Automatic z-correction for basis weight sensors
AssigneeHoneywell ASCa Inc.
InventorsReena Meijer Drees, Gertjan Hofman
Life of this patent
Estimating the term…
Abstract
Nuclear-based basis weight sensors are passline-sensitive. Error in measurement is induced when the sheet moves up and down in the gap between the radiation source and detector. A passline-insensitive basis weight sensor includes a triangulation sensor to measure the position of the sheet within the gap. The sensor and gap is characterized in the laboratory for its passline behavior over a range of basis weights. The curves are either parameterized or a lookup table is created for each weight and passline position and the data added to the sensor's processor. The basis weight measured can be automatically corrected to account for deviations from the passline or nominal path through the sensor.
Claims20
A method of measuring the basis weight of a moving sheet of material under test with a sensor that includes a basis weight gauge that includes a radiation source and radiation detector with a gap that is between the source and detector that defines a radiation path towards a sheet substrate and for detecting the amount of first radiation transmitted through the sheet substrate wherein the transmitted radiation that is detected being an initial measurement of the basis weight of the sheet substrate, said method comprising the steps of:
- (a) establishing a calibration for the material under test over a range of basis weights and positions within the gap using standards having a range of predetermined and stable basis weights to establish a library of calibration curves or look-up tables wherein the basis weight is the weight per unit area of the sheet of material and wherein step (a) of calibrating the material does not require consideration of the composition of the sheet of material;
- (b) moving the sheet of material under test through the gap to obtain an initial basis weight measurement wherein step (b) does not require measuring the thickness of the sheet material;
- (c) measuring the z-position of the sheet of material within the gap;
- and
- (d) determining a final basis weight measurement by correcting the initial basis weight measurement with the calibration, wherein the basis weight gauge is not recalibrated when the sheet of material changes in grade or thickness.
A sensor device for measuring the basis weight of a sheet of material under test that comprises:
- a basis weight gauge that includes a radiation source and radiation detector with a gap therebetween for directing radiation along a path towards a sheet of material and for detecting the amount of radiation transmitted through the sheet and generating a first signal that corresponds to the radiation transmitted, wherein the first signal corresponds to an initial basis weight measurement of the sheet, wherein the basis weight is the weight per unit area of the material under test;
- means for establishing a calibration for the material under test that comprises standards having a range of predetermined and stable basis weights;
- means for measuring the z-position of the sheet of material within the gap and deriving a correction factor corresponding to the position of the sheet;
- and
- means for adjusting the initial basis weight measurement by applying the correction factor wherein the means for adjusting the initial basis weight measurement comprises a processor and associated memory containing a library of basis weight calibration curves or look-up tables and the processor is not configured to measure the thickness of the sheet of material.
Dependencies are inferred from the claim text.