Optics: measuring and testing – Of light reflection
Reexamination Certificate
2000-09-22
2002-12-24
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Of light reflection
C356S388000
Reexamination Certificate
active
06498648
ABSTRACT:
The present invention relates to a procedure for taking a reference measurement, respectively for recalibrating an optical measuring device used in determining surface quality.
Devices employed to determine the quality of surfaces of a wide variety of products are known in the prior art. Since surface quality is a crucial characteristic for many products in providing the total overall impression of the product, the quality of these products' surfaces often takes on special significance. For this reason, measuring devices are employed in order to qualitatively and quantitatively determine the visual properties of a surface.
Such measuring devices are exposed to dust and other contaminations in particular, but not limited thereto, in the production environment, causing the optics of such a device to become dirtied over the course of time, which in turn changes its transmission properties and may yield erroneous measurements. Therefore, conventional devices undergo routine maintenance at regular intervals.
Another problem arising in surface determinations is that individual elements in the devices age. Especially when using thermal light sources which include filaments, a portion of the filament will vaporize over time, settling on the inside of the surrounding glass bulb and changing the transmission characteristics of the glass bulb such that the light emitted from the light source will exhibit an age-induced spectral change.
The relative position of the light-radiating elements and the sensors to one another can also vary due to the effects of vibrations or jarring impacts, etc., so that the geometrical relational ratios within a measuring device can vary over the course of time.
Consequently, in order to obtain high quality measurements, many of the measuring devices known in the prior art are calibrated, respectively recalibrated, on a frequent basis. In so doing, the measuring device is placed on a surface having known properties and these properties are then determined with said measuring apparatus. The user can then balance or calibrate the device to zero, respectively to a particular deflection, for example by changing potentiometer resistance, so that any deviations in the devices can be compensated for to a certain extent.
To simplify operational handling, automatic calibration procedures are also known in the prior art which automatically recalibrate the measuring device to the corresponding reference value after a reference surface has been measured.
A disadvantage of the known prior art procedures and devices, however, is that many operator errors are not detected. A user frequently relies on the automatic mechanisms of such devices instead of, for example, scrutinizing the optical devices himself and controlling whether said devices are dirtied.
It is therefore the task of the present invention to provide a procedure as indicated above in order to enable making a reliable and reproducible reference measurement for calibrating or recalibrating an optical measuring device.
This task is solved in accordance with the present inventive procedure as defined in claim
1
.
Further preferred embodiments of the invention constitute the subject matter of the subclaims.
A procedure according to the present invention for making a reference measurement is performed using an optical device which has at least a first illuminating means comprising at least one source of radiation and which is aligned at a predetermined angle to the measurement surface.
The optical device furthermore comprises at least a first and at least a second optical measuring means, both also aligned at a predetermined angle to the measurement surface and both receiving a portion of the light reflected from said measurement surface.
Both the first as well as the second optical measuring means in each case comprise at least one photo sensor which emits an electrical measurement signal which is in each case characteristic of the received, respectively reflected, light.
A control and evaluation means having at least one processor means and at least one memory means is additionally provided in the optical device in order to control the measurement sequence and to evaluate the measurement results. An output means is provided in the optical device for the outputting of the values.
The procedure according to the present invention using the optical device comprises the following steps which may be performed in the following or in a different order:
a) in a first step, the optical device and the reference surface are aligned with respect to one another; preferably, the optical device is placed upon the reference surface.
b) the first optical measuring means subsequently takes a measurement which is then preferably stored in the memory means.
c) a deviation parameter is derived from the measured value taken by the first measuring means and a first calibration value stored in the memory means which is characteristic of the first optical measuring means, said deviation parameter is a measure of the measured value's deviation from said first calibration parameter.
d) the next step entails the taking of a measurement with the second optical means.
e) after taking the measurement with the second measuring means, a second deviation parameter is derived from the measured value from said second measuring means and a second calibration parameter stored in the memory means which is characteristic of the second measuring means.
f) a variance parameter is derived from the first and the second deviation parameter, and
g) a subsequent warning signal is issued when the variance parameter either exceeds or falls short of a certain range, or when the variance parameter is greater than a predetermined value.
The procedure according to the present invention has numerous advantages.
Upon employing the optical device for the first time, which usually takes place while still in the production or quality control stage, the device is first adjusted by means of measuring reference standards and making the corresponding precision fine-tuning.
High-quality measuring devices need to be recalibrated at regular intervals in order to essentially equalize, respectively exclude, any changes in geometric circumstances. Therefore, reference surfaces are provided for many measuring devices which have specifically known and defined properties; these reference surfaces may also correspond to the reference standards of the original precision adjustment.
In conventional measuring devices, at least within the scope of the final inspection or the precision adjusting stage, the measuring device is preferably placed upon at least one reference surface and the device then measures said reference surface. The relevant measured value is then stored as the calibration parameter in a memory of the measuring device, respectively printed in the product specification. When such a measuring device needs to be recalibrated during the course of daily operation, it is then placed upon the relevant reference surface and measures the properties of said reference surface.
By comparing the values as thus determined with the calibration parameters stored in the memory means, respectively the printed calibration parameters, the device can be accordingly re-adjusted, thus allowing for a nullifying, at least to a certain extent, of effects as induced by contamination and other such similar factors.
However, it is frequently the case with measuring devices and procedures as known in the prior art for taking, respectively analyzing such a calibration or reference measurement, that these reference measurements are carried out incorrectly.
The procedure according to the present invention has the advantage with respect to the known methods that the measurement results of the first and of the second measuring means are subjected to a plausibility check, allowing for the avoiding of many erroneous reference, respectively calibration, measurements. It is not solely the problem that incorrect reference measurements need to be repeated in order to achieve high-quality meaningful m
BYK-Gardner GmbH
Pearne & Gordon LLP
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