The present invention relates to a lens image sensing apparatus used to detect, e.g., a hidden mark on a spectacle lens, a scratch on the lens surface, a foreign substance adhering on the lens, chipping or cracking of the lens, internal defects (striae, resin flow hysteresis, and weld lines) of the lens, and the optical characteristics of the lens.
A spectacle lens such as a progressive multifocal lens includes a plurality of convex (or concave) marks which are inscribed on it at reference positions spaced apart from the geometric center by predetermined distances and are called hidden marks (to be simply referred to as marks hereinafter). The spectacle lens is designed such that its geometric center, distance and near optical centers, and eyepoint position, for example, are calculated from the positions of these marks. For this reason, in edging the lens, an eyepoint position is detected from the positions of these marks, and a lens holder is mounted at the eyepoint position.
A spectacle lens image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2002-022599 is known to be used to detect the marks inscribed on the spectacle lens.
The spectacle lens image sensing apparatus includes a light source, half mirror, and image sensing device placed on the side of the convex surface of a test lens, and a condenser lens, imaging lens, and reflective screen placed on the side of the concave surface of the test lens. The convex surface of the test lens is irradiated with light from the light source to project images of the marks formed on the convex surface onto the reflective screen. The images reflected by the reflective screen are returned to the side of the convex surface of the test lens, formed again on the light-receiving surface of the image sensing device via the half mirror, and processed by an image processing device, thereby calculating, e.g., the geometric center and eyepoint position of the test lens. The reflective screen is formed by attaching a reflecting sheet coated with a fine powder of, e.g., glass or aluminum to a rotary plate in order to reflect light.
Unfortunately, it is often the case that marks are formed on the spectacle lens using different types of marking techniques such as printing, so they are hard to distinguish from the remaining portions due to their variation in sharpness. In addition, in recent years, as marks are inscribed in lighter colors, and high index lenses and colored lenses prevail, the differences in luminance between light beams having passed through the marks and those having passed through portions where no marks are inscribed (to be also referred to as non-mark portions hereinafter) have remarkably reduced. For this reason, it is demanded to develop a high-reliability apparatus which can obtain a sharp image by attaining a contrast higher than that attained by the conventional apparatus.
Furthermore, assume that the test lens is made of, for example, a thick bulk material (e.g., a strong-minus-power spectacle lens). In this case, if marks are formed on the periphery of the lens, this generates shadows of the marks and therefore makes it difficult to detect them. For this reason, it is also demanded to develop an apparatus which can easily detect marks formed on such a bulk material as well.
The present invention has been made to solve the above-described conventional problems and meet the above-described demands, and has as its object to provide a high-reliability lens image sensing apparatus which can obtain a sharp image with large differences in luminance between light beams transmitted through marks on a lens and those transmitted through non-mark portions on the lens.
In order to achieve the above-described object, the present invention provides a lens image sensing apparatus comprising a light source, an optical device including a collimator lens which converts light emitted by the light source into collimated light, and guides the collimated light to a convex surface of a test lens, a rotary reflector which reflects the light transmitted through the test lens back to the test lens, an image sensing device which receives the light that is reflected by the rotary reflector and transmitted through the test lens and the collimator lens again, an aperture stop arranged in an optical path between the collimator lens and the image sensing device, and a re-imaging lens provided between the aperture stop and the image sensing device, the rotary reflector including a sheet formed from a plurality of corner cube prisms.
In the present invention, since the corner cube prisms have three orthogonal total reflecting surfaces to have a retroreflection function, they reflect light emitted by the light source in the same direction as its incident direction. When a concave or convex mark is inscribed on the convex surface of the test lens, especially the periphery of this mark has a surface curvature different from that of the lens surface, so a light beam which enters this periphery diverges. Also, a light beam which enters the lens from a lens surface portion (non-mark portion) other than that where the mark is inscribed, is reflected by the corner cube prisms, and is transmitted through the periphery of the mark diverges on this periphery as well. Accordingly, light which is transmitted through the periphery of the mark, diverges, and returns in the same direction as its incident direction (such light will be referred to as diverging retroreflected light hereinafter) has a luminance lower than that of light which is transmitted through only the non-mark portion and retroreflected by the prisms (such light will be referred to as retroreflected light hereinafter). This means that a light beam converted into a collimated light beam by the collimator lens has a diameter significantly larger than that of a light beam converted into a collimated light beam by the collimator lens upon passing through only the non-mark portion. Hence, the illuminance on the light-receiving surface of the image sensing device becomes significantly lower in the mark portion than in the non-mark portion by setting the entrance pupil diameter of the re-imaging lens for forming an image of the test lens surface on the light-receiving surface of the image sensing device to be smaller than the diameter of a collimated light beam generated by the diverging retroreflected light and to be larger than the diameter of a collimated light beam generated by the retroreflected light. This makes it possible to sense a sharp image of the mark.
The present invention will be described in detail below with reference to embodiments shown in the accompanying drawings.
An example in which the test lens is a diverging progressive multifocal lens, and hidden marks (to be simply referred to as marks hereinafter) are formed on the convex surface of the lens will be given in this embodiment.
Referring to
The test lens 1 serving as a progressive multifocal lens includes a distance power measuring portion 6, a near power measuring portion 7, a portion for distance vision (distance portion) 8, a portion for near vision (near portion) 9, and a portion whose dioptric power continuously changes (progressive portion) 10.
The positions of the distance power measuring portion 6, the near power measuring portion 7, and an eyepoint 11 of the test lens 1 change depending on the lens design, and are determined at predetermined reference positions spaced apart from the geometric center O. For example, the eyepoint 11 is at a position spaced apart from the geometric center O to the upper side by a predetermined distance d1 (e.g., 2 mm), and a distance center 12 is at a position spaced apart from the position of the eyepoint 11 to the upper side by a predetermined distance d2 (e.g., 4 mm). Hence, the positions of the geometric center O and eyepoint 11 can be obtained by capturing and processing images of the marks 3A and 3B to calculate their position coordinates.
Referring to
The light source 31 is used to irradiate the test lens 1 to obtain sharp images of the marks 3A, 3B, and 3C, the number 4 indicating the addition power, and the identification mark 5, and is a monochromatic point source. The monochromatic point source is a general term including a laser light source that is a point source, and a light source, such as an LED, that can be substantially regarded to be a point source. Note that this embodiment exemplifies a red semiconductor laser as the point source.
The optical device 32 includes a condenser lens 33, transmission rotary scattering plate 34, half mirror 35, and collimator lens 36. The condenser lens 33 focuses the light beams L emitted by the light source 31. The transmission rotary scattering plate 34 is placed in front of the condenser lens 33. The half mirror 35 guides the light beams L transmitted through the transmission rotary scattering plate 34 toward the test lens 1. The collimator lens 36 is provided between the half mirror 35 and the test lens 1, and converts the light beams L from the light source 31 into collimated light beams L1.
The transmission rotary scattering plate 34 is used to eliminate any speckles and fringes, and serves as a transparent scatterer made of, e.g., glass. The transmission rotary scattering plate 34 is configured to be rotated by a driving motor (not shown) at the time of measuring the marks on the test lens 1 so as to scatter the light beams L from the light source 31. For this reason, the transmission rotary scattering plate 34 has a coarse surface 34a facing the half mirror 35, and is placed at a focal position P1 of the condenser lens 33.
The half mirror 35 has an appropriate transmittance and reflectance: it reflects the light beams L, which are emitted by the light source 31 and transmitted through the condenser lens 33 and transmission rotary scattering plate 34, toward the test lens 1, and transmits light beams L2 and L3 which return from the side of the test lens 1.
The collimator lens 36 is arranged in the optical path between the test lens 1 and the half mirror 35. The collimator lens 36 converts the light beams L, which are emitted by the light source 31, transmitted through the condenser lens 33 and transmission rotary scattering plate 34, and reflected by the half mirror 35, into the collimated light beams L1.
The test lens 1 is placed at a focal position P2 of the collimator lens 36 on its lower side.
An aperture stop 37, bandpass filter 38, re-imaging lens 39, image sensing device 40, and image processing device 41 are placed on the side of the half mirror 35 opposite to that of the test lens 1.
The aperture stop 37 is placed at a focal position P3 of the collimator lens 36 on its upper side, and limits the diameter of the light beam coming from the collimator lens 36. More specifically, the aperture stop 37 has a diameter which is smaller than that of a light beam from the mark 3C on the convex surface 1a of the test lens 1, and is larger than that of a light beam from a non-mark portion. However, the position of the aperture stop 37 is not limited to the focal position P3 of the collimator lens 36. The same function can also be realized by placing the aperture stop 37 at the position of the exit pupil of the collimator lens 36.
The bandpass filter 38 serves to transmit only light in the wavelength range of the light source 31 and cut off ambient light, and is provided between the aperture stop 37 and the re-imaging lens 39.
The re-imaging lens 39 focuses the light beams L2 and L3 having passed through the bandpass filter 38 on the image sensing device 40.
The image sensing device 40 includes a plurality of CCDs 40A which form a light-receiving surface, and is electrically connected to the image processing device 41. The CODs 40A are placed at a focal position P4 of the re-imaging lens 39. The focal position P4 of the re-imaging lens 39 is conjugate to the position of the convex surface 1a of the test lens 1 on the side of the collimator lens 36.
The lens image sensing apparatus 30 also includes a lens holding device 42 and rotary reflector 43 placed on the side of a concave surface 1b of the test lens 1.
The lens holding device 42 serves to chuck and fix the center of the concave surface 1b of the test lens 1, and includes a transparent plate 45 and a lens chucking cylinder 46 standing upright at the center of the upper surface of the transparent plate 45. The lens holding device 42 is configured to chuck and fix the center of the concave surface 1b of the test lens 1 on the upper surface of the lens chucking cylinder 46 by evacuating the lens chucking cylinder 46 using a vacuum pump. The lens chucking cylinder 46 has an outer diameter (e.g., 8 mm) small enough not to hamper projection of the marks 3A, 3B, and 3C, the number 4 indicating the addition power, and the identification mark 5 on the test lens 1.
The rotary reflector 43 serves to retroreflect the light beams L1 transmitted through the test lens 1 in the same directions as their incident directions, and includes a rotary plate 47 and a corner cube prism sheet 48 attached to the surface of the rotary plate 47.
The corner cube prism sheet 48 is made of plastic with a thickness of about 0.3 mm to 0.5 mm, includes a plurality of corner cube prisms (to be also simply referred to as prisms hereinafter) 49 formed on its surface, and is protected by a transparent protective film over the entire surface. The prisms 49 themselves are conventionally known prisms, which have three orthogonal total reflecting surfaces to have a function of reflecting the collimated light beams L1 transmitted through the test lens 1 in the same directions as their incident directions, i.e., a retroreflection function. The rotary reflector 43 is configured to be rotated at high speed (e.g., at 3,400 rpm) by a driving motor (not shown) in order to uniform its surface brightness and background, like the transmission rotary scattering plate 34.
Although the light source 31 emits innumerable light beams L,
Detection of the mark 3C on the test lens 1 by the lens image sensing apparatus 30 with the above-mentioned arrangement will be described next.
First, the test lens 1 is provided into the opening in the upper surface of the lens chucking cylinder 46 with the convex surface 1a facing up. Next, a vacuum exhaust device evacuates the lens chucking cylinder 46 to chuck and fix the test lens 1 in the opening in the upper surface of the lens chucking cylinder 46.
The light source 31 is turned on to emit light beams (red laser beams) L. The light beams L emitted by the light source 31 are focused by the condenser lens 33. The light beams L are converted into scattered light beams upon being transmitted through the transmission rotary scattering plate 34. The light beams L strike the half mirror 35, are reflected toward the test lens 1, and are further converted into collimated light beams L1 upon being transmitted through the collimator lens 36. The collimated light beams L1 become diverging light beams upon being transmitted through the test lens 1 from the convex surface 1a to the concave surface 1b (the collimated light beams L1 become converging light beams when the test lens 1 is a convex converging dioptric lens). At this time, the collimated light beam L1 which enters the test lens 1 from a lens surface portion (non-mark portion) other than that where the mark is inscribed strikes the prisms 49, is reflected by the prisms 49 in the same direction as its incident direction to the prisms 49. The light beam L2 is transmitted through the test lens 1 from the concave surface 1b, and returns to the convex surface 1a, as shown in
Referring to
The image sensing device 40 converts the light received by the CCDs 40A into an electrical signal, and sends it to the image processing device 41. The image processing device 41 processes the image information from the image sensing device 40 to identify a spectacle shop as the delivery destination using the mark 3C. Also, the image sensing device 40 receives the pieces of image information of, e.g., the marks 3A and 3B to calculate the positions of, e.g., the geometric center O and eyepoint 11 based on the pieces of position information of these marks 3A and 3B.
The detection of the mark 3C will be described in more detail herein with reference to
That is, in the lens image sensing apparatus 30 according to the present invention, using the corner cube prisms 49, the light beams L2, L5, and L6 transmitted through only the non-mark portion on the convex surface 1a in both the forward and backward paths are returned as retroreflected light beams with small degrees of diffusion, and focused on the light-receiving surface of the CCDs 40A. Using the corner cube prisms 49 as well, the light beams L3 and L4 transmitted through the periphery C of the mark 3C in at least one of the forward and backward paths are returned as diverging retroreflected light beams with large degrees of diffusion, and focused on the light-receiving surface of the CCDs 40A. When the retroreflected light beams L2, L5, and L6 and the diverging retroreflected light beams L3 and L4 are guided to the aperture stop 37, the retroreflected light beams L2, L5, and L6 pass through the aperture stop 37 without any losses because they have sufficiently small diameters. Hence, the retroreflected light beams L2, L5, and L6 can generate high illuminances of the mark on the light-receiving surface of the CCDs 40A. In contrast to this, the diverging retroreflected light beams L3 and L4 have diameters larger than that of the aperture stop 37, so they generate low illuminances of the mark on the light-receiving surface of the CCDs 40A because their losses due to factors associated with the aperture stop 37 are large. As a result, the lens image sensing apparatus 30 according to the present invention can obtain a mark image which is sharper and has a higher contrast than that obtained using the above-mentioned conventional reflective screen. This makes it possible to facilitate image processing, and, in turn, facilitate design of an image processing circuit.
As shown in
Since the transmission rotary scattering plate 34 is used in the present invention, generation of any speckles due to factors associated with the laser light source can be suppressed and prevented. Also, since the brightness of the surface of the corner cube prism sheet 48 in the image background is equalized by the rotary reflector 43, image processing can further be facilitated.
Even when the test lens 1 is a colored lens, it is possible to obtain a sharp image with high contrast as long as the mark has a shape which can obtain retroreflected light and diverging retroreflected light.
In the present invention, since the CCDs 40A of the image sensing device 40 are sufficiently set smaller than the test lens 1, the ratio between the focal length (f1) of the collimator lens 36 and the focal length (f2) of the re-imaging lens 39 (their lateral magnification) becomes sufficiently high. This makes it possible to set the longitudinal magnification sufficiently high as well, thus increasing the depth of focus. This has the advantage of minimizing defocusing at the time of observing a thick lens, thus reducing the shadows of the end face of a minus-power lens.
In the present invention, the light beams L emitted by the light source 31 are converted into the collimated light beams L1 by the collimator lens 36. However, if the light beams L are not converted into the collimated light beams L1, the exit light from the collimator lens 36 obliquely enters the end face of the test lens 1. Therefore, this incident light strikes and is reflected by the edge surface, does not become effective retroreflected light even when it is reflected by the prisms 49, and is not focused on the CCDs 40A of the image sensing device 40. This makes it impossible to obtain a sharp image. In contrast to this, if the light beams L are converted into the collimated light beams L1, the exit light from the collimator lens 36 enters the end face of a minus-power lens at a large incident angle. Therefore, this incident light is refracted toward the lens center without striking the edge surface, becomes retroreflected light upon being reflected by the prisms 49 after its transmission through the lens, travels back the way it came, and is focused on the CCDs 40A. This makes it possible to obtain a sharp image. When a conjugate optical system including the collimator lens 36 and re-imaging lens 39 is designed as a bilateral telecentric optical system, this is preferable because an image with the same barycentric position as an image free from defocusing can be obtained even if defocusing occurs upon fluctuation in thickness of the test lens 1.
Although image detection of the convex mark 3C has been described in this embodiment, the present invention is not limited to a convex mark, and a sharp image can also be obtained in the same way even by using a concave mark. That is, because a concave mark is symmetrical to a convex mark and has, on the periphery of its concave portion, a surface curvature quite different from that of the convex surface 1a of the test lens 1, light transmitted through the periphery has a large degree of diffusion and therefore becomes diverging retroreflected light, whereas light transmitted through the central portion of the concave portion has a small degree of diffusion and therefore becomes retroreflected light. This makes it possible to obtain a mark image with a clear contour shape and high contrast between the retroreflected light and the diverging retroreflected light.
In this embodiment, a corner cube prism sheet 48 is concavely curved on the light source side instead of being formed in a flat shape. Other constituent components in this embodiment are quite the same as the embodiment shown in
Assume that the corner cube prism sheet 48 is formed in a flat shape, as indicated by an alternate long and two short dashed line. In this case, a light beam L1 farther away from the center of a test lens 1 has a larger incident angle α on the surface of corner cube prisms 49. Thus, the corner cube prisms 49 exhibit low reflection efficiency. That is, a large light loss is generated, and this darkens the entire image. This means that a sharp image is hard to obtain when a mark is inscribed on the test lens 1 near its outer periphery.
To prevent this, the corner cube prism sheet 48 is concavely curved when viewed from the light source side. Then, the light beam L1 farther away from the center of the test lens 1 can have an incident angle β on the surface of the corner cube prisms 49, that is smaller than when the corner cube prism sheet 48 is flat. Thus, the corner cube prisms 49 exhibit high reflection efficiency, and this makes it possible to reduce a light loss. In this way, a sharp image can be obtained even when a mark inscribed on the test lens 1 near its outer periphery is used.
If the corner cube prism sheet 48 has too large a radius of curvature R, it has a shape close to that of a flat plate, and this lessens the effect produced by the corner cube prism sheet 48. If the corner cube prism sheet 48 has too small a radius of curvature R, a light beam which passes through the test lens 1 near its periphery enters the corner cube prism sheet 48 at a relatively large incident angle, and this generates a light loss. Hence, the corner cube prism sheet 48 is desirably designed to have a preferable value of the radius of curvature R in accordance with the lens dioptric power. If the light beam L1 which enters the convex surface 1a of the test lens 1 is a collimated light beam parallel to the optical axis, letting D (diopter) be the dioptric power of test lens 1, and M be the distance from the test lens 1 to the corner cube prism sheet 48, the radius of curvature R preferably has a value (R=(−1/D)+M) obtained by adding the distance M to the reciprocal of a negative value of the dioptric power D, or has its neighborhood. Note that if the light beam which enters the convex surface 1a of the test lens 1 is not collimated, the radius of curvature R can be set to a value obtained by adding a correction value that depends on the angle of divergence of the incident light beam to the radius of curvature R.
As has been described above, in a preferred embodiment of the present invention, the light source used is a monochromatic point source.
Also, in the preferred embodiment of the present invention, the corner cube prism sheet is concavely curved when viewed from the light source side to reduce a light loss. That is, when the corner cube prism sheet is flat, light transmitted through the test lens at a position farther away from the center of the test lens more obliquely enters the corner cube prism. This generates a light loss due to factors associated with the prism geometrical structure, and lowers reflection efficiency (the intensity ratio between the incident beam and the outgoing beam). This phenomenon is undesirable because it generates a decrease in image luminance on the outer periphery of the test lens, which exhibits especially high divergence, and deteriorates the detection sensitivity of a mark located near the outer periphery.
To suppress the influence of the foregoing fact, the corner cube prism sheet is concavely curved when viewed from the light source side. Hence, a light beam which passes through a diverging test lens at a position farther away from its center can have an incident angle on the corner cube prisms, that is smaller than when a flat sheet is used. This makes it possible to keep a light loss small enough to be ignored, and, in turn, makes it possible to sense a sharp image of even a mark inscribed on the test lens near its outer periphery.
A converging test lens shows a decrease in luminance on its outer periphery less conspicuous than a diverging test lens. In addition, the former lens has a converging optical path from the test lens to the corner cube prism sheet. Thus, even when the corner cube prism sheet is concavely curved, the light beam effective range on the prism sheet is limited to the vicinity of the center of the prism sheet, and the prism sheet has a small tilt angle within the range. For this reason, a decrease in reflectance is kept small enough to be ignored as compared with a case in which the prism sheet has a flat surface.
If the corner cube prism sheet is undesirably convexly curved when viewed from the light source side, a light beam transmitted through the outer periphery of a diverging test lens enters the corner cube prisms at a large incident angle, and this generates a large light loss and lowers reflection efficiency. This makes it impossible to sense a sharp image of the mark.
Also, in the preferred embodiment of the present invention, the optical device includes a condenser lens, transmission rotary scattering plate, and half mirror. The condenser lens focuses light emitted by the light source. The transmission rotary scattering plate scatters the light transmitted through the condenser lens. The half mirror guides the light transmitted through the transmission rotary scattering plate to the collimator lens, and further guides, to the aperture stop, the light which is transmitted through the test lens, strikes and is reflected by the rotary reflector, is transmitted through the test lens and collimator lens again, and returns.
Also, in the preferred embodiment of the present invention, the image sensing device includes a bandpass filter which transmits only light in the wavelength range of the light from the light source.
Since the bandpass filter transmits only light in the wavelength range of the light from the light source, it is possible to sense an image with high contrast with little influence of ambient light.
Moreover, in the preferred embodiment of the present invention, the image sensing device includes an image processing device which processes the image sensed by the image sensing device.
Number | Date | Country | Kind |
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334895/2007 | Dec 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2008/073398 | 12/24/2008 | WO | 00 | 6/22/2010 |