Method of optimal focusing for document scanner
View Patent ↗A method of optimal focusing for a document scanner is disclosed. The scanner includes an optical module movable in a given scanning direction to perform scanning operation over an area of a document in a scan line by scan line manner by being driven by an optical module moving mechanism under control of a control unit. The control unit includes a best focus value memory for storage of the best focus value for each scan line. The method includes the steps of moving the optical module to one of the scan lines of the document and retrieving the best focus value corresponding to the selected scan line. A focus adjusting mechanism is controlled by the control unit to move the optical module in a second direction to adjust the focus position of the optical module in accordance with the best focus value of the scan line. Once the optical module reaches the scan line, the operation of the optical module is temporarily suspended in order to have the vibration of the optical module damped out. Thereafter, a scanning operation is performed over the scan line.
1. A method of optimal focusing for a document scanner, wherein the scanner comprises an optical module movable to perform a scanning operation over an area of a document under control of a control unit, the method comprising the steps of:
(a) moving the optical module in a first direction substantially parallel to the document to a starting scan line of the document;
(b) moving the optical module in a second direction substantially perpendicular to the document for adjusting a focus position of the optical module with respect to the document in accordance with a best focus value corresponding to the selected scan line;
(c) temporarily suspending the optical module for a predetermined time period until a vibration of the optical module is damped out;
(d) scanning the selected scan line of the document; and
(e) moving the optical module to a next one of the scan lines of the document in the first direction and repeating steps (b) to (d) until all scan lines are done.
2. The method as claimed in claim 1 further comprising the step of performing a pre-scanning operation before the step (a) for establishing the best focus value for each scan line.
3. The method as claimed in claim 2 , wherein the pre-scanning operation is done by scanning a test sheet comprised of alternating black and white segments in order to obtain the best focus value for each scan line.
4. The method as claimed in claim 2 , wherein the best focus value is stored in a best focus value memory of the document scanner to be accessed by the control unit.
5. The method as claimed in claim 4 , wherein the best focus value memory stores at least one set of the best focus value.
6. A method of optimal focusing for a document scanner, wherein the scanner comprises an optical module movable to perform a scanning operation over an area of a document under control of a control unit, the control unit comprising a best focus value memory storing a best focus value corresponding to each scan line, the method comprising the steps of:
(a) moving the optical module in a first direction substantially parallel to the document to a starting scan line of the document;
(b) retrieving the best focus value corresponding to the scan line from the best focus value memory;
(c) moving the optical module in a second direction substantially perpendicular to the document for adjusting a focus position of the optical module with respect to the document in accordance with a best focus value corresponding to the selected scan line;
(d) temporarily suspending the optical module for a predetermined time period until a vibration of the optical module is damped out;
(e) scanning the selected scan line of the document; and
(f) moving the optical module to a next one of the scan lines of the document in the first direction and repeating steps (b) to (d) until all scan lines are done.
7. The method as claimed in claim 6 further comprising the step of scanning a test sheet comprised of alternating black and white segments in order to obtain the best focus value for each scan line.
8. The method as claimed in claim 6 , wherein the best focus value memory stores at least one set of the best focus value.