Image density detecting unit for image formation apparatus

An apparatus for copying a document onto a medium, comprising:

• light source means for directing light toward a document to be copied;
• rotating drum means for storing an image of said document in response to the projection of said image onto said drum means;
• developing means for transferring said stored image from said drum means to a medium, including means for controlling the density of said transferred image in response to a density control signal;
• first optical means for receiving a first portion of the light produced by said light source means and reflected by said document and projecting the resulting image of said document onto said drum means to form said stored image;
• second optical means for receiving a second portion of the light produced by said light source means and reflected by said document and for focusing said received second portion at a focal point;
• and
• light detecting means, optically coupled to said focal point, for producing said density control signal in response to the intensity of said focused light, wherein said second optical means includes:
• light transmission body means for receiving light reflected by substantially the entire width of said document, said body means including means for defining a curved surface toward which said received light is directed;
• first reflecting means, disposed on said curved surface, for focusing said received light at a point within said body means;
• and
• means for coupling said light focused at said point to said light detecting means.

An apparatus for copying a document onto a medium, comprising:

• light source means for directing light toward a document to be copied;
• rotating drum means for storing an image of said document in response to the projection of said image onto said drum means;
• developing means for transferring said stored image from said drum means to the medium, including means for controlling the density of said transferred image in response to a density control signal;
• first optical means for receiving a first portion of the light produced by said light source means and reflected by said document and for projecting the resulting image of said document onto said drum means to form said stored image;
• second optical means comprised of a transparent optical medium and including a light reflecting plate having a light incident plane and a light reflective surface, the cross-section of the light reflective surface being substantially quadric in configuration and said light reflective surface being uninterruptedly formed with respect to the light incident plane to permit light which is incident thereon to be directed onto a focal point;
• and
• light detecting means, optically coupled to said focal point, for producing said density control signal in response to the intensity of said focused light.

An apparatus for focusing light comprising:

• light transmissive solid body means for receiving light, said body means including means for defining a planar surface and means for defining a quadric surface, light incident upon said planar surface being transmitted through said body means toward said quadric surface;
• first reflecting means, disposed on said quadric surface, for focusing said light incident on said quadric surface toward a focal point within said body means;
• and
• light detecting means, at least partially embedded within said body means at said focal point, for detecting the intensity of light focused toward said point.