JP2575894B2 - Numerical control unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a machine tool such as a machining center,
The present invention relates to a numerical control device in which a tapper is attached to a main shaft, and tapping is performed by controlling the rotation of the tapper and the feed of the Z axis.

(Prior Art) When tapping is performed in a machining center or the like, it is necessary to precisely synchronize the rotation of a tapper attached to a main shaft with the feed speed of a Z-axis for controlling the feed of the tapper. Therefore, a control method has been realized in which the spindle rotation command and the Z-axis movement command are synchronized to synchronously control the spindle position and the Z-axis position to perform tapping processing (for example, Japanese Patent Application Laid-Open No. 63-123605). Gazette).

FIG. 5 shows the block configuration, in which the command input unit 1 supplies the depth of cut 1 and the screw pitch P to the position command generating unit 2 and also supplies the spindle rotational speed command SRM to the time constant determining means 3. The position command generator 2 is a main shaft rotation position command SR
Outputs P and Z-axis rotation position command ZRP synchronized with this,
These are input to the spindle control unit SC and the Z-axis control unit ZC, respectively. The spindle control unit SC and the Z-axis control unit ZC have almost the same configuration, and the rotation position command SR input from the position command generation unit 2
P and ZRP are subjected to acceleration / deceleration processing by the acceleration / deceleration processing units 10S and 10Z, respectively, and the same acceleration / deceleration is performed based on the time constant T ₀ determined by the time constant determination means 3 in order to maintain synchronization between the main shaft and the Z axis. Do. Spindle motor 4S has speed detector 5S and position detector
6S is connected and the spindle speed detection signal SS from the speed detector 5S
S is input to the adder / subtractor 14S via the speed detector 13S, and the spindle position detection signal SPS from the position detector 6S is input to the subtractor 11S. Further, a position detector 5Z is connected to the Z-axis motor 4Z. The Z-axis position detection signal ZPS from the position detector 5Z is input to the subtractor 11Z, and the speed detector 13Z
Is input to the adder / subtractor 14Z. The outputs of the acceleration / deceleration processing units 10S and 10Z are differentiated by differentiators 15S and 15Z to become velocity components, respectively, and added to the adders / subtractors 14S and 14Z, respectively. After being amplified by the amplifiers 12S and 12Z, they are input to the adders / subtractors 14S and 14Z, and the addition / subtraction results drive the main shaft motor 4S and the Z-axis motor 4Z via the power amplifiers 16S and 16Z.

In such a control method of the device, since the output torque of the spindle motor 4S for driving the spindle and the Z-axis motor 4Z for driving the Z-axis is finite, the acceleration of the spindle and the acceleration of the Z-axis are always less than a predetermined amount. Must be controlled. Therefore, there is a control method in which the acceleration is suppressed to a desired value by performing acceleration / deceleration processing on the position commands SRP and ZRP given to the spindle motor 4S and the Z-axis motor 4Z according to a predetermined acceleration / deceleration time constant. General. Then, for the purpose of synchronously controlling the positions of the main shaft and the Z axis, the main shaft and the Z axis are naturally subjected to acceleration / deceleration processing with the same acceleration / deceleration time constant.

The acceleration / deceleration time constant T ₀ in FIG. 5 is the spindle rotational speed command SRM input by the operator through the command input unit 1.
Is determined by the time constant determining means 3 in accordance with

(Problem to be Solved by the Invention) The acceleration / deceleration time constant T ₀ as described above is set and controlled in a fixed amount according to the acceleration time required to reach the spindle speed command SRM previously commanded. Was common.

However, the spindle motor 4S is generally in the base rotational speed N _B or decreases the output torque τ as shown in FIG. 6,
So if the user is for example used to command a spindle rotational speed N of the vicinity of the upper limit speed N _max, in the following base rotational speed N _B despite the much higher accelerations than the upper limit speed N _max obtained, very long, That is, a large acceleration / deceleration time constant had to be set. As a result, when such a long time constant is set during the tapping process, the seventh
As shown in the characteristics in the figure, the actual spindle speed is the upper limit speed.
There is a problem that the machining time does not reach _Nmax and the machining time becomes very long due to a long acceleration / deceleration time constant.

In this case, note that the spindle motor 4S is actually rotating at a low rotation speed, and at this actual rotation speed, a sufficiently large output torque τ can be output as shown in FIG. For example, by setting the rotation speed command of the spindle to be low and setting the acceleration / deceleration time constant to be small (short), it is possible to shorten the machining time as shown in the characteristics of FIG. However, if the spindle speed command is set too low or too high, the machining time becomes long. Therefore, it is necessary for the operator to calculate and issue the optimum rotation speed N each time. This operation is very troublesome for the operator, and there is a problem that a program error is easily induced.

In short, when tapping is performed in a machining center or the like, synchronous tapping in which the Z axis and the main axis are synchronously controlled by giving position commands synchronized to the main axis and the Z axis, respectively, is realized. In this case, it is necessary to execute the same acceleration / deceleration processing for the position commands for the main axis and the Z axis, and the acceleration / deceleration time constant is generally determined according to the commanded speed. However, if a high rotation speed is commanded, a long acceleration / deceleration time constant is selected, so that not only the actual spindle speed cannot reach the command value, but also the machining time becomes extremely long.

The present invention has been made under the circumstances described above,
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to automatically select an acceleration / deceleration time constant that minimizes a machining time in any tapping machining, thereby realizing high-speed and high-precision tapping machining. Is to provide.

(Means for Solving the Problems) The present invention synchronously controls the spindle position and the Z-axis position by synchronizing a spindle rotation command and a Z-axis movement command,
It is related to a numerical control device that performs tapping processing.
The above object of the present invention is a time constant determining means for determining an acceleration / deceleration time constant according to a commanded tap cutting depth and a screw pitch, wherein the acceleration / deceleration time constant is T, and the tap cutting depth is Where l is the thread pitch and P and K are constants, the rotation speed of the electric motor driving the spindle is within the range of the base frequency or less. In the range where the number of rotations is equal to or greater than the number of times of base, The acceleration or deceleration based on a data table of an acceleration or deceleration time constant that can be read in accordance with the tap depth and the screw pitch. This is achieved by providing a time constant determining means for determining a time constant, and performing acceleration / deceleration control of the main shaft and the Z axis based on the determined acceleration / deceleration time constant.

(Function) The present invention relates to a numerical control device that performs synchronous tapping by synchronizing commands for the main axis and the Z axis.
Acceleration / deceleration time constant determining means for determining the acceleration / deceleration time constant from the depth of cut of the tapper and the screw pitch is provided, and the acceleration / deceleration of the main shaft and the Z axis is determined by the acceleration / deceleration time constant determined by the acceleration / deceleration time constant. Perform control. When tapping, the acceleration / deceleration time constant that minimizes the processing time is automatically selected according to the specified tap depth and thread pitch. Can be. Further, the tapping process such that the processing time is always shortest can be realized only by the user instructing the tapper preparation depth and the screw pitch.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention in correspondence with FIG. The operator inputs a machining program, machining data, and the like via the command input unit 1. The cutting depth l and the thread pitch P of the tapper extracted from the inputted machining data are determined by the position command generating unit 2 and the time. Constant determination means 4
Is input to The position command generator 2 is a command for rotating the spindle.
An SRP and a Z-axis position command ZRP synchronized with the SRP are output and input to the spindle control unit SC and the Z-axis control unit ZC, respectively. In the spindle control unit SC and the Z-axis control unit ZC, the position commands SRP and ZRP are subjected to acceleration / deceleration processing by the acceleration / deceleration processing units 10S and 10Z, respectively. 4 performs the same acceleration / deceleration with the acceleration / deceleration time constant T output.

Here, an algorithm by which the time constant determining means 4 determines the acceleration / deceleration time constant T will be described. The time chart of the spindle rotation speed during the tapping process is as shown in FIG. 3. As is clear from the figure, assuming that the acceleration / deceleration time constant is T and the spindle rotation speed is N, the acceleration α of the spindle becomes α = N / T (1) Then, when the rotational speed N of the spindle motor 4S is below the base rotational speed N _B, as shown in FIG. 6, because it is the motor torque constant, a constant spindle acceleration alpha, which A ( Α) = N / T = A (2) Here, considering the rotation amount S of the main shaft in FIG. 3, this is equal to the area S of the triangle in the figure, and S = αT ² = AT ² (3). Here, the meaning of the spindle rotation amount S is as follows.
The number of rotations during the stop is shown. In the tapping process, S = 1 / P (4). Therefore, (3) and (4) because it is l / P = AT ² from the equation, the constant T during acceleration and deceleration is Becomes

As described above, the time constant determining means 4 determines the acceleration / deceleration time constant T from the tapper cutting depth 1 and the screw pitch P based on the above equation (5), so that the spindle motor 4S can output the maximum acceleration. Since acceleration → deceleration is performed, machining can be performed in the shortest time.

Further, the rotational speed of the spindle motor 4S is described a case where more than the base speed N _B. Spindle motor for simplicity
Assuming the 4S rotational speed and the spindle rotational speed are equal, the spindle condition for the motor 4S reaches the base speed N _B just is, S = l / P acceleration up to the base speed N _B as A ≧ N _B ² / A (6) That is, if the relationship between the cutting depth l and thread pitch P satisfies the above expression (6), the spindle motor 4S becomes the base rotational speed N _B above. In this range, the output torque τ of the spindle motor 4S is equal to the rotational speed N as shown in FIG.
Decreased with, the acceleration alpha shown in FIG. 3 is a α = A / N (N> N B) ...... (7). Here, the spindle rotation speed N is N = S / T from FIG. 3 (8), and therefore, from equations (7) and (8), Becomes Therefore, from the expressions (3), (4) and (9), Becomes Becomes In the case the spindle motor 4S said in the area above basal rotational speed N _B to (7) below is satisfied, the processing time is the shortest in the case of processing decelerates immediately from the acceleration as of Figure 3.

The time constant determining means 4 determines the acceleration / deceleration time constant T according to the above algorithm. This algorithm is shown in a flowchart in FIG. That is, first, the cutting depth l, screw pitch P and spindle acceleration A, base rotation speed
From the N _B , l / P ≧ N _B ² / A? In the above equation (8) is determined (step S
1), l / P performs the calculation of the time constant T by if smaller (5) than N _B ² / A (step S2). Also step
If l / P is equal to or more than N _B ² / A in S1, the time constant T is calculated according to equation (10).
Is calculated (step S3).

The acceleration / deceleration time constant T determined as described above is input to the acceleration / deceleration processing units 10S and 10Z, and the respective spindle rotational position commands
Performs acceleration / deceleration processing of SRP and Z-axis rotation position command ZRP. Then, the position commands of the main axis and the Z axis that have been subjected to the acceleration / deceleration processing are input to the subtracters 11S and 11Z, respectively, and the position feedback control is performed by the main axis position feedback signal SPS and the Z axis position feedback signal ZPS.
The other components of the spindle control unit SC and the Z-axis control unit ZC are based on the known technology as described above.

In addition to the algorithm described in the above embodiment, the time constant determining means 4 determines the relationship between the cutting depth l, the screw pitch P, and the acceleration / deceleration time constant T as shown by the characteristics in FIG. It is also possible to realize this by using the relationship between the expressions (5) and (10), that is, using a function data table with a broken line approximating the characteristics in the figure. In this case, according to the tap depth and the screw pitch, the time constant T of the data table which is obtained in advance as the address data is read.

Further, it is also possible to determine the time constant T by approximating the relational expression of the expressions (5) and (10) by, for example, the following approximate expression. That is, in step S2 of FIG. Also, in step S3, The time constant T is determined by the following approximate expression.

(Effects of the Invention) As described above, according to the numerical control device of the present invention, when any tapping is performed, machining is performed by simply instructing the minimum tapper cutting depth and screw pitch required for tapping. The acceleration / deceleration time constant that minimizes the time is automatically selected, and there is no need for the operator to input the spindle speed command.This greatly improves the operability when the operator inputs a machining program. Moreover, the processing efficiency can be maximized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flowchart for explaining an algorithm of a time constant determining means, FIG. 3 is a time chart of a spindle rotation speed, and FIG. FIG. 5 shows an example of a function data table for determination, FIG. 5 is a block diagram showing an example of a conventional numerical controller, FIG. 6 is a general speed torque characteristic diagram of a spindle motor driving a spindle, FIG. The figure is a time chart of the spindle rotation speed for explaining the operation at the time of performing tapping processing. 1 ... command input unit, 2 ... position command generation unit, 3, 4 ... time constant determination means, SC ... spindle control unit, ZC ... Z-axis control unit, 10
S, 10Z ... Acceleration / deceleration processing unit, 4S ... Spindle motor, 4Z ... Z
Shaft motor.

Claims (1)

(57) [Claims] 1. A synchronous control of a spindle position and a Z-axis position by synchronizing a spindle rotation command and a Z-axis movement command,
In a numerical control device for performing tapping processing, time constant determining means for determining an acceleration / deceleration time constant according to a commanded tap cutting depth and a thread pitch, wherein the acceleration / deceleration time constant is T, Depth l, thread pitch P, K
Is a constant, when the number of rotations of the electric motor driving the spindle is less than or equal to the number of base times. In the range where the number of rotations is equal to or greater than the number of times of base, The acceleration or deceleration based on a data table of an acceleration or deceleration time constant that can be read in accordance with the tap depth and the screw pitch. A numerical control device comprising a time constant determining means for determining a time constant, and performing acceleration / deceleration control of the main shaft and the Z axis based on the determined acceleration / deceleration time constant.