Research and development work on industrial robots goes back to the 1950s when developments took place in the field of NC machine tools. These machines had many building blocks in common with robots and the first prototype of an industrial robot from Unimation saw the light of day in 1960, and was in operation at Ford in 1961. The robots at the time were relatively simple with so called Point To Point (PTP) control and were primarily used in materials handling and machine tending, with spot welding coming shortly after for Robotic Arc Welding.
Still in the 1960s, Trallfa (now ABB Robotics) developed a robot for spray painting. The concept of programming and control of such a robot was quite different. The principle was that the programmer grabbed the robot end-effector and moved it in space and time while the robot recorded the motions. Typically, many such programs with quite short cycle times were made in a short time and the best one was selected for production. The method turned out to be a practical solution for the application in mind. It was tested on other applications as well in the 1970s, including arc welding, but with less success.
Most robots used at this time had hydraulic drives but demand from applications such as arc welding put on pressure to develop electric drive robots. In 1973, ASEA (now ABB Robotics) presented an all electric robot that shortly after that, this was used successfully in arc welding (6 kg payload) and spot welding (60 kg payload). Still, the motion control was rather simple and to overcome problems of generating straight line movements, a synchronized PTP (Point to Point) control was used so that all axes stop at the same time for a defined motion.
Trajectory generation of the welding torch in Cartesian coordinates was a major problem that needed to be solved so that robots could be used more efficiently in arc welding.
Robots had to be able to produce jerk-free motions in 3D space that can be defined according to common practice of using geometrical shapes in product design, i.e. linear and circular movements. At the time, however, the controllers did not have the necessary computing power to achieve this and the work around procedure was to define points along the weld joint. Depending on the necessary accuracy the distance between such points could vary, but in general there were about 30-40 mm between the points. The travel speed was defined by the time to travel between two points. For spot welding, the interpolation of a path was not so important as developments for robust and light spot welding guns.
Other important issues were related to fast and accurate communication between the robot controller and the welding power source and supporting peripherals such as automatic cleaning systems for the spot welding electrodes.
From mid-1970s a number of different robot applications were under constant testing and evaluation including deburring, polishing, gluing, cleaning of castings, and so on. Such work included development of peripheral equipment for use in robotic stations as well and integration of these to the robot controller.
In the area of robotic arc welding, servo controlled positioners were introduced with integrated motions of both the robot and the positioner. However, this integration was, and still is, in general limited to the joint space of the robot and the positioner as opposed to a real integration from a welding point of view where a relative motion of a welding torch along a weld joint (the object to be welded) is the actual requirement. Definition of such integrated motions requires a world model as normally used in modern systems for simulation and off-line programming of robots.
The introduction of positioners increased the use of the robot in many ways: objects could be oriented for better accessibility of the robot and better orientation of the weld that increases productivity and/or quality. Moreover, robots were mounted on moving tracks, usually a gantry with the robot hanging upside down. This increased not only the working space but also the complexity of the system. Products started to be designed for robotic welding taking advantage of the new technology by improvements in quality and productivity. Another important issue was soon to get a solution: how to decrease the usually long set up time between different products. Ideas based on the FMS (Flexible Manufacturing System) principles guided the design of new Robotic Arc Welding systems with automatic loading and unloading of fixtures on the positioner. This was further developed during the 1980s.
by Bolmsjo, GunnarView Profile; Olsson, Magnus; Cederberg, Per. The Industrial Robot29.2(2002)
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