Introduction: Automatic height sensing lets the film carriage follow the real top of each load instead of a fixed setting, and this guide follows the signal from sensor to carriage.
On a semi-automatic pallet stretch wrapping machine, automatic height sensing is one of the most misunderstood features. New operators often assume that "automatic" means the machine handles everything. In practice it automates one decision — how high the load reaches — while a person still places the pallet, attaches the film, presses start, and cuts the film at the end. The chain that makes it work is short and logical: a photoelectric sensor reads the top edge, the PLC interprets that reading, and the film carriage lift responds. Following that chain is the fastest way to understand both what the feature does and where the semi-automatic cycle still begins and ends with an operator.
How a Photoelectric Sensor Reads Pallet Load Height
Height detection on a turntable pallet stretch wrapper starts with a photoelectric sensor mounted on the mast. The sensor projects a light beam across the space the load will occupy. A tall stack blocks that beam; a short stack lets it pass over the goods and reach the receiver on the far side. As the film carriage travels upward during the wrap, the sensor keeps watching the beam, and the exact moment the beam changes state marks the top edge of the load. That change is the height reading. There is no tape measure, no operator counting cartons, and no limit switch pinned to a single fixed height that only suits one product. The value of that reading shows up whenever pallet heights vary during a shift. A warehouse might wrap a low pallet of dense parts in the morning and a chest-high pallet of light cartons in the afternoon. With a fixed setting, the machine would either wrap above the load and spend film on empty air, or stop short of the top and leave the upper layers loose — the part of a pallet load that most often shifts in transit. Mast height sets the working range rather than the reading itself. The TP-X165 arrives with a 2,400mm mast as standard, and can be built with a 2,800mm or 3,000mm mast for taller stacks. Within that range, the sensor reads the top edge in front of it whether the load is cartons, drums, bags, or a mixed stack, as long as the beam path stays physically clear.
How the PLC Turns Height Data Into Film Carriage Movement
A height reading on its own moves nothing. The PLC is the part that decides what the reading means for the rest of the cycle. On the TP-X165, the PLC sits in the control cabinet with an integrated display on the mast, and it runs the wrapping sequence from start to finish. The sensor contributes one input signal. The PLC holds the rest: the wrap pattern, the rotation speed, the film carriage travel, and the point at which the cycle ends. It also remembers the operator's settings, including independent counts for top and bottom reinforcement wraps, which is why a load can be wrapped heavily at the base and the top while the middle layers stay lighter. The action chain runs in a fixed order. The sensor detects the top edge; the PLC records that position and uses it as the turning point for the carriage; the carriage lift motor, driven by a variable frequency drive, decelerates, stops, and reverses; the turntable rotates at whatever speed the operator has set between 0 and 12 rpm; the PLC counts layers at the bottom and the top according to its two separate settings; and once the last layer is complete, the turntable returns to its loading position automatically. The variable frequency drive matters here for a practical reason. Ramping the carriage and turntable up and down smoothly instead of starting them abruptly keeps tall or top-heavy loads from lurching, which is exactly the kind of movement that loosens a stack before the film has a chance to hold it.
Why Automatic Height Sensing Does Not Make the Machine Fully Automatic
Anyone comparing pallet wrapper suppliers or stretch wrap machine manufacturers will notice that "automatic height sensing" and "semi-automatic operation" often appear in the same specification line. That pairing confuses people, because "automatic" sounds absolute. It is not. On this class of machine, the word describes one controlled action inside a cycle that a person starts and finishes. The sensor and PLC remove a manual judgement — how far up to wrap — but they do not load the pallet, do not attach the film to the load, do not cut the film when the wrap is done, and do not move the finished pallet away. A fully automatic line would need motorised infeed and outfeed conveyors, an automatic film attach and cut device, and a control system coordinating with whatever equipment sits upstream and downstream. That is a different machine class, and the TM-X165 is not it.
1. Which Operator Actions Still Start and Finish a Semi-Automatic Cycle
Every semi-automatic wrapping cycle is bookended by hand work. The operator places the pallet on the turntable — either lifted by forklift or pushed up a drive-up ramp with a pallet jack — then pulls the film from the carriage, attaches it to the load or the turntable, and steps back to press start. From that point the turntable rotates, the carriage travels, the sensor reads the load height, and the wrap layers build according to the settings. When the cycle finishes, the operator walks back in, cuts the film, presses the loose tail against the load, and removes the wrapped pallet. The machine's contribution is rotation, carriage travel, height detection, wrap counting, and reset; the operator's contribution is loading, film attachment, film cutting, and unloading.
2. How One-Button Start and Auto Reset Fit Into the Same Cycle
One-button start and automatic turntable reset are conveniences that shorten the hand work, not features that remove it. One-button start means the operator does not have to sequence the turntable, carriage, and wrap counts by hand, which reduces fumbling at the panel and makes the cycle repeatable from one pallet to the next. Auto reset returns the turntable to a defined loading position so the finished pallet always ends up where the next one begins, which keeps loading quick and predictable. Both features sit inside a cycle that a person still opens and closes, and both assume somebody is standing nearby — either watching the wrap or waiting to cut the film.
Conclusion
Automatic height sensing is best understood as a single link in a chain that runs from a photoelectric sensor, through PLC logic, to a variable frequency drive that moves the film carriage. The sensor finds the top edge of the load, the PLC turns that reading into carriage movement and wrap counts, and the machine returns the turntable to its start position when the cycle ends. What stays with the operator is the loading, the film attachment, and the film cutting. That combination is what makes the machine semi-automatic: it removes the guesswork about load height while leaving the decisions that need hands. Readers who want to see how PLC control, automatic height sensing, one-button start, and auto reset are documented together can review the TP-X165 specification listing as a concrete reference point.
FAQ
Q：How does automatic height sensing work on a pallet stretch wrapper?
A：A photoelectric sensor on the mast projects a beam across the load area, and the point where that beam changes state as the film carriage rises marks the top edge of the pallet load. The sensor sends that signal to the PLC, which uses it to set the turning point for the carriage. The result is that the wrap follows the actual load height rather than a height an operator had to enter or measure by hand.
Q：Is a pallet wrapper with automatic height sensing a fully automatic machine?
A：No. Automatic height sensing automates one part of the cycle — finding the top of the load. On a semi-automatic machine, the operator still places the pallet on the turntable, attaches the film before the cycle starts, presses the start button, and cuts and presses down the film when the wrap is complete. Full automation would add powered conveyors, automatic film attach and cut, and unattended pallet transfer.
Q：What does the PLC control in a semi-automatic pallet wrapping cycle?
A：The PLC runs the sequence. It accepts the sensor signal, commands the variable frequency drives that rotate the turntable and raise the film carriage, applies the independent top and bottom wrap counts set on the display, ends the cycle at the right point, and triggers the automatic turntable reset that returns the machine to its loading position. The embedded display keeps those settings and cycle status in one place.
Sources / References
MHI - The Industry That Makes Supply Chains Work
MHI - The Industry That Makes Supply Chains Work
Related Examples
Pallet stretch wrapping machine with pre-stretch function TP-X165
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