JP2005173431A - Autofocus device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an autofocus device of a linear motor system small in size and light in weight by realizing the position control of a focus lens without using a position sensor. <P>SOLUTION: The autofocus device is equipped with the focus lens 1 forming an image with incident light on the light receiving surface of an imaging device, a linear motor constituted of a magnet 4 and a driving coil 3 and generating driving force in the direction of an optical axis 100 in the driving coil 3 in accordance with a driving current supplied to the driving coil 3, a lens holder 2 to which the focus lens 1 and the driving coil 3 are attached and which can move in the direction of the optical axis 100, holder springs 8 and 9 energizing the lens holder 2 in the direction of the optical axis 100, and endpoint detection means 10 and 11 detecting that the lens holder 2 is positioned at the endpoint of a movable area. By using the detection means 10 and 11, the driving current obtained when the lens holder reaches the endpoint of the movable range or it starts moving from the endpoint is discriminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in an autofocus device that drives a focus lens using a linear motor to perform focus control.

  The autofocus device is a device that drives a focus lens in the optical axis direction and forms images of various subjects with different distances on an image sensor. A stepping motor, a linear motor, or the like is used for driving the focus lens. In particular, a linear motor system that linearly drives a focus lens using a drive coil and a magnet is suitable for miniaturization and weight reduction, and is often employed in an autofocus device such as a video camera (for example, Patent Document 1).

  FIG. 10 is a schematic diagram showing a configuration example of a conventional autofocus device adopting a linear motor system, and shows a cross section including an optical axis 100 of incident light from a subject with respect to the optical system unit M2.

  The lens holder 2 is a movable member having a cylindrical shape, and a focus lens 1 is attached to the inside thereof, and a drive coil 3 is attached to a side surface. When a driving current is supplied to the driving coil 3, a driving force parallel to the optical axis 100 is generated in the driving coil 3 due to the interaction between the magnetic field formed by the magnet 4 and the current flowing in the driving coil 3, and the lens holder 2 can be driven along the optical axis 100.

  The position sensor 6 is a sensor for detecting the position of the focus lens 1, and an MR (Magneto Resistance) sensor, a photo interrupter, or the like is used. The image sensor 5 is composed of a CCD (Charge Coupled Device), and an image of the subject formed by the focus lens 1 is output as a camera signal.

Since the in-focus state can be evaluated based on the camera signal, in the case of performing automatic focus control, the in-focus state is evaluated while moving the focus lens 1 and the subject is imaged on the image sensor 5. It is possible to determine the lens position that can be used. When the focus lens 1 is moved in this way, the detection signal of the position sensor 6 is used. Further, when performing fixed focus control, the focus lens 1 is moved to a lens position corresponding to a predetermined subject distance. In this case as well, lens drive control is performed based on the detection signal of the position sensor 6.
JP-A-7-239437

  As described above, in the linear motor system, a driving force corresponding to the supplied current is generated by supplying a current to the driving coil 3. For this reason, when the position control of the focus lens 1 is to be performed using a linear motor, the position sensor 6 for detecting the lens position is required. For this reason, there is a limit to miniaturization, weight reduction, and cost reduction of the autofocus device.

  On the other hand, if a holder spring for biasing the lens holder in the optical axis direction is provided, and the lens holder is driven to a position where the biasing force of the holder spring and the driving force of the driving coil 3 are balanced, the focus lens can be used without using the position sensor 6. It is considered that position control can be performed. However, in general, the biasing force of the spring has a large individual difference and also changes over time, so that there arises a problem that the accuracy of focus control is lowered.

  Further, the relationship between the driving current and driving force of the linear motor shows a hysteresis characteristic due to the influence of the residual magnetic flux. However, since this hysteresis characteristic also changes over time, there arises a problem that the accuracy of the focus control is lowered. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the size and weight of an autofocus device using a linear motor. It is another object of the present invention to provide such a small and light autofocus device at a low cost. It is another object of the present invention to provide an autofocus device that can perform focus control with high accuracy without using a position sensor that can detect the position of the entire movable region of the focus lens.

  The autofocus device according to the present invention includes a focus lens that forms an image of incident light on a light receiving surface of an image sensor, a magnet, and a drive coil. The drive coil is driven in the optical axis direction according to a drive current supplied to the drive coil. A linear motor that generates force, a focus lens and a drive coil, a lens holder that is movable in the optical axis direction, a holder spring that biases the lens holder in the optical axis direction, and the lens holder is positioned at the end point of the movable region And an end point detecting means for detecting that.

  With such a configuration, it is possible to determine the drive current when the moving lens holder reaches the end point or starts moving from the end point. For this reason, focus control can be performed in consideration of variations in motor characteristics and changes over time without using a position sensor that detects the position of the lens holder over the entire operating range. That is, high-precision focus control can be realized while reducing the manufacturing cost.

  In the autofocus device according to the present invention, the end point detection means regulates the movable region of the lens holder by abutting the end portion of the lens holder, and detects the contact state of the lens holder. Consists of parts. With such a configuration, it is possible to detect that the lens holder is at the end point of the movable region as a contact state, and thus it is possible to realize highly accurate focus control with a simple configuration.

  In the autofocus device according to the present invention, the lens holder has a detected terminal electrically connected to the drive coil at an end in the optical axis direction, and the holder abutting portion is the detected terminal. It has an end point detection terminal at the position where it contacts, and is configured to electrically detect the contact state of the lens holder. With such a configuration, the contact state of the lens holder with the holder contact portion can be electrically detected, so that the manufacturing cost can be reduced and the autofocus device can be downsized.

  Further, in the autofocus device according to the present invention, the holder spring is composed of a conductive member whose one end is attached to the end of the lens holder in the optical axis direction and supplies a drive current to the drive coil. A part of the holder spring on the lens holder side is used. With such a configuration, further cost reduction, size reduction, and weight reduction can be achieved.

  In addition, the autofocus device according to the present invention includes a characteristic data generation unit that generates characteristic data in which a drive current and a lens position are associated with each other based on a detection result of the end point detection unit, and a motor characteristic storage unit that stores the characteristic data. And a focus control means for determining the focal point by scanning the focus lens within the movable area based on the characteristic data held in the motor characteristic storage means, and moving the focus lens to the determined focal point. Configured. With such a configuration, high-precision automatic focus control can be performed in consideration of variations in motor characteristics and changes over time.

  In addition, the autofocus device according to the present invention includes a characteristic data generation unit that generates characteristic data in which a drive current and a lens position are associated with each other based on a detection result of the end point detection unit, and a motor characteristic storage unit that stores the characteristic data. And a focus control means for determining the drive current based on the characteristic data held in the motor characteristic storage means and moving the focus lens to the designated lens position. With such a configuration, high-precision fixed focus control can be performed in consideration of variations in motor characteristics and changes over time.

  According to the present invention, by providing the end point detection means for detecting that the lens holder is located at the end point of the movable region, the optical system unit having a simple configuration is used, taking into account variations in motor characteristics and changes over time. High-precision focus control can be performed. Therefore, the manufacturing cost of the optical unit can be reduced, and the size and weight can be reduced, and a small and lightweight autofocus device can be provided at low cost. In addition, an autofocus device can be incorporated into a portable device such as a cellular phone.

  FIG. 1 is a cross-sectional view showing a configuration example of a main part of an autofocus device according to Embodiment 1 of the present invention, and shows a cross section including an optical axis 100 of incident light from a subject with respect to the optical system unit M1. Has been. FIG. 2 is an exploded perspective view showing main parts constituting the optical system unit M1 of FIG.

  The lens holder 2 has a cylindrical shape with the optical axis 100 of incident light as a central axis, the focus lens 1 is attached to the hollow portion, and the drive coil 3 is attached to the outer side surface. The lens holder 2 is a movable member that can move in the direction of the optical axis 100, and a driving force in the direction of the optical axis 100 is applied by energizing the drive coil 3, and the lens holder 2 is drawn forward along the optical axis 100.

  The focus lens 1 is a lens for focus adjustment that collects incident light from a front subject and forms an image on the rear image sensor 5, and the lens holder 2 so that its central axis coincides with the optical axis 100. Installed inside. Since the subject distance, that is, the distance to the subject imaged on the image sensor 5 is determined by the focal distance inherent to the focus lens 1 and the distance from the focus lens 1 to the image sensor 5, the lens holder 2 is placed on the optical axis 100. If the subject distance is changed by moving in the direction, focus adjustment can be performed.

  The imaging element 5 has a light receiving surface on which incident light is collected by the focus lens 1 and is a photoelectric conversion element that converts a planar image formed on the light receiving surface into an electric signal, such as a CCD or CMOS image sensor. is there.

  The drive coil 3 and the magnet 4 constitute a linear motor that applies a driving force to the lens holder 2 and drives the lens holder 2. The drive coil 3 is made of a conductive wire wound around the side surface of the lens holder 2 in the circumferential direction.

  The magnet 4 is formed of a cylindrical permanent magnet fixed in an optical system housing 7 that houses the lens holder 2. The drive coil 3 is disposed in the hollow portion of the magnet 4, and the drive coil 3 is located in a magnetic field formed by the magnet 4. Therefore, if a current is supplied to the drive coil 3, a drive force parallel to the optical axis 100 is generated in the drive coil 3 due to the interaction between the magnetic field and the current, and the lens holder 2 can be linearly driven along the optical axis. .

  The holder springs 8 and 9 are elastic members for biasing the lens holder 2 in the direction of the optical axis 100. A holder spring 8 is attached to the front of the lens holder 2, and a holder spring 9 is attached to the rear of the lens holder 2. Therefore, when a driving current is supplied to the driving coil 3 to generate a forward driving force, the lens holder 2 moves to a position where the driving force balances with the restoring force of the holder springs 8 and 9 and stops. That is, since the lens position is determined by the drive current value, the position of the focus lens 1 can be controlled without using a position sensor.

  The holder abutting portion 12 is a holder regulating means that is provided on the inner side of the rear surface of the rear housing 7b and abuts the rear end portion of the lens holder 2 to regulate the movable region of the lens holder 2, and includes an optical system housing. 7 may be a part or a separate member. The holder abutting portion 12 has a cylindrical shape in order to secure an optical path for allowing incident light from the subject to reach the image sensor 5, and an end point detection terminal 11 described later is provided at the front end portion thereof. .

  The casing of the optical system unit M1 is configured by engaging the front casing 7a and the rear casing 7b. Further, the holder contact portion 12 restricts the rear side of the movable region of the lens holder 2, and the front side is restricted by the inner surface of the front casing 7a. In this specification, the lens position when the lens holder 2 is at the end point on the rear side of the movable region is referred to as a reference point Do, and the lens position when the lens holder 2 is at the front end point is referred to as a maximum extension point Dm.

  The holder abutting portion 12 is arranged so that the lens holder 2 abuts in a state where the lens holder 2 is urged rearward by the holder springs 8 and 9. That is, the movable region of the lens holder 2 is restricted by the holder contact portion 12 so as to be ahead of the position (neutral point) where the repulsive forces of the holder springs 8 and 9 are balanced in the absence of a drive current. Therefore, compared to the neutral state, the holder spring 8 is always contracted and the holder spring 9 is always extended, and the lens position immediately after the start of the autofocus device is the end point on the rear side of the movable region, that is, the reference point Do. It becomes.

  FIG. 3 is a plan view showing a configuration example of the holder springs 8 and 9. The holder springs 8 and 9 are plate springs formed by punching flat metal, and are constituted by coaxial outer ring 21 and inner ring 22, and three connecting springs 23 formed between both rings 21 and 22. Is done. Each connection spring 23 is a leaf spring that connects the rings 21 and 22 in a spiral manner while maintaining a central angle of 120 degrees. Therefore, when a compressive force or tensile force in the direction of the central axis is applied to both rings 21 and 22, the distance is changed by rotating relative to the central axis while maintaining a parallel state. That is, the holder springs 8 and 9 are springs that expand and contract in the central axis direction.

  The outer ring 21 of the front holder spring 8 is attached to the inside of the front surface of the front housing 7 a by the spacer 8 </ b> S, and the inner ring 22 is attached to the front end of the lens holder 2. Similarly, the outer ring 21 of the rear holder spring 9 is attached to the back inner side of the rear housing 7b by the spacer 9S, and the inner ring 22 is attached to the rear end of the lens holder 2.

  FIG. 4 is an explanatory view showing a state in which the drive coil 3 and the holder springs 8 and 9 are connected. The holder springs 8 and 9 are both made of a conductive member, are electrically connected to the drive coil 3, and are used as power supply lines that supply drive current to the drive coil 3. That is, the outer rings 21 of the holder springs 8 and 9 are respectively provided with power supply terminals 8T and 9T connected to a motor drive unit (not shown) for supplying a drive current. Further, one terminal 31 of the drive coil 3 is soldered to the inner ring 22 of the holder spring 8, and the other terminal 32 of the drive coil 3 is soldered to the inner ring 22 of the holder spring 9.

  The end point detection terminals 10 and 11 are voltage level detection means arranged at a position where the inner rings 22 of the holder springs 8 and 9 come into contact with each other, and the drive voltage applied to the drive coil 3 via the holder springs 8 and 9. To detect whether the lens holder 2 is positioned at the end point of the movable region. That is, the inner rings 22 of the holder springs 8 and 9 attached to both ends of the lens holder 2 serve as detected terminals, and the detected terminals are brought into contact with the end point detecting terminals 10 and 11 to electrically detect the end points. .

  The end point detection terminal 10 is provided at the contact position of the lens holder 2 inside the front surface of the front housing 7 a, and the end point detection terminal 11 is provided at the tip of the holder contact portion 12. The end point detection terminals 10 and 11 are ring-shaped terminals that secure an optical path of incident light from the subject and do not contact the outer ring 21 and the connecting spring 23 of the holder springs 8 and 9.

  FIG. 5 is a diagram for explaining the operation of the autofocus device according to the present embodiment. (A) in the figure is a diagram showing an example of the relationship between the drive current and the lens feed amount, (b) is the drive current and the detection voltage of the end point detection terminal 11, and (c) is the drive current. 6 is a diagram showing the relationship between the detection voltage of the terminal detection terminal 10 and the detection voltage. Note that directions A and B in the figure are the moving directions of the focus lens 1 shown in FIG. 1, and A is the feeding direction and B is the backward direction.

First, (a) will be described. The vertical axis of (a) is the lens feed amount, that is, the distance from the reference point Do to the focus lens 1. When no drive current is supplied, the focus lens 1 is at the last reference point Do (the origin in the figure). At this time, since the lens holder 2 is urged rearward by the holder springs 8 and 9, if the drive current is increased from this state, the focus is reached when the drive force exceeds the urging force of the holder springs 8 and 9. The lens 1 starts moving. i ₁ is the driving current at this time, that is, the current value at the start of feeding.

If the drive current is further increased, the feed amount increases in proportion to the excess of the current value i ₀ at the start of the feed. When the focus lens 1 reaches the maximum extension point Dm where the extension amount reaches the maximum, the extension amount does not change even if the drive current is increased thereafter. i ₂ is the driving current at this time, that is, the current value at the end of the feeding.

Next, even if the drive current is decreased from i ₂ , the focus lens 1 does not start moving for a while due to the influence of the residual magnetic flux. If the drive current is further reduced, the focus lens 1 starts moving. i ₃ is the drive current at this time, that is, the current value at the start of retraction.

Thereafter, if decreasing the driving current, the amount of feed in proportion to the decrease of the current value i ₃ at the start of retraction decreases. When the focus lens 1 reaches the reference point Do, the feed amount becomes zero, and thereafter, the feed amount does not change even if the drive current is decreased. i ₄ is the driving current at this time, that is, the current value at the end of the backward movement.

The drive current i ₄ at the end of the backward movement is smaller than the current i ₁ at the start of feeding. For this reason, in order to extend the focus lens 1 again, it is necessary to increase the drive current to i ₁ or more. The linear motor has such a hysteresis characteristic.

Next, (b) will be described. The end point detection terminal 11 can detect the applied voltage from the motor drive unit only when the inner ring 22 of the holder spring 9 is in contact. Therefore, when the case the drive current going to increase the driving current is less than i _1, when going to reduce the drive current voltage at the terminal 32 of the driving coil 3 when the driving current is less than i ₄ A level is applied.

Next, (c) will be described. The end point detection terminal 10 can detect the applied voltage from the motor drive unit only when the inner ring 22 of the holder spring 8 is in contact. Therefore, when the drive current is increased, the voltage at the terminal 31 of the drive coil 3 is when the drive current is i ₂ or more, and when the drive current is decreased, the drive current is i ₃ or more. A level is applied.

That is, if the end point detection terminals 10 and 11 are used, it can be detected that the focus lens 1 is located at the end point of the movable region. For this reason, it is possible to accurately obtain the drive currents i _{1 to} i ₄ at the start and end of the movement in the feeding direction A and the backward direction B without using a position sensor.

FIG. 6 is a diagram showing an example when the characteristics of the holder springs 8 and 9 are changed. If the repulsive force of the holder springs 8 and 9 is weak, the inclination of the characteristic (a) showing the lens extension amount with respect to the drive current becomes large. If the repulsive force of the holder spring 8 is weaker than the repulsive force of the holder spring 9, the characteristic (a) moves to the left. In any case, the drive current values i _{1 to} i ₄ are values corresponding to the motor characteristics. Therefore, if the drive current values i _{1 to} i ₄ are determined based on the voltage levels at the end point detection terminals 10 and 11, variations in characteristics of the holder springs 8 and 9 and changes with time can be compensated.

  As described above, the AF optical system M1 according to the present embodiment controls the lens position by the balance between the driving force of the driving coil 3 and the biasing force of the holder springs 8 and 9. For this reason, the motor characteristics referred to in this specification include not only the characteristics of the linear motor including the drive coil 3 and the magnet 4 but also the characteristics of the holder springs 8 and 9.

  FIG. 7 is a block diagram showing a configuration example of an autofocus device including the optical system unit M1 of FIG. This autofocus device includes an optical system unit M1, a signal amplification unit 50, a camera signal processing unit 51, an AF signal processing unit 52, an AF gate generation unit 53, a focus control unit 54, a characteristic data generation unit 55, and a motor characteristic storage unit 56. The motor drive unit 57 and the end point detection unit 58 are configured.

  The signal amplification unit 50 amplifies the camera signal output from the image sensor 5 to an appropriate signal level and outputs the amplified signal to the camera signal processing unit 51. The camera signal processing unit 51 performs predetermined signal processing on the camera signal to generate an image signal. For example, an image signal composed of a luminance signal and two color difference signals is output. The AF signal processing unit 52 evaluates the in-focus state based on the luminance signal output from the camera signal processing unit 51 and generates an AF evaluation signal. When the AF evaluation is performed in the AF signal processing unit 52, the AF gate generation unit 53 generates an AF gate signal that designates a part of the image area in the captured image area as an evaluation target.

  In general, an image shot in an in-focus state has a larger luminance difference between adjacent pixels than an image shot in an out-of-focus state, and the luminance signal contains a lot of high-frequency components. For this reason, if the high frequency component in the luminance signal is evaluated, the in-focus state can be evaluated. Here, it is assumed that the AF signal processing unit 52 obtains an AF integrated value as an AF evaluation signal. The AF integrated value is the sum of luminance differences between adjacent pixels, and is obtained for the image area designated by the AF gate signal.

The motor characteristic storage unit 56 stores characteristic data regarding the linear motor. The characteristic data is the characteristic of the lens position with respect to the driving direction and the driving current. Here, the driving currents i _{1 to} i ₄ at the start and end of the movement of the focus lens 1 shown in FIG. 5 are stored as the characteristic data. It is assumed that

  The focus control unit 54 instructs a drive current to the motor drive unit 57 to control the position of the focus lens 1. The motor drive unit 57 supplies drive current to the drive coil 3 in accordance with instructions from the focus control unit 54. The focus control unit 54 can perform automatic focus control and fixed focus control.

  The automatic focus control is a control for determining the focal point on the subject and moving the focus lens 1 to the focal point. When performing the automatic focus control, the focus control unit 54 sequentially changes the drive current value, moves the focus lens 1 at a predetermined pitch, and scans the entire movable region of the focus lens 1. During scanning of the focus lens 1, the focus control unit 54 monitors the AF signal from the AF signal processing unit 52. Then, after the scan is completed, the AF integrated value obtained for each lens position is compared, and the lens position where the AF integrated value is maximum is determined as the in-focus point. After the focal point is determined in this way, the focus lens 1 is moved to the focal point.

  In this case, the driving current at the start and end of scanning of the focus lens 1 is determined based on the characteristic data in the motor characteristic storage unit 56. Further, the change step width of the drive current corresponding to the movement pitch of the focus lens 1 is also determined based on the characteristic data. Furthermore, the drive current for moving the focus lens 1 to the in-focus point is also determined based on the characteristic data.

FIG. 8 is a diagram showing an example of the AF integrated value when the focus lens 1 is scanned over the entire movable region. The focal point is determined by changing the drive current from i ₁ to i ₂ for each predetermined step width. In this figure, it can be seen that the drive current i _a is the focal point. Therefore, in consideration of the hysteresis characteristics of the linear motor, the in-focus state can be obtained by driving the focus lens 1 to this in-focus point. For example, the drive current is set to i _a- (i ₂ -i ₃ ) to move to the focal point. Thereafter, by further narrowing the scan range and performing the same operation with a narrower pitch, the in-focus point can be determined more accurately.

In this way, when the focus lens 1 is moved in the extending direction to scan the entire movable region, the drive current at the start is i ₁ and the drive current at the end is i _2. Thus, scanning can be completed and current consumption can be reduced. Similarly, if scanning is performed by moving in the backward direction, the drive current at the start may be i ₃ and the drive current at the end may be i ₄ .

If the movable region of the focus lens 1 is known, the change step width of the drive current corresponding to the movement pitch of the focus lens 1 can be obtained based on the change width (i ₂ −i ₁ ) of the drive current. . Further, by grasping the accurate hysteresis characteristics of the linear motor based on the drive currents i _{1 to} i ₄ , it is possible to accurately drive the focal point determined by the scan of the focus lens 1.

  On the other hand, the fixed focus control is control for moving the focus lens 1 to a lens position where a predetermined subject distance is obtained. When performing the fixed focus control, the focus control unit 54 obtains a drive current value corresponding to the subject distance designated by the user using the characteristic data held in the motor characteristic storage unit 56, and obtains this drive current value. Output to the motor drive unit 57. For example, if the user specifies a close-up mode for reading a barcode, a drive current value corresponding to the subject distance in a predetermined close-up mode is obtained, and the focus lens 1 is controlled to the lens position. Is done. Note that the subject distance and the lens position correspond one-to-one if the focal distance of the focus lens 1 and the position of the image sensor 5 are determined.

  The end point detection unit 58 generates a first detection signal based on the voltage level of the end point detection terminal 11, and generates a second detection signal based on the voltage level of the end point detection terminal 10. These detection signals are generated by comparing the voltage levels of the end point detection terminals 10 and 11 with a predetermined threshold level, and are output to the characteristic data generation unit 55.

The characteristic data generation unit 55 monitors the detection signal from the end point detection unit 58 while scanning the focus lens 1, thereby driving current i ₁ at the start and end of movement in each movement direction of the focus lens 1. i ₄ is discriminated, and characteristic data including these drive currents i _{1 to} i ₄ is generated. The generated characteristic data is stored in the motor characteristic storage unit 56. Such generation of characteristic data is performed, for example, as an initial operation of the autofocus device.

Steps S101 to S110 in FIG. 9 are flowcharts showing an example of an initial operation of the autofocus device, and show an operation executed immediately after the autofocus device is turned on. In the autofocus device, the characteristic data generation unit 55 drives the focus lens 1 when activated to reciprocate the movable region. By this reciprocating operation, the drive currents i _{1 to} i ₄ are determined and stored in the motor characteristic storage unit 56 as characteristic data.

Immediately after activation of the autofocus device, the focus lens 1 is at the reference point Do, and the first detection signal is output from the end point detection unit 58. The characteristic data generation unit 55 increases the drive current by a predetermined step width from this state (step S101). As a result, when the focus lens 1 starts to move, the first detection signal is not output (step S102). Characteristic data generation section 55 as the current value i ₁ at the start of feeding the driving current at this time is stored in the motor characteristic storage section 56 (step S103).

Further, the drive current is increased, and when the focus lens 1 is extended to the maximum extension point Dm and the movement is finished, a second detection signal is output from the end point detection unit 58 (step S104). Characteristic data generation section 55 as the current value i ₂ at the end of feeding the driving current at this time is stored in the motor characteristic storage section 56 (step S105).

After determination of the current value i ₂ is gradually decreasing the driving current by a predetermined step width (step S106). Then, when the focus lens 1 starts moving and the second detection signal is not output, the drive current at that time is stored in the motor characteristic storage unit 56 as the current value i ₃ at the time of starting reverse (step S107, S108).

Further, the drive current is decreased, and when the focus lens 1 moves back to the reference point Do and ends its movement, the first detection signal is output again from the end point detection unit 58 (step S109). The characteristic data generation unit 55 stores the drive current at this time in the motor characteristic storage unit 56 as the current value i ₄ at the end of the backward movement (step S110).

  The characteristic data generation unit 55 performs the above processing as an initial operation, so that characteristic data is generated each time the autofocus device is activated. Therefore, even when the linear motor changes over time, the characteristic data of the focus lens 1 Position control can be performed with high accuracy.

  According to the present embodiment, the state where the focus lens 1 is located at the end point of the movable region is detected, and the position control of the focus lens is performed based on the detection result. For this reason, the autofocus device can be reduced in size and weight as compared with the case of using a position sensor for detecting the lens position for the entire movable region of the focus lens 1 without significantly reducing the control accuracy.

  In particular, in the present embodiment, the holder springs 8 and 9 are provided at both ends of the lens holder 2, and the drive current is supplied to the drive coil 3 via the holder springs 8 and 9. Therefore, it is only necessary to provide the end point detection terminals 10 and 11, and the optical system unit M1 can be greatly reduced in size and weight. As a result, since the size of the optical system unit M1 in the optical axis direction can be reduced to less than 10 mm, the autofocus device can be mounted on a thin portable device such as a mobile phone with a camera.

  In the present embodiment, as an example, the case where the applied voltage to the drive coil 3 is detected using the end point detection terminals 10 and 11 for performing voltage detection has been described. Although such a configuration is desirable from the viewpoint of miniaturization and weight reduction, the present invention is not necessarily limited to such a case. For example, end point detection may be performed using a piezoelectric sensor or the like.

It is sectional drawing which showed one structural example of the principal part of the auto-focus apparatus by Embodiment 1 of this invention. FIG. 2 is an exploded perspective view showing main parts constituting the optical system unit M1 of FIG. FIG. 6 is a plan view showing a configuration example of holder springs 8 and 9. It is explanatory drawing which showed a mode that the drive coil 3 and the holder springs 8 and 9 were connected. It is a figure for demonstrating operation | movement of the auto-focus apparatus by this Embodiment. It is the figure which showed an example when the characteristic of the holder springs 8 and 9 changed. It is the block diagram which showed one structural example of the auto-focus apparatus containing the optical system unit M1 of FIG. It is the figure which showed an example of AF integrated value at the time of making the focus lens 1 scan the whole movable region. It is the flowchart which showed an example of the initial operation | movement of an auto-focus apparatus. It is the schematic diagram which showed the structural example of the conventional autofocus apparatus which employ | adopted the linear motor system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Focus lens 2 Lens holder 3 Drive coil 4 Magnet 5 Image pick-up element 6 Position sensor 7, 7a, 7b Optical system housing | casing 8, 9 Holder spring 10, 11 End detection terminal 12 Holder contact part 21 Outer ring 22 Inner ring 23 Connection Spring 50 Signal amplification unit 51 Camera signal processing unit 52 AF signal processing unit 53 AF gate generation unit 54 Focus control unit 55 Motor drive unit 55 Characteristic data generation unit 56 Motor characteristic storage unit 57 Motor drive unit 58 Endpoint detection unit 100 Optical axis A Feeding direction B Backward direction i ₁ Driving current i at the start of movement in the feeding direction ₂ Drive current i at the end of movement in the feeding direction ₃ Driving current i at the start of movement in the backward direction ₄ End of movement in the backward direction Drive current

Claims (6)

A focus lens that focuses incident light on the light receiving surface of the image sensor;
A linear motor that includes a magnet and a drive coil, and generates a drive force in the optical axis direction in the drive coil in accordance with a drive current supplied to the drive coil;
A lens holder to which a focus lens and a drive coil are attached and movable in the optical axis direction;
A holder spring for urging the lens holder in the optical axis direction;
An autofocus device comprising: an end point detecting means for detecting that the lens holder is positioned at an end point of the movable region.   The end point detection means includes a holder contact portion that restricts a movable region of the lens holder by contacting an end portion of the lens holder and detects a contact state of the lens holder. The autofocus device according to 1. The lens holder has a detected terminal electrically connected to the drive coil at the end in the optical axis direction,
3. The autofocus device according to claim 2, wherein the holder contact portion has an end point detection terminal at a position where the detected terminal contacts, and electrically detects the contact state of the lens holder. The holder spring is composed of a conductive member whose one end is attached to the end of the lens holder in the optical axis direction and supplies a drive current to the drive coil.
The autofocus device according to claim 3, wherein a part of the holder spring on the lens holder side is used as the detected terminal. Based on the detection result of the end point detection means, characteristic data generation means for generating characteristic data in which the drive current and the lens position are associated with each other;
Motor characteristic storage means for storing the characteristic data;
Based on the characteristic data held in the motor characteristic storage means, the focus lens is scanned within the movable region to determine the in-focus point, and the focus control means to move the focus lens to the determined in-focus point. The autofocus device according to claim 1. Based on the detection result of the end point detection means, characteristic data generation means for generating characteristic data in which the drive current and the lens position are associated with each other;
Motor characteristic storage means for storing the characteristic data;
An autofocus device comprising: focus control means for determining a drive current based on characteristic data held in a motor characteristic storage means and moving the focus lens to a designated lens position.

Images