JPH0137878Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a control device for a machine tool that enables cutting temperature control and enables efficient cutting at high speed without abnormalities such as tool wear.

In recent years, machine tools have become NC (numerically controlled), and for example, lathes, milling machines, press machines, etc. are not only NC, but electric discharge machines are also becoming NC. ing. For example, in an NC lathe, the relative X between the workpiece and the cutting tool is controlled by the NC device and servo mechanism.
The amount of movement in the Y-axis direction, or even the diameter and rotational speed of the workpiece, is quantified, and this numerical information is used to simultaneously control the movement of the cutting tool, that is, the feed in the X-axis direction and the feed in the Y-axis direction. Alternatively, each side can be appropriately controlled according to a program to cut the contour of the workpiece as desired.

However, with conventional NC lathes like this, the cutting tool can only move in the direction and speed according to the program, so of course when the program settings are overloaded and the cutting is too heavy, etc. In the past, various adaptive control methods and means have been proposed in response to conditions such as changes in the material, vibration, noticeable tool wear, or increased cutting temperature at the cutting part. However, there is no one that can widely accommodate various aspects, and therefore, workers usually have to take appropriate measures. For example, when the cutting temperature of the cutting part is abnormally high, the annealing color of the chips,
Alternatively, judgments were made by visually observing the state of fumes caused by gasification of processing fluids, etc. These reactions are slow and indirect and do not give accurate values, resulting in
Proper and quick treatment is difficult, and it also causes abnormal wear of the tool bit, deteriorating workability.

[Purpose of invention]

Therefore, this device was devised by focusing on the above-mentioned problems of the conventional method. By detecting and determining the cutting temperature of the cutting part from time to time, the cutting state is controlled so that the cutting temperature is maintained within a predetermined tolerance range. A radiation thermometer that is placed facing the cutting part and measures the temperature of chips that are actually being generated during cutting (cutting temperature) and converts this measured temperature into an electrical signal, and this radiation temperature A preamplifier that amplifies the electrical signal output by the meter to reduce the influence of disturbances and increase sensitivity, and a low-pass filter that removes medium and high frequency components of the amplified signal input from the preamplifier and passes only low frequency signals. A comparator that compares the electric signal from this low-pass filter with a reference value and outputs a discrimination signal, an arithmetic circuit that outputs a command signal corresponding to the discrimination signal from this comparator, and a command signal generated by this arithmetic circuit. and a drive circuit for a drive motor that controls the rotational speed of the tool spindle, the relative machining feed rate between the tool and the workpiece, or the depth of cut so that the cutting temperature is within a predetermined range. The object of the present invention is to provide a control device for a machine tool that enables stable machining, extends tool life, and improves machining performance.

[Example of idea]

An example of this invention is shown below in Figures 1 and 2.
This will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of this invention, and shows a case where the invention is applied to a lathe. As mentioned above, when the cutting temperature (the temperature of the chips that are currently being generated during cutting) rises or falls during machining and changes to a temperature outside the predetermined range, the cutting temperature changes to a value within the predetermined range. The machining performance is improved by controlling the cutting conditions such as the machining feed rate so that the machining speed returns.

That is, in FIG. 1, reference numeral 4 denotes a radiation thermometer, the detection part of which is placed facing the cutting part during cutting, measures the temperature of chips (cutting temperature) that are currently being generated by cutting, and calculates the measured temperature. It is for converting into electrical signals. This thermometer 4 applies the principle that radiant energy increases rapidly as the temperature of a high-temperature object rises, and the telescope 1 detects the radiant energy of high-temperature chips by controlling and tracking its direction to the cutting part.
The thermoelectromotive force generated is collected by a lens, absorbed, or otherwise acted on a heat sensitive body such as a pyrometer bulb, phototube, photomultiplier tube, or thermocouple, and then, for example, increases the temperature of the heat sensitive body, and the generated thermoelectromotive force is converted into an electrical signal. The electrical signal output from the radiation thermometer 4 is input to a preamplifier 6, and the preamplifier 6 amplifies the electrical signal to reduce the influence of disturbances and increase sensitivity. As shown in FIG. 2, the amplified signal amplified by the preamplifier 6 corresponds to the constantly changing cutting temperature, so the amplified signal contains high frequency components and low frequency components. Since high frequency components are unfavorable for comparator 12, comparator 1
2, it is necessary to block input of high frequency components and input only low frequency components. Therefore, the high frequency components in the amplified signal input from the preamplifier 6 are removed by the low-pass filter 8, and the
Only low-frequency components of about Hz or lower, that is, low-frequency signals, are allowed to pass through. The low frequency signal outputted from the low pass filter 8 in this manner contains a large amount of DC components, which is preferable when comparing with a reference value. 10 is a DC amplifier that further amplifies this low frequency signal and outputs it to the comparator 12. The reference value is also input to the comparator 12 together with the amplified low frequency signal from the DC amplifier 10. Comparator 12
Then, the low frequency signal is compared with the reference value and a discrimination signal is output. That is, the reference value consists of an upper limit value and a lower limit value, and the range determined by these values is determined to correspond to the allowable range of cutting temperature.
When the level of the low frequency signal is between the upper and lower limits mentioned above, the discrimination signal S ₀ is output, and in other ranges, the discrimination signal S ₁₁ , S ₁₂ , S ₁₃ . . . S _1o , or
S ₂₁ , S ₂₂ , S ₂₃ , ...S _2o are output. Such a discrimination signal S ₀ , S _1o , or S _2o is input to the arithmetic circuit 14 . This arithmetic circuit 14 increases or decreases the NC control command signal based on the discrimination signal according to the program, and also receives feedback signals from rotation detectors 19A and 19B that detect the positions and rotational speeds of the drive motors 18A and 18B. The corrected signal is output to the drive circuit 16 after correction. The drive circuit 16 receives the command signal output from the arithmetic circuit 14 and controls the rotational speed of the workpiece W spindle 17, the relative machining feed or depth of cut between the tool 22 and the workpiece W at a predetermined cutting temperature. A drive signal is output to the drive motors 18A and 18B for adjustment control so that the drive signal is within the range. The drive motor 18A is a motor that adjusts and controls the machining or cutting feed of the tool 22 in the X-axis direction, and the drive motor 18B is a motor that rotationally drives the workpiece W. When these motors 18A and 18B are pulse motors, the rotation angle of the motor per command pulse is accurate, and the movement amount can be directly controlled by the number of command pulses, and the movement or rotation speed can be directly controlled by the command pulse frequency. device 19
A so-called open loop control system that does not require A and 19B can be used, but in order to achieve more accurate operation when the motors 18A and 18B are DC or AC servo motors, or even when pulse motors are used, the embodiment Detection devices 19A and 19B are provided, and these detection devices 19A and 19
From B onward, a feedback control method is adopted in which the feedback signal and the target value are compared and corrected. Both of the detection devices 19A and 19B detect the rotation angle or rotation speed, and a code plate such as an encoder is attached to the shaft of the motor 18A or the rotation main shaft 17 of the workpiece W, and the detection device 19A and 19B detect the rotation angle or rotation speed. Feedback signals are now available. Note that in order to detect the rotational speed, a rotational speed detector such as a finger speed generator is often provided separately from the detection devices 19A and 19B, and in the case of a milling machine, etc., the workpiece and the tool In addition to the two cross table axes X and Y for the relative position between and machining feed, the main axis Z for cutting feed of the rotary tool is added, or the four axes including the rotational drive axis of the main axis are controlled. The signals are combined and adjusted as appropriate.

Next, the effect will be explained.

FIG. 2 is a graph showing the relationship between cutting temperature and cutting time. During cutting, a stable state C is desirable in which the cutting temperature is maintained within the allowable temperature range.

However, if the cutting temperature rises during machining and shifts to unstable state A, for example, the rotation speed is excessive relative to the machining feed rate or depth of cut (relatively large value). , cutting resistance increases, the tool 22 wears significantly, and machining performance deteriorates. On the contrary, if the cutting temperature falls and shifts to unstable state B, for example, the rotation speed is excessive relative to the machining feed rate or depth of cut (a relatively small value). , leaving enough surplus power for cutting,
Processing efficiency will be low. In this way, when the cutting temperature is in the unstable state A or B, the rotational speed of the workpiece W spindle 17, the tool 22 and the workpiece W
It is necessary to adjust and control the relative machining feed rate or depth of cut between them so that the cutting temperature is within a predetermined range (here, t ₁ to _{t 2} °C). Therefore, in the control device of the present invention, when the cutting temperature rises or falls and exceeds the upper limit value t ₂ °C or the lower limit value t ₁ °C and becomes unstable state A or B, the radiation thermometer 4 detects this. , it is immediately detected as a value different from the previously detected value, and an electrical signal is output, inputted to the preamplifier 6 and amplified, and then applied to the low-pass filter 8. This low-pass filter 8 extracts only low-frequency components including DC components, and the comparator 12 compares this low-frequency signal with various reference values to generate a discrimination signal O, S _1o , or S _2o . is output. Based on this discrimination signal, the calculation circuit 14 performs calculation based on the program, and a command signal is output to the drive circuit 16 of the drive motors 18A and 18B, so that the cutting temperature decreases or increases and returns to within the allowable range. The circuit 16 controls the rotational speed of the workpiece W spindle 17, the relative machining feed between the tool 22 and the workpiece W, or the depth of cut.
Modified drive signals for motors 18A and 18B are output from.

In this way, by constantly detecting and determining the cutting temperature of the cutting part, the cutting condition is controlled so that the cutting temperature remains within the allowable range, and as a result, it becomes possible to control the cutting temperature and prevent abnormalities such as tool wear. is reduced, allowing for high-speed and efficient cutting.

[Effect of idea]

As is clear from the above explanation, according to this invention, by detecting and determining the cutting temperature of the cutting part from time to time, the cutting state can be controlled to keep the cutting temperature within an allowable range. Therefore, cutting can be performed under stable cutting temperature conditions at all times, and there is no abnormality such as abnormal increase in cutting force or tool wear, improving machining accuracy, extending tool life, and improving machining performance. Moreover, the effect of high-speed and efficient cutting can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a control device for a machine tool according to an embodiment of the invention, and FIG. 2 is a graph showing the relationship between cutting temperature and cutting time. 4... Radiation thermometer, 12... Comparator, 14...
Arithmetic circuit, 16... Drive circuit, 18A, 18B...
...Drive motor.

Claims (1)

[Scope of Claim for Utility Model Registration] A radiation thermometer that is placed facing the cutting part during cutting and measures the temperature of chips that are actually being generated during cutting (cutting temperature) and converts the measured temperature into an electrical signal; A preamplifier that amplifies the electrical signal output by the radiation thermometer to reduce the influence of disturbances and increase sensitivity, and a low-pass filter that removes the medium and high frequency components of the amplified signal input from the preamplifier and passes only low frequency signals. , a comparator that compares the electrical signal from this low-pass filter with a reference value and outputs a discrimination signal, an arithmetic circuit that outputs a command signal corresponding to the discrimination signal from this comparator, and a comparator that outputs a command signal corresponding to the discrimination signal from this comparator. drive a drive motor that receives a command signal to control the rotational speed of the workpiece or tool spindle, the relative machining feed rate or depth of cut between the tool and the workpiece so that the cutting temperature is within a predetermined range; A machine tool control device characterized by being equipped with a circuit.