Intensity control for a semiconductor laser of a laser beam printer

An intensity control device for a laser of a laser beam printer that produces a hard copy of image information by copy-processing a photosensitive surface scanned by the laser while it is in a scanning mode during which the laser is modulated by said image information, said intensity control device comprising:

• (a) means operative during a non-scanning mode of said laser for storing a first representation of a preset light intensity of said laser;
• (b) means for storing a second representation of a user selected image density for a hard copy produced by the printer;
• (c) means operative during a non-scanning mode of said laser for combining said first and second representations and thus forming a control voltage;
• and
• (d) control means responsive to said control voltage for producing a current that is supplied to said laser which thereby emits light whose intensity is dependent on both said first and second representations.

A method for controlling the intensity of a laser in a laser beam printer that produces a hard copy of image information by copy-processing a photosensitive surface scanned by the laser while it is in a scanning mode during which the laser is modulated by image information, said method comprising the steps of:

• (a) storing a first representation of a preset light intensity of said laser during a non-scanning mode of said laser;
• (b) storing a second representation of a user selected image density for a hard copy produced by the printer;
• (c) combining the first and second representations during a non-scanning mode of said laser for forming a control voltage;
• and
• (d) producing a current that is supplied to said laser in response to said control voltage whereby the intensity of light emitted by said laser is dependent on both of said representations.

A method for controlling the intensity of a laser in a laser beam printer that produces a hard copy of image information by copy-processing a photosensitive surface scanned by the laser while it is in a scanning mode during which the laser is modulated by image information, said method comprising the steps of:

• (a) generating a voltage V.sub.x representative of the intensity of light emitted by the laser;
• (b) generating a voltage V.sub.ref representative of a preset value of light intensity of said laser;
• (c) comparing V.sub.x with V.sub.ref and producing an output signal of one level when V.sub.ref >V.sub.x, and an output signal of another level when V.sub.x >V.sub.ref ;
• (d) sequentially incrementing a register while the output signal of said comparator remains at said one level;
• (e) converting the contents of said register to a control voltage;
• and
• (f) using said control voltage to control the level of current flowing through, and hence the intensity of light emitted by, the laser whereby the intensity of light produced by the laser increases in stepwise fashion to said preset value.