DE112018007736T5 - Numerical control device - Google Patents

Abstract

A numerical control device (100-1) includes a servo control unit (1) which has a motor (7) connected to a table (81) which is a driven member on which an object (90) is placed on the Based on a position command (200) drives so that a position of the table (81) follows the position command (200). The numerical control device (100-1) comprises: a cutting force output unit (2) that measures or estimates a cutting force (203) caused between the tool (101) and the object (90) and outputs the cutting force (203); a cutting force vector calculating unit (3) which calculates a cutting force vector based on the position of the table (81) and the cutting force (203); and a mechanical feature identification unit that identifies dynamic features of a mechanical system in relation to the cutting force (203). The numerical control device (100-1) is characterized by comprising a control characteristic changing unit (6) which controls the control characteristic of the servo control unit (1) based on the cutting force vector and the dynamic characteristics of the mechanical system generated by the unit (5) to identify the mechanical characteristic to be identified changes.

Description

Technical field

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

background

A numerically controlled machine tool is equipped with actuators and driven members including a table, a tool and the like that are driven by the actuators. The actuators are exemplified by a rotary servo motor, a linear servo motor and the like. The driven members operate by the actuators controlled in accordance with commands indicating positions, paths, speeds, torque commands and the like output from a numerical controller connected to the machine tool. In this way, an object to be machined, which is a workpiece fixed on the table, is machined by the tool. The control for driving a driven element so that the position of the tool with respect to the object to be machined exactly follows a commanded path, which is a commanded path, is referred to as path control or contour motion control. The path control or contour motion control is carried out by the numerical control device with high precision. When the path control or the contour motion control is performed, servomotors connected to one of two or more shafts, such as a main shaft and feed shafts, which are provided in the machine tool, and the position of the tool with respect to the object to be machined, operate controlled accordingly.

In the machine tool, a cutting force is generated in a region of the tool that is in contact with the object during a machining process for the object to be machined. In order to extend the life of the tool and improve the machining accuracy of the object, it is important to keep the cutting force constant. However, if the cutting tool is, for example, an end mill or a drill, the cutting blades provided on the shaft of the cutting tool are at a distance in the direction of rotation of the shaft, so that the cutting resistance at a contact area of the tool with the object to be processed fluctuates during a processing process actual processing of the object takes place 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 leads to disturbance of the control system of the servomotors that drive the main shaft and the feed shaft. If vibrations or the like are caused in the control of the servomotor connected to the feed shaft, for example by the fluctuation of the cutting force, a relative position of the tool in relation to the object to be processed also vibrates, and the processing accuracy or the processing surface quality deteriorates and in addition tool wear is accelerated. Patent Literature 1 discloses a method of machining objects in which a frequency band of a control system that controls a motor is set so that tool wear is within an allowable frequency band. According to the technique disclosed in Patent Literature 1, even if the fluctuation of a cutting resistance during a machining process causes disturbance in the control system, tool wear is kept within a certain range, machining quality is stabilized, and machining efficiency is improved.

Citation

Patent literature

Patent Literature 1: Laid-Open Japanese Patent Application No. 2013-250866

Summary

Technical problem

However, the method disclosed in Patent Literature 1 is problematic in that a narrower frequency band reduces the traceability of a tool position on a commanded path, which can adversely affect the machining accuracy.

The present invention has been made in view of the above circumstances, and aims to provide a numerical control device capable of preventing the lowering of traceability to a commanded path.

the solution of the problem

In order to solve the above problems and achieve the object, the present invention provides a numerical control device that controls a mechanical system configured to perform machining of an object to be machined with a tool used for machining the Object is used, the numerical control device comprising: a servo control unit for driving a motor connected to a driven element based on a position command so that a position of the driven element follows the position command, the object being set on the driven element; a cutting force output unit for measuring or estimating a cutting force caused between the tool and the object and outputting the cutting force; a cutting force vector calculating unit for calculating a cutting force vector based on the position of the driven member and the cutting force; a mechanical property identification unit for identifying dynamic properties of the mechanical system in relation to the cutting force; and a control characteristic changing unit for changing the control characteristic of the servo control unit based on the cutting force vector and the dynamic characteristics of the mechanical system identified by the mechanical characteristic identifying unit.

Advantageous Effects of the Invention

The present invention has an advantageous effect that the lowering of traceability to a commanded trajectory can be prevented.

Figure list

• 1 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a first embodiment of the present invention.
• 2 FIG. 13 is a diagram illustrating configurations of an engine and a mechanical system shown in FIG 1 are shown.
• 3 FIG. 13 is a diagram illustrating a configuration of a simulation response arithmetic unit shown in FIG 1 is shown.
• 4th Fig. 13 is a diagram showing a modification of that shown in 1 illustrated simulation response computing unit illustrated.
• 5 Fig. 13 is a first diagram for explaining information about mechanical properties calculated by a unit for identifying mechanical properties (illustrated in FIG 1 ).
• 6th Fig. 13 is a second diagram for explaining information on mechanical properties obtained from the in 1 unit for identifying mechanical properties.
• 7th FIG. 13 is a flowchart for explaining the operation of a control characteristic changing unit shown in FIG 1 is illustrated.
• 8th FIG. 13 is a first diagram showing an example in which positional disturbance is caused by cutting force at a machine end position (illustrated in FIG 1 ).
• 9 FIG. 13 is a second diagram illustrating an example in which spurious vibration is caused by cutting force in a machine end position (illustrated in FIG 1 ).
• 10 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a second embodiment of the present invention.
• 11 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a third embodiment of the present invention.
• 12th FIG. 3 is a block diagram of an engine and mechanical system shown in FIG 2 is illustrated and approximated by a two-inertial model.
• 13th Fig. 13 is a diagram illustrating an example of a hardware configuration of numerical control devices according to the first to third embodiments.

Description of the embodiments

A numerical control device according to embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not necessarily limited by these embodiments.

First embodiment. 1 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a first embodiment of the present invention. 2 FIG. 13 is a diagram illustrating configurations of an engine and a mechanical system shown in FIG 1 are shown. A numerical control device 100-1 generates a torque command 202 based on a position command 200 and a machine end position 201 and provides the generated torque command 202 to an engine 7th working in a machine tool 100 is provided to thereby create a mechanical system 8th to drive which is an object to be controlled. The numerical control device 100-1 includes a servo control unit 1 , a cutting force output unit 2 , a cutting force vector arithmetic unit 3 , a simulation response arithmetic unit 4th , a unit for identifying mechanical properties 5 , a unit for changing the control characteristic 6th and a subtraction unit 9 .

The servo control unit 1 is with the engine 7th connected and provides the torque command 202 to the engine 7th to thereby the mechanical system 8th to drive which is an object to be controlled. As in 2 illustrated includes the engine 7th a servo motor 71 and an engine position detector 72 . On a rotor 71a of the servomotor 71 is a wave 71b appropriate. A rotary encoder that is configured to provide a rotational position of the rotor 71a is detected for the engine position detector 72 used. The mechanical system 8th includes a table 81 , a ball screw nut 82 , a ball screw spindle 83 , a clutch 84 , a machine end position detector 85 and a machine end position detector head 86 . The ball screw spindle 83 of the mechanical system 8th is about the clutch 84 with the wave 71b of the servomotor 71 connected. The ball screw spindle 83 is with the ball screw nut 82 connected, and the table 81 , which is a driven element, is on the ball screw nut 82 attached. The table 81 is in the longitudinal direction of the ball screw spindle 83 movably supported by a guide mechanism which is not illustrated. The machine end position detector 85 and the machine end position detector head 86 serve as an encoder to detect a position of the table 81 , the one from the numerical control device 100-1 object to be controlled is. The machine end position detector 85 is for example a linear encoder and the machine end position detector head 86 is for example a linear encoder head. The ones in the servo control unit 1 entered machine end position 201 represents at least one of the pieces of information received from the engine position detector 72 detected rotational position of the rotor 71a and that from the machine end position detector 85 detected position of the table 81 Show.

The range of motion of the table 81 is by the machine end position detector 85 measured while the angle of rotation of the rotor 71a by the motor position detector 72 is measured. The servo control unit 1 however, it converts the angle of rotation of the rotor 71a to a length in the direction of movement of the table 81 by multiplying the angle of rotation with the pitch of a ball screw spindle, which is a movement distance of the table per revolution of the motor 7th and the result of the multiplication by an angle 2n [rad] for one revolution of the rotor 71a divided. The first embodiment is to have a value in the direction of movement of the table 81 by converting the angle of rotation of the rotor 71a in this value is obtained.

The feedback control that only comes from the motor position detector 72 as machine end position 201 uses detected position information is referred to as a semi-closed control loop. A control with feedback that is provided by both the motor position detector 72 detected position information as well as that by the machine end position detector 85 detected position information as machine end position 201 used, or a control with feedback that is only provided by the machine end position detector 85 using detected position information as the same is referred to as fully closed loop control. Both the semi-closed loop and the fully closed loop can be applied to the numerical control device according to the first embodiment 100-1 be applied. The following is an example of a configuration of the numerical control device 100-1 where the fully closed loop control is used. In addition, the position information used in the control is referred to below as the machine end position. Note that the configuration of the mechanical system 8th an example is that of the configuration of the mechanical system 8th not on the in 2 illustrated example is limited and that the numerical control device 100-1 can control a variety of mechanical systems.

The position command 200 and the machine end position 201 are in the in 1 illustrated servo control unit 1 entered. The servo control unit 1 generates a torque command 202 which causes the machine end position 201 the position command 200 follows. The servo control unit 1 receives a position deviation, which is, for example, a difference between the position command 200 and the machine end position 201 and performs an attitude control process such as proportional control of positional deviation to calculate a speed command. The servo control unit 1 also computes the torque command 202 by performing a speed control method such as proportional-integral control, for example, on the speed command, and giving the torque command 202 out.

One on the table while editing 81 set work object, the object to be processed 90 , for example, measures the in 1 illustrated cutting force output unit 2 a cutting force applied to a contact area of a tool 101 with the object to be edited 90 and gives a cutting force 203 off, ie information that indicates the measured cutting force.

For measuring the cutting force 203 For example, a load cell, a dynamometer or the like is used. A Load cell, dynamometer, etc. are measuring devices that measure the cutting force 203 can measure directly. Note that the cutting force 203 Can also be estimated from a motor current, and that a technique called a disturbance observer is used to measure the cutting force 203 can be estimated from the motor current. Alternatively, means for indirect measurement of the cutting force 203 for the cutting force output unit 2 instead of means for directly measuring the cutting force 203 be used.

The cutting force vector arithmetic unit 3 For example, calculates three cutting force vectors based on the measured cutting force 203 and the machine end position 201 . A first cutting force vector of the three cutting force vectors is a vector with respect to a direction parallel to a drive axis, such as an X-axis, a Y-axis or a Z-axis of a machine. In the following, the first cutting force vector is referred to as a cutting force vector in the direction of the machine axis. A second cutting force vector of the three cutting force vectors is a cutting force vector parallel to a feed direction of the tool 101 . In the following, the second cutting force vector is referred to as the cutting force vector in the tool feed direction. A third cutting force vector of the three cutting force vectors is a cutting force vector in a direction perpendicular to the feed direction of the tool 101 . Thereafter, the third cutting force vector is referred to as the cutting force vector in the vertical direction.

Here will be explained an example of a case where a dynamometer is used to measure the cutting force. In the case where the cutting force is measured with a dynamometer, the alignment of the dynamometer mounted on a machine is generally adjusted so that cutting forces are measured in directions that are parallel to individual drive axes of the machine, e.g. an X-axis , a Y-axis and a Z-axis of the machine. Therefore, the outputs of the dynamometer contain components of the cutting force vectors in the direction of the machine axis. Note that dynamometers are not limited to those capable of measuring cutting force vectors in the direction of the machine axis that correspond to the directions of three axes, and that some dynamometers are capable of only measuring one cutting force vector in the direction of the machine axis which corresponds to a direction of an axis among the X-axis, the Y-axis and the Z-axis. A cutting force in a certain direction for which the measurement is not performed is considered 0. In a controlled machine tool having five axes and five axes of rotation, the directions in which dynamometers are mounted can be changed depending on the orientations of the axes of rotation, and in this case the angles of the axes of rotation are used to calculate the cutting force vectors in the direction of the machine axis.

$$\text{Ft}=\left(\text{Fu}\right)$$

$$\text{Fn}=\text{F}-\text{Ft}$$

The cutting force vector arithmetic unit 3 can adjust the speed of movement of the shafts of a variety of tools 101 by differentiating the machine end position 201 to calculate. In a case where the machine tool 100 for example three tools 101 contains, calculates the cutting force vector arithmetic unit 3 the movement speed vector v with components of the movement speeds of the shafts of the three tools 101 . In addition, the cutting force vector arithmetic unit calculates 3 a cutting force vector Ft for the tool feed direction by Expression (1) and Expression (2). “U” represents a unit vector. “V” stands for a movement speed vector. "F" stands for a cutting force vector in the direction of the machine axis. "" represents an inner product. In addition, the cutting force vector arithmetic unit calculates 3 by Expression (1) and Expression (3), a cutting force vector Fn in the perpendicular direction. $$\text{u}=\text{v}/\left|\text{v}\right|$$

$$\text{Ft}=\left(\text{Fu}\right)$$

$$\text{Fn}=\text{F.}-\text{Ft}$$

Alternatively, the cutting force vector arithmetic unit 3 can be configured to calculate the cutting force vector in the tool advance direction and the cutting force vector in the perpendicular direction using speed feedback information used for speed control instead of the moving speeds obtained by differentiating the machine end position 201 can be obtained. In addition, the cutting force vector arithmetic unit calculates 3 the size of the cutting force vector F in the direction of the machine axis and uses the calculated size of the cutting force vector F in the direction of the machine axis as the size of the cutting force.

The cutting force vector arithmetic unit 3 further includes data indicating components of the cutting force vectors in the machine-axis direction corresponding to two or more axes and calculated from the current point of time to a point of time that is a predetermined time ago from the current point of time and calculates a power spectrum of the cutting force for each frequency using of the data held. Note that a power spectrum for frequency can be calculated by performing a Fourier transform.

The cutting force vector arithmetic unit 3 gives each cutting force vector, the magnitude of the cutting force, and a power spectrum of each component of the machine axis direction as cutting force vector information 204 to the unit for changing the control characteristic 6th out.

3 Fig. 13 is a diagram showing a configuration of the in 1 represents an illustrative simulation response computing unit. The simulation response arithmetic unit 4th simulates a response from the machine end position 201 based on the position command 200 , calculates a model position 205 which is the result of calculating an ideal position, which is the machine end position 201 should follow and gives the model position 205 out. The simulation response arithmetic unit 4th includes a unit for simulating the position control 41 and an integration arithmetic unit 42 . The unit for simulating the position control 41 leads to a difference between the position command 200 and an output of the integration computing unit 42 perform the same procedure as that of the servo control unit 1 performed position control procedures. The integration computing unit 42 receives the value of the machine end position 201 by integrating a result of the position control simulation unit 41 performed procedure and returns the value as a model position 205 out.

4th FIG. 13 is a diagram illustrating a modification of the simulation response arithmetic unit shown in FIG 1 is shown. One in 4th illustrated simulation response arithmetic unit 4A includes a speed control simulation unit 43 , an integration computer 44 and a proportionality constant arithmetic unit 45 in addition to the unit for simulating the position control 41 and the in 3 illustrated integration computing unit 42 . The simulation response arithmetic unit 4A calculated in addition to the model position 205 a model speed 208 having a value of the ideal speed of the mechanical system 8th indicates, and a model torque 209 that is, information indicating an ideal output of engine torque. The proportionality constant arithmetic unit 45 calculates the model torque 209 by taking a constant for the torque conversion to the model speed 208 added. Kpp, Kvp, Kvi, Kt and J each represent a constant of proportionality. S is a Laplace operator that represents the deviation. 1 / s stands for integration. The unit for simulating the position control 41 performs a typical proportional control. The speed control simulation unit 43 performs a typical proportional-integral control. The output of the speed control simulation unit 43 lies in an acceleration dimension. The output of the speed control simulation unit 43 is in the integration computer 44 entered and in two stages by the integration computer 44 and the integration arithmetic unit 42 integrated. The machine end position is simulated in this way. The output of the speed control simulation unit 43 is also used in the proportionality constant arithmetic unit 45 entered. The proportionality constant arithmetic unit 45 converts the output of the speed control simulation unit 43 into torque by getting the output of the speed control simulation unit 43 multiplied by the proportionality constant Kt.

The subtraction unit 9 calculates a positional disturbance 206 caused by a disturbance in the control of the cutting force and the like by the information provided by the simulation response arithmetic unit 4th calculated model position 205 from the machine end position 201 subtracted.

The unit for identifying mechanical properties 5 identifies the mechanical properties of the machine tool 100 in terms of cutting force 203 using position error 206 and the cutting force 203 . In the first embodiment, an example of the identification of a transfer function from the cutting force is given 203 until the position disturbance 206 in the control as a mechanical characteristic in relation to the cutting force 203 explained. Alternatively, the unit can be used to identify mechanical properties 5 be configured to instead of the positional disturbance 206 a speed disturbance, a torque disturbance and / or the like is calculated, the model speed 208 , the model torque 209 and / or the like is used that is supported by the in 4th illustrated simulation response arithmetic unit 4A and a transfer function of the cutting force 203 up to speed disturbance or a transfer function of the cutting force 203 until the torque failure is identified.

The unit for identifying mechanical properties 5 calculates a frequency transfer function by applying numerical processing such as Fourier transform to the cutting force 203 and the positional disturbance 206 performs. The unit for identifying mechanical properties 5 gives the calculated frequency transfer function as information about mechanical properties 207 to the unit for changing the control characteristic 6th out. 5 Fig. 13 is a first diagram for explaining the information on mechanical properties obtained from the in 1 illustrated unit for identifying mechanical properties can be calculated. The horizontal axis of 5 represents the logarithmic frequency and the vertical axis of 5 in the Gain expressed in decibels. In 5 the frequency transfer function is illustrated in a gain diagram. In the gain diagram, a resonance point appears as a positive peak and an anti-resonance point appears as a negative peak. 6th Fig. 13 is a second diagram for explaining the information on mechanical properties obtained from the in 1 unit for identifying mechanical properties. The horizontal axis of 6th represents the logarithmic frequency and the vertical axis of 6th the phase. In 6th the frequency transfer function is illustrated in a phase diagram. Alternatively, the frequency transfer function can also be illustrated in a Coquad diagram, the horizontal axis representing the logarithmic frequency and the vertical axis representing a real part and an imaginary part that result from the Fourier transformation.

As the disturbance in the control system, besides the disturbance by the fluctuation of the cutting force, there is also a disturbance by the friction and the positional disturbance 206 is also caused by friction. A typical example is quadrant projection caused when the direction of movement of a feed shaft is reversed at a quadrant switching position of a sheet. The unit for identifying mechanical properties 5 must remove the influence of friction to identify the mechanical properties related to the cutting force. For this reason, it is desirable to identify the mechanical properties related to the cutting force, except in the case that the influence of the friction caused when the direction of movement of the feed shaft is reversed or the influence of the friction that is caused when the feed shaft starts moving from a stopped state is significantly large.

The unit for changing the control characteristic 6th changes the frequency characteristics of the servo control unit 1 based on the from the cutting force vector arithmetic unit 3 calculated cutting force vector information 204 and that of the unit for identifying mechanical properties 5 identified information about mechanical properties 207 . In the case of path control, which takes place on two or more axes in the machine tool 100 is performed, a difference in set point response between the shafts being controlled causes a path error with respect to a commanded path. In the first embodiment, for the servo control unit 1 uses a two-degree degree of freedom control so that such a path error does not occur. The two-degree degree of freedom control is a control method in which two independent compensators are used for setpoint tracking and interference reduction. Since no path error occurs even if the frequency responses of compensators to reduce disturbance variables are different depending on the shaft to be controlled, the unit achieves to change the control characteristic 6th the reduction of disturbance variables by changing the frequency responses of disturbance response compensators, which are compensators for disturbance variable reduction. The interference response compensator is typically shown by a P controller (proportional controller), a PI controller (proportional-integral controller) or the like. As in this point, it enables the use of the two-degree degree of freedom control in the servo control unit 1 a reduction of the disturbances caused by the cutting force without causing a path error.

When there is a spike in the frequency transfer function indicated by the mechanical property identification unit 5 is identified, and the tip is a resonance point, vibration caused by the cutting force may occur in an area that can be observed in the machine end position. In the case of a fully closed loop control, vibrations occur in the motor 7th and the in 2 illustrated mechanical system 8th on; and in the case of a semi-closed loop control, vibrations occur in the motor 7th on. In these cases, the disturbance can be reduced by increasing the responsiveness of the disturbance response compensator at the resonance point, that is to say by increasing the control gain of the disturbance response compensator at the resonance point.

On the other hand, when a peak of the frequency transfer function is an anti-resonance point, vibrations caused by the cutting force may occur in an area that cannot be observed at the machine end position. For example, the object to be edited can 90 that on the table 81 is placed, the tool 101 and the like vibrate. In this case, the disturbance caused by the cutting force can be reduced by reducing the responsiveness of the spurious response compensator at the anti-resonance point, that is, by decreasing the control gain of the spurious response compensator at the anti-resonance point.

Next, the operation of the control characteristic changing unit will be discussed 6th explained. 7th FIG. 13 is a flow chart for explaining the function of the 1 illustrated unit for changing the control characteristic. First, the unit seeks to change the control characteristic 6th in that of the unit for identifying mechanical properties 5 calculated frequency transfer function (step S1) for a peak within a Frequency range of 1/2 the data sampling frequency. For example, if the sampling period corresponds to 1 kHz, the range for the peak value search is a range up to a frequency of 1/2 of 1 kHz, ie 0 to 500 Hz. Since aliasing occurs in the range from 500 Hz to 1 kHz, the unit leads to Change the control characteristics 6th does not perform the peak search.

The unit for changing the control characteristic 6th determines whether or not there is an anti-resonance point or a resonance point in the frequency transfer function (step S2). For example, the presence of an anti-resonance or resonance point is determined based on whether there is a first peak point where the gain value moves from decrease to increase or whether there is a second peak point where the gain value moves from increase to decrease .

If there is no antiresonance or resonance point in the frequency transfer function (step S2, No), the control characteristic changing unit repeats 6th the processes of steps S1 and S2.

If there is an anti-resonance point or a resonance point in the frequency transfer function (step S2, Yes), the control characteristic changing unit determines 6th whether the peak of the frequency transfer function is a resonance point or an anti-resonance point (step S3). For example, when there is the first vertex at which the gain value moves from decreasing to increasing, the unit for changing the control characteristic determines 6th that there is an anti-resonance point in the frequency transfer function. When the second vertex, at which the gain value changes from rise to fall, is present, the unit for changing the control characteristic provides 6th determines that there is a resonance point in the frequency transfer function. Note that if there is more than a first peak point during the scan, the unit for changing the control characteristic 6th stores the first peak points and determines the smallest of the stored first peak points as the anti-resonance point. If more than one second peak point is present during the scanning, the unit for changing the control characteristic stores the second peak points and determines the largest of the stored second peak points as the resonance point.

When a peak in the frequency transfer function is a resonance point (step S3, Yes), the control characteristic changing unit determines 6th whether that from the cutting force vector arithmetic unit 3 The calculated power spectrum of the cutting force at the peak frequency is equal to or greater than a threshold value or less than the threshold value (step S4).

If the power spectrum of the cutting force is smaller than the threshold value (step S4, No), the unit changes the control characteristic 6th an operation from step S8. If the power spectrum of the cutting force is equal to or greater than the threshold value (step S4, Yes), the unit for changing the control characteristic increases 6th the control gain of the spurious response compensator of the servo control unit 1 at the peak frequency (step S6).

If a peak in the frequency transfer function is an anti-resonance point in step S3 (step S3, No), the control characteristic changing unit determines 6th whether that from the cutting force vector arithmetic unit 3 The calculated power spectrum of the cutting force at the peak frequency is equal to or greater than a threshold value or less than the threshold value (step S5).

If the power spectrum of the cutting force is smaller than the threshold value (step S5, No), the unit changes the control characteristic 6th an operation from step S8. If the power spectrum of the cutting force is equal to or greater than the threshold value (step S5, Yes), the unit for changing the control characteristic lowers 6th the control gain of the spurious response compensator of the servo control unit 1 at the peak frequency (step S7). The unit for changing the control characteristic 6th repeats the processes from step S1 to step S7 until the peak value search within the frequency range to be scanned is completed (step S8).

The decision as to whether or not the frequency characteristic should be changed is made on the basis of the power spectrum of the cutting force in step S4, 5, since the coherence is low in a frequency range in which the cutting force is small, so that a peak in the Frequency transfer function cannot be calculated correctly with a certain probability and therefore an unnecessary change in the frequency characteristic must be prevented. In the method in step S4, 5, the power spectra of components for the machine axis direction, cutting force vectors of drive shafts, in which the control characteristics are to be changed, are used.

It should be noted that a frequency transfer function illustrated in the above-mentioned Coquad diagram can be used in the method of step S1. In the method in step S4, 5, the magnitude of the cutting force can be used instead of the power spectrum of the cutting force.

The means described below can initially be used for means for increasing the susceptibility of the control system to failure in step S6. As a first means, means for changing the control parameters of the spurious response compensator can be used, for example. The disturbance variable compensator of the servo control unit 1 is typically shown by a P controller, a PI controller and / or the like. In the case of PI control, for example, a proportional gain and an integration gain are control parameters of the spurious response compensator, and the control gain of the spurious response compensator can be increased by setting both the proportional gain and the integration gain to high values. With this method, however, the gain can increase in the entire frequency range of the spurious response compensators, which can lead to instability of the control system.

Second means described below can be used for the means for increasing a susceptibility to failure of the control system in step S6. A means for adding a filter for increasing the gain in a narrow band, that is to say an inverse band-stop filter for the spurious response compensator, can be used as a first means, for example. The inverse notch filter is expressed by, for example, a transfer function of Expression (4). s is a Laplace operator representing the deviation, and ω is an angular frequency in the middle of a range in which the gain should be increased. Q is a coefficient for determining a frequency band in which the gain should be increased, and a is a coefficient for determining the amount by which the gain should be increased. The gain at the frequency at which disturbance of the spurious response compensator occurs can be increased by setting ω as the peak frequency at the resonance point. $$\left(\text{<figure-callout id="2" label="s" filenames="DE112018007736T5\_0016.png" state="{{state}}">s</figure-callout>}2+\mathrm{\omega }\text{s / Q}+\mathrm{\omega }2\right)/\left(\text{<figure-callout id="2" label="s" filenames="DE112018007736T5\_0016.png" state="{{state}}">s</figure-callout>}2+\text{how}+\mathrm{\omega }2\right)$$

In addition, third means described below can be used for the means for increasing a susceptibility to failure of the control system in step S6. As a third means, for example means for using a bandpass filter that only passes frequency components within a certain range and does not pass frequency components other than the frequency components within the certain range, or a bandpass filter that only passes frequency components within a certain range and other frequency components than attenuates the frequency components within the specified range. By adding a component for the machine end position 201 is passed through the bandpass filter, the control parameters of the interference response compensator for the component are for the machine end position 201 passed through the band pass filter. In PI control, for example, a proportional gain and an integration gain are control parameters of the spurious response compensator, and both the proportional gain and the integration gain are set to high values. Since the control parameters are not changed in the case of components for the machine end position that do not pass the bandpass filter, the probability that the control system will become unstable is lower compared to the first means.

In step S7, the first means described below can be used. Means for changing control parameters of the spurious response compensator can be used, for example, as the first means in step S7. In the case that the spurious response compensator of the servo control unit 1 is adapted to the PI control, the proportional gain and the integration gain are set to low values.

Alternatively, a second means described below can be used in step S7. As the second means in step S7, means for adding a notch filter, which reduces the gain in a narrow band, to the spurious response compensator can be used as an example. The notch filter is expressed by expression (5), for example. s is a Laplace operator representing the deviation, and ω is an angular frequency in the middle of a range in which the gain should be lowered. Q is a coefficient for determining the frequency band in which the gain is to be lowered, and b is a coefficient for determining the amount by which the gain is to be lowered. The gain at the frequency at which a disturbance of the spurious response compensator occurs can be decreased by setting ω as the peak frequency at the resonance point. $$\left(\text{<figure-callout id="2" label="s" filenames="DE112018007736T5\_0016.png" state="{{state}}">s</figure-callout>}2+\text{bs}+\mathrm{\omega }2\right)/\left(\text{<figure-callout id="2" label="s" filenames="DE112018007736T5\_0016.png" state="{{state}}">s</figure-callout>}2+\mathrm{\omega }\text{s / Q}+\mathrm{\omega }2\right)$$

In addition, third means described below can be used in step S7. As a third means, means for using a bandpass filter that only passes frequency components within a certain range and does not pass frequency components other than the frequency components within the certain range, or a bandpass filter that only passes frequency components within a certain range and other frequency components than the frequency components can be exemplified as the third means attenuates within the specified range, be used. By adding a component for the machine end position 201 is passed through the bandpass filter, the control parameters of the interference response compensator for the component are for the machine end position 201 passed through the band pass filter. In PI control, for example, a proportional gain and an integration gain are control parameters of the spurious response compensator, and both the proportional gain and the integration gain are set to low values.

8th FIG. 13 is a first diagram illustrating an example in which spurious vibrations by the cutting force in the FIG 1 illustrated machine end position. In 8th is a tool path 300 which shows the machine end position changing at each moment and the cutting force vectors 310 at the respective positions of the changing machine end position are in 8th further illustrated by arrows. Note that in 8th only the cutting force vectors 310 are shown when the power spectrum of the cutting force at the peak frequency is equal to or higher than the threshold value.

9 FIG. 13 is a second diagram illustrating an example in which spurious vibration caused by the cutting force in the FIG 1 illustrated machine end position. In 9 is the parasitic vibration caused by the cutting force in relation to the position command 200 caused is illustrated enlarged. In 9 the direction of advance of the tool is indicated by an arrow D. As in 9 As illustrated, the surface property of the machined surface of the object to be machined is deteriorated by a side surface of the tool when spurious vibrations occur in a direction perpendicular to the advancing direction of the tool during the cutting process.

In the numerical control device 100-1 according to the first embodiment, the unit for changing the control characteristic changes 6th in the event of disturbance vibrations which worsen the surface quality of the machined surface, the disturbance response properties of the servo control unit 1 to reduce the parasitic vibrations. In addition, in the numerical control device 100-1 the processes of the cutting force vector arithmetic unit 3 , the unit for identifying mechanical properties 5 and the unit for changing the control characteristic 6th carried out in a predetermined period of time. This is because the cutting force responds to the change in a frequency to be changed based on the change in the machining position and the change in the states of the object to be machined, the tool and the machine after the machining is performed.

As described above, according to the numerical control device 100-1 In the first embodiment, since the transfer functions to be used to reduce the disturbance can be calculated sequentially during the machining process, the frequency response of the spurious response compensator is changed based on the cutting force vector information and the mechanical property information calculated during the machining process. In this way, the positional disturbance of the mechanical system caused by the cutting force can be reduced, the machining accuracy can be improved, and the tool wear can be reduced.

Since the transfer functions to be used to reduce the disturbances can be calculated sequentially during the machining process, it is after the numerical control device 100-1 In the first embodiment, it is not necessary to measure the frequency band in advance every time the cutting conditions change. For this reason, the frequency band need not be measured in advance, and any effort to change the frequency band accordingly is eliminated in the machining process, thereby making it possible for the user of the numerical control device 100-1 to relieve.

Since the machining operations of the cutting force vector arithmetic unit 3 , the unit for identifying mechanical properties 5 and the unit for changing the control characteristic 6th can be carried out in a predetermined time in the numerical control device 100-1 According to the first embodiment, the cutting force can be changed in accordance with the change in the machining position and the change in the states of the object to be machined, the tool and the machine caused by the execution of the machining.

If in the servo control unit 1 the numerical control device 100-1 In addition, if two-degree degree of freedom control is used in the first embodiment, the disturbance caused by the cutting force can be reduced without causing a path error.

In addition, according to the numerical control device 100-1 of the first embodiment, since the frequency band need not be made narrow in contrast to the conventional technique, the positional disturbances caused by the cutting force fluctuation are minimized, without reducing the ability of the tool position to follow the commanded trajectory.

Second embodiment. 10 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a second embodiment of the present invention. A numerical control device 100-2 according to the second embodiment comprises a display device 10 and a state input unit 11 in addition to the components used by the numerical control device 100-1 according to the first embodiment. In the second embodiment, components similar to those in the first embodiment are described using the same names and symbols as in the first embodiment.

The state input unit 11 enables a user of the numerical control device 100-2 , the condition for changing the control characteristic of the control characteristic changing unit 6th as well as information about whether the change in the control characteristic on the unit for changing the control characteristic 6th should be allowed or not. The condition for changing the control characteristic is, for example, the threshold of the power spectrum, the threshold of the magnitude of the cutting force or the like in the above-described machining processes in steps S4 and S5 of the unit for changing the control characteristic 6th .

In addition, an instruction code, generally referred to as G code, is used for a program for processing an object to be processed with the machine tool 100 used. The commands in G code include a position command (G00), a linear interpolating cutting command (G01), circular interpolating cutting commands (G02, G03), and the like. Typically, the position command (G00) is a command used at the time of no cutting. The user can set the condition for the unit to change the control characteristic 6th the control characteristic is allowed to change so that the state input unit 11 the unit for changing the control characteristic 6th the change of the control characteristic in the case of a position command or the unit for changing the control characteristic 6th enables the change of the control characteristic, for example in the case of a cutting command.

In addition, the status input unit 11 always change information on whether or not a change in the control characteristic is allowed, and the unit for changing the control characteristic 6th changes the control characteristics of the servo control unit 1 only if the change in the control characteristic is permitted and, for example, the condition for changing the control characteristic is met.

The display unit 10 shows part or all of the data of the information on mechanical properties 207 which is an output of the unit for identifying mechanical properties 5 and the cutting force vector information 204 , which is an output of the cutting force vector arithmetic unit 3 is on. The user of the numerical control device 100-2 can know this type of information that is on the display device 10 are displayed. For example, on the display unit 10 a unit length (e.g. 1 mm) of the in 7th illustrated tool path 300 displayed with a certain length. In addition, on the display unit 10 a unit force (1 N) of the in 7th illustrated cutting force vector 310 displayed with a certain length. With this, the user can check the magnitude and direction of the cutting force and know the state during the machining process and easily determine whether the control characteristic is in the control characteristic changing unit 6th should be carried out or not.

In addition, on the display unit 10 a unit size of the common logarithms in frequency on each of the in 5 illustrated gain diagrams and that in 6th phase diagram shown with a unit of length. Thereby, the user can check at what frequency vibrations are caused, know the state during the machining process, and easily determine whether the control characteristic is in the control characteristic changing unit 6th should be carried out or not.

As described above, the user uses after the numerical control device 100-2 according to the second embodiment, the state input unit 11 to specify the condition for the change of the control characteristic and to indicate the information on whether or not to allow the change of the control characteristic, thereby making it possible to prevent editing unintended by the user. In addition, on the display unit 10 the information on mechanical properties, information on cutting force vectors, and the like are displayed so that the user can easily determine whether or not change in the control characteristics is permitted.

Third embodiment. 11 Fig. 13 is a diagram illustrating a configuration of a numerical control device according to a third embodiment of the present invention. The use of a notch filter among the Conditions of vibration at frequencies contained in a control band for position commands is undesirable because the ability to follow a commanded path decreases. In view of this, in the case of vibrations at low frequencies included in a position control band, the vibration caused by the cutting force needs to be reduced in some other way. Therefore, in a numerical control device 100-3 according to the third embodiment, an adding unit 12th and a unit for calculating the disturbance correction amount 13th instead of the in 1 illustrated unit for changing the control characteristic 6th used. In the third embodiment, components similar to those in the first embodiment are described with the same names and symbols as in the first embodiment.

The unit for calculating the interference correction amount 13th estimates the disturbance caused by the cutting force and calculates a correction amount from the estimated disturbance based on the information on mechanical properties 207 and the cutting force vector information 204 . The calculated correction amount is made by the adding unit 12th to the position command 200 added, and an output of the adding unit 12th , ie a position command 200 , at which the correction amount has been added, is entered in the servo control unit 1 and the simulation response arithmetic unit 4th entered. The numerical control device 100-3 controls the machine tool 100 using the position command resulting from the addition 200 to thereby reduce the positional disturbance caused by the cutting force variation while minimizing the ability of the tool position to follow the commanded path, so that the deterioration in machining accuracy can be prevented.

12th FIG. 13 is a block diagram of the engine and the FIG 2 illustrated mechanical system which is approximated by a two-inertial model. In the in 12th illustrated model, K is a spring constant of an elastic element of the mechanical system 8th , C is the viscous coefficient of friction of a damping element of the mechanical system 8th , Jm is the inertia of the motor 7th and Jl is the inertia of the mechanical system 8th . The position of Jm is a simulated motor end position and the position of Jl is a simulated machine end position. Tm is a torque given by the servo motor 71 is output in accordance with a torque command, xl is a variable representing the machine end position, xm is a variable representing the motor end position, and s is a Laplace operator representing the deviation. The results of the Laplace transform of xm, xl and fc are expressed as XM, XL and Fc, respectively.

The elastic member K, the cushioning member C, and the like are changed according to the cutting force, so that a positional disturbance in table 81 is caused. Furthermore, the cutting force is transmitted through the elastic member K, the cushion member C, or the like, so that positional disturbance is caused even in the motor position. In the event that the engine 7th and the mechanical system 8th are modeled in a two-inertial model, the transfer function from the cutting force to the positional disturbance is expressed, for example, by expression (6). $$\text{G}\left(\text{s}\right)=1/\left(\text{J}1\text{<figure-callout id="2" label="s" filenames="DE112018007736T5\_0016.png" state="{{state}}">s</figure-callout>}2+\text{Cs}+\text{K}\right)$$

$$\text{GLPF}\left(\text{s}\right)=1/\left(\text{Ts}+1\right)$$

The unit for calculating the interference correction amount 13th identifies the coefficients in Expression (6) using, for example, a least squares method, a spectrum analysis method, a subspace method, or the like for the transfer function performed by the mechanical property identification unit 5 is identified. While the mechanical system 8th is approximated by a two-inertial model in the formula (6), the transfer function can be expressed in a lower or higher order model. The unit for calculating the interference correction amount 13th can calculate a disturbance caused by the cutting force by applying a filter of a type of the transfer function identified as described above to that of the cutting force output unit 2 measured cutting force 203 is applied. The calculated interference value resulting from this calculation also includes high frequency components. Since the high frequency components cannot be controlled, the unit for calculating the amount of interference correction removes 13th the high frequency components using a low pass filter for appropriate frequencies. The unit for calculating the interference correction amount 13th calculates the disturbances one after the other in a control cycle. The unit for calculating the interference correction amount 13th inverts a positive or negative value of the calculated disturbance to obtain the inverted disturbance as a correction amount. The correction is made in the adding unit 12th entered, and in the adding unit 12th the correction amount becomes the position command 200 added. The correction C is calculated by Expression (7) and Expression (8). F is a cutting force vector of the machine axis. T is a time constant of the low-pass filter. $$\text{C.}=-\text{GLPF}\left(\text{s}\right)\text{G}\left(\text{s}\right)\text{F.}$$

$$\text{GLPF}\left(\text{s}\right)=1/\left(\text{Ts}+1\right)$$

A factor that has an adverse effect on the surface finish of the machined surface, the vibration is in a direction perpendicular to the feed direction of the tool. In contrast to this, in the case of a correction in the feed direction of the tool, the speed of movement of the tool in the feed direction of the tool is no longer constant, which can have an adverse effect on the surface quality of the machined surface. In this situation, the unit leads to the calculation of the amount of correction for disturbance 13th the correction only takes place in one direction perpendicular to the feed direction of the tool. In this case, the cutting force vector Fn in the perpendicular direction specified in expression (3) may be used in place of the cutting force vector F in expression (7) in the machine axis direction.

As described above, the numerical control device 100-3 according to the third embodiment, reduce the spurious vibrations at low frequencies contained in the band for position control without reducing the ability to follow a commanded path. This extends the life of the tool and can improve the machining accuracy of the object to be machined. In addition, in the numerical control device 100-3 as well as in the numerical control device 100-1 according to the first embodiment, the machining operations of the cutting force vector arithmetic unit 3 , the unit for identifying mechanical properties 5 and the unit for changing the control characteristic 6th is performed in a prescribed period of time, thereby making it possible to change the cutting force depending on a change in the machining position and changes in the state of the object to be machined, the tool and the machine caused by performing machining.

13th Fig. 13 is a diagram illustrating an example of a hardware configuration of the numerical control devices according to the first to third embodiments. Any of the numerical control devices 100-1 , 100-2 and 100-3 contains a central processing unit (CPU) 51 that performs the arithmetic processing, a memory 52 from the CPU 51 is used as a work area, a storage device 53 that can store programs, information, and the like, an input device 54 receiving input from a user and a display device 55 . The memory 52 corresponds to: a volatile or non-volatile semiconductor memory, such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM) or an electrically erasable programmable read-only memory (EEPROM (registered trademark)); a magnetic disk; a flexible plate; an optical disk; a compact disc; a mini disc; or a digital versatile disc (DVD). Examples of the input device 54 include a keyboard and a mouse, and examples of the display device 55 include a monitor and a display. Notice that the input device 54 and the display device 55 can be integrated and implemented by a touch panel or the like.

The servo control unit 1 , the cutting force vector arithmetic unit 3 , the simulation response arithmetic unit 4th , the unit for identifying mechanical properties 5 , the unit for changing the control characteristic 6th , the subtraction unit 9 , the unit for calculating the amount of interference correction 13th and the adding unit 12th are from the CPU 51 implemented in the storage device 53 runs saved programs.

The configurations shown in the above embodiments are examples of the present invention and can be combined with other publicly known techniques and each can be partially omitted and / or modified without departing from the scope of the present invention.

List of reference symbols

1

Servo control unit;

2

Cutting force output unit;

3

Cutting force vector arithmetic unit;

4, 4A

Simulation response arithmetic unit;

5

Unit for identifying mechanical properties;

6th

Control characteristic changing unit;

7th

Engine;

8th

mechanical system;

9

Subtraction unit;

10

Display unit;

11

State input unit;

12th

Adding unit;

13th

Unit for calculating the amount of interference correction;

41

Unit for simulating position control;

42

Integration arithmetic unit;

43

Speed control simulation unit;

44

Integration computer;

45

Proportionality constant arithmetic unit;

51

CPU;

52

Storage;

53

Storage device;

54

Input device;

55

Display device;

71

Servo motor;

71a

Rotor;

71b

Wave;

72

Motor position detector;

81

Table;

82

Ball screw nut;

83

Ball screw spindle;

84

Coupling;

85

Machine end position detector;

86

Machine end position detector head;

90

object to be processed;

100

Machine tool;

100-1, 100-2, 100-3

numerical control device;

101

Tool;

200

Position command;

201

Machine end position;

202

Torque command;

203

Cutting force;

204

Cutting force vector information;

205

Model position;

206

Positional disorder;

207

Information on mechanical properties;

208

Model speed;

209

Model torque;

300

Tool path;

310

Cutting force vector.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• JP 2013250866 [0004]

Claims (9)

A numerical control device that controls a mechanical system configured to perform machining of an object to be machined with a tool used to machine the object, the numerical control device comprising: a servo control unit for driving a motor connected to a driven element based on a position command so that a position of the driven element follows the position command, the object being set on the driven element; a cutting force output unit for measuring or estimating cutting force caused between the tool and the object and outputting the cutting force; a cutting force vector calculating unit for calculating a cutting force vector based on the position of the driven member and the cutting force; a mechanical property identification unit for identifying dynamic properties of the mechanical system in relation to the cutting force; and a control characteristic changing unit for changing the control characteristic of the servo control unit based on the cutting force vector and the dynamic characteristics of the mechanical system identified by the mechanical characteristic identifying unit. Numerical control device according to Claim 1 wherein the mechanical property identification unit identifies frequency response characteristics of the servo control unit represented by gain and phase in a frequency range from the cutting force to the disturbance in a control system. Numerical control device according to Claim 2 wherein the control characteristic changing unit identifies a cause of a malfunction by searching the frequency response characteristics identified by the mechanical characteristic identifying unit for a resonance point or an anti-resonance point whose peak shapes of the frequency response characteristics are different from each other, and changing the frequency characteristics of the control system in accordance with the identified cause of the malfunction . Numerical control device according to Claim 2 or 3 wherein the control characteristic changing unit determines whether or not to change the frequency response characteristics based on the cutting force vector. Numerical control device according to one of the Claims 1 to 4th having a state input unit for inputting a condition for changing the control characteristic of the servo control unit to the control characteristic changing unit. A numerical control device that controls a mechanical system configured to perform machining of an object to be machined with a tool used to machine the object, the numerical control device comprising: a servo control unit for driving a motor connected to a driven element based on a position command so that a position of the driven element follows the position command, the object being set on the driven element; a cutting force output unit for measuring or estimating cutting force caused between the tool and the object and outputting the cutting force; a cutting force vector calculating unit for calculating a cutting force vector based on the position of the driven member and the cutting force; a mechanical property identification unit for identifying dynamic properties of the mechanical system in relation to the cutting force; and a disturbance correction amount calculating unit for calculating a correction amount with which a disturbance caused by the cutting force is to be corrected in a control system. Numerical control device according to Claim 6 wherein the unit for identifying mechanical properties identifies frequency response characteristics from the cutting force to the disturbance in the control system, and the unit for calculating the disturbance correction amount calculates the correction amount for correcting the disturbance by applying a transfer function type filter having the frequency response characteristics to the cutting force. Numerical control device according to Claim 6 or 7th wherein the disturbance correction amount calculating unit calculates the correction amount in a direction perpendicular to a feed direction of the tool based on the cutting force vector. Numerical control device according to Claim 2 , 3 , 4th , 6th , 7th or 8th , wherein the failure in the control system is a failure occurring in one of the Position command, a speed command and a torque command is included.

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