Patent Publication Number: US-2004041087-A1

Title: Multiple beam scanning device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a multiple beam scanning device for scanning a plurality of light beams in parallel across a light receiving member.  
       [0003] 2. Related Art  
       [0004] Image output devices including laser printers and digital copy machines often use a multi-beam scan optical system that writes image information by simultaneously scanning a plurality of laser beams in parallel across a photosensitive member. The multi-beam scan optical system is capable of achieving a higher output speed and higher image dot density than single-beam systems without increasing rotational speed of a polygon mirror for scanning the laser beams or the speed at which the light intensity of the laser beams is modulated. The number of laser beams that such a system simultaneously scans in parallel is referred to as the scan beam number. To match demand for increasingly high image output speed and high dot density, the scan beam number has increased from two to four and then to five. See  Applied Optics,  Vol. 36, No.  25 , September 1994. The scan beam number is expected to increase further in the future.  
       [0005] As disclosed in Japanese Patent-Application Publication No. HEI-2-160212, for example, semiconductor lasers are frequently used as the laser light source for emitting the laser beams because semiconductor lasers are easy to use and inexpensive. Also, each semiconductor laser can directly modulate the light intensity of the laser beam emitted from itself so that the plurality of laser beams can be modulated individually.  
       [0006] Conventionally, edge-emitting lasers (EELs) have been used as the semiconductor lasers. However, Japanese Patent-Application Publication No. HEI-5-294005 discloses also use of a vertical-cavity surface-emitting laser (VCSEL) as the semiconductor laser. VCSELs have the advantage in that 100 to 1,000 or more laser elements can be formed on the same substrate inexpensively and in a highly dense array so that images can be output at a high speed and high dot density by multi-beam scanning.  
       [0007] However, multi-beam scanning has a drawback in that quality of images can degrade or image information can be lost if even one of the laser light sources becomes defective, such as by emitting laser light with lower intensity than the others or by not emitting laser light at all. Accordingly, if any of the laser light sources breaks down, then the operation of the image output device must be stopped and the light source must be replaced with a properly operating one. Because image output operations must be stopped, this results in a loss in productivity. If the scan beam number, that is, the number of laser light sources, further increases in accordance with demand for higher speed and higher dot density, then the probability that any particular one of the laser light sources will break down will also increase. In this case, the resultant loss in productivity can no longer be ignored.  
       SUMMARY OF THE INVENTION  
       [0008] It is an objective of the present invention to overcome the above-described problems and also to provide a multiple beam scanning device that reduces the duration of time that image output operations are stopped because a laser light source breaks down or otherwise becomes defective and that reduces the time until the multiple beam scanning device can be brought back to proper operating condition, and to provide an image output device that includes the multiple beam scanning device.  
       [0009] In order to attain the above and other objects, the present invention provides a multiple beam scanning device for scanning a plurality of light beams across a light receiving member, and an image output device including a light receiving member and the multiple beam scanning device. The multiple beam scanning device includes an array light source including a plurality of a sub-array light sources, each sub-array light source emitting a plurality of light beams with independently modulated light intensity, and an optical unit that converges the light beams emitted from any one of the sub-array light sources and simultaneously scans the light beams in parallel and with equidistant spacing across the light receiving member.  
       [0010] There is also provided a multiple beam scanning device for scanning a plurality of light beams across a light receiving member, and an image output device including a light receiving member and the multiple beam scanning device. The multiple beam scanning device includes an array light source including a plurality of a sub-array light sources, each sub-array light source emitting a plurality of light beams with independently modulated light intensity, a selection unit that selects one of the sub-array light sources, and a drive unit that drives the selected one of the sub-array light sources to emit the light beams. The selection unit connects the selected sub-array light source to the drive unit. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] In the drawings:  
     [0012]FIG. 1 is a block diagram showing an image output device according to a first embodiment of the present invention; and  
     [0013]FIG. 2 is a block diagram showing an image output device according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
     [0014] Next, an image output device  100  that includes a multiple beam scanning device according to a first embodiment of the present invention will be described with reference to FIG. 1.  
     [0015] As shown in FIG. 1, the image output device  100  includes an array light source  10 , a first optical system  20 , a rotating polygon mirror  30 , a second optical system  40 , an optical detector  50 , and a light receiving member  60 . The light receiving member  60  is rotated at a fixed speed in a sub-scanning direction indicated by an arrow in FIG. 1.  
     [0016] The array light source  10  includes a substrate  5 , and two sub-array light sources  11 ,  12 . The sub-array light sources  11 ,  12  are integrally formed together. The sub-array light source  11  includes three edge-emitting lasers  111 ,  112 , and  113 . The sub-array light source  12  includes three edge-emitting lasers  121 ,  122 , and  123 . The edge-emitting lasers  111 ,  112 ,  113 ,  121 ,  122 , and  123  are aligned in a straight line on the substrate  5  and each is capable of emitting a laser beam with light intensity modulated independently from the other light beams. The three light beams from the sub-array light source  11  fall incident on the first optical system  20  as beam bundle B 1 . In the same way, the three light beams from the sub-array light source  12  fall incident on the first optical system  20  as beam bundle B 2 .  
     [0017] The first optical system  20  includes a collimator lens and a cylindrical lens and collects and collimates the beam bundle B 1  (B 2 ) from the array light source  10  and makes the beam bundle B 1  (B 2 ) image information writing laser beams  1 ,  2 ,  3 . The rotating polygon mirror  30  simultaneously deflects and scans the light beams  1 ,  2 ,  3  on a surface of the light receiving member  60 . The second optical system  40  includes a fθ lens which converges the scanned light beams  1 ,  2 ,  3  on the optical detector  50  and the light receiving member  60  as laser spots with a predetermined small diameter d 1 , d 2 , d 3 , respectively. By the manner states above, the light beams  1 ,  2 ,  3  are scanned repeatedly by the rotating polygon mirror  30 , in the direction (a main scanning direction) perpendicular to the moving direction of the light receiving member  60 . On the light receiving member  60 , the light beams with their spot diameter d 1 , d 2 , d 3  respectively are scanned in a main scanning direction, and form scan lines  21 ,  22 ,  23 , successively. The scan lines  21 ,  22 ,  23  have equivalent neighboring spacing in the sub-scanning direction. The optical detector  50  is for detecting the light beams (scan beams)  1 ,  2 ,  3  and is disposed adjacent to the light receiving member  60  at a position separated from a writing region, where image information is written by the light beams  1 ,  2 ,  3 .  
     [0018] As shown in FIG. 1, the image output device  100  also includes a reference clock generator  61 , a waveform shaping circuit  62 , a writing start signal generator  63 , a divider  64 , an image signal control system  73 , a laser drive system  81 , and a connection selection circuit  82 . The laser drive system  81  is for driving each of the laser elements  111 ,  112 ,  113 ,  121 ,  122 ,  123 . The laser drive system  81  includes an output circuit D connected to the connection selection circuit  82 . The output of the connection selection circuit  82  is connected to the laser elements  111 ,  112 ,  113  of the sub-array light source  11  through a circuit C 1  and to the laser elements  121 ,  122 ,  123  of the sub-array light source  12  through a circuit C 2 . Although the connection selection circuit  82  is capable of selecting either the circuit C 1  or the circuit C 2 , initially the connection selection circuit  82  is set to select the circuit C 1  so that the laser drive system  81  is initially connected to the sub-array light source  11 .  
     [0019] Next, operations performed in the image output device  100  to write image information on the light receiving member  60  will be explained.  
     [0020] When the laser beams  1 ,  2 , and  3  pass over the optical detector  50 , the optical detector  50  generates a scan beam detection signal  70 . The scan beam detection signal  70  is used both as a writing start signal  71  for starting operation to write image information and as a detection signal  72  for intensity of the light beams. Because the three laser beams  1 ,  2 , and  3  are aligned at a slant with respect to the sub-scan direction, the laser beams  1 ,  2 , and  3  pass by the optical detector  50  delayed one from the other by a predetermined time delay. Accordingly, the scan beam detection signal  70  has three pulses, which correspond to the three laser beams  1 ,  2 , and  3 . The amplitude of each beam detection signal indicates the intensity of the corresponding light beam  1 ,  2 , and  3 .  
     [0021] The waveform shaping circuit  62  shapes the writing start signal  71  into three consecutive pulse signals  621  and then send these pulses signals  621  to the writing start signal generator  63 . The writing start signal generator  63  generates a writing start signal  640  based on the pulse signals  621 . The divider  64  divides the writing start signal  640  into writing start signals corresponding to a number of scanning light beams and, in this case, outputs three writing start signals  641 ,  642 , and  643  to the image signal control system  73 . The writing start signals  641 ,  642 , and  643  correspond to the laser elements  111 ,  112 ,  113  ( 121 ,  122 ,  124 ), respectively. The image signal control system  73  is also input with a clock signal  611  from the reference clock generator  61  and an image information signal  731  from an external source. The image signal control system  73  arranges the image information signal  731  into light intensity modulation signals  651 ,  652 ,  653  according to the scanning light beams, that is, the number of scan beams, of the light receiving member  60 . Each light intensity modulation signal  651 ,  652 ,  653  includes a single scan line&#39;s worth of information in time sequence order for writing the corresponding one of the scan lines  21 ,  22 , and  23 . The light intensity modulation signals  651 ,  652 ,  653  are output to the laser drive system  81  in synchronization with the clock signal  611  and the writing start signals  641 ,  642 ,  643 .  
     [0022] Because the laser drive system  81  is connected to the sub-array light source  11  through the circuit C 1 , the laser elements  111 ,  112 , and  113  emit at total of three light beams for a single scanning. The light beams are intensity modulated based on the light intensity modulation signals  651 ,  652 , and  653 . The three light beams pass through the first optical system  20  as the beam bundle B 1  and fall incident on the rotating polygon mirror  30  as the image information writing laser beams  1 ,  2 , and  3 . The rotating polygon mirror  30  reflects the laser beams  1 ,  2 , and  3  simultaneously. The deflected laser beams  1 ,  2 , and  3  are converged by the second optical system  40  into laser spots d 1 , d 2 , d 3  and form scan lines  21 ,  22 , and  23  on the surface of the light receiving member  60 . An electrostatic latent image is formed on the surface of the light receiving member  60  by repeating the above-described operations.  
     [0023] Quality of printed images can be degraded or print information can be lost due to problems with even one of the laser elements  111 ,  112 ,  113 , such as intensity of one of the laser elements  111 ,  112 ,  113  dropping below a certain value or one of the laser elements  111 ,  112 ,  113  breaking down and not emitting light. When such a problem occurs, use of the sub-array light source  11  is stopped and switched to the sub-array light source  12 . As a result, in a manner similar to the beam bundle B 1  from the sub-array light source  11 , the beam bundle B 2  from the laser elements  121 ,  122 , and  123  of the sub-array light source  12  scans across the light receiving member  60  via the first optical system  20 , the rotating polygon mirror  30 , and the second optical system  40  as scan lines  21 ,  22 , and  23  to form an electrostatic latent image on the surface of the light receiving member  60 .  
     [0024] Next, the switching mechanism for switching between the sub-array light source  11  and the sub-array light source  12  will be, described. The switching mechanism includes a comparator  53 , a judgment unit  54 , a selection signal generator  55 , the optical detector  50 , and the connection selection circuit  82 .  
     [0025] The light intensity detection signal  72  from the optical detector  50  is sent to the comparator  53 . The comparator  53  outputs an output signal  531  based on the light intensity of the light beams  1 ,  2 , and  3 , that is, based on the amplitude of the pulses in the light intensity detection signal  72 . Described in more detail, the comparator  53  outputs a pulse when the amplitude of a pulse is within a predetermined range, but does not output a pulse when the amplitude of a pulse is outside the predetermined range. If the sub-array light source  11  is operating properly, then the amplitude all three pulses in the scan beam detection signal  70  will be within the predetermined range. Therefore, the resultant output signal  531  will have the normal waveform of three consecutive pulses as shown in FIG. 1. However, if the sub-array light source  11  is not operating properly because one or more of the laser elements  111 ,  112 ,  113  have broken down or for some other reason, then the amplitude of the corresponding pulse in the scan beam detection signal  70  will be outside the predetermined range. Therefore, the resultant output signal  531  will have one or more fewer pulses than the normal waveform.  
     [0026] The output signal  531  is input into the judgment unit  54 . The judgment unit  54  judges whether or not the sub-array light source  11  is operating normally based on whether the output signal  531  includes three consecutive pulses. The judgment unit  54  outputs a judgment signal  541  only when the judgment unit  54  judges that the sub-array light source  11  is operating improperly. The judgment unit  54  outputs no judgment signal  541  when the sub-array light source  11  is operating normally. When the selection signal generator  55  receives the judgment signal  541 , then the selection signal generator  55  generates and outputs a selection signal  551  to the connection selection circuit  82 . As a result, the connection selection circuit  82  switches connection from the circuit C 1  to the circuit C 2 . The output circuit D of the laser drive system  81 , which was connected to the sub-array light source  11  through the circuit C 1 , is connected to the sub-array light source  12  through the circuit C 2 , thereby bringing the sub-array light source  12  into operation condition.  
     [0027] The first optical system  20  has a sufficiently large aperture to pick up the light bundles B 1 , B 2  from the array light source  10 . Six laser beams form laser spots with a uniform spot diameter at equidistant spacing on the surface of the light receiving member  60 . Moreover, the multiple beam scanning optical system, which is mainly configured from the array light source  10 , the first optical system  20 , the rotating polygon mirror  30 , and the second optical system  40 , is designed to optimally prevent problems, such as scan line bowing, from occurring. The sub-array light sources  11 ,  12  are configured to both emit light beams of equivalent intensity and at an equivalent interspacing. Therefore, images written on the light receiving member  60  will have consistent quality regardless of which of the sub-array light sources  11 ,  12  is used.  
     [0028] Next, an image output device  200  according to a second embodiment of the present invention will be described with reference to FIG. 2.  
     [0029] The image output device  200  has the same basic configuration as the image output device  100  shown in FIG. 1, with the exception that the image output device  200  uses an array light source  10 A as its light source. The array light source  10 A is a two-dimensional array light source formed from nine integral laser elements  15  in a three-by-three flat array. The laser elements  15  are grouped into three sub-array light sources  16 ,  17 , and  18 . The sub-array light source  16  is configured from laser elements  161 ,  162 , and  163 , the sub-array light source  17  is configured from laser elements  171 ,  172 , and  173 , and the sub-array light source  18  is configured from laser elements  181 ,  182 , and  183 .  
     [0030] Each of the sub-array light sources  16 ,  17 , and  18  emits three laser beams that, in a manner similar to that of the first embodiment, scan across the light receiving member  60  via operation of the first optical system  20 , the rotating polygon mirror  30 , and the second optical system  40 . The method of writing image information on the light receiving member  60  is also the same as for the first embodiment so detailed explanation will be omitted.  
     [0031] If one of the laser light sources  161 ,  162 ,  163  becomes defective during write operations using the sub-array light source  16 , then the connection selection circuit  82  switches to the sub-array light source  17  on a judgment method similar to that described in the first embodiment. If one of the laser light sources  171 ,  172 ,  173  of the sub-array light source  17  becomes defective, then the connection selection circuit  82  switches to the sub-array light source  18  using a similar judgment process.  
     [0032] According to the above-described first and second embodiments, breakdown or other problems with the sub-array light source is detected based on the light intensity of each of the multiple beams, which is constantly detected during scanning operations. Therefore, the sub-array light source is constantly monitored, and problems with the sub-array light source can be promptly detected and electrical connection can be switched from the presently used array light source to another array light source.  
     [0033] Because operations can be quickly switched to use of a properly operating laser light source, the multiple beam scanning device can be easily returned to proper operation even if one of the laser elements becomes defective. There is no need to replace or repair the multiple beam scanning device or the entire image output device that uses the multiple beam scanning or to stop image output operations for long periods of time for repairs. High quality image output operations can be efficiently executed, and operation efficiency can be greatly increased. Problems that result from defective sub-array light sources, such as reduction in output image quality, can be prevented.  
     [0034] The image output device can be operated stably for long periods of time even if there is no future improvement in reliability of the individual laser elements from present levels. Accordingly, running costs can be greatly reduced compared to the convention configuration where the entire image output device needed to be replaced each time one of the laser elements became defective.  
     [0035] Because the operation of switching the sub-array light source is performed electrically, the switching is performed easily.  
     [0036] Because the plurality of sub-array light sources are integrally formed, the array light sources can be easily and precisely configured. Because each sub-array light source emits the same number of scan beams, the same image output controls can be used regardless of which sub array is presently being used. Because all of the sub-array light sources produce the same image quality, image quality can be maintained whether sub-array light sources are switched or not.  
     [0037] While the invention has been described in detail with reference to the specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.  
     [0038] For example, the embodiments describe the present invention applied to a multiple beam scanning device that includes three laser beams in each sub-array light source. However, according to the present invention, any optional number of laser beams can be used. For example, four or more laser elements may be needed in each sub array, depending on the specifications of the image output device. Note that the greater the number of laser elements, the greater the probability that output of any one of the laser elements will fluctuate or degrade. Therefore, the present invention is particularly effective when used in an image output device that includes array light source with a large number of laser elements.  
     [0039] The embodiments describe array light sources configured from laser elements that are integrally formed on the same substrate. However, sub-array light sources formed on separate substrates can be either integrated together or arranged separately and used with a common scanning optics system.  
     [0040] Vertical-cavity surface-emitting lasers (VCSEL) could be used as the laser elements rather than edge-emitting lasers (EELs).