| 摘要 |
PURPOSE:To increase the quality of a printed image by photoelectrically detecting the density of ink, which is recovered and recirculated for reuse, to add water thereto as necessary, whereby the density of ink can be maintained at a level in a predetermined range, and the ejection characteristics of ink and the angle of deflection of ink jet can be kept constant. CONSTITUTION:A transparent pipe portion 13 is provided in a circulation system 11 for ink 1, which includes an ink tank 2, an ink supply pump 3, a head 5 and a gutter 10. In this transparent pipe portion 13, the density of the ink 1 is detected photoelectrically at all times by a light emitting element 14 and a light receiving element 15. When the density of the ink 1 has reached the upper limit of a predetermined range of levels, a signal for operating a water supply pump 19 is outputted from a water supply circuit 17 to supply the water in the water tank 18 to the ink tank 2. As a result, the density of the ink is decreased. When the density of the ink has reached a level close to the lower limit, the supply of water is limited by a comparison circuit 16 and the water supply circuit 17. The supply of water is thereafter interrupted. |
