JPS6146261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contact detection device that electrically detects contact between a tool and a workpiece, and more specifically, a contact detection device that electrically detects contact between a tool and a workpiece. The present invention relates to a contact detection device that includes an excitation coil that generates magnetic flux surrounding an induced current path, and detects contact between a tool and a workpiece by increasing the current flowing through the excitation coil.

Generally, such contact detection devices eliminate idle cutting time,
It is used to detect tool breakage during machining, detect the cutting time of a workpiece, etc., but such contact detection devices are sensitive to changes in coil resistance due to fluctuations in power supply voltage, changes in ambient temperature, etc. Therefore, since the magnitude of the detection signal during non-contact varies considerably, in order to reliably detect contact, it is necessary to detect an increase in the detection signal based on the detection signal immediately before contact. To detect an increase in the detection signal using the detection signal immediately before contact as a reference, compare the detection signal with a signal delayed by a delay circuit to determine whether the detection signal has increased compared to the state a predetermined time ago. There is a method that detects an increase in the detection signal depending on whether the tool Since the contact detection signal will no longer be sent, it is necessary to transmit the contact signal while the tool and workpiece are in contact, such as when managing the tool life by integrating the time during which the workpiece and the tool are in contact. Such a method cannot be used when continuous discharge is required, making it difficult to perform reliable contact detection.

In view of these conventional problems, the present invention is designed to ensure contact detection even when it is necessary to send out contact detection continuously, and embodiments thereof will be described below with reference to the drawings.

FIG. 1 shows an example of a machine tool that processes a workpiece W by advancing and retracting a workpiece W provided on a table 12 that slides on a bed 11 with respect to a tool T attached to a spindle of a spindle head 10. An excitation coil 13 for contact detection is attached to the tip surface of the spindle head 10. Generally, a toroidal coil as shown in FIG. 2 is used as the excitation coil 13, and both ends of the excitation coil 13 are connected to an AC power source 14 via a current detection resistor R1. As a result, an annular magnetic flux is generated around the tool T, and when the tool T and workpiece W come into contact, an induced current flows through the induced current path 15 as shown by the broken line in FIG. When the induced current flows, the impedance of the exciting coil 13 decreases, so the current flowing through the exciting coil 13 increases, and the voltage generated across the current detection resistor R1 increases.

The contact detection circuit 16 performs contact detection by inputting an AC voltage signal generated across the current detection resistor R1 as a detection signal, and as shown in FIG. 3, includes an amplifier circuit 20, a rectifier circuit 21, It is composed of first and second differentiating circuits 22, 23, comparators 24, 25, and a flip-flop 26.The input detection signal is amplified to a predetermined level by an amplifier circuit 20, and then a rectifier circuit 21 and the first differentiating circuit 22 and the second differentiating circuit 2.
3 and given.

The first differentiating circuit 22 includes, for example, a rectifying circuit 21
a capacitor C1 connected between the non-inverting input of the comparator 24 and a resistor R1 connected between the non-inverting input of the comparator 24 and ground;
and a diode D1 connected in parallel with the rectifier circuit 21 so that the anode is on the ground side.When the DC signal output from the rectifier circuit 21 rises, it generates a positive pulse signal of a magnitude corresponding to the amount of rise. It is applied to the non-inverting input of the comparator 24. The positive reference voltage +VS output from the variable resistor VR1 is applied to the inverting input of the comparator 24, and when the positive pulse signal exceeds the reference voltage +VS, a signal is output from the comparator 24. flipflop 26
is applied to the set terminal S of. As a result, the flip-flop 26 is set and the contact signal TDS is output from the set output terminal Q.

On the other hand, the second differentiating circuit 23 includes a capacitor 02 connected between the rectifying circuit 21 and the inverting input of the comparator 25, a resistor R2 connected between the inverting input of the comparator 25 and the ground, and this It is composed of a resistor R2 and a diode D2 connected in parallel with the cathode on the ground side. When the DC signal output from the rectifier circuit 21 decreases, a negative signal of a magnitude corresponding to the amount of decrease occurs. Pulse signal to comparator 25
to the inverted input of. The non-inverting input of the comparator 25 is supplied with the negative reference voltage -VS output from the variable resistor VR2, and when the negative pulse signal becomes lower than the negative reference voltage -VS, the comparator 2
A signal is output from 5 and applied to the reset terminal R of the flip-flop 26, thereby resetting the flip-flop 26 and outputting the contact signal TDS.
transmission is stopped.

In addition, variable resistors VR1 and VR2 respond to minute fluctuations in the detection signal during contact, and the differentiating circuit 2
Positive and negative voltages that are larger by a predetermined amount than the peak values of the pulse signals outputted from 2 and 23 are adjusted so that they are outputted as positive and negative reference voltages +VS and -VS.

Therefore, when the amplitude of the detection signal increases significantly due to contact between the tool T and the workpiece W, and as a result, the output of the rectifier circuit 21 increases significantly as shown by A in FIG. 4a. A signal is output from the comparator 24 and the flip-flop 26 is set, and the amplitude of the detection signal is significantly reduced due to the separation of the tool T and workpiece W, so that the output of the rectifier circuit 21 becomes as shown in FIG. Flip-flop 26 is reset only when a significantly decreases as shown at B. Therefore, the flip-flop 26 is not reset erroneously due to a change in the contact state during contact, and a contact signal can be reliably sent while the tool T and workpiece W are in contact. Note that Fig. 4 a to f are respectively from point a to f in Fig. 3.
The signal waveform up to the point is shown.

In the above embodiment, if the set value of the reference voltage is increased in order to increase the stability against changes in the contact state during contact, the sensitivity of contact detection decreases. If the increase rate of the detected signal is small, the stability cannot be made very high. Figure 5 shows a contact detection circuit 16 that increases stability without reducing detection sensitivity.
This shows an embodiment in which peak value hold circuits 30, 31, voltage dividing circuit 32, comparator circuit 33, and one shot circuit 34 are provided between rectifier circuit 21 and first and second differentiating circuits 22, 23. A waveform shaping circuit configured as shown in FIG.

The peak value hold circuit 30 connected between the rectifier circuit 21 and the differentiating circuits 22 and 23 has a predetermined discharge time constant that is sufficiently longer than the fluctuation period of the detection signal during contact, and is shown in FIG. , b, DC signals that do not follow the rapid decrease in the detection signal during contact are applied to the differentiating circuits 22 and 23. On the other hand, the peak value hold circuit 31 connected between the rectifier circuit 21 and the voltage dividing circuit 32 has a discharge time constant set to be sufficiently longer than that of the peak value hold circuit 30, and is shown in FIGS. 6a to 6d. When a predetermined time ts elapses after the output of the rectifier circuit 21 returns to the state before contact due to separation of the tool T and workpiece W, the output b of the peak value hold circuit 30 becomes equal to the output d of the voltage dividing circuit 32. It goes down. As a result, a signal is output from the comparator circuit 33 to energize the one-shot circuit 34, and after a slight delay time td has elapsed, the one-shot circuit 34 outputs a pulse with a predetermined time width. The pulse from this one-shot circuit 34 is given as a reset signal to the peak value hold circuits 30 and 31 to reset the stored value.
When the output of 0 becomes less than the output of the voltage divider circuit 32, the output of the peak value hold circuit 30 suddenly becomes zero, which causes the second differentiator 23 and the comparator 25 to operate and flip-flop 26 to open. It will be reset. According to this, even if the output of the rectifying circuit 21 suddenly decreases due to a change in the contact state during contact, the voltage signals given to the differentiating circuits 22 and 23 do not follow this, so 2
No large negative pulses are sent out from the differentiating circuit 23. Therefore, even if the negative reference voltage is set to a small value, the flip-flop 26 will not be erroneously reset, and the stability can be increased without reducing the sensitivity of contact detection.

A first differentiator circuit that indirectly detects the magnitude of the current flowing in the induced current path and converts it into a voltage signal, and outputs a signal as the voltage signal increases, and a signal as the voltage signal decreases. a second differentiator circuit,
Since the memory element is set by the output of the first differentiating circuit, reset by the output of the second differentiating circuit, and outputs the contact signal while in the set state, the detection signal can be adjusted based on the detection signal immediately before the contact. In addition to being able to detect the increase in contact between the tool and the workpiece, it is possible to continue sending contact signals while the tool and workpiece are in contact. There is an advantage that contact detection can be performed reliably even when it is necessary to output a contact signal continuously while the contact is in contact.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is a schematic side view showing an example of a machine tool equipped with a contact detection device, and FIG.
Equivalent circuit diagram showing the relationship between the induced current path 15 and the induced current path 15, the third
The figure is a block diagram showing the specific configuration of the contact detection circuit 16 in FIG. 1, and FIG. 4 is a time chart showing the operating waveforms of each part of the contact detection circuit shown in FIG.
FIG. 5 is a block diagram showing a second embodiment of the contact detection circuit 16, and FIG. 6 is a time chart showing operating waveforms of various parts of the contact detection circuit shown in FIG. 10... Spindle head, 12... Table, 13... Excitation coil, 14... AC power supply, 16... Contact detection circuit, 2
1... Rectifier circuit, 22... First differentiation circuit, 23... Second
Differential circuit, 26...flip-flop, T...tool,
W...workpiece.

Claims (1)

[Claims] 1. An excitation coil that is disposed around a spindle of a machine tool and generates a magnetic flux that surrounds an induced current path that is short-circuited by contact between a tool and a workpiece that are electrically conductive. a detection circuit that indirectly detects the magnitude of the current flowing in the induced current path and converts it into a voltage signal; and a first differentiation circuit that detects an increase in the voltage signal output from the detection circuit. a second differentiating circuit for detecting a decrease in the voltage signal; and a second differentiating circuit that is set by the output of the first differentiating circuit and reset by the output of the second differentiating circuit, and outputs a contact signal while in the set state. A contact detection device comprising: a storage element for outputting data;