Mechanical Design Handbook

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Showing posts with the label Siemens NX

3-Position Synthesis with Inversion Method (Part 3)

In [ 3-Position Synthesis with Inversion Method - Part 2 ], we successfully determined the locations of the moving pivots (G and H) relative to our fixed ground pivots (O 2 and O 4 ). However, finding the points is only half the battle. Before we commit to manufacturing or detailed 3D modeling, we must verify that the mechanism actually moves smoothly between all three positions without locking up (toggle positions) or deviating from the path. Advertisement Constructing the Kinematic Chain Now that we have our four critical points (O 2 , O 4 , G, H), we need to "build" the mechanism links within the CAD Sketcher environment: Input Link (Link 2): Draw a solid line connecting the fixed ground O 2 to the moving pivot G. Output Link (Link 4): Draw a solid line connecting the fixed ground O 4 to the moving pivot H. Coupler Link (Link 3): This is the most important part. You must draw a rigid triangle connecting G, H, and the ...

3-Position Synthesis with Inversion Method (Part 2)

In the previous introduction , we established the problem: We have fixed mounting points (O 2 and O 4 ) on our machine base, and we need to design a linkage to hit 3 specific positions. Standard synthesis moves the pivots to fit the motion. In Kinematic Inversion , we do the opposite: we virtually move the ground to fit the coupler. By "freezing" the coupler in Position 1 and moving the ground relative to it, we can geometrically find the required link lengths. Advertisement Step 1: Setup the Constraints Start by drawing your known constraints in the CAD Sketcher (NX, SolidWorks, etc.): 1. The Fixed Ground Pivots (O 2 and O 4 ). 2. The 3 Desired Coupler Positions (A 1 B 1 , A 2 B 2 , A 3 B 3 ). Figure 1: The setup showing fixed grounds (bottom circles) and the target motion path (red lines). Step 2: Inverting Ground Pivot O 2 Now we perform the "Inversion." We need to find where the ground pivot...

3-Position Synthesis with Inversion Method (Introduction)

In our previous tutorials, such as [ 3-Position Motion Generation Synthesis with Alternate Moving Pivots ], we used a "standard" synthesis approach. We defined the moving coupler first, and the geometric construction dictated where the ground pivots (O 2 and O 4 ) had to be. But what if you don't have that freedom? Advertisement In real-world machine design, you often have a pre-existing frame or base. You cannot drill holes just anywhere; the ground pivots must be located at specific, available points. In this scenario, the standard method fails because it gives you valid kinematic solutions that might require mounting a pivot in thin air or inside a motor. The Solution: Kinematic Inversion To solve this, we use the Inversion Method . The Core Concept Instead of looking at the mechanism from the perspective of a stationary ground and a moving coupler, we invert our perspective. We pretend the Coupler is stationary...

Advanced Linkage Synthesis: 3-Position Motion with Alternate Pivots

In the previous post [ 3-Position Motion Generation Four-Bar Linkage Synthesis ], the locations of the fixed ground pivots (O 2 and O 4 ) were mathematically determined by the positions of points A and B. The Problem: Sometimes, these calculated fixed pivots land in impossible locations—inside another machine part, off the machine base, or too far away. The Solution: We use Alternate Moving Pivots . Instead of using the endpoints of the line AB, we create new points (C and D) that are rigidly attached to the moving body. By adjusting the location of C and D, we can steer the fixed pivots (O 2 and O 4 ) to desirable locations. Advertisement Step 1: Define the Desired Motion Draw the coupler link AB in its three design positions: A 1 B 1 , A 2 B 2 , and A 3 B 3 . Figure 1: Defining the three target positions. Sometimes standard pivot locations are invalid or obstructed. Step 2: Define Alternate Moving Pivots (C and D) ...

3-Position Linkage Synthesis: Motion Generation in CAD

In real-world engineering, a mechanism often needs to guide a part through more than just a start and end point. It usually requires passing through 3 specified positions to clear obstacles or perform complex tasks. This technique is known as 3-Position Motion Generation . We can extend the logic from our previous post [ Four-bar linkage Synthesis using CAD Sketcher ] to solve this problem geometrically within a modern CAD environment like Siemens NX, SolidWorks, or CATIA. Advertisement The Design Challenge Assume we must design a mechanism to move Link AB through three specific positions (A 1 B 1 , A 2 B 2 , A 3 B 3 ) while avoiding an obstacle (represented by the rectangle below). Figure 1: Defining the three target positions (A1B1, A2B2, A3B3) relative to the obstacle. Step-by-Step Synthesis 1. Define the Positions: Draw Link AB in its three design positions: A 1 B 1 , A 2 B 2 , and A 3 B 3 . 2. Geometric Synthes...

Geometric Synthesis of Four-Bar Linkages: A CAD Tutorial

In advanced Mechanism Design , engineers often face the challenge of moving a rigid body from one specific position to another. This process is known as Motion Generation Synthesis . While sophisticated solver software exists, you can perform this synthesis geometrically using the Constraint-Based Sketcher found in any modern CAD package like Siemens NX, SolidWorks, or CATIA. Advertisement The Goal: Moving a Line in a Plane Assume we need to design a 4-bar linkage that moves a coupler link from position AB (Start) to position A'B' (Target). Figure 1: Defining the Start Position (AB) and the Target Position (A'B'). Step-by-Step Geometric Synthesis The logic relies on finding the center of rotation for the moving points. 1. Locate the First Pivot (O 2 ): Draw a construction line connecting point A to A'. Then, create a Perpendicular Bisector of line AA'. Theory: Any point located on this...

NX Motion Simulation Part 5: Final Results & Digital Twin Verification

This is the moment of truth. In the previous posts, we moved from abstract mathematical derivations in Excel to the concrete setup of a 3D Digital Twin . Advertisement The result of our timing diagram design—utilizing overlapping motion with Fifth-Degree (3-4-5) Polynomial and Linear cam functions—is now fully integrated into the 3D model. We are no longer just guessing; we are validating the Mechatronics Design Workflow . The Power of "Spreadsheet Run" The simulation below was executed using the Kinematics environment in the Unigraphics (UG) NX4 Motion Simulation Module (now known as Simcenter 3D). By utilizing the "Spreadsheet Run" command, we are not just animating the assembly; we are driving the geometry with pure, precise data. Every frame of movement corresponds to a specific calculation row in our Excel sheet. This creates a direct data bridge, confirming that the complex polynomial curves we designed will phy...

NX Motion Simulation Part 3: Slider Joints & Linear Drivers

In [ Part 2 of this series ], we finished setting the driver for the revolute joint of the indexing mill. Now, we will set up the Punch Die . Advertisement Step 1: Setting up the Slider Joint The movement of the punch die is different from the indexing mill. It moves only in linear motion along the Z-axis. The joint for this kind of movement is called a "Slider" joint. Procedure: 1. Select Joint command. 2. Select "Slider" joint icon. 3. Select the "Die" link we created earlier. 4. Click "Orientation on the first link" → Select "Point". 5. Select the center point of the cylinder to define the joint origin. 6. Select "Vector" → Click the bottom face of the cylinder (defines the downward Z-axis). 7. Rename to "J_Die". 8. Click Ok. Step 2: Defining the Linear Driver Advertisement ...

NX Motion Simulation Part 2: Setting up Links and Joints

Let's continue from the previous post . Now it's time to visualize our previous calculation for the timing diagram of the indexing mill and punch die using 3D Motion Simulation in Unigraphics (UG) NX4 . Advertisement While we successfully created a 2D motion simulation in Excel , modern engineering demands a full Digital Twin . The UG NX4 Assembly model is prepared as shown below. The mating conditions of the assembly model follow the sketch shown in [ Timing Diagram (Part 1 - No Overlap Movement) ]. Step 1: Entering the Simulation Environment New to UG NX4 Motion Simulation ? No problem. Follow this step-by-step guideline. In the motion simulation environment , all commands are initially disabled. You must right-click on the assembly file and select New Simulation . This command creates the necessary files and organizes them automatically. Step 2: Defining the Kine...

NX Motion Simulation: Integrating Excel Timing Diagrams - Part 1

During the process of timing diagram design , I normally start with detailed calculations in an Excel spreadsheet to minimize acceleration while satisfying the required process cycle time. Advertisement Once I can visualize the preferred displacement, velocity, and acceleration profiles of the mechanisms in Excel, the question becomes: What's next? Shall I start manufacturing immediately? The answer is NO. In modern engineering, we use Digital Twin Technology to verify the design first. From Excel to 3D Simulation Currently, I use Unigraphics (UG) NX4 (now Siemens NX) to design the mechanical parts. When the assembly modeling is done, I use the assembly model to simulate the movement of mechanisms with the Motion Simulation Module . This step is critical for Virtual Commissioning . It helps confirm the timing diagram before releasing the design for manufacturing. It is especially useful when movements are combined in ...

Dynamic Simulation Tutorial: Setting up 3D Contact in UG NX4 Motion

Which software are you using in your mechanical design project? Advertisement 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. ...