Method and device for detecting errors in the signals of a...

Data processing: measuring – calibrating – or testing – Measurement system – Speed

Reexamination Certificate

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Reexamination Certificate

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06591217

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method and a device for safely monitoring the rotary motion of a shaft. The device comprises measuring means for recording a first and a second signal, wherein the first signal represents the motion characteristic of an angular position of a first reference point of said shaft and the second signal represents the motion characteristic of an angular position of a second reference point of said shaft, wherein said first and said second reference points are spaced apart one from the other by a rotary angle of said shaft, and wherein said device further comprises an evaluator which receives said first and said second signals.
An example of a rotary motion sensor that supplies such before-mentioned signals is, for instance, a resolver. Resolvers are well known in the art for recording rotary motions. They comprise a rotary transformer, the rotor of which is connected to the shaft which is to be monitored, and the stator of which comprises two separate windings arranged on the outer circumference of the shaft with an angular displacement of 90° one relative to the other. Being coupled in transformer fashion, the two stator windings are fed with a signal that is supplied via the rotor winding. The signals present at the output of the stator windings then represent the before-mentioned first and second signals. The function of a resolver will be described hereafter in more detail with reference to
FIGS. 2 and 3
.
For evaluation of resolver signals, complete circuits are known and available as integrated circuits (IC), as for example the integrated circuit No. AD2S80A available from Analog Devices. That IC is a so-called resolver/digital converter which calculates the rotary angle of the shaft from the resolver signals and presents the result as a digital numeric word at its outputs. In addition, a signal proportional to the rotary speed of the shaft is presented at an other output. Thereby, the known module generally allows to monitor the rotary speed of a shaft. However, this monitoring is not safe, since, for instance, a short circuit between two windings occurring in one of the stator windings cannot be detected reliably. Likewise, internal functional errors occurring in the integrated circuits cannot be safely detected, either. It is therefore possible, for example, that the integrated circuit fails due to some errors, thereby supplying a signal that indicates the shaft to be monitored at a standstill, although the shaft actually rotates at high speed.
Failsafe monitoring of rotary motions of shafts is necessary, for example, when the rotating shaft presents a risk for machine personnel or other machine elements. This is especially the case in situations where an operator has to work within the danger zone of a rotating shaft during set-up operations. The evaluation circuits for resolver signals known heretofore are not suited for safely monitoring the rotary motion of a shaft.
In order to ensure safe monitoring in such a case, it is known to arrange at least one additional rotation sensor at the shaft, in addition to the resolver. Usually, even two separate rotation sensors, for example incremental pickups, are employed today. In general, these additional rotation sensors merely serve to ensure safe monitoring of the rotary motion of the shaft. In addition, a resolver is frequently used as a third sensor for adjusting the rotary motion of the shaft during normal operation. An example of such a known arrangement will be explained hereafter with reference to FIG.
1
. As an evaluation device for safely monitoring of zero-speed conditions, or for safely monitoring a controlled low rotary speed of the shaft, a standstill monitoring relay called PDZ available from Pilz GmbH & Co., Ostfildern, Germany, may be used, for example; this monitoring relay is described in the company's Operating Instructions No. 19 161.
Another example of a device for safely monitoring a speed is described in DE-A-38 19 994. Said known device uses two separate inductive proximity pickups as sensors.
Using a plurality of additional sensors for safely monitoring the rotary motion of a shaft is expensive and negatively affects the costs of an installation to be monitored.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a device and a method of the before-mentioned kind which allow the rotary motion of the shaft to be safely monitored, even with only a single rotation sensor, especially a singly resolver.
It is another object of the invention to provide an arrangement having a rotating shaft, the rotation of which is controlled by a drive control, and a safety device for monitoring the rotation of the shaft, wherein said safety device is capable of safely stopping the rotational movement of the shaft, when an error is detected.
According to one embodiment, these and other objects are achieved by a device of the before-mentioned kind, wherein the evaluator comprises a comparator which is capable of comparing instantaneous values of the first and the second signals using a predefined geometric relation.
According to another embodiment, these objects are further achieved by a method of the before-mentioned kind, wherein instantaneous values of the first and the second signals are compared using a predetermined geometric relation.
According to the invention, instantaneous values of the first and the second signals are compared one with the other. Due to the fact that the signals are recorded at different reference points of the same shaft, there is a predetermined relation between such signals. As long as the operation of the monitoring device is free from errors, a comparison taking said relationship into account must always lead to a predictable result. Whenever a comparison between the two signals yields a different result than would be expected, an error has occurred in the monitoring device.
In this connection, the term “geometric relation” is understood as generally describing the predetermined relation between the instantaneous values of the two signals, which can be determined based on the geometric position of the reference points one relative to the other. This relationship may be graphically illustrated as a locus curve in a plane whose coordinates are defined by the instantaneous values of the two signals. If the actual shape of the locus curve derived from the recorded instantaneous values deviates from the expected shape of the locus curve, an error has occurred in the monitoring device.
It should be noted that, in principle, the method according to the invention can be employed for safe monitoring also when a plurality of separate sensors are used for recording the first and second signals. However, this is not required, since the method can be used with a single resolver for recording the rotary motion, because the described first and second signals are supplied by the resolver as such. Any possible error, as for example a short circuit between windings in one of the stator windings of the resolver, or failure of a component of the evaluator that will be described in more details in the following, any such possible error leads to a different result in the comparison between the instantaneous values as that one would have expected due to the predetermined relation between the two signals. Consequently, the method according to the invention can be employed for safely monitoring the rotary motion of a shaft with a single rotation sensor only, namely a resolver. The additional use of further sensors, such as incremental pickups, as usual heretofore, is no longer necessary.
According to a preferred embodiment of the invention, the comparator is capable of comparing concurrent instantaneous values of the first and the second signals.
This feature advantageously simplifies the predetermined relation between the instantaneous values of the first and the second signals so that the comparison between the instantaneous values can be realized more easily. This consequently reduces the effort required for both the developmen

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