Flat Article Conveyor

The present invention relates to a flat article conveyor and particularly relates to a conveyor for use in conjunction with automated circuit board manufacturing equipment where conveyors typically transport circuit boards between individual workstations.

In many manufacturing processes, it is conventional to transport an article between various workstations where different types of machines perform various operations on the article undergoing manufacture. For example, in the manufacture of printed circuit boards, many specialized manufacturing operations are performed at various and different workstations. Frequently, however, the boards are transported manually between the workstations. At each workstation, an operator typically removes a board from an input tote box, loads the board into the machine's fixture, waits for the machine to perform its specialized operation on the board and then removes the board from the fixture and disposes it into an output tote box. The tote boxes are, of course, manually moved between the workstations and this sequence of operations is repeated at each of the various workstations.

Automatic conveyance of articles between workstations is, of course, not new per se. However, specialized problems occur in efforts to convey articles, for example, printed circuit boards, in the automated manufacture thereof. For example, it is desirable that the boards be movable bi-directionally and with accuracy into predetermined positions after such movement. The magnitude and direction of forces acting on the moving circuit board must be maintained within predetermined levels. Access to the top and bottom of the boards must be virtually unlimited. Also, transfer problems occur when boards are transferred from one conveyor to the next or from one workstation to a conveyor or the converse. Such problems include boards jamming in the conveyor or electrostatic charge build-up on the board and sudden electrical discharge, which may cause damage to the circuit components of the board. Modularity of system components for serviceability and flexibility, together with low complexity and cost, are also considerations which must be addressed in the provision of a flat article conveyor of the type for transporting printed circuit boards.

One example of a prior flat article conveyor for conveying printed circuit boards between manufacturing workstations is described and illustrated in U.S. Pat. No. 4,561,819, issued Dec. 31, 1985. That patent alludes to various types of conveyors, for example, belt conveyors, push/pull devices, chain conveyors, and vibration conveyors, all of which have been used in the past and have met with limited degrees of success in minimizing or eliminating the foregoing and other problems associated with the conveyance of flat articles, e.g., printed circuit boards.

According to the present invention, there is provided a flat article conveyor particularly adapted for the conveyance of printed circuit boards between various types of workstations. More particularly, the conveyor hereof includes a pair of endless conveyor belts on respective opposite sides of the conveyor, each belt being disposed about pulleys or rollers at respective opposite ends of the conveyor. Inside portions of the belts are thus spaced laterally one from the other and serve as transport mechanism for the boards. In accordance with a particular aspect of this invention, the belts are disposed on edge and for movement about pulleys having substantially vertical axes adjacent opposite ends of the conveyor. Thus, each belt has a height dimension greater than its width dimension, the width dimension being transverse to the direction of movement of the conveyor and in the plane of movement of the articles along the conveyor. The opposite lateral edges or margins of the printed circuit boards rest on the upper edges of the laterally spaced belts.

The pulleys at opposite ends of each conveyor section on opposite sides of the conveyor have laterally outwardly projecting flanges at their lower ends for engaging and guiding the lower edge of the associated belt. The upper portions of the pulleys are otherwise free of projecting flanges or guides such that the area above the upper belt edge, particularly adjacent the pulleys, is free to support a margin of the printed circuit board on the conveyor. For reasons outlined in detail hereinafter, the upper edge of each belt is beveled or inclined in an outward and downward direction away from the pulleys, the beveled upper edges of the belts underlying the circuit boards supported therebetween on the upper edges of the belt.

The belts are preferably formed of a fiberglass-reinforced conductive rubber to provide a high coefficient of friction between the conveyor belts and the conveyed circuit board. This eliminates any need for pusher-type devices or squeezing or clamping of the board while the board is moving along the conveyor. Also, with such high coefficient of friction, the board may be transported in opposite directions simply by reversing the direction of the conveyor. It will be appreciated that the high coefficient of friction between the belt and the board, together with the known acceleration/deceleration profile of the belts, also affords accurate positioning of the board after rapid movement and prevents loss of registration of board position relative to belt position. Consequently, the acceleration and deceleration forces acting on the board may be maintained within predetermined levels.

Additionally, the on-edge conveyor belts are provided with upstanding, generally U-shaped, guides which receive the inner runs of the belts between the pulleys. The upstanding legs of the U-shaped guides between the belts terminate short of the upper edges of the belts so that the printed circuit board may be transported on the belt edge. The other upstanding legs of the guides within each endless belt extend upwardly above the upper belt edges to afford lateral guides for the printed circuit boards.

By providing a belt-on-edge configuration and mounting the boards on the upper thin edge of the belts, maximum access to the upper and lower surfaces of the boards is obtained. This is significant in certain printed circuit board manufacturing operations. Additionally, the beveled upper edge of the belt facilitates transfer of boards or flat articles from one conveyor to the next conveyor. More particularly, if adjacent transfer conveyors are slightly misaligned one with the other, either elevationally or laterally, the beveled configuration facilitates the transfer of boards from the feed conveyor to the receiving conveyor. For example, while conveyors of this type are normally disposed at the same elevation, it is possible due to different tolerances for the receiving conveyor to be slightly higher than the feed conveyor. In those circumstances, the board advances from the feed conveyor into contact with the beveled edges of the receiving conveyor. Those beveled edges assist in displacing the board vertically upwardly onto the flat upper edges of the belts of the receiving conveyor. Typically, of course, there is no problem if the receiving conveyor is slightly below the elevation of the discharging conveyor. The beveled edges also facilitate in much the same manner the transfer of boards which are warped from one conveyor to the next and whether or not the conveyers are misaligned.

As a further example, if adjacent conveyors are laterally misaligned, the longitudinally adjacent pulleys of the feed and receiving conveyors have heights which extend above the upper edge of the belts. Upon slight lateral misalignment of these conveyors, the leading edge or corner of the circuit board edge on one side of the discharge conveyor will engage the portion of the pulley on the corresponding side of the receiving conveyor above the belt thereof. The rotation of the receiving pulley tends to displace the board toward the center of the conveyor and align it between the side guides of the conveyor.

A further feature of the present invention resides in the bias applied to the belts to maintain the belts in contact with the underlying guides and the flanges of the pulleys. This enables the upper edges of the belts to remain free and unobstructed to receive the margins of the printed circuit boards. To achieve this, the axes of rotation of the pulleys on each of the opposite sides of the conveyor are slightly misaligned such that they converge towards one another below the conveyor. This causes the belts to bear or track against the bottom guides and the pulley flanges. This convergence of rotational axes may be accomplished by mounting each pulley for rotation about a single bearing carried by a pulley hub and located above the longitudinal centerline of the belt. Consequently, when the belt is driven, an off-center load is placed on the bearing, causing the bearing to shift to the loaded side of its raceway. This enables the outer race of the bearing and hence the pulley to rotate about an axis angularly related to the axis of the inner bearing race which is true vertical. Consequently, the outer races and, hence, the pulleys of each conveyor section, cant toward one another to provide downwardly slightly convergent axes of rotation. Thus, the entire upper edge of each belt is free for use as a support surface for the margin of the board obviating the need for upper belt guides or pulley flanges. That is, the belts are maintained seated against their underlying guides.

Additionally, by using conductive elastomer belts, conductive polymer belt guides, metal guide rollers and support frames, continuous bleed-off of any accumulated static electrical charge is assured. Additionally, the conveyors may be provided in usable sections of predetermined length, for example, on the order of 18 to 36 inches per section. Consequently, this modular aspect provides for individual positioning of the board and individual conveyor module serviceability.

Accordingly, in accordance with a preferred embodiment of the present invention, there is provided a conveyor for transport of articles having opposite side edges, comprising a flexible endless conveyor belt disposed along one side of the conveyor and spaced laterally from the opposite side of the conveyor, the belt extending generally parallel to the direction of travel along the conveyor, a pair of rollers mounted adjacent opposite ends of the conveyor for rotation about spaced, generally vertical, axes, the belt extending about the rollers and having, in cross-section, a depth dimension greater than its width dimension for supporting articles along its upper surface, the upper surface and the side of the belt closest to the opposite side of the conveyor being beveled to provide an inwardly facing beveled surface along the longitudinal extent of the belt.

In another preferred embodiment hereof, there is provided a conveyor for transport of articles having opposite side edges, comprising a flexible endless conveyor belt disposed along one side of the conveyor and spaced laterally from the opposite side of the conveyor, the belt extending generally parallel to the direction of travel along the conveyor, a pair of rollers mounted adjacent opposite ends of the conveyor for rotation about spaced, generally vertical, axes, the belt extending about the rollers and having, in cross-section, a depth dimension greater than its width dimension for supporting articles along its upper surface, a guide surface underlying the belt, the guide surface defining an elongated groove for receiving the belt with the height of the guide surface along the inside face of the conveyor belt being less than the depth dimension of the belt.

Accordingly, it is a primary object of the present invention to provide a novel and improved flat article conveyor which affords bi-directional movement and accuracy of positioning of the article, maximizes access to the top and bottom areas of the article, facilitates transfer of the article from adjacent in-line conveyors, as well as drain of any electrostatic charge from the articles being conveyed, provides modularity of system components and minimizes complexity and cost.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification and appended claims and drawings.

FIG. 1 is a plan view of a flat article conveyor constructed in accordance with the present invention;

FIG. 2 is a fragmentary end view of the flat article conveyor illustrated in FIG. 1;

FIG. 3 is a fragmentary enlarged cross-sectional view of the righthand pulley illustrated in FIG. 2;

FIG. 4 is a schematic illustration of the arrangement of the pulley axes along one side of the conveyor;

FIG. 5 is a fragmentary perspective view illustrating a transfer of an article from one conveyor section to the next along one side of the conveyor; and

FIG. 6 is an enlarged side elevational view of the pulleys illustrated in FIG. 5.

Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Referring now to the drawings, particularly to FIG. 1, there is illustrated a conveyor, generally designated 10, constructed in accordance with the present invention. Conveyor 10 has a discrete length, for example, on the order of 18 to 36 inches, and may be disposed in line with other conveyors of a similar or dissimilar nature or with manufacturing equipment at workstations, not shown, which perform work on the article being conveyed, in this instance, a printed circuit board, designated B. Each conveyor 10 may comprise laterally opposite conveyor sections S which may be mirror images one of the other. Referring now to both FIGS. 1 and 2, each conveyor section S includes a pair of end pulleys or rollers 12 mounted for rotation about generally vertical axes in a generally elongated frame 14. An endless conveyor belt 16 is disposed about end pulleys 12 and about a drive pulley 18 and a take-up pulley 20. A stepper motor 22 is disposed to drive pulley 18.

From a review of FIGS. 1 and 2, it will be appreciated that each endless belt 16 is disposed on its edge such that its height dimension is substantially greater than its width direction, the height and width dimensions being best illustrated in FIG. 3 by the designations h and w, respectively. Thus, the pair of endless belts 16 are spaced one from the other laterally across conveyor 10 such that the flat sides of the belt lie in opposition and lateral registry each with the other. The article B is disposed between the conveyor sections S such that the lateral margins along its underside bear on the upper edges of belts 16.

Referring now particularly to FIG. 3, each of the pulleys 12 is mounted for rotation about a generally vertical axis A.A. by a single ball bearing arrangement, generally designated 24, described in detail below. The inner race of ball bearing 24 is mounted on a hub 26 secured to a rigid structure or frame 28 by suitable means, such as a bolt 30. Importantly, each pulley 12 has a lower, laterally outwardly projecting flange 32 forming a lower guide surface for the lower edge of the associated pulley 12. Pulley 12 is otherwise clear of any other flanges or guides surfaces such that access to the upper edge of the belt may be provided.

For supporting and guiding the belt 16 between the end pulleys 12 of each conveyor section S, there is provided an upstanding generally U-shaped guide 34. Guide 34 is secured to the frame 14 and forms an elongated groove extending between end pulleys 12. The lower edge of the belt 16 rests on the base of segment 34 as the belt advances. The legs 35 of the guides 34 extend upwardly to straddle the belt. The inner leg 35 of each U-shaped guide terminates short of the upper edge of the belt. The other leg 37 of each guide 34 extends above the upper edge of the associated belt to guide the board B along the conveyor.

As will be apparent from the foregoing and a review of FIG. 3, the upper edge of each belt 16 is beveled at 38. Bevel 38 inclines inwardly and downwardly from upper edge 36 along the inside run of the belt in a direction toward the laterally opposite belt 16 of the opposite conveyor section.

Referring now to FIG. 4, there is schematically illustrated the bearings 24 for pulleys 12. It will be appreciated that bearings 24 are each located above a medial plane passing normal to the axis of rotation of the pulley and above the longitudinal centerline of the associated belt. It will also be appreciated that the outer race 40 (FIG. 3) of bearing 24 is secured to pulley 12 and that there is a tolerance between the outer and inner races 40 and 42, respectively. In the absence of an additional bearing, this tolerance enables pulley 12 to be canted such that its true axis of rotation is slightly offset from the vertical. With belt 16 tensioned about the pulleys, the pulleys will cant in the direction of belt tension such that, as illustrated in FIG. 4, the actual axes of rotation A.A. of the pulley 12 are about axes offset from true vertical (the true vertical axes being designated in FIG. 4 at T.A.). Axes A.A. therefore converge toward one another. The angle of offset of axes A.A. from the vertical is illustrated at .alpha. in FIG. 4. In this manner, the belt is maintained in engagement against the guide surfaces of the hubs, i.e., the flanges 32, and the base of U-shaped guides 34 such that the upper edges of the belts 36, on which the articles are transported, lie in a common horizontal plane as the belts move about the pulleys from end to end of the conveyor.

As noted hereinbefore, the belts are formed of a fiberglass-reinforced rubber. To maintain the upper edges of the belts in a common horizontal plane, the upper and lower edges of the belts are ground. In this manner, the upper and lower belt edges will lie in parallel planes and irregularities in the manufacture of the belts are avoided.

Referring now to FIGS. 5 and 6, there is illustrated one side of the sections of two conveyors disposed end-to-end whereby transfer of the article B may be effected from a feed conveyor onto a receiving conveyor, the articles B moving in the direction of the arrow illustrated in FIG. 5. As indicated previously, the conveyors disposed end-to-end as illustrated normally lie at a common elevation and are aligned laterally. However, there are instances where there are minor differences in elevation or lateral alignment of the feed and receiving conveyors due to tolerances in the set-up of the conveyors. By providing the beveled edge 38 on belts 16, the transfer of the article B from the feed conveyor to the receiving conveyor is facilitated.

For example, if there is a slight misalignment in the location of the feed and receiving conveyors such that the receiving conveyor is elevated slightly above the elevation of the feed conveyor, the forward or leading edge of the article B as it is transferred from the feed conveyor strikes or engages the beveled edges 38 of the belts 16 of the receiving conveyor. When the leading edge of the board strikes the beveled edge of the belts of the receiving conveyor, those beveled edges tend to lift the article as the belts advance, displacing the article upwardly such that its margin rests on the upper edges 36 of the belts rather than continue to engage the beveled edges. That is, the leading edge of the article engages the beveled edge 38 of the belts of the receiving conveyor as those belts are transposed from their curved condition about the pulley into the linear condition between the pulleys. This tends to elevate the article.

Similarly, should the article be warped, the same action occurs in the course of the transfer from the feed to the receiving conveyors. Consequently, even though adjacent-in-line transfer conveyors may be acurately aligned both elevationally and laterally one with the other, a warped article B may have its forward or leading edge drop downwardly as it leaves the feed conveyor prior to being engaged by the belts of the receiving conveyor. That edge, however, will strike the beveled edge of the belts of the receiving conveyor and a similar lifting action will occur.

Similarly, if slight lateral misalignment occurs between feed and receiving conveyor sections, one of the forward edges or corners of the board B will engage the corresponding pulley 12 on the same side of the receiving conveyor above the upper edge of its belt. The inside surface of the pulley is moving in the direction of travel and tends to shift the circuit board B laterally into a centered alignment on the receiving conveyor. From the foregoing, it will be appreciated that jamming between feed and receiving conveyors is substantially eliminated by the use of belts having beveled surfaces and arranged on pulleys in the manner indicated.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.