JPH07119892B2 - Electronic endoscope - Google Patents

Description

TECHNICAL FIELD The present invention relates to a so-called electronic endoscope including a solid-state image sensor in a tip rigid portion.

[Conventional technology]

Generally, in an image pickup apparatus using a solid-state image pickup element as an image pickup means, the resolution is determined by the number of picture elements of the image pickup element. However, if the area of one picture element is too small, the sensitivity of the whole element is lowered and Due to problems, it is difficult to increase the number of picture elements unnecessarily. In particular, when it is used in an extremely limited space inside the tip portion of an endoscope such as an electronic endoscope, the size of the entire image sensor has to be made very small, and it is more and more difficult to increase the number of picture elements. is there.
Therefore, how to improve the resolution in an electronic endoscope is an important issue.

As a means for increasing the resolution of the image pickup system, for example, Japanese Patent Publication Sho 56
As in the device described in Japanese Patent Application Laid-Open No. 40546, referred to as a pixel shift method, etc., a plurality of image pickup elements are arranged in a plane perpendicular to the optical axis of the imaging lens in a pitch of 1/2 pitch of the pixel with respect to the optical axis. , 1/3 pitch, etc. are arranged so as to be offset from each other, and the relative positions of the images in one pixel array and the other pixel array are different from each other. It is known that information of a portion corresponding to a position is obtained by the other image pickup element to improve the resolution.

[Problems to be solved by the invention]

However, in the endoscope, first of all, it is space-wise to dispose a plurality of solid-state image pickup devices, a beam splitter for guiding light to these solid-state image pickup devices, and the like in the rigid tip portion. Further, in this method, it is necessary to dispose a plurality of image pickup elements relatively in advance in order to set the image shift amount to a predetermined value. However, alignment accuracy for that purpose is required, and the image pickup system is assembled. There is a problem of making it troublesome.

An object of the present invention is to provide an electronic endoscope capable of increasing the resolution and being easy to assemble an optical system.

[Means and Actions for Solving Problems]

In the electronic endoscope according to the present invention, the imaging optical system includes an objective lens, a solid-state image sensor, and a prism system arranged in the optical path from the front lens of the objective lens or the cover glass to the solid-state image sensor. It is equipped with The prism system includes at least two adjacent prisms, one of which is an exit surface and the other of which is an entrance surface, both of which are surfaces inclined with respect to the optical axis. At least one is movable along the optical axis.

With this configuration, when the prism moves and the distance between the two prisms changes, the difference between the height of the light beam emitted from the one prism and the height of the light beam incident on the other prism changes accordingly, and the imaging The position of the image on the surface changes. Therefore, if the prism is oscillated back and forth at a desired cycle and images are taken near the + side maximum point and − side maximum point of the vibration, 2K times the vibration amplitude (K is a coefficient unique to the prism system). This is the same as arranging the image pickup elements by shifting by a distance equal to. Therefore, if the amplitude is appropriately determined according to the picture element interval, an image signal corresponding to the picture element and the portion between the picture elements can be obtained, and by appropriately combining these, a high-resolution image can be obtained. At that time, since the amplitude of the vibration may be adjusted after the assembly, there is an advantage that a troublesome work such as a case where the plurality of image pickup elements are displaced and attached is not required.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment.

FIG. 1 is a diagram showing a configuration of an electronic endoscope of a system in which R, G, B lights are sequentially irradiated as a first embodiment of the electronic endoscope of the present invention, and FIG. 2 is a timing chart for explaining its operation. Is.

In FIG. 1, reference numeral 1 indicates an endoscope tip portion,
An objective lens 2 (a front telecentric optical system with well-corrected chromatic aberration) and an illumination lens 3 are arranged in parallel at the tip thereof, and a line transfer type solid-state imaging device 4 is installed behind the objective lens 2. The received optical image is converted into a video signal V by the solid-state imaging device drive circuit 5, and the video signal V is sent to the next stage circuit via the preamplifier 6. Further, a vibrating prism system 30 and a liquid crystal shutter 31 are arranged between the objective lens 2 and the solid-state image sensor 4, and the image of the object is perpendicular to the optical axis on the light-receiving surface of the solid-state image sensor 4 as described later. It is designed to vibrate in any direction (Fig. 3). A light guide 7 such as an optical fiber bundle is disposed behind the illumination lens 3, and illumination light is emitted to the rear end face thereof with a rotary filter 8 interposed. Illumination light is emitted from the light source lamp 9 through the lens 10 onto the rotary filter 8, and this illumination light is alternately arranged on the filter 8 with an appropriate light shielding period as shown in FIG. The light is incident on the end face of the light guide 7 through the G (green) and B (blue) filters 8a, 8b and 8c. The rotary shaft of the rotary filter 8 is connected to a motor 14 via a transmission system 13, and a motor drive circuit 16 is controlled by a signal from a rotation detection element 15 provided in the motor 14 to keep the rotational speed of the motor 14 constant. ing. Further, a rotation detecting element 11 is provided on the outer peripheral portion of the rotary filter 8 so as to synchronize the reading from the solid-state image pickup device 4 and the rotation of the rotary filter 8.
On the other hand, the video signal V from the preamplifier 6 is further amplified.
After being amplified through 17, it is input to the multiplexer unit 18. The multiplexer section 18 is composed of three switches corresponding to the input R, G, B signals, and these switches are gate signals SG ₁ and SG for each switch from the synchronization signal generator 19.
₂ and SG ₃ are switched in sequence at a predetermined frame cycle to R,
A video signal corresponding to each color is supplied to each of the G and B frame memories 20, 21, and 22 via an A / D converter. Then, each color signal accumulated in each frame memory 20, 21, 22 is read out by the action of the synchronizing signal generator 19, and the respective delay circuits 23, 24,
After being passed through 25, they are further combined through mixers 26, 27 and 28 and a D / A converter, respectively, and are displayed in color on a color TV monitor 29.

In the above, the rotation detecting element 11 detects the intermediate position and the end position of the R, G, B filters arranged in the rotation filter 8 in the rotation direction thereof, and outputs the detection pulse Pr to the synchronization signal generator 19. send. Then, in the synchronization signal generator 19, the piezoelectric element actuator drive circuit 32 is controlled using the detection pulse Pr, and one prism of the vibrating prism system 30 is vibrated along the optical axis by the piezoelectric element actuator 33, whereby solid-state imaging is performed. The image of the object is vibrated on the light receiving surface of the element 4 in the direction perpendicular to the optical axis (FIG. 2).

FIG. 3 is a diagram showing the principle, but as shown in the figure, when the light beam is emitted from the fixed prism 30a of the vibrating prism system 30, it is refracted upward at its exit surface, and when it enters the vibrating prism 30b, its incidence The light is refracted again on the surface, becomes parallel to the original light, and is emitted from the vibration prism 30b. Because of this refraction,
When the distance between the two prisms 30a and 30b changes, the difference between the height of the incident light ray and the height of the emitted light ray of the prism system 30 changes. The amplitude of vibration of the actuator 33 is Δx, the refractive index of both prisms is n, the inclination angle of the exit surface of the fixed prism 30a (= the inclination angle of the entrance surface of the oscillation prism 30b) is θ, and the exit angle of the fixed prism 30a is θ ′. Then, the amplitude Δy of the optical axis emitted from the prism system 30 (amplitude of the image on the light receiving surface of the solid-state image sensor 4) is Given in. Therefore, the size of the piezoelectric element actuator 33 and the prisms 30a and 30b are adjusted so that Δy becomes a desired value.
It suffices to determine the refractive index of and the inclination angle of the surface. In the case of this embodiment, Δy is 1/4 of the pixel pitch of the solid-state image sensor 4.
Is.

Further, the synchronizing signal generator 19 creates a read clock signal CKr using the detection pulse Pr (FIG. 2) and controls the drive circuit 5 to store the charges accumulated in the solid-state image pickup device 4 for each of R, G and B. To the video signal V. In this case, it is only necessary to obtain an image signal representing the object image at the peaks and troughs of the vibration of the image, so that the peaks and troughs of the vibration fall within the accumulation time of the solid-state image sensor 4 as shown in FIG. The operation of the vibrating prism system 30 and the operation of the solid-state image sensor 4 are synchronized so that the read time from the solid-state image sensor 4 comes. That is, regarding the timing of the rotation of the rotary filter 8, the vibration of the image, and the imaging / reading, the accumulation time is within the time when the filter of one color of the rotary filter 8 is between the light guide 7 and the lens 10. The second read time and the first read time are synchronized with the middle part of the filter, and the second read time is synchronized with the light shielding part between the filter and another filter.

Further, the synchronization signal generator 19 controls the liquid crystal shutter drive circuit 34 using the detection pulse Pr to drive the liquid crystal shutter 31.
The liquid crystal shutter 31 is provided as an auxiliary and has the following role. As shown in FIG. 2, when the accumulation time is long, the image moves on the light receiving surface of the solid-state image sensor 4, so that the image signal obtained from the solid-state image sensor 4 stops at the peaks or troughs of vibration. Including components corresponding to other than the state,
When reproduced as it is, the image may appear slightly blurred. In order to avoid this, light should be incident on the solid-state imaging device 4 only when the image is very close to the peak or the bottom of the vibration. Therefore, if the liquid crystal shutter 31 is made to perform the transmission / shielding operation at the timing shown in FIG. 2, this is realized and the purity of the image signal is improved.

Further, the synchronization signal generator 19 uses the detection pulse Pr to generate the above-mentioned switch gate signals SG ₁ , SG ₂ and SG ₃ (second
(Fig.) The multiplexer section 18 is switched to input a video signal to each frame memory 20, 21, 22 for each R, G, B.

The frame memories 20, 21, 22 corresponding to R, G, B are respectively composed of two parts R ₁ , R ₂ ; G ₁ , G ₂ ; B ₁ , B ₂ and one part R ₁ , G ₁ , B ₁
The delay circuits 23, 24 and 25 are respectively connected to the. The delays of the delay circuits 23, 24 and 25 are all equivalent to 1/2 pitch of the picture element.

Since the electronic endoscope according to the present invention is configured as described above, while the object is illuminated with each color of R, G, B, reading from the solid-state image sensor 4 is performed twice each. And
For example, the image signal accumulated in the accumulation time A of FIG. 2 is stored in R ₁ of the memory 20, and the image signal accumulated in the accumulation time B is stored in R ₂ . The same applies to the other colors G and B.

Since the amplitude of the above as the image is the image signal to be and the solid-state imaging device 4 1/4 pitch of the picture element is accumulated only when the image is in the close proximity of the summit or valley of the vibration, R ₁ And R ₂
The image signal stored in is a signal shifted by 1/2 pitch of the picture element, that is, a signal that complements the other picture element.
Therefore, for example, as shown in FIG. 5, the solid-state image sensor 4 is a line transfer type, and an imaged signal including a peak to the right of the image in the horizontal scanning direction is stored in R ₁ , and a peak to the left is stored. If the imaged signal including it is stored in R ₂ , R ₁
By synthesizing the signal of _{2 with} the signal of R ₂ by delaying the signal of 1 1/2 pitch of the picture element, the signal of R ₁ and the signal of R ₂ are in a mutually complementary relationship. The delay circuit 23 and the mixer 26 are provided for this purpose, but the same effect can be obtained by delaying the read timing from R _{1 by} a half pitch of the picture element relative to the read timing from R ₂ . The same applies to the other colors G and B.

Thus, the electronic endoscope according to the present invention can obtain a high-resolution image because both the image signals corresponding to the picture element and the portion in between are obtained by the vibration of the image. Further, since the amplitude of the image vibration may be adjusted after the assembling, the optical system can be easily assembled.

FIG. 6 shows an image pickup optical system of the second embodiment, in which an objective lens 2 has a structure in which an oscillating prism 37 is sandwiched between two fixed prisms 35 and 36. The entrance surface 35a of the fixed prism 35 is perpendicular to the optical axis and the exit surface 35b is inclined, and the entrance surface 36a of the fixed prism 36 is inclined in the opposite direction to the exit surface 35b with respect to the optical axis. Moreover, the exit surface 35b is vertical. The entrance surface 37a of the vibrating prism 37 is inclined parallel to the exit surface 35b of the fixed prism 35, and the exit surface 37b is inclined parallel to the entrance surface 36a of the fixed prism 36.

FIG. 7 is a principle diagram of the prism system of the second embodiment. As shown in the figure, the light beam is refracted upward when it emerges from the fixed prism 35, and when it enters the vibrating prism 37, its incident surface 37 is shown.
The light is refracted at a and becomes parallel to the original light, and when exiting from the vibrating prism 37, it is refracted downward, and when entering the fixed prism 36, it is refracted at the incident surface 36a and becomes parallel to the original light and fixed again. The prism 36 is emitted. In this case, the relationship between the vibration amplitude Δx of the piezoelectric element actuator 33 and the amplitude Δy of the optical axis emitted from the prism system is as follows. Becomes However, n, θ and θ ′ are the same as in the first embodiment.

In the case of this example, the amplitude Δy is amplified by the magnification β in the optical system after the fixed prism 36, so that the amplitude of the image on the light receiving surface 2a of the solid-state imaging device 4 is β · Δy. Therefore, since the amount of image movement that is 2β times that in the case of the first embodiment can be obtained, the amplitude of the actuator 33 of the piezoelectric element can be set to Δx / 2β when the image amplitude is the same, and as a result, the piezoelectric element having a short length The actuator can be used, and an endoscope having a short rigid portion can be realized.

8 (a) and 8 (b) respectively show the structure of the image pickup optical system and the principle of the prism system of the third embodiment, in which the vibrating prism 37 is interposed between the two fixed prisms 35 and 36. In this configuration, the exit surface 35b of the first fixed prism 35 and the vibrating prism 3
The entrance surface 37a of the vibrating prism 37 and the exit surface 37b of the vibrating prism 37 and the entrance surface 36a of the second fixed prism 36 are parallel to each other. The normals of the exit surface 37b of 37 are set so as to be in planes perpendicular to the plane of the drawing.

In this case, the image vibration is Δy on the paper surface and Δz in the direction perpendicular to the paper surface. However, since Δy and Δz have the same phase, the image vibration is performed on a straight line having an inclination angle.

FIG. 8 shows a main part of a modification of the prism system of the third embodiment, which is obtained by cutting the vibrating prism 37 by a plane perpendicular to the light beam and dividing it into two vibrating prisms 37A and 37B. When the first vibrating prism 37A is moved back and forth, the image moves up and down in the plane of the paper, and when the second moving prism 37B is moved back and forth, the image moves in a direction perpendicular to the plane of the paper. If the angular frequency of vibration of the vibrating prism 37A is ω ₁ and the angular frequency of the second vibrating prism 37B is ω ₂ , then Δx ₁ sin (ω ₁ t +
φ ₁ ) and Δx ₂ (ω ₂ t + φ ₂ ) are proportional to the angular frequencies ω ₁ and ω _{2 of} each vibration, and the initial phase (two vibration prisms 37
Relative positional relationship between A and 37B) Depending on how φ ₁ and φ ₂ are determined, the movement trajectory of the light beam that exits the prism system can take various shapes such as straight lines, circles, and ellipses.

FIG. 10 shows an image pickup optical system of the fourth embodiment, in which the solid-state image pickup device 4 is arranged along the longitudinal axis direction of the endoscope, and between the objective lens 2 and the solid-state image pickup device 4. An optical path conversion prism system including a fixed prism 38 and a vibrating prism 39 is arranged. In this example, the vibrating prism
By vibrating 39 along the optical path (perpendicular to the optical axis of the objective lens 2) as shown by the arrow, the solid-state image sensor 4
The object image is vibrated on the light receiving surface of the.

Although the image is vibrated horizontally in the first embodiment, it can be vibrated vertically. In this case, a high resolution similar to that of the frame accumulation type can be obtained by a field accumulation type solid-state imaging device with a small number of vertical lines, but in this case, no special operation on the circuit is required. In the frame storage type solid-state image pickup device, the vibration method of the first embodiment can be used to further improve the resolution. It is also possible to improve the resolution in both vertical and horizontal directions by tilting the vibration direction.
In this case, the second field may be returned to the original position for a time corresponding to the distance of the horizontal component of the vibration and sandwiched between the scanning lines of the first field. Also, various other scans are possible.

Needless to say, the image pickup system shown in each of the embodiments is not limited to an endoscope and can be widely applied as an image forming optical system for an apparatus for obtaining an object image using a solid-state image pickup device such as a TV camera.

〔The invention's effect〕

As described above, the electronic endoscope according to the present invention has an important advantage in practical use that the resolving power can be increased and the optical system can be easily assembled.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration of a first embodiment of an electronic endoscope according to the present invention, FIG. 2 is a timing chart for explaining its operation, and FIGS. 3 and 4 are respectively. A sectional view of the vibrating prism system of the first embodiment and a front view of a rotary filter, FIG. 5 is an enlarged view of a main part of the solid-state image pickup device of the first embodiment, and FIG. 6 is an image pickup optical system of the second embodiment. FIG. 7 is a principle view of the prism system of the second embodiment, and FIGS. 8A and 8B are cross-sectional views showing the structure of the image pickup optical system of the third embodiment and the principle of the prism system, respectively. FIG. 9 is a perspective view of an essential part of a modification of the prism system of the third embodiment, and FIG. 10 is a sectional view of the image pickup optical system of the fourth embodiment. 1 ... End of endoscope, 2 ... Objective lens, 3 ... Illumination lens, 4 ... Solid-state image sensor, 5 ... Solid-state image sensor drive circuit, 6 ... Preamplifier, 7 ... Light guide, 8 ... … Rotating filter, 9 …… Light source lamp, 10 …… Lens, 11,15
...... Rotation detection element, 16 …… Motor drive circuit, 17 …… Amplifier, 18 …… Multiplexer section, 19 …… Synchronous signal generator,
20,21,22 …… Frame memory, 23,24,25 …… Daylay circuit, 26,27,28 …… Mixer, 29 …… Color TV monitor, 30…
… Vibration prism system, 31 …… Liquid crystal shutter, 32 …… Piezoelectric element actuator drive circuit, 33 …… Piezoelectric element actuator, 34 …… Liquid crystal shutter drive circuit, 35,36,38 …… Fixed prism, 37,39 …… Vibration prism.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 63-66526 (JP, A) JP 57-46211 (JP, A) JP 58-168031 (JP, A)

Claims (3)

[Claims] 1. An endoscope is provided with an objective lens, a solid-state image sensor, and a prism system arranged in an optical path between a front lens of the objective lens or a cover glass and the solid-state image sensor at a tip portion of an endoscope. In the electronic endoscope, the prism system includes a first prism having an exit surface inclined to the optical axis and a second prism having an incident surface inclined to the optical axis.
At least one of the first prism and the second prism is vibrated without being tilted along the optical axis by including at least a structure in which prisms are arranged in order, and thereby an image of an object on the light receiving surface of the solid-state imaging device is illuminated. An electronic endoscope characterized in that it is vibrated in a direction perpendicular to an axis, and an image is picked up by the solid-state image pickup device at a plurality of different points in a moving path of an image of the object due to the vibration. 2. A shutter means is provided on an optical path on an incident side of the solid-state image pickup element, and the shutter means is in an open state near both ends of a moving path of an image of the object in synchronization with the vibration of the prism, and in between. The electronic device according to claim (1), characterized in that the images at different positions of the moving path of the image are projected on the solid-state image sensor by setting the closed state. Endoscope. 3. A vibrating prism is attached to a piezoelectric actuator extending along an optical axis, and the prism is vibrated by changing a voltage applied to the piezoelectric actuator. The electronic endoscope according to claim (1).