This section provides overview, applications, and principles of photointerrupters. Also, please take a look at the list of 7 photointerrupter manufacturers and their company rankings.
A photointerrupter is an optical sensor that detects the passage or remaining amount of an object by blocking the light in the optical system.
Since it can detect the object to be detected in a non-contact manner, there is no wear and tear on the sensor due to physical contact such as friction, and it can be used for a long period of time at low cost.
A photointerrupter consists of a combination of a light emitter and a light receiver, and different optical systems are assembled depending on how each is arranged. These different optical systems determine the type of object that is suitable for detection.
The simplest use of photointerrupters is to detect the passage of an object. For example, they are used to detect the passage of coins and bills in ATMs and vending machines.
In automatic ticket gates, photo interrupters are used to detect the passage of a person, and the opening and closing of the gate are triggered by the touch of an IC card or the insertion of a ticket.
Other applications include detection of ink cartridges in printers and other devices and the detection of paper in multifunction machines and copiers.
Photointerrupters consists of a light emitter that emits detection light and a photodetector that receives the light. Infrared LEDs are often used as the light emitter, and for certain applications, ultraviolet LEDs are sometimes used. Photodiodes are also used as light receivers, converting the detected photons into electric current.
The principle of how photointerrupters detect objects is quite simple. Light emitted from the light emitter is monitored by the photodetector, and if there is a detected object in the light path, the light is intercepted, and the current from the phototransistor in the photodetector is reduced. This allows the detection of the passage of an object or the amount of remaining light.
Photointerrupters are available in various configurations, depending on the arrangement of the light emitter and photodetector. Those with light emitters and photoreceivers arranged to face each other are called transmissive photointerrupters, those that are connected and fixed at intervals are called integrated photointerrupters, and those that are not connected and the intervals can be freely changed are called separated photointerrupters.
The integrated type does not require any adjustment, such as optical-axis alignment, but has the characteristic of limiting the size of the detected object because the distance between the light emitter and receiver is fixed. On the other hand, the separated type allows the light emitter and receiver to be freely positioned, so there is little restriction on the size of the object, but strict optical-axis adjustment is required.
There are two main types of photointerrupters: the first is the "transmission type," in which the light emitter and receiver are placed directly opposite each other at a fixed distance, and the presence or absence and position of an object between the light emitter and receiver are detected. The other is a "reflective" photointerrupters, in which the light emitted from the light emitter is reflected by an object, and the reflected light is detected by the photodetector.
Since objects are detected when light is intercepted, stable detection of opaque objects is possible and highly reliable.
Detection of objects is performed by the reflection of light, so objects can be detected even if the detected object is far away from the light emitter and receiver.
When using transmission-type photo interrupters, care must be taken in cases where objects with high transmittance or objects that are smaller than the shape and dimensions of the light emitting and receiving surfaces are to be detected. When detecting these objects, even if the LED light is blocked by the object, it is not possible to block all light, and some light will be transmitted. If the light is transmitted, the light will be caught by the photodetector, and the object detection results will be affected.
When using reflective photointerrupters, the following two points should be considered:
Reflective photointerrupters are installed facing the outside world so that the photodetector can easily detect light, making it very susceptible to the effects of ambient light. If the disturbance light enters the photoreceptor, the detection result will be affected. Therefore, it is necessary to make the utmost effort to prevent the light from entering the detector.
Reflective photointerrupters may catch light not only from the detected object but also from background objects. Therefore, it is necessary to avoid placing objects in the background of the detected object as much as possible or to make the surrounding area dark.
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