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Revista de Engenharia Civil 2019, No. 56, 28-33
http://www.civil.uminho.pt/revista
Centre for Territory, Environment and Construction
Automated control systems for civil construction machinery using
RTK-GNSS: an implementation review
J.M. Lopesa, J.L.A. Trabancoa†
a Department of Geotechnics and Transportation, School of Civil
Engineering, Architecture and Urban Design, University of Campinas,
SP, Brazil
† Autor para correspondência: [email protected]
ABSTRACT Cronologia do artigo: The modernization of global
navigation satellite systems (GNSS) allowed us to obtain positions
in three dimensions with accurate precision. Techniques such as
real-time kinematic positioning (RTK) provide precise coordinates
in the field. All the progress has contributed to construction
works that make use of heavy machinery as a way to integrate these
positioning systems and ensure accuracy of performed activities
with increased productivity. A brief analysis on the implementation
of automated control systems for construction machinery with the
use of RTK-GNSS receivers is presented herein, as well as their
needs and advantages as to programming and operation. The commonly
automated machines (earthworks, compaction and machinery paving)
are classified here into three categories based on their
peculiarities and ability to integrate the system components.
Recebido a 07 junho 2017 Corrigido a 27 setembro 2018 Aceite a
11 abril 2019 Publicado a 27 maio 2019
Keywords: GNSS Global Positioning System Real-time kinematic
Machine Control Construction Machinery
1. Introduction
Until the 1990s, precision control of earthworks, compression
and paving was only possible through exhaustive work of surveying
teams that were present in the field during the entire execution of
activities. These teams used to make use of laser levels equipment
and universal total stations (UTS).
Even though it was created in the early 1970s, the Global
Navigation Satellite System (GNSS) came to operation only in the
1990s. As a revolution in human life, GNSS was valuable both for
those who needed positioning with precise coordinates, such as
surveyors, and civilian users who started using low-cost receivers
as an alternative to old printed maps. Nowadays it is hard to
imagine how construction demarcation of land would be performed
without the use of this technology.
The real-time kinematic (RTK) technique was the most significant
advance after the emergence of GNSS, as it allowed obtaining
precise data on the field without the need for post-processing the
data.
The possibility of integrating heavy construction machinery with
these systems emerged later on, in order to provide better control
of accuracy and precision during operation.
In the present study, we make a brief analysis on the
implementation of automated control systems for construction
machinery with the use of RTK-GNSS receivers. Although a particular
focus was given on earthmoving and paving surface compaction
machines, it is worth noting that RTK-GNSS technology can be
applied to various other constructions tools.
2. History of automated control machines
Until the advent of GNSS-operated machines such as excavators,
bulldozers, scrapers, drills, cement spreaders, compactors and
mixers, it was necessary an extensive work of a topography team
throughout the execution of activities in order to achieve high
accuracy and precision levels, using laser levels, theodolites and
total stations. Finally, with the development of automated laser
levels, control machines became more sophisticated, independent and
automated.
The rotating-beam levels can be mounted on tripods and are
equipped with pentaprisms that rotate 360 degrees at high speed and
at a right angle, emitting a beam of light through the work area.
Receivers installed on the machines receive the laser as a guide
and guarantee accuracy higher than 1cm at 100m.
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Revista de Engenharia Civil (2019) 56:28-33 29
This technology allows the control of leveling, and vertical and
horizontal characteristics of the plan (Roberts et al., 1999).
GNSS determines positions in three dimensions (3D, or latitude,
longitude and height) with millimeter accuracy. A few years ago the
biggest challenge when using this equipment was to ensure accuracy
in the definition of the height coordinate. Roberts et al. (1999)
were the pioneers to present GNSS-RTK as a valid system to automate
construction machinery blade. They presented the application of
RTK-GNSS applied to a bulldozer, and compared the system’s accuracy
with a laser level equipment. However, at that time the use of
mutual navigation satellite systems was not consolidated, but
nowadays it is consolidated the use of more than one constellation
satellites simultaneously (mainly GPS (Global Positioning System) +
Glonass (Globalnaya Navigatsionnaya Sputnikovaya Sistema)). This
practice increases the accuracy of all three coordinates by using
more satellites as a reference.
In addition, with the evolution of the technology its
application spread to several other areas. Examples of this is the
application of GNSS-RTK for monitoring crustal deformations
(Milyukov et al., 2010), for surveying in forests (Blum, 2015), for
deformation monitoring (Martín et al., 2015), for real-time
monitoring earth–rock dam material truck watering (Liu et al.,
2013), or associated with multipath reflectometry for determination
of snow depth at the site (Tabibi, Geremia-Nievinski, and Dam
2017).
3. GNSS
Global Navigation Satellite Systems are made of a constellation
of satellites in orbit around the Earth that emit signals that
allow us to determine precise coordinates across the globe. The
coordinates are determined based on the distance between the
satellites and the receiver. The emergence of GNSS was made
possible through the creation of GPS by the Americans and Glonass
by the Russians in the 1970s. Currently, the European Union, China
and Japan also have their own satellite positioning systems
(Galileo, Beidou, QZSS, respectively). India is also expected to
have their system complete and in orbit until the end of 2016
(Government of India, 2015).
These systems were created due to military interests. By the
year 2000, for example, the GPS system was Selective Availability
(SA), which consists in a programmed signal degradation tool for
civilians so that only the Army would have access to accurate
signals. Nevertheless, such degradation tool was discontinued and
in 2007 the US Government announced the creation of a new
generation of satellites, known as GPSIII, which lack the SA
resource. In addition, the US Government claimed no interest in
resuming with the degradation tool.
According to the US Government (2015) the GPS space segment
comprises 31 satellites in orbit, divided into legacy and
modernized satellites. The first to be launched were the Legacy
Satellites (between 1990 and 2004), operating at frequencies L1 C/A
(for civilian use) and L1/L2 P(Y) (for military use). Modernized
satellites make use of three communication frequencies, as follows:
L2C, L5 and L1C (the latter is the 4th generation of signal and
will only come into operation with the launch of GPS III
satellites).
L2C (Second Civil Signal): Operates at the frequency of 1227 MHz
and divides the frequency with two other military signals; L5
(Third Civil Signal): Operates at the frequency of 1176 MHz and is
designed to meet the security needs in transport. It is transmitted
in an exclusive band for aviation security services; L1C (Civil
Fourth Signal): It operates at the same frequency of the L1 signal
(1575 MHz), but should not be confused with the L1 C/A sign used by
legacy satellites. This frequency was created to allow the system
to make use of international collaboration while still ensures the
US national security. The L1C was originally created to be a shared
band with the Galileo, QZSS and Beidou (US Government, 2015).
GNSS receivers generally reach great accuracy when accompanied
of post-processing, that is,
when data obtained by the receiver have errors and ionospheric
refraction corrected by computer. However, it was necessary to have
even more precise data in the field in real time. The real-time
kinematic (RTK) technique has emerged as a great alternative to
solve this problem. Given its importance in automation of
construction machinery, following focus is given to this
technique.
4. GNSS real-time kinematic
The collection of GNSS data using real-time kinematic technique
allows the user to obtain accurate 3D
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positions (3 cm or less) without the need for the receiver to be
at a static position. This accuracy is possible due to corrections
of the coordinates that are sent via UHF radio by the fixed base
receiver to the rover, which is the receiver that may be moving
(Figure 1). A single base station can support an unlimited number
of rovers, and its scope is very wide and can meet an area within
20 km (12 miles), but the radio range is often more limited.
Figure 1 - RTK-GPS.
The fixed base must always be installed at a point with known
coordinates. By informing the
receiver the point coordinates, it can calculate the difference
(error) between both obtained by the fixed base. This information
is transmitted by radio to the rover, which applies the errors
already calculated to the coordinates that it is getting at the
moment, correcting them in real time (Figure 2).
Figure 2 - RTK-GPS correction.
The RTK technique may also have the bases with a radio antenna
replaced by available cellular
network (GSM, 3G, 4G, etc.) by installing a chip directly on the
rover. This technology known as NTRIP uses continuously operating
reference station (CORS) networks for corrections (Edwards et al,
2010; Mekik et al, 2011). This method allows the work be carried
out without the need for a fixed base in place, but limits its
operation within the signal coverage areas of telecommunication
companies, as well as their signal speed.
5. Automation components and operation
In the construction area, the most common machines equipped with
automated machinery control systems are earthworks, compactors and
pavers. Each of these has its characteristics and the requirements
of GNSS as well as the complexity of the installation of the
automation components, communication, calibration and pre-work
activities. The installation process of the components must be done
as much accurately as possible. Each installation error can relate
directly to the loss of precision of the activities to be
performed.
The GNSS receiver can be combined with other equipment to
control the machine, both level laser equipment and UTS. Angular
sensors are essential functioning parts of these systems as they
allow the control box to have the inclination information of each
part of the machine and consequently how
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the area is being modified by the blade, drum or screed.
Excavators and wheel loaders Earth moving machine, such as
excavators and wheel loaders, differs from bulldozers, scrapers
and graders by presenting a more dynamic movement of the bucket,
which prevents installation of the GNSS equipment directly on the
buckets. This feature makes the use of angle sensors important for
full control of machine movements. The angle sensor should be
installed in every part of the machine that will perform the
movement, e.g. in case of excavator, it should be installed in the
cabin, boom, stick and bucket. GNSS can be installed with single or
double receivers which should be installed on high masts on the
back of the booth, at the farthest point from the bucket, so that
sensitivity to simple movements is not noticed. All the information
from these sensors is received, compiled, and interpreted by a
control box installed in the cabin.
One of the most important stages of calibration of the equipment
is measuring the distances between the machine motion axes and
sensors when the machine is leveled and in early position, and also
at the initial position of the boom and the bucket at maximum reach
on the floor measured with the GNSS receiver (Figure 3).
Figure 3 - Excavator at maximum reach. Bulldozers, scrapers and
graders
The work done by these machines requires less dynamic movements
than those mentioned earlier. Because of this feature, it allows
the installation of GNSS receivers directly above the blade, in a
single or double form.
For calibration, it should be flush to a point with known
elevation, and it is important for the blade to be in its normal
working position, i.e., on the floor and in the same height as the
track of the machine.
Soil and asphalt compactors and pavers
Compression activities require great accuracy in their results
and GNSS applied to such processes can ensure and control the
compression quality more broadly.
In these activities, this system can also be used to obtain
information about the progress. Meehan et al. (2013) used
interpolation methods (Kriging and Inverse Distance Weighting
Methods) to create three-dimensional planes of compacted layers
using coordinates obtained by GNSS RTK. Given that GNSS data is
about point positions, the interpolation was shown to be an
excellent alternative for compaction control of large areas through
the creation of plans which represent the 3D compacted layers.
Compactors are typically equipped with only one GNSS receiver,
which may be installed above the cabin or close to the drum. In
this inclination sensor, compression and temperature can be added
to the system.
Pavers are machines that move straightforward at low speed and
have small range of movement of the screeds. The installation and
control of the equipment is very similar to compactors. GNSS
receivers can be installed in single or double way directly in the
screeds.
6. Automation in construction and its relationship with industry
4.0
When we compare the construction sector with the agricultural
sector or the industry sector, it is clear that those have passed
in recent years through a process of innovation and adoption of new
technologies that have allowed a greater automation of their
processes. The civil construction, was initially left behind
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by being composed of dynamic activities and by each activity
differs greatly from one work to another. However, society is
currently discussing the emergence of Industry 4.0, where physical,
cybernetic and biological meet, and their harmonious integration
allows for more and more intelligent decisions and actions to be
taken (Schwab, 2016). Industry 4.0 promises to affect all layers of
society by allowing "things" to be part of a network (also known as
the Internet of Things - IoT) and communicating by providing data.
A classic example of IoT is the hospital bed that recognizes that
the patient is moving abnormally and automatically triggers the
help of the nurses.
Such innovation will not exempt civil construction from its
benefits. Despite the precise blade control activities for earth
moving, compacting and paving still depend totally on the
positioning systems mentioned earlier in this paper, several
technological solutions have been used in the field in order to
increase the quality of construction activities and also to reduce
their costs. One of the main highlights is the remote monitoring
system, which aims to allow all machines and their parts to be
connected to the same network (Autodesk, 2015). In this way, it
would be possible to monitor the integrity of the equipment in real
time. This would allow managers to predict a possible equipment
failure, or need for supply. This type of system acts in the
prevention with the two main expenditures with equipment failures:
the one of stopped time for the repair of the machine in the field
and the waste of productive potential.
In addition to the technologies directed directly to the
machines, several others are already being used in the field. An
example of this is the use of drones to monitor the progress of
constructions as well as the individual activities of their workers
(Knight, 2015), single-task construction robots (STCRs) (Bock and
Linner, 2016), and 3D printing technologies in the field (Kothman
and Faber, 2016).
One of the great challenges for the rise of Fourth Revolution
technologies is security (and data privacy). The RTK-GNSS
technology discussed here has been widely used in agriculture
(Bangert et al., 2013, Jacobs et al., 2017) and associated with the
new technologies allows agricultural machines to operate in the
field autonomously. However, civil construction has a more dynamic
and busy working field, with several workers circulating between
the machines. Currently, although the technologies used in
agriculture allow the expansion to automation in construction, they
are not applied due to safety issues, so until the moment, there
are no fully autonomous machines working in civil construction
(Dadhich, Bodin and Andersson, 2016). Despite the delay in the use
of technology, the industry can still benefit from the advance of
Industry 4.0, which has as a priority robotization associated with
the concept of collaborative machines. These allow a worker to work
in collaboration with a highly productive robot, without their
safety being put at risk.
7. Discussion and conclusion
It is consensual that the advent of GNSS technologies has led to
major advances in several areas, including construction. The RTK
method also allowed obtaining real-time highly precise
coordinates.
When applied to the automated control of machines, RTK-GNSS can
still achieve good accuracy (+/- 3 cm), but other variables and
equipment can directly affect the quality of an automated work. As
all systems installed on machines do not operate only with GNSS
receivers, any error in system calibration, or even the
installation of ancillary components, can interfere with the
desired accuracy.
Obtaining good coordinates is a relatively easy task for
manufacturers of GNSS receivers. As this system is composed of
several components, communication between the different parts is
the main challenge to proper functioning. It can be noted that each
type of machine requires a different way of calibration, thus
requiring that the workers involved in such activities are properly
prepared and trained for the procedures, and above all, understand
the importance of each procedure.
The adoption of a RTK-GNSS machine control will require
excavation, paving and compaction projects to be made first, in
order to serve as a guide for the machines.
When the challenges of installation and operation are overcome,
machine control systems can result in significant increase in
productivity, allowing the contractor to decrease by up to three
times the runtime of the activities or the number of working
vehicles. Altogether, it demonstrates that although expensive this
system can pay for itself with middle-term productivity.
8. Acknowledgements
The authors thank the Coordination for the Improvement of Higher
Education Personnel (CAPES/Brazil – Process/Project
01-P-04376-2015) for financial support. The authors are also
grateful to Fernando Catrau (Trimble Brazil) for the support and
for provide information on Trimble machine operation.
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Revista de Engenharia Civil (2019) 56:28-33 33
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