Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-09-13
2003-04-15
Lee, Diane I. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462380, C359S199200
Reexamination Certificate
active
06547145
ABSTRACT:
BACKGROUND
The field of the present invention relates to optical systems for driving motors such as dithering or oscillating motor drive for producing a scanned beam in a data reading application.
Data reading devices, such as bar code scanners, read symbols such as those found on consumer and industrial products, including one-dimensional codes such as UPC code, EAN/JAN, Code 39 or two-dimensional codes such as PDF-417. Scanners may be stationary, handheld or combination stationary/handheld scanners. Typically a data reading device such as a bar code scanner illuminates a bar code and senses light reflected from the code to detect the bars and spaces of the code symbols and thereby derive the encoded data. In a common system, an optical beam of light, such as a laser beam produced by a laser diode is scanned over a scan angle so as to scan the laser spot across the item being read.
In applications requiring rapid scanning of an illumination beam, methods employed for rapidly and repetitively scanning the illumination beam across a scanned region include mirror dithering such as described in U.S. application Ser. No. 08/934,487 and light source dithering such as described in U.S. Pat. No. 5,629,510, both of which are hereby incorporated by reference. Dithering, i.e. rapid rotational oscillation of an illumination beam, causes the illumination beam to move rapidly back and forth generating a scan line. When this scan line illuminates a barcode, the resulting time dependent signal due to detected light scattered and/or reflected from the bars and spaces of the barcode is decoded to extract the information encoded therein.
FIG. 1
illustrates a dithering assembly
100
comprising an oscillating structure which has a resonant frequency determined by the effective spring constant of bending member
112
and the effective mass of the mirror/magnet assembly
110
and any components attached thereto. The dithering assembly
100
comprises a mirror/magnet assembly
110
, drive coil
106
, feedback coil
108
, bending member
112
, and mounting member
114
. The mirror/magnet assembly
110
comprises mirror
102
, mirror bracket
103
, drive magnet
104
and feedback magnet
105
. The drive coil
106
, feedback coil
108
and mounting member
114
may be part of or mounted within a housing (not shown) for dithering assembly
100
. The bracket
103
holds mirror
102
and is connected to mounting member
114
by bending member
112
, which may comprise a thin, flat sheet of flexible material which acts as a bendable spring.
Bending of member
112
results in pivoting/rotation of mirror/magnet assembly
110
about an axis substantially parallel to mirror
102
, perpendicular to the plane of FIG.
1
. The motion of mirror/magnet assembly
110
is driven by passing an oscillating drive current through drive coil
106
thereby generating an oscillating magnetic driving force on drive magnet
104
. The maximum amplitude of dithering motion of the mirror
102
occurs when the drive current oscillates at the resonant frequency of dithering assembly
100
, i.e., when the dithering assembly
100
is driven resonantly. It is important to drive the dithering assembly
100
resonantly to obtain the maximum dithering amplitude with minimum drive power consumption. It is also important that the position and length of the resulting scan line remain constant.
A feedback coil
108
positioned adjacent the mirror bracket
103
experiences an oscillating magnetic field due to motion of the feedback magnet
105
, which is attached to bracket
103
. The electrical potential developed across feedback coil
108
varies directly with time derivative of the magnetic flux at feedback coil
108
, and hence with the velocity of feedback magnet
105
and dithering mirror
102
. The zero crossings of the feedback potential, which occur when the mirror velocity is zero, are used to trigger switching of the polarity of the drive current in drive coil
106
, thereby reversing the drive force exerted on drive magnet
104
and mirror
102
. In this manner, the switching frequency of the drive force matches the resonant the frequency of the dithering motion of dithering assembly
100
and the drive force is in phase with the velocity for a resonantly driven system.
It is also possible to derive velocity feedback from a fixed Hall Effect sensor mounted adjacent a moving magnet, or from a piezoelectric element attached to the flexure such as disclosed in U.S. application Ser. No. 08/934,487.
There are several disadvantages with these feedback schemes such as requiring additional sensing hardware and control electronics, which add to the overall power consumption, cost, and/or complexity of the scanning system.
SUMMARY OF THE INVENTION
The present invention is directed to systems and methods for driving motors, such as those motors used to dither scan mechanisms in a scan module or scanning assemblies therefore. A preferred embodiment is directed to a resonantly driven dithering assembly employing feedback such as for scanning an illumination beam for a barcode scanner in which the velocity feedback signal is derived from the back-EMF of the actuator motor coil. The drive current is pulsed for a given duration commencing at a start point where the velocity of the dither mechanism is measured to be zero.
REFERENCES:
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patent: 5003164 (1991-03-01), Barkan
patent: 5097354 (1992-03-01), Goto
patent: 5168149 (1992-12-01), Devorkis et al.
patent: 5177631 (1993-01-01), Orlicki et al.
patent: 5280163 (1994-01-01), Barkan
patent: 5329103 (1994-07-01), Rando
patent: 5629510 (1997-05-01), Quinn et al.
patent: 5694237 (1997-12-01), Melville
patent: 5742042 (1998-04-01), Scofield
patent: 5874720 (1999-02-01), Dvorkis et al.
patent: 5874722 (1999-02-01), Rando et al.
patent: 6118569 (2000-09-01), Plesko
patent: 6152372 (2000-11-01), Colley et al.
U.S. patent application Ser. No. 08/934,487, filed Sep. 19, 1997, entitled “Dithering Assemblies for Barcode Scanners,” inventors: James Colley, James Ring, Patrick O'Donnell and Thomas Arends.
Coleman Edward P.
Colley James E.
Lee Diane I.
PSC Scanning Inc.
Stoel Rives LLP
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