JP5846400B2 - Machine tool and its thermal deformation correction method - Google Patents

Description

  The present invention relates to a machine tool and a method for correcting thermal deformation thereof, and more particularly to enabling a workpiece to be machined to a predetermined size even when the machine tool is thermally deformed.

  The applicant has proposed to measure the distance between the spindle and the turret using a linear sensor (Patent Document 1, Patent 4351379). If the linear sensor is composed of a scale made of a material with a low coefficient of thermal expansion, such as Invar alloy, and a sensor head that reads the scale, when one is fixed to the main shaft and the other is fixed to the turret, the main shaft and turret are not affected by temperature. Can be measured. When the spindle or turret is moved based on the measured distance, the workpiece can be machined without being affected by thermal deformation of the machine tool.

  Here is another prior art. Japanese Patent Application Laid-Open No. 2008-49425 discloses that the position of the cutting edge with respect to the spindle center is detected by a touch sensor. The touch sensor moves between a position on the spindle center and a position away from the spindle center, and can be used to measure the distance from the turret to the blade edge. The touch sensor and its haunting mechanism are called a tool setter. Patent Document 3 (Japanese Patent Laid-Open No. 2010-228011) discloses that a tool holder provided with a touch sensor is attached to a turret, and the turret and the work are moved relative to each other so that the touch sensor contacts both ends in the diameter direction of the work. Yes. This touch sensor is called an in-machine measuring device and can measure the size of a workpiece after processing. Then, the feed amount of the cutting edge for the next workpiece can be corrected so as to eliminate the machining error in the previous workpiece. However, this method cannot reduce the machining error in the first workpiece.

Patent 4351379 JP2008-49425 JP2010-228011

  Machine tools that perform precise machining are usually NC-controlled. Normally, the servo motor speed is monitored by an encoder other than the above-mentioned sensors, and the servo motor is controlled by the encoder signal to input commands. Execute. Therefore, how to combine the sensor signal not affected by temperature and the encoder signal to feed back to the servo motor becomes a problem.

  A basic object of the present invention is to reduce the influence of thermal deformation of a machine tool when machining a workpiece.

The machine tool of the present invention is an NC-controlled machine tool that measures the distance between the center of the spindle and the tool mounting portion using a scale and a sensor head,
A servo motor with an encoder that relatively moves the spindle and the tool mounting part;
A scale composed of a material having a low coefficient of thermal expansion compared to the machine part of the machine tool, and having a mark indicating the position;
A sensor head that measures the distance between the center of the spindle and the tool mounting portion by reading the mark on the scale;
A control device for moving the spindle or the tool mounting portion by controlling the servo motor based on the signal of the encoder,
The tool attachment portion is configured such that a tool having a cutting edge for cutting a workpiece attached to a spindle is attached.
The control device, when finishing the workpiece,
By moving the spindle or tool mounting part to the approach position just before finishing , the tool blade edge approaches the spindle center ,
At the approach position, the sensor head measures the distance between the spindle center and the tool mounting portion ,
The amount of movement of the spindle or tool mounting part in the finishing process is corrected by the correction amount based on the measured distance.
The finishing process is performed by further moving the spindle or the tool mounting portion from the approach position by the movement amount of the finishing process after correction.

According to the method for correcting thermal deformation of a machine tool according to the present invention, a scale composed of a material having a low thermal expansion coefficient compared to the machine part of the machine tool is read by the sensor head, and the distance between the spindle center and the tool mounting portion is read. Is a method of correcting thermal deformation of a machine tool by measuring
A tool having a cutting edge for cutting a workpiece attached to the spindle is attached to the tool attachment portion,
When finishing the workpiece,
Based on the signal of the encoder of the servo motor, moving the spindle or tool mounting part to the approach position immediately before the finishing process to bring the tool blade edge closer to the spindle center ;
Measuring a distance between a spindle center and a tool mounting portion by the sensor head at the approach position;
A step of correcting the movement amount of the spindle or tool mounting part in the finishing process by the correction amount based on the measured distance;
Based on the signal from the encoder of the servo motor, the finishing process is performed by further moving the spindle or the tool mounting portion from the approach position by the amount of the corrected finishing process.

  In the present invention, the distance between the spindle center and the tool mounting portion is measured by the sensor head at the approach position, and the movement amount of the spindle or the tool mounting portion in the finishing process is corrected by the correction amount based on the measured distance. The movement of the spindle or the tool mount is controlled by feeding back the encoder signal of the servo motor to the servo controller. The possibility that the thermal condition of the machine tool will change after the approach until the finishing process is completed is small because the time is very short. The workpiece can be machined to an accurate size by measuring the distance between the spindle center and the tool mounting portion at the approach position immediately before finishing. In addition, a measurement system including a scale having a low thermal expansion coefficient and a sensor head can be combined with a control system based on a signal from a conventional encoder. Materials having a low coefficient of thermal expansion include Invar alloys such as Super Invar alloy and Invar alloy, and other materials having a very low coefficient of thermal expansion are known, such as ceramics, glass, and plastic. In this specification, the description of the machine tool also applies to the thermal deformation correction method of the machine tool, and conversely, the description of the thermal deformation correction method of the machine tool also applies to the machine tool.

Preferably, the control device feedback-controls the servo motor so as to eliminate an error between a command value in a machining program and the signal of the encoder,
The correction amount is an error in the distance between the command center and the spindle center measured by the sensor head and the tool mounting portion at the approach position.
The control device corrects the amount of movement of the spindle or mounting part in the machining program by the correction amount in finishing machining, and feeds back the servo motor so as to eliminate the error between the corrected movement amount and the encoder signal. Control.

  By performing feedback control of the servo motor so as to eliminate the error between the command value and the encoder signal, the main shaft or the mounting portion moves. At the approach position, the encoder signal error due to thermal deformation of the machine tool is measured, and control is performed so that this error is eliminated by finishing.

Preferably, the machine tool is supported at one point on the bed and made of a material having a low coefficient of thermal expansion;
A first scale extending from the frame toward the main shaft, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A second scale extending from the frame to the tool mounting portion side, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A first sensor head that is provided on the spindle side and reads a position on the spindle side with respect to the frame by reading a magnetic mark of the first scale;
A second sensor head that is provided on the tool mounting portion side and reads the position of the tool mounting portion with respect to the frame by reading the magnetic mark of the second scale;
The control device is configured to measure the distance between the center of the spindle and the tool mounting portion based on the difference between the position obtained by the first sensor head and the position obtained by the second sensor head.

  The frame and the first and second scales can realize a scale that is substantially unaffected by thermal deformation of the machine tool, that is, a reference coordinate system. The scale is read by the first and second sensor heads, and the distance between the center of the spindle and the tool mounting portion can be measured by the difference between the signals of the two sensor heads without being affected by thermal deformation.

Preferably, the main axis is movable in an X direction orthogonal to the main axis center in the horizontal plane and a Z direction parallel to the main axis center in the horizontal plane,
The longitudinal direction of the frame extends parallel to the Z-axis,
The first scale and the second scale are arranged parallel to the X axis,
A third scale extending parallel to the Z-axis from the first scale, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A fourth scale provided parallel to the longitudinal direction of the frame, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A third sensor head that is provided on the main shaft side and reads a Z-axis coordinate on the main shaft side by reading a magnetic mark on the third scale;
A fourth sensor head that is provided on the tool mounting portion side and reads a Z-axis coordinate on the tool mounting portion side by reading a magnetic mark of the fourth scale;
The control device measures the Z-axis direction distance between the spindle end surface and the tool mounting portion based on the difference between the Z-axis coordinate obtained by the third sensor head and the Z-axis coordinate obtained by the fourth sensor head. It is configured.

  If it does in this way, the Z-axis direction distance between a spindle end surface and a tool attachment part can be measured by the independent measurement coordinate without the influence of the thermal deformation of a machine tool. Therefore, it can be machined according to the machining program along the Z-axis direction.

  Preferably, the control device is configured to retract the spindle or the mounting portion by a sum of a movement amount to the approach position after finishing and a movement amount in finishing before correction by the correction amount. Yes. In this way, the position to return by the correction amount measured at the approach position is changed, and the correction amount becomes effective at the actual time for the next actual machining.

Preferably, the machine tool further includes a touch sensor that generates a signal when coming into contact with the cutting edge of the tool, and a touch sensor retracting mechanism,
When the old tool is replaced with a new tool, the control device determines the distance between the spindle center and the tool mounting portion when the blade tip of the old tool contacts the touch sensor, and when the blade tip of the new tool contacts the touch sensor. The approach position is corrected by the difference between the center of the spindle and the distance between the tool mounting portions.

  In this way, changes in offset due to tool replacement can be corrected.

  Preferably, the control device of the machine tool uses the position of the spindle center read by the first sensor head as the spindle origin position when positioning the standard jig attached to the tool mounting portion and the spindle center relative to each other. The reading position of the first sensor head is corrected.

  In this way, the spindle origin position can be measured in the reference coordinate system. Accordingly, it is possible to correct an error caused by the main shaft falling down in a direction perpendicular to the axial direction of the main shaft in the horizontal plane.

Preferably, the machine tool further includes an in-machine measuring device for measuring a size of the workpiece chucked on the spindle, and the control device performs the finishing process between the intermediate finishing process and the remaining finishing after the tool change or at the start of the machine tool. The intermediate finishing process is performed by moving the spindle or tool mounting part to the middle of the finishing process. After the intermediate finishing process, the workpiece size is measured by the in-machine measuring device, and the target for the intermediate finishing process is reached. An error with respect to the size is obtained, and the moving amount of the spindle or the tool mounting portion in the remaining finishing is corrected so as to eliminate the obtained error.

  If it does in this way, it can process correctly from the first work at the time of starting after exchanging a tool or stopping a machine tool.

  Preferably, the control device includes a memory for storing a plurality of the correction amounts together with an operation history of the machine tool, and an analysis unit for outputting a result when a correction amount exceeding an allowable range determined by the operation history is detected. . For example, the correction amount is large immediately after the start of work or immediately after replacement of the tool, and the correction amount should be small when the thermal condition of the machine tool is stabilized by repeating machining with the same tool. Therefore, if the allowable range is determined based on the operation history of the machine tool and the correction amount is analyzed, tool life management and abnormality of the machine tool and the sensor system can be detected.

  Particularly preferably, the machine tool includes a temperature sensor, and the analysis unit determines the allowable range from an operation history and temperature of the machine tool, and the temperature is, for example, an air temperature and a temperature of each part of the machine tool. In this way, when the temperature is stable, the allowable range is narrowed, and when the temperature is changing, the allowable range is widened, and an abnormality can be accurately detected.

  Preferably, the control device is configured to latch the signal of the encoder when a signal from the sensor head arrives. In general, encoder signals are obtained at shorter time intervals than sensor head signals. Therefore, latching encoder signals based on sensor head signals effectively causes the sensor head signals and encoder signals to be simultaneously transmitted. Can be read.

It is a top view of the machine tool main body in the machine tool of an Example, and shows the conceptual structure of a control apparatus collectively. The perspective view of the machine tool main body of an Example. The principal part enlarged plan view of the machine tool of an Example The figure which shows the tool setter of an Example The figure which shows the in-machine measuring device of the Example The figure which shows the standard jig of the example Block diagram showing details of the read controller Block diagram showing details of correction unit The figure which shows the processing with the execution example Flow chart of basic routine in the embodiment Flow chart of tool exchange routine in the embodiment Flow chart of start-up routine in the embodiment

  In the following, an optimum embodiment for carrying out the present invention will be shown. The scope of the present invention should be determined according to the understanding of those skilled in the art based on the description of the scope of the claims, taking into account the description of the specification and well-known techniques in this field.

  The machine tool of an Example is demonstrated with reference to FIGS. 1 to 3 show an outline of a machine tool. The machine tool includes a machine tool main body 1 that is a machine part and a control device 2 that controls the machine tool main body 1, and the control is NC control. A spindle 6 is rotatably supported by a spindle stock 5 installed on a fixed bed 3 via a feed base 4. Further, a support base 26 is fixed to the bed 3, and the turret 7 is supported on the support base 26 so as to be capable of rotational indexing, that is, with high angular accuracy.

  The feed table 4 is moved by the servo motor 10 and the feed screw mechanism 11 along the X-axis guide 9 provided in the bed 3 along the X-axis direction perpendicular to the main axis O and the horizontal plane. As shown in FIG. 2, the headstock 5 is movable in the Z-axis direction parallel to the spindle center O along the Z-axis guide 13 provided on the feedtable 4, and the servomotor 14 and the feed screw mechanism 15 Moving. The spindle 6 is rotated by a spindle motor (not shown) built in the spindle base 5, and a chuck 17 is attached to the front end of the spindle 6 to chuck the workpiece W.

  The turret 7 is rotatable around the turret central axis T, and a plurality of tool holders 19 can be attached and detached. A tool 18 such as a bite and a rotary tool is attached to the tool holder 19. The turret 7 is fixed to the tip of the hollow shaft 7c that is rotatably supported by the support base 26, and an arbitrary tool holder 19 is attached to the main shaft 6 by rotating the hollow shaft 7c with an indexing motor (not shown). It is positioned at the opposite position. 1 and 2, only one tool 18 is shown, and the others are omitted. In the embodiment, the main shaft 6 moves in the X-axis and Z-axis directions, but the turret 7 may move. Further, the machine tool is a lathe in which the X axis and the Z axis move, but may be a machining center in which the X axis, the vertical Y axis, and the Z axis move.

  In the machine tool of the embodiment, the distance L between the spindle center O and the cutting edge is measured by a measurement system that is not thermally deformed. However, since it is difficult to directly measure the position of the blade edge, the distance between the end surface of the turret 7 on the spindle 6 side (the surface on the side where the tool holder 19 is fixed and the tool mounting surface) and the spindle center O is measured, and the turret is measured. The distance between the end face 7 and the blade edge is measured separately as shown in FIGS. And the workpiece | work W is processed by inputting the measured distance into the control apparatus 2 without the influence of the thermal deformation of a machine tool. A frame 30 is supported on the bed 3 at one point, and a scale 31 extending parallel to the X axis toward the lower part of the feed base 4 and a scale 32 extending parallel to the X axis along the central axis of the turret 7 are attached to the frame 30. It is fixed. Here, the one-point support means that the frame 30 is attached to one place of the bed 3 so that the frame 30 is not deformed by the thermal expansion of the bed 3. The frame 30 and the scales 31 and 32 are made of a material having a low thermal expansion coefficient such as a super invar alloy, and the material may be a simple invar alloy, glass, ceramics, liquid crystal polymer, or the like, and the thermal expansion is smaller than that of the bed 3. Use materials.

  The feed base 4 is provided with a sensor head 33 immediately below the spindle center O. For example, the magnetic marks on the scale 31 are read by four coils to obtain the X-axis coordinates. Since the scale 31 has a very low coefficient of thermal expansion, the X-axis coordinate of the feed base 4 with respect to the frame 30 can be measured independently from the influence of thermal deformation of the machine tool. The scale 32 extends into the turret 7 coaxially with the central axis of the turret 7 and is similarly provided with a magnetic mark. For example, a sensor head 34 having four coils reads the magnetic mark. Similarly, the scale 32 has a very low coefficient of thermal expansion, so that the X-axis coordinate of the turret 7 relative to the frame 30 can be measured without the influence of thermal deformation of the machine tool. The scale 32 and the sensor head 34 are protected by being placed inside the turret 7. The scales 31 and 32 may be attached to the feed base 4 and the support base 26, and the sensor heads 33 and 34 may be attached to the frame 30. A coordinate system that represents a position based on the frame 30 with little thermal deformation and is based on signals from the sensor heads 33 and 34 is referred to as a reference coordinate system.

  In the embodiment, the difference between the two obtained X-axis coordinates is used. The difference in the X-axis coordinates from the sensor heads 33 and 34 represents the distance from the tool mounting surface of the turret 7 to the spindle center O, and when the distance from the tool mounting surface of the turret 7 to the blade edge of the tool 18 is known, the blade tip to the spindle The distance L to the center O is known. If the distance L can be measured with a reference coordinate system based on the frame 30 that is not affected by the ambient temperature, heat generation of the machine tool, etc., the workpiece can be machined without being affected by thermal deformation of the machine tool. The position of the headstock 5 can also be measured by the encoder 20, and the coordinate system based on the signal of the encoder 20 is called a machine coordinate system. The control device 2 controls the servo controller 44 while correcting the machine coordinate system measured by the encoder 20 with the distance L in the reference coordinate system.

  When obtaining the Z-axis coordinates without the influence of thermal deformation, scales 35 and 36 and sensor heads 37 and 38 are provided. The scale 35 is attached to the scale 31 in parallel with the Z axis, for example, and the Z axis coordinates are read by the sensor head 37 provided on the feed base 4. For example, the scale 36 is attached to the frame 30 in parallel to the Z axis, but may be attached to the scale 32. The Z-axis coordinate is read from the scale 36 by the sensor head 38 provided on the support base 26. The scales 35 and 36 are made of a material having a low coefficient of thermal expansion such as a super invar alloy and provided with a magnetic mark, and the sensor heads 37 and 38 detect the magnetic mark with a plurality of coils. The difference between the two Z-axis coordinates is the Z-axis coordinate in the reference coordinate system, which represents the Z-axis coordinate of the headstock 5 with respect to the turret center axis T, and is the coordinate in the reference coordinate system that is not affected by thermal deformation.

  The control device 2 controls the machine tool body 1 by executing a machining program stored in the program memory 41 using an arithmetic control unit 43 including a CPU. The arithmetic control unit 43 includes a sequence control unit (not shown) that reads a machining program and interprets a command, a read control unit 46, a correction unit 47, an X-axis servo controller 44, and a Z-axis servo controller 45. . The arithmetic control unit 43 gives the X-axis command value Rx in the machining program to the X-axis servo controller 44 and gives the Z-axis command value Rz to the Z-axis servo controller 45. The servo controllers 44 and 45 feedback control the servo motors 10 and 14 so as to eliminate the error between the signals of the encoders 20 and 21 and the command value. The reading control unit 46 controls reading from the sensor heads 33 and 34. The correction unit 47 corrects an error in the machine coordinate system (error between the machine coordinate system and the reference coordinate system) based on the measurement value in the reference coordinate system, and inputs a correction amount to the servo controllers 44 and 45.

  FIG. 4 schematically shows a tool setter according to the embodiment. A touch sensor 52 is attached to the base 50, and the base 50 is located at a position where the detection surface of the touch sensor 52 coincides with the spindle center O and a position retracted from the machining area. Infested with. For example, an arm for turning the base 50 or a fluid pressure cylinder for moving the base 50 straightly is used for the appearance. When the X-axis coordinate in the reference coordinate system when the touch sensor 52 comes into contact with the tip of the tool 18 is obtained, the offset between the cutting edge position of the tool 18 and the turret 7 can be corrected. In order to accurately measure the absolute value of the offset, it is necessary to accurately position the base 50 in FIG. However, when the old and new cutting edge positions are continuously measured, if the position of the base 50 does not fluctuate during the measurement, the change in offset can be accurately obtained from the difference between the old and new cutting edge positions. Note that the procedure of FIG. 4 is defined by, for example, an M code in NC control. When the tool reaches the end of its life or some abnormality is recognized, the position of the base 50 is fixed, and the touch sensor 52 is held at a position that coincides with the spindle center O and replaced with a new tool. . At that time, the coordinates where the old and new tools come into contact with the touch sensor 52 are measured in the reference coordinate system, the difference is obtained, and the value is put in the correction term, so that the continuous processing from the old tool to the new tool can be performed. Can continue.

  FIG. 5 schematically shows the in-machine measuring apparatus of the embodiment, and the touch sensor 54 is attached to the tool holder 19. When the feed base 4 is moved in the Z-axis direction and the X-axis direction, the touch sensor 54 can be brought into contact with both ends of the workpiece W in the diameter direction. For example, the difference in the X-axis coordinates in the reference coordinate system between when the workpiece is represented by W and W ′ in FIG. 5 represents the diameter of the workpiece. Similarly, the inner diameter can be measured for a cylindrical workpiece. When the feed base 4 is moved in the Z-axis direction, the Z-axis coordinate of each part of the work can be measured in the reference coordinate system with one point of the work as a reference. The in-machine measuring device can determine the size of the workpiece after machining and measure the error from the command value. Automation can be achieved by using an in-machine measuring device as a function to compensate for discontinuous thermal displacement in the machine, such as after a long machine pause or tool change.

  FIG. 6 shows a standard jig 58 for obtaining the X-axis coordinate of the spindle origin in the reference coordinate system. The standard jig 58 and the tool holder 56 are made of a material having a low coefficient of thermal expansion such as a super invar alloy, and the standard jig 58 is a precision-processed round bar shape that is formed on the center of the standard jig 58 or on a specific surface thereof. Determine the spindle origin. For example, when using the touch sensor 52 positioned on the center of the spindle as shown in FIG. 4, the X-axis coordinate of the sensor head 33 when the touch sensor 52 is in contact with the standard jig 58 is used as the X-axis of the spindle origin. It can be regarded as coordinates. When the dial gauge 60 attached to the main shaft is used, it can be considered that the center of the standard jig 58 coincides with the main shaft center when the reading of the dial gauge does not change when the main shaft is rotated once. In this case, the X-axis coordinate of the sensor head 33 may be regarded as the X-axis coordinate of the main axis origin. The X-axis coordinates obtained as described above are stored in the log file as an offset of the spindle origin, and the signal of the sensor head 33 is corrected by this offset and used. The procedure of FIG. 6 can also be defined by M code, for example. The X-axis position of the principal axis center obtained by this method is the origin of the reference coordinate system.

  FIG. 7 shows the reading control unit 46, and shows a configuration for reading the signals of the encoders 20 and 21 simultaneously with the signals of the sensor heads 33 and 34. Reference numerals 62 to 65 denote memories, and the memories 64 and 65 are latch memories. The reading control unit 46 monitors the signal of the encoder 20, and when it reaches a predetermined value, instructs the sensor heads 33 and 34 to read the signal. At this time, when the signal of the movable sensor head 33 arrives, the signal from the encoder 20 is latched in the memory 64. Then, even when the servo motor 10 is operating, the signals of the sensor head 33 and the encoder 20 can be read at the same time, and an error due to the time difference between reading the signals does not occur. The signal from the sensor head 34 on the fixed side is almost constant regardless of time, and it is not necessary to accurately control the reading timing. When reading the Z-axis coordinates, the signal from the encoder 21 is similarly latched in the memory 65 when the signal from the sensor head 37 arrives. Also in this case, it is not necessary to accurately control the timing of reading the signal from the sensor head 38 on the fixed side. In order to eliminate an error due to a difference in reading time between the encoders 20 and 21 and the sensor heads 33 and 34, the servo motor can be temporarily stopped and the outputs of the encoders 20 and 21 and the sensor heads 33 and 34 can be read.

  FIG. 8 shows details of the correction unit 47, and the correction unit main body 70 corrects the X-axis command value and the Z-axis command value based on the X-axis coordinate and the Z-axis coordinate of the main axis with respect to the turret 7 in the reference coordinate system. These correction values, the difference between the old and new cutting edge positions at the time of tool replacement, the spindle center coordinates, etc. are stored in the log file 72. Further, the log file 72 stores machine tool events such as restart after a pause, tool replacement, spindle center coordinate measurement, machine maintenance, and the like, and further stores the temperature and the temperature of each part of the machine tool. The analysis unit 74 analyzes the correction value in the log file 72 with reference to the event of the machine tool, the air temperature, the temperature of the machine tool, and the like, and outputs to a monitor (not shown) if there is an abnormality.

  The correction amount is large immediately after the start of work in the morning and immediately after the replacement of the tool. If the workpiece is continuously processed thereafter, the correction amount should be gradually reduced. In addition, when the temperature change of the machine or the change of the air temperature is severe, the correction amount increases, and when the temperature change is small, the correction amount should decrease. Furthermore, the transition of the origin coordinate of the spindle is a transition of the inclination of the spindle with respect to the feed base. Therefore, the analysis unit 74 determines an allowable range for the correction amount from the operation history of the machine tool and the degree of temperature fluctuation, and outputs when the correction amount exceeds the allowable range. When the origin coordinate of the spindle changes by more than a predetermined value from the initial value, an output indicating that maintenance of the feed base 4 and the like is necessary is output.

  9 and 10 show the basic mechanism of processing. For example, it is assumed that the outer periphery of the workpiece is cut and a command is given by a G code. The approach with the code G00 ignores correction for thermal deformation and moves the feed base according to the command value while monitoring the encoder signal. The feed base moves from the left to the right in FIG. 9, and when the encoder signal reaches a predetermined value, it determines whether or not it is in position and reads the signals from the sensor heads on the spindle side and the turret side. As a result, the reference coordinates of the feed base 4 and the reference coordinates of the turret 7 are determined. The difference between the signals of the two sensor heads represents the distance between the turret and the feed base.

  The offset between the reference coordinates obtained by the sensor head 33 and the spindle center O has been measured by the operation of FIG. 6, and the signal of the sensor head 33 is corrected by the offset. In the following, it is assumed that the offset of the signal of the sensor head 33 has been corrected. Further, the offset between the blade tip position of the tool 18 and the turret 7 has been measured by the operation of FIG. 4, and the signal of the sensor head 34 is corrected by the offset between the blade tip and the turret. Hereinafter, similarly, it is assumed that the signal of the sensor head 34 has already been corrected for the offset. The difference between the signals of the sensor heads 33 and 34 represents the distance L between the turret and the feed base in the reference coordinate system.

  The change in the thermal condition of the machine tool during one finishing process is small, and the machine tool is almost thermally stable when a plurality of workpieces are processed continuously. Therefore, it is negligible that the error between the reference coordinate system and the machine coordinate system changes during finishing for the second and subsequent workpieces. For this reason, when the error of the machine coordinate system is obtained at the end of the approach and the movement amount of the machine coordinate system is corrected, finishing can be performed without the influence of thermal deformation. As shown in FIG. 9, in both the reference coordinate system and the machine coordinate system, the X coordinate increases as the cutting edge moves away from the spindle center. Assuming that the offset corrected sensor head 33 signal is Ps and the offset corrected sensor head 34 signal is Pt, Ps−Pt is the turret coordinate with respect to the spindle center in the reference coordinate system. Assuming that the machine coordinate obtained from the signal of the encoder 20 is Pm, the finishing feed amount is set so that the cutting edge is advanced to the spindle center side from the command value by an error ΔX = Pm− (Ps−Pt) between the machine coordinate and the reference coordinate. If corrected, machining can be performed to the size as per the machining program.

  When the cutting is finished, the error ΔX is ignored, and the feed base is returned by the sum of the approach and cutting feed command values. This eliminates errors in the machine coordinate system measured at the end of the approach. 9 and 10 are executed for each work until the machine tool is thermally stabilized. When the machine tool is thermally stable, it is executed for every work even if it is executed for all the works. Also good. When a plurality of machining operations are performed on a single workpiece while changing the position in the Z-axis direction, the reference coordinates are measured during movement in the Z-axis direction or at the end of the approach, and the feed amount in finishing is corrected.

  FIG. 11 shows the process for the first workpiece after the tool change. When the tool is replaced, the offset between the cutting edge position of the tool 18 and the turret 7 changes. In addition, the thermal conditions of the machine tool can change during tool changes. Therefore, as shown in FIG. 4, the difference between the new and old cutting edge positions is measured in the reference coordinate system, and the machine coordinate system is corrected according to the difference obtained by calculating the offset between the turret 7 and the cutting edge position in the reference coordinate system. Also, values such as the amount of tool wear in the machine coordinate system are corrected using a normal tool wear offset region. Therefore, the memory for correcting using the reference coordinate system and the memory for correcting tool wear use independent areas, and an operation of adding both at the time of actual machining is required. When the tool 18 is changed, not only the offset between the cutting edge position and the turret changes, but also factors such as sharpness may change. Therefore, the finishing process is divided into an intermediate finishing and a final finishing. After the intermediate finishing, the workpiece size is measured by the in-machine measuring device shown in FIG. 5 to obtain an error from the command value, and that amount is added as a correction at the final finishing. This eliminates the error as a total. If it does in this way, a work can be processed correctly from the first work after tool exchange, without the influence of thermal deformation. Moreover, the reference coordinates measured after intermediate finishing can be calibrated by the size of the workpiece measured by in-machine measurement.

  FIG. 12 shows the process for the first workpiece after the machine tool is started. Although the tool holder 19 is thermally deformed during the rest, the sensor heads 33 and 34 cannot measure this heat deformation. Therefore, intermediate finishing is executed after the approach is completed, and final finishing is executed so as to eliminate the difference between the command value in the machining program and the workpiece size measured by the in-machine measuring device. Also, as in the case of tool change, the reference coordinates measured after intermediate finishing are calibrated with the measured values of the workpiece measured by in-machine measurement, and the error is stored as a correction parameter and the movement amount in the machine coordinate system is corrected. To do.

  In the embodiment, the outer shape processing of the workpiece has been described, but other processing such as inner diameter processing may be performed. Further, in order to remove the influence of thermal deformation in the Z-axis direction in addition to the X-axis, the same processing may be performed by signals from the sensor heads 37 and 38. Furthermore, the type of machine tool is arbitrary, such as a compound lathe or a machining center. The influence of the thermal expansion of the workpiece itself is separately corrected by measuring the workpiece temperature or the like. The workpiece size after intermediate finishing may be measured manually. Further, even if the error is corrected so as to be eliminated by 100%, the magnitude of the error may be divided into a plurality of ranks, and correction values may be determined for each rank.

  The coefficient of thermal expansion is not zero even in a super invar alloy or the like. However, since the frame 30 and the scales 31 and 32 are supported by the bed 3 at one point, the thermal deformation can be easily obtained from the thermal expansion coefficient. For example, the temperature of the scales 31 and 32 is measured by a temperature sensor (not shown), and the product of the distance between the reading position of the sensor heads 33 and 34 and the frame 30, the difference from the reference temperature such as 20 ° C., and the linear thermal expansion coefficient length. Ask for. When the position obtained from the signals of the sensor heads 33 and 34 is corrected by this product, the influence of thermal expansion of the super invar alloy or the like can be eliminated.

In the embodiment, the following effects can be obtained.
1) By measuring the distance between the spindle center and the turret without being affected by heat, the influence of thermal deformation of the machine tool can be reduced. In addition, since a theoretical model is not used, correction is based on actual measurement values, so reliability is high.
2) The time from the end of the approach to the end of the finishing process is very short, and the machine coordinate system error is obtained at the end of the approach, and it can be accurately processed by eliminating the error in the finishing process.
3) By measuring the cutting edge position when changing the tool and performing intermediate finishing, it is possible to accurately machine from the first workpiece after changing the tool.
4) By performing intermediate finishing at the time of start-up after a stop, machining can be accurately performed from the first workpiece after start-up.
5) By analyzing the error tendency between the reference coordinate system and the machine coordinate system, it is possible to grasp the state of the machine tool and to perform maintenance before a machining error exceeding the allowable range occurs.
6) When the position of the spindle center is measured in the reference coordinate system as shown in FIG. 6, the error due to the spindle falling over the feed table can be corrected. In addition, it is possible to determine whether the maintenance of the machine tool is necessary or not from the transition of the reference coordinates around the spindle.

DESCRIPTION OF SYMBOLS 1 Machine tool main body 2 Control apparatus 3 Bed 4 Feed stand 5 Spindle base 6 Spindle 7 Turret 7c Hollow shaft 8 Bearing 9 X-axis guide 10, 14 Servo motor 11, 15 Feed screw mechanism 13 Z-axis guide 17 Chuck 18 Tool
DESCRIPTION OF SYMBOLS 19 Tool holder 20, 21 Encoder 26 Support stand 30 Frame 31, 32 Scale 33, 34 Sensor head 35, 36 Scale 37, 38 Sensor head 41 Memory 43 Arithmetic control part 44, 45 Servo controller 46 Reading control part 47 Correction part 50 Base 52, 54 Touch sensor 56 Tool holder 58 Standard jig 60 Dial gauge 62-65 Memory 70 Correction unit main body 72 Log file 74 Analysis unit L Distance between spindle center and cutting edge O Spindle center T Turret center axis W Workpiece

Claims (12)

An NC-controlled machine tool that measures the distance between the center of the spindle and the tool mounting section using a scale and a sensor head,
A servo motor with an encoder that relatively moves the spindle and the tool mounting part;
A scale composed of a material having a low coefficient of thermal expansion compared to the machine part of the machine tool, and having a mark indicating the position;
A sensor head that measures the distance between the center of the spindle and the tool mounting portion by reading the mark on the scale;
A control device for moving the spindle or the tool mounting portion by controlling the servo motor based on the signal of the encoder,
The tool attachment portion is configured such that a tool having a cutting edge for cutting a workpiece attached to a spindle is attached.
The control device, when finishing the workpiece,
By moving the spindle or tool mounting part to the approach position just before finishing, the tool blade edge approaches the spindle center,
At the approach position, the sensor head measures the distance between the spindle center and the tool mounting portion,
The amount of movement of the spindle or tool mounting part in the finishing process is corrected by the correction amount based on the measured distance.
A machine tool configured to perform the finishing process by further moving the spindle or the tool mounting portion from the approach position by the movement amount of the finishing process after correction. The control device feedback-controls the servo motor so as to eliminate an error between a command value in a machining program and the signal of the encoder,
The correction amount is an error in the distance between the command center and the spindle center measured by the sensor head and the tool mounting portion at the approach position.
The control device corrects the movement amount of the spindle or tool mounting portion in the machining program by the correction amount in finishing machining, and cancels the error between the corrected movement amount and the encoder signal. 2. The machine tool according to claim 1, wherein feedback control is performed. A frame made of a material having a low coefficient of thermal expansion, supported at one point on the bed of the machine tool;
A first scale extending from the frame toward the center of the main shaft, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A second scale extending from the frame to the tool mounting portion side, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A first sensor head that is provided on the spindle side and reads the position of the center of the spindle relative to the frame by reading the magnetic mark of the first scale;
A second sensor head that is provided on the tool mounting portion side and reads the position of the tool mounting portion with respect to the frame by reading the magnetic mark of the second scale;
The control device is configured to measure a distance between the center of the spindle and the tool mounting portion based on a position obtained by the first sensor head and a position obtained by the second sensor head. The machine tool according to claim 1 or 2. The main axis can move in the X direction orthogonal to the main axis center in the horizontal plane and the Z direction parallel to the main axis center in the horizontal plane,
The longitudinal direction of the frame extends parallel to the Z-axis,
The first scale and the second scale are arranged parallel to the X axis,
A third scale extending parallel to the Z-axis from the first scale, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A fourth scale provided parallel to the longitudinal direction of the frame, made of a material having a low coefficient of thermal expansion, and provided with a magnetic mark;
A third sensor head that is provided on the spindle side and reads a Z-axis coordinate on the spindle end face side by reading a magnetic mark of a third scale;
A fourth sensor head that is provided on the tool mounting portion side and reads a Z-axis coordinate on the tool mounting portion side by reading a magnetic mark of the fourth scale;
The control device measures the Z-axis direction distance between the spindle end surface and the tool mounting portion based on the difference between the Z-axis coordinate obtained by the third sensor head and the Z-axis coordinate obtained by the fourth sensor head. The machine tool according to claim 3, wherein the machine tool is configured.   The control device is configured to retract the spindle or the mounting portion by a sum of a movement amount to the approach position after finishing and a movement amount in finishing before correction by the correction amount. The machine tool according to claim 1, wherein It further includes a touch sensor that generates a signal when it comes into contact with the blade edge of the tool, and a touch sensor exit / retreat mechanism,
When the old tool is replaced with a new tool, the control device determines the distance between the spindle center and the tool mounting portion when the blade tip of the old tool contacts the touch sensor, and when the blade tip of the new tool contacts the touch sensor. 5. The machine tool according to claim 3, wherein the approach position is corrected by a difference between a center of the spindle and a distance between the tool mounting portions.   The control device uses the position of the spindle center read by the first sensor head when the standard jig attached to the tool attachment portion and the spindle center are positioned as the spindle origin position as a first sensor head. The machine tool according to claim 3, 4, or 6, wherein the machine tool is configured to correct the reading position. An in-machine measuring device that measures the size of the workpiece chucked on the spindle is further provided.
The control device divides the finishing process into an intermediate finishing process and a remaining finishing process after tool change or at the start of a machine tool,
Have the intermediate finishing process to move the spindle or tool mounting part to the middle of the finishing process,
After the intermediate finishing process, measure the size of the workpiece with the in-machine measuring device to obtain the error from the target size in the intermediate finishing process.
The system according to any one of claims 3, 4, 6, and 7, wherein the moving amount of the spindle or tool mounting portion in the remaining finishing process is corrected so as to eliminate the obtained error. Machine tools.   The control device includes a memory that stores a plurality of correction amounts together with an operation history of a machine tool, and an analysis unit that outputs a result when detecting a correction amount that is greater than or equal to an allowable range determined by the operation history. The machine tool according to claim 1.   10. The machine tool according to claim 9, further comprising a temperature sensor, wherein the analysis unit determines the allowable range from an operation history and temperature of the machine tool.   The machine tool according to any one of claims 1 to 10, wherein the control device is configured to latch the signal force of the encoder when a signal from the sensor head arrives. Compensates for thermal deformation of the machine tool by measuring the distance between the center of the spindle and the tool mount by reading the scale made of a material with a low thermal expansion coefficient compared to the machine part of the machine tool with the sensor head A way to
A tool having a cutting edge for cutting a workpiece attached to the spindle is attached to the tool attachment portion,
When finishing the workpiece,
Based on the signal of the encoder of the servo motor, moving the spindle or tool mounting part to the approach position immediately before the finishing process to bring the tool blade edge closer to the spindle center;
Measuring a distance between a spindle center and a tool mounting portion by the sensor head at the approach position;
A step of correcting the movement amount of the spindle or tool mounting part in the finishing process by the correction amount based on the measured distance;
A step of performing the finishing process by further moving the spindle or the tool mounting portion from the approach position by the amount of movement of the corrected finishing process based on the signal of the encoder of the servo motor. Correction method for thermal deformation.