JP2018027599A - Method for correcting machining error of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technical means capable of more appropriately correcting a machining error based on thermal deformation of a machine tool, in particular a lathe, without lowering the productivity.SOLUTION: A method for correcting a machining error of a machine tool, comprises: bringing the outer circumference 5 of a work chuck 4 attached to a main spindle into contact with a contact detection sensor 3a or a detection rod 3b attached at the tool attachment position 7 of a tool rest 14, 24; and by detecting a change in the relative positional relationship between the main spindle and the tool attachment position of the tool rest from the coordinates of the tool rest 14, 24 at the time of detecting the contact, determining a correction value with respect to the position of the tool rest 14, 24. The contact of the detection rod 3b with the chuck outer circumference 5 can be detected by detecting the rising of a position deviation, which is a difference signal between the position command given to a tool rest feed motor and a feedback signal by using the detection rod processed with high accuracy instead of using the contact detection sensor 3a.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a means for correcting a machining error of a workpiece due to thermal deformation of a machine tool.

  When a workpiece is machined with a machine tool, the temperature of each part of the machine changes due to the heat generated by the operation of the machine, and the machining accuracy of the workpiece to be machined changes due to the change in the thermal deformation of each part of the machine. Will fall).

  In order to correct the change in machining accuracy due to the temperature change of the machine itself over time, temperature sensors are attached to various parts of the machine, and a correction value is obtained by an arithmetic expression obtained by multiplying the detected temperature of each sensor by a coefficient obtained through experiments. Thus, machining is performed by correcting the moving position of the tool post with this correction value.

For example, n temperature sensors are attached to the lathe body where they are considered appropriate, and processing accuracy data when processing various workpieces and detected temperature data of each temperature sensor detected during processing. make use of,
Δx = a _1x t ₁ + a _2x t ₂ + a _3x t ₃ +... + A _nx t _n
Δy = a _1y t ₁ + a _2y t ₂ + a _3y t ₃ +... + A _ny t _n
Δz = a _1z t ₁ + a _2z t ₂ + a _3z t ₃ +... + A _nz t _n
The correction values Δx, Δy, and Δz in the X, Y, and Z axis directions are calculated using the following formula, and the position of the tool post in the X, Y, and Z axis directions specified by the machining program is calculated from time to time. Processing is performed by correcting with values.

In the above formula, t ₁ , t ₂ , t ₃ ... T _n are detected temperatures of n temperature sensors provided in the machine,
_{a 1x, a 2x, a 3x} ··· a nx, a 1y, a 2y, a 3y ··· a ny and _{a 1z, a 2z, a 3z} ··· a n is the detected temperature of each temperature sensor Is a coefficient in the X, Y, and Z axis directions multiplied by the value obtained by actually machining the workpiece.

JP-A-6-55415

  The types of workpieces processed by machine tools, their processing procedures, environmental temperatures, etc. are diverse and change over time. Therefore, even if processing is performed by calculating a correction value from the temperature of each part of the machine as described above, it is impossible to completely correct a processing error caused by thermal deformation of the machine. On the other hand, improvement in productivity and machining accuracy is a general requirement for machine tools, and further improvement is always required.

  This invention further improves the machining accuracy of a workpiece by providing technical means that can more appropriately correct machining errors based on thermal deformation of a machine tool, particularly a lathe, without reducing productivity. The challenge is to make it happen.

  This invention is capable of more accurately correcting a machining error in the radial direction of a workpiece by measuring a change in the relative positional relationship between the lathe spindle and the tool mounting position of the tool post in a timely manner. . In the present invention, the outer periphery 5 of the work chuck 4 attached to the spindle is brought into contact with the contact detection sensor 3a or the detection rod 3b attached to the tool attachment position 7 of the tool rests 14 and 24, and the tool at the time of contact detection. A change in the relative positional relationship between the spindle and the tool mounting position of the tool rest in the direction perpendicular to the spindle is detected from the coordinates of the stands 14, 24, and the tool rests 14, 24 instructed from the machining program based on the calculation including the detected value. The correction value for the position is obtained.

  As the contact detection sensor 3a, a known sensor generally called a touch sensor can be used. Further, instead of using such a sensor, a position deviation proposed in Patent Document 1 using a detection rod processed with high precision (preferably a round bar that is easy to process with high precision), that is, at the time of tool post feeding. The contact between the detection rod 3b and the chuck outer periphery 5 can be detected by detecting the rise of the position deviation, which is the difference signal between the position command given to the tool post feed motor and the feedback signal returned from the tool post feed motor. . According to the latter means, the present invention can be implemented without using an expensive contact detection sensor.

  In order to avoid detection errors based on errors in the roundness of the outer periphery of the chuck, it is preferable to stop the spindle at a predetermined phase and bring the contact detection sensors 3a to 3b into contact. Also, in order to avoid detection error due to cutting oil or chips adhering to the outer periphery of the chuck, two or more spindle stop phases are set, and the detection value in the first stop phase exceeds the threshold value. It is also possible to perform control by stopping the spindle at the stop phase determined as the next candidate.

  Since the present invention detects and corrects a change in dimension in the direction perpendicular to the spindle between the outer periphery 5 of the work chuck attached to the spindle and the tool mounting position 7 of the tool post, the workpiece is deformed based on the thermal deformation of the machine. It corrects machining errors in the radial direction. Since thermal deformation in the direction perpendicular to the spindle also changes depending on the position of the tool post in the Z-axis direction, the correction value is generally calculated using an arithmetic expression that includes a change in the relative positional relationship between the detected chuck outer periphery and the tool mounting position of the tool post. Should be computed. That is, the correction value is calculated by a calculation formula including a term including a change in the positional relationship between the chuck outer periphery and the tool mounting position of the tool rest in the direction perpendicular to the spindle detected by the method of the present invention as a variable δ in a conventionally known calculation formula. Calculate.

  The workpiece machining error is caused by a change in the relative positional relationship between the spindle center and the tool edge due to thermal deformation of the machine itself. The rise in the temperature of the spindle bearing accompanying the rotation of the spindle during turning is one of the main heat sources that cause thermal deformation of the machine. The headstocks 18 and 28 that support the main shaft are raised on the upper surfaces of the beds 11 and 21, and heat deformation in the rising direction of the main shaft stocks 18 and 28 increases due to heat generation of the main shaft bearings.

  In the structure in which the headstocks 18 and 28 rise in a direction perpendicular to the cutting direction of the tool (X-axis direction of the lathe), the influence of the displacement in the rising direction of the headstocks 18 and 28 on the machining error in the radial direction of the workpiece is small. However, in a lathe having a structure in which the rising directions of the headstocks 18 and 28 intersect with the cutting direction X of the tool as shown in FIGS. Directly affects.

  Further, in a compound lathe in which the tool rests 14 and 24 are moved also in the Y-axis direction to perform planar machining, grooving, drilling, etc., the displacement in the rising direction of the tool rests 14 and 24 becomes a machining error in the Y-axis direction. A big influence.

  In this invention, since the distance between the contact detection sensor 3a or the detection rod 3b mounted at the tool mounting position 7 of the tool post and the same location on the outer periphery 5 of the work chuck is directly detected, an error in the work diameter of the work and the Y-axis direction are detected. The machining position error can be corrected with high accuracy.

  Therefore, by using both the means of the present invention and the conventional correction means, it is possible to further increase the machining accuracy of the workpiece on the lathe.

Front view of the main part of the lathe of the first example Schematic side view of the lathe of the first example The flowchart which shows the setting procedure of the correction value in the lathe of the first example Front view of the main part of the lathe of the second example Schematic side view of the lathe of the second example The flowchart which shows the setting procedure of the correction value in the lathe of the 2nd example

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments of the present invention. A lathe 1 of the first embodiment shown in FIGS. 1 and 2 is a lathe whose vertical direction is the X-axis direction.

  In FIG. 2, a Z-axis moving table 12 is mounted on the upper surface of a bed 11 so as to be movable and positionable in the Z-axis direction (perpendicular to the plane of FIG. 2). A tall Y-axis moving table 13 is mounted so as to be movable and positionable, and a tool rest 14 is mounted on the front surface of the Y-axis moving table so as to be movable and positionable in the X-axis direction (vertical direction in FIG. 2). A tool motor 15 is mounted so as to be capable of swivel positioning in the direction of the B axis (around the Y axis). The rotor shaft (tool axis) of the tool motor 15 is oriented in a direction perpendicular to the Y axis. Tools (turning tools and rotary tools) are mounted on a tool chuck 17 provided at the tip of the rotor shaft of the tool motor 15 by an automatic tool changer (not shown). The touch sensor 3a shown in FIG. 1 is mounted on a tool magazine, and is attached to the tool chuck 17 by a tool changer at an appropriate time.

  The headstock 18 that supports the main shaft of the lathe according to the first embodiment rises upward with the lower back surface fixed to the front surface of the bed 11. The spindle not shown in the figure is pivotally supported on the upper part of the spindle stock 18. The spindle motor that rotates the spindle can fix the phase (angular position) at an arbitrary position instructed by a machining program or the like. The tool motor 15 can fix the rotor shaft at least at the origin phase. The workpiece is turned by attaching a turning tool to the tool chuck 17 of the rotor shaft fixed at the origin phase.

  A spindle bearing during turning that rotates the spindle at a high speed is one of the large heat sources during workpiece machining. The heat generated in the spindle bearing causes the spindle stock 18 to thermally expand. In the lathe having the structure shown in FIG. 2, it is considered that the direction of deviation of the spindle axis c due to the thermal expansion of the spindle stock 18 is substantially the direction indicated by the arrow d in FIG. The displacement of the spindle axis c in the arrow d direction changes the relative positional relationship between the workpiece and the tool in the X-axis direction and the Y-axis direction.

  In the NC device that controls the lathe, the correction value update procedure shown in FIG. 3 and the reference coordinates at the time of contact with the tool post, that is, the touch sensor 3 a mounted on the tool chuck 17 in the reference state is brought into contact with the outer periphery 5 of the work chuck 4. The coordinates of the tool post 14 are registered. The correction value update procedure shown in FIG. 3 is called at the start of workpiece machining and for each predetermined workpiece machining number when continuous automatic machining is performed.

  In the called correction value update procedure, the touch sensor 3a is mounted on the tool chuck 17 by the automatic tool changer, the spindle is stopped at the set phase, and the tool post is rapidly brought close to the contact detection start position. The contact detection start position is a position set as a position with a slight gap between the tip 6 of the touch sensor 3a and the outer periphery 5 of the work chuck 4 (see FIG. 1). Next, the feed motors in the Z-axis and Y-axis directions are stopped, and the tool post 14 is moved at a low speed in the X-axis minus direction (direction in which the tool post approaches the spindle axis c). If a touch detection signal is output from the touch sensor 3a during this movement, the X-axis coordinates of the tool rest 14 at that time are stored, and the tool rest 14 is stopped.

  If the difference δ between the detected coordinates of the tool rest 14 and the stored reference coordinates at the time of contact is within a predetermined threshold value, then the tool rest moves to the tool change position and the next machining is performed. A tool for mounting is mounted on the tool chuck 17.

  If the difference δ between the detected coordinates and the reference coordinates at the time of contact exceeds the threshold value, it is estimated that cutting fluid or chips are attached to the position to be detected on the outer periphery of the work chuck, and the spindle phase Is converted into the next candidate spindle phase, and the contact detection operation between the touch sensor 3a and the work chuck outer periphery 5 is performed again.

The computer incorporated in the NC unit is configured to detect the difference δ between the detected tool post coordinates and the reference coordinates at the time of contact and the detected temperatures t ₁ , t ₂ , t _3. Using t _n , new correction values Δx and Δy are calculated by, for example, the following equations.
Δx = a _1x t ₁ + a _2x t ₂ + a _3x t ₃ +... + A _nx t _n + b _x δ
_{Δy = a 1y t 1 + a} 2y t 2 + a 3y t 3 + ··· + a ny t n + b y δ

_{Here, t 1, t 2, t} 3 ··· t n, a 1x, a 2x, a 3x ··· a nx and _{a 1y, a 2y, a 3y} ··· a ny is the background section in a coefficient multiplied to their temperature when calculating the detected temperature and the correction value of the temperature sensor installed in the machine each unit described, b _x and b _y are the detected tool rest coordinate correction value updating step It is a coefficient in the X-axis direction and the Y-axis direction multiplied by the difference δ from the reference coordinate at the time of contact. The correction value Δz in the Z-axis direction may be obtained using the same arithmetic expression as before.

  When new correction values are calculated as described above, the correction values set in the NC device are updated, and command values given to the X-axis feed motor, Y-axis feed motor, and Z-axis feed motor of the tool post 14 Is corrected with the updated correction value, and the subsequent processing is performed.

  The lathe 2 of the second embodiment shown in FIGS. 4 and 5 is a lathe provided with a so-called slant type bed 21 and a turret tool post 24. A spindle not shown in the figure is pivotally supported on the upper part of a spindle stock 28 that rises in the vertical direction. In the lathe 2 of the second embodiment, the thermal deformation of the headstock due to the heat generated by the main shaft bearing is considered to displace the main shaft axis c in the direction indicated by the arrow d in FIG.

  The tool post 24 in the lathe 2 of the second embodiment can be moved and positioned only in the X-axis direction parallel to the upper surface of the bed 21 and the Z-axis direction which is the direction perpendicular to the paper surface of FIG. I do not have. A detection rod 3b made of a rod having a circular cross section precisely machined through an angle holder 27 is attached to one place 7 of the tool mounting position of the turret 26 of the tool post.

  FIG. 6 is a flowchart of the correction value update procedure in the lathe according to the second embodiment. The procedure of FIG. 6 differs from the procedure of FIG. 3 in that a detection bar 3b made of a metal bar having a circular cross section is used in place of the touch sensor, and the contact between the detection bar 3b and the outer periphery 5 of the work chuck 4 is determined as a blade. It is detected by monitoring the position deviation of the servo device of the feed motor that sends the table 24 in the X-axis direction, the detection rod 3b can be selected by the indexing rotation of the turret, and the B-axis and the Y-axis are not provided This is a difference.

  The called correction value update procedure in FIG. 6 is such that the turret 26 is rotated to index the detection rod 3b, the spindle is stopped at the set phase, the tool post is brought close to the contact detection start position, and the Z axis The direction feed motor is stopped, the X-axis feed motor is torque limited, and the tool post 24 is monitored while monitoring the position deviation which is the difference signal between the position command given to the feed motor and the feedback signal returned from the feed motor. Move at a low speed in the negative direction of the X-axis.

  Then, if a rising (abrupt increase) in position deviation is detected during this low speed movement, the tool rest is immediately stopped and the X coordinate of the tool rest at that time is read. The procedure after reading the tool post coordinates is the same as the procedure in FIG. 3 except that the correction value in the Y-axis direction is not calculated. Then, after setting a new correction value, the tool used in the subsequent process is determined by the rotation of the turret 26 and subsequent machining is started.

  As an example of a machine tool for carrying out the present invention, a lathe having two types of structures is illustrated, but of course, the lathe is not limited to these two types of structures, and a chuck and a tool that grips and rotates a workpiece are mounted. If it is a machine tool provided with a tool post, the present invention can be adopted as necessary to improve the machining accuracy.

3a Contact detection sensor 3b Detection rod 4 Work chuck 5 Work chuck outer periphery 7 Tool mounting position 14, 24 Tool post

Claims (4)

  An arithmetic expression that includes as a variable the difference from the reference coordinate of the tool rest coordinate when detecting contact between the contact detection sensor or detection rod attached to the tool mounting position of the tool rest and the fixed position on the outer periphery of the chuck that holds the workpiece A method for correcting a machining error of a machine tool, wherein the position command given to the tool post is corrected with the correction value calculated by the above.   The detection rod is a metal round bar, and the contact between the detection rod and the outer periphery of the work chuck is a difference signal between a position command given to the feed motor of the tool post and a feedback signal returned from the feed motor. The method for correcting a machining error of a machine tool according to claim 1, which is detected by detecting a sudden rise.   3. The machining error of the machine tool according to claim 1 or 2, wherein the contact between the contact detection sensor or detection rod and the outer periphery of the work chuck is performed in a state where the spindle on which the work chuck is mounted is stopped at a predetermined phase. Correction method.   The calculation formula includes a detection temperature of a temperature sensor attached to each part of a machine when contact detection between the contact detection sensor or detection rod and the outer periphery of the work chuck is performed. 3. A method for correcting a machining error of a machine tool according to 3.

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