News Column

Researchers Submit Patent Application, "Magnetic Field Measuring Device", for Approval

June 25, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Okamoto, Junichiro (Tokyo, JP); Takahashi, Arata (Tokyo, JP), filed on July 27, 2012, was made available online on June 12, 2014.

The patent's assignee is Asahi Kasei Microdevices Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "FIGS. 1A to 1C are diagrams for explaining a traditional magnetic encoder, in which a multipolar magnet and magnetic sensors such as Hall ICs as illustrated in FIG. 1A are used. In this case, Hall ICs 102a and 102b are placed such that the phase difference between each other's output pulses are offset by an electrical angle of 90 degrees. By taking such a configuration, it is possible to make a magnetic encoder able to detect a rotational direction.

"FIG. 2 is a block diagram of a Hall IC in general use, in which a Hall element 101, an amp 130, and a Schmitt circuit 131 are integrated. Such a Hall IC is broadly used in fields such as magnetic pulse encoders. The Hall IC operates to amplify the Hall electromotive force output in proportion to a magnetic field applied to the magneto-sensing surface of the Hall element 101 at the amp 130, subsequently make a comparison against an arbitrary threshold at the Schmitt circuit, and digitally output the result.

"Next, the principle of a magnetic encoder capable of detecting direction will be described. FIG. 1B represents the magnetic fields applied to Hall elements inside Hall ICs 102a and 102b and outputs of each Hall IC in the case where, provided that the state illustrated in FIG. 1A is an electrical angle of 0 degrees, the Hall ICs 102a and 102b are rotated therefrom about a magnet in the CCW direction. Also, FIG. 1C represents the magnetic fields applied to Hall elements inside Hall ICs 102a and 102b and outputs of each Hall IC in the case where, provided that the state illustrated in FIG. 1A is an electrical angle of 0 degrees, the Hall ICs 102a and 102b are rotated therefrom about a magnet in the CW direction. As the results demonstrate, it becomes possible to detect the rotational direction by taking the rising or the falling in the output of one of the Hall ICs as a trigger, and seeing whether the state of the output of the other Hall IC is high or low. In this example, the falling of the Hall IC 10b is set as the trigger.

"However, this configuration entails the use of two separate Hall ICs, and thus it is necessary to change the placement of the Hall ICs to match the pitch of the multipolar magnet, and the effects of assembly misalignment or the like cannot be ignored. For this reason, as a technique for improving the above, there exists a technique that, as in FIGS. 1 and 2 in Patent Literature 1, enables direction detection with one chip by using magnetic convergence plates made up of a magnetic body, and utilizing a property that the phases of a vertical magnetic field and a horizontal magnetic output in conjunction with the rotation of a multipolar magnet such as in FIG. 8 of Patent Literature 1 are offset by an electrical angle of 90 degrees with respect to an electromagnetic transducer magneto-sensing surface. This method improves the problems discussed above, and is an effective technique as a magnetic encoder or input device."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Technical Problem

"However, in applications such as wheel speed sensors broadly used in recent years, demands are rising for the sensor to be operable even if the distance between the multipolar magnet and the sensor is increased, or in other words even if the magnetic field strength applied to the sensor is in a low state, rising for less jitter in the output even in environments in which the magnetic noise disturbance is inferior, and also rising for output that accurately corresponds to the pole pitch of the multipolar magnet (generally called the output duty demand). As the magnetic flux density applied to the sensor from the multipolar magnet lowers, the effects of magnetic noise disturbance increase, degrading the output jitter and output duty. The technique of Patent Literature 1 discussed above does not mention such magnetic field noise disturbance.

"The present invention has been devised in light of such problems, and takes as an object to provide a magnetic field measuring device that is capable of eliminating the effects of magnetic noise disturbance, and furthermore is capable of duty output that is both low-jitter and accurate even if the magnetic field strength applied to the sensor device and produced by the object of detection is low, particularly in applications that detect the position, move, or rotation of an object of detection, such as a wheel speed sensor.

"Solution to Problem

"The present invention has been devised in order to achieve such an object, and the invention described in Claim 1 is a magnetic field measuring device that detects the strength of a magnetic field produced from a magnetic field-producing body, characterized by comprising: first to fourth magnetoelectric transducers; magnetic convergence plates made up of a magnetic body; and a calculation unit that calculates the strength of a magnetic field applied in a horizontal direction and/or a vertical direction with respect to a magneto-sensing surface of the magnetoelectric transducers; wherein the magnetic convergence plates are placed in the vicinity of the first to fourth magnetoelectric transducers so as to convert magnetic field vectors produced in a horizontal direction with respect to the magneto-sensing surface of the first magnetoelectric transducer and the magneto-sensing surface of the second magnetoelectric transducer into magnetic field vectors in a vertical direction with respect to the magneto-sensing surface of the first magnetoelectric transducer and the magneto-sensing surface of the second magnetoelectric transducer, and also in opposite directions at the respective magneto-sensing surfaces, and in addition, convert magnetic field vectors produced in a horizontal direction with respect to the magneto-sensing surface of the third magnetoelectric transducer and the magneto-sensing surface of the fourth magnetoelectric transducer into magnetic field vectors in a vertical direction with respect to the magneto-sensing surface of the third magnetoelectric transducer and the magneto-sensing surface of the fourth magnetoelectric transducer, and also in opposite directions at the respective magneto-sensing surfaces, and the calculation unit includes a first calculation block that adds or subtracts outputs from the first to fourth magnetoelectric transducers to output a calculation result.

"Also, the invention described in Claim 2 is a magnetic field measuring device that detects the strength of a magnetic field produced from a magnetic field-producing body, characterized by comprising: first to fourth magnetoelectric transducers; and a calculation unit that calculates the strength of a magnetic field applied in a horizontal direction and/or a vertical direction with respect to a magneto-sensing surface of the magnetoelectric transducers; wherein the calculation unit includes a first calculation block that adds or subtracts outputs from the first to fourth magnetoelectric transducers to output a calculation result, and a second calculation block that adds or subtracts outputs from the first to fourth magnetoelectric transducers to calculate a signal whose phase differs by 90 degrees from an output signal of the first calculation block to output a calculation result.

"Also, the invention described in Claim 3 is characterized in that, in the invention described in Claim 1 or 2, the first calculation block includes a first addition/subtraction block that adds or subtracts outputs from the first magnetoelectric transducer and the second magnetoelectric transducer to output a calculation result, a second addition/subtraction block that adds or subtracts outputs from the third magnetoelectric transducer and the fourth magnetoelectric transducer to output a calculation result, and a third addition/subtraction block that adds or subtracts output from the first addition/subtraction block and output from the second addition/subtraction block to output a calculation result.

"Also, the invention described in Claim 4 is characterized in that, in the invention described in Claim 1 or 2, the first calculation block includes a first addition/subtraction block that adds or subtracts outputs from the first magnetoelectric transducer and the third magnetoelectric transducer to output a calculation result, a second addition/subtraction block that adds or subtracts outputs from the second magnetoelectric transducer and the fourth magnetoelectric transducer to output a calculation result, and a third addition/subtraction block that adds or subtracts output from the first addition/subtraction block and output from the second addition/subtraction block to output a calculation result.

"Also, the invention described in Claim 5 is characterized in that, in the invention described in any of Claims 1 to 4, the calculation unit includes a second calculation block that adds or subtracts outputs from the first to fourth magnetoelectric transducers to calculate a signal whose phase differs from an output signal of the first calculation block.

"Also, the invention described in Claim 6 is characterized in that, in the invention described in Claim 5, the phase difference between an output signal from the first calculation block and an output signal from the second calculation block is 90 degrees.

"Also, the invention described in Claim 7 is characterized in that, in the invention described in Claim 5 or 6, the second calculation block includes a fourth addition/subtraction block that adds or subtracts outputs from the first magnetoelectric transducer and the second magnetoelectric transducer to output a calculation result, a fifth addition/subtraction block that adds or subtracts outputs from the third magnetoelectric transducer and the fourth magnetoelectric transducer to output a calculation result, and a sixth addition/subtraction block that adds or subtracts output from the fourth addition/subtraction block and output from the fifth addition/subtraction block to output a calculation result.

"Also, the invention described in Claim 8 is characterized in that, in the invention described in Claim 5 or 6, the second calculation block includes a fourth addition/subtraction block that adds or subtracts outputs from the first magnetoelectric transducer and the third magnetoelectric transducer to output a calculation result, a fifth addition/subtraction block that adds or subtracts outputs from the second magnetoelectric transducer and the fourth magnetoelectric transducer to output a calculation result, and a sixth addition/subtraction block that adds or subtracts output from the fourth addition/subtraction block and output from the fifth addition/subtraction block to output a calculation result.

"Also, the invention described in Claim 9 is characterized in that, in the invention described in any of Claims 1 to 8, the first to fourth magnetoelectric transducers are placed approximately linearly.

"Also, the invention described in Claim 10 is characterized in that, in the invention described in any of Claims 1 to 9, the calculation unit detects position, move, or rotation of the magnetic field-producing body.

"Also, the invention described in Claim 11 is characterized in that, in the invention described in Claim 10, the calculation unit detects position, move, or rotation of the magnetic field-producing body, on the basis of output from the first calculation block.

"Also, the invention described in Claim 12 is characterized in that, in the invention described in Claim 10 or 11, the calculation unit detects position, move, or rotation of the magnetic field-producing body, on the basis of a signal obtained by forming an output signal from the first calculation block into a pulse waveform.

"Also, the invention described in Claim 13 is characterized in that, in the invention described in any of Claims 5 to 8, the calculation unit detects position, move, or rotation of the magnetic field-producing body, on the basis of output from the first calculation block, and output from the second calculation block.

"Also, the invention described in Claim 14 is characterized in that the invention described in any of Claims 1 to 13 comprises a magnetic field-producing body, wherein the magnetic field-producing body is a movable and/or rotatable multipolar-magnetized magnet, or alternatively, a structure composed of a back-bias magnet installed in the vicinity of the first to fourth magnetoelectric transducers, and movable and/or rotatable gear teeth.

"Also, the invention described in Claim 15 is characterized in that the invention described in any of Claims 1 to 13 comprises a magnetic field-producing body, wherein the magnetic field-producing body is a structure composed of a back-bias magnet installed in the vicinity of the first to fourth magnetoelectric transducers, and movable and/or rotatable gear teeth, and the first to fourth magnetoelectric transducers are installed at positions between the back-bias magnet and the gear teeth.

"Advantageous Effects of Invention

"According to the present invention, it becomes possible to provide a magnetic field measuring device which is adaptable to applications that detect the position, move, or rotation of an object of detection, and additionally, is capable of eliminating the effects of magnetic noise disturbance in the case of detecting the position, move, or rotation of an object of detection, and furthermore is capable of duty output that is both low-jitter and accurate even if the magnetic field strength applied to the sensor device and produced by the object of detection is low.

BRIEF DESCRIPTION OF DRAWINGS

"FIG. 1A is a diagram for explaining a magnetic encoder of the related art;

"FIG. 1B is a diagram for explaining a magnetic encoder of the related art;

"FIG. 1C is a diagram for explaining a magnetic encoder of the related art;

"FIG. 2 is a block diagram of a Hall IC in general use in the related art;

"FIG. 3 is a configuration diagram for explaining respective embodiments given as a magnetic field measuring device according to the present invention;

"FIG. 4 is a side view of the magnetic convergence plate sensor unit 9 illustrated in FIG. 3;

"FIG. 5 is a diagram for explaining the role of the magnetic convergence plates illustrated in FIG. 3;

"FIG. 6 is a diagram illustrating internal signals of a detection field in a magnetic field measuring device according to the present invention;

"FIG. 7 is a diagram illustrating the placement relationship between an object of detection and Hall elements;

"FIG. 8 is a top view for explaining a magnetic field measuring device in Embodiment 1;

"FIG. 9A is a diagram illustrating the results of signal calculation for one electrical angle period;

"FIG. 9B is a diagram illustrating the results of signal calculation for one electrical angle period;

"FIG. 9C is a diagram illustrating the results of signal calculation for one electrical angle period;

"FIG. 10A is a diagram for explaining signal processing in Embodiment 1;

"FIG. 10B is a diagram for explaining signal processing in Embodiment 1;

"FIG. 11A is a diagram illustrating an output waveform from the output shaping unit illustrated in FIG. 6;

"FIG. 11B is a diagram illustrating an output waveform from the output shaping unit illustrated in FIG. 6;

"FIG. 12A is a diagram illustrating an example of a waveform in Examples 1, 2, and 3;

"FIG. 12B is a diagram illustrating an example of a waveform in Examples 1, 2, and 3;

"FIG. 12C is a diagram illustrating an example of a waveform in Examples 1, 2, and 3;

"FIG. 12D is a diagram illustrating an example of a waveform in Examples 1, 2, and 3;

"FIG. 13A is a top view for explaining another example of a magnetic field measuring device in Embodiment 1;

"FIG. 13B is a side view for explaining another example of a magnetic field measuring device in Embodiment 1;

"FIG. 14 is a top view for explaining a magnetic field measuring device in Embodiment 2;

"FIG. 15 is a top view for explaining a magnetic field measuring device in Embodiment 3;

"FIG. 16A is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16B is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16C is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16D is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16E is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16F is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16G is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 16H is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 17A is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 17B is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3;

"FIG. 17C is a diagram illustrating an example of a usable magnetic field convergence plate shape in Examples 1, 2, and 3; and

"FIG. 18 is a diagram illustrating internal signals of a detection field in a magnetic field measuring device according to the present invention."

For additional information on this patent application, see: Okamoto, Junichiro; Takahashi, Arata. Magnetic Field Measuring Device. Filed July 27, 2012 and posted June 12, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1252&p=26&f=G&l=50&d=PG01&S1=20140605.PD.&OS=PD/20140605&RS=PD/20140605

Keywords for this news article include: Electronics, Signal Processing, Asahi Kasei Microdevices Corporation.

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Source: Electronics Newsweekly


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