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Design, Analysis and Control of an Offshore Load Transfer System
1. Design, Analysis and Control
of an Offshore Load Transfer System
MAS501 Control Theory2- Autumn 2013
University of Agder
Grimstad Norway
Oreste Niyonsaba
Haocheng Su
Dimuthu Dharshana Arachchige
Bernard Sisara Gunawardana
Subodha Tharangi Ireshika
Jagath Sri Lal Senanayaka
2. Presentation Outline
Introduction and methodology
Crane kinematics
Control architecture in Labview
HIL Setup
Control architecture in Step 7
Results
Discussion and Conclusion
3. Introduction and methodology
Cranes are used in different Engineering activities
including offshore operations for transportation of loads
and personnel.
Control design needs improvement to meet some of the
main criteria such as automatic tool tip tracking among
others
Control system is aimed at maintaining the position of the
tool tip within one meter by one meter square relative to
an inertial frame of measurement is developed
Firstly, the desired tool path is achieved in Labview, then
the control architecture is programmed in Siemens Step7
TIA environment integrated with Siemens ET200 PLC.
4. Introduction and methodology
Control Architecture is plugged with crane boom to
achieve the desired movement
A DLL file is created by modeling HMF crane in
SimulationX in order to use it in Labview software as
shown if the figure below
5. Introduction and methodology
The desire is to implement the control architecture with
two P and PI controllers for controlling the tool tip
position
6. Crane kinematics from matlab
Kinematics plays a significient role to establish
the traslational relastionships between global
coordinate system and the coordinate system of
crane components.
Devided in to Forward kinematics, Inverse
kinematics, Forward Jacobian, Inverse Jacobian
and Actuator kinematics
7. Forward Kinematics
Utilized to find the change of
tool tip position when the
angular positions are given
Necessary to develop DH
(Denavit-Hartenberg) table
9. Forward Jacobian
Utilized to skecth the
velocities of the actucators
when the angular velocities
are known.
Maple was used to find the
parameters in the jacobian
matrix.
10. Inverse Jacobian
Angular velociteis when the toll tip
velocities are known.
It is obtained by differentiating the
inverse kinematics.
This part is also implemented in
both matlab and labview.
Inverse kinematics and inverse
Jacobian are crucial to convert the
reference positions and velocities of
the desired tool path into reference
angular positions and angular
velocities of two actuator joints.
11. Actuator kinematics
Used to derive relationships between angular movement of
the actuators and linear movements of the cylinders.
Actuator
Kinematics 2
Actuator
Kinematics 1
L3
L2
Law of Cosine
Analytical procedures are difficult
12. Polynomail Curve Fitting: ‘Polyfit’
Returns coefficients of the polynomial in descending powers.
L2 and Q2 Relation
L3 and Q3 Relation
140
40
120
20
100
0
80
-20
60
-40
40
-60
20
-80
0
-100
-20
-120
-40
-140
-60
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
-160
1.1
Root mean square error
Third order polynomial
Fifth order polynomial
1.2
1.3
1.4
1.5
1.6
0.0067
0.0037
1.7
1.8
1.9
2
2.1
13. Tool path in Labview
Operated in two segments
The path length (L) between the two locations and
angular position of the velocity vector are
geometrically found in order to guide the tool tip
along the shortest possible path
1. Initial position and target point
2. Reference square path
14. Tool point along the reference square path
Total Length of path s=3.914 m
s<L1
% First stretch
xDot=v;
zDot=0;
s<L1+L2
% First corner
x=R+L1+R*cos(q-pi/2);
z=R+R*sin(q-pi/2);
xDot=v*cos(q);
zDot=v*sin(q);
s<2*L1+L2)
% Second stretch
s<2*L1+2*L2)
% Second corner
s<3*L1+2*L2)
% Third stretch
s<3*L1+3*L2)
% Third corner
s<4*L1+3*L2)
% Fourth stretch
s<4*L1+4*L2)
% Fourth corner
Reference values for tool tip position and velocities are fed to
inverse Jacobian and inverse kinematics to configure the joint
angular movements .
15. Implementation of controllers in Labview
P_L2
PI_L2
P_L3
PI_L3
Propotional Gain
(P)
Integral Gain
(I)
P_L2 & P_L3
50
-
PI_L2 & PI_L3
0.05
0.001
20. Tasks of digital switches in PLC
Switch
Addre
Task
ss in
PLC
Manual(Man_Sw) I3.0
Tool tip is moved to any location in the xz plane with
respect to the actuator velocities given by analog inputs
Point(Point_Sw)
I3.2
Tool tip is moved through the shortest path from current
location to any given target location by changing the
velocity given by analog input 1
Auto(Auto_Sw)
I3.1
It is required to enable the point switch before enabling
the auto switch. Due to the limitation in actuator lengths,
it is not possible to run the given reference path starting
from any arbitrary location in the xz plane. Hence, the tool
tip is firstly moved to a defined point (2.0, 1.5) which is
within the scope of controlling the actuator lengths.
Thereafter, the tool tip is moved along the reference tool
tip path by enabling auto switch. Velocity of the tool tip
can be controlled by changing the analog input 1.
22. Digital switch configuration in main
controller block with SCL
Manual-1 Auto-1 Point-1
Manual-1 Auto-1 Point-0
Manual-1 Auto-0 Point-1
Manual-1 Auto-0 Point-0
Manual-0 Auto-1 Point-1
Manual-0 Auto-1 Point-0
Manual-0 Auto-0 Point-1
Manual-0 Auto-0 Point-0
23. Implementation of the point switch in Step 7
In order to achieve
the task of the
point switch,
point initializer
block and the
respective SCL
code is developed
The Initial
Integrator block is
used to calculate
the distance ‘ss’,
travelled by tool
tip along the
linear reference
path from stating
point to target
point
24. Implementation of auto switch in Step 7
‘path’ function is defined to configure the reference tool tip position and
reference velocity.
The reference tool path is implemented in Step 7 in SCL language
An integrator is used to calculate the distance travelled by tool tip along
the reference path, ‘s’.
25. Crane kinematics and PID controllers in Step 7
Inverse kinematics, Inverse jacobian and
actuator kinematics are developed in Step
seven as FC blocks and the same programs
used in labview were implemented in SCL
language.
Two P controllers and two PI controllers were
implemented with CONT_C block and
parameters were tuned accordingly.
Controller
P_L2
P_L3
PI_L2Dot
PI_L3Dot
400
400
0.05
0.05
Tuned values
P
I
0
0
0.01
0.01
26. LabView Results: Path
Test was sucessful
Maximum +/- 10 cm
deviation form
expected path
Reference Path
Actual Path
27. LabView Results: Controllers Operation
Actuator L2 position and velocity controllers
Actuator L3 position and velocity controllers
29. HiL Test Results : Manual and Start Point
Initialization Operations
Manual and tip point initialize(shortest path finder) control functions
to make the system operation more robust and safe.
Manual Mode Operation
Start Point Initialization Operations
30. HiL Test Results: Path
HiL test was very sucessful
Maximum +/-5 cm deviation form expected path( only in two edges).
Start Point Initialization Operations
Auto mode Actual Path
31. Real HMF Crane Test Results: Path
Real crane test was very sucessful
Maximum +/- 5 cm error in expected path
Approximate 35 cm offset in x direction.
HiL Test Actual Path
Real Test Actual Path
32. Why 35 cm Offset ?
There is 34.3 cm offset in x direction
of the coordinate systems used in dll
file and real crane.
33. Discussion and Conclusions
Lab view results were observed with +/- 5-10 cm deviation.
Possible resons could be computer programs were not used dedicated
hardware to run controllers and DLL model.
Modelling errors in DLL file and our sysem model
With HIL test we used dedicated hardware to run the controllers and
realtime tartget(DLL model). Maximum +/-5 cm deviation form expected
path( only in two edges) was observed. HiL Test was very sucessful.
Modelling errors in DLL file and our sysem model
With real experiment it was observed Maximum +/- 5 cm error in
expected path and 35 cm offset in x direction. Test was very successful.
Modelling errors in our system model.
There seems 35 cm offset in x direction of DLL model output than real
crane. We could solve this problem with little modification in system.
34. Discussion and Conclusions (Cont.)
Solution to the offshore load transfer system
2D -> 3D Solution
Reference target is required to get from sensors of floating platform
Tool tip target tracking operation
35. Discussion and Conclusions (Cont..)
A real engineering experience with 3 steps..
1) Numarial Modeling/Simulation :
Make the system with more software models(Lab view, dll model)
Less acuarate but easy to change and think.
2) HiL Method:
Make the sysem with more real equipments (PLC and switches) and
improved model sysems (DLL model run on real time labview,
Simulink model)
More acurate results and closer to reality.
It is cost saving safe method, befoure doing the actual task.
sucess of this method highly depend on acuracy of real system model.
Here the given DLL model was acurate as the real machine works
accordingly.
3) Real world test with actual devices (PLC, HMF real crane and real switches)
Solve the real world problem of offshore load transfer system