Feeder of a sheet-processing machine and method for operating a feeder of a sheet-processing machine

Abstract

Feeder (01) of a sheet-processing machine with a stacking table (06) designed to receive a stack of sheets (07), at least one singulation element (14) by which the uppermost sheet (03) of the sheet stack (07) can be detected in a singulation plane (15) and moved into a sheet guide plane (20) vertically spaced from the singulation plane (15), and at least one transport element (16) by which the respective sheet (03) can be transported in a transport direction (T) away from the sheet stack (07) into a downstream transport path, with a blowing device (18), wherein the blowing device (18) has a plurality of outlet openings (29),the are arranged at intervals perpendicular to the transport direction (T) and wherein the blowing device (18) for each sheet (03) of a sheet sequence is designed to generate a sequence of several blowing air bursts that begin at different times and are directed under the respective sheets (03), wherein the blowing device (18) for each sheet (03) is designed to generate a sequence of blowing air bursts from different outlet openings (29), in which outlet openings (29) arranged first in the region of the center of the sheet stack (07) and then outlet openings (29) spaced apart from the center of the sheet stack (07) each emit a blowing air burst.

Description

[0001] The invention relates to a feeder of a sheet-processing machine and a method for operating a feeder of a sheet-processing machine.

[0002] In sheet-processing machines, it is common practice to position the sheets intended for processing as a stack on a lifting and lowering stacking table. From the top of the stack, the sheets are separated and conveyed away in an overlapping, shingled stream. For this purpose, a sheet separator is positioned at the top of the stack. Its working elements, such as separating suction cups, transport suction cups, or a sensor foot, grip the topmost sheet of the stack in sync with the sheet-processing machine, separate it from the following sheet, and convey it in one direction. The airflow, which assists in gripping, separating, and conveying the sheets, is controlled by valve units that also adjust in sync with the sheet-processing machine's operating cycle.

[0003] When separating sheets from the stack, the sheet is first loosened from all sides at the feeder by continuous blowers. After suction by separating suction cups and separation by strippers, a burst of separating air is required to release the top sheet from the stack, allowing it to move freely. Along with numerous other elements and parameters, this burst of separating air is crucial for the quality of the sheet feed, especially for substrates with a basis weight of less than 135 grams per square meter. The direction, quality, quantity, and control of the separating air significantly influence the sheet feed and the printing rate.

[0004] In prior art solutions, the control of the supplied separating air is primarily achieved via cam-controlled piston valves or rotary valves. The required volume of separating air must be large enough to create an air cushion beneath the entire arc to be separated.

[0005] The volume of separating air introduced under each bow with the respective separating air pulse can be influenced by blowing pressure and blowing duration.

[0006] To generate a sufficiently large volume of separating air, prior art solutions operate with nominal pressures in the range of 1.2–1.4 bar, and the separating air pulse continues even when the transport suction device begins its movement cycle to remove the respective sheet. Higher pressures were avoided due to concerns about sheet deformation.

[0007] DE 198 15 104 A1 discloses a sheet separator in sheet feeders for singulating and feeding the uppermost sheet of a sheet stack, comprising separating suction cups that grasp the uppermost sheets in the rear area of ​​the sheet stack in the conveying direction and lift them approximately perpendicular to the sheet stack, transport suction cups that take over the sheets lifted by the separating suction cups and transport them in the conveying direction, and a sensor foot that rests on the rear area of ​​the sheet stack after the uppermost sheet has been separated.

[0008] DE 10 2005 054 138 A1 discloses a printing press for printing on sheets, comprising a feeder and printing units. The feeder has a separating blower or a loosening blower.

[0009] From DE 10 2020 107 836 B4, a sheet-processing machine is known with a feeder, a delivery unit, and one or more offset printing units and / or coating units arranged between the feeder and the delivery unit. The feeder includes a stacking chamber with a stacking support. In the stacking chamber, the separation of the top sheet from the sheet stack is assisted by blown air from separating blowers or by blown air from a pusher foot.

[0010] German patent DE 10 2011 120 475 A1 discloses a sheet feeder with two suction wheels. For singulation, a sheet at the top of the stack is lifted, and separating air is blown between the lifted sheet and the stack in a defined manner. This separates the upper sheet from the stack, and the separating air lifts it to an upper suction wheel.

[0011] DE 39 07 037 A1 discloses a device for sheet length measurement in a sheet-fed printing machine, consisting of suction air measuring nozzles which are aligned with the trailing edge of the sheet and which, in their connection with a suction air source, have switching elements in the circuit of the machine drive and in which a feeder aligns the sheets to be processed against stops for the leading edge of the sheet and lifts them from a stack of sheets with blasts of blowing air that begin at different times and are directed under the respective sheets.

[0012] The air blow times implemented in known solutions, which typically span 150 to 210 degrees of each machine cycle (which comprises 360 degrees), excite the sheet, causing it to oscillate, generating waves, vibrations, and instability. The sheet is therefore no longer lying flat, inevitably shortens unevenly due to the waves, and results in an irregular sheet arrangement on the conveyor table. As machine speed increases, the sheet overlap becomes increasingly imprecise, and sheets protrude from the arrangement. This leads to feeding problems and ultimately to jams.

[0013] The invention is based on the objective of creating a feeder for a sheet-processing machine and a method for operating a feeder for a sheet-processing machine.

[0014] In particular, the object of the invention is to provide a feeder for a sheet-processing machine and a method for operating a feeder for a sheet-processing machine that enables a smoother and, in particular, more uniform sheet travel with reduced wave formation.

[0015] The problem is solved according to the invention by the features of claim 1 or 13.

[0016] The advantages achievable with the invention consist in particular of increasing the functional reliability with which the feeder separates sheets from a stack of sheets.

[0017] In particular, the quality and uniformity of the underscaling and the staggering can be improved.

[0018] According to one embodiment, the flow velocity of the blown air expelled from the outlet openings can be adjusted more precisely.

[0019] The advantage of another embodiment can also be, in particular, that the application of separating air no longer has to depend on the speed of the production operation.

[0020] An embodiment of the invention is shown in the drawings and is described in more detail below.

[0021] It shows: Fig. 1 a schematic representation of a feeder with an indication of a transport path leading to one or more downstream processing units; Fig. 2 a detailed representation of a bow separator of the feeder with a blowing device.

[0022] The invention is described using the example of a feeder 01 of a sheet-processing machine, also referred to as a machine for processing substrate sheets 03 or sheet-processing machine, which can be designed as a printing machine, in particular as a sheet-fed offset printing machine.

[0023] A printing press, in particular a sheetfed offset printing press, comprises, in addition to the feeder 01 for supplying, for example, sheet-shaped substrate, in particular substrate sheet 03, or simply sheet 03, several printing units arranged one after the other in the substrate path, in particular printing on the same side of the substrate, in particular offset printing units, and a product delivery unit, e.g., a stack delivery unit. It may also include one or more coating units in the substrate path. Instead of several printing units, exactly one printing unit may also be provided. A perfecting unit, which enables double-sided printing, may also be part of the printing press, wherein all printing units upstream of the perfecting unit in the substrate path print on one side of the substrate and all printing units downstream of the perfecting unit in the substrate path print on the other side.

[0024] The printing units each comprise a form cylinder, which is driven, for example, either via a gear train from a main drive (not shown) that drives the majority of the printing units, or by a drive motor that is mechanically independent of the main drive. During production, which corresponds to printing, the form cylinders interact with one or more inking rollers of an inking unit and preferably with at least one dampening roller of a dampening unit.

[0025] The invention is not limited to sheet-processing machines designed as printing presses, but can be used on or be part of all types of sheet-processing machines.

[0026] In a preferred embodiment, the sheet-processing machine can be designed as a sheet-processing machine, e.g. embossing, cutting or in particular punching, with one or more units that mechanically process the sheets, e.g. with at least one punching or embossing unit or a stripping unit.

[0027] In an advantageous further development of the machine, it can also be designed as a hybrid machine, a sheet-processing machine with at least one die-cutting or embossing unit and, additionally, at least one printing unit located upstream of the die-cutting or embossing unit in the substrate or transport path. The product delivery, e.g., the stack delivery of such a machine, can also be designed to deliver bundles formed from sheets.

[0028] The transport path may also include further units such as a dryer, a paint shop, a calender, or other units acting on the sheet 03.

[0029] On the outflow side of the feeder 01, a conveying device 02, preferably in the form of a belt table 02, in particular a suction belt table 02, is connected in a transport direction T. This device takes the sheets 03 to be conveyed from the feeder 01 and, if necessary, feeds them downstream via further conveying devices to a single or first unit or assembly of the machine. The belt table 02 is, for example, designed as a suction belt table 02 and preferably comprises at least two rollers 19, of which only one is shown as the first when viewed downstream. One of these rollers is designed as a drive roller 19, and one or more others are designed as deflection rollers. A one- or multi-part table plate 21 extends between the rollers 19, which, for example, forms the multiply perforated top of a suction box 22.The two rollers 19 are enclosed by at least one conveyor belt 23, which, like the table plate 21 over which it extends, is perforated in many places so that it is not suctioned to the table plate 21, but a sheet 03 is drawn onto the conveyor belt 23. In the area where sheets 03 are approached, a roller 24, e.g., a timing roller 24, is provided above the entry-side roller 19 of the belt table 02 downstream of the feeder 01. This roller interacts with the roller 19 and / or the belt table 02 and presses the incoming sheets 03 against the belt table 02 in time with the arrival of the sheets 03.

[0030] In feeder 01, a stack 07, in particular a stack of sheets 07, is placed on a stacking table 06 provided in a stacking space 04. The stacking table 06 can be raised and lowered, in particular its height adjusted, for example by means of a first controllable drive 05, in order to hold the uppermost sheet 03 of the stack of sheets 07 at a fixed or only slightly variable height suitable for transferring the sheets 03 to the subsequent conveying device 02, regardless of the number of sheets 03 in the stack of sheets 07. In the illustration, the sheets 03 of the stack of sheets 07 lie directly on the stacking table 06; however, a pallet may also be located between the stack of sheets 07 and the stacking table 06, on which the stack of sheets 07 was transported to the stacking table 06 and placed there.

[0031] On the side of the stacking space 04 facing the transport direction T, a stop device 08, e.g., a one- or multi-part front stop 08, is provided, the stop surface of which, directed against the transport direction T, defines a vertical plane that serves as a stop for the leading edges, i.e., the edges that advance during transport, of the sheets 03 of the sheet stack 07. This stop device 08 does not extend vertically to the upper edge of the stack, but its vertical alignment is extended, as needed, by a stop surface of an active feed device 11, also referred to as a sheet flap 11. For this purpose, the feed device 11 is positioned between an active position, e.g., a pivoted position in which its stop surface is located in the transport path of a sheet 03 to be conveyed from the feeder 01, and an inactive position, e.g.,in a swung-away position in which it clears the transport path intended for transport, it can be moved, in particular pivoted.

[0032] Although other mechanisms are conceivable by which the arched flap 11 can be displaced between the two aforementioned positions, the arched flap 11 is preferably mounted in the springing point 01 so as to be pivotable about a pivot axis. For this purpose, for example, a support element 12, which acts as or is designed as a shaft 12, e.g., a flap shaft 12, is provided, which supports the arched flap 11.

[0033] The feeder 01 comprises various transport tools 14; 16 for removing individual sheets 03 from the sheet stack 07 and for transporting the sheets 03 onto or into the conveying device 02 downstream of the feeder 01. The transport tools 14; 16 are preferably accommodated in or encompassed by a so-called sheet separator 13.

[0034] The transport tools 14; 16 are preferably driven by separately controllable individual drives. The transport tool 14 is in particular a singulation element 14 for gripping a respective sheet 03 in a singulation plane 15 and for transferring the respective sheet 03 into a sheet guide plane 20 vertically spaced from the singulation plane 15. The singulation element 14 is in particular designed as a separating suction cup 14, more preferably as a spring suction cup 14.

[0035] Preferably, the sheet separator 13 also incorporates or includes a transport element 16, in particular a suction cup 16. The transport element 16 takes each sheet 03 from the singulating element 14 and transports it in a sheet guide plane 20 towards the conveying device 02. The singulating element 14 and / or the transport element 16 are formed in particular by a single or preferably by a plurality of suction cups 14; 16.

[0036] For example, several separating suction cups 14 can be arranged as a singulation device 14 on the sheet separator 13 in the area of ​​a rear edge of the sheet stack 07 in the transport direction T of the sheets 03 and can be moved essentially in a vertical direction. The rear edge of the sheet stack 07 or the rear edges of the sheets 03 represent the beginning of the transport path.

[0037] For example, several suction cups 16 are provided as transport elements 16. These are positioned closer to the front stop 08 on the sheet separator 13 when viewed in the transport direction T and are movable horizontally in and against the transport direction T. A further tool, particularly a so-called probe foot 17, can be provided as a component of the sheet separator 13. The probe foot 17 can be guided into the profile of the sheet stack 07. Preferably, the probe foot 17 is driven by a probe foot drive that moves the probe foot 17 between an upper and a lower end position. In the lower end position, the probe foot 17 rests on the top of the stack during production. Between the two end positions, the movement of the probe foot 17 can include a horizontal component in addition to the vertical one, and the probe foot 17 can, in particular, perform a pivoting movement.The button base 17 can also be designed as a blow nozzle for building up a supporting air cushion or can include a blow nozzle.

[0038] The sheet separator 13 is arranged in the feeder 01, in particular in a height-adjustable manner. A second controllable drive 10 is provided to implement the adjustment movement of the sheet separator 13.

[0039] In particular, at least one singulation device 14 and / or at least one transport device 16 and / or the blowing device 18 are components of the sheet separator 13, wherein the sheet separator 13 is assigned a controllable drive 10 for raising and lowering the sheet separator 13.

[0040] To facilitate the separation of each picked-up sheet 03 from the rest of the sheet stack 07, loosening blowers 26 can be arranged in the area of ​​the top of the sheet stack 07. The loosening blowers 26 can be arranged on the rear side of the stack, i.e., on the side opposite the transport direction T, in particular on the trailing edge of the stack 07. In addition to or as an alternative to an arrangement on the trailing edge of the stack 07 at the beginning of the transport path, loosening blowers 26 can also be arranged on both sides of the sheet stack 07 and designed to generate a blowing airflow directed towards the center of the stack. The loosening blowers 26 generate, in particular, a continuous blowing airflow during operation of the feeder 01.

[0041] In addition to the loosening blowers 26, or acting independently, a blowing device 18 is preferably provided at the beginning of the transport path in the area of ​​the trailing edge of the stack 07. The blowing device 18 is preferably fixed to a frame, but can also be mounted in a height-adjustable manner or be designed to be height-adjustable together with the sheet separator 13.

[0042] The blowing device 18 has a plurality of outlet openings 29, which are arranged at intervals between each other transversely to the transport direction T.

[0043] The outlet openings 29 are in particular a component of the respective separating air nozzles.

[0044] The outlet openings 29 can be equipped with means for selectively interrupting the blowing air supply to the outlet openings 29 or can cooperate with means for selectively interrupting the blowing air supply.

[0045] Preferably, all outlet openings 29 are connected via separate supply lines to a central air supply unit, and each supply line is assigned a means for selectively interrupting the air supply. The respective means for selectively interrupting the air supply can generate a jet of air exiting each outlet opening 29 by briefly lifting the interruption of the air supply in the respective supply line. In particular, the means for interrupting the air supply to individual outlet openings 29 are controllable, independently of other outlet openings 29, preferably by a central machine control system. Instead of individual outlet openings 29, groups of outlet openings 29 can also be equipped with means for interrupting the air supply or interact with them.

[0046] The outlet openings 29 can all have the same geometry or different geometries. In particular, the outlet openings 29 can be designed with oval geometries or with circular geometries.

[0047] In the case of outlet openings 29 with circular geometries, the diameter of the outlet openings is preferably less than six millimeters. In particular, the cross-sectional area of ​​the outlet openings 29 can be thirty square millimeters or less than thirty square millimeters.

[0048] The blowing device 18 can comprise pulse-controlled high-pressure valves. In particular, the means for selectively interrupting the blowing air supply can be formed by pulse-controlled high-pressure valves. The pulse-controlled high-pressure valves are preferably arranged between a compressed air generator and the outlet openings 29. Each such pulse-controlled high-pressure valve can be assigned exactly one outlet opening 29. Preferably, several outlet openings 29 are assigned to each such pulse-controlled high-pressure valve.

[0049] To control the air supply, the blowing device 18 can also include several cam-controlled valves or one or more rotary valves. In particular, one or more cam-controlled valves or rotary valves can be arranged between a compressed air generator and one or more outlet openings 29.

[0050] The blowing device 18 is designed for each sheet 03 of a sheet sequence to generate a sequence of several blowing air bursts that begin at different times and are directed under the respective sheet 03.

[0051] According to the design and arrangement of the blowing device 18, the blowing air pulses are directed at least approximately in the transport direction T.

[0052] To separate sheets 03 from the sheet stack 07, the uppermost sheet 03 in the sheet stack 07 is captured by the separating element 14, in particular by negative pressure in the separating plane 15, and then transported, in particular lifted, into the sheet guide plane 20, which is vertically spaced from the separating plane 15. It is sufficient if the uppermost sheet 03 is lifted on the side of the sheet stack 07 that faces away from the transport path downstream of the sheet stack 07.

[0053] The blowing device 18 emits several bursts of air for each sheet 03 transported from the singulation level 15, directed underneath the sheet 03. In other words, the emission of a sequence of blowing air bursts by the blowing device 18 is timed such that the blowing device 18 is activated to emit several blowing air bursts when a respective sheet 03 has passed the blowing device 18 vertically on its way into the sheet guide level 20.

[0054] Each air blast of a sequence of air blasts under a respective bow 03 begins either immediately before the respective bow 03 has arrived in the bow guidance plane 20 or exactly when the respective bow 03 has arrived in the bow guidance plane 20 or shortly after the respective bow 03 has arrived in the bow guidance plane 20.

[0055] A final burst of air in a sequence of bursts of air under a respective sheet 03 ends either at a time interval before the start of the transport movement of the transport element 16 for the transport of the respective sheet 03 or when the transport movement of the transport element 16 for the transport of the respective sheet 03 begins.

[0056] The total duration of the sequence of air blasts is significantly less than the time interval between the arrival of a respective bow 03 in the bow guidance plane 20 and the start of the transport movement of the transport element 16 for the transport of the respective bow 03.

[0057] Preferably, the blowing device 18 is designed to generate the temporally staggered blowing air pulses through different outlet openings 29.

[0058] In particular, the blowing device 18 can be configured for each sheet 03 to generate a sequence of blowing air bursts from different outlet openings 29, whereby outlet openings 29 arranged first in the region of the center of the sheet stack 07 and then outlet openings 29 spaced apart from the center of the sheet stack 07 each release a blowing air burst. With this control, an advantageously formed blowing air wedge is created, which reliably separates the sheets 03 and spreads them out laterally.

[0059] The blowing device 18 is preferably designed to generate sequences of blown air bursts in time with the sheet sequence. The time is defined as an angle of 360 degrees, so that a new time begins after each 360 degrees and the elements of the feeder 01 moving in time repeat their movements.

[0060] The duration of each individual burst of air in a sequence can be, in particular, forty-five degrees and accordingly extend over one eighth of a measure.

[0061] The duration of the air blasts can also range from twenty to seventy degrees or from thirty to sixty degrees.

[0062] The blowing device 18 can also be designed for each sheet 03 of a sheet sequence to generate blowing air bursts, the duration of which is the same for all sheets 03 of the sheet sequence and which therefore does not depend on the machine speed of the feeder 01 or the sheet-processing machine.

[0063] Preferably, the duration of the air blasts in this case is 25 milliseconds each, or is in the range of ten milliseconds to forty milliseconds.

[0064] The blowing device 18 can in particular be designed such that in the area of ​​at least one or all of the outlet openings 29 the air pressure of the respective blowing air pulse is equal to 1.5 bar or greater than 1.5 bar or equal to two bar or greater than two bar.

[0065] Accordingly, the central air supply unit generates an air pressure that is equal to 1.5 bar or greater than 1.5 bar or equal to two bar or greater than two bar.

[0066] Advantageously, the blowing device 18 is designed such that, in a sequence of blowing air bursts for a respective arc 03, the respective blowing air bursts begin offset from each other by a time in the range of one to five milliseconds.

[0067] The air blown between the layers of sheets by the blowing device 18 separates the sheet 03 from the stack of sheets 07 and forms an air cushion under the sheet 03, on which the sheet 03, driven by the horizontal movement of the transport element 16, is pushed over the sheet flap 11, which is then moved into the inactive position, onto the belt table 02.

[0068] In particular, the blowing device 18 generates a blowing air pulse for each arc 03 of an arc sequence, the duration and / or flow velocity of which is the same for all arcs 03 of the arc sequence. Reference symbol list 01 Investors 02 Conveyor system, belt table, suction belt table 03 Substrate arch, arch 04 Stacking room 05 Drive, first 06 Stacking table 07 Stacks, stacks of sheets 08 Stop device, front stop 09 - 10 Drive, second 11. Installation device, arched flap 12 Support element, shaft, flap shaft 13 sheet separators 14 Transport tool, singulation device, separating suction cup, spring suction cup, suction cup 15th level of isolation 16 Transport tool, transport element, trailing suction device, suction device 17 Pushbutton base 18 Blowing device 19 Roller, drive roller 20 Bow guide plane 21 Tabletop 22 Suction box 23 Conveyor belt 24-inch drum, timing drum 25 - 26 relaxation trumpets 27 - 28 - 29 Exit opening T Transport direction

Claims

[1] Feeder (01) of a sheet processing machine with a stacking table (06) designed to receive a stack of sheets (07), at least one singulation element (14) by which the uppermost sheet (03) of the sheet stack (07) can be detected in a singulation plane (15) and moved into a sheet guide plane (20) vertically spaced from the singulation plane (15), and at least one transport element (16) by which the respective sheet (03) can be transported in a transport direction (T) away from the sheet stack (07) into a downstream transport path, with a blowing device (18) wherein the blowing device (18) has a plurality of outlet openings (29),the are arranged at intervals perpendicular to the transport direction (T) and wherein the blowing device (18) for each sheet (03) of a sheet sequence is designed to generate a sequence of several blowing air bursts that begin at different times and are directed under the respective sheets (03), wherein the blowing device (18) for each sheet (03) is designed to generate a sequence of blowing air bursts from different outlet openings (29), in which outlet openings (29) arranged first in the region of the center of the sheet stack (07) and then outlet openings (29) spaced apart from the center of the sheet stack (07) each emit a blowing air burst. [2] Investors according to claim 1, characterized by , that the air blasts under the respective bow (03) are directed in the transport direction (T). [3] Investors according to claim 1 or 2, characterized by, that the blowing device (18) is designed to generate the temporally staggered blowing air pulses through different outlet openings (29). [4] Investors according to claim 1, 2 or 3, characterized by , that the air blasts of a sequence for each arc (03) begin offset from each other by a time in the range of one to five milliseconds. [5] Investors according to claim 1, 2, 3 or 4, characterized by , that the last burst of air of a respective sequence of bursts of air for a respective sheet (03) ends at a time interval before the start of the transport movement of the transport element (16) for the transport of the respective sheet (03) or ends when the transport movement of the transport element (16) for the transport of the respective sheet (03) begins. [6] Investors according to claim 1, 2, 3, 4 or 5, characterized by, that the blowing device (18) is designed to generate blowing air bursts in time with the arc sequence, wherein each arc sequence comprises 360 degrees and the duration of the blowing air bursts is forty-five degrees or in the range of twenty to seventy degrees or from thirty to sixty degrees or the duration of each blowing air burst is in the range of ten milliseconds to forty milliseconds. [7] Investors according to claim 1, 2, 3, 4, 5 or 6, characterized by , that the air pressure of the blowing air pulses in the area of ​​the outlet openings (29) is equal to 1.5 bar or greater than 1.5 bar or equal to two bar or greater than two bar. [8] Investors according to claim 1, 2, 3, 4, 5, 6 or 7, characterized by , that the outlet openings (29) each have an opening cross-section equal to thirty square millimeters or less than thirty square millimeters. [9] Investors according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized by, that the blowing device (18) comprises several pulse-controlled high-pressure valves. [10] Investors according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, characterized by , that the blowing device (18) comprises several cam-controlled valves or rotary slides. [11] Investors according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, characterized by , that the at least one transport element (16) runs back and forth in the transport direction (T) and is designed to transport a respective sheet (03) in the sheet guide plane (20). [12] Investors according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, characterized by , that the at least one singulation element (14) and / or the at least one transport element (16) and / or the blowing device (18) are part of a sheet separator (13), wherein the sheet separator (13) is assigned a controllable drive (10) for raising and lowering the sheet separator (13). [13] Method for operating a feeder (01) of a sheet-processing machine, in particular a feeder (01) according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein, for a sequence of sheets (03) lying as a stack (07) on a stacking table (06), the uppermost sheet (03) in the stack (07) is moved by at least one singulation element (14) from a singulation plane (15) forming the top of the stack (07) to a sheet guide plane (20) vertically spaced from the stack, at least on the side of the stack (07) that faces away from a transport path downstream of the stack (07), and a sequence of blown air pulses directed under the raised sheets (03) is generated.wherein the last burst of air in a sequence of bursts of air under a respective sheet (03) ends at a time interval from the start of the transport movement of the transport element (16) for the transport of the respective sheet (03) or ends when the transport movement of the transport element (16) for the transport of the respective sheet (03) begins. [14] Method according to claim 13, characterized by , that the duration of the air blasts is in the range of ten milliseconds to forty milliseconds and is the same for all arcs (03) of an arc sequence. [15] Method according to claim 13 or 14, characterized by that several bursts of air, beginning at different times, are directed under the raised arch (03). [16] Method according to claim 13, 14 or 15, characterized by , that several bursts of air are directed from different outlet openings (29) under the raised arch (03). [17] Method according to claim 13, 14, 15 or 16, characterized by , that under the raised arches (03) a first burst of air is released in the area of ​​the middle of the arch stack (07) and, at a time interval to the first burst of air, further bursts of air are released into areas spaced away from the middle of the arch stack (07) under the raised arches (03). [18] Method according to claim 13, 14, 15, 16 or 17, characterized by, that several bursts of air are directed from the same or different outlet openings (29) under the raised bow (03), beginning at different times from each other, wherein a first burst of air ends at a time interval before the start of the transport movement of the transport element (16) for the transport of the respective bow (03) or ends when the transport movement of the transport element (16) for the transport of the respective bow (03) begins and a second burst of air, beginning offset to or after the first burst of air, ends after the start of the transport movement of the transport element (16).

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