JPH03188320A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To enhance detection accuracy by winding an exciting coil around the fixed gear provided in opposed relation to a movable gear composed of a magnetic body and detecting the current flowing through the exciting coil to detect the movement of the movable gear. CONSTITUTION:A movable gear 40 composed of a magnetic body is provided on a rotary shaft and a large number of teeth 40a are formed on the outer periphery thereof at an equal pitch. A fixed gear 42 is provided in close vicinity to the movable gear 40 and a plurality of teeth 42a are formed on the gear 42 in opposed relation to the teeth 40a at the pitch equal to that of the teeth 40a. An exciting coil 44 is wound around the yoke part 42b of the fixed gear 42 and predetermined voltage is applied to the exciting coil 44 from an exciting circuit 46. When the movable gear moves, the change of the current flowing through the exciting coil 44 is detected by a current detection circuit 50 and, therefore, an angle of rotation can be known.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic encoder, and particularly to an improved magnetic encoder that can electrically detect the moving position of a movable body without contacting the movable body.

[Prior Art] Accurately detecting the current position of a rotating or linearly moving movable body is necessary in various industrial fields, and is particularly essential as a position detector for equipment that is subject to feedback control or synchronous control.

Such an encoder is used, for example, to detect the spindle rotational phase of a machine tool, the position of a feed table, or as a probe position detector of a coordinate measuring machine.

FIG. 8 shows a conventional photoelectric encoder. For example, in order to detect the rotational position of a rotating shaft 10, the rotating shaft 10 is provided with a plurality of light transmitting or light shielding slits 12 on its side surface. A circular plate 14 is fixed, and when this slit 12 moves together with the rotating shaft 10, the circular plate 14 is fixed.
The movement of the slit is electrically detected by a photoelectric element provided near 4.

In the illustrated conventional device, an index disk 16 is provided in parallel with the disk 14, and the index disk 16 has index slits 1 having a phase difference of 90 degrees.
6a and 16b are provided, and light emitting elements 18a and 18 are placed opposite to each other with the disk 14 and index disk 16 in between.
b. Electric signals having a phase difference of 90 degrees can be detected by the light receiving elements 20a and 20b as the slit 12 moves.

In addition, in the illustrated conventional device, in order to detect one rotation of the disk 14, the disk 14 and the index disk 16 are
Sub-slits 22 and 24 are respectively provided in the sub-slits 22 and 24, and one rotation of the disk 14 is detected in cooperation with the light-emitting element 26 and the light-receiving element 28.

FIG. 9 also shows a magnetic encoder as another conventional encoder, in which a gear 3 is attached to a rotating shaft (not shown).
0 is fixed, and magnetoresistive elements 32a and 32b are provided near this gear 30 with phases different by 90 degrees, and movement signals of the rotation axis are detected from the pixel elements 32a and 32b via preamplifiers 34a and 34b. Ru.

In this magnetic encoder, the gear 30 is made of a magnetic material, and the magnet 36 provided on the base of each of the magnetoresistive elements 32a, 32b causes the magnetoresistive element 3 to
Bias magnetic flux is supplied to 2a and 32b, and the magnetoresistive elements 32a and 32b convert the movement of the rotating shaft into an electric signal and detect it by the change in magnetic flux that occurs when the gear 30 made of the magnetic material moves.

[Problems to be Solved by the Invention] However, in the photoelectric encoder described above, the disk 14 is usually made of a material with excellent light transmission characteristics such as glass in order to form the light transmission or light shielding slits 12,22. As a result, there was a problem in that sufficient durability could not be maintained against external vibrations or shocks.

In addition, in the magnetic encoder, the magnetic resistance element 32a
, 32b, a magnet 36 for applying a magnetic bias to
As a result, iron powder, such as machine tools, etc.
There was a problem in that a large measurement error occurred in a work environment with a lot of chips.

Furthermore, each of the conventional devices described above has a problem in that the photoelectric element or the magnetoresistive element is easily affected by temperature, making it difficult to perform highly accurate measurements. The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a magnetic encoder with excellent environmental resistance, high reliability, and high measurement accuracy.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for moving a movable body such as a rotating shaft or a linear moving body without using a conventional semiconductor element such as a light emitting/receiving element or a magnetoresistive element. connected,
A magnetic fixed tooth is provided adjacent to a magnetic movable tooth having a plurality of teeth at an equal pitch on its outer periphery. Detect relative movement with.

To detect the relative movement, an excitation coil to which a voltage is applied from an excitation circuit is wound around the fixed teeth, and a current flowing through the coil is detected by a current detection circuit.

Therefore, according to the present invention, highly accurate position detection is possible by combining the excitation means, which is not easily influenced by the surrounding environment of the encoder, and the fixed teeth and movable teeth made of magnetic material.

Further, according to the present invention, a plurality of excitation coils provided with the excitation means and the current detection circuit are fixedly arranged, and the fixed teeth of these excitation coils are arranged with different phase differences with respect to the movable teeth. It is also possible to obtain detection signals having different phases, for example, 90 degrees different phases.

[Function] Therefore, according to the present invention, an alternating current signal or a pulse signal is normally applied to the excitation coil wound around the fixed tooth, and at this time, the signal changes depending on the relative position of the fixed tooth and the movable tooth. The coil current changes in accordance with the change in mutual inductance, and the current detection circuit detects this change in the coil current, thereby making it possible to detect the position or phase of the movable body.

Further, according to the present invention, a plurality of, for example, si
By obtaining an n-wave signal and a cosine-wave signal and dividing them using a well-known dividing circuit, it becomes possible to perform position detection with a sufficiently finer resolution than the fixed tooth and movable tooth pitches.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a preferred embodiment in which the magnetic encoder according to the present invention is configured as a rotary encoder, and a movable tooth 40 is connected to a rotating shaft (not shown), and this movable tooth 4θ usually It is made of magnetic material such as iron.

A plurality of teeth 4 are arranged at equal pitches on the outer periphery of the movable teeth 40.
0a is formed, and in the embodiment, this tooth 40a consists of an uneven surface.

On the other hand, a fixed tooth 42 is fixedly arranged adjacent to the movable tooth 40, and a plurality of teeth 42a are formed on a surface of the movable tooth 40 that faces the tooth surface 40a.

In the embodiment, the fixed teeth 42 are made of a magnetic material with high magnetic permeability and low core loss against high frequency magnetic fields, such as ferrite.

In addition, the fixed teeth 42 form a U-shaped yoke portion 42b in the embodiment, and two teeth 42a are provided at each end of the fixed teeth 42 at the same pitch and with the same phase as the plurality of teeth 40a of the movable teeth 40. It is formed of.

Therefore, it is understood that the magnetic coupling, that is, the magnetic resistance between the movable teeth 40 and the fixed teeth 42, changes significantly as the relative positions of the movable teeth 40 and the fixed teeth 42 change.

In this embodiment, an excitation coil 44 is wound around the yoke portion 42b of the fixed tooth 42.
A predetermined voltage is applied to 4 from an excitation circuit 46 such as an AC power source.

In the embodiment, this excitation circuit is comprised of a high frequency AC voltage source of, for example, about 500 kHz, and can excite the coil 44 at high frequency.

Further, the current flowing through the excitation coil 44 is detected by a current detection circuit 50 including a current transformer 48.

Therefore, as is clear from FIG.
The detected current i of the exciting coil 44 detected at is a current that lags behind the applied voltage V, and the delayed phase at this time is mainly influenced by the inductance of the exciting coil 44.

As described above, when the movable tooth 40 rotates, the relative position between the tooth 40a of the movable tooth 40 and the tooth 42a of the fixed tooth 42 changes, and due to the change in magnetic resistance between the two, the relative position changes according to the phase difference. It is understood that the delay phase of the detection current i changes.

Therefore, according to the present invention, it is possible to electrically detect the position of the movable tooth 40 with respect to the fixed tooth 42 by obtaining the phase difference of the detection current i or the amplitude change of the detection current i with respect to the applied voltage V.

Below, the detection operation of the embodiment shown in FIG. 1 will be explained based on FIG. 2.3.

In FIG. 2A, the tooth 40a of the movable tooth 40 is connected to the tooth 40a of the fixed tooth 42.
The relationship between the voltage V applied to the coil 44 and the coil current i at this time is as follows (
shown.

v=V cosωt −(1) where: ILcosωt IrS1nωt.

... (3) 1 φ-tan (IL / I r ) ω is the movable body 40
, the angular frequency of has a delayed characteristic, and its amplitude value is also determined by It and Ir.

The It and Ir are the movable tooth 40 and the fixed tooth 42.
It is understood that this changes depending on the relative positional relationship with the

FIG. 3A shows a state in which the opposing tooth surfaces of the movable tooth 40 and the fixed tooth 42 are furthest apart, and at this time, the tooth surfaces 40 of the movable tooth 40
A sufficiently larger magnetic resistance exists between the tooth surface 42a of the fixed tooth 42 than the state shown in FIG. 2A, and as a result, the magnetic flux guided to the movable tooth 40 side decreases, so that That is understood.

Furthermore, it is understood that at this time, since the inductance of the excitation coil 44 decreases, Ir increases.

As a result, the amplitude of current i decreases in the state of FIG. 3A,
On the other hand, it is understood that the delayed phase φ2 is greater than the phase φ1 in FIG. 2A.

FIG. 3B shows this state, and by comparing it with FIG. 2B, the relative position between the movable tooth 40 and the fixed tooth 42 is detected as a change in the amplitude or phase of the detection current 5 due to the rotation of the movable tooth 40.

As described above, according to the present invention, it is possible to measure the relative movement between the movable tooth 40 and the fixed tooth 42 using the detection current i of the exciting coil 44, and this detection is carried out by the current i as described above. It can be determined by the delayed phase φ or the amplitude change of the current i.

FIG. 4 shows a second embodiment of the magnetic encoder according to the present invention, and this embodiment is characterized in that four fixed teeth are provided at different phases with respect to the movable teeth. do.

The fixed teeth 142-1 to 142-4 in the second embodiment have the same structure as the single fixed tooth 42 shown in FIG. -1 to 144-4 are wound, to which an excitation circuit applies a predetermined voltage, and a coil current is detected from each excitation coil 144 by a current detection circuit including a current transformer.

In the second embodiment, the movable body is designated by the reference numeral 140.

FIG. 5 shows the phase of the four fixed teeth 142 in the second embodiment with respect to the tooth surface 140a of the movable tooth 140, and the fixed tooth 142-3 that is paired with the fixed tooth 142-1 is 1/1/2 of each other. A pair is created with a phase difference of 2p.

The remaining fixed teeth 142-2 and 142-4 form a set with a phase difference of 1/2p from each other, and have a phase difference of 1/4p with respect to the first set.

Therefore, in this embodiment, - set of fixed teeth 142-1,
142-3 forms the first detection pair, and a detection pair 1/4p apart from this detection pair is similarly connected to the fixed tooth 142-2.14.
2-4 forms a pair and Uke holds it.

FIG. 6 shows the overall detection circuit of the second embodiment.
-4 is detected by current detection circuits 150-1 to 150-4.

The outputs of different 1/2p phases from each part are differentially amplified by operational amplifiers 152-1 and 152-2, and it is possible to obtain a two-phase AC signal whose period is 1p of the fixed tooth 140. A sine output and a CO5 output are obtained by a phase difference of /4p, respectively.

As is clear from the figure, the excitation coil 144 is supplied with an alternating current voltage from a common excitation circuit 146 in the embodiment.

FIG. 7 shows an example of the detected current waveform of each part in the second embodiment, and the current of the excitation coil 144-1 is shown in FIG. Similarly, currents are detected in different phases.

The outputs of the current detection circuits 150-1 and 150-2 are shown in FIGS. 7(B) and 7(C), and the differential amplifier 15
2-1 appears in the output of FIG. 7(D).

Similarly, the output of the operational amplifier 152-2 is
), and as is clear from the figure, both outputs are obtained with a phase difference of 90 degrees, and it is possible to obtain a high-resolution detection circuit using a well-known signal dividing circuit using these two signals.

As described above, according to the present invention, it is possible to detect the position of the movable body without contacting the movable body, and by counting the detection output, the absolute amount of movement is obtained, and if necessary, the position of the movable body can be detected without contacting the movable body. It becomes possible to obtain a moving phase of .

In the above-mentioned embodiment, the excitation circuit is high-frequency AC! ? l
Although the S current is supplied to the excitation coil, this excitation circuit can also output pulse excitation using a pulse voltage, and it is also possible to digitally convert and process the instantaneous value of the output current.

[Effects of the Invention] As explained above, according to the present invention, the amount of rotation, rotational phase, or position of a movable body can be detected magnetically without contact, and this detection can be performed using fixed teeth made of magnetic material. Since this can be obtained by combining with an excitation means, it is possible to provide a device that is robust and has sufficient durability against temperature changes and other factors, and is suitable for use in machine tools and other poor working environments. It is also possible to perform a highly accurate detection operation without any failures.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a basic first embodiment of the magnetic encoder according to the present invention, Fig. 2A is an explanatory diagram of the operation in a state where the movable teeth and fixed teeth are close to each other in the first embodiment, Fig. 2B is a waveform diagram of the excitation voltage and detection current in Fig. 2A, Fig. 3A is an explanatory diagram of the action showing the state in which the movable teeth are farthest from the fixed teeth in the first embodiment, and Fig. 3B is a waveform explanatory diagram in Fig. 3A. , FIG. 4 is an explanatory diagram showing a second embodiment of the magnetic encoder according to the present invention having a plurality of fixed teeth, and FIG.
The figure is an explanatory diagram of the arrangement of movable teeth and fixed teeth in the second embodiment, FIG. 6 is a circuit configuration diagram in the second embodiment, and FIG.
Waveform diagrams of various parts in the embodiment, FIG. 8.9 are explanatory diagrams showing an example of a conventional encoder. 40.140 ... Movable tooth 42.142 ... Fixed tooth 44.144 ... Excitation coil 46.146 ... Excitation circuit

Claims (1)

[Scope of Claims] A movable tooth made of a magnetic material connected to a movable body and having a plurality of teeth at an equal pitch on its outer periphery; A fixed tooth made of a magnetic material on which teeth are formed, a coil that excites the fixed tooth, an excitation circuit that applies a predetermined voltage to the coil, and a current detection circuit that detects a current flowing through the coil, A magnetic encoder that detects the position of the movable body by detecting changes in coil current that occur when the movable body moves. (2) In the magnetic encoder according to claim (1), a plurality of fixed teeth are fixedly arranged adjacent to the movable teeth with different phase differences, and each of the fixed teeth includes an excitation coil, an excitation circuit, and a current detection circuit. A magnetic encoder characterized in that a plurality of coil currents having different phases are detected from each current detection circuit.