Systems and methods for improving the scan-line throughput of an image scanner using a modulated light source
View Patent ↗This disclosure provides systems and methods for decoupling the mechanical drive systems of image scanners from the exposure system. A light source, such as an array of light-emitting diodes (LEDs), may be modulated in order to maintain a constant exposure for each scan-line, regardless of the document velocity. Accordingly, the present systems and methods allow for continuous document scanning at varying speeds. An automatic document feeder may dynamically adjust the velocity of a document without negatively impacting the exposure of the image scan. As the velocity of the document is changed, the modulation rate of the light source may be adjusted to maintain a constant exposure.
1. A method for scanning a document, comprising:
illuminating at least a portion of a document with a light source, the light source configured to be modulated at a modulation rate including an on-time and an off-time each cycle;
determining an initial first velocity of the document relative to a scan bar, the scan bar including an array of image sensors for digitally reproducing the document as a sequence of scan-line rows;
determining first modulation rate of the light source based at least in part on the first velocity of the document relative to the scan bar, the on-time of the first modulation rate selected to obtain a first exposure level of each scan-line row at the first velocity;
modulating the light source at the first modulation rate; and
the array of image sensors capturing sequential scan-line rows of image data at a predetermined linear resolution using light emitted at the first modulation rate by the light source.
2. The method of claim 1 , further comprising:
determining a second modulation rate for the light source based on a detected change in velocity of the document relative to the scan bar from the first velocity to a second velocity, the second modulation rate including an on-time selected to maintain the first exposure level of each scan-line row at the second velocity;
modulating the light source at the second modulation rate; and
the array of image sensors capturing sequential scan-line rows of image data at the predetermined linear resolution using light emitted at the second modulation rate by the light source.
3. The method of claim 1 , further comprising dynamically adjusting the velocity of the document relative to the scan bar based on a capacity of a memory configured to store at least one of the sequence of scan-line rows.
4. The method of claim 3 , wherein the memory comprises a memory buffer configure to temporarily store a plurality of the sequence of scan-line rows for subsequent scan-line processing.
5. The method of claim 1 , wherein the light source comprises an array of light-emitting diodes (LEDs).
6. The method of claim 1 , wherein the light source comprises a xenon light source configured to be modulated with an on-time and an off-time.
7. The method of claim 1 , wherein the off-time of the modulation rate of the light source corresponds to a time period in which the light source is turned off.
8. The method of claim 1 , wherein the array of image sensors comprises an array of charge-coupled devices (CCDs).
9. The method of claim 1 , wherein the array of image sensors comprises an array of complementary metal-oxide-semiconductor (CMOS) sensors.
10. The method of claim 1 , wherein intensity of the light source is configured such that the first modulation rate comprises a 50% duty cycle based on the predetermined linear resolution and the initial first velocity.
11. The method of claim 1 , wherein the document comprises at least one of text, a picture, a graphic, a representation, and a photograph.
12. The method of claim 1 , wherein the document comprises at least one of cotton, a fabric, a fiber, paper, cardboard, a photograph, a slide, and a negative.
13. A image scanner comprising:
an automatic document feeder (ADF) configured to feed a document from a document source through an ADF path to a document destination;
a light source configured to illuminate at least a portion of the document with a modulated light at a modulation rate including an on-time and an off-time each cycle;
a scan bar including an array of image sensors configured to digitally reproduce the document as a sequence of scan-line rows as the document is fed through the ADF path; and
a calculation module configured to:
determine an initial first velocity at which the ADF is feeding the document through the ADF path; and
determine a first modulation rate of the light source based at least in part on the first velocity of the document through the ADF path, the on-time of the first modulation rate selected to obtain a first exposure level of each scan-line row at the first velocity.
14. The image scanner of claim 13 , wherein the calculation module comprises a look-up table.
15. The image scanner of claim 13 , wherein the calculation module is further configured to:
determine that the ADF is feeding the document through the ADF path at a second velocity; and
determine a second modulation rate of the light source based at least in part on the second velocity of the document through the ADF path, the on-time of the second modulation rate selected to maintain the first exposure level of each scan-line row at the second velocity.
16. The image scanner of claim 13 , further comprising a document velocity sensor configured to determine the velocity of the document through the ADF path.
17. The image scanner of claim 13 , further comprising a document adjustment module configured to dynamically adjust the velocity of the document through the ADF path based on a capacity of a memory configured to store at least one of the sequence of scan-line rows.
18. The image scanner of claim 17 , wherein the calculation module is configured to determine the velocity of the document through the ADF path based on a communication from the document adjustment module.
19. The image scanner of claim 17 , wherein the memory comprises a memory buffer configure to temporarily store a plurality of the sequence of scan-line rows for subsequent scan-line processing.
20. The image scanner of claim 13 , wherein the light source comprises an array of light-emitting diodes (LEDs).
21. The image scanner of claim 13 , wherein the light source comprises a xenon light source configured to be modulated with an on-time and an off-time.
22. The image scanner of claim 13 , wherein the off-time of the modulation rate of the light source corresponds to a time period in which the light source is turned off.
23. The image scanner of claim 13 , wherein the array of image sensors comprises an array of charge-coupled devices (CCDs).
24. The image scanner of claim 13 , wherein the array of image sensors comprises an array of complementary metal-oxide-semiconductor (CMOS) sensors.
25. The image scanner of claim 13 , wherein intensity of the light source is configured such that the first modulation rate comprises a 50% duty cycle based on the predetermined linear resolution and the initial first velocity.
26. The image scanner of claim 13 , wherein the document comprises at least one of text, a picture, a graphic, a representation, and a photograph.
27. The image scanner of claim 13 , wherein the document comprises at least one of cotton, a fabric, a fiber, paper, cardboard, a photograph, a slide, and a negative.
28. A image scanner comprising:
a translucent surface configured to receive a document;
a scan bar configured to translate from a first end of the document on the translucent surface to a second end of the document on the translucent surface, the scan bar including an array of image sensors configured to digitally reproduce the document as a sequence of scan-line rows as the scan bar translates from the first end of the document to the second end of the document;
a light source configured to illuminate at least a portion of the document with a modulated light at a modulation rate including an on-time and an off-time each cycle;
a calculation module configured to:
determine an initial first velocity of the scan bar relative to the document; and
determine a first modulation rate of the light source based at least in part on the first velocity of the scan bar, the on-time of the first modulation rate selected to obtain a first exposure level of each scan-line row at the first velocity.
29. The image scanner of claim 28 , wherein the calculation module comprises a look-up table.
30. The image scanner of claim 28 , wherein the calculation module is further configured to:
determine that the scan bar is translating at a second velocity relative to the document; and
determine a second modulation rate of the light source based at least in part on the second velocity of the scan bar, the on-time of the second modulation rate selected to maintain the first exposure level of each scan-line row at the second velocity.
31. The image scanner of claim 28 , further comprising a document velocity sensor configured to determine the velocity of the document through the ADF path.
32. The image scanner of claim 28 , further comprising a scan bar adjustment module configured to dynamically adjust the velocity of the scan bar relative to the document based on a capacity of a memory configured to store at least one of the sequence of scan-line rows.
33. The image scanner of claim 32 , wherein the calculation module is configured to determine the velocity of the scan bar relative to the document based on a communication from the document adjustment module.
34. The image scanner of claim 32 , wherein the memory comprises a memory buffer configure to temporarily store a plurality of the sequence of scan-line rows for subsequent scan-line processing.
35. The image scanner of claim 28 , wherein the light source comprises an array of light-emitting diodes (LEDs).
36. The image scanner of claim 28 , wherein the light source comprises a xenon light source configured to be modulated with an on-time and an off-time.
37. The image scanner of claim 28 , wherein the off-time of the modulation rate of the light source corresponds to a time period in which the light source is turned off.
38. The image scanner of claim 28 , wherein the array of image sensors comprises an array of charge-coupled devices (CCDs).
39. The image scanner of claim 28 , wherein the array of image sensors comprises an array of complementary metal-oxide-semiconductor (CMOS) sensors.
40. The image scanner of claim 28 , wherein intensity of the light source is configured such that the first modulation rate comprises a 50% duty cycle based on the predetermined linear resolution and the initial first velocity.
41. The image scanner of claim 28 , wherein the document comprises at least one of text, a picture, a graphic, a representation, and a photograph.
42. The image scanner of claim 28 , wherein the document comprises at least one of cotton, a fabric, a fiber, paper, cardboard, a photograph, a slide, and a negative.