Toner image fixing control process and apparatus in electrostatic copying machine

The copying rate of an electrophotographic copying machine of constant paper advance speed including a toner image fixing unit which is selectively preset to predetermined values in increment inverse relationship to the thickness of the copy sheets employed, so that copy sheets of greater thickness are fed to the fixing unit for lesser feed rate than the thinner standard sheets, whereby the copy sheets are adequately heated at the different thicknesses. Following the termination of a copy sequence of thicker sheets at reduced feed rate, the copy machine automatically reverts to its rate setting for standard thickness sheets. In copying with standard thickness sheets, the period of the first copying cycle is greater than that for subsequent sheets and the copying rate with the thicker sheets is the same as that for the first copy with standard thickness sheets. A microcomputer network with a rate selector switch programs the copying machine in the above manner.

BACKGROUND OF THE INVENTION 
The present invention relates generally to improvements in the control of 
the operation of an electrostatic copying machine and it relates 
particularly to an improved method and apparatus for fixing toner images 
in accordance with the thickness of the copy paper which is fed to a fuser 
at constant paper feeding speed. 
Sheets of copy paper employed in conventional electrostatic copying 
machines are generally limited to a narrow range of thicknesses (weights), 
for example, to the range of about 50 to 85 g/m.sup.2. The conventional 
office paper is included in this range. In recent years, however, there 
has been a demand for electrostatic copying machines which can be used 
with thicker papers weighting 100 to 160 g/m.sup.2, such as postal cards, 
labels, offset master sheets, etc., and such machines have become 
commercially available. The use of thick paper poses problems in the 
fixing of the copy as well as in the path of transport of the copy paper 
and in the image transfer station. In thermally fixing toner to a copy 
sheet for the development of a latent image, it is necessary to fuse the 
toner and heat the copy sheet to some extent at the same time. 
Accordingly, when the toner is to be fixed to the same degree on a copy 
sheet of conventional thickness and on a thicker copy sheet of different 
heat capacity, the latter requires a larger amount of heat in accordance 
with the difference in thickness. To meet this requirement, it has 
heretofore been a practice to set the fixing unit at a higher temperature 
only when using copy sheets of greater thickness, or to set the unit to a 
constant temperature at which the toner images can be fixed to thick 
sheets. With such a method, however, the fixing unit is not satisfactorily 
operable for thick copy sheets unless the unit has a heater of increased 
power capacity to compensate for a reduction in the temperature of the 
unit when continuously producing a plurality of copies. Especially in the 
case of copying machines adapted for a relatively short copy processing 
time wherein the copy processing time means the period of time consumed in 
processing each copy during a copying operation, for example, of about 20 
to 30 copies per minute, it is almost practically impossible to restrict 
the overall power consumption to the limit of the conventional household 
power supply (100 V, 15A in Japan; 115 V, 15A in U.S.). Additionally, the 
latter of the two methods mentioned above is uneconomical since the fixing 
unit, when operating for copy sheets of conventional thickness, consumes a 
larger quantity of heat than is needed. On the other hand, a copying 
machine has been proposed which is so controlled that the copy processing 
time is reduced in accordance with a reduction in the temperature of the 
fixing unit to maintain the unit at least at a temperature below which 
improper fixing will result (Japanese Laid Open Patent Application 
Tokkaisho No. 54-80135). Another copying machine has also been proposed in 
which a copying start instruction is given only when the detected 
temperature of the fixing unit is no lower than a reference temperature to 
permit no copying operation at temperatures that would cause improper 
fixing (Japanese Laid Open Patent Application Tokkaisho No. 54-109446). 
With these machines, however, the variations in the temperature of the 
fixing unit, namely, the drop and recovery of the temperature are allowed 
to spontaneously occur and influence the copying processing time interval, 
producing varying copy processing times. When such machine is featured by 
a short copying processing time, the performance of the machine is still 
unsatisfactory in that the copying operation requires indefinite varying 
times. 
SUMMARY OF THE INVENTION 
It is a principal object of the present invention to provide in an 
electrostatic copying machine an improved process and system by which 
toner images are optimumly fixed at a copying processing time 
predetermined in accordance with the thickness of the copy paper which is 
fed to a fuser at constant paper feeding speed, employed without 
necessitating increased power consumption and with overcoming the 
aforesaid disadvantages and drawbacks heretofore experienced. 
Another object of the present invention is to provide an improved process 
and system characterized by their reliability, efficiency and high 
adaptability and versatility. 
The present invention contemplates the provision in an electrostatic 
copying machine a toner fusion operation control process and system 
characterized in that at least when a plurality of copies are to be made 
with the use of copy sheets of varying thicknesses which are fed to a 
fuser at a constant speed, the interval or period of time for processing 
each copy during at least a continuous copying operation is set in 
respectively different modes in accordance with the thickness of the 
processed copy sheets, to process a sheet for a preset period of time 
longer than that for another sheet thinner than said sheet. 
Advantageously the different modes include a first copy processing mode 
having a predetermined processing time and a multi-copy processing mode 
having shorter processing times than the first copy processing mode, the 
continuous copying operation of the standard sheet proceeding in 
accordance with said multi-copy processing mode, the continuous copying 
operation of thick sheets proceeding in accordance with the first copy 
processing mode and a first copying operation of the standard sheet and 
the thick sheet being effected by the first copy processing mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Illustrated in FIG. 1 is an electrophotographic copying machine to which 
the present invention is applied and which includes a photoconductive drum 
2 rotatably mounted in a suitable portion of the main housing of copying 
machine 1. Arranged around the drum 2 in the known manner and of known 
construction are a sensitizing charger 3, a toner developing unit 4, a 
transfer charger 5, a separating charger 6, a separating pawl, a cleaning 
unit 8, etc. When the drum 2 is driven in a counterclockwise direction, 
the sensitizing charger 3 charges the surface of the drum, which is 
exposed to the image of an original (not shown) placed on a glass plate 10 
and scanned by an optical system 9 and projected onto drum 2. The latent 
electrostatic image formed on the drum surface is converted by the 
developing unit 4 to a toner image, which is then transferred by the 
transfer charger 5 onto a paper copy sheet 11 fed to the drum in timed 
relation with its rotation. The copy sheet 11 bearing the toner image is 
separated from the drum surface by the charger 6 and pawl 7 and fed to a 
fixing unit 14 comprising a heat roller 12 and a press roller 13. The 
image is fixed by the heat roller 12, and the copying sheet is discharged 
from the machine 1. With the drum 2 in continued rotation after the 
transfer of the image, the cleaning unit 8 removes the residual toner from 
the drum in preparation for the following copying cycle. 
As shown in FIG. 2 which illustrates variations in the surface temperature 
of the heat roller 12 of the fixing unit 14, after warm-up WU, the 
temperature overshoots as at OS and then settles at a set value TO. After 
a standby period SB, the machine is initiated onto a continuous operation 
CC for producing copies and as a consequence the temperature of the roller 
12 abruptly drops as at SD. At the same time, the heater is energized to 
gradully again raise the temperature since the amount of heat produced by 
the heater is greater than that absorbed by the copy paper 11. Indicated 
at TL is the lowest temperature of the heat roller 12 at which the toner 
can be properly fixed, and this temperature is dependent on the copy paper 
feeding speed, the type of the toner used, the kind of the copy paper and 
other parameters. To assure the proper fixing of the toner for making 
copies continuously at the temperature TO, the power consumption of the 
heater, and the other parameters must be so determined that the 
temperature resulting from the abrupt drop SD will not be lower than the 
temperature TL. 
Suppose the value TO, power consumption, etc. are set for a standard 
thickness copy paper, if copy paper of a different thickness, particularly 
copy paper of greater thickness and higher heat capacity than the standard 
paper, is then used in a continuous copying operation, the amount of heat 
removed by the paper increases to result in an improper or inadequate 
fixing of the toner. 
FIG. 3 shows the variations in the temperature of the heat roller 12 when 
thick copy paper is used for a continuous copying operation. The 
solid-line curve represents the temperature variations for the standard 
copy paper (about 50 to 85 g/m.sup.2). TO and TL are the same as those 
shown in FIG. 2. The dotted curve represents the temperature variations 
for the thick paper (about 100 to 160 g/m.sup.2). Since the lowest 
temperature TL' permitting the proper fixing of the toner for the thick 
paper is higher than TL for the standard paper by .alpha., the set 
temperature TO' is TO+.alpha.. 
However, when the machine is brought into a continuous operation with the 
use of the thick paper, the amount of heat absorbed or removed by each 
sheet is larger than is the case with the standard paper. Consequently 
there is a sharper temperature drop, as at SD, than in the latter case to 
a level which is lower than TL'. Moreover, recovery to the temperature 
setting TO' takes a longer period of time. This condition may be avoided 
by increasing the power consumption of the heater, or by setting TO' at a 
higher level, but in the former case, the conventional household power 
supply has great difficulty in affording the power needed for the overall 
copying machine. In the latter case (which poses a serious problem 
especially when the fixing unit includes a heat roller), it is difficult 
to elevate the temperature setting TO' to a very high level in view of the 
low heat conductivity of the heat roller 12 because of the non-adhesive 
coating (as of silicone rubber, Teflon, or the like) on the surface of the 
roller 12 is heatresistant at temperatures of up to about 210.degree. to 
260.degree. C. 
In view of the aforesaid limiting factors, the following experiment was 
conducted using a copying machine operable at a copy processing time of 30 
copies/min. (A4 size). With standard paper (80 g/m.sup.2), 200 copies were 
continuously produced at a copy processing time of 30 copies/min. at a 
temperature setting of 165.degree. C. (the lowest temperature for proper 
fixing being 160.degree. C.). With thick paper (152 g/m.sup.2), 100 copies 
were continuously produced at each of the copy processing times of 30 
copies/min., 18.5 copies/min. and 12 copies/min. at a temperature setting 
of 180.degree. C. (the lowest temperature for proper fixing being 
175.degree. C.). The standard paper copies and the thick paper copies 
obtained were checked for toner fixing performance, the latter at the 
varying copy processing times. As shown in detail in FIG. 4, the fixing 
unit 14 used comprises a press roller 13 which is of the internally heated 
type in view of the heat resistance of the heat roller surface. The fixing 
unit 14 comprises: 
Heat roller 12 which is 67 mm outside diameter and includes an aluminum 
pipe of 2 mm wall thickness having a 0.6-mm-thick RTV silicone rubber 
coating over the outer surface thereof and provided with a 100-V, 700-W 
upper heater lamp 15 in its interior; 
Press roller 13 which is of 73 mm outside diameter and includes an aluminum 
pipe of 2 mm wall thickness and having a 3.5-mm-thick RTV silicone rubber 
coating over the outer surface thereof and provided with a 100-V, 400-W 
lower heat lamp 16 which is de-energized only while the exposure lamp is 
on; and 
Temperature control thermistor 17 in contact with the surface of the heat 
roller 12 for the ON-OFF control of the upper heater lamp 15 by means of a 
suitable control network. 
The results of the experiment are listed in Table 1 on the next page. Note: 
Repeated ON-OFF of the heater indicates that the heater has restored the 
temperature set before the start of the continuous operation. 
TABLE 1 
__________________________________________________________________________ 
Copy 80 g/m.sup.2 
152 g/m.sup.2 
152 g/m.sup.2 
152 g/m.sup.2 
Item Paper 
Lowest fixable 
160.degree. C. 
175.degree. C. 
175.degree. C. 
175.degree. C. 
temperature 
Temperature 
165.degree. C. 
180.degree. C. 
180.degree. C. 
180.degree. C. 
Setting 
Copy processing 
30 copies/min. 
30 copies/min. 
18.5 copies/min. 
12 copies/min. 
time 
Number of 
200 100 100 100 
copies 
Fixing All 200 copies 
Faults in fixed 
All 100 copies 
All 100 copies 
performance 
with fixed 
images on 15th 
with fixed 
with fixed 
toner images 
and following 
images images 
copies 
Energiza- 
Continuously 
Continuously 
Continuously ON 
Continuously 
tion of ON for 1st to 
ON for all 100 
for 1st to 60th 
ON for 1st to 
heater 90th copies 
copies copies, followed 
35th copies, 
followed by by repeated ON- 
followed by 
repeated ON- OFF repeated ON- 
OFF OFF 
__________________________________________________________________________ 
The experiment results listed in Table 1 demonstrate that in the case of 
the thick paper, a great reduction in the temperature causes improper 
fixing despite the rise of the temperature setting and that insufficient 
power consumption of the heater delays the recovery of the temperature. It 
is also seen that at the same sheet feeding speed and at the same 
temperature setting with the same power consumption for the heater, an 
increase in the copy processing time interval, has some freedom for fixing 
the toner on copy paper. 
Thus it is useful to set the fixing unit at a higher temperature and 
increase the copy processing time interval for fixing the toner to thick 
paper which requires a larger amount of heat than the standard paper. 
However, if the copying machine has some freedom in its overall power 
consumption with no problem encountered in the durability of the fixing 
unit, there is no need to set the fixing unit to different temperatures 
for the standard paper and the thick paper, but the machine may be set at 
the same predetermined temperature for both the papers at which 
temperature the toner can be fixed also to the thick paper at a 
predetermined copy processing time interval, such that only the copy 
processing time interval for the standard paper is changed to the 
predetermined copy processing time interval for producing copies on the 
thick paper. 
According to the present invention which is based on the above findings, 
copy sheets are fed to a fuser at the same sheet feeding speed and the 
same fuser temperature, the copy processing time interval (namely the 
period of time consumed in processing each copy during a continuous 
copying operation) is set in different modes for copy sheets of different 
thicknesses in accordance with the thickness of the sheet to process thick 
sheets for a longer period of copy processing time interval than the 
standard sheets so that the toner is fixed to the thick sheets at a 
constant copy processing time interval established by the specified 
processing time. However, the copy processing time interval need not be 
set at many divided levels in strict accordance with the varying 
thicknesses of copy sheets since good results can be achieved when the 
copy processing time interval is set at two different values for the 
standard paper and the thick paper respectively or at three different 
values for three kinds of papers including another paper of intermediate 
thickness. 
Although the invention has been described above as applied to a fixing unit 
of the heat roller type, the invention is similarly useful for other heat 
fixing systems from the viewpoint of the transfer of heat from the fixing 
unit to the copy paper. 
There is hereinafter described an example of the present invention in which 
the copy processing time is set in accordance with the specific processing 
modes of the copying machine in relation to the thicknesses of copy 
papers. 
Generally with copying machines operable at a short copy processing time of 
about 20 to 30 copies/min., the copy processing time for the first copy is 
longer than for each of the second and following copies when making a 
multiplicity of copies due to the times required for the warm-up of the 
motor as well as of the exposure lamp, the erasing procedure for the 
photoconductive member, etc. While sheets of the standard paper are 
processed in the usual mode, sheets of thick paper are processed in a mode 
which utilized the difference in processing time between the first copy 
and the following copies of the standard paper mentioned above and in 
which the copying operation for the first copy of the standard paper is 
repeated for each thick copy instead of resorting to the multi-copy 
operation conducted for the second and subsequent copies of the standard 
paper. With this mode set for processing a multiplicity of thick copies, 
the number of copies made per unit time is reduced to provide the 
additional copy processing time for fixing the toner to the thick paper. 
Thus, as shown in FIG. 7 in the standard paper multi-copy processing mode 
the processing time T.sub.1 for the first copy is relatively long, for 
example, a rate of 18 copies/min., and each interval includes a standby or 
dormant period A.sub.1, a period B.sub.1 during which a paper sheet is 
advanced and processed, during which period the toner carrying sheet is 
exposed for a period C.sub.1 to the fuser. The subsequent copies in thin 
paper each have a shorter processing time T.sub.2, for example, 30 copies 
per minute, each including a dormant period A.sub.2 less than A.sub.1, 
paper advancing and processing period B.sub.2 and fuser exposure period 
C.sub.2 which are equal in duration to periods B.sub.1 and B.sub.2 
respectively. As seen in FIG. 8 which illustrates the timing sequence for 
the thick paper multiprocessing mode, each of successive processing time 
T.sub.3 is equal to the others and is equal to processing time T.sub.1, 
that is 18 copies/min. and each includes dormant period A.sub.3, paper 
advancing and processing period B.sub.3 and fuser exposure period C.sub.3 
equal to periods A.sub.1, B.sub.1 and C.sub.1 respectively. It should be 
noted that periods B.sub.1, B.sub.2 and B.sub.3 are equal and constant as 
are fuser exposure periods C.sub.1, C.sub.2 and C.sub.3, while hold up 
periods A.sub.1 and A.sub.3 are greater than periods A.sub.2. The speeds 
of advance of the copy sheets are equal and constant. 
When the copying machine is allowed to stand for a period of time (set by 
an autoreset timer) namely when no key input is given for a copying 
operation during such time period, the machine is automatically brought 
out of the thick copy processing mode and is set for the standard copy 
processing mode so as to avoid the following drawbacks. When the machine 
is allowed to stand in the former mode, power will be wasted. Since copies 
will be made much less frequently with thick sheets, it is likely that the 
next user will start the machine without noticing that it is set for thick 
sheets. High-temperature offset or like trouble would then occur. 
Referring to FIG. 5, a microcomputer designated by the reference numeral 
100 is incorporated in the electrophotographic copying machine for 
controlling various operation sequences carried out at a number of 
stations and by various devices. The microcomputer 100 comprises a central 
processing unit CPU, a random access memory RAM and a read only memory ROM 
which are connected to an input and output interface I/O and are 
constructed by one or more chips of large scale integrated (LSI). The 
central processing unit CPU includes an arithmetic-logic unit ALU, an 
accumulator ACC, a decoder DE, a program counter PC, a stack point SP and 
a timer T. 
The sequence control signal for each of the devices in the copying machine 
is generated in accordance with a program memorized in the read only 
memory ROM while a timing in which the read only memory ROM generates the 
sequence control signal is determined by the number of pulses counted in 
the counter. These pulses are produced by the timer T. Although the 
central processing unit CPU further includes flags F/F and a number of 
working registers, they are omitted from the drawings for the sake of 
brevity. A switch 101 connected to the interface I/O is provided on the 
control panel (not shown). The program of the computer 100 is set to the 
thick copy processing mode at "on" of switch 101, and is set to the 
standard copy processing mode at "off" of switch 101. 
FIG. 6 illustrates the control process described above and the flow chart 
shown therein is hereinafter described. When the program on microcomputer 
100 incorporated in the copying machine is started, an initial value is 
set at (1). It is assumed that the flag to be used subsequently is "0". At 
(2) judgment is made as to whether or not the print switch has been 
depressed. If it is not depressed, the flag for giving a copy order 
remains "0" at (3). If the print switch is on, the order turns to "1". At 
(4) judgment is made as to whether the copy order is "0" or "1". When the 
order is "0", the output from (4) is fed to (16). When it is "1", (5) 
judges whether the multiflag is "0" or "1". If the multiflag is "0", (6) 
performs the "preparation for making 1st copy only", and then (7) performs 
the "copying operation for 1st copy and common operation after 1st copy". 
If it is "1", the output form (5) is given to (7) which performs "copying 
operation for 1st copy and common operation after 1st copy" only. 
The multiflag is a flag of such nature that it is "0" only for making the 
1st copy and thick copies. At (8) judgment is made as to whether the 
photoconductive member has been completely exposed to the original image. 
When the exposure is judged as completed, (9) reduces the copy count. At 
(10) judgment is made as to whether the count has been reduced to "0", 
namely whether or not the number of copies set on the counter have been 
completed. If it is "0", "copying order" and "multiflag" are both changed 
to "0" at (14) and (15) respectively. When the count has not been reduced 
to the order of "0", namely if the machine is still in operation for 
making the specified number of copies, (11) judges whether or not the 
operation is for thick paper. In the case that it is not thick paper 
copying, the multiflag is set to "1" at (12). At (16) judgement is made as 
to whether or not the time set on the autoreset timer is up. 
The autoreset timer, although not shown in the flow chart, is set on the 
completion of a copying operation or in response to a key input. 
Completion of operation of the autoreset timer means that the copying 
machine has been allowed to stand for the period of time set on the timer. 
On completion of the timer operation, the machine is brought out of the 
thick copy processing mode into the standard copy processing mode at (17). 
Other necessary operations are conducted at (18), whereby one routine of 
the program is terminated. The program will be started again at (2). 
"Preparation for making 1st copy only" at (6) and "copying operation for 
1st copy and common operation after 1st copy" at (7), although shown in 
separate blocks in the flow chart, are not completely separate operations, 
but the illustration means that timers are set at different values, for 
example, for setting the pre-energization time for the exposure lamp. 
When the multiswitch is turned on upon setting the machine to produce a 
plurality of copies in the procedure of the flow chart described, the 
operation is started with "0" for the multiflag, which is processed at (6) 
to provide a copy processing time of 18.5 copies/min. On the other hand, 
if the multiflag is "1", the output is transmitted to (7) bypassing (6), 
affording a copy processing time of 30 copies/min. The first sheet of the 
standard paper is processed with the multiflag of "0" at the copy 
processing time of 18.5 copies/min. With completion of the first copy, the 
multiflag changes to "1" at (11), with the result that the second and 
following copies are processed at 30 copies/min. In the case of the thick 
paper the first copy is processed at 18.5 copies/min. with "0" for the 
multiflag. Since the multiflag is changed to "0" at (13) for the second 
and subsequent thick copies by "on" of the switch 101 on the control panel 
for specifying the thick paper, these following copies are processed at 
18.5 copies/min. 
With copying machines in which the copy processing time for the first sheet 
of standard paper is not longer than that for the second and following 
standard sheets (namely copy processing time for the first 
sheet.ltoreq.copy processing time for the second and following sheets) and 
which are unable to satisfactorily fix the toner to thick paper, the 
machine may be set in such a processing mode that the copy processing time 
for the thick paper is longer than for the standard paper when making a 
single copy and also when making a plurality of copies by a continuous 
operation. 
With the system and process of the present invention, copy paper is 
processed for a predetermined period of copy processing time in accordance 
with the thickness of the paper so that the reduction in the temperature 
of the heat roller due to the absorption of heat by the paper in each 
copying cycle is fully remedied before the subsequent cycle. Consequently 
copies with satisfactorily fixed toner images are produced at a constant 
copy processing time interval even with use of copy paper of increased 
thickness at the same sheet feeding speed without the necessity of setting 
the heater to a particular higher temperature. The power needed for the 
overall copying machine is thus readily available from the limited 
domestic power supply and waste of heat is minimized to effect energy 
savings since copies are made at a predetermined fixed temperature setting 
at a preset copy processing time interval in accordance with the thickness 
of the paper used. The copying machine is highly convenient in that copies 
on paper of a particular thickness are made at a constant copy processing 
time interval in a definite period of time. Since copy sheets of different 
thicknesses are processed for different periods of copy processing time 
intervals set in individually different modes in accordance with the 
thickness of the processed sheet, the machine is easily controllable with 
the use of the copy cycle already set for the machine, as it is or with a 
modification. The present invention accordingly facilitates the 
modification of existing copying machines. 
While there has been described and illustrated a preferred embodiment of 
the present invention, it is apparent that numerous alternations, 
omissions and additions may be made wthout departing from the spirit 
thereof.