Datum beam projecting apparatus for use with surveying equipment

A datum beam projecting apparatus for use with surveying equipment projects light rays emitted from a light source as the datum beam through a projecting lens system, wherein the apparatus uses a plane-parallel glass serving to compensate for tilt of the datum beam, thereby maintaining a direction of the projected datum beam constant with respect to a tilt of the apparatus. The plane-parallel glass is tiltably located in an optical path defined between the light source and the projecting lens system so that the following relationship may be satisfied: EQU tan .beta.=K tan .alpha. where .alpha. represents a tilt of the apparatus, .beta. represents a tilt of the plane-parallel glass and K is a constant. With the apparatus, a tilt of the data beam can be effectively compensated merely by tilting the plane-parallel glass by the angle .beta. corresponding to a predetermined times the tilt .alpha. of the apparatus, so that the complicated arrangement comprising concave lenses, prisms etc. usually required for compensation can be eliminated. Thereby, not only can the structure be simplified but also reliable precision can be obtained at a reasonable cost.

BACKGROUND OF THE INVENTION 
The present invention relates to a datum beam projecting apparatus for use 
with surveying equipment such as an optical leveling type to provide a 
datum level in construction surveying or the like. 
Although the datum beam projecting apparatus for surveying equipment should 
ideally be installed on a horizontal trestle, this apparatus has usually 
been installed, in practice, inevitably with a slight tilt and it has been 
required to compensate for such a tilt of the apparatus to achieve an 
effective projection of the datum beam. As an example of the well known 
apparatuses provided with means to maintain the direction in which the 
datum beam is projected constant by compensating for the tilt of the 
apparatus, Japanese Disclosure Gazette No. 1985-200117 discloses a datum 
beam projecting apparatus used with surveying equipment to project light 
rays emitted from a light source as the datum beam through a projecting 
lens system. This system includes a suspended reflector member of a 
complicated structure, for example, an erect prism or a Porroprism. 
Another example is disclosed in Japanese Disclosure Gazette (of Utility 
Model Application) No. 1986-105811, which includes a complicated structure 
comprising a pair of two-face reflectors individually suspended so that 
respective optical paths thereof extend perpendicularly to each other. 
Further, another example is disclosed in Japanese Disclosure Gazette No. 
1988-179208, which includes a projecting lens system comprising a convex 
lens fixed to the apparatus and a concave lens suspended in an intricated 
distance-relationship with said convex lens. However, all of such well 
known apparatuses are inconveniently intricate in their structures which, 
in turn, increase factors not only making the accuracy unreliable but also 
making the cost of manufacturing unacceptably high. 
SUMMARY OF INVENTION 
In view of the problems encountered by the prior art, the present invention 
basically resides in a datum beam projecting apparatus for use with 
surveying equipment to project light rays emitted from a light source as 
the datum beam through a projecting lens system. The apparatus uses a 
plane-parallel glass to compensate for tilt of the datum beam, thereby 
maintaining a direction of the projected datum beam constant with respect 
to a tilt of said apparatus and said plane-parallel glass is tiltably 
located in an optical path defined between the light source and the 
projecting lens system so that the following equation may be satisfied: 
EQU tan .beta.=K tan .alpha. 
where .alpha. represents a tilt of the apparatus, .beta. represents a tilt 
of the plane-parallel glass and K is a constant. 
Preferably, the plane-parallel glass is suspended with the tilt .beta. with 
respect to the tilt .alpha. of said apparatus. 
It is preferable to locate the plane-parallel glass in the optical path 
defined between the light source and the projecting lens system. 
It is also within a scope of the invention to locate the plane-parallel 
glass in the optical path including the projecting lens system. 
The apparatus can be arranged so that the datum beam is horizontally 
projected. 
The apparatus can be arranged so that the datum beam is projected 
vertically upward. 
The apparatus can be also arranged so that the datum beam is projected 
vertically downward. 
Preferably, a rotatable two-face reflector is provided in the optical path 
of the datum beam. 
Preferably, the two-face reflector is rotatably driven by an electromotor. 
Preferably, said rotatable two-face reflector is provided in the form of a 
two-face reflector unit adapted to be detachably mounted on the apparatus. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

EMBODIMENTS 
Before the present invention is described with respect to its detailed 
construction, operation thereof will be explained with reference to FIG. 
1. 
Referring to FIG. 1 which is a principle diagram illustrating an embodiment 
of the apparatus constructed in accordance with the present invention so 
as to project the datum beam in the horizontal direction, reference 
numeral 1 designates a light source, reference numeral 2 designates a 
projecting lens system of a focal distance f, and reference numeral 3 
designates a plane-parallel glass suspended at points C, D by suspension 
wire 4 extending from fixed points A, B. With the apparatus tilting by an 
angle .alpha., an optical axis H'--H' connecting the light source 1 to the 
projecting lens system 2 tilts by the angle .alpha. with respect to a 
horizontal datum line H--H while the plane-parallel glass 3 tilts by an 
angle .beta. with respect to the apparatus, and a virtual image 1' of the 
light source 1 is translated by a distance .delta. just onto the 
horizontal datum line H--H. Reference numeral 2' designates an optical 
center of the projecting lens system 2 and a letter d designates a 
thickness of the plane-parallel glass 3. Though the projecting lens system 
2 is shown and described here as comprising a single convex lens, it is 
obviously possible to combine a plurality of lenses to constitute the 
projecting lens system 2 and, in such a case also, even if there is any 
additional lens between the plane-parallel glass 3 and the light source 1, 
the virtual image 1' of the light source 1 will be translated by the 
distance .delta. under the effect of the plane-parallel glass 3, because, 
if said additional lens is a condensing lens, its condensing point will 
become a new light source 1 for said projecting lens system 2 and, if said 
additional lens is a diffusing lens, its diffusing datum point will become 
a new light source 1 for said projecting lens system 2. 
Referring to FIG. 1, said distance .delta. between the light source 1 and 
its virtual image 1' is expressed, on the basis of a geometrical 
relationship, by a following equation (1): 
EQU .delta.=f tan .alpha. (1) 
A translation .delta.' of the optical path due to the tilt .beta. of the 
plane-parallel glass 3 is expressed, on the basis of an optical 
relationship, by 
##EQU1## 
where n represents a refractive index of the plane-parallel glass 3. 
If the direction of the projected beam is kept on the horizontal datum line 
H--H independently of the tilt .alpha. of the apparatus, 
EQU .delta.'=.delta. (3) 
will be established. 
By substituting the equations (1) and (2) for the equation (3), a following 
equation (4) is derived: 
##EQU2## 
Here, n, f and d represent constants, respectively, so the equation (4) can 
be transformed into: 
##EQU3## 
Substitution of the equation (5) for the equation (4) gives: 
EQU tan .beta.=K tan .alpha. (6) 
Thus, by arrangement that the plane-parallel glass 3 tilts by the angle 
.beta. corresponding to K times the tilt .alpha. of the apparatus, the 
datum beam L can be compensated so as to maintain the direction of 
projected datum beam always in coincidence with the datum line. 
The present invention will be described in detail, by way of example, with 
reference to the accompanying drawing. 
Referring to FIG. 1 which is a principle diagram illustrating the 
embodiment of the apparatus constructed in accordance with the present 
invention so as to project the datum beam in a horizontal direction, as 
has already been described above in connection with the operation, 
reference numeral 1 designates a light source, reference numeral 2 
designates a projecting lens system of a focal distance f, and reference 
numeral 3 designates a plane-parallel glass suspended at points C, D by 
suspension wire 4 extending from fixed points A, B. With the apparatus 
tilting by an angle .alpha., an optical axis H'--H' connecting the light 
source 1 to the projecting lens system 2 tilts by the angle .alpha. with 
respect to a horizontal datum line H--H while the plane-parallel glass 3 
tilts by an angle .beta. with respect to the apparatus, and a virtual 
image 1' of the light source 1 is translated by a distance .delta. just 
onto the horizontal datum line H--H. Reference numeral 2' designates an 
optical center of the projecting lens system 2 and a letter d designates a 
thickness of the plane parallel glass 3. 
Though the projecting lens system 2 is shown and described here as 
comprising a single convex lens, it is obviously possible to combine a 
plurality of lenses to constitute the projecting lens system 2 and, in 
such a case also, even if there is any additional lens between the 
plane-parallel glass 3 and the light source 1, the virtual image 1' of the 
light source 1 will be translated by the distance .delta. under the effect 
of the plane-parallel glass 3, because, if said additional lens is a 
condensing lens, its condensing point will become a new light source 1 for 
said projecting lens system 2 and, if said additional lens is a diffusing 
lens, its diffusing datum point will become a new light source 1 for said 
projecting lens system 2. 
Between the tilt .beta. of the plane-parallel glass 3 and said tilt .alpha. 
of the apparatus, there is established a relationship as expressed by: 
EQU tan .beta.=K tan .alpha. (6) 
and 
##EQU4## 
where n represents a refractive index of the plane-parallel glass 3. FIG. 
2 is a principle diagram illustrating the embodiment of the apparatus 
constructed in accordance with this invention so as to project the datum 
beam L in a vertically upward direction, in which reference numeral 1 
designates a light source, reference numeral 2 designates a projecting 
lens system of a focal distance f, and reference numeral 3 designates a 
plane-parallel glass suspended at points C, D by suspension wire 4 
extending from fixed points A, B. With the apparatus tilting by an angle 
.alpha., an optical axis V'--V' connecting the light source 1 to the 
projecting lens system 2 tilts by the angle .alpha. with respect to a 
vertical datum line V--V while the plane-parallel glass 3 tilts by an 
angle .beta. with respect to the apparatus and, just as in the case of 
FIG. 1, a tilt of the vertically projected datum beam L can be effectively 
compensated merely by tilting the plane-parallel glass 3 by the angle 
.beta. corresponding to a predetermined times the tilt .alpha. of the 
apparatus. 
FIG. 3 is a principle diagram illustrating the embodiment of the apparatus 
constructed in accordance with this invention so as to project the datum 
beam L in a vertically downward direction, in which reference numeral 1 
designates a light source, reference numeral 2 designates a projecting 
lens system of a focal distance f, and reference numeral 3 designates a 
plane-parallel glass suspended at points C, D by suspension wire 4 
extending from fixed points A, B. With the apparatus tilting by an angle 
.alpha., the optical axis V'--V' connecting the light source 1 to the 
projecting lens system 2 tilts by the angle .alpha. with respect to the 
vertical datum line V--V while the plane-parallel glass 3 tilts by the 
angle .beta. with respect to the apparatus and, just as in the case of 
FIG. 1, a tilt of the vertically downward projected datum beam L can be 
effectively compensated merely by tilting the plane-parallel glass 3 by 
the angle .beta. corresponding to a predetermined times the tilt .alpha. 
of the apparatus. 
FIGS. 4 and 5 respectively illustrate suspending means for the 
plane-parallel glass 3, FIG. 4 illustrating the case of three-wire 
suspension and FIG. 5 illustrating the case of four-wire suspension. In 
both cases, the plane-parallel glass can be tilted both in the directions 
of X and Y. 
It should be understood that, in the embodiments of FIGS. 4 and 5, the 
suspension wire 4 may be replaced by the tape-like suspending means 
limiting the direction in which the plane-parallel glass 3 can be tilted 
to only one direction X or Y, as described in Japanese Disclosure Gazette 
(of Utility Model Application) No. 1986-105811. 
FIGS. 6 and 7 illustrate an embodiment of the apparatus constructed 
according to this invention comprising a two-face reflector 11 disposed in 
the optical path of the datum beam L and adapted to be rotated by an 
electromotor 13. This two-face reflector 11 is provided in the form of a 
two-face reflector unit 10 detachably mounted on a mounting frame 6 formed 
integrally with the apparatus 5. 
Referring to FIGS. 6 and 7, reference numeral 5' designates a screw by 
which the apparatus 5 is mounted on a given horizontal trestle. In the 
apparatus 5 of FIG. 6, as in the arrangement of FIG. 1 adapted to project 
the datum beam in the horizontal direction, the optical path connecting 
the light source 1, the projecting lens system 2 and plane-parallel glass 
3 in this order horizontally extends while, in the apparatus of FIG. 7, as 
in the arrangement of FIG. 2 adapted to project the datum beam vertically 
upward, the optical path connecting the light source 1, the projecting 
lens system 2 and the plane-parallel glass 3 in this order extends 
vertically upward. Reference numeral 3' designates a suspension frame for 
the plane-parallel glass 3. The two-face reflector unit 10 comprises an 
electromotor supporting frame 14 and cylindrical aperture plates 15 and 
contains therein the electromotor 13, the two-face reflector 11 and a 
supporting frame 12 for this refector. Said aperture plates 15 are detably 
mounted on the mounting frame 6 integral with the apparatus 5. The 
electromotor supporting frame 14 supports the electromotor 13 and the 
supporting frame 12 rotatably driven by the electromotor 13 integrally 
holds the two-face reflector 11 so that the two-face reflector 11 relects 
the datum beam L coming along the optical path defined by said light 
source 1, said projecting lens system 2 and the plane-parallel glass 3 in 
the direction perpendicular to said optical path and projects the beam 
through the aperture plates 15. Accordingly, the datum beam L reflected by 
the rotatable two-face reflector 11 is projected in a vertical plane 
defined by rotation of the vertical datum line V in the apparatus of FIG. 
6 while said datum beam L is projected in a horizontal plane defined by 
rotation of the horizontal datum line H in the apparatus of FIG. 7. 
The light source 1 which can be used in the apparatus of this invention is 
generally classified into two types, i.e., the diffusive ray type 
comprising a laser diode, light emitting diode etc. as used in the 
embodiments of FIGS. 1 through 7 for projection of the divergent rays L1, 
as seen in FIG. 8 (a), and the parallel ray type comprising, for example, 
HeNe laser adapted to project the parallel rays L2 as seen in FIG. 8 (b). 
When the light source 1 of said parallel ray type is employed, the parallel 
rays coming from the light source 1 are once condensed by the condensing 
lens 7 and then projected through the projecting lens system 2 as shown by 
FIG. 9 or the parallel rays coming from the light source 1 are once 
diffused by the diffusing lens 8 and then projected through the projecting 
lens system 2 as shown by FIG. 10. Referring to FIG. 9, reference numeral 
01 designates a condensing point of the condensing lens 7. In FIG. 9, the 
focus of the projecting lens system 2 is arranged to be in coincidence 
with said condensing point 01 and the plane-parallel glass 3 is located 
between the condensing point 01 and the projecting lens system 2. 
Referring to FIG. 10, reference numeral 02 designates a diffusion datum 
point. In FIG. 10, the focus of the projecting lens system 2 is arranged 
to be in coincidence with said diffusion datum point 02 and the 
plane-parallel glass 3 is located between the diffusing lens 8 and the 
projecting lens system 2. 
As will be apparent from the foregoing description, the apparatus of this 
invention enables a tilt of the datum beam to be effectively compensated 
merely by tilting the plane-parallel glass by the angle .beta. 
corresponding to a predetermined times the tilt .alpha. of the apparatus, 
so that the complicated arrangement comprising concave lenses, prisms etc. 
usually required for compensation can be eliminated and thereby not only 
can the structure be simplified but also the apparatus of a reliable 
precision can be obtained at a reasonable cost. Another advantage of this 
invention lies in that the datum beam can be compensated merely by 
suspension of the plane-parallel glass. Additionally, the direction of the 
projected datum beam can be set up in the horizontal, vertically upward or 
vertically downward direction according to the same principle and with the 
same construction, so the apparatus of this invention can be used, without 
any modification, with existing surveying equipment of various types 
intending to project the datum beam in various directions. Moreover, 
merely by incorporating the rotatable two-face reflector, there can be 
provided the apparatus adapted to project the datum beam in the horizontal 
or vertical plane. Finally, the two-face reflector unit rotatably driven 
by the electromotor may be detachably mounted on the apparatus to provide 
the appratus adapted to project the datum beam in the horizontal or 
vertical plane. The invention being thus described, it will be obvious 
that the same may be varied in many ways. Such variations are not to be 
regarded as a departure from the spirit and scope of the invention, and 
all such modifications as would be obvious to one skilled in the art are 
intended to be included within the scope of the following claims.