U.S. patent number 3,781,557 [Application Number 05/281,568] was granted by the patent office on 1973-12-25 for radiographic display system with cassette lock.
This patent grant is currently assigned to Raytheon Company. Invention is credited to Vitaliano Carugati, Sergio Colombo, Gianni Ferramola, Sergio Ferrari.
United States Patent |
3,781,557 |
Carugati , et al. |
December 25, 1973 |
RADIOGRAPHIC DISPLAY SYSTEM WITH CASSETTE LOCK
Abstract
A nuclear imaging device comprising a plurality of scanning
heads spaced apart in a predetermined configuration with the aid of
a support member that permits the individual scanning heads to scan
in parallel, antiparallel, and tomographic modes. The support
member which is driven in both X and Y directions is mechanically
connected with the stylus of a graphical X-Y plotter via a backlash
linkage. Displays are provided wherein the color of the ink dot on
printed paper or the intensity of the light projected on
photographic film are related to the nuclear particle count in a
preselectable manner.
Inventors: |
Carugati; Vitaliano (Cologno
Monzese-Milano, IT), Colombo; Sergio (Milan,
IT), Ferramola; Gianni (Milan, IT),
Ferrari; Sergio (Cernusco Sul Naviglio Milano, IT) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
26765339 |
Appl.
No.: |
05/281,568 |
Filed: |
August 17, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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81214 |
Oct 16, 1970 |
3735132 |
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Current U.S.
Class: |
250/363.02;
250/366; 250/363.08; 378/182 |
Current CPC
Class: |
G01T
1/1666 (20130101); G01T 1/1663 (20130101); A61B
6/4258 (20130101); G01T 1/2985 (20130101); G01T
1/166 (20130101) |
Current International
Class: |
G01T
1/29 (20060101); G01T 1/166 (20060101); G01T
1/00 (20060101); G01t 001/20 () |
Field of
Search: |
;250/71.5S,65R,68,320,366 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
|
3070695 |
December 1962 |
Stickney et al. |
3652852 |
March 1972 |
Miyazawa et al. |
|
Primary Examiner: Lawrence; James W.
Assistant Examiner: Willis; Davis L.
Parent Case Text
This is a division of application Ser. No. 81.214 filed Oct. 16,
1970 now U.S. Pat. No. 3,735,132.
Claims
What is claimed is:
1. In a radiographic imaging system wherein an image is produced on
a photographic film by means of a moving light stylus, the
invention comprising:
a light-tight box enclosing said photographic film, said
light-tight box having an opening for admitting light from said
stylus and a shield adapted to cover said opening for excluding
said light;
a structure for supporting said light-tight box in relation to said
stylus; and
a lock positioned on said light-tight box, said lock comprising an
elongated member slidably mounted for engaging alternately said
shield or said structure.
2. The device defined by claim 1 wherein said light-tight box is
slidably mounted within said structure to permit withdrawal of said
light-tight box through an opening in said structure, and said
shield is slidably mounted within said light-tight box to permit
withdrawal of said shield through said opening.
3. In combination:
means for scanning a source of radiation;
a source of light connected by a mechanical linkage to said
scanning means;
a photographic film container adapted to support a photographic
film for illumination by said source of light, said container
comprising a lock and having a slide for excluding light from the
container; and
a housing for supporting said container in spaced relation to said
source of light, said lock engaging said housing to secure said
container within said housing and releasing said slide for exposure
of said film by said source of light.
4. A device comprising in combination:
means for scanning a source of radiation;
a source of light connected by a mechanical linkage to said
scanning means;
a photographic film container adapted to support a photographic
film for illumination by said source of light, said container
comprising a lock and having a slide for excluding light from the
container;
a housing for supporting said container in spaced relation to said
source of light, said lock engaging said housing to secure said
container within said housing and releasing said slide for exposure
of said film by said source of light; and wherein
said source of light emits flashes of light having an intensity
related in a predetermined manner to the intensity of said
radiation, said device further comprising:
means for varying said predetermined manner; and
means for varying a repetition frequency of said light flashes as a
function of the scanning speed of said scanning means.
5. The device as defined by claim 4 wherein said mechanical linkage
has a predetermined amount of backlash to preclude the formation of
a scalloping effect in an image formed on said photographic film by
said source of light.
Description
BACKGROUND OF THE INVENTION
This invention relates to nuclear imaging devices and more
particularly to a means for recording data obtained from
simultaneous scans by a plurality of scanning heads.
In obtaining an image of a radioactive source it is frequently
convenient to use a plurality of scanning heads, for example, a
pair of scanning heads, in which the scanning heads may be arranged
for parallel scanning, antiparallel scanning or tomographic
scanning. In the situation where a human patient is being treated
with radio pharmaceuticals and a radiograph of the chest is to be
obtained, the scanning heads may be arranged to effect a parallel
scan in which one scanning head scans the upper portion of the
chest while the other scanning head scans the lower portion of the
chest, thereby providing radiographs of the entire chest in half
the time. Alternatively, it may be desirable to compare images
obtained from scanning the chest from a frontal view and also from
a rear view; in this case the scanning heads would be arranged in
antiparallel configuration in which one scanning head is positioned
above the patient and the other scanning head is positioned beneath
the patient. It may also be desirable to provide a tomographic
display which is accomplished by positioning the two scanning heads
side by side and at an angle to each other to provide two views of
a common source of radiation such that the two views are oriented
at an angle to each other. In these three situations it is
desirable that the two scanning heads be rigidly mounted relative
to each other to insure a correspondence between the imaging points
on the two radiographs provided by the two scanning heads, but
since the plurality of scanning heads are to be supported in a
fixed configuration by a rigid member, provision must also be made
for varying the orientation of these scanning heads to provide the
different modes of scanning, and furthermore, the scanning heads
must be connected to writing heads which provide the
radiographs.
An attempt to solve the foregoing problem was made by D. E. Kuhl as
shown in "Progress in Medical Radioisotope Scanning," pages 186 and
187, published by the U.S. Atomic Energy Commission, and in
"Clinical Scintillation Scanning," edited by L. M. Freeman and P.
M. Johnson, page 34, published by Harper & Row. Kuhl's scanning
apparatus comprises a large complex mechanism which is cumbersome
for a small hospital installation.
A further problem arises in the interpretation of the radiographs.
Radiographs are generally read visually and the interpretations
made from the radiograph are based on the capability of an observer
for reading these radiographs. In particular the observer must be
able to distinguish between radiations of higher and lower
intensities. While X-Y plots in color have been utilized, the
relationship between the selection of color or gray scale is preset
and cannot be varied to suit the particular situation or the
particular observer.
An additional problem commonly known as "scalloping" is found in
X-Y plots produced by imaging systems which are responsive to the
counting of nuclear particles, such as gamma ray photons, emitted
by the source of radiation. In such imaging systems the count of
the quanta of radiation are scaled such that a point is provided on
the radiograph for a specified number of counts. As the scanning
head is moved along during a scanning operation, the count is
accumulated so that at the end of some small region of the
radiograph, an image point or mark is printed upon the X-Y plot. At
the end of a scanning line when the direction of the scanning head
is reversed it becomes apparent that two image points will be
printed on the X-Y plot corresponding to the same X displacement,
these two points having different values in the X dimension. This
is the so-called scalloping effect, and it is desirable to provide
an imaging system which precludes this scalloping.
SUMMARY OF THE INVENTION
This invention provides for an imaging system in which a plurality
of transducers or scanning heads are mounted on a positioning means
comprising a rigid transport beam, a rigid frame rotatably mounted
thereon, and a plurality of arms slidably and rotatably attached to
the frame. Moving means are provided for moving the positioning
means in an X direction in which the main beam is displaced along
its axis and in a Y direction in which the transport beam is
displaced in a direction perpendicular to its axis. The transport
beam also mechanically moves a writing head which provides a
colored image on an XY plot, and is further connected to two
photoheads for providing two radiographs on photographic film, one
radiograph corresponding to each of the scanning heads, or
alternatively, to a combination of the data of two scanning heads.
The direct mechanical connection provides for the correlation of
data obtained from the scanning with position on the radiograph. A
backlash device interconnects the printing head with the main beam
such that upon a reversal in the scanning direction by the
transport beam there is a momentary lag in motion of the writing
head to permit the positioning means to move a short distance for
accumulating a count of nuclear particles before a mark is
imprinted on the X-Y plot. There is also disclosed means for
varying the responsivity of the color coding in a colored
radiograph as well as the responsivity of the gray code in a
photographic radiograph as a function of the count of the quanta of
radiant energy impinging upon the scanning heads.
In addition, this invention provides a film lock preventing
accidental exposure of a photographic radiograph and a means for
indicating when a writing head has been set for two high a writing
rate.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned objects and other features of the invention are
explained in the following description taken in connection with the
accompanying drawings wherein:
FIG. 1 is a pictorial representation, partially cut away to show
the drive mechanism, of the imaging system of the invention;
FIGS. 2A, 2B and 2C show various configurations for arranging the
scanning heads of the imaging system of the invention;
FIG. 3 is a block diagram showing the operation of the imaging
system;
FIGS. 4 and 4A are a block diagram and a timing diagram and a
timing diagram of a pulse height selector;
FIG. 5 is a block diagram of digital data processing equipment;
FIG. 6 is a block diagram of channel selection circuitry;
FIG. 7 is an isometric view of a writing head;
FIG. 8 is an isometric view of the drive mechanism which imparts a
scanning motion to the scanning heads;
FIGS. 9 and 10 are isometric and diagrammatic views of an
antiscalloping feature of the invention;
FIG. 11 is an isometric view, partially in section, of a photohead
and its transport mechanism;
FIG. 12 is a block diagram of a drive circuit for a writing
head;
FIG. 13 is a block diagram of a drive circuit for a photohead;
FIG. 14 is an isometric view of film cassettes showing a novel
lock; and
FIG. 15 is a schematic diagram of a control circuit for scanning
motors of the imaging system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1 there is shown an imaging system 20 in
accordance with the invention comprising a pair of scanning heads
22A and 22B which are pivotedly mounted by pivots 24A and 24B to a
corresponding pair of rachet arms 26A and 26B which are slidably
mounted within a C-frame 28. The C-frame 28 is pivotedly mounted by
pivot 30 to a transport beam 32 which is supported within a
carriage 34, partially shown in FIG. 1, for translational motion in
a direction parallel to the axis of the carrier beam 32,
hereinafter referred to as the X direction, and in a direction
perpendicular to the transport beam 32, hereinafter referred to as
the Y direction. The carriage 34 is mounted within a housing 36 in
a manner to be described with reference to FIG. 8. The transport
beam 32 enters the housing 36 via curtain 37. Writing heads 38A and
38B are affixed to the opposite end of the carrier beam 32 by means
of a backlash linkage 40 which permits printing of a radiographic
display upon a paper copy 42 while precluding the presence of the
well known scalloping affect. In addition, two photographic copies
of radiographs are formed by means of a pair of push rods 44 and 46
connected to the carrier beam 32 by means shown in FIG. 8 for
driving a corresponding pair of photoheads 50 and 52 over film
plates 54 and 56. The film plate 54 and 56 are contained within
light-tight boxes or cassettes 58 and 60 positioned within a
housing 62. The cassettes 58 and 60 are secured in a novel manner
by locks 64 which prevent accidental exposure of the film plates 54
and 56. The housing 62 and the housing 36 are supported by means of
a frame 66 which facilitates location of the imaging system within
a room such as the room of a hospital. The housing 36 has a hinged
section 67 to expose electronic equipment (not shown) located
therein.
Referring now to FIGS. 2A, 2B and 2C there are shown three methods
by which a patient 68 may be examined to produce a radiographic
image. A source of radiation is provided by a radio pharmaceutical
which may be ingested by the patient 68 and which then migrates
through the body of the patient 68 to accumulate in the organ of
the body which is to be observed. In FIGS. 2A and 2B the C-frame 28
has been rotated about pivot 30 with the aid of crank 70 (seen in
FIG. 1) to a horizontal position and tightened by knob 71A of FIG.
1. The two scanning heads 22A and 22B have been rotated to parallel
positions in FIG. 2A by means of the pivots 24A and 24B as seen in
FIG. 1 and tightened by knobs 71B and 71C. The scanning heads 22A
and 22B have been spaced apart a predetermined distance by means of
the rachet arms 26A and 26B which are driven respectively by rachet
cranks 72A and 72B of FIG. 1. With the arrangement of FIG. 2A two
separate radiographic images can be provided as by use of film
plate 54 and film plate 56 of FIG. 1 which taken together provide a
complete image of the chest of the patient 68 which has absorbed
the radio pharmaceutical. In this manner a radiographic image can
be obtained in half the time normally required, thereby permitting
a hospital to process an increased number of patients with a single
imaging system.
In FIG. 2B the scanning heads 22A and 22B are arranged by means as
described with reference to FIG. 2A in a manner permitting a
tomographic radiographic display in which the rays of radiation
emanating from an organ 74 such as a thyroid gland are observed
from two directions as is indicated by the angular orientation of
the two scanning heads 22A and 22B relative to each other. In the
situation of FIG. 22B as in the case of FIG. 2A the C-frame 28 has
been orientated in a horizontal position by means of the crank 70
and the rachet arms 26A and 26B have been positioned by means of
rachet drive gears 72A and 72B to provide the desired position of
the scanning heads 22A and 22B relative to each other.
In FIG. 2C the C-frame has been positioned in a vertical position
and the scanning heads 22A and 22B have been pivoted about pivots
24A and 24B to face each other in an antiparallel orientation such
that the rays of radiation emanating from the head of the patient
68 in a vertical direction are intercepted by the scanning rays 22A
while the rays of radiation emanating in the opposite direction are
intercepted by scanning head 22B. In this way radiographic images
of information obtained from the right side as well as the left
side of the patient 68 can be obtained.
Referring now to FIG. 3 there is shown a block diagram of the
imaging system 20. Two sources of data are provided by the scanning
heads 22A and 22B of FIG. 1, and the data is processed respectively
by channel 1 and channel 2 as shown in FIG. 3. The scanning heads
such as scanning head 22A has the well known form comprising a
collimator 90, a scintillator 92 and a photomultiplier 94 which is
separated from the scintillator by a glass plate 96. The
photomultiplier 94 comprises a photocathode 98 and an anode 100
which are maintained at a difference of potential of typically
1,000 volts by means of voltage source 102. A glass envelope 104
encloses the scintillator 92 as well as the photomultiplier 94 and
is further surrounded by a lead shield 106 for capturing stray rays
of radiation. Thus, the scanning head 22A is responsive to
X-radiation, gamma radiation and radiation of nuclear
particles.
A quanta of radiation, such as a gamma ray emitted from the organ
74 in the patient 68 of FIG. 2B, passing through the collimator 90
and impinging on the scintillator 92 causes optical photons to be
emitted from the scintillator 92. The optical photons are
intercepted by the photocathode 98 thereby emitting photoelectrons
which are accelerated across the difference of potential to the
anode 100 which results in an electrical signal to which amplifier
108 is responsive.
The amplifier 108 provides a pulse signal corresponding to each
quanta of radiant energy received by the scanning head 22A. Some of
these quanta of energy are due to background radiation and are of a
lower energy content than the quanta of energy, such as a gamma ray
photon, emitted from the organ 74 of FIG. 2B. Accordingly, a pulse
height selector 110, frequently referred to as a window, is
utilized to pass those pulse signals from amplifier 108 having an
amplitude indicating the presence of a quantum of energy emitted
directly from the organ 74. The pulse height selector 110 is preset
for the anticipated level of radiation associated with the radio
pharmaceutical administered to the patient 68 by means of a plug-in
module, hereinafter referred to as an isotope plug 112, positioned
on the housing 36 in FIG. 1 and described in further detail with
reference to FIG. 4.
The pulse signals provided by pulse height selector 110 are of
uniform amplitude suitable for processing by digital equipment such
as the data processor 114 which will be described in further detail
with reference to FIG. 5. The data processor 114 weighs the data
provided by the successive signal pulses from the pulse height
selector 110 and provides an output signal waveform which is
suitable for operating the writing heads 38A-B and the photoheads
50 and 52. Channel 2 comprises scanning head 22B (not shown in FIG.
3) and an amplifier and data processor corresponding to the
amplifier 108 and data processor 114 of channel 1. A selection and
a combination of the data of channel 1 and channel 2 are provided
by a channel selector 116 which is described in further detail with
reference to FIG. 6. For example, by means of the channel selector
116 the sum or the difference of the data of channel 1 and channel
2 may be provided to the writing heads 38A-B, or as a further
example, the data of channel 1 may be provided to operate the
photohead 50 while the data of channel 2 is provided to operate the
photohead 52 to provide simultaneously on film plate 54 and film
plate 56 of FIG. 1 radiographs corresponding to the radiation
incident upon the scanning heads 22A and 22B. The writing heads
38A-B provide either a black and white display or alternatively a
multicolor display, while the photoheads 50 and 52 provide a
photographic image of varying gray scale in response to the
radiation incident upon the scanning heads 22A and 22B. The
responsivity of the color selection in the case of the writing
heads 38A-B and the gray scale in the case of the photoheads 50 and
52 to the data provided by the channel selector 116 may be varied
in a novel manner by means of a predetermined functional
relationship which is preset by data enhancement circuits 118A-D in
the form of plug-in modules on the housing 36 as will be described
with reference to FIG. 7. As shown in FIG. 3, the data enhancement
circuits 118A-D connect respectively with writing head drivers 120A
and 120B and with photohead drivers 122A and 122B, described
respectively in FIGS. 12 and 13, to provide radiographs in which
the data is more readily interpreted.
Referring now to FIGS. 4 and 4A there are shown respectively a
block diagram of the pulse light selector 110 and a timing diagram
useful in explaining its operation. The pulse height selector 110
is responsive to signals from the amplifier 108, such signals being
shown illustratively in FIG. 4A by pulses 128 and 130. The two
pulses 128 and 130 are shown with their rise times exaggerated for
purposes of illustration. The intersection of pulse 128 with line
132 and the intersection of pulse 130 with line 133 are at the
minimum window voltage or threshold (shown as V.sub.th in the
figure) which is regarded as an acceptable input signal. Thus,
pulses provided by amplifier 108 having a peak value which is less
than this threshold value are presumed to occur in response to an
excessively low value of radiation incident upon the scanning head
22A such as might occur from Compton scattering in the vicinity of
the organ 74 of FIG. 2B. The intersection of pulse 130 and the line
134 is at a maximum value of window voltage, V.sub.max, of an
acceptable input signal. Thus, as exemplified by pulse 130, the
pulse 130 would be an unacceptable input signal in that it exceeds
this maximum voltage and is presumed to be produced in response to
an excessively high value of radiation incident upon the scanning
head 22A of FIG. 3 such as might be caused by an extra terrestrial
gamma ray. The pulse 128 of FIG. 4A represents an acceptable pulse
in that its peak amplitude is greater than the threshold voltage
yet less than the maximum voltage.
The pulse height selector 110 comprises a pair of comparators 136
and 138 which compare signals from amplifier 108 with respectively
the threshold window voltage and the maximum window voltage, and
provide output pulse signals (not shown) having leading and
trailing edges respectively occurring when an input pulse such as
pulse 130 crosses the threshold and the maximum window voltage
values. Reference voltages representing the threshold window
voltage and the maximum window voltage are provided respectively
along lines 140 and 142.
The comparators 136 and 138 drive respectively monostable or "one
shot" multivibrators 144 and 146 to provide pulses 148 and 150. The
leading edges of pulses 148 and 150 correspond respectively to the
time instants when the pulse 130 crosses the threshold window
voltage and maximum window voltage. The pulse 148 has a duration of
sufficient length such that the trailing edge of pulse 148 occurs
approximately at the midpoint of pulse 150.
Multivibrator 152 is a monostable or "one shot" multivibrator which
is triggered by the trailing edge of pulse 148 to produce an output
pulse 154 and is inhibited by pulse 150 such that when pulse 150 is
applied to the multivibrator 152 the output pulse 154 does not
appear. When the pulse 150 is present, it is applied to the
multivibrator 152 prior to the occurrence of the trailing edge of
pulse 148 and is, therefore, effective to inhibit the multivibrator
152. Thus, when an input signal pulse such as pulse 128 is present
an output pulse 154 is produced, however, when an input signal such
as pulse 130 is present the multivibrator 152 is inhibited so that
the pulse 154 is not produced. Also, in the event that an input
signal of peak value less than the threshold window voltage is
present, than none of the pulses 148, 150 and 154 is produced. In
this way the pulse height selector 110 selects those input signal
pulses having peak voltage values falling within the range of
values bounded by the threshold and maximum window voltages, and
provides output pulses 154 of uniform amplitude and duration
corresponding to each one of the input pulse signals having an
acceptable voltage value.
The reference voltages applied along lines 140 and 142 are obtained
via switch 156 from resistors 158A, 158B, 160A and 160B which form
a pair of voltage divider circuits, or alternatively, from
potentiometers 162 and 164. The voltage divider circuit of
resistors 158A and 158B, the voltage divider circuit of resistors
160A and 160B, and the potentiometers 162 and 164 are energized
from voltage source 166 so that either the voltage divider circuits
or the potentiometers may be utilized to provide the reference
voltages along lines 140 and 142. The switch 156 is mounted on the
housing 36 of FIG. 1. A novel plug in module hereinafter referred
to as an isotope plug 168, comprises the resistors 158A, 158B, 160A
and 160B, and is conveniently mounted on the housing 36 of FIG. 1
for operation of the imaging system 20 with the appropriate values
of window voltages for the pulse height selector 110.
Referring now to FIG. 5 there is shown a block diagram of the data
processor 114 which comprises a counter 178, a storage unit 180, a
digital-to-analog converter 182 and a clock 184. Counter 178 is a
digital counter responsive to successive pulses such as the pulse
154 from the pulse height selector 110 for counting these pulses
and providing a digital number indicating such count. The storage
unit 180 has the well known form of a group of flip-flops in
parallel connection with each of the output bits of the counter
178. A strobe pulse provided by clock 184 along line 186 initiates
the transfer of the digital number from the counter 178 to the
storage unit 180. Immediately after the strobe pulse on line 186, a
reset pulse is provided by clock 184 along line 188 to reset the
counter 178 to zero. The digital number in the storage unit 180 is
continuously applied to the digital-to-analog converter 182 which
provides an output voltage having a magnitude proportional to the
digital number stored in the storage unit 180. The analog output of
the digital-to-analog converter 182 corresponding to successive
changes in the digital number stored in the storage unit 180 is
shown illustratively by the voltage waveform 190. The pulse
repetition frequency of both the strobe pulse on line 186 and the
reset pulse on line 188 provided by clock 184 is set by the
scanning speed control knob 192 connected to the clock 184 and
located on the housing 36 of FIG. 1. The scanning speed control
knob 192 is also connected to the motor circuit of FIG. 15.
In operation, therefore, the data processor 114 is responsive to a
sequence of individual pulses 154 from the pulse height selector
110 to provide an analog voltage output, such as the voltage
waveform 190, in which the voltage amplitude corresponds to the
number of pulses 154 occurring within the interval between
successive reset pulses on line 188. Accordingly, the data
processor 114 functions as an integrator in which the voltage
waveform 190 is updated periodically at the frequency of the strobe
and reset pulses on lines 186 and 188. As will become apparent in
the description with reference to FIGS. 8 and 15, the speed at
which the scanning head 22A is moved for scanning is proportional
to the frequency of the clock 184, or equivalently the frequency of
the strobe and the reset pulses on lines 186 and 188, due to the
fact that the motor circuit of FIG. 15 and the clock 184 are both
connected to the scanning speed control knob 192. Thus, the count
accumulated in an interval between successive reset pulses on line
188 may equally well be regarded as the count accumulated over an
interval of scanning in the X direction, such interval being, for
example, 4 millimeters.
Referring now to FIG. 6 there is shown a schematic diagram of the
channel selector 116 which accepts input signals from channel 1 and
channel 2 and independently switches the signals by means of
switches 202, 204, 206 and 208 to writing head drivers 120A and
120B and photohead drivers 122A and 122B of FIG. 3. The input
signal from channel 1 on line 210 is provided by the data processor
114 of FIG. 3, and a corresponding signal from channel 2 on line
212 is provided by the data processor of channel 2. A summing
amplifier 214 and a difference amplifier 216 provide the sum and
difference of the signals on lines 210 and 212 such that the sum
signal appears on line 218 at the output of summing amplifier 214
and the difference signal appears on line 220 at the output of the
difference amplifier 216. The lines 218 and 220 connect with the
four switches 202, 204, 206 and 208 so that the sum and difference
signals may also be individually switched to the writing head
drivers 120A and 120B and also to the photohead drivers 122A and
122B. The four switches 202, 204, 206 and 208 are conveniently
mounted on the housing 36 to facilitate the selection of the
appropriate data to be displayed on the paper copy 42 and the film
plate 54 and 56 of FIG. 1.
Referring now to FIG. 7 there is shown an interior view of the
writing head 38A. Writing head 38B has the same form as writing
head 38A and is not shown in FIG. 7. A mark or imprint is made upon
the paper copy 42, seen also in FIG. 1, by means of a tapered rod,
preferably of steel, hereinafter referred to as a tapper 230. The
tapper 230 is affixed at its upper end to magnetic material not
shown in the drawing which is enclosed by a solenoid 232 so that
upon energization of the solenoid with an electric current provided
by the writing head driver 120A of FIG. 12 along wires 234, the
tapper 230 is drawn downwards toward the paper copy 42. A spring
236 affixed concentrically to the tapper 230 and also mounted to
the underside of the solenoid 232 withdraws the tapper 230 from the
paper copy 42 upon deenergization of the solenoid 232. The solenoid
232 and the tapper 230 are supported by a bracket 238 which in turn
connects with a frame member 239 of the backlash linkage 40 which
is seen also in FIGS. 8 and 9.
To provide a black and white radiograph, the paper copy 42
comprises preferably a pressure sensitive paper which when struck
by the tapper 230 produces a black mark at the point of impact. The
shape of the mark depends on the shape of the tip of the tapper 230
so that a dot or an elongated mark may be provided by an
appropriate selection of the tip of the tapper 230.
To provide a multicolor radiograph, a multicolored ink ribbon 240
is wound around two spools 242A and 242B, positioned on plate 244
and rotated in a well known manner by a small motor (not shown) and
is guided by struts 246, 247 and 248 across the tip of the tapper
230. Upon energization of the solenoid 232, the tapper strikes
against a portion of the ribbon 240 and thereby imparts a mark of
colored ink to the paper copy 42, the color of the ink depending on
the strip, such as a strip 250 containing blue ink, struck by the
tapper 230. The struts 246, 247 and 248 are mounted to the plate
244 which is pivotally mounted about the frame member 239 by means
of fingers 252 extending from the plate 244. A potentiometer 253 is
mounted to the frame member 239 such that its shaft, not shown,
connects with a finger 252 with the shaft axis coincident to the
pivot axis of the finger 252. The potentiometer 253 provides an
electrical signal, to be described with reference to FIG. 12, which
is responsive to the angle of pivot, or accordingly, the color of
the mark imprinted on the paper copy 42. The struts 246 and 247
have surfaces which are lower, respectively, outwardly and inwardly
along the centers of their axes to provide a uniform spacing of the
ribbon 240 relative to the tapper 230 independently of the pivoting
of plate 244. Pivoting of the plate 244 is provided by a sector
gear 254 affixed to the top of the plate 250, and a worm gear 255
meshing with the sector gear 254 and driven by a stepping motor
256. In response to electrical signals energizing the stepping
motor 256, as will be described with reference to FIG. 12, the
stepping motor 256 imparts a rotation to the worm gear 255 to pivot
the plate 244 for positioning the ribbon 240 beneath the tapper
230.
Referring now to FIG. 8 there is shown an isometric view of the
carriage 34 and push rods 44 and 46 partially seen in FIG. 1. The
carriage 34 comprises front plate 260, back plate 262, and four
connecting struts 264A-D. The transport beam 32 passes through an
aperture 266 in the front plate 260 and an aperture 268 in the back
plate 262. The carriage 34 is mounted on rails 270 and 272 for
motion in the Y direction by means of rollers 274 having a flat
surface and contacting rail 270 and by means of rollers 276 having
a concave surface and making contact with rail 272. The concavity
of the rollers 276 aids in positioning the carriage 34 upon the
rails 270 and 272. The push rods 44 and 46 are mechanically
connected to the transport beam 32 by means of a rigid member
referred to as hanger 278 which is rigidly affixed to the transport
beam 32. The push rods 44 and 46 are also slidably mounted within a
bracket 280 rigidly affixed to the back plate 262 for guiding the
push rods 44 and 46 through curtains 282 for positioning the
photoheads 50 and 52 seen in FIG. 1. The curtains 282 prevent the
entry of light into the cassettes 58 and 60 of FIG. 1 as the
carriage 34 moves back and forth during the scanning operation.
The carriage 34 is positioned in the X direction by means of a worm
drive 284 which comprises worm gear 286, traveler 288 affixed to
the front plate 160 and a chain drive 290 through which the worm
gear 286 is driven by motor 292. Upon energization of the motor
292, as will be described with reference to FIG. 13, the carriage
34 is displaced along the X direction, the amount of displacement
depending upon the amount of rotation of the worm gear 286.
The transport beam 32 is supported by the carriage 34 with the aid
of rollers 294 mounted on both the front plate 260 and the back
plate 262 around the apertures 266 and 268 in contact with each of
the four sides of the transport beam 32. The rollers 294 permit
movement of the transport beam 32 in the Y direction while the
transport beam 32 is displaced in the X direction by movement of
the carriage 34 in response to the worm drive 284.
The transport beam 32 is displaced in the Y direction by means of a
worm drive 296 which comprises a worm gear 298, a traveler 300
rigidly affixed to the transport beam 32 and a chain drive 302
through which the worm gear 298 is driven by motor 304. In response
to an exertation of motor 304 as will be described with reference
to FIG. 15 the transport beam 32 is moved back and forth in the Y
direction independently of its displacement in the X direction. In
this way the transport beam 32 receives both X and Y displacements
independently of each other to effect a scanning motion of the
scanning heads 22A and 22B as well as a scanning motion of the
backlash linkage 40, writing heads 38A and 38B and the push rods 44
and 46, all of which are seen in FIG. 1. It is noted that the
scanning motion of the writing heads 38A and 38B is identical to
that of the scanning heads 22A and 22B with the exception of the
slight displacement of the scanning heads 38A and 38B afforded by
the backlash linkage 40 for elimination of scalloping as will be
described with reference to FIGS. 9 and 10. The use of a single
mechanical connection, namely the transport beam 32 provides a
precise correlation between the position of the writing heads 38A
and 38B and the position of the scanning heads 22A and 22B.
Referring now to FIGS. 9 and 10 there are shown respectively a
cut-away view of the backlash linkage 40 and a diagrammatic view of
a radiograph explaining the scalloping mechanism. The backlash
linkage 40 comprises an outer shell 306 and frame member 239 to
which is affixed the writing heads 38A and 38B, the outer shell 306
being closed off by a cover plate 308. The outer shell 306 encloses
an end of the transport beam 32 and is in mechanical contact
therewith by means of roller assemblies 310 each of which has a
pair of rollers which ride along a track 314 on the transport beam
32. The transport beam 32 is hollow to permit the carrying of
electric wires within the transport beam for making connection
between the scanning heads 22A and 22B and the writing heads 38A
and 38B of FIG. 1, and accordingly, the outer shell 306 encloses
only the end portion of the transport beam 32 to permit electrical
wires to make entry into the interior of the transport beam as by
means of connector 316.
The amount of backlash provided by the backlash linkage 40 is equal
to the spacing between the cover 308 and a striker plate 318
mounted directly to the end of the transport beam 32. A drag rod
320 is affixed to the outer shell 306 and, as is shown in FIG. 8,
the drag rod 320 extends along the beam 32 and passes through a
fitting 322 affixed to the back plate 262 of the carriage 34. The
fitting 322 makes fictional contact with the drag rod 320 to supply
the drag force. Upon a reversal in the direction of travel of the
transport beam 32, as for example, when the transport beam 32 has
been moving in a direction towards the backlash linkage 40 and then
reverses direction, the striker plate 318 moves away from the cover
plate 308 until a spacing between the striker plate 318 and the
cover plate 308 is equal to the amount of scalloping to be negated,
for example, 6 millimeters. At this point the roller assemblies 310
reach the end of the respective tracks 314 and are contacted by the
back side of the striker plate 318 whereupon the roller assemblies
310 and the outer shell 306 proceeds to move along with the
transport beam 32 in the direction of the scanning heads 22A and
22B. As a second example, the transport beam 32 again reverses
direction to move towards the writing heads 38A and 38B in which
case there is again an interval of time when the outer shell 306 is
momentarily stationary as the transport beam 32 advances toward the
writing head 38A and 38B. The outer shell 306 remains stationary
until the striker plate 318 moves the distance of six millimeters
whereupon it strikes the cover plate 308 at which time the outer
shell 306 commences to move along in unison with the transport beam
32. The effect of the six millimeter backlash distance in
counteracting a scalloping effect will become apparent in the
description of the scalloping as will now be described with
reference to FIG. 10.
Referring now to FIG. 10 there is shown a diagrammatic
representation of a simplified view of the imaging system 20 which
is shown comprising a scanning head 22A, the backlash linkage 40
and a writing head 38A with a tapper 230, the scanning head 22A
being shown mechanically connected to the backlash linkage 40 by
means of a rigid connection representing the transport beam 32. For
simplicity the C-frame 28 and the rachet arm 26A of FIG. 1 have
been deleted. The imaging system 20 is shown forming an image on
the paper copy 42 in response to a test pattern 334 painted by way
of example with radioactive paint on a film 336 which is positioned
beneath the scanning head 22A. As the scanning head 22A moves in
both the X and Y directions, the tapper 230 provides a series of
image marks 338 which correspond to the paint marks 340 of the test
pattern 334. The arrows 342A and 342B trace the direction of
movement of the scanning heads 22A and the tapper 230. Assuming,
for the moment, that the backlash linkage 40 has been disabled, it
is observed that while the paint marks 340 of the test pattern 334
are arranged in regular rows and columns, the series of image marks
338 are also arranged in regular rows; however, the columns of the
series of image marks 338 have an irregular shape corresponding to
the well known scalloping effect. By way of example, the
displacement of the image marks 338 from their true columnar
positions is presumed to be 6 millimeters. The backlash linkage 40
is now presumed to be adjusted to provide 6 millimeters of backlash
distance whereupon the scalloping effect disappears.
The scalloping effect may be explained as follows. Recalling the
description of the data processor 114 with reference to FIG. 5, the
data provided along line 210 seen also in FIG. 3 is updated at the
repetition frequency of the reset pulse on line 188 from clock 184.
Or, equivalently, the data on line 210 is updated once during each
four millimeter scanning interval in the X direction. Now, with
reference to FIG. 10, is readily appreciated that each of the image
marks 338 may be delayed from its corresponding paint mark 340 by a
distance of up to six millimeters. Thus, when the transport beam 32
reverses direction the first image mark 338 to be placed in the new
row is offset by 6 millimeters, and similarly the remaining image
points 338 in that row are offset by the 6 millimeter distance. The
scalloping effect is cured with the aid of the backlash linkage 40
since on a reversal of direction of motion of the transport beam 32
the writing head 38A remains stationary until the scanning head 22A
and the transport beam 32 have advanced 6 millimeters in the X
direction whereupon the tapper 230 imprints an image mark 338 in
the correct columnar position.
Referring now to FIG. 11 there is shown a detailed isometric view
of the photohead 50 and a carriage 350 with portions of the figure
shown in section. Photohead 52 is identical to photohead 50 and is,
therefore, not shown in the figure. The photohead 50 is suspended
from the carriage 350 by means of a bracket 352 affixed to a
transport plate 354 which forms a part of the carriage 350. The
carriage 350 further comprises a pair of support rods 356 and 358,
by which the transport plate 354 is slidably supported in the X
direction, a roller assembly 360 and a roller assembly 362 affixed
to the ends of the support rods 356 and 358. Roller assemblies 360
and 362 comprise respectively concave surfaced rollers 364 and flat
surfaced rollers 366 for supporting the carriage 350 on rails 368
and 370 to provide motion in the Y direction. The concave surfaces
of the rollers 364 serve to position the carriage 350 on the rails
368 and 370.
The photohead 50 comprises an electronic flash lamp 372 which
flashes in response to an electric signal from the photohead driver
122A transmitted along electrical conductors 374. A lens 376
supported in spaced relationship to the flash lamp 372 by support
378 focuses light from the flash lamp 372 upon film plate 54 within
the cassette 58. An aperture plate 380 having a plurality of
apertures, such as aperture 381, of differing shapes is positioned
between the flash lamp 372 and the lens 376 to provide a desired
shape to the spot of light impinging upon the film plate 54. An
aperture is selected as follows. A motor 382 positioned within the
support 378 rotates the aperture plate 380 about shaft 384 via a
step down gear train 386 to position the desired aperture in front
of the flash lamp 372. A plurality of microswitches 388 positioned
on top of support 378 have arms 390 which engage cams 392 for
actuation of an individual one of the microswitches 388
corresponding to a desired aperture for deenergizing the motor 382
when the desired aperture is in position.
The carriage 350 is positioned in the X direction by means of push
rod 44, seen also in FIGS. 1 and 8, which engages the carriage 350
by means of a backlash linkage 394, the backlash linkage 394 being
provided to counteract the scalloping effect described earlier with
reference to FIGS. 9 and 10. The backlash linkage 394 comprises a
striker 396 slidably mounted within the transport plate 354 and
affixed to the push rod 44 which is slidably extended through end
portions 398A and 398B of the transport plate 354. A small amount
of friction is provided between the transport plate 354 and the
support rod 356, as for example, by means of a spring assembly 400,
indicated diagrammatically, which exerts a slight pressure upon the
support rod 356. In operation, the push rod 44, in response to
motion of the hanger 278, the transport beam 32 and the carriage 34
of FIG. 8, moves the carriage 350 in both the X and the Y direction
in precise synchronism with the motion of the writing heads 38A and
38B of FIG. 1. Upon reversal of motion in the X direction by push
rod 44, the transport plate 354 remains stationary momentarily
until the striker 396 has advanced a distance sufficient to
counteract the scalloping effect, as was explained with reference
to FIGS. 9 and 10, whereupon the striker 396 strikes the transport
plate 354 for resumption of motion of the transport plate 354. To
facilitate movement of the carriage 350 in the X direction, the
push rod 44 passes through the roller assembly 360, seen also in
FIG. 8, and slidably contacts the roller assembly 360 for urging it
in the X direction.
Referring now to FIG. 12 there is shown a block diagram of the
writing head driver 120A and the data enhancement circuit 118A
which is interconnected with the writing head driver 120A. The
writing head driver 120A accepts a signal from the channel selector
116 as shown in FIGS. 3 and 6, the input signal having an amplitude
proportional to the number of photons counted in a predetermined
interval as described earlier with reference to the description of
the data processor 114 of FIG. 5. The input signal is applied via a
variable gain amplifier 410 and switch 412 to a variable frequency
pulse generator 414 which is responsive to the amplitude of the
signal provided by the variable gain amplifier 410. The pulse
generator 414 provides a sequence of electrical pulses for
energizing the solenoid 232 of the writing head 38A, the sequence
of electrical pulses occurring at a pulse repetition frequency
linearly related to the amplitude of the signal provided by the
variable gain amplifier 410. Thus, the solenoid 232 drives the
tapper 230 of the writing head 38A with a repetition frequency, or
tapping rate, linearly related to the amplitude of the signal from
the channel selector 116. This linear relationship is dependent on
the scaling factor of the variable gain amplifier 410 as is set by
a knob 416 labled "density control" connecting with the variable
gain amplifier 410 and located on the housing 36 of FIG. 1. The
density control knob 416 is utilized to establish the spacing
between contiguous marks on the paper copy 42 of FIG. 10.
In an alternative mode of operation the switch 412 is operated to
connect the pulse generator 414 to a voltage source 418 which
provides a constant input voltage to the pulse generator 414 so
that the marks on the paper copy 42 of FIG. 10 are uniformly
spaced; this mode of operation is frequently useful when data is
presented in color on the paper copy 42.
An additional feature is provided by means of a comparator 420 and
a lamp 421 which indicates when the tapping rate provided by the
solenoid 232 becomes excessively high. The comparator 420 compares
the output voltage of the variable gain amplifier 410 to a
reference voltage on line 422 provided by a suitable source of
voltage (not shown). When the output voltage of the variable gain
amplifier 410 is greater than the reference voltage on line 422,
thus indicating that the pulse repetition frequency of the pulse
train provided by the pulse generator 414 exceeds the frequency
response of the solenoid 232 and the tapper 230. The comparator 420
provides an output voltage which energizes the lamp 421, located on
the housing 36, thereby providing an indication of the excessive
tapper repetition frequency.
The stepping motor 256 which positions the ribbon 240 described
earlier with reference to FIG. 7, is energized from the signal
provided by the channel selector 116 via the color data enhancement
circuit 118A and a color circuit 423 which comprises a pair of
comparators 424 and 426, a pair of gates 428 and 430, and a
feedback loop comprising the potentiometer 253 described with
reference to FIG. 7 and a difference amplifier 432. The input
signal is modified by the data enhancement circuit 118A to provide
an enhanced signal on line 434 in a manner to be described. The
stepping motors 256 is energized in the following manner: to
provide both clockwise and counterclockwise rotation. A pulse
generator 436 provides pulses to the windings of the stepping motor
256. The stepping motor 256 has a pair of windings, indicated
diagrammatically, for producing either clockwise or
counterclockwise rotation, the clockwise winding 438 and the
counterclockwise winding 440 being shown diagrammatically. The
clockwise winding 438 is energized with pulses from the pulse
generator 436 via the gate 428; and the counterclockwise winding
440 is energized with pulses from the pulse generator 436 by the
gate 430. As described earlier with reference to FIG. 7, the
voltage provided by the potentiometer 253 represents the position
of the plate 250 and ribbon 240 as well as the color of the ink
being utilized by the tapper 230. The desired color is represented
by the value of the voltage of the enhanced signal on line 434. The
difference amplifier 432 provides a signal representing the
difference of these two voltages. When the signal provided by the
difference amplifier 432 is greater than a reference 442 supplied
by a suitable voltage source (not shown) and applied to the
comparator 424, the comparator 424 provides a signal which enables
the gate 428 thereby passing pulses from the pulse generator 436 to
energize the clockwise winding 438. When the signals provided by
the difference amplifier 432 has a value of voltage lower than the
voltage of a reference 446 applied to the comparator 426, the
comparator 426 provides a signal which enables the gate 430 thereby
permitting pulses from the pulse generator 436 to energize the
counterclockwise winding 440. And, when the value of the voltage of
the signals provided by the difference amplifier 432 is less than
the voltage of the reference 442 and greater than the voltage of
the reference 446 then neither gate 428 or gate 430 is enabled and
the stepping motor 256 is deenergized and is not rotating. Thus,
the stepping motor 256 is able to provide the desired colors as
requested by the enhanced signal on line 434 to provide a colored
radiograph on the paper copy 42 of FIG. 1.
The data enhancement circuit 118A and the data enhancement circuit
118B, seen in FIG. 3, operate in the same fashion, and therefore,
the data enhancement circuit 118B is not shown in FIG. 12. The data
enhancement circuit 118A increases the responsivity of the color
drive circuit 423 to a preselected range of colors while decreasing
the responsivity of the color drive circuit 423 to other
preselected colors. This is in contradistinction to the signal
provided by the channel selector 116 which induces a uniform
responsivity of the color drive circuit 423 to the various colors.
The variation and responsivity occurs by virtue of the enhanced
signal on line 434. For example, in the absence of the data
enhancement circuit 118A there is a linear relationship between the
color selected and the amplitude of the signal provided by the
channel selector 116. Again, by way of example, it may be desirable
to emphasize those areas of a radiograph corresponding to high
intensity radiation which might be represented by warm colors such
as red, orange and yellow. In this case, the voltage of the
enhanced signal on line 434 would be of a relatively low value even
when the voltage of the signal provided by the channel selector 116
has risen to a moderately high value, but as the voltage provided
by the channel selector 116 rises to a higher value then the
voltage of the enhanced signal on line 434 would be observed to
rise sharply with the result that the colored radiograph provided
on the paper copy 42 of FIG. 1 would have cooler colors such as
green, blue, purple over most of the radiograph with the warmer
colors, red, orange and yellow appearing only at those spots
corresponding to high intensity radiation, thereby emphasizing
these spots of high intensity radiation.
To data enhancement circuit 118A comprises a series of comparators
of which three are shown in the drawing, the three comparators
being designated 448A, 448B and 448C. Each of these comparators
448A - C are provided with separate reference signals having
different values of voltage, three such reference signals being
shown in the Figure designated at 450A-C. The comparators 448A-C
provide output signals when their input signals on lines designated
respectively by 452A-C are greater than the voltages of the
respective reference signals 450A-C. The output signals of the
comparators 448A-C are summed together in a summing circuit 454 to
provide the enhanced signal.
The desired enhancement characteristic is provided by a plug-in
module hereinafter referred to as a color plug 456 which is located
on the housing 36 of FIG. 1. The color plug 456 comprises a series
of resistors 458A-C which function as a voltage divider of the
voltage provided by the channel selector 116, the values of the
various voltages obtained on the lines 452A-C depending on the
values of the various resistors such as the resistors 458A-C. Thus,
the use of the color plug 456 in combination with the comparators
448A-C and the summing circuit 454 provides the desired enhancement
characteristic to the signal of the channel selector 116 thereby
providing the desired responsivity of the color drive circuit 423
to the color command represented by the voltage value of the signal
of the channel selector 116.
Referring now to FIG. 13 there is shown a diagrammatic
representation of the photohead driver 122A, seen in FIG. 3, which
energizes the flash lamp 372 of FIG. 11. The circuit of the
photohead driver 122B of FIG. 3 is the same as that of 122A and is,
accordingly, not shown in FIG. 13. The flash tube 372 is of a well
known form comprising an anode 468, a cathode 470 and a grid 472. A
pulse generator 474 applies voltage pulses between the terminals of
the grid 472 and the cathode 470 to gate the flash tube 372 ON and
OFF. Light rays 476 are emitted when the flash tube 372 is gated on
by the pulse generator 474. The intensity of the light rays 476 is
dependent on the voltage impressed between the terminals of the
anode 468 and the cathode 470 by means of a variable gain amplifier
478. The gain of the amplifier 478 is varied by means of a knob 480
located on the housing 36 of FIG. 1 and connecting with the
variable gain amplifier 478.
The photohead driver 122A is responsive to the signal provided by
the channel selector 116 via switch 206 as indicated in FIG. 6, in
that the signal is applied to the variable gain amplifier 478 which
acts as a scaling factor to provide a voltage for energizing a
flash tube 372 which is linearly related to the amplitude of the
voltage provided by the channel selector 116. The photohead driver
122A is furthermore responsive to the signal from the channel
selector 116 in that the signal is applied to a summing circuit 482
and thereby combined with a second signal on line 484 to provide an
output voltage which is applied to the pulse generator 474. The
pulse repetition frequency of the pulse generator 474 is linearly
related to the voltage provided by the summing circuit 482 wo that
an increase in the signal voltage provided by the channel selector
116 results in an increase in the pulse repetition frequency of the
pulse generator 474 with a corresponding increase in the rate of
flashing of the light rays 476 of the flash tube 372.
The photohead driver 122A is also responsive to the scanning speed
of the transport beam 32 such that with increased scanning speeds
the flashing repetition frequency of the flash lamp 372 is
increased to provide an image density on the film plate 54 of FIG.
11 which is invariant with scanning speed. Since the flashing rate
of the flash tube 372 is sufficiently great such that the light
from the various flashes overlap on the film plate 54, as seen in
FIG. 11, a varying of the flash rate with the scanning speed
ensures an image density which is invariant with scanning speed.
Accordingly, a potentiometer 486 energized by a voltage source 488
is operated by the speed control knob 192, described with reference
to FIGS. 5 and 15, and generates the signal on line 484 for the
summing circuit 482, thereby providing the desired responsivity of
the photohead driver 122A to the scanning speed. The variable gain
amplifier 478 and the summing circuit 482 constitute the data
enhancement circuit 118C seen also in FIG. 3 and ensure that light
flashes from the flash tube 372 have an intensity and a pulse
repetition frequency dependent on the amplitude of the signal
provided by the channel selector 116.
Referring now to FIG. 14 are shown the locks 64 for the cassettes
58 and 60 of FIG. 1. The locks 64 comprises a bolt 496 slidably
mounted within a guide 498 for engaging channel 500 of the housing
62 seen in FIG. 1. Access to the bolt 496 in the form of a handle
is provided by a pin 502 extending outwardly from the bolt 496
through a slot 504 in the guide 498. The bolt 496 is positioned by
sliding the pin 502 in the slot 504. A slide 506 is provided in the
cassette 58 and 60 for protecting the film plate such as the film
plate 54 of FIG. 11 from light when the cassette is extracted from
the housing 62. The width of the slide 506 is such that the edge of
the slide clears the guide 498 of a cassette such as cassette 58
when the slide is removed from the cassette 58. However, when the
bolt 496 extends beyond this end of the guide 498 is catches the
edge of the slide 506 thereby preventing accidental removal of the
slide 506. Thus, the lock 64 provides a novel arrangement wherein
it secures the cassette 58 to the housing 62 of FIG. 1 or,
alternatively, releases the cassette 58 from the housing 62 while
engaging the slide 506. The front lip 508 of the slide 506 serves
as a handle for extracting the cassette 58 from the housing 62.
Referring now to FIG. 15 there is shown a schematic diagram of the
circuitry for energizing the motor 292 and 304 of FIG. 8 which
provide respectively movement of the transport beam 32 in the X
direction and movement of the carriage 34 in the Y direction. The
motor 292 is energized from a source of power 516 (shown
symbolically as a battery) supplied via a variable gain amplifier
518, a power-on switch 520 and a relay 522. The relay 522 is
energized from a source of power 524 via microswitches 526 and 528
and a set of contacts 530 of the relay 522 itself.
Returning momentarily to FIG. 8 the microswitches 526 and 528 are
seen located respectively on the front plate 260 and the back plate
262 of the carriage 34. The microswitches 526 and 528 are utilized
to initiate and to terminate the movements of the transport beam 32
in the X direction. A pair of scales 532 and 534 are mounted on the
transport beam 32. A pair of knobs 536 and 538 are slidably mounted
respectively on the scales 532 and 534 for setting the extreme
points of the scanning movement of the transport beam 32. The knob
536 serves as a cam for actuating the microswitch 526 when the knob
536 passes by the front plate 260. The knob 538 serves as a cam for
actuating the microswitch 528 as the knob 538 passes by the back
plate 262. Actuation of the microswitches 526 and 528 causes the
motor 292 to reverse direction as is shown on FIG. 15.
Returning now to FIG. 15 the relay 522 is shown deenergized and the
motor 292 is energized via the two sets of relay contacts 540 and
542. The motor 292 drives the transport beam 32 from the back plate
262 towards the front plate 260 in the manner described with
reference to FIG. 8. This movement of the transport beam 32
continues until the knob 538 actuates the microswitch 528 on the
back plate 262. As shown in FIG. 15 actuation of the microswitch
528 closes the circuit containing the source of power 524 thereby
energizing the relay 522 with the result that the motor 292 is
energized through another set of relay contacts 544 and 546 with
the result that electric current enters the winding (not shown) of
the motor 292 in the reverse direction thereby reversing the motor
direction of rotation. The motor may have by way of example, a
permanent magnet stator, and a rotor which is energized through a
commutator by an external current such that reversal of this
current, as in the case of the motor 292, results in a reversal of
the direction of rotation. Energization of the relay 522 also
closes the set of relay contacts 530 providing a second path of
energization of the relay with power from the source of power 524
via the microswitch 526. The reversed direction of the motor 292
now drives the transport beam 32 of FIG. 8 from the front plate 260
towards the back plate 262 so that the knob 538 is no longer
engaging the microswitch 528 with the result that the microswitch
528 opens one of the circuits energizing the relay 523. However,
the relay 522 remains energized via the microswitch 526. The
movement of the transport beam 32 continues until the knob 536
actuates the microswitch 526 on the front plate 260 thereby
breaking the circuit for energizing the relay 522. Thus, the relay
522 becomes deenergized and assumes the contact position shown in
FIG. 15. Accordingly, the motor 292 reverses direction such that
the transport beam 32 is again traveling in a direction from the
back plate 262 towards the front plate 260 thereby completing the
cycle in the X direction.
The motor 304 is energized by a source of power 556 via the
power-on switch 520, two sets of relay contacts 558 and 560 of
relay 562, and by the parallel combination of microswitches 526 and
528 and the relay 564. The relay 562 is energized from a source of
power 566 via a first circuit including microswitch 568 and a
second circuit including microswitch 570 and a set of contacts 572
of the relay 562 itself. It is noted that the motor 304 remains
deenergized until such time as either the microswitch 526 or
microswitch 528 is actuated. Thus, during a scanning movement of
the transport beam 32 the motor 304 is deenergized and the carriage
34 does not move in the Y direction. However, at the conclusion of
a single scan in the X direction when the transport beam 32
reverses direction, the microswitch 526 or the microswitch 528 is
actuated respectively by the knob 536 or the knob to effect the
reversal of direction of the transport beam 32. At the moment of
actuation of microswitch 526 or 528 the motor 304 is energized and
the carriage 34 is displaced in the Y direction in the manner
described with reference to FIG. 8. Energization of the motor 304
also results in an energization of the relay 564 with the
consequent closing of its set of contacts 574. The closure of the
contacts 574 in circuit with the counter-switch unit 576, seen also
in FIG. 8, retains the state of energization of the motor 304 even
after the microswitches 526 and 528 are no longer actuated by the
knobs 536 and 538. Thus, the motor 304 is able to position the
carriage 34 independently of the length of time that the
microswitches 526 and 528 are actuated.
The motor 304 is deenergized when the carriage 34 has been
displaced or indexed by a preset amount, this amount being set by
the counter-switch unit 576 which as shown in FIG. 8 is located on
the end of worm drive 284 and mounted on the housing 36. The
counter-switch unit 576 comprises a rotary member 578 directly
connected to the worm gear 286, and a stationary member 580
connected to the housing 36. The counter-switch unit 576 counts the
number of rotations of the worm gear 286 and opens its switch when
the prescribed count has been reached. The counter-switch unit 576
is of a well known form and may comprise, for example, a rotary
member 578 having a permanent magnet which actuates reed switches
(not shown) in the stationary member 580, the reed switches being
arranged in a counting circuit. Alternatively, the stationary
member 580 may comprise a magnetic coil pickup which energizes a
digital counter whenever the pickup coil is energized by the magnet
of the rotary member 578. Upon reaching the desired count the
counter-switch unit 576 opens its switch which deenergizes the
relay 564 thereby deenergizing the motor 304 so that the carriage
34 remains stationary at its new position.
When the carriage 34 has reached an extreme position in the Y
direction its motion must then be reversed to bring it back. The
motor reversal circuit for the motor 304 is similar to that
described earlier with reference to the motor 292. A scale 582,
seen in FIG. 8, is mounted to the rear of the housing 36. Two knobs
584 and 586 are slidably mounted on the scale 582 for setting the
extreme points of the indexing motion of the carriage 34. In one
extreme position in the Y direction of the carriage 34, the knob
584 serves as a cam to actuate the microswitch 568; and in the
other extreme position of the carriage 34 in the Y direction, the
knob 586 serves as a cam to actuate the microswitch 570. When the
relay 562 is deenergized, as shown in FIG. 15, the motor 304 being
energized through the sets of contacts 558 and 560 drives the
carriage 34, in the manner as described in FIG. 8, in a direction
towards the knob 584. When the microswitch 568 reaches the knob
584, the knob 584 acts as a cam which actuates the microswitch 568.
The actuation of the microswitch 568 closes the circuit containing
the source of power 566 to energize the relay 562. Upon
energization of the relay 562 the motor 304 receives electric
current through the sets of contacts 588 and 590 of relay 562,
rather than the sets of contacts 558 and 560, with the result that
current is applied in the reverse direction to the motor 304 which
then rotates in the reverse direction. Since the motor 304 is now
rotating in the reverse direction, the carriage 34 is now traveling
in a direction away from the knob 584 and towards the knob 586. The
energization of the relay 562 by the microswitch 568 has also
resulted in a closure of the set of contacts 572 which provides a
second path of energization of the relay 562 by the microswitch
570. Thereby, upon motion of the carriage 34 away from the knob 584
and the deactivation of the microswitch 568 the relay 562 remains
energized. Accordingly, the successive indexing operation of the
carriage 34 are performed with a direction of motion on the
carriage 34 away from the knob 584. The carriage 34 reaches the
other extreme of this motion; the knob 586 activates the
microswitch 570 breaking the second circuit of energization of the
relay 562. The deenergization of the relay 562 reverses the
direction of current to the motor 304 with the result that the
carriage 34 now proceeds to index in the reverse direction towards
the knob 584 thus completing the cycle.
It is understood that the above-described embodiment of the
invention is illustrative only and that modifications thereof will
occur to those skilled in the art. Accordingly, it is desired that
this invention is not to be limited to the embodiment disclosed
herein but is to be limited only as defined by the appended
claims.
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