Geometrical instruments – Gauge – Coordinate movable probe or machine
Reexamination Certificate
2001-01-16
2003-04-15
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Gauge
Coordinate movable probe or machine
C033S502000, C073S001790
Reexamination Certificate
active
06546640
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a traverse linearity compensation method and a rotational accuracy compensation method of a measuring device. More specifically, it relates to a traverse linearity compensation method of a measuring device having a linear movement mechanism, such as a roundness-measuring device and a roughness-measuring device, for compensating traverse linearity of the linear movement mechanism. It also relates to a rotational accuracy compensation method of a measuring device having a rotary mechanism such as a roundness-measuring device for compensating a rotational accuracy of the rotation mechanism.
2. Description of Related Art
When a workpiece is measured by a measuring device having a linear movement mechanism as a guide (reference) such as a roundness-measuring device and a roughness-measuring device, the resulted measurement data is a composition of a profile data of the workpiece and a mechanical accuracy of the linear movement mechanism (traverse linearity).
Similarly, when a workpiece is measured by a measuring device having a rotary mechanism as a guide (reference) such as a roundness-measuring device, the resulted measurement data is a composition of a profile data of the workpiece and the mechanical accuracy of the rotary mechanism (rotational accuracy).
In order to obtain a correct workpiece profile against the mechanical accuracy of the linear movement mechanism and the rotary mechanism, the traverse linearity of the linear movement mechanism or the rotational accuracy of the rotary mechanism has to be separated and removed from the measurement data.
Conventionally, a “straightness measurable roundness-measuring device”, Japanese Patent No. 2935603, has been proposed for separating and removing the traverse linearity of the linear movement mechanism from the measurement data.
The device has a rotary table for mounting a traverse linearity check gauge, a sensor for detecting a surface position of a side of the traverse linearity check gauge, a column for movably holding the sensor along the surface of the traverse linearity check gauge, a first storing means for storing data obtained by the sensor as a first data, a second storing means for storing data as a second data obtained by rotating the traverse linearity check gauge around a rotational axis of the rotary table by 180 degrees and by sensing the surface position of the same side of the traverse linearity check gauge, and a processor for calculating a linearity error compensation amount of the column based on the first data and the second data.
Since the above-described “straightness measurable roundness-measuring device”, Japanese Patent No. 2935603 employs so-called reversal method, which requires an initial measurement (the first measurement) and the second measurement conducted after rotating the rotary table by 180 degrees, and where the measurement locus has to be identical on the target workpiece surface, following problems accompanied.
It is extremely difficult to correctly set the workpiece during measurement and the setting requires skill. In addition, considerable number of steps, such as reversing the location of the sensor in conducting the two measurements is necessary therefor. Further, the guide of the sensor is not always in the regular condition (for instance, in the roundness measuring device, projection amount of an arm holding the sensor is not always the same), so that error is likely to be caused.
On the other hand, the following method is known for separating and removing the rotational accuracy of the rotary mechanism.
[Method 1] A spherical master workpiece having smooth surface, for instance, semispherical master workpiece (reference hemisphere) is measured and resulted measurement data is separated and removed from the workpiece measurement data as the rotational accuracy.
[Method 2] Phase difference method (multi step method), where measurement is conducted while shifting phase of a reference hemisphere by a predetermined pitch relative to a rotary table.
However, following problems occur in the above-described [method 1] and [method 2].
Since the reference hemisphere has its inherent profile error, reliability of [method 1] is not so high.
In [method 2], the reference hemisphere has to be measured while being shifted by a predetermined pitch relative to the rotary table. In order to shift the phase accurately, specially designed jig and skilled technique are required and a larger number of steps are required as the divisional number of the shift amount is increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a traverse linearity compensation method capable of overcoming the above-described disadvantage of the reversal method and obtaining highly reliable measurement data without modifying existing devices.
A traverse linearity compensation method of a measuring device according to the present invention employs following arrangement for achieving the above object.
The present invention is a traverse linearity compensation method of a measuring device having a linear movement mechanism, the method including: a traverse linearity data calculating step for measuring a master workpiece of which profile data is value-specified in advance while moving a sensor by the linear movement mechanism of the measuring device and for subtracting the value-specified profile data from the master workpiece measurement data to obtain a traverse linearity data of the linear movement mechanism; a workpiece measurement data calculating step for measuring a workpiece while moving the sensor by the linear movement mechanism of the measuring device to obtain a measurement data of the workpiece; and a workpiece profile calculating step for subtracting the traverse linearity data from the workpiece measurement data to obtain a true value data of the workpiece.
According to the above arrangement, the master workpiece of which profile data is value-specified in advance is measured while moving the sensor by the linear movement mechanism of the measuring device the traverse linearity data of the linear movement mechanism is obtained by subtracting the previously measured profile data from the master workpiece measurement data during the traverse linearity data calculating step. Subsequently, during the workpiece profile calculating step, the workpiece is measured while moving the sensor by the linear movement mechanism of the measuring device to obtain the workpiece measurement data. During the workpiece profile calculating step, the true value data of the workpiece is obtained by subtracting the traverse linearity data from the workpiece measurement data.
Accordingly, since only one measurement is necessary during the traverse linearity data calculating step, the disadvantage of the reversal method can be solved. Further, since the sensor guide is not required to be the same, more accurate compensation result can be obtained. Further, since the compensation is conducted by processing the workpiece measurement data, highly reliable measurement data can be obtained without special arrangement for the measuring device. Further, since the calculation of the traverse linearity data and the compensation of the traverse linearity data to the workpiece measurement data can be conducted by an application program independent of the measuring device, the data can be more accurately compensated by conducting processing such as averaging processing of the master workpiece measurement data (processing for obtaining average value of a plurality of master workpiece measurement data obtained by repeatedly measuring the same position under the same condition) for reducing electric noise and dispersion of the measurement data according to measurement environment.
In a traverse linearity compensation method of a measuring device having a linear movement mechanism according to the present invention, the method may include: a traverse linearity data calculating step f
Kojima Tsukasa
Okada Eiji
Omori Yoshiyuki
Tsuruta Atsushi
Fulton Christopher W.
Mitutoyo Corporation
Oliff & Berridg,e PLC
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