JPS6236826B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to tool breakage detectors.

Conventional tool breakage detectors detect machine tool vibration using a vibration detector attached to the machine tool.
Tool breakage was detected by detecting large vibrations when the tool broke.

However, simply monitoring the magnitude of machine tool vibration makes it difficult to distinguish between vibrations caused by spindle rotation stoppage and turret rotation that occur in addition to tool breakage, and vibrations caused by tool breakage. Hard to reach. Therefore, in order to reduce the influence of vibrations caused by stopping the rotation of the spindle or rotating the turret, this can be achieved by increasing the detection level and detecting only high vibrations. However, on the other hand, it has the disadvantage that low-level vibrations cannot be detected, which reduces the detection rate of tool breakage. On the other hand, if the level value is kept low, noise caused by causes other than tool breakage will be detected.
Signals to stop machining are issued frequently, reducing work efficiency.

The present invention has been made based on the above-mentioned drawbacks, and uses a detector to detect abnormal vibrations that occur during turning as an electric signal, as well as detect the rotation period of the spindle, and use these detected values to detect tool damage. An object of the present invention is to obtain a tool breakage detection device that detects tool breakage.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a vibration detector 1 is a detector made of, for example, a piezoelectric element, which is fixed to a lathe or a cutting tool and detects vibrations generated during turning as an electric signal. The vibration detector 1 is connected to an amplification circuit 2 that amplifies the electrical signal output from the vibration detector. A rectifying and smoothing circuit 3 is connected to the amplifying circuit 2, and rectifies and smoothes the amplified electrical signal by this circuit. A first comparator 4 is connected to the rectifying and smoothing circuit 3. The first comparator 4 compares the electrical signal input from the rectifying and smoothing circuit 3 with a set value A, and outputs a smoothed signal as the set value A.
When it becomes larger, one pulse is output to the next pulse interval detector 5. The pulse interval detector 5 detects the pulse interval output from the first comparator, and is connected to a subtracter 6. On the other hand, the main shaft rotation period detector 7 includes, for example, an encoder, detects the rotation period of the main shaft, and outputs it to the subtracter 6. The subtracter 6 is
The difference between the pulse interval value from the pulse interval detector and the period value of the spindle rotation from the rotation period detector 7 is calculated, and the absolute value of the calculated value is output to the second comparator 8. The second comparator 8 compares the absolute value output from the subtracter 6 with a set value B set in the second comparator, and outputs a control signal C if the absolute value is smaller than the set value. Output.

Next, the operation of the tool breakage detection device having the above configuration will be explained.

The vibration detector 1 detects abnormal vibrations generated by turning as an electrical signal, and the amplifier 2 amplifies this electrical signal. The electrical signal amplified by the amplifier 2 is rectified and smoothed by a rectification and smoothing circuit 3 and input to a first comparator 4 . The smoothed signal input to the first comparator 4 is compared with a set value A, and when the input signal becomes larger than the set value A, one pulse is output. Here, if the output from the rectifying and smoothing circuit 3 is examined using a recorder or an oscilloscope when machining continues with the cutting tool damaged, the output will be similar to the rotation period of the spindle as shown in Figure 2. There is an output due to large vibrations. This is because cutting after the tool breaks becomes an interrupted cutting process. The reason why abnormal vibrations occur intermittently during turning after tool breakage is as follows. That is, first, when the tool breaks, the first large abnormal vibration occurs. The tool damage at this time is relatively minor, such as chipping of the cutting edge, and if some of the cutting edges remain in normal condition, the depth of cut will change slightly depending on the amount of damage at the time of damage. do.
Therefore, a stepped portion is generated in the workpiece due to the damage. On the other hand, since the cutting tool is fed at a constant speed even after being worn out, cutting is performed with the aforementioned small depth of cut. However,
When the main shaft rotates once and the stepped portion of the workpiece hits the portion of the cutting tool remaining after chipping, the depth of cut increases rapidly. As a result, second chipping occurs and a second large abnormal vibration occurs. This also creates a stepped portion on the workpiece similar to the initial chipping. However,
Due to the stepped portion caused by this second chipping, a third chipping is induced again when the main shaft rotates once, and a third large abnormal vibration and a stepped portion of the workpiece are generated. Hereinafter, such chipping and the stepped portion of the workpiece induced by this chipping will occur intermittently every time the spindle rotates, that is, until the depth of cut of the cutting tool is averaged in synchronization with the rotation of the spindle. and occurs in a decaying manner. Based on these facts, we can compare the periodic large abnormal vibrations that occur during intermittent cutting due to tool breakage with the rotation period of the main shaft of the lathe, and if these periods approximately match, the cutting tool is damaged. It can be determined that there is a

The electric signal detected by the vibration detector 1 is compared with the set value A set in the first comparator 4, and only when a signal larger than the set value A is input, the pulse interval detection value 5 is changed to 1 pulse. is input. The pulse interval detection value 5 detects the pulse interval input from the first comparator 4 and outputs the interval value to the subtracter 6. On the other hand, the rotation period detector 7 detects the rotation period of the main shaft and outputs the period value to the subtracter 6. In the subtracter 6,
The difference between the pulse interval value from the pulse interval detector 5 and the rotation period value of the main shaft from the rotation period detector 7 is calculated as an absolute value, and the absolute value is output to the second comparator 8. The second comparator 8 compares the set value B with an absolute value, and if the absolute value is smaller than the set value, it determines that the tool is damaged and outputs a control signal C. By the above control signal C,
Immediately deal with damage to the cutting tool by stopping the feed of the cutting tool or issuing an alarm signal.

As described above, the present invention detects abnormal vibrations occurring during turning using a vibration detector, and compares the electrical signal obtained by the vibration detector with the set value of the first comparator. Then, the pulse interval value of the pulses output from this first comparator is detected by a pulse interval detector, and the rotation period value of the spindle is detected by the rotation period detector. The system is designed to detect damage to the tool. In other words, since the periodic value of abnormal intermittent turning vibrations caused by cutting tool damage has a relationship that roughly matches the rotational period of the spindle, the absolute value of the subtracted periodic value can be calculated as appropriate. By comparing it with the set value, it is possible to detect the damaged state of the cutting tool during turning, regardless of the turning conditions.
In particular, it is possible to accurately distinguish between tool damage and other vibrations, improving the detection rate of tool damage, and eliminating problems such as machining stops based on detection signals, thereby avoiding a decrease in work efficiency.

Note that a command value of the spindle rotation speed of a numerical control device or other control device may be used instead of the spindle rotation period detector.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a graph showing the waveform of the output signal from the first comparator. 1... Vibration detector, 3... Rectifying and smoothing circuit, 4... First
comparator, 5... pulse interval detector, 6... subtractor,
7... Rotation period detector, 8... Second comparator.

Claims (1)

[Claims] 1 A vibration detector that detects vibrations generated during turning and outputs an electrical signal, and compares the electrical signal obtained from the vibration detector with a set value and generates a pulse every time an electrical signal greater than this set value is input. a first comparator that outputs a signal; a pulse interval detector that detects the pulse interval of output pulses from the first comparator and outputs a pulse interval value; A rotation period detector that detects and outputs the period value, and calculates the absolute value of the difference between the pulse period value detected by the pulse period detector and the rotation period value detected by the rotation period detector. and a second comparator that compares the absolute value obtained from the subtracter with a set value and outputs a tool breakage signal when the absolute value is smaller than the set value. vessel.