Clutches are used to transmit torque in machines with rotating shafts. It may then be necessary for the machine that the subshafts connected by the clutch are coupled to one another in their zero position without being twisted in relation to one another or that the angle of twist through which the two subshafts are twisted is known.
In the case of releasable clutches the angle of twist must be redetermined after each new coupling. Such releasable clutches are used for example in gas and steam turbine power plants (GUD), in which the gas turbine is connected to the steam turbine by way of a shaft. The releasable clutch is disposed here between the gas and steam turbines. The determination of the angle of twist between the subshafts is of particular importance for the overall process of the power plant installation.
Until now the following procedure has generally been followed to measure an angle of twist for rotating shafts: Two shafts are connected to one another at any angle by way of a releasable clutch. The 0° positions of both shafts are defined by means of a zero mark, e.g. a notch. The two notches are twisted in relation to one another and span the required clutch angle.
The notches are measured computationally by means of optical or inductive sensors, it being possible to capture a temporally resolved signal by this means. A signal profile is obtained for each of the two subshafts. The clutch angle can now be calculated for a known rotation speed from the time difference between the signals of the two shafts.
The accuracy of the measured signal is imprecise due to the narrow signal width of the usual notches in the shaft and due to interference signals that are also present in some instances. Errors of +/−30° in total can in fact occur.
For the automated calculation of the clutch angle, the angle of the respectively first orders from an order analysis is to be determined from the difference. In practice a commercially available 2-channel FFT or order analyzer is used for this purpose, calculating the respective 1× phase values from the time signals and the respective 0° notches, the difference between which is used to calculate the clutch angle.
One disadvantage of the known methods for determining an angle between a first shaft section and a second shaft section is in particular the high level of inaccuracy of the calculation result. Signal interference, caused by network fluctuations for example, also produces inadequate results.