Feedback system

A feedback system for controlling properties of a single layer or multiple layer stack being applied on a blank or coated substrate by means of a vacuum coating process controlled by a plurality of process controllers, the feedback system comprising:

• at least one monitoring device for implementing at least two distinct measurement techniques for determining measurement signals at each of a plurality of locations spatially distributed over the coated substrate, wherein a first measurement technique is adapted for being applied simultaneously to a plurality of locations, and a second measurement technique is adapted for being applied to at least one location, one of the first and second measurement techniques being a spectral transmission measurement,
• at least one processing unit adapted for receiving the measurement signals, configured for determining, from the received measurement signals, actual values of a first layer property at the plurality of locations, and of a second layer property different from the first layer property at the at least one location, and/or for determining deviations between the actual first and second layer property values and desired layer property values,
• a controller for providing actuation signals for actuating the plurality of process controllers, and for generating further control signals to further drive at least one of the plurality of process controllers in the coating process based on the determined values and/or deviations between the actual layer property values and the desired layer property values and on knowledge from a layer model expressing layer parameters as a function of settings and/or variations of at least two of the plurality of process controllers, such that the properties of the layer stack lie within predetermined tolerance values.

A method for controlling properties of a single layer or multiple layer stack being applied on a blank or coated substrate by means of a vacuum coating process controlled by a plurality of process controllers, the method comprising:

• providing a model of a layer being applied on the substrate, the model expressing layer parameters as a function of settings and/or variations of at least two of the plurality of process controllers,
• initiating the coating process of the single layer or multiple layer stack, by driving the plurality of process controllers,
• measuring measurement signals in a plurality of locations spatially distributed over the coated substrate, thus determining at least one measurement signal at each of the measurement locations, the measuring being by at least two distinct measurement techniques, wherein a first measurement technique is applied simultaneously to a plurality of locations, and a second measurement technique is applied to at least one location, one of the first and second measurement techniques being a spectral transmission measurement,
• using the measurement signals and the knowledge from the layer model for determining actual values of at least two different layer properties at the plurality of locations, and/or for determining deviations between the actual layer property values and desired layer property values,
• further driving the plurality of process controllers in the coating process based on the determined values and/or deviations between the actual layer property values and the desired layer property values at the plurality of locations and on knowledge from the layer model, such that properties of the single or multiple layer stack being applied lie within predetermined tolerance values.