KR101614863B1 - auto focusing method using VCM actuator - Google Patents

Abstract

The present invention relates to a method of automatically adjusting a focus of a lens while increasing a lens position by using a voice coil motor (VCM) actuator to obtain a best focused optimal upward position value and lowering the lens position. The method includes the steps of: (a) setting a lens position as an upward position value according to a dummy code obtained by dividing each code value of the hysteresis table of the VCM actuator; (b) (C) repeating steps (a) and (b) with increasing the code value, and thereafter capturing and capturing an image captured with the code value And (d) setting a position of the lens based on the optimal upward position value in the downward characteristic of the hysteresis table. Minimizes spring ringing by improving linearity of spring movement of voice coil motor.

A voice coil motor (VCM), an actuator, an upward position value, a hysteresis table

Description

[0001] The present invention relates to an auto focusing method using a VCM actuator,

The present invention relates to a method of adjusting an auto-focus in a camera or a camera module.

It has become essential that a camera or a camera module recently has an auto focusing function.

Recently, the autofocus control method detects a high frequency component of an image acquired from an image sensor to acquire a focus value (FV) useful for focus adjustment, and moves the lens to a point where the FV reaches a maximum value. Such a method may be composed of a part for detecting the FV, a part for determining the moving position of the lens by evaluating the FV, and a part for controlling the lens. The most basic method for finding the maximum value of the FV is the mountain search method. Information on the focus control is obtained from the image signal obtained without a separate apparatus.

The voice coil motor (VCM) is an actuator that linearly moves the lens by using the Lorentz force generated by the induction magnetic force of the coil in the magnetic field of the permanent magnet. It is a system that precisely linearly moves a relatively short distance . However, when an auto focus (AF) algorithm is performed using a VCM actuator, when the auto focus (AF) command is received, hysteresis hysteresis. In the full-scan AF algorithm, the position of the lens is set based on the AF position code value in the downward characteristic after taking the AF position code value that the AF is optimized in the upward characteristic of the VCM. Since the upward position value and the downward position value are different from each other, the position of the lens should be set up and downward again. Such a voice coil motor has a spring structure, which causes a ringing phenomenon due to spring movement during AF.

The present invention provides an automatic focusing method that minimizes a springing phenomenon when the lens moves upward in an automatic focusing method using a VCM actuator.

A method of automatically adjusting the focus of a lens while acquiring a most focused optimal upward position value while lowering the lens position while upwardly moving the lens position using a voice coil motor (VCM) actuator according to an embodiment of the present invention (a) setting a lens position as an upward position value according to a dummy code obtained by dividing each code value of the hysteresis table of the VCM actuator, (b) setting a position of the lens at an upward position according to each code value of the hysteresis table, (C) repeating the steps (a) and (b) with increasing the code value, and then determining the position of the lens from the images captured according to the code value (D) determining a position of the lens based on the optimum upward position value in the downward characteristic of the hysteresis table; And a step of.

According to the automatic focus adjustment method using the VCM actuator according to the present embodiment, as the spring moving section according to each step of the upward movement of the lens is shortened, the linearity of the spring movement of the voice coil motor is improved to minimize the spring ringing phenomenon. The settling time and overshooting of the spring can be reduced.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and a duplicate description thereof will be omitted.

FIG. 1 is a graph showing characteristics of a VCM actuator, and FIG. 2 is a hysteresis characteristic graph of a VCM actuator.

Referring to FIGS. 1 and 2, it can be seen that the lens shift distance according to the current value is different between the upward position value and the downward position value. Here, the upward direction may denote advancement of the lens, and the downward direction may denote retraction of the lens. After taking the code value of the optimal upstream position value with optimal AF in the AF algorithm from the upward characteristic of the VCM, the position of the lens is set based on the code value in the downstream characteristic.

3 is a graph for explaining a full-scan type AF driving method.

Referring to FIG. 3, the position of the lens with respect to time is shown, and a code value of an optimum upward position value in which AF is optimally adjusted is taken from the upward characteristic of the VCM (see a) (See b), the upper lens position and the lower lens position are different from each other. Therefore, the optimal lens position can be set by taking the upward characteristic again (see c).

4 is a graph illustrating an AF driving method using the VCM actuator according to the present embodiment.

Referring to FIG. 4, a code value of the optimum upward position value indicating the position of the lens with respect to time is obtained from the upward characteristic of the VCM, and a dummy code such as two or three dummy codes code is added to the position of the lens, and the code value of the optimum up-position value is obtained (see d) by setting the position of the lens in a stepwise manner, and then the position of the lens is set based on the code value in the down- e) Since the upward position value and the downward position value are different from each other, the position of the optimal lens can be set by taking the upward characteristic again (see f).

5 is a block diagram showing a driver of the VCM actuator according to the present embodiment. 5, the driver 100 of the VCM actuator includes an interface unit 110, a memory 120, a dummy wave unit 130, an adder 140, a DAC 150, a reference 160, And an AMP 170.

The interface unit 110 receives an external signal. The memory 120 includes a hysteresis table according to the present embodiment. Here, the hysteresis table is a table showing the upward position value and the downward position value of the VCM actuator according to each code value.

Table 1 shows a hysteresis table stored in the memory 120 according to the present embodiment.

code Up position value Downward position value 60 27 47 66 42 63 72 57 79 78 72 93 84 86 107 90 100 120 96 113 133 102 125 145 108 137 156 114 149 166 120 160 176 126 169 185 132 179 192 138 188 200 144 196 205 150 202 208 156 205 212 162 209 214 168 213 216 174 215 218 180 218 220 186 221 221 190 222 222

The dummy wave unit 130 outputs a digital waveform according to a dummy code obtained by dividing each code value (actual code) of the hysteresis table to be added to each upward position value. For example, referring to Table 1, a code value 69 obtained by dividing the code value (actual code) between 66 and 72 of the hysteresis table is used as a dummy code, and a digital waveform corresponding thereto is output.

The adder 140 adds the waveform according to the code value of the hysteresis table and the digital waveform output from the dummy wave 130 according to the time transition.

The DAC 150 receives a digital signal and outputs an analog signal. In the present embodiment, the DAC 150 outputs a current as an analog signal. The reference 160 is a reference for converting a digital signal into an analog signal, and may include a current table according to a code value. The AMP 170 functions as a gain-booting buffer for the output of the DAC 150 and controls the current.

FIG. 6 is a flowchart illustrating an automatic focus adjustment method using the VCM actuator according to the present embodiment.

Referring to FIG. 6, an AF command signal for performing autofocus is received (S210). The position of the lens is set to an up position value according to a dummy code obtained by dividing each code value (actual code) of the hysteresis table (S220). For example, referring to Table 1, a code value 69 obtained by dividing the actual code of the hysteresis table between 66 and 72 is used as a dummy code, and an upward position value according to the code value 69 is used as a dummy code. Set the position. In this embodiment, the dummy code is generated by dividing each code value of the hysteresis table into two parts. However, each code value is divided into three or four parts to form a dummy code It will be apparent to those skilled in the art that the invention is not limited thereto.

Then, an image is captured and stored in an image sensor processor (ISP) (not shown) connected to the driver 100 of the VCM actuator by setting the lens position as an upward position value according to the code value of the hysteresis table (S230). The code value is increased until a full scan is performed according to the upward position value of all necessary code values and S220 and S230 are repeated to obtain the best focused upward position value among the stored images as the optimum upward position value. (S240). For example, an image sensor processor (ISP) can acquire an upstream position value of an image having the highest frequency among images stored as an optimal upstream position value.

Then, the position of the lens is set based on the optimum upward position value in the downward characteristic of the hysteresis table (S250).

FIG. 7 is a diagram showing a reduction in the ringing phenomenon of the VCM when performing AF using the VCM actuator according to the present embodiment. Referring to FIG. 7, according to the conventional AF driving method of the VCM actuator, the amplitude of the ringing phenomenon of the VCM spring is large (see a). In the AF driving method of the VCM actuator according to the present embodiment, it can be seen that the amplitude of the ringing phenomenon is greatly reduced (see b).

As used in this embodiment, the term " portion " refers to a hardware component such as software or an FPGA (field-programmable gate array) or ASIC, and 'part' performs certain roles. However, 'part' is not meant to be limited to software or hardware. &Quot; to " may be configured to reside on an addressable storage medium and may be configured to play one or more processors. Thus, by way of example, 'parts' may refer to components such as software components, object-oriented software components, class components and task components, and processes, functions, , Subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided in the components and components may be further combined with a smaller number of components and components or further components and components. In addition, the components and components may be implemented to play back one or more CPUs in a device or a secure multimedia card.

All of the functions described above may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), etc. according to software or program code or the like coded to perform the function. The design, development and implementation of the above code will be apparent to those skilled in the art based on the description of the present invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Accordingly, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

1 is a graph showing characteristics of a VCM actuator.

2 is a hysteresis characteristic graph of a VCM actuator.

3 is a graph for explaining a full-scan type AF driving method.

4 is a graph illustrating an AF driving method using the VCM actuator according to the present embodiment.

5 is a block diagram showing a driver of the VCM actuator according to the present embodiment.

FIG. 6 is a flowchart illustrating an automatic focus adjustment method using the VCM actuator according to the present embodiment.

FIG. 7 is a diagram showing a reduction in the ringing phenomenon of the VCM when performing AF using the VCM actuator according to the present embodiment.

DESCRIPTION OF THE REFERENCE SYMBOLS

100: driver of VCM actuator 110: interface part

120: memory 130: dummy wave section

140: Adder 150: DAC

160: Reference 170: AMP

Claims (4)

There is provided a method of automatically adjusting a focus of a lens while moving a lens position upward by using a voice coil motor (VCM) actuator to obtain a best focused optimal upward position value and lowering the lens position, (a) setting a position of a lens with an upward position value according to a dummy code obtained by dividing each code value of the hysteresis table of the VCM actuator; (b) capturing and storing an image by setting a position of the lens as an upward position value according to each code value of the hysteresis table including the dummy code; (c) repeating the steps (a) and (b) while increasing the code value, and obtaining the optimal upward position value from the captured images according to the code value; And (d) setting a position of the lens based on the optimal upward position value in a downward characteristic of the hysteresis table. The method according to claim 1, Wherein the optimal up position value is an up position value when the frequency of the captured images is the highest. The method according to claim 1, Wherein the setting of the position of the lens by the upward position value is a forward movement of the lens. The method according to claim 1, In the step (b) Wherein the image is captured and stored in an image sensor processor (ISP).

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