Sheet supply apparatus having an inverted V-shaped separation pad

A sheet supply apparatus is provided having a pressure plate for supporting sheets on a sheet supporting surface, a pick-up roller for feeding out the sheets supported by the pressure plate, a plate member for separating the sheets fed out by the pick-up roller one by one, and a separation pad provided on the sheet supporting surface of the pressure plate opposite the pick-up roller. The separation pad protrudes from the sheet supporting surface toward the sheets to contact frictionally the lower surface of the bottom-most sheet supported by the pressure plate. The separation pad has an upper surface which is higher at a portion opposing the pick-up roller than a portion downstream thereof, in a sheet feeding direction, relative to the sheet supporting surface of the pressure plate, to urge an end of a sheet fed out by the pick-up roller toward the pressure plate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a sheet supply apparatus for supplying a 
sheet (for example, printing sheet, transfer sheet, photosensitive sheet, 
electrostatic recording sheet, print sheet, OHP sheet, envelope, post 
card, sheet original and the like) from a sheet stacking portion to a 
sheet treating portion (for example, recording portion, reading portion, 
working portion and the like) in an image forming apparatus such as a 
recording device, i.e., a printer (as an information output device of a 
word processor, a personal computer and the like), a copying machine, a 
facsimile machine and the like, and a recording apparatus having such a 
sheet supply apparatus. 
2. Related Background Art 
In sheet supply apparatuses, it is required that stacked sheets are surely 
separated one by one and the separated sheet is positively supplied. In 
the past, there has been proposed a technique in which a pawl member is 
provided in association with a front corner of a sheet stack so that, when 
sheets are fed out by a sheet supply roller, only an uppermost sheet is 
flexed to ride over the pawl member, thereby separating the sheets one by 
one. However, in this technique, sheets having great resiliency (hard to 
be flexed) such as envelopes, post cards and the like cannot surely be 
separated one by one. 
On the other hand, there has been proposed a technique in which sheets hard 
to be flexed (for example, envelopes, post cards and the like) can be 
separated one by one (see Japanese Patent Appln. Laid-Open No. 3-284547). 
This technique will now be explained with reference to FIG. 11. A sheet 
stacking plate 201 for stacking sheets thereon is biased upwardly by a 
spring member 203. A free roller 204 for regulating an upper surface of 
the sheet stack is contacted with an upper surface of the sheet stack on 
the sheet stacking plate 201 to maintain the upper surface of the sheet 
stack below a guide surface 205. Further, an inclined surface 207 for 
separating sheets is disposed at a downstream side of the sheet stacking 
plate 201. 
A sheet supply roller 206 is constituted by a semi-circular roller having a 
large diameter portion and a small diameter portion (cut-out portion) so 
that, when the large diameter portion of the sheet supply roller is urged 
against an upper surface of the sheet stack on the sheet stacking plate 
201, one or several sheets are fed out. The sheets fed out by the sheet 
supply roller 206 abut against the inclined surface 207. In this case, an 
uppermost sheet rides over the inclined surface 207 while being flexed, 
thereby separating the uppermost sheet from the other sheet(s). Since tip 
ends of second and other sheets are pressed downwardly by an elastic force 
of the flexed uppermost sheet, these sheets cannot ride over the inclined 
surface 207. In this way, the sheets are positively separated one by one. 
However, in such a separating mechanism, since the elastic force generated 
in the uppermost sheet when the uppermost sheet is flexed around a contact 
point P between the sheet and the free roller 204 acts on the tip ends of 
the second and other sheets and affects a great influence upon the 
separation of the sheets, the inclination of the inclined surface 207 must 
be set in accordance with the flexural rigidity of the sheet. That is to 
say, when the sheets having great flexural rigidity are separated, the 
inclination of the inclined surface must be set smaller so that the fed 
out sheet is not deformed or folded; whereas, when the sheets having small 
flexural rigidity are separated, the inclination of the inclined surface 
must be set greater so that the second and other sheets can be fully held 
by the elastic force of the flexed uppermost sheet. 
Accordingly, when the inclination of the inclined surface 207 is set 
greater to separate the sheets (for example, envelopes, post cards and the 
like) having great flexural rigidity, for example, when copying sheets 
having a weight of 60-100 g/m.sup.2 try to be separated, the second and 
other sheets cannot be adequately held by the elastic force of the flexed 
uppermost sheet, with the result that the double-feed of sheets may occur. 
Thus, such an inclined surface cannot be used for the sheet having small 
flexural rigidity (such as plain sheet). 
To avoid this, there has been proposed a technique in which both sheets 
having different flexural rigidities can be separated by a single 
separation means. Now, this technique will be explained with reference to 
FIG. 12. A sheet stacking plate 301 on which sheets are stacked as a sheet 
stack is biased upwardly by a spring 302 so that, when a sheet supply 
roller 303 is contacted with an uppermost sheet in the sheet stack, 
several sheets are fed out by rotation of the sheet supply roller. 
An elastically deformable plate member 305 is disposed at a position where 
tip ends of the stacked sheets is regulated. The plate member 305 is 
formed from a plastic film or a metallic spring plate having predetermined 
flexural rigidity and can be elastically deformed when the sheets fed out 
by the sheet supply roller 303 abuts against the plate member. 
When the sheet supply roller 303 is rotated and the sheet stack on the 
stacking plate 302 is urged against the sheet supply roller 303 by a force 
of the spring 302 (upon releasing the sheet stacking plate by a release 
means (not shown)), the plate member is greatly flexed by the tip ends of 
the driven sheets. In this condition, the tip end of the uppermost sheet 
rides over the plate member while sliding on the latter, thereby 
separating the uppermost sheet from the other sheets. With this 
arrangement, various sheets having different rigidities can be separated. 
Incidentally, separation pads 306 for generating a double-feed preventing 
force by contacting with a last sheet are provided on a sheet stacking 
surface of the sheet stacking plate 302. The separation pads 306 are 
normally formed from elastic material such as rubber, artificial leather 
or the like. 
However, in the sheet supply apparatus having the construction shown in 
FIG. 12, when the sheet supply roller 303 is rotated, the separation pads 
306 may be elastically deformed to float. If the separation pads are 
deformed in this way, as shown in FIG. 13, the tip ends of the sheets are 
lifted, with the result that the deforming start position of the plate 
member 305 is elevated. In the separating method using the plate member 
305, since the sheets are separated by controlling the elasticity of the 
plate member 305, if the deforming start position is elevated, an amount 
of deformation of the plate member 305 is increased, with the result that 
two or more sheets may ride over the plate member simultaneously, thereby 
causing the double-feed. 
Further, even if the separation pads 306 are formed from material which is 
hard to be elastically deformed, due to inaccurate parallelism of the 
sheet stacking surface of the sheet stacking plate 302 and/or dispersion 
in thickness of the separation pads 306, the above-mentioned phenomenon 
(floating of the separation pad or pads) may occur, thereby causing the 
double-feed. Thus, this attempt is still unsatisfactory. 
SUMMARY OF THE INVENTION 
The present invention aims to eliminate the above-mentioned conventional 
drawbacks, and an object of the present invention is to positively prevent 
double-feed of sheets due to deformation of separation pad or pads 
provided on a sheet stacking plate. 
To achieve the above object, according to the present invention, there is 
provided a sheet supply apparatus comprising a sheet stacking means for 
stacking sheets, a sheet supply means for feeding out the sheets stacked 
on the sheet stacking means, a separation means for separating the sheets 
fed out by the sheet supply means one by one, and a friction separation 
pad means provided on a sheet stacking surface of the sheet stacking means 
in a confronting relation to the sheet supply means. Wherein the 
separation pad means is so shaped that a surface of the separation pad 
means opposed to the sheet supply means has an upstream side high level 
surface portion and a downstream side low level portion in a sheet 
supplying direction. 
The present invention further provides a recording apparatus comprising a 
sheet stacking means for stacking sheets, a sheet supply means for feeding 
out the sheets stacked on the sheet stacking means, a separation means for 
separating the sheets fed out by the sheet supply means one by one, a 
recording means for executing recording on the sheet separated by the 
separation means, and a friction separation pad means provided on a sheet 
stacking surface of the sheet stacking means in a confronting relation to 
the sheet supply means. Wherein the separation pad means is so shaped that 
a surface of the separation pad means opposed to the sheet supply means 
has an upstream side high level surface portion and a downstream side low 
level portion in a sheet supplying direction. 
With the arrangement as mentioned above, when the sheets stacked on the 
sheet stacking means are fed out by the sheet supply means, due to the 
configuration of the separation pad means, downstream ends of the sheets 
are not floating, with the result that the sheets can be sent to a proper 
position of the separation means. Thus, the poor separation of the 
separation means can be reduced. 
Further, when a contact width between the separation pad means and the 
sheet is smaller than a width of the sheet supply means, since the 
separating action is generated not only by contacting the sheet with the 
upper surface of the separation pad means but also by contacting the sheet 
with side edges of the separation pad means, the apparatus can be made 
compact and cheaper without reducing the separating ability of the 
separation pad means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
Entire Construction 
FIG. 1 is a perspective view of the entire recording apparatus A having a 
sheet supply apparatus B according to the present invention. 
A paper tray 1 also acts as a cover of the recording apparatus A and can be 
rotated around a rotary shaft (not shown) in a direction shown by the 
double-headed arrow. In use, the paper tray 1 is opened as shown in FIG. 
1. One or more sheets are set on the paper tray 1 with tip ends of the 
sheets being inserted into sheet supply opening 7. In this condition, the 
sheets are separated one by one by the sheet supply apparatus B disposed 
within the recording apparatus and the separated sheet is supplied to a 
recording portion C. A paper guide 2 can be slid left and right with 
predetermined friction to regulate side edges of the sheets stacked on the 
paper tray 1, thereby aligning the sheets. 
After an image is recorded on the sheet separated and supplied to the 
recording portion C by the sheet supply apparatus B, the sheet is 
discharged out of the recording apparatus A through a discharge opening 6. 
Key-tops 3 for handling the recording apparatus A include tact-switches 
for effecting ON/OFF of a power source, a sheet supplying operation, a 
sheet discharging operation and the like. A display 4 serves to display a 
sheet operating condition, a sheet setting condition, an error mode and 
the like. 
Sheet Supply Portion 
FIG. 2 is a sectional view of the recording apparatus A. A sheet stacking 
means for stacking the sheets S is constituted by a pressure plate 10 
which is biased upwardly (FIG. 2) by pressure springs 9. A pick-up roller 
(sheet supply means) 8 is disposed in a confronting relation to an 
uppermost sheet in the sheet stack S. 
In a sheet supplying condition, the uppermost sheet in the sheet stack S on 
the pressure plate 10 is urged against the pick-up roller 8 by biasing 
forces of the pressure springs 9, so that, by rotating the pick-up roller 
8, the sheets are fed out by friction. On the other hand, in a waiting 
condition as shown in FIG. 2, the pressure plate 10 is lowered in 
opposition to the biasing forces of the pressure springs 9 by means of a 
cam mechanism (not shown). Incidentally, the pick-up roller 8 is a 
so-called semi-circular roller having a cut-out portion, and, by waiting 
the pick-up roller in a condition as shown in FIG. 2, the sheet setting 
ability is improved. 
A separation pad 11 having predetermined coefficient of friction is 
attached to a sheet stacking surface of the pressure plate 10 by adhesive 
and the like so that the separation pad is contacted with a lowermost 
sheet in the sheet stack. The coefficient of friction of the separation 
pad is so selected that friction coefficient .mu.SS between the sheets 
becomes smaller than friction coefficient .mu.SP between the separation 
pad 11 and the sheet and friction coefficient .mu.SR between the pick-up 
roller 8 and the sheet becomes greater than the friction coefficient 
.mu.SP. Namely, 
.mu.SS&lt;.mu.SP&lt;.mu.SR 
Thus, when the number of sheets stacked on the pressure plate becomes few, 
it is possible to prevent the double-feed phenomenon that the lowermost 
sheet is fed out together with the sheet being fed by the pick-up roller 
8. 
A separation means for separating the sheets one by one is constituted by a 
plate member 21. The plate member 21 is elastically deformed when it is 
urged by the sheets fed by the pick-up roller 8, with the result that, 
when the uppermost sheet ridges over the deformed plate member 21, the 
uppermost sheet is separated from the other sheets. Incidentally, the 
plate member 21 is formed from synthetic resin film such as Myler. 
Now, the separation pad 11 will be fully explained with reference to FIGS. 
3 and 4. 
As shown in FIG. 3, the separation pad 11 has an inverted V-shaped section 
including a central portion protruded above the sheet stacking surface of 
the pressure plate 10 and is attached to the pressure plate 10 in such a 
manner that a surface 11a of a front portion of the separation pad 11 is 
inclined with respect to the sheet stacking surface of the pressure plate 
10 by an angle of .theta.. Further, the pick-up roller 8 is disposed in a 
confronting relation to the front surface 11a of the separation pad 11 
inclined by the angle of .theta.. 
With the arrangement of the separation pad 11 as mentioned above, in the 
sheet supplying operation, as shown in FIG. 4, the sheet urged against the 
rotating pick-up roller 8 by the biasing forces of the pressure springs 9 
and fed out by the pick-up roller is guided along the front surface 11a by 
the angle of .theta.. Thus, the fed sheet is not floating and abuts 
against the plate member 21 at a substantially constant position along the 
sheet stack. Accordingly, the deformed amount of the plate member 21 is 
stabilized, thereby preventing the poor sheet supply such as double-feed. 
A surface 11b of a rear (i.e. downstream) portion of the separation pad 11 
is inclined in an direction opposite to the inclining direction of the 
front surface 11a, so that, when sheets are loaded on the pressure plate 
10, even if the sheets are inserted along the sheet stacking surface of 
the pressure plate 10, the tip ends of the sheets cannot be caught by the 
rear end of the separation pad 11, and the sheets are surely loaded on the 
pressure plate since the tip ends of the sheets can easily ride over the 
separation pad 11 along the rear surface 11b. 
Further, as shown in FIG. 7, when a width of the separation pad 11 is set 
to be smaller than a width of the pick-up roller 8, due to the compactness 
of the separation pad, the apparatus can be made cheaper, and, the 
coefficient of friction of the separation pad 11 and the sheet can be made 
optimum and side edges of the separation pad 11 can contribute to separate 
the sheets, thereby obtaining the stable sheet separating ability. 
Incidentally, although the separation pad 11 is formed from a plate-shaped 
elastic member made of rubber, artificial leather, cork or the like and is 
attached to the pressure plate while bending the plate-shaped elastic 
member, the plate-shaped elastic member may be previously bent. 
Sheet Convey Portion 
As shown in FIG. 2, at an upstream side of the recording portion C which 
will be described later, there are disposed an LF roller 13, and a pinch 
roller 14 positioned below the LF roller and urged against the LF roller 
by a coil spring 15. Further, at a downstream side of the recording 
portion C, there are disposed a pair of discharge rollers 20 arranged 
along a sheet conveying direction, and a pair of discharge pinch rollers 
16 disposed below the respective discharge rollers 20 and urged against 
the respective discharge rollers by corresponding discharge coil springs 
17. 
With this arrangement, since the sheet is pushed upwardly by the pinch 
roller 14 and the discharge pinch rollers 16 up to lowermost points on 
peripheral surfaces of the LF roller 13 and of the discharger rollers 20. 
A distance between an upper surface of the sheet and a print head 18 
provided in the recording portion C can always be kept constant regardless 
of the thickness of the sheet. This permits the stable printing. 
Panel Board Portion 
As shown in FIGS. 5 and 6, at a downstream side of and above the sheet 
supply apparatus B, there is disposed a panel board 23 positioned near an 
operation surface. The panel board 23 is disposed immediately below the 
key-tops 3 so that force applied to the key-tops 3 are converted into 
electrical signals by detectors (not shown) on the panel board 23 for 
commanding the respective operations. 
A paper sensor 12 is attached to the panel board 23, which paper sensor 12 
serves to emit a detection signal in response to rotation of a paper 
sensor lever 12a protruded into a sheet path. Now, a relation between the 
paper sensor 12 and the LF roller 13. 
The sheet fed out by the pick-up roller 8 and separated by the plate member 
21 rotates the paper sensor lever 12a, with the result that the detection 
signal (for sheet) is outputted from the paper sensor 12. On the basis of 
this detection signal, by rotating the pick-up roller 8 by a predetermined 
amount, the sheet reaches the LF roller 13. In this case, by stopping the 
LF roller 13 or by rotating the LF roller in a reverse direction, the tip 
end of the fed sheet abuts against a nip between the LF roller 13 and the 
pinch roller 14 to form a loop in the sheet, thereby correcting the 
skew-feed of the sheet (registration operation). 
When the sheet is conveyed on the basis of the detection signal of the 
paper sensor 12 in this way, the sheet can be fed out with a correct 
distance between the LF roller and the pick-up roller, thereby avoiding a 
danger that the sheet does not reach the LF roller (and, thus, the 
skew-feed cannot be corrected) or the sheet is execessively penetrated 
into the nip to fold the sheet. 
Recording Portion C 
As shown in FIGS. 2 and 5, a carriage 19 on which the print head 18 is 
mounted is slidably supported on a guide shaft 31 disposed on a chassis 24 
along a longitudinal direction thereof and is driven by a carriage motor 
(not shown) and a carriage belt (not shown) in response to a recording 
signal. An HP sensor 28 for positioning the carriage 19 is attached to a 
carrier running portion of the chassis 24. The HP sensor comprises a 
photo-interrupter of permeable type which serves to detect the passing of 
a light shield plate of the carriage 19, thereby detecting the position of 
the carriage 19. 
The print head 18 is electrically connected to a controller board 22 (FIG. 
2) through a carriage flexible cable 32 so that the recording operation of 
the print head 18 is effected in response to a signal from the controller 
board 22. 
The recording method of the print head 18 is an ink jet recording method in 
which a selected electro-thermal converter is energized in response to the 
recording signal and, by growing a bubble in ink by heating the ink to 
exceed film boiling by means of the energized electro-thermal converter, 
the ink is discharged from a discharge opening, thereby executing the 
recording. 
Operation 
Next, the operation in the first embodiment will be explained. 
In the sheet supply apparatus B, the sheets stacked on the pressure plate 
10 are fed out by the pick-up roller 8 to reach the plate member 21. When 
the plate member is deformed and the uppermost sheet rides over the plate 
member, the uppermost sheet is separated from the other sheets. 
The separated and conveyed sheet is detected by the paper sensor 12, and, 
after detection, the sheet is conveyed by the predetermined amount, 
thereby correcting the skew-feed of the sheet by the LF roller 13. 
After the sheet is conveyed toward the discharge roller 16 and the 
registration of the sheet is completed, the sheet is further conveyed; 
meanwhile, the recording is effected on the sheet by means of the print 
head 18. After recording, the sheet is discharged out of the recording 
apparatus through the discharge opening 6 by means of the discharge 
rollers 16. 
Second Embodiment 
Now, a second embodiment of the present invention will be explained with 
reference to FIGS. 7 and 8. Incidentally, explanation of the same elements 
as those in the first embodiment will be omitted. 
The separation pad 11 is secured to the pressure plate 10 while deforming a 
plate-shaped member into an inverted V-shape. If the separation pad 11 is 
merely adhered to the sheet stacking surface of the pressure plate 10, 
when the sheet is fed out by the pick-up roller 8, the end of the sheet 
will be floating to float the entire sheet and/or the separation pad 18 
itself will be peeled from the pressure plate. To avoid this, in the 
second embodiment, front and rear ends of the separation pad 11 are held 
by shelves 111, 112 formed on the pressure plate 10. 
With this arrangement, when the sheet is fed out by the pick-up roller 8, 
it is possible to prevent the end of the sheet from floating and the 
separation pad 11 from being peeled, thereby achieving the stable sheet 
supply. Further, due to the provision of the shelf 112, when sheets are 
loaded on the sheet stacking surface of the pressure plate 10, the tip 
ends of the sheets are guided by the shelf 112, with the result that the 
tip ends of the sheets cannot be caught by the end of the separation pad 
11, thereby preventing the folding of the sheets and achieving the smooth 
loading of the sheets. 
Incidentally, since the operation of the sheet supply apparatus according 
to the second embodiment is the same as the first embodiment, explanation 
thereof will be omitted. 
Third Embodiment 
Next, a third embodiment of the present invention will be explained with 
reference to FIGS. 9 and 10. Incidentally, explanation of the same 
elements as those in the first embodiment will be omitted. 
A recess 101 is formed in the pressure plate 10 in a confronting relation 
to the pick-up roller 8. The separation pad 11 is secured within the 
recess 101 while deforming it into an inverted V-shaped as is in the 
second embodiment. Incidentally, the front and rear ends of the separation 
pad 11 is held by the shelves 111, 112 formed on the pressure plate 10, 
thereby preventing the peeling of the separation pad. 
Since the recess 101 has a dimension capable of receiving the pick-up 
roller 8, the pick-up roller 8 is not contacted with the sheet stacking 
surface of the pressure plate 10. Accordingly, when the sheets are urged 
against the pick-up roller 8 by the pressure springs 9, the load from the 
pressure springs 9 positively acts on the separation pad 11, with the 
result that the adequate friction force can be applied to the last sheet, 
thereby surely preventing the double-feed. 
As mentioned above, according to the present invention, when the sheet is 
fed out by the sheet supply means, due to the particular configuration of 
the separation pad, the front end of the sheet can be prevented from 
floating. As a result, since the sheet can reach the proper position on 
the separation means to reduce the occurrence of the poor separation of 
the separation means, the stable sheet supply can be realized and the 
reliable sheet supply apparatus can be provided.