Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-03-04
2001-10-09
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S192000, C700S057000
Reexamination Certificate
active
06301520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spindle end positional deviation correction system for machine tools, and particularly, it relates to a spindle end positional deviation correction System for compensating a deviation in axial position (Z-axis position) of a tool at a spindle, due such as to a thermal deformation of the spindle, in a machine tool of a numerical control type.
2. Description of Relevant Art
The machine tool generally has its spindle thermally deformed due to heat generation such as at bearings of the spindle as well as a spindle motor, during a long processing operation. In the numerical control machine tool, such a thermal deformation causes a coordinate position relationship between a spindle and a work table to be deviated in a Z-axis direction, resulting in a reduced processing accuracy. The coordinate position relationship between spindle and work table is caused to deviate in Z-axis direction, also by deflections of the spindle and bearings supporting the spindle, due to reaction forces of cutting actions, as well as by a contraction of the spindle due to a centrifugal force of the spindle in rotation, resulting in a reduced processing accuracy.
There have been made attempts over many years to compensate for the reduced processing accuracy in Z-axis direction due to a deformed spindle. In an attempt, body temperatures (such as at a spindle holding ram) of a machine tool were measured by temperature sensors and processed to estimate a quantity of thermal deformation in an axial direction of a spindle, and a (Z-axis) command for a position in the axial direction of the spindle was corrected in dependence on the estimation, to thereby compensate for the thermal deformation quantity in a canceling manner.
As another conventional art relevant to the present invention, there has been disclosed in Japanese Utility Model Application Laid-Open Publication No. (Hei)1-92347 a thermal positional deviation correction device, in which a thermal positional deviation in a radial direction of a spindle was measured by a non-contact type gap sensor provided at a housing end, and a (X-axis) position in the radiation direction of the spindle was corrected in dependence on a measured value of the gap sensor.
In general, the quantity of thermal deformation in an axial direction of a spindle is estimable from machine body temperatures. However, such an estimated quantity does not always represent the quantity of an actual deformation. Therefore, the positional deviation correction in axial direction of spindle may unsuccessfully depend on body temperatures, failing to achieve a spindle end positional deviation correction with a high accuracy.
Further, due to relatively large heat-mass dependent time constants such as of a spindle and a ram, it is difficult to perform the spindle end positional deviation correction with high accuracy, sometimes on a real time basis, and it actually is impossible to do so with a required precision.
The positional correction in axial direction of a spindle, so far as it depends on a machine body temperature, is thus applicable simply to a correction of a positional deviation due to a thermal deformation, and unable to correct positional deviations in axial direction of the spindle due to other causes.
In this respect, the thermal positional deviation correction device disclosed in the Japanese Utility Model Application'Laid-Open Publication No. (Hei)1-92347 is for correction of a radial (X-axis) position of a spindle, but not for that of an axial (Z-axis) position off spindle.
SUMMARY OF THE INVENTION
The present invention has been achieved with such points in view.
It therefore is an object of the present invention to provide a spindle end positional deviation correction system for machine tools, permitting a correction with an improved precision, on a real time basis as necessary, with respect to a positional deviation in an axial direction of a spindle due to a thermal deformation of the spindle and other factors.
To achieve the object, a first aspect of the invention provides a spindle end positional deviation correction system for machine tools including a spindle and a spindle holding member for holding the spindle to be rotatable relative thereto, the system comprising: a flange element provided on the spindle in a vicinity of an end of the spindle; a deviation detector, secured to the spindle holding member in opposite to a surface of the flange element in an axial direction of the spindle, for detecting in a non-contact manner a deviation of a gap in the axial direction between the deviation detector and the surface of the flange element; calculation means for calculating a correction value of an axial position of the spindle in accordance with the deviation of the gap detected by the deviation detector; and correction means for correcting a command responsible for the axial position of the spindle in accordance with the correction value calculated by the calculation means to compensate for an axial position of the end of the spindle.
According to the first aspect of the invention, in a (current) process in which a spindle rotates relative to a spindle holding member, a non-contact type deviation detector secured to the spindle holding member detects a (local or mean) deviation of an axial gap between therefrom to a (radial or annular) surface of a flange element provided on the spindle in a vicinity of a (front) end of the spindle, as it represents an occasional variation of an axial positional relationship between the end of the spindle that may be contracted or elongated due to a thermal deformation and other dynamic factors and an associated (reference) position of the spindle holding member that is representative of an (inherent or otherwise determined) axial position of (an entirety or an associated portion of) the spindle to be controlled with a command responsible therefor, and a (Z-axis correction value) calculation means calculates a correction value of the axial position of the spindle (not for an inherent control or other determination, but for a compensation described below) in accordance with the deviation of the axial gap detected by the deviation detector. Then, in (a real time manner in) the (current) process or in a (subsequent) process, a correction means corrects the command in accordance with the correction value calculated by the calculation means to compensate for an axial position of the end of the spindle (so that a positional deviation of the end of the spindle relative to a desired distance therefrom to a work piece is canceled e.g. by axially displacing the spindle holding member together with the spindle or by axially displacing the spindle alone).
Accordingly, there is achieved an improved processing precision.
According to a second aspect of the invention, the calculation means comprises first means for calculating a mean value of the respective deviations of the gap detected by the deviation detector within a time interval, and second means for calculating the correction value of the axial position of the spindle in accordance with the mean value calculated by the first means.
According to the second aspect of the invention, the calculation means includes a means for calculating a mean value of the deviations of the axial gap each respectively detected by the deviation detector within a certain interval of time (in which the spindle turns by e.g. one or more revolutions), and calculates the command correction value of the axial position of the spindle.
Accordingly, there is achieved an effective correction value essentially free from an occasionl detection of a false deviation.
According to a third aspect of the invention, the spindle is supported by a set of beatings at a pair of support portions thereof spaced from each other in the axial direction, and the flange element comprises a flange integrally formed on the spindle, between the end of the spindle and one of the support portions of the spindle nearer thereto.
According to the third aspect
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Grant William
Hartman Jr. Ronald D
Toshiba Kikai Kabushiki Kaisha
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