Dynamic control of individual spot exposure in an optical output device

In a method for obtaining a desired spot exposure on a photoreceptive medium from an optical output device including a laser light source, current supply means supplying current to the laser for driving the laser in accordance with a pulsed data signal switchable from below to above a laser threshold value so as to produce the light source output comprised of individual light pulses, switching means for terminating the laser current independently of the data signal, a photodetector for converting at least a portion of each of said individual light pulses into a photocurrent pulse, an integrator for determining the time-integral value of a full length of the photocurrent pulse, a threshold memory having a threshold memory value stored therein, a comparator for comparing the time-integral of the full length of the photocurrent pulse and the threshold memory value in the threshold memory, and a photoreceptive medium, the improvement comprising the steps of:

• determining the time-integral value of a photocurrent pulse to produce the desired spot exposure on the photoreceptive medium;
• setting the threshold memory value stored in the threshold memory to said time-integral value of a photocurrent pulse determined to produce the desired spot exposure on the photoreceptive medium in said determining step;
• and
• causing the current supplied to the laser to switch from above to below the laser threshold value independently of the data signal when the time-integral value of a full length of the photocurrent pulse becomes equal to or greater than the threshold memory value stored in the threshold memory, as set in said setting step.

An apparatus for dynamically controlling the exposure of individual spots in an optical output device, comprising:

• a light source;
• means for driving the light source in accordance with a pulsed data signal so as to cause the light source to emit output in the form of light pulses;
• means for terminating the light source output independently of the data signal;
• a photodetector for detecting at least a portion of the light emitted by the light source wherein the detected portion of the emitted light is comprised of individual light pulses, and for converting each of said detected light pulses into a photocurrent pulse;
• an integrator for determining the measure of energy in each of said detected light pulses by calculating the time-integral of a full length of the photocurrent pulse;
• a threshold memory;
• and
• a comparator for comparing the time-integral of the full length of the photocurrent pulse and the contents of the threshold memory;
• such that the means for terminating the light source output causes the light source to cease emitting light pulses when the time-integral of the full length of the photocurrent pulse becomes equal to or greater than the value of the contents of the threshold memory.

An improved printing apparatus including a light source, means for driving the light source in accordance with a pulsed data signal so as to cause the light source to emit light pulses, photoreceptor, means for moving the photoreceptor, means for charging the photoreceptor, means for forming a latent image on the photoreceptor, means for transferring the latent image to paper, means for erasing the latent image from the photoreceptor and for cleaning the photoreceptor, paper transport means, and means for fusing the image onto the paper, the improvement comprising:

• a photodetector for detecting at least a portion of the light emitted by the light source wherein the detected portion of the emitted light is comprised of individual light pulses, and for converting each of said detected light pulses into a photocurrent pulse;
• an integrator for determining the measure of energy in each of said detected light pulses by calculating the time-integral of a full length of the photocurrent pulse;
• a threshold memory;
• a switching means for terminating the laser current independently of the data signal, and
• a comparator for comparing the time-integral of the full length of the photocurrent pulse and the contents of the threshold memory;
• such that the switching means causes the light source to cease emitting light pulses when the time-integral of the full length of the photocurrent pulse becomes equal to or greater than the value of the contents of the threshold memory.