Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
2000-11-02
2003-04-22
Ellis, Christopher P. (Department: 3651)
Conveyors: power-driven
Conveyor section
Endless conveyor
C198S810040, C198S810020, C134S05600D, C134S0580DL, C134S0570DL
Reexamination Certificate
active
06550607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to warewashers which are used in commercial applications such as cafeterias and restaurants, and, more particularly, to a system for detecting jams which may occur in such warewashers.
BACKGROUND OF THE INVENTION
Commercial warewashers commonly include a housing area which defines the washing and rinsing area for dishes, pots pans and other wares. A conveyor is used to transport the wares through the warewasher from an input side to an output side. At the output side of the warewasher a ware receiving table/trough may extend several feet to allow cleaned wares to exit from the warewasher completely before being removed by kitchen personnel.
One potential problem with such warewashers is that improperly loaded wares or ware racks can shift during conveyance through the warewasher to a position which causes a jam in the conveying system. In this type of jam condition the mispositioned ware or rack physically prevents movement of the conveyor, and damage to the warewasher itself can occur.
The prior art includes techniques which attempt to account for this jam condition. For example, as shown in
FIG. 9
, one prior art drive arrangement
200
includes a drive motor assembly
202
which is attached to a pivotable motor mount
204
. The output of the drive motor assembly
202
is connected to a coupler
206
having a shaft
208
which extends through a bearing block
210
which is mounted to the tank shelf
211
(shown in dashed lines). The shaft
208
extends to a crank arm
212
. As the crank arm
212
rotates in a clockwise direction (looking from top to bottom along the rotational axis) it repeatedly engages a drive block
214
. The conveyor
216
includes a dog-type system that moves racks containing wares through the machine on tracks
218
in a stop and go fashion with every rotation of the crank arm
212
. The dogs
220
are attached to a cradle
222
that is suspended below the tracks
218
on four plastic slider blocks
224
. The cradle is made to oscillate back and forth in the direction of arrow
226
by the rotating crank arm
212
and drive block
214
, propelling the racks forward on every forward stroke of the cradle
222
. The drive block
214
runs in a channel formed by welding two L-shaped brackets together.
Anti-jam prevention is accomplished in the above-described prior art arrangement by mounting the entire drive motor assembly
202
on a pivot. The drive motor assembly
202
is mounted laterally to a movable motor mount
204
. The location of the drive motor assembly
202
is normally fixed by use of a die spring
228
which exerts a force sufficient to prevent pivoting under normal, acceptable operating conditions. When the cradle
222
encounters a jam situation, the crank arm
212
is prevented from rotating, causing the drive motor assembly
202
to pivot in a counterclockwise direction (looking from top to bottom along the rotational axis) against the force of spring
228
opening the contacts of an anti-jam switch
230
. When opened, the anti-jam switch
230
removes power from a contactor that then opens and removes power to the drive motor. The sensitivity of when the system trips is determined by setting of the die spring
228
and the setting of the anti-jam switch
230
.
The above-described anti-jam arrangement may not operate properly if power to the drive motor is hooked up in reverse polarity, causing the drive motor to run counterclockwise instead of clockwise (looking from top to bottom along the rotational axis). When this type of misconnection occurs the drive motor assembly attempts to rotate clockwise when a jam situation occurs. Because such clockwise rotation is not possible, the anti-jam switch will not be activated, potentially resulting in damage to the drive arrangement. Further, even when powered for proper rotation, in a jam situation, due to the time necessary for the drive motor to come to a stop, excessive forces in the arrangement can potentially result in damage to the drive arrangement.
A second potential problem with such warewashers is the build up of excess wares at the outlet end of the warewasher when kitchen personnel fail to remove cleaned wares in a timely fashion. The ware receiving table at the outlet end may include sidewalls and an end wall which prevents wares from tumbling onto the floor. However, if the wares are not removed quickly a back-up can occur in which wares exiting the warewasher may begin to collide with non-removed wares which are abutting against the end wall. This back-up type jam can result in undesired damage to the wares. Attempts to address this type of jam condition include the use of a table limit switch at the end of the ware receiving table which is triggered when wares exiting the warewasher reach the end of the table. Triggering of the switch then cuts power to the drive motor. However, some operators do not use the limit switch option, and instead attempt to rely on the anti-jam switch described above, which includes its own set of problems as previously noted.
Accordingly, it would be desirable to provide a warewasher jam detection system which addresses the aforementioned problems.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a warewasher jam detection system includes a conveyor drive arrangement having a drive motor assembly including a drive motor and an output shaft, and a rotatable slip clutch including an input side operatively connected for rotation by the drive motor assembly output shaft, an output side of the rotatable slip clutch operatively connected for driving a conveyor. At least one sensor is provided for producing an output indicative of rotation
on-rotation of the output side of the rotatable slip clutch, wherein non-rotation of the output side during rotation of the input side indicates a jam condition. Preferably the sensor is a non-contact type sensor such as a magnetic sensor, optical sensor or proximity sensor. A controller may be provided for receiving the sensor output signals and identifying a jam condition based upon the same, such that the controller can responsively stop the drive motor.
In one preferred arrangement the system may include at least a first sensor and a second sensor for detecting rotation
on-rotation of the output side of the rotatable slip clutch, with a defined spacing between the first and second sensors. First and second sensor tripping elements are positioned to the output side of the slip clutch, each positioned for tripping the first and second sensor when aligned therewith respectively. A spacing between the first and second sensor tripping elements is different than the defined spacing of the first and second sensors for preventing simultaneous tripping of the first and second sensors.
Still a further aspect of the invention provides a method of detecting a jam condition in a warewasher including a drive motor for driving a conveyor, where the method involves providing a slip clutch between the drive motor and the conveyor. A slip threshold of the slip clutch is set at a level to identify jam conditions and a sensor arrangement is provided for producing an output indicative of a movement state of an output side of the clutch. A jam condition is identified based upon the output produced by the sensor arrangement.
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patent: 5311894 (1994-05-01), Payzant
patent: 6056667 (2000-05-01), Sasaki
Edelmann David Charles
Watson Michael Thomas
Deuble Mark A.
Ellis Christopher P.
Premark FEG L.L.C.
Thompson Hine LLP
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