Apparatus and method for clutchless motor driven hand held scanner

The present invention provides a hand held scanner with a motorized drive capability. The motorized drive employs a clutchless motor system. In manual operation, the scanner operates as a standard non-motorized scanner in which the user can neither see nor feel any effects of the motor system. In the motorized mode, a worm gear mounted on the motor's drive shaft causes the drive gear/friction wheel assembly to engage the drive rollers.

BACKGROUND OF THE INVENTION 
This invention relates generally to image scanners. More specifically, the 
present invention relates to motorized movement of hand held scanners. 
Generally, hand held scanners contain a light source, a reflective element, 
a lens assembly, a detector array, and a set of rollers facilitating 
movement over an image to be scanned. In operation, the light source emits 
light onto the image. The light scattered from the image is reflected by 
the reflector and then focussed through the lens assembly onto the 
detector array. The detector array scans a single line at a time requiring 
continuous repositioning of the entire scanner in order to scan the entire 
image. Typically an operator manually moves the scanner over the image, 
which sometimes results in image scanner errors. Typical causes of errors 
include: (i) erratic hand movements due to shaking; (ii) varying scan 
speeds; (iii) movement which does not follow a straight vertical line 
along the paper; and (iv) the inability to maintain low speed during high 
resolution scans. 
A motorized scanner can alleviate the above problems. Most motorized 
scanners are large desk-top size devices in which the image to be scanned 
is held stationary, and the entire light/reflector/detector assembly is 
moved, similar to a copying machine. Although such a device reduces image 
scanner errors, it lacks portability and is often more expensive than hand 
held scanners. 
One device that combines the benefits of the hand held scanner with those 
of the desk-top scanner is shown in Taiwan Utility Model Application No. 
80212207. Two embodiments of the invention are shown. In the first 
embodiment, a power box containing a motor and gear assembly is manually 
brought into contact with the scanner's rollers. In the second embodiment, 
a "float gear" resides between the power box and the roller assembly. 
Under manual operation, the power box gear assembly is at rest and the 
rotation of the rollers does not cause the engagement of the float gear. 
In automatic operation, the power box assembly rotates, causing the float 
gear to engage the roller assembly. 
SUMMARY OF THE INVENTION 
The present invention provides a hand held scanner with the capability to 
either be operated manually, or with an internal motor. A clutchless motor 
system having a drive gear/friction wheel coupled to the scanner's rollers 
is employed. In manual operation, the scanner operates as a standard 
non-motorized scanner in which the user can neither see nor feel any 
effects of the motor system until the mechanization features are desired. 
According to the invention a hand held scanner is disclosed which includes 
a reversible motor. The motor's drive shaft is coupled to a worm gear. A 
driver assembly, including a drive gear and a friction wheel, is coupled 
to the motor assembly through the worm gear. When the motor is rotated in 
a first direction, the rotation of the worm gear causes the driver 
assembly to engage the scanner's roller. Once engaged, the rotation of the 
scanner's roller causes the scanner to move forward. When the direction of 
the motor's rotation is reversed, the driver assembly disengages from the 
scanner's roller. 
In the preferred embodiment, when manual operation is chosen, the motor 
drive system is completely disengaged from the scanner. The drive 
gear/friction wheel assembly does not contact any part of the scanner's 
roller assembly in this mode, therefore the user has complete freedom to 
move the scanner. In the manual mode, the hand scanner operates along the 
scan axis virtually identically to non-motorized versions. The motorized 
scanner of the preferred embodiment, operating in the manual mode, does 
not incur any additional internal wear due to the incorporation of the 
motor system. 
In the motorized mode, the user first positions the scanner in preparation 
for a scan. During this time the scanner operation is no different than 
that of a non-motorized scanner. Once the scanner is in place, the user 
starts the automatic scan by pressing a single button. The software then 
instructs the motor system to first, rotate at a reduced speed during 
which time the worm gear mounted to the motor's drive shaft rotates the 
drive gear causing the drive gear/friction wheel assembly to engage the 
drive roller and second, ramp up to normal operating speed during the 
actual scan (operating speed determined by required scan resolution). Once 
the scan is complete the user releases the button which causes the motor 
to stop and then automatically reverse in direction for a preselected 
number of steps, thus disengaging the drive gear/friction wheel assembly. 
The present invention, due to its clutchless motor system, minimizes 
possible wear and tear incurred by the scanner during manual operation. 
There is no contact between the drive assembly and the roller assembly 
during manual operation. This has the added benefit of allowing the 
scanner to be manually moved in either the forward or reverse direction 
along the scan axis.

DESCRIPTION OF A SPECIFIC EMBODIMENT 
FIG. 1 is an internal view of a scanner. Motor drive assembly 10 is shown 
in its normal operating configuration. Gear housing 12 serves a dual 
purpose; first, the drive gear/friction wheel assembly 22 is mounted 
within two slots in housing 12 and second, housing 12 acts as a protective 
cover, minimizing the collection of dust and other forms of contamination 
on the drive assembly's gears, thus helping to maintain its smooth 
operation. A light assembly 11 is also shown in this figure. Light 
assembly 11 contains the light source and the reflector element. Generally 
either a fluorescent light or an LED bar is used as the light source. 
Light scattered from an image is reflected into a lens assembly 13 which 
focusses the scattered light onto a detector array 14. 
FIG. 2 is a second view of the internal layout of the scanner shown in FIG. 
1, without the light assembly 11 and gear housing 12 in order to show the 
internal drive system of assembly 10. A worm gear 21 is mounted on the 
drive shaft of stepping motor 20. Worm gear 21 in turn drives a friction 
wheel assembly 22. In this figure, assembly 22 has engaged the scanner 
drive shaft and roller assembly 23. The rotation of assembly 23 causes the 
movement of scanner 25. 
FIGS. 3A-D show four perspectives of drive assembly 10. FIG. 3A is the top 
view of the assembly; FIG. 3B is the front view of the assembly; FIG. 3C 
is the side view of the assembly; and FIG. 3D is a skewed view of the 
assembly. Worm gear 21 is mounted directly onto the output shaft of motor 
20. As the worm gear 21 rotates, it imparts a force to drive gear 31. 
Shaft 32 of the drive gear/friction wheel assembly 22 is mounted in 
slotted housing 35, thus allowing the friction wheel to be either engaged 
or disengaged from drive roller 33. A drive roller 33 is mounted on main 
drive shaft 36. Scanner rollers 34, also mounted on drive shaft 36, rotate 
as drive roller 33 rotates, causing the scanner to move on its own power. 
FIG. 4 is a scanning system 400 embodying a preferred embodiment of the 
present invention. The scanning system 400 includes a computer system 450 
coupled to the hand held scanner 470. The computer system comprises a 
central processor 401, a system memory 402, an input device such as a 
keyboard 403, a fixed disk 404, a display 405, a scanner interface 406, a 
printer 407, and an input/output (I/O) controller 408. A system bus 415 
couples all the components of the computer system 450, providing a link 
between all of them. 
Scanner interface 406 couples computer system 450 to hand held scanner 470. 
Interface 406 provides pulses of a given polarity and rate to stepping 
motor 20. These pulses determine the direction of rotation of motor 20 and 
thus whether drive gear/friction wheel assembly 22 engages or disengages 
from drive roller 33. Interface 406 also controls the pulse rate ramping 
function, allowing for a gradual increase in pulse rate, thus providing a 
smooth transition from the manual mode of operation to that of the 
motorized mode. 
FIG. 5 is a flowchart showing the operation of the motorized scanner in the 
preferred embodiment. First the user manually positions the scanner at the 
beginning of the page to be scanned (step 500). Next the user selects the 
desired scanning resolution (step 510). The scan speed is computed based 
on this resolution. To begin scanning, the user presses a button on the 
scanner (step 520). Pressure is maintained on the scan button throughout 
the scanning operation (step 530). This pressure serves two purposes; 
first, to instruct the scanner to continue its scan and second, to supply 
downward pressure to the scanner. Note that under normal operating 
conditions the scanner's own weight applies sufficient downward pressure 
to the scanner's rollers do insure that they will not slip during the 
scanning operation. After the scan is complete, the user removes pressure 
from the scan button (step 540), thus automatically disengaging the motor 
drive. 
In a second embodiment, the scan button must only be pressed once to 
initialize the scan. The scan then continues for a set number of steps or 
for a set length of time, the length of the page defining the required 
number of steps or period of time. In this embodiment the user, prior to 
beginning the scan, selects the length of page to be scanned. The scanner 
is given sufficient weight to insure that it does not slip during the 
scanning operation. In a third embodiment, the scan speed selection, scan 
start, and scan end, are all performed remotely through commands entered 
using the computer keyboard. In a fourth embodiment, the scanner is only 
operable in the automatic/motorized mode. By removing the scanner's manual 
capability the scanner can be significantly simplified since there is no 
longer a need for the gear/encoder assembly 15 used to monitor scanner 
movement during manual operation. During motorized operation, the 
monitoring of the scanner's movement can be accomplished by either 
counting motor pulses or measuring a period of time. 
FIG. 6 is a flow chart illustrating the operation of the software in the 
preferred embodiment. In this embodiment all instructions necessary for 
motorized scanning are stored in ROM or in firmware and all of the 
required hardware is mounted within the body of the scanner. Thus the 
scanner does not require that any changes be made to the computer 
system/scan software to operate the scanner in the motorized mode. 
The software is initialized when the user presses the scan button mounted 
on the scanner (step 600). Once initialized, the software sends a pulse 
(square wave) to the stepper motor (step 610). The polarity is chosen so 
that the motor steps in a counterclockwise rotation. The pulse rate is 
purposefully chosen to be relatively slow so that the engagement of drive 
gear/friction wheel assembly 22 with drive roller assembly 23 is smooth. 
The period of time that pulses are being sent to the motor is monitored 
and compared to a predetermined value n (step 620). The value of n is 
chosen so that after the motor has been running for n nanoseconds, drive 
gear/friction wheel assembly 22 is completely engaged. 
After pulsing the stepper motor for a period of n nanoseconds, the pulse 
rate is increased (step 630) and a pulse is sent to the stepper motor 
(step 640). The ramping of the pulse rate continues until the stepper 
motor has been operating for a period of n+j nanoseconds (step 650). Once 
the operational period reaches a time of n+j nanoseconds, the pulses 
continue to be sent to the stepper motor with no further increase in rate 
(step 660) until the scan button is released (step 670). The constant 
pulse rate is determined by the user's resolution selection. When the scan 
button is released, the pulses first stop (step 675) and then a reverse 
polarity pulse is sent to the stepper motor (step 680) causing it to 
rotate in a clockwise fashion. Reverse polarity pulses continue to be sent 
to the stepper motor for a period of time i (step 685) at which time the 
program ends (step 690). 
FIG. 7 is an illustration of the stepper motor control sequence. At time 40 
the motor drive system is initialized. During the initial drive engagement 
period 41, the stepper motor rotates at a reduced speed counterclockwise 
for a predetermined period of time. The amount of time within period 41 is 
small, being sufficient to engage friction wheels 30 with drive roller 33. 
After drive roller 33 is engaged, the speed of the stepper motor ramps up 
to the normal speed as shown in time period 42. Once the scan has been 
completed, the drive motor stops its counterclockwise rotation and begins 
to rotate clockwise at a reduced speed for a predetermined period of time 
(period 43). The rotation during period 43 disengages the friction wheels 
30 from drive roller 33. 
FIG. 8 is a detailed view of drive assembly 10 illustrating the engagement 
procedure. Prior to engagement, space 50 separates friction wheels 30 and 
drive roller 33, thus allowing the drive rollers to rotate freely. After 
the motorized scanning mode has been selected, the drive shaft of stepping 
motor 20, to which worm gear 21 is attached, rotates at a reduced speed 
counterclockwise for a predetermined set of steps. The speed of motor 20 
is reduced during this period from its normal operating speed to insure a 
smooth engagement of friction wheels 30 with drive roller 33. As worm gear 
21 rotates, it imparts a force to the teeth of drive gear 31. This force 
causes drive gear 31 to rotate counterclockwise. Simultaneously this force 
causes drive gear 31 to move away from motor 20 and towards drive roller 
33. Drive gear 31 and friction wheels 30 are both mounted to shaft 32. 
Shaft 32 is contained in slot 35. As drive gear 31 and friction wheels 30 
rotate counterclockwise, the assembly `walks` down the ramps created by 
slot 35 until friction wheels 30 engage drive roller 33. 
FIG. 9 shows the drive assembly engaged. After friction wheels 30 engage 
drive roller 33, motor 20 ramps up to its scanning speed. After 
engagement, friction wheels 30 attempt to climb drive roller 33 due to the 
friction between friction wheels 30 and drive roller 33. This upward 
movement is stopped by the wedging effect of the friction wheel 30/drive 
gear 31 assembly between the drive roller 33 and the worm gear 21. 
Friction wheels 30 continue to rotate about shaft 32, imparting a force to 
drive roller 33, causing it to rotate clockwise about shaft 36. Scanner 
rollers 34 are also mounted to shaft 36 and therefore will also be forced 
to rotate in a clockwise fashion. The rotation of scanner rollers 34 cause 
the scanner to move in direction 60. 
FIG. 10 illustrates the disengagement procedure. After the scan has been 
completed, stepping motor 20 stops its counterclockwise motion and rotates 
clockwise for a predetermined period of time. The clockwise rotation of 
worm gear 21 causes drive gear 31 to rotate clockwise. Simultaneously this 
force causes the assembly comprised of drive gear 31 and friction wheels 
30 to walk up the ramp (direction 70), thus disengaging from drive roller 
33. Power to the motor is discontinued after a predetermined period of 
time. At this point the scanner rollers are completely free to move, 
unencumbered by the drive assembly which is now at the upper end of slot 
35. 
As will be understood by those familiar with the art, the present invention 
may be embodied in other specific forms without departing from the spirit 
or essential characteristics thereof. For example, initialization of the 
motorized scan mode could be selected by pressing a button on the scanner 
or by selecting a motorized scan mode using a computer and keyboard. 
Accordingly, disclosure of the preferred embodiment of the invention is 
intended to be illustrative, but not limiting, of the scope of the 
invention which is set forth in the following claims.