WO2006040792A1

WO2006040792A1 - Method for validating a spectral measure in a spectrometric measurement system

Info

Publication number: WO2006040792A1
Application number: PCT/IT2005/000598
Authority: WO
Inventors: Antonio Maccari
Original assignee: Antonio Maccari
Priority date: 2004-10-13
Filing date: 2005-10-12
Publication date: 2006-04-20
Also published as: EP1805491A1; ITPI20040075A1

Abstract

This invention permits to validate the measures registered by a hyperspectral measuring system, by means of at least one Reference made by a mosaic of pieces of different colours arranged ahead the item to be measured. In this way, during measurement, the system registers first the Reference, having known certified spectral values, then the item and, if required, when coming back, the Reference again, so as to register the error of measurement and/or even correct the spectrometric values of the sample.

Description

"METHOD FOR VALIDATING A SPECTRAL MEASURE IN A SPECTROMETRY MEASUREMENT SYSTEM"

Description Technical Field The present invention concerns the technical industrial sector relative to the production 'of measuring instruments, in particular precision measuring instruments. This invention meets the need to offer a validation of the objective measure, so as to know the degree of error, proper of any measurement, and possibly correct it. Background Art

Any measurement, even the one carried out _:by the most precise instrument, involves an error and it's important to know the degree of such an error in order to assess the reliability of the same measurement, since minor is the error, greatest is the precision of the instrument.

When using spectrometers, there is a defined method to assess the error of measurement executed by the same instrument. The error is assessed by definition of the "standard colours" having certified spectrometric values, thanks to an accurate measurement by high-precision instruments, therefore with a minimal error compared to the one at issue. Said criteria are the so-called "Certified Standards" and normally consist of ceramic tiles of- different colours. Among the most known and used in industry, we can cite BCRA criteria, consisting indeed of ceramic tiles of different colours properly selected. Therefore, the method currently used to verify the precision of an instrument consists in measuring the BCRA tiles with the instrument we want to assess and comparing its precision or error with the known criteria of the Certified Standards. The difference between the values expressed in CIELab so obtained and the values of the Certified Standards, is expressed in DeltaE and represents the error performed by the instrument under check. In order to assess the precision (or the error) of a traditional spectrometer, which normally measures over an area of about 4-6mm diameter through a small round window, we compare the measures provided by the Certified Standards . Such an assessment entails a great commitment both for the attention and for the time necessary to place the Certified Standards to their size and successively process the resulting spectrometric values. In addition, this assessment not only requires time, but it's only valid in the moment it is carried out, so it should be frequently repeated in order to keep the precision of the same instrument under watch. Nevertheless, in industrial practice this procedure is not regularly carried out, because of the time and the precious operative sources it requires, as any reference colour is registered separately. Consequently the measurements of the instrument lose reliability. Besides, once the error of the system is registered, there is no guarantee that the next measurement of a sample is affected by the same error (or precision) . Disclosure of invention

The present invention aims at eliminating the above-mentioned drawbacks, supplying a system capable of verifying, therefore validating the measure, during the same measurement. This invention reached these results providing a method for validating a measure in spectrometric measuring systems, comprising the following steps: a) to register the spectrometric measures, called VRR, of a reference system; b) to compare the spectrometric measures prefixed by the reference system, called VRP, with the spectrometric measures VRR registered in step a) ; c) to compute the difference between said prefixed spectrometric measures VRP of the reference system and said spectrometric measures VRR registered in step a) : this difference is called deltaE and represents the assessing error; d) to register the spectrometric measures of a sample to be measured, called VRC; e) to use said deltaE to validate the measure of the sample, characterized in that said assessing error deltaE is computed separately for any single registration of the spectrometric measures VRC of any sample to be measured.

According to a convenient practical solution, said registration of the spectrometric measures of the sample to be measured, called VRC, in step d) is carried out just before and/or after steps a) and b) .

The advantages resulting from the present invention essentially consist of the fact that no manual operations are required by the user; that all the Certified Standards are measured when registering the sample, before and/or after the measurement, in a time compatible with the measurement, so that the measurements of said Standards can be used to assess the validity of the same measurement. The spectrometer measures VRR of the reference system are registered by means of several reference colours having known prefixed spectrometric measures VRP.

According to a first practical solution, the spectrometric measures VRC registered by the sample are validated, i.e. they are considered valid measures, by the comparison of the registered deltaE with a prefixed value of deltaE, e.g. a maximum tolerance of the spectrometer fulfilling the analysis. For example, when the registered value of deltaE is minor than the prefixed value of deltaE, the spectrometric measures VRC registered by the sample are validated, i.e. they are considered valid measures.

Otherwise, according to a second practical solution, the spectrometric measures VRR can be used to correct the spectrometric measures VRC of the sample that is measured: for example it's possible to compute, by means of a suitable computing software, the correction to be made to the spectrometric measure VRC of the sample that is measured. In further convenient solutions of the present invention, the registration of said spectrometric measures VRR of the reference system is carried out on the same focal plane of the sample to be measured, in order to speed up and facilitate the same registration, so that it can be realized for any single sample. The registration of said spectrometric measures VRR of the reference system is carried out by registration of the spectrometric measures of a reference consisting of a tile or similar, having areas of different colours with prefixed known spectrometric values. Conveniently, the reference consisting of a tile or similar is made by a mosaic, formed by the BCRA certified tiles or equivalent, with known and certified VRP values, which comprises pieces of such a size that can be measured with a precision spectrometer. In addition, the reference has such a size that it is completely or at least partially included in the registering area of a spectrometric scanner, so that the registration of the spectrometric measure of all the reference colours is quite immediate. To this end, the pieces of the reference mosaic are arranged over one or more rows and the same reference includes at least a stripe of material that can be used as reference of white colour. In order to speed up the process, said registration of the spectrometric measures VRC of any sample to be measured can be carried out by shifting said sample through a registration area of the hyperspectral scanner, said reference being placed, referring to the direction of shift, at least in the area just before and/or next to the sample to be measured. In this way, the registration is carried out quickly and automatically, making measurement of deltaE possible for any registered sample. Preferably, said sample and/or said references are measured during the "outgoing" and/or "incoming" shift of the trolley through said registration area.

This invention also relates to a device for registering reference spectrometric values VRP, particularly by means of a spectrometer, characterized in that said device, called reference, consists of a tile or similar having several areas of different colours with prefixed known spectrometric values. Conveniently, the reference consisting of a tile or similar is made by a mosaic, formed by the BCRA certified tiles or equivalent, which comprises pieces of such a size that can be measured with a precision spectrometer.

In addition, the reference has such a size that it is completely or at least partially included in the registering area of a hyperspectral scanner, so that it can be registered after a passage in the registration area of the scanner. The pieces of the reference mosaic are arranged over one or more rows and the same reference includes at least a stripe of material that can be used as reference of white colour. According to different practical solutions, the reference comprises a non-volatile memory device for the sole identification of the same reference, storing a sole identifying number, so that the reference can be identified and associated without errors to the VRP values, since these values are measured by a high-precision spectrophotometer or spectrometer having minimal error compared to the spectrophotometer or spectrometer that follows the above described steps of method.

Furthermore, said non-volatile memory device stores the spectral data and/or the VRP values associated to every single tile and/or colour relative to the pieces of the mosaic. The reference comprises means to register and/or control the temperature of the same reference, and/or at least one component that allows the software controlling the process of spectral registration to measure the temperature of the same reference. In addition, the spectrometric values of the Certified Standards can be used to correct the number of the spectrometric values of the same sample in the case the error is included within the limits compatible with the method of correction. This solution is possible thanks to a system, hereinafter called "Certified Total Reference" (briefly "Reference") realized so as to provide such a control criteria of the measure that can be internally and automatically registered during the same process of registration of the sample. A system for validating the measure in spectrometric measuring systems, according to the present invention, comprises a mosaic formed by the BCRA tiles placed over the same focal plane of the sample to measure, so that measurement is carried out in a single phase, registering first the pieces of the mosaic and then the sample to measure, in order to validate the registered measure. Said registered measures are later processed and compared each other, possibly correcting the error of registration by means of a suitable electronic program. Conveniently, the Reference used in this system is made by a mosaic formed by the BCRA tiles or equivalent, comprising pieces of such a size that can be measured with precision spectrometer and so that the resulting mosaic is comprised in the registration area of the system of spectrometric measure. In other words, the size of the pieces must be large enough to be measured with a traditional precision spectrometer, but small enough to be grouped in a mosaic that the system can register, during the normal process of registration of the sample to be measured. A non-restrictive example is represented by a mosaic made of pieces of lOxlOmm arranged in tree rows of 4 elements each, plus one row of White material. A further example is a mosaic made of pieces of 10x4mm arranged in a single row of 12 elements.

The present invention permits to register the references before and after the registration of the sample, since it's placed in the area of the trolley preceding the sample to be measured. In this way, when the trolley moves forwards, we measure first the reference and later the sample, when the trolley moves backward to come back in its initial position for gathering a new sample, the reference can be measured again.

Thanks to this system, the error (or precision) of the measurement is verified both before and after the registration of the sample. In other words, the measure of the sample is validated, since the relative error (or precision) has been certainly verified.

Conveniently, a stripe of White material can be also placed next to the reference and used before any registration in order to measure the bright flow produced by the spotlight and use this information to compensate possible anomalies of the same spotlight. The use of white is a technique normally used and known as "Calibration". In traditional spectrometers it's not always carried out before any measurement, but this procedure would reduce the error. Conveniently, it's possible to insert in the Reference mosaic an electronic device holding a sole numeric code, so that the Reference can be identified and associated without errors to the values properly measured by a high-precision spectrophotometer. Such a numeric code is read by the software controlling the process of hyperspectral registration. Which guarantees that no errors are made associating wrong or obsolete spectrometric values to one or more pieces of the Reference mosaic.

Conveniently, it's possible to insert in the Reference mosaic a non-volatile memory device storing the data relative to the Certified Standards . Such a memory is read by the software controlling the process of hyperspectral registration. Which guarantees that no errors are made associating wrong or obsolete spectrometric values to one or more pieces of the Reference mosaic. Conveniently, it' s possible to insert in the Reference mosaic an electronic component, which allows the software controlling the process of hyperspectral or spectral registration to measure the temperature of the same Reference. Which is very important because some colours (red, yellow, orange) can vary their spectrum when temperature changes. Therefore it's important to known at which temperature the spectral measurement has been carried out.

Conveniently, the Reference data registered by the spectrometer when measuring can be stored together with the spectrometric data of the sample under measurement and thus sent to the programmed electronic system, otherwise they can be stored so that the spectrometer provides the user with an immediate visual and/or sound estimation of the validity of the spectrometric measurement, comparing the registered values of the Reference with the maximum (or minimum) values permitted. Conveniently, the spectrometric data of the Reference registered by the spectrometer when measuring can be stored together with the spectrometric data of the sample under measurement and thus sent to the programmed electronic system, otherwise they can be stored so as to be used to correct the spectrometric values of the same sample in the case the detected error is included within the limits compatible with the method of correction.

Conveniently, the correction can be fulfilled also after a long time, since the spectrometric image of the sample under measurement also contains the spectrometric data of the Reference registered by the spectrometer when measuring together with the certified spectrometric data of the same Reference. According to further solutions, the spectrometer can register separately the spectrometric measures VRR for any single colour, during the registration of the spectrometric measures VRR of the Reference, since the Reference consists of a tile having a mosaic of certified colours with known VRP value. The spectrometer measures the spectral value associated to any colour either by computation of a deltaE for any single colour or by computation of an average deltaE. In any case, the registered deltaE can be used to validate the measure, as above described.

The processing of the VRP values, i.e. of the prefixed (or certified) values of the Reference, can be either manual or automatic, for example: by reading an element of non-volatile memory associated to any Reference; by storing or loading different values for any Reference in the spectrometer, and retrieving them by computation of deltaE through an automatic reading of the element of non-volatile memory associated to the Reference; by reading a bar code and/or numeric code associated to any single Reference; by fixing manually the numeric code on the spectrometer by a user.

Brief description of drawings

The present invention can be better understood by every expert in this field, referring to the enclosed drawing, given as practical schematic example of a practical solution of the invention, but not to be considered restrictive.

- Fig. 1 is a schematic side view of a hyperspectral scanner showing: the measurement apparatus (1), the sliding surface (2), the base (3) where the items to be measured are placed, sliding under the apparatus (1), the device (4) constituting the instrument for the validation of the measure, consisting of a mosaic of different colours formed by the BCRA references. The base (3A) drafted with dotted lines shows the shift of the base (3) on the surface (2) .

Claims

1) Method for validating a measure in spectrometric measuring systems, comprising the following steps: a) to register the spectrometric measures, called VRR, of a reference system; b) to compare the spectrometric measures prefixed by the reference system, called VRP, with the spectrometric measures VRR registered in step a) ; c) to compute the difference between said prefixed spectrometric measures VRP of the reference system and said spectrometric measures VRR registered in step a) : this difference is .called deltaE and represents the assessing error; d) to register the spectrometric measures of a sample to be measured, called VRC; e) to use said deltaE to validate the measure of the sample; f) possibly to use said measures VRR registered in step a) to correct the spectrometric measures of the sample; characterized in that said assessing error deltaE is computed separately for any single registration of the spectrometric measures VRC of any sample to be measured.

2) Method as claimed in claim 1, characterized in that said registration of the spectrometric measures of the sample to be measured, called VRC, in step d) is carried out just before and/or after steps a) and b) . 3) Method as claimed in one or more of the above claims, characterized in that said spectrometer measures VRR of the reference system are registered by means of several reference colours having known prefixed spectrometric measures VRP.

4) Method as claimed in one or more of the above claims, characterized in that said registered deltaE is compared with a prefixed value of deltaE.

5) Method as claimed in claim 4, characterized in that the spectrometric measures VRC registered by the sample are validated, i.e. they are considered valid measures, by the comparison of said registered deltaE with a prefixed value of deltaE.

6) Method as claimed in claim 5, characterized in that the spectrometric measures VRC registered by the sample are validated, i.e. they are considered valid measures, when the registered value of deltaE is minor than the prefixed value of deltaE.

7) Method as claimed in claim 3, characterized in that said spectral values are used to correct the spectrometric measures VRC of the sample that is measured.

8) Method as claimed in one or more of the above claims, characterized in that the registration of said spectrometric measures VRR of the reference system is carried out on the same focal plane as the registration of the spectrometric measures VRC of the sample to be measured.

9) Method as claimed in one or more of the above claims, characterized in that the registration of said spectrometric measures VRR of the reference system is carried out by registration of the spectrometric measures of a reference consisting of a tile or similar, having areas of different colours with prefixed known spectrometric values. 10) Method as claimed in one or more of the above claims, characterized in that said reference consists of a tile or similar, made by a mosaic, formed by the BCRA certified tiles or equivalent.

11) Method as claimed in one or more of the above claims, characterized in that said reference consists of a tile or similar, made by a mosaic that comprises pieces of such a size that can be measured with a precision spectrometer.

12) Method as claimed in one or more of the above claims, characterized in that said reference has such a size that it is completely or at least partially included in the registering area of a spectrometric scanner.

13) Method as claimed in one or more of the above claims, characterized in that the pieces of the reference mosaic are arranged over one or more rows. 14) Method as claimed in one or more of the- above claims, characterized in that the same reference includes at least a stripe of material that can be used as reference of white colour.

15) Method as claimed in one or more of the above claims, characterized in that said registration of the spectrometric measures VRC of any sample to be measured can be carried out by shifting said sample through a registration area of a spectrometer.

16) Method as claimed in claim 15, characterized in that said reference is placed, referring to the direction of shift, at least in the area just before and/or next to the sample to be measured.

17) Method as claimed in one or more of the above claims, characterized in that said shift of the sample and of the reference is carried out by placing the sample and the reference on the same trolley sliding through a registration area of the hyperspectral scanner.

18) Method as claimed in claim 17, characterized in that, said sample and/or said references are measured during the "outgoing" and/or "incoming" shift of the trolley through said registration area.

19) Method as claimed in one or more of the above claims, characterized in that it comprises the following steps: a) to place a reference on a trolley; b) to place a sample to measure on said trolley; c) to move this trolley for the first time through the registration area of a spectrometric scanner, so permitting to register the spectrometric measures VRR of the reference and the spectrometric measures VRC of the sample to be measured.

20) Method as claimed in claim 19, characterized in that it also comprises the following steps: d) to move this trolley for the second time through the registration area of the hyperspectral scanner, so permitting to register the spectrometric measures VRR of the reference and the spectrometric measures VRC of the sample to be measured.

21) Method as claimed in claims 19 or 20, characterized in that it comprises also one or more of the characteristics claimed from claim 4 to 11.

22) Device for registering reference spectrometric values VRP, particularly by means of a spectrometer, characterized in that said device, called reference, consists of a tile or similar having several areas of different colours with prefixed known spectrometric values.

23) Device as claimed in claim 22, characterized in that said reference consists of a tile or similar, made by a mosaic, formed by the BCRA certified tiles or equivalent.

24) Device as claimed in one or more of claims from 22 to 23, characterized in that said reference consists of a tile or similar, made by a mosaic, formed by the BCRA certified tiles or equivalent, which comprises pieces of such a size that can be measured with a precision spectrometer. 25) Device as claimed in one or more of claims from 22 to 24, characterized in that said reference has such a size that it is completely or at least partially included in the registering area of a hyperspectral scanner. 26) Device as claimed in one or more of claims from 22 to 25, characterized in that the pieces of the reference mosaic are arranged over one or more rows.

27) Device as claimed in one or more of claims from 22 to 26, characterized in that the same reference includes at least a stripe of material that can be used as reference of white colour.

28) Device as claimed in one or more of claims from 22 to 27, characterized in that the reference comprises a non¬ volatile memory device for the sole identification of the same reference.

29) Device as claimed in one or more of claims from 22 to 28, characterized in that said non-volatile memory device stores a sole identifying number, so that the reference can be identified and associated without errors to the VRP values, since these values are measured by a high-precision spectrophotometer having minimal error compared to the hyperspectral scanner that follows the above described steps of method.

30) Device, as claimed in one or more of claims from 22 to 25, characterized in that said non-volatile memory device stores the spectral data and/or the VRP values associated to every single tile and/or colour relative to the pieces of the mosaic.

31) Device as claimed in one or more of claims from 22 to 30, characterized in that said reference comprises means to register and/or control the temperature of the same reference.

32) Device as claimed in one or more of claims from 23 to 31, characterized in that said reference comprises at least one component that allows the software controlling the process of hyperspectral registration to measure the temperature of the same reference.

33) Method as claimed in one or more of claims from 1 to 21, characterized in that it's used in combination with a device, or reference, as claimed in one or more of claims from 22 to 32.

34) System for registering the spectrometric data of a sample under check, characterized in that it comprises one or more steps of method as claimed in one or more of claims from 1 to 21 and/or in combination with a device, or reference, as claimed in one or more of claims from 22 to 32. The Reference data registered by the hyperspectral scanner when measuring can be stored together with the spectrometric data of the sample under measurement and thus sent to a programmed electronic system, otherwise they can be stored so that a suitable software program can process them in order to correct the spectrometric values of the same sample in the case the detected error is included within the limits compatible with the method of correction.