Machine tool spindle displacement compensation device and spindle displacement compensation method

Abstract

The objective is to provide a spindle displacement correction device and a spindle displacement correction method for a machine tool that correct spindle displacement caused by the supply condition of cooling oil to the spindle, and suppress spindle displacement, thereby suppressing a decrease in machining accuracy. [Solution] The spindle displacement correction device CD corrects the spindle displacement of a machining center M which comprises a spindle 3 rotatably supported within a spindle head 1 and a cooling device 6 that cools the spindle 3 by circulating temperature-controlled cooling oil within the spindle head 1. The device includes a displacement storage unit 15 that stores the correlation between the amount of cooling oil supplied to the spindle head 1 and the amount of displacement of the spindle 3, a displacement calculation unit 14 that calculates the amount of displacement of the spindle 3 corresponding to the amount of cooling oil supplied to the spindle head 1 based on the correlation stored in the displacement storage unit 15, and an NC device 13 that controls the movement of the spindle 3 in the opposite direction to the displacement direction based on a correction amount corresponding to the calculated value calculated by the displacement calculation unit 14.

Description

Technical Field

[0001] The present disclosure relates to a spindle displacement correction device and a spindle displacement correction method for correcting displacement of a spindle, particularly displacement in the axial direction and radial direction of the spindle, in a machine tool.

Background Art

[0002] In a machining center, which is an example of a machine tool, a tool is held on a spindle and a workpiece placed on a table is machined. Also, in a lathe, which is another example of a machine tool, a workpiece is held on a spindle and machined with a tool fixed to a tool post. In either example, it is needless to say that spindle displacement affects machining accuracy.

[0003] Spindle displacement is caused by thermal displacement due to heat generation of spindle bearings, motors, etc., spindle shrinkage due to centrifugal force during spindle rotation, change in the contact position of bearing rolling elements due to centrifugal force during spindle rotation in a spindle with a constant pressure preload structure, and displacement that occurs when switching the preload amount in a spindle with a fixed position preload structure. For example, in Patent Document 1, a method is disclosed in which the amount of thermal displacement is estimated based on the measured temperature and the thermal displacement is corrected based on the estimated value for thermal displacement due to heat generation of spindle bearings, motors, etc. In Patent Document 2, a method is disclosed in which the amount of displacement caused by spindle shrinkage due to centrifugal force during spindle rotation is estimated using a function with the spindle rotation speed as a variable, and the displacement is corrected based on the estimated value. In Patent Document 3, a method is disclosed in which the axial displacement amount of the spindle associated with the change in the contact position of bearing rolling elements due to centrifugal force during spindle rotation in a spindle with a constant pressure preload structure is calculated based on the correlation between the rotation speed of the spindle and the axial displacement amount of the spindle associated with the change in the contact position of bearing rolling elements, and the displacement is corrected based on the calculated value. In Patent Documents 4 and 5, a method is disclosed in which, for displacement that occurs when switching the preload amount in a spindle with a fixed position preload structure, the amount of displacement of the spindle that occurs for each preloading amount is stored in advance, and the spindle displacement is corrected so as to cancel out the stored displacement amount according to the preloading amount.

[0004] On the other hand, in recent years, there has been a growing demand for energy-saving in machine operation in order to realize a decarbonized society. For example, Patent Documents 6 and 7 disclose a method for reducing power consumption while reducing the thermal displacement of the spindle in a machine tool equipped with a cooling device for suppressing thermal displacement of the spindle, by appropriately stopping the cooling device that cools the cooling oil supplied to the spindle based on information such as spindle rotation speed and measured temperature. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] :Patent No. 3136464 [Patent Document 2] :Patent No. 3406765 [Patent Document 3] :Patent No. 3571505 [Patent Document 4] : Japanese Patent Application Publication No. 5-237704 [Patent Document 5] : Japanese Patent Application Publication No. 6-262485 [Patent Document 6] :Patent No. 6349276 [Patent Document 7] :Patent No. 6445395 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, when the cooling system is stopped and the supply of cooling oil to the spindle is stopped, and when the stopped cooling system is started and the supply of cooling oil to the spindle is restarted, the spindle is displaced in the axial direction, which is the so-called Z direction, and in the radial direction, which is the so-called Y direction. Figure 1 is a graph showing the axial displacement, with δz1 representing the amount of spindle displacement when the cooling system supplying cooling oil to the spindle is stopped and when the operation of the stopped cooling system is restarted. Figure 2 is a graph representing the radial displacement, with δy1 representing the amount of spindle displacement when the cooling system supplying cooling oil to the spindle is stopped and when the operation of the stopped cooling system is restarted.

[0007] However, the spindle displacements shown as δz1 and δy1 in Figures 1 and 2 are due to the operating state of the pump that supplies cooling oil to the spindle, and the cause of the spindle displacement shown as δz1 and δy1 is completely different from the spindle displacement that is subject to correction in Patent Documents 1 to 5. For this reason, it has been difficult to properly correct the displacement amounts δz1 and δy1 by applying known displacement correction methods and correction devices.

[0008] Furthermore, the spindle displacements shown as δz1 and δy1 in Figures 1 and 2 are independent of the operating state of the cooling system that cools the cooling oil. Therefore, as described in Patent Documents 6 and 7, even if the operating state of the cooling system is changed for the purpose of suppressing spindle displacement, it is not possible to suppress the spindle displacement.

[0009] Therefore, the present disclosure aims to provide a spindle displacement correction device and a spindle displacement correction method for a machine tool that correct spindle displacement caused by the supply state of cooling oil to the spindle and suppress spindle displacement, thereby suppressing a decrease in machining accuracy. [Means for solving the problem]

[0010] To solve the above problems, a first aspect of the present disclosure is a spindle displacement correction device for a machine tool comprising a spindle rotatably supported within a spindle head and a cooling device that cools the spindle by circulating a temperature-controlled fluid within the spindle head, characterized in that it comprises: a displacement storage unit that stores a correlation between the amount of fluid supplied to the spindle head and at least one of the axial displacement and radial displacement of the spindle; a displacement calculation unit that calculates at least one of the axial displacement and radial displacement of the spindle corresponding to the amount of fluid supplied to the spindle head based on the correlation stored in the displacement storage unit; and a control device that controls the movement of the spindle in the opposite direction to the displacement direction based on a correction amount corresponding to the calculated value calculated by the displacement calculation unit. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, the cooling device has a section in the pipeline that supplies fluid to the spindle head that has a cross-sectional area greater than the cross-sectional area of ​​the pipeline at the fluid discharge section of the cooling device. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, the correlation between the amount of fluid supplied to the spindle head and at least one of the axial displacement and radial displacement of the spindle is based on the axial displacement and radial displacement of the spindle when the amount of fluid supplied to the spindle head is 0. To solve the above problems, a second aspect of the present disclosure is a machine tool comprising a spindle rotatably supported within a spindle head and a cooling device that cools the spindle by circulating a temperature-controlled fluid within the spindle head, characterized in that a correlation between the amount of fluid supplied and at least one of the axial displacement and radial displacement of the spindle is stored, at least one of the axial displacement and radial displacement of the spindle corresponding to the amount of fluid supplied is calculated based on the stored correlation, and the spindle is controlled to move in the opposite direction to the displacement based on a correction amount corresponding to the calculated value calculated by the displacement calculation unit. [Effects of the Invention]

[0011] According to the present disclosure, the spindle displacement correction device calculates the displacement amount of the spindle corresponding to the supply amount of the fluid based on the correlation between the supply amount of the fluid that cools the spindle to the spindle head and the displacement amount of the spindle, and moves and controls the spindle in the direction opposite to the displacement direction based on the correction amount corresponding to the calculated calculated value. Therefore, regardless of the operating state of the machine tool, the spindle displacement associated with the change in the supply state of the fluid to the spindle due to the operating state of the cooling device can be corrected. Thereby, a decrease in machining accuracy can be suppressed. Furthermore, in the pipeline where the cooling device supplies the fluid to the spindle head, by having a section with a cross-sectional area larger than the cross-sectional area of the fluid discharge section in the cooling device, the spindle displacement that occurs when the supply amount of the fluid to the spindle head changes can be suppressed. Therefore, a decrease in machining accuracy can be suppressed.

Brief Description of the Drawings

[0012] [Figure 1] It is a diagram showing the change in the axial displacement caused by the change in the operating state of the cooling device. [Figure 2] It is a diagram showing the change in the radial displacement caused by the change in the operating state of the cooling device. [Figure 3] It is a configuration diagram of the machining center in the embodiment. [Figure 4] It is a flowchart showing the method for correcting the spindle displacement. [Figure 5] It is a flowchart showing the second method for correcting the spindle displacement. [Figure 6] It is a characteristic diagram showing the correlation between the supply amount of the cooling oil and the axial displacement and radial displacement of the spindle. [Figure 7] It is a diagram showing the change in the axial displacement caused by the change in the operating state of the cooling device when the spindle correction device of the present disclosure is applied. [Figure 8] It is a diagram showing the change in the radial displacement caused by the change in the operating state of the cooling device when the spindle correction device of the present disclosure is applied.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described based on the drawings. As shown in FIG. 3, a machining center M as a machine tool includes a spindle head 1, a column 2, a spindle 3, a bed 4, a table 5, a cooling device 6, and an NC device 13. Further, the machining center M includes a spindle displacement correction device (hereinafter referred to as a correction device) CD. The spindle head 1 is movable in a so-called Z-axis direction, that is, the vertical direction in FIG. 3, by a ball screw 9a, a nut 9b, and a motor 10. Also, the table 5 is movable in a so-called Y-axis direction, that is, the left-right direction in FIG. 3, by a ball screw 11a, a nut 11b, and a motor 12. The operation control of the machining center M is executed according to a command from an NC device 13 as a control device. The NC device 13 includes a CPU and a memory connected to the CPU, and realizes its operation by using them.

[0014] The spindle 3 is rotatably supported by the spindle head 1. The spindle head 1 includes, for example, a cooling oil passage 1a for cooling parts such as the spindle 3, a bearing (not shown) of the spindle 3, and a motor. The cooling oil passage 1a is connected to the cooling device 6 via a pipe 7. A fluid temperature-controlled by the cooling device 6 is circulated through the cooling oil passage 1a. In the present embodiment, the fluid is cooling oil. The temperature control of the cooling oil by the cooling device 6 is managed according to a temperature control command from the NC device 13. The cooling device 6 is for circulating the temperature-controlled cooling oil in the spindle head 1 to cool the spindle 3, and includes a pump for circulating the cooling oil through the pipe 7 and the cooling oil passage 1a. Also, a flow meter 16 for measuring the supply amount of the cooling oil is provided in the pipe 7 between the fluid discharge portion 6a of the cooling device 6 and the spindle head 1. Further, the pipe 7 is provided with a pipe 8 having a larger cross-sectional area than the pipe 7 between the flow meter 16 and the spindle head 1.

[0015] For example, as shown in part A of FIG. 1 and part B of FIG. 2, when the cooling device 6 is switched from the stop state to the operation state, a sudden change occurs in the flow rate of the cooling oil in the pipe 7 due to the discharge of the cooling oil at the time of pump startup, causing displacement in the axial direction and radial direction of the spindle 3. However, by providing a conduit 8 with a larger cross-sectional area than conduit 7, it is possible to suppress the rapid change in the flow velocity of the cooling oil in conduit 7. Therefore, the axial and radial displacement of the spindle 3 can be suppressed, and thus the decrease in machining accuracy can be suppressed.

[0016] The correction device CD comprises a displacement storage unit 15 and a displacement calculation unit 14. The correction device CD also includes an NC device 13. The displacement memory unit 15 stores the correlation between the axial displacement δz and radial displacement δy of the main shaft 3 in response to changes in the amount of coolant supplied. The displacement calculation unit 14 calculates the axial displacement δz and radial displacement δy of the main shaft 3 based on the correlation between the axial displacement δz and radial displacement δy of the main shaft 3 and the amount of coolant supplied measured by the flow meter 16.

[0017] Next, the method for correcting spindle displacement using the correction device CD will be explained based on the flowchart shown in Figure 4. First, as S1, it is confirmed whether there are any changes in the operating state of the cooling device 6, such as operation, stopping, and changes in the amount of cooling oil supplied as measured by the flow meter 16. The determination of changes in the state of the cooling device 6 is based on changes in the operation and stop commands from the NC device 13 to the cooling device 6, changes in the operation and stop signals obtained from the cooling device 6, and changes in the flow rate over a predetermined time period obtained by the flow meter 16.

[0018] In S1, if it is determined that there is a change in the operating state of the cooling device 6, then in S2, the amount of cooling oil supplied at the time the operating state of the cooling device 6 was determined, i.e., the timing when S1 was executed, is obtained. Next, in S3, as shown in Figure 6, based on the relationship between the amount of coolant supplied V stored in the displacement memory unit 15 and the axial displacement δz and radial displacement δy of the main shaft 3, the displacement calculation unit 14 calculates the axial displacement δz of the main shaft 3 as δz = δz1 and the radial displacement δy as δy = δy1 from the amount of coolant supplied V obtained in S2. The relationship between the cooling oil supply amount V and the axial displacement δz and radial displacement δy of the spindle 3 is derived based on the displacement of the spindle 3 when the cooling oil supply amount V to the spindle head 1 is zero, and is stored in the displacement memory unit 15 in advance. The relationship between the cooling oil supply amount V and the axial displacement δz and radial displacement δy of the spindle 3 may be derived, for example, from various information obtained during a test run conducted in advance, or from various information obtained from past machining history. Furthermore, if the relationship between the displacement of the spindle 3 and the cooling oil supply amount is clear, the case where the cooling oil supply amount is not zero may be used as the reference.

[0019] Subsequently, in S4, a correction amount corresponding to the axial calculation value δz calculated in S3 is sent from the NC device 13 to the motor 10, and the spindle head 1 is controlled to move in the opposite direction to the axial displacement. In this way, the correction device CD corrects the axial displacement of the spindle 3. Similarly, a correction amount corresponding to the radial displacement calculation value δy calculated in S3 is sent from the NC device 13 to the motor 12, and the table 5 is controlled to move in the opposite direction to the radial displacement. In this way, the correction device CD corrects the radial displacement of the spindle 3. Then, if there is no command to stop processing from the NC device 13 to the displacement calculation unit 14, the change in the operating state of the cooling device 6 is determined again in S1. If, in S1, it is determined that there is no change in the operating state of the cooling device 6, a correction amount based on the previous calculation value is output from the NC device 13.

[0020] Figures 7 and 8 show the axial and radial principal axis displacements when displacement correction of the principal axis 3 is performed based on the flowchart shown in Figure 4, under the same conditions as in Figures 1 and 2, except that conduit 8 is applied. Comparing Figure 1 and Figure 7, it can be seen that the displacement δz1' resulting from the change in the operating state of the cooling device 6 is smaller than the displacement δz1 shown in Figure 1. Similarly, comparing Figure 2 and Figure 8, it can be seen that the displacement δy1' resulting from the change in the operating state of the cooling device 6 is smaller than the displacement δy1 shown in Figure 2. Furthermore, the displacement when the cooling device changes from a stopped state to an operating state, as shown in section A' of Figure 7 and section B' of Figure 8, is also smaller than the displacement shown in section A of Figure 1 and section B of Figure 2, which indicate the timing of the change from the stopped state to the operating state of the cooling device 6.

[0021] In this way, the compensation device CD can compensate for spindle displacement caused by changes in the supply of cooling oil to the spindle head 1 due to the operating state of the cooling device 6, regardless of the operating state of the machining center M. This makes it possible to suppress a decrease in machining accuracy.

[0022] The correction device CD described above corrects the spindle displacement of a machining center M which comprises a spindle 3 rotatably supported within a spindle head 1 and a cooling device 6 that cools the spindle 3 by circulating temperature-controlled cooling oil within the spindle head 1. The device includes a displacement storage unit 15 that stores the correlation between the amount of cooling oil supplied to the spindle head 1 and the axial and radial displacement amounts of the spindle 3; a displacement calculation unit 14 that calculates the axial and radial displacement amounts of the spindle 3 corresponding to the amount of cooling oil supplied to the spindle head 1 based on the correlation stored in the displacement storage unit 15; and an NC device 13 that controls the movement of the spindle 3 in the opposite direction to the displacement direction based on a correction amount corresponding to the calculated value calculated by the displacement calculation unit 14.

[0023] Therefore, based on the correlation between the amount of cooling oil supplied to the spindle head 1 for cooling the spindle 3 and the amount of displacement of the spindle 3, the amount of displacement of the spindle 3 corresponding to the amount of cooling oil supplied is calculated, and the spindle 3 can be controlled to move in the opposite direction to the displacement direction based on the correction amount corresponding to the calculated value. As a result, regardless of the operating state of the machining center M, it is possible to correct the spindle displacement caused by changes in the supply state of cooling oil to the spindle 3 due to the operating state of the cooling device 6, thereby suppressing a decrease in machining accuracy.

[0024] Furthermore, a second method for correcting the spindle displacement using a correction device CD, which can more easily correct the displacement caused by the change between the operating and stopped states of the cooling device 6, as shown by δz1 in Figure 1 and δy1 in Figure 2, will be explained based on the follow chart shown in Figure 5. First, as S100, the axial displacement δz1 and radial displacement δy1 of the spindle 3 are stored in the displacement storage unit 15 when the cooling device 6 is in operation, based on the displacement of the spindle 3 when the amount of cooling oil supplied to the spindle head 1 is zero.

[0025] Next, in S101, it is confirmed whether the cooling device 6 is in operation. The determination of the operating status of the cooling device 6 is based on either an operation command or a stop command from the NC device 13 to the cooling device 6, or either an operation signal or a stop signal obtained from the cooling device 6. In S101, if it is determined that the cooling device 6 is operating, then in S102, the displacement calculation unit 14 calculates the axial displacement δz of the spindle 3 at the time the operating state of the cooling device 6 was determined, i.e., when S101 was executed, as δz = δz1, and the radial displacement δy as δy = δy1. The axial displacement δz1 and radial displacement δy1 are those stored in the displacement storage unit 15 in S100. On the other hand, if it is determined in S101 that the cooling device 6 is stopped, then in S103, the displacement calculation unit 14 calculates the axial displacement δz and radial displacement δy of the spindle 3 as zero.

[0026] Subsequently, in S104, a correction amount corresponding to the axial calculation value δz calculated in S102 or S103 is sent from the NC device 13 to the motor 10, and the spindle head 1 is controlled to move in the opposite direction to the displacement. In this way, the correction device CD corrects the displacement that occurred in the axial direction of the spindle 3. Similarly, a correction amount corresponding to the radial displacement calculation value δy calculated in S102 or S103 is sent from the NC device 13 to the motor 12, and the table 5 is controlled to move in the opposite direction to the displacement. In this way, the correction device CD corrects the radial displacement that occurred in the spindle 3. Then, if there is no command to stop processing from the NC device 13 to the displacement calculation unit 14, the change in the operating state of the cooling device 6 is determined again in S101.

[0027] According to the second spindle displacement correction method, the step of pre-storing the correlation between the amount of cooling oil supplied to the spindle head 1 and the amount of displacement of the spindle 3 can be omitted, making it possible to correct the spindle displacement more simply. Furthermore, the second spindle displacement correction method described above can be applied when the amount of cooling oil supplied to the spindle head 1 during the operation of the cooling device 6 remains constant at the timing of multiple displacement corrections.

[0028] In this disclosure, the explanation is based on the assumption that the vertical direction in Figure 3 is the Z-axis direction, the horizontal direction in Figure 3 is the Y-axis direction, and radial displacement occurs in the Y-axis direction. However, as described above, even when the Z-axis and Y-axis directions are defined in Figure 3 and the principal axis displacement occurs in the X-axis direction perpendicular to the plane of the paper, and when the principal axis displacement occurs in both the X-axis and Y-axis directions, the principal axis displacement correction by the correction device CD and the principal axis displacement suppression effect by the conduit 8 are still applicable.

[0029] Furthermore, the configuration of the spindle displacement compensation device and spindle displacement compensation method of this disclosure is not limited in any way to the embodiments described above, and can be modified as necessary without departing from the spirit of the invention. For example, the displacement calculation unit 14 and the displacement storage unit 15 may be built into the NC device 13. Furthermore, the machine tool does not have to be a machining center. Furthermore, the spindle can be either a tool spindle or a workpiece spindle. Furthermore, the fluid is not limited to cooling oil, and any cooling medium can be applied. [Explanation of Symbols]

[0030] 1...Spindle head, 3...Spindle, 6...Cooling device, 6a...Fluid discharge unit, 7...Pipeline, 8...Pipeline, 13...NC device (control device), 14...Displacement calculation unit, 15...Displacement memory unit, M...Machining center (machine tool), CD...Spindle displacement compensation device.

Claims

1. A spindle displacement compensation device for a machine tool, comprising a spindle rotatably supported within a spindle head, and a cooling device that cools the spindle by circulating a temperature-controlled fluid within the spindle head, A displacement storage unit that stores the correlation between the amount of fluid supplied to the spindle head and at least one of the axial displacement and radial displacement of the spindle, A displacement calculation unit calculates at least one of the axial displacement and radial displacement of the spindle corresponding to the amount of fluid supplied to the spindle head, based on the correlation stored in the displacement memory unit. A spindle displacement correction device for a machine tool, comprising: a control device that controls the movement of the spindle in the opposite direction to the displacement direction based on a correction amount corresponding to a calculated value calculated by the displacement calculation unit; and

2. The spindle displacement compensation device for a machine tool according to claim 1, characterized in that the cooling device has a section in the pipeline that supplies the fluid to the spindle head that has a cross-sectional area larger than the cross-sectional area of ​​the pipeline of the fluid discharge section of the cooling device.

3. The spindle displacement compensation device for a machine tool according to claim 1 or 2, characterized in that the correlation between the amount of fluid supplied to the spindle head and at least one of the axial displacement and radial displacement of the spindle is based on the axial displacement and radial displacement of the spindle when the amount of fluid supplied to the spindle head is 0.

4. A spindle rotatably supported within the spindle head, A machine tool comprising a cooling device that cools the spindle by circulating a temperature-controlled fluid within the spindle head, The correlation between the amount of fluid supplied and at least one of the axial displacement and radial displacement of the main shaft is stored. Based on the stored correlation, calculate at least one of the axial displacement and radial displacement of the main shaft corresponding to the amount of fluid supplied. A method for correcting spindle displacement of a machine tool, characterized by controlling the movement of the spindle in the opposite direction to the displacement direction based on a correction amount corresponding to the calculated value.

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