Sheet feeding apparatus

A bottom sheet feeder employing a vacuum feed assembly in conjunction with an air knife for separating and feeding sheets from a sheet stack. A self regulating blower input and output bleed valve assembly utilized in conjunction with a single blower regulates air flow through the blower to the air knife irrespective of the degree of air flow through the vacuum feed assembly caused by blockage thereof by the acquired sheets.

BACKGROUND OF THE INVENTION 
With the advent of high speed xerographic copy reproduction machines 
wherein copies can be produced at a rate in excess of three thousand 
copies per hour, the need for a document handler to feed documents to the 
copy platen of the machine in a rapid, dependable matter was recognized to 
enable full utilization of the reproduction machines potential copy 
output. A number of document handlers are currently available to fill that 
need. These document handlers must operate flawlessly to virtually 
eliminate the risk of damaging the originals and generate minimum machine 
shutdowns due to uncorrectable misfeeds or document multifeeds. It is in 
the initial separation of the individual documents from the document stack 
where the greatest number of problems occur. 
To provide a gentle yet positive feed, a vacuum feed belt assembly may be 
positioned beneath the stack of documents to be fed for acquiring the 
bottom document in the stack on the belts by vacuum and energizing the 
belts to pull the acquired document from under the stack into the document 
path of the document handler. To prevent misfeeds and multifeeds, an air 
knife may be positioned at the lead edge of the stack for injecting air 
between the documents in the stack to provide an air bearing between the 
document being fed and the remainder of the stack. This greatly reduces 
the force necessary to pull the bottom document from the stack and also 
minimizes the possibility of the adjacent document being pulled out from 
under the stack with the document being fed. 
To simplify the feed system, a single blower may be used to provide both 
positive and negative air pressure for the air knife and vacuum feed belt 
assembly respectively. 
However, if the sheet being fed is tightly drawn onto the vacuum feed belt 
assembly, the sheet will substantially block the flow of air to the inlet 
of the blower, thereby reducing the flow of air to the air knife below the 
level required to adequately lift the document stack and provide an air 
bearing between the sheet being fed and the remainder of the sheets in the 
stack. 
Conversely, prior to a sheet being pulled down onto the vacuum feed belt 
assembly, air flow to the blower may be essentially unrestricted, 
resulting in excess air flow to the air knife. It is therefore the object 
of this invention to provide a sheet feeder having an automatic self 
compensating air flow control valve to provide the desired air flow 
through the system at all times. 
SUMMARY OF THE INVENTION 
A sheet feeder for separating and feeding the bottom sheet in a sheet 
stack, including a plurality of vacuum feed belts spaced below the surface 
of the sheet stack tray, positive air pressure means being provided for 
air flotation of the stack to reduce the weight of the stack on the bottom 
sheet thereof. A single blower is utilized to provide the sub-atmospheric 
pressure for the vacuum feed means and the air supply for air flotation. 
To provide optimum air flow in the system, a self actuating 
vacuum-pressure bleed valve is interconnected with the blower inlet and 
outlet.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, there is illustrated an automatic document 
handler 1 for installation above the exposure platen 3 of a xerographic 
reproduction machine. The document handler is provided with a document 
tray 5 to be explained more fully hereinafter, adapted for supporting a 
stack of documents 7 face up. A vacuum belt-corrugating feeder mechanism 9 
is located below the document tray for acquiring and corrugating the 
bottom document in the stack and forwarding the document to take away roll 
pair 11 after an air knife 12 has had time to separate sheet 1 from the 
rest of the stack. The document is then fed by take-away roll pair 11 
through document guide 13 to feed-roll pair 15 and under platen belt 17 
onto the platen of the copy machine for reproduction. After exposure of 
the document, it is fed off the platen by belt 17 into guide 19 and 
feed-roll pairs 21 and 23 either to an inverter mechanism 25 or back to 
the document stack through the feed-roll pair 27. A diverter 29 is 
provided to divert the document either to the inverter or to the feed roll 
pair 27. The inverter comprises a three roll arrangement 31 and a closed 
inverter pocket 33. If the document is to be inverted it is fed through 
the lower two rolls of the three roll inverter into the pocket. When the 
trail edge of the document clears the nip of the lower two rolls in the 
three roll inverter, the stiffness of the sheet will cause the trail edge 
to straighten up into the nip of the upper two rolls of the inverter at 
which time it will be fed into roll pair 27 and back into the document 
stack. The inverter pocket illustrated is sized such that when the leading 
edge of the document contacts the end of the pocket, the document will 
buckle slightly within the upper portion of the pocket 33, the buckle 
thereby providing the required force to feed the trailing edge of the 
document into the upper roll pair of the inverter rolls for feeding the 
sheet toward roll pair 27. If desired, an open ended inverter pocket could 
be utilized having a feed roll pair associated therewith for feeding the 
document back into the upper roll pair in a positive manner rather than 
relying on the sheet buckle to feed the document thereto. 
The document handler is also provided with a sheet separator finger 35 as 
is well known in the art to separate the documents to be fed from those 
documents returned to the document handler. Upon removal of the last 
document from beneath sheet separator finger 35, the finger 35 drops 
through a slot provided in the tray, suitable sensors are provided to 
sense that the last document in the set has been removed from the tray and 
the finger is then rotated in a clockwise direction to again come to rest 
on the top of the documents in the stack prior to subsequent recirculation 
of the document set. 
Referring more particularly to FIGS. 2, 3 and 4 wherein the sheet 
separator-feeder is more clearly illustrated, there is disclosed a 
plurality of feed belts 37 supported for movement on feed belt rolls 38, 
39, and 40. Spaced within the run of the belts 37 there is provided a 
vacuum plenum 41 having openings 43 therein adapted for cooperation with 
perforations 45 in the belts 37 to provide a vacuum for pulling the bottom 
document in the document stack onto the belts 37. The belts are located 
below the surrounding support surface so that the sheet being fed is 
pulled down from the bottom of the sheet stack. The gap formed between 
sheets one and two provide for entry of the separating air flow from the 
air knife 12. The air knife 12, comprised of pressurized air plenum 50 
having a plurality of air jet openings 51, is provided to inject air into 
the pocket formed between the document pulled down against the feed belt 
and the documents thereabove to provide an air cushion or bearing between 
the stack and the bottom document to minimize the force necessary for 
removing the bottom document from the stack. 
By suitable valving and controls (not shown), a delay may be provided 
between the time the vacuum is applied to pull the document onto the belts 
and the start up of the feed belts to assure that the bottom document is 
captured on the belt before belt movement commences and to allow time for 
the air knife to separate sheet 1 from any sheets that were pulled down 
with it. 
By reference to FIGS. 1, 2 and 4 it can be seen that the document tray 5 is 
provided with a depressed portion or pocket 53 behind the feed belt 
assembly. This pocket serves a number of purposes. First, space is 
provided for the forward portion of the bottom document to be pulled down 
onto the feed belt assembly as previously mentioned. When the bottom 
document is pulled into this space, an envelope type opening or pocket is 
created between the bottom sheet and the remainder of the sheets in the 
stack. Air injected into this space from the air knife produces an air 
bearing between the bottom sheet and the remainder of the stack to allow 
easy removal of the bottom sheet from beneath the stack. Flow of air from 
the pocket is restricted by the partial seal or flow restricton caused by 
supporting the major portion of the stack weight on the edge portions of 
the tray surrounding the pocket. 
To further increase the efficiency of the system, the stack tray is 
provided with a rearward tilt as seen in FIGS. 1 and 2. When flotation air 
is provided under the stack or between the first and second sheets, 
gravity will allow the sheets to settle or float back against the rear 
tray wall. Thus, the sheet being removed is pulled uphill while gravity 
helps hold the remainder of the sheets back, helping to prevent 
multifeeds. 
By reference to FIG. 1, it can be seen that a single blower unit 55 is 
utilized to provide sub-atmospheric pressure in plenum 41 and pressurized 
air to air knife 12. The air flow through blower 55 is partially 
controlled by the actual operation of the feeder in that when a sheet is 
acquired on the vacuum belts, a restriction of air flow to the blower is 
caused by the sheet, thereby reducing the output of air supplied to the 
air knife. Thus in certain circumstances, depending upon the paper weight 
and therefore the ability of the sheet being fed to conform to the 
apertures in the feed belt assembly vacuum plenum, the sheet being fed 
acts as a control valve for the system. However, further control of the 
air flow through the system may be desirable. Therefore, a control valve 
57, best illustrated in FIG. 3 is provided to assure adequate air flow to 
the air knife under circumstances where the sheet being fed substantially 
blocks off flow of air to the blower and also to prevent excessive air 
flow to the air knife prior to sheet acquisition on the feed belts. 
By reference to FIG. 3, it can be seen that a two chambered valve assembly 
is provided, the first chamber 58 having an inlet 59 communicating with 
the vacuum feed belt assembly plenum and an outlet 61 for communication 
with the inlet to the blower 55. The valve assembly is also provided with 
a second chamber 62 having an inlet 63 for communication with the output 
side of blower 55 and an output port 65 for communication with the air 
knife plenum. A vacuum bleed port 67 having a cooperating valve 69, and a 
pressurized bleed port 71 having a valve 73 associated therewith are 
interconnected by a lever arm 75 for reasons to be hereinafter explained. 
The lever arm 75 is pivoted at 77 and biased in a counterclockwise 
direction by suitable means such as spring 79. 
Under conditions wherein very little air blockage is encountered at the 
vacuum feed belt assembly, air flow into port 59 through port 61 to the 
inlet of the blower will be at a level such that minimum vacuum will be 
produced within chamber 58. Valve 69 will therefore remain closed as 
illustrated which will result in valve 73 being open to bleed some of the 
air flow from the output of blower 55 to prevent excessive air discharge 
from air knife 12 and minimize sheet blow away in the sheet stack which 
could result from unrestricted flow of air through the blower. 
In the event that the air apertures in the vacuum feed belt assembly are 
substantially blocked by a sheet closely conforming to the top surface of 
the feed belt assembly, and minimum air flow is provided to the inlet of 
the blower and therefore to the air knife, the vacuum produced in chamber 
58 will cause valve 69 to be pulled up by the reduced pressure. This will 
allow flow of air into chamber 58 to increase the flow of air through 
blower 55. When valve 69 opens, valve 73 which is interconnected thereto 
through lever 75 will close, thereby preventing the bleed of air from the 
output of the blower to provide the entire blower output to the air knife. 
If should be understood that under certain circumstances, both valves 69 
and 73 will be positioned somewhere between fully open and fully closed 
due to the variation in input and output pressures of the blower. 
Utilizing this valve, the input and output of blower 55 is closely 
controlled to provide optimum vacuum for the feed belt assembly and 
optimum air flow for the air knife without extensive adjustments or 
controls. Thus the sheet feeder is capable of handling a wide variety of 
sheet weights and stiffness due to the control exerted on the system by 
the automatic air flow control valve 57. The valve 57 is also provided 
with an air shut off valve plate 80. With the disclosed system, the blower 
is operated continuously and air flow to the blower is controlled by 
opening and closing valve plate 80. At the start of the feed cycle, the 
valve plate is opened, allowing air flow through the system to provide the 
required vacuum and high pressure air for the air knife. After the bottom 
sheet has been fed, the valve plate 80 is closed to allow return of the 
previously exposed sheet to the tray without interference from the air 
knife flow. 
It can be seen from the forgoing that an efficient, gentle yet positive 
bottom sheet feeder is provided through the use of the disclosed control 
valve, the air flow through the vacuum transport is maximized while the 
air flow through the air knife is minimized prior to sheet acquisition on 
the feed belts. Further, the valve maximizes air flow through the air 
knife and compensates for reduced air flow through the vacuum transport 
following sheet acquisition. 
While I have described the preferred embodiment of my invention, it is to 
be understood that the invention is not limited thereto but may be 
otherwise embodied within the scope of the following claims.