1. Field of the Invention
The present invention relates to a printing apparatus that forms an image by reciprocating a carriage mounting a print head and more particularly to an ink jet printing apparatus and an ink jet printing method capable of using a relatively thick print material such as a tray accommodating a compact disc.
2. Description of the Related Art
Ink Jet printing apparatus are currently being applied not only to rectangular sheets of paper or strips of rolled paper but also to other print materials having a variety of two-dimensional shapes and thicknesses For example, even small and thick materials such as CD-R's, DVD's and cards are printed with various images and characters by putting on their surfaces a print material suited for ink jet printing and printing images and characters there (in the following, these materials to be printed on are generally called compact discs (CD's).
In conventional general-purpose ink jet printing apparatus, when a material such as CD is to be printed, if a general transport path for paper is used, various problems will arise, including bad feeding performance because of its high stiffness, the CD sustaining scores, and the CD failing to be transported because of a relatively long distance between feed rollers. To deal with these problems, the conventional apparatus use a dedicated path for tray different from the general paper transport path.
Since trays have a greater thickness than that of general paper, the tray transport path is set almost horizontal and, from a standpoint of user's maneuverability, often configured to accept a tray from a front side of the printing apparatus as opposed to a back side from which paper is usually loaded. In this configuration, whether the tray is loaded in the transport path is usually not directly detected by a sensor. This is because the use of a configuration that enables detection of the presence or absence of a tray loaded from the opposite direction makes a reduction in size and cost of the apparatus difficult.
Meanwhile, in ink jet printing apparatus capable of printing such materials as CD's, an ink jet printing method that performs printing by scanning an ink ejecting print head mounted on a carriage along with the carriage is widely adopted. Thanks to many advantages, such as an ease with which an image can be formed in colors and at an increased resolution and low operation noise, the ink jet printing apparatus are in widespread use.
In such ink jet printing apparatus, setting a distance (or gap) between ink ejection openings in a print head and a print medium such as CD to an optimum value constitutes an important factor in forming a vivid and crisp image. When print media such as CDs are used in particular, since they are thicker than ordinary print media such paper and films, the print head must be set farther apart from a print medium support surface than when ordinary print media are used, to provide an optimum gap.
To provide an optimum gap between the print medium and the print head or ink ejection openings of the print head, it is common practice to change a position of a shaft that guides and supports a carriage mounting the print head according to the thickness of the print medium by activating a drive mechanism or eccentric cam provided on the shaft. In this case, the gap between the print head and the print medium is generally controlled by providing a rotary encoder or the like to a drive shaft of a pulse motor or DC motor, a drive source for the drive mechanism and eccentric cam, and controlling the motor according to a detected revolution of the drive shaft. The gap between the print head and the print medium is also controlled by using an optical or magnetic sensor that detects the gap.
These conventional techniques, however, have the following drawbacks.
(1) If a sensor for detecting the movement of a drive mechanism or for detecting the distance (gap) between a print medium, such as CD and tray, and the print head is provided to control the gap, it is difficult to minimize the cost of an ink jet printing apparatus.
(2) The provision of such a sensor requires a space and members for installing it and also lead wires for electrical connection of the sensor, making the inner construction of the printing apparatus complex and its size reduction difficult.
(3) If, to avoid the above problems, the dedicated sensor in not used, it is then not possible to check whether a gap control mechanism such as the one described above is working normally.