Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-05-03
2001-11-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S822000, C359S819000, C341S010000
Reexamination Certificate
active
06324023
ABSTRACT:
This application is U.S. National Phase Application of PCT International Application PCT/JP99/03186.
TECHNICAL FIELD
The present invention relates to a position detecting device for detecting the position of an object, and more specifically, relates to a position detecting device employing magnetoresistive (MR) elements which is suitable when high-resolution position detection is required, and relates to a lens barrel for a camera, video camera, or the like, incorporating such a position detecting device.
BACKGROUND ART
In general, a magnetoresistive (MR) element is an element which utilizes a phenomenon in which the application of magnetic flux to a thin film pattern of an iron-nickel alloy, a cobalt-nickel alloy, or the like changes its magnetoresistance. Position detecting devices incorporating this kind of magnetoresistive elements are widely used in conjunction with a magnetic recording medium (e.g., ferrite or plastic magnet) for enabling detection of the position of the magnetic recording medium. Specifically, a sinusoidal reproduction output can be obtained by utilizing the change in the magnetic flux due to the movement of the magnetic recording medium. By processing the output waveform, the relative or absolute position of the magnetic recording medium is obtained with a high accuracy. This kind of position detecting device is disclosed in Japanese Laid-open Publication No. 1-203922, for example, and a position detecting device which has a configuration as shown in
FIG. 12
is widely implemented in apparatuses for consumer or industrial use.
FIG. 13
is a perspective view showing the general structure of a position detecting device incorporating a magnetoresistive element, and
FIG. 14
is its front view. On the surface of a magnetic recording medium
201
is provided a magnetic pattern
202
, which in magnetized so as to have N poles and S poles with a predetermined period &lgr;. It has a structure such that a holder
204
, which is integrally formed with magnetoresistive elements, is placed so as to oppose the magnetic recording medium
201
with predetermined spacing therefrom.
The operation principle of magnetoresistive elements is now explained with reference to
FIGS. 15A through 15E
. The change in the resistance of a magnetoresistive element in response to magnetic flux has the characteristics an shown in
FIG. 15A
, such that the resistance changes in proportion to the magnitude of the magnetic flux regardless the direction of the magnetic flux, and reaches saturation at a certain value. On a sensor face
205
of a holder
204
, two magnetoresistive units R
1
and R
2
are disposed with an interval &lgr;/2, which is equal to half of the period &lgr; of the magnetic pattern
202
, or an electrical angle of 180° along the direction of movement of the magnetic recording medium
201
.
Now, a case is considered where the magnetic recording medium
201
moves, and magnetic flux B whose magnitude changes in sinusoidal waves as shown in
FIG. 15B
is applied to the magnetoresistive units R
1
and R
2
. If such magnetic flux B is applied to the magnetoresistive units R
1
and R
2
, the resistance values of the magnetoresistive units R
1
and R
2
vary with the period &lgr;, with a phase difference of &lgr;/2 as shown in FIG.
15
C.
Therefore, as shown in
FIG. 15D
, if these magnetorsistive units R
1
and R
2
are serially connected, and a voltage V in applied from a DC power supply
210
, an output E
1
can be obtained at a connection point
211
. As shown in
FIG. 15E
, the output E
1
is a sine wave output having the period &lgr;.
Now, as understood from
FIGS. 15A
,
15
B, and
15
E, the amplitude of the sine wave output E
1
increases or decreases corresponding to the amplitude of the magnetic flux B. This means that, if the spacing between the sensor face
205
and the magnetic recording medium
201
becomes wider, the amplitude of the magnetic flux B, which changes in accordance with the motion of the magnetic recording medium
201
, becomes smaller, so that the sine wave output E
1
also becomes smaller. In order to detect the position of the magnetic recording medium by processing the sine wave output E
1
, a high signal-to-noise ratio is required. Thus, it is necessary to increase the amplitude of the sine wave output E
1
. Therefore, it is necessary to decrease the distance between the sensor face
205
and the magnetic recording medium
201
so as to increase the amplitude of magnetic flux B.
At the same time, as seen from
FIG. 15A
, the resistance change of a magnetoresistive element saturates at a certain value. If the amplitude of the magnetic flux B is too large, the resistance of the magnetoresistive element reaches saturation. Therefore, the amplitude of sine wave output E
1
can only increase so much. On the contrary, the saturation of the resistance change amount gives rise to an expanse of areas in which the resistance remains unchanged despite changes in the magnetic flux and the output E
1
is distorted.
As is understood from the above, it is necessary to adjust the distance between the sensor face
205
and the magnetic recording medium
201
to a predetermined distance known as a reference gap amount in order to increase the amplitude of the sine wave output E
1
while preventing distortion of the sine wave output E
1
.
The foregoing is a description of the principle of magnetic flux change detection. Now, a method for determining the moving direction of magnetic recording medium
201
will be explained, employing, four magnetoresistive units R
1
, R
2
, R
3
, and R
4
shown in FIG.
16
. The magnetoresistive units R
3
and R
4
are disposed with an interval of &lgr;/2 along the moving direction of the magnetic recording medium
201
, in a manner similar to the magnetoresistive units R
1
and R
2
.
A pair of magnetoresistive units R
3
and R
4
are disposed with an interval of ¼&lgr;, i.e., an electrical angle of 90°, with regard to the pair of magnetoresistive units R
1
and R
2
, and electrically connected as shown in FIG.
17
. Then, if a voltage V is applied from a DC power supply
210
, a phase-A output Ea is obtained at an output terminal
212
, and a phase-B output Eb is obtained at an output terminal
213
. As shown in
FIG. 18
, the phase-A output Ea and the phase-B output Eb are shifted from each other by an electrical angle of 90° (¼&lgr;), so that their phases advance differently depending on whether the moving direction of magnetic recording medium
201
is positive or negative. Based on this, it is possible to determine the moving direction of the magnetic recording medium
201
.
On the other hand, the amount of resistance change of a magnetoresistive element is as small as 2%. In an actual position detecting device, it is commonplace to dispose a plurality of the same phase magnetoresistive elements with the distance &lgr; in order to increase the amount of resistance change. That is, as shown in
FIG. 19
, eight magnetoresistive units R
11
, R
12
, R
21
, R
22
, R
31
, R
32
, R
41
, and R
42
are used. Here, the magnetoresistive units R
11
and R
12
are disposed with the distance &lgr; along the moving direction of the magnetic recording medium
201
, so as to be equivalent to the magnetoresistive unit R
1
shown in FIG.
17
. The pair of magnetoresistive units R
11
and R
12
and the pair of magnetoresistive units R
21
and R
22
are disposed with an interval of &lgr;/2 so as to be equivalent to the magnetoresistive units R
1
from R
2
shown in FIG.
17
.
The four magnetoresistive elements, i.e., the magnetoresistive units R
11
, R
12
, R
21
, and R
22
and the magnetoresistive units R
31
, R
32
, R
41
, and R
42
are disposed with an interval of ¼&lgr;. The magnetoresistive elements disposed in such a pattern are equivalent to the electrical circuit of
FIG. 17
, and yet twice as much magnetoresistance change is obtained.
Among lens barrels used in cameras or video cameras and the like, a barrel is known in which the lens is moved by a linear motor when zooming or focusing. When moving the lens usin
Nagaoka Eiichi
Terasaka Takushi
Epps Georgia
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
Thompson Tim
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