Measuring and testing – Rotor unbalance – Dynamic
Reexamination Certificate
2001-03-07
2003-10-14
Williams, Herzon (Department: 2856)
Measuring and testing
Rotor unbalance
Dynamic
C073S457000, C073S460000
Reexamination Certificate
active
06631640
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for measuring a dynamic balance of a tested member, capable of measuring the imbalance to be removed of a tested member which should have a predetermined dynamic imbalance remaining therein.
That is, in case a dynamic balance of a crank shaft for an engine of an automobile, for example, is to be measured, it must be taken into account that, when a crank shaft is rotated with being built in an automobile, several additional members such as a piston, a connecting rod and so on are mounted thereto.
In other words, it is meaningless to measure a dynamic imbalance of a tested crank shaft itself. It should rather be measured whether there is the imbalance to be removed of a tested crank shaft for allowing the crank shaft to be rotated without vibrating when the related members are mounted thereto.
In order to measure such an imbalance of a tested member as described above, there have been employed the following three methods.
In a first method, a plurality of dummy rings corresponding to the imbalance to remain are attached to respective portions of the crank shaft, when rotated to determine correction amounts and angle positions therefor.
In a second method, a crank shaft is connected on a vibration stand to a spindle which carries a dummy weight equivalent to the predetermined imbalance to remain, when rotated to determine correction amounts and angle positions therefor.
In a third method, a crank shaft itself is rotated without attaching any dummy ring or dummy weight, and the imbalance of the rotating crank shaft is detected by a vibration sensor as an analogue signal which is then converted to digital signal by an A/D converter (Analogue-Digital converter). Thereafter, a numerical calculation is conducted based on the detected digital value and a digital dummy value obtained in advance and corresponding to the imbalance to remain, i.e., the latter is subtracted from the former, thereby finding an initial imbalance and deciding correction amounts and angle positions therefor.
It should be noted here that the balance adjustment of the crank shaft after the above described measurement based on the above described correction amounts and angular positions is performed by making a drill hole at the optimum position with the optimum depth on the counter weight of the crank shaft.
However, the above described first method requires attaching and detaching of dummy rings for each crank shaft to be measured. Further, when crank shafts of various types are to be measured by the same measuring apparatus, different dummy rings for different types have to be respectively prepared and replaced each time. Moreover, for these reasons, it is difficult to automate the measurements with this method.
Although the second method does not require attaching or detaching of dummy rings for respective crank shafts, it requires replacing dummy weights when different type crank shafts are to be measured by the same measuring machine.
The third method requires neither attaching nor replacing of dummy rings or dummy weights so that it is suitable for automation of the measurements, but is hard to attain measurements with high accuracy because of the following reasons.
That is, the imbalance data obtained by a vibration sensor is the sum of the imbalance to remain and that to be removed as described above. Although the imbalance to remain is different depending on the type of a crank shaft, some reaches a level of several thousand gcm. In contrast, the imbalance to be removed is rather smaller, i.e., generally of a level of several hundred gcm.
Accordingly, the maximum size of the imbalance data obtained by the vibration sensor comes to several thousand and several hundred gem.
On the other hand, the voltage which can be inputted to the A/D converter is usually limited to below ±5V, and the full scale of the input range of the A/D converter should be made to correspond to the possible maximum value of the imbalance data measured by the above sensor.
By doing so, however, the imbalance measurable per one digit by the A/D converter becomes larger (i.e., the resolution of the A/D converter becomes low) as the above maximum value becomes larger and, hence, the measurement with the resolution higher than the above becomes impossible. That is, the resolution becomes worse due to the presence of the relatively large imbalance to remain, and therefore the measurement with high accuracy for the imbalance to be removed becomes difficult.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for measuring a rotational balance of a tested member which should have a predetermined imbalance remaining therein, capable of accurately detecting the imbalance to be removed, without requiring a dummy ring, a dummy weight or the like.
The measuring method of the present invention is such that the digital dummy value information equivalent to a dummy portion is stored in a memory in advance and a rotation sensor detects the rotational angular position of the body of rotation as a workpiece and, in response to this rotational angular position, digital dummy value information is read out from the memory, accompanied by which these pieces of information are converted to an analogue dummy signal and then the analogue vibration signal obtained by detecting the rotational vibration amount of the body of rotation by a rotational vibration sensor and the analogue dummy signal are synthesized so as to obtain the analogue signal of the initial imbalance portion by removing the dummy portion from the imbalance portion, after which this analogue signal is digital-converted so as to obtain the digital initial imbalance value.
The above described digital dummy information is desirably stored in a memory for each different type of the apparatus and which is, every time the type of the workpiece changes, made to switch over to the dummy value information corresponding to the type changed. In this manner, an automatic measurement becomes possible while the workpieces of different types may follow on the same measuring apparatus. Morever, when the initial analogue imbalance signal is digitalized, it is desirable that the approximate maximum value of the initial analogue signal is made to correspond to the full scale measurable by the A/D converter. Also, the analogue signals are preferably divided into components orthogonal to each vibration direction, which are generated by the cosine waveform and the sine waveform completely synchronized with the body of rotation, respectively.
The rotational balance measuring apparatus of the present invention is provided with a rotational support portion for supporting the body of rotation as a work, which is provided with an electrical motor capable of rotatingly driving this body of rotation. Also, a rotation sensor for detecting the rotational angular position of the body of rotation is provided and a vibration sensor for obtaining an analogue vibration signal by detecting the vibration of the above described body of rotation through the rotational support portions provided. On the other hand, a memory for storing the dummy value information as a digital data of the imbalance to be left over in the body of rotation is provided and a controller for outputting the above described dummy value information based on the rotational angular position signal from the above described rotation sensor is provided. With this outputted digital dummy value information inputted, a D/A converter for converting this information to an analogue dummy signal is installed and a wave synthesizing circuit is installed where the analogue dummy signal obtained here and the analogue vibration signal from the above described rotation sensor are inputted and wave-synthesized so as to obtain an analogue initial imbalance signal by removing the analogue dummy signal portion from the analogue vibration signal. To this wave synthesizing circuit, a A/D converter is connected where the analogue initi
Kokusai Keisokuki Kabushiki Kaisha
Pitney Hardin Kipp & Szuch LLP
Saint-Surin Jacques
Williams Herzon
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