JP6842146B2 - How to correct machine tool machining errors - Google Patents

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 accompanying change in thermal deformation of each part of the machine (generally). Will decrease).

In order to correct the change in machining accuracy due to the time-dependent temperature change of the machine itself, temperature sensors are attached to various parts of the machine, and the correction value is calculated by the calculation formula obtained by multiplying the detected temperature of each sensor by the coefficient obtained by the experiment. Therefore, the moving position of the tool post is corrected by this correction value and the processing is performed.

For example, n temperature sensors are attached to the main body of a lathe at appropriate locations, and data on machining accuracy when machining various workpieces and data on the detected temperature of each temperature sensor detected during machining are collected. make use of,
Δx ＝ a _1x t ₁ ＋ a _2x t ₂ ＋ a _3x t ₃ ＋ ・ ・ ・ ＋ an _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 obtained by a calculation formula such as, and the position of the tool post in the X, Y, and Z axis directions specified in the machining program is calculated at each time. It is corrected by the value and processed.

In the above equation, t ₁ , t ₂ , t ₃ ... t _n are the detection temperatures of n temperature sensors installed 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 It is a coefficient in the X, Y, and Z axis directions that is multiplied by, and is a value obtained by actually processing the workpiece.

Japanese Unexamined Patent Publication No. 6-55415

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

The present invention further improves the machining accuracy of a workpiece by providing a technical means capable of more appropriately correcting machining errors due to thermal deformation of a machine tool, particularly a lathe, without reducing productivity. The challenge is to let them do it.

The present invention makes it possible to more accurately correct the machining error in the radial direction of the workpiece by timely measuring the change in the relative positional relationship between the spindle of the lathe and the tool mounting position of the tool post. .. In the present invention, the outer circumference 5 of the work chuck 4 mounted on the spindle is brought into contact with the contact detection sensor 3a or the detection rod 3b attached to the tool mounting positions 7 of the tool rests 14 and 24, and the blade at the time of contact detection. The change in the relative positional relationship between the spindle and the tool mounting position of the tool post in the direction perpendicular to the spindle is detected from the coordinates of the tables 14 and 24, and the tool post 14 and 24 commanded by the machining program based on the calculation including the detected value. The correction value for the position of is obtained.

As the contact detection sensor 3a, a well-known sensor generally called a touch sensor can be used. Further, instead of using such a sensor, a detection rod processed with high accuracy (preferably a round rod that can be easily processed with high accuracy) is used, and the position deviation proposed in Patent Document 1 and the like, that is, at the time of feeding the tool post 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, the contact between the detection rod 3b and the chuck outer circumference 5 can be detected. .. According to the latter means, the present invention can be carried out without using an expensive contact detection sensor.

In order to avoid a detection error based on an error in the roundness of the outer circumference of the chuck, it is preferable to stop the spindle at a predetermined phase and bring the contact detection sensor 3a to the detection rod 3b into contact with each other. Further, in order to prevent cutting oil and chips from adhering to the outer circumference of the chuck and causing a detection error, 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 control that the spindle is stopped at the stop phase determined as the next candidate at that time to perform detection.

According to the present invention, a change in the dimensions of the outer circumference 5 of the work chuck mounted on the spindle and the tool mounting position 7 of the tool post in the direction perpendicular to the spindle is detected and corrected. It corrects the machining error in the radial direction. Since the thermal deformation in the direction perpendicular to the spindle also changes depending on the position of the tool post in the Z-axis direction, in general, the correction value is a correction value including the change in the relative positional relationship between the detected outer circumference of the chuck and the tool mounting position of the tool post. Should be calculated. That is, the correction value is calculated by a conventionally known calculation formula including a term including a change in the positional relationship between the outer circumference of the chuck and the tool mounting position of the tool post detected by the method of the present invention in the direction perpendicular to the spindle as a variable δ. Calculate.

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

In a structure in which the headstocks 18 and 28 rise in a direction orthogonal to the cutting direction of the tool (X-axis direction of the lathe), the displacement of the headstocks 18 and 28 in the rising direction has an effect on the machining error in the radial direction of the workpiece. small. However, in a lathe having a structure in which the rising directions of the headstocks 18 and 28 intersect the cutting direction X of the tool at the same direction or diagonally as shown in FIGS. 2 and 5, the displacement in the rising direction of the headstock causes a machining error. It has a direct effect.

Further, in a compound lathe in which the tool rests 14 and 24 move in the Y-axis direction to perform flat surface machining, grooving, drilling, etc., the displacement of the tool post 14 and 24 in the rising direction causes a machining error in the Y-axis direction. It has a big influence.

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

Therefore, by using the means of the present invention and the conventional correction means in combination, the machining accuracy of the work on the lathe can be further improved.

Front view of the main part of the lathe of the first example Schematic side view of the lathe of the first example A flowchart showing a procedure for setting a 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 Flow chart showing the procedure for setting the correction value in the lathe of the second example

Hereinafter, the present invention will be specifically described with reference to the drawings showing examples of the present invention. The 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 the bed 11 so as to be movable and positioned in the Z-axis direction (direction perpendicular to the paper surface in FIG. 2), and the Z-axis moving table is mounted in the Y-axis direction (horizontal direction in FIG. 2). A tall Y-axis moving table 13 is mounted on the front surface of the Y-axis moving table, and a tool post 14 is mounted on the front surface of the Y-axis moving table so as to move and position in the X-axis direction (vertical direction in FIG. 2). The tool motor 15 is mounted so that it can be swiveled and positioned in the B-axis (Y-axis) direction. The rotor shaft (tool shaft) of the tool motor 15 faces in a direction orthogonal to the Y-axis. The tools (turning tools and rotary tools) are mounted on the 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 the tool magazine and is timely mounted on the tool chuck 17 by the tool changing device.

The headstock 18, which pivotally supports the main shaft of the lathe of the first embodiment, has a lower back surface fixed to the front surface of the bed 11 and stands up upward. The spindle not shown in the figure is pivotally supported on the upper part of the headstock 18. The spindle motor that rotationally drives the spindle can fix the phase (angle position) at an arbitrary position commanded by a machining program or the like. Further, the tool motor 15 can fix the rotor shaft at least in the origin phase. The turning of the work is performed by mounting the turning tool on the tool chuck 17 of the rotor shaft fixed at the origin phase.

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

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

In the called correction value update procedure, the touch sensor 3a is attached to 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 circumference 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 (the direction in which the tool post approaches the spindle axis c). If a contact detection signal is output from the touch sensor 3a during this movement, the X-axis coordinates of the tool post 14 at that time are memorized and the tool post 14 is stopped.

If the difference δ between the detected coordinates of the tool post 14 and the stored reference coordinates at the time of contact is within a predetermined threshold value, the tool post then moves to the tool change position and performs the next machining. The tool for this purpose is attached to the tool chuck 17.

When 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 have adhered to the position to be detected on the outer circumference of the work chuck, and the spindle phase Is converted to the next candidate spindle phase, and the contact detection operation between the touch sensor 3a and the work chuck outer circumference 5 is performed again.

The computer built into the NC device has the difference δ between the detected coordinates of the tool post and the reference coordinates at the time of contact, and the detection temperatures of the temperature sensors of each part of the machine detected during the execution of the detection procedure t ₁ , t ₂ , t ₃ ... Using t _n , the new correction values Δx and Δy are calculated by, for example, the following equation.
Δx = a _1x t ₁ + a _2x t ₂ + a _3x t ₃ + ... + _anx 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 that is multiplied by the difference δ from the reference coordinates at the time of contact. The correction value Δz in the Z-axis direction may be obtained by the same calculation formula as in the conventional case.

When the new correction value is calculated as described above, the correction value set in the NC device is updated, and the command value given to the X-axis feed motor, the Y-axis feed motor, and the Z-axis feed motor of the tool post 14. Is corrected with the corrected correction value after the update, 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. The spindle not shown in the figure is pivotally supported on the upper part of the spindle 28 that rises in the vertical direction. In the lathe 2 of the second embodiment, it is considered that the thermal deformation of the spindle base due to the heat generation of the spindle bearing displaces the spindle axis c in the direction of arrow d in the figure, that is, in the upward direction.

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 in the Z-axis direction which is the direction perpendicular to the paper surface in FIG. Not prepared. A detection rod 3b made of a rod material having a circular cross section, which is precisely machined via an angle holder 27, is mounted at one location 7 of the tool mounting position of the turret 26 of the tool post.

FIG. 6 is a flowchart of the correction value updating procedure in the lathe of the second embodiment. The procedure of FIG. 6 is different from the procedure of FIG. 3 in that a detection rod 3b made of a metal rod having a circular cross section is used instead of the touch sensor, and the contact between the detection rod 3b and the outer circumference 5 of the work chuck 4 is a blade. It is detected by monitoring the position deviation of the servo device of the feed motor that sends the base 24 in the X-axis direction, the detection rod 3b can be selected by the indexing rotation of the turret, and it does not have the B-axis and the Y-axis. It is a difference due to the fact.

In the called correction value update procedure of FIG. 6, the turret 26 is rotated to index the detection rod 3b, the spindle is stopped at the set phase, the tool post is rapidly brought close to the contact detection start position, and the Z axis is used. The tool post 24 is operated while stopping the feed motor in the direction, limiting the torque of the X-axis feed motor, and 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 low speed in the minus direction of the X axis.

Then, when the rise (rapid rise) of the position deviation is detected during this low-speed movement, the turret is immediately stopped, and the X coordinate of the turret at that time is read. The procedure after reading the coordinates of the tool post is the same as the procedure of 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 the subsequent machining is started.

As an example of a machine tool for carrying out the present invention, a lathe having two types of structures has been illustrated, but of course, the lathe is not limited to these two types of structures, and a chuck and a tool that grip and rotate the work are mounted. If the machine tool is equipped 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 circumference 7 Tool mounting position 14, 24 Tool post

Claims (2)

The contact detection sensor or detection rod mounted at the tool mounting position of the tool post and the fixed position on the outer circumference of the work chuck that grips the work are brought into contact with each other with the spindle on which the work chuck is mounted stopped at a predetermined phase. , and correcting a position command to be given to the tool rest with the correction value calculated by the arithmetic expression including a difference from the reference coordinates of the tool rest of coordinates when it detects the contact as a variable, of the machine tool How to correct machining errors. The operation according to claim 1, wherein the calculation formula is a calculation formula including the detection temperature of the temperature sensor attached to each part of the machine when the contact detection sensor or the detection rod and the outer periphery of the work chuck are detected. How to correct machine tool machining errors.

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