JPH0122177B2 - - Google Patents

Description

[Detailed description of the invention]

Japanese Patent Application No. 53-1594 (Japanese Patent Publication No. 54-17226) filed by the present applicant discloses a low-inertia rotating drum for conveying flexible sheets such as paper. . The drum has two longitudinal slots disposed in its surface, each connected to an interior segment by a spaced port extending into the slot. Valve systems are used to independently control vacuum to these slots through these internal segments. The spacing of these slots around the circumference of the drum is based on the size of the sheets being processed. A charged corona is positioned relative to the drum and attracts the sheet to the drum by electrostatic attraction. The drum of the previously described invention handles sheets of one size and requires the use of a corona to attract the sheets to the drum. No. 4,202,542 shows a sheet transport apparatus that includes a low inertia rotating drum for manipulating materials of multiple sizes. The drum has a plurality of longitudinally spaced sets of ports formed in its surface. These ports are precisely spaced from each other around the surface of this drum, with one set of ports allowing vacuum to be applied to the leading edge of the sheet, while only one of the other set of ports The ports provide vacuum to the trailing edge of the sheet according to the dimensions of the sheet circumferentially around the drum. Additionally, the sheet transport system controls how many of these two sets of ports are to apply vacuum according to the size of the paper along the length of the drum. A rotary valve is used to control the flow rate of the vacuum according to the dimensions of the seat. Thus, although the drum of the invention processes sheets of many different sizes, it requires a rotary valve to control the flow rate of the vacuum. The present invention is an improvement over the drums of the above-mentioned patents and patent applications; the drum of the present apparatus does not require an adsorption corona and/or a valve to control the vacuum. The drum of the present invention handles sheets of a wide variety of sizes and can be used with the configurations described in any of the patents and patent applications mentioned above. The present invention relates to a document transport device, and more particularly to a drum-type document feed device in which a sheet of flexible material (such as a sheet of paper) is attracted to a transport drum and a processing drum. The use of rotating drums to convey sheet material is known in the prior art. These rotating drums are often used in printing equipment. In addition to their transport function, these drums hold the sheet material during the printing process. Additionally, prior art printing devices include paper handling mechanisms for loading and unloading sheets of paper onto this drum. A necessary component of this prior art printing device is the means used to suction the sheet onto the drum. This prior art often used mechanical fingers to clamp the sheet onto the drum. For example, US Pat. No. 2,451,079 describes a rotating drum for holding sheets in a facsimile printing machine. This drum has two rows of pins arranged in a straight line. The two rows of pins are circumferentially spaced and extend outwardly from the surface of the drum. One row of pins securely secures the leading edge of the sheet, and the other row of pins securely secures the trailing edge of the sheet. The loading plate and stripping bar are positioned with respect to this drum. The stacking plate loads the sheets onto the drum, and the stripping bar strips the sheets from the drum. Although this above-described mechanical clamping device works well for its intended purpose, it tends to be rather slow and complicated. This low speed results in a fairly long response time for this mechanical device to clamp and release sheets. Therefore, this printing drum with mechanical fingers for gripping the sheet is used in relatively slow performance printing equipment. For high performance printing equipment, this prior art typically uses pneumatic and/or electrostatic means to clamp the sheet to the drum. Typically, prior art printing devices use corona means as the source of this electrostatic force. Examples of prior art printing devices using a combination of pneumatic and corona means to attract sheets to a printing drum are disclosed in the specifications of the above-mentioned patent applications. For pneumatic equipment, the usual method is to use segmented drums to convey the sheet. Vacuum to pick up and/or remove the sheet is selectively applied to different regions or segments of the drum. The drum is shown segmented so that segments of the drum may or may not have a vacuum during each operating time of the apparatus. US Pat. No. 3,545,746 is an example of this prior art segmented drum. This patent describes a document transport device consisting of a hollow cylindrical transport drum and document loading and unloading means arranged with respect to this drum. The cylindrical surface of the drum is provided with longitudinal slots and circumferential slots. The inside of this drum is communicated with the atmosphere through communication holes. A static partition divides the interior of this drum into two pneumatically independent compartments. By rotating the drum and applying a vacuum to one of the compartments, the document is rotated with the drum within limits determined by the dimensions of the evacuated compartment. US Pat. No. 4,145,040 is another example of this prior art segmented vacuum drum. This drum is adapted to convey flexible sheets. The drum is formed with working suction areas or sectors for gripping these sheets. The drum consists of an inner fixed cylindrical member and an outer rotating cylindrical member. This fixed cylindrical member is equipped with a suction source and a pressure source. Both the suction source and the pressure source are interchanged around the circumference of this fixed cylindrical member. The suction source is fitted via a groove to the outer surface of the inner cylindrical member. Similarly, this pressure source communicates via a recess formed in the surface of this internal fastening member. This sector of the external rotating member is provided with an array of apertures. These openings interconnect the inner surface of the fixation member with the outer surface. A common duct interconnects the series of openings to this groove or this recess. Each duct is equipped with a piston. This piston controls the pressure (positive or negative) on these openings. A vacuum (negative pressure) and/or a blast of air (positive pressure) is applied to a sector of the drum as the outer member is rotated relative to the inner member. It is known in the prior art to use valves as a means of controlling vacuum flow to the working segments of the drum. For example, U.S. Pat.
No. 3,663,012 and No. 3,466,029 disclose a segmented vacuum transfer drum, and valves are used to control the vacuum to the working sectors of the drum. Although the use of pneumatic means or a combination of pneumatic and electrostatic means is a significant improvement over the use of mechanical tools for securing sheets to the drum, this prior art pneumatic document feeder still It has some drawbacks. First of all, this segmented drum design tends to be complex. This complexity increases as the number of sheet sizes that the transport device operates on increases. Complex valving is typically required with this prior art pneumatic system. This valving is necessary to select which ports receive flow at any particular time. The valve arrangement increases as the size of the seat it operates on increases. Another requirement for the valve system is that the system must know the paper size in order to have the vacuum applied to a given port. This requires operator intervention to select the seat size or the use of logic circuitry to sense the seat size. Furthermore, with respect to the valve system, the operator must be extremely careful in selecting the valve and positioning the valve with respect to the drum. Both valve selection and valve positioning are important because the response time of this drum is directly based on both variables. Because of these complexities, this prior art pneumatic document transport device has fairly low reliability. Another prior art problem area lies in the type of vacuum equipment used. As previously mentioned, the vacuum system is necessary to evacuate the drum. In other words, the vacuum device generates a force to clamp the sheet to the drum. The problem in this field is
This results from the fact that in this type of vacuum device there is a wide variation in the vacuum between loaded and unloaded conditions of the drum. For example, in no-load conditions (no paper on the drum) this vacuum is quite low. At load conditions (paper on the drum) this vacuum is substantially high. This wide variation in vacuum has several undesirable effects. First of all, there is a large imbalance between these vacuum requirements for attracting and retaining sheets to this drum. usually,
A fairly high flow rate is required for adsorption and a fairly low vacuum power is required for retention. Therefore, it is necessary to recognize that there is a strict relationship between the vacuum systems that generate these vacuum requirements and to design the vacuum system that minimizes this unbalanced combination. Up to this point, the prior art has failed to recognize and recommend the interrelationship between these vacuum requirements (in the drum) and the design of the vacuum equipment. Additionally, this high vacuum tends to damage the sheets on this drum. Very importantly, in some types of applications such as inkjet printing, this high vacuum is simply unacceptable. The reason for this is that this high vacuum sucks this ink through the paper. This prior art attempts to solve this problem by using a relief valve to reduce this pressure in the drum. Needless to say, the use of this relief valve tends to complicate the device and increases cost. It is an object of the present invention to provide a sheet transport and retention system that is much more efficient than previously designed sheet transport and retention systems. Another object of the invention is to provide a non-segmented drum for handling sheets of multiple sizes. Yet another object of the present invention is to provide a vacuum drum that provides a relatively uniform vacuum during loaded and unloaded conditions. The invention works by creating a variable flow area on the surface of the drum when loading a sheet and creating a variable vacuum force area on the drum surface during the period that the sheet is retained on the drum. To achieve this mentioned above. These vacuum forces and flow areas are highest in the predetermined areas, particularly where the leading and trailing edges of the sheet are attracted to the drum. The vacuum force and flow rate are generated by slots and communication holes located in the surface of the drum. By varying the dimensions of these slots and the number and/or dimensions of these holes, these variable vacuum force and flow regions are created. The sheet transport and holding device of the present invention includes a low inertia rotating drum that holds sheets of paper of variable size. The drum is journalled at both ends for rotation. A plurality of spaced apart elongated slots are formed on the cylindrical surface of the drum. These slots are arranged longitudinally and circumferentially of the drum. These slots are arranged along the length of the drum to hold sheets of three different sizes.
These slots around the circumference of the drum are configured into a leading edge slot and a plurality of trailing edge slots. The leading edge slots hold the leading edge of sheets of all sizes, and each trailing edge slot holds the trailing edge of sheets of different sizes. The spacing between these leading edge slots and these trailing edge slots is determined by the dimensions of the sheets. A high flow, low vacuum blower is connected to this drum. Communication ports or holes are formed in these slots. These holes communicate this vacuum to the surface of the drum. In one feature of the invention, one or more arcuate grooves are arranged circumferentially of the drum. One or more stripping fingers cooperate with these slots to strip sheets from the drum. In another feature of the invention, the number and/or size of the holes are greatest in the leading and trailing edge slots. Furthermore, in another feature of the invention, the elongated load guide means are arranged with respect to the surface of this drum. The guide means exerts a force to force the sheet to follow the surface of the drum. As used herein, the term "pump" refers to a type of air compressor that is characterized as a conventional high pressure, low flow type device of the positive displacement type. As used herein, the term "blower" refers to a type of air compressor that is characterized as a conventional high flow type device of the negative displacement (dynamic) type. Although the invention can be used in any environment where flexible sheet material is transported, the invention is well suited for use in a printing environment and will therefore be described in the context of a printing process. However, this should not be construed to limit the scope of the invention as it is possible in this prior art to adapt the invention for use in other environments without departing from the scope and spirit of the invention. 1 and 4, there is shown a document handling device 10 in accordance with the teachings of the present invention. For simplicity of explanation, common parts in the figures are designated by common reference numbers. Also, common parts such as retaining frames, mechanical couplings, bearings, etc. are omitted from the figures. It is believed that these omitted parts would be readily procurable by those of ordinary skill in this mechanical art, and furthermore, these omitted parts are illustrated in the figures and hereinafter described in the description of the invention. make it easier. This document handling device 10 has a rotating drum 1 with low inertia.
Contains 2. This drum has a cylindrical outer frame 14
and end members 16 and 18 are fixedly attached to opposite ends of the cylindrical shell. As will be explained next, the tubular member 20 is connected to this drum 12.
brings negative pressure inside. As shown more clearly in FIG. 2, the shaft 22 is attached to the end member 18. A set of conventional bearings and mechanical couplings (not shown) are coupled to shaft 22 and tubular member 20, respectively. The bearing is fixedly mounted on the machine frame (not shown). A drive motor (not shown) is coupled to shaft 22. The drum is therefore journalled for rotation in bearings (not shown) and rotated in the direction of arrow 24 by the drive motor (not shown). Vacuum chamber 26 is connected to tubular member 20 . A blower 28 is connected to this vacuum chamber via a tube 30. As will be described later, the inside of this drum 12 is exhausted by this blower. Seal member 32 is positioned around tubular member 20 and prevents leakage of negative pressure to the atmosphere. In a preferred embodiment of the invention, the blower is a low vacuum, high flow blower. Still referring to FIG. 1, a loading station 32 and an unloading station 34 are positioned relative to the surface of the rotating drum. This loading station functions as a stack of sheets 36 placed on a holding tray 38.
This is to sequentially stack flexible sheet-like members such as paper sheets. The top sheet of the stack is fed along guide channel 40, where its leading edge is first attracted to a predetermined area on the cylindrical surface of the drum. In the direction of rotation of this drum, downstream from this loading area,
An arcuate elongated guide member 42 is positioned relative to the cylindrical surface of the drum. The function of this guide member is to exert a force on the sheet so that it follows the surface of the drum 12. The guide member has a length approximately equal to the length of the drum and extends in a direction parallel to the axis of rotation of the drum. In a preferred embodiment of the invention, the spacing between the cylindrical surface of the drum and the inner surface of the guide member is approximately 0.05 cm. As shown in FIG. 1, a sheet of paper 44 is firmly attracted to the cylindrical surface of this drum. The sheets on the drum are processed by a processing station (not shown) positioned relative to the drum and between the loading station and the unloading station. The processing station may be an inkjet head that writes readable characters on the paper as it passes through the processing station. After processing, this sheet 44 and other similarly situated sheets are stripped from the drum by a plurality of stripping fingers 46. As shown more clearly in FIG. 2, the stripping fingers are lowered into cooperation with a plurality of circumferential grooves 48 formed circumferentially in the drum. These removed sheets advance over the upper surface of this guide member 50 and onto the output tray 52. The operator can then remove the processed sheet from the output tray. Although in a preferred embodiment of the invention a plurality of circumferential grooves and a plurality of mechanical stripping fingers are used to remove the sheet from the drum, only one groove and one stripping finger are used. I know that it will happen. It is therefore clear that any number of grooves and associated stripping fingers can be used to remove the treated sheet from the surface of the drum. Referring to FIG. 4, a cross-sectional view of the perspective view shown in FIG. 1 is shown. As previously mentioned, parts in this perspective view that are common with parts previously shown in FIG. 1 are designated by the same reference numerals. As previously mentioned, these sheets (not shown) are fed sequentially from the holding tray 38 along the guide groove 40 to the cylindrical surface of this drum 12. This sheet stacking is assisted by an elongated guide member 42. A pair of feed rollers 50 and 52 are respectively disposed in the sheet feed path. These feed rollers are mounted such that a fairly small gap separates them. This gap is small enough to allow the sheet to pass freely between it. Feed roller 50 is coupled to a solenoid 56 via mechanical coupling means 54 . This solenoid is connected to a control device 60 by a conductor 58. As will now be described, when a control signal is output on conductor 58, the solenoid pivots feed rollers 50 and 52, respectively, to nip a sheet positioned between them. . The sheet is then fed onto the surface of the drum. Paper gates 62 are pivotally mounted in the paper path and downstream from feed rollers 50 and 52, respectively. This solenoid is connected to control device 60 by a conductor 68. In operation,
A paper sheet (not shown) is fed by a feeding mechanism (not shown)
is fed from the top of the stack of paper in the bin 38. For example, the paper feeding mechanism may be a paper feeding mechanism called Shingler and described in US Pat. Nos. 4,113,245 and 4,175,741. The sheet passes through the gap between feed rollers 50 and 52 and the leading edge of the sheet is stopped by a sheet gate 62. An enable signal is output on conductors 58 and 68, respectively. This signal on conductor 68 operates solenoid 66. As a result of this operation, this paper gate 6
2 is pivoted from the leading edge of this sheet. Similarly,
This signal on conductor 58 operates solenoid 56. At this time, the solenoid 56 pushes the feed roller 50 downward, thereby bringing the sheet into contact with both feed rollers. The roller 50 is then rotated counterclockwise by rotating means (not shown), thereby causing the drum 12 to
The sheet is fed onto the cylindrical surface of the drum 12 synchronously in position and surface speed. Typically, the drum is decelerated during loading operations, increased in speed during processing operations, and decelerated again when sheets are removed from the drum. In other words, the paper is fed onto this drum at a first speed. Paper is processed on this drum at a second speed. Typically, this second speed is faster than this first speed. Still referring to FIG. 4, the stripping fingers 46 are generally conical in shape with an upper sloped surface and a bottom surface of the cone having a concave surface for cooperating with the outer periphery of the drum. have These stripping fingers are fixedly connected to the shaft 70.
Shaft 70 is connected to solenoid 74 via mechanical coupling means 72 . A conductor 76 connects this solenoid to controller 60. In operation, a control signal is output from controller 60 onto conductor 76 . This signal activates the solenoid 74 and the shaft 70 is rotated clockwise so that the stripping fingers are lowered into the groove. Of course, if a single groove and stripping finger are used, then the stripping finger is lowered into the single groove. The sheet on this drum therefore rides along the upper sloped surface of the fingers 46 over the guide member 50 and onto the tray 52. At this point, it will be appreciated that several other types of loading devices can be used without departing from the scope of the invention. For example, the loading mechanism may be the loading mechanism described in the above-mentioned cross-referenced US patent application. Similarly, other types of sheet unloading mechanisms can be used to unload sheets from this drum. As previously mentioned, the means used to attract the sheet to the drum is a vacuum. Second
As shown in Figures 3 and 5, a plurality of slots and holes are used to control and communicate the vacuum to the surface of the drum 12. In FIG. 2, this drum is shown in its normal (removed) configuration. FIG. 3 shows a cross-sectional view of this drum of FIG. In FIG. 5, this drum is shown in removed form. In this removed display configuration, the drum occupies a flat rectangular area. It can be seen that the illustration in FIG. 5 emphasizes these slot and communicating port structures. This structure is capable of generating a vacuum area of variable force on the cylindrical surface of the drum. No valves or other prior art segmentation is required to establish this variable force vacuum area on this drum. As previously mentioned, common parts in the figures are indicated by common reference numerals. As can be seen in the figures, the drums are mated at longitudinal scribe line 74 and circumferential scribe line 76. Typically, the leading edge 78 (see FIG. 1) of the sheet is aligned with respect to or parallel to the scribe line 74. The rotation of the drum is in the direction of arrow 80. Typically, the longitudinal dimension of the sheet is aligned with the longitudinal score line. Similarly, the width of the sheet is generally aligned with the circumferential score line 76. It will be appreciated that this sheet alignment may be reversed without departing from the scope of the invention. Further referring to FIGS. 2, 3 and 5,
The entire cylindrical surface of the drum has a plurality of elongated slots formed therein. The function of these slots is to apply a vacuum across the width of the paper. The slots are arranged in linear and spaced relationship along the longitudinal and circumferential axes of the drum. For ease of explanation, the slots are numbered in ascending order diametrically opposite to the direction of rotation of the drum. For example, slot 86 is shown as this leading edge slot. The slot generates a vacuum force that attracts the leading edge of the sheet to the drum. Slots 88-102 are intermediate slots and attract the center portion of the sheet to the drum. Slots 104 and 106 are the trailing edge slots.
The function of these slots is to attract the trailing edge of the sheet to this drum. Additionally, the widths (dimensions) of these slots vary. In particular, the leading edge slot 86 is connected to the intermediate slots 88-10.
Wider than 2. Similarly, this trailing edge slot 10
4 and 106 are wider than these intermediate slots. This can generate a slightly higher vacuum force at the trailing edge of this sheet. Further referring to FIGS. 2, 3 and 5,
The slots are arranged in linear rows spaced longitudinally and circumferentially of the drum. The slots are also arranged in groups both longitudinally and circumferentially of the drum. Each set or group is adapted to hold sheets of different sizes. For example, a first group of slots (indicated by reference numerals 108 and 118) extend along the length of the drum and are located between scribe line 76 and dashed line 110. The first group of slots also extends circumferentially of the drum and is defined by score line 74 and trailing edge slot 106. This first group of slots holds a first size of sheet, referred to as a 216 mm x 279 mm sheet. Similarly, the second group of slots (reference number 1
21 and 116) are defined in the circumferential dimension of this drum by the score line 74 and the trailing edge slot 104. This second group of slots holds sheets of a second size, designated as international paper A4. The dimensions of this A4 paper are approx.
It is 210mm x 297mm. Finally, this third group of slots (indicated by reference numbers 114 and 118) is 216 mm x 356
Hold a sheet of third dimension in mm. This third group of slots is defined along the longitudinal direction by dashed line 111 and score line 76 and along the circumferential direction by score line 74 and trailing edge slot 106. There is. Although FIG. 5 shows that the drum can hold three different sizes of paper, this cannot be construed as a limitation on the scope of the invention. Therefore, it is possible in this prior art to design the surface of this drum to hold more or less than three sizes of paper. In other words, these slots can be configured to hold sheets of various sizes. As is clear from the foregoing, the circumferential dimensions of this drum hold sheets with a specific width (say 216 mm). Similarly, this distance, designated as reference numeral 116, holds a sheet having a second width, such as what is referred to as A4 paper. A4 paper is the designation given internationally to sized paper. Of course, any other configuration can be designed to hold other types of sheets without departing from the scope of the invention. A plurality of circumferential grooves 113 are arranged around the circumference of the drum. The stripping fingers cooperate with these circumferential grooves to remove sheets from the drum. Although multiple grooves are shown in FIG. 5, only a single groove is used in one embodiment of the invention. Further referring to FIGS. 2, 3 and 5,
A plurality of communication ports 120 are formed in the cylindrical surface of the drum. These communicating ports, sometimes referred to as holes, interconnect the interior of the drum to the cylindrical surface. The function of these holes is to provide a vacuum from the interior of the drum to the exterior surface. the quantity and/or of these holes;
The dimensions are such that regions of variable flow rate are created on the cylindrical surface of this drum. As shown in the figures, a relatively high number and/or size of holes are shown in this leading edge slot 86. Therefore, a fairly high flow rate is generated in this area which attracts the leading edge of the sheet. Similarly, a significantly higher number and/or size of holes are located in trailing edge slots 104 and 106, respectively.
Therefore, a fairly high flow rate is generated in this trailing edge region to adsorb the trailing edge of these sheets. The number of holes in this intermediate slot 80-102 is low and therefore a region of significantly lower flow rate is located between these rows. In other words, the number of holes in the intermediate slot is less than the number of holes in the leading and/or trailing edge slots. Although not shown in FIG. 5, in a preferred embodiment of the invention,
The number and/or size of holes in the trailing edge slot are larger than those in the leading edge slot. This creates an area of higher flow (suction) at the trailing edge of the sheet than at the leading edge. It can be seen that the leading edge and trailing edge areas of this drum are the most critical areas for sheet attraction and retention. To adsorb the leading and trailing edges of this sheet, high flow rates are required and provided by large port flow areas (ie, number of holes and/or hole size). To hold the leading and trailing edges of this sheet, some vacuum force is required and provided by the wide slots. Regions inboard of the leading and trailing edge regions have lower flow rates and vacuum force requirements for suction and retention. The type of vacuum device used in the present invention interacts with the widths of these slots and the flow areas of the ports to meet the adsorption and retention requirements of these various regions. This is performed very effectively in loaded conditions (sheets loaded) and unloaded conditions (sheets not loaded). Although FIGS. 2, 3, and 5 illustrate specific combinations of slots and holes with respect to specific designs, they are not limiting to the scope of the invention.
It will be appreciated that the number of holes, the number of slots, the size of the holes and the size of the slots may be varied within the skill of the art without departing from the scope of the invention. For example, the following table shows hole sizes, slot sizes, etc. for typical drums. However, it will be appreciated that variations in the number of holes and slots may be made within the skill of the art without departing from the scope of the invention.

【table】

【table】

Table 1 shows these slots in detail. This table is interpreted in conjunction with FIG. These rows in this table and figure are numbered 86-106. These columns in this table represent various characteristics of these slots. This column 1 details the width of these slots when counting from right to left. Column 2 represents the displacement of the slot in the circumferential and longitudinal directions of this drum. This circumferential displacement is measured at an angle starting from this scribe line 74. This longitudinal displacement is measured in length units starting from the scribe line 76. Segment 1 is the first segment closest to this scribe line 76. Segment 2 is the closest segment to the first segment, and the other segments also have this relationship. Column 3 represents the length of each segment. Table 2 shows these communication holes in detail. In this table, column 1 represents the diameter of these communicating holes. The total quantity represents the total number of communicating holes per line. The other column represents the number of through holes per segment. Referring to FIG. 6, there is a diagram illustrating the relationship between a conventional vacuum pump (as used in prior art evacuated vacuum systems) and a blower suitable for use with the present invention. This diagram is helpful in understanding the variations in vacuum generated on the surface of a rotating drum. This diagram also helps in understanding the problems discussed above with respect to this prior art evacuated vacuum device. In Figure 6, the vacuum pressure (where A is the magnitude of the vacuum pressure in pounds per square inch (PSI)) is
The conversion constant 0.07031 for expression in units of Kg/cm ² ) is expressed in units of Kg/cm ² and is plotted along the ordinate of the diagram. Similarly, this flow rate (where B is the conversion constant 0.02832 for expressing the flow rate in cubic feet per minute (CFM) in units of m ³ /min) is expressed in units of m ³ /min. and is plotted along the abscissa of this chart. Curve 120 represents these operating characteristic curves for a 0.9 horsepower blower. Similarly, curve 122 represents these operating characteristic curves for a 1.0 horsepower vacuum pump. As can be seen from this diagram, the operating characteristic curve of the vacuum pump is parallel to the ordinate of the diagram to a considerable extent. In other words, the vacuum pump has a fairly low flow rate and a fairly high vacuum pressure. However, the operating characteristic curve of the blower has a fairly high flow rate and a fairly low vacuum pressure. Data regarding these operating curves for blowers and vacuum pumps of similar output can be obtained from the respective manufacturers. Curve 124 represents the operating characteristics of the drum without paper being picked up. This curve was plotted for a representative drum with a particular arrangement of slots and holes. Curve 126 represents a characteristic curve for a drum with a certain size of paper adsorbed. When using a vacuum pump, the operating point of this vacuum device is the point where its characteristic curve intersects the characteristic curves of the unloaded drum (no paper is adsorbed) and the loaded drum (paper is adsorbed), respectively. If a blower is used, it is located at the intersection where its characteristic curve intersects the characteristic curves of the unloaded drum and the loaded drum, respectively. As can be seen from this diagram, the characteristic curve of the unloaded drum intersects the characteristic curve of the blower at intersection point 3. By drawing a horizontal line from this point of intersection to the ordinate of this diagram, the effective vacuum pressure developed in the slot of the unloaded drum is determined. Similarly, intersection point 4 indicates the operating point for a paper-loaded drum when a speed blower is used. Again, the horizontal line drawn from the intersection to the ordinate of this diagram indicates the vacuum pressure available in the slot of this drum. As can be seen from the two vacuum pressures, the effective pressure between the no-load and loaded conditions is approximately constant. This indicates that for optimal operation, a vacuum system that includes a blower with a fairly high flow rate and a fairly low vacuum pressure is highly desirable. Using a similar analysis, it can be seen that intersection point 1 and intersection point 2 represent the respective operating points of the drum when the prior art vacuum pump is used to evacuate the drum. It can be seen that there is a wide variation between the vacuum pressure generated on the drum between no-load and loaded conditions. This is an undesirable condition and therefore conventional vacuum pumps are not suitable for use in the evacuation system of the paper transport system unless the drum is segmented and a vacuum relief mechanism is used. An advantage of the present invention is that it allows sheets of various sizes of flexible material to be manipulated by a non-segmented vacuum drum.

[Brief explanation of drawings]

1 is a perspective view of a document handling and holding device in accordance with the teachings of the present invention; FIG. 2 is a perspective view of a printing drum; FIG. 3 is a cross-sectional view of the printing drum; and FIG. 4 is a cross-sectional view of the document handling device. , FIG. 5 is a perspective view of the developed vacuum drum, and FIG. 6 is a chart showing the characteristics of different vacuum devices. 12...Drum, 20...Tubular member, 28...
Blower, 86... Slot for leading edge, 104, 10
6... Trailing edge slot, 88, 90, 92, 9
4, 96, 98, 100 and 102...intermediate slot, 120...communication port.

Claims (1)

[Scope of Claims] 1. A sheet conveying and holding device which is a device for conveying a flexible sheet, and which comprises the following elements (a) to (c). (a) A rotary drum with low inertia and a cylindrical surface for holding the sheet. A plurality of slots each having an elongated shape parallel to the longitudinal direction of the cylindrical surface are arranged in a matrix in the longitudinal direction and circumferential direction of the cylindrical surface. Each slot has at least one slot for communicating the interior of the rotary drum with the cylindrical surface.
The number of communication ports in each slot with which the leading edge and the trailing edge of the sheet should respectively contact is larger than the number of communication ports in other slots. selected. (b) A low-vacuum, high-flow blower connected to the rotary drum so as to exhaust the inside of the rotary drum. (c) A motor connected to the rotary drum so as to rotate the rotary drum.