GB2528236A - Print removal devices and methods - Google Patents

Abstract

A print removal device 100 comprises a paper feed system 11 to receive and feed printed paper though the device; a print removal head having a controllable optical output such as a laser output 3 for removing print from said paper; and a head drive system 6 to scan said print removal head over said paper as said paper is fed through the device. The print removal head further comprises a sensor 4, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output. The device further comprising a control system 9, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper. The device may also include a particle removal system 5 to capture nanoparticles from the removed print.

Description

Print Removal Devices and Methods

FIELD OF THE INVENTION

This invention relates to apparatus and methods for removing print from paper ("unprinting").

BACKGROUND TO THE INVENTION

We have previously described a combination of laser pulse length and wavelength which optimises the removal of toner ink from white paper, in Leal-Ayala DR. and Allwood J.M., "Paper re-use: Toner-print removal by laser ablation", International Conference on Digital Printing Technologies (2010), pages 6-9; and also in Leal-Ayala, D. R., Allwood, J. M., Schmidt, M., & Alexeev, I. (2012), "Toner-print removal from paper by long and ultrashoit pulsed lasers", Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 468(2144), 2272-2293. Figure 8, which is taken from the Proc. Roy. Soc. paper, illustrates the relationship between wavelength, pulse length and paper damage, showing that the optimum wavelength is in the visible, around the green, and that the optimum pulse length is in the range 1- 4Ons. Further background prior art can be found in U52012/0268799 and US2004/0080787; JP2005/292747A also appears to describe a paper sheet regenerating device.

Despite this general background, there is need to solve various practical engineering problems in order to make a practical, low-commercial device.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provided a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; wherein said print removal head further comprises a sensor, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output; the device further comprising a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

Embodiments of the above described print removal device avoid the need for complex and expensive image processing and instead use an arrangement with a direct functional coupling between the print sensing and laser ablation: in embodiments the ablation head is scanned and as it is scanned an optical detection system on the head detects the print and directly controls the laser (optionally compensating for a short time delay). This quasi-direct control avoids the need for 2D image capture and processing thus potentially providing a substantial cost saving and improved unprinting speed. Preferably, but not essentially, the print sensor is mounted on the print removal head, and preferably the sensor is directed towards a region close to the region of laser ablation. In embodiments a delay device, preferably memory but in principle a counter or timer, provides a delay between print detection and laser ablation to compensate for the lateral displacement between the sensing and ablation and the consequent delay due to head movement. Where the spacing between the sensing and ablation is more than one ablation pixel, memory may be employed to store the one or a few intermediate pixels to provide a first in -first out buffer for the ablation data.

In preferred embodiments the paper feed system feeds paper past the head in a first, feed direction and the head is scanned in a second, perpendicular, scanning direction.

Alternatively, however, the paper may be fed stepwise through the device, in which case the head may be scanned into perpendicular directions rather than just in a single direction. In embodiments the paper feed system feeds paper through the device from an input port to an output port but in other arrangements an input and/or output paper tray or hopper may be internal and the paper feed system may feed the paper internally through the device.

The laser may be mounted within the device and the laser output is provided to the print removal head via transmission optics, for example a fibre optic, but in other embodiments the laser is mounted on the print removal head. The laser may be a continuous laser or a pulse laser; in the former case a shutter may be employed to control the laser output for selective unprinting.

In some preferred embodiments two print sensors are provided, one for either side of the laser output (in the scanning direction) so that the head may be operated bi-directionally for increased scanning speed. Thus in embodiments the head drive system is arranged to scan the head in a substantially continuous boustrophedonic motion. Preferably in such an arrangement the head drive is arranged so that the head overshoots the boundary of the paper slightly at each side so that the relevant sensor is correctly positioned for the start of the next scanning pass across the paper.

Preferably the head is moved at a rate no greater than the product of a pixel dimension in the scanning direction and the frequency of operation of the laser -that is preferably the scanning speed is matched to the frequency of laser operation. Preferably the laser output provides a peak laser pulse power of at least 50KW, more preferably at least 80KW or 90KW, over the area of an unprinting pixel.

In embodiments the device is configured to unprint both sides of a sheet of paper simultaneously. It is preferable for the paper to be supported in the unprinting region and in embodiments double-sided unprinting is achieved by providing a paper support with a slot longitudinally aligned along the scanning direction so that a second print removal head under the paper can sense and ablate print.

Optionally the unprinter may include an additional sensor, for example a 1D line sensor, to sense the presence of an entire blank line along the scanning direction.

When such a blank line is sensed the control system can control the paper feed system to skip past the blank line. This can speed up the unprinting process since a typical printed page will often include many blank lines.

In a related aspect the invention provides a method of removing print from paper, the method comprising: providing a print removal head having a controllable optical output for removing print from paper; moving printed paper and said print head relative to one another in a first direction; scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; scanning a sensor in tandem with said print removal head in said second direction; and controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.

The invention further provides a print removal device, the device comprising: a print removal head having a controllable optical output for removing print from paper; means for moving printed paper and said print head relative to one another in a first direction; means for scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; means for scanning a sensor in tandem with said print removal head in said second direction; and means for controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.

The invention also provides processor control code for a controller to implement the above-described devices and methods, in particular on a data carrier such as a disk, CD-or DVD-ROM, programmed memory such as read-only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. Code (and/or data) to implement embodiments of the invention may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code. As the skilled person will appreciate such code and/or data may be distributed between a plurality of coupled components in communication with one another.

Operation of a print removal device such as that previously described results in ablated toner particles, as well as some water vapour and carbon dioxide. By way of example, for black toner the ablated toner typically comprises a mixture of polymer (polyester) resin and pigment; the pigment typically comprises iron oxide. The ablated material comprises nanoparticles, typically with a median maximum dimension of less than l000nm, 500nm, or 200nm. For example typical ablated toner particles comprise iron oxide with a size distribution extending over the range lOnm to 200nm, typically with a peak in the 1O-2Onm range. It is therefore important in embodiments of the device to include a particle removal system, for safety and, potentially, also reuse of the ablated toner material.

Thus in a further aspect the invention provides a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a laser output for removing print from said paper; and a particle removal system to capture nanoparticles from said removing of said print.

In a preferred embodiment the particle removal system comprises an inlet nozzle mounted on the print removal head (or at least to move together with the head (and directed towards the point of removal of the print by the laser. This inlet nozzle may then be connected to a suction device and to a nanoparticle receptacle or bag, preferably incorporating a nanoparticle filter such as an HEPA filter to remove nanoparticles from the discharged air.

In preferred embodiments the nanoparticle receptacle bag has a self-sealing air inlet, for safe handling. In one arrangement this is provided by a set of moveable leaves which engage with a male member of an air duct of the particle removal system -so that the receptacle or bag can be pushed over the air-duct to form a sealed coupling.

Preferably the end of the air-duct has an asymmetric cross-sectional shape which matches a corresponding shape defined by the pattern of moveable leaves or flaps (or other sealing arrangement), to reduce the risk of accidental opening of the receptacle or bag. In another approach the self-sealing arrangement comprises a displaceable sealing member which is displaced to open the air inlet on attachment of the receptacle or bag and which is displaced to close the air inlet when the receptacle/bag is removed.

In a simple embodiment the receptacle/bag may have an attachment portion with a moveable shutter which slides out of the way when the attachment portion is slid across the end of the relevant air duct.

The skilled person will appreciate that features of the above described aspects and embodiments of the invention can be combined in the permutation.

In a still further aspect the invention provides a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; a point or line sensor for sensing print on said paper; means for providing relative motion between said paper and said sensor; and a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

In embodiments the sensor may be a line sensor for sensing a line of print (along the scanning direction). The control system may then comprise a buffer to store one or more lines of sensed unprinting pixels prior to the line of print arriving at the print removal head. Optionally the control system may then be configured to control the paper feed system responsive a signal from the sensor to skip past a blank line on the paper. Again, features from other previously described aspects/embodiments of the invention may be included in the device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is diagrammatically illustrated, by way of example, in the accompanying drawings, in which: Figures la to ic show, respectively, a perspective view of an unprinter according to an embodiment of the invention, a perspective view of a first example of an unprinter head, and a perspective view of a second example of an unprinter head; Figures 2a to 2c show, respectively, a side view of a paper feed system, a view from above of the paper feed system, and an illustration of paper positioning under the unprinting head; Figure 3 shows a vertical cross-section view through an unprinting head according to an embodiment of the invention; Figures 4a to 4c show, respectively, a laser system for the head of Figure 3, a toner detection system for the head of Figure 3, and a head positioning system; Figure 5 illustrates, schematically, an optical sensor for toner detection for the unprinting head of Figure 3; Figures 6a to 6d show, respectively, evolution of a toner sensing signal as the unprinting head is scanned over printed paper, a schematic illustration of an unprinting pixel and laser spot, unprinting pixel geometry/definitions, and a flow diagram of an unprinting procedure implemented by an unprinter controller in an embodiment of the invention; Figure 7 shows an ablated toner extraction system according to an embodiment of the invention; Figure 8 shows examples of wavelength and pulse length operating regions illustrating a preferred region of operation for unprinting; Figure 9 shows a variant of an unprinter employing a line/array sensor for detecting printed toner; Figure 10 shows example configurations in which the laser is mounted separately to the unprinting head; and Figure 11 shows an example of a preferred unprinting scan pattern in embodiments of the invention; and Figures 12a to 12c show cross-sectional views through an embodiment of an unprinter according to the invention illustrating, in particular, a colour toner residue collection system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Broadly speaking we will describe a system that uses a laser device in combination with a positioning sensor for effectively removing toner print from paper. We will also describe a method for detecting the location of toner particles in the form of printed features (e.g. characters or images) on the surface of paper and then removing them by laser ablation. The laser ablation of toner particles is a process that consumes less energy than paper recycling. The laser system is selected to produce the high energy radiation required to remove toner particles without paper damage or discolouration.

The high energy light is preferably directed through vacuum sealed optics to a toner containing suiface. The positioning of the printed surface under the laser radiation is preferably done by a positioning system that includes a scanning device that feeds data to an algorithm that then positions the target area. The positioning sensor detects the position of the toner on a white paper background by means of light reflection. The positioning may be done by mechanical means by a paper feeding system and then by moving the laser system to the required location along the paper.

We will first outline the various aspects of an example unprinter, then describe these in more detail. Thus Figure la shows an unprinter 100 according to an embodiment of the invention. The unprinter comprises a laser power unit 1 providing power to a laser source 3. The laser is cooled by laser cooling unit 13. An unprinter head of the device also includes a toner position detector 4 and an air extraction model 5; the head is moved by a seivo motor 6. A stepper motor 7 drives the paper feed which loads paper from input tray 11 and transports the paper over paper feed rollers 10. The unprinter is powered by a main power unit 12 and controlled by a controller 9, which interfaces to a visual display/user interface B. The controller may comprise a processor operating under control of processor control code stored in non-volatile memory to implement and control the operations described later. The unprinter also includes an ablated toner extraction system 2.

Figure lb shows details of the unprinting head, in this example comprising a laser source 1 and laser optics 2 focusing the laser onto the region of an unprinting pixel.

The head includes a toner detector/sensor 3 and a head support 4 for mounting and positioning the head. In preferred embodiments a toner particle extraction nozzle is also provided (not shown in Figure ib). Figure ic shows an alternative arrangement in which a toner detector/sensor 3 is located to either side of the laser ablation region.

Figure 2a shows the paper feed system; comprising paper feed rollers 1 to transport paper from an input tray 2. The rollers 1 are driven by a stepper rotor (shaft) 3 and chain 4. In Figure 2b reference numeral 3 labels the unprinting scanning access and reference numeral 4 an input paper tray sensor. Figure 2b also shows a second sensor 5 adjacent to the unprinting axis (X), and a paper exit sensor 6. In Figure 2c reference numeral 2 labels a guide rail for the unprinting head and refelence numeral 3 labels a belt drive for moving the head in the X direction, transverse to the direction of paper feed; paper is moved in the Y direction 4.

Figure 3 illustrates components of an example unprinting head comprising, as before, a laser source 1, laser optics 2, toner sensor 3, and head guide/stage support 4.

Figure 4a illustrates an example unprinting head incorporating a laser source 1 coupled to laser optics 2 (preferably under vacuum), which include a focusing lens 3 to focus the optical output 4 onto a target on printing area 6 of paper 5. A cable 7 connects the laser 1 to a power supply and electronic control unit.

Referring to Figure 4b, an example tonel detection system comprises an LED emitter 2 and photodiode 3 supported on a mount 1 and defining an optical path 4 for detecting toner over a target unprinting region 6 on paper 5. An electrical connection 7 couples a sensor to a power supply and the unprinter controller.

Figure 4c shows the head positioning system comprising head supporUpositioning rods 1, 2, a support wheel 3 running in a guide 5 on the lower rod 2 (wheel 3 provides support but in embodiments is not used to drive the head). The head is driven laterally by a belt 8 which engages with a 2 stroke mount 4 and is driven by motor 7.

Figure 5 shows a simplified schematic diagram of the toner sensor of Figure 4b.

Figure 6a illustrates the evolution of a signal at successive points (1), (2) and (3) as the head moves across the surface of paper 9 bearing toner in region 8. The toner detection area of the sensor is labelled 7; at stages (1), (2) and (3) the detection area is respectively free from toner, partially covered by toner, and fully covered by toner. The sensor is calibrated to zero for a signal from the region of the paper free from toner as indicated by level 4; the signal level increases 5 as the paper is displaced in the X (or Y) direction over the toner, increasing to a maximum 6 when the detection area is entirely covered by toner.

Figure Gb illustrates a region of paper 1 showing the laser spot area 2 (the toner detection area preferably corresponds), and an unprinting pixel 3.

Figure 6c illustrates the labelling of unprinting pixels, described further later, and Figure 6d shows a (simplified) unprinting procedure, referring to the coordinates shown in Figure 6c. Thus the paper feed system passes paper through the device, unprinting pixels in the scanning head movement direction (index j), and unprinting rows of pixels in the paper feed direction (index i). The controller successively increments over the pixels, determines whether toner is present, if so unprinting, if not incrementing to the next pixel, finally outputting the unprinted paper.

Figure 7 shows an ablated toner extraction system, with a schematic illustration of an intake nozzle 1 having an air conduit to a fan 2, and thence to a HEPA filter porous bag 3 and exhaust port 4. Preferably the porous bag 3 has a self-sealing closure 3a, for example comprising a shutter displaced when the bag is fitted as shown in the inset sketch and/or comprising a set of moveable flaps or leaves opened when the bag is fitted.

Figure 8 is taken from the Leal et al paper (ibid).

Figure 9 shows a variant of the unprinter in which, rather than the toner sensor being mounted on the head, a line or array-type toner sensor 6 is provided to sense an entire row of pixels in the head scanning direction. The line sensor 6 is prior to the unprinting head in the paper feed direction; as illustrated paper 4 is carried by rollers 1 from sensor 6 towards unprinting head 5 mounted on guide rail 2, driven by belt 3.

Figure 10 illustrates a variant of the unprinter in which the laser source 1 is remote from the unprinting head and coupled to the head by, for example, an optical fibre 4 or a flexible arm 5 with internal guide mirrors 6. The unprinting head comprises laser optics 2 (preferably under vacuum) including a focusing lens 3.

Figure 11 illustrates scanning of the unprinting head in one embodiment, in which the head scans alternately in opposite directions along the unprinting axis. Thus in this example preferably the head has a pair of sensors for sensing toner, ito either side of the ablation output.

Figures 12a to i2c show cross-sectional views through an embodiment of an unprinter according to the invention illustrating, in particular, separate, removeable, black and colour toner residue collection receptacles. The optical toner sensing system may be configured to distinguish black (on white) toner from colour printing and means may be provided to selectively provide ablated toner to either a black or a colour toner receptacle, for example by selectively activating one of two different suctions devices (fans) for each of the two collection systems (which may have a separate or shared collection nozzle). It will be appreciated that although we have described separate black and colour toner collection, more generally a selective toner collection system may separately collect between any two different, distinguishable types of toner.

Now, referring again to Figure 1, embodiments of the unprinter' preferably comprise three main systems within an enclosure, which is preferably substantially light-proof for safety: i. the laser system, which conducts the laser radiation to the surface of the printed paper; ii. the positioning system, which ensure that the laser radiation is directed to a previously scanned area containing toner on the surface of the paper; and iii. the vaporized toner removal system, which continuously absorbs and filters any possible residues from the process.

The laser and positioning systems are the core unprinting mechanism; these systems work together and are mechanically guided by their own positioning mechanisms. The enclosure contains those systems together with the required electronics for them to function. The three main systems are described in turn below.

Laser system: The laser system comprises a laser source; experiments have shown that this may have a relatively low pulse energy, and pulse energy of greater than 0.lmJ can be suitable (for example a pulse energy of 0.37 mJ was found effective in laboratory tests). The skilled person will appreciate that since pulse energy divided by the pulse length defines the peak power, low peak pulse energies are preferably used together with short pulses. Nonetheless for speed/larger unprinting pixel sizes a higher energy pulsed laser may be preferred, for example with a pulse energy of at least 200mJ, preferably 400mJ up to l200mJ or greater. The laser may be, for example: a Q-switched Nd:YAG laser (532nm), a Q-switched ruby laser (694nm), a Q-switched alexandrite laser (755nm), an argon laser, a carbon dioxide laser, an Er:YAG laser, a fiber laser, a semiconductor laser, a diode laser, or a combination thereof. Preferably a Q-Switched laser with peak output wavelength around 532nm is used. The output wavelength(s) is/are preferably situated at a value or values corresponding to one or more wavelengths highly absorbed by toner particles. A preferred wavelength may be selected in combination with a laser pulse duration according to the graph in FIG 8 (Leal et al., ibid). The wavelength is preferably in the range 250nm to 1200nm (for example 266nm to 1064nm), and the pulse duration may be from Dm5 to 2Ons, preferably 4ns to 8ns for 532nm. These values help to preserve paper whiteness and the integrity of the cellulose fibers (see Leal-Ayala etal., ibid).

The laser beam is directed through an optical path to a target surface containing toner particles on printed paper. These optics are preferably assembled at low pressures (vacuum) <SOombar, preferably <200mbar to avoid air ionization and improve optical transmission. The optics guide the laser beam from the laser source to the surface of the printed paper, and define an illumination area on its surface. The laser beam is focused by a focusing lens (FIG4A:3) onto the surface containing print. The area of the laser spot is determined by the distance from the paper at which the lens is positioned; the area of the laser spot corresponds to a circle with a diameter selected from 1mm to 5cm, and preferably 5mm for total area of 19.6mm2. In principle, however, smaller sizes, for example down to 0.01 mm or less, may be employed -smaller spot sizes may, for example, help to increase unprinting resolution. The size (diameter) of the laser spot area may be chosen in accordance with the laser power output provided by the laser system.

Positioning system: The positioning system of the unprinter comprises the toner position detector, the laser positioning mechanism, the paper feeding system and a scanner signal processing to coordinate the actions of these elements for successful removal of print. The integrated unprinting action mechanism is coordinated by an algorithm as follows: position the detection system over a given area of the paper; if toner print is detected store value and continue process until laser system is positioned onto the previously scanned location; if print was detected there fire laser and unprint. The algorithm finishes when the entire printed surface has been scanned and unprinted. The detection of toner print on the surface is done by the toner position detector. The position is stored and the displacement of the unprinting head in the X and Y directions over the paper surface (FIG 2B), is performed by the laser positioner and the feeding system respectively. Fig 2c shows the paper positioning under the unprinting head in the X and Y directions.

The laser system includes a positioning system to determine the position of toner particles on the target surface. In embodiments this comprises a light emitting element and a light detecting element and optical components to align the light paths (FIG 4B).

The light emitting element preferably comprises a light emitting diode (LED) with peak wavelength emission selected from 600nm to 2000nm, preferably a peak wavelength emitted at the peak sensitivity wavelength of the detecting element. The detecting element is preferred to have peak sensitivity values in the near infrared or visible red light from 600nm to 2000nm. The detecting element may comprise one or more lnGaAs photodiodes (sensitivity range 700nm to 1700nm), PIN photodiodes (max response 940nm), side-looking infrared detectors, or phototransistors. A preferred combination comprises a photodiode with peak sensitivity at 940+I-2Onm and an LED infrared emitter with peak emitting wavelength at 940+I-2Onm. Both the emitter and detector are preferably geometrically arranged as in the configuration shown in FIG4B.

The detector and emitter are inclined at an angle selected from 0° to 60° from the normal to the surface of the paper. The angle and distance from the paper surface determine the target unprinting area (FIG4B:6). A configuration is preferred in which the inclination angle of the light emitter and detector is -30° from a normal to the surface of the paper in opposite direction to each other. The scanning may also be adjusted by means of optical elements accompanying the emitter and detector, such as lenses. The area is selected in accordance to the unprinting laser spot area. In embodiments the unprinting laser spot area may have a maximum dimension (or diameter for a circular spot) in the range 1mm to 3cm and may be, for example, a circle of 5mm diameter with 19.6mm2 area. In principle however the maximum dimension, or diameter for a circular spot, may be smaller, for example down to 0.01mm (in principle a diffraction limited spot), or larger, for example up to Scm or more (depending upon the laser power). The combination of photodetector and photo emitter can be substituted by integrated optical detector/phototransistor. The presence or absence of toner on the surface of the paper is detected by the difference in signal detected from the photodetector after the emitted light has been reflected from the surface of the paper. The signal is transmitted by means of electrical connections to the main control unit via an electronic circuit similar to, but not limited to, the one depicted in FIGS. The intensity of the signal is calibrated to 0 for a white paper surface containing no printed tonner. As the toner print is positioned in the area of detection of the toner detection system, the reflected light from the white paper surfaces decreases in intensity due to the darkness of the toner print. This results in an increase of the signal as illustrated in FIG6. When there is no toner the signal is set to 0 (S=0, FIG6:1), whereas when all the surface of the detection area is covered by tonner the signal will acquire a maximum value (S=Max, FIG6:3). Values in between (Max...0) correspond to an area partially covered by toner print (FIG6:2).

The laser head of the laser unit is positioned on a guiding stage (FIG4C). The stage comprises two guides for cylindrical rods or guiding rails (10mm diameter) attached to the main body of the unprinter. One of them includes a support wheel to support the weight of the unprinting head mechanically attached to this laser positioner (FIG4C:3,5). The laser positioner is attached to a toothed belt (FIG4B:8) to drive the unprinter head along the width of an the paper sheet. The unprinter dimensions are preferable compatible with an A4 paper size but are not limited to this and may be selected from standard sizes of A series, B series, C series or US series (e.g. legal, letter, envelope, A3, A2, B3, B4, B2). The carriage and unprinter dimensions may be defined in accordance with these paper sizes. A rubber toothed band is driven by a motor which is fixed on the side of the paper feeding system (FIG4B:7). The belt material is preferably a fabric or woven steel wires embedded in an elastic material.

The wire or fabric reinforcement reduces elasticity horizontally for a precise positioning of the unprinting head. This movement is defined as the movement along the X direction while the movement of the paper sheet by the feeding system provides movement in the Y direction (FIG 2B).

For the signal processing it is useful to define certain geometrical measures. The area given by the laser optics and toner detection system corresponds to a circle of diameter D' and defined as A=(rrD2/4). In order to ensure complete removal of toner print under the area of incidence of the laser bean,, an square area smaller than the laser spot area is defined as an unprinting pixel' and called U' hereafter. These definitions are graphically depicted in FIG6B. The square area U (FIG6B:3) is entirely contained in the laser or detection system area such as the center of the square U and circle A (FIG6B:2) are the same point. The area U is preferable -63% of the area A. The sides of the square L' measure D/2112 or less, preferably the dimensions that match 63% of the area of the circle. The dimensions of the printed paper are defined in terms of the unprinting pixels as depicted in FIG6C. The rectangular piece of paper is divided into a grid of unprinting pixels, the number of unprinting pixels in the X direction of the paper is defined as n' and the number of unprinting pixels in the Y direction is defined as k'.

The location of an unprinting pixel along the X direction is defined as the position and the location along the Y direction as the th position. A given unprinting pixel can be described in unprinting coordinates as xj,yj as highlighted in FIG6C.

The main control unit processes the information from all the unprinter components and executes the required actions for successful unprinting as follows: The paper is fed to the unprinter and the toner detector in the unprinted head is positioned on the first unprinting pixel (i.e. x1,y1), the detector is moved along the Y axis and X axis by the motors described in the paper feed system and laser position system sections respectively. The paper feed sensors establish the edges of the paper and then the toner detector area is centered on the unprinting pixel. From that point the displacement of the paper and unprinting head proceeds in steps of distance L along X and Y. The toner detector system first records the signal information from the current unprinting pixels, then stores it and continues. When the laser head is positioned on the pixel that produced S>0 the laser beam is triggered and all the toner on the area is removed. In the illustrated embodiment the centre of the laser spot area is 5 unprinting pixels apart from the toner detection area (5D12112). These steps are coded into an algorithm contained in the control unit which stores all the geometries ensuring that all surface of the paper has been scanned and unprinted.

Unprinting parameters The unprinting parameters used for unprinting are defined as follows: An unprinting energy density (UED) is defined as the unprinting intensity (ia) divided by the unprinting speed (V1): UED=1JV where I,, is the laser intensity in terms of the pixel area defined above (lccl) and defined as: I=PP/A1 and, I=PP/A where PP is the laser peak power given by the laser pulse energy E divided by the pulse length p1 of the laser as: PTh-E/p/ Laser energy parameters E are typically provided by the laser manufacturer in millijoules mJ and pulse lengths p1 in nanoseconds ns respectively. The unprinting speed V is the pixel length L (defined in function of the laser spot area diameter 0) multiplied by the laser frequency f: V1=fL Example parameters are 0= 150pm and f-l5Hz with pI=4ns and E/A=1.6J/cm2. The diameter may be small, for example down to 0.01mm (diffraction limited spot), or larger, for example up to 5cm or more (depending upon the laser power). The frequency of operation may be, for example, from 1Hz up to 1MHz or more.

In embodiments the unprinter V1preferred parameter range is 0. 1mm/s to 2x106mm/s; in embodiments the unprinter has a characteristic UED from about O.O8kWs/mm3 to 1x1O"kWs/mm3.

Paper feed system: 1. Overview: the unprinting device has a line along which un-printing takes place, described in this document as the unprinting axis [FIG2B:3], beneath the unprinter head [FIG2B:3]. A page passes through the un-printing axis a line (of unprinting pixels) at a time. Paper is transported from the input tray across the un-printing axis by a set of, for example, eight plastic rollers located on the sides of the paper path (four on each side), as shown in FIG2A: 1 and FIG2B: 1.

Paper motion through the un-printing axis is a succession of linefeed -stop actions to each new line. This allows the unprinter head [FIG1AB] on its carriage to detect and un-print one line per pass. The width of the line is determined by the laser spot area (See "Laser optics" section).

2. Feeder mechanism: the eight rollers [FIG2A:1 and FIG2B:1] are simultaneously rotated by the action of a cog chain [FIG2A:4] that engages with the DC stepper motor shaft [FIG2A:3]. To insert a page the feeder system first needs to detect the presence of paper in the input tray to start the process.

After this the feed rollers pick the page up and propel it forward in a continuous movement until reaching the un-printing area, where a signal is produced to switch from continuous to linefeed -stop motion for un-printing.

3. Motor drive: motor drive for the feed rollers is provided by a stepper motor [FIG1AA:7] capable of producing short steps to move the paper in lines not wider than the laser spot area width (See "Laser optics" section).

4. Control sequence and sensors: three sensors provide the intelligence required to control the paper feed system: i) an electro-mechanical limit switch located at the paper input tray to mechanically detect the presence of paper and trigger an electrical signal [FIG2B:4]; ii) an infrared photo-emitter and detector pair located near the unprinting axis [FIG2B:3] to detect the presence of paper in this area to switch from continuous paper feed movement to line by line step movements [FIG2B:5]; iii) and a second infrared photo-emitter and detector pair located at the exit of the paper path to notify the system about the end-of the unprinting operation [FIG2B:6]. This provides the useful feedback on what the paper path is doing and helps to coordinate the activation of the paper feed motor. The command sequence is the following: i) un-printing sequence activated by user; ii) paper detection process: if positive activate main feed motor in continuous movement mode, if negative wait; üi) when feed motor is activated wait for un-printing area detection signal to switch into line by line step movement; iv) wait for paper-out signal to finalise process and switch-off main feed motor.

5. Paper input tray: the paper input tray is where paper is deposited prior to unprinting [FIG1AA:11]. When the unprinting sequence is initiated, paper is propelled into the machine in a linear movement, starting at the paper input tray [FIG1A:11], located at the front of the machine, through the opening at the front of the unprinter, across the unprinting axis [FIG2B:3], and out through the back of the unprinter. This movement has enough clearance at the back to avoid a collision between the exiting paper and external objects.

Vaporised toner residues extraction system The toner residues extraction system has five main components [FIG7], as folows: 1. An intake nozzle embedded in the unprinting head [FIGT:1]; 2. An electric motor and fan [FIG7:2]; 3. A HEPA filter porous bag capable of capturing particles of down to 10 nm diameters [F137:3]; in preferred embodiments the filter captures particles in a size (average lateral dimension) range of lOnm to 200nm; 4. An exhaust port [FIG7:4]; 5. A housing that contains all components [FIG7:5].

The DC motor is attached to the fan [FIG7:2], which has angled blades that force air foiward as they turn, toward the exhaust port. Captured toner particles from the unprinting area are driven forward through the intake nozzle [FIG1A:5] and captured in the porous bag [FIG7:3] before air flows out of the housing [FIG7:5] through the exhaust pod [FIG7:4]. The fan creates suction, creating a partial vacuum inside the toner residues extraction system, sucking ambient air into the intake nozzle because of the pressure difference. The HEPA filter porous bag [FIG7:3] acts as an air filter, allowing air to pass but small collecting the toner debris.

Unprinter housing The unprinting device has eleven main components within a common housing [FIG1A], as follows: 1. Laser power unit [FIGIA:1]: this power supply provides the voltage for the laser tubes contained within the laser head [FIG1A:3], with a highly regulated current output to ensure optical stability. The power supply adjusts laser tube voltage to maintain a fixed discharge current. The core component of the power supply is a transformer connected backwards to step-up voltage.

2. Vaporised toner residues extraction system [FIG1A:2]: this is the system in charge of collecting and filtering out toner residues generated during the unprinting process. More details given in "Vaporized toner residues extraction system" section.

3. Laser source [FIGIA:3 and FIGIAB:1]: This component is the part of the laser system where the laser beam is generated and fired during unprinting.

More details in the "laser system section".

4. Toner position detector [FIG1A:4 and FIG1AB:3]: This component is part of the laser system. It determines the position of the toner on the paper to control the laser firing process. More details in the "laser system section".

5. Air extraction nozzle [FIGIA:5]: This component is part of the toner residues extraction system [FIG7]. It has an opening at the end of the intake port where air enters the passageway that conducts it towards the porous bag for filtration.

More details in the "Vaporised toner residues extraction system" section.

6. Laser guide servomotor [FIGIA:6]: this servomotor allows for precise control of angular position, velocity and acceleration. Preferably this comprises a brushless DC electric motor coupled to a sensor for position feedback and a closed-loop controller. This servomotor controls the motion and positioning of the laser system in the unprinting area.

7. Paper feed rollers DC stepper motor [FIGIA:7]: a brushless DC stepper motor divides a full rotation into a number of steps by having multiple electromagnets arranged around a central gear-shaped piece of iron. An external microcontroller energises the electromagnets to attract the gear's teeth by magnetic attraction, effectively rotating the gear step by step. This allows the motor to rotate and hold its position in an easy way, without the need for any feedback sensor, effectively controlling the paper's feed into the unprinting area by propelling the paper forward in small line by line steps. This motor provides motion for the eight paper feed rollers during unprinting.

8. Electronic visual display [FIGIA:8]: this is an active liquid crystal display that works as the interface between the user and the machine. A series of options are given to the user through this display before commencing the unprinting sequence, triggered by the user through the display.

9. Main control unit [FIG1A:9]: this unit contains the electronic systems required to control all aspects of the machine: i) display electronics; ii) laser system control; üi) paper feed system control; iv) and vaporised toner residues extraction system. It is mainly composed of one or more microprocessors programmed with the command sequences to coordinate all these functions.

10. Paper feed rollers [FIGIA:10]: These components are part of the paper feed system [FIG2A:1 and FIG2B:1]. They are responsible for transporting paper from the input tray into the unprinting area. More details in the "Paper feed system" section.

11. Paper input tray LFIGIA:1 1] This component is part of the paper feed system [FIG2A:2 and FIG2B:2]. It is the area where paper is initially located prior to the beginning of the unprinting process. More details in the "Paper feed system" section.

12. Main power unit [FIGIA:12]: This power supply provides the voltage for all peripheral components of the machine, including: i) the laser system servomotor; ii) the paper feed system DC motor controlling the rollers; iii) the vaporised toner residues extraction system fan; iv) other electronic components such as sensors and the electronic display.

13. Laser cooling unit [FIGIA:13]: The laser unit generates heat that should be removed from the laser system to avoid overheating. An ambient cooling system is preferably added for this purpose, comprising, for example, a high-performance copper heat exchanger for use with water, integrated with a fan, pump, and a tank in a metal chassis.

In another configuration, the toner detection system is detached and separate from the unprinting head and comprises a linear array of detectors that scan along the paper X direction as shown in FIG9. The values for each unprinting pixel are stored and processed, feeding the toner position to the laser system on the moving unprinting head. Then, the control unit directs the paper to under the laser system via the feed system using the same algorithm. Finally, the laser is triggered removing the ink on the selected pixels.

The positioning detection system may comprise a commercial optical detector such as the Fairchild Semiconductor QRD113/4 reflective object sensor. In embodiments it is located on the unprinting head or on the array described above. In embodiments the light emitter of the detection system comprises a low power red laser.

The high power laser light may be generated adjacent the laser power supply unit and guided to the laser optics on the unprinter head from this external source by means of an optical fiber, collimated fiber, or mirrors inside a guiding arm comprising hollow tubes, as depicted on FIG1O.

The toner detection system is place on the X axis of displacement aligned with the laser head, and preferably on both sides of the head, so that when the laser head is driven by the positioning motors, the detection system simultaneously detects the toner ink on the paper surface as it moves from -X to +X. Thus in embodiments the unprinter head contains two toner print sensors located one on each side of the unprinting optical output along the unprinting axis, and the head moves sidewise scanning in the +X direction and in the -X direction as shown in FIG1 1.

We now describe the functional operation of an embodiment of the unprinter. The user instigated functions are as follows: 1. The user switches the machine ON (or wakes the machine up).

2. The user loads printed paper in the input paper tray (component 11 in FIG la).

3. The user interacts with the user interface (component 8 in FIG la, e.g. electronic display, mechanical button, or voice recognition) to give the command that executes the unprinting sequence.

4. After the end of the unprinting sequence, the user collects the paper from the paper output tray (for example, behind the machine).

At start-up and during unprinting operation the Unprinter performs a sequence of functions as follows: 1. When the user switches on the machine (or wakes it up), the unprinter checks the status of all peripheral systems, ie. the control unit sends an activation signal and then expects to receive and read a return signal from all unprinter components, which are provided with a feedback loop. An activation signal is sent to all systems (laser, air extraction, paper feed system, laser positioning system) to check ON status. If all systems return an ON signal, the user interface displays a READY message.

2. The loading tray holds paper (which may be of different sizes, but one size at a time) in a position where the paper feed system can load the paper to the machine.

The paper tray has an adaptable size switch. The position of this switch (which is moved according to the paper size) defines the number of pixels that is contained within one page based on the coordinates n' and k" (See FIG 6C).

3. When the unprinter receives an unprinting command the user interface sends command to the main electronic control unit system which then checks that conditions for unprinting are met: i. Paper tray contains paper: The control unit checks the status of the sensor (electromechanical switch or optical) located at the paper input tray. If tray contains paper then the signal is ON, if not then it is OFF. If the signal is OFF the control unit sends the user interface a message prompting to load paper on tray (display, light, or sound). If the signal is ON check next condition.

ii. Check laser status and position laser head to initial position: Check for laser power unit status (ON, OFF). If OFF turn ON and message user to wait while the optimum laser operation temperature is reached. If ON proceed to next step: Send signal to laser positioning rotor to position laser in reference start position (outside first pixel area -1OL [L is defined below], at coordinates X0,Y0 [Fig 6c]) iii. Check paper feed rotors (Fig 1) for ON signal (if OFF send error message). If ON go to next step.

iv. Check laser positioning rotor for ON signal (if OFF send error message). If ON go to next step.

v. Check air extraction system (Fig 7) for ON signal (if OFF send error message). If ON, go to the next step.

vi. If all previous steps OK send ON signal, proceed to next step.

4. Air extractor begins continuous extraction: The ON signal continues and the air extractor operates until an OFF signal is received.

5. Paper loading to unprinting area (Fig 2b): The paper feed rotor starts to operate in continuous mode: the plastic rollers on the sides start displacing a sheet of paper at a time until the front edge of the sheet of paper reaches the unprinting axis sensor (electromechanial or optical, see component 5 in Fig 2b, or Fig 11) to indicate sheet is at the right position. If paper is not detected (OFF) keep feeding with rollers, if OFF is received after a given warning length then send error. If paper is detected (ON) proceed to next step.

6. Start unprinting sequence (algorithm, see FIG6D).

a. The laser positioning rotor starts to operate continuously at a given speed which is no greater than the laser frequency (pulses per second, fl multiplied by pixel length 12' (where pixel length L" is preferably smaller than the laser spot size L, and the pixel area is less than 63% of the laser spot area).

b. When toner detector on laser head is over the first pixel (X1, Vi) a signal reading (S) is taken (see FIG6) and compared to a reference signal (SO) corresponding to a not printed area (alternatively, the user previously executes calibrate command and inputs a not printed paper sheet with the same characteristics as the desired printed sheet to unprint to record SO).

c. If S-SO> 0 a signal is sent to the control unit which starts a counter that triggers the laser after the laser head has moved by 5 pixels (the laser is spaced 5 pixel lengths apart from toner sensor, see FIG3). This acquisition process continues until cn pixels have been scanned for toner (Xi...n, Yi).

d. Then the motor continues to the END position (n+10 pixels), when this position is reached a signal is sent to the control unit which in return sends a signal to the paper feed system to move the paper forward by activating rotors and displacing the paper one pixel length L'.

e. Then, the laser positioning system rotor moves until the second toner sensor (on the other side of laser head) is positioned over the pixel corresponding to (Xn, Y2). The signal is sampled and the laser positioning rotor moves, scanning all pixels in the X direction until the start position is reached again, then the laser head is moved to the starting, reference position.

f. The process repeats (move, scan, move, unprint) until pixel (Xn, Yn) is reached (Fig ii). When unprinting is complete a paper extraction action is executed.

7. Paper extraction: Send signal to paper feed rotor to displace paper out until outlet paper sensor stops detecting paper (if outlet sensor has not detected paper by the last pixel Xn, Yn, keep moving rotor until paper is detected and then continue until paper stops been detected again).

8. Repeat steps 3 onward until input paper tray sensor is OFF.

9. Control unit displays "Ready" message in the user interface, switches fan OFF and starts timer to switch main power OFF after X minutes of the machine being idle.

Thus, broadly speaking, embodiments of the invention provide a laser system that works in combination with a sensor/positioning system. The sensor/positioning system processes spatial information defining the location of colour toner on a white paper surface. The area where toner is detected is then placed under the axis of the unprinting head and under the ablation spot of a high energy laser for removal. The laser light is preferably guided through high transmission optics for minimal energy loss. The dark toner on white background is detected by means of light reflection by a position scanner system, preferably comprising an incident light source and a photodetector. The incident light source may be a NIR (near infrared) LED with a focusing lens that provides a fixed illumination area. In embodiments light is reflected from the surface of the paper at an angle to meet the photodetector. The photodetector may comprise a single pixel detector spatially arranged to scan over a fixed area for later ablation. The spatial information may be processed by an algorithm that positions the laser system along the paper and the paper itself by means of a paper feed system, for example a roller, for ablation of the detected toner.

No doubt many other effective alternatives will occur to the skilled person. For example, although preferred embodiments of the system use a laser to ablate the print, in principle an alternative light source may be employed, provided that it is of sufficient power, and the invention contemplates the substitution of the laser by such an alternative light source. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims (24)

1. CLAIMS: 1. A print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; wherein said print removal head further comprises a sensor, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output; the device further comprising a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.
2. 2. A print removal device as claimed in claim 1 wherein said head is scanned in a scanning direction and wherein said sensor is displaced from a position of said laser output along said scanning direction.
3. 3. A print removal device as claimed in claim 2 comprising two said sensors, one displaced to each side of said laser output along said scanning direction, and wherein said head drive system is arranged to scan said head bi-directionally along said scanning direction.
4. 4. A print removal device as claimed in claim 2 or 3 wherein said control system comprises a delay device to control said laser output to fire after a delay from detection of said print on said paper by said sensor or sensors.
5. 5. A print removal device as claimed in any preceding claim wherein said head drive system is configured to scan said head at a rate no greater than the product of a pixel dimension in a scanning direction of said head and a frequency of operation of said laser.
6. 6. A print removal device as claimed in any preceding claim wherein said controllable laser output provides a peak laser pulse power of at least 50KW over the area of a unprinting pixel.
7. 7. A print removal device as claimed in any preceding claim wherein said head drive system is configured to scan said head in a substantially continuous boustrophedonic motion.
8. 8. A print removal device as claimed in any one of claims 1 to 7 further comprising a paper support having a slot longitudinally aligned along said scanning direction and a second said head beneath said slot, such that the device is configured to remove print from both sides of said paper simultaneously.
9. 9. A print removal device as claimed in any preceding claim further comprising an additional sensor to sense a blank line along said scanning direction, wherein a said blank line comprises a line without print on said paper; and a blank line skipping controller to control said paper feed system to skip past an identified blank line.
10. 10. A method of removing print from paper, the method comprising: providing a print removal head having a controllable optical output for removing print from paper; moving printed paper and said print head relative to one another in a first direction; scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; scanning a sensor in tandem with said print removal head in said second direction; and controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.
11. 11. A print removal device, the device comprising: a print removal head having a controllable optical output for removing print from paper; means for moving printed paper and said print head relative to one another in a first direction; means for scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; means for scanning a sensor in tandem with said print removal head in said second direction; and means for controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.
12. 12. A print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a laser output for removing print from said paper; and a particle removal system to capture nanoparticles from said removing of said print.
13. 13. A print removal device as claimed in claim 12 further comprising a head drive system to scan said print removal head over said paper as said paper is fed through the device; and wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.
14. 14. A print removal device as claimed in claim 12 or 13 wherein said particle removal system comprises a removable receptacle or bag, preferably incorporating a nanoparticle filter.
15. 15. A print removal device as claimed in claim 14 wherein said receptacle or bag has self-sealing air inlet configured to self-seal on removal of said receptacle or bag from said particle removal system.
16. 16. A print removal device as claimed in claim 16 wherein said self-sealing air inlet comprises plurality of moveable leaves configured to engage with a male member of an air duct of said particle removal system.
17. 17. A print removal device as claimed in claim 15 or 16 wherein said self-sealing air inlet is configured to engage with a male member of an air duct of said particle removal system, and wherein said male member and said self-sealing inlet each have a matching, non-symmetrical cross-sectional shape.
18. 18. A print removal device as claimed in claim 15, 16 or 17 wherein said self-sealing air inlet comprises a displaceable sealing member, configured to be displaced to open the air inlet on attachment of said air inlet to an air conduit of said particle removal system and to be displaced to close the air inlet on removal of said receptacle or bag.
19. 19. A self-sealing receptacle or bag for the print removal device of any one of claims 12 to 18, wherein said receptacle or bag has self-sealing air inlet configured to self-seal on removal of said receptacle or bag from said particle removal system.
20. 20. The print removal device as claimed of any one of claims 1 to 9 and 11, further comprising a particle removal system to capture nanoparticles from removal of said print, in particular wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.
21. 21. A print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; a point or line sensor for sensing print on said paper; means for providing relative motion between said paper and said sensor; and a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.
22. 22. A print removal device as claimed in claim 21 wherein said sensor comprises a line sensor for sensing a line of print on said paper and wherein said control system comprises a buffer to store one or more lines of sensed unprinting pixels prior to said line of print arriving at said print removal head.
23. 23. A print removal device as claimed in claim 21 or 22 wherein said control system is configured to control said paper feed system responsive a signal from said sensor to skip past a blank line on said paper.
24. 24. The print removal device as claimed in claim 21, 22 or 23, further comprising a particle removal system to capture nanoparticles from removal of said print, in particular wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.