Spring      15

Design  Assesment  Board  Report      

   

National  University  of  Sciences  And  Technology  

Pakistan  Navy  Engineering  College  

 Project  Title  

   Design  and  implementation  of  a  Robotic  manipulator  for  Remotely  Operated  Vehicle  

 

Project   Members      

Wasiq  Saleem   2011-­‐-­‐-­‐NUST-­‐-­‐-­‐PNEC-­‐-­‐-­‐BE-­‐-­‐-­‐372  

Fazeel  Ayaz   2011-­‐-­‐-­‐NUST-­‐-­‐-­‐PNEC-­‐-­‐-­‐BE-­‐-­‐-­‐364  

 

Project   Advisor      

CDR  Dr.  Attaullah  Memon            

     

Certificate    

This is to certify that the Design Assessment board entitled, “Design and implementation of a Robotic manipulator for Remotely Operated Vehicle” submitted by Wasiq Saleem and Fazeel Ayaz in partial fulfillment of the requirements for the award of Final Year Project of Bachelor of Engineering Degree in Electronics Engineering at Pakistan Navy Engineering College (PNEC), National University of Sciences & Technology (NUST) is an authentic work carried out by them under my supervision and guidance.

To the best of our knowledge, the matter embodied in this Report has not been submitted to any other University/Institute for the award of any Degree or Diploma.

CDR. DR. Attaullah Memon Assistant Professor Department of Electronics & Power engineering Pakistan Navy Engineering College Dated: 26th Mar 2015

Table  of  Contents  

ABSTRACT 5  

INTRODUCTION 6  

STRUCTURE  OF  THE  ARM 7  

GRIPPER 7  ELBOW 8  MATERIAL  OF  FABRICATION 9  Method  of  Fabrication  

Controlling  Mechanism   18  

SERVO  MOTOR 19    

 

 

     ABSTRACT  

 

A robot is a system combining many subsystems that interact among themselves as well as with the environment in which the robot works. In robotics, end effectors/gripper is a device at the end of a robotic arm, designed to interact with the environment. Gripper is an end effectors or tool to grasp any physical. To achieve this function we intend to integrate a simple linkage actuation mechanism. The gripper to be used in our robotic manipulator performs basic function of picking, holding and grasping of objects by means of a DC motor. The design and flexibility of a human hand is the main tool in designing our robotic manipulator. It can be function near to human’s ability of grasping and manipulation if coupled with wrist and elbow.

Robots are normally used in conjunction with auxiliary devices such as machines and fixtures but in our case it is ROV. Due to technological advancement robot has become an integral device, hence it has can be used where presence of human is not feasible. The gripper can perform the basic function of picking, holding, rotating and grasping of objects by means of a DC motor.

Introduction:    Oceans are an attractive environment because of abundant mineral resources, energy, space, and so on, and recently lots of research is being carried out in this field. However, the extreme conditions such as high water pressure, invisibility and non-oxygen become great barriers for human to access directly. Underwater robotic manipulator are designed and fabricated in a way in perform efficiently like human arm, hence replacing their need. In order to realize underwater robotics, the intelligence and accuracy of robots are crucial factors to be researched and ROVs are the new tools for major underwater exploration operations. The need for ROVs to perform more and more complex task and to propagate in areas where humans can’t is an inspiration in terms of research and work done in this field. Therefore, manipulators which are mounted on ROVs are expected to play a crucial role for complex tasks

A robotic manipulator is a mechanical structure functioning like a human arm. It is programmed to function in a matter in which we want it to. During designing of this arm, links are connected via joints allowing either a linear motion or a rotational motion in various planes. In industrial robots sensor are used for feedback which indicates the controller about the hardness by which the gripping is done by arm or directs the arm in directions in which it should move to perform the task or even tells the system about presence of object in front of it.

Various aspects needs to be considered while designing a robotic arm that are torque calculation for motor used, amount of weight it can carry, interfacing to remote controller, ways for interfacing it with ADC (analog-to-digital converter).We have designed this robotic arm using servos, ATmega32 microcontroller with interfacing analog joystick controller.

STRUCTURE  OF  THE  ARM:  The mechanical design of a robotic arm is based on a robotic manipulator with similar function like a human arm. In order to establish a generalized operating systems and the technological systems for the analysis, design, integration and implementation of a humanoid robotic arm.

Gripper:

It is the mentor of the robotic arm we intend to fabricate, as it will enable us to do all the required underwater tasks.

Features of aluminum gripper

• Sleeves in the joints improve rigidity and eliminate the need for adjustment. • A specific gear ratio increases gripping torque while utilizing the full travel of

the servo. • A spring loaded clutch protects the servo gear train while providing spring

tension for gripping objects.

3D CAD Model of our Robotic Manipulator

Elbow

The material we are using for this part is made of Aluminum, which is light and cheap. To support the structure and to maintain it balance during movement rods are inserted between the arm in horizontal direction. About 90% of the whole space, which this elbow takes, is empty which makes the weight of the robotic arm quite low. When ROV is working in the water the structure of the robotic arm can vibrate a little because of the pressure inside water to overcome this problem the Aluminum parts are thin so they can stretch a bit making them elastic.

The Elbow joint was of primary importance in the design of our robotic arm. Due to the weight of the arm and its overall length, the imposing moment on this joint is substantial.

This part should be made to attach the Arm firmly with ROV. The position of the elbow will not change during movement of the Arm and because it has to sustain all the load of the rest of the Arm the Gear Ration is kept high. The dimensions are kept small in order to make space for the rest of the electronics that are to be attached with the ROV.

This part of the robotic arm has to bear the entire load that is on rest of the arm. The material to be used for this is also aluminum.

Why chose Aluminum? Pure aluminum is a silvery-white metal with many desirable characteristics. It is light, non toxic (as the metal), non magnetic and non sparking. It is decorative. It is easily formed, machined, and cast. Alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Strength depends on purity. 99.996 per cent pure aluminum has a tensile strength of about49 mega Pascal (MPa), rising to 700 MPa following alloying and suitable heat treatment. Although not found free in nature, Aluminum an abundant element in the earth’s crust. A key property is low density. Aluminum is only one-third the weight of steel. Aluminum and most of its alloys are highly resistant to most forms of corrosion. The metal’s natural coating of aluminum oxide provides a highly effective barrier to the ravages of air, temperature, moisture and chemical attack. Aluminum is a superb conductor of electricity. This property allied with other intrinsic qualities has ensured the replacement of copper by aluminum in many situations. Aluminum is non-magnetic and non-combustible, properties invaluable in advanced industries such as electronics or in offshore structures. Aluminum is non-toxic and impervious, qualities that have established its use in the food and packaging industries since the earliest times. Other valuable properties include high reflectivity, heat barrier properties and heat conduction.

The metal is malleable and easily worked by the common manufacturing and shaping processes.

   

Wire cutting process:  The Design process of our Robotic arm is completed. We finally have what we wanted. The last thing that remains is the process of manufacturing the arm.There are two things that are of great concern for us while manufacturing the Robotic arm , (i) The process should be accurate , (ii) It should not take a very long time.  Advantages  of  Wire  cutting  process:    

1) Efficient Production Capabilities - Because of the precision and high-speed of machines.

2) Reliable Repeatability - The constant reliability of wire EDM is one of the greater advantages of this process. Because the programs are computer generated and the electrode is constantly being fed from a spool (the wire electrode is used only once), the last part is identical to the first part. The cutter wear found in conventional machining does not exist. In addition, tighter machining tolerances can be maintained without additional cost.

3) Reduced Costs - The high-speed cutting Wire EDM machines of today have

dramatically reduced costs for many manufactured parts. Conventional machining often leaves sharp edges and burrs, but a radius can be made with Wire EDM without any additional cost. This eliminates a filing or sanding operation.

4) Unlimited Possibilities - Many parts can be economically produced with wire EDM, such as: precision gages and templates, keyways, shaft and collet slots, splitting tubes, gears, internal splines, hexes, cams, extrusion molds, punches and dies from one piece of tool steel, short run stampings from stacked material, and many other exotic shapes.

5) Exotic Materials - Wire EDM can cut any electrically conductive material hard

or soft. In fact, the EDM manufactures use hardened D2 to rate the cutting speed of their machines. Hardened D2 cuts faster than cold roll steel. What can become a nightmare with conventional machining, does not faze wire EDM at all.

How does Wire EDM work?

1) EDM stands for "Electrical Discharge Machine".

2) An electrical charge is applied to an electrode, a brass wire, copper, sterling, or graphite.

3) The electrode then makes a electrical connection with the steel.

4) A spark jumps from the electrode to the work piece and disintegrates the

steel with a controlled electrical charge.

5) This process happens thousands of times per second. The mirror image of the electrode is formed in the work piece.

   

The various stages we went through while designing is frequently depicted in these sequence of events.    

   

   

   

   

   

     

 

Laser Cutting The laser cutting process uses a strong focused laser beam, produced by a laser diode. The high energetic laser beam heats the surface of the material and melts.Laser cutting offers a high precision, CNC controlled method of cutting plastic, metallic and thin ceramic components. It is a mechanised, thermal, non-contact process capable of cutting most materials with a high degree of precision and accuracy.

Advantages of Laser cutting:

• Laser light can be well focused from 2" (50 mm) to .007" (.2 mm). • Variable cutting speeds. • laser cutting is used in the most diverse areas, specifically wherever high

accuracy for the component geometry and the cut edge is required. • Minimum material is melted and the laser energy is used very efficiently. • No material deformation due to contactless material processing • Clean cut edges without burr or dust formation.

Disadvantages of Laser cutting:

• When using the laser-cutting process for plastic, the fumes that the plastic produces when melted can be toxic. This means that the machine will need to be placed in a well-ventilated environment, which can take a lot of time and money to create.

• Rate of production is not consistent when laser cutting is used. It highly

depends on thickness of the workpiece, type of material, and type of laser used.

• Carelessness in adjusting laser distance and temperature may lead to burning of some materials. Certain metals tend to discolor if the intensity of the laser beam is not as per requirement

3D printing 3D printing (or additive manufacturing, AM) is any of various processes used to make a three-dimensional object. In 3D printing, additive processes are used, in which successive layers of material are laid down under computer control. These objects can be of almost any shape or geometry, and are produced from a 3D model or other electronic data source. A 3D printer is a type of industrial robot.

Advantages

• Additive manufacturing gives great freedom in design.

• Metal 3D printing can produce highly customized parts with added improved functionalities that are not possible through traditional processes.

• Different types of alloys suits perfectly the needs of lightweight applications.

• Mixing different raw materials as titanium, aluminium, stainless steel or nickel

based alloys and constantly discovering new alloys with various strength and temperature resistance is close to impossible trough conventional manufacturing methods.

• Doesn’t require any additional tooling.

Controlling  Mechanism  During early discussions we thought to use BLDC motors to provide controlling for the robotic arm. BLDC motors have high torque and normal BLDC motors can lift up to 10 kg of load from the ground. But the idea of using BLDC motors was punctured because they require very high current and since our arm would be working in the water about 10’s of amperes of current could damage the whole system if some fault occurs. Other problem with BLDC motor was it’s complex controlling mechanism. We needed Hall sensors to detect the position of the poles inside the BLDC motors to keep the motor rotating as we desire. Further problems that forced us to use servo motor was that we couldn’t find our required BLDC motor on internet and in different markets in Karachi. Using Servo motors comforted us in many ways.

Advantages for us for using servo motors: • It was easy to find the best one which suited our project. • The controlling mechanism was simple. • Servomotors that are used in boats are water proof (Water proof servo motor

was a bonus for us). • We easily decided what number of servo motors do we need • Servo motors required less current than first chosen BLDC motors. • We had a good past experience on working with servo motors (we had done

many mini projects before in which we used servo motors). • Servomotors don’t cost much. • No additional motor controlling drivers were required .We only needed a micro

controller and a power supply. • Servos are best for robotics.

At the start of our project we decided to make a 3D robotic arm but due to the flexibility in controlling which servomotors provided we shifted to a higher level, we decided to make a 4D robotic manipulator.

When we are working with servomotor the speed of rotation becomes a main problem. As the load increases the speed of the servomotor slows down. In order to maintain the speed we had to decrease the load by decreasing the weight of the arm. That was also a reason why we decided to use Aluminum instead of other metal. Our decision was to use Vigor VSD-11YMB HV servo motor which has maximum torque of 40 kgf.cm.

  After when we had selected which servo motor are we using we searched more and more on servo motors because we wanted to make our robotic arm suitable for our ROV. Before going into further detail I would like to explain first about servo motors. Servo motors:

Servo refers to an error sensing feedback control, which is used to correct the performance of a system. Servo or RC Servo Motors are DC motors equipped with a servo mechanism for precise control of angular position. The RC servomotors usually have a rotation limit from 90° to 180°. But servos do not rotate continually. Their rotation is restricted in between the fixed angles. The Servos are used for precision positioning. They are used in robotic arms and legs, sensors canners and in RC toys like RC helicopter, airplanes and cars.

The Servomotors come with three wires or leads. Two of these wires are to provide ground and positive supply to the servo DC motor. The third wire is for the control signal. These wires of a servomotor are color coded. The red wire is the DC supply lead and must be connected to a DC voltage supply in the range of 4.8V to 6V.The black wire is to provide ground. The color for the third wire (to provide control signal) varies for different manufacturers. It can be yellow (in case of Hitec), white

(in case of Futaba), brown etc. Unlike DC motors, reversing the ground and positive supply connections does not change the direction (of rotation) of a servo. This may, in fact, damage the servomotor. That is why it is important to properly account for the order of wires in a servomotor.

  Servo Control program - Moves a Servomotor through a range of positions in response to the position of a Potentiometer attached to an Analog input. #include <Servo.h> // Comes with Arduino IDE /*-----( Declare Constants and Pin Numbers )-----*/ #define ServoPINone 9 #define ServoPINtwo 3 #define ServoPINthree 5 #define ServoPINfour 6 #define PotPinone A1 // Analog input 0 (zero) #define PotPintwo A1 // Analog input 1 (one) #define PotPinthree A2 // Analog input 2 (two) #define PotPinfour A3 // Analog input 3 (three) #define ServoMIN 88 // Don't go to very end of servo travel #define ServoMAX 98 // which may not be all the way from 0 to 180. Servo myservo_one; // create servo object to control a servo Servo myservo_two; Servo myservo_three; Servo myservo_four

  int PotValueone; // User moves the pot. int PotValuetwo; int PotValuethree; int PotValuefour; int Positionone; // variable to store the servo position int Positiontwo; int Positionthree; int Positionfour; void setup() { myservo_one.attach(ServoPINone); // attaches the servo on pin 9 to the servo object myservo_two.attach(ServoPINtwo); myservo_three.attach(ServoPINthree); myservo_four.attach(ServoPINfour); } void loop() { //for servo one PotValueone = analogRead(PotPinone); // Get the value as user moves pot Positionone = map(PotValueone, 0, 1023, ServoMIN , ServoMAX); // scale it to use it with the servo (value between MIN and MAX) myservo.write(Positionone); // tell servo to go to position

  // for servo two PotValuetwo = analogRead(PotPintwo); Positiontwo = map(PotValuetwo, 0, 1023, ServoMIN , ServoMAX); myservo.write(Positiontwo); //for servo three PotValuethree = analogRead(PotPinthree); Positionthree = map(PotValuethree, 0, 1023, ServoMIN , ServoMAX); myservo.write(Positionthree); // for servo four PotValuefour = analogRead(PotPinfour); Positionfour = map(PotValuefour, 0, 1023, ServoMIN , ServoMAX); myservo.write(Positionfour); delay(100); // wait for the servo to reach the position }

 

 Circuit  Diagram  

     

 

Using Joystick in place of potentiometer

How does it work? To provide a controller to our servo controlling mechanism we need something that varies with it’s resistance (because using simple potentiometers for this purpose is not a grand idea).Now, Let’s imagine a volume control or other knob. These controls are generally made from potentiometers, which are variable resistors. By connecting the potentiometer as a voltage divider, we can get a varying voltage out of the device, which can be fed to an Arduino microprocessor. This allows the servos to rotate the way we want.

The joystick which we intend to use now contains two potentiometers. These potentiometers connected with a gymbal mechanism that separates the "horizontal" and "vertical" movements. (If the joystick is flat on a table, these movements are more "front / back" and "left / right", but you get the idea.) The potentiometers are the two blue boxes on the sides of the joystick. If moved the joystick while watching the center shaft of each potentiometer, it can be seen that each of the potentiometers pick up movement in only one direction. Clever, isn't it!

Gimbal Mechanism:

The problems that we extensively confronted with the designing of this project were, that we as students of Electronics Engineering were not familiar with all the stuff related to mechanics. We only knew basics mechanical physics which we studied in high school. This all meant that we had to do a lot of research work in order to develope a perfect design that would suit the ROV.

Both of us never heard these words gimbal mechanism. This is one of those things that we came over for the first time.

A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be

 

used to allow an object mounted on the innermost gimbal to remain independent of the rotation of its support (e.g. vertical in the first animation). For example, on a ship, the gyroscopes, shipboard compasses, stoves, and even drink holders typically use gimbals to keep them upright with respect to the horizon despite the ship's pitching and rolling

Gimbal mechanism allows us to control two servos with a single joystick. It also allowed us to limit the number of joystick to only 2 joysticks for four servos. If this was not the case and we had to go with four joysticks in one controller board then we had to design a large controller which would then look very ugly.

This joystick also contains a switch which activates pushed down on the cap. The switch is the small black box on the rear of the joystick. If pushed down on the cap,we can see a lever pushing down on the head of the switch. The lever works no matter what position the joystick is in. Cool!

Transmission  meduim:  There  are  two  types  of  transmission  meduim  (i)  wired  and  (ii)  wireless.  The  second  group  under  Mr.  Noman  Ashraf  which  is  designing  ROV  has  stick  towards  a  wired  medium  for  transferring  data.They  have  planned  to  bind  all  the  power  and  the  signal  wires  togather  and  attach  it  with  ROV  as  a  single  cable.So,  as  they  have  demanded  we  can’t  go  for  a  wireless  channel  because  other  wise  we  would  have  ROV  that  will  be  controlled  by  a  wired  mechanism  and  a  Robotic  arm  attached  that  will  be  controlled  via  wireless  channel.There  are  other  reasons  for  why  a  wire  medium  is  better  for  this  project.        

 

 Wireless  medium  for  this  project  is  not  suitable  in  all  situations  shown  below:  

1) Very  expensive    

2) Will  require  more  power.    

3) Water  is  good  absorber  for  radio  wave  under  water.    

4) Not  good  for  long  distance  experiments.    

5) The  wireless  network  would  be  slower.    To  cope  with  the  above  situation  we  require  under  water  wired  communication.  

Ethernet  Cable(Cat-­‐5):  Category 5 cable (cat 5) is a twisted pair cable for carrying signals. This type

of cable is used in structured cabling for computer networks such as Ethernet.

The cable standard provides performance of up to 100 MHz and is suitable

for10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet).

Cat 5 is also used to carry other signals such as telephony and video.This cable is

commonly connected using punch-down blocks and modular connectors. Most

category 5 cables are unshielded, relying on the balanced line twisted pair design

and differential signalling for noise rejection.

Category 5 has been superseded by the category 5e (enhanced)

specification and category 6 cable.

     

           

 

   Cable  standard  The specification for category 5 cable was defined in ANSI/TIA/EIA-568-A.

Each of the four pairs in a cat 5 cable has differing precise number of twists per metre to minimize crosstalk between the pairs. Although cable assemblies containing 4 pairs are common, category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs.

The cable is available in both stranded and solid conductor forms. The stranded form is more flexible and withstands more bending without breaking. Permanent wiring (for example, the wiring inside the wall that connects a wall socket to a central patch panel) is solid-core, while patch cables (for example, the movable cable that plugs into the wall socket on one end and a computer on the other) are stranded.

The specific category of cable in use can be identified by the printing on the side of the cable.

 

   Most Category 5 cables can be bent at any radius exceeding approximately four times the outside diameter of the cable. The maximum length for a cable segment is 100 m which is enough for this project .

Applications  This type of cable is used in structured cabling for computer networks such as Ethernet over twisted pair. Cat 5 is also used to carry other signals such as telephony and video.

 

Power Supply: About 48V(DC) and 40A(max) will be available for us from the main power supply board.The reason for these limitations are that since we are working under water we cant allow very high currents and voltages under water.There are two problems now, (i) 48V is much greater than our operating voltage that is 5-7 V ,so we have to step down the voltage using DC-DC converters.(ii)40A is for whole ROV so the current is also limited.

First we will look at how much current is available to us

Component Current required (max) Operating voltage

Thrusters 10A x 4 12V

Camera 2A x 2 12V

Lights 0.5 x 2 24V

Servo motors 4Ax4 5-7V

Arduino microcontroller 0.5A x 2 5V

 

Figure below shoes wave form of a step down converter.

The output voltage and current of a DC-DC converter is the average of the above waveforms. As t1 gets smaller average value decreases and so the output voltage.

Value of the Load Current and voltage at output

The value of k(duty cycle) is between 0-1.If k decrease the output voltage will also decrease. But the current will increase by amount 1/k , this is because the power at input is equal to the power at output.

 

By decreasing the voltage at the output the current rating of the supply can be increased by the same ratio. For example if the whole robotic arm requires 20A and 5V then this would be equal to 48V and 2A.We can increase the current at the output by decreasing the voltage using buck converters.

48V to 24V Step Down Regulator

Takes 48V input and outputs 24V.The maximum output current is 10A.It water proof and has high conversion efficiency. Working temperature is between -40 °C ~ +85 °C. Features:

• Stable performance, waterproof, Damp-proof & anti-shock protection

• With output short circuit protection, Overheat protection

• Input voltage: DC 48V

• Output voltage: 24V

 

• Output power: 240W • Rated output current: 10A • Conversion efficiency: up to 95% • Applications: Bus, CMB, large trucks, motor car, solar power, bus display, taxi

advertising screen, car audio, LCD TV, LED, intercom and monitoring system.

 

Buck  DC  Voltage  Converter  24V  to  5V  

 

Features:

Input voltage: DC 24V Output voltage: DC 5V Output Current: 10A MAX Enough power, stable performance Efficiency: more than 96% Used in Motors, audio, gps navigation, surveillance, LED car display, air conditioning, electric fans, solar energy, photovoltaic energy, DVD, LED lights, motors, pumps, electrical appliances and industrial equipment .

             

 

Application   • Science ! Seafloor mapping ! Rapid response to oceanographic and ! Geothermal events ! Geological sampling

• Environment ! Long term monitoring (e.g., hydrocarbon Spills, radiation

leakage, pollution) ! Environmental remediation ! Inspection of underwater structures, including pipelines,

dams, etc.

• Military ! Shallow water mine search and disposal ! Submarine off-board sensors

• Ocean mining ! Ocean survey and resource assessment and oil industry ! Construction and maintenance of undersea structures

• Other applications ! Ship hull inspection and ship tank internal inspection ! Nuclear power plant inspection ! Underwater communication & power cables installation

and inspection ! Entertainment-underwater tours ! Fisheries-underwater ranger

   

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