Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2000-10-12
2003-06-03
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S862610
Reexamination Certificate
active
06571631
ABSTRACT:
TECHNICAL FIELD
This invention relates to a displacement sensor composed of a force sensor, an acceleration sensor or the like, which is capable of performing a precision measurement, and a mobile data collecting apparatus suited to be used for, among others, an on-vehicle navigation system utilizing the displacement sensor.
BACKGROUND ART
Displacement sensors of this type have heretofore been known. For example, Japanese Patent Publication (Unexamined) No. 8-248059 discloses a three-dimensional acceleration sensor comprising a weight part and detection parts arranged point-symmetrically at positions equidistantly away in a three-dimensional direction from the center of gravity of the weight part, a three-dimensional acceleration applied to the weight part being detected by the detectors.
The above-mentioned publication discloses sensors of the following types. The first one is of the type in which a piezoelectric element is utilized in a detection part and an acceleration applied in various directions by an adjustment torque screw for clamping or sandwiching a weight part with a constant pressure is detected as an analogous variation in voltage by the piezoelectric element (piezoelectric type acceleration sensor). The second one is of the type in which a magnetic sensor is utilized in a detection part and which includes an electromagnet with the magnetic sensor fixed thereto and a control unit module for it. An amount of displacement of the magnetic body is detected as the variations in magnetic field by the magnetic sensor. Then, the amount of displacement is pulse-width modulated so as to be fed back to the electromagnet and the pulse-width modulation is monitored to detect an acceleration (electromagnetic type acceleration sensor). The third one is of the type which includes a weight part having a magnet of magnetic characteristics, serving as an inertial body and in which a detection part includes magnets three-dimensionally opposedly arranged in an inner surface of a case and a magnetic coil module. With the weight part kept floated within the case under the effect of magnetic suspension from six directions caused by the magnets and the magnetic coil module, the variations in magnetic flux caused by positional change of the weight part are converted into an electric signal and detected as an acceleration (magnet type sensor).
However, the above-mentioned techniques have the following shortcomings.
In the case where a sensing part (weight part) of an acceleration sensor contacts a separate substance (detection part) as in the case with the piezoelectric type acceleration sensor, mechanical errors caused by frictional force thereof are liable to occur.
Even in the structure in which the weight part is balanced in a hollow interior as in the case with the electromagnetic type speed sensor, modulation errors and conversion errors during the pulse-width/electric power conversion are liable to occur because the controlling of the electric power supplied to the electromagnetic coil is performed by means of pulsewidth modulation. This makes it difficult to obtain a precision detection.
Moreover, in any one of the above-mentioned types, there is not only a need of analog processing, such as synchronous rectification and smoothing, amplification, integration and the like but also a need of A/D conversion, for detection of an acceleration. Consequently, it is difficult to obtain more than a certain degree of accuracy because of its non-linearity. Moreover, the circuitry becomes large and the cost is increased. In addition, operation tends to be unstable because it is susceptible to the fluctuations in temperature and power supply.
The present invention has been accomplished in view of the abovementioned shortcomings. It is, therefore, a technical problem to be solved by the present invention to provide a displacement sensor which is precise and inexpensive.
Mobile data collecting apparatuses of the above-mentioned type have heretofore been known, as well. A typical example is disclosed in Japanese Patent Publication (Unexamined) No. 8-43113, in which an absolute position is detected utilizing radio waves from a GPS (Global Positioning System). Another example is disclosed in Japanese Patent Publication (Unexamined) No. 8-297033, in which a position on the ground is computed utilizing a combination of various kinds of sensors (an acceleration sensor, an angular acceleration sensor and an inclination sensor).
However, the former has such shortcomings that it becomes unable to be used in a tunnel, under an elevated railroad and in a room because it uses radio waves coming from an artificial satellite. On the other hand, the latter has such shortcomings that big errors occur depending on accuracy of the sensors and the positions where they are attached, the number of component parts of the sensors and the circuits are increased and therefore, the cost is inevitably increased.
In view of the above situation, it is, therefore, another technical problem to be solved by the present invention to provide a mobile data collecting apparatus which can be used even in a place where radio waves coming from an artificial satellite do not reach, in which errors are lessened and which is inexpensive.
DISCLOSURE OF INVENTION
As mentioned above, the present invention has been accomplished in view of the shortcomings inherent in the prior art. It is, therefore, an object of the present invention to provide a displacement sensor which is precise and inexpensive and a mobile data collecting apparatus which can be used even in a place where radio waves coming from an artificial satellite do not reach, in which errors are lessened and which is inexpensive.
In a first embodiment of the present invention, a displacement sensor includes a moving member (
10
) composed of a magnetic material; a pair of stators (
11
,
12
) each composed of a magnetic material and arranged opposed to each other with respect to the moving member (
10
), the stators (
11
,
12
) including driving coils (
13
,
14
) and position detectors (
15
,
16
) corresponding to the driving coils (
13
,
14
), respectively; and a control unit (
30
) for driving, based on a detection output coming from the position detectors (
15
,
16
), the driving coils (
13
,
14
) with an electric power corresponding to intervals (d
1
, d
2
) between the moving member (
10
) and the stators (
11
,
12
) so that the moving member (
10
) is balanced at an intermediate position between the stators (
11
,
12
) and for computing a force (F) or acceleration (G) applied to the moving member (
10
) with a driving electric power of the driving coils (
13
,
14
).
In a second embodiment of the present invention, one pair or more of the stators (
11
,
12
) are disposed opposed to each other on each plane of the moving member (
10
) in triaxial directions X, Y, Z.
In a third embodiment of the present invention, a displacement sensor includes a spherical moving member (
10
) composed of a magnetic material; three pairs of stators (
11
,
12
) each composed of a magnetic material and arranged opposed to each other in triaxial directions X, Y, Z, with respect to the moving member (
10
), the stators (
11
,
12
) including driving coils (
13
,
14
) and position detectors (
15
,
16
) corresponding to the driving coils (
13
,
14
), respectively; and a control unit (
30
) for driving, based on a detection output coming from the position detectors (
15
,
16
), the driving coils (
13
,
14
) with an electric power corresponding to intervals (d
1
, d
2
) between the moving member (
10
) and-the stators (
11
,
12
) so that the moving member (
10
) is balanced at an intermediate position between the stators (
11
,
12
) and for computing a force (F) or acceleration (G) applied to the moving member (
10
) with a driving electric power of the driving coils (
13
,
14
).
In a fourth embodiment of the present invention, a shield .(
23
) composed of a non-magnetic body is interposed between and adjacent to the stators on the X-, Y- and Z-axis.
In a fifth embodiment of the present
Chapman John E.
FDK Corporation
Wenderoth , Lind & Ponack, L.L.P.
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