Patent Application
20080087147
The accompanying drawings illustrate presently various embodiments of the invention, and assist in explaining the principles of the invention.
a is a block diagram showing the input stages of a typical inserter system.
b is a block diagram showing the input stages of a typical inserter system including a right-angle turn.
An embodiment of the present invention will now be described. It is to be understood that this description is for purposes of illustration only, and is not meant to limit the scope of the claimed invention. For the purposes of assessing blade life, the following sequence is executed when a cutter is new, or when a new blade set is installed in a cutter.
First, the blade is commanded to execute a very slow constant velocity profile without paper. Preferably, this commanded profile takes roughly 2 seconds to traverse 360 crank degrees. The output of the digital filter that commands the output current of the amplifier driving the servo motor (which is coupled to the crank) is captured and stored. The plot of the digital filter output is commonly referred to as a DAC plot (digital to analog conversion). Since the input signal to the amplifier is proportional to the output current and the input current into the motor is proportional to the generated motor torque, a DAC plot provides an accurate representation of the instantaneous torque applied at the crankshaft.
The second step in this sequence is to insert paper between the upper and lower blades, and the upper blade is commanded to execute the identical motion profile as before, but while cutting paper. Again the DAC plot is captured and stored. Typical exemplary DAC plots with and without paper are shown in
Third in this sequence is to subtract the “No Paper” DAC signature from the “With Paper” DAC signature, resulting in a DAC signature of the instantaneous torque required of the crank motor to cut paper only, negating the effect of friction for the crank-rocker mechanism. A slow profile is preferably chosen for this procedure, at least in order to minimize the effects of overcoming inertia which could possibly add noise to these signals, particularly if the servo gains for the motor/amplifier system are set high.
As the blade set wears, this same procedure is executed to generate updated blade signatures. In order to compare signatures, a figure of merit must be determined based on the DAC signatures. As the blade set wears, it will take additional force to cut paper, much like it takes more effort to cut material with dull scissors. This figure of merit value will increase as the blade set wears, and end of blade life will be declared once it reaches a predetermined threshold value. Any number of methods can be used to determine a figure of merit. One such method is to sum the squares of each of the DAC values within the plot during the crank displacements where cutting is taking place (roughly 40 to 165 degrees).
For example, by using the sum of squares method, a particular blade set measured at 1 million blade cycles and 8 million blade cycles results in a figure of merit that increases from 6926 to 7793, respectively. At 8 million, the blades still cut reliably.
Once an end life figure of merit is determined empirically from field data, the cutter control system can, upon command or automatically as per an established schedule, execute this procedure and compute a new updated figure of merit. This figure of merit can be used to ultimately output a value that indicates what percentage of blade life is remaining, much like that of an ink jet cartridge.
More sophisticated methods may be utilized to determine a figure of merit with higher confidence levels. For example, statistical methods like Analysis Of Variances (ANOVA), may be used once sufficient data on blade signatures is captured across many cutters and blade usages. Regardless of the methods chosen, statistical methods will help reduce the effects of noise, in order to arrive at a more accurate assessment of blade life.
Turning now to
Algorithms for implementing this system for testing blade sharpness can be realized using a general purpose or specific-use computer system, with standard operating system software conforming to the method described above. The software product is designed to drive the operation of the particular hardware of the system. A computer system for implementing this embodiment includes a CPU processor 880 or controller, comprising a single processing unit, multiple processing units capable of parallel operation, or the CPU can be distributed across one or more processing units in one or more locations, e.g., on a client and server. The CPU may interact with a memory unit 810 having any known type of data storage and/or transmission media, including magnetic media, optical media, random access memory (RAM), read-only memory (ROM), a data cache, a data object, etc. Moreover, similar to the CPU, the memory may reside at a single physical location, comprising one or more types of data storage, or be distributed across a plurality of physical systems in various forms.
It is to be understood that all of the present figures, and the accompanying narrative discussions of preferred embodiments, do not purport to be completely rigorous treatments of the methods and systems under consideration. A person skilled in the art will understand that the steps of the present application represent general cause-and-effect relationships that do not exclude intermediate interactions of various types, and will further understand that the various structures and mechanisms described in this application can be implemented by a variety of different combinations of hardware and software, and in various configurations which need not be further elaborated herein.
