1. Field of the Invention
The present invention relates to an image generating apparatus for generating an image on recording paper through an electrophotographic or xerographic process.
2. Description of the Related Art
As the processing speed of personal computers and workstations has increased on recent years, it has also been increasing demand to speed up the processing of an image generating apparatus based on a xerographic process. With such an image generating apparatus as mentioned above, when a polygon mirror included in an exposure optical system is increased in its rotational speed, it is possible to speed up its printing operation. In the prior art, however, the increased rotational speed of the polygon mirror has already reached its limit. For this reason, as another additional speeding-up measure, a plurality of semiconductor lasers for forming an electrostatic latent image on a photoconductor drum are provided to realize a simultaneous recording system.
An arrangement and operation of a prior art image generating apparatus having a plurality of semiconductor lasers will be explained in the following. FIG. 11 is an arrangement of an exposure optical system having a plurality of semiconductor lasers therein in the prior art. The exposure optical system of FIG. 11 includes first and second semiconductor lasers 21 and 22, which are positioned so that laser beams emitted from the lasers 21 and 22 are crossed perpendicularly to each other. A collimator lens 23 for making the input light beams parallel is positioned in a beam exit direction of the first semiconductor laser 21, and a collimator lens 24 is similarly positioned on a beam exit direction of the second semiconductor laser 22. Disposed on light exit sides of the collimator lenses 23 and 24 is a beam splitter 25 which functions to deflect the laser beam of the first semiconductor laser 21 to a direction perpendicular thereto, transmit the laser beam of the second semiconductor laser 22 therethrough and guide the beams onto a surface of a polygon mirror 26. The polygon mirror 26, which is disposed on a rotatary axis of a polygon motor (not shown in the drawing) rotating at a high speed, acts to cause the laser beams received from the first and second semiconductor lasers 21 and 22 to be scanned on a photoconductor drum 1. Disposed between the polygon mirror 26 and the photoconductor drum 1 are on f lens 27 for reducing the diameter of the laser beams reflected on the polygon mirror 26 to a predetermined value as well as on a reflecting mirror 28.
With this image generating apparatus, image data corresponding to 2 lines can be recorded at a time in a main scanning direction B of the photoconductor drum 1 from the 2 laser beams received from the first and second semiconductor lasers 21 and 22.
Further, FIG. 12 shows a control block diagram of a prior art image generating apparatus having 2 semiconductor lasers. FIG. 13 is a detailed circuit diagram of a first image data selective output means in the prior art image generating apparatus. In FIG. 12, an image data generating means 31 generates image data (bit map data) on the basis of image information received from a host computer (not shown). A memory means 32 stores therein the image data generated by the image data generating means 31. Further, a first image data selective output means 37 and a second image data selective output means 38 act to extract the image data from the memory means 32 and output it to a first exposure energy control means 35 and a second exposure energy control means 36, respectively. The first and second exposure energy control means 35 and 36 respectively control exposure energy (light emission time, light emission power) of the first and second semiconductor lasers 21 and 22 incorporated in first and second exposure means 33 and 34 (which will be explained later).
The first and second exposure means 33 and 34, which include the first and second semiconductor lasers 21 and 22, respectively, irradiate laser beams on the photoconductor drum 1 to form an electrostatic latent image on the photoconductor drum 1.
An output control means 39, on the basis of a printing operation reference signal, controls the operation of the sequential output of the image data stored in the memory means 32 to the first and second image data selective output means 37 and 38. Further, a clock generating means 40 generates a clock (which will be referred to as the video clock) that is used as a reference to the output operation of the first and second semiconductor lasers 21 and 22.
Explanation will now be made as to the operation of the image generating apparatus having the above arrangement. In FIG. 11, image data is optically modulated by the first and second semiconductor lasers 21 and 22 so that output laser beams of the respective semiconductor lasers are converted by the collimator lenses 23 and 24 to collimated or parallel light and then input to the beam splitter 25. The beam splitter 25 in turn deflects by 90 degrees the laser beam received from the first semiconductor laser 21 and then guides it to the polygon mirror 26; whereas the beam splitter 25 transmits the laser beam received from the second semiconductor laser 22 therethrough and then guides it to the polygon mirror 26. The polygon mirror 26, while rotated by the polygon motor (not shown), scans the laser beams received from the first and second semiconductor lasers 21 and 22 at a predetermined angle. The laser beams are further input to the f lens 27 where the laser beams are reduced in diameter to a predetermined diametered single beam, and then the single beam is scanned by the reflecting mirror 28 on the photoconductor drum 1 in the direction (main scanning direction) shown by an arrow B. In this case, the photoconductor drum 1 is rotating at a constant speed Vp (mm/sec.) in a direction shown by an arrow A.
FIG. 14 is a diagram for explaining how image data is generated in the prior art image generating apparatus. As shown in FIG. 14, picture elements (pixels) 30 each having an illustrated diameter are formed by the laser beam issued from the second semiconductor laser 22 on the first raster scan line, while picture elements (pixels) 29 each having the same diameter as that of the pixel 30 are formed by the laser beam issued from the first semiconductor laser 21 on the second raster scan line. The above operation is sequentially repeated in a direction shown by an arrow C so that the laser beam issued from the second semiconductor laser 22 forms pixels of the odd-numbered raster scan lines, whereas the laser beam issued from the first semiconductor laser 21 forms pixels of the even-numbered raster scan lines. As a result, printing can be realized at a speed of twice as fast as the case of using a single semiconductor laser.
Explanation will next be made as to specific control operation when image data having a main scan (horizontal scanning) resolution of 600 dpi and a feed scan (vertical scanning) or sub-scan resolution of 600 dpi is output to the photoconductor drum 1. FIG. 15 is a timing chart of the first image data selective output means of the prior art image generating apparatus, and FIG. 16 is a diagram showing a relationship between pixel formation and laser emission time in the prior art image generating apparatus.
In FIG. 12, the image data generating means 31, on the basis of image information received from the host computer (not shown), generates image data (bit map data) and stores it in the memory means 32. On the basis of a printing operation reference signal (not shown), the output control means 39 controls the memory means 32 to cause the memory means 32 to output the first and second raster scan lines of the image data therefrom to the second and first image data selective output means 38 and 37 respectively. That is, as shown in FIG. 13, a semiconductor memory (DRAM) 41 within the memory means 32 is connected to a parallel/serial converter 42 within the first image data selective output means 37 through a bus 8 bits of D7-D0. The output control means 39 generates a predetermined address and sends it to the DRAM 41 to read out image data at the address, and loads the read-out image data to the parallel/serial converter 42 under a signal LD.
The image data of D7-D0 loaded into the parallel-to-serial converter 42, as shown in FIG. 15, in synchronism with a video clock f received from the clock generating means 40, serially outputs the image data (starting from D7 and ending in D0) from a serial output terminal Q7 to the first exposure energy control means 35 as a laser beam emission signal of the second raster scan line.
Further, the output control means 39 outputs the next address to read out image data at the address from the DRAM 41. The similar operation to the above is repeated to cause the parallel-to-serial converter 42 to sequentially output the image data of the fourth raster scan line as a laser beam emission signal.
Similarly, the second image data selective output means 38 sequentially outputs the image data of the first raster scan line to the second exposure energy control means 36 as serial image data.
The first and second exposure energy control means 35 and 36, according to the received image data, send the respective laser beam emission signals of predetermined emission time and power to the first semiconductor laser 21 of the first exposure means 33 and also to the second semiconductor laser 22 of the second exposure means 34 for modulation, respectively. As shown in FIG. 15, the laser beam emission time of the first and second semiconductor lasers 21 and 22 is usually set at a period time of the video clock f, so that such a predetermined size (beam diameter) of pixel dots as shown in FIG. 16 is formed. In the drawing, the black dot or circle denotes the presence of the pixel output and the white dot or circle denotes the absence of the pixel output.
In the case of the prior art image generating apparatus having the aforementioned arrangement, in order to obtain a high quality of such text image as characters or lines, it is necessary to increase its pixel density or resolution. FIG. 17 is a timing chart of the first image data selective output means of the prior art image generating apparatus when the apparatus is operated in a high-density record mode, and FIG. 18 shows a relationship between the laser beam emission signal and formed pixels with the same high resolution. For example, when the resolution in the main scanning direction B is changed from 600 dpi to 1200 dpi as shown in FIG. 18, it is necessary to set the frequency of the video clock at twice (2 fHz) as shown in FIG. 17.
However, this also requires the other circuits to operate at a speed of twice the previous operational speed, which also increases noise such as unnecessary irradiation. In this way, this involves a problem in which the circuit costs become high.
In order to obtain a high quality of image such as a photograph, further, it is necessary to increase or enhance its pixel density or gray shade property (gradient). For enhancing the gray shade property, it is required to divide exposure energy into a plurality of stages of energy. However, the division of exposure energy into such a plurality of stages by one scan of the semiconductor laser involves the complication of the control circuit, thus disadvantageously increasing the circuit costs.
It is accordingly an object of the present invention to provide an image generating apparatus which can produce a high quality of image without the need for increasing the frequency of a video clock and can provide gray shade display with use of a simple control circuit.
In accordance with the present invention, there is provided an image generating apparatus which has a plurality of exposure means for optically modulating image data to record a plurality of main scanning lines of the image data on a recording medium through a single main scanning operation, and which comprises image data selective output means for selecting the image data corresponding to the plurality of exposure means from the image data forming one of the main scanning lines and outputting the selected image data to the respective exposure means; and control means for controlling the operation of the image data selective output means in such a manner that the plurality of exposure means perform sequential scanning operation over the one main scanning line based on the image data issued from the image data selective output means to record the image data.
In the image generating apparatus of the present invention, one of the main scanning lines of image data is recorded through a plurality of scanning operations of the plurality of exposure means. For this reason, even when the number of pixels of one main scanning line is increased, the number of image data to be recorded for one main scanning line by one exposure means can be maintained as in the prior art. Accordingly, high-density image formation can be implemented through a plurality of recording operations of the plurality of exposure means over the image data without the need for increasing the frequency of a video clock for generating the timing of irradiation or illumination of an exposure light beam from one exposure means.
In accordance with the present invention, there is also provided an image generating apparatus which has a plurality of exposure means for optically modulating image data to record a plurality of main scanning lines of the image data on a recording medium through a single main scanning operation, and which comprises image data division/output means for dividing the image data forming one of the main scanning lines into predetermined gray shade levels of image data and outputting the divided image data to the respective exposure means; and control means for controlling the operation of the image data division/output means in such a manner that the plurality of exposure means perform sequential scanning operation over the one main scanning line based on the image data issued from the image data divisional/output means to record the image data.
In the image generating apparatus of the present invention, the image data division/output means divides the image data into different gray shade levels of image data and outputs them to the plurality of exposure means. The respective exposure means form pixels allowing the gray shade display according to the gray shade levels of the received image data. In addition, image data are recorded based on the different-level gray shade display through a plurality of scanning operations of the plurality of exposure means over one main scanning line. Since one exposure means can perform the gray shade display as controlled to a constant exposure condition, the gray shade display can be realized through easy-to-control operation.
In accordance with a first aspect of the present invention, there is provided an image generating apparatus which has a plurality of exposure means for optically modulating image data to record a plurality of main scanning lines of the image data on a recording medium through a single main scanning operation, and which comprises image data selective output means for selecting the image data corresponding to the plurality of exposure means from the image data forming one of the main scanning lines and outputting the selected image data to the respective exposure means; and control means for controlling operation of the image data selective output means in such a manner that the plurality of exposure means perform sequential scanning operation over the one main scanning line based on the image data issued from the image data selective output means to record the image data.
Thus, high-density image formation can be carried out without the need for increasing the frequency of a video clock signal for controlling the timing of exposure operations of the respective exposure means.
In accordance with a second aspect of the present invention, in the image generating apparatus of the first aspect, a plurality of the image data selective output means are provided for the plurality of exposure means, and the control means performs the control operation in such a manner that as a main scanning position of the plurality of exposure means advances by one line in a sub-scanning direction perpendicular to the main scanning direction, the plurality of exposure means simultaneously record the image data on a plurality of main scanning lines based on the image data issued from the image data selective output means.
Therefore, when the plurality of exposure means are advanced by an amount of each one line in the sub-scanning direction through the repetitive main scanning operation, one main scanning line of image data can be recorded through the scanning operations of the plurality of exposure means, and thus high-density image formation can be realized without the need for increasing the frequency of the video clock signal.
In accordance with a third aspect of the present invention, in the image generating apparatus of the first or second aspect, the image data selective output means includes change-over means for switching between a first mode in which a plurality of main scanning lines of image data to be simultaneously recorded are output to the associated exposure means and a second mode in which the image data selective output means selects image data corresponding to the plurality of exposure means from the image data of one main scanning line and outputs the selected image data to the respective exposure means.
Thus, selection can be made between the normal operation of image formation of plural lines and the high-density image formation operation.
In accordance with a fourth aspect of the present invention, there is provided an image generating apparatus which has a plurality of exposure means for optically modulating image data to record a plurality of main scanning lines of the image data on a recording medium through a single main scanning operation, and which comprises image data division/output means for dividing the image data forming one of the main scanning lines into predetermined gray shade levels of image data and outputting the divided image data to the respective exposure means; and control means for controlling operation of the image data division/output means in such a manner that the plurality of exposure means perform sequential scanning operation over the one main scanning line based on the image data issued from the image data division/output means to record the image data.
Therefore, the gray shade display using the plurality of exposure means can be realized through simple control operation while eliminating the need for changing the exposure conditions of one exposure means.
In accordance with a fifth aspect of the present invention, in the image generating apparatus of the fourth aspect, the plurality of exposure means, on the basis of image data received from the image data division/output means, irradiate exposure light beams having different exposure energies on the recording medium and overlap the exposure light beams issued from the plurality of exposure means with respect to predetermined pixels to record the image data of the different gray shade levels.
Thus, image gray shade display can be realized by making different the exposure energies of the plurality of exposure means.
In accordance with a sixth aspect of the present invention, in the image generating apparatus of the fourth or fifth aspect, a plurality of image data division/output means are provided for the plurality of exposure means.
Therefore, when the respective image data division/output means output image data to the associated exposure means according to the gray shade levels, gray shade display can be realized.
In accordance with a seventh aspect of the present invention, in the image generating apparatus of any of the fourth to sixth aspects, the image data division/output means includes change-over means for switching between a first mode in which a plurality of main scanning lines of image data to be simultaneously recorded are output to the associated exposure means and a second mode in which the image data division/output means divides image data of one of the main scanning lines into predetermined gray shade levels of image data and outputs the divided image data to the respective exposure means.
Thus, change-over can be carried out between the normal mode of image formation by the simultaneous scanning operation of a plurality of lines and the image formation mode based on the gray shade display.