JPH0223301B2 - - Google Patents

Description

Detailed Description of the Invention The present invention allows an induced current to flow in a loop-shaped secondary circuit formed on a machine tool when a tool attached to a rotating spindle comes into contact with a workpiece. The present invention relates to a contact detection device that detects contact between a tool and a workpiece by electrically detecting the flow of this induced current.

Generally, in such a contact detection device, the bearing supporting the main shaft is inserted in series in the secondary circuit through which an induced current flows, so if an oil film forms on the bearing and the inner and outer rings of the bearing become electrically insulated, Even if the tool contacts the workpiece, no induced current flows in the secondary circuit, making it impossible to detect contact between the tool and the workpiece.

For this reason, conventionally, as a means to bypass the insulation resistance caused by the oil film of the bearing,
A brush was provided that contacted the outer surface of the spindle and was electrically connected to the spindle head, but with this type, the brushes would wear out if the machine tool was operated for a long period of time, so the I had to replace the brush.

The present invention has been made in view of these conventional problems, and includes a capacitance adding member (hereinafter simply referred to as capacitance) that is electrically connected to the spindle head and is attached to the outer surface of the spindle or the rotating shaft that is electrically connected to the spindle. The purpose of this invention is to bypass the insulation resistance generated in the bearing by arranging additional members (referred to as additional members) close to each other in a non-contact manner, thereby eliminating the need for maintenance of such a bypass means.

Embodiments of the present invention will be described below based on the drawings. In FIG. 1, reference numeral 10 denotes a main spindle head of a machine tool, and the main spindle head 10 includes a main spindle 11 with a tool T attached to its tip, and a pair of bearings 12 disposed at a predetermined distance in the axial direction. , 13. A gear G1 is integrally fixed to the rear end of this main shaft 11, and this gear G1
is meshed with a gear G3 attached to the output shaft of the main shaft drive motor 16 via a gear G2 supported on the main shaft head 10 via the rotating shaft 15.

Reference numeral 17 denotes a capacity adding member that is loosely fitted on the outside of the main shaft 11 between the pair of bearings 12 and 13, and is attached to the main shaft head 10 with a metal bolt or the like.
The spindle head 10 is electrically connected to the spindle head 10. The main shaft 1 bored in this capacity adding member 17
The through hole concentric with 1 is formed to have a diameter slightly larger than the outer diameter of the main shaft 11, for example, by about 10 μm to 100 μm in radius, and its axial length is equal to the inner peripheral surface of the capacity adding member 17. It is made as long as possible so that the area facing the outer peripheral surface of the main shaft 11 is as wide as possible.

Due to this capacitance adding member 17, a capacitance Cb is generated between the main shaft 11 and the inner circumferential surface of the capacitance adding member 17.
0, this capacitance Cb is the insulation resistance based on the oil film generated on the bearings 12 and 13, as shown in Figure 2.
It exists in a parallel relationship with Ri.

The inner circumferential surface of the capacitance adding member 17 and the outer circumferential surface of the main shaft 11 are parallel flat plates and can be considered equivalent to a capacitor. The length of is l,
Letting d be the gap between the capacity adding member 17 and the main shaft 11, the value is calculated by the following equation.

Cb=1/36π×10 ⁹ ×2πrl/d=rl/1.8d×10 ¹⁰ (F) However, in the above equation, radius r, length l, gap d
The unit of is (m).

For example, the inner radius r of the capacity adding member 17 is 100
mm, length l is 200 mm, and gap d is 10 μm,
The capacitance Cb is 0.11μF.

On the other hand, 20 has a main shaft 11 mounted on the front surface of the main shaft head 10.
The excitation coil 20 is a toroidal excitation coil disposed so as to surround the outer periphery of the excitation coil 20. The excitation coil 20 is connected to an excitation AC power source 21 via a detection resistor Rd. As a result, a magnetic flux surrounding the main shaft 11 is excited in the excitation coil 20, and the main shaft 11
When the tool T contacts the workpiece W placed on the machine tool opposite to it, the machine body, spindle head 10, bearings 12, 13, spindle 11, tool T,
An induced current flows through a loop-shaped secondary circuit 22 formed by the workpiece W. As a result, the current flowing through the exciting coil 20 increases and the detection resistor
The voltage across Rd increases, and in response, the contact detection circuit 23 sends out a contact detection signal TDS.

As mentioned above, the bearings 12 and 13 are connected in series to the secondary circuit 22 through which the induced current flows, but the insulation resistance Ri based on the oil film generated on the bearings is bypassed by the conductive property of the capacitance Cb. , when the tool T contacts the workpiece W, a large short-circuit current flows through the secondary circuit 22, and the rate of voltage rise across the detection resistor Rd increases at the time of contact, increasing the contact between the tool T and the workpiece W. Can be detected sensitively and reliably.

For example, set the frequency of the excitation AC power supply 21 to 2M.
Hz, the impedance Zc of the capacitance Cb of 0.11μF is 0.7Ω, and the spindle 11 and spindle head 10, which are electrically isolated by the insulation resistance Ri,
This means that electrical continuity can be established between the two with a sufficiently small electrical resistance.

Therefore, when the tool T contacts the workpiece W, a large induced current flows through the secondary circuit 22, and it is possible to reliably detect that the tool T has contacted the workpiece W.

In addition, in the above embodiment, the capacity adding member 17
By supplying a fluid with a higher dielectric constant than air to the gap between the inner circumferential surface of the main shaft 11 and the outer circumferential surface of the main shaft 11, a larger capacitance can be added using a capacitance adding member of the same shape. For example, when lubricating oil such as spindle oil is supplied, since the dielectric constant of the lubricating oil with respect to air is about 2, the capacitance that can be added by the capacitance adding member can be almost doubled.

Further, the capacitance adding member may be provided on a rotating shaft 15 that rotates together with the main shaft 11 and is in electrical conduction with the main shaft 11, as shown by the two-dot chain line in FIG.

As described above, in the present invention, the capacitance adding member is electrically connected to the spindle head that supports the spindle in proximity to the outer surface of the spindle or the rotating shaft that is in electrical continuity with the spindle. By providing a capacitance between the spindle head and the spindle, the electrical conductivity based on this capacitance bypasses the insulation resistance of the oil film that occurs on the bearing. Therefore, even without maintenance, the effect of bypassing the insulation resistance of the oil film continues semi-permanently, and there is an advantage that no maintenance is required.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a longitudinal sectional view of the spindle head, and FIG. 2 is an equivalent electrical circuit diagram of the contact detection device. 10...Spindle head, 11...Spindle, 12,1
3... Bearing, 15... Rotating shaft, 17... Capacitance addition member, 20... Excitation coil, 21...
Excitation power supply, 22...Secondary circuit, T...Tool, W...
...Workpiece.

Claims (1)

[Claims] 1 A coil is arranged so as to generate an induced current in a loop-shaped secondary circuit formed on the machine tool by contact between the workpiece and the tool of the spindle rotatably supported on the spindle head, and this coil is connected to an alternating current. In a contact detection device connected to a power source and equipped with a signal detection means for detecting a change in an electrical signal caused by the presence or absence of the contact, an outer surface of the main shaft or a rotating shaft that is in electrical continuity with the main shaft is provided. A capacitance adding member is disposed close to each other so that the main shaft or rotating shaft and the capacitance adding member are electrically connected by capacitance, and further the capacitance is A contact detection device characterized in that an additional member is attached to the spindle head in electrical continuity.