Image forming apparatus and recording method

Abstract

To enhance a color optical density of a secondary color in a recording medium having three or more color development layers.SOLUTION: A printing head is controlled by changing a ratio of heat energy that is applied by N-printing heads to each of predetermined areas to total amounts of heat energy that is applied by the N-printing heads to the predetermined areas, in accordance with a combination of color development layers in which the N-printing heads develop colors for a predetermined area of an imaging member on the basis of image data.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and a recording method. [Background technology]

[0002] Up until now, in recording with a thermal printhead, monochrome printing using thermal paper and color printing using an ink ribbon have been widely used. Meanwhile, in recent years, color recording using paper equipped with multiple color developing layers has been proposed and has become widespread as a simple means of printing photographs, etc. The multiple color developing layers each require different heating temperatures and heating times to develop color, and a color image is recorded by utilizing these differences to develop a specific color developing layer (see Patent Documents 1 and 2).

[0003] Furthermore, Patent Document 3 discloses that in order to print high gradation black data at high density, a printing medium is heated twice using two thermal heads. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2013-506582 [Patent Document 2] Patent No. 4677431 [Patent Document 3] JP 2010-201693 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the methods of Patent Documents 1 and 2, in secondary colors in which the topmost and bottommost layers of three or more color-producing layers are simultaneously produced, the middle layer prevents erroneous color production, so the topmost and bottom layers cannot be heated sufficiently, resulting in a problem of low color production density of the secondary colors.

[0006] In addition, in the method of heating the same color-forming layer described in Patent Document 3 twice, the color density of the secondary color cannot be increased.

[0007] The present invention has been made in view of the above problems, and an object thereof is to increase the color density of secondary colors in a recording medium having three or more color-forming layers.

Means for Solving the Problems

[0008] The present invention includes a first printing head and a second printing head arranged in a first direction that apply thermal energy to an image member having M (M≧3) color-forming layers each having different color-forming characteristics and coloring in response to the applied thermal energy, N (2≦N<M) printing heads, moving means for relatively moving the image member and the printing heads in a direction intersecting the first direction, RBG data control means for controlling each of the N printing heads based on image data to apply thermal energy from the printing heads to the image member, The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, The control means changes the ratio of the thermal energy applied to a predetermined region of the image member by each of the N printing heads to the total amount of thermal energy applied to the predetermined region by the N printing heads according to the combination of the color-forming layers that the N printing heads cause to color in the predetermined region of the image member based on the image data the control means controls the first print head and the second print head so that the yellow color-forming layer is colored by applying more thermal energy from the second print head than from the first print head, and the cyan color-forming layer is colored by applying more thermal energy from the first print head than from the second print head, and the control means controls the first print head and the second print head so that, when the R, G, B values ​​of the image data satisfy R>G and R>B, the magenta color-forming layer is colored by applying more thermal energy from the second print head than from the first print head, and, when the R, G, B values ​​of the image data do not satisfy R>G and R>B, the control means controls the first print head and the second print head so that the magenta color-forming layer is colored by applying more thermal energy from the first print head than from the second print head. and is characterized by doing so.

Effects of the Invention

[0009] According to the present invention, the color density of secondary colors can be increased in a recording medium having three or more color-forming layers.

Brief Description of the Drawings

[0010] [Figure 1] It is a diagram for explaining an image member according to a first embodiment. [Diagram 2] It is a diagram for explaining the color-forming characteristics in the image member according to the first embodiment. [Diagram 3] It is a diagram for explaining a configuration example of a printing head according to the first embodiment. [Figure 4] 1 is a diagram showing a cross-sectional configuration of an image forming apparatus according to a first embodiment. [Diagram 5] 1 is a diagram illustrating an example of a system configuration according to a first embodiment. [Figure 6] FIG. 4 is a sequence diagram of a print service according to the first embodiment. [Figure 7] FIG. 1 is a diagram for explaining a configuration of a conventional heating pulse. [Figure 8] FIG. 4 is a diagram showing distribution of heating pulses to two rows of heads according to the first embodiment. [Figure 9] 4 is a flowchart of a process during image formation according to the first embodiment. [Figure 10] 13 is a diagram showing the distribution ratio of heating pulses to two rows of heads according to the second embodiment. FIG. [Figure 11] FIG. 11 is a diagram showing distribution of heating pulses to two rows of heads according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] This embodiment will be described in detail below.

[0012] <First embodiment> [Image material] 1 is a conceptual diagram for explaining the configuration of an imaging member according to the present embodiment. In addition, in the present embodiment, an infrared imaging method using infrared rays as a heat source for the image forming apparatus is described, but other methods and heat sources may be used.

[0013] In Fig. 1, the image member 10 on which the image is formed is composed of, from the bottom layer, a light-reflecting substrate 12, an image-forming layer 18, a spacer layer 17, an image-forming layer 16, a spacer layer 15, an image-forming layer 14, and a protective film layer 13. The image-forming layers 14, 16, and 18 are generally yellow, magenta, and cyan, respectively, during full-color printing, but may be other color combinations. In other words, in the example of Fig. 1, image-forming layers (color-developing layers) corresponding to three colors are provided, but more image-forming layers may be provided as long as M (M≧3) image-forming layers are provided.

[0014] Each image forming layer is initially colorless (before image formation), but changes to a corresponding color when heated to a specific temperature called the activation temperature of each image forming layer. In this embodiment, the color development characteristics for color development in each image forming layer are different. The order of colors of the image forming layers in the image member 10 (order of stacking) can be selected arbitrarily. One suitable color order is as described above. Another suitable order is an order in which the three image forming layers 14, 16, and 18 are a cyan color developing layer, a magenta color developing layer, and a yellow color developing layer, respectively. In this embodiment, an example in which the layers are configured in the above-mentioned order of yellow, magenta, and cyan will be described. In FIG. 1, the image forming layers are stacked to the same thickness, but this is not limited to this, and the thickness may differ depending on the color (color material).

[0015] As shown in FIG. 1, a spacer layer is provided between each of the image forming layers. The thickness of the spacer layer may be determined according to the color development characteristics of each image forming layer, the thermal conduction characteristics and thermal diffusivity of each layer, etc. For example, each spacer layer may be made of the same material or different materials. The function of the spacer layer is to control the thermal diffusion within the image member 10. Preferably, the spacer layer 17 is at least four times thicker than the spacer layer 15 when the spacer layer 17 is made of the same material.

[0016] All layers disposed on substrate 12 are substantially transparent prior to imaging. If substrate 12 is a reflective color (e.g., white), the color image formed by imaging member 10 is viewed through overcoat layer 13 against the reflective background provided by substrate 12. The transparency of each layer deposited on substrate 12 allows the human eye to see the combination of colors printed on each of the imaging layers.

[0017] In this embodiment, the three image-forming layers 14, 16, and 18 in the imaging member 10 are disposed on the same side of the substrate 12, although some of the image-forming layers may be disposed on opposite sides of the substrate 12.

[0018] In this embodiment, the imaging layers 14, 16, and 18 are processed at least in part independently by varying two adjustable parameters in the imaging device: temperature and time. These parameters are controlled by the print head temperature and time when heat is applied to the imaging member 10 to form an image in the desired imaging layer. That is, by controlling the temperature and time applied to the imaging member 10, a desired density of color can be developed in the desired imaging layer.

[0019] In this embodiment, each of the image forming layers 14, 16, and 18 is treated by applying heat while the print head is in contact with the top layer of the imaging member 10, i.e., the protective film layer 13 shown in FIG. 1. The color development characteristics of each image forming layer according to this embodiment will be described. The activation temperatures of the image forming layers 14, 16, and 18 are Ta3, Ta2, and Ta1, respectively. In this case, the activation temperature (Ta3) of the image forming layer 14 is higher than the activation temperature (Ta2) of the image forming layer 16, and is also higher than the activation temperature (Ta1) of the first image forming layer 18. The relationship between the activation (color development characteristics) of each image forming layer will be described later with reference to FIG. 2.

[0020] Heating of the image forming layers located farther from the print head (i.e., the protective film layer 13) is delayed by the time required for heating because of conduction and diffusion to those layers through each spacer layer. Therefore, even if the temperature applied from the print head to the surface of the image member 10 (i.e., the protective film layer 13) is substantially higher than the activation temperature of the image forming layers located lower (layers farther from the print head), heating due to heat diffusion by each layer is delayed. This makes it possible to control the heating to the activation temperature for the image forming layers closer to the print head while not activating the image forming layers below it. Therefore, when processing (coloring) only the image forming layer 14 closest to the protective film layer 13, the print head heats up to a relatively high temperature (Ta3 or higher) in a short time. In this case, both the image forming layers 16 and 18 are insufficiently heated, and coloring (activation) of these layers is not performed.

[0021] Activation of only the imaging layer closer to substrate 12 (in this case, imaging layer 16 or 18) is accomplished by heating for a sufficiently long period of time at a temperature lower than the activation temperature of the imaging layer further from substrate 12 (e.g., imaging layer 14). In this way, when the lower imaging layer (imaging layer 16 or 18) is activated, the higher imaging layer (e.g., imaging layer 14) is not activated.

[0022] As noted above, heating of the image member 10 is preferably accomplished using a thermal print head, although other methods may be used, such as any known means, such as a modulated light source (such as a laser).

[0023] [Color development characteristics] 2 is a diagram for explaining the relationship between the heating temperature and heating time required to treat the image forming layers 14, 16, and 18 that compose the imaging member 10. In FIG. 2, the vertical axis indicates the heating temperature at the surface of the imaging member 10 that contacts the print head, and the horizontal axis indicates the heating time. The heating time here will be explained as being the same as the temperature supplied by the print head.

[0024] The region 21 indicates a relatively high heating temperature and a relatively short heating time. In this embodiment, the region 21 corresponds to the yellow of the image forming layer 14. That is, when the energy shown in the region 21 is supplied to the image forming layer 14, color development (image formation) is performed. The region 22 indicates an intermediate heating temperature and an intermediate heating time. The region 22 corresponds to the magenta of the image forming layer 16. That is, when the energy shown in the region 22 is supplied to the image forming layer 16, color development (image formation) is performed. The region 23 indicates a relatively low heating temperature and a relatively long heating time. The region 22 corresponds to the cyan of the image forming layer 18. That is, when the energy shown in the region 23 is supplied to the image forming layer 18, color development (image formation) is performed. The time required for imaging (color development) of the image forming layer 18 is substantially longer than the time required for imaging the image forming layer 14.

[0025] The activation temperature selected for the imaging layers is, for example, within the range of about 90° C. to about 300° C. The activation temperature (Ta1) of the imaging layer 18 is preferably as consistently low as possible for thermal stability of the imaging member 10 during shipping and storage, and is preferably about 100° C. or higher. The activation temperature (Ta3) of the imaging layer 14 is preferably consistently high, and is preferably about 200° C. or higher, for activation of the imaging layers 16, 18 by heating through this layer. The activation temperature (Ta2) of the imaging layer 16 is between Ta1 and Ta3, and is preferably between about 140° C. to about 180° C.

[0026] In addition, even when energy is applied to each image forming layer within the corresponding region, the density of the color formed varies depending on the position within the region. For example, when energy is applied to the image forming layer 16 within the region 22, an image with a higher density is formed when a temperature closer to Ta3 is applied than when a temperature closer to Ta2 is applied, even if the heating time is the same. The same is true when the heating time varies.

[0027] [Print head] The printhead of this embodiment includes a substantially linear array of resistors that extend across the width of the image, the printhead extending in a direction perpendicular to the transport direction of the image member 10 (the width of the image member 10) and the resistors disposed along the width of the image member 10.

[0028] By supplying a current to a resistor in the print head, the resistor acts as a heat source, and the image member 10 is transported while receiving heat from the resistor in the print head, so that each image forming layer forms an image. As described above, in this embodiment, the resistor is configured to be capable of irradiating infrared rays. The time during which heat is applied to the image member 10 by the print head typically ranges from about 0.001 to about 100 milliseconds per line of the image. The upper limit is set in consideration of the printing time, while the lower limit is defined by the constraints of the electronic circuit (not shown). The intervals between dots forming an image are generally in the range of 100 to 600 lines per inch in both the transport direction and the width direction of the image member 10, and may be different in each direction.

[0029] FIG. 3 is a diagram showing an example of the configuration of the print head and the image member 10 during image formation according to this embodiment. In FIG. 3(a), the image member 10 is transported to the right during image formation. The width direction of the image member 10 corresponds to the depth direction in FIG. 3(a). The print head 30 includes a glaze 32 on a base 31. In this embodiment, the glaze 32 further includes a convex glaze 33. The resistor 34 is disposed on the surface of the convex glaze 33 and is disposed so as to contact the image member 10 transported in the transport direction. The convex glaze 33 may have another shape or may not be provided. In that case, the resistor 34 is configured to contact the image member 10. It is preferable that a protective film layer (not shown) is formed on the resistor 34, the glaze 32, and the convex glaze 33. The combination of the glaze 32 and the convex glaze 33, which are generally made of the same material, is hereinafter referred to as the "glaze of the print head".

[0030] A base 31 and a heat sink 35 are provided on the glaze 32. The base 31 is in contact with the heat sink 35 and is cooled by a cooling section such as a fan (not shown). The image member 10 will be in contact with the printhead glaze which is typically longer than the length of the actual heating resistor in the transport direction. A typical resistor has a length in the transport direction of the image member 10 of about 120 microns, while the thermal contact area of ​​the image member 10 with the printhead glaze in a typical case is 200 microns or more.

[0031] 3(b) is a diagram showing an example of an arrangement of resistors 34 in the width direction. A plurality of resistors 34 are arranged in the width direction, so that the resistors 34 have a fixed length in the width direction of the image member 10, and an image of one line is formed along this arrangement. In the example shown below, an image is formed line by line while the image member 10 is transported in the transport direction.

[0032] [Image forming device] FIG. 4 is a cross-sectional view showing an example of the configuration of an image forming apparatus according to this embodiment. The image forming apparatus 40 includes the following components: a first print head 30 on the upstream side of the conveyance of the image member 10, a second print head 31 on the downstream side of the conveyance of the image member 10, a storage section 41, a conveying roller 42, a first platen 43, a second platen 44, an outlet 45, a first temperature sensor 46, and a second temperature sensor 47. The storage section 41 can store a plurality of image members 10, and the image members 10 can be replenished by opening and closing a cover (not shown). During printing, the image member 10 is sent to the first print head 30 by the conveying roller 42, and an image is formed between the first platen 43 and the first print head 30. Next, the image member 10 is sent to the second print head 31, and after an image is formed between the second platen 44 and the second print head 31, it is discharged from the outlet 45 to complete printing. A first temperature sensor 46 is provided around the nip between the first print head 30 and the first platen 43 to detect the temperature supplied by the first print head 30. A second temperature sensor 47 is provided around the nip between the second print head 31 and the second platen 44 to detect the temperature supplied by the second print head 31. The object detected by the first temperature sensor 46 and the second temperature sensor 47 may be, for example, the temperature of the resistor 34 (heat source) of the first print head 30 and the second print head 31, or the surface temperature of the imaging member 10. Furthermore, the first temperature sensor 46 and the second temperature sensor 47 may be configured to detect the environmental temperature of the image forming apparatus 40.

[0033] The transport speed of the image member 10 is controlled according to the speed of image formation, the resolution during image formation, etc. For example, when forming a high-resolution image, the transport speed may be slower than when forming a low-resolution image. Also, when priority is given to printing speed, the transport speed may be increased and the resolution may be decreased.

[0034] In the present embodiment, the image member is conveyed by the conveying roller, but the print head and the image member may be moved relatively in a direction intersecting with the arrangement direction of the resistors 34 of the print head. Therefore, the print head may be moved.

[0035] [System Configuration] Fig. 5 is a diagram showing an example of the overall configuration of a system according to this embodiment. As shown in Fig. 5, the system according to this embodiment includes the image forming apparatus 40 shown in Fig. 4 and a personal computer (PC) 50 as its host device.

[0036] The PC 50 includes the following components: a CPU (Central Processing Unit) 501, a RAM (Read Only Memory) 502, a HDD (Hard Disk Drive) 503, a communication I / F 504, an input device I / F 505, and a display device I / F. Furthermore, each component is connected to each other via an internal bus so that they can communicate with each other. The CPU 501 executes processing in accordance with programs and various data stored in the HDD 503 and RAM 502. The RAM 502 is a volatile storage device that temporarily stores programs and data. Furthermore, the HDD 503 is a non-volatile storage device that stores programs and data.

[0037] The communication I / F 504 is an interface that manages communication with an external device, and here controls transmission and reception of data with the image forming apparatus 40. The connection method for transmitting and receiving data here can be a wired connection such as USB, IEEE1394, or LAN (Local Area Network), or a wireless connection such as Bluetooth (registered trademark) or WiFi (registered trademark). The input device I / F 505 is an interface that controls a HID (Human Interface Device) such as a keyboard or mouse, and accepts input from a user's input device. The display device I / F 506 controls display on a display device such as a display (not shown).

[0038] The image forming apparatus 40 includes a CPU 401, a RAM 402, a ROM 403, a communication I / F 404, a first head controller 405, a second head controller 406, an image processing accelerator 407, a first temperature sensor 46, and a second temperature sensor 47. Furthermore, each part is connected to each other so as to be able to communicate with each other via an internal bus. The CPU 401 executes the processing of each embodiment described later in accordance with the programs and various data stored in the ROM 403 and the RAM 402. The RAM 402 is a volatile storage and temporarily stores the programs and data. Moreover, the ROM 403 is a non-volatile storage and stores table data and programs used in the processing described later.

[0039] The communication I / F 404 is an interface that manages communication with an external device, and in this case, controls the transmission and reception of data between the PC 50 and the first head controller 405. The first head controller 405 controls the heating operation of the first print head 30 shown in FIG. 3 based on the recording data, and the second head controller 406 controls the heating operation of the second print head 31 shown in FIG. 3 based on the recording data. Specifically, the first head controller 405 can be configured to read the control parameters and the first head recording data from a predetermined address of the RAM 402. The second head controller 406 can be configured to read the control parameters and the second head recording data from a predetermined address of the RAM 402. Then, when the CPU 401 writes the control parameters and the recording data to a predetermined address of the RAM 402, the first head controller 405 starts a process, and the first print head 30 is heated. Similarly, the second head controller 406 starts a process, and the second print head 31 is heated.

[0040] The image processing accelerator 407 is configured by hardware and executes image processing faster than the CPU 401. Specifically, the image processing accelerator 407 can be configured to read parameters and data required for image processing from a predetermined address of the RAM 402. Then, when the CPU 401 writes the above parameters and data to a predetermined address of the RAM 402, the image processing accelerator 407 is started and a predetermined image processing is performed. Note that the image processing accelerator 407 is not necessarily an essential element, and the above table parameter creation processing and image processing may be executed only by the processing by the CPU 401 according to the specifications of the printer, etc. Also, the first temperature sensor 46 detects the ambient temperature of the resistor 34 of the first print head 30 as shown in FIG. 4, and the second temperature sensor 46 detects the ambient temperature of the resistor 34 of the second print head 31, and provides each temperature information to the CPU 401, etc. Based on the acquired temperature information, the CPU 401 generates a control parameter for controlling the heat generation of the resistor 34 of the first head and the resistor 34 of the second head. The detailed control will be described later.

[0041] In this embodiment, the image forming device 40 and the PC 50 are described as different devices, but for example, they may be integrated into a system, or the image forming device 40 may be integrated into a system with an imaging device (not shown). Also, although a PC has been given as an example of the host device, this is not limiting, and for example, a mobile terminal such as a smartphone, a tablet terminal, or an imaging device may be used.

[0042] [Print service] Fig. 6 shows a sequence when a print service is performed in the system according to this embodiment. In Fig. 6, S601 to S605 show processing in the PC 50, and S611 to S616 show processing in the image forming device 40. Also, in Fig. 6, dashed arrows show data transmission and reception. Each step is realized by the CPU of each device reading and executing a program or the like stored in a storage unit. This sequence starts when a user wants to perform printing.

[0043] In S611, after the image forming apparatus 40 is powered on, it confirms that it is capable of printing and goes into a standby state, ready to provide a printing service.

[0044] On the other hand, in S601, the PC 50 executes print service discovery. The print service discovery here may be configured to search for peripheral devices according to user operations, or to periodically search for an image forming device that is in a state where it can provide a print service. Alternatively, the PC 50 may be configured to make an inquiry when the PC 50 and the image forming device 40 are connected.

[0045] In step S612, upon receiving the print service Discovery from the PC 50, the image forming apparatus 40 notifies the PC 50 in response that it is a device that can provide the print service.

[0046] In S602, when the PC 50 receives a notification from the image forming apparatus 40 that the print service can be provided, the PC 50 requests printable information from the image forming apparatus.

[0047] In step S613, the image forming apparatus 40 notifies the PC 50 of information on the printing services that the image forming apparatus 40 can provide in response to the request for printable information from the PC 50.

[0048] Upon receiving the printable information from the image forming apparatus 40, the PC 50 constructs a user interface for creating a print job based on the printable information in S603. Specifically, based on the printable information of the image forming apparatus 40, the PC 50 appropriately displays the designation of the print image, print size, printable paper size, etc., and provides appropriate options to the user via a display (not shown). Then, settings from the user are accepted via an input device (not shown) such as a keyboard.

[0049] In S604, the PC 50 issues a print job based on the settings received from the user, and transmits it to the image forming apparatus 40.

[0050] In S614, image forming apparatus 40 receives the print job from PC 50.

[0051] In S615, the image forming apparatus 40 analyzes and executes the received print job. Details of image formation for a print job according to this embodiment will be described later.

[0052] When the printing is completed, in S616, the image forming apparatus 40 notifies the PC 50 of the printing completion. Then, the processing on the image forming apparatus 40 side is completed, and the image forming apparatus 40 goes into a standby state.

[0053] In S605, the PC 50 receives the print completion notification and notifies the user of the same, completing the process on the PC 50 side.

[0054] In the above description, various types of information are transmitted by making a request from the PC 50 to the image forming apparatus 40, and the image forming apparatus 40 responds to the request. However, the communication is not limited to the above-described so-called pull-type communication, and may be a so-called push-type communication in which the image forming apparatus 40 spontaneously transmits information to one or more PCs 50 on the network.

[0055] (Conventional head control) First, as a comparative example of the present invention, a conventional print head is used to explain signals used for heating control. FIG. 7 shows an example of a signal pattern (heating pulse) corresponding to each color applied to the print head of a conventional image forming apparatus. FIG. 7 shows examples of colors to be developed in the image member 10 in one pixel and the configuration of the heating pulse at that time. From the top, yellow (Y), magenta (M), cyan (C), and green (G) are shown. In FIG. 7, the heating pulse for one pixel is composed of eight sections (p0 to p7), and the length of one section is Δt0. In other words, the time of the heating pulse required to form one pixel is Δt0×8 sections (p0 to p7). In other words, the number of cycles of the pulse in the eight sections is used to develop the color of one pixel, and the color development is controlled by the pulse signal train included in this.

[0056] In FIG. 7, the signal shows two values, High and Low (ON and OFF). When it is High, heating is performed by the resistor 34, and when it is Low, heating is not performed. The color development is controlled by controlling the pulse width and number of pulses contained in the heating pulse for each color. In this embodiment, the pulse width of each pulse is adjusted by PWM (Pulse Width Modulation) control. As shown in FIG. 7, the starting point of each section will be described as the rising timing of the pulse (ON timing).

[0057] For example, when yellow (Y) is developed, in order to realize the region 21 (relatively high heating temperature and relatively short heating time) shown in FIG. 2, heating for a time of Δt1 is performed a total of two times with an interval. When magenta (M) is developed, in order to realize the region 22 (intermediate heating temperature and intermediate heating time) shown in FIG. 2, heating for a time of Δt2 is performed a total of three times with an interval. The interval between the first pulse and the second pulse here is (Δt0-Δt2). Similarly, when cyan (C) is developed, in order to realize the region 23 (relatively low heating temperature and relatively long heating time) shown in FIG. 2, heating for a time of Δt3 is performed a total of five times with an interval. The interval between the first pulse and the second pulse here is (Δt0-Δt3). By providing this interval, the temperature of the image member 10 is prevented from rising above the target temperature (activation temperature). In other words, the target temperature is maintained by controlling the ON and OFF times.

[0058] In FIG. 7, for ease of understanding, Δt1=Δt2×2=Δt3×4 and the total time of the heating pulses applied to the print head 30 is the same for any color that is to be developed. t1 to t3 and Ta1 to Ta3 shown below correspond to those shown in FIG.

[0059] Heating time is Heating time t2>Y Δt1+Δt0>t1 t3>M heating time Δt2+Δt0×2>t2 Heating time of C Δt3+Δt0×4>t3 The relative relationship of the heating time is as follows: Heating time of Y < Heating time of M < Heating time of C Here, Y, M, and C refer to the image-forming layers 14, 16, and 18.

[0060] Here, the energy (amount of heat) applied to the image member 10 by the print head 30 is thermally conducted to the glaze 32 (and convex glaze 33) of the print head 30, the base 31, the heat sink 35, and the like shown in FIG. 3 during the interval time of each signal. Therefore, the temperature of the image member 10 drops during the interval time. Similarly, the amount of heat conducted into the image member 10 is also propagated to the periphery, such as the platen 43 shown in FIG. 4, and the temperature of the image member 10 drops by that amount. As a result, when the input energy (amount of heat) is the same, the peak temperature due to heating is Y>M>C Here, Peak temperature of Y>Ta3 Ta3>M peak temperature>Ta2 Ta2>C peak temperature>Ta1 By controlling it in this way, it is possible to produce each of the colors Y, M, and C independently.

[0061] Next, the heating pulses that control the color development of the secondary colors red (R), green (G), and blue (B) will be described. Here, the N-order color means a color expressed by developing and combining N color materials (image forming layers). The heating pulses are controlled so that red (R) develops in the order of yellow (Y) → magenta (M). In other words, the image of red (R) is formed by developing the image forming layer 14 corresponding to yellow (Y) and the image forming layer 16 corresponding to magenta (M). Similarly, the heating pulses are controlled so that blue (B) shown in FIG. 7 develops in the order of magenta (M) → cyan (C). However, if the heating pulses are controlled so that green (B) shown in FIG. 7 develops in the order of yellow (Y) → cyan (C), an intermediate heating temperature and intermediate heating time will occur, causing the image forming layer 16 corresponding to magenta (M) to develop erroneously. Therefore, the heating time for Δt1 is reduced by one time, and similarly the heating time for Δt3 is reduced by one time, and by providing OFF timing intervals in sections p1, p2, and p3, a cooling period is created and the erroneous color development of magenta (M) is avoided. However, because the total number of heating times for Δt1 and Δt3 is reduced, a highly colored green cannot be realized on the image member. In this way, in order to create a cooling time for the image member in a configuration with a single print head, it is necessary to use the OFF timing of the heating pulse within one pixel.

[0062] (Heating Pulse According to This Embodiment) Next, the basic configuration of the signal pattern (heating pulse) according to this embodiment will be described with reference to FIG. 8. In FIG. 8, Δt0, Δt1, and Δt3 will be described as being the same as those in FIG. 7 for the sake of simplicity. In this embodiment, two print heads, a first print head 30 and a second print head 31, are used to form a highly colored green (G) image. The heating pulse of the first print head 30 in FIG. 8 is the same as the cyan (C) heating pulse in FIG. 7, and the heating pulse of the second print head 31 is the same as the yellow (Y) heating pulse in FIG. 7. The image member is heated using the first print head 30, and then the image member is heated using the second print head 31. Since the image member is cooled while being transported by the first print head 30 and the second print head 31, the cyan (C) heating time Δt1×5 and the yellow heating time Δt3×2 can be applied to the image member, respectively, and there is no need to reduce the heating time as in FIG. 7. As a result, compared to the green (G) heating pulse in FIG. 7, heating for a time period of Δt1 is increased by one, and heating for a time period of Δt3 is increased by one, thereby making it possible to realize a highly colored green color on the image member.

[0063] The control of image formation according to this embodiment will be described below. In this embodiment, a signal (pulse signal) for applying a current to the resistor 34 of the first print head 30 is output from the first head controller 405 to perform heating control to form an image. Next, a signal (pulse signal) for applying a current to the resistor 34 of the second print head 31 is output from the second head controller 406 to perform heating control to form an image.

[0064] [Processing flow] Fig. 9 is a flow chart of image processing for implementing a heating pulse according to this embodiment. The flow shown in Fig. 9 is executed in step S615 in Fig. 6. This flow is implemented, for example, by the CPU 401 of the image forming apparatus 40 reading and executing programs and data contained in the ROM 403, etc. Note that this process may be configured so that part of it is executed by the image processing accelerator 406.

[0065] In S901, the CPU 401 acquires image data in the print job received in S614 in Fig. 6. Here, the description will be given assuming that the image data is acquired page by page.

[0066] In S902, the CPU 401 performs a decoding process on the image data. If the image data is not compressed or encoded, this process may be omitted. The image data becomes RGB data through the decoding process. Examples of the RGB data include standard color information such as sRGB and adobe (registered trademark) RGB. In this embodiment, the image data has 8-bit information for each color, with a value range of 0 to 255, but may be composed of a different number of bits, such as 16 bits.

[0067] In S903, the CPU 401 performs color correction processing on the image data. The color correction processing may be performed on the PC 50 side, or may be performed within the image forming apparatus 40 when color correction is performed to match the image forming apparatus 40. The image data after the color correction processing is RGB data, but at this point, it is assumed that the data is in a format of RGB specialized for the image forming apparatus 40, that is, a so-called device RGB format.

[0068] In step S904, the CPU 401 performs luminance / density conversion on the image data using a three-dimensional lookup table. In a typical thermal printer, for example, the RGB signal of the image data is used to convert the luminance / density of the image data into the following: C=255-R M=255-G Y=255-B On the other hand, in the case of pulse control according to this embodiment, for example, the control parameters of magenta constituting a single color of magenta (M) and the control parameters of magenta constituting a suitable color of red (R) are different. Therefore, in order to set the two separately, it is desirable to perform luminance density conversion using a three-dimensional lookup table. Note that the conversion may be performed by any method, but here, an example using a three-dimensional lookup table, which is more preferable, will be described.

[0069] In this embodiment, luminance / density conversion is performed using a three-dimensional lookup table as follows. In the function 3D_LUT[R][G][B][N] of the three-dimensional lookup table used below, the variables R, G, and B are input with RGB data values, and the variable N is specified as one of C, M, and Y to be output. Here, 0, 1, and 2 are specified as C, M, and Y, respectively. C=3D_LUT[R][G][B][0] M=3D_LUT[R][G][B][1] Y=3D_LUT[R][G][B][2]

[0070] The above 3D_LUT is composed of 50,331,648 data tables of 256×256×256×3. Each data corresponds to the pulse width applied to p0 to p7 in FIG. 8. In order to reduce the amount of data in the lookup table, for example, the number of grids may be reduced from 256 to 17, and the result may be calculated by an interpolation operation using 14,739 data tables of 17×17×17×3. Of course, other than 17 grids, a suitable number of grids such as 16 grids, 9 grids, and 8 grids may be set as appropriate. Any method such as known tetrahedral interpolation may be used as the interpolation method. In this embodiment, the three-dimensional lookup table is defined in advance and is held in the ROM 403 of the image forming apparatus 40.

[0071] By using the above three-dimensional lookup table, it is possible to set the control parameters for yellow (Y), magenta (M), and cyan (C) that make up each color individually. In other words, it is possible to set the control parameters for the yellow and magenta that make up red (R), the cyan and yellow that make up green (G), the magenta and cyan that make up blue (B), and the yellow, magenta, and cyan that make up black (K) independently. This allows for more precise control of color development, which contributes to improved color reproducibility.

[0072] In S905, the CPU 401 performs output correction on the converted image data. First, the CPU 401 calculates the pulse width for achieving the density of each C, M, and Y using a conversion table corresponding to each color. c, m, and y indicate the pulse width corresponding to the values ​​of C, M, and Y, respectively. The conversion table (conversion formula) here is defined in advance and is held in the ROM 403 of the image forming apparatus 40, etc. c=1D_LUT[C] m=1D_LUT[M] y=1D_LUT[Y]

[0073] Here, the maximum value of the pulse width indicated by c is Δt3 in FIG. 7. The maximum value of the pulse width indicated by m is Δt2 in FIG. 7. The maximum value of the pulse width indicated by y is Δt1 in FIG. 7. Since the image forming apparatus 40 can modulate the color intensity in the image member 10 by modulating the pulse width, when the above-mentioned c, m, and y are smaller than the maximum values, the pulse width can be shortened appropriately to achieve the desired gradation. This process may be performed by using a known means.

[0074] Furthermore, the CPU 401 modulates the heating pulse according to the temperature of the imaging member 10 (or the first print head 30) acquired by the temperature sensor 46 and the temperature of the imaging member 10 (or the second print head 31) acquired by the temperature sensor 47. Specifically, the CPU 401 controls the pulse width of the heating pulse used to reach the activation temperature to be shortened as the temperature detected by the temperature sensors 46 and 47 increases. This processing may be performed using a known means. In addition, the temperature of the imaging member 10 may not only be acquired by the temperature sensors 46 and 47, but may also be controlled based on the estimated temperatures by estimating the temperatures of the imaging member 10, the first print head 30, and the second print head 31 in the PC or the image forming device 40. The method of temperature estimation is not particularly limited, and any known method may be used.

[0075] In S906, in the cmy data generated in S905, the c data is distributed to the first print head 30 and the y data is distributed to the second print head 31 to generate recording data to be used for printing. The m data may be distributed to either the first print head 30 or the second print head 31. For example, the m data can be distributed as follows. In the case of red (R) and blue (B), high color development can be achieved with the heating pulse shown in FIG. 7. Therefore, when coloring red (R), the m data is distributed to the second print head 31, which is the same as the y data. Also, when coloring blue (B), the m data is distributed to the first print head 30, which is the same as the c data. Alternatively, the m data may be distributed half to the first print head 30 and half to the second print head 31.

[0076] In S907, in accordance with the recording data generated in S906, the CPU 401 controls the first print head 30 via the first head controller 405, and controls the second print head 31 via the second head controller 406. By controlling the Y heating pulse, M heating pulse, and C heating pulse shown in Fig. 7, a desired color is formed on the image member.

[0077] In S908, CPU 401 determines whether printing of the page is complete. If it is complete (YES in S908), this processing flow ends, and the processing of the next page or the processing of S616 in Fig. 6 proceeds. If it is not complete (NO in S908), the processing proceeds to S902, and image formation processing for the page continues.

[0078] As explained above, in the example of Fig. 8, heating for a time period of Δt1 is performed twice in total, and heating for a time period of Δt3 is performed five times in total. Compared to the green (G) heating pulse shown in Fig. 7, heating for a time period of Δt1 is performed once more per pixel, and heating for a time period of Δt3 is performed once more. As a result, the amount of thermal energy required to achieve a highly colored green color can be applied to the image member, and a highly colored green color can be achieved.

[0079] In the first embodiment, the ratio of the heat energy applied to the image member from the first print head and the second print head is changed according to the combination of the color-developing layers, out of the total amount of heat energy applied to a specific region of the image member, in this case one pixel. By doing so, it is possible to obtain an image with high color development.

[0080] Also, when only one coloring layer is to be colored, all data may be distributed to either the first print head or the second print head.

[0081] <Second embodiment> In the above first embodiment, an example was described in which a cyan (C) heating pulse was allocated to the first print head and a yellow (Y) heating pulse was allocated to the second print head. In this embodiment, an example in which a cyan (C) heating pulse, a magenta (M) heating pulse, and a yellow (Y) heating pulse are distributed to the first head and the second head using a three-dimensional lookup table will be described with reference to FIG.

[0082] In FIG. 10, 1001 indicates the distribution ratio of c data and 1002 indicates the distribution ratio of y data in the cmy data generated in S905 to the first print head 30 and the second print head 31. 1003 and 1004 indicate the ratio of applying a cyan (C) heating pulse to the first print head 30 and applying a yellow (Y) heating pulse to the second print head 31, as shown in the first embodiment. 1005 distributes to the first print head 30 and the second print head 31 at a ratio of 50:50, which is the same as applying a pulse to realize a conventional halftone green twice to the first print head 30, the second print head 31, and the image member. Distribution to the first print head 30 and the second print head 31 is performed in s906 shown in FIG. 9. In this embodiment, distribution is performed using a three-dimensional lookup table as follows. In the three-dimensional lookup table function 3D_LUT[R][G][B][N] used below, the variables R, G, and B are input with RGB data values, and the variable N is specified as the output C, M, or Y. Here, it is assumed that 0, 1, and 2 are specified as C, M, and Y, respectively.

[0083] cp=3D_LUT[R][G][B][0] mp=3D_LUT[R][G][B][1] yp=3D_LUT[R][G][B][2] From the calculated distribution ratios cp, mp, yp of the first print head 30, c1, m1, y1 of the first print head 30 and c2, m2, y2 of the second print head 31 are calculated using the following equations. c1=c×cp / 100, c2=c-c1 m1=m×mp / 100, m2=m-m1 y1=y×yp / 100, y2=y-y1

[0084] The above 3D_LUT is composed of 50,331,648 data tables of 256 x 256 x 256 x 3. Each data corresponds to the distribution ratios cp, mp, and yp of the first print head (values ​​are 0 to 100). In each data, the distribution ratio of cp is specified as 1001 in FIG. 10 regardless of the value of the RGB data, and similarly, the distribution ratio of 1002 is specified for yp. For mp, the distribution ratio of 1002 is specified for the grid where R>G and R>B according to the RGB data, and the distribution ratio of 1001 is specified for the other grids. That is, in the color-developing layer of the image-forming layer of the image member 10, cooling time for the image member is required to develop non-adjacent cyan (C) and yellow (Y), so cyan (C) is mainly heated by the first print head, and yellow (Y) is mainly heated by the second print head. On the other hand, because magenta (M) is adjacent to yellow (Y) and cyan (C), in red (R), yellow (Y) and magenta (M) are heated more by the second print head than by the first print head. In blue (B), magenta (M) and cyan (C) are heated more by the first print head than by the second print head.

[0085] A specific distribution method will be described using Figure 11. Figure 11 shows an example in which red (R), green (G), and blue (B) cmy data is distributed to a first print head 30 and a second print head 31. In Figure 11, Δt0, Δt1, Δt2, and Δt3 will be described as being the same as in Figure 7 for the sake of simplicity.

[0086] Red (R) is (R,G,B)=(255,0,0), so the relationship R>G and R>B is satisfied. Therefore, in the function 3D_LUT[R][G][B][N] that specifies the distribution ratio, a ratio of 1001 is specified for cp, and a ratio of 1002 is specified for mp and yp. The m data is distributed to the first print head 30 and the second print head in a ratio of 33:66, and the y data is distributed to the first print head 30 and the second print head in a ratio of 0:100.

[0087] Green (G) is (R,G,B)=(0,255,0), so the relationship of R>G and R>B is not satisfied. Therefore, in the function 3D_LUT[R][G][B][N] that specifies the distribution ratio, the ratio of 1001 is specified for cp and mp, and the ratio of 1002 is specified for yp. The c data is distributed to the first print head 30 and the second print head in a ratio of 60:40, and the y data is distributed to the first print head 30 and the second print head in a ratio of 0:100. By changing the distribution ratio from 1005 to 1003 and 1004 in FIG. 10, it is possible to achieve even higher green color development, and the distribution ratio that gives the highest green color development is when the distribution ratio is 1003 and 1004. However, as shown in FIG. 8, the first print head turns on the heating pulse a total of five times per pixel, while the second print head turns on the heating pulse a total of two times per pixel. This causes the first print head to deteriorate faster. As shown in Figure 11, the first print head turns on the heating pulse a total of three times per pixel, while the second print head turns on the heating pulse a total of four times per pixel, making it possible to make the number of times the heating pulse is turned on uniform. By distributing Δt3 of the c data to the first and second print heads as shown in Figure 11, it is possible to prevent degradation of only one of the print heads while achieving a higher color development than with conventional green.

[0088] Similarly, blue (B) does not satisfy the relationship of R>G and R>B because (R,G,B)=(0,0,255). Therefore, in the function 3D_LUT[R][G][B][N] that specifies the distribution ratio, a ratio of 1001 is specified for cp and mp, and a ratio of 1002 is specified for yp. The c data is distributed to the first print head 30 and the second print head in a ratio of 60:40, and the m data is distributed to the first print head 30 and the second print head in a ratio of 100:0. Considering the positional deviation of the first print head 30 and the second print head 31, the distribution ratio of both the c data and the m data is larger for the first print head 30 than for the second print head 31, as in this embodiment, so that the color development position deviation is less likely to occur.

[0089] In order to reduce the amount of data in the lookup table, for example, the number of grids may be reduced from 256 to 17, and the result may be calculated by an interpolation operation using 17×17×17×3 (14739) data tables. Of course, other than 17 grids, the number of grids may be set appropriately, such as 16 grids, 9 grids, and 8 grids. Any known method such as tetrahedral interpolation may be used as the interpolation method. In this embodiment, the three-dimensional lookup table is predefined and stored in the ROM 403 of the image forming apparatus 40. Alternatively, a method may be used in which a plurality of three-dimensional lookup tables with different distribution ratios are predefined in the ROM 403, and the CPU 401 determines the three-dimensional lookup table to be used depending on the number of times the print head is turned on.

[0090] As described above, by changing the data distribution ratio to the two print heads depending on the content of the image data, it is possible to suppress misalignment of color development and prevent one of the print heads from deteriorating faster than the other.

[0091] (Third embodiment) In the above description, an example of printing on an image member 10 having three color-forming layers has been described. However, the above method can also be applied to a recording device that records on an image member having four or more color-forming layers that have different color-forming characteristics and produce different colors, and that causes two or more layers to produce colors in the same pixel.

[0092] For example, consider a case where an image recording member has a yellow color-forming layer, a green color-forming layer, a magenta color-forming layer, and a cyan color-forming layer arranged in the aforementioned order from the side to which energy is applied. These color-forming layers have different color-forming characteristics, and the green color-forming layer forms at a lower temperature than the yellow color-forming layer and a higher temperature than the magenta color-forming layer.

[0093] When recording an image on such an image member, if a coloring layer that is separated from the image member is colored in the same pixel, the coloring layer that is separated from the image member is recorded by a different print head, similar to S906 in FIG. 9 of the first embodiment. Specifically, when a yellow coloring layer and a magenta coloring layer are colored, when a yellow coloring layer and a cyan coloring layer are colored, or when a green coloring layer and a cyan coloring layer are colored, the thermal energy for coloring one coloring layer is applied to the image member by the first print head, and the thermal energy for coloring the other coloring layer is applied to the image member by the second print head. In this embodiment, the coloring layer that is separated from the side to which energy is applied is recorded by the first print head, and the coloring layer that is closer to the side to which energy is applied is recorded by the second print head. When other coloring layers are colored, the coloring layer adjacent to the coloring layer that is colored by the first print head is colored by the first print head, and the coloring layer adjacent to the coloring layer that is colored by the second print head is colored by the second print head. As an example, a case will be described in which the yellow color layer is developed by the second print head, and the cyan color layer is developed by the first print head. The green color layer is adjacent to the yellow color layer, so it is developed by the second print head, and the magenta color layer is adjacent to the cyan color layer, so it is developed by the first print head. If it is adjacent to both the color layers developed by the first and second print heads, it may be developed by either print head, or it may be distributed between the first and second print heads.

[0094] When three or more color layers are to be colored, the color layer data to be recorded by dividing the print head may be determined based on the amount of data, or the color layer to be divided may be determined in advance.

[0095] As described above, in addition to the method of the first embodiment in which a print head is completely separated for each color layer, a method of changing the distribution ratio according to data as in the second embodiment can also be applied.

[0096] The four color-producing layers are not limited to the above-mentioned color-producing layers, but may be layers having other color-producing properties or emitting other colors. [Explanation of symbols]

[0097] 10 Image material 14, 16, 18 Image forming layer 30, 31 Print head 34 Resistance 45 Temperature Sensor 40 Image forming device

Claims

1. N (2≦N<M) print heads including a first print head and a second print head arranged in a first direction, each of which applies thermal energy to an image member having M (M≧3) color-forming layers each having a different color-forming characteristic and which develop color in response to the applied thermal energy; a moving means for relatively moving the image member and the print head in a direction intersecting the first direction; a control means for controlling each of the N print heads based on image data, which is RGB data, to apply thermal energy from the print head to the image member; Equipped with The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, the control means changes a ratio of heat energy applied to the predetermined region of each of the N print heads relative to a total amount of heat energy applied to the predetermined region by the N print heads in accordance with a combination of color layers caused to develop by the N print heads in a predetermined region of the image member based on the image data, and controls the first print head and the second print head so that the yellow color layer is developed by applying more heat energy from the second print head than from the first print head, and the cyan color layer is developed by applying more heat energy from the first print head than from the second print head, an image forming apparatus characterized in that the control means controls the first print head and the second print head so that, when the R, G, and B values ​​of the image data satisfy R>G and R>B, the magenta color layer is colored by applying more thermal energy from the second print head than from the first print head, and, when the R, G, and B values ​​of the image data do not satisfy R>G and R>B, the magenta color layer is colored by applying more thermal energy from the first print head than from the second print head.

2. 2. The image forming apparatus according to claim 1, wherein the control means outputs a signal pattern for controlling the thermal energy applied to the image member by the print head, and the signal pattern specifies a heating temperature and heating time for the image member by a pulse width and a pulse number.

3. 3. The image forming apparatus according to claim 1, wherein the N print heads are two print heads, the first print head which first applies thermal energy to the image member, and the second print head which secondly applies thermal energy to the image member.

4. The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, An image forming apparatus as described in any one of claims 1 to 3, characterized in that, when at least two color layers including a cyan color layer are caused to color, the control means controls the first printing head and the second printing head so that the amount of thermal energy applied to the cyan color layer is greater for the first printing head than for the second printing head.

5. The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, 5. An image forming apparatus according to claim 1, wherein the control means controls the first print head and the second print head so that the cyan color layer is developed by the first print head and the yellow color layer is developed by the second print head.

6. The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, An image forming apparatus as described in any one of claims 1 to 5, characterized in that, when the cyan color-forming layer and the yellow color-forming layer are caused to develop, the control means controls the first printing head and the second printing head so that more than half of the amount of thermal energy applied to the cyan color-forming layer is applied to the image member by the first printing head, and all of the amount of thermal energy applied to the yellow color-forming layer is applied to the image member by the second printing head.

7. applying thermal energy to an image member having M (M≧3) color layers each having different coloring characteristics and coloring in response to the applied thermal energy, based on image data which is RGB data, by N (2≦N<M) print heads including a first print head and a second print head arranged in a first direction; A recording method in which the image member and the print head are moved relatively in a direction intersecting the first direction, comprising: The M color forming layers are layered in the order of a yellow color forming layer, a magenta color forming layer, and a cyan color forming layer from the side to which thermal energy is applied by the print head, based on the image data, a ratio of thermal energy applied to the predetermined region of each of the N print heads relative to a total amount of thermal energy applied to the predetermined region by the N print heads is changed in accordance with a combination of color layers caused to develop by the N print heads in a predetermined region of the image member based on the image data, and the first print head and the second print head are controlled so that the yellow color layer is developed by applying more thermal energy from the second print head than from the first print head, and the cyan color layer is developed by applying more thermal energy from the first print head than from the second print head, to form an image on the image member; a recording method for forming an image on the image member by controlling the first print head and the second print head so that, when the R, G, and B values ​​of the image data satisfy R>G and R>B, the magenta color-forming layer is colored by applying more thermal energy from the second print head than from the first print head, and, when the R, G, and B values ​​of the image data do not satisfy R>G and R>B, the magenta color-forming layer is colored by applying more thermal energy from the first print head than from the second print head.

Images