The cutter must travel with the strip
A flying cutter cannot remain stationary while a moving strip passes through it. During cutting, its carriage must follow the strip's movement. A master/slave relationship lets the controller express that travel as a ratio rather than repeatedly generating unrelated targets.
A master can be a physical encoder axis or a virtual axis that provides a common reference. A virtual master is useful when several machine mechanisms should follow one commanded production phase. If the product slips relative to a motor encoder, that master measurement may still be unsuitable for product tracking.
Calculate the relationship
For an ideal engaged gear:
slave_position = master_position * slave_master_ratio + phase_offset
slave_velocity = master_velocity * slave_master_ratioAt ratio 0.25, 400 master units correspond to 100 slave units. A negative ratio reverses the coordinate direction. Ensure compatible scaling: a master in degrees and a slave in millimetres needs a ratio with the corresponding physical meaning, not a unitless number copied from another machine.
The phase offset sets the relative position relationship. Equal velocities do not prove the carriage is at the correct cutting location. Synchronization requires the relevant position and velocity conditions under the installed operation.
Engagement is an operation
MC_GearIn requests coupling, but its allowed initial state and synchronization behavior are vendor-specific. In Beckhoff Tc2_MC2, basic MC_GearIn couples at standstill; moving-master synchronization uses other documented operations. Do not assume that a familiar block name guarantees a flying-cutter engagement ramp.
Before engagement, specify the master condition, slave position, available synchronization distance and permissible dynamics. Observe the block's synchronization status and completion contract before allowing the cutting action. A Busy indication is not proof of a valid synchronized window.
MC_GearInPos and related families address position-related engagement where supported. Their precise inputs, timing and options belong to the vendor library. Inputs visible in a declaration may be reserved or unimplemented; Beckhoff documents such restrictions on its basic GearIn interface.
Decoupling does not define the next move
MC_GearOut ends the relationship under its vendor rules. It must not be assumed to stop the slave. A flying cutter commonly needs a defined deceleration or return move after leaving the cutting window. Issue that operation through the same owner/arbiter and account for the interruption of synchronization.
If the master faults or stops unexpectedly, decide how the slave responds. Consider a carriage near its stroke end and a vertical synchronized load. An ideal ratio formula has no knowledge of physical limits, torque capability or safety requirements.
Coupling bench
Change the master angle and observe the slave demand with ratio 0.25. Increase the master angle by 400 degrees and verify a 100-degree increment in slave demand. Try a negative ratio and add an offset. The picture represents the mathematical relationship only; it does not run MC_GearIn or model engagement ramps.
The benchmark readout lets you distinguish a ratio change from an offset change. A ratio changes demand slope as the master progresses. An offset moves the whole position relationship. Changing either abruptly in a real running machine can require a controlled transition.
Flying-cut exercise
Describe the stages: wait for a valid product, prepare slave position, engage with the master, confirm synchronization, permit cut within its window, disengage and return. Include missing product, failed synchronization and master interruption. State the measured product reference and the evidence required before cutting.
Calculate a 1:1 slave/master linear relationship at a strip speed of 300 mm/s. The slave needs 300 mm/s during the synchronized segment, plus the acceleration and return capacity required by the cycle. The engaged ratio alone is insufficient for motor sizing.
References
Beckhoff MC_GearIn documents standstill coupling and unimplemented interface options. PLCopen motion control defines synchronized-motion families. TryPLC's ST engine currently rejects gear commands; use a vendor runtime for their lifecycle tests.