Method and apparatus to monitor and control sheet characteristics on a creping process
The invention embodies methods and apparatuses to monitor and control the characteristics of a creping process. The method involves measuring optical properties of various points along a creped paper sheet and converting those measurements into characteristic defining data. The invention allows for determining the magnitude and distribution of crepe structures and their frequency and distribution. This allows for the generation of information that is accurate and is much more reliable than the coarse guessing that is currently used in the industry. Feeding this information to papermaking process equipment can result in increases in both quality and efficiency in papermaking.
1. A method of measuring the geometric characteristics of a crepe structure on a paper sheet, the method comprising the steps of:
generating data values representing characteristics of positions on a paper sheet by repeatedly emitting at least two emission beams against each of the positions on the paper sheet and reflecting the two beams off of the positions and into a sensor constructed and arranged to absorb and measure the intensity of the reflected emission beams, wherein the positions on the crepe structure on the paper sheet lie along a substantially straight line extending in a substantially cross machine direction,
correcting the measured intensity of the data values by using an n th order polynomial fit,
performing a row-by-row smoothing operation of the corrected data values using a filter algorithm,
identifying positive to negative transitions within the smoothed data values, and
correlating the identified positive to negative transitions with previously identified values known to correspond to particular geometric dimensions to determine geometric features of the crepe structure, said determined geometric features comprising a beginning and ending of a crepe feature.
2. The method of claim 1 wherein the emission beams are illuminating light and the sensor is a digital camera coupled to a microscope.
3. The method of claim 1 wherein the emission beams are projected at an angle oblique to the machine direction.
4. The method of claim 1 wherein the emission beams are projected at an angle relative to the plane of the paper sheet.
5. The method of claim 1 wherein the filter algorithm is one selected from a list consisting of FFT, Butterworth, Savitsky-Golay, and any combination thereof.
6. The method of claim 1 further comprising the steps of determining a crepe frequency size distribution and converting the crepe frequency size distribution into a length scale.
7. The method of claim 1 further comprising the step of using more than one filtering algorithm and evaluating results of the filtering algorithms to determine the characteristics of free fiber ends of the paper sheet.
8. The method of claim 1 further comprising the step of recognizing periodicity of peaks in the measured intensity data and using the periodicity to determine the softness of the creped paper sheet.
9. The method of claim 1 further comprising the step of recognizing dispersion of peaks in the measured intensity data and using the dispersion to determine the softness of the creped paper sheet.
10. The method of claim 1 further comprising the step of measuring both sides of the paper sheet, the method utilizing a shutter on each side of the paper sheet, the shutters on both sides constructed and arranged to block the impact of an emission beam against a position on one side of the paper sheet when an emission beam is impacting against the other side and also to alternate between which side is having the emission impacts against.
11. The method of claim 1 in which the measured characteristics are input into a system which has online control of at least a process equipment in a papermaking process, the system constructed and arranged to modify the settings of the process equipment if the measured characteristics are outside of a predetermined acceptable range to induce further measured characteristics to conform to the predetermined acceptable range.
12. An apparatus for measuring the geometric characteristics of a crepe structure on a paper sheet, the apparatus comprising:
at least two emission sources constructed and arranged to emit emission beams against positions on a paper sheet,
at least one sensor constructed and arranged to absorb and measure the intensity of the reflected emission beams, and
at least one data processing device constructed and arranged:
to generate data values representing characteristics of positions on a paper sheet by repeatedly emitting, to correct the measured intensity of the data values by using an n th order polynomial fit,
to perform a row-by-row smoothing operation of the corrected data values using a filter algorithm,
to identify positive to negative transitions within the smoothed data values,
and to correlate the identified positive to negative transitions with previously identified values known to correspond to particular geometric dimensions to determine geometric features of the crepe structure, said determined geometric features comprising a beginning and ending of a crepe feature.