FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13)
1. TITLE OF INVENTION MACHINE TOOL
2. APPLICANT(S)

a) Name : MITSUBISHI HEAVY INDUSTRIES, LTD.
b) Nationality : JAPANESE Company
c) Address : 16-5, KONAN 2-CHOME,
MINATO-KU, TOKYO 1088215, JAPAN
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

TECHNICAL FIELD
The present invention relates to a machine tool that machines an object by moving the object and a tool relative to each other.
BACKGROUND ART
Machine tools of recent years have faced ever-growing demand for higher machining accuracy. The accuracy in machining performed by a machine tool depends significantly on the geometrical precision of the machine tool itself, such as: the smoothness of the moves oi members such as the table on which the workpiece is mounted, and the saddle that supports the main spindle; the straightness of the moves of the above-mentioned members; the parallelism and the squareness of the movement with respect to the center line of the main spindle. To put it differently, the machining accuracy is determined by the precision of the relative positions of the tool and the workpiece to each other while the machining is being performed.
In addition, to achieve high accuracy in machining a workpiece, it is necessary for the machine tool itself to maintain high dimensional precision. What is important to achieve the above-mentioned purpose includes not only the positional precision of such structural bodies that form parts of the machine tool, for example, the table and the saddle, but also such structural bodies that support the above-mentioned members and that serve as the reference for the moves of the above-mentioned members, specifically, the bed and the column. For this reason these structural bodies that form parts of the machine tool are designed so as to be stiff enough not to be deformed by stress or the like, and are specially designed so as not to be affected by vibration.
A machine tool, however, suffers inevitably from the influence of the heat generated by the machine tool, per se, or from the influence of the temperature of its surroundings. Such an influence sometimes leads to thermal expansion of the

structural bodies that form parts of the machine tool, and eventually to the deformation of the machine tool. To be more specific, while a machine tool is in operation, various motors, the tool, the workpiece, and the like produce heat, and the heat thus produced is transferred to the structural bodies. The heat thus transferred causes the thermal deformation of the machine tool. In addition, the temperature of the atmosphere in which the machine tool is set up, and the distribution of such temperature is not uniform from one point to another. Accordingly, the temperature varies depending on the portion of the structural body, i.e., the front, rear, right-hand side, left-hand side, upper or lower portion. Such variation of the temperature within a single structural body results in thermal deformation, such as leaning and warping. Such thermal deformation of the structural body may probably make the main spindle lean to a side and result in an unsatisfactory precision level in machining a workpiece.
For this reason, various measures have been conventionally taken for the accuracy in machining a workpiece, which is affected by the heat generated by the machine tool itself and a temperature environment of the machine tool. Machine tools with such measures to counter the above-mentioned problem are disclosed, for example, in Patent Documents 1 and 2.
Patent Document 1: Japanese Patent Application Publication No. Hei 4-82649 Patent Document 2: Japanese Patent Application Publication No. Hei. 6-39682
DISCLOSURE OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
In a machine tool, multiple structural bodies allow three-dimensional movement of a main spindle that supports the tool, along the axes. The movement of the main spindle sometimes causes deformation of the structural bodies.

For example, in such a machine tool as a horizontal boring machine, a saddle that supports the main spindle is movably supported on a sidewall of a column, which is also capable of moving. Accordingly, particularly in a large-sized machine tool that has a tall column and a heavy saddle, the deformation (leaning) oi the column becomes greater as the saddle moves upwards. Such greater deformation makes it difficult to maintain the straightness with which the saddle moves upwards and downwards. In addition, when the column moves, the movement of the column affects the straightness of a bed that supports the movement. Accordingly, the column moves as experiencing angular deviations (pitch, roll, and yaw), resulting in deformation (leaning) of the column. As a consequence, an error may possibly occur with respect to the leading-end position of the main spindle, thereby resulting in an unsatisfactory precision level in machining a workpiece.
Conventional machine tools, however, have nothing to counter the above-described deformation that derives from the movement of the main spindle in the axial directions, so that the machining of a workpiece may possibly be done with only an unsatisfactory precision level. In order to achieve a higher level of machining accuracy, it is believed that consideration should be given to not only the thermal deformation of the structural bodies caused by the heat produced by the machine tool itself and the temperature environment of the machine tool but also the deformation of the structural bodies caused by the movement of the main spindle in axial directions.
The present invention, which has been made to solve the above-described problem, aims to provide a machine tool capable of preventing the machining accuracy from being lowered even when the column is deformed due to the movement of the main spindle in the axial directions.
MEANS FOR SOLVING THE PROBLEM

A machine tool according to a first invention to solve the above-mentioned problem is a machine tool which moves a tool and an object to be machined relative to each other so as to machine the object the machine tool characterized by comprising:
a saddle rotatably supporting a main spindle having the tool detachably fitted
thereto;
a column movably provided and movably supporting the saddle ;
column-deformation detecting means for detecting deformation of the column
caused by movement of at least one of the saddle and the column; and
correcting means for correcting movement of at least one of the tool and the object
on the basis of detection results of the column-deformation detecting means.
A machine tool according to a second invention to solve the above-mentioned problem is characterized in that the column-deformation detecting means includes:
a portion to be measured which hangs vertically down in the column; and measuring means for measuring the distance between the column and the measured portion.
A machine tool according to a third invention to solve the above-mentioned problem is characterized in that the column-deformation detecting means includes damping means for damping the vibration of the portion.
A machine tool according to a fourth invention to solve the above-mentioned problem is characterized in that the column-deformation detecting means includes:
a container which is attached to the column and which stores a viscous fluid;
a hanging member which hangs vertically down in the column by means of wires;
a first bar-shaped member, the upper end of which is supported by the hanging
member with a spherical bushing, and which includes a portion to be measured;
a second bar-shaped member, the upper end of which is supported by the hanging

member with a spherical busliing, and the lower end of which is immersed in the viscous fluid stored in the container; and
a distance sensor which is attached to the column and which measures the distance from the distance censor to the portion.
A machine tool according to a fifth invention to solve the above-mentioned problem is characterized in that the column-deformation detecting means is provided inside the column.
EFFECTS OF THE INVENTION
Therefore, according to the machine tool of the present invention, even when the column is deformed by the movement oi the main spindle in the axial directions, the lowering of the machining accuracy can be prevented by executing correction on the movement of at least one of the tool and the object to be machined on the basis of the detected deformation amount of the column.
BRIEF DESCRIPTION OF THE DRAWINGS
[Fig. 1] Fig. 1 is a schematic perspective view of a machine tool according to an embodiment of the present invention.
[Fig. 2] Fig. 2 is a general configuration view illustrating a column-deformation detection apparatus.
[Fig. 3] Fig. 3 is a cross-sectional view of a column.
[Fig. 4] Fig. 4 is a schematic view illustrating how the column is deformed in the X-axis direction.

[Fig. 5] Fig. 5 is a schematic view illustrating how the column is deformed in the Z-axis direction,
BEST MODE FOR CARRYING OUT THE INVENTION
A machine tool according to an embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 is a schematic perspective view of a machine tool according to an embodiment of the present invention. Fig. 2 is a general configuration view illustrating a column-deformation detection apparatus. Fig. 3 is a cross-sectional view of a column. Fig. 4 is a schematic view illustrating how the column is deformed in the X-axis direction. Fig. 5 is a schematic view illustrating how the column is deformed in the Z-axis direction. In each of the drawings, the directions indicated by X, Y, and Z (W) represents the orthogonal three axial directions that are orthogonal to one another, and represents, specifically, the front-to-rear direction of the machine tool, the up-and-down direction of the machine tool, and the width direction of the machine tool, respectively. In addition, the embodiment that will be described below is an application of a machine tool according to the present invention to a large-sized horizontal boring machine.
As Fig. 1 shows, a machine tool 1 which is a large-sized horizontal boring machine includes a bed 11 that is fixed to the floor. A left-and-right pair of guide rails 12a and 12b that extend in the X-axis direction are formed in the top surface of the bed 11. A column base 13 is supported by the guide rails 12a and 12b so as to be capable of sliding in the X-axis direction. A hollow column 14 stands on top of the column base 13. Accordingly, the column base 13 (column 14) can be moved in the X-axis direction by driving column driving means that includes such members as an unillustrated column driving motor and an unillustrated column-feeding threaded mechanism.

A left-and-right pair of guide rails 15a and 15b that extend in the Y-axis direction are formed in the front-side surface of the column 14 (a sidewall 14b to be described later). A saddle 16 is supported by the guide rails 15a and 15b so as to be capable of sliding in the Y-axis direction. Accordingly, the saddle 16 can be moved in the Y-axis direction by driving saddle driving means that includes such members as an unillustrated saddle driving motor and an unillustrated saddle-feeding threaded mechanism.
A guide portion 17 is formed in the saddle 16 so as to penetrate the saddle 16 in the Z-axis direction. A ram 18 is supported in the guide portion 17 so as to be capable of sliding in the Z-axis direction. Accordingly, the ram 18 can be moved in the Z-axis direction by driving ram driving means that includes such members as an unillustrated ram driving motor and an unillustrated ram-feeding threaded mechanism.
A main spindle 19 is supported in the ram 18. The main spindle 19 thus supported is capable of rotating and of sliding in the W-axis direction. A tool T that actually performs a predetermined kind of machining is detachably fitted to the leading end of the main spindle 19. Accordingly, the main spindle 19 can be rotated about the W-axis by driving main-spindle rotating means that includes such members as an unillustrated main-spindle rotating motor. In addition, the main spindle 19 can be moved in the W-axis direction by driving main-spindle driving means that includes such members as an unillustrated main-spindle driving motor and an unillustrated main-spindle-feeding threaded mechanism.
A table bed 21 fixed to a portion of the floor is provided at a side of the bed 11. A rear-and-front pair of guide rails 22a and 22b that extend in the Z-axis direction are formed in the top surface of the table bed 21. A table base 23 is supported by the guide rails 22a and 22b so as to be capable of sliding in the Z-axis direction. In addition, in the upper portion of the table base 23, a rotary table 24 is supported so as to be capable of rotating. A workpiece (object to be machined) W is detachably

mounted on the top surface of the rotary table 24. Accordingly, the table base 23 (rotary table 24) can be moved in the Z-axis direction by driving table driving means that includes such members as an unillustrated table driving motor and an unillustrated table-feeding threaded mechanism. In addition, the rotary table 24 can be rotated about the Y-axis by driving table rotating means that includes such members as an unillustrated table rotating motor.
An NC apparatus (correcting means) 50 is provided in the machine tool 1, and controls the machine tool 1 as a whole. The NC apparatus 50 is connected to each of the above-mentioned driving means and oi the above-mentioned rotating means and the like. The NC apparatus 50 thus connected changes in which direction and how fast each of the tool T and the workpiece W moves. The NC apparatus 50 also adjusts how much each of the tool T and the workpiece W moves and rotates. Thus, the NC apparatus 50 performs the positioning control on both the tool T and the workpiece W, and also performs the indexing control on the workpiece W. Accordingly, the tool T and the workpiece W are moved relatively to each other, so that a predetermined shape is machined in the workpiece W.
As Figs. 2 and 3 show, the column 14 includes an upper wall 14a and sidewalls 14b, 14c, 14d, and 14e, and is formed as a hollow structure. Inside the column 14 thus formed, a column-deformation detection apparatus (column-deformation detecting means) 30 is supported so as to be suspended vertically from the bottom surface of the upper wall 14a.
The column-deformation detection apparatus 30 includes two flexible wires 31. The two end portions of each of the wires 31 are attached to the bottom surface of the upper wall 14a. A hanging member 33 is suspended by the wires 31 with passed-through members 32. Suspended bars (a first bar-shaped member and a second bar-shaped member) 35 and 36 are attached to the hanging member 33 respectively with spherical bushings 34. The material and the diameter of each of the wires 31 can be selected arbitrarily. Nevertheless, the wires 31 may preferably

have a stiffness that is low enough to always hang vertically down even when the column 14 is deformed and leans to a side.
Measured members 37 and 38 are provided respectively in the middle portion in the axial direction, oi the suspended bar 35 and at the lower end of the suspended bar 35. Paces to be measured (portions to be measured) 37a and 37b are formed in the measured member 37 while faces to be measured (portions to be measured) 38a and 38b are formed in the measured member 38. Each of the faces to be measured 37a and 38a is formed as a plane that is orthogonal to the X-axis direction while each of the faces to be measured 37b and 38b is formed as a plane that is orthogonal to the Z-axis direction. In addition, a weight 39 is provided at the lower end of the suspended bar 36.
An up-and-down pair of distance sensors (measuring means) 40a and 40b are provided to the internal surface of the sidewall 14b, and are opposed respectively to the faces to be measured 37a and 38a. In addition, an up-and-down pair of distance sensors (measuring means) 41a and 41b are provided to the internal surface of the sidewall 14e, and are opposed respectively to the faces to be measured 37b and 38b. The distance sensors 40a, 40b, 41a, and 41b are non-contact type sensors. The distance sensor 40a always measures the distance from itself to the face to be measured 37a, and the distance sensor 40b always measures the distance from itself to the face to be measured 38a. In addition, the distance sensor 41a always measures the distance from itself to the face to be measured 37b, and the distance sensor 41b always measures the distance from itself to the face to be measured 38b. Moreover, the NC apparatus 50 is connected to the distance sensors 40a, 40b, 41a, and 41b. The distances measured by the distance sensors 40a, 40b, 41a, and 41b (the detection results) are inputted into the NC apparatus 50.
An oil pan (container) 42 is supported on the internal surface of the sidewall 14d with an unillustrated supporting member. Oil 43, which is a highly viscous fluid, is stored in the oil pan 42, and the suspended bar 36 is immersed in the oil 43 stored in

the oil pan 42. Note that the oil pan 42 and the oil 43 together form damping means.
Accordingly, the NC apparatus 50 calculates out the amount of X-axis-direction deformation (the amount of X-axis-direction leaning) of the column 14 from the difference between the distance from the distance sensor 40a to the face to be measured 37a, which is measured by the distance sensor 40a, and the distance from the distance sensor 40b to the face to be measured 38a, which is measured by the distance sensor 40b. In addition, the NC apparatus 50 calculates out the amount of Z-axis-direction deformation (the amount of Z-axis-direction leaning) of the column 14 from the difference between the distance from the distance sensor 41a to the face to be measured 37b, which is measured by the distance sensor 41a, and the distance from the distance sensor 41b to the face to be measured 38b, which is measured by the distance sensor 41b. Then, the NC apparatus 50 performs the positioning control on the tool T and the workpiece W on the basis of the amount of X-axis-direction deformation and the amount of Z-axis-direction deformation of the column 14 thus calculated out. The positioning control is performed for the purpose of correcting the driving of each of the driving means so that a predetermined shape is machined in the workpiece W.
In addition, even when the suspended bars 35 and 36 are made to vibrate together with the hanging member 33 by such causes as disturbance vibration, the vibration of the suspended bar 36 is quickly damped by the oil 43 stored in the oil pan 42. Accordingly, the vibration of the suspended bar 35 is also damped in an instant.
When a workpiece W is machined by the machine tool 1, the workpiece W is firstly mounted on the top surface of the rotary table 24, and then the table base 23 is moved in the Z-axis direction so that the workpiece W is moved to the machining position. Then, while the tool T is being rotated by the main spindle 19, the following motions of the members are selectively carried out as needed: the column 14 is moved in the X-axis direction; the saddle 16 is moved in the Y-axis direction;

the ram 18 is moved in the Z-axis direction; and the main spindle 19 is moved in the W-axis direction. Besides, the rotary table 24 is rotated as necessary to perform indexing rotation on the workpiece W. In this way, the workpiece W is machined by the tool T.
As described above, while the workpiece W is being machined, the tool T has to be moved in at least one of the X-axis, Y-axis, Z-axis, and W-axis directions. Deformation of the column 14 is more likely to occur particularly when the tool T is moved in the X-axis direction and/or the Y-axis direction than in the other cases. As the column 14 is deformed, an error of the leading-end position of the main spindle 19 may probably occur, resulting in lower machining accuracy.
Specifically, the machine tool 1 represented by a horizontal boring machine has a structure that the saddle 16 rotatably supporting the main spindle 19 is supported by the sidewall 14b of the column 14. With this structure, a movement of the saddle 16 in the Y-axis direction makes the column 14 lean in the X-axis direction, with the joint point of the column base 13 and the column 14 as the reference position, as shown in Fig. 4. When the machine tool 1 is a large-sized one in particular, the column 14 becomes taller and the saddle 16 becomes heavier. Accordingly, as the saddle 16 moves upwards, the deformation of the column 14 becomes greater. As a consequence, the straightness of the up-and-down movement of the saddle 16 cannot be maintained.
In addition, when the column 14 (column base 13) is moved, on the bed 11, in the X-axis direction, such a movement of the column 14 affects the straightness of the bed 11 and the guide rails 12a and 12b. Accordingly, the column 14 moves experiencing angular deviations (pitch, roll, and yaw). As a consequence, the column 14 leans in the Z-axis direction with the joint point between the column base 13 and the column 14 serving as the reference, as Fig. 5 shows.

Moreover, as Fig. 3 shows, the sidewalls 14b and 14d of the column 14 differ from each other in the wall thicknesses, since the guide rails 15a and 15b are formed in the sidewall 14b. The thick-walled sidewall 14b and the thin-walled sidewall 14d differ from each other in the heat capacity. Accordingly, when heat is produced in such members as the driving means, the rotating means, the tool T, and the workpiece W, and/or when a change occurs in the temperature of the atmosphere in which the machine tool 1 is set up, the sidewall 14d with a small heat capacity is more likely to be thermally deformed than the sidewall 14b with a large heat capacity. As a consequence, the column 14 leans in the X-axis direction.
The occurrence of the deformation of the column 14 in X-axis direction and/or in the Z-axis direction may probably cause an error of the leading-end position of the main spindle 19, resulting in a lower accuracy in machining a workpiece W. Accordingly, in the machine tool 1, the column-deformation detection apparatus 30 is provided in the column 14 so as to always detect directly the deformation of the column 14 occurring in a complex way.
Specifically, suppose a case where the saddle 16 is moved in the Y-axis direction and the column 14 is thus deformed in the X-axis direction, and a case where the heat produced by the machine tool 1 itself and the temperature change in the atmosphere in which the machine tool 1 is set up cause thermal deformation of the column 14 in the X-axis direction. In these cases, the distance from the distance sensor 40a to the face to be measured 37a is measured by the distance sensor 40a, and the distance from the distance sensor 40b to the face to be measured 38a is measured by the distance sensor 40b. Then, the measured distances thus obtained are inputted into the NC apparatus 50, and the difference between the measured distances thus inputted is calculated out by the NC apparatus 50. Subsequently, on the basis of the calculated-out difference between the measured distances, the NC apparatus 50 calculates out the amount of deformation of the column 14 in the X-axis direction. On the basis of this deformation amount thus calculated out, the NC apparatus 50 corrects the driving of each driving means and thus performs the positioning control

on the tool T and on the workpiece W.
In addition, suppose a case where the column 14 is moved in the X-axis direction and the column 14 is thus deformed in the Z-axis direction. In this case, firstly, the distance from the distance sensor 41a to the face to be measured 37b is measured by the distance sensor 41a, and the distance from the distance sensor 41b to the face to be measured 38b is measured by the distance sensor 41b. Then, the measured distances thus obtained are inputted into the NC apparatus 50, and the difference between the measured distances thus inputted is calculated out by the NC apparatus 50. Subsequently, on the basis of the calculated-out difference between the measured distances, the NC apparatus 50 calculates out the amount of the deformation of the column 14 in the Z-axis direction. On the basis of this deformation amount thus calculated out, the NC apparatus 50 corrects the driving of each driving means and thus performs the positioning control on the tool T and on the workpiece W.
As has been described thus far, according to the machine tool of the present invention, when the workpiece W is machined by the tool T, the column-deformation detection apparatus 30 detects the deformation of the column 14 in the X-axis direction and in the Z-axis direction caused by the movements of the column 14 and the saddle 16. After that, on the basis of the detection results, the NC apparatus corrects the driving of each driving means and thus performs the positioning control on the tool T and the workpiece W. Accordingly, the lowering of the machining accuracy can be prevented.
In addition, in the column-deformation detection apparatus 30, the upper ends of the suspended bars 35 and 36 are supported by the hanging member 33 respectively with the spherical bushings 34 while the hanging member 33 hangs down with the wires 31. Besides, the lower end oi the suspended bar 36 is immersed in the oil 43 stored in the oil pan 42. Accordingly, even when disturbance vibration occurs in the column 14, the vibration of the suspended bars 35 and 36 can be damped in a

short time, and thus the suspended bars 35 and 36 can be held in a stationary state in a vertical direction. As a consequence, the distance sensors 40a, 40b, 41a, and 41b can measure, directly, quickly, and correctly, their respective distances to the corresponding faces to be measured 37a, 37b, 38a, and 38b of the measured members 37 and 38. Moreover, provision of the column-deformation detection apparatus 30 inside the column 14 results in space saving. Accordingly, it is not necessary to make the size of the machine tool 1 unnecessarily large.
INDUSTRIAL APPLICABILITY
The present invention is applicable to a thermal-deformation preventing structure configured to prevent the machining accuracy from being lowered by the thermal deformation of the column fixed in a machine tool such as a machining center.

WE CLAIM:
[1] A machine tool which moves a tool and an object to be machined relative to each other so as to machine the object, the machine tool characterized by comprising:
a saddle rotatably supporting a main spindle having the tool detachably fitted thereto;
a column movably provided and movably supporting the saddle; column-deformation detecting means for detecting deformation of the column caused by movement of at least one of the saddle and the column; and
correcting means for correcting movement of at least one of the tool and the object on the basis of detection results of the column-deformation detecting means.
[2] The machine tool according.to claim 1 characterized in that the column-deformation detecting means includes: ' a portion to be measured which hangs vertically down in the column; and measuring means for measuring the distance between the column and the measured portion.
[3] The machine tool according to claim 2 characterized in that the column-deformation detecting means includes damping means for damping the vibration of the portion.
[4] The machine tool according to claim 1 characterized in that the column-deformation detecting means includes:
a container which is attached to the column and which stores a viscous fluid; a hanging member which hangs vertically down in the column by means of wires; a first bar-shaped member the upper end of which is supported by the

hanging member with a spherical bushing, and which includes a portion to
be measured;
a second bar-shaped member, the upper end of which is supported by the
hanging member with a spherical bushing, and the lower end of which is
immersed in the viscous fluid stored in the container; and
a distance sensor which is attached to the column and which measures the
distance from the distance censor to the portion.
[5] The machine tool according to any one of claims 1 to 4 characterized in that the column-deformation detecting means is provided inside the column.