Apparatus and method of measuring web feeding velocity by using single field encoder

Patent metadata

Field	Value
Publication number	US-9784756-B2
Application number	US-201414273745-A
Country	US
Kind code	B2
Filing date	May 9, 2014
Priority date	May 10, 2013
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

A method of measuring feeding velocity of a web, on which a scale having pitches different from pitches of a mask are formed, is provided. The method includes: calculating a number of vibrations of a moiré image of light passing through the mask and the scale; calculating pitches of the scale of the fed web based on the calculated number of vibrations of the moiré image; averaging the pitches of the scale so that a change in a pitch between adjacent timings among the calculated pitches of the scale is minimized; extracting first signals corresponding to our phases for one pitch based on the averaged pitches of the scale; calculating two second signals for forming a Lissajous circle from the first signals; and calculating an angle of the Lissajous circle by the two second signals and then calculating the feeding velocity of the web by using the calculated angle.

First claim

What is claimed is:

1. A method of measuring feeding velocity of a web, on which a scale having pitches different from pitches of a mask are formed, the method comprising:
detecting a light passing through the mask and the scale by an image sensor;
calculating a number of vibrations of a moiré image of the light passing through the mask and the scale;
calculating pitches of the scale of the fed web based on the calculated number of vibrations of the moiré image;
averaging the pitches of the scale so that a change in a pitch between adjacent timings among the calculated scale pitches of the scale is minimized;
extracting first signals corresponding to our phases for one pitch based on the averaged pitches of the scale;
calculating two second signals for forming a Lissajous circle from the first signals corresponding to 4 phases;
correcting the Lissajous circle by correcting the two second signals; and
calculating an angle of the Lissajous circle by the two second signals, and then calculating the feeding velocity of the web by using the calculated angle.

2. The method of claim 1 , wherein
the calculating of the number of vibrations of the moiré image includes extracting only a low band vibration number component in the signal generated by the image sensor, and then calculating the number of vibrations of the moiré image based on the extracted low band vibration number component.

3. The method of claim 2 , wherein
the calculating of the number of vibrations of the moiré image includes performing Fast Fourier Transform on the low band vibration number component, or performing auto-correlation and then Fast Fourier Transform on the low band vibration number component.

4. The method of claim 1 , wherein the calculating of the number of vibrations of the moire image adopts at least one of a Gaussian window and a second order polynomial regression method in a log scale of a Fast Fourier Transform graph in order to improve accuracy of calculating the number of vibrations of the moire image.

5. The method of claim 1 , wherein
the calculating pitches of the scale of the fed web based on the calculated number of vibrations of the moiré image includes calculating the number of vibrations of the scale by Equation below, and then calculating the pitches of the scale based on the calculated number of vibrations of the scale:
f s =f r −f b

wherein f s is a spatial frequency of the scale, f r is a spatial frequency of the mask, and f b is a frequency of the moiré image, and the Equation corresponds to a case where an interval of a grating of the mask is larger than that of a grating of the scale, and a case where the interval of the grating of the scale is larger than that of the grating of the mask, wherein for the case where the interval of the grating of the scale is larger than that of the grating of the mask, a negative (−) sign in the Equation is changed to a positive (+) sign.

6. The method of claim 1 , wherein
the averaging of the pitches of the scale includes processing a pitch at a specific time and pitches at a plurality of precedent times before the specific time by a least squares method to calculate the processed pitch as an averaged pitch of the scale, arithmetically averaging the pitch at the specific time and the pitches at the plurality of precedent times to calculate the arithmetically averaged pitch as the averaged pitch of the scale, or selecting the pitch at the specific time as the averaged pitch of the scale.

7. The method of claim 6 , wherein the method further includes
averaging signal intensities of the first signals corresponding to four phases (0 °, 90 °, 180 °, and 270°)for one pitch based on the averaged pitch of the scale, and the two second signals for forming the Lissajous circle are calculated by Equations below:
wherein
u 1 =I 0 -I 180 ,
u 2 =I 90 -I 270 ,

Herein, u 1 and u 2 are the two second signals,
I 0 is a signal intensity at a phase of 0°,
I 90 is a signal intensity at a phase of 90°,
I 180 is a signal intensity at a phase of 180°, and
I 270 is a signal intensity at a phase of 270°.

8. The method of claim 1 , wherein
a signal quality is calculated by Equation below after the correcting of the Lissajous circle, and when the signal quality is equal to or smaller than a predetermined threshold value, the calculated signal quality is ignored and a signal quality of a previous time zone is used:

S
⁢

⁢
Q

=

1
-

∑

i
=
1

n
p

,
ave

⁢

d
i

n
p

,
ave

wherein SQ is the signal quality,
d i is a distance to a circle having a radius of 1 at a point corresponding to the signal based on an i th pitch after the correction of the Lissajous circle, and
n p ,ave is the number of signals facilitating a determination of the Lissajous circle.

9. The method of claim 1 , wherein
when there is a point at which the calculated feeding velocity of the web is changed, a plurality of image sensors having different characteristics are provided to receive signals of the light passing through the scale before and after the point at which the calculated feeding velocity of the web is changed, respectively.

10. The method of claim 1 , wherein
the light passing through the mask and the scale is detected by a single image sensor in which a plurality of detection units are integrated.

11. An apparatus for measuring feeding velocity of a web, on which a scale having a different pitch from a pitch of a mask is formed, the apparatus comprising:
a light source configured to provide collimated light to the mask side;
a single image sensor in which a plurality of detection units for detecting light emitted from the light source to pass through the scale are integrated; and
a calculation unit configured to calculate feeding velocity of the web by using the signals detected by the single image sensor,
wherein the calculation unit calculates the pitch of the scale of the fed web based on the detected signals, extracts first signals corresponding to four phases for one pitch based on the calculated pitch of the scale, forms a Lissajous circle by using the first signals corresponding to the four phases, corrects the Lissajous circle by correcting two second signals from the first signals corresponding to the four phases, and then calculates the feeding velocity of the web by using the formed Lissajous circle.

Assignees

• Korea Mach & Materials Inst

Inventors

• Kang Dongwoo
• Lee Taik Min
• Lee Seung-Hyun
• Choi Young Man
• Yoon Deokkyun
• Kim Kwang-Young
• Jo Jeongdai

Classifications

• G01P3/54 Primary

  by measuring frequency of generated current or voltage · CPC title

• G01P3/486 Primary

  delivered by photo-electric detectors · CPC title

• G01P3/68

  using optical means, i.e. using infrared, visible, or ultraviolet light (G01P3/80 takes precedence {; by reflection of waves G01S17/58}) · CPC title