Incremental printing of symbolic information – Thermal marking apparatus or processes – Density control
Reexamination Certificate
2001-11-13
2004-08-31
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Density control
C347S194000, C400S120120
Reexamination Certificate
active
06784908
ABSTRACT:
This application claims benefit of Japanese Application No. 2000-350117 filed in Japan on Nov. 16, 2000, Japanese Application No. 2000-350118 filed in Japan on Nov. 16, 2000, Japanese Application No. 2000-350119 filed in Japan on Nov. 16, 2000, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printer such as a sublimable type thermal printer having a freely attachable or detachable battery as a power supply for printing operation. More particularly, the present invention relates to a printer capable of correcting a current to be conducted to a thermal head for the purpose of stabilizing a printing density. The printer thus achieves printing with stable image quality ensured, offers improved performance, and contributes to realization of a low-cost compact design.
2. Description of the Related Art
In recent years, heat-sensitive heat-transfer printers capable of presenting high-definition images owing to the ability to print images full of colors have been widely adopted as devices that produce hardcopies of images received from a personal computer, a camera-built-in video tape recorder, an electronic still camera, or the like.
As far as a conventional heat-sensitive heat-transfer printer is concerned, print paper as well as an ink sheet is pressured against and sandwiched between a platen roller and a thermal head. The ink sheet is produced by applying a plurality of heat-sublimable color dyes to a base film, and positioned so that the heat-sublimable dyes will stick to the print paper. A plurality of heating elements are arranged on one side of the thermal head. When a current is conducted to the thermal head, the heating elements appropriately generate heat according to print data. Consequently, the heat-sublimable dyes are heated through the base film. This causes the heat-sublimable dyes to sublime. Eventually, the heat-sublimable dyes are transferred to the paper for the purpose of printing.
In the past, many proposals have been made of the foregoing types of printer and intended to improve printing quality and reduce costs. For example, Japanese Unexamined Patent Application Publication No. 5-238046 describes a battery-driven printer and Japanese Unexamined Patent Application Publication No. 7-195729 describes a heat-sensitive heat-transfer recording device.
The battery-driven printer described in the Japanese Unexamined Patent Application Publication No. 5-238046 has a rechargeable battery as a power supply that permits photo-printing. When photo-printing is not performed, a rectified dc voltage source composed of an ac rectifier, a switching unit, a voltage control unit, and a secondary rectifier, is used to charge the rechargeable battery. During photo-printing, the rechargeable battery discharges to supply power required to perform photo-printing. A voltage drop stemming from the discharge is detected. The voltage control unit controls the rectified dc voltage source so that the rectified dc voltage source will develop a dc voltage corresponding to the voltage drop. The voltage control unit then uses a charging/superposition switching unit and a superposition unit to superpose the output of the rectified dc voltage source on the output of the battery for correction. The voltage control unit thus stabilizes the power to be supplied from the battery to improve a quality of photo-printing.
Moreover, the heat-sensitive heat-transfer recording device described in the Japanese Unexamined Patent Application Publication No. 7-195729 performs thermal recording using a thermal head. An incorporated photo-printing voltage sensing unit detects a voltage applied to the thermal head, then, it develops a voltage to be applied to the thermal head based on an output voltage of a voltage adding circuit.
The voltage adding circuit adds up an output voltage of a peak-value detecting unit, which detects a peak value of an output voltage of the photo-printing voltage sensing unit, and a voltage set by a photo-printing voltage setting unit. In other words, the voltage applied to the thermal head is detected and then is controlled in order to stabilize the output voltage of the thermal head. Thus, a printing density is stabilized.
Furthermore, other proposals intended to improve printing quality include, for example, a proposal for a density/gray scale controlled printer described in Japanese Unexamined Patent Application Publication No. 6-91916 and a proposal for an image forming device described in Japanese Unexamined Application Publication No. 2000-135809.
The density/gray scale controlled printer described in the Japanese Unexamined Patent Application Publication No. 6-91916 conducts a current to heating resistance elements and records an image on print paper using the energy of heat generated from the heating resistance elements. Power is compensated based on the counted number of conducting elements. Thus, excellent color reproducibility is guaranteed on a constant basis all the time.
Moreover, the image forming device described in the Japanese Unexamined Application Publication No. 2000-135809 adopts a thermal head designed for a heat-transfer printer or a heat-sensitive printer in efforts to prevent occurrence of an uneven density among lines. Incidentally, the uneven density is attributable to the fact that the larger the number of heating resistance elements driven simultaneously among all heating resistance elements is, the smaller a current to be fed to each heating resistance element is. Herein, the number of all heating resistance elements is the same as the number of dots constituting one line. In the image forming device, calculation is performed using photo-print data representing one line. Consequently, a density can be corrected based on the pulse duration of current conduction pulses. Moreover, occurrence of an uneven density such as a white streak created between lines can be prevented.
Incidentally, there is a demand for printers that are inexpensive and able to produce high-definition prints. Moreover, printers that are compact, lightweight, and portable are strongly demanded so that printing can be performed at any time in any place.
In order to realize a portable printer capable of satisfying the above demands, the printer must be able to be driven using a battery alone. In this case, since the printer can be used even in places where an ac power supply is unavailable, its usefulness improves. When an emphasis is put on image printing, a heat-transfer printer such as the aforesaid sublimable printer is preferred because it offers high image quality.
However, the heat-transfer printer requires a large amount of power for heat-transfer printing. Moreover, since the capacity of a battery power supply is limited, occurrence of a voltage drop during use is unavoidable. As long as an ac power supply can be used, an applied voltage is held constant and unevenness in printing image quality is limited. However, when an attempt is made to use a battery alone to perform heat-transfer printing, a large obstacle must be overcome. Namely, a large voltage drop dependent on the degree of exhaustion of the battery must be coped with, and satisfactorily stable image quality must be attained.
In consideration of the above demands, the battery-driven printer described in the Japanese Unexamined Patent Application Publication No. 5-238046 is unacceptable, though it can maintain a predetermined photo-printing voltage all the time. Namely, the battery-driven printer has a drawback that it must be powered using an ac power supply but cannot be driven with a battery alone.
Moreover, the heat-sensitive heat-transfer recording device described in the Japanese Unexamined Patent Application Publication No. 7-195729 employs an assembly that detects a voltage applied to a thermal head, controls the applied voltage so that an output voltage of the thermal head will remain constant, and thus stabilizes a printing density. In addition, a peak-value detecting unit is employed for detecting the peak of
Olympus Corporation
Pokotylo John C.
Straub & Pokotylo
Tran Huan
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