JPH0132026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a contact detection method for machine tools that electrically detects the presence or absence of contact between a spindle head and a workpiece support device that are in an electrically conductive relationship and that are relatively approaching or separating from each other. It is related to the device.

Some conventional contact detection devices use induction coils, which are wound around an iron core that is placed around an object that moves relative to each other, such as the spindle head of a machine tool. At the same time as the two objects are excited, the secondary current path is closed by contact between the two objects, and the presence or absence of the contact is determined by detecting a change in the excitation current of the primary coil accompanying the closure of the secondary current path. A primary side detection method is known. Such a coil constitutes the primary winding of a transformer, and the closed loop secondary current path formed by the contact becomes a 1-turn secondary winding, and the winding ratio to the primary winding is very small. Therefore, the change is very small compared to the change in the excitation current of the primary winding. For this reason, such a primary side detection method has a problem in that the degree of change in the signal during contact and non-contact cannot be made very large. In addition, when there is light contact between the sharp cutting edge of the tool inserted into the spindle and the workpiece,
It is extremely difficult to cause a large induced current to flow through the secondary side, and it is also difficult to increase detection sensitivity in such cases.

In particular, since the main shaft supported by a rolling bearing is present in the secondary current path, bearings lubricated with an oil film have a relatively high electrical resistance and reduce the secondary induced current. A brush was required to contact the main shaft as a means of bypassing electrical resistance. The electrical resistance of such a bearing has been an obstacle to increasing detection sensitivity in devices that use the primary side detection method.

The present invention attempts to detect on the secondary side in place of the conventional primary side detection method, and in particular actively utilizes the electrical resistance of the bearing to detect the secondary current path due to contact between two objects. The purpose is to detect the potential difference that occurs across the bearing electrical resistance based on the current flowing through the bearing.

Embodiments of the present invention will be described below based on the drawings. 10 is a spindle head of a machine tool equipped with an automatic tool changer, and 11 is a bearing 12, 1 attached to this spindle head 10.
A rotating main shaft 11 is rotatably supported at 3 and 14, and a through hole 15 is bored in the center of the rotating main shaft 11, and a tool socket 16 for removably receiving a tool T is provided at one end of the through hole 15. It is formed. A clamp bar 17 is inserted through the through hole 15, and an engaging portion 17 is provided at one end of the clamp bar 17 to engage with a pull stud 18 protruding from the end of the tool T.
a, the other end of which protrudes from the rear end of the rotating main shaft 11, and a spring 19 formed by stacking a plurality of disc springs is arranged on the outer periphery of the central portion. One end of this spring 19 engages with the engagement step portion 11a of the rotating main shaft 11, and the other end engages with the engagement step portion 11a of the rotating main shaft 11.
The tool T is engaged with a flange portion 20 protruding from
A pressing force in the direction of pulling in is applied to the clamp bar 17. Projecting end 17 of the clamp bar 17
An unclamping cylinder 21 is arranged opposite to b and is fixed to the spindle head 10. The piston 22 fitted into the cylinder 21 has piston rods 23 and 24 protruding from it.
A contact member 25 that contacts the protruding end 17b of the clamp bar 17 is rotatably supported at the tip of the clamp bar 17. A through hole 26 is bored through the contact member 25, the piston 22, and the piston rods 23, 24, and insulating bushes 30, 31, 32 made of an insulator are fixed to the through hole 26. A holding rod 28 made of a conductive material and holding a brush 27 at one end is inserted into the holes of the insulating bushes 30, 31, and 32. A spring 29 is provided between the large diameter portion 28a of the holding rod 28 and an insulating bushing 32 fixed to the end of the piston rod 24.
is compressed and inserted, pressing the brush 27 against the end surface of the clamp bar 17. The contact position between the brush 27 and the clamp bar 17 coincides with the center of rotation of the rotating main shaft 11, and a contact member 17c made of a copper alloy is embedded in the contact surface on the clamp bar 17 side. A keyway 28b is carved along the axis of the holding rod 28, and an insulating bushing 32 fixed to the end of the piston rod 24 is inserted into this keyway 28b.
An engaging pin 24a provided protrudingly engages to prevent rotation and allows movement in the axial direction.
In order to unclamp the tool T, the piston 22 moves forward from the state shown in the figure, and the abutting member 25 moves against the clamp bar 1.
When the spring 2 moves until it comes into contact with the end face of 7,
9 is compressed, and the holding rod 28 maintains contact with the brush 27 and does not move. The conductor 33 and spindle head 10 connected to the end of this holding rod 28
The conductive wire 34 connected to is connected to input terminals 41 and 42 of a detection circuit 40 that detects a potential difference.

An annular groove 10b is formed in the bearing housing 10a which protrudes from the front surface of the spindle head 10 and is concentric with the spindle.As shown in FIG. The wound induction coil 35 is housed, and the holding plate 36 made of insulating material
It is installed at. When this induction coil 35 is excited by an AC power supply 37, a magnetic flux surrounding the rotating main shaft 11 is formed along the annular iron core, and a secondary current flowing in the direction of the main shaft axis is induced. As a secondary circuit through which this secondary current flows, when the tool T and workpiece W come into contact, the machine body, the spindle head 10, and the bearing 1
2, 13, 14, a closed loop current path 38 is formed through the rotating main shaft 11, and a current flows therethrough. If the tool T and workpiece W do not come into contact, such a closed loop will not be formed and no secondary current will flow.

As a result, a voltage drop based on the electric resistance R of the bearings 12, 13, and 14 occurs due to the current flowing through the current path 38 as a secondary coil for the induction coil 35, and the voltage drop between the rotating main shaft 11 and the main spindle head 10 is caused.
A potential difference occurs between the two. Electrical resistance R of this bearing
has the largest resistance in the current path 38, and is several hundreds of ohms during rotation of the main shaft, and therefore produces the most significant potential difference. This potential difference is generated between the rotating spindle 11, the holding rod 28 which is in a conductive relationship via the clamp bar 17 and the brush 27, and the spindle head 10 which is in a conductive relationship with the workpiece W through the machine body. The potential difference is led to input terminals 41 and 42 of the detection circuit 40 via conductive wires 33 and 34, and the level of the potential difference is determined. If there is no contact between the tool T and the workpiece W, no secondary current will flow, so the potential difference will be zero, and the detection circuit 40 will not issue a contact detection signal. When the tool T and workpiece W come into contact, a secondary current flows and a potential difference is generated, so the detection circuit 40 outputs a contact detection signal in response to this potential difference.

In this way, in the present invention, the voltage drop due to the resistance R of the bearing is detected, and the resistance R of the bearing is the same as that of the tool T, which has the largest resistance in the current path 38.
If there is no contact between the workpiece and the workpiece W, the potential difference is zero, but if contact occurs and a secondary current flows, a potential difference is generated, so the rate of change in the signal appears large and the detection sensitivity can be increased. Moreover, it has the effect of being able to reliably detect the state in which the sharp cutting edge of the tool lightly contacts the workpiece W.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a longitudinal cross-sectional view of the main part of the spindle head, and FIG. 2 is an equivalent electric circuit diagram. 10...Spindle head, 11...Rotating main shaft, 12,1
3, 14...Bearing, 17...Clamp bar, 27
... Brush, 28 ... Holding rod, 35 ... Induction coil, 37 ... AC power supply, 38 ... Current path, 4
0...detection circuit, T...tool, W...work.

Claims (1)

[Claims] 1. A spindle head having a spindle rotatably supported via a bearing and a workpiece support device supporting a workpiece are electrically connected through the machine body, and as the two move toward each other relative to each other, In a machine tool in which a closed-loop current path is formed by contact, an electromagnetic coil that is excited to induce an induced secondary current is arranged in this current path, a brush is brought into contact with the main shaft, and the brush and the Conductive wires are connected to the spindle head, respectively, and detection means is provided for detecting a voltage drop due to the electrical resistance of the bearing connected between these conductive wires and interposed in series in the closed loop current path. Contact detection device for machine tools. 2. The contact detection device for a machine tool according to claim 1, wherein the electromagnetic coil includes an annular core through which a portion of the spindle head is inserted, and an excitation coil wound around the core.