JP2012011509A - Thermal displacement correcting method and thermal displacement correcting device of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal displacement correcting method and the like of a machine tool capable of highly accurately correcting thermal displacement with a simple construction.SOLUTION: A supporting rigidity estimating part 54 estimates supporting rigidity Kh in a horizontal direction and supporting rigidity Kv in a vertical direction changed by passing time to a column 10 on the basis of a thermal extension amount ΔL and a temperature change amount Δt of a member 15 (the column 10) acquired by a thermal extension amount acquiring part 52 and a temperature change amount acquiring part 53. When the supporting rigidities Kh and Kv greatly affecting an attitude of the column 10 are changed by passing time, the supporting rigidity estimating part 54 once estimates supporting rigidities Kh and Kv changed by passing time on the basis of a thermal extension amount ΔL and a temperature change amount Δt and a thermal displacement amount deriving part 55 determines a thermal displacement amount ΔM1h in the horizontal direction and a thermal displacement amount ΔM1v in the vertical direction of the column 10 on the basis of the supporting rigidities Kh and Kv. Thereby, accuracy of the thermal displacement amount ΔM1h in the horizontal direction and the thermal displacement amount ΔM1v in the vertical direction can be heightened and highly accurate thermal displacement correction can be made possible with a simple construction.

Description

  The present invention relates to a thermal displacement correction method and a thermal displacement correction apparatus for a machine tool.

  A machine tool processes a workpiece by controlling the position of each drive shaft by a control device. In this machine tool, the support that supports the moving body may be thermally deformed due to heat generation due to internal factors such as machining by a tool or rotation of a motor and heat transfer due to external factors such as room temperature fluctuations in the installation environment. Since the thermal deformation of the support affects the position of the moving body, the processing accuracy may be reduced.

  Therefore, for example, Patent Document 1 discloses a thermal displacement correction device (attitude control device) in the following machine tool. This apparatus detects a displacement due to a temperature change generated on a wall surface of a support (column) by a strain sensor (displacement sensor) installed on the wall surface of the support. Then, according to the detected displacement value, a control signal is output to the thermal actuator installed on the wall surface of the support body, and the wall surface of the support body is heated or cooled to control expansion and contraction of the wall surface of the support body. Hold in place.

  For example, Patent Document 2 discloses a thermal displacement correction method for the following machine tools. This method detects the temperature change of the support that is affected by the heat source, and uses the detected temperature change to achieve a behavior that is almost the same as the thermal behavior of a thermal displacement of a machine tool having a thermal characteristic such as a certain time constant. The temperature change is calculated. And a processing error is correct | amended based on the thermal displacement obtained using the function which defines the relationship between the calculated calculated temperature change and the above-mentioned thermal displacement.

JP-A-4-82649 (page 3, upper right column, line 18 to lower left column, line 7, FIG. 1) Japanese Patent Laid-Open No. 9-108992 (paragraph 0010, FIG. 1)

  The conventional thermal displacement correction device described in Patent Document 1 is a device that detects the tilt of the support by a strain sensor and raises the support by a thermal actuator. In this device, in order to increase the positional accuracy of the support. Requires a very large number of strain sensors and thermal actuators, and tends to be complicated and expensive.

  Moreover, in the conventional thermal displacement correction method described in Patent Document 2, the thermal displacement of the support can be corrected by measuring the temperature. Here, in general, the elongation amount and posture due to the thermal deformation of the support are determined by the balance between the force generated by the thermal deformation of the support and the static rigidity of the support. However, in the thermal displacement correction method described in Patent Document 2, it is assumed that the static rigidity and restraint conditions of the support do not change.

  Thus, for example, a rolling guide that is provided between the support and the rail on the bed and supports the support in a movable manner is worn during repeated movements, so that the preload in the guide is reduced and the support rigidity is deteriorated over time. Therefore, the thermal displacement correction method described in Patent Document 2 may be difficult to perform highly accurate thermal displacement correction.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermal displacement correction method and a thermal displacement correction apparatus for a machine tool that can correct thermal displacement with higher accuracy with a simple configuration.

(Machine tool thermal displacement compensation method)
In order to solve the above problems, the structural features of the invention relating to the thermal displacement correction method for a machine tool according to claim 1 are:
A support body that is supported by a base of a machine tool so as to be movable in a horizontal direction, moves relative to the base based on a first command position, and a support rigidity with respect to the base changes with time; In a thermal displacement correction method for a machine tool, comprising: a movable body supported so as to be movable in a vertical direction and moving relative to the support body based on a second command position;
Before and after thermal deformation of the support, a thermal extension amount acquisition step of acquiring a horizontal thermal extension amount of a thermal extension inspection point set on the support;
Before and after thermal deformation of the support, a temperature change acquisition step of acquiring a temperature change of a temperature inspection point set on the support;
A support stiffness estimation step of estimating a horizontal support stiffness and a vertical support stiffness that have changed over time with respect to the support, based on the thermal extension amount and the temperature change amount;
A thermal displacement amount derivation step for obtaining a thermal displacement amount of the support based on the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support; and
A correction value calculating step of calculating a correction value for the second command position based on the thermal displacement amount;
A correction step of correcting the second command position of the movable body by the correction value;
It is to provide.

The structural feature of the invention described in claim 2 is that in claim 1,
When the support is supported at two support points in the horizontal direction on the base of the machine tool, the thermal extension amount acquisition step is performed at the thermal extension inspection set between the two support points. The horizontal thermal expansion amount of the point is acquired, and the temperature change acquisition step is to acquire the temperature change amount of the temperature inspection point set on one side or both sides of the thermal extension inspection point in the horizontal direction. .

The structural feature of the invention described in claim 3 is that in claim 2,
When the support is supported by a rolling guide at the two support points, the support rigidity estimation step is based on the acquired amount of thermal expansion and the amount of temperature change, and the time-dependent change with respect to the support is performed. The horizontal support stiffness is estimated, and the vertical support stiffness is estimated assuming that the horizontal support stiffness is equal to the vertical support stiffness that has changed over time with respect to the support.

The constitutional feature of the invention described in claim 4 is that in claim 2,
The support stiffness estimation step is a time-dependent change with respect to the support, based on a relational expression between the thermal extension amount and the temperature change amount stored in advance and the acquired thermal extension amount and the temperature change amount. Estimating the horizontal support stiffness and the vertical support stiffness.

The structural feature of the invention according to claim 5 is the structure according to any one of claims 1 to 4,
The thermal expansion amount acquisition step is to acquire the thermal expansion amount based on the strain of the support measured by a strain sensor arranged at the thermal expansion inspection point.

The constitutional feature of the invention according to claim 6 is the structure according to any one of claims 1 to 5,
The thermal displacement amount derivation step includes the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support, and the temperature change on the sliding surface of the support that occurs as the moving body moves. The amount of thermal displacement of the support is obtained from the amount.

(Machine tool thermal displacement compensation device)
In order to solve the above problem, the structural features of the invention relating to the thermal displacement correction device for a machine tool according to claim 7 are:
A support body that is supported by a base of a machine tool so as to be movable in a horizontal direction, moves relative to the base based on a first command position, and a support rigidity with respect to the base changes with time; In a thermal displacement correction device for a machine tool, comprising: a movable body supported so as to be movable in a vertical direction and moving relative to the support body based on a second command position;
Before and after thermal deformation of the support, a thermal extension amount acquisition means for acquiring a horizontal thermal extension amount of a thermal extension inspection point set on the support;
Before and after thermal deformation of the support, a temperature change amount acquisition means for acquiring a temperature change amount of a temperature inspection point set in the support;
A support stiffness estimating means for estimating a horizontal support stiffness and a vertical support stiffness that have changed over time with respect to the support, based on the thermal extension amount and the temperature change amount;
A thermal displacement amount deriving means for obtaining a thermal displacement amount of the support based on the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support;
Correction value calculating means for calculating a correction value for the second command position based on the thermal displacement amount;
Correction means for correcting the second command position of the movable body by the correction value;
It is to provide.

  According to the first aspect of the invention, the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support estimated in the support stiffness estimation step are acquired in the thermal extension amount acquisition step and the temperature change amount acquisition step. It is set as the structure estimated based on the thermal expansion amount and temperature variation of a support. When the horizontal support stiffness and the vertical support stiffness, which greatly affect the posture of the support, change with time, it is difficult to accurately estimate the thermal displacement of the support with only the temperature change of the support. However, as in the present invention, the horizontal support stiffness and the vertical support stiffness that have changed over time based on the amount of thermal expansion and temperature change are once estimated, and the horizontal support stiffness and the vertical support stiffness are estimated. Since the thermal displacement amount of the support is obtained based on the above, the accuracy of the thermal displacement amount can be increased, and more accurate thermal displacement correction can be performed with a simple configuration.

  According to the invention of claim 2, the thermal elongation amount acquisition step acquires the thermal elongation amount of the thermal elongation inspection point set in the middle between the two support points in the horizontal direction supporting the support, and the temperature change amount The acquisition process is configured to acquire the temperature change amount of the temperature inspection point set on one side or both sides of the thermal extension inspection point in the horizontal direction. The thermal extension amount at the thermal extension inspection point set in the middle between the two support points can increase the accuracy in estimating the horizontal support stiffness that has changed over time. And the temperature change amount of the temperature test point in the vicinity can also improve the precision in estimating the horizontal support rigidity which changed with time. In particular, by setting the temperature inspection points on both sides of the thermal extension inspection point, it is possible to further increase the estimation accuracy of the horizontal support stiffness that has changed over time.

  According to the invention which concerns on Claim 3, the support body is set as the structure currently supported by the base of the machine tool by the rolling guide. The change over time of the support rigidity due to, for example, a decrease in the preload of the rolling guide generally changes similarly in the vertical direction and the horizontal direction. Therefore, by estimating the support stiffness in the horizontal direction that has changed over time, the support stiffness in the vertical direction that has changed over time can be easily estimated. Therefore, the thermal displacement amount of the support can be obtained with high accuracy based on the horizontal support stiffness and the vertical support stiffness that have changed over time.

  According to the invention according to claim 4, the support rigidity estimation step is based on the relational expression between the amount of thermal expansion and temperature change stored in advance and the acquired amount of thermal expansion and temperature change. The horizontal support stiffness and the vertical support stiffness that have changed over time are estimated. Since the relational expression between the amount of thermal expansion and the amount of temperature change is expressed as a coefficient with the support rigidity in the horizontal direction or the support rigidity in the vertical direction as a coefficient, the relational expression corresponding to the acquired amount of thermal extension and temperature change is As a result, it is possible to easily estimate the horizontal support stiffness and the vertical support stiffness that have changed over time. Therefore, the thermal displacement amount of the support can be obtained with high accuracy based on the horizontal support stiffness and the vertical support stiffness that have changed over time.

  According to the invention which concerns on Claim 5, the thermal expansion amount acquisition process is set as the structure which acquires thermal expansion amount based on the distortion | strain of a support body measured by the distortion sensor arrange | positioned at the thermal expansion inspection point. The strain sensor may be, for example, a strain gauge that changes the internal resistance value due to the expansion and contraction of the support and measures the strain based on the change in the resistance value. And a thermal expansion amount acquisition process measures the distortion accompanying the thermal deformation of a support body, and can detect the thermal expansion amount of a support body from this distortion.

  According to the invention of claim 6, the thermal displacement amount deriving step is configured to obtain the thermal displacement amount of the support body from the temperature change amount on the sliding surface of the support body generated by the movement of the moving body. The support is thermally expanded and deformed due to thermal effects such as machining of the machine tool and changes in environmental temperature. In particular, the heat generated by the movement of the supporting moving body greatly affects the thermal deformation of the supporting body. Therefore, the thermal effect of the machine tool may be the thermal effect on the sliding surface of the support body on which the moving body moves. Thereby, the deformation | transformation shape of a support body can be linearly approximated as this sliding surface. Therefore, it is possible to calculate a correction value for the sliding surface and perform more appropriate thermal displacement correction.

  According to the seventh aspect of the invention, the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support estimated by the support stiffness estimation means are acquired by the thermal extension amount acquisition means and the temperature change amount acquisition means. It is set as the structure estimated based on the thermal expansion amount and temperature variation of a support. When the horizontal support stiffness and the vertical support stiffness, which greatly affect the posture of the support, change with time, it is difficult to accurately estimate the thermal displacement of the support with only the temperature change of the support. However, as in the present invention, the horizontal support stiffness and the vertical support stiffness that have changed over time based on the amount of thermal expansion and temperature change are once estimated, and the horizontal support stiffness and the vertical support stiffness are estimated. Since the amount of thermal displacement of the support is obtained based on the above, the accuracy of the amount of thermal displacement can be increased, and more accurate thermal displacement correction can be performed.

  Further, the other characteristic portions of the machine tool thermal displacement correction method of the present invention can be similarly applied to the machine tool thermal displacement correction apparatus of the present invention. And the effect in this case also has the same effect as the effect as the thermal displacement correction method for the machine tool.

It is a perspective view showing the whole machine tool composition concerning an embodiment of the invention. It is a block diagram which shows the numerical control apparatus of the machine tool of FIG. FIG. 2 is a schematic side view of a part of the column of the machine tool in FIG. 1, showing a mounting position of a strain sensor and a temperature sensor. It is a figure showing the support rigidity of the ball guide with respect to a column. It is a graph showing the relational expression of the amount of thermal expansion and the amount of change in temperature with the support stiffness as a coefficient for obtaining the support stiffness of the ball guide with respect to the column that has changed over time. It is a figure for demonstrating derivation | leading-out of the thermal displacement amount and calculation of a correction value in the thermal displacement amount derivation | leading-out part and correction value calculation part of a numerical controller.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of a thermal displacement correction method and a thermal displacement correction apparatus for a machine tool according to the present invention will be described with reference to the drawings. As a machine tool, a three-axis machining center will be described as an example. That is, the machine tool is a machine tool having three rectilinear axes (X, Y, Z axes) orthogonal to each other as drive axes. A thermal displacement correction device for a machine tool according to an embodiment will be described with reference to FIGS. FIG. 1 is an overall view of a machine tool. FIG. 2 is a block diagram showing a numerical control device (thermal displacement correction device) of a machine tool. FIG. 3 is a schematic side view of a part of a column of a machine tool.

  As shown in FIG. 1, the machine tool 1 includes a bed 2, a column 10 (corresponding to a “supporting body” of the present invention), a saddle 20 (corresponding to a “moving body” of the present invention), a rotating spindle 30, a table 40, and a numerical control device 50 (corresponding to the “thermal displacement correction device” of the present invention) shown in FIG. 2. The workpiece W is a workpiece to be processed by the machine tool 1. The bed 2 is installed on the floor surface, and a pair of rails 3 extending on the upper surface in the X-axis direction (horizontal direction) and a pair of rails extending in the Z-axis direction (horizontal direction) orthogonal to the X-axis direction. 4 is provided.

  The column 10 has a pair of guide grooves 10a extending in the X-axis direction on the bottom surface, and the pair of guide grooves 10a extends in the X-axis direction so as to be movable in the X-axis direction with respect to the bed 2. The ball guides 11 (corresponding to “rolling guides” and “support points” of the present invention) are fitted on the pair of rails 3, and the bottom surfaces are in close contact with the top surface of the bed 2. As shown in FIG. 3, the ball guide 11 is a guide in which balls 11a that support in a 45 ° direction at four locations, up, down, left and right, are arranged.

  The column 10 slides in the X-axis direction along the upper surface of the bed 2 while being guided by the rail 3 by the rotational drive of an unillustrated X-axis motor fixed to the bed 2. The column 10 is a support that supports the saddle 20 so as to be slidable in the Y-axis direction. The Y-axis direction perpendicular to the X-axis direction and the Z-axis direction is provided on the sliding surface 10b (side surface parallel to the X-axis). A pair of rails 5 extending in the (vertical direction) is provided.

  On the side surface 10c (side surface parallel to the Z-axis) orthogonal to the sliding surface 10b of the column 10, as shown in FIG. 3, one thermal extension inspection point P1 and two temperature inspections are performed in order to perform thermal displacement correction. Points P2 and P2 are set, a strain sensor 12 (corresponding to the “strain sensor” of the present invention) such as a strain gauge is attached to the thermal extension inspection point P1, and a thermistor or the like is attached to the temperature inspection points P2 and P2. A first temperature sensor 13 (corresponding to a “temperature sensor” of the present invention) is attached. The thermal extension inspection point P1 is set in the middle of the ball guide 11 on the pair of rails 3 on the side surface 10c of the column 10, and the temperature inspection points P2 and P2 are set on both sides in the horizontal direction of the thermal extension inspection point P1. ing.

  The strain sensor 12 detects the strain of the column 10 at the installed location and outputs a signal corresponding to the strain to the numerical controller 50. Each first temperature sensor 13 detects the temperature of the column 10 at each installed location, and outputs a signal corresponding to the temperature to the numerical controller 50. Alternatively, the temperature inspection point P2 may be set only on one side in the horizontal direction of the thermal extension inspection point P1, and one first temperature sensor 13 may be attached thereto.

  In order to perform thermal displacement correction, a plurality of (six in this example) second temperature sensors 14 such as thermistors are installed inside the sliding surface 10b of the column 10 as shown in FIG. Each of the second temperature sensors 14 has a reference inspection point Pa0, a first inspection point Pa1, and a second inspection point Pa2 inside the sliding surface 10b of the column 10, and a third inside the back surface 10d of the column 10. The inspection points Pa3, the fourth inspection point Pa4, and the fifth inspection point Pa5 are installed at a total of six locations. The reference inspection point Pa0, the first inspection point Pa1, and the second inspection point Pa2 are about 20% high, about 40% high, and about 80% high with respect to the total height of the column 10 from the bed 2. Is set to The third inspection point Pa3, the fourth inspection point Pa4 and the fifth inspection point Pa5 are also about 20% high, about 40% high and about 80% high with respect to the total height of the column 10 from the bed 2. Is set. Each second temperature sensor 14 detects the temperature of the column 10 at each installed location, and outputs a signal corresponding to the temperature to the numerical controller 50.

  Since this column 10 is thermally deformed by the thermal influence of the machine tool 1 such as heat generation due to internal factors such as machining with tools and rotation of the motor and external factors such as room temperature fluctuations in the installation environment, the numerical control device Reference numeral 50 denotes a correction target for the thermal displacement of the saddle 20 accompanying the thermal deformation of the column 10. Since the ball guide 11 that supports the column 10 is a rolling guide, unlike the sliding guide and the static pressure guide, the ball guide 11 is worn during repeated movements, so that the preload in the guide decreases, and the support rigidity with respect to the column 10 changes with time. Therefore, in this embodiment, the thermal displacement correction is performed by estimating the support stiffness that has changed over time with respect to the column 10 based on the thermal expansion amount and the temperature change amount acquired from the strain sensor 12 and the first temperature sensor 13. Yes. As the rolling guide, in addition to the ball guide 11, for example, a needle guide may be used. Details of the thermal displacement correction will be described later.

  The saddle 20 is formed with a pair of guide grooves 20a extending in the Z-axis direction on the side surface 20b facing the sliding surface 10b of the column 10 and is movable in the Y-axis direction with respect to the column 10 The guide groove 20 a is fitted into a pair of rails 5 extending in the Y-axis direction, and the side surface 20 b is in close contact with the sliding surface 10 b of the column 10. The saddle 20 slides in the Y-axis direction along the sliding surface 10b of the column 10 while being guided by the rail 5 by the rotational drive of a Y-axis motor (not shown) fixed to the column 10. The saddle 20 is a moving body that moves in the Y-axis direction while rotatably supporting the rotary spindle 30 around the axis.

  The rotation spindle 30 is rotatably provided by a spindle motor (not shown) housed in the saddle 20 and supports a tool 31. The tool 31 is fixed to the tip of the rotary spindle 30 and rotates with the rotation of the rotary spindle 30. Further, the tool 31 moves in the X-axis direction and the Y-axis direction with respect to the bed 2 as the column 10 and the saddle 20 move. The tool 31 is, for example, a ball end mill, an end mill, a drill, a tap, or the like.

  The table 40 is provided on a pair of rails 4 extending in the Z-axis direction so as to be movable in the Z-axis direction with respect to the bed 2. The table 40 moves in the Z-axis direction while being guided by the rail 4 by the rotational drive of a not-illustrated Z-axis motor fixed to the bed 2. The table 40 is provided with a jig 41 for fixing the workpiece W on the upper surface, and is a feed base for moving the workpiece W in the Z-axis direction. In such a machine tool 1, the column 10, the saddle 20, and the table 40 are controlled to move to the command position based on the command position by the control device 50. Thereby, the tool 31 is moved relative to the workpiece W for processing.

  The numerical control device 50 is a device that corrects thermal displacement due to the thermal influence of the machine tool 1 and controls each axis motor, main shaft motor, and the like based on NC data. explain. As shown in FIG. 2, the numerical controller 50 includes a control unit 51, a thermal expansion amount acquisition unit 52, a temperature change amount acquisition unit 53, a support stiffness estimation unit 54, a thermal displacement amount derivation unit 55, and a correction. A value calculation unit 56, a correction unit 57, and a memory 58 are included. Here, the control unit 51, the thermal expansion amount acquisition unit 52, the temperature change amount acquisition unit 53, the support rigidity estimation unit 54, the thermal displacement amount derivation unit 55, the correction value calculation unit 56, and the correction unit 57 are individually hardware components. It can be configured by software, or can be configured by software.

  The control unit 51 controls the drive motor 60 such as each axis motor and spindle motor based on the input NC data. As a result, the numerical controller 50 controls the movement of the column 10, the saddle 20, and the table 40, controls the rotation of the rotary spindle 30, and relatively moves the tool 31 that is driven to rotate with respect to the workpiece W. Is going.

  As described above, the numerical control device 50 is a thermal displacement correction device that corrects the thermal displacement due to the thermal effect of the machine tool 1 based on the support stiffness that has changed over time with respect to the column 10. That is, the numerical controller 50 estimates the support stiffness that has changed over time with respect to the column 10, calculates a correction value corresponding to the thermal deformation of the column 10 due to the thermal effect of the machine tool 1 based on the support stiffness, and this correction value. Based on the above, the control of the drive motor 60 by the control unit 51 is corrected to achieve high processing accuracy.

  The thermal extension amount acquisition unit 52 is a thermal extension amount acquisition unit that acquires the thermal extension amount of the thermal extension inspection point P1 before and after thermal deformation of the column 10. The temperature change amount acquisition unit 53 is a temperature change amount acquisition unit that acquires the temperature change amounts of the two temperature inspection points P2 and P2 before and after thermal deformation of the column 10. The support stiffness estimator 54 is a support stiffness estimator that estimates the support stiffness Kh in the horizontal direction and the support stiffness Kv in the vertical direction that have changed over time with respect to the column 10 based on the amount of thermal expansion and the amount of temperature change.

  The thermal displacement amount deriving unit 55 is thermal displacement amount deriving means for obtaining the thermal displacement amount of the column 10 based on the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time with respect to the column 10. The correction value calculator 56 is a correction value calculator that calculates a correction value for the command position of the saddle 20 (corresponding to the “second command position” of the present invention) based on the thermal displacement amount of the column 10. The command position is a value output for controlling each axis motor based on the NC data input by the control unit 51. The correction unit 57 is a correction unit that corrects the command position of the saddle 20 with the calculated correction value.

  The operation of the numerical controller 50 having the above configuration will be described. Here, as shown in FIG. 4, the column 10 is considered to be supported by a horizontal spring 11b having a support rigidity Kh and a vertical spring 11c having a support rigidity Kv by ball guides 11 on a pair of rails 3. . Therefore, in the following description, between the ball guides 11 on the pair of rails 3, it is assumed that the spring force F is applied from the horizontal spring 11 b to both ends of the virtual member 15 having the length L and the cross-sectional area A. A horizontal support stiffness Kh that has changed over time with respect to the column 10 is estimated.

  And since the ball | bowl guide 11 has the ball | bowl 11a arrange | positioned up and down and right and left, it is thought that the influence of the rigidity fall by abrasion of the ball | bowl 11a is received equally to the up and down, right and left. Therefore, it is estimated that the vertical support rigidity Kv with respect to the column 10 that has changed over time is equal to the horizontal support rigidity Kh with respect to the column 10 that has changed over time.

  First, in the thermal elongation amount acquisition step, the thermal elongation amount of the thermal elongation inspection point P1 before and after thermal deformation of the column 10 is acquired. That is, the thermal extension amount acquisition unit 52 inputs a signal of strain ε before and after thermal deformation of the member 15 from the strain sensor 12 attached to the thermal extension inspection point P1, and stores the member 15 stored in advance in the memory 58. Is obtained, and the thermal expansion amount ΔL (= εL) of the member 15 is acquired.

  Further, in the temperature change amount acquisition step, the temperature change amounts of the two temperature inspection points P2 and P2 before and after thermal deformation of the column 10 are acquired. That is, the temperature change amount acquisition unit 53 outputs the signals of the temperatures t1, t2 and t11, t12 before and after thermal deformation of the member 15 from the first temperature sensors 13, 13 attached to the two temperature inspection points P2, P2. Each is input, and the average value ((t1−t2) + (t11−t12)) / 2 of the temperature differences t1−t2 and t11−t12 is acquired as the temperature change amount Δt of the member 15.

  Then, in the support stiffness estimation step, the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time with respect to the column 10 are estimated based on the thermal expansion amount ΔL and the temperature change amount Δt. That is, the support rigidity estimation unit 54 inputs the thermal expansion amount ΔL of the member 15 and the temperature change amount Δt of the member 15 from the thermal expansion amount acquisition unit 52 and the temperature change amount acquisition unit 53 and is stored in the memory 58 in advance. The length (L) of the member 15, the cross-sectional area A of the member 15, and the Young's modulus E of the member 15 are read out, and an expression (5 ) To estimate the support stiffness Kh, and then estimate the support stiffness Kv in the vertical direction with respect to the column 10 which has changed over time.

Here, it will be described that the horizontal support stiffness Kh that has changed with time with respect to the column 10 is expressed by Expression (5). First, from the Hooke's law, the spring force F of the spring 11b is expressed by equation (1) by the horizontal support stiffness Kh that has changed over time with respect to the column 10 and the thermal expansion amount ΔL of the member 15.
F = Kh · ΔL / 2 (1)

Further, from the Hooke's law, the spring force F of the spring 11b is such that the sectional area A of the member 15, the Young's modulus E of the member 15, the thermal expansion amount ΔL of the member 15, and the member 15 before and after thermal deformation of the member 15. It is represented by the formula (2) by the original thermal extension amount ΔLt.
F = A · E (ΔLt−ΔL) / L (2)

Therefore, the horizontal support stiffness Kh that has changed with time with respect to the column 10 is expressed by the equation (3) from the equations (1) and (2).
Kh = 2 · A · E (ΔLt−ΔL) / (L · ΔL) (3)

The original thermal expansion amount ΔLt of the member 15 before and after the thermal deformation of the member 15 is expressed by the equation (4) by the thermal expansion coefficient α of the member 15, the length L of the member 15, and the temperature change amount Δt of the member 15. It is represented by
ΔLt = α · L · Δt (4)

Therefore, the horizontal support stiffness Kh that has changed over time with respect to the column 10 is expressed by the equation (5) from the equations (3) and (4). Since the vertical support rigidity Kv of the column 10 that has changed with time is equal to the horizontal support rigidity Kh of the column 10 that has changed with time, the support rigidity Kh is directly used as the support rigidity Kv.
Kh = 2 · A · E ((α · Δt / ΔL) − (1 / L)) (5)

  Further, the support rigidity estimation unit 54 inputs the thermal expansion amount ΔL of the member 15 and the temperature change amount Δt of the member 15 from the thermal expansion amount acquisition unit 52 and the temperature change amount acquisition unit 53 and is stored in the memory 58 in advance. Based on the graph showing the relational expression between the thermal expansion amount ΔL and the temperature change amount Δt with the support stiffness K as a coefficient as shown in FIG. The stiffness Kv may be estimated.

  That is, the value of the thermal expansion amount ΔL with respect to the temperature change amount Δt tends to increase as the support rigidity K decreases as K2> K0> K1, but by obtaining a graph representing these relational expressions in advance, Based on the obtained thermal expansion amount ΔL of the member 15 and the temperature change amount Δt of the member 15, it is possible to estimate the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time with respect to the column 10.

  Here, the thermal displacement correction in the present embodiment is targeted for correction of the thermal displacement at the tip of the rotary spindle 30 accompanying the thermal deformation of the column 10 due to the thermal effect of the machine tool 1. Therefore, first, in the thermal displacement amount deriving step, the thermal displacement amount of the column 10 is estimated. In other words, the thermal displacement amount deriving unit 55 inputs temperature signals before and after thermal deformation of the column 10 from each second temperature sensor 14 provided at each inspection point Pa0 to Pa6, and is known based on each temperature signal. The amount of thermal displacement of the column 10 is estimated by this method.

  Then, in the correction value calculation step, the correction value is calculated by converting the thermal displacement amount of the column 10 into the thermal displacement amount at the tip of the rotary spindle 30. That is, the correction value calculation unit 56 inputs the horizontal support stiffness Kh and the vertical support stiffness Kv of the column 10 that have changed over time from the support stiffness estimation unit 54, and is a known method based on the support stiffnesses Kh and Kv. Thus, the correction value is calculated by converting the thermal displacement amount of the column 10 into the thermal displacement amount at the tip of the rotary spindle 30. In this way, the numerical control device 50 allows the rotation spindle to accompany the thermal deformation of the column 10 taking into account the horizontal support stiffness Kh and the vertical support stiffness Kv of the column 10 that have changed over time during machining of the machine tool 1. The accuracy of processing is improved by sequentially correcting the thermal displacement at the tip of 30.

  Further, as another example of the thermal displacement correction in the present embodiment, the thermal displacement of the saddle 20 due to the thermal deformation of the column 10 due to the thermal effect of the machine tool 1 is targeted for correction. In order to simplify the explanation, as shown in FIG. 6, the column 10 is assumed to be thermally deformed so as to bend in the Z-axis direction on the table 40 side due to thermal influence. In other words, of the deformation of the column 10 due to thermal influence, the thermal displacement related to the deformed shape projected on the YZ plane is the correction target. Therefore, in the thermal displacement correction, the correction value of the drive shaft in the moving direction (Y-axis direction) of the saddle 20 as a moving body and the drive shaft in the moving direction (Z-axis direction) of the table 40 are calculated.

  Therefore, in the thermal displacement amount derivation step, the thermal displacement amount of the column 10 is obtained based on the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time with respect to the column 10. That is, the thermal displacement amount deriving unit 55 receives the horizontal support stiffness Kh and the vertical support stiffness Kv of the column 10 that have changed over time from the support stiffness estimation unit 54, and is provided at the first inspection point Pa1, for example. The temperature signals before and after the thermal deformation of the column 10 are respectively input from the second temperature sensor 14 and the horizontal thermal displacement amount ΔM1h, the vertical thermal displacement amount ΔM1v, and the temperature change amount at the first inspection point Pa1. Based on the known method, a horizontal thermal displacement amount ΔM1h and a vertical thermal displacement amount ΔM1v at the first inspection point Pa1 are obtained, and the first displacement point Pb1 with respect to the first inspection point Pa1 is specified.

  Similarly, the second displacement point Pb2 with respect to the second inspection point Pa2 is also specified based on the horizontal thermal displacement amount ΔM1h, the vertical thermal displacement amount ΔM1v, and the amount of temperature change at the second inspection point Pa2, for example. . Then, an equation C of a straight line passing through the first displacement point Pb1 and the second displacement point Pb2 is obtained and stored in the memory 58. The above-described thermal displacement amount derivation step is merely an example, and the thermal displacement amount can be derived by a known method, and is not limited to this step.

  In the correction value calculation step, a correction value for the command position of the saddle 20 is calculated. Therefore, first, the correction value calculation unit 56 obtains the command position Pyz of the saddle 20 in the numerical controller 50. Next, the correction value calculation unit 56 reads the equation C of the straight line passing through the first displacement point Pb1 and the second displacement point Pb2 from the memory 58, associates the command position Pyz of the saddle 20 with the equation C, and corrects the correction value. Ry and Rz are calculated. In the correction step, the command position Pyz of the saddle 20 is corrected by the correction values Ry and Rz. That is, the correction unit 57 corrects the command position Pyz output from the control unit 51 to the correction command position PYZ based on the correction values Ry and Rz input from the correction value calculation unit 56.

  Thereby, in addition to the command position of the saddle 20, the command position of the table 40 is also corrected, and the workpiece W is further moved by the correction value Ry in the Y-axis direction and further moved by the correction value Rz in the Z-axis direction. It will be processed at the processing position. In this way, the numerical control device 50 allows the saddle 20 to accompany the thermal deformation of the column 10 taking into account the horizontal support stiffness Kh and the vertical support stiffness Kv of the column 10 that have changed over time during machining of the machine tool 1. By successively correcting the thermal displacement, the processing accuracy is increased.

  As described above, according to the present embodiment, the support rigidity estimation unit 54 calculates the horizontal direction support rigidity Kh and the vertical direction support rigidity Kv with respect to the column 10 as the thermal expansion amount acquisition unit 52 and the temperature change amount. It is estimated based on the thermal expansion amount ΔL and the temperature change amount Δt of the member 15 (column 10) acquired in the acquisition unit 53. When the horizontal support stiffness Kh and the vertical support stiffness Kv that greatly affect the posture of the column 10 change with time, it is possible to estimate the thermal displacement amount of the column 10 with high accuracy only by the temperature change amount Δt of the column 10. Have difficulty.

  However, the support stiffness estimation unit 54 temporarily estimates the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time based on the thermal expansion amount ΔL and the temperature change amount Δt, and the thermal displacement amount deriving unit 55 Based on the horizontal support rigidity Kh and the vertical support rigidity Kv, the horizontal thermal displacement amount and the vertical thermal displacement amount of the column 10 are obtained. Therefore, the accuracy of the horizontal thermal displacement amount and the vertical thermal displacement amount can be increased, and more accurate thermal displacement correction can be performed with a simple configuration.

  Further, according to the present embodiment, the thermal extension amount acquisition unit 52 acquires the thermal extension amount ΔL of the thermal extension inspection point P <b> 1 set in the middle between the two ball guides 11 in the horizontal direction that support the column 10. The temperature change amount acquisition unit 53 acquires the temperature change amount Δt of the temperature inspection points P2 and P2 set on one side or both sides of the thermal extension inspection point P1 in the horizontal direction. The thermal extension amount ΔL at the thermal extension inspection point P1 set in the middle between the two ball guides 11 can improve accuracy in estimating the horizontal support rigidity Kh that has changed over time.

  Further, the temperature change amount Δt of the temperature test points P2 and P2 in the vicinity thereof can also be improved in accuracy in estimating the horizontal support stiffness Kh that has changed over time. In particular, by setting the temperature inspection points P2, P2 on both sides of the thermal extension inspection point P1, it is possible to further increase the estimation accuracy of the horizontal support stiffness Kh that has changed over time.

  Further, according to the present embodiment, the column 10 is supported on the bed 2 by the ball guide 11. The change in the support stiffness with time due to, for example, a decrease in the preload of the ball guide 11 generally changes similarly in the vertical and horizontal directions. Therefore, by estimating the support stiffness Kh in the horizontal direction that has changed over time, the support stiffness Kv in the vertical direction that has changed over time can be easily estimated. Therefore, the thermal displacement amount of the column 10 can be obtained with high accuracy based on the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time.

  Further, according to the present embodiment, the support stiffness estimation unit 54 is based on the relational expression between the thermal expansion amount ΔL and the temperature change amount Δt stored in advance and the acquired thermal extension amount ΔL and the temperature change amount Δt. Thus, the horizontal support rigidity Kh and the vertical support rigidity Kv of the column 10 that have changed over time are estimated. Since the relational expression between the thermal extension amount ΔL and the temperature change amount Δt is expressed by a formula using the horizontal support stiffness Kh or the vertical support stiffness Kv as a coefficient, the acquired thermal extension amount ΔL and temperature change amount Δt By obtaining the relational expression corresponding to, the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time can be easily estimated. Therefore, the thermal displacement amount of the column 10 can be obtained with high accuracy based on the horizontal support stiffness Kh and the vertical support stiffness Kv that have changed over time.

  Further, according to the present embodiment, the thermal displacement amount deriving unit 55 obtains the thermal displacement amount of the column 10 from the amount of temperature change in the sliding surface 10a of the column 10 generated by the movement of the saddle 20. The column 10 is thermally expanded and deformed by the thermal effect of the machine tool 1. In particular, heat generated by the movement of the supporting saddle 20 greatly affects the thermal deformation of the column 10. Therefore, assuming that the thermal effect of the machine tool 1 is the thermal effect on the sliding surface 10a of the column 10 on which the saddle 20 moves, the deformed shape of the column 10 can be linearly approximated as this sliding surface 10a. Therefore, it is possible to calculate a correction value for the sliding surface 10a and perform more appropriate thermal displacement correction.

  In the above-described embodiment, the column 10 is configured to be supported by the ball guide 11 in which the balls 11a that are supported in the 45 ° direction are arranged at four positions, upper, lower, left, and right. If the preload in the guide decreases and the support rigidity with respect to the column 10 changes with time, for example, two balls are supported vertically at the top and bottom and horizontally supported at two positions on the left and right. Even in the case of the ball guide, it is possible to similarly estimate the support stiffness that has changed over time with respect to the column 10.

  In addition, the strain sensor 12 is provided in the middle of the ball guides 11 disposed on the pair of rails 3 so as to acquire the thermal expansion amount. However, the strain sensor 12 has a cross section in a direction orthogonal to the longitudinal direction of the rails 3. Even if it is provided in the central portion, the amount of thermal expansion can be obtained in the same manner, and it is also possible to estimate the support rigidity of the column 10 that has changed over time.

  Further, the thermal displacement correction has been described as being due to thermal deformation of the column 10 as a support. On the other hand, the thermal displacement correction method of the present invention is applied to a member that supports the tool 31 or the workpiece W and causes thermal displacement due to the thermal influence of the machine tool 1, such as the saddle 20 or the table 40. Can do. In addition, the machine tool 1 has been described by taking a three-axis machining center as an example. On the other hand, the machine tool 1 may be, for example, a 5-axis machining center having a rotation axis (A, B axis). Even in such a configuration, the same effect can be obtained.

1: Machine tool, 2: Bed, 3, 4, 5: Rail 10: Column (support), 10b: Sliding surface, 11: Ball guide, 12: Strain sensor, 13: First temperature sensor, 14: First 2 Temperature sensor 20: Saddle (moving body)
30: Rotating spindle 31: Tool 40: Table 41: Jig 50: Control device (thermal displacement correction device) 51: Control unit 52: Thermal elongation acquisition unit 53: Temperature change acquisition unit 54: Support stiffness estimation unit, 55: thermal displacement amount derivation unit, 56: correction value calculation unit, 57: correction unit, 58: memory, 60: drive motor W: workpiece, P1: thermal extension inspection point, P2: temperature inspection point

Claims (7)

A support body that is supported by a base of a machine tool so as to be movable in a horizontal direction, moves relative to the base based on a first command position, and a support rigidity with respect to the base changes with time; In a thermal displacement correction method for a machine tool, comprising: a movable body supported so as to be movable in a vertical direction and moving relative to the support body based on a second command position;
Before and after thermal deformation of the support, a thermal extension amount acquisition step of acquiring a horizontal thermal extension amount of a thermal extension inspection point set on the support;
Before and after thermal deformation of the support, a temperature change acquisition step of acquiring a temperature change of a temperature inspection point set on the support;
A support stiffness estimation step of estimating a horizontal support stiffness and a vertical support stiffness that have changed over time with respect to the support, based on the thermal extension amount and the temperature change amount;
A thermal displacement amount derivation step for obtaining a thermal displacement amount of the support based on the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support; and
A correction value calculating step of calculating a correction value for the second command position based on the thermal displacement amount;
A correction step of correcting the second command position of the movable body by the correction value;
A method for correcting thermal displacement of a machine tool, comprising: In claim 1,
When the support is supported at two support points in the horizontal direction on the base of the machine tool, the thermal extension amount acquisition step is performed at the thermal extension inspection set between the two support points. A horizontal thermal expansion amount of a point is acquired, and the temperature change amount acquiring step acquires a temperature change amount of the temperature inspection point set on one side or both sides of the thermal extension inspection point in the horizontal direction. A thermal displacement correction method for machine tools. In claim 2,
When the support is supported by a rolling guide at the two support points, the support rigidity estimation step is based on the acquired amount of thermal expansion and the amount of temperature change, and the time-dependent change with respect to the support is performed. The horizontal support stiffness is estimated, and the vertical support stiffness is estimated by assuming that the horizontal support stiffness is equal to the vertical support stiffness that has changed over time with respect to the support. Displacement correction method. In claim 2,
The support stiffness estimation step is a time-dependent change with respect to the support, based on a relational expression between the thermal extension amount and the temperature change amount stored in advance and the acquired thermal extension amount and the temperature change amount. A thermal displacement correction method for a machine tool, wherein the horizontal support stiffness and the vertical support stiffness are estimated. In any one of Claims 1-4,
The thermal extension correction method for a machine tool, wherein the thermal extension amount acquisition step acquires the thermal extension amount based on strain of the support measured by a strain sensor arranged at the thermal extension inspection point. . In any one of Claims 1-5,
The thermal displacement amount derivation step includes the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support, and the temperature change on the sliding surface of the support that occurs as the moving body moves. A thermal displacement correction method for a machine tool, wherein the thermal displacement amount of the support is determined from the amount. A support body that is supported by a base of a machine tool so as to be movable in a horizontal direction, moves relative to the base based on a first command position, and a support rigidity with respect to the base changes with time; In a thermal displacement correction device for a machine tool, comprising: a movable body supported so as to be movable in a vertical direction and moving relative to the support body based on a second command position;
Before and after thermal deformation of the support, a thermal extension amount acquisition means for acquiring a horizontal thermal extension amount of a thermal extension inspection point set on the support;
Before and after thermal deformation of the support, a temperature change amount acquisition means for acquiring a temperature change amount of a temperature inspection point set in the support;
A support stiffness estimating means for estimating a horizontal support stiffness and a vertical support stiffness that have changed over time with respect to the support, based on the thermal extension amount and the temperature change amount;
A thermal displacement amount deriving means for obtaining a thermal displacement amount of the support based on the horizontal support stiffness and the vertical support stiffness that have changed over time with respect to the support;
Correction value calculating means for calculating a correction value for the second command position based on the thermal displacement amount;
Correction means for correcting the second command position of the movable body by the correction value;
A thermal displacement correction apparatus for machine tools, comprising:

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