Print gap adjustor in a serial printer

A decentering collar to hold and rotate a carriage by a fixed decentering amount. The position the carriage is moved relatively by rotation of the decentering collar to one of two positions having the same height with respect to the center of rotation of the decentering collar in the direction of the print paper feed. From these two positions, a position can be selected by operation of the adjustment lever that is appropriate for the thickness of the print paper.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a printer, in particular, to a technology for 
adjusting the interval between the print surface of the print paper and 
the print head during printing on the print surface of the print paper. 
2. Description of Related Art 
When the thickness of the print paper changes in a printer, the print 
quality becomes uneven due to the change in the interval between the print 
surface of the print paper and the print head. To compensate, a printer is 
known wherein a mechanism is provided to adjust the interval between the 
print surface of the print paper and the print head by changing the 
posture of the print head so that the interval between the print surface 
of the print paper and the print head is kept uniform. Hereafter, 
adjustment of the interval between the print surface of the print paper 
and the print head in this type of printer will be described with 
reference to FIGS. 4-6. 
FIG. 4(a) is a side view showing the positional relationship between the 
print paper 34, print head 35 and carriage 33 during printing on the 
surface of a print paper having a normal thickness; FIG. 4(b) shows a 
positional relationship between an angle adjustment lever 41 and a guide 
plate 42 (support member) as shown in FIG. 4(a); FIG. 5(a) is a side view 
showing a positional relationship between the print paper 34, print head 
35 and carriage 33 during printing on the surface of a print paper with a 
thicker-than-normal thickness; FIG. 5(b) shows a positional relationship 
between the angle adjustment lever 41 and the guide plate 42 (support 
member) as shown in FIG. 5(a); and FIG. 6 is a magnified side view of the 
print head unit 35 of FIG. 5(a). 
The printer 31 comprises the carriage 33 to hold the ink cartridge 32 which 
stores printing ink and the print head 35 for printing on the print 
surface of the print paper 34. The carriage 33 is supported by the guide 
shaft (guide member) 36 and moves linearly back and forth along the print 
line on the print paper 34 while facing the print paper 34. The angle 
adjustment lever 41 is provided in the back part of the carriage 33 
abutting the guide plate 42 and supporting the carriage 33 in such manner 
that the posture of the carriage 33 is adjusted by rotating the angle of 
adjustment lever 41. 
In the printer 31 having the structure described above, the angle 
adjustment lever 41 abuts the guide plate 42 vertically, or at a right 
angle, when printing on the print surface of the print paper 34 with 
normal thickness. In this state, the print head 35 is kept parallel to the 
print paper 34 to maintain a predetermined amount of interval between the 
nozzle surface of the print head 35 and the print surface of the print 
paper 34, as shown in FIGS. 4(a) and 4(b). In order to print on the print 
surface of a print paper 34 having a thicker-than-normal thickness, the 
angle adjustment lever 41 is rotated clockwise (as shown in FIG. 5(b)). 
This causes the carriage 33 to pivot about guide shaft 36 and changes the 
posture of the print head 35 as the interval between the nozzle surface of 
the print head 35 and the print surface of the print paper 34 expands in 
such manner that the interval is as shown in FIG. 5(a). In this manner, 
the interval between the print surface of the print paper 34 and the print 
head 35 is adjusted even when printing on the print surface of the print 
paper 34 having a thicker-than-normal thickness. 
However, in printing on the print surface of the print paper 34 having a 
thicker-than-normal thickness in the printer 31 described above, the 
carriage 33 is made to pivot amount the guide shaft 36, causing the 
posture of the print head 35 to tilt to produce the adjustment in the 
interval between the print paper 34 and the print head 35. This results in 
an unequal distance between each part of the surface of the print head 35 
facing the print paper 34 and the print surface of the print paper 34 
(FIG. 6). The result is a failure to achieve highly accurate printing, 
thus making it difficult to obtain uniform print quality. 
There are also wire dot matrix printers having print head position 
controlling mechanisms as described above, however, they too are unable to 
perform high quality printing. Examples of this type of printer are 
disclosed in U.S. Pat. Nos. 4,676,675 and 5,156,464, which are expressly 
incorporated by reference herein. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a printer capable of producing 
uniform printing quality by eliminating tilting of the print head relative 
to the print surface of the printing paper when adjusting the interval 
between the print surface of the print paper and the print head. 
In order to achieve the purpose described above, the printer of the 
invention is capable of adjusting the interval between the print paper and 
the print head for printing on the print paper according to the thickness 
of the print paper and comprises: a carriage holding the print head and 
moving linearly back and forth along the print line on the print paper; a 
guide member to guide the carriage to move linearly back and forth; a 
decentering collar to be fitted on the external surface of the guide 
member in such a manner that the collar is allowed to slide and rotate and 
to hold the carriage such that the carriage is allowed to rotate with the 
center which is shifted by a predetermined decentering amount with respect 
to the center of rotation on the external surface of the guide member; and 
a positioning member to position the decentering collar in at least two 
rotational positions among various rotational positions of the decentering 
collar sliding on the external surface of the guide member such that the 
heights corresponding to the shifted position in the direction of feeding 
the print paper become the same, wherein adjustment of the interval 
between the print paper and the print head is enabled by moving the 
carriage toward or away from the print paper through rotation of the 
decentering collar around the guide member. 
For example, the positioning member is provided in the decentering collar 
and comprises: an adjustment lever provided in the decentering collar and 
rotating with the decentering collar; and a position determining member to 
determine a relative position between the adjustment level and the 
carriage, wherein the shift amount of the center of rotation to hold the 
carriage can be determined by the position determining member. 
The position determining member can comprise a protrusion and a hole, for 
example, provided on the surface where the adjustment lever and the 
carriage face each other in such manner that the protrusion and the hole 
can mesh with one another. 
In a printer structured in the manner described above, the carriage moves 
toward and away from the print paper by making the decentering collar 
rotate around the guide member according to the thickness of the print 
paper, enabling adjustment of the interval between the print surface of 
the print paper and the print head to maintain a uniform interval, hence a 
uniform print quality is obtained regardless of the thickness of the print 
paper. 
Moreover, because the decentering collar can be made to rotate differently 
according to the thickness of the print paper, at least two positions can 
be selected and established for the height of the decentering position in 
the direction of the feeding the print paper with respect to the center of 
the rotation of the decentering collar. Hence, the interval between the 
print paper and the print head is adjusted according to the thickness of 
the print paper without changing the posture of the print head. In this 
case, the distance between each part on the surface of the print head and 
the print surface of the print paper is held constant. Hence, a decline in 
the print quality due to tilting of the print head can be eliminated 
enabling uniform print quality. 
Furthermore, because the decentering position of the decentering collar is 
determined by the protrusion and the hole which can engage with each 
other, selection and establishment of each of at least two points where 
the height in the direction of feeding the print paper can be maintained 
at the decentering position with respect to the center of rotation of the 
decentering collar.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Hereafter, an embodiment of the invention will be described with reference 
to the drawings. FIGS. 1 and 2 are side views of an ink-jet type printer 
of the embodiment of the invention. FIG. 1 shows the positional 
relationship between the print paper 3, the print head 4 and the 
decentering collar 5 in printing on the print surface of the print paper 3 
with a normal thickness. FIG. 2 shows the positional relationship between 
the print paper 3', the print head 4 and the decentering collar 5 in 
printing on the print surface of the print paper 3 with a 
thicker-than-normal thickness. FIG. 3 is a drawing showing the decentering 
position of the decentering collar 5 due to rotation and movement of the 
print head 4 and the carriage 2. 
The printer 1 of the invention comprises the carriage 2 which moves (driven 
by a driving motor, not shown) linearly back and forth along the print 
line on the print paper facing the print paper 3. The carriage 2 holds a 
print head 4 which executes printing by ejecting ink onto the surface of 
the medium being printed. The carriage 2 has the decentering collar 5 
which moves the carriage 2 by its rotation. The ink used for printing is 
stored in an ink cartridge 6 mounted on the carriage 2. The carriage 2 is 
axially supported by a guide shaft (guide member) 7 which is anchored 
between the chassis side boards (not shown) in such manner that the 
carriage 2 moves linearly back and forth and rotates freely. The carriage 
2 and the posture of the print head 4 are maintained by the guide plate 
holding units 2c,2d, placed in the lower part of the back side of the 
carriage 2, that hold from both surfaces of the guide plate (holding 
member) 8 which is anchored between the chassis side boards. A platen 9 is 
provided on the opposite side of the print surface of the print paper 3 to 
hold the print paper 3. 
A paper feeding roller 10 transports the print paper 3 by rotation. Tension 
rollers 11,12 are provided adjacent the paper feeding roller 10 to make 
contact with or to separate from the paper feeding roller 10 and assist in 
the transport of the print paper 3 by holding the print paper 3 against 
the paper feeding roller 10. A paper discharge roller 13 and a paper 
discharge tension roller 14, to discharge the print paper 3, are also 
provided. The paper feeding roller 10, tension rollers 11,12, paper 
discharge roller 13, and paper discharge tension roller 14 are supported 
between the chassis side boards (not shown) so as to be able to rotate 
freely. A driving mechanism (not shown), that receives the rotation power 
from the driving motor (not shown), is connected to the paper feeding 
roller 10 and the paper discharge roller 13. 
A cylindrical unit 5c is provided on the decentering collar 5 and is fitted 
(socket joined) to the external surface of the guide shaft 7 to slide and 
rotate freely. Moreover, the cylindrical unit 5c holds the carriage 2 to 
rotate freely. The decentering collar 5 is formed in such a manner that 
the center of rotation A of the decentering collar 5, that is, the center 
of the guide shaft 7 (hereafter, center A) possesses a predetermined 
decentering amount between the center of rotation B (hereafter, center B) 
with respect to the carriage 2. Rotation of the decentering collar 5 
causes the carriage 2 to move substantially horizontally, that is, toward 
and away, with respect to the print surface of the print paper 3. In order 
to properly determine the position of the carriage 2, which moves by the 
rotation of decentering collar 5, protrusions 2a,2b are formed on the 
surface of the carriage 2 adjacent an adjustment lever 5a of the 
decentering collar 5. A hole 5b is provided in the adjustment lever 5a to 
engage with the protrusions 2a,2b to fix the carriage 2 and the adjustment 
lever 5a. 
Hereafter, the operation of the printer 1 having the structure described 
above will be described. In the printer 1, the adjustment lever 5a of the 
decentering collar 5 is rotated according to the thickness of the print 
paper 3 and the position of the print head 4 is determined by the 
engagement of the hole 5b of the adjustment lever 5 with either protrusion 
2a or protrusion 2b of the carriage 2. When the print paper 3 is 
transported to the place between paper feeding roller 10 and the tension 
rollers 11,12 by a paper feeding device (not shown), the carriage 2, which 
is in the stand-by mode at the home station, that is, at a stand-by 
position during the intervals between print operations, begins linearly 
back and forth printing movement driven by the driving motor (not shown). 
Hence, the print head 4 moves facing the print surface of the print paper 
3 maintaining a constant interval with the print paper 3. The print head 4 
injects ink particles onto the print surface of the print paper 3 and 
executes printing opposite the platen 9 positioned between the paper 
feeding roller 10 and the paper discharge 13. When the print head 4 
completes printing over the entire print surface of the print paper 3, the 
print paper 3 is discharged from the printer 1 by the paper discharge 
roller 13 and the paper discharge tension roller 14 and the carriage 2 
returns to the home station. 
Next, the selection and establishment of the positions of the carriage 2 
and print head 4, which is positioned by the rotation of the decentering 
collar 5, will be described. As explained above, the decentering collar 5 
is formed in such a manner that the center B possesses a predetermined 
decentering amount with respect to center A, hence, when the adjustment 
lever 5a is rotated clockwise from the position shown in FIG. 1 to the 
position shown in FIG. 2, the center B rotates around the center A. The 
carriage 2, being rotatably held by decentering collar 5, moves with the 
rotation of the center B by an amount equal to the displacement of the 
center B around the center A. The positions to which the center B rotates 
around the center A, that is center B and center B' shown in FIG. 3, have 
the same height relative to the direction of feed of the print paper 3. 
The guide plate 8 and the guide plate holding units 2c,2d are relatively 
fixed with respect to the direction of feed of the print paper in either 
of the two positions above (center B,B' in FIG. 3) so that the print head 
4 is held parallel to the print surface of the print paper 3 while 
printing. 
By establishing the printing positions in the above-stated manner, the 
position B and the second position B' (FIG. 3) have the same height in the 
direction of the feed of the print paper 3 with respect to the center A. 
Hence, the carriage 2 and the print head 4 are maintained parallel to the 
print surface of the print paper 3 at both positions without changing the 
set-up of the guide plate 8 and the guide plate holding units 2c,2d. 
Moreover, as long as the height of each position in the direction of feed 
of the print paper 3, with respect to the center A, is the same, the 
above-mentioned effect is obtained and the amount of movement of the 
carriage 2 and the print head 4 can be made large by selecting and setting 
the positions such that the displacement from one position to the other 
position is large. 
The protrusions 2a,2b of the carriage 2 and the hole 5b of the adjustment 
lever 5a are provided so that the positions of carriage 2 and the print 
head 4 are predetermined at the above-described positions B, B' by the 
engagement of a protrusion 2a,2b and the hole 5b. Of the two positions 
above, the one B in which the interval between the print surface of the 
print paper 3 and the print head 4 is narrow is determined by the 
engagement of the hole 5b and the protrusion 2a and is used to execute 
printing on the print surface of a print paper 3 having a normal thickness 
(the solid line position of lever 5a in FIG. 3). The second position B', 
where the interval between the print surface of the print paper 3 and 
print head 4 is wide, is determined by the engagement of the hole 5b and 
the protrusion 2b and is used to execute printing on the print surface of 
a print paper 3 with a thicker-than-normal thickness (the position of 
broken line ever 5a' in FIG. 3). By using the protrusions 2a, 2b and the 
hole 5b, the selection and setting of the two positions described above 
can be done properly and easily. 
In this manner, the carriage 2 moves to contact or retreat from the print 
paper 3 by rotating the decentering collar 5, provided in the carriage 2, 
of the printer 1 of the present embodiment and the interval between the 
print surface of the print paper 3 and print head 4 can be adjusted. By 
selecting and the setting of the two positions where the heights in the 
direction of feed of the print paper 3, with respect to the center of 
rotation A of the decentering collar 5, of the center of rotation B of the 
cylindrical unit 5c, which moves by rotation of decentering collar 5, the 
print head 4 can be moved to an appropriate print position without 
changing the orientation of the print head 4. By doing so, the distance 
from each part of the surface of the print head 4 facing the print paper 3 
to the print surface of the print paper 3 is made equal, resulting in 
uniform printing quality. Moreover, by fixing the rotation of decentering 
collar 5a by the engagement of the protrusions 2a,2b of the carriage 2 
with the hole 5a of the adjustment lever 5a and by setting adjustment 
lever 5a to be fixed in one of the above two positions, selection and 
setting of positions of the print head 4 to execute printing can be 
accomplished properly and easily. 
The invention is not limited to the above-mentioned structure and various 
modifications are possible. For example, for the protrusions 2a, 2b and 
hole 5b for fixing rotation of the adjustment lever 5a, it is not 
necessary that protrusions 2a,2b be provided on the carriage 2 and the 
hole 5b be provided in the adjustment lever 5a. It is permissible to 
provide a protrusion 5g (FIG. 3(a)) on the adjustment lever 5 and holes on 
the carriage 2 or, alternatively, protrusions 5h, 5h' (FIG. 3(b)) on the 
adjustment lever 5a by widening the adjustment lever 5a and a single hole 
on the carriage 2. Moreover, although an ink jet type printer is used to 
describe the invention, the invention can be applied to other printers 
where it is necessary to have the face of the print head 4 and print paper 
3 parallel to one another.