Closed loop lateral and skew control

According to aspects illustrated herein, a method, a system, and a printmaking device for performing closed loop lateral and skew control of a sheet is provided. The printmaking device includes a feed path, printing module, and sheet registration system. First, the feed path moves the sheet in a process direction past the lateral sensor. Next, the sheet is registered by measuring a lateral position of one side edge of the sheet at a fixed reference using the lateral sensor and determining a lateral position error of the sheet using the lateral position measurement. After that, a sheet angular velocity is calculated based on the lateral position error using the registration controller. Then, the lateral position error is corrected using the at least one pair of registration nips to adjust the sheet by applying the sheet angular velocity to the sheet.

TECHNICAL FIELD

This disclosure relates to apparatus, systems, and methods of accurately registering a sheet in a media handling assembly, such as a printing system or a printmaking device. The disclosure specifically provides a method for closed loop lateral control of a sheet in an agile registration system.

BACKGROUND

Agile registration systems receive a mis-registered sheet at the input and deliver the sheet registered to a downstream “agile” registration datum, such as a photoreceptor or a drum. Typically, agile registration systems provide for approximately 2 or 3 degrees of movement between input and output.FIG. 1shows an example of an agile registration system10. In order to deliver the sheets downstream, the agile registration system10uses stationary nips12,14to impart x-direction velocity vectors v0(16) and v1(18) on a sheet20. The average of the velocity vectors16,18(v1+v0)/2 provides an x-direction process direction) motion to the sheet. The difference between the velocity vectors16,18(v1−v0) provides a rotation of the sheet20. The sheet10is transported downstream and adjusted along a feed path22prior to entering a device.

When the sheet20enters the nips12,14of the agile registration system10, the velocities are set equal to the sheet velocity of the sheet20along the upstream feed path22to ensure correct hand-off between the sheet20and the upstream feed path22of the sheet20. Agile registration begins after a sensor detects the sheet20. The system10shown includes two lead edge sensors24,26configured to report the time-of-arrival t0and the process position x0(28) and angle β0(30) of the sheet20. The system10further includes a lateral sensor32reports the lateral position y0(34) of the sheet20. In many cases, the lead-edge-center28or lead-edge-side34is considered the point that is being registered since simple geometric calculations may be used to yield values for the initial conditions of the registration point from sensor measurements.

To ensure the paper is delivered at the correct time and in the correct position, velocity profiles of both nips12,14must be computed. The velocity profiles v1(t) and v0(t) at the a time, t=tf, and may be represented by xf, yf, and βf, with the velocity at the delivery location usually matching the velocity of the downstream device.

FIG. 2(40) provides the system10with a sample trajectory42of the sheet20along the feed path22from arrival44of the sheet20at the nips12,14during agile registration to the delivery46of the sheet20at the downstream device. Note, the trajectory of sheet20through the nip center48is curved, illustrating the correction to the position of the sheet20over time. The position of the sheet20is corrected to be in the proper lateral position by changing the lateral position and the skew of the sheet20. As disclosed in U.S. Pat. No. 5,887,996 to Castelli et al., a skew in the sheet20results in both a skew error and lateral error. Hence, a lateral controller may be used to move the sheet20such that the skew error and lateral error are corrected.

Current strategies for sheet registration use sensors to take snap shots of the sheet as the agile registration begins, as shown on the trajectory as the arrival44of the sheet20, to determine the appropriate location of the sheet at the delivery location, as shown on the trajectory as the delivery46of the sheet20. The problem with such systems is that there is no verification or follow-up sensoring to ensure the sheet10really ends up at the delivery location in the correct position. When inaccuracies in any of the programmed inboard and outboard nip velocities and/or input sheet position result in registration errors in the process, lateral, and skew measurements. Thus, there is a need for a method of reducing the lateral error overtime using a single low-cost sensor.

SUMMARY

According to aspects illustrated herein, there is provided a printmaking device for performing closed loop lateral and skew control of a sheet using a single lateral sensor in a sheet registration system is provided. The printmaking device includes a feed path, a printing module, and a sheet registration system. The feed path is adapted to move the sheet of paper, the sheet including a first edge, a second edge and a first side edge and a second side edge therebetween. The first edge is approximately parallel to the second edge. The printing module is configured to print an image on the sheet. The sheet registration system is along the feed path and includes a lateral sensor, a registration controller, and at least one pair of registration nips. The lateral sensor is configured to measure the lateral position of the first side edge of the sheet at a fixed reference along the feed path to determine a lateral position error of the first side of the sheet. The registration controller is configured to calculate an angular velocity based on a lateral position error. The registration controller is operatively connected to the lateral sensor. The at least one pair of registration nips are along the feed path and operatively connected to the registration controller. The at least one pair of registration nips are configured to apply the angular velocity to the sheet. The feed path moves a first side of the sheet in a process direction past the lateral sensor and the first side of the sheet is registered by: measuring a first lateral position of the first side edge of the sheet at a first fixed reference along the feed path using the lateral sensor; determining a first lateral position error of the first side of the sheet using the first lateral position measurement; calculating a first sheet angular velocity based on the lateral position error using the registration controller; correcting the lateral position error using the at least one pair of registration nips to adjust the sheet by applying the first sheet angular velocity to the sheet.

According to other aspects illustrated herein, there is provided a method for performing closed loop lateral and skew control of a sheet using a single lateral sensor in a sheet registration system. The method includes the following steps. Moving the sheet along a feed path in a process direction to the sheet registration system. The sheet having a first edge, a second edge, and a first side edge and a second side edge therebetween. Measuring a first lateral position of the first side edge of the sheet at a first fixed reference along the feed path using the lateral sensor. Determining a first lateral position error of the first side of the sheet using the first lateral position measurement. Calculating a first sheet angular velocity based on the lateral position error. Correcting the lateral position error by applying the first sheet angular velocity to adjust the sheet.

According to other aspects illustrated herein, there is provided a system for performing closed loop lateral and skew control of a sheet using a single lateral sensor. The system includes a feed path, a lateral sensor, a registration controller, and at least one pair of registration nips. The feed path is configured to move the sheet in a process direction. The sheet having a first edge, a second edge, and a first side edge and a second side edge therebetween. The lateral sensor is configured to measure the lateral position of the first side edge of the sheet at a fixed reference along the feed path to determine a lateral position error of the first side edge. The registration controller is configured to calculate an angular velocity based on a lateral position error. The registration controller is operatively connected to the lateral sensor. The at least one pair of registration nips along the feed path and operatively connected to the registration controller. The at least one pair of registration nips configured to apply the angular velocity to the sheet. The feed path moves a first side of the sheet in a process direction past the lateral sensor. The first side of the sheet is registered by: measuring a first lateral position of the first side edge of the sheet at a first fixed reference along the feed path using the lateral sensor; determining a first lateral position error of the first side of the sheet using the first lateral position measurement; calculating a first sheet angular velocity based on the lateral position error using the registration controller; correcting the lateral position error using the at least one pair of registration nips to adjust the sheet by applying the first sheet angular velocity to the sheet.

Additional features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the disclosure.

DETAILED DESCRIPTION

The method, system, and printmaking device disclosed herein provide for performing closed loop lateral and skew control of a sheet using a single lateral sensor.

As used herein, the term “sheet” encompasses, for example, one or more of a usually flimsy physical sheet of paper, heavy media paper, coated papers, transparencies, parchment, film, fabric, plastic, or other suitable physical print media substrate on which information can be reproduced.

As used herein, the phrase “printmaking device” encompasses any apparatus, such as a digital copier, a bookmaking machine, a facsimile machine, and a multi-function machine, which performs a printing outputting function for any purpose.

As used herein, the phrase “feed path” encompasses any apparatus for separating and/or conveying one or more sheets into a substrate conveyance path inside a printmaking device.

As used herein, the phrase “process direction” refers to a direction that the feed path moves a sheet.

As used herein, the phrase “lead edge” refers to the edge of a sheet that first advances along the substrate conveyance path.

As used herein the phrase “printing module” refers to a marking device that uses marking technologies, such as xerographic, inkjet, and offset markings.

As used herein, the phrase “sensors” refer to a sensor that detects the position of a sheet edge. It may use intensity or brightness of light or other physical phenomena. For example, the sensor may be an optical sensor.

As used herein, the phrase “fixed reference” refers the alignment and configuration of the sensor, which points at a non-changing location to where the sensor collects information. The reference is a fixed reference because the sensor will only detect activity at the configured location. For example, a fixed reference may be a specific location on the feed path and the sensor may detect when a sheet is at that specific location.

As used herein, the term “skew” refers to an angular error in the placement of an image printed onto a sheet.

As used herein, the terms “register” and “registration” refer to determining the proper alignment of a sheet and/or a printing apparatus with respect to a fixed reference.

As used herein, the phrases “controller” and “registration controller” refer to a device capable of collecting data from sensors, analyzing data, and controlling movement of registration nips.

As used herein, the term “closed loop registration” refers to continuous or repeated monitoring and/or adjustment of a sheet during the registration of the sheet. Closed loop registration allows feedback to be obtained throughout the registration process to help ensure the sheet is being adjusted properly and/or remains on the correct path of movement.

As used herein, the term “open loop registration” refers to receiving an input and adjusting the sheet based on the input. No additional feedback is received after the input. For example, a system may measure and/or determine the position of the sheet at one instance during the registration process and adjust the sheet based on that one instance without receiving additional feedback or measurements thereafter.

With reference toFIG. 3, a method50for closed loop lateral and skew control during registration of a sheet using a single lateral position sensor is provided. Step52moves a sheet along a feed path in a process direction to a sheet registration system. The sheet has a first edge, a second edge, and a first side edge and a second side edge therebetween. Next, step54, measures a first lateral position of the first side edge of the sheet at a first fixed reference along the feed path using the lateral sensor, and a first lateral position error of the first side of the sheet is determined using the first lateral position measurement in step56. The lateral sensor may be attached to a controller, for example, a closed loop lateral controller.

After that, step58, calculates a sheet angular velocity based on the lateral position error. The sheet angular velocity may be calculated by the controller. The lateral position error is corrected in step60by applying the sheet angular velocity to adjust the sheet. The sheet may be adjusted using a pair of nips and/or using any method known to one skilled in the art. For example, if a pair of nips are used the speed of one or more of the nips may be increased and/or decreased in order to correct the lateral position error of the sheet. The method50may further be designed to measure the arrival time of the first side edge of the sheet at the fixed reference and adjust the process position to ensure that the sheet arrives at the registration datum within a designated time interval after the arrival time (i.e., “on time”), as shown in step62.

The method50ofFIG. 3may further include the steps of inverting and refeeding the sheet on a second side and repeating the steps52-62on the second side of the sheet. When two-sided or duplex printing is being performed the arrival time of the first side edge of the sheet will be measured on both the first and second sides of the sheet, with each having a different arrival time, but the fixed reference may be two distinct fixed reference locations, i.e., a first and a second fixed reference, or the same fixed reference, depending on the registration system. Similarly, the registration datum for the first and second sides of the sheet may be two separate datums or the same datum, depending on the registration system.

The angular velocity may be calculated using any method known to one skilled in the art. The Examples of equations used to find the angular velocity, omega, include: (1) omega=(proportional gain)*(Y-direction error); (2) omega=(proportional gain)*(Y-direction error)+gain*(derivative of Y-direction error); and (3) omega=f (Y-direction error). Devices capable of calculating angular velocity based on the lateral position error include, but are not limited to, a proportional controller, or a Proportional Integral and Derivative (PID) controller. The method50ofFIG. 3and angular velocity equations are designed (but not limited to) to be used as a fine registration method, i.e., a method for correcting small errors in the lateral position of the sheet.

Moreover, it is contemplated that the method50may be used in combination with a coarse registration method. If used in combination with a coarse registration method, the sheet may be registered using a known registration method, such as an open loop lateral and skew registration method, prior to the initiation of the fine registration method50ofFIG. 3. For example, after the coarse registration is completed, the sheet would proceed in the process direction to the fixed reference. Once the sheet reaches the fixed reference, the method50may be performed to determine and correct the lateral position error of the first side of the sheet.

As may be appreciated by one skilled in the art, the course registration method used to determine the correct position the sheet at a fine registration line may include one of the following known methods: determining a lateral position error by subtracting an actual lateral position from a desired lateral position; using a set of trapezoidal profiles; and/or using the angular velocity of the sheet relative to nips in a registration system to determine the sheet position error. U.S. Pat. No. 5,094,442 by Kamprath et al. U.S. Pat. Nos. 6,533,268 and 6,575,458 disclose alternative mechanisms for adjusting a sheet's lateral position with an appropriate actuator. These contemporary methods more generally disclose that the nip assemblies can be used to move the sheet in three degrees of freedom, i.e. process, lateral, and skew, in order to achieve proper sheet registration.

Referring toFIG. 4, a system70for use with the method50ofFIG. 3for performing closed loop lateral and skew control of a sheet72using a single lateral sensor74in a sheet registration system is provided. The system70includes a feed path76, a lateral sensor74, a registration controller78, and at least one pair of registration nips, shown as one pair of nips80,82. The feed path76is configured to move the sheet72in a process direction84. The sheet72having a first edge86, a second edge88, and a first side edge90and a second side edge92therebetween.

The lateral sensor74is configured to measure a lateral position of the first side edge90of the sheet72at a fixed reference96(or fine registration line) along the feed path76to determine a lateral position error of the first side94of the sheet72. The lateral sensor74is operatively connected to the registration controller78. The registration controller78is configured to calculate the sheet angular velocity. For example, the registration controller78may be a closed loop lateral controller, a proportional controller, or a proportional integral and derivative controller (PID).

The registration controller78is also operatively connected to the pair of registration nips80,82, which are located along the feed path76. The pair of registration nips80,82may adjust the sheet72by applying the sheet angular velocity to the sheet72. For example, the sheet angular velocity may result in slowing down and/or speeding up the speed of one or more of the nips80,82to correct the lateral position error.

In operation, the feed path76moves the first side94of the sheet72in a process direction84past the lateral sensor74and the first side94of the sheet72is registered. The registration is performed using the following steps. First, measuring the lateral position of the first side edge90of the sheet72at a first fixed reference96along the feed path76using the lateral sensor74. After that, determining a first lateral position error of the first side94of the sheet72using the first lateral position measurement. Next, calculating a first sheet angular velocity based on the lateral position error. The first sheet angular velocity may be calculated by the registration controller78. Then, correcting the lateral position error using the one pair of registration nips80,82to adjust the sheet72by applying the first sheet angular velocity to the sheet72. The registration may further include measuring the arrival time of the first side edge90of the sheet72at the first fixed reference96and adjusting the process position to ensure that the sheet72arrives at the registration datum98within a designated time interval after the arrival time.

The system70may further be configured for two-sided or duplex printing, as shown inFIG. 5. During duplex printing, the system70inverts and refeeds the sheet72on a second side100. The sheet72is shown being inverted such that the first side edge90of the sheet72remains along the same edge of the feed path76. However, as one skilled in the art will appreciate, the sheet72may also be inverted such that the first side edge90and the second side edge92are switched. Although not shown herein, the system would operate in the same manner except opposing side edges90,92would be measured during the duplex printing.

Once the sheet72is inverted and refed, the feed path76moves the second side100of the sheet72in the process direction84past the lateral sensor74, and the second side100of the sheet72is registered. The second side100of the sheet72is registered by measuring a second lateral position of the first side edge90of the sheet72at a second fixed reference102along the feed path76using the lateral sensor74, and determining a second lateral position error of the second side100of the sheet72using the second lateral position measurement. A second sheet angular velocity is calculated based on the second lateral position error using the registration controller78. Then, the second sheet angular velocity is applied to the sheet72using the one pair of registration nips80,82to adjust the sheet72to correct the lateral position error. After that, the registration may further include measuring the arrival time of the first side edge90of the sheet72at the second fixed reference102and adjusting the process position to ensure that the sheet72arrives at the registration datum104within a designated time interval after the arrival time.

When two-sided or duplex printing is being performed the fixed reference may include two distinct fixed reference locations, i.e., a first and a second fixed reference96,102, or the same fixed reference, depending on the system. Similarly, the registration datum for the first and second sides94,100of the sheet72may be two separate datums98,104or the same datum, depending on the printmaking device. As may be appreciated by one skilled in the art, the same lateral edge sensor74may be used to register both sides of the sheet72or a different lateral edge sensor74may be used to register each side of the sheet72, depending on the system.

The system70ofFIGS. 4-5, may further be configured to perform open loop lateral and skew registration prior to the sheet72reaching the first fixed reference96. The lateral and skew registration may be performed using any method as will be appreciated by one skilled in the art. The performance of open loop lateral and skew registration may be performed during coarse registration as described above and be used to provide the sheet72to the system70in condition for fine registration as described herein.

FIGS. 6-7provide graphs110,120that plot the lateral position and skew movement of a fixed portion of the sheet72as the method50ofFIG. 3corrects the lateral error of the sheet72. Note how correction of the lateral position requires adjusting the skew of the sheet72. In particular,FIG. 6plots the lateral position measurements in millimeters (mm). The graph110shows the initial lateral position error as 0.5 mm prior to 0.05 seconds (112) and then shows the lateral position error as approximately 0.0 mm at 0.3 seconds (114).FIG. 7plots the skew measurements in millirads (mrad). The graph120shows the initial skew as 2 mrad prior to 0.05 seconds (122), and then shows the skew as approximately 0.0 mrad at 0.3 seconds (124).

FIG. 8provides a printmaking device150for use with the method50and system70ofFIGS. 3-5. The printmaking device150includes a feed path76, one or more printing modules152, and a sheet registration system70. The feed path76is adapted to move the sheet72. The sheet72includes a first edge86, a second edge88and a first side edge90and a second side edge92therebetween, where the first edge86is approximately parallel to the second edge88. The printing module152is configured to print an image on the sheet72. The printing module152may then send the sheet72to another printing module152as shown inFIG. 10, or move the sheet72along the feed path76in the printmaking device150.

Prior to reaching the printmaking module152, the feed path76moves the sheet72past the sheet registration system70. The sheet registration system70includes a lateral sensor74, a registration controller78, and at least one pair of registration nips, shown as one pair of registration nips80,82. The feed path76is configured to move the sheet72in a process direction84. The sheet72having a first edge86, a second edge88, and a first side edge90and a second side edge92therebetween.

The lateral sensor74is configured to measure a lateral position of the first side edge90of the sheet72at a fixed reference96(or fine registration line) along the feed path76to determine a lateral position error of the first side edge90of the sheet72. The lateral sensor74is operatively connected to the registration controller78. The registration controller78is configured to calculate the sheet angular velocity. For example, the registration controller78may be a closed loop lateral controller, a proportional controller, or a proportional integral and derivative controller (PID).

The registration controller78is also operatively connected to the pair of registration nips80,82, which are located along the feed path76. The pair of registration nips80,82may adjust the sheet72by applying the sheet angular velocity to the sheet72. For example, the sheet angular velocity may result in slowing down and/or speeding up the speed of one and/or both of the nips80,82to correct the lateral position error.

In operation, the feed path76moves the first side94of the sheet72in a process direction84past the lateral sensor74and a first side94of the sheet72is registered. The registration is performed using the following steps. First, measuring a first lateral position of the first side edge90of the sheet72at a first fixed reference96along the feed path76using the lateral sensor74. After that, determining a lateral position error of the first side94of the sheet72using the first lateral position measurement. Next, calculating a first sheet angular velocity based on the first lateral position error. The first sheet angular velocity may be calculated by the registration controller. Then, correcting the lateral position error using the one pair of registration nips80,82to adjust the sheet72by applying the first sheet angular velocity to the sheet72. The registration may further include measuring the arrival time of the first side edge90of the sheet72at the first fixed reference96and adjusting the process position to ensure that the sheet72arrives at the registration datum98within a designated time interval after the arrival time.

The printmaking device150may further be configured for two-sided or duplex printing, using the system70as shown inFIG. 5. During duplex printing, the sheet72is inverted and refed on a second side100. The feed path76moves the second side100of the sheet72in the process direction84past the lateral sensor74and the second side100of the sheet72is registered. The second side100of the sheet72is registered by measuring a second lateral position of the first side edge90of the sheet72at a second fixed reference102along the feed path76using the lateral sensor74, and determining the second lateral position error of the second side100of the sheet72using the second lateral position measurement. A second sheet angular velocity is calculated based on the second lateral position error using the registration controller78. Then, the second sheet angular velocity is applied to the sheet72using the one pair of registration nips80,82to adjust the sheet78to correct the second lateral position error. After that, the registration may further include measuring the arrival time of the first side edge90of the sheet72at the second fixed reference102and adjusting the process position to ensure that the sheet72arrives at the registration datum104within a designated time interval after the arrival time.

When two-sided or duplex printing is being performed the arrival time of the first side edge90of the sheet72will be measured on both the first and second sides94,100of the sheet72, with each having a different arrival time. The fixed reference may also be two distinct fixed reference locations, i.e., a first and a second fixed reference96,102, or the same fixed reference, depending on the system. Similarly, the registration datum for the first and second sides94,100of the sheet72may be two separate datums98,104or the same datum, depending on the printmaking device. As may be appreciated by one skilled in the art, the same lateral edge sensor74may be used to register both sides of the sheet72or a different lateral edge sensor74may be used to register each side of the sheet72, depending on the system.

The printmaking device150FIG. 8, may further be configured to perform open loop lateral and skew registration prior to the sheet72reaching the first fixed reference96of the sheet registration system70. As will be appreciated by one skilled in the art, the lateral and skew registration may be performed using any known method. The performance of open loop lateral and skew registration may be performed during coarse registration as described above and be used to provide the sheet72to the system70in condition for fine registration as described herein.

The printmaking device150may further include one or more printing modules152for use with modular overprint systems in printmaking devices.FIGS. 9-10provide examples of a printmaking devices160,170with a printing module162, which may be used with the method50and system70ofFIGS. 3-5. See U.S. patent application Ser. No. 12/364,675, filed on Feb. 3, 2009, contents of which are incorporated herein by reference.

Specifically,FIG. 9provides an example of a portion of the printmaking device160containing the printing module162. The printing module162is connected to a processor164in the printmaking device, which may include and/or be operatively connected to a registration controller78as described herein. The printing module162is capable of printing on the sheet72and the processor164is capable of controlling the printmaking device160and/or printmaking module162. The printing module162and the processor164are operatively connected to facilitate proper printing on the sheet72.

FIG. 10provides an example of a configuration of multiple printing modules162configured for use together with a printmaking device170. In such configuration, each printing module162may include a structure forming a portion of the feed path76and printing hardware to place printing material of a predetermined type (“type” referring to color or some other attribute, such as MICR properties) on the sheet72passing through the feed path76: in any other significant aspects, all printing modules162are substantially identical in design. In this way, by providing a given number of printing modules162along a common sheet path and providing different types of printing material in each printing module162, the overall printing making device170can effectively be custom made.

For example, the design ofFIG. 10contains four printing modules162, providing a “full color” printer, one with black toner and the others with cyan, magenta, and yellow toners respectively, may be provided. However, as will be appreciated by one skilled in the art additional types of toner for a hexachrome and/or other special-purpose printer may also be added to the configuration. Moreover a “stack” of two sets of printing modules162, along with input modules172, fuser modules174, and sheet exit modules176, for a high-productivity color printer may be provided.

The benefit of the method, system, and printmaking device provided herein include use of a single low cost lateral edge sensor to determine a lateral position error in a closed loop registration process. By using a single low cost sensor, this disclosure ensures that the sheet72is delivered to the registration datum at the proper time and position without requiring multiple expensive sensors. Moreover, since the single lateral sensor is used with a closed loop registration process, the sheet72is monitored to provide more accuracy than other open loop registration processes.

It will be appreciated that variations of the above-disclosed and other features and functions, or alternative thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. In addition, the claims can encompass embodiments in hardware, software, or a combination thereof.