Exposure control system for photocomposition machines

In a photocomposition machine comprising continuously movable font means for successively presenting individual characters of at least one font of characters at a projection location and variable magnification lens means for projecting an individual character of said font means at a selected point size to a photosensitive receptor, an exposure control system comprising:

• a projection light source means for producing a light flash during movement of said individual character through the projection location, said light flash having an output intensity variable relative to an applied electrical energy;
• means for storing a digital number having a value alterable in response to a change in the selected point size;
• digital-to-analog conversion means for converting said digital number to an analog signal;
• energy storage means for storing electrical energy responsive to a D.C. charging signal;
• means responsive to the analog signal for storing in the energy storage means electrical energy having a magnitude determined by the value of said analog signal, said means including:
• i. regulator means responsive to said analog signal for producing a regulator signal having a magnitude proportional to the analog signal;
• ii. oscillator means for generating a relatively low voltage oscillating signal;
• iii. voltage converting means responsive to both said relatively low voltage oscillating signal and said regulator signal for formulating a third, oscillating, input signal having at least one characteristic varied according to the magnitude of the regulator signal, said converting means including a transformer means for transforming said third signal to a high voltage oscillating signal, whereby at least said one characteristic of said high voltage oscillating signal is varied according to the magnitude of the regulator signal;
• and
• iv. rectifying means for rectifying said high-voltage oscillating signal to produce said D.C. charging signal, said rectifying means connected to said energy storage means for charging said energy storage means with a magnitude of energy determined by said one characteristic;
• and
• trigger means for applying the energy stored by said storage means to said light source means when the individual character is in the projection location, whereby the intensity of the light flash can be varied over a wide range by changing the value of the digital number.