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Showing posts from November, 2010

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VFD vs Soft Starter for Conveyors: Preventing Gearbox Failure

You selected the right AGMA Class gearbox . You calculated the belt tension perfectly. But the moment you hit "Start," the belt snaps or the gearbox makes a terrifying clunk. The culprit is likely your Starting Method . In conveyor systems, the starting torque profile matters more than steady-state power. Note: We previously discussed VFDs as Energy Savers for pumps and fans. For conveyors, however, the goal is not lowering your electric bill—it is preventing your gearbox from exploding. Table of Contents 1. The Physics of Shock Loads 2. Why Soft Starters Stall Conveyors 3. The VFD Torque Advantage 4. Comparison: Cost vs. Protection 5. Final Verdict Advertisement 1. The Physics of Shock Loads When an AC induction motor starts Direct-On-Line (DOL), it draws 600% to 800% of its rated current (Inrush Current). More importantly, it produces a sudden spike known as Locked-Rotor Torqu...
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Roberts straight-line mechanism

Figure 1: A modern linear ball slide (like this THK model) is the contemporary solution for precise straight-line motion. Many modern engineering applications require components to move in a precise linear fashion, known as " straight-line motion ". Today, we take this for granted. We can simply purchase an off-the-shelf Linear Motion Guide that moves a device accurately along a rail with low friction. The Historical Challenge: Making a Straight Line However, in the late 17th and early 18th centuries—before the development of high-precision milling machines—it was extremely difficult to manufacture long, perfectly flat surfaces. Creating a sliding joint without significant backlash was nearly impossible. During that era, engineers had to rely on Linkages . Much thought was given to the problem of attaining a straight-line motion using only revolute (hinge) connections, which were much easier to manufacture. The most famous early result was...

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...