Despite the long road ahead for Offline Programming (OLP), misconceptions persist. In the welding industry, much robot programming still requires tedious, point-by-point manual work on instructional pegboards. Many remember the history of robotics development, where robots promised much but failed to deliver. Dreamers and doers alike have strived to exceed expectations.
Simulation and offline programming software are also evolving, becoming smarter, faster, more flexible, and more reliable. This is a new era that values ease of use, and offline programming software vendors are gradually unveiling the mysteries of robotics technology.
Most simulation and offline programming solution providers will tell you that it's not an either-or choice; simulation and offline programming can go hand in hand. However, this doesn't mean they are interchangeable. You can perform simulation without offline programming, but without simulation, you cannot use offline programming.
Figure 1: Offline programming software uses calibration data from robot kinematics, external axis, and workpiece positioner to accurately simulate the robot welding process. Image credit: Centitech.
Robot simulation is a three-dimensional representation of a robot cell or production line. It visually demonstrates how a robot moves along a set path or trajectory from one XYZ coordinate to another. It can include multiple robots mounted on external axes, can be used in conjunction with multi-axis workpiece positioners, and can be coordinated on an assembly line. However, all these movements and plans become more complex.
“Many customers who buy robots think they behave like computer numerical control (CNC). That’s not the case,” says Albert Nubiola, CEO of RoboDK. “CNC programming is easy. The workspace is correctly defined. It’s like a cube.” However, robots have a spherical workspace, and due to joint limitations and robot singularities (points where robot motion is mathematically unpredictable), there are some types of movements you simply can’t do. Offline programming helps avoid mistakes when programming robots.
In robotic machining, there can be hundreds or even thousands of points, Nubiola continued, “No one can program point by point using a tutorial tool. You definitely need software to program offline.”
Simulation can be used for proof-of-concept purposes, such as sales tools for robot integrators, to demonstrate how a robot system works. Through simulation, users can detect potential conflicts between robots, tools, fixtures, and any safety barriers.
Simulation can analyze joint constraints, singularities, and range issues. Furthermore, it can reveal a range of remarkable problems, saving time and money in the long run. Offline programming uses simulation to output specific robot code, which can be loaded onto the actual robot's controller and run the program. A post-processor translates the programming code into a language the robot can understand. Robot manufacturers have their own proprietary programming languages, meaning third-party software must be multilingual.
Benefits of Offline Programming
The main driving force behind offline programming is reducing robot downtime, which is the time required to manually program a robot point by point using instructional widgets, as well as the costs associated with machine downtime and programmer labor.
“If end users manually program robots on the teaching pendant (online), they have to stop production to program the parts,” said Rob House, sales director at Octopuz. “The advantage of using offline programming is that you can program while in production, you can program your second, third, or fifth parts offline in the software, and then switch programs and restart your production once you’re ready to start a new process.”
Offline programming is best suited for complex path planning applications requiring a large number of points, such as welding, trimming, laser cutting, deburring, thermal spraying, spraying, laser cladding, and additive manufacturing. Offline programming is not particularly useful for simple pick-and-place applications, assembly, packaging, and palletizing. While these applications can still be programmed using offline software, users may not achieve a return on investment. If the process only involves four to five points, then manual programming is more economical.
“If you spend as much time on offline programming software as you do on tutorial widgets for each new component, then there’s no benefit to it,” said Garen Cakmak, senior director at Hypertherm Robotics Software. “For robots in highly mixed, low-volume environments, the software needs to be simple and easy to use.”
Improving usability is a top priority for these software developers. However, simulation and offline programming are meaningless if they cannot accurately reflect reality.
Figure 2: In railway maintenance, processes involving hundreds or thousands of repetitive actions can be streamlined by using collaborative robots with offline programming, potentially saving months of manual programming time. Image source: Hypertherm Robotics Software Company
Calibrate and do not deviate
For offline programming to work, the virtual world must match the real world. This means that the simulation must accurately represent the physical robot unit.
“The virtual environment in offline programming software must perfectly replicate the actual work cells in the shop floor, but this is not the case in most cases,” said Helmut Ziewers, vice president of digital factory solutions at Centit. “The discrepancy between the computer-aided design (CAD) model and the physical part corresponding to that model can be small or large, especially when the tools used are not particularly perfect. We still see a major problem where people think these jobs cannot be done offline because of these discrepancies.” However, these discrepancies are not insurmountable, so calibration is crucial.
Figure 3: In arc welding work cells, offline programming can halve programming time and reduce robot downtime, thus helping to meet production demands. Image source: Octopuz.
“Even with deviations of only a few millimeters or centimeters, you can create any number of offline programs,” Ziewers said. “They will never be exactly the same. We must know exactly how the robots in the shop are set up, and there absolutely cannot be any deviations, otherwise offline programming will not work. Toolpaths and trajectories will always be off.”
Crown Equipment, a manufacturer of powered forklifts, encountered this problem. Their factory in Roding, Germany, has several complex robotic welding systems with external and multi-axis workpiece positioners. Faced with production bottlenecks caused by time-consuming manual robot programming, Crown decided to explore the feasibility of offline programming. Their journey was not without its challenges. Some on the Crown team were skeptical, while others were eager to try offline programming.
Figure 4: NASA is developing a new inspection system with offline programming software for path planning of its simulated robots. This system uses collaborative robots equipped with infrared cameras to test for defects in composite aircraft structures. Image credit: RoboDK
Cenit was one of two suppliers involved in the benchmark study. Ziewers stated that they used CAD drawings provided by Crown Automation Integrator and created virtual robotic work cells in their software. Based on these drawings, they created robot programs and ran them on the physical work cells.
Cenit engineers went to the Crown plant in person to physically calibrate the work cells. “We found dimensional discrepancies,” Ziewers said. “We utilized these discrepancies in the software and then adjusted the offline program based on the new settings in the virtual world.” This perfectly matched the physical settings of the shop floor, and the robot program functioned well.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
