Cutting – Processes
Reexamination Certificate
2000-04-07
2001-05-29
Rachuba, M. (Department: 3724)
Cutting
Processes
C083S062000, C083S062100
Reexamination Certificate
active
06237455
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and method or sensing the position of knives in a cutting machine.
BACKGROUND OF THE INVENTION
Cutting machines that include a rotatable knife older to which are clamped a plurality of cutting knives are well known in the wood machining industry. Wood to be processed in the form of raw logs or processed lumber is fed into the cutting machines and the rotating knives rapidly convert the logs or lumber into chips, flakes, particles or other products. Examples of such machines used in the forest products industry include:
1) chippers and hogs used in saw mills, pulp mills, chipping plants and mobile units to make pulp chips or mulch;
2) planners, matchers, milling machines and routers used in lumber mills to finish the surface of lumber or in manufacturing plants to shape wood;
3) waferizers and flakers used to make particles or flakes for manufacture of wood products such as oriented strand board (OSB) and particle board.
The cutting machines described above employ numerous different configurations with respect to knife clamping arrangements, however, they are all governed by the same design considerations.
The knives are subjected to large centrifugal forces and the knife clamping force must be sufficient to retain the knives in place. Furthermore, in performing their cutting action, the knives tend to be pulled from or pushed into the knife clamp and the knife clamping force must be sufficient to overcome these forces. A safety hazard exists if knives come loose during operation of the cutting machine as the rotation speed of the knives tends to throw them outwardly with great force. In addition, the rotating knives often come into close proximity with stationary parts of the cutting machine and even slight movements of the knives can cause collisions and resulting catastrophic failure of the cutting machine.
The position and condition of the cutting knife edge is important in the cutting process. Particularly when flakes or chips are being formed, the position and sharpness of the knife edge is vital to the quality of product being produced. The knife edges dull and retract with use making it necessary to sharpen and reposition the knives periodically which requires stopping the cutting machine to gain access to the knives.
It is readily apparent from the foregoing discussion that cutting knife position is an important element of cutting machine design and operation. It is recognized that it would be advantageous to be able to monitor the position of the cutting knives in a cutting machine to prevent failures, to assist in scheduling of regular maintenance and sharpening of equipment and to ensure product quality. Visual inspection of the knives during operation is not possible as the configuration, presence of guard screens, size and rotating speed of cutting machines generally prevents an operator from observing the knives while the machine is working.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a knife projection monitoring system that permits rapid and efficient inspection of the cutting knives particularly during operation. Applicant has developed a knife projection monitoring system that functions to ensure that cutting knives are installed properly and that knives remain in their proper position during use. In addition, the system permits knives to be easily monitored for changing or sharpening as necessary. The system relies on stationary sensors that generate a signal containing information about the rotating knife holder and knives of the cutting machine. The signals are analyzed to isolate the position of each of the cutting knives and to determine the projection of each knife while the cutting machine is operating. The actual projection of the knives is compared to desired pre-set limits, and, if the limits are exceeded, a warning can be sent to the operator to prompt appropriate corrective action or a signal can be sent from the system to the cutting machine to shutdown automatically.
In a first aspect the present invention provides a knife projection sensing system for cutting machines having a rotatable surface adapted to retain a plurality of cutting knives comprising:
at least one sensor mountable to the cutting machine to be stationary with respect to the rotatable surface for generating a signal capable of indicating the position of each cutting knife as the knives rotate past the at least one sensor;
processing means in communication with the at least one sensor for analyzing the signal generated to determine the projection of each knife from a reference surface and to determine if the projection of at least one of the plurality of cutting knives deviates outside preset desirable limits; and
means for communicating the projection status of the knives to an operator.
Preferably, the system includes a visual display using indicator lights or an audible alarm to notify the operator. In addition, a printer interface allows a printer to be connected to the system so that a hardcopy of knife projection distances over time can be produced as a permanent record for future analysis or for maintenance purposes.
In a further aspect the present invention provides a method for monitoring the position of cutting knives in a cutting machines having a rotatable surface adapted to retain a plurality of cutting knives comprising the steps of:
detecting the cutting knives using at least one stationary sensor as the knives rotate past the sensor, the sensor generating a signal capable of indicating the position of each cutting knife;
analyzing the signal generated by the at least one stationary sensor to determine the projection of each knife from a reference surface; and
comparing the projection of each knife with preset desirable limits to determine if at least one of the knives exceeds the limits.
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Irwin James Gary
Mierau Cameron Dean
CAE Machinery Ltd.
Rachuba M.
Townsend and Townsend / and Crew LLP
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