Reference jig for use in mounting lens components in positions, and lens mounting method using such jig

A reference jig for positioning and fixing a lens or lenses in a predetermined position on a lens support structure, the reference jig including for positioning and fixedly bonding a plural number of lens components on a lens mounting surface of the support structure: a plate-like main body having a predetermined thickness and detachably fixable on the lens mounting surface of the support structure; registration members provided contiguously to the main body and engageable with reference walls of the lens support structure to hold the main body in registered position relative to the lens support structure; and notched positioning wall portions each formed in the main body and abuttingly engageable with at least two transversely opposite corner portions of a lens component to hold same in a predetermined position on the lens support structure.

FIELD OF THE INVENTION 
1. Field of the Art 
This invention relates to a reference jig particularly suitable for use in 
mounting and fixing a plural number of lens components of an optical 
system in predetermined positions on a lens support structure in the 
fabrications of a beam scanner, a photostatic copier or the like, and a 
method of fixedly mounting lenses exactly in position on a lens support 
structure by the use of such a reference jig. 
2. Description of the Prior Art 
For instance, the optical systems, which are used on laser beam scanners 
for scanning a laser beam transversely along a scanning surface at a 
predetermined speed, usually employ truncate lenses which need to be fixed 
in predetermined positions on a lens support structure. In mounting the 
lens components of this sort on a lens support structure, the positioning 
of the lenses requires extremely high accuracy. Especially in a case where 
a plural number of lens components are to be mounted, each one of the lens 
components has to be positioned on a lens mounting surface of a support 
structure with strict accuracy free of inclinations in vertical and 
horizontal directions and exactly in predetermined positional relationship 
with other lens components to maintain an air spacing of a predetermined 
width therebetween. 
Therefore, as an expedient for positioning and fixing each lens component 
exactly in position on a lens mounting surface, it has been the 
conventional practice to resort to the so-called positioning projections 
which are provided in predetermined positions on a lens mounting surface 
in such a manner as to hold each lens component in position. After 
mounting the lens component in abutting engagement with the positioning 
projections, they are fixed in position by caulking the respective 
positioning projections. 
These positioning projections are relatively small in size because they 
have to be provided in receded positions away from the effective surface 
of the lens, namely, away from an area to be scanned by a laser beam. 
Therefore, it is extremely difficult to position the respective lens 
components by means of such projections. Particularly, the projections, to 
be caulked after positioning the lens components, are required to have a 
relatively small wall thickness despite a serious problem in that they are 
susceptible to deformation and might cause deviations of the lens mounting 
position when a lens component is pressed thereagainst for positioning 
purposes. There may also arise a problem in that the caulking operation 
for fixation of lens components might cause undesirable inclinations of 
the lens components. 
Another expedient which has been resorted to in the art is to provide 
stepped walls on a lens mounting surface by a prior machining operation, 
using stepped wall surfaces as reference surfaces in positioning the lens 
components. In this case, the lens components can be mounted in position 
simply by pressing them against the surfaces of stepped reference walls, 
and can be fixed in position by the use of an adhesive. However, the 
necessity for cutting out the reference walls on the lens support 
structure by a prior machining operation, coupled with the difficulty of 
forming high reference walls, makes the lens positioning and fixing job 
difficult and complicates the machining process of the lens support 
structures. 
In short, the prior art lens positioning and fixation means which relies on 
lens positioning mechanisms provided on a lens, support structure itself 
requires a complicated machining operation for the lens support structure, 
failing to provide an optimum construction from the standpoint of the lens 
positioning job. 
SUMMARY OF THE INVENTION 
The present invention contemplates solving the drawbacks or problems of the 
prior art as mentioned above, and has as its object the provision of a 
lens positioning means which permits positioning of a lens or a number of 
lenses on a lens mounting surface of a support structure with extremely 
high accuracy and in a facilitated manner. 
It is another object of the present invention to provide a lens positioning 
and fixation means which permits mounting of a lens or lenses accurately 
on a lens support structure without providing any lens positioning or 
fixing mechanism on the part of the lens support structure. 
In accordance with the present invention, there is provided, for achieving 
the above-stated objectives, a reference jig for positioning and fixing a 
lens or lenses in a predetermined position on a lens support structure, 
the reference jig comprising for positioning and fixedly bonding a plural 
number of lens components on a lens mounting surface of the support 
structure: a plate-like main body having a predetermined thickness and 
detachably fixable on the lens mounting surface of the support structure; 
registration members provided contiguously to the main body and engageable 
with reference walls of the lens support structure to hold the main body 
in registered position relative to the lens support structure; and notched 
positioning wall portions each formed in the main body and abuttingly 
engageable with at least two transversely opposite corner portions of a 
lens component to hold the same in a predetermined position on the lens 
support structure. 
In accordance with the present invention, there is also provided a method 
of positioning and fixing a plural number of lens components on a lens 
mounting surface of a support structure by the use of a reference jig 
having a plate-like main body of a predetermined thickness detachably 
fixable on the lens mounting surface of the support structure, 
registration members provided contiguously to the main body and engageable 
with reference walls of the lens support structure to hold the main body 
in registered position relative to the lens support structure, and notched 
positioning wall portions formed in the main body and abuttingly 
engageable with at least two transversely opposite corner portions of each 
lens component to hold the same in a predetermined position on the lens 
support structure, the method comprising: abuttingly engaging the 
registration members with the reference wall surfaces of the lens support 
structure to hold the main body in registered position thereon; applying 
an adhesive at least to lens mounting positions on the lens support 
structure or to the lens component; mounting and fixedly bonding the lens 
components in the respective predetermined positions on the lens mounting 
surface with the corner portions of each lens component in abutting 
engagement with the positioning walls of the main body of the reference 
jig; and removing the reference jig from the lens support structure after 
fixation of the lens component.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereafter, the invention is described more particularly by way of preferred 
embodiments of the invention with reference to the accompanying drawings. 
In the following embodiments, the invention is applied to an operation for 
mounting a couple of truncate lenses on a lens support structure to be 
used for a scanning optical system of a laser beam scanner. 
Referring first to FIG. 1, indicated at 1 is a platelike lens support 
structure with a predetermined thickness. In order to mount a couple of 
truncate lens components 2 and 3 as shown in FIG. 2, the lens support 
structure 1 is provided with lens mounting portions 4 and 5 on a lens 
mounting surface 1a on the front side of the support structure 1 as 
indicated by imaginary lines in FIG. 1. In addition to the lens mounting 
surface 1a which is of course a precision-machined surface with an 
extremely high degree of smoothness, the support structure 1 is provided 
with precision-machined reference wall surfaces including a reference wall 
surface 1b which is provided at least at one lateral side of the support 
structure 1 in a direction parallel with the axes of the lens components 2 
and 3, and a reference wall surface 1c which is provided at one end of the 
support structure 1 in a direction parallel with the lens components 2 and 
3. 
In the following description, those sides of the truncate lenses 2 and 3 
which are to be abutted against the lens support structure are referred to 
as the lower or bottom side, and the opposite sides of the lens components 
are referred to as the upper or top side, respectively. The inner sides of 
the lens components 2 and 3 which face each other are referred to as inner 
sides 2a and 3a, and the opposite outer sides of the lens components are 
referred to as outer sides 2d and 3d. The lateral sides between the inner 
and outer sides of the lens components 2 and 3 are referred to as lateral 
sides 2b and 2c and lateral sides 3b and 3c, respectively. Each of the 
truncate lenses 2 and 3 has a flat surface at least on the bottom side 
thereof. 
According to the invention, a reference jig 10 as shown in FIG. 3 is used 
for mounting the truncate lens components 2 and 3 on the lens support 
structure of the above-described construction. After positioning the 
truncate lenses 2 and 3 exactly and correctly in predetermined positions 
on the lens mounting surface 1a by the use of the reference jig 10, the 
respective lenses are fixed in position by an adhesive means. 
When mounting the lenses 2 and 3 by the use of the reference jig 10, 
firstly it is necessary to position and fix the reference jig 10 on the 
lens support structure 1 correctly in an extremely stable state. Besides, 
after mounting the lens components 2 and 3, the reference jig 10 has to be 
removed. Therefore, the reference jig 10 is provided with three 
registering projections 12a to 12c on the lower side of its main body 11 
of a predetermined thickness, namely, on the lower side of its main body 
11 to be abutted on the lens mounting surface 1a of the support structure 
1. The registering projection 12a is abuttingly engageable with the 
reference wall surface 1b, while the registering projections 12b and 12c 
are similarly abuttingly engageable with the reference wall surface 1c. 
Therefore, simply by placing the reference jig 10 on the lens support 
structure 1 with the registering projections 12a to 12c in abutting 
engagement with the reference wall surfaces 1b and 1c, the jig 10 can be 
easily held in a correctly registered position relative to the lens 
support structure 1. For fixing the reference jig 10 in the registered 
position on the lens support structure 1, it is advantageous to utilize 
mounting holes 6 which are bored in the lens support structure 1 
originally for the purpose of mounting the laser beam scanner on a bracket 
or other support body. To this end, the reference jig 10 is provided with 
screw holes 13 in alignment with the mounting holes 6, and screws 7 are 
threaded thereinto from the lower side of the lens support structure 1 to 
fix them to each other. 
The reference jig 10 is formed of a suitable thickness, preferably, of a 
thickness substantially the same as that of the truncate lens components 2 
and 3, and is provided with notched portions defining a first lens 
positioning portion 14 for one truncate lens 2 and a second lens 
positioning portion 15 for the other truncate lens 3. These first and 
second lens positioning portions 14 and 15 are arranged to hold the 
truncate lenses 2 and 3 in position by abutting engagement with two 
transversely opposite corner portions of the corresponding lens. Namely, 
the corner portions 20 and 21 formed by the inner side 2a and the lateral 
sides 2b and 2c of the lens component 2 are abutted against positioning 
walls 14a and 14b and positioning walls 14c and 14d, respectively. On the 
other hand, the corner portions 30 and 31 formed by the inner side 3a and 
the lateral sides 3b and 3c of the lens component 3 are abutted against 
positioning walls 15a and 15b and positioning walls 15c and 15d, 
respectively. Therefore, the positioning walls 14a to 14d as well as the 
positioning walls 15a to 15d are dimensioned with strict accuracy to hold 
the lens components 2 and 3 correctly in position. Similarly, the line 
which interconnects the positioning walls 14a and 14c and the line which 
interconnects the positioning walls 15a and 15c are high accuracy lines to 
define an air spacing of a predetermined width between the lenses 2 and 3. 
Besides, the positioning wall surfaces are buff-finished surfaces or 
provided with an anti-friction coating to prevent frictional abrasion of 
the lens components 2 and 3 which might otherwise be caused by sliding 
contact with the positioning wall surfaces when positioning them on the 
support structure. 
By the use of the reference jig 10 of the above-described construction, the 
lens components 2 and 3 are mounted and fixed in position on the lens 
support structure 1 in the manner as follows. 
Firstly, the reference jig 10 is set on the lens mounting surface 1a of the 
support structure 1. For this purpose, the reference jig 10 is placed on 
the lens support structure, abutting its registering projection 12a 
against the reference wall surface 1b of the lens support structure 1 and 
then the registering projections 12b and 12c against the reference wall 
surface 1c. Nextly, the screws 7 are inserted into the mounting holes 6 
from the lower side of the lens support structure 1, threading them into 
the screw holes 13 in the main body 11 of the reference jig 10 thereby 
firmly fastening the reference jig 10 to the lens support structure 1 in a 
correctly registered position relative to the latter. 
In this state, an adhesive is applied on the lens mount portions 4 and 5 
for fixation of the truncate lenses 2 and 3 on the lens support structure 
1. The adhesive may be applied over the entire areas of the lens mount 
portions 4 and 5 or may be deposited at a plural number of necessary spots 
on the lens mount portions 4 and 5. The formation of such adhesive spots 
contributes to simplification of the adhesive feed process. Instead of or 
in addition to the lens mount portions 4 and 5, the adhesive may be 
applied to the lower sides of the lens components 2 and 3 to be placed in 
abutting engagement with the lens mount portions 4 and 5, respectively. 
Nextly, the lens components 2 and 3 are mounted in the respective positions 
at the first and second notched lens positioning portions 14 and 15 of the 
reference jig 10. At this time, the corner portions 20 and 21 of the lens 
component 2 as well as the corner portions 30 and 31 of the lens component 
3 are fitted in position by engagement with the positioning walls 14a to 
14d of the lens positioning portion 14 or the positioning walls 15a to 15d 
of the lens positioning portion 15. As a result, the lens component 2 is 
fitted into the lens positioning portion 14 of the reference jig 10 as the 
inner and lateral sides 2a and 2b of the corner portion 20 of the lens 
component 2 and the inner and lateral sides 2a and 2c of the opposite 
corner portion 21 are guided in along the positioning walls 14a and 14b 
and the opposite positioning walls 14c and 14d, respectively. On the other 
hand, the lens component 3 is fitted into the lens positioning portion 15 
of the reference jig 10 as the inner and lateral sides 3a and 3b of the 
corner portion 30 of the lens component 3 and the inner and lateral sides 
3a and 3c of the opposite corner portion 31 are guided in along the 
positioning walls 15a and 15b and the positioning walls 15c and 15d, 
respectively. Consequently, the lens components 2 and 3 are positioned in 
the respective lens mount portions 4 and 5 as shown in FIG. 5. 
In this instance, the reference jig 10 is arranged to abut against the lens 
components 2 and 3 only at its positioning walls which engage the inner 
corner portions 20 and 21 of the lens 2 and the inner corner portions 30 
and 31 of the lens 30, leaving the outer sides 2d and 3d of the respective 
lenses open. Accordingly, the lens components 2 and 3 can be fitted into 
the lens positioning portions 14 and 15 in an extremely facilitated manner 
simply by urging the lenses into the respective positions from the open 
outer sides as indicated by arrows in FIG. 5. However, if simply placed in 
the lens positioning portions 14 and 15, the lens components 2 and 3 might 
be in a deviated state in the directions of arrows B in FIG. 6 or in a 
tilted state as indicated by arrows T in the same figure. Therefore, it is 
desirable to push in the lens components 2 and 3 with a finger in the 
direction of arrows P, preferably at an angle of about 45.degree., at a 
position in the vicinity of the ridge between the outer side 2d and the 
top side of the lens 2 and at a position in the vicinity of the ridge 
between the outer side 3d and top side of the lens 3, respectively. By so 
doing, the lens component 2 is correctly located in the predetermined 
position of the lens mount portion 4, with the lower side of the lens 2 in 
engagement with the lens mounting surface 1a of the lens support structure 
1, the inner side 2a in engagement with the positioning walls 14a and 14c, 
the lateral side 2b in engagement with the positioning wall 14b, and the 
opposite lateral side 2c in engagement with the positioning wall 14d. 
Similarly, the lens component 3 is located exactly in the predetermined 
position on the lens mount portion 5, with the lower side of the lens in 
engagement with the lens mounting surface 1a of the support structure 1, 
the inner side 3a in engagement with the positioning walls 15a and 15c, 
the lateral side 3b in engagement with the positioning wall 15b, and the 
opposite lateral side 3c in engagement with the positioning wall 15d. Even 
if a relatively large force were applied to the lenses 2 and 3 when 
pushing them as described above, it would not cause positional deviations 
of the reference jig 10 since the jig 10 is fixed in an extremely stable 
state. Instead, the pushing force contributes to spread the adhesive 
applied on the lens mount portions 4 and 5, smoothing out irregular 
portions of the applied adhesive layer. Even in a case where the adhesive 
is dropped in spots on part of the lens mount portions 4 and 5, it can be 
uniformly spread out by the pushing force to preclude minute inclinations 
of the lens components 2 and 3 which might be caused by irregularities in 
thickness of the applied adhesive layer. The reference jig 10 which is 
formed substantially in the same thickness as the lenses 2 and 3 ensures 
stable push-in operation. 
Consequently, the lens components 2 and 3 can be mounted correctly on the 
lens mount portions 4 and 4 in an extremely facilitated manner without 
requiring any meticulous skill, and they can be fixed in position free of 
inclinations in vertical and horizontal directions to maintain an air 
spacing of a predetermined width between the lens components 2 and 3 as 
indicated by arrow A in FIG. 4. 
The adhesive is allowed to set after mounting the lens components 2 and 3 
in the respective positions on the lens mount portions 4 and 5, and then 
the reference jig 10 is removed from the lens support structure 1. Upon 
removal of the jig 10, there is obtained an assembly which has the lens 
components 2 and 3 mounted and fixed exactly in predetermined positions on 
the lens mount portions 4 and 5 on the lens mounting surface 1a of the 
support structure 1 as shown particularly in FIG. 7. The removed reference 
jig 10 can be used again for mounting similar lens components 2 and 3 on 
another lens support structure 1. Thus, a single reference jig 10 can be 
used repeatedly for making similar lens assemblies. 
Although a couple of lens components are mounted on a lens support 
structure in the foregoing embodiment, there is no particular restriction 
with regard to the number of lens components to be mounted on the support 
structure. In a case where the lens mounting surface contains stepped 
surfaces, the abutting surface of the reference jig is preferred to have 
complimentarily stepped surfaces. Further, the lens components to be 
mounted on a lens support structure are not restricted to the truncate 
type and may be collimator lenses or may be of other types including 
lenses with a flatly cut bottom surface, namely, may be of any other type 
as long as they have a flat surface on the bottom side to be placed on the 
lens mounting surface of the support structure.