JPH0617369Y2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention relates to an image pickup apparatus having an automatic focus adjustment function, which is preferably used in a video camera or the like.

2. Related Art FIG. 8 is a side view of the vicinity of a lens unit 1 used in a conventional video camera or the like.

The lens unit 1 includes an afocal lens 2 for adjusting an angle of view, a master lens 3 for focusing, and the like. In a direction opposite to the afocal lens 2 of the master lens 3, a solid-state image sensor 4 for converting light into a video signal is provided. Is located.

FIG. 9 is a flowchart of a processing procedure of automatic focus adjustment (hereinafter, abbreviated as auto focus) according to the related art.
Hereinafter, with reference to FIG. 8 and FIG. 9, an autofocus processing procedure will be described.

In step m1, a high frequency band filter (hereinafter abbreviated as HPF) extracts a high frequency band signal component from the carrier component of the video signal output from the solid-state image sensor 4, and detects the peak value a of this high frequency component. To do.

In step m2, the master lens 3 is displaced in the arbitrary direction along the optical axis by a predetermined distance, and in step m3, the peak value b of the high frequency component is detected again. The relationship between the peak level of the output of the HPF and the movement amount of the lens, that is, the relative distance between the solid-state image sensor 4 and the master lens 3 is as shown by the curve l1 in FIG. When the focus position of the master lens 3 is on the surface of the solid-state image sensor 4,
The peak level of the HPF output is at point P shown in FIG.

At step m4, the peak value a obtained at step m1
Is compared with the peak value b obtained in step m3, and in step m5 it is determined whether or not the following equation | ab− | K ... (1) is satisfied. That is, the peak values a, b
It is judged whether or not the difference between is within a certain range (K in this case), and if so, the process proceeds to step m6.

At step m6, since the difference between a and b is within a certain range, it is determined that the master lens 3 is located at the focal position. As a result, the master lens 3 is stopped.

In step m5, if the difference between the peak values a and b exceeds a certain range, the process proceeds to step m8, and in step m8 the magnitudes of the peak values a and b are compared. Go to m9.

At step m9, the peak value b after displacement of the master lens 3 is smaller than the peak value a before displacement, so that the distance between the master lens 3 and the image sensor 4 is further away from the focusing distance. Therefore, in order to adjust the focus, the master lens 3 is displaced in the direction opposite to the direction displaced in step m2 (see the peak values (a) and (b) of the rear pinned area B in FIG. 10).

If a <b in step m8, the process proceeds to step m10. In step m10, since the peak value b after displacement of the master lens 3 is larger than the peak value a before displacement, the master lens 3 is set at the focal position. The master lens 3 is further displaced in the direction displaced in step m2 (see peak values (a) and (b) of the front pinned area A in FIG. 10).

After displacing the master lens 3 in steps m9 and m10, the process returns to step m3 and the same operation as described above is repeated. This series of operations is repeated until the difference between the peak values of the master lens 3 before and after the displacement falls within a certain range, that is, until the focus is achieved.

Problems to be Solved by the Invention In such a conventional technique, when displacing the master lens 3 in step m2, the determination of the displacement direction is governed by chance and does not necessarily occur. Therefore,
There is no problem if the displacement direction of the master lens 3 is the same as the focusing direction, but if it is the opposite direction, the displacement direction must be reversed at that time point and directed toward the focusing direction. That is, when the master lens 3 is moved in a direction opposite to the focusing direction by a driving mechanism such as a motor, the image is further blurred from the current state and then moves toward the focusing direction, and the responsiveness of the autofocus function is reduced. There is a problem of deterioration.

An object of the present invention is to solve the above problems and provide an image pickup apparatus having a good responsiveness of the autofocus function.

MEANS TO SOLVE THE PROBLEMS The present invention relates to a lens 11, an image pickup element 12 on which an optical image of a subject formed by the lens 11 is formed, and which is converted into an electrical video signal, and the lens 11 and the image pickup element 12 are relatively arranged. A motor 25 that displaces the image sensor 12 in the optical axis direction, a piezoelectric element 16 that reciprocally displaces the image sensor 12 in the optical axis direction, a filter 20 that extracts only a high frequency band from the output of the image sensor 12, and an output from the filter 20. In response to the output of the peak value detector 21 and the peak value detector 21 for detecting the peak values c and d, the difference between the peak values c and d at each of the two positions due to the reciprocal small displacement of the image pickup device 12 is determined in advance. When the value is less than the specified value K, the motor 2
5 is stopped, and when the difference between the peak values c and d exceeds the predetermined value K, the focus of the lens 11 is the image sensor 12
The control means 22 and 24 for deciding the displacement direction of the optical axis direction which matches with, and driving the motor 25 to focus, and the blanking period of the screen scanning of the image sensor 12 are detected, and the piezoelectric element 16 is detected during that period. And a means for generating a voltage for driving the piezoelectric element 16, and the minute displacement operation of the piezoelectric element 16 is performed during a blanking period of screen scanning of the image sensor 12.

Operation According to the present invention, before the motor 25 is driven to relatively displace the lens 11 and the image pickup device 12, the image pickup device 12 is reciprocally slightly displaced in the optical axis direction by the piezoelectric element 16, and two A peak value detector 21 detects the peak values c and d of the output through the filter 20 that extracts only the high frequency band from the image sensor 12 at each position, and the difference between the peak values c and d at these two positions is When the value is a predetermined value K, the driving of the motor 25 is stopped assuming that the lens is in focus, and when the difference exceeds the predetermined value K, the lens 11 is determined based on the peak values c and d at the respective positions. Determines the displacement direction in the optical axis direction in which the focal point of the
To drive. In this way, the responsiveness of the autofocus function can be improved.

In particular, according to the present invention, the small displacement operation of the piezoelectric element 16 is
This is performed during the blanking period of the screen scanning of the image sensor 12, and even if the displacement amount of the image sensor 12 is large, the image does not blur at all, and the high frequency components can be compared during that time.

Embodiment FIG. 1 is a system diagram showing a basic configuration of an image pickup apparatus 10 which is an embodiment of the present invention. The image pickup apparatus 10 includes a lens unit 11, an image pickup element 12 arranged facing the lens unit 11, and realized by a CCD (charge coupled device) or the like. The lens unit 11 includes an afocal lens 13 for adjusting an angle of view and a master lens 14 for focusing, and the afocal lens 13, the master lens 14 and the image pickup device 12 are provided.
Are arranged so that their centers coincide with the optical axis in this order.

Further, on the side opposite to the master lens 14 of the image sensor 12,
An image pickup device 1 is provided with a flat plate-shaped element base 15.
The piezoelectric element 16 is inserted between the element 2 and the element base 15, and the imaging element 12 and the piezoelectric element 16 are provided by the plurality of screws 17 and the spring 18 wound around the screws 17.
Are fixed to the element base 15. As will be described later, the plurality of springs 18 are arranged so that even if the piezoelectric element 16 expands and the imaging element 12 is displaced, the surface of the imaging element 12 is always perpendicular to the optical axis. Those with uniform power are selected.

FIG. 2 is a block diagram showing the electrical structure of the imaging device 10. The image pickup device 12 is connected to the CPU 22 via an amplifier 19, a high frequency band filter (hereinafter abbreviated as HPF) 20 and a peak value detector 21.
The CPU 22 is connected to the piezoelectric element 16 via a piezoelectric element drive circuit 23, and is connected to a motor 25 via a motor drive circuit 24. The motor 25 is arranged so as to displace the master lens 3 in the optical axis direction.

The light reflected by the subject is imaged on the image pickup element 12 via the lens unit 11, and the image information of the light is converted into an electric image signal by the image pickup element 12. The video signal is voltage-amplified by the amplifier 19 and then input to the HPF 20. The HPF 20 takes out only the high frequency band of the amplified video signal, detects the peak value of this high frequency component by the detector 21, and gives it to the CPU 22. The CPU 22 activates the piezoelectric element drive circuit 23 or the motor drive circuit 24 according to the information. As a result, the piezoelectric element 16
Expands and pushes up the image sensor 12, and the motor 25 displaces the master lens 3.

FIG. 3 is a system diagram showing a state where the piezoelectric element 16 has expanded. The piezoelectric element 16 expands in volume by being energized by the piezoelectric element drive circuit 23, and changes from the thickness D1 in the optical axis direction (see FIG. 1) to the thickness D2 (D1 <D2. ). This allows the piezoelectric element 16 to be screwed 17
And image pickup element 12 integrally fixed by a spring 18
Is slightly displaced toward the master lens 14 against the spring force of the spring 18. If the power supply is deenergized in this state, the piezoelectric element 12 is reduced to its original volume, and the image pickup element 12
Is returned to its original position by the spring bias of the spring 18 (see FIG. 1) (hereinafter, this original position is referred to as a reference position).
This allows the image sensor 12 to be arbitrarily displaced within a fixed range.

Further, the master lens 14 can be arbitrarily displaced by a motor 25 (not shown in FIG. 3) in a direction parallel to the optical axis toward the image sensor 12 and in the opposite direction. Focusing can be achieved by arbitrarily displacing the image pickup device 12 and the master lens 14.

FIG. 4 is a flow chart of the autofocus system according to this embodiment, and FIGS. 5, 6, and 7 are schematic views showing the states of focus, front focus, and rear focus of the master lens 14 and the image sensor 12, respectively. FIG. The autofocus method of this embodiment will be described below with reference to this flowchart.

In step n1, the video signal from the image sensor 12 is extracted through the amplifier 19 and the HPF 20 to obtain the high frequency component of the amplified video signal. The peak value c of this high-frequency component is detected by the peak value detector 21 and given to the CPU 22 for storage. In step n1, the image sensor 12 is assumed to be at the reference position.

In step n2, the piezoelectric element 16 is driven to displace the image pickup element 12 toward the master lens 14 by a predetermined minute distance, and in step n3, the peak value d of the high frequency component is detected again, After being temporarily stored by the CPU 22, the image sensor 12 is returned to the reference position in step n4. It should be noted that the minute distance is selected so that the blur cannot be visually recognized in the image. Moreover, each figure of FIG. 5 to FIG.
(1) shows the state of step n1, and each figure (2) shows the state of step n3.
Is the state of.

In step n5, the peak values c and d are compared with each other to determine whether or not the following expression | c−d | ≦ k (2) is satisfied. That is, it is determined whether the difference between the peak value c and the peak value d is less than or equal to the constant value k, and if the difference is smaller than the constant value K, the process proceeds to step n6.

In step n6, the amount of change in the peak value with respect to the small amount of displacement of the image sensor 12 is smaller than the constant value k, so it is determined that the image is in focus (see FIG. 5).

At step n7, the peak values c and d stored at step n1 and step n3 are erased and the process returns to step n1.
That is, the subject moves or the video camera 10
If is moved, the focus is lost, so the operations from step n1 to step n5 are repeated. If the subject and the video camera 10 do not move, step n1
From step n7 to step n1 again.

If the difference between the peak values c and d is larger than the constant value k in step n5, it is determined that the focus is not achieved, so the process proceeds to step n8, and in step n8, the magnitude correlation between the peak values c and d is compared, and c If <d, proceed to step n9.

In step n9, the image sensor 12 is set to the master lens 1
As a result of the slight displacement in the direction approaching 4, it was determined that the peak value had increased (see the front pinned area A in FIG. 10), so this state is as shown in FIG. Is determined to be between the image pickup device 12 and the image pickup device 12. Hereinafter, this state is called a front pin.

In step n10, since it is determined that the front focus, that is, the focus position F is between the master lens 14 and the image sensor 12, the master lens 14 is moved toward the image sensor 12. That is, the master lens 14 is changed so that the focus position F is on the image sensor 12.

If c> d in step n8, the process proceeds to step n11.

In step n11, it is determined that the peak value has decreased as a result of the slight displacement of the image sensor 12 in the direction approaching the master lens 14 (see pin area B after FIG. 10), and this state is shown in FIG. Thus, the focus position F is determined to be on the opposite side of the image sensor 12 from the master lens 14. Hereinafter, this state is called a rear pin.

In step n12, since it is determined to be the rear pin, the master lens 14 is moved in the direction away from the image sensor 12. That is, the master lens 14 is displaced so that the focus position F is on the image sensor 12.

In step n13, step n10 or step
After moving the master lens 14 at n12, the peak value e of the high frequency component of each pixel is detected again and is temporarily stored in the CPU 22.

In step n14, it is checked whether or not the difference between the peak value d obtained in step n3 and the peak value e obtained in the previous step is smaller than a constant value K. If smaller, the process proceeds to step n6 and it is determined that focusing is achieved. If the difference between the peak values d and e is larger than K, the process proceeds to step n15.

In step n15, as a result of moving the master lens 14 once, it is determined that the focus is not sufficient yet. Therefore, the master lens 14 is further moved in the same direction as the one moved to step n13. , And then return to step n13. In this way, the operation of this loop is continued until the difference between the peak values d and e becomes smaller than the constant value K, and when it becomes smaller than the constant value K, the process proceeds to step n6 and it is determined that the focus is achieved.

In this way, by slightly displacing the image sensor 12 before moving the master lens 14, the image sensor 12
The direction in which the master lens 14 should be moved can be determined after determining whether the upper imaging state is the front focus or the rear focus. Therefore, it becomes possible to displace the master lens 14 in the direction in which it is reliably focused.

Since the expansion coefficient of the piezoelectric element 16 is proportional to the applied voltage, the amount of blurring cannot be detected by calculating the depth of focus (the range that can be regarded as the in-focus state on the imaging surface) from the aperture value of the current lens. It is possible to change the minute change amount.

Further, the minute displacement operation (one reciprocation) of the image sensor 12 by the piezoelectric element 16 may be performed during the blanking period of the screen scanning. In this way, even if the amount of displacement of the image sensor 12 is large, the image does not blur at all, and it becomes possible to compare the high frequency components during that time.

The image pickup device 12 is composed of, for example, a CCD as described above, and has a large number of independent pixels formed in a mosaic pattern on a silicon substrate. Screen scanning is performed by applying a scanning pulse to these pixels in a circuit manner and reading out the photocharges accumulated in the pixels one after another. Such CCD configurations are well known to those skilled in the art. In order to perform a minute displacement operation of the image pickup device 12, which is a CCD, by the piezoelectric element 16, for example, the piezoelectric element 16 is inverted and synchronized with a scan pulse for screen scanning of the image pickup device 12 and during the blanking period of the screen scan. In step n2, a voltage is applied to the piezoelectric element 16 to energize the piezoelectric element 16, and the voltage is not applied to deenergize the power to perform a minute displacement operation of the piezoelectric element 16. it can.

As described above, according to the present invention, after changing the relative distance between the image pickup means and the optical system by the drive means, a signal of a level relating to the image formation state of the optical image in the image pickup means output by the image pickup means, By comparing with the signal of the level output from the image pickup unit before the change, the image formation state in the image pickup unit can be identified. This makes it possible to quickly execute the operation corresponding to the identified image formation state.

Further, since the change in the relative distance between the image pickup means and the optical system is minute, this operation has almost no influence on the image forming action of the image pickup apparatus.

[Brief description of drawings]

FIG. 1 is a system diagram showing the basic configuration of an embodiment of the present invention,
FIG. 2 is a block diagram showing the electrical structure of the image pickup apparatus 10,
FIG. 3 is a system diagram showing the expanded state of the piezoelectric element, FIG. 4 is a flow chart for explaining the autofocus system according to this embodiment, and FIG. 5 is a schematic view of the in-focus state of the master lens 14 and the image sensor 12. 6 is a diagram showing the front pinned state of the master lens 14 and the image sensor 12, FIG. 7 is a diagram showing the rear pinned state of the master lens 14 and the image sensor 12, and FIG. 8 is a diagram showing the prior art. FIG. 9 is a side view, FIG. 9 is a flow chart for explaining the conventional autofocus method, and FIG. 10 shows the relationship between the output of the HPF and the relative distance between the master lens 14 (3) and the image sensor 16 (4). It is a graph. 10 ... Imaging device, 11 ... Lens unit, 12 ...
Image sensor, 13 ... Afocal lens, 14 ... Master lens, 16 ... Piezoelectric element

Claims (1)

[Scope of utility model registration request] 1. A lens (11), an image pickup device (12) for forming an optical image of a subject by the lens (11) and converting it into an electric image signal, a lens (11) and an image pickup device (12). A motor (25) that relatively displaces the and (a) in the direction of the optical axis, and a piezoelectric element that reciprocally displaces the image sensor (12) in the direction of the optical axis.
(16), a filter (20) that extracts only the high frequency band from the output of the image sensor (12), and a peak value detector (21) that detects the peak value (c, d) of the output from the filter (20) In response to the output of the peak value detector (21), the peak value at each of the two positions due to the reciprocal small displacement of the image sensor (12)
When the difference between (c, d) is less than a predetermined value K, the motor (2
When the driving of 5) is stopped and the difference between the peak values (c, d) exceeds the predetermined value K, the focus of the lens (11) is the image sensor (12).
The control means (22, 24) that drives the motor (25) to focus by deciding the displacement direction of the optical axis direction that matches the optical axis direction and the blanking period of the screen scanning of the image sensor (12), and And a means for generating a voltage for driving the piezoelectric element (16) during the period, the micro-displacement operation of the piezoelectric element (16) is performed during the blanking period of the screen scanning of the image sensor (12). Image pickup device.