Control device for a machine tool with C-axis functionality

Abstract

To prevent oscillation caused by the inherent vibration of a mechanical brake or the influence of brake torque when a state of the mechanical brake changes.SOLUTION: When a machine control unit 7 changes a brake operation command to switch a state of a mechanical brake 6 while performing C-axis control, brake torque of the mechanical brake 6 when the brake operation command is switched with the brake operation command as input is estimated from an operation delay time, a rise time, a release delay time, and a fall time by a control parameter changing unit 25. The control parameter changing unit 25 outputs a feedback control parameter adapted to the estimated brake torque to a feedback control unit 28, and outputs a feedforward control parameter coefficient adapted to the estimated brake torque to a feedforward control unit 17.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a control device for a machine tool having a function of controlling a C-axis by using a mechanical brake provided in a spindle or a motor that drives the spindle.

Background Art

[0002] In machining using a lathe or a machining center that performs milling, there are two types of machining using position control of a spindle (hereinafter referred to as "C-axis control"): indexing machining and generating machining. In indexing machining, the spindle is positioned at a desired angle, and the spindle angle is fixed using a mechanical brake provided in the spindle.

[0003] Generating machining is a method of performing milling or the like while controlling the locus of the spindle. When the machining load is small, the mechanical brake is released to improve machining accuracy. When performing heavy cutting with a large machining load, a technique is known in which the mechanical brake is driven at a low pressure to generate a low brake torque, thereby improving cutting ability or preventing machining chatter (for example, Patent Document 1).

[0004] In the device described in Patent Document 1, when the mechanical brake is set to a low-pressure brake, the feedback gain in servo control is reduced compared to when the mechanical brake is released. This prevents oscillation due to the natural vibration of the mechanical brake or the influence of the brake torque.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Figure 3 shows the time evolution of brake operation commands, brake torque, and servo control parameters. The horizontal axis in Figure 3 represents time.

[0007] As shown in Figure 3, in reality, there is a time required for the hydraulic system and other components to operate between the transmission of a brake operation command (upper part of Figure 3) to the mechanical brake and the response of the brake torque. In addition, the rise in brake torque may be gradual (middle part of Figure 3). Therefore, if control parameters are switched instantaneously as in the prior art, the control parameters will not match the slowly changing state of the machine, and when the state of the mechanical brake changes, there is a problem of oscillation due to the influence of the natural vibration of the mechanical brake and the brake torque.

[0008] The objective of this invention is to prevent oscillation caused by the natural vibration and brake torque of a mechanical brake when the state of the mechanical brake changes. [Means for solving the problem]

[0009] One aspect of the present invention is a control device for a machine tool having a C-axis function, characterized by comprising: a motor for driving a spindle; a mechanical brake attached to the spindle or the motor, capable of changing the brake torque and releasing the brake; a mechanical control unit that outputs a brake operation command to the mechanical brake; an encoder for detecting the position of the motor; a position command generation unit that outputs a C-axis control position command for the spindle from a higher level; a feedback control unit that calculates a torque command for the motor by feedback control so that the position detection value of the encoder follows the position command; a current control unit that takes the torque command of the motor as input and supplies current so that the torque generated by the motor follows the torque command; and a control parameter changing unit that, when the mechanical brake is operated while the C-axis is being controlled, takes the brake operation command as input and changes the C-axis control parameters of the feedback control unit, taking into account the response delay of the mechanical brake, the rise time and fall time of the brake torque.

[0010] The control method by the feedback control unit may be a method of performing PID control from the position error between the position of the C axis and the position command, or a P-PI control method in which a speed command is calculated from the position error by P control, the speed of the C axis is detected in a subsequent stage, and PI control is performed to follow the speed command.

[0011] A control device for a machine tool having a C-axis function further includes a feedforward control unit that performs feedforward control based on the position command, in addition to the feedback control unit, so that the C-axis follows the position command, and the control parameter changing unit may change the C-axis control parameters of the feedforward control unit when the mechanical brake is operated while the C-axis is being controlled, taking into account the response delay of the mechanical brake, the rise time and fall time of the brake torque.

[0012] The control method by the feedforward control unit may include at least one feedforward control method from among: a first method of differentiating the position command to calculate a feedforward velocity command and adding it to the velocity command of the P-PI control; a second method of calculating a feedforward acceleration command by second-order differentiating the position command and adding a control input to the feedback control input such that the C axis generates an acceleration corresponding to the feedforward acceleration command; and a third method of performing reversal compensation control so that the position error is reduced when the C axis reverses direction.

[0013] The control parameter changing unit includes a brake state simulation unit that takes the brake operation command as input and estimates the brake torque of the mechanical brake in response to the switching of the brake operation command, and a parameter interpolation unit that outputs feedback control parameters to the feedback control unit according to the estimated brake torque estimated by the brake state simulation unit. The brake state simulation unit may estimate the brake torque of the mechanical brake from the torque command, and the parameter interpolation unit may output feedback control parameters that match the estimated brake torque to the feedback control unit.

[0014] The control parameter changing unit includes a brake state simulation unit that takes the brake operation command as input and estimates the brake torque of the mechanical brake in response to the switching of the brake operation command; a parameter interpolation unit that outputs a feedback control parameter to the feedback control unit according to the estimated brake torque estimated by the brake state simulation unit; and a parameter coefficient selection unit that takes the brake operation command as input and selects a feedforward control parameter coefficient in response to the switching of the brake operation command, or interpolates the feedforward control parameter coefficient with respect to the estimated brake torque as input and outputs it to the feedforward control unit. The brake state simulation unit estimates the brake torque of the mechanical brake from the torque command, the parameter interpolation unit outputs a feedback control parameter that matches the estimated brake torque to the feedback control unit, the parameter coefficient selection unit outputs a feedforward control parameter that matches the brake operation command or the estimated brake torque to the feedforward control unit, and the feedforward control unit may multiply the compensation parameter of the inversion compensation control by the feedforward control parameter coefficient.

[0015] The brake state simulation unit may, when estimating the brake torque, have the position command generation unit output a command to rotate the C-axis at a constant speed, thereby operating the mechanical brake when the C-axis rotates at a constant speed, and estimating the response delay, the rise time and fall time of the brake torque from the torque command.

[0016] The brake state simulation unit receives the torque command as input and updates the estimated brake torque response according to the response delay, rise time, and fall time of the brake torque, which are estimated each time. The change time of the feedback control parameter or feedforward control parameter coefficient may be made variable.

[0017] The brake state simulation unit may select linear interpolation or exponential interpolation as the interpolation method for the rise time and fall time of the brake torque.

[0018] When abnormal noise or vibration occurs when the feedback control parameter or feedforward control parameter coefficient is changed in a state where the brake state simulation unit selects exponential interpolation, linear interpolation may be selected.

Advantages of the Invention

[0019] According to the present invention, it is possible to prevent oscillation caused by the natural vibration of the mechanical brake or the influence of the brake torque when the state of the mechanical brake changes.

Brief Description of the Drawings

[0020] [Figure 1] It is a block diagram showing the configuration of the system according to Embodiment 1 of the present invention. [Figure 2] It is a block diagram showing the configuration of the control parameter change unit 8. [Figure 3] It is a diagram showing the time response of the brake torque and the servo control parameter during the brake operation during linear interpolation. [Figure 4] It is a diagram showing the time response of the brake torque and the servo control parameter during the brake operation during exponential interpolation. [Figure 5] It is a block diagram showing the configuration of the feedback control unit 3, and is a block diagram for explaining PID control. [Figure 6] It is a block diagram showing the configuration of the feedback control unit 3, and is a block diagram for explaining P-PI control. [Figure 7] It is a block diagram showing the configuration of Embodiment 1 including the feedforward control unit 17. [Figure 8] It is a block diagram showing the configuration of the feedforward control unit 17. [Figure 9] It is a block diagram showing the configuration of the control parameter change unit 25. [Figure 10] It is a block diagram showing the configuration of the system according to Example 2 of the present invention. [Figure 11] It is a block diagram showing the configuration of the control parameter changing unit 23. [Figure 12] It is a diagram showing the time response of the estimation operation according to Example 2 of the present invention. [Figure 13] It is a block diagram showing the configuration of Example 2 including the feedforward control unit 17. [Figure 14] It is a block diagram showing the configuration of the control parameter changing unit 26. [Figure 15] It is a block diagram showing the configuration of the control parameter changing unit 25. [Figure 16] It is a block diagram showing the configuration of the control parameter changing unit 26. ​​​​​​​​​​​​​​​​​​​​​​​​​The feedback control unit 3 outputs a feedback torque command to the current control unit 4 through feedback control corresponding to the position error output from the subtractor 50.

[0026] The current control unit 4 controls the current flowing to the motor 5 so that the torque generated by the motor 5 follows the feedback torque command. The motor 5 drives the spindle by generating torque with the current supplied from the current control unit 4.

[0027] The mechanical control unit 7 controls the mechanical brake 6, which is provided on the motor 5 or spindle, by outputting a brake operation command to the mechanical brake 6.

[0028] The mechanical brake 6 is driven by a hydraulic system in response to a brake operation command output from the mechanical control unit 7. The state of the mechanical brake 6 can be switched to one of the following depending on the brake operation command: a released state in which the brake is not applied, a low-pressure brake state in which the brake is applied weakly, or a high-pressure brake state in which the brake is applied strongly to fix the C-axis.

[0029] In the following example 1, we will describe the case where the change time for the C-axis control parameter is fixed.

[0030] The control parameter changing unit 8 receives a brake operation command output from the mechanical control unit 7 as input, estimates the brake torque of the mechanical brake 6 when the brake operation command is switched based on that brake operation command, and outputs feedback control parameters to the feedback control unit 3.

[0031] The specific configuration of the control parameter changing unit 8 will be described with reference to Figure 2. Figure 2 is a block diagram showing the configuration of the control parameter changing unit 8.

[0032] The control parameter modification unit 8 includes a brake state simulation unit 9 and a parameter interpolation unit 10.

[0033] The brake state simulation unit 9 receives a brake operation command output from the mechanical control unit 7 as input. Based on the brake operation command, the brake state simulation unit 9 simulates the brake torque during low-pressure braking, taking into account the response delay of the mechanical brake, the rise time of the brake torque, and the fall time of the brake torque, and calculates the low-pressure braking ratio, which it then outputs to the parameter interpolation unit 10.

[0034] As shown in Figure 3, there is a delay between the transmission of the low-pressure brake operation command (upper part of Figure 3) and the response of the brake torque, and it also takes time for the brake torque to rise and fall. Therefore, if the brake torque changes in proportion to time, the brake torque will change with a delay from the time the low-pressure brake operation command is transmitted, as shown in the middle part of Figure 3 (in the example shown in Figure 3, the brake torque increases).

[0035] The low-pressure braking ratio is 0% when the brake is released, and 100% when the low-pressure brake is engaged. The low-pressure braking ratio is a response that simulates the brake torque (middle panel of Figure 3) in accordance with the low-pressure brake operation command (upper panel of Figure 3).

[0036] The parameter interpolation unit 10 receives the low-pressure braking ratio output from the brake state simulation unit 9 as input, and interpolates the feedback control parameters for states between the brake release state and the low-pressure braking state based on that low-pressure braking ratio, as shown in the lower part of Figure 3. That is, when the low-pressure braking ratio is 0%, the parameter interpolation unit 10 outputs the feedback control parameter S1 for the brake release state, and when the low-pressure braking ratio is 100%, it outputs the feedback control parameter S2 for the low-pressure braking state. When the low-pressure braking ratio is 50%, the parameter interpolation unit 10 outputs the average value of the feedback control parameter S1 for the brake release state and the feedback control parameter S2 for the low-pressure braking state.

[0037] When the brake torque changes exponentially with respect to time, the brake torque in response to the low-pressure brake operation command (upper part of Figure 4) changes as shown in the middle part of Figure 4. In this case, the brake state simulation unit 9 simulates the low-pressure brake ratio corresponding to the brake torque shown in the middle part of Figure 4. The parameter interpolation unit 10 interpolates the feedback control parameters according to the parameters represented by the curve between S1 and S2, as shown in the lower part of Figure 4.

[0038] Since the change time for the C-axis control parameters is fixed, the change time and response delay time can be determined by pre-measuring the rise and fall times of the brake torque on the actual machine.

[0039] Furthermore, the choice between linear and exponential interpolation of parameters is determined based on the measured motor torque and the presence or absence of abnormal noise during the interpolation operation. When achieving low-pressure braking, the motor torque balances with the brake torque with a delay due to feedback control. Therefore, exponential interpolation is more likely to match the measured motor torque than linear interpolation. Exponential interpolation also has the advantage of lower computational load. However, with exponential interpolation, the slope of the parameter at the start of interpolation is steeper than with linear interpolation, which can easily lead to unstable control. Therefore, if abnormal noise or vibration occurs during operation when exponential interpolation is selected, linear interpolation should be chosen.

[0040] The detailed configuration of the feedback control unit 3 can be described as follows:

[0041] Figure 5 shows the first configuration of the feedback control unit 3. Figure 5 is a block diagram of this first configuration. In the first configuration, PID control is implemented. The subtractor 50 calculates the position error by subtracting the position detection value detected by the encoder 2 provided on the motor 5 from the position command, and outputs the calculated position error to the P control unit 11, the I control unit 12, and the D control unit 13. The P control unit 11 performs proportional control, the I control unit 12 performs integral control, and the D control unit 13 performs differential control, and their respective control inputs are output to the adder 51. The adder 51 calculates the feedback torque command by adding the control inputs output from the P control unit 11, the I control unit 12, and the D control unit 13, and outputs the calculated feedback torque command to the current control unit 4.

[0042] Figure 6 shows the second configuration of the feedback control unit 3. Figure 6 is a block diagram of this second configuration. In the second configuration, P-PI control is realized. The subtractor 50 calculates the position error by subtracting the position detection value detected by the encoder 2 provided on the motor 5 from the position command, and outputs the calculated position error to the position control unit 14. The position control unit 14 calculates the speed command from the position error using P control, and outputs the calculated speed command to the subtractor 52. The differentiator 15 calculates the speed detection value by differentiating the motor position detection value, and outputs the calculated speed detection value to the subtractor 52. The subtractor 52 calculates the speed error by subtracting the speed detection value from the aforementioned speed command, and outputs the calculated speed error to the speed control unit 16. The speed control unit 16 calculates the feedback torque command using PI control based on the input speed error, and outputs the calculated feedback torque command to the current control unit 4.

[0043] By setting the feedback control parameters calculated by the control parameter changing unit 8 into the feedback control unit 3, each control parameter of the feedback control unit 3 can be changed according to the state of the mechanical brake 6.

[0044] Another example of a control device configuration may be one that implements feedforward control. Figure 7 shows an example of such a configuration. The control device shown in Figure 7 includes a feedforward control unit 17 that performs feedforward control based on a position command. The feedforward control unit 17 generates a feedforward torque command by feedforward control according to the position command, outputs the generated feedforward torque command, and calculates a speed command which is output to the feedback control unit 28. The adder 53 generates a torque command by adding the feedback torque command and the feedforward torque command, and outputs the generated torque command to the current control unit 4.

[0045] Figure 8 shows the detailed configuration of the feedforward control unit 17. The detailed configuration of the feedforward control unit 17 can be described below as follows:

[0046] In the first configuration, the feedforward control unit 17 calculates a velocity command from the position command using a differentiator 18, inputs the calculated velocity command to a differentiator 19, and adds it to the input to the subtractor 52. Figure 17 shows the detailed configuration of the feedback control unit 28. In addition to the P-PI control described above, the feedforward control unit 17 adds the velocity command output by the feedforward control unit 17 to the subtractor 52 to calculate the velocity error, and outputs the calculated velocity error to the velocity control unit 16. The method realized by the first configuration corresponds to an example of the first method.

[0047] In the second configuration, the feedforward control unit 17 calculates an acceleration command from the velocity command using a differentiator 19, multiplies this value by a constant K20 proportional to the inertia of the drive system to calculate an acceleration torque command that generates the acceleration command, and outputs the calculated acceleration torque command as a feedforward torque command. The method realized by the second configuration corresponds to an example of the second method.

[0048] In the third configuration, the feedforward control unit 17 calculates an inversion compensation torque command using the inversion compensation calculation unit 21 and outputs the calculated inversion compensation torque command as a feedforward torque command. The inversion compensation calculation unit 21 calculates the inversion compensation torque command using known techniques such as inversion projection compensation according to the position command. The method realized by the third configuration corresponds to an example of the third method. As will be described in detail later, the inversion compensation calculation unit 21 has compensation parameters in the low-pressure brake state and uses the value obtained by multiplying these parameters by the feedforward control parameter coefficient output by the parameter coefficient selection unit 22 for compensation.

[0049] At least one configuration from the first, second, and third configurations is adopted. That is, at least one method from the first, second, and third methods is performed. A combination of multiple methods from the first, second, and third methods may be performed by adopting a combination of multiple configurations from the first, second, and third configurations.

[0050] For example, when using both the second and third configurations, the adder 54 adds the acceleration torque command and the reversal compensation torque command, and the command obtained from this addition is output as a feedforward torque command.

[0051] The control parameter changing unit 25 shown in Figure 7 estimates the brake torque of the mechanical brake 6 when the brake operation command is switched based on the brake operation command, outputs the feedback control parameter to the feedback control unit 28, and outputs the feedforward control parameter coefficient to the feedforward control unit 17.

[0052] Figure 9 shows the configuration of the control parameter modification unit 25. Figure 9 is a block diagram showing the configuration of the control parameter modification unit 25. The parameter coefficient selection unit 22 receives a brake operation command as input, selects a feedforward control parameter coefficient to multiply the feedforward control parameter according to the brake operation command, and outputs the selected feedforward control parameter coefficient to the feedforward control unit 17.

[0053] When the feedforward control unit 17 performs compensation for inversion protrusions to reduce position errors (inversion protrusions) during C-axis reversal, it is necessary to switch the compensation parameters according to the state of the mechanical brake 6. In the low-pressure brake state, brake torque is applied, so compensation for inversion protrusions is necessary. However, in the brake release state, brake torque is not applied, so compensation for inversion protrusions is reduced, and in the high-pressure brake state, compensation parameters are selected to disable compensation for inversion protrusions. Therefore, the feedforward control unit 17 is given compensation parameters for the low-pressure brake state, and a value of 1 is selected as the feedforward control parameter coefficient when the low-pressure brake state is in the high-pressure brake state, 0 when the high-pressure brake state is in the high-pressure brake state, and a value between 0 and 1 is selected when the brake is released. By outputting the feedforward control parameter coefficient selected in this way to the feedforward control unit 17, the feedforward control can be appropriately switched according to the brake state.

[0054] In the above-described embodiment, the case in which the parameter coefficient selection unit 22 selects feedforward control parameter coefficients based on the brake operation command was explained. As shown in Figure 15, the low-pressure brake ratio output by the brake state simulation unit 9 may be input to the parameter coefficient selection unit 27, and the feedforward control parameter coefficients may be calculated to change over time according to the low-pressure brake ratio and output to the feedforward control unit 17.

[0055] The response delay, rise time, and fall time of the brake torque generated by the mechanical brake 6 may change due to aging of the hydraulic system, brake pads, etc. In Example 2, we will describe a case where the change time of the C-axis control parameter, which was fixed in Example 1, is variable.

[0056] The difference between Example 2 and Example 1 is that, as shown in Figures 10 and 11, the motor torque command is additionally input to the control parameter change unit 23 and the brake state simulation unit 24.

[0057] To update the brake torque response delay, rise time, and fall time to reflect changes over time, the brake torque estimation operation involves switching between a low-pressure brake state and a brake release state while the C-axis is moving at a constant speed, and measuring the time response of the low-pressure brake operation command and the motor torque command.

[0058] Figure 12 shows the time responses of the motor speed, motor torque command, low-pressure brake operation command, and brake torque in this estimated operation. In the estimated operation, the low-pressure brake is switched ON and OFF while the C-axis is moving at a constant speed, so the brake torque is generated with a delay from the low-pressure brake operation command, and a motor torque command that balances the brake torque is generated in order to move at a constant speed. Therefore, as shown in Table 1 below, various times can be estimated from the relationship between the low-pressure brake operation command and the motor torque command.

[0059] This estimation method assumes operation in a state where the center of gravity is balanced and no workpiece is being gripped. However, it is also conceivable to perform estimation when the gripped workpiece is eccentric and the center of gravity is unbalanced, and the motor torque command during C-axis movement at a constant speed changes within one rotation of the C-axis. In this case, the motor torque command for one rotation of the C-axis with the low-pressure brake OFF can be stored in a memory or other storage device. Then, the motor torque after the low-pressure brake operation command is ON can be compared with the stored motor torque command, and various times can be estimated in the same way as above based on the difference in torque at the same phase.

[0060] [Table 1]

[0061] The reason for rotating the C-axis at a constant speed is that, in the estimated operation, a motor torque command that balances the brake torque is generated, allowing the brake torque to be estimated from the motor torque command. Furthermore, by rotating at a constant speed, acceleration and deceleration torque are not required, and the factors influencing the motor torque command can be limited solely to the influence of the brake torque.

[0062] By simulating brake torque in the brake state simulation unit 24 using the updated parameters mentioned above, it is possible to respond to changes in brake torque due to aging and other factors, and to stably control the C-axis.

[0063] Furthermore, in the second embodiment, as shown in Figure 13, the control device may also include a feedforward control unit 17 that performs feedforward control based on a position command.

[0064] The control parameter change unit 26 receives brake operation command and torque command as input, estimates the brake torque of the mechanical brake 6 when the brake operation command is switched, outputs feedback control parameters to the feedback control unit 28, and outputs feedforward control parameter coefficients to the feedforward control unit 17.

[0065] Figure 14 is a block diagram showing the configuration of the control parameter changing unit 26. The parameter coefficient selection unit 22 receives a brake operation command as input, selects a feedforward control parameter coefficient to be multiplied by the feedforward control parameter according to the brake operation command, and outputs the selected feedforward control parameter coefficient to the feedforward control unit 17.

[0066] In addition, as in Example 1, as shown in Figure 16, the low-pressure braking ratio output by the brake state simulation unit 24 may be input to the parameter coefficient selection unit 27, and the feedforward control parameter coefficients may be calculated to change over time according to the low-pressure braking ratio and output to the feedforward control unit 17.

[0067] Furthermore, in the above-described embodiment, a method for generating a feedforward torque command based on a position command in the inversion compensation calculation unit 21 in order to realize inversion compensation control was explained. When using the P-PI control shown in Figure 6, the inversion compensation calculation unit 21 may generate an inversion compensation position command and an inversion compensation speed command from the position command using known techniques, and feedforward control may be realized by adding the inversion compensation position command to the subtractor 50 or adding the inversion compensation speed command to the subtractor 52.

[0068] According to the control devices of each embodiment described above, the braking state of the mechanical brake is estimated by considering the response delay of the mechanical brake and the rise and fall times of the brake torque, and the feedback control parameters and feedforward control parameters are appropriately changed. This makes it possible to prevent oscillation due to the natural vibration of the mechanical brake or the influence of the brake torque when the state of the mechanical brake changes.

[0069] For example, when the machining load in a generation process is small, the mechanical brake can be released to improve machining accuracy. Conversely, when performing heavy cutting with a large machining load, the mechanical brake can be driven at low pressure to generate low braking torque, thereby improving cutting performance and preventing machining chatter.

[0070] The configuration of the control device according to each of the embodiments described above can be realized using hardware resources such as a processor and electronic circuits, and devices such as memory may be used as necessary in its realization. Furthermore, the configuration of the control device according to each embodiment may be realized by a computer. In other words, all or part of the configuration of the control device according to each embodiment may be realized through the cooperation of hardware resources such as the CPU (Central Processing Unit) and memory of a computer and software (programs) that define the operation of the CPU, etc. The program is stored in the storage device of the control device according to each embodiment via a recording medium such as a CD or DVD, or via a communication path such as a network. As another example, the configuration of the control device according to each embodiment may be realized by a DSP (Digital Signal Processor) or an FPGA (Field Programmable Gate Array), etc. [Explanation of Symbols]

[0071] 1 Position command generation unit, 2 Encoder, 3, 28 Feedback control unit, 4 Current control unit, 5 Motor, 6 Mechanical brake, 7 Mechanical control unit, 8, 23, 25, 26 Control parameter change unit, 9, 24 Brake state simulation unit, 10 Parameter interpolation unit, 11 P control unit, 12 I control unit, 13 D control unit, 14 Position control unit, 15, 18, 19 Differentiator, 16 Speed ​​control unit, 17 Feedforward control unit, 20 Constant K proportional to the inertia of the drive system, 21 Inversion compensation calculation unit, 22 Parameter coefficient selection unit, 27 Parameter coefficient selection unit, 50, 52 Subtractor, 51, 53, 54 Adder.

Claims

1. The motor that drives the spindle, A mechanical brake, mounted on the main shaft or the motor, which allows for changing the brake torque and releasing the brake, A mechanical control unit that outputs a brake operation command to the aforementioned mechanical brake, An encoder for detecting the position of the motor, A position command generation unit that outputs a position command for the C-axis control of the main spindle from a higher level, A feedback control unit calculates a torque command for the motor by feedback control so that the position detection value of the encoder follows the position command, A current control unit receives a torque command from the motor as input and supplies current so that the torque generated by the motor follows the torque command, When the mechanical brake is operated while the C-axis is being controlled, the control parameter changing unit takes the brake operation command as input and modifies the C-axis control parameters of the feedback control unit, taking into account the response delay of the mechanical brake, the rise time and fall time of the brake torque. A control device for a machine tool having a C-axis function, characterized by having the following features.

2. The control method by the feedback control unit is a method of performing PID control based on the position error between the position of the C axis and the position command, or a P-PI control method in which a speed command is calculated from the position error by P control, the speed of the C axis is detected in a subsequent stage, and PI control is performed to follow the speed command. A control device for a machine tool having a C-axis function as described in feature 1.

3. In addition to the feedback control unit, the system further includes a feedforward control unit that performs feedforward control based on the position command so that the C-axis follows the position command. The control parameter changing unit modifies the C-axis control parameters of the feedforward control unit when the mechanical brake is operated while the C-axis is being controlled, taking into account the response delay of the mechanical brake, the rise time and fall time of the brake torque. A control device for a machine tool having a C-axis function as described in feature 2.

4. The control method by the feedforward control unit includes at least one feedforward control method from among: a first method of differentiating the position command to calculate a feedforward velocity command and adding it to the velocity command of the P-PI control; a second method of calculating a feedforward acceleration command by second-order differentiation of the position command and adding a control input to the feedback control input such that the C axis generates an acceleration corresponding to the feedforward acceleration command; and a third method of performing reversal compensation control so that the position error is reduced when the C axis reverses direction. A control device for a machine tool having a C-axis function as described in feature 3.

5. The control parameter changing unit is A brake state simulation unit that takes the brake operation command as input and estimates the brake torque of the mechanical brake in response to the switching of the brake operation command, A parameter interpolation unit outputs feedback control parameters to the feedback control unit according to the estimated brake torque estimated by the brake state simulation unit, It has, The brake state simulation unit estimates the brake torque of the mechanical brake from the torque command, The parameter interpolation unit outputs feedback control parameters that are suitable for the estimated brake torque to the feedback control unit. A control device for a machine tool having a C-axis function as described in claim 1 or 2.

6. The control parameter changing unit is A brake state simulation unit that takes the brake operation command as input and estimates the brake torque of the mechanical brake in response to the switching of the brake operation command, A parameter interpolation unit outputs feedback control parameters to the feedback control unit according to the estimated brake torque estimated by the brake state simulation unit, A parameter coefficient selection unit that takes the brake operation command as input to select a feedforward control parameter coefficient for switching the brake operation command, or takes the estimated brake torque as input to calculate a feedforward control parameter coefficient that changes over time, and outputs the selected or calculated feedforward control parameter coefficient to the feedforward control unit, It has, The brake state simulation unit estimates the brake torque of the mechanical brake from the torque command, The parameter interpolation unit outputs feedback control parameters that are suitable for the estimated brake torque to the feedback control unit. The parameter coefficient selection unit outputs a feedforward control parameter coefficient that matches the brake operation command or the estimated brake torque to the feedforward control unit. The feedforward control unit multiplies the compensation parameter of the inversion compensation control by the feedforward control parameter coefficient. A control device for a machine tool having a C-axis function as described in feature 4.

7. When estimating the brake torque, the brake state simulation unit operates the mechanical brake when the C-axis rotates at a constant speed, based on the position command generation unit outputting a command to rotate the C-axis at a constant speed, and estimates the response delay, the rise time and fall time of the brake torque from the torque command. A control device for a machine tool having a C-axis function as described in feature 6.

8. The brake state simulation unit takes the torque command as input and updates the estimated brake torque response according to the response delay, rise time, and fall time of the brake torque, which are estimated each time, and makes the change time of the feedback control parameter or feedforward control parameter coefficient variable. A control device for a machine tool having a C-axis function as described in feature 6.

9. The brake state simulation unit selects linear interpolation or exponential interpolation as the interpolation method for the rise time and fall time of the brake torque. A control device for a machine tool having a C-axis function as described in feature 6.

10. The brake state simulation unit, when exponential interpolation is selected and the feedback control parameter or feedforward control parameter coefficient is changed, selects linear interpolation if abnormal noise or vibration occurs. A control device for a machine tool having a C-axis function as described in feature 9.

Images