Have you ever wondered how you can optimize the quality of weld seams in series production? Are you annoyed by rejects or rework? If you use welding robots including laser triangulation in your production, for example, you know that precise welds are essential – not only for stability, but also for the efficiency and cost-effectiveness of your processes. There are different sensors available and the question is: how many lines are better for your application? A sensor with one or three lines?
In our last blog post “When welding tolerances become a trip to hell”, we explained how you can overcome all the challenges posed by specified position tolerances in welding. In this article, we want to follow on that and focus on the next question: What are the differences between sensors with one laser line and sensors with three lines? We will give you a basic overview so that you can better evaluate the technology and find the right solution for your needs right from the start.
Among other methods, optical seam tracking systems operate on the basis of laser triangulation (light section method). More precisely, it is called laser line triangulation, but for simplicity, we will refer to it using the shorter term.
Think of the sensor as an eye that observes the workpiece and its surface. To do this, the sensor head projects a fine red laser beam onto the workpiece, creating a visible line.
The light is reflected, and a specialized camera inside the sensor head captures the reflected line from a specific angle. By analyzing this angle, the camera can determine the exact position and shape of the line on the workpiece. Since the distance and angle (triangulation angle) between the camera and the laser projector are fixed, the camera precisely knows its position relative to both the laser and the workpiece. The camera can therefore draw conclusions about the exact position and shape of the weld seam from the distortion of the reflected line. In real time, the sensor collects data on the joint – i. e. its position, width, and depth – and transmits this information to the welding system's control unit. The system then uses this data to precisely guide the welding torch along the seam and immediately compensate for any deviations.
To summarize:
In the world of laser triangulation, two approaches have become established: sensors with one line and sensors with three lines.
Both methods have specific advantages and disadvantages and are suitable for different applications. Ultimately, the choice of process depends on what you need the sensor for – the specific welding task, the component, and the precision requirements of the seam.
To give you a better overview, we want to compare the two methods and explain their respective pros and cons.
Advantages:
Disadvantages:
Advantages:
Disadvantages:
The following table provides a comprehensive comparison of the key differences between a single-line sensor, such as the iST ARC weld seam tracking sensor from ABICOR BINZEL, and a three-line sensor:
The difference between single-line and three-line sensors is largely related to their applications and technical limitations. Sensors with three or even five lines were originally developed for applications where speed was more critical than precision. However, in practice, the additional information from three or more lines is often not usable.
The reason: Most standard industrial robots, such as those from ABB, Fanuc, KUKA, or Yaskawa, are designed to process data from a single-line sensor. Transmitting additional measurements from multiple lines to the controller offers little benefit since only a limited number of measurements per second can be processed.
In addition, a single-line sensor uses the entire available laser power, resulting in a stronger signal compared to distributing it across three lines. This can be beneficial when dealing with very high arc intensities, which may partially outshine the sensor signal. Such conditions occur, for example, in plasma welding or high-performance MAG welding.
Furthermore, modern single-line sensors feature software filters that ensure consistent measurements. These filters detect and correct incorrect measurements, for example, over tack welds, so that a single line is generally sufficient to achieve precise and reliable results. Another point: While a three-line sensor provides additional measurements for plausibility checks, these are only useful if all three lines can simultaneously capture the weld seam – which is often not possible for smaller or more complex components.
Tip: When selecting a sensor, consider not only the technical specifications but also the requirements of your application. In most cases, a well-configured single-line sensor can provide all the relevant information without the added complexity of a three-line sensor.
The choice between a single-line and a three-line sensor strongly depends on the application. However, for most robotic arc welding processes, the single-line sensor offers better conditions: it is efficient, flexible, and delivers data at a speed that the robot controller can process. While three-line measurement can theoretically provide more information, the interfaces required to utilize it are often lacking. Additionally, modern software options can handle many of the tasks that a three-line sensor is intended for.
What experiences have you had with optical seam tracking? Feel free to share your thoughts in the comments or contact us!
Curious for more? If you want to learn about the challenges of welding tolerances and how to manage them, check out our article “When welding tolerances become a trip to hell”.