Note: Descriptions are shown in the official language in which they were submitted.
CA 02111200 1998-06-01
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Electronic high-speed camera
The invention relates to an electronic high-speed camera for
the recording of fastly moved objects, including visualized
events, comprising a plurality of separate semiconductor video
sensors arranged in the imaging beam path of an optical imaging
system and connected to associated image memories.
In a known device for electronic image recording (DE-PS 24 60
625) fastly occuring events as, e.g., the progress of an
elctric arc, are recorded in a front-light mode by means of
optoelectronic semiconductor image converters like photocells,
phototransistors or even photodiodes which are arranged in a
line or in a matrix with several lines behind a lense system
and which are interrogated cyclically one after the other.
Further, high-speed film cameras with rotary drums, mirrors or
prisms are used for the photographic recording of fastly moved
objects, including visualized events (e.g. flows). These have a
drawback in that the photograms cannot be judged and evaluated
but after the exposure of the film. Therefore, a direct
interference in the event in the light of the photograms is not
possible. The entirely electronic Cranz-Schardin camera
according to the Review of Scientific Instruments, Vol 62 No.
2, pp. 364 to 368, Bretthauer et al. "An Electronic Cranz-
Schardin Camera", certainly furnishes an immediately available
sequence of videograms; it is, however, not provided for a
front-light imaging operation. This backlight mode high-speed
camera can be equipped with a plurality of semiconductor video
sensors connected to associated image memories, which sensors
are arranged in a circle around a mirror pyramid, each of the
mirror surfaces thereof being assigned to one of the video
sensors and to one of a plurality of light emitting diodes
arranged in a circle beyond the object to be recorded and being
cyclically pulse-operated one after the other.
However, for a photographic recording of fastly moved objects
and visualized events, especially single or not periodical
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events, a high-speed camera is required which can operate both
in the backlight mode and in the front-light mode dependent on
the kind of the object. - -
The invention is based on the problem to devise an electronic
high-speed camera which operates without wear and which can be
used both in the backlight mode and in the front-light mode
without modification of its optoelectronic recording system.
Preferably, the videograms shall be available i -~;ately
(screen, printer) and shall be suitable as computer file for a
direct electronic evaluation.
The electronic high-speed camera according to the invention in
solving said problem comprises an optoelectronic recording
system with a plurality of separate semiconductor video sensors
connected to associated image memories and an optical imaging
system imaging the im~ge of the object on the video sensors and
comprising a camera objective common to the video sensors and a
mirror pyramid which faces the objective with its pyramid tip
and lies with its axis in the optical axis of the camera
objective. The video sensors are arranged in a circle around -
the optical axis of the objective and the mirror py~
comprises a plurality of mirror surfaces assigned in each case
to one of the video sensors. To each of the ~ideo sensors a
triggerable electronic shutter means is assigned.
This optoelectronic recording system is suitable without
modification for both the front-light mode and the backlight
mode. For the backlight operation an optical backlight system
is arranged in series, the ob~ect being located in the beam
path thereof. Herein, a plurality of lumped flashlight sources
are arranged in a circle before the optical backlight system
which can be imaged through the optical backlight system and
through the camera objective each on one of the mirror
surfaces, the shutter means being synchronized with the
flashlight sources.
In this way, the electronic high-speed camera of the invention
: . .
can be o~erated in two different modes, due to its novel
optical and electronic arrangement. In the backlight mode, the
camera operates according to a modified Cranz-Schardin
principle. The modification lies in that the semiconductor
S video sensors each have not an objective of its own but the
camera has only one camera objective cl -n to all video
sensors each being able to furnish a two-~;~~nciional image
whereby the construction as well as the ad~ustment are
substantially simplified. In the ~ront-light mode in which the
optical backlight system and the flashlight sources are
uncoupled, the beam of rays is simultaneously projected to all
video sensors due to the beam splitting effect of the
objective-mirror ~yl, id arrangement. These video sensors are
activated cyclically one after the other by their shutter
electronics in such a way that thereby an image sequence
results which can be stored in the image memories, which can be
combined in an image memory unit with respective several image
memory inputs, and can be processed in a preferably connected
image processor.
The flashlight sources can, e.g., be spark light sources, they
are, however preferably pulse operated light emitting idiodes or
laser diodes which especially emit visible light. The
flashlight sources can be synchronized with the image memories.
The video sensors, each designed as a detector matrix, are
preferably synchronized with eachother and with the image
memories. The shutter means are preferably asynchronously
triggerable and synchronized with the image memories. For very
short shutter intervals, the shutter means can be designed as
image intensifier placed in front of the video sensors.
Preferably, a freely proyl~ ~hle sequenzer, controlling the
shutter means, the image memories and in a given case the
flashlight sourceB i6 connected thereto for optimal conditions
and interference possibilities. Preferahly, eight video sensors
are provided; however, also fewer or more video sensors can be
used.
The advantages reached by the invention consist especially in
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that, with a relatively simple construction, one can produce
high-speed backlight videograms and high-speed front-light
videograms. Further, the camera allows an on-line observation
in both modes. The recorded images can, with a respective
layout of the camera, electronically be stored, transferred,
evaluated, processed and ; -~;ately be printed. The camera is
not subjected to ~ch~n; cal wear (has no movable parts) and has
no consumption of materials (no film, developer and so on).
10 The invention is illustrated by means of embodiments being -
obvious from the drawings at least schematic.
The figures 1 and 2 show two embodiments of the optoelectronic
recording system of an electronic high-speed camera according
lS to the invention. Figs. 3 and 4 show the structure of the
camera in the bac~light mode (fig. 3) and in the front-light
mode (fig. 4). Fig. 5 indicates the electronic circuit diagram
of the high-speed camera according to the invention.
20 The optoelectronic recoxding system of the high-speed camera of --
fig. 1 has a nearly potshaped casing with a camera ob~ctive 3, ;
; behind which in the casing a mirror pyramid 1 is disposed
coaxially with respect to the objective 3, the pyramid tip
thereof facing the objective 3 and the mirror surfaces thereof
deflecting the optical rays to the video sensors 2 arranged on
a circle around this mirror pyramid with the center of the -
circle on the axis of the mirror pyramid 1, the video sensors
being perpendicularly aligned to the axis thereof. The number
of the mirror surfaces of the mirror pyramid 1 coincides with
the number of the video sensors. Half of the aperture angle of
the thought cone comprising the side edges of the mirror
pyramid 1 amounts preferably to 45~. The deflection of the beam
path causes a tilting and a reflection of the images. In order
to compensate for the tilting, the sensors are turned around ;
their own optical a~es each by an angle of 360~ per number of
the sensors. The reflection of the images can be retransformed
by hardware (e.g. by reversely reading out of the image lines)
or by software by means of the image processor. However, the
--~ f . ~ .L ~
tilting and the reflection can also be avoided in an optical
way by a double deflection of the beam path. Fig. 2 shows a
variant of the optoelectronic recording system 1, 2 and 3 in
which the rays deflected by the side surfaces of the mirror
pyL~ i d 1 are deflected again by the additional mirrors 12
which are arranged inclined by 45~ with respect to the optical
axis according to fig. 2. The number of these mirrors 12
coincides with the number of sensors as well. In this variant,
the video sensors are preferably arranged in such a way, that
their active surfaces are lying in a plane perpendicular to the
optical axis of the camera, which is the case in fig. 2,
according to which the sensors 2 are arranged at the bottom of
the casing in a circle and are aligned with the mirrors 12 in
parallel with the optical axis.
The video sensors 1 each comprise electronic shutter means 7
(fig. 5), the shutter interval of which preferably is very
short. These shutter means operate asynchronous, i.e. an image
is ; ~iately recorded after appearance of an external trigger
signal and is distributed. The image is then stored in an image
memory 8, to which an image processor is connected. The number
of the image memory inputs (channels) corresponds to the number
of sensors 2. The shutter means 7 of the sensors 2 and of the
image memories 8 are triggered by a sequencer 11. This
sequencer 11 generates a series of pulses after an electrical
or manuell start signal and a trigger signal of the object. The
number, the ch~nnel number and the spacing between the pulses
can be freely programmable.
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This pulse sequence must often be synchronized with the object
(event) to be videographed. In case of an object the function
of which can be triggered or synchronized by an electrical
signal, it is triggered or synchronized by a trigger signal
generated by the sequencer 11. In the other cases a trigger
signal is derived from the object and is delivered to the
sequencer 11.
The camera operates in two modes: in the backlight mode (fig.
.9
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3) it operates according to the Cranz-Schardin principle
(Zeitschrift fur Physik 56 (1929), pages 147-183). This
principle, however, was modified by another optical
arrangement. The modification lies in that the camera comprises
an objective 3 common to all video sensors whereby both, the
construction and the adjustment are substantially simplified.
In this arrangement, the light is generated by pulse-operated
flashlight point sources 4. Preferred as light sources are high
efficiency LEDs. These LEDs can be coupled to photoconductors
and can electrically directly (without conducting cable) be
connected tc the pulse amplifier 10 (fig. 5). Thereby, a
favourable shape of the light output with a small diameter is
obtained and the emitted light becomes substantially uniformer.
Further, the distortion of the electrical control pulses is
avoided which can be caused b~ the unmatching of the diode
cable. The light sources, the number of which coincides with
that of the video sensors 2 (e.g. eight), are arranged on a
common circle, the center of which is lying in the axis of the
optical system, and are aligned in parallel with the axis of
the optical system. They mostly are at the focus distance of
the first lense 5a of the optical backlight system 5. The ~;
object to be videographed is situated in the parallel beam of
light resulting thereby. After passage through and around the
object, the light is prefocussed by the second lense 5b of the
optical system 5. Thereby, the light is collected in the camera
objective 3 and the light losses are reduced. The distance
between the mirror pyramid 1 and the camera objective 3 is
selected such that the light sources are sharpl~ imaged on the
respectively corresponding mirror surface of the mirror pyramid
1. As this is the narrowest spot of the beam path, the images
are optimum separated from each other by the mirror pyramid 1.
The photoactive faces of the video sensors are lying in
tangential planes of a circle the radius of which is preferably
selected such that the sum of the radius and of the dis~ance
between the objective 3 and the tip of the mirror pyramid 1 is
equal to the distance of the image plane from the objective.
Thereby, a sharp image of the object on the respective sensor
is ensured.
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After ~he starting pulse and, depen~nt on the kind of the
object, after initiating the event by the object trigger signal
generated by the sequencer 11 or after an object trigger signal
given to the sequencer from the object, a sequential lighting
of the light sources, controlled by the sequencer 11, occurs.
The lighting of each light source corresponds to the imaging of
the object on the video sensor assigned to this light source.
In this way, an image sequence results on the video sensors 2
which is taken over by the image -,~y 8 due to the image
memory trigger signal, subsequently generated by the sequencer,
and is stored. If also the shu~ter means 7 of the video
sensors 2 are triggered by the sequencer in synchronism with
the lighting of the light sources, the dynamics and the
signal/noise ratio of the stored images are substantially
increased. This is preferably used if the exposures must be
performed in the presence of stray light (e.g. daylight). In
this case, the outside light will affect the image oniy during
the active shutter interval (e.g. 0.1 ms) and not during the
whole integration interval ~40 ms at CCIR standards).
The ~ framing rate of the camera in the backlight mode
depends on the -~1 flash succession frequency of the light
sources. The flash succession frequency obtainable at the
present time with the V-MOS-controlled light emitting diodes is
about 10 NHz. When using laser light sources, substantially
higher framing rates can be obtained.
In the front-light mode (fig. 4) the object 6 is sLmultaneously
imaged on all video sensors 2, due to the beam-splitting effect
of the mirror pyramid. The optical, mechanical and electrical
arrangement of the optoelectronic recording system 1, 2, 3 of
the camera according to fig. 1 and 2, respectively, ~ ~in~
unchanged. After the starting pulse and depending on the kind
of the object after initiating the event by the object trigger
signal generated by the sequencer or after a object trigger
signal given to the sequencer from the object, a seguential
activation of the shutter means 7 of the video sensors occurs,
controlled by the sequencer 11. The image sequence obtAine~ in
3 ~
8 : :
this way is taken over by the image memory 8 and is stored due ~.
$o the trigger signal subsequently generated by the sequencer
11 .
The ~-~i framing rate of the camera in the front-light mode
is dependent on the ~i n 1 shutter interval of the video
sensors 2. The shortest shutter interval obtainable at the :
present time is abol-t 0.1 ms correspo~ing to a maximum framing ~-
rate of 10 kHz (without temporary overlapping). At short
shutter intervals, the ob~ect must be illuminated to a greater
extent. Substantially higher f. ing rates without
proportionally increased illumination can, however, be realized
by a layout of each of the video sensors 2 with an image
intensifier taking charge of the shut$er function.
