Ink and dampening solution determination in offset printing

A method of operating an offset printing press including the steps of:

• directing a light source at a moving component;
• detecting light scattered from said moving component and forming an intensity signal thereof;
• storing a record of one or more positions representing non-imaging areas;
• data processing said scattered intensity signal to identify the presence of ink at at least one of the positions;
• and
• adjusting the ink and/or dampening liquid controls of the press to avoid scumming when onset of conditions indicative of scumming is detected.

An instrument for determining the occurrence of scumming in an offset printing press, including:

• a light source for directing light at an offset printing plate, the light source being of a known intensity;
• a light detector for receiving light scattered from said plate and producing an intensity signal thereof;
• and
• a data processor storing a record of one or more positions representing non-imaging areas, and processing said scattered intensity signal to identify the presence of ink at said positions.

A method of operating an offset printing press including the steps of

• (a) directing a beam of light onto an offset printing plate of the press having image areas carrying printing ink and non-image areas carrying a dampening liquid, the beam being incident on the offset printing plate to be scattered therefrom and specularly reflected therefrom,
• (b) detecting the scattered light and providing a corresponding first signal representative of the intensity of detected scattered light,
• (c) detecting the specularly reflected light and providing a corresponding second signal representative of the intensity of the detected reflected light
• (d) processing the first signal to identify when the light falls on image areas,
• (e) using data from processing the first signal to filter the second signal to provide an output signal when the light is directed on a non-image area, the output signal indicating the amount of dampening liquid present on the printing plate, and
• (f) controlling a supply of ink to the image areas of the printing plate using the first signal, the first signal indicating the thickness of ink present on the printing plate.

Apparatus for controlling an offset printing press having

• (i) means for directing a beam of light onto an offset printing plate of the press having image areas carrying printing ink and non-image areas carrying a dampening liquid, the beam being incident on the offset printing plate to be scattered therefrom and specularly reflected therefrom,
• (ii) means for detecting the scattered light and providing corresponding first signal representative of the intensity of detected scattered light,
• (iii) means for detecting the specularly reflected light and providing a corresponding second signal representative of the intensity of the detected reflected light,
• (iv) means for processing the first signal to identify when the light fails on image areas,
• (v) means for using data from processing the first signal to filter the second signal to provide an output signal when the light is directed on a non-image area, and the output signal indicating the amount of dampening liquid present on the printing plate, and
• (vi) means for controlling a supply of ink to the image areas of the printing plate using the first signal, the first signal indicating the thickness of ink present on the printing plate.

A method of operating an offset printing press including the steps of

• (g) directing a beam of light onto an offset printing plate of the press having image areas carrying printing ink and non-image areas carrying a dampening liquid, the beam being incident on the offset printing plate to be scattered therefrom and specularly reflected therefrom,
• (h) detecting the scattered light and providing a corresponding first signal representative of the intensity of detected scattered light,
• (i) detecting the specularly reflected light and providing a corresponding second signal representative of the intensity of the detected reflected light
• (j) processing the first signal to identify when the light falls on image areas,
• (K) using data from processing the first signal to filter the second signal to provide an output signal when the light is directed on a non-image area, the output signal indicating the amount of dampening liquid present on the printing plate, and
• (l) providing a synchronisation signal for synchronising data acquisition with the press operation and determining spatial positions on the printing plate.

Apparatus for controlling an offset printing press having

• (i) means for directing a beam of light onto an offset printing plate of the press having image areas carrying printing ink and non-image areas carrying a dampening liquid, the beam being incident on the offset printing plate to be scattered therefrom and specularly reflected therefrom,
• (ii) means for detecting the scattered light and providing a corresponding first signal representative of the intensity of detected scattered light,
• (iii) means for detecting the specularly reflected light and providing a corresponding second signal representative of the intensity of the detected reflected light,
• (iv) means for processing the first signal to identify when the light fails on image areas,
• (v) means for using data from processing the first signal to filter the second signal to provide an output signal when the light is directed on a non-image area, and the output signal indicating the amount of dampening liquid present on the printing plate, and
• (vi) synchronisation means for providing a synchronisation signal for synchronising data acquisition with the press operation and determining spatial positions on the printing plate.