JPS63305211A - Magnetic encoder that determines absolute position - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to determining an absolute value using a movable element having multipole magnetized magnetic encoder magnetic poles and a magnetoresistive element, and in particular to improving response speed. is fast.

The present invention relates to a magnetic encoder capable of battery backup, and is applicable to either rotary type or linear type magnetic encoders.

[Prior Art] When performing positioning in various automatic devices, a means is required to measure the rotation angle and movement amount of a motor, etc., and to convert these into electrical signals. For this purpose, devices called encoders are often used.

For example, regarding rotary encoders, there are two types: an incremental type that measures the number of pulses generated during nine revolutions, and an absolute type that reads a code recorded on the rotor. Furthermore, there are two types of detection methods: optical and magnetic, but in i&Kan, incremental magnetic encoders, which are inexpensive and have excellent reliability, are increasingly being used.

Figure 3 shows a conventional general rotary magnetic encoder 1.
This is an explanatory diagram of a magnetic encoder magnetic pole 2 in which the outer periphery is magnetized with 2 N poles and 2 S poles alternately and at fine pitches.
A magnetoresistive element (MR sensor) 5 is disposed to face the magnet rotor 3 having a radial gap 4 therebetween. Note that the magnet rotor 3 may be an integral type made of magnets.
1 [It may be formed by applying a magnetic layer to the outer periphery of a suitable rotor drum.

The N pole 2N and S pole 2S of the magnetic encoder magnetic pole 2 are each magnetized to have a width of λ (equal to the width expressed by 2π in electrical angle).

In addition, the magnetoresistive element 5 is assumed to be a ferromagnetic magnetoresistive effect element, for example. First, in order to explain the principle of the magnetic encoder 1, it is a wire formed of a ferromagnetic thin film that constitutes the magnetoresistive element 5. The magnetoresistive element 6 will be explained using FIG. 4.

This magnetoresistive element 6 is formed by forming a Ni-Co metal thin film (ferromagnetic metal thin film) with a thickness of approximately several thousand amperes on a substrate such as glass by means such as vacuum evaporation or etching. 5 can be formed.

As shown in FIG. 4, if the magnetoresistive element 6 is arranged so that the direction of the current I flowing through it and the magnetic field (magnetic flux) 7 are perpendicular, the magnetic flux 7 will be directed from the north pole 2N to the south pole. Extreme 2S
Head to.

As shown in FIG. 5, this magnetoresistive element 6 causes a decrease in resistance value due to a horizontal magnetic flux 7X in a magnetic field 7, where 7Y indicates a longitudinal magnetic flux.

The rate of change in resistance of the magnetoresistive element 6 at this time is several percent, and when the width of one magnetic pole of the magnetic encoder magnetic pole 2 is λ, the change rate of the resistance of the magnetoresistive element 6 at the positions λ/4 and 3λ/4 is Assuming that the resistance value is R2 and the resistance change value is Δr, the phase θ of the magnetic pole (2N or 2S) and the magnetoresistive element 6 (−phase θ is when the magnetic pole widths 2N and 2S are respectively set to 2π in electrical angle) The resistance value R(θ) is.

It can be expressed as R(θ)=R−Δr−cosθ (1).

The lateral magnetic flux (magnetic field) 7X is related to the nine phases θ and the distance between the magnetoresistive element 6 and the magnetic encoder pole 2, and the magnetoresistive element 6 also takes a resistance value R corresponding thereto.

In the case of the magnetoresistive element 5, unlike other magnetic sensors such as Hall elements, in the center of the magnetic field (the magnetic field state at the middle of the N pole 2N and the S pole 2S), there is no magnetic field (N pole 2N
Similar to the magnetic field shape n) at the boundary between the south pole 2S and the south pole 2S, there is a characteristic that the output signal does not change.

Since it is not possible to obtain the A-phase and B-phase magnetic echoer signals with the magnetoresistive element 5 having one magnetoresistive element 6 as described above, four magnetoresistive elements 6a are used as shown in FIG.

6b, 6a', and 6b' are formed sequentially shifted by λ/4 to obtain A-phase and B-phase magnetic encoder signals.

This magnetoresistive element 5 includes two magnetoresistive elements 6a, 6a' and B to obtain an A-phase magnetic encoder signal.
Magnetoresistive elements 6b and 6b' are formed to obtain phase magnetic encoder signals.

When the width of one magnetic pole (N pole 2N or S pole 2S) of the magnetic encoder magnetic pole 2 is λ (2π in electrical angle), the magnetoresistive elements 6a and 6a' have opposite phases to each other.
They are formed with a width offset of /2.

Similarly, the magnetoresistive elements 6b and bo are formed to be shifted by a width of λ/2 so that they have opposite phases.

Also magnetoresistive elements 6a and 6b, and 6a'' and 6b
' are formed to be shifted from each other by a width of λ/4.

Therefore, the magnetoresistive elements 5 are sequentially shifted by ^/4 pitch,
Magnetoresistive elements 6a, 5b.

6a' and 6b' are formed.

As a circuit for processing the magnetic encoder signal from the magnetoresistive element 5 formed in this manner, a circuit as shown in FIG. 7, for example, is used.

This magnetic encoder signal processing circuit 8 includes resistors 9-1.
. . , 9-4 constitutes a bridge to convert a resistance change into a voltage change, and comparators 10-1 and 10-2 are used to convert the resistance change into a voltage change, as shown in FIG. 8(a).

It is possible to obtain two rectangular wave encoder signals 11-1 and 11-2 having different phases by 90 degrees as shown in FIG.

By counting the rectangular wave encoder signals 11-1, 11-2 with a counter, the rotation angle of the magnetic encoder can be measured.

[Problems to be Solved by the Invention] In order to increase the resolution by 2 in the magnetic encoder as described above, the magnetization pitch of the magnetic encoder magnetic poles must be made extremely fine.

The finer the magnetization pitch, the more difficult it is to achieve fine magnetization and the more difficult it is to manufacture, so the rotor diameter had to be increased. The air gap also needs to be narrowed according to the magnetic pole width.

High-precision bearings were required, and there was a risk of damage due to vibration, etc.

Furthermore, a magnetic encoder with a high resolution generates a large number of pulses per rotation, which limits the frequency band of the signal processing circuit.

The maximum allowable rotational speed had to be low. This also applies to linear magnetic encoders.

[Means for the invention to solve] The present invention has been made in view of the above circumstances.

For example, by measuring the absolute position within one magnetic pole of a mover having a magnetic encoder magnetic pole with multi-pole magnetization on its surface,
Regarding the rotary magnetic encoder, it is possible to realize a rotary magnetic encoder with high resolution without increasing the diameter of the magnet rotor or reducing the maximum rotational speed.

In addition, by connecting the magnetic resistance element that counts the number of passing magnetic encoder magnetic poles of the magnet rotor and the electronic circuit for counting to a backup power source that supplies power even when the power is turned off, the absolute position can be determined as soon as the power is turned on. It was created for the purpose of making it possible to display images.

[Specific Means for Achieving the Problems of the Invention] The object of the present invention is to provide a movable element having magnetic encoder magnetic poles in which a large number of north and south poles are alternately magnetized on one surface, and to provide a magnetic encoder of the movable element. Two sets of magnetoresistive elements disposed opposite to the magnetic poles, a means for counting the number of passing magnetic encoder magnetic poles using one set of the magnetoresistive elements, and another set of the magnetoresistive elements. This can be achieved by including means for measuring the absolute value of one of the magnetic encoder magnetic poles.

[Effect] The present invention is a magnetic encoder that allows the absolute value to be determined.

It is constructed by adding a magnetic resistance element and a signal processing circuit that electrically subdivide the minimum resolution pitch to a relatively low-resolution magnetic encoder.

Magnetic encoders have low resolution, so one magnetization pitch only needs to be large.1 For example, in the case of a rotary magnetic encoder, a small diameter magnet rotor can be used, so it can be mass-produced compactly and at low cost. Since absolute values are output, pulse counting errors do not occur, and the low-resolution magnetic encoder can be used without problems up to its maximum rotational speed.

[Embodiments] Although the present invention is also applicable to linear magnetic encoders, since the explanation will be redundant, in the embodiments shown below, a rotary magnetic encoder will be explained.

FIG. 1 is a circuit block diagram showing an embodiment of a rotary magnetic encoder in which the absolute value of the present invention can be determined.As shown in FIG.
These are formed as one magnetoresistive element 12A), and one magnetoresistive element 12-
1 four magnetoresistive elements 12-1a, 12-1b
.

Direct current is applied to 12-1a' and 12-1b', and resistors 13-1°..., 13-
4 constitutes a bridge to convert the resistance change into a voltage change, and the comparator 14-1.14-2 generates two rectangular wave magnetic encoder signals 11-1.11 with different 90' phases as shown in FIG. -2 is obtained.

By applying these rectangular wave encoder signals 11-1, 11-2 to the double rotation direction discrimination circuit 15, right rotation pulses and left rotation pulses are obtained. By adding
Get the current rotation angle.

Note that +V bac indicates a positive power supply terminal connected to a battery backup power supply (not shown).

V b a e indicates a negative power supply terminal connected to a battery backup power source (not shown), and the double rotation direction discrimination circuit 15 and up/down counter 16 is also supplied with power.

The other magnetoresistive element 12-2 has an RO in which a table of sine and cosine numbers is recorded with the result of counting the number of pulses obtained by the 9 oscillator 17 by the counter 18 as an address.
M19-1.19-2 and convert it to DA converter 2
Analogized by 0-1.20-2 and amplifier 21-1
．． The sine and cosine waves amplified by 21-2 are applied.

Magnetoresistive elements 12-2a, 12-2b, 12-2a', 12-2b of each magnetoresistive element 12-2
' is the resistor 22-1. ..., 22-4 constitute a bridge, and the output voltage of each bridge is connected to the resistor 23-
1. . . , 23-4 and the operational amplifier 24, it is possible to obtain an AC signal whose phase is shifted by the rotation angle with respect to the applied AC signal.

The comparator 25 detects the zero-crossing point of the AC signal, and the address value at the rising edge of the rectangular wave of the magnetic encoder signal is taken into the D-FF 26, so that a minute rotation angle of less than one magnetic pole width of the magnetic encoder magnetic pole 2 can be electrically calculated. It can be obtained as a signal.

The upper digits of the rotation angle counting result are stored in the up/down counter 16.
The lower digits are obtained by the up/down counter 16, which are separated by separate magnetoresistive elements 12-1, 12-
2, the upper digits are not necessarily raised or lowered when a carry-over or carry-down occurs from the lower digits. Therefore, the correction circuit 27 is used to make the occurrence of carry-over/carry-down of the lower digits coincide with the value of the upper digits.

This is because a doubling circuit is used in the rotational direction discrimination circuit 15, which can be constructed at low cost, in the measurement of upper digits.

The up/down counter 16 is one of the magnet rotors 2.
The value changes by rotation by /2 magnetic pole width. On the other hand, for the lower digits, the full scale is the rotation of one magnetic pole width of the magnet rotor 2.

Therefore, the least significant bit of the up/down counter 16 and the least significant bit of the D-FF 26 indicate the same value, if they are different.

All you need to do is correct the upper measurement result by +1 or -1.
The determination whether to perform a 1 correction or a -1 correction is made by looking at the second bit from the most significant bit of the lower measurement result.

That is, if this bit is 1, it is determined that the upper measurement value has been counted up even though the lower measurement result is about to be carried forward.

Correct the upper measurement value by -1.

Conversely, if this bit is O, it is determined that the upper measured value has counted down even though the lower measured value is about to fall, and the upper measured value is corrected by +1. There is.

The maximum number of revolutions that can be measured with this magnetic encoder is determined by the direction discrimination circuit 15 that measures the upper order and the up/down counter 1.
However, the frequency of the pulses processed here is the number of revolutions multiplied by the resolution divided by the number of pulses of the lower measurement, so the absolute value of the present invention can be determined. A rotary magnetic encoder is capable of faster response than a normal incremental type rotary magnetic encoder.

Furthermore, since the absolute position is displayed on the lower measurement side, by batch leavering up only the upper measurement side, even if the power is cut off, the absolute position can always be displayed at the same time as the power is turned on.

[Effect of the invention] The present invention is a magnetic encoder that can determine the absolute value.

Not only can high-resolution encoders be made smaller;

It has the advantage of being capable of high-speed response, being easy to manufacture, and being mass-produced at low cost. In addition, it has excellent features such as being able to display the absolute position as soon as the power is turned on by backing up only a portion with a battery.

[Brief explanation of drawings]

Fig. 1 is a circuit block diagram of a magnetic encoder according to the present invention that allows absolute values to be determined, Fig. 2 is an explanatory diagram of a magnetoresistive element used in the magnetic encoder, and Fig. 3 is a schematic diagram of a conventionally known incremental type rotary magnetic encoder. 4 to 6 are explanatory diagrams of the relationship between the magnetic encoder magnetic poles and the magnetoresistive element of the magnetic encoder, FIG. 7 is an explanatory diagram of the magnetic encoder processing circuit of the magnetic encoder, and FIG. It is an encoder signal waveform diagram obtained from the same magnetic encoder. [Explanation of symbols... Rotary magnetic encoder, 2... Magnetic encoder magnetic pole, 3... Magnet rotor. 4... Air gap, 5... Magnetoresistive element. 6.6a, 6a', 6b, 6b' --- Magnetoresistive element, 7... Magnetic field, 8... Magnetic encoder signal processing circuit. 9-1. ..., 9-4...Resistor. 10-1.10-2...Comparator. 11-1.11-2...Magnetic encoder signal. 12-1.12-2... Magnetoresistive element. 12-1a, 12-1a', 12-1b, 12-1b
', 12-2a, 12-2a', 12-2b, 12
-2b'... Magnetoresistive element. 13-1. ..., 13-4...resistor. 15...Double multiplier type direction discrimination circuit. 16... Up/down counter, 17... Oscillator,
18...Counter. 19-1.19-2・-・ROM, 20-1゜20-2
...DA converter. 21-1.21-2...Amplifier. 22-1. ..., 22-4...resistor. 24... operational amplifier, 25... comparator, 26
...D-FF, 27...correction circuit. 28...Battery backup circuit.

Claims (2)

[Claims] (1) A movable element having magnetic encoder magnetic poles with a large number of N-pole and S-pole magnetic poles alternately magnetized on the surface thereof, and two sets of magnetic resistors arranged opposite to the magnetic encoder magnetic poles of the movable element. a means for counting the number of passing magnetic encoder magnetic poles using one set of the magnetic resistance elements; and a means for counting the number of passing magnetic encoder magnetic poles using one set of the magnetic resistance elements, and measuring an absolute value of one magnetic pole of the magnetic encoder magnetic poles using another set of the magnetic resistance elements. A magnetic encoder for determining an absolute value, characterized in that it has means. (2) A magnetic resistance element for measuring the number of passing magnetic encoder magnetic poles of the movable element and an electronic circuit for counting the magnetic resistance element,
Claim No. 1 characterized in that the device is connected to a backup power source that supplies power even when the power is cut off.
) A magnetic encoder that allows you to determine the absolute value listed in the item.