Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1999-02-08
2002-04-09
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C250S578100
Reexamination Certificate
active
06369918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to scanners in which the integration period is not an integer multiple of the step period. In particular, the invention relates to timing a resume after a pause for scanners in which the integration period is not an integer multiple of the step period.
2. Description of the Related Art
Scanners generate data at a rate proportional to a processor clock signal. The duration of a scan is thus the amount of data to scan divided by the rate. The amount of data to scan is determined by the horizontal resolution, the horizontal size, the vertical resolution, and the vertical size. Scanners transfer the scanned data to an associated device (usually a computer) at a rate generally less than the processor clock speed. Thus, data accumulates at the scanner faster than it can be transferred. Many scanners include a buffer to hold the accumulated data.
Unfortunately, the accumulated data backlog is often greater than a desired size for the buffer. Such desired size is usually measured by cost, with a large enough buffer to hold the largest possible data accumulation being expensive and usually inefficient because often the largest possible data backlog will not be generated. A typical solution, instead, is to provide a moderately-sized buffer and then pause generation of the scanned data until the buffer has been emptied.
The amount of time the scanner takes to process one line of an image is called the integration period. An “integration signal” is a series of pulses spaced apart from one another by the integration period. A horizontal sensor in the scanner reads one line of the image. Data processing hardware in the scanner uses the integration signal to time its processing of the data from the sensor.
A stepper motor moves the sensor vertically down the image. (Some scanners move the image instead of the sensor, and some scanners move a vertical sensor horizontally, but the principles are the same.) A “step” is a unit of vertical movement. (Some scanners move the sensor in units of microsteps, but the principles are the same.) The amount of time the scanner takes to move one step is called the step period. A series of pulses spaced apart from one another by the step period is called the step signal. So, the step signal drives the stepper motor.
Many scanners have sensors that are physically configured to scan an image at 600 dots per inch (DPI) or an integer fraction thereof: 300, 200, 150, 120, 100, 85.71, and 75 DPI. (Other resolutions are generally made by scanning at the next higher resolution and then processing the line data in software to reduce it to the desired resolution.) Many scanners also prefer to scan at the same vertical resolution as horizontal resolution. In such a situation the scanner is set such that one step is {fraction (1/600)}th of an inch, and the scanner takes an integer number of steps per integration period.
FIG. 1
illustrates the movement of a sensor driven by a stepper motor that takes an integer number of steps per integration period. The x-axis shows time in processor clock periods, and the y-axis shows distance in lines. Line
32
shows the progress of the sensor as it moves over the lines. Integration signal
20
has a period equal to the time the scanner takes to process one line, so the pulses of integration signal
20
define the lines. Pulses of step signal
22
cause the sensor to move one step. The illustrated relationship between integration signal
20
and step signal
22
is such that the sensor moves one step per integration period, which for many scanners indicates the highest vertical and horizontal resolution of 600 DPI. Similarly, two pulses of step signal
22
per integration period would indicate that the sensor moves twice as far in one line, so each line would have a doubled vertical dimension and the scan would be at 300 DPI.
Region
28
is the area in which the sensor moves across lines of the image and detects the light levels thereof. In the middle of the sixth line, pause signal
24
goes high to indicate that the buffer is about to be full and the scanner should stop scanning. The scanner continues processing line six, although other scanners may be configured to stop processing immediately. If the scanner is scanning at more than one step per integration period then the stepper motor should continue stepping until the line has been completed, otherwise the partial data of the line may have to be discarded and the line re-scanned in its entirety upon resuming.
Upon de-assertion of the step signal
22
pulse, at the end of the sixth line, the data valid signal
26
goes low to indicate that the sensor has completed scanning line six, the last line to be scanned before the pause. Any light levels the sensor detects at this point should not be transferred into the buffer.
Ideally, the sensor would pause right at the start of line seven, because the pulses of step signal
22
could be paused at that point. However, the physical characteristics of the stepper motor and the sensor, such as the mass of the sensor and the finite torque of the stepper motor, result in nonideal conditions. These nonideal conditions may cause the sensor to continue moving into line seven, resulting in an inaccurate sensor position upon resuming. Similarly, nonidealities affect the resuming of sensor movement as well, causing the sensor to move with a nonuniform velocity when it is first restarted. This further increases distortion of the resulting scan.
Many scanners solve these problems by moving the sensor backward over previously-scanned lines during a pause. This solves the continued movement problem because the sensor can move backward enough to compensate for the continued forward movement. It solves the nonuniform velocity problem because the sensor can reach a constant velocity after accelerating over the previously-scanned lines.
As shown in
FIG. 1
, in region
30
the step signal
22
pulses three times after pause signal
24
goes low, moving the sensor backward three lines. Pulses of the integration signal
20
may continue, if desired, even though no valid data is being generated.
In region
34
, no pulses of step signal
22
are generated as the scanner waits for the buffer to empty. Pulses of the integration signal
20
may continue, if desired. Near the end of region
34
, the pause signal
24
changes to indicate that the buffer is no longer full and the scanner can resume moving and generating data.
In region
38
, pulses of step signal
22
resume. These three pulses are to move the sensor forward again (over the reversed lines of region
30
).
In region
40
, after the three pulses of step signal
22
(in region
38
), the data valid signal
26
goes high to indicate that the sensor is now at line seven, the correct line to resume generating data.
As detailed above, the scanner having the movement shown in
FIG. 1
takes an integer number of steps (specifically, one step) per integration period. However, not all scanners take an integer number of steps per integration period, for example, as described in U.S. patent application Ser. No. 09/166,871 entitled “Apparatus, Method, and Computer Program for Increasing Scanner Data Throughput”, assigned to the owner of the present application and incorporated herein by reference. A scanner that takes a non-integer number of steps per integration period will have resuming problems not solved by scanners such as those described above, as detailed in FIG.
2
.
FIG. 2
illustrates the movement of a sensor driven by a stepper motor that takes a non-integer number of steps per integration period. The x-axis, y-axis, line
32
, integration signal
20
, pause signal
24
, and data valid signal
26
are as described above regarding FIG.
1
. Step signal
50
has a period slightly longer than that of integration signal
20
; specifically, seven step pulses per eight integration pulses.
The first difference from
FIG. 1
is that, in region
30
, the sensor moves into line seven because the stepper motor does not generat
Hamilton Frederick McGuire
Tom Ronald Hou Kern
Grant II Jerome
National Semiconductor Corporation
Pillsbury & Winthrop LLP
Worku Negussie
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