Method and system for calculating misalignment of rotational body

• US 8,306,776 B2
• Filed: 06/30/2008
• Issued: 11/06/2012
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Mitsubishi Power Limited (Mitsubishi Heavy Industries, Ltd.)
• Original Assignee: Mitsubishi Heavy Industries, Ltd.
• Inventors: Ihara, Keisuke, Sakae, Toshiyuki
• Primary Examiner(s): Teixeira Moffat, Jonathan C
• Assistant Examiner(s): HENSON, MISCHITA L
• Application Number:
  US12/678,018
• Publication Number:
  US 20100241394A1
• Time in Patent Office: 1,590 Days
• Field of Search: 702150-151, 702/154
• US Class Current: 702/151
• CPC Class Codes: G01B 21/24 for testing alignment of axes

Abstract

In a method of calculating misalignment of a rotational body, radial displacement values are measured using a displacement gauge. A calculation part performs the steps of deriving radial displacement amounts of the rotational body for at least four or more measurement points along an outer surface while rotating the rotational body, selecting three arbitrary points to calculate a circle, calculating circle values for all the measurement points, calculating differences between the calculated circle values and the radial displacement amounts as error amounts, summing the error amounts to derive a total error amount, repeating circle calculation for different combinations and calculating a total error amount for each calculated circle, selecting a circle with a minimum total error amount as a most probable circle, and calculating deviation between the center of the most probable circle and the center of rotation of the rotational body.

Claims

1. A method of calculating misalignment of a rotational body, said method comprising the steps of:

measuring radial displacement values using a displacement gauge;

deriving, by a calculation part, radial displacement amounts of the rotational body for at least four or more measurement points along an outer surface in a circumferential direction based on the measured values measured by the displacement gauge while rotating the rotational body;

selecting, by the calculation part, three arbitrary points among all the measurement points to calculate a circle from the radial displacement amounts and measured angles;

calculating, by the calculation part, circle values for all the measurement points from the calculated circle;

calculating, by the calculation part, differences between the calculated circle values and the radial displacement amounts as error amounts at the measurement points;

summing, by the calculation part, the error amounts to derive a total error amount;

repeating, by the calculation part, circle calculation for different combinations of three measurement points among all the measurement points and calculating, by the calculation part, a total error amount for each calculated circle;

selecting, by the calculation part, a calculated circle with a minimum total error amount among obtained total error amounts for all combinations as a most probable circle; and

calculating, by the calculation part, deviation between the center of the most probable circle and the center of rotation of the rotational body as misalignment data of the most probable circle.

2. The method according to claim 1, wherein the misalignment data of the most probable circle includes a misalignment amount and a misalignment angle.

3. The method according to claim 1, wherein a measured value at a measurement point corresponding to a most probable circle error amount that is a difference between the calculated circle value and the radial displacement amount on the most probable circle is recognized as an abnormal value when the most probable circle error amount exceeds a reference value.

4. The method according to claim 3, wherein the measured value recognized as the abnormal value is remeasured to obtain a remeasured value and the measured value is replaced with the remeasured value when the most probable circle error amount exceeds the reference value.

5. The method according to claim 1, wherein the rotational body is a gas turbine rotor.

6. A system for calculating misalignment of a rotational body, comprising:

an input part that sets at least four or more measurement points in one turn of the rotational body;

a deflection amount detection part that derives radial displacement amounts of the rotational body for the at least four or more measurement points along an outer surface in a circumferential direction of the rotational body based on measured values measured by a displacement gauge;

a storage part that stores the radial displacement amounts derived by the deflection amount detection part and measured angles at the measurement points; and

a calculation part that calculates misalignment data of a most probable circle of the rotational body based on data stored in the storage part,

wherein the calculation part

selects three arbitrary points among all the measurement points stored in the storage part to calculate a circle from the radial displacement amounts and the measured angles,

calculates circle values for all the measurement points from the calculated circle,

calculates differences between the calculated circle values and the radial displacement amounts as error amounts at the measurement points,

sums the error amounts to derive a total error amount,

repeats circle calculation for different combinations of three measurement points among all the measurement points and calculates a total error amount for each calculated circle,

selects a calculated circle with a minimum total error amount among obtained total error amounts for all combinations as the most probable circle, and

calculates deviation between the center of the most probable circle and the center of rotation of the rotational body as misalignment data of the most probable circle.

7. The system for calculating misalignment of a rotational body according to claim 6, wherein the calculation part includes an abnormal value determination part that recognizes, as an abnormal value, a measured value at a measurement point corresponding to a most probable circle error amount that is a difference between the calculated circle value and the radial displacement amount on the most probable circle when the most probable circle error amount exceeds a reference value.

8. The system for calculating misalignment of a rotational body according to claim 7, wherein the calculation part includes a measured value updating part that calls up a remeasured value obtained by the deflection amount detection part from the storage part and replaces the measured value with the remeasured value when the most probable circle error amount exceeds the reference value.