Measuring and testing – Rotor unbalance – Dynamic
Reexamination Certificate
2003-05-16
2004-09-07
Williams, Hezron (Department: 2856)
Measuring and testing
Rotor unbalance
Dynamic
C073S001140, C700S279000
Reexamination Certificate
active
06786093
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to balancing apparatus that measures dynamic imbalance of a rotating body by detecting vibration transmitted to the balancing apparatus from the rotating body.
Vibration due to imbalance in a rotating body has been a serious problem in many industrial fields. In order to prevent such vibration, it is required to dynamically balance the rotating body.
Some types of rotating body, however, are required to have a certain dynamic imbalance so as to allow a system to which the rotating body belongs being dynamically balanced as a whole. For example, a crank shaft, to which pistons or the like are to be coupled, should have dynamic imbalance that cancels the dynamic imbalance generated by the pistons or the like so that serious vibration does not occur in an engine.
The dynamic imbalance of a rotating body is generally measured with balancing apparatus. The rotating body is dynamically balanced by adding or removing mass thereto so as to cancel the measured imbalance.
If the rotating body is required to have a certain imbalance, mass is added to the rotating body, which mass balances with the desired dynamic imbalance, so that only the deviation of the dynamic imbalance from the desired dynamic imbalance will be measured by the balancing apparatus. For example, if the crank shaft is to be measured, a dummy ring having the same mass as the piston is mounted to each crank pin during the measurement.
The above-mentioned method for measuring dynamic imbalance of a crank shaft, however, requires manually mounting and removing dummy rings whenever a new crank shaft is to be measured, which makes automation of the measuring process difficult, and also increases the time required for the measurement.
Therefore, there is a need for balancing apparatus that is capable of measuring deviation of the dynamic imbalance of a crank shaft from the desired dynamic imbalance thereof without requiring mounting dummy rings to the crank shaft.
Balancing apparatus measures the dynamic imbalance of a rotating body by detecting the vibration transmitted to such balancing apparatus from the rotating body with a vibration pick-up. However, the sensitivity of the vibration pick-up, and also the vibration characteristic of the balancing apparatus, may change over time and in accordance with ambient temperature variation. Accordingly, calibration of the balancing apparatus should be carried out regularly to ensure correct measurement.
Conventionally, calibration of such balancing apparatus is performed by providing to the balancing apparatus a standard rotating body having no dynamic imbalance, attaching a weight of known mass onto the standard body, rotating the standard body to measure the dynamic imbalance thereof, and comparing the measurement result with the dynamic imbalance calculated from the mass and position of the weight attached to the standard body.
However, it is difficult to automate conventional calibration of balancing apparatus, since the calibration process requires manually attaching the weight onto the standard body.
Further, if dynamic imbalance is to be measured for a plurality of balancing planes of the rotating body, the calibration should be carried out for each balancing plane. That is, the calibration should be carried out several times with the weight being attached to the standard body in a different balancing plane each time. In this case, the weight has to be manually attached and removed from the standard body several times which increases the time required for the calibration.
Therefore, there is a need for balancing apparatus that is capable of performing calibration without requiring use of a weight.
In some cases, the vibration characteristic of the balancing apparatus changes significantly, due, for example, to mechanical defects. Since correct measurement of dynamic imbalance cannot be achieved in such cases, there is also a need for balancing apparatus that is capable of automatically detecting such significant changes in vibration characteristic.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide balancing apparatus that is capable of measuring deviation of dynamic imbalance of a rotating body from desired dynamic imbalance thereof without requiring manually mounting a weight to the rotating body.
It is yet another object of the present invention to provide balancing apparatus that is capable of performing calibration thereof without requiring manually mounting a weight to a dynamically balanced rotating body utilized for calibration.
It is yet another object of the present invention to provide balancing apparatus that is capable of automatically detecting abnormal vibration characteristics.
According to an aspect of the present invention, there is provided balancing apparatus for rotating a body to be measured with a rotating mechanism so that the body vibrates due to the dynamic imbalance thereof. The vibration of the body is transmitted to a vibration member and then detected by a sensor. A vibrator is coupled to the vibration member. In one embodiment of the present invention, the vibrator is for canceling a predetermined vibration of the vibration member. For example, the vibrator applies to the vibration member a vibration, which is an inverse of an ideal vibration that will be generated in the vibration member by an ideal body having an ideal dynamic imbalance. In this way, the ideal vibration in the vibration member can be canceled, and by detecting the vibration remaining in the vibration member, the balancing apparatus can determine the deviation of the dynamic imbalance of the body being tested from the ideal dynamic imbalance.
A memory device may be provided to the balancing apparatus for holding data representing vibration, which will be generated in the vibration member by the ideal body, so that the vibrator can easily obtain data necessary for vibrating the vibration member as described above. It should be noted, the data can be prepared and stored into the memory device by mounting the ideal body to the rotating mechanism, rotating the ideal body to cause vibration to the vibration member, and then detecting the vibration of the vibration member by the sensor.
Optionally or additionally, the balancing apparatus may have a processor for carrying out calculation for determining dynamic imbalance of the body from the output of the sensor. The processor also performs modification of a coefficient utilized in the above-mentioned calculation. As is well known to those skilled in the art, the modification of such a coefficient can be achieved by generating vibration in the vibration member with a rotating body having known dynamic imbalance, and determining the magnitude of the output of the sensor detecting the vibration of the vibration member. In the balancing apparatus of the present invention, however, the modification of the coefficient is carried out by utilizing a dynamically balanced reference body, instead of a body having known dynamic imbalance. A reference vibration is further applied to the vibration member by the vibrator. The reference vibration is substantially identical to a vibration that will be caused to the vibration member by rotating the reference body carrying a predetermined weight at a predetermined location. The data for generating such reference vibration may be held in a memory device of the balancing apparatus.
In the balancing apparatus arranged as described above, the modification of the coefficient, or calibration of the balancing apparatus, can be performed without actually attaching the weight to the reference body, which allows not only shortening of time required for the calibration but also automation of the calibration.
Optionally or additionally, the balancing apparatus may have a controller for determining whether the balancing apparatus has a defect that seriously reduces the vibration transmitted from the body to the sensor. The controller determines whether such a defect exists based on vibration detected by the sensor while
Hanley John
Kokusai Keisokuki Kabushiki Kaisha
Pitney Hardin LLP
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