Background

[0001] Print medium advance sensors are used in printers to track print medium advance. Some low-cost print medium advance sensors are temperature-sensitive and prone to error when operating in temperature conditions that differ from a reference temperature corresponding to an initial calibration of the sensor. As a result, printing quality may suffer at temperatures different from the reference temperature.

Description of Drawings

[0002] The following detailed description will best be understood with reference to the drawings, wherein:

[0003] Fig. 1 shows a schematic diagram of a printer according to an example;

[0004] Fig. 2 shows a schematic diagram of a print medium advance controller according to an example;

[0005] Fig. 3 shows a flow diagram of a method of measuring print medium advance in a printer according to an example; and

[0006] Fig. 4 shows a schematic diagram illustrating predefined compensation relations between raw print medium advance values and compensated print medium advance values according to some examples.

Description of Examples

[0007] Fig. 1 shows a schematic diagram of a printer 10 according to an example. The printer 10 may be, may include, or may be part of a desktop printer, a large format printer, a plotter or the like, for example. The printer 10 may be a 2D printer or a 3D printer. The printer 10 may be an inkjet printer.

[0008] The printer 10 may print a print medium 14 with a printing fluid. In the example described, the printing fluid may be an ink, such as a black or color ink, including CMYK inks, and white ink. The ink may be a latex ink or another type of ink. In other examples, the printing fluid can be a type of conditioning fluid used in inkjet type printers, including 2D and 3D printer.

[0009] In the example described, the print medium 14 may a printable material, which can be a sheet-like material, such as paper, cardboard, plastic, fabric or the like. The printer 10 may comprise at least one printheads 12 to print the print medium 14. Each of the printheads 12 may comprise a corresponding plurality of printing nozzles to fire the printing fluid on the print medium 14. According to some examples, the printer 10 may be configured to print a print medium 14 having a width from 50 cm to 500 cm, preferably from 61 cm (24 inches) to 320 cm (126 inches).

[0010] The at least one printhead 12 may print the print medium 14 in a print zone 16 of the printer, which may be defined as a region of the printer in which the print medium 14 may be printed by the at least one printheads 12. The at least one printheads 12 may be arranged in a movable carriage, which may be movable in a carriage movement direction, which may be perpendicular to a print medium advance direction A in which the print medium 14 may advance during a printing process. This may allow the at least one printhead 12 to print the print medium 14 over a width of the print medium 14 or over a portion thereof.

[0011] According to some examples, the print zone 16 may comprise or may correspond to a vacuum system (not shown) used to maintain an arrangement of the print medium 14 in a plane corresponding to the advance direction A by means of a vacuum.

[0012] The print medium 14 may move through the printer 10 in the print medium advance direction A, for example conveyed by a print medium conveyor 18 of the printer 10. The print medium conveyor 18 may comprise a motor to convey the print medium 14 in the print medium advance direction A, such that the print medium 14 is moved with respect to the printer 10 in order to be printed. The print medium conveyor 18 may comprise rolling elements, a conveyor belt, a stepper motor and the like. The print medium conveyor 18 may move the print medium 14 to be printed with respect to the printer 10 in the advance direction A so that different longitudinal regions of the print medium 14 can be printed by the printheads 12 in the print zone 16, as the print medium 14 moves in the advance direction A.

[0013] The printer 10 comprises a print medium advance controller 100, an example of which is separately shown in Fig. 2. The print medium advance controller 100 may be hardware-based or software-based. The print medium advance controller 100 may be integrated within the printer 10, as in the example shown in Fig. 1 , or may be arranged as an external component connected to the printer.

[0014] The print medium advance controller 100 may comprise a print medium advance sensor 110 configured to provide a row print medium advance value corresponding to an advance movement of the print medium 14 in the advance direction A of the printer 10. The print medium advance sensor 110 may be configured as a rotatable sensor, which may be in direct contact with the print medium 14 and configured such that when the print medium 14 moves in the advance direction A, this movement causes a corresponding rotation of the print medium advance sensor 110.

[0015] The print medium advance sensor 110 may be or comprise a rolling element arranged in contact with the print medium 14. According to some examples, the print medium advance sensor 110 may be or comprise a rotary encoder. According to some examples, the print medium advance sensor 110 may also be involved in driving in advance movement of the print medium 14 in the advance direction A. The rolling element may be in direct contact with the print medium 14. The print medium advance sensor 1 10 may provide the raw print medium advance value based on a rotation of the rolling element caused by an advance movement of the print medium 14.

[0016] The print medium advance controller 100 may further comprise a processor 130 containing executable instructions which, when executed by the processor 130, cause the processor 130 to obtain from the print medium advance sensor 110 a raw print medium advance value corresponding to an advance movement of the print medium 14 according to an initial calibration relation between movements of the print medium advance sensor 110 and movement of the print medium 14 in the advance direction A. Said original calibration relation may have been provided to the processor 130 by a manufacturer of the printer, for example as part of an manufacturing or calibration process of the printer 10 in a manufacturing line thereof. The original calibration relation may be stored in a storage device 140, which may be comprised in the print medium advance controller 100 or connected thereto, in particular to the processor 130.

[0017] According to an example, the initial calibration relation may for example determine that a rotation of the print medium advance sensor 110 by an angle a, for example a=180°, corresponds to a given translation x of the print medium 14 in the advance direction A, for example x=30 mm.

[0018] The processor 130 may be configured to obtain from the print medium advance sensor 110 said raw print medium advance value.

[0019] As a consequence of temperature variations in the print zone 16 of the printer 10, a real relation between movements of the print medium advance sensor 110 and movements of the print medium 14 in the advance direction A may deviate from the original calibration relation. For example, the original calibration relation may have been defined for a temperature of the print zone 16 of 25°C, and at a given point in time, the printer 10 may be operating with a temperature in the print zone 16 anywhere from 15°C to 35°C. This may for example be due to thermally induced variations in a diameter of a rolling element of the print medium advance sensor 110. This may cause malfunctioning of the printer 10 due to wrong assumptions by the processor 130 as to the relative position of the print medium 14 with respect to the at least one print head 12 and may result in printing misalignment. For example, with temperature changes, the processor 130 may assume, when relying on the initial calibration relation, an advance of the print medium 14 in the advance direction, that is actually different from a real advance of the print medium 14.

[0020] To address this issue, the processor 130 may be configured to obtain a temperature value and to determine a compensated print medium advance value for the raw print medium advance value based on the temperature value and on a corresponding predefined compensation relation between raw print medium advance values and compensated print medium advance values for a temperature corresponding to the temperature value.

[0021] One or more of such predefined compensation relations may be stored in the printer 10, for example stored in the storage device 140 of the printer medium advance controller 100. Each predefined compensation relation may reflect a pre-computed relation between raw print medium values and real (compensated) print medium advance values for a corresponding temperature.

[0022] According to some examples, the storage device may store a first predefined compensation relation corresponding to a first temperature, for example of 15°C, a second predefined compensation relation corresponding to a second temperature, for example of 20°C, a third predefined compensation relation corresponding to a third temperature, for example of 25°C, a fourth predefined compensation relation corresponding to a fourth temperature, for example of 30°C, and a fifth predefined compensation relation corresponding to a fifth temperature, for example of 35°C. The number of predefined compensation relations stored in the storage device 140 may be greater than five and may be adapted to a desired level of printing accuracy. One of the predefined compensation relations stored in the storage device 140 may correspond to the initial calibration relation.

[0023] Each predefined compensation relation may be determined via measurement, for example by a manufacturer of the printer 10, under controlled temperature conditions. According to some examples, each of the predefined compensation relations may comprise a corresponding lookup table or a corresponding mathematical function, for example a non-linear function.

[0024] Each of the predefined compensation relations may link to each raw print medium advance value, for a corresponding temperature value, a corresponding compensated print medium advance value. Thus, different predefined compensation relations corresponding to different temperature values may relate one same raw print medium advance value to different respective compensated print medium advance values.

[0025] The processor 130 may choose the predefined compensation relation to be used among a plurality of available predefined compensation relations based on the temperature value.

[0026] The print medium advance controller 100 may further comprise a temperature sensor 120 configured to provide the temperature value to the processor 130. The temperature sensor 120 may be arranged close to the print medium advance sensor 110, for example within the print zone 16, such that the temperature value provided by the temperature sensor 120 may correspond to a temperature of operation of the print medium advance sensor 110 or to a temperature in the print zone 16. The temperature sensor 120 may be configured to measure the temperature of air surrounding the print medium advance sensor 110 and to provide the temperature value corresponding to such measured temperature.

[0027] According to some examples, the processor 130 may be configured to obtain the temperature value during a begin of print job process or during a print job process performed by the printer 10.

[0028] The temperature value obtained by the processor 130 and used to obtain the compensated print medium advance value may correspond to a temperature difference between a temperature of operation of the print medium advance sensor 1 10, for example measured by the temperature sensor 120, and a reference temperature. The reference temperature may correspond to a temperature for which the initial calibration relation was designed.

[0029] Fig. 3 shows a schematic flow diagram of a method 200 of measuring print medium advance in a printer according to an example. The method may be a computer-implemented method, for example implemented by the processor 130 of the print medium advance controller 100 of the printer 10 shown in Figs. 1 and 2. The method 200 may be implemented at a user end.

[0030] At 204, the temperature value T is obtained. The temperature value T may be provided by the temperature sensor 120 and may correspond to a temperature of operation of the print medium advance sensor 1 10. The temperature value T may be obtained as a measurement by the temperature sensor 120.

[0031] At 206, a raw print medium advance value X is obtained. The raw print medium advance value X may be provided by the print medium advance sensor 110 based on an initial calibration relation, which may be stored in the storage device 140. The initial calibration relation may have been the find for a given reference temperature. The raw print medium advance value X may be obtained as a measurement by print medium advance sensor 110.

[0032] At 208, the processor 130 determines a compensated print medium advance value X’ as a function of the temperature value T and of the raw print medium advance value X. This may comprise choosing, based on the temperature value T, one of a plurfality of predefined compensation relations that may be stored in the printer 10, in particular in the storage device 140, and determining the compensated print medium advance value X’ corresponding to the raw print medium advance value X according to the chosen predefined compensation relation X’=f(X,T).

[0033] The method 200 may be performed depending on the fulfilment of a condition 202. For example, stages 204-208 may be performed in predefined time intervals, such as every 1 , 10, 20, 30, 60 or 120 minutes, or every time the printer 10 performs a printing process. According to some examples, the method 200 may be performed or repeated when the obtained temperature value T differs from a reference temperature value by at least a predetermined temperature threshold. The method 200 may be performed when the obtained temperature value T differs from the reference temperature value, for example from a reference temperature value of 25°C, by 5°C or more, i.e., when the obtained temperature value T corresponds to a temperature below 20°C or above 30°C.

[0034] According to some examples, the method 200 may be performed during a begin of print job process or during a print job process performed by the printer 10.

[0035] The processor 130 may provide the compensated print medium advance value without using any optical sensors.

[0036] According to some embodiments, the predefined compensation relations may define corrections of the initial calibration relation.

[0037] Fig. 4 shows predefined compensation relations between raw print medium advance values and compensated print medium advance values for different temperatures over a range from 15°C to 35°C, represented along the horizonal axis. The values of the vertical axis of Fig. 4. correspond to respective ratios between a raw print medium advance value determined by the print medium advance sensor 110 and a real advance of the print medium 14 in the advance direction 14, both quantities being expressed in mm. The values of the real advance of the print medium may have been experimentally measured under controlled temperature conditions, for example during a development or manufacturing process of the printer 10.

[0038] The processor 130 may obtain, for a given raw print medium advance value, the corresponding compensated print medium advance value by using a predefined compensation relation like the compensation relation shown in Fig. 4. However, other compensation relations, possibly more complex, may be used in other related examples. [0039] According to the example shown in Fig. 4, for a temperature of 25°C, a compensation relation between the raw print medium advance values and the compensated print medium advance values corresponds to an initial calibration relation, for which the ratio between the raw print medium advance values determined by the print medium advance sensor 110 and the real advance of the print medium 14 in the advance direction 14 is 1. In other words, the initial calibration relation is reliable for a temperature of 25°C.

[0040] For a temperature of for example 17°C, a corresponding compensation relation between the raw print medium advance values and the compensated print medium advance values defines that the raw print medium advance value must be compensated with a factor 1/1 .008. Thus, for a raw print medium advance value of 1 mm, the compensated print medium advance value at a temperature of 17°C may be 0.992 mm. This may imply that, without the compensation, the print medium advance sensor would be measuring an advance of the print medium greater than a real advance of the print medium possibly due to a thermally induced reduction in a diameter of a rolling element of the print medium advance sensor 110.

[0041] For a temperature of for example 31 °C, a corresponding compensation relation between the raw print medium advance values and the compensated print medium advance values defines that the raw print medium advance value must be compensated with a factor 1/0.994. Thus, for a raw print medium advance value of 1 mm, the compensated print medium advance value at a temperature of 17°C may be 1 ,006 mm. This may imply that, without the compensation, the print medium advance sensor would be measuring an advance of the print medium smaller than a real advance of the print medium possibly due to a thermally induced increase in a diameter of a rolling element of the print medium advance sensor.

[0042] The method 200 and the print medium advance controller 100 according to the presently discussed examples allow automatically compensating measurements performed by the print medium advance sensor 110 based on temperature values, thereby providing a better calibration of the print medium advance sensor adjusted to real printing conditions and thereby allowing for better printing quality and improved robustness, in particular despite temperature variations and without the intervention of a user.

[0043] Advantageously, the method 200 may be used in combination with a relatively simple print medium advance sensor 110, since the method 200 may allow compensating thermally-induced errors to which the print medium advance sensor 110 may otherwise be prone, in particular offline and/or in real time. As a result, manufacturing costs with respect to the print medium advance sensor 110 can be reduced and the printer 10 can be manufactured with increasing printing accuracy without substantially increasing manufacturing costs.

[0044] Further, the method 200 and the print medium advance controller 100 allow reducing waste of print medium and print fluid, since the compensated print medium advance values can be obtained without dedicating print medium or print fluid to printing calibration plots. Additionally, down-time of the printer 10 due to maintenance tasks can be reduced and an overall user experience can be improved.

[0045] The description is not intended to be exhaustive or limiting to any of the examples described above. The printer, method and user interface disclosed herein can be implemented in various ways and with many modifications without altering the underlying basic properties. The methods and user interface can be implanted in a printer as shown in Fig. 1 , including variations of that printer and other types of printers, as outlined above. Moreover, the aspects of the printer, the methods and the user interface described herein can be combined, in total and in part, and can be modified within the scope of the following claims.