Abstract:
A flat stroke bi-directional conveyor for conveying object, granular and powder material. The unit utilizes the skewed sine wave trough stroke principle using primary eccentric counterweights wheels driven by a motor running at the secondary speed and equipped with the secondary eccentric counterweight wheels. The forces not in line with the trough stroke are absorbed with an isolation spring mounted between the drive assembly and the base.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to vibrating conveyors, and more particularly, to a vibratory conveyor of the flat stroke design, capable of conveying in both the forward and reverse flow direction.  
         BACKGROUND OF THE INVENTION  
         [0002]    Two-way flat stroke vibratory conveyors or feeders have substantial applications in a variety of fields. One typical application is in foundry operations wherein, for example, foundry castings may be delivered to a conveyor energized to feed the castings to one end or the other, depending upon where it is desired to locate the castings. Another typical application is in the bulk operations of granular materials wherein, for example, sugar, sand, stone, flour, cement, and various other chemical compounds may be delivered to one end or the other in the same way. Additionally, the conveyors may also move combinations of these object, granular and powder materials.  
           [0003]    A conventional two-way flat stroke conveyor made according to the prior-art will typically include a motor powered drive system that includes four drive shafts having pairs of eccentric counterweight wheels connected via an elaborate belt connection. This drive is coupled to an elongated bed with an upwardly facing, generally horizontal conveying or feeding surface terminating at opposite ends. In operation the two sets of eccentric counterweight wheels are driven such that the wheels in each set rotate in opposite direction and the two sets are 90° out of phase relative to one another. When the motor powers the drives, a cyclic vibratory force is produced and the output displacement is transferred to the bed to create material flow. If one were to plot the sum of the stroke versus stroke angle of the sets of eccentric counterweight wheels, the result would be a skewed or biased sine wave in the direction of material flow. By reversing the rotation of the system, the skewed sine wave is reversed and the material flow is reversed.  
           [0004]    This prior art conveyor poses a number of problems, the greatest of which is the complexity of the drive on what is essentially a brute force system. In other words, as the drive consists of four shafts with pairs of eccentric counterweight wheels, and the wheels, bearings and shafts must be large to transfer the forces, the result is a complex belt drive system with great maintenance and alignment difficulties.  
           [0005]    U.S. Pat. No. 5,934,446 to Thomson (incorporated herein by reference) attempts to address these problems with a vibratory conveyor that includes a generally horizontal, elongated conveying surface connected to a base by generally vertically arranged, resilient slats. A drive is mounted to the surface and includes two rotary eccentric shafts coupled in series and set 90° out of phase for vibrating the surface in a generally horizontal direction by imparting a cyclic vibrating force in the form of a skewed sine wave. In other words, the drive, through the connecting drive slats, imparts a horizontal force to the trough, causing it to vibrate in the horizontal direction.  
           [0006]    Essentially, the conveyor in the Thomson patent is tuned, through the reactor slats, to approximately 7% above the primary shaft rpm. This design, as such, takes advantage of the sub-resonant natural frequency and reduces the forces to the drive bearings as well as reducing the motor size requirements as compared to the prior art. In other words, the primary horizontal eccentric force and stroke is amplified and the lessor secondary eccentric wheel force is transmitted in a brute force manner, resulting in a smaller skewing stroke component. However, the disadvantage of the Thomson patent remains its drive complexity and space limitation with respect to both manufacture and maintenance costs.  
           [0007]    Accordingly, it is a general object of the present invention to provide a new and improved flat stroke bi-directional conveyor.  
           [0008]    Another general object of the present invention is to overcome those deficiencies of the flat stroke conveyors of the prior art.  
           [0009]    It is a more specific object of the present invention to provide an improved flat stroke bi-directional conveyor which utilizes the skewed sine wave principle to transfer force to the conveying bed.  
           [0010]    It is another object of the present invention to provide an improved conveyor which utilizes less and smaller component parts, as compared to current practice, thereby greatly reducing manufacture and maintenance costs.  
         SUMMARY OF THE INVENTION  
         [0011]    The invention is generally directed to a bi-directional vibratory conveyor having a trough with an upper conveying surface for transferring energy to convey material along the surface. The drive assembly includes a drive shaft with a primary counterweight and a driven sheave, a motor shaft with a secondary counterweight and a driver sheave, a timing belt connecting the sheaves and a motor having a reversible output connected to the motor shaft for causing a direction of rotation that produces both horizontal and vertical energy components. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The features of the present invention which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identifying like elements, and in which:  
         [0013]    [0013]FIG. 1 is a side elevation view of a flat stroke bi-directional conveyor made according to the principles of the present invention with certain parts omitted for clarity purposes.  
         [0014]    [0014]FIG. 2 is a cross-sectional top plan view of the bi-directional conveyor made according to the principles of the present invention taken along lines  2 - 2  of FIG. 1.  
         [0015]    [0015]FIG. 3 is a cross-sectional frontal view of the bi-directional conveyor made according to the principles of the present invention taken along lines  3 - 3  of FIG. 1.  
         [0016]    [0016]FIG. 4 is a cross-sectional rear view of the bi-directional conveyor made according to the principles of the present invention taken along lines  4 - 4  of FIG. 1.  
         [0017]    [0017]FIG. 5 is a cross-sectional rear view of the bi-directional conveyor made according to the principles of the present invention taken along lines  5 - 5  of FIG. 1.  
         [0018]    [0018]FIG. 6 is a graph plotting stroke versus stroke angle of the primary and secondary counterweights as well as the combined sum of the two frequencies showing the skewed sinusoidal stroke.  
         [0019]    [0019]FIG. 7 is a graph of the combined sum of the two frequencies of FIG. 6 when the motor rotation is reversed.  
         [0020]    [0020]FIG. 8 is a depiction of the eccentric counterweight wheel positions every 90° of counter-clockwise rotation of the secondary wheels.  
         [0021]    [0021]FIG. 9 is a depiction of the eccentric counterweight wheel positions every 90° of clockwise rotation of the secondary wheels.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    An exemplary embodiment of a flat stroke bi-directional conveyor or feeder is illustrated in the drawings and will be described herein as a conveyor, it is understood that the terms conveyor and feeder are synonymous for purposes of the present application. Referring now to the drawings, and particularly to FIG. 1, a conveyor  10  constructed in accordance with the invention is seen to basically include a base  12 , which may be mounted on the underlying terrain as, for example, the floor of a building, a table structure or the like. Supported about the base  12  is a generally horizontal, elongated, trough  14  having opposed ends  16  and  18 , as well as an upper conveying surface  20 . The trough  14  is supported about the base  12  by a series of vertically arrayed, vertical resiliency members  22 , for example a rocker leg and coil spring combination, or, preferably vertical leaf spring slats of conventional construction that are secured to both the underside of the trough  14  and to the base  12  at spaced locations via fabricated structural brackets  24  and fabricated brackets  26  respectively.  
         [0023]    The drive assembly, FIG. 2, consists of a structural drive fabricated horizontal rectangular box  28  and is preferably opened at the top and bottom. Two flange bearings  30  are mounted on each longitudinal side holding a lateral drive shaft  32  which in turn supports two primary eccentric counterweights  34 . A preferably totally enclosed and non-ventilated heavy duty reversible shaker motor  36  is bolted at one end of the drive box  28  so that the motor shaft  38  is lateral and horizontal to the elongated trough  14 . Two secondary eccentric counterweights  40  are mounted on the motor shaft  38 . The two primary eccentric counterweights  32  are driven by a synchronous timing belt  42  and driver and driven sprocket system are respectively longitudinally aligned whereby the driver sheave  44  is mounted on the motor shaft  38  and the driven sheave  46  is mounted on the primary drive shaft  32 . The drive assembly is attached to the trough  14  with a horizontal resiliency member  48 , preferably a leaf spring slat connected to the drive at the opposite end of the drive motor  36  and attached to a trough drive bracket  50  that is in turn connected to the trough  14 . Lastly, a spring  52  is connected to the bottom side of the drive and at the opposite end to the base  12 .  
         [0024]    Thus far, FIGS. 1 and 2 have been shown and described to give the overall look and general structure of the principle components of the present invention. Turning now to the cross-sectional views of FIGS. 3-5, the functional aspects of the principle components of the present invention are shown and described. Referring to FIG. 3, the front of the drive assembly is shown with respect to its position above the base  12  and beneath the trough  14  as supported by the spring  52 . Within the drive box  28  is the shaker motor  36  which drives motor shaft  38 . The two secondary eccentric counterweights  40  rotate about the shaft  38  upon the motor  36  generating rotational power to the shaft  38 . Also, coupled to and rotating with the motor shaft  38  is the driver sheave  44 . The driver sheave  44  in turn rotates the driven sheave  46  through timing belt  42 . In the preferred embodiment, the driven sheave  46  is preferably twice the diameter of the driver sheave  44 , thereby causing the primary eccentric counterweights  34  to rotate at half the speed of the secondary eccentric counterweights  40 . Although, multiple combinations may provide the desired results, these speeds of rotation are preferably 300 r.p.m. and 600 r.p.m. respectively.  
         [0025]    Referring now to FIG. 4, the rear of the drive assembly is shown with respect to its positions above the base  12  and beneath the trough  14  as supported by the spring  52 . The previously discussed rotation of the driven sheave  46  in turn rotates the lateral drive shaft  32 , which is supported within the drive box  28  by flange bearings  30 , thereby causing the two primary eccentric counterweights  34  to rotate about the drive shaft  32 . The primary eccentric counterweights  34  and the secondary eccentric counterweights  40  are timed so that the primary eccentric counterweights  34  are horizontal when the secondary eccentric counterweights  40  are vertical i.e. lag the primary eccentric counterweights by 90°. The spring  52  illustrated in FIGS. 1-4 as being connected to the bottom side of the drive assembly and the opposite end connected to the base  12  serves a dual purpose. First, the spring  52  is sized to isolate and help support the drive assembly from the base  12  and accordingly nearly eliminates the vertically induced forces transmitted to the ground. In other words, the forces of the wheels not in line with the trough stroke (infra) are absorbed via this spring. Second, the spring  52  supports the drive assembly weight in order to relieve pre-loading the horizontal leaf spring slat  48 .  
         [0026]    Finally, FIG. 5 illustrates the coupling of the base  12  and the trough  14  through the leaf spring slats  22  that are connected thereto by fabricated structural brackets  24  and fabricated brackets  26  respectively. These leaf spring slats  22  are sized so that the total spring rate sets the single mass natural frequency of the elongated trough  14  mass at preferably about seven percent (7%) over the primary running frequency. Furthermore, the leaf spring slats  22  are positioned vertically with respect to the base  12  and trough  14  so that the direction of the vibratory motion is horizontal and parallel to the elongated trough  14 .  
         [0027]    With the general structure and function of the component parts shown and described with respect to FIG. 1-5, FIGS. 6-9 are now discussed as they relate to the general operation of the present invention. During operation and when the motor  36  is turned on to rotate the motor shaft  38  in a counter-clockwise manner, the secondary eccentric counterweights  40  and the primary eccentric counterweights  34  transfer energy through the horizontal leaf spring slat  48 , the trough drive bracket  50 , and ultimately the trough  14  in the form of a modified sinusoidal skewed stroke pattern as shown in FIG. 6. This stroke pattern has been termed a “skewed sine wave” in that the slope of one side of each wave is shallower than the slope of the other side of the wave. Thus, if the stroke pattern illustrated by FIG. 6 is being applied to the components in the manner illustrated in FIGS. 1-5, movement of the trough  14  to the right, that is toward the end  18 , will be relatively slow while the return movement toward the other end  16  will be relatively fast. In this case, conveying will be to the right because the slow movement to the right will allow the material being conveyed to frictionally engage and be advanced in that direction by the conveying surface  20  of the trough  14 . On the other hand, the fact that the return is so rapid, and the fact that the material still contains momentum energy from the rightward stroke will result in little or no reverse movement during the return stroke. The net result will be conveying of the material to the right.  
         [0028]    When the operation is as in FIG. 7, the opposite will occur. By reversing the motor rotation, the sinusoidal skewed stroke is biased to the left and the material flow is reversed to the left. As above, but stated differently, the stroke is skewed, now to the left, so that the trough movement to the left takes approximately twice the time which results in a low enough acceleration force, to promote material conveyance during the portion of the cycle as the return movement to the right does. The result is a biased impulse to the left causing material on the trough to be conveyed to the left.  
         [0029]    As shown and described, it is the transfer of energy of the counterweights to the trough that produces the material flow. The present invention provides this forward material flow because the eccentric counterweight wheels are aligned such that the secondary wheels lag the primary wheels by 90° when the primary wheels are in line with the line of action of the trough stroke. The 90° offset fixed eccentric counterweight wheels are further capable of producing reverse material flow because the offset run in the opposite direction changes from a lagging profile to a leading profile resulting in reversing the skewed sinusoidal stroke.  
         [0030]    This lagging/leading 90° offset is best illustrated with respect to FIGS. 8 and 9 respectively. FIG. 8 shows a step-wise representation  54  of the relative positions of the primary  34  and secondary  40  eccentric counterweights for every 90° counter-clockwise rotation  56  of the secondary eccentric counterweights  40 . The phase illustration  58  to the right of the nine-step series  54  shows the positions of the wheels where the maximum strokes occur when the material flow is from left to right. Similarly, FIG. 9 shows a step wise representation  60  of the relative positions of the primary  34  and secondary  40  eccentric counterweights for every 90° clockwise rotation  62  of the secondary eccentric counterweights  40 . The phase illustration  64  to the right of the nine-step series  60  shows the positions of the wheels where the maximum strokes occur when the material flow is from right to left.  
         [0031]    From the foregoing, it will be appreciated that a flat stroke bi-directional vibratory conveyor made according to the invention produces a number of advantages over the prior art apparatus. For one, wheel sizes are greatly reduced without loss of stroke force. More particularly, the present invention utilizes a 2:1 frequency ratio and a 1:3 eccentric force ratio that results in the wheel sizes to be [(2×2)×1]:[1×3] or a 4:3 ratio for wheel size. Furthermore, the size of the wheels are even smaller because the present invention&#39;s lower frequency stroke is amplified by the sub-resonant tuned frequency of the trough, thereby further reducing the 4:3 ratio to around 1.75:3 ratio. In other words, by adapting the motor to the secondary frequency, motor eccentric counterweight wheels are small, and further, the primary eccentric counterweight wheels are minimized because of the sub-resonant tuning of the conveyor.  
         [0032]    By way of example, assume that the conveyor trough natural frequency is set to be around 7% above the primary frequency. So, if the primary frequency is 300 rpm then the trough frequency is set to 320 rpm. The combined result is that the primary running frequency of 300 rpm is amplified as a sub-resonant natural frequency single mass conveyor system. The primary and secondary counterweight wheels have approximately the same brute force stroke. Because the primary natural frequency is close to the primary running speed, the trough stroke amplifies by a factor of about three times the brute force stroke.  
         [0033]    It will therefore be appreciated that a flat-stroke bi-directional conveyor made according to the principles of the present invention provides considerable advancements over the aforementioned deficiencies of the prior art.  
         [0034]    While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true sprit and scope of the invention.