Rotating shaft vibration monitor

• US 5,438,882 A
• Filed: 09/09/1994
• Issued: 08/08/1995
• Est. Priority Date: 01/25/1993
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Zimmerman, Paul J., Karim-Panahi, Khosrow, Terhune, James H.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): BIEGEL, RONALD L
• Application Number:
  US08/303,541
• Time in Patent Office: 333 Days
• Field of Search: 73/862.324, 73/862.326, 73/862.327, 73/862.195
• US Class Current: 73/862.324
• CPC Class Codes: G01H 1/10 of torsional vibrations
• CPC Class Codes: G01H 9/00 Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
• CPC Class Codes: G01L 3/109 involving measuring phase difference of two signals or pulse trains
• CPC Class Codes: G01L 3/12 involving photoelectric means

Abstract

A non-contact system and method for measuring torsional wave propagation along a rotating shaft as well as static angular deflection due to a constant applied torque. The relative twist angle between two cross-sectional portions of the rotating shaft separated by a predetermined distance is detected over time and then the axial variation of torque along the rotating shaft is determined as a function of relative twist angle. Detection is carried out electro-optically using a pair of photodetectors and bands of reflective marks adhered on the circumferential surfaces of the two cross-sectional portions. Axial variation of torque is determined by determining variations in the phase difference between pulse trains output by the photodetectors.

Claims

1. A system for monitoring an effect of torque on a rotating shaft, comprising:

first detectable means circumferentially arranged on an outer surface of said rotating shaft at a first axial location thereof and having a property which varies repeatedly about a circumference;

second detectable means circumferentially arranged on the outer surface of said rotating shaft at a second axial location thereof and having a property which varies repeatedly about said circumference, said second axial location being separated from said first axial location by a predetermined distance;

first detecting means for outputting a first electrical signal which varies in dependence on a first local value of said repeatedly varying property for a portion of said first detectable means located opposite to a window of said first detecting means;

second detecting means for outputting a second electrical signal which varies in dependence on a second local value of said repeatedly varying property for a portion of said second detectable means located opposite to a window of said second detecting means; and

processing means for computing a wave number of a torsional wave propagating axially in said rotating shaft in dependence on variations in a difference in phase angles between said first and second electrical signals.

2. The rotating shaft monitoring system as defined in claim 1, further comprising first means for directing light onto said first detectable means such that light reflected therefrom impinges on said first detecting means and second means for directing light onto said second detectable means such that light reflected therefrom impinges on said second detecting means.

3. The rotating shaft monitoring system as defined in claim 2, wherein said repeatedly varying property is reflectivity, and said first and second detecting means respectively comprise first and second photodetectors for outputting an electrical signal in response to the impingement of light reflected from said first and second detectable means respectively.

4. The rotating shaft monitoring system as defined in claim 3, further comprising a first focusing lens arranged between said first photodetector and said first detectable means and a second focusing lens arranged between said second photodetector and said second detectable means.

5. The rotating shaft monitoring system as defined in claim 1, wherein said first and second detectable means are arranged so that when said shaft is stationary, said varying properties of said first detectable means have a constant phase relationship with said varying properties of said second detectable means.

6. The rotating shaft monitoring system as defined in claim 1, wherein said first and second electrical signals comprise first and second pulse trains respectively, and said processing means comprise means for quantizing the time intervals between corresponding pulses of said first and second pulse trains.

7. The rotating shaft monitoring system as defined in claim 6, further comprising means for displaying the first and second pulse trains superimposed on each other.

8. The rotating shaft monitoring system as defined in claim 6, wherein said processing means further comprises means for determining the relative twist angle between first and second cross-sectional portions of said rotating shaft at said first and second axial locations over time in dependence on said quantized time intervals, and further comprising means for displaying first and second wave patterns showing the variation of said relative twist angle over time for said first and second cross-sectional portions.

9. A system for monitoring an effect of torque on a rotating shaft, comprising;

a first plurality of detectable means circumferentially distributed along an outer surface of said rotating shaft at a first axial location thereof;

a second plurality of detectable means circumferentially distributed at said equal intervals along the outer surface of said rotating shaft at a second axial location thereof, said second axial location being separated from said first axial location by a predetermined distance;

first detecting means for outputting a pulse in response to each event wherein one of said first plurality of detectable means is located at a first predetermined angular position opposing said first detecting means, said pulses output by said first detecting means forming a first pulse train;

second detecting means for outputting a pulse in response to each event wherein one of said second plurality of detectable means is located at a second predetermined angular position opposing said second detecting means, said pulses output by said second detecting means forming a second pulse train;

processing means for computing a wave number of a torsional wave propagating axially in said rotating shaft in dependence on variations in a difference in phase angles between corresponding pulses of said first and second pulse trains, and

first means for directing light onto said rotating shaft at said first axial location such that light reflected by said first detectable means impinges on said first detecting means and second means for directing light onto said rotating shaft at said second axial location such that light reflected by said second detectable means impinges on said second detecting means.

10. The rotating shaft monitoring system as defined in claim 9, wherein said first and second detecting means respectively comprise first and second photodetectors for outputting an electrical signal in response to the impingement of light reflected from said first and second detectable means respectively, further comprising a first focusing lens arranged between said first photodetector and said first detectable means and a second focusing lens arranged between said second photodetector and said second detectable means.

11. A system for monitoring an effect of torque on a rotating shaft, comprising:

a first plurality of detectable means circumferentially distributed along an outer surface of said rotating shaft at a first axial location thereof;

a second plurality of detectable means circumferentially distributed at said equal intervals along the outer surface of said rotating shaft at a second axial location thereof, said second axial location being separated from said first axial location by a predetermined distance;

first detecting means for outputting a pulse in response to each event wherein one of said first plurality of detectable means is located at a first predetermined angular position opposing said first detecting means, said pulses output by said first detecting means forming a first pulse train;

second detecting means for outputting a pulse in response to each event wherein one of said second plurality of detectable means is located at a second predetermined angular position opposing said second detecting means, said pulses output by said second detecting means forming a second pulse train;

processing means for computing a wave number of a torsional wave propagating axially in said rotating shaft in dependence on variations in a difference in phase angles between corresponding pulses of said first and second pulse trains, wherein said processing means comprise means for quantizing the time intervals between corresponding pulses of said first and second pulse trains and means for determining the relative twist angle between first and second cross-sectional portions of said rotating shaft at said first and second axial locations respectively over time in dependence on said quantized time intervals, and

means for displaying first and second wave patterns showing the variation of said relative twist angle over time for said first and second cross-sectional portions.

12. A method for monitoring an effect of torque on a rotating shaft, comprising the steps of:

detecting the time at which predetermined circumferential portions of said rotating shaft at a first axial location thereof reach a first predetermined angular position;

outputting a first electrical signal which varies as a function of detection of said predetermined circumferential portions at said first predetermined angular position;

detecting the time at Which predetermined circumferential portions of said rotating shaft at a second axial location thereof reach a second predetermined angular position;

outputting a second electrical signal which varies as a function of detection of said predetermined circumferential portions at said second predetermined angular position;

computing a wave number of a torsional wave propagating axially in said rotating shaft in dependence on variations in a difference in phase angles between said first and second electrical signals, wherein said first electrical signal comprises a first train of electrical pulses and said second electrical signal comprises a second train of electrical pulses and said variations in a difference in phase angles are determined by quantizing the time intervals between corresponding pulses of said first and second pulse trains; and

determining the relative twist angle between first and second cross-sectional portions of said rotating shaft at said first and second axial locations respectively over time in dependence on said quantized time intervals, and displaying first and second wave patterns showing the variation of said relative twist angle over time for said first and second cross-sectional portions.

13. The rotating shaft monitoring method as defined in claim 12, further comprising the steps of:

arranging a first plurality of detectable means along the circumferential surface of said rotating shaft at said first axial location thereof; and

arranging a second plurality of detectable means along the circumferential surface of said rotating shaft at said second axial location thereof,

wherein said first and second detectable means are arranged so that when said shaft is stationary, said first detectable means have a constant phase relationship to said second detectable means.

14. The rotating shaft monitoring method as defined in claim 13, wherein said first and second detectable means are reflective, and said first and second trains of electrical pulses are output by first and second photodetectors in response to the detection of light reflected from said first and second detectable means.