Thermal displacement correction device and thermal displacement correction method for machine tool

Abstract

To exactly calculate a thermal displacement correction amount despite that a reference point of thermal contraction changes during rotation restriction of a main spindle, in performing correction.SOLUTION: A thermal displacement correction device 20 of an NC vertical type machining center 1 comprises: temperature sensors 8, 9 and a temperature measuring unit 21 that can measure temperatures of a housing supporting a main spindle and the main spindle; a correction amount calculation unit 22 for calculating a thermal displacement correction amount by estimating thermal displacement of the main spindle, from the temperature information measured with the temperature measuring unit 21; and an NC device 10 which calculates an axis correction movement amount of a feed shaft of the main spindle on the basis of the thermal displacement correction amount estimated by the correction amount calculation unit 22, and outputs a correction command to a correction object shaft. The correction amount calculation unit 22 determines whether or not rotation of the main spindle is restricted by a clamp mechanism, on the basis of the information from the NC device 10, and calculates a respective thermal displacement correction amount that varies according to the presence / absence of restriction by the clamp mechanism.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an apparatus and method for compensating for thermal displacements occurring in a machine tool. [Background technology]

[0002] Generally, machine tools have heat sources (for example, the rolling bearings of the main shaft) in various parts due to the characteristics of the machine, and the heat generated in these heat sources is transmitted to various parts of the machine, causing thermal deformation of the machine components.Since thermal deformation has a significant effect on machining accuracy, the conventional methods of preventing it have been widely adopted, which include cooling the heat-generating parts, or estimating and correcting the thermal displacement based on the temperature information of the thermally deformed parts. As the latter thermal displacement correction method, Patent Document 1 discloses a technology in which the temperature of the thermally deformed part is measured based on the output of a temperature sensor, and in a steady state where the temperature is saturated, the thermal displacement is estimated based on the instantaneous value of the measured temperature, and in a transient state after the operating conditions change, the thermal displacement is estimated over time, and the thermal displacement is corrected by an NC device based on each estimated value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3136464 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in the spindle unit 30 shown in Fig. 2, the spindle 31 is supported by a housing (here, a sleeve 32) via a plurality of bearings 37A-37D that constrain one end (left side of Fig. 2) of the spindle 31 in the radial and axial directions and rotatably support it, and a cylindrical roller bearing 38 that constrains the other end (right side of Fig. 2) of the spindle 31 in the radial direction and supports it rotatably and axially. Milling and drilling can be performed by attaching a rotating tool to the tip of the spindle 31 and rotating it with the spindle motor 12. Furthermore, a clamp mechanism 60 that mechanically constrains the rotation of the spindle 31 is provided on the left side of the spindle 31, and turning can be performed with a turning tool attached to the tip of the spindle 31 while the rotation of the spindle 31 is constrained by the clamp mechanism 60. When the spindle 31 rotates, the temperature rises and the spindle expands due to heat generated by the bearings 37A-37D and the spindle motor 12. In particular, the spindle expands in the axial direction from the support parts of the multiple bearing groups as base points, and the expansion from the support parts to the tip of the spindle has a large effect on machining accuracy, so that thermal displacement compensation is performed by a known method. However, when the spindle 31, which has thermally expanded due to the spindle rotation, is stopped and thermally contracts, if the rotation of the spindle 31 is mechanically restrained by the clamp mechanism 60, the axial movement of the spindle 31 is also restricted by the clamp mechanism 60, so the base point for contraction of the spindle 31 shifts. Therefore, the tool position during clamping cannot be accurately corrected, and machining accuracy in turning becomes insufficient.

[0005] Therefore, the present disclosure aims to provide a thermal displacement compensation device and a thermal displacement compensation method for a machine tool that can accurately calculate the amount of thermal displacement compensation and perform compensation even if the base point of thermal contraction changes while the spindle is restrained from rotating, thereby enabling high-precision turning processing. [Means for solving the problem]

[0006] In order to achieve the above object, a first configuration of the present disclosure is a machine tool including a spindle rotatably supported within a housing via a bearing, a clamping mechanism capable of mechanically restricting rotation of the spindle within the housing, and a control device that controls the rotation of the spindle and the operation of the clamping mechanism, a temperature measuring means for measuring temperatures of the housing and the spindle; a compensation amount calculation means for calculating a compensation amount for thermal displacement of the spindle from temperature information measured by the temperature measurement means; a compensation command means for calculating an axis compensation movement amount of a feed axis of the spindle based on the thermal displacement compensation amount calculated by the compensation amount calculation means, and outputting a compensation command to an axis to be compensated, The correction amount calculation means determines whether or not the rotation of the spindle is constrained by the clamp mechanism based on information from the control device, and calculates the thermal displacement correction amount, which differs depending on whether or not the rotation of the spindle is constrained by the clamp mechanism. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, when rotation of the spindle is constrained by the clamp mechanism, the correction amount calculation means calculates a base point of thermal displacement of the spindle based on the axial support rigidity of a restraining portion of the spindle constrained by the clamp mechanism and the axial support rigidity of a bearing portion of the spindle supported by the bearing, and calculates the thermal displacement correction amount based on the base point. In order to achieve the above object, a second configuration of the present disclosure is a machine tool including a spindle rotatably supported within a housing via a bearing, a clamping mechanism capable of mechanically restricting rotation of the spindle within the housing, and a control device that controls the rotation of the spindle and the operation of the clamping mechanism, a temperature measuring step of measuring temperatures of the housing and the spindle; a compensation amount calculation step of calculating a compensation amount for thermal displacement of the spindle from the temperature information acquired in the temperature measurement step; a compensation command step of calculating an axis compensation movement amount of a feed axis of the spindle based on the thermal displacement compensation amount calculated in the compensation amount calculation step, and outputting a compensation command to an axis to be compensated, The correction amount calculation step is characterized in that it is determined whether or not the rotation of the spindle is constrained by the clamp mechanism based on information from the control device, and the thermal displacement correction amount, which differs depending on whether or not the rotation of the spindle is constrained by the clamp mechanism, is calculated. Effect of the Invention

[0007] According to the present disclosure, the amount of thermal displacement correction is calculated according to the change in the base point of thermal contraction while the spindle is constrained from rotating, so that the correction can be performed accurately. Therefore, turning can be performed with high accuracy when the spindle is clamped. [Brief description of the drawings]

[0008] [Figure 1] This is a configuration diagram of an NC vertical machining center and a thermal displacement compensation device. [Diagram 2] FIG. 2 is a central vertical cross-sectional view of the main shaft. [Diagram 3] 3(A) and (B) are cross-sectional views of the bearing portion of FIG. 2. [Figure 4] FIG. 4 is an explanatory diagram showing thermal displacement of a spindle. [Diagram 5] 4 is a flowchart of a thermal displacement correction method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a configuration diagram of an NC vertical machining center (hereinafter simply referred to as a "machining center"), which is an example of a machine tool, provided with a thermal displacement compensation device, and FIG. 2 is a central vertical cross-sectional view of a spindle. The machining center 1 includes a swivel table 3 supported on a bed 2 so as to be movable in the left-right direction (Y-axis) on the page and capable of rotating, a column 4 fixed to the bed 2, a saddle 5 supported on the column 4 so as to be movable in the direction perpendicular to the page (X-axis), and a spindle head 6 supported on the saddle 5 so as to be movable in the up-down direction (Z-axis) on the page. The spindle head 6 is movable in three translational axes relative to a workpiece W fixed to the swivel table 3. The spindle head 6 houses a spindle unit 30 which rotatably supports a downward spindle 31, and a tool 7 can be attached to the lower end of the spindle 31. The spindle head 6 is provided with temperature sensors 8 and 9.

[0010] The NC device 10 of the machining center 1 controls the servo motors 11 of each axis to move the spindle head 6 relative to the workpiece W in accordance with the machining program, and controls the rotation of the spindle motor 12 that rotates the spindle 31. The workpiece W can be cut by rotating the tool 7 together with the spindle 31. A clamp mechanism 60 capable of clamping / unclamping the rotation of the spindle 31 is provided within the spindle unit 30. The NC device 10 can perform turning of the workpiece W by using the clamp mechanism 60 to stop the spindle 31 and the tool 7 from rotating, and rotating the swivel table 3.

[0011] The thermal displacement correction device 20 includes a temperature measurement unit 21 that measures the temperature of the spindle 31 and the sleeve 32 serving as a housing for supporting the spindle 31 via temperature sensors 8 and 9, a correction amount calculation unit 22 that calculates a thermal displacement correction amount based on temperature information acquired by the temperature measurement unit 21, a recording unit 23 that records the thermal displacement correction amount calculated by the correction amount calculation unit 22 and various parameters, and an NC device 10. The NC device 10 calculates the compensation movement amount for each feed axis based on the thermal displacement compensation amount input from the compensation amount calculation unit 22, and outputs a compensation command to the servo motor 11 of the axis to be compensated. Here, the temperature sensors 8, 9 and the temperature measurement unit 21 serve as the temperature measurement means of the present disclosure, the correction amount calculation unit 22 serves as the correction amount calculation means of the present disclosure, and the NC device 10 serves as the control device and correction command means of the present disclosure.

[0012] As shown in Fig. 2, spindle unit 30 contained in spindle head 6 has a hollow spindle 31 and a sleeve 32 surrounding spindle 31. For convenience, the left side in Fig. 2 will be described as the front and the right side as the rear. A front housing 33 and a rear housing 34 are fixed to the inner surface of the sleeve 32. The front housing 33 and the rear housing 34 are cylindrical, and the spindle motor 12 is accommodated between the two housings 33, 34. The spindle motor 12 has a stator 35 fixed to the inner surface of the sleeve 32, and a rotor 36 fixed to the spindle 31 inside the stator 35. A first bearing 37A, a second bearing 37B, a third bearing 37C, and a fourth bearing 37D are arranged at a predetermined interval in the front-rear direction between the main shaft 31 and the front housing 33. A fifth bearing 38 is arranged between the main shaft 31 and the rear housing 34.

[0013] As shown in FIG. 3(A), the first to fourth bearings 37A to 37D are angular ball bearings consisting of an outer ring 39 fixed to the inner surface of the front housing 33, an inner ring 40 fixed to the outer surface of the main shaft 31, a plurality of spherical rolling elements 41 interposed between the outer ring 39 and the inner ring 40, and a retainer 42 that rotates together with the rolling elements 41 using the inner surface of the outer ring 39 as a guide surface and holds the rolling elements 41 at a fixed distance from each other. Outer ring spacers 43, 43... fixed to the inner surface of the front housing 33 are interposed between adjacent outer rings 39, 39 in the front and rear of each of the first bearing 37A to the fourth bearing 37D. Inner ring spacers 44, 44... fixed to the outer surface of the main shaft 31 are interposed between adjacent inner rings 40, 40 in the front and rear of each of the first bearing 37A to the fourth bearing 37D. A first annular protrusion 45 is provided on the rear end of the front housing 33 behind the fourth bearing 37D. The first annular protrusion 45 abuts against the outer ring 39 of the fourth bearing 37D. A front retaining lid 46 is provided at the front end opening of the front housing 33. The front retaining lid 46 presses the outer rings 39 and the outer ring spacers 43 of the first to fourth bearings 37A to 37D toward the first annular protruding portion 45. A front step 47 is formed on the outer periphery of the main shaft 31 in front of the first bearing 37A, where the outer diameter of the main shaft 31 changes from a large diameter to a medium diameter. The inner ring 40 of the first bearing 37A abuts against the front step 47. A first retaining nut 48 is screwed into the first annular protrusion 45 in the rear of the fourth bearing 37D. The first retaining nut 48 presses the inner rings 40 and the inner ring spacers 44 of the first to fourth bearings 37A to 37D toward the front step 47.

[0014] As shown in Figure 3 (B), the fifth bearing 38 consists of an outer ring 49 fixed to the inner surface of the rear housing 34, an inner ring 50 fixed to the outer surface of the main shaft 31, a plurality of roller-shaped rolling elements 51 interposed between the outer ring 49 and the inner ring 50, and a retainer 52 that rotates together with the rolling elements 51 using the inner surface of the outer ring 49 as a guide surface and holds the rolling elements 51 at a fixed distance from each other. A second annular protrusion 53 is provided on the front end of the rear housing 34, in front of the fifth bearing 38. The second annular protrusion 53 abuts against the outer ring 49 of the fifth bearing 38. A rear retaining lid 54 is provided at the rear end opening of the rear housing 34. The rear retaining lid 54 presses the outer ring 49 of the fifth bearing 38 against the second annular protrusion 53. A rear step 55 is formed on the outer periphery of the main shaft 31 in front of the fifth bearing 38, where the outer diameter of the main shaft 31 changes from a medium diameter to a small diameter. Inner ring spacers 56, 56 fixed to the outer surface of the main shaft 31 are interposed in front of and behind the inner ring 50 of the fifth bearing 38. The front inner ring spacer 56 is interposed between the rear step 55 and the inner ring 50 of the fifth bearing 38. A second retaining nut 57 is screwed into the rear retaining cover 54 in the rear of the fifth bearing 38. The rear inner ring spacer 56 is interposed between the second retaining nut 57 and the inner ring 50 of the fifth bearing 38. The second retaining nut 57 presses the inner ring 50 of the fifth bearing 38 and each inner ring spacer 56 toward the rear step 55.

[0015] A clamp mechanism 60 is provided in front of the spindle unit 30. The clamp mechanism 60 includes an annular tooth profile 61 formed on the left end surface of the front holding cover 46, a rear clutch 62 provided on the front surface of the spindle 31 radially inside the front holding cover 46 and having a tooth profile similar to that of the tooth profile 61, and a front clutch 63 disposed in front of the front holding cover 46 and the rear clutch 62 and having a tooth profile that meshes with the tooth profiles of the front holding cover 46 and the clutch 62 simultaneously. The front clutch 63 is disposed so as to be movable forward and backward, and a first oil chamber 64 and a second oil chamber 65 are formed in front and behind the front clutch 63. When hydraulic pressure is supplied to the second oil chamber 65, the front clutch 63 is in the forward position shown by the solid line in Fig. 2 and is separated from the teeth of the front holding cover 46 and the rear clutch 62 (unclamped state). When hydraulic pressure is supplied to the first oil chamber 64, the front clutch 63 is in the backward position shown by the two-dot chain line and is engaged with the teeth of the front holding cover 46 and the rear clutch 62 (clamped state). This restricts the rotation of the main shaft 31.

[0016] Next, the thermal displacement of the main shaft 31 will be described with reference to FIG. The axial thermal displacement of the rotating main shaft 31 expands and contracts with P2 in Fig. 4 as the base point. P2 is the point where the main shaft 31 is supported by the first to fourth bearings 37A to 37D. The thermal displacement Δf of the front end of the main shaft at this time is expressed by the following equation (1).

[0017]

number

[0018] On the other hand, when the rotation of the main shaft 31 is restricted by the clamp mechanism 60 after the main shaft 31 has stopped, the front clutch 63 clamps the front retaining cover 46 and the rear clutch 62 at the base point P1, restricting the movement of the main shaft 31 in the axial direction. Therefore, the base point (neutral point of thermal displacement) of the contraction of the axial thermal displacement of the main shaft 31 transitions from P2 to P3 in Fig. 4. This P3 is determined by the axial support rigidity of the rear side of the main shaft supported by the first to fourth bearings 37A to 37D, the axial support rigidity of the front side of the main shaft supported by the clamp mechanism 60, the clamp position P1 of the main shaft 31, and the support span L between P1 and P2, which are set in advance, and is expressed by the following formula (2).

[0019]

number

[0020] The thermal displacement δc of the front end of the spindle during clamping is expressed by the following formula (3): Note that, as a result of the clamping operation, the clamp position changes from one point P1 to two points between P1 and P2, generating a force that suppresses the thermal displacement in the axial direction. However, since Kr and Kf are sufficiently small compared to the axial rigidity of the spindle 31, this can be ignored.

[0021]

number

[0022] Next, the calculation of the thermal displacement correction amount (hereinafter simply referred to as the "correction amount") by the correction amount calculation unit 22 will be described with reference to the flowchart of FIG. First, in step (hereinafter referred to as "S") S-11, correction parameters are obtained from the recording unit 23, and in the following S-12, support stiffness information between the spindle and the sleeve is obtained from the recording unit 23. Next, in S-13, information on each temperature measured by the temperature measuring unit 21 is obtained (temperature measurement step). Next, in S-14, information on the clamping of the spindle 31 by the clamping mechanism 60 is obtained from the NC device 10. Next, in S-15, it is determined whether or not the spindle 31 is clamped based on the clamp information of the spindle 31 acquired in S-14. If it is not determined that the spindle 31 is clamped, in S-16, a correction amount Δf, which is a thermal displacement, is calculated by the method of formula (1) (correction amount calculation step).

[0023] On the other hand, if it is determined in S-15 that the spindle 31 is clamped, the correction amount δc is calculated based on the formula (3) in S-17 (correction amount calculation step). In S-18, it is determined whether or not to continue calculating the correction amount, and if so, the process returns to S-13 to acquire temperature information, whereas if not, the process ends. In this way, either the correction amount δf or the correction amount δc is selected and calculated depending on whether the spindle 31 is clamped or not. Therefore, the NC device 10 calculates the correction movement amount of each axis according to either the correction amount output from the correction amount calculation unit 22, and outputs a correction command to the servo motor 11 of the axis to be corrected (correction command step).

[0024] As the temperature of the spindle 31 drops due to the spindle being stopped, the spindle 31 tries to contract, but while the spindle is clamped, the clamp mechanism 60 restricts the movement of the spindle 31 and restrains the spindle 31 together with the first to fourth bearings 37A to 37D, so that a tensile force acts on the spindle 31. The force generated here causes elastic deformation of the support system, and the point at which the spindle 31 and the spindle support system are not thermally displaced relative to each other due to thermal deformation (neutral point of thermal displacement) shifts from the vicinity of the first to fourth bearings 37A to 37D to the front of the spindle 31. As a result, while the spindle is clamped, the thermal displacement differs from that estimated with the vicinity of the first to fourth bearings 37A to 37D as the neutral point of thermal displacement, causing a correction error and deteriorating the machining accuracy of the turning process. In contrast, according to the thermal displacement compensation device 20 and thermal displacement compensation method of the machining center 1 of the above embodiment, the compensation amount calculation unit 22 judges whether the rotation of the spindle 31 is constrained by the clamp mechanism 60 based on information from the NC device 10, and calculates different compensation amounts depending on whether the spindle 31 is constrained by the clamp mechanism 60. Therefore, the transition of the thermal displacement neutral point while the spindle 31 is clamped can be estimated based on the support stiffness between the spindle and the sleeve, and compensation errors can be reduced. This allows turning to be performed with high accuracy while the spindle 31 is clamped.

[0025] The machine tool is not limited to the vertical machining center described above, and the present disclosure can also be applied to horizontal machining centers, multi-tasking machines, etc. In addition, in the above embodiment, the thermal displacement compensation device is incorporated into the machine tool together with the NC device, but it is also possible to perform thermal displacement compensation by providing other devices besides the NC device outside the machine tool and communicating with the NC device via wired or wireless communication. [Explanation of symbols]

[0026] 1 NC vertical machining center, 2 bed, 3 swivel table, 4 column, 6 spindle head, 7 tool, 10 NC device, 11 servo motor, 12 spindle motor, 20 thermal displacement compensation device, 21 temperature measurement unit, 22 compensation amount calculation unit, 23 recording unit, 30 spindle unit, 31 spindle, 32 sleeve, 33 left housing, 34 right Housing, 37A~37D··first to fourth bearings, 38··fifth bearing, 43··outer ring spacer, 44, 56··inner ring spacer, 46··front retaining cover, 47··front step portion, 48··first retaining nut, 54··rear retaining cover, 55··rear step portion, 57··second retaining nut, 60··clamping mechanism, 61··tooth profile, 62··rear clutch, 63··front clutch, W··work, P1~P3··base point.

Claims

1. The present invention is provided in a machine tool including a spindle rotatably supported within a housing via a bearing, a clamping mechanism capable of mechanically restricting rotation of the spindle within the housing, and a control device for controlling the rotation of the spindle and the operation of the clamping mechanism, a temperature measuring means for measuring temperatures of the housing and the spindle; a compensation amount calculation means for calculating a compensation amount for thermal displacement of the spindle from temperature information measured by the temperature measurement means; a compensation command means for calculating an axis compensation movement amount of a feed axis of the spindle based on the thermal displacement compensation amount calculated by the compensation amount calculation means, and outputting a compensation command to an axis to be compensated, a compensation amount calculation means for calculating a compensation amount for thermal displacement, the compensation amount being different depending on whether or not the rotation of the spindle is constrained by the clamping mechanism, based on information from the control device, and the compensation amount being different depending on whether or not the rotation of the spindle is constrained by the clamping mechanism.

2. 2. The thermal displacement compensation device for a machine tool according to claim 1, wherein, when rotation of the spindle is constrained by the clamp mechanism, the compensation amount calculation means calculates a base point of thermal displacement of the spindle based on the axial support rigidity of a restraining portion of the spindle constrained by the clamp mechanism and the axial support rigidity of a bearing portion of the spindle supported by the bearing, and calculates the thermal displacement compensation amount based on the base point.

3. A machine tool including a spindle rotatably supported within a housing via a bearing, a clamping mechanism capable of mechanically restricting rotation of the spindle within the housing, and a control device for controlling the rotation of the spindle and the operation of the clamping mechanism, a temperature measuring step of measuring temperatures of the housing and the spindle; a compensation amount calculation step of calculating a compensation amount for thermal displacement of the spindle from the temperature information acquired in the temperature measurement step; a compensation command step of calculating an axis compensation movement amount of a feed axis of the spindle based on the thermal displacement compensation amount calculated in the compensation amount calculation step, and outputting a compensation command to an axis to be compensated, a correction amount calculation step of determining whether or not the rotation of the spindle is constrained by the clamp mechanism based on information from the control device, and calculating the thermal displacement correction amount, which differs depending on whether or not the rotation of the spindle is constrained by the clamp mechanism.

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