Method and apparatus for compensating for skewing of documents

Abstract: The skew angle of a sheet (39) (e.g., business form or other document) is detected by providing two sensors (40, 40') spaced from each other a known distance along a straight line perpendicular to the direction (A) of conveyance of the sheet. If there is a skew, the distance travelled by the sheet leading edge (44) between sensings by the sensors is determined, and the skew angle calculated from its tangent. First and second independent drive rollers (35, 36) under the sheet are driven in opposite directions of rotation to compensate for the skew angle. The rollers preferably act in conjunction with a controller (42) (computer) to not only reorient the sheet to compensate for the skew, but also to rotate the document through a significant angle (e.g., 90 o ) to give the sheet a second orientation different from its initial orientation (e.g., from portrait to landscape).

Description: This application relates to an improvement of the invention disclosed in our European Application No. 92304108.1 (EP-A-0512827). In the handling of sheets, particularly documents such as business forms, as a sheet is being conveyed in a particular direction, often the leading edge thereof will become skewed -- that is, the leading edge is not perpendicular to the direction of conveyance, but assumes a particular angular orientation (a skew angle). If the sheet is skewed when presented to a device for rotating it through a finite angle, such as described in the above-mentioned application, then the sheet will not be rotated to a second orientation which is the desired orientation, but will differ by the skewed angle (either being greater or lesser than desired) by the amount of the skew angle. If the document --with the leading edge not positioned as desired -- is then fed into a pressure sealer, such as the Moore commercial "Speedisealer" (Registered Trade Mark) pressure seal system, the pressure rolls may pass over only a portion of the edge, thus sealing only a half or a third of the edge of the document, which could result in reject of the form, or the form could be damaged when mailed or otherwise handled. In this, and in many other situations, it is thus important to have the form positioned so that the leading edge thereof is perpendicular to the direction of conveyance into a piece of equipment. Xerox Disclosure Journal; Vol. 12; No. 4; July/August 1987; Rochester; NY; USA; pages 205 - 206; R.W. Huggins; "Skew detector and method of correction", discloses a method and apparatus for detecting the angle of skew of a document travelling in a first conveyance direction and correcting the skew so that the document continues travelling in the conveyance direction with its leading edge now correctly perpendicular to that first direction. According to the present invention, a method and apparatus are provided for simply and effectively correcting the skew angle of sheets by compensating for the skew angle during rotation of the sheet through a finite angle while repositioning the sheet (e.g. from landscape to portrait mode or vice versa). According to one aspect the invention provides apparatus for rotating a sheet, comprising: a conveyance surface on which a sheet, having a first orientation, travels in a first conveyance direction (A); first and second rollers for engaging a sheet travelling on said conveyance surface and spaced from each other in a second direction, generally transverse to said first direction; first and second drive means, operatively driving said first and second rollers, respectively, independently of each other; sensing means for sensing the leading edge of a sheet, having said first orientation, said sensing means further comprising means for sensing if the leading edge of the sheet is skewed with respect to its intended first orientation in which the leading edge is normal to the first conveyance direction; control means for controlling the speed and direction of rotation of said drive means and in response to a determination that the leading edge is skew, arranged to control the speed and direction of rotation of said drive means to compensate for the skew orientation of the sheet leading edge; characterised in that the control means are arranged to rotate the sheet through a predetermined angle of rotation of at least substantially 90 degrees and are arranged to simultaneously add or subtract the angle of skew (a) from the predetermined angle so that the sheet is rotated to a second orientation in which said leading edge has been displaced by a significant angle from its intended first orientation so that the sheet is rotated to the desired predetermined second orientation, with the skew automtically compensated for. In another aspect the invention provides a method of re-orienting a sheet having a skew using first and second drive means, rotating first and second rollers, respectively, independently of each other, and first and second sensors, comprising the steps of: (a) feeding the sheet in a first direction, and in a first orientation with a leading edge intended to be normal to the first direction, to a location adjacent the first and second rollers, at which the rollers engage the sheet; (b) at a location adjacent the first and second rollers, sensing the leading edge of the sheet with the sensors; (c) if the leading edge reaches one sensor before it reaches the other sensor, determining the distance of movement of the sheet in the first direction between sensor activations; (d) utilizing the distance determined from step (c), calculating the angle of skew of the leading edge of the sheet; (e) in response to (d), controlling the drive means continuously and without interruption to correct for skew; and characterised by controlling the speed and direction of rotation of the rollers, so that the rollers rotate the sheet through a significant angle to dispose the sheet in a desired second orientation in which the leading edge is no longer the leading edge in the first direction, and with the skew simultaneously compensated for. The rollers rotate the sheet through a predetermined angle even if the sheet is not originally skewed, so that it has the second orientation whether or not the sheet is originally skewed. There may also be the further step after step (e), of conveying a sheet in the first direction. Step (b) is preferably practiced at a location less than one-half of the dimension of the sheet in the first direction when it has the first orientation, and under the sheet while step (e) is practiced. The drive means are preferably reversible motors, such as D.C. stepper motors. The sensing means comprise first and second sensors spaced from each other a predetermined distance in the second direction in a line on a center line perpendicular to the first direction, and are preferably spaced apart the same distance as the rollers in center lines parallel to them, and downstream from them. An embodiment of the invention is described by way of example only with reference to the accompanying drawings of which:- BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side schematic view, partly in cross-section and partly in elevation, of operative components of the apparatus according to the invention; FIGURE 2 is a schematic plan view illustrating the operation of the apparatus as a skewed sheet is being handled thereby; FIGURE 3 is an enlarged detail view comparable to that of FIGURE 2 showing the skew in more detail; FIGURE 4 is a view like that of FIGURE 2 only showing the document after it has been rotated through 90 o from landscape mode to portrait mode, with compensation for the skew angle; and FIGURE 5 is a logic flowchart illustrating an exemplary operation of the apparatus according to the invention and which can be substituted for the flowchart of FIGURE 9 of the parent application. DETAILED DESCRIPTION OF THE DRAWINGS In the description of the drawings, the same reference numerals will be utilized as were provided in the European Application 92304108.1 the disclosure of which has been incorporated by reference herein. Exemplary apparatus according to the invention is shown generally by reference numeral 10 in FIGURE 1. The apparatus includes a generally horizontal conveying surface 15 along which sheets are fed in the direction of arrow A (a first direction). While the surface 15 is generally horizontal, it can have a positive or negative slope. An axis 19 is provided perpendicular to the direction A, and a hold-down strap 20 of relatively flexible material may be utilized to hold the sheets (39) on the surface 15. In order to continuously convey sheets in direction A, it is preferred to provide some sort of a conveyer, not shown in the drawings. For pivotal movement about the axis defined by the rod 19, a nip wheel 24 may be provided, connected by arms 26 to the rod 19. First and second drive means -- the drive means 31 illustrated in FIGURE 1, and a comparable drive means in the opposite side of the rollers 35, 36 (not shown) are provided for driving the rollers 35, 36. The drive means, such as the drive 31, are preferably reversible motors, such as conventional D.C. stepping motors (motors of the PX245 series from Oriental Motor Company Ltd.). The rollers 35, 36 are rotatable about shafts that define a common, in-line axis 33' (see FIGURE 2), which is perpendicular to the direction A. The rollers 35, 36 have peripheral surfaces 37, 38, and they are mounted so that the peripheral surfaces 37, 38 extend upwardly through the surface 15 and are operatively engaged by the nip wheels (e.g., 24). The rollers 35, 36 are spaced a relatively short distance in the direction of axis 33', in any event a distance significantly less than the width of a sheet 39 to be acted on thereby (e.g., spaced about 5.08-10.16 cm (2-4 inches)). The rollers 35, 36 are clamped to the shafts 33, 34. The rollers 35, 36 must be lightweight so that they have minimum inertia since they must be reversed in a fraction of a second. Yet the rollers 35, 36 must have a durable circumferential surface which has a high coefficient of friction, and a small footprint. Preferably the rollers 35, 36 are of aluminum or ABS plastic. The rollers 35, 36 may also have a roughened circumferential surface (especially if of aluminum), or a synthetic or natural rubber O-ring, or like elastomeric material, may extend around the circumferential surfaces of the rollers 35, 36. Located downstream, in the first direction A, of the first rollers 35, 36 are sensing means for sensing the leading edge 44 (see FIGURES 2 and 3 in particular) of sheet 39. The sensing means preferably comprise first and second sensors 40, 40'. As illustrated in the drawings, the sensors 40, 40' are preferably disposed on a center line which is parallel to the line 33', and perpendicular to the direction A, and the sensors 40, 40' are preferably spaced from each other in the horizontal direction perpendicular to the direction A the same distance that the rollers 35, 36 are spaced in the direction of axis 33' (e.g., 5.08-10.16 cm (2-4 inches)). The sensors 40, 40' are connected by lines 41 (e.g., fiber optic cables) with a microprocessor CPU 42, which in turn is connected via lines 43 with the motor 31 and the comparable motor for roller 36. While the location of the edge sensors 40, 40' downstream in the direction A of the rollers 35, 36 is not particularly critical, it must be adjacent the rollers 35, 36 and a distance from the rollers in the first direction A which is less than half the shortest dimension of the sheet 39 in the direction A. Also, the sensors 40, 40' should be under the sheet 39 during rotation of the sheet 39 (if the apparatus is used for positively always rotating the document or like sheet) to prevent the sensors 40, 40' from the detecting an edge falsely. The sensors 40, 40' may be photosensors, or any other desirable conventional type of sensor which can sense a leading edge 44 of a sheet 39. For example, the sensors 40, 40' and related hardware may comprise commercially available fiber optic cable, and FEP-PAD 6 series microswitch, and devices in the MFOD (receiver) and MFOE (transmitter) series from Motorola. When a leading edge 44 is skewed as illustrated in FIGURES 2 and 3, it will pass and be detected by one of the sensors 40, 40' before the other. For the example illustrated in FIGURES 2 and 3, the leading edge 44 will be sensed by the sensor 40 first and then by the sensor 40'. The time between sensing may be measured. Knowing this time and then calculating the distance y (see FIGURE 3) based upon that time and the knowledge of the speed of conveyance of the sheet 39, the skew angle α can be calculated. By sensing the distance y itself by utilizing an incremental encoder driven by a shaft which also drives rollers or conveyance mechanisms which cause the actual travel of the document, angle α can also be calculated. Once the distance y is determined, since the distance x is known, the angle α can be calculated since the tangent of α = y ÷ x . For example, if the sensors 40, 40' having a spacing of 5.08 cm (2.0 inches), and the distance y is determined to be 0.0635 cm (.025 inches), then the tangent of the skew angle α is equal to 0.0635 (0.025) divided by 5.08 (2), equals 0.0125, resulting in an angle α of .72° (or 43 minutes of arc). If the stepper motors 31, etc., have a step resolution of 0.0635 cm (0.025 inches), that means that the compensation of one step -- either to compensate for a clockwise skew (as illustrated in FIGURES 2 and 3), or a counterclockwise skew (if sensor 40' is covered first) -- must occur. The calculation of the skew angle α necessary to be compensated for is preferably accomplished by the microprocessor 42, or like components of the computer controller as described in the parent application. FIGURE 4 illustrates the rotation of the sheet 39 from the landscape mode to the portrait mode, with compensation for the skew angle α. As illustrated in FIGURE 4, after receiving input from the sensors 40, 40', which sense the leading edge 44 of the document 39 and determine its skew angle, the microprocessor 42 controls the motor 31 and its counterpart for the roller 36 to rotate them with the directions of rotation illustrated in FIGURE 4, and continues rotation of the rollers 35, 36 until the sheet 39 is in the portrait mode, that is, at a 90° angle of rotation from the position illustrated in FIGURE 2 and with the skew angle α compensated for. The rollers 35, 36 are rotated at high speed, that is on the order of 12 x 10 4 mm (400 feet) per minute, in this case the rotation being accomplished merely by effecting reverse rotation of the roller 36, which occurs for the necessary amount of time to rotate the sheet 39 ninety degrees while compensating for the skew angle α. FIGURE 5 illustrates a simple logic flowchart for control of the CPU 42 with software which -- if the invention is practiced in the entire system of the above EP application -- may be substituted for the logic flowchart of Figure 9 therein. At decision block 49, it is determined whether or not there is a skew of the sheet 39. If there is no skew, then the steps in blocks 53, 54 are practiced just like in the above EP application. In block 60, the time between sensing is either recorded, or the distance y is directly recorded from an incremental encoder. If the time is recorded, then the distance y is calculated from the speed of travel of the document 39. In any event, once the distance y is measured or determined, at block 61 the tangent of the skew angle α is calculated, and then when the counter is loaded with a count for 90 degrees of rotation, the skew angle is compenated for at block 62. Then at block 63 one of the motors is reversed (e.g., motor 31) as required to rotate the business form 39 to the desired second orientation (FIGURE 4). In a method of the invention, first a sheet 39 is fed, with the leading edge 44 and in the first orientation (FIGURES 2 and 3), in a first direction A to a location adjacent the rollers 35, 36, at which location the rollers 35, 36 engage the sheet 39. At a location adjacent the rollers 35, 36 the sensors 40, 40' sense the leading edge 44 of the sheet 39. If the leading edge 44 reaches one sensor (e.g., 40) before it reaches the other (40'), the distance "y" of travel of the sheet 39 in the first direction A between sensor activations is determined (either directly by an incremental coder, or by measuring the time between sensor activations and knowing the speed of conveyance of the sheet 39). Then, utilizing the distance "y" from the last step, the angle of skew α of the leading edge 44 of the sheet is calculated (by calculating a tangent) utilizing a CPU 42 or the like. In response to this calculation of the skew angle, the drive means are controlled to, in turn, control the speed and direction of rotation of the rollers 35, 36 so that the rollers 35, 36 rotate the sheet 39 to compensate for the skew angle α to dispose the sheet 39 in a desired second orientation. In the practice of the invention the sheet 39 is rotated a large angle of rotation so as to reorient the sheet 39 in a very different orientation, for example, from the landscape orientation of FIGURE 2 to the portrait orientation of FIGURE 4. This is accomplished at the same time that the skew angle is compensated for, for example, by rotating the roller 36 in the direction illustrated by an arrow in FIGURE 4 so that -- in the specific embodiment illustrated -- the document 39 is rotated counterclockwise 90 degrees from the position illustrated in FIGURE 2, plus the skew angle α. It will thus be seen that according to the present invention a simple yet effective method and apparatus have been illustrated for compensating for the skew angle of a sheet while simultaneously rotating the sheet through a large angle so that it has a significantly different orientation. While the method and apparatus according to the invention are particularly useful in the feeding of business forms to a pressure sealer, such as the Moore Speedisealer ® pressure system, they are applicable to a wide variety of different types of sheets and for a wide variety of different types of apparatus.

Claims: Apparatus for rotating a sheet, comprising: a conveyance surface (15) on which the sheet (39), having a first orientation, travels in a first conveyance direction (A); first and second rollers (35, 36) for engaging the sheet travelling on said conveyance surface and spaced from each other in a second direction, generally transverse to said first direction; first and second drive means (31), operatively driving said first and second rollers, respectively, independently of each other; sensing means (40, 40') for sensing the leading edge (44) of the sheet, having said first orientation, said sensing means further comprising means for sensing if the leading edge (44) of the sheet is skewed with respect to its intended first orientation in which the leading edge is normal to the first conveyance direction; control means (42) for controlling the speed and direction of rotation of said drive means and in response to a determination that the leading edge is skew, arranged to control the speed and direction of rotation of said drive means to compensate for the skew orientation of the sheet leading edge; characterised in that the control means (42) are arranged to rotate the sheet through a predetermined angle of rotation of at least substantially 90 degrees and are arranged to simultaneously add or subtract the angle of skew (α) from the predetermined angle so that the sheet is rotated to a second orientation in which said leading edge has been displaced by a significant angle from its intended first orientation so that the sheet is rotated to the desired predetermined second orientation, with the skew automatically compensated for. Apparatus according to claim 1 characterised in that said sensing means comprises first and second sensors (40, 40') spaced from each other a predetermined distance, preferably equal to the distance between the first and second rollers (35, 36) in said second direction, and lying on a line perpendicular to said first direction and downstream of the rollers; Apparatus according to claim 1 or claim 2 characterised in that said control means (42) comprise means for calculating the angle of skew of the leading edge (44) of a document based upon the distance of travel of the leading edge from when one sensor (40) detects it to when the other sensor (40') detects it. Apparatus according to any of claims 1 to 3 characterised in that said control means (42) include computer means for controlling said drive means (31) to effect rotation of the sheet (39) by driving the first roller (35) so that the tangential velocity thereof is in the first direction, and by driving the second roller (36) so that the tangential velocity thereof is in a third direction. Apparatus according to any of claims 1 to 4 characterised by conveyance means associated with said conveyance surface (15) for delivering a sheet (39) to said first and second rollers (35, 36) and sensors (40, 40') and for transporting said sheet away from said first and second rollers and sensors, in said first direction (A). A method of re-orienting a sheet (39) having a skew using first and second drive means (31), rotating first and second rollers (35, 36), respectively, independently of each other, and first and second sensors (40, 40'), comprising the steps of: (a) feeding the sheet (39) in a first direction (A), and in a first orientation with a leading edge (44) intended to be normal to the first direction, to a location adjacent the first and second rollers (35, 36), at which the rollers engage the sheet (39); (b) at a location adjacent the first and second rollers (35, 36), sensing the leading edge (44) of the sheet (39) with the sensors (40, 40'); (c) if the leading edge (44) reaches one sensor (40) before it reaches the other sensor (40'), determining the distance of movement of the sheet (39) in the first direction between sensor activations; (d) utilizing the distance determined from step (c), calculating the angle of skew (α) of the leading edge (44) of the sheet (39); (e) in response to (d), controlling the drive means (31) continuously and without interruption to correct for skew; and characterised by controlling the speed and direction of rotation of the rollers (35, 36), so that the rollers rotate the sheet (39) through a significant angle to dispose the sheet in a desired second orientation in which the leading edge is no longer the leading edge in the first direction (A), and with the skew compensated for. A method according to claim 6 wherein step (d) is practiced by calculating the tangent of the skew angle (α). A method according to claim 6 or claim 7 wherein step (b) is practiced at a location less than one-half the dimension of a sheet (39) in the first direction (A) when it has the first orientation, and under the sheet while step (e) is practiced.

Inventors: KALISIAK MICHAEL S, KALISIAK, MICHAEL S.
Applicants: MOORE BUSINESS FORMS INC, MOORE BUSINESS FORMS, INC.
Application year: 1992
Main classification: B65H7
IPC codes: B65G47, B65H7, B65H9