Electrical computers and digital data processing systems: input/ – Input/output data processing
Reexamination Certificate
1998-07-02
2001-09-04
Lee, Thomas (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
36, 36, 36, C408S008000, C318S561000
Reexamination Certificate
active
06286055
ABSTRACT:
BACKGROUND OF THE INVENTIONS
1. Field of the Invention
The present invention relates to an error compensating device for calibrating a movement accuracy of a movable unit of a numerical control machine tool and successively compensating an error during its movement.
2. Description of the Prior Art
For recent numerical control machine tools, high working precision is intended, and many new technologies have been developed and utilized. The new technologies are based on the concept of a machine tool structure having a high rigidity in order to prevent dynamic movement disturbance from occurring even during a high-speed movement and a highly reproducible movement mechanism is employed so as to always exhibit similar behavior during the repetition of the movement. However, even when such a design countermeasure is taken, the movement error cannot be completely eliminated because of the thermal deformation of the machine tool structure or the like. Therefore, after the completion of the machine tool, a calibrating operation called calibration is usually performed as required at certain time intervals to measure machine movement errors, and the measurement results are stored and held in a numerical control device. In actually operating and controlling the machine tool, these errors are reflected in control information to compensate an operating command so that the actual movement may not cause the errors.
In a usual calibration method, special measuring apparatus such as a laser interferometer, a dial gauge or the like is mounted on the machine tool. However, it is difficult to collectively and automatically measure various movement errors such as roll, pitch, yaw or the like of a movement axis, the degree of movement parallelism, movement perpendicularity or the like and right angles among a plurality of movement axes or other movement errors. Therefore, a setting-up operation exclusive for each error measurement is manually performed, and errors are measured and verified taking a relatively long period of time (at least several hours) in the present situation.
Also, in a precise calibrating operation, when utilizing light measurement as a measuring means, in principle a distance is generally measured based on a light wavelength.
In the above calibration method, the machine tool is occupied during every calibrating operation, the method can not be used during normal working operation, and the machine operation rate is decreased. Therefore, the calibrating operation can not be performed frequently. Also, to prevent the measuring accuracy from being varied by external disturbances such as temperature variation or occurrence of vibration in the measuring environment during the measuring operation, a remarkably stable measuring environment needs to be secured.
Also, even the machine tool developed basing on the above-mentioned new design concept inevitably has an error which can not be eliminated so completely as the error caused by the machine thermal deformation. It is known that this error generally takes irregular and complicated behavior as time elapses. It is also known that this behavior variation gradually takes place for a comparatively long period of time from several ten minutes to several hours. Therefore, when the calibrating operation in the conventional method is carried out at time intervals from several ten minutes to several hours, the machine movement error can be effectively compensated. However, this is not actually possible in view of the secured operation rate of the machine tool.
Further, since the accuracy of measurement based on the light wavelength is easily affected by temperature, air turbulence, humidity or the like, there is a problem that the measurement can not be easily utilized in a general factory environment where machine tools are operating.
On the other hand, because a demand for improvement in product quality is getting severe year by year, development of new technology for solving these shortcomings of the conventional calibrating method is desired.
An object of the present invention is to solve the above-mentioned problems, to detect a spatial movement error of a machine tool changing with elapsed time caused by the thermal deformation of the machine tool, abrasion of a movement mechanism or deterioration of assembly accuracy in the normal operation condition including a working operation without being influenced even by the general factory environment, to control the movement of the machine tool while compensating the machine movement error based on the result of detection, and to operate the machine tool with high accuracy.
SUMMARY OF THE INVENTION
The present invention has been developed in order to solve the above-mentioned problems.
The first aspect of the present invention is directed to an error compensating device in a numerical control machine tool which comprises a movable unit position detecting means for detecting a position along a predetermined control axis of a movable unit controlled along the axis, a movement condition detecting means for detecting a movement condition of the movable unit, a movement error calculating means for calculating a machine movement error by the use of the movement condition, and a movement error compensating means for compensating the movement error on the basis of the movement error.
The second aspect of the present invention is directed to the error compensating device which has a first movement condition memory means for previously storing the movement condition to be detected by the movement condition detecting means and wherein the movement error calculating means has a function of calculating the movement error from a difference between the movement condition stored in the first movement condition memory means and the movement condition at the present time.
The third aspect of the present invention is directed to the error compensating device which has a second movement condition memory means for storing, as required, the movement condition detected by the movement condition detecting means and wherein the movement error calculating means has a function of calculating the movement error from a difference between the movement condition stored in the second movement condition memory means and the movement condition at the present time.
The fourth aspect of the present invention is directed to the error compensating device wherein the movement error compensating means has a function of performing continuous compensation of the machine movement error by adding an error compensation quantity to a position command value.
The fifth aspect of the present invention is directed to the error compensating device wherein the movement condition detecting means detects displacement of the movable unit at a specific point in a direction of a movement axis from a movement basis on a coordinate axis different from the movement axis, and the movement error calculating means calculates the movement error on the basis of the detected displacement.
The sixth aspect of the present invention is directed to the error compensating device wherein for the sake of the detection of the movement condition, there are used a reference position beam generator installed to generate a reference position beam in parallel with the direction of the movement axis, and a movable unit two-dimensional detecting element installed on the movable unit for detecting the displacement from the movement basis on the coordinate axis different from the movement axis by the use of the reference position beam from the reference position beam generator.
The seventh aspect of the present invention is directed to the error compensating device wherein the detection of the movement condition includes the detection of torsion of the movable unit on the movement axis based on the displacements from the movement basis which are separately detected at two movable unit two-dimensional detecting elements installed on one movable unit.
The eighth aspect of the present invention is directed to the error compensating device wherein a movement end two-dimensiona
Matsumiya Sadayuki
Morita Naoki
Yamamoto Kyoichi
Yamazaki Kazuo
Lee Thomas
Okuma Corporation
Oliff & Berridg,e PLC
Schuster Katharina
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