The conveniences provided by portable printers have made them widely used in the modern business settings for many years. For instance, a person supervising rental car returns often wears a portable printer on his/her belt for printing car rental information or for communicating information to his/her rental car company's main computer. By virtue of carrying a portable printer, the person may print out return information and/or receipts at the parking lot where the rental cars are returned, without the need of going back to the rental office to complete the transactions. The portable printers, thus, save tremendous amounts of time and trouble for customers and they dramatically improve efficiencies of many business transactions.
There are many different designs of portable printers available on the market. However, only two forms of printing mediums, namely, a separate-sheet form or a medium-roll form, are predominantly used for all printers, whether portable or not. Each printer thus has its specifically designed feeding mechanism to receive either one form of the printing medium, or both. For a typical small-sized portable printer, the medium-roll form is the principal printing medium form used.
The printing medium may be made of sheets of paper or labels attached to protective backings. For the separate-sheet printing medium form, each sheet of paper or each label is separately fed into the printer for printing. Conversely, the medium-roll form of a printing medium is formed by a continuous paper or label strip fed into the printer by a roller feeding mechanism built into the printer. The continuous strip may have periodic perforations to facilitate tearing the strip of the printing medium apart. Alternatively, other tearing mechanisms may be adopted by the printer to tear the strip of the printing medium roll.
Having a medium roll as the printing medium form is particularly desirable for most portable printers. Preferably, a portable printer should be small and lightweight, as compared to a regular non-portable printer. Moreover, the portable printer is often designed to print simple receipts, or similar business records. Thus, there is less need of using standard-size business papers for the portable paper. In addition, the medium-roll form is easier to handle for a small size printing medium. As a result, most portable printers use the medium-roll form printing mediums.
A conventional portable printer generally has a print head for forming images on the printing medium, a platen for pressing the printing medium against the print head and for moving the printing medium, a feeding mechanism for feeding the printing medium to the print head, and a door to be opened for accessing or replacing the printing medium. The feeding mechanism often comprises a medium roller for mounting a printing medium roll thereon, and a motor for rotating the platen and/or the medium roller to move the printing medium toward the print head.
As the printing medium passes through the portable printer, the printing medium needs to be carefully aligned throughout an internal medium path of the portable printer for a good quality printout. The internal medium path starts from the printing medium roll to the print head and the platen until the printing medium comes out of the portable printer. Thus, the platen of the portable printer should be aligned with the print head to press and move the printing medium properly. The medium roller also has to be carefully situated in the portable printer in order to assure the alignment of the printing medium with the print head. Otherwise, skipped printings, double printings, paper jam, and many other problems might happen due to the misalignment problem of the printing medium in the portable printer. As a result, the print head, the platen, and the medium roller are typically positioned in the vicinity of each other, and a conventional portable printer typically has a single bracket for holding the print head and the platen together to reduce the likelihood of misalignment problems.
Placing the print head and the platen on a single bracket does reduce the likelihood of misalignment problems for a conventional portable printer. It, however, has drawbacks of inconvenience in replacing the printing medium, for it necessitates threading the printing medium between the print head and the platen. Also, the medium roller of the conventional printer is often positioned inside the portable printer and is hard to reach. Thus, to replace a printing medium in the conventional portable printer, a user has to open the printer door, take off a used printing medium roll, insert a new printing medium roll, carefully thread the strip of the new medium roll between the platen and the print head, and then close the door of the portable printer. These steps, taken as a whole, are quite time-consuming to perform. It is particularly inconvenient if the portable printer is mounted on the belt of the user, such as the person supervising the rental car returns. To replace the printing medium roll in the conventional portable printer, that person will necessarily have to take the printer off the belt and have it reinstalled on the belt after reloading the printing medium roll.