The most commonly used robot configurations are articulated robots, SCARA robots, Delta robots and Cartesian coordinate robots, (aka gantry robots or x-y-z robots). In the context of general robotics, most types of robots would fall into the category of robotic arms (inherent in the use of the word manipulator in the above-mentioned ISO standard). Robots exhibit varying degrees of autonomy:
Some robots are programmed to faithfully carry out specific actions over and over again (repetitive actions) without variation and with a high degree of accuracy. These actions are determined by programmed routines that specify the direction, acceleration, velocity, deceleration, and distance of a series of coordinated motions. Other robots are much more flexible as to the orientation of the object on which they are operating or even the task that has to be performed on the object itself, which the robot may even need to identify.
For example, for more precise guidance, robots often contain machine vision sub-systems acting as their “eyes”, linked to powerful computers or controllers. Artificial intelligence, or what passes for it, is becoming an increasingly important factor in the modern industrial robot. George Devol applied for the first robotics patents in 1954 (granted in 1961).
The first company to produce a robot was Unimation, founded by Devol and Joseph F. Engelberger in 1956, and was based on Devol’s original patents. Unimation robots were also calledprogrammable transfer machines since their main use at first was to transfer objects from one point to another, less than a dozen feet or so apart.
————————————————-Technical descriptionDefining parameters* Number of axes – two axes are required to reach any point in a plane; three axes are required to reach any point in space. To fully control the orientation of the end of the arm (i.e. the wrist) three more axes (yaw, pitch, and roll) are required. Some designs (e.g. the SCARA robot) trade limitations in Degrees of freedom which is usually the same as the number of axes. * motion possibilities for cost, speed, and accuracy.
* Kinematics – the actual arrangement of rigid members and joints in the robot, which determines the robot’s possible motions. Classes of robot kinematics include articulated, cartesian, parallel and SCARA. * Carrying capacity or payload – how much weight a robot can lift. * Speed – how fast the robot can position the end of its arm. This may be defined in terms of the angular or linear speed of each axis or as a compound speed i.e. the speed of the end of the arm when all axes are moving. * Acceleration – how quickly an axis can accelerate.
Since this is a limiting factor a robot may not be able to reach its specified maximum speed for movements over a short distance or a complex path requiring frequent changes of direction. * Accuracy – how closely a robot can reach a commanded position. When the absolute position of the robot is measured and compared to the commanded position the error is a measure of accuracy. Accuracy can be improved with external sensing for example a vision system or Infra-Red.
See robot calibration. Accuracy can vary with speed and position within the working envelope and with payload (see compliance). * Repeatability – how well the robot will return to a programmed position. This is not the same as accuracy. It may be that when told to go to a certain X-Y-Z position that it gets only to within 1 mm of that position. This would be its accuracy which may be improved by calibration. But if that position is taught into controller memory and each time it is sent there it returns to within 0.1mm of the taught position then the repeatability will be within 0.1mm.
Accuracy and repeatability are different measures. Repeatability is usually the most important criterion for a robot and is similar to the concept of ‘precision’ in measurement – see Accuracy and precision. ISO 9283  sets out a method whereby both accuracy and repeatability can be measured. Typically a robot is sent to a taught position a number of times and the error is measured at each return to the position after visiting 4 other positions. Repeatability is then quantified using thestandard deviation of those samples in all three dimensions.
A typical robot can, of course make a positional error exceeding that and that could be a problem for the process. Moreover the repeatability is different in different parts of the working envelope and also changes with speed and payload. ISO 9283 specifies that accuracy and repeatability should be measured at maximum speed and at maximum payload. But this results in pessimistic values whereas the robot could be much more accurate and repeatable at light loads and speeds.
Repeatability in an industrial process is also subject to the accuracy of the end effector, for example a gripper, and even to the design of the ‘fingers’ that match the gripper to the object being grasped. For example if a robot picks a screw by its head the screw could be at a random angle. A subsequent attempt to insert the screw into a hole could easily fail.
These and similar scenarios can be improved with ‘lead-ins’ e.g. by making the entrance to the hole tapered. * Motion control – for some applications, such as simple pick-and-place assembly, the robot need merely return repeatably to a limited number of pre-taught positions. For more sophisticated applications, such as welding and finishing (spray painting), motion must be continuously controlled to follow a path in space, with controlled orientation and velocity. * Power source – some robots use electric motors, others use hydraulic actuators.
The former are faster, the latter are stronger and advantageous in applications such as spray painting, where a spark could set off an explosion; however, low internal air-pressurisation of the arm can prevent ingress of flammable vapours as well as other contaminants. * Drive – some robots connect electric motors to the joints via gears; others connect the motor to the joint directly (direct drive). Using gears results in measurable ‘backlash’ which is free movement in an axis.
Smaller robot arms frequently employ high speed, low torque DC motors, which generally require high gearing ratios; this has the disadvantage of backlash. In such cases the harmonic drive is often used. * Compliance – this is a measure of the amount in angle or distance that a robot axis will move when a force is applied to it. Because of compliance when a robot goes to a positioncarrying its maximum payload it will be at a position slightly lower than when it is carrying no payload. Compliance can also be responsible for overshoot when carrying high payloads in which case acceleration would need to be reduced.
Robot programming and interfaces
Offline programming by ROBCAD
A typical well-used teach pendant with optional mouse
The setup or programming of motions and sequences for an industrial robot is typically taught by linking the robot controller to a laptop, desktop computer or (internal or Internet) network. Software: The computer is installed with corresponding interface software. The use of a computer greatly simplifies the programming process. Specialized robot software is run either in the robot controller or in the computer or both depending on the system design.
There are two basic entities that need to be taught (or programmed): positional data and procedure. For example in a task to move a screw from a feeder to a hole the positions of the feeder and the hole must first be taught or programmed. Secondly the procedure to get the screw from the feeder to the hole must be programmed along with any I/O involved, for example a signal to indicate when the screw is in the feeder ready to be picked up. The purpose of the robot software is to facilitate both these programming tasks. Teaching the robot positions may be achieved a number of ways: Positional commands
The robot can be directed to the required position using a GUI or text based commands in which the required X-Y-Z position may be specified and edited. Teach pendant: Robot positions can be taught via a teach pendant.
This is a handheld control and programming unit. The common features of such units are the ability to manually send the robot to a desired position, or “inch” or “jog” to adjust a position. As of 2005, the robotic arm business is approaching a mature state, where they can provide enough speed, accuracy and ease of use for most of the applications. Vision guidance (aka machine vision) is bringing a lot of flexibility to robotic cells.
According to the International Federation of Robotics (IFR) study World Robotics 2012, there were at least 1,153,000 operational industrial robots by the end of 2011. This number is estimated to reach 1,575,000 by the end of 2015. For the year 2011 the IFR estimates the worldwide sales of industrial robots with US$8.5 billion.
Including the cost of software, peripherals and systems engineering the annual turnover for robot systems is estimated to be US$25.5 billion in 2011 hese industrial robots play a vital role in manufacturing industries, and there is a bright and wide future for these robots. Despite the enormous work put in by the earlier researchers, there is an immense scope for research for further development in this field.
The feature applications of robots are seen in the following fields: Coal minesWaste disposalsSecurityAgriculturalUtilities , Military and Fire fighting operationsUnder seaTeachingBank tellersMedicalSpace