JPH0132023B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting tool breakage, particularly when the same type of machining cycle is repeatedly executed.
The present invention relates to a detection method for detecting breakage of the tool in one machining cycle in the next machining cycle.

In machining processes such as drilling and tapping using numerically controlled machine tools, the machining program is usually configured to sequentially machine several to even several dozen pieces of one workpiece.

The present applicant previously filed Japanese Patent Application No. 131848/1984,
In No. 107906, etc., a method is disclosed that takes a drill or a milling cutter as an example of a tool and detects breakage of the tool in advance or immediately after breakage during actual cutting. Of these, the former method successively compares the actual cutting current value i of the spindle motor that rotates the drill as a tool with the actual cutting current value i0 during normal drilling stored in memory etc. When α=i/i0 exceeds the value of a predetermined system parameter K, it is determined that there is a breakage.

However, in this method, it is necessary to modify the value of the parameter K to some extent depending on the diameter of the drill that is the tool, and even if the diameter is the same for the types of tools, such as a drill and a tap. The values of K are different. Furthermore, in cases where the ratio α is close to the value of the parameter K and therefore the determination is delicate, a breakage determination may not be made even though the tool is actually broken (such a case may be caused by the selection of the value of the parameter K). In the next machining cycle, the tool that broke in the previous cycle will be used as is.Therefore, this method detects the tool breakage during the machining process. For each broken tool, the next machining cycle will proceed as is, and if several dozen such machining cycles continue, the machining time that follows is completely wasted. It turns out that.

Next, in order to clarify the gist of the present invention, problems with the conventional method will be explained with reference to FIGS. 1 to 4. FIG. 1A is a block diagram illustrating the progress of the process when tapping is performed continuously when a tap is used as the tool. In FIG. 1A, 11 indicates a start command for the main shaft motor for tap rotation. Reference numeral 12 indicates a tap processing process, and this processing process consists of two steps, the first of which is the tap T1 as shown in FIG.
is moved in rapid traverse to the reference line Ref (separated by a certain distance from the surface of the workpiece W) directly above the prepared hole H1. In the second step, the tap is sent downward from the same line Ref in a cutting feed state for tapping into the prepared hole H1 of the workpiece W. Note that normally, the tap T1 is already in a normal rotation state before reaching the line Ref as shown by the arrow.

Reference numeral 13 is a reverse rotation command for the main shaft motor, and this command causes the tap T1 to stop its downward movement, including its forward rotation, and then proceed to the tap removal step 1.
At step 4, the main shaft rotates in the opposite direction, and the tap T1 is moved upward. When the tap T1 returns to the line Ref in FIG. 2 in the tap removal step 14, the main shaft motor is commanded to rotate in the forward direction in step 15, and the tap machining shown in step 12 is started again.

However, for the next tap machining, the tap T1 is relatively moved to the line Ref immediately above the next prepared hole H2 with respect to the workpiece W, as shown in FIG. (First step in the machining process of the prepared hole H2) During this time, the tap T1 remains in the forward rotation state.

FIG. 1B is a block diagram of a circuit for detecting the spindle motor current i. Reference numeral 21 denotes a motor current detecting section which can detect the current using a shunt current or a current transformer (CT) method.

22 is an RMS circuit that performs root mean square processing on the signal detected by the detection unit 21, and 23 is a low-pass filter that filters high frequency components of the RMS circuit output. The state in FIG. 2 shows the state in which the tapping process for the prepared hole H1 has been completed and the tap T1 has returned to the line Ref. The condition is, for example, from the other pilot hole H2
Fast-forward horizontally to the position directly above the same hole H2.
This shows the state in which screw machining has started.

' indicates that the tap T1 was moved to a position above another prepared hole H2' while being broken from its base during the machining process.

Characteristics of tap machining The load current (main spindle motor current) during cutting is similar to that of drilling.

Since the rotation and feed of the tap are synchronized, there is a nearly one-to-one correspondence between the shape of the type and the cutting conditions when the workpiece material is the same.

Normally, a torque limiter is used in tap machining, so if chips become entangled and the cutting torque increases, the tap becomes idle. However, in reality, tap breakage occurs quite often. This is because the force applied to the tool (tap) is not only cutting torque but also a wide range of factors such as bending moment and vertical force, and misalignment and tilting of the prepared hole can also cause this.

Figure 3 is a measurement waveform diagram depicting changes in the spindle motor current in a video graph when tap machining of 8 mmφ is sequentially performed on a workpiece with a pre-drilled hole, and this figure will now be explained. Then, in the same figure, the waveform data of three consecutive tap machinings of , respectively, shows that normal machining has been performed, and each waveform part a, a of ,
Subscripts of b, c, d, e, f, g (numbers 1, 2,
3) correspond to , respectively, and the same alpha alphabet indicates the corresponding waveform portion of each machining cycle.

The waveform part aj (j = 1, 2, 3) is a part of the tap machining process, and regarding the tap T1, it is cutting feed, but it has not yet reached the pilot hole of the workpiece, and on the other hand, the spindle motor current i As shown in the figure, is relatively close to the reference level RL (for example, the value when the spindle rotation is stopped) and is in a state of idle cutting. The next waveform portion bj (j=1, 2, 3) is a substantial part of the tapping process and shows that the prepared hole is actually tapped by the tap T1. The first step of the above-mentioned tapping process,
To show the correspondence with the second step, the tap processing step is (aj+bj), but the first step is a part of aj. The next waveform part Cj (j=1, 2, 3) shows the transition part when moving from the tapping process to the tapping process. The main shaft motor was reversed to prevent tapping.

The waveform dj (j=1, 2, 3) corresponds to the starting current when the main shaft motor starts to rotate in reverse.

The next waveform portion ej (j=1, 2, 3) corresponds to a so-called tapping operation, and the main shaft motor current i in the reverse rotation state has a larger variation range than in the idle (aj) state.

The next waveform portion fj (j = 1, 2, 3) corresponds to the transition state of the spindle motor from reverse rotation to forward rotation, and the next waveform portion fj (j = 2, 3, 4) corresponds to the transition state of the spindle motor from reverse rotation to forward rotation. It corresponds to the instantaneous starting current when it starts rotating.

In the same figure, for example, there is a difference in the time interval between a2 and a3 because the distances to the next prepared hole position on the workpiece are different, and the main shaft motor, that is, the tap T1, continues to rotate in the normal direction during that time. be.

Figure 4 shows that two tap machining operations are performed consecutively, and if a breakage occurs during the first tap machining, and the breakage cannot be detected using only the method using the system parameter K described above, the second tap machining process is performed. This explains how the result is that no processing is performed.

In the figure, gn is the starting current waveform when the spindle motor rotates forward in the n-th tap machining, an, bn are idle cutting and actual cutting waveforms, cn is the waveform in the transition state from forward rotation to reverse rotation, and dn is the reverse rotation. The starting current during rotation, en is the waveform diagram in the tap removal state, fn is the waveform in the transition state from reverse rotation to forward rotation, and gn+1 is the normal rotation starting current waveform for the next tap machining. Below an+
1,bn+1,cn+1,dn+1,en+1,fn+1,
gn+2 indicates a waveform portion corresponding to each alpha bet, with only the subscript n changed to n+1.

A in FIG. 4 is a signal corresponding to the forward rotation state of the main shaft motor, and B is a signal corresponding to the forward/reverse rotation conversion of the motor (including the reverse/forward rotation conversion).

Now, in the waveform part bn of the same figure, if the peak value of the waveform when tap T1 breaks at time tBR is ip, and if the system parameter K set for breakage determination is K=K1, then ip>K1 holds true. Therefore, it is possible to immediately form a breakage determination signal, but if K=K2 is set, ip<K2 and this conventional method cannot detect it. Moreover, when breakage occurs, ip cannot be a constant value depending on the cutting conditions at that time, and when K=K3, it is possible that breakage is determined even though no breakage occurs. Therefore, the value of parameter K is K2
It is not easy to decide where to set it between K3 and K3. Now let's consider the case where K=K2 is set. In this case, the next n+1 tap machining command is issued despite the breakage of tap T1. However, as seen in the waveform portions an+1 to bn+1, the motor current value i does not actually increase and remains at the current value i0 corresponding to the idle cutting state. Further, the waveform portion en+1 corresponding to tap removal also corresponds to the idle cutting state and is different from the waveform portion en. In this way, if breakage occurs and it cannot be detected, the tap machining process in which subsequent commands are issued one after another will be issued without actually being machined. Furthermore, in Fig. 4, conventionally, the spindle motor current value i is checked one by one to determine whether, for example, the level has changed from waveform part an to waveform part bn, and therefore whether actual cutting has started after that. function, iK2 was determined only when i(bn)>i(an).
However, in order to determine the state during the machining cycle in this manner, various determination conditions regarding i must be determined in advance as a program. Furthermore, various constraints must be taken into account when setting time conditions for when to perform the above-mentioned judgment calculations.

The present invention was made in view of the above-mentioned problems, and its purpose is to detect that the tool is broken in the next machining cycle when a tool breaks in a certain machining cycle. Therefore, the waveform part an+1 to bn in Figure 4
We propose a new tool breakage detection method that avoids wasteful processes such as +1 and en+1. Therefore, in the present invention, we use time interval signals that include at least the actual cutting process of each machining cycle. It is determined that the tool has already broken depending on whether the current value of the tool rotation spindle motor exceeds a predetermined level value. One of the features of the present invention is that it is free from the need for delicate adjustment of the system parameter K as in the past when setting the level value for the determination and forming the starting conditions for the determination calculation. I have to.

Examples of the present invention will be described below. In this example, tap processing will be described in detail, but the technical idea described here is not limited to tapping.

In other words, (a) tapping and tapping are always interposed between reverse rotation of the motor and forward rotation of the motor. (b) If the tap breaks from the base, the motor current value will not increase.

Based on the facts (a) and (b), breakage of the tap is detected by comparing it with a predetermined current value.

As a time interval signal for comparison and judgment, if a forward rotation signal from the NC device or a reverse rotation signal is obtained, pay attention to the time from the start of forward rotation to the start of reverse rotation, and check whether cutting was performed during that time. Judge by.
Also, forward/reverse signal (SiGNAL=MO3→MO4 or MO4
→MO3) is determined based on whether or not cutting was performed during the three occurrences.

In the above example, the motor current value i is compared with the reference value while the time interval signal exists, but the point is that it is only necessary to check whether or not cutting has been performed during that time. It is also possible to determine whether cutting or non-cutting is to be done based on the vibration waveform of the tool being used.

The determination process in the case where a forward/reverse signal is given from the NC device in the above-mentioned example will be explained with reference to the flowchart shown in FIG.

In Figure 5, step (hereinafter referred to as ST) 1
The breakage detection program is started. In ST2, the contents of the counter CNTR are set to 0. next
At ST3, whether the main shaft motor is rotating in the forward direction or the reverse direction, that is, the rotation state is c1 in Figure 3,
It is determined whether it is in a transition state like f1. this
If NO in ST3, return to ST3 and check whether there is a transition state. If ST3 is YES, the next
Move to ST4 and add +1 to the contents of counter CNTR. Therefore, CNTR is now 1. then
Move to ST5 and check whether it is cutting or not. In this cutting check, the value of the level iCHKL below the values K1, K2, and K3 shown in FIG. 4 is compared with the current value i of the main shaft motor. this level
It is sufficient that iCHKL is larger than the value io during idle cutting, and there is no need to take into consideration delicate value settings as in the case of K1 to K3 mentioned above.

If i>iCHKL>io in ST5, ST5 is
The result is YES, and the process moves to ST6, where the contents of the counter CNTR are set to 0.

ST7 and ST8 are program steps for determining wear and breakage of the tool (tap) during cutting, and may be performed using the motor current method according to the above-mentioned Japanese Patent Application No. 52-131848, or by detecting other vibrations. It may also be possible to detect wear and breakage. In ST7
If YES, the tool is determined to be worn and wear treatment is performed.
The process moves to ST7A, and if YES in ST8, the process moves to breakage processing ST8A via the confluence point B. When ST8 is NO
Moving to ST9, it is checked whether one tapping cutting process has been completed. If it is not finished yet, return to ST8 again. (ST7 is executed only once at the beginning) When the process is finished in ST9, the process moves to ST10 and checks whether all the tapping processes have been completed. With ST10
If NO, the process returns to the confluence point A' and returns to the first step ST5 to check for the next tapping process.

If YES in ST10, end in ST11.

If NO in ST5, the process moves to ST12, where it is checked whether a change in the rotational direction of the spindle motor has been given.

If YES in ST12, move to ST13 and start counter
The contents of CNTR are further incremented by +1.

Next, the process moves to ST14, where it is checked whether the value of the counter CNTR is 3 or not, and if it is 2 or 1, the process returns to the confluence point A'.

If ST14 is YES, it is determined that the item is broken.
Move to the breakage processing program routine of ST8A.

As explained above, in the flowchart of Fig. 5, it is checked in ST5 whether or not cutting has started, and if NO, ST12, ST13,
If the contents of the counter CNTR are successively +1 and successively become 3 through each step of ST14, that is, if the rotation direction of the spindle motor is changed twice in a row but the cutting level is not reached, the previous machining cycle In this way, it is determined that it has broken.

As explained above, in the present invention, tool breakage is detected in the machining cycle following the machining cycle in which the tool broke, thereby avoiding the continuation of wasteful machining cycles. be able to.

Furthermore, in the present invention, the detection level at the time of detection in the next machining cycle can be set to a rough level that can be distinguished from the idle cutting state, so problems such as the conventional setting of the system parameter K do not occur.

Furthermore, in the present invention, there are two states in one machining cycle, excluding transition states such as forward and reverse, idle cutting and actual cutting, and the motor current i is compared with the set level during a time interval that includes both of these states. Therefore, there is no need to set strict conditions as in the past regarding the timing of comparison.

This means that, for example, signals such as MO3 and MO4, which are normally given as external signals by a numerical control device, can be used as time interval signals for detecting tool breakage.

Furthermore, in the present invention, it is also possible to take advantage of the fact that, particularly in the tap machining sequence, the rotation direction is always changed twice in one machining cycle, such as from forward/reverse to reverse/forward. Furthermore, the present invention can be combined with a conventional method (current or vibration method) for detecting breakage during a machining cycle to achieve even more reliable breakage detection.

[Brief explanation of drawings]

Figure 1A is a diagram explaining the progress of each process in tap machining, Figure 1B is a circuit block diagram for measuring the spindle motor current i, and Figure 2 is a diagram showing the relationship between the tap and the workpiece in tap machining. , Fig. 3 is a diagram explaining the spindle motor current waveform when tap machining is performed continuously, and Fig. 4 is a diagram explaining the current waveform of the main shaft motor current in the case where the tap breaks during the first machining cycle. FIG. 5, a diagram showing waveforms, is a flowchart illustrating a group of program commands for detecting breakage according to the present invention. 11...Motor start, 12...Tap processing, 1
3...Motor reverse command, 14...Tap removed, 1
5...Motor forward rotation command.

Claims (1)

[Claims] 1. In a tool breakage detection method in machining, in which the workpiece is cut forward when rotating in the forward direction, and the tool is pulled out when rotating in the reverse direction, a change signal in the rotational direction of the main shaft of the tool is taken out from a numerical control device, and the signal is detected in advance. Therefore, a signal (i1) is set to a value larger than the machining signal value (i0) corresponding to the idle cutting state by the tool, and the spindle rotation direction change signal includes the actual cutting time in the middle. A tool breakage detection method that determines that the tool is broken when a cutting signal i measured during a predetermined number of extractions is smaller than i1.