Title: Proximity detector and radiography system
Abstract: Certain embodiments of the present invention provide a proximity detector having a simple configuration and an imaging system including the proximity detector. In an embodiment, a proximity detector mainly comprises: a single electrode mounted on a subject-side end of a movable member; a current feeding device for feeding a constant current to an electrostatic capacitor formed between the electrode and a ground; a discharging device for releasing charge from the electrostatic capacitor at intervals of a certain cycle; a binary-coding device for binary-coding the potential at the electrode relative to a ground based on a threshold; and a smoothing device for smoothing an output signal of the binary-coding device.
Patent Number: 6,985,556 Issued on 01/10/2006 to Shanmugavel, et al.
| Inventors:
|
Shanmugavel; Giridharan (Bangalore, IN);
Krishnaswami; Hariharan (Bangalore, IN)
|
| Assignee:
|
GE Medical Systems Global Technology Company, LLC (Waukesha, WI)
|
| Appl. No.:
|
639882 |
| Filed:
|
August 13, 2003 |
Foreign Application Priority Data
| Dec 27, 2002[JP] | 2002-379671 |
| Current U.S. Class: |
378/117; 378/197; 324/678; 324/687; 250/363.02 |
| Current Intern'l Class: |
H05G 1/54 (20060101) |
| Field of Search: |
378/91,114,117,196,197,205
324/661,662,668,663,678,679,686,687,658
340/540,541,561,562
250/363.02,363.03,363.04,363.05,363.08
|
References Cited [Referenced By]
U.S. Patent Documents
| 5166679 | Nov., 1992 | Vranish.
| |
| 5212621 | May., 1993 | Panter.
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| 5363051 | Nov., 1994 | Jenstrom.
| |
| 5373245 | Dec., 1994 | Vranish.
| |
| 5583909 | Dec., 1996 | Hanover.
| |
| 5651044 | Jul., 1997 | Klotz.
| |
| 5726581 | Mar., 1998 | Vranish.
| |
| 5764145 | Jun., 1998 | Hansson.
| |
| 5805658 | Sep., 1998 | Hum.
| |
| 5883935 | Mar., 1999 | Habraken.
| |
| 5964478 | Oct., 1999 | Stanley.
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| 6020812 | Feb., 2000 | Thompson et al.
| |
| 6079738 | Jun., 2000 | Lotito.
| |
| 6260879 | Jul., 2001 | Stanley.
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| 6307384 | Oct., 2001 | Havey.
| |
| 6348862 | Feb., 2002 | McDonnell.
| |
| 6408051 | Jun., 2002 | Habraken.
| |
| 6430259 | Aug., 2002 | Meek et al.
| |
| 6445294 | Sep., 2002 | McDonnell.
| |
| 6661239 | Dec., 2003 | Ozick.
| |
| 2003/0132763 | Jul., 2003 | Ellenz.
| |
| Foreign Patent Documents |
| 2693555 | Jan., 1994 | FR.
| |
Primary Examiner: Glick; Edward J.
Assistant Examiner: Kao; Chih-Cheng Glen
Attorney, Agent or Firm: McAndrews, Held & Malloy, Ltd., Vogel; Peter J., Dellapenna; Michael A.
Goverment Interests
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[Not Applicable]
MICROFICHE/COPYRIGHT REFERENCE
[Not Applicable]
BACKGROUND OF THE INVENTION
The present invention relates to a proximity detector and a radiography system,
and more particularly, to a proximity detector for detecting the proximity of a
movable unit to a subject using proximity sensing and to a radiography system including
the proximity detector.
Imaging systems, such as x-ray radiography systems, are typically positioned
close to a patient or subject to be imaged in order to provide desired imaging
information. One type of radiation imager is a mobile C-arm system. In the medical
field, the mobile C-arm system may be used for general surgery, orthopedic procedures,
pain management procedures, vascular procedures, and cardiac procedures, for example.
Typically, the mobile C-arm has an x-ray source mounted at one end of a mainframe
and a detector, such as an image intensifier, mounted at the other end of the mainframe.
The mobile C-arm may be moved in relation to the object, such as a patient, to
be imaged.
Motorized motion of any of the axes of a mobile C-arm system poses possible
risks to the patient and to the imaging system and other equipment. It is desirable
to prevent or minimize collisions between the mobile C-arm and the object. A possibility
of collision exists whether the C-arm is moved through automated trajectory tracking
or through direct user input from a user interface device. It is therefore desirable
to prevent or minimize collisions when the mobile C-arm is controlled by both an
external user and by an automated system. A method and system for preventing collision
between a mobile C-arm and an object would be highly desirable.
Imaging systems typically use one of two types of anti-collision sensors:
contact sensors and proximity sensors. A contact sensor may use a bumper. The contact
sensor detects a change in pressure resulting when the bumper contacts the object.
A proximity sensor detects the presence of an object within a given distance
from
a movable part of the C-arm imaging apparatus. A proximity sensor may be a capacitive
proximity sensor. Typically, a plurality of capacitive sensor plates are used.
A multiplexor selectively electrically couples the sensor plates and a capacitive
sensing processing unit. Conventional sensor systems may also incorporate shielding
to prevent detection of components in the imaging apparatus.
Proximity detection may be enhanced using two additional electrodes. One
electrode may be used as a receiver. The other electrode is used as a transmitter
and attached to the face of the x-ray detector, such as an image intensifier. Proximity
detection with the two electrodes is based on a radio frequency (RF) coupling between
the transmitting and receiving electrodes.
Current proximity sensor systems use several sensor plates. The sensor plates
are placed around the x-ray detector (e.g., image intensifier) and in the face
of the detector. Scanning circuitry includes a multiplexor to accommodate the plurality
of sensor plates. The scanning circuitry increases overhead on sensing circuitry
for the imaging system. U.S. Pat. No. 5,651,044, to Klotz et al., relates to one
such multi-plate proximity sensor system.
Additionally, proximity sending is currently performed using RF coupling
with both a transmitter and receiver. Capacitance is detected by a change in an
electromagnetic field created by the transmitter when an object passes near the transmitter.
Current proximity sensors are limited by the complexity of electronic circuitry.
Complex, additional electrical circuitry impacts the cost, maintenance, and performance,
for example, of the imaging system. Current sensor systems are also limited by
distances between sensors and imaging system components. That is, operating constraints
limit the distance between a proximity sensor and an image intensifier, for example.
Additionally, current sensor systems are limited by the use of an electromagnetic
field for proximity detection. Furthermore, capacitive proximity sensing has not
been used with a mobile C-arm apparatus.
Thus, a need exists for an improved proximity sensing mechanism using capacitive
sensing techniques on a mobile C-arm apparatus.
BRIEF SUMMARY OF THE INVENTION
Certain embodiments of the present invention provide a proximity detector
having a simple configuration and an imaging system including the proximity detector.
In a certain embodiment, the imaging system includes a movable member capable of
approaching a subject and a proximity detector. The proximity detector indicates
an approach of the movable member within a certain distance of the subject based
on an electric field. The proximity detector includes an electrode mounted on the
movable member, a current feeding device for feeding a current to an electrostatic
capacitor formed between the electrode and a ground, and a discharging device for
releasing charge from the electrostatic capacitor at intervals of certain cycle.
The proximity detector may also include a binary-coding device for binary-coding
a potential at the electrode relative to a ground based on a threshold and a smoothing
device for smoothing an output signal of the binary-coding device. The electrode
may include two conductive layers electrically isolated from each other. The current
may be fed to an outer layer of the conductive layers. Identical voltages may be
applied to the outer and inner layers. The imaging system may also include an x-ray
irradiating device and an x-ray receiving device supported by the movable member.
The x-ray irradiating device and x-ray receiving device may be positioned opposed
to each other with a space therebetween. The x-ray receiving device may include
in image intensifier. The movable member may be a C-arm. The electrode may be formed
along a perimeter of a receiving surface of the x-ray receiving device. The electrode
may also be formed over an outer periphery of the x-ray receiving device and a
perimeter of a receiving surface thereof.
In a certain embodiment, the proximity detector includes an electrode positioned
on a surface, a current feeding device for feeding a current to an electrostatic
capacitor formed between the electrode and a ground, a discharging device for releasing
charge from the electrostatic capacitor at intervals of a certain cycle, and a
proximity detection triggering an alert based on a threshold. The alert may be
an alarm, a report, and/or a command, such as a motion halt command. In an embodiment,
the current fed to the electrostatic capacitor may be a constant current.
The proximity detector may also include a binary-coding device for binary-coding
a potential at the electrode relative to a ground based on a threshold, and a smoothing
device for smoothing an output signal of the binary-coding device. The electrode
may include two conductive layers electrically isolated from each other. The current
may be fed to an outer layer of the conductive layers, and a voltage may be applied
to the outer and inner layers. In an embodiment, the proximity detector uses a
ramp and pedestal method to detect a change in capacitance.
In an embodiment, the proximity detector may be used with an x-ray irradiating
device and an x-ray receiving device supported by a supporting device. The x-ray
irradiating device and x-ray receiving device may be positioned opposed to each
other with a space therebetween. The electrode may be formed along a perimeter
of a receiving surface of the x-ray receiving device. The electrode may also be
formed over an outer periphery of the x-ray receiving device and a perimeter of
a receiving surface thereof.
In a certain embodiment, the method for proximity detection includes positioning
an electrode on a surface, forming an electrostatic capacitor between the electrode
and a ground, feeding a current to the electrostatic capacitor, releasing a charge
from the electrostatic capacitor at certain intervals, comparing a voltage across
the electrode to a reference signal to form a proximity detection signal, and triggering
an alert if the proximity detection signal does not satisfy a certain threshold.
The method may also include generating a binary signal based on the voltage and
the reference signal, and smoothing the binary signal to form a proximity detection
signal. Additionally, the method may include positioning a patient and triggering
an alert when the surface approaches the patient within a certain threshold distance
based on the proximity detection signal.
In an embodiment, since the single electrode is adopted, the configuration of
a sensor is simplified. Moreover, a constant current is fed to the electrostatic
capacitor formed between the electrode and a ground. Charge is released from the
electrostatic capacitor at intervals of a certain cycle. A potential at the electrode
relative to a ground is binary coded based on a threshold. An output signal of
the binary-coding device is smoothed in order to produce a detection signal. This
results in the simplified configuration of an electric circuit.
In an embodiment, the electrode has two conductive layers electrically isolated
from each other. The constant current is fed to an outer layer of the conductive
layers, and a voltage same as one applied to the outer layer is applied to an inner
layer. In this case, sensitivity to be attained in proximity detection improves.
In an embodiment, the electrode is formed along a perimeter of a receiving surface
of the x-ray receiving device, so that the adverse effect on incident x-rays may
be minimized. In an embodiment, the electrode is formed over a periphery of the
x-ray receiving device and a perimeter of a receiving surface thereof. In this
case, while the adverse effect on incident x-rays may be minimized, the area of
the electrode may be increased.
In an embodiment, the supporting device supports the x-ray irradiating device
and x-ray receiving device at respective ends of a C-arm. In this case, diverse
accesses to a subject are permitted. In an embodiment, the x-ray receiving device
includes image intensifier so that the sensitivity to incident x-rays may be improved.
Certain embodiments of the present invention provide a proximity detector
having a simple configuration and an imaging system including the proximity detector.
Claims
What is claimed is:
1. An imaging system, said imaging system comprising:
a movable member capable of approaching a subject; and
a proximity detector, said proximity detector indicating an approach of said
movable member within a certain distance of said subject based on an electric field,
said proximity detector comprising:
an electrode mounted on said movable member;
a current feeding device for feeding a constant current to an electrostatic capacitor
formed between said electrode and a ground; and
a discharging device for releasing charge from said electrostatic capacitor at
intervals of a certain cycle,
wherein said electrode comprises two conductive layers electrically isolated
from each other, and said constant current is fed to an outer layer of said conductive
layers, and a voltage equal to a first voltage applied to said outer layer is applied
to an inner layer.
2. The system of claim 1, wherein said proximity detector further comprises:
a binary-coding device for binary-coding a potential at said electrode relative
to a ground based on a threshold; and
a smoothing device for smoothing an output signal of said binary-coding device.
3. The system of claim 1, further comprising an x-ray irradiating device and
an x-ray receiving device supported by said movable member, said x-ray irradiating
device and said x-ray receiving device positioned opposed to each other with a
space there between.
4. The system of claim 3, wherein said electrode is formed along a perimeter
of a receiving surface of said x-ray receiving device.
5. The system of claim 3, wherein said electrode is formed over an outer periphery
of said x-ray receiving device and a perimeter of a receiving surface thereof.
6. The system of claim 3, wherein said x-ray receiving device comprises an image intensifier.
7. The system of claim 1, wherein said movable member comprises a C-arm.
8. The system of claim 1, wherein said imaging system comprises a sensing circuit
mounted on the same movable member as the electrode.
9. A proximity detector, said proximity detector comprising:
an electrode positioned on a surface of a movable member;
a current feeding device for feeding a constant current to an electrostatic capacitor
formed between said electrode and a ground;
a discharging device for releasing charge from said electrostatic capacitor at
intervals of a certain cycle; and
a proximity detection device triggering an alert based on a threshold,
wherein said electrode comprises two conductive layers electrically isolated
from each other, and said constant current is fed to an outer layer of said conductive
layers, and a voltage equal to a first voltage applied to said outer layer is applied
to an inner layer.
10. The proximity detector of claim 9, wherein said alert comprises at least
one of an alarm, a log, and a motion halt command.
11. The proximity detector of claim 9, wherein said proximity detector further comprises:
a binary-coding device for binary-coding a potential at said electrode relative
to a ground based on a threshold; and
a smoothing device for smoothing an output signal of said binary-coding device.
12. The proximity detector of claim 9, wherein the proximity detector is used
with an x-ray irradiating device and an x-ray receiving device supported by a supporting
device, said x-ray irradiating device and said x-ray receiving device positioned
opposed to each other with a space therebetween.
13. The proximity detector of claim 12, wherein said electrode is formed along
a perimeter of a receiving surface of said x-ray receiving device.
14. The proximity detector of claim 12, wherein said electrode is formed over
an outer periphery of said x-ray receiving device and a perimeter of a receiving
surface thereof.
15. The proximity detector of claim 9, wherein said proximity detector uses a
ramp and pedestal method to detect a change in capacitance.
16. The proximity sensor of claim 9, wherein said proximity detector comprises
a sensing circuit positioned on the same movable member as the electrode.
17. A method for proximity detection, said method comprising:
positioning an electrode on a surface of a movable member, wherein said electrode
comprises two conductive layers electrically isolated from each other;
forming an electrostatic capacitor between said electrode and a ground;
feeding a constant current to said electrostatic capacitor, wherein said feeding
step feeds said constant current to an outer layer of said conductive layers;
releasing a charge from said electrostatic capacitor at certain intervals;
comparing a voltage across said electrode to a reference signal to form a proximity
detection signal;
triggering an alert if said proximity detection signal does not satisfy a certain
threshold; and
applying a voltage equal to a first voltage applied to said outer layer to an
inner layer.
18. The method of claim 17, wherein said comparing step further comprises:
generating a binary signal based on said voltage and said reference signal; and
smoothing said binary signal to form a proximity detection signal.
19. The method of claim 17, further comprising:
positioning a patient; and
triggering an alert when said surface approaches said patient within a certain
threshold distance based on said proximity detection signal.
20. The method of claim 17, wherein said positioning step further comprises positioning
a sensing circuit on the same surface movable member as the electrode.
Description
RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. 119 to Japanese Patent
Application No. JP2002-379671, filed on Dec. 27, 2002, to Giridharan Shanmugavel
and Hariharan Krishnaswami.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 illustrates a configuration of a radiography system used in accordance
with an embodiment of the present invention.
FIG. 2 illustrates an electrode used in a proximity detector in accordance with
an embodiment of the present invention.
FIG. 3 illustrates an enlarged sectional view of a portion of the x-ray receiver
including the electrode used in accordance with an embodiment of the present invention.
FIG. 4 shows a block diagram of a proximity detector used in accordance with
an embodiment of the present invention.
FIG. 5 illustrates a timing diagram for actions performed by the proximity detector
in accordance with an embodiment of the present invention.
FIG. 6 depicts a relationship between a distance and a detection signal used
in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
For the purposes of illustration only, the following detailed description references
a certain embodiment of an x-ray radiography system using a C-arm. It is understood
that the present invention may be used with other imaging systems, such as a mobile
C-arm system or other imaging modality.
FIG. 1 illustrates a configuration of a radiography system used in accordance
with an embodiment of the present invention. The radiography system includes a
table
100, a gantry
200, and an operator console
300.
The table
100 has a tabletop
102. A subject P of radiography is
positioned on the tabletop
102. The tabletop
102 is supported by
a base
104. An advancing/withdrawing mechanism, a raising/lowering mechanism,
and a tilting mechanism are incorporated in the base
104. The mechanisms
advance, withdraw, raise, lower, and/or tilt the tabletop
102.
The gantry
200 includes an arc-shaped C-arm
206 for supporting
an x-ray irradiator
202 and an x-ray receiver
204. The irradiator
202 and receiver
204 are located opposed to each other. The arm
206
is supported by a stand
208.
The x-ray irradiator
202 has a built-in x-ray tube and irradiates x-rays
towards the x-ray receiver
204. The x-ray receiver
204 has a built-in
image intensifier and receives the x-rays irradiated from the x-ray irradiator
202. The x-ray receiver
204 is, for example, generally, shaped like
a cylinder.
The x-ray irradiator
202 is an example of an embodiment of an x-ray irradiating
device included in the present invention. The x-ray receiver
204 is an example
of an embodiment of an x-ray receiving device included in the present invention,
and is also an example of an embodiment of a movable member included in the present
invention. The arm
206 is an example of an embodiment of a supporting device
included in the present invention.
The support structure or gantry
200 has an isocenter in an interspace
between the x-ray irradiator
202 and x-ray receiver
204. The isocenter
is equivalent to a center of an arc of the arm
206.
A feeding or positioning mechanism incorporated in the stand
208 moves
the
arm
206 along an arc, for example, whereby the x-ray irradiator
202
and x-ray receiver
204 rotate with the isocenter as a center while maintaining
the opposed relationship. Using the advancing/withdrawing mechanism incorporated
in the arm
206, the x-ray receiver
204 may be advanced or withdrawn
in the direction of the isocenter. A degree of advancing, withdrawing, raising,
lowering, and/or tilting the tabletop
102 may be adjusted so that a radiographic
center of the subject P will coincide with the isocenter.
The operator console
300 serves as a user interface, such as a mechanical
interface, computer interface, joystick, or other interface. The operator console
300 may include information processing equipment, for example, a computer
and peripheral equipment. The operator console
300 controls the table
100
and gantry
200 in response to a user-entered command. The operator console
300 may also facilitate radiography or other imaging or processing.
In an embodiment, the radiography system includes a proximity detector. An embodiment
of the proximity detector will be described below. FIG. 2 illustrates an electrode
used in a proximity detector in accordance with an embodiment of the present invention.
As shown in FIG. 2, an electrode
210 is mounted on one end of the x-ray
receiver
204. In an embodiment, the end of the x-ray receiver
204
is an end on the side facing the subject P, that is, on the receiving surface-side.
In an embodiment, the electrode
210 is formed over a perimeter of a receiving
surface of the x-ray receiver
204 and a periphery of an end of the x-ray
receiver
204. In an embodiment, the receiving surface of the x-ray receiver
204 and the peripheral surface of the end thereof are covered with an enclosure
made of an insulating material, for example, a plastic. The electrode
210
may also be covered with an enclosure made of an insulating material (not shown).
FIG. 3 illustrates an enlarged sectional view of a portion of the x-ray receiver
including the electrode
210 used in accordance with an embodiment of the
present invention. As shown in FIG. 3, the electrode
210 has two conductive
layers
212 and
214. The conductive layers
212 and
214
are stacked up with an insulating layer
216 between them. The conductive
layers
212 and
214 are layers of conductors made of, for example,
copper or aluminum. The electrode
210 may be formed using, for example,
a flexible printed-circuit board.
In an embodiment, the electrode
210 is formed as a single electrode. The
electrode
210 is composed of a portion mounted on the receiving surface
of the x-ray receiver
204 and a portion mounted on the peripheral surface
of the end of the x-ray receiver
204. After the portions are mounted on
the x-ray receiver
204, the corresponding conductive layers included in
the portions may be electrically coupled to each other. This also results in an
electrically single electrode. Alternatively, the electrode
210 may be mounted
on the receiving surface of the x-ray receiver
204.
FIG. 4 shows a block diagram of a proximity detector used in accordance with
an embodiment of the present invention. As shown in FIG. 4, the electrode
210
serves as one electrode of an electrostatic capacitor having a ground as the other
electrode. Both the subject P and the x-ray receiver
204 have a ground potential.
The conductive layer
212 forms a capacitor together with the subject P,
while the conductive layer
214 forms a capacitor together with the x-ray
receiver
204. Hereinafter, the conductive layers
212 and
214
may be called electrodes.
A constant current source
402 is connected to the electrode
212.
The constant current source
402 is an example of an embodiment of a current
feeding device included in the present invention. Assuming that the electrostatic
capacitance of the capacitor is C, the relationship between a current I and a voltage
v developed across the electrode
212 is provided as follows:
##EQU1##
In an embodiment, since the current I is a constant current, the voltage v increases
linearly with the passage of time. The slope of the increase in the voltage is
1/C. That is, the slope is inversely proportional to the electrostatic capacitance C.
A discharging circuit
404 is connected to the electrode
212. The
discharging circuit
404 is an example of an embodiment of a discharging
device used in accordance with an embodiment of the present invention. The discharging
circuit
404 releases charge from the capacitor formed with the electrode
212 at intervals of a certain cycle. The release of charge brings the voltage
v to a zero level periodically. Due to the repetition of charging and discharging,
the voltage v assumes a sawtooth wave having the certain cycle (e.g., a ramp and
pedestal waveform).
In an embodiment, the slope of the sawtooth wave in one direction of progress
thereof is inversely proportional to the electrostatic capacitance C. The electrostatic
capacitance C increases with a decrease in the distance d between the electrode
212 and subject P. The slope of the sawtooth wave diminishes with the decrease
in the distance d between the electrode
212 and subject P.
The voltage v across the electrode
212 is applied to the electrode
214
via a voltage repeater
406. The voltage repeater
406 is realized
with a high-impedance amplifier that produces a gain of, for example, +1. The voltage
repeater
406 produce potential at the electrode
214 equal to the
potential at the electrode
212. If the potentials at the electrodes
212
and
214 are equal, no electric field is formed between the electrodes
212
and
214. Then, an electric field around the electrode
212 may be
formed on the subject side of the electrode
212. The field formed on the
side of the electrode
212 toward the subject P allows proximity detection
to be carried out in excellent sensitivity. In an embodiment, an electric field
around the electrode
214 is formed on the x-ray receiver side of the electrode
214.
The voltage v across the electrode
212 is applied to a comparing circuit
408. The comparing circuit
408 produces a binary signal w, which
signifies whether an input signal is larger, using a reference signal REF. The
binary signal w is smoothed by a smoothing circuit
410 and transmitted as
a proximity detection signal s. The comparing circuit
408 is an example
of an embodiment of a binary-coding device used in accordance with an embodiment
of the present invention. The smoothing circuit
410 is an example of an
embodiment of a smoothing device used in accordance with an embodiment of the present invention.
The foregoing electric circuit may be incorporated in, for example, the enclosure
covering the x-ray receiver
204. The electrode
210 may be formed
with a flexible printed-circuit board extended to a certain degree. The electric
circuit is then formed as a printed circuit on the extension of the electrode
210.
In an embodiment, the proximity detector is constructed as a unit.
FIG. 5 illustrates a timing diagram for actions performed by the proximity detector
in accordance with an embodiment of the present invention. Referring to FIG. 5,
(1) indicates timing of the voltage v, and (2) to (4) indicate timings of the binary
signal w and proximity detection signal s.
As shown in FIG. 5, the voltage v assumes a sawtooth wave having a certain cycle.
The slope of the sawtooth wave in one direction of progress diminishes along with
a decrease in the distance d between the electrode
212 and subject P, as
indicated with, for example, oblique lines v
1, v
2, and v
3
in FIG. 5.
Binary signals w
1, w
2, and w
3 indicate whether respective
sawtooth waves v
1, v
2, and v
3 are larger than the reference
signal REF. In an embodiment, duty ratios of the binary signals w
1, w
2,
and w
3 are in order of increasing magnitude.
In an embodiment, proximity detection signals s
1, s
2, and s
3
result from smoothing of the respective binary signals w
1, w
2, and
w
3. In an embodiment, signal strengths of the proximity detection signals
s
1, s
2, and s
3 are in order of increasing magnitude.
FIG. 6 depicts a relationship between a distance and a detection signal used
in accordance with an embodiment of the present invention. A proximity detection
signal s with a signal strength increasing with a decrease in the distance d may
be produced. A degree of proximity of the x-ray receiver
204 to the subject
P may be determined based on the signal strength of the proximity detection signal
s. The proximity detection signal s may be used to trigger a proximity alarm or
prevent contact of the x-ray receiver
204 or other system component with
the subject P through verification based on a threshold TH corresponding to a limit
DL of proximity (for example, by halting motion of the arm
206).
For example, a patient is placed on the tabletop
102 that is positioned
between the x-ray receiver
204 and the x-ray irradiator
202 mounted
on the C-arm
206. A gantry moves the C-arm
106. Moving the C-arm
106 positions the x-ray receiver
204 and the x-ray irradiator
202
at desired locations with respect to the patient. The x-ray receiver
204
may be positioned near the patient in order to improve resulting image quality.
The proximity detector may use a ramp of peak voltage 5V and a frequency of 100
kHz. The reference voltage
250 may be set at 4V, for example. When the peak
of the voltage ramp drops below the reference voltage
250, a signal is sent
indicating the presence of a human body in the proximity of the capacitive proximity
sensing circuit mounted on the x-ray receiver
204 or other component of
the radiography system. When the proximity detector detects the presence of the
patient, a motor moving the C-arm
206 may be stopped or slowed to avoid
a collision with the patient.
For example, a patient is placed on the tabletop
102 that is positioned
between the x-ray receiver
204 and the x-ray irradiator
202 mounted
on the C-arm
206. A gantry moves the C-arm
106. Moving the C-arm
106 positions the x-ray receiver
204 and the x-ray irradiator
202
at desired locations with respect to the patient. The x-ray receiver
204
may be positioned near the patient in order to improve resulting image quality.
The proximity detector may use a ramp of peak voltage 5V and a frequency of 100
kHz. The reference voltage may be set at 4V, for example. When the peak of the
voltage ramp drops below the reference voltage, a signal is sent indicating the
presence of a human body in the proximity of the capacitive proximity sensing circuit
mounted on the x-ray receiver
204 or other component of the radiography
system. When the proximity detector detects the presence of the patient, a motor
moving the C-arm
206 may be stopped or slowed to avoid a collision with
the patient.
While the invention has been described with reference to certain embodiments,
it will be understood by those skilled in the art that various changes may be made
and equivalents may be substituted without departing from the scope of the invention.
In addition, many modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from its scope. Therefore,
it is intended that the invention not be limited to the particular embodiment disclosed,
but that the invention will include all embodiments falling within the scope of
the appended claims.
*
