WO2001038209A1

WO2001038209A1 - A high stroke, highly damped spring system for use with vibratory feeders

Info

Publication number: WO2001038209A1
Application number: PCT/US2000/041613
Authority: WO
Inventors: Harold E. Patterson
Original assignee: Fmc Technologies, Inc.
Priority date: 1999-11-29
Filing date: 2000-10-26
Publication date: 2001-05-31
Also published as: JP2001151328A; AU2619701A

Abstract

A vibratory conveying feeder (10) includes a trough (11) mounted by springs (27) and spring assembly (106) to a base (39) with a vibratory driver (50) bonded to the base and connected to the trough. The springs include a first vertically oriented spring (27) at a front of the conveyor connected between the base and the trough and a second spring assembly (106) arranged between the trough and the base and arranged along a line about 20° to the horizontal. The second spring assembly (106) is removably mountable in the base of the conveying feeder to facilitate repair and/or replacement of the spring assembly. This configuration facilitates configuring the conveying feeder for different types of applications, including conveyance of different types of materials at various feed rates.

Description

A HIGH STROKE, HIGHLY DAMPED SPRING SYSTEM FOR USE WITH VIBRATORY FEEDERS

Field of the Invention

The present invention relates to vibratory feeders and particularly to two mass electromagnetic vibratory feeders for conveying materials.

Background of the Invention

This invention relates to a substantial improvement of an existing high stroke, highly damped spπng system design disclosed in U.S. Patent No. 5,967,294 granted to Harold E. Patterson and Bπan V. Mclntyre. Many applications for vibratory feeders require high conveying feed rates Feed rates on a vibratory feeder are a function of the operating frequency (number of vibration cycles per second), stroke (displacement magnitude) of the conveying surface, and the stroke angle with respect to a hoπzontal reference plane. In a two-mass, electromagnetic vibratory feeder a longitudinal conveying member, the trough, is usually disposed above a base member and connected to the base member by means of a system of spπngs. The spπngs are connected to the trough and base members at an angle, such that the spπng connection of the trough would be displaced a distance from a vertical reference that passes through the center of the spπng connection on the base member. An armature of an electromagnet is connected to one of the base or trough members, usually the trough member, and the electromagnet core and coil is connected to the other The base member is usually isolated from its support structure by coil spπngs, or elastomer spπngs to minimize unwanted forces from being transmitted into the support, and surrounding structures.

When an electπc current is caused to flow through the magnet, the armature and magnet pole faces are rrutually attracted to each other, causing the spπngs to deflect, and displacing the trough and base from their rest position When the current is removed, the magnet releases, and the energy stored in the spπng system by deflection, causes the trough and base to return to their rest positions and onward to a deflection in an opposite direction to a maximum position where the trough and base will once again change directions back toward the rest position. If the current is then reapphed, the process is repeated If the current is turned on and off at a uniform rate, the trough and base will be deflected at that rate, or frequency.

Typically, electromagnetic dπven vibratory feeders are operated at a frequency determined by the power line frequency, or at half of the power hne frequency by use of a diode rectifier, or by use of a permanent magnet as part of the electromagnetic drive system. Examples of such feeders are those manufactured by FMC Corporation of Homer City, Pennsylvania, under the trade name SYNTRON In such feeders, the frequency is fixed at 120 Hz or 60 Hz in North Ameπca, and 100 Hz or 50 Hz (usually 50 Hz) in most other countries of Europe or Asia. Since the frequency at which these feeders operate is fixed, only the stroke and stroke angle can typically be adjusted to optimize the feed rate. The stroke magnitude of these feeders is constrained by the amount of magnetic force available to deflect the spπng system, and ultimately by the stress limitations of the spπng system and the structural members of the feeder.

The two-mass feeder takes advantage of the natural amplification of the stroke due to resonance, by adjusting the natural frequency of the mass/spπng system to be close to that of the operating frequency. This assures that there will be sufficient power available to operate the feeder with a reasonably sized electromagnet Typical maximum stroke values for these feeders operating at 60 Hz is 0.0625 inches to about 0 1 inches, and at 50 Hz, is about 0.09 inches to about 0.144 inches.

The equation for acceleration of the trough, assuming sinusoidal motion may be stated as: Equation #1 , = N² • A, /70400 where a_] = the acceleration of the trough along the linear dπve line, N = the operating frequency m cycles per mmute; A, = the stroke of the trough in inches; and 70400 is a constant derived from equation simplification, and conversion to the unit measure value as shown above. For the trough strokes and frequencies given, the accelerations at both 60 Hz and 50Hz range from 1 1.5 g's, to 18 g's. As can be seen, the acceleration is heavily influenced by the operating frequency, because the acceleration vanes with the square of a change m frequencies, but vanes only proportionally to a change m stroke.

Feed rate is also dependent on the angle at which the acceleration is applied to the trough member of the feeder. As the trough is linearly accelerated along a path defined by the spnng angle, any point on the trough is therefore subjected to both a honzontal and a vertical component of the acceleration. The vertical component, again assuming sinusoidal motion, may be expressed Equation #2 «, = a_t sin (α) where Ω_V = the vertical component of the trough acceleration a_t in g's; α - the spnng angle

As the trough is accelerated, a particle resting on the trough surface will be accelerated with the trough, and at a point where the vertical acceleration of the particle exceeds -1 g, the particle will separate from the trough's surface, taking flight. The particle, by force of gravity, will return to the trough surface displaced at some distance from the point where it took flight, depending on the amount of acceleration and the angle at which it was applied. Starting with a spπng angle of 0, the feed rate would, for practical purposes, also be zero, as only the hoπzontal component of the trough acceleration would be present As the spπng angle increases, the feed rate also increases, until the optimum feed rate for that combination of frequency, stroke and spπng angle is reached. At some angle, the feed rate would start to decrease again, and will continue to decrease as the spπng angle decreases, with violent bouncing of the matenal being conveyed as the spπng angle approaches 90° If the particles separated from the trough return to be m contact with the trough within the same vibration cycle, but at a point on the trough acceleration curve where the particle can be again accelerated to the same level as the previous cycle, it is referred to as the "first stable feed zone". Likewise, if the particle leaves the trough, and comes back m contact with the trough in the next vibration cycle, again at a point on the trough acceleration curve where it can stabilize, it would be referred to as conveying in the "second stable feed zone", and so on for particles landing m three or four vibration cycles. There exists between these stable feed zones acceleration regions where the particle cannot be uniformly accelerated between landings. In these unstable zones, feed rate is indeterminate by calculation, but the net result in practice is a decrease from the feed rate obtained just pπor to the unstable zone.

While very high feed rates can be realized from operation in the higher stable feed zones, there are practical reasons that make such operation difficult. These regions are very sensitive, because small changes in feed angle, stroke, surface friction, etc., can result in major changes to the feed rate, for example. Also, at the acceleration levels involved, it would be difficult to design structures and spnng systems for such high frequency electromagnetic equipment, and have the structures and spnng systems survive the stress levels involved For these reasons, electromagnetic feeders are usually limited to operation m the first or second stable feed zones.

Another concern of operating a feeder in higher acceleration regions is the possible damage to the material being conveyed from high impact speed between the mateπal particles and the trough surface, as mateπal particles, accelerated by gravity, land back on the trough after flight. As an accelerated particle separates from the trough surface m flight, depending on its acceleration and hence its flight time, it may land back on the trough surface such that the velocity of the trough adds to the velocity of the particle when they collide, resulting m a high impact force. It is necessary, therefore, to choose combinations of frequency, stroke and feed angle that minimizes impact speed without sacrificing too much feed rate. In the case where the frequency is fixed and the stroke is controllable, it is important to select a feed angle that results in the best compromise between impact speed and feed rate. Often concerns about product damage from high impact collisions between the material and the trough preclude operation m the second and higher feed zones.

In order to have uniform rate along the entire length of the trough member of the feeder, it is advantageous that the feed angle and stroke be uniform along the entire length of the trough member, as well. In order to accomplish this, it has been suggested that the dnve force could be applied along a linear, angular path, such that it passes through the center of gravity of the base mass, trough mass, and the effective center of gravity of the system as a whole. By so aligning the drive force, in theory, the trough and base masses would not generate inertial forces about their respective mass centers to form a force couple that would cause the feeder to rotate or to pitch longitudinally on its isolation system.

In practice, it is difficult to align the center of gravity because of the constraints imposed by the geometry of the feeder and its installation constraints. Balancing weights would be required to mount onto the base or trough, as the case may be, to align the center of gravity. The balancing weights add unwanted mass to the feeder, add to cost, and detract from its performance

Often, as in the case of small feeders used to feed product to vertical weigh scales, it would be virtually impossible to dynamically balance the feeder, because the space limitations of the scale require a feeder with an extremely short base. Prior patents such as U.S. Patent Nos. 3,216,556, 4,260,052 and

4,356,91 1 descnbe methods and apparatus to compensate for the dynamic mertial force couple. These devices compensate by independently adjusting the feeder spπng angles relative to one another, such that they cause a rotation of the trough that opposes the rotation caused by the mertial force couple. With this method, however, it is difficult to adjust the spπng angles correctly to achieve uniform motion, and each individual feeder manufacturer requires its own unique adjustment. This requirement for adjustment adds considerable cost to manufactuπng, making it difficult to compete m a high volume, low cost market. Also, the adjustable spπng angle feature places geometric restraints on the feeder design, such as a minimum length requirement, making it difficult to be adapted for use m a weigh scale feeder. For a weigh scale feeder it is important to be able to reduce the size of the feeder, advantageous because such would enable the scale manufacturer to reduce the height and overall size of the equipment, making such equipment more cost effective.

Another problem often encountered m applying electromagnetic feeders, particularly where a high stroke feeder is required to start and stop frequently, is that mateπal continues to feed for an instant after the electπc power is removed from the feeder magnet This phenomena is known as "coasting", and is caused by the combination of inertia and low spnng system damping, and can be a problem for the user, particularly m a weighing application, where the overfeed can add up in lost mateπal and lost revenue. External damping means can be added to the feeder to reduce the coasting problem, such as adding dash pots and the like, but since dampers use energy, there often is insufficient power to maintain the high stroke required for the desired feed rate while m operation

Also, another source of overfeeding after shutoff is that due to the angle of repose of the matenal, if the mateπal is poured from a container onto a surface unconstrained, it will form a conical pile. The angle formed between the base of the pile and its slope, is the angle of repose for that mateπal. If the bed depth of the feed is very deep, as might be required with lower feed rate feeders in order to maintain capacity, and the feeder is stopped, mateπal falls from the discharge lip of the trough until the angle of repose of the mateπal has been reached Often m the past, mechanical gates have been used to prevent matenal from discharging due to this phenomenon, but again this adds to increased equipment costs. Another concern of users of these feeders include the requirement in some applications of a sanitary service type of construction, for example for food as feed mateπal, with few if any places allowable where particles of feed material can collect. Other concerns include: the ease of cleaning the feeder, an effective vibration isolation of the feeder that minimizes any forces being transmitted to the feeder support structure, a low maintenance with easy access to adjustment devices, and a low operating noise level.

It would be desirable to provide a vibratory feeder that advantageously addresses the above concerns and would be useful in meeting the requirements of the vertical and linear weigh scale feeder markets. In these vertical and linear weigh scale feeder markets there exists a large and diverse application base that require custom features for the feeder trough geometry (i.e. it's length, width, height, shape etc.) resulting in a broad range of trough weights and sizes that must be accommodated by the feeder dπve. Also, to obtain desired feed rates over such a range of feeder applications and trough designs becomes a challenge, as does the need to maintain structural mtegπty of the feeder trough at the same time.

Addressing these needs and the other objects, features, and advantages of this invention are evident from the following descπption of a preferred embodiment of this improvement invention, with reference to the accompanying drawings. Summary of the Invention

The present invention is an improvement to the design disclosed in U.S. Patent No. 5,967,294 which contemplates additional features that address the broad range of trough weights and sizes that must be accommodated by the feeder dπve.

In the design of the present invention, the conveyor includes a base (such as disclosed in U.S. Patent No. 5,967,294) having a hoπzontal portion, and a rising vertical portion at the rear of the base. The πsmg vertical portion includes a front facing surface which is angled backwards toward the rear of the base and which includes an obliquely arranged cavity therein. The cavity of the present invention is of a rectangular shape, square in the disclosed embodiment, that is milled entirely through the rising vertical portion of the base from the front facing surface through to the rear of the base. As in U.S. Patent No. 5,967,294, a trough is mounted over the base and supported by a first vertical spπng on one side of the base and a second obliquely arranged spπng held withm the cavity and extending toward the trough at between 10° and 45°, and preferably at about 20° to the hoπzontal. Said obliquely arranged spπng consists of two elastomer spπng elements sandwiched between and bonded to two outer steel compression plates and a middle steel spπng connecting bracket The spπng is pressed into the cavity such as to compress the elastomer spnng elements by a known amount so as not to let the elastomer spπng elements go into tension dunng operation of the feeder. Also, the rate of the second spπng can be adjusted to be up to 90% of the total spring rate, to allow more flexibility in handling heavier and longer feeder troughs, and represents an even greater portion of the spπng rate required for the entire feeder, so that a damping coefficient for the feeder is achieved that is more than three times that of some known feeders of the same size and capacity Further, the feeder of the improvement invention is designed to take advantage of operation at lower input power frequencies and higher trough amplitudes of up to 0.25 ms. for even greater flexibility in maintaining high feed rates over the range of trough designs, while minimizing damaging feed product impact speeds, and while maintaining structural integnty of the trough through reduced accelerations

Other features and advantages of the present improvement invention will be apparent from the following detailed descπption, the accompanying drawings, and the appended claims Brief Description of the Drawings

Figure 1 is a side view of the U.S. Patent No. 5,967,294 vibratory feeder invention, with portions removed for clarity, and provided for comparison and reference purposes; and Figure 2 is a diagrammatic side view of the vibratory feeder drive, with portions removed for clarity, illustrating the improvements of the present invention. Detailed Description of the Preferred Embodiments

While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described presently preferred embodiments with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated.

Figure 1 illustrates a two-mass electromagnetic vibratory feeder which embodies the invention of U.S. Patent No. 5,967,294, and is included for reference and comparison purposes. U.S. Patent No. 5,967,294 is herein incorporated by reference.

Figure 1 illustrates a two-mass electromagnetic vibratory feeder 10 as disclosed in U.S. Patent No. 5,967,294. This vibratory feeder 10 would be particularly useful for weigh scale applications. A trough 1 1 is supported by ribs 12, 13 which are in turn connected to a mounting bracket 14. The mounting bracket 14 is supported on a mounting pedestal 15. The pedestal 15 is connected to a spring-mounting bracket 16. The pedestal 15 is typically connected to the spring mounting bracket 16 by threaded studs protruding from blind tapped holes extending from the mounting bracket 16 (not shown) and connected to the mounting pedestal 15 with suitable washers and nuts.

The mounting pedestal 15 is used as a means for the weigh scale manufacturer to seal the drive section of the scale feeder from the scale head for sanitary concerns. A circular plate (not shown) having cutouts to receive the mounting pedestal 15 is positioned above the feeder drive. The mounting pedestal 15 protrudes through the cutout and is sealed from below by means of a soft rubber boot (not shown) connected between the mounting pedestal 15 and the circular plate.

The trough 1 1 is bolted to the mounting pedestal 15 using suitable mounting hardware (not shown). On an outside face of one end of the spπng mounting bracket 16, one or more leaf spπngs 27 are connected by means of a spπng clamp bar 23a and a plurality of countersunk Allen-head fasteners 28 which pass through the spπng mounting bracket 16 and are threaded into tapped holes of the electromagnet armature 29. The other end of the spπng mounting bracket 16 is bent to facilitate its connection to a tab 30 on a hub 32 of an annular elastomer spnng assembly 35. The spnng assembly 35 also includes an annular elastomer spπng element 36 which extends to an annular surface 37 withm the cavity 38.

An L-shaped base casting 39 supports the spπng mounting bracket 16 via the spπngs 27,36. The inner surface 36a of spπng element 36 is cemented to the hub 32, while its outer surface 36b is cemented into a cavity 38 which is machined into an upstanding leg 39a of the feeder base casting 39, such that its longitudinal axis 36c is perpendicular to the slope of an upper front facing surface 39b of the leg 39a of the feeder base casting 39. The front facing surface 39b of the feeder base casting 39 slopes upward and away from the vertical axis in a direction to the rear of the feeder, such that the angle A formed between this edge and a vertical line is between 10° and 45 ° and preferably about 20° Thus, the longitudinal axis 36c is set at between 10° and 45 °, and preferably about 20° to the horizontal. In the center bottom of cavity 38, a hole is dnlled to form a channel 40 which in turn is obliquely connected to a further channel 42 formed by drilling a hole extending axially upward through a dnlled and tapped mounting hole 43 used to connected to a rear coil spnng isolator 44 to the feeder base casting 39 The remaining end of the leaf spnng assembly 27 is connected to a bottom leg 39c of the feeder base casting 39, at a lower front face 39b thereof, utilizing a second spπng clamp bar 23b and Allen-head fasteners 28.

The magnet core and coil assembly 50, consisting of iron laminations 52, a polyurethane molded and encapsulated coil 58 wound on the laminations, and magnet mounting/adjusting bracket 60, is mounted to the feeder base casting 39

The lower portion of the magnet core and coil assembly 50, is mounted within a through cavity 62 of the feeder base casting bottom leg 39c, and the magnet mounting/adjustment bracket 60 is mounted on the machined flat surfaces 70 formed by the upper longitudinal edges of the through cavity 62. Fasteners 71 pass through slotted holes (not shown) in the magnet mounting/adjustment bracket 60 and are threaded into drilled and tapped holes in the machined flat surface 70 to connect the magnet core and core assembly 50 to the feeder base casting 39. The pole face 73 of the magnet core and coil assembly 50, is aligned to be uniformly parallel with the magnet armature 29 that is mounted to the spnng mounting bracket 16, utilizing the slotted holes of the magnet/mounting adjusting bracket 60, and held m place by tightened fasteners 71 , thus forming a uniform air gap 75 between the pole face 73 and a face 29a of the magnet armature 29.

Two circular cutouts 76 are machined in the lower front corners of the feeder base casting 39, forming a plate 78 in each corner between the upper surface of the feeder base casting 39, and the top of the cutout. Holes are dnlled m the center of each cutout through the plates 78 thus formed. Two front coil spπng isolators 80 are mounted in the cutout 76 of the feeder base casting 39, and connected to the feeder base casting 39 by means of the fasteners 84 passing through the holes 86, and tightened m place using acorn nuts 88.

The rear coil spπng isolator 44 is mounted in a recess 90 machined perpendicularly into the rear center of feeder base casting 39, by means of a fastener 92, threaded into the drilled and tapped hole 43 m the center of the recess 90. A slot 93, to position and provide a strain relief means for the electromagnet power cord (not shown), is machined in the bottom of the feeder base casting 39, extending longitudinally from the rear of the feeder base casting 39, to the edge of through cavity 62, where the slot is enlarged to accommodate connection to the magnet coil.

Figure 2 illustrates the improvements to the two-mass electromagnetic vibratory feeder dnve 105 of the present invention. This vibratory feeder drive

105 is an improvement of the feeder dπve of U.S. Patent No. 5,967,294 for weigh scale applications because the improvements allow more flexibility in handling a broader range of trough geometry and weights while maintaining high feed rates, and minimizing damaging feed product impact speeds. Also, the design maintains structural integnty of the trough through reduced accelerations.

A trough (as shown m Figure 1 ) is supported by πbs which are m turn connected to a mounting bracket. The mounting bracket is supported on a mounting pedestal. The pedestal is connected to the spπng-mountmg bracket 16, all as shown m Figure 1. The pedestal is typically connected to the spπng mounting bracket 16 by threaded studs protruding from blind tapped holes extending from the mounting bracket 16 and connected to the mounting pedestal with suitable washers and nuts.

As m Figure 1 (and U.S. Patent No. 5,967,294), the mounting pedestal is used as a means for the weigh scale manufacturer to seal the dπve section of the scale feeder from the scale head for sanitary concerns. A circular plate (not shown) having cutouts to receive the mounting pedestal is positioned above the feeder dπve 105. The mounting pedestal protrudes through the cutout and is sealed from below by means of a soft rubber boot (not shown) connected between the mounting pedestal and the circular plate.

The trough is bolted to the mounting pedestal using suitable mounting hardware. On an outside face of one end of the spπng mounting bracket 16, one or more leaf spπngs 27 are connected by means of the spπng clamp bar 23a and the plurality of countersunk Allen-head fasteners 28 which pass through the spring mounting bracket 16 and are threaded into tapped holes of the electromagnet armature 29.

One end of a spnng connecting bracket 102, of an obliquely mounted spπng assembly 106, is bent to facilitate its connection to the remaining end of the spπng mounting bracket 16 Through holes 107 in the spπng connecting bracket 102 are aligned with matching through holes 108 m the spπng mounting bracket 16, and suitable fasteners (not shown) placed m the through holes are used to fasten the two brackets together. The spπng assembly 106 also includes two rectangular shaped elastomer spnng elements or blocks 101 sandwiched between and bonded, by glumg or vulcanizing, to two outer rectangular shaped steel compression plates 100, and a middle rectangular shaped steel spπng connecting bracket 102, such that one surface of one elastomer spπng element 101 is bonded to the surface of one steel compression plate 100, while the opposite surface of said elastomer spπng element 101 is bonded to the surface of one side of the steel spπng connecting bracket 102. Likewise, one surface of the remaining elastomer spπng element 101 is bonded to the surface of the opposite side of the steel spπng connecting bracket 102, while the opposite surface of said remaining elastomer spπng element 101 is bonded to the surface of one side of the remaining steel compression plate 100. The spπng assembly 106 is then pressed into a rectangular shaped cavity 103 such to compress the elastomer spπng elements 101 by a known amount so as not to let the elastomer spπng elements go into tension dunng opeiation of the feeder.

Unlike the feeder dnve disclosed m U.S. Patent No. 5,967,294, where the obliquely arranged spπng assembly disclosed an elastomer element having fixed dimensions for length and thickness, the length of the spπng assembly 106 may be vaπed as indicated in Figure 2 by dashed lines 110. Also, by using thicker or thinner plates for the steel compression plates 100, and the spπng connecting bracket 102, the elastomer spnng elements 101 may be made thicker or thinner to be able to vary the initial spnng rate of the assembly 106. It would also be possible to enlarge the size of the cavity 103 by machining to enlarge the design of the spnng assembly 106 for special applications as may be required.

The L-shaped base casting 39 supports the spπng mounting bracket 16 via the spπngs 27, and the spπng assembly 106. The rectangular cavity 103 is machined completely through the upstanding leg 39a of the feeder base casting

39, such that its longitudinal axis 109 is perpendicular to the slope of an upper front facing surface 39b of the leg 39a of the feeder base casting 39. The front facing surface 39b of the feeder base casting 39 slopes upward and away from the vertical axis in a direction to the rear of the feeder, such that the angle A formed between this edge and a vertical line is between 10° and 45° and preferably about 20° Thus, the longitudinal axis 109 is set at between 10° and 45°, and preferably about 20° to the honzontal.

The dnlled and tapped mounting hole 43 is used to connect the rear coil spnng isolator 44 to the feeder base casting 39. The remaining end of the leaf spnng assembly 27 is connected to the bottom leg 39c of the feeder base casting

39, at the lower front face 39b thereof, utilizing the second spπng clamp bar 23b and Allen-head fasteners 28

The magnet core and coil assembly 50, consisting of iron laminations 52, the polyurethane molded and encapsulated coil 58 wound on the laminations, and the magnet mounting/adjusting bracket 60, is mounted to the feeder base casting 39. The lower portion of the magnet core and coil assembly 50, is mounted within a through cavity 62 of the feeder base casting bottom leg 39c, and the magnet mounting/adjustment bracket 60 is mounted on the machined flat surfaces 70 formed by the upper longitudinal edges of the through cavity 62 Fasteners 71 pass through slotted holes (not shown) m the magnet mounting/adjustment bracket 60 and are threaded into drilled and tapped holes in the machined flat surface 70 to connect the magnet core and core assembly 50 to the feeder base casting 39 The pole face 73 of the magnet core and coil assembly 50, is aligned to be uniformly parallel with the magnet armature 29 that is mounted to the spπng mounting bracket 16, utilizing the slotted holes of the magneϋmounttng adjusting bracket 60, and held in place by tightened fasteners 71 , thus forming a uniform air gap 75 between the pole face 73 and the face 29a of the magnet armature 29.

Two circular cutouts 76 are machined m the lower front corners of the feeder base casting 39. Holes 43 are drilled and tapped in the center of each cutout. Two front coil spnng isolators are mounted in the cutouts 76 of the feeder base casting 39, and connected to the feeder base casting 39 by means of the fasteners 92.

The rear coil spnng isolator 44 is mounted in a recess 90 machined perpendicularly into the rear center of feeder base casting 39, by means of a fastener 92, threaded into the drilled and tapped hole 43 in the center of the recess 90 A slot 93, to position and provide a strain relief means for the electromagnet power cord (not shown), is machined in the bottom of the feeder base casting 39, extending longitudinally from the rear of the feeder base casting 39, to the edge of through cavity 62, where the slot is enlarged m expanding slot to accommodate connection to the magnet coil

In order to address the need to apply a broad range of trough weights and sizes that must be accommodated by the feeder dπve, more flexibility is required from the feeder drive design. As the troughs become heavier, more spring rate is required, but since the dπve must also be able to carry light weight troughs as well, provision must be made to accommodate a broad range of spnng rates while maintaining the desirable damping effects of the design While the spnng rate could be changed by adding more or less of the fiber glass spπngs 27 it would defeat the damping feature needed to reduce coasting. The heavier the trough the greater the coasting phenomena due to its greater inertia, therefore varying the size of the elastomer spπng assembly 106 to increase or decrease rate and damping as required solves this problem. Since the elastomer spnng assembly 106 with it's high damping coefficient now provides up to 90% of the total spnng rate of the feeder, a damping coefficient for the feeder is achieved that is more than three times that of some known feeders of the same size and capacity.

The elastomer spring assembly 106 is only pressed into the cavity 103, and is replaceable. The cavity 103 is sized to have an opening smaller than the height of the uncompressed elastomer spring assembly 106 by an amount equal to the required precompression of the elastomer spring assembly 106 so that the elastomer spring elements are prevented from going into tension as the feeder strokes back and forth during operation. If the elastomer springs were allowed to go into tension they would over heat and melt, particularly at the edges of the bonded areas, and eventually destroy themselves. The greater the stroke, the greater the amount of precompression is required and also the thicker the elastomer element 101 must be.

As noted, by using thicker or thinner plates for the steel compression plates 100, and the spring connecting bracket 102, the elastomer spring elements 101 may be made thicker or thinner to be able to accommodate a wide range of strokes (precompression) providing a design flexibility improvement.

Also, the spring rate must be tuned to the trough weight, i.e., the heavier the trough the greater the spring rate must be to maintain the required tuning relationship close to resonance, as disclosed in U.S. Patent No. 5,967,294. The length of the spring assembly 106 can be made longer or shorter, as indicated by the dashed lines 1 10 in Figure 2, to change the initial spring rate to provide more flexibility to handle a broad range of trough weights.

The force required to press the spring assembly 106 into the cavity 103 and precompress the elastomer spring elements 101 is sufficient to hold the spring assembly 106 in place as the feeder operates, in contrast to the spring elements disclosed in U.S. Patent No. 5,967,294 which were epoxied in place. This adds to the flexibility of the feeder of the invention, by allowing springs to be changed, for example, to repair a damaged spring, or to change the spring rate of an existing feeder to accommodate a change to the trough weight. Another area in utilizing the flexibility of the spπng assembly 106 is the ability to accommodate much longer trough members than those depicted m U.S. Patent No. 5,967,294. Such long trough members produce a force couple, created by the mertial unbalance due to misalignment of the center of gravity of the feeder trough and base. The force couple would result m unwanted pitching of the frough if it were not for the compensation created by the dynamic rotational effect of the combination of the vertical spπng 27 and the spπng assembly 106, where the elastomer spπng elements 101 can be made long and thinner to maintain the required spπng rate and stroke, while producing a longer moment arm and increased damping.

Also, the feeder of this invention, due to the flexibility of the spπng assembly 106, is capable of operating at lower frequencies (speeds). Operation at lower frequencies is often advantageous as it is possible to find stroke, stroke angle, and frequency combinations that result m high feed rates, low impact speeds, and lower accelerations. Such operation usually lies in the first stable feed zone providing stable feed rates, as well as the low impact speed resulting in reliable feeder application. Also, the characteπstics of many feed matenals, such as leafy or spongy mateπal, respond much better to the long strokes at lower frequencies. The spπng assembly 106 of this invention allows the use of thicker, longer elastomer elements 101 required to obtain the required strokes involved, over a large range of trough geometry's and weights. Available controls (not shown in the figures) such as the sub line frequency control model UMC-1 from FMC Corporation of Homer City Pa., the ATAC control available from T.S. Engineeπng Inc. of Eastlake Oh., and the vertical weigh machine's controller from Yamato Scale Co. of Japan are capable of producing the required operating power frequencies. Controls such as the ATAC and that of Yamato Scale's are capable of providing continuously vanable frequency output, which is advantageous because subtle changes, such as aging of the elastomer spπng that might result in a drop off of feed rate over time, can be compensated for by changing the operating frequency to keep the relationship between operating frequency and the natural frequency of the feeder such to maintain feed rate. Some controls such as the control in the Yamato Scale can automatically maintain the required relationship between the feeder natural frequency and the operating speed by closely monitoring the feed rate. From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1. A vibratory conveyor, compnsmg; a base having a spnng cavity; a trough; a vibratory dnve mounted to said base and connected to said trough to impart vibration thereto; a first spπng connected to said trough at one end thereof and to said base at an opposite end thereof, and a second spnng connected at one end to said frough, said second spπng arranged with a spπng axis at an angle to hoπzontal, said second spπng including at least one elastomer block press-fit into said spπng cavity.

2. The vibratory conveyor according to claim 1, wherein said second spnng compnses about 90% of a total spπng rate including said first spnng and said second spπng. 3. The vibratory conveyor according to claim 1, wherein said second spπng compnses a connecting bracket connected to said trough, first and second compression plates, and first and second elastomer blocks, said elastomer blocks adhesively affixed to said connecting bracket and each of said elastomer blocks adhesively secured to one of said compression plates, which are pressed to the sidewalls of said cavity.

7. The vibratory conveyor according to claim 1 , wherein said second spπng is shdably removable from said spπng cavity.

8. The vibratory conveyor according to claim 7, wherein said at least one elastomer block is rectangular. 9. The vibratory conveyor according to claim 1 , wherein said second spπng compnses a connecting bracket mechanically connected to said trough, ar^r' said at least one elastomer block compnses two elastomer blocks secured to said connecting bracket on opposite sides thereof and compressed withm said spπng cavity in a direction normal to said spπng axis.

10. The vibratory conveyor according to claim 9, wherein said elastomer blocks are compressed by said spring cavity in a direction normal to said spring axis and are compressed by an amount to always be in compression during each stroke of said vibratory conveyor.

11. The vibratory conveyor according to claim 1 , wherein said at least one elastomer block is compressed by said spring cavity in a direction normal to said spring axis and is compressed by an amount to always be in compression during each stroke of said vibratory conveyor.