12. Path Finding - Overview
Tutorial
This tutorial will look at an overview of the general path finding settings and the different path finding options available to use across all path finding methods.
Prerequisites and Resources
Before starting with the tutorial, ensure to have the KUKA KR8 example cell downloaded and imported into Verbotics Weld. This cell is available to download here.
This walkthrough also uses the path finding overview example project which can be downloaded here.
Video Tutorial
Step by Step Guide
Step 1: Types of Path Finding
Load example project 1 in verbotics weld, then navigate to the weld settings. Now, navigate down the list of settings until you find the Path Finding Example Setting. This is an example of a generic path finding setting. Looking at the details of this setting, you should notice one of the first settings available to adjust is the type. This allows you to specify the method of path finding the robot should use when this setting is applied.
Verbotics supports 4 types of path finding:
Touch Sense
Nozzle Sense
Laser 1D
Laser 2D
Path Finding Types
The ability to use each of these will depend on your robot’s capabilities and how the robot has been set-up. For example, the KUKA KR8 being used in this tutorial has touch sense set-up, and also has an additional 1D laser sensor attached and connected. You’ll see this has directly affected the options in the type drop-down box. Which should show touch sense and laser 1D as available, and leave the remaining 2 options greyed out and unavailable.
KUKA KR8 with Touch and Laser 1D
Each path finding type shares a common set of options which you can see listed under General, as well as an additional set of unique options listed below this. For this tutorial, you’ll be focussing on the common settings in general.
General Path Finding Settings
Step 2: Accounting for Displacement Error with Part Accuracy
Start with the first path finding setting you can adjust, this being part accuracy. The part accuracy option let’s you set the range to conduct a search in depending on how accurate you believe your part to be. To see how accuracy impacts a sensing motion, there are 2 path finding settings labelled “PartAc10mm” and “PartAc20mm”. Looking at these settings, you should see that each setting has had a part accuracy of +- 10mm and 20mm respectively.
Part Accuracy Slider
Return to the viewer, and select welds 1 and 2 which have both been planned using these 2 settings. The sensing marking for each weld should appear, and comparing the 2 side-by-side, you’ll notice the circle marking for weld 2 is significantly larger than weld 1.
Note
The sensing motions can be made visible by enabling touch sense. This is found in view->touch sense
This circle represents the area to conduct the searching motion within when accounting for displacement error. Increasing the value for part accuracy increases the radius of this search area to compensate for parts with lower accuracy.
High Part Accuracy |
Low Part Accuracy |
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Weld 1 is an example of when the part is known to be placed accurately, and in this scenario is known to be no more than 10mm from its expected position. However for weld 2, it’s assumed the part isn’t going to be this accurate, and as such its setting has increased the value of part accuracy option to account for a larger error, this time at most +-20mm.
While the part accuracy option can be increased to larger values, this can sometimes cause planning difficulties if used on smaller parts. Look at the failed weld labelled Weld 2b, which is an example of when this occurs. This weld has had the PartAc 50mm applied and has failed to plan its path finding motions
Right click on weld 2b and open the edit calibration window. This menu allows you to manually edit path finding motions. Select the first touch and click the pick button, you’ll find that no matter where we try to place the path finding operation, the area can’t fit on the part face.
Path Finding Motion Un-placeable
A sense must be able to fit within the bounds of a part face in order to avoid path finding errors. For this example, a +-50mm potential error results in the sense not fitting and hence being impossible to plan a successful sensing motion. In these cases, you may be required to improve the accuracy of your part’s positioning in the real world.
However, it’s also important to ensure if you set your part accuracy to a value of +-10mm for example, that your part is definitely within that area, as otherwise the sensing operation could miss entire features and determine sub-optimal values for offsets.
Sensing motions and how they are performed is explained in our Path Finding reference documentation,.
Part 3: Sense Distance and Sensed Components
Return back to weld settings and you’ll see the next option you can set is labelled sense. With this, you can limit what type of components should be sensed, by default this is set to weldable parts only but you can also specify to include all parts, or to only sense weld faces or weld parts.
For this example, we’ve created the Weldable Only and the All Parts path finding settings.
Return to the viewer and now select welds 3 and 4. We’ve set weld 3 to only search weldable parts, while weld 4 uses a path finding setting that allows it to conduct a search on any part. While both welds show senses conducted along the plate being welded, notice only weld 4 conducts a third sense on the un-weldable plate in the centre.
All Parts |
Weldable Only |
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Moving on, the next option to look at is the maximum sense distance, return to weld settings and navigate to the first example setting created for this, this is labelled as Max Sense 20mm.
With maximum sense distance, you can limit how far away a sense action can be from the current path finding location. For this, you’ll see one setting with this set to 20mm and one left at the default value of 100mm.
Return back to the viewer and select welds 5 and 6, which have had the 20mm and 100mm settings applied to each respectively. Upon closer inspection of these welds, you should see that with weld 5 on the left, the sensing motions shown are kept within a much closer distance to the path finding location, which is represented by the green ball. However, weld 6 on the right has its motions much more further away from the path finding location, which is further evident by looking at the sensing operation planned on the plate between welds 5 and 6.
20mm |
100mm |
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Part 4: Spacing between Sense Operations
For the final 2 options, return to the viewer and navigate to the small spacing settings. At the bottom of the general settings you’ll find 2 values related to the spacing of each sensing operation.
Using minimum spacing and maximum spacing, you can specify the allowable space between each sensing operation. You should find 2 final example settings related to this, these named small spacing and large spacing. Return to the viewer and explore these now.
Select welds 7 and 8, and you’ll find that with the small spacing setting applied, weld 7 has 4 sensing operations all spaced closely, whereas weld 8 on the other hand has only 3 sensing operations as with the minimum spacing set to 100mm, could only fit 3 operations along the length of a 200mm weld.
Small Spacing |
Large Spacing |
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That covers all the common operation available to adjust for path-finding, further details on the path finding operations can be found here.