JPH1047351A - Air bearing spindle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air bearing spindle which can remove a sensor output drift by a temperature. SOLUTION: A spindle 1 is supported in a housing 3 on a static pressure bearing 2, the spindle 1 is driven to rotate by a motor 4, a sensor coil 9 is provided on one end side of the spindle 1 facing it, a dummy coil 10 is arranged to be opposed to a dummy target 11 near the coil 9. By subtracting an output of the dummy coil 10 from an output from the sensor coil 9, a temperature drift is removed, and a displacement detection signal of the spindle without an influence by a temperature change is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air bearing spindle, and more particularly, to an air bearing spindle for detecting a displacement of a spindle in a spindle in which a spindle is supported in a housing by a fluid bearing including the air bearing.

[0002]

2. Description of the Related Art Conventionally, there is a problem that a small hole is easily broken during machining because the diameter of a tool is small. For this reason, attempts have conventionally been made to monitor the machining state to prevent overload applied to the tool, or to detect or predict the breakage of the tool. Some devices detect a reaction force by displacement of a main shaft. In particular, when the main shaft is supported by a hydrostatic bearing, vibration during rotation caused by the bearing can be extremely reduced, so that even a minute machining reaction force can be detected as a displacement of the shaft.

FIG. 3 is a diagram showing an example of such a spindle. In FIG. 3, a main shaft 1 is supported by a housing 3 by a hydrostatic bearing 2, and is driven to rotate by a motor 4. A displacement gauge 5 is provided at one end of the main shaft 1, and a drill 6 is attached to the other end. The displacement meter 5 detects the displacement of the main shaft, and outputs the displacement to the outside via the displacement detection circuit unit 7.

[0004]

The air bearing spindle capable of forming a small-diameter hole as shown in FIG. 3 is often operated at a high speed, so that the motor 4 generates heat during rotation and generates heat during rotation. Heat generation due to friction loss from bearings,
When a sensor is built into the spindle due to the effect of temperature change of the coolant of the housing 3 or the like, the sensor is affected to some extent by the temperature or thermal expansion of the spindle. Conventionally, this thermal change of the sensor section is not so large as to the detection sensitivity, and thus has not been a problem.

However, when the built-in sensor requires higher detection sensitivity or is used at a higher rotation speed, the output drift due to the temperature of the sensor has been regarded as a problem.

[0006] It is, therefore, a primary object of the present invention to provide an air bearing spindle that can eliminate drift in sensor output due to temperature.

[0007]

The invention according to claim 1 is
In an air bearing spindle for detecting a displacement of a main shaft of a spindle which supports a main shaft in a housing by an air bearing, a displacement sensor provided on the spindle and detecting displacement of the main shaft, and a displacement sensor provided near the displacement sensor and having a temperature of the displacement sensor A pseudo sensor for removing the drift and a detection circuit for removing a temperature drift from an output of the displacement sensor based on an output of the pseudo sensor and outputting a signal indicating a displacement of the main shaft are provided.

According to the second aspect of the present invention, a dummy target is provided to face the pseudo sensor of the first aspect.

In the invention according to claim 3, the detection circuit of claim 1 is built in the housing.

[0010]

FIG. 1 is a sectional view showing a spindle according to an embodiment of the present invention, and FIG. 2 is a block diagram of a sensor circuit. 1, a main shaft 1, a hydrostatic bearing 2, a housing 3, and a motor 4 are configured in the same manner as in FIG. 3, and a sensor core 8 is attached to the housing 3 at one end of the main shaft 1. A sensor coil 9 for detecting displacement of the main shaft 1 and a dummy coil 10 for canceling a temperature drift of the sensor coil 9 are attached to the sensor core 8. In addition, a member called a dummy target 11, which is substantially equivalent to the main spindle 1, is fixedly installed on the sensor core 8 at a position facing the dummy coil 10. Each coil is connected to a displacement detection circuit unit 12, which converts the distance between each coil 9, 10 with the target 11 into a DC voltage and outputs a difference between the two DC voltages.

The displacement detection circuit section 12 is configured as shown in FIG. That is, the oscillation circuit 13 oscillates a sine wave and supplies the sine wave to the sensor unit 14. The sensor section 14 is composed of two resonance circuits 15 and 16 in which the sensor coil 9 and the dummy coil 10 shown in FIG. An eddy current is generated in the target 11 facing the target, and its inductance changes depending on the distance between the target and the coil and the temperature around the coil.

In one embodiment of the present invention, the target of the sensor coil 9 is the main shaft 1, and the dummy coil 10 has a dummy target 11 fixed thereto. As a result, the inductance of the sensor coil 9 changes due to two factors, the position of the main shaft 1 and the temperature, and the dummy coil 10
Will change only with temperature. Due to the change of these inductances, each resonance circuit 15, 1
6, the resonance points of the respective resonance circuits 15, 16 change accordingly.
Changes the amplitude of the sine wave.

The sine wave whose amplitude has changed is supplied to the rectifier circuit 1 in the subsequent stage.
The voltage is converted into a DC voltage by 7 and 18, and the difference between the output on the sensor side and the output on the dummy side is output by the differential circuit 19. As a result, the change in inductance due to the sensor coil 9 is caused only by the change in the axis, and it is possible to output a stable change in the main shaft 1 with respect to temperature. A low-pass filter 20 for removing high-frequency noise is provided at the subsequent stage of the differential circuit 19, and after high-frequency noise unnecessary for displacement of the main shaft 1 is removed, the low-pass filter 20 outputs the noise to the outside.

In the example shown in FIG. 1, since the dummy target 11 is fixed to the tip of the dummy coil 10, the gap between the coil and the target is determined by the processing size of the dummy target portion, and variation between products is reduced. Can be reduced.

If the displacement detection circuit shown in FIG. 2 is housed in the housing 3 and the distance between the sensor and the sensor is shortened, the influence of the change in inductance due to the cable can be prevented.

[0016]

As described above, according to the present invention, the displacement sensor is provided at one end of the spindle to detect the displacement of the main shaft, and the pseudo sensor is provided near the displacement sensor, and the pseudo sensor is provided based on the output of the pseudo sensor. The temperature drift is removed from the output of the displacement sensor to output a signal indicating the displacement of the spindle, so that the change due to temperature is canceled,
Only the displacement of the main shaft can be taken out.

[Brief description of the drawings]

FIG. 1 is a sectional view of a spindle according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of a displacement detection circuit unit shown in FIG.

FIG. 3 is a longitudinal sectional view of a conventional air bearing spindle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 2 Hydrostatic bearing 3 Housing 4 Motor 6 Drill 8 Sensor core 9 Sensor coil 10 Dummy coil 11 Dummy target 12 Displacement detection circuit part 13 Oscillation circuit 14 Sensor part 15, 16 Resonance circuit 17, 18 Rectification circuit 19 Differential circuit 20 Low pass filter

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location G01B 21/00 G01B 21/00 A

Claims (3)

[Claims] 1. An air bearing spindle for detecting a displacement of the main shaft of a spindle that supports the main shaft in a housing by an air bearing, a displacement sensor provided on the spindle and detecting a displacement of the main shaft, a vicinity of the displacement sensor. A pseudo sensor for removing a temperature drift of the displacement sensor, and a detection of removing a temperature drift from an output of the displacement sensor and outputting a signal indicating a displacement of the main shaft based on an output of the pseudo sensor. Air bearing spindle with circuit. 2. The method according to claim 1, wherein a dummy target is provided to face the pseudo sensor.
Air bearing spindle. 3. The air bearing spindle according to claim 1, wherein said detection circuit is built in said housing.