| 摘要 |
PROBLEM TO BE SOLVED: To provide an apparatus for detecting the residual quantity of ink in an ink jet printer in which the detection accuracy can be enhanced by increasing the tolerance of the incident angle of light to the interface at a prism part and the tolerance of distance to the prism part. SOLUTION: A prism part 61 is provided on the bottom face of each ink tank 15a-15d and the prism part 61 is provided with a first inclination interface 61a for refracting incident light from a light emitting element 62 located on the outside of a recording sheet in the widthwise direction thereof, a second inclination interface 61b for reflecting or refracting the incident light refracted on the first inclination interface, a third inclination interface 61c for reflecting or refracting the light reflected on the second inclination interface, and a fourth inclination interface 61d for refracting the light reflected on the third inclination interface to be in parallel with the incident light from the light emitting element. Angle of the first inclination interface is set such that the incident angle of light to the second inclination interface is altered to 52 deg. which is the substantially middle value of a critical angle range of 42 deg.-63 deg. and the apical angle at the prism part is set at 104 deg. so that the lights reflected on the first and second inclination interfaces impinge on the prism part at an incident angle of the substantially middle value of a critical angle range. |
