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Posts Tagged ‘SW2009’

Most of you have no idea and perhaps don’t even care about the fact that I adopted a little kitten about a month ago. What can I say? If you are a smart person, unlike moi, you’ll avoid visiting the pet store while the local cat rescue is showing off their adoptable cats. But I admit I would’ve probably ended up adopting the kitten anyway, eventually…

I named him Troubles because it suits his personality. He’s always in the mood for mischief and looking for ways to get into all sorts of places.  Unfortunately for me, one of his favorite places to explore is inside my kitchen cupboards, where I keep the aluminum foil, the sugary cereal, and other goodies. Up until a couple of days ago, I used to think I had the situation under control thanks to the leftovers of the childproof latches I had installed on those cupboard doors to keep my own kids out of them. That’s when I contemplated in horror how the cat managed to push the latch down and swing the cupboard door open.  Wait a minute?  I thought those things were supposed to be hard to open even for a small child! Not that it requires a lot of effort, but, I mean, how strong is a cat, anyway?

Motivated by this question, I decided to make a simple model of a childproof latch and use SolidWorks Simulation to estimate the force that is required in order to push the latch down and open the cupboard door.  First of all, the kind of latch I’m talking about is a simple vinyl one, such as the one in this picture.

The long narrow piece goes attached to the inside top corner of the cupboard door and there’s a small piece that goes secured to the frame of the cupboard, and that will serve as a stop for the latch. When the child attempts to open the door, the latch will get trapped by the other piece, allowing the door to open only partially, unless the latch is pushed down enough for its tip to pass underneath the other piece.  I’m not so good at explaining this, but I’m sure most everyone has seen one of these before.

So this is what I did… I made a very simple model of the latch, as you see here. My model included some filleted edges, but they are not really necessary or useful for this analysis, as you will see in a bit, so I decided to suppress the fillets and run an analysis without them.  Doing this usually makes the calculations easier and faster, and the results aren’t affected, unless, of course, there’s a concentration of stress in the corners and you are interested in knowing   the stresses precisely in the filleted areas.

Next thing I needed to do was create a new Simulation study using this configuration without fillets, and establish some boundary conditions.  I applied a fixed geometry fixture to the back of the rectangular plate, to simulate how it would be securely attached to the cupboard door, unable to rotate, slide or move in any direction. This is done simply by right clicking on Fixtures and selecting Fixed Geometry from the menu.

I applied a second fixture to this study. This fixture makes the study slightly unusual, because what I was used to do was to apply some boundary conditions (usually some fixed geometry) and then a force and that’s it, let SolidWorks calculate stresses, displacements, etc. due to that force. In this case, however, I’m trying to find the magnitude of a force that will generate a certain known displacement, and this second fixture is going to help me in that task.

I knew I needed the very tip of the latch to displace some 5 mm down, so I used an advanced fixture to specify this translation.  If you right click on Fixtures and select Advanced Fixture, you’ll open a property manager where you’ll be able to choose from several different advanced fixtures available. In this case, I used Use Reference Geometry.  At first, I made the mistake of thinking that what I wanted was for the that small rectangular face on the tip of the latch (shown in pink) to displace down 5 mm along the vertical face adjacent to it (shown in green), and so I used those two faces to define the fixture, as you can see in the image. 

This, however, was a mistake because, after meshing the model and running the simulation, it produced the following result.  Notice something funny about this image? Look closely. If you were paying attention, you probably noticed that both faces remain parallel to their original positions throughout the deformation process, which is not the way you expect the latch would deform when pushed down. You can see it clearly in the image, as the original model has been superimposed on the deformed one.

So, I tried again, only this time I used different entities to define the fixture. Instead of a face, I used an edge on the tip of the latch.  I specified that I needed that edge to translate 5 mm down in a direction normal to the Top plane, as you can see in the following image. 

Well, that seemed to do the trick! After meshing the model and running the simulation, I obtained results that were more like what I was expecting.

By the way, in case I haven’t mentioned it before, I don’t have Simulation Premium, I was running this analysis in SolidWorks Simulation, but even though SolidWorks Simulation is usually limited to the small displacement kind of analysis (linear analysis), where the deformation of the model is so small it really can’t be noticed by the naked eye, it is also possible to solve some large displacement, non-linear problems, as well,  and obtain some accurate results, provided that there is no permanent deformation.  This one is a large displacement kind of problem, since 5 mm is an extremely noticeable deformation, however, this deformation doesn’t appear to be permanent, since the maximum stress is way below the yield point for this material.  To run an analysis making use of the large displacements option, simply right click the analysis name on the tree, select Properties, Options, and check the option Large Displacement, as you see in this image.  However, if you don’t select this option yourself and, while running the simulation, SolidWorks Simulation detects that this is a problem where large displacements are involved, it will give you a warning about it and ask you about running the simulation using this option. Don’t ignore the warning, since it can lead to incorrect results.

Once the stress distribution was calculated, I was able to estimate the force necessary to push the latch down 5 mm by right clicking on the Results folder and selecting List Result Force from the menu. I selected the rectangular face of the tip (in green), clicked Update, and found that the magnitude of the force should be approximately 5.5 lbs, applied normal to this face. 

I checked these findings by running an analysis the “typical” way, applying a force of 6 lbs normal to that same face, and the displacements plot showed the kind of large displacements I was expecting, once again with a maximum stress way below the yield point.  One thing to notice here is that if you look at the stress distribution plot for this problem I just talked to you about, you’ll see that the magnitude of the stress appears to be higher on the particular edge that was used to define the second fixture, when compared to the stress on rest of the latch’s tip, that is. This, I think is a consequence of applying the fixture using the edge, and not necessarily relevant, but I could be wrong.

I must confess that the arms were quite a challenge for me.  My result is not perfect, I know, but I think it’s close enough.  Not so bad for a beginner, at least? Anyway, I had tried doing a surface sweep, but it didn’t look good, so I went with more lofts.  I started by creating some more geometry (What a surprise!).  I sketched a spline on the Top plane, following the silhouette of the arm when seen from above (assuming the funkey is lying on its back).

I used that spline and the sketch of the parting line I had made for the body to create a parting line for the arm as a projected line of the two.

Next, I created a couple of sketches on the Front plane to help shape the lower and upper half of the arm when seen from the side.  Here’s the sketch for the lower half of the arm. It’s a spline sketched on the Front plane. Its endpoints are coincident to endpoints of a 3D sketch that is a copy of the parting line for the arm that was  just created previously. To make that copy simply open a 3D sketch, select the projected curve that is the parting line for the arm and use Convert Entities.  The spline is also tangent to a couple of construction lines which are perpendicular to the sketch of the parting line for the body, as you can see in this image.

My next step was to create three planes parallel to the Right plane where I would sketch cross sections of the lower half of the arm, as you can see here. These cross sections will be used as guide curves for a lofted surface, just like with the foot.

Each of these cross sections is a two point spline. There’s a piercing relation between one endpoint of the spline and the sketch of the lower half of the arm that was created previously and another piercing relation between the other endpoint of the spline and the 3D sketch that is a copy of the arm’s parting line. The spline is also made tangent to those two construction lines you see there, one vertical and one horizontal.

After I had my cross sections ready, I created a surface loft, using the sketch of the lower half of the arm and the 3D Sketch that is a copy of the arm’s parting line as profiles, and the cross sections I just created as guide curves.

The upper half of the arm was also modeled in a very similar way, with a surface loft between an upper half arm sketch and the arm’s parting line, only in this case I didn’t use any guide curves. I realized that for the kind of surface I wanted to create, the results were the same if I simply adjusted the start/end constraints to be Normal to Surface for the upper half sketch (with the end tangent length adjusted to 0.17) and Direction Vector for the parting line (with end tangent length adjusted to 0.54). The direction vector, by the way, was defined by one of the construction lines in one of the cross sections I sketched for the lower half loft. According to the Help document, Start and End Constraint applies a constraint to control tangency to the start and end profiles. Normal to Profile applies a tangency constraint normal to the start or end profile, while Direction Vector applies a tangency constraint based on a selected entity used as a direction vector. The tangent length controls the amount of influence on the loft. The effect of tangent length is limited up to the next section.

 

At this point, the arm looked pretty much like a fin. I trimmed the upper and lower halves using the rest of the body as the trimming tool. The purple area is the part of the surface that will be kept.

To finish shaping the arm from a fin to something more funkey-like, I created a third surface loft.  I started off with more auxiliary geometry. First, I created three planes parallel to the Front plane where I would sketch profiles for the loft (shown in purple). Two of these profiles are splines with a piercing relation to a 3D sketch copy of the arm’s parting curve (shown in yellow), and the third one of them is a point coincident with that 3D sketch copy of the arm’s parting line.

Next, I created a lofted surface using those three profiles and the 3D sketch copy of the parting line as a guide curve.

Then I trimmed this surface using the upper half of the “fin” as a trimming tool. The purple area is the part of the surface that was kept.

I trimmed the new surface and the upper half of the “fin” using a sketch as the trimming tool, as you see in the image. The idea was to remove a section from both surfaces and create a new surface that will blend them together (more or less) nicely at the elbow. The purple areas, as usual, are the ones being kept.

To blend both surfaces at the elbow, I decided to use a surface loft. I tried the Filled Surface first, but I didn’t get nice results.  So, I created a 3D sketch and converted the right edge of the hole in the “fin”  to use it as one of the profiles for the surface loft. Then, I made the surface loft, using the 3D sketch I just created and the edge of the other surface as profiles, and a copy of the arm’s parting line as the guide curve. Notice that the Start and End constraints for both profiles as Tangent to Face. This setting was the one that produced the smoothest results, without puckering at the corner where both profiles meet.

The next step was to take care of the funkey’s “hand”. First, I opened a sketch in the same plane where I had sketched the biggest cross section for this surface loft, converted the edge of the surface as you see in the image and joined the ends with a line to form a closed boundary for a planar surface.

Then used Planar Surface command with the sketch I just created.

I trimmed this planar surface using the body as the trimming tool. Again, the purple area is the one that’s kept.

 

Next, I trimmed the planar surface again, this time using the fin as the trimming tool. The purple area is the one that is being kept. In this case, you don’t see the portion of surface that is discarded because it’s extremely small, but enough to make other features such as Knit fail.

Now I trimmed the upper half of the “fin” using the lofted surface as a trimming tool. In this case, the area in purple is the one being discarded.

At this point, I discovered a tiny hole right in the corner where the surfaces meet that needed to be filled; otherwise it would prevent the knit surface feature from working. I used Fill Surface to patch it.

After patching the hole, I knitted all the arm surfaces together, including the tiny patch, and trimmed them using the body of the funkey as trimming tool. The area in purple is the one that is kept.

Then I mirrored the arm with respect to the Front plane. And then I trimmed the funkey’s body using the arms as trimming tools. This had to be done in two separate trims; one for each arm. Then simply knitted all three surfaces together: the two arms and the rest of the body.

I filleted the edges of the “hands” using a variable radius fillet. Notice the different values for the fillet at each one of the control points.

After patching the bottom of the funkey and the neck with a couple of planar surfaces, all that was left to do was to make the head, but that was easy, all I had to do was revolve three arcs and then trim the surfaces with respect to each other.

Wow! That was some long post! I didn’t think there would be so much to say about this model, and I simplified a lot to avoid making it way too long. If anyone needs the model, I’ll be glad to share it, of course. I apologize with those of you who are experts at surfacing if my model is too amateurish for you, but as I said before, I’m just getting started.

I think I like surfacing…

 

In this second part of my blog post I’ll show you how I worked the funkey’s feet. The feet were made in a very similar way to the body, with lofted surfaces, but I didn’t use Fill Surface to create a patch in this case, just the lofted surface.

First of all, I created a plane that was parallel to the Right plane and used it to trim the bottom of the body, using the Trim Surface command with the plane as the trimming tool. This plane will also be where the spline that is the shape for the bottom of the feet will be sketched.

Next, I created some auxiliary geometry. First, I created an axis between the Front and Top planes. The purpose of creating this axis is to use it as a reference when creating the plane of symmetry for the foot, which needs to be 130 degrees from the Top plane and pass through that axis.

 

Once I had a plane of symmetry for the foot, I sketched a spline on the plane I used to trim the bottom of the body (I called it Funkey bottom plane); this spline is the silhouette of the foot when seen from below.  Notice that I sketched only one half of the silhouette and mirrored it with respect to a construction line that would be collinear with the foot’s plane of symmetry. This is because having the whole shape of the bottom of the foot helped me visualize how wide and/or long to make the feet.  Once again, I don’t have many dimensions, but I do have some relations in place. Notice the two construction lines that are perpendicular to the line of symmetry. The spline was made to be tangent to these two lines at each end.

Next, I sketched a spline on the foot’s plane of symmetry. This spline will give me the shape of the foot when seen from the side. I made the endpoints of the spline coincident with the endpoints of the one I had sketched previously and, once again, the spline is tangent to those two construction lines you see there at both ends.

That construction line that appears at 0.12 in from one of the sides is there simply to help me create a series of planes perpendicular to the symmetry plane and that will be needed to sketch cross sections of the foot.  In this image you can see the planes and the cross sections that were sketched on each one of them.

Each one of these cross section sketches is a two point spline. There’s a piercing relation between one endpoint of the spline and the sketch of the bottom of the foot, and another piercing relation between the other endpoint of the spline and the sketch of the silhouette of the foot when seen from the side that was created previously.  The spline is made tangent to those two construction lines you see there, one vertical, and one horizontal.

Once I had my cross sections ready, I used them to create a surface loft using the sketch of the side view of the foot and only half of the spline in the sketch of the bottom of the foot as profiles (use the selection manager to pick only half of the spline and not the whole sketch). The cross sections I sketched previously were used as guide curves. Notice that the start and end conditions were set to Normal to Curve. It doesn’t always work this way, but in this particular case, it made the loft look a lot smoother.  Now, I know there’s a singularity right where the two profiles meet, so perhaps in the future I should try using a patch like I did for the body, although it doesn’t look bad this way.

Next, I mirrored the lofted surface with respect to the foot’s plane of symmetry.

And mirrored the result with respect to the Front plane.

Next I simply trimmed the surfaces using Trim Surface.  I used the option Mutual Trim, which means that both surfaces will work as trimming tools and will be trimmed by each other at the same time. It also means that the resulting surfaces will be knitted together.  Notice that there are three surfaces as trimming tools: the body and the two feet. The areas in purple will be kept and the areas in green will be discarded.

When you’re on the road with a dog, one thing you learn pretty quickly is that your choices for food are limited because most places won’t allow dogs inside, not even little lap dogs.  I think we must’ve visited every single fast food place along I-70 on the way to Ohio and every single one along I-80 on the way back. Too much junk food!  Master Andrew seemed pleased, however, since he managed to collect a few of those little toys called Funkeys that came included with his kid’s meal.  I borrowed this one as my inspiration for a surfacing exercise.

This one is my version of the funkey. It doesn’t look exactly the same, but I’m excited no matter what. I know it’s not perfect and there’s probably a bunch of things I should’ve or could’ve done differently. I certainly appreciate comments and corrections, but remember I’m just a novice at surfacing, so go easy on me.

This has the potential of becoming a huge post, so I’ll probably have to break it down in pieces. Let’s start with the body.

The first thing I did was to create some geometry that would help me build the shape of the funkey. I sketched a spline on the Top plane that would follow the silhouette of the funkey’s body when seen from the front or from the top if you think of it as laying down on its back.  I only needed one half of the silhouette, since I was planning on taking advantage of the symmetry by constructing only half of the body and mirroring it with respect to the Front plane.

On the Front Plane, I sketched a spline that would be the parting line for the body when seen from the side. I don’t really have much knowledge of plastic mold design, but I observed the toy and the parting line followed this curvy shape all along the body.  Notice that I almost have no dimensions on my sketches and almost all of them are under defined. This was really an exercise and I was constantly dragging and moving spline handles and points, but I suppose that you could define the sketch completely if that’s what you wish to do.

Next, I used Insert, Curve, Projected, to create the parting line for the body as the projection of the first and second splines I had sketched previously.  Make sure to use the option Sketch on Sketch for this one. The curve created this way is a spline and it’s a 3D sketch because it’s not resting on any plane.

I sketched a third spline on the Front plane. This will be the sketch that follows the shape of the lower half of the body when seen from the side (Front plane).  Again, I don’t really have dimensions because I was constantly playing with the shape of the body, but I have a few relations in place. First there’s a piercing relation between this spline and a circle that I sketched on a plane I called Neck Plane.  The funkey has a circular neck.  By adding relations between the splines and this circle I’m trying to help shape the transition.  On the other end of the sketch, you’ll notice some construction lines and some tangent and perpendicular relations.  One of the construction lines is tangent to the parting line created previously. Another construction line was made perpendicular to the first one and the new spline (lower half sketch) is made tangent to this second line.  I wanted to add draft, and that’s why you see another two lines separated by a 2 degrees angle. My plan was to make my spline tangent to this other construction line, but the shape wasn’t really good, so I decided not to try to add draft, at least until I practice more and learn proper ways to do it.  By the way, those grey lines you see between the points of the spline are what is called the control polygon. I find that I have a better time controlling the shape of a spline by dragging the points in the control polygon than by manipulating the handles. To see the polygon, just right click on the spline and select Display Control Polygon.

 

Next, I created a series of planes, parallel to the Right plane that would help me sketch cross sections of the body. The purpose of these cross sections was to aid me in the process of creating a surface loft.

Each one of the sections was a two point spline. One end of the spline had a piercing relation to the parting line (the 3D sketch created as a projected line) and the other end had a piercing relation to the lower half sketch.  The spline was made tangent to a vertical line on one side and a horizontal line on the other.

Next, I used the cross sections as profiles to create a surface loft, and the parting line and lower half sketch as the guide curves.

This gave me part of the lower half of the body, but there was still some of it left to do. I decided to use Fill Surface to build a patch on that area. You know, when I think about it, there’s other things I could’ve done, like a loft surface to fill up that part or simply change the way I did the loft, by using the parting line and lower sketch as profiles and the cross sections as guide curves. I probably would’ve needed less guide curves too, as many guide curves tend to make the result a bit bumpy. Yes, there’s other things I could’ve done, but I wanted to practice with fill surface so I went this way.

The first thing I needed to do was to create these two auxiliary surfaces you see here.

The edges of these three surfaces were then used as boundaries for the patch created with Fill Surface. Notice the curvature control for each of the edges. Two of them are Tangent and one is Contact.  According to the help document, “Contact creates a surface within the selected boundary. Tangent creates a surface within the selected boundary, but maintains the tangency of the patch edges. Curvature creates a surface that matches the curvature of the selected surface across the boundary edge with the adjacent surface.”  These settings worked for me because those were the ones that made the result look the smoothest, but I’ve found that you have to experiment with it a bit sometimes.

After this step, I hid the auxiliary surfaces, knitted the two lofts together and mirrored the result with respect to the Front plane.

 

The upper half of the body was made in exactly the same way, leading to this result.

Next, I created a plane parallel to the Neck Plane and used it to trim the surfaces, by using the Trim Surface command, with the plane as the trimming tool.

 

After knitting both halves together, I proceeded to create the neck.  First, I extruded a surface using the same circle I had sketched previously on the Neck Plane.

I trimmed this surface using a line I sketched on the Front Plane. I had previously segmented this line using Tools, Sketch Tools, Split Entities.

The idea was to partition the extruded surface in four equal parts to facilitate a loft between its edges and the edges of the rest of the body. As you can see in the image below, this surface loft uses the edges of both surfaces as profiles and the lower half sketch and a copy of the parting line (made by using Convert Entities on a 3D sketch) as guide curves.

I did something similar for the other edge, except now using the upper half sketch; instead of the lower half sketch.

After that, I simply knitted both edges and mirrored the result with respect to the Front plane.

What I ended up with was this gourd-like shape that would be the body of my funkey. I know it’s not perfect. I played with the profiles and splines for a bit, trying to make it look a bit better. It could be smoother, but it’s a good start, I guess.  Next time, I’ll show you what I did for the rest of the funkey.

Just as promised, here is the video of the second part of what was going to be my presentation at the local SWUG.  This one deals with Free Motion, changing component properties and changing the orientation and camera views during the animation.  By the way, I added a new option to the controls of the video. If you notice, there’s a button in the video control bar that will allow you to select from a floating table of contents and choose exactly what part of the video you want to watch. I hope someone out there finds this video useful. There’s a third and last part coming soon. Enjoy!