxi-

  1.2065 mm. Thus positioned, the effective south pole on the left side of the frame 26 is still placed closer to the steel washer 62 than the north pole N of the magnet 30. This is always true because the distance Y is smaller at the half of X, where X is the distance between the adjacent poles of the magnet 30. Therefore,

  when the current to the field winding 54 ends, the attrac-

  The upper magnetic bearing between the effective south pole on the left side of the frame 26 and its associated steel washer 62 provides a force to return the frame 26 to its first position. This

  strength is increased by the magnetic attraction that exists between the

  to be the effective south pole of frame 26 and its associated steel washer

  64. In the example of engine shown above, each washer pos-

  preferably an outer diameter of 9.525 mm, an internal diameter

  born of 5.08 mm and a thickness of 0.254 mm. The magnetic attraction between each washer and its associated effective pole can be increased or decreased by decreasing or increasing, respectively, the diameter

the hole in each washer.

  The armature 26 can be moved to the right, that is,

  say to a third position, by connecting the field winding 56 to a DC power source. Thus excited, the head portion 44 of the outlet bar 36 moves in contact with the inner surface of the end cap 52 after having traveled a distance

  Y. As soon as the field winding 56 is de-energized, the magnetic force

  that greater that exists between the effective south pole of the frame 26 and its associated washer 64, compared to that which exists between the effective north pole N of the magnet 32 and the washer 64, moves the frame

  25 again in his original position or first position.

  Reference is now made to FIGS. 3 and 4 of the drawing, in which another embodiment of an engine has been shown.

linear, 10 '.

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  The linear motor 10 'is substantially identical to the motor

  shown in Figures 1 and 2, with a major difference

  that is to say that the two steel washers 62 and 64 have been replaced by a single steel washer 74, which is located on the coil 12 'in the position previously occupied by the cheek 16. The operation of the linear motor 10 'is substantially identical to that of the motor 10 except that in this embodiment it is the larger magnetic force exerted between the effective north pole and the single steel washer 74 which displaces the motor. armature 26 either of the second or of the third positions again in the first position. For example, the excitation of the field winding 54 by a direct current has the effect of moving the armature 26 to the left by a distance Y, in the second position in which the effective south pole on the left of the armature 26 is in contact with the inner surface of the end cap 48, as shown in FIG. 4. However, the effective north pole 70 is still placed closer to the steel washer 74 than either effective south poles of the armature because Y is less than one half of X 'where X' is the distance between two effective poles. Therefore, when the field winding 54 is de-energized, the greater magnetic attraction between the effective north pole 70 and the washer 74 provides the force necessary to send the armature 26 to its central or first position. The excitation of the field winding 56 has for

  effect of moving the armature 26 to the right in its third position.

tion.

  Referring now to Figure 5 of the drawing in which there is shown yet another variant of a linear motor 100, the

  motor being represented in a first position or position

  cited. The motor 100 comprises a cylindrical coil 102 having a pair of annular cheeks 104 and 106 between which is wound a field winding 108. A cylindrical end portion 110 extending on one side of the cheek 104 is provided with an opening 112 which forms a continuation of a passage 114 of cylindrical shape. A washer 116, made of a magnetically

  permeable such as mild steel, is mounted on the part of ex-

  tremity 110 and retained in place on it by an end cap

  118. The end cap 118 has an opening 120 for

  putting the passage of a portion of the cylindrical shaft portion 122 of an output arm 124. The output arm 124 comprises a head 126 having a diameter greater than that of the opening 120 and -9-

  slightly smaller than that of the opening 112 and the passage 114.

  The open end of the passage 114 is closed by a plate 128 pos-

  seducing a recessed portion 130. The recessed portion 130 is sufficiently

  spaced apart from the armature end of the motor to

  tact between them when the latter is returned to the position shown in Figure 5, hereinafter called the first position. The coil 102, the end cap 118, the plate 128 and the arm of

  output 124 are preferably made of Delrin.

  A cylindrical frame 132 is slidably received

  within the opening 112 and the passage 114. The armature - 132 consists of a permanent magnet, preferably formed of cobaltsamarium, having its north-effective pole (N) and its effective south pole (S ) aligned axially with the passage 114. The effective south pole S of the armature is fixedly secured by any suitable means to the head 126 of the output arm 124. When the armature 132 is in its initial position or first position as shown in the figure, the steel washer 116 is placed so as to surround and align with

  with the effective south pole S of frame 132.

  The field winding 108 is energized by connecting an electrical cable 134 to a DC power source. Thus excited a magnetic field is produced to provide a force driving the armature 132 to the left (according to Figure 5) over a distance Y (which is less than half of X) at which it is stopped in its second

  position by the inner surface of the end cap 118. When

  that the armature 132 is placed in its second position, the effective south pole S is still placed closer to the steel washer 116 than

  is the North Pole effective N, thus having a magnetic attraction

  When the field winding 108 is de-energized, this larger magnetic attraction between the effective south pole S and the washer 116 provides the force that automatically returns the armature 132 to its first position. The recessed portion 130 of the plate 128 allows the armature to momentarily exceed its first position without causing any potential damage to the armature 132. Although the armature 132 has been shown with its

  effective south pole in alignment with puck 116, one must understand

  that the poles could be reversed, as in all

double magnet motor cases.

  Because some changes can be made to the

  above without departing from the framework and spirit of the invention.

  tion, it is understood that the above description of a mode of

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  embodiment and its variants is given by way of example in no way limiting. For example, the two field windings, of the embodiments shown in FIGS. 1 to 4, could be replaced by a single field winding and the movement of the armature from the first position to the second position could take place, in response to the flow of DC current through the field winding, in one direction while reversing the DC flow could move the armature of the

  first position in the third position.

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Claims (16)

  Linear motor characterized in that it comprises means for supporting electrically conductive means, said support means comprising means defining a passage extending axially to said support means, an armature mounted inside said passage for an axial movement relative to said support means between a first and a second position, said frame comprising a permanent magnet whose poles are oriented along said passage, electrically conductive means wound on said support means, for moving said frame of said   first position to said second position when they are electrically   triply excited, means mounted on one end of said   armature for transmitting the movement of said armature to a disc   positive driven by them, means for limiting the movement of said armature along said passage during the excitation of said electrically conductive means, and means made of a ferrous material mounted on said support means substantially in alignment with one of effective poles of said armature, when   said armature is in its said first position for automatic-   return said armature to said first position during the   de-energizing said electrically conductive means.   2. Linear motor according to claim 1, characterized in that said means formed of a ferrous material comprise a disk having an opening through which a portion of   said frame is designed to pass.   Linear motor according to claim 2, characterized by   the fact that the distance crossed by said armature in its movement   from said first position to said second position is less than   than half the distance between the effective opposite poles of said armature.   4. Linear motor according to claim 3, characterized in that said support means and said limiting means   are formed of a non-magnetic material.   Linear motor according to claim 3, characterized by   the fact that said armature further comprises a second permanent magnet;   and a core, said core being placed between said first permanent magnet and said second permanent magnet, the common poles of said magnets being in contact, the opposite axial end faces of said core thereby forming a frame having effective common poles at its ends. axial and an effective pole of opposite polarity placed 2458934   at a point approximately half the distance between ends of said core.   6. linear motor according to claim 5, characterized in that it further comprises second output means mounted on one end of said armature opposite to that to which-   said first output means are mounted to transmit the movement   said frame to a device to be driven.   7. linear motor according to claim 6, characterized in that said electrically conductive means are excitable so as to move said armature from said first position to a third position, said third position being in a direction   substantially opposite to that taken by said armature in its movement   from said first position to said second position.   8. linear motor according to claim 7, characterized in that said first effective pole of said frame is a pole   located substantially midway between the opposite ends   of said core and that said disk is in alignment with said first effective pole when said armature is in said first position.   Linear motor according to claim 8, characterized in that said electrically conductive means comprise first and second field windings, said first field winding being capable of being excited to move said armature from said first position to said second position and said second field winding being able to be excited to move   said armature from said first position to said third position   tion. 10. linear motor according to claim 5, characterized in that said permanent magnets are made from   of a material containing a rare earth.   i1. Linear motor according to claim 2, characterized in that the distance crossed by said armature in its   moving from said first position to said second position   is less than half the length between the magnet poles. 35 ticks of said permanent magnet.   Linear motor according to Claim 11, characterized   in that said support means and said limiting means   are formed from a non-magnetic material.   13. Linear motor according to claim 11, characterized in that said frame further comprises a second permanent magnet and a core, said core being placed between said first permanent magnet and said second permanent magnet, the common poles of said magnets. being in contact with the opposite axial end faces of said core thereby forming an armature having effective common poles at its axial ends and an effective pole of   opposite polarity placed at a point substantially equal to half of the   between the ends of said core.   14. linear motor according to claim 13, characterized in that it further comprises second output means mounted on one end of said armature opposite that to which said first output means are mounted, to transmit the   movement of said armature to a device to thereby lead.   Linear motor according to Claim 14, characterized   in that said electrically conductive means is capable of   may be excited to move said armature of said   first position to a third position, said third position   being in a direction substantially opposite to that taken by said armature in its movement from said first position to said second position.   Linear motor according to claim 15, characterized   in that it further comprises a second disk provided with an opening   formed from a ferrous material, through which a portion of said armature is adapted to pass as said armature moves between said first and said third positions, said disks being mounted on said support structure in relation thereto   transverse to said armature and substantially aligned with   with and surrounding opposite ends of said armature   when said armature is in its said first position for self-   to move said armature from said third position to said first position upon de-excitation of said means electrically conductive.   17. Linear motor according to claim 16, characterized in that said electrically conductive means comprise   first and second field windings, said first winding   field member being energizable to move said armature from said first position to said second position and said second field winding being energizable to move said armature from said first position to said third position. -14- 2458934   18. Linear motor according to claim 13, characterized in that said permanent magnets are formed from a material containing a rare earth. Mr NONY