JP5317855B2 - Geomagnetic sensor correction device and orientation display device - Google Patents

Description

  The present invention relates to a correction device for a geomagnetic sensor that corrects geomagnetic data detected by a geomagnetic sensor and a direction display device using the correction device.

  When a geomagnetic sensor is mounted on an electronic device, the geomagnetic sensor is easily affected by magnetism other than geomagnetism generated from a circuit of the electronic device or a magnetic part. For example, in an azimuth display device in which a geomagnetic sensor is attached to a display of a fluorescent display tube, when the current flowing through the fluorescent display tube is changed to change the brightness of the display screen, the geomagnetic sensor is generated by magnetic noise generated from the fluorescent display tube. The detected value of fluctuates and correct orientation data may not be obtained.

  In response to this, measures have been taken such as blocking the magnetic field around the geomagnetic sensor and reducing the current flowing through the fluorescent display tube. However, when the magnetic field is interrupted around the geomagnetic sensor, there is a possibility that the measurement of the geomagnetism itself may be hindered, and it is necessary to use a special material for shielding. Further, when the current flowing through the fluorescent display tube is reduced, the brightness of the display screen is lowered, and thus visibility is lowered.

  As a conventional technique for removing the influence on the geomagnetic sensor due to magnetism other than geomagnetism, there is a mobile phone disclosed in Patent Document 1, for example. This mobile phone has table data in which each of a plurality of operation states of its own circuit is associated with an offset value indicating the direction and magnitude of magnetism that affects the geomagnetic sensor other than geomagnetism in each operation state. Pre-held. When using a geomagnetic sensor, this mobile phone detects the operation state of its own circuit and identifies a corresponding offset value, and based on this offset value and the direction and magnitude of magnetism detected by the magnetic sensor. Calculate the direction of geomagnetism.

JP 2005-315650 A

  Conventionally, as described above, offset value table data associated with each operation state of its own circuit is provided. In this table data, it is considered that an offset value obtained by a prior experiment in which the operation state of the circuit of the own device is changed is registered. However, in practice, it is rare that the operation state is set exactly the same as that in the preliminary experiment. For this reason, in the method of referring to the table data in which the offset value at the time of the preliminary experiment is fixedly registered, there is a high possibility that a deviation occurs between the offset value of the table data and the actual value. Cannot be corrected.

  For example, when an operation state not included in the table data is set, a deviation occurs between the offset value of the table data and the actual value. Further, if an attempt is made to register an offset value corresponding to a more detailed change in the operating state, the capacity of the table data inevitably increases, and memory resources are unnecessarily consumed.

  In a azimuth display device with a geomagnetic sensor attached to the display of a fluorescent display tube, when the brightness of the screen of the fluorescent display tube is changed, geomagnetic data detected by the geomagnetic sensor due to magnetic noise generated from the fluorescent display tube It changes slowly with a certain time constant. Such a so-called transient state cannot be corrected by referring to the table data of the offset value corresponding to the operation state determined in advance by a prior experiment as in Patent Document 1.

  The present invention has been made to solve the above-described problems, and can correct the geomagnetic data of the geomagnetic sensor affected by the magnetic noise with high accuracy, and change of the geomagnetic data due to the magnetic noise. It is an object of the present invention to provide a correction device for a geomagnetic sensor and an azimuth display device using the same, which can be corrected accurately even in a transient state.

A correction apparatus for a geomagnetic sensor according to the present invention includes a first correction formula for calculating a correction value of output fluctuation of a geomagnetic sensor caused by magnetism emitted from a magnetic generator according to an operation, and correction in a transient state of output fluctuation storage means for storing a second correction equation to calculate the value, using a first correction equation storing means, thereby correcting the output variation by calculating the correction value of the output of the geomagnetic sensor in accordance with the operation And a correction unit that corrects the output fluctuation in the transient state up to the calculated correction value using the second correction formula of the storage unit .

According to the present invention, the output fluctuation of the geomagnetic sensor according to the operation is calculated using the first correction formula for calculating the correction value of the output fluctuation of the geomagnetic sensor caused by the magnetism emitted from the magnetic generator according to the operation. In addition to performing correction , the output fluctuation in the transient state is corrected using the second correction formula for calculating the correction value in the transient state of the output fluctuation . By doing in this way, there exists an effect that the fluctuation | variation of the geomagnetic data of the geomagnetic sensor resulting from the magnetic noise emitted from magnetic generators, such as a fluorescent display tube, can be correct | amended accurately.

It is a perspective view which shows the vehicle-mounted display to which the correction | amendment apparatus and azimuth | direction display apparatus of the geomagnetic sensor by Embodiment 1 of this invention were applied. It is a functional block diagram which shows the structure of the vehicle-mounted display of FIG. It is a figure which shows the example of a display of geomagnetic data. It is a figure which shows the intensity | strength of the magnetic noise according to the brightness of the screen of a fluorescent display tube. It is a figure which shows an example of the influence by magnetic noise. 3 is a flowchart showing a flow of correction processing of geomagnetic data according to the first embodiment. It is a figure which shows the relationship between the type | formula which shows magnetic noise intensity | strength, and its correction formula. It is a figure which shows the result of having calculated | required the correction value with respect to the magnetic noise of FIG. 4 according to the brightness setting from the correction formula. It is a flowchart which shows the flow of the correction | amendment process of the geomagnetic data by Embodiment 2 of this invention. It is a figure which shows typically the time-sequential change of the coordinate value of the y-axis direction of the geomagnetic data according to the brightness setting of the screen of a fluorescent display tube. It is a figure for demonstrating an example of the correction formula showing the transient state of geomagnetism.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing an in-vehicle display to which a correction device for a geomagnetic sensor and a direction display device according to Embodiment 1 of the present invention are applied. In FIG. 1, a vehicle-mounted display 1 includes a geomagnetic sensor 2 and a display main body 3. The geomagnetic sensor 2 is attached to, for example, the top surface of the display main body 3. In the example of FIG. 1, two-dimensional coordinates are set with the y-axis being the direction perpendicular to the display screen of the fluorescent display tube 4 and the x-axis being the parallel direction.

  A fluorescent display tube (magnetic generator) 4 is used for displaying information on the in-vehicle display 1. For example, a microcomputer (hereinafter referred to as a microcomputer) built in the display main body 3 calculates an orientation based on geomagnetic data detected by the geomagnetic sensor 2, and this orientation information is displayed on the display screen of the fluorescent display tube 4. To display. Here, the above-described two-dimensional coordinates are applied to the display screen of the fluorescent display tube 4, and the arrow direction in FIG. 1 corresponds to the y-axis direction.

  In addition, the in-vehicle display 1 displays not only the direction information but also vehicle information such as fuel efficiency and cruising distance of the vehicle on which the vehicle is mounted, music information of radio and other media, outside temperature information, altitude and pressure information, and the like. It can be displayed on the display screen of the fluorescent display tube 4.

FIG. 2 is a functional block diagram showing the configuration of the in-vehicle display of FIG. In FIG. 2, the in-vehicle display 1 includes a geomagnetic sensor 2 and a display main body 3. The display main body 3 includes a fluorescent display tube 4 and a microcomputer 5.
The brightness of the screen of the fluorescent display tube 4 is controlled by changing the duty ratio of a pulse (rectangular wave) having a predetermined frequency output from the microcomputer 5. At this time, the magnetic field fluctuates according to the amount of current supplied to the fluorescent display tube 4, and magnetic noise is generated. The microcomputer 5 is configured such that a built-in CPU (not shown in FIG. 2) executes a program stored in a ROM (Read Only Memory) 8, thereby causing a control unit (correction unit, control unit) 6 and a calculation processing unit (correction). Means) 7 functions.

  The control unit 6 calculates display data indicating the direction (direction vector) based on the geomagnetic data detected by the geomagnetic sensor 2 and displays the display data on the fluorescent display tube 4, and the screen of the fluorescent display tube 4 as described above. It is a component that also performs brightness setting. FIG. 3 is a diagram showing a display example of geomagnetic data. When a coordinate system as shown in FIG. 3 is considered, if the intensity of geomagnetism detected by the geomagnetic sensor 2 is (x, y), true north is (0, 100) and true west is (-100, 0). ), And the southeast can be represented by (100, -100) or the like.

  The calculation processing unit 7 is a component that corrects geomagnetic data detected by the geomagnetic sensor 2 using a correction formula stored in the ROM 8 or the external ROM 8a. In addition, the calculation processing unit 7 uses a correction formula stored in the ROM 8 or the external ROM 8a, and changes the geomagnetic data transiently due to magnetic noise corresponding to the screen brightness of the fluorescent display tube 4 set by the control unit 6. Is corrected.

  A ROM (storage means) 8 stores in advance a correction formula for correcting the influence of magnetic noise from the fluorescent display tube 4 on the geomagnetic data, and the correction data calculated by the calculation processing unit 7 using the correction formula. Is stored. The external ROM (storage means) 8a is, for example, a ROM prepared separately from the microcomputer 5 inside the display main body 3, or a semiconductor memory connected to the outside of the display main body 3 by USB (Universal Serial Bus). The same data and correction formula as in the ROM 8 are stored.

  The influence of magnetic noise generated in the fluorescent display tube 4 on the geomagnetic data according to the brightness setting of the screen of the fluorescent display tube 4 can be specified in advance by experiments. For this reason, it is possible to create the correction formula in advance. In the first embodiment, the correction formula is assumed that magnetic noise of constant intensity and direction is generated from the fluorescent display tube 4 by setting the brightness of the screen of the fluorescent display tube 4 (duty ratio = 0 to 100%). The case where it created is shown.

  FIG. 4 is a diagram showing the intensity of magnetic noise corresponding to the brightness of the screen of the fluorescent display tube. FIG. 4 shows an example in which magnetic noise is generated in a direction perpendicular to the screen of the fluorescent display tube 4, that is, in a true north (y-axis) direction. If the brightness of the screen of the fluorescent display tube 4 is duty ratio = 100% under the influence of magnetic noise when facing the west direction at present, the control unit 6 of the microcomputer 5 as shown in FIG. Deviation (error) occurs in the direction calculated by. The influence of such magnetic noise is small in a region where the geomagnetism is relatively strong, but in a region where the geomagnetism is weak, the influence of the magnetic noise becomes large, and there is a high possibility that an error occurs in the measurement result of the geomagnetism.

  On the other hand, the magnetic noise shown in FIG. 4 can be mathematically expressed as y = −0.2d. Here, d is the duty ratio of the output waveform that controls the brightness of the screen of the fluorescent display tube 4. In the present invention, it is possible to correct the geomagnetic data with high accuracy by using the correction formula obtained from the formula for specifying the magnetic noise as described above.

Next, the operation will be described.
FIG. 6 is a flowchart showing a flow of correction processing of geomagnetic data according to the first embodiment, and shows the correction processing in the in-vehicle display of FIG.
First, when the vehicle-mounted display 1 is activated, the control unit 6 prohibits updating the azimuth display (step ST1). At this time, the calculation processing unit 7 reads the previous setting value (duty ratio) from the ROM 8 or the external ROM 8a, and checks the current setting value of the screen brightness of the fluorescent display tube 4 (step ST2).

  Next, the calculation processing unit 7 reads the correction formula (a) (first correction formula) from the ROM 8 or the external ROM 8a (step ST3), and according to the brightness setting of the screen of the fluorescent display tube 4, the correction formula ( A correction value (b) is calculated from a) (step ST4). As shown in FIG. 7, when the intensity of the magnetic noise generated from the fluorescent display tube 4 can be expressed as y = −ad, the correction expression y = is stored in the ROM 8 as a correction expression (a) for canceling out the magnetic noise intensity. ad is stored. Here, d is the duty ratio of the output waveform that controls the brightness setting of the screen of the fluorescent display tube 4, and a is a proportional constant of the magnetic noise intensity with respect to the duty ratio d.

  In FIG. 4, since the intensity of magnetic noise can be expressed by y = −0.2d, y = 0.2d is used as the correction equation (a). FIG. 8 shows the result of obtaining the correction value (b) corresponding to the brightness setting from this correction formula.

  When the calculation processing unit 7 calculates a correction value corresponding to the current brightness setting from the correction formula (a), the calculation processing unit 7 outputs this to the control unit 6 as geomagnetic data. Thereby, the control unit 6 calculates the direction corrected according to the brightness setting of the screen of the fluorescent display tube 4, and generates the direction display data indicating the direction (step ST5). When creating the corrected azimuth display data, the control unit 6 sets the azimuth display update permission (step ST6), and updates the azimuth display on the screen of the fluorescent display tube 4 (step ST7).

  Subsequently, the control unit 6 shifts to a state where it is determined whether or not the brightness setting of the screen of the fluorescent display tube 4 has been changed (step ST8). If the brightness setting is not changed (step ST8; NO), the determination state is maintained. In addition, when the power supply of the vehicle-mounted display 1 is turned off, the control unit 6 saves the current brightness setting in the ROM 8 or the like.

  When the user changes the brightness setting using an input device (not shown in FIG. 2), the control unit 6 determines that there is a change in the brightness setting (step ST8; YES), and prohibits updating of the azimuth display. (Step ST9).

  Next, the calculation processing unit 7 calculates a correction value (b ′) corresponding to the changed brightness setting from the correction equation (a) that has already been read (step ST10). Thereafter, the calculation processing unit 7 outputs the correction value (b ′) to the control unit 6 as geomagnetic data. Thereby, the control part 6 calculates the azimuth | direction corrected according to the brightness setting of the screen of the fluorescent display tube 4, and produces the azimuth | direction display data which show this azimuth | direction (step ST11).

  When the control unit 6 creates the azimuth display data subjected to the correction according to the changed brightness setting, the control unit 6 sets the azimuth display update permission (step ST12), and updates the azimuth display on the screen of the fluorescent display tube 4. (Step ST13). Thereafter, the control unit 6 again shifts to a state in which it is determined whether or not the brightness setting of the screen of the fluorescent display tube 4 has been changed.

  As described above, according to the first embodiment, the correction formula (a) for calculating the correction value of the output fluctuation of the geomagnetic sensor 2 caused by the magnetism emitted from the fluorescent display tube 4 according to the brightness setting of the screen. Is used to correct the output fluctuation of the geomagnetic sensor 2 according to the brightness setting of the screen of the fluorescent display tube 4. In this way, the geomagnetic data affected by the magnetic noise from the fluorescent display tube 4 can be accurately corrected.

  In addition, according to the first embodiment, the in-vehicle display 1 uses the fluorescent display tube 4, the geomagnetic sensor 2, and the magnetism emitted from the fluorescent display tube 4 according to the brightness setting of the screen of the fluorescent display tube 4. The calculation processing unit 7 that functions as a correction device that corrects the output fluctuation of the caused geomagnetic sensor 2, and the direction is measured based on the output value of the geomagnetic sensor 2 corrected by the calculation processing unit 7 and displayed on the fluorescent display tube 4. And a control unit 6 that performs. With such a configuration, the influence of magnetic noise from the fluorescent display tube 4 can be corrected, so that an error in azimuth display can be prevented.

  Further, according to the first embodiment, when the brightness setting of the screen of the fluorescent display tube 4 is changed, the calculation of the correction value (b ′) by the correction formula (a) and the correction value (b ′) are performed. Updating of the azimuth display is prohibited for a certain time sufficient to complete the correction processing of the azimuth display data used. By doing in this way, it is possible to prevent misdirection display.

  In the first embodiment, as shown in FIG. 7, the case where an approximate correction formula using one linear function is used as the correction formula (a) for magnetic noise is shown. If a mathematical expression that accurately reproduces the magnetic noise intensity according to the brightness setting is possible, a correction expression may be set accordingly. For example, when the magnetic noise intensity is approximated by a combination of two or more linear functions or an n-th order function (n is an arbitrary natural number), a correction with higher accuracy can be performed by using an approximate correction formula that cancels this. An effect is obtained.

Embodiment 2. FIG.
In the second embodiment, correction in a transient state of changes in geomagnetic data due to magnetic noise will be described. For the sake of simplicity of explanation, details of the correction processing will be described by taking as an example a case where the hardware configuration is basically the same as that of the first embodiment (FIGS. 1 and 2). As a matter different from the first embodiment in the second embodiment, a correction formula for correcting the transiently changing geomagnetic data is stored in the ROM 8 or the external ROM 8a.

Next, the operation will be described.
FIG. 9 is a flowchart showing a flow of correction processing of geomagnetic data according to the first embodiment of the present invention. Here, the processing from step ST1 to step ST10 is the same as that in the first embodiment, and a description thereof will be omitted.

  When the calculation processing unit 7 calculates the correction value (b ′) corresponding to the changed brightness setting, the transient processing correction formula (a ′) is obtained from the ROM 8 or the external ROM 8a according to the correction value (b ′). (Second correction formula) is read (step ST11a). Hereinafter, as in the first embodiment, a case where magnetic noise occurs in a direction perpendicular to the screen of the fluorescent display tube 4, that is, in the true north (y-axis) direction will be described as an example.

  FIG. 10 is a diagram schematically showing a time-series change in the coordinate value in the y-axis direction of the geomagnetic data according to the brightness setting of the screen of the fluorescent display tube. Even when the brightness setting of the screen is changed, the geomagnetism does not change instantaneously due to the influence of magnetic noise according to the changed brightness setting, but via a state with a time constant (transient state) It is common to do.

  The example of FIG. 10 shows the case where the brightness setting is changed from 0% to 100% at a certain time T1. In this case, the geomagnetism changes to a change amount corresponding to the correction value (b ′) due to magnetic noise corresponding to the brightness setting with a duty ratio of 100%, but this change is a transient during the period of ΔT (= T2−T1). Go through the state.

  The transient change of the geomagnetic data due to the magnetic noise according to the brightness setting of the screen of the fluorescent display tube 4 can be specified in advance by experiments, and a correction formula (a ′) representing the transient state of the geomagnetic data due to the magnetic noise is previously set. Can be created.

  Therefore, in the second embodiment, the correction formula (a ′) representing the transient state is associated with the correction value (b ′) (final point of geomagnetism) according to the brightness setting of the screen of the fluorescent display tube 4. ) Is stored in the ROM 8 or the ROM 8a, and the correction formula (a ′) is read and the correction in the transient state is performed when the brightness setting after the change is within the range in which the geomagnetism changes transiently.

  Further, a plurality of correction expressions (a ′) approximating each transition stage in the transient state are stored in the ROM 8 or the ROM 8a, and the correction is performed based on the correction value (b ′) calculated by the correction expression (a). A correction formula (a ′) that approximates the transition stage with the value (b ′) as the final reaching point is selected and used for correction.

  Returning to the description of FIG. 9, when the calculation processing unit 7 reads the correction formula (a ′), the calculation processing unit 7 uses the brightness setting before and after the change and the correction formula (a ′) to reach the correction value (b ′). The correction value (b ″) of the geomagnetic data in the transient state is calculated (step ST12a). FIG. 11 is a diagram for explaining an example of a correction formula representing a transient state of geomagnetism. In the example of FIG. 11, a correction formula (a ′) that approximates a change in geomagnetic data with a linear function is shown.

  The calculation processing unit 7 calculates the correction value (b ″) as a point on the straight line according to the correction formula (a ′) at each time until the time T2, and outputs the correction value (b ″) to the control unit 6 as correction data. Thereby, the control part 6 calculates the direction by which correction | amendment according to the brightness setting of the screen of the fluorescent display tube 4 was made, and produces the direction display data which shows this direction (step ST13a).

  When the control unit 6 creates the azimuth display data that has been corrected according to the changed brightness setting, the control unit 6 sets the azimuth display update permission (step ST14a), and updates the azimuth display on the screen of the fluorescent display tube 4. (Step ST15a). In this way, the direction in the transient state of the geomagnetic data is sequentially displayed.

  When the control unit 6 updates the azimuth display, the calculation processing unit 7 calculates the correction value (b ″) calculated using the correction formula (a ′) using the correction formula (a) in step ST10. It is determined whether or not the correction value (b ′) corresponding to the current brightness setting matches (step ST16a). At this time, if it is determined that the two correction values match (step ST16a; YES), the control unit 6 shifts to a state in which whether or not the brightness setting of the screen of the fluorescent display tube 4 is changed is determined in step ST8. .

  On the other hand, if it is determined that the two correction values do not match (step ST16a; NO), the control unit 6 determines that the geomagnetic data is still in a transient state, and prohibits updating of the azimuth display (step ST17a). The process from step ST12a is repeated.

  As described above, according to the second embodiment, when the brightness setting of the screen of the fluorescent display tube 4 is changed, the calculation processing unit 7 outputs the output of the geomagnetic sensor 2 using the correction formula (a). While calculating the correction value, the output fluctuation in the transient state up to the calculated correction value is corrected using the correction formula (a ′). By doing so, as in the first embodiment, it is possible to accurately correct the fluctuation of the geomagnetic data of the geomagnetic sensor 2 caused by the magnetic noise, and further the output of the geomagnetic sensor 2 due to the magnetic noise. The output can be accurately corrected even in a transient state.

  In the second embodiment, as shown in FIG. 11, the case where an approximate correction equation using one linear function is used as the correction equation (a ′) representing the transient state has been described. If it is possible to formulate the transient state of the geomagnetic data according to the accuracy, it may be set. For example, the transient state may be approximated by a combination of two or more linear functions, or an n-order function (n is an arbitrary natural number), and correction is performed with higher accuracy than in the case of simple approximation by a linear function. An effect is obtained.

  DESCRIPTION OF SYMBOLS 1 In-vehicle display, 2 Geomagnetic sensor, 3 Display main-body part, 4 Fluorescent display tube (magnetic generator), 5 Microcomputer, 6 Control part (correction means, control means), 7 Calculation processing part (correction means), 8 ROM (memory | storage) Means), 8a External ROM (storage means).

Claims (3)

A first correction formula for calculating a correction value of the output fluctuation of the geomagnetic sensor caused by magnetism emitted from the magnetic generator according to the operation, and a second correction formula for calculating a correction value in a transient state of the output fluctuation; Storage means for storing
Using the first correction formula of the storage means to calculate the correction value of the output of the geomagnetic sensor according to the operation and correct the output fluctuation, and using the second correction formula of the storage means, A correction device for a geomagnetic sensor, comprising: correction means for correcting output fluctuations in a transient state up to the calculated correction value . The magnetic generator is a fluorescent display tube,
Operation, the correction device of the geomagnetic sensor of claim 1 Symbol mounting, characterized in that said a brightness setting of the screen of fluorescent display tubes. A fluorescent display tube;
A geomagnetic sensor,
A correction device of the geomagnetic sensor of claim 1 Symbol placement to correct the output variations of the geomagnetic sensor due to a magnetic emitted from the fluorescent display tube according to the brightness setting of the screen of the fluorescent display tube,
An azimuth display apparatus comprising: control means for measuring an azimuth based on the output value of the geomagnetic sensor corrected by the correction apparatus and displaying the azimuth on the fluorescent display tube.

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