JPH01276017A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To eliminate an error caused by eccentricity and to detect a rotation angle with a high resolution by providing two pieces of magnetic sensors which are aligned to the same phase on two positions separated by roughly a semicircle of the periphery of a magnetic drum, and obtaining an output value from its composite output. CONSTITUTION:A magnetic drum 22 has a shape of a hollow cylindrical member, and attached to a rotation axis, etc. by using the inside surface 26. On the peripheral of the drum 22, a housing 30 of a magnetic encoder 20 is provided as a still member, and this housing 30 forms a fitting member of a magnetic sensor, and two magnetic sensors 40 are attached to two position separated by about 180 deg., respectively, on its peripheral fitting surface 32. Each sensor 40 is provided with a bracket 42 and a thin film magneto-resistance element 44 which is installed therein, and this element 44 is opposed to the outside peripheral surface 24 which is brought to multiple magnetization of the drum 22 through a void of the gap quantity which is selected in advance. According to such constitution, from a composite output from both, an exact rotation angle detecting signal by which eccentric errors caused by eccentricity are negated mutually is obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic sensor having a multi-pole magnetized magnetic drum and a thin film magnetoresistive element disposed opposite to the drum at a stationary position with an air gap therebetween. With regard to magnetic encoders consisting of elements, in particular, correction of errors mixed into the rotation angle detection force signal output from the magnetic sensor element as the magnetic drum rotates due to the unavoidable eccentricity of the magnetic drum with respect to the rotation axis. This invention relates to an improved structure of a magnetic encoder.

[Conventional technology]

2. Description of the Related Art Along with optical encoders, magnetic encoders have already been provided as encoder devices for detecting the rotational output of rotating devices such as motors. This magnetic encoder is a magnetic sensor that includes a multi-pole magnetized magnetic drum and a thin film magnetoresistive element (hereinafter referred to as MR element) deposited on the magnetic drum, which is disposed opposite to the magnetic drum in a non-contact manner with an air gap in between. Since the MR element of the magnetic sensor has the characteristic that its electrical resistance changes according to changes in the magnetic field, changes in AC electrical output (usually , voltage change) and detects rotation.

The conventional configuration of the above-mentioned magnetic encoder is such that a magnetic drum is rotatably supported by a bearing via a rotating shaft, and one magnetic sensor is arranged at one stationary position around the magnetic drum. For that one magnetic sensor, 1/4 of the multipolar magnetization pitch (λ) of the magnetic drum
By providing two sets of MR elements with a mechanical phase shift equal to 100 degrees, and taking the difference between the electrical outputs of both MR elements, an alternating output waveform centered around the neutral level is formed to detect rotation. It allows for incremental detection. Furthermore, by adjusting the amount of air gap between the magnetic drum and the magnetic sensor, it is possible to form the electrical output waveform from the magnetic sensor into a substantially sinusoidal waveform. Especially in the case of a high-resolution encoder, this sine waveform can be formed into a substantially sinusoidal waveform. By interpolating, a high-resolution pulse signal can be obtained.

[Problem to be solved by the invention]

However, the configuration of the conventional magnetic encoder described above assumes that the magnetic drum and the magnetic sensor are arranged concentrically with respect to the rotation axis, but in reality, the geometric center of the magnetic drum and the rotation center are arranged concentrically. It is unavoidable that eccentricity occurs during processing and assembly, and due to this eccentricity of the magnetic drum, the electrical output output from the magnetic sensor as the magnetic drum rotates is not accurate to the center of rotation. A rotation angle error occurs with respect to the rotation angle amount. To explain this with reference to FIG. 4, the magnetic drum 12 is formed as a cylindrical member with a radius r and whose outer peripheral surface is magnetized with NSS multipolar magnetism at a constant pitch. A magnetic sensor 14 is disposed at and the two constitute a magnetic encoder. At this time, the magnetic drum 12 is mounted on, for example, a rotating shaft (not shown), and the rotating shaft is supported by a pair of bearings, so that the magnetic drum 12 is rotatable. Accordingly, the magnetic sensor 14 is configured to send out a rotation angle detection force. For processing and assembly reasons, the geometric center O° of the magnetic drum 12, which is the center of the outer cylindrical surface of the magnetic drum 12, is the center of the bearing 0.
If the magnetic drum 12 is eccentric by a minute amount ΔX relative to the magnetic drum 12, when the magnetic drum 12 makes a half turn in the direction of the arrow P with respect to the center 0, a rotation corresponding to 1/2 of the total circumferential length will occur. However, in reality, the rotation length of the magnetized circumferential surface is, for example, only rotating from point A to point B on the circumference in Figure 4 to point 0. , angular error Δθ
(in radians), the following error occurs.

Δθ=x-'1cos-'(Δx/r)... (1)
At this time, assuming that the eccentricity ΔX is 0.01 mm and the radius r of the cylindrical magnetic drum 12 is 50 mm, the outer circumferential surface of the magnetic drum 12 has a multipolar magnetic field with an electrical angle detection force of 3000 mm. If it is magnetized by the amount of pulse/rotation, the angular error will be approximately 0.02° (approximately 0.2 pulses) (4 pulses error) by introducing these values into equation (1) above. In other words, corresponding to a rotation of 180°,
As mentioned above, an angular error of approximately 0.02° occurs as a negative amount.

Further, even when rotating in the opposite direction C-DA in the direction of arrow P'' in FIG. 4, the same amount of angular error will occur as a positive amount for a rotation of 180 degrees.

Such angular errors become a problem when trying to obtain a high-resolution pulse signal by interpolating the electrical output signal that is the angle detection force of the magnetic encoder, and when the detection unit angle is minute, A problem arises in that the ratio of the detected angle error to the unit angle becomes large (becomes large) and the detection accuracy becomes low.

Therefore, it is an object of the present invention to solve these problems.

Another object of the present invention is to solve the above problems by structurally improving a magnetic encoder.

[Means of solution and action]

That is, in view of the above-mentioned object, the present invention includes a magnetic drum that is multipolar magnetized and rotatably supported, and a thin film magnetoresistive element that is disposed opposite to the magnetic drum at a stationary position with an air gap interposed therebetween. In the magnetic encoder, two magnetic sensor elements electrically aligned in the same phase are provided at two positions approximately half a circumference apart around the magnetic drum, and the two magnetic sensor elements The present invention provides a magnetic encoder that corrects rotational angle detection errors due to the eccentricity of the magnetic drum using an output that is the sum of the outputs of the sensors. , the angular errors are corrected so as to cancel each other out in the electrical signal state, and the signal from which the eccentric component is removed is used as the practical signal, so the amount of eccentricity is equivalent to zero. Hereinafter, the present invention will be explained according to embodiments shown in the drawings.

〔Example〕

FIG. 1 is a front view of a magnetic encoder according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line nn in FIG. 1, and FIG. 3 is a diagram for determining the setting positions of two magnetic sensors. FIG. 2 is a graph diagram of an output waveform observed in FIG.

Referring to FIGS. 1 and 2, the magnetic encoder 20 according to the embodiment of the present invention has a magnetic drum 22 in the center, and the magnetic drum 22 has a multi-pole magnetic field (
In this embodiment, the magnets (N, S magnetism) are alternately magnetized at a constant pitch in the circumferential direction, and the magnets are magnetized using methods such as applying magnetic paint for boat fishing and e.g. The magnetic drum 22 has the shape of a hollow cylindrical member, and is attached to a rotating shaft or other rotating part using an inner surface 26.

A housing 30 of the magnetic encoder 20 is provided as a stationary member around the magnetic drum 22, and this housing 30 forms a mounting member for the magnetic sensor 40.
Two magnetic sensors 40 according to the present invention are mounted on the circumferential mounting surface 32 of the housing 30 at two positions approximately 180 degrees apart.

These two magnetic sensors 40 include a bracket 42 and an MR element 44 attached to the bracket 42. It faces the multi-pole magnetized outer circumferential surface 24 at. Here, according to the present invention,
Two magnetic sensors 40 arranged one above the other in FIGS. 1 and 2
As mentioned above, the magnetic drums 22 are spaced approximately 180" apart in order to eliminate the influence of eccentricity errors in the rotation of the magnetic drum 22. However, this arrangement requires that the mechanical arrangement be spaced 180 degrees apart. This is not inevitable, and the two magnetic sensors 40 output electric signals indicating angular position detection values as the magnetic drum 22 rotates (the output of the MR element 44 is generated by electromagnetic interaction with the multipolar magnetization of the magnetic drum surface 24, An alternating current signal is output, and the alternating current signal can be made into a substantially sinusoidal output signal by adjusting the amount of the air gap. In this way, the influence of eccentricity that occurs when only a single magnetic sensor 40 is arranged is corrected and eliminated.

Note that the upper magnetic sensor 4 in FIGS. 1 and 2
0 as the first magnetic sensor and the lower magnetic sensor 40 as the second magnetic sensor, in order to set the phase of the electrical output values of both to have a gap of 180 @, for example, the first , one of the second magnetic sensors 40 is attached to the housing 30
and fix the other side with screws to the mounting surface 32 of the housing 30 in the vicinity of a position approximately half a circumference away from the mounting surface 32 of the housing 30.
0, while monitoring the electrical signals output from the respective MR elements 44 of both magnetic sensors 40, and searching for a position where the phases of the two substantially match,
- When the magnetic sensor 40 is aligned, the other magnetic sensor 40 can also be fixed with screws.

To explain the above-mentioned positioning operation of the two magnetic sensors 40 more specifically, for example, while viewing the electrical output waveform from the MR element 44 of the first magnetic sensor 40 on a well-known oscilloscope, the trigger is applied. fixed, and then a second magnetic sensor is applied to the waveform of the fixed first magnetic sensor 40.
When the electrical output waveform from the MR element 44 of the magnetic sensor 40 is observed on the same oscilloscope, the magnetic drum 2
A shifter appears in the output waveform of the second magnetic sensor 40 due to the influence of the eccentricity of the second magnetic sensor 40 as shown schematically in FIG.
A first magnetic sensor 40 is located approximately at the center within the jitter width.
By adjusting the position of the second magnetic sensor 40 in small increments so that the output waveform of Two magnetic sensors 40 thus obtained
By adding the output signals of , as described above, the angle detection error due to the influence of eccentricity can be removed and corrected.

A signal line 50 in FIG. 1 is a signal line from each MR element 44 of the two magnetic sensors 40 to take out an electrical output signal indicating a detected value of the rotation angle.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the magnetic sensor that sends the angle detection force as an electrical signal to the magnetic drum in a magnetic encoder is placed at two positions approximately half a circumference apart around the magnetic drum. Since the output value of the encoder is obtained by adding the outputs of the two magnetic sensors, the rotation angle detection error due to the eccentricity of the magnetic drum can be reduced. By interpolating the corrected output, it is possible to increase the resolution of rotation angle detection using a magnetic encoder. Therefore, this type of magnetic encoder can be applied to rotation detection in machine tools and other industrial machines to detect rotation angle with high resolution.

[Brief explanation of the drawing]

Fig. 1 is a front view of a magnetic encoder according to an embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 is a diagram for determining the setting positions of two magnetic sensors. FIG. 4 is a schematic front view illustrating problems caused by the configuration of a conventional magnetic encoder. 20... Magnetic encoder, 22... Magnetic drum,
24... Outer peripheral surface, 40... Magnetic sensor, 44...
MR element.

Claims (1)

[Claims] 1. Consisting of a multi-pole magnetized magnetic drum and a rotatably supported magnetic drum, and a magnetic sensor element having a thin film magnetoresistive element placed opposite the magnetic drum at a stationary position with an air gap in between. In the magnetic encoder, two magnetic sensor elements electrically aligned in the same phase are provided at two positions approximately half a circumference apart around the magnetic drum, and the output of the two magnetic sensors is combined to generate the A magnetic encoder characterized in that a rotation angle detection error due to eccentricity of a magnetic drum is corrected.