Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2000-04-05
2003-12-23
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S375000
Reexamination Certificate
active
06666375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to position-encoding devices (generally abbreviated “encoders”), particularly rotary encoders (also sometimes referred to as “code wheels”). Even more specifically, the present invention provides rotary encoder devices useful for ink-jet hard copy apparatus where accurate positioning of motor driven subsystems, such as pen servicing elements and transports for accurately advancing the printing medium through a printing-zone, is required.
2. Description of Related Art
An encoder generally has two main elements that are subject to relative movement. One of the elements is extended along the direction of relative movement that is to be measured and has marked graduations that are, in effect, arrayed along that direction of movement. The other element is positioned to sense relative passage of such graduations and in response to produce a signal indicative of the movement and which can be translated into a position reckoning. Both linear and rotary encoders are known in the art. “Resolution” is the ability of the system to properly and reliably distinguish each graduation from adjacent ones. This ability may also be described as the readability of the graduations through interpretation of the signals transmitted, or the precision with which the signals correspond to the passage of graduations passed the sensing element. A typical encoder subsystem comprises a optical detector device (reflective or transmissive) mounted in conjunction with a graduated encoder disk acting as a light interrupter to generate signals indicative of the relative position.
Ink-jet printers create text and images as arrays of a very large number of computer-controlled placements of individual, minute, ink droplets on a printing medium that is computer-control advanced in very small steps through the printer during the ink deposition process. Encoders are used to determine positioning of print media relative to the ink jet writing instrument. Other subsystems of an ink-jet printer, such as the positioning of movable service station elements, can employ relatively low resolution encoders directly mounted to a DC drive motor.
For example, rotary encoders can be used to establish image positioning on a print medium as shown in
FIG. 1
(Prior Art) herein from U.S. Pat. No. 5,598,201 filed on Jan. 31, 1994, and by Stodder et al. for a DUAL-RESOLUTION ENCODING SYSTEM FOR HIGH CYCLIC ACCURACY OF PRINT-MEDIUM ADVANCE IN AN INKJET PRINTER (issued Jan. 28, 1997, assigned to the common assignee and incorporated by reference herein).
Referring to
FIG. 1
(Prior Art), two rotary encoders
41
,
51
are linked through a gear train
21
. The gear train
21
consists of a spur
22
on a shaft
12
of the print-medium drive platen/roller
11
, and a pinion
23
that engages the spur
22
and rides on a shaft of a motor
31
. The motor
31
, train
21
and roller
11
together advance
13
a piece of printing medium
1
longitudinally relative to a printhead, or pen
71
. The pen
71
is mounted for transverse motion
72
to mark on the medium
1
at coordinate positions established orthogonally by the medium advance
13
and pen motion
72
. Each encoder
41
,
51
includes a respective encoder disk
42
,
52
and encoder sensor
43
,
53
. One encoder disk
42
is on the platen shaft
12
and the other disk
52
is on the motor shaft
32
. Accordingly, the encoder disk
52
has a mechanical advantage relative to the platen
11
. In operation, encoder signals
44
,
54
from respective encoders
41
,
51
are transmitted to digital electronic controller for
61
for processing which in turn provide signals
62
to control the platen
11
motion and pen
71
motion
72
. Relatively low resolution disks
42
,
52
can be employed by use of quadrature signal generation and digital signal processing techniques.
Commercially available products such as the Hewlett-Packard™ DeskJet™ models
720
and
722
C incorporate an optical encoder wheel on the axle of the print media advance tires. Note that in addition to the illustrated mechanical type paper transport subsystem, endless-loop, vacuum belt, print media transports are also employed in ink-jet printers for moving the media through a printing-zone; the belt position in the printing zone at a given time relative to a printhead is critical to image formation. It will also be recognized by those skilled in the art that document scanners and other hard copy apparatus such as facsimile machines that may incorporate scanning subsystems may use the same type media advance system as a simple computer printer. The present invention may be employed in such other types of hard copy apparatus where incremental advance of the media must be coordinated with other subsystems.
In printers, the accuracy of position determinations along the advance direction of the medium is limited by the positional accuracy of the encoder system graduations. In fact, in printing with a digitally manipulated matrix of very small droplets of ink, for example at a resolution of 1200 dots-per-inch or greater, precision in alignment of the print media with the printhead is a key factor of resultant print quality.
In general, opaque disks used for encoders are preferably made of metal, providing sturdiness of construction, punched through with light transmitting slits. Metal encoder disks are relatively expensive. Moreover, metal type encoder disks are inherently a low resolution mechanism as punching processes attempting to form high resolution graduations can bend or deform the material. Chemical etching or precision laser cutting of the slits are relatively expensive manufacturing techniques.
In other known rotary encoders, a printed film technology is employed. Printed films can achieve very precise encoder lines through photolithographic processes performed on a thin plastic film. Thus, relatively high resolution position encoding can be achieved. However, these films employed are generally too thin to attach directly to a rotating shaft. Therefore, a separate piece part for a hub and attachment manufacturing step is required. Thus, this is a moderately expensive solution.
Moreover, the printed graduation marks can be scratched from stamped plastic, and to a lesser extent on films, leading to encoder subsystem failures.
Heavier plastic disks with molded through holes are difficult to achieve due to the precise mating of mold halves required to achieve holes without flash. Moreover it is difficult to push material in to fill apertures where desired. Thus, through hole type encoders are capable of only relatively low resolution.
Generally, it is also known in the art to provide relatively thick, transparent material, encoder disks with graduation marks using silk screening or photochemistry. The known processes for simply printing a pattern on an inflexible surface also has problems. Pad printing of lines results in varying line thicknesses depending on ink quantity and pressure; controlling run-out (the abbreviation for tolerance problems known to occur in rotating disk technologies) presents difficulties for printing alignment; smudging and voids can occur, reducing the process yield. Hot stamping, or coated foil transfer, using a heated die in the shape of the desired graduation marks, presents the same issues; moreover, ink bridging the small gap between marks can occur.
Therefore, there is a need for providing a relatively low cost encoder having equivalent resolution capabilities to that provided by the prior art.
For convenience in describing the art and the present invention, all types of ink-jet hard copy apparatus are sometimes hereinafter referred to as “printers;” all types, sizes, and compositions of print media are also referred to as “paper;” all compositions of colorants are sometimes referred to as “ink;” and all embodiments of an ink-jet writing instruments are simply referred to as a “pen;” no limitation on the scope of the invention is intended nor should any be implied.
SUMMARY OF THE INVENTION
In
Buck David F. D.
Harriman Douglas L.
Walker Donald G.
Frech Karl D.
Hewlett--Packard Development Company, L.P.
LandOfFree
Rotary encoders does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rotary encoders, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rotary encoders will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3128221