JPS59201748A - Apparatus for detecting breakage of cutting tool - Google Patents

Abstract

PURPOSE:To enable the occurrence of a tool breakage to be securely detected by detecting a cutting load force, controlling tool feed speed when said force exceeds the upper or lower limit value of the steady load reference value and stopping a machine tool when said force exceeds an abnormal load reference value. CONSTITUTION:When a cutting load force exceeds the upper limit value Tmax of a teady load reference value, the signal from an upper limit comparating circuit 3 is sent to the input of a control circuit 6 to reduce tool feeding speed and the cutting load force through a tool control unit 7 so that said force becomes lower than the upper limit value Tmax. And when the tool reaches a small cutting allowance portion, the cutting load force is reduced to be lower than the lower limit value Tmin of the steady load reference value. Then the signal from the lower limit value comparing circuit 9 is sent to the control circuit 6 so that the tool feeding speed is accelerated by the control unit 7 and the cutting load force becomes larger than the lower limit value Tmin. Next, in the breakage of the tool, the cutting load force abruptly increases to exceed the upper limit value Tmax and further the abnormal load reference value X. Then, the comparing circuit 9 generates the output signal to operate a machine tool stopping unit 10 for judging securely the breakage of the tool.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cutting tool loss detection device that detects tool loss during cutting. In recent years, automatic machine tools such as NO machines have been widely used to save labor in machining. Its application has gradually expanded to include the processing of workpieces with complex shapes. Therefore, when machining these complex-shaped parts, it is necessary to set and maintain appropriate machining conditions in order to obtain precise machining accuracy. However, if a tool breaks during cutting, especially during unattended operation, proper machining conditions cannot be maintained, and as a result, a large number of workpieces with defective finished surfaces are produced. In some cases, damage to the workpiece,
Furthermore, there is a great risk of breaking the machine tool and causing serious damage.

Therefore, various methods for early detection of this type of tool damage have been proposed. For example, there is a method that focuses on the fact that cutting temperature, vibration, cutting load force, etc. change due to tool chipping, and indirectly detects tool chipping by measuring and processing these signals. Among these methods, the method that focuses on the cutting load force compares the standard cutting load value during normal cutting with the cutting load value during actual cutting, and calculates when the actual cutting load value deviates from the standard cutting load value. It determines that the tool has been damaged and stops the machine tool.

However, with this method, in the case of so-called free-form surface cutting, in which parts with different cross-sectional shapes are continuously cut,
Not necessarily valid. FIG. 1 shows the relationship between cutting time and cutting load force in the case of cutting a self-contained curved surface. As shown in the drawing, when cutting is performed using a normal tool, the cutting load force changes as shown by the dotted line in the drawing in response to changes in the machining allowance of the workpiece and changes in the surface shape of the cutting part. do. On the other hand, a in the figure
If a tool breakage occurs in the area and cutting is continued using the broken tool after that, a large cutting load force will be shown as shown by the solid line. However, the increase in cutting load force at the time of tool breakage, which is shown by the solid line after point a in the figure, occurs when cutting a part with a large cutting surface using a normal tool, which is shown by the dotted line from point b onwards. less than the increase in cutting load generated. Therefore, in such a case, it is impossible to determine tool damage based on the occurrence of a large cutting load value as in the conventional method. In this way, with the conventional method, it is difficult to determine whether a specific increase in load force is due to tool breakage, increased machining allowance, or cutting of a specially shaped part. However, it was difficult to accurately detect the occurrence of tool breakage.

The present invention aims to eliminate the above-mentioned drawbacks of the method that focuses on cutting load force, and to provide a cutting tool chipping detection device that can reliably detect the occurrence of tool chipping.

That is, the present invention includes a first comparator circuit that detects the cutting load force and outputs an output when the upper limit value or the lower limit value is exceeded; a control circuit that receives the signal and outputs an immediate response signal; a tool control device that receives the output of the control circuit and controls the tool feed rate; A cutting machine characterized by comprising a second comparison circuit that outputs an output when the abnormal load reference value is exceeded, and a machine tool stop device that stops the machine tool in response to the output of the second comparison circuit. This is a tool defect detection device for

According to the device of the present invention, by controlling the tool feed rate in accordance with the cutting load force, the cutting load force can be leveled and its fluctuation range can be kept within a narrow fixed range. the result,
The large increase in cutting load force that occurs when a tool breaks can be clearly distinguished from the increase in cutting load force caused by a change in the cutting stock or cross-sectional area of a normal tool, making it possible to reliably determine the occurrence of tool breakage. be able to.

At the same time, within the range of the leveled cutting load force,
Since the tool feed rate can be maximized, cutting efficiency can be increased.

The detection unit in the present invention includes a sensor connected to a main shaft motor or a tool feed motor of a cutting machine and detects the load current or electric power of these motors. The cutting load force is calculated based on these load force currents or voltages. Note that the signal detected by the sensor is further converted into a voltage or torque signal and output as required.

The first comparison circuit in the present invention includes an upper limit comparison circuit and a lower limit comparison circuit. An upper limit value of the steady reference load value is set in advance in the upper limit comparison circuit, and a signal is output when the input output of the detection section exceeds the upper limit value. In addition, the lower limit value of the steady load reference value is set in advance in the lower limit comparison circuit, and a signal is output when the output of the input detection section exceeds the lower limit value. .

The steady load reference value has a certain range consisting of variations in the cutting load force of the tool.

The control circuit in the present invention is a circuit that receives the signal output from the first comparison circuit and controls the tool.

The second comparison circuit in the present invention is an abnormal load reference value comparison circuit, in which an abnormal load reference value is set in advance, and a signal is generated when the input and output of the t-detector exceeds the abnormal load reference value. It is now output.

The abnormal load reference value is a value larger than the steady load reference value.
This value was measured in advance as the cutting load force value that would occur when a tool breakage occurred.

Embodiments of the present invention will be described based on the drawings. FIG. 2 is a block diagram schematically showing the apparatus of the present invention.

1 is a cutting load force detection unit, 2 is a steady load reference upper limit setting circuit in which the upper limit of the steady load reference value is input and set in advance, 8 is a comparison circuit for the steady load reference upper limit value, and 4 is a steady load A steady load reference value lower limit setting circuit in which the lower limit of the reference value is input and set in advance, 5 a comparison circuit for the steady load reference lower limit value, 6 a control circuit, and 7 a tool control that decelerates or accelerates the tool feed speed. The device 8 is an abnormal load reference value setting circuit in which an abnormal load reference value is input and set in advance;
Reference numeral 9 indicates an abnormal load reference value comparison circuit, and IO indicates a machine tool stop device for stopping the machine tool.

Next, the operation of the apparatus configured as described above will be explained based on FIG. 3. FIG. 3 shows the variation in cutting load force with respect to the passage of cutting time when cutting is performed using the apparatus of the present invention. First, if the tool is in good condition, as cutting continues and a portion with a large machining allowance is cut, the cutting load force extracted based on the load current of the machine tool's spindle motor will increase, and the upper limit of the steady load reference value will increase. approaches the value Tmax.

The output signal of such a detection section 1 is always inputted to a comparator circuit 3 for steady load reference value upper limit value. The cutting load force exceeds the upper limit Tmax of the steady load reference value. As a result, the tool cutting load force decreases, and the upper limit of the steady load reference value Tm
Go below the ax.

And, conversely, if cutting takes place in the area with less machining allowance - ζ,
The cutting load force decreases, and the lower limit of the steady load reference value Tm1n
approach. When the cutting load force falls below the lower limit value Tm1n of the steady load reference value, a signal is output from the lower limit comparison circuit 9, and via the input/output of the control circuit 6, the tool control device 7 controls the feed rate of the tool. is accelerated, and the cutting load force becomes larger than the lower limit value Tm1n of the steady load reference value.

As described above, when the tool is normal, the cutting load force is set to the upper limit value Tmax (for example, torque value of 8.0 to 8.5~·m) and the lower limit value Tm1n (for example, torque value As shown by the solid line below, the cutting load force increases rapidly within the range of 6.0 to 7.5 Kg・m.
exceeds and further increases, a signal is output from the abnormal load reference value setting circuit 9, the machine tool stop device IO is activated, the machine tool is immediately stopped, and cutting with the defective tool is stopped.

As described above, according to the present invention, tool damage can be quickly and reliably determined, thereby making it possible to prevent serious troubles from occurring.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the relationship between cutting time and cutting load force in the case of conventional free-form surface cutting, FIG. 2 is a block diagram showing the outline of the present invention device, and FIG. 3 is the present invention device FIG. 2 is an explanatory diagram showing the relationship between cutting time and cutting load force in one case in which free-form surface cutting is performed using a cutting machine. 1: Detection unit 2: Steady load reference upper limit setting circuit 8: Steady load reference upper limit comparison circuit 4: Steady load reference lower limit setting circuit 5: Steady load reference value comparison circuit 6: Control circuit 7: Tool control device 8: Abnormal reference value setting circuit 9: Comparison circuit for abnormal reference value 10: Machine tool stopping device Patent applicant Toyota Central Research Institute Co., Ltd. (RI) 2S) Fig. 1 Fig. 3 Cutting time 2nd round

Claims (1)

[Claims] A detection unit that detects cutting load force, and a first comparison that compares the output of the detection unit with a steady load reference value having preset upper and lower limit values, and outputs an output when the upper or lower limit value is exceeded. a control circuit that receives the output of the detection unit and the output of the first comparison circuit and outputs a responsive signal; and a tool control device that receives the output of the control circuit and controls the tool feed rate; a second comparison circuit that compares the output of the detection section with an abnormal load reference value set in advance to be larger than the steady load reference value, and outputs an output when the abnormal load reference value is exceeded; A cutting tool defect detection device comprising: a machine tool stop device that stops a machine tool when the machine tool is stopped.