The present invention relates to a winding apparatus for winding a paper web, comprising
The invention also relates to a method for winding a paper web comprising the steps of
The invention also relates to an equipment in a winding apparatus for winding a paper web, for measuring and controlling a distance between a roll of paper being wound and a support member, which winding apparatus comprises
In the continuous manufacture of paper in a paper machine the paper web is wound onto reel spools to form finished rolls of paper, i.e. parent rolls. To facilitate subsequent processing of the parent rolls, it is essential to ensure that each parent roll is formstable and substantially circular-cylindrical in shape. It is important also to ensure that winding takes place in such a manner that the properties the paper web acquired during production, such as stretchability and bulk, are not lost. When winding creped soft paper with low grammage and density known as high-bulk tissue, for instance, it is desirable that the pressure between adjacent layers of paper in the parent roll is as low as possible, as well as being substantially constant through the whole parent roll. However, at the same time, sufficient pressure must be applied to prevent the parent roll from “telescoping” or becoming deformed in some other way.
In order to control the winding it is common to form a nip between the roll of paper being wound and a support member such as a surface winding drum or an endless belt. The roll of paper and the support member thus form a nip through which the paper web passes. By controlling the linear load between the roll of paper and the support member, i.e. the ratio of the force acting between the roll and the support member, and the width of the roll of paper, the pressure between adjacent layers of paper in the roll of paper is controlled.
A good control of the linear load is thus important in order to obtain rolls of paper of high quality. The linear load is usually measured using force sensing elements such as load cells or pressure transducers arranged between the carriage supporting the roll of paper and the stand of the winding device. However, this method has the drawback that the signal generated by the linear load in the force sensing element risks being drowned in signals caused by friction forces and inertia forces from the rotating roll of paper. In conventional winding devices having a primary system and a secondary system it is particularly difficult to control the linear load in the primary system and when transferring the roll of paper from the primary system to the secondary system.
U.S. Pat. No. 6,036,137 describes a reel-up utilizing the fact that a given linear load between a roll of paper and a support member in the form of a surface winding drum can be correlated to the radial indentation of the roll of paper where it abuts the surface winding drum. The reel-up comprises a measuring device having a first sensor that measures the increasing diameter of the roll of paper by measuring the distance between a known position of the winding drum and the cylindrical surface of the roll of paper. The measuring device also comprises a second sensor that measures the distance between the axis of the roll of paper and a known second position relative to the axis of the surface winding drum. The measured values are supplied to a control unit in which the indentation of the roll of paper is calculated and compared with a desired indentation corresponding to an optimal linear load. If the discrepancy between measured and desired indentation is too great, the desired indentation is set by a controlled regulation of the distance between the axis of the surface winding drum and the axis of the roll of paper. Examples of suitable sensors mentioned in U.S. Pat. No. 6,036,137 are laser-based sensors which measure said distance using triangulation or interferometry techniques. In order to unequivocally determine the radius and axis position of the roll of paper, therefore, two location-separated distance sensing systems must be used. This is a drawback since a common detailed calibration of the two systems is necessary in order to obtain accurate values for the radius and axis position of the roll of paper.
The object of the present invention is to provide a winding apparatus which remedies the above-mentioned drawback and enables simple, accurate and reliable calculation of the radius and axis position of a roll of paper being wound, thereby enabling simple, accurate and reliable control of the distance between the roll of paper and the support member.
The winding apparatus in accordance with the invention is characterized in that the winding apparatus further comprises a measuring and controlling equipment comprising
The method in accordance with the invention is characterized by the further steps of
The equipment in accordance with the invention is characterized in that it comprises
According to the invention the fact is exploited that the equation for said line contains explicit information concerning the radius and axis position of the roll of paper. Placing and aligning the light-emitting member and the camera so that the projection of the line in the camera forms a curve allows the equation of the line to be calculated, given that the positions of the camera and the light-emitting member are known. The radius and axis position of the roll of paper can then be calculated from the equation of the line.
The radius and axis position of the roll of paper is preferably calculated continuously during winding, and the information is used for positioning the roll of paper at a desired distance from the support member. The linear load between the roll of paper and the support member can thus be continuously controlled.
The light-emitting device preferably emits luminous laser light. The light-emitting member may comprise a laser-prism arrangement that emits a curtain of light forming a coherent light track as a visible line. Alternatively the light-emitting member may comprise a plurality of lasers that emit laser beams illuminating the line pointwise.
Said analysis comprises preferably the steps of digitalizing the depicted line, identifying a plurality of points on the depicted line, calculating the equation of the line on the basis of the mutual positions of these points and calculating the radius and axis position of the roll of paper from the equation of the line. For accuracy of the calculation it is preferable for the line to have as large an extension as possible in the circumferential direction of the roll of paper.
The invention will be described in the following in more detail with reference to the drawings.
The principle of the invention will be described in more detail in the following with reference to
The reel-up includes a measuring and controlling equipment which comprises a light-emitting member 6 in the form of a laser, that emits a focused laser beam, and a prism that spreads the laser beam to a flat light curtain. This laser-prism arrangement, in the following called “linear laser” is arranged above the surface winding drum 2 and the roll 4 of paper and emits said light curtain in one plane, in the following called “illumination plane”. Where the illumination plane encounters the roll 4 of paper the linear laser 6 illuminates the roll 4 of paper creating a visible line 7 on the cylindrical surface 8 of the roll 4 of paper. In other words the linear laser emits a line-shaped light pattern onto the roll 4 of paper.
The normal direction of the illumination plane forms substantially a right angle to the machine direction (MD) of the reel-up and an angle of approximately 90° to the axial direction of the roll 4 of paper, i.e. the normal direction of the illumination plane substantially coincides with the cross direction (CD). The line 7 thus describes a circle arc that has a radius of curvature from which the radius of the growing roll 4 of paper can be calculated, and a centre of curvature corresponding to the position of the axis of the roll 4 of paper. The line 7 thus contains information as to the radius and axis position of the roll 4 of paper, from which information the indentation of the roll 4 of paper can be calculated, provided that the radius and axis position of the surface winding drum 2 are known.
The measuring and controlling equipment comprises a receptive system or light detection device. In the embodiments shown the receptive system is in the form of a reproducing optical system, that includes a camera 9. The measuring and controlling equipment also comprises a control unit 10 connected to the camera 9 and comprising an image analyzer. The camera 9 is placed at a distance from the linear laser 6 and aligned so that its optical axis forms an angle in the interval of 15 to 45° to the illumination plane. The camera 9 thus depicts the line 7 as a curve. Provided that the position and alignment of the camera 9 are known, the image analyzer calculates the radius and axis position of the roll 4 of paper on the basis of the depicted line 7. Provided that the radius and axis position of the surface winding drum 2 are known, the control unit 10 then calculates the distance between the roll 4 of paper and the surface winding drum 2, which gives the indentation of the roll 4 of paper. The control unit 10 compares the calculated distance between the roll 4 of paper and the surface winding drum 2 with a predetermined, desired distance between the roll 4 of paper and the surface winding drum 2, which corresponds to a desired indentation of the roll 4 of paper. If the calculated distance deviates from the desired distance, the control unit 10 sends a distance-correcting signal to said actuator which then moves the reel spool 3 closer to or further away from the surface winding drum 2 so that the desired indentation is obtained.
During the winding process the radius of the roll 4 of paper is constantly growing. In order for the measuring and controlling equipment to maintain the desired indentation the axis of the paper roll 4 need to move away from the surface winding drum 2 in a controlled manner. The speed of this movement of the axis of the roll 4 of paper away from the surface winding drum 2 needs to be relatively higher at an early stage of the winding process due to a relatively small radius of the roll 4 of paper at this early stage. However, at a later stage of the winding process the speed of the movement needs to be relatively lower due to a relatively large radius of the roll 4 of paper.
The control unit 10 preferably also calculates the peripheral speed of the growing roll 4 of paper by multiplying the radius calculated by the image analyzer, by the speed of rotation of the roll 4 of paper that is obtained from the drive unit of the reel spool 3 or drive unit of the reel spool 3 (not shown). If the calculated peripheral speed deviates from a desired peripheral speed, the control unit 10 sends a signal correcting the rotational speed to the drive unit which then adjusts the speed of rotation so that the desired peripheral speed is obtained.
The linear laser 6 preferably illuminates the growing roll 4 of paper throughout the winding process so that the indentation and peripheral speed of the roll 4 of paper can be continuously controlled.
The depicted line 7 is preferably digitalized at an early stage in the image analyzer of the control unit 10, or alternatively already in the camera 9, and the continued processing in the image analyzer then takes place in digital form. The image analyzer preferably comprises a microprocessor for this processing. The algorithm that calculates the equation of the line 7 preferably comprises the steps of identifying a plurality of evenly distributed points along the line 7, after which the radius of curvature and centre of curvature of the line 7 are calculated in known manner on the basis of the relative positions of the points. It will be recognized that, from the point of view of accuracy, the line 7 should be as long as possible. The linear laser 6 enables illumination of half the circumference of the roll 4 of paper and, in general, the extension of the line 7 in circumferential direction of the roll 4 of paper should be as great as possible. Since the line 7 describes an arc, at least three points must be used in the algorithm in order to unambiguously define the radius of curvature and centre of curvature. However, more points are preferably used for increased accuracy. Other known algorithms to determine the radius of curvature and centre of curvature of a curve with the aid of an image analyzer may alternatively be used.
In an alternative process, the light curtain also illuminates the surface winding drum 2 creating a second visible line 11 on the cylindrical surface 12 of the surface winding drum 2. In other words the linear laser also emits a line-shaped light pattern onto the surface winding drum 2. In this case the camera 9 is aligned to depict the first line 7 as well as the second line 11. The radii of curvature and centres of curvature of the lines 7, 11 are calculated in the image analyzer in the same manner as described above. The control unit 10 then calculates the distance between the surface winding drum 2 and the roll 4 of paper, after which the indentation of the roll 4 of paper is calculated. In this process the indentation of the roll 4 of paper is thus obtained directly without the need for previous knowledge of the radius or axis position of the surface winding drum 2.
In the embodiment shown in
Consequently a first group of lasers 13a illuminates the roll 4 of paper pointwise along the line 7, and a second group of lasers 13b illuminates the surface winding drum 2 pointwise along the line 11. In other words, the first group of lasers 13a emits a first light pattern onto the roll 4 of paper and the second group of lasers 13b emits a second light pattern onto the surface winding drum 2, said first and second light patterns having the shape of luminous points following the line 7 and 11, respectively. The illuminated points 14, 15 on the lines 7, 11 are depicted by the camera 9. The image analyzer of the control unit 10 calculates the radii of curvature and centres of curvature in known manner, on the basis of the relative positions of the points 14, 15, after which the indentation and peripheral speed of the roll 4 of paper are calculated to constitute a basis for any control signals to said actuator and drive unit, respectively. The advantage of this embodiment is that a set of lasers is normally cheaper than the technically more complicated laser-prism arrangement.
To be able to calculate the indentation and peripheral speed of the roll 4 of paper as described above it is required that the camera 9 is positioned and directed so that it depicts the lines 7, 11 as curves. In other words, the position of the camera 9 must be separate from the illumination plane. If the camera 9 were to be arranged in the illumination plane the projections of the lines 7, 11 in the camera 9 would be straight and the image analyzer would be unable to calculate said radii of curvature or centres of curvature.
In principle the measuring method is independent of the alignment of the illumination plane and the camera, provided the reproducing requirements as to curvature of the depicted lines are fulfilled. However, it is preferred that the light-emitting member be aligned so that the normal direction of the illumination plane substantially forms a right angle to the machine direction in order to avoid that the geometry of the depicted lines and calculation of the radii and centres of curvature becomes unnecessarily complicated. The normal direction of the illumination plane may thus be permitted to form an angle in the interval of 0-90° to the cross direction, and the optical axis of the camera may be permitted to form an angle to the illumination plane which is also in the interval of 0-90°. An alternative to the alignments of the light-emitting member and the camera as described in
If the light-emitting member comprises a set of lasers the lasers need not be arranged so that their laser beams define a single plane, i.e. a flat surface. Theoretically it is possible to determine the radius and centre of curvature of the roll of paper also in the case when the laser beams define some form of curving surface. In this case, however, the calculations would be relatively complicated.
The method in accordance with the invention is also suitable for use with reel-ups where the support member is a member other than a surface winding drum.
The light-emitting member and the depicting optical system may be placed in various ways in relation to the roll of paper.
The light-emitting member and camera may thus be placed in a number of different ways. However, the condition is, as mentioned above, that the light-emitting member and camera are positioned and aligned so that the light-emitting member illuminates the roll of paper and possibly also the surface winding cylinder along lines on their cylindrical surfaces, and that the lines depicted by the camera are curves. Provided these requirements are fulfilled the light-emitting member and camera may be placed inside the width of the paper web, as shown in
It is recognized that the invention can be combined with conventional technology. The radius of the roll of paper may be calculated in accordance with the invention, for instance, while the axis position of the roll of paper may be measured with a conventional position transducer, preferably one connected to the control unit.
The measuring and controlling equipment should preferably operate with visible light, preferably visible laser light. However, it will be recognized that the invention is not only limited to light-emitting members and receptive or reproducing optical systems that operate in the visible range of wave lengths, i.e. 390-770 nanometer. Measuring systems operating in the ultraviolet, infrared or other ranges of wave lengths may also be used. A condition is, however, that the electromagnetic waves have such physical properties that the detection of a distinct line on the cylindrical surface of the roll of paper is possible. Consequently the concepts “light” and “optical” shall not be interpreted here to be associated only with visible electromagnetic waves.
The invention has been described above in connection with a reel-up, however, it should be understood that the invention also is applicable to all types of winding apparatus wherein a nip load is to be controlled during a web winding process, for instance a rewinding machine.
Number | Date | Country | Kind |
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0200691-4 | Mar 2002 | SE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/SE03/00363 | 3/5/2003 | WO |
Number | Date | Country | |
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60369177 | Apr 2002 | US |