JP7647451B2 - MACHINE TOOL, CONTROL METHOD, CONTROL PROGRAM, AND STORAGE MEDIUM - Google Patents

Description

The present invention relates to a machine tool, a control method, a control program, and a storage medium.

Patent Document 1 discloses a machine tool equipped with a magazine that stores tools to be attached to a spindle. The magazine has multiple grips on its outer periphery that hold the tools. The magazine is connected to a motor using a reduction gear. During a tool replacement operation, the machine tool controls the drive of the motor to position the tool to be replaced directly under the spindle.

Patent No. 4767925

When multiple tools are held unevenly on one part of the outer periphery of the magazine, the gravity acting on the tools increases the unbalanced torque, which is the torque of the load on the motor and reducer when the magazine stops. The tooth surface of the reducer may elastically deform due to the increase in unbalanced torque. In such a case, even if the rotation amount of the magazine motor is controlled by an encoder, a misalignment occurs in the reducer, and the grip holding the tool to be replaced may not be positioned in the correct replacement position.

The object of the present invention is to provide a machine tool, a control method, a control program, and a storage medium that can ensure the accuracy of the tool changing operation even if the unbalanced torque applied when the tool magazine is stopped increases due to the gravity acting on the tool.

The machine tool according to the first aspect of the present invention is a machine tool including a tool magazine that stores a plurality of tools and a spindle on which one tool from the plurality of tools stored in the tool magazine is attached, characterized in that it includes a motor that is a drive source for the tool magazine, a torque detection unit that detects a torque value of the motor, an acquisition unit that acquires a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is positioned to attach and detach a tool to and from the spindle, and a position of a tool to be attached to the spindle based on the torque value detected by the torque detection unit when the motor is stopped or driving the tool magazine, and a control unit that controls the motor using the correction amount acquired by the acquisition unit.

When multiple tools are stored unevenly on one part of the outer periphery of the tool magazine, the unbalanced torque, which is the load torque applied to the motor when the tool magazine is stopped, increases due to gravity acting on the tools. When the number of tools stored in the tool magazine is increased, or when the tool magazine stores large tools, the unbalanced torque increases further. As the unbalanced torque increases, the tool magazine stops at an angle different from the rotation angle due to deformation, etc. In such a case, the machine tool can correctly position the tool at the tool change position and ensure the accuracy of the tool change by correcting the rotation angle of the tool magazine by a correction angle equivalent to the increase in the torque value. In addition, since the machine tool can reliably move the tool to the tool change position, the tool can be reliably attached to the spindle, reducing the possibility of failure of the tool change operation and the possibility of the tool being dropped and damaged in the event of a failure.

In the first aspect, the acquisition unit may calculate the correction amount when the torque value detected by the torque detection unit is equal to or greater than a predetermined first value. When the torque value is less than the first value, there is a possibility that the accuracy of the tool replacement operation can be sufficiently ensured without correcting the position of the tool magazine, so the machine tool can omit the process for correction.

In a first aspect, the machine tool includes a position detection unit that detects the position of the tool magazine, and a memory unit that associates and stores the position of the tool magazine detected by the position detection unit while the tool magazine is moving with the torque value detected by the torque detection unit when the tool magazine is at that position, and the acquisition unit may calculate the correction amount based on the position of the tool magazine and the torque value stored in the memory unit. The machine tool stores the position and torque value of the tool magazine detected while the tool magazine is moving, and when a tool to be replaced is moved to a tool replacement position, the machine tool can move the tool magazine with high accuracy by determining the correction amount for the movement of the tool magazine from the stored values.

In the first aspect, the acquisition unit may calculate the correction amount when the difference between the maximum and minimum torque values detected by the torque detection unit is equal to or greater than a predetermined second value. When the difference between the maximum and minimum torque values is less than the second value, there is a possibility that the accuracy of the tool replacement operation can be sufficiently ensured without correcting the position of the tool magazine, so the machine tool can omit the process for correction.

In a first aspect, the tool magazine may include a reducer, and the acquisition unit may calculate the correction amount based on stiffness values of the tool magazine and the reducer and the torque value detected by the torque detection unit. By using the stiffness values of the tool magazine and the reducer to calculate the correction amount, the machine tool can further improve the accuracy of the tool changing operation.

The control method according to the second aspect of the present invention is a control method for controlling a machine tool having a tool magazine storing a plurality of tools and a spindle on which one tool from among the plurality of tools stored in the tool magazine is attached, and is characterized in that it comprises a torque detection step for detecting a torque value of a motor that is a drive source of the tool magazine, an acquisition step for acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where a tool is attached to or detached from the spindle, and a position of a tool to be attached to the spindle, based on the torque value detected in the torque detection step when the motor is stopped or driving the tool magazine, and a control step for controlling the motor using the correction amount acquired in the acquisition step. The second aspect provides the same effect as the first aspect.

In the second aspect, a position detection process is provided for detecting the position of the tool magazine, and a storage process is provided for correlating and storing the position of the tool magazine detected in the position detection process while the tool magazine is moving with the torque value detected in the torque detection process when the tool magazine is at that position, and in the acquisition process, the correction amount may be calculated based on the position of the tool magazine and the torque value stored in the storage process. Therefore, the same effect as in the first aspect is achieved.

A control program according to a third aspect of the present invention causes a computer that controls a machine tool having a tool magazine that stores a plurality of tools and a spindle on which one tool from among the plurality of tools stored in the tool magazine is attached to execute a torque detection process that detects a torque value of a motor that is a drive source of the tool magazine, an acquisition process that acquires a correction amount that corrects the deviation between a tool exchange position, where the tool magazine is positioned to attach and detach a tool to and from the spindle, and the position of a tool to be attached to the spindle, based on the torque value detected in the torque detection process when the motor is stopped or driving the tool magazine, and a control process that controls the motor using the correction amount acquired in the acquisition process. The third aspect provides the same effects as the first aspect.

A storage medium according to a fourth aspect of the present invention stores a control program for causing a computer controlling a machine tool having a tool magazine storing a plurality of tools and a spindle on which one tool from among the plurality of tools stored in the tool magazine is attached to execute a torque detection process for detecting a torque value of a motor that is a drive source of the tool magazine, an acquisition process for acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where a tool is attached to or detached from the spindle, and the position of a tool to be attached to the spindle, based on the torque value detected in the torque detection process when the tool magazine is stopped or while the motor is driving, and a control process for controlling the motor using the correction amount acquired in the acquisition process. According to the fourth aspect, the same effect as the first aspect is achieved.

FIG. FIG. 2 is a block diagram showing the electrical configuration of the machine tool 1. FIG. 11 is an explanatory diagram of correction of a turning angle of the tool magazine 20. FIG. 4 is a flowchart of a tool replacement process according to the first embodiment. 13 is a flowchart of a tool replacement process according to a second embodiment. 10 is a graph showing the relationship between the turning angle of the tool magazine 20 and the turning torque Tt.

A first embodiment of the present invention will be described. In this embodiment, the left/right, front/back, and up/down directions of the machine tool 1 will be described with reference to the directions of the arrows shown in the figure. The left/right, front/back, and up/down directions of the machine tool 1 are the X-axis, Y-axis, and Z-axis directions, respectively. The orientation of the tool changer 15 also follows this pattern.

The configuration of the machine tool 1 will be described. As shown in Figures 1 and 2, the machine tool 1 includes a base 2, a column 5, a spindle head 7, a spindle 9, a control box 6, a workbench 10, a tool changer 15, and the like. The base 2 is an approximately rectangular parallelepiped iron base extending in the front-to-rear direction. The column 5 is disposed on the rear side of the upper surface of the base 2. The spindle head 7 (see Figure 2) can be raised and lowered along the front surface of the column 5. The spindle 9 is disposed rotatably inside the spindle head 7. The spindle 9 has a mounting hole (not shown) that opens downward. The mounting hole is located at the bottom of the spindle head 7. The tool 4 is fixed to the tool holder 3. The tool holder 3 is detachably mounted in the mounting hole of the spindle 9. The spindle head 7 includes a gripping mechanism (not shown) inside. The gripping mechanism grips the tool holder 3 mounted in the mounting hole. The gripping mechanism releases its grip in response to the elevation and lowering of the spindle head 7. In the following description of this embodiment, the tool 4 and the tool holder 3 are collectively referred to as the tool 4. The spindle 9 is rotated by the drive of a spindle motor 52 (see FIG. 3) provided on the spindle head 7. The tool 4 rotates integrally with the spindle 9.

The control box 6 houses a numerical control device 40 (see Figure 3). The numerical control device 40 controls the operation of the machine tool 1. The work table 10 is located approximately in the center of the top surface of the base 2 and is located below the spindle head 7. The work table 10 is movable in the X-axis and Y-axis directions. The workpiece (not shown) is fixed to the top surface of the work table 10 with a jig (not shown). The machine tool 1 moves the work table 10 and the spindle head 7 relatively in three axes, the X-axis, Y-axis, and Z-axis, and brings the tool 4 into contact with the workpiece to perform cutting on the workpiece.

The tool changer 15 includes a tool magazine 20 and a plurality of grip arms 25. The tool magazine 20 is disk-shaped and made of aluminum alloy. The tool magazine 20 is substantially circular with its front surface tilted slightly downward. The tool magazine 20 includes a shaft portion 21 at the center of the rear surface, which protrudes toward the column 5. A pair of frames 8 extend forward from both the left and right sides of the upper front surface of the column 5. The support base 18 is fixed to the tip of the pair of frames 8. The support base 18 includes a shaft support portion 19 at the front surface. The shaft support portion 19 supports the shaft portion 21 so that it can rotate. The support base 18 includes a reducer 56 fixed to the upper portion. The reducer 56 includes a plurality of gears and cams (not shown). The magazine motor 55 is fixed to the upper portion of the reducer 56. The drive shaft of the magazine motor 55 is connected to the shaft portion 21 via the reducer 56. The reducer 56 reduces the rotational force of the magazine motor 55 and transmits it to the shaft portion 21. The column 5 supports the tool magazine 20 via a pair of frames 8.

The grip arms 25 are arranged radially along the outer periphery of the tool magazine 20. There are 28 grip arms 25. The grip arms 25 hold the tools 4 in a freely attachable and detachable manner. The state in which the grip arms 25 hold the tools 4 is called the state in which the tool magazine 20 stores the tools 4. The tool magazine 20 has a plurality of fulcrum tables 70 arranged at equal intervals along the outer periphery of the back surface. The fulcrum tables 70 are arranged corresponding to the respective positions of the grip arms 25. The fulcrum tables 70 support the corresponding grip arms 25 so that they can swing between the column 5. The tool holding portion 26 is provided at the tip of the grip arm 25 and is approximately U-shaped in a plan view. The tool holding portion 26 holds the tools 4 in a detachable manner. The middle portion of the grip arm 25 on the column 5 side rotatably supports the roller 27. When the spindle head 7 rises and falls, the roller 27 slides on the cam surface of the cam 11. The cam 11 is fixed along the right end of the front surface of the spindle head 7. The cam surface of the cam 11 has a straight section 11A that extends vertically and an inclined section 11B that slopes diagonally backward from the end of the straight section 11A.

The tool magazine 20 rotates around the shaft portion 21. The tool changer 15 rotates the tool magazine 20 to position a specific tool 4 at the tool change position. The tool change position is where the tool magazine 20 attaches and detaches the tool 4 to the spindle 9, and is the lowest position of the tool magazine 20. In the tool change operation, the tool changer 15 swaps the tool 4 attached to the spindle 9 with the tool 4 at the tool change position.

The operation panel 46 (see FIG. 3) is disposed on the outer wall of a cover (not shown) that covers the machine tool 1. The operation panel 46 includes a display unit 47 (see FIG. 3) and an input unit 48 (see FIG. 3). The display unit 47 displays various screens, abnormality information, etc. based on commands from the numerical control device 40. The input unit 48 accepts input of various information, operation instructions, etc., and outputs the input information to the numerical control device 40.

The tool changing operation will be explained. As shown in FIG. 2, the spindle head 7 starts to rise to the ATC origin, which is a position where the tool magazine 20 can be rotated. The roller 27 of the grip arm 25 at the tool changing position slides on the cam surface of the cam 11, in the order of the straight section 11A and the inclined section 11B. By sliding on the inclined section 11B, the roller 27 moves to the column 5 side. Therefore, the grip arm 25 swings counterclockwise around the fulcrum table 70 as viewed from the right side. The tool holding section 26 moves toward the spindle 9 and holds the tool 4 attached to the spindle 9. The gripping mechanism inside the spindle head 7 releases the grip on the tool 4, so that the tool 4 can be removed from the spindle 9. With the tool holding section 26 holding the tool 4, the spindle head 7 rises further, and the tool 4 comes out of the spindle 9. The roller 27 moves downward away from the inclined section 11B of the cam 11. The spindle head 7 then stops at the ATC origin.

The tool magazine 20 rotates to position the target tool at the tool change position. The target tool is the tool to be next mounted on the spindle 9. The tool holding portion 26 of the grip arm 25 at the tool change position holds the target tool. The target tool is located below the mounting hole of the spindle 9.

The spindle head 7 starts descending from the ATC origin. The tool 4 enters the mounting hole of the spindle 9. The gripping mechanism grips the tool 4, so that the tool 4 cannot be removed from the spindle 9. The spindle head 7 continues to descend. The roller 27 of the grip arm 25 at the tool change position slides from bottom to top on the inclined portion 11B of the cam 11. The grip arm 25 swings clockwise around the fulcrum 70 when viewed from the right side. The roller 27 slides from bottom to top from the inclined portion 11B of the cam 11 to the straight portion 11A. Because the roller 27 is in contact with the straight portion 11A, the grip arm 25 maintains its position with the tool holding portion 26 separated in front of the tool 4. The spindle head 7 continues to descend and stops at the target position, completing the tool change operation.

The electrical configuration of the machine tool 1 will be described with reference to FIG. 3. The numerical control device 40, which controls the machine tool 1, includes a CPU 31, a ROM 32, a RAM 33, a storage device 34, an input/output unit 35, and drive circuits 41 to 45. The CPU 31, the ROM 32, the RAM 33, and the storage device 34 are electrically connected to the input/output unit 35. The CPU 31 controls the numerical control device 40. The ROM 32 stores various programs including a main program. The main program executes main processing. The main processing reads the NC program line by line and executes various operations. The NC program is composed of multiple lines including various control commands, and controls various operations including the axis movement of the machine tool 1, tool replacement operation, etc., on a line-by-line basis. The ROM 32 may be a rewritable EEPROM or flash memory. In this case, the various programs may be stored in a storage medium such as a CD-ROM or flash memory, and copied to the ROM 32 and introduced into the numerical control device 40. The RAM 33 temporarily stores various information. The storage device 34 is non-volatile and stores various data such as NC programs, default values, and threshold values. The CPU 31 can store in the storage device 34 NC programs input by the operator through the input unit 48 of the operation panel 46, as well as NC programs read in via external input.

The drive circuit 41 is connected to the Z-axis motor 51 and the encoder 61. The drive circuit 42 is connected to the spindle motor 52 and the encoder 62. The drive circuit 43 is connected to the X-axis motor 53 and the encoder 63. The drive circuit 44 is connected to the Y-axis motor 54 and the encoder 64. The drive circuit 45 is connected to the magazine motor 55 and the encoder 65 that drives the tool magazine 20. The Z-axis motor 51, the spindle motor 52, the X-axis motor 53, the Y-axis motor 54, and the magazine motor 55 are all servo motors. The drive circuits 41 to 45 receive commands from the CPU 31 and output drive currents to the corresponding motors 51 to 55, respectively. The drive circuits 41 to 45 receive encoder information from the encoders 61 to 65 and perform feedback control of the position and speed. The encoder information includes various information such as torque monitor values, speed, and position. The encoder information can be read by the CPU 31 via the input/output unit 35. The input/output unit 35 is electrically connected to the grip detection unit 66 and to the display unit 47 and input unit 48 of the operation panel 46, respectively. The grip arm 25 has an identifier that can be detected by the grip detection unit 66. The grip detection unit 66 detects the identifier of the grip arm 25 that is in the tool change position. Note that the grip detection unit 66 detects the identifier not only when the grip arm 25 is exactly in the tool change position. In other words, the grip detection unit 66 detects the identifier of the grip arm 25 that is closest to the tool change position.

Referring to FIG. 4, the correction of the rotation angle of the tool magazine 20 during a tool exchange operation will be described. During a tool exchange operation, the numerical control device 40 rotates the tool magazine 20 and moves the target tool 4A to be exchanged to the lowest tool exchange position. The tool magazine 20 has 28 grip arms 25, and the position interval between adjacent grip arms 25 in the circumferential direction is called the pitch. One pitch is 2π/28 [rad]. The numerical control device 40 calculates the rotation angle according to the pitch difference between the grip arm 25 currently at the tool exchange position and the grip arm 25 holding the target tool 4A, and controls the drive circuit 45. The drive circuit 45 drives the drive shaft of the magazine motor 55 by an amount of rotation corresponding to the rotation angle based on the encoder information from the encoder 65.

As shown in FIG. 4(A), the tool magazine 20 may hold multiple tools 4 biased toward a portion of the outer periphery. In such cases, the center of gravity G of the tool magazine 20 is shifted from the rotation center 22 due to the gravity acting on the multiple tools 4, and is located on the side of the tool magazine 20 where the tools 4 are biased, toward the outer periphery. When the tool magazine 20 is stopped, the unbalanced torque, which is the torque of the load acting on the magazine motor 55 and the reducer 56, increases according to the position of the center of gravity G due to the weight of the tools 4, the degree of bias in the arrangement of the tools 4, etc.

As shown in FIG. 4B, the numerical control device 40 rotates the tool magazine 20 clockwise when viewed from the front, for example, by 9 pitches, in order to move the target tool 4A to the tool change position. Even if there is an influence of unbalanced torque, the drive circuit 45 uses feedback control to correctly drive the drive shaft of the magazine motor 55 to an amount of rotation equivalent to a rotation angle of 9 pitches. On the other hand, the tooth surface of the reducer 56 may be elastically deformed due to an increase in unbalanced torque. In such a case, even if the drive shaft of the magazine motor 55 is driven to the correct amount of rotation, the elastic deformation of the reducer 56 may cause the tool magazine 20 to rotate more than the rotation angle. The position of the target tool 4A shifts from the tool change position.

As shown in FIG. 4(C), the numerical control device 40 performs angle correction of the tool magazine 20 to correctly position the target tool 4A, which has shifted in position due to the elastic deformation of the reducer 56, at the tool exchange position. The amount of elastic deformation of the reducer 56 corresponds to the magnitude of the unbalanced torque. The magnitude of the holding torque for the magazine motor 55 to hold the rotation of the drive shaft in a stopped state increases or decreases according to the unbalanced torque. Therefore, the numerical control device 40 detects the holding torque of the magazine motor 55 and performs angle correction of the tool magazine 20 based on the holding torque. That is, the numerical control device 40 determines the angle by which the tool magazine 20 has rotated due to an increase in the unbalanced torque based on the holding torque, rotates the tool magazine 20 counterclockwise when viewed from the front, and positions the target tool 4A at the tool exchange position.

The tool change process will be described with reference to FIG. 5. The CPU 31 of the numerical control device 40 interprets the NC program block by block and generates a tool change command, then reads out and executes the program stored in the ROM 32 to execute the tool change process. The CPU 31 determines the pitch difference between the grip arm 25 currently at the tool change position and the grip arm 25 holding the target tool 4A, calculates the rotation angle of the tool magazine 20, and stores it in the RAM 33 (S1). The ROM 32 stores the rotation angle for one pitch in advance.

The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to move the spindle head 7 to the ATC origin (S2). The CPU 31 instructs the drive circuit 45 to drive the magazine motor 55 to start rotating the tool magazine 20 (S3). The drive circuit 45 uses feedback control to accurately drive the drive shaft of the magazine motor 55 by an amount of rotation corresponding to the rotation angle. When the amount of rotation of the drive shaft of the magazine motor 55 reaches the amount of rotation corresponding to the rotation angle, the CPU 31 stops driving the magazine motor 55 to stop the rotation of the tool magazine 20 (S4).

The CPU 31 acquires a torque monitor value as encoder information of the magazine motor 55 from the drive circuit 45 (S5). The acquired torque monitor value is a holding torque Th for the magazine motor 55 to hold the drive shaft in a stopped state. The CPU 31 judges whether the holding torque Th is equal to or greater than a first value set in advance (S6). The first value is a specified value that is a pre-measured value of the holding torque when the tooth surface of the reducer 56 is elastically deformed by the unbalanced torque. If the holding torque Th is less than the first value (S6: NO), the tooth surface of the reducer 56 is elastically deformed but does not affect the positioning accuracy. Therefore, the tool magazine 20 does not rotate too much, and the target tool 4A is placed at the tool exchange position. The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to lower the spindle head 7. The gripping mechanism grips the target tool 4A and attaches the target tool 4A to the spindle 9 (S10). The spindle head 7 then descends further and stops at a specified position, completing the tool change operation.

On the other hand, if the holding torque Th obtained after the tool magazine 20 is rotated in the tool changing operation is equal to or greater than the first value (S6: YES), the tooth surface of the reducer 56 may be elastically deformed. Even if the drive shaft of the magazine motor 55 is driven accurately by an amount of rotation equivalent to the turning angle, the tool magazine 20 may be rotated too much due to the elastic deformation of the reducer 56, and the target tool 4A may be positioned offset from the tool changing position. The CPU 31 calculates a correction angle θ for correcting the offset between the tool changing position and the position of the grip arm 25 that holds the target tool 4A based on the holding torque Th, and stores the calculated correction angle θ in the RAM 33 (S7). The correction angle θ is calculated using the following formula:
θ=k·Th
The coefficient k is a fixed value, expressed in units of [rad/N·m], that represents the rigidity of the reducer 56 and the tool magazine 20. The coefficient k is stored in advance in the ROM 32 or the storage device 34.

The CPU 31 instructs the drive circuit 45 to drive the magazine motor 55 to start rotating the tool magazine 20 (S8). The drive circuit 45 uses feedback control to accurately drive the drive shaft of the magazine motor 55 by the amount of rotation corresponding to the correction angle θ. When the amount of rotation of the drive shaft of the magazine motor 55 reaches the amount of rotation corresponding to the correction angle θ, the CPU 31 stops driving the magazine motor 55 and stops the rotation of the tool magazine 20 (S9). The tool magazine 20 places the target tool 4A at the tool exchange position. The CPU 31 drives the Z-axis motor 51 to lower the spindle head 7. The gripping mechanism grips the target tool 4A and attaches the target tool 4A to the spindle 9 (S10). The spindle head 7 further descends and stops at a predetermined position, completing the tool exchange operation.

As described above, when a plurality of tools 4 are stored unevenly on a part of the outer circumference of the tool magazine 20, the unbalanced torque, which is the load torque applied to the magazine motor 55 when the tool magazine 20 is stopped, increases due to gravity acting on the tools 4. When the number of tools 4 stored in the tool magazine 20 is increased or when the tool magazine 20 stores large tools 4, the unbalanced torque increases further. As the unbalanced torque increases, the tool magazine 20 stops at an angle different from the rotation angle due to deformation, etc. In this case, the machine tool 1 can correctly position the tool 4 at the tool exchange position and ensure the accuracy of the tool exchange by correcting the rotation angle of the tool magazine 20 by the correction angle θ equivalent to the increase in the torque value. In addition, since the machine tool can reliably move the tool to the tool exchange position, the tool can be reliably attached to the spindle, and the possibility of failure of the tool exchange operation and damage due to the tool falling in the event of failure can be reduced.

When the holding torque Th is less than the first value, it is possible to ensure sufficient accuracy in the tool replacement operation without correcting the position of the tool magazine 20, so the machine tool 1 can omit the process for correction.

The machine tool 1 can further improve the accuracy of the tool changing operation by using a coefficient k based on the rigidity of the tool magazine 20 and the reducer 56 to calculate the correction angle θ.

In the above description of the first embodiment, the magazine motor 55 is an example of a motor of the present invention. The CPU 31 that executes the process of S5 is an example of a torque detection unit of the present invention. The CPU 31 that executes the process of S7 is an example of an acquisition unit of the present invention. The CPU 31 that executes the processes of S8 and S9 is an example of a control unit of the present invention.

A second embodiment of the present invention will be described. The second embodiment is a modified version of the first embodiment. In the second embodiment, the turning torque Tt applied to the magazine motor 55 when the tool magazine 20 turns is measured in advance, and a correction angle θ corresponding to the pitch of the turning during the tool changing operation is calculated based on the turning torque Tt. The machine tool 1 of the second embodiment has the same configuration as the first embodiment, and executes the tool changing process shown in FIG. 6.

Prior to executing the tool replacement process, the operator edits the magazine information when a new tool 4 is attached to the tool magazine 20 or when a tool 4 is replaced. The magazine information is information indicating the holding state of each of the multiple grip arms 25. The storage device 34 stores, as magazine information, a grip number that identifies the grip arm 25 in the tool magazine 20, tool information, and a rotation torque Tt (described later) in association with each other. The numerical control device 40 displays a magazine information editing screen (not shown) on the display unit 47, and the operator edits the magazine information via the input unit 48. When the operator finishes editing the magazine information, the numerical control device 40 updates the magazine information in the storage device 34.

The tool change process of the second embodiment will be described with reference to FIG. 6. The CPU 31 of the numerical control device 40 interprets the NC program block by block and generates a tool change command, then reads and executes the program stored in the ROM 32 to execute the tool change process. The CPU 31 determines whether the magazine information has been updated (S21). If the magazine information has been updated (S21: YES), the CPU 31 determines that there has been a change in the arrangement of the tools 4 held by the tool magazine 20, and instructs the drive circuit 45 to drive the magazine motor 55 to start rotating the tool magazine 20 (S22). The CPU 31 waits until the rotation angle of the tool magazine 20 reaches one pitch based on the encoder information (S23: NO).

If the tool magazine 20 has rotated one pitch (S23: YES), the CPU 31 acquires a torque monitor value as encoder information of the magazine motor 55 from the drive circuit 45 (S24). The acquired torque monitor value is the load applied by the magazine motor 55 to rotate the tool magazine 20, i.e., the rotation torque Tt. The CPU 31 identifies the grip arm 25 at the tool exchange position based on the detection result of the grip detection unit 66, updates the magazine information by associating the acquired rotation torque Tt with the grip number of the identified grip arm 25, and stores it in the storage device 34 (S25).

Based on the encoder information, the CPU 31 determines whether the rotation angle of the tool magazine 20 has reached half a revolution since the start of rotation (S26), and if not (S26: NO), the process proceeds to S23. The CPU 31 repeats the processes of S23 to S26, acquiring the rotation torque Tt each time the tool magazine 20 rotates by one pitch, and updates the magazine information in the storage device 34 by associating it with the grip number of the grip arm 25 that is in the tool change position at the time of acquisition.

When the rotation angle of the tool magazine 20 reaches half a revolution (S26: YES), the CPU 31 calculates the rotation torque Tt corresponding to the grip numbers of the half revolution for which no correspondence has been established between the grip numbers and the rotation torque Tt. The CPU 31 updates the magazine information and stores it in the storage device 34 (S27).

The tool magazine 20 is circular. Therefore, as shown in FIG. 7, if the position of the center of gravity G deviates even slightly from the rotation center 22, a graph with the rotation torque Tt on the vertical axis and the rotation angle on the horizontal axis will draw a sine curve. The amplitude of the sine wave represents the gravitational component acting on the center of gravity G, and the phase of the sine wave represents the position of the center of gravity G relative to the rotation center 22. Therefore, once the rotation torque Tt for half a revolution of the tool magazine 20 is obtained, the CPU 31 can estimate the shape of the sine wave by calculation and determine the rotation torque Tt for the remaining half revolution. Details of the calculation to estimate the sine wave are known and will not be described here.

As shown in FIG. 6, the CPU 31 calculates the load variation based on the magazine information. The load variation is the maximum value of the turning torque Tt minus the minimum value of the turning torque Tt. The load variation represents the amplitude of the above-mentioned sine wave, i.e., the magnitude of the gravitational component acting on the center of gravity G. The CPU 31 stores the calculated load variation in the storage device 34 (S28).

The CPU 31 obtains the pitch difference between the grip arm 25 currently at the tool exchange position and the grip arm 25 holding the target tool 4A, calculates the rotation angle of the tool magazine 20, and stores it in the RAM 33 (S31). The ROM 32 stores the rotation angle for one pitch in advance. The CPU 31 judges whether the load fluctuation stored in the storage device 34 is equal to or greater than a preset second value (S32). The second value is a specified value that is a pre-measured value of the load fluctuation of the rotation torque when the tooth surface of the reducer 56 is elastically deformed by the unbalanced torque. If the load fluctuation is less than the second value (S32: NO), the tooth surface of the reducer 56 is elastically deformed but does not affect the positioning accuracy. Therefore, the tool magazine 20 does not rotate too much, and the target tool 4A can be placed at the tool exchange position. The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to move the spindle head 7 to the tool exchange position (S35). The CPU 31 instructs the drive circuit 45 to drive the magazine motor 55 to start rotating the tool magazine 20 (S36). The drive circuit 45 uses feedback control to accurately drive the drive shaft of the magazine motor 55 by the amount of rotation corresponding to the rotation angle. When the amount of rotation of the drive shaft of the magazine motor 55 reaches the amount of rotation corresponding to the rotation angle, the CPU 31 instructs the drive circuit 45 to stop driving the magazine motor 55 and stop the rotation of the tool magazine 20 (S37). The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to lower the spindle head 7. The gripping mechanism grips the target tool 4A and attaches the target tool 4A to the spindle 9 (S38). The spindle head 7 further descends and stops at a predetermined position, and the tool changing operation is completed.

On the other hand, if the load fluctuation of the turning torque Tt is equal to or greater than the second value (S32: YES), the tooth surface of the reducer 56 may be elastically deformed. Even if the drive shaft of the magazine motor 55 is driven accurately by an amount of rotation equivalent to the turning angle, the elastic deformation of the reducer 56 causes the tool magazine 20 to turn too much, and the target tool 4A is positioned offset from the tool changing position. The CPU 31 calculates a correction angle θ for correcting the offset between the tool changing position and the position of the grip arm 25 holding the target tool 4A based on the turning torque Tt, and stores the calculated correction angle θ in the RAM 33 (S33). The correction angle θ is calculated by the following formula:
θ=Σ{k・(Tt(i)−Ta)}
The coefficient k is a fixed value representing the rigidity of the reducer 56 and the tool magazine 20, and is expressed in units of [rad/N·m]. The coefficient k is stored in advance in the ROM 32 or the storage device 34. i represents a grip number and is an integer value. All grip numbers passing through the tool exchange position during the tool exchange operation, from the grip number of the grip arm 25 currently at the tool exchange position to the grip number of the grip arm 25 holding the target tool 4A, are substituted for i. The average turning torque Ta is the average value of the turning torque Tt obtained when the tool magazine 20 is turned in a state in which no tool 4 is held. The average turning torque Ta is measured in advance and stored in the ROM 32 or the storage device 34. The center of gravity G of the tool magazine 20 is at the rotation center 22 in a state in which no tool 4 is held. Even in this state, when the magazine motor 55 turns the tool magazine 20, a turning torque due to the viscous resistance of the reducer 56 or the like is generated. Therefore, in calculating the correction angle θ, the CPU 31 uses the average turning torque Ta, which is the average value of the turning torque Tt for each pitch, as a parameter to correct the positional deviation of the target tool 4A caused by the unbalanced torque.

The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to move the spindle head 7 to the ATC origin (S35). The CPU 31 instructs the drive circuit 45 to drive the magazine motor 55 to start rotating the tool magazine 20 (S36). The drive circuit 45 drives the drive shaft of the magazine motor 55 accurately by the rotation amount corresponding to the rotation angle through feedback control. When the rotation amount of the drive shaft of the magazine motor 55 reaches the rotation amount corresponding to the rotation angle, the CPU 31 further instructs the drive circuit 45 to correct the rotation amount of the drive shaft of the magazine motor 55. The drive circuit 45 drives the drive shaft of the magazine motor 55 accurately by the rotation amount corresponding to the correction angle θ through feedback control. When the rotation amount of the drive shaft of the magazine motor 55 reaches the rotation amount corresponding to the correction angle θ, the CPU 31 instructs the drive circuit 45 to stop driving the magazine motor 55 and stop the rotation of the tool magazine 20 (S37). The CPU 31 instructs the drive circuit 41 to drive the Z-axis motor 51 to lower the spindle head 7. The gripping mechanism grips the target tool 4A and attaches the target tool 4A to the spindle 9 (S38). The spindle head 7 further descends and stops at a predetermined position, completing the tool changing operation.

When the tool replacement process is executed without the operator replacing the tool 4 or updating the magazine information (S21: NO), the CPU 31 transitions to S31, and makes the judgment in S32 using the load fluctuation value stored in the storage device 34.

As described above, the machine tool 1 rotates the tool magazine 20 in advance and stores the grip number corresponding to the grip arm 25 of the tool magazine 20 and the rotation torque Tt as magazine information. The correction angle θ for the amount of correction when moving the target tool 4A to be replaced is calculated based on the rotation torque Tt for each pitch stored as magazine information, so that the tool magazine 20 can be rotated with high precision.

When the load fluctuation, which is the difference between the maximum and minimum values of the turning torque Tt, is less than the second value, it is possible to ensure sufficient accuracy in the tool changing operation without correcting the position of the tool magazine 20, so the machine tool 1 can omit the processing for correction.

In the above description of the second embodiment, the CPU 31 that executes the process of S24 is an example of a torque detection unit of the present invention. The CPU 31 that executes the process of S33 is an example of an acquisition unit of the present invention. The CPU 31 that executes the processes of S36 and S37 is an example of a control unit of the present invention. The CPU 31 that executes the process of S23 is an example of a position detection unit of the present invention. The storage device 34 that stores magazine information is an example of a storage unit of the present invention.

The present invention can be modified in various ways. The number of tools 4 that can be held in the tool magazine 20 is set to 28 as an example, but the number can be changed as appropriate, and may be, for example, 24. The machine tool 1 may be configured without a reducer 56. The correction angle θ is calculated using a formula, but may be calculated using a table created by measuring torque values corresponding to the correction angle θ in advance. In S6 of the first embodiment, the CPU 31 judges whether the holding torque Th is equal to or greater than a first value, but this judgment does not have to be made. In the second embodiment, the CPU 31 associates the grip number with the turning torque Tt for a half rotation of the tool magazine 20, but may also perform this for the entire rotation. In S32 of the second embodiment, the CPU 31 judges whether the load fluctuation of the turning torque Tt is equal to or greater than a second value, but this judgment does not have to be made. In S24 of the second embodiment, the CPU 31 acquires the turning torque Tt for each pitch in the rotation of the tool magazine 20, but may also acquire the turning torque Tt for every multiple pitches, for example, every three pitches. Alternatively, the CPU 31 may obtain the turning torque Tt each time the tool magazine 20 turns a predetermined angle, for example, each time it turns 1/8π. In S36 and S37 of the second embodiment, the CPU 31 turns the tool magazine 20 by the turning angle and then turns it by the correction angle θ to perform the correction, but the turning angle may be corrected in advance by the correction angle θ, and in S36 and S37, the tool magazine 20 may be rotated by the corrected turning angle.

1 Machine tool 4 Tool 9 Spindle 10 Work table 20 Tool magazine 31 CPU
34 Storage device 55 Magazine motor 56 Speed reducer

Claims (13)

A machine tool including a tool magazine that stores a plurality of tools and a spindle to which one tool from among the plurality of tools stored in the tool magazine is attached,
A motor that is a drive source of the tool magazine;
a torque detection unit that detects a torque value of the motor;
an acquisition unit that acquires a correction amount for correcting a deviation between a tool exchange position , where the tool magazine is positioned to attach or detach a tool to or from the spindle, and a position of the tool to be attached to the spindle, based on the torque value detected by the torque detection unit when the tool magazine is stopped after the tool magazine is rotated by the drive of the motor;
a control unit that controls the motor using the correction amount acquired by the acquisition unit. The machine tool according to claim 1, characterized in that the acquisition unit calculates the correction amount when the torque value detected by the torque detection unit is equal to or greater than a predetermined first value, and does not calculate the correction amount when the torque value is less than the first value . A machine tool including a tool magazine that stores a plurality of tools and a spindle to which one tool from among the plurality of tools stored in the tool magazine is attached,
A motor that is a drive source of the tool magazine;
a torque detection unit that detects a torque value of the motor;
an acquisition unit that acquires a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where the tool is attached to or detached from the spindle, and a position of the tool to be attached to the spindle, based on the torque value detected by the torque detection unit during rotation of the tool magazine by the drive of the motor when an arrangement of the tools held in the tool magazine is changed;
a control unit that controls the motor using the correction amount acquired by the acquisition unit;
A machine tool comprising: a position detection unit for detecting the position of the tool magazine;
a storage unit that stores a position of the tool magazine detected by the position detection unit during rotation of the tool magazine by at least half a revolution by the drive of the motor and the torque value detected by the torque detection unit when the tool magazine is at the position, in association with each other,
The machine tool according to claim 3 , wherein the acquisition unit calculates the correction amount based on the position of the tool magazine and the torque value stored in the memory unit. The machine tool according to claim 4, characterized in that the acquisition unit calculates the correction amount when a difference between a maximum value and a minimum value of the torque value detected by the torque detection unit is equal to or greater than a predetermined second value, and does not calculate the correction amount when the difference is less than the second value . The tool magazine includes a reducer,
The machine tool according to any one of claims 1 to 5 , wherein the acquisition unit calculates the correction amount based on stiffness values of the tool magazine and the reducer and the torque value detected by the torque detection unit. 1. A method for controlling a machine tool including a tool magazine that stores a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached, comprising the steps of:
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is positioned to attach and detach a tool to and from the spindle, based on the torque value detected in the torque detection step when the tool magazine is stopped after the tool magazine is rotated by the drive of the motor;
and controlling the motor using the correction amount acquired in the acquisition step. 1. A method for controlling a machine tool including a tool magazine that stores a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached, comprising the steps of:
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where the tool is attached to and detached from the spindle, and a position of a tool to be attached to the spindle, based on the torque value detected in the torque detection step during rotation of the tool magazine by the drive of the motor when an arrangement of tools held in the tool magazine is changed;
a control step of controlling the motor using the correction amount acquired in the acquisition step;
A control method comprising: a position detection step of detecting a position of the tool magazine;
a storage step of storing a position of the tool magazine detected in the position detection step during at least half a rotation of the tool magazine by the drive of the motor and a torque value detected in the torque detection step when the tool magazine is at the position, in association with each other,
9. The control method according to claim 8 , wherein in the obtaining step, the correction amount is calculated based on the position of the tool magazine and the torque value stored in the storing step. A computer for controlling a machine tool including a tool magazine storing a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached,
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is positioned to attach and detach a tool to and from the spindle, based on the torque value detected in the torque detection step when the tool magazine is stopped after the tool magazine is rotated by the drive of the motor;
and a control step of controlling the motor using the correction amount acquired in the acquisition step. A computer for controlling a machine tool including a tool magazine storing a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached,
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where the tool is attached to and detached from the spindle, and a position of a tool to be attached to the spindle, based on the torque value detected in the torque detection step during rotation of the tool magazine by the drive of the motor when an arrangement of tools held in the tool magazine is changed;
a control step of controlling the motor using the correction amount acquired in the acquisition step;
A control program for executing the above. A computer for controlling a machine tool including a tool magazine storing a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached,
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is positioned to attach and detach a tool to and from the spindle, based on the torque value detected in the torque detection step when the tool magazine is stopped after the tool magazine is rotated by the drive of the motor;
a control step of controlling the motor using the correction amount acquired in the acquisition step. A computer for controlling a machine tool including a tool magazine storing a plurality of tools and a spindle to which one tool selected from the plurality of tools stored in the tool magazine is attached,
a torque detection step of detecting a torque value of a motor which is a drive source of the tool magazine;
an acquisition step of acquiring a correction amount for correcting a deviation between a tool exchange position, where the tool magazine is a position where the tool is attached to and detached from the spindle, and a position of a tool to be attached to the spindle, based on the torque value detected in the torque detection step during rotation of the tool magazine by the drive of the motor when an arrangement of tools held in the tool magazine is changed;
a control step of controlling the motor using the correction amount acquired in the acquisition step;
A storage medium storing a control program for executing the above.

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