Automatic control system for construction machinery

An automatic control system comprises a construction machine provided on a construction site and equipped with a ground leveling implement and a target; a survey unit for projecting a beam of tracking light toward the target and receiving reflected tracking light from the target to determine a coordinate position of the target; a storage unit for storing finished-plane height data corresponding to coordinate positions; a computation unit for determining a finished target height at the coordinate position of the target and for computing a deviation between the finished target height and a measured target height; and a transmitter for transmitting the deviation toward the construction site. The survey unit operates in a finished-height data drive mode in which the tracking light is moved vertically so that the height of the tracking light at the horizontal coordinate position is at the finished target height. The construction machine has a receiver for receiving the deviation and a height control unit for controlling a height of the ground leveling implement according to the received deviation data.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improvement in an automatic control 
system for construction machines which automatically perform leveling of 
ground and paving. The construction machines are used in the civil 
engineering and construction field and include, for example, motor 
graders, pavers, and bulldozers. 
2. Description of the Related At 
In the civil engineering and construction field, the ground leveling 
implements of a construction machine, such as a blade and a screed, are 
automatically controlled in performing ground leveling and paving. 
In the system for automatically controlling a ground leveling implement 
that is used in a construction machine, a ground leveling string 
corresponding to a finished cross section is stretched over the 
construction site in order to obtain an expected fished surface. The 
interval between the ground leveling string and the ground leveling 
implement is detected with a contact type cantilever or a non-contact type 
ultrasonic sensor. Based on the detection result, the ground leveling 
implement is controlled so as to follow the ground leveling string. 
However, the system for automatically controlling a ground leveling 
implement so that the implement follows a ground leveling string requires 
a great deal of labor to stretch a ground leveling string over a 
construction site. 
Hence, there has been proposed an automatic control system for construction 
machinery which is capable of automatically controlling a ground leveling 
implement and obtaining an expected finished surface without stretching a 
ground leveling string over a construction site. 
An example of the aforementioned automatic control system is shown in FIG. 
1. In the figure, reference numeral 1 denotes a bulldozer which is a 
construction machine for leveling a construction site, 2 a rotating laser 
unit installed in a construction site, 3 a blade which is a ground 
leveling implement, 4 a pole attached to the blade 3, and 5 a laser sensor 
fixed to the pole 4. 
The rotating laser unit 2 forms a reference plane Rs at a position of a 
predetermined height (h) away from a finished plane 6 by means of a 
generated laser beam. The blade 3 is controlled so that the laser light 
from the rotating laser unit 2 strikes against the vertical center Ho of 
the laser sensor 5 (center Ho in the height direction of the laser sensor 
5), by an oil pressure control unit 7 serving as ground leveling implement 
control means. In this way, the ground of a construction side is leveled 
to an expected finished plane 6. According to this automatic control 
system for construction machines, a ground leveling operation and a paving 
operation can be simply performed compared with an operation of stretching 
a ground leveling string over a construction site. 
However, in the case where the ground 6' and finished plane 6 of a 
construction site have a complicated configuration with undulations and 
inclination, the rotating laser unit 2 has to be reinstalled as shown in 
FIG. 2 in order to obtain the reference plane Rs. For this reason, in the 
case of the leveling and paving of complicated ground contours 
reinstalling the rotating laser unit 2 will be troublesome. 
Hence, another system for automatically controlling the construction 
machine 1 has been proposed. This system employs an automatic tracking 
type survey unit (also called a total tracking station), which is 
available as "AP-L1" manufactured by TOPCON. The automatic tracking type 
survey unit measures a distance to a target, a horizontal angle between a 
reference direction and a direction in which the target exists, and a 
vertical angle between a reference height and a direction in which the 
target exists, and tracks the target. 
FIG. 3 illustrates an example of the system for automatically controlling a 
construction machine by employing an automatic tracking type survey unit. 
In the figure, reference numeral 8 denotes an automatic tracking type 
survey unit, which is installed at the known coordinate point O of a 
construction block. The survey unit 8 is connected to a personal computer 
(PC) 9, which is in turn connected to a radio transmitter 10. A bulldozer 
1 is provided with a blade 3, a pole 4 attached to the blade 3, an oil 
pressure control unit 7, a prism 11 attached to the pole 4 as a target to 
be tracked, and a radio receiver 12. 
The PC 9 stores finished-height data that defines the desired elevation of 
the finished ground surface at each coordinate position. The height of the 
finished surface is usually expressed by an elevation or height relative 
to a known reference such as sea level. The survey unit 8 tracks the prism 
11 with a tracking light L and measures the distance from the known 
coordinate position O to the prism 11 and the horizontal angle between a 
reference direction and a direction in which the prism 11 exists. Based on 
the measured distance and horizontal angle, the survey unit 8 computes at 
least the horizontal coordinate position of the prism 11 (target) relative 
to the known coordinate O. The computed horizontal coordinate position 
data is transferred from the survey unit 8 to the PC 9. 
The PC 9 calls out finished-height data corresponding to the computed 
horizontal coordinate position. Then, the PC 9 transfers the 
finished-height data to the radio transmitter 10. The radio transmitter 10 
transmits the finished-height data to the radio receiver 12. The oil 
pressure control unit 7 controls the blade 3, based on the finished-height 
data received by the radio receiver 12. The blade 3 digs or cuts ground so 
that the ground has a designed fished height. 
The system for automatically controlling a construction machine with the 
automatic tracking type survey unit 8 has an advantage that a complicated 
finished ground surface can be created without increasing the number of 
steps, because the blade 3 is controlled based on the finished-height 
data. 
Incidentally, the conventional automatic total tracking station 8 is 
constituted so that it tracks a target in both a horizontal direction and 
a vertical direction. The automatic total tracking station 8 detects the 
target position of the target, such as prism 11, through a telescope and 
feeds back the offset quantity i.e., offset between the target position 
and the optical axis center of the barrel portion of the telescope to a 
horizontal-vertical drive servo motor. In this way, the automatic total 
tracking station 8 is controlled so that the optical axis center tracks 
the target. However, there is a limit to the response time, and in the 
case where the vibration cycle of the target is fast, the station 8 cannot 
follow it and a dead zone will occur. Also, in the conventional tracking 
control system, the height of the ground leveling implement 3 is 
controlled based on finished height data, and if the height of the ground 
leveling implement 3 changes, the tracking light follows this change. 
Because the tracking light follows the change, there are cases where the 
tracking station 8 will give rise to a hunting phenomenon. Therefore, when 
the construction machine 1 travels on a desert road surface, there is the 
possibility that the vertical vibration, will cause an error in the 
position detection. 
In addition, since the ground leveling implement 3 itself of the 
construction machine 1 has a specific response speed and is automatically 
controlled, control is repeated between the construction machine 1 and 
total tracking station 8. This repetitive control causes a degradation in 
finished-height precision. Generally, in the case of the construction 
machine 1 which performs leveling of ground and paving, vertical 
(height-direction) finishing precision is required. This requirement 
hinders the use of the automatic total tracking station 8. 
Another automatic control system has been proposed in U.S. patent 
application Ser. No. 08/658655 (filed on Jun. 5, 1996) now U.S. Pat. No. 
5,771,978. The automatic total tracking station 8 tracks a target only in 
a horizontal direction and does not track it in a vertical direction. In 
this automatic control system, the total tracking station 8 is provided 
with a fan laser having a horizontal rotation or spread, and the 
horizontal coordinate position of a target is detected by horizontal 
tracking. The finished height data at the detected horizontal coordinate 
position is read out of storage, and the tracking station projects the fan 
beam to the designed height (finished height) at the detected horizontal 
coordinate position. The construction machine 1 is provided with a laser 
sensor, and this sensor detects the fan beam. Based on the difference 
between the vertical (height-direction) center of the laser sensor and the 
vertical position at which the fan beam was radiated on the laser sensor, 
the ground leveling implement is controlled so that the fan beam radiates 
the center of the laser sensor. 
According to the aforementioned structure, one can obtain a finished height 
with a high degree of accuracy without being influenced by the vibration 
of the construction machine 1, because vertical tracking is based on 
finished height data, not the vertical position of a moving target. Also, 
vertical direction control of the ground leveling implement 3 of the 
construction machine 1 occurs only if the fan laser light is controlled so 
that it can be received at the vertical center of the laser sensor, and 
there is the advantage that control equal to or greater than the 
conventional control based on a rotating laser can be easily achieved. 
However, in the aforementioned control system, for controlling the ground 
leveling implement 3 of the construction machine 1, an additional fan 
laser light source must be provided and, therefore, there is a 
disadvantage that the survey unit 8 becomes complicated structurally. 
Furthermore, in order to give construction information, such as the 
inclination of the ground leveling implement 3, to the operator of the 
construction machine 1, additional communication means for communicating 
the construction information is required, as with the control system 
employed in the conventional automatic total tracking station. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an automatic control 
system for a construction machine which is cable of performing automatic 
construction of high precision height by improving the operation of the 
aforementioned conventional automatic total tracking station, without 
providing an additional light emitting source such as a fan laser light 
source in a survey unit. 
To achieve this end, there is provided an automatic control system 
comprising: a construction machine provided on a construction site and 
equipped with a ground leveling implement and a light reflecting target; a 
survey unit placed at a known point for radiating a beam at light toward a 
center of the target and receiving light reflected from the target to 
determine a coordinate position of the construction machine and a measured 
target height; storage means for storing finished-plane height data 
corresponding to coordinate positions; computation means for determining a 
finished target height (height of the target when the implement is at the 
finished height) and for computing a deviation between the finished target 
height and the measured target height; and transmission means for 
transmitting the deviation to the construction machine. In the automatic 
control system, the survey unit can operate in a finished-height data 
drive mode in which the tracking light is moved vertically so that the 
height of the tracking light at the horizontal coordinate position is at 
the finished target height, and the construction machine is provided with 
reception means for receiving the deviation and height control means for 
controlling a height of the ground leveling implement so that it becomes 
the finished-plane height, based on the deviation received by the 
reception means. 
The transmission means may modulate the tracking light to transmit the 
deviation data to the reception means. 
The transmission means and the reception means may be constituted by a 
radio communication unit. 
The survey unit may have an automatic vertical tracking mode in which the 
rotation means is controlled so that an optical axis center of a 
lens-barrel portion provided in the survey unit coincides with a vertical 
center of the target. When the deviation is outside a predetermined range, 
the survey unit is switched from the finished-height data drive mode to 
the automatic vertical tracking mode. 
Preferably, the target is provided integrally in the ground leveling 
implement, and the ground leveling implement and the target is controlled 
by the height control means. 
Preferably, when data on the coordinate position of the target is input 
from the survey unit to the computation means, the computation means 
controls a rotation means, in the survey unit to move the light beam to 
the desired height at the measured coordinate position. 
The deviation data may be employed as construction evaluation information. 
The survey unit includes means for measuring a distance from the installed 
position thereof to the target.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 4, there is shown a total tracking station according to 
an embodiment of the present invention. In the figure, reference numeral 
20 denotes a base portion and 21 a main body portion. The main body 
portion 21 is horizontally rotated (i.e., rotated in a horizontal plane) 
on a vertical axis G by horizontal rotation means 22. The main body 
portion 21 has a display portion 23 and a pair of support portions 24. The 
support portions 24 are connected together by a horizontal shaft 25. The 
horizontal shaft 25 is provided with a lens barrel portion 26, which is in 
turn vertically rotated (i.e., rotated in a vertical plane) on the 
horizontal shaft 25 by vertical rotation means 27. The quantity of 
horizontal rotation of the main body portion 21 and the quantity of 
vertical rotation of the lens barrel portion 26 are detected by a rotary 
encoder (not shown). 
The lens barrel portion 26 includes a tracking and measuring unit portion 
30, as shown in FIG. 5. The tracking and measuring unit portion 30 
comprises a horizontal tracking-light generating portion 28 and a light 
wave distance meter (EDM) portion 29 which measures a distance to a target 
(prism). 
The tracking and measuring unit portion 30 has an objective lens 32 which 
is shared by a tracking operation and a distance measuring operation. The 
EDM portion 29 is constituted by a first light emitting element 29a, a 
second light emitting element 29b, and a split mirror 29c. The distance 
measuring light P1, emitted from the first light emitting element 29a and 
modulated with a specific frequency, is reflected by the reflecting 
surface 29d of the split mirror 29c and the reflecting surface 33a of A 
dichroic mirror 33. The reflected light P1 is passed through the lower 
half of the objective lens 32 and is guided to a prism 34 (see FIG. 6) 
which is a target. The modulated light, reflected by the prism 34, is 
condensed by the upper half of the objective lens 32 and is reflected by 
the reflecting surface 38a of the dichroic mirror 33. The light reflected 
by the dichroic mirror 33 is reflected by the reflecting surface 29e of 
the split prism 29c and is guided to the second light emitting element 
29b. 
The EDM portion 29 is equipped with a processing circuit (not shown). The 
processing circuit measures the phase difference between an emitted-light 
signal modulated with a specific frequency and a received-light signal, 
and measures the distance to the prism 34, from the measured phase 
difference. The dichroic mirror 33 is equipped with a second reflecting 
surface 33b, which in turn transmits the distance measuring light P1 
emitted from the first light emitting element 29a and reflects tracking 
light P2 to be described later. 
The tracking-light generating portion 28 has a two-dimensional scanning 
portion for moving a laser light beam P2 in a two-dimensional direction of 
X-Z. The two-dimensional scanning portion, as shown in FIG. 7, is 
constituted by a laser diode 28A, a collimator lens 28B for converting 
laser light (tracking light P2) emitted from the laser diode 28A to a 
collimated beam of light, and acoustic-optic elements 28C and 28D crossing 
each other at right angles. Since the two-dimensional scanning portion is 
well known in the prior art, an illustration thereof is omitted. For the 
illustration of the scanning portion, see FIG. 3 of Japan Laid-Open Patent 
Publication No. HEI 5-322569. Note that the scanning operation may also be 
performed by a combination of a rotational polygon mirror and a 
galvanometer mirror. 
The scanning beam (tracking light) P2 emitted from the two-dimensional 
scanning portion is reflected by a first mirror 35a and a second mirror 
35b. The reflected light is passed through a center hole 36 of the 
objective lens 32 and is directed toward the prism 34. The tracking laser 
light P2 reflected by the prism 34 is focused by the entire surface of the 
objective lens 32, is reflected by the reflecting surface 33b of the 
dichroic mirror 33, and is focused on a light receiving element 37. The 
wavelength of the tracking light P2 is different from that of the distance 
measuring light P1 emitted from the light emitting element 29a. 
The position detection of the prism 34 is performed as follows: 
As shown in FIG. 8, a predetermined area is scanned in a raster fashion in 
an X-Z direction by the scanning light P2 emitted from the two-dimensional 
scanning portion of the tracking portion 28. When the scanning light P2 
strikes against the prism 34, it is reflected. The reflected light 
(tracking light) P2, as described above, is focused by the objective lens 
32 and returns to the light receiving element 37. A processing circuit 
(not shown) detects the timing at which a received-light signal was 
received during scanning, and measures the X-direction deviation .DELTA.X 
and Z-direction deviation .DELTA.Z of the center position (tracking 
center) 34a of the prism 34 relative to a scanning center 38. The measured 
deviations .DELTA.X and .DELTA.Z are converted to the horizontal 
rotational quantity of the support portion 24 and the vertical rotational 
quantity of the lens barrel 26, respectively, which are in turn fed back 
to the horizontal rotation means 22 and vertical rotation means 27. In 
this way, the automatic tracking type total station 80 (FIG. 6) can be 
controlled so as to be aligned with the center 34a of the prism 34. The 
objective lens 32 and eyepiece 39 as a whole constitute a telescope. The 
operator can align the survey unit 80 with a target (prism 34) through the 
telescope. The survey unit 80 is equipped with a finished-height data 
drive mode and an automatic vertical (height-direction) tracking mode. 
These modes will be described later. 
The total tracking station 80 has an incorporated central processing unit 
(CPU), which functions as part of the processing circuit (not shown). The 
incorporated CPU computes the horizontal coordinate position and height 
coordinate position of the target prism 34), based on the distance to the 
prism 34, horizontal angle, and vertical angle obtained by measurement. 
The computed horizontal coordinate position is displayed on the display 
portion 23 and also is output to an input-output port 40 (FIG. 4). The 
input-output port 40 is usually constituted by RS-232C and is connected to 
an external personal computer (PC) 41. The PC 41 transmits and receives 
data between it and the CPU of the total tacking station 80. In this 
embodiment, the PC 41 controls the operating mode of the total tracking 
station 80. 
The pole 4, attached to the ground leveling implement 3, is provided with a 
light receiving unit 46 shown in FIG. 9. The exterior circumferential 
portion 47 of the light receiving unit 46 is provided with a plurality of 
prisms 34 over the entire circumference at predetermined intervals. With 
this, the total tracking station 80 can track the bulldozer 1 even when 
the direction of the bulldozer 1 is changed by 360 degrees. 
In the case of the laser beam scanning, the spread angle of the laser beam 
itself is narrow, so the energy density of the laser beam is high. 
Therefore, even when a target is far away from the survey unit 80, it can 
be tracked. 
The operating procedure will hereinafter be described. 
The prism 34 is installed on the ground leveling implement 3 of the 
construction machine 1 at a predetermined height from the lower edge 3a of 
the implement 3 by employing the pole 4 (FIG. 6). Next, the automatic 
total tracking station 80 is installed on a known coordinate point O at a 
dear place in the construction site. The automatic total tracking station 
is connected to the PC 41 in which the three-dimensional design data 
(finished-height data defined as a height of a finished surface 
corresponding to each horizontal coordinate position) of the construction 
site has been stored. The inputs to the PC 41 are the horizontal 
coordinate position of the known point of the automatic total tracking 
station 80, the machine height, and the target height from the lower edge 
3a of the ground leveling implement 3 to the vertical center position 34a 
of the prism 34. The operation of the automatic total tracking station 80 
is started toward the prism 34. 
The automatic total tracking station 8 always tracks horizontal movement of 
the prism 34. The EDM portion 29 measures a distance to the prism 34 
referenced to a known point. At this time, an up-and-down direction is not 
tracked. Consequently, there are cases where the position of the prism 34 
is not on the distance measuring axis. In such cases, measurement of 
distance will be possible if the distance measuring light P1 of the EDM 
portion 29 has an appropriate spread. 
The horizontal coordinates X and Y of the prism 34 are calculated from the 
angle data and distance data of the rotary encoder (not shown) of the 
automatic total tracking station 80 and are output to the PC 41. 
The PC 41 compares the calculated coordinates X and Y with design data 
(finished-height data) and computes finished target height (height of a 
vertical center of the target 34 when the implement is not the finished 
height. As shown in FIG. 14, the survey unit measures the horizontal 
coordinate position 82 of the prism 34 and the measured target height 84. 
The finished-height data at the horizontal coordinate position 82 defines 
a finished height 86 of the finished ground level 6 relative to point O. 
The height 88 of the prism 34 above the bottom 3a of the implement is 
added to the finished height 86 to determine the finished target height 
90. The difference between the measured target height 84 and the finished 
target height 90 is a deviation .DELTA.Z 92. The deviation .DELTA.Z is the 
amount of ground that has to be removed or filled to bring the existing 
ground surface 6' to the finished ground level 6 defined by the 
finished-height data.) at the horizontal coordinates. The PC 41 outputs an 
instruction to the rotation means 27 to adjust the height of the tracking 
light P2 of the automatic total tracking station 80 so that the height of 
the tracking light P2 at the horizontal coordinate position is the 
finished target height 90, as shown in dashed lines at point 94 in FIG. 
14. The automatic total tracking station 80 rotates the lens barrel 26 in 
the vertical direction according to the instruction. 
At the time the rotation of the lens barrel 26 ends, the PC 41 calculates 
the vertical deviation of the prism 34, i.e., the deviation .DELTA.Z 92 
(FIG. 14). The detected vertical deviation is output to a radio 
transmitter 10. At the same tine, this deviation data is output to the PC 
41 as construction evaluation data. The PC 41 records the construction 
evaluation data on the memory thereof. The radio transmitter 10 outputs 
deviation data to a radio receiver 12. The radio receiver 12 outputs the 
deviation data to the drive control unit of the oil pressure control unit 
7. The oil pressure control unit 7 controls the ground leveling implement 
3 up and down according to the deviation data so that the desired height 
of the finished surface is graded. 
In the control system according to the present invention, the 
aforementioned operation is repeated each time the automatic total 
tracking station 80 measures distance. In this way, ground 6' is cut or 
dug by the ground leveling implement 3 and is finished to an expected 
finished plane 6. 
According to this mode of operation of the present invention, the automatic 
total tracking station 80 does not vertically track the target (prism 34) 
installed in the ground leveling implement 3 of the construction machine 1 
because it vibrates and is controlled up and down. Instead the station 80 
follows the design data (finished-height data) transmitted from the PC 41. 
Therefore, high precision construction becomes possible. In addition, the 
automatic total tracking station 80 always detects the vertical deviation 
.DELTA.Z of the prism 34, and therefore, if the deviation is recorded and 
stored, it can be used as construction evaluation data. 
In this embodiment, while the target has been scanned and tracked by the 
tracking light P2, the present invention is not limited to this. For 
example, a two-dimensional CCD sensor, a 4-split element, may be provided 
in the light receiving element 37 for performing a tracking operation. In 
such a case, the scanning-light generating portion 28 shown in FIG. 5 is 
replaced with a light source portion having a suitable spread angle. That 
is, a scanning mechanism is unnecessary. 
In the above case, the tracking light P2 emitted from the light source is 
radiated through the objective lens 32 to the prism 34 and is reflected by 
the prism 34. The reflected tracking light P2 passes through the objective 
lens 32 again and is focused and projected on the light receiving element 
37. The projected image on the light receiving element 37 is detected and 
then is fed back to a servo system, thereby performing automatic tracking. 
FIG. 10 illustrates an alternative to the scanning mechanism which uses a 
4-split element 37A employed as the light receiving element 37. The 
4-split element 37A consists of four light receiving surfaces 37B through 
37E, and the center thereof is disposed so as to be aligned with an 
optical axis. The tracking light P2, reflected by the prism 34 and 
projected on the light receiving surfaces 37B through 37E, generates four 
outputs proportional to the projected areas on the light receiving 
surfaces 37B through 37E. Therefore, from the four outputs of the light 
receiving surfaces 37B through 37E the displaced position of the tracking 
light P2 can be detected. According to this control system, the tracking 
light P2 from the survey unit 80 is not radiated toward the light 
receiving element 37, rather a light source for tracking is disposed near 
the prism 34. The image, formed by the light source for tracking, is 
received by the 4-split sensor 37A (two dimensional CCD) serving as the 
light receiving element 37 of the survey unit 80, and the deviation 
between the optical center axis and the position at which the image was 
received is received, thereby tracking a target. 
In aforementioned control system, a beam scanning mechanism is not required 
and therefore the survey unit 80 becomes structurally simple, but tracking 
light with a certain degree of spread becomes necessary in order to 
reliably irradiate the prism 34 or automatic total tracking station 8 
itself, so the trackable range will be limited. 
Incidentally, in the construction prior to final finishing, high precision 
is not required and construction is repeated many times. With the 
repetition of the operation, a land creating operation is gradually 
performed as the design data (finished-height data) requires. That is, in 
an initial stage of construction, the road surface in the present 
condition is often considerably offset from a designed value. According to 
the aforementioned embodiment, a height of the tracking target 34 where it 
would be when the implement is at the finished surface 6 at a target 
horizontal coordinate position is always indicated by the tracking light 
P2. Therefore, when a ground level for rough finishing is considerably 
offset from a designed height and firmer than other ground levels, the 
prism 34 can depart from a tracking range so measurement of distance 
becomes impossible. In the case where a ground level for rough finishing 
is uniformly offset up or down from a finished surface height, the prism 
34 can be kept within the tracking range by adding a predetermined offset 
to the finished surface height. However, in the case where land with a 
complicated configuration is leveled, a great number of prisms 34 must be 
arranged in an up-and-down direction or the spread angle of the distance 
measuring light P1 must be enlarged. Consequently, the control system 
becomes complicated and the cost is increased. 
According to the following embodiment, when a ground level for rough 
finishing is considerably offset from a designed height, construction can 
be accurately performed without arranging a great number of prisms 34 in 
an up-and-down direction, even if the ground for rough finishing is 
partially firmer than the ground at other places. 
The distance measuring light P1 of the EDM 29 usually has a spread angle of 
a few minutes. Therefore, if the prism 34 exists in this spread angle 
range, measurement of distance can be performed. For example, when the 
spread angle is 5 minutes and the prism 34 is 50 m off, the beam spread is 
about 7 cm. Therefore, if the deviation is within .+-.3.5 cm, measurement 
of distance can be performed. Therefore, if construction is performed 
within .+-.3.5 cm relative to a designed value with a single ground 
leveling operation, distance can be measured at all times and there will 
be no problem. 
However, in the case where the present road surface condition is bad and, 
for example, there are many places offset from the designed data 
(finished-height data), or when ground is partially firm and therefore 
construction cannot be performed within .+-.3.5 cm with a single ground 
leveling operation, the tracking light P2 may not strike the prism 34 and 
therefore the light receiving element 37 will not be able to receive the 
tracking light P2. 
Incidentally, the automatic total tracking station 80 always detects the 
vertical position of the prism 34. Therefore, the automatic total tracking 
station 80 can know how the present construction condition is offset from 
the design data (finished-height data). 
Hence, the automatic total tracking station 80 is constituted so that if a 
ground leveling operation is beyond a predetermined range (for example, 
.+-.3 cm), vertical tracking as well as horizontal tracking is 
automatically started as in a standard automatic total tracking station. 
More specifically, the automatic total tracking station 80 is switched from 
a finished-height data drive mode (described above) to an automatic 
vertical tracking mode when the aforementioned vertical deviation .DELTA.Z 
of the prism 34 exceeds .+-.3 cm. The vertical rotation means 27 deflects 
the tracking light P2 so that it is positioned at the vertical center 
position 34a of the prism 34. In other words, the vertical rotation means 
27 deflects the tracking light P2 so that the center of the optical axis 
of the lens-barrel portion 26 coincides with the vertical center position 
34a of the target, thus tracking the target (prism 34). 
Even in this case, the deviation data .DELTA.Z (difference between a 
measured target height and a finished target height) transmitted from the 
automatic total tracking station is used as control data by the implement 
controller to control the height of the implement. The height deviation 
data is transmitted from the radio transmitter 10 to the radio receiver 
12. 
In the above case, although the automatic total tracking station 80 also 
performs vertical tracking and, therefore, precision is degraded, no 
hindrance will arise because this operation is originally performed when 
ground is considerably offset from the design data (finished-height data). 
For ground with a considerable offset the design data (finished height 
data), the ground leveling operation is repeated by the aforementioned 
method. If the offset from the design data is within a constant range (for 
example, .+-.2 cm) in a succession, the automatic total tracking station 
80 will stop the vertical tracking and will be switch to the 
finished-height data drive mode again. 
In addition, if the vertical tracking servo response is reduced to such a 
degree as not to follow vibration of a heavy machine (construction 
machine) and fine deviation is corrected with the vertical deviation 
.DELTA.Z (shown in FIGS. 8 and 14), precision will be enhanced. 
In the foregoing description, the deviation data .DELTA.Z has been 
transmitted or to the construction machine 1 by the radio transmitter 10 
and the received by radio receiver 12. However, if optical communication 
means described hereinafter is employed, the deviation data .DELTA.Z can 
be transferred to the construction machine 1 without being subjected to 
communication jamming and interference. 
That is, in this further alternative embodiment, the deviation data 
.DELTA.Z) is modulated to the tracking light P2 and sent, and the tracking 
light P2 is demodulated by a light receiving element 45 shown in FIG. 11, 
thereby taking out finished-height data. 
In the case where two-dimensional raster scanning is performed as shown in 
FIG. 8, if it is assumed that horizontal scanning time for one line is 0.1 
msec and the number of vertical scan lines is 100, it will take 10 msec to 
complete the scanning operation. After completion of the scanning 
operation, the tracking light P2 is returned to the center position 38 of 
the target and then modulation for data communication is performed. 
The light receiving signal is processed by a subsequent electric circuit. 
In the case where the light receiving element 45 is disposed above the 
prism 34, preferably the scanning beam P2 from the automatic total 
tracking station 80 is not returned to the target center position 38 but 
is returned to the light receiving element 45 slightly above the target 
center position 38, in order to accurately perform reception. How the 
scanning beam P2 is deflected upward from the target center can be easily 
calculated, because the offset value H1 between the prism 34 and the light 
receiving element 45 is known and also the distance to the prism 34 has 
been measured by the automatic total tracking station 80 itself. In this 
embodiment, vertical tracking is not performed but is controlled by design 
data (finished height data). Therefore, the position of the prism 84 fixed 
to the pole 4 and the position of the light receiving element 45 are not 
always the same position relative to a collimated axis. Even in this case, 
when a scanning operation for tracking is performed, it can be judged how 
the prism 34 is displaced from a collimated axis. Therefore, it will be 
sufficient if the scanning beam P2 is deflected to the displaced 
direction. 
FIGS. 12(a) and 12(b) show an example of data modulation performed by a 
tracking light scanning method. FIG. 12a shows a signal modulated by an 
ASK method. In FIG. 12a, T1 represents an interval during which the 
position of the prism 34 is detected by performing a raster scanning 
operation for tracking. T2 represents an interval during which the 
scanning beam P2 is deflected to the light receiving element 45. T3 
represents an interval during which data communication is performed. 
In the period T3 of FIG. 12a, reference character S denotes a synchronous 
pattern representing the start of blocks of data, and a1, a2, a3, . . . 
represent serial data bits, respectively. The data bits are partitioned by 
data bit 0 having the same width so that data bit 1 does not continue in 
succession. In this example, in order to easily detect the synchronous 
pattern S, the width is a few times greater than each width of data bits 
a1, a2, a3, . . . . The data bits following the synchronous pattern S 
indicate binary data (for example, 1, 0, 1, . . . ). 
FIG. 12b shows a modulation circuit. In the figure, reference numeral 55 
denotes an oscillator and 56 a gate circuit. The oscillator 55 outputs a 
carrier wave, and the gate circuit 56 performs ASK modulation on the 
serial data transmitted from the PC 41. A drive circuit 57 causes the 
laser diode 28A to emit light, while modulating the laser diode, based on 
serial data. The tracking light P2 is data-modulated with the deviation 
data .DELTA.Z. The deviation data .DELTA.Z thus is sent to the light 
receiving element 45. In this way, deviation data is transmitted to the 
light receiving element 45. In this embodiment, the width of the 
synchronous pattern S is 1 msec, the width of each data bit is 0.1 msec, 
and the partition width is 0.1 msec. The tie required for data 
communication of 10 data bits is 3 msec. On the other hand, since the 
raster scanning time for a tracking operation is 10 msec, the time during 
transmission does not become a problem. 
Although the tracking light P2 is incident upon the light receiving element 
45 during a raster scanning operation, this does not hinder detection of 
the synchronous pattern S, because the tracking light is not incident in 
succession compared with the synchronous pattern S. Also, the distance 
measuring light P1 of the EDM portion 29 is likewise incident upon the 
light receiving element 45. In this case, if a carrier wave frequency 
different from the modulation frequency (usually 15 Mhz and 75 Mhz) of the 
EDM portion 29, for example, 500 khz is employed as a frequency for data 
modulation, frequencies can be discriminated from each other by a filter 
circuit (not shown). 
The light, received by the light receiving element 45, is amplified to an 
appropriate level by an amplifier 50, as shown in FIG. 11. Then, the 
carrier wave is removed by an envelope detector 51 and is shaped by a 
waveform shaping circuit 52. The shaped light is input to a computer 53. 
The computer 53 detects the synchronous pattern S in which data bits 1's 
continue at more than a constant interval, and from the timing at which 
the detected synchronous pattern S rises, it is judged whether the input 
signal, input for every constant interval, is a 0 or a 1. With this, data 
is demodulated. After demodulation, the computer 53 outputs the 
demodulated data to a display 54 or an output connector (not shown). 
A description will next be made of the case where the 4-split element 37A 
is used. 
In the case where the 4-split element 37A is used as the light receiving 
element 37, tracking and communication do not need to be performed in a 
time-division manner, because the tracking light P2 is always radiated on 
the prism 34 and the light receiving element 37. In this case, since the 
data-modulated tracking light P2 is reflected by the prism 34 and returns, 
data is not detected but the synchronous pattern S emitted stably is 
detected when light is received by the 4-split element 37A. Based on the 
signal level of the detected synchronous pattern S, the received position 
of the tracking light P2 is detected For example, as shown in FIG. 13, the 
output of the light receiving surface 37b of the 4-split element 37A is 
amplified to an appropriate level by an amplifier 58. After amplification 
the carrier wave is removed by an envelope detector 59, the tracking beam 
P2 is shaped by a waveform shaping circuit 60 and is sent to the PC 41. 
The PC 41 detects the synchronous pattern S where data bits 1's continue 
more than a constant interval. The output of an A/D converter (not shown) 
at that time is fetched. Likewise, the light receiving surfaces 37C 
through 37E are processed with similar circuits. From the A/D conversion 
output values of the light receiving surfaces 37B through 37E, the 
received position of the tracking beam P2 is computed and then is fed back 
to a servo system. In this embodiment, the survey unit 80 can track the 
target while transmitting data. 
As previously described, optical communication becomes possible by carrying 
data with the tracking light and installing a light receiving element near 
the prism 34 (target), and consequently, a radio communication unit is not 
required. In the aforementioned embodiments, although ASK modulation and 
demodulation have been employed, other known methods may be employed. For 
example, a PSK method may be utilized as a modulation method. 
While the present invention has been described with reference to preferred 
embodiments thereof, the invention is not to be limited to the details 
given herein, but may be modified within the scope of the appended claims.