1. Field of the Invention
This invention relates an automatic paper loading mechanism and method for printers, and more particularly to an improved automatic paper loading mechanism and method in which a bail roller can be automatically retracted to a release position so as not to be an obstruction during the paper feeding and can be automatically pivotally moved to a loading position after completion of the paper feeding.
2. Description of the Prior Art
A printer is widely known in which a desired printing operation is performed on a sheet paper or a tractor paper wound on a platen as a printing head is moved forwardly and backwardly along the platen, the printing head being such as of the dot, thermal or ink jet type.
According to this known printer, automatically loading the sheet paper or tractor paper was particularly useful to improve the operativity of the printer; heretofore, various automatic paper loading mechanisms have been put to practical use.
In such known automatic paper loading, the paper is manually inserted into a paper feed unit and is then automatically advanced by the paper feed unit until its top end arrives at a predetermined position on a platen. During that time, the paper is pressed against the platen in a correct posture by means of a bail roller, which would be inconveniently a significant obstruction.
Generally, before the automatic paper loading, this bail roller is pivotally moved by hand to a release position in which it is spaced from the platen. At that time the bail roller is manually moved by a bail-roller lever so that the position of the bail roller is restricted to facilitate the manipulation of the bail-roller lever. Usually, since the bail roller is located above the platen in confronting relation thereto, a blank area of the paper between the printing head and the bail roller must be set large.
Further, pivotally moving the bail roller by hand necessarily causes the bail-roller lever to project from a printer casing, thus resulting in an increased size of the printer and also in leakage of printing noise from an opening in the printer casing through which opening the bail-roller lever extends.
To this end, following mechanisms have hitherto been proposed to automatically pivotally move the bail roller during the automatic paper feeding.
Each of Japanese Patent Laid-Open Publications Nos. 73978/1987 and 162577/1987 discloses a printer in which a bail roller is operatively connected to an exclusive motor so that the bail roller is automatically released from a platen and returned thereto during the paper loading.
Japanese Patent Laid-Open Publications Nos. 21278/1985 and 62579/1987 and Japanese Utility Model Laid-Open Publications Nos. 130446/1986, 85448/1986 and 152444/1986 individually disclose a structure in which a bail roller is pivotally moved between a loading position and a loading position by utilizing the driving force of a carriage carrying a printing head.
Further, Japanese Patent Laid-Open Publication No. 49465/1988 discloses a mechanism in which the drive force for paper feeding is transmitted to the bail roller by means of a pivoting gear so that the bail roller is pivotally moved between a loading position and a release position as the pivotal movement of the bail roller is controlled by the printing-head carrier (carriage).
However, with the foregoing prior art arrangement, since the exclusive motor or solenoid is used only for pivotal movement of the bail roller, it would necessarily increase the entire size and weight of the printer, thus making the printer expensive.
In the prior art structure in which the bail roller is pivotally moved by utilizing the driving force of the carriage, because paper loading must be conducted with the bail roller lever held outside the printing area so that the carriage retains the bail roller in the release position, it would be impossible to conduct the centering of the carriage during paper feeding.
Consequently, since a paper being fed to the bail roller cannot be pressed by the carriage, the paper can be easily jammed at the bail roller.
Further, because the pivotal movement of the bail roller is determined depending on the amount of movement of the carriage, it is relatively difficult to define the correct release position.
For another problem, in the prior art arrangement equipped with a conventional clutch unit utilizing a pivoting gear, partly because only the forward rotating force of the paper feed driving force is utilized to release the bail roller, and partly because this release driving can be controlled by a cam in a predetermined release pattern, fine control of the pivotal movement of the bail roller.
When the bail roller is driven only by the forward rotating force of the paper feed driving force, especially when high-concentration printing is conducted as the paper is slightly backwardly moved, and when printing is conducted in a laterally split manner, the paper is the bail roller cannot be retained in the release position so that fine printing control such as top margin printing cannot be achieved.