Sensor and sensing method

Abstract

The present invention relates to a sensor (1), more particularly but not exclusively to a motion sensor for sensing the position of a first moving part of a device relative to a second part of the device.The present invention discloses a sensor comprising a static magnetic field generator (2) for generating a static magnetic field, and a movable magnetic conductive part (3) movable to influence the static magnetic field, the difference in influence being indicative of the position of the magnetic conductive part (3).

Description

[Technical field]

[0001] <Field of the Invention> The present invention relates to sensors, and more particularly, but not exclusively, to motion sensors for sensing the position of a first moving part of a device relative to a second part of the device. [Background technology]

[0002] <Background of the invention> A motion sensor ("encoder") detects the rotation and / or linear displacement of a first part of a device, e.g., a shaft, relative to a second part of the device, e.g., a body. Rotary encoders detect rotation, and linear encoders detect linear displacement.

[0003] Rotary encoders detect the rotation angle, rotation speed, direction, and position of a shaft, and include mechanical, optical, magnetic, capacitive, and inductive encoders.

[0004] A magnetic encoder has a rotor and a sensor. The rotor is fixed to a shaft and rotates with the shaft. The rotor is a series of magnets containing alternating, evenly spaced north and south poles around its circumference. As the shaft rotates with the rotor fixed, the sensor detects the change in position of the rotor's north and south poles. Figure 1 below is a diagram of a magnetic encoder with multiple north and south poles evenly spaced around the shaft. Figure 2 is a diagram of a magnetic encoder where the magnet has only one north and one south pole. Figure 1 TIFF2024539404000002.tif59169Figure 2 TIFF2024539404000003.tif74169

[0005] U.S. Patent Application No. US6857782B2, entitled "Magnetic encoder and wheel bearing assembly using the same," filed in the name of Takayuki Norimatsu and assigned to NTN Corporation, discloses a magnetic encoder that can increase the air gap between the magnetic encoder and a magnetic sensor. The magnetic force generated thereby can be easily controlled qualitatively. The wheel bearing assembly includes a magnetic encoder. The magnetic encoder includes a metal core and an elastic member integrated with the metal core in a ring shape. The elastic member is made of an elastic material mixed with powder of a magnetic material, and has a plurality of different magnetic poles arranged alternately in the circumferential direction. The Shore hardness of the elastic member is Hs90 or more. A wheel bearing assembly using a magnetic encoder as a component of a seal unit is also provided.

[0006] U.S. Patent Application No. US20110101964A1, entitled "Magnetic Encoder Element for Position measurement," assigned to Infineon Technologies AG, discloses a magnetic encoder element for use in a position measurement system including a magnetic field sensor for measuring position along a first direction. The encoder element includes at least one first track including a material that provides a magnetic pattern along the first direction, the magnetic pattern being formed by a remanent magnetization vector having a variable magnitude that depends on position along the first direction. The gradient of the remanent magnetization vector is such that a resulting magnetic field in a corridor above the first track and at a predetermined distance above the plane includes a magnetic field component perpendicular to the first direction whose sign does not change along the first direction.

[0007] US Patent Application No. 20140116132A1, entitled "Device for measuring angle and angular velocity of distance and speed", filed in the name of Heinrich Acker and assigned to Continental Teves AG, discloses a device for measuring the angle and angular velocity of a moving part. The device comprises a sensor that is or can be placed stationary and an encoder that is or can be placed on the moving part and generates, together with the sensor, a modulated signal to be demodulated by the sensor. For the frequency measurement required to measure the angular velocity / speed, the encoder has a structure reproducing a periodic pattern and interrupted by at least one index area for angle / distance measurement. In the index area, the encoder has an alternative pattern different from the periodic pattern according to at least one physical variable detectable by the sensor, but also allowing a frequency measurement in the index area.

[0008] U.S. Patent No. 5,302,893A, entitled "Magnetic encoder having a magnetic recording medium containing barium-ferrite," filed in the name of Yoshimura Kuniaki and assigned to Hitachi Metals, Ltd., discloses a coating-type magnetic recording member for use in a magnetic encoder including a non-magnetic substrate and a magnetic recording medium carried on the non-magnetic substrate. The magnetic recording medium is a magnetic film made of a magnetic paint containing magnetic barium ferrite powder. The magnetic encoder includes a magnetic recording member on which magnetic recording is performed and a magnetic sensor disposed opposite the magnetic recording medium.

[0009] U.S. Patent Application No. US10876861B2, entitled "Inductive Position Detector" filed in the names of Mark Anthony Howard and Darran Kleit and assigned to Zettlex (UK) Limited, discloses an inductive detector provided for measuring the relative position of a body along a measurement path. The detector includes an inductive target disposed along the measurement path, a laminated antenna disposed facing a portion of the target, and electronic circuitry disposed along the measurement path, wherein the inductance of at least one winding in the antenna is continuously varied in proportion to the relative position of the target and the antenna.

[0010] Celera Motion discloses the Zettlex inductive encoder (https: / / www.celeramotion.com / Zettlex / ), which uses a contactless induction method. Instead of the transformer of traditional inductive sensors, the Zettlex encoder uses a printed circuit. The encoder has two main parts, each shaped like a flat ring: a stator and a rotor. The stator is powered and measures the angular position of a passive rotor. Large encoders house all the associated electronics in the stator, while for small encoders, these electronics are distributed across the stator and a separate remote electronic circuit board found in the cable assembly. The large bore and low axial height allow for easy integration with through shafts, slip rings, direct drive motors, optical fibers, pipes or cables.

[0011] One of the difficulties with polarised magnets is that the magnet cannot be polarised precisely: the exact position or angle of the shaft where the polarised magnet is attached cannot be measured precisely. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0012] <Subject of the present invention> SUMMARY OF THE DISCLOSURE It is an object of the present invention to provide a sensor which at least partially alleviates the above-mentioned difficulties. [Means for solving the problem]

[0013] <Summary of the Invention> According to the present invention, there is provided a sensor comprising a static magnetic field generator (or a stationary magnetic field generator) for generating a static magnetic field (or a stationary magnetic field) and a movable magnetically conductive part that is movable to influence the static magnetic field, the difference in influence indicating the position of the magnetically conductive part.

[0014] It is provided that the static (or stationary) magnetic field generator is an electromagnet and / or a magnet.

[0015] An electromagnet and / or magnet is provided that is affixed to a printed circuit board ("PCB").

[0016] It is further provided that the electromagnet has a power source.

[0017] It is provided that the electromagnet is part of the oscillator.

[0018] Electromagnets and / or magnets are provided which generate an oscillation frequency suitable for adaptation and measurement using a microprocessor.

[0019] A magnetic conductive portion is provided to be associated with a first portion of an object, the position of which is provided to be detected.

[0020] The first portion is provided for movement relative to a second portion of the object.

[0021] It is provided that the first part is a shaft.

[0022] It is further provided that said magnetically conductive part is arranged around at least a portion of the shaft.

[0023] It is further provided that the movable magnetically conductive part is a magnetically conductive ring arranged around the shaft.

[0024] A movable magnetically conductive ring is provided off-centre with the axis.

[0025] It is further provided that a portion of the surface of the movable magnetic conductive ring is inclined and / or irregular.

[0026] It is further provided that the major faces of the movable magnetic conductive ring are inclined.

[0027] It is provided that the movable magnetic conductive ring is wedge-shaped in side view.

[0028] It is further provided that the movable magnetic conductive ring is constructed from ferrite.

[0029] It is further provided that the magnets and / or electromagnets are spaced apart from at least one side of the ferrite ring.

[0030] A printed circuit board is provided disposed about at least a portion of the axis.

[0031] - a static (or stationary) magnetic field generator generating a static magnetic field; - a movable magnetic conductive part influencing a static magnetic field; - detecting a difference in the effect of the sensor on a static magnetic field. Or, a static magnetic field generator for generating a static magnetic field; a movable magnetic conductive part which exerts a static magnetic field; a sensor that detects the difference in effect on a static magnetic field.

[0032] - a static magnetic field coil generating a magnetomotive force; - the stationary magnetic conductive part having a low magnetic resistance; - a movable magnetic conductive part having a low magnetic resistance; - an air gap with high magnetic resistance connecting the stationary magnetic conductive part and the moving magnetic conductive part to create a magnetic path; - a moving magnetic conductive part changes the air gap to affect the flow of magnetic flux; - a sensor detecting a difference in magnetic flux flow for a given magnetomotive force. Or, - a static magnetic field coil that creates a magnetomotive force; a static magnetic conductive part having a low magnetic resistance; a movable magnetic conductive part having low magnetic resistance; - an air gap with high magnetic resistance connecting the stationary magnetic conductive part and the movable magnetic conductive part, thereby creating a magnetic path; having - the movable magnetic conductive part changes the air gap as it moves, thus influencing the flow of magnetic flux; - A sensor that detects the difference in magnetic flux flow for a given magnetomotive force Further comprising Sensing method.

[0033] A further step of the present invention provides that a movable magnetically conductive part moves with the first part of the object, the position of which is detected.

[0034] A further step of the present invention provides for the movable magnetic conductive portion to rotate off-center about the first portion.

[0035] A further step of the present invention provides the inductance of the static magnetic field coil to be sensed.

[0036] These and other features of the invention are described in greater detail below. [Brief description of the drawings]

[0037] Embodiments of the invention will now be described, by way of example only, with reference to the drawings in which: [Figure 1] FIG. 1 shows a top view of a first embodiment of a sensor. [Diagram 2] FIG. 2 shows a side view of the sensor of FIG. [Diagram 3] FIG. 3 shows a top perspective view of a second embodiment of the sensor. [Figure 4] FIG. 4 shows a side view of the sensor of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] <Detailed Description of the Drawings> 1 and 2, a sensor is generally designated by the reference numeral 1.

[0039] The sensor 1 comprises three static magnetic field generators 2, in this case magnetic field coils, each forming part of an independent oscillator. The oscillators and the associated magnetic field coils 2 are connected to a power source, e.g. a battery (not shown). Each oscillator oscillates at a nominal frequency of 5 MHz determined by a tank circuit formed by a fixed capacitor and a magnetic field coil, the inductance of which varies with the rotation of the shaft. The capacitors are standard surface mount components with a fixed capacitance, and the variable inductance is established by a winding of the associated magnetic field coil with an associated variable magnetic flux path.

[0040] The oscillator and associated field coils 2 are fixed to a printed circuit board ("PCB") 5. The PCB 5 is generally C-shaped in top view to allow easy mounting about an axis. The field coils are evenly spaced at 90 degree intervals around the inner edge of the PCB 5.

[0041] A magnetically conductive part 3 is disposed at a distance from an upper surface of the magnetic field coil 2, forming an air gap 8 between the upper surface of the magnetic field coil and a lower surface of the magnetically conductive part 3. A part of the magnetically conductive part 3 is located on (or over) a part or parts of the magnetic field coil 2. The magnetically conductive part 3 is a ferrite ring, which avoids eddy current losses. The ferrite ring 3 is fixed off-centre on the axis 4.

[0042] The axis 4 extends through the centre of the PCB 5 .

[0043] Each oscillator and associated magnetic field coil 2 is buffered with a voltage comparator which generates a high speed digital signal for transmission to a 32-bit binary counter within a common microprocessor (not shown).

[0044] A second embodiment of the sensor 1 is shown in FIGS.

[0045] In this embodiment, a ferrite ring 3 is split into two halves that are fastened together to form a ring. The ferrite ring 3 has a sloped underside. The ferrite ring 3 is attached to a bobbin 7 with a radial offset. The bobbin 7 is split into two halves that are fastened together to form a ring-like disk that holds the ferrite ring.

[0046] Also, instead of three oscillators, six oscillators are fixed to PCB5.

[0047] In use, the oscillators receive power from a battery or any other suitable power source. Each oscillator drives its associated field coil to form a local magnetic circuit with magnetic flux flowing through the air gap and the ferrite ring, as shown in Figure 2.

[0048] Because the ferrite ring is fixed off-center on the axis, it extends unevenly over the magnetic field coil: in a first position, the ferrite ring spans a larger portion of the magnetic field coil on the left side of the PCB and a smaller portion of the magnetic field coil on the right side of the PCB (see FIG. 1).

[0049] Each magnetic field coil generates a local magnetic force that induces magnetic flux in a local magnetic circuit, as shown in Figure 2. Each magnetic circuit has a specific variable reluctance, which in turn causes the magnetic field coil to have a specific variable inductance that affects the oscillation frequency of the associated oscillator.

[0050] A 32-bit counter determines the number of pulses generated by each oscillator during a precise period of time. The microprocessor uses these count values ​​to adjust a model of the system until the best match between the predicted and observed counts occurs, thus generating the angular position of the ferrite rings, and therefore the angular position of the shaft.

[0051] The shaft rotates in a given direction, rotating the ferrite ring in sync to a new position. The above process for achieving a change in the magnetic field continues, and thus the angular position of the rotating shaft can be continuously determined in real time. This process results in an absolute angle encoder capable of real time operation in both clockwise and counterclockwise directions at high speeds.

[0052] The second embodiment described herein is expected to be convenient to use. Compared to the prior art, the system and method described herein is more accurate in that it uses electromagnets instead of polarized permanent magnets. Also, multiple sensors are used in conjunction with a system model, allowing the algorithm to achieve very high resistance and accuracy to radial and axial misalignment of the rotor and stator, temperature drift, and long-term variations due to aging.

[0053] It will be appreciated by those skilled in the art that many other embodiments of the invention, including both rotary and linear position sensors, are possible without departing from the scope of the invention. For example, the nominal oscillation frequency at which the oscillators drive their associated magnetic field coils need not be 5 MHz, but may be lower or higher. It may be increased to 50 MHz to increase resolution by a factor of ten, or may be decreased to reduce EMI emissions. Similarly, the bit count of a binary counter in a microprocessor may be increased to improve resolution, or decreased to reduce element count.

Claims

1. 1. A sensor comprising: a static magnetic field generator for generating a static magnetic field; and a movable magnetically conductive portion movable to influence said static magnetic field, the difference in influence indicating the position of said movable magnetically conductive portion.

2. 2. The sensor of claim 1, wherein the static magnetic field generator is an electromagnet forming part of an oscillator that produces an oscillation frequency suitable for adaptation and measurement using a microprocessor.

3. The sensor of claim 1 , wherein the movable magnetic conductive portion is associated with a first portion of an object to detect the position of the object.

4. The sensor of claim 3 , wherein the first portion is a shaft.

5. The sensor of claim 4 , wherein the movable magnetically conductive portion is disposed about a portion of the shaft.

6. The sensor of claim 1 , wherein the movable magnetically conductive portion is a movable magnetically conductive ring disposed about the axis.

7. The sensor of claim 6 , wherein the movable magnetic conductive ring is off-center on the axis.

8. The sensor of claim 6 , wherein the movable magnetic conductive ring is inclined over a portion of its surface.

9. 7. The sensor of claim 6, wherein the movable magnetic conductive ring is irregular over a portion of its surface.

10. The sensor of claim 6 , wherein the movable magnetic conductive ring is tapered on its major sides.

11. The sensor of claim 6 , wherein the movable magnetic conductive ring is constructed from ferrite.

12. The sensor of claim 2 , wherein the electromagnet is spaced from at least one side of the movable magnetic conductive ring.

13. The sensor of claim 6 , wherein a printed circuit board is disposed about at least a portion of the axis.

14. - generating a magnetomotive force by means of a static field coil; - providing a static magnetically conductive part with low magnetic resistance; - providing a movable magnetically conductive part with low magnetic resistance; - forming an air gap with high magnetic resistance connecting said stationary magnetically conductive part and said moving magnetically conductive part, thereby creating a magnetic path; - moving said movable magnetically conducting part and, as it moves, changing said air gap and thereby influencing the flow of magnetic flux; - detecting said difference in flow of magnetic flux for a given magnetomotive force by means of a sensor; having Sensing method.

15. The method of claim 14 including detecting the inductance of the static magnetic field coil.

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