Transfer a part, then prove it arrived
The teaching cell has an infeed conveyor, a horizontal pusher and an XY transfer gantry. A part reaches the loading sensor, the pusher transfers it into a fixture and the gantry carries it to an unload location. The machine must distinguish a completed axis command from a completed transfer.
The course's individual benches support isolated command and mathematical investigations. They do not execute this entire cell or its safety system. The capstone is a design-and-test exercise to take into an appropriate vendor simulator before any physical commissioning.
Define coordinates and permissions
Use a units sheet for every axis: physical mechanism, encoder location, transmission ratio, units, positive direction, reference method and valid workspace. Define gantry machine and workpiece frames. Name the product reference used by conveyor tracking if the gantry must pick from a moving belt.
Before automatic operation, establish drive readiness, coordinate validity, tooling readiness and the absence of conflicting ownership. Safety permission is supplied by the validated safety design; ordinary program conditions do not replace it.
Write the machine sequence
- Wait for a valid product at load and a clear receiving fixture.
- Accept a pusher absolute move to the transfer station.
- Monitor Done, CommandAborted and Error; record a bounded timeout.
- Confirm the transferred product with the receiving sensor.
- Return the pusher under a separately accepted operation.
- Permit the gantry pick when the pusher and tooling are clear.
- Execute the coordinated gantry path in the correct frame.
- Confirm unload and return to the next permitted state.
Every step needs entry conditions, an owned operation and a completion definition. A sensor already high at entry may represent the previous product or a stuck signal. Decide how the machine identifies a new product and rejects stale confirmations.
Compare two gantry requirements
A pick-and-place transfer may care only that the tool avoids fixtures and reaches its endpoint. A dispensing path cares about the geometry throughout travel. The latter needs coordinated path control, speed planning and a defined corner tolerance. Independently starting X and Y point moves cannot be assumed to satisfy it.
On the path bench, verify a straight line from (0,0) to (300,400) mm. At half completion, position is (150,200). For ideal 100 mm/s path speed, the components are 60 and 80 mm/s. Then specify the acceleration, workspace and tool-clearance checks absent from this analytic model.
Recovery table
| Interruption | Information to preserve | Next permitted action |
|---|---|---|
| Pusher move aborted | Replacing command and actual position | Defined interruption state |
| Product confirmation missing | Motion result and sensor/product identity | Inspect or reject, not automatic success |
| Gantry command refused | ErrorID, frame and target | Diagnose before issuing a new request |
| Home validity lost | Maintenance/power event and feedback status | Re-establish reference before coordinate moves |
| Stop held | Stop request and axis state | Release under restart policy, then accept new travel |
A fault reset does not imply a product is safely recoverable or the cell can resume. Require the physical-state checks specified for that interruption.
Safety boundaries
MC_Stop, MC_Halt and MC_Power are ordinary motion-control operations, not certified safety functions. A guard or emergency stop needs the risk-assessed safety response using suitable hardware and validated logic. STO removes torque-producing capability under its defined safety function; it is not electrical isolation and does not by itself hold a vertical load. SS1 and related drive safety functions have their own certified implementation and validation requirements.
Use ISO 12100 for risk assessment and the applicable ISO 13849-1 or IEC 62061 method for the safety-related control system. IEC 61800-5-2 addresses drive safety functions. The installed products, architecture and validation determine what is achievable; a course worksheet cannot certify the machine.
Capstone acceptance record
Run normal transfer, blocked receiving fixture, missing product confirmation, command interruption, held Stop and invalid reference cases. For each, record request ID, state transitions, accepted target, feedback and final outcome. Add a restart test with Start already held when a fault clears, and verify that your chosen restart policy is respected.
Finish with a vendor-specific implementation sheet: controller, motion library version, drive, supported blocks, BufferMode restrictions, homing options, task period and safety-system reference. An advanced learner should be able to explain why each operation is selected and which evidence permits the next machine step.
References
PLCopen motion control covers single-axis, homing and coordinated specifications. CODESYS coordinated group setup provides a vendor implementation example. Use current manufacturer safety manuals for the exact drive and safety option.