CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/287,895, filed May 1, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to devices for adjusting the lateral position of a moving belt. In one aspect, the invention relates to a belt positioning assembly for automatically adjusting the position of a belt during operation of a belt filter press. 
     2. Description of the Related Art 
     Belt filter presses are utilized to remove liquid from a mixture of liquid and solid material, leaving a relatively dry, solid “cake” for disposal or further processing. The belt filter press comprises a frame and an assembly of rollers that support and drive an upper continuous belt and a lower continuous belt that are in operable communication with each other. The belts are permeable to allow the extrusion of the liquid therethrough. The mixture is first placed on the lower belt, then “sandwiched” between the upper and lower belts. The belts and the retained mixture then pass through a wedge section where the mixture is evenly distributed between the belts, and an initial volume of liquid is removed. The belts then pass through a series of progressively smaller diameter rollers where the retained mixture is compressed for further liquid removal. The belts are then separated and the dry “cake” is removed from the belts, generally by a scraping apparatus. The belts then pass through one or more belt washers, after which the process is repeated. The liquid from the extrusion and belt washing processes are collected for disposal. 
     The belts must remain in alignment relative to the rollers and to each other for proper filter press operation and dewatering of the material. The belts are typically aligned at the beginning of the operation. Any misalignment that occurs during operation of the filter press generally necessitates a shutdown of the filter press so that the belts can be realigned. 
     SUMMARY OF THE INVENTION 
     The invention comprises a device for adjusting the lateral position of an endless belt. It includes a sensor for detecting the lateral position of an endless belt relative to a predetermined position; a roller disposed adjacent to the endless belt; a controller operatively connected to the sensor and to the roller, and an air bellows operably connected to the controller to move the roller laterally in response to a signal from the controller. The volume of air in the bellows is controlled by an air valve and the controller signals the air valve to open and close to adjust the air volume in the air bellows so that the controller will automatically cause the roller to urge the endless belt toward the predetermined position when the sensor detects that the lateral position of the endless belt is away from the predetermined position. Preferably, the sensor comprises an inductive proximity transducer and comprises a wheel disposed against an edge of the belt in rotational communication therewith. The sensor signals the lateral position of the endless belt to the controller, which is preferably a computer. 
     In another aspect of the invention, a device for adjusting the lateral position of an endless belt disposed to move over a roller in a given direction comprises a sensor for detecting the lateral position of the endless belt relative to a predetermined position; an air bellows operably connected to at least one end of the roller in a position to adjust the position of the roller relative to the belt by expansion or contraction of the bellows; and a controller operatively connected to the sensor and to the air bellows. The controller will automatically cause the air bellows to expand or contract, thereby adjusting the position of the roller to urge the endless belt toward the predetermined positioned when the sensor detects that the lateral position of the endless belt is away from the predetermined position. 
     The air bellows urges the one end of the roller to move in the given direction to cause the belt to move laterally relative to the roller. In this case, the air bellows is positioned in the given direction. There can be a first air bellows and a second air bellows, where the second air bellows is positioned in the given direction opposite the one end of the roller from the first air bellows. Either way, an air valve is preferably positioned between the controller and the air bellows, and the controller automatically causes the air bellows to expand or contract by signaling the air valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side elevation view of a schematic of a belt filter press illustrating the configuration of belts adjustable by the belt positioning assembly according to the invention; FIG. 2 is a perspective view of a belt control assembly for the belt filter press of FIG.  1 . 
     FIG. 3 is a perspective view of a belt adjustment assembly for the belt filter press of FIG.  1 . 
     FIG. 4 is a plan view of a portion of the belt control assembly of FIG. 2 showing a sensor arm, inductive proximity switches, stops, and a mounting bracket. 
     FIG. 5 is a schematic view of the electrical and fluid connections of the belt control assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The embodiment of the claimed invention described herein is based upon the invention&#39;s use in a belt filter press. It will be readily apparent to one of ordinary skill in the art that the invention can be used in any application requiring automatic adjustment of the lateral position of a moving belt. Thus, the invention is not limited to use in a belt filter press. 
     Referring now to FIG. 1, a belt filter press  10  according to the invention comprises a frame  12 , an upper belt  14 , a lower belt  16 , a waste placement apparatus  18 , liquid catch pans  20 , belt washers  22 , a wedge section  24 , a primary roller  26 , secondary rollers  28 , upper belt guide rollers  30 , lower belt guide rollers  32 , and a belt alignment assembly  34 . It will be readily understood by one skilled in the art that the belt filter press of FIG. 1 will also comprise suitable belt tensioning devices, belt drives, and controls, which for purposes of this disclosure will not be described herein. As with a conventional belt filter press, the belt filter press  10  of FIG. 1 extrudes liquid from a mixture of solid and liquid material by “sandwiching” the mixture between the two belts  14 ,  16 , passing the belts over the wedge section  24  and around the wing roller  26  and secondary rollers  28 , and discharging the dewatered solids upon separation of the belts  14 ,  16 . 
     The belts in a conventional belt filter press are typically maintained in tension. As the belts travel through the belt filter press, they can move laterally on the guide rollers. This lateral movement may be sufficiently great that the belts contact the frame or other components, or the dewatering process is otherwise adversely affected. When this occurs, the belt filter press must typically be shut down to realign the belts. Referring to FIGS. 2-4, a belt control assembly  160  according to the invention comprises a contact wheel  164 , a lever arm  166 , at least one inductive proximity switch  184 , and a bracket  178 . The lever arm  166  comprises a wheel arm  170  and a sensor arm  174 . Intermediate the wheel arm  170  and the sensor arm  174  is a pivot bearing  172  provided with a pivot aperture  176  therethrough. The wheel arm  170  is an elongated member extending from the pivot bearing  172  and terminating in a free end  175  to which is rotatably attached the contact wheel  164  using a suitable wheel bearing  168 . The wheel arm  170  has an orthogonal bend intermediate the free end  175  and the pivot bearing  172 . Extending in a generally opposite direction from the wheel arm  170  is the sensor arm  174 . The sensor arm  174  comprises a generally flat, elongated member. The bracket  178  comprises a base  179  and parallel, upstanding opposing flanges  181 . The base  179  is provided with at least one suitable aperture or slot  185  for mounting the bracket  178  to the frame  12 . Each flange  181  is provided with an adjustable stop  182 . In the preferred embodiment, the stop  182  comprises a bolt that is threaded into a threaded aperture in the flange  181 . The flanges are provided with switch apertures  183  adapted to receive and retain at least one inductive proximity switch  184 . A suitable switch is the model number PKW-ON-1H inductive proximity sensor supplied by Automationdirect.com of Cumming, Ga. The inductive proximity switch  184  generates an electrical sensing field, and the switch is activated by the presence of the lever arm  166  in the field. A spring  180  extends from the lever arm  166  to one of the flanges  181 . The switch  184  is connected by a suitable electrical cable  186  to a suitable control module  188 . 
     The bracket  178  is fixedly attached to the frame  12  so that the contact wheel  164  is in operable communication with the belt  14 ,  16 . The spring  180  will maintain the wheel  164  in contact with the belt  14 ,  16 . As the belt  14 ,  16  moves longitudinally, the wheel  164  will follow the lateral displacement of the belt  14 ,  16 . Movement of the wheel  164  in response to the lateral movement of the belt  14 ,  16  will pivot the lever arm  166  about the pivot bearing  172 , which will displace the sensor arm  174 . With the sensor arm  174  in its centered position, the switches  184  will be in an unactuated or “switch off” condition. If the sensor arm  174  moves into the sensing field of one of the switches  184 , the switch  184  will be actuated to a “switch on” condition, sending a signal to the control module  188 . 
     The belt  14 ,  16  is supported on at least one adjustable belt guide roller  30 ,  32 . The roller  30 ,  32  is journaled into a conventional roller bearing  190  that is housed in a bearing housing  192 . An adjustable roller bearing assembly comprises a conventional roller bearing  190 , a bearing housing  192 , a frame mounting plate  198 , a bellows plate  194 , and a bellows  196 . The bellows plate  194  is rigidly mounted to the bearing housing  192 . The bellows  196  is rigidly mounted between the bellows plate  194  and the frame mounting plate  198 . The frame mounting plate  198  is rigidly mounted to the frame  12 . The bearing housing  192  is not mounted to the frame  12  and is able to move relative thereto. The adjustable roller bearing assembly is adapted so that expansion of the bellows  196  will shift the bearing housing  192  laterally and will move the roller  30 ,  32  laterally. As shown in FIG. 5, the bellows  196  is fluidly connected through an air valve  200  and suitable fittings to a supply of pressurized air  202 . The air supply  202  is also operably connected through the air valve  200  to the control module  188 . Alternatively, the bearing housing  192  can be operatively connected to a motor (not shown), such as an electric motor or a hydraulic motor, through, for example, a rack and pinion gear, for lateral adjustment of the position of the bearing housing in response to the operation of the motor in response to a signal from the control module. 
     If the switch  184  is in the “switch on” condition, the signal from the switch  184  sent to the control module  188  will be processed to actuate the air valve  200  to direct air from the pressurized air supply  202  to the bellows  196 . Depending upon which switch  184  is in the “switch on” condition, pressurized air will be supplied to one of the bellows  196 . Expansion of the bellows  196  will cause the bearing housing  192  to shift laterally, moving the roller laterally, and adjusting the belt  14 ,  16  to the desired position. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing description and drawings without departing from the spirit of the invention.
A device for adjusting the lateral position of an endless belt comprises a sensor for detecting the lateral position of the endless belt relative to a predetermined position, a roller disposed adjacent to the endless belt, and a controller operatively connected to the sensor and to the roller by way of an air bellows, wherein the controller will automatically cause the air bellows to move the roller to urge the endless belt toward the predetermined positioned when the sensor detects that the lateral position of the endless belt is away from the predetermined position.