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Let the part drive the robot

Let the part drive the robot

Ten years ago, CNC programming required the accumulation of teaching points by actually moving the machine in teach mode. Today's CNC programs eliminate this stage; machines are programmed directly from within a graphic environment which includes the ability to design parts and fixtures, visualize a tool path, and perform simulations. Now-adays, nobody would consider writing CNC programs one line at a time. Yet most industrial robots, although they are in the most advanced echelon of modern manufacturing, are still programmed using a teach pendant.

A new add-in for SolidWorks, called RobotWorks, presents a novel approach. RobotWorks uses the 'wisdom' built into SolidWorks parts and assemblies to generate the robot's trajectory with accuracy and speed, far beyond any teach pendant.

Features to the rescue. Consider arc welding, where a welding torch is pointed at a seam between parts at about half the angle. The outcome of this operation is a bead that looks like a chamfer. In fact, SolidWorks provides a "Weld symbol" which looks just like the "chamfer icon." So why not create a chamfer and drive along it?

Compare the effort of teaching the robot hundreds of points to trace this shape, with creating a chamfer around it, which takes three seconds, and making a robot path to follow it, which takes 30 seconds more. This is the idea behind the RobotWorks program.

Other SolidWorks features resemble motion by definition. Sweep is 'moving a sketch along a curve,' so for our purposes the side faces of the sweep are tracks. A simple extrude is 'moving a sketch along a straight line.' For every 'track' or path in mind, there is a suitable feature.

Save your face. In robotics, we need to provide the location of the robot tool (paint nozzle, welding torch, glue gun, etc.) in terms of translation (XYZ) and rotation (angles around X,Y, and Z) within the robot coordinate system. Aline or an edge has only a direction vector, because a body can rotate freely around it, so an angular orientation is not defined. A face, however, has defined vectors at any point.

By analyzing the geometry of the part, RobotWorks is able to create a complete path based on the faces. Therefore, the accuracy of the path no longer depends on the dexterity of the robotics expert or his ability to eyeball a position. Continuous path robots that weld, cut, paint, seal, polish, sew, slit, trim, and de-burr, always follow a part contour or a prescribed path on a part-usually along a face or an edge. They are the hardest to program, and therefore, they will benefit the most from following a geometry.

Not all parts are equal. Your part geometry will usually dictate most of the path. However, the robot tool may be far away from the part or the worktable. What do we do with the spaces between faces? We create guide parts.

Unlike other parts in the assembly, there is no need to produce them, or to make a dimensioned drawing for them. They are in the assembly merely in order to have the robot tool ride on their back. You make them from a simple sketch, extruded, swept, or lofted, and mate them to real parts to create a complete path. If you do not create any guide parts, the program will create straight-line motions between the parts for you.

In summary, SolidWorks has become the mainstream CAD of choice in many industries and plants. A PC and Windows NT are no longer strangers on a production floor. We accept computer-operated machinery around us as a fact of life. Yet robot programming is still associated with "big bucks" and many "white collar" hours in the "blue collar" zone.

Design engineers know their parts. If they already design in SolidWorks, the next natural step is to get manufacturing engineering and robotics people into it too, as a natural extension of the design. With RobotWorks, users can now e-mail a robot trajectory to any robot on the planet and shorten time to market considerably.

To download RobotWorks, visit www.compucraftltd.com.

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