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...
In the previous post [3-Position Motion Generation Four-Bar Linkage Synthesis], the locations of the fixed ground pivots (O2 and O4) 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 (O2 and O4) to desirable locations.
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Step 1: Define the Desired Motion
Draw the coupler link AB in its three design positions: A1B1, A2B2, and A3B3.
Figure 1: Defining the three target positions. Sometimes standard pivot locations are invalid or obstructed.
Step 2: Define Alternate Moving Pivots (C and D)
This is the critical step. We attach a "virtual" rigid shape to line AB to define new points C and D.
Figure 2: Defining alternate moving pivots C and D relative to the coupler AB using rigid triangles.
Procedure:
1. Draw points C1 and D1 relative to A1B1.
2. Replicate this geometry for positions 2 and 3.
3. Use Geometric Constraints (Equal Length, Fixed Angle) to ensure the triangle ABC is identical in all three positions.
Step 3: Synthesize Fixed Pivot O2
Now we treat C as our moving pivot instead of A.
- Draw construction lines from C1 to C2 and C2 to C3.
- Construct perpendicular bisectors for both lines.
- The intersection is the fixed pivot O2.
- Draw Link 2 as line O2C1.
Step 4: Synthesize Fixed Pivot O4
Figure 3: Locating the fixed ground pivots O2 and O4 using the bisectors of the alternate pivot paths.
Repeat the process for point D.
- Bisect lines D1D2 and D2D3.
- The intersection is the fixed pivot O4.
- Draw Link 4 as line O4D1.
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Step 5: Construct the Mechanism
Figure 4: Building the final kinematic chain. The coupler is now a rigid triangle connecting the moving pivots to the functional link AB.
- Draw line O2M equal to O2C1.
- Draw line O4N equal to O4D1.
- Draw the rigid coupler triangle M-N-A-B. Ensure it is dimensionally identical to the shape C1-D1-A1-B1.
- Apply an angular driving dimension (e.g., 20 degrees) to the input link.
Simulation and Verification
Figure 5: Setting up the animation dimension to verify the motion path.
Use the Animate Dimension command to sweep the input angle. You should see the target line AB pass perfectly through all three desired positions.
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