All About Touch Sensing

Posted on August 24, 2023 by Andrew

Path finding (or path calibration) is the ability of a robot to use sensors to account for differences between where it expects a welding path, and where it actually is. For offline programming it’s a critical feature as the 3D CAD model will never exactly match the real world. It also allows to account for part variations and robot inaccuracies. Without path finding, robot programs need to be manually touched up to put the weld in the exact right spot. This is why Verbotics includes automatic path finding - so you don’t have to spend the time to do this.

Touch sensing is the most common sensing technology our customers use for path finding. But what is touch sensing, and what are the pros and cons compared to some other options?

A robot using touch sensing to find the welding path.

What is touch sensing?

Put simply, touch sensing is where the robot uses the welding wire or nozzle to ``touch’’ the part, and detect exactly where it is. It starts at a certain position, then drives along a direction until the welding power source detects electrical contact with the part. It then records the position where the touch was, and compares this with the expected position to offset the welding path.

Verbotics includes some smarts to analyse your part geometry, and understand where is the best places on your part to touch sense. It then combines a number of touch senses to offset the path in different axes, as well as to allow touch sensing small features and to minimise cycle time. Our path finding documentation has more detailed information about how this works.

What are the pros and cons?

The biggest pro of touch sensing is that it does not require any additional sensor hardware. Most robot and power source combinations support touch sensing out of the box, and it’s typically easy to set up.

The second major advantage is that you’re sensing and welding with the same thing - the welding wire. This means that you are not having to exactly calibrate the relationship between a sensor and the welding wire.

Touch sensing does have a few drawbacks. One major one is the impact on cycle time - each touch can be time consuming, and you also need to cut the wire at regular intervals. Another issue is that the surfaces being touched need to allow electrical continuity to be detected - so painted surfaces can be a challenge.

A final issue is that touch sensing is sensitive to the position of the welding wire. The wire needs to be a known length, and it can cause issues if the wire is bent, or moves in and out while the robot moves.

What considerations do I need for touch sensing?

When considering touch sensing with Verbotics, it’s good to confirm that your welding power source and robot have the required capability. As mentioned above, touch sensing requires a consistent and known wire length to work best. To do this you’ll need a wire cutter as part of your robot system. We also reccommend that you consider a wire brake, particularly for large robots. This will stop the wire moving in and out as the robot moves.

Robot using a wire cutting station.

How do I program for touch sensing in Verbotics?

The good news is that touch sensing is fully automatic in Verbotics Weld! The software will pick where to put each touch based on your 3D part model and settings. If you want, you also have exact control to pick where each touch should be placed.

Automatically planned touch sense path finding inside Verbotics Weld.

If you’d like to learn more about touch sensing in Verbotics or arrange a demonstration, please contact us.