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Optical encoder — from a slit disk to a digital count

光学式エンコーダ — スリット円盤がデジタルの数値になるまで

An optical encoder measures rotation angle as a digital number. It has three parts: a slit disk (a disk with many small openings called slits), a light source (an LED), and a photodetector (a part that senses light).

Turn the disk below. When a slit passes the reading station, light passes through and reaches the detector, so the output is ON. When the solid part blocks the light, the output is OFF. This on–off signal is a series of pulses. By counting pulses, we measure the angle.

Try this ▸ Press Play, or drag the disk with the mouse to turn it by hand. Watch one slit reach the LED: the beam turns bright, the detector lights up, the output jumps to 1, and the counter adds one.

▶ を押すか、円盤をドラッグして手で回してください。 スリット数 N を変えると分解能が変わります。
55°/s
16

Slit disk & reading station

LED → slit → photodetector / スリット円盤・透過光・受光器

Photodetector output & counter

Square-wave pulses, counted in real time / 受光器の出力信号とカウンタ

0 pulses counted
パルス計数 (since reset)
Pulses / revolution 1回転あたり
16
Resolution 分解能
22.5°
Measured rotation 計測回転量
0°
Output now 現在の出力
0

Notice ▸ The pulse train looks the same for CW and CCW, so a single detector cannot tell the direction of rotation. The two-phase encoder (next slide) adds a second detector to solve this.