Geometrical instruments – Indicator of direction of force traversing natural media – Magnetic field responsive
Reexamination Certificate
2002-08-26
2004-11-16
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Magnetic field responsive
C033SDIG001, C368S010000
Reexamination Certificate
active
06817106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic equipment, and more specifically, relates to an electronic equipment such as an electronic wrist watch having a built-in function of an electronic compass.
2. Description of the Prior Art
In recent years, electronic wrist watches have been made multifunctional through the advancement of digital techniques, semiconductor manufacturing techniques, and the like. For instance, there is known an electronic wrist watch having a built-in function of an electronic compass that detects terrestrial magnetism and displays a compass direction (north). This electronic wrist watch has a built-in magnetic sensor with which terrestrial magnetism is sensed.
In such an electronic wrist watch, in general, 12 o'clock direction is set as an X axis and 3 o'clock direction is set as a Y axis, and a magnetic sensor is arranged for each coordinate axis. A compass direction (north) is calculated using a detection value (voltage value) concerning a magnetic field (terrestrial magnetism) detected for each axis and the calculated compass direction is displayed.
Also, the display of this compass direction (north) is, for instance, performed for ten seconds in the case where a user selects an electronic compass function. There is a probability that the direction of the wrist watch placed on the user's arm is changed during this display operation (for ten seconds), so that measurement is repeated at predetermined intervals and display is performed.
As this magnetic sensor, there is known a so-called flip-type magneto-resistance sensor. This flip-type magneto-resistance sensor includes a bridge circuit constructed of four magneto-resistance elements. The sensor also includes a flip coil that is formed using an aluminum wiring layer at a position at which the flip coil overlaps each magneto-resistance element in a cross-sectional direction. The magneto-resistance element is an element whose resistance value is changed by a magnetic field, and the resistance value is changed inversely with a square by a magnetic field.
In such a flip-type magneto-resistance sensor, a magnetic substance constituting each magneto-resistance element is magnetized in a predetermined direction by pulse-shaped flip current to drive a flip coil. Following this, the bridge circuit is driven, thereby detecting a voltage value that is changed by the effect of terrestrial magnetism. The flip coil has a function of refreshing the magnetization of the magneto-resistance elements each time measurement is performed.
In general, there is used flip current that is several hundred to one ampere and has a pulse width of several [&mgr;sec] to several ten [&mgr;sec]. This pulse width corresponds to the aforementioned predetermined intervals during measurement. In the case where the compass direction (north) is displayed for ten seconds, for instance, terrestrial magnetism is measured at several [&mgr;sec] to several ten [&mgr;sec].
Also, the flip current has a characteristic that the reproducibility of a detection value concerning a magnetic field that is obtained each time flip driving is performed is degraded in accordance with the reduction of a pulse width. Respective samples have different threshold values concerning this pulse width. Therefore, in many cases, in consideration of variations due to mass production, there is used a construction where flip driving is performed while setting the pulse width at a fixed value of 10 [&mgr;sec].
It should be noted here that the aforementioned flip-type magneto-resistance sensor that detects changes of a magnetic field with reference to a single axis is disclosed in PCT/EP94/01789 (U.S. Pat. No. 5,521,501 B, JP 8-503778 A).
However, the magnetic sensor used in a conventional electronic equipment, such as an electronic wrist watch, exhibits different minimum pulse widths of flip current for respective samples. Therefore, if flip driving is performed by uniformly setting the pulse width at a fixed value of 10 [&mgr;sec], the pulse current becomes larger than electromagnetic energy that is required to magnetize the magnetic resistance elements and to reset the magnetization, which leads to a problem in that the pulse current is wasted and efficiency is reduced.
For instance, even in the case of a sample for which a stable magnetic field detection output is obtained even at 2 [&mgr;sec], driving is performed at the fixed value of 10 [&mgr;sec] at all times, so that there occurs a problem in that a pulse current of 8 [&mgr;sec] corresponding to the difference is wasted and efficiency is reduced. This imposes limitations on the reduction of flip driving power.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made to solve the problems described above, and the object of the present invention is to provide an electronic equipment having a built-in electronic compass that detects terrestrial magnetism using a magnetic sensor, which is drivable with efficiency, and displays a compass direction (north).
In order to achieve the above-mentioned object, according to the present invention, there is provided an electronic equipment comprising: a magnetic sensor that detects terrestrial magnetism; a compass direction calculation means for determining a compass direction by performing calculation on a detection value of the magnetic sensor; a compass direction display means for displaying the compass direction determined by the compass direction calculation means on a screen; and a reset means for resetting the magnetic sensor by having a magnetic field with a pulse waveform generated at predetermined intervals prior to detection of the terrestrial magnetism, characterized in that the electronic equipment comprises: a comparison means for comparing a detection value, which is detected by the magnetic sensor each time the reset means performs the resetting, with a detection value concerning the displayed compass direction; a reproducibility judgment means for judging that there exists reproducibility if a matching result is obtained as a result of the comparison, and judging that there exists no reproducibility if a non-matching result is obtained; and a pulse width setting means for setting a short pulse width for a magnetic field for resetting the magnetic sensor if there exists reproducibility.
With this construction, it becomes possible to change the pulse width of flip current in accordance with the electromagnetic energy that is required to magnetize and reset magneto-resistance elements. As a result, it becomes possible to perform flip driving in accordance with variations of a pulse width of flip current due to samples and to efficiently supply pulse current without causing waste. Accordingly, with the technique of the present invention, it becomes possible to provide an electronic equipment having a built-in electronic compass that detects terrestrial magnetism using a magnetic sensor, which is drivable with efficiency, and displays a compass direction (north).
Note that, it is preferable that the reproducibility judgment means stores a reproducibility existing flag if there exists reproducibility and stores a reproducibility non-existing flag if there exists no reproducibility. It is preferable that after a first detection of the terrestrial magnetism, the reproducibility judgment means temporarily sets the flag to the reproducibility non-existing flag.
Also, after a first detection of the terrestrial magnetism, the pulse width setting means may set a short pulse width during a second detection of the terrestrial magnetism. Further, an electronic equipment may comprise a flag conformation means that confirms the flag prior to the second and subsequent detections of the terrestrial magnetism and has the pulse width setting means set a long pulse width if the flag stored during a previous confirmation is the reproduciblity non-existing flag. In this case, it is preferable that the flag confir
Adams & Wilks
Fulton Christopher W.
Seiko Instruments Inc.
Smith R. Alexander
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