U.S. patent application number 13/370646 was filed with the patent office on 2012-06-07 for position detection apparatus and medical-device-position detection system.
This patent application is currently assigned to Olympus Corporation. Invention is credited to Atsushi KIMURA, Ryoji SATO, Akio UCHIYAMA.
Application Number | 20120143047 13/370646 |
Document ID | / |
Family ID | 37771465 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120143047 |
Kind Code |
A1 |
KIMURA; Atsushi ; et
al. |
June 7, 2012 |
POSITION DETECTION APPARATUS AND MEDICAL-DEVICE-POSITION DETECTION
SYSTEM
Abstract
A position detection apparatus and a medical-device-position
detection system that have improved position detection accuracy are
provided by setting high amplification for the position detection
apparatus. The position detection apparatus includes a circuit that
has at least one embedded coil (10a) and that is provided inside an
object (10) to be detected; a first magnetic-field generating unit
(11) for generating a first magnetic field in the region where the
embedded coil (10a) is disposed; a magnetic-field detecting unit
(5, 12) for detecting an induced magnetic field generated at the
embedded coil (10a) by the first magnetic field; and a second
magnetic-field generating unit (23) for generating a second
magnetic field having a phase substantially opposite to the phase
of the first magnetic field.
Inventors: |
KIMURA; Atsushi; (Tokyo,
JP) ; UCHIYAMA; Akio; (Kanagawa, JP) ; SATO;
Ryoji; (Tokyo, JP) |
Assignee: |
Olympus Corporation
Tokyo
JP
|
Family ID: |
37771465 |
Appl. No.: |
13/370646 |
Filed: |
February 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11571232 |
Sep 30, 2008 |
8140145 |
|
|
PCT/JP2006/316082 |
Aug 16, 2006 |
|
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13370646 |
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Current U.S.
Class: |
600/424 |
Current CPC
Class: |
A61B 1/041 20130101;
G01V 3/105 20130101; A61B 1/00158 20130101; A61B 5/062
20130101 |
Class at
Publication: |
600/424 |
International
Class: |
A61B 5/05 20060101
A61B005/05 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2005 |
JP |
2005-242359 |
Claims
1. A medical-device-position detection system comprising: a medical
device including a circuit having at least one embedded coil, and a
magnet; a first magnetic-field generating unit for generating a
first magnetic field; a magnetic-field detecting unit for detecting
an induced magnetic field excited at the embedded coil by the first
magnetic field; and a second magnetic-field generating unit for
generating a second magnetic field having a phase substantially
opposite to the phase of the first magnetic field, wherein the
second magnetic-field generating unit is configured to generate a
third magnetic field for controlling the position and orientation
of the magnet included in the medical device.
2. The medical-device-position detection system according to claim
1, wherein the magnetic-field detecting unit and the second
magnetic-field generating unit are arranged on substantially the
same flat surface.
3. The medical-device-position detection system according to claim
1, wherein an object to be detected is a capsule medical
device.
4. The medical-device-position detection system according to claim
3, wherein the capsule medical device includes a container for
holding a medication to be administgered to a subject.
5. The medical-device-position detection system according to claim
1, wherein the second magnetic-field generating unit is provided
with a moving mechanism for moving a position of at least one of a
mutually-induced-magnetic-field generating coil for generating a
mutually induced magnetic field by the first magnetic field and a
second magnetic-field generating coil positioned in the vicinity of
the magnetic-field detecting unit.
6. The medical-device-position detection system according to claim
5, wherein the moving mechanism is configured to move the position
of the mutually-induced-magnetic-field generating coil so as to
minimize the intensity of a magnetic-field-intensity signal being
output from the magnetic-field detecting unit and being associated
with a combined magnetic field of the first magnetic field and the
second magnetic field.
7. The medical-device-position detection system according to claim
1, wherein an object to be detected is a tubular medical
device.
8. The medical-device-position detection system according to claim
7, wherein the tubular medical device is a catheter or an
endoscope.
9. The medical-device-position detection system according to claim
7, wherein the embedded coil is provided substantially at a tip of
the tubular medical device.
10. The medical-device-position detection system according to claim
7, wherein the embedded coil is provided at an intermediate section
of the tubular medical device.
11. The medical-device-position detection system according to claim
1, wherein the second magnetic-field generating unit is positioned
in the vicinity of the first magnetic-field generating unit and
includes a mutually-induced-magnetic-field generating coil for
generating a mutually induced magnetic field by the first magnetic
field and a second magnetic-field generating coil positioned in the
vicinity of the magnetic-field detecting unit, and the
mutually-induced-magnetic-field generating coil and the second
magnetic-field generating coil are electrically connected in
series.
12. The medical-device position detection system according to claim
1, wherein the second magnetic-field generating unit includes a
mutually-induced-magnetic-field generating coil for generating a
mutually induced magnetic field by the first magnetic field.
13. The medical-device-position detection system according to claim
11, wherein the mutually-induced-magnetic-field generating coil and
the first magnetic-field generating unit are arranged on
substantially the same flat surface.
14. A medical-device-position detection system comprising: a
medical device including a circuit having at least one embedded
coil, and a magnet; a first magnetic-field generating unit for
generating a first magnetic field; a magnetic-field detecting unit
for detecting an induced magnetic field excited at the embedded
coil by the first magnetic field; and a second magnetic-field
generating unit for generating a second magnetic field having a
phase substantially opposite to the phase of the first magnetic
field, wherein the position and orientation of the magnet included
in the medical device is controlled based on the second magnetic
field generated by the second magnetic-field generating unit.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation under 37 C.F.R.
.sctn.1.53(b) of prior application Ser. No. 11/571,232 filed Dec.
22, 2006, entitled POSITION DETECTION APPARATUS AND
MEDICAL-DEVICE-POSITION DETECTION SYSTEM, the entire contents of
which are incorporated by reference herein, and is a 35 U.S.C.
.sctn..sctn.371 national phase conversion of PCT/JP2006/316082
filed 16 Aug. 2006, which claims priority from Japanese patent
application 2005-242359 filed 24 Aug. 2005, both of which are
herein incorporated by reference. The PCT International Application
was published in the Japanese language.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a position detection
apparatus and a medial-apparatus-position detection system.
[0004] 2. Description of Related Art
[0005] Recently, there has been research and development of
swallowable capsule medical devices (objects to be detected), as
represented by capsule endoscopes and the like, that are swallowed
by a subject to enter the subject's body, where they traverse a
passage in the body cavity to capture images of a target site
inside the passage in the body cavity.
[0006] To guide such a capsule medical device to a predetermined
position in a passage in the body cavity, currently, the position
of the capsule medical device in the passage in the body cavity
must be detected and a solution to guide the capsule medical device
is required.
[0007] One known solution to guide the capsule medical device is to
control the position of the capsule medical device by installing a
magnet inside the capsule medical device and externally applying a
magnetic field.
[0008] One known method of detecting the position of the capsule
medical device is a magnetic position detection method. A known
magnetic position detection method is a technology of determining
the position of an object to be detected by externally applying a
magnetic field to the object to be detected that includes an
embedded coil and detecting the magnetic field generated by an
induced electromotive force with an external magnetic sensor (for
example, Japanese Unexamined Patent Application Publication No.
HEI-6-285044 and Tokunaga, Hashi, Yabukami, Kouno, Toyoda, Ozawa,
Okazaki, and Arai, "High-resolution position detection system using
LC resonant magnetic marker", Magnetics Society of Japan, 2005, 29,
p. 153-156.
BRIEF SUMMARY OF THE INVENTION
[0009] The above-mentioned Patent Document 1 discloses a technology
of externally positioning a substantially rectangular-solid-shaped
magnetic field source having three magnetic-field generating coils
whose axes intersect orthogonally and positioning three
magnetic-field detecting coils having magnetic-field receiving
coils whose axes also intersect orthogonally inside a medial
capsule. According to this technology, an induced current is
generated at the magnetic-field detecting coils by an alternating
magnetic field generated by the magnetic field source so as to
detect the positions of the magnetic-field detecting coils, i.e.,
the position of the medical capsule, based on the generated induced
current.
[0010] However, according to the above-described technology, the
intensity of the alternating magnetic field generated by the
magnetic field source and the intensity of the induced current
generated at the magnetic-field detecting coils are proportional.
Therefore, there is a problem in that, to improve the detection
efficiency, the intensity of the alternating magnetic field has to
be increased by the same extent.
[0011] In Non-Patent Document 1, a position detection system
including an excitation coil for generating an alternating magnetic
field, an LC resonance magnetic marker for generating an induced
magnetic field by receiving the alternating magnetic field, and a
detecting coil for detecting the induced magnetic field are
disclosed. According to this position detection system, since the
LC resonance magnetic marker resonates at a predetermined frequency
depending on additional capacitance and parasitic capacitance, by
setting the frequency of the alternating magnetic field to the
predetermined frequency, the intensity of the induced magnetic
field can be significantly increased compared to that of other
frequencies, and thus, the detection efficiency increases.
[0012] However, for the system according to Non-Patent Document 1,
the detecting coil captures the alternating magnetic field
generated by the excitation coil, in addition to the induced
magnetic field generated by the LC resonance magnetic marker.
[0013] It is known that, in a position detection process, the
induced magnetic field can be detected by subtracting an
alternating magnetic field measured when an induced magnetic field
is not present since the induced magnetic field to be detected is a
very small magnetic field compared to the above-mentioned
alternating magnetic field.
[0014] This operation is carried out, for example, after an analog
signal, such as the detected alternating magnetic field, is
converted into a digital signal by an analog-to-digital (A/D)
converter. The analog signal captured by the detection coil is
input to the A/D converter after an amplification process. However,
as described above, the analog signal output from the detection
coil includes more signals associated with the alternating magnetic
field than signals associated with the induced magnetic field.
[0015] For this reason, when the signals associated with the
induced magnetic field are amplified to a level sufficient for
position detection (when the gain of the amplifier is increased),
there is a possibility that the amplifier will be saturated. As a
result, there is a problem in that the signals associated with the
induced magnetic field cannot be amplified to a sufficient
level.
[0016] In general, the setting of the amplification of the
amplifier is set on the basis of the intensity of the alternating
magnetic field such that the amplifier does not become saturated.
Therefore, there is problem in that, with respect to the signals
associated with the induced magnetic field, the amplification is
kept low and the position detection accuracy of the LC resonance
magnetic marker, i.e., the position detection accuracy of the
position detection system, is sacrificed.
[0017] The present invention has been conceived in light of the
problems described above. Accordingly, it is an object of the
present invention to provide a position detection apparatus and a
medical-device-position detection system with improved position
detection accuracy by setting high amplification for the position
detection apparatus.
[0018] To achieve this object, the present invention provides the
following solutions.
[0019] A first aspect of the present invention provides a position
detection apparatus including a circuit provided inside an object
to be detected, the circuit including at least one embedded coil; a
first magnetic-field generating unit for generating a first
magnetic field; a magnetic-field detecting unit for detecting an
induced magnetic field generated at the embedded coil by the first
magnetic field; and a second magnetic-field generating unit for
generating a second magnetic field having a phase substantially
opposite to the phase of the first magnetic field.
[0020] According to the first aspect, the second magnetic field
having a phase substantially opposite to the phase of the first
magnetic field that is generated by the second magnetic-field
generating unit can cancel out the first magnetic field at the
position of the magnetic-field detecting unit. In other words, the
intensity of a combined magnetic field of the first magnetic field
and the second magnetic field that are detected by the
magnetic-field detecting unit can be minimized (for example, set to
zero) and the magnetic-field detecting unit can capture only the
induced magnetic field.
[0021] Therefore, for example, when the output from the
magnetic-field detecting unit is amplified, high amplification can
be set based on the output associated with the induced magnetic
field, and the accuracy of position detection of the object to be
detected can be increased.
[0022] By positioning the second magnetic-field generating unit in
the vicinity of the magnetic-field detecting unit, the second
magnetic field can be more easily canceled out at the position of
the magnetic-field detecting unit.
[0023] According to the present invention, it is desirable that the
second magnetic-field generating unit is position in the vicinity
of the first magnetic-field generating unit and includes a
mutually-induced-magnetic-field generating coil for generating a
mutually induced magnetic field by the first magnetic field and a
second magnetic-field generating coil positioned in the vicinity of
the magnetic-field detecting unit, and the
mutually-induced-magnetic-field generating coil and the second
magnetic-field generating coil are electrically connected in
series.
[0024] In this way, the mutually-induced-magnetic-field generating
coil that is positioned in the vicinity of the first magnetic-field
generating unit receives the first magnetic field generated at the
first magnetic-field generating unit and generates a mutually
induced magnetic field as a second magnetic field. The phase of the
mutually induced magnetic field is opposite to that of the first
magnetic field. At this time, since the
mutually-induced-magnetic-field generating coil is electrically
connected in series to the second magnetic-field generating coil
position in the vicinity of the magnetic-field detecting unit, a
second magnetic field whose phase is substantially opposite to that
of the first magnetic field is generated. As a result, the second
magnetic field whose phase is substantially opposite to that of the
first magnetic field can be generated by a simple configuration and
the intensity of the second magnetic field can be increased at the
position of the magnetic-field detecting unit. Therefore, the first
magnetic field can be more reliably canceled out at the position of
the magnetic-field detecting unit.
[0025] According to the present invention, it is desirable that the
second magnetic-field generating unit is provided with a moving
mechanism for moving the position of at least one of the
mutually-induced-magnetic-field generating coil and the second
magnetic-field generating coil.
[0026] By providing a moving mechanism that can move the position
of at least one of the mutually-induced-magnetic-field generating
coil and the second magnetic-field generating coil (hereinafter,
referred to as "mutually-induced-magnetic-field generating coil or
the like") and adjusting the position of the
mutually-induced-magnetic-field generating coil or the like, the
intensity of the second magnetic field at the position of the
magnetic-field detecting unit can be adjusted.
[0027] According to the above-described configuration, it is
desirable that the moving mechanism moves the position of the
mutually-induced-magnetic-field generating coil so as to minimize
the intensity of a magnetic-field-intensity signal associated with
a combined magnetic field of the first magnetic field and the
second magnetic field that are output from the magnetic-field
detecting unit.
[0028] In this way, since the position of the
mutually-induced-magnetic-field generating coil is adjusted by the
moving mechanism so as to minimize the intensity of the
magnetic-field-intensity signal associated with the combined
magnetic field, the intensity of the magnetic-field-intensity
signal associated with the combined magnetic field of the first and
second magnetic fields can be minimized at the position of the
magnetic-field detecting unit.
[0029] According to the above-described configuration, it is
desirable that the moving mechanism moves the position of the
second magnetic-field generating coil so as to minimize the
intensity of a magnetic-field-intensity signal being output from
the magnetic-field detecting unit and being associated with a
combined magnetic field of the first magnetic field and the second
magnetic field.
[0030] In this way, since the position of the second magnetic-field
generating coil is adjusted by the moving mechanism so as to
minimize the intensity of the magnetic-field-intensity signal
associated with the combined magnetic field, the intensity of the
magnetic-field-intensity signal associated with the combined
magnetic field of the first and second magnetic fields can be
minimized at the position of the magnetic-field detecting unit.
[0031] According to the present invention, it is desirable that the
second magnetic-field generating unit includes a phase adjusting
unit for generating a signal having a substantially reversed phase
from a signal for magnetic field generation, a
second-magnetic-field-generating-coil driving unit for amplifying
the signal, and a second-magnetic-field generating coil for
generating a second magnetic field from the amplified signal that
is positioned in the vicinity of the magnetic-field sensor.
[0032] In this way, since the phase adjusting unit for generating a
signal having a substantially reversed phase from a signal for
magnetic field generation is provided as a component, a second
magnetic field having a phase substantially opposite to that of the
first magnetic field can be more reliably generated, and since the
second-magnetic-field-generating-coil driving unit for amplifying
the signal is provided as a component, the second magnetic field
can be generated with a predetermined magnetic field intensity.
Therefore, a second magnetic field capable of canceling out the
first magnetic field can be generated more reliably.
[0033] According to the present invention, it is desirable that the
second magnetic-field generating unit includes a phase adjusting
unit for generating a signal having a substantially reversed phase
from a signal for magnetic field generation, a
second-magnetic-field-generating-coil driving unit for amplifying
the signal, and a second-magnetic-field generating coil that is
positioned in the vicinity of the magnetic-field sensor and that
generates a second magnetic field from the amplified signal, and it
is desirable that the second-magnetic-field-generating-coil driving
unit adjusts the intensity of the second magnetic field based on a
magnetic-field-intensity signal output from the magnetic-field
detecting unit so as to minimize the signal intensity.
[0034] In this way, since the intensity of the second magnetic
field is adjusted on the basis of the above-described
magnetic-field-intensity signal such that the
magnetic-field-intensity signal is minimized, the intensity of the
combined magnetic field of the first magnetic field and the second
magnetic field can be minimized at the magnetic-field detecting
unit.
[0035] According to the present invention, it is desirable that a
display unit for displaying a magnetic-field-intensity signal
output form the magnetic-field detecting unit.
[0036] In this way, the magnetic-field-intensity signal output from
the magnetic-field sensor can be confirmed sequentially on the
display unit.
[0037] A second aspect of the present invention provides a
medical-device-position detection system including a medical device
having a circuit having at least one embedded coil and a magnet; a
first magnetic-field generating unit for generating a first
magnetic field; a magnetic-field detecting unit for detecting an
induced magnetic field excited at the embedded coil by the first
magnetic field; and a second magnetic-field generating unit for
generating a second magnetic field having a phase substantially
opposite to the phase of the first magnetic field and a third
magnetic field for controlling the position and orientation of the
medical device by acting upon the magnet.
[0038] According to the second aspect of the present invention,
since the third magnetic field acts upon the magnet so as to guide
the medical device, the medical device can be guided to a
predetermined position while confirming the position of the medical
device.
[0039] Furthermore, since the phase of the second magnetic field is
substantially opposite to the phase of the first magnetic field,
the first magnetic field can be canceled out at the position of the
magnetic-field detecting unit. In other words, the intensity of the
combined magnetic field of the first magnetic field and the second
magnetic field that are captured by the magnetic-field detecting
unit can be minimized (for example, set to zero), and the
magnetic-field detecting unit can capture only the induced magnetic
field. Thus, the position detection accuracy can be improved.
[0040] In the position detection apparatus and the
medical-device-position detection system according to the present
invention, since the alternating magnetic field can be canceled out
at the position of the magnetic-field sensor by a reversed-phase
magnetic field whose phase is substantially opposite to the phase
of the alternating magnetic field that is generated at the
reversed-phase-magnetic-field generator, for example, amplification
can be set high on the basis of the output associated with the
induced magnetic field when amplifying the output from the
magnetic-field sensor. Thus, it is advantage in that the accuracy
of the position detection of the object to be detected can be
improved.
[0041] Since the alternating magnetic field can be more easily
canceled out at the position of the magnetic-field sensor by
positioning the reversed-phase-magnetic-field generator in the
vicinity of the magnetic-field sensor, the amplification of the
position detection apparatus can be set high. Thus, it is advantage
in that the position detection accuracy can be improved.
[0042] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0043] FIG. 1 is a schematic view illustrating the outline of a
position detection apparatus according to a first embodiment of the
present invention.
[0044] FIG. 2 is a circuit diagram showing the circuitry
constituted of a coupled coil and a reversed-phase magnetic field,
shown in FIG. 1.
[0045] FIG. 3 illustrates other positional relationships of the
coupled coil and a magnetic-field generating coil, and the
reversed-phase magnetic field and a magnetic-field sensor, which
are shown in FIG. 1.
[0046] FIG. 4 illustrates the intensity of the magnetic field
viewed from the side of a position measurement device shown in FIG.
1.
[0047] FIG. 5 is a schematic view illustrating the outline of a
position detection apparatus according to a second embodiment of
the present invention.
[0048] FIG. 6 is a schematic view illustrating the outline of a
position detection apparatus according to a third embodiment of the
present invention.
[0049] FIG. 7 is a schematic view illustrating the outline of a
position detection apparatus according to a fourth embodiment of
the present invention.
[0050] FIG. 8 is a schematic view illustrating the outline of a
position detection apparatus according to a fifth embodiment of the
present invention.
[0051] FIG. 9 is a block diagram showing the overall structure of a
guidance magnetic-field generating coil shown in FIG. 8.
[0052] FIG. 10 is a circuit diagram illustrating the connection
between a guidance-magnetic-field generating coil and
guidance-magnetic-field-generating-coil driving unit.
DETAILED DESCRIPTION OF THE INVENTION
(Position Detection Apparatus)
First Embodiment
[0053] A position detection apparatus according to a first
embodiment of the present invention will be described below with
reference to FIGS. 1 to 4.
[0054] FIG. 1 is a schematic view illustrating the outline of a
position detection apparatus according to the first embodiment.
[0055] As shown in FIG. 1, a position detection apparatus 1 is
mainly formed of a magnetic-field generating coil (first
magnetic-field generating unit) 11 that generates an alternating
magnetic field (first magnetic field); a magnetic-field sensor
(magnetic-field detecting unit) 12 that detects an induced magnetic
field generated by an embedded coil 10a installed on an object 10
to be detected; a driving unit 3 that is used for driving control
of the magnetic-field generating coil 11; a detecting unit
(magnetic-field detecting unit) 5 that processes a signal output
from the magnetic-field sensor 12; a reversed-phase-magnetic-field
generating coil (second magnetic-field generating unit, second
magnetic-field generating coil) 23 that generates a reversed-phase
magnetic field (second magnetic field); and a coupled coil (second
magnetic-field generating unit, mutually-induced-magnetic-field
generating coil) 22.
[0056] An example of the object 10 to be detected is a capsule
medical device that is put into the body of a subject to perform
medical procedures.
[0057] As shown in FIG. 1, in the object 10 to be detected, an
object closed circuit (not shown) including the embedded coil 10a
and a capacitor having a predetermined capacity (not shown) is
constructed, and an LC resonance circuit that brings about
resonance at a predetermined frequency is provided.
[0058] As described above, the LC resonant circuit can be used as
an object closed circuit, or if a predetermined resonance frequency
can be achieved with parasitic capacitance in the embedded coil
10a, the embedded coil 10a alone, with both ends open, can form the
object closed circuit.
[0059] The magnetic-field generating coil 11 is formed in a
substantially planar shape and is electrically connected to the
driving unit 3.
[0060] The driving unit 3 is mainly composed of a signal generating
unit 13 that outputs an alternating signal having a frequency of
the alternating magnetic field generated at the magnetic-field
generating coil 11 and a magnetic-field-generating-coil driving
unit 14 that drives the magnetic-field generating coil 11 by
amplifying the alternating signal input from the signal generating
unit 13.
[0061] The magnetic-field sensor 12 is constructed of a plurality
of detecting coils 12a disposed in a substantially planar shape.
Each of the detecting coils 12a is electrically connected to a
detecting unit 5. The magnetic-field sensor 12 is disposed opposite
to the magnetic-field generating coil 11, and the object 10 to be
detected is interposed between the magnetic-field sensor 12 and the
magnetic-field generating coil 11.
[0062] The detecting unit 5 is mainly composed of a filter 15 for
cutting unwanted frequency components contained in an output signal
(magnetic-field-intensity signal) from the detecting coils 12a; an
amplifier 16 for amplifying the output signal from which unwanted
components are cut; a DC converter 17 for converting the amplified
output signal from an AC signal to a DC signal; an A/D converter 18
for converting the DC-converted output signal from an analog signal
to a digital signal; and a CPU 19 for performing computational
processing based on the output signal converted into a digital
signal.
[0063] When a plurality of the magnetic-field sensor 12 is disposed
around the object 10 to be detected, a magnetic-field-sensor
switching unit 20 for selecting an output signal of a predetermined
detecting coil 12a among the output signals from all detecting
coils 12a is provided between the magnetic-field sensor 12 and the
filter 15. By providing the magnetic-field-sensor switching unit
20, only output signals of the detecting coils 12a that are
required for position detection can be selected to reduce the
computational load of the CPU 19. Examples of output signals
required for position detection are output signals having high
signal intensity and output signals from the detecting coils 12a at
positions close to the object 10 to be detected.
[0064] A memory 21 for saving an output signal acquired while the
object 10 to be detected is not present is connected to the CPU 19.
By arranging the memory 21, it is easier to subtract an output
signal acquired while the object 10 to be detected is not present
from an output signal acquired while the object 10 to be detected
is present. For this reason, only an output signal associated with
the induced magnetic field generated by the embedded coil 10a on
the object 10 to be detected can easily be detected.
[0065] An example of the DC converter 17 is an RMS converter.
However, the DC converter 17 is not limited and any known AC-DC
converter may be used.
[0066] FIG. 2 is a circuit diagram illustrating the circuitry
constituted of the coupled coil and a reversed-phase-magnetic-field
generating coil, as shown in FIG. 1.
[0067] The coupled coil 22 is constituted of a coil formed in a
substantially planar shape, and, as shown in FIGS. 1 and 2, is
electrically connected to the reversed-phase-magnetic-field
generating coil 23 to constitute a closed circuit. Furthermore, as
shown in FIG. 1, the coupled coil 22 is disposed in such a manner
as to be magnetically coupled with the magnetic-field generating
coil 11 by being positioned opposite to the magnetic-field
generating coil 11 and in the vicinity thereof. Moreover, the
coupled coil 22 is disposed at a position opposite to the object 10
to be detected with respect to the magnetic-field generating coil
11.
[0068] The reversed-phase-magnetic-field generating coil 23 is
constituted of a coil formed in a substantially planar shape, and
as shown in FIGS. 1 and 2, is electrically connected in series with
the coupled coil 22 to constitute a closed circuit. Furthermore, as
shown in FIG. 1, the reversed-phase-magnetic-field generating coil
23 is disposed in such a manner as to be electrically coupled with
the magnetic-field sensor 12 by being positioned opposite to the
magnetic-field sensor 12 and in the vicinity thereof. Moreover, the
reversed-phase-magnetic-field generating coil 23 is disposed at a
position opposite to the object 10 to be detected with respect to
the magnetic-field sensor 12, which is interposed between the
reversed-phase-magnetic-field generating coil 23 and the object 10
to be detected.
[0069] The positional relationship between the coupled coil 22 and
the magnetic-field generating coil 11 or the positional
relationship between the reversed-phase-magnetic-field generating
coil 23 and the magnetic-field sensor 12 can be switched.
Furthermore, if the coupled coil 22 has an air core and is shaped
so as to accommodate therein the magnetic-field generating coil 11,
then the coupled coil 22 and the magnetic-field generating coil 11
may be arranged on substantially the same flat surface, as shown in
FIG. 3. In addition, if the reversed-phase-magnetic-field
generating coil 23 has an air core and is shaped so as to
accommodate therein the magnetic-field sensor 12, then the
reversed-phase-magnetic-field generating coil 23 and the
magnetic-field sensor 12 may be arranged on substantially the same
flat surface.
[0070] The operation of the position detection apparatus 1 with the
above-described structure will now be described.
[0071] First, at the driving unit 3, as shown in FIG. 1, an AC
signal having a predetermined frequency is generated in the signal
generating unit 13, and the AC signal is output to the
magnetic-field-generating-coil driving unit 14. The
magnetic-field-generating-coil driving unit 14 amplifies the input
AC signal to a predetermined intensity. The amplified AC signal is
output to the magnetic-field generating coil 11. The magnetic-field
generating coil 11 forms an alternating magnetic field therearound
as a result of the AC signal being supplied.
[0072] When the magnetic flux of the alternating magnetic field
intersects the object 10 to be detected, a resonant current with a
predetermined frequency is induced in the object closed circuit
having the embedded coil 10a installed therein. When a resonant
current is induced in the object closed circuit, it causes the
embedded coil 10a to form therearound an induced magnetic field
having a predetermined frequency.
[0073] Since the magnetic fluxes of the above-described alternating
magnetic field and the induced magnetic field intersect the
detecting coils 12a of the magnetic-field sensor 12, the detecting
coils 12a capture a magnetic flux generated by adding the magnetic
fluxes of both the magnetic fields and generate an output signal
that is an induced current based on a change in the intersecting
magnetic fluxes. An output signal of each detecting coils 12a is
output to the detecting unit 5.
[0074] In the detecting unit 5, the output signal that has been
input is first input to the magnetic-field-sensor switching unit
20. The magnetic-field-sensor switching unit 20 passes only an
output signal used for position detection of the object 10 to be
detected therethrough and cuts out other output signals.
[0075] Examples of a method of selecting an output signal include
selecting output signals with high signal intensity, outputting
signals from the detecting coils 12a positioned near the object 10
to be detected, or the like.
[0076] Only an output signal used for position detection may be
selected by arranging the magnetic-field-sensor switching unit 20
between the magnetic-field sensor 12 and the filter 15, as
described above. Alternatively, by causing the
magnetic-field-sensor switching unit 20 to switch the connection
among a plurality of detecting coils 12a, the output signals from
all detecting coils 12a may be input to the detection section 5 in
a time-division manner. Furthermore, by connecting the line between
the filter 15 and the A/D converter 18 to a plurality of detecting
coils 12a, it is not necessary to use the magnetic-field-sensor
switching unit 20 or select an output signal. Thus, no particular
restrictions are applied.
[0077] The selected output signal is input to the filter 15, and
frequency components in the output signal that are not used for
position detection, for example, low-frequency components, are
removed. The output signal from which unwanted components are
removed is input to the amplifier 16 and is then amplified so as to
have an input level appropriate for the A/D converter 18 downstream
thereof
[0078] The amplified output signal is input to the DC converter 17,
and the output signal, which is an AC signal, is converted into a
DC signal. Thereafter, the output signal is input to the AID
converter 18, and the output signal, which is an analog signal, is
converted into a digital signal.
[0079] The output signal converted into a digital signal is input
to the CPU 19. On the other hand, the output signal acquired from
the memory 21 connected to the CPU 19 while the object 10 to be
detected is not present is input to the CPU 19.
[0080] In the CPU 19, an output signal associated with the induced
magnetic field is obtained by calculating the difference between
both the output signals that have been input, and computation for
identifying the position of the embedded coil 10a, namely the
position of the object 10 to be detected, is carried out based on
the obtained output signal associated with the induced magnetic
field. For the computation for identifying the position, a known
computation method can be used, and no particular restrictions are
applied.
[0081] The operation of the coupled coil 22 and the
reversed-phase-magnetic-field generating coil 23, which are the
main subject matters of the present invention, will now be
described.
[0082] Since the coupled coil 22 is positioned in a matter such as
to be magnetically coupled with the magnetic-field generating coil
11, the magnetic flux of the alternating magnetic field generated
by the magnetic-field generating coil 11 passes through the coupled
coil 22. When the intensity of the magnetic field of the
alternating magnetic field varies, an induced electromotive force
is generated in the coupled coil 22, i.e., an electromotive force
that forms a magnetic field having a direction in which variations
in the magnetic field intensity are cancelled out, namely, a
reversed-phase magnetic field with a phase opposite to that of the
above-described alternating magnetic field.
[0083] Since the coupled coil 22 and the
reversed-phase-magnetic-field generating coil 23 are electrically
connected in series to form a closed circuit, an induced current
based on the induced electromotive force generated at the coupled
coil 22 is also applied to the reversed-phase-magnetic-field
generating coil 23.
[0084] When the induced current is applied to the
reversed-phase-magnetic-field generating coil 23, the
reversed-phase magnetic field is generated around the
reversed-phase-magnetic-field generating coil.
[0085] The distributions of the magnetic field intensities of the
magnetic fields generated by the magnetic-field generating coil 11,
the coupled coil 22, and the reversed-phase-magnetic-field
generating coil 23 will now be described.
[0086] FIG. 4 illustrates the distributions of the magnetic fields
in FIG. 1 viewed from the side of the position detection apparatus
1. The intensity distribution of the alternating magnetic field
generated by the magnetic-field generating coil 11, as represented
by a dotted line A in FIG. 4, is such that the intensity is
maximized at a position L11 where the magnetic-field generating
coil 11 is disposed, and the intensity decreases away from this
position.
[0087] The intensity distribution of the reversed-phase magnetic
field generated by the coupled coil 22 and the
reversed-phase-magnetic-field generating coil 23, as represented by
a dashed dotted line B in FIG. 4, is such that the intensity is
maximized between a position L22 where the coupled coil 22 is
disposed and a position L23 where the reversed-phase-magnetic-field
generating coil 23 is disposed, and the intensity decreases away
from L22 and L23 (left of L22 and right of L23, in FIG. 4). As
shown in FIG. 4, the intensity of the reversed-phase magnetic field
is lower than the intensity of the alternating magnetic field and
the phase thereof is a substantially reversed phase of the
alternating magnetic field.
[0088] The intensity distribution of the combined magnetic field of
the above-described alternating magnetic field and revered-phase
magnetic field, as represented by a solid line C in FIG. 4, is such
that the intensity is maximized at the position L11 where the
magnetic-field generating coil 11 is disposed, and the intensity is
substantially zero at a position L12 where the magnetic-field
sensor 12 is disposed, which is a position closer to the coupled
coil 22 than the position L23 where the
reversed-phase-magnetic-field generating coil 23 is disposed. Since
the phase of the reversed-phase magnetic field is opposite to the
phase of the alternating magnetic field, these magnetic fields
cancel out each other.
[0089] Therefore, the phase of the combined magnetic field and the
phase of the alternating magnetic field are the same on the side
closer to the position L11, where the magnetic-field generating
coil 11 is disposed than the position L12, whereas the phase of the
combined magnetic field is opposite to the phase of the
reversed-phase magnetic field on the side closer to the position
L23, where the reversed-phase-magnetic-field generating coil 23 is
disposed.
[0090] The position L22, where the coupled coil 22 is disposed, to
the position L23, where the reversed-phase-magnetic-field
generating coil 23 is disposed, may be determined such that the
output of the magnetic-field sensor 12 is minimized or set to
substantially zero by measuring the combined magnetic field
intensity in advance or such that the output is minimized or set to
substantially zero by observing the output of the magnetic-field
sensor 12. The positions are not particularly limited.
[0091] According to the above-described structure, the
above-described alternating magnetic field can be canceled out at
the position of the magnetic-field sensor 12 by the above-described
reversed-phase magnetic field generated by the coupled coil 22 and
the reversed-phase-magnetic-field generating coil 23. In other
words, as shown in FIG. 4, since the intensity of the combined
magnetic field of the alternating magnetic field and the
reversed-phase magnetic field captured by the detecting coils 12a
of the magnetic-field sensor 12 can be minimized or set to
substantially zero, the detecting coils 12a can capture only the
above-described induced magnetic field.
[0092] Therefore, when the output signals from the detecting coils
12a are amplified at the amplifier 16, the level of amplification
can be set high based on the output signal associated with the
induced magnetic field, and the position detection accuracy of the
object 10 to be detected can be improved.
[0093] By positioning the reversed-phase-magnetic-field generating
coil 23 in the vicinity of the magnetic-field sensor 12, the
alternating current can be easily canceled out at the position of
the magnetic-field sensor 12.
[0094] By positioning the coupled coil 22 in the vicinity of the
magnetic-field generating coil 11 and magnetically coupling the
coupled coil 22 to the magnetic-field generating coil, an induced
electromotive force that forms a reversed-phase magnetic field
having a phase substantially opposite to the phase of the
alternating magnetic field can be generated at the coupled coil 22.
By using the reversed-phase-magnetic-field generating coil 23 that
is electrically connected to the coupled coil 22 in series, the
alternating magnetic field can be more reliably canceled out at the
magnetic-field sensor 12.
[0095] As described above, the reversed-phase-magnetic-field
generating coil 23 that is a special coil for generating a
reversed-phase magnetic field may be disposed. Alternatively, for
example, when a magnetic-field generating coil used for guiding the
object 10 to be detected is provided, the position and orientation
of the magnet installed in the object 10 to be detected is
controlled by the magnetic field (third magnetic field) generated
by the magnetic-field generating coil, and the position and
orientation of the object 10 to be detected is controlled, so long
as the magnetic-field generating coil used for orientation control
is connected as shown in FIG. 2, the magnetic-field generating coil
used for orientation control may also be used as a
reversed-phase-magnetic-field generating device.
[0096] For example, so long as an opposing coil is disposed in a
manner such as to satisfy Helmholtz conditions and a low-impedance
driving device is connected, the same functions as those according
to the first embodiment may be achieved.
[0097] As described above, the position detection apparatus 1 may
include only a closed circuit including at least the embedded coil
10a inside the object 10 to be detected or, depending on the usage,
may be used as an image-acquisition unit formed of a CCD and a CMOS
for imaging the body cavity of the patient or a capsule medical
device in which a container for holding medication to be received
by the patient is installed, and no particular restrictions are
applied.
[0098] The object 10 to be detected may be provided as a tubular
medical device, such as a catheter or an endoscope, and a closed
circuit including the embedded coil 10a may be installed at
substantially the tip thereof or at an intermediate section
thereof
Second Embodiment
[0099] A position detection apparatus according to a second
embodiment of the present invention will be described below with
reference to FIG. 5.
[0100] The basic configuration of the position detection apparatus
according to this embodiment is the same as that in the first
embodiment; however, the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof are different from those in the first embodiment. Thus, in
this embodiment, only the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof shall be described with reference to FIG. 5, and the
description of the structures of other components shall be
omitted.
[0101] FIG. 5 is a schematic view illustrating the outline of the
position detection apparatus according to this embodiment.
[0102] The same components as those in the first embodiment are
denoted with the same reference numerals, and thus will not be
described.
[0103] As shown in FIG. 5, a position detection apparatus 101 is
mainly formed of a magnetic-field generating coil 11 that generates
an alternating magnetic field; a magnetic-field sensor 12 that
detects an induced magnetic field generated by an embedded coil 10a
installed on an object 10 to be detected; a driving unit 3 that is
used for driving control of the magnetic-field generating coil 11;
a detecting unit (magnetic-field detecting unit) 105 that processes
a signal output from the magnetic-field sensor 12; a
reversed-phase-magnetic-field generating coil (second
magnetic-field generating unit, second magnetic-field generating
coil) 123 that generates a reversed-phase magnetic field; and a
coupled coil (second magnetic-field generating unit,
mutually-induced-magnetic-field generating coil) 22 that is
electrically connected to the reversed-phase-magnetic-field
generating coil 123.
[0104] The detecting unit 105 is mainly composed of a filter 15 for
cutting unwanted frequency components contained in an output signal
from the detecting coils 12a; an amplifier 16 for amplifying the
output signal from which unwanted components are cut; a DC
converter 17 for converting the amplified output signal from an AC
signal to a DC signal; an A/D converter 18 for converting the
DC-converted output signal from an analog signal to a digital
signal; and a CPU 19 for performing computational processing based
on the output signal converted into a digital signal.
[0105] When a plurality of the magnetic-field sensor 12 is disposed
around the object 10 to be detected, a magnetic-field-sensor
switching unit 20 for selecting an output signal of a predetermined
detecting coil 12a among the output signals from all detecting
coils 12a is provided.
[0106] A memory 21 for saving an output signal acquired while the
object 10 to be detected is not present and a display unit 124 for
displaying the magnetic field intensity captured by the
magnetic-field sensor 12 as a numerical value or a graph are
connected to the CPU 19. By providing the display unit 124,
magnetic-field-intensity signals output from the magnetic-field
sensor 12 can be confirmed sequentially.
[0107] The reversed-phase-magnetic-field generating coil 123 is
constituted of a coil formed in a substantially planar shape, and,
as shown in FIG. 5, is electrically connected to the coupled coil
22 to constitute a closed circuit. Furthermore, as shown in FIG. 5,
the reversed-phase-magnetic-field generating coil 123 is disposed
opposite to the magnetic-field sensor 12, and the magnetic-field
sensor 12 is interposed between the object 10 to be detected and
the reversed-phase-magnetic-field generating coil 123.
[0108] At the lower edge of the reversed-phase-magnetic-field
generating coil 123 a moving mechanism 125 for supporting the
reversed-phase-magnetic-field generating coil 123 in a manner such
that the reversed-phase-magnetic-field generating coil 123 is
movable towards or away from the magnetic-field sensor 12. The
moving mechanism 125 is mainly composed of a pair of moving rails
125a positioned substantially orthogonal to the surface of the
magnetic-field sensor 12 and supporting parts 125b disposed such
that they are slidable on the moving rails 125a. The supporting
parts 125b hold the lower edge of the reversed-phase-magnetic-field
generating coil 123 by grips.
[0109] As described above, as a moving mechanism, a description has
been given of an embodiment of the moving mechanism 125 constituted
of the moving rails 125a and the supporting parts 125b; however,
the moving mechanism 125 is not limited to being constituted of a
combination of the moving rails 125a and the supporting parts 125b,
and other known moving mechanisms may be used.
[0110] The operation of the position detection apparatus 101 with
the above-described structure will now be described.
[0111] The steps of generating an alternating magnetic field around
the object 10 to be detected, detecting an induced magnetic field
generated at the embedded coil 10a, and determining the position of
the object 10 to be detected by the CPU 19 are the same as those in
the first embodiment. Thus, descriptions thereof shall be
omitted.
[0112] An output signal associated with a combined magnetic field
input to the CPU 19 is output to the display unit 124. The display
unit 124 displays the intensity of the output signal that is input
and that is associated with the combined magnetic field as a
numerical value or a graph.
[0113] The position of the reversed-phase-magnetic-field generating
coil 123 is adjusted by the moving mechanism 125 based on the
intensity of the output signal associated with the combined
magnetic field that is displayed on the display unit 124 such that
the intensity is minimized or set to substantially zero. More
specifically, the reversed-phase-magnetic-field generating coil 123
is moved, together with the supporting parts 125b on the moving
rails 125a, towards or away from the magnetic-field sensor 12 while
maintaining the direction of the central axis.
[0114] According to the above-described structure, by providing the
moving mechanism 125 that can move the position of the
reversed-phase-magnetic-field generating coil 123 and by adjusting
the position of the reversed-phase-magnetic-field generating coil
123, the intensity of the combined magnetic field at the position
of the magnetic-field sensor 12 can be adjusted to a minimum value
or substantially zero.
[0115] Since the position of the reversed-phase-magnetic-field
generating coil 123 is changed based on the output signal
associated with the combined magnetic field displayed on the
display unit 124 such that the output signal is minimized or set to
substantially zero, the intensity of the combined magnetic field at
the position of the magnetic-field sensor 12 can be reliably set to
a minimum value or substantially zero.
[0116] As described above, the reversed-phase-magnetic-field
generating coil 123 may be provided with the moving mechanism 125,
and the reversed-phase-magnetic-field generating coil 123 may be
movable; the coupled coil 22 may be provided with the moving
mechanism 125, and the coupled coil 22 may be movable; or the
coupled coil 22 and the reversed-phase-magnetic-field generating
coil 123 both may be movable. Thus, no particular restrictions are
applied.
Third Embodiment
[0117] A position detection apparatus according to a third
embodiment of the present invention will be described below with
reference to FIG. 6.
[0118] The basic configuration of the position detection apparatus
according to this embodiment is the same as that in the second
embodiment; however, the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof are different from those in the second embodiment. Thus, in
this embodiment, only the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof shall be described with reference to FIG. 6, and the
description of the structures of other components shall be
omitted.
[0119] FIG. 6 is a schematic view illustrating the outline of the
position detection apparatus according to this embodiment.
[0120] The same components as those in the second embodiment are
denoted with the same reference numerals, and thus will not be
described.
[0121] As shown in FIG. 6, a position detection apparatus 201 is
mainly formed of a magnetic-field generating coil 11 that generates
an alternating magnetic field; a magnetic-field sensor 12 that
detects an induced magnetic field generated by an embedded coil 10a
installed on an object 10 to be detected; a driving unit 3 that is
used for driving control of the magnetic-field generating coil 11;
a detecting unit 105 that processes a signal output from the
magnetic-field sensor 12; and a reversed-phase-magnetic-field
generating coil (second magnetic-field generating unit, second
magnetic-field generating coil) 223 that generates a reversed-phase
magnetic field.
[0122] The reversed-phase-magnetic-field generating coil 223 is
constituted of a coil formed in a substantially planar shape, and
as shown in FIG. 6, is electrically connected with a control unit
(second magnetic-field generating unit) 225. Furthermore, as shown
in FIG. 6, the reversed-phase-magnetic-field generating coil 223 is
positioned opposite to the magnetic-field sensor 12 and is disposed
such that the magnetic-field sensor 12 is interposed between the
object 10 to be detected and the reversed-phase-magnetic-field
generating coil 223.
[0123] The control unit 225 is mainly formed of a phase adjusting
unit 226 for receiving an output from the signal generating unit 13
and a reversed-phase-magnetic-field-generating-coil driving unit
(second magnetic-field-generating-coil driving unit) 227 for
receiving an output from the phase adjusting unit 226.
[0124] The phase adjusting unit 226 is configured to generate a
reversed-phase signal having a substantially reversed phase based
on an AC signal input from a signal generating unit 13. The
reversed-phase-magnetic-field-generating-coil driving unit 227 is
configured to amplify the input reversed-phase signal to a
predetermined intensity, that is to carry out amplitude adjustment.
The amplified reversed-phase signal is output to the
reversed-phase-magnetic-field generating coil 223.
[0125] The operation of the position detection apparatus 201 with
the above-described structure will now be described.
[0126] The steps of generating an alternating magnetic field around
the object 10 to be detected, detecting an induced magnetic field
generated at the embedded coil 10a, and determining the position of
the object 10 to be detected by the CPU 19 are the same as those in
the first embodiment. Thus, descriptions thereof shall be
omitted.
[0127] An output signal associated with a combined magnetic field
input to the CPU 19 is output to the display unit 124. The display
unit 124 displays the intensity of the output signal that is input
and that is associated with the combined magnetic field as a
numerical value or a graph.
[0128] The amplification of the
reversed-phase-magnetic-field-generating-coil driving unit 227 is
adjusted based on the intensity of the output signal associated
with the combined magnetic field that is displayed on the display
unit 124 such that the intensity is minimized or set to
substantially zero. When the intensity of the reversed-phase signal
supplied to the reversed-phase-magnetic-field generating coil 223
changes, the intensity of the reversed-phase magnetic field
generated by the reversed-phase-magnetic-field generating coil 223
also changes. Therefore, a reversed-phase magnetic field having an
intensity that cancels out the alternating magnetic field can be
generated.
[0129] According to the configuration described above, since a
reversed-phase signal having a substantially reversed phase is
generated from the AC current used for generating the alternating
magnetic field at the phase adjusting unit 226, a magnetic field
having a phase substantially opposite to that of the alternating
magnetic field can be generated more reliably. Since the
reversed-phase signal is amplified by a predetermined amplification
at the reversed-phase-magnetic-field-generating-coil driving unit
227, a reversed-phase magnetic field having an intensity that can
cancel out the alternating magnetic field can be generated at a
predetermined position. Therefore, at the position of the
magnetic-field sensor 12, a reversed-phase magnetic field that can
cancel out the alternating magnetic field more reliably can be
generated.
[0130] By positioning the reversed-phase-magnetic-field generating
coil 223 in the vicinity of the magnetic-field sensor 12, the
alternating magnetic field can be more easily canceled out at the
position of the magnetic-field sensor 12.
Fourth Embodiment
[0131] A position detection apparatus according to a fourth
embodiment of the present invention will be described below with
reference to FIG. 7.
[0132] The basic configuration of the position detection apparatus
according to this embodiment is the same as that in the third
embodiment; however, the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof are different from those in the third embodiment. Thus, in
this embodiment, only the structures of the
reversed-phase-magnetic-field generating coil and the periphery
thereof shall be described with reference to FIG. 7, and the
description of the structures of other components shall be
omitted.
[0133] FIG. 7 is a schematic view illustrating the outline of the
position detection apparatus according to this embodiment.
[0134] The same components as those in the third embodiment are
denoted with the same reference numerals, and thus will not be
described.
[0135] As shown in FIG. 7, a position detection apparatus 301 is
mainly formed of a magnetic-field generating coil 11 that generates
an alternating magnetic field; a magnetic-field sensor 12 that
detects an induced magnetic field generated by an embedded coil 10a
installed on an object 10 to be detected; a driving unit 3 that is
used for driving control of the magnetic-field generating coil 11;
a detecting unit (magnetic-field detecting unit) 305 that processes
a signal output from the magnetic-field sensor 12; and a
reversed-phase-magnetic-field generating coil (second
magnetic-field generating unit, second magnetic-field generating
coil) 323 that generates a reversed-phase magnetic field.
[0136] The detecting unit 305 is mainly composed of a filter 15 for
cutting unwanted frequency components contained in an output signal
from the detecting coils 12a; an amplifier 16 for amplifying the
output signal from which unwanted components are cut; a DC
converter 17 for converting the amplified output signal from an AC
signal to a DC signal; an A/D converter 18 for converting the
DC-converted output signal from an analog signal to a digital
signal; and a CPU 319 for performing computational processing based
on the output signal converted into a digital signal. The CPU 319
is configured to output control signals to a phase adjusting unit
and a reversed-phase-magnetic-field-generating-coil driving unit,
described below.
[0137] The reversed-phase-magnetic-field generating coil 323 is
constituted of a coil formed in a substantially planar shape, and
as shown in FIG. 7, is electrically connected with a control unit
(second magnetic-field generating unit) 325. Furthermore, as shown
in FIG. 7, the reversed-phase-magnetic-field generating coil 323 is
positioned opposite to the magnetic-field sensor 12 and is disposed
such that the magnetic-field sensor 12 is interposed between the
object 10 to be detected and the reversed-phase-magnetic-field
generating coil 223.
[0138] The control unit 325 is mainly formed of a phase adjusting
unit 326 for receiving an output from the signal generating unit 13
and a reversed-phase-magnetic-field-generating-coil driving unit
(second magnetic-field-generating-coil driving unit) 327 for
receiving an output from the phase adjusting unit 326.
[0139] The phase adjusting unit 326 is configured to generate a
reversed-phase signal having a phase misaligned from a phase of an
AC signal based on the AC signal input from a signal generating
unit 13 and the control signal input from the CPU 319. The
reversed-phase-magnetic-field-generating-coil driving unit 327 is
configured to amplify the input reversed-phase signal to a
predetermined intensity, that is to carry out amplitude adjustment,
based on the control signal input from the CPU 319. The amplified
reversed-phase signal is output to the
reversed-phase-magnetic-field generating coil 323.
[0140] The operation of the position detection apparatus 301 with
the above-described structure will now be described.
[0141] In this embodiment, first, the CPU 319 outputs a control
signal for setting the phase of the reversed-phase signal to be
generated to be misaligned by substantially 180.degree. to the
phase adjusting unit 326. In addition the CPU 319 outputs a control
signal for changing the amplitude of the reversed-phase signal to
the reversed-phase-magnetic-field-generating-coil driving unit 327
every time measurement is carried out. In other words, while
changing the intensity of the reversed-phase magnetic field, output
signals associated with the combined magnetic field of the
alternating magnetic field and the mutual magnetic field are
obtained and stored in a memory 21.
[0142] The CPU 319 selects the amplification corresponding to the
smallest signal intensity from the series of output signals
obtained by changing the amplification and outputs a control signal
for amplifying the reversed-phase signal with the selected
amplification to the reversed-phase-magnetic-field-generating-coil
driving unit 327. In addition, the CPU 319 outputs a control signal
for changing the misalignment of the phase of the reversed-phase
signal little by little from substantially 180.degree. every time
measurement is carried out. In other words, output signals
associated with the combined magnetic field are obtained while
changing the phase of the reversed-phase magnetic field and are
stored in the memory 21.
[0143] Then, the CPU 319 selects the phase of an output signal
having the weakest signal intensity among the output signals stored
in the memory 21.
[0144] Subsequently, the position detection apparatus 301 amplifies
the reversed-phase signal having a phase determined according to
the procedure described above by the amplitude described above, and
uses a reversed-phase magnetic field generated by this amplified
reversed-phase signal.
[0145] The steps of generating an alternating magnetic field around
the object 10 to be detected, detecting an induced magnetic field
generated at the embedded coil 10a, and inputting the output signal
associated with the combined magnetic field to the CPU 319 are the
same as those in the first embodiment. Thus, descriptions thereof
shall be omitted.
[0146] According to the structure described above, the CPU 319 can
determine settings for the phase adjusting unit 326 and the
reversed-phase-magnetic-field-generating-coil driving unit 327 that
set the intensity of the combined magnetic field captured by the
magnetic-field sensor 12 to a minimum value or substantially zero.
Therefore, compared to determining these settings manually, the
settings can be determined in a less amount of time.
Fifth Embodiment
[0147] A fourth embodiment of the present invention will be
described below with reference to FIGS. 8 to 10.
[0148] The basic configuration of a medical magnetic inductance and
position detection system according to this embodiment is the same
as that in the first embodiment; however, the structures of the
guidance-magnetic-field generating coil and the periphery thereof
are different from those in the first embodiment. Thus, in this
embodiment, only the structures of the guidance-magnetic-field
generating coil and the periphery thereof shall be described with
reference to FIGS. 8 to 10, and the description of the structures
of other components shall be omitted.
[0149] FIG. 8 is a schematic view illustrating the outline of the
position detection apparatus according to this embodiment.
[0150] The same components as those in the first embodiment are
denoted with the same reference numerals, and thus will not be
described.
[0151] As shown in FIG. 8, a position detection apparatus 401 is
mainly formed of a magnetic-field generating coil 11 that generates
an alternating magnetic field; a magnetic-field sensor 12 that
detects an induced magnetic field generated by an embedded coil 10a
installed on an object 10 to be detected; and
guidance-magnetic-field generating coils 413A, 413B, 414A, 414B,
415A, and 415B that generates an induced magnetic field for guiding
the object 10 to be detected to a predetermined position in the
body cavity.
[0152] A driving unit 403 for driving control of the magnetic-field
generating coil 11 is provided on the magnetic-field generating
coil 11, and a detecting unit 405 for processing a signal output
from the magnetic-field sensor 12 is provided on the magnetic-field
sensor 12.
[0153] The driving unit 403 is mainly composed of a signal
generating unit 423 that outputs an alternating signal having a
frequency of the alternating magnetic field generated at the
magnetic-field generating coil 11 and a
magnetic-field-generating-coil driving unit 424 that drives the
magnetic-field generating coil 11 by amplifying the alternating
signal input from the signal generating unit 423.
[0154] The detecting unit 405 is mainly composed of a filter 425
that cuts unwanted frequency components contained in an output
signal from the detecting coils 12a; an amplifier 426 that
amplifies the output signal from which unwanted components are cut;
a DC converter 427 that converts the amplified output signal from
an AC signal to a DC signal; an A/D converter 428 for converting
the DC-converted output signal from an analog signal to a digital
signal; a CPU 429 that performs computational processing based on
the output signal converted into a digital signal; and a
magnetic-field-sensor switching unit 430 that selects a
predetermined output signal of the magnetic-field sensor 12 among
all output signals from the magnetic-field sensor 12.
[0155] A memory 431 for saving an output signal acquired while the
object 10 to be detected is not present is connected to the CPU
429. By arranging the memory 431, it is easier to subtract an
output signal acquired while the object 10 to be detected is not
present from an output signal acquired while the object 10 to be
detected is present. For this reason, only an output signal
associated with the induced magnetic field generated by the
embedded coil 10a can easily be detected.
[0156] An example of the DC converter 427 is an RMS converter.
However, the DC converter 427 is not limited and any known AC-DC
converter may be used.
[0157] The guidance-magnetic-field generating coils 413A and 413B,
the guidance-magnetic-field generating coils 414A and 414B, and the
guidance-magnetic-field generating coils 415A and 415B are each
disposed opposite to each other in a manner such as to satisfy
Helmholtz conditions. Therefore, spatial intensity gradients are
not generated in the magnetic fields generated by the
guidance-magnetic-field generating coils 413A and 413B, the
guidance-magnetic-field generating coils 414A and 414B, and the
guidance-magnetic-field generating coils 415A and 415B, and uniform
magnetic fields are generated within the induction range.
[0158] The central axes of the guidance-magnetic-field generating
coils 413A and 413B, the guidance-magnetic-field generating coils
414A and 414B, and the guidance-magnetic-field generating coils
415A and 415B are each disposed so as to orthogonally intersect
each other and are disposed in a manner such as to form a cubic
spaces inside the coils. The cubic space is the operation space of
the object 10 to be detected, as shown in FIG. 8.
[0159] FIG. 9 is a block diagram illustrating the outline structure
of the guidance-magnetic-field generating coils of FIG. 8. FIG. 10
is a circuit diagram illustrating the connection of the
guidance-magnetic-field generating coils, shown in FIG. 9, and
magnetic-field-generating-coil driving units.
[0160] For the pairs of the guidance-magnetic-field generating
coils 413A and 413B, the guidance-magnetic-field generating coils
414A and 414B, and the guidance-magnetic-field generating coils
415A and 415B, the coils in each pair are electrically connected to
each other.
[0161] As shown in FIGS. 9 and 10,
guidance-magnetic-field-generating-coil driving units 413C, 414C,
and 415C are electrically connected such that outputs thereof are
input to the pairs of the guidance-magnetic-field generating coils
413A and 413B, the guidance-magnetic-field generating coils 414A
and 414B, and the guidance-magnetic-field generating coils 415A and
415B, respectively. The guidance-magnetic-field-generating-coil
driving units 413C, 414C, and 415C are electrically connected such
that signals from signal generating units 413D, 414D, and 415D are
input thereto, respectively. The signal generating units 413D,
414D, and 415D are electrically connected such that control signals
from a guidance control unit 416 is input thereto. The guidance
control unit 416 is electrically connected such that a signal from
an input device 417 that receives an instruction for the guidance
direction of the object 10 to be detected from the outside is input
thereto.
[0162] The operation of position detection of the medical magnetic
inductance and a position detection system 401 having the structure
described above will now be described. First, the operation of
position detection of the object 10 to be detected by the medical
magnetic inductance and a position detection system 401 will be
described.
[0163] First, at the driving unit 403, as shown in FIG. 11, an AC
signal having a predetermined frequency is generated in the signal
generating unit 423, and the AC signal is output to the
magnetic-field-generating-coil driving unit 424. The
magnetic-field-generating-coil driving unit 424 amplifies the input
AC signal to a predetermined intensity.
[0164] The amplified AC signal is output to the magnetic-field
generating coil 11. The magnetic-field generating coil 11 forms an
alternating magnetic field therearound as a result of the AC signal
being supplied.
[0165] When the magnetic flux of the alternating magnetic field
intersects the object 10 to be detected, a resonant current with a
predetermined frequency is induced in the object closed circuit
having the embedded coil 10a installed therein. When a resonant
current is induced in the object closed circuit, it causes the
embedded coil 10a to form therearound an induced magnetic field
having a predetermined frequency.
[0166] Since the magnetic fluxes of the above-described alternating
magnetic field and the induced magnetic field intersect the
magnetic-field sensor 12, the magnetic-field sensor 12 capture a
magnetic flux generated by adding the magnetic fluxes of both the
magnetic fields and generate an output signal that is an induced
current based on a change in the intersecting magnetic fluxes. An
output signal of the magnetic-field sensor 12 is output to the
detecting unit 405.
[0167] In the detecting unit 405, the output signal that has been
input is first input to the magnetic-field-sensor switching unit
430. The magnetic-field-sensor switching unit 430 passes only an
output signal used for position detection of the object 10 to be
detected therethrough and cuts out other output signals.
[0168] Examples of a method for selecting an output signal include
selecting output signals with high signal intensity, output signals
from the magnetic-field sensor 12 positioned near the object 10 to
be detected, or the like.
[0169] Only an output signal used for position detection may be
selected by arranging the magnetic-field-sensor switching unit 430
between the magnetic-field sensor 12 and the filter 425, as
described above. Alternatively, by causing the
magnetic-field-sensor switching unit 430 to switch the connection
among a plurality of magnetic-field sensors 12, the output signals
from all magnetic-field sensors 12 may be input to the detection
section 405 in a time-division manner. Furthermore, by connecting
the line between the filter 425 and the A/D converter 428 to a
plurality of magnetic-field sensors 12, it is not necessary to use
the magnetic-field-sensor switching unit 430 or select an output
signal. Thus, no particular restrictions are applied.
[0170] The selected output signal is input to the filter 425, and
frequency components in the output signal that are not used for
position detection, for example, low-frequency components, are
removed. The output signal from which unwanted components are
removed is input to the amplifier 426 and is then amplified so as
to have an input level appropriate for the A/D converter 428
downstream thereof
[0171] The amplified output signal is input to the DC converter
427, and the output signal, which is an AC signal, is converted
into a DC signal. Thereafter, the output signal is input to the AID
converter 428, and the output signal, which is an analog signal, is
converted into a digital signal.
[0172] The output signal converted into a digital signal is input
to the CPU 429. On the other hand, the output signal acquired from
the memory 431 connected to the CPU 429 while the object 10 to be
detected is not present is input to the CPU 429.
[0173] In the CPU 429, an output signal associated with the induced
magnetic field is obtained by calculating the difference between
both the output signals that have been input, and computation for
identifying the position of the embedded coil 10a, namely the
position of the object 10 to be detected, is carried out based on
the obtained output signal associated with the induced magnetic
field. For the computation for identifying the position, a known
computation method can be used, and no particular restrictions are
applied.
[0174] The operation of guiding the capsule medical device will now
be described.
[0175] First, a movement that is to be applied to the object 10 to
be detected for remote operation of the object 10 to be detected is
input to an input device 417. The input device 417 outputs a signal
to the guidance control unit 416 based on the input information.
Based on the input signal, the guidance control unit 416 generates
a control signal for generating a magnetic field for moving the
object 10 to be detected, and outputs it to signal generating units
413D, 414D, and 415D.
[0176] In the signal generating units 413D, 414D, and 415D, signals
output to the guidance-magnetic-field-generating-coil driving units
413C, 414C, and 415C are generated based on the input control
signal. The guidance-magnetic-field-generating-coil driving units
413C, 414C, and 415C amplify the current of the input signals and
cause the current to flow in the guidance-magnetic-field generating
coils 413A and 413B, the guidance-magnetic-field generating coils
414A and 414B, and the guidance-magnetic-field generating coils
415A and 415B, respectively.
[0177] As described above, it is possible to generate an induced
magnetic field in an area near the object 10 to be detected by
causing electric current to flow in the guidance-magnetic-field
generating coils 413A and 413B, the guidance-magnetic-field
generating coils 414A and 414B, and the guidance-magnetic-field
generating coils 415A and 415B. With this generated magnetic field,
the magnet in the object 10 to be detected can be moved, and
accordingly, the object 10 to be detected can be moved by moving
the magnet.
[0178] The operation when a mutually induced magnetic field is
generated by the guidance-magnetic-field generating coils 413A and
413B, the guidance-magnetic-field generating coils 414A and 414B,
and the guidance-magnetic-field generating coils 415A and 415B,
which is the main subject matter of the present invention, will now
be described.
[0179] The guidance-magnetic-field generating coil 413A and the
guidance-magnetic-field generating coil 413B, the
guidance-magnetic-field generating coil 414A and the
guidance-magnetic-field generating coil 414B, and the
guidance-magnetic-field generating coil 415A and the
guidance-magnetic-field generating coil 415B are electrically
connected in series. Therefore, when the magnetic flux of the
alternating magnetic field having varying magnetic field intensity
intersects one of the guidance-magnetic-field generating coils 413A
and 413B, one of the guidance-magnetic-field generating coils 414A
and 414B, and one of the guidance-magnetic-field generating coils
415A and 415B, an induced electromotive force is generated in the
coils through which the magnetic flux passes, i.e., an
electromotive force that forms a magnetic field having a direction
in which variations in the magnetic field intensity are cancelled
out, namely, a reversed-phase magnetic field with a phase opposite
to that of the above-described alternating magnetic field.
[0180] Since the guidance-magnetic-field generating coils 413A and
413B, the guidance-magnetic-field generating coils 414A and 414B,
and the guidance-magnetic-field generating coils 415A and 415B are
electrically connected in series to form closed circuits, an
induced current based on the induced electromotive force generated
at one of the pairs of coils is applied to the other coils of the
guidance-magnetic-field generating coils 413A and 413B, the
guidance-magnetic-field generating coils 414A and 414B, and the
guidance-magnetic-field generating coils 415A and 415B.
[0181] When the induced current is applied to the other coils, the
reversed-phase magnetic field is generated around the other
coils.
[0182] Since the guidance-magnetic-field generating coils 413A,
413B, 414A, 414B, 415A, and 415B are normally set to have a low
output impedance, the above-mentioned current based on induced
electromotive force is applied and a magnetic field having a phase
substantially opposite to the phase of the position-detection
magnetic field can be generated. Since the guidance-magnetic-field
generating coils 413A, 413B, 414A, 414B, 415A, and 415B are
connected in series to the two opposing guidance-magnetic-field
generating coils 413A and 413B, there is an effect of canceling out
even in the vicinity of the magnetic-field sensor 12, in the same
way as in the first embodiment. For example, as shown in FIG. 8,
the guidance-magnetic-field generating coil 413A functions as the
coupled coil according to the first embodiment, and a magnetic
field having a phase that is opposite to the position-detection
magnetic field is generated also from the guidance-magnetic-field
generating coil 413B connected in series with the
guidance-magnetic-field generating coil 413A. In other words,
without particularly providing a coupled coil and a
reversed-phase-magnetic-field generating coil, the
position-detection magnetic field generated in the vicinity of the
magnetic-field sensor 12 can be canceled out by adjusting the
positions of the coils.
[0183] The pair of position detecting coils may be combined with
the guidance-magnetic-field generating coil pairs B and C.
[0184] Three pairs of position detecting coils, which is the same
number of guidance-magnetic-field generating coils, may be
positions so as to cancel out the position-detection magnetic field
of the magnetic-field sensor unit.
[0185] According to the above-described structure, the
position-detection magnetic-field generating coil 11 generates a
position-detection magnetic field for inducing an induced magnetic
field in the embedded coil 10a of the object 10 to be detected. The
induced magnetic field generated by the embedded coil 10a is
detected by the magnetic-field sensor 12 and is used to detect the
position or orientation of the object 10 to be detected having the
embedded coil 10a.
[0186] Furthermore, the induced magnetic fields generated by the
three pairs of guidance-magnetic-field generating coils 413A and
413B, guidance-magnetic-field generating coils 414A and 414B, and
guidance-magnetic-field generating coils 415A and 415B act on the
magnet provided in the object 10 to be detected to control the
position and orientation of the object 10 to be detected. Here,
since the three pairs of guidance-magnetic-field generating coils
413A and 413B, guidance-magnetic-field generating coils 414A and
414B, and guidance-magnetic-field generating coils 415A and 415B
are arranged such that the directions of their central axes are
orthogonal to one another, the magnetic force lines of the induced
magnetic fields can be oriented in any three-dimensional direction.
As a result, the position and orientation of the object 10 to be
detected including the magnet can be controlled
three-dimensionally.
[0187] The technical field of the present invention is not limited
to the aforementioned embodiments, and various modifications may be
applied within the scope thereof without departing from the gist of
the invention.
[0188] For example, in the embodiments described above, one of each
of a magnetic-field generating unit, magnetic-field sensor,
reversed-phase-magnetic-field generating coil, and so on are
provided, and a configuration in which these are positioned on a
substantially straight line is described. However, the structure is
not limited, and a plurality of magnetic-field generating coil and
so on may be provided, and these may be positioned on a plurality
of straight lines. The number and position are not particularly
limited.
* * * * *