JPS635214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tool chipping detection device that can automatically detect when a tool is chipped during cutting or the like.

In milling machines and the like, numerical control and tracing control are performed to save labor in machining. In order to improve the machining accuracy of the workpiece, automatic machine tools that perform numerical control or tracing control detect when a tool breaks and use this detection signal to stop the machine tool or issue an alarm. need to occur. Many proposals have been made to date for this purpose. In particular, recently, with the development of various detectors and signal processing techniques, there has been increasing interest in detection during milling, that is, in-process detection methods and devices.

Conventional tool chipping detection focuses on the fact that cutting resistance, cutting temperature, vibration, spindle motor current, acoustic emission, etc. change due to tool chipping, and measures these signals. A method has been used in which tool defects are indirectly detected through processing.

However, in such an indirect detection method, the detected signal, cutting force, cutting Signals such as temperature, vibration, spindle motor current, and acoustic emission are constant, and if there is a signal change when a tool breaks, it can be clearly distinguished, making it possible to detect it.

However, in numerical control or profile control machining, the shape of the workpiece generally changes in a complex manner, and this results in uneven depth of cut, cutting width, etc., so even during normal cutting, There was a problem in that the detection signal fluctuated so much that it was difficult to distinguish it from a case where a tool was missing. That is, the conventional tool defect detection device is not suitable for practical use in the above-mentioned machining, and requires a person to monitor the cutting state during machining, which is a major obstacle to unmanned machining.

This invention eliminates such obstacles and enables indirect detection of tool breakage during machining, which can be applied to many types of machine tools and can accommodate different cutting conditions depending on the shape of the workpiece. It is an object of the present invention to provide a tool defect detection device.

The tool chipping detection device of the present invention utilizes the power or current (power consumption or current consumption) value of the spindle motor of a machine tool during cutting, and detects when a tool is chipped.
We extract the characteristic waveforms included in level value fluctuations, that is, the waveforms associated with rapid rises due to tool breakage and declines due to machining heat, capture the time width (period) of these waveforms, and perform calculation processing. By doing this, tool damage can be automatically determined.

Next, this invention will be explained using figures. FIG. 1 shows the relationship between the cutting time and the power or current value of the spindle motor in a cutting machine. In numerical control or copy control machining, the power or current of the spindle motor during the cutting process under normal conditions fluctuates and is unstable, but when a defect occurs,
It shows characteristic behavior. Figure 1 shows this state. As shown in this figure, the level during normal cutting (the part to the left of a in the figure) is such that the shape of the workpiece changes complexly and the depth of cut is Non-uniform machining causes fluctuations and instability.

However, the part beyond a in Figure 1 (the right part) shows the state when the tool is missing, and since the power or current consumed by the spindle motor further increases or decreases, it can be distinguished from the previous situation. . When a tool breaks, the power or current changes characteristically because the broken part is caught between the workpiece and the tool, or because an overload is temporarily applied to the tool during the breaking process. , the power or current increases rapidly, and then,
As a result of this, the cutting resistance decreases as the cutting heat increases, resulting in a rapid drop.

The present invention has been made based on such a theory, and provides a detection device that captures the characteristic waveform change of electric power or current and detects that point as the time when a tool breaks. It is.

Next, an embodiment of the present invention will be explained with reference to FIG. 2. 1 is a power or current detection section,
Connected to the main shaft motor of a cutting machine (not shown),
It constantly detects power or current.
A machine tool control circuit 3 is connected downstream of the detection section 1 via a tool loss detection section 2, which will be described in detail next.

The tool loss detection section 2 has a CR circuit section 4, an increase value comparator 5, and a maximum level value comparator 6 connected to the input side. The detection section 1 shapes the detected signal, converts it into a voltage, and sends it to the tool loss detection section 2. CR of tool missing detection part 2
The circuit section 4 differentiates the output signal waveform of the detection section 1, and outputs a signal when the reference value at the time of rising and falling is reached. The rise value comparator 5 is
Based on the differential output of the CR circuit section 4 and the voltage from the detection section 1, the difference between the detection voltage when the differential output exceeds the rising reference value and the detection voltage when the differential output changes from positive to negative is the set value V. It outputs a signal when it exceeds the limit. In addition, the highest level value comparator 6 is CR
The detected voltage value when the differential output of the circuit section 4 changes from positive to negative is detected, and a signal is output when it exceeds the level T at the time of a defect.

A flip-flop circuit 7 and a waveform calculation circuit 8 are connected to the rear stage of the CR circuit section 4, and one input terminal of an AND circuit 9 is connected to the rear stage of the waveform calculation circuit 8. At the other input terminal of the AND circuit 9,
The output side of the above-mentioned increase value comparator 5 is connected. The output side of the AND circuit 9 is connected to the input end of the machine tool control circuit 3 together with the above-mentioned maximum level value comparator 6. 10 is a waveform time width threshold setting circuit section, and 11 is a waveform time width signal circuit section. The waveform time width signal circuit section 11 supplies the signal from the waveform time width threshold setting circuit section 10 corresponding to the loss to the waveform operation circuit 8 as a control signal for the waveform operation circuit 8.

Next, to explain the operation of this device configured in this way, first, we tested the rising value comparator 5 and the highest level value comparator 6 in response to sudden changes in power or current as described above. Set it to be sensitive. This can be done by monitoring the time width t, the rise value V, the differential value of rise and fall dV/dt, and the highest level value T of the waveform in FIG.

The power or current of the machine tool spindle motor is detected by a detection unit 1, shaped here, and converted into voltage. The CR circuit section 4 of the tool chipping detection section 2 outputs a signal when the differential value of the output signal waveform of the detector 1 reaches the reference value (dV/dt) for rising and falling, and the flip-flop circuit 7 outputs a signal when the differential value of the output signal waveform of the detector 1 reaches the reference value (dV/dt) for rising and falling. A rectangular wave signal is output that rises depending on the signal corresponding to the reference value and falls depending on the signal corresponding to the falling reference value. The next-stage waveform calculation circuit 8 measures the waveform time width t of the rectangular wave signal output from the flip-flop circuit 7, and compares it with the waveform time width at the time of a loss output from the waveform time width signal circuit section 11. Identify whether it is unique to the time of loss.

As a result, if the waveform is compatible, the waveform time width threshold setting circuit section 10, the waveform time width signal circuit section 11, and the waveform calculation circuit 8 measure the waveform time width t, and calculate the time characteristic at the time of loss. If it is determined whether the waveform has a width and if both the rise value V of the waveform matches the initial setting threshold value, the AND circuit 9
The machine tool control circuit 3 is operated through the machine tool control circuit 3 to perform an emergency stop of the machine tool. Further, as in the present embodiment, if the level T is detected and a signal of tool loss is obtained from the comparison with the highest level value by the highest level value comparator 6, more reliable detection can be achieved.

As an actual example of when a tool breaks, the differential value when ascending and descending when cutting steel is ±3.0Kg・m/sec±4.0
Kg·m/sec, and the waveform time width t is 0.5 seconds to 1.5 seconds. On the other hand, cast iron is ±2.0Kg・m/sec~±4.0
Kg·m/sec, and t is 0.5 seconds to 1.5 seconds as in the case of steel. Steel as a further example of this
To explain the case of SKD11, the differential values during rising and falling are +3.7 Kg·m/sec and -4.0 Kg·m/sec, and the waveform time width t is 0.9 seconds. Also cast iron
In FC20, the values are +3.6Kg·m/sec and -3.0Kg·m/sec, and the waveform time width t is 1.3 seconds. Note that the above-mentioned differential value is obtained by converting the electric power or current value into torque.

As described above in detail along with the embodiments, according to the present invention, tool damage can be detected by analyzing the behavior of each signal during the cutting process. In the above embodiment, each block is described as a separate unit, but it is possible to replace part or all of these with a microcomputer, a minicomputer, or the like.

Since the present invention is constructed as described above, it is possible to accurately determine whether a tool is missing and to stop the operation of the tool.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between power or current value and cutting time, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1...detection section, 2...tool missing detection section, 3...
Machine tool control circuit, 4...CR circuit section, 7...
Flip-flop circuit, 8... Waveform calculation circuit.

Claims (1)

[Claims] 1 A detection unit that detects changes in the power or current of the machine tool spindle motor when a tool is missing, and a CR circuit that calculates the differential value of the output signal of the detection unit and outputs a signal when the differential reference value is reached during upward and downward movements. Department and
A flip-flop circuit outputs a rectangular wave signal that rises in response to a signal corresponding to a rising reference value from the CR circuit section and falls in response to a signal corresponding to a falling reference value; A tool defect detection device includes a waveform calculation circuit that determines whether or not this is a pre-stored defect characteristic, and a machine tool control circuit connected to the waveform calculation circuit.