| 摘要 |
PROBLEM TO BE SOLVED: To detect that a guide roller is positioned at a reference position, and facilitate maintenance operation with a simple structure. SOLUTION: A drive motor is formed so as to detect variation from the reference position of the guide rollers 35 by a detecting means 40, and return the respective guide rollers 35 at a speed proportional to the variation from the reference position to the upper limit position of each of the guide rollers 35 when it is determined that the respective guide rollers 35 exceed, for example, the upper limit position of a detecting range. When the detecting means 40 determines that the respective guide rollers 35 are moved down to the upper limit position and included in the detecting range, the drive motor is controlled so as to return the respective guide rollers 35 to the reference position at the speed proportional to the variation to the reference position of the respective guide rollers 35 within the detecting range, and the downward movement of a holding frame 34 is stopped when the respective guide rollers 35 are returned to the reference position.
|
