1. 9th
International DAAAM Baltic Conference
INDUSTRIAL ENGINEERING -
24-26 April 2014, Tallinn, Estonia
AUTOMATION OF AN EXCAVATOR BOOM MOVEMENT
IN 3-DIMENSIONS
Liukkonen, J.; Knuuttila, P.; Nguyen, T.; Ingale, S.; Kiviluoma, P. & Kuosmanen, P.
Abstract: Mass stabilization is the process
of mixing binder into soil to improve its
strength and stiffness. Stabilization is
carried out using a specialized tool
attached at the end of an excavator boom.
The purpose of this project is to automate
the boom movement of a mini excavator to
better understand how automation affects
the speed and accuracy of the system. The
movement was automated using
AT90CAN128 microcontroller connected
by CAN bus to proportional valves which
control the hydraulic cylinders of the boom
based on the angle feedback from the
resolvers. It was possible to move the
bucket attached at the end of the boom
reliably from point to point inside the
reachable space of the excavator.
Keywords: mass stabilization, robotic
excavator, PID control, kinematics
1. INTRODUCTION
Mass stabilization is the process of
hardening soft soil by mixing in a binding
agent. Mass stabilization unit consists of
one human operated excavator and a
separate binding agent tank [1
]. Typically
large areas need to be stabilized and
maintaining a consistent quality during this
process is a difficult and time consuming
task. The repetitive nature of the process
suggests substantial benefits in
automatizing the task.
This research focuses on automating the
boom movement. The purpose is to reduce
the effect of control movements of the
operator to achieve more accurate and
efficient result of mass stabilization.
Independent movement of the excavator
together with the tank is left out of this
research. The research builds on the
previous studies carried out by Martikainen
et al. [2
] and Kiviranta [3
]. The goal is to
extend the results of one-dimensional
movement of the bucket tip by Martikainen
et al. into full three-dimensional
movement. Other groups such as Lee et al.
[4
] have also conducted research into
automated boom movement for automated
levelling work.
2. METHODS
The excavator used in the project (JCB
Micro 800) is automated using
electrohydraulic valves (Sauer-Danfoss,
PVED-CC Series 4) and resolvers
(Axiomatic AXRES-CO-V2-1X-H) which
are connected through CAN bus to a
microcontroller (AT90CAN128). The
electrohydraulic valves of the excavator
allow operation of the boom using a
microcontroller and resolvers attached to
each joint which provide accurate
information of the joint angles. Since the
original diesel engine of the excavator had
been replaced with an electric motor, the
resolvers were connected by twisted pair
cables to minimize the electromagnetic
interference.
A printed circuit board and the supporting
electronics were built to interface the
microcontroller with the electrohydraulic
valves and the resolvers. Bucket tip
coordinates specified in the custom made
PC software were supplied to the
microcontroller via serial port. In the

2. microcontroller, a software PID controller
adjusts the flow for each valve based on
the difference between the reference angle
and the current angle for each joint. The
control messages for the valves are sent
through CAN bus and define the flow and
spool drive direction. Figure 1 has a
flowchart of the interaction between the
system components.
Fig 1. System schematic. The interaction
between system components.
The desired path for the bucket tip is
determined by an array of waypoints. Each
waypoint consists of x, y and z coordinates
of point O3 as illustrated in Figure 2. These
waypoints can be converted into joint
angles by using inverse kinematics
equations presented by Koivo [5
].
Equation 1 describes the angle of the
excavator boom slew joint








 
D
ox
D
oy
p
p1
1 tan , (1)
where D
oyp is the y coordinate of point O3
and D
oxp the x coordinate. Equation 2 gives
the angle of the link 2 around the Z1 axis
     
  






















2
3
2
2
22
2
2
3
2
2
22222
21
1
2
4
tan
tan
aadp
aadpdpa
d
p
D
oz
D
oz
D
oz
D
oz

, (2)
where D
ozp is coordinate of point O3.
Parameters a2 and 3a describe lengths of
link 2 and 3, and d used to shorten the
equation is defined as
    111 sincos appd D
oy
D
ox   . (3)
where a1 is the length of link 1. All the link
lengths are given in Table 1.
Table 1. Link lengths of the excavator boom.
a 1 0.180
a 2 1.340
a 3 0.945
a 4 0.460
Link length (m)
Equation 3 gives the angle of the link 3
around the Z2 axis.








 
222
221
3 tan
adcps
dspc
D
oz
D
oz
 (4)
Finally, equation 4 gives the angle of
coordinate frame O4 around the Z3 axis
 324 2   dgb , (5)
where b is the angle between the bottom
of the bucket and the X4 axis. The digging
angle dg describes the angle between the
bottom of the bucket and horizontal ground
plane.

3. Fig. 2. The assignment of the coordinate
systems[5
].
For the purposes of this small scale
prototype, the bucket is kept perpendicular
to the ground to mimic the orientation of
the power mixer. Thus, determining the
final position of the bucket tip requires
three joint angles, namely 1 , 2 , 3 and the
digging angle of the bucket dg . It directly
follows that the x and y coordinates of the
bucket edge are the same with joint 4. The
bucket length thus defines the difference in
the z coordinate.
The waypoints are preloaded into the
microcontroller memory via serial port.
The reachability of each point is checked
before coordinates are sent to ensure a
predictable operation of the excavator. The
reachable space of the excavator boom can
be calculated when the link lengths and the
minimum and maximum angles of each
joint are known.
The reachable space can be visualized by
plotting a slice of the 3D space according
to Figure 3. This method is also very
suitable for graphical user interface where
the user can clearly see the reachable plane
for a given z coordinate of the bucket tip.
Fig 3. A slice of the reachable space of the
excavator and an illustration of the orientation
of all the boom links when the bucket tip is in
coordinates (0.8, 1.5, 0.1).
The area to be stabilized can be divided
into rectangular pieces. The mixing head is
kept at roughly constant depth as it is
moved through the soil. The system
parameters can be optimized if the largest
rectangle for a given depth (z coordinate) is
known. The dimensions of the rectangle
with the largest area can be derived as
2222
8228
2
1
kRkkRxrect  (6)
and
 kkRyrect 38
4
1 22
 , (7)
where R is the reach of the excavator and k
is the radius of the unreachable area close
to the excavator as illustrated in Figure 4.
Fig 4. The rectangle inside a slice of the
reachable space. The white area depicts area the
excavator boom can reach for a given constant
height of the bucket tip. The slew joint axis is at
the origin.

4. 3. TEST PLAN
Testing the accuracy and speed of the
automatic operation is important for
quantifying the possible performance gains
in mass stabilization. To test the accuracy,
a strategy for moving from one waypoint to
the next must be devised. A waypoint
strategy is characterized by the placement
of the waypoints, e.g., the distance between
the waypoints, and the tolerances
associated with each waypoint. Each
waypoint has a surrounding tolerance
radius associated with it. If the resolvers
indicate the bucket tip to be within the
radius, the control algorithm then directs
the bucket tip to move to the next
waypoint. Modifying these factors will
result in changes in performance measures.
The goal was to find an optimal waypoint
strategy within this control framework.
To determine the value of the usable
tolerances, the accuracy of the system has
to be measured.
Before the tolerances can be measured the
resolvers must be calibrated. The system
was calibrated by measuring the maximum
and minimum readings for each resolver.
The actual angles of the boom joints were
then calculated by measuring the height of
each joint from level floor and using
trigonometric relationships to obtain the
maximum and minimum joint angles
corresponding to the resolver values.
4. RESULTS
In order to determine the reliability of the
resolver data, the real position of the
bucket tip was measured from five
different points and the results were
compared with the position indicated by
the resolver data and the kinematics
equations. The comparisons are shown
below in figures 5 and 6. The bucket joint
angle 4 was not included in the
measurements. The bucket was always set
so that the line from the bucket joint to the
bucket tip was perpendicular to the ground.
Fig 5. Box-Whisker plot for the joint angle error
of the resolvers. The error in degrees of 1 was
between [0.5, 4.98]. 2 had error between [0.65,
4.85] and the error of 3 was between [-0.44, -
6.24].
Fig 6. Box-Whisker plot for position error of the
bucket tip. The error in x-direction was between
[-14.2, 3.2], for y-direction the error was between
[-10, 2.8], and for z-direction [-1.2, 5.1].
The joint angles had errors less than 6
degrees for all the joint angles. The
absolute error in distance was on the
average 11.33 cm or 6.43%. The standard
deviation was 4.05 cm or 2.8%. The
resolver data were concluded to be
sufficiently accurate for this application
based on the comparison.
The calibration step is crucial for achieving
high accuracy and these results could
perhaps be further improved.
5. CONCLUSIONS
The initial test results showed that the
boom can be reliably moved within the
reachable space of the excavator when no
external forces act on the boom. However,

5. the excavator is used in this research
primarily as a test platform for automated
boom movement and it cannot be used for
mass stabilization as the excavator joints
do not tolerate large lateral loads.
Currently, an important next step would be
to develop a system for monitoring the
forces applied to boom and the power
mixer unit to avoid damage to the tool
when encountering hard obstacles, such as
rocks hidden in the soil. Beyond that, the
problem of autonomous movement of the
excavator and binding agent tank must also
be solved to achieve full automation.
6. REFERENCES
[1] Ingles, O. G., and Metcalf, J. B., Soil
Stabilization Principles and Practice,
Butterworth and Company Publishers
Limited, London, 1972.
[2] Martikainen, J., Pahlsten J., Söderena
P. & Ubiagege C., “Automation in Mass
Stabilization,” 2013, 8th
International
DAAAM Baltic Conference (Speech).
[3] Kiviranta, J., Instrumentation of an
Automated Excavator, Master’s Thesis,
Helsinki University of Technology, Espoo,
2009.
[4] Lee, C. S., Bae, J., and Hong, D.,
“Contour Control for Leveling Work with
Robotic Excavator,” Int. J. Precis. Eng.
Man., 2013, 14, 2055–2060.
[5] Koivo, A. J., “Kinematics of
Excavators (backhoes) for Transferring
Surface Material,” J. Aerosp. Eng., 1994,
7, 17–32.
7. CORRESPONDING ADDRESS
Panu Kiviluoma, D.Sc. (Tech.)
Aalto University School of Engineering,
Department of Engineering Design and
Production
P.O. Box 14100
00076 Aalto, Finland
Phone: +358 50 433 8661
E-mail: panu.kiviluoma@aalto.fi
http://edp.aalto.fi/en/
8. ADDITIONAL DATA ABOUT
AUTHORS
Liukkonen, Jere, B.Sc. (Tech)
Phone: +358 45 112 5028
E-mail: jere.liukkonen@aalto.fi
Knuuttila, Pekka, B.Sc. (Tech)
Phone: +358 40 560 9767
E-mail: pekka.knuuttila@aalto.fi
Nguyen, Tien, B.Sc. (Tech)
Phone: +358 44 096 4507
E-mail: tien.vannguyen@aalto.fi
Ingale, Saurabh, B.Sc. (Tech)
Phone: +358 41 483 3068
E-mail: saurabh.ingale@aalto.fi
Kuosmanen, Petri, D.Sc. (Tech.), Professor
Aalto University School of Engineering,
Department of Engineering Design and
Production
P.O. Box 14100
00076 Aalto, Finland
Phone: +358 9 470 23544
E-mail:petri.kuosmanen@aalto.fi