WO2021000294A1

WO2021000294A1 - Apparatus for detection of angular movement of a ferromagnetic vane

Info

Publication number: WO2021000294A1
Application number: PCT/CN2019/094586
Authority: WO
Inventors: Ioannis Anastasiadis; Renan LIU; Ming Li
Original assignee: Hamlin Electronics (Suzhou) Ltd.
Priority date: 2019-07-03
Filing date: 2019-07-03
Publication date: 2021-01-07

Abstract

A new magnetic circuit design arrangement is presented for the detection of angular movement of a ferromagnetic vane. This arrangement is based on the symmetric properties of magnetic field distribution. The proposed arrangement is easily implemented and will operate within the requirements of the application, independent of the shape of the vane and the angular movement of the vane. Moreover, the design will work regardless of whether the sensor is mounted on a bracket composed of a ferromagnetic or non-ferrous material.

Description

Apparatus For Detection Of Angular Movement Of A Ferromagnetic Vane

Background of the Invention

Embodiments of flap-type switches typically consist of a permanent magnet, a magnetic sensor, for example, a Hall effect sensor, and a vane, composed of a ferromagnetic material. The magnetic sensor and magnet are placed spaced at specific distances along a direction normal to the magnetization of the magnet. The ferrous vane is rotated about to a pivot point and passes through the air-gap between the magnet and magnetic sensor. The magnetic sensor detects the angular movement of the vane by detecting the presence of the ferrous vane between the magnet and the magnetic sensor, which diminishes the magnetic field sensed by the magnetic sensor.

A prior art version of a flap-type switch is shown in FIG. 1, with view (A) showing a schematic side view have the switch and view (B) showing a detail, with dimensions, of view (A) . The switch shown in FIG. 1 comprises an 8 x 8 x 5 mm magnet. The magnetization of the magnet is along a longitudinal direction as shown in FIG. 1. The distance between the magnet and the magnetic sensor is relatively large, at approximately 9 mm. As a result, it is necessary for this configuration to use only large rare earth magnets (i.e., neodymium or samarium-cobalt) . The configuration shown in FIG. 1 works fine when the sensor is mounted on or in close proximity to a non-ferrous material such as aluminium. However, the sensor fails to operate when the sensor is mounted on or in close proximity to a ferromagnetic material, such as iron. As it is often desirable that the switch operate in close proximity to a ferromagnetic material, for example, by mounting on bracket comprised of a ferromagnetic material, a revised design that works when in close proximity to ferromagnetic material is necessary.

Summary of the Invention

A revised design of the magnetic switch which operates in close proximity to ferromagnetic materials is presented. The revised design is based on the symmetric properties of magnetic field distribution. The main benefit of the revised design is that it is easily implemented, and the revised design operates within the requirements of the application, independent of the shape of the vanes and the angular direction of movement. Moreover, the revised design will work regardless of whether the switch is mounted on or in close proximity to ferromagnetic materials. As such, the revised design maybe mounted on a ferromagnetic bracket.

Brief Description of the Drawings

FIG. 1, view (A) is a side schematic view of the arrangement of components comprising a prior art magnetic switch. View (B) is an enlarged view of the schematic view of view (A) showing dimensions of the prior art design.

FIG. 2 shows how the presence of a ferromagnetic material affects the field distribution of the magnet.

FIG. 3 shows how the presence or absence of a magnetic vane between the magnet and the magnetic sensor affects the field distribution of the magnet.

FIG. 4, View (A) is a side schematic view of the arrangement of components comprising a magnetic switch having of the revised design of the present invention, which will work in the presence of a ferromagnetic bracket. View (B) is an enlarged view of the schematic view of View (A) showing dimensions and tolerances of the revised design.

FIG. 5 shows the differences between the prior art design and the revised design with respect to the spacing between the magnet and the ferromagnetic bracket.

FIG. 6 shows the differences between the prior art design and the revised design with respect to the spacing between the magnet and the magnetic sensor.

FIG. 7 shows the differences between the prior art design and the revised design with respect to the spacing between the magnetic sensor and the vane.

FIG. 8 shows the differences between the prior design and the revised design with respect to the spacing between the vane and the magnet.

FIG. 9 shows a magnetic profile of the revised design when mounted on a ferromagnetic bracket and when mounted on a non-ferrous bracket.

FIG. 10 shows components of the sensor mounted on a printed circuit board.

FIG. 11 shows a housing for the device.

Detailed Description

Flap sensor applications typically consist of a permanent magnet, a magnetic sensor (e.g. a Hall effect sensor) and a vane, which is made of a ferromagnetic material such as a low-carbon steel material or, more often, a magnetic stainless-steel material (due to anti-corrosion capabilities) . The magnetic sensor and magnet are placed at a distance from each other along a direction normal to the magnetization of the magnet (i.e. normal to a longitudinal line along which the North/South poles of the magnet lie) .

Without the presence of ferrous vane, the field distribution from a magnet along the normal axis is given by:

For the design of the air-gap between the magnet and the magnetic sensor, and to provide a selection of the correct magnet, the following equation also needs to be taken into account:

As can be seen from the equation, the magnetic field at a distance r from the magnet loses its strength according to the reciprocal of the square root of the distance, r.

The vane is rotatably mounted such that it can rotate between a neutral position (rotated approximately 45°) and an engaged position (rotated approximately 0°) wherein the vane is positioned between the magnetic sensor and the magnet. When in the engaged position, the field distribution is concentrated on the vane and, therefore, the measured magnetic field strength at the magnetic sensor is significantly reduced.

The revised design of the sensor, in accordance with the above equations, arranges the magnet and magnetic sensor in a symmetric orientation. The magnetization of the magnet is along a longitudinal direction with the North and South poles oriented as shown in FIG. 4. Depending on the application and the relative distances, the magnet may composed of either a rare earth material or a hard-ferrite material.

Magnetic flux lines exit from the North pole of the magnet and return to the South pole of the magnet. Flux lines always follow the path of least resistance. As such, the flux lines will follow the shortest path through a medium. When a ferromagnetic material is located near by the magnet, fluxes have a tendency to accumulate to the ferromagnetic material instead of travelling around ferromagnetic material in the air-space between the North and South poles. The flux lines use the ferrous material to shorten their journey back to magnet. Therefore, when the sensor is placed on ferromagnetic bracket, the magnetic flux lines shorten their distribution in space, from the North pole to the South pole, and the magnetic profile of the sensor application changes. This is the reason why the prior art sensor fails to operate when in close proximity to a ferromagnetic material.

FIG. 2 shows a comparison between an unimpeded field distribution of the magnet, in view (A) and the field distribution of the magnet when it is in close proximity to a ferromagnetic material, in view (B) . In view (A) , where there is no ferromagnetic material for the magnetic flux lines to pass through, the magnetic flux lines spread homogeneously in the space around the magnet. In view (B) , however, where a ferromagnetic material is present, for example, a bracket, the majority of the magnetic flux lines pass through the ferromagnetic material. The magnetic flux lines will always take the shortest possible path to travel from the North pole to the South pole of the magnet. Any ferromagnetic material which is located close to magnet can create a “short-cut” for the magnetic flux lines to close the path.

FIG. 3, view (A) shows the magnetic field distribution when the vane is in the engaged position at 0° rotation, located substantially between the magnet and the magnetic sensor, with and without the presence of the ferromagnetic material bracket. View (B) of FIG. 3 shows a magnetic field distribution with the vane at the neutral position at 45° rotation, such that the vane is no longer in between the magnet and the magnetic sensor.

It can be seen from FIG. 3 that the vane (which is made from ferromagnetic material) accumulates the magnetic flux lines and therefore changes the field strength that the magnetic sensor senses. Is It also reveals that the field is distributed near the ferromagnetic materials (i.e., the vane and the bracket) and the Hall sensor therefore measures and a significantly smaller magnetic field strength.

The prior art sensor fails to work properly in the presence of the ferromagnetic bracket. In particular, at extreme temperatures and mechanical tolerances, the sensor will not provide correct output results when mounted on ferromagnetic material.

The revised design, shown in FIG. 4, is best described in terms of differences from the prior art design. While the arrangement of components may appear similar between the revised design the prior art design, the changes in spacing of the components is significant and provides the desired functionality of allowing the revised design sensor to work in the presence of the ferromagnetic bracket.

FIG. 5 shows the first difference between the revised design and the prior art design. In the revised design, the magnet has been shifted up away from the ferromagnetic bracket. In the prior art design, the magnet was placed approximately 1.48 mm from the ferromagnetic bracket, while in the revised design, the magnet is placed approximately 1.98 mm from the ferromagnetic bracket, with a tolerance of ± 0.5 mm. While most of the flux will still past through the ferromagnetic material, until the material is saturated, the greater distance between the magnet and the is ferromagnetic bracket will allow more of the magnetic field to be sensed by the magnetic sensor.

FIG. 6 shows that the distance between the magnet and the magnetic sensor has been decreased in the revised design. In the prior art sensor, the distance was approximately 8.89 mm, while, in the revised design, the distance is approximately 6.89 mm with a tolerance of +. 25 mm and -. 5 mm. Due to the presence of the ferromagnetic bracket, less magnetic field travels in and around the space between the magnet and the magnetic sensor. As such, moving the magnet and magnetic sensor closer together will allow the magnetic sensor to measure more magnetic field.

FIG. 7 shows that the distance between the magnetic sensor and the vane has been decreased. These changes were made for the same reasons as the changes shown in FIG. 6. In the prior art design, the magnetic sensor and the vane were approximately 3.80 mm apart, while in the revised design, the magnetic sensor and the vane are proximally 1.21 mm apart, with a tolerance of ± 0.5 mm.

FIG. 8 shows that the vane in the revised design has shifted such that it is further away from the magnet than in the prior art design. Because both the vane and the bracket are composed of a ferromagnetic material, if the vane and bracket are too close together the majority of the magnetic field will pass through the vane and the bracket. In the prior art design, the vane and the magnet were proximally 3.09 mm apart, while in the revised design, the vane and magnet are approximately 3.68 mm apart with the tolerance of ± 1 mm.

Lastly, FIG. 4 shows that the longitudinal distance between the magnet and the magnetic sensor have been changed. In the prior art design, the magnetic sensor was positioned approximately opposite the center of the magnet, such that when the vane was in the 0° position, the vane was directly underneath the magnetic sensor. This orientation creates issues with mechanical tolerances in the revised design. As such, in the revised design, the magnetic sensor is offset from the magnet such that when the vane is oriented at the 0° position, it is no longer directly underneath the magnetic sensor.

FIG. 9 shows the magnetic profile of the revised design both when mounted on a ferromagnetic bracket and when mounted on a non-ferrous bracket. The two profiles are close, showing that the revised design of the present application can operate in both modalities.

The proposed symmetrical arrangement of the revised design assures that the sensor works correctly in all temperature variations from -40℃ two +150℃. The revised design can operate with any vane design and thickness (within accepted limits due to mechanical tolerances) . Due to the relative position of the magnet and the magnetic sensor, the vane can rotate clockwise or counter-clockwise and still provide similar angular results.

In preferred embodiments of the invention, a magnetic sensor is a Hall effect sensor. A typical Hall effect sensor useful for this purpose is the Micronas Hall chip HAL1509. In the absence of magnetic field (i.e., when the vane is between the magnet and the Hall-chip) the output of this switch is low, whereas under high external magnetic field (absence of the vane) , the output is high. In alternate embodiments, an xMR magnetic sensor may be used.

In preferred embodiments, as shown in FIG. 10, the magnetic sensor and any components necessary to power and/or read signals from the magnetic sensor may be mounted on a printed circuit board. Also, in preferred embodiments, and as shown in FIG. 11, the printed circuit board may be housed in a plastic or polymer housing which also houses the magnet and provides a pivot point about which the vane can rotate. The plastic housing may be mounted on the ferromagnetic bracket, as shown in FIG. 11.

Claims

A flap-type sensor comprising:

a magnetic field sensor;

a magnet, wherein the magnet and magnetic field sensor are disposed along a line normal to a longitudinal line along which the north and south poles of the magnet lie; and

a vane composed of a ferromagnetic material and rotatably mounted such that the vane may rotate between a neutral position and an engaged position approximately between the magnetic field sensor and the magnet such that magnetic flux lines from the magnet pass substantially through the vane;

wherein the separation between the magnet and the magnetic field sensor along the normal line is approximately 6.89 mm with a tolerance of +. 25 mm and -. 5 mm.
The sensor of claim 1 wherein the separation between the vane, when in the engaged position, and the magnetic sensor along the normal line is approximately 1.21 mm with a tolerance of ± . 5 mm.
The sensor of claim 2 wherein the separation between the vane, when in the engaged position, and the magnet along the normal line is approximately 3.68 mm with a tolerance of ±1 mm.
Sensor of claim 3 wherein the magnetic sensor is mounted on a printed circuit board.
The sensor of claim 4 wherein the printed circuit board and the magnet are housed in a housing, the housing also providing a pivot point about which the vane rotates.
The sensor of claim 5 wherein the housing is mounted on a bracket comprised of a ferromagnetic or non-ferrous material.
The sensor of claim 6 wherein the separation between the magnet and the bracket is a proximally 1.98 mm with a tolerance of ± . 5 mm.
The sensor of claim 1 wherein the magnetic sensor is a Hall effect sensor.
The sensor of claim 1 wherein the magnet is composed of a rare earth material.
The sensor of claim 1 wherein the longitudinal positioning of the magnet and the magnetic sensor are such that when the vane is in the engaged position, the vane is not directly between the magnet and the magnetic sensor.