The present invention relates generally to a paper feeding device for feeding sheets of paper in a feeder or sorter.
There are essentially two types of feeders for use for after-treatment of sheets of paper in printing machines and copiers, viz. friction feeder and vacuum feeders. In friction feeders, individual sheets are picked from piles of sheets by a rotary feeding roll abutting against and pulling the top sheet from the pile, wherein a subjacent friction block normally retains subjacent sheets of the pile. Friction feeders are robust and in general reliable in operation, but occasion-ally more than one sheet at a time may happen to be picked mistakenly. The feeding rolls may also leave marks in the sheets. In vacuum feeders, sheets are picked from piles by the fact that the top sheet of the pile is sucked against a conveyor belt for transportation of the sheet to subsequent further processing. The vacuum feeder does not have the disadvantages mentioned above of the friction feeder, but the function thereof is more sensitive and a vacuum feeder is considerably more expensive than a friction feeder.
A vacuum feeder picks individual sheets of paper from a paper stack. First, the uppermost sheets of papers are separated by means of separation air and levitation air which are blown into the upper portion of the stack of papers. As the uppermost sheet of paper is separated it is lifted towards a vacuum unit comprising vacuum belts, which are rotating around a suction unit. Thereby, the uppermost sheet of paper is pulled from the stack of papers.
A drawback of prior art vacuum feeding machines is the mechanical solutions used for determining where over time a homogenous stack of papers is present. Between the homogenous stack of papers and the vacuum belts there is an area, the separation area, where air and paper are mixed. The position of the homogenous stack of papers controls the operation of the elevator which lifts the stack of papers at the same rate as the vacuum feeding machine feeds the paper sheets, i.e, at the rate which the uppermost paper sheet is removed from the stack of papers. These mechanical designs puncture the air bed which is built up over time in the separation area, which increases the risk of double feedings.
An object of the present invention is to provide a paper feeding device wherein the position of a homogenous stack of papers can be determined without puncturing the air bed in the separation area.
According to a first aspect of the invention there is thus provided a paper feeding device comprising a storage surface for a stack of papers, the storage surface having a leading edge, a trailing edge, and a first and a second side edge and being adapted to be move vertically between a first, lower end position and a second, upper end position. The device further comprises a vacuum feeder for feeding papers from their position on the storage surface and imparting a horizontal displacement on an uppermost sheet of paper. The device further comprises a blower arrangement adapted to provide a curtain of air separating the uppermost sheet of paper from the rest of the stack of papers. The device further comprises a sensor arrangement arranged to determine where the upper paper sheets in the stack of papers provided on the elevator start to separate from the rest of the paper sheets, the sensor arrangement comprising a plurality of infrared reflective sensors arranged in at least one vertical row.
In one embodiment, the infrared sensors are arranged in two parallel rows. In some embodiments, the two parallel rows with sensors are vertically displaced relative to one another, in order to achieve a higher resolution from the sensors.
A paper processing machine comprising a paper feeding device according to the invention is also provided.
The invention is now described, by way of example, with reference to the accompanying drawings, in which:
In the following, a detailed description of a paper feeding device according to the invention will be given. Special references given in the description, such as “up” or “down”, refer to directions during normal operation of the device.
Reference is first made to
The paper feeding device 10 further comprises adjustable paper guides for positioning of the stack of papers 12. Thus, four side guides 15a are provided, two on each side edge 14c, 14d of the storage surface 14 and an end guide 15b is provided at the trailing edge 14b of the storage surface 14. Thus, the side guides 15a are provided along the first and second side edges 14c, 14d and somewhere between the leading edge 14a and the trailing edge 14b of the storage surface 14. The side guides 15a cooperate so that the side guides on the different sides move an equal distance to keep the stack of papers 12 centrally positioned on the elevator 14 with respect to the longitudinal axis of the paper feeding device. The movable end guide 15b is adapted to control the length of the storage surface 14, by changing the distance between the leading edge 14a and the end guide 15b. Typically, the guide is positioned such that the papers are as close as possible to the leading edge 14a, which means that the stack of papers 12 abuts a stopping plate 13 at the leading edge 14a of the storage surface 14. The operating position of the stack of papers 12 is shown in
A vacuum feeder 16 extends across essentially the entire with of the stack of papers 12 and comprises in the shown embodiment five feeding belts 16a provided around a suction box 16b adapted to, during operation, generate an under-pressure to make a sheet of paper from the stack of papers adhere thereto for subsequent transportation by means of the feeding belts. Thus, the vacuum feeder 16 is provided for the feeding of papers from their position on the storage surface 14 and imparts the uppermost sheet of paper 12a a horizontal displacement to the left, as shown in the figures. It is also shown that the stack of papers 12 is centred with respect to the vacuum feeder 16.
The paper feeding device 10 also comprises a blower arrangement in the form of pairs of side blower units 18 adapted to provide a flow of air separating the uppermost sheet of paper 12a from the rest of the stack. The blower units are provided on the upper portion of the side guides 15a. This means that they are provided along the first and second side edges 14c, 14d of the storage surface 14 and somewhere between the leading edge 14a and the trailing edge 14b thereof.
Each side blower unit 18 is preferably provided with a fan and a nozzle having a slot-shaped exhaust opening substantially horizontal or orientated substantially parallel to the storage surface. The nozzle will now be described with reference to
In the embodiment shown in
It is seen in
The blower arrangement also comprises a front blower unit 20 mounted in front of the stack of papers 12, i.e., along the leading edge 14a of the storage surface 14. When a paper sheet is moved by the vacuum feeder 16 it will pass above the front blower unit 20. The front blower unit 20 provides multiple air flows, preferably four, by means of a respective air opening. Each of the air openings is made up of a first portion 20a and a second portion 20b, see
The air openings are designed such that the air from each air opening is separated into two different cones in order to obtain a turbulent air flow. Approximately 60% of the air creates a first air cone 20a′ with a height of 10 mm when it impinges the stack of papers 12 at a distance of about 10 mm. The remaining air, i.e. approximately 40% of the air, creates a second air cone with a similar, although approximately 50% smaller, geometry, but which is vertically displaced approximately 5 mm in relation to the first air cone. In this way, the front blower unit 20 will cover a larger vertical distance from the vacuum belts 16a. The major part of the total air, flow, i.e. the approximately 60% that constitute the first air cone, is directed at a steeper angle than the 40% that constitute the second air cone towards the vacuum belts 16. This is due to the separation at the top part of the stack of papers is more important than separation at a lower portion of the stack of papers, since the final separation of the paper sheets happens close to the vacuum belts 16a, i.e. close to the top of the stack of papers.
Referring to
The paper feeding device 10 also comprises a sensor arrangement 22, shown in detail in
The sensor arrangement 22 preferably also comprises 16 auxiliary IR diodes 22b, which provide extra IR light and which can be controlled depending on the requirements, and is used especially when the natural lighting conditions are insufficient. In
At start of operation of the paper feeding device 10 a homogenous stack of papers cover eight of the 16 sensors 22a of the sensor arrangement 22. A calibration is then performed to make the sensor arrangement independent of the type of paper medium and colour. The position of the homogenous stack of papers, i.e., where the papers start to separate, is determined by the position where the reflection detected by the sensors 22a falls below a predetermined threshold value, such as 15%. Thus, the position of the homogenous stack of papers is determined by the vertical position of the uppermost sensor 22a detecting a reflection above the threshold value.
The auxiliary IR diodes 22b are operated when no reflection above a predetermined threshold value, such as 15%, is detected by the reflective sensors 22a at the calibration thereof, which in other words mean that the IR diodes 22b are operated only when the original lighting conditions are insufficient to achieve a detection above a certain threshold value. Thus, the operating mode is automatically determined at the start of operation, in the sense that the IR diodes 22b are either used, i.e. turned on, or not use, i.e. turned off.
During operation the sensor arrangement 20 performs sampling at regular intervals, in the preferred embodiment every 20 ms, starting at the top and progressing downward. When the sensor arrangement identifies a reflection value which is above the threshold value, this position is submitted to the control unit controlling the operation of the paper feeding device 10. This value is used for controlling the operation of the elevator arrangement controlling the vertical position of the storage surface 14. This is due to the reflection value being indicative of how tightly packed the papers in the stack of papers are, and as such the reflection value will be higher at a bottom part of the stack of papers than at the top of the stack of papers during operation of the paper feeding device, since the paper sheets are more tightly packed at the bottom of the stack of papers.
Again referring to
Before operation of the paper feeding device but after the stack of papers 12 has been placed on the elevator 14, the first and second distance meters 24a, 24b perform at least one measurement of the distance from the respective distance meter and the respective paper guide, in order to determine the size of the paper sheets in the stack of papers 12. It is preferred that multiple measurements are performed by each distance meter, such as 10 measurements, and that subsequently an averaging is performed. The values Sx and Sy, respectively, are stored and the paper size can be calculated as follows.
The width of the papers in the stack of papers 12 is determined by the first distance meter 24a. When the side guides 15a are in their rearmost position, i.e., accommodating a maximum width, they are in a basic position. In the present embodiment this accommodates a maximum width Wmax of 360.0 mm. This basic position is connected to a basic distance DWbase from the first distance meter 24a and the surface of the side guide 15a facing towards the first distance meter 24a, for example 20.0 mm. When performing a measurement by the first distance meter 24a a distance value DWmeasured is obtained. It should be noted that the distance value DWmeasured is always at least as large as the distance value DWbase.
It has already been mentioned that the associated side guides 15a move an equal distance in order to centre the stack of papers 12. Thus, if one side guide 15a moves a distance Δ towards the stack of papers 12, the accommodated width is decreased by 2×Δ. These relationships can be used to calculate the accommodated width Waccomodated of the stack of papers 12 as follows.
W
accomodated
=W
max−2×(DWmeasured−DWbase)
For example, given the values in the above example, if the measured distance DWmeasured is 95.0 mm, the width of the papers in the stack of papers 12 is calculated to 360.0−2×(95.0−20.0)=210.0 mm.
The length of the papers in the stack of papers 12 is determined by the second distance meter 24b. This is provided at a fixed distance DLbase from the leading edge 14a of the storage surface, which is the same as the position of a stopping plate 13 or wall to which the stack of papers 12 abuts in during operation of the device for feeding papers. When the end guide 15b is in a position accommodating a maximum length, it is in a basic position. In the present embodiment this position accommodates a maximum length Lmax of 660.0 mm. When performing a measurement by the second distance meter 24b from the distance meter 24b to the side of the end guide 15b facing towards the distance meter 24b, a distance value DLmeasured is obtained. It has already been mentioned that the second distance meter 15b is positioned a distance DLbase from the position of a stopping plate 13 or wall to which the stack of papers 12 abuts in during operation, i.e., the leading edge of the stack of papers 12. This can be used to calculate the accommodated length Laccomodated of the stack of papers 12 as follows.
L
accomodated=(DLmeasured+DLbase)
For example, given the values in the above example, if the measured distance DLmeasured is 197 mm, the length of the papers in the stack of papers 12 is calculated to 197.0+100=297.0 mm.
Referring to
The upper paper stops 26 are divided into two parts, and it preferably has a gap in between the parts, see
In
Preferred embodiments of a paper feeding device have been described. It will be appreciated that these can be modified without departing from the inventive idea as defined by the appended claims. Thus, although . . . .
Number | Date | Country | Kind |
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1650440-9 | Apr 2016 | SE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/SE2017/050323 | 3/31/2017 | WO | 00 |