Method of detecting a length of sheet of a printer

Abstract: The invention relates to a method of detecting a length of sheet of a printer, comprising the step of: detecting the sheet length by use of an optical sensor (5) when inserting said sheet, according to the invention said sensor (5) is moved while steering clear of undetectable portions of said sheet, thus detecting the sheet length.

Description: Detailed Description of the Invention: [Field of Industrial Application] The present invention relates to a method of detecting a length of sheet of a printer. [Prior Art] Known is a printer in which a length of sheet inserted is detected, and the number of printing lines is set corresponding to the length thereof. Based on a sheet length detecting method, an optical sensor fixed in a specific position judges an existence or non-existence of the sheet while taking in the sheet. A sheet length is obtained based on the judgment result. [Problems to be Solved There is caused, however, a drawback to the conventional detecting method. The sensor is fixed, and hence, when ruled lines are printed beforehand on the sheet, the sensor is incapable of detection of sheet at the ruled line printed portions. A judgment of non-existence of sheet comes out. A misjudgment about a length of sheet is given, and it follows that the number of printing lines is mistakenly set. It is an object of this invention to provide a method of detecting a length of sheet of a printer, which is capable of accurately detecting the sheet length. [Means for Solving the Problems] To obviate the foregoing problems, according to the present invention, there is provided a method of detecting a length of sheet of a printer, comprising the step of: detecting the sheet length by use of an optical sensor when inserting the sheet, characterized in that the sensor is moved while steering clear of undetectable portions of the sheet, thus detecting the sheet length. Preferably, the optical sensor is mounted on a carrier of a printing head. [Embodiment] One embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram illustrating the principal portion of a printer. The numeral 1 represents an opening through which a sheet is taken in and discharged; 2a, 2b rollers for taking in and discharging the sheet; 3 a printing head; 4 a carrier for moving the printing head 3; 5 an optical sensor for judging existence or non-existence of the sheet, composed of light emitting/receiving elements and mounted on the carrier 4; 6 a platen colored in, e.g., black to make the platen itself optically distinguishable from the sheet; and 7 a guide rod for supporting the carrier 4. FIG. 2 is a block diagram depicting the principal portion of the printer. The same numerals as those of FIG 1 indicate the same components. Designated at 8 is a control circuit for controlling operations of the printer as a whole. The numeral 9 denotes a printing means constructed of the printing head 3 and the carrier 4; 10 an LF (Line Feed) motor for driving the rollers 2a, 2b; 11 an LF counter for counting the number of line feeds in accordance with a rotary quantity of the LF motor 10; and 12 a storage means for storing positional data of the carrier 4. Referring next to FIGS. 3 and 4, the operation of detecting a sheet length will be described. To start with, the carrier 4 moves in response to an intake instruction of the sheet, whereby the sensor 5 is placed in a predetermined position, e.g., at the center (step A). Next, the rollers 2a, 2b are rotated in an intake direction. When the sheet has already been inserted into the opening 1, the sheet is taken in with rotations of the rollers 2a, 2b (step B). It is assumed that a line 13 is, as illustrated in FIG. 5, printed beforehand on the sheet. The sheet is being taken in, and when the sensor 5 judges an existence of sheet, the LF counter 11 is reset. In this state, the LF counter 11 effects counting corresponding to the rotary quantity of the rollers 2a, 2b (step C). Moe specifically, as illustrated in FIG. 5a, the sheet moves in an arrowed direction. The sensor 5 judges the existence of sheet. Subsequently, the sheet is further taken in, and when the line 13, as depicted in FIG, 5b, enters a monitor region of the sensor 5, the sensor judges a non-existence of sheet. When giving a judgment of the non-existence of sheet, a confirmation thereof is performed (step D) The confirming operation at the step D will be explained in conjunction with a flowchart of FIG. 4. On making a judgment of the non-existence of sheet, the rollers 2a, 2b stop rotating, and the intake of the sheet stops, correspondingly. The LF counter 11 likewise ceases to count (step A'). Next, the carrier 4 moves to the home position (step B'). With this movement, the sensor 5 judges the existence of sheet because of the monitor region deviating from the line 13. At this moment, the positional data of the carrier 4 is stored in the storage means 12. The carrier 4 stops in the home position. Thereafter, as depicted in FIG. 5c, the carrier 4 resumes its movement to a position indicated by the positional data stored in the storage means 12 (step C'). The operation reverts to a routine of FIG. 3. The rollers 2a, 2b resume their rotations. The intake of the sheet continues, and the LF counter 11 also continues to count (step E). After the terminal of sheet has been taken in, and when making a judgment of the non-existence of sheet, the operation comes back again to a routine of FIG. 4. In this case, even when moving the sensor 5 in accordance with the step B', the judgment of the existence of sheet is not given. Hence, the carrier 4 moves back to the initial monitoring position (step D'). In the judgment as to the existence or non-existence of sheet in the next routine of FIG. 3, the non-existence of sheet is judged. The sheet length is set based on a count value of the LF counter 11 at that time (step F). The sheet length is detected by the operations discussed above. A printing format is set based on this sheet length. Printing is then effected. Note that in the embodiment given above, when changing the sheet existence judgment to the non-existence judgment, the carrier 4 moves to the home position in the confirming operation. The process is not, however, limited to this. For instance, the carrier 4 temporarily moves to the home position and further to the right end. The existence or non-existence of sheet may thereafter be detected. With this arrangement, even if the line 13 is printed up to the left end of sheet, the existence of sheet can be judged on condition that there is a space at the right end of sheet. More accurate judgment about the sheet length can be made. [Effect of the Invention] According to the present invention, if the sheet includes portions, i.e., the printed portions in which the sensor can not judge the existence of sheet, the sensor moves to steer clear of such portions. In this manner, the existence or non-existence of sheet is judged. It is therefore possible to accurately detect the sheet length. [Brief Description of the Drawings] FIG. 1 is a schematic diagram illustrating the principal portion of a printer; FIG. 2 is a block diagram depicting the principal portion of the printer; FIG. 3 is a flowchart of assistance in explaining the operation of detecting a sheet length; FIG. 4 is a flowchart of assistance in explaining the operation of detecting the sheet length; and FIG. 5 is an explanatory diagram showing the operation of detecting the sheet length. 5: sensor.

Claims: A method of detecting a length of sheet of a printer, comprising the step of: detecting the sheet length by use of an optical sensor when inserting said sheet, characterized in that said sensor is moved while steering clear of undetectable portions of said sheet, thus detecting the sheet length. The method as set forth in claim 1, wherein said optical sensor is mounted on a carrier of a printing head.

Inventors: IKEDA KAZUAKI C O SEIKOSHA CO, IKEDA, KAZUAKI, C/O SEIKOSHA CO., LTD.
Applicants: SEIKOSHA KK, SEIKOSHA CO., LTD.
Application year: 1992
Main classification: B41J29
IPC codes: B41J29, B41J11, B41J13, B65H7