Design, Analysis and Controlof an Offshore Load Transfer

System

Oreste Niyonsaba Haocheng Su

Dimuthu Dharshana Arachchige Bernard Sisara Gunawardana

Subodha Tharangi Ireshika Jagath Sri Lal Senanayaka

MAS501 Control Theory2- Autumn 2013University of Agder Grimstad Norway

Introduction and methodology

Crane kinematics

Control architecture in Labview

HIL Setup

Control architecture in Step 7

Results

Discussion and Conclusion

Presentation Outline

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.

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

Introduction and methodology

The desire is to implement the control architecture with two P and PI controllers for controlling the tool tip position

Introduction and methodology

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

Crane kinematics from matlab

Utilized to find the change of tool tip position when the angular positions are given

Necessary to develop DH (Denavit-Hartenberg) table

Forward Kinematics

Utilized to sketch the angular position(q2,q3) when the tool tip position (x,z)is known.

Inverse Kinematics

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.

Forward 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.

Inverse Jacobian

Actuator kinematicsUsed to derive relationships between angular movement of the actuators and linear movements of the cylinders.

Actuator Kinematics 1

Actuator Kinematics 2

𝒒𝟑

𝒒𝟐

Law of Cosine q

L ??? Analytical procedures are difficult 

L2

L3

Polynomail Curve Fitting: ‘Polyfit’

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2-60

-40

-20

0

20

40

60

80

100

120

140L2 and Q2 Relation

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1-160

-140

-120

-100

-80

-60

-40

-20

0

20

40L3 and Q3 Relation

𝑳𝟐=−𝟎 .𝟎𝟎𝟐𝟏∗𝒒𝟐𝟓+𝟎 .𝟎𝟏𝟒𝟗∗𝒒𝟐

𝟒−𝟎 .𝟎𝟒𝟑𝟔∗𝒒𝟐𝟑+𝟎 .𝟎𝟐𝟏𝟖∗𝒒𝟐

𝟐+𝟎 ,𝟑𝟒𝟔𝟒∗𝒒𝟐+𝟏.𝟐𝟗𝟏𝟒𝑳𝟑=−𝟎 .𝟎𝟎𝟏𝟏∗𝒒𝟑

𝟓+𝟎 .𝟎𝟎𝟏𝟏∗𝒒𝟑𝟒+𝟎 .𝟎𝟏𝟎𝟗∗𝒒𝟑

𝟑+𝟎 .𝟎𝟏𝟎𝟗∗𝒒𝟑𝟐+𝟎 .𝟑𝟎𝟐𝟕∗𝒒𝟑+𝟏 .𝟗𝟐𝟐𝟗

Returns coefficients of the polynomial in descending powers.

Root mean square error Third order polynomial 0.0067

Fifth order polynomial 0.0037

Operated in two segments

Tool path in Labview1. Initial position and target point 2. Reference square path

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

Tool point along the reference square path

Reference values for tool tip position and velocities are fed to inverse Jacobian and inverse kinematics to configure the joint angular movements .

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 corners<3*L1+2*L2) % Third stretchs<3*L1+3*L2) % Third corners<4*L1+3*L2) % Fourth stretchs<4*L1+4*L2) % Fourth corner

Total Length of path s=3.914 m

Implementation of controllers in Labview

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

P_L2

Harware-In-Loop;Labview,PLC & Real Time Target

TCP/IP configuration

Data Communication

Communication between Step7 and Labview

Configuration of the PLC

Siemens ET200S PLC

Configuration of the PLC

Tasks of digital switches in PLC

Switch Address in

PLC

Task

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.

Digital switch configuration

Manual Auto Point Output

1 1 1 No operation

1 1 0 No operation

1 0 1 No operation

1 0 0 Manual switch is enabled

0 1 1 No operation

0 1 0 Auto switch is enabled

0 0 1 Point switch is enabled

0 0 0 No operation

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

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

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’.

Crane kinematics and PID controllers in Step 7

Controller Tuned valuesP I

P_L2 400 0P_L3 400 0PI_L2Dot 0.05 0.01PI_L3Dot 0.05 0.01

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.

LabView Results: Path

Test was sucessful

Maximum +/- 10 cm deviation form expected path

Reference Path Actual Path

LabView Results: Controllers Operation

Actuator L2 position and velocity controllers Actuator L3 position and velocity controllers

HiL Test Results: Expected Path

Manual and tip point initialize(shortest path finder) control functions to make the system operation more robust and safe.

HiL Test Results : Manual and Start Point Initialization Operations

Manual Mode Operation

Start Point Initialization Operations

HiL test was very sucessful Maximum +/-5 cm deviation form expected path( only in

two edges).

HiL Test Results: Path

Start Point Initialization Operations Auto mode Actual Path

Real crane test was very sucessful Maximum +/- 5 cm error in expected path Approximate 35 cm offset in x direction.

Real HMF Crane Test Results: Path

HiL Test Actual Path

Real Test Actual Path

There is 34.3 cm offset in x direction of the coordinate systems used in dll file and real crane.

Why 35 cm Offset ?

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.

Discussion and Conclusions

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

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

Discussion and Conclusions (Cont..)

Thank You..!!