Image forming apparatus having a plurality of image forming stations including devices and receiving sections for detachably receiving the devices

An image forming apparatus such as color electrophotographic printer has a plurality of image forming stations. Each image forming station includes an image forming cartridge and a toner cartridge mounted therein. The toner cartridge has a corresponding first engagement portion. The image forming cartridge has a receiving section with a corresponding second engagement portion. The receiving section detachably receives the corresponding toner cartridge therein with the second engagement portion fittingly engaging the first engagement portion. The first and second engagement portions are of a construction that they can be polarized such that the first engagement portions engage the second engagement portions in different engagement relations when the devices are received in the receiving sections, each of the toner cartridges being received in a corresponding one of the receiving sections. Such an engagement construction may also be applicable to the image forming cartridge and the receiving section formed in the body of the printer which receives the image forming cartridge. The image forming cartridges and the receiving sections are polarized such that they are fittingly engaged with each other in different engagement relations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image processing apparatus. 
2. Description of Related Art 
An electrophotographic printer is one of widely used image processing 
apparatuses and incorporates an image processing cartridge detachably 
mounted to the printer. The image processing cartridge includes a 
developer cartridge detachably mounted thereto. The image processing 
cartridge is a generally cylindrical container and holds toner therein. 
The toner is discharged through holes formed in the container which are 
adapted to open and close, and is supplied to the developing roller of the 
image processing cartridge. The developing roller then supplies the toner 
to the electrostatic latent image on the drum to develop the electrostatic 
latent image into a toner image. 
The toner image is then transferred by the transfer roller to the print 
medium and subsequently fused on the print medium. The medium is then 
discharged out of the printer after fixing. 
An electrophotographic printer designed to form color images incorporates 
image processing cartridges for the respective primary colors, and a 
developer cartridge for a specific color is detachably received in a 
cartridge-receiving section of the corresponding image processing 
cartridge. Deficiency of color printing systems involving separate 
developer cartridges for the constituent colors is in the inadvertent 
misplacement of the toner cartridges in the printer. Misplacement of the 
cartridges destroys printed color images. 
Therefore, the developer cartridges are designed to be in different shape 
according to color, thereby preventing inadvertent misplacement of the 
developer cartridges. 
Toners of the respective colors are not necessarily consumed at the same 
rate. It is quite often that a particular color is used more than any 
other colors. Colors used more than other colors depend on individual 
print data and therefore it is difficult to predict what color or colors 
should be manufactured more than other colors. Moreover, if the toner 
cartridges are different in shape according to colors, then it is 
difficult to determine how many unfilled cartridges should be manufactured 
for each color. 
However, a conventional electrophotographic printer requires an image 
processing cartridge and a developer cartridge for each primary color. 
Manufacturing developer cartridges different in shape necessarily 
increases the number of kinds of cartridges and manufacturing costs. 
In order to solve this drawback, electrophotographic printers has been 
proposed where the developer cartridge and the mounting construction 
therefor are of the same design and shape for all the toner colors, and 
one of ribs or the like formed at a specific area in the developer 
cartridge is cut off to selectively polarize the cartridge for a 
corresponding color. However, once the ribs are cut off, the individual 
cartridges become different shapes. If they are to be recycled, separately 
storing the developer cartridges according to shape is difficult and 
therefore adds cost to the recycled containers. This construction does not 
lend itself to recycling. 
SUMMARY OF THE INVENTION 
The present invention is to solve the aforementioned drawbacks of the 
conventional electrophotographic printers. 
An object of the invention is to provide an image processing apparatus 
where image quality is not destroyed due to inadvertent misplacement of 
the developer cartridges, and the toner cartridges can be recycled and 
manufactured at low cost. 
Another object of the invention is to provide an image processing apparatus 
where the toner cartridges and image processing cartridges for the 
respective colors are built only by assembling a limited number of 
standardized parts in different ways. 
An image forming apparatus has a plurality of image forming stations. Each 
image forming station includes an image forming cartridge and a toner 
cartridge mounted therein. The toner cartridge has a corresponding first 
engagement portion. The image forming cartridge has a receiving section 
has a corresponding second engagement portion. The receiving section 
detachably receives the corresponding toner cartridge therein with the 
second engagement portion fittingly engaging the first engagement portion. 
The first and second engagement portions are of a construction that they 
can be polarized such that the first engagement portions engage the second 
engagement portions in different engagement relations when the devices are 
received in the receiving sections, each of the toner cartridges being 
received in a corresponding one of the receiving sections. 
This engagement construction may also be applicable to the image forming 
cartridge and the receiving section formed in the body of the printer 
which receives the image forming cartridge. The image forming cartridges 
and the receiving sections are polarized such that they are fittingly 
engaged with each other in different engagement relations. 
Further a cope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific example, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
Embodiments of the invention will be described in detail with reference to 
the drawings. 
First Embodiment 
FIG. 1 illustrates a general construction of a color electrophotographic 
printer. 
Referring to FIG. 1, an electrophotographic color printer 11 includes four 
printing stations for forming yellow, magenta, cyan, and black images, 
respectively, aligned in this order from a print medium insertion side to 
a print medium discharge side. Each of the printing station includes an 
image forming cartridge with a toner cartridge for a corresponding color. 
Mounted at the printing stations are image processing cartridges 12Y, 12M, 
12C, and 12B, respectively. 
The image forming cartridges 12Y, 12M, 12C, and 12B are of the same 
construction and therefore only the cartridge 12Y will be described and 
the description of the other cartridges is omitted. 
The image forming cartridge 12Y includes an LED head, photoconductive drum 
16, charging roller 17, developing roller 19, developing blade 20, sponge 
roller 21, and developer cartridge 22. The LED head 13 illuminates the 
photoconductive drum 16 in accordance with image data. The charging roller 
17 uniformly charges the surface of the photoconductive drum 16. A toner 
container 18 holds toner of a corresponding color therein. The developing 
roller 19 develops an electrostatic latent image formed on the charged 
surface of the photoconductive drum 16 into a toner image. The developing 
roller 19 is in contact with a developing blade 20. The developing roller 
19 also in contact with a sponge roller 21 and receives toner from the 
sponge roller 21. The developer cartridge 22 is detachably mounted to the 
cartridge 12Y via a mounting construction provided in the cartridge 12Y. A 
developing station is constituted of the toner container 18, developing 
roller 19, developing blade 20, sponge roller 21, and developer cartridge 
22. The image forming cartridges 12Y, 12M, 12C, and 12B include a lower 
housing 23 and upper housings 24Y, 24M, 24C, and 24B, respectively. 
Disposed at a lower part of the electrophotographic printer is a paper 
feeding mechanism 71. A print medium is fed by a feed roller 72 from a 
paper tray to a registry rollers 73. The registry roller 73 in turn feeds 
the print medium to a transport belt 74 which runs in a direction shown by 
arrow B. The print medium is attracted to the transport belt 74 and 
travels through the respective image forming cartridges 12Y, 12M, 12C, and 
12B mounted to the respective stations, passing between the 
photoconductive drum 16 and the transfer roller 75 of the respective image 
forming cartridge so that images of corresponding colors are superposed 
one over the other on the print medium. After having passed through all of 
the image forming cartridges, the image printed on the medium becomes a 
full color toner image. The full color toner image is then fixed at the 
fixing station 76. 
The operation of the electrophotographic printer 11 will now be described. 
Upon activation of the printing operation, the print medium is advanced by 
the feed roller 72 from the paper tray. When the leading edge of the print 
medium has reached the registry rollers 73, the feed roller 72 is stopped 
by a clutch mechanism, not shown, while the print medium is being 
transported further by the registry rollers 73. 
When the leading edge of the print medium has reached the transport belt 
74, the transport belt 74 attracts the print medium thereto and transports 
the print medium to the yellow image forming cartridge 12Y. At this time, 
the LED head 13 is energized at predetermined timings in accordance with 
the image data and illuminates the surface of the photoconductive drum 16 
to form an electrostatic latent image on the surface. The photoconductive 
drum 16 is rotated in a direction shown by arrow A. When the electrostatic 
latent image reaches the developing roller 19, the developing roller 19 
applies the toner to the photoconductive drum 16 to develop the 
electrostatic latent image into a toner image. 
Subsequently, the toner image on the photoconductive drum 16 is transferred 
to the print medium by the transfer roller 75. In this manner, the yellow 
toner image is transferred to the print medium. Likewise, magenta, cyan, 
and black toner images are subsequently formed by the image forming 
cartridges 12M, 12C, and 12B, respectively, and transferred by the 
corresponding transfer rollers 75 to print one over the other on the print 
medium, thereby forming a full color toner image. The print medium is 
subsequently transported to the fixing station 76 where the toner image is 
fixed into a full color image, and the print medium is ejected out of the 
fixing station 76. 
The developer cartridge 22 will now be described. 
FIG. 2 is a perspective view of a developer cartridge according to the 
first embodiment of the invention. FIG. 3 is a cross-sectional view of the 
developer cartridge taken along lines 3--3 of FIG. 2. 
As shown in FIGS. 1 and 2, a cylindrical inner case 33 opens at both 
longitudinal ends thereof and is closed by a cap 34 at one end and closed 
by another cap 31 formed of a white, semitransparent, or transparent 
material. The cap 31 slidably fits over the inner case. The cap 34 has a 
lever 35 formed in one piece construction with the cap 34. A cylindrical 
outer case 32 rotatably holds the inner case 33 therein. Rotation stoppers 
37 project from the outer case diametrically at two circumferential 
locations. The cap 31 is formed with four cutouts 31b into which the 
stoppers 37 are fitted so that the cap 31 is placed in position relative 
to the outer case 32. The cutouts are located relative to the central axis 
of the cylindrical cap 31 to diametrically oppose each other. 
The outer case 32 and inner case 33 are formed with an opening 32a and an 
opening 33a therein, respectively, and the toner in the inner case 33 can 
be discharged when the inner case has been rotated till the openings 32a 
and 33a are aligned with each other. Once the developer cartridge 22 has 
been mounted to the cartridge-receiving section in a corresponding image 
forming cartridge, for example, 12Y, the cap 34 and inner case 33 can be 
rotated together relative to the outer case 32 when the lever 35 is 
rotated. When the lever 35 has been rotated to a position where the 
openings 32a and 33a are aligned each other, the toner in the inner case 
33 is cascaded into the toner container 18 through the openings 32a and 
33a. The developer cartridge 22 is mounted to the cartridge-receiving 
section such that the rotation stoppers 37 lie in a horizontal plane with 
the openings 32a facing down. 
The cap 31 is formed with a groove-like recess 31a in its circular end 
surface 31c. The recess 31a radially extends substantially from the center 
of the circular surface 31c. 
FIGS. 4, 5, 6, and 7 are side views of the yellow, magenta, cyan, and black 
developer cartridges according to the first embodiment. 
Referring to FIGS. 4-7, the toner container 18 (FIG. 1) is disposed at the 
lower parts of the figures. FIG. 4 shows the developer cartridge 22 for 
yellow toner. The cutouts 31b in the cap 31 are engaged with the rotation 
stoppers 37 of the outer case 32 such that when the developer cartridge 32 
is positioned with the opening 22a facing down, the recess 31a extends 
upwardly from the center of the circular end surface of the developer 
cartridge 22. 
For the developer cartridge 22 for magenta toner, the cutouts 31b are 
engaged with the rotation stoppers 37 as shown in FIG. 5 such that when 
the developer cartridge 22 is positioned with the opening 32a facing down, 
the recess 31a extends in a direction of travel of the print medium shown 
by arrow T, upstream of the center of the circular end surface 31c of the 
developer cartridge 22. 
For the developer cartridge 22 for cyan toner, the cutouts 31b are engaged 
with the rotation stoppers 37 as shown in FIG. 6 such that when the 
developer cartridge 22 is positioned with the opening 32a facing down, the 
recess 31a extends downwardly. 
For the developer cartridge 22 for black toner, the cutouts 31b are engaged 
with the rotation stoppers 37 as shown in FIG. 7 such that when the 
developer cartridge 22 is positioned with the opening 32a facing down, the 
recess 31a extends in the direction of travel of the print medium shown by 
arrow T, downstream of the center of the circular end surface of the 
developer cartridge 22. 
The cartridge-receiving sections in which the developer cartridges 22 are 
received will now be described. FIGS. 8, 9, 10, and 11 illustrate the 
cartridge-receiving sections of the image forming cartridges for yellow, 
magenta, cyan, and black, respectively, when seen in a direction shown by 
arrow R in FIG. 12. 
The cartridge-receiving sections are generally long, semi-cylindrical in 
shape and includes a support 62, an engagement wall 63, and a wall 64. The 
engagement wall 63 and the wall 64 are oppositely formed at longitudinal 
ends of the cartridge-receiving section. The engagement wall 63 has a 
projection 24b that project inwardly of the cartridge-receiving sections. 
A semi-cylindrical support 62 receives and supports the developer 
cartridge 22 from under the developer cartridge. The engagement wall 63 
and the wall 64 are of generally round plate-like shape. When the 
developer cartridge 22 is mounted in the cartridge-receiving section, the 
wall 64 opposes the cap 34, the engagement wall 63 opposes the cap 31 of 
the developer cartridge 22, and the projection 24b engages the recess 31a 
in the developer cartridge 22. Stopper-receiving edges 24c receive and 
support the rotation stoppers 37 of the developer cartridge 22 from under 
when the developer cartridge 22 is mounted into the receiving section. 
A retainer 24a is formed on top of the engagement wall 63 and projects 
inwardly of the cartridge-receiving section. When the developer cartridge 
22 is received in the receiving section, the retainer 24a engages the 
circumference of the cap 31 from above to prevent the developer cartridge 
22 from rising. 
As shown in FIG. 8, the projection 24b for the yellow image forming 
cartridge 12Y projects into the cartridge-receiving section and extends 
upwardly from the center of the circular surface of the engagement wall 
63. As shown in FIG. 9, the projection 24b for the magenta image forming 
cartridge 12M extends in the direction T of travel of the print medium, 
upstream of the center of the circular surface of the engagement wall 63. 
As shown in FIG. 10, the projection 24b for the cyan image processing 
cartridge 12C extends downwardly from the center of the circular surface 
of the engagement wall 63. As shown in FIG. 11, the projection 24b for the 
black image forming cartridge 12B extends in the direction T of travel of 
the print medium, downstream of the center of the circular surface of the 
engagement wall 63. 
FIG. 12 illustrates the developer cartridge 22 for cyan when a user 
attempts to mount it into the receiving section of the upper housing of 
the image forming cartridge 24Y for yellow. 
The projection 24b of the receiving section extends upwardly from the 
center of the engagement wall 63 while the recess 31a of the cap 31 
extends downwardly from the center of the cap 31. Therefore, the 
projection 24b cannot enter the recess 31a, preventing the developer 
cartridge 22 from being received into the receiving section. 
Likewise, if the user attempts to mount the developer cartridge 22 for 
magenta or black into the cartridge-receiving section for the developer 
cartridge 22 for yellow toner, these developer cartridges 22 interfere 
with the projections 24b which are oriented in directions different from 
the direction in which the recess 31a of the developer cartridges extends. 
FIG. 13 illustrates the developer cartridge 22 for yellow when it has been 
mounted into the receiving section of the upper housing of the yellow 
image forming cartridge 24Y. The projection 24b of the receiving section 
extends upwardly from the center of the engagement wall 63 and the recess 
31a also extends upwardly from the center of the cap 31. Thus, when the 
developer cartridge 22 for yellow is introduced into the receiving 
section, the projection 24b is smoothly received into the recess 31a, 
thereby preventing inadvertent misplacement of the developer cartridge 
during the manufacture of the printer. 
As mentioned above, the cap 31 is mounted to the outer case 32 at angularly 
different positions relative to the rotation stopper 37 of the developer 
cartridge 22 according to the color of the toner contained therein. This 
construction eliminates the need for manufacturing the developer 
cartridges 22 of different shapes depending on toner colors, and lends 
itself to the standardization of the cartridge construction and lowers the 
manufacturing cost of the printer 11. 
Assembling the caps 31 to the outer cases 32 at different angular positions 
relative to the rotation stoppers 37 polarizes the developer cartridges 
such that the developer cartridges are accepted only by corresponding 
cartridge-receiving sections. Thus, developer cartridges for one color 
after use can be reassembled to make developer cartridges for another 
color by simply assembling the standardized parts in different ways. This 
makes recycling of the developer cartridge 22 easy and practical, 
facilitating the storage of the components as well as lowering the printer 
cost. 
Only the developer cartridge 22 is formed with cutouts 31b, so that caps 31 
can be arranged in different ways. However, the projection 24b can be made 
as a separate part and the engagement wall 63 may be formed with holes or 
the like so that the projection 24b can be detachably mounted to the 
holes, thereby allowing mounting of the projection 24b in different 
directions. 
Second Embodiment 
In the first embodiment, the projections 24b are oriented in different 
directions depending on the colors of toner contained in the developer 
cartridges. The orientations of the projections 24b are fixed, and 
therefore the cartridge-receiving section cannot be standardized. A second 
embodiment solves this drawback. 
FIG. 14 is a perspective view of an image forming cartridge according to 
the second embodiment. 
The image forming cartridges 12Y, 12M, 12C, and 12B are of the same 
construction and therefore only the image forming cartridge 121Y for 
yellow will be described. 
The engagement wall 63 is formed with a large-diameter hole 24e in its 
center, two small-diameter holes 24d vertically diametrically opposing 
with respect to the large-diameter hole 24e, and two small-diameter holes 
24d horizontally diametrically opposing with respect to the large-diameter 
hole 24e. An engagement piece 40 has a large-diameter projection 40a and a 
small-diameter projection 40b which project parallel to each other. 
The large-diameter projection 40a fits into the large-diameter hole 24e and 
the small-diameter projection 40b fits into one of the four small-diameter 
holes 24d depending on which developer cartridge the receiving section 
receives thereinto. In this manner, the cartridge-receiving section can be 
polarized to accept only a developer cartridge of a corresponding color. 
FIGS. 15, 16, 17, and 18 illustrate the image forming cartridges for 
yellow, magenta, cyan, and black, respectively. 
As shown in FIG. 15, the engagement piece 40 for the yellow image forming 
cartridge 12Y extends upwardly from the center of the circular surface of 
the engagement wall 63. As shown in FIG. 16, the engagement piece 40 for 
the magenta image forming cartridge 12M extends in the direction T of 
travel of the print medium, upstream of the center of the circular surface 
of the engagement wall 63. As shown in FIG. 17, the engagement piece 40 
for the cyan image forming cartridge 12C extends downwardly from the 
center of the circular surface of the engagement wall 63. As shown in FIG. 
18, the engagement piece 40 for the black image forming cartridge 12B 
extends in the direction T of travel of the print medium, downstream of 
the center of the circular surface of the engagement wall 63. 
The operation for mounting the developer cartridge 22 to the receiving 
section is the same as that in the first embodiment and therefore detailed 
description thereof is omitted. 
The image forming cartridges are initially mounted in the printer at the 
factory, and therefore, the engagement pieces 40 are assembled to the 
image forming cartridges by the assembly worker. The image forming 
cartridges may be also sold alone and mounted into the printer by the 
user, in which case the engagement piece 40 is mounted by the user to an 
appropriate position according to the user's desired color of toner. 
The engagement wall 63 and developer cartridge 22 are formed with holes 24d 
and cutouts 31b, respectively, so that both engagement piece 40 and cap 31 
can be arranged in different ways. However, either the engagement wall 63 
or developer cartridge 22 may be formed with no holes or cutouts so that 
the developer cartridge or the image forming cartridge assembled for a 
specific color of toner cannot be reassembled for another color. 
Third Embodiment 
In the aforementioned second embodiment, the engagement wall 63 accepts 
only one projection 40. A third embodiment is directed to the engagement 
wall 63 which accepts more than one projections. 
FIGS. 19, 20, and 21 are perspective views of the image forming cartridge, 
developer cartridge, and engagement piece of the third embodiment, 
respectively. 
The image forming cartridges 12Y, 12M, 12C, and 12B are of the same 
construction and therefore only the yellow image forming cartridge 12Y 
will be described. 
As shown in FIGS. 19-21, a developer cartridge 42 has engagement pieces 43a 
and 43b which are detachably mounted to one end surface of the developer 
cartridge 42. A cartridge-receiving section 66 of the image forming 
cartridge 12Y has engagement projections 44a and 44b which are detachably 
mounted to the engagement wall 66. 
As shown in FIGS. 20 and 21, the developer cartridge 42 has a plurality of 
pairs of holes 45, holes in each pair being aligned vertically, and the 
engagement wall 66 has a plurality of pairs of holes 46, holes 46 in each 
pair being also aligned vertically. A total of eight holes 45 and a total 
of eight holes 46 are provided. Engagement pieces 43a and 43b each can be 
selectively fitted into any pair of holes 45 while engagement pieces 44a 
and 44b each can be selectively fitted into any pair of holes 46. The 
engagement pieces 43a-43b and 44a-44b are mounted during the manufacture 
of the printer. 
The engagement pieces 43a-43b and engagement pieces 44a-44b are mounted so 
that they do not interfere with each other when the developer cartridge is 
attached into the cartridge-receiving section. A total of 6 different 
combinations of locations of the engagement pieces can be made so that the 
developer cartridges and cartridge-receiving sections can be polarized in 
six different ways. For the same reason as in the second embodiment, the 
engagement pieces 43a-43b and 44a-44b may be mounted at the factory or in 
the field by the user. 
While the first to third embodiments have been described with respect to 
the electrophotographic printer 11, the construction may also be 
applicable to copying machines and printing apparatuses using developer 
cartridges, or to ink jet printers, copying machines, and other printing 
apparatuses using ink cartridges. 
Although the engagement walls 63 and 66 are formed to oppose the 
longitudinal end surfaces of the developer cartridges 22 and 42, 
respectively, the engagement pieces may be formed at any other locations 
that oppose part of the developer cartridges. 
The engagement wall 66 and developer cartridge 42 are formed with holes 46 
and holes 45, respectively, so that both engagement pieces 44a-44b and 
43a-43b can be arranged in different ways. However, either the engagement 
wall 66 or developer cartridge 42 may be formed with no holes therein so 
that the engagement pieces are provided at fixed locations and cannot 
detachably reassembled for different ways. 
Fourth Embodiment 
In the first to third embodiments, the image forming cartridges 12Y, 12M, 
12C, and 12B are each mounted to a corresponding mounting location which 
is provided in the electrophotographic printer 11. There is possibility of 
image forming cartridges being misplaced when the user replaces a 
plurality of image forming cartridges at a time. Such a misplacement 
destroys the quality of a printed color image. 
A fourth embodiment is directed to a construction where inadvertent 
misplacement of the image forming cartridges is prevented when the image 
forming cartridges are mounted to the printing stations. FIG. 22 is a 
perspective view, illustrating the image forming cartridge immediately 
before the image forming cartridge is mounted to the printing station. 
FIG. 23 is a perspective view, illustrating the body of an 
electrophotographic printer. 
The image forming cartridges 12Y, 12M, 12C, and 12B are of the same 
construction and therefore only the image forming cartridge 12Y is 
described. The image forming cartridge 12Y includes an upper housing 24Y 
with a developer cartridge mounted thereon and a lower housing 23, and is 
assembled to the electrophotograhic printer from above. There are provided 
engagement pieces 50a-50b and engagement pieces 52a-52b for polarizing the 
image forming cartridges and corresponding cartridge-receiving sections, 
respectively, to prevent inadvertent misplacement of the image forming 
cartridges into the electrophotographic printer. The engagement pieces 
50a-50b and engagement pieces 52a-52b are mounted such that they do not 
interfere with each other when the image forming cartridge is attached 
into the printer. A total of 6 different combinations of locations of the 
engagement pieces can be made so that the developer cartridges and 
cartridge-receiving sections can be polarized in six different ways. 
Each of the engagement pieces 52a and 52b has parallel projections 72 and 
is detachably fitted into a pair of holes 51a formed in the 
cartridge-receiving section 51. The image forming cartridge 12Y has 
engagement pieces 50a and 50b. Each of the engagement pieces 50a and 50b 
has two parallel projections 71 and is detachably mounted into a pair of 
holes 23a formed in a side surface of a lower housing 23. The 
cartridge-receiving section 51 on the body of the printer is formed with a 
wide recess 51c and a narrow recess 51b therein. The wide recess 51c is 
formed with a plurality of pairs of holes 51a, each pair including 
vertically aligned two holes 51a. 
The lower housing 23 is formed with a plurality of pairs of holes 23a, each 
pair including two vertically aligned holes and engagement pieces 71 are 
fitted into pairs of holes 23a. A total of eight holes 23 and a total of 
eight holes 51a are provided. Two engagement pieces 50a and 50b and two 
engagement pieces 52a and 52b are selectively fitted into any two pairs of 
holes 23a and holes 51a, respectively. Therefore, six different 
combinations are possible in polarizing the image forming cartridges 
according to toner color. 
The engagement pieces 50a-50b and engagement pieces 52a-52b are mounted 
such that they do not interfere with each other when the image forming 
cartridge is mounted to the body of the printer. 
FIGS. 24-27 are side views of the image forming cartridges for yellow, 
magenta, cyan, and black, respectively. FIGS. 28-31 illustrate 
cartridge-receiving sections for image forming cartridges for yellow, 
magenta, cyan, and black. 
FIGS. 24-27 show engagement pieces 50a and 50b which have been mounted to 
the holes in the lower housing 23. A print medium travel in a direction 
shown by arrow T. FIGS. 24, 25, 26, and 27 show the positions of the 
engagement pieces 50a and 50b for yellow, magenta, cyan, and black, 
respectively, mounted to the lower housing 23. 
FIGS. 28, 29, 30, and 31 show the positions of the engagement pieces 52a 
and 52b for yellow, magenta, cyan, and black, respectively. As is clear 
from FIGS. 24-31, the image forming cartridges for yellow, magenta, cyan, 
and black can be received into corresponding cartridge-receiving sections 
without inadvertent misplacement. 
For example, if the user attempts to mount the image forming cartridge for 
yellow into the cartridge-receiving section for magenta, the engagement 
piece 50b interfere with the engagement piece 52b, preventing the user 
from misplacing the image forming cartridge for yellow. For the same 
reason as in the second embodiment, the engagement pieces may be mounted 
at the factory or in the field by the user. 
For example, an electrophotographic printer 11 using a plurality of image 
forming cartridges requires that the respective image forming cartridges 
are spaced apart very accurately. Therefore, a main frame is usually made 
of a metal material and the side frame having the cartridge-receiving 
section 51 formed therein is molded from a resin. According to the fourth 
embodiment, the construction of the side frame can be the same for all the 
colors and therefore allows standardization of the side frame and improves 
production efficiency of the side frame. 
The cartridge-receiving section 51 and image forming cartridge 12 are 
formed with holes 51a and holes 23a, respectively, so that both engagement 
pieces 52a-52b and 50a-50b can be arranged in different ways. However, the 
either cartridge-receiving section 51 or image forming cartridge 12 may be 
formed with no holes so that the engagement pieces are provided at fixed 
locations and cannot detachably be reassembled for different ways. 
Fifth Embodiment 
FIG. 32 is a perspective view of the cartridge-receiving section 51 
according to a fifth embodiment. FIG. 33 is a cross-sectional side view 
taken along lines 33--33 FIG. 32. FIG. 34 illustrates the on-off states of 
the switches for the respective colors. FIG. 35 is a block diagram showing 
the controlling unit of the cartridge-receiving sections 51. 
Just as in the fourth embodiment, each of the image forming cartridges 12Y, 
12M, 12C, and 12B has the engagement pieces 50a and 50b detachably fitted 
into the holes 23a. The cartridge-receiving section 51 is provided with 
micro switches SW1-SW4 in alignment with the pair of holes 23a. When the 
image forming cartridge is mounted in the cartridge-receiving section 51, 
the engagement pieces 50a and 50b push the lever of the micro switch 
opposing the engagement pieces. Thus, a set of four switches SW1-SW4 
provides a four-bit binary signal which expresses a specific combination 
of locations of the engagement pieces 50a and 50b. This four-bit binary 
signal is sent to the controller 55 shown in FIG. 35 so that the 
controller 55 can indicate to the user what toner color of 
image-processing cartridge has been mounted in the cartridge-receiving 
section 51. The controller 55 may also indicate to the user when the image 
forming cartridge is misplaced. The controller 55 sends image data via a 
driver 58a, 58b, 58c, 58d to an LED head 13a, 13b, 13c, 13d only when the 
cartridge-receiving sections 51 has received the corresponding image 
forming cartridges. 
Modification 1 of the Fifth Embodiment 
FIG. 36 is a perspective view of a modified cartridge-receiving section 51 
according to a fifth embodiment. FIG. 37 is a cross-sectional side view 
taken along lines 37--37 FIG. 36. The modified cartridge-receiving section 
51 may have holes 51a into which engagement pieces 52a and 52b of the same 
construction as those in the fourth embodiment are fitted. When the 
engagement piece is fitted into the holes 51a, the engagement piece pushes 
the lever of a corresponding switch to switch on. Thus, the controller 55 
can detect the location of the engagement pieces 52a and 52b, and 
indicates to the assembly personnel whether the engagement pieces 52a and 
52b have been properly assembled. 
While the fourth and fifth embodiments have been described with respect to 
the electrophotographic printer 11, the construction may also be 
applicable to copying machines and printing apparatuses using image 
forming cartridges, or to ink jet printers, copying machines, and other 
printing apparatuses using ink cartridges. 
Although the cartridge-receiving section 51 is formed on the side frame to 
oppose the longitudinal end surface of the image forming cartridge, the 
cartridge-receiving section 51 may be formed at any other location where 
the cartridge-receiving section opposes part of the developer cartridge. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims. 
Modification 2 of the Fifth Embodiment 
Modification 2 differs from the fifth embodiment in the operation of the 
controller 55. The controller 55 receives the signals from switches 
SW1-SW4 and can therefore identify receiving sections into which the 
respective image forming cartridges of yellow, magenta, cyan, and black 
are mounted. In other words, the image forming cartridges of yellow, 
magenta, cyan, and black can be correctly identified by the controller 55 
regardless of which receiving section each cartridge is placed into. Since 
the receiving sections are identified in terms of color, the controller 55 
can determine print data which should be supplied to each of the drivers 
58a-58d for first to fourth LED heads 13a-13d. This modification relieves 
the users of the problem where the respective image forming cartridges 
must be placed into corresponding receiving sections.