JPS608178B2 - Contact detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides 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. A contact detection device that includes a coil that generates a magnetic flux that surrounds an induced current path, extracts a current signal flowing through this coil as a detection signal, and detects contact between a tool and a workpiece based on an increase in this detection signal. The purpose of this is to enable stable contact detection without being affected by fluctuations in power supply voltage or temperature drift, and to send a contact detection signal while the tool and workpiece are in contact. The object is to enable tool breakage to be detected by monitoring the contact detection signal.

Generally, such a contact detection device is used for dry cut removal and tool breakage detection, but in such a contact detection device, detection during non-contact is caused by fluctuations in power supply voltage, changes in coil resistance due to changes in ambient temperature, etc. Since the magnitude of the signal varies, in order to reliably detect contact, it is necessary to detect an increase in the detection signal based on the detection signal before contact. In order to detect an increase in the detection signal based on the detection signal before contact, there is a method of differentiating the detection signal to extract the change in the detection signal, and a comparison of the detection signal with a signal in which the detection signal is delayed by a delay circuit. There is a method of detecting an increase in the detection signal based on whether the detection signal has increased compared to the state a predetermined time ago, but in both of these methods, the signal is detected only immediately after the detection signal increases. If the detection signal is stabilized when the tool is in complete contact with the workpiece, the contact detection signal will no longer be sent. Therefore, when contact detection is performed using these methods, the contact detection signal must be monitored. A disadvantage arises in that it becomes impossible to detect tool breakage. The present invention has been made in view of these points, and includes a storage circuit that stores a detection signal with a predetermined delay, and compares the signal stored in this signal storage circuit with the detection signal to determine whether the detection signal is a signal. A contact detection signal is output when the signal exceeds the signal stored in the memory circuit, and at the same time as the contact detection signal is sent out, a switching element provided on the input side of the signal memory circuit or inside the signal memory circuit is activated. This feature is characterized in that the detection signal after contact is not stored in the signal storage circuit.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an example of a machine tool that processes a workpiece W by advancing and retracting the 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. A 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 this coil 13, and both ends of this coil 13 are connected to an AC power source 14 via a current detection resistor RI. 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 conductive current flows, the impedance of the coil 13 decreases, so the current flowing through the coil 13 increases, and the voltage generated across the current detection resistor RI increases. The contact detection circuit 16 includes a current detection resistor RI.
Contact detection is performed by inputting an alternating current voltage signal generated at both ends of the circuit as a detection signal, and as shown in FIG. 3, two peak value hold circuits 20, 21 and the detection signals stored in these peak value hold circuits 20 and 21, and the detection signal stored in the peak value hold circuit 20 is higher than the detection signal stored in the peak value hold circuit 21. A comparator 23 outputs a contact detection signal TDS when the signal becomes large, and a switching element 24 is connected before the peak value hold circuit 21 and prevents the detection signal from being applied to the peak value hold circuit 21 after contact. , comparator 2
3, and an inverter 25 which deenergizes the relay 24 when the contact detection signal TDS is outputted.

The peak value hold circuits 20 and 21 are shown in FIGS. 4 and 5, and have almost the same circuit configuration, including comparison circuits 30 and 40, integration circuits 31 and 41, and inverting amplifier circuits 32 and 42. and a diode D for blocking backflow,
and a negative feedback resistor Rf.

The difference between the two is the integration circuits 31 and 41. In the integration circuit 31 of the peak value hold circuit 20, the charging time constant setting resistor R13 and the discharging time constant setting resistor R14 are both composed of resistors of about IKQ. The discharge time constant is a few S.
The peak value hold circuit 21 is set to ~ number S.
In the integrating circuit 41, the resistor for setting the specific number during charging is composed of a high resistance of 100 KQ, and the charging time constant is several hundred.
The discharge time constant of the capacitor C is determined by the insulation resistance of the capacitor C and the input resistance of the oven amplifier OP2, with no discharge resistor connected. Furthermore, since the input voltage divided by the resistors R13 and R14 is applied to the capacitor C of the integrating circuit 31, when the tool T is not in contact with the workpiece W, the voltage shown in FIGS. As shown in FIG. 2, the output of the peak value hold circuit 20 is lower than the output of the peak value hold circuit 21, and the contact detection signal TDS is not output from the comparator 23. In this state, when the tool T contacts the workpiece W and the amplitude of the detection signal increases as shown in FIG. The corresponding value is output to the comparator 23.

On the other hand, the capacitor C of the peak value hold circuit 21
Since the voltage does not rise immediately, when the tool T and workpiece W come into contact, the output voltage of the peak value hold circuit 20 exceeds the output voltage of the peak value hold circuit 21, as shown in FIGS. 6b and 6c. , the contact detection signal TDS is output from the comparator 23. As a result, the feed rate of the workpiece W is switched, etc. On the other hand, when the contact detection signal TDS is output from the comparator 23, the relay 24 is deenergized, and after a slight delay time d, the contact 24 of the relay 24
Since a is opened, no detection signal is given to the peak value hold circuit 21.

As a result, the voltage of the capacitor of the peak value hold circuit 21 is maintained at the value immediately after contact, and a signal corresponding to this voltage is output to the comparator 23. Therefore, even if the tool T and workpiece W are in complete contact and the detection signal no longer changes, the transmission of the contact detection signal will not be stopped, and while the tool T is in contact with the workpiece W. A contact detection signal TDS is output. Then, when the tool T and workpiece W no longer come into contact due to the retreat of the workpiece W or the breakage of the tool T, and the amplitude of the detection signal becomes small, the charging voltage of the capacitor C of the peak value hold circuit 20 immediately becomes a low value, and the peak value The voltage becomes lower than the output voltage of the hold circuit 21.

As a result, the contact detection signal TDS is no longer output from the comparator 23, and if tool breakage is detected by monitoring the contact detection signal TDS, tool breakage is detected.
Furthermore, when the contact detection signal TDS is no longer sent, the relay 24 is energized and the contact 24a of the relay 24 is closed again, so that the detection signal is again given to the peak value hold circuit 21. At this time, if the detection signal is higher than before contact due to fluctuations in the power supply voltage, capacitor C is charged with a time constant of several seconds, and if the detection signal is lower than before contact, Capacitor C
The capacitor C is discharged with a time constant determined by the insulation resistance of the amplifier OP2 and the input resistance of the amplifier OP2. Thereby, the voltage of the capacitor C is corrected to a value corresponding to the magnitude of the detection signal after the tool T and workpiece W are separated, and the next contact detection can be performed reliably. In the above embodiment, the contact detection is performed by applying the detection signal to two peak value hold circuits having different charge/discharge time constants, and comparing the detection signals stored in the two peak value hold circuits with a comparator. However, as shown in FIG. 7, if the detection signal is rectified by a rectifier circuit 26 and converted into a DC signal, the peak value hold circuit 20' may not be necessary. Also,
The peak value hold circuit 21 may be a sample hold circuit having a predetermined charging time constant. Furthermore, the relay 24 may be an analog switch, and these switching elements may be placed in a different location in the machine where the detection signal can be prevented from being stored in the peak value hold circuit 21, such as between the diode D and the resistor R17 in FIG. You can also connect to. As described above, the contact detection device of the present invention includes a signal storage circuit that stores detection signals with a predetermined delay, and
The signal stored in the signal storage circuit is compared with the detection signal, and when the detection signal exceeds the signal stored in the signal storage circuit, a contact detection signal is output. At the same time, a switching element provided on the input side of the signal storage circuit or inside the signal storage circuit is activated to prevent the detection signal after contact from being stored in the signal storage circuit, so that detection is performed based on the detection signal before contact. Not only can an increase in the signal be detected, but the contact detection signal can continue to be sent out while the tool and workpiece are in contact.

Therefore, there is an advantage that not only contact detection can be ensured, but also tool breakage can be detected by monitoring the contact detection signal.

[Brief explanation of the drawing]

Fig. 1 is a schematic side view showing an example of a machine tool equipped with a contact detection device according to the present invention, Fig. 2 is an equivalent circuit diagram showing the Aya Tsutomu detection coil and the induced current path, and Fig. 3 is the same as that shown in Fig. 1. Block diagrams showing the specific configuration of the contact detection circuit 16, FIGS. 4 and 5, are the peak value hold circuit 20 in FIG.
, 21 is an electric circuit diagram, FIG. 6 is a timing chart for explaining the operation of the contact detection circuit 16, and FIG.
The figure is a block diagram showing another embodiment of the contact detection circuit 16. 10... Spindle head, 11... Bed, 1
2...Nerfle, 13...Touch detection coil, 14...Father flow power supply, 16...Touch detection circuit, 20, 21...Peak value hold circuit, 23
...Comparator, 24...Relay, 25.
...Inverter, R1...Resistor for current detection, T...Tool, W...Workpiece. Oh? Picture spear and picture o3 picture spear 4 figure oak picture fang 6 figure picture

Claims (1)

[Claims] 1. A coil that generates a magnetic flux that surrounds an induced current path that is short-circuited by contact between a tool and a workpiece that are in an electrically conductive relationship, and is placed around the spindle of a machine tool, and this coil is connected to an alternating current. a detection circuit that extracts a current signal that is excited by the coil and that flows through the coil as a detection signal; a signal storage circuit that stores the detection signal output from this detection circuit with a predetermined delay time constant; Comparing the stored detection signal and the detection signal output from the detection circuit, and outputting a contact detection signal when the detection signal output from the detection circuit exceeds the detection signal stored in the signal storage circuit. a switching element provided between the detection circuit and the signal storage circuit or inside the signal storage circuit to prevent the detection signal from being stored in the signal storage circuit; and a contact detection signal output from the comparator. and a control circuit that operates the switching element while the switching element is being switched.