automated barge unloading

8/8/2019 Automated Barge Unloading

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Automated Barge Unloading

ME 230Real-time Programming for Mechanical Control Systems

University of California, Berkeley

Final Project

Joshua Cemenska

Mike Mueller


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Table of Contents

INTRODUCTION .........................................................................................................................................................................3

DEMONSTRATION ....................................................................................................................................................................3

FEATURES / SPECIFICATIONS............................................................................................................................................8

TASK DIAGRAM.........................................................................................................................................................................8

STATE DIAGRAMS ....................................................................................................................................................................9

MACHINE CONTROL....................................................................................................................................................................9MOTOR SETPOINT PROFILERS ................................................................................................................................................. 10GUI ............................................................................................................................................................................................. 10PID ..............................................................................................................................................................................................10PWM........................................................................................................................................................................................... 11VELOCITY MEASUREMENT ......................................................................................................................................................11

PVCS

TATED

IAGRAM.............................................................................................................................................................. 12

SOFTWARE .................................................................................................................................................................................12

GRAPHICAL USER INTERFACE .......................................................................................................................................14

IMPLEMENTATION ISSUES ................................................................................................................................................15

CONCLUSION.............................................................................................................................................................................15


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Introduction

With the rise of just-in-time manufacturing, reliability of the supply chain and thelogistics governing the flow of goods has become mission-critical for many businesses. Our

final project simulates the large mechatronic container crane systems (like those found in the

Port of Oakland) used to unload containers from barges. Arrangement of containers on ships isdeliberate, allowing the use of robotics and automation to speed unloading at the port.

A six degree-of-freedom robot arm is used to simulate the container crane system. We

use Coca-Cola cans in place of semi-sized containers. Cans can be stacked two high, to simulate

the multiple layers of containers commonly found on barges. Our mechatronic system canremove any container desired. If a container is inaccessible due to the fact that it has a container

resting on top of it, the mechatronic system can rearrange the containers to allow for the bottom

container removal.

Demonstration

Our demonstration allows a user with no prior training to operate the barge unloading

mechatronic system. The user simply points and clicks on the desired container and the robot

removes the containers. The robot will automatically rearrange containers as necessary to carryout the users objective. Our setup assumes that containers are in a predetermined location. Our

assumption is not unrealistic in that containers are positioned on the boat in a predetermined,

optimized way to allow for ease of loading/unloading and to allow a ship to contain the greatestnumber of containers.

Figure 1: The five container setup used throughout our demonstration. Cans are configured into

three columns. Two of the columns are stacked two cans high.


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Figure 2: The robot has been commanded to pick up the bottom diet Coke can. The robot first removes the top

diet Coke can to allow access to the bottom can.

Figure 3: Having moved the top diet Coke can to a temporary storage position, the robot now grabs the

desired bottom diet Coke can.


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Figure 4: The robot gives the can a shake to determine whether it is empty or full. This diet Coke can is full,

and thus it is placed as shown.

Figure 5: The robot now retrieves the diet Coke can from the temporary storage position.


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Figure 6: To complete the move, the robot now returns the stored can to its initial position (now at the lower

level).

Figure 7: The robot can also identify empty cans. Here, the robot will pick up the right-most Mountain Dew

can.


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Figure 8: Here, the robot shakes the can to determine whether it is full or empty. Based on the resistance, the

robot realizes that this can is empty.

Figure 9: In contrast to the full can scenario, the robot moves the empty can towards the edge of the table.


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Figure 10: The robot drops the empty can off the table, allowing it to be automatically discarded into a trash

can.

Features / Specifications

Reliable and repeatable removal of individual cans

Point-and-click graphical user interface Removal of containers at various z-positions (multi- layer removal) Rearrangement of containers to allow full access

Automatic tracking of repositioned containers Automatic determination of full / empty containers (damage detection)

Configuration preferences for three, four, or five containers

Task Diagram

The task diagram illustrates the relationships between distinct events that take place in parallel.

Tasks have been divided into a top-level machine control, motor movement task, and GUI task.Separate tasks are also used to implement PID control, PWM, the setpoint profiler, and the

velocity measurement.


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State Diagrams

Each state diagram illustrates a task. Only one state is active for a given task at a time.

Machine Control

Software

Hardware

PID

Motor Movement GUI

Motor 1SetpointProfiler

Task Diagram

Machine Control

PWM

Amp

Motor

Encoder

Motor 2SetpointProfiler

Motor nSetpointProfiler

VelocityMeasurement

PID

PWM

Amp

Motor

Encoder

VelocityMeasurement

PID

PWM

Amp

Motor

Encoder

VelocityMeasurement

Motor Movement State Diagram

Power up

UprightEntry:

Action:

Move from Uprightto Home

Entry:Action: Follow profile

Start=1

Home

Entry:

Action:

At home

Set Sequence

Entry:Determine ifbottom covered,set sequence

(movement)

Move to can

Entry: Loadprofile

Action: Followprofile for eachmotor

Sequenceset

Grab can

Entry:

Action: Closegrip

Move to homeEntry: Load profile

Action: follow profile

Move to targetEntry: set target

load profile

Action: Followprofile

Full IDEntry: Setup

move

Action: Executemove; averageDC

Drop canEntry:

Action: Open

grip

Return homeEntry: Load

profile

Action: Followprofile

At home

Grip openMovedone

Movedone

At homeCan = chosen

Grip closed

Selectcan Move

done

At homeCan = covered


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Motor Setpoint Profilers

GUI

PID

On

Entry: DisplayGUIAction:

Off

Entry: Show GUI

Action:

GUI State Diagram

exit =1

Power up

display =1

Profiler On

Entry:Action: Produceout ut values

Motor Setpoint Profiler State Diagram

Power up

PID OnEntry:Action:Calculate loopoutput

PID State Diagram

Power up


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PWM

Velocity Measurement

The PID, PWM, and velocity measurement, tasks have been combined into a single task, the

PVC (proportional velocity control). The state diagram incorporating all three subtasks is shownbelow.

VelocityMeasurment

Entry:Action: Readvelocity

Velocity Measurement State Diagram

Power up

OffEntry: Turnoutput offAction:

OnEntry: Turn outputon

Action:

PWM State Diagram

time >duty cycle

Power up

time > PWM cycle time


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PVC State Diagram

Software

Control of the robotic manipulator was implemented in Java using state transition logic.

Encoder positions of the robotic manipulator were monitored in order to determine a series of

motions suitable to grasp each can. A home position and a ready position were created toallow for ease of repeatability. The home position put the robot into a fully upright position,

while the ready position placed the robot in a position from which it could easily grasp any

desired can.

HoldEntry: No operation

Action: No operation

AccelEntry: Adjust setpoint

Action: Calculate dutycycle

Decelerate

Entry: Adjust setpointAction: Calculate DutyCycle

Constant VelEntry: Stop motorsAction: Calculate duty

cycleTime > RiseTime + Time at Max

Stop == 1

Zero the positionEntry: No operationAction: Calculate dutycycle

Start_Move ==1

Reach 0

Move to 0command Time > RiseTime +

Start Time


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Figure 11: The 'home' position

Figure 12: The ready position


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Implementation of the control portion of the software requires the use of a proportional-integral-derivative (PID) controller, pulse-width modulation, a setpoint profiler, and velocity

measurement.

Each object is created in a top-level file named Run. Because there are 6 motors in the robotic

arm there are 6 PID controllers, 6 pulse-width modulation objects, and 6 velocity measurementobjects. Each velocity measurement object has a boxcar filter. There are many more setpoint

profilers because each motor has the ability to make several movements; each movement is madeby following a distinct setpoint profile.

Not depicted in the task diagram, there is a motor movement object that sets the setpoint profilerfor each of the motors. A movement is simply a collection of profiles for specific motors, and it

specifies the order in which the motors should successively execute their individual movements.

The movement is called by the machine control in order to set the profilers and order of motor

execution.

The program is constructed such that the user chooses a can from using the GUI, which is

explained in the next section. This triggers the machine control to identify the chosenmovement, which lines up the profiles for each of the motors for that movement. This happens

in the state entitled Set Sequence. Set Sequence specifies the movement to the chosen can and

the movement from the can to back to the home position.

If the GUI-selected can is covered by another can the robot first moves the covering can to a

temporary holding position. Then it returns for the chosen can. When the robot is holding the

chosen can in the home position it makes 1 move to determine whether the can is full or empty.If the can is heavier then it is identified as full and is then moved to the target position. If the

can is lighter then it is identified as empty and is discarded into a trash pile. If the chosen can

was originally covered then the robot returns the covering can to the position that the chosen canpreviously was occupying. The robot arm then returns to home to await the next GUI

command.

Graphical User Interface

All commands used throughout the state transition logic aspects of the software have

been migrated to a graphical user interface to allow operation to occur through a simpler point-

and-click interface. The graphical user interface adds a layer on top of the implementing code.Removal does not prevent operation of the software. Rather, reversion to manual entry of

commands is required.


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Figure 13: The Graphical User Interface. The robotic arm is controlled by a point-and-click interface. The red

Coca-Cola buttons each represent a can.

Figure 14: The Configuration Menu. The GUI allows the user to set preferences as to the number of containers

on board and removes the controls for cans that are absent. Here, the default five-can configuration has been

altered to reflect the presence of just three cans.

Implementation Issues

Our primary implementation issue was coding for repeatable, reliable performance.Subtle differences in the initial position of the robotic manipulator or slight error in coding the

encoder positions could produce drastic errors over many moves and long time periods. To

overcome this difficulty, we created home and ready positions; these positions can be easily

reached from any state and can be precisely and accurately attained each time.

Conclusion

This project has tied together many of the lessons learned throughout the course. We

successfully implemented a real-time control system that serves as a model for similar systems

operating on large mechatronic systems to solve real-world problems. We utilized the principles


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of object-oriented programming including hierarchical design and code reuse, and successfullydeveloped our system using Java. We successfully broke down a complex set of requirements

into small building blocks that were more easily managed successfully debugged those blocks

until they were consistent and reliable, and then integrated the many pieces together. Our project

serves as a demonstration of the complementary nature of object-oriented programming

principles with real- time control systems. We hope the lessons learned from this project willallow us to achieve similar success in future control system software design.

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