A fork sensor (also known as a slot sensor) is a photoelectric sensor designed in a U-shaped or fork-shaped housing, where the emitter and receiver are built into opposite arms of the fork. It’s used to detect the presence, position, or movement of small objects that pass through the slot. Because the emitter and receiver are factory-aligned in a single compact body, fork sensors offer high precision, easy installation, and reliable operation without the need for external alignment.
The working principle of a fork sensor is based on the through-beam photoelectric detection method. The emitter (usually an infrared or visible LED) sends a continuous light beam to the receiver (a phototransistor or photodiode). When an object — such as a label, paper edge, wire, or packaging material — passes through the fork gap, it interrupts the light beam. This interruption causes a change in the sensor’s output signal, which can then be processed by a PLC or controller to perform an action like counting, cutting, or positioning.
Fork sensors are widely used in label detection, packaging machines, printing, textile, and electronics assembly lines, where high-speed and accurate detection of small parts or materials is essential. They come in various slot widths (typically from 2 mm to 220 mm) and can detect transparent, reflective, or opaque objects depending on the light type and sensitivity settings.
In simple terms, a fork sensor works like a light gate — when something passes through the “U” and blocks the beam, the sensor immediately detects it. It’s a compact, plug-and-play sensor that provides fast, reliable, and maintenance-free detection, making it one of the most commonly used optical sensors in modern automation systems.