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INERTIAL CONVEYOR SYSTEM
This is a continuation-in-part application based upon parent application Ser. No. 07/470,844, filed Jan. 25, 5 1990, U.S. Pat. No. 5,046,602.
FIELD OF INVENTION
This invention relates generally to systems for the transport of articles via a conveyor, and more particu- 10 larly to a transport conveyor system utilizing the inertia of the articles themselves for movement along the conveyor to a destination point, the conveyor system having provision for minimizing vibration.
BACKGROUND ART 15
Conveyors systems are utilized in many industries, typically including the manufacturing and packaging industries. These conveyor systems can be of many types, such as continuous belt conveyors, shaker (iner- 20 tial) conveyors, etc. Often the articles being transported must be deposited upon further conveyor units as in the case of a change in direction of the transfer. In the case of the continuous belt type conveyor, when articles are to be deposited upon another belt there is often a drop 25 of several inches due to the size of the rollers/wheels that carry the belt. For some types of articles that are fragile, such as foodstuffs, this drop is detrimental. In the case of the shaker- or inertial-type conveyors, very little drop distance can be provided such that there is no 30 damage to the articles being transferred- Also, the tray in this latter type of conveyor can be made of materials that will not be damaged by the material being transferred and, more importantly, will not contaminate the materials being transferred. 35
A problem that has been encountered in the prior art is the matter of the vibration that often occurs with the devices for inertial-type conveyors. The principle of these conveyors is to cause vibration of the transfer tray such that during a "forward" stroke, the articles are 40 moved with the tray. Then, during the "return" stroke, the inertia of the articles causes them to remain in motion slipping along the tray as the tray is returned. To accomplish this, the tray oscillation is produced by a wide number of mechanisms. Some of these create sub- 45 stantial vibration such that the machine must be firmly attached to a support surface.
A number of mechanisms have been devised to produce the tray oscillation and, in some of the designs, to minimize the vibration. Typically of these prior art 50 devices are those shown and described in U.S. Pat. Nos. 218,757 issued to F. Martin, Jr. on Aug. 19, 1879; 1,843,282 issued to E. Horn et al on Feb. 2, 1932; 3,212,630 issued to K. M. Allen et al on Oct. 19, 1965; 4,019,626 issued to H. J. Kamner on Apr. 26, 1977; and 55 4,339,029 issued to D. A. Wilson On Jul 13, 1982.
Still other references that may be material relative to the present invention are U.S. Pat. Nos.: 3,476,234 issued to K. L, M. Allen, et al on Nov. 4, 1969; 3,817,370 issued to J. P. Cox on Jun. 18, 1974; 4,436,199 issued to 60 K. Baba, et al on Mar. 13, 1984; and 4,567,979 issued to R. A. Hoehn on Feb. 4, 1986. In particular, the '234 Allen reference uses two conveyor members that are driven longitudinally by a single drive means, with one conveyor member used to counter the vibration of the 65 other. As each conveyor moves in a first direction, it is moved downwardly; then, as it is moved in the opposite direction, it is moved upwardly to advance any material
supported thereon. The structure provides a generally back-and-forth vibratory motion, with a tossing motion being given to the conveyors and thus to the material. Both conveyor members have the same acceleration in each direction of motion as they are driven by a common crankshaft-eccentric mechanism.
All of these known systems must be designed for the transport of a specific article on the conveyor, with the exception of those described in the '626 and '019 patents which can be modified for specific products. However, even with the effort to minimize vibration, each of these devices does produce undesirable vibration (and thus noise) during operation. Further, some of these systems (e.g., the '234 reference) will damage fragile items being transported on the tray thereof. While these patents describe the principles of inertial conveyance, several are constructed without an understanding of these principles.
Accordingly, it is an object of the present invention to provide an inertial-type convey system that substantially eliminates vibration effects of the operating mechanism.
Another object of the present invention is to provide means for offsetting a reaction force produced by the acceleration of the conveyor tray and for offsetting a couple produced by that reaction force to thereby eliminate vibrational effects.
It is another object of the present invention to provide an inertial conveyor system utilizing a counterbalance (counterweight) means to offset the reaction force produced by the moving of the conveyor tray means so as to substantially eliminate vibration effects of the operating mechanism.
It is also an object of the present invention to provide a conveyor system using a counterweight means to overcome vibration where the weight of the counterweight means is substantially equal to the weight of the conveyor tray means and wherein the center of mass of the counterweight means is matched to the center of mass of the conveyor tray means along a common line of action in order so as to provide for offsetting the reaction force and the couple produced by the acceleration of the conveyor tray means.
These and other objects of the present invention will become apparent upon a consideration of the drawings which are referenced below and a complete description thereof.
SUMMARY OF INVENTION
In accordance with the present invention, there is provided in the preferred embodiment an inertial conveyor system wherein a plurality of rotatable cam surfaces and cam followers provide simultaneous reciprocating longitudinal movement of a conveyor tray means and a counterweight means, with the counterweight means moving in a direction opposite the movement of the conveyor tray means. The conveyor tray means and the counterweight means are constructed such that the reaction force of the conveyor tray means equals the reaction force of the counterweight means, and the couple (rotational force) of the conveyor tray means equals the couple of the counterweiqht means (where reaction force is mass times acceleration and couple is the reaction force times.distance from a common reference point). These equalities are satisfied, in one embodiment, when the conveyor tray means and the counterweight means have substantially the same weight and when the center of mass of the conveyor tray means and
FIG. 1 is a side elevation of a general conveyor system that incorporates the features of the present invention, this drawing illustrating approximately one-half of the system.
FIG. 2 is an end elevation of the general conveyor ^ system of FIG. 1.
FIG. 3 is a side elevation of the drive mechanism as utilized in the general conveyor system of FIG. 1 to substantially eliminate vibration, and showing the relationship of this drive mechanism to the tray of the conveyor system. In this FIG. 3 (and in FIG. 4) surfaces are shaded using color symbols to distinguish between the components that produce movement of the conveyor tray, the components that move the counterweight, and the components that relate to both movements.
FIG. 4 is an end elevation of the apparatus shown in FIG. 3.
FIG. 5 is series of plots representing acceleration, velocity and cam height as a function of rotation of a ^ cam utilized to produce the inertial motion to articles handled on the conveyor of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring first to FIGS. 1 and 2, shown therein is the general form of the inertial conveyor system of the present invention. It has a frame 12 which typically has a pair of side supports 14,16 extending substantially the length of the device, with a plurality of upright legs 18, 40 18A, etc. that terminate in plate-like feet 20, 20A, etc. to provide adequate support upon a surface 22. If desired, these feet can be attached to the support surface. Appropriate cross-braces 24, 24A, etc. are typically used. It will be understood, however, that the shape and over- 45 all construction of the frame 12 can be changed without departing from the scope of the present invention.
A plurality of upright supports 26, 26A, etc. are fixedly attached to the top edge of the side supports 14, 16. These upright supports typically support bars 28, 50 28A, etc. passing across the frame 12, with upright leveling arms 30, 30A, etc. adjustably mounted from the support bars using coupling means 32, 32A, etc. Guide members 34, 34A, etc. are typically attached to the upper ends of these leveling arms, with these guide 55 members engaging slideways 36, 36A, etc. attached to (or forming part of) the bottom of a conveyor pan or tray 38 as part of a conveyor tray means 39. Also attached to the top edge of the side supports 14, 16 is a mechanism 40 for the operating components utilized to 60 create the reciprocating motion of the conveyor tray means 39, as well as the reciprocating motion of a counterweight means 42. As is the case of the components of the frame 12, the other general tray support components discussed are not considered unique relative to the 65 present invention except for the details given hereinafter with regard to the content of the enclosure 40 and the counterweight means 42.
Referring now to FIGS. 3 and 4, shown therein are the components used in accordance to the present invention to achieve oscillatory axial movement of a conveyor tray means 39, including pan 38, and counterweight means 42, the counterweight means being a preferred form of means to offset a reaction force produced by the means 39 moving tray 38. In order to distinguish the various components as related to the movement of the tray means and counterweight means, component shading is used in these figures. Components (i.e., the tray means) associated with only tray movement are shaded with closely spaced diagonal lines, components associated with only counterweight means movement are shaded as with closely spaced diagonal lines in an opposite direction, and components associated with both movements are shaded with vertical dashed lines.
This mechanism 40 is housed in an enclosure 50, primarily so that adequate lubrication can be provided. A shaft 52, driven by any suitable rotating means, traverses this enclosure where it is journalled in bearing/seal units 54, 54A. A cam member 56 is attached to this shaft within the enclosure. This cam member 56 typically is fabricated from nylon or has a nylon outer surface. Of course, other suitable materials can be used. The cam member has cam surfaces 58, 58A at opposite ends, with these surfaces being uniformly spaced apart. In addition, a second pair of cam surfaces 60, 60A are provided on the periphery of the cam member, with these surfaces also being uniformly spaced apart. The particular contour of these cam surfaces 58, 58A, 60, 60A will be discussed in detail hereinafter.
In the particular embodiment illustrated in FIG. 3, the cam surfaces 58, 58A are utilized to drive the pan or tray 38 of the conveyor. Accordingly, cam followers 62, 62A are mounted on a reciprocatable member 64 (a second set of followers and reciprocatable member are also used, see FIG. 4) that passes through appropriatelybushed openings in the enclosure 50. These cam followers typically have rollers in contact with the surfaces of the cam member. Opposite ends of the reciprocatable member 64 are attached to pan supports 66,66A that are fixedly attached to the tray 38 with any suitable means. The cam followers, the reciprocatable member(s) 64, the pan supports 66, 66A, and the pan or tray 38 make up the conveyor tray means 39. Thus, as the cam member 56 is rotated, cam followers 62, 62A move axially as they follow the contour of cam surfaces 58, 58A and, accordingly, move the member 64 axially to cause the tray to move longitudinally. As- discussed below, the contours of the cam surfaces 58, 58A determine the distance of travel as well as the velocity and acceleration of the tray 38.
Cam followers 68, 68A (also typically with rollers) are attached to another reciprocatable member 70 (a second similar member is shown in FIG. 4), and these cam followers track the cam surfaces 60, 60A. Thus, as the cam member is rotated, the member 70 is caused to reciprocate. This member 70 passes through appropriately-bushed openings in both the enclosure 50 as well as the tray supports 66, 66A. Attached at opposite ends of the member 70 are support means for the counterweights. These support means include cross-brace members 72, 72A and upright members 74, 74A, etc. (see FIG. 4). Attached to these upright members is a counterweight 76. A second counterweight 76A is on the opposite side of the tray as shown in FIG. 4. Although not shown, the position of the counterweights
76, 76A can be adjusted relative to the upright members 72, 72A so as to adjust the center of mass of the counterweight means 42 relative to the center of mass of the conveyor tray means 39. In this manner, the center of mass of these two means can be made to move along a 5 common line of action during operation of the conveyor system. As indicated above, this is one embodiment for matching the reaction force and the couple of the two portions of the present invention.
The cam followers 58, 68A, the member(s) 70, the 10 counterweight supports 72, 72A, 74, 74A and the counterweights 76, 76A make up the counterweight means 42. By this construction, the counterweight means 42 is moved in the opposite direction from movement of the tray means 39 to offset the reaction force produced by 15 means 39 in moving the tray 38. By the choice of the cam surfaces 60, 60A the counterweight means can be moved with the proper distance, acceleration and velocity to negate vibration that would be caused by the movement of the tray 38. 20
The weight of the two counterweights 76, 76A is chosen, in combination with their actuating means, to be approximate the weight of the moving tray 38 and its actuating means. Furthermore, the shape and position of the counterweights are chosen so that the center of 25 mass of the counterweight means 42 moves along a line of action that is common with the movement of the center of mass of the tray means 39. This matching of the weights and centers of mass substantially negates undesirable vibration. 30
A typical relationship between acceleration and velocity of a tray (for a given R.P.M.) is depicted in FIG. 5 as a function of the contour of the cam member during a complete rotation thereof. The values of velocity and acceleration (which is the derivative of velocity) of the 35 tray or pan are shown as being cross-hatched with the indications where there is negative velocity and negative acceleration in addition to the positive values thereof. These values are those that would be experienced when a cam member is used having a two inch 40 stroke and the forward stroke is about 270° with the return stroke being about 90°. As discussed hereinafter, other proportions of forward and return strokes can be used effectively. Of course, other stroke lengths can be used also. In order to understand the effect of the pan 45 movement upon products carried thereon, the velocity of the product is indicated with a dashed line adjacent the velocity of the pan.
Portions of the velocity curves of the pan and the product articles for a previous and following rotation of 50 the cam member are shown to assist in this understanding of product movement by inertia. In this embodiment, the cam member initially (in a given revolution of the cam member) provides a constantly increasing velocity that results in a constant acceleration. The accel- 55 eration achieved during at least a major portion of the forward stroke is chosen such that the frictional contact (due to the coefficient of friction of the product and of the pan) between product articles on the tray and the surface of the tray causes the product articles to move 60 in the same direction as the tray with the same velocity. The acceleration during this forward stroke can be limited (by cam shape and R.P.M.) to that at which frictional contact of the product articles and the tray is not overcome as discussed in the afore-referenced pa- 65 tent application Ser. No. 07/470,844. If necessary, this coefficient of friction can be determined by measuring the angle of repose which is the maximum angle at
which the product will stay in place. Typical values are 31° for a coefficient of friction of 0.6 to 11 + ° for a coefficient of friction of 0.2.
As illustrated in FIG. 5, as the 270° of the cam member is approached, the velocity of the pan is rapidly decreased resulting in a rather sudden change in acceleration to a negative acceleration. A small transition of, for example, 2° on the cam member provides a small "slope" to the acceleration changes as indicated at A, B and C. This reduces "hammer-type" noise. The product articles, however, continue to move across the surface of the tray due to their inertia as the tray direction is reversed. The velocity of the product articles is gradually reduced during the return stroke of the pan due to frictional effect. This return stroke (in this embodiment) occurs over a period of about 90° of rotation. For about one-half of this return stroke, the nearly linear increase of velocity in the opposite direction produces the nearly constant (but negative) acceleration with this acceleration being sufficient to completely overcome frictional forces between the articles and the tray so that, as indicated, the product articles continue to move forward by inertia. As the velocity during the return stroke returns to a zero value before beginning the forward stroke, the acceleration again changes direction and is a rather constant but large value. When the cam member has completed one full revolution and is started on the next revolution the product articles are again accelerated when the pan velocity reaches a point where the pan and product articles move together.
In this FIG. 5 the general contour of a cam member is depicted for a two-inch stroke. In order to prevent a too severe angle of attack of cam followers on a cam having a two-inch stroke, the cam member typically has an 8-inch diameter. When only a one-inch stroke is required, this diameter can be smaller. It will be understood, however, that other stroke values can be used as well as other divisions of forward and reverse directions during each revolution of the cam member. Generally, the forward stroke is about 200° to about 280° of a revolution with the return stroke being essentially all of the remaining portion of a revolution of the cam member. Also, the cam surfaces can be altered to provide substantially constant velocity during the forward stroke as long as the resultant ever-increasing acceleration on the forward stroke moves the articles in the same direction as the tray, with the acceleration on the return stroke being greater than this value of the forward stroke.
Since there is a portion of the rotation of the cam member in the forward stroke where the velocity of the product articles is reducing, there is some inefficiency in the transport of the product. It can be seen that during a time Ti the articles are being carried forward on the pan. Then during a time T2 the product articles are being carried forward by their own inertia. The lost time T3, with this particular proportion of forward and return strokes, is nearly 90° of rotation.
In order to reduce this lost time and thus more efficiently transfer product articles, it has been found that for most products a forward stroke during about 226° and a return stroke of about 134° substantially improves the throughput of the system. In addition, about a 2° transition between the change in acceleration is effective in reducing some of the noise generated by the system due to moving mechanical components. When product articles exhibiting higher than average coefficients of friction are being moved, any detrimental effect