Abstract:
An overhead rotatably powered conveyer drive shaft has ridges inter-engaged with skewed driven wheels mounted for free rotation on a load carrying carriage to trace a helical loci of engagement and improve traction. The ridges are preferably extruded to be parallel. The driven wheels may also have extruded parallel ridges or have an elastic peripheral surface deformed elastically into spaces between adjacent drive shaft ridges during normal conveying to provide the inter-engaging.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The field of the invention is that of overhead conveyers having fixed axis, rotatable drive shafts engaging skewed driven wheels of a carriage to provide the carriage conveying force, wherein the carriage is supported by the drive shaft and/or a fixed support rail. 
   2. Description of the Related Art 
   The present invention relates to overhead conveyors of the type disclosed in U.S. Pat. No. 5,806,655 issued Sep. 15, 1998 to Tabler, in U.S. Pat. No. 5,785,168 issued Jul. 28, 1998 to Beall, Jr., in U.S. Pat. No. 4,203,511 issued May 20, 1980 to Uhing, in U.S. Pat. No. 3,164,104 issued Jan. 5, 1965 to Hunt, and in U.S. Pat. No. 3,850,280 issued Nov. 26, 1974 to Ohrnell. 
   Conventional rotating shaft driven overhead conveyors are limited in the amount of weight they may carry or the incline/decline they may traverse, without the carriage undergoing an uncontrolled slippage, particularly between the drive shaft and the driven wheels, Therefore, overhead conveyors for loads or inclines too great for the rotating shaft driven overhead conveyer are generally of a different type, for example a power and free chain driven conveyor. 
   Shaft driven overhead conveyors have many advantages over the heavier load type conveyors such as the power and free conveyor; such advantages including quietness, cleanliness, less repair, easy diversion of load carrying carriages, buffering, speed variation along the conveying path, and generally greater flexibility in design. 
   This well known slippage problem of the rotatable drive shaft type of overhead conveyor has been partially solved by sand-blasting and then anodizing aluminum drive shafts, which adds expensive processing to the manufacturing. Though this is an improvement for some applications, in many cases, it is not enough. 
   In addition to ascents and to a lesser extent, descents, the problem arises in other circumstances, for example: when a carriage with spaced apart trolleys for a single load (two trolleys being used to carry a greater load than can be carried with a single trolley) passes through a switch. Where a carriage traveling straight on one line, is switched to travel on another line, a trolley passing through the switch may not be powered, so that the rear trolley is the sole drive into the switch and the front trolley is the sole drive out of the switch. In such a situation, the driving power is cut in half through the switch and slippage is more likely to occur, for example when the load is particularly heavy in the high load overhead conveyor of U.S. Pat. No. 5,785,168 issued Jul. 28, 1998, whose disclosure is incorporated herein in its entirety, by reference. 
   Therefore, there is a need to increase drive friction between the drive shaft and driven rollers of the rotatable drive shaft type of overhead conveyor systems at least at selected locations of a system where a slippage problem is most likely to occur. 
   SUMMARY OF THE INVENTION 
   One or more driven wheels are rotatably mounted on the carriage for rotation about one or more drive axes, each of which is non-parallel and non-perpendicular to the shaft axis. Each driven wheel engages a peripheral portion of the drive shaft with sufficient traction so as to form a helical loci of engagement about the periphery of the drive shaft during rotation of the drive shaft about the shaft axis to power the carriage along the conveying path in a direction of the conveying path dependent upon a direction of rotation of the drive shaft. Traction is improved by ridges of the drive shaft inter-engaging with the driven wheel, particularly with an elastic and/or rigid ridged driven wheel. There are advantages of production time and cost when the drive shaft ridges are extruded parallel to the shaft axis during the manufacturing of the shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a schematic drawing of a conveyer system according to the present invention embodiment; 
       FIG. 2  is a view taken on a plane parallel to the axis of rotation of one of the rotatable drive shafts of  FIG. 1 , showing the drive shaft or a portion thereof and a pair of driven wheels engaged therewith; 
       FIG. 3  is a view taken on a plane parallel to the axis of rotation of one of the rotatable drive shafts of  FIG. 1 , showing another drive shaft or another portion or the  FIG. 2  drive shaft; 
       FIG. 4  is an end view, perpendicular to the plane of  FIG. 2 , showing the engagement between a partially shown driven wheel and a partially shown drive shaft, of  FIG. 1 , in more detail; 
       FIG. 5  is a complete end view of the drive shaft taken from the right end as seen in  FIG. 2 ; 
       FIG. 6A  shows a plurality of cross-sectional shapes for the ridges of the drive shaft and/or the driven wheels; 
       FIG. 6B  shows a plurality of cross-sectional shapes for the ridges of the drive shaft and/or the driven wheels; and 
       FIG. 7  is an end view, perpendicular to the plane of  FIG. 3 , showing engagement between a partially shown driven wheel of elastic material and a partially shown rigid ridged drive shaft, of  FIG. 1 , in more detail. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
   The overhead conveying system  10  of an exemplary embodiment of the invention may be of any of the types shown in the above-mentioned patents. 
   By way of a specific best mode example, the embodiment shown in the drawing is of the type wherein a plurality of carriages and loads  17  (one being shown) travel along a conveying direction  26  as they are supported on a fixed support rail  16  by a plurality of freely rotating support wheels  20 ,  21 . The fixed support rail  16  has its longitudinal extent or axis  29  extending parallel to the conveying direction  26 . 
   Each carriage  17  has a plurality of biased mountings  30 , for example a combined lost-motion connection and compression spring mount  30  (not shown in detail), which biases freely rotatable driven wheels  18 ,  19  respectively into engagement with an adjacent one of the rotatable drive shafts  13 . 
   Each of the rotatable drive shafts  13  is mounted on a rigid frame (not shown in this embodiment but shown in the above-referenced patents) for rotation about a shaft axis  28  that is parallel to the axes  26  and  29 , which axes  28  and  29  may include curved portions to go up, down or around corners. A drive unit  31 , for example having an electric, hydraulic or pneumatic motor and a transmission and controls (not shown herein, but disclosed in the above-referenced patents), rotates the rotatable drive shaft at the desired speed about the shaft axis  28 , the rotatable drive shaft may be made up of a plurality of extruded aluminum or synthetic plastic material sections, for example. All of the structure descried so far with specific reference to  FIG. 1  is conventional. 
   According to the embodiment, the drive shaft  13  and preferably also the driven wheels  18 ,  19  are provided with novel features that improve the traction between them, which is particularly useful for moving heavy loads, moving loads upward, or accelerating/decelerating loads from rest or a steady state speed. 
   In the embodiment, particularly as shown in  FIG. 2  and  FIG. 3 , the outer peripheral surface of the drive shaft  13  is substantially cylindrical.  FIG. 2  shows a portion of the drive shaft  13  of  FIG. 1 , enlarged to more than twice actual size for showing details of the peripheral outer surface. More particularly, the outer, substantially cylindrical, surface of the drive shaft  13  has a plurality of ridges  23 ,  24 , which ridges are parallel to each other and spaced about the periphery for at least a portion of the length of the drive shaft where increased traction is desired. 
   The ridges  23 ,  24  are most preferably extruded. That is, their cross-section perpendicular to the shaft axis (also the extrusion axis) is uniform throughout the length as measured along the direction of the axis of the drive shaft  13  and thereby they are parallel to each other. Additionally, each of the ridges  23  of  FIG. 2  lie entirely within a respective flat plane that passes through the axis of the drive shaft  13 , which is most preferred as being of least expense to manufacture. Each of the ridges  24  of  FIG. 2  lie along a twisted or helical path and accordingly each lies entirely within a respective twisted plane that passes through the axis of the drive shaft  13 . Twisting the shaft  13  as it is being extruded may make the ridges  24 . Most preferably, the entire shaft  13 , not including the nose  22 , is unitarily or one piece extruded, although the outer periphery with the ridges  23 ,  24  may be extruded onto a pre-extruded shaft. 
   Conventional bullet noses  22  are provided at one or both terminal ends of the drive shafts  13 , particularly at an entrance end to lead in the driven wheels  18 ,  19  and compress their bias springs of the mountings  30 . The bullet noses of the embodiment may have their greatest diameter portion of a diameter defined by the peaks of the ridges  23  as in  FIG. 2  or optionally equal to the diameter defined by the valleys of the ridges  24  as in  FIG. 3 , for example. 
   The driven wheels  19  are formed with ridges  31  that are complementary to the ridges  32  of the drive shaft  13  and they inter-engage, as shown in  FIG. 4 . While only a set of wheels  19  are shown in  FIG. 2 , it is to be understood that an identical set of wheels  18  is also present as shown in  FIG. 1 , but outside of the illustration in  FIG. 2 . 
   In  FIG. 2 , the ridges  23  of the driven wheels  18 ,  19  are skewed by an angle relative to the axis of rotation  27  of the driven wheels  19  that is equal to the angle of skew of the axis  27  relative to the axis of rotation of the driven shaft  13 . With the twisted or helical ridges of  24  of  FIG. 3 , the driven wheels  18 ,  19  have their ridges parallel to the axis  27 , and the angle of the twist of ridges  24  relative to the shaft axis  28  is the same as the angle between shaft axes  27  and  28 . Of course, other complementary angles may be provided and, although not shown, the ridges  23  may be skewed relative to the axis  27  and the ridges  24  may be skewed relative to the axis  28  by the same or a different angle, although such a construction would probably be at an increased cost relative to the disclosed embodiments. 
   In  FIGS. 4 and 5 , the ridges  23 ,  24  have a rectangular cross-section.  FIGS. 6A and 6B  show a plurality of different cross-sectional shapes for the ridges that may be used in place of one or more of the rectangular ridges of  FIG. 4 . These shapes may be used in any combination. Ridges  23 A,  24 A,  23 B,  24 B are parallelograms that will grip more in one rotational direction than the other. Ridges  23 C,  24 C,  23 D,  24 D are rounded and will grip the same in both rotational directions while producing less wear on the driven wheels. Ridges  23 E,  24 E,  23 K,  24 K are sharp like serrations, and will grip the same in both rotational directions while producing more grip and more wear on the driven wheels than will the rounded ridges  23 C,  24 C,  23 D,  24 D. Ridges  23 F,  24 F,  23 G,  24 G are triangles that will grip more in one rotational direction than the other. Ridges  23 H,  24 H are of a random ill-defined cross-sectional shape. Ridges  23 I,  24 I are trapezoidal and will grip less than the trapezoidal ridges  23 J,  24 J. 
     FIG. 7  shows the shaft  13 , which may be constructed in any one of the previously disclosed examples, inter-engaging with a driven wheel  19  that has an elastic outer periphery, which may be a rubber or polyurethane tire extruded on the shaft or a part of a one-piece homogeneous elastic shaft. Elastic, as used herein, refers to a material that elastically deforms (non-permanent deformation) by contact with the ridges of the shaft  13  and then returns to its prior shape when such contact ceases, that is, no permanent set takes place within the normal life of the elements. Although not shown, the shaft may also or alternatively have an elastic outer array of ridges. 
   Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.