New measurement and control technology in tunnelling - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 269

6.5.2 Steering with laser beam and active target
As an example of a modern steering control system for tunnel boring machines, the SLS-T
(steering control system for tunnel boring machines with segment lining) system from the
company VMT is now described:
The system consists of the following components (see Fig. 6-27):
- A laser theodolite with servostation.
- An active target (ELS) with integrated roll and inclination instrument.
- An industrial PC with monitor for the control position.
- A microprocessor interface box (“Yellow Box”).
Figure 6-27 Components of the SLS-T system from VMT.
The system enables permanent monitoring of the position of a tunnel boring machine. The
ELS has a light-sensitive sensor surface to localise the laser point and is fixed to the shield
body. The position of the ELS is included in the construction of the shield machine. The
point of contact of the laser beam on the target can be surveyed relative to the machine
axis. A two-axis inclinometer for simultaneous measurement of the longitudinal attitude
and roll of the machine is also integrated into the ELS. With an intelligent sensor system,
the exact yaw angle is determined as the deviation between the longitudinal axis of the
target and the laser beam. The offsets in horizontal and vertical directions are transmitted
to the computer with the roll, yaw and pitch angles and used to determine the attitude and
height. All values are determined every two to three seconds and the results are shown
graphically and in numbers at the control position in relation to the planned tunnel align-
ment or the already calculated correction curve (see Fig. 6-28).