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 rotary encoders are widely used. Hamamatsu manufacturers Si photodiodes, photo ICs, LEDs, and so on that are suitable for such encoders and also provides customization of these devices.
Rotary encoders can be classified into two types: magnetic/electric induction type and optical type. The optical type detects rotation angles by detecting the on/off signals of light. This is achieved by placing a code wheel with fine pitch slits between a light emitter (e.g., LED) and photosensor (e.g., photodiode) and blocking and transmitting light.
High accuracy detection requires several features. For the photosensor Si diode, which makes up the encoder, photo detecting chip arrangement that supports complicated slip patterns and high-speed response are required. For the light emitting LED, uniform irradiation is required. Hamamatsu provides light emitters and photo sensors for both transmissive and reflective encoders.
Through-holes can be formed on Si photodiode chips by applying MEMS technology. This allows a 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.
Example in which an LED is mounted inside a through-hole of a Si photodiode
It is possible to mount a Hamamatsu fiber optic plate (FOP) to the photosensitive area of a Si photodiode. Combining an FOP and Si photodiode allows the lens to focus at a position that is higher by the amount of the FOP thickness than the normal photosensitive surface. This makes it easier to mount a slip plate or other components closer to the photosensitive surface. Moreover, the photosensitivity directivity can be adjusted by using an FOP with a low NA.
Example of a Si photodiode with an FOP
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 a Si photodiode with a light-shielding film
Higher reliability than those of previous confinement type LEDs was achieved by refining the crystal structure of the confinement type LED chip. Further, it possible to design light emission diameters that meet customer needs. (Hamamatsu LEDs are normally provided as package products. Bear chip products are provided separately. If you require them, contact us.)
Example of a confinement type LED chip design (unit: μm)
Example of a confinement type LED
Operating temperature: -30 to +105 ℃
Storage temperature: -40 to +105 ℃
Packing method: 100 pcs/bag
Operating temperature: -30 to +85 ℃
Storage temperature: -40 to +100 ℃
Packing method: 2000 pcs/reel
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