Product engineering and manufacturing has several aspects related to it, and one of which is digital product development. The aim of digital product development is to model the design virtually and conduct all studies related to the design digitally, so that we expend least amount of effort in creating it, in real life and with minimum resources. For example, in case you are designing a piston, you may want to simulate mechanical load conditions, and analyse the maximum stress and keep it under elastic limit of the material.
Depending upon the product that you are modelling, your design requirements may change. For example, before manufacturing an engine, it may be of interest to find if the different parts would clash with each other during the motion. Or you may wish to graph valve position with respect to crank rotation etc.
I like to watch videos online, and am fond of the work and products created by Matthias Wandel. I thought, I would take one of his invention, model it in Catia and demonstrate some of the example study that you may do with Catia. So, the post in an attempt to demonstrate Catia's capabilities and the kind of studies that you can do using this. Pantorouter is a product that utilizes pantograph design and uses it to cut wooden shapes with the help of wood router. If you are not familiar with pantograph, you can read more about it here and here.
So, here's how I went about doing this.
1. Creating the sketch to study dynamics of the mechanism
If you see Matthias' Pantorouter, the links he uses are not very clear in video and pictures, So I thought, I would first create a reference sketch before modeling the links and other different parts like table router, pattern etc. The sketch is such that, the motion traced by the point on the longest line is double the scale of the motion done by the mid point, where we intend to have the tracing pin. Below you can see that sketch and how it moves. This is done using animate constraints. This provides us a sanity check and we can see that the centre point where we intend to mount the router, does indeed trace a circle (in white D=25mm) that's half the diameter of the point that's tracing the bigger circle (in green D=50mm).
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| Pantorouter Mechanism analysis using sketch |
We can change the scale of motion, by changing the link lengths and can do a sanity check by comparing the sizes. The sketch provides an easy way to make changes and study the kind of impact it will have on the motion. The useful points derived from the sketch can be used directly for designing parts and can be used for modeling links etc. We can already see that the bottom-most link is such that it will collide with the base on which it mounts, if it is not offset by some distance. so those kind of considerations are done beforehand.
This reference sketch is also important from the view point that if the links won't have same centre distances as this sketch has, then the mechanism won't work as intended. The reference sketch also works as a template and helps make design changes easily.
2. Using the reference sketch to model parts
Modeling parts is straight forward. For this, I saw the images and modeled it as I saw fit. I am not a wood worker, so this was not a detailed design, so different joints and joining techniques etc. that may be used were not taken into consideration. The different parts that I modeled are:
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| Pantorouter - Modeled in Catia |
- Base - This is part on which the slide and table are mounted. So in a sense it is the largest and main part.
- Table - Table is the part on which the wood part is clamped so that it can be worked with.
- Slide - Slide is used for mounting links which carry and move the router. It also has provision for mounting the pattern.
- Router - The router was not modeled, but was instead imported as STEP file from an online directory of parts.
- Pin - The pin will trace the pattern, and it is with respect to this movement, the router will move and machine wood.
- Router clamp - This is used to clamp router to the link arm that carries the router.
- Router bit - The bit can be replaced and there's a point created on the bit, which will be used to trace the movement it makes.
- Links - There are a few link arms that make up the mechanism and help make the movement.
- Drawer slides - Drawer slides were also imported as STEP files from an online parts directory.
Below you can see how the different parts come together and work as a mechanism. The parts were first assembled (leaving the constraint that we needed for mechanism). Subsequently, assembly constraints were used to create joints and simulation was created in DMU kinematics workbench.
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| Pantorouter 3D mechanism |
3.
Tracing the centre point of the router bit
The router bit can be seen in green, the movement made by the center of the bit will help us confirm the path that it is tracing. At this point, it's not really needed and is redundant, since we made the mechanism after seeing how it works in 2D. Nonetheless, this can be done. To do this, first we need to compile the simulation and generate a replay. After the replay is generated, it will be shown in the specification tree. Subsequently, we can generate movement by tracing point, line etc. To my surprise, I made a mistake while designing links and found the path generated by router bit was not aligned with table. I tracked this mistake by creating a drawing of the assembly, and found that the link holding router was not equidistant from the end.
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| Mistake made - Router was not at the centre, it was corrected |
I corrected the mistake and the router carrying link was remodeled. Below you can see the path traced by centre point of the router bit after the correction was made. The size is half of the pattern and is as expected.
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| Path traced by centre of router bit shown in black |
4. Swept volume generated by router bit
This replay we generated in previous step, will also be used to generate the volume swept by the router bit. We can better visualize the volume that the router bit will remove by creating the swept volume generated by router bit. Below you can see the volume swept by router bit. The file generated by Catia is a .cgr file. Unfortunately, the file is generated independent of the assembly file as you can see below. However, you can call the file by using existing component tool, as you do in an assembly and see it in reference to the other parts.
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| Swept volume generated using router bit with reference to the table on which the part will be placed. Subsequently, volume placed with respect to parts. |
There's no direct way of using the volume for design purposes, however it has other uses. For example if you are designing a machine, or trying to visualize some robot arm movement, you may want to have the swept volume information. To keep a safe distance or for the purpose of designing other parts, assemblies etc.
5. Clash analysis
During the process of designing parts and assembly, there's no way to find if the parts will collide during the operation. However, after the simulation is created and mechanism operates with full range of motion, we can check for clash or interference between parts. You can turn clash detection on while the simulation is taking place and it will show you the parts and portion that clash in red outline (see it below)
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| Clash regions in the Pantorouter can be seen in red outline |
There is another way to comprehensively analyse clash in the assembly between all parts. You can find the clash tool in Space analysis toolbar. This will reveal all components in clash or contact. You can also set clearance parameters and filter parts as per criteria. This makes analysing parts easy. A thing should be kept in mind is that this does not reveal how the parts will interact when they move. So, you may also want to dynamically check for clashes between parts while running the simulation.
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| Dialogue box for checking clash, contact, clearance in Pantorouter |
Below you can see the router bit tracing another pattern.
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| Router bit tracing another pattern |
