Release Date:2026.09.18 Page views:0

How does a photoelectric encoder "see" motion? Breaking down the core principles in one ar

Imagine: a humanoid robot's fingers nimbly grasp an egg, a high-end CNC machine tool cuts metal with micron-level precision, and a printer precisely feeds hundreds of sheets of paper per second — behind these seamless movements, there is an invisible "referee" issuing commands in real time.

This "referee" is the optical encoder.

It is known as the "heart" and "sensory nerve" of motion control. Without it, robots would lose balance, motor rotation would lose step, and precision equipment would become scrap metal.

So how exactly does an optical encoder "see" motion? Today, we use one article to thoroughly break down its core principles.

How does a photoelectric encoder "see" motion? Breaking down the core principles in one article

1. What Is an Encoder? Why Is It So Important?

Simply put, an encoder is a sensor that converts mechanical motion (angle, position, speed) into electrical signals.

You can think of it as the "eyes" and "odometer" of mechanical equipment — it constantly watches where a mechanical part is turning and how fast, then reports in real time to the controller via electronic signals, and the controller adjusts commands accordingly, forming closed-loop control.

Without encoder feedback, servo motors would just "spin blindly"; with precise encoder feedback, there is precise motion control for industrial automation, robotics, and new energy vehicles.

According to operating principles, encoders are mainly divided into three categories: optical, magnetic, and capacitive/inductive. Among them, optical encoders, with advantages such as high precision, strong anti-interference ability, and fast response speed, occupy about 50% of the market share and are the absolute mainstream in mid-to-high-end applications.

2. Four-Step Breakdown: The Complete Chain of How an Optical Encoder "Sees" Motion

The operating principle of an optical encoder can be summarized in four key steps: emit light → modulate light → sense light → solve/compute. Let's look at them step by step.

Step 1: Light Emission — The light source emits a stable beam

Everything starts with light.

The light source of an optical encoder is usually an LED (light-emitting diode) or a laser (VCSEL). It needs to continuously emit a stable, uniform beam that shines onto the code wheel behind it.

There is a technical detail here: the stability of light directly affects measurement accuracy. Ordinary designs use external resistors to control LED current, while high-end solutions such as Kewei's use a built-in self-developed constant-current IC to control LED current, ensuring better light emission consistency and longer lifespan. This is especially critical in high-speed or high-temperature scenarios.

Step 2: Light Modulation — The code wheel modulates light into a "light-and-dark code"

The light emitted by the light source meets the most core precision component of the encoder — the code wheel (grating disk).

The code wheel is a disk engraved with extremely fine, uniform alternating light-transmitting and opaque stripes. When the code wheel rotates with the mechanical shaft, each stripe is like a small window that continuously opens and closes: the light-transmitting area lets light pass, and the opaque area blocks it.

Thus, the originally constant light beam, after passing through the rotating code wheel, is modulated into alternating light-and-dark "optical pulse signals."

There is a key parameter here: resolution (LPI, Lines Per Inch), which is the number of stripes engraved per inch. The higher the resolution, the finer the stripes, the smaller the minimum angle the code wheel can divide, and the higher the measurement accuracy.

Kewei's products support up to 600LPI resolution, while mainstream competing products on the market are usually 360LPI. This means that at the same code wheel size, Kewei encoders can achieve higher-precision position detection.

Step 3: Light Sensing — The photodetector converts optical signals into electrical signals

The light-and-dark optical pulses modulated by the code wheel then shine onto a photodetector (PDIC, Photo Diode Integrated Circuit).

The photodetector is an array of precision photosensitive elements that can convert changes in optical signal intensity into changes in electrical signal intensity — when there is light, current is generated (high level); when there is no light, current weakens (low level). In this way, continuous rotational mechanical motion is converted into strings of electrical pulse signals.

The design quality of the photodetector directly affects the stability of the final output waveform. For example, Kewei uses a 7-8 group PD array design, which, compared with the common 4-group PD design of competitors, can achieve higher resolution and more stable waveform output.

Step 4: Computation — The signal processing circuit "translates" motion information

The last step, and the most critical one: the signal processing circuit interprets and calculates the electrical pulses.

By calculating the number of pulses received per unit time, the rotational speed can be obtained; by accumulating the total number of pulses, the rotation angle or linear displacement can be obtained; by determining the phase sequence of the A and B signals (90 degrees apart), the rotation direction can also be accurately determined.

In addition, encoders are also divided into two main types:

Incremental encoder: measures relative position changes, data resets to zero after power-off, suitable for measuring speed and direction.
Absolute encoder: measures absolute position, can still remember the position value after power-off, suitable for scenarios requiring precise positioning.

3. Technology Evolution: From "Independent Component" to "Integrated Sensing, Driving, Control, and Computing"

Traditional encoders are just a "sensor," responsible for collecting data and reporting it. But modern motion control systems have increasingly high requirements — they not only need to "perceive," but also to "think" and "decide."

This is the origin of integrated intelligent encoders.

Industry leaders such as Kewei are upgrading encoders from a single sensing unit to an intelligent system integrating sensing units, communication modules, drive control, microprocessors, and algorithm software. This "sensing, driving, control, and computing" integrated solution gives encoders intelligent closed-loop capabilities such as real-time data acquisition, analysis and adaptive control, and fault warning, and is especially suitable for cutting-edge application scenarios such as humanoid robots, collaborative robots, and integrated joint motors.

4. Back to the Starting Point: Why Do We Need Domestic Optical Encoders?

Back to the original question: How does an optical encoder "see" motion?

The light-emitting element emits a beam → the code wheel modulates it into light-and-dark optical signals → the photodetector converts optical signals into electrical pulses → the signal processing circuit computes speed, position, and direction — these four steps constitute the complete chain of how an optical encoder perceives motion.

The principle may not sound complicated, but to perfect every step — the light source must be stable, the code wheel precise, the detector sensitive, and the algorithm accurate — and to maintain long-term reliability in industrial environments with high vibration, high temperature, and high electromagnetic interference, tests full-chain technical capabilities from chip design and optical design to packaging, testing, and algorithm software.

For this reason, the high-end optical encoder market has long been monopolized by Japanese and German brands. The efforts of Chinese companies such as Kewei are precisely aimed at breaking this pattern — using independently developed technology to let China-made motion control systems truly have their own "eyes."

In the following articles, we will further interpret: when the era of humanoid robots arrives, how big will the market be for these "eyes"? Can the technical strength of Chinese companies compete with international giants? Stay tuned.

Source: Kewei Semiconductor (Zhuhai) Co., Ltd.

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How does a photoelectric encoder "see" motion? Breaking down the core principles in one ar

1. What Is an Encoder? Why Is It So Important?

2. Four-Step Breakdown: The Complete Chain of How an Optical Encoder "Sees" Motion

3. Technology Evolution: From "Independent Component" to "Integrated Sensing, Driving, Control, and Computing"

4. Back to the Starting Point: Why Do We Need Domestic Optical Encoders?

What sensors are required for a printer

The production of humanoid robots is expected to exceed 100000 units this year. Where will the 54 en

Photoelectric Sensors Move Towards Single‑Chip Integration – Proximity and Ambient Light Detection C

Why Dual‑Encoder Design Is Common in Humanoid Robot Joints

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