Support device for travel assembly

A support device for supporting on a guide shaft a travel assembly moving along the guide shaft, comprising at least two sliding bearings equipped with V shaped grooves, and separate bearings disposed opposite the respective sliding bearings across the guide shaft. The support device supports the travel assembly on the guide shaft by pinching the guide shaft between the sliding bearings and the separate bearings.

FIELD OF THE INVENTION 
This invention relates to a support device which supports on a shaft a 
travel assembly moving along the guide shaft. 
This travel assembly is used when moving an exposure optical system which 
is designed to expose and scan an original document in the original reader 
for printers and so on, or when similarly moving an exposure optical 
system in a copying machine. 
RELATED ART STATEMENT 
Heretofore, such various supports for the travel assembly have been 
proposed as follows: 
According to Japanese Utility Model Laid-Open Publication No. 
Sho-54-181949, as shown in FIG. 8, the travel assembly is supported on a 
guide shaft 104 by sliding bearings 102 and 103 on one side, and at the 
same time on another guide shaft 106 through rollers 105 on the other 
side. This way of supporting is common, but necessitates clearances on the 
order of 0.02 to 0.08 mm between the sliding bearings 102 and 103 and the 
guide shaft 104 to move the travel assembly 101. While a wire 107 is 
pulling the travel assembly, the assembly can move by the amount of the 
above clearances, thus creating a fluctuation of travel speed and a degree 
of vibration. To avoid this, FIG. 8 employs a spring 108 and another wire 
109 to push the travel assembly toward the direction of advance to 
compensate for the play. This method, however, has the disadvantage that a 
large amount of running resistance must be overcome. 
Japanese Patent Laid-Open Publication No. Sho-55-121430 employs a magnet 
instead of the spring 108 and the wire 109 in FIG. 8, in which the 
magnetic force of the magnet again presses the travel assembly in the 
direction of advance in order to reduce play. This method also produces a 
fairly large amount of running resistance. 
According to Japanese Utility Model Publication No. Sho-57-10845, as shown 
in FIG. 9, the travel assembly is supported on a guide shaft 104 by a 
so-called double-cone type roller 110 and another roller 111 on its one 
side (left), and on the other guide shaft 106 by the other rollers 112 on 
the other side (right). The roller 111 is pushed against the guide shaft 
104 by a spring or the like (not shown). 
This method uses the double-cone type roller 110, which permits the 
clearance between the guide shaft 104 and the rollers 110 and 111 to be 
reduced nearly to zero, thus reducing running resistance. The position of 
the travel assembly, however, may shift as the rollers wear, or noise may 
be raised as the rollers rotate. 
According to Japanese Utility Model Publication No. Sho-57-25216, as shown 
in FIG. 11, the travel assembly 101 is provided with two V-shape type 
sliding bearings 113 on its one side, and supported on a guide shaft 104 
by these V-shape type bearings and a roller 114. The system is illustrated 
in FIG. 11. 
In this figure, pulling a wire 107 in the direction of A or B allows the 
travel assembly 101 to be moved respectively in the direction of AA or BB 
along the guide shaft 104. In short, this method causes the travel 
assembly 101 to be supported at three points by the roller 114 and the 
V-shape grooves 115 on the bearings 113. 
With this kind of support device, when the wire 107 is pulled, a force 
couple is applied to the travel assembly 101, which cause the assembly to 
float up from the guide shaft 104. For instance, when the wire is pulled 
in the direction of A, a force couple Ma acts on the travel assembly 101, 
which in turn causes the groove 115 on the right side to slide against the 
guide shaft 104. As shown in FIG. 12, the force couple exerts such a force 
on the assembly that the groove 115 on the right side is pushed out in the 
direction of S, which causes the right-side slope of the right groove 115 
to ride on the guide shaft 104, thus resulting in the travel assembly 101 
floating up in the direction of T or upward in the drawing. 
When using the travel assembly for copy scanning by means of an exposure 
optical system, such a float-up of the travel assembly as described above 
can cause difficulties because of the inability to accurately position the 
requisite optical image. 
OBJECT AND SUMMARY OF THE INVENTION 
In view of the above, it is the object and purpose of the invention to 
provide a support device for a travel assembly which can keep the travel 
assembly from floating up from a guide shaft and can allow smooth travel. 
In a support device for supporting on a guide shaft a travel assembly which 
moves along the guide shaft, the aforesaid object can be accomplished by 
providing at least two first bearings having V-shape grooves fixedly 
secured on the travel assembly, and slidably in contact with the guide 
shaft as well as second bearings also fixedly secured to the travel 
assembly, and disposed respectively oppositely to at least two of the 
first bearings across the guide shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 7 is a sectional side view of an example of a document reader using a 
support device of a travel assembly according to the invention. 
In this device, the beam of the reflected image produced by illuminating by 
lamps 52 an original document 51 placed on a glass document support member 
50 is projected to form the image on a line sensor 57 through a first 
mirror 53, a second mirror 54, a third mirror 55, and a lens 56, and the 
original image is read by the line sensor 57 using a so-called CCD (charge 
coupled device) or the like. 
When reading the original 51, the lamps 52 and the first mirror 53 travel 
together as a unit, in the direction of F shown by the arrow, from the 
positions shown by the full lines in the figure. At the same time, the 
second mirror 54 and the third mirror 55 also travel together as one piece 
in the direction of F shown by the arrow similarly but at half the speed. 
Therefore, the lamps 52 and the mirrors 53 to 55 respectively arrive at 
the relative positions shown by broken lines in the figure. 
The sub-scan for the original 51 is performed by the travel of the lamps 52 
and the respective mirrors 53 to 55 in the direction of F, and the 
main-scan thereof is accomplished by the self-scan of the line sensor 57, 
which results in reading of the original 51 in two dimensional state by 
the line sensor 57 to be converted into electric signals. 
As mentioned above, the lamps 52 and the mirrors 53 to 55 travel of 
sub-scan for the original 51, and a first travel assembly 1 in FIG. 1 is 
dedicated to the travel of the lamps 52 and the first mirror 53, while a 
second travel assembly 2 in FIG. 1 is dedicated to the travel of the 
second and third mirrors 54 and 55. Because the lamps 52 and the first 
mirror 53 travel twice as fast as the second and third mirrors 54 and 55, 
the first travel assembly 1 travels faster than the second travel assembly 
2, which results in the change of the relative disposition of the first 
travel assembly 1 and the second travel assembly 2 within the end limits 
of the second travel assembly 2. In this connection, the direction F shown 
by the arrow in FIG. 1 is the same as shown by the like reference sign in 
FIG. 7. 
Both of the first travel assembly 1 and the second travel assembly 2 are 
provided with supports representing embodiments according to the 
invention, which are different from each other. From now on, each of the 
embodiments is separately described. 
First, as shown in FIG. 2, which is a sectional view of FIG. 1 taken along 
line II--II, two first bearings 5a and 5b provided with V shaped grooves 4 
in contact with a guide shaft 3 are fixed on the first travel assembly 1. 
Numeral 6 designates screws fixing the first bearings 5a and 5b to the 
first assembly 1. The distance between the bearings 5a and 5b is set to a 
proper value l1. From now on, l is defined as the bearing-to-bearing 
distance. 
In FIG. 1, a bracket portion 1a extending downwardly is formed 
approximately in the center of the first travel assembly 1, and a flat 
spring 7 working as pressing means is fixed by screws 8 to the lower 
portion of the bracket portion 1a. The flat spring 7 provides projections 
7a and 7b spaced by a distance approximately the same as the 
bearing-to-bearing distance l1 at both longitudinal ends, with the bracket 
portion 1a at the center, and rollers 9a and 9b working as second bearings 
are rotatably installed respectively on these projections. 
The first bearings 5a and 5b and the rollers 9a and 9b are disposed 
opposite to each other across the guide shaft 3, and further the rollers 
9a and 9b are properly pressed against the guide shaft 3 by the flat 
spring 7. As a result, the travel assembly 1 is slidably held between the 
first bearing 5a and the roller 9a, and further between the other first 
bearing 5b and the other roller 9b, namely being held slidably at the two 
points. 
As the first travel assembly 1 is supported in this manner on the guide 
shaft 3 by means of two sets of bearings facing each other, the first 
travel assembly 1 is kept from floating up from the guide shaft 3 by the 
action of the pressing force of the rollers 9a and 9b, and can run 
smoothly, even if a force couple acts thereon as described concerning 
FIGS. 11 and 12. 
The force of the flat spring 7 is set to be just enough to prevent 
floating, because too strong a spring force causes too high a running 
resistance when the first travel assembly 1 moves in the direction of F. 
More specifically, the spring force should be just large enough to prevent 
the first travel assembly from being lifted, taking into account the 
design maximum couple (Ma; FIG. 11). 
So far the description concerns the first embodiment according to the 
invention applied to the first travel assembly 1, and from now on it 
concerns the second embodiment according to the invention applied to the 
second travel assembly 2. In FIG. 1, the second travel assembly 2 is 
equipped with two first bearings 15a and 15b spaced by a 
bearing-to-bearing distance l2 longer than the bearing-to-bearing distance 
l1 for the first travel assembly 1. As shown in FIG. 3, the second 
embodiment is similar to the first embodiment in that the first bearing 
15b (15a) has a V-shaped groove 14 in contact with the guide shaft 3 and 
is fixed by screws 6 to the second travel assembly 2. But, the difference 
between the first and second embodiments lies in that the second bearings 
placed opposite to the first bearings 15a and 15b across the guide shaft 3 
are not rollers but sliding bearings 19a and 19b. 
With the second bearings comprising the sliding bearings 19a and 19b, when 
a force couple (FIG. 11) acting on the travel assembly 2 is about to cause 
the second travel assembly 2 to lift up from the guide shaft 3, float-up 
of the travel assembly 2 is prevented as well, because the sliding 
bearings 19a and 19b come into contact with the guide shaft 3. 
In addition, if the sliding bearings 19a and 19b are set too tightly 
against the guide shaft 3, the running resistance of the second travel 
assembly 2 can be too high, resulting in a failure to assure smooth 
running thereof. Therefore it is desirable that a proper gap be 
established between the sliding bearings 19a,19b and the guide shaft 3. 
However, too large a gap may allow the second travel assembly 2 to lift. 
Experiments have revealed the most suitable gap to be about 0.02 to 0.05 
mm. 
The two embodiments described above have respective characteristics. 
Firstly, the first embodiment attached to the first travel assembly 1 is 
particularly useful for a short bearing-to-bearing distance l1. Generally, 
the extent of the lifting of the travel assembly is in inverse proportion 
to the bearing-to-bearing distance (e.g. l1 in FIG. 1). In other words, a 
short bearing-to-bearing distance allows the bearings to be easily lifted 
and the degree of the lifting is also large. Therefore, it is desirable 
that the gap between the second bearings (e.g. 9a and 9b in FIG. 1) and 
the guide shaft should be set as small as possible, and if possible, they 
should be in contact with each other, in order to prevent lifting. In the 
case of the first embodiment or with a short bearing-to-bearing distance, 
using the sliding bearings 19a and 19b as the second bearings as seen in 
the second embodiment is not practical because of the large running 
resistance as mentioned above. However, using the rollers 9a and 9b as the 
second bearings in the first embodiment can adequately suppress the 
lifting of the travel assembly with a minimum of running resistance. 
Secondly, the second embodiment attached to the second travel assembly 2 is 
especially effective for a long bearing-to-bearing distance l2 and 
benefits from low cost. The aforesaid description shows that in general 
the result of longer bearing-to-bearing distance is that the bearings are 
hardly lifted and the degree of the lifting is small. So, in this case, 
contact of the second bearings (e.g. 19a and 19b in FIG. 1) and the guide 
shaft is not practically required. In this connection, using rollers for 
the second bearings as shown in the first embodiment, and placing of the 
flat spring 7 to press the rollers to the guide shaft could result in high 
cost, thus being undesirable. 
So far, the angles .theta..sub.1 and .theta..sub.2 of the V shaped groove 4 
(FIG. 2) in the first embodiment and the V shaped groove 14 (FIG. 3) in 
the second embodiment have not been explained. In the embodiment in FIG. 
1, wherein the bearing-to-bearing distance l1 in the first embodiment is 
shorter than that l2 in the second embodiment, it is preferred that the 
angle .theta..sub.1 of the groove in the first embodiment be smaller than 
that angle .theta..sub.2 of the groove in the second embodiment. The order 
of 60.degree. and 90.degree. is employed respectively for .theta..sub.1 
and .theta..sub.2. 
The reason is as follows. As seen in FIG. 12, in the case of a small angle 
of the V shaped groove, it is harder to lift the slant face of the V 
shaped groove 115 from the guide shaft 104, even when a force couple acts 
on the travel assembly 101 in FIG. 11. So, it is desirable to keep the 
angle .theta..sub.1 of the groove small in the first embodiment in which 
the short bearing-to-bearing distance tends to promote lifting of the 
travel assembly. 
However, setting a small angle .theta..sub.1 or .theta..sub.2 of the groove 
of the first bearing results in more difficult machining and also in 
inaccurate dimensions of the travel assembly 1 or 2 in the vertical 
direction (the vertical direction in FIGS. 1 to 3). As a result, it is 
desirable to avoid setting the angles of the grooves of the first bearings 
smaller than needed. 
As mentioned above, by changing the degree of the angle .theta..sub.1 or 
.theta..sub.2 of the first bearings 5a and 5b or 15a and 15b, according to 
the bearing-to-bearing distance l1 or l2, effective prevention of lifting 
can be properly obtained for respective cases. On the other hand, if the 
degree of the angle .theta..sub.1 of the groove is set different from that 
.theta..sub.2 of the groove, the positions P (in FIG. 2) on which the 
first bearings 5a and 5b are in contact with the guide shaft 3 in the 
first embodiment, and the positions Q (in FIG. 3) on which the first 
bearings 15a and 15b are in contact with the guide shaft 3 in the second 
embodiment, can be different from each other. This means that if the first 
bearings 5a and 5b for the first embodiment, and the first bearings 15a 
and 15b for the second embodiment happen to slide on the same guide shaft 
3 at the same time, the sliding loci of the respective bearings result in 
different lines on the guide shaft 3. As a result, the guide shaft wears 
out less and has a longer service life in comparison with the case in 
which both of the different first bearings slide on the same line. 
In FIGS. 7 and 1, the bearing-to-bearing distance l1 between the first 
bearings 5a and 5b supporting the first travel assembly 1 carrying the 
lamps 52 and the first mirror 53 and travelling a longer distance is set 
short (in the first embodiment), while the bearing-to-bearing distance l2 
between the first bearings 15a and 15b supporting the second travel 
assembly 2 carrying the second and third mirrors 54 and 55 and travelling 
a shorter distance (the second embodiment) is set long, and further the 
first travel assembly 1 is placed within the end limits of the second 
travel assembly 2. The purpose is to make the overall width W of the 
device as short as possible in comparison with the length L of sub-scan of 
the original 51 in FIG. 7. Therefore, if there is no such dimensional 
restriction for the overall width W, it is possible to provide two pieces 
of the same first travel assemblies 1 and the same supports thereof (the 
first embodiment) on the same guide shaft in juxtaposition, as well as to 
attach the lamps 52 and the mirror 53 to one first travel assembly and the 
mirrors 54 and 55 to the other one. 
In this case, assuming that the bearing-to-bearing distances of the 
supports for the both travel assemblies are set equal, it is desirable to 
preset different degrees of angles of V shaped grooves in both supports in 
order to extend the life of the guide shaft 3, as previously described. 
The following description concerns the third embodiment according to the 
invention, referring to FIG. 4. A travel assembly 21 shown in this figure 
can support one combination of the lamps 52 and the first mirror 53 or the 
other combination of the second and third mirrors 54 and 55 shown in FIG. 
7. For example, the lamps 52 and the first mirror 53 are mounted on one 
travel assembly 21, and further the second and third mirrors 54 and 55 are 
mounted on the other travel assembly 21. The travel assemblies 
respectively can travel along the guide shaft 3 in the direction of F in 
FIG. 7. But, one travel assembly carrying the lamps 52 and the first 
mirror 53 moves twice as fast as the other travel assembly carrying the 
second and third mirrors 54 and 55. The direction F in FIG. 4 is identical 
to the direction shown by the like sign in FIG. 7. 
The travel assembly 21 has two bearings 25a and 25b spaced the distance L 
from each other which respectively are equipped with V shaped grooves 24 
in contact with the guide shaft 3 at the points pp, as shown in FIG. 5. 
In FIG. 4, a bracket portion 21a extending downwardly at about the center 
of the travel assembly 21 is formed, and arms 26a and 26b are pivotally 
secured to the lower portions thereof. FIG. 6 shows in detail how the arms 
26a and 26b are secured. 
In FIG. 6, sleeves 27 are fixed into the bracket portion 21a by means of 
set screws 28, and a one-way clutch 30a is force-fitted into one sleeve 
27. The arm 26a is secured on the left end of a clutch shaft 31 inserted 
through the one-way clutch 30a. At the right end of the clutch shaft 31, a 
set screw 32 fitted thereinto prevents the clutch shaft 31 from slipping 
out. In FIG. 4, the one-way clutch 30a permits the arm 26a to rotate 
clockwise but prevents the arm 26a from rotating counterclockwise. 
FIG. 6 shows mainly the arms 26a at the left side in FIG. 4, the other arm 
26b, at the right side is secured similarly. However, the one-way clutch 
30b for the arm 26b works differently--the one-way clutch 30b permits the 
arm 26b at the right side to rotate counterclockwise but prevents it from 
rotating clockwise. 
At the other ends of the right and left arms 26a and 26b, rollers 29a and 
29b, such as antifriction bearings, ball bearing or other bearings, are 
rotatably supported opposite the bearings 25a and 25b across the guide 
shaft 3. Tension springs 35 working as elastic means are engaged between 
pins 33a and 33b fixed to the right and left arms 26a and 26b, and pins 
34a and 34b secured to the travel assembly 21. As mentioned above, the 
left arm 26a is designed to rotate only clockwise, and the right arm 26b 
only counterclockwise, so that the left arm 26a is given the clockwise 
rotation tendency, and the right arm 26b the counterclockwise rotation 
tendency by the positive action of the tension springs 35. These rotation 
tendencies work in such directions that both the rollers 29a and 29b swing 
respectively toward the mating bearings 25a and 26b, and cause the right 
and left rollers 29a and 29b to get into close contact with the guide 
shaft 3 by the force of the springs 35. 
As a result, the travel assembly 21 moves on the guide shaft while being 
held between two sets of the bearing 25a and the roller 29a, as well as 
the bearing 25b and the roller 29b, which are respectively opposite each 
other across the guide shaft 3. While the travel assembly 21 is running, 
the running resistance is remarkably reduced thanks to the rotation of the 
both rollers 29a and 29b. Too strong a force of the springs 35, however, 
is not desirable, because too excessive a force of the rollers in pressing 
against the guide shaft 3 induces too large a running resistance, 
resulting in difficulties. So, the force of the springs 35 should be set 
to a proper degree just enough to keep the running resistance low as well 
as to effectively prevent lifting of the travel assembly 21. 
When a force couple acts on the travel assembly 21 (Ma in FIG. 11), the 
travel assembly 21 tends to lift itself from the guide shaft 3 upwardly, 
as described referring to FIG. 12. Simultaneously, each of the rollers 29a 
and 29b is relatively moved downwardly in FIG. 4 by means of the guide 
shaft 3, which results in the left arm 26a (holding the roller 29a) being 
pushed counterclockwise while the right arm 26b (holding the roller 29b) 
is being pushed clockwise. 
The arms, however, have no possibility of rotating in the directions in 
which they are pushed because the left arm 26a is prevented from rotating 
counterclockwise by the one-way clutch 30a, and the right arm 26b from 
rotating clockwise by the one-way clutch 30b as already mentioned above. 
In other words, even if a lifting force acts on the travel assembly 21 the 
assembly cannot be lifted from the guide shaft 3 because of these 
preventive measures. Thus, the travel assembly 21 is both kept from 
lifting and is allowed to run smoothly. 
Even if the guide shaft 3 and the bearings 25a and 25b wear from long use, 
the travel assembly 21 is still kept from lifting because continued 
contact of the guide shaft 3 and the rollers 29a and 29b is ensured by the 
springs 35. 
Additionally, in determining the angle .theta. of the groove (FIG. 5), the 
same consideration apply as in determining the angles .theta..sub.1 and 
.theta..sub.2 in FIG. 2. In other words, the groove angle .theta. should 
not be set unnecessarily small only with the prevention of the lifting of 
the travel assembly 21 in mind, but reasonably set on the basis of the 
bearing-to-bearing distance and other factors. In addition to the 
bearing-to-bearing distance, the weight, the running speed and the running 
characteristics (the so-called allowable value of jitters) of the travel 
assembly 21 should be taken into consideration. 
According to the inventor's experiments, the angle of 40.degree. to 
90.degree. is optimum for effective prevention of lifting of the travel 
assembly 21 and also for keeping the running resistance small. More 
particularly, the angle .theta. of 70.degree. to 90.degree. is ideal for a 
long bearing-to-bearing distance, and the angle .theta. of 40.degree. to 
60.degree. for a short bearing-to-bearing distance. 
It will be clear to those skilled in the art that various changes may be 
made in the invention without departing from the spirit and scope thereof 
and therefore the invention is not limited by that which is shown in the 
drawings and described in the specification but only as indicated in the 
appended claims.