Abstract:
A tandem printer with a mechanism for fine substrate-position correction, comprising: a first printing station; a second printing station; a rotatable element, rotating at a given rotation rate, that receives the substrate after printing thereon by the first printing station and transfer the substrate toward the second printing station; a sensor which measure the position of an edge of the substrate during its transfer from the first printing station to the second printing station; and a controller, which applies a corrective step change in angular position of the rotatable element responsive to the measurements of the sensor, without changing the general rotation rate of the rotatable element.

Description:
RELATED APPLICATIONS 
     The present application is a U.S. national application of PCT/IL99/00600, filed 7 Nov. 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to printing systems and more particularly to tandem printing systems for printing variable information using two or more printing stations and including a paper-position correction mechanism. 
     BACKGROUND OF THE INVENTION 
     Tandem printing systems, that is printing systems with two or more printing engines, are well known, both for duplex printing and for multi-colour, single-side printing, with each colour being printed with a different one of a tandem series of printing engines. Such systems are known both for conventional and electronic printing. However, such systems depend on a very accurate transmission and edge alignment of the paper. 
     In systems of rollers and belts, a mismatch in transmission and edge alignment may occur for various reasons. The rollers may be slightly off centre, the paper may slip or creep off is its hold, there may be diameter variations, for example, because of different paper thickness and the belts may stretch as a result of heat or age. To achieve the accuracy required in tandem printing, these misalignments must be corrected. 
     SUMMARY OF THE INVENTION 
     One aspect of some preferred embodiments of the invention relates to a tandem printer with a mechanism for fine paper-position correction. 
     Preferably, the tandem printer has a motive system comprising a rotatable element which rotates at a given rotation rate and on which the paper is mounted, wherein a step angular displacement to the rotatable element brings the paper into alignment, without changing the rotation rate of the rotatable element. 
     Preferably, a paper sensor measures the position of the paper. The measurements are reported to a controller which applies the step, angular displacement to the rotatable element, in addition to the continuous rotation, responsive to the measurements of the sensor. 
     Preferably, the motive system also comprises a flexible strip, for example, a timing belt, which transfers motion at a constant rotation rate from a driving roller to the rotatable element, wherein a step displacement to the flexible strip induces the step angular displacement to the rotatable element. The axis of the flexible strip is defined as the line connecting the centre of the rotatable element and the driving roller. 
     Preferably, the step displacement of the flexible strip is provided by linear motion of two pulleys located upstream and downstream of the rotatable element, wherein as one pulley presses onto the flexible strip, requiring slack, the other pulley pulls away from the flexible strip, releasing slack. The transfer of flexible-strip slack from one pulley to the other provides the step displacement of the flexible strip. 
     Preferably, the tandem printer comprises means for providing the required linear motion to the pulleys. 
     In some preferred embodiments of the invention, means for providing linear motion to the pulleys comprises a rod having two edges on which the two pulleys are mounted. The rod is preferably situated perpendicular to the axis of the flexible strip, with one pulley, at one edge, pressing against the flexible strip upstream of the rotatable element, at a first point, and the other pulley, at the other edge, pressing against the flexible strip downstream of the rotatable element, at a second point. Movement of the rod up and down in a direction generally, perpendicular to the axis of the flexible strip provides the required linear motion to the pulleys. 
     Alternatively, means for providing linear motion to the pulleys comprises a shaft on which one pulley is mounted, pressing against the flexible strip at a first point and a spring-loaded device (for example, a spring-loaded piston-cylinder device) on which the other pulley is mounted, in partial compression, pressing against the flexible strip at a second point, wherein the first and second points are upstream and downstream of the rotatable element, in any order, reasonably far from any rotating elements associated with the flexible strip. Linear movement of the shaft provides the linear motion to the pulley mounted on it. The response of the spring-loaded device to the release or demand in slack provides the motion of the other pulley. 
     Preferably, a stepper motor provides the motion for the pulleys. In some preferred embodiments an eccentric shaft is used to convert the motor motion to linear motion. Alternatively, any of a slider-crank mechanism, a piston-cylinder mechanism, or a turning-screw mechanism may be used. Alternatively still, any other method of providing linear motion, known to persons versed in kinematics, may be used. 
     Preferably, the motor is activated by a controller which determines when the paper is out of alignment and the magnitude and direction of the misalignment. 
     In some preferred embodiments, the section of the flexible strip adjacent to the first point and the section of the flexible strip adjacent to the second point are parallel. For small displacements, the step angular displacement of the rotatable element is symmetric for upward and downward linear displacements of the pulleys. 
     Preferably, the step angular displacement of the rotatable element is given as a function (which may be empirical) of the linear displacement of the pulleys. Alternatively, a lookup table is used. 
     In some preferred embodiments of the invention, the tandem printer comprises a duplex printer for printing on both sides of paper while inverting it. Alternatively, the tandem printer comprises a multicolour printer of single side printing, with each colour being printed with a different one of the tandem series of printing engines. 
     In some preferred embodiments of the invention, the tandem printer comprises any conventional printer, such as a printer which prints directly from plates. Alternatively, the tandem printer comprises any of a lithographic printer, an electrostatic printer, or an electronic printer. 
     There is thus provided, in accordance with a preferred embodiment of the invention a tandem printer with a mechanism for fine substrate-position correction, comprising: 
     a first printing station; 
     a second printing station; 
     a rotatable element, rotating at a given rotation rate, that receives the substrate after printing thereon by the first printing station and transfers the substrate toward the second printing station; 
     a sensor which measures the position of an edge of the substrate during its transfer from the first printing station to the second printing station; and 
     a controller, which applies a corrective step change in angular position of the rotatable element responsive to the measurements of the sensor, without changing the general rotation rate of the rotatable element. 
     Preferably, the sensor which measures the position of an edge of the substrate is situated on the rotatable element. 
     Alternatively, the sensor which measures the position of an edge of the substrate is adjacent to the rotatable element. 
     In a preferred embodiment of the invention, the tandem printer also comprises: 
     a transfer system which transfers the substrate from the first printing station to the second printing station, in which the rotatable element is comprised; 
     the transfer system further comprising: 
     a flexible strip, travelling at a given rate and providing motion to the rotatable element, wherein a corrective step displacement of the flexible strip induces the corrective step change in angular position of the rotatable element. 
     Preferably, the flexible strip rotates at a constant rate. 
     Preferably, the flexible strip is a timing belt. 
     In a preferred embodiment of the invention, the tandem printer also comprises at least one pulley that provides the corrective step displacement of the flexible strip. 
     In a preferred embodiment of the invention, the at least one pulley comprises: 
     two pulleys, situated along the flexible strip, one upstream and one downstream of the rotatable element, said pulleys pressing into the flexible strip at a first point and a second point, respectively, wherein when pressure of one pulley is partially released, the other pulley takes up the thus produced slack, providing the corrective step displacement of the flexible strip. 
     In a preferred embodiment of the invention, the tandem printer also comprises a rod, comprising two points, to which the two pulleys are attached, one at each edge, wherein linear movement of the rod provides the motion of the pulleys into and away from the flexible strip. 
     Preferably, the tandem printer also includes a motion provider for the rod, comprising: 
     an eccentric shaft to which the rod is attached; and 
     a motor which provides motion to the eccentric shaft, 
     wherein the motor is activated by the controller. 
     Alternatively, the tandem printer includes a motion provider for the rod, comprising: 
     a slider-crank mechanism, wherein the rod is attached to the slider and moves in the same direction as the slider; and 
     a motor which provides motion to the slider-crank mechanism, 
     wherein the motor is activated by the controller. 
     Alternatively, the tandem printer includes a motion provider for the rod, comprising: 
     a piston-cylinder mechanism, wherein the rod is attached to the piston and moves in the same direction as the piston; and 
     a motor which provides motion to the piston-cylinder mechanism, 
     wherein the motor is activated by the controller. 
     Alternatively still, the tandem printer includes a motion provider for the rod, comprising: 
     a turning-screw mechanism, wherein the rod is attached to the screw and moves in the same direction as the screw; and 
     a motor which provides motion to the turning-screw mechanism, 
     wherein the motor is activated by the controller. 
     Preferably, the motor is a stepper motor. 
     In another preferred embodiment of the invention, the tandem printer also comprises: 
     a shaft on which one of the two pulleys is mounted, pressing against the flexible strip at a first point; and 
     a resilient device on which the other pulley is mounted, resiliently pressing against the flexible strip at a second point, 
     wherein linear movement of the shaft provides motion of the pulley at the first point, and the response of the resilient device to release or demand in slack provides motion of the pulley at the second point. 
     Preferably, the shaft is an eccentric shaft and including: 
     a motor which provides motion to the eccentric shaft, 
     wherein the motor is activated by the controller. 
     Preferably, the tandem printer also includes a motion provider for the shaft, comprising: 
     a slider-crank mechanism, wherein the shaft is connected to the slider and moves in the same direction as the slider, and 
     a motor which provides motion to the slider-crank mechanism, 
     wherein the motor is activated by the controller. 
     Alternatively, the tandem printer also includes a motion provider for the shaft, comprising: 
     a piston-cylinder mechanism, wherein the shaft is connected to the piston and moves in the same direction as the piston; and 
     a motor which provides motion to the piston-cylinder mechanism, 
     wherein the motor is activated by the controller. 
     Alternatively still, the tandem printer also includes a motion provider for the shaft, comprising: 
     a turning-screw mechanism, wherein the shaft is connected to the screw and moves in the same direction as the screw; and 
     a motor which provides motion to the turning-screw mechanism, 
     wherein the motor is activated by the controller. 
     Preferably, the motor is a stepper motor. 
     In a preferred embodiment of the invention, the two pulleys are substantially identical. 
     In a preferred embodiment of the invention, the section of the flexible strip adjacent to the first point and a section of the flexible strip adjacent to the second point are parallel to each other. 
     In a preferred embodiment of the invention, the tandem printer comprises a duplex printer for printing on both sides of the paper while inverting it. 
     Alternatively, the tandem printer comprises a multicolour printer of single-side printing, with each colour being printed with a different one of the tandem series of printing engines. 
     In a preferred embodiment of the invention, the tandem printer is a conventional printer which uses plates. 
     Alternatively, the tandem printer is an electrostatic printer. 
     Alternatively, the tandem printer is an electronic printer. 
     Alternatively, the tandem printer is a lithographic printer. 
     In a preferred embodiment of the invention, a multi-engine printer with a mechanism for fine substrate-position correction, is provided, comprising at least 3 printing engines, wherein each adjacent pair of printing engines comprises a first printing station and a second printing station, of the tandem printer described herein. 
     There is further provided, in accordance with a preferred embodiment of the invention a tandem printing method while applying a fine positional correction to a substrate, comprising: 
     printing on a substrate by a first printing station; 
     transferring the substrate from the first printing station toward a second printing station, comprising: 
     mounting the substrate on a rotatable element of a substrate-transfer system; and 
     moving the substrate by rotating the rotatable element at a given rotation rate; 
     measuring the angular position of an edge of the substrate on the rotatable element; and 
     applying a step angular displacement to the rotatable element, responsive to the measurement, without changing the rotation rate of the rotatable element. 
     Preferably, rotating the rotatable element at a given rotation rate comprises rotating the rotatable element by a flexible strip; and 
     applying the step angular displacement to the rotatable element comprises applying a step displacement to the flexible strip. 
     Preferably, applying the step displacement to the flexible strip comprises any of a positive and negative step displacements to the flexible strip, thus inducing any of a clockwise and a counterclockwise step angular displacements to the rotatable element. 
     Preferably, applying the positive step displacement to the flexible strip comprises: 
     releasing flexible strip slack upstream of the rotatable element; and 
     taking up flexible strip slack downstream of the rotatable element; and 
     applying the negative step displacement to the flexible strip comprises: 
     releasing flexible strip slack downstream of the rotatable element; and 
     taking up flexible strip slack upstream of the rotatable element. 
     Preferably, the method also includes using a lookup table to calculate a necessary step displacement of the flexible strip in order to achieve a desired step angular displacement of the rotatable element 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the following detailed description of the preferred embodiments of the invention and from the attached drawings, in which same number designations are maintained throughout the figures for each element and in which: 
     FIG. 1 is a schematic illustration of a tandem printer comprising a correctional mechanism for correcting a paper position, in accordance with a preferred embodiment of the invention; and 
     FIG. 2 is a schematic illustration of a tandem printer comprising another correctional mechanism for correcting a paper position, in accordance with another preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIG. 1 which is a schematic illustration of a tandem printer  10  having a roller assembly  20  for paper inversion and transfer and a correctional mechanism  30 , in accordance with a preferred embodiment of the invention. 
     Preferably, tandem printer  10  comprises a first printing station  11 , comprising an impression roller  12  and at least one first printing engine  16  associated with it, and a second printing station  13 , comprising an impression roller  14  and at least one second printing engine  18  associated with it. In the system shown, each of printing engines  16  and  18  comprises an intermediate transfer member (ITM)  15  and  17  respectively. The image is transferred to ITM or  17  and then to paper  40  on the respective impression roller. Alternatively, no ITM is used, and each of printing engine  16  and  18  comprises a photoconductive drum  15  or  17  respectively. The image is preferably formed on photoconductive drum  15  or  17  and transferred to paper  40  on the impression roller. For two side printing, one side of a paper  40  is printed while it is on impression roller  12 , by first printing engine  16 , and an opposite side of paper  40  is printed while it is on impression roller  14 , by second printing engine  18 . For multicolour, single side printing, each colour is printed with a different one of the tandem series of printing engines, such as printing engines  16  and  18 . 
     In a preferred embodiment of the invention, roller assembly  20  inverts the paper and transfers it from impression roller  12  to impression roller  14 . In a preferred embodiment of the invention, the “rollers” of roller assembly  20  are rotary arms, rather than rollers, each with vacuum nipples that attach themselves to the paper. Generally, the nipples are evenly distributed along the length of the paper and extend through the width of it. The paper pick-off system, which removes the paper from one roller and transfers it to the other, comprises a vacuum pick-off system, as one set of nipples lets go and the other takes over. The rotary-arm “rollers” and the vacuum nipples and vacuum paper pick-off system associated with them are described in PCT patent application, PCT/IL98/00553, “Printing System” filed on Nov. 11, 1998, in the Israel receiving office, whose disclosure is incorporated herein by reference. Alternatively, conventional rollers may be used. The exact configuration of the paper transfer and (or) inversion system may differ from that shown, since the inversion is applicable to many transfer/inversion and perfecta or perfecta-like systems known in the art. 
     Typically, after the first image (which may be coloured or black and white) is transferred onto the first side of paper  40 , paper  40  is transferred from impression roller  12  to a roller R 1  of assembly  20 . From roller R 1 , which rotates in a clockwise direction, paper  40  is transferred to a perfecting roller R 2 , which, during the transfer from roller R 1  to roller R 2 , rotates in the counterclockwise direction. 
     Preferably, perfecting roller R 2  is controlled by a servo motor (not shown) capable of moving at different angular velocities, clockwise and counterclockwise. Preferably, the purpose of perfecting roller R 2  is to invert the paper. Additionally, perfecting roller R 2  corrects the position of paper  40  for the following reason: Impression rollers  12  and  14  are each controlled by a separate engine and slight errors are introduced by a system that controls their relative rotation. Perfecting roller R 2  corrects for slight variations in angular velocities and in phases, responsive to measurements of a first paper sensor  22  which senses the position of the leading edge of paper  40  (before inversion). An error of 1-2 mm in the position of the paper may be encountered and corrected by the servo motor using the following method: 
     After receiving paper  40 , servo-controlled roller R 2  changes its direction to clockwise, and changes its velocity to correct for any error in the position of paper  40 , bringing the trailing edge of paper  40  exactly to a pick-up point of a roller R 3 , rotatable counterclockwise. 
     As roller R 3  picks up the trailing edge of paper  40 , the trailing edge becomes the new leading edge, and paper  40  is inverted. It is noted that the paper is still referenced to its original leading edge. 
     The next transfer, from roller R 3 , rotatable counterclockwise to a roller R 4 , rotatable clockwise, involves a second paper sensor  24  which determines the position of the new tailing edge (previous leading edge) of paper  40 , close to the transfer point from R 3 , as it is transferred onto roller R 4 . Second paper sensor  24  may be situated on roller R 4  or it may be adjacent to roller R 4 . From roller R 4 , the paper is transferred to impression roller  14 . Exact synchronisation between the image on impression roller  14  and paper  40  cannot be performed when paper  40  reaches impression roller  14 ; in general, the image is already on ITM (or photoconductive drum)  17  to produce an image on the second side of paper  40  when it reaches impression roller  14  at a precise time and angular position of impression roller  14 . Thus, any correction in synchronisation must be made to the position of paper  40  before it reaches impression roller  14 . 
     In the following discussion, the term pulley, as used here, refers to a wheel, possibly with a grooved rim, in direct contact with the flexible strip, preferably, a timing belt, to drive it,or to be driven by it. The term tension pulley refers to a wheel, possibly with a grooved rim, in direct contact with the flexible strip, to keep the flexible strip under tension. Preferably, roller R 4  and a roller R 5  are in communication with each other through a flexible strip  26 , wherein a driving pulley  28  is mounted on roller R 5  and moving continuously with it at a constant rotation rate, and a driven pulley  32  is mounted on roller R 4  and moving continuously with it at the same (or proportional) constant rotation rate as that of R 5 . As used herein, the generic term flexible strip means a smooth belt, or a timing belt, or a cable, or a bead cable, or an endless chain. The term pulley may mean a sprocket 
     An axis  27  of flexible strip  26  is defined as the line connecting the centres of R 4  and R 5 . A tension pulley  34  serves as a tension to flexible strip  26 . (Tension pulley  34  is optional, and may be eliminated.) Alternatively, two or more tension pulleys  34  may be used.) Correctional mechanism  30  is associated with flexible strip  26  and roller R 4 . Note that correction mechanism  30  does not affect roller R 5 , the driver, since the motion of roller R 5  is controlled by a driving mechanism (not shown), which is commonly driven by, or synchronously driven with impression rollers  14  and/or  12 , at a constant rotation rate. Only driven pulley  32  of roller R 4  is free to respond to corrections. 
     Preferably, correctional mechanism  30  comprises a correctional tension pulley  38 , mounted on an shaft  46 . Motion is provided by a stepper motor  42 , which moves shaft  46  and correctional tension pulley  38  so that they travel up or down a specific amount. At an “equilibrium position”, correctional tension pulley  38  presses against flexible strip  26  at a first point, downstream of roller R 4 , producing an indentation in the profile of flexible strip  26 . A tension pulley  44  mounted on a spring-loaded device  45  in partial compression, presses against flexible strip  26  at a second point, upstream of roller R 4 , and produces a second indentation in the profile of flexible strip  26 . Spring loaded device  45  may be a spring-loaded piston-cylinder device. Alternatively, another spring-loaded device may be used. Alternatively, another method of resiliently pressing tension pulley  44  against flexible strip  26  may be used. 
     Preferably, when second paper sensor  24  determines that a positional correction to paper  40  is required, the controller activates stepper motor  42  which drives shaft  46  and correctional tension pulley  38 . Step angular displacement of roller R 4  is provided as follows: 
     When shaft  46  moves up, pressing correctional tension pulley  38  deeper against flexible strip  26  at the first point, downstream of roller R 4 , a demand for slack at the first point is created. In response, spring-loaded device  45  on which tension pulley  44  is mounted, compresses, pulling tension pulley  44  away from flexible strip  26  and releasing the slack that is to needed downstream. Flexible strip  26  moves in a clockwise direction, producing a step angular displacement to roller R 4  in the clockwise direction. 
     When shaft  46  drives correctional tension pulley  38  away from flexible strip  26 , slack in flexible strip  26  is created at the first point, downstream of roller R 4 . Spring compression of spring-loaded device  45  is released somewhat; tension pulley  44  presses deeper against flexible is strip  26  at the second point, gathering the slack that was released downstream. Flexible strip  26  moves a step in a counterclockwise direction, producing a step angular displacement to roller R 4  in the counterclockwise direction. Note that the pressure of spring-loaded tension pulley  44  on flexible strip  26  is such that pulley  38  is always in contact with flexible strip  26 . Note also that the situation described may be reversed; pulley  38  my be spring loaded or otherwise resiliently pressed against flexible strip  26  and tension pulley  44  may be driven by shaft  46 . 
     Reference is now made to FIG. 2 which is a schematic illustration of a tandem printer  60  having a roller assembly  20  for paper inversion and transfer and another correctional mechanism  50 , in accordance with another preferred embodiment of the invention. 
     In FIG. 2, the step linear displacement of flexible strip  26  is provided by two correctional tension pulleys  48  and  52 , mounted on the two ends of a rod  54  and connected to a shaft (not shown) which is driven by stepper motor  42 . Rod  54  is situated inside flexible strip  26 , perpendicular to axis  27 , with correctional tension pulleys  48  and  52  pressing against flexible strip  26  at two points, A and B, upstream and downstream of roller R 4 . 
     Preferably, step angular displacement of roller R 4  is provided as follows: 
     When rod  54  moves up or down, one or the other of correction pulleys  48  or  52  is pressed deeper against flexible strip  26 , requiring more slack, while the other is pulled away from flexible strip  26 , releasing slack The transfer of slack provides the step displacement of flexible strip  26 , in the direction of the increased indentation, producing a step angular displacement to roller R 4  in that direction. 
     In some preferred embodiments of the invention, as shown, correctional tension pulleys  48  and  52  are external to flexible strip  26 . Alternatively, they are internal to flexible strip  26 . Note that pulleys  48  and  52  are always in contact with flexible strip  26 . In some preferred embodiments of the invention, two tension pulleys  34  are used. Alternatively, only one tension pulley  34  is used. Alternatively still, no tension pulley is used. 
     The following discussion applies to the embodiments of both FIGS. 1 and 2. 
     Preferably, the step angular displacement of roller R 4  is given as a function (which may be empirical) of the linear displacement. Alternatively, the step angular displacement of roller R 4  is determined from a lookup table 100. 
     In some preferred embodiments, the section of the flexible strip adjacent to the first point and the section of the flexible strip adjacent to the second point are parallel. 
     For some configurations, small step angular displacements of roller R 4  are symmetric for upward and downward displacements of tension pulleys  38  and  44  or tension pulleys  48  and;  52 . More generally, they are not. 
     Preferably, there is only one sheet of paper on roller R 4  at any time. Preferably, the total travel time of paper  40  on roller R 4  is about 0.4-0.5 seconds, and the order of magnitude of the correction time by correctional mechanism  30  is 0.05-0.1 seconds. Preferably, the order of magnitude of the positional correction of paper  40  by correctional mechanism  30  is about 0.5 mm. 
     In some preferred embodiments, roller assembly  20  comprises more rollers or fewer rollers, depending on the distances between impression roller  12  and impressions roller  14 . 
     In some preferred embodiments, a multi-printing system, comprising more than two printing engines, may be used, wherein a correctional mechanism such as correctional mechanism  30  or correctional mechanism  50  is positioned between any two adjacent printing engines. 
     In some preferred embodiments an eccentric shaft is used to convert the motion of stepper motor  42  to linear motion. Alternatively, any of a slider-crank mechanism, a piston-cylinder mechanism, or a turning-screw mechanism may be used. Alternatively still, any other method of providing linear motion, known to persons versed in kinematics, may be used. 
     In some preferred embodiments of the invention, as shown in FIGS. 1 and 2, the tandem printer comprises a duplex printer for printing on both sides of paper while inverting it Alternatively, the tandem printer comprises a multicolour printer of single side printing, with each colour being printed with a different one of the tandem series of printing engines. Where the tandem printer is a multicolour printer of single side printing, perfecting roller R 2  and first paper sensor  22  are eliminated as the paper is not inverted. Alternatively, an additional roller (not shown) is provided and an operator may choose, preferably, with a keystroke at a control panel, whether to invert the paper, wherein the paper then passes through perfecting roller R 2 , or not to invert the paper, wherein the paper then passes through the additional roller. 
     In some preferred embodiments of the invention, the tandem printer comprises any conventional printer, such as a printer which prints directly from plates. Alternatively, the tandem printer comprises any of a lithographic printer, an electrostatic printer, or an electronic printer. 
     The present invention has been described using non-limiting detailed descriptions of preferred embodiments thereof that are provided by way of examples and are not intended to limit the scope of the invention. Variations of embodiments described will occur to persons of the art. Similarly, combinations of features of different embodiments within the scope of the claims will occur to persons of the art. These are still within the scope of the invention. The terms “comprise,” include,” and “have” or their conjugates, when used herein, mean “including but not necessarily limited to.” The scope of the invention is limited only by the following claims: