JP2012056066A - Thread cutting control method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for attaining alteration of main shaft rotation speed during thread cutting, which is not conventionally attained since a phase error of a main shaft and a feed shaft is generated by alteration of the main shaft rotation speed even though chatter damaging a thread and generated during thread cutting can be suppressed by alteration of main shaft rotation speed, in thread cutting for moving the feed shaft synchronizing with the main shaft rotation speed.SOLUTION: Upon thread cutting instruction, the speed of the feed shaft is formed from a main shaft rotation instruction and a time constant, an acceleration and deceleration type and position loop gain of the main shaft and the feed shaft are made to be same to eliminate the phase error of the main shaft and the feed shaft to the change of the main shaft rotation speed. Thus alteration of the main shaft rotation speed during thread cutting is made attainable.

Description

  The present invention relates to a threading control method and apparatus for performing threading by moving a threading tool driven by a feed shaft by controlling the feed shaft in synchronization with rotation of a main shaft.

  Thread cutting using a numerical control (NC) device rotates the spindle while the workpiece is fixed by a chuck provided on the spindle, and also feeds a feed axis that drives a servo motor to send a thread cutting tool. This is realized by controlling and feeding the thread cutting tool in the feed axis direction (Z-axis direction). At this time, the feed shaft (servo motor) feeds the tool in synchronism with the rotation of the main shaft, thereby processing a desired screw.

First, the prior art of this threading control will be described with reference to FIG.
The speed of the rotating spindle is appropriately input by the operator in order to change the spindle speed command S commanded by the NC machining program and the spindle speed commanded by the NC machining program at the spindle speed creation unit 203. It is created by multiplying with the spindle override 202. The generated spindle rotation speed is subjected to acceleration / deceleration of the spindle by the spindle speed acceleration / deceleration processing unit 204, and the spindle control unit 205 controls the spindle motor 206. The spindle motor 206 is provided with an encoder, and the thread cutting feed creation unit 208 multiplies the feedback rotational position data from the encoder by the pitch P analyzed by the program analysis unit 207 of the NC machining program, thereby providing a feed rate. Create F. If the increment value of the feedback rotation position data of the spindle from the encoder per unit time is ΔS, the speed of the feed shaft is F = P × ΔS.

  Servo acceleration / deceleration is applied to this feed rate by the feed rate acceleration / deceleration processing unit 209, and the servo control unit 210 controls the servo motor 211 to move the thread cutting tool in the Z-axis direction to cut the screw. Controls the feed axis that moves the tool. In threading, the feed shaft needs to pass through the same thread groove path many times with respect to the rotation position (phase) of the main shaft, so one rotation signal (Z phase signal) generated every rotation of the main shaft is used as a reference. The feed axis starts to move.

By the way, when chattering occurs during this threading, chattering can be suppressed by changing the cutting speed of the feed shaft. In thread cutting for calculating the speed of the feed shaft from the main shaft rotation speed, the cutting speed of the feed shaft can be changed by changing the main shaft rotation speed. Usually, the spindle rotation speed can be changed by spindle override.
However, if the spindle rotational speed changes, the position of the feed shaft deviates from the previous thread groove path with respect to the rotational position (phase) of the spindle. Since threading requires the feed shaft to go through the same path many times with respect to the rotation position (phase) of the spindle, if there is a phase error (deviation) of the feed axis with respect to the rotation position (phase) of the spindle, screw accuracy Will be reduced. This phase error occurs during acceleration / deceleration when the spindle rotation speed and the feed axis speed change. For this reason, during thread cutting, the spindle speed cannot be changed substantially, for example, the spindle override cannot be fixed or changed 100%.

  To solve this problem, when the spindle speed is changed during thread cutting after the start of threading, the relative phase error between the spindle position and the feed axis position during thread cutting is calculated, and the relative phase is calculated. There has been proposed a method of correcting the phase error between the main shaft and the feed shaft by calculating the amount of movement of the feed shaft based on the pseudo main shaft position in which the error amount is compensated for the main shaft position (see Patent Document 1).

  Japanese Patent No. 3926737

  However, in the invention described in Japanese Patent No. 3926737, the feed speed is created from the pseudo main spindle position in which the phase error amount is compensated for the feedback position of the main spindle. Time delay. Therefore, even with the technique proposed in the present invention, there is a problem that a minute delay of the feed shaft occurs at the moment when the spindle override is changed, and the accuracy of the screw is deteriorated.

  The present invention has been made to solve such a problem, and a thread cutting control method that does not deteriorate the thread machining accuracy even if the spindle rotation speed is changed during the thread cutting after starting the thread machining, and The purpose is to obtain the device.

  The threading control method according to the present invention calculates the moving amount of the feed shaft to be synchronized with the rotation of the spindle from the spindle speed command, and makes the time constant, the acceleration / deceleration type, and the position loop gain of the spindle and the feed shaft the same. Is to do.

  Further, the thread cutting control method according to the present invention performs multi-stage acceleration / deceleration according to the speed fluctuation region when the spindle rotational speed is changed during thread cutting.

  The threading control device according to the present invention calculates the amount of movement of the feed shaft that is synchronized with the rotation of the spindle from the spindle speed command in the threading control device that performs threading by moving the threading tool in synchronization with the rotation of the spindle. Means for setting the time constants and acceleration / deceleration types of the main shaft and the feed shaft to be the same, and means for setting the position loop gains of the main shaft and the feed shaft to be the same.

  The thread cutting control device according to the present invention performs multi-stage acceleration / deceleration according to the speed fluctuation region when the spindle rotational speed is changed during thread cutting.

  According to the present invention, even if the spindle rotation speed is changed during the thread cutting after the start of the thread cutting process, the screw machining accuracy does not deteriorate, and as a result, the spindle rotates during the thread cutting after the thread cutting process starts. You can change the number.

  In addition, since the spindle is controlled by multistage acceleration / deceleration, the spindle speed rises quickly, and the response is improved.

1 is a block diagram showing an NC apparatus according to Embodiment 1 of the present invention. It is a figure which shows the spindle speed waveform produced with the NC apparatus which concerns on Example 1 of this invention. It is a figure which shows the feed shaft speed waveform produced with the NC apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the calculation delay time of threading control. It is a figure for demonstrating the delay at the time of acceleration / deceleration. It is a figure for demonstrating the follow-up delay of a motor. It is a figure which shows an example of the multistage acceleration / deceleration of the NC apparatus which concerns on Example 2 of this invention. It is a flowchart which shows operation | movement when performing multistage acceleration / deceleration of the NC apparatus which concerns on Example 2 of this invention. It is a block diagram which shows an example of the conventional threading control.

Example 1.
A first embodiment of the present invention will be described below with reference to FIGS. In this embodiment, the threading control method and the apparatus are applied to the NC apparatus.
1 is a block diagram showing an NC apparatus according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 103 denotes a spindle rotational speed command S commanded by the NC machining program and a spindle rotational speed commanded by the NC machining program. This is a spindle speed creation unit that creates a spindle rotational speed command F by multiplying with a spindle override 102 that is appropriately input by an operator to change. The spindle speed is actually converted into a change amount ΔS of the spindle position per unit time (change amount of the spindle angle per unit time) by the spindle speed creation unit 103. A spindle speed acceleration / deceleration processing unit 104 performs acceleration / deceleration processing on the spindle speed created by the spindle speed creation unit 103 based on the acceleration / deceleration time constant t1 set as a parameter so as to obtain linear inclination data. is there.

  A spindle speed acceleration / deceleration processing unit 112 performs acceleration / deceleration processing so that, for example, S-shaped data is obtained by applying an acceleration / deceleration filter to the acceleration / deceleration process performed by the spindle speed acceleration / deceleration processing unit 104. 113 is a spindle control parameter change for threading that adjusts so that the position loop gain of the spindle is the same as the position loop gain of the feed axis (the axis for moving the thread cutting tool by moving the thread cutting tool in the Z-axis direction). , 105 is a spindle control unit for controlling the position of the spindle motor 106 based on the output from the spindle speed acceleration / deceleration processing unit 112, 106 is a spindle motor for rotating the spindle, and an encoder is attached to the detection data of this encoder. Is fed back to the spindle control unit 105, and the position of the spindle control unit 105 is controlled.

Reference numeral 107 denotes a program analysis unit for analyzing the NC machining program, and 108 denotes a spindle rotational speed command F created by the spindle speed creation unit 103 and the spindle speed acceleration / deceleration processing unit 104 and an analysis by the program analysis unit 207 of the NC machining program. This is a thread cutting feed creating unit that creates a feed shaft speed F (= P × S) by multiplying the pitch P. The feed shaft speed F is actually converted into a change amount ΔS of the spindle position per unit time (change amount of the spindle angle per unit time) by the spindle speed creation unit 103 in practice. Is the feed shaft speed of ΔS × P.
A feed speed acceleration / deceleration 109 performs acceleration / deceleration processing by applying an acceleration / deceleration filter so that the same acceleration / deceleration pattern as the spindle acceleration / deceleration pattern can be obtained with respect to the feed axis speed created by the thread cutting feed creation unit 108. The processing unit 114 is a threading feed axis control parameter changing unit that adjusts the position loop gain of the feed axis to be the same as the position loop gain of the main shaft. 110 is based on the output from the feed axis speed acceleration / deceleration processing unit 109. A spindle control unit that servo-controls the servo motor 111, 111 is a servo motor that rotates the feed shaft, and an encoder is attached to the servo control unit 110 by feeding back the detected data of the encoder to the servo control unit 110. Servo controlled.

  In this embodiment, the thread cutting feed creation unit 108 calculates the movement amount of the feed shaft synchronized with the spindle from the spindle speed command, and the feed speed acceleration / deceleration processing units 104, 112, and 109 Thread feed spindle control parameter change section 113 and thread cut feed axis control parameter change section 114 have the same position loop gain for the spindle and feed axis. The means to set is set.

  As described above, in this embodiment, the thread cutting feed speed is not created from the spindle feedback data, but the thread cutting feed speed is created from the spindle rotational speed command. In addition, the same acceleration / deceleration time constants and acceleration / deceleration filter (acceleration / deceleration type) are adopted for the spindle and feed axis, and for thread cutting so that the position loop gain of the spindle and feed axis is the same. Adjustment is performed by the spindle control parameter changing unit 113 and the threading feed shaft control parameter changing unit 114.

Next, the function and effect of the NC device configured as described above will be described.
That is, there are three factors that cause phase errors due to changes in the spindle speed.
As a first factor, there is a phase error caused by a calculation delay time. In the conventional thread cutting, as described above, the speed of the feed shaft is created from the feedback data ΔS of the encoder of the spindle motor 206 and the pitch P. Further, since data is exchanged between the NC and the amplifier per unit time of communication, the change in speed is reflected in the servo motor 211 after the speed of the spindle motor 206 is actually changed. As shown, there will be a deviation of several communication unit times between the NC and the amplifier. As a result, a phase error between the main shaft and the feed shaft occurs.

However, in this embodiment, the thread cutting feed creation unit is not created from the spindle rotational speed command created by the spindle speed creation unit 103 and the spindle speed acceleration / deceleration processing unit 104, but the thread cutting feed rate is not created from the feedback position data of the spindle. Since the feed axis command is created at 108, the spindle speed change command and the feed axis speed change command have the same timing.
For this reason, there is no calculation delay time of the feed shaft with respect to the main shaft, and no phase error occurs.

  The second factor that causes a phase error due to changes in the spindle speed is the phase error that occurs during acceleration / deceleration of the speed due to the acceleration / deceleration time constant between the spindle and feed axis and the acceleration / deceleration filter (acceleration / deceleration type). is there. When the speed is changed, the changed speed is reached in the time of the set acceleration / deceleration filter (acceleration / deceleration type) and acceleration / deceleration time constant, causing a delay. If the acceleration / deceleration time constants and acceleration / deceleration filter (acceleration / deceleration type) of the main shaft and feed shaft are different, the acceleration / deceleration delay amount is also different, resulting in a phase error between the main shaft and the feed shaft, resulting in loss of synchronization. This will be explained with reference to FIG. 5. When the acceleration / deceleration filter (acceleration / deceleration type) is a linear acceleration / deceleration time constant t, the acceleration / deceleration delay amount d1 due to the speed change ΔS is d1 = ΔS × t / 2. It can be seen that the amount of delay changes depending on the acceleration / deceleration time constant.

However, in this embodiment, since the same acceleration / deceleration time constant and acceleration / deceleration filter (acceleration / deceleration type) are set for the main shaft and the feed axis, phase errors due to acceleration / deceleration do not occur.
This will be explained with reference to FIGS. 1 to 3. When the spindle speed is changed from S1 to S2 by the spindle override 102, the speed data created by the spindle speed creating unit 103 is the step shown in FIG. It becomes the speed data that makes the rise at. By setting an acceleration / deceleration time constant t1 in the spindle speed acceleration / deceleration processing unit 104 for this data, linear inclination data as shown in FIG. 2B is created. The thread cutting feed creation unit 108 creates a feed rate from the spindle speed S and the pitch P created by the spindle speed acceleration / deceleration processing unit 104, and the feed rate F becomes F = P × S, as shown in FIG. The feed rate data is created.

  The feed rate acceleration / deceleration processing unit 109 applies an adjustment filter to the feed rate. For example, when an S-shaped acceleration / deceleration filter is set in the feed speed acceleration / deceleration processing unit 109, S-shaped acceleration / deceleration data as shown in FIG. In this embodiment, in order to make the acceleration / deceleration time constant and acceleration / deceleration type the same, the acceleration / deceleration processing unit 112 further performs acceleration / deceleration processing for applying the same acceleration / deceleration filter as the feed axis to the spindle speed. Spindle speed data as shown in FIG. 2 (c) is created. As a result, the command data output to the spindle motor 106 (FIG. 2C) and the command data output to the servo motor 111 (FIG. 3C) have the same form, and F = P × S also during acceleration / deceleration. The relationship never breaks down. Thereby, a phase error due to acceleration / deceleration does not occur.

A third factor that causes a phase error due to a change in the spindle speed is a phase error that occurs due to a follow-up delay between the actual spindle motor and the servo motor during acceleration / deceleration. When the speed changes, the speed of the command output to the motor is accelerated and decelerated as described above. However, the actual operation of the motor is further delayed as shown in FIG. 6 with respect to the command subjected to the acceleration / deceleration. Even if the amount of follow-up delay between the spindle motor and the servo motor at the time of acceleration / deceleration is different, a phase error between the spindle and the feed shaft occurs and the synchronization is lost. Here, when the position loop gain of the motor is G, the follow-up delay amount d2 of this motor is a linear acceleration / deceleration filter (acceleration / deceleration type).
d2 = ΔS / G
Thus, it can be understood that the follow-up delay amount of the motor is due to the position loop gain.

However, in this embodiment, since the position loop gains of the main shaft and the feed shaft are the same, the phase error due to the tracking delay does not occur.
This will be explained with reference to FIG. 1. In this embodiment, when a threading command is issued, the threading position loop gain can be set as a parameter for each of the spindle motor 106 and the servomotor 111. Therefore, the threading spindle control parameter is changed. In part 113 and threading feed axis control parameter changing part 114, the position loop gains of spindle motor 106 and servo motor 111 are changed to the same loop gain. The spindle control unit 106 and the servo control unit 111 control the motors 106 and 111 according to the set loop gain. As a result, the error due to the follow-up delay of the motor can be eliminated, and no phase error occurs.

Example 2
Next, a second embodiment of the present invention will be described mainly with reference to FIGS.
That is, when the rotational speed of the main shaft is high, the torque is small, so that rapid acceleration is not possible. Since the acceleration / deceleration time constant must be set so that it can follow even when the number of revolutions is high, the acceleration / deceleration time constant of the spindle inevitably increases and the responsiveness to changes in speed becomes worse.
Therefore, in the second embodiment, at the time of threading, the spindle speed acceleration / deceleration processing unit 104 performs multistage acceleration / deceleration, thereby increasing the rise of the spindle speed and improving the response.
FIG. 7 shows the relationship between the spindle speed of multistage acceleration / deceleration and the acceleration / deceleration time constant. FIG. 8 is a flowchart when performing multi-stage acceleration / deceleration as shown in FIG. In FIG. 7, acceleration is performed with acceleration / deceleration time constant 81 when the spindle rotation speed is within 84, acceleration / deceleration time constant 82 when the spindle rotation speed is within 84 to 85, and acceleration / deceleration time constant 83 when the spindle rotation speed is within 85 to 86. Shows that you can. Here, 86 is the maximum rotational speed of the spindle motor, and this speed is not exceeded. The spindle rotation speeds 84 to 86 and the acceleration / deceleration time constants 81 to 83 can be set by parameters.

  In the case of the second embodiment, the spindle speed acceleration / deceleration processing unit 104 operates as shown in FIG. That is, in step 1, it is determined whether threading is in progress by referring to the threading command. If not, the process proceeds to step 3 to set a normal acceleration / deceleration time constant. If threading is in progress, the process proceeds to step 2 to determine whether the previous spindle speed is the same as or lower than the spindle rotational speed 84. In step 2, when the previous spindle speed is equal to or lower than the spindle speed 84, the process proceeds to step 4 where an acceleration / deceleration time constant 81 is set, and the previous spindle speed is the same as or higher than the spindle speed 84. If so, go to step 5. In step 5, it is determined whether or not the previous spindle speed is equal to or lower than the spindle rotational speed 85. If the previous spindle speed is equal to or lower than the spindle rotational speed 85, the process proceeds to step 4 to add. When the deceleration time constant 82 is set and the previous spindle speed is equal to or higher than the spindle rotation speed 85, the routine proceeds to step 7 where the acceleration / deceleration time constant 83 is set. Then, after setting these acceleration / deceleration time constants, the process proceeds to step 8 to create the spindle speed.

  According to the second embodiment, since the main shaft rotation speed is 84 and the main shaft rotation speed is low, the torque is large and the acceleration is relatively rapid with a short acceleration / deceleration time constant such as the acceleration / deceleration time constant 81. I do. On the other hand, when the main shaft rotation speed is in the high range of 85 to 86, the torque is small, so that a relatively slow acceleration is performed with a long acceleration / deceleration time constant like the acceleration / deceleration time constant 83. In this way, by using multistage acceleration / deceleration, acceleration can be performed with an acceleration / deceleration time constant suitable for the speed region, and the responsiveness of changing the spindle speed when chatter occurs can be improved.

As described above, according to these embodiments, the feed axis command is created not from the feedback position data of the spindle but from the spindle rotation speed command, and therefore the phase due to the calculation time delay error of the feed axis with respect to the spindle. There is no error. In addition, since the acceleration / deceleration time constants and acceleration / deceleration types of the spindle and feed axis are the same at the time of threading command, no phase error occurs at the command level during acceleration / deceleration. In addition, since the position error gain of the main shaft and the feed axis are the same and the following error of the motor is the same, no phase error due to the following error occurs.
For this reason, even if the spindle rotation speed is changed by the spindle override, no phase error occurs, and the thread machining accuracy does not decrease. Therefore, the spindle rotation speed can be freely changed during thread cutting.
In addition, since the spindle is controlled by multistage acceleration / deceleration, the spindle speed rises faster, which in turn improves responsiveness.

  The thread cutting control method and the apparatus according to the present invention are suitable for use when it is desired to change the spindle rotational speed during the thread cutting after starting the thread cutting without deteriorating the thread machining accuracy.

  101 Spindle speed, 102 Spindle override, 103 Spindle speed creation unit, 104 Spindle speed acceleration / deceleration processing unit, 105 Spindle control unit, 106 Spindle motor, 107 Program analysis unit, 108 Thread cutting feed creation unit, 109 Feed rate acceleration / deceleration processing unit , 110 Servo control unit, 111 Servo motor, 112 Spindle speed acceleration / deceleration processing unit, 113 Threading spindle control parameter changing unit, 114 Threading feed axis control parameter changing unit.

Claims (4)

  In a threading control method in which threading is performed by moving a threading tool driven by the feed axis by controlling the feed axis in synchronization with the rotation of the spindle, the feed axis synchronized with the rotation of the spindle from the spindle speed command is controlled. A threading control method characterized by calculating a moving amount and performing threading processing with the same time constant, acceleration / deceleration type, and position loop gain of a spindle and a feed axis.   The threading control method according to claim 1, wherein when the spindle rotational speed is changed during threading, multistage acceleration / deceleration is performed in accordance with a speed fluctuation region.   In a threading control device that performs threading by moving a threading tool in synchronization with the rotation of the spindle, a means for calculating the amount of movement of the feed axis that is synchronized with the rotation of the spindle from the spindle speed command, A threading control device comprising: means for setting the constant and acceleration / deceleration type to be the same; and means for setting position loop gains for the spindle and the feed axis to be the same.   4. The thread cutting control device according to claim 3, wherein when the spindle rotational speed is changed during thread cutting, multistage acceleration / deceleration is performed in accordance with a speed fluctuation region.

Images