Objective optical system for three-dimensional scanners and three-dimensional scanner

Abstract

To provide an objective optical system for three-dimensional scanners with which it is possible to improve the accuracy of measuring the three-dimensional surface shape of an object.SOLUTION: An objective optical system 3 for three-dimensional scanners includes an objective lens system 30. The objective lens system 30 is composed of a lens L1 having negative power, a lens L2 having positive power, a lens L3 having negative power, a lens L4 having positive power, a lens L5 having positive power, and a lens L6 having negative power, in order from the object side to the image side. The lens L3 and the lens L4 constitute a doublet. The lens L4 is a biconvex lens. The radius of curvature of the image-side surface of the lens L4 is 30 mm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an objective optical system for a three-dimensional scanner that acquires data on the three-dimensional surface shape of an object, and a three-dimensional scanner.

Background Art

[0002] In recent years, in the dental field, in order to digitally design prostheses and the like on a computer, it is necessary to acquire three-dimensional data on the surface shape of teeth, and three-dimensional scanners (intraoral scanners) have been put into practical use. For example, Patent Document 1 (Japanese Patent No. 5654583) discloses a three-dimensional scanner including a light source, a pattern generation means, a lens system including a lens that moves along an optical axis, and a camera. In this three-dimensional scanner, the lens is reciprocally moved along the optical axis to scan the light having the pattern that has passed through the pattern generation means and the lens, and the light having the pattern is irradiated onto the surface of the object, and the object is imaged by the camera. The image of the object captured by the camera is processed to obtain data on the three-dimensional surface shape of the object.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the object is a tooth, the material of the tooth surface is enamel. Since enamel is translucent, when imaging a tooth with a three-dimensional scanner, the intensity of the light reflected or scattered by the tooth is very weak. Therefore, it is necessary to increase the light amount of the light source. However, when the light amount of the light source increases, the light emitted from the light source is reflected by the surface of the lens constituting the lens system and enters the camera, resulting in ghosts in the image obtained by the camera. When ghosts occur, the measurement accuracy of the three-dimensional surface shape of the object decreases. The same problem exists not only when the object is a tooth but also when the reflected light or scattered light from the object is very weak.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide an objective optical system for a three-dimensional scanner and a three-dimensional scanner capable of improving the measurement accuracy of the three-dimensional surface shape of an object.

Means for Solving the Problems

[0006] The objective optical system for a three-dimensional scanner of the present disclosure includes an objective lens system. The objective lens system is composed of a first lens having a negative power, a second lens having a positive power, a third lens having a negative power, a fourth lens having a positive power, a fifth lens having a positive power, and a sixth lens having a negative power, in order from the object side to the image plane side. The third lens and the fourth lens constitute a cemented lens. The fourth lens is a biconvex lens. The radius of curvature of the image plane side surface of the fourth lens is 30 mm or less.

[0007] The three-dimensional scanner of the present disclosure includes the objective optical system for a three-dimensional scanner of the present disclosure.

Effects of the Invention

[0008] According to the objective optical system for a three-dimensional scanner of the present disclosure and the three-dimensional scanner of the present disclosure, the measurement accuracy of the three-dimensional surface shape of an object can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 8A

Figure 8B

Figure 8C

Figure 9A

Figure 9B

Figure 9C

Figure 10A

Figure 10B

Figure 10C

Figure 11

Figure 12

Figure 13

Figure 14

Modes for Carrying Out the Invention

[0010] [Outline of the Embodiment]

[0011] The outline of the embodiment of the present disclosure will be described by way of enumeration.

[0012] The objective optical system for a three-dimensional scanner according to this embodiment includes an objective lens system. The objective lens system is composed of, in order from the object side to the image plane side, a first lens having a negative power, a second lens having a positive power, a third lens having a negative power, a fourth lens having a positive power, a fifth lens having a positive power, and a sixth lens having a negative power. The third lens and the fourth lens constitute a cemented lens. The fourth lens is a biconvex lens. The radius of curvature of the image plane side surface of the fourth lens is 30 mm or less.

[0013] Since the radius of curvature of the image plane side surface of the fourth lens is 30 mm or less, the light emitted from the light source and reflected by the image plane side surface of the fourth lens diverges. Therefore, the light reflected by the image plane side surface of the fourth lens and incident on the optical sensor decreases. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0014] In the objective optical system for a three-dimensional scanner according to this embodiment, the second lens is a biconvex lens. The radius of curvature of the image plane side surface of the second lens is 30 mm or less.

[0015] Since the radius of curvature of the image plane side surface of the second lens is 30 mm or less, the light emitted from the light source and reflected by the image plane side surface of the second lens diverges. Therefore, the light reflected by the image plane side surface of the second lens and incident on the optical sensor decreases. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0016] In the objective optical system for a three-dimensional scanner according to this embodiment, the sixth lens is a negative meniscus lens with a convex surface facing the image side. The radius of curvature of the image plane side surface of the sixth lens is 40 mm or less.

[0017] Since the radius of curvature of the image-side surface of the sixth lens is 40 mm or less, the light emitted from the light source and reflected by the image-side surface of the sixth lens diverges. Therefore, the light reflected by the image-side surface of the sixth lens and incident on the optical sensor decreases. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0018] In the objective optical system for the three-dimensional scanner according to the present embodiment, the objective lens system satisfies the following conditional expression (1), 0.5 < |a / b| < 1.4 …(1) However, a: The distance on the optical axis from the image plane to the image-side surface of the sixth lens, b: The radius of curvature of the image-side surface of the sixth lens, where.

[0019] Therefore, the light reflected by the image-side surface of the sixth lens and incident on the optical sensor decreases. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0020] In the objective optical system for the three-dimensional scanner according to the present embodiment, the objective lens system satisfies the following conditional expression (2), 4.0 < |c / d| < 14.0 …(2) However, c: The distance on the optical axis from the image plane to the image-side surface of the first lens, d: The radius of curvature of the image-side surface of the first lens, where.

[0021] Therefore, the light reflected by the image-side surface of the first lens and incident on the optical sensor decreases. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0022] In the objective optical system for a three-dimensional scanner according to this embodiment, the fifth lens is a moving lens that moves along the optical axis. The objective lens system is a variable focal length lens system whose focal length changes as the fifth lens moves along the optical axis.

[0023] Therefore, the depth of focus of the objective optical system for a three-dimensional scanner can be made shallow, and the measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0024] The objective optical system for a three-dimensional scanner according to this embodiment further includes a quarter-wave plate disposed on the object side of the objective lens system and a polarization beam splitter disposed on the image plane side of the objective lens system.

[0025] Therefore, the optical path from the light source to the object and the optical path from the object to the optical sensor can be separated. The optical path from the light source to the object and the optical path from the object to the optical sensor can share the objective lens system.

[0026] The three-dimensional scanner according to this embodiment includes the objective optical system for a three-dimensional scanner according to this embodiment.

[0027] Therefore, the light emitted from the light source, reflected by the objective optical system for a three-dimensional scanner, and incident on the optical sensor is reduced. Ghosts in the image captured by the optical sensor are reduced or eliminated. The measurement accuracy of the three-dimensional surface shape of the object can be improved.

[0028] [Details of the Embodiment]

[0029] Based on the drawings, the details of the embodiment of the present disclosure will be described below. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated. At least some of the configurations of the embodiments described below may be arbitrarily combined.

[0030] Referring to FIG. 1, the three-dimensional scanner 1 is a device that obtains data on the three-dimensional surface shape of the object 50. The three-dimensional scanner 1 is, for example, an intraoral scanner for obtaining data on the three-dimensional surface shape of intraoral tissues (e.g., teeth). Note that even an intraoral scanner may obtain data on the three-dimensional surface shape not only of the teeth in the oral cavity but also of the gums, mucosa, fabricated dental prostheses, scan bodies for implants, orthodontic devices, or various dental laboratory products. Further, the three-dimensional scanner 1 of the present embodiment is not limited to an intraoral scanner, and can be applied to other three-dimensional scanners, such as a three-dimensional scanner that images the inside of a person's ear to obtain data on the three-dimensional surface shape inside the outer ear.

[0031] [Configuration of the Three-Dimensional Scanner 1]

[0032] Referring to FIGS. 1 and 2, the three-dimensional scanner 1 includes a handpiece 2 and a computer 45.

[0033] The handpiece 2 irradiates the object 50 (e.g., a tooth) with light having a pattern such as a line pattern or a checker pattern, and detects the reflected light or scattered light from the object 50. The handpiece 2 includes a housing 10, a light source 13, an illumination optical system 14 for the three-dimensional scanner, an objective optical system 3 for the three-dimensional scanner, and an optical sensor 39. The handpiece 2 may further include a movement mechanism 34, a lens position detector 35, and a controller 40.

[0034] The housing 10 houses the light source 13, the illumination optical system 14 for the three-dimensional scanner, the objective optical system 3 for the three-dimensional scanner, the movement mechanism 34, the lens position detector 35, the optical sensor 39, and the controller 40.

[0035] Referring to FIG. 1, the light source 13 includes a light emitting surface 13a. The light source 13 emits light (for example, white light) for illuminating the object 50 from the light emitting surface 13a. The light source 13 is, for example, a light emitting diode (LED). The output of the light source 13 is preferably 3 W or more, and may be 4 W or more. Therefore, even when the intensity of the light reflected or scattered by the object 50 is weak as in the case where the object 50 is a tooth, the object can be brightly illuminated with the light emitted from the light source 13, so that the measurement accuracy of the three-dimensional surface shape of the object 50 can be improved.

[0036] Referring to FIG. 1, the illumination optical system 14 for a three-dimensional scanner includes an illumination lens system 15 and a reticle 16. The illumination optical system 14 for a three-dimensional scanner may further include a polarizer 19.

[0037] The illumination lens system 15 makes the intensity distribution of the light from the light source 13 more uniform. The illumination lens system 15 is composed of a lens L11 and a lens L12 in order from the light source 13 side to the object side. The lens L11 has a positive power. The lens L11 is a biconvex lens. The lens L11 is made of glass. The lens L12 has a positive power. The lens L12 is an aspherical lens. The light source side surface of the lens L12 is aspherical. The object side surface of the lens L12 may be aspherical. Although the lens L12 is a biconvex lens as a whole, in the paraxial region, it is a negative meniscus lens with the convex surface facing the object side. The lens L12 may be made of plastic or glass.

[0038] The reticle 16 is a pattern generation unit that gives an intensity pattern such as a line pattern or a checker pattern to the light emitted from the light source 13 to generate light having a pattern (hereinafter also referred to as "pattern"). The reticle 16 generates light having a pattern that is irradiated onto the surface of the object 50. The reticle 16 includes a transparent plate 17 and a light-shielding pattern layer 18 disposed on the transparent plate 17. For example, the transparent plate 17 is a glass plate, and the light-shielding pattern layer 18 is a chromium layer. The light-shielding pattern layer 18 has a pattern such as a line pattern or a checker pattern. The light-shielding pattern layer 18 is disposed, for example, on the first surface of the transparent plate 17 distal from the light source 13.

[0039] The polarizer 19 converts the light emitted from the light source 13 into linearly polarized light. The polarizer 19 is, for example, a polarizing film disposed on the second surface of the transparent plate 17 proximal to the light source 13.

[0040] Referring to FIG. 1, the objective optical system 3 for a three-dimensional scanner includes an objective lens system 30. The objective optical system 3 for a three-dimensional scanner may further include a beam splitter 20, a phase plate 37, and a mirror 38.

[0041] Referring to FIG. 1, the beam splitter 20 is an optical component that separates the optical path from the light source 13 to the object 50 and the optical path from the object 50 to the optical sensor 39. The beam splitter 20 is disposed on the image plane side of the objective lens system 30. The beam splitter 20 is disposed between the objective lens system 30 and the illumination optical system 14 for a three-dimensional scanner, and is also disposed between the objective lens system 30 and the optical sensor 39. The beam splitter 20 directs the illumination light from the light source 13 toward the object 50, and directs the reflected light or scattered light from the object 50 toward the optical sensor 39. The beam splitter 20 may be a polarizing beam splitter 21.

[0042] Referring to FIG. 1, the objective lens system 30 sends light having a pattern emitted from the light source 13 and passing through the reticle 16 to the object 50, and sends light reflected or scattered from the object 50 to the optical sensor 39. The objective lens system 30 is composed of a lens L1, a lens L2, a lens L3, a lens L4, a lens L5, and a lens L6 in order from the object side to the image plane side. The lens L1, the lens L2, the lens L3, the lens L4, the lens L5, and the lens L6 respectively correspond to the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens of the present disclosure. The configuration of the objective lens system 30 will be described in detail later.

[0043] The lens L5 may be a movable lens that can move along the optical axis AX by a moving mechanism 34 described later. The objective lens system 30 may be a variable focal length lens system whose focal length changes as the lens L5 moves along the optical axis. By changing the position of the lens L5 along the optical axis AX, the focal plane position of the light from the light source 13 (for example, the light having a pattern) changes from the shortest focal position F1 closest to the exit end face of the handpiece 2 (housing 10), through the intermediate focal position F2, to the longest focal position F3 farthest from the exit end face of the handpiece 2 (housing 10). Note that generally, there are an object-side focus and an image-side focus, but the focal position described in this specification means the object-side focus unless otherwise specified.

[0044] Referring to FIG. 1, the phase plate 37 is disposed on the object side of the objective lens system 30. The phase plate 37 is, for example, a quarter-wave plate. The phase plate 37 converts the first linearly polarized light passing through the objective lens system 30 into circularly polarized light, and the phase plate 37 converts the circularly polarized light reflected or scattered by the object 50 into second linearly polarized light having a polarization orthogonal to the first linearly polarized light.

[0045] Referring to FIG. 1, the mirror 38 is disposed on the object side of the objective lens system 30. More specifically, the mirror 38 is disposed on the object side of the phase plate 37. The mirror 38 reflects the light emitted from the light source 13 and passing through the objective lens system 30 toward the object 50. The mirror 38 reflects the light reflected or scattered by the object 50 toward the objective lens system 30. The objective optical system 3 for the three-dimensional scanner is a projection optical system that projects the light from the light source 13 onto the object 50, and is an imaging optical system that transmits the reflected light or scattered light from the object 50 to the optical sensor 39.

[0046] Referring to FIGS. 1 and 2, the moving mechanism 34 moves the lens L5 along the optical axis AX. The moving mechanism 34 is, for example, a linear guide including a slider (not shown), a ball screw (not shown), and a motor (not shown). The lens L5 is fixed to the slider. The slider is guided by the ball screw and is movable relative to the ball screw. The motor rotates the ball screw. When the ball screw rotates, the slider moves relative to the ball screw, and the lens L5 moves along the optical axis AX.

[0047] Referring to FIGS. 1 and 2, the lens position detector 35 detects the position of the lens L5 corresponding to the focal plane position of the light (for example, light having a pattern) from the light source 13. The lens position detector 35 is, for example, an optical encoder that detects the position of the lens L5.

[0048] Referring to FIGS. 1 and 2, the optical sensor 39 detects the light that is reflected or scattered by the object 50 and passes through the objective optical system 3 for the three-dimensional scanner. The optical sensor 39 is, for example, an image sensor such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor that images the object 50 and acquires an image of the object 50.

[0049] Referring to FIG. 2, the controller 40 transmits a drive signal to the light source 13 to control the light emission state of the light source 13. The controller 40 transmits a drive signal to the moving mechanism 34 to move the lens L5. The controller 40 receives a signal regarding the position of the lens L5 corresponding to the focal plane position of the light (e.g., light having a pattern) from the light source 13 from the lens position detector 35.

[0050] The controller 40 processes the image of the object 50 acquired by the optical sensor 39 to calculate data on the three-dimensional surface shape of the object 50. Specifically, the controller 40 calculates data on the three-dimensional surface shape of the object 50 from the position of the lens L5 corresponding to the focal plane position of the light (e.g., light having a pattern) from the light source 13 and the image acquired by the optical sensor 39 at each focal plane position.

[0051] The light having a pattern, which is emitted from the light source 13 and obtained through the reticle 16, is irradiated onto the object 50 through the objective optical system 3 for the three-dimensional scanner. When the lens L5 moves along the optical axis AX, the focal plane position of the light having a pattern changes. The optical sensor 39 detects the light reflected or scattered from the object 50 at each focal plane position. By the optical sensor 39, a two-dimensional image of the object 50 at each focal plane position is acquired. The controller 40 associates the two-dimensional image of the object 50 with the position of the lens L5 corresponding to the focal plane position of the light having a pattern, and stores the combination of the two-dimensional image of the object 50 and the position of the lens L5 in a memory (not shown). The controller 40 reads out the combination from the memory and stacks the two-dimensional images of the object 50 according to the focal plane positions corresponding to each of the two-dimensional images. The X coordinate position and the Y coordinate position of the object 50 are calculated from the two-dimensional image at the focal plane position. The Z coordinate position of the object 50 is calculated from the position of the lens L5. Thus, the controller 40 calculates data on the three-dimensional surface shape of the object 50.

[0052] The controller 40 can output data on the three-dimensional surface shape of the object 50 to the computer 45. The controller 40 can receive information such as settings and commands from the computer 45. The controller 40 includes a processor (e.g., a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), etc.), a ROM (Read Only Memory) that stores a program and data for the operation of the processor, a RAM (Random Access Memory) that functions as a work area for the processor, and an input / output interface that is responsible for input / output of signals with peripheral devices, etc. The program executed by the controller 40 may be provided after being fixedly recorded on a tangible recording medium such as a CD-ROM, a DVD-ROM, or a semiconductor memory, or may be provided via a communication network as a data signal superimposed on a carrier wave.

[0053] At least a part of the arithmetic processing for processing the image of the object 50 captured by the optical sensor 39 to obtain data on the three-dimensional surface shape of the object 50 may be executed by software or may be realized by dedicated hardware separate from the processor. Also, at least a part of the processor or the hardware may be incorporated inside the handpiece 2. Although a cable for communicably connecting the handpiece 2 to the computer 45 is depicted in FIG. 2, the handpiece 2 may be communicably connected to the computer 45 by wireless communication without providing the cable.

[0054] The data of the three-dimensional surface shape of the object 50 obtained by the controller 40 is transmitted to the computer 45. The computer 45 performs rendering processing on the data of the three-dimensional surface shape of the object 50 on the display unit, generates a two-dimensional image of the object 50 viewed from an arbitrary viewpoint, and displays it. The display unit may be a display built into the computer 45, a stationary display connected to the computer 45, or a wearable display (for example, a head-mounted display or a glasses-type display) communicably connected to the computer 45, etc.

[0055] In this embodiment, the controller 40 processes the image captured by the optical sensor 39 to obtain the data of the three-dimensional surface shape of the object 50. However, the computer 45 may also process the image captured by the optical sensor 39 to obtain the data of the three-dimensional surface shape of the object 50.

[0056] The three-dimensional scanner 1 may further include a power supply device (not shown) for supplying power to drive the light source 13, the moving mechanism 34, the lens position detector 35, the optical sensor 39, the controller 40, and the like.

[0057] Taking the case where the three-dimensional scanner 1 of this embodiment is used as an intraoral scanner as an example, the operation of the three-dimensional scanner 1 will be described.

[0058] Insert the tip of the handpiece 2 into the oral cavity. The controller 40 transmits a drive signal to the light source 13 to cause the light source 13 to emit light. The light emitted from the light source 13 passes through the illumination lens system 15 to make the intensity distribution of the light more uniform. The light passes through the polarizer 19 and is converted into linearly polarized light. The light passes through the reticle 16 and is converted into light having a pattern. The light having a pattern passes through the polarizing beam splitter 21, the objective optical system 3 for the three-dimensional scanner, and the phase plate 37, is reflected by the mirror 38, and irradiates the object 50 (for example, a tooth). The controller 40 transmits a drive signal to the moving mechanism 34 to reciprocate the lens L5 along the optical axis AX. Due to the movement of the lens L5, the focal plane position of the light having a pattern changes. The controller 40 receives a signal regarding the position of the lens L5 corresponding to the focal plane position of the light from the light source 13 (for example, the light having a pattern) from the lens position detector 35.

[0059] The light reflected or scattered from the object 50 is reflected by the mirror 38, passes through the phase plate 37 and the objective optical system 3 for the three-dimensional scanner, is reflected by the polarizing beam splitter 21, and enters the optical sensor 39. The optical sensor 39 detects the light reflected or scattered from the object 50 at each focal plane position. An optical sensor 39 acquires a two-dimensional image of the object 50 at each focal plane position. The controller 40 associates the two-dimensional image of the object 50 with the position of the lens L5 corresponding to the focal plane position of the light having a pattern, and stores the combination of the two-dimensional image of the object 50 and the position of the lens L5 in a memory (not shown). The controller 40 reads out the combination from the memory and stacks the two-dimensional images of the object 50 according to the focal plane positions corresponding to the respective two-dimensional images. In this way, the controller 40 calculates the data of the three-dimensional surface shape of the object 50.

[0060] [Configuration of the Objective Optical System 3 for the Three-Dimensional Scanner]

[0061] Figures 3 to 5 respectively show the optical configurations of the objective optical system 3 for a three-dimensional scanner according to Embodiments 1 to 3. FIG. 6 shows the optical configuration of the objective optical system 3b for a three-dimensional scanner according to the comparative example. As shown in FIG. 1, the objective optical system 3 for a three-dimensional scanner according to Embodiments 1 to 3 and the objective optical system 3b for a three-dimensional scanner according to the comparative example each include an objective lens system 30, a phase plate 37, a mirror 38, and a beam splitter 20. In each of FIGS. 3 to 6, "W" represents the shortest focal length state, "M" represents the intermediate focal length state, and "T" represents the longest focal length state.

[0062] (Embodiment 1)

[0063] Referring to FIG. 3, the objective lens system 30 of the objective optical system 3 for a three-dimensional scanner according to Embodiment 1 includes, in order from the object side to the image plane side, a first lens group G1 having a positive power, a second lens group G2 having a positive power, and a third lens group G3 having a negative power. When the objective optical system 3 for a three-dimensional scanner changes from the shortest focal length state (W) to the longest focal length state (T), the first lens group G1 and the third lens group G3 are fixed, and the second lens group G2 moves toward the image plane IM side along the optical axis AX. The image plane IM is the light receiving surface of the optical sensor 39.

[0064] The first lens group G1 to the third lens group G3 in Embodiment 1 are each configured as follows when each lens is viewed in the paraxial surface shape, in order from the object side.

[0065] The first lens group G1 includes a negative meniscus lens L1 with a convex surface facing the object side, a biconvex positive lens L2, a biconcave negative lens L3, and a biconvex positive lens L4. The positive lens L2 is an aspherical single lens. The negative lens L3 and the positive lens L4 are joined to each other to form a joined lens having a positive power. The aperture stop ST is disposed on the image plane side of the positive lens L4.

[0066] The second lens group G2 includes a biconvex positive lens L5. The positive lens L5 is an aspherical single lens.

[0067] The third lens group G3 consists of a negative meniscus lens L6 with its convex surface facing the image plane side. The negative meniscus lens L6 is an aspherical single lens.

[0068] (Example 2)

[0069] Referring to FIG. 4, the objective lens system 30 of the objective optical system 3 for a three-dimensional scanner according to Example 2 includes, in order from the object side to the image plane side, a first lens group G1 having a positive power, a second lens group G2 having a positive power, and a third lens group G3 having a negative power. When the objective optical system 3 for a three-dimensional scanner changes from the shortest focal length state (W) to the longest focal length state (T), the first lens group G1 and the third lens group G3 are fixed, and the second lens group G2 moves toward the image plane IM side along the optical axis AX. The image plane IM is the light receiving surface of the optical sensor 39.

[0070] In Example 2, the first lens group G1 to the third lens group G3 are each configured as follows when each lens is viewed with a paraxial surface shape, in order from the object side.

[0071] The first lens group G1 consists of a negative meniscus lens L1 with its convex surface facing the object side, a biconvex positive lens L2, a biconcave negative lens L3, and a biconvex positive lens L4. The negative meniscus lens L1 is an aspherical single lens. The positive lens L2 is an aspherical single lens. The negative lens L3 and the positive lens L4 are joined to each other to form a joined lens having a positive power. The positive lens L2 is an aspherical single lens. The aperture stop ST is disposed on the image plane side of the positive lens L4.

[0072] The second lens group G2 consists of a biconvex positive lens L5. The positive lens L5 is an aspherical single lens.

[0073] The third lens group G3 consists of a negative meniscus lens L6 with its convex surface facing the image plane side. The negative meniscus lens L6 is an aspherical single lens.

[0074] (Example 3)

[0075] Referring to FIG. 5, the objective lens system 30 of the objective optical system 3 for a three-dimensional scanner according to Embodiment 3 includes, in order from the object side to the image plane side, a first lens group G1 having a positive power, a second lens group G2 having a positive power, and a third lens group G3 having a negative power. When the objective optical system 3 for a three-dimensional scanner changes from the shortest focal length state (W) to the longest focal length state (T), the first lens group G1 and the third lens group G3 are fixed, and the second lens group G2 moves toward the image plane IM side along the optical axis AX. The image plane IM is the light receiving surface of the optical sensor 39.

[0076] The first lens group G1 to the third lens group G3 in Embodiment 3 are each configured as follows when each lens is viewed with a paraxial surface shape, in order from the object side.

[0077] The first lens group G1 includes a negative meniscus lens L1 with a convex surface facing the object side, a biconvex positive lens L2, a biconcave negative lens L3, and a biconvex positive lens L4. The positive lens L2 is an aspherical single lens. The negative lens L3 and the positive lens L4 are joined to each other to form a joined lens having a positive power. The aperture stop ST is disposed on the image plane side of the positive lens L4.

[0078] The second lens group G2 includes a biconvex positive lens L5. The positive lens L5 is an aspherical single lens.

[0079] The third lens group G3 includes a negative meniscus lens L6 with a convex surface facing the image plane side. The negative meniscus lens L6 is an aspherical single lens.

[0080] (Comparative Example)

[0081] Referring to FIG. 6, the objective lens system 30 of the objective optical system 3b for a three-dimensional scanner according to the comparative example includes, in order from the object side to the image plane side, a first lens group G1 having a positive power, a second lens group G2 having a positive power, and a third lens group G3 having a negative power. When the objective optical system 3 for a three-dimensional scanner changes from the shortest focal length state (W) to the longest focal length state (T), the first lens group G1 and the third lens group G3 are fixed, and the second lens group G2 moves toward the image plane IM side along the optical axis AX. The image plane IM is the light receiving surface of the optical sensor 39.

[0082] The first lens group G1 to the third lens group G3 in the comparative example are each configured as follows when each lens is viewed with a paraxial surface shape, in order from the object side.

[0083] The first lens group G1 includes a negative meniscus lens L1 with a convex surface facing the object side, a biconvex positive lens L2, a negative meniscus lens L3 with a convex surface facing the object side, and a biconvex positive lens L4. The negative meniscus lens L1 is an aspherical single lens. The positive lens L2 is an aspherical single lens. The negative meniscus lens L3 is an aspherical lens. The negative meniscus lens L3 and the positive lens L4 are joined to each other to form a cemented lens having a positive power. The aperture stop ST is disposed on the image plane side of the positive lens L4.

[0084] The second lens group G2 includes a biconvex positive lens L5. The positive lens L5 is an aspherical single lens.

[0085] The third lens group G3 includes a biconcave negative lens L6. The biconcave negative lens L6 is an aspherical single lens.

[0086] (Numerical Examples, Numerical Comparative Examples)

[0087] Hereinafter, while contrasting with the optical configuration of the objective optical system 3b for a three-dimensional scanner according to the comparative example, the optical configuration of the objective optical system 3 for a three-dimensional scanner according to the embodiment will be specifically described with reference to construction data and the like. Numerical Examples 1 to 3 are numerical examples corresponding to Examples 1 to 3 described above, respectively. The numerical comparative example is a numerical example corresponding to the comparative example described above.

[0088] In Numerical Examples 1 to 3 and the numerical comparative example, as surface data, in order from the left column, the surface number (object: object surface, stop: aperture stop ST, image: image surface IM), radius of curvature r (mm), axial surface interval d (mm), refractive index nd with respect to the d line (wavelength 587.56 nm), and Abbe number νd with respect to the d line are shown. The surface with an asterisk (*) attached to the surface number i is an aspherical surface, and its surface shape is defined by the following formula (AS) using a local orthogonal coordinate system (x, y, z) with the surface vertex as the origin. As aspherical data, aspherical coefficients and the like are shown. In the aspherical data of Numerical Examples 1 to 3 and the numerical comparative example, the coefficients of the terms not shown are 0, and for all data, e-n = ×10 -n is used. z=(c·h 2 ) / [1+√{1-(1+K)·c 2 ·h 2}]+Σ(Aj·hj) …(AS) However, h: height in the direction perpendicular to the z-axis (optical axis AX) (h 2 =x 2 +y 2 ), z: sag amount in the direction of the optical axis AX at the position of height h (with respect to the surface vertex), c: curvature at the surface vertex (reciprocal of the radius of curvature r), K: conic constant, Aj: j-th aspherical coefficient, is defined.

[0089] As various data, the focal length (Fl, mm), F-number (Fno.), half field angle (ω, °), image height (y’max, mm), overall lens length (TL, mm), back focus (BF, mm), and variable axial surface interval (di (i: surface number), mm) of the entire system in each of the shortest focal length state (W), intermediate focal length state (M), and longest focal length state (T) are shown. Also, as lens group data, the focal length (mm) of each lens group is shown. However, the back focus BF represents the distance from the image side surface of lens L6 to the light receiving surface of the optical sensor 39 in terms of the air equivalent length. The overall lens length TL is the distance from the object side surface of the phase plate 37 to the light receiving surface of the optical sensor 39.

[0090] The spherical aberration diagrams from Fig. 7A to Fig. 10C represent the spherical aberration amount for the d-line (wavelength 587.56 nm) (shown by the solid line), the spherical aberration amount for the C-line (wavelength 656.28 nm) (shown by the dashed-dotted line), and the spherical aberration amount for the g-line (wavelength 435.84 nm) (shown by the broken line) by the deviation amount (unit: mm) of the focal position in the optical axis AX direction from the paraxial image plane. The vertical axis represents the value obtained by normalizing the incident height to the pupil by its maximum height (i.e., relative pupil height).

[0091] In the aberration diagrams from Fig. 7A to Fig. 10C, the broken line T represents the tangential image plane for the d-line by the deviation amount (unit: mm) of the focal position in the optical axis AX direction from the paraxial image plane, and the solid line S represents the sagittal image plane for the d-line by the deviation amount (unit: mm) of the focal position in the optical axis AX direction from the paraxial image plane. The vertical axis represents the value obtained by normalizing the ray height at the image plane by its maximum image height (i.e., relative image height).

[0092] In the distortion aberration diagrams from Fig. 7A to Fig. 10C, the horizontal axis represents the distortion for the d-line as the ratio of the actual image height to the ideal image height (unit: %), and the vertical axis represents the value obtained by normalizing the ray height at the image plane by its maximum image height (i.e., relative image height).

[0093] Numerical Example 1 Unit: mm Surface Data Surface Number r d nd vd object infinity d0 1 infinity 2.000 1.5231 58.57 2 infinity 2.897 3 31.150 2.000 1.7432 49.34 4 21.020 8.370 5* 109.750 4.500 1.5163 64.07 6* -24.430 30.230 7 -31.480 1.500 1.6889 31.08 8 55.000 5.500 1.5163 64.14 9 -21.790 0.000 10 (stop) infinity d10 11* 27.110 4.000 1.497 81.55 12* -53.360 d12 13* -17.840 2.000 1.6935 53.19 14* -26.230 3.780 15 infinity 15.000 1.5163 64.14 16 infinity 3.600 image infinity Aspherical data Surface number K A4 A6 A8 A10 5 0 -9.3862342e-06 -3.1657448e-07 6.4068205e-09 -7.3421905e-11 6 0 -6.3718423e-06 -1.9499159e-07 3.6018514e-09 -4.8025073e-11 11 0 -1.3037796e-05 9.4621713e-08 -2.4143316e-09 1.0625811e-11 12 0 -1.5522299e-06 6.7137294e-08 -2.0280225e-09 8.6495021e-12 13 0 3.0431800e-04 -3.0073855e-06 5.1638006e-08 -4.8182191e-10 14 0 2.6881064e-04 -2.4546334e-06 4.4542610e-08 -4.2465792e-10 Variable axis upper surface interval W M T d0 21.77 35.68 56.43 d10 15.35 20.97 26.59 d12 25.35 19.73 14.11 Various data W M T Fl 37.01 42.45 49.01 Fno. 4.02 3.71 3.57 ω 5.02 5.35 5.44 y’max 5.918 5.918 5.918 TL 126.018 126.018 126.018 BF 17.2725 17.2725 17.2725 Lens group data Group (surface) Focal length 1 (3 - 9) 62.1 2 (11 - 12) 36.8 3 (13 - 14) -89.1

[0094] Numerical example 2 Unit: mm Surface data Surface number r d nd vd object infinity d0 1 infinity 2.000 1.4585 67.82 2 infinity 3.884 3* 16.600 2.500 1.7432 49.34 4* 11.650 5.370 5* -322.340 4.500 1.5163 64.14 6* -17.800 33.230 7 -47.630 1.500 1.6889 31.08 8 43.390 5.500 1.5163 64.14 9 -22.760 0.000 10 (stop) infinity d10 11* 28.530 4.000 1.497 81.55 12* -60.130 d12 13* -22.240 2.000 1.6935 53.21 14* -38.760 3.780 15 infinity 15.000 1.5163 64.14 16 infinity 3.600 image infinity Aspherical data Surface number K A4 A6 A8 A10 3 0 -1.1144264E-04 1.9277627E-06 -3.6868517E-08 2.1036287E-10 4 0 -1.7729887E-04 3.9692775E-06 -7.5098606E-08 4.4804034E-10 5 0 -6.6546445E-05 1.7347126E-06 -1.4356059E-08 1.5015450E-10 6 0 -4.3833867E-05 6.4506594E-07 -1.5182637E-08 2.9170575E-10 11 0 1.2262494E-06 -2.5592432E-07 8.2051549E-09 -1.1856975E-10 12 0 1.1662703E-05 -3.3228424E-07 1.0215521E-08 -1.4907518E-10 13 0 2.9583489E-04 -5.1835300E-06 9.7288581E-08 -1.1142106E-09 14 0 2.7486941E-04 -4.7507676E-06 9.2137539E-08 -1.0931852E-09 Aspherical data Surface number A12 3 0 4 0 5 -1.8087881E-12 6 -2.7031191E-12 11 6.0365102E-13 12 7.7304291E-13 13 0 14 0 Variable-axis surface interval W M T d0 20.20 34.30 54.83 d10 15.35 20.97 26.59 d12 25.35 19.73 14.11 Various data W M T Fl 35.60 40.64 46.60 Fno. 3.96 3.68 3.75 ω 4.98 5.36 5.48 y’max 5.918 5.918 5.918 TL 127.568 127.568 127.568 BF 17.2725 17.2725 17.2725 Lens group data Group (surface) Focal length 1 ( 3- 9) 60.8 2 ( 11- 12) 39.5 3 ( 13- 14) -79.2

[0095] Numerical example 3 Unit: mm Surface data Surface number r d nd vd object infinity d0 1 infinity 2.000 1.4585 67.82 2 infinity 3.884 3 38.145 2.500 1.7432 49.34 4 25.143 9.370 5* 150.675 4.500 1.5163 64.14 6* -23.783 29.230 7 -24.659 1.500 1.6889 31.08 8 91.563 5.500 1.5163 64.14 9 -18.927 0.000 10 (stop) infinity d10 11* 26.530 4.000 1.497 81.55 12* -58.908 d12 13* -18.632 2.000 1.6935 53.21 14* -28.040 3.780 15 infinity 15.000 1.5163 64.14 16 infinity 3.600 image infinity Aspherical data Surface number K A4 A6 A8 A10 5 0 -1.8022262E-05 4.0343714E-08 1.9347573E-10 -1.6696317E-11 6 0 -8.6164897E-06 8.6150978E-08 -1.0306947E-09 -5.0090729E-12 11 0 -8.2557157E-06 -4.4224134E-08 -7.5808074E-10 1.6572697E-12 12 0 4.3722024E-06 -8.8475127E-08 -1.7664905E-10 -1.1230085E-12 13 0 2.6794556E-04 -3.1916158E-06 6.7692084E-08 -6.3705635E-10 14 0 2.3320309E-04 -2.7087808E-06 6.0291783E-08 -5.6234723E-10 Variable axis upper surface interval W M T d0 20.20 34.30 54.83 d10 15.35 20.97 26.59 d12 25.35 19.73 14.11 Various data W M T Fl 36.60 41.91 48.27 Fno. 3.97 3.67 3.56 ω 5.05 5.38 5.43 y’max 5.918 5.918 5.918 TL 127.568 127.568 127.568 BF 17.2725 17.2725 17.2725 Lens group data Group (surface) Focal length 1 (3 - 9) 61.9 2 (11 - 12) 37.4 3 (13 - 14) -87.7

[0096] Numerical comparison example Unit: mm Surface data Surface number r d nd vd object infinity d0 1 infinity 2.000 1.4585 67.82 2 infinity 2.304 3* 82.823 2.500 1.7432 49.34 4* 32.068 6.950 5* 37.306 4.500 1.5167 64.07 6* -58.968 33.232 7* 42.447 1.500 1.6895 31.02 8 17.209 5.500 1.5163 64.14 9 -760.000 0.000 10 (stop) infinity d10 11* 23.863 4.000 1.497 81.55 12* -80.927 d12 13* -46.181 1.740 1.5167 64.07 14* 127.303 3.783 15 infinity 15.000 1.5163 64.14 16 infinity 3.600 image infinity Aspherical data Surface number K A4 A6 A8 3 -1.0079048E-01 8.5694708E-06 -2.2707395E-07 1.9684923E-09 4 -2.7071945E-01 -1.7708561E-05 -3.4555373E-07 3.0206995E-09 5 2.5334010E-01 -1.1535385E-05 -2.3844823E-08 -8.5790734E-10 6 -2.9158070E-02 1.9767953E-05 5.0906818E-08 -1.1282814E-09 7 -2.1572252E-01 1.2684949E-05 -4.3350501E-09 4.7233304E-12 11 8.2462459E-02 -1.2903455E-05 -5.4775825E-09 -7.6159055E-11 12 9.6547336E-02 6.2177997E-06 -6.2694346E-09 -3.6071346E-11 13 -3.0507895E-02 2.4032391E-05 -1.5363422E-07 1.5532824E-09 14 7.3198600E-04 3.6005177E-07 -1.5372145E-09 8.8349921E-11 Variable axis upper surface interval W M T d0 20.20 34.30 56.56 d10 15.35 20.97 26.59 d12 25.61 19.73 14.37 Various data W M T Fl 31.60 36.29 41.90 Fno. 3.99 3.69 3.54 ω 5.39 5.85 5.93 y’max 5.918 5.918 5.918 TL 127.568 127.568 127.568 BF 17.2725 17.2725 17.2725 Lens group data Group (surface) Focal length 1 (3 - 9) 63.6 2 (11 - 12) 37.6 3 (13 - 14) -65.4

[0097] Table 1 shows the numerical values of Numerical Example 1 to Numerical Example 3 and the numerical comparison example. Table 2 shows the conditional formula corresponding values of Numerical Example 1 to Numerical Example 3 and the numerical comparison example.

Table 1

Table 2

[0098] Figures 11 to 13 show the ghost images formed on the optical sensor in Numerical Example 1 to Numerical Example 3. Figure 14 shows the ghost image formed on the optical sensor in the numerical comparison example. It can be seen from Figures 11 to 14 that the ghosts in Numerical Example 1 to Numerical Example 3 are more suppressed than in the numerical comparison example.

[0099] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims be included.

Explanation of Signs

[0100] 1 Three-dimensional scanner, 2 Handpiece, 3, 3b Objective optical system for three-dimensional scanner, 10 Housing, 13 Light source, 14 Illumination optical system for three-dimensional scanner, 15 Illumination lens system, 16 Reticle, 17 Transparent plate, 18 Light-shielding pattern layer, 19 Polarizer, 20 Beam splitter, 21 Polarizing beam splitter, 30 Objective lens system, 34 Moving mechanism, 35 Lens position detector, 37 Phase plate, 38 Mirror, 39 Optical sensor, 40 Controller, 45 Computer, 50 Object, AX Optical axis, G1 First lens group, G2 Second lens group, G3 Third lens group, IM Image plane, L1, L2, L3, L4, L5, L6, L11, L12 Lenses.

Claims

1. An objective optical system for a three-dimensional scanner, comprising an objective lens system, wherein the objective lens system in order from the object side to the image plane side, a first lens having a negative power, a second lens having a positive power, a third lens having a negative power, a fourth lens having a positive power, a fifth lens having a positive power, and a sixth lens having a negative power, wherein the third lens and the fourth lens form a cemented lens, the fourth lens is a biconvex lens, and a radius of curvature of an image plane side surface of the fourth lens is 30 mm or less. The objective optical system for a three-dimensional scanner.

2. the second lens is a biconvex lens, and a radius of curvature of an image plane side surface of the second lens is 30 mm or less. The objective optical system for a three-dimensional scanner according to claim 1.

3. the sixth lens is a negative meniscus lens with a convex surface facing the image side, and a radius of curvature of an image plane side surface of the sixth lens is 40 mm or less. The objective optical system for a three-dimensional scanner according to claim 1.

4. the objective lens system satisfies the following conditional expression (1). The objective optical system for a three-dimensional scanner according to claim 1; 0.5 < |a / b| < 1.4... (1) provided that a: the distance on the optical axis from the image plane to the image plane side surface of the sixth lens, b: the radius of curvature of the image plane side surface of the sixth lens, is.

5. the objective lens system satisfies the following conditional expression (2). The objective optical system for a three-dimensional scanner according to claim 1; 4.0 < |c / d| < 14.0...(2) However, c: The distance on the optical axis from the image plane to the image plane side surface of the first lens, d: The radius of curvature of the image plane side surface of the first lens, and it is as follows.

6. The fifth lens is a moving lens that moves along the optical axis, The objective lens system is a variable focal length lens system whose focal length changes when the fifth lens moves along the optical axis. The objective optical system for a three-dimensional scanner according to claim 1.

7. A quarter-wave plate disposed on the object side of the objective lens system, and a polarization beam splitter disposed on the image plane side of the objective lens system. The objective optical system for a three-dimensional scanner according to claim 1.

8. A three-dimensional scanner comprising the objective optical system for a three-dimensional scanner according to any one of claims 1 to 7.

Images