encoder encoder

Encoder

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.

What are optical encoders?

There are two types of optical rotary encoders, “transmissive type” and “reflective type”. In the transmissive type, a chord wheel engraved with fine slits is fitted between a light emitter and a photosensor. It detects 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 chord wheel. It detects rotation angle from the reflection/non-reflection of light.

In order to structure a high accuracy encoder, the light emitter must have the ability to emit light uniformly. For the photosensor, photo detecting chip arrangement that supports complicated slit patterns and high-speed response are required.

Hamamatsu can provide light emitters and photosensors for both transmissive type and reflective type encoders.

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Photodiodes for encoders

 

Features of Hamamatsu photodiodes for encoders

1. Unique semiconductor process

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.

2. Optimum sensitive design

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.

3. Extensive package/mounting technology

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.

Package lineup

■ COB package

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

■ Chip carrier package

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

Photo IC for encoder

 

Customization

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.
 

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

 

Example 1: Example photo IC in which the photodiode and LED are integrated (monolithic structure)

This is an example of Hamamatsu converting to photo IC a photodiode and peripheral circuit discretely configured by a customer.

■ Block diagram

■ Product image

■ Image of LED mounting (cross section)

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

We realized noise reduction with a circuit structure that considers 1/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 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

FOP mounting

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. (Patent: JP 6383460 B)

■ FOP example

■ FOP directivity

■ Example of Si photodiode with FOP

Low-reflectance light-shielding film

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

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 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.

  • 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 unique semiconductor process using on Hamamatsu unique semiconductor process technology, Hamamatsu manufacturers output, highly reliable LED that are suitable for light emitters for encoders.

2. Various product formats

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.

Improvement of liability by refining the crystal structure: current confinement type LEDs (point source LEDs)

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

Product examples:

Package lineup

■ High reliability, high collimation CAN package

  • Operating temperature: -30 to +105 ℃
  • Storage temperature: -40 to +105 ℃
  • Packing method: 100 pcs/bag

■ Compact, narrow directivity COB package

  • Operating temperature: -30 to +85 ℃
  • Storage temperature: -40 to +100 ℃
  • Packing method: 2000 pcs/reel

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