JP2710549B2 - Gap tracking type magnetic length measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gap-following magnetic length measuring apparatus, and more particularly to a gap-following magnetic measuring apparatus for measuring displacement magnetically by a magnetic scale graduated with magnetic lattice fringes and a magnetic head having a variable measuring span. It relates to a length measuring device.

[0002]

2. Description of the Related Art In order to detect displacement in a non-contact manner, a device which measures a distance from an appropriate origin as a length along a magnetic scale and outputs a change in the length as a displacement has been put into practical use. In a conventional example of this type of apparatus shown in FIG. 5A, a magnetic scale 1 has a magnetic pole 2 regularly magnetized at a constant pitch, and moves in parallel with the magnetic scale 1 across a gap d1. Each time 3 intersects the magnetic flux of each magnetic pole 2, it outputs a voltage signal corresponding to the change in magnetic flux. Magnetic scale 1
If the distance from the above appropriate reference point (not shown) is measured as a length along the magnetic scale 1, a change in the length can be detected as a displacement.

[0003]

However, the length measuring device of FIG. 5A has a disadvantage that an error occurs when the gap d between the magnetic scale 1 and the head 3 becomes small. When the gap d has an appropriate size like d1 in FIG. 5A, the magnetic flux density from the magnetic pole 2 of the magnetic scale 1 is equal to the magnetic flux detection span ± V _{m of the} head 3 (FIG. 5B). ), And the magnitude of the output voltage V of the head 3 corresponds to the magnetic flux density in the head 3. Therefore, the entire range of the magnetic flux detection span becomes the effective measurement range R of the displacement.

On the other hand, when the head 3 approaches the magnetic scale 1 too much as shown in FIG.
Magnetic flux density from and beyond the magnetic flux detecting span ± V _m of the head 3 (see the broken line curve in FIG. 5 (B)), the magnitude of the output voltage V saturation magnetic flux is generated in the head 3 does not correspond to the magnetic flux density Things are coming. For example, in the case of the curve of FIG. 5B, the magnetic flux density in the head 3 is the magnetic flux detection span ± V _m
When beyond increases, the output of the head 3 be varied as the magnetic flux density in the range of span indicated by the broken line is constant at this time + V _m or -V _m, between the output voltage flux density Is lost. Accordingly, the effective measurement range R of the displacement is significantly narrowed as shown. This means that the effective range of the measurement is greatly reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gap-following magnetic length measuring apparatus which can accurately measure even when a gap between a magnetic scale and a head fluctuates.

[0006]

Referring to FIG. 1, a gap-following magnetic length measuring apparatus according to the present invention comprises: a magnetic scale 1 having magnetic poles 2 regularly magnetized at a constant pitch; In a magnetic length measuring device comprising a head 3 which moves with a gap from the scale 1 and generates a signal corresponding to the intersection with the magnetic flux of the magnetic pole 2 and a counter 4 which counts a signal from the head 3, A configuration including a distance meter 6 for measuring a gap between the scale 1 and the head 3 and a span adjusting means 5 for adjusting a magnetic flux measurement span of the head 3 according to an output of the distance meter 6 is used.

Referring to FIG. 2, preferably, an amplifier 8 for amplifying a signal from the head 3 is provided between the head 3 and the counter 4, and the output of the distance meter 6 is output by the span adjusting means 5. The magnetic flux measurement span of the head 3 is adjusted by controlling the gain of the amplifier 8 in accordance with the following equation.
As shown in FIG. 4, the head 3 includes a saturable core 12 having an exciting winding 14 and a core 10 having a signal winding 13 in series with the saturable core 12. The magnetic flux measurement span of the head 3 may be adjusted by controlling the current of the exciting winding 14 in accordance with the output of the head 3.

[0008]

Referring to the embodiment of FIG. 2, in the case of using a magnetic sensor 3 having a relatively small output without saturation and using an amplifier 8 to amplify the output of the magnetic sensor 3 and adding it to the counter 4, the distance The distance d between the magnetic scale 1 and the magnetic sensor 3 is measured by a distance meter 6 such as an engineering type, an acoustic type, or a mechanical contact type, and a gain control circuit 7 is used by using a signal of the measured distance. Controls the gain of the amplifier 8.
For example, the distance d between the magnetic scale 1 and the magnetic sensor 3 is found to be about d1 shown in FIG. 5A by the distance meter 6, and the magnetic flux detection span ±
If it is determined in advance that V _m is appropriate, the magnetic flux detection span ± V _m according to the signal of the gap d1 from the distance meter 6.
The gain of the amplifier 8 is controlled via the gain control circuit 7 so as to obtain If the distance meter 6 finds that the gap d has been reduced to d2 in FIG. 5 (B) and it is predetermined that the magnetic flux detection span ± _VL is appropriate for this gap d2,
According to the signal of the gap d2 from the distance meter 6, the magnetic flux detection span ±
Amplifier 8 through gain control circuit 7 so that V _L can be obtained.
To control the gain. Thus, even if the gap d between the magnetic scale 1 and the magnetic sensor 3 fluctuates, the magnetic flux detection span of the magnetic sensor 3 is controlled in accordance with the fluctuation of the gap d, so that the magnetic measurement without error due to magnetic saturation. A long device is realized.

Here, it is not always necessary to predetermine the magnetic flux detection spans ± V _m , ± _VL, etc., and they may be selected by trial and error during operation.

Therefore, the object of the present invention is to provide a "gap-following magnetic length measuring apparatus capable of measuring accurately even when the gap between the magnetic scale and the head fluctuates".

[0011]

FIG. 3 shows an example of a contact type distance meter 6 which can be used in the present invention. One end of the leaf spring 18 is fixed to a strain detector 19 serving as a distance sensor, and the other end protrudes from the strain detector 19 and held so as to be in contact with an object to be measured (not shown).
When the gap d between the strain detector 19 and the object to be measured is equal to or less than a predetermined length, the other end of the leaf spring 18 comes into contact with the object to be measured, causing distortion. Since this distortion is a function of the gap d between the distortion detector 19 and the object to be measured, the distance d can be determined by the distortion detected by the distortion detector.

FIG. 4 shows another embodiment of the present invention. The magnetic sensor 3 has a pair of cores 10, and one end of each core has a head magnetic pole 11 for measuring the length along the magnetic scale 1.
Is provided. A saturable core 12 is provided at the other end of the core 10, a signal winding 13 is wound around the core 10, and a saturable core 12 is provided.
The excitation winding 14 is wound around the. The reason why the pair of cores 10 is used is to determine the moving direction. Signal winding 13 for each core
Are connected to the counter 4 via a bandpass filter 16, and each excitation winding 14 is connected to an excitation circuit 15. The above structure belongs to the prior art. According to the invention, the distance meter 6 is mounted on the core 10, and the excitation circuit 15 functions as the span adjusting means 5 in this case. The magnetic flux of the head 3 is detected by controlling the exciting current supplied to each exciting winding 14 via the exciting circuit 15 in accordance with a signal from the distance meter 6 regarding the gap d between the magnetic scale 1 and the head 3. The span is adjusted according to the change in the gap d. Even when the gap d fluctuates, magnetic saturation in the head 3 is prevented, and high-precision length measurement is ensured.

[0013]

As described in detail above, the gap-following magnetic length measuring apparatus of the present invention adjusts the magnetic flux detection span of the head according to the change in the gap between the magnetic scale and the head. There is a remarkable effect that the length and displacement can be measured accurately even when the gap between the head and the head fluctuates.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of an embodiment of the present invention using gain control of an amplifier.

FIG. 3 is a schematic explanatory view of an example of a mechanical distance meter.

FIG. 4 is an explanatory diagram of an embodiment using an excitation circuit.

FIG. 5 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

1 magnetic scale 2 magnetic pole 3
Head 4 Counter 5 Span adjusting means 6
Rangefinder 7 Gain control circuit 8 Amplifier 10
Core 11 Head pole 12 Saturable core 13
Signal winding 14 Excitation winding 15 Excitation circuit 16
Band filter 18 Leaf spring 19 Strain detector.

Claims (3)

(57) [Claims] A magnetic scale having magnetic poles regularly magnetized at a constant pitch; a head moving from the magnetic scale with a gap therebetween to generate a signal corresponding to an intersection with a magnetic flux of the magnetic pole; In a magnetic length measuring device comprising a counter for counting a signal from the head, a distance meter for measuring a gap between the magnetic scale and the head, and a magnetic flux measurement span of the head following the output of the distance meter. A gap-following magnetic length measuring device having a span adjusting means for adjusting. 2. The magnetic length measuring apparatus according to claim 1, wherein the head includes a saturable core with an exciting winding and a core with a signal winding in series with the saturable core, and the distance meter is provided by the span adjusting means. And a gap-following magnetic length measuring device which controls the current of the exciting winding according to the output of the magnetic field measuring device. 3. The magnetic length measuring device according to claim 1, further comprising: an amplifier for amplifying a signal from the head between the head and the counter, wherein the span adjusting means responds to the output of the distance meter. A gap-following magnetic length measuring device that controls the gain of an amplifier.