JPS6334019A - Tap processing control device - Google Patents

Abstract

PURPOSE:To shorten a processing time and to improve screw precision, by a method wherein a time lag correcting circuit is situated to the acceleration deceleration circuit of an axis-Z servo motor, and control is effected so that a ratio of an axis-Z feed speed to the number of revolutions of a spindle is always adjusted to a thread pitch. CONSTITUTION:When, with a shifting device 18 shifted to the side (a), a device is brought into a spindle position control mode, according to a processing program 15, an NC control device 16 outputs a position control command to a spindle position control circuit 17 through an acceleration deceleration circuit 24, and to an axis-Z position control circuit 20 through a correction circuit 26 having index function characteristics responding to and following up the initial legs of an acceelration deceleration circuit 25 and the control circuit 17. The control circuits 17 and 20 receives signal feedback from a position encoder 12 and a pulse encoder 23, and performs synchronous control of rotation of an AC spindle motor 13 and an axis-Z step motor 22 through servo circuits 19 and 21, respectively. This constitution enables a ratio F/S of a feed speed F in the direction of an axis-Z to a spindle rotation speed S to be always held at a thread pitch P, shortening of a processing time, and improvement of screw precision.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention has the following advantages: The present invention relates to a tapping control device that performs accurate tapping.

(Prior Technology) Machining centers that can perform milling using contour control, drilling and tapping using various fixed cycles have been developed and are now being used in many factories. The tapping operation performed by this machining center involves attaching the tapper to the spindle, operating the Z-axis feed motor to bring the tip of the tapper close to the entrance of the hole drilled in the workpiece, and rotating the spindle to move the Z-axis. The feed motor continues to operate to cut the tapper into the hole and cut a thread on the inner surface of the hole. When the thread has been cut to a predetermined length, the spindle is rotated in the opposite direction, and the Z-axis feed motor is also rotated in the reverse direction to remove the tapper.

By the way, in conventional machining centers, the tapping operation is not controlled by linking the spindle motor and the two-axis feed motor, and the spindle and Z-axis are controlled independently.
For example, the speed of each Z-axis feed motor was independently controlled by determining the rotation speed of the Z-axis feed motor according to the rotation speed of the spindle.

However, in tapping, the Z-axis feed per revolution of the spindle must be equal to the thread pitch of the collar.
It is required that the conditions be met. In other words, if P is the pitch of the thread of the tapper, F is the feed rate of the Z-axis, and S is the rotation speed of the spindle, then P=F/S... (1) When performing tapping, When the power tap pitch P is given, determine the spindle rotation speed S while considering the processing conditions of the machine, etc., calculate the Z-axis feed rate from F=PXS, and calculate P=F/S in the above equation (1). The control circuit that controls the spindle only rotates the spindle to achieve the given S, and also controls the feed of the Z axis. The control circuit only moves the axis so that the feed rate becomes F, and does not necessarily communicate with the other circuit to perform control.
It is not intended to perform processing while satisfying the conditions of /S.

゛ In particular, when machining the bottom of a hole, the rotation of the spindle and the feed of the shaft both decelerate and stop, and then move in the opposite direction while accelerating, and force acceleration and deceleration are handled independently. , P=F/S will not be satisfied. For this reason, a spring is installed inside the holder of the tapper to make the tapper expandable and retractable to correct the feed. That is, (1) Z-axis feeding motor stops)-13 Thread cutting of the tapper continues until the spindle motor decelerates and stops, and the tapper extends. (2) The actual spindle motor rotation speed has an error from the set rotation speed, so it expands when pushing in and contracts when pulling up. (3) The Z-axis feed motor reverses while the spindle motor is decelerating or stopping. Pull the tapper in the opposite direction to stretch it. (4) While the spindle motor is accelerating in reverse, the Z-axis feed motor is rotating in reverse and the tapper is extended by pulling it in the opposite direction. However, such control causes damage to the threads and impairs the dimensional accuracy of the screws. Further, since an unreasonable force is applied to the tapper, an inconvenience arises in that the expensive tapper may be damaged.

By the way, recently, due to improvements in the performance of spindle motors and spindle motor control circuits, spindle motors are not used normally for turning the spindle, that is, used only for speed l control, but are now being used like servo motors. It has also become possible to use it by controlling both position and speed. In other words, conventionally, when turning the spindle to perform turning, the spindle motor is connected to the spindle, and when positioning the spindle at a certain angle to perform drilling, the spindle motor and spindle are connected. Previously, the servo motor was separated and used by connecting it to the spindle, but now the spindle motor can be used by itself for turning or for positioning. A schematic block diagram for performing such control is shown in FIG. A comparator that compares the output signal of the deceleration circuit a with the feedback signal of the position detector j that detects the moving position of the spindle i, C is an error counter that counts the position deviation amount, and d corresponds to the rotation speed of the spindle. A control circuit that calculates the voltage, e is a switch for position control and speed control, f is a D/A converter, and g is an amplifier into which the output signal of the D/A converter and the speed detection signal of the spindle motor are input. be.

A control device that uses such a spindle motor control circuit to perform a tapping operation as described below has been developed.

That is, when performing tapping, as shown in FIG. 4, the table l pushes up the workpiece 2 during the tapping operation and lowers the workpiece 2 when cutting is completed, that is, the speed in the Z-axis direction. The feed speed is F [mm/m i
n], the rotational speed of the spindle, that is, the rotational speed of the tap 3, is S [rpm], and the beach 2 of the screw 4 is P, then by transforming equation (1) between these, F=S-P.
... If the relationship (2) is always obtained, the tap 3 will push forward while cutting the thread into the hole 5 without expanding or contracting, and when the tap 3 is reversed, it will also be pulled out without expanding or contracting. That's why. Therefore, when performing a tapping operation, the tap 3 starts cutting from the tap depth dt, P, and P, and then finishes cutting dt.

Determine the number of rotations N required until the process is completed (N = 7-), and calculate the total cutting length using the following formula.

πX d By the way, the cutting speed when tapping a normal stop hole is 8 m/min or less, and the cutting speed when the material to be cut is light metal and the tap is made of carbide is 25 m/min or less. Then, the cutting time T is obtained from the following equation (3) using this cutting speed.

T = sentence / V e ... (4
) Substituting equation (3) into equation (4), N/T=Ns
By substituting equation (4) into T, S is obtained by the following equation.

C 3=7 possible - (5) After obtaining the rotation speed S of the tap in this way, (2)
According to the formula, the feeding speed F in the Z-axis direction is synchronized with the rotational speed S to perform the tapping operation.

As a related control between the spindle motor and the Z-axis motor, it is possible to perform linear interpolation between the two axes, the spindle and the Z-axis, to improve the precision of tapping.For example, as shown in Figure 5, As shown, the Z-axis feed rate Fz,
Given data S on the Z-axis travel amount Z and spindle rotation speed, the Z-axis and spindle can be linearly interpolated by controlling their respective travel amounts and feed speeds, as shown in Figure 6. Linear interpolation between the Z-axis and the spindle using the above-mentioned movement amount and feed rate means that the relationship of P=F/S in the above-mentioned equation (1) is always maintained.

FIG. 7 is a block diagram showing the control relationship between the two axes, the Z-axis and the spindle. In FIG.
The axis acceleration/deceleration circuit A3 is a position control circuit with a gain Gz. Further, Bl is a circuit for generating an interpolation command Fs by distributing pulses of the spindle, B2 is a spindle acceleration/deceleration circuit with a time constant Ts, and B3 is a spindle position 21 control circuit with a gain Gs. As shown in L, in order to maintain the relationship P=F/S in equation (1), the time constants of the acceleration/deceleration circuits of the Z-axis and spindle and the time constants of the position control circuit (position control loop gain) must be the same value, i.e., Tz=Ts ・
... (6) Gz=Gs ...
Control is performed so that (7) is achieved.

Normally, Gz=20 to 40 (sec=) in many cases, but it can only be raised to Gs=5 to 20 (see'), so tap processing is performed by linear interpolation between the spindle and the Z axis. Sometimes, by lowering Gz, Gs
The value of Gz is changed to match. The outputs of the spindle and Z-axis acceleration/deceleration circuits are completely (1
) relationship of P=F/S is maintained.

(Problem to be Solved by the Invention) If each Z-axis and spindle position control circuit is a first-order lag element expressed by the transfer function /(Ts+1), then as mentioned above, Gz=Gs By doing so, the movement of the Z-axis servo motor and spindle motor is (
1) Control is performed so that the relationship of P=F/S in the equation is maintained.

However, in an actual control system, the transfer functions of the Z-axis and spindle position control circuits are not as simple as a first-order delay, but have a complicated form. This is because there is a difference in torque constant between the spindle motor and the Z-axis servo motor, and there is a difference in movement between the Z-axis servo motor and the spindle motor. This difference can be expressed as follows. That is, if the transfer function of the position control circuit is approximated to a second-order lag, then this transfer function Gz
is, Gz=ωn2/ (S2+2ζωnS+ωn2)...
(8) However, ωn: natural frequency of the second-order lag system ζ: can be expressed as a damping coefficient. Here, the difference in characteristics such as torque constant appears as a difference in damping coefficient, and as shown in FIG. 8, the response of the second-order delay element to the ramp input becomes larger as ζ becomes larger.

The Z-axis servo motor has better responsiveness than the spindle motor, so even if Gs=Gz, P
=F/S relationship could not be maintained. Therefore, the present invention corrects the input to the position control circuit for the Z-axis servo motor with good response, and as a result, the Z-axis servo motor
This invention provides a control system for tapping in which the movement of a shaft servo motor is matched with the movement of a spindle motor so that the relationship P=F/S can always be maintained.

(Means for Solving the Problems) In order to improve the conventional drawbacks as described above, the present invention provides a first motor that drives a spindle and a second motor that drives a workpiece in the spindle axial direction. The time constant of the acceleration/deceleration circuit of the first motor is Tz, the gain of the position control circuit is Gz, and the time constant of the acceleration/deceleration circuit of the second motor is Ts.
, when the gain of the position control circuit is Gs, Tz=Ts.

In a tap machining control device, a linear interpolation command generation circuit satisfying the condition of Gz=Gs is provided in the control circuit of the first and second motors, and a tapper machine provided on the spindle performs tapper machining on a workpiece. A correction circuit having an exponential characteristic that follows the initial delay of the first motor control circuit is inserted into the acceleration/deceleration circuit of the second motor, so that P=F/S, where P: tapper thread pitch F : To provide a tapping control device that satisfies the Z-axis feed rate S and the rotational speed of the varnish spindle.

(Function) The present invention provides a correction circuit having time delay response in the Z-axis top control circuit so that the movement of the Z-axis motor and spindle motor always holds P=F/S. Since it is controlled, tapping and rolling on the workpiece can be performed precisely.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of the general configuration of the present invention. In the figure, an output shaft 14 of an AC spindle motor 13 is connected via a coupling device 11 to a spindle lO attached to the tip of a tap 3, and the position of the tap 3 is detected by a position coder 12. Ru. Also,
The table l is connected to a table driving AC motor 22 and driven in two axial directions at a feed rate fm. Reference numeral 16 denotes a numerical control device, into which a cannibal program 15 is input from an external storage device such as a bubble memory, and according to this cannibal program, machining command signals are sent to the AC spindle motor 13.
is issued to the table driving AC motor 22. 24 is an acceleration/deceleration circuit for the AC spindle motor 13, 17 is a spindle position control circuit, 18'' is a cutting device, which is switched and controlled by the numerical control device fi16, 19 is a spindle servo circuit, and 25 is a cutting device. Table drive AC motor 22 Acceleration/deceleration circuit, 26 is primary 8 related to unfired Ill
These correction circuits include a Z-axis position control circuit 20, a Z-axis servo circuit 21, and a pulse coder 23 for determining the rotational position and speed of the AC motor 22 for driving the table.

Next, the operation of this control device will be explained.

When the contact point of the device 18 is connected to the a side and the spindle position control mode is set, the control program 15 will cause
The NC device 16 operates and sends a position control command to the acceleration/deceleration circuit 2.
4 to the spindle position control circuit 17. A position signal from a position coder 12 that detects the position of the spindle 10 is input to the spindle position control circuit 17, and a deviation signal between the two is input to the spindle servo circuit 19. The AC spindle motor 13 is digitally controlled by an output signal from a spindle servo circuit 19.

On the other hand, the output signal from the NC control device 16 is input to the Z-axis position control circuit 20 via the acceleration/deceleration circuit 25 and the correction circuit 26, and the Z-axis position control circuit 20 controls the position of the table driving AC motor 22. The output signal from the pulse coder 23 to be detected is compared with the command signal from the NC control device 16, and an error signal is applied to the Z-axis servo circuit 21. The table driving AC motor 22 is digitally controlled by an output signal from the Z-axis servo circuit 21. At this time, the AC spindle motor and the table drive motor are driven synchronously by a command signal from the NC control device.

In the embodiment of J shown in FIG. 1, the acceleration/deceleration circuit 25 of the AC motor 22 for driving the table is used to correct the difference in response between the Z-axis motor and the spindle motor shown in FIG. After that, a correction circuit 26 for temporary delay is provided. That is, as explained in FIG. 7, the acceleration/deceleration circuit A of the Z-axis motor and spindle motor
2. Since the time constants Tz and TS of B2 are made equal, and the gains Gz and Gs of position control circuits A3 and B3 are made equal, as shown in FIG. 8, the slope angles of the respective waveforms are made equal. However, at the beginning of operation, the AC spindle motor 13, which has a small torque constant, has an exponential delay with respect to the AC motor 22 for driving the table. For this reason, a correction circuit that causes an exponential delay is inserted into the acceleration/deceleration circuit 25 of the AC motor 22 for driving the table, which has a large torque constant, etc., to correct the input to the position control circuit 20, and as a result, As shown in Figure 2, the time constant Tz on the Z-axis servo motor side is matched with the time constant Ts on the spindle side, and the movement of this is matched to the movement of the spindle motor, so that the relationship P=F/S is always maintained. This is to ensure that the

(Effects of the Invention) As explained above, according to the present invention, the movement of the Z-axis servo motor and spindle motor is always controlled by P=F/S (where P is the screw pitch and F is the feed in the Z-axis direction. The speed can be controlled so as to maintain the relationship between the rotational speed of the spindle (S is the rotational speed of the spindle), and effects such as shortening of machining time and improvement of welding accuracy can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic blow diagram of the present invention, Fig. 2 is a block diagram showing changes in input signals in various parts of the embodiment of the present invention, Fig. 3 is a block diagram showing a conventional example, and Fig. 4 is a thread cutting diagram. An explanatory diagram for explaining the operation, Figures 5 and 6 are explanatory diagrams of the operation, Figure 7 is an explanatory diagram of another conventional example, and Figure 8 is the response difference in position control between the spindle motor and the Z-axis motor. FIG. lO・・Spindle, 13・AC spindle motor,
16...Numerical control device, 17.Fist spindle position control circuit, 19Φ.Spindle servo circuit, 20-ΦZ-axis position control circuit, 21..Z-axis servo circuit, 22..Table drive AC motor, 24 and 25.・Acceleration/deceleration circuit, 2
6. Dispute correction circuit. Patent Applicant Fanuc Co., Ltd. Agent Patent Attorney Minoru Tsuji\to <Australian Procedural Amendment (Touken October 6, 1985 Patent Application No. 175869, Title of Invention: Tapping Processing Control Device, Amendment) Relationship with the case involving the person who filed the patent application Patent applicant name: Faner 2 Ri Co., Ltd. Representative: Seiemon Inaba, agent address: IO1 3-14 Kanda Ogawa-cho, Chiyoda-ku, Tokyo, Japan Figure 1 of the drawing originally attached to the petition As shown in the engraving and attached sheet (no changes to the content)

Claims (1)

[Claims] A first motor that drives a spindle and a second motor that drives a workpiece in the spindle axial direction, the time constant of the acceleration/deceleration circuit of the first motor being Tz, and position control. The gain of the circuit is Gz, and the time constant of the acceleration/deceleration circuit of the second motor is Ts.
, when the gain of the position control circuit is Gs, linear interpolation command generation circuits satisfying the conditions Tz=Ts, Gz=Gs are provided in the control circuits of the first and second motors, and the control circuits are connected to the tapper provided on the spindle. In a tapping control device that performs tapper processing on a workpiece, a correction circuit having an exponential characteristic that follows the initial delay of the first motor control circuit is inserted into the acceleration/deceleration circuit of the second motor, and P =F/S where P: tapper thread pitch F: Z-axis feed speed S: spindle rotation speed.