Presentation Slide Show For Final Year Project

Research: Robotic Arm

The robot arm is probably the most mathematically complex robot you could ever build. As such, this tutorial can't tell you everything you need to know. Instead, I will cut to the chase and talk about the bare minimum you need to know to build an effective robot arm. 


Degrees of Freedom (DOF) 
The degrees of freedom, or DOF, is a very important term to understand. Each degree of freedom is a joint on the arm, a place where it can bend or rotate or translate. You can typically identify the number of degrees of freedom by the number of actuators on the robot arm. Now this is very important - when building a robot arm you want as few degrees of freedom allowed for your application!!! Why? Because each degree requires a motor, often an encoder, and exponentially complicated algorithms and cost. 


Denavit-Hartenberg (DH) Convention 
The Robot Arm Free Body Diagram (FBD) 

The Denavit-Hartenberg (DH) Convention is the accepted method of drawing robot arms in FBD's. There are only two motions a joint could make: translate and rotate. There are only three axes this could happen on: x, y, and z (out of plane). Below I will show a few robot arms, and then draw a FBD next to it, to demonstrate the DOF relationships and symbols. Note that I did not count the DOF on the gripper (otherwise known as the end effector). The gripper is often complex with multiple DOF, so for simplicity it is treated as separate in basic robot arm design. 4 DOF Robot Arm, three are out of plane: 3 DOF Robot Arm, with a translation joint: 5 DOF Robot Arm: Notice between each DOF there is a linkage of some particular length. Sometimes a joint can have multiple DOF in the same location. An example would be the human shoulder. The shoulder actually has three coincident DOF. If you were to mathematically represent this, you would just say link length = 0.   Also note that a DOF has its limitations, known as the configuration space. Not all joints can swivel 360 degrees! A joint has some max angle restriction. For example, no human joint can rotate more than about 200 degrees. Limitations could be from wire wrapping, actuator capabilities, servo max angle, etc. It is a good idea to label each link length and joint max angle on the FBD. (image credit: Roble.info) Your robot arm can also be on a mobile base, adding additional DOF. If the wheeled robot can rotate, that is a rotation joint, if it can move forward, then that is a translational joint. This mobile manipulator robot is an example of a 1 DOF arm on a 2 DOF robot (3 DOF total). Robot Workspace The robot workspace (sometimes known as reachable space) is all places that the end effector (gripper) can reach. The workspace is dependent on the DOF angle/translation limitations, the arm link lengths, the angle at which something must be picked up at, etc. The workspace is highly dependent on the robot configuration. Since there are many possible configurations for your robot arm, from now on we will only talk about the one shown below. I chose this 3 DOF configuration because it is simple, yet isnt limiting in ability. Now lets assume that all joints rotate a maximum of 180 degrees, because mostservo motors cannot exceed that amount. To determine the workspace, trace all locations that the end effector can reach as in the image below. Now rotating that by the base joint another 180 degrees to get 3D, we have this workspace image. Remember that because it uses servos, all joints are limited to a max of 180 degrees. This creates a workspace of a shelled semi-sphere (its a shape because I said so). If you change the link lengths you can get very different sizes of workspaces, but this would be the general shape. Any location outside of this space is a location the arm cant reach. If there are objects in the way of the arm, the workspace can get even more complicated. Here are a few more robot workspace examples:   Cartesian Gantry Robot Arm   Cylindrical Robot Arm   Spherical Robot Arm   Scara Robot Arm   Articulated Robot Arm Mobile Manipulators A moving robot with a robot arm is a sub-class of robotic arms. They work just like other robotic arms, but the DOF of the vehicle is added to the DOF of the arm. If say you have a differential drive robot (2 DOF) with a robot arm (5 DOF) attached (see yellow robot below), that would give the robot arm a total sum of 7 DOF. What do you think the workspace on this type of robot would be? Force Calculations of Joints This is where this tutorial starts getting heavy with math. Before even continuing, I strongly recommend you read the mechanical engineering tutorials for statics anddynamics. This will give you a fundamental understanding of moment armcalculations. The point of doing force calculations is for motor selection. You must make sure that the motor you choose can not only support the weight of the robot arm, but also what the robot arm will carry (the blue ball in the image below). The first step is to label your FBD, with the robot arm stretched out to its maximum length.

Choose these parameters: weight of each linkage weight of each joint weight of object to lift length of each linkage

Next you do a moment arm calculation, multiplying downward force times the linkage lengths. This calculation must be done for each lifting actuator. This particular design has just two DOF that requires lifting, and the center of mass of each linkage is assumed to be Length/2. Torque About Joint 1:
M1 = L1/2 * W1 + L1 * W4 + (L1 + L2/2) * W2 + (L1 + L3) * W3
Torque About Joint 2:
M2 = L2/2 * W2 + L3 * W3
As you can see, for each DOF you add the math gets more complicated, and the joint weights get heavier. You will also see that shorter arm lengths allow for smaller torque requirements.

Too lazy to calculate forces and torques yourself? Try my robot arm calculatorto do the math for you.

Forward Kinematics Forward kinematics is the method for determining the orientation and position of the end effector, given the joint angles and link lengths of the robot arm. To calculate forward kinematics, all you need is highschool trig and algebra. For our robot arm example, here we calculate end effector location with given joint angles and link lengths. To make visualization easier for you, I drew blue triangles and labeled the angles. Assume that the base is located at x=0 and y=0. The first step would be to locate x and y of each joint. Joint 0 (with x and y at base equaling 0):
x0 = 0 y0 = L0
Joint 1 (with x and y at J1 equaling 0):
cos(psi) = x1/L1 => x1 = L1*cos(psi) sin(psi) = y1/L1 => y1 = L1*sin(psi)
Joint 2 (with x and y at J2 equaling 0):
sin(theta) = x2/L2 => x2 = L2*sin(theta) cos(theta) = y2/L2 => y2 = L2*cos(theta)
End Effector Location (make sure your signs are correct):
x0 + x1 + x2, or 0 + L1*cos(psi) + L2*sin(theta) y0 + y1 + y2, or L0 + L1*sin(psi) + L2*cos(theta) z equals alpha, in cylindrical coordinates
The angle of the end effector, in this example, is equal to theta + psi.Too lazy to calculate forward kinematics yourself? Check out my Robot Arm Designer v1 in excel. Inverse Kinematics Inverse kinematics is the opposite of forward kinematics. This is when you have a desired end effector position, but need to know the joint angles required to achieve it. The robot sees a kitten and wants to grab it, what angles should each joint go to? Although way more useful than forward kinematics, this calculation is much more complicated too. As such, I will not show you how to derive the equation based on your robot arm configuration. Instead, I will just give you the equations for our specific robot design:
psi = arccos((x^2 + y^2 - L1^2 - L2^2) / (2 * L1 * L2)) theta = arcsin((y * (L1 + L2 * c2) - x * L2 * s2) / (x^2 + y^2)) where c2 = (x^2 + y^2 - L1^2 - L2^2) / (2 * L1 * L2); and s2 = sqrt(1 - c2^2);
So what makes inverse kinematics so hard? Well, other than the fact that it involvesnon-linear simultaneous equations, there are other reasons too. First, there is the very likely possibility of multiple, sometimes infinite, number of solutions (as shown below). How would your arm choose which is optimal, based on torques, previous arm position, gripping angle, etc.? There is the possibility of zero solutions. Maybe the location is outside the workspace, or maybe the point within the workspace must be gripped at an impossible angle. Singularities, a place of infinite acceleration, can blow up equations and/or leave motors lagging behind (motors cant achieve infinite acceleration).And lastly, exponential equations take forever to calculate on a microcontroller. No point in having advanced equations on a processor that cant keep up. Too lazy to calculate inverse kinematics yourself? Check out my Robot Arm Designer v1 in excel. Motion Planning Motion planning on a robot arm is fairly complex so I will just give you the basics. Suppose your robot arm has objects within its workspace, how does the arm move through the workspace to reach a certain point? To do this, assume your robot arm is just a simple mobile robot navigating in 3D space. The end effector will traverse the space just like a mobile robot, except now it must also make sure the other joints and links do not collide with anything too. This is extremely difficult to do . . . What if you want your robot end effector to draw straight lines with a pencil? Getting it to go from point A to point B in a straight line is relatively simple to solve. What your robot should do, by using inverse kinematics, is go to many points between point A and point B. The final motion will come out as a smooth straight line. You can not only do this method with straight lines, but curved ones too. On expensive professional robotic arms all you need to do is program two points, and tell the robot how to go between the two points (straight line, fast as possible, etc.). For further reading, you could use the wavefront algorithm to plan this two point trajectory. Velocity (and more Motion Planning) Calculating end effector velocity is mathematically complex, so I will go only into the basics. The simplest way to do it is assume your robot arm (held straight out) is a rotating wheel of L diameter. The joint rotates at Y rpm, so therefore the velocity is
Velocity of end effector on straight arm = 2 * pi * radius * rpm
However the end effector does not just rotate about the base, but can go in many directions. The end effector can follow a straight line, or curve, etc. With robot arms, the quickest way between two points is often not a straight line. If two joints have two different motors, or carry different loads, then max velocity can vary between them. When you tell the end effector to go from one point to the next, you have two decisions. Have it follow a straight line between both points, or tell all the joints to go as fast as possible - leaving the end effector to possibly swing wildly between those points. In the image below the end effector of the robot arm is moving from the blue point to the red point. In the top example, the end effector travels a straight line. This is the only possible motion this arm can perform to travel a straight line. In the bottom example, the arm is told to get to the red point as fast as possible. Given many different trajectories, the arm goes the method that allows the joints to rotate the fastest. Which method is better? There are many deciding factors. Usually you want straight lines when the object the arm moves is really heavy, as it requires the momentum change for movement (momentum = mass * velocity). But for maximum speed (perhaps the arm isn't carrying anything, or just light objects) you would want maximum joint speeds. Now suppose you want your robot arm to operate at a certain rotational velocity, how much torque would a joint need? First, lets go back to our FBD: Now lets suppose you want joint J0 to rotate 180 degrees in under 2 seconds, what torque does the J0 motor need? Well, J0 is not affected by gravity, so all we need to consider is momentum and inertia. Putting this in equation form we get this: torque = moment_of_inertia * angular_acceleration breaking that equation into sub components we get: torque = (mass * distance^2) * (change_in_angular_velocity / change_in_time) and change_in_angular_velocity = (angular_velocity1)-(angular_velocity0) angular_velocity = change_in_angle / change_in_time Now assuming at start time 0 that angular_velocity0 is zero, we get torque = (mass * distance^2) * (angular_velocity / change_in_time) where distance is defined as the distance from the rotation axis to the center of mass of the arm: center of mass of the arm = distance = 1/2 * (arm_length) (use arm mass) but you also need to account for the object your arm holds: center of mass of the object = distance = arm_length (use object mass) So then calculate torque for both the arm and then again for the object, then add the two torques together for the total: torque(of_object) + torque(of_arm) = torque(for_motor)And of course, if J0 was additionally affected by gravity, add the torque required to lift the arm to the torque required to reach the velocity you need. To avoid doing this by hand, just use the robot arm calculator. But it gets harder . . . the above equation is for rotational motion and not for straight line motions. Look up something called a Jacobian if you enjoy mathematical pain =P

Arm Sagging Arm sagging is a common affliction of badly designed robot arms. This is when an arm is too long and heavy, bending when outwardly stretched. When designing your arm, make sure the arm is reinforced and lightweight. Do a finite element analysis to determine bending deflection/stress such as I did on my ERP robot:

Keep the heaviest components, such as motors, as close to the robot arm base as possible. It might be a good idea for the middle arm joint to be chain/belt driven by a motor located at the base (to keep the heavy motor on the base and off the arm). The sagging problem is even worse when the arm wobbles between stop-start motions. The solve this, implement a PID controller so as to slow the arm down before it makes a full stop. Sensing Most robot arms only have internal sensors, such as encoders. But for good reasons you may want to add additional sensors, such as video, touch, haptic, etc. A robot arm without video sensing is like an artist painting with his eyes closed. Using basic visual feedback algorithms, a robot arm could go from point to point on its own without a list of preprogrammed positions. Giving the arm a red ball, it could actually reach for it (visual tracking and servoing). If the arm can locate a position in X-Y space of an image, it could then direct the end effector to go to that same X-Y location (by using inverse kinematics). If you are interested in learning more about the vision aspect of visual servoing, please read the Computer Vision Tutorials for more information. Haptic sensing is a little different in that there is a human in the loop. The human controls the robot arm movements remotely. This could be done by wearing a special glove, or by operating a miniature model with position sensors. Robotic arms for amputees are doing a form of haptic sensing. Also to note, some robot arms have feed back sensors (such as touch) that gets directed back to the human (vibrating the glove, locking model joints, etc.).

Tactile sensing (sensing by touch) usually involves force feedback sensors andcurrent sensors. These sensors detect collisions by detecting unexpected force/current spikes, meaning a collision has occurred. A robot end effector can detect a successful grasp, and not grasp too tight or too lightly, just by measuring force. Another method would be to use current limiters - sudden large current draws generally mean a collision/contact has occurred. An arm could also adjust end effector velocity by knowing if it is carrying a heavy object or a light object - perhaps even identify the object by its weight.

http://www.societyofrobots.com/robot_arm_tutorial.shtml

Work Plan

The time frame allocated for this research study is 11 months. It will start in January S1’2012 and is projected to be completed in November S2’2012. The Gantt chart for the project and its milestone are shown as in Table 1.

ID	Task Name	Duration(days)	Start	End
1	Start	70	1-16-12	4-12-12
2	Introduction	22	1-16-12	2-7-12
3	Discuss about project area	2	1-16-12	1-18-12
4	Choose the title	1	1-16-12	1-16-12
5	Discuss project with advisor	1	1-16-12	1-16-12
6	RESEARCH	18	1-16-12	2-3-12
7	Research project	4	1-16-12	1-20-12
8	Proposal guidline	10	1-16-12	1-26-12
9	Methodology	3	2-1-12	1-3-12
10	Technology	1	2-6-12	2-6-12
11	Survey the component part	5	2-7-12	2-12-12
12	Listing component	5	2-7-12	2-12-12
13	Meeting with advisor	43	2-14-12	4-5-12
14	Discuss about the project	6	2-14-12	2-20-12
15	Remark the component	9	2-22-12	3-2-12
16	Survey the price and the function	9	2-22-12	3-2-12
17	Creating slide presentation	11	3-1-12	3-11-12
18	Set up the information	11	3-2-12	3-12-12
19	Progres report due	10	3-29-12	4-12-12
20	Presentation Day	1	4-12-12	4-12-12

Intelligent Fire Fighting System

Introduction

Firefighting is the act of extinguishing fires. A firefighter fights fires to prevent loss of life, and/or destruction of property and the environment. Firefighting is a highly technical skill that requires professionals who have spent years training in both general firefighting techniques and specialized areas of expertise.

The word robot was derived from Czech word robota which means “a forced laborer” then later a well known Russian science fiction writer Isaac Asimov coined the word robotics. From there on various different developments are being successfully done till date in the field of robotics in the form of teleoperated manipulators, humanoids , micro robots etc. as the trend of the industry is moving from the current state of automation to robotization . Thus the robot technology is advancing rapidly. Now a days the most commonly used robots in industry is a robotic manipulator or a robotic arm .Robotic arm is basically an open closed kinematics chain of rigid links interconnected by movable joints. The end of the arm is connected to the end-effectors. The end-effector maybe a tool and its fixture or a gripper or any other device to do the work. The end-effector is similar to the human hand with or without fingers.

Objective

The purpose of our project is to extinguish a flame in a certain amount of time and having to get through an obstacle course all at once. The robot has to see a line without crossing it. Touch a wall without knocking it down and identifying a flame and extinguishing it.

Benefits / Contributions

Firefighters' goals are to save life, property and the environment. A fire can rapidly spread and endanger many lives; however, with modern firefighting techniques, catastrophe is usually, but not always, avoided. To prevent fires from starting, a firefighter's duties include public education and conducting fire inspections.

Because firefighters are often the first responders to people in critical conditions, firefighters provide many other valuable services to the community they serve, such as:

• Emergency medical services, as technicians or as licensed paramedics, staffing ambulances;
• Hazardous materials mitigation (HAZMAT);
• Vehicle Rescue/Extrication;
• Search and rescue;
• Community disaster support.
• Fire Risk Assessments

Additionally, firefighters also provide service in specialized fields, such as:

A hose team training to fight an aircraft fire aboard a US aircraft carrier, 2006.

• Aircraft/airport rescue;
• Wildland fire suppression;
• Shipboard and military fire and rescue;
• Tactical paramedic support ("SWAT medics");
• Tool hoisting;
• High Angle Rope Rescue;
• Swiftwater Rescue.

In the US, firefighters also serve the Federal Emergency Management Agency (FEMA) as urban search and rescue (USAR) team members.

Problem Statement

The robot must be able to identify victims and deliver an air tank, fire blanket and homing beacon to their location in order to extend their lives while the firefighters attempt to control the blaze.  In order to be able to exist in such harsh conditions the robot must be heat resistant and water resistant. The main goal of this project is to save lives.  If the robot can successfully aid in the rescue of victims who would have otherwise perished in a fire this groups goals have been met.

Literature Review

              The history of firefighting can be dated back to the times of Ancient Egypt where hand pumps were used to fight fires.  However, it wasn’t until 1699 in France, that firefighting became modernized.   Here, François du Mouriez du Périer introduced the first commercially provided fire pumps to the City of Paris.  In the 1800’s helmets were introduced to protect the firefighters.  The first steam powered fire engine was used in Cincinnati Ohio on April 1, 1853.  This was also the first full time paid fire department in the United States.  However, in 1907, the first internal combustion engine fire engines were developed.  These lead to the extinction of the steam engine fire engine by 1925.

             Today, fire companies are both paid and volunteer.  The technology is far more advanced than in the earlier times.  Firefighters wear full heat resistant gear and are equipped with oxygen tanks and high pressure fire houses.  Companies such as AFT (Advanced Firefighting Technology) are working to make firefighting safer and more effective with low-pressure Water Mist and CAFS (compressed air foam systems).

            The London based company, Qinetiq has been commissioned to deploy a team of three robots to respond to fires where Acetylene gas is present.  When this gas is present in canisters, firefighters are forced to sit back and watch the fire until after the gas has exploded.  The three robots each have a specific job and can keep the human fire fighters out of danger. Other companies, Brazilian based ARMTEC, Las Vegas based InRob and iRobot, inventors of the Roomba, have also been developing robot technology for firefighting.  The technology is far from perfect however and will be continuously developed in the coming years.