GB2184914A

GB2184914A - Image recording method

Info

Publication number: GB2184914A
Application number: GB08700615A
Authority: GB
Inventors: Satoru Tomita
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1984-01-13
Filing date: 1985-01-03
Publication date: 1987-07-01
Also published as: GB2185652B; GB8700614D0; GB2185653B; GB2185652A; GB8700616D0; GB8700615D0; GB2184914B; GB2185653A

Abstract

An image recording method capable of allowing an optical scan type electrophotographic recording apparatus to record images with a high resolution. The pulse width of video data adapted to modulate a light beam is varied. An optimum light beam scanning condition is provided which causes the pulse width of binary video data to be controlled to suitably vary the power of an exposing beam such that a latent image potential difference at a boundary between an image portion and a non-image portion is increased to enhance electrostatic contrast, thereby recording images with a high resolution. The ratio of the widths of a latent image line in a direction parallel to, and perpendicular to the summing direction lies between 1.0 and 1.2. <IMAGE>

Description

1 GB2184914A 1 SPECIFICATION elaborated to free a laser printer from the

in tricacy of construction of its optical system Image recording method (Japanese Patent Laid-Open Publication No.

58-108864) and other problems. In the pro BACKGROUND OF THE INVENTION 70 posed apparatus, to simplify a light source

The present invention relates to an image re- and an optical system, a light source com cording method for an optical scan type elec- prises a phosphor dot array tube having an trophotographic recording apparatus and, fur- array of phosphor elements arranged in the ther, to an image recording method for an main scan direction in correspondence with optical scan type electrophotographic record- 75 pixels. Light issuing from phosphor dot tube ing apparatus of the kind which uses minute and modulated by binary video data is passed light emitting segments as a light source. through an imaging system toward a photo Generally, in a laser printer or like optical conductive element, which is fed in the sub scan type electrophotographic recording appa- scan direction, to provide a latent image ther ratus, a light beam modulated by binary video 80 eon, the latent image being developed to re data is manipulated to sequentially expose a cord data associated with the video data.

photoconductive element to form a latent im- However, due to the use of minute, light age electrostatically thereon. The problem en- emitting phosphor elements as a light source, countered with this kind of image recording is the above-described prior art method limits that because the pulse width of video data 85 the available potential of latent images and, per pixel and, therefore, the ratio of a light thereby, electrostatic contrast. This is apt to beam exposing time to a one-pixel scanning cause the resolution in the subscan direction time is fixed, the latent image potential in an to fluctuate due to gitter on the surface of the image portion which borders a non-image por- photoconductive element, greatly effecting the tion is lowered due to building and failing of 90 quality of the entire recorded images.

the latent image potential. Such causes the In addition, the dot array tube scheme can image to be developed to have different pixel not accomplish a sufficient resolution, particu diameters in the main scan and subscan direc- larly sufficient reproducibility of hairlines such tions and, thereby, considerably lowers the as one-dot lines. Specifically, because with re resolution. Especially, when it comes to docu- 95 spect to the main scan direction the intensity ment images, characters are prevented from distribution of the fight issuing from the regu appearing clear-cut. larly arranged light emitting elements has great Japanese Patent Laid-Open Publication No. influence and because, with respect to the 56-8112/1981 discloses an implementation subscan direction, the light emitting elements for an optical scan type electrophotographic 100 emit light at a predetermined timing associated recording apparatus which modulates the with the movement of the photoconductive pulse width of video data in order to eliminate element in the subscan direction, in the case thinning of images which is apt to occur dur- of recording hairlines such as one-dot lines, ing positive-to-positive recording, which develthe width of the lines to be developed differs ops unexposed portions. However, it fails to 105 from the main scan direction to the subscan improve the quality of recorded images when direction thereby deteriorating the resolution.

a countermeasure is provided against thinning in the main scan direction only. That is, it SUMMARY OF THE INVENTION cannot offer a desirable image quality unless a It is therefore a first object of the present countermeasure covering both the main scan 110 invention to provide an image recording and subscan directions is provided in due con- method which allows an optical scan type sideration of gitter occurring on a photocon- electrophotographic recording apparatus to re ductive element, developing method, develop- cord images with a high resolution.

ing characteristics, etc. In that case, reproduci- It is a second object of the present inven bility on a one-dot line basis is very important. 115 tion to provide an image recording method Meanwhile, the countermeasure against which allows an optical scan type electropho thinning and a measure for an improvement in tographic recording apparatus of the type us resolution, which the present invention con- ing minute light emitting segments as a light templates, are contradictory to each other; the source to provide latent images with consider anti-thinning measure is not always advan- 120 able electrostatic contrast.

tageous in enhancing or stabilizing the image It is a third object of the present invention quality. That is, whether the recording be to provide an image recording method which negative-to-positive which develops exposed allows an optical scan type electrophotogra portions or positive-to-negative which devel- phic recording apparatus to record high resolu ops unexposed portions, attaching importance 125 tion images which have the same pixel dia to the resolution rather than anti-thinning is meter both in the main scan and subscan di advantageous from the viewpoint of improve- rections.

ment or stabilization of the image quality. It is a fourth object of the present invention An optical scan type electrophotographic re- to provide an image recording method which cording apparatus has been proposed which is 130 allows an optical scan type electrophotogra- 2 GB2184914A 2 phic recording apparatus of the type using In another aspect of the present invention, minute light emitting elements as a light in an image recording method using an optical source to record high resolution images which scan type electrophotographic recording appa have the same pixel diameter in both the main ratus which modulates by binary video data scan and subscan directions. 70 light issuing from minute light emitting seg It is a fifth object of the present invention ments which are associated with pixels, to provide an image recording method which passes the modulated light through an imaging allows an optical scan type electrophotogra- system to a surface of a photoconductive ele phic recording apparatus to record images ment to form an electrostatic latent image, with desirable reproducibility on a one-dot line 75 and develops the latent image to record data basis by controlling the formation of a latent associated with the video data, there is pro image during exposure. vided the improvement wherein a pulse width It is a sixth object of the present invention of video data is varied such that a ratio pylp, to provide an image recording method which where p. indicates a ratio of a beam diameter allows an optical scan type electrophotogra- 80 ina main scan direction to a pixel pitch in the phic recording apparatus of the type using main scan direction and p, indicates a ratio of minute light emitting elements as a light a beam diameter in a subscan direction to a source to record high resolution images excelpixel pitch in the subscan direction satisfies a lent in reproducibility on a one-dot line basis condition 0.6:5 pylp;,:5 1.0, and that a pro by controlling the formation of a latent image 85 duct of the ratio py and a ratio of Tp of an during exposure. exposig time to a one-pixel scanning time at a It is another object of the present invention boundary between an image portion and a to provide a generally improved image recordnon-image portion satisfies a condition 0.5:5 ing method. 1),. - Tp:5 1. 5.

In one aspect of the present invention, in an 90 In another aspect of the present invention, image recording method using an optical scan in an image recording method using an optical type electrophotographic recording apparatus scan type electrophotographic recording appa which includes a device for varying a pulse ratus, there is provided the improvement width of video data which modulate a light wherein a light beam scans such that a ratio beam, there is provided the improvement 95 1c11p where lp indicates a width of a latent wherein a light beam scans such that at a image line substantially parallel to a developing boundary between an image portion and a direction and lc indicates a width of a latent non-image portion a ratio of a light beam ex- image line substantially perpendicular to the posing time to a one-pixel scanning time satideveloping direction satisfies a condition 1.0 sfies a condition 0.2:5 Td:s 1.1. 100:s 1c11p:5 1.2.

In another aspect of the present invention, In another aspect of the present invention, in an image recording method using an optical in an image recording method using an optical scan type electrophotographic recording appa- scan type electrophotographic recording appa ratus which modulates by binary video data ratus which modulates by binary video data light issuing from minute light emitting seg- 105 light issuing from minute light emitting seg ments which are associated with pixels, ments which are associated with pixels, passes the modulated light through an imaging passes along the modulated light through an system to a surface of a photoconductive ele- imaging system to a surface of a photocon ment to form an electrostatic latent image, ductive element to form an electrostatic latent and develops the latent image to record data 110 image, and develops the latent image to re associated with the video data, there is pro- cord data associated with the video data, vided the improvement wherein a pulse width there is provided the improvement wherein a of video data for modulating the light issuing light beam scans such that a ratio 1c11p where from the light emitting segments is varied. lp indicates a width of a latent image line In another aspect of the present invention, 115 substantially parallel to a developing direction in an image recording method for an optical and lc indicates a width of a latent image line scan type electrophotographic recording appasubstantially perpedicular to the developing di ratus, there is provided the improvement rection satisfies a condition 1. 0:5 1c11p:5 wherein a light beam scans such that a ratio 1.3.

plp,, where & indicates a ratio of a beam dia- 120 The above and other objects, features and meter in a main scan direction to a pixel pitch advantages of the present invention will be in the main scan direction and py indicates a come apparent from the following detailed de ratio of a beam diameter in a subscan direc- scription taken with the accompanying draw tion to a pixel pitch in the subscan direction ings.

satisfies a condition 1.0:5plp, 1.5, and that 125 a product of the ratio py and a ratio Td of an BRIEF DESCRIPTION OF THE DRAWINGS exposing time by the light beam to a one-pixel Figure 1 is a schematic view of an ordinary scanning time at a boundary between an im- optical scan type electrophotographic record age portion and a non-image portion satisfies ing apparatus to which the first, third and fifth a condition 0.5:5 p;, Td:5 1.5. 130embodiments of the present invention are ap- 3 GB2184914A 3 plied; posure energy distribution resulted when a Figure 2 is a graph showing a relationship pixei-by-pixel grid pattern was drawn; between a relative potential and a relative dis- Figure 17 is a view of surface potential dis tance associated with a pattern which was tribution on a photoconductive element associ exposed at every two pixels in the main scan 70 ated with Fig. 16 direction in the first and second embodiments; Figures 18A and 18B are graphs showing Figure 3 is a graph showing a relative po- relative potentials with respect to a relative tential and a relative beam diameter provided distance in the subscan direction and that in by fully exposing lines in the horizontal scan the main scan direction provided by p, of direction; 75 about 0.94 in accordance with the fifth em Figure 4 is a graph showing a relationship bodiment of he present invention; between a relative potential difference and a Figures 19A and 19B are graphs showing pixel frequency duty associated with a pattern relative potentials with respect to a relative which was exposed at every two pixels in the distance in the subscan direction and that in main scan direction; 80 the main scan direction provided by p, of Figure 5 is a graph showing a relationship about 1. 18; between a potential contrast and a pixel fre- Figures 20A and 208 are graphs showing quency duty; relative potentials with respect to a relative Figure 6 is a schematic view of an optical distance in the subscan direction and that in scan type electrophotographic recording appa- 85 the main scan direction provided by p, of ratus using a phosphor dot array tube as a about 1.42; light source and to which the second, fourth Figures 21A-21C show respectively a distri and sixth embodiments of the present inven- bution of relative exposure energy G as tion are applied; viewed in the main scan direction, a distribu- Figure 7 is a perspective view of an 90 tion of relative potentials as viewed in the example of the phosphor dot aray tube shown main scan direction, and a distribution of rela in Fig. 6; tive potentials as viewed in the subscan direc Figures BA and BB are graphs showing relation, each being associated with a case tive potentials with respect to a relative dis- wherein a potential distribution provided by tance in the subscan direction and that in the 95 drawing a pixel-by- pixel grid pattern is sub main scan direction provided by 1),, of about stantially equal in both the main and subscan 0.94 in accordance with the third embodi- directions; ment; Figures 22A-22C show respectively a distri Figures 9A and 98 are graphs showing rela- bution of relative exposure energy Q as tive potentials with respect to a relative dis- 100 viewed in the main scan direction, a distribu tance in the subscan direction and that in the tion of relative potentials as viewed in the main scan direction provided by 1jy of about main scan direction, and a distribution of rela 1. 18; tive potentials as viewed in the subscan direc Figures 10A and 10B are graphs showing tion, each being associated with a case relative potentials with respect to a relative 105 wherein a ratio between latent image line distance in the subscan direction and that in widths provided by drawing a pixel-by-pixel the main scan direction provided by 1), of grid pattern satisfies a condition in accordance about 1.42; with the present invention; Figure 11 is a two-dimensional view of ex- Figures 23A and 238 are graphs showing posure energy distribution resulted when a 110 relative potentials with respect to relative dis pixel-by-pixel grid pattern was drawn; tances in the subscan direction and those in Figure 12 is a view of surface potential dis- the main scan direction provided by p, of tribution on a photoconductive element associ- about 0.94 in accordance with the sixth em ated with Fig. 11; bodiment of the present invention; Figures 13A and 13B are graphs showing 115 Figures 24A and 24B are graphs showing relative potentials with respect to a relative relative potentials with respect to relative dis distance in the main scan direction and a rela- tances in the subscan direction and those in tive distance in the subscan direction provided the main scan direction provided by p, of by p, of about 0.94; about 1. 18; Figures 14A and 14B are graphs showing 120 Figures 25A and 25B are graphs showing relative potentials with respect to a relative relative potentials with resepct to relative dis distance in the main scan direction and that in tances in the subscan direction and those in the subscan direction provided by p, of about the main scan direction provided by py of 1. 18; about 1.42; Figures 15A and 15B are graphs showing 125 ' Figures 26A and 26B show respectively a relative potentials with respect to a relative distribution of relative exposure energy Q as distance in the main scan direction and that in viewed in the main scan direction and a distri the subscan direction provided by py of about bution of relative potentials as viewed in the 1.42; main scan direction, each being associted with Figure 16 is a two-dimensional view -of ex- 130 a case wherein a distribution of potentials pro- A__ 4 GB2184914A 4 vided by drawing a pixel-by-pixel grid pattern struction, images are recorded in a predeter is substantially equal in both the main and mined density which depends upon the scann subscan directions; and ing rate of the laser beam in the main scan Figures 27A and 278 show respectively a direction an the linear velocity of the drum 22 distribution of relative exposure energy Q as 70 in the subscan direction. Alternatively, a beam viewed in the main scan direction and a distriemanating from a gas laser may be modulated bution of relative potentials as viewed in the by means of an acoustooptical modulator in main scan direction, each being associated response to binary data.

with a case wherein a ratio between latent Referring to Fig. 2, there is shown a charac- image line widths provided by drawing a pixel- 75 teristic associated with a pattern provided by by-pixei grid pattern satisfies a condition in exposing a photoconductive element at every accordance with the present invention. two pixels in the main scan direction (i.e. a stripe pattern repeating at every one of black DESCRIPTION OF THE PREFERRED EMBODI- and white lines which extend in the subscan

MENTS 80 direction). In Fig. 2, the abscissa shows a While the image recording method of the relative distance which is a ratio of each expo present invention is susceptible of numerous sure distance to a pixel pitch in the main scan physical embodiments, depending upon the direction, while the ordinate shows a relative environment and requirements of use, sub- potential which is a ratio of each exposed sur stantial numbers of the herein shown and de- 85 face potential to a surface potential of the scribed embodiments have been made, tested uniformly -charged drum 22. A parameter in and used, and all have performed in an emi- the plot of Fig. 2 is a pixel frequency duty, nently satisfactory manner. i.e., a ratio of an exposure time to a one- pixel A first embodiment of the present invention exposure time, which is varied over a range of elaborated to achieve the first object will be 90 10-150%.

described first. It will be seen from Fig. 2 that as the pixel An image recording method in accordance frequency duty increases, the bottoms of the with the first embodiment is implemented by surface potential become shallower and the means which is capable of varying the pulse peaks, lower. This implies that the pixel fre- width of video data which modulate a light 95 quency duty constitutes one of various condi beam in an optical scan type electrophotogra- tions which allow the boundaries between phic recording apparatus. Light beam scanning black and white in recorded images, or image is effected such that the ratio of a light beam and non-image portions, to appear clear-cut exposing time to a one-pixel scanning time and set up adequate black and white line satisfies a condition which will be described at 100 widths, and that an adequate pixel frequency boundaries between image portions and non- duty exists in the above- discussed range.

image portions, so that the latent image po- For the selection of an adequate pixel fre tential in the image portions may be increased quency duty, it is a primary requisite to deter at the boundaries. mine an adequate range of the ratio of the In this particular embodiment, in recording 105 beam diameter to the pixel pitch. Fig. 3 images by such an optical scan type electro- shows a curve representative of ratios be photographic recording apparatus as one 10 tween the peak of surface potential on the shown in Fig. 1, an optimum light beam drum 22 resulted from the full exposure of scanning condition is provided which is such lines in the main scan direction and the sur- that the pulse width of binary image data is 110 face potential on the drum 22 resulted from controlled to suitably vary the power of an zero exposure energy. In Fig. 3, the abscissa exposing beam to enhance the latent image indicates a relative beam diameter which is potential difference at a border between image the ratio of a beam diameter to a pixel pitch and non-image portions and, thereby, the in the main scan direction and the ordinate, a electrostatic contrast, thereby providing re- 115 relative potential. It is known by experience corded images with high resolution. that a relative potential lower than about 0.2 In the recording apparatus 10 shown in Fig. is desirable in which case, as shown in Fig. 3, 1 a light source 14 which comprises a laser the beam diameter to pixel pitch ratio is larger diode is turned on and off by binary data 12 than about 1.0.

to produce a directly modulated laser beam 120 As shown in Fig. 4, the ratios shown in Fig.

16. The laser beam 16 is routed through an 2 may be represented in relation to the pixel optical scanning system and compensating opfrequency duties employing the relative beam tical system 18 to sequentially illuminate in a diameter as a parameter. In this instance, it is main scan direction a drum-like photoconduc- known by experience that a relative potential tive element 22 which is fed in a subscan 125 higher than about 0.6 is desirable. This, coup direction and deposited with a uniform charge led with the previously mentioned beam dia by a charger 20. The resulting latent image meter to pixel pitch ratio which is larger than formed on the drum 22 is developed by a about 1.0, provides an adequate pixel fre developing unit 24 and, then, transferred to a quency range as indicated by hatching in Fig.

paper 26 in a transfer station. In this con- 130 4.

GB2184914A 5 In Fig. 5, there is shown a relationship be- image potential in the image portion. This al- tween a potential contrast and a pixel frelows an optical scan type electrophotographic quency duty with respect to the various rela- recording apparatus to record images with a tive beam diameters. In this case, experience high resolution.

teaches that the potential contrast is desirable 70 Hereinafter will be described a second em if higher than about 60%. Such a desirable bodiment of the present invention elaborated range of potential contrast and the previously to achieve the second object.

stated relative beam diameters provide an The method in accordance with the second adequate pixel frequency duty range as indi- embodiment is applicable to an optical scan cated by hatching in Fig. 5. 75 type electrophotographic recording apparatus Therefore, considering conditions essential which uses minute light emitting segments for recording, i.e., that the potential contast such as phosphors or light emitting diodes and potential difference of latent images be (LEDs), modifies light emanating therefrom by large and, in addition the exposure potential binary video data, scans a photoconductive be kept low and stable, the relationships 80 element with the modulated light to form an shown in Figs. 4 and 5 teach that the opti- electrostatic latent image thereon, and turns mum range of pixel frequency duty is the latent image to a visible image. The 20-110%. method is implemented by means which is Thus, in this particular embodiment, scann- capable of varying the pulse width of video ing by the light beam is effected such that, 85 data which modulate light emanating from the assuming that the ration of the light beam light-emitting elements. The pulse width of vi exposure time to the one-pixel scanning time deo data is varied such that the ratio of an is Td, it satisfies a predetermined condition at, exposing time to a one- pixel scanning time in particular, the boundaries between image satisfies a given condition which will be de- and non-image portions, as shown below: 90 scribed at boundaries between image and non- 0.2:5 Td:5 1.1 image portions, thereby increasing the latent If the pulse width of binary video data is image potential in image portions adjacent to selected within the adequate pixel frequency non-image portions.

range as described above, images will be re- In this particular embodiment, in recording corded with high contrast and resolution, 95 images by such an optical scan type electro whether the recording mode be positive-to- photographic recording apparatus as one positive or negative-to-positive. In addition, shown in Fig. 6, generally 30, an optimum the areas of image and non-image portions exposure condition is provided which is such become similar to those of video data so that that the pulse width of binary video data for various factors detrimental to sharpness, such 100 modulating light output from minute light em as thickening and thinning of lines, are effec- itting segments is varied to enhance the latent tively reduced. Experimentarily, in positive-to- image potential difference at a border between positive recording, the best images were image and non-image portions and, thereby, achieved at the developing level of 150V and electrostatic contrast, thereby recording imin the pixel frequency duty range of 60-70%. 105 ages with a high resolution.

In the foregoing description, attention has In the recording apparatus 30 shown in Fig.

been paid exclusively to pixel frequency duty 6, phosphor elements arranged in lines in a which greatly effects recording quality. Howphosphor dot array 34 pixel by pixel in the ever, because various other factors such as main scan direction are turned on and off by scanning rate, beam power and developing 110 binary data 32 to produce directly modulated devel have influence on recording quality, they fine beams. The beams are routed through an also have to be taken into consideration in optical imaging system 36 to illuminate in the selecting an optimum pixel frequency duty so main scan direction a drum- like photoconduc that the quality of recorded images may be tive element 40 which is fed in a subscan further enhanced. 115 direction and deposited with a uniform charge The method in accordance with the illustra- by a charger 38, thereby sequentially exposing tive embodiment may be practiced with any of the drum surface line by line. A latent image various means which will not be shown or resulting from the exposure is turned to a vis described. In any case, it can readily be prac- ible image by a developing unit 42 and, then, ticed by modifying the ratio of an exposure 120 transferred to a paper 46 by a transfer unit time to a one-pixel scanning time at a bound44. The reference numeral 48 in Fig. 6 desig ary between image and non-image portions, or nates a cleaner for removing residual toner pulse width of binary video data, in response particles from the drum surface after the to binary video data. transfer.

As described above, the image recording 125 Referring to Fig. 7, a specific construction method in accordance with the first embodi- of the phosphor dot array 34 is shown which ment varies the pulse width of binary video comprises an array of phosphor elements 52 data within an adequate pixel frequency duty arranged in a face glass 50 pixel by pixel, and range at a boundary between image and non- drive integrated circuits (ICs) 54 built in a sin image portions, thereby increasing the latent 130 gle substrate 58 integrally with terminals 56.

6 GB2184914A 6 The phosphor dot aray 34 serving as a light tential (uniform) associated with zero exposure source may be replaced by an array of LEDs energy, and the relative exposure energy Q each constituting a pixel. the ratio of actual exposure energy to maxi The various plots shown in Figs. 2-4 and mum exposure energy. For illustration, Figs.

discussed in relation with the first embodiment 70 8B, 9B and 10B share the same data.

are directly applicable to the second embodi- The curves shown in Figs. 8A and 8B were ment as well. provided by a ratio p. of a beam diameter in Therefore, considering conditions essential the main scan direction to a pixel pitch in the for recording, i.e., that the potential contrast main scan direction which was about 0.94. In and potential difference of latent images be 75 Fig. 8A, the frequency duty Td which is the large and, inaddition, the exposure potential ratio of an optical beam exposure time to a be kept low and stable, the relationships one-pixel scanning time is varied while, in Fig.

shown in Figs. 4 and 5 teach that the opti- 8B, a ratio p, of a beam diameter in the sub mum range of pixel frequency duty is scan direction to a pixel pitch in the subscan 20-110%._ 80 direction. The characteristics indicated by bold Thus, in accordance with this particular em- lines are associated with a condition wherein bodiment, the pulse width of video data is the potential distribution is analogous in both varied such that, assuming that the ratio of an the main scan and subscan directions and, in exposure time to a one-pixel scanning time is such a condition, there are provided p,,=0.94, Td, it satisfies a predetermined condition at, 85 p,= 1.18 and Td=0.6 and, thereby, a light in particular, the boundaries between image beam condition plp,= 1.255 and a light beam and non-image portions, as shown below: scanning condition p,. Td=0.564. The -bearn 0.2:c Td -< 1. 1 diameter- referred to is defined by a sectional As described above, the image recording shape in a position which is e-2 (about method in accordance with the second em- 90 13.5%) of a peak of a beam intensity distribu bodiment varies the pulse width of binary vi- tion having a Gaussian distribution.

deo data within an adequate pixel frequency The curves shown in Figs. 9A and 913 re duty range at a boundary between image and sulted from a ratio I);, of the beam diameter in non-image portions, thereby increasing the la- the main scan directi on to the pixel pitch in tent image potential in the image portion and, 95 the main scan direction which was about thereby, the electrostatic contrast. This allows 1.18. In Fig. 9A, the frequency duty Td which an optical scan type electrophotographic re- is the ratio of a light beam exposing time to a cording apparatus, especially one which uses one-pixel scanning time is varied while, in Fig.

miniature fight-emitting segments as a light 9B, the ratio py of a beam diameter in the source, to record images with a high resolu- 100 subscan direction to a pixel pitch in the sub tion. scan direction is varied. The characteristics in A third embodiment contemplated to dicated by bold lines are associated with a achieve one third object of the present invencondition wherein the potential distribution in tion will be described. the main scan direction is analogous to that in Where an optical scan type electrophotogra- 105 the subscan direction and, in such a condition, phic recording apparatus such as one shown there are provided 1),= 1. 18, p,= 1.42 and in Fig. 1 is constructed to electrostatically Td0.7 and, thereby, a light beam condition form a latent image on a photoconductive ele1),11)f 1.203 and a light beam scanning condi ment by exposing it to a light beam modu- tion 1),. Td=0.826.

lated by binary video data, the method in ac- 110 The curves shown in Figs. 10A and 10B cordance with third embodiment sets up a resulted from a ratio 1), of the beam diameter light beam condition and a light beam scann- in the main scan direction to the pixel pitch in ing condition which makes the pixels in an the main scan direction which was about image to be developed have the same dia- 1.42. In Fig. 10A, the frequency duty Td meter both in the main scan and subscan di- 115 which is the ratio of a light beam exposing rections. time to a one-pixel scanning time is varied Referring to Figs. 8A, 8B, 9A, 9B, 10A and while, in Fig. 1013, the ratio p, of a beam 1013, there are shown examples of relative po- diameter in the subscan direction to a pixel tentials V and relative exposure energy Q in pitch in the subscan direction is varied. The relation to relative distances X and Y in the 120 characteristics indicated by bold lines are as main scan and subscan directions in an expo- sociated with a condition wherein the potential sure pattern which comprises one line in each distribution in the main scan direction is analo of the main scan and subscan directions, pro- gous to that in the subscan direction and, in vided by varying the light beam condition and such a condition, there are provided p;,=1.42, the light beam scanning condition in various 125 p.=1.65 and Td=0.8 and, thereby, a light ways. The relative distance X or Y represents beam condition plp,= 1. 162 and a light beam a ratio of distance to each pixel pitch in the scanning condition p,. Td= 1. 136.

main scan or subscan direction, the relative By selecting other suitable values of p;, to potential V a ratio of a surface potential on provide other various parameters p, and Td, the drum 22 after exposure to a surface po- 130 potential distributions which are analogous in 7 GB2184914A 7 the main scan and subscan directions will be beam scarinting condition. However, because obtained. the quality of recorded images also depends It will be understood from the above analy- upon other various factors such as scanning sis and by experience that if 1.0 < plp,, < rate, beam power and developing level, such 1.5 and 0.5 < p,. Td < 1.5 are satisfied, a 70 various factors need also be taken into ac potential distribution substantially analogous in count in the selection of pylp, and p, Td if the main scan and subscan directions in prac- higher quality images are desired. The control tice is achievable. over Td is readily practicable by modifying the Referring to Figs. 11 and 12, a two-dimenpulse width of binary video data at boundaries sional distribution is shown which is associ- 75 between image and non- image portions.

ated with one of the various conditions dis- As described above, the method in accor cussed hereinabove. Fig. 11 represents a dis- dance with the third embodiment sets up a tribution of exposure energy Q provided when particular light beam condition and a particular a grid pattern'is drawn pixel by pixel under light beam scanning condition which make the conditions p,= 1. 18, py= 1.42 and 80 each pixel recorded by an optical scan type Td=0.7. Fig. 12 shows a surface potential electrophotographic recording apparatus identi distribution on a photoconductive element ascal in diameter in the main scan and subscan sociated with the exposure energy distribution directions, thereby allowing images to be re of Fig. 11. Although the graphs of Figs. 11 corded with an excellent resolution.

and 12 are the results of computer simulation, 85 A fourth embodiment of the present inven it has been proved by experiments that when tion directed to achieving the fourth object will a latent image is formed on a photoconductive be described.

element under the above conditions and then The method in accordance with the fourth turned to a visible image, lines of the resulting embodiment is applicable to, for example, the grid are substantially identical in width in the 90 optical scan type electrophotographic record main scan and subscan directions. ing apparatus 30 shown in Figs. 6 and 7 As described above, in accordance with the which is of the type using, as a light source, method of the third embodiment, where an the phosphor dot array tube 34 having phos optical scan type electrophotographic record- phor elements arranged in an array in the main ing apparatus is operated to record an image, 95 scan direction on a pixel basis. When a light a latent image associated with binary video beam modulated by binary video data 32 and data is formed electrostatically on a photocon- output from the dot array tube 34 is to be ductive element under a particular light beam focused onto the surface of the photoconduc condition and a particular light beam scanning tive element 40, which is fed in the subscan condition which provide a potential distribution 100 direction, the method of the fourth embodi analogous in the main scan and subscan direc- ment provides a specific light beam condition tions. The method, therefore, allows images and a specific light beam scanning condition to be recorded always with a high resolution which make the pixels in the resulting image and with the same pixel diameter in the main equal in diameter in the main scan and sub scan and subscan directions. 105 scan directions.

As described above, in accordance with the Referring to Figs. 13A, 1313, 14A, 1413, method of the third embodiment, when an op- 15A and 1513, there are shown examples of tical scan type electrophotographic recording relative potentials V and relative exposure en apparatus is operated to record an image, a ergy Q in relation to relative distances X and latent image associated with binary video data 110 Y in the main scan and subscan directions in is formed electrostatically on a photoconduc- an exposure pattern which comprises one line tive element under a particular light beam con- in each of the main scan and subscan direc dition and a particular light beam scanning tions, provided by varying the light beam con condition which provide a potential distribution dition and the light beam scanning condition in analogous in the main scan and subscan direc115 various ways. The relative distance X or Y tions. The method, therefore, allows images represents a ratio of a distance to each pixel to be recorded always with a desirable resolu- in the main scan or subscan direction, the tion and with an equal diameter both in the relative potential V a ratio of a surface poten main scan and subscan directions. tial on the drum after exposure to a surface Basically, the pixel diameters in the main 120 potential (uniform) associated with zero expo scan and subscan directions can be controlled sure energy, and the relative exposure energy if g, p, and Td are determined at the step of Q a ratio of actual exposure energy to maxi forming a latent image on a photoconductive mum exposure energy. Here, Figs. 13A, 14A element. This particular embodiment, which and 15A share the same data for illustration provides a potential distribution analogous in 125 purpose.

the main scan and subscan directions, is ef- The curves shown in Figs. 13A and 13B fectively applicable to both positive-to-positive were provided by a ratio p, of a beam dia recording and negative-to-negative recording. meter in the subscan direction to a pixel pitch The third embodiment described has con- in the main scan direction which was about centrated to a light beam condition and a light130 0.94. In Fig. 13A, the ratio p, of a beam 8 GB2184914A 8 diameter in the main scan direction to a pixel tribution of exposure energy Q provided when pitch in the main scan direction is varied a grid pattern is drawn pixel by pixel under while, in Fig. 1313, the ratio Tp of a light the conditions py =-- 1. 18, px =d 1.42 and Tp beam exposing time to a one-pixel scanning d 0.7. Fig. 17 shows a surface potential dis time is varied. The characteristics indicated by 70 tribution on a photoconductive element associ-' bold lines are associated with a condition ated with the exposure energy distribution of wherein the potential distribution is analogous Fig. 16. Although the graphs of Figs. 16 and in the main scan and subscan directions and, 17 are the results of computer simulation, it in such a condition, there are provided py - has been proved by experiments that when a 0.94, p, - 1.18 and Tp - 0.6 and, thereby, 75 latent image is formed on a photoconductive a light beam condition pylpx c:d 0.797 and a element under the above conditions and then light beam scanning condition p Tp 0.564. turned to a visible image, lines of the resulting The -beam diameter- referred to is defined grid are substantially identical in width in the by a sectional shape in a position which is e-2 main scan and subscan directions.

(about 13.5%) of a peak of a beam intensity 80 As described above, in accordance with the distribution having a Gaussian distribution. method of the fourth embodiment, when an The curves shown in Figs. 14A and 14B optical scan type electrophotographic record resulted from a ratio py of a beam diameter in ing apparatus is operated to record an image, the subscan direction to pixel pitch in the sub- a latent image associated with binary video scan direction which was about 1.18. In Fig. 85 data is formed electrostatically on a photocon 14A, the ratio p, of a beam diameter in -the ductive element under a particular light beam main scan direction to a pixel pitch in the condition and a particular light beam scanning main scan direction is varied while, in Fig. condition which provide a potential distribution 14B, the ratio Tp of a light beam exposing analogous in the main scan and subscan direc- time to a one-pixel scanning time is varied. 90 tions. The method, therefore, allows images The characteristics indicated by bold lines are to be recorded always with a desirable resolu associated with a condition wherein the po- tion and with the same pixel diameter in the tentiai distribution is analogous in the main main scan and subscan directions.

scan and subscan directions and, in such a Basically, the pixel diameters in the main condition, there are provided py c-- 1.18, 1), 95 scan and subscan directions can be controlled 1.42 and Tp ct 0.7 and, thereby, a light if 1), py and Tp are determined at the step of beam condition pyll), - 0.831 and a light forming a latent image on a photoconductive beam scanning condition py. Tp =t-, 0.826. element. This particular embodiment, which The curves shown in Figs. 15A and 15B provides a potential distribution analogous in resulted from a ratio p, of a beam diameter in 100 the main scan and subscan directions, is ef- the subscan direction to a pixel pitch in the fectively applicable to both positive-to-positive subscan direction which was about 1.42. In recording and negative-tonegative recording.

Fig. 15A, the ratio p., of a beam diameter in The third embodiment described has con the main scan direction to a pixel pitch in the centrated to a light beam condition and a light main scan direction is varied while, in Fig. 105 beam scanning condition. However, because 1513, the ratio Tp of a light beam scanning the quality of recorded images also depends time to a one-pixel scanning time is varied. upon other various factors such as scanning The characteristics indicated by bold lines are rate, beam power and developing level, such associated with a condition wherein the po- various factors need also be taken into ac tential distribution is analogous in the main 110 count in the selection of p,ll),, and p,. Tp if and subscan directions and, in such a condi- higher quality images are desired.

tion, there are provided py = 1.42, p;, =-- 1.65 The control over Td is readily practicable by and Tp=0.8 and, thereby, a light beam condimodifying the pulse width of binary video data tion pylp, f-- 0.861 and a light beam scanning at boundaries between image and non-image condition py. Tp f-- 1. 136. 115 portions.

By selecting other suitable values of py to As described above, the method in accor- provide other various parameters p., and Tp, dance with the third embodiment sets up a potential distributions which are analogous in particular light beam condition and a particular the main scan and subscan directions will be light beam scanning condition which make obtained. 120 each pixel recorded by an optical scan type It will be understood from the above analy- electrophotographic recording apparatus, parti sis and by experience that if 0.6 s pylp;,:s cularly one which uses minute light emitting 1.0 and 0.5:5 py - Tp::5 1.5 are satisfied, a segments as a light source, identical in dia potential distribution substantially analogous in meter in the main scan and subscan direc the main scan and subscan directions in prac- 125 tions, thereby allowing images to be recorded tice is achievable. with an excellent resolution.

Referring to Figs. 16 and 17, a two-dimen- A fifth embodiment of the present invention sional distribution is shown which is associ- elaborated to achieve the fifth object will be ated with one of the various conditions dis- described.

cussed hereinabove. Fig. 16 represents a dis- 130 Where an optical scan type electrophotogra- 9 GB2184914A 9 phic recording apparatus such as one 10 tribution and, in such a condition, there are shown in Fig. 1 is constructed to electrostati- provided & -- 1. 18, py cn:t 1.42 and Td =:

cally form a latent image on the drum 22 by 0.7. In this case, by changing the ratio py of a exposing it to a light beam modulated by bi- beam diameter in the subscan direction to a nary video data, the method in accordance 70 pixel pitch in the subscan direction from 1.42 with the fifth embodiment sets up a particular to 1.30 as represented by a bold line in Fig.

light beam condition which confines the ratio 11913, the latent image line width lc in the sub between a width lp of a latent image line sub- scan direction can be made greater than one stantially parallel to the developing direction in the main scan direction and the ratio 1c11p and a width lc of the same substantially per- 75 can be confined to the previously mentioned pendicular to the developing direction to an range.

optimum range of 1.0:5 1c11p:5 1.2. The curves shown in Figs. 20A and 20B Referring to Figs. 18A, 1813, 19A, 11913, resulted from a ratio p., of a beam diameter in 20A and 2013, there are shown examples of the main scan direction to a pixel pitch in the relative potentials V and relative exposure en- 80 main scan direction which was about 1.42. In ergy Q in relation to relative distances X and Fig. 20A, the ratio Td of a light beam expos Y in the main scan and subscan directions in ing time to a one-pixel scanning time is varied an exposure pattern which comprises one line while, in Fig. 2013, the ratio p, of a beam each of the main scan and subscan directions, diameter in the subscan direction to a pixel provided by varying the light beam condition 85 pitch in the subscan direction is varied. The and light beam scanning condition in positive- characteristics indicated by dotted lines in to-positive recording in various ways. The Figs. 20A and 20B share substantially the relative distance X or Y represents a ratio of same potential distribution and, in such a con a distance to each pixel pitch in the main scan dition, there are provided p, =t 1.42, p, -- or subscan direction, the relative potential V a 90 1.65 and Td = 0.8. In this case, by changing ratio of a surface potential on the drum 22 the ratio 1), of a beam diameter in the subscan after exposure to a surface potential (uniform) direction to a pixel pitch in the subscan direc associated with zero exposure energy, and the tion from 1.65 to 1.42 as indicated by a bold relative exposure energy Q a ratio of actual line in Fig. 20B and the pixel frequency duty exposure energy to maximum exposure en- 95 Td from 0.8 to 0.7 as indicated by a bold line ergy. in Fig. 20A, the latent image line width lc in The curves shown in Figs. 18A and 18B the subscan direction can be made greater were provided by a ratio p., of a beam dia- than one in the main scan direction and the meter in the main scan direction to a pixel ration 1c11p can satisfy the condition con- pitch in the main scan direction which was 100 cerned.

about 0.94. In Fig. 18A, the pixel frequency Further, if 1), is suitably varied so that, in the duty Td which is the ratio of an optical beam manne c16scried, the ratio p. of a beam dia exposing time to a one-pixel scanning time is meter in the subscan direction to a pixel pitch varied while, in Fig. 1813, the ratio p, of a in the subscan direction and/or the pixel fre beam diameter in the subscan direction to a 105 quency duty Td associated with a potential pixel pitch in the subscan direction is varied. distribution which is substantially identical in The characteristic indicated by a dotted line in the main scan and subscan directions is Fig. 18A and one indicated by a bold line in varied, the ratio 1c11p will satisfy the same Fig. 18B share substantially the same potential condition.

distribution and, in such a condition, there are 110 Taking one of the various conditions de provided l);, -- 0.94, py =t 1.18 and Td=-- 0.6. scribed so far for example, a two-dimensional In this case, by changing the pixel frequency distribution will be analyzed. When a pixie-by duty Td from 0.6 to 0.7 as indicated by a pixel grid pattern is drawn under the condi bold line in Fig. 18A, the latent image line tions l);, c-- 1.18, py = 1. 42 and Td 0.7 so width lc in the subscan direction can be made 115 that one dot line in each of the main and greater than one in the main scan direction subscan directions may be evaluated under and the ratio 1c11p can be confined to the the same conditions, the distributions shown previously mentioned range. in Figs. 21A-21C hold if the potential distribu The curves shown in Figs. 19A and 19B tion is substantially identical in the main and resulted from a ratio p., of a beam diameter in 120 subscan directions, and the distributions the main scan direction to a pixel pitch in the shown in Figs. 22A-22C if the line width ratio main scan direction which was about 1.18. In satisfies the condition 1. 0:5 1c11p:S 1.2.

Fig. 19A, the ratio Td of a light beam expos- Figs. 21A and 22A show distributions of rela ing time to a one-pixel scanning time is varied tive exposure energy Q each viewed in the while, in Fig. 1913, the ratio p, of a beam 125 main scan direction, Figs. 21B and 22B distri diameter in the subscan direction to a pixel butions of relative potentials each viewed in pitch in the subscan direction is varied. The the main scan direction, and Figs. 21C and characteristic indicated by a bold line in Fig. 22C distributions of relative potentials each 19A and one indicated by a dotted line in Fig. viewed in the subscan direction.

19B share substantially the same potential dis- 130 It will be apparent from the drawings that GB2184914A 10 the portion labeled A and B in Figs. 21 B, tube 34 is to be focused onto the surface of 21C, 22B and 22C represent lines extending the drum 40, which is fed in the subscan in the subscan direction, the potential being direction, the method in accordance with the slightly lower in the portions A than in the sixth embodiment provides a light beam condi- portions B. Needless to mention, the potential 70 tion and a light beam scanning condition distribution width is wider in the portions B which confine the ratio between the width lc than in the portions A. of a latent image line substantially parallel to The above analysis, coupled with experi- the developing direction and the width lc of a ence, teaches that if the ratio of the latent latent image line substantially parallel to the image line widths satisfy the condition 1.0:5 75 developing direction to an otimum range of 1c11p:5 1.2, images can be recorded with 1.0:5 1c11p:s 1.3.

desirable reproducibility dot on a one-dot line Referring to Figs. 23A, 2313, 24A, 2413, basis. 25A and 2513, there are shown examples of Concerning negative-to-positive recording, as relative potentials V and relative exposure en- distinguished from the above-described posi- 80 ergy Q in relation to relative distances X and tive-to-positive recording, it is necessary in Y in the main scan and subscan directions in tendency that the condition for setting up the an exposure pattern which comprises one line relation between line widths in the main scan in each of the main scan and subscan direc and subscan directions be inverted. In such a tions, provided by varying the light beam con case, too, the ratio]clip associated with an 85 dition and the light beam scanning condition in image portion needs to satisfy the previously positive-to-positive recording in various ways.

mentioned condition. While the method in ac- The relative distance X or Y represents a ratio cordance with this particular embodiment is of a distance to each pixel pitch in the main applicable to both the positive-to-positive re- scan or subscan direction, the relative poten cording and negative-to-negative recording, the 90 tial V a ratio of a surface potential on the application to postive-to-positive recording will drum after exposure to a surface potential prove particularly effective in view of the fact (uniform) associated with zero exposure en that the reproducibility of hairlines are inher- ergy, and the relative exposure energy Q a ently fair in the case of negative-to-positive ratio of actual exposure energy to maximum recording. The increase in the line width in the 95 exposure energy.

direction substantially perpendicular to the de- The curves shown in Figs. 23A and 23B veloping direction will be greately effected by were provided by a ratio py of a beam dia developing characteristics and velocity charac- meter in the main scan direction to a pixel teristics of a photoconductive element and, pitch in the main scan direction which was therefore, the ratio 1c11p has to be selected 100 about 0.94. In Fig. 23A, the ratio I);, of a taking such characteristics have into con- beam diameter in the main scan direction to a sideration. pixel pitch in the main scan direction is varied As described above, the method in accorwhile, in Fig. 2313, the pixel frequency duty Tp dance with the fifth embodiment selects an which is the ratio of a ligth beam exposing exposing beam diameter and/or a pixel fre- 105 time to a one-pixel scanning time is varied.

quency duty in an optical scan type electro- The characteristic indicated a dotted line in photographic recording appartus such that the Fig. 23A and one indicated by a bold line in latent image fine width in a direction substan- Fig. 23B share substantially the same potential tially perpendicular to the developing direction distribution and, in such a condition, there are becomes greater than in a direction substanprovided py=0.94, I).,= 1. 18 and Tp=0.6. In tially parallel to the same. Hence, even if the this case, by changing the beam diameter in image width is somewhat disturbed by fluctua- the main scan direction to the pixel pitch in tions in developing characteristics, moving the main scan direction from 1. 18 to 1.30 as velocity of a photoconductive element and indicated by a solid line in Figs. 2313, the line other factors, the method allows even a hair- 115 width]c in the subscan direction can be made line such as a one-dot line to be desirably greater than one in the main scan direction reproduced only if the line width ratio is pre- and the ratio 1c11p can be confined to the determined in consideration of the fluctuations. previously mentioed range.

A sixth embodiment directed to achieving The curves shown in Figs. 24A and 24B the sixth embodiment will be described. 120 were provided by a ratio py of a beam dia The method in accordance with the sixth meter in the subscan direction to a pixel pitch embodiment is applicable to, for example, the in the subscan direction which was about optical scan type electrophotographic record- 1. 18. In Fig. 24A, the ratio p,, of a beam ing apparatus 30 shown in Figs. 6 and 7 diameter in the main scan direction to a pixel which is of the type using, as a light source, 125 pitch in the main scan direction is varied the phosphor dot array tube 34 in which while, in Fig. 2413, the pixel frequency duty Tp phosphor elements are arranged in an array in is varied. The characteristic indicated by a the main scan direction in a pixel configura- bold line in Fig. 24A and one indicated by a tion. When a light beam modulated by binary dotted line in Fig. 24B share the substantially video data 32 and output from the dot array 130same potential distribution and, in such a con- GB2184914A 11 dition, there are provided py= 1. 18, px= 1.42 width is wider in the portions B than in the and Tp=0.7. In this case, by changing the portions A.

pixel frequency duty Tp from 0.7 to 0.6 as The above analysis, coupled with experi indicated by a bold line in Figs. 2413, the line ence, teaches that if the line width ratio sati width lc in the subscan direction can be made 70 sfies the condition 1. 0:: 1c11p:5 1.3, images greater than one in the main scan direction can be recorded with desirable reproducibility and the ratio 1c11p can be confined to the on a one-dot line basis.

previously mentioned range. Concerning negative-to-positive recording, as The curves shown in Figs. 25A and 25B distinguished from the above-described posi- were provided by a ratio p, of the beam diative-to-positive recording, it is necessary in meter in the subscan direction to the pixel tendency that the condition for setting up the pitch in the subscan direction which was relation between the line widths in the main about 1.42. In Fig. 25A, the ratio px of the scan and subscan directions be inverted. In beam diameter in the main scan direction to such a case, too, the ratio 1c11p associated the pixel pitch in the main scan direction is 80 with an image portion needs to satisfy the varied while, in Fig. 2513, the pixel frequency previously mentioned condition. While the duty Tp is varied. The characteristic indicated method in accordance with this particular em a dotted line in Fig. 25A and one indicated by bodiment is applicable to both the positive-to a dotted line in Fig. 25B share a substantially positive recording and negative-to-positive re identical potential distribution and, in such a 85 cording, the application to positive-to-positive condition, there are provided p,=1.42, recording will prove particularly effective in &=1.65 and Tp=0.8. In this case, by chang- view of the fact that the reproducibility of ing the pixel frequency duty Tp from 0.8 to hairlines are inherently fair in the case of nega 0.7 as indicated by a bold line in Figs. 25B tive-to-positive recording. The increase in line and the ratio & of the beam diameter in the 90 width and the direction substantially perpendi main scan direction to the pixel pitch in the cular to the developing direction will be main scan direction as indicated by a bold line greatly effected by developing characteristics in Fig. 25A from 1.65 to 1.42, the latent and velocity characteristics of a photoconduc image line width lc in the subscan direction tive element and, therefore, the ratio 1c11p has can be made greater than that in the main 95 to be selected taking them into account.

scan direction and the ration 1c11p can be co- As described above, the method in accor nfined in the previously mentioned range. dance with the sixth embodiment selects an Further, if 1), is suitably varied so that, in the exposing beam diameter and/or a pixel fre manner descried, the ratio p, of a beam dia- quency duty in an optical scan type electro meter in the main scan direction to a pixel 100 photographic recording apparatus, particularly frequency duty Tp and/or a pixel pitch in the one which uses miniature light emitting seg main scan direction associated with a potential ments as a light source, such that the latent distribution which is substantially identical in image line width in a direction substantially the main scan and subscan directions is perpendicular to the developing direction be- varied, the ratio 1c11p will satisfy the previ105 comes larger than one in a direction substan ously presented condition. tially parallel to the same. Hence, even if the Taking one of the various conditions de- image width is somewhat disturbed by fluctua scribed so far for example, a two-dimensional tions of developing characteristics, moving distribution will be analyzed. When a pixie-byvelocity of a photoconductive element and pixel grid pattern is drawn under the condi- 110 other factors, the method allows even a hair tions py= 1. 18, p,= 1.42 and Tp =0.7 so that line such as a one-dot line to be desirably one-dot line in each of the main and subscan reproduced only if the line width ratio is pre directions may be evaluated under the same determined in consideration of the fluctuations.

conditions, the distribution shown in Figs.

Claims

26A and 26B hold if the potential distribution 115 CLAIMS is substantially

identical in the main scan and 1. In an image recording method using an subscan directions, and the distributions optical scan type electrophotographic record shown in Figs. 27A and 27B if the the line ing apparatus, the improvement wherein a width ratio satisfies the condition 1.0:5 1c11p light beam scans such that a ratio 1c11p where 55:5 1.3. Figs. 26A and 27A show distributions 120 lp indicates a width of a latent image line of relative exposure energy Q each viewed in substantially parallel to a developing direction the main scan direction, Figs. 26B and 27B and lc indicates a width of a latent image line distributions of relative potentials each viewed substantially perpendicular to the developing in the main scan direction. direction satisfies a condition 1.0:5 1c11p:5 It will be apparent from the drawings that 125 1.
2.

the portions labeled A and B in Figs. 26B and 2. The improvement as claimed in claim 1, 27B represent lines extending in the subscan wherein the developing direction is substan direction, the potential being slightly lower in tially coincident with an intended direction of the portions A that in the portions B. Need- movement of a photoconductive element.

less to mention, the potential distribution 130
3.The improvement as claimed in claim 1, 12 GB2184914A 12 wherein a factor for determining the ratio 1c11p comprises at least one of an exposing beam diameter and a pixel frequency duty.
4. The improvement as claimed in claim 2, wherein a factor for determining the ratio 1c11p comprises at least one of an exposing beam diameter and a pixel frequency duty.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained.