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Archive for October, 2009

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.

Hey there! If you are wondering (and even if you are not) why this blog has been so empty as off lately, just let me tell you that everyone in my family, including me, has been sick on and off with some sort of flu or cold. I’m sick of it (no pun intended)!  So, that’s how with kids staying home sick and in between fevers and coughs, my days have been as boring and unproductive as they could ever get.  Every now and then, however, I get a chance to go online and check out the forums for something interesting or fun.  This little post right here caught my fancy. It’s just a bunch of SolidWorks users sharing pictures of what they do with the software. Yeah, I know, nothing new, but I like to look at it just the same.  I wish I could add something of mine in there, but what I’ve done so far isn’t really worth it of being among those images and is not even for real work, but only for fun or for this blog.  I’m so dying to try out my wings in the real world! I know I said before I didn’t feel like taking a full time job at this time because of my family situation, but perhaps some freelancing or tackling a small project…  Hmmm, I don’t know, right now it all feels like it will never happen and I will simply continue doing this as a hobby until Hell freezes over…  By the way, have I told you that feeling sick has a depressing effect on me?

Oh, I almost forgot! My brother is on the look for 3D modeling software for his personal use.  He’s not looking into SolidWorks, mainly because he can’t afford it and also because he’s in the area of architecture and doesn’t feel SolidWorks would be what he needs. After spending quite a long time convincing him that AutoCAD 2010, even with all the bells and whistles it’s been given, is NOT a 3D modeling software, he decided to take a look into other software, such as Rhino, and I must admit he’s got me curious about it. Well, it seems so affordable that if it’s really something useful for mechanical /product design, I may save my pennies and get a copy for my personal use.  So here are some questions for you:  Do you use Rhino combined with SolidWorks? If so, what is your experience with it? What kind of design have you done that you used Rhino for and what part did SolidWorks play in the rest of the design? Did you need other software of addins?

The weekend seemed very short and I apologize for not putting this up earlier, like I said I would, but I wanted to spend time with my husband, who had just come back from a long trip to Japan, and celebrate both our birthdays while he was here for a couple of days before he had to go back to Japan for a trade show.  Every year is the same: he’s travelling during the week of his birthday, by the end of September, and again during mine, the first week of October. It never fails! But I don’t complain, because God has blessed our family by giving him a great job, and that’s plenty.

Anyway…  Transforming the plain round head of the funkey into a mouse’s head began by changing the sketch for the revolved surface from an arc (spherical head) to a partial ellipse (oval shaped head).  I also changed the axis of revolution, just tilted it up a bit.

Next step was to modify the ears. Instead of revolving the sketch 360 degrees as before, I only revolved it 180 degrees and then thickened the surface to a solid, by using the command Thicken, then mirrored the ear with respect to the Front plane and filleted the edges.

On the Top plane I made a sketch to aid me in the process of shaping the mouse’s snout. I used the sketch to trim the face’s surface with it. In the image, you can see the surface I’m removing in purple and the sketch appears in blue on the Top plane. Notice that there is a projection of this sketch on the back of the head, but I didn’t select that surface to be removed as well.

After trimming the surface, I patched the hole with a new surface using Fill Surface.  I didn’t really want to just patch the hole; I wanted this surface to have a more pronounced shape, different to that of the face. My goal was to create the nose of the mouse, so I thought if I added a point as a constraint curve (the one you see in the image), the new surface would have to pass by that point and I’d be able to shape it that way into a mouse’s snout. Well, the idea was good in part, but you can’t really depart that much from the original shape by using this method, or else the Fill Surface will fail. This is as far as I was able to locate that point.  I get a bump in the surface, but not so much for a mouse’s nose.

And this is where I decided to try my luck with the Freeform tool.  By the way, before you read any further, I would like you to take a look at a very nice video that Mark Biasotti shared with all the community through the SolidWorks Discussion Forums. You can find the video at: http://files.solidworks.com/special-videos/freeform demo.zip  This video explains in more detail how to use the Freeform tool.

Did you check out the video? Great! Now I’ll tell you how I used Freeform with my mouse.  First of all, I established that the boundary conditions at the edges would be Contact. Why? Well, because I wanted to deform that surface considerably and I knew the result would certainly not be tangent or have the same curvature of the face, but that was OK with me. For your own projects, however, you may want to keep the edges tangent or have the same curvature, so keep an eye on that.  I also established that the deformation would be symmetrical with respect to the Front plane by choosing Direction 1 Symmetry. What this means is that whatever I do to one side of the surface will automatically be done to the other side, thus making my work easier.  Notice the plane of symmetry in the middle of the nose. In this particular case, the plane is coincident with the Front plane of the model.

Next, I added a few curves (they appear in green in the image) by clicking on Add Curves and placing them pretty much wherever I thought I needed them.  On most of these curves, I also placed a few points, by clicking on Add Points and placing them over the curves I had just added previously. Each one of these points would allow me to push and pull from it, thus deforming the surface. Pulling a point in one of these curves will affect the appearance of the rest of the surface, at least up to the next curve. It sounds complicated, but each one of the points also has a Triad that gives you some control over the whole deformation process. You can either pull directly on the screen or enter numerical values for each axis direction in the property manager.

While you are at it, if you take a closer look at the edges of the surface being deformed, you’ll notice some arrows/vectors. If you click on them, a Triad will show up and by manipulating this Triad you’ll be able to adjust the tangency and vector direction of the surface right at the edges.  This will also affect the look of the rest of the surface.

So, basically, this is what I did with Freeform. I spent a few minutes pushing and pulling, adding and removing points. Just dynamically changing the surface until it looked the way I wanted it. I wasn’t really worried about creating the best of surfaces at this point, or if the mouse would be able to be manufactured or not; I just wanted the looks. Nevertheless, with some effort and perhaps a sketch or two to guide the deformation, I believe better results can be achieved with this tool.

Moving on with the rest of the mouth. Before deforming the surface, I had made an offset copy of it to serve as the back of the mouse’s mouth, by using the Offset Surface tool, as you see here.

Then, once the surface had been deformed, I trimmed it again using another sketch I made, again on the Top plane. This sketch will help me shape the smiling mouth. You can see the sketch in blue and the purple area is the surface to keep.

Once I had the gap for the mouth, I opened a 3D sketch and placed a two-point spline from corner to corner, like you see here.

I used this 3D sketch to create a couple of surfaces using Fill Surface. This is one of them.

And this is the other one.

Notice that the surfaces intersect the one for the back of the mouth that was previously created using Offset surface.  It’s time for some trimming.

First, I trimmed both new surfaces against the one I had created for the back of the mouth. In the image you see the parts in purple are the areas to keep and the surface in black is the one for the back of the mouth, used as the trimming tool.

I trimmed the back of mouth surface against the other two in a very similar way and then knitted all three surfaces together.

The eyes were made in a very similar way to the mouth. First, using a sketch to trim part of the surface of the face…  The sketch appears in blue and the area in purple is the one being removed.

I then opened a 3D sketch, converted the edge of the snout, thus creating a spline, and trimmed the spline  to the edges of the eye hole, like you see here. This sketch will be used to loft a surface for the eye.

This is the loft for the eye. As you see here, the lofted surface was created between the edge of the eye hole and the 3D sketch. I added a start constraint using the Top plane to define Direction Vector. I just wanted to give the eye some volume and make it look like it was popping out of the face.

The rest of the features for the face are fairly simple. The black little nose was made using a surface revolve and the teeth are just a couple of extrusions.

I’m still fascinated by the Freeform tool, however. I want to explore it further and see what else it can do and what other applications it can have, but most importantly, learn to control it a lot better than this in order to achieve the best results possible.

Hey! It’s been quite some time since I updated this blog. I’ve been engrossed in a refresher of Chemistry and Materials Science, in hopes of better understanding about manufacturing processes of plastic products. Back in the day, I used to love Chemistry, and I think I wasn’t so bad at it, although some people may disagree with me, all because of a one-time tiny accident that left the lab stinking like rotten eggs for a couple of months. Anyway…  Today or tomorrow I’ll write about this model you see here, which is a modification of my original funkey. The inspiration came from a brief conversation with my brother. He’s an architecture student in Mexico, and he was telling me about how our sister, a graphics designer, had requested his help in creating the 3D model of a mouse to include in some sort of advertisement. He showed me samples of the renderings he had made, and that was enough to get me going. I had to have my own mouse!

I didn’t really spend much time in modifying this model; I didn’t have more than a couple of hours to spare.  So, basically I reshaped the head (partial ellipse instead of an arc), made a few trims, lofts, and filled surfaces here and there, and most importantly, shaped the snout using Freeform command.  I’ll explain all that in more detail in my next post.

Now, I’m not sure this mouse could even be manufactured as it is. I just wanted the looks, and it was also a good exercise in the use of the Freeform command. I used to feel much intimated by it, but I’m finding that it’s not really that hard, and the best of all is that I can go back and edit the Freeform anytime I want. Perhaps with a bit more practice I will be able to model really neat stuff.  I didn’t have a layout of some kind to guide myself in shaping the snout, so I just pulled and pushed until it looked good to me. I know it could look much better than that…

Now, please, somebody tell me this does look like a mouse!  I was never the artistic or creative one of the family, you know?

Tell you more soon!