Imaging device

Abstract

Provided is an imaging device enabling precise adjustment of the focal position.　This imaging device comprises: a frame that has a cylindrical part protruding from a position surrounding a through hole penetrating in the axial direction, and a male thread on the outer peripheral surface of the cylindrical part; an image sensor that has a light receiving surface for receiving light that has passed through the through hole; a lens that faces an object on the opposite side of the frame from the image sensor and forms an image of the object on the light receiving surface; a lens holder that is housed in the inner periphery of the cylindrical part and movable in the axial direction integrally with the lens; a biasing member that biases the lens holder in a direction away from the image sensor; a holder cap that has an inner peripheral surface having a female thread threadedly engaged with the male thread and an outer peripheral surface having a driven gear, and restricts the movement of the lens holder in the direction away from the image sensor; and a drive mechanism that moves the holder cap in the axial direction with respect to the frame by transmitting driving force to the driven gear so as to rotate the holder cap.

Description

Imaging device

[0001] The present invention relates to an imaging device.

[0002] Conventionally, cameras have been known that include an image sensor and a lens that forms an image of a subject on the light receiving surface of the image sensor. For such cameras, there is a technique for keeping the position of the lens constant relative to the image sensor (see, for example, Patent Document 1).

[0003] Special Publication No. 2022-522039

[0004] However, when cameras are installed outdoors where there is a large temperature difference between day and night or summer and winter, such as with surveillance cameras, differences in the expansion coefficients of each component can cause a shift in the focal position, resulting in a blurred image formed on the light receiving surface.For this reason, with cameras used for such purposes, it is difficult to obtain high-resolution images simply by keeping the positions of the image sensor and lens constant, as in Patent Document 1.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging device that allows precise adjustment of the focal position.

[0006] In order to solve the above problem, the imaging device of the present invention is characterized by comprising: a frame having a cylindrical portion that protrudes toward a subject at a position surrounding a through hole that penetrates in the axial direction, and a male thread on the outer peripheral surface of the cylindrical portion; an image sensor having a light receiving surface that receives light that has passed through the through hole and that is positioned further from the subject than the frame; a lens that faces the subject on the opposite side of the frame from the image sensor and forms an image of the subject on the light receiving surface; a lens holder that is housed in the inner circumference of the cylindrical portion and is movable in the axial direction together with the lens; a biasing member that biases the lens holder in a direction away from the image sensor; a holder cap that has an inner peripheral surface with a female thread that screws onto the male thread and an outer peripheral surface with a driven gear, and that restricts movement of the lens holder in a direction away from the image sensor; and a drive mechanism that transmits a driving force to the driven gear to rotate the holder cap, thereby moving the holder cap in the axial direction relative to the frame.

[0007] According to the present invention, it is possible to obtain an imaging device that allows precise adjustment of the focal position. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0008] FIG. 1 is an external perspective view of a surveillance camera; FIG. 2 is a diagram showing main components of an imaging device; FIG. 3 is an exploded perspective view of a frame, a lens, a lens holder, a biasing member, and a holder cap; FIG. 4 is an exploded perspective view of a biasing member; FIG. 5 is a longitudinal sectional view of an imaging device; FIG. 6 is a diagram showing main components of a drive mechanism; FIG. 7 is a diagram showing a hardware configuration of an imaging device; FIG. 8 is a diagram showing another example of a biasing member; and FIG. 9 is a diagram showing another example of a drive mechanism.

[0009] Hereinafter, an embodiment of the invention will be described with reference to the drawings. This embodiment realizes a highly versatile surveillance camera 1 and imaging device 10, which contributes to "9. Build resilient infrastructure, promote inclusive and sustainable industrialization, foster innovation and build resilient infrastructure" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0010] [Overall Configuration of Surveillance Camera 1] Fig. 1 is a perspective view of the exterior of surveillance camera 1. Surveillance camera 1 is a camera that is installed on a ceiling or wall and monitors its surroundings. More specifically, surveillance camera 1 captures images of surrounding subjects and outputs image signals (e.g., still image signals, moving image signals). Typically, surveillance camera 1 according to this embodiment may be installed outdoors where the temperature changes greatly. As shown in Fig. 1, surveillance camera 1 mainly comprises a housing 2, a dome 3, and an imaging device 10.

[0011] The housing 2 houses the components of the surveillance camera 1, including the imaging device 10. The housing 2 is fixed to a ceiling or a wall. The dome 3 is a translucent material that transmits light. The dome 3 has the outer shape of a part of a sphere (typically a hemisphere). The dome 3 protrudes from an opening provided in the housing 2. The imaging device 10 is housed inside the housing 2. The imaging device 10 photoelectrically converts light incident through the dome 3 to generate an image signal, and outputs the generated image signal to an external device (for example, a monitoring terminal such as a computer or recorder).

[0012] [Configuration of Imaging Device 10] Figure 2 is a diagram showing the main components of the imaging device 10. Figure 3 is an exploded perspective view of the frame 11, lens 15, lens holder 16, biasing member 17, and holder cap 18. As shown in Figures 2 and 3, the imaging device 10 includes the frame 11, cover 12, image sensor 13, color filter 14, lens 15, lens holder 16, biasing member 17, holder cap 18, drive mechanism 19, home position sensor 20 (see Figure 7), image processing board 21 (see Figure 7), and motor control board 22. Note that the motor control board 22 alone, or the combination of the image processing board 21 and the motor control board 22, is an example of a control unit.

[0013] The frame 11 is a member that supports the components (12-22) of the imaging device 10. As shown in FIG. 3 , the frame 11 is composed of a disk portion 23 and a cylindrical portion 24. The disk portion 23 has a disk-like outer shape with a front surface and a back surface. A through-hole 25 that penetrates the disk portion 23 in the axial direction is formed in the disk portion 23. The cylindrical portion 24 has a cylindrical outer shape. Both ends of the cylindrical portion 24 in the axial direction are open. The cylindrical portion 24 protrudes from the disk portion 23 toward the subject at a position that surrounds the through-hole 25.

[0014] In this specification, the direction in which the cylindrical portion 24 protrudes is referred to as the "axial direction," the direction perpendicular to the axial direction is referred to as the "radial direction," and the direction of the circumference of a circle centered on the axial direction is referred to as the "circumferential direction." Furthermore, within the axial direction, the direction away from the image sensor 13 (in other words, the direction toward the subject) is referred to as the "subject-facing direction," and the direction toward the image sensor 13 (in other words, the direction away from the subject) is referred to as the "sensor-facing direction." Furthermore, of the surfaces of each component facing the axial direction, the surface facing the subject is referred to as the "front surface," and the surface facing the sensor is referred to as the "back surface." Furthermore, the axial direction may coincide with the direction of the optical axis of the image sensor 13. The optical axis of the image sensor 13 refers, for example, to the imaging direction of the image sensor 13 (more specifically, the direction toward the center of the angle of view of the image sensor 13).

[0015] A male thread 26 is formed on the outer peripheral surface of the cylindrical portion 24. The cylindrical portion 24 also has a ring portion 27 that protrudes radially inward from the inner peripheral surface and extends circumferentially at the end facing the sensor in the axial direction. The ring portion 27 may be formed around the entire inner peripheral surface of the cylindrical portion 24, or may be formed on a portion of the inner peripheral surface of the cylindrical portion 24 in the circumferential direction.

[0016] The ring portion 27 has a plurality of recesses 28 (only one of which is shown in FIG. 2 ). The recesses 28 are recessed from the surface of the ring portion 27 toward the image sensor 13. The recesses 28 are provided at positions spaced apart (more specifically, equally spaced) around the circumference of the ring portion 27. In this embodiment, the recesses 28 are provided at three locations spaced apart at 120° intervals, but may be provided at four or more locations. The recesses 28 accommodate one end of the biasing member 17. More specifically, one end of the biasing member 17 abuts against the innermost surface of the recesses 28.

[0017] The cover 12 is attached to the frame 11 at a position closer to the subject than the frame 11 (more specifically, the disk portion 23). This forms an internal space between the frame 11 and the cover 12 that houses some of the components (15-19, 22) of the imaging device 10. The cover 12 also has an opening 29 that exposes the lens 15.

[0018] The image sensor 13 is a collection of multiple pixels arranged in a matrix on its light-receiving surface. The image sensor 13 photoelectrically converts light that has passed through the lens 15 to generate an image of the subject. The image sensor 13 then outputs an image signal representing the generated image to the image processing board 21. The image sensor 13 is, for example, a complementary metal-oxide-semiconductor (CMOS) or a charge-coupled device (CCD). The color filter 14 separates the light that has passed through the lens 15 into individual colors and causes them to enter the image sensor 13. Note that the color filter 14 is optional.

[0019] The image sensor 13 is disposed at a position facing the through-hole 25 and farther from the subject than the frame 11. The color filter 14 is disposed between the frame 11 and the image sensor 13. As a result, light that has passed through the lens 15 passes through the through-hole 25, is dispersed by the color filter 14, and enters the image sensor 13.

[0020] The lens 15 is disposed axially opposite the image sensor 13 across the frame 11, facing the subject. That is, the lens 15 is disposed axially at a predetermined distance (a focal length, described below) from the image sensor 13. The lens 15 focuses light emitted from the subject onto the light-receiving surface of the image sensor 13, thereby forming an image of the subject on the light-receiving surface of the image sensor 13. The lens 15 is composed of, for example, a light-focusing portion 30 and a threaded portion 31. The light-focusing portion 30 is a convex lens that focuses light incident through the dome 3 onto the light-receiving surface of the image sensor 13. The threaded portion 31 is a cylindrical portion extending axially from the back surface of the light-focusing portion 30. A male thread 32 is formed on the outer circumferential surface of the threaded portion 31.

[0021] The lens holder 16 holds the lens 15. The lens holder 16 is housed on the inner periphery of the cylindrical portion 24. The lens holder 16 is configured to be movable in the axial direction integrally with the lens 15. The lens holder 16 is configured, for example, with a holder main body 33 and a flange portion 34.

[0022] The holder main body 33 has a cylindrical outer shape. The outer dimensions of the holder main body 33 are set to be the same as or slightly smaller than the inner diameter of the cylindrical portion 24. In other words, the holder main body 33 is a clearance fit into the cylindrical portion 24. A female thread 35 is formed on the inner peripheral surface of the holder main body 33. The male thread 32 and the female thread 35 are screwed together, thereby integrating the lens 15 and the lens holder 16.

[0023] Furthermore, a plurality of grooves 36 are formed on the outer peripheral surface of the holder main body 33. The grooves 36 are formed at positions corresponding to the plurality of recesses 28 when the lens holder 16 is housed in the cylindrical portion 24. In other words, when the lens holder 16 housed in the cylindrical portion 24 is viewed from the axial direction, the recesses 28 are located on extensions of the grooves 36. The grooves 36 are recessed radially inward from the outer peripheral surface of the holder main body 33 and extend over the entire axial area of ​​the holder main body 33. The grooves 36 house the biasing member 17.

[0024] The flange portion 34 is a portion that protrudes radially outward from the end of the subject-facing surface of the holder main body 33 and extends circumferentially. The flange portion 34 may be formed around the entire outer periphery of the holder main body 33, or may be formed on a portion of the outer periphery of the holder main body 33 in the circumferential direction. The outer dimension of the flange portion 34 is set to be larger than the inner diameter dimension of the cylindrical portion 24. The other end of the biasing member 17 abuts against the back surface of the flange portion 34.

[0025] The biasing member 17 biases the lens holder 16 in a direction away from the image sensor 13. The biasing members 17 are provided at at least three locations spaced apart in the circumferential direction around the lens holder 16. More specifically, one end of the biasing member 17 abuts against the ring portion 27 (more specifically, the inner surface of the recess 28), the other end abuts against the flange portion 34, and extends along the recessed groove 36. FIG. 4 is an exploded perspective view of the biasing member 17. As shown in FIG. 4, the biasing member 17 is composed of a pipe member 37, a plunger 38, and a coil spring 39.

[0026] The pipe member 37 has a cylindrical outer shape. The pipe member 37 has openings at its distal and proximal ends in the axial direction (hereinafter referred to as "distal opening 37a" and "proximal opening 37b"). The distal opening 37a has a ring portion that protrudes radially inward and continues circumferentially, allowing a small-diameter portion 38a (described later) to pass through while preventing a large-diameter portion 38b (described later) from passing through. That is, the diameter of the distal opening 37a is larger than that of the small-diameter portion 38a and smaller than that of the large-diameter portion 38b. Meanwhile, the proximal opening 37b allows the plunger 38 (the small-diameter portion 38a and the large-diameter portion 38b) and the coil spring 39 to pass through. That is, the diameter of the proximal opening 37b is larger than that of the large-diameter portion 38b and the coil spring 39. After the plunger 38 and the coil spring 39 are housed inside the pipe member 37, the proximal opening 37b is closed by a lid (not shown) or by crimping.

[0027] The plunger 38 is a long, rod-shaped member extending in the axial direction. The plunger 38 has a small-diameter portion 38a and a large-diameter portion 38b. The small-diameter portion 38a has a smaller diameter than the large-diameter portion 38b. The small-diameter portion 38a is connected to the axial end of the large-diameter portion 38b and extends further in the axial direction. That is, a step is formed between the small-diameter portion 38a and the large-diameter portion 38b, which engages with the ring portion of the distal end opening 37a. The plunger 38 is housed in the pipe member 37 from the base-end opening 37b, with the small-diameter portion 38a at the front. This allows the small-diameter portion 38a of the plunger 38 to protrude and retract from the distal end opening 37a. Note that "protruding and retracting" does not require the entire small-diameter portion 38a to be retracted into the pipe member 37; it is sufficient that the amount of protrusion from the distal end opening 37a changes.

[0028] The coil spring 39 is housed inside the pipe member 37 on the proximal end opening 37b side of the plunger 38. The coil spring 39 biases the plunger 38 in a direction that causes the small diameter portion 38a to protrude from the distal end opening 37a. The coil spring 39 according to this embodiment is an example of an elastic member. However, specific examples of the elastic member are not limited to the coil spring 39, and may include rubber, a balloon, etc.

[0029] The biasing member 17 configured as described above is housed in the recessed groove 36, with the tip of the small-diameter portion 38a protruding from the tip opening 37a abutting against the ring portion 27 (more specifically, the back surface of the recessed portion 28), and the base end of the pipe member 37 (i.e., the closed base-end opening 37b) abutting against the flange portion 34. The biasing member 17 biases the lens holder 16 in a direction away from the image sensor 13 and expands and contracts in accordance with the axial movement of the lens holder 16. The pipe member 37 is completely housed in the recessed groove 36 and does not come into contact with the inner wall of the cylindrical portion 24 when it expands and contracts. Furthermore, the diameter of the small-diameter portion 38a of the plunger 38 is smaller than the outer dimension of the pipe member 37, so it does not come into contact with the inner wall of the cylindrical portion 24 when it expands and contracts.

[0030] The holder cap 18 is fitted onto the cylindrical portion 24. The holder cap 18 moves in the axial direction by rotating due to a driving force transmitted from the drive mechanism 19. The holder cap 18 also restricts the movement of the lens holder 16 housed inside the cylindrical portion 24 in a direction away from the image sensor 13. The holder cap 18 mainly includes a cap main body 40 and a restricting portion 41.

[0031] The cap body 40 has a cylindrical outer shape with both axial ends open. An internal thread 42 that is threaded onto the external thread 26 is formed on the inner peripheral surface of the cap body 40. A driven gear 43 to which a driving force is transmitted from the drive mechanism 19 is formed on the outer peripheral surface of the cap body 40. The driven gear 43 is, for example, a spur gear.

[0032] The restricting portion 41 is provided at the end of the subject-facing surface of the cap body 40. The restricting portion 41 protrudes radially inward from the inner peripheral surface of the cap body 40 and has a ring-shaped outer shape that is continuous in the circumferential direction. The inner diameter dimension of the restricting portion 41 is smaller than the outer dimension of the flange portion 34 of the lens holder 16 and larger than the diameter of the threaded portion 31 of the lens 15. In other words, the restricting portion 41 abuts against the flange portion 34 to restrict axial movement of the lens holder 16 and allows the threaded portion 31 to pass through.

[0033] Furthermore, notches 44 are formed in parts (two parts in this embodiment) of the regulating portion 41 in the circumferential direction. The notches 44 are spaces for passing a nozzle that applies adhesive between the lens 15 and the lens holder 16. Furthermore, a holding portion 46 that holds a magnet 45 is formed on the outer circumferential surface of the cap body 40. The magnet 45 is a detection target that is detected by the home position sensor 20.

[0034] The drive mechanism 19 generates a drive force for rotating the holder cap 18 under the control of the motor control board 22, and transmits the generated drive force to the holder cap 18. The drive mechanism 19 is supported on the surface of the frame 11 (disk portion 23). Details of the drive mechanism 19 will be described later with reference to FIG. 6.

[0035] The home position sensor 20 outputs a position signal to the motor control board 22 according to the position of the lens 15 relative to the light receiving surface of the image sensor 13. The home position sensor 20 is mounted on the motor control board 22, for example, and disposed facing the holder cap 18 at a predetermined radial distance. The home position sensor 20 is a magnetic sensor that detects the magnetic force generated by the magnet 45 and outputs a position signal when the holder cap 18 rotates and the magnet 45 approaches closest to it (hereinafter, the position of the lens 15 and holder cap 18 at this time will be referred to as the "home position"). However, the specific method for detecting the position of the lens 15 by the home position sensor 20 is not limited to the example described above.

[0036] [Assembly Procedure of the Imaging Device 10] Fig. 5 is a longitudinal cross-sectional view of the imaging device 10. More specifically, Fig. 5 is a cross-sectional view of the imaging device 10 taken along two cross sections passing through the center of the cylindrical portion 24 and each of the two biasing members 17. First, the image sensor 13, color filter 14, and drive mechanism 19 are attached to the frame 11, the motor control board 22 is attached to the cover 12, and the biasing members 17 are press-fit into the grooves 36 of the lens holder 16.

[0037] Next, the lens holder 16 is inserted into the holder cap 18 from the opposite side to the restricting portion 41, with the flange portion 34 at the front. The threaded portion 31 of the lens 15 is inserted into the holder cap 18 from the restricting portion 41 side, and the male thread 32 of the threaded portion 31 is screwed into the female thread 35 of the lens holder 16. This integrates the lens 15, lens holder 16, and holder cap 18. The light-collecting portion 30 of the lens 15 and the flange portion 34 of the lens holder 16 are arranged on opposite sides of the restricting portion 41 in the axial direction.

[0038] Here, adhesive is applied between the threaded portion 31 and the inner peripheral surface of the lens holder 16 from a nozzle inserted through the notch 44 of the holder cap 18. This firmly integrates the lens 15 and the lens holder 16 so that their relative positions do not change. Meanwhile, the integrated lens 15 and lens holder 16 are configured to be slightly movable in the axial direction relative to the holder cap 18. Furthermore, the holder cap 18 is configured to be rotatable relative to the integrated lens 15 and lens holder 16. Furthermore, a space is formed between the lens holder 16 and the holder cap 18 so that the cylindrical portion 24 can enter.

[0039] Next, the cylindrical portion 24 is inserted between the lens holder 16 and the holder cap 18 (in other words, the lens holder 16 is inserted into the cylindrical portion 24 and the holder cap 18 is inserted onto the cylindrical portion 24), and the male thread 26 of the cylindrical portion 24 is screwed into the female thread 42 of the cap body 40. This attaches the lens 15, lens holder 16, and holder cap 18 to the frame 11. At this time, one end (the tip of the small diameter portion 38a) of the urging member 17 attached to the lens holder 16 is housed in the recess 28 and abuts against the inner surface of the recess 28. Furthermore, the cover 12 is attached to the frame 11 so as to cover the lens 15, lens holder 16, and holder cap 18, and the imaging device 10 is assembled.

[0040] [Description of Movement of Imaging Device 10] The flange portion 34 of the lens holder 16 abuts against the restricting portion 41 due to the biasing force of the biasing member 17. This positions the lens holder 16 (lens 15) in the axial direction. That is, the light receiving surface of the image sensor 13 and the lens 15 are positioned in the axial direction. At this time, an axial gap D is formed between the tip (protruding end) of the cylindrical portion 24 and the flange portion 34.

[0041] Furthermore, when the holder cap 18 is rotated in the first direction by the drive mechanism 19, the holder cap 18 moves in a direction approaching the image sensor 13 (downward in FIG. 5 ) along the spiral of the engaged male screw 26 and female screw 42. As a result, the integrated lens 15 and lens holder 16 are pushed by the holder cap 18 and move in a direction approaching the image sensor 13 against the biasing force of the biasing member 17. As a result, the gap D becomes smaller.

[0042] Furthermore, when the holder cap 18 is rotated by the drive mechanism 19 in a second direction opposite to the first direction, the holder cap 18 moves in a direction away from the image sensor 13 (upward in FIG. 5 ) along the spiral of the engaged male thread 26 and female thread 42. As a result, the integrated lens 15 and lens holder 16 move in a direction away from the image sensor 13 due to the biasing force of the biasing member 17. As a result, the gap D becomes larger.

[0043] [Configuration of Drive Mechanism 19] Fig. 6 is a diagram showing the main components of the drive mechanism 19. As shown in Fig. 6, the drive mechanism 19 mainly includes a gear case 47, a motor 48, a drive gear 49, a first intermediate gear 50, a first worm gear 51, a first support shaft 52, a second intermediate gear 53, a second worm gear 54, and a second support shaft 55.

[0044] The gear case 47 is supported by the frame 11 on the surface of the disc portion 23. The gear case 47 houses a drive gear 49 and a first intermediate gear 50 in a space formed between the gear case 47 and the frame 11. The gear case 47 also supports both ends of a motor 48 and a first support shaft 52. The drive gear 49, the first intermediate gear 50, and the second intermediate gear 53 are spur gears. The first worm gear 51 and the second worm gear 54 are so-called "screw gears" in which a helical (screw-shaped) gear is formed on the outer circumferential surface of a rod-shaped member.

[0045] The motor 48 is a drive source that generates a drive force to rotate the holder cap 18. The motor 48 is, for example, a stepping motor. However, specific examples of the drive source are not limited to a stepping motor. The motor 48 is supported by the gear case 47 with its output shaft 56 oriented axially. The drive gear 49 is fixed to the output shaft 56 of the motor 48 and rotates in conjunction with the rotation of the motor 48. The drive gear 49 is also disposed closer to the disk portion 23 than the motor 48 (in other words, closer to the image sensor 13).

[0046] The first intermediate gear 50 and the first worm gear 51 are integrated by a first support shaft 52. More specifically, the first support shaft 52 penetrates the center of the first intermediate gear 50 in the thickness direction and penetrates the center of the first worm gear 51 in the extension direction. The first support shaft 52 extends parallel to the output shaft 56 (i.e., in the axial direction). Both ends of the first support shaft 52 are supported by the gear case 47.

[0047] The second intermediate gear 53 and the second worm gear 54 are integrated by a second support shaft 55. More specifically, the second support shaft 55 penetrates the center of the second intermediate gear 53 in the thickness direction and penetrates the center of the second worm gear 54 in the extension direction. The second support shaft 55 extends in a direction perpendicular to the axial direction. Furthermore, both ends of the second support shaft 55 are supported by a pair of supports 23a, 23b provided on the surface of the frame 11 (disc portion 23).

[0048] The first intermediate gear 50 meshes with the drive gear 49. The first intermediate gear 50 and the first worm gear 51 rotate together. The second intermediate gear 53 meshes with the first worm gear 51. The second intermediate gear 53 and the second worm gear 54 rotate together. The second worm gear 54 meshes with the driven gear 43. As a result, the driving force of the motor 48 is transmitted to the driven gear 43 via the output shaft 56, the drive gear 49, the first intermediate gear 50, the first worm gear 51, the second intermediate gear 53, and the second worm gear 54.

[0049] The drive gear 49 has a number of teeth Z1, the first intermediate gear 50 has a number of teeth Z2, the second intermediate gear 53 has a number of teeth Z3, and the driven gear 43 has a number of teeth Z4. The number of teeth of each spur gear (49, 50, 53, 43) is set, for example, to satisfy Z1 < Z2 < Z3 < Z4. As a result, the rotation of the motor 48 is decelerated by (Z2 / Z1) times between the drive gear 49 and the first intermediate gear 50, by Z3 times between the first worm gear 51 and the second intermediate gear 53, and by Z4 times between the second worm gear 54 and the driven gear 43. In other words, the reduction ratio of the drive mechanism 19 according to this embodiment is (Z2 / Z1) × Z3 × Z4. However, the relationship between the numbers of teeth is not limited to the above example. As another example, Z1 < Z3 < Z2 < Z4 may be satisfied.

[0050] [Hardware Configuration of Imaging Device 10] Fig. 7 is a hardware configuration diagram of the imaging device 10. As shown in Fig. 7, the imaging device 10 includes an image processing board 21 and a motor control board 22. The image processing board 21 and the motor control board 22 are integrated circuit products in which various electronic components are integrated on a single chip configured by an integrated circuit. The image processing board 21 and the motor control board 22 include, for example, a memory, a CPU (Central Processing Unit), an ISP (Image Signal Processing), etc. The image processing board 21 and the motor control board 22 may be a single board or separate boards.

[0051] The image processing board 21 outputs the image signal output from the image sensor 13 to an external device. The image processing board 21 may also calculate the degree of change in the focal position from the image signal output from the image sensor 13 and output the calculated degree of change in the focal position to the motor control board 22. The motor control board 22 drives the motor 48 as described below based on the position signal output from the home position sensor 20 or the degree of change in the focal position output from the image processing board 21.

[0052] The focal length of the lens 15 is predetermined, for example, depending on the shape and material of the light-collecting unit 30. Generally, light from an object at infinity can form a sharp, focused image on an image plane at a distance approximately equal to the focal length. Light from a nearby object (an object at a finite distance) can form a sharp, focused image on an image plane at a distance greater than the focal length. In other words, if the axial distance between the lens 15 (more specifically, the light-collecting unit 30) and the light-receiving surface of the image sensor 13 is a distance that allows the image of the object to be properly focused on the light-receiving surface, a sharp image will be formed on the light-receiving surface (a so-called in-focus state).

[0053] Since the linear expansion coefficients of the components of the surveillance camera 1 differ from component to component, the position of the light receiving surface of the image sensor 13 (the image plane position of the image sensor 13) changes as the distance between the components of the surveillance camera 1 changes due to temperature changes. Furthermore, expansion or contraction of the light-collecting unit 30 changes the focal length of the lens 15. Thus, a shift in the focal position of the surveillance camera 1 occurs due to temperature changes in the installation environment of the surveillance camera 1. The shift in the focal position of the surveillance camera 1 corresponds to a combination of the amount of change in the focal length of the lens 15 and the amount of change in the image plane position of the image sensor 13. Therefore, to adjust the shift in the focal position due to temperature changes in the installation environment of the surveillance camera 1 (i.e., to adjust the focus), the motor control board 22 executes the following process.

[0054] As an example, the motor control board 22 stores a table showing the correspondence between the temperature at the installation position and the rotation amount (number of steps of the stepping motor) of the motor 48 from the home position. The rotation amount stored in the table corresponds to the movement amount of the holder cap 18 required to correct the deviation of the focal position due to temperature. This rotation amount is determined in advance, for example, through experimentation or simulation. The motor control board 22 then rotates the motor 48 until the holder cap 18 reaches the home position, and then further rotates the motor 48 by an amount corresponding to the temperature at the installation position. The temperature at the installation position may be detected by a temperature sensor (not shown) or obtained from an external device connected via a cable.

[0055] As another example, the motor control board 22 may rotate the motor 48 in a direction that eliminates the shift in the focal position based on the degree of the shift in the focal position calculated by the image processing board 21. As yet another example, the image processing board 21 may further calculate the amount of rotation (number of steps) of the motor 48 required to eliminate the calculated shift in the focal position, and output this to the motor control board 22. The motor control board 22 may then rotate the motor 48 by the amount of rotation calculated by the image processing board 21.

[0056] [Effects of the embodiment] According to the above embodiment, the holder cap 18 is moved axially along the threaded male screw 26 and female screw 42, so that the amount of movement of the holder cap 18 can be finely adjusted. Furthermore, the lens holder 16 is positioned in the axial direction by the biasing member 17 and the restricting portion 41, so that the lens 15 and the lens holder 16 can be precisely positioned in accordance with the axial movement of the holder cap 18. As a result, an imaging device 10 can be obtained that allows precise adjustment of the focal position.

[0057] Furthermore, according to the above embodiment, by biasing the lens holder 16 at three circumferentially spaced locations, it is possible to prevent the lens 15 and the lens holder 16 from tilting when the focal position is adjusted, and as a result, it is possible to prevent the image formed on the light receiving surface of the image sensor 13 from becoming blurred when the focal position is adjusted.

[0058] Furthermore, according to the above embodiment, by configuring the biasing member 17 as shown in Figure 4, the coil spring 39 does not come into sliding contact with the side surface of the recessed groove 36 of the lens holder 16 and the inner circumferential surface of the cylindrical portion 24 when the biasing member 17 expands or contracts, thereby preventing the spring constant from becoming unstable due to sliding resistance. This stabilizes the load applied by the coil spring 39, and the drive torque of the motor 48 is not overwhelmed by the load, allowing the holder cap 18 to be moved stably. As a result, it is possible to prevent the image formed on the light-receiving surface of the image sensor 13 from becoming blurred when adjusting the focus position.

[0059] Furthermore, according to the above embodiment, by accommodating the biasing member 17 in the recess 28 and the recessed groove 36, it is possible to prevent the lens 15 and the lens holder 16 from rotating in conjunction with the rotation of the holder cap 18. As a result, it is possible to prevent the image formed on the light receiving surface of the image sensor 13 from becoming blurred when the focal position is adjusted.

[0060] Furthermore, according to the above embodiment, by including the worm gears 51 and 54 in the drive mechanism 19, the rotation of the motor 48 can be significantly decelerated before being transmitted to the holder cap 18, allowing for fine adjustment of the movement amount of the holder cap 18. As a result, an imaging device 10 can be obtained that allows for precise adjustment of the focal position. Furthermore, the focal position can be adjusted using a motor 48 with a small torque.

[0061] Furthermore, according to the above embodiment, by laying out the components (47 to 55) of the drive mechanism 19 as shown in FIG. 6, it is possible to obtain a high reduction ratio in a small space.

[0062] Furthermore, according to the above embodiment, by adjusting the focal position based on the position signal of the home position sensor 20 or the image signal of the image sensor 13, it is possible to appropriately correct changes in the focal position due to changes in temperature.

[0063] [Modification 1] Fig. 8 is a diagram showing another example of the biasing member 57. As shown in Fig. 8, the biasing member 57 according to Modification 1 has a cylindrical outer shape. The biasing member 57 is disposed between the ring portion 27 of the frame 11 and the flange portion 34 of the lens holder 16 so as to surround the holder main body 33. The biasing member 57 biases the lens holder 16 in a direction away from the image sensor 13. The biasing member 57 may be, for example, a coil spring or cylindrical rubber. According to Modification 1, the recess 28 and the recessed groove 36 can be omitted.

[0064] [Modification 2] Fig. 9 is a diagram showing another example of the drive mechanism 19. Note that components common to Fig. 6 are given the same reference numerals, and detailed description thereof will be omitted.

[0065] 9A , the drive mechanism 19 may be configured such that the second intermediate gear 53, the second worm gear 54, and the second support shaft 55 are omitted. A drive gear 49 fixed to an output shaft 56 of a motor 48 meshes with the first intermediate gear 50, and a first worm gear 51 that rotates integrally with the first intermediate gear 50 meshes with the driven gear 43.

[0066] 9(B), the drive mechanism 19 may be configured without the first intermediate gear 50, the first worm gear 51, the first support shaft 52, the second intermediate gear 53, the second worm gear 54, and the second support shaft 55. The drive gear 49 meshes with the driven gear 43.

[0067] In this way, by obtaining the required reduction ratio and then omitting some of the components (50 to 55), the number of components can be reduced, and the imaging device 10 can be made smaller and lighter.

[0068] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention.

[0069] Some or all of the above embodiments may be described as, but are not limited to, the following supplementary notes: (Supplementary Note 1) An imaging device comprising: a frame having a cylindrical portion that protrudes toward a subject at a position surrounding a through-hole that penetrates the imaging device in the axial direction and a male thread on an outer peripheral surface of the cylindrical portion; an image sensor having a light-receiving surface that receives light that has passed through the through-hole and that is positioned farther from the subject than the frame; a lens that faces the subject on the opposite side of the frame from the image sensor and forms an image of the subject on the light-receiving surface; a lens holder that is housed in an inner circumference of the cylindrical portion and is movable in the axial direction together with the lens; a biasing member that biases the lens holder in a direction away from the image sensor; a holder cap that has an inner peripheral surface that has a female thread that screws onto the male thread and an outer peripheral surface that has a driven gear, and that restricts movement of the lens holder in a direction away from the image sensor; and a drive mechanism that transmits a drive force to the driven gear to rotate the holder cap, thereby moving the holder cap in the axial direction relative to the frame.

[0070] (Appendix 2) In the imaging device described in Appendix 1, the cylindrical portion has a ring portion that protrudes radially inward from its inner surface and extends circumferentially, and the lens holder has a flange portion that protrudes radially outward from its outer surface and extends circumferentially, and the imaging device is characterized in that it comprises a plurality of the biasing members at at least three circumferentially spaced locations, one end of which abuts against the ring portion and the other end of which abuts against the flange portion, and which bias the lens holder in a direction away from the image sensor.

[0071] (Appendix 3) In the imaging device described in Appendix 2, the ring portion has a plurality of recesses each spaced apart in the circumferential direction, the lens holder has grooves extending in the axial direction at positions on the outer peripheral surface of the lens holder corresponding to each of the plurality of recesses, and each of the plurality of biasing members has one end accommodated in the recess and extends along the groove.

[0072] (Appendix 4) In the imaging device described in Appendix 2, the biasing member is characterized in that it has a pipe member having an opening at one end in the axial direction, a plunger housed in the pipe member so as to be able to protrude and retract from the opening, and an elastic member housed in the pipe member and biasing the plunger in a direction to protrude from the opening.

[0073] (Appendix 5) In the imaging device described in Appendix 1, the drive mechanism has a motor that generates a drive force, a drive gear that is fixed to the output shaft of the motor and rotates, a first intermediate gear that meshes with the drive gear, a first worm gear that rotates integrally with the first intermediate gear, a second intermediate gear that meshes with the first worm gear, and a second worm gear that rotates integrally with the second intermediate gear and meshes with the driven gear, wherein the first intermediate gear has a greater number of teeth than the drive gear, and the second intermediate gear has a greater number of teeth than the first intermediate gear and a fewer number of teeth than the driven gear.

[0074] (Appendix 6) In the imaging device described in Appendix 5, the drive mechanism further includes a first support shaft that integrates the first intermediate gear and the first worm gear and extends in the axial direction parallel to the output shaft of the motor, a second support shaft that integrates the second intermediate gear and the second worm gear and extends in a direction perpendicular to the axial direction, and a gear case that houses the drive gear and the first intermediate gear and supports the motor, wherein both ends of the first support shaft are supported by the gear case, and both ends of the second support shaft are supported by the frame.

[0075] (Appendix 7) In the imaging device described in Appendix 1, the drive mechanism has a motor that generates a drive force, a drive gear that is fixed to the output shaft of the motor and rotates, an intermediate gear that meshes with the drive gear, and a worm gear that rotates integrally with the intermediate gear and meshes with the driven gear, and the intermediate gear has a greater number of teeth than the drive gear and a smaller number of teeth than the driven gear.

[0076] (Appendix 8) In the imaging device described in Appendix 1, the drive mechanism has a motor that generates a drive force, and a drive gear that is fixed to the output shaft of the motor and meshes with the driven gear, and the drive gear has fewer teeth than the driven gear.

[0077] (Supplementary Note 9) The imaging device according to Supplementary Note 1 further comprises: a sensor that outputs a position signal according to the position of the lens relative to the light receiving surface; and a control unit that drives the drive mechanism based on the position signal output from the sensor.

[0078] (Supplementary Note 10) The imaging device according to Supplementary Note 1, further comprising a control unit that drives the driving mechanism based on an image signal output from the image sensor.

[0079] DESCRIPTION OF SYMBOLS 1: Surveillance camera 2: Housing 3: Dome 10: Imaging device 11: Frame 12: Cover 13: Image sensor 14: Color filter 15: Lens 16: Lens holder 17, 57: Urging member 18: Holder cap 19: Drive mechanism 20: Home position sensor 21: Image processing board 22: Motor control board 23: Disk portion 23a, 23b: Support portion 24: Cylindrical portion 25: Through hole 26, 32: Male screw 27: Ring portion 28: Recess 29: Opening 30: Light collecting portion 31: Threaded portion 33: Holder body 34: Flange portion 35, 42: Female screw 36: Groove 37: Pipe member 37a: Tip opening 37b : Base end opening 38 : Plunger 38a : Small diameter portion 38b : Large diameter portion 39 : Coil spring 40 : Cap body 41 : Restricting portion 43 : Driven gear 44 : Notch 45 : Magnet 46 : Holding portion 47 : Gear case 48 : Motor 49 : Drive gear 50 : First intermediate gear 51 : First worm gear 52 : First support shaft 53 : Second intermediate gear 54 : Second worm gear 55 : Second support shaft 56 : Output shaft

Claims

1. An imaging device comprising: a frame having a cylindrical portion that protrudes toward a subject at a position surrounding a through hole that penetrates the device in the axial direction, and a male screw on the outer surface of the cylindrical portion; an image sensor having a light receiving surface that receives light that has passed through the through hole and that is positioned further from the subject than the frame; a lens that faces the subject on the opposite side of the frame from the image sensor and forms an image of the subject on the light receiving surface; a lens holder that is housed on the inner circumference of the cylindrical portion and is movable in the axial direction together with the lens; a biasing member that biases the lens holder in a direction away from the image sensor; a holder cap that has an inner peripheral surface that has a female screw that screws onto the male screw and an outer peripheral surface that has a driven gear, and that restricts movement of the lens holder in a direction away from the image sensor; and a drive mechanism that transmits a drive force to the driven gear to rotate the holder cap, thereby moving the holder cap in the axial direction relative to the frame.

2. An imaging device according to claim 1, wherein the cylindrical portion has a ring portion that protrudes radially inward from its inner peripheral surface and extends circumferentially, and the lens holder has a flange portion that protrudes radially outward from its outer peripheral surface and extends circumferentially, and the imaging device is provided with a plurality of the urging members at at least three circumferentially spaced locations, one end of which abuts against the ring portion and the other end of which abuts against the flange portion, urging the lens holder in a direction away from the image sensor.

3. An imaging device according to claim 2, wherein the ring portion has a plurality of recesses each spaced apart in the circumferential direction, the lens holder has recessed grooves extending in the axial direction at positions on the outer peripheral surface of the lens holder corresponding to each of the plurality of recesses, and each of the plurality of biasing members has one end housed in the recess and extends along the recessed groove.

4. An imaging device according to claim 2, wherein the biasing member comprises a pipe member having an opening at one end in the axial direction, a plunger housed in the pipe member so as to be able to protrude from the opening, and an elastic member housed in the pipe member and biasing the plunger in a direction that causes it to protrude from the opening.

5. An imaging device according to claim 1, wherein the drive mechanism comprises a motor that generates a drive force, a drive gear that is fixed to the output shaft of the motor and rotates, a first intermediate gear that meshes with the drive gear, a first worm gear that rotates integrally with the first intermediate gear, a second intermediate gear that meshes with the first worm gear, and a second worm gear that rotates integrally with the second intermediate gear and meshes with the driven gear, wherein the first intermediate gear has a greater number of teeth than the drive gear, and the second intermediate gear has a greater number of teeth than the first intermediate gear and a fewer number of teeth than the driven gear.

6. An imaging device according to claim 5, wherein the drive mechanism further comprises: a first support shaft that integrates the first intermediate gear and the first worm gear and extends in the axial direction parallel to the output shaft of the motor; a second support shaft that integrates the second intermediate gear and the second worm gear and extends in a direction perpendicular to the axial direction; and a gear case that houses the drive gear and the first intermediate gear and supports the motor; both ends of the first support shaft are supported by the gear case; and both ends of the second support shaft are supported by the frame.

7. An imaging device according to claim 1, wherein the drive mechanism comprises a motor that generates a drive force, a drive gear that is fixed to the output shaft of the motor and rotates, an intermediate gear that meshes with the drive gear, and a worm gear that rotates integrally with the intermediate gear and meshes with the driven gear, and wherein the intermediate gear has a greater number of teeth than the drive gear and a smaller number of teeth than the driven gear.

8. An imaging device according to claim 1, wherein the drive mechanism comprises a motor that generates a drive force, and a drive gear that is fixed to the output shaft of the motor and meshes with the driven gear, and the drive gear has fewer teeth than the driven gear.

9. An imaging device according to claim 1, further comprising: a sensor that outputs a position signal according to the position of the lens relative to the light receiving surface; and a control unit that drives the drive mechanism based on the position signal output from the sensor.

10. An imaging device according to claim 1, further comprising a control unit that drives the driving mechanism based on an image signal output from the image sensor.

Images