JPS5997829A - Method of detecting tool abnormality - Google Patents

Abstract

PURPOSE:To detect the abnormality of a tool through a method of comparing the load on normal maching with the load varied due to aging effect, without causing any erroneous detection at the time of switching the cutting condition, by interrupting the function of judging occurrence of abnormality for the predetermined period, when the cutting condition is switched. CONSTITUTION:During the signal monitoring period which continues from the start of cutting to the end of cutting of cutting start/end signals J, the monitoring of signals is interrupted during the time T1 following a cutting start signal and the time T2 following a high-speed cutting start signal. During these hours, any variation in comparison signals exceeding allowable variation ranges is determined not to be judged as the occurrence of abnormality. Further-more, the monitoring of signals is equally interrupted from the point a T3 hour before the cutting end signal to the cutting end signal. Thereby any erroneous judgement caused by the instability of signals on switching the cutting condition can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the occurrence of an abnormality in cutting work with a machine tool. especially.

(1) Successively compare the load fluctuation over time (reference signal) memorized during normal cutting with the load fluctuation during actual cutting (comparison signal), and check whether the deviation amount of the comparison signal with respect to the reference signal exceeds the permissible fluctuation range. The present invention relates to a method for setting an interval in which the comparison signal and the reference signal are to be successively compared when putting into practical use a tool abnormality detection method that determines whether or not an abnormality has occurred.

A conventional example of this type of method is shown in FIG. In the figure.

Reference numeral 1 denotes a load detection device, which converts a load (for example, morph current) caused by driving the main shaft or feed shaft of a machine tool into a signal (for example, a voltage signal) that can be recorded in the memory bag M2. Reference numeral 8 denotes a comparison device, which compares a signal port detected by load detection during actual operation with a reference signal C already stored.

Reference numeral 4 denotes a delay device, which outputs one alarm signal when the input signal E continues to occur for longer than a separately set delay time G (when a certain predetermined condition is satisfied).

In such a configuration, a start signal (2) (not shown) is used to store the change over time in the normal load detected by the load detection device 1 along the path shown by the solid line in the figure in the storage device 2 as a reference signal. The storage is terminated by a stop signal (not shown). Detection of overload in subsequent work is carried out along the path shown by the dotted line in Figure 1 between the start signal and the stop signal.

The value of the signal port obtained by load detection is successively compared with the value of the standard signal C corresponding to that time, and the load signal (
When the amount of deviation of the comparison signal (comparison signal) deviates from a separately set tolerance range, an overload signal is output. Then, when the overload signal (e) continues for more than a separately set delay time (t), one alarm signal is generated.

Here, the allowable range 1 is set as a percentage or an absolute amount of load (for example, α ampere), with the reference signal value corresponding to the time to be compared being 100%.

Since this method compares the load fluctuation with the reference signal over time, it is possible to monitor the condition in detail, including sequence malfunctions.Furthermore, a delay circuit is installed to detect abnormal conditions after a certain period of time has elapsed. It has the advantage that it is less susceptible to the effects of power supply noise, for example, in that it generates an alarm signal only when the alarm signal is generated.

However, when this method is applied to actual cutting work on site, there is a first-order problem due to the method of setting the interval for successive comparison of the comparison signal and the reference signal.

That is, if the cutting conditions change during one continuous cutting process (this is often the case in hole machining, especially deep hole machining), the entire process cannot be monitored properly.

About this.

This will be explained with reference to FIG.

FIG. 2 shows the signal state during actual drilling of a certain hole. ■ and ■ are observations after converting the relay contact signals instructing start/end of cutting and start/end of high-speed cutting into voltage signals, respectively, and arrows a + b + c in Figure 2.
Each operation is performed at the times indicated by .

■ is the observed current of the main shaft motor at that time,
■ is the feed shaft motor current.

As can be seen from FIG. 2, the signal level suddenly changes (or relatively largely fluctuates) when the cutting conditions are changed (immediately after the start of cutting, immediately after the start of high-speed cutting, and immediately before the end of cutting).

This is indicated by a ■ mark in the figure.

In this way, the tool abnormality detection method explained in FIG.
When applied to cutting work that shows signal changes as shown in the figure,
Misjudgments were made at the points marked with ■ in Figure 2 (even though no tool abnormality had occurred).

(judged as abnormal) occur frequently. This is because the signal levels of both the reference signal and the comparison signal are unstable at the portions marked with ■.

In view of the problems of the conventional tool abnormality detection method by monitoring the load over time, the present invention aims to provide an effective method that can be applied to actual cutting work in the field. This method is characterized by preventing erroneous determinations by interrupting the determination of whether an abnormality has occurred for a preset period of time (immediately after the start of cutting, immediately after the start of high-speed cutting, immediately before the end of cutting, etc.).

Hereinafter, one embodiment of the present invention will be explained based on the drawings.

FIG. 8 is a diagram showing changes in the switching signal and motor current, similar to the above-mentioned FIG. However, among these, T1 time from the cutting start signal,
Signal monitoring is suspended for 72 hours from the high-speed cutting start signal.

That is, during this time, even if the comparison signal mentioned above fluctuates beyond the permissible fluctuation range, it is not determined that an "abnormality has occurred". Furthermore, signal monitoring is similarly interrupted from 78 hours before the cutting end signal until the cutting end signal.

By doing so, it is possible to avoid erroneous determinations caused by signal instability when switching cutting conditions.

Incidentally, THI T2 can be set based on the rising time of the signals (2) and (2), respectively. T8 can be set by monitoring a number of data from the total number of data sampling and the data sampling interval at the time of storing the reference signal to a number of data corresponding to T8.

An example of setting TI, T2+'rs is shown in FIG. In addition, in Figure 4, the same symbols as in Figure 1 are attached to the same specifications as in Figure 1.

It has a function. That is, 1 is a load detection device, 2 is a storage device, 8 is a comparison device, and 4 is a delay device.

Reference numeral 5 denotes a gate device, which is opened and closed by a gate control signal O, and allows and cuts off an overload signal E.

Gate control signal 9 is not shown in this embodiment, but is created by hardware or software, and controls the gate device 5 only during the time period corresponding to 'r, , 'r, , T9 in FIG. 3. The gate device 5 is manually operated to close. By doing this, T...
T2. In the time zone 'r8, even if the comparison signal mentioned above fluctuates outside the allowable fluctuation range, the overload signal ■
is not input to the delay device H4, and it is possible to prevent it from being determined that "an abnormality has occurred".

In this embodiment, a cutting process in which cutting conditions are changed as shown in FIG. 8 was explained as an example, but it is of course applicable to other cutting processes without changing the gist of the present invention. be.

As explained above, by adopting the method according to the present invention, even in machining where the cutting conditions are switched during machining, erroneous detection when switching between two conditions will not occur (
, it becomes possible to put into practical use a tool abnormality detection method based on a comparison method with the change in load over time during normal machining.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional method, and FIG. 2 is a diagram illustrating problems with the conventional method. FIG. 8 is a diagram for explaining the present invention, and FIG. 4 is a block diagram showing implementation-1 according to the present invention. DESCRIPTION OF SYMBOLS 1... Load detection device, 2... Storage device, 8... Comparison device, 4... Delay device, 5... Gate device. (9) 13

Claims (1)

[Claims] During cutting operations that are performed according to an automatic cutting program that includes the workpiece, tool type, and cutting conditions, changes in the load applied to the drive system over time are stored in advance as a reference signal, and further variations are tolerated based on the reference signal. The range is set, the deviation of the corresponding load from the reference signal is monitored in subsequent cutting operations under the same conditions, and the presence or absence of tool abnormality is determined based on whether the deviation is within the variation tolerance range. A tool abnormality detection method characterized in that the determination of whether an abnormality has occurred is temporarily interrupted when cutting conditions are changed during a cutting process.