Magnetic Encoder Disk

"Joint Perception" in Robots: Unveiling How Magnetic Encoder Disks Grant Robots Agile Movements

In science fiction movies, robots can perform high-difficulty actions such as dancing, performing surgery, or even parkour. Behind this capability lies a critical component: the joint. For modern robots—whether industrial manipulators or humanoid robots—each joint requires not only powerful "muscles" (motors) but also acute "nerves" to perceive angles and positions. The core of these "nerves" is the protagonist of our discussion today: the magnetic encoder disk.

What is an Encoder? The Robot's "Proprioception"

Imagine being able to accurately touch your nose with your eyes closed. This is possible because your muscles and joints feed position information back to your brain. In the realm of robotics, an encoder plays a similar role. It is a sensor that converts mechanical motion (such as rotational angle and speed) into electrical signals, providing critical position, velocity, and direction data to the robot's control system, thereby optimizing overall system performance .

Currently, there are three main types of encoder technologies: optical, magnetic, and capacitive. For a long time, optical encoders have been a popular choice in the market due to their high precision. They operate like a precision CD player, determining position by reading transparent and opaque lines on a coded disk .

However, optical encoders face several inherent challenges in robotic applications:

1. Susceptibility to Contamination: Dust and oil can obstruct the optical path, leading to signal loss .

2. Susceptibility to Vibration: The glass disks used in optical encoders are prone to breakage during high-speed robot motion or impacts .

3. Size and Power Consumption: High-resolution optical encoders typically have larger form factors and higher power consumption .

Against this backdrop, magnetic encoders have begun to shine in the field of robotic joints, leveraging their unique advantages.

Magnetic Encoder Disks: "Mapping" Motion with Magnetic Fields

The structure of a magnetic encoder is similar to that of an optical encoder, but it utilizes magnetic fields instead of light beams . Its core component is a magnetic encoder disk. This small disk features an array of alternating magnetic poles (akin to countless tiny north and south poles).

As the disk rotates with the motor shaft, these alternating magnetic fields are detected by nearby magnetoresistive sensors or Hall sensors. The sensors convert the magnetic field variations into electrical signals, which are then processed by circuitry to calculate the precise position of the shaft .

If we liken an optical encoder to "reading a grating," then a magnetic encoder is like "interpreting a magnetic field map."

Why Do Robotic Joints Favor Magnetic Encoders?

In recent years, with the surge in embodied intelligence and humanoid robots, magnetic encoders have become a favored choice in joint module design for several reasons:

1. Inherent Robustness, Unfazed by Harsh Environments
   Robotic joints are often filled with lubricating grease and may operate in dusty environments. Optical encoders can have their "vision" blurred under such conditions. In contrast, magnetic encoders, being non-contact magnetic field sensors, are "immune" to dust, oil, and moisture, offering high reliability and excellent resistance to vibration and shock .

2. Compact Size and Flat Structure

   Modern robotic joints strive for "integrated power modules," requiring high integration of motors, reducers, and drives. Magnetic encoders eliminate the need for bulky light sources and optical lens systems; the chips and disks can be made very thin, facilitating "miniaturized, lightweight, and flat" joint designs .

3. Breakthroughs in High Resolution for Precision Force Control

   It was once commonly said that magnetic encoders lagged behind optical ones in precision. However, this is changing. At the 2024 China Hi-Tech Fair (CHTF), domestic manufacturers showcased high-precision magnetic encoder disks achieving 19-bit or even 20-bit resolution . For instance, by arranging complex magnetic pole pairs—such as "126 poles on the inner ring and 128 poles on the outer ring"—on a very small disk, sensors can detect extremely minute movements. This enables robots to perform delicate operations, such as assembling precision parts .

4. Cost Advantages and Localization Benefits

   For a long time, the market for high-resolution (e.g., 19-bit, 20-bit) magnetic encoders was dominated by foreign companies, making them expensive with long lead times—a classic example of a technology bottleneck . Today, domestic companies like Yuzhi Power Technology have achieved breakthroughs. Their technology has reached world-class levels, while costs have been reduced to one-half or two-thirds of imported products, significantly lowering the manufacturing cost for domestic robots .

Technological Frontiers: From "Single-Turn" to "Multi-Turn," From "Sensing" to "Intelligent"

As robot application scenarios expand, magnetic encoder technology continues to evolve:

• Absolute Position Memory: High-end magnetic encoders now support "multi-turn" functionality. Even if a robot joint is moved by an external force after power loss, the encoder, powered by a battery, can record the number of turns and immediately know the absolute position upon restart, eliminating the need for re-homing .

• Anti-Interference Algorithms: To counter the strong electromagnetic interference generated by running motors, modern magnetic encoder chips (e.g., those employing AMR technology) integrate dynamic angle error compensation algorithms, ensuring stable signal output even in noisy environments .

• Innovations in Disk Manufacturing: Precision magnetization has traditionally been a major challenge for magnetic disks. Now, through unique techniques like "one-time magnetization," the accuracy of domestically produced magnetic disks has been significantly enhanced, laying a solid foundation for high-precision robot joints .

If the motor is the heart of a robot, then the magnetic encoder, incorporating a high-precision disk, is the robot's "proprioceptive nerve." It not only allows the robot to perceive its own posture but also grants it the ability to operate stably and precisely in complex environments.