Patent Application
20220001675
Dye sublimation printers may print on a medium using a printhead with heating elements. The printhead may heat up, causing dye or other printing materials to evaporate and be absorbed by or deposited on the medium. The amount of heat generated may affect the amount of dye printed to the medium. For example, when using a yellow dye, a higher heat may result in a darker yellow on the medium.
Various examples will be described below referring to the following figures:
Dye sublimation printers may experience thermal smear due to thermal energy accumulation. While there may be a delay between printing rows of an image, the delay may be insufficient for the printhead or heating elements to diffuse their heat to the environment. When printing subsequent rows, there may be a thermal energy accumulation based on the printing of prior rows. This may cause subsequent rows to be printed more darkly. For example, when attempting to print a uniform block of color, the later-printed rows may be darker due to the accumulated thermal energy of prior rows being added to the heat generated by the heating elements of the printhead. When transitioning from printing a dark section of an image to a lighter section, the accumulated thermal energy may also cause the initial rows of the lighter section to be printed more darkly, eventually reaching the proper shade of color as the heat diffuses and the heating elements reach a lower temperature.
Calculating an estimated thermal energy accumulation during printing may allow for correction of the heating of heating elements when printing subsequent rows. A long-term thermal energy accumulation and a short-term thermal energy accumulation may be calculated, combined together, and used to modify the amount of heat to be generated by the heating elements. The thermal energy accumulations may be calculated on-the-fly while printing the image. The thermal energy accumulations may use scaled running totals or be based on a select set of data points in order to limit the use of memory and computation time.
Heating the heating element may cause evaporation of a dye and absorption of the dye by a medium to print the first pixel. The heating element, printhead, or printing environment may retain thermal energy from the heating of the heating element to print the first pixel. The heat from heating the heating element to print the second pixel may be added to the retained thermal energy, affecting the amount of dye absorbed in printing of the second pixel. The thermal energy may be accumulated after printing the second pixel and affect the printing of subsequent pixels. Such an effect may be corrected by calculating an estimated thermal energy accumulation and controlling the heating element based on the estimated thermal energy accumulation.
In various examples, a heating element may be heated by receiving a pulse wave, the number of pulses controlling the heat generated by the heating element. Based on an accumulated thermal energy in printing the first pixel, the number of pulses sent to the heating element may be adjusted to generate a corrected amount of heat. The adjustment may be to reduce the number of pulses.
In various examples, the number of pulses provided to the heating element may be increased or decreased based on a temperature of the printhead. The printhead may be preheated to reach an operational temperature. The printing may be paused between printing of images to allow dissipation of the temperature. If printing a light image, the number of pulses provided may be increased to account for dissipation of heat that may place the printhead outside an operational temperature range during printing.
The controller 220 may be coupled to the memory 230 and the row of heating elements 210, such as via a bus. The controller 220 may comprise a microprocessor, a microcomputer, a microcontroller, a field programmable gate array (FPGA), or discrete logic. The controller 220 may execute machine-readable instructions that implement the methods described herein.
The memory 230 may include a hard drive, solid state drive (SSD), flash memory, electrically erasable programmable read-only memory (EEPROM), or random access memory (RAM). The memory 230 includes control heating element instructions 240 and calculate thermal energy instructions 250. The calculate thermal energy instructions 250 may cause the processor to calculate an estimated thermal energy accumulation during printing. The control heating element instructions 240 may control the amount of heat generated by the heating elements in the printing process, which may be modified based on the estimated thermal energy accumulation. The instructions 240, 250 may be for execution by the controller 220.
The apparatus 200 may include a dye sublimation printer. The row of heating elements 210 may be part of a printhead. The apparatus 200 may include other elements, such as a motor to move the medium across the printhead, a pump to provide a flow of dye to the printhead, or color ribbons to provide dye for transfer to the medium.
A heating element 212, 214, 216 may include a resistor through which an electrical signal flows to heat up the resistor. The electrical signal may include a voltage pulse wave. When the voltage is high, the resistor may heat up. Control of the number of pulse waves sent to the resistor within a specific duration of time may control the heating of the heating element. A larger number of pulse waves may cause the heating element to generate a higher heat. In various examples, the duty cycle, current value, or voltage value of the pulse wave may be controlled.
In various examples, the apparatus 200 may print using multiple dyes, such as magenta, cyan, yellow, and black dyes. The different colors may be printed using different color ribbons. Different color ribbons may be used to provide different darkness of colors, such as a dark yellow and a light yellow color ribbon, which may improve the range or quality of printed colors. The apparatus 200 may implement a single-pass or multi-pass solution to print using the multiple dyes. The apparatus 200 may include multiple rows of heating elements 210 to print using the different dyes.
Calculating thermal energy accumulation may include calculating a short-term thermal energy accumulation and calculating a long-term thermal energy accumulation, which may be combined. A short-term thermal energy accumulation includes the thermal energy accumulated along a heating element and its adjacent heating elements during printing of the last few rows of pixels. The number of rows of pixels considered may vary with specific implementations. Additional heating elements beyond the directly adjacent heating elements may be considered in estimating a short-term thermal energy accumulation. In various examples, the short-term thermal energy accumulation may consider the directly adjacent heating elements for the last five rows of printed pixels.
A long-term thermal energy accumulation includes one specific heating element and the accumulated thermal energy since beginning the printing of an image. The long-term thermal energy accumulation may be calculated across the printing of multiple images.
In various examples, thermal energy accumulations, including a long-term thermal energy accumulation and a short-term thermal energy accumulation, may be calculated for the various heating elements 212, 214, 216 in the row of heating elements. For example, the long-term thermal energy accumulation for heating element 212 may be different from the long-term thermal energy accumulation for heating element 214, as the heating elements 212, 214 may have been heated by different amounts during printing of an image. While the two heating elements 212, 214 may consider heating of the other heating element 212, 214 as part of calculating the short-term thermal energy accumulation, the thermal energy accumulations may be different and lead to different adjustments in the control of the heating elements 212, 214. This may be because the short-term thermal energy accumulation calculation for heating element 214 accounts for heating of heating element 216, which may not be used to calculate the short-term energy accumulation of heating element 212.
In various examples, apparatus 200 may include a temperature sensor, such as a thermistor. The thermistor may measure an ambient temperature of the environment, a temperature of the medium, a temperature of the printhead, or another temperature related to the printing process. The control of the row of heating elements 210 may be based on the temperature measured by the temperature sensor. The temperature may be used in calculating the accumulated thermal energy, such as modifying the diffusion rate during pauses based on the ambient temperature.
In various examples, the calculation of the thermal energy accumulation may be based on the time between printing rows of pixels. The amount of heat diffused may vary depending on the length time between printing the rows, as there may be a pause in sending pulses to the heating elements of the printhead.
The row including pixel 350 may be the first row of an image 300 being printed. The row including pixel 375 may be the current row of the image 300 to be printed. The estimated thermal energy accumulation for the heating element printing column 320 pixels may be calculated. The estimated thermal energy accumulation may include a long-term thermal energy accumulation and a short-term thermal energy accumulation.
The long-term thermal energy accumulation may be calculated as indicated by arrow 377. The heat values used in printing pixels 350, 370, 371, 372, 373, 374 may be combined to determine a long-term thermal energy accumulation. The heat values may be based on the number of pulses provided to the heating element or an intensity of the pixel. One example equation for calculation of a long-term thermal energy accumulation may be:
In the equation above showing an example of calculating a long-term thermal energy accumulation, a indicates the column of the pixel to be printed, and b indicates the row of the pixel to be printed. T indicates the long-term thermal energy accumulation at the specified column and row position. D indicates the amount of thermal energy diffusion to the environment based on pauses between sending the pulses to the heating element or between printing the rows of pixels. I indicates the intensity of the pixel being printed at the current position. The intensity may be represented by the number of pulses sent to the heating element. M indicates the midpoint, where the pixel being printed stops absorbing energy from the thermal energy of the printhead and starts adding to the thermal energy of the system. Printing of higher intensities may add exponentially more thermal energy accumulation. For example, when the intensity is represented as an 8-bit number indicating the number of pulses sent to the heating element, the midpoint may be the value 128, for half the potential number of pulses. Depending on the particular printer, the M value used may differ from half the number of pulses, as the printing may begin adding thermal energy at a higher or lower number of pulses. The M value may be determined empirically through testing. The M value may be determined as part of a calibration or self-calibration procedure. S indicates a scaling factor to be used.
Using such an equation, the long-term thermal energy accumulation for a specific heating element may be stored as one number and updated as the pixels are printed. Tracking the long-term thermal energy accumulations across a row of 1,256 heating elements may use 1,256 numbers. For example, before printing pixel 350, the long-term thermal energy accumulation may be zero, as no prior pixels were printed in the image 300. After printing pixel 350, the long-term thermal energy accumulation may be calculated based on the intensity (I) and midpoint (M) of pixel 350 and the scaling factor. Absent a prior printed row of pixels, the long-term accumulated thermal energy for this heating element from the prior row (Ta(b−1)) and the amount of diffusion (D) may be considered zero. After printing pixel 370, the long-term thermal energy accumulation may be calculated by using the long-term thermal energy accumulation calculated after printing pixel 350 as the long-term thermal energy accumulation for the prior row (Ta(b−1)). The intensity (I) and midpoint (M) values for pixel 370 may be used to finish the equation, resulting in an updated long-term thermal energy accumulation. This produces a running, scaled average of the thermal energy added by the printing of pixels by a specific heating element. Thus, the long-term thermal energy accumulation prior to printing pixel 375 may be based on the thermal energy accumulated from the prior printing of pixels 350, 370, 371, 372, 373, 374 by the specific heating element.
In various examples, corner cases may be handled, such as if the image 300 includes light sections, so that the thermal energy diffusion (D) is able to sufficiently diffuse the long-term thermal energy accumulation, comparable to the calculations for pixel 350, where there may not be a long-term thermal energy accumulation from a prior row.
In various examples, the intensity (I) and midpoint (M) values may be based on the number of pulses to be provided in printing a pixel. These values may be scaled as appropriate.
The short-term thermal energy accumulation may be calculated by combining the thermal energy accumulated from printing of the last five pixels 370, 371, 372, 373, 374 by the specific heating element and the last five pixels 360, 361, 362, 363, 364, 380, 381, 382, 383, 384 printed by its neighboring heating elements. This may be due to bleed effects as the heat generated by one heating element bleeds over to its neighboring heating elements. This can be seen in
One example equation for calculating a short-term thermal energy accumulation may be:
In the equation above, T indicates the short-term thermal energy accumulation, a indicates the column of the pixel to be printed, and b indicates the row of the pixel to be printed. Σ indicates a summation, in this case from 1 to 5 to do a scaled average based on the intensities of the five recently printed pixels for a particular column. M indicates the midpoint. I indicates the intensity of the pixel printed at the column and row position. Sn indicates a scaling factor. The scaling factor may be different for the different prior rows of pixels, giving more weight to recently printed pixels. The scaling factor may also be different for the three summations.
Using the above short-term thermal energy accumulation equation as an example, the short-term thermal energy accumulation may be calculated by adding together a scaled average of the five most-recently printed pixels 360, 361, 362, 363, 364 in the column to the left, a scaled average of the five most-recently printed pixels 370, 371, 372, 373, 374 in the current column, and a scaled average of the five most-recently printed pixels 380, 381, 382, 383, 384 in the column to the right.
In various examples, a larger or smaller number of recently printed pixels may be used. For example, one set of pixels from the prior row may be used, instead of sets of pixels from the five prior rows.
The long-term thermal accumulation and short-term thermal accumulation may be scaled and added together into an estimated thermal accumulation. The number of pulses to send to the heating element to print pixel 375 may be adjusted based on the estimated thermal accumulation.
In various examples, the intensity of the pixel to be printed may be modified based on the short-term thermal energy accumulation. For example, an equation such as the following equation may be used:
I
modified
=I−(Aa−1−M)S1−(Aa−M)S2−(Aa+1−M)S3
In the equation above, Imodified indicates a modified intensity value to use in printing the pixel 375. I indicates the original intensity value for printing the pixel 375. A indicates a moving average of the thermal energy accumulation from printing the last few pixels for a specific column, where Aa is the column containing pixel 375, and Aa−1 and Aa+1 are for the columns to either side. S indicates scaling factors that may be used, which may be different for the different columns. For example, S2 for the column containing pixel 375 may be weighted more heavily. M indicates a modification for the midpoints of the printed pixels. Imodified may be modified by the calculated long-term thermal energy accumulation, or Imodified may be converted into a pulse wave or number of pulses, that is modified by the long-term thermal energy accumulation.
While certain variables, such as I, S, and M were used in the different equations, their values may be different in the different equations. For example, the M may be different for calculating the intensity, as it is accounting for a running average of multiple pixels, while it may account for one pixel when calculating the short-term thermal energy accumulation. The specific equations mentioned here are examples to assist with the explanation, and other equations may be used or may be more convenient in calculating the intensities or thermal energy accumulations.
In various examples, the thermal energy accumulations, including short-term and long term accumulations, may be updated during the printing process. For example, after printing pixels 360, 370, 380 the thermal energy accumulations may be calculated or updated for the respective heating elements. After printing pixels 361, 371, 381, the thermal energy accumulations may be calculated or updated again for the respective heating elements. This may be performed as the rows of pixels are printed in order to correct printing of the next row of pixels based on the accumulated thermal energy at various heating elements. The thermal energy accumulations may be updated based on the prior thermal energy accumulations and the number of pulses provided as new pixels are printed.
Calculating the estimated thermal energy after this fashion may utilize less memory or computation power than other methods. The long-term thermal energy accumulation may use one data value for a heating element that is kept current during the printing process. The short-term thermal energy accumulations may store five data values for a heating element, or some other number of prior pixels, as the data values may be shared with neighboring heating elements.
Calculating the estimated thermal energy accumulation may include calculating a short-term accumulated thermal energy and a long-term accumulated thermal energy. The long-term accumulated thermal energy may be based on a running, scaled average indicating the heat generated by a heating element when printing prior pixel rows of the image. The long-term accumulated thermal energy may include thermal energy accumulated across images, such as when images are printed back-to-back.
The short-term accumulated thermal energy calculations may include calculating a scaled average indicating the heat generated by a heating element and additional heating elements on either side. The short-term accumulated thermal energy calculation may calculate such a scaled average for the last row or printed pixels or for a larger number of rows.
The above discussion is meant to be illustrative of the principles and various examples of the present disclosure. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/024945 | 3/29/2019 | WO | 00 |
