JPH0588004A - Focal variable lens and focusing device thereof - Google Patents

Abstract

PURPOSE:To provide the ideal focal variable lens which is substantially free from aberrations and the control method which can make response at a high speed. CONSTITUTION:An optically transparent liquid material is sealed between two sheets of elastically deformation high-molecular films or between the high- molecular films 3 and a transparent plate 1. Since the high-molecular films 3 are elastically change to a parobolic shape, a ideal lens having no aberrations is constituted. Since the curvature of radius of the high-molecular films 3 changes according to amt. of the liquid material to be pack, the focal variable lens of the focal distance varying according to the amt. of liquid material to be packed is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable focus lens capable of high-speed focus control and a control method therefor.

[0002]

2. Description of the Related Art When imaging an object, it is necessary to move a lens system in the optical axis direction to form an image of the object on a photosensitive surface. On the other hand, as a method of fixing a lens and capturing an image, a method of capturing an image using a variable focus lens is known, and for example, a polymer gel lens described in JP-A-1-260401 proposed by the present applicant is It is known. Since the focal length of this variable focus lens is controlled according to a drive signal from the outside, it is possible to image a moving object with the lens fixed, and to use it as a visual sensor for an industrial robot, for example. You can

[0003]

The variable focus lens system proposed by the present inventor changes the focal length by causing a non-uniform phase transition of polymer gel in response to an electric field, for example.
For example, it has a great advantage that it can be used as a visual sensor of an industrial robot.

However, the polymer gel lens system has a drawback that the response to the control signal of the polymer gel lens is slow and it is difficult to adapt to a system requiring high-speed control. The focusing operation of the image capturing video camera includes a method of measuring a distance and a method of processing the captured image signal, and the latter is adopted as a general method. In the image signal processing method, in order to reduce the image signal noise, it is necessary to add a plurality of operation signals, so that the focusing time becomes long.
Further, in order to determine the direction of focus control, it is necessary to compare at least three image signals with different focal lengths, which is a cause of increasing the focusing time by the image signal processing method.

Further, in the conventional video camera, in order to reduce the aberration of the image pickup lens, a large number of lenses have to be used in combination, and there is a drawback that the lens system becomes large.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, to perform focus control at high speed, and especially when an object is moving, a moving object can be imaged at high speed, and the size and weight are reduced. And a focus control method thereof.

[0007]

A variable focus lens according to the present invention comprises a first and a second light transmissive surface which are arranged so as to face each other, and a space between the first and the second light transmissive surfaces. An optically transparent liquid material that is hermetically filled in the liquid crystal, and a control mechanism that controls the filling amount of the liquid material, and at least one of the first and second light transmissive surfaces can be elastically deformed. It is characterized in that it is made of a polymer film and the focal length is changed based on the filling amount of the liquid material.

The focus control device for a variable focus lens according to the present invention has first and second surfaces which are arranged so as to face each other and at least one surface of which is made of an elastically deformable polymer film. And a focus control device for a variable focus lens, which has an optically transparent liquid material hermetically filled between the first and second surfaces, and whose focal length changes according to the filling amount of the liquid material, A control mechanism for controlling the filling amount of the liquid material, an imaging device for imaging an object through the variable focus lens, and a differentiating circuit for generating a distance differential signal based on a video signal generated from the imaging device. The filling amount of the liquid material is controlled based on a differential signal output from the differentiating circuit.

[0009]

When the optically transparent liquid material is enclosed between the elastically deformable polymer film and the transparent plate, the polymer film is elastically deformed into a convex shape. As a result of simulating the shape of the polymer film at this time, it was found that the polymer film was a paraboloid centered on an axis passing through the center. From this result, if a transparent liquid material is enclosed in the space defined between the transparent plate and the optically transparent polymer elastic film, an ideal lens with almost no aberration can be realized. Moreover, by using a transparent film having an appropriate elastic tension as the polymer film, it is possible to realize a lens that is hardly affected by gravity even if the lens is arranged vertically. Further, since the radius of curvature of the polymer film changes according to the amount of the liquid material enclosed, it is possible to realize a variable focus lens with almost no aberration by controlling the amount of the enclosure appropriately.

At the time of focus control of the variable focus lens, a control signal is generated based on the contrast of an image picked up by the lens, and the amount of the liquid material enclosed is controlled based on this control signal, so that the focus control can be performed at high speed. Can be done.

[0011]

1 is a sectional view showing the structure of an example of a variable focus lens according to the present invention. In this example, a variable focus lens called a back type lens will be described. Fig.1 (a) shows the state of acting as a convex lens, and Fig.1 (b)
Shows the state of acting as a concave lens. A transparent plate 1 which is an optically transparent parallel plate is used, and an O-ring 2 acting as a spacer is fixedly adhered onto the transparent plate 1. An optically transparent and elastically deformable polymer film 3 is adhered and fixed to the spacer 2. As the polymer film 3, for example, a polystyrene film having a thickness of 30 μm can be used.
Two small holes 2a and 2b are formed in the spacer 2, and tubes 4a and 4b are connected to these small holes, respectively. Tube 4a
And 4b and the pores 2a and 2b, an optically transparent liquid material such as dimethyl silicone oil 5 is inserted into the space defined by the transparent plate 1, the elastic polymer film 3 and the spacer 2. Here, the refractive index of each member is about 1.5 for the transparent substrate 1 and the polystyrene film, and the refractive index of dimethyl silicone oil 5 is about 1.6. When the amount of silicone oil 5 as a transparent liquid material is gradually increased, the polymer film 3 elastically deforms, and as shown in FIG. 1 (a), the polymer film 3 has a convex parabolic or spherical shape. Transforms into. As a result, the transparent plate 1, the polymer film 3 and the silicone oil 5
This forms a plano-convex lens. Then, since the radius of curvature of the polymer film 3 changes according to the filling amount of the silicone oil 5, the focal length as a lens changes according to the change in the radius of curvature. As a result, a variable focus lens whose focal length changes according to the filling amount of silicon oil is configured. Further, as shown in FIG. 1B, when the filling amount of the silicone oil 5 decreases, the polymer film 3 becomes a concave surface, and as a result, the variable focus lens according to the present invention can function as a concave lens.

FIG. 2 is a diagram showing an example of a focus control system for a variable focus lens according to the present invention. An image of an object 11 is picked up by an image pickup device 12 through a variable focus lens 10. As the image pickup device 12, a CCD camera (built-in 1/2 inch CCD element, effective pixel 376H × 488V) can be used. The video signal from the image pickup device 12 is input to a central processing unit (CPU) 13 via a pixel capturing board. The CPU 13 processes the video signal to generate a lens drive signal. still,
The detailed operation will be described later. The variable focus lens 10 has 2
The conduits 14a and 14b are connected to each other, and the conduit 14a is connected to a gear pump 16 and an oil tank 17 via a first solenoid valve (three-way valve) 15, respectively. Similarly, the conduit 14b is also connected to the gear pump 16 and the oil tank 17 via the second solenoid valve (three-way valve) 18, respectively. A step motor 19 is connected to the gear pump 16, and the step motor 19 is driven by the step motor 19.
Is controlled by a drive signal supplied from the CPU 13 via the drive circuit 20. To reduce the radius of curvature of the lens surface of the variable focus lens 10 to obtain a short focal length, the gear pump 16
The silicone oil from the oil tank 17 is the gear pump
16, through the first solenoid valve 15 and the conduit 14a, the focus variable lens is driven. On the other hand, when the long focal length is set, the silicone oil of the lens 10 is driven so as to be discharged to the oil tank 17 via the second solenoid valve 18, the gear pump 16, and the first solenoid valve 15.

Next, the focus control method will be described. Book
In the example, the focus detection method is the video signal contrast.
Is used to control the maximum value. Should be imaged
Object 11 is divided into white and black at the center, as shown.
Use the target object. In the present invention, the image from the image pickup device 12 is
Differentiated value obtained by differentiating the audio signal strength with a position function
Focus error detection is performed based on Therefore, in this example,
5 image signals in the horizontal direction, that is, 5H at the center of the screen
The signals from 50V pixels are used, and these pixel signals are averaged.
The signal processing is performed by using the obtained one. In addition,
For example, the differential differentiation method can be used. Actual focus
At the time of control, 90% of the differential value at the time of focusing is set to D_f, About 70%
The value of D_tAs D_tGear pump 16 until reaching
Supply 1 cc of silicone oil each time from _tTo
After reaching, control to supply 0.1cc each, and_fReached
When it does, it can be determined that it is in focus. CPU
Connect the pre-flop switch 21 to 13 and
Connect the relay 22 to the flip-flop switch, and
-22 from the first and second solenoid valves 15 and 18
Generates control signals for controlling each. And lens 10
When increasing the filling amount of silicone oil in oil tank
17 → Second solenoid valve 18 → Gear pump 16 → First
The solenoid valve 15 → lens 10 flow path is formed
In order to control the filling amount and decrease the filling amount, the lens 10 → second
Solenoid valve 18 → Gear pump 16 → First solenoid
Control so that the flow path from valve 15 to tank 17 is formed.
It

Next, the focus control operation will be described.
First, it is assumed that the object 11 moves from the focus position so as to approach the lens, and the focal length of the lens 10 is too long. The CPU 13 obtains the differential value at the current position from the video signal and stores it in the memory. Next, a minute amount of silicon oil is supplied to the lens 10, the differential value is obtained again, and the value is stored in the memory. Then, the previously stored differential value and the calculated differential value are compared, and the difference is calculated (the differential value of this time is subtracted from the previous differential value). In this case, since the focal length of the lens is shortened by supplying silicon oil, the lens shifts to the focusing direction, the differential value increases, and the differential value difference becomes negative. Then, if the comparison result is negative, a control signal is generated from the CPU 13 to the step motor 19 so as to supply silicon oil to the lens 10.
Next, the differential value is obtained again, the value is stored and compared with the previous differential value, and if the difference is negative, the silicone oil is further supplied. Repeat this operation,
When the obtained differential value reaches D _f , it is determined that the in-focus state is achieved. On the other hand, similarly to the case where the object 11 moves far away from the lens 10, a minute amount of silicon oil is first supplied to the lens 10 to obtain a differential value from the video signal and a comparison process is performed. When the object 11 moves away from the in-focus position, the focal length of the lens 10 is short, so that the supply of silicon oil further shortens the focal length of the lens 10, and as a result, the difference between the differential values becomes positive. If the comparison result is positive, the CPU is the lens
Generates a control signal that reduces the silicone oil filling the 10. Upon receiving this control signal, the flow paths of the first and second solenoid valves 15 and 18 are switched, and the lens 10
Silicone oil inside is reduced by one step. Next, the differential value is obtained again and the comparison process is performed. When the comparison result is positive, the operation is further executed, or when the differential value reaches D _f , it is determined that the focus is reached. With this configuration, the focus variable lens can be automatically focus controlled by a simple operation. In this example, since the silicone oil is supplied and discharged using the gear pump and the two solenoid valves, the response may be slightly delayed, but the silicone oil can be supplied and discharged at a higher speed. If so, sufficient high-speed response can be achieved.

FIG. 3 is a diagram showing a modification of the focus control system for a variable focus lens according to the present invention. The same members as those used in FIG. 2 will be described with the same reference numerals. In this example, one syringe 30 and one linear pulse motor 31 are used to supply and discharge silicone oil. A control signal is supplied from the CPU 13 to the drive circuit 20, and the drive circuit 20 supplies a drive pulse to the linear pulse motor 31. Then, the syringe 30 moves in the direction of arrow a or b according to the operation of the linear pulse motor to increase or decrease the filling amount of the silicone oil filled in the lens 10. In this example,
The maximum filling amount and the minimum filling amount of the silicone oil in the lens 10 are determined in advance, and the filling amount of the silicone oil is controlled between the maximum filling amount and the minimum filling amount. In focus control, first, a differential value is obtained and stored in a memory. And
A minute amount of silicone oil is supplied to the lens 10 to obtain a differential value, the differential value obtained is compared with the differential value stored in the memory, and the difference is obtained (the differential value at this time is calculated from the previous differential value). Subtract). It is determined from the sign of the obtained difference whether the silicone oil should be supplied or reduced. If the difference is positive, the defocus amount is increased by supplying the silicone oil, and therefore the CPU 13 supplies the control signal for reducing the silicone oil of the lens 10 to the drive circuit 20. Then, the drive circuit 20 continuously drives the linear pulse motor 31 until the minimum filling amount is reached. On the other hand, CPU
During this period, a differential signal is obtained from the video signal for each pulse and sequentially stored in the memory. Since the maximum differential value (in the focused state) exists in the differential signals sequentially stored, the position when the maximum differential value occurs, that is, the number of pulses, is obtained. Next, the silicone oil is reversely supplied to the position where the maximum differential value is generated, and the lens 10 is focused. On the other hand, when a negative differential value difference is generated in the comparison comparison of the first differential value, the defocus amount is reduced by the supply of silicon oil, and therefore the CPU controls the lens 10 to increase the filling amount of silicon oil. A signal is supplied to the drive circuit 20 and driven until the maximum filling amount is reached. According to this structure, it is possible to respond to the movement of the object at an extremely high speed.

FIG. 4 shows the relationship between the supply amount of silicon oil and the measured differential value and time when the focus control is actually performed using the focus control system shown in FIG. Figure 4
(a) shows L = 67 cm from the long focus position, and
The experimental result when an object at a position of = 37 cm is focused is shown. Further, FIG. 4 (b) shows an experimental result when an object at L = 37 cm is focused from the long focus position and further an object at a position L = 67 cm is focused. As is clear from the results of this experiment, it takes about 1 second to focus at L = 67 cm from the position L = 67 cm, and from the position L = 37 cm to L = 67 cm.
It takes about 2 seconds to focus at the position. From this experimental result, it is possible to perform focus control at an extremely high speed by using the variable focus lens and the focus control method thereof according to the present invention.

Next, the performance of the back type lens according to the present invention will be evaluated. When liquid is injected into the back type lens, the film surface is deformed into a convex shape. Therefore, the lens surface shape is calculated by assuming that the pressure acting on the liquid and the drag force due to the tension on the film surface are balanced. The evaluation will be described with reference to the schematic diagram shown in FIG. Here, FIG. 5 (a) shows the flexure of a circular polymer film uniformly stretched under uniform load, and FIG. 5 (b) shows the tension acting on the polymer film in a cross section parallel to the rz plane. Show. Let us assume that the center of the lens surface is O, and consider a fan-shaped region defined by Oabcd.

Where Oa = Ob = r and ab = bc
= Dr, the angle between Oa and Ob is a minute angle dθ,
Let W be the pressure acting per unit area of the liquid, T be the surface tension of the polymer film, and z be the amount of displacement in the optical axis direction.
The equation of the balance on the lens surface is given by the following equation.

[0019]

[Equation 1] By rearranging equation (1), the following equation holds.

[0020]

[Equation 2] Equation (2) is the differential equation for the deflection of the polymer film. Solving equation (2) for Z, the following equation holds.

[0021]

[Equation 3] Here, C ₁ and C ₂ are integration constants. In a back-type lens, Z has a finite value when r = 0,
C ₁ = 0. Further, when r = R, Z = 0, so that C ₂ = −WR ² / 4T. Therefore, the displacement Z of the polymer film in the optical axis direction is given by the following equation.

[0022]

[Equation 4] Where γ represents the lens radius,

[Outer 1] Need to meet. As is clear from this equation (4),
The lens surface defined by the polymer film is a parabolic surface rotated about the optical axis. Now, assuming that the curvature in the radial direction and the curvature in the circumferential direction near the center of the polymer film (parabolic surface) are R (r) and R (θ), respectively, the following equation is established. 1 / R (r) =-d ² z / dr ² = W / 2T (5) 1 / R (θ) =-1 / r ・ dz / dr = W / 2T (6) To establish. R (r) = R (θ) = 2T / W (7) As is apparent from the equation (7), the region near the center of the polymer film can be approximated to a spherical surface.

Next, the influence of gravity when the lens is arranged so that the lens surface is vertical will be examined. As shown in FIG. 6, a lens in which the vertical cross section of the lens is extended to infinity was examined. The lens deflection equation in this case is defined by the following equation. Here, the distance in the optical axis direction is x, and the plane orthogonal to the optical axis is the yz plane.

[0024]

[Equation 5] Here, ρ is the density of the enclosed liquid material, and g is the gravitational constant. Under the boundary condition of z = 0 when y = 0,2 (8)
Solving the equation for z,

[0025]

[Equation 6] Here, when the ratio of the pressure W due to the injection of the liquid material and the maximum pressure difference 2ρgγ due to the weight is set to K (= W / 2ρgγ),
The following equation holds.

[0026]

[Equation 7] FIG. 7 shows the result of calculating the lens surface shape in consideration of the influence of gravity on various values of K. In FIG. 7, the position of the center of the polymer film is indicated by a black circle. As is clear from FIG. 7, when K = 30, the influence of gravity becomes almost zero, and an ideal lens surface can be formed.

The present invention is not limited to the above-described embodiments, but various modifications and changes can be made. For example, in the above-described embodiment, the plano-convex lens or plano-concave lens is configured by enclosing the transparent liquid material between the transparent plate and the polymer film.
It is also possible to use a single polymer film and enclose a transparent liquid material between these films to form a biconvex lens.

Further, although the plane parallel plate is used as the transparent plate in the above-mentioned embodiments, it is also possible to construct a two-lens convex lens system or concave lens system by using a transparent plate in the form of a convex lens or a concave lens. is there.

Further, although silicon oil is used as the liquid material in the above-mentioned embodiments, a polymer gel such as PMMA can also be used. When the polymer gel is used, for example, the polymer gel can be used by once shaping it into a spherical or parabolic shape and then coating the lens surface with an elastically deformable polymer film.

[0030]

As described above, according to the present invention, since the elastically deformable polymer elastically deforms in a parabolic shape, it is possible to realize an ideal variable focus lens with almost no aberration. Further, according to the present invention, the focal length can be freely controlled only by changing the filling amount of the transparent liquid material to be filled, so that the focus control can be performed at high speed.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an example of a variable focus lens according to the present invention.

FIG. 2 is a diagram showing a control system of a variable focus lens according to the present invention.

FIG. 3 is a diagram showing a modified example of the control system of the variable focus lens according to the present invention.

FIG. 4 is a graph showing a relationship between time, a differential value, and a supply amount of a liquid material in the control system shown in FIG.

FIG. 5 is a schematic diagram in lens performance evaluation.

FIG. 6 is a schematic diagram in lens performance evaluation when lenses are arranged vertically.

FIG. 7 is a graph showing a relationship between a factor K and a lens center displacement amount.

[Explanation of symbols]

 1 Transparent plate 2 Spacer 3 Polymer film 4a, 4b Tube 10 Focus variable lens 11 Object 12 Imaging device 13 CPU 15, 18 Solenoid valve 16 Gear pump 17 Tank 19 Step motor 20 Drive circuit

Claims (3)

[Claims] 1. A first and a second light-transmissive surface which are arranged to face each other, and an optically transparent liquid material which is hermetically filled between the first and the second light-transmissive surfaces. And a control mechanism for controlling the filling amount of the liquid material, wherein at least one of the first and second light transmissive surfaces is formed of an elastically deformable polymer film, and the filling of the liquid material is performed. A variable focus lens characterized in that the focal length is changed based on the amount. 2. The variable focus according to claim 1, wherein the first surface is made of an optically transparent plate, and the second surface is made of an elastically deformable polymer film. lens. 3. First and second surfaces which are arranged so as to face each other and at least one surface of which is made of an elastically deformable polymer film, and a seal is provided between the first and second surfaces. A focus control device for a variable focus lens, comprising a filled and optically transparent liquid material, the focal length of which varies according to the filling amount of the liquid material, and a control mechanism for controlling the filling amount of the liquid material. An image pickup device for picking up an image of a subject through the variable focus lens; and a differential circuit for generating a distance differential signal based on a video signal generated by the image pickup device, based on the differential signal output from the differential circuit. A focus control device for a variable focus lens, wherein the filling amount of the liquid material is controlled.