JPS6116581B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tool abnormality monitoring method, and in particular, it stores changes in the spindle motor current during trial cutting as reference data, and stores changes in the spindle motor current during re-cutting with the stored reference data. The present invention relates to a tool abnormality monitoring method for determining tool abnormality by comparison.

Conventionally, as one of the above-mentioned tool abnormality monitoring methods, data on spindle motor current changes over the entire period from when the spindle motor is started until it is stopped, without considering whether the tool is in the cutting state or not, has been used. A method of comparison with reference data is used. This tool abnormality monitoring method has a problem in that the memory capacity of the reference data becomes enormous.

In addition, in the case of small-diameter tools or light cutting, the difference between the current level during cutting and the spindle motor current level during no-load rotation is small, that is,
Since the current value used for pure cutting is smaller than the current value during no-load rotation, monitoring the absolute level of the spindle motor current will prevent the effects of changes in the current level during no-load rotation due to power fluctuations, etc. This poses a problem in that it is easy to receive errors, resulting in erroneous judgments.

Another conventional tool abnormality monitoring method is
It determines whether the tool is in the cutting state based on electrical continuity between the tool and the workpiece, and only when the tool is in the cutting state, changes in the spindle motor current are compared with reference data to monitor tool abnormalities. There is a method to do this.

In this method, when the material to be cut produces long and narrow chips, if the chips are wrapped around the tool, conduction may occur even when the tool and the material to be cut are far apart. , which makes monitoring inaccurate. The tool breakage detection device using this method is
This poses a practical problem because the position at which the tool is sent out from the reference position and becomes conductive may vary each time due to elongated chips generated by cutting.

Another conventional tool abnormality monitoring method is
There is a method in which the no-load rotation state of the spindle motor is continued for a certain period of time by a dwell or the like, and tool abnormalities during cutting are monitored based on the level of the spindle motor current during that time purely based on the current required for cutting.

This method has the problem that monitoring of tool abnormalities becomes inaccurate when the spindle motor changes speed during cutting because the current level when the spindle motor rotates under load changes depending on the rotation speed. If we use a method to determine the current level during no-load rotation every time the main shaft motor changes speed,
It becomes necessary to restrict machining until the current value stabilizes, which reduces machining efficiency.
No favorable results are obtained.

In view of the above-mentioned problems with the conventional type, the main object of the present invention is to track changes in spindle motor current in a tool abnormality monitoring method that determines tool abnormalities based on reference data during trial cutting. Based on the idea of determining the current level during load rotation every time before cutting begins and determining the cutting state, we compared the value of the spindle motor current required for pure cutting only when the tool is in the cutting state with reference data. The purpose is to make it possible to reliably determine tool abnormalities even in the case of small-diameter tools or light cutting, and to reduce the memory capacity of reference data.

In the present invention, tool abnormality monitoring involves storing changes in spindle motor current during trial cutting as reference data, and comparing changes in spindle motor current with the stored reference data during recutting to determine tool abnormality. In the method, the no-load rotation current level and cutting current level of the spindle motor are determined from changes in the spindle motor current using a smoothing circuit with a short time constant and a smoothing circuit with a long time constant, and the no-load rotation The current level during no-load rotation is subtracted from the cutting current level of the spindle motor when it is in the cutting state based on the judgment result. A tool abnormality monitoring system is provided, which is characterized in that a current value obtained by the method is compared with the stored reference data to thereby detect a tool abnormality.

A tool abnormality monitoring device used in a tool abnormality monitoring method as an embodiment of the present invention is shown in FIG. In Figure 1, 1 is an NC machine tool, 2
is a tool abnormality monitoring device.

The tool abnormality monitoring device 2 includes a primary smoothing circuit 21,
Secondary smoothing circuit 22, subtraction circuit 23, no-load rotation current memory 24, comparison circuit 25, cutting state judgment data memory 26, cutting state judgment circuit 27, mode switching circuit 28, reference data memory 29, abnormality detection data memory 30 , a tool abnormality detection circuit 31, and an alarm signal generation circuit 32 are provided. The mutual connections and functions of circuits and the like in the tool abnormality monitoring device 2 will be explained below.

As shown in FIG. 1, a spindle motor current detection signal from the NC machine tool 2 is connected to a primary smoothing circuit 21. In the primary smoothing circuit 21,
Changes in the spindle motor current are smoothed by a relatively short time constant sufficient to eliminate pulsation components. The output of the primary smoothing circuit 21 is connected to a secondary smoothing circuit 22 and a subtraction circuit 23. Secondary smoothing circuit 22
In this case, the main shaft motor current is smoothed by a relatively long time constant. The output of the secondary smoothing circuit 22 is connected to a comparison circuit 25.

The output of the primary smoothing circuit 21 and the output of the no-load rotation current value memory 24 are connected to the subtraction circuit 23 . The output of the subtraction circuit 23 is connected to a cutting state determination circuit 27. The output of the subtraction circuit 23 and the output of the cutting state determination data memory 26 are connected to the cutting state determination circuit 27 . In the cutting state determination circuit, a signal indicating whether or not the tool is in the cutting state is generated, and this signal is supplied to the current memory 24 during no-load rotation.

The current memory during no-load rotation also includes a comparator circuit 2.
5 is connected to the comparator circuit 25, and conversely, the output of the no-load rotation current memory 24 is connected to the comparator circuit 25.
The no-load rotation current memory 24 receives the output signal of the secondary smoothing circuit 22 during no-load rotation via the comparison circuit 25 according to the signal from the cutting state determination circuit 27. The minimum value of the output signal of the circuit 22 is determined by this, and this minimum value is stored as the current value during no-load rotation.

In the subtraction circuit 23, the difference between the output signal of the primary smoothing circuit 21 and the output signal of the no-load rotation current memory 24 is determined, and the signal of this difference is supplied to the cutting state determination circuit 27. In the cutting state determination circuit 27, the output of the subtraction circuit 23 and the output of the cutting state determination circuit data memory 26 are compared to determine whether or not the tool is in the cutting state. The output of the cutting state determination circuit 27 is connected to a mode switching circuit 28.

In the mode switching circuit 28, a teaching cutting mode and a monitoring cutting mode are selected. In the teaching cutting mode, the output signal of the subtraction circuit 23 is supplied via the cutting state determination circuit 27 and is supplied to the reference data memory 29 via the mode switching circuit 28. In the reference data memory 29, the above signal is stored as reference data. Also,
In the monitoring cutting mode, the cutting state determination circuit 2
The signal supplied from 7 is transmitted to the tool abnormality detection circuit 31 via the mode switching circuit 28.

The tool abnormality detection circuit 31 includes the output of the mode switching circuit 28 as well as the reference data memory 28.
and the output of the abnormality detection data memory 30 are connected. In the tool abnormality detection circuit 31,
Mode switching circuit 28 when the tool is in the cutting state
A signal of the current value purely required for cutting supplied from the controller is compared with reference data stored in the reference data memory 29, and it is determined whether or not a tool abnormality has occurred based on the data from the abnormality determination data memory 30. will be held. When the occurrence of a tool abnormality is detected, the tool abnormality detection circuit 31 supplies an output signal to the alarm signal generation circuit 32 and activates the alarm signal generation circuit 32. The alarm signal generation circuit 32 is
In response to the signal from the tool abnormality detection circuit 31, a signal indicating the occurrence of tool abnormality is supplied to the NC machine tool.

FIGS. 2 1 to 4 show various current waveforms showing changes in the spindle motor current during cutting.

The operation of the tool abnormality monitoring device 2 shown in FIG. 1 will be explained below using the current waveform diagram shown in FIG. Figure 2 1
shows a typical change in spindle motor current in the case of small-diameter tools or light cutting. As shown in FIG. 2 1, the current change in the above case has an extremely large peak value immediately after startup, and thereafter the current value decreases until the current value I ₀ during no-load rotation.
decreases to When the tool enters the cutting state, the spindle motor current increases by the amount of current required for cutting. In the case of a small-diameter tool or light cutting, this increase in the spindle motor current I _V is smaller than the current value I ₀ during no-load rotation.

FIG. 2 shows an example of a case where a tool abnormality occurs due to the above-mentioned change in the spindle motor current. For example, if the tool wears out, the current required for cutting increases. Also, if the tool breaks,
The main shaft motor current temporarily increases and then decreases to the current value during no-load rotation. The tool abnormality monitoring device 2 shown in FIG. 1 detects the occurrence of tool abnormality by monitoring abnormalities in changes in the spindle motor current as described above.

As shown in FIG. 1, a detection signal of the spindle motor current is supplied from the NC machine tool 1 to the primary smoothing circuit 21 of the tool abnormality monitoring device 2. The current detection signal from the NC machine tool 1 includes a pulsating component as shown in FIG. 2. Primary smoothing circuit 21
has a relatively short time constant, thereby eliminating the pulsating component in the spindle motor current detection signal and obtaining a smoothed change curve of the spindle motor current as shown in FIG. This smoothed current variation is referred to below as the cutting current level.

The current detection signal smoothed in the primary smoothing circuit 21 is further supplied to the secondary smoothing circuit 22,
It is smoothed with a longer time constant than in the primary smoothing circuit. As described above, the current level during no-load rotation is determined from the main shaft motor current signal smoothed in the secondary smoothing circuit 22. This current level during no-load rotation is Y ₁ ,
Denoted as Y ₂ , Y ₃ . In FIG. 2, the cutting current levels are indicated as X ₁ , X ₂ , and X ₃ . As shown in FIG. 2, the difference between the two current levels, ie, Zi=Xi-Yi, when the tool is in the cutting state, indicates the change in the current value required for cutting. This Zi is obtained as the output of the subtraction circuit 23 and supplied to the cutting state determination circuit 27.

The determination circuit 27 determines whether or not the tool is in a cutting state based on the change in Zi. From the time when it is determined that the cutting state is reached until one cutting process is completed, that is, T ₁ ,
For each period shown as T ₂ and T ₃ , the current value required for cutting, Zi=Xi-Yi, is compared with pre-stored reference data. Therefore, the current value to be stored as the reference data is sufficient only for the period in which the cutting state is in progress, and the memory capacity of the reference data can therefore be small.

The current level Yi during no-load rotation is determined as described above each time one cutting period is completed. Therefore, even if the main shaft motor current during no-load rotation changes due to power supply fluctuations or the like, it is possible to prevent erroneous determination from occurring.

According to the present invention, in a tool abnormality monitoring method for determining tool abnormality based on reference data during trial cutting, occurrence of tool abnormality can be reliably detected in the case of small-diameter tools or light cutting. The memory capacity of the reference data can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a tool abnormality monitoring device used in a tool abnormality monitoring system as an embodiment of the present invention, and Fig. 2 1 to 4 explain the operation of the tool abnormality monitoring device of Fig. 1. FIG. 4 is a current waveform diagram showing changes in main shaft motor current used for this purpose. Explanation of symbols, 1: NC machine tool, 2: Tool abnormality monitoring device, 21: Primary smoothing circuit, 22: Secondary smoothing circuit, 23: Subtraction circuit, 24: Current memory during no-load rotation, 25: Comparison circuit, 26 : Cutting state judgment data memory, 27: Cutting state judgment circuit, 28: Mode switching circuit, 29: Reference data memory, 30:
Abnormality detection data memory, 31: Tool abnormality detection circuit, 32: Alarm signal generation circuit.

Claims (1)

[Claims] 1. A tool that stores changes in spindle motor current during trial cutting as reference data and compares changes in spindle motor current with the stored reference data during recutting to determine tool abnormality. In the abnormality monitoring method, the no-load current level and the cutting current level are detected for each cutting state during trial cutting, and the current value obtained by subtracting the no-load current level from the cutting current level is stored in memory and reused. During cutting, the no-load current level and the cutting current level are detected for each cutting state, these two levels are used to determine whether or not the machine is currently in the cutting state, and based on the determination result, it is determined whether the machine is currently in the cutting state. A tool abnormality monitoring method characterized in that, at times, a tool abnormality is detected by comparing a current value obtained by subtracting a no-load current level from a cutting current level of the spindle motor with a current value stored in the memory. .