Densitometer for a liquid developer material

A printing machine of the type in which the reduction in specular reflectance of a member having a liquid deposited on a portion thereof is detected, wherein the improvement includes:

• means for projecting light rays, in the visible spectrum, onto the portion of the member having the liquid deposited thereon;
• a first condenser lens interposed between said projecting means and the portion of the member having the liquid deposited thereon so that collimated light rays are projected thereon;
• means for detecting the total reflectivity of the portion of the member having the liquid deposited thereon and the diffuse component of the total reflectivity of the portion of the member having the liquid deposited thereon and generating a total signal proportional to the total reflectivity and a diffuse signal proportional to the diffuse component of the total reflectivity of the liquid, said detecting means includes a photosensor array;
• a second condenser lens interposed between said detecting means and the member having the liquid deposited thereon for receiving the light rays reflected therefrom, said photosensor array comprises a central photosensor positioned to receive the total light rays transmitted through said second condenser lens, and at least one edge photosensor positioned about the periphery of said central photosensor to receive the diffuse component of the light rays transmitted through said second condenser lens;
• and
• means, responsive to the difference between the total signal and the diffuse signal, for generating a specular signal proportional to the specular component of the total reflectivity.

A densitometer adapted to measure the reduction in the specular component of the reflectivity of a surface having a liquid deposited on a portion thereof, including

• a collimating lens;
• a light source positioned to project light rays, in the visible spectrum, through said collimating lens onto the portion of the surface having the liquid deposited thereon;
• a collector lens positioned to receive the light rays reflected from the portion of the surface having the liquid deposited thereon;
• a photosensor array positioned to receive the light rays transmitted through said collector lens and generating a total signal proportional to the total reflectivity of the portion of the surface having the liquid deposited thereon and a diffuse signal proportional to the diffuse component of the total reflectivity of the portion of the surface having the liquid deposited thereon;
• and
• control circuitry, electrically connected to said photosensor array, for comparing the total signal and the diffuse signal to determine the difference therebetween for generating a specular signal proportional to the specular component of the total reflectivity of the surface having the liquid deposited thereon.