Patent ID: 8439476

Claim:
A method of adjusting the optical axis of an ink droplet detecting device, the ink droplet detecting device including a light emitting element that emits light, a light emitting element holder that holds the light emitting element and includes a light-emission-side holder shaft portion, a light receiving element for detecting an ink droplet discharge failure that receives scattered light after a light beam formed by the light emitted from the light emitting element collides with an ink droplet, a light receiving element holder that holds the light receiving element and includes a light-reception-side holder shaft portion, and a base member to which the light emitting element holder and the light receiving element holder are preliminarily positioned by the light-reception-side holder shaft portion and the light-emission-side holder shaft portion and then fixed, the light emitting element holder being held to the base member such that the rotation of the light emitting element holder about the light-emission-side holder shaft portion can be adjusted and the light receiving element holder being held to the base member such that the sliding of the light receiving element holder in the axial direction of the light-reception-side holder shaft portion perpendicular to a direction in which the rotation of the light emitting element holder is adjusted can be adjusted, the method comprising: positioning the ink droplet detecting device with the light-emission-side holder shaft portion and the light-reception-side holder shaft portion and fixing the ink droplet detecting device to an optical axis adjusting device; supplying power to turn on the emission of the light emitting element and a detecting circuit of a position adjusting light receiving element; rotating the light emitting element holder, and detecting that the light beam formed by the light which is emitted from the light emitting element is incident on a positioning target provided in the light receiving element for detecting a discharge failure, from an output value of the position adjusting light receiving element; duly fixing the light emitting element holder to the base member; and when the incidence of the light beam on the positioning target is not detected from the output value of the position adjusting light receiving element even though the light emitting element holder is rotated, sliding the light receiving element holder to adjust the height of the light receiving element holder, rotating the light emitting element holder again, and repeating the adjustment of the height of the light receiving element holder and the adjustment of the rotation of the light emitting element holder until the light beam is incident on the positioning target.