essay with robot

Essay on Robots: Top 17 Essays | Intelligent Machines | Engineering

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Essay on Robots

Essay Contents:

Essay on the Reasons for Using Robots

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Essay # 1. Definition of Robot:

Robot, once a creature of science fiction, is today a reality. It is the off-shoot of the second industrial revolution. Robot can be defined as a programmable multifunction manipulator designed or intelligent machine to move material, parts, tools, or specialised devices through variable programmed motions for the performance of variety of tasks.

Today’s robots 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 given objective and constraints, and develops action decisions for the robot actuators.

Robots are more flexible in terms of ability to perform new tasks or to carry out complex sequences of motion than 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.

Industrial robots (tough and tireless) are capable of handling a variety of jobs right from material handling to complex assembly tasks. They perform hazardous and monotonous tasks with tireless precision. They improve productivity and reduce manufacturing costs. They can perform complex jobs. They can even cope with changing conditions in the workplace, when fitted with sensors and adaptive controls.

Essay # 2. Basic Elements of Robots :

The basic elements of industrial robots are manipulator, controller, end effector, sensors and energy source. (Refer Fig. 38.1).

The manipulator comprising of base, arm and wrist are the most obvious parts of the robot. The robot’s movements are executed by the mechanical parts like links, power joints, and transmission system along with internal sensors housed within the manipulator.

The controller acts like a brain of robot. It performs the functions of storing and sequencing data in memory, initiating and stopping the motions of the manipulator, and interacting with the environment.

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 configurations.

Sensors to sense the environment are essential for intelligent robots.

Energy source is required to cause movement of the manipulator arm. They may take the form of electrical, hydraulic or pneumatic devices.

Essay # 3. General Structure of Robot:

Figure 38.13 shows a general structure of an advanced robot. The operational unit consists of articulated mechanical system (AMS), (comprising of rigid links and kinetic joint), transmission system and actuators (which control the configuration of each articulation). The internal sensors are provided to indicate the position, velocity and forces of the end effector. The external sensors are provided to sense the environment.

The structural analysis program provides the user with integrated interactive processing from structural analysis to strength evaluation, by means of a pre-processor for graphics, geometrical modeling, finite element modeling and output graphic functions to be used for displaying the deformation quantity, indicating equi-stress lines, stress diagrams, excess stress, dynamic response and animation.

This system displays the element division diagrams and the vibration characteristics of the entire robot as a result of the frequency response calculation for the component parts of the robot system. In the design stage the strength and rigidity of each part are analysed, while the dynamic characteristics of the entire system are predicted and evaluated for lighter weight and higher rigidity.

ii. Mechanical Design of a Robot :

The mechanical design of a robot is an iterative process involving evaluation and choice among a large number of engineering and technical considerations in several disciplines.

A purely static, rigid-body approach to design is not sufficient and factors like mechanical system stiffness, natural frequencies, control system compatibility also need to be considered. A robot should be designed to have only the flexibility it needs to perform the range of tasks for which it is intended.

The various design consideration are:

(i) System Specification:

It includes range, reach, work envelope, load capacity.

(ii) System Configuration:

It includes the joint configuration, number of degrees of freedom, joint travel range, drive configuration.

(iii) System Performance:

It includes system velocity and acceleration, repeatability, resolution, accuracy, component life and duty cycle. Detailed design of major components concerns the robot structures, robot joints, actuators, transmission, wiring and routing of cables and hoses. One should evaluate the possible flexibility of the robot, grippers, tools, and peripheral units and integrate all components to one system.

Essay # 6. Classification of Robots:

Broadly three classes of robots could be considered:

(i) Pre-Programmable/Re-Programmable General Purpose Industrial Robots:

These operate fully by programmed computer control. These are most useful for all structured operations, i.e. activities whose motion and work handling requirements are known before hand and thus can be programmed.

The robot is taught before-hand to perform the necessary action in the teach mode. The robot can then take over and execute the operation repetitively such as in welding, painting, assembly of components for mass manufacturer, loading/unloading of jobs into and from machine tools, etc.

(ii) Tele-Operated, Man-Controlled Robots or Man-in-the-Loop Manipulator:

These differ from totally machine-controlled robots in the sense that the advantage of presence of man is taken in situations where it is not possible to anticipate all the motion and handling requirements in such details as to render them programmable or teachable for machine control. This type of requirement is found in hazardous locations.

The servo-driven master-slave manipulator with force feedback, or vehicle mounted heavy duty multi-axis power manipulator performs the necessary work in hazardous environment, taking commands from a human controller who can manipulate the slave arms at the scene of operation from safe location, relying for viewing on closed circuit television.

(iii) Intelligent Robots:

These are very advanced, state of the art robots and possess sufficient artificial or machine intelligence, somewhat analogous to the sensory perception of the neuro-muscular coordination that human beings are capable of.

Such intelligent robots can not only explore the environment on their own machine perceptions and evaluate them in real time, but also execute the necessary motor functions matching the action of their sensory inputs.

Advanced robots have been built with mobility to not only move over floors but also to climb, ability to avoid obstacles, high power-to-weight ratios, compactly assembled, with on board sensors, instruments and power supplies.

According to another general method of classification robots are classified as:

(i) Special purpose, designed and produced for a limited range of specific jobs, like welding, painting, casting, assembling, material handling etc.

(ii) General purpose of universal robots designed and produced to perform a wide variety of jobs. These may be non-servo-controlled, servo-controlled or sensory type depending on sophistication.

Essay # 7. Specifications of Robot:

i . Work Envelope:

Work envelope or work volume of a manipulator is defined as the envelope or space within which the robot can manipulate the end of the wrist. It depends on the number of types of joints, physical size of the joints and links and the ranges of various joints.

The shape of work volume is dependent upon the configuration of robot, for example, polar configuration has partial sphere as work space, cartesian coordinate configuration robot has a rectangular work space, and a cylindrical robot has a cylindrical work envelope.

ii . Load Carrying Capacity:

It is dependent on the physical size and construction of robot, and also on the capability to transmit force and torque to the end effector in the wrist.

iii . Speed:

It varies from one point to other and it can be programmed into cycle so that different portions of cycle are performed at different speeds as desired. Maximum speed may be of the order of 2m/sec. In fact more important than speed is the accelerating and decelerating capability in a controlled manner. Robot may hardly achieve its top rated speed in view of its operation in a confined area.

iv . Repeatability:

It is the measure of the robot’s ability to position an object at a previously taught point in the work envelope. Due to inherent errors present (particularly due to mechanical sources), the robot will not be able to return to exact programmed point.

v . Control Resolution:

It refers to the capability of the system (both controller and the positioning device) to divide the range of total movement into closely spaced points than can be identified. Thus it would represent the minimum noticeable movement achievable. It may be mentioned that controller can generate pulses of very small duration but the positioning device should be able to respond and change its position accordingly.

In such a case:

Essay # 8. Types of Joints of a Robot:

A joint permits relative motion between two links (or arms) of a robot. It provides controlled relative movement between two (input and output) links. Usually one joint provides the robot with one degree of freedom. The robots are usually classified according to the number of degrees of freedom possessed by them.

Various types of mechanical joints are:

(i) Linear Joint (Type L Joint):

It permits linear sliding motion between two links whose axes are parallel.

(ii) Orthogonal Joint (Type O Joint):

In this case the two links are perpendicular to each other but motion between them at the joint is linear sliding type.

(iii) 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.

(iv) Twisting Joint (Type T Joint):

It permits rotatory motion between two links, the axis of rotation being parallel to the axes of the two links.

(v) 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 joint, and the axis of output link is perpendicular to the axis of rotation.

Essay # 9. Control Systems for Robots :

Actuators (pneumatic, electrical, or hydraulic type) are used to move the joints of robots. Electric actuators may be d.c. servo motors or stepping motors. These are preferred type due to compatibility with computers, non-dependence on air or oil supply from outside source.

These are very common for sophisticated robots due to higher accuracy. Pneumatic cylinders are used for smaller robots as in material handling applications. Hydraulic actuators are used to exert high torque and greater speed.

The type of actuator, position and speed sensors, feed-back systems, etc., determine the dynamic response characteristics of the manipulator. Robot’s cycle time is dependent on the speed of response. It may be mentioned that while robots with greater stability are slower in response, the less stable system may tend to oscillate near the set value.

Microprocessor based controllers are used. A hierarchical structure approach is followed, i.e. each joint is actuated by its own controller, and a supervisory controller is used to coordinate the combined actuation of the joints and sequences of the motions.

Depending on sophistication desired, the robot control system may be:

(i) Simple Interlocked System:

This employs no servo control to achieve precise positioning. It is used for simple operations like pick-and-place. Limit switches are used for sequencing the actuation of the joints to complete the cycle.

(ii) Point-to-Point Control with Play Back Facility:

In this system, the various positions/locations, and the sequence to be followed in a cycle are programmed in the memory. The locations and their sequence are played back during the operation. Feed-back control is used to ascertain that desired location is attained.

(iii) Continuous Path Control:

The memory is big to hold information regarding locations of path. In this case path taken by the arm to reach final location is controlled. Servo control is used to maintain continuous control over the position and speed of the manipulator.

(iv) Intelligent Robot:

These can take own decisions when things go wrong during the cycle. These can interact with their environment, communicate with human beings, make computations during the motion cycle, incorporate advanced sensors like machine vision.

Essay # 10. Kinematic Control of Robots:

The various ways in which the robots could be controlled are:

(i) Non-Servo Control:

Non-servo-controlled robots move their arms in an open loop fashion between exact end positions on each axis, or along predetermined trajectories in accordance with fixed sequence. Such controls could be executed either by sequence controllers or by limit switches.

In latter type, more than one position is defined along an axis by indexable stops inserted or withdrawn automatically. A sequence type control steps through a number of pre-set logic steps, which causes one or more joints to move until the appropriate limit switch on the axis is reached.

(ii) Servo-Controlled Robots:

These incorporate feedback devices on the joints or actuators of the manipulator which continuously measure the position of each axis. These have much more manipulative quality and can position the end effector anywhere within the total work envelope.

These could be further classified as:

(a) Point-to-Point Control:

In this system each joint is controlled by an independent position servo with all joints moving from position to position independently. In it, each joint or axis of the robot is moved individually until the combination of joint positions yields the desired position of the end effector.

The way each joint is to move to achieve final position is practiced before-hand and stored in a memory device. As per this stored information each joint runs freely at its maximum or limited rate until it reaches its final position.

Point-to-point motion could be controlled independently in sequence joint control, uncoordinated joint control, or terminally co-ordinated joint control. In sequential joint operation one joint is activated at a time, while all other axes are immobilised.

A single joint may operate more than once in a sequence associated with such a motion. The resulting path of the manipulator end effector will thus have a zig-zag form associated with the motion directions of the manipulator joints.

It results in immediate simplification in the control. However, it causes longer point-to-point motion time. In uncoordinated joint control, the motions are not coordinated, in the sense that if one joint has made some fraction of its motion it does not imply that all other joints will have made the same fractions of their respective motions. When each joint reaches its final position, it holds and waits until all the joints have completed their motions.

Due to non-coordination of motion between joints, the path and velocity of end effector between points is not easily predicted. Terminally co-ordinated joint control is the most useful type of point-to-point control. In it the motion of individual joints are co-ordinated so that all joints attain their final position simultaneously.

It is used primarily in applications where only the final position is of interest and the path is not a prime consideration. Where the continuous path of the end effector is of primary importance to the application, then continuous path control is used.

(b) Continuous Path Control:

It is used where continuous path of the end effector is of primary importance. Continuous path motions are produced by interpolating each joint control variable from its initial value to its desired final value.

Each joint is moved the maximum amount required to achieve the desired final positions to give the robot tool a controlled predicted path. All the joint variables are interpolated to make the joints complete their motions simultaneously, thus giving a co-ordinated joint motion.

Depending on the quantum of information used in the motor control calculation the basic categories of continuous path control techniques are:

(i) Servo control approach (controller has a stored representation of the path to be followed, and the drive signals to the robot’s motors are determined by performing all calculations based on the past and present path tracking error);

(ii) Preview control or feed forward control. (It uses some knowledge about how the path changes immediately ahead of the robot’s current location, in addition to the past and present tracking error used by the servo-controller); and

(iii) Path planning or trajectory calculation approach (controller is fed with a complete description of the manipulator from one point to another. It uses a mathematical physical ‘model’ of the arm and its load, and pre-computes an acceleration profile for every joint, predicting the nominal motor signals that should cause the arms to follow the desired path).

Continuous path control requires lot of memory space to store all the axis positions needed to smoothly record the desired path. In practice, the device is moved actually through the desired path manually and the position of each axis is recorded on a constant time base, thus, generating continuous time history of each axis position.

Essay # 11. Expected Qualities in Robots :

The qualities expected in robots are listed below:

(i) Vision:

The utility of robots will increase several folds by incorporation of vision systems. Vision systems capable of identifying the part for pick up by pattern recognition data based on object’s silhouette have been developed.

Such systems can transform the position and orientation of the object into robot co-ordinates enabling the robot to acquire the object in a known manner. Other type of vision systems can recognise different objects. For each part, a number of distinguishing geometric features can be delineated, including area, perimeter, centre of gravity, number of holes and maximum and minimum radii.

In another vision system, a fibre sensor is used to look at a seam to be welded and automatically adjusts the robot’s weld path.

(ii) Tactile Sensing:

Robots with tactile sensor can identify an object and perform the function based on the referenced data. Grippers have been developed which can pick up any shape of objects and at the same time not exert enough force to crush them.

(iii) Mobility:

Usually the robot stands in a single station for the bulk of factory requirements. However, to handle intermittent and asynchronous demands, compact mobile device which could move in complex paths and access large areas economically has been developed.

(iv) Other Important Qualities in the Process of Development in Robots are:

Computer interpretation of the visual and tactile data, multiple appendage hand-to-hand co-ordination, minimised spatial intrusion, general purpose hands, man-robot voice communication, total self-diagnostic fault tracing, inherent safety, interaction with other technologies, etc.

Essay # 12. Performance Testing of Robots :

Usually following tests are performed on robots to judge their suitability.

(i) Geometric Values:

These include:

(a) Workspace:

Workspace, i.e. the envelope reached by the centre of the interface between the wrist and the tool, using all available axis motions.

(b) Static Behaviour:

It is indication of the deformation of a fixed robot structure under different load cases.

The repeatable accuracy that can be achieved at nominal load and normal operating temperature. This is based on two types of errors, viz., repeatability and reversal error.

(d) Path Accuracy:

The path accuracy of a path- controlled robot indicates at what level of accuracy programmed path curves can be followed at nominal load. The typical errors in path accuracy of a robot are: path accuracy or mean-path dispersion error, trailing error or mean-path deviation, overshoot during acceleration/deceleration.

(e) Reproduction of Smallest Steps:

With very low velocities, the slip-stick effect may become serious and it is hard to control.

(f) Synchronous Travel Accuracy:

(For cases where robot has to perform tasks synchronous to a moving conveyor) as in spray painting and assembly.

(g) Long-Term Behaviour:

It provides information on the time required to achieve thermal stability.

(ii) Kinematic Values:

These include cycle time, speed, and acceleration. It involves measuring of attainable cycle times for a defined sequence in different areas of the working space.

(iii) Power and Noise Values:

Usually measured in decibel at a distance of one metre from the working space.

(iv) Thermal Values:

Changes in temperature effect deviation of the structure.

(v) Dynamic Values:

It involves determination of dynamic behaviour of simple components and the total structure. The response of the robot structure is elicited by the following excitation methods—shaker (sinus, random), hammer (impact), snapback (impact), drives (sinus, random).

Essay # 13. Sensors for Robots :

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. The key to the success of closed loop control systems used in robots, in terms of accuracy, reliability and stability relies upon the type, complexity, resolution of the sensor.

It must be remembered that best sensory power has been bestowed by nature in the homomorphic creatures. It is the aim of engineers to attain similar perfection for robots. In order to enable robot perform its duties by understanding the environment around it, sensors provide information like.

(i) Recognition data (to understand the shape, size and features of the object).

(ii) Orientation data (the position of the object in relation to the robot arm co-ordinates in the absolute mode).

(iii) Physical interaction data (to understand the intensity interaction between the end effectors and the object).

The various types of sensors used for this purpose are:

(i) Force sensors (these measure the three mutually orthogonal forces and three orthogonal torques at the tips of the fingers of robot).

(ii) Inertial sensors (these feel the gravity and acceleration generated reaction torques).

(iii) Tactile sensors (these respond to contact forces arising between themselves and objects—used to warn the manipulator of robot to avoid collision when the end effector is near the object).

(iv) Visual sensors (with the use of triangulation or any other algorithm these help in determining the co-ordinates of the object before it is grasped.)

(v) Binary sensors micro-switches, magnetic switches, bimetallic thermal switches, etc. These are used to sense the presence/absence of a part.

(vi) Analog sensors thermocouples, linear variable differential transformers, strain gauges, piezo-electric sensors. These are used when the magnitude of quantity is desired.

(vii) Sensor arrays include pressure sensitive arrays or optical arrays used on the fingers and palm of a gripper. This requires considerable signal processing with a dedicated microprocessor.

Essay # 14. Precautions in the Use of Robots :

Before taking a decision to install a robot, it is important that its use be justified as it costs a lot. Plenty of work should exist for each robot. It is safest to employ robots first on simpler jobs and then put them to complex jobs after gaining experience.

The repetitive tasks, such as picking up heavy parts from one conveyor and placing them on another conveyor, can be easily programmed. Grippers are selected depending on the shape and size of the parts. It is possible to equip them with sensors and computer controls. These can then search the parts for out of position also.

In machine loading and unloading applications, the machines may be grouped around a robot and the robot picks up a part from an incoming conveyor and loads it into a NC lathe and then transfer it to drilling machine, inspect on table, and finally place it on an outgoing conveyor. Thus a system of machines with a robot can be converted into automatic production system.

All operations requiring worker intervention can be completely eliminated. If the shape or size of the part gets changed significantly after machining, then double grippers can be used on robots. To avoid any damage, the gripper of robot must hold the parts securely, exerting sufficient gripping force. Universal grippers are also available for handling parts of different size and shape.

A very nice application of robots is in cleaning of castings, deburring of machined parts, and polishing of parts which is usually fatiguing monotonous, dirty, noisy and sometimes hazardous. In a typical operation, the robot may be programmed to pick up casting from conveyor, presenting it to a rotary cut off wheel or saw removing gates and rise’s, then to a floor stand grinder for removing external flash, then to a grinding head that cleans the interior of the casting and then returning to the second conveyor. All machines should be located and grouped within easy reach of the robot. Stations of such type can handle a wide variety of castings of different shapes and sizes simply by changing programs.

Robots also find wide applications in assembly jobs, spot welding and arc welding. It is observed that robotic welders are about three times more productive than human operators. Robots can also be mounted on tracks so that they can automatically move from one station to another. It is essential to follow safety guidelines strictly in design and operation of robots to avoid any accidents.

Essay # 15. Applications of Robots :

Robots would find successful applications in following situations:

(i) Repetitive operation.

(ii) Other justifications for doing away with manual handling.

(iii) Handling hot or heavy work pieces.

(iv) Production limited by human performance and for endurance.

(v) Quality adversely affected by inconsistent manual handling.

(vi) Where parts have to be repeatedly oriented in the same position.

(vii) Part geometries must permit mechanical handling.

The most useful application of robot is for processes involving hazardous, unpleasant work environment like heat, sparks, fumes, etc. Typical applications in this regard could be die casting, shot welding, spray painting, forging, etc.

The other useful field for use of robots is involving repetitive work cycle which is tiring, fatiguing and boring for operator. Robots give consistent and repeatable results. Robots are essential for applications involving handling of heavy parts or tools.

Industrial robot applications usually involve several pieces of hardware (conveyors, pallets, machine tools, fixtures, etc.) in addition to the robot. Several robots and associated hardware may have to be integrated into a single work-cell.

Layout of the equipment in cell deserves greater attention for optimum results. Various types of layouts may involve centering around single robot, various robots arranged in line, or robots may be mobile. In manufacturing applications, robots may be used to handle tools and work pieces, processing operations, assembly and inspection.