JPH05188069A - Tachometer using eddy current effect - Google Patents

Abstract

PURPOSE: To measure in a relatively large temperature range with reliability by forming a rotor extending in an axial direction in a pot-like state, and selecting a magnetic field in an air gap continuously in a predetermined allowable range so that a web substantially completely pass through the field in an axial direction. CONSTITUTION: Magnetic field measuring units 12a, 12b measure magnetic field strength at a position where a rotor is out of an air gap, and a measuring circuit 13 forms a signal representing the number of revolutions of the rotor 10 from the measured value. The rotor 10 has a web 10.2 which is extended in the axial direction and rotated, and is formed in a pot-like state. The relative position of the rotor 10 to a magnetic field generator 11 and the length of the web 10.2 of the rotor are set so that the web 10.2 substantially completely passes the magnetic field in the air gap 11.3 continuously in the predetermined allowable range in the axial direction. Thus, a tachometer in which the measurement with reliability is conducted even in a relatively large temperature range and the responding sensitivity is very high is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tachometer utilizing the eddy current effect, which has a magnetic field generating device having an air gap, a rotor, a magnetic field measuring device and a measuring circuit. The rotor is to rotate through the gap,
The magnetic field measuring device is for measuring the magnetic field strength at a position where the rotor goes out of the air gap or at a position where it enters the air gap, and the measurement circuit outputs a signal representing the number of rotations of the rotor from the measured value. The present invention relates to a tachometer using the eddy current effect that is formed.

[0002]

2. Description of the Related Art DE-A1673439 discloses a tachometer utilizing the eddy current effect. This tachometer has a magnetic field generating device having an air gap, a rotor, a magnetic field measuring device, and a measuring circuit, wherein the rotor rotates through the air gap, The magnetic field measuring device is for measuring the magnetic field strength at a location where the rotor goes out of the magnetic field or a location where it enters the magnetic field, and the measurement circuit forms a signal representing the rotation speed of the rotor from the measured value. It is characterized by that.

The magnetic field generator in this tachometer is
It consists of a magnet core and two permanent magnets. The two permanent magnets have the gap between them. At least one magnetic sensor is used in the magnetic field measuring device. This magnetic sensor measures a magnetic field by an arbitrary method. Advantageously, two or four sensors are provided, which are connected synthetically to form a half bridge or a full bridge as a differential type sensor. When two sensors are provided, each one is arranged near both ends of the air gap when viewed in the circumferential direction of the rotor. When the rotor is stationary, the bridge is balanced by zero balancing as follows. That is, the balance is adjusted so that the output signal indicating the rotation speed becomes zero.

The tachometer utilizing the eddy current effect has the following advantages. This means that the tachometer can already reliably detect very low rpms. As such, the tachometer is particularly suitable for use in various servo drive systems, which may be used, for example, in adjustable moving elements of tool machines or steering systems of motor vehicles.

In order to measure very low rpms, the typical conventional method uses a specially configured tachometer. However, in order for such a tachometer to operate reliably, it should usually be finely designed and carefully manufactured. In order to compensate for temperature-dependent shaft length variations, a tachometer is typically used with a servomotor and a bellows-type connecting member (F).
must be connected via an altenbergkupplung). This is especially true in the technical field of automotive engineering. This is because relatively large temperature differences have to be taken into account in this technical field.

Under significant temperature fluctuations (for example, the servo drive system in the technical field of automobile engineering mentioned above is frequently subjected to such significant temperature fluctuations), the eddy current effect type of the type described at the beginning is used. A tachometer cannot be realized. This is because in order to ensure that the rotor does not get caught in the restricted section of the air gap within the entire axial tolerance, the air gap must be chosen very large. However, if the air gap is chosen to be large, the obstructive effect on the magnetic field used for the measurement increases. Besides, the magnetic field strength is reduced.
This leads to a decrease in response sensitivity.

[0007]

An object of the present invention is to provide a tachometer utilizing the eddy current effect so that the tachometer can be reliably measured even in a relatively large temperature range. Is.

[0008]

According to the present invention, the above object is to provide a rotor for a magnetic field generating device, wherein the rotor has a web that extends in the axial direction and has a rotating web. And the web length of the rotor are selected and solved so that the web continuously and almost completely penetrates the magnetic field in the air gap within a predetermined tolerance in the axial direction.

By making measurements with a web extending axially in the rotor, the web is completely and continuously penetrated by the magnetic field in the air gap at all axial positions of the rotor. Becomes This ensures that the measurement is almost completely unaffected by the axial position of the rotor. The axial position of this rotor is
It depends to a great extent on the occasional temperature.

Since most of the magnetic sensors have a predetermined temperature characteristic change, the measuring circuit of the tachometer has a temperature compensating function for compensating for such temperature characteristic change. It is advantageous to be

Due to the additional web on the rotor in the tachometer according to the invention, the moment of inertia of the rotor is increased. Therefore, in order to keep this moment of inertia at a small absolute value, it is advantageous to construct the rotor with a plastic member. In this case at least one of the webs
Two peripheral walls are metal-coated.

If a magnet core is used in the magnetic field generator, high measurement sensitivity is obtained when scanning the web. The boundary surface of this magnet core extends in the radial direction,
And / or the magnet core is U-shaped on both sides of the web as seen in the axial direction of the rotor and has legs directed towards the web.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The tachometer according to FIGS. 1 and 2 comprises a rotor 10 with a rotor disk 10.1 and a rotor web 10.2, a magnet core 11.1 and four permanent magnets 11.2. Magnetic field generator 11 and sensor 12
A magnetic field measuring device having two magnetoresistive elements as a and 12b and a measuring circuit 13 are used.

From the plan view of FIG. 2, the magnet core 1 is shown.
1.1 has a limiting partition in the radial direction when viewed in the direction of the axis 14 of the rotor 10, and the magnet core 1
It can be seen that 1.1 is configured in a U-shape on both sides of the web 10.2, and further has legs pointing towards the web 12. Each of the four legs is fitted with one of the four permanent magnets 11.2.
In this case, the polarities of these permanent magnets 11.2 are arranged as follows. In other words, in the two outer legs the north pole is arranged towards the web 10.2, whereas in the two inner legs the south pole is arranged towards the web 10.2. .. The polarity of the magnet can be selected in reverse. Two sensors 12 at each end of the two outer legs
One of a and 12b is embedded. However, these sensors can also be mounted on the ends of the legs.

The rotor 10 is made of plastic and has a metal coating 10.3 on the outside of the web 10.2. However, such coatings can also be arranged on the inside or on both sides. When the web 10.2 passes and moves through the gap 11.3 of the magnet core 11, that is, when the rotor 10 rotates,
Eddy currents are induced. The magnetic field generated by the eddy current is directed so that the magnetic field of the air gap is strengthened at the position where the metal coating 10.3 exits from the air gap 11.3, while the magnetic field of the air gap is weakened at the entrance side. Be oriented to. In other words, on the outlet side, the magnetic poles try to hold back the metal coating that is trying to get out of the air gap, whereas on the inlet side the magnetic poles prevent the metal coating from entering the air gap. Is adjusted. The faster the rotor 10 rotates, that is, the faster the moving movement of the metal coating 10.3 through the air gap 11.3,
The magnetic field will be more different and this field will be measured by the two sensors 12a, 12b.

As can be seen in FIG. 1, the web 10.2, together with the metallic coating 10.3, projects entirely through the air gap 11.3. This protrusion is selected as follows. That is, even if the rotor 10 moves upward in the axial play frame, for example due to thermal expansion (based on the configuration of FIG. 1), the magnetic flux ratio in the air gap remains substantially constant. To be selected. The reason why this magnetic relationship is kept unchanged is that the web, together with its metallic coating, completely penetrates the magnetic field of the air gap.

The measuring circuit 13 shown only as a single block in FIG. 1 is shown in a basic block circuit diagram in FIG. Furthermore, the measuring circuit 13 is shown in FIG. 4 as a detailed circuit diagram with some modifications made to the simple block circuit diagram of FIG. According to this circuit diagram, the sensors 12a and 12b are supplied with a constant current from the constant current source 15. Each of the sensors 12a and 12b includes a respective compensation circuit 1 for offset correction and temperature compensation.
Differential amplifiers 16a through 16 through 7a through 17b
connected to b. In the output amplifier 18, the signal 16a
And 16b are formed and output as a signal indicating the rotation speed ω of the rotor 10. A zero-balance adjusting circuit 19 is further provided for outputting an output signal having a value of 0 when the rotor 10 is stationary. Reference is made to FIG. 4 for the construction of the circuit portions 15-19. From this figure, we can simply see the following. That is, it can be seen that the offset correction is performed by the potentiometers P1a and P1b of the respective compensation circuits 17a and 17b, and the zero balance adjustment is performed by the potentiometer P2 of the zero balance adjustment circuit 19. For temperature compensation, temperature-dependent resistors NTCa and NTCb are provided in the compensation circuits 17a and 17b, respectively. These resistors are selected so that their temperature characteristic changes substantially correspond to the temperature characteristic changes of the sensors 12a and 12b. At least these temperature dependent resistors are mounted such that they always have substantially the same temperature as the sensors 12a and 12b. However, the entire measuring circuit 13
It can be placed in good heat exchange relationship with the magnet core 11 and the accompanying sensor.

Using a rotor having a web diameter of 5 cm,
33 μV / (U / min) when a magnetic resistance element is used as a sensor when the magnetic field strength is 270 mT
Was measured, and the response sensitivity was 17 μV / (U / min) when the Hall sensor was used.

[0020]

According to the present invention, reliable measurement can be performed even in a relatively large temperature range, and a tachometer with extremely high response sensitivity can be achieved.

By making measurements with a web extending axially in the rotor, the web is completely and continuously penetrated by the magnetic field in the air gap at all axial positions of the rotor. Becomes This ensures that the measurement is almost completely independent of the axial position of the rotor. The axial position of the rotor depends to a great extent on its temperature.

Since most of the magnetic sensors have a certain temperature characteristic change, the measuring circuit of the tachometer has a temperature compensation function for balancing such temperature characteristic change. Is advantageous.

The additional web in the rotor of the tachometer according to the invention increases the rotor's moment of inertia. Therefore, in order to maintain this moment of inertia at a small absolute value, it is advantageous to construct the rotor with a plastic member. In this case at least one of the webs
Two peripheral walls are metal-coated.

If a magnetic core is used in the magnetic field generator, high measurement sensitivity is obtained when scanning the web. The limiting section of the magnet core extends in the radial direction and / or the magnet core is U-shaped on both sides of the web when viewed in the axial direction of the rotor and is oriented towards the web. Has a leg.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional view of a rotor of a tachometer, a magnetic field generator, and a magnetic field measuring device taken along line I-I of FIG. 2, and a block diagram of a measuring circuit.

2 is a partial cross-sectional view of the rotor, the magnetic field generator and the magnetic field measuring device according to FIG. 1, taken along the line II-II in FIG.

3 is a block circuit diagram of a measuring circuit for detecting the rotational speed of the rotor of the tachometer according to FIG.

FIG. 4 shows in detail a measuring circuit similar to the basic circuit of FIG.

[Explanation of symbols]

 10 Rotor 10.1 Rotor Disk 10.2 (Rotor) Web 10.3 Metallic Coating 11 Magnetic Field Generator 11.1 Magnet Core 11.2 Permanent Magnet 11.3 Air Gap 12a Magnetoresistive Element (Sensor) 12b Magnetoresistive Element (sensor) 13 Measurement circuit 14 Axis 15 Constant current source 16a Differential amplifier 16b Differential amplifier 17a Compensation circuit 17b Compensation circuit 18 Output amplifier 19 Zero balance adjuster

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Robert Klot Germany Federal Republic of Bezigheim-Otmarsheim Buhlgartenweg 20 Ar (72) Inventor Manfred Strohmann Karlsruhe 31 Bonner Strasse 15

Claims (5)

[Claims] 1. A tachometer utilizing the eddy current effect, comprising: a magnetic field generator (11) having a gap (11.3), a rotor (10), and a magnetic field measuring device (12a, 12b) and-a measuring circuit (13), the rotor (10) rotates through the air gap, and the magnetic field measuring device (12a, 12b) has the rotation. The magnetic field strength is measured at a position where the child goes out of the air gap or a position where the child enters the air gap, and the measurement circuit (13) forms a signal representing the rotation speed of the rotor from the measured value. In the tachometer utilizing the eddy current effect, the rotor (10) has a web (10.2) extending in the axial direction and rotating, and is configured in a pot shape, and a magnetic field generator is provided. Relative position of rotor (10) with respect to (11) The length of the web (10.2) of the rotor, the web (1
Eddy current effect type rotation, characterized in that 0.2) is selected so as to almost completely penetrate the magnetic field in the air gap (11.3) within a predetermined allowable range in the axial direction. Speedometer. 2. The magnetic field generator (11) comprises a magnet core (11.1) having a limiting partition extending in the radial direction when viewed in the axial direction of the rotor. The described tachometer. 3. The magnet core (11.1) is U-shaped on both sides of the web when viewed in the direction of the axis (14) of the rotor and faces the web (10.2). The tachometer according to claim 1 or 2, further comprising a leg portion. 4. The tachometer according to claim 1, wherein the rotor (10) is a plastic member in which at least a peripheral wall of the web is metal-coated. 5. The temperature compensation circuit (17a, 17b, NTCa, NTC) for balancing the temperature characteristic change of the magnetic field measuring device (12a, 12b).
The tachometer according to any one of claims 1 to 4, which has b).