US3643384A

US3643384A - Vibratory apparatus

Info

Publication number: US3643384A
Application number: US806079A
Authority: US
Inventors: Max Isaacson; Benjamin Smilg
Original assignee: Vibrodyne Inc
Current assignee: Tailored Systems Inc
Priority date: 1969-03-11
Filing date: 1969-03-11
Publication date: 1972-02-22
Anticipated expiration: 1989-02-22
Also published as: DE2011404A1; GB1298274A; FR2037984A5

Abstract

A vibratory finishing machine includes an elongated container supported at longitudinally spaced intervals for oscillator movement at a predetermined natural frequency and on an effective axis offset laterally to a vertical plane extending through the center of the container. In one form, the container consists of longitudinally aligned and rigidly connected sections each supported by a plurality of aligned spring beams mounted on a corresponding frame section so that each container section has substantially the same natural frequency of oscillation. A pair of opposing magnets are mounted on each frame section to effect vibration of an armature rigidly connected to the corresponding container section, and each armature is generally aligned with the corresponding spring beams. Each pair of magnets is separately controllable to provide for varying the amplitude of oscillation of each container section. The container may also be enclosed to provide a ball mill or may be provided with end openings for progressive finishing an elongated part.

Description

nite States Patent isaacson et al.

Primary Examiner-l-larold D. Whitehead Attorney]acox & Meckstroth [54] VEBRATORY APPARATUS ABSTRACT A vibratory finishing machine includes an elongated container 221 Filed: Mar. 11, 1969 21 Appl.No.: 806,079

supported at longitudinally spaced intervals for oscillator movement at a predetermined natural frequency and on an effective axis offset laterally to a vertical plane extending through the center of the container. in one form, the container consists of longitudinally aligned and rigidly connected sec tions each supported by a plurality of aligned spring beams mounted on a corresponding frame section so that each room [52] US. [51] int. [58] Field oli tainer section has substantially the same natural frequency of References oscillation. A pair of opposing magnets are mounted on each frame section to effect vibration of an armature rigidly connected to the corresponding container section, and each armature is generally aligned with the corresponding spring beams. Each pair of magnets is separately controllable to provide for varying the amplitude of oscillation of each container section. The container may also be enclosed to provide a ball mill or may be provided with end openings for progressive finishing an elongated part.

15 Claims, 7 Drawing Figures VIBRATORY APPARATUS BACKGROUND OF THE INVENTION In the finishing of a long article or part, as for example, the deburring and stress relieving of a 30-foot aluminum spar for an aircraft wing, it is common to sand or polish the edges of the spar manually to form radii on the edges for preventing cracks which could possibly lead to subsequent fatigue failure.

This manual finishing operation involves substantial man hours which significantly increases the cost of the wing.

While small parts, for example, under 3 feet in length, may be successfully deburred, polished or otherwise finished in a power operated vibratory finishing machine such as the machine disclosed in Isaacson et al. U.S. Pat. No. 3,173,664, longer parts are usually finished manually due to the lack of suitable vibratory finishing equipment which will accommodate and effectively finish an elongated part.

When the vibratory finishing machine disclosed in the above patent is extended substantially in length to accom modate a long part, the desirable lightweight tub or container will bend or flex when vibrated thereby absorbing vibratory energy and preventing uniform treatment of the part by the media within the container. On the other hand, if the elongated container is constructed sufficiently rigid to eliminate significant flexing or breathing and weaving of the container, the weight or mass of the container becomes excessive and a substantial increase in the energy is required to vibrate or oscillate the container.

In other types of vibratory finishing machines such as those which employ a container supported by coil springs and vibrated by rotating eccentric weights, a substantial increase in the length of the container presents the same problems of flexing or excessive mass of the container and of obtaining uniform treatment of a part inserted into the media within the container.

SUMMARY OF THE INVENTION The present invention is directed to an improved vibratory finishing apparatus of the basic form disclosed in the above patent and which may be conveniently assembled to provide for effectively and uniformly finishing a part of essentially any length. Thus as one important feature, the vibratory apparatus of the invention provides for obtaining uniform treatment of a long part along its entire length. In addition, the apparatus provides for selectively controlling the amplitude of vibration of the container at spaced intervals along its length to accommodate long parts having a nonuniform cross section and regions of increased mass which require greater vibratory energy to obtain the desired finishing treatment of the part.

In accordance with one embodiment of the invention, the vibratory finishing machine or apparatus incorporates an elongated container having a U-shaped cross-sectional configuration. The container is formed of a plurality of container sections each supported along one edge portion by a plurality of longitudinally spaced and aligned spring beams mounted on a corresponding frame section. The container sections oscillate on an effective axis provided by the aligned spring beams. At least one pair of magnets are mounted on each frame section in opposing relation, and an armature is rigidly connected to each container section and supported between the corresponding magnets in alignment with the corresponding spring beams so that a substantial uniform gap is obtained between the armature and each magnet for providing a more efficient flux path.

The apparatus of the invention also provides for connecting auxiliary springs between a frame section and its corresponding container section in spaced relation to the effective pivot axis to aid in supporting the container for oscillation at the predetermined natural frequency. Each container section and its supporting spring structure are tuned to substantially the same resonant or natural frequency of oscillation so that the container sections may be rigidly connected together, and the transfer of forces or stresses between adjacent container sections is essentially eliminated.

As mentioned above, the vibratory apparatus of the invention also provides for varying the amplitude of vibration at selected intervals along the length of the container. This is accomplished by providing a separate voltage control for each pair of magnets mounted on each frame section of the vibratory apparatus.

In accordance with another embodiment of the invention, the container system, the spring means, and the armatures are arranged so that the armatures lie substantially in the plane defined by the effective pivot axis and the center of gravity of the container system. Furthermore, the armatures are located at the center of percussion of the vibrating container system and thus minimize the stresses in the spring beams and their supports. The center of percussion may be defined as that point in a mechanical rotatable system at which a force may be applied suddenly without producing a shock on the axis of rotation. The location of the center of percussion and consequently the position of the armature is determined from the following formula:

l=I/X where l distance from the armatures to pivotal axis 1 mass moment of inertia of the complete container system about the pivotal axis X distance from the center of gravity of the container system to the pivotal axis A further embodiment of the invention provides for progressively finishing an elongated part. This is accomplished by forming openings within opposite end walls of the container and providing removable partitions within the container for supporting and guiding the part as it is directed through the openings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of apparatus constructed in accordance with the invention;

FIG. 2 is an end view of the apparatus shown in FIG. 1, with a portion of the forward end wall broken away;

FIG. 3 is a fragmentary section taken generally on the line 33 of FIG. 4;

FIG. 4 is a front elevational view of the apparatus taken generally on the line 44 of FIG. 1, with portions broken away to show details of construction;

FIG. 5 is a diagrammatic vertical section of vibratory apparatus constructed in accordance with another embodiment of the invention;

FIG. 6 is a diagrammatic view similar to FIG. 5 and showing a different longitudinal section; and

FIG. 7 is a diagrammatic axial section of vibratory apparatus constructed in accordance with another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the vibratory finishing apparatus shown in FIGS. 1-4, an elongated frame 20 incorporates a plurality of frame sections 22 each including a pair of spaced vertical walls 23 rigidly connected by a pair of crossmembers 24, a plate member 26 and a support bar 28. A plurality of reinforcing members 29 extend between the bar 28 and the plate member 26 within each frame section. A U-shaped recess 311 is formed in the upper portion of each wall 23, and a set of

resilient support feet

32 and 33 extend downwardly from the crossmembers 24 of each frame section.

An elongated tub or container 35 extends horizontally within the recesses 31 of the frame sections 22 and includes a set of end container sections 36 connected by an intermediate container section 38. Each of the

container sections

36 and 33 includes a U-shaped wall 40, and the end sections 36 each include a vertical end wall 42 rigidly connected to the wall 40. A flange 43 projects outwardly from the upper edges of the

walls

40 and 42, and mating flanges 44 are formed on both ends of the center section 38 and on the inner ends of the end sections 36 for rigidly securing the sections together by a series of bolts 46. Suitable gaskets (not shown) are located between adjacent flanges 44 to form watertight seals between the container sections, and a resilient liner (not shown) such as polyurethane covers the inner surface of each container section. As shown in FIG. 1, the container 35 is tilted by the additional length of the rear feet 33 relative to the front feet 32 so that the upper flange 43 lies substantially horizontal.

A longitudinally extending bar 48 is rigidly secured to the upper portion of the wall 40 of each

container section

36 and 38, and a plurality of reinforcing ribs 49 extend from each bar 48 around the underneath surface of each wall 40 to add rigidity to each container section without adding significant weight. Each

container section

36 and 38 is supported by a plurality of longitudinally aligned and generally flat spring beams 50 having upper end portions rigidly secured to the corresponding bar 48 by a clamping plate 51 and a series of screws 52. The lower end portions of each set of spring beams 50 are rigidly secured to the crossbar 28 of the corresponding frame section 22 by clamping plates 53 having tapped holes for receiving a series of screws 54 extending through the bar 28.

In addition to the spring beams 50, the outer end portion of each container section 36 is supported by a spring beam 55 having an I-configuration. The lower flange of each spring beam 55 is secured to the adjacent end wall 23 by a series of screws 56, and the upper flange is rigidly connected to the adjacent end wall 42 of the container 35 by screws 57. Referring to FIG. 2, the end spring beams 55 are longitudinally aligned with the intennediate spring beams 50 and cooperate therewith to form a virtual or effective pivot axis on which the container 35 oscillates at a predetermined natural frequency as will be explained later. I

Referring to FIGS. 2 and 4, a series of downwardly projecting brackets 62 are rigidly secured to the walls 40 of the

container sections

36 and 38 adjacent the reinforcing ribs 49. A pair of auxiliary tension springs 65 are connected to each bracket 62 and extend in opposite directions to corresponding eyebolts 66 extending through flanges rigidly secured to the adjacent vertical walls 23. Nuts 68 are threaded on the eyebolts 66 and provide for selectively controlling the forces exerted by the springs 65 on the container 35 according to the load of media M received within the container 35. These auxiliary tension springs can be used to position the armature with respect to the magnets in order to maintain a uniform gap regardless of the load of media in the container and to reduce the static and dynamic loads carried by the spring beams.

Each of the

container sections

36 and 38, the supporting

spring beams

50 and 55 and the corresponding tension spring 65 are designed and tuned to provide a predetermined resonant or natural frequency of oscillation. As mentioned in the above patent, this predetermined frequency is preferably slightly greater than 3,600 cycles per minute when the apparatus is to be operated from a 60-cycle AC power supply. As a result of the separate tuning of each container section, the transfer of forces or stresses between adjacent

container sec tions

36 and 38 is minimized when the container 35 is oscillated to effect orbital movement of the media M within the container 35.

A pair of opposing electromagnets 70 are supported by the cross plate 26 of each frame section 22 in laterally offset relation to a vertical plane extending through the center of the container. and each magnet 70 is-rigidly secured by a set of screws 72 to a pair of parallel spaced support blocks 73 adjustably mounted on the plate 26 by a set of screws 74.

Lock screws

76 and 77 and nuts 78 rigidly secure the blocks 73 to the cross plate 26 after the precise position of each magnet 70 is determined.

A pair of spaced vertical support members 79 (FIG. 4) are rigidly secured to the wall 40 of each of the

container sections

36 and 38, and a laminated barlike armature 80 is rigidly connected to each pair of support members 79. Each armature 80 extends between the adjacent parallel faces 82 of the corresponding pair of magnets 70 and, as shown in FIG. 3, is positioned in alignment with the spring beams 50 and 55 so that a substantially uniform gap is defined between each side of the armature and the adjacent magnet face 82. Thus the faces 82 of the magnets 70 lie within parallel spaced planes, and the effective pivot axis 60 extends between these planes.

Referring to FIG. 2, a female electrical receptacle 85 is mounted on each frame section 22 and is connected by wires to the corresponding electromagnets 70. Each receptacle 85 is adapted to receive a plug 86 which is connected by wires 87 to a controller 90 incorporating a variable voltage transformer (not shown) having a control knob 92 providing for varying the voltage of the power supplied to the magnets 70 and thereby provide for varying the amplitude of oscillation of the corresponding container section.

A circular opening 95 (FIG. 2) is formed within each end wall 42 of the container 35 and is adapted to receive a circular closure 96 carried by an arm 97 pivotally connected to a bracket 98 secured to the end wall 42. A handle 100 is pivotally supported by each bracket 98 and is connected by a link to the adjacent arm 97 to provide for opening and closing the closure member 96 and locking it in its closed position by an overcenter toggle action.

In accordance with another embodiment of the invention, diagrammatically illustrated in FIGS. 5 and 6, a pair of laterally spaced parallel elongated containers are rigidly connected by a cross member 106, and each container 105 has a U-shaped cross-sectional configuration generally similar to the container 35 shown in FIG. 1. The containers 105 are supported by a plurality of longitudinally spaced spring beams each having an I-configuration. The upper flange of each spring beam 110 is rigidly secured to the crossmember 106, and the lower flange is rigidly secured to a frame 112. Thus the effective pivot axis 114 for the oscillatory movement of the containers 105 and the effective center of gravity 115 for the containers 105 lie within a vertical plane.

A dusttight cover 118 is removably mounted on each container 105 to adapt the containers for use as ball mills for grinding a material into-a powder. For this application, the containers 105 may be lined with a ceramic material, and ceramic balls provide the media. A pair of vertical support members 120 (FIG. 6) project downwardly from the crossmember 106 between each pair of spring beams 110 and support an armature 122 which extends between a pair of electromagnets 125. Preferably, the armature 122 is located at the center of percussion 126 to minimize the stresses in the spring beams 110 and in their supports.

Referring to FIG. 7 which shows another embodiment of the invention, an elongated container 130 has a U-shaped crosssectional configuration and is supported for oscillatory movement at a predetermined natural frequency by a series of Iongitudinally spaced spring beams (not shown) secured to an elongated frame 132. The container 130 includes opposite vertical end walls 134 having aligned openings 136 for receiving an elongated part P to be surface finished, such as an aluminum spar for an aircraft wing.

A series of

partitions

138 and 140 are positioned within the container 130, and each partition can be conveniently removed simply by lifting the partition from the container. Each of the

partitions

138 and 140 support a flexible member 142 for guiding the part P-as it is progressively advanced through the container 130, and a screen 143 is provided within the lower portion of each end partition 138 to provide for drainage of water and sludge from the container 130 through bottom outlets 144 formed within the end portions of the container.

If a portion of the media used in the container 130 escapes past one of the end guide members 142, it flows through the corresponding outlet 144 and onto a screening device 145 where media particles of predetermined size are separated from the sludge and returned to the container 130 by a suitable conveyor 146. When it is desired to clean the container 130, the

partitions

138 and 140 are removed and the media is fed through the outlets 144 onto the screening devices 145. As

shown in FIG. 1, the long container 35 may be effectively reinforced without adding significant mass by securing one or more rigid tie members 150 across the flanges 43 of the container 35 intermediate its end portions. Each tie member is easily removable by releasing a clamping screw 151 so that a long part to be finished may be conveniently inserted into the media M.

From the drawings and the above description, it becomes apparent that a vibratory finishing apparatus constructed in accordance with the invention provides desirable features and advantages. For example, the support of the elongated container 35 for uniform oscillatory movement by the plurality of aligned spring beams 50 located at longitudinally spaced intervals along the side of the container, enables a container 35 of essentially any length to be constructed according to the length of a part to be finished. Thus, if the part to be finished was an aluminum wing feet in length, the container would be somewhat greater than 30 feet and be supported at longitudinally spaced intervals along its entire length by a series of the spring beams so that flexing or weaving of the long container would be essentially eliminated when the container was oscillated at substantially its predetermined natural frequency by a series of magnets 70 positioned in pair at longitudinally spaced intervals along the frame supporting the container.

Another important feature of the vibratory apparatus of the invention is provided by the construction of the frame 20 and container 35 in modules or sections. That is, the support of each container section on its corresponding frame section for oscillatory movement at substantially the same predetermined resonant or natural frequency and the mounting of at least one pair of magnets 70 on each frame section for oscillating the corresponding container section at this frequency, enables the apparatus to be conveniently assembled to a selected length simply by inserting additional intermediate container sections 38 and corresponding frame sections 22 between the end container sections 36 and frame sections 22.

The module construction wherein each container section has the same length, also simplifies lining the inner surface of each container section with a wear-resistant resilient material.

' For example, with the use of only one size mold, a polyurethane lining may be cast in place within each container section. This eliminates the need for molds of various lengths according to the different lengths of containers 35. As illustrated in FIG. ll, if spring beams 50 are employed to support the end portions of each end container sections 36 in addition to the spring beams 55, the intermediate spring beam 50 for each end container section 36 may be eliminated. The primary purpose of the spring beams is to compensate for the additional mass added to the container 35 by the end walls 42. The spring beams 50 provide the primary support for the container 35.

Another important advantage of the vibratory apparatus of the invention is provided by the separate voltage controller 90 for each pair of magnets 70. Thus when a part to be finished is not uniform in cross section and has a region of greater mass at some point along its length, the voltage for the magnets corresponding in location to the region of greater mass may be increased so that the energy for oscillation of the container 35 in the region of the greater mass is correspondingly increased to provide the desired finishing ofthe part.

The tilted position of the container 35 and the construction of the front wall being higher than the rear wall provides another advantage of the invention. That is, this arrangement minimizes the mass moment of inertia of the container on the effective axis of oscillation and thereby provides for minimizing the thickness of the spring beams 50 and 55 and the stresses on the beams during oscillation. Moreover, the tilted position of the container 35 provides for orbiting a large volume of media M at a rapid rate.

The embodiment shown in FIGS. 5 and 6 provides a further advantage. That is, the arrangement of the components so that the vibratory impulses for minimum stresses and optimum efficiency of operation. The embodiment shown in FlG. 7 provides still another feature. That is, the openings 136 within the end walls 134 of the oscillatory container R30 enable a long part P to be progressively fed through a media within the con tainer to effect progressive finishing of the part. Moreover, the removable partitions 113th and M0 provide for guiding the part P through the container 130 and also for simplified cleaning of the container.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. Vibratory apparatus comprising a frame, an elongated container including opposite end portions connected by an intermediate portion and defining a chamber adapted to receive a load to be vibrated, a pair of spring beams mounted on said frame and connected to said end portions of said container, means positioning said spring beams to support said container for oscillatory movement on an effective pivot axis extending longitudinally outboard of said chamber, at least one intermediate spring member mounted on said frame and connected to said intermediate portion of said container, and said intermediate spring member cooperating with said spring beams to aid in supporting said intermediate portion of said container for oscillatory movement at the same frequency and amplitude as said end portions of said container, and poweroperated means for oscillating said container at a frequency corresponding substantially to the resonant frequency of said container when loaded.

2. Apparatus as defined in claim ll wherein said poweroperated means comprise a plurality of longitudinally spaced pairs of opposed electromagnets, an armature extending between each said pair of electromagnets and rigidly connected to said container, and separate control means for independently varying the voltage to each said pair of electromagnets.

3. Apparatus as defined in claim 1 wherein said spring member comprise a generally flat spring beam cooperating to form said effective axis of oscillation.

4. Apparatus as defined in claim 1 wherein said container has a generally U-shaped cross-sectional configuration, and a rigid tie member extends laterally across the top of said intermediate portion of said container for effectively reinforcing said container intermediate said end portions without adding significant mass to said container.

5. Vibratory apparatus comprising a frame, a container defining a chamber adapted to receive a load of parts and media to be vibrated, a plurality of elongated spring beams mounted on said frame and supporting said container for oscillatory movement at a predetermined natural frequency and on an effective pivot axis offset laterally from a vertical plane extending through the center of said container, a pair of electromagnets mounted on said frame in opposed relation generally below said container, an armature extending between said electromagnets and connected to said container, and said electromagnets and said armature being positioned to locate said armature in substantially longitudinal alignment with said spring beams and laterally offset from said plane in the same direction as said pivot axis to provide a substantially uniform gap between said armature and said electromagnets during the oscillatory movement of said container.

6. Apparatus as defined in claim 5 including a pair of said containers extending in horizontally spaced parallel relation, means rigidly connecting said containers, a plurality of said spring beams positioned to support both said containers for oscillation on the same said effective axis disposed outboard of said containers, and said effective axis of oscillation and the effective center of gravity of said containers defining a generally vertical plane.

7. Vibratory apparatus comprising a frame including a plurality of frame sections disposed in substantially aligned relation, a container including a plurality of container sections connected in substantially aligned relation to define an elongated chamber adapted to receive a load to be vibrated, means mounted on said frame sections and supporting the corresponding said container sections for oscillatory movement at a predetermined natural frequency and on an effective pivot axis offset laterally outboard of said chamber, said natural frequency of oscillation of each said container section being substantially the same, power-operated means for oscillating each said container section at a frequency corresponding substantially to the resonant frequency of said container section when loaded, and means for adjustably controlling said power-operated means for each said container section.

8. Apparatus as defined in claim 7 wherein said poweroperated means for each said container section comprise a pair of electromagnets mounted on each said frame section in opposed relation, an armature extending between said electromagnets and rigidly connected to the corresponding said container section, and each said armature being ofiset from a generally vertical plane extending through the center of said container and in the same direction as said effective pivot axis.

9. Apparatus as defined in claim 8 including separate control means for a plurality of said pairs of electromagnets to provide for independently varying the voltage to each said pair of electromagnets to control the amplitude of oscillation of the corresponding said section of said container.

10, Apparatus as defined in claim 1 including a plurality of longitudinally spaced said intermediate spring beams connecting said intermediate portion of said container to said frame.

11. Apparatus as defined in claim 1 wherein said spring member comprises a coil spring positioned to exert a lifting force on said container in spaced relation to said pivot axis.

12. Apparatus as defined in claim 11 including a plurality of longitudinally spaced said coil springs extending between said container and said frame.

13. Apparatus as defined in claim 1 wherein said poweroperated means comprise a pair of electromagnets mounted on said frame in opposed relation, an armature extending between said magnets, and said armature being positioned generally within a plane defined by said spring beams.

14. Apparatus as defined in claim 7 wherein said supporting means for each said section of said container, include a plurality of generally flat spring beams, and said spring beams for all said container sections being aligned.

15. Vibratory apparatus comprising a frame including a plurality of frame sections disposed in substantially aligned relation, a container including a plurality of corresponding container sections connected in substantially aligned relation to define an elongated chamber adapted to receive a load of parts and media to be vibrated, a plurality of elongated spring beams mounted on each said frame section and supporting the corresponding said container section for oscillatory movement on an effective pivot axis offset laterally from a vertical plane extending through the center of the container sections, a pair of electromagnets mounted on each said frame section in opposed relation generally below the corresponding said container section, an armature extending between each pair of magnets and connected to the corresponding said container section, and each pair of electromagnets and the corresponding said armature being positioned to locate said armature in substantially longitudinal alignment with the corresponding said spring beams and laterally offset from the center plane of said container sections in the same direction as said pivot axis.

Claims

1. Vibratory apparatus comprising a frame, an elongated container including opposite end portions connected by an intermediate portion and defining a chamber adapted to receive a load to be vibrated, a pair of spring beams mounted on said frame and connected to said end portions of said container, means positioning said spring beams to support said container for oscillatory movement on an effective pivot axis extending longitudinally outboard of said chamber, at least one intermediate spring member mounted on said frame and connected to said intermediate portion of said container, and said intermediate spring member cooperating with said spring beams to aid in supporting said intermediate portion of said container for oscillatory movement at the same frequency and amplitude as said end portions of said container, and power-operated means for oscillating said container at a frequency corresponDing substantially to the resonant frequency of said container when loaded.

2. Apparatus as defined in claim 1 wherein said power-operated means comprise a plurality of longitudinally spaced pairs of opposed electromagnets, an armature extending between each said pair of electromagnets and rigidly connected to said container, and separate control means for independently varying the voltage to each said pair of electromagnets.

8. Apparatus as defined in claim 7 wherein said power-operated means for each said container section comprise a pair of electromagnets mounted on each said frame section in opposed relation, an armature extending between said electromagnets and rigidly connected to the corresponding said container section, and each said armature being offset from a generally vertical plane extending through the center of said container and in the same direction as said effective pivot axis.

10. Apparatus as defined in claim 1 including a plurality of longitudinally spaced said intermediate spring beams connecting said intermediate portion of said container to said frame.

13. Apparatus as defined in claim 1 wherein said power-operated means comprise a pair of electromagnets mounted on said frame in opposed relation, an armature extending between said magnets, and said armature being positioned generally within a plane defined by said spring beams.