Patent Grant
8474968
1. Field of the Invention
Embodiments of the present invention relate to an inkjet apparatus that ejects and applies ink to an object using an inkjet head.
2. Description of the Related Art
An inkjet printer disclosed in U.S. Pat. No. 5,428,384 preliminarily raises the temperature of a sheet by heating the sheet from the reverse side using two heaters, thereby promoting the drying of ink applied to the sheet. The two heaters are a drive roller having a built-in preheating lamp, and a halogen lamp provided under a supporting surface in a print region.
In general, there is a time-lag from when a heater is powered on to when a predetermined amount of heat radiation is reached. If a command to drive the heater is given at the start of printing, the temperature of a part of the sheet passing during the time-lag until temperature rise is lower than desired. In the part, image unevenness such as color unevenness due to incomplete drying of ink may occur. The inkjet printer disclosed in U.S. Pat. No. 5,428,384 is provided with two heating units and preheats a sheet before printing. Providing two heaters increases power consumption and complicates the structure. The larger the printer, the more noticeable this problem.
The inkjet printer disclosed in U.S. Pat. No. 5,428,384 heats a sheet from the reverse side to dry ink droplets on the face. Such a drying method has the following problems. When the sheet used has a large thickness or is made of a highly heat-insulating material (for example, when the sheet is a resin plate or a thick vinyl sheet), it is difficult to efficiently apply heat to ink on the face of the sheet, and high-speed printing is hindered. In the case of a sheet having an adhesion layer on the reverse side thereof, such as a sheet of wall paper, the glue of the adhesion layer may be melted by heating the reverse side of the sheet. The melted glue causes a sheet conveyance jam.
On completion of printing, sheet conveyance is stopped, and the heating by the heater is also stopped. The heater continues to radiate heat due to residual heat even after being stopped. For this reason, the sheet at rest immediately below the heater continues to be heated. If the sheet surface temperature exceeds permissive temperature, the sheet may deform. This phenomenon is particularly noticeable in the case where the sheet is made of a heat-sensitive material such as plastic.
One disclosed aspect of the embodiments prevents image deterioration due to partial temperature drop of a sheet at the start of printing. One disclosed aspect of the embodiments prevents deformation of a sheet due to partial temperature rise of the sheet after printing.
In an aspect of the embodiments, an inkjet apparatus includes a roller pair that moves a sheet, an inkjet head that applies ink to the sheet being conveyed by the roller pair, a heating unit that heats the sheet at a location downstream of the roller pair in the direction in which the sheet moves, a cooling unit that cools the sheet at the location, and a control unit that, in a stopped state where the sheet is not moving, performs control so that the sheet is heated by the heating unit and cooled by the cooling unit at the same time and that, when the sheet starts moving after the stopped state in order for the inkjet head to apply ink to the sheet, performs control so that the sheet continues to be heated by the heating unit and is cooled by the cooling unit at a lower power than in the stopped state.
In another aspect of the embodiments, an inkjet apparatus includes a roller pair that moves a sheet, an inkjet head that applies ink to the sheet being conveyed by the roller pair, a heating unit that heats the sheet at a location downstream of the roller pair in the direction in which the sheet moves, a cooling unit that cools the sheet at the location, and a control unit that, in a moving state where the sheet is moving while the inkjet head is applying ink to the sheet, performs control so that the sheet is heated by the heating unit and that, when the sheet stops moving after the moving state, performs control so that the sheet is heated by the heating unit at a lower power and cooled by the cooling unit at a higher power than in the moving state.
According to one disclosed aspect of the embodiments, a sheet coming at the start of printing the temperature of which is lower than a predetermined temperature may be immediately heated to the vicinity of the predetermined temperature. That is, image deterioration due to partial temperature drop of a sheet at the start of printing may be prevented. According to one disclosed aspect of the embodiments, by increasing the power of the cooling unit after printing, the temperature rise of a sheet due to residual heat of the heating unit may be prevented, and therefore the deformation of the sheet may be prevented.
Further features of the embodiments will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An inkjet printer using a large-sized sheet will be described as an embodiment of the present invention. One disclosed aspect of the embodiments may be applied not only to printers but also to other inkjet apparatuses for various purposes that apply ink to an article using an inkjet method. One disclosed aspect of the embodiments may be widely applied to heating devices that heat a moving article (not limited to a sheet) in order to regulating the temperature thereof.
One disclosed feature of the embodiments may be described as a process which is usually depicted as a flowchart, a flow diagram, a timing diagram, a structure diagram, or a block diagram. Although a flowchart or a timing diagram may describe the operations or events as a sequential process, the operations may be performed, or the events may occur, in parallel or concurrently. In addition, the order of the operations or events may be re-arranged. A process is terminated when its operations are completed. A process may correspond to a method, a program, a procedure, a method of manufacturing or fabrication, a sequence of operations performed by an apparatus, a machine, or a logic circuit, etc.
An unused roll sheet 6 is attached to a sheet supply unit 5. The roll sheet 6 is a continuous sheet wound into a web. The roll sheet to be used has a large size, for example, a sheet width of several meters. The sheet S supplied from the sheet supply unit 5 is nipped between a conveying roller pair including a conveying roller 1 to which a rotational drive force is given, and a pinch roller 2 rotating dependently. The conveying roller 1 and the pinch roller 2 have a length corresponding to the maximum sheet width. The conveying roller 1 and the pinch roller 2 may be divided into a plurality of segments. The pinch roller 2 is supported by an arm 3 and is pressed against the conveying roller 1 by elastic force. The arm 3 also has a length corresponding to the pinch roller 2.
The sheet S is conveyed by the rotation of the conveying roller 1 and moves in the sub-scanning direction (leftward in
The inkjet head 7 may use any one of a method using heaters, a method using piezoelectric elements, a method using electrostatic elements, and a method using MEMS elements. In this embodiment, emulsion ink (dispersal ink) may be used. By heating ink droplets ejected onto the sheet, emulsion ink forms a film and is solidified and fixed to the surface of the sheet. For this purpose, as described later, a heating unit that heats the sheet S is provided.
By alternately repeating the reciprocation of the inkjet head 7 by the carriage 8 (main scanning) and the conveyance of the sheet (sub-scanning), a two-dimensional ink image is formed serially on the sheet S. The printed sheet S is ejected in the Y direction in
Above the print unit, a heating unit for heating the sheet on the platen 4 and a cooling unit for cooling the sheet on the platen 4 are provided. The positional relationship between the heating unit and the cooling unit is such that they heat and cool the sheet to regulate the sheet temperature at a predetermined position (temperature regulating region) on the downstream side of the conveying roller pair. By appropriately controlling the power of the heating unit and the cooling unit, the surface temperature of the sheet may be regulated. The specific control method will be described later.
The heating unit includes a rod-like heater 10 elongated along the main scanning direction, and a reflector 11 covering a part of the periphery of the heater 10. The heater 10 is a heat source that converts input electric energy into electromagnetic waves (heat rays of infrared rays or far-infrared rays in this embodiment) and radiates them, such as a halogen heater or a sheathed heater. By regulating the amount of input energy, the amount of heat radiation may be changed. The reflector 11 reflects heat rays radiated from the heater 10, thereby deflecting them in substantially one direction. It is ideal that the reflector 11 have a parabolic cross-section at the focus of which the heater 10 is located, and the heater-side surface thereof be smooth like a mirror surface. However, the cross-section of the reflector 11 is not limited to a parabolic cross-section as long as the reflector 11 may deflect heat rays substantially toward the sheet. The reflector is made of a material that resists high temperatures, for example, stainless steel or aluminum. Some of the heat rays radiated from the heater 10 head directly to the platen 4, and the other heat rays are reflected by the reflector 11 and directed mainly to the platen 4. Using the reflector 11, heat rays are concentrated on the sheet on the platen 4. The heating unit applies heat rays (energy for drying ink) to the entire print region substantially uniformly in the main scanning direction. The heat rays radiated from the heating unit are directed to the sheet, and some of them are directed to the upstream side of the platen 4. However, because the pinch roller 2 and the arm 3 are located upstream of the platen 4, many of the heat rays are blocked by them and do not reach the sheet. For this reason, before the sheet reaches the platen 4, the temperature rise of the sheet is small.
The cooling unit includes a blower fan 13 and a duct 14 (not shown in
Thus, the heating unit heats the entire main scanning width region substantially uniformly, and the cooling unit cools the entire main scanning width region substantially uniformly, and therefore the temperature of the sheet is unlikely to be uneven in the main scanning direction.
In the vicinity of the reflector 11, a temperature sensor 12 (not shown in
The print sequence in the above configuration is based on serial print in which a two-dimensional ink image is formed serially on the sheet S by alternately repeating the reciprocation of the inkjet head 7 by the carriage 8 (main scanning) and the conveyance of the sheet (sub-scanning). In the main scanning in the serial print, a so-called multipath print method is used in which the carriage 8 applies ink to the same part of the sheet a plurality of times while reciprocating, thereby completing an image. In the case where emulsion ink is used, ink applied to a part of the sheet by the inkjet head 7 in a main scanning (path) needs to be dried to form a film before ink is applied to the same part in the next main scanning (path). If film formation of emulsion ink has not been completed before the next main scanning, superimposed inks mix with each other and cause image deterioration due to bleeding or aggregation.
For this reason, the heating unit irradiates the sheet S with heat rays to heat the sheet surface while the carriage 8 is reciprocating in the printing operation. In a region where heat rays are not blocked by the carriage 8 and the inkjet head 7, a surface of the sheet S to which ink is applied is irradiated with heat rays from the heating unit. A part of the sheet is not irradiated with heat rays because heat rays are blocked by the carriage 8 and the inkjet head 7 that are moving. However, because the carriage 8 moves at a substantially constant speed, the accumulated heat ray irradiation to a region of the sheet S to which ink is applied is averaged in the main scanning direction, and therefore the region is heated substantially uniformly in the main scanning direction.
The operation of the heating unit and the cooling unit and the resulting sheet surface temperature changes will be described with reference to
In parts (a) and (b) of
The interval from time 0 to t1 (t1′) is a period when the sheet surface is heated by the heating unit until the surface temperature of the sheet at rest rises from an initial sheet surface temperature T1 (for example, 30° C.) to T2 (for example, 60° C.). During this period, sheet conveyance is stopped in a state where the leading edge of the sheet is located on the platen 4. It takes time for the heater to reach a predetermined temperature after the heater is powered on. As shown in part (b) of
The relationship between W1 and W2 may be expressed as W1=W2−ΔWfs (ΔWfs: the amount of heat removed from the sheet surface by the cooling by the cooling unit). The time (t1) required for the heater 10 to reach the amount W2 of heat radiation is longer than the time required to reach the amount W1 (<W2) of heat radiation by Δt (=t1−t1′). Therefore, the time when the sheet surface reaches the predetermined sheet surface temperature T2 is later than in the comparative example by Δt1.
The interval from time t1 (t1′) to t2 is the period from when the sheet surface temperature reaches the target temperature T2 till when ink is ejected from the inkjet head to start the printing operation. The interval between time t1 and t2 is a mere waiting time and is therefore preferably as short as possible. At least the output of the heater 10 is feedback-controlled so that the sheet surface temperature detected by the temperature sensor 12 is maintained within a predetermined temperature range centered on temperature T2. In the case where cooling is performed at the same time (solid line), the output D2 of the blower fan 13 continues to be maintained as shown in part (c) of
At time t2, the printing operation is started. At this time, as shown by the solid line in part (b) of
Simultaneously with the start of printing, the conveying roller 1 starts rotating, and new parts of the sheet are conveyed sequentially onto the sheet supporting surface of the platen 4. As described above, many of the heat rays from the heater 10 are blocked by the pinch roller 2 and the arm 3 from reaching the sheet. Therefore, the surface temperature of a coming part of the sheet has not reached T2.
The heater output (the amount W1 of heat radiation) in the comparative example may not heat the moving sheet to the sheet surface temperature T2 in the temperature regulating region. That is, as shown by the dashed line in part (a) of
In contrast, in this embodiment, at a stage before time t2 and in a stopped state where the sheet is not moving, the control unit performs control so that in the temperature regulating region, the sheet is heated by the heating unit (the amount of heat radiation: W2) and cooled by the cooling unit (the amount of cooling: ΔWfs) at the same time. At time t2, the control unit 100 performs control so that in the temperature regulating region, the sheet continues to be heated by the heating unit (the amount of heat radiation: W2) and cooled by the cooling unit at a lower power than in the stopped state. The amount ΔWfs of cooling is equal to the amount ΔWp of heat required to raise the temperature of the low-temperature part of the sheet coming from the upstream side. The term “equal” means not only strictly equal but substantially equal, and is interpreted to have such a meaning throughout this specification.
Thus, the temperature drop of the sheet passing through the temperature regulating region immediately after the start of printing (during Δt2) is small, and good printing may be performed from the leading edge of the sheet. Metaphorically speaking, by depressing both the gas pedal and the brake before printing and releasing only the brake as soon as the printing is started, a quick start is achieved without time-lag. Because a quicker response may be obtained by releasing the brake than by further depressing the gas pedal, the effective amount of heating is increased instantly as soon as the printing is started.
As described above, in a stopped state where the sheet is not moving, the control unit performs control so that the sheet is heated by the heating unit and cooled by the cooling unit at the same time. After the stopped state and when the sheet starts moving in order for the inkjet head to apply ink to the sheet, the control unit performs control so that the heating by the heating unit is continued and the cooling by the cooling unit is at a lower power than in the stopped state.
During the printing after the start of printing, the sheet surface temperature is maintained within a predetermined narrow temperature range centered on temperature T2 by feedback-controlling the heating unit on the basis of the detection of the temperature sensor 12. For any reason, during printing, the sheet surface temperature may rise beyond the predetermined temperature range despite the control of the heating unit. If the sheet surface temperature significantly exceeds T2 during printing, the blower fan 13 of the cooling unit may be activated to perform cooling.
Returning to
To prevent such a problem, in this embodiment, the blower fan 13 is activated when the printing is completed. In the case where the blower fan 13 operates during the printing, the output of the blower fan 13 is increased when the printing is completed. Let ΔWfe denote the amount of heat removed from the sheet surface by the blower fan 13. The output of the blower fan 13 (fan output D3) is set so that ΔWfs (=ΔWp)<ΔWfe. Thus, as shown by the solid line in part (a) of
In this embodiment, the sheet S is heated by the heating unit with heat rays not from the reverse side but from the face to which ink is applied. For this reason, even if the sheet used has a large thickness or is made of a highly heat-insulating material, ink is efficiently dried, and high-speed printing is achieved. In the case where a sheet having an adhesion layer on the reverse side thereof, such as a sheet of wall paper, is used, the reverse side of the sheet is not heated, and therefore the glue of the adhesion layer is prevented from melting, and a sheet conveyance jam is prevented from being caused by the melted glue.
As described above, in a moving state where the sheet is moving while the inkjet head is applying ink to the sheet during printing, the control unit performs control so that the sheet is heated by the heating unit. After the moving state and when the sheet stops moving, the control unit performs control so that the sheet is heated by the heating unit at a lower power and cooled by the cooling unit at a higher power than in the moving state.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-191207 filed Aug. 27, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-191207 | Aug 2010 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5428384 | Richtsmeier | Jun 1995 | A |
| 6059406 | Richtsmeier et al. | May 2000 | A |
| 7538299 | Spence et al. | May 2009 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20120050372 A1 | Mar 2012 | US |
