JP2004202594A - Numerical control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the cycle time of a working cycle by reducing an incomplete thread part. <P>SOLUTION: An acceleration-deceleration parameter (an acceleration-deceleration curve and a time constant) 1 for ordinary cutting is set. An acceleration-deceleration parameter (an acceleration-deceleration curve and a time constant) 2 for optimal threading work is stored in a table to a combination of a main spindle rotating speed and the lead length of a screw. A servo parameter 1 of the ordinary cutting and a servo parameter 2 for the threading work are set as a servo parameter of a servo control part 32. When reading in a switching command to the threading work, a parameter is switched to the acceleration-deceleration parameter 2 read out of the table on the basis of the main spindle rotating speed and the lead length, and is switched to the servo parameter 2, and the threading work is performed. When instructing the switching command to the ordinary cutting, the parameter is switched to the acceleration-deceleration parameter 1 and the servo parameter 1, and optimal ordinary cutting work is performed. An incomplete thread part can be shortened in a specific length, and the threading cycle time is shortened. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a numerical control device suitable for thread cutting.
[0002]
[Prior art]
The workpiece is attached to the main shaft and rotated, and the cutting tool (thread cutting tool) attached to the tool rest opposite to the workpiece is moved in a cutting direction (X-axis) perpendicular to the rotation of the workpiece and parallel to the rotation. 2. Description of the Related Art Numerically controlled lathes that perform drive control in a feed direction (Z axis) to perform required machining are widely used.
[0003]
Thread cutting in such a numerically controlled lathe, a thread cutting tool is attached to the tool post, and a predetermined cut is set by feeding and driving the tool post in the X-axis direction with the X-axis feed motor and the X-axis feed screw. This is performed by controlling the feed of the tool post in the Z-axis direction at a predetermined pitch by a Z-axis feed motor and a Z-axis feed screw in synchronization with the rotation phase of the workpiece held by the chuck.
[0004]
Further, in a general numerically controlled machine tool, there is known a method of performing processing control using parameters such as a servo gain such as a position loop gain and a speed loop gain and an acceleration / deceleration time constant according to processing conditions and control conditions as optimal control parameters. (For example, see Patent Document 1).
There is also known an apparatus in which parameters of an acceleration / deceleration curve are changed in accordance with a cutting feed speed to perform optimal acceleration / deceleration control (see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-11-231914 [Patent Document 2]
JP 2001-321309 A
[Problems to be solved by the invention]
In thread cutting, at the start and end of thread cutting, there is an “incomplete screw” part caused by a delay in servo follow-up and acceleration and deceleration. The length of the thread increases.
In order to eliminate the effect of the imperfect thread part on the processed product, the necessary extra margin is required outside the product so that cutting starts after the moving speed of the threading tool in the Z-axis direction reaches the set speed. ”, The thread machining must be started / terminated, and this increase in length hinders an increase in thread cutting speed, and causes a longer cycle time of the machining cycle.
[0007]
In the case of thread cutting, unlike normal cutting, the start-up part and the end part are not provided for the product, so even if the stability of the machine operation is somewhat impaired, the start-up and cut-up time is short. By doing so, shortening the incompletely threaded portion greatly contributes to improvement in cycle time.
Also, depending on the machine, acceleration or deceleration is generally required in order to reduce acceleration / deceleration shock due to acceleration limitation.
[0008]
Acceleration / deceleration requires an acceleration / deceleration time constant, but having an acceleration / deceleration time constant causes a delay amount that is a function of the acceleration / deceleration time constant. Become. That is, during the acceleration / deceleration time, the Z-axis feed speed of the thread cutting tool does not reach the set value, and the speed does not reach the speed corresponding to the spindle speed (the rotation speed of the workpiece), so that an incomplete thread portion occurs. Will be. In addition, the higher the spindle speed, the greater the number of incompletely threaded portions. To reduce the length of this incomplete thread, start the Z-axis feed of the thread cutting tool before starting cutting the workpiece, and start thread cutting before and after the end of acceleration. Therefore, the cycle time of the machining cycle is lengthened by the time corresponding to the acceleration / deceleration.
Therefore, an object of the present invention is to provide a numerical control device suitable for thread cutting in which incomplete thread portions are reduced and the cycle time of a machining cycle is reduced.
[0009]
[Means for Solving the Problems]
The numerical control device according to the present invention is configured such that at least one of the servo control parameters in the servo control unit that controls the servo motor that drives the tool feed axis is different from the parameter value for threading and the parameter value for threading. A parameter storage means for storing parameter values, and a thread cutting command, the parameter value for thread cutting stored in the parameter storage means being read and set in the servo motor control unit, and a command for processing other than thread cutting. Setting means for reading a parameter value different from the parameter value for thread cutting stored in the parameter storage means and setting the parameter value in the servo motor control section. The servo control parameters are a position and speed feedforward gain, a position loop gain, and a speed loop gain. Also provided is acceleration / deceleration data storage means for storing data in which the type of acceleration / deceleration and the acceleration / deceleration time constant correspond to the combination of the spindle speed at the time of threading and the lead of the screw. The acceleration / deceleration type and the acceleration / deceleration time constant for the combination of the spindle speed at the time of thread cutting and the screw lead are read from the acceleration / deceleration data storage means, and the acceleration / deceleration processing is performed by switching to the read acceleration / deceleration data. I did.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Generally, in a machine tool, there are speeds and accelerations that are permissible for the machine. Also, the motor for driving the machine has an allowable speed and acceleration based on its own load or the load on the machine shaft. Based on these conditions, a servo system is selected for each machine. In a normal cutting process, there are servo parameters such as an optimum servo gain set for a servo control unit of a servo motor that drives a tool feed axis in order to realize an optimum machined surface.
[0011]
On the other hand, in the thread cutting, the length of the incompletely threaded portion increases when the servo parameters used in the above-described normal cutting are used. In order to reduce the number of parts, servo parameters for starting the axis movement at the limit speed and the limit acceleration are used.
[0012]
Therefore, in the present embodiment, the servo parameters for normal cutting other than thread cutting and the servo parameters for thread cutting are stored in the storage unit, and the servo parameters to be used are determined depending on whether the thread cutting or the normal cutting. Try to switch.
[0013]
Further, when starting the threading process at the limit of the speed and acceleration, smoothness is required at the acceleration start portion. It is necessary to realize a partially smooth speed change by applying acceleration / deceleration to an acceleration start portion or a transition portion to a steady speed based on an optimum speed curve. Further, as described above, the length of the incomplete screw portion changes depending on the acceleration / deceleration time. For example, when performing linear acceleration / deceleration, the linear acceleration / deceleration time constant is set to T, and when the tool post is moved at the command speed F in the Z-axis direction to perform thread cutting, the length of the incomplete thread portion accompanying the acceleration / deceleration is set. Becomes F * T / 2. That is, the value of the imperfect thread portion depends on the feed speed F and the time constant T of the thread cutting tool.
[0014]
Therefore, in the present embodiment, a table of the acceleration / deceleration type (acceleration / deceleration curve) and time constant corresponding to the combination of the two elements of the spindle rotation speed, the screw lead, and the time constant is created. To obtain the acceleration / deceleration curve and the time constant to perform the acceleration / deceleration control. In this way, an incomplete thread portion independent of the speed of the thread cutting tool is obtained.
[0015]
FIG. 3 is an example of an acceleration / deceleration control parameter table at the time of thread cutting, which is set and stored in the numerical controller used in the present embodiment. In this example, the speed curve during acceleration (speed curve) and its time constant, the speed curve during deceleration (speed curve) and its time constant, according to the spindle rotation speed, the length of the screw, and the length of the lead of the screw Is set. In the example shown in FIG. 3, the speed curve and the time constant during acceleration / deceleration are changed depending on the length of the screw. However, the length of the screw does not always need to be considered. In this embodiment, the table is made in consideration of the length of the screw for more accuracy. The acceleration / deceleration speed curves (speed curves) set in this table are linear acceleration / deceleration, bell-shaped acceleration / deceleration, and exponential acceleration / deceleration, but other than these, linear functions, multidimensional functions, combinations thereof, etc. An arbitrary speed curve is created and set.
[0016]
As types of acceleration / deceleration, for example, linear acceleration / deceleration, bell acceleration / deceleration, exponential acceleration / deceleration, and the like are already known. FIG. 4 shows an example of the velocity curve and its function.
FIG. 4A shows an example of linear acceleration / deceleration, in which acceleration is performed linearly and deceleration is performed linearly with respect to the commanded speed Fc. The acceleration time constant is a target set speed after the start of acceleration. This is the time t1 required to reach Fc. The deceleration time constant is the time from the start of deceleration until the speed reaches the next speed (speed 0 in the example in the figure) (in the example of FIG. 4A, the deceleration time constant is also set to t1). Is shown).
[0017]
Until the time t reaches the time constant t1 after the acceleration is started, the speed is linearly accelerated by a function of “F (t) = K ₁ · t”. After the set speed Fc is reached, "F (t) = Fc" is maintained at this set speed Fc. Then, at the time of deceleration, the vehicle is linearly decelerated by a function of “F (t) = K ₂ · (t−t ₂ ) + Fc”.
[0018]
FIG. 4B shows an example of exponential function acceleration / deceleration. In this case, the time constant at the time of acceleration is T1, and the time constant at the time of deceleration is T2. until the time t1 to reach the Fc is function _{"F (t) = K 1 ·} (1-e (-t / T1)) " is accelerated exponentially at a rate F (t) represented by. After reaching the set speed Fc, the value is held at this value, and at the time of deceleration, an exponential function is given by a speed F (t) represented by a function “F (t) = Fc · e ^{((t2−t) / T2)} ”. Is decelerated.
[0019]
FIG. 4C shows an example of bell-shaped acceleration / deceleration. In this case, the time constant is Tc (in the example shown in FIG. 5C, the same time constant is used during acceleration and deceleration), and the basic function of the speed curve is used. An acceleration curve is composed of OA “F (t) = 2Fc · t ² / Tc ² ” and a function AB obtained by inverting the function OA in a point-symmetric manner at the time of Tc / 2. The curve OB is a left-right inverted shape.
[0020]
FIG. 1 is a functional block diagram of a main part of a numerical controller 10 according to an embodiment of the present invention and a machine tool controlled by the numerical controller 10. The configuration of the numerical control device 10 and the configuration of the machine tool are almost the same as those of the conventional numerical control device and the configuration of the conventional lathe machine tool. In the RAM), the servo parameters for the normal cutting and the servo parameters for the thread cutting of the servo control unit described above are set. Another difference is that the acceleration / deceleration parameters during normal cutting and the acceleration / deceleration control parameter table during thread cutting described above are stored.
[0021]
First, the servo parameters include position, speed feed forward gain, position gain, speed loop gain, feed forward coefficient, and the like. These servo parameters 1 for normal cutting are used for various types of machines determined for each machine as in the past. It is determined by a servo selection calculation based on the constants and the load conditions applied to the drive motor, and the determined parameters are actually input to the control device, and are finely adjusted experimentally and verified. Further, as the servo parameters 2 for threading, these servo parameters are similarly obtained and determined so as to start the axis movement at the limit speed and the limit acceleration. In particular, it is desirable that the position, velocity, feed forward gain, and feed forward coefficient be different from ordinary servo parameters for cutting.
[0022]
The servo parameters obtained here are automatically input to storage means (determined memory area on the control device 10) in the numerical control device 10 manually or by a program. FIG. 1 shows a diagram in which a normal cutting servo parameter is stored as a servo parameter 1 and a thread cutting servo parameter is stored as a servo parameter 2 in the storage unit 14 of the parameter setting unit.
[0023]
Further, the table shown in FIG. 4 is set and registered in the parameter storage unit 14 as the acceleration / deceleration parameter for ordinary cutting processing as the acceleration / deceleration parameter 1 and the acceleration / deceleration parameter for thread cutting as the acceleration / deceleration parameter 2.
[0024]
After setting the parameters in this manner, the machining is started. However, a command to switch to thread cutting or a command to switch to normal cutting is read from the machining program 11 stored in a storage unit or the like in the numerical controller. Then, the interpolation / distribution processing unit of the numerical control device 10 performs a parameter switching process 12a, and performs a parameter setting switching process corresponding to the processing according to the read normal cutting or threading.
[0025]
FIG. 2 is a flowchart of a process executed by the processor of the numerical controller according to the present embodiment. In the machining program, before the thread cutting command, together with the command code for switching to thread cutting, or before the command for switching to thread cutting, the spindle rotation speed, the lead of the screw and, in this embodiment, the length of the screw are set. And program it. In addition, when transitioning to normal cutting, a normal cutting switching command (return command from thread cutting) is programmed to switch between thread cutting mode and normal cutting mode. When the power is turned on to the numerical controller 10, the acceleration / deceleration curve and the time constant of the acceleration / deceleration parameter 1 for normal cutting are set by the initial setting. Parameter 1 is set.
[0026]
The processor of the numerical controller 10 reads one block from the machining program 11 (step 100), determines whether the command of the read block is a command to switch to threading (step 101), and is not a command to switch to threading. In this case, it is determined whether the command is a command for switching to normal cutting (step 102), and if it is not a command for switching to normal cutting, the command read as in the past is executed (step 103), and the process returns to step 100. Hereinafter, if a command to switch to thread cutting or normal cutting is not read out, the processing of steps 100 to 103 is repeatedly executed, and the processing instructed in each block of the program is executed.
[0027]
That is, the interpolation / distribution processing unit 12 outputs a movement command corresponding to the spindle rotation speed commanded by the program 11 to the spindle control unit 20, and the spindle control unit 20 outputs the movement command and the rotation speed of the spindle motor 22. Speed loop control is performed based on a feedback signal from the position coder 23 to be detected, and the spindle motor 22 is driven via the spindle amplifier 21 so as to match the commanded spindle rotational speed.
[0028]
When a command to the tool feed axis is read from the machining program, the interpolation / distribution processing unit 12 outputs a movement command to the acceleration / deceleration processing unit 13 at predetermined intervals based on the read command, and performs acceleration / deceleration processing. The unit 13 executes a speed curve calculation process 13 a determined by the set acceleration / deceleration parameter 1 and outputs the movement command subjected to the acceleration / deceleration process to the servo control unit 30. The servo control unit 30 calculates the servo command 1 based on the movement command, the position attached to the servomotor 32 that drives the feed shaft, the position from the speed detector 33, and the speed feedback signal. Performs feedforward processing of position and speed, position and speed loop processing, and current loop processing, and drives and controls the servomotors 32 (only one servomotor is shown in FIG. 1) of each feed axis via the servo amplifier 31. I do.
The drive control of the spindle motor 22 and the servo motor 32 described above is the same as that of the related art.
[0029]
On the other hand, if the command of the block read in step 100 is determined to be a command to switch to thread cutting, the acceleration is decelerated from the table based on the commanded spindle rotational speed, the screw lead, and the screw length. The type of acceleration / deceleration at the time (speed curve) and the acceleration / deceleration parameter 2 of the time constant are read out and set as parameters for the speed curve calculation processing of the acceleration / deceleration processing unit 13 (step 104).
[0030]
Further, the servo parameter 2 for threading is set in the servo control unit 30. That is, the value of the servo parameter 30a such as the position gain of the position and speed feedforward processing of the servo control unit 30, the speed feedback gain, the position feedforward gain, the speed feedforward gain, and the feedforward coefficient is used as the servo parameter 2 The value is switched (step 105). Then, the process returns to step 100. Since the command for the thread cutting is issued after the command for switching to the thread cutting, the command sequentially read from each block is executed in step 103, and the acceleration of the acceleration / deceleration parameter 2 for the thread cutting described above is performed. At this time, acceleration / deceleration control is performed based on a speed curve during deceleration (speed curve) and its time constant, and a movement command is output to the servo control unit 30. Based on the movement command, the position attached to the servomotor 32 that drives the feed shaft, the position from the speed detector 33, and the speed feedback signal, the servo control unit 30 sets the servo for threading that has been set. According to the parameter 2, the position and speed feedforward processing, the position and speed loop processing, and the current loop processing are performed, and the servo motors 32 of the respective axes are driven and controlled via the servo amplifier 31.
[0031]
In this manner, the acceleration / deceleration is controlled by the acceleration / deceleration parameter 2 for thread cutting, the servo control is performed by the servo parameter 2 for thread cutting, the servo motors of the respective axes are driven, and the thread cutting is executed. Then, when the thread cutting is completed and a switching command to the normal cutting (a return command from the thread cutting) is read, the process proceeds from step 102 to step 106, where the acceleration / deceleration parameter 1 for the normal cutting is read, and the numerical value is read. The acceleration / deceleration parameter of the acceleration / deceleration curve calculation processing 13a performed by the acceleration / deceleration processing unit 13 of the control device 10 is switched to the read acceleration / deceleration parameter 1.
[0032]
Further, the servo parameter 1 for normal cutting is read out, and the position gain, speed feedback gain, position feed forward gain, and speed feed forward of the position, speed loop processing, position and speed feed forward processing executed by the servo controller 30 are performed. The servo parameters 30a such as the gain and the feedforward coefficient are switched to the read servo parameter 1 (step 107).
Thereafter, the processing of steps 100 to 103 is executed based on the machining program 11, and normal cutting is performed.
[0033]
As described above, when the command to switch to threading is read from the machining program, the parameter is switched to the threading acceleration / deceleration parameter 2, and the acceleration / deceleration control is performed. 30a is switched, and servo control such as loop control of position, speed, and current is performed, and the servo motor 32 is driven and controlled. Further, when a switching command to the normal cutting is read from the machining program, the acceleration / deceleration control is performed by switching to the acceleration / deceleration parameter 1 for the normal cutting, and the servo control unit is changed to the servo parameter 1 for the normal cutting. The 32 servo parameters 32a are switched, and the servo control such as the position and the speed loop is performed, so that the drive of the servo motor 32 is controlled.
As a result, screw machining with less incomplete thread portions and machining other than thread cutting with an optimal machined surface are simultaneously realized.
[0034]
In the above-described embodiment, the acceleration / deceleration parameter 2 for thread cutting is selected according to the rotation speed of the spindle, the length of the screw, and the lead length of the screw. You may make it select by three elements.
[0035]
【The invention's effect】
According to the present invention, the speed curve and the time constant of the acceleration / deceleration control are automatically set to the optimum values in accordance with the rotation speed of the spindle and the lead of the screw. Can be. In addition, the margin of the outside of the thread product is reduced, and the cycle time of the thread cutting cycle is shortened. Further, an optimum machined surface can be obtained even in ordinary cutting.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a main part of a numerical control device according to an embodiment of the present invention and a machine tool controlled by the numerical control device.
FIG. 2 is a flowchart of a process executed by a processor of the numerical controller according to the embodiment.
FIG. 3 is an example of an acceleration / deceleration control parameter table during thread cutting used in the embodiment.
FIG. 4 is an explanatory diagram of speed curves of linear acceleration / deceleration, bell acceleration / deceleration, and exponential acceleration / deceleration.
[Explanation of symbols]
Reference Signs List 10 Numerical control device 22 Spindle motor 23 Position coder 32 Servo motor 33 Position / speed detector

Claims (3)

Parameter storage for storing, for at least one of the servo control parameters in the servo control unit that controls the servomotor for driving the tool feed axis, a parameter value for threading and a parameter value different from the parameter value for threading. Means,
In accordance with a thread cutting command, the parameter value for thread cutting stored in the parameter storage means is read and set in the servo motor control unit. In accordance with a command other than thread cutting, the thread cutting stored in the parameter storage means is performed. Setting means for reading a parameter value different from the parameter value for processing and setting the parameter value in the servo motor control unit. The numerical control device according to claim 1, wherein the servo control parameters are a position and a speed feedforward gain, a position loop gain, and a speed loop gain. Acceleration / deceleration data storage means for storing data corresponding to the type of acceleration / deceleration and the acceleration / deceleration time constant for the combination of the spindle speed at the time of thread cutting and the screw lead,
When the threading process is commanded, the type of acceleration / deceleration and the acceleration / deceleration time constant for the combination of the spindle speed and the screw lead at the time of threading are read from the acceleration / deceleration data storage means, and are switched to the read acceleration / deceleration data. 3. The numerical controller according to claim 1, wherein the numerical controller performs a deceleration process.

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