The challenge: cut the strip on the fly without stopping the coil, and stack at high cadence
A Spanish manufacturer of metal components for the appliance industry asked us to automate a flying shear and servo-stacking line. The plant processes rolled coil that feeds continuously from a decoiler-straightener group and must be cut into variable-length pieces at high speed, without slowing the strip feed, and then deposited onto neatly arranged stacks ready for shipment.
The technical challenge had two sides. On one side, the shear must kinematically synchronise with the moving strip throughout the cutting phase: travel at the same linear speed as the material, execute the cut cycle, return to its home position and be ready for the next shot, all within tens of milliseconds and with no deviation that would cause burrs or out-of-tolerance pieces. On the other side, the stacker had to execute coordinated trajectories synchronised with the piece output rate and reorganise its pattern according to the production recipe selected at the HMI.
The client was coming from a previous installation with discontinuous mechanical cutting: the line had to stop the strip for each cut, which limited throughput and generated high energy consumption from the repeated start/stop cycles of the feed drive. The specification called for continuous strip movement and recipe changeover times under two minutes.
Why Motion Control, and why Siemens S7-1500T
Flying shear is one of the canonical scenarios where Motion Control is not optional: synchronisation between the strip feed axis (a virtual master derived from the measuring encoder) and the shear axis (the slave) must run at the controller firmware level, not at application-program level. Any latency introduced by the PLC cyclic execution would degrade cut quality.
For this class of applications Siemens offers the S7-1500T technology CPU, which extends the standard S7-1500 PLC with advanced technology objects: TO_SynchronousAxis, TO_Cam, TO_LeadingAxisProxy, electronic cam profiles and MC_CamIn / MC_GearIn instructions. These blocks make it possible to implement electronic cam, electronic gearing and sector-based synchronisation without leaving the TIA Portal environment and without resorting to a dedicated external motion controller. Selecting the S7-1500T over a SIMOTION-based solution was justified by native integration with the rest of the machine PLC, unified programming in TIA Portal, deterministic 1 ms IRT cycle over Profinet and immediate availability.
For the actuators we selected Siemens SINAMICS S210 servo drives, a family designed specifically for Motion Control over Profinet IRT, with servomotor auto-identification and guided commissioning from the CPU itself. The matching SIMOTICS S-1FK2 servomotors carry an absolute multi-turn encoder and one-cable connection to the drive.
Control system architecture
The system revolves around an S7-1500T CPU (CPU 1515T-2 PN) acting as the single line controller: it handles sequential logic, the HMI, plant communications and — most importantly — the motion technology objects. Field devices connect over Profinet with two differentiated traffic classes:
- Profinet IRT (Isochronous Real-Time) at a 1 ms cycle for the four SINAMICS S210 drives, ensuring the deterministic synchronisation required by the technology objects.
- Profinet RT for distributed peripherals (ET 200SP) handling digital I/O, auxiliary encoders and the TP1500 Comfort Panel HMI.
Four servo-driven axes
The line integrates four Motion Control axes managed from the technology CPU:
- Axis 1 — Shear (slave in electronic cam): SINAMICS S210 servomotor synchronised with the virtual master through TO_SynchronousAxis and a cam profile generated in TIA Portal. During the cut phase the axis tracks the strip's linear speed with a following error below 0.1 mm.
- Axis 2 — Strip feed (virtual master axis): derived from the incremental measuring encoder mounted on the idler roller after the straightener. The signal is processed as a virtual master to which the shear axis and the length-measurement axis hook in via gearing.
- Axis 3 — Stacker X axis: S210 servomotor for longitudinal positioning of the stacking head, handled with TO_PositioningAxis using jerk-limited profiles to minimise mechanical oscillation.
- Axis 4 — Stacker Z axis: S210 servomotor with electromagnetic brake for vertical travel, coordinated with the X axis through point-to-point interpolation.
The critical block: the flying-shear electronic cam
The heart of the project is the electronic cam profile that synchronises the shear with the strip. The cam was designed as a displacement(master) function made of three sectors:
- Approach sector: acceleration of the shear from its waiting position up to strip speed, with a fifth-order polynomial profile that keeps acceleration continuous and differentiable.
- Synchronised cut sector: linear speed identical to the master axis (effective 1:1 gear ratio) over a configurable angular sector matching the programmed piece length, during which the cutting head executes the pneumatic cycle on the moving strip.
- Return sector: deceleration, disengagement from the master with MC_PhasingRelative, return to home position and re-engagement ready for the next shot.
The complete profile is stored as a TO_Cam technology object and re-tuned at runtime as a function of the piece length set in the recipe — no need to recompile the PLC program. The operator can vary the length from 250 mm up to 2,500 mm at the HMI and the system automatically recalculates the cam parameters.
Functional safety integrated into the drive
Machine safety is solved with the Safety Integrated functions embedded in the SINAMICS S210 drives: Safe Torque Off (STO), Safe Stop 1 (SS1) and Safe Operating Stop (SOS), certified to SIL 2 / PL d. Emergency stop and guard interlocks trigger SS1 on the four axes through the Profisafe bus, removing the need for external safety relays in series with the power side and reducing total stopping time. The risk assessment was documented per ISO 13849-1 and the critical loops were validated with Siemens Safety Evaluation Tool.
TIA Portal programming: project structure
The application was programmed in TIA Portal V18 with a modular architecture by subsystem. Each subsystem lives in its own program block with a clean interface of inputs, outputs and parameters, so the client's maintenance team can work on one part without risk of impacting the others. The structure was organised as:
- OB_MotionControl — motion organisation block executed every 1 ms, synchronised with the IRT cycle of the Profinet bus.
- FB_FlyingShear — flying-shear function block: cam management, MC_CamIn commands, following-error supervision and diagnostics.
- FB_StackerKinematics — stacker kinematics: point-to-point trajectory calculation, pile-recipe management, software-based collision supervision.
- FB_RecipeManager — recipe manager: piece length, thickness, pieces per stack, dynamic cam parameters, target cycle time.
- FB_LineSequence — line sequencer: global state, transitions, run/stop conditions, alarm management per ISA-18.2.
The project includes a diagnostic module embedded in the Comfort Panel HMI that shows in real time the following error of each axis, the active cam curve, absolute positions and the status of the safety functions. This lets the client's maintenance team diagnose issues without opening TIA Portal.
Commissioning and on-site validation
Commissioning ran in three phases with a documented methodology, after a workshop FAT where the virtual master axis was simulated with a pulse generator to validate cam behaviour without real material.
- Individual axis tuning: autotuning of each SINAMICS S210 from TIA Portal, adjustment of filters and friction compensation. Validation with step and ramp setpoints.
- Cam validation in dry run: execution of the cam profile without strip, verification of the shear's following error with the built-in Trace of the S7-1500T. Iteration on the approach-polynomial parameters.
- Real-material trials: three days of supervised production starting with longer piece lengths (less demanding) and progressively going down to the worst case (250 mm at maximum strip speed). Dimensional tolerance measured on each piece with a digital caliper, plus burr inspection.
- Signed SAT: Site Acceptance Test protocol with the client's production manager, including process capability (Cpk) measurement over 500 consecutive pieces.
Results and deliverables
- Significant throughput increase compared with the previous discontinuous-cut line, thanks to continuous strip operation and electronic-cam synchronisation.
- Dimensional tolerance within specification across the full programmable length range, with Cpk validated at SAT and shear following error below 0.1 mm under nominal conditions.
- Recipe changeover times under two minutes: electronic-cam adjustment is parametric, with no mechanical intervention and no PLC code modification.
- Full documentation handover: Eplan schematics, list of technology objects, operator and maintenance manuals, TIA Portal project backup and ISO 13849-1 safety-function documentation.
- Internally maintainable line: the client's team can adjust recipe parameters, read detailed diagnostics from the HMI and swap any servo drive leveraging SIMOTICS S-1FK2 auto-identification.
- Post-delivery support: annual contract with secure remote access and 24 h SLA, within our standard control system maintenance offering.
Why this project is a good representation of what we do
A Motion Control project is not won with the Siemens catalogue — it is won by understanding the process kinematics, choosing the right architecture (technology CPU vs SIMOTION, electronic cam vs application-level programming) and being able to tune the axes on-site until the part comes out within tolerance. That requires hands-on experience with TIA Portal technology objects, fluency with the Trace tool and SINAMICS filter tuning, and a method to deliver FAT, SAT and safety documentation as signed deliverables.
If you have a line that involves multi-axis synchronisation, flying shear, electronic cam or any scenario where the standard PLC cycle falls short, share the details with us. We will assess technical feasibility and project scope at no obligation, within our standard PLC programming and industrial automation offering.