Patent ID: 8770705

Claim:
A droplet discharge detection device comprising: a head array unit in which plural nozzles are arranged in a line; a light emitter configured to emit a light beam in a direction in which the nozzles are arranged, wherein the light emitter is disposed at a first end portion of the head array unit and the light emitter has an aperture for limiting a diameter of a light beam; and a light receiver configured to receive a scattered light beam of the light beam generated by a droplet, wherein the light receiver is disposed at a second end portion of the head array unit, the second end portion being opposite to the light emitter of the head array unit, wherein, when a first direction in which the droplet is discharged from the nozzles is set to be an X direction, and when a second direction that is perpendicular to the X direction and that is perpendicular to the direction in which the nozzles are arranged is set to be a Y direction, a formula below is satisfied, ∫ X 1 X 2 ∫ Y 1 Y 2 ( Asc 2 +2 Adf·Asc· cos[2π( L df −L sc )/λ]) dX PD dY PD >0, wherein, in the formula, the Y PD is a Y-coordinate of a position in the Y direction on a light receiving surface of the light receiver, the [Y 1 , Y 2 ] is an effective detection range in the Y direction on the light receiving surface of the light receiver, the X PD is an X-coordinate of the position in the X direction on the light receiving surface of the light receiver, the [X 1 , X 2 ] is an effective detection range in the X direction on the light receiving surface of the light receiver, the L df is a first optical path length of a diffracted light beam from a center of the aperture of the light emitter to the light receiving surface of the light receiver, the A df is a first amplitude of the diffracted light beam, the A sc is a second amplitude of the scattered light beam, the L sc is a second optical path length of the scattered light beam from the center of the aperture of the light emitter to the light receiving surface of the light receiver, and the λ is the wavelength of the light beam.