JPH01301017A - Tapping control method - Google Patents

Abstract

PURPOSE:To eliminate deformation of ridge and to shorted working cycle time by carrying out tapping operation with the control mode being switched from position control to torque or thrust control. CONSTITUTION:Upon entering into tapping operation according to an instruction on a cutting program, tap tool position and feeding speed to be determined through a feeding shaft motor 200 are detected respectively through a position detector 2 and a speed detector 5 thus carrying out normal position control at first. Upon contact of the tap tool with a work, a switching means 12 is switched to the side of a torque command set value storing section 13 so as to switch the control mode from position control to torque or thrust control thus controlling drive torque of the feed shaft motor 200 through an amplifier 10 corresponding to the difference between a torque command set value S13 being set in the storing section 13 and a torque signal S8 detected through a torque detector 8. By such arrangement, the feed shaft can be moved freely according to the thread pitch of a rigid tap tool with no deformation of the ridge and the machining time can be shortened.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides an effective method for drilling screw holes in a workpiece by installing a tap tool on a numerically controlled (hereinafter referred to as NC) machine tool that performs position control. This invention relates to a tapping control method.

(Prior Art) Conventionally, in order to make a screw hole in a workpiece (tapping process), the shaft of a tap tool 100 is mounted on a tap holder 101 as shown in FIG.
A is pressed into the hole 103 pre-drilled in the workpiece 102 in the direction of the arrow F in the figure, and the tap holder 101 is pressed.
This is done by manually rotating the handle 104 and threading it.

At this time, for example, he would make two turns to the right, then half a turn back to the left, and then ask his father to make two turns while removing the chips with his hands. As you can see from this tap, the tap tool 100 itself has a position with respect to the workpiece 102, and when considering each pitch mountain, it has a position for each pitch mountain regularly by the pitch. . However, this manual method is time consuming and has poor precision in thread machining, so a method of automatically tapping with an NC machine tool is usually used.

FIG. 8 is a side view showing the machining section when tapping is performed with an NC machine tool, and the rotation of the feed shaft motor 200 causes the feed shaft ball screw 201 and the pole screw nut 202 to
A spindle head 203 that ascends or descends along a sliding surface 204 via a spindle head 203, a spindle 210 that is rotated by a spindle motor (21 (IA)) located inside this spindle head 203, and a tool that can be attached to this spindle 210. A holder 211 and a tap tool 212 inserted and fixed in this tool holder 211
It consists of The tapping tool 212 is configured to tap a work 220 fixed to a table 221 as the feed shaft 200 rotates while being rotated by the main shaft 210.

FIG. 1θ is a block diagram showing an example of a control system that realizes a conventional feed axis control method that can be applied to such NC machine tools.
a subtracter 3 that subtracts the position detection value S2 detected by the position detector 2 from 1, an amplifier 4 that amplifies the position deviation value S3 that is the output of this subtracter 3, and a speed command that is the output of this amplifier 4. A subtracter 6 that subtracts the speed detection value S5 detected by the speed detector 5 from the value S4, an amplifier 7 that amplifies the speed deviation value S6 that is the output of this subtracter 6, and a torque that is the output of this amplifier 7. Torque detector 8 from command value S7
(Detects the current flowing through the feed shaft motor 200 and converts it into torque.) A subtracter 9 subtracts the detected torque value S8, and the output of the subtractor 9 is the feed shaft motor current value S9. is amplified by amplifier lO and sent to feed shaft motor 2.
00, torque is generated and the required speed and position of the feed shaft can be obtained. In this case, it always operates to make the position deviation value S3 zero, but
Even if the position deviation value S3 does not become the stem for some reason, the speed command value S4 is generated (because St-52≠O), so as a result, torque is generated in the feed shaft motor 200 and the position deviation is reduced. It acts to flatten the value S3.

Next, a description will be given of tapping processing in which the feed shaft is used to perform synchronization control with the rotation angle of the main shaft 210.

FIG. 11 is a block diagram showing an example of a control device that implements this synchronous control method, and the same components as in FIG. In this control device, a function generator 1 generates a rotational speed command value Sl' for the main shaft 210 and a position command value Sl' for the feed axis, and inputs each command value to each axis control system. The feed axis position command value S1 is input to the subtracter 3 of the control device, thereby controlling the feed axis as described above. On the other hand, the control system on the spindle 210 side operates from the rotation angle command value S1° of the spindle 210 to the rotation angle detector 2°.
A subtracter 3° that subtracts the raw glaze rotation angle S2° detected by , and a position deviation value S3° that is the output of this subtractor 3°.
and a spindle rotation speed detector 5° based on the spindle rotation speed command value S4°, which is the output of this amplifier 4°.
A subtractor 6 that subtracts the rotational speed detection value S5° detected at
° and the rotational speed deviation value S6 which is the output of this subtractor 6°
The torque detected by the main shaft torque detector 8° (detects the current flowing through the main shaft motor 21QA and converts it into torque) from the torque command value S7° which is the output of this amplifier 7°. It has a subtracter 9° for subtracting the detected value S8°. Then, the main shaft motor current value S9°, which is the output of the subtractor 9°, is amplified by the amplifier 10° and flows to the main shaft motor 210A, generating torque.
The structure is such that the required rotation speed and one rotation angle can be obtained.

(Problems to be Solved by the Invention) The synchronous control method using the control device shown in FIG. 11 described above has no problems theoretically, but it has the following problems in practice. In other words, the properties required for the spindle 210 are different from the properties required for the feed axis, so even if you simply attach a 2° rotation angle detector to the spindle 210 and perform angle control, the spindle 2
The control performance of No. 10 is worse than that of the feed axis. To overcome this drawback, using a servo motor for the spindle 210 is conceivable for small machine tools, but it is not common.
Furthermore, if a servo motor is used for the main shaft 210, the characteristics required of the main shaft, such as small size, high rotational speed, high output, and constant output characteristics, cannot be satisfied.

As described above, in order to synchronously control the main shaft 210 and the feed shaft, it is necessary to match the control characteristics of these two glazes, and conventionally, the control characteristics of the feed shaft have been lowered to the level of the main shaft 210. However, generally by lowering the control characteristics, there is a tendency to become weaker against load fluctuations on each axis, so-called disturbances.
A tracking error occurs on each axis, resulting in a tracking area difference during synchronous control, which appears as deformation of the thread after machining.

FIG. 12 shows the positional relationship between the tap tool 212 and the workpiece 220, and FIG. 13 shows the positional relationship between the rotational speed of the main shaft 210 and the feed shaft. Assuming that the starting point of the tapping process is SP and the ending point of the tapping process is E, a solid line connecting these two fixed points becomes a locus of values generated by the function during synchronous control. Further, in FIG. 13, the main shaft rotation angle at 21 points is Pl, and the feed shaft position is PmZ. From the starting point SP of tapping processing, the function generation values are Sp, P+, P2s",
It outputs Pn-+, Pn, and Ep, and stops at the end point EP. Next, in order to pull out the tap tool 212, the function generation values are Ep, Po, Pn-+, -, P2. PI and SP are output. Here, since the control characteristics are lowered, the curve follows as shown by the broken line. The slope of the solid line connecting the two fixed points becomes the pitch amount of the tapping tool 212, but the following trajectory like the broken line will put a load on the thread being machined during tapping. . When the value of the follow-up error (the shaded area shown in FIG. 13) of this follow-up trajectory increases, deformation of the workpiece being machined, so-called bulging of the thread, occurs. Furthermore, the tracking error of the tracking trajectory is SP+Pl+'2+..."+P11-1+P
11+EP direction, Ep, Po in the opposite direction
, Po−+, ”, P2. P+ and Sp will take different tracking trajectories, and there is a possibility that the threads will be crushed during the drawing process.

This will be explained in more detail with reference to FIG.

Here, the representative points of the function generation values are represented by Pk-1 and Pk, and the distribution value of the command value on the spindle side is Pkt, the distribution value on the feed axis side is Pkz, and the same goes for Pk-1 below. do. Then, the position of the tap tool 212 at the point of -1+Pk is set as Pk-1 "+Pk" in the above, and the distribution values of each axis are the same as in the above method. The thrust direction of the command value for the tap tool 212 is the vector Pk-IPk in the figure.
Since the thrust of the tap tool is in the direction of the vector Pk-1'Pk, this slope θ is expressed as the vector Pk-1'Pk.
Since there is a deviation angle from IPk to vector Pk-1p,
A phenomenon occurs in which the thread being machined is deformed due to thrust acting in a direction other than the direction in which it should be cut.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a tapping system that can completely eliminate the collapse of threads due to tracking errors without changing the control characteristics of the main spindle and the feed axis. The objective is to provide a control method. In other words, thread collapse in tapping occurs when the rotation angle of the main spindle and the position of the feed axis are synchronously controlled, and the tracking error of each axis causes an error in the thread pitch of the tapping tool itself. This is caused by the large thrust acting on the screw extension. As a countermeasure against this problem, it is common to improve the control characteristics of the main axis and feed axis to improve the followability of each axis to the command value, but in the present invention, the position control of the feed axis is performed during tapping. By switching to torque control only occasionally and generating torque of the feed shaft in a direction that helps move the tool position corresponding to the thread pitch amount of the tap tool itself according to the rotation angle of the main shaft, the control characteristics of the two axes are not improved. The purpose is to completely eliminate the collapse of screw threads due to tracking errors.

(Means for Solving the Problems) The present invention relates to a tapping control method for an NG machine tool that performs position control, and the above object of the present invention is to perform tapping machining by switching the control mode from position control to torque or thrust control. It is achieved by doing.

(Function) The tapping control method of the present invention generates torque in a direction that aids tapping by controlling the feed axis, and uses the conventionally used position detection values and speed detection values to monitor abnormal operations and separate sequences. By using it as a point detection means, it is possible to eliminate deformation of the screw thread caused by a tracking error of each axis during synchronization control of the rotation angle of the main shaft and the position of the feed shaft. In particular, in Fig. 14, the torque command value of the spindle during cutting with a tap tool is used to control the torque of the feed axis such that it always coincides with the vector Pk-IPk direction in the figure, or a torque control close to that, and The machining shape is left to the trajectory shape of the tap tool itself. Therefore, by controlling the trajectory shape of the tap tool itself, the rotation angle of the spindle, and the position control of the feed axis, there is no deformation of the screw thread that would occur based on a difference in the shape of the trajectory being followed. In addition to the above method, it is also possible to improve the situation by switching the position control of the feed shaft to torque control.

(Example) FIG. 1 shows the tapping control method of the present invention at N of FIG.
10 is a block diagram illustrating an example of a feed axis control device realized for a C machine tool, corresponding to FIG. 10, in which the same components are given the same reference numerals and a description thereof will be omitted. This control device is newly equipped with a torque command setting value storage section 13 in which the numerical value of the torque command value T1 is written in advance, and a torque command value switching means 12 that switches the torque command value to T1 at a predetermined switching timing. It is provided. Note that each numerical value for control, such as a position detection value, a speed detection value, a torque detection value, and each corresponding command value, etc., are controlled by software, so that they can all be monitored. The switching timing is generated by software processing corresponding to the torque command value monitoring part in the flowchart shown in FIG. Furthermore, Figs. 3fA) and 3(B) are block diagrams showing an example of a synchronous control device for the feed axis and the main spindle that realizes the tapping control method of the present invention, and the control system for the main spindle is shown in Fig. 11. The same control system as that of the spindle is used.

In such a configuration, an example of its operation will be explained with reference to the time chart of FIG. 4 and the flow chart of FIG. 2. The time chart in FIG. 4 shows the main shaft rotational speed, the speed of the feed shaft, and the torque command value of the feed shaft. In addition, the fourth
In the figure, the numbers ``■'' to ``■'' correspond to the positions ``■'' to ``■'' of the tip of the tap tool 212 in FIG. When an NC machine tool performs machining according to an NC cutting program and there is a tapping process in the cutting program, the tapping tool 212 is fixed to the spindle 21 (l) in advance, and the tapping process is performed during the cutting program. When a machining command is given, tapping machining is performed in the following steps SPI to SP4.

Step SPI (SPII-5P13): Assuming that the spindle head 203 is positioned and stopped at the 0 point, the torque of the feed shaft motor 200 at that time is T. shall be. Considering the equation for the balance of the movable portion of the spindle head 203 in the +2 direction, it is expressed by the following equation (1).

F7o± fStation-W・0 ・・・・・・・・・
(1) However, F'to is the thrust in the +2 direction generated by the feed shaft motor torque To, W is the weight of the spindle head moving part, ±f static is the static friction force that the spindle head moving part receives from the sliding surface guide, +f static is the frictional force generated when the spindle head 203 is positioned from the +2 direction to the 12th direction, and -f static is the frictional force generated when the spindle head 203 is positioned from the 12th direction to the +2 direction.

When the tapping process starts from ① according to a command on the cutting program, normal position control is first performed, and the spindle head 203 begins to descend at a descending speed Vdow□, which is one depression. In the preprocessing of step 5P11, the torque command fixed value T
l, T2, falling speed setting value V,. lol. , rotation speed N (rev) until the main shaft 210 stops, screw thread pinch P
(+nm/rev), JZ-NXP is set as the distance °C required for stopping the spindle 210. The feed shaft is accelerated and decelerated by normal position control until the descending speed reaches Vdown in FIG. 4. Immediately after starting from the 0 point, monitor whether or not the torque command value TI has fallen below (
Step 5P12). After this, tap tool 212 at 0 point
contacts the workpiece 220. At this time, the torque command value suddenly changes and tends to exceed the torque command set value T1 to the negative side. At this 0 point, switch the control mode of the feed axis from "position control" to "torque control" (step 5P13)
.

Step SP2 (SP21 to 5P26): After the switching to torque control in step 5P13 is completed, point ■゛ (
The main @21O starts rotating at the same physical position as the 0 point (step SP21). Here, the main shaft 2100
When the tap tool 212 starts to bite into the workpiece 220 normally at the start of rotation, the following relationship (2) is established.

v −p X N/1000 ・−・−
・-・(2) However, P is the thread pitch amount [mm/rev], and N is the spindle rotation speed [mm/rev].
RPM], U is the moving speed of the feed axis [m/m1nl,

Therefore, using the relationship in equation (2) above, the tap tool 21
It is also possible to detect whether the workpiece 2 is biting into the workpiece 220 normally or not (Step 5P22), or an error (Step 526). Further, in FIG. 4, the resistance F'down that the tap tool 212 receives from the workpiece 220 during tapping is expressed by the following equation (3) based on the balance of the spindle head movable part.

F'a. Yu. 10F A, ◆fStationary-W-0...
...(3) However, Fa is the +2-direction thrust generated by the feed shaft motor torque T1, W is the weight of the spindle head moving part, and +f static is the +ZZnO static friction that the spindle head moving part receives from the sliding surface guide. power, is.

Here, assuming that f stationary valve is 0, the above (1), (3
), the following equation (4) is derived.

F'davn-FTO-FTI...
...(4) Here, the obtained resistance F゛. Since wn was solved by the drag force that the tap tool 212 receives from the workpiece 220, if the thrust force that the workpiece 220 receives from the tap tool 212 is Fdown, the drag force Fdown is expressed by the following equation (5).
It is expressed as

F. . -4'dow.・・・・・・・・・
・(5) Therefore, it can be seen that both have the same thrust force with only opposite directions.

By the way, the value of the torque command setting value T used in step SPI is calculated as follows.

TI -To"ko 4aow.-TO"Tdo
lol.・(6) Here, 0 is a constant for converting the thrust force into feed shaft motor torque, F down is the thrust value when it comes into contact with the workpiece 220 with +ZZnO acting thrust as a plus, and Tdown is Fdo
lol. The torque command value of the feed axis at is .

Note that the thrust value Fdow. is a value that can be set as a parameter before tapping, and since contact is made in the negative direction, Fdown <o.

FIG. 4 shows an embodiment in which the torque of the feed shaft is controlled using the fixed value T1 shown by the above equation (6), but as another example, the rotation speed of the main shaft 210 is detected and the torque command value of the feed shaft is T
A method of calculating 1 can also be considered. That is, TI-To" ko・Fao-, +k+・No
-(7).

However, k is a proportionality constant, and No is a detected value of the rotation speed of the main shaft 210. In the case of this example, during the tapping process, -
or N so that No<O. Set the sign of .

Another possible method is to calculate the torque command value TI of the feed shaft from the torque command value of the main shaft 210 while the tap tool 212 is cutting. That is, T+ = To+ko 'Faown + (k2/ko
) T, ・(a)k2・P/(π・D)
...(9).

However, T is the main @21O that occurs while the tap tool 212 is cutting.
P is the thread pitch amount of the tap tool 212 [ma+/revl], and D is the pitch circle diameter of the tap tool 212 [mml].

Therefore, during tapping processing, the thrust value Fdow to be brought into contact with the workpiece 220 is determined based on the management number on the software of the tapping tool 212. , proportionality constant ko, + , thread pitch ff1P of the tap tool 212, pitch circle diameter D (k2
is determined by equation (9)) and whether the thread is a right-hand thread or a left-hand thread must be set in advance.

However, depending on the embodiment, it is not necessary to set all of the above.

Next, the rotation of the main shaft 210 is stopped at the 0 point (step 5
P24, 5P25), this stop position control is performed by the main shaft 21
Determine in advance the number of revolutions required to stop the rotation of 0, and multiply by the screw pitch amount P to obtain the distance l of the feed axis! ! When tλ is determined and a point obtained by subtracting the distance 7111 from the coordinate value of the 0 point is detected, control is performed to perform deceleration processing of the spindle rotation speed.

Therefore, in order to improve the accuracy of the stop position, the main @21
It is sufficient to control the rotation angle of 0. In this case, controlling the rotation angle of the main shaft 210 means controlling the rotation angle of the main shaft 210. By accurately controlling the rotation speed of the main spindle 210 from when the Thf1210 is decelerated until it stops, the purpose is to improve the accuracy of the stopping position of tapping processing, so the main spindle and feed as in the conventional technology described above are Since the purpose is not to synchronize with the axis, it is used in a different way. Therefore,
Even if the control characteristics of the rotation angle control of the spindle are somewhat low, the screw thread will not be deformed. That is, in this embodiment, it is not necessarily necessary to control the rotation angle of the main shaft depending on the required machining accuracy of the thread bottom.

Step 5P3 (SP31 to 5P33): Next, the fourth
At the ■° point in the figure (the physical position is the same as the 0 point, but the time is different, it is distinguished), the torque command setting value of the feed axis is changed from T1 to T2 (step 5P31).

Next, step 5P32 is entered in which the main shaft 210 is rotated in the opposite direction to the direction in which it was rotated in step SP2, and the tap tool 212 is pulled out. At this time, the torque command setting value is changed from T1 to T2. This torque command set value T2 is expressed by the following equation (lO).

T2-To+ko'Fu, -To+Tup+*+++++
(10) However, pup is the thrust value that raises the spindle head 203, and Tup is F
The feed axis torque command value for generating up is as follows.

Here, the thrust value Fllp is a value set in advance like Fdown. For simplicity, Fup=Fd. lol
, may also be used.

In the other embodiment described in step SP2, this step S
P3 is expressed by the following equations (11) and (12), respectively. That is, when detecting the rotation speed of the main @111210 and finding the torque command value of the feed axis, T2-To+ko-Ful, 10 kl・N
...... (11), and when calculating the torque command value T of the feed axis from the torque command value of the main shaft 210 during tap tool withdrawal, T24o"ko'Fup" (k2/kO)T- ---
(12). In FIG. 4, the step SP
2 using the above equation (6), and step SP3 using the above equation (10) to control the torque of the feed shaft as shown in Fig. 3.
Combinations with other embodiments are also possible. For example, step S
When using equation (8) above in P2, as shown in Figure 5, (1
2) A torque distribution calculator 14 that performs the calculation shown in equation 2) is newly provided compared to FIGS. 3(A) and 3(B).

While receiving a thrust in the +Z direction due to the torque command value T calculated by the above equation (lO), the tap tool 212 moves upward in the +2 direction at a speed V shown by the above equation (2) as the main shaft rotates. Equation (2) holds true while the blade of the tap tool 212 is engaged with the machined thread, but when the tap tool 212 comes out of the workpiece 220, the torque command value of the feed shaft is T2, so the main shaft Acceleration α acts on the moving part of the head. The movement method of the spindle head movable part is as follows (13
) is expressed by the formula.

FT2-f-W-M・α・・・・・・
・(13) However, FTup is the +Z-axis direction thrust generated in the spindle head movable part by the feed shaft torque command value Tup, -f! JJ is the dynamic friction force in two directions that the moving part of the spindle head receives from the sliding surface guide,
M is the mass of the spindle head moving part.

Therefore, at the 0 point, acceleration α acts on the spindle head movable portion, increasing the rising speed. This speed is monitored by software from point ■° onwards.

The rising speed vup is obtained by multiplying the spindle rotational speed command value reversed in step SP3 by the screw pitch amount P, and when the above-mentioned monitored speed becomes, for example, (1,1 to 1.2) XVup or more, (1, 1-1.2) Switch the control mode from "torque control" to the original "position control" so as to control the speed of XVup (step 5P33).

In this embodiment, the above switching is performed by monitoring the detected speed of the feed axis, but in another embodiment,
It is also conceivable to memorize the position data when the tap tool 220 is contacted in step SPI, and use this position as a switching mark when pulling out the tap tool 212.

Step SP4 (SF41.5P42): Since the feed axis is under normal position control, it is easy to stop the feed axis at the zero point. Normally, the positions of the 0 point and the 0 point in the Z direction are the same. Further, the rotation of the main shaft 210 may be stopped at any timing, if necessary, from immediately after the tap tool 212 is removed from the workpiece 220 at the 0 point. In Figure 4,
The figure shows that the spindle 210 is still rotating after the spindle head 203 has been positioned at the zero point.

This embodiment shows the most basic example, but as an applied example, in the operations of steps SPI to SP4, especially in the case of a small diameter tap, cutting due to breakage of the tap tool, etc.
Although a return operation may be performed, it is also conceivable to carry out this control while performing the feed shaft torque control in steps SP2 and SF3, and equivalently to perform step SP2. Furthermore, as an example of reducing the machining cycle time, the main shaft 210 is rotated in step SPl, and using the rotation speed N and the thread pitch P of the tap tool 212,
Let the feed rate V shown by the above formula (2) be Vdown,
Follow the feed axis and lower it.

The method for detecting contact with the workpiece is as follows: (1) Sudden change and direction of change in the torque command value of the feed axis (2) Sudden change and direction of change in the torque command value of the spindle (2) A method of detecting contact with the workpiece using either or both of them, and then entering processing in step SP2 can also be considered. Further, there is also a means of using an AE sensor or the like to detect the above-mentioned contact.

If the thrust force shown in equation (8) is performed during tapping, the function generator will be in charge of only 1° in Fig. 5, and when considered at any point on the cutting edge of the tapping tool, Fig. 6 As shown in Fig. 7, thrust is generated only by the rotation angle command value of the spindle in the direction of the trajectory that should always be machined. Deformation is completely eliminated. In other words, the thrust of the two axes is generated from the two command values, which is equivalent to one-axis control, and the control is performed so that the thrust is always generated at the cutting edge of the tap tool 212 in the direction P in FIG. 7.

Also, in the above equation (8), when the main shaft rotates, 2Ts
>> Fdown ---(14), and the influence of Fdown on the thrust direction P in FIG. 7 is almost eliminated. Therefore, the thrust angle deviation as explained in FIG. 14 does not occur. This is because thrust is always applied in the direction in which the tap tool itself should cut, without having to re-instruct the machining trajectory shape from the control system. The deformation of will disappear. Accordingly, conventionally there have been the following limitations in order to reduce the difference in tracking errors between the main spindle and the feed axis.

(1) Sudden acceleration/deceleration restriction of the spindle (2) Control of high-speed machining during synchronous control However, it is easy to increase the load on the tap tool to an appropriate level, and as a result, high-precision machining can be performed in a short time comparable to conventional methods. This was made possible by the control performance of the spindle. (8)
Similar effects can be obtained using thrust control methods other than those using the above principle.

(Effects of the Invention) As described above, according to the control method of the present invention, the feed shaft can move freely according to the thread pitch amount of the jit tap tool, thereby eliminating deformation of the thread and reducing the machining cycle time. It can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus for realizing the method of the present invention, FIG. 2 is a flowchart showing an example of its operation, and FIG.
Figures (A) and (B) are block diagrams showing an example of a combination of a feed shaft to which the control method of the present invention is applied and a main shaft to which position (angle) control is applied; FIG. 5 is a block diagram showing another embodiment of the present invention; FIGS. 6 and 7 are diagrams for explaining the present invention in detail; Figure 8 is a diagram showing how tapping is performed by an NC machine tool to which the wood invention can be applied, Figure 9 is a diagram showing how tapping is performed by a human, and Figure 10 is a diagram showing a conventional feed axis control system. FIG. 11 is a block diagram showing a conventional synchronization control system for the rotational speed of the main spindle and the position of the feed axis, and FIGS. 12 to 14 are diagrams for explaining tapping processing. 1.1'...Function generator, 2,2°...Position detector, 3,6,9゜3゛,6°,9°...Subtractor, 4,7
, 10, 4°, 7°, lO'...Amplifier, 5.5゛・
・・Speed detector, 8,8°・・Torque detector, 13・
...Torque command setting value storage section, 100, 212...Tap tool, 210...Main φ thread, 220...Work. Applicant's agent Yu Yasugata 3 2nd normal rotation ↑ Spindle rotation Maki Hayabusa 6 已υ (ri axis position!

Claims (1)

[Claims] 1. A tapping control method for a numerically controlled machine tool that performs position control, characterized in that tapping is performed by switching the control mode from position control to torque or thrust control. . 2. A claim in which tapping processing is started according to a command on a cutting program, the control mode is automatically switched during the processing process, and the control mode is automatically returned to the original state by the end of the processing process. The tapping control method according to item 1. 3. The tapping control method according to claim 1, wherein after switching the control mode, the detected position value and the detected speed value are used for monitoring an abnormal state, detecting a break point of an operation sequence, etc. 4. The tapping control method according to claim 1, wherein the torque command value for the feed shaft torque control is calculated using the torque command value of the main shaft during cutting by the tapping tool. 5. The tapping control method according to claim 1, wherein the torque command value during torque control of the feed shaft is set to a fixed value or a value proportional to the spindle rotation speed based on the appropriate load torque of the tapping tool.