The invention relates to an apparatus for printing a substrate with at least one coloured mass.

Such an apparatus is known in diverse embodiments. Use is made of a printing roller, on the periphery of which is arranged a printing stencil through which coloured mass is supplied making use of squeegee means. Via the openings in the stencil, which are ordered in a precisely predetermined pattern, the desired printing is applied to the stencil which passes over the printing roller in a printing pinch. After applying the coloured mass to the substrate in one or more printing operations, the substrate undergoes a further number of processes performed in-line.

Known apparatus comprise means to limit the amount of coloured mass in a reservoir to a determined maximum level. Replenishing of the reservoir takes place when the amount of mass in the reservoir falls below a predetermined minimum level.

Other known apparatus separate the coloured mass from the substrate such that only little or even no coloured mass is transferred onto the substrate. It is an object of the invention to provide a printing apparatus which is embodied such that no more coloured mass is supplied to the reservoir added to a printing station than is required for printing a predetermined number of metres of substrate and that no more substrate is printed than is required according to the order specification.

In order to realize this and other objectives the invention provides an apparatus for printing a substrate, for instance paper, fabric or foil, with at least one coloured, liquid or pasty mass, which apparatus comprises:

(1) a printing station;

(2) transporting means for carrying the substrate along the printing station;

(3) a main reservoir for the coloured mass;

(4) an auxiliary reservoir of known capacity which is connected via controllable supply means to the main reservoir and which is placed and adapted to supply coloured mass to the printing station; (5) measuring means for determining the amount of coloured mass required to print a substrate of known length;

(6) information input means for entering and storing

- the total remaining length of substrate for printing, and - the capacity of the auxiliary reservoir; and

(7) control means connected to these measuring means for interrupting the supply of coloured mass from the main reservoir to the auxiliary reservoir at or after the moment at which the coloured mass present in the auxiliary reservoir is sufficient to print the remaining length of substrate.

A preferred embodiment of the apparatus according to the invention has the special feature that the apparatus comprises a central control unit, forming part of which are:

(1) a first memory for the information generated by the measuring means;

(2) a second memory for the information generated by information input means;

(3) comparing means for comparing the content of the first and that of the second memory; and (4) the control means.

In a particular embodiment the apparatus has the special feature that the measuring means are adapted to divide the coloured mass supplied in a given time period during operation of the apparatus by the length of substrate printed in this time period.

In another embodiment the apparatus has the special feature that the measuring means are adapted to update and use historic data concerning the combination of coloured mass, printing station and substrate. In yet another variant the apparatus has the charac¬ teristic that the measuring means are adapted for a statistical analysis of the available historic data and the spreading capacity of the printing, the absorption of

95/32863 PC17NL95/00182

3 coloured mass by the substrate and the viscosity of the coloured mass.

Finally, the apparatus can have the special feature that prior to the end of an operational cycle the printing station is first rendered inoperative and the transporting means are then rendered inoperative after the last printed part of the substrate has undergone all in-line operations with a maximum time duration.

An apparatus can be constructed according to the following specification.

A database is built up in which the following data is stored:

- different stencils for use in a printing station, wherein for each stencil is specified what percentage of the surface allows through coloured mass.

- coloured masses, wherein the viscosity of each individual coloured mass is known.

- different substrates, with the absorption factor per individual substrate, optionally for different coloured masses.

- after each print order the following is stored per used stencil: the amount of coloured mass consumed per unit length of substrate, a code for the colour and a code for the substrate. At the start of production it is determined in advance for each stencil how much coloured mass is situated in an auxiliary reservoir filled to the maximum. The number of substrate units for printing is also known.

At the start of production, after each occasion that a reservoir is replenished and after any possible change in the number of metres of substrate for printing, the central control unit decides whether replenishing of the auxiliary reservoir from the main reservoir must be blocked or whether the blocking must be discontinued. These decisions are taken per stencil on the basis of the consumption of coloured mass per metre of substrate, the known capacity of the auxiliary reservoir and the total remaining length of substrate still to be printed.

The consumption per unit length of substrate is determined as follows.

- replenishing has already taken place at least once during this printing cycle. - the consumption per metre at that moment has been determined by dividing at least approximately the total quantity of mass by the total length of printed substrate.

- if replenishing of the auxiliary reservoir has not yet taken place during this printing cycle, but is there historic data available concerning the combination of stencil, coloured mass and substrate, then the consumption per unit length is derived from the historic data.

- if the combination is as such unknown, but historic data is however available concerning the substrate, the stencil and the coloured mass, the use per unit length of substrate which can be anticipated is then calculated with statistical techniques and on the basis of parameters such as spreading capacity, absorption and viscosity.

The operating cycle is ended when the required length of substrate has been printed in accordance with the order or when an operative gives the apparatus this stop instruction. The coloured mass is separated from the substrate at the location of the printing station such that the substrate is no longer printed. The substrate is further transported by the transporting means under the control of the central control unit until it has undergone all in-line operations with which a maximum time duration is associated.

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