The packaging jaw follows a cycle
A jaw closes while a product passes the sealing station, stays closed for part of the cycle and opens before the next product. Its slave motion is not a constant ratio to the master. An electronic cam describes slave position as a function of master position: y = f(x).
The master can represent machine phase, often expressed over a repeating cycle. The cam table maps that phase to a slave coordinate. Scaling and offsets adapt the relationship, while interpolation determines what happens between table points. A larger number of points does not automatically produce acceptable derivatives.
Read more than the position plot
Cam slope converts master velocity into slave velocity. Cam curvature contributes to slave acceleration:
v_slave = f'(x) * v_master
a_slave = f''(x) * v_master² + f'(x) * a_masterWith unchanged geometry and constant master speed, doubling speed doubles slave velocity and quadruples slave acceleration. A cam that worked at half production speed can exceed torque or acceleration limits at full speed.
If position joins continuously but slope jumps, the ideal slave velocity jumps. If curvature jumps, acceleration changes abruptly. Check periodic joins, dwell boundaries and table switching, not just whether the graph looks smooth from a distance.
A rise, dwell and return
The teaching bench uses a cosine rise from 0 to 80 mm over 0 to 120 degrees, a dwell to 180 degrees, a return to zero by 300 degrees and another dwell to the end of the cycle. This exposes the relationship without implying that it is a production-ready jaw cam.
The cosine rise has zero slope at its ends, but its acceleration joins to a dwell need examination. A different profile can make acceleration or jerk continuous at the expense of other peak demands. Choose continuity from the mechanical requirements and cycle time, then calculate the resulting limits.
A dwell keeps slave position unchanged while master phase advances. It can correspond to a process window, but sealing force, tooling temperature and product presence remain separate process conditions. A cam position alone does not establish them.
Select and engage the table
MC_CamTableSelect, MC_CamIn and MC_CamOut are common families, with vendor-specific table representations and lifecycle details. Define when the selected table becomes active, how the slave joins its demand and what happens at the first periodic wrap.
Switching tables while running needs explicit activation and continuity rules. A new table with a different value at the current phase can demand an abrupt position change. Phase adjustment and scaling options also need supported update mechanisms. Do not edit a running table behind an accepted operation unless the library documents that behavior.
TryPLC does not execute these cam blocks in its ST runtime. The bench calculates slave demand directly from master phase; it does not simulate table selection, engagement, drive following error or torque saturation.
Bench investigation
Switch the coupling bench to Electronic cam. Scrub master phase through 0, 60, 120, 180, 240 and 300 degrees. The expected slave demands are 0, 40, 80, 80, 40 and 0 mm. Repeat the cycle beyond 360 degrees and inspect the repeated demand.
Return to gear mode and compare the graph implied by a constant ratio. A gear's linear relationship cannot provide a dwell followed by a return within the same increasing master cycle.
Exercises
Design a jaw demand with a longer closed dwell. Explain what must change in rise/return timing if the cycle remains 360 degrees. Calculate how doubling constant master speed changes velocity and acceleration demand. Then name the conditions required before switching from a cleaning cam to a production cam.
For a vendor lab, export the table's position, velocity and acceleration demands, record the interpolation method and verify the join at the periodic boundary. Compare actual feedback and command demand under the drive's approved test procedure.
References
Beckhoff camming documentation describes start modes, activation and switching options. PLCopen motion control provides the common synchronized-motion framework.