Mechanism for centering rolls of paper stock supplied for printing

An improved mechanism for centering a roll of paper stock for printing in a portable printer is provided, in which the printer has a housing with a cavity and an opening from a side thereof to provide a receptacle for the roll. The centering mechanism includes a spindle disposed in the cavity toward the opening and mounted in the housing for rotation about an axis, and a pair of arms coupled to each other to move in opposite directions with respect to a center between the arms. The arms engage the two opposing ends of the roll when received on the spindle for centering the roll on the spindle. The arms are coupled to each other by a rack and pinion assembly which moves the arms in opposite direction to each other responsive to a force applied by an operator to one of the arms when a roll is received on the spindle.

DESCRIPTION 
1. Field of the Invention 
The present invention relates to a mechanism for centering rolls of paper 
stock on a spindle which is especially useful in a portable printer, and 
particularly to, a mechanism for automatically centering rolls of paper 
stock in different widths. The mechanism provided by the invention is 
especially adapted for use in a portable label printer which is carried by 
an operator and may be hand held, and more especially such printers which 
are loaded from a side of the housing of the printer. 
2. Background of the Invention 
Conventional portable label printers generally use a roll of wound stock 
material, such as paper, which is loaded into the printer such that paper 
from the roll will properly feed and be aligned with a print head for 
printing by the print head. It is usually desired to provide in such 
printers a facility for using rolls having different width paper, such 
that labels of different widths may be printed. The widths may range 
between one and several inches. 
To accommodate the range of roll widths, the print head is of a length 
sufficient to print along the widest width paper. With a roll loaded into 
the printer, the print head is yieldably biased by springs against a 
platen over which the paper is fed. Printing quality may be reduced if the 
bias varies across the width of the paper. Thus, maintaining uniform bias 
on the print head over the entire width is desirable. If the paper is not 
aligned on the platen, the edge of the paper may be presented to the print 
head causing it to tilt and distort the uniformity of the bias. To resolve 
this problem in a portable label printer, the roll should be centered in 
the printer along its width with respect to the print head, such that the 
bias will be even over the paper from the roll regardless of the paper's 
width. 
Typically, centering a roll in a printer has utilized a top-loading scheme 
in which the roll is located in a printer cavity and two rotatable spindle 
members are urged by spring or springs into the tubular core of the roll 
to move the roll into a center position. It is often difficult to load the 
roll using this scheme, since an operator must physically separate the two 
spindle members from each other while simultaneously orienting the core of 
the roll such that each member will fit into the core when released. If 
the roll's core is not properly oriented between the two members, the roll 
will not be properly aligned when the members collapse together under the 
spring force. Misalignment of the roll can also cause the printer to 
malfunction in feeding paper from the roll and in printing on the paper. 
Further, due to the compactness of the printer, the printer cavity is 
small which can cause difficulty for the operator to insert his or her 
fingers to drop and maneuver the roll in the cavity. This centering scheme 
is used, for example, in label printers manufactured by Eltron 
International of Simi Valley, Calif., of model no. P2242. Side loading of 
rolls into printers has been shown in U.S. Pat. Nos. 5,267,800 and 
5,447,379. However, centering of rolls of different widths has required 
manipulation and is not as operator friendly as desirable. 
In addition, the top-loading scheme limits the size of the roll, i.e., the 
amount of paper stock wound on the roll, due to the narrow dimensions of 
the top opening through which the roll is received into the printer's 
cavity. Thus, depending on the amount of printer use, rolls frequently 
need to be replaced with new rolls, which can make the printer more costly 
to operate. A further drawback is that the roll is generally not 
sufficiently secured in the printer and can easily misalign due to jarring 
of the printer. 
SUMMARY OF THE INVENTION 
Accordingly, it is the principal object of the present invention to provide 
an improved mechanism which automatically centers a roll of paper stock on 
a spindle, thereby facilitating loading of rolls of different widths for 
printing in a printer. 
It is another object of the present invention to provide an improved 
mechanism for centering a roll of paper stock in a portable printer in 
which the roll is side-loaded into the housing of the printer. 
It is yet another object of the present invention to provide an improved 
mechanism for centering a roll in a portable printer which can reliably 
center rolls having different width paper and can easily be loaded by an 
operator. 
Briefly described, the present invention includes a mechanism for centering 
a roll of stock in a portable printer which prints upon the stock from the 
roll. The roll may be a paper stock of adhesive back labels wound upon a 
tubular core, or other media wound on a roll. A housing of the printer has 
a cavity, and an opening from a side thereof to provide a receptacle for 
the roll. The centering mechanism includes a spindle disposed in the 
cavity toward the opening and mounted in the housing for rotation about an 
axis, and a pair of arms coupled to each other to move in opposite 
directions with respect to a center between the arms. The arms engage the 
two opposing ends of the roll when received on the spindle for centering 
the roll on the spindle about the center. The arms are coupled to each 
other by a rack and pinion assembly of the centering mechanism which moves 
the arms in opposite directions to each other. 
One of the arms is provided by a first guide (the inner edge guide) facing 
one end of the roll. The other arm is provided by a projecting member and 
a second guide (the outer edge guide) which faces the other end of the 
roll and may lie adjacent to the projecting member. The rack and pinion 
assembly includes a first rack member coupled to the first guide to be 
moveable therewith, and a second rack member coupled to the projecting 
member to be moveable therewith. A pinion is engagable with the first and 
second rack members to move the first and second rack members in opposite 
directions to each other. The pinion can rotate about a fixed position in 
the housing which determines the center between the first and second 
guides of the arms. 
To center a roll, an operator pushes the second guide onto the spindle 
after a roll is placed on the spindle. In response, the second guide 
applies a force against the roll as it is received on the spindle, thereby 
moving the roll along the spindle. This force moves the first and second 
rack members in opposite directions to each other by the force being 
conveyed against the first guide, via said roll, or the projecting member, 
via the second guide, until both the second guide lies adjacent the 
projecting member, and the first guide lies adjacent the roll.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the figures, a portable compact label printer 10 is shown 
having a housing 12 with a front portion 14, a rear portion 15, a top 
portion 16, and opposing sides portions 17 and 18. Side 18 has an opening 
19 through which a roll 22 is mounted into a cavity 20 in housing 12. Roll 
22 is a roll of stock material 22d, such as adhesive backed paper carried 
on a web which is wound on a tubular core 22a, or may be any other media. 
A cover 18a is hingedly connected to housing 12 such that it closes 
opening 19 in side 18, as shown in FIG. 3. Cover 18a is not shown in FIGS. 
1, 2, and 4 for purposes of illustrating the invention. 
A mechanism is provided in housing 12 for automatically centering roll 22 
as it is loaded from side 18 into cavity 20. The centering mechanism 
includes a spindle 24 in cavity 20 which is mounted on a shaft (not shown) 
protruding about half the length of housing 12 toward opening 19 from a 
side wall 23 of cavity 20. Spindle 24 has an internal bearing (not shown), 
which is coupled by a screw and washer to the end of this shaft, to allow 
spindle 24 to freely rotate along axis 26 as indicated by arrows 27. The 
shaft may have steps of decreasing diameters from side wall 23 toward 
opening 19 to prevent spindle 24 from cantilevering as it rotates. The 
internal bearing may be a self-lubricating plastic bearing mounted about 
halfway in spindle 24. The length of spindle 24 is longer than the widest 
possible width of roll 22, defined by the length of core 22a between 
opposing ends 22b and 22c of the roll. 
In cavity 20, the centering mechanism further includes an inner edge guide 
28, a projecting member 30, and an outside edge guide 32. Inner edge guide 
28 has a flange 28a which extends into cavity 20 and faces end 22b of the 
roll when the roll is loaded via its core 22a onto spindle 24. Outer edge 
guide 32 has a hub 32a and a circular flange 32b which extends from hub 
32a. Flexible fingers 32c extend from hub 32a generally perpendicular to 
the surface of flange 32b and have raised areas or tabs 32d (FIG. 2). Hub 
32a is slidable along spindle 24 with fingers 32c facing towards the side 
wall 23. With roll 22 on spindle 24, flange 32b faces end 22c of the roll. 
Flange 32a has an outer rim or end 32e which can adjacently lie against 
projecting member 30 when outer edge guide 32 slides along the spindle 
toward side wall 23. The projecting member 30 extends into cavity 20 so as 
not to interfere with the loading of roll 22 on spindle 24. Also, the 
circular diameter of flange 32b is larger than the diameter of roll 22, 
such that a section 30d of projection member 30 will engage rim 32c during 
centering of the roll on spindle 24. Cavity 20 may have an interior 
generally contoured to allow outer edge guide 32 to slide along a 
substantial length of the spindle 24 from opening 19. 
The centering mechanism has a rack and pinion assembly 33 which couples the 
inner edge guide 28 and projecting member 30 to each other, and enables 
them to move in opposite directions from each other approximately parallel 
to axis 26 of the spindle. The rack and pinion assembly 33 is shown in 
FIG. 3 with a rear cover 15a removed. Assembly 33 has upper and lower rack 
members 34a and 34b which are located in slots 35a and 35b, respectively. 
Rack members 34a and 34b each have an "L" or "T" shaped edge 38 which 
rides in slots 35a and 35b, respectively. Edge 38 is illustrated as "L" 
shaped in FIGS. 3 and 3A. Arrows 36a and 36b represent the linear motion 
of each rack member 34a and 34b in their respective slot, which is also 
approximately parallel with axis 26 of the spindle. At one end of rack 
34b, projecting member 30 is attached through a window 36 (FIG. 1) in 
cavity 20 by a screw 30b threaded into member 30, as shown in FIG. 3A. 
Pins 30a are provided to assist in aligning projecting member 30 on rack 
member 34b via holes 30c. Inner edge guide 28 is similarly attached to the 
end of rack 34a through window 37 (FIG. 1). Other attachment means or 
additional screws maybe used to attach inner edge guide 28 and projecting 
member 30 to their respective rack members. Racks 34a and 34b each engage, 
via their teeth 40, opposite sides of a pinion 39, such that they move in 
opposite directions within their respective slots responsive to rotation 
of pinion 39. 
Pinion 39 includes a circular flange 39a to retain rack members 34a and 34b 
in slots 35a and 35b, respectively, and a gear (not shown) having teeth 
which engage teeth 40 of rack members 34a and 34b. Preferably, flange 39a 
and this gear are part of a single molded assembly. Pinion 39 rotatably 
mounted to housing 12 by a screw 39b threaded into the housing which 
extends through a boss (or a washer) and the center of pinion 39. Screw 
39b may be a tapered head or shoulder screw. 
Ribs 41 may be provided in housing 12 under rack member 34b to provide a 
level path for motion in slot 35b. Similarly, ribs may be provided under 
rack member 34a to provide a level path for motion in slot 35a. Also, 
raised ribs 42 may be provided in housing 12 to provide a gap between rear 
cover 15a and the rack and pinion assembly 33 when the cover is closed. 
Cover 15a may be attached by screws, through holes 15b, and hinges 15c 
into aligned holes 44 and slots 46, respectively, in housing 12. 
Projecting member 30, attached to rack member 34b, and inner edge guide 28, 
attached to rack member 34a, move in opposite direction to each other 
toward and away from a center position between them. The center position 
is determined by the mounted location of pinion 39 in the housing 12. The 
extent of the reciprocal opposite movement of inner edge guide 28 and 
projecting member 30 is determined by the size of windows 37 and 36, 
respectively, along the direction of such movement. In this manner, inner 
edge guide 28 represents one of a pair of arms of the centering mechanism, 
while outer edge guide 32 with the projecting member 30 represent the 
other of the pair of arms when the outer edge guide is slid onto spindle 
24 against projecting member 30. The pair of arms is coupled to the rack 
and pinion assembly 33, and thus coupled to each other, to move in 
opposite directions with respect to the center between the arms. The arms 
engage the opposing ends 22b and 22c of roll 22 when the roll is received 
on the spindle 24 to center the roll about the center position determined 
by the location of pinion 39, as described in more detail below. 
To center roll 22, an operator pushes the outer edge guide 32 onto spindle 
24 while placing a roll on the spindle (or after placing a roll on the 
spindle), such that fingers 32c of hub 32a are oriented in the direction 
of side wall 23 and the fingers lie between the spindle and the inner 
surface of core 22a of the roll. In response to the external force of the 
operator on outer edge guide 32, the outer edge guide applies a force 
against the roll, thereby moving the roll along spindle 24. This force 
moves the first and second rack members 34a and 34b in opposite directions 
through rotation of pinion 39 by the force being conveyed either against 
the inner edge guide 28, via the roll, or projecting member 30, via the 
outer edge guide 32, until both the outer edge guide lies adjacent the 
projecting member, and the inner edge guide lies adjacent the roll. Thus, 
the roll can easily be loaded and centered in housing 12. 
Whether the force applied to the outer edge guide 32 is conveyed to 
projecting member 30 or to the inner edge guide 28 depends on the width of 
roll 22 and the position of the inner edge guide when the roll is first 
placed on spindle 24. For example, when the projecting member 30 meets the 
outer edge guide 32 before the roll 22 is adjacent the inner edge guide 
28, the outer edge guide will push the projecting member toward side wall 
23, until the other end 22b of the roll meets the flange 28a of the inner 
edge guide as the inner edge guide moves away from side wall 23. However, 
if the roll 22 meets the inner edge guide 28 before the outer edge guide 
32 meets the projecting member 30, the roll will push the inner edge guide 
toward side wall 23 as it is moved along the spindle, until the outer edge 
guide meets projecting member 30 as the projecting member moves away from 
side wall 23. In either case, the roll is automatically centered when the 
roll can no longer be pushed any farther into the housing. The opposing 
motion of the inner edge guide and the projecting member is achieved via 
the rack and pinion assembly 33 described earlier. Accordingly, rolls of 
different widths may automatically be centered in housing 12 while 
eliminating the possibility of a misaligned roll. In the preferred 
embodiment, rolls may vary from 1 to 4 inches in width between its ends 
22b and 22c (FIG. 2). 
After centering roll 22, it is locked or held in place on spindle 24 by 
fingers 32c which are pressured against the inner surface of core 22a by 
the force of spindle 24 against the fingers. Tabs 32d on fingers 32c 
extend into the material of the core, if such material is compliant, to 
grip the core. Preferably, the outer diameter of spindle 24 is tapered 
toward opening 19 in cavity 20 to reduce the space between the spindle and 
the core as the outer edge guide 32 slides toward side wall 23 on the 
spindle, thereby pressuring the fingers 32c and tabs 32d outwards toward 
the core 22a of the roll. FIG. 4 is similar to FIG. 1 and shows roll 22 
loaded and centered in housing 12. The roll is centered in the housing 
with respect to the position of pinion 39 in the housing. In other words, 
the roll is centered about the middle point of an imaginary line between 
the inner and outer edge guides 28 and 32, where the imaginary line is 
approximately parallel to the axis 26 of the spindle. In the figures, the 
middle point is aligned with the center of the pinion 39. However, the 
centered location of the roll along this imaginary line may be adjusted, 
such as by changing the location where the projecting member or inner edge 
guide is attached to their respective racks, or by moving the position of 
the pinion 39 in the housing. 
After the roll is spent, its core 22a may be easily removed from housing 
12. Generally, the operator can pull the outer edge guide 32 off spindle 
24 and the core of the spent roll will be retained on the outer edge guide 
by fingers 32c. A new roll can then be loaded and automatically centered 
as described above. 
The housing 12 of the printer has a platen roller 48 with a rubber surface 
which is rotatably mounted in bearings between side 18 and side wall 23. A 
motor (not shown) in the housing is coupled to one end of the platen 48 to 
drive the platen such that when the paper stock 22d from roll 22 is 
threaded around the platen the paper is pulled from roll as the roll 
freely rotates on spindle 24. A print head (not shown) is located in a 
hinged top cover 16a (FIG. 3), such that when cover 16a is closed in 
housing 12, the print head extends over a substantial length of the platen 
48 and is centered in relation to the center position of the rack and 
pinion assembly 33. Thus, the center of the paper from rolls of different 
paper widths loaded in housing 12 will be identical with respect to the 
print head. The print head may be a thermal print head which is controlled 
to print indica on the paper as the paper is pulled by platen 48. 
Electronics is provided in the printer for controlling the operation of 
the print head and rotation of the platen 48, which may be responsive to 
switches 49 (FIG. 3). The motor and electronics are powered by a battery 
(not shown) in the housing. Straps 50 through rings 51 mounted to housing 
12 may facilitate carrying of the printer by an operator, such as on a 
belt. 
From the foregoing description, it will be apparent that there has been 
provided an improved mechanism for centering rolls of paper stock supplied 
for printing in a portable printer. Variations and modifications in the 
herein described system in accordance with the invention will undoubted 
suggest themselves to those skilled in the art. Accordingly, the foregoing 
description should be taken as illustrative and not in a limiting sense.