Optical device

Abstract: An optical device reads the information such as bar codes (6) on an object. A light-emitting element (2) emits a read-beam. A lens cover (8) has an inclined surface (8a) that is at an angle with the read-beam (2a) and reflects the read-beam (2a) toward a bar code (6), the read-beam (2a) emerging as a reflected-beam (3a) after reflection from the surface of the bar code (6). The reflected-beam (3a) contains a component directly reflected from the bar code (6) and a component randomly reflected by the white and black areas of the bar code (6). An optical system in the form of a lens (5) is arranged between the lens cover (8) and the light-emitting element (2), and converges the read-beam (2a) to the bar code (6). The inclined surface (8a) is also at an angle with the reflected-beam (3a) and reflects the reflected-beam (3a) toward a second optical system in the form of a lens (5) which in turn converges the reflected-beam (3a) emerging from the inclined surface (8a) to a light-sensing element (3). The light-sensing element detects the reflected-beam (3a). The inclination angle of the inclined surface (8a) may be selected such that more randomly reflected light is contained in the reflected-beam (3a) than the directly reflected light.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to optical devices such as photo-interrupters that are utilized for bar code reading and object detection. DESCRIPTION OF RELATED ART Figs. 23 and 24 show a conventional reflective-type photo-interrupter 20 equipped with a light-emitting unit and a light-sensing unit. This unit reflects the preamble of the independent claims. The light-emitted from the light-emitting unit is reflected off an object surface and is then detected by the light-sensing unit. In this conventional photo-interrupter 20, light-emitting chip 2 and light-sensing chip 3 are mounted to a head 4 by some method such as gold wire bonding. This photo-interrupter is further provided with a lens 5 which focuses a read-beam emitted from light-emitting element 2 on the object surface and converges a reflected-beam from the object surface on the light-sensing element 3, and a case which houses various members of the unit and blocks ambient light from coming into the unit, and a lens cover 18 for protecting the lens 5. When reading a bar code 6 using reflection-type photo-interrupter 20 of the aforementioned construction, the bar code 6 is moved above the reflective-type photo-interrupter 20, or the reflective-type photo-interrupter 20 is moved above bar code 6, thereby reading the bar code 6. When the read-beam is converged to a certain spot on a white area of the bar code 6, the amount of the reflected-beam is large and therefore the light-sensing chip 3 receives a more amount of light. This results in an increase in the photo-current generated by the light-sensing chip 3. Also, when the read-beam is focused at a certain spot on a black area of the bar code 6, the amount of the reflected-beam is small, resulting in a relative decrease in the photo-current generated by light-sensing chip 3. In this manner, the bar code pattern is converted into a varying photo-current generated by the light-sensing chip 3. In order to realize a small sized photo-interrupter, the distance from the light-emitting chip 2 and light sensing chip 3 to the bar code 6 is preferably as short as possible. The focal length of the lens 5 can be shortened by decreasing the radius of curvature of the lens 5, thereby decreasing the distance from the light-emitting chip 2 and light-sensing chip 3 to the bar code 6. However, the radii of curvature of the lens 5 smaller than a certain value cause larger aberrations of the lens 5, making it difficult to distinguish between the white and black areas as well as reducing the depth of focus. A reduced depth of focus makes it difficult to accurately read the bar codes when the bar codes are moving in the direction of the optical axis of the read-beam. Therefore, the distance from the light-emitting chip 2 and light sensing chip 3 to the bar code 6 cannot be shorter than a certain minimum value. This limitation prevents package reduction of an apparatus incorporating photo-interrupter 20. Also, for a reflection-type photo-interrupter such as the one shown in Figs. 23 and 24, the light-emitter and light-sensor are placed in a mirror relation for ease of manufacture. With this construction, the light directly reflected (referred to as direct reflection hereinafter) from the bar codes enters directly the light-sensing chip. The intensity of the direct-reflection is more sensitive to the luster of the medium on which the bar code is printed than to the black and white areas of the bar code. Thus, the bar codes on a very lustrous object cannot be read properly. In order to accurately read such bar codes, the sensor is tilted relative to the bar code as shown in Fig. 25 so that the reflected-beam contains a less amount of direct-reflection with an increased ratio of scattered light to the direct-reflection. However, a tilted photo-interrupter occupies a larger space within the housing of the interrupter, presenting a problem in assembly into the apparatus. Thus, incorporating such a photo-interrupter in the apparatus is an obstacle to miniaturizing the apparatus. In EP0377973, a bar code scanner is disclosed wherein a second optical system for collecting light reflected by the bar code is tilted with respect to a first optical system, leading to the same problems regarding the physical size of the device discussed above. Other examples of prior devices are shown in EP 0669592 and EP0475675, which disclose arrangements where a scanning mirror is provided for reflecting light emitted by a light-emitting device, directing it onto a region of the barcode, and for directing light reflected from the barcode region towards the light sensitive device. In EP0669592, a prism is provided between a converging lens and the position of the light emitting and light sensitive devices, so that the light emerging from the light emitting device and the light travelling towards the light sensitive device is reflected. By altering the direction of propagation, the use of a prism allows the size of the reader to be reduced without causing a corresponding diminution in depth of field. In EP0475675, the scanning mirror is arranged to produce a similar reduction in physical size. SUMMARY OF THE INVENTION The present invention was made in view of the problems noted above. An object of the invention is to provide an optical device which lends itself to the miniaturization of apparatus. Another object of the invention is to provide an optical device which ensures that for example bar codes are reliably read regardless of the luster of the surface of a medium on which the bar code is printed. An optical device according to the invention comprises a housing, a light-emitting element for emitting a first beam of light towards an object, a light-sensing element for sensing a second beam of light, the second beam of light being the reflection of first beam of light from a surface of the object, a first optical system, having a first optical axis, arranged to converge the first beam of light substantially on the surface of the object, a second optical system arranged to converge the second beam of light substantially to the said light-sensing element, said second optical system having a second optical axis that is oblique to the axis of the first optical system, and a reflector having a reflecting surface that reflects the first beam of light towards the surface of the object and reflects the second beam of light towards said light-sensing element via said second optical system, wherein the reflector is formed by part of said housing. The invention further provides a method of reading a bar code comprising illuminating an object having the bar code thereon with light from a source, collecting light reflected by the object and detecting the intensity of the reflected light bearing the bar code data, wherein the light illuminating the object passes through a first optical system positioned between the light source and the object, the light returned from the object passes through a second optical system located between the object and a light sensing element, and the light passing through both optical systems is reflected by a reflector and said optical systems have optical axes that are oblique to one another, wherein the reflector is formed by part of a housing in which said optical systems are located, having an inclined surface where the angle of inclination has been selected so that the second optical system preferentially collects light bearing data concerning the bar code, rather than specular reflections from the object bearing the bar code. In an embodiment of the invention, a light-emitting element (2) emits a first beam of light or read-beam (2a). A lens cover (8) has an inclined surface (8a) that is at an angle with the read-beam (2a) and reflects the read-beam (2a) toward a bar code (6), the read-beam (2a) emerging as a second beam of light or reflected-beam (3a) after reflection from the surface of the bar code (6). The reflected-beam (3a) contains components directly reflected from the bar code (6) and randomly reflected by the white and black areas of the bar code (6). An optical system in the form of a lens (5) is arranged between the lens cover (8) and the light-emitting element (2), and converges the read-beam (2a) to the bar code (6). The inclined surface (8a) is also at an angle with the reflected-beam and reflects the reflected-beam (3a) toward a second optical system in the form of a lens (5) which in turn converges the reflected-beam (3a) emerging from the inclined surface (8a) to a light-sensing element (3). The light-sensing element sensing the reflected-beam (3a). The inclination angle of the inclined surface (8a) may be selected such that more randomly reflected light is contained in the reflected-beam (3a) than the directly reflected light. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention as defined in the appended claims will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Figs. 1 and 2 are sectional views showing the construction of the optical device related to a first embodiment in this invention; Fig. 3 is a perspective view illustrating the optical axes of the read-beam and reflected beams in the first embodiment; Fig. 4 is another perspective view of the first embodiment, illustrating the directions of the light incident on and reflected by the bar code; Fig. 5 compares a conventional optical device with an optical device according to the first embodiment, when assembled in an apparatus; Figs. 6 and 7 illustrate the construction of an optical device according to a second embodiment; Fig. 8 illustrates the detail of the mounting projection of the optical device of the second embodiment; Fig. 9 illustrates a chassis to which the optical device of the second embodiment is assembled: Fig. 10 is a perspective view of the optical device of the second embodiment when assembled to the chassis in Fig. 9; Fig. 11 is a cross sectional view showing the photo-interrupter of the second embodiment assembled in the chassis of Fig. 9; Figs. 12 and 13 illustrate an optical device according to a third embodiment; Figs. 14 and 15 are perspective views of the third embodiment, illustrating the directions of the light incident on and reflected by the bar code; Fig. 16 illustrates the operation of the lens cover of the third embodiment; Figs. 17 and 18 illustrate the construction of an optical device according to a fourth embodiment; Fig. 19 illustrates the optical device according to the fourth embodiment; Fig. 20 illustrates the construction of the optical device according to a fifth embodiment; Fig. 21 illustrates the construction of the optical device according to a sixth embodiment; Fig. 22 illustrates the construction of the optical device according to a seventh embodiment. Figs. 23 and 24 illustrate the construction of a conventional photo-interrupter; and Fig. 25 illustrates the position of a conventional photo-interrupter relative to an object. DETAILED DESCRIPTION OF THE INVENTION First embodiment Figs. 1 and 2 are sectional views of an optical device (photo-interrupter 10) according to a first embodiment of present invention. Referring to Figs. 1 and 2, a light-emitting chip 2 emits a read-beam, and a light-sensing chip 3 for sensing the read-beam reflected off the surface (herein referred to as "reflected-beam") of a bar code 6 as an object to be read. The bar code 6 includes white and black areas as shown. The light-emitting chips 2 and light-sensing chip 3 are mounted on a head 4. A lens 5 is held above the light-emitting chip 2 and light-sensing chip 3, and includes a lens section 5a and lens section 5b, the lens 5a focusing the read-beam from light-emitting chip 2 on the bar code 6 and the lens 5b focusing the reflected-beam on the light-sensing chip 3. A lens cover 8 is disposed on the lens 5. A case 1 houses the head 4, lens cover 8, and other associated components, not shown, therein. The above two lens sections 5a and 5b have optical axes 2a and 3a, respectively, which are somewhat oblique to each other. A lens cover 8 is made of a transparent material such as glass or resin, and has a surface 8a which is inclined at 45 degrees with respect to the plane PLo including the two optical axes 2a and 3a of the lens 5. The plane PLo is also substantially parallel to the surface of the bar code 6. Fig. 3 is a perspective view of the optical axes 2a an 2b of the read-beam and reflected beam, respectively. The read-beam emitted from light-emitting chip 2 is converged by the lens 5, and is then reflected by the inclined plane 8a of the lens cover 8 to the bar code 6. Since the inclination angle of the inclined surface 8a is 45 degrees, the read-beam and reflected-beam are in a plane substantially perpendicular to the surface of the bar code 6 as shown in Fig. 4. The reflected-beam contains diffused reflection (randomly reflected light) and direct reflection Dr, and travels in the optical path 3a back to the photo-interrupter 10. Then, the components representing the information on the bar code 6 are redirected by the inclined surface 8a of the lens cover 8 toward the lens section 5b which in turn focuses the light to the light-sensing chip 3. For instance, with a lens cover 8 having a refractive index N of 1.5, the light incident upon the inclined surface 8a is totally reflected if the angle of incidence, i.e., α 1 is greater than 41.8 degrees. As shown in Fig. 2, the reflected-beam from the bar code 6 is redirected by the inclined surface 8a of the lens cover 8 by reflection. This construction offers a shorter distance d3 from the photo-interrupter 10 to the bar code 6 while still maintaining a sufficient optical distance d1+d2. Therefore, as shown in Fig. 5, when assembled in an apparatus, the construction of the first embodiment requires a distance d4 in the direction in which the read-beam illuminates the bar code 6, while the conventional construction requires a distance d5 longer than the distance d4. Thus, the construction of the first embodiment lends itself to the miniaturization of an apparatus into which the photo-interrupter 10 of this construction is installed. It is to be clearly understood that the photo-interrupter 10 of the embodiment takes a smaller space defined by a chassis 15 than the conventional photo-interrupter 80. The use of the lens cover 8 of the aforementioned geometry not only protects the lens 5 but also functions the same way as a prism, and therefore eliminates the prism which was needed for redirecting the read-beam in the conventional apparatus. Therefore, equipping an apparatus with this type of photo-interrupter 10 allows cost reduction. Second embodiment Figs. 6 and 7 are sectional views of a photo-interrupter as an optical device according to a second embodiment. This embodiment applies to the photo-interrupter 20 just as the first embodiment described above. Structural elements in Figs. 6 and 7 similar to or corresponding to those in Figs. 1 and 2 have been given the same reference numerals. Referring to Fig. 6, a head 4 supports a light-emitting chip 2 and a light-sensing chip 3. A lens 5 is held above the light-emitting chip 2 and light-sensing chip. A lens cover 8 is held on the lens 5. A case 1 houses the head 4 having the chips 2 and 3 mounted thereon, lens 5, and other associated components, not shown therein. The photo-interrupter 20 has a mounting projection 7 by which the photo-interrupter 20 is positioned in place when the photo-interrupter 20 is assembled to a chassis 11 of an apparatus as shown in Fig. 9. The chassis 11 is not transparent to light, preventing ambient light from entering the apparatus. The mounting projection 7 is on the surface of the photo-interrupter 20 opposing the bar code 6. The mounting projection 7 is a cylinder of a transparent material. As shown in Fig. 8, the diameter L2 of the mounting projection should be large enough so as not to block the read-beam having a diameter D1 when the read-beam emerges the mounting projection 7. The shaded area represents the divergence of light. Also, the diameter L2 is selected to be as large as the components of the reflected-beam that would fall on the light-sensing element 3 are not blocked. If the interior surface is highly reflective, the diameter should be as small as possible so that only the light converged by the lens 5 enters the light-emitting chip. The chassis 11 of an apparatus into which the photo-interrupter 20 is formed with a mounting hole 12 therein. To connect the chassis 11 to the photo-interrupter 20, the mounting projection 7 is inserted into the mounting hole 12, as shown in Fig. 10. When the diameter of the mounting hole 12 is such that the mounting projection 7 snugly fits thereinto, the photo-interrupter 20 is firmly connected to block 11. Such a diameter facilitates the assembly operation of the photo-interrupter 20. On the other hand, if the diameter of hole 12 allows for some play, the position of the photo-interrupter 20 can be easily adjusted after insertion of the mounting projection 7, in which case the photo-interrupter 20 is fixedly assembled to the chassis 11 by a suitable method such as bonding by an adhesive, melting, or holding with the other structural elements of the chassis 11. The photo-interrupter 20 is assembled to the chassis 11 with the mounting projection 7 which also functions as the optical path for the read-beam and reflected-beam. The read-beam emerging the photo-interrupter 20 is more accurately positioned relative to the chassis 11 when the photo-interrupter 20 is positioned with reference to the mounting projection 7 than with reference to other part, e.g., near the head 4, of the photo-interrupter 20. The use of mounting projection as a positional reference minimizes variations in optical characteristics. Fig. 11 is a cross-sectional side view of the apparatus into which the photo-interrupter 20 is assembled. Referring to Fig. 11, the read-beam and reflected-beam are output and input, respectively, through the mounting projection 7 which serves as a positional reference when the photo-interrupter 20 is assembled to the chassis 11. Therefore, even if the position of the rest of the photo-interrupter 30 changes slightly relative to chassis 11, the focus position of photo-interrupter 30 relative to the chassis 11 will not shift. While the second embodiment has been described with reference to the mounting projection 7 in the form of a cylinder, the mounting projection may be other shapes in which case the shape of the hole 12 is in accordance with the shape of the mounting projection 7. In addition, rotation of the photo-interrupter, if not desired, can be prevented by forming the mounting projection 7 in the form of, for example, a prism. Third embodiment If the inclination angle of the incline surface 8a of the first embodiment is set at 45 degrees, the read-beam travels in the plane substantially perpendicular to the surface of the bar code 6 as shown in Fig. 4 and the direct reflection travels back together with diffused reflection in the same plane entering the lens cover 8. The direct reflection may reach the light-sensing element 3. The third embodiment solves this problem. Figs. 12 and 13 are sectional views of an optical device according to a third embodiment of the present invention. Components in Figs. 12 and 13 corresponding to those in Figs. 1, 2, 6, and 7 have been given the same or similar reference numerals. Referring to Fig. 12, a head 4 supports a light-emitting chip 2 and a light-sensing chip 3 thereon. A lens 5 is held above the light-emitting chip 2 and light-sensing chip. A case 1 houses the lens 5, head 4, and other associated components, not shown. A lens cover 8 is held on the lens 5 and has a mounting projection 7 formed therewith. The mounting projection 7 is on the surface of the photo-interrupter 30 opposing the bar code 6. The inclined surface 8a of the lens cover 8 of the photo-interrupter 30 shown in Fig. 13 is at angles α 2 other than 45 degrees, e.g., 55 degrees, with the plane including the two optical axes 2a and 3a, as opposed to the inclined surface 8a of the photo-interrupter 20 shown in Figs. 6 and 7 which is at an angle α 1 at 45 degrees with the plane including the two optical axes. It is to be noted that this angle α 2 is such that a significant amount of direct reflection will not enter the mounting projection 7. If the angle α 2 is larger than 45 degrees, the read-beam travels along the optical axis 2a in a plane PL1 in Fig. 14 and the diffused reflection travels along the optical axis 3a in the plane PL1 while the direct reflection travels along an optical axis Dr in a plane PL2. The planes PL1 and PL2 make an angle  1 with the surface of the bar code 6. As shown in Fig. 16, the reflected-beam shown in solid line enters the mounting projection 7 and is converged by the lens 5 to the light-sensing element 3. Some of the direct reflection shown in dotted line enters the mounting projection 7 but is not converged by the lens 5 to the light-sensing element 3. Thus, the direct reflection will not reach the light-sensing element 3. If the angle α2 is smaller than 45 degrees, the read-beam travels along the optical axis 2a in a plane PL3 in Fig. 15 and the diffused reflection is reflected back along the optical axis 3a in the plane PL3 into the mounting projection 7 while the direct reflection travels along an optical axis Dr in a plane PL4. The planes PL3 and PL4 make an angle  2 with the surface of the bar code 6. Here again, some of the direct reflection enters the mounting projection 7 but is not converged by the lens 5 to the light-sensing element 3. Thus, the direct reflection will not reach the light-sensing element 3. The angles  1 and  2 are shown somewhat larger than actual values in order to clearly illustrate the planes in which the light incident upon the bar code 6 and light reflected by the bar code 6 travel. The angle α 2 varies depending on the diameter of the mounting projection 7 and the distance from the mounting projection 7 to the bar code 6. As described above, a large portion of the direct reflection is directed in a direction different from the direction in which the scattered light directed to the light-sensing element. Thus, the light incident upon the light-sensing element 3 contains the direct reflection and scattered light in different proportion with greatly increased ratio of the scattered light to the direct reflection. The intensity of direct reflection is high but varies depending not only on the black and white surfaces of the bar code but also on the luster of the object on which the bar code is printed. For example, if the area concerned is black and the surface is glossy, the intensity becomes high making it difficult to distinguish between the black and white surfaces. On the other hand, the intensity of the diffused reflection is low, but is not affected significantly by the luster of the surface. Therefore, if the ratio of the scattered light to the direct reflection is increased, the overall intensity of the light incident upon the light-sensing element 3 decreases but becomes less sensitive to the luster of an object to be measured. The signal-to-noise ratio of the light incident upon the light-sensing element 3 can therefore be increased. If the inclination angle α 2 of the surface 8a is increased or decreased from 45 degrees, the percentage of the direct reflection in the reflected-beam can be reduced. As mentioned above, if the refraction index of the lens cover 8 is, for example, 1.5 and the incidence angle (i.e. inclination angle) is 41.8 degrees or more, the read-beam is totally reflected. Therefore, the inclination angle α 2 can be set between 41.8 degrees and 45 degrees. The inclination angles α 2 other than 45° cause the read-beam to be incident on the bar code at an angle α 3 other than 90°, causing the light directly reflected by the lustrous surface of the bar code 6 to travel in such directions as not to enter the mounting projection 7. However, if the surface of the bar code 6 is not substantially parallel to the plane including the optical axes of the lens 5, a significant amount of direct reflection may travel back in the plane including the read-beam. Thus, it is desirable that the inclination angle α 2 be 45 degrees or larger. An inclination angle of the surface 8a other than 45 degrees increases the ratio of the scattered light contained in the light reflected by the bar code 6, and therefore improves the signal-to-noise ratio of the light incident upon the light-sensing element 3. The inclination angle of the surface 8a greater than 45 degrees ensures that the light is totally reflected, so that no part of light passes through the surface 8a to the outside of the photo-interrupter. Fourth embodiment Figs. 17 and 18 are sectional views of an optical device according to a fourth embodiment. Structural elements in Figs. 17 and 18 similar to or corresponding to those in Figs. 1, 2, 6, 7, 14 and 15 have been given the same reference numerals. Figs. 17 and 18 illustrate a photo-interrupter 40 of the fourth embodiment. Referring to Fig. 17, a head 4 supports a light emitting chip 2 and light sensing chip 3 thereon. Over the light emitting chip 2 and light sensing chip 3 is held a lens 5. A lens cover 8 is mounted on the lens 5. A case 1 houses the head 4, light emitting chip 2 and light sensing chip 3, lens 5, lens cover 8, and other associated components, not shown. The lens cover 8 has two inclined surfaces 8a and 8c, substantially parallel to each other. Referring back to Fig. 1, the optical distance from the bar code 6 to the bottom surface 8b of the lens cover 8 in contact with the lens 5 is d1+d2. In Fig. 18, the optical distance from the bar code 6 to the bottom surface 8b is a+b+c. However, the use of two surfaces 8a and 8c makes the physical distance D, from the bar code 6 to the bottom surface 8b, shorter by the distance a while still maintaining the optical distance a+b+c. The distance a can be determined at will by adjusting the space between two inclined surfaces 8a and 8c. Therefore, these two surfaces 8a and 8c may be advantageously used in reducing the overall size of an apparatus which incorporates the photo-interrupter 40. If the mounting space of the photo-interrupter 40 is limited by obstacles 11-13 in the apparatus as shown in Fig. 19 into which the photo-interrupter 50 is incorporated, then the aforementioned two surfaces 8a and 8c provide a detour of light, increasing degrees of freedom in designing the apparatus. The shorter physical distance D resulting from the two surfaces 8a and 8b is an advantage to miniaturizing the apparatus. Fifth embodiment The first to fourth embodiments have been described with reference to a reflection type photo-interrupter to which the present invention is applied. A fifth embodiment is directed to the construction of a light-emitting element 50 and a light-sensing element 50a as shown in Fig. 20. Fig. 20 illustrates the light-emitting element 50. The light-emitting element 50 and the light-sensing element 50a are of much the same construction and differ only in that the light emitting chip 2 and a light-sensing element 3 are interchanged. The solid lines indicate the light emitted by the light-sensing element 50 and the dotted lines indicate the light coming in the light light-sensing element 50a. The light-emitting element 50 includes a light emitting chip 2 and a package 21 which is made of a transparent resin and houses light emitting chip 2 therein. The package 21 includes an inclined surface 22 which functions as a reflecting surface in the same way as the inclined surface 8a formed, for example, on the lens cover 8 shown in Fig. 1. The light-sensing element 50a includes a light sensing chip 3 in place of the light emitting chip 3 in the light-emitting element 50. The surface 22 formed on a part of the package 21 for the light-emitting element 50 and the light-sensing element 50a offers more degrees of freedom of the arrangement thereof. Therefore, an apparatus incorporating the light-emitting element 50 and/or the light-sensing element 50a can realize package reduction. Sixth embodiment A sixth embodiment is directed to the construction of a light-emitting element and a light-sensing element which have two inclined reflecting surfaces. Fig. 21 illustrates a light-emitting element 60 and a light-sensing element 60a according to the sixth embodiment. The solid lines indicate the light emitted by the light-sensing element 60 and the dotted lines indicate the light coming in the light-sensing element 60a. The light-emitting element 60 and the light-sensing element 60a are of much the same construction and differ only in that the light emitting chip 2 and a light-sensing element 3 are interchanged. This light-emitting element 60 includes a package 21 in the form of, for example, a transparent resin in which a light-emitting chip 2 is molded. The package has two inclined surfaces that function as a reflecting surface similar to the surfaces 8a and 8c in the fourth embodiment (Fig. 18). The light-sensing element 60a has the light sensing chip 3 in place of the light sensing chip 3 in the light-emitting element 60. If the mounting space of the light-emitting element 60 or the light-sensing element 60a is limited by obstacles in the apparatus in which the elements 60 or 60a is incorporated, then the two surfaces 23 and 24 provide a detour of light so that the obstacle 14 is cleared. The construction increases degrees of freedom in designing the apparatus. The package 21 having the two inclined surfaces 23 and 24 is an advantage to miniaturizing the apparatus into which the light-emitting element 60 and/or the light-sensing element 60a is incorporated. Seventh embodiment Fig. 22 illustrates a photo-interrupter 70 according to a seventh embodiment. The seventh embodiment includes a reflecting mirror 25 in place of the inclined surface 8a of the aforementioned first to fourth embodiments. Referring to Fig. 22, a head 4 supports a light-emitting element 2 and light-sensing element 3 thereon. A lens 5 is held over the head 4 arid has two sections as in the first embodiment, only one being shown in the figure. One of the two sections has an optical axis in line with the optical axis of the read-beam and the other has an optical axis in line with the optical axis of the scattered light incident on the light-sensing element 3. A case 1' has an inclined wall on its top and a mirror 25 placed on the interior side of the inclined wall. The case 1' also has an opening 8d covered by a lens cover 8' through which the read-beam emitted from the light-emitting element 2 emerges and the reflected-beam enters. The mirror 25 reflects the read-beam converged by the lens 5 to direct the read-beam to the bar code 6. The mirror 25 also directs the reflected-beam from the surface of the bar code 6 to the lens 5 which in turn converges the light to light-sensing chip 3. The photo-interrupter 70 is advantageous in that a small sized apparatus incorporating the photo-interrupter 99 is manufactured at lower costs. Setting the angle of the inclined surface of the case 1' to other than 45 degrees improves the proportion of direct reflection and scattered light contained in the reflected-beam with increased ratio of scattered light to the direct reflection, increasing the signal-to-noise ratio of the reflected-beam. While the first to seventh embodiments have been described with reference to the bar code 6, the invention also applies to objects, for example, a label having letter printing.

Claims: An optical device comprising: a housing; a light-emitting element (2), emitting a first beam of light (2a) towards an object; a light-sensing element (3), sensing a second beam of light (3a), the second beam of light being the reflection of the first beam of light from a surface of the object; a first optical system (5a), having a first optical axis, arranged to converge the first beam of light substantially on the surface of the object; a second optical system (5b) arranged to converge the second beam of light substantially to the said light-sensing element (3), said second optical system having a second optical axis that is oblique to the first optical axis; and a reflector (8) having a reflecting surface (8a) that reflects the first beam of light towards the surface of the object and reflects the second beam of light towards said light-sensing element via said second optical system characterised in that the reflector is formed by part of said housing. The optical device of claim 1, further including a light-blocking member (1, 11) for preventing ambient light from entering the optical device. The optical device of claim 1, wherein said reflector (8) has an additional reflecting surface (8c) for reflecting the first beam of light and the second beam of light to change directions of travel of the first beam of light and the second beam of light. The optical device of claim 3, wherein the additional reflecting surface (8c) is parallel with the inclined surface (8a) and the first beam of light and second d beam of light are reflected by the inclined surface (8a) and the additional reflecting surface (8c). The optical device of claim 1, wherein said first and second optical systems are lenses (5a, 5b). The optical device of claim 1, wherein said reflector (8) is a transparent cover (8) having a flat surface (8a) that serves as the inclined reflecting surface (8a). The optical device of claim 6, wherein the transparent cover (8) has a projection (7) by means of which the optical device is positioned relative to an external apparatus when said device is assembled to the external apparatus. The optical device of claim 1, wherein said reflector is a mirror (25). The optical device of claim 1, wherein the second beam of light contains direct reflection and diffused reflection and the reflecting surface is at an angle with the first and second beams of light, the angle being such that more diffused reflection is contained in the second beam of light than the direct reflection. A method of reading a bar code comprising: illuminating an object (6) having the bar code thereon with light (2a) from a source (2); collecting light (3a) reflected by the object (6); and detecting the intensity of the reflected light bearing the bar code data; wherein the light (2a) illuminating the object (6) passes through a first optical system (5a) positioned between the light source (2) and the object (6), the light (3a) returned from the object (6) passes through a second optical system (5b) located between the object (6) and a light sensing element (3), the light passing through both optical systems is reflected by a reflector (8a) and said optical systems (5a, 5b) have optical axes that are oblique to one another; characterised in that the reflector (8) is formed by part of a housing in which said optical systems (5a, 5b) are located, having an inclined surface (8a) where the angle of the inclination has been selected so that the second optical system (5b) preferentially collects light bearing data concerning the bar code, rather than specular reflections from the object bearing the bar code. The optical device of claim 5, wherein said two lenses (5a, 5b) are formed in one piece.

Inventors: HAGIMOTO MITSURU, HAGIMOTO, MITSURU
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1997
Main classification: G06K7
IPC codes: G06K7