Patent Publication Number: US-2023158549-A1

Title: Vibrating screening feeder and method of use

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This is a Continuation application of U.S. application Ser. No. 17/130,339 filed on Dec. 22, 2020 which is a Continuation of U.S. Ser. No. 15/741,655 filed on Jan. 3, 2018 now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of industrial vibrating screens for separating small elements from large elements, such as in the case of coal or stone. 
     BACKGROUND OF THE INVENTION 
     In the handling of particulate bulk material, there are numerous ways for conveying such material and feeding it over an open end of the conveyor to a desired point of delivery. This invention is concerned with a conveyor or feeder vibrated as a free mass, i.e., the trough or conveyor is suitably isolated from the ground so that it may be vibrated in response to an oscillating force, as distinguished from a mass which is positively connected to the exciting force, as, for example, by driving the conveyor through an arm rigidly connected to a fixed stroke eccentric drive. 
     Vibrating screens are in use in numerous industrial situations where the necessary separation of dust and fine particles of a given product is necessary. For example, electrical utility companies burn coal, which must be delivered to the boilers in almost powdered form and screening of the coal aggregate is necessary in very great volumes. 
     Conventional mechanical means operate by varying the frequency or the stroke of the feeder. An exception to mechanical means for adjusting rates of feed is in the case of an electromagnetic drive for a feeder, in which case the frequency or the voltage of the applied pulsating current applied to the electromagnetic drive is varied. However, in this type of device the vibrations per minute used are generally above 1800 cycles per minute and have relatively short strokes with the result that such feeders are limited to bulk materials of the more free-flowing type as distinguished from those which are characterized as damp or viscous. 
     Mechanical means may include a variable rate spring device such as an air bag interposed in the drive with the pressure in the air bag being adjustable to effect the change of spring rate, or some form of mechanical adjustment of the drive motors angularity or position relative to the pan. There have been many attempts, in vibratory feeders, to utilize some form of adjustable feed rate control using electrical phenomena, but to date none of these have been successful for a number of reasons. The electromagnetic type vibrators have high energy losses and are restricted to essentially high frequency and short stroke combinations. Low frequency, long stroke devices have been conceived that utilize adjustable frequency A.C. drives, multi-speed, and/or multi-winding A.C. motors, or adjustable voltage D.C. drives which have not met with success because of high initial cost, and the cost of maintenance due to brush wear, commutator problems and the like. 
     Induced conveying improves material handling in applications where different kinds of solid fuels are used to produce heat in a boiler with a vibrating stoker grate that burns it. The vibratory feeders and screens induce the fuel&#39;s movement instead of forcing it. This avoids squeezing and bunching the fuel. The Particles remain loose which facilitates more efficient burning. Some power plant boilers are fired by fuels such as coal meeting a demanding specification wherein the fuel met the designation of “steam coal” having a particle size, density, and moisture content specified for efficient combustion. 
     When fuel is scarce because of shortages uncleaned run-of mine (ROM) coal and the waste coals such as culm, gob, silt, or high moisture “wet” coal are burned, especially in countries having economic difficulties. The biomass fuels of bagasse, wood waste such as bark, chips, shavings, and sawdust fuel is used to fire boilers. Refuse derived fuels (RDF) which is shredded municipal waster and whole or shredded rubber tries can also be sources of fuel. Density and moisture content are difficult to control. The induced vertical flow and induced conveyance flow provided by vibrating feeders, screens, and conveyors are used because these fuels are usually obstinate to flow from storage. 
     Generally, a vibrating screen is fixedly mounted in a screen housing with supporting frame work. The screen housing is then supported above a fixed base by springs or rotatable arms. The screen housing is caused to vibrate by some sort of drive which shakes the housing. Some drives are fixed to the base and connected by a crank journal to the vibrating screen housing. The prior art illustration shown in  FIG.  1    shows a fixed base member  102 , a motor  112  and a crank journal  114  driving a vibrating screen housing  108  which is movable relative to the fixed base  102  about rotating arms  104  with damper springs  20 . Other drives consist of a motor fixed to the vibrating screen housing driving eccentric weights which then cause the screen housing to vibrate. These units have inherent disadvantages such as difficulty of changing or repairing motor drives and large energy consumption. 
     In the vibratory industry, vibratory conveying apparatus such as vibrating feeders, vibrating conveyors, vibrating screens, vibrating heat transferring fluidized beds, attrition mills, and the like, were all powered by a well-known and popular driving method called the “Single Input” or “Brute Force” type of drive. A single pair of rotating eccentric weights is the sole source of the input power in this kind of drive. Being installed directly across from one another, a single pair of eccentric weights rotating in opposite directions vibrate the vibratory conveying apparatus with a linear or “back and forth”, straight line motion. As the load carrying capability of the conveying apparatus increased over the years, the weight of the rotating eccentric weights also necessarily increased in size, and the horsepower demand of the electric motor utilized to rotate the eccentric weights increased accordingly. 
     When more input power is needed to move heavier loads along the length of the conveying trough, more rotating eccentric weight force and horsepower are needed. Consequently, the rotatable eccentric weights become larger and heavier and have a greater force output. Likewise, the electrical windings in the vibratory motor increase in size to produce more horsepower. This increase in eccentric weight force output and the respective vibratory motor horsepower has approached the point that the vibratory motors are presently as large as practical to manufacture or to utilize on a vibratory conveying type of apparatus. 
     Electric motor applications attempt to match motor torque operating characteristics with load torque characteristics. Conventional electric motor applications teach that an AC. squirrel cage motor is not to be used for adjustable speed drive, because the load torque requirements are such that when an attempt is made to substantially alter speed through change in voltage, the motor is overloaded and will burn out, except in the case when the motor drives a fan or a pump which is used in moving a fluid, wherein the load torque requirements are consistent with the thermal capability of a squirrel cage motor. 
     In the present invention it is possible to use an A.C. squirrel cage motor and adjust the voltage thereon to vary the feed rate of the vibratory system is because the vibratory system is of the free mass, natural frequency type, that is, the motor exciter drive is a part of a natural frequency vibratory system and the vibratory system is isolated from ground, as distinguished from a vibratory system which is driven positively from a fixed stroke rotary eccentric member as best described by Applicant prior U.S. Pat. No. 3,251,457 for a Method and Apparatus for Driving Vibratory Devices which issued in 1965 and is incorporated by reference herein in its entirety. 
     As the system operates below natural frequency, the mass inertia vector is diminished, the spring effect is diminished, the damping losses are diminished, and the applied force is subdivided into a horizontal and vertical component, with the horizontal component matching the damping losses, and the vertical component acting in opposition to the spring effect. This in itself creates a mechanical impedance on the motor resulting in the stroke of the feeder being diminished, and explains why the current drawn by the motor, which is proportional to the damping losses, diminishes as one moves below natural frequency. Therefore, an AC. squirrel cage motor may be used effectively to change the speed of the motor and a natural frequency resulting in a free mass vibratory system. 
     Watts, volts, amperes, and stroke characteristics vary exponentially in relation to speed, and that a small change in speed causes a marked change in feed rate, current, and watts, which explains why the feed rate can be changed in this manner without burning up the motor. The load torque characteristics of the motor are being matched with the load torque demands of the vibratory mass system. 
     It is the objective of this invention to operate as near the peak of the curve as is possible for maximum feed and normal load conditions. As a practical matter, the spring rates are chosen for a load condition to have the system operate when the vibrating screening feeder is carrying a normal load. As voltage is reduced on the motor to move from maximum feed rate to a lesser feed rate, the frequency and&#39; stroke are both reduced until a zero feed rate is approached. 
     It is contemplated that a fixed rate spring will be used for tuning the vibratory mass to the frequency of the oscillatory drive. It is possible that a variable rate spring might in some instances be used to approximate the natural frequency of the system. The control of frequency and stroke would be accomplished by dropping the voltage on the AC squirrel cage motor. 
     An auto-transformer has shown in prior art  FIG.  19    provides a way to adjust the voltage on the AC motor. Other ways in which the voltage may be regulated is, for example, by the use of solid state type control including a gating transistor. 
     Another common problem with vibrating screens occurs when screens become jammed or clogged with aggregate material. This clogging slows or stops throughput causing costly shutdown for screen cleaning and unclogging. The instant invention includes a pulsing solution to dislodge contaminants from the screens. 
     SUMMARY OF THE INVENTION 
     A continuous, steady flow of the supply of the incoming bulk solid such as coal, ore, wood waste, or the like is required as feed material for optimal control and screening performance of the feeding and screening system. It is recommended that the vibrating screening feeder be installed under the outlet of a storage bin or silo or surge bin. The outlet of the steady feed source must be interfaced with the vibrating screening feeder inlet chute that connects to the feed bin. The chute typically includes a baffle of 30 to 60 degrees and preferably about 45 degrees to help convert the vertical feed flow into the inlet to a horizontal or near horizontal flow and spread across the full width of the vibrating screen feeder feed plate. The screen media is usually woven wire of perforated plate with longitudinal side clamps, flap plastic squares or any standard screen media. Three screening decks are typically used in the apparatus; however, it is contemplated that additional decks may be added. The passed unders (under sized particles) collecting pan is disposed beneath the screening plates and extends the full width and length of the screen for collecting and conveying all of the passed unders to an outlet located near to the end of the screen. The collecting pan includes an outlet for discharging the passed unders located near the end of the screens and can be full width or converging. The means for powering the vibrating screening feeder is accomplished by an AC motor rotating unbalanced eccentric weights combined with sub-resonant tuned steel coil drive springs which are attached to the end of a longitudinal counterbalanced support base which is a longitudinal structure which can be cut into sections that are bolted together if necessary. The instant invention concentrates and nests the steel drive coils in selected positions or locations connecting the screening unit to the longitudinal counterbalance support base. 
     A vibrating conveyor screening and feeding process for conveying materials includes a bed having an inlet end and an outlet end on which material is adapted to be conveyed in a direction. A plurality of drive springs each have a first end attached to the bed and a second end attached to a support. Each drive spring is adapted to compress and extend along a line of stroke. A plurality of stabilizers attaches to the bed, each one being more rigid in a direction transverse to the line of stroke than the stabilizer is rigid in the direction of the line of stroke. A first vibratory motor has a first rotatable eccentric weight adapted to state about a first axis. A second vibratory motor has a second rotatable eccentric weight adapted to rotate about a second axis. A third vibratory motor has a third rotatable eccentric weight adapted to rotate about a third axis. A fourth vibratory motor has a fourth eccentric weight adapted to rotate about a fourth axis. The first and second axis are located substantially in a first plane and the third and fourth axis are located substantially in a second plane. The second plane is non-coplanar with the first plane and the first and second axis are spaced apart from the third and fourth axis along the direction the material is conveyed. The eccentric weights are free-wheeling with respect to one another. The vibratory motor is adapted to operate at substantially the same operating speed and to provide an output force generally perpendicular to its axis of rotation. The rotatable eccentric weights are adapted to accumulatively synchronize with one another without being rotationally coupled to one another such that the combined resulting output force of the first pair of rotatable eccentric weights is generally parallel to the line of stroke and the combined resulting output force of the second pair of rotatable eccentric weights is generally parallel to the line of stroke. The vibratory motors operate to rotate the eccentric weights, such that the rotating eccentric weights accumulatively synchronize and accumulatively add their output forces and their respective power outputs and thereby vibrate the bed along the line of stroke at a vibration frequency. The vibratory motors operate at substantially the same selected operating speed which approaches 
     being equal to, or is less than, the natural frequency of the drive springs which are vibrating the bed. 
     A novel feature of the instant invention is based on the electrical control enabling a full zero to maximum output adjustment by means of adding a standard variable frequency (VFD) combined with adjustable timers so that a vibratory stroke required screening has an automatic capability of a momentary “pulsing” to 60 hertz (or higher) for a brief time of usually 3 to 5 seconds, which generates a vigorous vibratory action “spurt” or “pulse” to the entire screening body similar to a dog shaking off water. The pulsing action is usually automatically repeated to keep the screen media clear of “pegging” or being blinded by lumps or particles stuck in the openings or to break free accumulated layers of adhesive and cohesive particles that try to stick or adhere to the surface of the screening media and the passed unders collecting pan below it. 
     Another novel feature of the present invention is the feedback control operation of the vibrating screening feed based upon the throughput capacity of the equipment it is feeding. For instance, if feeding a rock crusher, a standard 4 to 20 ma direct current (D.C.) signal can be used to automatically control the vibrating screening feeder&#39;s variable frequency (VFD) control of the screening feeder. The closed loop of the control circuit monitors the amps drawn by the rock crusher to control the feed rate of the vibrating screening feeder by increasing or decreasing the output of the fed from the vibrating screening feeder. Thus, the amps pulled by the equipment being fed will control the rate of feed. The variation form zero to maximum TPH output and the repeated “pulsing” of making the motor with eccentric weights to go faster and then return to a slower, steady speed is accomplished with the 3 phase alternating current (A.C.) squirrel cage motor. 
     Another feature facilitating processing of sticky feed material is a cross bar with water spray nozzles which can optionally be used when adhesive and cohesive bulk solids are being screened to clean the sticking particles to the screening surface of the collecting pan underneath. 
     Use of stainless steel or other alloys which tend to resist sticky residues are also useful to eliminate sticky residue and agglomerates. Coatings such as TEFLON may also be used to treat the surface of equipment to resist sticky residue. 
     The vibrating screening feeder is dust tight having a bolted top cover with quick opening view ports add to the screen body. Enclosed vertical chutes are added to the discharge end. Flexible connections also seal the inlet and the outlets. 
     In accordance with features of the invention, the vibration drive isolation assembly includes a longitudinally extending longitudinal counterbalance member. A plurality of drive springs are supported by the longitudinal counterbalance member. The drive springs are distributed across the width and the length of the enclosed screening unit. At least one vibratory motor or mechanism is installed on the proximate end of the longitudinal counterbalance member. A plurality of isolation springs support the longitudinal counterbalance member. 
     Induced conveying is accomplished by imparting a proper stroke at the needed frequency to move the load. The result is a conveying motion that is induced instead of being forced. It can be a very gentle type of movement or when necessary, a very sharp, reacting type of vibration which can be produced by using an appropriate stroke angle. A helical or elliptical stroke pattern will convey the material in a circular path resulting in a backspin on the particle. A linear stroke is the most efficient one to use for unidirectional movement which moves the material in a straight line. The vibratory action does most of the work. When vibrated, the inner particle friction of the moved material is reduced. 
     A particle can be vibrated and conveyed over a hard surface by means of a series of repetitive “hops”. Each “hop” is a cycle. The distance hopped is directly related to the unit&#39;s stroke length and the angle at which it is applied. The “hops” per unit of time is the operating frequency which is usually expressed in “cycles per minute” or (CPM). 
     An alternative vibratory motor embodiment suitable as a drive means for the vibratory screening feeder utilizes a double extended shaft with eccentric weights installed on both ends of the shaft and are cumulatively considered as a single rotatable eccentric weight. Vibratory motors equipped with shaft mounted eccentric weights will be emphasized herein, but other jack shaft driven combinations can also be used such as v-belts and the like. In either instance, the pair of rotatable eccentric weights are installed on and become an integral part of the conveying assembly. 
     It is an object of this invention to provide a vibrating screen for separating of at least two particle sizes of aggregate in a continuous flow process. 
     It is an object of this invention to provide a vibrating screen for separating of at least two particle sizes of aggregate in a continuous flow process which has a low horsepower to tonnage throughput ratio as compared to other separation processes. 
     It is an object of this invention to provide a vibrating screen which includes a periodic cleaning and unclogging of the screens wherein the speed of the drive motors is periodically and briefly changed by a nominal amount for a short time to dislodge blockages. 
     It is an object of this invention to provide a vibrating screen which provides motors located in an easy to maintain location at one end of the vibrating screen unit. 
     It is an object of the present invention to provide an electrically controlled, a vibratory drive powered by electric motors or high frequency electromagnets that are combined with steel coil springs that are sub-resonant tuned (enabling drive springs to drive harder under loaded conditions), to provide a vibrating screen for unidirectional material movement whereby the vibratory drive is the prime mover of the material (induced conveying) as opposed to conventional vibratory feeds which depend upon the force of gravity (induced vertical flow) as the prime mover of the material. 
     It is an object of the present invention to convey and screen material in response to applied vibratory action via a free force vibratory input combined with subresonant tuned springs to reduce interparticle friction and stratify the material into layers by particle size. 
     It is an object of the present invention to utilize the principle of resonance or natural frequency and to subresonant tune the drive springs to produce more under load whereby the machine&#39; operating frequency is always kept below or under the resonant point of all the drive springs. 
     It is an object of the present invention to provide a vibratory feeder and screen apparatus whereby the dynamic acceleration is the same in both directions of the back and forth movement of its vibratory motion versus a reciprocating motion that moves forward slowly and then accelerates rapidly on its return stroke. 
     It is an object of the present invention to provide a vibratory feeder capable of screening wet bulk solids that are adhesive and cohesive. 
     It is an object of the present invention to provide a vibrating feeder and vibrating screen assembly which can tolerate variation in moisture content. 
     It is an object of the present invention to incorporate a drive system for a vibratory feeder and conveyor powered by one or more electric motors with input power provided by eccentric weights rotated by each motor, a linear stroke pattern, a wide range of operating frequencies, electrically adjustable output with zero to maximum output by variable voltage, with the stroke and frequency simultaneously changed, subresonant operational tuning, longitudinal counterbalanced vibratory force isolation, and capable of smooth repetitive starts and stops. 
     It is an object of the present invention to provide a drive system having three primary components comprising a steel coil drive spring that produces the portion of the load that opposes the vibratory motion, a plurality of flat bar stabilizers guide the motion, and the motor produces the remaining portion of the load that resists it. 
     It is an object of the present invention to provide an energy efficient drive system for the vibrating feeder and screen apparatus. 
     It is an object of the present invention to provide a screening deck for: cleaning unit pieces by removing clinging particles such as adhered sand or trimming edges; for washing by mounting rows of liquid sprays directly over the screen medium, a bulk solid or a unit piece so the liquid spray such as water, oil, surfactant, defactant, or other washing action; sizing to separate flakes and sizes; scalping to remove oversize particles; removing undersize particles; grading; de-liquefying; de-sliming by washing the clinging fines from freshly crushed lumpy materials; rinsing; de-watering; and draining. 
     It is an object of the present invention to include an underside pan for recollecting all the passed unders. 
     It is an object of the present invention to utilize conveying surfaces dynamically counterbalanced and isolated with isolation springs to reduce motor power consumption by 50 to 70 percent compared to conventional motors achieving the same performance. 
     It is an object of the present invention to utilize multiple small low HP motors with synchronized rotating eccentric weights in place of larger higher HP motors. 
     It is an object of the present invention to provide a “dust-tight” vibrating screen design. 
     It is an object of the present invention to provide an unidirectional induced conveying apparatus counterbalanced with isolator springs to support it. 
     It is another object of the present invention to provide an extremely simple and practical way to adjust frequency and stroke, in the drive for vibrating devices combined with mechanical impedances which are purposely built into the vibrating mass system. 
     A further objective of the invention is to provide an electric drive for vibratory equipment which lends itself to simplified remote control for changing the frequency and the stroke of the vibratory equipment. 
     A still further object of the invention is to make use of an A.C. squirrel cage induction motor which is well known to have rugged performance characteristics, low maintenance costs and low initial costs as compared to other electrical motors which are capable of adjustable speeds. 
     Other objects, features, and advantages of the invention will be apparent with the following detailed description taken in conjunction with the accompanying drawings showing a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the views wherein: 
         FIG.  1    is a side view of a prior art vibrating conveyor showing a fixed base member, a motor and a crank journal driving a vibrating screen housing which is movable relative to the fixed base about rotating arms with damper springs; 
         FIG.  2    is a side elevational view of the vibrating screening feeder unit illustrating natural frequency vibrating screening feeder in which the exciter motor is suspended from the vibratory mass system and acts in parallel with the drive springs which are selected to give the system natural frequency characteristics; 
         FIG.  3    is a view of a section of the vibrating screening feeder showing the screening unit connecting to drive springs mounted on brackets supported by the longitudinal counterbalance support base; 
         FIG.  4    is an end view of the vibrating screening feeder showing the screening unit connecting to a plurality of drive springs mounted in a row across the width of the screening unit and longitudinal counterbalance support base which is supported by a plurality of horizontal coil steel isolation springs supporting the longitudinal counterbalance support base on a base and showing a plurality of motors mounting on the end of the longitudinal counterbalance support base; 
         FIG.  5    is a perspective view of the vibrating screening feeder unit of the present invention showing the screening unit side walls and pan having brackets connecting to a plurality of drive springs mounted in a row across the width of the screening unit and longitudinal counterbalance support base; 
         FIG.  6    is an elevated perspective view of the vibrating screening feeder unit showing the discharge chutes extending from the rear end of the present invention; 
         FIG.  7    shows that when the drive springs  20  are expanded, the rocker springs  24  are flexed upward. 
         FIG.  8    shows that when the drive springs are compressed, the rocker springs  24  are flexed downward. 
         FIG.  9    shows a vibratory motor with rotatable eccentric weights.; 
         FIG.  10    shows the vibratory motor of  FIG.  9    including extra weights added to the shaft; 
         FIG.  11    is an end view of a vibrating screening feeder unit showing the storage bin positioned above the vibrating screening feeder and connecting the bin outlet to the feeder inlet interfacing chute; 
         FIG.  12    is a side view of the vibratory screening feeder showing a chute connecting the bin to the feeder inlet and the screening unit supported by the longitudinal counterbalance on drive springs and the longitudinal counterbalance supported on the base with steel coil isolation springs; 
         FIG.  13    is an end view of the vibrating screening feeder showing the motors attaching to the end of the longitudinal counterbalance, a row of isolation springs supporting the screening unit above the longitudinal counterbalance and the drive springs on the outside of the row extending across the screening unit supported by the longitudinal counterbalance; 
         FIG.  14    is an elevated side view of the vibratory screening feeder showing a chute connecting the bin to the feeder inlet and the screening unit supported by the longitudinal counterbalance on drive springs and the longitudinal counterbalance supported on the base with steel coil isolation springs wherein the longitudinal counterbalance is angled downward at a 15 degree angle with respect to the base; 
         FIG.  15    is an elevated side view of the vibratory screening feeder of  FIG.  16    showing a chute connecting the bin to the feeder inlet and the screening unit supported by the longitudinal counterbalance on drive springs and the longitudinal counterbalance supported on the base with steel coil isolation springs wherein the longitudinal counterbalance is angled downward at a 15 degree angle with respect to the base and showing the optional water spray bars and discharge connection to a crusher; 
         FIG.  16    is an end view showing the connection of the vibrating screening feeder to the crusher and the discharge chute; 
         FIG.  17    is a side elevational view showing the drive of this invention applied to a natural frequency vibratory feeder where the springs are in series with the motor drive. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the  FIGS.  1 - 17   , a vibrating screening feeder system  1  includes a vibratory storage bin  8  feeding a vibrating screening feeder unit  10  feeding and crusher  70  for oversized material. The intermediate storage bin  8  is positioned above the vibrating screening feeder  10  connecting the bin outlet  102  to the feeder inlet interfacing chute  104 . The size of the bin  8  is determined by the throughput to maintain a maximum feed rate to the vibratory screening feeder  10  and ensure an appropriate amount of storage to enable it to continuously operate at its rated TPH (ton per hour) capacity. The bin&#39;s outlet  102  is positioned close to the feeder inlet  103  separated by the feed plate  105 . Preferably the bin  8  is a vibratory bin or hopper having the capability to shake accumulations or bridging particles from the sidewalls to effect a smooth flow of feed to the vibratory screening conveyor  10 . The following U.S. Patents are incorporated by reference herein are some of the vibratory hoppers which may be useful for utilization with the present invention: U.S. Pat. Nos. 3,261,592; 3,257,040; 5,046,643; 4,960,229; 3,735,963; 4,744,893; 4,899,669; and 4,844,289. 
     As shown in  FIGS.  2 , and  11   , a chute  104  or stove pipe can be used to connect the bin to the feeder inlet  104 . On “start-up” the top section or cover is temporally removed to permit the adjustment of the “mat depth” flowing into the vibrating screening feeder  10 . When adjusted properly, full width spreading is obtained and the cover  56  is reinstalled over the unit. Also shown are the horizontal coil steel isolation support springs  22  which are nested in sets and mounted to support members  23  extending across the width of the conveyor. The isolation springs  22  rest on a base, floor or other immobile support surface. A alternate motor  50  is shown mounted to the longitudinal counterbalance  26 . 
       FIG.  13    is an end view of the vibrating screening feeder showing the motors attaching to the end of the longitudinal counterbalance, a row of isolation springs  22  supporting the screening unit above the longitudinal counterbalance and the drive springs  20  on the outside of the row extending across the screening unit supported by the longitudinal counterbalance. The vibrating screening feeder  10  shown includes 200 drive springs  20  are arranged in sets of two rows each extending across the width of the conveyor attaching to the conveyor bed frame or integral body/frame support members  18  supported at a 45 degree angle by brackets  19  mounted on the top of the longitudinal counterbalance support base  26 . Each drive spring or coil is equivalent to ½ HP. Thus, 200 drive springs provide the equivalent of 100 HP of driving force to the vibrating screening feeder  10 . 
     As shown in  FIG.  14   , the vibratory screening feeder shows a chute connecting the bin to the feeder inlet and the screening unit supported by the longitudinal counterbalance on drive springs and the longitudinal counterbalance supported on the base with steel coil isolation springs wherein the longitudinal counterbalance is angled downward at a 15 degree angle with respect to the base. 
       FIG.  15    is an elevated side view of the vibratory screening feeder of  FIG.  14    showing a chute  104  connecting the bin  8  to the feeder inlet and the screening unit  10  supported by the longitudinal counterbalance on drive springs  20  and the longitudinal counterbalance supported on the base with steel coil isolation springs  22  wherein the longitudinal counterbalance is angled downward at a 15 degree angle with respect to the base and showing the optional 450 gallon per minute (GPM) water spray bars  52  and valve  54  and discharge connection  44  to a crusher  70  for minus 7 millimeter material.  FIG.  16    is an end view showing the connection of the vibrating screening feeder to the crusher  70  and the discharge chute  44 . 
     The vibrating screening feeder  10  consists or comprises a trough or pan defined by a bottom floor  11 , side walls  12  and  13 , and a rear end wall  14 , with the forward end wall  15  including chutes  40 ,  42 , and  44  in fluid engagement with downstream processing equipment. The processed feed material is delivered to a desired conveyor or process equipment point at some selected rate of speed. The vibrating screening unit  10  is mounted on support members  18  which are carried at selected points at the front and rear portions of the a vibrating screening feeder  10  mounted beneath the trough, bed, or pan  11 . 
     The drive springs  20  are preferably selected with K factors, that is, spring rates which are appropriately related to the frequency of the motor drive, the mass of the motor drive component, and the total mass of the driven vibratory system, so that under normal synchronous speed of the drive motor, the springs  20  will be at or near natural frequency with the system. For ideal operation, the vibratory system with its exciter drive is designed to operate at, as close to, the natural frequency of the system as illustrated by the stroke-frequency curve of FIG. 7 of U.S. Pat. No. 4,015,705 wherein the natural frequency is at the peak of the curve. 
     It will be understood that the drive springs  20  are also designed so that lateral forces transverse to the longitudinal axis of the vibrating screening feeder  10  are absorbed by the lateral deflections of the springs  20 . Of course, if desired dual motors having the same characteristics as the motor  30 , except for being each one-half the horsepower of the single motor, may be used in place of the single motor  30 , in which case they are driven in opposite directions and have their motor housings rigidly joined together in a manner well known in the art so as to cause the rotating weights to phase together and cancel out the lateral forces while producing a resultant linear stroke. 
     A motor  30  for vibrating the vibrating screening feeder  10  at a selected frequency and stroke for moving particulate material on the pan  11  toward the discharge end  14  of the feeder. The motor drive in the present invention is capable of adjusting the rate of feed by varying the frequency and the stroke of the vibratory system. 
     An unexpected surprising and unique relationship exists between the characteristics of the vibratory system and the driving motor, whereby it is possible to vary not only the frequency, but also to simultaneously vary the stroke of a natural frequency vibrating feeder or similar vibratory system merely by changing the voltage on the A.C. motor  30 . An A.C. squirrel cage motor has always been thought of as essentially a constant speed motor (except, of course, a multi speed or multi-winding A.C. motor)one which could not have its speed effectively varied by voltage control. The variable load requirements of a free mass, natural frequency, vibratory system in relation to speed are similar to those of a fan or a fluid pump and that it is possible to use variations in the voltage applied to the A.C. squirrel cage motor as an effective means for controlling the feeding rate of this type of vibratory system, and that, surprisingly, this can be accomplished without motor overload. 
     The ability to control feeder rate merely by voltage control lends itself to the remote control of systems of this type, and is far more convenient than attempting to adjust or vary the rate of the force-transmitting spring units interposed between the motor  30  and the vibrating screening feeder  10 . 
     The motor drive  30  comprises a single alternating current squirrel cage induction motor which is supported on the end of the longitudinal counterbalance  26  from a motor mount bracket rigidly secured thereto. The motor has a squirrel cage rotor, and is thereby characterized as one which does not have brushes. For convenience the type of A.C. motor will hereinafter be referred to simply, as an A.C. squirrel cage motor, and is to be distinguished from a variable speed A.C. motor having multiple windings or multipoles for speed control. 
     As shown best in  FIGS.  9 - 10   , at each end of the shaft  33  of the motor  30  an eccentric weight  52  is mounted, and usually these weights are fixed to the shaft in parallel relationship, although in some instances, it may be desirable to vary their angular relative positions to achieve adjustment of the effective eccentric mass operating on the vibratory system, or adjusting weights  54  may be added to or subtracted from the eccentric weights, as required. Shrouds cover the ends of the motor to protect personnel from the revolving eccentric masses. 
     The motor  30  is supported on the longitudinal counterbalance in such a manner that the exciting oscillatory force supplied by the eccentrically weighted motors is applied to the vibratory conveyor screening unit  9  along a fixed angle of attack. This angle of attack is ordinarily on the order of from 20 to 40 degrees, and it will be seen that as an oscillating force is applied to the vibrating screen  9  along this axis, the particulate on the vibrating screen  9  is caused to move toward the open end of the vibrating screen  9  by what might be termed a hopping action. As the frequency of the oscillating force is reduced and/or as the stroke is reduced, the rate of feed is correspondingly reduced and it is desirable to have this rate of feed variable between zero, or substantially zero, and the maximum rate of feed. 
     It is an accepted fact in the natural frequency vibrating system field (as for example in the type of feeder shown in Klemencik Patent No. 2,725,984) that one can normally determine whether the system is operating in natural frequency by checking the current draw on the motor, because, when the system is operating at true natural frequency, the current draw is at a minimum. Conversely, to the extent that a system of this type is not operating at natural frequency, the power requirements go up, and this is reflected in increased current draw, regardless of whether one is operating above or below the point of natural frequency. Contrary to conventional teachings, when the present invention is operating in natural frequency, the current drawn by the motor is at its maximum, and, as the frequency (i.e. speed) of the motor is changed by dropping the voltage, the current decreases. As one moves below natural frequency with the system the current going through the motor drops rather than rises, as might normally be expected. It is possible to effectively vary the feed rate of a vibratory conveying or feeding system from-substantially zero to its maximum feed rate, merely by adjusting the voltage of an A.C. squirrel cage motor. This of course can conveniently be done with an auto transformer, such as shown in  FIG.  17   . 
     The vibrating screening feeder is adapted to be driven by a plurality of accumulatively phased pairs of free-wheeling rotatable eccentric weights. The accumulative force output produced by the rotating eccentric weights will be a unified amount equal to the sum of all the multiple pairs of eccentric weights. The respective power outputs of the motors turning these eccentric weights will also accumulatively add. This wanted “phasing” of multiple pairs of rotating eccentric weights will only occur when used in conjunction with properly stabilized, sub-resonant tuned, stiff drive springs. 
     The accumulative phasing of a plurality of pairs of rotating eccentric weights is applicable to vibratory conveyors of the non-balanced type, which must be rigidly fixed to their support structure. It is also applicable to vibratory conveying machines that are dynamically counterbalanced and provided with isolation springs. The longitudinal counterbalance can be one single longitudinal assembly, or the longitudinal counterbalance can be sectionalized in a plurality of sections as shown in Dumbaugh U.S. Pat. No. 4,149,627. It is important to note the vibrating screen  9  must employ the sub-resonant tuned springs kind of vibratory drive configuration that is properly stabilized for this wanted multiple phasing of a plurality of pairs of rotatable eccentric weights to occur. 
     The multiple pairs of rotatable eccentric weights are installed on and become an integral part of the conveying trough assembly of the conveying apparatus when the vibratory conveying apparatus is the “non-balanced” type. This means its longitudinal counterbalance frame is rigidly “fixed” to a robust stationary foundation. Conversely, when the vibratory conveyor is “dynamically counterbalanced”, the pair of rotatable eccentric weights can be installed on either the conveying trough or on a counterbalancing member. When the conveying apparatus is longitudinal counterbalanced, the pair of rotatable eccentric weights are almost always installed on the counterbalancing member. 
     Method of Use: 
     A continuous, steady flow of the supply of the incoming bulk solid such as coal, ore, wood waste, or the like is required as feed material for optimal control and screening performance of the feeding and screening system. It is recommended that the vibrating screening feeder  10  be installed under the outlet of a storage bin or silo or surge bin  8 . The outlet  102  of the steady feed source must be interfaced with the vibrating screening feeder inlet chute  104  that connects to the feed bin  8 . The chute typically includes a baffle of 30 to 60 degrees and preferably about 45 degrees to help convert the vertical feed flow into the inlet to a horizontal or near horizontal flow and spread across the full width of the vibrating screen feeder feed plate  17 . 
     The screen media  53  is usually woven wire or a perforated plate with longitudinal side clamps, flap plastic squares or any standard screen media. Three screening decks, a (top deck  50 , a middle deck  55 , and a bottom deck  58 ), and a bottom trough or pan  11  are typically used in the vibrating screening feeder  10 ; however, it is contemplated that additional decks may be added. The passed “unders” (under sized particles) collecting pan  11  is disposed beneath the screening plates and extends the full width and length of the screen for collecting and conveying all of the passed “unders” to an outlet located near to the end of the screen. The collecting pan  11  includes an outlet  44  for discharging the “passed unders” located near the end of the screens and can be full width or converging. The means for powering the vibrating screening feeder is accomplished by motorized an AC motor rotating unbalanced eccentric weights combined with sub-resonant tuned steel coil drive springs which are attached to the end of a counterbalanced support base which is a longitudinal structure which can be cut into sections that are bolted together if necessary. The instant invention concentrates and nests the steel drive coils  20  in rows at selected positions or locations connecting the screening unit to the longitudinal counterbalance support base  26 . 
     The electrical control enables a full zero to maximum output adjustment by means of adding a standard variable frequency (VFD) combined with adjustable timers so that a vibratory stroke of about 2 Gees for the require screening (50 Hz at for about 25 seconds) has an automatic capability of a momentary “pulsing” to(60 hertz (or higher) for a brief time of usually 3 to 5 seconds), which generates a ver vigorous vibratory action “spurt” or “pulse” to the entire screening body similar to a dog shaking off water. The novel pulsing action is usually automatically repeated to keep the screen media clear of “pegging” or being blinded by lumps or particles)stuck in the openings) or to break free accumulated layers of adhesive and cohesive particles that try to “stick” or adhere to the surface of the screening media and the passed “unders” collecting pan  11  below it. 
     A novel feature of the present invention is the control of the vibrating screening feed by the equipment it is feeding. For instance, if feeding a rock crusher  70 , a standard 4 to 20 ma D.C. signal automatically controls the vibrating screening feeder&#39;s variable frequency (VFD) control of the vibrating screening feeder  10 . The closed loop of the control circuit comprises or consists of monitoring the amps drawn by the rock crusher to control the feed rate of the vibrating screening feeder by increasing or decreasing the output of the fed from the vibrating screen. Thus, the amps pulled by the equipment being fed will control the rate of feed. The variation form zero to maximum TPH output and the repeated “pulsing” of making the motor with eccentric weights to go faster and then return to a slower, steady speed is accomplished with the 3 phase A.C. squirrel cage motor. 
     More particularly, there is provided a vibrating screen unit  9  comprising, consisting of, or consisting essentially of a generally rectangular vibrating screen housing  79  supported by a fixed base  4  defining a longitudinal counterbalance  26  by a plurality of upward extending isolation support coil springs  22  fixedly attaching to a top surface of the longitudinal counterbalance  26  and fixedly attached to a bottom surface of the generally rectangular frame  8 . The intermediate frame  8  has triangular shaped support members  18  defining alternating large and small triangular abutments extending upward therefrom. The large triangular abutments have a first side forming about a forty-five degree angle with a top surface of the longitudinal counterbalance  26 . The first side of the large triangular abutment  18  have a drive coil spring  20  extending upward therefrom at about a forty-five degree angle with a top surface of the longitudinal counterbalance  26 . The small triangular abutment has two spaced apart leaf spring rockers  24  extending upward at about a forty-five degree angle with the top surface of the longitudinal counterbalance  26 . The first side of the large abutment faces toward the second side of the small abutment. A generally rectangular vibrating screen housing  79  has at least two rows of downward extending trapezoidal abutments on a bottom surface thereof. The trapezoidal abutments fixedly connect on a third side to free ends of the upward extending drive coils  20  and on a fourth side to free ends of the upward extending leaf springs. The vibrating screen housing  79  has at least one screen and preferably a plurality of screens extending the width and length thereof and at least two output apertures formed therein. The longitudinal counterbalance support base  26  has a plurality of motors  30  mounted at a front end  15  thereof. The motors have output shafts extending from top and bottom ends with eccentric weights mounted on the shafts in mechanical time with one another. A programmable motor control unit is capable of driving the motors with the weights synchronized with one another and capable of driving the motors at a selected speed and of periodically changing the speed for a selected time interval by a selected amount. 
     The present application provides a vibrating screen for separating different sizes of aggregate in a continuous flow process wherein aggregate flows into a hopper, down onto one end of a vibrating screen, and is transported over the screen by vibration of the screen. Fine and medium sized portions of the aggregate fall through the first screen to a second screen. Only fine portions fall through the second screen. Thus the aggregate is separated into three grades of material. The vibrating screen is rotatably connected to a moveable intermediate base member by a plurality of leaf springs fixedly connected at about a forty-five degree angle between the longitudinal counterbalance  26  and the vibrating screen frame unit  9  and a plurality of coil springs called ‘drive springs’  20  which are connected at 45 degrees with the leaf springs between the longitudinal counterbalance and the vibrating screen. The longitudinal counterbalance in turn is supported above a fixed base member by vertical coil springs  22 . The longitudinal counterbalance includes a number of electric motors  30  which have eccentric weights connected directly to the shafts. When the motors are running the spinning eccentric weights cause the vibrating screening frame  10  to vibrate at a frequency consistent with the speed of the motors. The speed of the motors can be varied to give a different vibrating frequency. 
     The mostly horizontal left and right motion of the intermediate base member therefore causes a left to right and an up and down motion of the vibrating screen housing  79 . It can also be seen that, primarily, the ‘drive springs’  20 , and to a smaller degree, both the leaf springs  24  and the drive springs  20 , store and release energy every cycle of movement. This system of springs establishes a harmonic system which tries to maintain a frequency of movement of the system. This storing and releasing of energy allows for a more efficient system with fewer and smaller drive motors for a given throughput of aggregate. 
     The motors  30  are variable speed and run at one selected speed most of the time. Periodically, however, the speed is changed by a selected amount for a selected period of time and then returned to normal. This change in speed dislodges jams or clogs that occasionally occur in the process, due to density and particle variance, moisture, and so forth. The vibrating screen of the present invention gives superior performance where moist aggregate is an issue. 
     A programmable motor controller easily accomplishes this periodic cycle of motor speed change. A user can easily change the cleaning cycle time and amount of speed change, as desired. 
     The preferred embodiment includes an input hopper  100  with a vibratory motor  31  to vibrate the provide consistent feed rate of aggregate onto the vibrating screens. Another preferred embodiment has a hopper without a separate vibratory drive motor and wherein the gap between the bottom of the hopper is adjusted manually to give an ideal flow of aggregate over the input end of the vibrating screen. This hopper is preferably fitted with a device which strikes the side of the hopper periodically or whenever a bridging or clogging of aggregate is detected. 
     It is anticipated that a feed box may be used between the hopper and the vibratory screen comprising a short length conveying trough utilized at the inlet end of the conveyor where the incoming bulk solid needs to be stratified to avoid abrasive wear from impacting and the unnecessary blinding of the screen medium on its upstream extremity. The feed to the screening unit needs to be uniform and with a reasonable spread across its width. 
     Referring now to the drawings, the vibration drive isolation system or assembly is arranged to minimize vibration to exterior plant equipment. Vibration drive isolation system includes a longitudinal counterbalance member  26 , a plurality of drive springs  20  supported by longitudinal counterbalance member  26  and a plurality of isolation springs  22  supporting the longitudinal counterbalance member  26 . A structural steel base  4  supports the isolation springs  22 . The vibration unit has a variable speed motor control capable for adjusting the vibration intensity. 
     Both the time between oscillations and the intensity of the oscillation can be controlled with an easy control panel adjustment of controller. They require no mechanical adjustment of eccentrics. 
     The electric motors  30  of the vibratory drive assembly are attached to the dynamic counter-balance  261  and positioned at the front end  15  or under the combination of the steel coil drive springs  20  and multiple flat bar type of stabilizers. The assembly is supported from the longitudinal counter-balance  26  by the appropriately spaced isolating springs  22  mounted in compression and appropriately spaced along its length. The vibratory motors with shaft mounted eccentric weights  80  are either installed on each side of the counter-balance  26  as shown in  FIG.  7   , or combined together, and placed at the front end  15  of the counter-balance. 
     The steel coil type drive springs  20  are distributed across the width and along the length of the underside of the screen unit  9 . The drive springs  20  are combined with flat bar type stabilizers  24  to assure a uniform stroking action. The flat bar type stabilizers  24  are used to guide the movement of the stiff drive springs  20 . 
     The drive springs  20  are sub-resonant tuned to cause them to inherently work harder under load, where sub means under and Resonant means natural frequency. Therefore, “Sub-resonant” means the maximum running speed of the vibratory motors  30  is always under the natural frequency of the combined drive springs. For example, if the top motor speed is 570 RPM, which in this instance is the same as CPM, then the natural frequency of all the drive springs  182  would be, for example, 620 CPM. While 570 CPM is preferred, other frequencies such as 720 CPM, 900 CPM or 1200 CPM, might be useful for various applications. 
     The axial centerline of the steel coil drive springs  20  is provided in line with the wanted stroke angle, but the axial centerline of the stabilizer  24  is perpendicular to the stroke angle. By utilizing paralleled counter-balance  26  as a longitudinal configuration, the enclosed vibrating screening feeder  10  is dynamically counter-balanced. The structural Natural Frequency of the counter-balance assembly will be at least 1.4 times the maximum speed of the motors, but preferably will exceed it. In this instance, the RPM of the motor  30  is the same as the vibrating CPM of the enclosed vibrating screening feeder  10 . 
     Relatively soft steel coil type isolation springs  22  are used to support the longitudinal counter-balance  26  which in turn supports the enclosed vibrating screening unit  9  above it. Preferable needed input power is proved by three phase, A-C squirrel cage vibratory motors  30 . Electrical adjustment of conveying speed is provided by the controller implements either as a variable voltage or an adjustable frequency type of electrical control. The conveying speed of the ash over the vibrating screening feeder  10  can be electrically adjusted. 
     In operation, the vibratory motor(s)  30  are energized and the shaft mounted eccentric weights are accelerated to full speed. The force output of the rotating eccentric weights excites or induces all the stiff steel coil drive springs  20  and flat bar stabilizers  24  to vibrate back and forth in a straight line. The speed (RPM) of the vibratory motors  30  is the same as the vibrating frequency (CPM) of the drive springs  20 . This happens even though the natural frequency of the drive springs  20  is above the motor speed. Consequently, the enclosed vibrating screening feeder  10  vibrates at a prescribed amount of linear stroke at the wanted angle, which is usually 45 degrees. As an equal reaction to the vibratory movement of feeder  10 , the counter-balance member  26  inherently moves in an opposite direction. Thus, the opposing dynamic forces cancel one another. The counter-balance  26  freely moves or floats on top the soft isolation springs  22  supporting it. 
     A resulting directional, straight line stroke on the enclosed unit induces the particles to unidirectional move forward simultaneously over the screens and pan. This particle movement is the result of a series of hops or pitches and catches by the applied vibration. Normally, the particles first settles on screen. Then, it is gradually moved forward by repetitive on and off cycles of applied vibration. For example, the particles are moved 3 feet every 6 minutes. Alternatively, the particle movement over the screen surfaces could be electrically adjusted via adjustment of motor operation by controller to provide, for example, a conveying speed of 0.5 FPM. The particles conveyed on the screens discharges into vertical chutes. The particle sifting that fall through any openings in the screens drop onto the bottom conveying pan  11 . When the vibratory conveying action is applied, these particles move forward. Eventually, these particles fall down through outlets located near the discharge end of the screening unit  9 . 
     The vibrating screening feeder  10  includes a plurality of vibratory motors  30  placed relatively close together on the front end  15  of the longitudinal counterbalance  26 . In one embodiment, a total of six vibratory motors are disposed transversely across from one another with respect to the longitudinal width of the vibrating screening feeder  10 . Each vibratory motor includes a rotatable eccentric weight. Since the rotating eccentric weights are located on the top and bottom of each motor, a total of twelve individual eccentric weights would be involved, but all of the eccentric weights on a single motor are considered herein to be a single eccentric weight. The eccentric weight attached to one of the vibratory motors in a pair of vibratory motors is substantially equal in size to the eccentric weight attached to the other vibratory motor in the pair of vibratory motors. Each motor is rated 45-60 HP, which would make a total of 270-300 HP provided by the six vibratory motors although other sizes of motors can be used. While electric motors are preferred, air motors or hydraulic motors can also be used. 
     Each vibratory motor preferably has the substantially same size eccentric weight attached thereto, such that each vibratory motor and eccentric weight produce substantially the same force output during operation. 
     All six motors synchronize and provide an accumulatively phased force output equal to the sum of the individual force outputs of all of the eccentric weights. The proper phasing of the eccentric weights happens if each pair of motors is started separately, or in any combination, or all started at the same time. These motors would still try to “phase” even if the rotation was different when these six motors are working in conjunction with sub-resonant tuned steel coil drive springs that have flat bar type stabilizers to guide their stroke line. 
     The goal is to make the load carrying vibrating screening feeder  10  to vibrate at a prescribed stroke of, for example, one-half inch at a frequency of 570 cycles per minute (CPM), which is the same as the rotational speed of the motors at 570 revolutions per minute (RPM). In other words, the operating frequency of the conveying apparatus  10  in CPM is the same as the RPM of the motors. 
     After being energized at the same time all six the motors accelerate the rotatable eccentric weights installed on the top and bottom shaft extension of the motors. While the weights are accelerating, a slight “shimmy” or shudder-like movement may be present. After all six motors have reached full speed, the stroke on the conveying trough assembly begins to grow steadily from, for example, from one-eighth inch to the desired maximum of one-half inch in about twenty seconds. Thus, the three pairs of motor combinations require about ten to twenty seconds after being energized to accelerate the eccentric weights and to properly “phase” or to accumulatively synchronize the outputs of the eccentric weights. 
     All of the rotating eccentric weights may have exactly the same force output. If any of these motors is de-energized, then the resulting stroke on the vibrating screening feeder will decrease from its maximum amount. 
     The “phased” or synchronized eccentric weights on the vibratory motors excite or prompt the steel coil drive springs  20  to move back and forth, or compress and extend, in a straight line of stroke. That “line” is guided by the flat bar type stabilizers  24  installed at 90 degrees or perpendicular to the axial centerline of the steel coil drive springs  20 . The vibratory screening unit  9  positioned on top of the drive spring brackets vibrates back and forth in reaction to the movement of the longitudinal counterbalance  26  below. This is in keeping with Newton&#39;s Law of an “equal and opposite reaction”. Stabilization of the drive springs  20  must be relatively rigid in a direction transverse to the line of stroke and relatively weak in the direction of stroke. For example, the flat bar stabilizer  24  may be five inches wide across its transverse width and only one-eighth inch thick in the direction of the stroke. If the drive springs  20  are not rigidly stabilized in a direction transverse to the line of stroke, then the rotating eccentric weights may not synchronize. The stabilizers  24  may be formed in other configurations than as flat bars so long as the stabilizer is relatively rigid in a direction transverse to the line of stroke and relatively weak in the direction of stroke. The vibratory motors are tilted or inclined from horizontal to agree with the stroke line and the installed inclined angle of the drive springs  20 . 
     The entire apparatus vibrates very smoothly and quietly when all six motors are up to their full speed. The amount of vibratory stroke remains constant or steady. A given amount of bulk solid, such as foundry sand, in the vibrating screening feeder installed above the longitudinal counterbalance  26  can be conveyed forward at a steady speed of, for example, approximately forty feet per minute (FPM). 
     In another embodiment, the stiff steel coil drive springs  20  have a combined natural frequency that is always above the maximum speed of the motors being utilized. “Sub” means “under” and “resonant” means “natural frequency”. Therefore, “sub-resonant” means to maintain the top running speed of the motor (for example, 600 RPM or CPM) to always be under the “natural frequency” of all the steel coil drive springs  20  (for example, 650 CPM) when the vibratory conveyor  10  is in the “no load” state or empty condition. When a load is applied to the vibrating screening feeder the “natural frequency” of all the installed drive springs  20  will inherently reduce in response to the added weight of the load (for example, to 625 CPM). Because the natural frequency of the drive springs  20  has decreased (from 650 to 625 CPM), and moved closer to the motor speed (600 RPM or CPM), the entire drive configuration works harder. The more the natural frequency of the drive springs decreases because of additional load being added to the vibrating screening feeder, the more close the natural frequency of all the drive springs  20  comes to the running speed of the motors. Thus, the drive configuration works even harder. This is the advantage of “sub-resonant” tuning. 
     Consequently, the stiff steel coil drive springs  20  in combination with the six motors inherently drive harder when load is applied to the vibrating screening feeder  10 . Therefore, the use of “sub-resonant” tuning takes advantage of the principal of “natural frequency”. However, it should be noted this kind of drive configuration does not normally operate in “natural frequency”. 
     The objective is to make the respective force outputs of the eccentric weights to “pull” the screens of the vibrating screening feeder  10  in tension from the discharge end as compared to “pushing” the inertial mass in compression from the inlet end. The same relationship is wanted from the total number of drive springs  20  installed that help to make the apparatus vibrate. This is the reason the collective forces from both the rotating eccentric weights and the drive springs should place the overall length of the vibratory apparatus in tension as compared to being in compression. More simply stated, the vibratory apparatus is dynamically being “pulled” instead of being “pushed”. 
     When an electrical means for adjusting the operating stroke and frequency of the vibratory machine is wanted, it is preferred to be large enough to control the total combination of paired motors installed on the vibratory apparatus. To ensure each of those individual controllers are responding to the same electrical pilot signal (usually 4 to 20 ma D.C.) to ensure each of the motors is rotating at the same speed throughout the range of adjustment. This maybe accomplished by use of a common electrical potentiometer on either the variable voltage or the frequency inverter type of electrical controls. The simultaneous adjustment of the operating stroke and frequency by means of a variable voltage electrical control as outlined in U.S. Pat. Nos. 3,251,457 and 4,015,705 can be successfully utilized. As a substitute for the variable voltage control, a frequency inverter can also be utilized. 
     Since these motors are combined with sub-resonant tuned drive springs  20  that are properly stabilized by stabilizers  24 , the plurality of motors requires less work output to align with the movement of the stiff drive springs  20  than it would be to try to be “out of step” or not phased or accumulatively synchronized with all the sub-resonant tuned drive springs  20 . 
     The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modification will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention and scope of the appended claims. Accordingly, this invention is not intended to be limited by the specific exemplification presented herein above. Rather, what is intended to be covered is within the spirit and scope of the appended claims.