Photo-Fork Sensor (Slot Sensor)
A U-shaped optical sensor with emitter and receiver built into opposite tines — detects objects passing through the gap.
Use this when…
- Detecting individual sheets, labels, or thin film in a gap
- Counting encoder disc slots for position feedback
- Detecting the presence of a circuit board or thin part
Label applicator
Photo-forks detect label gaps on a backing liner, timing the applicator head to peel and place each label precisely.
PCB handling
Slot sensors detect the leading edge of circuit boards entering a solder wave machine, starting the conveyor-speed synchronisation.
A photo-fork sensor — also called a slot sensor or fork sensor — is a self-contained through-beam sensor shaped like the letter U. The emitter sits in one tine and the receiver sits in the opposite tine, with a precisely defined gap between them. Any object passing through the slot interrupts the beam, switching the output.
Because the emitter and receiver are mechanically fixed relative to each other, there is no alignment step during installation. This makes photo-forks extremely repeatable and reliable in high-speed applications where positional accuracy matters.
The slot width is fixed at manufacture — typically 3 mm to 30 mm depending on the model. Choosing the right slot width is critical: too wide and thin objects may pass without reliable detection; too narrow and thicker parts will jam.
Photo-forks are the sensor of choice for label-gap detection on liner-less and liner-backed webs, for encoder disc reading (the slots or slots-and-teeth trigger the sensor to produce a pulse train), and for edge detection on thin films.
Electrically they follow the same NPN/PNP, NO/NC conventions as other discrete sensors. Most photo-forks output a clean square wave at high speed — models rated for 50 kHz switching are common for encoder applications.
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