Dampening water quantity measuring apparatus and dampening water adjusting method

Abstract

In a dampening water measuring apparatus, light emitted from a semiconductor laser has its beam expanded by an objective lens, and is then reflected by a beam splitter to irradiate a non-image area on a surface of a printing plate P. The laser beam reflected from the non-image area on the surface of the printing plate passes through the beam splitter, and enters a CCD camera. The CCD camera measures speckle intensity of the incident laser diffused light, and transmits measurements to a controller through an interface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

FIG. 1 is a schematic view showing a principal portion of a printing machine according to this invention;

FIG. 2 is a schematic view of a dampening water measuring apparatus according to this invention; and

FIG. 3 is a graph showing a relationship between quantity of dampening water and speckle intensity of laser diffused light reflected from a surface of a printing plate.

Claims

1. A dampening water adjusting method comprising: a measuring step for emitting a laser beam from a laser source to a non-image area on a surface of a printing plate before supplying dampening water to the printing plate, and measuring speckle intensity of laser diffused light reflected from the surface of the printing plate;a dampening water supplying step for emitting a laser beam from the laser source to the non-image area on the surface of the printing plate while supplying dampening water from a dampening water feeder to the printing plate, and measuring speckle intensity of laser diffused light reflected from the surface of the printing plate; andan adjusting step for adjusting a feed rate of dampening water from said dampening water feeder so that the speckle intensity of the laser diffused light measured in said dampening water supplying step exceed the speckle intensity of the laser diffused light measured in said measuring step.

2. A dampening water adjusting method as defined in claim 1, wherein: when the speckle intensity of the laser diffused light measured in said dampening water supplying step is approximately equal to the speckle intensity of the laser diffused light measured in said measuring step, the feed rate of dampening water is determined insufficient, and said adjusting step is executed to increase the feed rate of dampening water; andwhen the speckle intensity of the laser diffused light measured in said dampening water supplying step is less than the speckle intensity of the laser diffused light measured in said measuring step, the feed rate of dampening water is determined excessive, and said adjusting step is executed to decrease the feed rate of dampening water

3. A dampening water adjusting method comprising: a measuring step for varying a feed rate of dampening water in a range including a proper feed rate between an excessive feed rate and an insufficient feed rate while emitting a laser beam from a laser source to a non-image area on a surface of a printing plate, and measuring a relationship between quantity of dampening water and speckle intensity of laser diffused light reflected from the surface of the printing plate;a dampening water supplying step for measuring speckle intensity of laser diffused light reflected from the surface of the printing plate in a state of emitting a laser beam from the laser source to the non-image area on the surface of the printing plate while supplying dampening water from a dampening water feeder to the printing plate; andan adjusting step for adjusting the feed rate of dampening water from said dampening water feeder, based on the relationship between quantity of dampening water and speckle intensity of laser diffused light measured in said measuring step, and the speckle intensity of the laser diffused light measured in said dampening water supplying step.

4. A dampening water adjusting method as defined in claim 3, wherein: the speckle intensity of the laser diffused light measured in said measuring step is divided into three regions consisting of a high, first region, a low, third region, and an intermediate, second region between the first and the third regions;when the speckle intensity of the laser diffused light measured in said dampening water supplying step is in said first region, the feed rate of dampening water is determined proper;when the speckle intensity of the laser diffused light measured in said dampening water supplying step is in said second region, the feed rate of dampening water is determined insufficient, and said adjusting step is executed to increase the feed rate of dampening water; andwhen the speckle intensity of the laser diffused light measured in said dampening water supplying step is in said third region, the feed rate of dampening water is determined excessive, and said adjusting step is executed to decrease the feed rate of dampening water.

5. A dampening water quantity measuring apparatus for measuring a feed rate of dampening water supplied to a printing plate, comprising: a laser source for emitting a laser beam to a non-image area on a surface of the printing plate;an imaging device for measuring speckle intensity of laser diffused light reflected from the surface of the printing plate; anda controller for measuring a quantity of dampening water based on the speckle intensity of the laser diffused light measured by said imaging device.

6. A dampening water quantity measuring apparatus as defined in claim 5, wherein said controller is arranged to determine that the quantity of dampening water is optimal when the speckle intensity substantially attains a maximum.