WO1999049479A2

WO1999049479A2 - Solenoid plunger having attenuated external magnetic flux

Info

Publication number: WO1999049479A2
Application number: PCT/US1999/005640
Authority: WO
Inventors: Ryan S. Porter; Jeffrey M. Brooke; William R. Blessing
Original assignee: Plasmon Lms, Inc.
Priority date: 1998-03-20
Filing date: 1999-03-17
Publication date: 1999-09-30
Also published as: WO1999049479A3

Abstract

A plunger assembly includes a plunger disposed in a coil for movement relative to the coil when the coil is energized, and a non-magnetic end portion coupled to the plunger, the end portion disposed externally to the coil for reducing external magnetic flux generated by the coil when energized.

Description

SOLENOID PLUNGER HAVING ATTENUATED EXTERNAL MAGNETIC FLUX BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to solenoid plungers and, more particularly, to a solenoid plunger with a non-magnetic clevis for attenuating magnetic flux.

2. Description of the Related Art Solenoids are generally used to mechanically actuate a plunger by inducing a magnetic field. Typically, a plunger is comprised of a magnetic material, 10 such as a bar or rod. The plunger is surrounded by a coil having a plurality of turns about the plunger. When the coil is energized, current flows through the coil and the plunger is magnetized. A mutual action of the field in the solenoid on the magnetic poles created on the plunger causes the plunger to move within the solenoid. This force becomes zero only when the magnetic centers of the plunger and the solenoid coincide. If a load is applied to the plunger, work will be done until the force to be overcome is equal to the force that the solenoid exerts on the plunger.

Referring to FIG. 1, a conventional solenoid and plunger assembly 10 is shown. A solenoid body 12 includes a coil 14 which is an insulated electrical conductor wrapped in a plurality of turns about an interior portion 16 of solenoid body. A plunger 18 is dimensioned and configured to fit within interior portion 16 of solenoid body 12. When coil 14 is energized, plunger is magnetized. Since a portion of plunger 18 extends beyond coil 14, strong magnetic flux lines 20 are produced and a magnetic field is created that extends outward from assembly 10.

When solenoids are used around devices that are sensitive to magnetic flux, additional hardware is often used in the form of magnetic shielding, either to contain or reroute the flux generated by the solenoid or in the form of a shield for the sensitive device to shield the device from the ambient flux field created by the energized solenoid. Another way to reduce magnetic flux is to increase the distance between the source of the magnetic field and the sensitive device.

Mumetal is a metal often used to implement the above mentioned shielding. Mumetal is more expensive than most sheet metal fabrication materials. Mumetal is a magnetic material with a high permeability (the ability to carry magnetic flux) and very little tendency to retain a magnetic field when de-energized. That is the mumetal will not become magnetic when exposed to strong magnetic fields.

Therefore, a need exists for a solenoid and plunger assembly that provides reduced external magnetic flux. A further need exists for a solenoid and plunger assembly that does not require magnetic flux shielding or require a distance be maintained between the assembly and a magnetically sensitive device.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a plunger assembly includes a plunger for being positioned in a coil. The plunger moves relative to the coil when the coil is energized, and a non-magnetic end portion is coupled to the plunger and is disposed externally to the coil and for reducing external magnetic flux generated by the coil when energized.

In alternate embodiments of the plunger assembly, the non-magnetic end portion may be aluminum, brass, plastic or any other rigid material without magnetic properties. The non- magnetic end portion may be stainless steel, and the non-magnetic end portion may include attachment means for mechanically coupling to a device to be actuated. The non-magnetic end portion may further include a clevis. The non-magnetic end portion may engage the magnetic plunger through any mechanical means that does not remove significant magnetic material from the plunger body. Exemplary coupling means include threading, press fitting, bonding, welding and pinning.

Another illustrative embodiment includes an assembly for actuating a plunger with a magnetic field. A magnetic element for producing magnetic flux for actuating the plunger is included. The magnetic element is housed in a solenoid body wherein the plunger is disposed within the magnetic element and when the magnetic element produces magnetic flux, the plunger moves relative to the magnetic element. A non-magnetic end portion is coupled to the plunger and disposed externally to the magnetic element for reducing external magnetic flux emanating from the magnetic element, the non-magnetic end portion attaches to a member for causing movement of the member.

In alternate embodiments of the assembly, the non-magnetic end portion may be aluminum, stainless steel any structural non-magnetic material. The non-magnetic end portion may also include a clevis for mechanically coupling to the member. The solenoid body may be tubular. The non-magnetic end portion may threadedly engage the plunger. The magnetic element may be a coil.

Another illustrative embodiment of the present invention includes an assembly for use with magnetic media having attenuated magnetic flux. A magnetically sensitive device for recording and retrieving magnetic data is included with at least one solenoid assembly proximally located relative to the magnetically sensitive device. The at least one solenoid assembly includes: a solenoid body housing a coil therein; a plunger disposed within the coil and being actuated by the coil when energized; the plunger extending within the coil and a non-magnetic end portion coupled to the plunger; the end portion positioned externally to the coil for reducing external magnetic flux generated by the coil when energized; and for providing attachment to a mechanically actuated member of the magnetically sensitive device.

The non-magnetic end portion is preferably aluminum or stainless steel. The nonmagnetic end portion may include a clevis and engages the plunger. The assembly may include a video recorder and the magnetically sensitive device may be a head assembly.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS The invention will be described in detail in the following description of preferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a prior art solenoid showing magnetic flux lines; FIG. 2 is a perspective view of a plunger assembly in accordance with the present invention; FIG. 3 is a perspective view of the plunger assembly of FIG. 2 in accordance with the present invention with parts separated;

FIG. 4 is a cross-sectional view of a solenoid assembly in accordance with the present invention showing magnetic flux lines;

FIG. 5 is an isometric view of a magnetic storage device having solenoid assemblies in accordance with the present invention;

FIG. 6 is an isometric view of a solenoid assembly having a plunger assembly in accordance with the present invention; and FIG. 7 is an isometric view with parts separated of the solenoid assembly in accordance with the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to solenoid plungers and, more particularly, to a solenoid plunger with a non-magnetic clevis for attenuating external magnetic flux. Rather than control a geometry of a flux field generated by a solenoid assembly through the use of shields and magnetic flux shunts, etc., the present invention locally reduces a strength of and the external flux field generated by the solenoid assembly without compromising the performance of the solenoid assembly. The solenoid assembly works by generating a magnetic field within a coil which then magnetically attracts (or repels, if permanent magnets are present in the design) a pole piece or plunger made of ferrous material into (or out to) the geometric confines of a coil within a solenoid body. A toroidal-shaped flux field normally emanates from an exposed portion of the plunger and returns through an opposite end of the solenoid body. However, for the solenoid assembly to function as designed, it is only necessary for the material of the plunger contained within the coil when fully inserted within the solenoid body to have magnetic properties. Any portion of the plunger external to the coil is outside the range of coil influence and is usually only needed to attach the plunger to a device or devices to be driven by the solenoid assembly and therefore can have non-magnetic properties. The present invention employs non-magnetic materials for portions of the plunger outside of the range of coil influence. In this way, reduced external magnetic flux is realized. This aspect of the present invention is particularly useful for devices where reduced magnetic fields are desired, for example in magnetic storage devices.

Referring now to the drawings in which like numerals represent the same or similar components throughout the many views and initially to FIGS. 2 and 3, a perspective view of a plunger assembly 100 is shown in accordance with the present invention. Plunger assembly 100 includes a plunger portion 102 and a clevis portion 104. Plunger portion 102 is comprised of a ferro-magnetic material, for example iron or carbon steel. In preferred embodiments, plunger portion is made from cold drawn steel and in particularly preferred embodiments 12L14 cold drawn steel which may contain lead to provide improved machinability of the material. To reduce corrosion plunger portion may be provided with a coating or plating, for example nickel plating which may be provided electrolessly onto plunger portion 102. Plunger portion 102 has a first end portion 106 having a tapered or conical end 108. Conical end 108 may be tapered at varying taper angles to provide different stroke lengths and forces dependent on the application. For example, a flat end (no taper) on plunger portion 102 provides a short stroke and high force while a taper angle of 600 provides a larger stroke and a lower force.

Plunger portion 102 has a second end portion 110 adapted to receive clevis portion 104. In a preferred embodiment, second end portion 110 forms a threaded hole 112 which is configured and dimensioned to threadedly receive a threaded end portion 114 (FIG. 3) of clevis 104. Threaded hole 112 and threaded end portion 114 may be further secured using an adhesive compound, such as a commercially available thread locking compound. Other methods of attaching clevis 104 to plunger portion 102 are contemplated, for example, pins, snaps, clasps, welding, press fitting, bonding and the like.

Clevis 104 provides a connection point between plunger portion 102 and equipment or devices to be mechanically actuated by plunger portion 102 during use. Clevis 104 includes a non-magnetic material in accordance with the present invention. This nonmagnetic material may be, for example aluminum, preferably aluminum 6061 or stainless steel, preferably 303 stainless steel. Clevis 104 may include any structural material without magnetic properties, for example, brass, plastic, etc.

Clevis 104 is configured to mechanically couple to a linkage or member (not shown in FIGS. 2 and 3). In one embodiment, clevis 104 forms a slot 116 having an open end 118 for receiving the linkage therein. Clevis 104 further includes a hole 120 therethrough such that a pin (not shown) may connect clevis 104 to the linkage. Clevis 104 may be replaced with devices that support other attachment configurations. For example, clevis 104 may be replaced by a link, a pusher, a joint, etc. Referring to FIG. 4, a solenoid assembly 200 is shown in accordance with the present invention. A solenoid body 202 includes a coil 204 which is an insulated electrical conductor wrapped in a plurality of turns about an interior portion 206 of solenoid body 202. Plunger assembly 100 is dimensioned and configured to fit within interior portion 206 of solenoid body 202. When coil 204 is energized, plunger portion 102 is magnetized. Solenoid assembly 200 provides for inward motion of plunger assembly 100 when coil 204 is energized. It is preferred that plunger portion 102 is dimensioned such that its length remains within coil 104 while being energized. In this way clevis 104, which is non-magnetic, extends beyond coil 204. When coil is energized, clevis 104 is not magnetized and external magnetic flux is reduced relative to conventional devices. Referring to FIG. 1 and FIG. 4, strong magnetic flux lines 21 of FIG. 1 are rerouted by the present invention to provide a reduced or weaker magnetic field 210 as shown in FIG. 4. Areas in the proximity of flux lines 21 and 210 are area which may affect magnetically sensitive devices.

The present invention provides a reduced external magnetic field which is advantageously utilized in devices where it is desirable to have low magnetic flux. One such device is a magnetic storage device, such as a video player/recorder, a cassette player/recorder or the like. Referring, to FIG. 5, a magnetic tape assembly 300 is shown. Magnetic tape assembly 300 is used for reading and writing data to a magnetic storage tape (not shown). A head assembly 302 is a magnetically sensitive device which is used for reading and writing magnetic data from and to the magnetic storage tape. A solenoid assembly 304 is used to advance and retract a roller bearing 306. Roller bearing 306 contacts the tape which is guided by guides 308 to engage or disengage the tape from a write portion of the head assembly 302. A second solenoid assembly 305 is used to actuate a brush plate 307 used to periodically brush debris from head assembly 302. Solenoid assembly 304 includes clevis 104 which is coupled to a plunger portion (not shown) within a solenoid body 310. A linkage 312 is pivotally attached to clevis 104 by a pin 314. Due to the proximity between solenoid assembly 304 and head assembly 302 and the flux paths present within assembly 300, the present invention advantageously reduces external magnetic fields generated by solenoid assembly 304 and provides for improved performance of head assembly 302.

Referring to FIGS. 6 and 7, solenoid assembly 304 is shown in greater detail. FIG. 6 shows an assembled solenoid assembly 304, and FIG. 7 shows solenoid assembly 304 with parts separated. Solenoid body 310 includes a coil disposed therein. A bracket 404 is provided with a washer 406, and they are secured to solenoid body 310 with a nut 402. A compression spring 408 is used to bias plunger assembly 100 out of solenoid body 3 1Q. Plunger assembly 100 includes plunger portion 102 and clevis 104 in accordance with the present invention. Pin 314 supports a collar 410 for compressing spring 408, and pin 314 secures linkage or lever 312. Linkage 312 pivotally attaches to a shaft 412 on a roller housing 414. Roller housing 414 supports a rod 416 which forms an opening 418 for connecting to a pin 420 on linkage 312. Rod 416 is coupled to roller bearing 306 to provide engagement or disengagement as described above. When the coil is energized, plunger portion 102 is magnetized and is pulled into solenoid body 310 against the biasing force of spring 408. This movement pivots linkage 312 on shaft 412 which retracts rod 416 thereby retracting roller bearing 306.

Although the present invention has been described having a tubular solenoid assembly, other geometries are contemplated for the solenoid body and the plunger portion. As described the clevis of the present invention may be replaced by coupling devices having other geometries and methods of attachment to the plunger portion. Further, the present invention may be used independently or in conjunction with devices other than those set forth above. These devices include equipment or assemblies where it is desirable to have reduced magnetic flux, such as telecommunications equipment, computers, etc.

Having described preferred methods of a novel solenoid plunger having attenuated external magnetic flux (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.

Claims

WHAT IS CLAIMED IS: 1. A plunger assembly comprising: a plunger disposed in a coil for movement relative to the coil when the coil is energized; and a non-magnetic end portion coupled to the plunger, the end portion disposed externally to the coil for reducing external magnetic flux generated by the coil when energized.

2. The plunger assembly as recited in claim 1, wherein the non-magnetic end portion is aluminum.

3. The plunger assembly as recited in claim 1, wherein the non-magnetic end portion is non-magnetic stainless steel.

4. The plunger assembly as recited in claim 1, wherein the non-magnetic end portion includes attachment means for mechanically coupling to a device to be actuated.

5. The plunger assembly as recited in claim 1, wherein the non-magnetic end portion includes a clevis.

6. The plunger assembly as recited in claim 1, wherein the non-magnetic end portion threadedly engages the plunger.

7. An assembly for actuating a plunger with a magnetic field comprising: a magnetic element for producing magnetic flux for actuating the plunger, the magnetic element being housed in a solenoid body wherein the plunger is disposed within the magnetic element and when the magnetic element produces magnetic flux, the plunger moves relative to the magnetic element; and a non-magnetic end portion coupled to the plunger and disposed externally to the magnetic element for reducing external magnetic flux emanating from the magnetic element, the non-magnetic end portion attaches to a member for causing movement of the member.

8. The assembly as recited in claim 7, wherein the non-magnetic end portion is aluminum.

9. The assembly as recited in claim 7, wherein the non-magnetic end portion is non- magnetic stainless steel.

10. The assembly as recited in claim 7, wherein the non-magnetic end portion includes a clevis for mechanically coupling to the member.

11. The assembly as recited in claim 7, wherein the solenoid body is tubular.

12. The assembly as recited in claim 7, wherein the non-magnetic end portion threadedly engages the plunger.

13. The assembly as recited in claim 7, wherein the magnetic element includes a coil.

14. An assembly for use with magnetic media having attenuated magnetic flux comprising: a magnetically sensitive device for recording and retrieving magnetic data; at least one solenoid assembly proximally located relative to the magnetically sensitive device wherein the at least one solenoid assembly includes: a solenoid body housing a coil therein; a plunger disposed within the coil and being actuated by the coil when energized, the plunger extending within the coil; and a non-magnetic end portion coupled to the plunger, the end portion positioned externally to the coil for reducing external magnetic flux generated by the coil when energized and for providing attachment to a mechanically actuated member of the magnetically sensitive device.

15. The assembly as recited in claim 14, wherein the non-magnetic end portion is aluminum.

16. The assembly as recited in claim 14, wherein the non-magnetic end portion is non- magnetic stainless steel.

17. The assembly as recited in claim 14, wherein the non-magnetic end portion includes a clevis.

18. The assembly as recited in claim 14, wherein the non-magnetic end portion threadedly engages the plunger.

19. The assembly as recited in claim 14, wherein the assembly includes a device for magnetic media data transfer and the magnetically sensitive device is a head assembly.