US 5,854,680 A · Photoelectric densitometer

Abstract

A description is given of a photoelectric measuring device by means of which the light reflected from a measuring point on a printed product is detected, and the corresponding measured signals are processed for the purpose of indicating quality data. A measuring instrument of this type, having at least one illumination device and measuring channels, is an improvement over the prior art in order to expand its possible uses, with a construction which is cost-effective and stable when handled. In accordance with the invention, this is achieved with an illumination device which has a spectral intensity distribution which corresponds to the number of spectral ranges provided for the irradiation of the measuring point. The light from the sequentially drivable illumination devices irradiates the measuring point. The light reflected from the measuring point is detected and converted into a reflective signal which is processed to determine ink density values. The photoelectric measuring device is designed, in particular, as a densitometer, preferably being made using light-emitting diodes (LEDs). Interference filters are additionally used in order to match the spectral intensities of the diodes to the spectral ranges which are provided for obtaining ink density values.

Claims20

Dependent claims

A method of measuring a density of ink at an area of a printed product comprising the steps of generating a predetermined sequence of incident beams of light having different spectral intensity distributions;

irradiating the measuring area with the incident beams of light, a portion of every incident beam of light being reflected by the measuring area to produce reflected beams of light;
collecting the reflected beams of light;
generating reflectance signals, each reflectance signal being correlated to an intensity of a respective reflected beam of light;
generating from the reflectance signals an ink density signal;
and generating at least one dark phase during the sequence of incident beams of light in which the measuring area is not irradiated with the incident beams of light, a dark phase reflectance signal being generated during the at least one dark phase and used as an offset value for generating the ink density signal.

2 more elements

A photoelectric densitometer for measuring an area of a printed product, comprising:

a plurality of illumination devices for irradiating the measuring area with incident beams of light, a portion of every incident beam of light being reflected by the measuring area to produce reflected beams of light;
a photoelectric converter collecting the reflected beams of light and generating reflectance signals, each reflectance signal being correlated to an intensity of a respective reflected beam of light;
an evaluator, connected to the photoelectric converter, for evaluating the reflectance signals to generate an ink density signal;
a controller connected to the plurality of illumination devices for activating each one of the plurality of illumination devices in a predetermined sequence, at least one of the plurality of illumination devices generating a light having a different spectral intensity distribution than the other individual illumination devices;
wherein the controller sequentially activates the individual illumination devices with at least one dark phase during which the measuring area is not irradiated with the incident beams of light, a dark reflectance signal being generated during the at least one dark phase and used as an offset by the evaluator when generating the ink density signal.

2 more elements

A photoelectric densitometer for measuring an area of a printed product, comprising:

a plurality of illumination devices, including light-emitting diodes (LEDs) of different spectral intensity distribution, at least one illumination device generating a light having a different spectral intensity distribution from the other illumination devices, for irradiating the measuring area with incident beams of light, a portion of every incident beam of light being reflected by the measuring area to produce reflected beams of light;
a controller connected to the plurality of illumination devices for sequentially activating the plurality of illumination devices, wherein there is at least one dark phase during which the measuring area is not irradiated with any incident beams of light;
a photoelectric converter collecting the reflected beams of light and generating reflectance signals, each reflectance signal being correlated to an intensity of a respective reflected beam of light, a dark phase reflectance signal being generated during the at least one dark phase;
an evaluator, connected to the photoelectric converter, for evaluating the reflectance signals to generate an ink density signal, the dark phase reflectance signal being used as an offset by the evaluator when generating the ink density signal;
a second photoelectric converter collecting the incident beams of light, and generating incidence signals, each incidence signal being correlated to an intensity of a respective incident beam of light, the second photoelectric converter connected to the evaluator, wherein evaluator evaluates the incidence signals for adjusting the ink density signal.

2 more elements

Dependencies are inferred from the claim text.

Photoelectric densitometer

Life of this patent

Photoelectric densitometer

Life of this patent

Abstract

Claims20