METHOD AND APPARATUS FOR MONITORING CONDITION OF CUTTING BLADES

• US 3,809,870 A
• Filed: 06/08/1972
• Issued: 05/07/1974
• Est. Priority Date: 06/08/1972
• Status: Expired due to Term

• Current Assignee: Gary J. Kimmet, Ronald E. Auble
• Original Assignee: Gary J. Kimmet, Ronald E. Auble
• Inventors: Kimmet, Gary J., Auble, Ronald E.
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US05/260,875
• Time in Patent Office: 698 Days
• Field of Search: 235/151.3,150.1,151.31 444/1 340/261,267 73/104,105,101,67,67.2,67.3 83/72,522 324/77B,77D
• US Class Current: 702/34
• CPC Class Codes: B23F 23/12 Other devices, e.g. tool holders; Checking devices for controlling workpieces in machines for manufacturing gear teeth
• CPC Class Codes: B23Q 17/0947 Monitoring devices for measuring cutting angles
• CPC Class Codes: E21C 35/00 Details of, or accessories for, machines for slitting or completely freeing the mineral from the seam, not provided for in groups E21C25/00 - E21C33/00, E21C37/00 or E21C39/00
• CPC Class Codes: G01N 3/58 Investigating machinability by cutting tools; Investigating the cutting ability of tools
• CPC Class Codes: G05B 2219/37525 Mean, average values, statistical derived values

Abstract

Method and apparatus for monitoring the condition of a cutter on a cutting machine while it is being used and for indicating when the cutter wear rate has increased sufficiently to economically require removal for replacement and/or servicing. During at least a portion of an actual cutting operation on the machine, the power being consumed by the cutting machine drive motor is monitored and a frequency spectrum of the monitored power consumption is obtained therefrom. At least part of this power consumption frequency spectrum is then integrated to provide a wear rate index value (called a '"'"''"'"''"'"''"'"'wear number'"'"''"'"''"'"''"'"') which, when compared with previous wear rate index values, may be used as an indication of the relative wear rate for the corresponding cutter. Both an analog embodiment and a combination analog and digital embodiment of apparatus are disclosed for performing the method. To minimize statistical fluctuations, provisions are also made for averaging over several different measurement or sampling periods. An exemplary set of rules is given for processing the wear index values and determining whether or not cutter wear is sufficient to warrant removing the cutter for re-sharpening and/or other servicing.

Claims

1. A method for automatically monitoring the condition of cutters on a cutting machine which is driven by a driving motor, said method comprising the steps of:

producing an electrical signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, automatically machine processing said electrical signal to derive a frequency spectrum therefor, and automatically machine integrating at least part of said frequency spectrum to automatically produce a wear index value output indicative of the condition of the cutters being used by said cutting machine.

2. A method as in claim 1 further comprising, after said producing step, the step of substantially filtering out of said electrical signal, all frequency components in excess of a predetermined frequency range.

3. A method as in claim 2 wherein said predetermined frequency range of said electrical signal comprises 1-50 Hz.

4. A method as in claim 1 further comprising the step of blocking the D.C. component of said electrical signal before said automatic machine processing step.

5. A method for monitoring the condition of cutters on a cutting machine which is driven by a driving motor, said method comprising the steps of:

producing a signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, processing said signal to derive a frequency spectrum therefor, and integrating at least part of said frequency spectrum to produce a wear index value indicative of the condition of the cutters being used by said cutting machine, said producing step comprising generating an analog signal representative of the power being consumed by sAid motor, and processing said analog signal with an analog-to-digital converter to produce digital signals representative of the magnitude of power being consumed by said motor at successive discrete time intervals during at least part of a cutting operation on said cutting machine.

6. A method as in claim 5 wherein said processing step comprises:

digitally computing a Fourier transform using said digital signals to provide a digitally valued frequency spectrum of the power being consumed by said motor.

7. A method as in claim 6 wherein said integrating step comprises:

digitally integrating said digital valued frequency spectrum to produce a digital wear number indicative of the condition of said cutter.

8. A method as in claim 7 further comprising the steps of:

comparing the just computed said digital wear number to at least one previously computed wear number value to detect when the cutters need to be removed for servicing.

9. A method as in claim 8 further comprising:

comparing the number of parts which have been cut by said cutters to a predetermined maximum fail-safe number to indicate a need for cutter removal if said maximum fail-safe number has been exceeded even though said wear-number may not indicate such need.

10. A method for monitoring the condition of cutters on a cutting machine which is driven by a driving motor, said method comprising the steps of:

producing a signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, processing said signal to derive a frequency spectrum therefor, and integrating at least part of said frequency spectrum to produce a wear index value indicative of the condition of the cutters being used by said cutting machine, said producing step comprising generating an analog signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, passing said analog signal through a low pass filter, effectively blocking said analog signal during other than said cutting operations if it is then being produced, and effectively blocking any D.C. component of said analog signal to produce an output signal representing only the significant A.C. components of variations in the power being consumed by said motor during a cutting operation on said cutting machine.

11. A method as in claim 1 wherein said automatic machine processing step comprises:

automatically performing an apparatus generated frequency analysis of said signal to automatically determine which frequency components are present and the magnitude thereof.

12. A method as in claim 11 wherein said automatic machine integrating step comprises automatically integrating and summing within apparatus at least one of said frequency components to automatically produce a wear index value indicative of cutter wear rate.

13. A method as in claim 12 further comprising:

automatically comparing said wear index value within apparatus to a predetermined level which is sufficient to require removal and providing an output indication from said apparatus of this condition if said predetermined level is exceeded.

14. A method as in claim 13 further comprising:

automatically inhibiting said output indication from said apparatus if less than a predetermined minimum number of parts have been cut with said cutters thereby preventing possible spurious output indications.

15. A method as in claim 13 further comprising:

automatically forcing said output indication from said apparatus if more than a predetermined maximum number of parts have been cut with said cutters thereby providing a fail-safe output indication from said apparatus even though said predetermined level may not be exceeded.

16. A method as in claim 1 wherein said automatic machine processing and integrating steps are automatically performed in computing apparatus means which are time-shaRed by a plurality of cutting machines.

17. Apparatus for monitoring the condition of cutters on a cutting machine which is driven by a driving motor, said apparatus comprising:

means for producing a signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, means for processing said signal to derive a frequency spectrum therefor, and means for integrating at least part of said frequency spectrum to produce a wear index value indicative of the condition of the cutters being used by said cutting machine.

18. Apparatus as in claim 17 further comprising:

means for substantially filtering out of said signal, all frequency components in excess of a predetermined frequency range.

19. Apparatus as in claim 18 wherein said predetermined frequency range comprises 1-50 Hz.

20. Apparatus as in claim 17 further comprising:

means for blocking the D.C. component of said signal.

21. Apparatus as in claim 17 wherein said means for producing comprises:

means for generating an analog signal representative of the power being consumed by said motor, analog-to-digital converter means connected to receive said analog signal and to produce digital signals in response thereto which are representative of the power being consumed by said motor at successive discrete time intervals during at least part of a cutting operation on said cutting machine.

22. Apparatus as in claim 21 wherein said means for processing comprises:

means for digitally computing a Fourier transform using said digital signals to provide a digitally valued frequency spectrum of the power being consumed by said motor.

23. Apparatus as in claim 22 wherein said means for integrating comprises:

means for digitally integrating said digitally valued frequency spectrum to produce a digital wear number indicative of the condition of said cutters.

24. Apparatus as in claim 23 further comprising:

means for comparing the just computed said digital wear number to at least one previously computed wear number value to detect when the cutters need removal for servicing.

25. Apparatus as in claim 24 further comprising:

means for comparing the number of parts which have been cut by said cutters to a predetermined maximum fail-safe number to indicate a need for cutter removal if said maximum number has been exceeded even though said wear number may not indicate such need.

26. Apparatus as in claim 17 wherein said means for producing comprises:

means for generating an analog signal representative of the power being consumed by said motor during at least part of a cutting operation on said cutting machine, a low pass filter connected to pass the low frequency components (approximately 1-50 Hz) of said analog signal, gate means for blocking said analog signal during other than said cutting operations if it is then being produced, and A.C. coupling means for blocking any D.C. component of said analog signal to produce an output signal representing only the significant A.C. components of variations in the power being consumed by said motor during a cutting operation on said cutting machine.

27. Apparatus as in claim 17 wherein said means for processing comprises:

means for performing a frequency analysis of said signal to determine which frequency components are present and the magnitude thereof.

28. Apparatus as in claim 27 wherein said means for integrating comprises:

means for integrating and summing said frequency components to produce a wear index value indicative of the cutter wear rate.

29. Apparatus as in claim 28 further comprising:

means for comparing said wear index value to a predetermined level which is sufficient to require removal and for providing an indication of this condition if said predetermined level is exceeded.

30. Apparatus as in claim 29 further comprising:

means for inhibitiNg said indication if less than a predetermined minimum number of parts have been cut with said cutters thereby preventing possible spurious indications.

31. Apparatus as in claim 29 further comprising:

means for forcing said indication if more than a predetermined maximum number of parts have been cut with said cutters thereby providing a fail-safe indication even though said predetermined level may not be exceeded.