Method and apparatus for monitoring machine performance

• US 5,523,701 A
• Filed: 06/21/1994
• Issued: 06/04/1996
• Est. Priority Date: 06/21/1994
• Status: Expired due to Term

• Current Assignee: Martin Marietta Energy Systems, Inc. (Martin Marietta Corporation)
• Original Assignee: Martin Marietta Energy Systems, Inc. (Martin Marietta Corporation)
• Inventors: Castleberry, Kimberly N., Smith, Stephen F.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): KHOSRAVI, KOURO
• Application Number:
  US08/263,344
• Time in Patent Office: 714 Days
• Field of Search: 324/772, 324/117 H, 324/545
• US Class Current: 324/765.01
• CPC Class Codes: B23Q 17/0961 by measuring power, current or torque of a motor
• CPC Class Codes: G01M 13/00 Testing of machine parts
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 2219/37094 Hall sensor
• CPC Class Codes: G05B 2219/37285 Load, current taken by motor
• CPC Class Codes: G05B 2219/37508 Cross correlation
• CPC Class Codes: G05B 2219/50185 Monitoring, detect failures, control of efficiency of machine, tool life
• CPC Class Codes: G07C 3/00 Registering or indicating the condition or the working of machines or other apparatus, other than vehicles

Abstract

Machine operating conditions can be monitored by analyzing, in either the time or frequency domain, the spectral components of the motor current. Changes in the electric background noise, induced by mechanical variations in the machine, are correlated to changes in the operating parameters of the machine.

Claims

1. An apparatus for monitoring operating parameters of a machine rotated by an electric motor, comprising:

means for sensing current drawn by the electric motor and producing an electric signal having a mechanically-induced random noise component which varies in accordance with a mechanical condition of the machine; and

means for correlating changes in the mechanically-induced random noise component to changes in the mechanical condition of the machine.

2. An apparatus according to claim 1, wherein the sensing means is a current transformer.

3. An apparatus according to claim 1, wherein the sensing means is a low value dropping resistor in series with at least one lead wire of the motor.

4. An apparatus according to claim 1, wherein the sensing means is a Hall effect sensor.

5. An apparatus according to claim 1, wherein the correlating means includes a spectrum analyzer.

6. An apparatus according to claim 1, wherein the correlating means comprises an amplifier connected to the sensing means, a demodulator connected to an output of the amplifier, an analog-to-digital converter connected to an output of the demodulator, and a computer for producing a frequency domain spectrum of the motor current.

7. An apparatus according to claim 1, wherein the machine is a cutting machine and the condition is tool sharpness and depth of cut.

8. An apparatus according to claim 1, wherein the correlating means comprises an amplifier connected to the sensing means, an analog-to-digital converter connected to an output of the amplifier, and a computer for producing a frequency domain spectrum of the motor current.

9. A method for monitoring operating parameters of a machine rotated by an electric motor, comprising the steps of:

sensing current drawn by the electric motor;

producing an electric signal from the sensed current, the electric signal having a mechanically-induced random noise component which varies in accordance with a condition of the machine; and

correlating changes in the mechanically-induced random noise component to changes in the mechanical condition of the machine.

10. A method according to claim 9, wherein the sensing step comprises attaching a current transformer to a lead of the electric motor.

11. A method according to claim 9, wherein the sensing step comprises connecting a dropping resistor in series with at least one lead wire of the motor.

12. A method according to claim 9, wherein the sensing step comprises positioning a Hall-effect sensor near a current supply of the electric motor.

13. A method according to claim 9, wherein the correlating step comprises amplifying the electric signal, demodulating the amplified signal, converting the demodulated signal from analog to digital, and performing a frequency transform on the digital signal.

14. A method according to claim 9, wherein the correlating step comprises amplifying the electric signal, converting the amplified signal from analog to digital, and performing a frequency transform on the digital signal.

15. A method according to claim 9, wherein the correlating step comprises amplifying the electric signal, converting the demodulated signal from analog to digital, and performing a frequency transform on the digital signal.