Patent Application
20130027489
1. Field of the Invention
The present invention relates to a printing apparatus in which a print head applies ink to a recording medium to perform printing.
2. Description of the Related Art
In a serial print system which forms an image while reciprocating a print head, multipass bidirectional printing is known in which printing is performed by performing reciprocal scanning a plurality of times on the same area of the sheet. In this system, a time interval between printing at the time of the first scanning and printing at the time of the second scanning in any continuous two-times scanning is different according to the distance from a position where a carriage inverts its driving direction. For this reason, before an ink droplet applied on the sheet in the first scanning permeates the sheet and is then fixed to the sheet, printing is performed by the second scanning, so that an image at that portion may deteriorate as an uneven streak depending on the characteristics of the sheet.
Japanese Patent Application Laid-Open No. 07-047695 discusses a solution to the above problem such that the carriage is caused to wait for a predetermined time period until the next scanning is started after the forward or backward scanning is ended.
The waiting time period from the end of a scanning to the start of the next scanning merely means the stop of a printing operation. For that reason, it is important to reduce the waiting time as much as possible to improve a print throughput.
An aspect of the present invention is directed to a printing apparatus capable of reducing the deterioration of an image due to an insufficient dryness without sacrificing print throughput.
According to an aspect of the present invention, a printing apparatus includes a printing unit configured to apply ink to a recording medium while reciprocating a print head with respect to the recording medium, and a drying unit configured to apply energy for accelerating dryness to the recording medium to which the ink is applied by the print head. The drying unit applies more energy at edges of a range within which the printing unit moves on the recording medium than at a middle of the range.
According to an exemplary embodiment of the present invention, there is provided a printing apparatus capable of reducing the deterioration of an image due to an insufficient dryness without any sacrifice of print throughput. Further, electric power required for drying ink can be minimized.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
It is presumed that the recording medium for use in the inkjet printing apparatus according to the present exemplary embodiment is the one made of water repelling vinyl chloride without a receiving layer (hereinafter referred to as recording medium without a receiving layer). A general recording medium with a receiving layer may be used. It is also presumed that the ink in use includes a large amount of polymer emulsion with a property in which moisture in the ink is evaporated by applying heat to the recording medium and the ink is softened and encapsulated. The ink is encapsulated on the recording medium to enable improving weather resistance, water resistance, and scratch resistance of an image.
The printing unit forms an image in a serial print system method in which a carriage 6 repeats the reciprocal scanning of a print head 7 in the main scanning direction (X direction) on the recording medium, which is conveyed on a platen 2 in the sub-scanning direction (Y direction) by step feed.
The platen 2 is mounted on a casing 1. The casing 1 includes a suction unit 4 for suctioning a recording medium 3. The carriage 6, which is reciprocated in the main scanning direction, is supported by a main rail 5 arranged along the longitudinal direction of the casing 1. The carriage 6 is provided with the inkjet print head 7. An energy generation element for discharging ink from the nozzles of the print head 7 may be any of a heating element, a piezoelectric element, an electrostatic element, and a microelectromechanical system (MEMS) element.
A carriage motor 8 is a drive source for moving the carriage 6 in the main scanning direction and the rotation driving force thereof is transmitted to the carriage 6 by a belt 9. A position where the carriage 6 is in the main scanning direction is detected by a linear encoder. The linear encoder includes a linear encoder pattern 10 attached to the casing 1 and a reader (not illustrated) which optically, magnetically, or mechanically reads the encoder pattern 10 and is mounted on the carriage 6.
The recording medium conveyance unit feeds a recording medium, conveys the recording medium in the printing unit, and handles the recording medium at the time of collecting the recording medium. A long continuous recording medium of a recording medium is supplied as a roll member 23 wound onto a spool 18 in a roll shape. The spool 18 includes a torque limiter 19 for exerting a brake force (back tension) on the recording medium 3. The recording medium drawn out from the roll member 23 is supplied to the lower portion of the printing unit (the casing 1) from the front to the rear of the apparatus.
The recording medium 3 supplied to the lower portion of the casing 1 is supplied onto the platen 2 from the rear to the front while winding the casing 1. The recording medium 3 on the platen 2 is conveyed along the sub-scanning direction (direction indicated by an arrow Y in
The recording medium on which an image is printed by the print head 7 of the printing unit is wound and collected by a spool 20. The recording medium wound in a roll shape around the spool 20 forms a roll member 24. The spool 20 is rotated by a winding motor 21 and includes a torque limiter 22 for exerting a winding tension on the recording medium 3.
If the recording medium without a receiving layer is used, the drying unit radiates energy for drying the ink applied to the recording medium in a short time period. The drying unit has a heater 25 provided immediately above the platen 2 and in a position higher than the carriage 6. The heater 25, as described below, is divided into a plurality of heater elements (five elements in the present exemplary embodiment) along the longitudinal direction. The heater 25 is covered by a heater cover 26. The heater cover 26 causes a mirror inside the cover to reflect the heat (infrared to far-infrared) of the heater to direct the heat toward the recording medium surface and physically protects the heater.
The heater 25 is positioned immediately above the platen 2 and radiates thermal energy to the area where the print head 7 is reciprocated. When the ink discharged from the print head 7 reaches the print surface, the carriage 6 immediately leaves there, and the applied ink is exposed to the thermal energy radiated by the heater 25. This accelerates the evaporation and dry of moisture of the ink promptly after printing is performed. The thermal energy of the heater 25 evaporates moisture and dissolves specific components in the ink to cover the color materials of the ink with the specific components. Thus, the ink can be firmly fixed even to the recording medium without a receiving layer to form an image high in weather resistance.
The control unit acquires information about a period of time required until printing is performed in the next scanning after printing is performed in the previous scanning (hereinafter referred to as an interscanning time) for each of the five areas on the recording medium 3 corresponding to the five heater elements. For example, when an image with two bands illustrated in
As described above, insufficient thermal energy to be provided for dryness produces image unevenness. However, excessively increasing temperature on the recording medium increases the power consumption of the apparatus, which is not desirable. This also increases the temperature of the recording head to probably affect the discharge performance and lifetime of nozzles. Furthermore, if the recording medium in use is a material weak against heat, such as vinyl chloride, excessive heating may deform the recording medium and cause damage such as creases.
The image unevenness prominently occurs in bidirectional printing in which printing is performed in both of forward and backward scanning while the carriage is reciprocated. On the other hand, the image unevenness slightly occurs in unidirectional printing in which printing is performed in either of forward or backward scanning while the carriage is reciprocated. The reason is described below with reference to
In the case of bidirectional printing, in the five divided areas on the recording medium, the nearer an edge area is to the reversing position of scanning (return position), the shorter the interscanning time. For this reason, the possibility that ink is applied in the next scanning before ink applied in the previous scanning is sufficiently dried in the end area is higher than in the other areas. This phenomenon prominently occurs as temperature becomes lower. The ink applied in the previous and the next scanning forms a dot in which adjacent dots are mixed with each other as illustrated in
In the case of unidirectional printing, on the other hand, a time sufficient enough to dry the ink applied in the precious scanning is allowed and the next scanning is performed. For this reason, the ink applied in the previous and the next scanning does not interfere with each other. Every dot in one image is formed in a dot shape as illustrated in
In the range in which the print head moves for scanning on the recording medium, for example, the heating value of the heater in the drying unit is set such that, the smaller the area is in the minimum value of the interscanning time, the higher the temperature on the recording medium becomes. Table 1 illustrates a relationship between the minimum value of the interscanning time and the temperature on the recording medium.
The reason the minimum value of the interscanning time is referenced is described below. In general, inkjet printing uses multipass printing in which an image is formed by scanning the same area on the recording medium more than once. When the bidirectional printing and the multipass printing are performed, as illustrated in
In both edges of scanning where the large and small time differences are alternated, the scanning small in the interscanning time causes a problem, so that the amount of energy applied to the vicinity of both edges (the heating value of the heater) is determined based on the above. Alternatively, the amount of energy applied to the vicinity of both edges may be alternately increased and decreased every scanning.
The advantage of the present exemplary embodiment is described by comparing the present exemplary embodiment (in
The interscanning time for each area can be acquired by measuring the time using a timer or calculating the time. If the time is acquired by calculation, the time can be determined from a scanning speed, a distance from edges of an image, a distance from a print head reversing portion, and a print head reversing time. An example of a calculation formula for determining the interscanning time T is represented by the following equation (1):
Interscanning time T=(distance from a print head reversing portion)×2/(average scanning speed)+(print head reversing time). (1)
The temperature of the recording medium can be controlled to a predetermined temperature by using feedback control or open loop control. For the feedback control, the temperature of the recording medium surface is measured by a temperature sensor to control the output of each heater. For the open loop control, the relationship between the temperature of the recording medium previously determined by an experiment and a heater output is obtained and stored to set the heater output to a predetermined temperature.
The configuration of the heater is not always limited to the above form. For example, such a form may be provided that the heater is formed of a long and thin single element, a shutter for shielding heat is provided for each segmented area, and heat applied to the recording medium is adjusted according to a time period for which the shutter is opened. Alternatively, such a form may be provided that the heater can be moved along the scanning direction.
A drying unit for giving energy for accelerating dryness for the recording medium to which ink is applied by a printing unit may be used irrespective of a form for providing thermal energy (infrared to far-infrared) by a heater. For example, such a form may be provided that the recording medium is irradiated with electromagnetic waves, such as ultraviolet ray, infrared ray, or microwave, or provided with air current (warm wind with low humidity) to accelerate dryness by providing energy.
As described above, the ink applied in the previous and the next scanning interferes with each other on the recording medium to produce the image unevenness. The probability that the image unevenness is produced in an area where dot density is low is relatively low because the probability that the ink applied in the previous and the next scanning is adjacent to each other is low.
Weighting of temperature control on the recording medium performed according to the interscanning time for each area may be performed according to the dot density for each area. If the dot density is low, the temperature control on the recording medium is not performed according to the interscanning time for each area and the temperature control on the recording medium is performed according to the interscanning time for each area as the dot density becomes high. Table 2 illustrates an example of a relationship among the dot density, the minimum value of the interscanning time, and temperature on the recording medium.
Thus, the minimum value of the interscanning time and the temperature of the drying unit are controlled according to the dot density for each area to allow power consumption to be reduced and temperature in the apparatus to be further prevented from increasing.
Another modification is described below with reference to
Table 4 illustrates an example of a relationship between recording medium target temperature and power applied to the drying unit according to the carriage speed.
According to the exemplary embodiment described above, a printing apparatus capable of preventing the deterioration of an image due to an insufficient dryness without any sacrifice of print throughput can be realized. Further, Power required for drying ink can be reduced.
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 modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Application No. 2011-166761 filed Jul. 29, 2011, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-166761 | Jul 2011 | JP | national |
