JP7510259B2 - Thermal displacement countermeasure structure for machine tool feed shaft - Google Patents

Description

The present invention relates to a structure for preventing thermal displacement of the feed shaft of a machine tool, and in particular to a structure that uses a low thermal expansion material to prevent thermal displacement of a structure caused by a heat source such as the spindle of a machine tool.

In conventional machine tools, heat sources such as heat from the driven motor and frictional heat from the rotation of the bearings cause the expansion of structures such as the spindle head, displacing the mechanical position of the tool at the tip of the spindle, resulting in a shift in the relative position between the tool and the workpiece, making it difficult to perform high-precision machining. In order to eliminate the displacement of the mechanical position of the tool due to the thermal expansion of the spindle head, etc., the machine is warmed up before machining the workpiece, and machining, dimensional measurement, and correction are repeated (see, for example, Patent Document 1), or a displacement sensor or temperature sensor is provided, and the command position by the NC is corrected based on the detected displacement and temperature (see, for example, Patent Document 2).

JP 2012-091261 A Japanese Patent Application Laid-Open No. 10-138091

However, in the conventional example in which a warm-up operation is performed as described in the above-mentioned Patent Document 1, not only does it require the operator to be highly skilled, but there is also the problem that it is not possible to expect a reduction in processing time. In addition, in the conventional example in which the command position by the NC is corrected based on the detection results by the sensor as described in Patent Document 2, a complex system is used and multiple coefficients must be calculated from the measurement results, which requires complex processing by the NC.

The present invention was made in light of the above-mentioned circumstances, and its purpose is to provide a technology that can reduce warm-up operations and shorten processing time as a countermeasure against thermal displacement of the feed axes of machine tools, and that uses a simple mechanism to enable accurate detection of the axis position without the need for complex calculations or measurements.

As a result of extensive research into countermeasures against thermal displacement of the feed axes of the above-mentioned machine tools, the inventors have come up with a new and useful idea that uses a simple mechanism and does not require complex calculations or measurements, making the detection section of the position detector that detects the axis position less susceptible to the effects of thermal displacement, thereby reducing warm-up operations and shortening machining times.

That is, the thermal displacement countermeasure structure for the feed shaft of a machine tool according to the present invention comprises a structure made of a metal material having a predetermined thermal expansion coefficient and capable of moving the feed shaft in the axial direction while holding the feed shaft, a low thermal expansion material formed in a long plate shape and having a thermal expansion coefficient lower than the thermal expansion coefficient of the metal material in the longitudinal direction of the long plate and having tensile rigidity in the longitudinal direction, the low thermal expansion material being interposed so that the longitudinal direction is along the axial direction of the structure, and a position detector, wherein a detection portion of the position detector is fixed to the low thermal expansion material, and a mounting bracket is provided for fixing one end side of the low thermal expansion material in the longitudinal direction to the structure, and the mounting bracket is structured to be easily elastically deformed in the axial direction,
a means for fixing an end portion of the low thermal expansion material opposite to the one end portion in the longitudinal direction to the structure, the means being provided separately from the mounting metal fitting;
The low thermal expansion material is characterized in that it is capable of absorbing relative thermal displacement between the low thermal expansion material and the structure.
In this way, the low thermal expansion material is made of a material that has both a low thermal expansion coefficient and rigidity in the length direction (thermal expansion direction), such as CFRP.

The present invention provides a technology that makes it possible to reduce the warm-up period and shorten processing time by designing the detection section of the shaft position detector to be less susceptible to thermal displacement, and that uses a simple mechanism to enable accurate shaft position detection without the need for complex calculations or measurements.

1A is an overall view of the thermal displacement countermeasure structure for the feed axis of a machine tool according to a first embodiment of the present invention, including a spindle head, which is a structure capable of holding a spindle as a feed axis so as to be rotatable at high speed while moving it in the axial direction, a low thermal expansion material, a position detector, and mounting hardware; FIG. 1B is an enlarged view of the end of the spindle head to which the low thermal expansion material is fixed; FIG. 1C is an enlarged view of the end of the spindle head to which the low thermal expansion material is fixed; and FIG. 1D is an enlarged view of the fixing part of the detection part of the position detector to the spindle head. FIG. 1 is a diagram showing the main components of a spindle head, a low thermal expansion material, and a mounting bracket, as well as how each component is assembled together, in a thermal displacement countermeasure structure for a feed axis of a machine tool according to a first embodiment of the present invention, in which (a) is an enlarged view of the spindle head, (b) is a diagram showing the front side of the mounting bracket, (c) is a diagram showing the back side of the mounting bracket, (d) is a diagram showing the state in which the detection unit of a position detector is attached to the front side of the mounting bracket and is also attached to the low thermal expansion material for ease of understanding (note that in reality, the detection unit and a linear scale are combined to form the position detector, and the detection unit is not removed and attached to the mounting bracket alone), (e) is a diagram showing the assembly shown in (d) fixed to the spindle head, (f) is an enlarged view of the mounting bracket and position detector in (e), and (g) is an enlarged view of the end of the spindle head in (e). 1A and 1B are diagrams for explaining the effect of a thermal displacement countermeasure structure for a feed axis of a machine tool according to a first embodiment of the present invention, in which (a) is an overall view, (b) is an enlarged view showing the structure in its natural state, and (c) is an enlarged view illustrating the case in which the spindle head is extended due to thermal expansion. 5A and 5B are diagrams showing main parts of a thermal displacement countermeasure structure for a feed axis of a machine tool according to a second embodiment of the present invention, in which (a) is a front view of the mounting bracket, (b) is an oblique view of the mounting bracket, (c) is an oblique view of the mounting bracket from the front side, (d) is an oblique view of the state in which the mounting bracket is used to attach CFRP material and the detection unit of the position detector to the spindle head, (e) is an enlarged view of the mounting bracket and position detector in (d), and (f) is an enlarged view of the end of the spindle head in (d).

1 is a diagram for explaining a thermal displacement countermeasure structure for a feed axis of a machine tool according to a first embodiment of the present invention, in which (a) is an overall view of the thermal displacement countermeasure structure including the Z axis of the machine tool, a low thermal expansion material, a position detector, and mounting hardware, (b) is an enlarged view of the end of the spindle head to which the low thermal expansion material is fixed, (c) is an enlarged view of the end of the spindle head to which the low thermal expansion material is fixed, and (d) is an enlarged view of the fixing part of the detection part of the position detector to the spindle head. First, in order to facilitate understanding of the present invention, the schematic configuration of a feed axis (Z axis) as an example to which the present invention is applied will be described with reference to the above FIG. 1(a). A structure (spindle head) 10 that houses a spindle 12 so that it can rotate at high speed is made of a metal material having a predetermined thermal expansion coefficient, and is driven in the (Z) axis direction (up and down in the figure) by the axis drive part (linear motor, magnet unit and coil unit) 14. In addition, the spindle head 10 and the shaft drive unit 14 slide in the (X) axis direction (left and right direction in the figure) on the structure (part of the column) 18 by the saddle (carrier) 16. Furthermore, the structure (part of the column) 18 can be configured to be movable in the Y axis direction, but the description and illustration of this will be omitted. In this configuration, the spindle head 10 is driven in the (Z) axis direction (up and down direction in the figure), and the tool 12A attached to the tip of the spindle 12 makes cuts in the workpiece (not shown). Here, a feedback position detector 20 is used to control the spindle head 10 in the (Z) axis direction, and the linear scale 22 of this position detector 20 is fixed to the saddle 16 side, and the detection unit 24 is fixed to the spindle head 10 side. In addition, 26 is an LM guide, and 28 is an LM block.

However, in the above configuration, heat sources such as heat from the motor (not shown) that rotates the spindle 12 at high speed and frictional heat caused by the rotation of the internal bearings (not shown) cause thermal expansion, particularly at the tip side of the spindle head 10, which is a structure. Since the position of the shaft is fed back using position information detected by a feedback position detector, thermal displacement occurring between the detection unit of the position detector and the tool causes a shift in the relative position between the tool 12A at the tip of the spindle 12 and the workpiece (not shown), making it difficult to perform high-precision machining. For this reason, in the past, measures were taken such as warming up the machine to eliminate the effects of thermal expansion before machining, measuring each time with a temperature sensor or the like in a complex system configuration, and making corrections taking the results into account. Therefore, in order to enable accurate detection of the machining position using a simple mechanism without the need for complex calculations or measurements, the heat countermeasure structure of the present invention was applied.

Figure 2 shows the main components of the spindle head, low thermal expansion material, and mounting bracket in the thermal displacement prevention structure for the feed axis of a machine tool according to the first embodiment of the present invention, as well as how each part is assembled together, where (a) is an enlarged view of the spindle head, (b) is a view showing the front side of the mounting bracket, (c) is a view showing the back side of the mounting bracket, (d) is a view showing the detection part of the position detector attached to the front side of the mounting bracket and also attached to the low thermal expansion material for ease of understanding (note that in reality, the head part and linear scale are combined to form the position detector, and the detection part is not removed and attached to the mounting bracket alone), (e) is a view of the assembly shown in (d) fixed to the spindle head, (f) is an enlarged view of the mounting bracket and the detection part of the position detector in (e), and (g) is an enlarged view of the end of the spindle head in (e). That is, the structure for preventing thermal displacement of the feed axis of a machine tool according to a first embodiment of the present invention (not shown in its entirety, see FIG. 1(a) for part of its column, etc.) comprises a spindle head 10 which is a structure for housing a spindle 12 to enable high speed rotation and is made of a metal material having a prescribed thermal expansion coefficient, CFRP material 30 which serves as a low thermal expansion material and has a thermal expansion coefficient lower than that of the metal material and is inserted along the axial direction of the spindle head 10, and a position detector 20, and a mounting bracket 40 is provided which connects a detection unit 24 of the position detector, the low thermal expansion material (CFRP material 30), and the spindle head 10, and a relatively thin portion 40A of the mounting bracket 40 is elastically deformed to absorb relative thermal displacement between the low thermal expansion material (CFRP material 30) and the spindle head 10. That is, in the first embodiment of the present invention, as shown in FIG. 1(a), a long, L-shaped CFRP material 30 [see FIG. 2(d)] as a low thermal expansion material having a lower thermal expansion coefficient than that of the spindle head 10 is inserted along the (Z) axial direction (the up-down direction in the figure) at the tip side of the spindle head 10 made of a metal material having a predetermined thermal expansion coefficient as described above, and a mounting bracket 40 is provided to connect the detection unit (head portion) 24 of the position detector 20, the low thermal expansion (CFRP) material 30, and the spindle head 10, and a relatively thin portion 40A [see FIGS. 2(b) and 2(c)] of the mounting bracket 40 is elastically deformed to absorb relative thermal displacement between the low thermal expansion (CFRP) material 30 and the spindle head 10. That is, by connecting the end of the spindle head 10 and the detection unit 24 of the position detector with a low thermal expansion (CFRP) material 30, thermal displacement occurring between the tip of the tool 12A and the detection unit 24 of the position detector is suppressed. In addition, the thermal displacement of the spindle head 10 caused by the heat of the spindle 12 and the relative displacement between the low thermal expansion (CFRP) material 30 are absorbed by a specially shaped mounting bracket 40.

Next, the heat countermeasure structure according to the first embodiment of the present invention will be described in more detail.
[composition]
In the heat countermeasure structure according to the first embodiment of the present invention, a groove 10h [see FIG. 2(a)] is formed in the center (the center in the thickness direction of the spindle head 10) of the end surface of the position detection side (the right side in the example shown in FIG. 1(a)) of the approximately half of the tip side of the spindle head 10, and a CFRP material 30 as a long plate-shaped low thermal expansion material is inserted into this groove 10h. Then, the rear side of a mounting metal fitting 40 having a shape shown in FIG. 2(b)(c) is attached so as to straddle the CFRP material 30 as shown in FIG. 2(d). In addition, both sides of the rear side of this mounting metal fitting 40 are attached to the above-mentioned end surface of the spindle head 10 as shown in FIG. 1(d) and FIG. 2(e). Furthermore, the detection unit (head unit) 24 of the position detector 20 is placed and attached to the center of the upper surface of the mounting metal fitting 40 as shown in FIG. 1(a)(d).

[Mounting bracket shape]
2B and 2C, the mounting bracket 40 is generally formed in a substantially rectangular flat plate shape, and has a mounting surface 42 on which the detection unit (head unit) 24 of the position detector 20 is placed and attached, and screw holes 42a, 42b at the center of the longitudinal direction on the top (front) side. Also, mounting surfaces 44, 44 for the spindle head 10 and two screw holes 44a, 44b are provided on both longitudinal sides of the bottom (back) side, and a mounting surface 46 for the CFRP material 30 and five screw holes 46a are provided at the center. Also, the mounting bracket 40 has notches (constrictions) 48A, 48B formed in the illustrated shape penetrating the thickness direction, so that relatively thin portions 40A are formed at both longitudinal ends.

[How to install the position detector, mounting bracket, and CFRP material]
As shown in Fig. 2(d), the CFRP material 30 is in the form of a long plate with an end 30e bent at a right angle to have a generally L-shape, and fastening holes 30a, 30a are formed in the bent end 30e for corresponding locations on the spindle head 10, and a fastening hole 30c for the spindle head 10 is also formed in the vicinity of the bent end 30e. First, as shown in Fig. 2(d), a mounting bracket 40 on which the detection unit (head unit) 24 of the position detector is placed and fixed is attached to the opposite end of the CFRP material 30. The CFRP material 30 (assembly) with the mounting bracket 40 attached in this manner is inserted into the spindle head 10 in which corresponding fastening holes are formed, as shown in Fig. 2(e), and is fixed by bolts to the fastening holes 30a, 30a and fastening hole 30c as shown in Fig. 2(g). The mounting bracket 40 is attached to the spindle head 10 through two screw holes 44a, 44b on each of the mounting surfaces 44, 44 to the spindle head 10. As shown in Fig. 1(d) and Fig. 2(f), the detection section (head section) 24 of the position detector 20 is placed and attached to the center of the upper surface of the mounting bracket 40, and as shown in Fig. 2(g), it is fixed by bolts. In this embodiment, the low thermal expansion material (CFRP material 30) is formed into a substantially L-shape, but it does not necessarily have to be L-shaped, and other shapes such as a flat plate shape may be used as long as the end can be firmly fixed to the structure (spindle head 10).

Also, as shown in Figures 1(b) and (c), a groove 10h for mounting the CFRP material 30 is formed on the position detection side of the spindle head 10 before the CFRP material 30 is attached, and an assembly in which a mounting bracket 40 carrying the head portion 24 of the position detector is further attached to the CFRP material 30 is embedded and inserted into the groove 10h of the spindle head 10 as shown in Figure 1(c), thereby completing the heat countermeasure structure according to an embodiment of the present invention.

[Action and Effect]
3A and 3B are diagrams for explaining the function and effect of the thermal displacement countermeasure structure for the feed axis of the machine tool according to the first embodiment of the present invention, in which (a) is an overall view, (b) is an enlarged view showing the natural state, and (c) is an enlarged view showing the case where the spindle head is thermally expanded and extended. In the configuration described above with reference to Figs. 1 and 2, the spindle side of the spindle head 10, which is a structure, thermally expands due to heat sources such as heat generated by a motor (not shown) that rotates the spindle 12 at high speed and frictional heat generated by the rotation of an internal bearing (not shown). However, since the CFRP material 30, which is a low thermal expansion material, has a thermal expansion coefficient smaller than that of the spindle head 10, the position of the detection part (head part) 24 of the position detector mounted on the central part of the upper surface of the mounting bracket 40 attached to the base end side of the CFRP material 30 is not easily affected by the thermal expansion of the spindle side of the spindle head 10. The mounting surfaces 44, 44 of the mounting bracket 40 to the spindle head 10 are pulled in the thermal expansion direction, so that the thin portion 40A is elastically deformed to absorb the relative thermal displacement between the CFRP material 30 and the spindle head 10. That is, the mounting bracket 40 is a member that has anisotropy of elastic deformation, that is, elastic deformation only in its longitudinal direction (in the thermal expansion direction when mounted to the spindle head 10) due to the notches (constrictions) 48A, 48B. In this embodiment, the mounting bracket 40 is formed in the shape shown in the figure, but is not limited to this shape, and the mounting bracket 40 may have another shape as long as it has a shape that is easy to elastically deform only in its longitudinal direction (in the thermal expansion direction when mounted to the spindle head 10) due to the notches (constrictions) or the like, as shown in the second embodiment (modified example) below.

[Modification]
4A and 4B are diagrams showing the main parts of the thermal displacement countermeasure structure for the feed shaft of a machine tool according to the second embodiment (modification) of the present invention, where (a) is a front view of the mounting bracket, (b) is a perspective view of the mounting bracket, (c) is a perspective view of the mounting bracket from the front side, (d) is a perspective view of the state in which the CFRP material and the position detector are attached to the spindle head using the mounting bracket, (e) is an enlarged view of the mounting bracket and the position detector in (d), and (f) is an enlarged view of the end of the spindle head in (d). That is, in the thermal displacement countermeasure structure for the feed shaft of a machine tool according to the second embodiment of the present invention, a mounting bracket 400 having a shape as shown in Fig. 4A, (b), and (c) is used. The mounting bracket 400 has a notch 408A cut in the thickness direction from the front side over the entire width, and a notch 408B cut in the thickness direction from the back side over the entire width. Therefore, by using this mounting bracket 400, it is possible to absorb the relative thermal displacement of the CFRP material 30, which is a low thermal expansion material, and the spindle head 10 serving as the feed shaft head portion by elastically deforming the relatively thin portions shown in Figures 4(a) and (c). Note that this mounting bracket 400 is not used to place and attach the detection portion (head portion) 24 of the position detector 20, but is used to fix one end side 30k of the CFRP material 30 to the spindle head 10 as shown in Figure 2(e), and the fixing holes 402, 404 are used to fix the one end side 30k of the CFRP material 30 to the mounting bracket 400 with a bolt or the like, and the fixing holes 406A, 406B are used to fix the one end side 30k of the CFRP material 30 to the spindle head 10 with a bolt or the like as shown in Figure 4(e). That is, in this embodiment, the detection portion (head portion) 24 of the position detector 20 is placed and attached directly to the CFRP material 30 without using the mounting bracket 400 .

As described above, the thermal displacement countermeasure structure for the feed shaft of a machine tool according to the first embodiment of the present invention includes a feed shaft structure (spindle head) made of a metal material having a predetermined thermal expansion coefficient, a low thermal expansion material having a thermal expansion coefficient lower than that of the metal material and inserted along the axial direction of the feed shaft, and a mounting bracket for fixing the detection part of the shaft position detector and one end side of the low thermal expansion material to the structure, characterized in that the mounting bracket has a thin portion to make the detection part of the position detector less susceptible to the effects of thermal displacement and to absorb the relative thermal displacement between the low thermal expansion material and the feed shaft head part. On the other hand, in the thermal displacement countermeasure structure for the feed shaft of a machine tool according to the second embodiment of the present invention, the detection part of the position detector is placed and attached directly to the low thermal expansion material without the use of a mounting bracket. As a general concept including both of these embodiments, the present invention is defined as a thermal displacement countermeasure structure for a feed shaft of a machine tool, which includes a feed shaft structure (spindle head) made of a metal material having a predetermined thermal expansion coefficient, a low thermal expansion material having a thermal expansion coefficient lower than that of the metal material and inserted along the axial direction of the feed shaft head, and a mounting bracket capable of absorbing the relative thermal displacement between the low thermal expansion material and the feed shaft head, which makes the detection unit of the position detector less susceptible to the thermal displacement of the head, and makes it possible to absorb the relative thermal displacement between the low thermal expansion material and the feed shaft head by providing a mounting bracket that is easily deformed in the axial direction of the head.

In the first and second embodiments described above, CFRP material is used as the low thermal expansion material, but any material other than CFRP, such as Super Invar, may be used as long as it has a thermal expansion coefficient lower than that of the feed shaft structure (spindle head) made of a material having a predetermined thermal expansion coefficient. However, it is preferable to use a material that has both a low thermal expansion coefficient and rigidity in the length direction (thermal expansion direction). In other words, since it is fixed to the feed shaft structure (spindle head), it would be meaningless if it were to stretch mechanically by being pulled by the feed shaft structure (spindle head), so it is preferable to use a material that has mechanical rigidity (strength) in the pulling direction.

10 Structure (spindle head), 12 Spindle, 12A Tool, 14 Axis drive unit, 16 Saddle (carrier), 18 Structure (column), 20 Position detector, 22 Linear scale, 24 Detector, 26 LM guide, 28 LM block, 30 Low thermal expansion material (CFRP material), 40 Mounting bracket, 40A Thin section

Claims (1)

A thermal displacement countermeasure structure for a feed shaft of a machine tool, comprising: a structure made of a metal material having a predetermined coefficient of thermal expansion, capable of moving the feed shaft in the axial direction while holding the feed shaft; a low thermal expansion material formed in a long plate shape, having a coefficient of thermal expansion in the length direction of the long plate lower than the coefficient of thermal expansion of the metal material, and having tensile rigidity in the length direction, the low thermal expansion material being interposed so that the length direction is along the axial direction of the structure; and a position detector, wherein a detection unit of the position detector is fixed to the low thermal expansion material, and a mounting bracket is provided for fixing one end side of the low thermal expansion material in the length direction to the structure, the mounting bracket being structured to be easily elastically deformed in the axial direction,
a means for fixing an end portion of the low thermal expansion material opposite to the one end portion in the longitudinal direction to the structure, the means being provided separately from the mounting metal fitting;
A thermal displacement countermeasure structure for a feed shaft of a machine tool, characterized in that the structure is capable of absorbing relative thermal displacement between the low thermal expansion material and the structure.

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