Method and apparatus for measuring small variations in the speed of rotating shafts

• US 3,885,420 A
• Filed: 03/06/1974
• Issued: 05/27/1975
• Est. Priority Date: 03/06/1974
• Status: Expired due to Term

• Current Assignee: John F. Wolfinger
• Original Assignee: John F. Wolfinger
• Inventors: Wolfinger, John F.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Kreitman, Stephen A.
• Application Number:
  US05/448,605
• Time in Patent Office: 447 Days
• Field of Search: 73/70.1,70,71.4,71,71.2,67,67.2,136A 324/161,83R
• US Class Current: 73/650
• CPC Class Codes: G01H 1/10 of torsional vibrations

Abstract

Method and apparatus for measuring torsional vibrations in a rotating shaft. A detection device is connected to provide output pulses at a rate proportional to the instantaneous angular velocity of the shaft. The pulses are compared in a phase detector with pulses produced by a voltage controlled oscillator which oscillator is adjusted to produce pulses at a frequency corresponding to the average angular velocity of the shaft. The phase detector generates an output signal proportional to the instantaneous phase difference between the two pulse inputs which output signal varies as a function of variations in the frequency of pulses from the detection device. The output signal is therefore representative of torsional vibrations in the shaft. The output signal may be filtered to produce a signal having an instantaneous amplitude and frequency corresponding to the torsional vibrations.

Claims

1. Apparatus for detecting instantaneous torsional vibrations in a rotating shaft, said apparatus comprising:

first means for generating a first signal at a frequency proportional to the instantaneous angular velocity of said shaft;

second means for generating a second signal at a frequency proportional to the average angular velocity of said shaft; and

third means connected to receive said first and second signals and responsive thereto to produce a third signal having an average value proportional to the phase difference between said first and second signals.

2. The apparatus as defined in claim 1 and including:

fourth means connected to receive said third signal and responsive thereto to produce a fourth signal having an amplitude and frequency corresponding to said instantaneous torsional vibrations of said shaft.

3. The apparatus as defined in claim 1 wherein said first means comprises:

an annular member mounted for rotation with said shaft, said member having a plurality of circumferentially spaced elements;

a probe mounted adjacent said member, said probe being responsive to rotation of said member to provide a pulse signal as each of said plurality of elements passes by said probe, and a zero-crossing detector connected to receive said pulse signal and responsive thereto to produce said first signal.

4. The apparatus as defined in claim 1 wherein said third means comprises:

a flip-flop circuit connected to be reset by said first signal and to be set by said second signal, said flip-flop circuit producing said third output signal comprising a plurality of pulses, each of said pulses having a pulse width proportional to the phase difference between said first and second signals.

5. The apparatus as defined in claim 1 wherein said second means comprises a voltage controlled oscillator.

6. The apparatus as defined in claim 5 and including a feedback loop for passing predetermined frequency components of said third signal to said oscillator, said oscillator being responsive to said predetermined frequency components to adjust the frequency of said second signal.

7. The apparatus as defined in claim 6 wherein said feedback loop includes a serially connected low-pass filter.

8. A method for measuring torsional vibrations in a rotating shaft comprising the steps of:

generating a first signal at a frequency proportional to the instantaneous angular velocity of said shaft;

generating a second signal at a frequency proportional to the average angular velocity of said shaft; and

comparing the phase relationship between said first and second signals to produce a third signal having an average value proportional to the phase difference between said first and second signals.

9. The method as defined in claim 8 and including the step of filtering said third signal to produce a fourth signal having an amplitude and frequency corresponding to the amplitude and frequency of torsional vibrations in said shaft.