ROBOTICS

Introduction

Robotics is a science of designing and building robots suitable for real life application in automated manufacturing and other non-manufacturing environments

A robot is a device that is built to independently perform actions and interact with its surroundings.

A robot is a reprogrammable, multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.” (Robot Institute of America)

The word Robot originates from ‘Robota’ means Slave or mechanical item that would help its master

OR “A robot is a one-armed, blind idiot with limited

memory and which cannot speak, see, or hear.”

Robot ranges from toys to automated assembly lines

Functions of Robot

Classified into three categories: “Sensing” the environment by external

sensorE.g.- Vision, touch, voice, proximity etc.

“Decision making” based upon information received from sensors

“Performing” the task decided

Advantage

Working in adverse conditions Providing repeatability and consistency Increasing productivity Achieving more accuracy Lifting and moving heavy loads Working in unfavourable hours

Disadvantage

Initial installation cost is very high Lack of capability to respond in

emergency Replace human workers, causing

unemployment

Types of Robot

There are many ways how you could possibly define different types of robots

Types of robots by application Types of robots by locomotion and

kinematics Types of robot by control

Non Servo control Servo Control etc.

Types of robots by application

Robots do a lot of different tasks in many fields and the number of jobs , So there are:

Industrial robots - Industrial robots are robots used in an industrial manufacturing environment. Usually these are articulated arms specifically developed for such applications as welding, material handling, painting and others.

Domestic or household robots - Robots used at home. This type of robots includes many quite different devices such as robotic vacuum cleaners, robotic pool cleaners, sweepers, gutter cleaners 

Medical robots - Robots used in medicine and medical institutions. First and foremost - surgery robots. Also, some automated guided vehicles and maybe lifting aides.

Service robots - These could be different data gathering robots, robots made to show off technologies, robots used for research, etc. 

Military robots - Robots used in military. This type of robots includes bomb disposal robots, different transportation robots, reconnaissance drones.

Entertainment robots - These are robots used for entertainment. This is a very broad category. It starts with toy robots such as robosapien or the running alarm clock and ends with real heavyweights such as articulated robot arms used as motion simulators. 

Space robots - This type would include robots used on the International Space Station, Canadarm that was used in Shuttles, as well as Mars rovers and other robots used in space.

Types of robots by locomotion and kinematics

1. Stationary robots (including robotic arms with a global axis of movement) 

1.1 Cartesian/Gantry robots 

1.2 Cylindrical robots 

1.3 Spherical robots 1.4 SCARA robots 1.5 Articulated robots (robotic arms) 1.6 Parallel robots 

2. Wheeled robots 2.1 Single wheel (ball) robots 2.2 Two-wheel robots 2.3 Three and more wheel robots 

3. Legged robots 3.1 Bipedal robots (humanoid robots) 3.2 Tripedal robots 3.3 quadrupedal robots 3.4 hexapod robots 3.5 other number of legs 

4. Swimming robots 5. Flying robots 6. Mobile spherical robots (robotic balls) 7. Swarm robots

Cartesian robots

Typical Cartesian robots have 3 linear axes of freedom which are perpendicularly oriented at each other

Because of their rigid structure, this type of robots usually can offer good levels of precision and repeatability. 

This type of robots are also easier to program Cartesian robots are the simplest of all

stationary robots Because of their relative simplicity, if

compared to other types of robots that could do similar tasks, Cartesian robots are ought to be cheaper than their counterparts

 It still won't be able to make movements needed for some tasks, like welding

Also, its footprint can be quite large compared to other robots that could do the same task

So, it can be very effective for tasks where extensive tool orientation is not required . For example - gluing, soldering, possibly sewing, pick and place operations etc.

Gantry robots

 Although it is a part of Cartesian robot but Gantry robots should be discussed separately because of their distinctive structure and their possible applications

As, movement along the x axis takes place between two beams which are directed in the x direction.

The carriage on the y axis can move along it between aforementioned x axis beams.

The tool can be lowered down from the carriage, thus forming the z axis movement The work envelope is similar with other robots of

Cartesian type, however, a gantry robot usually encloses its work envelope from the outside. The only part of the robot that interferes with its work space is its z axis and the tool

As, robot stands firmly on four "legs". If those legs are strong enough, the robot can lift very heavy weights. This is the most prominent use of a gantry robot - a lifter-mover. So, Gantry robots can be used for pick and place

tasks that could include packaging, assembly and others.

It can be used as a platform for other robots. For example, a 6-axes robotic arm can be

mounted upside-down as a tool on a gantry robot's Z axis.

Cylindrical robot

The cylindrical robot type is one of the rarest nowadays

 It has three axes of movement - two of which are linear and one - circular. So, usually robots of this type can move

along Z and Y axes and rotate along Z axis

This, basically, forms a cylindrical coordinate system - hence it has a cylindrical work envelope.

The most usual set of applications in which they are used, where the cylindrical work envelope combined with horizontal tool orientation is required. For example - specific handling and

assembly tasks or spot welding.

Spherical robots

Spherical robots, sometimes regarded as polar robots, are stationary robot arms with spherical or near-spherical work envelopes that can be positioned in a polar coordinate system.

 These robots are more sophisticated than Cartesian and cylindrical robots, while control solutions are less complicated than those of articulated robot arms

 It has two rotary joints and one linear to form spherical work envelope

There can be more than three joints but these three are the basic ones that form the work envelope

 Joints would add more flexibility, but wouldn't radically change the reachable area For example, if the gripper could rotate, this

would be a 4-axis robot while the work envelope wouldn't change at all

Joint Arm/ Articulated Robot

A Jointed Arm robot has three rotational axes connecting three rigid links and a base

Jointed Arm robot is frequently called an anthropomorphic arm because it closely resembles a human arm. 

The first joint above the base is referred to as the shoulder. The shoulder joint is connected to the upper arm, which is connected at the elbow joint.

Jointed Arm robots are suitable for a wide variety of industrial tasks, ranging from welding to assembly

There are actually three different types of joint arm robots: (a) Pure Spherical (b) Parallelogram spherical and (c) cylindrical

SCARA Robots

SCARA stands for Selective Compliance Assembly Robot Arm

It is a subclass of a joint cylindrical arm manipulator robot

It is a combination of the articulated arm and the cylindrical robot.

This robot has more than three axes. It is used widely in assembly operations

requiring insertion of objects into holes. The rotary axes are mounted vertically

rather than horizontally. This configuration minimizes the robot's

deflection when it carries an object while moving at a programmed speed.

The basic configuration of a SCARA is a four degree-of-freedom robot with horizontal positioning accomplished by a combined Theta 1 and Theta 2 motion, much like a shoulder and elbow held perfectly parallel to the ground.

SCARAs are know for their fast cycle times, excellent repeatability, good payload capacity and a large workspace

For flexible, high speed parts assembly and handling, SCARA is one of the most useful and flexible automation tools available

Robot Configurations

Types of robot by control

There are only two basic types of robots: “SERVO CONTROLLED & NON-SERVO CONTROLLED

Non-servo robots are inexpensive, easy to understand and easy to set up,

Also called as limited sequence robot, end point robots, pick and place robots or bang bang robots

implemented by setting limits or mechanical stops for each joint and sequencing the actuation of each joint to accomplish the cycle

No control over the motion at the intermediate points, only end points are known

Programming accomplished by setting desired sequence of moves adjusting end stops for each axis accordingly the sequence of moves is controlled by a “squencer”, which

uses feedback received from the end stops to index to next step in the program

Low cost and easy to maintain, reliable relatively high speed repeatability of up to 0.01 inch limited flexibility typically hydraulic, pneumatic drives

Servo controlled robots

Servo controlled robots have a wide range of capabilities.

Perform multiple point to point (PTP) transfers or can move along a Continuous path (CP) .

Most servo controlled robots use jointed arm mechanism and can be programmed to avoid an obstruction.

Programming can be rather sophisticated Complete servo controlled robot system is

relatively expensive

Closed Loop control used to monitor position, velocity (other variables) of each joint

Another Classification Based on Control Systems

Point-to-point (PTP) control robot: is capable of moving from one point to another point.

The locations are recorded in the control memory.

PTP robots do not control the path to get from one point to the next point.

Common applications include component insertion, spot welding, hole drilling, machine loading and unloading, and crude assembly operations.

Continuous-path (CP) control robot: with CP control, the robot can stop at any specified point along the controlled path.

All the points along the path must be stored explicitly in the robot’s control memory.

Typical applications include spray painting, finishing, gluing, and arc welding operations.

Controlled-path robot: the control equipment can generate paths of different geometry such as straight lines, circles, and interpolated curves with a high degree of accuracy.

All controlled-path robots have a servo capability to correct their path

Robot Drive Systems

A robot will require a drive system for moving their arm, wrist, and body. A drive system is usually used to determine the capacity of a robot. For actuating the robot joints, there are three different types of drive systems available such as:

Electric drive system, Hydraulic drive system, and Pneumatic drive system.

Electric Drive System:

The electric drive systems are capable of moving robots with high power or speed.

The actuation of this type of robot can be done by either DC servo motors or DC stepping motors.

It can be well – suited for rotational joints and as well as linear joints.

The electric drive system will be perfect for small robots and precise applications.

It has got greater accuracy and repeatability.

The one disadvantage of this system is that it is slightly costlier.

An example for this type of drive system is Maker 110 robot.

Pneumatic drive system

The pneumatic drive systems are especially used for the small type robots, which have less than five degrees of freedom.

It has the ability to offer fine accuracy and speed.

This drive system can produce rotary movements by actuating the rotary actuators.

The translational movements of sliding joints can also be provided by operating the piston.

The price of this system is less when compared to the hydraulic drive.

The drawback of this system is that it will not be a perfect selection for the faster operations.

Hydraulic Drive System:

The hydraulic drive systems are completely meant for the large – sized robots.

It can deliver high power or speed than the electric drive systems.

This drive system can be used for both linear and rotational joints.

The rotary motions are provided by the rotary vane actuators, while the linear motions are produced by hydraulic pistons.

The leakage of hydraulic oils is considered as the major disadvantage of this drive.

An example for the hydraulic drive system is Unimate 2000 series robot.

WRIST

Typically has 3 degrees of freedom Roll involves rotating the wrist about the

arm axis Pitch up-down rotation of the wrist Yaw left-right rotation of the wrist

End effector is mounted on the wrist

WRIST MOTIONS

End effectors

An end effector is a device or tool that's connected to the end of a robot arm where the hand would be.

The end effector is the part of the robot that interacts with the environment.

The structure of an end effector and the nature of the programming and hardware that drives it depend on the task the robot will be performing.

Some of examples are

End Effectors are categorise into two major types: Grippers Tools

GRIPPERS: Angular closing and parallel closing

grippers are the most common of all end effectors.

Simple angular closing grippers are nothing more than air operated pliers while simple parallel closing grippers are essentially air operated vices.

Applications of Robots

Industrial Application Material Handling

Material transfer application Machine loading and unloading applications Pelletizing application

Processing Applications Arc Welding Spot Welding Spray painting Paint scraping

Assembly Applications The assembly task Peg-in-hole assembly

Inspection applications Sensor based application Vision based application Testing

Non Industrial Application Home Sector Health care Service Sector Agriculture and farms Research and Exploration

Robot Selection

The technical features are the prime considerations in the selection of a robot.

1. Degrees of freedom 2. Control system to be adopted 3. Work volume 4. Load-carrying capacity 5. Accuracy and repeatability

The characteristics of robots generally considered in a selection process include

1. Size of class Micro (x <=1 m) Small (1 < x <= 2 m) Medium (2 < x <= 5 m) Large (x > 5 m) 2. Degrees of freedom: the cost of increases with

increasing number of DOF. 3. Velocity 4. Actuator type

5. Control mode 6. Repeatability 7. Lift capacity 8. Right-Left traverse 9. Up-down-traverse 10. In-out-traverse 11. Yaw 12. Pitch 13. Roll 14. Weight of the robot