Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
1999-09-29
2001-05-29
Valenza, Joseph E. (Department: 3651)
Conveyors: power-driven
Conveyor section
Endless conveyor
Reexamination Certificate
active
06237752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to conveyors and, more particularly, relates to a method and apparatus for detecting misalignment of a conveyor.
2. Discussion of the Related Art
A conveyor belt assembly typically comprises a plurality of pulleys, at least one of which is powered, that is mounted onto a frame, and an elastic material (or conveyor belt) that is wrapped around the pulleys. In the event that the conveyor belt assembly is being used to transport the load over long distances, additional support pulleys or rollers may be placed underneath the conveyor belt. The conveyor belt becomes operational when the pulleys rotate, thereby moving the conveyor belt forward.
In order to ensure that the force of the pulley will be sufficient to drive the conveyor belt, the conveyor belt is placed under tension so that friction between the conveyor belt and the drive pulley is sufficient to ensure that the conveyor belt does not slip against the surface of the pulley. The typical conveyor belt is therefore of an elastic material, such as a reinforced rubber composite. However, uneven loading of the belt, belt material inhomogeneity, and unequal temperature distribution across the belt can cause the belt to stretch unevenly, thereby causing the belt to slide laterally with respect to the pulleys and become misaligned during use, resulting in damaged belt edges and a shorter belt life. A misaligned belt could also, in some situations, damage the load.
Devices have been implemented in the past to detect a misaligned conveyor belt. One such device comprises a bronze disc that is placed adjacent at least one side of the belt such that, when the belt becomes misaligned, it rubs against the disc, thereby generating heat that is conducted through the disc. A thermocouple embedded in the disc measures the heat and outputs voltage signals to a programmable controller that processes the signals to measure the temperature. A threshold temperature is programmed into a human machine interface and communicated to the controller via an analog circuit such that, when the measured temperature exceeds the threshold temperature, the controller activates an alarm signal that is detectable by a user.
Several disadvantages are associated with this device. First, the output of this device requires a long response time in detecting the misalignment of the conveyor belt. Specifically, a significant amount of time elapses while frictional forces between the belt and disc generate heat and while the generated heat is conducted through the bronze disc to the thermocouple. During this delay, the conveyor belt may become increasingly misaligned. Additionally, no back-up sensors exist on this device to allow a user stationed at a location remote from a conveyor belt to make a reliable determination that the belt has become misaligned. For example, the user may be unsure that the temperature sensor is functioning properly. Finally, in order to test the operability of the sensor, the bronze disc must be manually heated until the measured temperature exceeds the threshold temperature. This process is cumbersome and inefficient.
The need has therefore arisen to provide a method and apparatus for detecting a misaligned conveyor belt with a quick response time that incorporates back-up features, and allows a user to easily perform diagnostics to ensure the operability of the detection apparatus.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method and apparatus for detecting a misaligned endless conveyor, such as a conveyor belt, with a quick response time.
It is a second object of the invention to provide a misaligned conveyor detection assembly that provides more than one indication of whether the conveyor is misaligned.
It is a third object of the invention to provide a misaligned conveyor detection assembly that is connected to a communication network to allow real time adjustment of threshold values to perform diagnostics, to reduce wiring costs, and to increase the reliability of the system by having fewer connectors and cables.
It is a fourth object of the invention to provide a misaligned conveyor detection assembly that permits automatic termination of conveyor operation if the conveyor becomes misaligned.
In accordance with a first aspect of the invention, when used in conjunction with an endless conveyor belt, a misaligned conveyor belt detection assembly comprises a misalignment contact apparatus that is positioned adjacent at least one edge, and preferably both edges, of a conveyor belt. The misalignment contact apparatus preferably comprises a thermally conductive material, such as a bronze disc, with an embedded heat sensor, such as a thermocouple, to measure the heat generated during operation of the conveyor. The heat sensor outputs voltage signals, corresponding to the measured temperature, to a network interface located within a housing. An insulation layer also may be positioned between the contact apparatus and the housing to minimize heat transfer to the housing. A mounting plate is disposed between the insulation layer and the contact apparatus. The housing, insulation layer, and mounting plate are all mechanically connected to one another, and the mounting plate is further connected to the contact apparatus on one side and to a frame on the other side.
When the conveyor belt becomes misaligned, it rubs against the contact apparatus, thereby causing it to vibrate. Because the housing is in mechanical communication with the contact apparatus, the housing also vibrates. A vibration sensor, such as an accelerometer, is disposed within the housing and outputs a signal indicative of a measured vibration level, which is sent to the network interface. Preferably, the network interface samples output from the vibration sensor at predefined time intervals, computes an average of the measured vibration values over that interval, and compares the average to a predetermined threshold level to determine whether the conveyor belt is misaligned. Because the vibration detection does not incorporate the time delays typically associated with thermal conduction, a fast response time is associated with the detection of the misaligned conveyor belt based on vibration.
The network interface may comprise a microprocessor that processes the measured temperature and vibration signals and computes respective measured temperature and vibration values. The microprocessor then compares these values with respective predetermined threshold values that are inputted into a human machine interface located remotely from the detection assembly.
In accordance with a second aspect of the invention, the network interface preferably comprises outputs that are connected via a serial communication link to indicate the status of the conveyor belt and reduce the wiring cost. In accordance with a preferred embodiment, independent temperature and vibration alarms, located on the human machine interface, are activated to indicate that the conveyor belt has become misaligned. Once both alarms are activated, the user may have conclusive grounds for determining that the conveyor belt has become misaligned. If, for example, the temperature alarm is activated without the vibration alarm, the user may elect to conduct further investigation before determining that the conveyor belt has become misaligned.
In accordance with a third aspect of the invention, the network interface and human machine interface may be connected to a serial communication network, thereby allowing a user to adjust the temperature and vibration threshold values by inputting the new values into the human machine interface. These values are then sent to the network interface. As a result, when testing the operability of the detection assembly, the temperature and/or vibration thresholds may be appropriately set such that the measured ambient values would trigger the alarm when the detection assembly is operational. Therefore, if the alarms are not triggered when the th
Forman Adam J.
Gerasimow A. M.
Horn John J.
Reliance Electric Technologies LLC
Valenza Joseph E.
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