Linear Actuator

Abstract

A linear actuator of the solenoid type comprising a primary coil adapted to be powered by an A.C. electrical source, a cylindrical magnetic shield surrounding the exterior of the coil, a magnetic central core member extending through the interior of the coil, an end disc disposed at one end of the cylindrical shield and an armature including a central opening to receive the core member spring biased to form an air gap which when closed completes a magnetic circuit including the core member, the shield and the end disc. Disposed within the interior of the shield is a secondary coil, induced by the change in the magnetic flux generated by the primary coil during each electrical cycle, shielded from the primary coil by a saturating or shading disc. Thus as the primary coil is energized the armature is pulled in closing the magnetic circuit and drawing the centrally located core member towards any side of the central opening thereof to advance the core member along with the armature. When the signal in the primary coil decays the secondary coil is induced to magnetically latch the core member thereto while the armature is released to advance along the core member.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to solenoid actuators, and more particularly to A.C. powered solenoid actuators for producing linear motion.

2. Description of the Prior Art:

In many control applications, and particularly in applications were remote actuation of large valves is required, the electrical power requirements of a solenoid activating such large valves is often prohibitive and many A.C. solenoids have been developed in the past which integrate a plurality of cycles in order to produce a linear motion of a particular amplitude. This integrating effect by which an alternating electrical current is converted or rectified to a linear motion reduces the current load at any one time through the solenoid coil thus allowing a small current load to activate large linear motions. A further requirement of such actuators is that they be adaptable to any desired actuation rate in order to complement various control systems and that they be linear in response. Accordingly various schemes such as an introduction of dither and the like, have been introduced in the past to reduce the mechanical nonlinearities of solenoids. Heretofore all such linear actuators operated on the mechanical ratchet principle such that repetitive mechanical contact was experienced during the actuation cycle and continual maintenance was required to replace worn out mechanical parts. Furthermore mechanical contacts generally exhibit nonlinear responses, such as the transition from static to coulomb friction. Thus the presence of mechanical structure in the solenoid typically presented unfavorable characteristics of response requiring extensive corrective efforts.

SUMMARY OF THE INVENTION

Accordingly it is the general purpose and object of the present invention to provide a linear A.C. actuator which electro-magnetically latches along its pull-in cycle to produce an integrated pull-in motion at a predetermined rate. Other objects of the invention are to alternately couple a primary and a secondary magnetic circuit to the core member of the solenoid where the primary magnetic circuit advances the core while the secondary magnetic circuit induced by the primary magnetic circuit provides forces holding the core in any position while the primary magnetic circuit is decaying.

Briefly these and other objects are accomplished within the present invention by a spring loaded armature spring biased to present an air gap in a magnetic circuit around a primary coil. When the primary coil is energized the armature is pulled in to close the air gap thus increasing the permeance of the magnetic circuit. Extending through the interior of the magnetic coil and through the center of the armature is a central core member which forms the actuating structure of the solenoid completing the magnetic circuit around the primary coil. In the first embodiment the central core member, of the actuator, of the solenoid is substantially longer than the longitudinal dimension of the primary coil, extending from the coil at both ends. Thus when the primary coil is energized only relatively weak centering forces are generated on the core member. In this manner the core member is latched to the armature during its pull-in motion when the primary coil is energized. Accordingly the motion of the central core member is directly tied to the motion of the armature when the armature is pulled in by the magnetic field of the primary coil. In order to preclude oscillation of the central core along with the oscillations of the armature a secondary magnetic circuit is provided comprising a secondary coil, disposed in concentric relationship around the central core member, which is induced by the decay of the primary magnetic circuit. Accordingly as the primary magnetic circuit decays a current is induced into the secondary coil forming a secondary magnetic circuit which fixes the location of the central core while the primary magnetic circuit has decayed. The inductive phase relationship between the primary magentic circuit and the secondary magnetic circuit rectifies the motion of the central core member thus producing linear actuation which is an integral of the number of electrical alternations passed through the primary coil. The respective ends of the central core are further provided with end stops which on one end depress the armature against the adjacent structure of the magnetic circuit when the linear motion is completed, thus closing the magnetic circuit to provide a substantially large permeance. This particular feature reduces the holding current requirements when the actuator is at its extreme position. When the core is in its extreme position the armature is maintained in its closed position through the A.C. voltage fluctuations by virtue of the out of phase holding action of the secondary magnetic circuit.

In a second embodiment the central core member is conformed to telescope into the armature on the interior of the primary coil. The armature is spring biased by a cup spring to form an air gap between the distal end thereof and the end plate of the housing forming the primary magentic circuit around the primary coil. Thus as the primary coil is energized the core and the armature are drawn together and move as a unit as the armature is pulled in to close the air gap. The tractive forces acting on the core assist the pull in. Similar to the first embodiment of a secondary coil provides a latching magnetic circuit during the decay of the primary magnetic circuit thus providing the rectification in the primary circuit necessary to advance the core member into the coil. In order to provide a higher reactance magnetic circuit during the fully advanced state of the core member a projection is formed concentric therewith which extends beyond the armature to close the magnetic circuit when fully abutting against the end plate within the interior of the primary coil. This closure of the magnetic circuit establishes a substantial inductive reactance on the primary coil thus reducing the current draw when fully advanced.

Other objects and features of the invention will become apparent from consideration of the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment of a linear actuator constructed according to the present invention;

FIG. 2 is a cross-sectional view of the linear actuator shown in FIG. 1 advanced to an intermediate position;

FIG. 3 is yet another partial cross-sectional view of the linear actuator shown in FIG. 1 as fully advanced to the extreme end of its travel;

FIG. 4 is a cross-sectional view of yet another embodiment of a linear actuator constructed according to the present invention;

FIG. 5 is a cross-sectional view of a linear actuator shown in FIG. 4 advanced to an intermediate position; and

FIG. 6 is a cross-sectional view of a linear actuator shown in FIG. 4 advanced to the extreme of its travel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1, 2 and 3, a linear actuator generally designated as 10 comprises a primary coil 11 adapted to be energized by any convenient A.C. power source and formed to describe an annular structure including a central cavity 12 having received therein a cylindrical central core member 15 forming the core of the solenoid.

The core member 15 is dimensionally substantially longer than the longitudinal dimension of the coil 11 extending at both ends thereof from the central cavity defined by the coil. Disposed around one protruding end of member 15 is a floating armature 20 generally shaped in the form of a disc extending from an outwardly protruding neck 19 including a central bore conformed to the outer dimensions of member 15. Armature 20 is retained in position by nonmagnetic retainers 21 extending from the outer peripherial surface of an external ferrous cylindrical shield 22 disposed in surrounding relationship around coil 11, being urged by an armature spring 23 compressed between the armature 20 and the adjacent end of the coil 11 away from the end of shield 22, thereby forming an air gap for providing an alterable permeance interval between the armature 20 and shield 22 when the coil is energized. At the opposite end shield 22 abuts a circular end plate 24 including a central opening 25 also conformed to receive the core member 15, being affixed to said shield in concentric alignment therewith.

In this manner a toroidal magnetic circuit is formed enclosing coil 11 where the central core member 15 forms the center of the toroid and where the magnetic loop is closed by the armature 20, the cylindrical shield 22 and the disc 24. When coil 11 is energized, i.e., when the current passed through coil 11 is high during the A.C. cycle, the magnetic field conducted through these elements develops attractive forces between the armature 20 and the end of shield 22 urging the armature towards the shield 22 to close the air gap therebetween. Concurrently the attractive magnetic forces draw the central core against the inner wall of the protruding neck 19 of the armature where static friction maintains the core and armature fixed in mutual position as the armature 20 is drawn towards the shield 22 to close the air gap therebetween. It is contemplated that the centering strength of the magnetic circuit on the central core member 15 is effectively low compared to the latching strength of the static friction against the adjacent inner surface of the neck 19 of armature 20, thereby effectively latching the central core to the action of the armature such that the central core moves along with the armature. Disposed intermediate between the disc 24 and the adjacent end of coil 11 is a secondary coil 30 shielded from coil 11 by a shielding disc 31 which is dimensionally sized to saturate when coil 11 is energized. Thus the secondary coil 30 is induced at a phase lag of 90 degrees behind the induced magnetic field generated by coil 11, thereby generating a secondary magnetic field through disc 24, shield 22, disc 31 and the adjacent part of the central core member 15 which is at its peak when coil 11 is de-energized or is decaying. This secondary magnetic circuit latches core 15 in its advanced position, similar to the latching of the armature, when the primary magnetic circuit is decaying, i.e., when the armature is released, thereby allowing armature 20 to advance on core 15 while core 15 is maintained in position. In this manner two alternative magnetic circuits are formed which alternately latch the core to the armature and to the secondary coil 30 thereby advancing the core along with the armature during the energization of the primary magnetic circuit and latching the core to the secondary magnetic circuit when the primary magnetic circuit is de-energized. It is to be noted that due to the phase relationship between the primary and the secondary magnetic circuit the strongest field developed by the secondary magnetic circuit occurs when the primary magnetic circuit is essentially open-looped by the air gap developed between armature 20 and shield 22. Thus a rectification effect takes place whereby a core of substantially longer dimensions than the solenoid coil is advanced through the solenoid coil according to the number of cycles imposed across the primary and secondary magnetic circuit. At the extreme ends of travel the core is engaged by stops including a circular disc 35 proximate the advanced end thereof and a plastic, deformable O-ring 36 at the collapsed end. Accordingly as the core is advanced to a point where disc 35 closes the magnetic circuit between the armature 20 and core member 15 driving the armature against the end of shield 22 to form a magnetic circuit of high permeance.

In operation core 15 is advanced by the alternating latching cycles of the central core with armature 20 and with the secondary magnetic circuit formed by disc 24, shield 22 and shading disc 31. The core is wholly unencumbered between the end stops and is therefore advanced by the free floating armature during the energized state of the primary circuit. As the electrical signal in the primary coil 11 decays the shaded secondary magnetic circuit latches to the core, holding it in place while the floating armature is returned to its original position by the spring 23. During this return of armature period the primary magnetic circuit is at a low flux density and therefore generates lower latching forces than the latching forces generated by the secondary magnetic circuit. Thus on the return cycle of the armature the core is latched in the advanced position relative the secondary magnetic circuit, producing an effective rectification of the linear motion of the core. At the extremely advanced position or as shown in FIG. 3, the armature is held in its closed position both during the energized and the decayed states of the primary circuit, where the direct metal to metal contact of the various elements forms a magnetic circuit of relatively high permeance thus generating a high inductive reactance in the primary coil to reduce the holding power requirements. Upon de-energization of the primary coil magnetic unlatching allows for an unrestricted return of the core member to its initial or unloaded position.

As shown in FIGS. 4, 5 and 6, a second embodiment of the present invention generally designated by the numeral 50 includes a central core 55 concentrically telescoped into a movable tubular armature 60 within the interior of a primary coil 61. A casing 62 encloses the primary coil 61 having disposed therein a secondary or shading coil 65 in surrounding relationship with core 55 and intermediate the extreme end of casing 62 and the adjacent end of coil 61. Armature 60 is urged inwardly into the central cavity formed by coil 61 by a cup spring 70 abutting against a disc 71 affixed to casing 62 in substantially opposing relationship with the exposed end of core 55. Cup spring 70 further includes a central opening 72 conformed to receive a reduced extension 56 on the adjacent end of core 55 to provide direct contact between core 55 and the end disc 71 at the extremely advanced end of travel of core 55. Disc 71 further includes a threadable end stop 75 through which adjustment can be made on the extremes of the motion of armature 60. On the opposite end casing 62 further includes a nonferrous sleeve 77 concentrically receiving core 55 being conformed to mate with the core for providing an abutting structure for the core member when the secondary coil 65 is energized thus, similar to the first embodiment, latching the core during the decay of the magnetic circuit developed by the primary coil 61. Similar to the first embodiment the secondary coil or the shading coil 65 has a saturating disc interclosed between the adjacent end of coil 61 and coil 65 to provide for the local magnetic path necessary to generate a local flux in the magnetic circuit around the secondary coil 65. On the exterior of casing 62 a return spring 80 is compressed between a spring retainer 81 engaged at the free end thereof to core 55, such that upon de-energization of the primary coil the core is extracted from the interior of coil 61.

The operation of this embodiment is substantially similar to the operation of the first embodiment where the magnetic field generated by the primary coil urges the armature to abut against the end stop 75 thereby reducing the air gap formed therebetween, carrying along with this motion the central core 55. Upon decay of the primary magnetic circuit the secondary magnetic circuit induced through coil 65 is energized, substantially out of phase with the primary coil, to latch the core in position when the primary magnetic circuit is de-energized. When fully advanced to a closed position the extension 56 of core 55 protrudes through the opening in the cup spring 70 to make direct contact with the face of the end stop 75, thereby providing a direct contact reducing all air gaps in the magnetic circuit formed by casing 62, disc 71 and core 55. In this manner a closed circuit of substantially high permeance is formed in the fully advanced position thereby generating large inductive reactance in the primary coil and reducing the primary coil power requirements in the fully advanced position. At this time the out of phase secondary magnetic circuit mitigates the force fluctuations, due to the cyclic character of A.C. energization, to provide quiet holding against an external load including the return spring 80.

Some of the many advantages of the present invention should now be readily apparent. The invention utilizes a secondary or shading magnetic circuit which is induced by the action of the primary coil and which forms a peak flux during the decay period of the primary coil thereby providing for a latching action when the primary coil is decaying. In this manner no mechanical accessories are necessary to rectify the alternating motion of the core thereby reducing the mechanical wear usually attendant with actuators of this kind.

Obviously many modifications and variations are possible in the light of the above teachings. It is therefore intended that the scope of the invention be determined by the appended claims.

Claims

The embodiments of the invention in which an exclusive property or

1. Apparatus for producing linear motion of an amplitude proportional to the number of cycles of an electrical A.C. signal supplied thereto, comprising:

a primary coil adapted to receive an electrical A.C. signal for developing a primary magnetic flux according to the current level thereof;

a secondary coil disposed in inductive proximity with one end of said primary coil for developing a secondary magnetic flux when said primary magnetic flux is changing;

magnetic armature means disposed proximate the other end of said primary coil, including spring means for urging thereof to a predetermined position relative said primary coil, for being displaced from said predetermined position concurrent with the production of said primary magnetic flux; and

a magnetic core means disposed in magnetic proximity with said armature means, said primary coil and said secondary coil to be drawn towards the adjacent surface of said armature and along with said armature during the development of said primary magnetic flux and to be drawn towards the adjacent surface of said secondary coil during the development of said

2. Apparatus according to claim 1, further comprising:

magnetic circuit means disposed to contact at one end thereof the distal surface of said armature means when said armature means is drawn towards said primary coil, and terminating at the other end thereof proximate said core means and said secondary coil, said magnetic circuit means being conformed around said primary and secondary coils, for concentrating said

3. Apparatus according to claim 2, wherein:

said primary coil, secondary coil and armature means including central opengins in concentric alignment; and

said core means including a magnetic cylindrical structure conformed to be

4. Apparatus according to claim 3, further comprising:

retainer means disposed from said magnetic circuit means for selective limiting of the separation of said armature means from said primary coil

5. Apparatus according to claim 4, further comprising:

end stop means connected to said core means for providing abutting magnetic structure between said core means and said armature means when said core

6. Apparatus according to claim 4, further comprising:

end stop means formed on said core means for abutting said magnetic circuit

7. Apparatus for producing linear motion corresponding to the number of cycles of received electrical A.C. signal, comprising:

a primary electrical coil conformed to describe an annular structure and adapted to receive an electrical A.C. signal;

a cylindrical magnetic central core member conformed to be received in the central opening of said primary coil;

a floating magnetic armature disposed at one end of said primary coil including a central opening conformed to receive said core member disposed concentric with said primary coil proximate one end thereof;

a cylindrical magnetic shield formed to receive said primary coil and said central core member;

spring means disposed between said armature and said primary coil for urging said armature away from said primary coil; and

a secondary elecrical coil disposed in inductive proximity with said primary coil and conformed to describe an annular structure receiving said

8. Apparatus for producing linear motion of an amplitude proportional to the number of cycles of an electrical A.C. signal supplied thereto, comprising:

a primary coil adapted to receive the electrical A.C. signal for producing a magnetic flux according to the current level thereof including a first central opening;

a magnetic shield disposed on the exterior of said primary coil;

a secondary coil disposed within said shield for magnetic induction at one end of said primary coil including a second central opening concentric with said first central opening;

a magnetic central core member disposed to extend into said first and second central opening of said primary and secondary coil;

magnetic structure means disposed between said shield and said core member including saturating means disposed intermediate said primary coil and said secondary coil for forming a magnetic circuit thereacross;

a movable armature disposed at the other end of said primary coil including a third central opening conformed to receive said central core member and extending at the periphery thereof to contact said shield; and

spring means operatively connected between said armature and said shield

9. Apparatus according to claim 8, further comprising:

a nonmagnetic spacer interposed between said armature and the exposed surface of said magnetic structure means.