In the joints of industrial robots such as machine tools, numerous servo motors are used to accurately control their operations. To detect the direction, angle and speed rotation of servo motors, optical encoders are widely used. Hamamatsu manufactures Si photodiodes, photo ICs, image sensors, LEDs, and so on that are suitable for optical encoders and also provides products that meet customer's needs.
■ Structure of servo motor
■ Configuration example
There are two types of optical rotary encoders. One is "transmission type" and the other one is "reflection type". In the transmission type, a code wheel engraved with fine slits is placed between a light emitter and a photosensor, and the rotation angle is detected from the on/off signal made by transmitting/blocking light. In the reflection type, the light emitter and the photosensor are placed on the same side as the code wheel and the rotation angle is detected from the reflection/non-reflection of light.
To ensure a highly accurate encoder, the light emitter is required performance to emit light uniformly. Also, the photosensor needs a high-speed response, as well as a chip arrangement that supports complicated slit patterns.
Hamamatsu can provide light emitters and photosensors for both types of encoders (transmission type / refrection type).
Using on Hamamatsu unique semiconductor process technology, we manufacturer high-sensitivity, low-noise, highly-reliability photodiodes that are suitable for encoders. Further, we have 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 near 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.
we can suggest a variety of package/mounting solutions such as the combined mounting of the LED and photodiode, and the miniaturization of photodiode packages.
■ COB package
■ Chip carrier package
Hamamatsu offers customized photo ICs according to the customers' encoder specifications. Below are our track record and examples of customizations of photo ICs for reflective encoders.
This is an example of Hamamatsu photo ICs integrating a photodiode and peripheral circuit that were discretely discretely configured by a customer.
■ Block diagram
■ Product image
■ Image of LED mounting (cross section)
Noise reduction has been achieved through circuit configuration that measures against I/F noise and thermal noise.
Through-holes can be formed on Si photodiode chips by applying MEMS technology. This allows to mount a point source LED (current confinement type LED) used in reflective encoders inside a hole of a Si photodiode chip. Further, it is possible to align the height of the LED emitter surface and photosensitive area surface of the Si photodiode by adjusting the thickness of Si photodiode chip.
■ Through-hole example
■ Example of an LED mounted inside a through-hole of a Si photodiode
The reflectance of metal wiring and parts other than the photosensitive area can be reduced by applying light-shielding film on the surface of the Si photodiode through special processing. As a result, the S/N ratio can be improved.
■ 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 encoders. Number of pixels from 64 ch to 4096 ch are available.
Pixel size, number of pixels, and package types are all customizable. If you have any requests, please contact our sales.
Hamamatsu has unique semiconductor process technology and manufactures high-light output and high-reliability LED suitable for light emitters of encoders.
Hamamatsu produces and provides various types of LEDs for a wide variety of applications including automotive, industrial, and consumer. For optical encoders, we provide collimated LEDs that can irradiate low-focus/dispersion, uniform collimated light suitable for constructing high accuracy encoders.
Higher reliability than previous LEDs was achieved by improving the crystal structure of the point source LED chip. Further, it is 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 point source LED chip design (unit: μm)
■ Example of a point source LED
■ Effect of stray light countermeasures due to side light shading
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