Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
2003-02-28
2004-12-14
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
C073S862626, C073S780000
Reexamination Certificate
active
06829953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to capacitive sensors, and more specifically relates to a sensor structure in which tilt, acceleration, etc., can be detected on the basis of a capacitance change between a fixed electrode and a movable electrode.
2. Description of the Related Art
FIG. 14
shows a known capacitive sensor which uses a capacitance change.
The sensor shown in
FIG. 14
includes a pair of plates
1000
and
1003
which face each other. Electrodes
1001
and
1002
are formed on the plate
1000
, which is fixed, and an electrode
1004
is formed on the plate
1003
, which is movable and has flexibility. The electrode
1004
serves as a movable electrode which rotates with respect to the fixed electrodes
1001
and
1002
. In addition, a weight
1005
is attached to the flexible plate
1003
, and when the sensor tilts or when an external force is applied to the sensor, the flexible plate
1003
is distorted due to the weight
1005
, so that the capacitances P between the fixed electrode
1001
and the movable electrode
1004
and between the fixed electrode
1002
and the movable electrode
1004
. Accordingly, the tilt, the external force, etc., is detected by determining the capacitance changes.
In the above described construction, the movable plate
1003
is initially deflected due to the weight of the weight
1005
. Thus, the gap between the movable plate
1003
and the fixed plate
1000
cannot be easily maintained.
In addition, signals based on the detected capacitances include not only the capacitance changes due to the distortion of the movable plate
1003
but also offset capacitances corresponding to the capacitance increase caused by the displacement of the movable electrode
1004
. The offset capacitances are large when the tilt angle
0
of the sensor is small since the moving direction of the movable plate
1003
is close to the direction of gravity, and are small when the sensor is in an approximately vertical position since the moving direction of the movable plate
1003
is close to the direction perpendicular to the direction of gravity.
Accordingly, when the sensor is tilted, a capacitance Pa of a capacitor A constructed by the movable electrode
1004
and the fixed electrode
1001
and a capacitance Pb of a capacitor B constructed by the movable electrode
1004
and the fixed electrode
1002
vary in accordance with the tilt angle &thgr; of the sensor, as shown in
FIG. 15
along curves having maximum values when the tilt angle &thgr; is about ±30°. Accordingly, when the tilt of the sensor is detected, the detection range is ±30°, which is extremely small. In addition, as shown in
FIG. 15
, the difference between Pa and Pb (Pa−Pb) varies along an ‘S’ shape having maximum and minimum values when the tilt angle &thgr; of the senor is ±&thgr;
0
(that is, ±F
0
in terms of the force applied to the weight
1005
). The tilt angle &thgr;
0
, at which Pa−Pb has the maximum and minimum values is generally about 60° (although this varies with the construction of the sensor), and even when the tilt of the sensor is detected on the basis of the difference between the capacitances, the detectable angle range is about ±60°, which is still small.
In addition, when the sensor is attached to an external device, there is a problem in that the sensor cannot be attached with sufficient freedom since the detection range of the tilt angle, etc., is small.
Furthermore, since the capacitances P vary in accordance with a force applied to the weight
1005
along curves having maximum values, when the tilt angle &thgr; is determined on the basis of a capacitance change, calculations to compensate for the capacitance change due to the vertical displacement of the movable electrode
1004
must be performed. Thus, complex calculations must be performed by using an expensive processing circuit, and the detection accuracy is degraded due to the compensation calculation.
SUMMARY OF THE INVENTION
In view of the above-described situation, an object of the present invention is to provide a capacitive sensor which can be attached with sufficient freedom and which can detect a force applied to a weight on the basis of a capacitance between a fixed electrode and a movable electrode-without compensating for the vertical displacement of a movable member.
In order to attain this object, a capacitive sensor according to the present invention includes a fixed board which is provided with a fixed electrode unit consisting of one or more electrodes; a movable member provided with a movable electrode unit consisting of one or more electrodes which faces the fixed electrode unit with a gap therebetween, the movable member being rotatable with respect to the fixed board; a weight provided on the movable member; and a retaining element which is disposed between the fixed board and the weight and retains the movable member in a rotatable manner. At least one of the movable electrode unit and the fixed electrode unit includes a plurality of electrodes, and the movement of the movable member is detected on the basis of capacitances between the one or more electrodes of the movable electrode unit and the one or more electrodes of the fixed electrode unit change in accordance with the movement of the movable member.
In the above-described construction, the movable member smoothly rotates (or seesaws) around a retaining point at which the retaining element retains the weight. Since the movable member is directly or indirectly retained by the retaining element, the movable member is not displaced due to the weight of the weight and a gap between the movable member and the fixed board is maintained constant at the retaining point irrespective of the tilt of the sensor. Therefore, the capacitance between the fixed electrode unit and the movable electrode unit changes linearly in one-to-one correspondence with the tilt angle of the sensor over the range from −90° to +90° at a maximum. In addition, even when the sensor is attached in an inclined manner, the tilt from the position at which the sensor is attached, an external force, etc., can be detected. Therefore, the sensor can be attached with sufficient freedom. In addition, since the capacitance change linearly in one-to-one correspondence with the tilt or the external force and do not have maximum values, the detection range can be increased. Furthermore, since the movable member is retained by the retaining element, the movable member is not displaced in the vertical direction. Accordingly, calculations to compensate for such a displacement can be omitted, so that the detection accuracy can be prevented from being degraded due to the compensation calculations.
The retaining element can be formed integrally with the fixed board. In such a case, the positional relationship between the retaining element and the fixed electrode unit can be set more accurately and the detection accuracy of the capacitance can be improved compared to the case in which the retaining element is formed separately. In addition, the number of components can be reduced, so that the costs can be reduced.
In this case, the movable member preferably have a concave portion for receiving an end portion of the retaining element at a position where the movable member is in contact with the retaining element. Accordingly, the retaining point at which the retaining element retains the movable member is fixed by the concave portion, so that the positional accuracy of the movable member and the fixed board can be improved. In addition, when the movable member and the fixed board are positioned such that they are parallel to each other while the sensor is in a horizontal position, that is, in a neutral state, offsets are not easily generated. Furthermore, since the movable member always rotates around the same retaining point, stable detection accuracy can be obtained.
The retaining element may also be formed integrally with the weight. In such a case, the positional relationship be
Hasegawa Kazuo
Hashimoto Daiichi
Ishiguro Katsuyuki
Ono Yasuichi
ALPS Electric Co. Ltd.
Bayer Weaver & Thomas LLP
Lefkowitz Edward
Martir Lilybett
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