JPH11332209A - Linear actuator with built-in position sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear actuator with a built in position sensor which can be constructed so as to have a small and compact form. SOLUTION: An opening 4 from which an operation rod 2 protrudes is formed in the tip part of a linear actuator 1. A detection rod 7 is attached to the outer circumference the operation rod 2 which is moved reciprocally through the aperture 4. A detection head 8 is attached to the inner circumference of a slide bearing 5 attached to the inner circumference of the opening 4. A magnetic induction position sensor 6 is composed of the detection rod 7 and the head 8. The linear actuator with the position sensor which can be smaller and more compact than a linear actuator with a position sensor consisting of a differential transformer or a magnetic or optical encoder which is attached to the outside of a housing 3 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear actuator having a magnetic induction type position sensor.

[0002]

2. Description of the Related Art In general, a linear actuator is provided with a position sensor for detecting a moving amount or a moving position of an operating rod. As a position sensor, for example, a sensor using a differential transformer is known.
The position sensor extends the arm from the operating rod in a direction perpendicular to the axis thereof and transmits the movement amount of the operating rod to a position sensor attached to the actuator body.

[0003]

The linear actuator provided with the position sensor has a problem that the size of the device is correspondingly increased since the position sensor is mounted on the side surface of the housing.

When the operating rod is bent, it is amplified by the lever principle via the arm and transmitted to the position sensor. As a result, the error included in the detection result by the position sensor increases, and it is not possible to expect high-precision, high-resolution detection.

[0005] An object of the present invention is to propose a linear actuator having a position sensor which can be made compact and compact and which can detect with high accuracy and high resolution.

[0006]

In order to solve the above-mentioned problems, the present invention provides a linear actuator which reciprocates linearly in a predetermined range of an operating rod slidably supported by a slide bearing. Wherein a position sensor having the following configuration is provided for detecting a movement position of the operating rod.

That is, the position sensor has a detection rod and a detection head. The detection rod includes a magnetic body and a non-magnetic body having the same width and arranged along the moving direction of the operation rod. The detection head comprises five primary induction coils arranged along the moving direction of the operating rod, and first to fourth secondary induction coils arranged also along the moving direction of the operating rod. And

Further, one of the detection head and the detection rod is attached to the slide bearing, and the other of the detection head and the detection rod is attached to the operating rod. Further, when the operating rod moves while an AC voltage is applied to the primary side induction coil, the induced voltage generated in the first and third secondary side induction coils is changed to the second and fourth secondary side induction coils. The magnetic material and the non-magnetic material, and the first to fourth components so that the phase is shifted by 90 degrees with respect to the induced voltage generated in the side induction coil.
Of the secondary side induction coil is set.

In the position sensor having this configuration, for example, a sine waveform induced voltage is generated in the first and third secondary induction coils, and a cosine waveform is generated in the second and fourth secondary induction coils. Induced voltage is generated. Therefore, for example, a signal indicating the moving position of the operating rod can be generated based on the zero cross point of the composite wave of these output voltages and the zero cross point of the voltage waveform applied to the primary side induction coil.

Here, if the components of the position sensor are arranged in the output side opening of the linear actuator, the components of the position sensor can be easily replaced from the outside.

When the position sensor of the present invention is incorporated into a linear motor, the rotor of the linear motor can also be used as a component of the position sensor. Therefore, the position sensor can be incorporated into the linear motor in a compact form. .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a linear actuator to which the present invention is applied will be described with reference to the drawings.

FIG. 1 shows a main part of the linear actuator of the present embodiment. The general structure of the linear actuator 1 can be the one generally used, and can be used as it is. A motor, a reduction mechanism for reducing the output rotation, and a reduced rotation output output from the motor are converted into a linear reciprocating motion. And a working rod that performs a linear reciprocating motion by the converting mechanism. In the drawing, a tip portion of the linear actuator 1 is shown, and an opening portion 4 of a linear actuator housing 3 from which a tip portion of an operating rod 2 projects is formed. On the inside, a cylindrical slide bearing 5 is attached. The operating rod 2 is supported by the slide bearing 5 so as to be slidable in the direction of the axis 2a.

Here, a magnetic induction type position sensor 6 for detecting the moving position of the operating rod 2 is arranged at the tip of the linear actuator 1. The position sensor 6 includes a detection rod 7 attached to the operation rod 2 and a detection head 8 attached to the inner peripheral surface of the opening 4 of the housing 3 so as to surround the distal end of the operation rod 2. .

The detection rod 7 is arranged at a constant pitch on the axis 2a.
Are formed in a cylindrical shape in which five magnetic rings 71 to 75 arranged in the direction of are fixed by a non-magnetic body 76. Non-magnetic material 76
Can be made of a material such as a metal or a resin,
An appropriate material may be selected according to the processing accuracy, lubricity and other required performance.

The detection head 8 is arranged such that the axis 2a is
Ring-shaped primary induction coils 8 arranged in the directions of
1 to 85, and four ring-shaped secondary induction coils 91 to 94 arranged therebetween.

Here, nine induction coils 81 to 85 and 91 to 94 are arranged at equal intervals between a distance p from one magnetic ring on the detection rod 7 side to an adjacent magnetic ring. An AC voltage is applied to the four primary-side induction coils 81 to 85 to form a magnetic field extending in the direction of the axis 2a. When the detection rod 7 linearly moves integrally with the operation rod 2 in this magnetic field, the magnetic rings 71 to 75 of the detection rod 7 and the non-magnetic material portion formed therebetween are alternated. To each induction coil 81-85, 91-
Go through 94. As a result, the magnetic field changes and an induced voltage is generated in the secondary induction coils 91 to 94.

Here, the primary side induction coils 81 to 85 have the same winding direction and are connected to each other in series. On the other hand, the secondary induction coils 91 to 9
4, the first and third secondary induction coils 9
1, 93 are connected in series so as to be mutually reverse-wound, and similarly, the second and fourth secondary induction coils 92,
94 are connected in series so that they are oppositely wound.

As a result, assuming that the AC voltage applied to the primary side induction coils 81 to 85 is V = Asinωt and the linear displacement of the rod is x,
The induced voltage obtained from the secondary induction coils 91 and 93 is V1 = Asinωt · sinx, and the induced voltage obtained from the second and fourth secondary induction coils 92 and 94 is V2 = Asinωt · cosx, The waveforms are shifted by 90 degrees from each other.

Therefore, these secondary induction coils 91 to 91
The induced voltage waveform generated at 94 and the primary induction coil 81
The moving position of the operating rod 2 can be detected based on the AC voltage waveforms applied to .about.85. That is, these voltages V
The combined wave of 1, V2 is V3 = Asin (ωt ± x), and the linear displacement x can be detected as a phase difference between the combined wave and the carrier wave V applied to the primary side induction coil.

In the present embodiment, the detection rod 7 is mounted on the operation rod 2 and the detection head 8 is mounted on the housing 3. However, the arrangement may be reversed.

In the linear actuator 1 with the built-in position sensor constructed as described above, unlike the position sensor composed of a differential transformer, the position sensor can be built in the front end portion of the linear actuator 1. Increase can be suppressed.

A detection head 8, which is a component of the position sensor 6, is attached to the opening 4 of the housing 3. Therefore, it is easy to access the portion of the detection head 8 from the outside, and there is an advantage that maintenance such as coil replacement is facilitated.

(Modification of Detecting Rod) Here, in the case where a configuration in which the cylindrical detecting rod 7 is attached to the outer periphery of the operating rod 2 is adopted, in order to reduce the outer diameter of a portion composed of these combinations. It is desirable to do as follows.

That is, as shown in FIG. 2, instead of using a magnetic ring having a circular cross section, a magnetic ring 71a having a semicircular cross section is used. Alternatively, a magnetic ring having a horizontally long elliptical cross section is used. By doing so, it is possible to suppress an increase in the outer diameter of the distal end portion of the operating rod 2 to which the detection rod 7 is attached.

(Another Configuration Example of Position Sensor) FIG. 3 shows another configuration example of the position sensor 6. In the position sensor 6A shown in this figure, a non-magnetic ring 7 having the same cross-sectional shape as a magnetic ring 71b having a rectangular cross-section
6b are disposed adjacent to each other in the axial direction, and these constitute a detection rod 7A.

On the housing 3 side, four magnetic pole pins 11 to 14 are attached vertically toward the detection rod 7A, and primary induction coils 21 to 24 are mounted on the base sides of the magnetic pole pins 11 to 14, respectively. Is wound. Each magnetic pole pin 11-14
Are wound on the distal end side thereof.

FIG. 4 shows each of the secondary induction coils 31 to 34.
And the arrangement relationship between the magnetic ring 71b and the non-magnetic ring 76b. As shown in this figure, the secondary-side induction coils 31 and 33 are arranged at a pitch of half the pitch from one magnetic ring 71b to the next magnetic ring. The remaining secondary induction coils 32 and 34 are arranged at positions shifted by a half pitch with respect to these secondary induction coils 31 and 33.

As a result, when the induced voltage waveforms obtained from the secondary induction coils 31 and 33 are sine waves, the induced voltage waveforms obtained from the secondary induction coils 32 and 34 are cosine shifted by 90 degrees. It becomes a waveform. Therefore, a detection signal indicating the movement position of the operating rod 2 can be generated based on these outputs.

The position sensor 6A configured as described above is particularly suitable for use as a position sensor in a linear motor. That is, some of the components of the linear motor can be used as the components of the position sensor, so that the position sensor can be compactly configured in the linear motor. On the other hand, in a conventional linear motor, a configuration in which an optical or magnetic linear encoder is externally mounted for position detection and position control is generally adopted. In this configuration, a detection unit having a length corresponding to the stroke of the linear motor is required, and this is a factor that increases the price of the linear motor system. In particular, when high resolution is required, the price of the sensor affects the price of the entire system, and therefore, it is an important factor that the sensor can be manufactured at low cost.

Also, since the optical or magnetic linear encoder is externally attached to the linear motor, when a vibration is generated in a table or the like driven by the linear motor, the vibration is amplified and transmitted to the linear encoder. This causes a detection error to increase. However, in the position sensor 6A of this example, since the portion corresponding to the slit of the linear encoder can be substituted by the rotor of the linear motor, only the detection head needs to be added.

[0032]

As described above, in the linear actuator with a built-in position sensor of the present invention, a magnetic induction type position sensor is formed between the operating rod and the housing. There is no need to externally attach to the housing, unlike the position sensor used or the magnetic or optical linear encoder. Therefore, the linear actuator with the position sensor can be configured to be small and compact.

Further, according to the present invention, unlike an externally mounted position sensor, the detection error does not increase due to external vibrations or the like, so that high-precision and high-resolution detection can be performed.

Further, since the components such as the coil of the position sensor are attached to the opening of the housing, there is an advantage that maintenance work such as replacement of the coil can be simplified.

Furthermore, when the present invention is applied to a linear motor, some of the components of the position sensor can be used as the components of the linear motor, so that the position sensor can be assembled compactly. The advantage is also obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a distal end portion on the output side of a linear actuator to which the present invention is applied.

FIG. 2 is an explanatory diagram showing another example of a detection rod which is a component of the position sensor of FIG.

FIG. 3 is a configuration diagram showing another example of the position sensor of FIG. 1;

FIG. 4 is an explanatory diagram showing an arrangement relationship of each coil of the position sensor of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Linear actuator 2 Operating rod 3 Housing 4 Opening 5 Slide bearing 6, 6A Position sensor 7, 7A Detection rod 71-75 Magnetic substance ring 76 Non-magnetic substance 88A Detection head 21-24, 81-85 Primary induction coil 31- 34, 91-94 Secondary side induction coil

Claims (3)

[Claims] 1. A linear actuator which reciprocates linearly within a predetermined range of an operating rod slidably supported by a slide bearing, comprising a position detecting sensor for detecting a moving position of the operating rod. The position detection sensor includes a detection rod and a detection head, and the detection rod includes a magnetic body and a non-magnetic body having the same width arranged along a moving direction of the operating rod, and the detection head Comprises five primary induction coils arranged along the moving direction of the operating rod, and first to fourth secondary induction coils similarly arranged along the moving direction of the operating rod. One of the detection head and the detection rod is attached to the slide bearing, and the detection head and the front of the detection rod are attached to the operation rod. The other of the detection rods is attached, and when the operating rod moves while applying an AC voltage to the primary side induction coil, the induced voltage generated in the first and third secondary side induction coils is Second and fourth
The arrangement relationship between the magnetic material and the non-magnetic material and the first to fourth secondary induction coils is set such that the phase is shifted by 90 degrees with respect to the induced voltage generated in the secondary induction coil. A linear actuator with a built-in position sensor, wherein a position signal indicating a moving position of the operating rod is generated based on an induced voltage generated in the first to fourth secondary induction coils. 2. The device according to claim 1, wherein the detection head or the detection rod attached to the slide bearing is located at an output side opening of a linear actuator housing from which the operating rod projects. A linear actuator with a built-in position sensor. 3. A linear motor comprising the position sensor according to claim 1.