Measuring and testing – Frictional resistance – coefficient or characteristics
Reexamination Certificate
1999-02-01
2001-11-27
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Frictional resistance, coefficient or characteristics
Reexamination Certificate
active
06321586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a device to automatically measure the static coefficient of friction (SCOF) on a moving conveyor belt and a means to initiate in-process reinstatement of the SCOF, if a reduction below the design range is detected.
2. Description of the Prior Art
The SCOF is an important parameter in the design of a certain class of machines having conveyors where obtaining necessary accelerations of conveyed parts is completely dependent only on the value of the SCOF, and also where the normal force acting on the conveyor does not exceed the weight of the conveyed part. This conveyor type will be referred to as non positive drive, with no normal force enhancement or for the purposes of discussion, a type three conveyors (A more complete discussion of conveyor types will be explained later in this disclosure)
The reason why this class of conveyor is considered in the design of postal equipment is because this configuration is relatively simple, which yields a design that is low cost and more reliable.
Since the net result of SCOF measurement will directly lead to the cleaning of the conveyor surface, it can be argued that this can be accomplished by regular maintenance procedure on the part of Postal Service personnel. Even though this improvement can be approached in this way (at least theoretically), in practice it can never be optimized when compared to an in-process determination, and also since conveyor cleaning is almost never done in postal facilities since it generally would be done at the expense of mail sorting production time.
This invention is therefore important because it can significantly improve the production efficiency of the type three conveyor, by permitting the use of SCOF values which are significantly greater than those presently being used. The in-process aspect of this procedure will also mean that valuable maintenance time need not be devoted to conveyor cleaning. The potential of a significantly greater SCOF together with the already obvious advantages of low cost and reliability can result in a significant discriminator in improving the competitive position of machines incorporating the invention.
In the design of the type three conveyor production cycle, the acceleration and deceleration portions of the cycle are developed such that selected accelerations do not exceed the value of the SCOF during initial delivery of mail to the conveyor from induction stations, during subsequent constant velocity transporting, or during the critical process of exiting from the carrier cells into the designated sort bins. The net result of not accelerating (or decelerating) the conveyor beyond the limits established by the SCOF, is that synchronismn is maintained throughout the sortation process between the conveyor and the mail being conveyed. In other words, system throughput and sort accuracy are completely dependent on the established minimum acceptable value of the SCOF.
The SCOF is normally measured statically and off-line, by either of several standard (manual) methods. In general, these manual methods are used to obtain data which are then used to define acceptable values for the SCOF, and in turn are then used as a parameter in the dynamics equations of the conveying process. In the design of the SPBS (Small Parcel And Bundle Sorter), the acceleration rates were based upon SCOF values available with new (uncontaminated) belt surfaces which then were reduced by at least 40%, in anticipation of subsequent surface contamination during mail sortation. Conveyor surface contamination is primarily due to a deposition of airborne dust and oil and also embedded debris typical in a postal mail processing facility. This reduction from the ideal value of the SCOF guarantees that synchronous operation will be maintained even in the presence of dirty belts but also results in a significant compromise from the ideal production rates possible if the conveyor belts were consistently maintained at values close to the maximum ideal available value of the SCOF. The single most important advantage of this invention is that it can substantially eliminate the need to reduce the initially higher acceleration rate available, by not permitting the conveyor belt to be significantly contaminated, and thereby realizing the advantage of higher acceleration/deceleration rates which result in proportionately greater throughput and improved sort accuracy.
An objective of this disclosure is to describe a method of SCOF measurement which would be totally automated, and in-process, being performed on a moving conveyor.
A further objective of this disclosure is to describe a method of automated SCOF measurement which is performed under dynamic conditions, as opposed to the traditional manual methods of SCOF measurement which are obtained under static equilibrium conditions. This unique difference in obtaining the value of the SCOF is the key to realizing the benefits of in-process determination of this parameter which directly lead to automated improvement in process control.
Measurement of the SCOF will be remote, using electrical transducers, whose output will be identical to the value obtained by the standard manual methods. The remote measurement of SCOF is not used to the knowledge of the applicants in any postal sorting machine. This in-process, automated scheme would yield the advantage of assessing the SCOF in an ongoing method of evaluating the process in an effort to obtain greater productivity and process control. The information will be utilized to correct the process if a small degradation in the SCOF design range is detected, and also before the process is adversely affected by such degradation. Since the value of the SCOF generally decreases due to contamination of the conveyor drive surface, any method which can dynamically measure the SCOF in-process and which can reinstate the SCOF substantially to its original design range, can significantly improve the productivity of the process. In practice the SCOF measurement obtained with new belts (completely uncontaminated) cannot be completely reinstated after cleaning due to some surface changes resulting from the cleaning process. Actual tests indicate however, that a significant increase in the SCOF is realized as a result of cleaning.
In respect to sorting machines, this benefit will be to improve throughput or sort accuracy. The objective of this disclosure is to describe a method to obtain these benefits.
The SCOF is defined here as the maximum value of the force required to move a piece of mail relative to the conveyor surface, divided by the weight of the mail. Explained in physical terms, it is the result of obtaining the threshold value of slip of the mail relative to the conveyor surface, resulting in the start of undesirable asynchronous movement of mail relative to the conveyor surface. Since this threshold value is a ratio of two forces, the SCOF is a non dimensional parameter.
In general, the acceleration/deceleration portions of the production cycle are designed such that the value of the SCOF is not exceeded since when this threshold is crossed, the dynamic coefficient of friction (DCOF) dominates and its value is significantly smaller than the SCOF. Predictions related to the arrival of mail pieces at defined positions in a sortation cycle, either in successful delivery onto carrier cells from an induction station or in successful exiting of mail into the correct sort bin are best determined under conditions of synchronous delivery. This is due to the fact that this process yields the minimum process time, and therefore, the maximum productivity.
A description of some typical conveyor types used in mail processing is helpful in identifying the specific conveyor category which will benefit the most by this-invention. In general, three types of conveyors are used to transport mail:
(1) Positive drive conveyors using cleats attached to the conveyor surface; the driving cleat provides unlimited acceleration of transported mail, but a cons
Bader Clifford J.
Wojtowicz Edward A.
Davis Octavia
Fuller Benjamin R.
Lockheed Martin Federal Systems, Inc.
Perman & Green LLP
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