In the joints of machine tools and industrial robots, numerous motors are used to accurately control their operations. To accurately detect the rotation angle of those motors, optical encoders are widely used. Hamamatsu manufacturers Si photodiodes, photo ICs, image sensors, LEDs, and so on that are suitable for optical encoders and also provides customization of these devices.
There are two types of optical rotary encoders: transmissive type and reflective type. In the transmissive type, a code wheel engraved with fine slits is fitted between a light emitter and a photosensor. This type of encoder detects the rotation angle from the on/off signal made by transmitting/blocking light. In the reflective type, the light emitter and the photosensor are placed on the same plane as the code wheel. This type detects the rotation angle from the reflection/non-reflection of light.
To ensure a highly accurate encoder, the light emitter must have the ability to emit light uniformly. Also, the photosensor must have a high-speed response, as well as a chip arrangement that supports complicated slit patterns.
Hamamatsu can provide light emitters and photosensors for both transmissive type and reflective type encoders.
Using on Hamamatsu unique semiconductor process technology, Hamamatsu manufacturers high-sensitivity, low-noise, highly reliable photodiodes that are suitable for photosensors for encoders. Further, Hamamatsu has a proven track record of manufacturing numerous industrial photodiodes.
Hamamatsu can manufacture photodiodes with high sensitivity for the wavelength of the light source to be used, from visible light to infrared light.
A higher S/N can be expected by optimizing the sensitivity for the LED used in the optical encoder.
Hamamatsu supplies various package products for many applications including automotive, industrial, and consumer.
Hamamatsu can suggest a wide variety of package/mounting solutions such as the combined mounting of the LED (used in the optical encoder) and photodiode and the miniaturization of photodiode packages.
■ COB package
■ Chip carrier package
Hamamatsu offers customization of photo ICs according to the specifications of the encoder the customer will structure. Below are examples of Hamamatsu’s initiatives and customizations of photo ICs for reflective encoders.
This is an example of Hamamatsu converting to photo IC a photodiode and peripheral circuit discretely configured by a customer.
■ Block diagram
Example block diagram of a customized photo IC that combines a photodiode, LED, and peripheral circuits.
■ Product image
External appearance of a customized photo IC that combines a photodiode, LED and peripheral circuits.
■ Image of LED mounting (cross section)
We realized noise reduction with a circuit structure that considers 1/f noise and thermal noise.
Through-holes can be formed on Si photodiode chips by applying MEMS technology. This allows a current confinement type LED used in reflective encoders and the like to be mounted inside a hole of a Si photodiode chip. Further, the thickness of Si photodiode chip can be adjusted to align the height of the LED emitter to that of the photosensitive area of the Si photodiode.
■ Through-hole example
■ Example in which an LED is mounted inside a through-hole of a Si photodiode
The reflectance of metal wiring and components other than the photosensitive area can be reduced by applying light-shielding film to the surface of the Si photodiode through special processing. Improvement to the S/N ratio can be expected.
■ Reflectance vs. wavelength (reference value)
The reflectance of near infrared light often used in optical encoders is reduced significantly.
■ Example of Si photodiode with light-shielding film
CMOS linear image sensors with rectangular pixels, high line rate, and a global shutter function are appropriate for absolute track reading of linear encoders.
Hamamatsu offers image sensors with various numbers of pixels and pixel sizes, according to the resolution and response speed needed for each encoder. Supports number of pixels from 64 ch to 4096 ch.
Pixel size, number of pixels, and package are all customizable. If you have any requests, please contact our sales.
Hamamatsu unique semiconductor process using on Hamamatsu unique semiconductor process technology, Hamamatsu manufacturers output, highly reliable LED that are suitable for light emitters for encoders.
Hamamatsu produces and provides various types of LEDs for a wide variety of applications including automotive, industrial, and consumer. For optical encoders, Hamamatsu provides collimated LEDs that can irradiate low-focus/dispersion, uniform collimated light suitable for constructing high accuracy encoders.
Higher reliability than those of previous current confinement type LEDs was achieved by refining the crystal structure of the current confinement type LED chip. Further, it possible to design light emission diameters that meet customer needs.
* Hamamatsu LEDs are normally provided as package products. If you wish to request a bare chip product, please contact our sales.
■ Example of a current confinement type LED chip design (unit: μm)
■ Example of a current confinement type LED
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