Field Of The Invention

The present invention relates generally to a document handling apparatus and, more particularly, to a document handling apparatus that registers sheets.

Background Of The Invention

Customized documents are commonly used in the form of deposit slips, checks, and other types of bank drafts and personalized documents. The use of these types of documents has become widespread throughout the world and many institutions, such as banks and credit unions, are dependent upon these documents for efficient operation. The widespread use of these customized documents has led to numerous efforts to develop systems that can print them fast and without error.

Conventional financial document printing processes typically use a collator and either a printer or a press. The financial documents, including checks, are produced by transporting a pre-printed stock of paper through the printing system at which time customized characters and images are printed on the sheet. Examples of characters and images include, but are not limited to, names, addresses, characters that are to be located in a pre¬ printed box, and computer readable codes such as account numbers and check numbers.

During production, sheets of the stock paper or print media are transported through the printing system. The sheets will pass through the printer at which time a print engine will print the characters or images. Many systems include a registration mechanism in order to align the document with the print engine. Alignment can be very important, especially when trying to align customized information with preprinted characters and images.

Alignment is also important when printing machine readable codes, which must be accurately aligned so that scanners at institutions such as banks can accurately and quickly scan the printed documents.

A difficulty is that the registration techniques used in many current machines have only marginal accuracy that does not provide the required standard of quality required during high-precision printing such as printing machine readable code or aligning customized information with preprinted characters and images. Additionally, many registration systems and assemblies can act as a bottle neck of a printing system that slows down the production of financial documents. When the throughput of the machine is increase, the registrations systems may loose accuracy, which is unacceptable in high-precision printing.

Therefore, there is a need for a registration system that increases the accuracy and productivity of the overall document-handling process in a printing system.

Summary Of The Invention

In one embodiment of the present invention is directed to an apparatus for registering a sheet being transported along a path. The sheet has a leading edge. The apparatus is configured to align the sheet so that the leading edge is substantially perpendicular to the path. The apparatus comprises a first sensor arranged and configured to detect the leading edge and generate a first signal in response to detection of the leading edge. A second sensor is arranged and configured to detect the leading edge and generate a second signal in response to detection of the leading edge. First and second roller pairs arranged and configured to nip the sheet. First and second motors arranged to rotate the first and second roller pairs, respectively. Circuitry is linked to the first and second sensors and the first and second motors. The circuitry is configured to receive the first and second signals and cause a speed differential between the first and second motors, thereby aligning the sheet.

In another embodiment of the present invention comprises a track for transporting sheets to a printer,

and a collator having a plurality of retainers. Each retainer is arranged and configured to hold stack of sheets. The collator is arranged and configured to pick sheets from one of the retainers and present the picked sheet to the track. A registration assembly has a roller arrangement for rotating the sheet being transported along the track from a first position in which the sheet is not in angular alignment with the printer to a second position in which the sheet is in angular alignment with the printer.

Yet another embodiment of the present invention comprises a carriage configured to move laterally to the path. The carriage includes a transport mechanism configured to engage a sheet having a side edge. A motor is operably connected to the carriage. The motor is arranged and configured to move the carriage. A sensor is arranged and configured to detect the side edge of a sheet engaged by the transport mechanism and generate a signal in response thereto. Circuitry is operably connected to the sensor and the motor. The circuitry is arranged and configured to control the motor in response to the signal generated by the sensor, thereby causing the motor to move the carriage so that the side edge of the sheet is in a predetermined position.

Brief Description Of The Drawings Other aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: FIG. 1 is an illustration of a printing system including a collator module, a printing module, and a stacker module,-

FIG. 2 is a front elevational view of a registration system used in the printing system shown in FIG. 1,- FIG. 3 is a top plain view of the registration system shown in FIG. 2,-

FIGS. 4 and 5 show a paper sensor that is a component of the registrations sensor shown in FIGS. 2 and 3;

FIG. 6 is a functional block diagram of the programmable controller,- FIG. 7 is a functional block diagram of a remote control unit shown in FIG. 6;

FIG. 8 is a functional block diagram of a timer daughter board shown in FIG. 6.

While exemplary implementations of the present invention, as illustrated in these figures, can be modified and altered in various ways, it should be understood that the intention is not to limit the invention to the particular embodiment described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description Of The Drawings FIG. 1 illustrates a system for creating documents, such as checks, deposit slips and other customized forms used in the finance industry. While the principles of the present invention are not so limited, it has been discovered that the present invention is particularly advantageous for this type of application. Hence, the implementations and embodiments embodying the principles of the present invention will be described in this context.

Referring to FIG. 1, the system can be viewed as including three main modular sections: a collator 100, a printer 102, and a stacker 104. Each of these sections operates under the control of a programmed controller (not shown in FIG. 1) , such as a conventional business computer that controls the selection (or "picking") of print medium sheets from the various retainers 106 in the collator 100 for processing by the printer 102. After the printing stage, the printer 102 feeds the printed sheets to the

stacker 104, which stacks the printed sheets according to a programmed arrangement as dictated by the programmed controller.

The collator 100 includes a plurality of retainers (or hoppers) 106a-106h for storing groups of documents. Each retainer 106a-106h can hold a different type of print media sheets. The collator 100 is a document handling apparatus having a side portion 122 and a rear portion 124 that are adjacent to and substantially perpendicular to one another. The collator 100 also includes a plurality of retainers 106a-106h. Each retainer 106a-106h is formed by a tray assembly 128a-128h, respectively, that may hold a stack 130a-130h of print media sheets. Examples of print media sheets that can be used in the present printing system include standard paper, self-carbonizing paper, preprinted check stock ready for customization, and other forms and materials ready for customization. Referring to the stack 130a, each stack has a leading edge 132, first side edge 134, second side edge 136, rear edge 138, and bottom (not shown) .

Each retainer I06a-106h has an associated pair of adjustable edge guides 140a-140p for helping to control the sheets, and an associated elevator assembly (not shown) that is housed in the rear portion 124 of the collator 100. Each elevator assembly is arranged and configured to move an associated tray assembly 106a-106h up and down in order to maintain the top of the stack 130a-130h, respectively, at an appropriate level. Each elevator has a motor and an encoder. Each retainer 106a- 106h also has an associated pick mechanism assembly (not shown) that is housed in the side portion 122 of the collator 100. Each pick mechanism has a stepper motor and an encoder. A vertical track is housed in the side portion 122 of the collator 100. Each pick mechanism assembly is arranged and configured to pick the top sheet from the

stack 130a-130h and feed it into the vertical track, which then transports the picked sheet to the first track assembly 112. Additionally, the collator 100 has various switches, sensors, and solenoids that work in conjunction with internal mechanism such as the elevators, pick mechanism, and vertical track.

The first track assembly 112 is operably connected between the output of the collator 100 and the input of the printer 102. The first track assembly 112 includes a plurality of transport belts 113 that are configured to transport sheets of print media from the collator 100 to the printer 102. The second track assembly 114 also includes a plurality of transport belts 115 and is operably connected between an output of the printer 102 and an input of the stacker 104. A touch screen 118 provides an interactive and graphical user interface for the programmed controller that controls the collator 100, printer 102, stacker 104, and first and second track assemblies 112 and 114. The printer 102 includes a print engine (not shown) configured to print on sheets of print medium and a registration assembly 1000 configured to receive sheets being transported by the first track assembly 112. The stacker 104 stacks the sheets fed from the second output track 114. The stacker will place the sheet on a dolly (not shown) that is positioned within the stacker's base 116. After the stack is complete, the operator can remove the dolly and push it to another area of the production facility so that production of the check books can be completed.

The collator 100, first track assembly 112, printer 102, second track assembly 114, and stacker 104 form a path along which sheets are transported. The print engine can print characters and images on the sheets as they are printed along the path. The registrations mechanism 103 aligns the sheets being transported along the path with

the print engine so that the printed characters and images are properly positioned on the sheets.

Referring now to FIGS. 2 and 3, the registration assembly 1000 positions the sheet being transported along the path so that the sheet is properly aligned with the printer 102 and the print engine within the printer. The registration assembly 1000 adjusts both the skew and lateral position of the sheet. This function is very important, especially when the sheet is a preprinted form and the printer 102 is adding new characters that need to be properly aligned on the form. This function is also important when printing machine readable codes that must be properly aligned in order to maintain the accuracy of scanners that are used to read the documents. The registration assembly includes a frame 1002 that has a horizontal member 1004 extending between first and second vertical members 1006 and 1008. A vertical motor bracket 1010 is mounted on the horizontal member 1004 and supports a carriage motor 1012. The carriage motor 1012 drives a ball screw mechanism 1014 that includes a nut 1016. The carriage motor 1012 and ball screw mechanism 1014 form a motor arrangement. Additionally, a lower rail 1016 has one end 1018 connected to the vertical motor bracket 1010 and an opposite end 1020 supported by mounts 1022 and 1024. The lower rail 1016 supports a carriage 1026.

The carriage motor 1012 is linked to and controlled by a servo controller (not shown) . In turn, the servo controller is linked to the control system. One type of servo controller that can be used is model number PRO 450 controller, which is manufactured by Reliance Electric of Eden Prairie, Minnesota. This servo controller may include an amplifier such as model number BSA 15, which is also manufactured by Reliance Electric. Such servo controllers are well known in the art.

The carriage 1026 includes an upper rail 1028 that slidable engages the lower rail 1016. A horizontal plate

1030 is mounted on the upper rail 1028, and first and second motor brackets 1032 and 1034 are mounted on the horizontal plate 1030. The first and second motor brackets 1032 and 1034 support first and second stepper motors 1036 and 1038, respectively. The first and second stepper motors 1036 and 1038 are linked to the control system.

First and second lower rollers 1040 and 1042 are connected to first and second rods 1044 and 1046, respectively, which are rotatably mounted on the first and second motor brackets 1032 and 1034, respectively. First and second belts 1048 and 1050 transmit motive power from the first and second stepper motors 1036 and 1038, respectively, to the first and second lower rollers 1040 and 1042, respectively. The diameter of the first and second lower rollers 1040 and 1042 is approximately +/- 0.0005 of an inch of each other.

A platen 1052 is supported above the horizontal plate 1030 by brackets 1054 and 1056. Flanges 1058 and 1060 extend upward from the platen 1052, and a rod 1062 extends between the flanges 1058 and 1060. First and second upper rollers 1064 and 1066 are rotatably mounted on the rod 1062 such that the first upper roller 1064 engages the first lower roller 1040 and the second upper roller 1066 engages the second lower roller 1042. The first upper roller 1064 and the first lower roller 1040 form a first roller pair. The second upper roller 1066 and the second lower roller pair 1042 form a second roller pair.

The first upper roller 1064 includes a central roller 1068 that is surrounded by an o-ring 1070, which provides a tapered rim and minimizes the contact area between the first upper roller 1064 and the first lower roller 1040. Similarly, the second upper roller 1066 has a central roller 1072 and an o-ring 1074. An advantage of minimizing the contact between the upper rollers 1064 and 1066 and the lower rollers 1040 and 1042 is that the sheet

being registered will more easily move when the skew is being adjusted.

The first and second roller pairs are positioned on opposite sides of the path and form a roller arrangement. The first roller pair will grip or pinch one side of the sheet and the second roller pair will grip or pinch the opposite side of the sheet. First and second sensors 1076 and 1078 are connected to the platen 1052 and are positioned proximate the first and second roller pair, respectively. Each sensor 1076 and 1078 includes a gap 1080 and 1082, respectively, and has a light emitter/detector arrangement (not shown) such that the sensors 1076 and 1078 can detect the presence or absence of a sheet in the gaps 1080 and 1082. Thus, the first and second sensors can detect the leading and trailing edges of the sheet as it is being transported along the path. The first and second sensors 1076 and 1078 are linked to the control system.

A third sensor 1084 is substantially similar to the first and second sensors 1076 and 1078. However, the third sensor 1084 is mounted on a bracket 1088, which is connected to the horizontal member 1004 of the frame 1002. Thus, the third sensor 1084 does not move with the carriage 1026. The third sensor 1084 is linked to the servo controller. The third sensor 1084 is slightly offset from the first sensor 1076. Thus, the third sensor 1084 can be used to register the side edge of the sheet being transported.

In operation, the first and second stepper motors 1036 and 1038 rotate at a substantially similar and predetermined speed so that the first and second roller pairs rotate and transport the sheets at approximately the same speed as the printer 102. Thus, the first and second roller pairs will slow the sheets being transported along the first track assembly 112 and reduce the gap between consecutive sheets picked from the collator 100 so that

the gap is compatible with the print engine that is used in the printer 102.

As the sheet is being transported, it will pass through the first and second roller pairs and the leading edge will trip the first and second sensors 1076 and 1078. There is angular error if the sheet is skewed. In this first position, the leading edge of the sheet is not perpendicular to the path and will trip the first and second sensors 1076 and 1078 at different times. The control system can measure the interval between the moments when the first and second sensors 1076 and 1078 are tripped. In response, the control system will create a speed differential between the first and second stepper motors 1036 and 1038 by increasing the speed of one stepper motor 1036 or 1038 and decreasing the speed of the other stepper motor 1038 or 1036. The controller will also cause a phase differential between steps in the first and second stepper motors 1036 and 1038.

The magnitude of the speed change for the first and second stepper motors 1036 and 1038 is approximately the same so that the mean speed of the sheet will remain substantially the same as it is being rotated. Once the sheet is shifted to a second position wherein the leading edge is substantially perpendicular to the transport path, the first and second stepper motors 1036 and 1038 are returned to substantially the same speed and the phase differential between the steps is returned to approximately zero.

The registration assembly 1000 also shifts the sheet from side to side so that the sheet's side edge is placed in a predetermined position that is aligned with the printer 102. When the leading edge of the sheet is detected by either the first or the second sensors 1076 or 1078, the control system will activate the servo system and the carriage motor 1012 will move the carriage 1026 toward the third sensor 1084. When the third sensor 1084 detects the side edge of the sheet, it will send a signal

to servo controller. The servo controller will then stop moving the carriage 1026 and the lateral position of the sheet will be properly aligned with the printer 102.

An alternative form of lateral registration is to move the carriage 1026 laterally until the third sensor

1084 detects the sheet and then move the carriage 1026 in the opposite direction until the sheet moves out of the third sensor's 1084 detection.

Referring to FIGS. 4 and 5, the paper sensor 1076 includes housing 486 that defines a cavity 488 and is molded from clear LEXSAN brand material. Housing 486 has a rear portion 490, an upper portion, and a lower portion 492. Rear portion 490 has a face 496. Upper and lower portions 492 and 494 define the gap 430 through which sheets can pass. A cover 498 is operably connected to housing 486 and seals the cavity 488. Cover 498 can be sonically welded to housing 486.

Housing 486 also defines a recess 500 that receives a square nut 502 and a slot 504 that exposes the threaded hole 506 of square nut 508. Cover 498 secures square nut 502 in the recess 500. Alternatively, the paper sensor 428 is mounted by mating square nut 502 with an appropriately sized threaded post or bolt. For example, bracket 248 of pick mechanism assembly 180a might have a projecting threaded post for mounting paper sensor 428. Cover 498 and housing 486 also define a bolt passage 514 through which a mounting bolt can pass.

Additionally, housing 486 has a first protrusion 510 that projects from face 496 of rear portion 490. A second protrusion 512 may project from cover 498. Either first or second protrusion 510 or 512 can mate with a slot defined in the structure on which paper sensor 428 is mounted. Mating either first or second protrusions 510 or 512 will prevent the paper sensor 428 from rotating and moving out of alignment with the path.

A light-sensitive sensor 520, an emitter LED 522, a potentiometer 524, an indicator LED 526, and a capacitor

528 are mounted on a flexible circuit board 518 that is positioned in cavity 488 of housing 486. Emitter LED 522 is positioned in the upper portion 494 of the housing 486 and the light-sensitive sensor 520 is positioned in the lower portion 494 of the housing 486.

The light-sensitive sensor 520 is an intelligent signal processing sensor to which the emitter LED 522 is slaved. The light-sensitive sensor 520 provides a pulsed power signal to the slaved emitter LED 522, which emits a signature in the form of a step wave function. Emitter LED transmits the signature across gap 430. The light- sensitive sensor 520 is sensitive to the signature of the emitter LED 522, but has a low sensitivity to a continuous wave of light. The light-sensitive sensor 520 thus has a low sensitivity to ambient light conditions including bright lights. A signal output 530 is operably connected to the control system and provides a signal to the control system whenever light-sensitive sensor 520 does not detect the signature from the emitter LED 522. The ligh - sensitive sensor 520 can be implemented using a light modulation photo integrated circuit, Model No. S4282, manufactured by Hamamatsu Corp., of Japan.

The potentiometer 524 sets the sensitivity between the emitter LED 522 and the light-sensitive sensor 520. If multiple paper sensors 428 are used, the potentiometer

524 can be adjusted to standardize the response of all the paper sensors 428. This adjustment enables accommodation of lot differentials for the light-sensitive sensors 520 and emitter LED 522. Indicator LED 526 is visible through housing 486 and provides a visual mimic of the light-sensitive sensor 520 condition for diagnostic purposes . When working properly, indicator LED 526 emits a visible light when light-sensitive sensor 520 detects the signature emission from emitter LED 522. Indicator LED 526 does not emit a visible light when light-sensitive sensor 520 does not detect the signature emission from emitter LED 522. Thus,

a technician can test the paper sensor 428 by manually cycling light-sensitive sensor 520 on and off and observing indicator LED 526. The light-sensitive sensor 520 can be cycled by blocking it with an opaque object such as a sheet of paper.

Paper sensors 1078 and 1078 are substantially similar to paper sensor 1076 and is not described in detail for purposes of brevity and clarity.

Referring to FIG. 6, the programmable controller includes a central control unit 716, a plurality of remote control units 732a-732o, and timer daughter boards 735a and 735b. The central control unit 716, which is a system controller, can be implemented using an IBM-compatible personal computer having a microprocessor 718, which is a first processor, and a coprocessor board 720. Coprocessor board 720 includes a co-microprocessor 724, which is a second processor, and RAM 722. The microprocessor 718 and co-microprocessor 724 communicate through RAM 722. The control unit 716 also includes a serial communication controller 726 that is linked to both the microprocessor 718 and the coprocessor board 720. The serial communication controller 726 provides a communication interface between the central control unit 716 and a daisy chain-type local area network (daisy chain network) 731. Additionally, touch screen 118 is communicatively linked to microprocessor 718 and provides a user interface for central control unit 716.

The microprocessor 718 allows an operator to create and edit jobs for running on the printing system described herein. Additionally, microprocessor 718 creates and rasterizes print images that are printed by printer 100. The print images are created from format and image data that can be input from the system manager 730 or downloaded from remote sites such as customer locations. Co-microprocessor 724 performs real-time functions, can be implemented using a 80188 type coprocessor, and receives sequence table and retainer configuration

14 information from the microprocessor 718. Co- microprocessor 724 uses this information to schedule picks from the various retainers 106a-106h. Additionally, the co-microprocessor 724 determines error recovery strategies, generates error recovery signals, and records mechanical performance. Examples of errors to which the co-microprocessor 724 will respond include an empty retainer, a failure to pick a sheet from a retainer, a jammed sheet, overlapping sheets were picked from a retainer, a retainer is holding the incorrect type of sheets, and the sheets are improperly positioned within the retainer.

Remote control units (RCU) 732a-732o are coupled to the daisy chain network 731. RCTJs 732a-732i form a collator controller and are physically located in the collator 100. RCUs 732a-732h control the elevator assemblies and pick mechanism assemblies in collator 100. RCU's 732j and 732k control the first and second stepper motors 1036 and 1038, respectively. RCU 732i controls track assembly 112, the vertical track of the collator 100, and the carriage motor 1012. Control of the carriage motor 1012 is via the servo controller. RCUs 7321 and 732m form a printer controller and provide control for the printing mechanisms in the printer 102. RCUs 732n and 732o form a stacker controller and provide control for the stacker 104. The central control unit 716, RCUs 732a- 732o, and the timer daughter boards 735a and 735b form the programmed controller. Timer daughter boards 735a and 735b are linked to RCUs 732j and 732k, respectively. Additionally, central control unit 716 is coupled to a local area network 728, which can be any type of conventional network. A system manager 730 is also linked to local area network 728. System manager 730 is an IBM- compatible personal computer, which monitors and controls multiple printing systems as described herein. System manager 720 also provides snapshots of the current status of various modules such as the collator 100, printer 102,

stacker 104. Additionally, the system manager 730 generates job lists and allows users to create and edit collation sequences, printer jobs, images for printing, and fonts. Another advantage of system manager 730 is that it can be configured to display mechanical performance statistics of the various modules and also efficiency statistics of operators.

Referring to FIG. 7, RCU 732a includes a serial communication controller (SCO 740, a microprocessing unit 738, a motor controller 762, a stepper motor controller 764, a sensor interface 768, a switch interface 766, external/internal status display 770, a latch 772 and interface circuitry 774a-774d for various solenoids, a connector 752 for additional electronics such as a timer daughter board 735a or 735b, an address/data bus 736, or a servo controller.

SCC 740 provides an interface to daisy chain network 731, which includes a receive twisted pair 746, a transmit twisted pair 748, and an address bus 750. SCC 740 is linked to test interface 742. Test interface 742 provides an interface for test equipment and communicates according to the RS 232 protocol. Test equipment can be connected to connector 744. As will be described in more detail below, daisy chain network 731 includes a third twisted pair 757 for transmitting track encoder pulses. One type of SCC that can be used is model 85C30, which operates at 8 MHz.

Microprocessing unit 738 is linked to the address/data bus 736 and includes a microprocessor such as an 80188 model, a 32K x 8 static RAM, and a programmable readable memory. Microprocessing unit 738 provides processing power for RCU 732a and includes a microprocessor (not shown) , a static RAM (not shown) , and a PROM (not shown) . The elevator motion encoder for measuring movement of the elevator for the retainer 106a is linked to microprocessing unit 738. In the case of RCU 732i, a track encoder for measuring movement of belts in

the vertical track assembly and the belts 113 of the first track assembly 112 is linked to both the microprocessing unit 738 and driver 754. Driver 754 and receiver 756 provide an interface between microprocessing unit 738 and the third twisted pair 757. Third twisted pair 757 provide a dedicated communication link for transmitting encoder pulses from the track encoder to the central control unit 716 and the RCUs 732a-732h in the collator 100. In this configuration, the encoder pulses a communication without being delayed by other messages that are being transmitted along the daisy chain network 731.

Motor controller 762 and stepper motor controller 764 are linked to the address/data bus 736, but are optically isolated. Motor controller 762 is linked to and controls the motor of the elevator assembly. One type of motor controller that can be used is model 33033 for controlling a brushless DC motor. Stepper motor controller 764 is linked to and controls stepper motor of pick mechanism assembly 180a. One type of stepper motor controller that can be used is model L297.

Switch interface 766 is linked to the address/data bus 736 and provides an interface for various switches that are used in the elevator and pick mechanism. Sensor interface 768 is linked to address/data bus 736 and provides an interface for various sensors for detecting events such as errors, the presence of a sheet at a particular location, or the position of a movable mechanism.

Internal/external status display 770 is linked to the address/data bus 736, driven by an octal flip flop (not shown) , and enabled by an 8-bit latch (not shown) . Internal/external status display 770 includes an internal set of eight light-emitting diodes (not shown) and an external set of eight light-emitting diodes (not shown) . Both sets of diodes are arranged in a vertical bar graph and display identical codes that a technician can use for diagnostic purposes. The external set of diodes are

17 visible to an operator. The internal set of diodes are mounted directly on the RCU circuit board. Latch 772 is linked to address/data bus 736 and provides an interface to solenoid control circuits 774a-774d each of which controls a solenoid that is used to actuate various mechanical mechanisms such as pneumatic valves.

RCUs 732a-732o are detachably mounted programmable circuits. RCUs 732b-732o are substantially similar to RCU 732a. Referring to Fig. 8, the timer daughter board 735a includes a programmable gate array 1090 that is linked to a connector 1092. The connector 1092 is attached to connector 752 of RCU 732j . One type of programmable gate array that can be used is chip number ISPLSI 1016, which is manufactured by Lattice Corporation. In turn, the first and second sensors 1076 and 1078 are linked to the programmable gate array 1090. The timer daughter board 735b is substantially identical to the timer daughter board 735a and is also similarly linked to the first and second sensors 1076 and 1078.

The timer daughter boards 735a and 735b perform substantially identical functions and operate in parallel. When either the first or second sensor 1076 or 1078 detects the leading edge, it generates a signal that is detected by the programmable gate array 1090. In response to the signal, a counter internal to the programmable gate array 1090 begins to count. The counter continues to count until either the other sensor 1078 or 1076 detects the leading edge of the sheets and generates a signal or the counter overflows.

The programmable gate array 1090 is configured to operate on a 2 MHz clock. In contrast, RCUs 732j and 732k operate on a 4 MHz clock and thus increment the first and second stepper motors 1036 and 1038 on that basis. Thus, the count made by the programmable gate array 1090 corresponds to only half the number of steps made by the first and second stepper motors 1036 and 1038 and one half

the time interval between triggering the first and second sensors 1076 and 1078.

Once the counter stops counting, the programmable gate array 1090 sends an interrupt signal to the RCUs 732j and 732k and then communicates the count to the RCUs 732j and 732k. The RCUs 732 and 732k use this information to calculate the change in speed and phase of the first and second stepper motors 1036 or 1038, respectively, required to rotate the sheet and correct the angular error. RCU's 732j and 732k then adjust the speed and phase of the first and second stepper motors 1036 and 1038, respectively, until the angular error of the sheets is corrected. Once the leading edge of the sheet is substantially perpendicular to the path, the RCU's 732j and 732k return the first and second stepper motors 1036 and 1038, respectively, to their default speed.

When correcting angular error, RCU 732j will increase the speed of the first stepper motor 1036 and RCU 732k will decrease the speed of the second stepper motor 1038 if the second sensor 1078 detects the leading edge before the first sensor 1076. Similarly, RCU 732j will decrease the speed of the first stepper motor 1036 and RCU 732k will increase the speed of the second stepper motor 1038 if the first sensor 1076 detects the leading edge of the sheet before the second sensor 1078 detects the leading edge. The RCU's 732j and 732k will not adjust the speed and phase of the first and second stepper motors 1036 and

1038, respectively, if there is not a detectable time interval between the moments that the first and second sensors 1076 and 1078 detect the leading edge of the sheet .

An advantage of this architecture is that all of the calculations are accomplished in the time domain, which negates the need to convert the count to distance. Another advantage is that the count does not need to be divided by two in order to determine the velocity change required by each of the stepper motors 1036 and 1038. The

reason that dividing the count is not required is that the clock speed of the programmable gate array is half that of the RCUs 732j and 732k. The count only corresponds to one half the steps made by the stepper motors 1036 and 1038 and thus one half the angular error of the sheet. Thus, the number of mathematical operations required by the RCUs 732j and 732k is reduced.

Reducing the number of required calculations in turn reduces the response time of the RCUs 732j and 732k. Thus, the delay between detection of the leading edge of the sheets and speed and phase adjustment of the first and second stepper motors 1036 or 1038 is minimized and angular error of the sheet is adjusted very quickly. Such a quick response time is very important when the sheets are being transported along the path very quickly and there is only a short time period in which the sheet engages the registration assembly 1000.

Although adjusting the speed of both the first and second stepper motors 1036 and 1038 is discussed, it is contemplated that angular error could also be corrected by adjusting the speed of only one of the stepper motors 1036 or 1038.

Those skilled in the art will readily recognize that these and various other modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein, without departing from the true spirit and scope of the present invention which is set forth in the following claims.