JP6880322B2 - Numerical control device - Google Patents

Description

The present invention relates to a numerical control device that controls a machine tool.

A numerically controlled machine tool includes an actuator and a driven body such as a table or a tool driven by the actuator. The actuator is a rotary servo motor, a linear servo motor, or the like. The driven body operates by controlling the actuator according to a command indicating a position, a path, a speed, a torque, and the like output from a numerical control device connected to the machine tool. As a result, the workpiece to be machined, which is fixed to the table, is machined by the tool. The control for driving the driven body so that the position of the tool with respect to the workpiece accurately follows the command locus, which is the commanded path, is called locus control or contour motion control. Trajectory control or contour motion control is precisely performed by a numerical control device. By executing the trajectory control or the contour motion control, the servomotors connected to each of the plurality of axes such as the spindle and the feed axis provided in the machine tool operate to control the position of the tool with respect to the workpiece.

In a machine tool, when machining a work piece, a cutting force is generated at a portion where the tool comes into contact with the work piece. In order to extend the life of the tool and improve the machining accuracy of the workpiece, it is important to keep the cutting force constant. However, when the cutting tool is, for example, an end mill or a drill, the cutting blades provided on the shaft of the cutting tool are arranged apart from each other in the direction of rotation of the shaft. The cutting resistance in the work fluctuates, and the machining to the workpiece is performed intermittently. Therefore, when a cutting tool such as an end mill or a drill is used, it is difficult to keep the cutting force constant, and the fluctuation of the cutting force causes disturbance of the control system of the servomotor that drives the spindle and the feed shaft. When the control system of the servo motor connected to the feed shaft vibrates due to fluctuations in cutting force, the relative position of the tool with respect to the workpiece also becomes vibrating, and the machining accuracy or surface quality deteriorates. Not only does it, but the tool wears out. Patent Document 1 discloses a technique for processing a workpiece by setting the frequency response band of a control system for controlling a motor to a frequency response band such that tool wear is within an allowable range. According to the technique disclosed in Patent Document 1, even if a disturbance occurs in the control system due to fluctuations in cutting resistance during machining, tool wear is suppressed within a certain range and machining quality is stabilized. At the same time, the processing efficiency is improved.

Japanese Unexamined Patent Publication No. 2013-250866

However, the technique disclosed in Patent Document 1 has a problem that the narrowing of the frequency response band may reduce the followability of the tool position to the command locus, which may adversely affect the machining accuracy.

The present invention has been made in view of the above, and an object of the present invention is to obtain a numerical control device capable of suppressing a decrease in followability to a command locus.

In order to solve the above-mentioned problems and achieve the object, the numerical control device of the present invention is a numerical control device that controls a mechanical system that processes a workpiece by a tool that processes the workpiece, and is a position. A servo control unit that drives a motor connected to the driven body so that the position of the driven body on which the workpiece is provided follows the position command based on the command is provided. The numerical control device measures or estimates and outputs the cutting force generated between the tool and the workpiece, and the cutting force that calculates the cutting force vector based on the position of the driven body and the cutting force. It is equipped with a vector calculation unit and a mechanical characteristic identification unit that identifies the dynamic characteristics of the mechanical system with respect to the cutting force. The numerical control device is characterized by including a control characteristic changing unit that changes the control characteristics of the servo control unit based on the cutting force vector and the dynamic characteristics of the mechanical system identified by the mechanical characteristic identification unit.

According to the present invention, there is an effect that a decrease in followability to a command locus can be suppressed.

The figure which shows the structure of the numerical control apparatus which concerns on Embodiment 1 of this invention. The figure which shows the structure of the motor and the mechanical system shown in FIG. The figure which shows the structure of the simulated response calculation part shown in FIG. The figure which shows the modification of the simulated response calculation part shown in FIG. FIG. 1 for explaining the machine characteristic information calculated by the machine characteristic identification unit shown in FIG. FIG. 2 for explaining the machine characteristic information calculated by the machine characteristic identification unit shown in FIG. A flowchart for explaining the operation of the control characteristic changing unit shown in FIG. FIG. 1 shows an example in which disturbance vibration is generated at the machine end position shown in FIG. 1 due to a cutting force. FIG. 2 shows an example in which disturbance vibration is generated at the machine end position shown in FIG. 1 due to a cutting force. The figure which shows the structure of the numerical control apparatus which concerns on Embodiment 2 of this invention. The figure which shows the structure of the numerical control apparatus which concerns on Embodiment 3 of this invention. A block diagram of the motor and mechanical system shown in FIG. 2 approximated by a two-inertia model. The figure which shows the hardware configuration example of the numerical control apparatus which concerns on Embodiments 1 to 3.

Hereinafter, the numerical control device according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a diagram showing a configuration of a numerical control device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the motor and the mechanical system shown in FIG. The numerical control device 100-1 generates a torque command 202 based on the position command 200 and the machine end position 201, and gives the generated torque command 202 to the motor 7 provided in the machine tool 100 to control the mechanical system. Drive 8. The numerical control device 100-1 includes a servo control unit 1, a cutting force output unit 2, a cutting force vector calculation unit 3, a simulated response calculation unit 4, a mechanical characteristic identification unit 5, a control characteristic change unit 6, and a subtraction unit 9.

The servo control unit 1 is connected to the motor 7, and by giving the torque command 202 to the motor 7, the mechanical system 8 to be controlled is driven. As shown in FIG. 2, the motor 7 includes a servomotor 71 and a motor position detector 72. A shaft 71b is provided on the rotor 71a of the servomotor 71. As the motor position detector 72, a rotary encoder that detects the rotational position of the rotor 71a is used. The mechanical system 8 includes a table 81, a ball screw nut 82, a ball screw 83, a coupling 84, a mechanical end position detector 85, and a mechanical end position detector head 86. The ball screw 83 of the mechanical system 8 is connected to the shaft 71b of the servomotor 71 via the coupling 84. A ball screw nut 82 is fitted to the ball screw 83, and a table 81, which is a driven body, is fixed to the ball screw nut 82. Table 81, by a guide mechanism (not shown), a ball screw 83 is movably supported in the extension building direction. The machine end position detector 85 and the machine end position detector head 86 are encoders for detecting the position of the table 81, which is the control target of the numerical control device 100-1. The mechanical end position detector 85 is, for example, a linear encoder, and the mechanical end position detector head 86 is, for example, a linear encoder head. The machine end position 201 input to the servo control unit 1 is information indicating the rotation position of the rotor 71a detected by the motor position detector 72 and information indicating the position of the table 81 detected by the machine end position detector 85. At least one of them is shown.

The mechanical end position detector 85 measures the moving distance of the table 81, whereas the motor position detector 72 measures the rotation angle of the rotor 71a. However, by multiplying this rotation angle by the ball screw lead, which is the table movement distance per rotation of the motor 7, and dividing by the angle of one rotation of the rotor 71a, 2π [rad], the rotor 71a in the servo control unit 1 The rotation angle of is converted into the length of the table 81 in the moving direction. In the first embodiment, it is assumed that a value obtained by converting the rotation angle of the rotor 71a into the moving direction of the table 81 is used.

Feedback control that uses only the position information detected by the motor position detector 72 as the machine end position 201 is called semi-closed loop control. As the machine end position 201, feedback control using both the position information detected by the motor position detector 72 and the position information detected by the machine end position detector 85, or the machine end position detector 85 detected. Feedback control that uses only position information is called full closed loop control. Either semi-closed loop control or fully closed loop control may be applied to the numerical control device 100-1 according to the first embodiment. Hereinafter, a configuration example of the numerical control device 100-1 to which the full closed loop control is applied will be described. In the following, the position information used for feedback control will be referred to as the machine end position. The configuration of the mechanical system 8 is an example, and the configuration of the mechanical system 8 is not limited to the example shown in FIG. 2, and the numerical control device 100-1 can control a plurality of mechanical systems. is there.

The position command 200 and the machine end position 201 are input to the servo control unit 1 shown in FIG. The servo control unit 1 generates a torque command 202 that causes the machine end position 201 to follow the position command 200. For example, the servo control unit 1 obtains a position deviation which is a difference between the position command 200 and the machine end position 201, executes a position control process such as proportional control for the position deviation, and calculates a speed command. Further, the torque command 202 is calculated and output by executing a speed control process such as proportional integration control for the speed command.

The cutting force output unit 2 shown in FIG. 1 measures, for example, the cutting force generated at the contact portion of the tool 101 with the workpiece 90 when the workpiece 90 provided on the table 81 is machined, and measures the measured cutting force. The cutting force 203, which is the information to be shown, is output.

For the measurement of the cutting force 203, for example, a load cell, a power meter, or the like is used. A load cell, a power meter, or the like is a measuring instrument capable of directly measuring a cutting force 203. The cutting force 203 can also be estimated from the motor current, and when the cutting force 203 is estimated from the motor current, a method called a disturbance observer is used. The cutting force output unit 2 may use a means for indirectly measuring the cutting force 203 instead of a means for directly measuring the cutting force 203.

The cutting force vector calculation unit 3 calculates, for example, three cutting force vectors based on the measured cutting force 203 and the machine end position 201. Of the three cutting force vectors, the first cutting force vector is a vector based on a direction parallel to the drive axis such as the X-axis, Y-axis, and Z-axis of the machine. Hereinafter, the first cutting force vector is referred to as a machine axial cutting force vector. Of the three cutting force vectors, the second cutting force vector is a cutting force vector parallel to the feed direction of the tool 101. Hereinafter, the second cutting force vector is referred to as a tool feed direction cutting force vector. Of the three cutting force vectors, the third cutting force vector is a cutting force vector in the direction perpendicular to the feed direction of the tool 101. Hereinafter, the third cutting force vector is referred to as a vertical cutting force vector.

Here, an example in which the cutting force is measured using a power meter will be described. When measuring cutting force using a power meter, generally, by adjusting the direction of the power meter installed in the machine, the drive shafts of the machine, such as the X-axis, Y-axis, and Z-axis, are extended. The cutting force in the direction parallel to the direction of vibration is measured. Therefore, the output from the power meter includes a component of the machine axial cutting force vector. The power meter is not only capable of measuring the mechanical axial cutting force vector corresponding to the directions of the three axes, but also the mechanical axis corresponding to the direction of one of the X-axis, Y-axis, and Z-axis. Some can measure only the directional cutting force vector. Then, the cutting force in the unmeasured direction is regarded as 0. In a 5-axis control machine having five rotation axes, the installation direction of the power meter may change depending on the direction of the rotation axis. In such a case, the angle of the rotation axis is the cutting force vector in the machine axis direction. Used for calculation.

The cutting force vector calculation unit 3 can calculate the moving speed of each axis of the plurality of tools 101 by differentiating the machine end position 201. When the machine tool 100 includes, for example, three tools 101, the cutting force vector calculation unit 3 calculates a movement speed vector v whose component is the movement speed of each axis of the three tools 101. Further, in the cutting force vector calculation unit 3, the tool feed direction cutting force vector Ft is calculated by the equations (1) and (2). “U” is a unit vector. “V” is a moving speed vector. "F" is a machine axial cutting force vector. "・" Indicates the inner product. Further, in the cutting force vector calculation unit 3, the vertical cutting force vector Fn is calculated by the equations (1) and (3).
u = v / | v | ... (1) formula Ft = (F · u) ... (2) formula Fn = F-Ft ... (3) formula

The cutting force vector calculation unit 3 uses the speed feedback information used for speed control instead of the moving speed obtained by differentiating the machine end position 201 to obtain the tool feed direction cutting force vector and the vertical cutting force vector. It may be configured to calculate. Further, the cutting force vector calculation unit 3 calculates the magnitude of the machine axial cutting force vector F, and sets the calculated magnitude of the machine axial cutting force vector F as the magnitude of the cutting force.

Further, the cutting force vector calculation unit 3 holds data indicating the components of the machine axial cutting force vector corresponding to each of the plurality of axes calculated from the present time to the time point retroactive to a certain time, and the held data. Is used to calculate the power spectrum of the cutting force for each frequency. The power spectrum with respect to frequency can be calculated by performing a Fourier transform.

The cutting force vector calculation unit 3 outputs the power spectrum of each component of each cutting force vector, the magnitude of the cutting force, and each machine axial cutting force vector to the control characteristic changing unit 6 as the cutting force vector information 204. ..

FIG. 3 is a diagram showing the configuration of the simulated response calculation unit shown in FIG. The simulated response calculation unit 4 simulates the response of the machine end position 201 based on the position command 200, calculates and outputs the model position 205, which is the calculation result of the ideal position that the machine end position 201 should follow. The simulated response calculation unit 4 includes a position control simulation unit 41 and an integration calculation unit 42. The position control simulating unit 41 executes the same processing as the position control processing performed by the servo control unit 1 with respect to the difference between the position command 200 and the output of the integration calculation unit 42. The integration calculation unit 42 obtains the value of the machine end position 201 by integrating the processing result of the position control simulation unit 41 and outputs it as the model position 205.

FIG. 4 is a diagram showing a modified example of the simulated response calculation unit shown in FIG. The simulated response calculation unit 4A shown in FIG. 4 includes a speed control simulation unit 43, an integral calculation unit 44, and a proportional constant calculation unit 45 in addition to the position control simulation unit 41 and the integration calculation unit 42 shown in FIG. In addition to the model position 205, the simulated response calculation unit 4A calculates the model speed 208 indicating the ideal speed value of the mechanical system 8 and the model torque 209 which is information indicating the ideal output of the motor torque. .. The proportional constant calculation unit 45 calculates the model torque 209 by integrating the constant for torque conversion with the model speed 208. Each of Kpp, Kbp, Kvi, Kt and J shows a proportionality constant. s is a Laplace operator that represents the derivative. 1 / s represents the integral. In the position control simulating unit 41, general proportional control is performed. In the speed control simulation unit 43, general proportional integration control is performed. The output of the speed control simulation unit 43 is in the dimension of acceleration, and the output of the speed control simulation unit 43 is input to the integration calculation unit 44, and is integrated in two stages by the integration calculation unit 44 and the integration calculation unit 42. This simulates the machine end position. Further, the output of the speed control simulation unit 43 is input to the proportional constant calculation unit 45. The proportional constant calculation unit 45 converts the output of the speed control simulation unit 43 into torque by multiplying the output of the speed control simulation unit 43 by the proportional constant Kt.

The subtraction unit 9 calculates the position disturbance 206 caused by the disturbance to the control such as the cutting force by subtracting the model position 205 calculated by the simulated response calculation unit 4 from the machine end position 201.

The machine characteristic identification unit 5 identifies the mechanical characteristics of the machine tool 100 with respect to the cutting force 203 by using the position disturbance 206 and the cutting force 203. In the first embodiment, an example of identifying a transfer function from the cutting force 203 to the position disturbance 206 in the control system as the mechanical characteristics with respect to the cutting force 203 will be described. The mechanical characteristic identification unit 5 calculates the speed disturbance, torque disturbance, etc. by using the model speed 208, the model torque 209, etc. calculated by the simulated response calculation unit 4A shown in FIG. 4 instead of the position disturbance 206. , The transfer function from the cutting force 203 to the velocity disturbance, or the transfer function from the cutting force 203 to the torque disturbance may be identified.

The mechanical property identification unit 5 performs numerical processing such as Fourier transform on the cutting force 203 and the position disturbance 206 to calculate the frequency transfer function. The mechanical characteristic identification unit 5 outputs the calculated frequency transfer function as mechanical characteristic information 207 to the control characteristic changing unit 6. FIG. 5 is a diagram for explaining the machine characteristic information calculated by the machine characteristic identification unit shown in FIG. The horizontal axis of FIG. 5 represents the logarithmic frequency, and the vertical axis of FIG. 5 represents the gain represented by the decibel value. In FIG. 5, the frequency transfer function is represented by a gain diagram. In the gain diagram, the resonance point appears as a positive peak and the antiresonance point appears as a negative peak. FIG. 6 is a second diagram for explaining the machine characteristic information calculated by the machine characteristic identification unit shown in FIG. The horizontal axis of FIG. 6 represents the logarithmic frequency, and the vertical axis of FIG. 6 represents the phase. In FIG. 6, the frequency transfer function is represented by a phase diagram. The frequency transfer function can also be represented by a coquad diagram whose horizontal axis is a logarithmic frequency and whose vertical axis is represented by a real part and an imaginary part after Fourier transform.

Disturbances in the control system include disturbances due to friction in addition to disturbances due to fluctuations in cutting force, and positional disturbance 206 is also generated by friction. As a typical example, there is a quadrant protrusion that occurs when the moving direction of the feed axis is reversed at the quadrant switching position of the arc. In the mechanical property identification unit 5, it is necessary to remove the influence of friction in order to identify the mechanical property with respect to the cutting force. Therefore, it is desirable to identify the mechanical properties for the cutting force unless the influence of friction generated when the moving direction of the feed shaft is reversed or the influence of friction generated when the feed shaft starts moving from the stopped state is large.

The control characteristic changing unit 6 changes the frequency characteristics of the servo control unit 1 based on the cutting force vector information 204 calculated by the cutting force vector calculation unit 3 and the mechanical characteristic information 207 identified by the mechanical characteristic identification unit 5. I do. In the locus control performed on two or more axes in the machine tool 100, if the target value responsiveness of the controlled axes is different, a locus error occurs with respect to the command locus. In the first embodiment, since such a trajectory error does not occur, the servo control unit 1 employs two-degree-of-freedom control. The two-degree-of-freedom control is a control method that uses two independent compensators to follow the target value and suppress disturbance. Since no locus error occurs even when the frequency response of the compensator for disturbance suppression differs depending on the control axis, the control characteristic changing unit 6 changes the frequency response of the disturbance response compensator, which is a compensator for disturbance suppression. As a result, disturbance suppression is realized. The disturbance response compensator is generally composed of a P (Proportional) controller, a PI (Proportional Integral) controller, and the like. That is, by adopting the two-degree-of-freedom control in the servo control unit 1, it is possible to suppress the disturbance due to the cutting force without causing a locus error.

If there is a peak in the frequency transfer function identified by the machine characteristic identification unit 5 and this peak is the resonance point, there is a possibility that vibration due to the cutting force is occurring in the range observable at the machine end position. is there. In the case of full closed loop control, vibration is generated in the motor 7 and the mechanical system 8 shown in FIG. 2, and in the case of semi-closed loop control, vibration is generated in the motor 7. In this case, the disturbance can be suppressed by increasing the responsiveness of the disturbance response compensator at the resonance point, that is, increasing the control gain of the disturbance response compensator at the resonance point.

On the other hand, when the peak of the frequency transfer function is the antiresonance point, vibration due to the cutting force may occur in a range that cannot be observed at the mechanical end position. For example, there is a possibility that the workpiece 90, the tool 101, etc. installed on the table 81 are vibrating. In this case, the disturbance due to the cutting force can be suppressed by lowering the responsiveness of the disturbance response compensator at the antiresonance point, that is, lowering the control gain of the disturbance response compensator at the antiresonance point.

Next, the operation of the control characteristic changing unit 6 will be described. FIG. 7 is a flowchart for explaining the operation of the control characteristic changing unit shown in FIG. First, the control characteristic changing unit 6 searches for a peak in the frequency range of 1/2 of the data sampling frequency in the frequency transfer function calculated by the mechanical characteristic identification unit 5 (step S1). For example, when the sampling period is 1 kHz, the range for searching for a peak is a range up to 1/2 of 1 kHz, that is, 0 to 500 Hz. Since aliasing occurs in the range from 500 Hz to 1 kHz, the control characteristic changing unit 6 does not search for the peak.

The control characteristic changing unit 6 determines whether or not an anti-resonance point or a resonance point exists in the frequency transfer function (step S2). For example, depending on whether or not there is a first peak point at which the gain value changes from decreasing to increasing, and whether or not there is a second peak point where the gain value changes from increasing to decreasing, the antiresonance point or resonance point of the resonance point. The presence or absence is judged.

When the anti-resonance point or the resonance point does not exist in the frequency transfer function (steps S2 and No), the control characteristic changing unit 6 repeats the processes of steps S1 and S2.

When the frequency transfer function has an anti-resonance point or a resonance point (steps S2, Yes), the control characteristic changing unit 6 determines whether the peak of the frequency transfer function is an anti-resonance point or an anti-resonance point (step S2, Yes). Step S3). For example, when there is a first peak point at which the gain value changes from decreasing to increasing, the control characteristic changing unit 6 determines that an antiresonance point exists in the frequency transfer function. When there is a second peak point at which the gain value changes from increasing to decreasing, the control characteristic changing unit 6 determines that the resonance point exists in the frequency transfer function. When a plurality of first peak points are present during scanning, the control characteristic changing unit 6 stores the plurality of first peak points, and determines that the lowest of them is an antiresonance point. When a plurality of second peak points are present during scanning, the control characteristic changing unit 6 stores the plurality of second peak points and determines that the largest of them is the resonance point.

When the peak of the frequency transfer function is a resonance point (steps S3, Yes), the control characteristic changing unit 6 determines whether the power spectrum of the cutting force at the peak frequency calculated by the cutting force vector calculation unit 3 is equal to or greater than the threshold value. It is determined whether the frequency is less than the threshold value (step S4).

When the power spectrum of the cutting force is less than the threshold value (steps S4 and No), the control characteristic changing unit 6 performs the process of step S8. When the power spectrum of the cutting force is equal to or greater than the threshold value (step S4, Yes), the control characteristic changing unit 6 raises the control gain of the disturbance response compensator of the servo control unit 1 at the peak frequency (step S6).

In step S3, when the peak of the frequency transfer function is an antiresonance point (steps S3, No), the control characteristic changing unit 6 has the power spectrum of the cutting force at the peak frequency calculated by the cutting force vector calculation unit 3. It is determined whether it is equal to or greater than the threshold value or less than the threshold value (step S5).

When the power spectrum of the cutting force is less than the threshold value (steps S5 and No), the control characteristic changing unit 6 performs the process of step S8. When the power spectrum of the cutting force is equal to or greater than the threshold value (steps S5 and Yes), the control characteristic changing unit 6 lowers the control gain of the disturbance response compensator of the servo control unit 1 at the peak frequency (step S7). The control characteristic changing unit 6 repeats the processes from steps S1 to S7 until the search for the peak is completed within the frequency range of the scanning target (step S8).

The reason why whether or not to change the frequency characteristics is determined by the power spectrum of the cutting force in steps S4 and S5 is that the peak of the frequency transfer function is correct because the coherence is low in the frequency region where the cutting force is small. This is because there is a high possibility that the calculation has not been completed and unnecessary changes in frequency characteristics are prevented. In the processing of steps S4 and 5, the power spectrum of each component of the mechanical axial cutting force vector corresponding to the drive shaft whose control characteristics are changed is used.

In the process of step S1, the frequency transfer function shown in the above-mentioned coquad diagram may be used. Further, in the processing of steps S4 and 5, the magnitude of the cutting force may be used instead of the power spectrum of the cutting force.

As a means for enhancing the disturbance response of the control system in step S6, the first means described below may be used. As a first means, it can be exemplified to change the control parameters of the disturbance response compensator. The disturbance response compensator of the servo control unit 1 is generally composed of a P controller, a PI controller, and the like. For example, in the case of PI control, the proportional gain and the integrated gain become control parameters of the disturbance response compensator, and both the proportional gain and the integrated gain are set to high values to increase the control gain of the disturbance response compensator. be able to. However, in this method, the gain in the entire frequency range of the disturbance response compensator increases, and the control system may become unstable.

As a means for enhancing the disturbance response of the control system in step S6, the second means described below may be used. As a second means, it can be exemplified that a filter for increasing the gain in a narrow band, that is, a reverse notch filter is added to the disturbance response compensator. The inverse notch filter is represented by, for example, the transfer function of Eq. (4). s is the Laplace operator representing the derivative, and ω is the angular frequency at the center of the range for increasing the gain. Q is a coefficient for determining the frequency band for increasing the gain, and a is a coefficient for determining the amount for increasing the gain. By setting ω as the frequency of the peak of the resonance point, the gain at the frequency at which the disturbance of the disturbance response compensator is occurring can be increased.
(S ² + ω s / Q + ω ² ) / (s ² + as + ω ² ) ... Equation (4)

Further, as a means for enhancing the disturbance response of the control system in step S6, a third means described below may be used. As a third means, a bandpass filter that passes only frequencies in a specific range and does not pass frequencies other than the specific range, or passes only frequencies in a specific range and does not pass frequencies other than the specific range. It can be exemplified by using a bandpass filter that attenuates the frequency of. By passing the machine end position 201 through the bandpass filter, the control parameters of the disturbance response compensator for the machine end position 201 that has passed through the bandpass filter are changed. For example, in the case of PI control, the proportional gain and the integrated gain are control parameters of the disturbance response compensator, and both the proportional gain and the integrated gain are set to high values. Since the control parameters are not changed for the mechanical end position that does not pass through the bandpass filter, the control system is less likely to become unstable than the first means.

In step S7, the first means described below may be used. As the first means of step S7, changing the control parameter of the disturbance response compensator can be exemplified. When the disturbance response compensator of the servo control unit 1 is PI controlled, low values are set for the proportional gain and the integrated gain.

Further, in step S7, the second means described below may be used. As the second means of step S7, it can be exemplified that a notch filter for lowering the gain in a narrow band is added to the disturbance response compensator. The notch filter is represented by, for example, Eq. (5). s is the Laplace operator representing the derivative, and ω is the angular frequency at the center of the range in which the gain is lowered. Q is a coefficient for determining the frequency band for lowering the gain, and b is a coefficient for determining the amount for lowering the gain. By setting ω as the frequency of the peak of the resonance point, the gain at the frequency at which the disturbance of the disturbance response compensator is generated can be lowered.
(S ² + bs + ω ² ) / (s ² + ω s / Q + ω ² ) ... Equation (5)

Further, in step S7, the third means described below may be used. As a third means, a bandpass filter that passes only frequencies in a specific range and does not pass frequencies other than the specific range, or passes only frequencies in a specific range and does not pass frequencies other than the specific range. It can be exemplified by using a bandpass filter that attenuates the frequency of. By passing the machine end position 201 through the bandpass filter, the control parameters of the disturbance response compensator for the machine end position 201 that has passed through the bandpass filter are changed. For example, in the case of PI control, the proportional gain and the integrated gain are control parameters of the disturbance response compensator, and both the proportional gain and the integrated gain are set to low values.

FIG. 8 is FIG. 1 showing an example in which disturbance vibration is generated at the machine end position shown in FIG. 1 due to a cutting force. FIG. 8 shows a tool locus 300 representing a machine end position that changes from moment to moment, and FIG. 8 shows an arrow indicating a cutting force vector 310 at each machine end position that changes. Note that FIG. 8 shows only the cutting force vector 310 when the power spectrum of the cutting force at the peak frequency is equal to or greater than the threshold value.

FIG. 9 is FIG. 2 showing an example in which disturbance vibration is generated at the machine end position shown in FIG. 1 due to a cutting force. In FIG. 9, the disturbance vibration due to the cutting force with respect to the position command 200 is enlarged and displayed. In FIG. 9, the feed direction of the tool is indicated by an arrow D. As shown in FIG. 9, if disturbance vibration occurs in a direction perpendicular to the feed direction of the tool during cutting, the surface properties of the machined surface of the workpiece to be machined on the side surface of the tool deteriorate.

In the numerical control device 100-1 according to the first embodiment, when the disturbance vibration that deteriorates the surface properties of the machined surface occurs in this way, the disturbance response characteristic of the servo control unit 1 is changed by the control characteristic changing unit 6. As a result, disturbance vibration is reduced. Further, in the numerical control device 100-1, the processing of the cutting force vector calculation unit 3, the mechanical characteristic identification unit 5, and the control characteristic change unit 6 is performed at a constant cycle. This is to make the cutting force correspond to the change of the frequency to be changed by the change of the machining position and the change of the state of the workpiece, the tool and the machine due to the cutting.

As described above, according to the numerical control device 100-1 of the first embodiment, the transfer function used for disturbance suppression can be sequentially calculated during the cutting process, so that the cutting force vector information and the mechanical characteristics calculated during the cutting process can be calculated. The frequency response of the disturbance response compensator can be modified based on the information. As a result, it is possible to suppress the position disturbance of the mechanical system due to the cutting force, improve the accuracy of machining, and suppress the wear of the tool.

Further, according to the numerical control device 100-1 of the first embodiment, since the transfer function used for the disturbance suppression can be sequentially calculated during the cutting process, it is not necessary to measure the frequency response band in advance every time the cutting conditions change. Therefore, the pre-measurement of the frequency response band becomes unnecessary, and the trouble of changing the appropriate frequency response band at the time of cutting is eliminated, and the burden on the user of the numerical control device 100-1 can be reduced.

Further, in the numerical control device 100-1 of the first embodiment, each processing operation of the cutting force vector calculation unit 3, the machine characteristic identification unit 5, and the control characteristic change unit 6 is performed at a constant cycle, so that the machining position is determined. The cutting force can be changed in correspondence with the change and the change in the state of the workpiece, the tool and the machine due to the cutting process.

Further, when the servo control unit 1 of the numerical control device 100-1 of the first embodiment adopts the two-degree-of-freedom control, it is possible to suppress the disturbance due to the cutting force without causing a locus error.

Further, according to the numerical control device 100-1 of the first embodiment, it is not necessary to narrow the frequency response band as in the prior art, so that the cutting force fluctuates without deteriorating the followability of the tool position to the command locus. The generated disturbance can be suppressed.

Embodiment 2.
FIG. 10 is a diagram showing a configuration of a numerical control device according to a second embodiment of the present invention. The numerical control device 100-2 according to the second embodiment includes a display unit 10 and a condition input unit 11 in addition to the configuration provided by the numerical control device 100-1 according to the first embodiment. In the second embodiment, the same components as those in the first embodiment will be described using the same names and symbols as those in the first embodiment.

In the condition input unit 11, the user of the numerical control device 100-2 specifies a condition for changing the control characteristic in the control characteristic changing unit 6 and whether or not to allow the control characteristic to be changed in the control characteristic changing unit 6. can do. The conditions for changing the control characteristics include, for example, a threshold value of the power spectrum and a threshold value of the magnitude of the cutting force in the processing operations of step S4 and step S5 of the control characteristic changing unit 6 described above.

A command code generally called a G code is used as a program for processing a workpiece using the machine tool 100. The G code includes commands such as a positioning command (G00), a linear interpolation cutting command (G01), and an arc interpolation cutting command (G02, G03). Generally, the positioning command (G00) is a command used during non-cutting. In the condition input unit 11, for example, the control characteristic change unit 6 changes the control characteristic in the case of a positioning command, or the control characteristic change unit 6 changes the control characteristic in the case of a cutting command. The user can specify the permission condition for changing the control characteristic by the change unit 6.

Further, the condition input unit 11 can always change whether or not to allow the change of the control characteristic. For example, only when the change of the control characteristic is permitted and the condition for changing the control characteristic is satisfied. , The control characteristic change unit 6 changes the control characteristic of the servo control unit 1.

On the display unit 10, the machine characteristic information 207 which is the output of the machine characteristic identification unit 5 and a part or all the data of the cutting force vector information 204 which is the output of the cutting force vector calculation unit 3 are displayed. The user of the numerical control device 100-2 can grasp the information displayed on the display unit 10. For example, on the display unit 10, the unit length (for example, 1 mm) of the tool locus 300 shown in FIG. 7 is displayed with a specific length. Further, the unit force (1N) of the cutting force vector 310 shown in FIG. 7 is displayed on the display unit 10 with a specific length. As a result, the user can confirm the magnitude and direction of the cutting force, grasp the situation during the cutting process, and easily determine whether or not the control characteristic change unit 6 should change the control characteristic. Can be done.

Further, the display unit 10 displays the unit amount of the common logarithm of each frequency of the gain diagram shown in FIG. 5 and the phase diagram shown in FIG. 6 in unit length. As a result, the user can confirm at which frequency the vibration is occurring, grasp the situation during cutting, and easily determine whether or not the control characteristic change unit 6 should change the control characteristic. it can.

As described above, according to the numerical control device 100-2 according to the second embodiment, whether or not the user specifies the condition for changing the control characteristic from the condition input unit 11 and permits the change of the control characteristic. By specifying the heel, it is possible to prevent unintended processing by the user. Further, by displaying the machine characteristic information, the cutting force vector information, and the like on the display unit 10, it is possible to easily determine whether or not the user should change the control characteristics.

Embodiment 3.
FIG. 11 is a diagram showing a configuration of a numerical control device according to a third embodiment of the present invention. When a notch filter is used for vibration of a frequency included in the position control band, it is not desirable because the followability to the command locus is lowered. Therefore, regarding the low frequency vibration included in the control band, it is necessary to suppress the vibration caused by the cutting force by different methods. Therefore, in the numerical control device 100-3 according to the third embodiment, the addition unit 12 and the disturbance correction amount calculation unit 13 are used instead of the control characteristic changing unit 6 shown in FIG. In the third embodiment, the same components as those in the first embodiment will be described using the same names and symbols as those in the first embodiment.

The disturbance correction amount calculation unit 13 estimates the disturbance caused by the cutting force based on the mechanical characteristic information 207 and the cutting force vector information 204, and calculates the correction amount from the estimated disturbance. The calculated correction amount is added to the position command 200 by the addition unit 12, and the output of the addition unit 12, that is, the position command 200 to which the correction amount is added is input to the servo control unit 1 and the simulated response calculation unit 4. The numerical control device 100-3 controls the machine tool 100 by using the position command 200 to which the correction amount is added, thereby suppressing the decrease in the followability of the tool position to the command trajectory and fluctuating the cutting force. By suppressing the disturbance caused by the above, it is possible to suppress a decrease in processing accuracy.

FIG. 12 is a block diagram in which the motor and the mechanical system shown in FIG. 2 are approximated by a two-inertia model. In the model shown in FIG. 12, K is the spring constant of the elastic element of the mechanical system 8, C is the viscous friction coefficient of the damping element of the mechanical system 8, Jm is the inertia of the motor 7, and Jl is the mechanical system. 8 inertias. The position of Jm simulates the position of the end of the motor, and the position of Jl simulates the position of the end of the machine. Tm is the torque output by the servomotor 71 according to the torque command, xl is a variable indicating the machine end position, xm is a variable indicating the motor end position, and s is a Laplace operator representing differentiation. xm, the xl and fc, those Laplace transform to _X M, _{X L} and Fc.

Positional disturbance occurs in the table 81 due to changes in the elastic element K, damping element C, and the like due to the cutting force. Further, since the cutting force is transmitted by the elastic element K, the damping element C, and the like, the position disturbance occurs at the motor position. When the motor 7 and the mechanical system 8 are modeled by a two-inertia model, the transfer function from the cutting force to the position disturbance is expressed by, for example, Eq. (6).
G (s) = 1 / (Jls ² + Cs + K) ... Equation (6)

The disturbance correction amount calculation unit 13 identifies each coefficient of the equation (6) with respect to the transfer function identified by the mechanical property identification unit 5 by using, for example, the least squares method, the spectrum analysis method, the subspace method, or the like. In Eq. (6), the mechanical system 8 is approximated to a two-inertia model, but the transfer function may be expressed by a lower-order or higher-order model. The disturbance correction amount calculation unit 13 calculates the disturbance generated by the cutting force by applying the transfer function type filter identified as described above to the cutting force 203 measured by the cutting force output unit 2. be able to. The calculated value of the disturbance calculated here also includes a high frequency component. Since the high frequency component cannot be controlled, the disturbance correction amount calculation unit 13 removes the high frequency component by using a low-pass filter having an appropriate frequency. The disturbance correction amount calculation unit 13 calculates the sequential disturbance in the control cycle. The disturbance correction amount calculation unit 13 reverses the calculated positive and negative values of the disturbance, and sets the disturbance after the inversion as the correction amount. The correction amount is input to the addition unit 12, and the correction amount is added to the position command 200 in the addition unit 12. The correction amount C is calculated by the equations (7) and (8). F is a machine axis cutting force vector. T is the time constant of the low-pass filter.
C = -G _LPF (s) G (s) F ... (7) formula G _LPF (s) = 1 / (Ts + 1) ... (8) formula

It is the vibration in the direction perpendicular to the feed direction of the tool that adversely affects the surface properties of the machined surface. On the other hand, when the correction is performed for the feed direction of the tool, the moving speed of the tool with respect to the feed direction of the tool becomes not constant, which may adversely affect the surface properties of the machined surface. Therefore, the disturbance correction amount calculation unit 13 corrects only in the direction perpendicular to the feed direction of the tool. In this case, the vertical cutting force vector Fn shown in the equation (3) may be used instead of the mechanical axial cutting force vector F in the equation (7).

As described above, according to the numerical control device 100-3 according to the third embodiment, it is possible to suppress low-frequency disturbance vibration included in the position control band without deteriorating the followability to the command locus. As a result, the tool life can be extended and the machining accuracy of the workpiece can be improved. Further, in the numerical control device 100-3, the processing operations of the cutting force vector calculation unit 3, the mechanical characteristic identification unit 5, and the control characteristic change unit 6 are constant, as in the numerical control device 100-1 according to the first embodiment. Since it is performed in the cycle of, the cutting force can be changed correspondingly by the change of the machining position and the change of the state of the workpiece, the tool and the machine due to the cutting.

FIG. 13 is a diagram showing a hardware configuration example of the numerical control device according to the first to third embodiments. The numerical control devices 100-1, 100-2, 100-3 are a CPU (Central Processing Unit) 51 that performs arithmetic processing, a memory 52 that the CPU 51 uses for a work area, and a storage device 53 that can store programs, information, and the like. And an input device 54 for receiving input from the user, and a display device 55. The memory 52 is a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Online Memory), an EEPROM (registered trademark), an Electrically volatile memory, or an EEPROM (registered trademark). This includes semiconductor memory, magnetic disk, flexible disk, optical disk, compact disk, mini disk, and DVD (Digital Versaille Disk). The input device 54 is exemplified by a keyboard and a mouse, and the display device 55 is exemplified by a monitor and a display. The input device 54 and the display device 55 may be integrated and realized by a touch panel or the like.

The CPU 51 stores the servo control unit 1, the cutting force vector calculation unit 3, the simulated response calculation unit 4, the mechanical characteristic identification unit 5, the control characteristic change unit 6, the subtraction unit 9, the disturbance correction amount calculation unit 13, and the addition unit 12. It is realized by executing the program stored in 53.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 Servo control unit, 2 Cutting force output unit, 3 Cutting force vector calculation unit, 4, 4A simulated response calculation unit, 5 Mechanical characteristic identification unit, 6 Control characteristic change unit, 7 Motor, 8 Mechanical system, 9 Subtraction unit, 10 Display unit, 11 condition input unit, 12 addition unit, 13 disturbance correction amount calculation unit, 41 position control simulation unit, 42 integration calculation unit, 43 speed control simulation unit, 44 integration calculation unit, 45 proportional constant calculation unit, 51 CPU, 52 Memory, 53 Storage Device, 54 Input Device, 55 Display Device, 71 Servo Motor, 71a Rotor, 71b Shaft, 72 Motor Position Detector, 81 Table, 82 Ball Screw Nut, 83 Ball Screw, 84 Coupling, 85 Machine End Position detector, 86 Machine end position detector head, 90 Work piece, 100 Machine, 100-1, 100-2, 100-3 Numerical controller, 101 Tool, 200 Position command, 201 Machine end position, 202 Torque Command, 203 Cutting Force, 204 Cutting Force Vector Information, 205 Model Position, 206 Position Disturbance, 207 Mechanical Characteristic Information, 208 Model Speed, 209 Model Torque, 300 Tool Trajectory, 310 Cutting Force Vector.

Claims (9)

A numerical control device that controls a mechanical system that processes the workpiece with a tool that processes the workpiece.
A servo control unit that drives a motor connected to the driven body so that the position of the driven body on which the workpiece is provided follows the position command based on the position command.
A cutting force output portion to the cutting force measured or estimated and outputs generated between the workpiece and the tool,
A cutting force vector calculation unit that calculates a cutting force vector based on the position of the driven body and the cutting force.
A mechanical characteristic identification unit that identifies the dynamic characteristics of the mechanical system with respect to the cutting force,
A control characteristic changing unit that changes the control characteristics of the servo control unit based on the cutting force vector and the dynamic characteristics of the mechanical system identified by the mechanical characteristic identification unit.
A numerical control device characterized by being provided with. The numerical control device according to claim 1, wherein the mechanical characteristic identification unit identifies the frequency response characteristic of the servo control unit indicated by a gain and a phase in a frequency region from a cutting force to a disturbance of a control system. .. The control characteristic changing unit identifies a disturbance factor by searching for a resonance point or an antiresonance point in which the peak shapes of the frequency response characteristics are different from each other in the frequency response characteristic identified by the mechanical characteristic identification unit. The numerical control device according to claim 2, wherein the frequency characteristics of the control system are changed according to the identified disturbance factor. The numerical control device according to claim 2 or 3, wherein the control characteristic changing unit determines whether or not the frequency response characteristic can be changed based on the cutting force vector. The numerical control device according to any one of claims 1 to 4, wherein the control characteristic changing unit is provided with a condition input unit for inputting a condition for changing the control characteristic of the servo control unit. A numerical control device that controls a mechanical system that processes the workpiece with a tool that processes the workpiece.
A servo control unit that drives a motor connected to the driven body so that the position of the driven body on which the workpiece is provided follows the position command based on the position command.
A cutting force output portion to the cutting force measured or estimated and outputs generated between the workpiece and the tool,
A cutting force vector calculation unit that calculates a cutting force vector based on the position of the driven body and the cutting force.
A mechanical characteristic identification unit that identifies the dynamic characteristics of the mechanical system with respect to the cutting force,
A disturbance correction amount calculation unit that calculates a correction amount that corrects the disturbance of the control system caused by the cutting force, and a disturbance correction amount calculation unit.
A numerical control device characterized by being provided with. The mechanical characteristic identification unit identifies the frequency response characteristics from the cutting force to the disturbance of the control system.
The sixth aspect of claim 6, wherein the disturbance correction amount calculation unit calculates a correction amount for correcting disturbance by applying a transfer function type filter exhibiting the frequency response characteristic to the cutting force. Numerical control device. The numerical control device according to claim 6 or 7, wherein the disturbance correction amount calculation unit calculates a correction amount in a direction orthogonal to the feed direction of the tool based on the cutting force vector. The numerical control according to claim 2, 3, 4, 6, 7 or 8, wherein the disturbance of the control system is a disturbance included in any one of the position command, the speed command and the torque command. apparatus.

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