Robotics

INTRODUCTION

ROBOTICS

The term “Robotics” means a science which enables us to design and manufacture “Robots”. These robots may be meant for real life applications in automated manufacturing processes or non-manufacturing activities.
Historically, origin of the terms “Robotics” is related to a French author “Isac Asimov” who gave the following three popular rules of Robotics.
1. A robot may not injure a human being or through inaction, allow one to come to harm.
2. A robot must obey the orders given to it by human beings except where such orders would conflicts with the first law.
3. A robot must protect its own existence as long as such protection does not conflict with the first or second law.

ROBOTS

A “Robot” is any mechanical device operated automatically to perform in a seemingly human way. A garage door opener, which automatically opens the door by remote control is also a robot, obviously this is not an industrial robot.
The robot institute of America (RIA) defines industrial robots as:-
“A robot is a programmable, multi-functional manipulator designed to move material, parts or specialized devices through variable programmed motions for the performance of a variety of tasks.”
Today’s robot are fitted with a variety of sensors (like vision, ranging, force-torque, touch, proximity etc) sending the sensory information to the computer which processes them subject to give objective and constraints and develops action decisions for the robot actuators. Robots are more flexible of ability to perform new tasks or to carry out complex sequence of motion then other categories of automated manufacturing equipment. Generally speaking, robots are machines with some degree of intelligence and operated under the control of a mini or micro-computer.

REASONS FOR USING ROBOTS:-
1. The reasons for introducing into a production process could be:-
2. It relives man of hazardous or fatiguing tasks.
3. It brings improvements in product consistency & quality.
4. In countries short of labour, it brings in saving from labour reductions. It increases the output without increasing the labour force.
5. Robots will lead the way into areas of technology where man has not entered so far.

OBJECTIVES OF USING INDUSTRIAL ROBOTS:-
The use of industrial robots is increasing day by day with a view to achieve the following objectives:-
1. To increase productivity
2. To raise the quantity level of products.
3. To minimize the labour requirement.
4. To reduce production time.
5. To remove existing manufacturing processes.
6. To enhance the life of production machines.
7. Thus, to minimize the loss of man-hours on account of accidents and diseases.

CONSTRUCTION / BASIC ELEMENTS OF ROBOTS:
A robot carries a large number of components, of which the main components are the following:-
1. BASE: Base is the bottom most position of the robot which may be fixed or mobile.
2. MANIPULATOR ARM: The manipulator comprising of base, arm & wrist are the most obvious parts of the robot. The robots movements are executed by the mechanical parts like links, power joints and transmitting system along with internal sensors housed within the manipulators (or) the manipulator (mechanical) unit is much like a human arms and wrist that carries a tool to perform work. The tool may be a welding head, a spray gun or a gripper containing on-off jaws depending upon the specific application of the robot. It has a number of degrees of freedom of movement to reach a point with a specific orientation in space.
3. GRIPPER /END EFFECTOR: End effector is the tool, a sort of gripper, which directly interacts with the job. Grippers are being designed to handle a wide range of part configuration or it function to holding a piece or a tool, depending upon the application of the robot.
4. DEVICES: It is also known as actuators; they move the manipulator arm & end effectors to the required position in space.
5. CONTROLLER: The controller acts like a brain of robot. It performs the function of storing and sequencing data in memory, initiating and stopping the motion of the manipulator and interacting with the environment. It delivers commands to the actuator with the help of hardware & software support.
6. SENSORS: They perform dual function:
1. To act as feedback devices to direct further actions of the manipulator arm and the end effectors.
2. To interact with the robot’s working environment.

DEGREE OF FREEDOM:
Vertical Motion: The entire manipulator arm can be moved up & down vertically either by means of the shoulder swivel, i.e. turning it about a horizontal axis or by sliding it in a vertical slide.
Radial Motion: Radial movement i.e. in and out movement, to the manipulator arm is provided by elbow extension by extending it & drawing back.
Rotational Motion: Clockwise or anticlockwise rotation about the vertical axis to the manipulator arm is provided through arm sweep.
Pitch Motion: It enables up & down moment of the wrist & involves rotational moment as well. It is also known as wrist bend.
Roll Motion: Also known as wrist swivel. It enables rotation of wrist.
Yaw: Also called wrist yaw. It facilitates rightward or leftward swiveling movement of the wrist.

TYPES OF JOINTS:-
A joint permits relative motion between two links of a robot. It provides controlled relative movement between two (input/output) links. Usually one joint provides the robot with one degree of freedom. The robot is usually classified to the number of degree of freedom possessed by them. Various types of mechanical joints are:-
1. Linear Joint (Type “L” Joint)-
It permits linear sliding motion between two links whose axes are parallel to each other.
2. Orthogonal Joint (Type “O” Joint)-
In this case the two links are perpendicular to each other but motion between them at the joints is linear sliding types.
3. Rotational Joint (Type “R” Joint)-
It provides rotational relative motion of the joints, with the axis of rotation perpendicular to the axes of two links.
4. Twisting Joint (Type “T” Joint)-
It permits rotator motion between to links, axis of rotation being parallel to the axis of the two links.
5. Revolving Joint (Type “V” Joint)-
It also provides rotary motion, but the axis of the input link is parallel to the axis of rotation of the joints, and the axis of output link is perpendicular to the axis of rotation.

CONFIGURATIONS OF ROBOTS
1. POLAR COORDINATE BODY AND ARM ASSEMBLY:-
It is also known as spherical coordinate system. A robot designed and built around this configuration carries two angular (rotary) motions and one radical (linear) motion, as shown in figure. Since this is achieved by three joints T, R & L it is represented by “TRL” rotation. Here the wrist assembly arm (sliding type) can be actuated relative to body (L-joint) or rotated about vertical axis (T-joint) or also rotated about a horizontal axis (R-joint).
2. CYLINDRICAL CONFIGURATION:-
It can be achieved by various combinations like TLO. In this cylindrical configuration the robot carries two linear motions and one rotary motion. The body of the robot is a vertical column & attached to the base, which can rotate about a vertical axis to provide the rotary motion (T joint). The arm can slide up and down to provide one linear motion in the vertical direction (L joint) i.e. parallel to the axis of the column rotation. Also, the arm can slide in and out to provide the second linear motion (O Joint).
3. CARTESIAN COORDINATE BODY AND ARM ASSEMBLY:-
Since all motions in this case are liner type, it is also called rectilinear robot or x-y-z robot. The robot with this type of configuration i.e. designed and built with this type of coordinate system has sliding motions along the three standard orthogonal axes x,y & z as shown in fig. The slide moving along the x-axis enable a right and left motion, that along the y-axis a forward and backward motion and the one along the z-axis an up & down motion. Thus with proper movements of the slides along these three coordinate axes the robot arm can reach any point in its cubic volume in space i.e. any point in its cubic volume in space i.e. over any point on a rectangular shaped components within the said volume.
4. REVOLUTE COORDINATE SYSTEM:-
This type of configuration is also known with some other names, like anthropomorphic configuration, articulated configuration or jointed arm configuration. In appearance, it very much resembles a human arm, as shown in fig. Just like the human arm, the robot arm in this configuration comprises a no. of straight parts, which are connected together by means of different joints in the same way as the different parts of human arm, which carry joints at shoulders, elbows and wrists. The whole arm is mounted on the base which can be rotated about a vertical axis (Z-axis). Also, the arm can rotate about a horizontal axis, provided by the shoulder joint. The arm link can also rotate about another horizontal axis, provided by the elbow joints. This enables the arms to extend or retract. Further, the last link of the arm (wrist) can rotate about a horizontal axis provided by the wrist joint. Other smaller components of the wrist have some additional movements also. All these motions together enable the arm to reach any location in space within the workspace or work envelope of this type of robot, which is quasispherical.
5. SCARA BODY AND ARM ASSEMBLY:-
SCARA body and arm assembly (selective compliance assembly robot arm) can be achieved by VRO joints. This is similar to the jointed arm robot except that the shoulder and elbow rotation axes are vertical. It is very well suited to perform insertion tasks such as for assembly in a vertical direction requiring side to side adjustment to make the two parts properly. Because of minimal orientation requirements, wrist assembly can be avoided.

TYPES OF ROBOTS
Generally industrial robots can be broadly classified into two main groups as follows:-
a. GENERAL PURPOSE: General purpose robots are those which standard designs and parts and are readily available. They can be easily adopted to the user’s requirements by attaching suitable end effectors or fingers to them according to the requirements of the work, such as a part picking operation, welding operation, spray painting etc. since such robots are mass produced, they are cheaper.
b. SPECIAL PURPOSE: Against this, special purpose robots are tailor made to specific job requirement. The ultimate user to feed this requirements and based on them, these robots are specially designed and built to cater to such specific needs. Obviously, their designing and manufacturing consumes a lot of time. As such, they can not be readily available in market. Also because they can not be manufactured on mass scale, their price is bound to be higher.

DETAILS ABOUT
a. END EFFECTORS: An end effectors is a device which is attached to the robot’s wrist to perform a specific task. Its design depends on the shape and size of parts to be held. The task might be work part handling, spot welding, spray paintings, end effectors may be classified as
b. GRIPPERS: A robot interacts with its surroundings by manipulating objects and tools to fulfill a given task. The robot gripper (end of arm tooling) becomes a link between computer controlled arm and the world around it. Grippers are used to hold either work parts (in pick and place operation, machine loading or assembly work) or tools.
These are
1. Suction or vacuum gripper in which suction cups are used to hold flat objects.
2. Magnetized gripper is used for holding ferrous objects.
3. Hooks used to lift parts off conveyors.

SENSORS
In the pursuit of imparting more and more artificial intelligence to a robot in order to bring its operation nearer to that of a human being, efforts continue to be made for improving its sensing abilities i.e. its vision, hearing, feeling by touching other objects, vision and coordination between its hand and eye. These objectives are achieved by using different types of sensors. To carry out its task, a robot must have access to information on predetermined parameters of the environment. Sensors are used to provide this information.
Some of these sensors are known as internal state sensors & they are used for measuring position, velocity and accelerations of end effectors or the joints of a robot. The other class of sensors are external state sensors, determines the relationships of the robot with its environments and the objects handled by it. Some of the devices used for this purpose include proximity devices, electromagnetic sensors etc.

ROBOT PROGRAM:
There are three types of programmed employed in robot:-
a. Manual Method:- This type of programmed is employed for simple robot & which have relative shorter work cycle. These methods are employed to the robot which is performing the task like pick & place & loading & unloading etc.
b. Walk Through Method: These type of programmed are applicable for the robot which are performing the operation like arc welding & spray paintings. Here the programmer initially moves the arm & head of the robot & after that all the operation which are done by the operator are recorded by the robot memory.
c. Lead Trough Method (Teach Pendant Method): In this type of method, a teach pendant which is a small hand held with a switch & dials is used to control the robots physical movement. After the operation is done by the teach pendant all are recorded by the computer memory.
d. Off Line Programming Method: In this type of method the preparation of robot program off line, in a manner similar to NC m/c programming.

APPLICATION
• Welding: mostly spot welding and arc welding in automobile.
• Spray Painting:-robots are used for spray painting of automobile bodies and bodies of a number of home appliances.

ADVANTAGES
• Save human operators from likely health hazards due to toxic fumes and mist, noise, fire etc.
• Consistency of paint layer over the entire surface.
• Saving in energy consumed.
• Higher productivity.
• Substantial saving in consumption of paint.
• Mechanical Loading & Unloading: Robots are used for loading of stock parts & unloading of finished parts on CNC machine tool die casting m/c, injection & transfer plastic m/c.
• Material Handling & Transfer: Robots are used for shifting an object from one location to the other like:
1. Palletizing & depelletizing
2. Transfer of blanks from on incoming conveyor to the machine tool for further processing.
3. Transfer of parts from one conveyor to the other.

BIBLIOGRAPHY
 Production Technology By O.P Khanna
 Production Technology By R.K.Jain
 Workshop Technology By B.S Raghubanshi
By S.K.Hazra Choudhury
 Production Technology By R.B. Gupta
 Internet
 Process Manufacturing & CIM By P. Grobor