Method and system for determining the wear of a drill bit in real time

• US 4,228,514 A
• Filed: 04/16/1979
• Issued: 10/14/1980
• Est. Priority Date: 04/16/1979
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Weiss, Roger E.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/030,061
• Time in Patent Office: 547 Days
• Field of Search: 364/475, 364/474, 364/111, 364/551, 73/104
• US Class Current: 702/34
• CPC Class Codes: G01N 3/58 Investigating machinability by cutting tools; Investigating the cutting ability of tools
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 19/4163 Adaptive control of feed or cutting velocity without NC B23Q15/12

Abstract

A method and a system are disclosed for determining the wear of a drill bit in real time. At a predetermined point prior to engagement of the drill bit with the workpiece, a first rotational speed of the drill bit is ascertained. Upon exit of the drill bit from the workpiece a second rotational speed is determined. Measurement of these two rotational speeds enables a determination to be made of the loss of energy resulting from the drilling operation. This loss in energy is used to produce a measure of drill bit wear.

Claims

1. A method for ascertaining the wear of a drill bit during the performance of a drilling operation on a workpiece comprising the steps of:

monitoring with a position monitoring device positions of said drill bit prior to engagement with and after emergence from said workpiece;

determining a first rotational speed of said drill bit at the position indicated by said position monitoring device prior to engagement with said workpiece;

storing temporarily said first rotational speed of said drill bit;

determining a second rotational speed of said drill bit at the position indicated by said position monitoring device following emergence of said drill bit from said workpiece;

measuring the elapsed time between said first and second rotational speed determinations;

determining the amount of energy expended during said drilling operation from said first and second rotational speed determinations and said elapsed time; and

generating a measure of the wear of said drill bit from said energy determination.

2. The method in accordance with claim 1 wherein said position monitoring step further includes the steps of:

storing temporarily a predetermined height position of said drill bit spaced apart from said workpiece;

measuring an actual height position of said drill bit with respect to said workpiece;

monitoring said actual measured height position and a direction of travel of said drill bit with respect to said workpiece;

decoding direction of travel information so that said actual measured height position is decremented by a predetermined unit of height as said drill bit approaches said workpiece and is incremented by a predetermined unit of height as said drill bit recedes from said workpiece;

comparing said actual measured height position of said drill bit with respect to said workpiece and said predetermined height position of said drill bit spaced apart from said workpiece; and

generating an output signal when said actual measured height position and said predetermined height position correspond.

3. The method in accordance with claim 1 wherein said rotational speed determining step further includes the steps of:

illuminating with light energy a spindle having affixed therein said drill bit;

absorbing a first portion of said light energy by light energy absorbing means which extend approximately halfway around the circumference of said spindle and adhere thereto;

detecting a second portion of said light energy reflected from said spindle in a region adjacent that having said light energy absorbing means adhering thereto;

counting a number of transitions occurring between said reflected light energy and said absorbed light energy; and

measuring, concurrently with said counting step, an elapsed time corresponding to said number of transitions.

4. Apparatus for ascertaining the wear of a drill bit during the performance of a drilling operation on a workpiece, the apparatus including:

means for monitoring positions of said drill bit prior to engagement with said workpiece and after emergence from said workpiece;

means, responsive to said position monitoring means, for determining a first rotational speed of said drill bit at the indicated position prior to engagement with said workpiece and a second rotational speed of said drill bit at the indicated position after emergence from said workpiece;

means for storing temporarily said first rotational speed of said drill bit;

means for measuring an elapsed time between said first and second rotational speeds;

means, responsive to said speed determining means, said rotational speed storing means and said time measuring means, for determining the amount of energy expended during said drilling operation based on said first and second rotational speeds and said elapsed time, said means further generating a measure of the wear of said drill bit based on said energy determination.

5. The apparatus in accordance with claim 4 wherein said position monitoring means comprises:

means for storing temporarily a predetermined height position of said drill bit spaced apart from said workpiece;

means for measuring an actual height position of said drill bit with respect to said workpiece;

means, responsive to said height position measuring means, for monitoring said actual measured height position and a direction of travel of said drill bit with respect to said workpiece;

means, responsive to said height position measuring means, for decoding direction of travel information so that said actual measured height position is decremented by a predetermined unit of height as said drill bit approaches said workpiece and is incremented by a predetermined unit of height as said drill bit recedes from said workpiece;

means, responsive to said actual measured height position monitoring means and said predetermined height position storing means, for comparing said actual measured height position of said drill bit with respect to said workpiece and said predetermined height position of said drill bit spaced apart from said workpiece; and

means, internal to said comparing means, for generating an output signal when said actual measured height position and said predetermined height position correspond.

6. The apparatus in accordance with claim 5 wherein said predetermined height position storing means comprises:

a plurality of flip-flops arranged in parallel; and

means for coupling a multibit digital signal representing said predetermined height position to said plurality of flip-flops such that separate bits in said signal are coupled to separate flip-flops.

7. The apparatus in accordance with claim 5 wherein said actual measured height position monitoring means comprises:

a plurality of up/down counters each having a separate input for an up-count signal and a separate input for a down-count signal and each counter further having a separate output for a borrow signal and a separate output for a carry signal; and

means for coupling said counters to one another such that said borrow signal output is coupled to said down-count signal input and said carry signal output is coupled to said up-count signal input.

8. The apparatus in accordance with claim 5 wherein said direction of travel information decoding means comprises:

first, second and third inverters, said first inverter output coupled to said third inverter input;

first and second multivibrators each of which has an input coupled to an output of said second inverter;

means for controlling the time duration of signals produced by said first and second multivibrators;

first, second, third and fourth NAND gates each of which has a pair of inputs, said first NAND gate inputs coupled to said first inverter output and said second multivibrator output, said second NAND gate inputs coupled to said first multivibrator output and said third inverter output, said third NAND gate inputs coupled to said second multivibrator output and said third inverter output, and said fourth NAND gate inputs coupled to said first inverter output and said first multivibrator output;

first and second NOR gates, each of which has a pair of inputs, said first NOR gate inputs coupled to said first and second NAND gate outputs and said second NOR gate inputs coupled to said third and fourth NAND gate outputs; and

a flip-flop having first and second inputs coupled to said first and second NOR gate outputs, respectively.

9. The apparatus in accordance with claim 4 wherein said speed determining means comprises:

means for illuminating with light energy a spindle having affixed therein said drill bit;

means, extending approximately halfway around the circumference of said spindle and adhering thereto, for absorbing a first portion of said light energy produced by said illuminating means;

means for detecting a second portion of said light energy produced by said illuminating means which energy is reflected from said spindle in a region adjacent that having said absorbing means adhering thereto;

means for counting a number of transitions occurring between said reflected light energy and said absorbed light energy; and

means for measuring an elapsed time corresponding to said number of transitions.

10. The apparatus in accordance with claim 9 wherein said elapsed time measuring means comprises:

clock means; and

means, responsive to said clock means, for accumulating a number of clock pulses corresponding to said number of transitions.

11. The apparatus in accordance with claim 10 wherein said counting means comprises:

means for storing temporarily a number of spindle revolutions to be sampled; and

means, responsive to said number of spindle revolutions storing means, for controlling the number of clock pulses accepted by said accumulating means.

12. The apparatus in accordance with claim 11 wherein said number of spindle revolutions storing means comprises:

an up/down counter;

means for coupling a binary representation of said number of spindle revolutions to be sampled to said up/down counter; and

means for controlling the loading of said binary representation of said number of spindle revolutions to be sampled into said up/down counter.

13. The apparatus in accordance with claim 11 wherein said clock pulse controlling means comprises:

a multivibrator having an input coupled to said number of spindle revolutions storing means;

a NOR gate having a pair of inputs one of which is coupled to a first output from said multivibrator and the other of which is coupled to said means for controlling the loading of said binary representation of said number of spindle revolutions to be sampled into said up/down counter;

first and second flip-flops coupled to an output of said NOR gate and to each other; and

a two input AND gate, one input coupled to said reflected light energy detecting means and the other input coupled to an output of said second flip-flop, said AND gate being enabled during a time interval encompassing said number of spindle revolutions to be sampled and disabled when a counted number of spindle revolutions equals the number of such revolutions to be sampled thereby causing said multivibrator and said first and second flip-flops to change state and disable said synchronous binary counter in said accumulating means.

14. The apparatus in accordance with claim 10 wherein said accumulating means comprises:

a synchronous binary counter; and

a plurality of binary counters coupled in tandem with each other and with said synchronous binary counter.

15. The apparatus in accordance with claim 10 wherein said clock means comprises:

an oscillator; and

a plurality of binary counters connected in tandem with said oscillator.

16. The apparatus in accordance with claim 4 further including:

display means; and

means for selecting which spindle out of n spindles is to have selected information associated therewith presented on said display means.

17. The apparatus in accordance with claim 4 further including:

means for calibrating a spindle, said calibrating means comprising

a current probe;

a low-pass filter coupled in series with said current probe;

a level detector coupled in series with said low-pass filter;

means for storing temporarily a number of spindle revolutions to be sampled;

clock means;

means for accumulating a number of clock pulses produced by said clock means; and

means, responsive to said number of spindle revolutions storing means and coupled to said level detector, for controlling the number of clock pulses accepted by said accumulating means.

18. The apparatus in accordance with claim 17 wherein said number of spindle revolutions storing means comprises:

an up/down counter;

means for coupling a binary representation of said number of spindle revolutions to be sampled to said up/down counter; and

means for controlling the loading of said binary representation of said number of spindle revolutions to be sampled into said up/down counter.

19. The apparatus in accordance with claim 18 wherein said clock means comprises:

an oscillator; and

a plurality of binary counters connected in tandem with said oscillator.

20. The apparatus in accordance with claim 19 wherein said accumulating means comprises:

a synchronous binary counter; and

a plurality of binary counters coupled in tandem with each other and with said synchronous binary counter.

21. The apparatus in accordance with claim 20 wherein said clock pulse controlling means comprises:

a multivibrator having an input coupled to said number of spindle revolutions storing means;

a NOR gate having a pair of inputs one of which is coupled to a first output from said multivibrator and the other of which is coupled to said means for controlling the loading of said binary representation of said number of spindle revolutions to be sampled into said up/down counter;

first and second flip-flops coupled to an output of said NOR gate and to each other; and

a two input AND gate, one input coupled to said reflcted light energy detecting meand and the other input coupled to an output of said second flip-flop, said AND gate being enabled during a time interval encompassing said number of spindle revolutions to be sampled and disabled when a counted number of spindle revolutions equals the number of such revolutions to be sampled thereby causing said multivibrator and said first and second flip-flops to change state and disable said synchronous binary counter in said accumulating means.