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| Home > Articles > Industrial Robots - A Reprogrammable Multi-functional Manipulator |
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Industrial Robots - A Reprogrammable Multi-functional Manipulator |
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These robots are evolving in two directions. In massive factories, making complex products such as automobile and aircraft, the individual robot may dissolve as a separate unit as sensors, computers, manipulators, and machine tools are combined. In smaller operations, the robot will remain a separate unit and with even larger memory and simpler programming to perform more diverse functions. For example, a single robot may feed a machine tool, move pallets and raw material, and inspect parts. Robots today, with vision, use pattern-recognition techniques in which image signals provided by TV camera "eyes" are compared with those stored in computer memory to discriminate between various types of objects. The robot systems therefore can discriminate and select a single part from randomly spaced parts on a pallet or a conveyor belt. With pattern-recognition, distinctive parts of the object silhouette are sensed and operated on with sophisticated software algorithms. In this manner, the data is compared with stored information to identify the part and determine its position and orientation. Other systems may use pattern-matching techniques in which the basic shape of the object is compared with that stored in the computer memory. Most vision systems are generally limited to 2D applications in which details are discriminated on the basis of silhouette. The next refinement is a more advanced 3D perception sensitive enough to guide the robot through even the most complex task. The most sophisticated systems use stereo vision analogous to human sight. Another variation identifies 3D shapes by the way a beam of light deforms as it strikes an object.
In addition to vision, the sense of touch also is essential in some applications. Many robots have a rudimentary tactile sense provided by switches that detect the presence or absence of an object in the grippers. Also grip-controlling sensors can provide force-feedback signals that enable the system to control how tightly an object is grasped. Compliant mechanisms on the grippers permit the robot to "jiggle" parts together with an action similar to that which a human uses in groping for hole locations or the proper fit of parts not precisely aligned.
Tactile work is also aimed at developing highly sensitive systems that will enable robots to handle parts more delicately and execute more complex maneuvers. One of these methods analyses the torque applied to the robot arm joint. A more sensitive system has an array of piezoelectric material on the grippers that produces an electric current, in fact voltage, when compressed. Another system uses flexible conductive skin that produces a signal when an object forces it against an underlying array of electrodes. Research in robotics has also led to development of voice data entry systems. These systems enable a programmer to instruct robot verbally or to enter the requirements for a specific task on the shop-floor. Speech synthesisers may be incorporated to permit the robot to verbally feed data back to the programmer or operator. One of the goals of artificial intelligence is to integrate these sensory systems with more sophisticated computer software to enable robots to make limited decisions. Given adequate computer power, these robots can even take appropriate actions not provided by their programmers and modify their controlling software accordingly. For instance, a robot might conclude that a task could be performed more efficiently than the method given by the programmer.
Given sufficient mobility, such robots could perform the widest possible range of tasks in a CAM system. With this in mind, various methods of robot locomotion have been developed. One six legged robot resembles a large insect and is quite stable on rough terrain. Each leg joint is independently powered and provides position and rate feedback to the computer system which controls their movements. Other robots have been developed with two, three or four legs. Some robots being worked on have wheel type locomotion and sophisticated guidance systems. The robots laser-range finder eyes, gyrocompass, and optical-encoded odometer enable it to self-navigate in a totally alien environment. As our experience with robots increases, we are finding out that they affect other functional areas in some anticipated ways. In spot welding components, for example, engineers traditionally have overdesigned manufacturing specifications by calling for more welds than are really needed, anticipating that the human welder would miss one or two welds with the onset of fatigue or distractions on the job. Robots in contrast never miss a weld and consequently engineers are rethinking their traditional overdesign practices. While the robots computer programs and operational specifications do not reside in the manufacturing database of most organisations as of date, the computer integrated manufacturing concept is aimed toward doing so in the future.
Robot applications in foundry
Most robot applications in the foundry are associated with saving labour, working in dangerous or obnoxious conditions and smoothing workflow. The earliest robot applications in metal casting probably occurred in die-casting operations. Since 1962, robots have been unloading die casting machines and handling scrap. In the basic operation, the robot removes the casting from the die-casting machine and places it on a conveyor or in a container. In more complex applications, the robot unloads the casting, quenches it, and places it in a trim press. One robot can be set up between two machines to tend them alternatively. A robot can operate as fast as the machine cycles (which is a function of casting solidification time). Obtaining maximum benefits from robots includes the automatic spraying of the die lubricant and ladling of molten metal. Properly set up, robots perform on a consistent basis and maintain optimum operating conditions. Casting production increase due to robot applications have been as high as 200% to 300%. Typical paybacks for robots in die-casting are 1.5 to 2 years in advanced production system for a one shift / double machine unload (or a two shift / single machine unload). The payback for a two shift / double machine unload is about twice as fast (i.e. one year). An area of the foundry that is now receiving special attention for robot utilisation is the finishing room, especially in European and Japanese foundries. Analysis of complete production finishing operations shows that, this is a very attractive area for automation due to high labour intensity and efficient working conditions.
The cell layout design shown in Figure 3 consists of one robot and four specially designed cutting and grinding tools. The tools are hydraulically driven, one at a time, from a central unit. An automatic mechanism within each tool compensates for wear on the wheel, so that the robot finds the working point of the wheel at exactly the same location.
The operator positions the castings on the incoming conveyor. The casting passes through a dedicated press that removes the main riser. At the same time, specific contours are stamped as preference areas for the robot arm. The casting then moves to a set location within the working envelope of the robot. The casting is picked up by the robot using dedicated hydraulic grippers and is successively worked against different cutting and grinding tools, until the cycle is complete and the part is released on the outgoing accumulator.
This brief discussion of robot applications in the foundry does not imply that the task is simple. A thorough analysis of the project is necessary if parts are to be handled automatically, kept within tolerances, and with some flexibility.
Robot for surgeon
Scientists in Britain have developed a robot that can help surgeons perform delicate knee operations quickly and safely. The active constrained robot - Acrobot - was invented at Londons Imperial College of Science Technology and Medicine by a team of doctors and researchers. Acrobot is particularly useful for knee operations where access to the joints is restricted and, although it has been developed principally for knee surgery, the device could also be applied to a range of surgical tasks. The two-stage process uses an ultrasound probe to identify the pieces to be removed. Then the computer-controlled robotic arm (known as Probot) does not cut it but activates a diathermic electrode to vaporise the tissue. The procedure reduces blood loss and takes 15 minutes or less, while the surgeon monitors the operation on screen using the robots camera.
A robot must have the ability to adopt to many different kinds of jobs in many different industris and perform these jobs with some degree of dextrity and flexibility in motions. In contrast, fixed or special purpose automation is less universal and includes machines designed to do one particular job in one specific industry.
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| Posted : 10/26/2005 |
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