In automation design, the choice between a Stepper Motor and a Servo Motor is often decided by budget. But looking at the price tag alone is a mistake that leads to machine failure. Steppers are excellent for holding loads stationary (high holding torque). Servos are kings of high-speed motion. If you choose a stepper for a high-speed application, it will lose torque and "miss steps." If you choose a servo for a simple low-speed application, you have wasted $500. This guide explains the physics behind the choice. Table of Contents 1. Open Loop vs. Closed Loop (The Risk) 2. The Torque Curve: Speed Kills Steppers 3. Inertia Mismatch 4. Selection Summary Advertisement 1. Open Loop vs. Closed Loop (The Risk) The biggest difference is not the motor itself, but how it is controlled. Figure 1: Steppers run "blind" (Open Loop). Servos use an encoder to verify position (Closed Loop). ...
Which software are you using in your mechanical design project?
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I have been using Solid Edge 3D CAD software for 1-2 years for my mechanical design projects in the past. But now, according to the standardization in my design organization, I have to switch to use Unigraphics software instead, or we call it in short as "UG NX4" (the latest versions are simply called NX).
To be honest, at first, I still liked Solid Edge because I think I can make modeling and assembly in Solid Edge faster and easier than in UG. But one of the good things for UG is the Motion Simulation module that helps me simulate the movement of mechanical assemblies before releasing for manufacturing. I know that Solid Edge also has this kind of simulation module, but I didn't have a chance to use it (no license). So in this post, I would like to share how easy it is to set up motion simulation in UG NX4.
Let's start with a very simple modeling.
I would like to see how the cylinder moves when it is pushed by the rotating lever. So I start by making UG modeling as shown above. Those parts can be "features" in a single UG file or the assembly of several UG files.
Once the assembly is ready, I can then start "Motion Simulation".
At Motion Navigator, right-click and select "New Simulation".
UG NX4 will show the pop-up Motion Joint Wizard window for automatic setting of joints for simulation. For this example, I just click the cancel button in order to set the links and joints manually.
Next, what I have to do is to set necessary links and joints for motion simulation. I have to start with the creation of links. Parts or features that cannot be moved and have no contact with other parts can be excluded from the link setting. In the example, the fixed column can be excluded from link setting. I can leave it as it is, just for showing purposes only.
First, I would set the lever as a link in motion simulation by clicking at the "link" icon and selecting the lever and renaming it as "lever".
Do the same thing for the cylinder and the block.
Why do I need to set the block as a link?
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I have to set the block as a link even though it is not moving because I would like to set the 3D contact between the cylinder and the block, otherwise, the cylinder will fall down during simulation! I have to also select "fix the link" for the block in order to prevent falling down when the simulation starts.
At Motion Navigator, I can see the links and joints I've created. We can see that though I don't set the joint for each link yet, there is a "J001" joint at the Motion Navigator pane because UG NX4 creates a "fixed joint" automatically when we select "fix the link" during the creation of the link.
Next, I create a revolute joint and set the motion driver for the lever. This step is very important. The point and direction of the joint must be correct i.e. Z-axis should be the axis of rotation.
Then I create the 3D Contact between the cylinder and the block and also between the lever and the cylinder.
Then we're ready to start simulation. But we have to make sure that the solver environment is "Dynamics" not "Kinematics" because I would like to see the effect of 3D contact. (Click at the calculator icon).
Next, start motion simulation by clicking at "Animation" and set time = 1 and step = 100 and see the result.
Watch the following video for the result.
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