Light bead generating apparatus

A light bead generating apparatus has a point light source (11) and a variable optical system (12, 13) of variable focal length, by means of which the point light source (11) is imaged via a light deflecting apparatus (24) in an image plane (14). The variable optical system is formed by two circular cylindrical mirrors (12', 13') which are crossed relative to one another, which have variable focal lengths in the direction of their circular cylinder axes (17', 18') and which are adjustable. They are illuminated by the image forming light beam (19, 19') in the direction of the optical axes (15).

FIELD OF THE INVENTION 
The invention relates to a light bead generating apparatus, having a point 
light source and a variable optical system of variable focal length by 
means of which the point light source is imaged, preferably via a light 
deflecting device such as a mirror wheel, at an image surface with a 
magnification scale predetermined by the variable optical system. 
DESCRIPTION OF PRIOR ART 
Such light bead generating apparatuses are generally used in scanning 
apparatuses where a light beam, in particular a laser beam, is deflected 
onto a surface to be scanned, for example by means of a mirror wheel, and 
there generates a light bead, in particular a circular light bead, which 
executes a periodic scanning movement. The light deflecting apparatus can 
thereby preferably generate a V-shaped scanning movement of the light beam 
(DE patent 36 00 578), preferably via an F-.theta.-objective, or can 
generate a scanning beam (DE-PS 23 40 688) which is displaced parallel to 
itself by means of a concave mirror. 
With scanning problems, where the surfaces to be scanned, for example code 
markings applied to articles, can be arranged at very different distances 
from the light bead generating apparatus, the light bead which is set to 
be sharp on the surface of the image surface has a greatly differing size, 
depending on the spacing of the image surface from the light deflecting 
apparatus. However, since it is important when scanning codes consisting, 
for example, of bars, that the size of the light bead has a predetermined 
relationship to the width of the code bars, one has already formed an 
image of the point light source by means of a variable optical system, 
i.e. an optical system of variable focal length, on the image surface 
(U.S. Pat. No. 4,920,255). This makes it possible to always generate the 
same size of light bead on the image surface, independently of the 
distance between the light deflecting apparatus and the image surface. 
Known variable objectives consist of a plurality of lenses which are 
arranged to be displaceable relative to one another in the direction of 
the optical axis in order to be able to change the focal length. Such 
variable objectives are, however, costly, and above all take up a lot of 
space in the direction of the optical axis, because the space for the 
axial displacement of the lenses must be available. 
OBJECT OF THE INVENTION 
The object of the present invention is to provide a light bead generating 
apparatus of the initially named kind with which light beads of different 
size and preferably also of different shape can be generated at the image 
surface without using a plurality of lenses which are displaceable 
relative to one another in the direction of the optical axis. 
SUMMARY OF THE INVENTION 
In order to satisfy this object there is provided an apparatus of the 
initially named kind which is characterized in that the variable optical 
system is formed by two crossed cylindrical optical systems with variable 
focal length in the direction of their cylindrical axes which are 
displaceably connected in the direction of their cylinder axes and are 
sequentially illuminated by image forming light beams at points where the 
cylinder axes of the two cylindrical optical systems stand optically 
perpendicular to one another. 
The concept underlying the invention is thus to be seen in the fact that 
two cylindrical optical systems, which are crossed in the area of the beam 
path are used in place of a spherical or parabolic optical system. The 
change of the focal length is effected in that each cylindrical optical 
system is equipped with different focal lengths along its cylinder axis so 
that different focal lengths can be realized without problem by a shift of 
the two cylindrical optical systems in the direction of their cylinder 
axes which are crossed in the region of the light passage, i.e. 
perpendicular to the optical axis. It has proved to be particularly 
advantageous that the two cylindrical optical systems can indeed have the 
same focal length at the points where they are struck by the image forming 
light beam, so that on the whole they act in the same way as a parabolic 
or spherical optical system, but can also have different focal lengths, so 
that elliptical light beads with different eccentricities can also be 
generated in place of a circular light bead. When arranging the two 
cylindrical optical systems relative to one another, attention should 
merely be paid to the fact that the cylinder axes stand at least 
substantially perpendicular to one another at the points where they are 
illuminated by the image forming light beam, so that the two cylindrical 
optical regions at these points jointly have the effect of a parabolic or 
spherical optical system. 
The cylindrical optical systems can be cylindrical lenses or cylindrical 
mirrors. Cylindrical mirrors are, however, preferred for manufacturing 
reasons. 
Furthermore, the cylindrical optical systems can be straight or circular. 
The circular shape is preferred for space reasons and also to achieve 
simple adjustability. In this respect, very many different cylindrical 
lens focal lengths can be accommodated in compact manner on a circular 
disc in accordance with claim 6. By arranging the disc on a rotary shaft 
the setting of different focal lengths can, moreover, take place without 
problem. 
At each point of the cylindrical optical systems the optical axes can be 
arranged along the cylinder axis relative to the axis of rotation. 
A particularly preferred embodiment facilitates the manufacture of the 
circular, cylindrical mirror disc by an injection molding process. The 
mold half of the injection mold which forms the cylindrical mirror can 
thus be withdrawn in the direction of the axis of rotation in simple 
manner from the cylindrical mirror after it has been injection molded. 
With the apparatus of the invention it is ultimately possible to effect any 
desired changes of focal length along the cylindrical axis. 
If a continuous increase or decrease of the focal length takes place around 
the total circumference of the circular disc, then a step-like change of 
the focal length results at one point of the circumference. 
Manufacture is made easier, while the optical accuracy required for the 
generation of a sharp light bead is ensured. 
Another embodiment is advantageous for realizing space saving folded beam 
paths, in particular when using cylindrical mirrors.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In accordance with FIG. 1 a narrow, parallel image forming light beam 19 of 
circular cross sections starts from a point light source 11 symbolized as 
a gap with an incandescent lamp 26 arranged behind it, with the image 
forming light beam having a diameter of 0.5 to 1 mm and striking a 
cylindrical lens 12 perpendicular to its cylinder axis 17 and also 
parallel to its optical axis 15 which stands perpendicular to the cylinder 
axis 17. 
At a small distance behind the first cylindrical lens 12 there is located a 
second cylindrical lens 13 whose cylinder axis 18 stands at a right angle 
relative to the cylinder axis 17 of the first cylindrical lens 12 and 
which is likewise so arranged with its optical axis that the image forming 
light beam 19' which emerges from the cylindrical lens 12 strikes onto the 
surface of the cylindrical lens 13 parallel to the optical axis 15. At a 
distance behind the second cylindrical lens 13 there is provided an image 
surface 14 on which the two crossed cylindrical lenses 12, 13 jointly 
generate a light bead 23 which is a sharp image of the point light source 
11. 
In accordance with the invention the focal length of the cylindrical lenses 
12, 13 changes continuously along the cylinder axes 17, 18, which is 
illustrated by a curvature of the cylindrical lens surfaces, which reduces 
from one end to the other. Moreover, the two cylindrical lenses 12, 13 are 
displaceable in the direction of the double arrows 27, 28, i.e. in the 
direction of the cylindrical lens axes 17 and 18 respectively in such a 
way that points of different focal length can be selectively shifted to 
the position of the image forming light beam 19, 19'. 
The manner of operation of the described light bead generating apparatus is 
as follows: 
Through a suitable shift of the cylindrical lenses 12, 13 in the direction 
of the double arrows 27, 28, a desired focal length of the cylindrical 
lenses 12, 13 can in each case be selected for the image forming light 
beam 19, 19' in such a way that either circular light beads 23 of 
different sizes can be realized in accordance with FIG. 2a or elliptical 
light beads 23', 23" of different sizes can be realized in accordance with 
FIG. 2b. In order to obtain circular light beads 23 of different sizes in 
accordance with FIG. 2a, the focal lengths of the cylindrical lenses 12, 
13 must have the same focal length at the points at which they are 
traversed by the image forming light beams 19, 19'. The elliptical light 
beads 23', 23", having different eccentricities in accordance with FIG. 
2b, can be obtained if the image forming light beams 19, 19' traverse 
points of the two cylindrical lenses 12, 13 having different focal lengths 
to a greater or lesser degree. 
In order to obtain a trouble-free sharp image of the light beads 23, 23', 
23" on the image surface 14, the overall arrangement consisting of the 
cylindrical lenses 12, 13 of the point light source 11 can be displaceably 
mounted on a suitable holder in the direction of the double arrow 29, i.e. 
of the optical axis 15. However, the linear shift of the cylindrical 
lenses 12, 13 in the direction of the double arrows 27, 28 must remain 
possible. 
In the preferred embodiments of FIGS. 3 and 4 a laser diode 11 generates 
the image forming light beam 19 via a beam broadening optical system 22, 
which strikes the marginal region of a circular, cylindrical mirror disc 
21 at an angle of ca. 20.degree., the disc being rotatable about an axis 
of rotation 20 standing perpendicular to the circular plane. In the edge 
region of the circular disc 21, which is illuminated by the image forming 
light beam 19, there is located a circular cylindrical mirror 12 arranged 
concentrically to the axis of rotation 20, with a circular cylinder axis 
17'. 
In accordance with FIG. 5 the radius of curvature of the cylindrical mirror 
12' changes continuously in the direction of the circumference and indeed 
in the direction of the arrow in the reducing sense, so that at one point 
16 of the periphery a jump in curvature, i.e. a step change, takes place. 
In this manner the focal length of the cylindrical mirror 12' increases 
continuously in the circumferential direction in the direction of the 
arrow. The radii of curvature can, for example, change continuously from 
300 mm to 1200 mm. 
Thus, at each point of the circumference there is a cylindrical mirror 
region of different focal length, with the optical axis 15 of each of 
these regions extending parallel to the axis of rotation 20. 
In accordance with FIGS. 3 and 4 the image forming light beam 19 is 
reflected at a circumferential point of the cylindrical mirror 12' and 
reaches the marginal region of a further, similar circular, cylindrical 
mirror disc 21, as an image forming light beam 19' which has already been 
influenced by the cylindrical mirror 12', with the further similar 
circular, cylindrical mirror disc 21 likewise being rotatable about an 
axis of rotation 20 parallel to the optical axes 15 and being arranged 
parallel to the first cylindrical mirror 12'. The circular cylindrical 
mirror axis 18' again extends concentrically to the axis of rotation 20 of 
the cylindrical lens 13'. 
It is important that at the point of incidence of the image forming light 
beam 19' the cylindrical axis 18' of the cylindrical mirror 13' stands 
normal to the optical axis 17' of the cylindrical mirror 12' at the point 
of incidence of the image forming light beam 19, i.e. is crossed relative 
to it, so that the two illuminated cylindrical mirror regions jointly have 
the action of a spherical lens. As one can recognize from FIGS. 3 and 4, 
the two cylindrical mirrors 12', 13' are thus respectively illuminated by 
the image forming light beams 19 and 19' at two points displaced by 
90.degree. relative to one another. 
The image forming light beam 19' is reflected as an image forming light 
beam 19" from the cylindrical mirror 13' to a mirror wheel 24, the axis of 
rotation 30 of which stands perpendicular to the plane defined by the 
image forming light beams 19, 19', 19". The light beam 19"' reflected by 
the mirror wheel 24 executes a V-shaped scanning movement as a result of 
the rotation of the mirror wheel 24 in the direction of the arrow and 
generates the desired light bead 23 on a concavely arched image surface 
14. By suitable rotation of the two cylindrical mirrors 12', 13' about the 
axes of rotation 20, 20' it is possible to realize different focal lengths 
of the cylindrical mirrors 12', 13' and thus to achieve different sizes 
and shapes of the light bead 23 in the sense of FIGS. 2a and 2b. 
Whereas, in accordance with the illustration in continuous lines in FIGS. 3 
and 4, the circular, cylindrical mirror discs 21 of FIG. 5 are so formed 
that the channel-like cylindrical mirror 12' or 13' is located on an end 
phase of the circular disc, in such a way that the optical axis 15 at each 
point of the circumference extends parallel to the axis of rotation 20, or 
perpendicular to the relevant end face of the circular disc 21, it is 
possible, in accordance with the broken line illustrations in FIGS. 3 and 
4 or in accordance with FIG. 6, to design the circular, cylindrical mirror 
disc 21' also in such a way that the cylindrical mirrors 12', 13' are 
located on the outer circumference of the circular, cylindrical mirror 
discs 21. In this case the optical axes 15 at each circumferential 
position represent extensions of the radii of the circular disc 21' at 
this point. The cylindrical mirror axes 17' and 18' respectively are again 
circles concentric to the axis of rotation 20', which are, however, 
located somewhat radially outside of the outer circumference of the 
circular, cylindrical mirror disc 21'. 
When arranged in the beam path of FIGS. 3 and 4, the rotational axes 20' of 
the circular, cylindrical mirror disc 21' must stand perpendicular to the 
axis of rotation 20 of the embodiment shown in solid lines. In other 
respects, the condition also applies here that the points on the 
circumference of the circular disc 21' which are struck by the image 
forming light beams 19, 19' are displaced relative to one another by 
90.degree. respectively. 
The cylindrical mirrors 12', 13' can, however, also be so arranged on the 
circumference of a circular, cylindrical mirror disc 21" in the manner 
which can be seen from FIG. 7. In this case, the optical axes 15 at each 
circumferential position stand, for example, at an angle .alpha. of 
45.degree. relative to the axis of rotation 20". Any other angle .alpha. 
(see also FIGS. 3 and 4) between 0.degree. and 90.degree. is also 
conceivable. 
The embodiment of FIG. 7 has the advantage that when manufacturing the 
circular, cylindrical mirror disc 21" in an injection mold, the mold half 
forming the cylindrical mirror 12' or 13' can be lifted upwardly without 
problem away from the circular disc 21" in the direction of the axis of 
rotation 20". It is accordingly expedient to design the circular, 
cylindrical mirror disc 21" in such a way that no undercuts are present 
relative to the axis of rotation 20, so that the circular disc 21" can be 
manufactured in a single injection molding process without burrs. 
In the preferred embodiment of the circular light bead generating apparatus 
of the invention with circular, cylindrical mirror discs 21, 21', 21", the 
decisive advantage lies in the fact that the different focal length 
settings of the two cylindrical lenses 12', 13' can not only be realized 
independently of one another, but also by a simple rotational movement 
about the axes 20, 20', 20". 
In order to make the light bead sharp, the arrangement consisting of the 
laser diode 11 and the beam widening optical system 22 can be displaceably 
arranged in the direction of the double arrow 29' in accordance with FIGS. 
3 and 4.