JPH0260963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for detecting the mutual contact between a tool and a workpiece that are electrically connected through a support such as a bed or a table and that move relatively toward or away from each other. This invention relates to a mechanical contact detection device.

Conventionally, in the above-mentioned contact detection devices for machine tools, a toroidal coil is arranged to surround a support such as a bed or table, and this is excited with an alternating current voltage to detect contact between the tool and the workpiece. An induced current is caused to flow through a support such as a bed or table, and the flow of excitation current through a support such as a bed or table is detected by an increase in the current flowing through the coil, and the tool and workpiece are It was designed to determine if there was contact.

However, in such conventional devices, an initial current of a certain level depending on the impedance of the coil flows through the coil even when the tool and the workpiece are not in contact, making it difficult to detect contact between the tool and the workpiece with high sensitivity. In this case, it is necessary to reduce the resistance of the induced current path and increase the current change upon contact.

Therefore, when detecting contact between a tool mounted on a spindle and a workpiece that moves relative to this tool using a contact detection device for a machine tool such as the one described above, a bearing for supporting the spindle is used. The resistance generated in the contact must be bypassed using a brush with very low contact resistance, which not only makes the bypass brush expensive, but also increases the contact resistance of the brush, which may make it impossible to reliably detect contact. Ta.

The present invention has been made in order to eliminate such conventional problems.A detection coil having an annular magnetic core in a shape that surrounds the induced current path is provided in addition to the excitation coil, and the present invention is designed to eliminate the problems of the conventional method. By detecting the flow of current using this detection coil, contact between the tool and the workpiece can be reliably detected even when the resistance value of the induced current path is large. .

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

FIG. 1 shows an example of a processing machine in which a workpiece W placed on a table 15 sliding on a bed 13 moves forward and backward with respect to a tool T attached to a spindle 12 of a spindle head 11. , the electrical resistance of the bearing supporting the spindle 12 is bypassed by the brush 16.

Reference numeral 20 indicates an excitation toroidal coil in which a coil 27 is wound around the entire circumference of an annular iron core 26 as shown in FIG. It is fixed like this, several K
It is excited by an AC power source 21 of Hz to several tens of KHz. This causes an alternating current to flow through the toroidal coil 20, generating a closed annular magnetic flux passing through the center of the toroidal coil winding. This magnetic flux includes the tool T, spindle 12, brush 16, spindle head 11, processing machine body 10, table 15, and workpiece W.
Because it surrounds a part of the current path 23 formed by the
1. An induced current flows through the processing machine body 10, table 15, and workpiece W.

On the other hand, 22 is a detection coil having the same configuration as the excitation coil 20, and is disposed so as to surround the center of the spindle head 11 at a certain distance from the tip surface of the spindle head 11. A shielding portion 24 that performs magnetic shielding is protruded between the spindle head 11 and the shaft head 22 so as to surround the outer periphery of the spindle head 11 . Therefore, the magnetic flux leaked from the coil 20 hardly acts directly on the detection coil 22 to generate an electromotive force on the detection coil 22, and the tool T and workpiece W are not in contact with each other, and the current path 23 In a state where no induced current flows, the output of the detection coil 22 becomes substantially zero.

In addition, when the tool T and workpiece W come into contact, the current path 23
When an induced current flows, a magnetic field induced by the induced current is generated around the outer periphery of the spindle head 11, and as a result, an alternating current flows through the winding of the detection coil 22, and an alternating current is generated from the detection coil 22. A voltage signal is output.

FIG. 2 is an equivalent circuit showing the relationship between the excitation coil 20 and the detection coil 22, in which the current path 23 is one
The resistance value of the current path 23, which is shown as a turn coil and is a combination of the contact resistance of the brush 16 and the contact resistance between the table 15 and the processing machine main body 10, is R.
It is shown in As is clear from this circuit, the excitation coil 20 and the current path 23 constitute a N:1 transformer, and the current path 23 and the detection coil 22 constitute a 1:1 transformer.
It constitutes N transformers. Therefore, if the input impedance Zi of the circuit connected to the output of the detection coil 22 is large to some extent and almost no current flows through the detection coil 22, the only current flowing through the current path 23 is the excitation current. It becomes a very small value, and the voltage drop due to the resistor R almost disappears.
Therefore, the magnitude of the voltage output from the detection coil 22 hardly changes even if the magnitude of the resistor R changes.

In FIG. 1, 25 is a determination circuit that determines whether the tool T is in contact with the workpiece W based on whether or not an AC voltage is output from the detection coil 22, and includes an input amplifier circuit with high input impedance; It consists of a rectifier circuit, a comparison circuit, etc.
In this way, since contact can be determined based on the presence or absence of AC voltage, contact between the tool T and the workpiece W can be reliably detected despite variations in the output voltage of the AC power supply 21 that excites the excitation coil 20. .

Note that the excitation coil 20 and the detection coil 2
The mounting position of 2 is not limited to the position of the above embodiment, and may be placed anywhere as long as both the excitation coil 20 and the detection coil 22 surround the current path 23. In addition, in the above embodiment, a shielding portion 24 was provided between the excitation coil 20 and the detection coil 22 so that both coils could be mounted close to each other, but the detection If the coil 22 is mounted apart from the excitation coil 20 so that the magnetic flux leaking from the excitation coil 20 does not directly act on the detection coil 22,
The shielding part 24 may not be provided.

Furthermore, the excitation coil 20 need only be capable of generating magnetic flux surrounding the induced current path, and the detection coil 22 only need to be capable of detecting with high sensitivity the magnetic field generated around the induced current path by the induced current. good. Therefore, the excitation coil 20 and the detection coil 22 may be formed by winding a coil 27' around a part of the annular iron core 26, as shown in FIG.

The embodiment shown in FIG. 5 is an application of the present invention to a grinding machine, and the grindstone G is electrically conductive.
This grindstone G includes a grindstone shaft 34, a grindstone stand 35, a bed body 36, a table 37, a workpiece support device 38,
A conductive relationship with the workpiece W is maintained via 39. In this case, the excitation coil 20 is arranged so as to surround the grindstone shaft 34 on the side of the grindstone G, and the detection coil 22
are arranged around the outer periphery of the excitation coil 20 with the magnetic shielding part 24 interposed therebetween.

As described above, in the present invention, the closed loop current path formed by the contact between the tool and the workpiece, that is, the tool and the workpiece, and the processing machine main body 10 and the bed main body 36 that electrically conduct them. An excitation coil having a coil wound around an annular magnetic core surrounding the current path is disposed in either of the above, and a detection coil having a coil wound around a magnetic core having a shape surrounding the current path is also disposed. Since contact is detected using the signal from this detection coil, the output signal from the detection coil will be close to zero when the tool and workpiece are not in contact, indicating that there is no contact between the tool and workpiece. increases the output signal from a value close to zero to a predetermined value. Therefore, it is possible to reliably distinguish between a non-contact state and a contact state, and compared to a system that detects contact based on a slight change in the level of the excitation current, the resistance of the induced current path is large and the AC voltage output at the time of contact is large. This has the advantage that contact between the tool and workpiece can be reliably detected even if the resistance of the induced current path is quite large. Therefore, in a processing machine or a grinding machine that uses such a contact detection device to detect contact between a spindle tool and a workpiece, the contact resistance of the brush that bypasses the resistance of the spindle affects the contact detection sensitivity. It has the advantage of not being affected.

Furthermore, magnetic flux is generated to surround the induced current path, and a detection coil is arranged to surround the induced current path, so when the tool and workpiece come into contact, a large excitation current is generated in the induced current path. In addition to being able to detect the flow of an induced current with high sensitivity, it has the advantage of being able to reliably detect contact between a tool and a workpiece without exciting the excitation coil at high frequency. Therefore, it is not necessary to use a high frequency power source that is likely to cause radio wave interference as an AC power source.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic side view of a processing machine equipped with a contact detection device, and FIG.
The figure shows an equivalent circuit showing the relationship between the excitation coil 20 and the detection coil 22 in Fig. 1, Fig. 3 shows the structure of the excitation coil 20 and the detection coil 22, and Fig. 4 shows the excitation coil 20 and the detection coil. 2
FIG. 5 is a schematic plan view of a grinding machine in which the contact detection device according to the present invention is applied to the grinding machine. DESCRIPTION OF SYMBOLS 10... Processing machine main body, 11... Spindle head, 12... Spindle, 15... Table, 16... Brush, 20...
Excitation coil, 21... AC power supply, 22... detection coil, 23... current path, 24... shielding part, 25... discrimination circuit, 34... grinding wheel shaft, 35... grinding wheel head, 36... bed body, 37... table, G... conductive Grindstone, T...Tool, W...Workpiece.

Claims (1)

[Claims] 1 A device that detects contact between a tool and a workpiece that are electrically connected through a support such as a bed or table and that approach or move away from each other,
an excitation coil that is arranged so as to surround a part of the current path formed by the tool, the workpiece, and the support such as the bed or table, and is wound around a ring-shaped magnetic core that surrounds the current path; a detection coil arranged so as to surround a part of the current path and having a coil wound around an annular magnetic core surrounding the current path; and an output of the detection coil that detects an induced current flowing in the current path. A contact detection device for a machine tool, characterized in that the contact detection device for a machine tool is provided with a discriminating means for discriminating whether the tool and the workpiece have contacted each other.