Abstract:
A conveyor for materials uses a gearset to generate horizontal differential conveying motion in a conveying member. The conveying motion includes an advancing stroke in a conveying direction and a retracting stroke in a direction opposite to the conveying direction. The linear velocity of the retracting stroke is greater than the linear velocity of the advancing stroke to move materials along the conveying member in the conveying direction. The gearset is preferably a ring gear and a pinion.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is directed generally to a conveyor for materials. In one aspect, the invention relates to a device and method for generating a horizontal differential motion for conveying materials. In another aspect, the invention relates to a horizontal differential motion conveyor in which a gearset is used to generate a conveying motion. In yet another aspect, the invention relates to a horizontal differential motion conveyor in which a ring gear and a pinion are used to generate a conveying motion. In a further aspect, the invention relates to a horizontal differential motion conveyor having a conveying motion which has an advancing stroke and a retracting stroke, wherein a linear velocity of the retracting stroke is greater than a linear velocity of the advancing stroke. In yet a further aspect, the invention relates to horizontal differential motion conveyor having a conveying motion which can be described by an approximation of a sawtooth waveform.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many production processes require the products being processed to be conveyed from one place to another place. Some products, such as dry cereals, snack chips, and the like, are very fragile and must be handled carefully. Belt conveyors are not well suited to this environment because they are difficult to clean. Vibratory conveyors oscillate at an acute angle to the conveying direction in order to convey the product. These conveyors bounce the product as it is conveyed, which causes the product to break and a residue to build up on the conveying surface.  
           [0003]    To overcome these problems, conveyors have been developed which use a horizontal differential motion to propel the product along a conveying surface. Horizontal differential motion is the resultant of the superposition of two sinusoidal waveforms which result in a second order approximation of a sawtooth waveform. A sawtooth waveform  100 , overlaid with a typical horizontal differential motion waveform  102 , is shown in FIG. 1. The horizontal differential motion waveform can be expressed as a Fourier series having two harmonics by the expression: 
           ƒ(θ 1 ,θ 2 )=2 sin(θ 1 )−sin(2θ 2 ) 
           [0004]    wherein:  
           [0005]    θ 1 =phase angle of the first harmonic waveform; and  
           [0006]    θ 2 =phase angle of the second harmonic waveform.  
           [0007]    Descriptively, the above equation provides that the primary harmonic function has two times the amplitude of the secondary harmonic function, while the secondary harmonic function is at twice the frequency of the primary harmonic function. Further, the secondary harmonic function is moving in the opposite direction from the primary harmonic function.  
           [0008]    The resulting motion is made up of a series of oscillations, parallel to the conveying direction, which propels a product without causing the product to bounce on the conveying surface. The oscillations are made up of a slower advancing stroke and a faster retracting stroke. The slower advancing stroke moves in the conveying direction and carries the product with it. The faster retracting stroke causes the product to slide across and advance along the conveying surface by overcoming the friction between the product and the conveying surface. Repeating this motion causes the product to be conveyed, in the conveying direction, along the conveying surface. The conveying speed for this type of conveyor is increased by increasing either the amplitude or the frequency of the horizontal differential motion.  
           [0009]    Most horizontal differential motion conveyors typically use two sets of two rotating, eccentrically-weighted shafts to produce the desired motion. The shafts in each set rotate in opposite directions to counteract any vertical force component. This arrangement results in a horizontal resolution of the two force functions, which are each simple harmonics, but combine to produce a second order approximation of a sawtooth function. Examples of horizontal differential motion conveyors which use counter-rotating weighted shafts can be found in U.S. Pat. Nos. 5,392,898 and 5,584,375 to Burgess et al. A further example of this type of horizontal differential motion conveyor is the Slipstick® conveyor, which is manufactured by Triple/S Dynamics, Inc. of Dallas, Tex.  
           [0010]    As stated above, one way to improve the conveying speed is to increase the oscillation amplitude. In a counter-rotating shaft conveyor, increases in oscillation amplitude require large increases in the mass of the eccentric weights used to generate the differential force, since the stroke of this type of conveyor is proportional to the mass of the eccentric weights. The mass used to generate the horizontal differential motion must also be oscillated, thus the efficiency of the conveyor is diminished due to the added drive mass. Accordingly, the excursion or linear displacement of the conveyor is limited, from a practical standpoint, to one inch or less. Further, larger housings are required when the mass of the eccentric weights is increased. Another method for increasing the conveying speed is to increase the oscillation frequency. Increases in the oscillation frequency, however, cause increases in the forces which are resisted by the conveyor supports. For these reasons, counter-rotating shaft conveyors do not lend themselves to miniaturization.  
           [0011]    Other drive unit configurations have been employed to produce a horizontal differential conveying motion. A drive unit using cams and cam followers is disclosed in U.S. Pat. No. 5,046,602 to Smalley et al. This design is inherently complex, and wear on the contacting surfaces results in a comparatively high level of required maintenance. In addition, a drive unit employing a bent universal joint is disclosed in U.S. Pat. Nos. 5,351,807 and 5,699,897 to Svejkovsky. This configuration results in a rather large load being passed through the small bearings in the universal joint. Reversals of the load on the drive train can also cause damage to the universal joint. Further, a significant amount of space is required to house the shaft, bearings, gear reducer, and other elements of the drive.  
           [0012]    Thus, a need exists for a horizontal differential motion conveyor having a drive unit which can be made compact and thereby lends itself to miniaturization. Further, a need exists for a horizontal differential motion conveyor having a drive unit which can produce large amplitudes, and thus, greater conveying speeds. Yet another need exists for a horizontal differential motion conveyor having a drive unit which is simple and requires little maintenance. Yet a further need exists for a horizontal differential motion conveyor having a drive unit which is tolerant of load reversals on the drive unit.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    The present invention is a new and advantageous device and method for generating a horizontal differential motion for conveying materials. The device generates a horizontal differential conveying motion substantially only in a direction parallel to a conveying direction. The conveyor of the present invention can be made compact and, thus, lends itself to miniaturization. The drive unit of the present invention can generate large amplitudes, thereby producing greater conveying speeds. The drive unit of the present invention is simple, requires little maintenance, and is tolerant of load reversals.  
           [0014]    According to one aspect of the present invention, a device for generating a horizontal differential motion includes a first connection for attaching the device to a second device, such as a conveying member. The first connection is rotatable about a first axis of rotation. Further, the first axis of rotation is rotatable about a second axis of rotation. By rotating the first connection about the first axis of rotation while rotating the first axis of rotation about the second axis of rotation, a horizontal differential motion is produced.  
           [0015]    According to another aspect of the present invention, a method of generating a horizontal differential conveying motion includes the steps of rotating the first connection about the first axis of rotation while rotating the first axis of rotation about the second axis of rotation. The motion generated by these steps is transmitted to a second device, such as a conveying member, from a location corresponding to the first connection.  
           [0016]    According to yet another aspect of the present invention, a conveyor is provided having a drive unit, comprising a gearset, which generates a conveying motion substantially only in a conveying direction. The conveying motion has an advancing stroke in the conveying direction and a retracting stroke in a direction opposite to the conveying direction. The linear velocity of the retracting stroke is larger than that of the advancing stroke so as to move material being conveyed along a conveying member in the conveying direction.  
           [0017]    Further, according to another aspect of the present invention, the conveying member is elongated in shape and has a longitudinal axis which is substantially parallel to the conveying direction.  
           [0018]    According to yet a further aspect of the present invention, the gearset of the drive unit includes a ring gear and a pinion.  
           [0019]    According to another aspect of the present invention, a plot of the conveying motion with respect to time is an approximation of a sawtooth waveform.  
           [0020]    According to yet another aspect of the present invention, a conveyor is provided having a power source which rotates a pinion engaged with a ring gear. A conveyor linkage is attached to a face of the pinion and to a conveying member. As the power source rotates the pinion, a conveying motion is generated having an advancing stroke in a conveying direction and a retracting stroke in a direction opposite to the conveying direction. The linear velocity of the retracting stroke is larger than that of the advancing stroke so as to move material being conveyed along a conveying member in the conveying direction.  
           [0021]    According to a further aspect of the present invention, a pitch radius of the ring gear is approximately equal to three times a pitch radius of the pinion.  
           [0022]    According to yet a further aspect of the present invention, a distance between a first axis of the pinion and an second axis of the ring gear is approximately two times a distance between the location where the conveyor linkage is attached to the face of the pinion and the first axis of the pinion.  
           [0023]    According to still a further aspect of the invention, the conveying motion can be described by the function: 
           ƒ( t )=2 sin(ω 1   t )−sin(2ω 2   t ) 
           [0024]    wherein:  
           [0025]    ω 1 =an angular velocity of the first axis of the pinion about the second axis of the ring gear; and  
           [0026]    ω 2 =an angular velocity of a first connection of the conveyor linkage on the face of the pinion about the first axis of the pinion.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0027]    Other advantages and features of the invention will become more apparent with reference to the following detailed description of the presently preferred embodiment thereof in connection with the accompanying drawings, wherein like reference numerals have been applied to like elements, in which:  
         [0028]    [0028]FIG. 1 is a graph illustrating a sawtooth waveform and an approximation of a sawtooth waveform;  
         [0029]    [0029]FIG. 2 is a plan view of a drive unit and a conveyor of the present invention;  
         [0030]    [0030]FIG. 3 is a schematic view of a drive unit of the present invention;  
         [0031]    [0031]FIG. 4 is a plan view of a drive unit of the present invention;  
         [0032]    [0032]FIG. 5 is a schematic view of the drive unit of FIG. 4 and a corresponding plot of a horizontal differential motion produced by the drive unit.  
         [0033]    [0033]FIG. 6 is a graph showing relationships between table movement or displacement and the distance between the first connection and the first axis;  
         [0034]    [0034]FIG. 7 is a plot showing the locations of the pinion and the first connection according to one embodiment of the present invention wherein the distance between the first connection and the first axis is 25.4 mm (1.0 inches);  
         [0035]    [0035]FIG. 8 is a plot showing the locations of the pinion and the first connection according to another embodiment of the present invention wherein the distance between the first connection and the first axis is 15.7 mm (0.6 inches);  
         [0036]    [0036]FIG. 9A is a schematic view of one embodiment of conveyor of the present invention;  
         [0037]    [0037]FIG. 9B is a graph showing a waveform corresponding to the embodiment of FIG. 9A;  
         [0038]    [0038]FIG. 10A is a schematic view of another embodiment of the present invention;  
         [0039]    [0039]FIG. 10B is a graph showing a waveform corresponding to the embodiment of FIG. 10A;  
         [0040]    [0040]FIG. 11A is a schematic view of yet another embodiment of the present invention;  
         [0041]    [0041]FIG. 11B is a graph showing a waveform corresponding to the embodiment of FIG. 11A;  
         [0042]    [0042]FIG. 12A is a schematic view of a further embodiment of the present invention; and  
         [0043]    [0043]FIG. 12B is a graph showing a waveform corresponding to the embodiment of FIG. 12A.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0044]    Referring to the drawings, and FIG. 2 in particular, shown therein is a conveyor of the present invention having a conveying member  110  and a drive unit  112 . The conveying member  110  can be configured in a variety of shapes but is preferably elongated with a longitudinal axis  114  which is substantially parallel to a conveying direction  116 .  
         [0045]    The drive unit  112  of the present invention generates the conveying motion substantially only in a conveying direction  116  so as to move materials along the conveying member  110  in the conveying direction  116 . An alternate conveying direction can be a direction opposed to the conveying direction  116 .  
         [0046]    Referring now to FIG. 3, the drive unit  112  of the present invention is comprised of a first connection  200 , a first axis  202 , and a second axis  204 . The first axis  202  and the second axis  204  are generally perpendicular to the view shown by FIG. 3. A horizontal differential motion is achieved by rotating the first connection  200  about the first axis  202  in a first direction at an angular velocity ω 2  while rotating the first axis  202  about the second axis  204  in a second direction, counter to that of the first direction, at an angular velocity ω 1 . The line L 1  represents a linkage from the first connection  200  to an exemplary outputted horizontal differential motion waveform  206 . The first axis  202  is located a distance D 1  away from the second axis  204 , and the first connection  200  is located a distance D 2  away from the first axis  202 . In a preferred embodiment, the distance D 1  from the second axis  204  to the first axis  202 , in a plane perpendicular to both the first axis  202  and the second axis  204 , is approximately two times the distance D 2  from the first connection  200  to the first axis  202 . The resulting horizontal differential motion can be described as a Fourier series by the function: 
         ƒ( t )=2 sin(ω 1   t )−sin(2ω 2   t ) 
         [0047]    wherein:  
         [0048]    t=time;  
         [0049]    ω 1 =an angular velocity of the first axis  202  about the second axis  204 ; and  
         [0050]    ω 2 =an angular velocity of the first connection  200  about the first axis  202 .  
         [0051]    Descriptively, the above function defines a waveform which has two harmonic components. The first component (2 sin(ω 1 t)) has twice the amplitude of the second component (sin(2ω 2 t)), while the second component has twice the frequency of the first component. Further, the second component is moving in the opposite direction from the first component.  
         [0052]    [0052]FIG. 4 shows a preferred embodiment of the present invention, wherein the drive unit housing  113  is shown in phantom. The drive unit  112  includes a power source  118 , such as an electric motor (shown in phantom); a gearset  120 ; and a motor linkage  122 . The gearset  116  comprises a pinion  124  engaged with a ring gear  126 . The pinion  124  has an outer surface  128  with a plurality of teeth  130 . Similarly, the ring gear  126  has an inner surface  132  with a plurality of teeth  134 . At any given time, a subset of the plurality of pinion teeth  130  engages a subset of the plurality of ring gear teeth  134 .  
         [0053]    The power source  118  is connected to the pinion  124  by a motor linkage  122  so as to cause the pinion  124  to rotate about a second axis  136  as the pinion  124  rotates about a first axis  138 . The first axis  138  and the second axis  136  correspond to the first axis  202  and the second axis  204 , respectively, of FIG. 3. The second axis  136  is collinear with a center axis of the ring gear  126 , and the first axis  138  is collinear with a center axis of the pinion  124 . A conveyor linkage  140  is connected at a first end  142  to a face  144  of the pinion  124  at a fixed distance away from the first axis  138 . The first connection  148  between the first end  142  of the conveyor linkage  140  and the face  144  of the pinion  124  allows the conveyor linkage  140  to rotate in a plane perpendicular to the first axis  138  and the second axis  136 . The first connection  148  corresponds to the first connection  200  of FIG. 3. A second end  146  of the conveyor linkage  140  is attached by a second connection  149  to the conveying member  110  so as to also allow the conveyor linkage  140  to rotate in a plane perpendicular to the first axis  138  and the second axis  136 .  
         [0054]    Referring now to FIG. 5, the ring gear  126 , the pinion  124 , and the conveyor linkage  140  are shown in schematic form. In a preferred embodiment of the present invention, the pitch radius R 1  of the ring gear  126  is approximately three times the pitch radius R 2  of the pinion  124 . Further, the distance D 1  from the first axis  138  to the second axis  136 , in a plane perpendicular to the first axis  138  and the second axis  136 , is approximately two times the distance D 2  from the first connection  148  at the first end  142  of the conveyor linkage  140  on the face  144  of the pinion  124  to the first axis  138 . As the power source  118  (shown in FIG. 4) causes the pinion  124  to rotate clockwise about the first axis  138  and to rotate counterclockwise about the second axis  136 , a horizontal differential motion is produced at the first connection  148 . A plot of this horizontal differential motion, which is an approximation of a sawtooth waveform, is shown in FIG. 5. This motion can be described as a Fourier series by the formula: 
         ƒ( t )=2 sin(ω 1   t )−sin(2ω 2   t ) 
         [0055]    wherein:  
         [0056]    t=time;  
         [0057]    ω 1 =an angular velocity of the first axis  138  about the second axis  136 ; and  
         [0058]    ω 2 =an angular velocity of a connection  148  at the first end  142  of the conveyor linkage  140  on the face  144  of the pinion  124  about the first axis  138  of the pinion  124 .  
         [0059]    Descriptively, the above formula defines a waveform which has two harmonic components. The first component (2 sin(ω 1 t)) has twice the amplitude of the second component (sin(2ω 2 t)), while the second component has twice the frequency of the first component. Further, the second component is moving in the opposite direction from the first component.  
         [0060]    [0060]FIG. 6 illustrates a correlation between the distance D 2  and the movement or excursion of the conveying member  110  resulting from the horizontal differential motion generated by the drive unit  112  for one embodiment of the present invention. As the distance D 2  is varied from 15.7 mm (0.6 inches) to 25.4 mm (1.0 inch), the excursion increases from about 101.6 mm (4.0 inches) to about 114.3 mm (4.5 inches), and the overall shape of the motion curve changes to one having two distinct peaks. The formation of these peaks indicates that the horizontal differential motion reverses briefly during the overall cycle, which can improve the conveying characteristics of the device.  
         [0061]    Referring now to FIG. 7, wherein the locations of the first connection  148  through one rotational cycle of one embodiment of the present invention are shown. The distance D 2  from the first connection  148  to the first axis  138  is 25.4 mm (0.6 inches). The circle  208  corresponds to the inner surface  132  of the ring gear  126 . Each of the circles  210  (only one circle  210  is indicated in FIG. 7) corresponds to the outer surface  128  of the pinion  124  as the first axis  138  rotates about the second axis  136  at intervals A-S of one revolution of the power source  118 . Each of the circles  212  (only one circle  212  is indicated in FIG. 7) corresponds to locations of the first connection  148  as the first connection  148  rotates about the first axis  138 , also at intervals A-S, during one revolution of the power source  118 .  
         [0062]    Similarly, in reference to FIG. 8, the locations of the first connection  148  through one rotational cycle of another embodiment of the present invention are shown. In this embodiment, distance D2, from the first connection  148  to the first axis  138 , is 15.7 mm (0.6 inches). The circle  208 ′ corresponds to the inner surface  132  of the ring gear  126 . Each of the circles  210 ′ (only one circle  210 ′ is indicated in FIG. 8) corresponds to the outer surface  128  of the pinion  124  as the first axis  138  rotates about the second axis  136  at intervals A′-T′ of one revolution of the power source  118 . Each of the circles  212 ′ (only one circle  212 ′ is indicated in FIG. 8) corresponds to locations of the first connection  148  as the first connection  148  rotates about the first axis  138 , also at intervals A′-T′, during one revolution of the power source  118 .  
         [0063]    Acceleration generated by the device of the present invention is affected by the angular position of the first connection  148  with respect to the first axis  138 , the second axis  136 , and the second connection  149 . Referring now to FIG. 9A, the device of the present invention is shown wherein the second axis  136 , the first axis  138 , the first connection  148 , and the second connection  149  are all positioned on a line L 0  at the start of the motion cycle. FIG. 9B shows the acceleration at the second connection  149  with respect to the rotation of the power source  118  (e.g., motor) in degrees. The acceleration peaks, declines to a lower acceleration, and peaks again, wherein the values corresponding to each of the acceleration peaks are generally equal.  
         [0064]    Referring now to FIG. 10A, the device of the present invention is shown wherein the first axis  138  and the second axis  136  fall on a line L 1  which is parallel to a line L 2  defined by the first connection  148  and the second connection  149 . The first connection  148  is rotationally offset about the first axis  138  as compared to the arrangement shown in FIG. 9A. The first connection  148  is rotationally offset such that an angle between a line L 3 , defined by the first axis  138  and the first connection  148 , and the line L 2  is approximately 30°. This arrangement produces a horizontal differential motion which has an increased first acceleration peak and a decreased second acceleration peak within each cycle, as shown in FIG. 10B.  
         [0065]    [0065]FIG. 11A depects a configuration which is similar to that of FIG. 10A, wherein lines L 4 -L 6  generally correspond to lines L 1 -L 3 , respectively, of FIG. 10A. In this configuration, the angle between line L 5  and line L 6  is approximately 60°, which results in a horizontal differential motion having a further increase in the first acceleration peak and a decrease in the second acceleration peak, as shown in FIG. 11B.  
         [0066]    This progression is continued, as shown in FIG. 12A, wherein lines L 7 -L 9  generally correspond to lines L 1 -L 3  in FIG. 10A and lines L 4 -L 9  in FIG. 11A, respectively. The angle between line L 8  and L 9  is approximately 90°, which further accentuates the first acceleration peak and reduces the second acceleration peak of the horizontal differential motion, as shown in FIG. 12B.  
         [0067]    The conveyor of the present invention can be used in many conveying applications, for example, but not limited to, straight and curved path conveying, split flow conveying, singulating, de-shingling, and size control screening.  
         [0068]    Although the present invention has been described with reference to a presently preferred embodiment, it will be appreciated by those skilled in the art that various modifications, alternatives, variations, etc., may be made without departing from the spirit and scope of the invention as defined in the appended claims.