“DESIGN AND ANALYSIS OF SINGLE ARM ROBOT”

ABSTRACT

Robot is a machine to execute different task repeatedly with high

precision. Thereby many functions like collecting information and studies about

the hazardous sites which is too risky to send human inside. Robots are used to

reduce the human interference nearly 50 percent. Robots are used in different types

like fire fighting robot, metal detecting robot, etc. Robot manufacturers, like many

other manufacturers, are today experiencing ever increasing competition in a

global market. For many of the robot manufacturers' customers, a key component

in their strategy for greater efficiency has been robot automation. This is not case

for the robot manufacturers themselves, who traditionally have little in-house

production and an assembly process where merely marginal savings can be made

through robot automation. Another way to improve the odds of being one of the

fittest in this struggle for survival is instead to speed up the time to market for new

products by shortening lead times in the development process this should of course

be achieved without lowering any requirements with regard to quality and

performance. However, stricter requirements often increase the cost and a key

factor for success is finding the most profitable balance between quality,

performance, and cost. The main objective of the project is to design and analysis

of single arm robot for 10 kg payload. The corresponding deflections, stresses and

strains for that load will be find out by using the method of finite element analysis

(FEA).Here the design of robot arm to be assigned by using pro-e wildfire 5.0 and

then the analysis of arms to be done by using ansys 11.0.

LITERATURE REVIEW “MODELLING AND STUDY OF MOTION CONTROL SYSTEM FOR MOTORIZED ROBOT ARM USING MAT LAB AND ANALYSIS OF THE ARM BY USING ANSYS”

K. MANOJ KUMAR & CH. SAMBAIAH,

In this paper the Motion control is one of the technological

foundations of industrial automation. Putting an object in the correct place with the

right amount of force and torque at the right time is essential for efficient

manufacturing operation. In the present work modeling of control system for

motorized robot arm with a single degree of freedom is done. The results of the

control system are also described. The control algorithm was developed by

MATLAB software which is widely used in controlling application. In this system

the DC motor moves the robot arm to the desired angular position in accordance

with the input given.

Keywords: Robotic Arm, Transient analysis, Beam Specifications, Control

System, FEA, ANSYS

“A COMPREHENSIVE STATIC AND MODAL ANALYSIS OF”5R”KINEMATIC CHAINS USING VIRTUAL TECHNIQUES”

GABRIEL MUNTEANU, ADRIAN GHIORGHE

An important characteristic for the field of industrial robotics

is the positioning precision of end effectors. Due to the progress of the computer

technologies and control systems, the accuracy has significantly improved in the

last years. Still, there is a continuous need for machines to provide higher accuracy

mechanisms and kinematic chains or to adjust the systems already built in order to

adequate it to reach to a better precision of the tasks. The current paper shows the

results of a comprehensive analysis applied for RRR-RR robotic system already

build including two versions of static analysis and modal analysis, using the

modern virtual instruments. The main stages pursued was: design of the

mechanisms and kinematic chains for each rotation joint, in accordance with the

real robot, modelling of the connections and the mesh for each element and

surface, simulation and model analysis using FEM specialized instruments. A final

indication about the characteristics to improve is presented.

“OPTIMIZATION DESIGN FOR THE STRUCTURE OF AN RRR TYPE INDUSTRIAL ROBOT”

ADRIAN GHIORGHE

The current paper shows a methodology to determine the optimum

values for the design parameters considering the criteria of reducing the material

used to build the structure of industrial robot, using a structural optimization and

topology algorithm. This analysis is based on the finite element method (FEM) and

consists in completion of the design model using the dimensional data as

parametric design variables to which restriction conditions have been applied in

order to achieve the object function. A recurrent FEM analysis using different

parameters for the design variables was applied in order to assess an optimum

composition of the object function.

“COMPARATIVE ANALYSIS FOR LINK CROSS-SECTION OF MANIPULATOR ARMS”

DR. AHMED ABDUL HUSSAIN ALI, DLER OBED RAMADHAN

The stresses and deflections in robot arm was analyzed using ANSYS

software package. Industrial robot analyzed in this work consists of three arms that

have 2-DOF. The analysis of each arm had been made separately.The maximum

stress and deflection have been analyzed for a static applied at one end of the arm

while has the other end fixed. Links of various cross-sections having same masses,

length, and material properties to make a choice of the shape that gives a high

stiffness to weight ratio have been examined. After specifying the best section for

the arms of the robot an optimization process began to determine the dimensions of

the arms sections which give the least deformation this had been done by the aid of

a program build up by using the MATHCAD software package. In the beginning

the program finds the optimum section in which the stress in the members not

exceeds the allowable stress and finds the total weight of the robot after that the

program begins to change the dimensions to satisfy the condition of minimum

deflection of the whole robot after that the program estimates the best choices of

the dimension for each section that gives the minimum weight and deflection.

INTRODUCTION

A robotic arm is a robotic manipulator, usually programmable, with similar

functions to a human arm. The links of such a manipulator are connected by joints

allowing either rotational motion or translational displacement. The links of the

manipulator can be considered to form a kinematic chainman robot may be

designed to perform any desired task such as welding, gripping, spinning etc.,

depending on the application. For example robot arms in automotive assembly

lines perform a variety of tasks such as welding and parts rotation and placement

during assembly. A rotation of 99 degrees is given to the robot arm in a minimum

time (.02seconds) by supplying power to the robot arm using a switch. Further the

arm will settle down with critical damping to an angle of 90degrees. The FE modal

analysis has been performed for the robotic arm to find the natural frequency.

Transient analysis is performed to note the displacement, velocity and

accelerations during its Motion. However, the use of feedback can lead to an

unstable system whose output may oscillate or even go to infinity with a small

input signal. Stability determination is therefore an important design consideration.

One specification for absolute stability requires that the poles of the transfer

function must be in the left half of the s-plane. Absolute stability, often specified in

the frequency domain, is essential and necessary but not sufficient.

Frequency domain specifications relating to relative system stability may also be

given. For relative stability, a certain phase margin and gain margin may be

specified to ensure that the system will remain stable although some parameters

change due to temperature changes, aging or other environmental changes.If a

system is stable, then other performance criteria, specified in either the time or

frequency domain, may be considered to meet the performance requirements.

Short-term, or transient, response specifications such as rise-time or percent

overshoot to a unit step function input may be given. Fortunately, the advance

control calculation can be solved with the help of using MATLAB software.In

industrial automation the control of motion is a fundamental concern. Putting an

object in the correct place with the right amount of force and torque at the right

time is essential for efficient manufacturing operation. Feedback comparison of the

target and actual positions is done in motion control system. This comparison

generates an error signal that may be used to correct the system, thus yielding

repeatable and accurate results. The goal is to design a compensation strategy so

that a voltage of 0 to 10 volts corresponds linearly of an angle of 0 degrees to an

angle of 90 degrees.

INTRODUCTION.

The techniques of analysis and simulation of mechanical systems using the

finite element method allows researchers and mechanical engineers to build

mathematical models and to analyze the static and dynamic behavior of the

structural elements directly on the computer, and optimization alculations,

simulations, studies of similarity, etc.Approximate numerical solutions, obtained

through modeling for the proposed problems, have the following key advantages:

• It can be applied to bodies and real phenomena, regardless of their degree of

complexity;

• are converge to solutions of proposed problems (results may be obtained with the

desired accuracy;

• You can view the pictures, charts, graphs - intuitive and more diverse than in the

case of exact solutions;

• allows to obtain a solution in a reasonable time;

• are economically advantageous.

It is a work environment that integrates design and analysis, in order to achieve

optimized products, shortening manufacturing cycle. It has the capability to create

optimized versions of the products, reducing the need to manufacture a prototype

to validate the results. The challenge that robot manufacturing industry must face

today is the speed of response to market demands. The key is to produce

efficiently, at a low price and high quality in record time. Specialized companies

provide an information technology solution that helps companies in various areas

to reduce time from manufacturing to sales while reducing the costs dramatically.

Specialists allow customers to eliminate real prototypes and laboratory tests in the

design phase, while they check and improve their processes and products.

Optimized structural design for the structures of the industrial robots have to meet

certain criteria regarding dimensional design and shape, material consumption and

adapt this to the functional requirements. For an optimized design of the robot

structure the engineers normally consider all the aspects of industrial applications

where the structure will be integrated. Specific requirements are related to the

resistance of the elements, not to oversize the structure but also to guarantee

minimum criteria of stability and security in operation and to fit the material and

its shape with the above mentioned criteria. It is required to correlate all these with

the kinematic model of the joints and from this basis to establish the loads and to

build a dynamic model to determine the behavior from this point of view. The

actual progress in the field of topological optimization – [1], [2], [3], [4], [5] is

determined by the software progress in optimization on the basis of FEM, using the

new approach that reaches a high accuracy of the results obtained from a system of

equations, whose size depends on the complexity of the model examined and

whose solution require an efficient numerical method to calculate. The research

indicates also as a major possibility to improve the characteristics of the structures,

the use of new materials, while the modern methods for optimized design of a

robot structure involve the use of CAD programs and finite element analysis

(CAD-FEM). Different material databases are available for assessment within the

virtual model. This kind of verification of the components and complete structure

of robots becomes compulsory requisite in modern design as well as in

optimization program.

INTRODUCTION Robot is an integral part in automating the flexible manufacturing system that one greatly in demand these days. Robots are now more than a machine, as robots have become the solution of the future as cost labor wages and customers' demand. Even though the cost of acquiring robotic system is quite expensive but as today's rapid development and a very high demand in quality with IS0 (International Standard Organization) standards, human are no longer capable of such demands. Research and development of feature robots is moving at a very rapid pace due to the constantly improving and upgrading of the quality standards of products.Robot and automation is employed in order to replace human to perform those tasks that are routine, Dangerous, dull, and in a hazardous area. In a world of advanced technology today. Automation greatly increases production capability. Improve product quality and lower reduction cost. It takes just a few people to program or monitor the computer and carry out routine maintenance.

MATERIAL SELECTION AND CONSIDERATIONS

The most suitable material to fabricate the structure of the arm has to be

light and strong. Otherwise, the servo motor will not be able to pull up the arm and

to perform the desired turning degree. Among the materials that can be considered

to fabricate the structure are aluminum, Perspex, plastic polymer and carbon fiber.

In choosing the fabrication materials, the aspect of availability of the materials, the

overall cost and the flexibility to be shaped, should also be taken into

consideration. Thus among the four materials considered, the aluminum is the most

ideal material to be chosen as fabrication material.

OBJECTIVES

The main objective in completing the project is to achieve the standards that

have been set.

COMPONENTS OF A ROBOT MANIPULATOR A robot manipulator system often consists of links, joints, actuators,

and controllers [Robotics Second Edition, Man Zhihong, 2004].

JOINTS The rotary joints and the sliding of prismatic joints allow the links to

move in the robot work space. In robot system, the number of degrees-of-freedom

is determined by the number of independent joint variables [Man Zhihong, 2004].

"CRS Robotics", the automation laboratory robot has 3 DOF. It's inexpensive, easy

to program and limited load capacity [Handbook of Industrial Robotics, Shimon

Y.Nof, 1999]. "IVAX SCARA" robotic arm produced by FEEDBACK has 4 DOF,

it is primarily used in industrial areas such as pick & place and automated

palletizing [Darryl Wai, 2004]. "Teleoperate Anthropomorphic Robotic Arms" has

5 DOF and the concept is Similar to the industrial robotic arm in the factory. It is

suitable for pick and place Object with limited load capacity [Karl Williams,

20041. Through all the research that I've done I have chose 5 DOF for my robotic

arm because 5 DOF has the similar Movement and features like human arm. But

the more number of DOF the more Complex the robotic arm.

Translational motionLinear joint (type L)Orthogonal joint (type O)Rotary motionRotational joint (type R)Twisting joint (type T)Revolving joint (type V)

Robot Links and Joints

September 21st, 2011 yog

In a robot, the connection of different manipulator joints is known as Robot Links, and the integration of two or more link is called as Robot Joints. A robot link will be in the form of solid material, and it can be classified into two key types – input link and output link. The movement of the input link allows the output link to move at various motions. An input link will be located nearer to the base.

Different types of robot joints:

The Robot Joints is the important element in a robot which helps the links to travel in different kind of movements. There are five major types of joints such as:

Rotational joint Linear joint Twisting joint Orthogonal joint Revolving joint

Rotational Joint:

Rotational joint can also be represented as R – Joint. This type will allow the joints to move in a rotary motion along the axis, which is vertical to the arm axes.

Linear Joint:

Linear joint can be indicated by the letter L – Joint. This type of joints can perform both translational and sliding movements. These motions will be attained by several ways such as telescoping mechanism and piston. The two links should be in parallel axes for achieving the linear movement.

Twisting Joint:

Twisting joint will be referred as V – Joint. This joint makes twisting motion among the output and input link. During this process, the output link axis will be vertical to the rotational axis. The output link rotates in relation to the input link.

Orthogonal Joint:

The O – joint is a symbol that is denoted for the orthogonal joint. This joint is somewhat similar to the linear joint. The only difference is that the output and input links will be moving at the right angles.

Revolving Joint:

Revolving joint is generally known as V – Joint. Here, the output link axis is perpendicular to the rotational axis, and the input link is parallel to the rotational axes. As like twisting joint, the output link spins about the input link.

ACTUATORS

Actuators are devices that cause rotary joints to rotate or drive prismatic

joints to slide along their motion axes. The most used robot drivers are stepper

motor and DC servo motor. The stepper motor movements can be very precise but

stepper motor is open loop type that is the control computer computes the number

of pulses required for the desired movement and dispatches the command to the

robot without checking whether the robot actually completes the motion

commanded. "IR Transreceiver Robotic Arm" used 4 stepper motor to control the

direction and generate a Pulse Width Modulation. "Robotic Arm Control System"

used 4 unit of DC motor to drive each joint of the robotic arm used for speed and

position control application. The second type of robot actuator is dc servo. These

robots invariably incorporate feedback loops from the driven components back to

the driver. Thus the control system continuously monitors the positions of the robot

components, compares these positions with the position desired by the controller

and check any differences or error conditions. "Teleoperate anthropomorphic

Robotic Arm" used 8 servo motors overall to control the arm. That is 2 large scale

servos to control shoulder to provide torque needed to lift the rest of the arm as

well as any object that it may be grasping, 1 large scale servo to control the

rotating base and another one large scale servo to control elbow. While 3 standard

servos used to control the wrist and one more standard servo to control the gripper.

As a conclusion on the actuators, I'm going to use servo motor as my robotic arm

driver since servo motor is a continuous device, thereby making possible a

smoother and continuously controllable movement.

Making Sense of Actuators

Now that we learned about robotics in general in Lesson 1 and decided on the robot to make in Lesson 2, we will now choose the actuators that will make the robot move.

What is an actuator?

An “actuator” can be defined as a device that converts energy (in robotics, that energy tends to be electrical) into physical motion. The vast majority of actuators produce either rotational or linear motion. For instance, a “DC motor” is therefore a type of actuator.

Choosing the right actuators for your robot requires an understanding of what actuators are available, some imagination, and a bit of math and physics.

Rotational Actuators

As the name indicates, this type of actuators transform electrical energy into a rotating motion. There are two main mechanical parameters distinguishing them from one another: (1) torque, the force they can produce at a given distance (usually expressed in N•m or Oz•in), and (2) the rotational speed (usually measured in revolutions per minutes, or rpm).

AC Motor

AC (alternating current) is rarely used in mobile robots since most of them are powered with direct current (DC) coming from batteries. Also, since electronic components use DC, it is more convenient to have the same type of power supply for the actuators as well. AC motors are mainly used in industrial environments where very high torque is required, or where the motors are connected to the mains / wall outlet.

DC Motors

DC motors come in a variety of shapes and sized although most are cylindrical. They feature an output shaft which rotates at high speeds usually in the 5 000 to 10 000 rpm range. Although DC motors rotate very quickly in general, most are not strong (low torque). In order to reduce the speed and increase the torque, a gear can be added.

To incorporate a motor into a robot, you need to fix the body of the motor to the frame of the robot. For this reason motors  often feature mounting holes which are generally located  on the face of the motor so they can be mounted perpendicularly to a surface. DC motors can operate in clockwise (CW) and counter clockwise (CCW) rotation. The angular motion of the turning shaft can be measured using encoders or potentiometers.

Geared DC Motors

A DC gear motor is a DC motor combined with a gearbox that works to decrease the motor’s speed and increase the torque. For example, if a DC motor rotates at 10 000 rpm and produces 0.001 N•m of torque, adding a 256:1 (“two hundred and fifty six to one”) gear down would reduce the speed by a factor of 256 (resulting in 10 000rpm / 256 = 39 rpm), and increase the torque by a factor of 256 (0.001 x 256 = 0.256 N•m). The most common types of

gearing are “spur” (the most common), “planetary” (more complex but allows for higher gear-downs in a more confined space, as well as higher efficiency) and “worm” (which allows for very high gear ratio with just a single stage, and also prevents the output shaft from moving if the motor s not powered). Just like a DC motor, a DC gear motor can also rotate CW and CCW. If you need to know the number of rotations of the motor, an “encoder” can be added to the shaft.

R/C Servo Motors

R/C (or hobby) servo motors are types of actuators that rotate to a specific angular position, and were classically used in more expensive remote controlled vehicles for steering or controlling flight surfaces. Now that they are used in a variety of applications, the price of hobby servos has gone down significantly, and the variety (different sizes, technologies, and strength) has increased.

The common factor to most servos is that the majority only rotate about 180 degrees. A hobby servo motor actually includes a DC motor, gearing, electronics and a rotary potentiometer (which, in essence,  measures the angle). The electronics and potentiometer work in unison to activate the motor and stop the output shaft at a specified angle. These servos are generally have three wires: ground, voltage in, and a control pulse. The control pulse is usually generated with a servo motor controller.  A “robot servo“ is a new type of servo that offers both continuous rotation and position feedback. All servos can rotate CW and CCW.

Industrial Servo Motors

An industrial servo motor is controlled differently than a hobby servo motor and is more commonly found on very large machines. An industrial servo motor is usually made up of a large AC (sometimes three-phase) motor, a gear down and an encoder which provides feedback about angular position and speed. These motors are rarely used in mobile robots because of their weight, size, cost and complexity. You might find an industrial servo in a more powerful industrial robotic arm or very large robotic vehicles.

Stepper Motors

A stepper motor does exactly as its name implies; it rotates in specified “steps” (actually, specific degrees). The number of degrees the shaft rotates with each step (step size) varies based on several factors. Most stepper motors do not include gearing, so just like a DC motor, the torque is often low. Configured properly, a stepper can rotate CW and CCW and can be moved to a desired angular position. There are unipolar and bipolar stepper motor types. One notable downside to stepper motors is that if the motor is not powered, it’s difficult to be certain of the motor’s starting angle.

Adding gears to a stepper motor has the same effect as a adding gears to a DC motors: it increases the torque and decreases the output angular speed. Since the speed is reduced by the gear ratio, the step size is also reduced by that same factor. If the non geared down stepper motor had a step size of 1.2 degrees, and you add a gear down of 55:1, the new step size would be 1.2 / 55 = 0.0218 degrees.

Linear Actuators

A linear actuator produces linear motion (motion along one straight line) and have three main distinguishing mechanical characteristics: the minimum and maximum distance the rod can move “a.k.a. the “stroke”, in mm or inches),  their force (in Kg or lbs), and their speed (in m/s or inch/s).

 

DC Linear Actuator

A DC linear actuator is often made up of a DC motor connected to a lead screw. As the motor turns, so does the lead screw. A traveller on the lead screw is forced either towards or away from the motor, essentially converting the rotating motion to a linear motion. Some DC linear actuators incorporate a linear potentiometer which provides linear position feedback. In order to stop the actuator from destroying itself, many manufacturers include limit

switches at either end which cuts power to the actuator when pressed.  DC linear actuators come in a wide variety of sizes, strokes and forces.

 

Solenoids

Solenoids are composed of a coil wound around a mobile core. When the coil is energized, the core is pushed away from the magnetic field and produces a motion in a single direction. Multiple coils or some mechanical arrangements would be required in order to provide a motion in two directions. A solenoid’s stroke is usually very small but their speed is very fast. The strength depends mainly on the coil size and the current going trough it. This type of actuator is commonly used in valves or latching systems and there is usually no position feedback (it’s either fully retracted or fully extended).

Muscle wire

Muscle wire is a special type of wire that will contract when an electric current traverses it. Once the current is gone (and the wire cools down) it returns to its original length. This type of actuator is not very strong, fast or provides a long stroke. Nevertheless, it is very convenient when working with very small parts or in a very confined space.

Pneumatic and Hydraulic

Pneumatic and hydraulic actuators use air or a liquid (e.g. water or oil) respectively in order to produce a linear motion. These types of actuators can have very long strokes, high force and high speed. In order to be operated they require the use of a fluid

compressor which makes them more difficult to operate than regular electrical actuators. Because of they high force speed and generally large size, they are mainly used in industrial environments.

 

 

Choosing an Actuator

To help you with the selection of an actuator for a specific task, we have developed the following questions to guide you in the right direction.

It is important to note that there are always new and innovative technologies being brought to market and nothing is set in stone. Also note that an single actuator may perform very different task in different contexts. For instance, with additional mechanics, an actuator that produces linear motion may be used to rotate an object and vice versa (like on a car’s windshield wiper).

(1) Is the actuator being used to move a wheeled robot?

Drive motors must move the weight of the entire robot and will most likely require a gear down. Most robots use “skid steering” while cars or trucks tend to use rack-and-pinion steering. If you choose skid steering, DC gear motors are the ideal choice for robots with wheels or tracks as they provide continuous rotation, and can have optional position feedback using optical encoders and are very easy to program and use. If you want to use rack-and-pinion, you will need one drive motor (DC gear is also suggested) and one motor to steer the front wheels). For stirring, since the rotation required is restricted to a specific angle, an R/C servo would be the logical choice.

 

(2) Is the motor being used to lift or turn a heavy weight?

 

Lifting a weight requires significantly more power than moving a weight on a flat surface. Speed must be sacrificed in order to gain torque and it is best to use a gearbox with a high gear ratio and powerful DC motor or a DC linear actuator. Consider using system (either with worm gears, or clamps) that prevents the mass from falling in case of a power loss.

(3) Is the range of motion limited to 180 degrees?

If the range is limited to 180 degrees and the torque required is not significant, an R/C servo motor is ideal. Servo motors are offered in a variety of different torques and sizes and provide angular position feedback (most use a potentiometer, and some specialized ones use optical encoders). R/C servos are used more and more to create small walking robots.

(4) Does the angle need to be very precise?

Stepper motors and geared stepper motors (coupled with a stepper motor controller) can offer very precise angular motion. They are sometimes preferred to servo motors because they offer

continuous rotation. However, some high-end digital servo motors use optical encoders and can offer very high precision.

(5) Is the motion in a straight line?

Linear actuators are best for moving objects and positioning them along a straight line. They come in a variety of sizes and configurations. Muscle wire should be considered only if your motion requires very little force. For very fast motion, consider pneumatics or solenoids, and for very high forces, consider DC linear actuators (up to about 500 pounds) and then hydraulics.

Tools

In order to compute the strength (or torque), and speed required for your application, many (rather complex) computations are required involving the physics of the machine to be created. In order to simplify the design process, we have put together a few tools that can help you out.

DC Drive Motor Selector (useful for robots with wheels or tracks). Also consult the Drive Motor Sizing Tutorial for further details.

Robot Leg Torque Tutorial Robot Arm Torque Calculator

Practical Example

In lesson 1 we determined the objective of our project would be to get a better understanding of mobile robots, while keeping the budget to about $200 to a maximum of $300. In lesson 2 we decided we wanted a small tank (on tracks) that could operate on top of a desk.

First, let us determine the type of actuators that would be required by answering the five aforementioned questions:

1. Is the actuator being used to move a wheeled robot?Yes. A DC gear motor is the suggested type of actuator and skid steering is appropriate for a tank, which means that each track will need it;s own motor.

2. Is the motor being used to lift or turn a heavy weight?No, a desktop rover should not be heavy.

3. Is the range of motion limited to 180 degrees?No, the wheels need to urn continuously.

4. Does the angle need to be precise?No, our robot does not require positional feedback.

5. Is the motion in a straight line?No, since we want the robot to turn and move in all directions.

Since rotating a wheel needs rotational motion, we could quickly eliminate all linear actuators and choose a DC gear motor. The next logical question was “which one?”A search online shows that there are not too many track systems intended for small robots, which in itself would restrict which motors we could consider.

The Currently Available Track Systems

 

At 2″ and 3″ wide, the Lynxmotion tracks are more intended for medium sized robots, so we’ll omit them.

The price does fall within the budget though.

The Vex Tank Tread Kit is definitely a good option, but it would restrict us to one specific motor.

The Tamiya Track and Wheel Set is definitely a good option, and would limit our choices to Tamiya motors  and gearboxes. This would also be within the budget.

There are several Johnny Robot Track Kits, one for a Hitec continuous rotation servo (which is essentially a gear motor in a servo’s body) another for a Futaba continuous rotation servo, one for Tamiya motors and another for Pololu or Solarbotics motors. This is definitely a good option and also within our budget. Mainly because of aesthetic and motor compatibility reasons, we are going to stick with this choice.

There is always the option of hacking a toy such as an R/C tank and convert it into a robot.  This option would also give us compatible motors, however, the objective is to design our own robot and not hack another product.

CONTROLLERS Controllers are the most important components in a robot system. If a

robot has n Joints, n controllers are needed to control all joint actuators. Robot

controllers used to solve the problem how robot actuators are driven to achieve a

desired performance. A robot control system is actually the integration of

electronic hardware and software. The task of software is to use some control

algorithms to compute the control signals while the control hardware can then

provide the control signals to the actuators. "IR Transreceiver Robotic Arm"

applied stepper motor controller to control the direction and generate a PWM. The

direction of and the PWM output is then sent to the stepper motor driver. In this

controller design, the programmable PIC16F84 is use to generate the desired

signals. UCN5804 IC is used to drive the stepper motors. By incorporating stepper

motor controller into the design, the PIC can control multiple stepper motor

"Teleoperate Anthropomorphic Robotic Arm" used serial servo controller to

control robot arm via serial connection to a PC or directly from the onboard PIC

16F84 microcontroller.

The PIC is programmed to listen for any incoming serial communication from the

host computer then set the servos to the positions received and update the servos

with their positional information so that the servos will hold their positions [Karl

Williams, 2004]. I'm going to choose servo motor controller for my robotic arm

since I'll use servo motor to drive my robotic arm and the advantage of using servo

motor already explain under actuators topic above.

Different levels of robot controller

October 20th, 2011 yog

A robot controller is used to decrease the errors of control signal to zero or somewhere close to zero. It can be classified into six different types namely:

ON – OFF control Proportional control Integral control Proportional – plus – Integral control (P – I) Proportional – plus – Derivative control (P – D) Proportional – plus – Integral – plus – Derivative control (P – I – D)

According to the application, anyone of these controllers can be used. The functions of each controller are described briefly below.

ON – OFF control:

The element in the ON – OFF controller offers two control methods such as:

Complete OFF Complete ON

m(t) = M1, if e(t) > 0

m(t) = M2, if e(t) < 0

Where,

m(t) denotes the control signal created by the controller. e(t) denotes the error on the controller. In most of the cases either M1 or M2 will be 0.

The purpose of an ON – OFF control is to protect the controller from swinging with very high frequency. This is made possible by moving the error through several ranges before the operation starts. Here, the range is considered as the differential gap.

Proportional control:

A control signal produced by this controller is proportional to the error. It is basically used as an amplifier by means of a gain (Kp). This is represented as:

m(t) = Kp e(t)

The transfer function will be:

M(s) / E(s) = Kp

The proportional controller will be best suited for providing smooth control action.

Integral control:

A control signal produced by the integral controller is altered at a rate proportional to the error (i.e.) the control signal maximizes quickly if the error is big, and the control signal maximizes slowly if the error is small. This can be represented as:

m(t) = Ki ∫ e(t) dt

Here, the Ki denotes the integrator gain.

The transfer function will be:

M(s) / E(s) = Ki / s

Here, the 1/s is used for integration.

Proportional – plus – Integral control (PI):

The PI controller is used to overcome two major issues. They are:

The integral control is capable of offering zero errors, but it is set back with its slow response.

The proportional control provides error while counteracting a load on the system.

This can be represented as Kp.

m(t) = Kp e(t) + Kp / Ti ∫ e(t) dt

Here,

Kp is used to adjust the proportional and integrator gain.

Ti is used to adjust only the integrator gain.

The transfer function will be:

M(s) / E(s) = Kp (1 + 1 / Ti s)

Proportional – plus – Derivative control (PD):

The control signal produced by the PD controller is proportional to the rate of change of the error. This method is used rarely because of its incapability to provide output without the change of error. An advantage is that it can give changes with faster responses. This can be represented as

m(t) = Kp e(t) + Kp Td de(t) / dt

The transfer function will be:

M(s) / E(s) = Kp (1 + Tds)

Proportional – plus – Integral – plus – Derivate control (PID):

The PID controller integrates three control actions, and it is the most frequently used controller. It is because of its fast response, and low steady – state error. This controller can be represented as

m(t) = Kp e(t) + Kp / Ti  ∫ e(t) dt + Kp Td de(t) / dt

The transfer function will be:

M(s) / E(s) = Kp (1 + 1 / Tis + Tds)

Gripper types and choice of gripper typeThe robotic gripper is one of the most important parts in a robotic system. The gripper is thedevice between the robot and the work piece. The selection of the gripper in a robotic systemis therefore very important. There are many different types of grippers and a wide variety offactors to consider. The most common types of grippers are: jaw-type, vacuum and magneticgrippers, the types of grippers can also be categorized into three main groups; single-surfacegrippers, clamping grippers and flexible grippers [2].To decide which type of the grippers is

most suitable for picking up the parts and place the parts to the next station, a description of

the different gripping techniques and a conclusion will be presented in this chapter

Gripper typesAs described earlier the gripper types can be categorized into three main groups. The threemain categories will be described here.2.1.1 Single-surface grippersWhen only one surface of the component is available, the single-surface grippers’ matchesperfect for gripping this types of components. These types of grippers are useful for grippinglight and heavy weight and flat components which are difficult to handle by other means. Thegripper types that are included in single-surface grippers are magnetic, vacuum and adhesivegrippers. These types of grippers are gripping the components by pulling force rather than apushing force which is more common for robotic-grippers [3]. The adhesive type of gripperwill not be discussed here because they are usually used for picking up fabric or similarmaterial.2.1.1.1 Magnetic grippersThere are two types of magnetic grippers, permanent-magnets and electro-magnets. Themagnetic grippers are only suitable for picking up ferrous objects and are very easy to controlfor picking and releasing. A permanent-magnet is an object that is made from a magnetizedmaterial. The permanent magnets require a mechanism for releasing the gripped object asshown in figure 2. [4]Figure 2 Permanent Magnet, picture taken from [4] page 204

5In addition to permanent magnets, a magnetic field can be electrically generated. Themagnetic field is generated by a wire wounded into a coil. When the electricity is passingthrough the wire the magnetic field becomes active and the field disappears when theelectricity is gone. The electromagnetic lifters are often used for picking up various iron andsteel scraps. They are common in the manufacturing industries. Some objects can bemagnetized when picking with electromagnets but that problem can be reduced by connectingthe electromagnets to alternating current. The electromagnetic grippers can pick up andrelease objects in few seconds which is beneficial when the time matters. Other benefits withelectromagnetic grippers are that they can be dimensioned for very big forces. [4]2.1.1.2 Vacuum grippersVacuum-grippers become in suction cups, the suctions cups is made of rubber. The suctioncups are connected through tubes with underpressure devices for picking up items and forreleasing items air is pumped out into the suction cups. The under pressure can be createdwith the following devices:Vacuum pumpsEjectorsSuction bellowsPneumatic cylindersThe vacuum grippers use suction cups (vacuum cups) as pick up devices. There are differenttypes of suction cups and the cups are generally made of polyurethane or rubber and can beused at temperatures between -50 and 200 °C. The suction cup can be categorized into four

different types; universal suction cups, flat suction cups with bars, suction cups with bellowand depth suction cups as shown in figure 3.Figure 3 Different types of suction cups, picture taken from [5] page 204

6The universal suction cups are used for flat or slightly arched surfaces. Universal suction cupsare one of the cheapest suction cups in the market but there are several disadvantages withthis type of suction cups. When the under pressure is too high, the suction cup decreases a lotwhich leads to a greater wear.The flat suction cups with bars are suitable for flat or flexible items that need assistance whenlifted. These types of suction cups provides a small movement under load and maintains thearea that the underpressure is acting on, this reduces the wear of the flat suction cup with bars,this leads to a faster and safer movement.Suction cups with bellows are usually used for curved surfaces, for example when separationis needed or when a smaller item is being gripped and needs a shorter movement. This type ofsuction cups can be used in several areas but they allow a lot of movement at gripping andlow stability with small underpressure. The depth suction cup can be used for surfaces that arevery irregular and curved or when an item needs to be lifted over an edge. [5]Items with rough surfaces (surface roughness ≤ 5 μm for some types of suction cups) or itemsthat are made of porous material will have difficulty with vacuum grippers. An item withholes, slots and gaps on the surfaces is not recommended to be handled with vacuum grippers.The air in the suction is sucked out with one of the techniques described earlier, if the materialis porous or has holes on its surface, it will be difficult to suck out the air. In such cases theleakage of air can be reduced if smaller suction cups are used. Figure 4 shows different typesof suction cups. [4]Figure 4 Different types of suction cups from Anver, picture taken from [6]

72.1.2 Clamping grippersTwo-jaw grippers and three jaw-grippers are related to clamping grippers and occurfrequently in manufacturing factories. Clamping grippers can be designed relatively simple,therefore the price can be cheaper. Clamping grippers straps the object that is being picked upby applying pressure internally or externally to more than one of the object surfaces. Thistype of grippers is driven pneumatic or hydraulic. For smaller object that doesn’t need bigforces the pneumatic technique is used and for heavy object that requires big forces thehydraulic technique is used. The pneumatic technique is more common because of the lowprice, low weight, and ease of use. [2]2.1.2.1 Two and three jaw grippersTwo-jaw gripper is the simplest type of jaw grippers. Two-jaw gripper consists with twogripping fingers that apply pressure externally or internally on the object depending on thejaw design. Depending on shape and size of the object the jaw-fingers can be designeddifferent for an accurately and securely movement. The two-jaw grippers can be used forlarge and small objects. The mechanics for the movement of the jaw-fingers can includelinkage, cams, pinion and actuators, and as described earlier pneumatic and hydrauliccylinders.When the shapes get more complex than the two-jaw gripper can handle, the three-jaw gripperis option for objects with more complex shapes. The three-jaw grippers consist with threegripping fingers and apply pressure like the two-jaw grippers. The three-jaw grippers aremore complex and therefore more expensive than two-jaw grippers. Figure 5 presents two and

three jaw grippers. [2]Figure 5 Two and Three-jaw grippers from Schunk, picture taken from [7]

82.1.3 Flexible grippersFlexible grippers consist with several linkages on each finger and two or several fingers. Eachlinkage have normally an individual steering, this types of grippers can be compared with thehuman hand. The flexible grippers are indented to handle a number of different items. Avariety of these grippers have been produced by various researches. Multi fingered grippersthat are related to flexible grippers are like a human hand lookalike gripper with more thantwo fingers. This type of gripper can grasp object with very complex shapes because of thelinkages in the fingers that can be controlled individually. The fingers in these types ofgrippers can be simulated after the shape of the object that will be grasped. Other types offlexible grippers are soft grippers, bladder grippers and adjustable-jaw grippers. Figure 6shows a multi fingered gripper. [2]Figure 6 A multi fingered gripper, picture taken from [8] page 321

2.2

MODELING OF ROBOTIC ARM

DC motor is used to drive a robot arm horizontally as shown in Fig. 3. The

link has a mass, M=5Kg, length L=1 m, and viscous damping factor D = 0.1.

Assume the system input is a voltage signal with a range of 0 volts. This signal is

used to provide the control voltage and current to the motor. The motor parameters

are given below. The goal is to design a compensation strategy so that a voltage of

0 to 10 volts corresponds linearly of an angle of 0° to an angle of 90°. The required

response should have an overshoot below 10%,a settling time below 3 second and

a steady state error of zero.

Kinematic diagram of robot associated co ordinate system

Model of single arm robot

.

BASIC MANIPULATOR GEOMETRIES In this section, I look at some basic arm geometries. As I said before, a robot arm or manipulator is composed of a set of joints, links, grappers and base part. The joints are where the motion in the arms occurs, while the links are of fixed construction. Thus the links maintain a fixed relationship between the joints. The joints may be actuated by motors or hydraulic actuators. There are two sorts of robot joints, involving two sorts of motion. A revolute joint is one that allows rotary motion about an axis of rotation. An example is the human elbow. A prismatic joint is one that allows extensions or telescopic motion. An example is a lescoping automobile antenna.There is some types of manipulator kinematic below.

ROBOT CONFIGURATIONS

(a) Cartesian robot

(b) Cylindrical robot

.

(c) Scara robot

(d) Polar robot

(e) Spherical robot

(f) Jointed arm