Sheet feed device for a selectable print speed image forming device having a time delayed pick-up roller

In a sheet feed device for image forming equipment, a sheet feed section and a register section are each provided an exclusive drive arrangement. The sheet feed section starts feeding a sheet toward the register section in response to a feed start signal generated in an image forming section. The time for causing the sheet feed section to stop feeding a sheet or the time for causing the register section to start driving the sheet is delayed in matching relation to a print speed. As a result, the sheet feed section provides a sheet with a sufficient slack while the register section brings the sheet into accurate register with an image and can change the position of an image on the sheet in the top-and-bottom direction.

BACKGROUND OF THE INVENTION 
The present invention relates to a sheet feed device for a printer, copier 
or similar image forming equipment. 
It is a common practice with a sheet feed device of image forming equipment 
to feed a stack of sheets one by one from a rack or table toward a pair of 
register rollers movable into and out of contact with each other. The 
register rollers drive the sheet to an image forming section where an ink 
drum or a photoconductive element, for example, is located. In this type 
of sheet feed device, a pick-up roller associated with the rack is rotated 
in such an amount that the sheet moves a distance greater than the 
distance between the pickup roller and the register roller pair. Hence, 
after the leading edge of the sheet has abutted against the register 
roller pair, the leading edge portion of the sheet is sequentially 
slackened until the pick-up roller stops rotating. This allows the 
register roller pair to start driving the sheet at an accurate time and 
corrects the skew of the sheet which may occur during transport, despite 
the difference between the coefficient of friction of the sheet and that 
of the pick-up roller and the irregularity in the transport resistance of 
the path. The sheet feed device may be provided with a drive source 
implemented by a motor which drives the ink drum or the photoconductive 
element, a speed changing mechanism in the form of a gear train 
interlocked with the drive source, a cam for bringing the register roller 
pair into and out of contact, and a drive transmission mechanism for the 
cam. 
The sheet feed device of the type described has various problems left 
unsolved, as follows. To begin with, the structure for driving the pick-up 
roller and register roller needs a great number of parts and is not easy 
to design due to complexity. Although such parts may be accurately 
assembled as designed, it is likely that the interlocked relation is 
disturbed due to their mechanical wear and fatigue as the device is 
repetitively operated. Then, even when the pick-up roller is rotated a 
predetermined amount, the actual displacement of the sheet becomes short 
and prevents the sheet abutting against the register roller pair from 
being sufficiently slackened. If the abutment of the sheet against the 
register roller pair which is based on the slack or elasticity of the 
sheet is not sufficient, the register roller pair is apt to start feeding 
the sheet at an unexpected time or to fail to correct the skew of the 
sheet. This brings the sheet out of register with an image provided on the 
ink drum or the photoconductive element. The misregister of the sheet and 
image is particularly serious when the print speed or the copy speed is 
changed. 
Another function available with the register roller pair is to change the 
position on the sheet where an image begins to be transferred in a range 
corresponding to the upstream side with respect to a sheet feed direction, 
i.e., in the top-and-bottom direction. With this function, it is possible 
to change the area of a blank portion or margin to be formed at opposite 
ends of the sheet with respect to the sheet feed direction. This can be 
done if the time when the register roller pair starts feeding the sheet is 
changed. However, the register roller having such a function has to be 
provided with a number of constituents for transmitting a drive force from 
the drive source associated with the ink drum or the photoconductive 
element, as stated earlier. Moreover, the register roller needs a cam for 
changing the drive timing thereof, a drive source for operating the cam, 
an encoder or a sensor for determining the current displacement of an 
image in the top-and-bottom direction, noticeably scaling up and 
complicating the structure. In addition, since the interengagement of the 
constituent parts is apt to get out of order, the displacement of an image 
which can be set is limited to a certain range, resulting in low 
resolution. Therefore, to change the displacement, it is sometimes 
necessary to change the design itself. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a sheet feed 
device for image forming equipment which has a simple construction made up 
of a minimum number of parts, reduces the influence of aging of 
constituent parts, and slackens a sheet stably. 
It is another object of the present invention to provide a sheet feed 
device for image forming equipment which has a simple construction made up 
of a minimum number of parts, reduces the influence of aging of 
constituent parts, and feeds a sheet over a constant distance. 
It is another object of the present invention to provide a sheet feed 
device for image forming apparatus which has a simple construction made up 
of a minimum number of parts, reduces the influence of aging of 
constituent parts to facilitate the change in the displacement of an image 
on a sheet, and allows the displacement to be set with free resolution. 
In accordance with the present invention, in a sheet feed device for image 
forming equipment and having a rack on which sheets are stacked, a pick-up 
section for feeding uppermost one of the sheets from the rack while 
separating it from the others, and a register section located upstream of 
an image forming section with respect to an intended direction of sheet 
feed, the device feeding the sheet toward the register section in response 
to a feed start signal from the image forming section, there are provided 
a sheet sensor for sensing the sheet being fed from the rack toward the 
register section, speed selecting means for entering a period of time 
necessary for an image to be formed at the image forming section, and a 
controller connected at an input to the sheet sensor and speed selecting 
means and at an output to a driver included in the pick-up section for 
controlling, on receiving a signal from the sheet sensor, an amount of 
drive of the pickup section in matching relation to information entered on 
the speed selecting means. 
Also, in accordance with the present invention, in a sheet feed device of 
the type described, there are provided speed selecting means for entering 
a period of time necessary for an image to be formed at the image forming 
section, and a controller connected at an input to the speed selecting 
means and at an output to a driver included in the register section for 
controlling, on receiving a feed start signal from the register section 
derived from the image forming section, an amount of drive of the register 
section in matching relation to information entered on the speed selecting 
means. 
Further, in accordance with the present invention, in a sheet feed device 
for image forming equipment and having a rack on which sheets are stacked, 
a pick-up section for feeding uppermost one of the sheets from the rack 
while separating it from the others, and a register section located 
upstream of an image forming section with respect to an intended direction 
of sheet feed, the device feeding the sheet toward the register section in 
response to a feed start signal from the image forming section and feeding 
the sheet from the register section toward the image forming section in 
response to a feed start signal from the register section derived from the 
image forming section, there are provided a sheet sensor for sensing the 
sheet being fed from the rack toward the register means, speed selecting 
means for entering a period of time necessary for an image to be formed at 
the image forming section, a first control circuit connected at an input 
to the sheet sensor and speed selecting means and at an output to a driver 
included in the pick-up section and a driver included in the register 
section for controlling, on receiving a signal from the sheet sensor, an 
amount of drive of the pick-up section in matching relation to information 
entered on the speed selecting means, and a second control circuit 
connected at an input to the sheet sensor and speed selecting means and at 
an output to the driver included in the register section for controlling 
an amount of drive of the register section in response to a feed start 
signal from the register section derived from the image forming section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 of the drawings, image forming equipment to which a 
sheet feed device embodying the present invention is applied is shown. As 
shown, the equipment is implemented as a printer 1 having a hollow 
cylindrical ink drum 2. A cut stencil or master 3 is wrapped around the 
drum 2 by a clamp mechanisin, not shown. An ink supply mechanism, not 
shown, is disposed in the drum 2 to feed ink to the master 3. As a sheet 
is laid on the master 3, the ink is transferred to the sheet via the cuts 
of the master 3. The drum 2 is rotated by a drive motor 4 in a direction 
indicated by an arrow in the figure. An arrangement of causing a sheet to 
be picked up at a sheet feed section, which will be described, is 
associated with the drum 2. Specifically, a screen member 2A is affixed to 
the surface of the drum 2 while a pick-up roller trigger sensor 5 is 
disposed on the path which the screen member 2A moves. The pick-up roller 
trigger sensor 5 will be described later specifically in relation to a 
control system. 
A sheet feed section 6, a register section 7 and a pressing section 8 are 
sequentially arranged from the upstream side to the downstream side, i.e., 
to a position preceding the drum 2 with respect to a sheet feed direction 
A, constituting an arrangement for feeding sheets to the drum 2. To 
discharge a sheet S to which an image has been transferred from the master 
3, a separator 9, a roller pair 9A and a tray 10 are located downstream of 
the drum 2 in the sheet feed direction A. The separator 9 removes the 
sheet S from the master 3 of the drum 2. The sheet S removed by the 
separator 9 is transported by the roller pair 9A toward the tray 10. 
The sheet feed section 6 has a rack 6A to be loaded with a stack of sheets 
S, and a pick-up roller 6B for feeding the uppermost sheet from the rack 
6A while separating it from the others. As shown in FIG. 2, a one-way 
clutch 6C is mounted on a shaft 6B1 which supports the pick-up roller 6B, 
allowing the roller 6B to rotate only clockwise as viewed in the figure. 
On rotating clockwise, the pick-up roller 6B feeds the sheet S contacting 
the lower part of the roller 6B. A separating mechanism, not shown, 
separates the uppermost sheet S from the others on the basis of a 
difference in the coefficient of friction between the pick-up roller 6B 
and the sheets and a difference in the coefficient of friction between the 
wall of the rack 6A adjoining a sheet outlet and the sheets S. 
The rotation of the drive motor 4, FIG. 1, is transmitted to the pick-up 
roller 6B. Specifically, as shown in FIG. 3, an electromagnetic clutch 12 
is connected to the shaft 6B1 at the driven side thereof while a driven 
gear 11 is affixed to the drive side of the clutch 12. A belt 13 is passed 
over a belt pulley 13A and to which the rotation of the drive motor 4 is 
transmitted. A drive gear 14 is supported coaxially with the belt pulley 
13A and held in mesh with the drive gear 11. The clutch 12 is usually held 
in a deenergized state. As the clutch 12 is energized, it couples the 
drive side and the driven side so as to rotate the shaft 6B1 via the drive 
gear 14 and driven gear 11. At this instant, the previously mentioned 
one-way clutch 6C regulates the direction of rotation of the shaft 6B1. 
The register section 7 has a pair of register rollers 7A and 7B which 
respectively are disposed below and above a sheet transport path. In the 
illustrative embodiment, the rotation of the drive motor 4 is transferred 
to the lower register roller 7A to rotate it. Further, the drive force 
from the motor 4 causes the lower register roller 7A to periodically move 
into and out of contact with the upper register roller 7B via a moving 
mechanism, not shown. For example, a cam having a particular profile is 
included in the moving mechanism and causes the register roller 7A to 
contact the register roller 7B before the leading edge of the sheet S fed 
by the pick-up roller 6B reaches the register section 7. After the 
register roller 7A has been brought into contact with the register roller 
7B, the rotation of the motor 4 is transmitted to the roller 7A. Then, the 
register roller 7B is rotated by the underlying register roller 7A. The 
register rollers 7A and 7B are rotated in particular directions to drive 
the sheet S in the direction A at their contact position. 
The electromagnetic clutch 12 of the sheet feed section 6 is controlled by 
a controller 15 shown in FIG. 4. The controller 15 is mainly constituted 
by a microcomputer which executes arithmetic and logical operations for 
print processing. The pick-up roller trigger sensor 5, speed selecting 
means 16 and a sheet sensor 17 are connected to the input of the 
controller 15 via an input/output interface, not shown. The clutch 12 is 
connected to the output of the controller 15. The pick-up roller trigger 
sensor 5 is implemented by a photosensor and located in close proximity to 
the surface of the drum 2. As shown in FIG. 5, when the screen member 2A 
affixed to the surface of the drum 2 blocks the optical path of the sensor 
5, the sensor 5 generates a trigger signal. The trigger signal is used to 
set up the timing for causing the pick-up roller 6B to start picking up 
the sheet S. 
The speed selecting means 16 is implemented by, for example, numeral keys 
provided on an operation panel 1A, FIG. 1. The speed selecting means 16 
may be operated to change the print speed, i.e., the rotation speed of the 
motor 4. The sheet sensor 17 precedes the register section 7 in the sheet 
feed direction A, FIG. 2, and senses the leading edge of the sheet S being 
driven toward the register section 7 from the sheet feed section 6. 
On receiving the signal from the pick-up roller trigger sensor 5, the 
controller 15 energizes the electromagnetic clutch 12 to transfer the 
rotation of the drive motor 4 to the pick-up roller 6B. Then, the 
controller 15 causes the pick-up roller 6B to stop rotating at a 
particular time in response to a signal from the sheet sensor 17 
responsive to the leading edge of a sheet S fed from the rack 6A. In this 
manner, the controller 15 controls the amount of drive of the pick-up 
roller 6B. For this purpose, the controller 15 stores delay times each 
being associated with a particular print speed and defining the time when 
the clutch 12 should be restored to a deenergized state. Specifically, one 
of the delay times matching the print speed is selected, and on the elapse 
of the delay time a signal for deenergizing the clutch 12 is generated. In 
the illustrative embodiment, the lower the print speed, the longer the 
delay time is. 
A specific operation of the controller 15 will be described with reference 
to FIG. 6. On the start-up of the printer 1, the controller 15 stores or 
registers delay times each defining a particular time when the pick-up 
roller 6B should stop rotating in matching relation to a print speed, 
i.e., a particular time when the electromagnetic clutch 12 should be 
restored from an energized state to a deenergized state. As a print start 
command is entered on, for example, the operation panel 1A. FIG. 1, the 
controller 15 selects one of the stored delay times matching a print speed 
entered on the speed selecting means 16. Then, the controller 15 
determines whether or not a signal from the pick-up roller trigger sensor 
5 has arrived. When the signal from the sensor 5 arrives, the controller 
15 energizes the clutch 12. As a result, the rotation of the drive motor 4 
is transmitted to the shaft 6B1 of the pick-up roller 6B via the belt 13, 
drive gear 14, and driven gear 11. As the pick-up roller 6B feeds the 
uppermost sheet S from the rack 6A, the controller 15 determines whether 
or not the sheet sensor 17 has sensed the leading edge of the sheet S. As 
the sheet sensor 17 senses the leading edge of the sheet S, the controller 
15 delays the time for deenergizing the clutch 12 by the above-mentioned 
delay time from that instant. 
In the illustrative embodiment, the delay time increases with the decrease 
in print speed. Therefore, the sheet S can be paid out in a constant 
amount although the moving speed of the sheet S changes with the print 
speed. This maintains the slack of the sheet S to occur after abutment 
against the register roller pair 7 constant. After the amount of rotation 
of the pick-up roller 6B has been controlled as stated above, the 
controller 15 determines whether or not a print end command has been 
entered. If the answer of this decision is negative, the controller 15 
repeats the above processing. Such a procedure is repeated until a print 
end command arrives. 
An alternative embodiment of the present invention will be described 
hereinafter. In this embodiment, the register section 7 is not driven by 
the drive motor 4 associated with the drum 2, but by an exclusive drive 
source in terms of the amount of rotation and the time for rotation. 
Specifically, the embodiment uses a pulse motor 18 (see FIG. 1) for 
driving the lower register roller 7A under the control of the controller 
15. As shown in FIG. 7, a register roller trigger sensor 19 is connected 
to the input of the controller 15 in place of the pick-up roller trigger 
sensor 5 and sheet sensor 17, FIG. 4. A driver for driving the pulse motor 
driver 18 is connected to the output of the controller 15. The register 
roller 7A is movable into and out of contact with the overlying register 
roller 7B, as in the previous embodiment. The register roller trigger 
sensor 19 is implemented as a photosensor located in a different phase 
from the pick-up roller trigger sensor 5. When the screen member 2A of the 
drum 2 blocks the optical path of the sensor 19, the sensor 19 generates a 
trigger signal or feed start signal meant for the register section 7. 
Before the controller 15 causes the register section 7 to start feeding 
the sheet S in response to the feed start signal from the sensor 19, it 
sets a delay time for delaying the time when the register section 7 should 
start feeding the sheet S in matching relation to the print speed. 
Specifically, the controller 15 delays the time for starting driving the 
pulse motor 18 so as to bring the sheet S into register with the master 3 
wrapped around the drum 2. Assuming that the feed speed of the is register 
section 7 is constant, the delay time is selected such that the time for 
causing the register section 7 to feed the sheet S advances as the print 
speed increases. 
A reference will be made to FIG. 8 for describing a specific operation of 
the controller 15 in the above embodiment. On the start-up of the printer 
1, the controller 15 stores or registers delay times each defining a 
particular time for causing the register section 7 to start feeding the 
sheet S, i.e., the time for starting rotating the pulse motor 18. As a 
print start command is entered on, for example, the operation panel 1A. 
FIG. 1, the controller 15 selects one of the stored delay times matching a 
print speed entered on the speed selecting means 16. Then, the controller 
15 determines whether or not a signal from the register roller trigger 
sensor 19 has arrived. On receiving a signal from the register roller 
trigger sensor 19, the controller 15 starts driving the pulse motor 18 
when the delay time selected elapses. As a result, the register section 7 
starts feeding the sheet S abutting against the sheet S toward a position 
where the pressing section or roller 8 and the drum 2 contact each other. 
The amount of rotation of the pulse motor 18 is selected on the basis of 
the size of the sheet S such that the register section 7 continuously 
feeds the sheet S until the trailing edge of the sheet S moves away from 
the section 7. On reaching such an amount of rotation, the pulse motor 18 
is deenergized. 
Another embodiment of the present invention will be described in which the 
controller 15 controls both of the pick-up roller 6B and lower register 
roller 7A shown in FIG. 2. In this embodiment. the electromagnetic clutch 
12, FIGS. 2 and 3, and the pulse motor 18, FIG. 1, are used to drive the 
pick-up roller 6B and the lower register roller 7A, respectively. As shown 
in FIG. 9, the pick-up roller trigger sensor 5, speed selecting means 16, 
sheet sensor 17 and register roller trigger sensor 19 are connected to the 
input of the controller 15. Drivers for driving the electromagnetic clutch 
12 and pulse motor 18 are connected to the output of the controller 15. 
The controller 15 energizes the electromagnetic clutch 12 in response to a 
signal from the pick-up roller trigger sensor 5 and then starts rotating 
the pulse motor 18 in response to a signal from the register roller 
trigger sensor 19. Before executing this step, the controller 15 
determines a delay time matching the print speed for each of the clutch 
and pulse motor 18, i.e., a delay time for delaying the deenergization of 
the clutch 12 and a delay time for delaying the start of drive of the 
motor 18. 
A reference will be made to FIG. 10 for describing a specific operation of 
the controller 15 in the above embodiment. On the start-up of the printer 
1, the controller 15 stores or registers delay times each defining a 
particular time when the pick-up roller 6B should stop rotating in 
matching relation to a print speed, i.e., a particular time when the 
electromagnetic clutch 12 should be restored from an energized state to a 
deenergized state. As a print start command is entered on, for example, 
the operation panel 1A, FIG. 1, the controller 15 selects one of the 
registered delay times which matches information entered on the speed 
selecting means 16. Then, the controller 15 determines whether or not a 
signal from the pick-up roller trigger sensor 5 has arrived. When the 
signal from the sensor 5 arrives, the controller 15 energizes the clutch 
12. As a result, the rotation of the drive motor 4 is transmitted to the 
shaft 6B1 of the pick-up roller 6B via the belt 13, drive gear 14, and 
driven gear 11. As the pick-up roller 6B feeds the uppermost sheet S from 
the rack 6A, the controller 15 determines whether or not the sheet sensor 
17 has sensed the leading edge of the sheet S. As the sheet sensor 17 
senses the leading edge of the sheet S, the controller 15 delays the time 
for deenergizing the clutch 12 by the above-mentioned delay time from that 
instant. 
Also, the controller 15 selects one of the stored delay times meant for the 
pulse motor 18 and matching a print speed entered on the speed selecting 
means 16. Then, the controller 15 determines whether or not a signal from 
the register roller trigger sensor 19 has arrived. On receiving a signal 
from the register roller trigger sensor 19, the controller 15 starts 
driving the pulse motor 18 when the delay time selected elapses. As a 
result, the register section 7 starts feeding the sheet S abutting against 
the sheet S toward a position where the pressing section or roller 8 and 
the drum 2 contact each other. The amount of rotation of the pulse motor 
18 is selected on the basis of the size of the sheet S such that the 
register section 7 continuously feeds the sheet S until the trailing edge 
of the sheet S moves away from the section 7. On reaching such an amount 
of rotation, the pulse motor 18 is deenergized. On completing the control 
over the rotation of the pulse motor 18, the controller 15 determines 
whether or not a print end command has been entered. The controller 15 
repeats the above procedure until a print end command arrives. 
In this embodiment, the pick-up roller trigger sensor 5 and register roller 
trigger sensor 19 may be implemented by a single sensor. In such a case, 
on receiving a signal from, for example, the pick-up roller trigger sensor 
5, the controller 15 will cause the register roller 7A to contact the 
register roller 7B, set a longer delay time for delaying the start of 
drive of the pulse motor 18 than in the above-stated case, and then 
execute the processing described above. 
Hereinafter will be described another alternative embodiment of the present 
invention in which the timing for starting feeding the sheet S from the 
register section 7 is used to change the position to start transferring an 
image on the sheet S. It is often desired to change the size of the blank 
area or margin at the leading edge of the sheet S with respect to the 
sheet feed direction in matching relation to the configuration of a 
printing. In this embodiment, when the operator enters a particular size 
in the top-and-bottom direction which corresponds to the margin of 
interest, a controller 150. FIG. 11, sets up a displacement of the sheet S 
required to implement such a size in terms of the time for causing the 
register section 7 to start driving the sheet S. FIG. 11 shows a control 
arrangement for setting up the displacement of the sheet S. The controller 
150, like the controller of FIG. 4, is mainly constituted by a 
microcomputer. 
Assume that the embodiment controls the rotation of the pick-up roller 6 of 
the sheet feed section 6 via the electromagnetic clutch 12, as in the 
arrangement of FIG. 2. Then, as shown in FIG. 11, the pick-up roller 
trigger sensor 5, speed selecting means 16, sheet sensor 17, register 
roller trigger sensor 19 and displacement selecting means 20 are connected 
to the input of the controller 150. Connected to the output of the 
controller 150 are the electromagnetic clutch 12 and the driver for the 
pulse motor 18. The controller 150 stores a table listing print speeds and 
corresponding delay times meant for the clutch 12, as stated earlier. In 
addition, the controller 150 stores a table listing delay times for 
changing the time for starting driving the pulse motor 18 in response to a 
signal from the register roller sensor 19 on the basis of information 
entered on the displacement selecting means 20 and print speed. By 
selecting a particular delay time out of this table, the controller 150 
determines the time for actually starting driving the pulse motor 18. FIG. 
12 shows a specific table showing print speeds (a&lt;b&lt;c&lt;d) and corresponding 
displacements of the sheet S, on the assumption that the displacement is 
variable on a 1 millimeter basis. 
A specific operation of the controller 150 will be described with reference 
to FIG. 13. As shown, on the start-up of the printer 1, the controller 150 
stores or registers delay times each defining a particular time when the 
pick-up roller 6B should stop rotating in matching relation to a print 
speed, i.e., a particular time when the electromagnetic clutch 12 should 
be restored to an energized state to a deenergized state. At the same 
time. the controller 150 stores delay times each being associated with a 
particular time for starting driving the register section 7 in relation to 
a displacement. As a print start command is entered on, for example, the 
operation panel 1A, FIG. 1, the controller 15 selects one of the 
registered delay times matching information entered on the speed selecting 
means 16. Then, the controller 15 determines whether or not a signal from 
the pick-up roller trigger sensor 5 has arrived. When the signal from the 
sensor 5 arrives. the controller 15 energizes the clutch 12. As a result, 
the rotation of the drive motor 4 is transmitted to the shaft 6B1 of the 
pick-up roller 6B via the belt 13, drive gear 14, and driven gear 11. As 
the pick-up roller 6B feeds the uppermost sheet S from the rack 6A, the 
controller 15 determines whether or not the sheet sensor 17 has sensed the 
leading edge of the sheet S. As the sheet sensor 17 senses the leading 
edge of the sheet S, the controller 15 delays the time for aleenergizing 
the clutch 12 by the above-mentioned delay time from that instant. Also, 
the controller 15 selects a particular delay time for delaying the time 
for starting feeding the sheet S from the register section 7 and matching 
the determined displacement of the sheet S and print speed. On the elapse 
of this delay time, the controller 15 brings the register roller 7A into 
contact with the register roller 7B and then rotates it. At this instant, 
the sheet S is held in abutment against the register section 7 and 
provided with a slack determined by the time for stopping the rotation of 
the pick-up roller 6B. The slack of the sheet S remains the same at any 
print speed, as stated earlier. The register section 7 starts driving such 
a sheet S on the elapse of the above-mentioned delay time to change the 
position of the sheet S relative to the position of the master 3. As a 
result, the sheet S is provided with a desired margin at the leading edge 
thereof. 
FIG. 14 is a timing chart representative of a specific relation between 
delay times (Ta, Tb, Tc and Td) associated with the end of rotation of the 
pick-up roller 6B and delay times (T'a, T'b, T'c and T'd) associated with 
the feed start at the register section 7. In FIG. 14, the delay times 
meant for the register section 7 correspond to the delay times shown in 
FIG. 11. 
As stated above, by delaying the time for causing the register section 7 to 
start driving the sheet S, it is possible to change the position on the 
sheet S where the image of the master 3 begins to be transferred. FIGS. 
15A, 16A and 17A each shows the master 3 and sheet S in a particular 
transfer start position while FIGS. 15B, 16B and 17B each shows the 
leading edge of the sheet S and the leading edge of the image of the 
master 3 in a particular position. In these figures, the delay time is 
sequentially increased in the incrementing order of figure numbers. 
Specifically, the margin at the leading edge of the sheet S (displacement 
in the top-and-bottom direction) is sequentially increased with the 
increase in the delay time. 
In summary, it will be seen that the present invention provides a sheet 
feed device in which a sheet feed section and a register section can each 
be controllably driven by exclusive means. The device, therefore, 
simplifies drive transmission mechanisms for the sheet feed section and 
register section. This prevents the amount of sheet feed from becoming 
unstable due to the wear and fatigue of mechanical parts and prevents a 
sheet from being brought out of register with an image at an image forming 
station. Even when the displacement of a sheet is changed to change the 
position on a sheet where an image begins to be transferred, it is 
possible to control the sheet feed start timing by the register section 
which is subjected to exclusive drive control. Hence, any desired 
displacement of a sheet in the top-and-bottom direction can be set by a 
simple arrangement. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof. For example, while the present invention has been 
shown and described in relation to the ink drum of a printer, it is, of 
course, practicable with a photoconductive element incorporated in an 
electrophotographic copier or printer.