GB2155701A - Electromagnetic vibratory exciter - Google Patents

Abstract

An electromagnetic vibratory exciter (12) for use in vibratory equipment incorporates a free mass (60) housed in an elongated housing (20) having electromagnets (26) mounted inboard at each end of the housing. The free mass is supported for longitudinal movement in the housing and the mass carries a pair of armatures (72) for co-operation with the electromagnets. An air gap is maintained during operation between the electromagnets and the armature through the use of elastomeric compression elements (44), (46) interposed between the electromagnetic housing and the armatures of the free mass. The elastomeric compression elements being non-linear spring means having contoured surfaces. <IMAGE>

Description

SPECIFICATION Electromagnetic vibratory exciter This invention concerns electromagneticvibratory exciters for use in imparting vibratory excitation into a host mass for use, for instance, in vibratory conveyor equipment, bin hoppers and chutes for bulk material transport and metered delivery.

Electromagnetic vibratory drive units have been extensively used in industry to ensure the smooth flow of bulk materials from storage bins, hoppers and delivery chutes. Electromagnetic vibratory drive units are also used in vibratory feeders forfeeding various bulk materials to mixers, grinders, crushers, packaging machinery, batching, grading or mixing stations.

The electromagnetic exciters are coupled to a delivery trough which is vibrated by the exciter to control material flow along the chute, trough, or pan.

In general electromagnetic powered vibratory systems are two mass designs each mass carrying either the magnets orthe armature. The two masses are connected by springs that normally are sized to have the system utilize resonance amplification of the motion. Electromagnets produce useful forces only when the pole faces are in close proximity to each other such as one tenth inch (.1") or less. The attraction force increases approximately with the inverse of the gap squared. The system motion is divided between the two masses inverse to theirweightthat is, the lighter mass moves proportionatelyfurther.The masses move in opposite directions as the air gap between pole faces increases and decreases.

Provisions must therefore be made to prevent the pole faces from striking as they move close to the minimum gap and the magnetforce is approaching its peak.

The instant invention provides an electromagnetic vibratory exciter which incorporates a totally enclosed free mass carried inside an elongated housing. The housing includes a pair of end caps each receiving a potted electromagnet. The end caps are separated by a housing tube secured between them.

The free mass is suspended by elastomeric shear springs insidethe housing tube equidistantfrom each end cap. A pair of armature assemblies are integral with the free mass, one armature at each end ofthe generally elongated free mass.

Rubbercompression elements are interposed between and normally spaced apart from the free mass and the electromagnet retaining end caps. These non-linearsprings help to avoid armature strike and store the input energy during electromagnet conduction resulting in high efficiency.

The electromagnets are sequentially energized through a remotely located controllerthat is connected to thefirst electromagnet retaining end cap. An armored conduit extends from the first end cap to the second end cap. Upon energization ofthe electromagnets in sequence the free mass will be moved longitudinally th rough the housing and into contact with the elastomeric compression elements and will cycle back and forth responsive to electromagnet energization and de-energization.Thefrequency of operation is close to the natural frequency over a broad range ofdriven weights to utilize resonance.

The apparatus and operation ofthe invention will be readily understood through a perusal of the following description in conjunction with the drawing figures wherein: Figure lisa simplified illustration of a feedertrough to which the electromagnetic exciter has been mounted; Figure 2 is an exploded view of the invention with some components broken away; Figure 3 is an elevation view of Figure 2 with some components broken away and sectioned for clarity; Figure 4 is an end view ofthe device of Figure 2 with part of the housing broken away and sectioned; Figure 5 is a side elevation view of 5-5 of Figure 4; Figure 6 is a graph showing the frequency response range of the electromagnetic exciter; Figure 7 is a graph showing the energy output of the electromagnet; Figure 8 is an elevation view of an elastomeric compression element;; Figure 9 is a plan view of an elastomeric ring; Figure 10 is a partially sectioned elevation view of the ring of Figure 9.

A bulk material handling trough generally 10 in Figure 1 provides a typical application for the electron magnetic vibratory exciter of the invention. The exciter, generally 12, will be fastened to the trough by means such as fasteners 14. Asupply conduit 16 will extend from the electromagnetic exciter to a control module typically remotely stationed.

The mechanical aspects of the invention can be easily understood by studying Figure 2 which is a projected view of the electromagnetic excite. general- ly 12. The exciter is a unitized closed structure having a housing tube 20 which may be of sturdy structural material such as aluminum. First and second end caps 22 and 24 respectively, act as magnet housings each containing a potted electromagnet such as 26 in end cap 24. The end caps 22 and 24 are placed on opposite ends ofthe housing tube 20. In one embodiment studs such as 30 are secured with fasteners such as 32 to securely maintain the housing's integrity. The housing is an elongated container that is sealed against intrusion due to its construction. This containerized housing provides the possibility of an explosion proof housing that is not possible with more conventional electromagnetic exciters.

The first end cap 22 is provided with an electrical conduit terminal 28to accept the supply conduit 16.

Figure 5 shows conduit 34 running between the first and second end caps 22 and 24for carrying the wire bundle 36 used to provide electrical pulsestothe electromagnet 26.

Thefirst end cap 22 may also be provided with threaded apertures such as 40 to provide one method of mounting the electromagnetic exciter generally 12 to the apparatus to be vibrated.

Looking at Figures 2,3 and 4, parts solidly carried inside the housing can be identified. Electromagnet 26, as well as its twin carried at the opposite end of the This print embodies corrections made under Section 117(1) of the Patents Act 1977.

housing tube 20 (not visible) and its electrical supply wires from the bundle 36, as well as cover plate 42 are clearly shown.

Inside the housing tube and attached to each end cap are elastomeric compression elements such as pairs of identical elements 44 and 46 making up spring elementsthatfunction as non-linear elements in this system. The pairs differfrom each other in the thickness of the elastomeric components.

Afirst pair44 of elastomeric compression elements are bonded orotherwise suitably affixed to a backing plate such as 50 which in turn is mounted by fastening means to the inside face ofthe end plate at each end of the housing tube. A cap of fabric reinforced material may be integral with the elastomeric body portion.

The cap would eliminate relative motion between the elastomerandthe mounting plate 76 during spring compression. The second pair 46 of elastomeric compression elements 46 are also suitably affixed to a similar backing plate but may have shims, one shown as 52, interposed between the backing plate and the endcaptowhich it is mounted. The elastomeric compression elements are symmetrically arranged so that pair members are on diametrically opposite sides ofthe longitudinal axis ofthe diametrically opposite sides ofthe longitudinal axis of the housing. The thickness ofthe elastomeric compression elements and the shims associated therewith are variables that can be changed in orderto provide desirable operat- ing characteristics of a specified electromagnetic exciter.The stacking height of each pair of elastomeric compression elements at each end ofthe housing may be differentfrom the other pair atthe same end so that better control ofthe non-linear aspect ofthis spring means is possible. The elastomeric compression elements provide a non-linearstiffening rate and self-limiting deflection ofthe device.

The elastomericcompression elements such as 44 can be fabricated with a crowned surface such that he thickness ofthe elastomeric compression element is not uniform through its relative length. Figure 8 shows an elastomeric compression element 100 having a crowned portion 102 that may be an exaggeration of the degree ofthe crown portion but is representative ofthe concept. Multiple crowns and concave portions are also posibilities contemplated by the inventors as is a "stepped" embodimentwhere there would be more radical demarcations between the thicker and thinner portions ofthe elastomeric compression element.

Alternative embodiments may include fewerthan or more than the four elements shown in the presentation ofthe preferred embodiment. Other embodiments of elastomeric compression elements are also contemplated by the invention For instance, Figure 9 shows a single elastomericcompression element 104 that is basically an elastomeric ring with a central aperture such as 106, that may be of a shape other than that as shown as long as it accomodates the armature 80 which could also be of a shape otherthan the generally rectangular shape as depicted in the drawings. The eiastomeric ring could be suitably affixed to backing plates such as 52, for example, or could be attached to a unitary backing plate such as 108.The backing plate is optional as the ring 104 could be attached directly to the interior of the end caps orto the mounting plate 76.

Figure 10 shows a partially sectioned embodiment in side elevation view of Figure 9 with a crowned portion shown as 110 and different height crown portions such as 112. The top surface could be of many configurations including a flat surface, a wave form surface with crowns and concave sections of various dimensions alternating around the ring ora "stepped" surface of various heights alternating around the ring. Figure 10 is not presented as a limiting feature but is exemplary of the undulating surface possibilities contemplated by the inventors. A cap offabric reinforced material may also be integral with these embodiments of elastomeric rings.

It should be noted thatthe housing tube and end caps as well as all the equipment and parts mentioned above are part of the driven mass in the vibrating system since they are integrally connected together in the assemblied embodiment.

A free mass generally 60 is totally enclosed and suspended inside the housing tube 20 between the end caps 22 and 24. Figures 2and 3 are helpful in identifying its parts. First and second shear springs 54 and 56 are pressed into the interior of the elongated nousing tuee 2Oto suspend the + ruse mass generally 60.

The free mass includes a central melr,ter 62 of a generaiNy eWongate configuration having apertured wall porticns defining a pair of recesses such as 64.

This free mas; is supported by and functionally secured to the inside aperturesofthefirstand second shearspnngs. Retainer means such asthreaded rod 66 is provided to retain tuning weights such as 70 which may be held in place by fasteners.

The tuning weights such as 70 are important to this invention as they are an interchangeabie element that enables changes in theweight ofthe free mass even thoughthegeneral sizesandcomponentconfigura- tion ofthe electromagnetic exciter remains constant.

Tuning weights can be changed withoutthe need of changing or adjusting the rate of the supporting springs during tuning. Thus exciters of different capacities can be manufactured from common com ponents to advantageously utilize economies of scale.

Universal tuning is made possible bythe proper selection ofthe natural frequency ofthe free mass and the springs 54 and 56. This universal tuning allows the exciter to deliver rated power regardless of the weight ofthe driven memberto which it is attached.

Afterthetuning weights are in position the flange plates such as 72 are suitably fastened to the opposite ends ofthe central member 62. Armature assemblies generally 74, including a mounting plate 76 and a generally rectangular armature 80 are fastened to the flange plate 72. An alternative method of assembly would beto eliminate the mounting plates and mount the armatures directly to the flange plates 72.

Upon assembly ofthe electromagnetic exciter an air gap 82 exists between the face of the armatures such as 80 and the faces ofthe electromagnets such as 26 when in a static state. Upon actuation the air gap will cyclically decrease and increase but the pole faces will not strike if proper spring selection has been made.

It should be mentioned, as is obvious from the drawing figures, that components on the interiorof the housing aresymetricallysimilaron each end ofthe central member. The symmetry resulting from this structure and the dual opposing electromagnets is beneficial to good exciter operation. Figures 6 and 7 graphically display the advantages gained through the embodiment presented herein.

Figure 6 graphically represents the universal tuning advantage ofthe exciter. The frequency ratio on the x-axis shows that maximum amplitude occurs where the operating frequency ofthe exciter and the natural frequency ofthe system are the same. The included portion ofthecurve betweenAand B representsthe operating region for an exciter of a given free mass applied to a broad range of driven weights. The exciter is tuned, by judicious selector ofthe tuning weights, such that the natural frequency of the system is equal to the operating frequency of the exciter. That would mean that the exciter would be tuned so thatthe frequency ration is between A and B for a broad range of driven weights. The resonance amplification in this range is at least five.

The exciter would continue to perform efficier :ly to super-resonance represented where line B intersects the curve. The resonance amplification factor would again be five. In summary it is apparentthatthis exciter is closeto resonance over a broad weight range of driven masses.

Without the compression elements the pole faces would strike atthe higher amplification factors. Line C showsthefull system deflection which is maintained by these elements.

In Figure 7 the electrical power pulse timing and the force produced by the electromagnet is graphically depicted. Each electromagnet is energized once per mechanical cycle. Although not shown in the drawing figures a controller will be remotely mounted from the exciter and designed to supply each electromagnet sequentially with a pulse of electrical energy timed appropriately to energize each electromagnet. The static air gap A at the right side ofthe graph depicts a position where the armature free mass is equally spaced apart from the electromagnets. Proceeding to the left ofthe graph towards the minimum air gap the duration of the electrical pulse to the electromagnet is shown by the curve designated as broken line C.The force produced by the electromagnet is shown by curve D while the area under the curve is the energy output of the magnet. The electromagnet is energized during the deflection of the free mass towards the electromagnets in the zone from Eto B (the minimum air gap). As the air gap opens current continues to flow backto pointFthereforethe net energy produced is that indicated by the crosshatched area under the curve. This energy is that stored in the compression springs 44 and 46. Electromagnet coils designed for energization in the manner described make it possible to store significantly more energy per cycle then the designs ofthe prior art.

Depending on the design ofthe compression elements this stored energy resulting from the initial impact ofthe free mass directed toward the compression element provides approximately 30% ofthe force needed to accelerate the free mass in the opposite direction. This results in an electrical power savings and the attendant cost benefit. Since the compression elements are non-linear any armature striking can be avoided through proper selection oftheelements.

Claims (13)

1. An electromagnetic vibratory exciter including an exciter body having a plurality of electromagnet means directed toward the inside of said exciter body and a free mass supported for longitudinal movement in said exciter body, the improvement comprising: non-linear spring means carried in said exciter body, one of said non-linear spring means inboard and longitudinally adjacent one of each of said plurality of electromagnet means, said non-linear spring means having contoured surfaces.

2. The invention in accordance with Claim 1 wherein said non-linear spring means is an elastomeric compression element having a crowned surface.

3. The invention in accordance with Claim 1 wherein said non-linear spring means is an elas tomericcompression element having crowned portions and concave portions alternating along its surface.

4. The invention in accordance with Claim 1 wherein said contoured surface is a stepped surface.

5. The invention in accordance with Claim 1 wherein said non-linear spring means is an elastomeric ring.

6. The invention in accordance with Claim 4 wherein said ring has crowned surface portions and concave portions alternating around said ring.

7. The invention in accordance with Claim 5 wherein said ring has a stepped surface with different elevations alternating around said ring.

8. An elastomeric non-linear spring means for use in an electromagnetic exciter comprising: a block of elastomeric material having a contoured surface.

9. The invention in accordance with Claim 8 wherein said surface is a crowned surface.

10. The invention in accordance with Claim 7 wherein said contoured surface is a stepped surface having different spring thicknesses.

11. The invention in accordance with Claim 8 wherein said block of elastomeric material is an elastomeric ring having an undulating surface.

12. The invention in accordance with Claim 11 wherein said undulating surface is a series of steps alternating in elevation around said ring.

13. An electromagnetic vibratory exciter as claimed in Claim 1 and substantially as described with reference to or as shown bythedrawings.