Metal cutting tool failure event sensor

• US 5,319,357 A
• Filed: 06/08/1992
• Issued: 06/07/1994
• Est. Priority Date: 06/08/1992
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Carmichael, Jerry H., Diei, Edward N., Hayashi, Steven R.
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US07/895,320
• Time in Patent Office: 729 Days
• Field of Search: 340/680, 340/683, 73/104, 73/660, 364/508, 364/474.17, 364/551.02
• US Class Current: 340/680
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 2219/37245 Breakage tool, failure
• CPC Class Codes: G05B 2219/37434 Measuring vibration of machine or workpiece or tool
• CPC Class Codes: G05B 2219/37493 Use of different frequency band pass filters to separate different signals
• CPC Class Codes: G08B 21/187 Machine fault alarms

Abstract

Breaking of a cutter insert in a multiple insert metal cutter is detected by selecting a periodic vibration generated electrical signal having components which track individual insert contribution. These components are filtered to provide RMS values whose predetermined ratio values indicate insert breakage.

Claims

1. A method of determining a metal cutting tool failure event during a metal cutting procedure, comprising the steps of:

(a) obtaining an electrical low frequency forced vibration signal from a cutting tool during its cutting process;

(b) passing said signal through electronic filters to provide a residual signal;

(c) electronically determining an RMS value of each of said low frequency signal and said residual signal;

(d) passing said RMS values into a value comparison processor which determines a ratio value of ##EQU3## (e) generating a tool failure event electrical signal when said ratio value is greater than a predetermined value.

2. The invention as recited in claim 1, wherein said cutting tool is a multiple cutting edge tool and said failure event is a breakage of one cutting edge of said cutting tool.

3. The invention as recited in claim 1, wherein said cutting tool is a multiple cutter insert tool and said failure event is a breakage of one insert of said cutting tool.

4. The invention as recited in claim 1, wherein said cutting tool is mounted in a spindle of a metal cutting machine and said low frequency forced vibration signal is obtained by an accelerometer having a flat response in the range of about 5 to about 1000 Hz., said accelerometer being positioned on said metal cutting machine.

5. The invention as recited in claim 1, wherein said electronic filters include a d.c. filter, a synchronous filter, a notch filter, and an MAV (mean-absolute-value) filter for each RMS determination.

6. A method of detecting a multiple cutting edge metal cutting tool failure event during a metal cutting operation, comprising the steps of:

(a) generating an electrical low frequency (LF) base signal caused by operation of a cutting tool;

(b) filtering said LF base signal through a d.c. filter and a first MAV (mean-absolute-value) filter to remove and d.c. bias and to determine a first RMS value signal;

(c) passing a branch of an output from said d.c. filter together with a tool rotation tachometer signal from said cutting tool through s synchronous filter which only passes an electrical signal of a rotational tool frequency at harmonics of said cutting tool;

(d) passing a branch of an output signal from said synchronous filter through a second MAV filter to determine a second RMS value signal;

(e) passing said first and second RMS value signals into a comparison processor to determine a ratio of the signals which provides a first threshold value;

(f) passing another branch of the output signal from said synchronous filter together with an electrical signal, having a magnitude corresponding to a quantity of cutting edges on said cutting tool, through a multi notch filter to provide a residual signal which will contain any noise present in said LF signal and passed by said d.c. filter and said synchronous filter and caused by said cutting tool if damaged;

(g) passing the residual signal from said notch filter to a third MAV filter to determine a third RMS value signal;

(h) passing an output signal from each of said third and said second MAV filters to a comparison processor to determine a ratio of the signals which provides a second threshold value; and

(i) initiating a tool failure event signal when said second threshold value exceeds a predetermined value.

7. The invention as recited in claim 6, wherein said cutting tool comprises multiple cutting inserts and said tool failure event signal is initiated when a breakage of one of said inserts occurs.

8. A metal cutting tool failure event sensor, comprising:

means for sensing a vibration in a cutting machine tool having a multiplicity of cutting inserts and for generating a vibration base signal responsive to said sensed vibration;

a d.c. filter to receive said vibration base signal and to provide a d.c. filter output signal without d.c. bias;

a first MAV (mean-absolute-value) filter coupled to said d.c. filter to provide an RMS value of said d.c. filter output signal;

a synchronous filter for receiving a spindle tachometer signal and coupled to said d.c. filter for receiving said d.c. filter output signal, said synchronous filter providing a synchronous filter output signal;

a second MAV filter coupled to said synchronous filter to provide an RMS value of said synchronous filter output signal;

a first comparison processor coupled respectively to said first MAV filter and to said second MAV filter to calculate a first ratio defined by said synchronous filter output signal RMS value over said d.c. filter output signal RMS value;

a notch filter coupled to said synchronous filter to provide a residual signal which will contain any noise caused by at least one of said multiplicity of cutting inserts if damaged;

a third MAV filter coupled to said notch filter to provide an RMS value of said residual signal; and

a second comparison processor coupled respectively to said second MAV filter and to said third MAV filter to calculate a second ratio defined by said synchronous filter output signal RMS value over said residual signal RMS value, said second comparison processor generating an alarm signal if the second ratio exceeds a predetermined threshold value.

9. The sensor of claim 8, wherein said first comparison processor compares the first ratio to another predetermined threshold value and discontinues signal processing through said notch filter, said third MAV filter and said second comparison processor if the first ratio is less than the other predetermined threshold value.

10. A metal cutting tool failure event sensor, comprising:

p1 a vibration sensor to sense a vibration in a cutting tool having a multiplicity of cutting inserts and to generate a vibration base signal responsive to said sensed vibration;

a d.c. filter for receiving said vibration base signal and for providing a d.c. filter output signal without d.c. bias;

a synchronous filter for receiving a spindle tachometer signal and coupled to said d.c. filter for receiving said d.c. filter output signal, said synchronous filter providing a synchronous filter output signal;

a first MAV (mean-absolute-value) filter coupled to said synchronous filter to provide an RMS value of said synchronous filter output signal;

a notch filter coupled to sid synchronous filter to provide a residual signal which will contain any noise caused by any one of said multiplicity of cutting inserts being damaged;

a second MAV filter coupled to said notch filter to provide an RMS value of said residual signal; and

a first comparison processor coupled respectively to said first MAV filter and to said second MAV filter to calculate a first ratio defined by said synchronous filter output signal RMS value over said residual signal RMS value, said comparison processor generating an alarm signal if said ratio exceeds a predetermined threshold value.

11. The sensor of claim 10, further comprising:

a third MAV (mean-absolute-value) filter coupled to said d.c. filter to provide an RMS value of said d.c. filter output signal; and

a second comparison processor coupled respectively to said first MAV filter and said third MAV filter to calculate a second ratio defined by said synchronous filter output signal RMS value over said d.c. filter output signal RMS value and said second comparison processor compares the second ratio to another predetermined threshold value and discontinues signal processing through said notch filter, said second MAV filter and said first comparison processor if the second ratio is less than the other predetermined threshold value.