Continuous-Path Control

The continuous-path control is used when the action the robot must provide occurs at all times between points, such as spray painting, continuous cutting, continuous welding, or continuous gluing. Since this type of robot must follow a precise path when it's spray painting, each location in the path the robot takes to move from point to point is recorded during the programming phase of the project and replayed when the robot is in the run phase. ill. 1 shows an example of a continuous-path robot that's used for spray painting.

Above: ill. 1 Example of a continuous-path robot.

The continuous-path robot also can be used in a gluing process where it must place a bead of glue around a complex contour like the clear lens of a headlight assembly for an automobile. In this application the glue is placed on the clear lens, and then the lens is placed against the remainder of the headlight assembly (the shell) where it's allowed to dry. The types of headlights commonly used on automobiles today have very complex contours to fit the design of the automobile to aid in aerodynamics. If one looks at a variety of headlamps on cars today notice that the path around the lens may be irregular with many curves. During the programming phase of the project, the robot is moved around the path with its gluing head in the correct position just above the surface. The technician who programs the robot puts the robot in teach mode, which disables the servomotors and allows the robot to be manually pulled through the path. This action would be similar to the process if the technician has a glue gun in hand and moved around the path placing glue in the correct position. Even though the servos are de-energized during this process, the encoders of each axis are still energized and they record the exact path as the robot is pulled through its program. During this teaching process the robot controller is recording every single point in this path as well as the speed at all times as the technician pulls the robot around the contours. The robot controller also keeps track of when the glue gun is turned on to dispense glue and when it's turned off at any points while the robot is moving around the path. When the program is in the replay mode, the robot will follow the exact path at the exact speed the technician used while the robot was being taught.

This type of robot is fairly easy to program because no special programming language is needed to get the robot to repeat the exact path it was taught. The main drawback of this type of controller is that this type of programming requires large amounts of memory to record the exact path the robot was taught as well as the speed during each part of the program.