JPS61140908A - Automatic focus adjusting device in endoscope - Google Patents

Abstract

PURPOSE:To permit automatic focus adjustment without controlling mechanical movement by determining, by calculation, the modulating level of the modulation signal when the data giving the max. space frequency is obtd. CONSTITUTION:The video signal from a solid state image pickup element 17 is subjected to digital processing and the three primary color signals converted to analog signals are introduced to an adder 33. A fast Fourier transformer 34 resolves the signal to the space frequency component with the horizontal scanning line of each frame and a memory 35 accumulates these sets of the data in frame units, determines the max. space frequency data among the same by calculation and compares the calculated result with the data in the next frame period. An arithmetic circuit 36 determines the max. space frequency data obtd. in an optimum focusing position by repeating such calculation and introduces the same into a ROM37. The focusing data which determines such quantity of modulation of a driving source 40 as to set a liquid crystal lens 16 in the focusing state is read out of the ROM37. The focus is thus automatically adjusted and the focusing is executed in a short period.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic focus adjustment device for an endoscope, and particularly to an endoscope that uses a solid-state image sensor to adjust focus using a liquid crystal lens.

[Technical background of the invention]

In general, optical observation devices and optical photographing devices such as endoscopes, cameras, and television cameras are capable of photographing and photographing objects clearly.
To enable observation, a focus detection means is provided to detect whether the imaging position of the imaging optical system of the device is in focus, and the output of this detection means is used to automatically move and set the optical system to the focus position. There are things that have functions.

FIG. 2 is an explanatory diagram showing the principle of an example of the focus detection means as described above, in which 1 is a light source, 2 is a light receiving element having a pinhole 3, and the light from the light source 1 is exchanged. The light shielding surface 2*IfC of the element 3 is irradiated and passes through the pinhole 3 to the light receiving surface 2b side. A photographic/observation lens 4 is provided at a predetermined position on the side of the light receiving surface 2b, and irradiates light from a light source 1 that has passed through the pinhole 3t onto a subject (not shown) via a lens 4yk.

In this configuration, if the object is in focus at the position already indicated by the code, but the object is too close and the object is too fast, the positions are indicated by a and c, respectively. show. The light reflected at the position of the symbol passes through the photographic/observation lens 4 and becomes the convergence point (convergence point) at the position of the pinhole 3, so the light reaches the photocathode 2b around the pinhole 3. do not. On the other hand, the light reflected at the position a has a convergence point at the rear position of the pinhole 3, so the light reaches the photocathode 2b on the outer periphery of the pinhole 3 as shown in the figure, and a signal for this light is output. be done. Similarly, the light reflected at the position C has already converged at the position in front of the pinhole 3, and then spreads out, so the light reaches the photocathode 2b, and the light receiving element 2 outputs a signal for this light. be done.

Therefore, by moving the observation/taking lens 4 based on the output of the light receiving element 2, it is possible to form a focused light image on the imaging film or eyepiece set at the same position as the light receiving element 2. It is possible.

Incidentally, in recent years, an endoscope is being developed that uses a purely electronic method to obtain an image of a subject without using a photographic film or a relay lens. An effective means for this purpose is a solid-state imaging device such as a COD or MO8 type image sensor.

However, in an endoscope that uses a solid-state image sensor as described above, the configuration explained in FIG. It was necessary to adjust the insertion amount of the endoscope and move the objective lens from the proximal side so that it was connected to the light-receiving surface of the element. However, adjusting the insertion amount of the endoscope has the disadvantage of causing unnecessary pain to the patient, and moving the objective lens from the proximal side has the disadvantage of complicating the structure. .

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and it is possible to automatically adjust the focus and always obtain clear images in an endoscope using a solid-state image sensor without performing mechanical movement control. An object of the present invention is to provide an automatic focus adjustment device for an endoscope.

[Summary of the invention J! ! ] In order to achieve the above object, an automatic focus adjustment device according to the present invention includes a liquid crystal lens that is provided in the head of an endoscope and functions as an objective lens, and a focus sweep variable function for the liquid crystal lens when searching for a focus. a liquid crystal drive source that applies a modulation signal to sweep its focal point; a solid-state image sensor that receives a light image from a subject through a liquid crystal lens to which the signal of this drive source is applied; Frequency decomposition means decomposes this signal into a spectrum of spatial frequencies in a predetermined scanning direction, spectral data from this means is supplied, and the maximum spatial frequency is determined based on these data. and a modulation level detection means for calculating the modulation level of the modulation signal when the given data is obtained.

[Embodiments of the invention]

Hereinafter, the present invention will be described with reference to illustrated embodiments.

FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the present invention.

In FIG. 1, reference numeral 11 is a head section of an endoscope, 12 is a video signal processing section, 13 is a display device, 14 is an automatic focus adjustment section according to the present invention, and 15 is an illumination light source section.

Inside, the endoscope head section 11 includes a liquid crystal lens 16. It is mainly composed of a solid-state image sensor 17 such as a COD and a light guide table 18. The liquid crystal lens 16 is a cover glass ll
The lens is disposed at the rear of the lens a, and its focal length can be varied by a liquid crystal driving source, which will be described later. Its structure is
There are outer transparent plates 16 on both sides of the transparent plate 161 located in the center.
The liquid crystal cells 164, 16s are sealed with 2,163, and the electrodes 16s, 167.16 on both sides of each liquid crystal cell 164, 165 are sealed.
Among the inner electrodes 167.16g, a signal from the drive source 40 is commonly applied to the inner electrodes 167.16g, while the outer electrodes 166.8.
169 f7c are each connected to the ground point. Further, the solid-state image sensor 17 has its light-receiving surface 171 facing the liquid crystal lens 16, and is driven by a drive signal from a drive circuit 172, and its output is taken out via a preamplifier 173.

Further, the light guide cable 18 irradiates the object with illumination light from the light source section 15 via the lens 19. This light source unit 15 is a color plane sequential illumination type light source that reflects light from a light source 20 with a reflection plate 21 and supplies the reflected light to the incident end of a light guide cable 18 via a tricolor plate 22 and a lens 23. Reference numeral 24 denotes a rotational drive body that rotates the three-color plate 221. Accordingly, the subject is sequentially illuminated with red, green, and back primary color light.

The video signal processing section 12 first receives the video signal from the preamplifier 173 at the analog/digital converter 25, and then sends the digital signal for one frame to three frame memories 27R, 28G, and 29B via the changeover switch 26. Read in color plane sequentially. Each frame memory 27R, 28
G, 29B are digital-to-analog converters 30B,
RGB signals are supplied to the display device 13 via 31G and 32B.

The automatic focus adjustment section 14 includes each digital-to-analog converter 30.
The outputs of R, 31G, and 32B are received by an adder 33, and the adder 33 combines the respective primary color signals to create a luminance signal. The output of adder 33 is introduced into memory 35 via fast Fourier transformer 34 . In this memory 35, data representing a spectrum for each spatial frequency detected by the fast Fourier transformer 34 is written as digital data in frame sequence, and the read data is supplied to an arithmetic circuit 36. This arithmetic circuit 36 performs an arithmetic operation to set the liquid crystal lens 16 at a focal length that provides this data, based on the data representing the highest spatial frequency component from the set of data for each frame from the memory 35. , this calculation result is supplied to the ROM 37 in the form of address data. That is, the ROM 37 digitally stores a large amount of focus data for setting the focal length.

This corresponds to a level (quantity) IC that modulates the output signal of the drive source 40 of the liquid crystal lens 16 via the . Changeover switch 41
The analog voltage from the digital-to-analog converter 38 is selected at the time of focusing, and the sweep voltage from the sweep voltage generation circuit 39 is selected at the time of focus search. That is, the sweep voltage generation circuit 39 modulates the drive source 40 according to its output voltage, and the focal length of the liquid crystal lens 16 is swept (searched) using the modulation signal from the drive source 40 obtained thereby.

Then, when the spectrum data representing the maximum spatial frequency component described above is detected, the changeover switch 41 supplies the voltage from the digital-to-analog converter 38 to the drive source 40. The switching control signal for the changeover switch 41 uses, for example, a pulse signal synchronized with the generation of address data to the ROM 36.

The present invention is configured as described above, and its operation will be explained next. The present invention sweeps and varies the focus of the liquid crystal lens 16 so that the image from the object is focused on the light-receiving surface 171 of the solid-state image sensor 17, and thereby optimizes the focus based on the signal obtained from the solid-state image sensor 17. This is to detect and set the focus.

(1) Focus sweep At the beginning, the head portion of the endoscope, that is, the liquid crystal lens 16 is held still at a predetermined distance from the subject.

Focus sweep is performed in this state. The focus sweep is performed by controlling the drive source 40 by the sweep voltage generation circuit 39. In this control method, when an AC signal generator is used as the drive source 40, the output signal of the drive source 40 is controlled by the voltage from the sweep voltage generation circuit 39.
It is modulated by M.

Further, when a frequency signal generator is used as the drive source 40, the output signal of the drive source 40 is subjected to FM modulation with the voltage from the sweep voltage generation circuit 39.

Such a drive signal from the drive source 40 is transmitted to the liquid crystal lens 16.
By applying voltage between each electrode 167, 168 and 16g, 169, the focus of the liquid crystal lens 16 is swept variable within a predetermined range, and the liquid crystal lens 16 whose focal length is sweep variable is applied to the solid-state image sensor 17. This means that the subject image rays that have passed through the lens are incident. Therefore, the solid-state image sensor 17 receives a different image for each frame that sequentially changes from an out-of-focus state to an in-focus state.

(2) Detection of focus state The video signal thus obtained by the solid-state image sensor 17 undergoes digital processing by the video signal processing circuit 12, and the three primary color signals converted to analog signals from the output terminal are sent to the adder 3.
3 will be introduced. When these primary color signals are combined, the adder 3
3 provides a luminance signal, the output of which is supplied to a fast Fourier transformer 34. The fast Fourier transformer 34 decomposes the video signal for each frame into spatial frequency components for, for example, one specific horizontal scanning line, and outputs the spectrum data for each frame. The memory 35 stores these data in a frame manner, calculates the maximum spatial frequency data among the data obtained in the frame period, and uses the obtained result as temporary reference data in the next frame period. Wait for the data to be obtained. Similar calculations are then performed on the data in this frame period, and the results are compared with the maximum spatial frequency data obtained in the previous frame period. The arithmetic circuit 36 repeats such arithmetic operations to obtain the maximum spatial layer wave number data obtained at the optimal focus position, and introduces, for example, the address content of the memory 35 in which the data is stored into the ROM 37. In this case, R
Focusing data that determines the amount of modulation of the drive source 40 that sets the liquid crystal lens 16 in a focused state is read out from the OM 37.

This data is converted into a voltage amount by the digital-to-analog converter 3B, and when the changeover switch 41 is switched, the drive source 40
can apply a drive signal having a modulation amount based on data from the ROM 37 to the liquid crystal lens 16JC. In this way, a clear image of the subject can be obtained from the solid-state image sensor 17 due to the focused state of the liquid crystal lens 16.

Note that even if the distance conditions between the endoscope head and the subject differ, the data is stored in the memory 34 in the order of addresses corresponding to changes in the sweep voltage. The spatial frequency data is accumulated at a predetermined address corresponding to the distance condition, and the modulation amount data obtained thereby also takes a value according to the change in distance.

Furthermore, if the image on the display device 13 is temporarily fixed and displayed during the sweep, and spectral data for several frames are detected during this period, the image will not become blurred.

Furthermore, even under anesthesia, the digestive system is constantly moving,
If the operator drives the focusing while inserting or moving the tip of the endoscope, the tip may flicker and be difficult to see. Therefore, by fixing the image every 10 frame scans and performing inverse Fourier transform to cut the low frequency components of the compensated signal, the image that has been subjected to edge enhancement processing is output to a monitor display device and displayed. On the other hand, during this 10 frame scanning period, the liquid crystal lens is driven by a sweep voltage, and when the optimum focus voltage of 1 is detected, the 1 frame of my signal captured by the voltage application at that time is displayed on the monitor during the next 10 frames. By outputting the image to the device, the above-mentioned flickering can be prevented.

In the above embodiment, the luminance signal that has passed through the adder 33 is used as a signal for spectral decomposition, but it is also possible to use one of the primary color signals. Further, the means for obtaining the spatial frequency data of the luminance signal is not limited to the fast Fourier transform means.

Furthermore, the unfocused focus setting means may be applied to optical instruments other than endoscopes.

〔Effect of the invention〕

As explained above, according to the present invention, since the focus is automatically adjusted, the structure of the endoscope is simplified without requiring any mechanical configuration, and manual adjustment while viewing the monitor image is not required. This has the effect of enabling focusing in a short time and reducing pain for the patient.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the present invention, and FIG. 2 is an explanatory diagram illustrating an example of a conventional automatic focus adjustment method. 11... Endoscope tip, 12... Image processing circuit,
13...Display device, 14...Automatic focus adjustment section. 15...Light source part, 16...Liquid crystal lens, 1
7...Solid-state camera element 25...Analog digital 3
0R, 31G, 32B...Digital analog converter,
33... Adder, 34... Fast Fourier transformer, 35... Memory, 36... Arithmetic circuit 37... ROM, 3g... Digital analog converter, 39... Sweep voltage generation Circuit, 40... Drive source. Agent Patent Attorney Susumu Ito 'Figure 1 Figure 2

Claims (4)

[Claims] (1) A liquid crystal lens installed in the head of the endoscope and functioning as an objective lens, and a liquid crystal drive source that sweeps the focus by applying a modulation signal for variable focus sweep to the liquid crystal lens during focus search. , a solid-state image sensor that receives a light image from the subject through a liquid crystal lens to which a signal from the drive source is applied, a display means that processes the video signal obtained from the solid-state image sensor and displays it on a screen, and a focus search device. At times, a video signal obtained from the solid-state image sensor is supplied, and a frequency decomposition means for decomposing this signal into a spectrum of spatial frequencies in a predetermined scanning direction, and spectral data from this means are supplied, and based on these data, modulation level detection means for calculating the modulation level of the modulation signal when data giving the maximum spatial frequency is obtained; An automatic focus adjustment device for an endoscope, characterized in that the focus of a lens is adjusted. (2) The display means fixedly displays a signal obtained when the liquid crystal lens is in a focused state for a predetermined period, and the focus of the liquid crystal lens is swept during this period. An automatic focus adjustment device in an endoscope according to item 1. (3) The automatic focus adjustment device for an endoscope according to claim 1, wherein the liquid crystal drive source generates an AC signal whose amplitude is modulated by the output of the modulation level detection means. (4) The automatic focus adjustment device for an endoscope according to claim 1, wherein the liquid crystal drive source generates an alternating current signal that is frequency-modulated by the output of the modulation level detection means.