Data recovery device for printer

A data recovery device is employed in a printer using a continuous form recording medium for reprinting data after printing has been interrupted. In the data recovery device, the number of pages remaining in a predetermined area of the feed path of the recording medium is counted. A plurality of page buffers are sequentially read out and printed. The printing operation is controlled such that the one of the data storing means from which the data is read out and printed by the printing means is identified based on the number of the pages remaining in the predetermined area.

BACKGROUND OF THE INVENTION 
The present invention relates to a data recovery device for reprinting data 
that has not been printed on recording paper due to a paper jam or the 
like in a printer. 
A laser printer is generally provided with a data recovery function for 
reprinting pages that have not been printed when recording paper becomes 
unusable in the course of printing because of paper jamming and the like. 
In a printer using a cut sheet, sheets of recording paper are independent 
of each other and consequently it is only necessary to reprint the page 
that has suffered from a jam. 
In the case of a printer using a continuous form recording sheet, however, 
the preceding and the following page may also suffer when a paper jam 
occurs and those pages may also become unsuable. As a result, unlike the 
printer using a cut sheet, which is designed to recover data on only one 
page, in case of the printer using a continuous recording sheet, 
recovering data on only one page may be insufficient. 
In order to completely reproduce the data thus unprinted because of a jam, 
the maximum number of pages which may be affected by the jam in the 
printer could always be recovered. However, the maximum number of pages 
could not necessarily be recovered, depending on the position to which the 
paper has been fed. In this case, those pages that have been unaffected by 
the jam may be reprinted and this inconveniently results in wasting paper. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an improved data 
recovery device for a printer using a continuous form recording sheet 
which is capable of eliminating waste of recording paper. 
For the above object, according to the invention, there is provided a data 
recovery device employed in a printer using a continuous form recording 
medium for reprinting data after printing has been interrupted to 
The recovery device includes a counting mechanism for counting the number 
of printed pages remaining in a predetermined area of the feed path of the 
recording medium, and 
a plurality of data storing devices for storing printing data on a page 
basis, the number of the plurality of data storing devices being larger 
than at least the maximum value of the number of pages capable of 
remaining in the printer. 
A printing device for sequentially reading the data stored in the data 
storing devices and printing the data onto corresponding pages of the 
recording medium, and 
a control mechanism for restarting sequentially printing the data from the 
data stored in one of the data storing means which is identified based on 
the number of the pages counted by the counting means after printing 
performed by the printing devices has been are also provided. 
According to another aspect of the invention, there is provided a printer 
using a continuous form recording medium comprising a data recovery device 
for reprinting data after printing has been interrupted, 
The device includes a counting mechanism for counting the number of printed 
pages of the recording medium remaining in a predetermined area of the 
feed path of the recording medium, and 
a plurality of data storing devices for storing printing data on a page 
basis, the number of the plurality of data storing devices larger than at 
least the maximum value of the number of pages capable of remaining in the 
printer. 
Also provided is a printing mechanism for sequentially reading the data 
stored in the data storing devices and printing the data onto 
corresponding pages of the recording medium 1, 
a detection mechanism for detecting an error condition of printing 
operation of the printer and 
a control mechanism for restarting sequentially printing the data from the 
data stored in one of the data storing devices which is identified based 
on the number of the pages counted by the counting mechanism when the 
error condition is detected by the detection mechanism.

DESCRIPTION OF THE EMBODIMENTS 
A printer 100 shown in FIG. 1 is a laser beam printer employing an 
electrophotographic image transfer system. The printer 100 comprises, in 
sequence, a transfer unit 10 including a photoconductive drum 11, a 
tractor unit 20 having an endless belt 21 for feeding a recording sheet, 
and a fixing unit 30 having a pair of rollers 31, 32 for heating and 
pressing an unfixed toner image, in order to fix it on the recording 
sheet. Light carrying printing data from a host computer or the like is 
emitted from a laser scanning unit (LSU) 13, the charged circumferential 
surface of a photoconductive drum 11 is exposed to the light, and a latent 
image is formed on the circumferential surface of the photoconductive drum 
11. Toner is adhered to the circumferential surface of the photoconductive 
drum 11 to develop a toner image by use of a developing unit 14. Then the 
toner image is transferred onto the recording sheet at a transfer charger 
15, and the image thus transferred is fixed by a fixing unit 30. The 
printer 100 employs the electrophotograhic image transfer system, and so 
it is designed to be a page printer which starts printing after the 
printing data for one page is accumulated. The laser scanning unit 13 is 
secured to an upper cover UC. The upper cover UC is rotatably disposed on 
the main body of the printer 100 so that it can be rocked around a pivot 
axis P. 
This printer 100 uses a continuous form recording sheet FP, which is known 
as fan-fold sheet. The fan-fold sheet is a foldable continuous sheet 
having feed holes at both side ends, and perforated tear lines along which 
the recording sheet FP is easily cut off. Projections are provided on the 
endless belt 21 which are to be fitted to the feed holes of the continuous 
form recording sheet FP. The continuous form recording sheet FP is fed 
from a feed port 1 to a discharge port 2. It should be noted that the 
printer 100 is designed to print pages between perforations in order to 
prevent printed data from being torn apart when the recording sheet FP is 
torn off at the perforated tear lines. 
In case of a printer using a cut-sheet, the distance between transferring 
position and fixing position is not so important because printing data for 
one page is printed onto one sheet of recording paper. On the other hand, 
in a printer using a continuous sheet, if the portion of the sheet 
carrying unfixed toner image is caused to pass through the fixing position 
and fixed, the paper may be wasted to the extent of the distance between 
transfer and fixing positions. Consequently, it is necessary to determine 
the portion of the sheet carrying a toner image to be fixed. In other 
words, it is necessary to determine the portion carrying an unfixed toner 
image to be remained in the printer between the transfer and fixing 
positions. 
When the printing quality is taken into consideration, the interruption and 
resumption of transfer and fixing should preferably be made at the 
perforations, where data is not printed. For this reason, the distance 
between the transfer position and fixing position is preferably arranged 
equal to the length of one page, so that the perforations are located at 
the transfer and fixing positions when printing is stopped. 
As arranged above, the portion carrying an unfixed toner image for one page 
remains between the transferring and fixing positions, in a standby state, 
when the printing is terminated. When another page is printed, the unfixed 
toner image is fixed and the remaining page is discharged. In this way, 
waste of paper due to the fixing of every transferred image becomes 
avoidable. 
The distance between the transferring and fixing positions of this printer 
100 is set to eleven inches long for the continuous recording sheet having 
a page length that is eleven inches long. 
The transfer unit 10 comprises a charger 12 for charging a photoreceptor 
material on the circumferential surface of the photoconductive drum 11 
with electricity, the laser scanning unit 13 for exposing the 
photoconductive drum 11 to light, a developing unit 14 for adhering toner 
on to the latent image formed on the photoconductive drum 11, a transfer 
charger 15 for charging the recording sheet FP with electricity to cause 
to toner image to be transferred to the recording sheet FP, a cleaning 
unit 16 for removing the residual toner on the drum, and a discharging LED 
17 for totally exposing the photoconductive drum 11 to light, so as to 
removing the charge thereon. 
The photoconductive drum 11 should be exchanged after being used for 
printing a certain number of pages, since its properties will deteriorate 
and it will fail to provide clear printing. For example, a limit of use is 
set at approximately 20,000 pages. The number of printed pages are 
electrically counted and recorded in a counter by a control system which 
will be described later. This counter is reset when an upper cover UC is 
shut after a new photoconductive drum 11 is installed. 
An outwardly protruting projection (not shown) is provided on a new 
photoconductive drum 11. As the projection presses down a reset switch, 
not shown, on the body side, the control system can detect that the new 
photoconductive drum 11 is placed in position. The projection retracts 
when the operation is started and an indication of the new drum disappears 
from the display. The control system resets the counter when the upper 
cover UC is shut after the reset switch is turned on. 
The laser scanning unit 13, which is secured to the upper cover UC, 
continuously deflects ON/OFF-modulated beams from a semiconductor laser 
(not shown) by means of a polygon mirror 13a. The laser beams are 
converged by means of a f.theta. lens (not shown), reflected by a beam 
bender 13b so that scanning lines are formed on the photoconductive drum 
11, then an electrostatic latent image is formed on a dot basis, as the 
drum rotates. 
The developing unit 14 comprises a toner case 14a in which toner is 
accumulated, a developing roller 14b for adhereing the toner onto the 
circumferential surface of the photoconductive drum 11, provided at the 
lower end of the case 14a, and a piezoelectric sensor acting as a low 
toner sensor 14c for detecting the presence or absence of the toner in the 
case 14a. 
In normal text printing, the printing of letters are started from the 
left-hand side of paper so that the frequency of use of toner normally 
tends to become high in portion corresponding to the left-hand side of the 
paper. For this reason, the toner low sensor 14c is provided in the 
portion corresponding to the left-hand side of the paper where the toner 
consumption is large. 
Conventionally, two dry development methods are generally known. One of 
them is a so-called monocomponent development method, and the other is a 
two-component development method. 
In the two-component development method, carrier is mixed with the toner, 
and stirred at a relatively high speed by a scraper or the like, in order 
to charge the toner. 
On the other hand, in the monocomponent development method, toner is fed to 
a developing roller or the like, without using carrier for charging the 
toner. This monocomponent development method is disclosed in the U.S. Pat. 
No. 3,909,258. However, there is a problem in this monocomponent 
development method. That is, the toner tends to form the block in a toner 
box. In order to overcome the above problem, an improved monocomponent 
development method, in which a relatively small amount of carrier is mixed 
with the toner, is disclosed in the U.S. Pat. No. 4,640,880. With the 
mixture of a small amount of carrier with the toner, lubrication between 
the toner grains is improved, which prevents the toner from forming 
blocks. It should be noted that the mixture of the carrier with the toner 
does not affect the chargeability of the toner. In this improved 
monocomponent development method, the main function of the scaper is to 
feed the toner to the developing roller or the like. Accordingly, the 
scraper rotates relatively slowly in the toner box. 
A scraper 19 is provided in the toner case 14a. The scraper 19 slowly 
rotates to supply the toner therein to the developing roller 14b. The 
scraper 19 is, as shown in FIG. 3, composed of a rotary shaft 19a to be 
driven by a main motor, and four pieces of blades 19b, 19c, 19d, 19e 
fitted such that the angle between the surfaces of the blades 19b and 19c 
is 90 degrees, that of the blades 19b and 19d is 180 degrees, and that of 
the blades 19 and 19 is 270 degrees. In this specification, this angle 
will be called a mounting angle, i.e., the mounting angles, with respect 
to the blade 19b, of the blades 19c, 19d, and 19e are 90 degrees, 180 
degrees, and 270 degrees, respectively. The blades 19b through 19e are 
driven to rotate in the direction of an arrow shown in FIG. 3. 
Since the four blades are arranged to have different mounting angles, it 
becomes possible that the load applied when the toner is forced out is 
one-quarter of the conventional scraper having all the blades set to have 
the same mounting angles. Consequently, the load applied to the motor 
decreases and fluctuates less with the scraper of this embodiment, thus 
suppressing noise generation. 
By sequentially making the mounting angles of the blades of the scraper 19 
different, as stated above, a certain amount of toner can be gradually 
moved to a portion corresponding to the right-hand side of the paper as 
the scraper 19 slowly rotates. 
When toner consumption in the portion corresponding to the right-hand side 
of the paper increases as it is used for an graphic output, for instance, 
a low toner condition is left undetected by the low toner sensor 14c. In 
such a case, as the conventional scrapers do not function to move the 
toner in the manner stated above, carrier may be transferred onto the 
circumferential surface of the photoconductive drum 11. 
According to the scraper in this printer 100, the occurrence of the carrier 
being transferred on the photoconductive drum 11 is avoided even when the 
toner consumption is large on the side where the toner low sensor 14c is 
not provided. 
The transfer charger 15 is secured to an arm 15a which can be rotated by a 
cam mechanism around a pivot shaft L1. Moreover, a pair of guide rollers 
18a, 18b are integrally secured to the arm 15a, the guide rollers 18am18b 
being laterally positioned so that the continuous form recording sheet FP 
is nipped therebetween. 
When printing is started, it is necessary to idly rotate the 
photoconductive drum 11 without feeding the recording sheet until the 
exposed portion of the photoconductive drum 11 is located at the transfer 
position. In this case, the arm 15a is moved down to lower the guide 
rollers 18a, 18b, and accordingly, the recording sheet FP is retracted 
from the circumferential surface of the photoconductive drum 11. The life 
of the photoreceptor material is thus prevented from being shortened 
because of wear. In addition, the paper is also prevented from being 
soiled by residual toner on the photoconductive drum 11. 
An opening is formed in the transfer charger 15. The opening of the 
transfer charger 15 is arranged so that its rearward half, in the feeding 
direction of the recording sheet FP, is covered with a Mylar film 15b. The 
discharging area, which is uncovered, of the transfer charger 15 is 
arranged at the upstream side in the rotational direction of the 
photoconductive drum 11 with respect to the contact portion between the 
photoconductive drum 11 and the recording sheet FP. 
Conventionally, the whole opening of a transfer charger has been left 
opened for charging. With such a setting, however, transfer efficiency 
tends to vary considerably as ambient humidity changes. 
By narrowing the discharge area, corona discharge efficiency can be 
increased to prevent toner from being reversely charged under the 
influence of the corona discharge. Moreover, the period of time in which 
the recording sheet FP contacts the photoconductive drum 11 under 
pressure, after the toner image is transferred thereto, can be set to be 
longer than that of conventional printers. As a result, transfer 
efficiency in the whole humidity range can be vastly improved. Experiments 
show that the transfer efficiency is improved to a great extent, 
especially when humidity is low. It is also possible to arrange the 
transfer charger 15 itself in towards the upstream side in the sheet feed 
direction, in order to prolong the period of time for applying pressure 
after transfer. 
The toner adhering the photoconductive drum 11 is not totally removed 
therefrom after the termination of the transferring process. As the 
residual toner is unnecessary for next printing, it is removed by a 
cleaning unit 16. The waste toner thus removed is stored in a waste toner 
box 60, detachably fitted to the side of the photoconductive drum 11, as 
shown in FIG. 2. 
When a certain amount of waste toner is accumulated in the waste toner box 
60, it overflows into the printer, unless it is discarded. The waste toner 
may soil the inside of the printer if printing is started without the 
waste toner box 60. 
In conventional printers, sensors have been used to respectively detect the 
presence or absence of such a waster toner box 60 and the full condition 
of the waster toner box 60. The problem is that the plurality of sensors 
thus required tends to render the control system complicated. 
In the printer according to the present embodiment, only one sensor is used 
to detect both conditions. 
FIG. 4 illustrates the detecting mechanism. The waste toner box 60 is 
movably inserted while being guided by the body. The waste toner box 60 
being is vertically movable. An actuator 62 is rotatably pivoted via a 
fulcrum 61 on the body such that a contact portion 62a is located at a 
position where the bottom side of the waste toner box 60 is located. A 
fan-shaped portion 62b is provided at the other end of the rod 62, and a 
light-shading (or blocking) wall 62c is formed on the arcuate peripheral 
edge of the fan-shaped portion. The light-shading wall 62c is capable of 
crossing the space between a light receiving element and a light emitting 
element of a photo-interrupter 63. 
If the waste toner box is not attached, the rod 62 revolves clockwise due 
to its own weight as shown by a continuous line of FIG. 4, so that its 
contact portion 62a ascends and the light-shading wall 62c is located 
under the photo-interrupter 63. In this state, the photo-interrupter 63 
produces a signal indicating that no rays of light are shaded (or blocked) 
and the control system determines that an error relating to the waste 
toner box 60 has occurred. 
When the waste toner box 60 is attached, the contact portion 62a is forced 
down by the weight of the box and the rod is rotated counter-clockwise up 
to a substantially horizontal state, as shown by a broken line of FIG. 4. 
The light-shading wall 62c is thus moved to a position where it screens 
the photo-interrupter 63. In this state, the photo-interrupter produces a 
signal indicating that the rays of light are shaded or blocked and the 
control system determines that no error relating to the waste toner box 60 
has occurred. 
When waste toner box 60 is filled with waste toner, the contact portion of 
the rod descends due to the weight of accumulated toner, as shown in FIG. 
5, and the light-shading wall 62c moves up to the left-hand side of the 
photo-interrupter 63. In this state, the control system again determines 
that an error relating to the waste toner box 60 has occurred. 
In this way, one sensor can be used to detect both that the waste toner box 
60 is not installed, and that the waste toner box 60 is filled with waste 
toner. Although this sensor is arranged so as to monitor the presence or 
absence of the waster toner box and the amount of waste toner from the 
balance in weight between the rod 62 and the waste toner box 60, it is 
possible to employ a spring or the like to hold the balance as well as the 
dead weight of the rod 62. 
The tractor unit 20 is arranged so that, as shown in FIG. 2, the two 
endless belts 21, 21, stretched between a driving shaft 23 22 and a driven 
shaft 23 are driven by the main motor 40 via a field clutch (not shown), 
hereinafter called the F clutch) and a gear train (not shown) provided in 
a gear box 41. 
The gear train extending from the main motor 40 up to the drive shaft 23 in 
the tractor unit 20 is arranged so that the continuous recording sheet FP 
is fed at the velocity of 50 mm/sec. if the tractor unit 20 is 
independently feed the recording sheet FP. Moreover, the gear train 
contains a unidirectional clutch which races with a predetermined 
resistance in compliance with a tension when the paper is drawn at a rate 
higher than 50 mm/sec. to prevent the papaer from overdriving the motor 
40. 
The driven shaft 22 is connected with a disc 25 via a chain 24. The disc 25 
is rotatable in response to the rotation of the driven shaft 22. As shown 
in FIG. 6, the disc 25 is provided with slits 25a which are spaced from 
each other by predetermined distance. The disc 25 is positioned (i.e., 
received) between the light emitting member and the light receiving member 
of the photo-interrupter 26, and a pulse corresponding to the amount of 
movement of the recording sheet FP is obtainable. The photo-interrupter 26 
is hereinafter called the PFS (Paper Feed Sensor,) with its output 
constituting the PFS pulse. 
The PFS pulse is outputted such that when the recording sheet is fed by 1/2 
inch, one pulse is outputted. Further, the signal corresponding to the 
slit portion 25a and the signal corresponding to the portion other than 
the slit 25a correspond to the perforated lines of the continuous 
recording sheet FP and the non-perforated portion, respectively. 
However, the positional relation between the disc 25, used for generating 
the PFS pulse, and a base plate on which the photo-interrupter 26 is 
mounted, may not be the same in individual printers because of assembly 
errors. If the slits 25a formed in the disk 25 are rectangular in the 
radial direction, the pulse width thus outputted may vary, depending on 
where the photo-interrupter 26 has detected the slits 26a, in the radial 
direction of the disc 26, and depending on shift in the relative radial 
position between the disc 25 and the photo-interrupter 26. 
As this printer is arranged so that the paper feed error is judged from the 
detection of the PFS pulse, the variation of the pulse width may result in 
misjudgement on the error. 
For this reason, the slit 25a formed in the disc 25 is fan-shaped so that 
its width gradually increases toward the circumference of the disc. In 
other words, the slit 25a is defined by a pair of radii of the disc 25. 
With this fan shape, the width of the pulse thus outputted can be unified 
(i.e., the ratio between slit 25a and the non-slit portion remains 
constant) irrespective of the position where the photo-interrupter has 
detected the slit in the radial direction of the disc 25, thus preventing 
misjudgement of an error. In addition, the assembly precision required is 
eased and hence assembly workability is improved. 
Sensors for detecting paper errors will be subsequently described. 
In a conventional laser printer using cut sheets, two sensors are provided 
along a sheet feed path to detect the jamming of recording sheet. Paper 
errors are detected when the sheet does not pass the down-stream side 
sensor a predetermined time after it passed the up-stream side sensor. 
Since there are no breaks in the continuous recording sheet, the 
aforementioned method of detection cannot be utilized in a printer using a 
continuous recording sheet. 
In this printer 100, there are provided four kinds of sensors for detecting 
the presence or absence of the paper along the sheet feed path. The sheet 
empty and paper jamming conditions are detected by detecting the changing 
of a sheet feed speed and the lifting up of the sheet. 
The first sensor is an empty sensor 50 provided between the feed port 1 and 
the transfer unit 10. This printer 100 does not print on the portion 
adjacent to the perforated lines, which is used as a break between pages. 
The perforated lines are located right under the photoconductive drum 11 
of the transfer unit 10 and at the position of the fixing rollers 31, 32 
when printing is stopped in this printer 100. The sheet empty condition 
can be detected from the output of the empty sensor 50 when the last page 
of the recording sheet FP is located in the printer. Moreover, it is 
detectable, by counting the PFS pulses, what portions of the recording 
sheet are positioned at the transfer unit 10, at the fixing unit 30, and 
further at the empty sensor. Consequently, counting of the PFS pulse and 
the output of the empty sensor 50 can be used to detect the recording 
sheet FP being torn off at a non-perforated portions. 
The second sensor comprises skew sensors 51, 51 provided between the fixing 
unit 30 and the tractor unit 20. The skew sensors 51, 51 are used for 
detecting the skew and cutting-off of the continuous recording sheet FP. 
The sensors 51, 51 are capable of detecting the sheet when at least one 
side thereof lifts up. 
The third sensor is a top sensor 52 provided in the central part of the 
sheet between the skew sensors 51, 51. The top sensor 52 is used for 
detecting the leading end of the paper when printing is started. After the 
predetermined number of pulses have been counted, after the leading end of 
the recording sheet FP passes the top sensor 52, the leading end thereof 
reaches the fixing unit 30, whereas the following perforations are 
positioned at the transfer unit 10. 
The fourth sensor is a jam sensor 53 provided in the upper cover UC, 
substantially opposite to the top sensor 52 with the sheet feed path 
therebetween. The jam sensor 53 is used for detecting the sheet, when the 
sheet is jammed in the fixing unit 30, and the central part of the 
recording sheet swells out to contact the jam sensor 53. 
The fixing unit 30 comprises a heat roller 31 provided in the upper portion 
of FIG. 1, and a press roller 32. The continuous recording sheet FP is 
nipped between the rollers 31, 32, and is pressed against the heat roller 
31 by the press roller 32 with a predetermined pressure. In the heat 
roller 31, a heating halogen lamp, and a thermistor for temperature 
detection are provided. 
The heat roller 31 is driven by the main motor 40 to rotate via the F 
clutch and the gear train and is arranged so that, when the continuous 
recording sheet FP is held between the rollers 31, 32, it is fed at the 
speed of 75 mm/sec.. As a result, the continuous recording sheet FP is 
actually driven by the fixing unit 30, whereas the tractor unit 20 mainly 
functions to prevent skewing of the continuous recording sheet FP. 
If the continuous recording sheet FP is kept pressed against the heat 
roller 31 while printing is in the standby state, the paper may be 
scorched by the heat of the heat roller 31. In order to avoid scorching of 
the sheet, in this printer 100, the press roller 32, facing the heat 
roller 31, is made vertically movable so that the continuous sheet is 
retracted from the heat roller 31 when printing is in standby state. 
In the meantime, the rocking of the press roller 32 and that of the 
transfer charger 15 are implemented by the same drive means. 
A general liquid crystal display panel heretofore in use is, as shown in 
FIG. 7, built by mounting two glass plates 72, 73 on a substrate 70 via 
conductive rubber member 71 and nipping a layer of liquid crystal 74 
between the glass plates 72, 73. Moreover, the edges of the glass plates 
are enclosed with a frame 75, which is secured to the substrate 70. The 
substrate 70 is secured with screws onto the body so that the display 
panel can be viewed through an opening 76. 
The arrangement stated above, however, has posed a problem in that the 
large number of parts makes it troublesome to assemble the display unit. 
In liquid crystal display unit 170 of this embodiment, there is provided a 
stepped portion at the peripheral edge of the opening 76 of the body as 
shown in FIG. 8. While the glass plates 72, 73, between which the liquid 
crystal layer 74 is inserted, are directly mated with the stepped portion 
76a, the combination is secured with screws onto the body. With this 
arrangement, the frame can be omitted, so that the number of parts becomes 
reducible. 
FIG. 9 shows a control circuit of the printer. 
This circuit comprises a controller 81 for developing the printing data 
received from a host computer into a map on a dot basis and outputting the 
map, and a driver 82 comprising two CPU's: one of which, A-IC 83, is 
mainly for controlling printing; and the other, B-IC 84, is mainly for 
performing error detection. 
The controller board 81 is equipped with buffers B1 through B6 whose 
capacity is large enough to develop printing data equivalent in volume to 
six pages. Data are successively written to these buffers B1, B2, B3 . . . 
B6, B1 . . . in this order, when printing is started, and are transmitted 
to the driver board in the same order. The controller 81 and the driver 
board 82 are connected via a video interface (VIDEO I/F) for transmitting 
various data as well as printing data. The controller 81 requests the 
driver to carry out the printing operation when at least data equivalent 
to one page is stored in the buffer. 
When continuous printing is desired, data equivalent to two preceding pages 
which had been printed, is held in the buffers for reprinting purposes. 
When data storage is started from the buffer B1, for instance, the data 
stored in the buffers B1, B2 are hold therein until the buffer B3 
completely outputs its data. New data is written to the buffer B1 at the 
time the outputting of the data stored in B4 is started. 
The data recovery function will subsequently be described. 
The printer 100 in this embodiment is designed to transfer from the buffer 
the data for the pages which incompletely printed in the normal way when a 
jam occurs during printing, when paper empty is detected at portions other 
than a perforation line, or when the upper cover UC is released during 
printing. 
FIG. 13 illustrates the relation of the transfer portion, the fixing 
portion and the discharge portion in the printer 100 to continuous form 
recording sheet being fed therein. 
When printing performance is taken into consideration, it is preferred that 
the interruption and restarting of transfer and fixing is implemented at 
the perforation line where printing is not to be made. For this reason, 
the perforation line is located at a page break between the transferring 
and the fixing portions, when the printing operation is stopped, as the 
interval between the transferring and the fixing portions is set 
equivalent to one page. Consequently, the paper equivalent in space to one 
page remains between the transfer portion and the fixing portion when the 
standby condition is maintained after the normal printing operation is 
terminated. When data equivalent to the following one page is transferred 
or when FF (Form Feed: turning pages) is requested, the preceding page is 
fixed and discharged. 
Since the printer 100 in this embodiment is to be operated on the 
assumption that the page length (a length between two perforation lines) 
of the continuous recording sheet preimarily used is 11-inch long, the 
interval between the transfer and the fixing portions is set at 11 inches. 
In addition, the interval between the fixing portion and the discharge 
portion is L. 
When a jam occurs during printing in the printer, at least the page 
positioned between the transfer and the fixing portions needs recovering. 
However, it is highly probable that the paper might be damaged because of 
a jam as it passes through the discharge port after passing the fixing 
unit. In this example, it has therefore been arranged that all the pages 
positioned between the transfer unit and the discharge port are to be 
recovered. 
As the number of pages so positioned varies with the operation in progress, 
the number of pages to be reprinting is determined on the driver 82 side 
in accordance with the state in which the recording sheet is being fed. 
The decision made on which one of the pages is being printed is based on 
the PFS pulse on the driver side. 
There are four kinds of page count to be transferred from the driver to the 
controller: page count `0` denotes no recovery; `1` the reprinting of a 
page being transferred; `2` the reprinting of the page being transferred 
and the preceding one; and `3` the reprinting of the page being 
transferred and the preceding two pages. 
When new continuous paper is set in the printer, the upper cover UC is 
closed with the leading end of the recording sheet mated with the tractor 
unit 20 and the paper is fed until it is inserted into the fixing unit 30. 
When the PFS pulse is counted for a predetermined number of unless after 
the leading end of the recording sheet has passed the top sensor, the 
leading end thereof reaches the fixing unit 30 and the following 
perforation line is located at the transfer portion. However, the 
recording sheet may not be held when the press roller ascends even though 
the leading end of the recording sheet has reached the fixing unit. 
When the recording sheet is set, an additional page of the paper is loosely 
fed so as to locate the border between the first and the second pages at 
the fixing portion as shown in FIG. 13(a). As a result, the preceding two 
blank pages are discharged and the third page is intended for printing. 
When printing is started, fixing of the third page is started. When the 
fixing of the third page is terminated as shown in FIG. 13(b), image 
transferring to the fourth page and discharging of the third page are 
executed. If the recording sheet is located between the positions shown in 
FIG. 13(a) and FIG. 13(b), only the third page is positioned between the 
transfer unit and the discharge port and intended for printing. Therefore, 
`1` is the page count needed for recovery when a jam occurs in this case. 
The third and the fourth pages are positioned between the transfer unit and 
the discharge port, and intended for printing until fixing on the third 
page end, as and the transferring to the fourth page shown in FIG. 13(c) 
after the state of FIG. 13(b). Therefore, `2` is the page count needed for 
recovery when a jam occurs in this case. 
When fixing of the fourth page and the transferring of the fifth page are 
completed halfway, the third page is discharged from the discharge port as 
shown in FIG. 13(d). As shown in FIG. 13(e), fixing on the fourth page and 
the transfer of the fifth page are terminated as the printing operation 
progresses further. 
The third, the fourth and the fifth page are positioned between the 
transfer unit and the discharge port, and intended for printing when the 
recording sheet is located between the positions shown in FIGS. 13(c) and 
(d). Therefore, `3` is the page count needed for recovery when a jam 
occurs in this case. Similarly, the fourth and the fifth page are those 
positioned between the transfer unit and the discharge port and indented 
for printing when the sheet is located between the positions shown in 
FIGS. 13(d) and (e). Therefore, `2` is the page count needed for recovery 
when a jam occurs in this case. 
When printing is continuously carried out further, the positional condition 
of the recording sheet shown in FIGS. 13(c)-(e) are repeated and the page 
count is switched between `2` and `3`. 
FIG. 14 is a flowchart for use in determining the page counts described 
above. The process shown therein is carried out every time interval which 
is set as a timer interruption process with respect to the main sequence 
of the printer, for instance. In this case, the page count PAGE is reset 
to 0 when power is supplied or when the upper cover UC is opened. 
The driver 82 decides whether or not the perforation lines as the border 
lines between pages passes the transfer unit in Step S.1 and increments 
the page count in S.2 when it passes there. In S.3, the driver 82 decides 
whether or not FF (Form Feed or sheet feed) is executed and increments the 
page count PAGE in S.4 when it is executed. The FF is a process which 
forces the unfixed portion to be fixed before being discharged while 
printing is paused. This process can be requested by the host computer or 
with the operation panel, and further, is automatically performed when the 
sheet empty is detected as the empty sensor is turned on. 
In steps S.5 through S.7, the page count PAGE `2` is restored at a point of 
time the page that has passed the fixing unit is discharged from the 
discharge port after the page count PAGE reaches `3` because of the 
increment in step S.2. 
The setting of the page count can be effected in accordance with the state 
in which the paper proceeds as shown in FIG. 13 through the process shown 
in the flowchart FIG. 14. 
The A-IC 83 is connected with a high voltage circuit to which provides 
biases to which the charger 12 and the like in the transfer unit 10 are 
connected, and further, a drive system, including the main motor 40, the F 
clutch 41, the halogen lamp in the heat roller 31 are connected to the 
A-IC to be controlled thereby. 
A thermistor 85 for detecting the temperature of the heat roller 31, a 
cover sensor 86 for detecting the opening and closing of the upper cover 
UC, and the PFS sensor (or photo-interrupter) 26 are connected to the A-IC 
as the sensors for supplying data to the A-IC. 
The heat roller 31 is controlled so as to have a high temperature as the 
fixing temperature only during printing, and a low temperature as the 
standby temperature when the printer is in a standby state to save power 
and to prevent the printer temperature from rising. 
Power is supplied to the halogen lamp provided in the heat roller 31, and 
acting as a heat source, from the power supply 87 for supplying 100 volts 
a.c. The power supply is turned ON and OFF by a signal from A-IC 83. A-IC 
83 receives an analog output from the thermistor provided adjacent to the 
heat roller 31 and executes A/D conversion so as to execute temperature 
control. 
The temperature control is effected with an allowance (i.e. range) of 
approximately .+-.5 degrees. As a result, the actual temperature of the 
heat roller 31 fluctuates within upper and lower limits as shown in FIG. 
10. Accordingly, there is a difference in the time required to lower the 
temperature to a certain value depending upon the actual temperature of 
the heat roller 31. If the actual temperature of the heat roller 31 is at 
the upper limit of the fixing temperature range, the time required to 
lower the temperature to the certain temperature is relatively long, 
while, if the actual temperature is at the lower limit of the fixing 
temperature range, the time is relatively short. In other aspect words, 
the temperature of the heat roller 31, after a predetermined time has 
past, differs, depending upon the temperature of the heat roller 31 when 
the temperature began to be lowered. It is obvious that more warm-up time 
will be required to raise the temperature of the heat roller 31 to the 
operable (fixing) temperature from the lower temperature than from the 
higher temperature. 
FIG. 11 shows the difference between two cases when the temperature of the 
heat roller 31 is lowered to a predetermined temperature set between the 
fixing and the standby temperatures. Point A shows a point where the 
temperature falls to a predetermined temperature, by being lowered from 
the lower limit of the fixing temperature, and point B shows a point where 
the temperature falls to a predetermined temperature after being raised to 
the upper limit, then lowered from the upper limit. In this example, there 
are approximately 30 seconds between point A and B. 
In the printer of this embodiment, when the temperature is lowered from the 
fixing temperature to the standby temperature, the temperature is first 
raised to the upper limit of the fixing temperature before being lowered. 
In this way, the temperature is prevented from being lowered from a 
relatively low temperature within the fixing temperature range so that the 
warm time required to raise the temperature up to the fixing temperature 
again, can be shortened. 
The B-IC 84 is connected with the semiconductor laser of the laser scanning 
unit 13 and an EEPROM 88 for storing printer life data. 
As to means for inputting data to the B-IC 84, the empty sensor 50, the 
skew sensor 51, the top sensor 52 and the jam sensor 53 and are primarily 
connected to the B-IC 84 which are concerned with the paper feeding. In 
addition, the B-IC 84 is connected with the waste toner sensor for warning 
of the presence or absence of the waste toner box 60 and the amount of 
accumulated waste toner, and the toner low sensor 14C for warning the 
shortage of toner, which are provided in the transfer unit 10 and 
constitute the sensors concerned with toner. 
As to the toner low sensor, in a conventional laser printer, it is common 
practice to set the sensor to output a low level signal when no toner is 
detected. With this arrangement, however, the problem is that when the 
sensor is disconnected, the low level signal indicating the low toner 
condition cannot be detected. In other word, the disconnection of the 
sensor and the toner-sufficient condition cannot be distinguished in the 
conventional printer. 
In this embodiment, the toner low sensor 14coutputs a high level signal 
when toner low is detected, while the B-IC 84 receives the signal in a 
pull-up state by use of a pull-up resistance 89 for receiving the signal 
in the pull-up state. 
HIGH is thereby inputted to the B-IC 84 when toner low is detected by the 
sensor 14c, when disconnection occurs in the sensor system and when the 
developing unit 14 installed with the toner low sensor 14c is not attached 
to the printer 100. In other words, a number of symptoms can 
simultaneously be detected with one sensor 14c. 
The toner low sensor 14c comprises the piezoelectric element incorporated 
in the bottom surface of the toner case 14a and it outputs a LOW level 
signal on sensing the pressure applied by the toner accommodated in the 
toner case 14a; and a HIGH level signal without such pressure. 
When sufficient toner is stored in the toner case 14a, the toner is always 
placed on the piezoelectric element serving as the toner low sensor 14c, 
despite the operation of the scraper 19, and the LOW level signal is 
always outputted. On the other hand, when the amount of toner is low, the 
HIGH level signal is outputted irrespective of the operation of the 
scraper 19. 
If the toner case 14a is substantially half filled with the toner, the 
toner is alternately placed on and swept off of the toner low sensor 14c 
as the scraper 19 slowly rotates, thus causing alternative output of the 
LOW and HIGH signals. Monitoring the duty ratio of the output of the toner 
low sensor 14c, the B-IC 84 judges the amount of the toner to be low when 
the HIGH signal exceeds 80 percent. 
As the toner is not supplied to the developing roller 14b by the scraper 19 
immediately after power is supplied, the output of the toner low sensor 
during the first three seconds, for two rotations of the scraper, is 
ignored. After the elapse of the three seconds, the toner low sensor 14c 
starts monitoring. Misjudgement of a low toner condition can thereby be 
prevented before the operation of the scraper 19, when power is supplied. 
The A-IC 83 and the B-IC 84 controls the printer 100 by exchanging data via 
a plurality of signal lines. From the B-IC 84 to the A-IC 83, transmitted 
are signals such as a signal indicating that the B-IC 84 is in a standby 
state, a STOP signal for immediately stopping the operation of each unit 
of the printer 100 when an emergency (i.e., urgent) error occurs, even if 
printing is being executed, and a PAUSE signal for stopping the operation 
of each unit after the predetermined operations, when a less urgent error 
occurs. 
On the other hand, error signals indicating errors in the drive system are 
transmitted from the A-IC 83 to the B-IC 84. 
The B-IC 84 analyzes the errors detected by itself and the errors 
transmitted for the A-IC 83 thereto, then determines their degrees of 
emergency in accordance with predetermined standards. The B-IC 84 selects 
the STOP or PAUSE signal depending on the degree of emergency, and then 
transmits the signal to the A-IC 83. The less urgent errors are the errors 
of a toner overflow, a toner low and a paper empty, while the other errors 
are treated as emergency errors. 
One hundred volts a.c. is applied to the printer, the control system being 
driven at 5 volts d.c., the driving system, such as the motor being driven 
at 24 volts d.c.. When a main switch 90 of the printer 100 is turned off, 
the voltage gradually drops from 24 volts d.c. to ultimately 0 volt as 
shown by a broken line in FIG. 12. 
The 5 volts d.c. power supply for the control system is so designed that 
more than 90 percent of the rated voltage (i.e. 4.5 volts d.c.) is held at 
least 20 msec. for storing data after the main power supply is turned off. 
If the voltage becomes less than 90 percent of the rated voltage, the 
control system may fail to control driving system. 
As to 24 volts d.c. power supply for the driving system, the voltage tends 
to fluctuate while it drops because of the operation of a protection 
circuit on the power supply side. Further, the control system does not 
operate as 5 volts d.c. is cut off at that point in time, which may cause 
vibration of the motor, and hence malfunctions. 
In this printer 100, the voltage applied to the driving system is 
instantaneously dropped from 24 volts d.c. to 0 volt upon turning off the 
100 volts a.c. main power supply 87, in order to prevent the 
aforementioned malfunctions. A relay is provided between the power supply 
and the driving system as a switch for the function stated above. The 
relay operates to cut off 24 volts d.c. either when a power good signal 
(PGS) representing the presence of the main power 87 supply is cut off of 
when the upper cover is opened. 
By instantaneously dropping the voltage from 24 volts d.c. to 0 volt as 
above, the driving system is stopped while the control system functions 
with 5 volts d.c. being applied. Moreover, the fluctuation of the voltage 
is prevented while it is dropping. Consequently, the motor is prevented 
from vibrating and hence malfunctioning. 
Laser printers are generally provided with a data recovery function for 
reprinting a blank page due to jamming or the like. 
Although a reference has been made to the use of continuous sheet whose 
page length is 11 inches long in the embodiment shown, a continuous sheet 
whose page length is 12 inches long may also be used by changing a counter 
for counting PFS pulses therefor. 
If 12-inch page length sheet is used in this printer 100, some additional 
arrangements may also be considered such that the last page carrying an 
unfixed toner image is discharged when printing is terminated, that the 
page remaining in the printer 100 is fed when printing is restarted, or 
that a perforated line is located at the fixing unit with the portion one 
inch from the next perforation being located at the transfer unit 14. 
As set forth above, the optimum number of pages can be retained for data 
recovery, in accordance with the state in which the paper progresses 
according to the present invention, whereby the paper is prevented from 
being wasted, whereas data recovery fit for the use of continuous form 
recording sheet can be implemented. 
The present disclosure relates to subject matters contained in Japanese 
Patent Application No. HEL 1-293712 (filed on Nov. 10, 1989) and No. HEI 
2-98225 (filed on Apr. 11, 1990), which are expressly incorporated herein 
by reference in their entireties.