JP3558508B2 - Control device for NC machine tool - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an NC machine tool.
[0002]
[Prior art]
In a machine tool such as a machining center or a lathe, when a cutting tool and a workpiece are relatively moved to cut the workpiece, so-called chattering may occur between the blade and the workpiece. is there.
Chatter is self-excited vibration in which undulations having a certain regularity occur between the blade and the workpiece.
When this chatter occurs, the vibration of the machine gradually increases, and this vibration undesirably causes the cutting surface of the workpiece to be defective or an excessive load on the drive system.
[0003]
Generally, the vibration frequency of the chatter has a magnitude corresponding to the natural frequency of a mechanical system including a machine tool, a cutting tool, and a workpiece.
For example, when a cutting tool is attached to a spindle and rotated as in milling, chatter increases when the rotation speed of the spindle approaches the natural frequency of the mechanical system.
Chatter is also induced when the feed speed of the workpiece to the cutting tool is set to a certain speed.
Conventionally, when chatter occurs or when chatter is expected to occur, the operator must reduce the rotational speed of the spindle to an extent that chatter is empirically suppressed, The feed speed was reduced.
[0004]
[Problems to be solved by the invention]
However, if only the rotation speed of the spindle or only the feed speed is changed in order to suppress the chatter, the state of the cutting surface also changes before and after the rotation speed or the feed speed of the spindle is changed.
For example, in a cutting tool having a plurality of blades such as a milling cutter and an end mill, if one of the rotation speed and the feed speed of the spindle is changed, the feed amount per workpiece per blade is changed. Therefore, the state of the cutting surface varies, and the quality of the cutting surface varies in the same workpiece.
Conventionally, it is necessary for an operator to always monitor whether chatter occurs during machining and to determine the rotation speed and the feed speed of the main spindle, which makes it difficult to automate the machining.
[0005]
The present invention has been made in order to solve the conventional disadvantage, and it is possible to suppress chatter vibration generated between a cutting tool and a workpiece in an NC machine tool, and to make the state of a cutting surface uniform. It is an object of the present invention to provide a control device for an NC machine tool, which is capable of approaching to the above, and which enables automation of processing.
[0006]
[Means for Solving the Problems]
The present invention is a control device for an NC machine tool having a spindle for rotating a tool or a workpiece, and a feed axis for relatively moving the workpiece and the tool, wherein the rotation speed of the spindle and the feed rate are controlled. By changing the feed speed of the shaft, vibration suppressing means for suppressing vibration generated between the tool and the workpiece by processing the workpiece by the tool, and A constant load range control means for controlling a load applied to the main shaft and the feed shaft by machining to a predetermined range by changing a rotation speed of the main shaft and a feed speed of the feed shaft; The means and the constant load range control means change the rotation speed of the spindle and the feed speed of the feed shaft while keeping the rotation speed of the spindle and the feed speed of the feed shaft constant. It has the means.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First embodiment
Description of NC device
FIG. 1 is an explanatory diagram illustrating a configuration of an NC device to which the present invention has been applied. Note that the NC device NC is described as being capable of controlling a main shaft and three feed axes of X, Y, and Z axes.
In FIG. 1, an NC apparatus 1 according to the present embodiment includes an NC program analysis / command distribution unit 4, an auxiliary control unit 6, servo control units 12 to 14 for X, Y, and Z axes, X, Y, It has Z-axis servo drivers 15 to 17, a spindle control unit 21, and a spindle driver 22.
X, Y, and Z axis servo motors 18 to 20 are connected to the X, Y, and Z axis servo drivers 15 to 17, respectively. The X, Y, and Z-axis servo motors 18 to 20 are provided with rotational position detectors 18a to 20a such as optical rotary encoders.
A spindle motor 23 is connected to the spindle driver 22. The spindle motor 23 is provided with a rotational speed detector 23a such as a tacho generator or an optical encoder.
Further, a vibration detector 31 and a start / stop switch 33 are connected to the auxiliary control unit 6.
[0017]
The NC program analysis processing / command distribution unit 4 analyzes (decodes) the NC program 35 to convert the trajectory data into a position command to be moved for each feed axis, and also provides necessary control information such as a feed speed F and an acceleration. Outputs information etc. in block units (code units). Further, it outputs the rotational speed S and acceleration information of the spindle motor 23 specified in the NC program 35 as control information in block units.
[0018]
The auxiliary control unit 6 changes the block-based control information output from the NC program analysis processing / command distribution unit 4 into a predetermined form or adds new control information and outputs it. The detailed processing contents of the auxiliary control unit 6 will be described later.
[0019]
The NC program 35 is generally created by a CAD system or an automatic programming system, and is downloaded to the NC device 1 via a predetermined storage medium or by communication means.
[0020]
Each of the X, Y, and Z axis servo controllers 12 to 14 includes a position loop, a speed loop, and a current loop.
The position loop receives, for example, a position command (movement amount), which is control information in block units, converts them into position commands per unit time, and outputs the position command per unit time and the servomotors 18 to. A proportional operation is performed on the deviation from the position feedback signals from the rotational position detectors 18a to 20a for detecting the rotational position of the motor 20 (a position loop gain is multiplied), and this is output as a speed command for a speed loop.
The speed loop performs, for example, a proportional operation and an integral operation on a deviation between the speed command and a difference value (speed feedback signal) for each sampling time of the position feedback signal from the rotational position detectors 18a to 20a to generate a torque command. This is output to the current loop.
The current loop performs, for example, a current command by performing a proportional operation on a deviation between the output torque signal of each servo motor 18 to 20 converted from the drive current of each axis servo motor 18 to 20 and the torque command. The signals are converted into predetermined electric signals and output to the servo drivers 15 to 17.
Although the axis servo controllers 12 to 14 are realized by software in the present embodiment, they can also be realized by hardware.
[0021]
Each of the axis servo drivers 15 to 17 outputs a drive current obtained by amplifying the current command from each of the axis servo controllers 12 to 14 to each of the axis servo motors 18 to 20.
Each of the axis servo motors 18 to 20 is driven according to a drive current output from each of the axis servo drivers 15 to 17.
[0022]
The rotation position detectors 18a to 20a provided in the respective axis servo motors 18 to 20 output detection pulses corresponding to the rotation amounts of the respective axis servo motors 18 to 20 to the respective axis servo controllers 12 to 14.
As the rotational position detectors 18a to 20a, for example, an incremental type rotary encoder or an absolute type rotary encoder can be used. When an incremental type rotary encoder is used, since the rotary encoder outputs a position signal for each rotation as a rotation pulse signal, the number of rotation pulse signals must be managed in each axis servo control unit 12 to 14. Thereby, the absolute positions of the servomotors 18 to 20 can be managed.
With the above configuration, it is possible to control the rotational position of each axis servo motor 18-20.
[0023]
The spindle control unit 21 includes a speed loop and a current loop. That is, the spindle control unit 21 calculates a deviation between the rotation speed command of the spindle motor 23 obtained from the NC program analysis processing / command distribution unit 4 and the rotation speed signal from the rotation speed detector 23a, and performs a proportional operation. Then, an integral operation is performed to generate a torque command, which is output to a current loop.
The current loop performs, for example, a proportional operation on a deviation between the output torque signal of the spindle motor 23 converted from the drive current of the spindle motor 23 and the torque command to generate a current command, and outputs the current command to the spindle driver 22.
The spindle control unit 21 is realized by software in the present embodiment, but can also be realized by hardware.
The spindle driver 22 has, for example, a current control circuit including a PWM (pulse width modulation) inverter circuit, and controls the speed of the spindle motor 23 according to a current command output from the spindle control unit 21.
In the present embodiment, the case where the spindle control unit 21 is provided inside the NC device 1 has been described. However, the present invention is applied to a case where the spindle control unit 21 is provided separately from the NC device 1. Even if it is, it is applicable.
[0024]
The vibration detector 31 detects vibration generated between the tool driven by the spindle motor 23 and the workpiece.
As the vibration detector 31, for example, an acceleration sensor, an AE (acoustic emission) sensor, a sound sensor, or the like can be used.
The start / stop switch 33 is a switch operated by a worker provided in the NC device 1.
[0025]
Each function of the NC apparatus 1 shown in FIG. 1 is realized by, for example, hardware having a configuration as shown in FIG.
In FIG. 2, a microprocessor 41 includes a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, interface circuits 44, 45, 46, a graphic control circuit 47, a display device 48, a keyboard 49, a software key 50, and the like. And connected via a bus.
The microprocessor 41 controls the entire NC device 1 according to a system program stored in the ROM 42.
[0026]
The ROM 42 has programs for realizing the NC program analysis / command distribution unit 4, the auxiliary control unit 6, the servo control units 12 to 14, the spindle control unit 21, and the like, and a program for controlling the entire NC device 1. Is stored.
The RAM 43 downloads programs stored in the ROM 42 and stores various NC programs, data, and the like.
[0027]
The graphic control circuit 47 converts the digital signal into a signal for display and supplies the signal to the display device 48.
As the display device 48, for example, a CRT display device or a liquid crystal display device is used. The display device 48 displays the shape, the processing conditions, the generated processing program, and the like when the operator creates the processing program interactively using the software key 50 or the keyboard 49.
The operator can input data according to the content (interactive data input screen) displayed on the display device 48.
On the screen of the display device 48, operations or data received on the screen are displayed in a menu format. Which item of the menu is selected is pressed by pressing a software key 50 below the menu.
The keyboard 49 is used to input data necessary for the NC device 1.
The above-described start / stop switch 33 is realized by, for example, the software key 50 or the keyboard 49.
[0028]
The interface circuit 44 converts a control command such as a position command output from the microprocessor 41 into a predetermined signal and outputs the signal to each axis servo driver 15 to 17.
Further, the interface circuit 44 sequentially counts the detection pulses from the position detectors 18 a to 20 a provided in the respective axis servo motors 18 to 20, and outputs the count value to the microprocessor 41.
The interface circuit 45 converts a control command such as a speed command output from the microprocessor 41 into a predetermined signal and outputs the signal to the spindle driver 22.
The interface circuit 46 converts the analog signal detected by the vibration detector 31 into a digital signal and outputs the digital signal to the microprocessor 41.
[0029]
Example of NC machine tool
Here, before describing the auxiliary control unit 6 of the NC apparatus 1 in detail, an example of a machining center as an NC machine tool to which the NC apparatus of the present embodiment can be applied will be described.
FIG. 3 is a configuration diagram showing an example of a machining center to which the NC device of the present embodiment can be applied.
The machining center shown in FIG. 3 is a so-called gate-type machining center, and is movably supported on the cross rail 37 by a cross rail 37 movably supported at both ends by respective axes of a column-shaped column 38. A headstock 55 is provided movably in a vertical direction (Z-axis direction) via a movable member 54.
[0030]
A female screw (not shown) is formed in the movable member 44 through the cross rail 37 in the horizontal direction, and a ball screw 61 is screwed into the female screw. A Y-axis servomotor 19 is provided at an end of the ball screw 61, and the ball screw 61 is driven to rotate by the Y-axis servomotor 19.
The rotation of the ball screw 61 allows the movable member 54 to move in the Y-axis direction, whereby the headstock 55 moves in the Y-axis direction.
[0031]
Further, a female screw (not shown) is formed in the movable member 54 in the vertical direction, and a ball screw 62 is screwed into the female screw. The Z-axis servo motor 20 is provided at an end of the ball screw 62. The ball screw 62 is rotationally driven by the Z-axis servomotor 20, whereby the headstock 55 movably provided on the movable member 54 is moved in the Z-axis direction.
[0032]
A spindle motor 31 is built in the headstock 55, and the spindle motor 31 rotationally drives a tool T such as an end mill provided at the tip of the headstock 55.
An X-axis table 35 is provided below the main shaft 55 so as to be movable in the X-axis direction. The X-axis table 35 is provided with an X-axis servo motor 18 via a feed mechanism including a ball screw and a female screw. It is connected.
The X-axis table 35 is moved in the X-axis direction by the rotation of the X-axis servo motor 18.
[0033]
The drive control of the X, Y, and Z axis servo motors 18, 19, and 20 is performed by the NC device 1 described above.
A female screw portion (not shown) is formed in the portal column 38, and the cross rail 37 is moved up and down by rotating a ball screw 32a screwed into the column screw 38 by a cross rail elevating motor 32.
Further, the tool T can be replaced with various tools by an automatic tool changer (ATC) 39, and various attachments can be replaced with various tools by an automatic tool changer (AAC) 40.
The above-described vibration detector 31 is installed on the headstock 55, and when chatter vibration occurs during machining by the tool T, the chatter vibration can be detected.
[0034]
Next, an example of cutting of a workpiece by the NC device 1 and the machining center described above will be described.
4A and 4B are views showing a state in which the upper end surface of the workpiece W is finish-cut by the end mill T. FIG. 4A is a top view, and FIG. 4B is a side view.
The workpiece W shown in FIG. 4 has a column portion R1 and a flange portion R2 formed continuously with the column portion R1.
In order to finish-cut the upper end face Fw of the flange portion R2 of the workpiece W having such a shape by the rotating end mill T, the end mill T is moved along the XY plane by a predetermined cutting amount in the Z-axis direction. This is performed by moving at a constant feed speed.
[0035]
At this time, a state in which the end mill T is located on the flange R2 of the workpiece W on the upper end face Fw as shown by the position PA and a state in which the end mill T is located on the support R1 of the workpiece W as shown by the position PB. appear.
In the workpiece W having the above-described shape, the mechanical rigidity of the flange R2 is lower than that of the support R1. Therefore, the frequency of chatter vibration generated during cutting is different between the case where the end mill T is located on the flange R2 and the case where it is located on the support R1.
Therefore, for example, when the end mill T moves from above the flange R2 of the workpiece W to above the support R1, or from above the support R1 to the flange R2, the amplitude of the chatter vibration suddenly increases. May be large.
This is considered because the rotation speed of the end mill T approaches the natural frequency of the cutting system including the end mill T and the workpiece W.
The shape of the workpiece W shown in FIG. 4 is merely an example, and the more the workpiece W has a more complicated shape, the more the above-mentioned chatter vibration is likely to occur.
[0036]
In the related art, when chatter vibration suddenly increases, the worker reduces the rotational speed of the end mill T to keep it away from the natural frequency of the cutting system, thereby suppressing chatter vibration.
However, when reducing the rotation speed of the end mill T, the feed speed in the X-axis and Y-axis directions of the end mill T was not changed.
For this reason, the state of the cut surface of the workpiece W by the end mill T before and after the change of the rotation speed of the end mill T is different, and it is difficult to make the quality of the cut surface constant, and there is a problem that it is desired to make the cut surface uniform. .
[0037]
Control method of the present invention
Here, control performed by the NC apparatus 1 according to the present embodiment to solve the above-described problem will be described.
When chatter vibration is generated or increased while cutting the workpiece W while feeding the end mill T in a predetermined feed axis direction, as shown in FIG. The rotation speed S of T (spindle motor 23) is reduced to a predetermined value. At the same time, the feed speed F of the feed shaft being driven during cutting is reduced so that the ratio with the rotation speed S of the end mill T is kept constant.
FIG. 6 shows a speed command pattern in the spindle control unit 21 and the servo control units 12 to 14 of each axis.
[0038]
In the example shown in FIG. 6, the rotation speed S and the feed speed F of the spindle motor 23 are reduced to 50% at the time t1, and the feed speed F before the change is returned at the time t2.
With such a control, the rotational speed of the end mill T is separated from the natural frequency of the cutting system, so that chatter vibration is suppressed.
In addition, since the ratio between the rotation speed S of the end mill T and the feed speed F of the feed shaft is kept constant, the feed amount of the end mill T with respect to the workpiece W per one blade is the rotation speed S and the feed amount. The speed F is kept the same before and after the speed is changed.
As a result, the state of the cut surface of the workpiece W by the end mill T before and after the change of the rotation speed of the end mill T can be substantially the same, and the quality of the cut surface of the workpiece W can be kept constant. It is possible to do.
[0039]
Further, as another control method, when chattering vibration is generated or increased while cutting the workpiece W while feeding the end mill T in a predetermined feed axis direction, in order to suppress this, For example, as shown in FIG. 7, it is possible to suppress chatter vibration by modulating the rotational speed S of the spindle motor 23 in a sine wave shape.
For example, when the rotation speed S for driving the spindle motor 23 is 2000 rpm and the feed speed F of the feed shaft is 1000 mm / min, a sine wave command having an amplitude of ± 200 rpm and a period T is added to the rotation speed command of 2000 rpm. At the same time, a sine wave command having an amplitude of ± 100 mm / min and a period T is added to a feed speed command of 1000 mm / min. Note that each sine wave command is added to the feed speed command and the rotation speed command so that the phases become equal.
As a result, the ratio between the rotation speed S of the spindle motor 23 and the feed speed F of the driven feed shaft is always constant.
In order to prevent the displacement of the feed axis, the length of the sine wave command is always an integral multiple of one cycle so that the integral value of the sine wave command added to the feed speed command and the rotation speed command becomes zero. In addition, information on the cycle and amplitude of the sine wave command can be specified in advance with predetermined parameters in the NC device 1, for example.
As a result, the state of the cut surface of the workpiece W by the end mill T can be substantially the same before and after the modulation of the rotation speed of the end mill T, and the quality of the cut surface of the workpiece W can be kept constant. It is possible to do.
[0040]
The method of determining the time t2 in FIGS. 6 and 7 is, for example, such that when the time set in advance by the predetermined parameter in the NC device 1 has passed, the modulation of the rotation speed S and the feed speed F is stopped, The modulation of the rotation speed S and the feed speed F may be stopped when the magnitude of the rotation speed S and the feed speed F are decreased, or the modulation of the rotation speed S and the feed speed F may be stopped when the processing for each block of the NC program is completed.
Further, in the present invention, it is possible to keep the rotation speed S and the feed speed F modulated until the predetermined machining is completed without setting the time t2 in FIGS. 6 and 7.
[0041]
Explanation of auxiliary control unit
Here, FIG. 5 is an explanatory diagram illustrating a configuration of the auxiliary control unit 6 of the NC device 1.
In FIG. 5, the auxiliary control unit 6 includes a control information change unit 6a, a data storage unit 6b, and an input unit 6c.
[0042]
The control information changing unit 6a controls the chattering vibration during the above-mentioned cutting process and controls information for keeping the quality of the cut surface constant in units of blocks output from the NC program analysis processing / command distribution unit 4. The control information is output to the respective axis servo controllers 12 to 14 and the main spindle controller 21 after changing and correcting the control information or adding new control information.
[0043]
The data storage unit 6b holds data necessary for correcting the control information in the control information changing unit 6a or adding new control information.
[0044]
When the control signal 33s is input from the start / stop switch 33 to the input unit 6c, the start signal ST1 to the control information change unit 6a is turned on in response thereto. Therefore, when the operator appropriately operates the start / stop switch 33, the start signal 6s output from the input unit 6c is turned on / off.
Further, a detection signal 31s of the vibration detector 31 is input to the input unit 6c.
For example, as shown in FIG. 8, when the chatter vibration increases and the amplitude of the detection signal 31 s of the vibration detector 31 exceeds the range of the predetermined threshold Vth, the input unit 6 c activates the control information change unit 6 a. The signal ST1 is turned on.
[0045]
Here, the processing content of the auxiliary control unit 6 will be described based on the flowchart shown in FIG.
First, the control information changing unit 6a acquires control information in block units from the NC program analysis processing / command distribution unit 4 (step S1).
The control information in block units from the NC program analysis processing / command distribution unit 4 input to the control information change unit 6a includes, for example, the feed amount (movement amount) of each feed axis of X to Z axes, the feed speed F, and the main spindle. The rotation speed S of the motor 23 is an example. The control information is output from the NC program analysis / command distribution unit 4 in code units (block units) such as a command code for linear cutting feed.
[0046]
Next, the control information changing section 6a determines whether or not the activation signal ST1 from the input section 6a is turned on (step S2).
When the start signal ST1 from the input unit 6a is in the off state, the control information from the NC program analysis / command distribution unit 4 is used as it is as a normal control mode according to the command of the NC program created in advance. Output to the control units 12 to 14 and the spindle control unit 21 (step S4).
[0047]
When the activation signal ST1 from the input unit 6a is in the ON state, that is, when the vibration detector 31 detects a vibration equal to or more than the threshold value Vth, or while feeding the end mill T in the predetermined feed axis direction, When chatter vibration occurs or increases during cutting of the object W and the operator operates the start / stop switch 33 to turn it on, the start signal ST1 to the control information changing unit 6a is turned on. And the vibration suppression control mode is executed (step S3).
When the control shown in FIG. 6 is performed, when the start signal ST1 is input from the input unit 6c, the feed speed F and the rotation speed S are reduced to a speed reduction rate previously stored in the data storage unit 6b, for example, 50%. The control information is sent to the axis servo controllers 12 to 14 and the spindle controller 21.
[0048]
Each of the axis servo controllers 12 to 14 calculates a movement command (speed command) per unit time based on the changed feed speed F and movement amount.
At this time, if the movement command per unit time changes abruptly, there is a possibility of giving an impact to the NC machine tool. Therefore, as shown in FIG. 6, the speed is reduced at a constant rate during a predetermined time. . In addition, when accelerating to the speed before the change, the speed is similarly increased at a constant rate during a predetermined time.
When the feed speed F is changed from 1000 mm / min to 500 mm / min, which is a half, the movement command per unit time is reduced to half before the change.
[0049]
At the same time, the spindle control unit 21 calculates a speed command for rotating the spindle motor 23 based on the changed rotation speed S.
As in the case of the axis servo controllers 12 to 14, if the speed command suddenly changes, the main spindle controller 21 may adversely affect the NC machine tool. Therefore, as shown in FIG. To be decelerated during. In addition, when accelerating to the speed before the change, the speed is similarly increased at a constant rate during a predetermined time.
[0050]
For example, when performing the control shown in FIG. 7, information on the cycle and amplitude of the sine wave command to be added is sent to each of the axis servo controllers 12 to 14 and the spindle controller 21. That is, information for creating a sine wave command to be added to the speed command before the change is added to the control information and sent to each of the axis servo controllers 12 to 14 and the spindle controller 21.
Note that the information on the cycle and amplitude of the sine wave command can be specified in advance using predetermined parameters in the NC device 1.
[0051]
When the above-described operation is completed, the process returns to step S1 again, and the control information in block units is acquired from the NC program analysis / command distribution unit 4.
[0052]
In the present embodiment, the start of the vibration suppression control mode is performed by the start signal ST1 from the input unit 6c, but the end of the vibration suppression control mode is determined by operating the start / stop switch 33 when the start / stop switch 33 is operated. It can be done by turning it off.
On the other hand, when the vibration suppression control mode is activated by the vibration detection by the vibration detector 31, the vibration suppression control mode is terminated, for example, when the execution of one command code (block) is completed, the vibration suppression control mode is terminated. Alternatively, it may be configured to return to the normal control mode according to the NC program created in advance.
It is also possible to return to the normal control mode when a preset number of command codes are executed in the data storage unit 6c, or to return to the normal control mode after a preset time has elapsed. Various embodiments are conceivable.
[0053]
Further, as a method of starting and stopping the vibration suppression control mode, it is possible to instruct the NC program to start and stop the vibration suppression control mode in advance.
That is, a command code (for example, a G code or an M code) for starting and stopping the vibration suppression control mode is specified in advance, and the control information changing unit 6a of the auxiliary control unit 6 recognizes the command code and recognizes the command code in FIG. Alternatively, a configuration may be employed in which the vibration suppression control described in FIG. 7 is executed.
[0054]
In this embodiment, as a method of modulating the rotation speed S of the main shaft and the feed speed F of the feed shaft, as described in FIGS. 6 and 7, a method of reducing the speed, a method of modulating the speed in a sine wave shape, and the like. However, the present invention is not limited to this. When chatter vibration occurs or increases, the rotation speed of the main shaft may be separated from the natural frequency of the mechanical system (cutting system). The rotation speed of the main shaft and the feed speed of the feed shaft may be further increased.
Further, the method of modulating the rotation speed S of the main shaft and the feed speed F of the feed shaft may be configured to be set in advance by parameters set in the NC device.
[0055]
As described above, according to this embodiment, the vibration detector 31 detects the occurrence of chatter vibration provided in the NC machine tool, and the vibration suppression control mode of the auxiliary control unit 6 can be automatically activated. Can be automated.
Further, since the start / stop of the vibration suppression control mode of the auxiliary control unit 6 can be performed only by the operator operating the start / stop switch 33, the operator does not need to adjust the speed of the main shaft and the feed shaft, and can perform work. Simplified.
Further, according to the present embodiment, the vibration suppression control mode of the auxiliary control unit 6 can be started and stopped by the command code specified in the NC program created in advance. Vibration suppression in an area where vibration is expected to occur can be automatically performed in advance.
[0056]
In the present embodiment, the case where the present invention is applied to a machining center has been described. However, the present invention is also applicable to an NC lathe that rotates a workpiece W by a spindle and feeds a tool. .
[0057]
Second embodiment
FIG. 10 is an explanatory diagram showing the configuration of the second embodiment of the NC apparatus to which the present invention is applied, and FIG. 11 is an explanatory diagram showing the internal configuration of the auxiliary control unit in FIG.
The NC device shown in FIG. 10 is configured such that the drive current values If and Is flowing through the respective axis servomotors 18 to 20 and the main shaft motor 23 are fed back to the auxiliary control unit 6.
That is, the drive current flowing through each of the axis servomotors 18 to 20 and the spindle motor 23 is detected by each of the axis servo drivers 15 to 17 and the spindle driver 22 and is fed back to the auxiliary control unit 6, as shown in FIG. The drive current values If and Is are read into the control information change section 6a of the control section 6, respectively.
[0058]
Further, the auxiliary control unit 6 has a so-called adaptive control function in addition to the function described in the first embodiment.
That is, when the load torque applied to each of the axis servomotors 18 to 20 and the spindle motor 23 is out of the preset range, the auxiliary control unit 6 sets the load torque applied to each of the axis servomotors 18 to 20 or the spindle motor 23 to a predetermined value. Can be changed based on the rotational speed S of the main shaft and the feed speed F of the feed shaft specified in advance by the NC program so that the speed falls within a predetermined range. It has a control function.
[0059]
By having such an adaptive control function, for example, it is possible to prevent an excessive load from being applied to the spindle motor 23 or the servomotors 18 to 20 during cutting.
At the same time, the rotational speed S of the spindle or the feed speed F of the feed shaft is increased or decreased so that the load torque applied to the spindle motor 23 or the servomotors 18 to 20 during machining falls within a predetermined load torque range. In addition, the processing time can be reduced.
Note that various adaptive control algorithms for realizing such adaptive control have already been proposed, and a description thereof will be omitted.
[0060]
However, when the rotational speed S of the main shaft or the feed speed F of the feed shaft is independently changed so that the load torque at the time of machining falls within the range of the allowable load torque by the above-described adaptive control function, the above-described chattering vibrations may occur. Similarly to the above, the state of the cut surface of the workpiece W is different before and after the change of the rotation speed of the end mill T or before and after the change of the feed speed F, and the quality of the cut surface is not constant.
[0061]
Therefore, in the present embodiment, when the adaptive control function is activated, the control information changing unit 6a of the auxiliary control unit 6 changes the ratio between the rotation speed S of the main shaft and the feed speed F of the feed shaft while keeping the ratio constant. I do.
That is, when the load torque applied to the spindle motor 23 is not in the predetermined range, or when the load torque applied to each of the axis servos 18 to 20 is not in the predetermined range, the rotation of the spindle motor 23 or each of the axis servos 18 to 20 is performed. When the speed is changed to keep the load torque within a predetermined range, the ratio is simultaneously changed while keeping the ratio between the rotation speed S of the main shaft and the feed speed F of the feed shaft constant. The speed change amount can be calculated by, for example, an adaptive control algorithm.
As a result, the state of the cutting surface of the workpiece W by the end mill T before and after the change of the rotation speed S of the end mill T and the feed speed F of the feed shaft can be substantially the same. It is possible to make the quality of the cutting surface constant.
[0062]
The ratio between the rotation speed S of the main shaft and the feed speed F of the feed shaft can be the ratio between the rotation speed S and the feed speed F specified in the NC program. It is also possible to set in advance in the data storage unit 6b.
[0063]
【The invention's effect】
Advantageous Effects of Invention According to the present invention, chatter vibration generated between a cutting tool and a workpiece in an NC machine tool can be suppressed, the state of a cutting surface can be made uniform, and automation of machining can be easily performed. Become.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of an NC apparatus to which the present invention is applied.
FIG. 2 is an explanatory diagram illustrating an internal configuration of an auxiliary control unit in FIG. 1;
FIG. 3 is a configuration diagram illustrating an example of a machining center to which the NC device according to the present embodiment can be applied;
4A and 4B are views showing a state in which the upper end surface of a workpiece is finish-cut by an end mill, wherein FIG. 4A is a top view and FIG. 4B is a side view.
FIG. 5 is an explanatory diagram illustrating a configuration of an auxiliary control unit of the NC device.
FIG. 6 is an explanatory diagram illustrating an example of a control method in a vibration suppression control mode.
FIG. 7 is an explanatory diagram showing another example of the control method in the vibration suppression control mode.
FIG. 8 is an explanatory diagram illustrating an example of a method of detecting vibration of an input unit in an auxiliary control unit.
FIG. 9 is a flowchart illustrating an example of processing contents in an auxiliary control unit.
FIG. 10 is an explanatory diagram showing a configuration of an NC device according to a second embodiment of the present invention.
11 is an explanatory diagram showing an internal configuration of an auxiliary control unit shown in FIG.
[Explanation of symbols]
2 ... NC device
4: NC program analysis processing / command distribution unit
6 ... Auxiliary control unit
12-14 ... Each axis servo control unit
15-17: Each axis servo driver
18-20 ... Each axis servo motor
21: Spindle control unit
22 ... Spindle driver
23: Spindle motor
31 ... Vibration detector
33 ... Start / stop switch

Claims (1)

A control device for an NC machine tool having a main shaft for rotating a tool or a workpiece, and a feed shaft for relatively moving the workpiece and the tool,
By changing the rotation speed of the main shaft and the feed speed of the feed shaft, a vibration suppressing unit that suppresses vibration generated between the tool and the workpiece by machining the workpiece by the tool,
A load constant range control means for controlling the load applied to the spindle and the feed shaft by the processing of the workpiece by the tool to fall within a predetermined range by changing the rotation speed of the spindle and the feed speed of the feed shaft. , And
The NC machine tool has a means for changing the rotation speed of the main shaft and the feed speed of the feed shaft while maintaining the rotation speed of the main shaft and the feed speed of the feed shaft constant. Control device.

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