[2] An optical sensoris a device that detects and converts light intensity into electric signals, operating not only via visible light but also invisible light (e.g., near-infrared rays, which can't be perceived by human eyes). They're used factory automation, security systems, automatic doors, and screen brightness adjustment in smartphones.
Meaning of the name "Optical" refers to relate to sight, light, or study of optics. So an optical sensor's name refers to its ability to use light to detect something's presence/physical changes.
[2] They primarily consist of a light emitter and light receiver.
Light from the emitter hits an object and the light receiver detects the reflected/transmitted light's intensity to detect the object’s presence. This used to confirm if a product is on a factory production line, measure the number of motor rotations, measure dimensions, and more. They perform high-precision detection in place of human eyes to contribute to quality confirmation and industrial machinery automation.
[2] Non-contact measurement: Optical sensors detect objects without physical contact. This enables measurement without damaging objects, thus being suited for delicate materials and surfaces as well as in environments for hygiene management. They are also effective at detecting moving objects and in challenging environments like high temperatures/pressure. Compared to contact sensors, they undergo less friction and deterioration and have the advantage of longer service lives. They are often used in fields needing clean environments like food industries, pharmaceuticals, and semiconductor manufacturing.
Fast response: Since they operate at the speed of light, optical sensors can respond at extremely fast speeds, on the level of microseconds. This makes them well-suited for use on high-speed production lines and quality control systems. For example, they can detect small flying particles or accurately position fast-moving products. They are also suitable for real-time feedback control and high-speed counting. This high speed is also leveraged to control industrial robots and detect paper jams in high-speed printers.
Wide detection range: Optical sensors make use of the rectilinear propagation of light to detect objects across a wide range, from short to long distances. The use of lenses and mirrors makes it possible to widen detection ranges even further or focus them on smaller areas. This characteristic allows optical sensors to perform a variety of tasks, from detecting small parts to measuring the position of large objects. And because a single sensor can cover a wide area, the number of sensors can be reduced to contribute to cost savings. They are used in various fields such as entry detection systems for buildings and object detection in large warehouses.
Various detectable properties: Optical sensors can detect not only the presence of an object but various properties such as its color, transparency, reflectivity, and shape. This versatility makes them suitable for complex tasks such as product quality control, categorization, and identification. For example, the food industry uses them to detect foreign objects and the automotive industry uses them to check quality of paint jobs, etc. They are also used to optically read information such as barcodes and QR codes. Moreover, by selecting light wavelengths, optical sensors can utilize not only visible light but also infrared and ultraviolet light for detection.
Sensitive to environmental factors: Optical sensors are easily affected by environmental factors such as surrounding light conditions, dust, moisture, and vibration. Appropriate positioning and protection are necessary. Especially in places where lighting conditions can change such as outdoors or in factories, measures to prevent detection errors are important. Filters and careful sensor positioning can reduce the effects of these factors. Measures such as improving the sensor’s dust and water resistance and adding temperature compensation can also help. In addition, regular maintenance and calibration are important for maintaining stable performance.
The main optical sensor types are photodiodes, phototransistors, and photoelectric sensors.
Light-to-Electricity Converters
Photodiodes: Change light into an electric current. They react very fast and are used in remote controls and light meters.
Phototransistors: Act like photodiodes but include built-in signal amplification for stronger electrical outputs.
Photoconductive cells (Photoresistors): Change their internal resistance when light hits their surface, often used in automatic night lights.
Industrial detection systems
A through-beam sensor uses a separate emitter and receiver facing each other to detect objects when the light beam breaks.
A retro-reflective sensors bounces a light beam off a reflector and spot items when that reflection is interrupted.
A diffuse-reflective sensor projects light that bounces directly off the target object back to the sensor.
[1] Wikipedia
[3] Dexerials