JPH04240044A - Correction method for working error and machine tool - Google Patents

Abstract

PURPOSE:To correct the straightness error of an X, Z axial each table at real time, by measuring the straightness error of one part of the table to the rectilinear direction of the other part of the table, and superposing by the straightness error quantity on the positional command of the other part of the table. CONSTITUTION:A 1st straightness error detector 27 which measures the displacement in a Z axial direction of an X axial table 23 and a 2nd straightness error detector 29 which measures the displacement in the X axial direction of a Z axial table 24 are provided. Then, the respective straightness error signal obtained during the work is transmitted to an NC device, and the straightness errors of the X, Z axial both tables 23, 24 under working are corrected at real time, with their being superposed on the NC command of the other part of the table via an interface.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool that can control two axes simultaneously and a method for correcting machining errors therefor.

0002

2. Description of the Related Art An ultra-precision lathe is one of the multi-axis simultaneous control machine tools that requires high machining accuracy.

FIG. 1 shows an embodiment of an ultra-precision lathe. X, Z
Each axis table is arranged perpendicularly on a stone surface plate (16). The X-axis table (13) is equipped with a tool post (12) and moves straight in the direction of the spindle's rotation radius, and the Z-axis table (14) is equipped with a spindle (10) that rotates the workpiece (15) and moves straight in the direction of the spindle's rotation axis. Go straight to. The position of each table is simultaneously controlled on two axes by the NC device (20) according to NC data, and it is possible to turn the workpiece (15) into a spherical or aspherical rotating shape.

FIG. 5 shows an example in which a laser interference position feedback system is used to control the positioning of the table of this ultra-precision lathe. The laser beam emitted from the laser oscillator (57) installed on the stone surface plate (56) is sent to the beam splitter (58).
), the beam is split into two orthogonal laser beams, which enter a laser interferometer (59), are bent in the straight direction of each table, and enter a reflecting mirror (60) on each table. The laser light travels back and forth between the reflecting mirror (60) and the laser interferometer (59) and enters the laser interferometer (59) again to form interference light. The interference light enters a receiver (61), and the position of each table is detected by a built-in photoelectric element. Each table is positioned by feeding back the obtained position signal to the position control section of each table.

[0005] Straightness is required for the linear movement of both the X- and Z-axis tables in such an ultra-precision lathe. However, in reality, there is a straightness error due to the method of the table guide surface, the machining accuracy of the table, and disturbances to the workpiece and table. For example, as shown in Figures 4 and 6, when the position of the cutting edge is controlled to point P, the X-axis table has a straightness error of ΔZ in the Z-axis direction, and the Z-axis table has a straightness error of ΔX in the X-axis direction due to the above reasons. If it occurs, it actually starts from point P.

The cutting edge is positioned at point Q, which is separated by . If such straightness errors are left unaddressed, the ideal shape (NC command) shown by the dotted line in FIG. 7 will be machined into a shape having an error as shown by the solid line. In other words, if the positioning accuracy of each table is simply improved using a laser interference position feedback system or the like, positioning errors due to table straightness errors will remain.
High-precision machining cannot be performed.

[0007]

[Problems to be Solved by the Invention] The present invention provides a machining error correction method and method that enables machining of an ideal shape by correcting straightness errors during machining of each X-axis and Z-axis table in real time. The purpose is to provide machine tools that

[0008]

[Means for Solving the Problems] The present invention eliminates the straightness error by superimposing the straightness error in the direction of the other axis on each table of the X and Z axes by the amount of the error on the NC command of the opposing table. This is a processing error correction method that attempts to compensate and achieve the above objective.

The present invention also provides a first straightness error detector that measures the displacement of the X-axis table in the Z-axis direction, and a second straightness error detector that measures the displacement of the Z-axis table in the X-axis direction. This machine tool attempts to achieve the above object by transmitting each straightness error signal obtained during machining to an NC device and superimposing it on the NC command of the other table via an interface.

0010

[Function] By adopting this machining error correction method, the straightness errors of both the X and Z axis tables during machining can be corrected in real time, and therefore the machine tool can process the ideal shape in response to NC commands. Become.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment in which a straightness error detector is installed in the ultra-precision lathe shown in FIG. A target (26) having a length longer than the stroke of the X-axis table (23) is fixed to the tool rest (22) of the X-axis table (23) so that its longitudinal direction is orthogonal to the Z-axis. The straightness error ΔZ during the linear movement of the X-axis table (23) is measured by a straightness error detector (27) installed on a stone surface plate facing the target (26).
is detected as a displacement from the X axis. Similarly, a target (28) with a length longer than the stroke of the Z-axis table (24) is fixed to the Z-axis table (24) so that its longitudinal direction is perpendicular to the X-axis.
The straightness error ΔX is detected by a straightness error detector (29) installed opposite the target (28). For example, if a laser interferometric measurement system is used as the straightness error detector (27, 29), and a reflecting mirror is fixed on each table parallel to the axis as a target (26, 28), high-precision straightness error measurement can be performed. It is possible. These straightness error detectors (27
, 29) has a function of outputting the measured values ΔX and ΔZ in real time during processing.

FIG. 3 is a block diagram of the error correction system of this embodiment. Inside the broken line is the configuration of a general NC device,
This controls the two axes simultaneously by distributing commands from the position command unit (31) to the X and Z axis table position control units, and receives position signals from the position detector (36) that measures the position of each table. is fed back to the position control section (33, 34) of each axis for position control. In contrast, this embodiment further includes a straightness error detector for each table and an interface (38) for transmitting the obtained straightness error signal to the NC device (30). Now, when a machining program is given from a paper tape or internal memory, the NC device (30
) transmits corresponding position commands to the X-axis and Z-axis position control units (33, 34) to drive the drive motors (35) of each table. Here, the position detection signal of each table obtained by the position detector (36) is fed back to each position control section (33, 34) to continuously control the position. At this time, the Z-axis direction straightness error ΔZ of the X-axis table measured by the straightness error detector (37) facing the target on the tool rest, and the straightness error detector (37) facing the target on the Z-axis table The X-axis direction straightness error ΔX of the Z-axis table measured by (37) is transmitted to the interface (38). From the interface (38), -Δ is given to the position command to the X-axis table.
A correction signal of -ΔZ is transmitted in response to position commands to the X and Z axis tables. Therefore, a command value in which the correction signal and the position command are superimposed is input to the position control section of each table.

FIG. 4 is a diagram showing the locus of the cutting edge according to this embodiment. The position command section transmits a command for the ideal plane shown by the broken line to the position control section. Since each of the X- and Z-axis tables has a straightness error as described above, if only the position control of each table is performed, the cutting edge will draw a trajectory having an error as shown by the solid line. Therefore, in the present invention, the position of the blade edge is compensated for the ideal plane by superimposing the straightness errors (-ΔX, -ΔZ) on the position commands (X, Z) of each table. As a result, ultra-precision turning becomes possible.

Although this embodiment relates to a machining error correction method for an ultra-precision lathe with simultaneous two-axis control, the same effect can be achieved with any machine tool that simultaneously controls orthogonal two-axis tables (column heads). can get.

[0016]Also, a laser interference position feedback system was used as a detector for positioning errors of the table; however,
Any measuring device capable of highly accurate measurement can be applied regardless of whether it is a contact type or a non-contact type. For example, a capacitance type, a differential transformer type, or an eddy current type displacement meter may be used.

[0017]

[Effects of the Invention] As detailed above, according to the present invention, X
, it is possible to provide a machining error correction method capable of correcting straightness errors of each Z-axis table in real time, and a machine tool capable of high shape precision machining.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram (perspective view) of an ultra-precision lathe.

FIG. 2 is a diagram showing a machining error detection system according to an embodiment of the present invention.

FIG. 3 is a block diagram of an error correction system according to an embodiment of the present invention.

FIG. 4 is a diagram showing the X and Z components of a machining error vector and their composite vector.

FIG. 5 is a schematic diagram (top view) of a laser interference position feedback system installed on an ultra-precision lathe.

FIG. 6 is a diagram showing the occurrence of straightness errors in the X and Z axis tables.

FIG. 7 is a diagram showing a machining error of a workpiece caused by a straightness error.

[Explanation of symbols]

10...Main shaft spindle, 11...Cutter, 12...Turret, 1
3...X-axis table, 14...Z-axis table, 15...workpiece, 16...stone surface plate, 17...NC device, 18...vibration isolation table, 20
...Main shaft spindle, 21...Cutter, 23...X-axis table,
24... Z-axis table, 25... Workpiece, 26... Target, 27... Straightness error detector, 28... Target, 29...
Straightness error detector, 30... NC device, 31... Position command section, 32... Pulse distribution section, 33... X-axis position control section, 34...
Z-axis position control unit, 35...Table drive motor, 36...Position detector, 37...Straightness error detector, 38...Interface, 50...Main shaft spindle, 51...Cutter, 53...X
Axis table, 54... Z-axis table, 55... Workpiece, 56
... Stone surface plate, 57 ... Laser oscillator, 58 ... Beam splitter, 59 ... Laser interferometer, 60 ... Reflector, 61 ... Receiver.

Claims (2)

[Claims] Claim 1: In a machining error correction method for a machine tool that simultaneously controls orthogonal two-axis tables, the straightness error of one table with respect to the linear direction of the other table is measured, and the straightness error of the other table is adjusted by the amount of the straightness error. A machining error correction method characterized by compensating by superimposing it on a position command. 2. A Z-axis table on which a spindle for rotating a workpiece is mounted, which moves straight in the direction of rotation of the spindle; and an X-axis table, which is installed orthogonally to the Z-axis table, fixes a cutter, and moves straight in the direction of the rotation radius of the spindle. In a machine tool that can turn into a rotating shape by simultaneous NC control,
a first straightness error detector that detects a straightness error of the X-axis table in the Z-axis direction; a second straightness error detector that detects a straightness error of the Z-axis table in the X-axis direction; The straightness error signal detected by the detector is N
A machine tool comprising: an interface for transmitting a signal to a C device; and means for superimposing a straightness error signal from the interface on a position command for each table.