Encoder

What are optical rotary encoders?
Photodiodes for encoders
Photo ICs for encoders
Example of special processing applied to Si photodiodes and photo ICs (customization)
Applying image sensors to linear encoders
LEDs for encoders

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

What are optical rotary encoders?

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).

Photodiodes for encoders

Features of Hamamatsu photodiodes for encoders

1. Unique semiconductor process

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.

2. Optimum sensitive design for users' applications

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.

3. Extensive package/mounting technology

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.

Package lineup

■ COB package

Operating temperature: -40 to +100 ℃
Storage temperature: -40 to +100 ℃
Packing method: 1000 pcs/reel

Package example: S13773

■ Chip carrier package

Operating temperature: -40 to +100 ℃
Storage temperature: -40 to +100 ℃
Packing method: 100 pcs/tray or 1000 pcs/tray

Package example: S14833

Photo ICs for encoders

Customization

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.

Monolithic structure of photodiode and peripheral circuit　⇒　Contributes to reduce the number of parts and mounting space on the customer's side
Multifunctionalization using I2C　⇒　Enables multifunctionalization such as electron volume
Built-in LED and LED driver　⇒　Enables light receiving and emitting photo ICs with LEDs placed in the center of the chip
Variation correction for variations in reference values (current, voltage) by trimming

Example 1: Example of photo ICs intergating the photodiode and LED (monolithic structure)

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

External appearance of a customized photo IC that combines a photodiode, LED and peripheral circuits.

■ Image of LED mounting (cross section)

Image of LED mounting (cross section).

Example 2: Example of instrumentation amplifier (1/f noise, thermal noise considered)

Noise reduction has been achieved through circuit configuration that measures against I/F noise and thermal noise.

Example of special processing applied to Si photodiodes and photo ICs (customization)

Through-hole formation (MEMS processing)

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

Low-reflectance light-shielding film

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

Applying image sensors to linear encoders

CMOS linear image sensors with rectangular pixels, high line rate, and a global shutter function are appropriate for absolute track reading of linear encoders.

Various product formats

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.

Example: CMOS linear image sensor S15611

Rectangular pixel (7 × 200 µm)
Line rate
1024 ch all-pixel readout: 34 kHz
260 ch partial readout: 100 kHz
Global shutter
12-bit digital output

LEDs for encoders

Features of Hamamatsu LEDs for encoders

1. Unique semiconductor process

Hamamatsu has unique semiconductor process technology and manufactures high-light output and high-reliability LED suitable for light emitters of encoders.

2. Various product lineup

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.

Improvement of reliability by improving the crystal structure: Point source LEDs (Current confinement type LEDs)

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)