Machinery TwinBuild a flying shear
The signature cam application, synchronize a carriage to a moving web and cut on the fly.
A flying shear cuts continuously moving material: a carriage accelerates, matches the web speed exactly while the cut happens, then returns. It is the canonical test of cam design, and of whether your PLC's camming is phased right.
What you'll build
- A web of material moving at constant speed (line path with a series of product marks)
- A shear carriage on a linear axis, cam-driven
- A blade with a simple cut animation (state machine or second cam)
- One master variable driving it all, the digital line shaft
1. The master
Create Line_Master, MasterTime 0…360, speed to taste. In Online mode this later maps to the real line-shaft position, nothing else changes.
2. The web
A line path along the machine direction. Drive its movement variable from the master via a Copy function scaled so one master cycle = one product pitch. Use the series trick or several offset followers for repeating product marks.
3. The carriage cam, the heart of it
New cam profile, master 0…360, slave = carriage position:
| Master | Segment | Purpose |
|---|---|---|
| 0–100° | Poly5, 0 → sync-start, end velocity = web speed in slave-units/master-degree | Accelerate to match |
| 100–170° | Straight at web-speed slope | Synchronization window, the cut happens here |
| 170–300° | Poly5 back to 0, entry velocity matched, zero end conditions | Return |
| 300–360° | Straight, dwell at 0 | Wait for next cycle |
The one non-negotiable: the Straight zone's slope equals the web's speed in the same units, and the Poly5 boundary velocities match it on both ends. Verify the velocity plateau in the visualizer.
Create Shear_Carriage as a Motion Cam variable (this cam, master Line_Master) and bind it to the carriage object's travel axis.
4. The cut
A state machine: Wait → (variable transition: master enters the sync window) → Cut (SetValue blade down + timer) → Retract → Wait. Bind a product mark's visibility to a post-cut flag if you want the web to visibly separate.
5. Watch it fail, then fix it
Deliberately shift the sync window 20°, the blade now cuts a moving target at the wrong speed and the scene shows exactly the smeared, dragging cut a real machine would produce. This is the class of bug the twin exists to catch: phase errors that are invisible in a variable table and obvious in 3D.
Going online
Map Line_Master to the PLC's virtual master axis (From Connection) and the twin now validates the PLC's cam tables, see HIL workflow.