Image forming apparatus

Abstract: A laser beam scanning unit (53) adapted for scanning laser beams on a surface of a charged image bearing member (5) is provided. The laser beam scanning apparatus (53) comprises a semiconductor laser array (21) having a plurality of light emitting portions (21a) and a rotating polygon mirror (3) adapted for deflecting laser beams emitted from the light emitting portions to the image bearing member (5). The light emitting portions (21a) are disposed two-dimensionally on a surface of the semiconductor laser array. The lighting and the amount of light of the light emitting portions (21a) are discretely controlled by a control unit (60).

Description: Technical Field The present invention relates to an image forming apparatus for scanning laser beams and thereby forming a latent image on a image bearing member. Related Art Heretofore, a large number of image forming apparatuses for forming a static latent image on a image bearing member with a laser beam and for printing the image on a paper at a high speed by a electrophotographic process have been used as output units of computers, facsimile machines, multi-functional copy machines, and so forth. In recent years, there has been an urgent need for improving the output speeds of these apparatuses. Accordingly, the apparatuses have been actively improved. For example, an image forming apparatus using a rotating polygon mirror type deflecting unit deflects one laser beam with each facet and draws one scanning line. Thus, to increase the number of scanning lines in a particular time period, provided that the number of small mirror surfaces of the rotating polygon mirror is constant, the number of rotations should be increased. On the other hand, provided that the number of rotations is constant, the number of mirror surfaces of the rotating polygon mirror should be increased. To increase the number of rotations of the rotating polygon mirror, a dynamic or static bearing using pneumatic or hydraulic power is required. These bearings are expensive and difficult to handle. Thus, they are difficult to use in conventional laser printers. In contrast, provided that the number of mirror surfaces of the polygon mirror is increased, since the deflection angle becomes small, the length of the optical path following the deflecting unit becomes large. In addition, the diameter of collimated laser beams entering into an image forming optical system becomes large in proportion to the length of the optical path. Thus, the sizes of the lens and the rotating polygon mirror become large. In particular, when a high resolution is required, since the number of scanning lines are increased, the number of rotations of the polygon mirror and the length of optical path should be further increased. This situation also applies to the case where the deflecting unit is not a rotating polygon mirror. In this case, the scanning frequency and the length of the optical path following the deflecting unit increase. To solve these problems, an exposing technique for writing a plurality of scanning lines with a plurality of laser beams in one scanning sequence has been developed. This technique is referred to as a multi-beam exposing technique. To obtain a plurality of laser beams, a plurality of gas laser (for example, He-Ne) oscillators are used as a light source. In addition, a technique wherein a laser beam generated by one oscillator is time-divided into a plurality of portions by an acousto-optical modulator (AOM) or the like has been developed. As a technique for simplifying the construction of the unit and decreasing the size thereof, for example, as disclosed in Japanese Patent Laid-Open Publication Serial No. SHO 54-7328, a semiconductor laser array where a plurality of light emitting portions for radiating laser beams are integrally disposed on one device is used as a light source. Next, an image forming apparatus using a semiconductor laser array will be described. An image forming apparatus uses a laser array integrally disposed on one substrate as a light source. A beam radiating point of each light emitting portion is disposed at an edge of a semiconductor device substrate. A plurality of laser beams are collimated by a common collimator lens so that they have a particular diameter. Thereafter, the collimated laser beams are introduced into one facet of the rotating polygon mirror (deflecting unit). As the facet rotates, the laser beams are deflected. Next, the laser beams are spotted as an image through an image forming lens. Then, the image spot exposes the image bearing member and thereby a static latent image is formed. Next, in accordance with the electrophotographic process, the latent image is developed, transferred onto a paper, and then fixed. In addition, as disclosed in Japanese Patent Laid-Open Publication Serial No. SHO 54-158251, to decrease the distance of each adjacent scanning line scanned on the image bearing member at a time, the light emitting portions of the laser array are disposed at particular angles to the scanning plane. A scanning optical system of an image forming apparatus using a semiconductor laser array which has been conventionally used is disclosed in for example Japanese Patent Laid-Open Publication Serial No. HEI 3-248114. A semiconductor laser array 501 is disposed on an object side focal position of a collimator lens 502. At the image side focal position of the collimator lens 502, an aperture stop 503 is disposed. On the other hand, there is still another need of an image forming apparatus using such a semiconductor laser array which can scan laser beams at a high speed and with a high resolution. However, the conventional image forming apparatus has not satisfactorily accomplished a high-speed and high-resolution laser beam scanning technique. Disclosure of the Invention The present invention has been made with consideration of the above described points. An object of the present invention is to provide a compact image forming apparatus for scanning laser beams with a high resolution. A first feature of the present invention is an image forming apparatus, comprising a image bearing member for forming a static latent image on a surface thereof, a charting unit for charging the surface of the image bearing member, a laser beam scanning unit for scanning a plurality of laser beams on the charged surface of the image bearing member, and a developing unit for causing a developing agent to adhere on the scanned surface of the image bearing member, wherein the laser beam scanning unit comprises a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, a collimator lens for collimating laser beams emitted from the light emitting portions, and a deflecting unit for deflecting the laser beams, wherein an aperture stop is disposed on an optical path midway between the semiconductor laser array and the deflecting unit, and wherein the following relations are satisfied st f ≤ 0.12 ( D d ) 2.3 + 0.17 D d ≤ 2 where f is the focal length of the collimator lens, s is the distance between a deflecting unit side focal point of the collimator lens and the aperture stop, t is the distance between a light emitting portion spaced farthest from an optical axis of the collimator lens and the optical axis, D is the diameter of the aperture stop, and d is the diameter of each of the collimated beams. A second feature of the present invention is an image forming apparatus, comprising a image bearing member for forming a static latent image on a surface thereof, a charging unit for charging the surface of the image bearing member, a laser beam scanning unit for scanning a plurality of laser beams on the charged surface of the image bearing member, and a developing unit for causing a developing agent to adhere on the scanned surface of the image bearing member, wherein the laser beam scanning unit comprises a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, a collimator lens for collimating laser beams emitted from the light emitting portions, and a deflecting unit for deflecting the laser beams, wherein an aperture stop is disposed on an optical path midway between the semiconductor laser array and the deflecting unit, and wherein the following relations are satisfied st f ≤ 0.06 ( D d ) 2.9 + 0.08 D d ≤ 2 where f is the focal length of the collimator lens, s is the distance between a deflecting unit side focal point of the collimator lens and the aperture stop, t is the distance between a light emitting portion spaced farthest from an optical axis of the collimator lens and the optical axis, D is the diameter of the aperture stop, and d is the diameter of each of the collimated beams. A third feature of the present invention is a laser beam scanning apparatus, comprising a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, a collimator lens for collimating the laser beams emitted from the light emitting portions, and a deflecting unit for deflecting the laser beams, wherein an aperture stop is disposed on an optical path midway between the semiconductor laser array and the deflecting unit, and wherein the following relations are satisfied st f ≤ 0.12 ( D d ) 2.3 + 0.17 D d ≤ 2 where f is the focal length of the collimator lens, s is the distance between a deflecting unit side focal point of the collimator lens and the aperture stop, t is the distance between a light emitting portion spaced farthest from an optical axis of the collimator lens and the optical axis, D is the diameter of the aperture stop, and d is the diameter of each of the collimated beams. A fourth feature of the present invention is a laser beam scanning apparatus, comprising a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, a collimator lens for collimating the laser beams emitted from the light emitting portions, and a deflecting unit for deflecting the laser beams, wherein an aperture stop is disposed on an optical path midway between the semiconductor laser array and the deflecting unit, and wherein the following relations are satisfied st f ≤ 0.06 ( D d ) 2.9 + 0.08 D d ≤ 2 where f is the focal length of the collimator lens, s is the distance between a deflecting unit side focal point of the collimator lens and the aperture stop, t is the distance between a light emitting portion spaced farthest from an optical axis of the collimator lens and the optical axis, D is the diameter of the aperture stop, and d is the diameter of each of the collimated beams. Brief Description of the Drawings Fig. 1 is an optical side view showing the construction of portions adjacent to a light source of a conventional scanning optical system; Fig. 2 is an optical side view showing a laser scanning optical system of a sixth embodiment of the image forming apparatus in accordance with the present invention; Fig. 3 is an optical side view showing the construction of portions adjacent to a light source of a conventional optical system; Fig. 4 is an optical side view describing that a beam is vignetted by a collimator lens; Fig. 5 is an optical side view showing a beam which passes through an aperture stop disposed at a focal point of a collimator lens; Fig. 6 is an optical side view showing a beam which passes through an aperture stop disposed at other than a focal point of a collimator lens; Fig. 7 comprises charts showing distributions of beam sectional intensity in the case where a beam is vignetted; Fig. 8 is a side view showing the image forming apparatus; and Fig. 9 is an optical side view showing the construction of portions adjacent to a light source of a scanning optical system. Embodiment of Image Forming Apparatus 1. Comparison with Related Art Before describing a first embodiment of the present invention, so as to easily understand the conception thereof, the related art thereof will be described. A scanning optical system of an image forming apparatus using a semiconductor laser array which has been conventionally used is disclosed in for example Japanese Patent Laid-Open Publication Serial No. HEI 3-248114. A semiconductor laser array 501 is disposed on an object side focal position of a collimator lens 502. At the image side focal position of the collimator lens 502, an aperture stop 503 is disposed. However, in this related art, since the position of the aperture stop is limited to the image side focal position of the collimator lens, the degree of freedom of designing an optical system is low. Moreover, in a conventional optical system, a holding frame of a lens is sometimes used for an aperture stop. However, according to the related art, such a construction cannot be accomplished. 2. Construction of the Present Invention Fig. 8 is a schematic diagram showing the construction of an image forming apparatus of the present invention. Next, this image forming process will be described. A charger 551 applies an equal electric charge to an image bearing member 507. A scanning optical system 552 exposes and scans the image bearing member 507, thereby forming a latent image thereon. Thereafter, a developing unit 553 adheres a developing agent on the latent image so as to form a visible image. An image transferring unit 554 transfers the developing agent, which constructs the visible image, on a transfer material 555 such as a paper. Thereafter, a fixing unit 556 heats and melts the developing agent and fixes it on the transfer material 555. Fig. 2 is a schematic diagram showing the construction of a scanning optical system of the embodiment of the present invention. A plurality of beams emitted from a semiconductor laser array 501 are collimated by a collimator lens 502. The resultant beams enter one of deflecting surfaces 505 of a rotating polygon mirror 504 which is a deflecting unit through an aperture stop 503. As the polygon mirror 504 rotates, emitted beams are deflected and scanned. The resultant beams are imaged on the image bearing member 507 through an image forming lens 506. In Figs. 2 and 9, the aperture stop 503 is disposed on the optical path midway between the semiconductor laser array 501 and the deflecting unit 504. When the focal length of the collimator lens 502 is f; the distance from the deflecting unit 504 side focal point of the collimator lens 502 to the aperture stop 503 is s; the distance from the optical axis of the collimator lens 502 to the optical axis of a light emitting portion which is most spaced from the optical axis of the collimator lens 502 is t; the diameter of the aperture stop 503 is D; and the diameter of a collimated beam is d, then the relations given by the following formulas can be obtained. st f ≤ 0.12 ( D d ) 2.3 + 0.17 D d ≤ 2 Alternatively, instead of the formulas (1) and (2), the relations given by the following formulas can be obtained. st f ≤ 0.06 ( D d ) 2.9 + 0.08 D d ≤ 2 Generally, the spread angles of output beams of a semiconductor laser 501 deviate to some extent depending on a light emitting portion for use. In addition, the diameters of beams collimated by the collimator lens 502 also deviate. However, when the aperture stop 503 is disposed at the position where the cross sections of the beams are nearly matched and the diameter of the aperture stop 503 is almost the same as or slightly smaller than the diameter of each collimated beam, the diameter of each collimated beam which passed through the aperture stop 403 becomes equal. As a result, the diameter of each spot imaged on the image bearing member 505 becomes equal. Thus, a stable and high printing quality can be obtained. The printing quality does not deviate from product to product. The beam spread angles and the diameters of beams are represented as an intensity distribution of cross sections of beams. The intensity distribution accords with a Gaussian distribution. The beam spread angle represents a full width of the angle at which the center intensity is halved. On the other hand, the spot diameter represents a position where the intensity becomes l/e 2 times the center intensity. Next, an effect where the beam diameters are equalized by an aperture stop 503 will be described. When laser beams are limited by the aperture stop 503, they are diffracted as a characteristic of wave optics. When the center of the aperture stop accords with the center of an incident beam and the effect of diffraction is considered, the diameter d0 of an image spot on the image bearing member 505 can be expressed by the following formula. d 0 = kλf D where k is a constant; λ is the wavelength of a laser beam; f is the focal length of the image forming lens; and D is the diameter of the aperture stop. When the ratio of the diameter d of a beam entered into the aperture stop and the diameter D of the aperture stop is represented as a cutting ratio T = d / D, the constant k can be calculated by the following formula (refer to "LASER & OPTICS GUIDE II", JAPAN Melles Griot K.K). k = 1.6449 + 0.6460 (T-0.2816) 1.821 - 0.5320 (T-0.2816) 1.891 As an example, when the diameter D of the aperture stop is 1 and the diameter d of each incident beam deviates in the range of 1 ± 20 %, the deviation of the diameter of each image spot is limited in the range from -3.1% to +5.9 %. Thus, the aperture stop has an effect for decreasing the deviation of the diameter of each image spot. The distribution of intensity of the cross sections of beams collimated by the collimator lens 502 nearly accords with a Gaussian distribution. As shown in Fig. 4, when a collimated beam passes through the aperture stop 503, the periphery of the beam is vignetted. Thus, the power of the beam which passed through the aperture stop 503 decreases. As shown in Fig. 5, when the aperture stop 503 is disposed at the position of the deflecting unit side focal point of the collimator lens 502, since all the center axes of the beams which passed through the aperture stop 503 are matched, the power decrease of each beam which passed through the aperture stop 503 is equal. However, when the position of the aperture stop 503 is limited to the position of the deflecting unit side focal point of the collimator lens 502, the degree of freedom of designing the optical system decreases. As shown in Fig. 6, when the aperture stop 503 is disposed at a position apart from the deflecting unit side focal point of the collimator lens 502, the center axes of a plurality of beams which passed through the aperture stop 503 are not matched each other. Thus, when a beam 511a which travels along an optical axis 510 of the collimator lens 502 and a beam 511b which travels with an inclination to the optical axis 510 pass through the aperture opening 503, they are vignetted in different manners. Fig. 7 shows the difference of the vignetting manners. Fig. 7 (a) shows the vignetting manner of the beam 511a, while Fig. 7 (b) shows the vignetting manner of the beam 511b. In these figures, the portions of intensity distributions of cross sections of beams which are vignetted by the aperture stop are hatched. The powers of beams which passed through the aperture stop 503 differ one by one. In this condition, the power of the beam 511a is larger than that of the beam 511b. When the difference between these powers exceeds a predetermined level, uneven density takes place on a printed paper. However, when this difference is in a particular range, a substantially good printing quality can be obtained. Thus, the allowable range where the aperture stop can be disposed is present. When the condition represented by the formula (1) is satisfied, the fluctuation of powers of beams which passed through the aperture stop 503 can be suppressed to 20 % or less. However, since the formula (1) is an approximate formula, it is satisfied under the condition of the formula (2). On the other hand, when the condition represented by the formula (2) is satisfied, the fluctuation of powers of beams which passed through the aperture stop 503 can be suppressed to 5 % or less. Likewise, the formula (3) is an approximate formula. Thus, this formula is satisfied under the condition of the formula (4). According to an experiment conducted by the applicant of the present invention, when only letters and lines are printed with the image forming apparatus, if the fluctuation of powers of image spots is approximately 20 % or less, a good printing quality can be obtained. If the fluctuation is larger than 20 %, the printing quality is degraded. On the other hand, when half tone patterns of graphic images or small dots are printed, the fluctuation of powers of image spots results in uneven density of printed images. To obtain a good printing quality, the fluctuation should be limited to approximately 5 % or less. Thus, the conditions given by the formulas (1) and (2) are suitable for image forming apparatuses which only print letters and lines. On the other hand, the conditions given by the formulas (3) and (4) are suitable for image forming apparatus which print not only letters, but half tones and mesh dots. According to the above-mentioned conditions, the aperture stop 503 can be disposed at any position in a wide range on the optical path between the semiconductor laser array 511 and the deflecting unit 503. Thus, the degree of freedom of designing an optical system is increased. Alternatively, the holding frame of the collimator lens 502 can be used as the aperture stop. In other words, since an independent aperture stop is not necessary, the number of constructional elements can be decreased. Next, a position of the aperture stop 503 which satisfies the above-mentioned conditions will be specifically described with a system shown in Fig. 9. Now, consider the case where a surface light emitting type semiconductor laser array is used as the semiconductor laser array 501. The surface light emitting type semiconductor laser is a semiconductor laser where the center axes of beams emitted are nearly perpendicular to the surface of a device substrate. In the surface light emitting type semiconductor laser array 501, the spread angles of laser beams emitted therefrom can be set to 10 degrees or less and the distance of each adjacent light emitting portion can be set to 0.05 mm or less. Now, consider the semiconductor laser array 501 having two light emitting portions. The distance t between the light emitting portions 512a and 512b is set to 0.05 mm and the light emitting portion 512a is disposed on an optical axis 510 of the collimator lens 502. The lighting and the amount of light of the light emitting portions 512a and 512b are controlled by a control unit 560 (see Fig. 2). Beams emitted from the light emitting portions 511a and 511b are referred to as beams 511a and 511b, respectively. When the spread angle  of each radiated beam is 10 degrees; the focal length f of the collimator lens 502 is 10 mm; and the distance h from the collimator lens 502 to the deflecting surface 505 of the rotating polygon mirror is 50 mm, then the diameter d of the beams becomes 3.0 mm. Now, assume that the center of the aperture stop 503 is present on the optical axis 510 and that the diameter D of the aperture stop 503 is equal to the beam diameter d. Since D/d = 1, both the conditions given by the formulas (19) and (21) are satisfied. According to the condition given by the formula (18), since s ≤ 58 mm, the aperture stop 503 can be disposed at any position midway between the collimator lens 502 and the deflecting surface 505 of the rotating polygon mirror. On the other hand, according to the condition given by the formula (20), since s ≤ 28 mm, the aperture stop 503 can be disposed at any position midway between the deflecting surface 505 side focal point of the collimator lens 502 and the position 28 mm right of the deflecting surface 505. In addition, even if the number of light emitting portions which are disposed in line is increased and thereby the value of t becomes large, provided that the conditions given by the formulas (1) and (2) are satisfied, when the number of the light emitting portions is 12 or less, the aperture stop 503 can be disposed. On the other hand, according to the conditions given by the formulas (3) and (4), when the number of light emitting portions is six or less, the aperture stop 503 can be disposed at the position of the collimator lens 502. When the aperture stop 503 can be disposed at the position of the collimator lens 502, since the holding frame of the collimator lens 502 can be used as an aperture stop, an independent aperture stop is not necessary and thereby the number of constructional elements of the scanning optical system can be decreased. 3. Effects As described above, according to the present invention, an aperture stop is disposed on an optical path midway between a semiconductor laser array and a deflecting unit in the conditions given by the formulas (1) and (2). Thus, even if the spread angles of the beams deviate, the diameters of the image spots can be kept equal. Thereby, a stable and high printing quality can be obtained. In addition to a high printing quality of letters and lines, an aperture stop can be disposed on an optical path at any position in a wide range between a semiconductor laser array and a deflecting unit. Alternatively, a holding frame of a collimator lens can be used as an aperture stop. As a result, the degree of freedom of designing an optical system is improved. Moreover, an aperture stop is disposed on an optical path midway between a semiconductor laser array and a deflecting unit in the conditions given by the formulas (3) and (4). Thus, even if the spread angles of the beams deviate, the diameters of the image spots can be kept equal. Thereby, a stable and high printing quality can be obtained. In addition to a high printing quality of not only letters and lines, but half tone images and mesh points, an aperture stop can be disposed on an optical path at any position in a wide range between a semiconductor laser array and a deflecting unit. Alternatively, a holding frame of a collimator lens can be used as an aperture stop. As a result, the degree of freedom of designing an optical system is improved. Industrial Utilization The image forming apparatus according to the present invention can print data on papers at a high speed by using an electrophotographic process. The image forming apparatus can be used as an output unit of a computer, a facsimile machine, a multi-functional copy machine, and so forth.

Claims: An image forming apparatus, comprising: a image bearing member (507) for forming a static latent image on a surface thereof; a charging unit (551) for charging the surface of said image bearing member (507); a laser beam scanning unit (552) for scanning a plurality of laser beams on the charged surface of said image bearing member (507); and a developing unit (553) for causing a developing agent to adhere on the scanned surface of said image bearing member (507); wherein said laser beam scanning unit comprises: a semiconductor laser array (501) having a plurality of light emitting portions for emitting laser beams; a collimator lens (502) for collimating laser beams emitted from said light emitting portions; and a deflecting unit (504) for deflecting the laser beams; wherein an aperture stop (503) is disposed on an optical path midway between said semiconductor laser array (501) and said deflecting unit (504); and wherein the following relations are satisfied st f ≤ 0.12 (D) d 2.3 + 0.17 D d ≤ 2 where f is the focal length of said collimator lens (502); s is the distance between a deflecting unit (504) side focal point of said collimator lens (502) and said aperture stop (503); t is the distance between a light emitting portion spaced farthest from an optical axis of said collimator lens (502) and said optical axis; D is the diameter of said aperture stop (503); and d is the diameter of each of said collimated beams. An image forming apparatus, comprising: a image bearing member (507) for forming a static latent image on a surface thereof; a charging unit (551) for charging the surface of said image bearing member (507); a laser beam scanning unit (552) for scanning a plurality of laser beams on the charged surface of said image bearing member (507); and a developing unit (553) for causing a developing agent to adhere on the scanned surface of said image bearing member (507); wherein said laser beam scanning unit comprises: a semiconductor laser array (501) having a plurality of light emitting portions for emitting laser beams; a collimator lens (502) for collimating laser beams emitted from said light emitting portions; and a deflecting unit (504) for deflecting the laser beams; wherein an aperture stop (503) is disposed on an optical path midway between said semiconductor laser array (501) and said deflecting unit (504); and wherein the following relations are satisfied st f ≤ 0.06 (D) d 2.9 + 0.08 D d ≤ 2 where f is the focal length of said collimator lens (502); s is the distance between a deflecting unit (504) side focal point of said collimator lens (502) and said aperture stop (503); t is the distance between a light emitting portion spaced farthest from an optical axis of said collimator lens (502) and said optical axis; D is the diameter of said aperture stop (503); and d is the diameter of each of said collimated beams. A laser beam scanning apparatus, comprising: a semiconductor laser array (501) having a plurality of light emitting portions for emitting laser beams; a collimator lens (502) for collimating the laser beams emitted from said light emitting portions; and a deflecting unit (504) for deflecting the laser beams; wherein an aperture stop (502) is disposed on an optical path midway between said semiconductor laser array (501) and said deflecting unit (504); and wherein the following relations are satisfied st f ≤ 0.12 (D) d 2.3 + 0.17 D d ≤ 2 where f is the focal length of said collimator lens (502); s is the distance between a deflecting unit (504) side focal point of said collimator lens (502) and said aperture stop (503); t is the distance between a light emitting portion spaced farthest from an optical axis of said collimator lens (502) and said optical axis; D is the diameter of said aperture stop (503); and d is the diameter of each of said collimated beams. A laser beam scanning apparatus, comprising: a semiconductor laser array (501) having a plurality of light emitting portions for emitting laser beams; a collimator lens (502) for collimating the laser beams emitted from said light emitting portions; and a deflecting unit (504) for deflecting the laser beams; wherein an aperture stop (502) is disposed on an optical path midway between said semiconductor laser array (501) and said deflecting unit (504); and wherein the following relations are satisfied st f ≤ 0.06 (D) d 2.9 + 0.08 D d ≤ 2 where f is the focal length of said collimator lens (502); s is the distance between a deflecting unit (504) side focal point of said collimator lens (502) and said aperture stop (503); t is the distance between a light emitting portion spaced farthest from an optical axis of said collimator lens (502) and said optical axis; D is the diameter of said aperture stop (503); and d is the diameter of each of said collimated beams.

Inventors: INOUE NOZOMU, KOGA YOSHIRO, KURIHARA HAJIME, TAKADA KYU, INOUE, NOZOMU, KOGA, YOSHIRO, KURIHARA, HAJIME, TAKADA, KYU, INOUE, NOZOMU, C/O SEIKO EPSON CORP., KOGA, YOSHIRO, C/O SEIKO EPSON CORP., KURIHARA, HAJIME, C/O SEIKO EPSON CORP., TAKADA, KYU, C/O SEIKO EPSON CORP.
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1992
Main classification: H04N1
IPC codes: H04N1, G02B26, G06K15, B41J2