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safety implications. Today sees greater availability of lower-cost and increas- ingly capable solutions. Consider each system on its own merit, as not all vision/laser solutions offer the same capabilities.
Laser-scanning technologies fall into the categories of 1D, 2D, 3D, spot, line and circle. All frequently combine with some form of CCD-style camera to capture images for processing with algorithms. Such setups usually are managed by a host PC (often combined with the camera as a space saver) that calculates the input data and produces the necessary output for the robot to execute its task.
To ensure the effective deploy- ment of vision/laser solutions, ask the following:
• When sizing up the task, what is the smallest object or feature to be tracked/detected?
• When viewing the feature or part, what level of measurement accuracy is required to meet the process criteria?
• What size of field of view is required to capture essential informa- tion when tracking?
• What is the speed of recognition and processing time required to meet output-cycle requirements?
When selecting the right laser/cam- era combination, consider environ- mental aspects. Temperature, vibration, illumination and humidity all can affect the quality and reliability of results. Note that some cameras are best suited for static capture and others perform better for linear tracking.
The combination of process-head and component geometry also may dictate what size lens and camera arrangement can be installed on the end of the robot arm. Time spent with quality 3D-simulation software is very important. Simulating the movement of the robot and its end-of-arm-tooling minimizes risk by thoroughly identi- fying what welds can be accessed, as well as any potential compromises that may arise with certain camera/lens configurations. Beyond the physical constraints, determine whether your company has the expertise to configure
Advancements in sensing technology enables accurate tracking of unique and difficult weld seams, resulting in new opportunities to employ robotic welders.
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the equipment, and the level of the support that’s needed for system start- up and operation.
Seam-Tracking Technology Propels Automated Welding
When looking to track the seam and/or volume-fill a continually chang- ing joint configuration, vision and laser are not ideal tracking methods. Instead, a through-the-arc approach may mean the difference between producing a repeatable, quality joint via automa- tion, or completely abandoning the automation option altogether.
Through-the-arc-tracking has evolved considerably in recent years, with reliable, fast and accurate tracking of a weld joint becoming second nature to a robot. In practice, through-the- arc sensing monitors the arc in order to track the seam, using impedance— resistance to an electrical circuit— rather than simple volts or amps. Doing so provides more reliable values for producing accurate data.
ABB’s WeldGuide III software pro- vides an example of how seam tracking works. It operates by introducing a weave pattern, which is freely program- mable in time, geometry, symmetry and amplitude. The robot controller library also holds a default set of weave
patterns. Actual tracking of the joint is achieved by monitoring the imped- ance of the arc as the weld wire weaves from side to side, and the rules of the chosen or programmed weave data determine how the robot reacts. The changing impedance is used to modify, in real-time, the wire-feed speed (amps and fill ratio) and robot travel speed. This combination of attributes greatly increases the variety of workable joints and materials.
Seam tracking requires no external apparatus to execute its tasks, providing a viable option for joint types with access challenges that have previously precluded the use of bolt-on equip- ment. And, in simple economics, the capital investment of through-the-arc sensing can be as little as 10 percent of a comparable vision or laser solution.
A top-performing through-the-arc seam tracking setup provides the com- bined benefits of economics, technical capability and physical geometry. While the ratio of investment to capa- bility for this type of seam tracking solution has been well established over the years, recent process advance- ments have continued to push the boundaries of capability in addressing the problems of the ever-changing joint configuration.