DESCRIPTION

The invention relates to printers and, more particularly, to printers having document alignment mechanisms.

Generally document alignment in printers is achieved by constraining documents the printer can handle to be of a certain size and to move along a printing path defined by physical constraints such as rails, slots, studs or the like.

However, the use of such a defined printing path is not suitable for certain printing applications. One example of such an application is printers for printing banking passbooks where it is preferable for an operator to be able to insert the passbook into the printer. Such passbooks can vary in both size and thickness. Nevertheless in prior art such printers document alignment is achieved by an abutment against which an operator must position the document to be printed. The printing mechanism is arranged to print the document at a position which is defined in relation to this abutment.

Printers are known having alignment mechanisms for aligning documents inserted therein, the alignment mechanism comprising: document positioning means; means to determine the skew of the document; and a control system for controlling the positioning means in response to signals from the detectors so that the document is aligned for printing.

For example, US 4,833,591 describes a mechanism for deskewing moving envelopes fed from a conveyor. In this system an array of optical sensors arranged across the path of the envelope determines the document skew from changes in the number of occluded sensors and calculates the correction needed. The result of this calculation is used to change the velocity of one of the drive motors which feed the envelope to a printing position until the number of occluded sensors is stable.

This system has the problem that the position of the envelope after this alignment operation is not checked. Furthermore, a relatively long paper path is required in order that a difference in the driving

velocities of the driving motors result in a sufficient change in the orientation of the envelope.

This invention is directed to providing an improved such deskewing mechanism which would be particularly suitable for, but not limited to, use in a printer for printing banking passbooks. For this application it is desirable that the printer have a short paper path and be capable of handling a wide variety of document sizes and thicknesses.

Accordingly, the invention provides a printer of the above type characterized in that the positioning means is arranged to rotate an inserted document substantially about a stationary point.

This provides a deskewing mechanism which is suited for a passbook printer since the rotation of the document about a stationary point enables the printer to be designed with a short paper path.

In a preferred embodiment, the skew determining means comprises first and second detectors for detecting an edge of an inserted document at spaced positions; and the control means is responsive to the first detector detecting the presence of the edge first to cause the positioning means to rotate the document in a first sense and responsive to the second detector detecting the presence of the edge first to cause the positioning means to rotate the document in a second sense until the document is aligned.

Preferably the positioning means are also capable of moving the document in a direction substantially perpendicular to that in which the detection positions are spaced. In this case, the control system is preferably arranged to cause the positioning means to drive the document until both the first and second detectors has detected the presence of the document edge and to determine the amount by which the positioning means is to rotate the document from the distance the document needs to be moved in said direction from the point at which one of the first and second detectors detects the presence of the edge to the point at which the other of the first and second detectors detects the presence of the edge.

This provides a particularly simple and convenient way of employin the pair of detectors to determine the skew of the document.

Moreover, the control system can be arranged to determine that the document is aligned by moving the document over the first and second sensors and determining the distance the document needs to be moved in a direction perpendicular to that in which the positions of the detectors are spaced from the point at which one of the first and second detectors detects the presence of the edge to the other of first and second detectors detects the presence of the edge.

In the way the same pair of detectors are used to determine whethe the deskewing operation has been successful and provides the ability for the spaced detectors to continuously monitor the orientation of the document. Therefore, it is possible to be certain of the position of t document after the alignment operation.

The positioning means can comprise two spaced rollers arranged to be driven either in opposite directions or in the same direction. Advantageously, the positioning means comprises two sets of rollers eac set comprising upper and lower rollers, wherein the upper and/or lower rollers are spring loaded and an inserted document is driven by a nip between the upper and lower rollers. The spring loading of the rollers enables the printer to handle documents of varying thickness.

In a particularly preferred form of the invention the printer comprises a third detector arranged between the first and second detectors and the control system is responsive to the third detector an only one of the first and second detectors detecting the edge to determine that the document is excessively misaligned and reject the document.

Viewed from another aspect, the invention also provides a method for operating a printer of this type comprising the steps of:

(a) driving an inserted document in a direction substantially perpendicular to that in which the detection positions are spaced until both the first and second detectors have detected the presence of the document edge;

(b) determining the amount by which the positioning means is to rotat the document from the distance the document needs to be moved in said direction from the point at which one of the first and second detectors detects the presence of the document edge until the other of the first and second detectors detects the presence of the edge;

(c) rotating the document by the determined amount;

(d) driving the inserted document over the first and second detectors in said direction until both the first and second detectors have detecte the presence of the document edge; (e) determining the whether the document is aligned from the distance the document needs to be moved in said direction from the point at whic one of the first and second detectors detected the presence of the document edge until the other of the first and second detectors detecte the presence of the edge,- (f) repeating the above steps, if necessary, until the document is aligned.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 shows a perspective view of a printer,- Figure 2 shows a top view of a printer,-

Figure 3 shows the document alignment mechanism of a printer,-

Figure 4 shows an exploded view of a sensor bar;

Figure 5 is a schematic diagram showing the configuration of the sensor and pressure rolls in a printer,- Figure 6 is a schematic diagram showing the configuration of the sensor and pressure rolls in a printer- Figures 7 and 8 are flow diagrams illustrating the operation of t printer.

Referring to Figures 1 and 2 a printer for printing banking passbooks comprises a dot matrix printhead 100 of conventional type mounted on a carriage on drive belt 110. In operation a document is inserted by the operator into document insertion chute 120 and the prin head moves backwards and forwards over the document under the control o suitable control logic, printing onto the document as it does so.

Figure 1 is a perspective view of the printer and Figure 2 is a t view of the same printer from a direction perpendicular to the paper path, which is slanted slightly upwards when the printer is in a normal table top position.

The printer includes a document alignment mechanism which compris document sensor bar 130 and stepper motors 140 and 150. The document

alignment mechanism is shown in more detail in Figure 3. The mechanism comprises left and right side plates 300 and 310. Stepper motors 140 and 150 and sensor bar 130 are mounted on the side plates. Sensor bar 130 includes upper pressure rolls 320, release arm 330 and four photoelectric sensors, whose positions are indicated at 340. Motors 140 and 150 are mechanically connected via drive belts 350 and pulleys to lower drive shafts 360 on both sides of the sensor bar.

The upper pressure rolls 320 are mounted using a pair of springs to create the load against the lower feed rolls which are driven from the stepper motors 140 and 150. The springs also serve to create the load for the friction drive rolls.

Figure 4 shows an exploded view of the sensor bar 130 in which can be seen left and right lower drive shafts and pulleys 360 and 370, upper rolls 320 and release arm 330.

Figures 5 and 6 are schematic diagrams showing the configuration o the feed rolls and geometrical layout of the sensors 340. The printer also includes left and right document edge sensors mounted on the print head which are not shown in Figure 6.

The document alignment mechanism itself includes four sensors: document present sensor 600, left and right skew sensors 610 and 620 respectively and error detect sensor 630.

In this embodiment, the sensors are photoelectric sensors of conventional type which, when occluded or blocked by an object, sense a change in the amount of light received and provide a signal indicative o the presence of the object. It will be understood that the edge of a document passing over the sensors may be detected either by the sensor becoming occluded when previously it was not or by an occluded sensor being exposed to light by no longer being covered by the document. The possibility that other types of detector may be employed is not excluded.

Stepper motors 140 and 150 operate in conjunction with the sensors under the control of a control system which includes a memory, a microprocessor and appropriate microcode stored in the memory.

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Figure 7 and" 8 are flow charts showing the deskewing and error detection operations. The system works as follows:

When the operator inserts a document, either a single or multi-co cut form or a banking passbook, on document insertion chute 120, The steps shown generally in Figure 7 at 700 are performed. The insertion the document causes the document present sensor 600 shown in Figures 5 and 6 to be blocked. Blocking of the document present sensor causes a variable DP in the program to take the binary value 1.

In response to detection of the blocking of the document present sensor, the control system starts the alignment motors 140, 150 and mov the document forwards. The document is caught by the nip between the lower feed rolls 360, 370 and the upper pressure rolls 320 in the alignment mechanism.

The document/passbook is fed into the printer as far as the left, right and error detect sensors, 610, 620 and 630 shown in Figures 5 and 6. The controller tracks which one of the left or right sensor detects the presence of the document first, and how many microsteps it takes fo the other sensor to detect the presence of the document. Blocking of t left, right and error sensors causes the variables LA, RA and CA respectively referred to in Figures 7 and 8 to take the value 1.

The error detect sensor 630 located halfway between the left and right sensors is used in the steps denoted generally by 710 in Figure 7 to detect a document/passbook that is inserted by the operator with too much initial skew or offset from document insertion chute centre line. The control system determines whether only one of the left and right sensors has been blocked in conjunction with the error sensor. If that is the case the document or passbook will be ejected and the operator h to reinsert the document.

In principle, the alignment mechanism can handle any initial skew but physical limitations within the printer prohibit such operation and therefore the error sensor is used to set a limit for initial skew.

The microprocessor divides the number of microsteps between blocking of the left and right sensors by two and drives motor 1 half t distance forward and motor 2 half the distance backwards or vice versa

depending on which of the left and right sensors was blocked prior to th other.

After the document has been deskewed once it is then fed to the left and right sensors again and the microprocessor calculates the difference, if any, in detection between the left and right sensors. The microprocessor determines if it is within a range for an acceptable ske If the skew is within range both motors 140 and 150 move the document forward into position beneath the print head 100.

If the document is not within the acceptable tolerance, the deskewing process, as explained above, is repeated twice to try to desk the document to within the tolerance. The deskewed range or level is defined in the microcode and can be set to a value appropriate for the printing application.

If the alignment mechanism is not capable of deskewing a document to within the defined tolerance, for example if the document has a torn leading edge or a binder hole punched at the leading edge, the document is ejected, and the operator will have to reinsert the document again.

When the document/passbook has reached the print station the prin head moves across the document/passbook. The two sensors mounted on th print head detect the left and right edges of the document. The home position of the print head is known, and the distance between home position and either the left or right document edge is used by the microprocessor to determine the first print position on the document. The first print position varies with respect to print head's home position depending how well the document/passbook has been centred on t document insertion chute.

The printer can be programmed to use either the left or right document edge as a starting point for printing according to the printing application .