Densitometer for measuring developability

An apparatus for measuring the reflectivity of a selected region of a surface covered at least partially with particles;

• including:
• means for generating a first signal proportional to the diffuse component of the total reflectivity of the selected region of the surface covered at least partially with particles and a first reference signal proportional to the diffuse component of the total reflectivity of a region of the surface without particles thereon, said generating means generates a second reference signal proportional to the specular component of the total reflectivity of the region of the surface without particles thereon, a third reference signal proportional to the specular component of the total reflectivity of the selected region of the surface with black particles thereon, and a fourth reference signal proportional to the diffuse component of the total reflectivity of the selected region of the surface with black particles thereon;
• and
• means for determining a control signal as a function of the difference between the first signal and the first reference signal, said determining means determines a constant of proportionality as a function of the first reference signal, the second reference signal, the third reference signal and the fourth reference signal with the control signal being determined as a function of the constant of proportionality.

An electrophotographic printing machine of the type in which the reflectivity of a selected region of a moving photoconductive member covered at least partially by marking particles is detected, wherein the improvement includes:

• means for generating a first signal proportional to the diffuse component of the total reflectivity of the selected region of the photoconductive member covered at least partially with marking particles and a first reference signal proportional to the diffuse component of the total reflectivity of a region of the photoconductive member without particles thereon said generating means generates a second reference signal proportional to the specular component of the total reflectivity of the region of the surface without particles thereon, a third reference signal proportional to the specular component of the total reflectivity of the selected region of the surface with black particles thereon, and a fourth reference signal proportional to the diffuse component of the total reflectivity of the selected region of the surface with black particles thereon;
• and
• means for determining a control signal as a function of the difference between the first signal and the first reference signal, said determining means determines a constant of proportionality as a function of the first reference signal, the second reference signal, the third reference signal and the fourth reference signal with the control signal being determined as a function of the constant of proportionality.

An infrared densitometer for measuring the reflectivity of a selected region of a moving photoconductive member covered at least partially with marking particles, including

• a collimating lens;
• a light source positioned to project light rays through said collimating lens onto the moving photoconductive member with or without marking particles thereon;
• a collector lens positioned to receive the light rays reflected from the moving photoconductive member;
• a photosensor array positioned to receive the light rays transmitted through said collector lens and generating a first signal propotyional to the diffuse component of the total reflectivity of the selected region of the photoconductive member with marking particles covering at least a portion thereof and a first reference signal proportional to the diffuse component of the total reflectivity of a region of the photoconductive member without marking particles thereon;
• and
• control circuitry, electrically connected to said photosensor array, for determining a control signal as a function of the difference between the first signal and the first reference signal.

An infrared densitometer for measuring the reflectivity of a selected region of a moving photoconductive member covered at least partially with marking particles, including:

• a collimating lens;
• a light source positioned to project light rays through said collimating lens onto the moving photoconductive member with or without marking particles thereon;
• a collector lens positioned to receive the light rays reflected from the moving photoconductive member;
• a photosensor array positioned to receive the light rays transmitted through said collector lens and generating a first signal proportional to the diffuse component of the total reflectivity of the selected region of the photoconductive member with marking particles covering at least a portion thereof and a first reference signal proportional to the diffuse component of the total reflectivity of a region of the photoconductive member without marking particles thereon, said photosensor array generates a second reference signal proportional to the specular component of the total reflectivity of the region of the photoconductive member without particles thereon, a third reference signal proportional to the specular component of the total reflectivity of the selected region of the photoconductive member with black particles thereon, and a fourth reference signal proportional to the diffuse component of the total reflectivity of the selected region of the photoconductive member with black particles thereon;
• and
• control circuitry, electrically connected to said photosensor array, for determining a control signal as a function of the difference between the first signal and the first reference signal, said control circuitry determines a constant of proportionality as a function of the first reference signal, the second reference signal, the third reference signal and the fourth reference signal with the control signal being determined as a function of the constant of proportionality.

A method of measuring the reflectivity of a selected region of a photoconductive member covered with diffusely reflecting marking particles, including the steps of:

• generating reference voltages proportional to the specular and diffuse components of the total reflectivity of the selected region of the photoconductive member without marking particles thereon and covered at least partially with black marking particles;
• determining a constant of proportionality as a function of the reference voltages generated in said step of generating and the diffuse reflectivity of black marking particles;
• generating a voltage proportional to the diffuse component of the total reflectivity of the selected region of the photoconductive member with diffusely reflecting particles covering at least a portion thereof;
• and
• determining the portion of the selected region of the photoconductive member that is covered with diffusely reflecting marking particles as a function of the constant of proportionality and the voltage proportional to the diffuse component of the total reflectivity of the region of the photoconductive member without marking particles thereon.