BACKGROUND

[0001] In some printing systems, a detector arrangement is used to detect light reflected from a surface of a substrate to be printed in order to perform measurements and/or calculations. For example, the arrangement may often be used for detecting the edge of the substrate, or for aligning printheads in the printing apparatus. In the present disclosure such optical detector may also be used to detect possible printing fluid leakages.

[0002] Several issues may trigger a printing fluid leakage, for example, a lack of proper cleaning of a printhead may cause a partial block of nozzles that, in turn, may increase the internal pressure of the printhead and printing fluid may leak from the printhead from its lateral walls. Also, failed pressure regulators or mechanical bumps may trigger such printing fluid leakages. Printing fluid leakages usually results in media waste and may cause damage to other elements of the printing system.

BRIEF DESCRIPTION OF DRAWINGS

[0003] Examples will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0004] Figure 1 is an example schematic of a printing system including leak monitoring;

[0005] Figure 2 is a printing system according to an example;

[0006] Figure 3 is a schematic figure illustrating the measurements obtained by an example leakage sensor of a printing system;

[0007] Figure 4 is a flowchart illustrating an example leak detection method; and

[0008] Figure 5 is a simplified schematic of an example of a machine-readable medium and a processor.

DETAILED DESCRIPTION [0009] In some print systems, printing fluid, such as ink, may be deposited from a printing fluid distributor, also referred to as a printhead, onto a printable substrate, such as paper, cardboard, plastics material, glass, latex and the like. In some examples, a print system may include multiple printheads, for example one printhead for each color of printing fluid that it prints. In one example, a print apparatus may be capable of printing four colors (e.g. cyan, magenta, yellow and black) and may, therefore, include four printheads. Print systems may, in other examples, include a different number of printheads. Each printhead may be referred to with reference to the color of printing fluid (for example, ink) that it deposits. For example, a print system may include a cyan printhead, a magenta printhead, a yellow printhead and a black printhead. Some print apparatuses may include a printhead capable of printing white ink onto a substrate; this may be referred to as a white printhead. The print system may, in some examples, include an additive manufacturing apparatus for generating three-dimensional objects by forming layers of build material on a print bed. In such examples, the printing fluid may comprise build material, fusing agents, detailing agents or the like.

[0010] The printhead(s) may, in some examples, be housed or located within a carriage of the print system. The carriage may reciprocate over the substrate, along a scan axis of the print system. For example, the carriage may move over the width of the substrate, or over a region of the substrate (e.g. a printable region). The printheads may deposit printing fluid in a controlled manner as the carriage and the printheads are moved over the substrate. In other examples, the printhead(s) and/or the carriage housing the printhead(s) may remain stationary while the substrate moves relative to the printhead(s).

[0011] A print system may include a detector arrangement or sensor arrangement for use in printing operations, or print management operations, such as printhead maintenance operations, e.g., printhead wiping and/or capping. Such a detector arrangement may include one or several light sources and a light detector or sensor for detecting light from the light sources, which has been reflected off a reference surface which may be the substrate or a surface within a service station. Such detector may be used as a printing fluid leak detector.

[0012] The printing fluid leak detector may be housed within or otherwise attached to the carriage carrying the printhead(s). Thus, the detector may move across a width of the substrate with the printhead(s). In other examples, the substrate and/or the service station may move while the detector arrangement remains stationary [0013] A surface or printing fluid of a particular color, or wavelength, reflects just light of that particular color, or wavelength; light of colors/wavelengths other than the particular color/wavelength is absorbed by the substrate or printing fluid. Therefore, light of some colors will reflect from the substrate or printing fluid to a greater extent than light of other colors. Furthermore, light of some colors is, when reflected from the surface or printing fluid, likely to be more easily distinguishable than light of other colors. Put another way, the intensity of light reflected from the surface or printing fluid of a particular color may vary depending on the color of the light used.

[0014] Therefore, it may be advantageous to reflect light of a particular color off a reference surface, depending on the color of the printing fluid that would like to be detected. The present disclosure provides a mechanism capable of determining a printing fluid leak and, also, determining the particular printing fluid color based on use of an appropriate light source to use for each different color of printing fluid, depending on the color of the substrate to be printed on.

[0015] Figure 1 is a schematic drawing illustrating an example of printing system 1000 comprising a printing fluid leak detector 112 according to the present disclosure. The system 1000 is to identify a reference surface with printing fluid in a location that, in normal conditions, would lack the presence of printing fluid, therefore, being indicative of a printing fluid leak. The printing system 1000 comprises a printing fluid distributor 111 for depositing printing fluid of a particular color onto a printable substrate. Such printing fluid distributor may also be known and referred to herein as a printhead. In some examples, the printing fluid may comprise liquid ink, toner or other non-marking fluids, such as fixers and/or optimizers.

[0016] The functions that may be performed by the leak detector 112 (i.e. , the light source 113 and the light sensor 114) may be performed at any time. In some examples, such functions may be performed before a printing operation commences. For example, a leak detection may be performed using the leak detector 112 when the carriage is located on a service station that is remote to the printable region. In particular, the leak detection may be performed using the capping station as a reference surface upon uncapping the printheads or during other servicing operations.

[0017] As discussed above, the printing system 1000 may comprise one or several light sources 113. When a plurality of light sources 113 is used, each light source 113 may emit light a particular wavelength towards the reference surface. In some examples, the light sources may comprise light emitting diodes (LEDs). The plurality of light sources 304 may, in one example, comprise four LEDs - a red LED, a blue LED, a green LED and an orange LED. Having a plurality of light sources 113 allows having measurements for different wavelengths as to ensure that printing fluid leaks of several colors of printing fluid can be detected.

[0018] The sensor 114 detects light from each of the plurality of light sources 304, which has been reflected from the reference surface. Thus, light from each light source 113 is reflected off the reference surface and detected by the sensor 114. In some examples, the plurality of light sources 113 are such that just one light source emits light at a time. The light sources 113 may, for example, emit pulses of light in a series, such that each light source emits light in turn. The sensor 114 (e.g. a photosensor) may, in some examples, comprise a diffuse sensor.

[0019] The print system 1000 further comprises processing apparatus 115. The processing apparatus 115 may be in communication with the printing fluid distributor 111 , the plurality of light sources 113, and/or the sensor 114. In some examples, the processing apparatus 115 may control or operate the printing fluid distributor 111 , the plurality of light sources 113, and/or the sensor 114. For example, the processing apparatus 115 may control the printing fluid distributor 111 of the print apparatus 300 to deposit printing fluid in an intended manner. The processing apparatus 115 may control the light plurality of light sources 113 to emit light in a controlled and intended manner. The processing apparatus 115 may communicate with the sensor 114 to receive data received by the sensor 114. The processing apparatus 115 may perform various functions of the methods that will be described with reference to figures 4 and 5.

[0020] The processing apparatus 115 may be any combination of hardware and programming to implement the functionalities described herein. These combinations of hardware and programming may be implemented in a number of different ways. In certain implementations, the programming for the processing apparatus 115, and its component parts, may be in the form of processor executable instructions stored on at least one non- transitory machine-readable storage medium and the hardware for the engines may include at least one processing resource to execute those instructions. The processing resource may form part of the printing system, or a computing device that is communicatively coupled to the printing system. In some implementations, the hardware may include electronic circuitry to at least partially implement the processing apparatus 115. For example, the processing apparatus 115 may comprise an application-specific integrated circuit that forms part of a printing device within the printing system.

[0021] According to some examples, the processing apparatus 115 is to determine, for each of the plurality of light sources 113, an intensity of light reflected from the reference surface. Thus, the processing apparatus 115 may determine the intensity of the light received by the sensor 114 that has reflected from a portion of the reference surface. The processing apparatus 115 is further to compare the measured intensity or radiation (or intensities, in the case of multiple light sources 113) to an expected intensity radiation associated to the reference surface and determining the presence of a printing fluid leakage based on the comparing, e.g., if the measured intensity is above or below an acceptable range associated to the expected intensity, a leak may be identified.

[0022] In an example, as described above the expected intensity may be a threshold intensity range. In other examples, the expected intensity may be an intensity profile associated to the reference surface, the profile may comprise a plurality of expected intensities for a plurality of carriage positions.

[0023] The radiation sources (e.g. the LEDs) and the sensor for receiving reflected radiation may be located on or in a carriage carrying the printheads. In this way, the radiation sources and the sensor can move (partially or entirely) over a width of the substrate. This provides a convenient mechanism by which the radiation source and sensor can move to different positions relative to the substrate, so that radiation from each radiation source can be directed towards and reflected from different portions of the printing system, e.g., a print zone that is to receive printable media or a service zone wherein servicing operations in a service station such as spitting, wiping and/or capping are performed. In some examples, the carriage carrying the radiation sources and the sensor may perform a pass over the reference surface while directing and detecting radiation from a first radiation source, then a further pass over the reference surface while directing and detecting radiation from a second radiation source, and so on, until radiation from each of the plurality of radiation sources has been reflected from the reference surface and detected by the sensor.

[0024] The sensor 114 to detect radiation that has been reflected from the reference surface may be any suitable sensor, such as a photosensor. In some examples, the radiation source(s) and sensor may form part of, or function as, a diffuse sensor arrangement. In a diffuse sensor arrangement, the radiation sources and the sensor may be located in the same housing or form part of the same unit. Each radiation source may emit radiation that diffuses over a range of directions. The substrate reflects part of the emitted radiation towards the sensor.

[0025] Figure 2 illustrates an example of a printing system comprising a leak detector. In the example, as shown in the upper drawing, the printing system comprises a printhead module 110 configured to reciprocate along a scan axis (not shown) in a scanning direction S. The printhead module 110 is to reciprocate between a printable zone wherein a substrate may be provided to receive the printing fluid and a service station 200 wherein maintenance or servicing operations may be performed to elements within the printhead module 110.

[0026] The middle drawing is a detail of view A-A’ of the upper drawing wherein the service station is shown in more detail from the top. As can be seen from the figure, the service station 200 comprises a spitting station 213 with a pair of spit rollers for receiving printing fluid from the printheads that is expelled for servicing purposes. Also, the service station 200 may comprise other maintenance elements such as wipers, blades, or others. The service station 200 further comprises a plurality of caps 211 for capping the printheads during inactivity periods thereby preventing the printing fluid from drying on the nozzle surface of the printheads which may possibly block the printheads.

[0027] In the present example, the service station may be used for determining possible leaks on the printheads, in particular, a capping zone 210 wherein the caps 211 are placed may be used as a reference surface for determining possible leaks of printing fluid, e.g., by performing measurements in a series of swaths by a series of measurement lines 210 at a series locations within the service station.

[0028] The bottom drawing illustrates view B-B‘ of the upper drawing wherein the printhead module 110 is shown in more detail from below. As shown, the printhead module 110 comprises a plurality of printheads 111 for ejecting printing fluid onto a printable medium as to generate an image. Each of the plurality of printheads 111 has a respecitive cap 211 on the service station 200.

[0029] Further, the printhead module 110 comprises a leakage detector 112 comprising a light source and an optical sensor. The optical sensor is to detect an intensity of radiation which has been reflected from a reference surface remote to a printing surface comprising the printable medium, and is connected to a processing apparatus (not shown). The processing apparatus receives the intensity of radiation detected by the optical sensor, determine an expected intensity radiation, for example, by pulling it from a memory resource; and determine, based on the measured intensity radiation and the expected intensity radiation, a printing fluid leakage.

[0030] In an example, the processing apparatus calculates a deviation of the measured intensity radiation from the expected intensity radiation. If the measured intensity radiation deviates from a determined value, it is indicative that a printing leak has occurred.

[0031] In a further example, the processing apparatus may have the capability to determine a color of the printing fluid leakage based on the deviation. For example, the leakage detector may comprise a plurality of light sources of different wavelengths and the sensor may measure a plurality of intensities of radiation from each the plurality of sources and, given that light is absorbed differently depending on the color that it is reflected from, based on the plurality of intensities, the processor may determine the color of the reference surface from which light is reflected. Then, if a printing fluid leak is present, the processor may determine the color of the printing fluid.

[0032] In yet another example, the leak detector may successively irradiate the reference surface with each of plurality of light sources and the sensor may measure each reflected intensity of radiation of each light source as to determine the presence of printing fluid leakage and the color of the printing fluid associated to the leakage.

[0033] In this case, the leak detector 112 may direct radiation from a plurality of radiation sources onto the patch of printing fluid and onto the reference surface. In some examples, the radiation sources may comprise light sources, such as light emitting diodes (LEDs). In other examples, other radiation sources may be used. For example, radiation sources capable of emitting ultraviolet (UV) radiation and/or infrared (IR) radiation may be used. The plurality of radiation sources may, in some examples, each emit radiation having a different wavelength or frequency and, therefore, each may appear a different color. In some examples, the plurality of radiation sources may comprise four radiation sources: a red radiation source, a blue radiation source, a green radiation source and an orange radiation source. The radiation sources (e.g. LEDs) may be such that radiation (e.g. light) from each radiation source is directed towards the substrate, and radiation reflected from the substrate can be received by a light detector or sensor. In some examples, an optical component, such as a lens, may be associated with a radiation source, or with multiple radiation sources, to aid the directing of the radiation towards the substrate in an intended manner. In a particular example, a leak of white printing fluid may be present in a printing system. Light from a plurality of light sources - for example a red LED, a blue LED, a green LED and an orange LED - is directed onto a reference surface comprising the leak of printing fluid. The sensor detects the radiation reflected from each LED in turn, and the intensity of the reflected light is measured for both: light reflected from the white leak, and light reflected from the reference surface. The difference between the intensity of light reflected from the white leak and light reflected from the reference surface may then be determined for each LED, and one of the LEDS may be selected based on the determined intensities. In some examples, the LED that corresponds to the largest difference or range between the intensities may be identified and selected. Thus, for leak detections of this particular color, the selected LED may be used, as its light, after reflecting from the white leak, is the most distinguishable (e.g. the brightest) relative to the reference surface.

[0034] Figure 3 shows measurements obtained with a leak detector according to an example of the present disclosure. In particular, figure 3 illustrates three scenarios: a first scenario 301 wherein no leak is determined in the capping station; a second scenario 302 in which a leak is present that spans a complete cap; and a third scenario 303 shows a measurement in which a leak of printing fluid is detected on the borders of a cap.

[0035] In the first scenario 301 , the measurement signal (in this case, the radiation intensity shown at the left of the figure) is taken by the leak detector as the carriage moves along a swath direction, thereby measuring along a measuring line 212.

[0036] During non-operational periods, the printhead module is normally capped in the capping station or otherwise positioned in the service station, therefore, providing a suitable reference for performing measurements to determine possible leaks on the printhead module, e.g., due to an excessive pressure therein. Back to figure 3, each printhead is associated to a respective cap 211 , 211A, 211 B, 211C, 211 D, 211 E, therefore, if a leak is detected in a determined cap, the printhead which is leaking may also be easily identified. The first scenario 301 illustrates a scenario in which no leakage of printing fluid is detected by the leak detector. In particular, the measurement at the right indicates the intensities of radiation determined by the optical sensor after an irradiation by a light source on the reference surface 210. The measurement indicates several pairs of peaks 311 A, 311 B, 311C, 311 D, 311 E corresponding to each of the measured caps 211A, 211 B, 211 C, 211 D, 211 E, i.e., the caps that are captured by the measuring line 212. [0037] Each pair of peaks corresponds to a difference in height within the reference surface but none of such peaks exceeds a threshold intensity that may be correlated to a printing fluid leakage, therefore it is within an expected intensity range.

[0038] In some examples, a measurement signal such as the one of the first scenario (without printing fluid leak) may be used as a radiation signature 311 F and may define a range of expected intensities, e.g., radiations that are within a range of 20% over or below the radiation signature are considered to be the expected intensity, a measurement exceeding the expected intensity is considered to be a printing fluid leakage.

[0039] In the second scenario 302, a leaked cap 211A’ is represented by the texture therein. In the measurement signal it is shown that a portion 311 A’ associated to the leaked cap 211 A shows a substantial increase in the measured intensity for this cap whereas all other measured caps remain within the expected intensity radiation ranges, for example, substantially unchanged with respect to the radiation signature 311 F. A processing apparatus (not shown) is to receive the measured intensity for the leaked cap 211A’ and compare it to an expected intensity which may be associated to a signature intensity or an otherwise defined threshold intensity and, based on such comparison determine that a leak has occurred over the leaked cap 211 A.

[0040] As previously discussed, there are two possibilities for determining which printhead within the printhead module may be responsible for the printing fluid leak. In a first example, the cap 211 A may be correlated to a printhead 311 that is the printhead that rests on such a cap, therefore, the printhead 311 is responsible for the printing fluid leak. In other example, the reference surface may be radiated with light sources of different intensities and based on the magnitude of the intensity received by the plurality of light sources, the color of the leaked printing fluid may be determined and may be correlated to a printhead (or a plurality of printheads, if several printheads of the same color are installed on the printing system).

[0041] The third scenario 303 shows a case in which a further leaked cap 211A” is leaked with printing fluid but only on the borders thereof. In this case, as can be seen from the measured intensity on the right, there are a pair of peaks 311A” that exceed the expected intensity.

[0042] Figure 4 illustrates an example method for determining leaks of printing fluid within a printing system. The method comprises directing 401 radiation from a radiation source onto the reference substrate. As previously explained, the radiation sources may comprise light sources, such as light emitting diodes (LEDs). In other examples, other radiation sources may be used. For example, radiation sources capable of emitting ultraviolet (UV) radiation and/or infrared (IR) radiation may be used. The plurality of radiation sources may, in some examples, each emit radiation having a different wavelength or frequency and, therefore, each may appear a different color. In some examples, the plurality of radiation sources may comprise four radiation sources: a red radiation source, a blue radiation source, a green radiation source and an orange radiation source. The radiation source may comprise a plurality of radiation elements (e.g. LEDs) and may be such that radiation (e.g. light) from each radiation source is directed towards the reference surface, and radiation reflected from the reference surface can be received by a light detector or sensor. In some examples, an optical component, such as a lens, may be associated with a radiation source, or with multiple radiation sources, to aid the directing of the radiation towards the substrate in an intended manner.

[0043] In some examples, directing radiation from a plurality of radiation sources may comprise directing radiation from each of the plurality of radiation sources in turn. For example, each radiation source may be activated (e.g. pulsed) for a short, defined period in turn.

[0044] The method further comprises detecting 402, using a sensor, radiation from the radiation source which has been reflected from the reference surface. The sensor may comprise a light detector or radiation detector as mentioned above. The sensor is to be positioned such that radiation directed from the radiation sources reflects from the substrate towards the sensor.

[0045] Further, the method comprises measuring 403 an intensity of the radiation reflected from the reference surface, i.e., a measured intensity of radiation. In some examples, the sensor may include components or functionality capable of measuring the intensity of several radiation sources when it receives the reflected radiation from each source. In other examples, the sensor may be in communication with another component (e.g. processing circuitry or a processing apparatus) to measure the intensity of the radiation received by the sensor.

[0046] Once the radiation intensity has been measured, the method includes comparing 404 an expected intensity radiation associated to the reference surface and the measured intensity of radiation from the reference surface and determining 405 based on the comparison if there is a fluid leakage.

[0047] It should be noted that, in some examples, the sensor and the radiation source are coupled to a reciprocating printing carriage and wherein the method comprises moving the carriage to the reference surface being the reference surface remote to a printing surface. For example, the reference surface may be a surface within a service station such as a capping station comprising caps for a plurality of printheads.

[0048] Moreover, the expected intensity radiation may be a threshold radiation or a range of expected radiations based on a radiation signature obtained, e.g., during a calibration routine performed in an environment without leaks. Such a radiation signature may comprise a plurality of intensity radiation points along the reference surface.

[0049] According to a further aspect, the present disclosure relates to a machine- readable medium. Figure 5 is a simplified schematic of an example of a processor 500 and a machine-readable medium 501. The processor 500 and the machine-readable medium 501 may communicate with one another. The machine-readable medium 501 comprises instructions which, when executed by the processor 500, cause the processor to perform functions associated with blocks of the method described herein. In some examples, the machine-readable medium 501 comprises instructions (e.g. light source operating instructions 502) which, when executed by the processor 500, cause the processor to operate a light source or a plurality of light sources to emit light onto a reference surface. The machine-readable medium 501 comprises instructions (e.g. measurement obtaining instructions 503) which, when executed by the processor 500, cause the processor to obtain, for the light source (or light sources), a measurement of an intensity of radiation reflected from reference surface by an optical sensor. The machine-readable medium 501 comprises instructions (e.g. leakage determining instructions 504) which, when executed by the processor 500, cause the processor to determine, based on the obtained measurements, a printing fluid leakage, e.g., by comparing the measured intensity of radiation with an expected intensity of radiation.

[0050] In an example, the machine-readable medium 501 may comprise instructions to cause the processor to determine a deviation between the measured intensity of radiation and an expected intensity of radiation which may be, e.g., an intensity of radiation exceeding a pre-determined threshold value or a deviation from a pre-defined radiation signature and, based on the determination, determining a printing fluid leakage color. [0051] Also, the machine-readable medium 501 may comprise instructions to, before operating the light source, instructing to move a carriage comprising the light source, the optical sensor and a plurality of printheads towards the reference surface being the reference surface, e.g., a surface within the service station such as the capping station.

[0052] Examples in the present disclosure can be provided as methods, systems or machine-readable instructions, such as any combination of software, hardware, firmware or the like. Such machine-readable instructions may be included on a computer readable storage medium (including but is not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0053] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the flows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions.

[0054] The machine-readable instructions may, for example, be executed by a general-purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine-readable instructions. Thus, functional modules of the apparatus and devices may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term ‘processor’ is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors.

[0055] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0056] Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices realize functions specified by flow(s) in the flow charts and/or block(s) in the block diagrams.

[0057] Further, the teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure.

[0058] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above- mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims. Features described in relation to one example may be combined with features of another example.

[0059] The word “comprising” does not exclude the presence of elements other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0060] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.