Modular conveyor belt sealed sprocket drive system
TECHNICAL FIELD 
     This invention relates to modular link conveyor belt systems and more particularly it relates to sprocket drive mechanisms therefor. 
     BACKGROUND 
     Plastic modular link conveyor belts are ideally suited for processing foods, chemicals and other critical products that must be protected from environmental contamination, such as bacteria, oil or accumulated dust, dirt and grime. In such environments the belt and belt drive systems need to be sanitized or cleaned frequently, and this is difficult and possibly dangerous when the drive system is located inaccessibly. Also, conventional drive systems using sprocket teeth often employ rough surfaces, crevices and corners tending to accumulate contaminants. In such environmental operating conditions, it has been difficult with prior art systems to meet the critical requirements for cleanliness and sanitation because of the presence of sprocket drive teeth and accompanying drive mechanisms in modular link belt drive systems. Consider that because of the mechanical requirements to bear loads and to rotate for long times sprocket gear teeth and accompanying drive mechanisms require lubrication, which encourages vapors and grime inconsistent with sanitation and lack of contamination. Thus, it is a significant problem when contaminants are present, even in trace quantities and where sprockets and drive systems take configurations that tend to breed pockets of contaminants and which are very difficult to reach and clean. 
     Furthermore sprocket drive systems often employ mechanisms which are subject to excessive wear in the environment of modular link belt operations, where abrasive residue from the belt can significantly shorten operating life. 
     Additionally safety to operating and service personnel is a problem. However, conventional prior art sprocket drive mechanisms for conveyor belts have drive gears, pulleys and like mechanisms which may not be adequately protected from the possibility of encounter with clothing, tools, loads or even personal body parts such as hands which can be damaged or eyes into which damaging materials could be thrown. 
     It is therefore an objective of this invention to provide improved sprocket drive systems in modular conveyor belt systems which produce less contamination and which are more readily cleaned and sanitized. 
     Another object of the invention is to provide sprocket drive systems with longer operating life. 
     Still another object is to provide sprocket drive systems with improved safety to operating and service personnel. 
     Other objects, features and objectives of the invention will be found throughout the following description, drawings and claims. 
     DISCLOSURE OF THE INVENTION 
     Substantially all the operating hazards dangerous to personnel are eliminated from the belt drive mechanisms as well as the propensity to accumulate or spread contaminants such as bacteria grease or grime. Thus by closing and sealing in the sprocket drive system mechanism, a conveyor belt system is made more acceptable for environmental control in processing food or chemical products. 
     Also, operating conditions are improved by compactness of the drive mechanisms into a modular element in accordance with this invention. This reduces friction and packing space, and expedites servicing with simple modular replacement of drive mechanisms with compact modules. 
     The drive modules are made substantially universal in character by accommodation of various belt sprocket configurations with easily accessible and replaceable sprocket discs. The discs are light weight, thereby reducing power and inertia for better operating conditions, yet sturdy and strong in their assigned duty of driving loaded belts. The discs are further capable of accommodating dynamic stresses of loaded belts under various environmental conditions including curved paths, radical temperature changes and unbalanced loading, by means of free lateral movement transverse to the belt if desired. 
     All these advantages are achieved by mounting sprocket teeth upon a hollow rotating member internally housing the driving mechanism, typically a substantially cylindrical hermetically sealed drum, which is typically driven by an internally disposed electric motor and drive gear train. The drum when hermetically sealed prevents leakage of oil, vapor or worn off residue into the atmosphere. Likewise it eliminates dirt, dust and abrasives from the drive mechanism thus providing longer life expectations. 
     The sprocket teeth are preferably formed on light weight hollow disc like rings mated on the outer rotating drum peripheral surface of the driving module and keyed for rotation with the drum. Shaped drum surfaces, preferably octagonally sculptured, advantageously drive and key the rings for location along the drum axis to mesh with belt drive apertures individually or in sets. Discs are readily provided and positioned to conform to the sprocket drive spacings and teeth configurations for a variety of different belts. The sprocket rings are mountable with at least a degree of free axial movement to accommodate dynamic belt conditions encountered from unbalanced loading, movement around curves and significant temperature changes, thereby increasing belt life and reliability. 
     Other features and advantages will be evident from the following text. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, wherein like features are given similar reference characters in the several views to facilitate comparison: 
     FIG. 1 is a fragmental side view sketch of a modular link conveyor belt sprocket drive system wherein the belt is conveyed by sprocket teeth in the direction of the arrow, 
     FIG. 2 is a side perspective view of a modular belt sprocket drive mechanism embodiment of the invention, with comparative fragmental cutaway segment emphasizing construction details of the hollow outer drum used in accordance with this invention to carry the sprocket teeth, and 
     FIG. 3 is a perspective, cut away sketch of a typical motor drive embodiment afforded by this invention. 
    
    
     THE PREFERRED EMBODIMENTS 
     With respect to FIG. 1, it is seen that modular link conveyor belt 15 is driven toward the right by means of sprocket teeth 16 in the rotatable sprocket wheel 17, which may be in the form of a drum, disc or series of spaced discs. This sprocket wheel 17 is keyed on a drive shaft by a non-circular and preferably symmetrical central bore 19, in this embodiment defined as an octagon with flat planar sides 18. 
     As seen in FIG. 2, a series of sprocket discs 20 are arranged in paired sets 21, 22, 23 axially along the outer peripheral surface 25 of a hollow body member 28 in the form of a substantially cylindrical pipe 29 with a smooth cylindrical interior surface in this embodiment. The outer peripheral surface has eight flattened surfaces 30 arranged in octagon configuration for mating with octagon shaped aperture surfaces 18 of the individual sprocket discs 20. 
     The discs 20 and disc sets 21, etc. may have sprocket tooth shapes and spacings to mate with various modular belt configurations of various widths. The outer hollow body member 28 as shown in both FIGS. 2 and 3 is rotatable coaxially about a supporting shaft 40, which is anchored to a suitable frame, thus making the externally disposed stationary service compartment 45 accessible for receiving lubricating fluid at port 46 and electrical connections at terminals 47. The hollow member 28 has end plates 48, 49 to form an enclosed drum assembly capable of hermetic sealing to prevent dust and grime or conveyor belt residue from entering into the interior, and for preventing internal grease, grit or vapors from entering the environment in which the conveyor belt is working. 
     In the drum interior 50, as shown in FIG. 3, is mounted the conveyor belt electrical drive motor 51, having the conventional stator member 52 mounted on the stationary inner wall 56 and the conventional armature 53 mounted on the rotatable shaft 54 journalled for rotation in bearing 55. Thus, the motor drives the planetary gear train 57 having individual gears journalled in bearings 58, etc. thereby to rotate the drum end panel 49 and thus the outer hollow drum cylindrical member 28. Variations from this particular electrical motor driven mechanism can be made without departing from this invention. Alternative forms of such mechanisms are known in the art, such as shown in Chung U.S. Pat. No. 4,082,180, Apr. 4, 1978 and Besel, et al. U. S. Pat. No. 3,064,797, Nov. 20, 1962. Also, more than eight sides, say 20 are possible, especially for large diameter sprockets. 
     Although fewer drum sides 30 could be used, the octagonal configuration including the rounded corners 60 has significant advantage in that the peak to valley ratio of wall thickness is reduced and a thinner, lighter shell is rotatable with less energy. The even number of surfaces is thus symmetrically disposed for good balance. However, if it is desirable to radially key the sprocket discs 20 in a particular position, one such surface (18, 30) may be made asymmetrical by being shorter, longer, or shallower, etc. The thin walls also provide a better dissipation of internal heat from the drive mechanism, which can also be aided by internal lubricant-cooling fluids supplied and monitored at the port 46. 
     It is evident that the mechanism is easily cleaned and sanitized in the absence of any rough surfaces, crevices and corners that tend to accumulate dirt, grease or grime. The sprocket discs, particularly when freely axially movable can also be easily moved or removed from the drum for cleansing and sanitation. A preferable drum surface material would be anodized aluminum, since it is light weight and non-corrosive, or stainless. 
     Having therefore advanced the state of the art with improved sprocket drive systems for modular conveyor belts, those novel features setting forth the spirit and nature of the invention are set forth with particularity in the following claims.