Abstract:
An article conveyor having live rollers driven by a polymeric driven pad which has a wear indicator element co-extruded with the driven pad. The element is visually distinct from the pad and has converging sides in the driven pad so that wear on the pad is indicated by the amount of the wear element visible to an observer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements in article conveyance systems having roller bed assemblies frictionally powered by plastic driver pads carried on a chain drive mechanism. 
     2. Description of the Prior Art 
     Abell U.S. Pat. No. 4,588,073, and Wiggers &amp; Alderink U.S. Pat. No. 5,176,246 (both owned by the assignee of this invention) disclose padded chain drives for roller conveyors. In these conveyors, the pads are moved into engagement with the rollers to drive the rollers and advance articles on the conveyor and are disengaged from the rollers when the conveyor is not moving articles. The pads are positioned on the chain link drive and advance with the drive chain. Geib U.S. Pat. No. 5,984,082 also is directed to a padded chain drive for a roller conveyor. 
     The pads conventionally are resilient, thermoplastic polyurethane elastomers. As such, they are subject to wear from frictionally engaging the rollers. Thus the pads require periodic maintenance and replacement. However, it has always been difficult to determine when the driver pad has worn enough to require replacement. The common practice is to use calipers or height gauges to measure the driver pad height and thus determine when the minimum height is reached when replacement is required. Both of these processes are difficult to use, particularly the calipers, and both measure only in one place and not over the entire length of pad. Since the chains and pads extend for hundreds of feet in some conveyors, it is apparent that it is difficult, if not virtually impossible to be sure the measurement has been made at the thinnest place, i.e., the place where the pad is most likely to fail. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly it is a principal object of this invention to provide a driver pad which has a built-in system for determining wear on the pad. This is achieved in the present invention by co-extruding the driver pad with a visually distinct wear element embedded in, the same composition as, and integral with the remainder of the polymer pad, but preferably of a different color. 
     The majority of the pad is of one color and the visually distinct wear element part of the pad is of a distinctly different color. The colored portion. preferably is substantially triangular in shape with the base of the triangle oriented toward the conveyor rollers. The sides of the wear element converge toward each other in the pad when viewed in cross-section. Thus, the width of the colored surface indicates the relative wear on the driver pad and if there is no color present, the pad needs replacement. 
     Since the colored segment extends the entire length of the pad and chain, one can observe the entire pad from a single viewing point while the chain is moving. Alternatively, once can walk the length of the pad and observe its total condition by visual observation. 
    
    
     These and other objects, benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification and drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, where like numbers and letters refer to like parts wherever they occur: 
     FIG. 1 is a fragmentary plan view of the conveyor showing the drive chain drive sprocket and the drive of the rollers in the area of the sprocket; 
     FIG. 2 is an enlarged transverse sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged sectional detail of the mounting of the pad on the roller chain; 
     FIG. 4 is an enlarged vertical sectional view of the pad of this invention in an unworn state; 
     FIG. 4A is an enlarged vertical sectional view of the pad of FIG. 4 in a partially worn state; and 
     FIG. 4B is an enlarged vertical sectional view of the pad of FIG. 4 in a worn state ready for replacement. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The present invention is specifically designed for application to the conveyor assemblies shown in Patent Nos. 4,588,073 and 5,176,246, both of which are incorporated herein by reference. FIGS. 1,  2  and  3  are exemplary of the conveyor mechanisms to which the present invention is applicable. This invention also is applicable to the conveyor pad and drive assembly shown in Pat. No. 5,984,082, which also is incorporated herein by reference. 
     Referring now to FIG. 1, the general construction of a load transportation conveyor has been illustrated at the end portion where the drive mechanism for the load bearing rollers is shown. The conveyor includes special channel-shaped side rails  11  held in spaced parallel positions by spaced cross channels  12  which are secured (see FIG. 2) to the vertical webs of the side rails  11  by tabs  13  that engage in the webs just above the bottom out-turned flange  14  of the side rails  11 . While FIG. 1 does not show a full complement of load supporting rollers  15 , it is intended to show in a schematic way the drive for the rollers  15  which includes an approaching length of a drive assembly  16  and a return length  16 A of that same drive assembly after these lengths have passed around a driven sprocket  17 . 
     The view of FIG. 2 shows a transverse sectional elevation of the construction of FIG.  1 . In this view the side rails  11  support the load carrying rollers which are mounted with the projecting axles resting in slots on the side rails  11 . The spacer channels  12  are seen to support lifting means  18  of a well known character with which the drive assembly  16  is associated for the purpose of lifting or lowering the drive assembly  16 . The system normally is operated so that the lifts  18  are actuated to raise the roller drive assembly  16  into contact with the under side of the load supporting rollers  15 . The return length  16 A is known as a “return track” and is always out of contact with the rollers  15 . 
     In the conveyor the drive assembly  16  is shown in FIG.  3  and embodies a guide track which extends continuously along the conveyor length. The guide track carries an equally elongated low friction track  21  which is formed with flanges  22  which project laterally to embrace the side walls of the guide track  20 . The roller chain drive assembly  16  embodies a system of side links  24  which are oriented in horizontal planes with roller elements  25  captured between the links by vertically directed axles  26 , thereby allowing the chain assembly to follow a path which traverses the driver sprocket  17 . In this arrangement, each axle  26  for the roller elements  25  is elongated so its upper end is exposed to a suitable extent to be inserted into apertures in the bottom of an elongated high friction drive pad  27 . The pad is hollow so that the upper surface  27 A is able to flex when it is lifted by the lifts  18  to engage the under side of the load supporting rollers  15 . The pad  27  is provided with apertures for the axles  26  of each chain roller to thereby maintain a better contact over the pad flexture as it transverses the driver sprocket  17 . 
     It has been found that the top surface  27 A of the drive pad  27  wears during operation of the conveyor  10 . This is caused by the frictional wear from engaging and driving the rollers  15 . Over time, the hollow pad  27  will become thinner and the wear will lessen the friction drive to the rollers enough to stall the rollers, thus interferring with the operation of the conveyor  10 . Any lost time in moving goods because of drive pad malfunction is costly and defeats the purpose of installing high speed, high tech conveyor systems. To avoid this problem, pads have to be manually inspected using calipers or gauges, which is costly of manpower and difficult to achieve over the length of the pad. 
     FIG. 4 shows an enlarged view of the improved driver pad  27  of this invention which obviates the problem of normally checking the pad  27  for wear. The pad  27  is made of polyurethane, preferably of Shore A hardness of about 85 to about 90. The pad  27  has curved outer side walls  30 , a flat top drive surface  31  which engages the rollers  15 , a recessed flat bottom surface  32  and two ribs  33  between the side walls  30  and the recessed bottom surface  32 . The center  34  of the pad  27  is hollow and defined by a flat bottom  35  and an arcuate inner surface  36 . The portion of the pad  27  between the top drive surface  31  and the inner surface  36  is formed by a co-extrusion process wherein a wear indicator insert  40  is extruded with the remainder of the pad  27 , but is of a different contrasting color than the remainder of the pad  27 . 
     The composition of the wear indicating element insert  40  is the same as the remainder of the pad  27  and it is integral with the remainder of the pad  27  due to the co-extrusion process. 
     The element  40  preferably is triangular in shape so that it indicates the degree of wear on the pad  27 . The base  41  of the triangular element  40  defines all or a substantial part of the top surface  31  of the virgin pad  27  and the converging sides  42  taper to an apex  43  inside the pad  27 . The apex  43  is sufficiently deep in the pad  27  to provide good wear, but is spaced from the center opening inner surface  36  a sufficient distance to provide sufficient drive to the rollers for the pad  27  to function for a time sufficient for inspectors to determine the wear on the pad  27  and replace it. Preferably, the depth of the apex  43  (denoted by the distance “A” in FIG. 4) is from about to about          0.063   0.178                   to                 about                   0.063   0.118                            
     of the top wall thickness between the top surface  41  and the arcuate inner surface  36  (denoted by the distance “B” in FIG.  4 ). 
     FIG. 4A shows the pad  27  in a condition of partial wear with a smaller colored base  41 A visible compared to the remainder of the top drive surface  31 . 
     When there is no wear color present (FIG.  4 B), the driver pad  27  is fully worn and needs replacement. These observations can be made along the entire length of the driver pad  27 , even by an observer at one location, and can be made while the conveyor is running. The ease of making these wear observations, as compared to a manual measuring operation, encourage replacing the drive pad  27  as part of a preventable maintenance program, rather than checking and replacing when a problem occurs. 
     While a preferred embodiment of the invention has been disclosed, it is understood that modifications are encompassed in this disclosure which are substantial equivalents and are to be included within the scope of this invention. For example, the driver pad  27  may be a series of short sections rather than one continuous length as disclosed in U S. Pat. No. 4,588,073. The wear indicating element  40  can be trapezoidal in shape. 
     The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. It is recognized, however, that various modifications are possible within the scope of the invention as claimed.