30-04-2011, 03:00 PM
SUBMITED BY :
JIGAR P PATEL
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ROBOTICS
Robotics is a prominent component of manufacturing automation which will affect human labour at all levels, from unskilled workers to professional engineers and mangers of production. It is possible; perhaps likely, that robotics will become a field, like today’s computer technology, which is pervasive throughout our society.
Robotics technology is controlled by means of programming, and the ability to program a robot is dependent on its level of technology. Successful implementation of robotics in useful applications is obviously a function of the technology and programming. Today, robots are highly automated mechanical manipulators controlled by computers.
An industrial robot is a reprogrammable, multifunctional manipulator designed to move materials, parts , tools, or special devices through variable programmed motions for the performance of a variety of tasks.
Today the human analogy of an industrial robot is very limited. Robots do not look like humans, and they do not behave like humans. Instead, they are one-armed machines which almost operate from a fixed location on the factory floor. Future robots are likely to have a greater number of attributes similar to the attributes of humans. They are likely to have grater sensors capabilities, more intelligence, a higher level of manual dexterity(skill in using one’s hands), and a limited degree of mobility(movable). There is no denying that the technology of robotics is moving in a direction to provide these machines with more and more capabilities like those of humans.
Science fiction has no doubt contributed to the development of robotics, by planting ideas in the minds of young people who might embark on careers in robotics, and by creating awareness among the public about this technology.
Automation and robotics are two closely related technologies. In an industrial context, we can define automation as a technology that is concerned with the use of mechanical, electronic, and computer-based systems in the operation and control of production. Examples of this technology include transfer lines, mechanized assembly machines, feedback control systems (applied to industrial processes), numerically controlled machine tools, and robots. Accordingly, robotics is a form of industrial automation.
There are three broad classes of industrial automation: fixed automation, programmable automation, and flexible automation. Fixed automation is used when the volume of production is very high and it is therefore appropriate to design specialized equipment to process the product very efficiently and at high production rates. Programmable automation is used when the volume of production is relatively low and there are a variety of products to be made. In this case, the production equipment is designed to be adaptable to variations in product configuration.
Of the three types of automation, robotics coincides most closely with programmable automation. An industrial robot is a general-purpose, programmable machine which possesses certain anthropomorphic, or humanlike, characteristics. The most typical humanlike characteristic of present-day robots is their movable arms. The robot can be programmed to move its arm through a sequence of motions in order to perform some useful task.
ASIMOV LAWS OF ROBOTICS
There are three laws of Robotics by Asimov and they are:
1. A robot may not injure a human being or , through inaction, allow a human to be harmed.
2. A robot must obeys orders given by humans except when that conflicts with the First Law.
3. A robot must protect its own existence unless that conflicts with the First or Second Laws.
Robotics is an applied engineering science that has been referred to as a combination of machine tool technology and computer science.
ROBOT ANATOMY:-
Robot anatomy is concerned with the physical construction of the body, arm, and wrist of the machine. Most robots used in plants today are mounted on a base which is fastened to the floor. The body is attached to the base and the arm assembly is attached to the body. At the end of the arm is the wrist. The wrist consists of a number of components that allow it to be oriented in a variety of positions. Relative movements between the various components of the body, arm, and wrist are provided by a series of joints.
Attached to the robot’s wrist is a hand. The technical name for the hand is “end effector”. The end effector is not considered as part of the robot’s anatomy. The arm and body joints of the manipulator are used to position the end effector, and the wrist joints of the manipulator are used to orient the end effector.
GENERAL CONDITIONS OF ROBOT
The following conditions may be used as guidelines for using robots:
(a) Hazardous(risky) or uncomfortable working conditions
In situations where there are potential dangerous or health hazards (like heat, radiation, toxicity, etc.). robots may be used. Some of the examples are hot forging, die casting, spray painting and so on.
(b) Difficult handling
If the work piece or tool involved in the operation is awl ward in shape or of heavy type it is possible for the robot to do this type of work more easily.
© Repetitive task
If the work cycle consists of a sequence of elements which do not vary from cycle to cycle it is possible that the robot can be programmed to do the job. It reduces workers’ boredom of monotonous work.
(d) Continuous working
If machine is working for more hour or days or month then it is require that making it automatic.
SELECTION OF A ROBOT
A Robot nay be distinguished from other types of automation by the fact that it can be programmed and reprogrammed to suit the varying demands of production as and when they occur. Clearly no single robot will be useful for all of the applications. Today Industrial robots are available in a wide range of capabilities and price ranges and are being used in a variety of manufacturing operations. The following factors be considered in determining whether or not a robot is the right choice on a particular job.
• Complexity of the operation – Avoid extremes of complexity.
• Degree of disorder – Disorder is deadly.
• Production rate – Robots are generally no faster than people.
• Production volume – For very short range use people. For very long runs, use fixed automation.
• Justification. If it does not make rupees, it does not make sense.
• Long term potential – If I only need one I am better off with none.
• Acceptance – If people don’t want make it.
Before using and selection a robot is necessary to examine how the company needs/characteristics like market conditions, production methods, organizational climate react with the basic robot characteristics like flexibility, consistency, speed and environmental differences etc.
Finally, in the selection of robot the user has to be concerned about cost, number and types of axes of motion, power drive, logic memory, programming, maintenance, environment, physical size and weight, cycle rate. In addition robot system characteristics should also be considered.
BASIC ELEMENTS OF ROBOTS
The elements which are common to all robots can be considered as the basic elements and are as follows:
a) Manipulator: It is the most obvious part of the robot and mainly consists of a base, an arm and wrist. Within the manipulator are the mechanical parts like joints, transmission lines, internal sensors which execute the robot movements in any number of degrees of freedom. The movement of the manipulator can be described in relation to its coordinate system which may be cylindrical, spherical, Cartesian or anthropomorphic. Depending on the controller, movement can be servo or non-servo controlled and can be point-to-point motion or continuous path motion.
b) Controller: It is the brain of a robot and is based on a computer or a system of computers. Its major functions are to store, to sequence and to position the data in memory, to initiate and stop motions of manipulator as per instructions given to interact with the environment. The controller will have two components, namely, the hardware and the software.
c) End effectors
d) Sensors
e) Energy source: Movement of manipulator arm requires energy and this is supplied by energy source. Depending on load range and type of application, it may be electrical, hydraulic or pneumatic. For small and medium sized robots electrical source is generally employed. For bigger size robots where load is also large, hydraulic source is used. Where accuracy requirement is less, pneumatic energy source is preferable.
ROBOTS AND ITS CLASSIFICATION
A robot is defined as a mechanical system which has flexible motion functions analogous to the motion functions of living organism. It combines such motion functions with intelligent functions, and which acts in response to the human will. In this context intelligent functions mean the ability to perform at least one of the following:
• Judgement
• Recognition
• Adaptation
• Learning
Robots may be classified in many ways. Some of them are as follows:
A) Based on level of sophistication
B) Based on manipulative function
C) Based on manipulator geometry
D) Based on motion characteristics
E) Based on type of control
F) On the basis of technology involved
G) According to method of input of information and teaching Robots are classified as under:
• Manual Manipulator
• Fixed sequence Robot
• Variable sequence Robot
• Playback robot
• Numerically controlled (NC) Robot
• Intelligent Robot
ROBOT PHYSICAL CONFIGURATIONS
Industrial robots come in a variety of shapes and sizes. They are capable of various manipulators and they possess different motion systems. Commercially available industrial robots have one of the following configurations:
(a) Polar co-ordinate configuration: This configuration also goes by the name of spherical coordinate. The workspace within which it can move its arm is a partial sphere. The robot body has base and pivot that can be used to raise or lower a telescoping arm. It has two rotary axes combined with a linear axis. The base axis is a rotary axis with a second rotary axis providing vertical motion. The linear axis makes the radius of the sphere. The working envelop is the area between a large sphere defined by the maximum extension of the linear axis and a small sphere defined by its minimum extension.
(b) Cylindrical Coordinate configuration: Here the robot body is a vertical that swivels about a vertical axis. The arm consists of several orthogonal slides which allow the arm to be moved up or down and in and out with respect to the body. The base axis is a rotary axis. It is commonly used in material handling system. The working envelop of the robot is a cylindrical section.
© Cartesian Co-ordinate configuration: A robot which is considered around this configuration consists of three orthogonal slides. The three slides are parallel to the x, y and z axes of the Cartesian coordinate system. By appropriate movements of these slides, the robot is capable of moving its arm to any point within its three – dimensional rectangular shaped work space. The base axis of a Cartesian system is often extended to enlarge the working volume or to move the robot from one position to another. Its geometry usually has rigid structural path that mechanically transfers loads to the robot base, providing stiffness and load carrying capacity. Its motion are linear and they are usually of a lower velocity than rotary motions.
(d) Jointed arm configuration: It is similar of three rigid members connected by two rotary joints and mounted on a rotary base. It is similar to human arm in appearance. Straight members are connected by joints which are analogous to the human shoulder, elbow and wrist. Robot arm can be rotated to provide the robot with the capacity to work within a quasi-spherical space. It has low resolution which depends on arm length. It can move at high speeds.
BASIC ROBOT MOTIONS
Whatever the configuration, the purpose of the robots is to perform a useful task. To do the task, the robot arm must be capable of moving the end effector through a sequence of motions and positions.
There are six basic motions or degrees of freedom which provide with the capability to move the end effector through the required sequence of motions. All industrial robots are not equipped with such type of six degrees motions. Out of these six motions, three motions are provided to arm and body and rest are wrist motions.
(a) Arm and body motions
Arm and body motions include three motions, such as vertical, radial and rotational.
(i) Vertical traverse: This motion include up and down movements of the arm about a pivot in which the entire arm id pivoted about a horizontal axis or moving the arm along the vertical axis.
(ii) Radial traverse: This motion includes in and out movements of the arm.
(iii) Rotational traverse: With the help of this motion, the robots are capable of rotating about a vertical axis or the right-left swivel of the arm.
It determines the complexity of the aggregate movements, capable of arm movements which defines the robot’s reach or work envelop.
(b) Wrist Motions
A typical wrist will have swivel (roll), pitch (bend), and yaw see fig.
- Wrist swivel: It is rotation of the wrist in a plane perpendicular to the end of the arm.
- Wrist bend: Bend or pitch is rotational movements in a vertical plane or up or down movements of the wrist.
- Wrist Yaw: Yaw is a rotation in a horizontal plane through the arm or right-left swivel of wrist. The main significance of wrist movements is the ability to orientate the gripper or any other form of arm tooling. An additional axis of motion is also possible, by putting the robot on a track or slide.
