servo based 5 axis robotic arm project report

A PROJECT REPORT ON

Servo Based 5 Axis Robotic Arm

A Project Report on Servo based 5 Axis Robotic Arm

ROBO INDIA | www.roboindia.com 1

Chapter 1 Introduction

The word robot is derived from the Czechoslovakian term robota which is generally

translated as forced labor. This means that the original conception of a robot, as far the

etymology of the word is concerned, was to be a capable servant. It was first used in the

play by the Czechoslovakian author Karel Capek entitled R.U.R. (Rossum's Universal

Robots). In the play, robots were portrayed as small, artificial and anthropomorphic

creatures strictly obeying their master's orders. From this humble conception, many

authors began getting inspirations from the concept of a robot. The most famous of all

the authors that wrote about robots is Isaac Asimov. He was the one who formulated the

four laws of robots:

1. A robot may not injure humanity, or through inaction, allow humanity to come to

harm.

2. A robot may not injure or harm a human being, or through inaction, allow a

human being to come to harm.

3. A robot must obey orders given to it by human beings, except where such orders

would conflict the 0th or 1st law.



4. A robot must protect its own existence as long as such protection does not

conflict with the previous laws. As time passed, people began formulating an

encompassing definition of a robot.

As currently defined, robots exhibit three key elements:

1. Programmability, implying computational or symbolic manipulative capabilities

that a designer can combine as desired (a robot is a computer)

2. Mechanical capability, enabling it to act on its environment rather than merely

function as a data processing or a computational device (a robot is a machine).

3. Flexibility in that it can operate using a range of programs and manipulates and

transport materials in a variety of ways.

This kind of description does not sway too far from what really most robots in the world

are doing. Most robots used nowadays are designed for heavy, repetitive manufacturing

work. They are specifically designed to handle certain tasks that are difficult, dangerous,

or to boring to human beings. Robots can do more work more efficiently than humans

can since robots are precise. They always do the same task with such precision over and

over no matter how long they have worked. Robots nowadays are becoming more and

more important in most industries of the world.

The most common of all these manufacturing robots is the robot arm. A typical robot

arm is made up of seven segments joined by six joints. Usually a servo motor is used in

order to track the movement of the robot arm. The reason for this is quite obvious since

servo motors are designed to move in exact increments unlike DC motors. With such

configurations, a computer may be able to control or manoeuvre the robot very

precisely, repeating exactly the same environment over and over again.

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

a human arm. Servo motor is used for joint rotation. It has about same number of

degree of freedom as in human arm. Humans pick things up without thinking about the

steps involved. In order for a robot or a robotic arm to pick up or move something,

someone has to tell it to perform several actions in a particular order — from moving

the arm, to rotating the “wrist” to opening and closing the “hand” or “fingers.” .So, we

can control each joint through computer interface



Some advanced robot arms make use of sensors like motion and pressure sensors in

order for it to detect foreign obstacles and avoid breaking or dropping what it is

carrying. Robot arm also vary with the type of end effector that they are using. The kind

of end effector that a particular robot arm is using is very much dependent on the kind

of task the robot is designed for:

1. Blowtorches for auto assembly lines robots.

2. Drills for metal application robots.

3. Spray paints for decoration oriented robots.

4. For welding purpose.

5. For pick and place applications.

Fig.1 | ProE model of our Robotic Arm



1.1 Specifications

Our robotic arm is having following features and specification.

1. Degree of Freedom: 5

2. Payload Capacity(Fully Extended) : 100gm

3. Maximum Reach(Fully Extended) : 25cm

4. Rated speed(Adjustable) : 0-0.3 m/s

5. Joint speed(Adjustable) : 0-60 rpm

6. Hardware interface : USB

7. Control Software : computer interface(GUI)

8. Shoulder Base Spin : 180°

9. Shoulder Pitch : 180°

10. Elbow Pitch : 180°

11. Wrist Pitch : 180°

12. Wrist spin: 180°

13. Gripper Opening(Max) : 8cm

1.2 Salient Features

1. The arm has six servos which are controlled through the use of only one

microcontroller Atmel Atmega16.

2. The arm could grab things approximately in a hemisphere of 50cm and is robust

made completely with an aluminium sheet of 2.5mm.

3. The arm is very user friendly because of the computer interface developed by us,

even layman could operate it.

4. It can lift objects up to weight of 100 gm.

5. The base is equipped with high torque servo.

6. The GUI is platform free and dosent require any tool like MATLAB. A single setup

file that can be executed on any both windows operating system i.e. 32/64 bits.

7. The controlling hardware is using USB that makes it ultra-portable. Unlike to the

old systems of serial ports.

8. Keeping the design of robotic arm gripper simple, as well as implementing the

gripping mechanism without using gears and with one servo motors.

9. The gripper is equipped with micro servo which makes it lighter.



Chapter 2

Objective

The main objectives of the project are (1) to be able to design and construct a robot arm,

and (2) to be able to control the robot arm using a computer through a keyboard and

mouse. The first object is very straightforward it requires the modern designing

capacities. The complete robotic arm was first designed and assembled in designing

software. We have used Wildfire ProEngineer to design 3D model of the robot. The

model is designed as per the actual dimensions of the robot. After designing and

assembling the robot in ProE, Drawings are exported. Our objective is to construct

physical parts of the robot and them assemble them as we assembled in the ProE. The

second objective requires a working knowledge of PC to hardware communication.

Additional hardware components aside from the robot arm like opt isolator circuits and

limit switches will be implemented in order to facilitate the safe control of the arm.

An additional objective will be to program the robot arm to do a simple task. This

option, if to be implemented with accuracy and precision, requires a more challenging

task of familiarizing the science of kinematics both forward and reverse kinematics.

However, the implementation used for the automation of this robot arm is time-based.

This means that when automating the robot arm, a program records the length of time



of a certain joint from moving from one position to another. This kind of automation,

however, is not very accurate or precise since it doesn’t take into consideration the

actual load that the arm is carrying.



Chapter 3

Methodology

The following block diagram explains working of the system, later we shall discuss all of

the components of the diagram.

Fig.2 | Block diagram



Chapter 4

Parts designing and assembly

This chapter elaborate the designing of robotic arm parts and assembling them in

Wildfire ProEngineer.

4.1 Introduction to ProE

Pro/ENGINEER Tool Design Option(TDO) is the essential 3D CAD tool for professional

designers who need to rapidly create higher quality mold inserts, casting cavities, and

patterns. Using Pro/ENGINEER Tool Design Option’s powerful parametric surfacing

capabilities, engineers can easily create even the most complex parting surfaces with

unprecedented ease. By automating many time-consuming, complex processes,

Pro/ENGINEER TDO enables us to focus less on tedious tasks and more on creating

innovative, top quality tool designs. Easy Interfaces for Mold and Casting

Pro/ENGINEER Tool Design Option features a variety of 3D CAD tools specifically

engineered to accelerate the design of molds and castings. With its robust functionality

and two easy-to-use process-driven GUIs – one for molds and one for castings –

engineers can quickly develop inserts, casting cavities and patterns, regardless of the

complexity of geometry. Since the 3D models we create in Pro/ENGINEER automatically

reference your mold and casting designs in Pro/ENGINEER TDO, any changes we make



are instantly reflected in our tooling and patterns, which further speeds up the product

development process.

4.1 Designing servo

Fig.3 | ProE model of Servo

Fig.4| Wireframe and hidden lines of servo model.



4.2 Dimension of Servo are as follows.

4.2.1 Servo 17 Kg Torque:

A (mm) 46

B (mm) 40

C (mm) 41

D (mm) 20

E (mm) 55

F (mm) 29

4.2.2 Servo 6.8 Kg Torque:

A (mm) 44.2

B (mm) 40

C (mm) 41

D (mm) 20

E (mm) 55

F (mm) 29

4.2.3 Servo 4.5 Kg Torque (Standard servo):

A (mm) 46

B (mm) 41

C (mm) 42

D (mm) 21

E (mm) 56

F (mm) 29



4.3 Base Part

Fig.5 | Base of Robotic Arm

Fig. 6 | Wireframe and hidden lines of base model.



4.4 Servo Shaft

Fig.7 | Base of Robotic Arm

Fig.8 | Wireframe and hidden lines of servo shaft model.



4.5 Gripper stand

Fig.9 | Gripper Stand

Fig. 10 | Gripper Base Drawing (dimensions are in mm)



4.5 Wrist stand

Fig.11 | wrist (Top) Stand

4.6 Linking rod 1

Fig .12 | Linking Rod 1



Fig.13 | Drawing of linking Rod 1. (Dimensions are in mm)



4.7 Linking rod 2

Fig.14 | Lining Rod 2



Fig.15 | Drawing Linking rod 2. (Dimension are in mm)

4.8 Servos’ base stand

Fig. 16 |Base Servo’s stand



Fig. 17 | Drawings Base Servo’s stand (dimensions are in mm)



4.9 Base assembly

Fig. 18 | Base Assembly

4.10 Linking rod assembly

Fig.19 | Assembly of connecting links



4.11 Gripper assembly

Fig.20 | Gripper Assembly

Fig. 21 | Gripper Assembly with wrist servo



4.12 Final assemblies

Fig. 22 | Final Assembly 1

Fig.23 | final Assembly 2



Chapter 5

The parts & Interfacing

We have seen the designing and assembly of the parts in ProE. Here we will have

detailed discussion about the parts used in robotic arm.

5.1. Servo

A Servo is a small device that has an output shaft. This shaft can be positioned to specific

angular positions by sending the servo a coded signal. As long as the coded signal exists

on the input line, the servo will maintain the angular position of the shaft. As the coded

signal changes, the angular position of the shaft changes. In practice, servos are used in

radio controlled airplanes to position control surfaces like the elevators and rudders.

They are also used in radio controlled cars, puppets, and of course, robots.

Fig.24 | A Futaba S-148 Servo

http://www.seattlerobotics.org/guide/images/servo1.jpg



Fig. 25 | servo notations

Servos are extremely useful in robotics. The motors are small, as we can see by the

picture above, have built in control circuitry, and are extremely powerful for their size.

A standard servo such as the Futaba S-148 has 42 oz/inches of torque, which is pretty

strong for its size. It also draws power proportional to the mechanical load. A lightly

loaded servo, therefore, doesn’t consume much energy. The guts of a servo motor are

shown in the picture below.

Fig.26 | Servo disassembled

http://www.seattlerobotics.org/guide/images/servo3c.jpg



Fig.27 | Servo circuit

So, how does a servo work? The servo motor has some control circuits and a

potentiometer (a variable resistor, aka pot) that is connected to the output shaft. In the

picture above, the pot can be seen on the right side of the circuit board. This pot allows

the control circuitry to monitor the current angle of the servo motor. If the shaft is at the

correct angle, then the motor shuts off. If the circuit finds that the angle is not correct, it

will turn the motor the correct direction until the angle is correct. The output shaft of

the servo is capable of travelling somewhere around 180 degrees. Usually, its

somewhere in the 210 degree range, but it varies by manufacturer. A normal servo is

used to control an angular motion of between 0 and 180 degrees. A normal servo is

mechanically not capable of turning any farther due to a mechanical stop built on to the

main output gear.

The amount of power applied to the motor is proportional to the distance it needs to

travel. So, if the shaft needs to turn a large distance, the motor will run at full speed. If it

needs to turn only a small amount, the motor will run at a slower speed. This is called

proportional control.

How do we communicate the angle at which the servo should turn? The control wire is

used to communicate the angle. The angle is determined by the duration of a pulse that

is applied to the control wire. This is called Pulse Coded Modulation. The servo expects

to see a pulse every 20 milliseconds (.02 seconds). The length of the pulse will

determine how far the motor turns. A 1.5 millisecond pulse, for example, will make the

motor turn to the 90 degree position (often called the neutral position). If the pulse is

shorter than 1.5 ms, then the motor will turn the shaft to closer to 0 degrees. If the pulse



is longer than 1.5ms, the shaft turns closer to 180 degrees. So we generate the desired

pulse with the help of microcontroller.

Fig.28 | Servo pulses

5.2 Servo wiring and interface

The Servo uses three wires: white carries the control signal, red carries power (usually

4.8 V to 6 V), and black is ground.

Fig.29 | Servo wirings

Black Red

White or yellow



5.3 The controller

Robotic arm controller comprises several electronic components. Here we will

discuss the important parts of the circuit.

5.3.1 The microcontroller (Atmega 16)

The ATmega16 is a low-power CMOS 8-bit microcontroller based on the AVR

enhanced RISC architecture. By executing powerful instructions in a single clock

cycle, the ATmega16 achieves throughputs approaching 1 MIPS per MHz

allowing the system designer to optimize power consumption versus processing

speed.

Fig.30 | Atmega 16 Pinout diagram.



Fig.31 | Block diagram of Atmega 16

The AVR core combines a rich instruction set with 32 general purpose working

registers. All the 32 registers are directly connected to the Arithmetic Logic Unit

(ALU), allowing two independent registers to be accessed in one single

instruction executed in one clock cycle. The resulting architecture is more code

efficient while achieving throughputs up to ten times faster than conventional

CISC microcontrollers. The ATmega16 provides the following features: 16K bytes

of In-System Programmable Flash Program memory with Read-While-Write



capabilities, 512 bytes EEPROM, 1K byte SRAM, 32 general purpose I/O lines, 32

general purpose working registers, a JTAG interface for Boundary scan, On-chip

Debugging support and programming, three flexible Timer/Counters with

compare modes, Internal and External Interrupts, a serial programmable USART,

a byte oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional

differential input stage with programmable gain (TQFP package only), a

programmable Watchdog Timer with Internal Oscillator, an SPI serial port, and

six software selectable power saving modes. The Idle mode stops the CPU while

allowing the USART, Two-wire interface, A/D Converter, SRAM, Timer/Counters,

SPI port, and interrupt system to continue functioning. The Power-down mode

saves the register contents but freezes the Oscillator, disabling all other chip

functions until the next External Interrupt or Hardware Reset. In Power-save

mode, the Asynchronous Timer continues to run, allowing the user to maintain a

timer base while the rest of the device is sleeping. The ADC Noise Reduction

mode stops the CPU and all I/O modules except Asynchronous Timer and ADC, to

minimize switching noise during ADC conversions. In Standby mode, the

crystal/resonator Oscillator is running while the rest of the device is sleeping.

This allows very fast start-up combined with low-power consumption. In

Extended Standby mode, both the main Oscillator and the Asynchronous Timer

continue to run. The device is manufactured using Atmel’s high density non-

volatile memory technology. The On chip ISP Flash allows the program memory

to be reprogrammed in-system through an SPI serial interface, by a conventional

non-volatile memory programmer, or by an On-chip Boot program running on

the AVR core. The boot program can use any interface to download the

application program in the Application Flash memory. Software in the Boot Flash

section will continue to run while the Application Flash section is updated,

providing true Re ad-While-Write operation. By combining an 8-bit RISC CPU

with In-System Self-Programmable Flash on a monolithic chip, the Atmel

ATmega16 is a powerful microcontroller that provides a highly-flexible and cost-

effective solution to many embedded control applications. The ATmega16 AVR is

supported with a full suite of program and system development tools including:

C compilers, macro assemblers, program debugger/simulators, in-circuit

emulators, and evaluation kits.



5.3.1.1 Pin Description of ATmega 16.

VCC: Digital supply voltage.

GND: Ground.

Port A (PA7..PA0): Port A serves as the analog inputs to the A/D

Converter. Port A also serves as an 8-bit bi-directional I/O port, if the A/D

Converter is not used. Port pins can provide internal pull-up resistors

(selected for each bit). The Port A output buffers have symmetrical drive

characteristics with both high sink and source capability. When pins PA0

to PA7 are used as inputs and are externally pulled low, they will source

current if the internal pull-up resistors are activated. The Port A pins are

tri-stated when a reset condition becomes active, even if the clock is not

running.

Port B (PB7..PB0): Port B is an 8-bit bi-directional I/O port with internal

pull-up resistors (selected for each bit). The Port B output buffers have

symmetrical drive characteristics with both high sink and source

capability. As inputs, Port B pins that are externally pulled low will source

current if the pull-up resistors are activated. The Port B pins are tri-stated

when a reset condition becomes active, even if the clock is not running.

Port C (PC7..PC0): Port C is an 8-bit bi-directional I/O port with internal

pull-up resistors (selected for each bit). The Port C output buffers have


capability. As inputs, Port C pins that are externally pulled low will source

current if the pull-up resistors are activated. The Port C pins are tri-stated

when a reset condition becomes active, even if the clock is not running. If

the JTAG interface is enabled, the pull-up resistors on pins PC5(TDI),

PC3(TMS) and PC2(TCK) will be activated even if a reset occurs.

Port D (PD7..PD0): Port D is an 8-bit bi-directional I/O port with internal

pull-up resistors (selected for each bit). The Port D output buffers have


capability. As inputs, Port D pins that are externally pulled low will source

current if the pull-up resistors are activated. The Port D pins are tri-stated

when a reset condition becomes active, even if the clock is not running.



RESET: Reset Input. A low level on this pin for longer than the minimum

pulse length will generate a reset, even if the clock is not running.

XTAL1: Input to the inverting Oscillator amplifier and input to the

internal clock operating circuit.

XTAL2: Output from the inverting Oscillator amplifier.

AVCC: AVCC is the supply voltage pin for Port A and the A/D Converter. It

should be externally connected to VCC, even if the ADC is not used. If the

ADC is used, it should be connected to VCC through a low-pass filter.

AREF: AREF is the analog reference pin for the A/D Converter.

5.3 Serial Communication:

Serial communication is a way enables different equipments to communicate with their

outside world. It is called serial because the data bits will be sent in a serial way over a

single line.

A personal computer has a serial port known as communication port or COM Port used

to connect a modem for example or any other device, there could be more than one COM

Port in a PC.

Serial ports are controlled by a special chip called UART (Universal Asynchronous

Receiver Transmitter). Different applications use different pins on the serial port and

this basically depend of the functions required. If we need to connect our PC for

example to some other device by serial port, then we have to read instruction manual

for that device to know how the pins on both sides must be connected and the setting

required.

5.3.1 Advantages of Serial Communication

Serial communication has some advantages over the parallel communication. One of the

advantages is transmission distance, serial link can send data to a remote device more

far then parallel link. Also the cable connection of serial link is simpler then parallel link

and uses less number of wires.



Serial link is used also for Infrared communication, now many devices such as laptops &

printers can communicate via inferred link.

5.3.2 Communication methods

There are two methods for serial communication, Synchronous & Asynchronous.

5.3.2.1 Synchronous serial communication:

In Synchronous serial communication the receiver must know when to “read” the next

bit coming from the sender, this can be achieved by sharing a clock between sender and

receiver.

In most forms of serial Synchronous communication, if there is no data available at a

given time to transmit, a fill character will be sent instead so that data is always being

transmitted. Synchronous communication is usually more efficient because only data

bits are transmitted between sender and receiver, however it will be more costly

because extra wiring and control circuits are required to share a clock signal between

the sender and receiver.

5.3.2.2 Asynchronous serial communication:

Asynchronous transmission allows data to be transmitted without the sender having to

send a clock signal to the receiver. Instead, special bits will be added to each word in

order to synchronize the sending and receiving of the data.

When a word is given to the UART for Asynchronous transmissions, a bit called the

“Start Bit” is added to the beginning of each word that is to be transmitted. The Start Bit

is used to alert the receiver that a word of data is about to be sent, and to force the clock

in the receiver into synchronization with the clock in the transmitter.



Fig.32 | Example of serial data transmission

After the Start Bit, the individual bits of the word of data are sent, each bit in the word is

transmitted for exactly the same amount of time as all of the other bits

When the entire data word has been sent, the transmitter may add a Parity Bit that the

transmitter generates. The Parity Bit may be used by the receiver to perform simple

error checking. Then at least one Stop Bit is sent by the transmitter.

If the Stop Bit does not appear when it is supposed to, the UART considers the entire

word to be garbled and will report a Framing Error.

5.4 USB to Serial Converter

Since latest computers and laptops don’t come with serial ports. Because the popularity

of the USB. So we are using USB to serial converter. That makes our project ultra-

portable. A typical USB to serial converter creates a comport on the computer or laptop

and connects that comport to the external world.

Fig.33 | USB to Serial Converter.



5.5 Software

The software we have got, is very easy to use. It requires the comport no. to

the robotic arm controller is attached. The complete operations of the arm

con be controlled through the drag bar or by entering value in the text box.

This software provide axis wise control.

Fig.34 | Robotic Arm Controller.



Chapter 6

The Construction

Till now we have seen all of the parts, design and assembly of the robot. Now we can

construct the robotic arm as per our designs. We took out the drawings and

manufactured the parts from aluminium sheet and ACP sheet.

Then assembled these parts as we have seen in the ProE assembly. Here we are show

some pic of the assembly.

Fig35 |. Assembly of Base.



Fig.36 | After connecting link rod 1 and link rod 2 to the base.

Gripper is equipped with micro servo, two gears and some kinematic links. The bottom

view shows all these in gripper assembly.

Fig.37 | Gripper top view.



Fig.38 | the gripper assembly bottom view

Fig.39 | The final assembly



Chapter 7

References

1. Atmega 16 data sheet.

2. USB to serial data sheet.

3. Futaba servo mannuals.

4. PWM Generation guide from Atmel.

servo based 5 axis robotic arm project report

Engineering