Robot Magnetic Encoder Sensor: How Domestic Magnetic Code Discs Break The Import Monopoly?

Inside the joints of industrial robots, on the shafts of servo motors, and at every motion node of humanoid robots, there hides an inconspicuous yet vital component – the magnetic encoder. It acts as the robot’s “joint nerve,” capturing speed, position, and angle in real time, converting mechanical motion into electrical signals, and enabling every precise turn and grasp.

At the heart of a magnetic encoder lies the magnetic code disc (also called a magnetic ring or drum) – a circular magnetic component patterned with alternating N/S poles. As the disc rotates with the shaft, the magnetic sensor detects changes in the magnetic field to compute angle and speed. Compared with traditional optical encoders, magnetic encoders offer non-contact measurement, immunity to dust and oil, vibration resistance, wide operating temperature range, and long service life, making them increasingly dominant in industrial automation and robotics.

I. Why is “domestic substitution” a must?

Though small, magnetic encoders are a classic bottleneck technology. For years, high-precision 19-bit or even 20 bit magnetic encoders required for humanoid robots, new energy vehicles, and many other sectors have relied entirely on imports from Europe – not only expensive but also subject to long lead times. Domestic magnetic encoders once struggled with insufficient accuracy, and the manufacturing of high-end magnetic code discs was long controlled by foreign giants.

Fortunately, this situation is changing. With continuous breakthroughs in magnetic materials, precision magnetisation, and integrated moulding, Chinese companies are steadily improving the performance of high-precision magnetoresistive sensors and magnetic code discs, accelerating the domestic substitution. In 2024, the market size of China’s magnetic encoder industry reached approximately RMB 1.114 billion, growing 8.37% year-on-year.

II. Three technical hurdles for domestic magnetic code discs

Manufacturing a high-performance magnetic code disc for robot magnetic encoders requires overcoming three core technical challenges:

1. Moulding precision – The dimensional accuracy of the disc directly affects the encoder’s resolution and signal stability. Traditional multi-piece assembly or post-processing methods introduce assembly errors that cannot meet the micron-level precision demanded by robot joints.

2. Magnetisation uniformity and complexity – High-precision magnetic encoders typically require dozens or even over a hundred pairs of N/S poles. During magnetisation, every pole must be identical in strength, position, and angle – any tiny deviation leads to angular measurement errors.

3. 100% outgoing inspection – Before a magnetic code disc is installed into a robot, it must undergo rigorous magnetic field waveform testing to ensure its output signal meets design specifications. Without full inspection, there is no consistency or reliability.

III. SDM: A one-stop breakthrough from magnetic materials to magnetic encoder sensors

Amid the wave of domestic substitution, SDM Magnetics (Hangzhou) Co., Ltd. has forged an independent, full-chain path from magnetic materials to magnetic encoder sensors.

In the field of robot magnetic encoder sensors, SDM has built a complete technical loop of integrated injection moulding → magnetic-printing point magnetisation → full magnetic-field waveform inspection, with each step reflecting the ultimate pursuit of precision and consistency.

Integrated injection moulding: from “assembly” to “monolithic casting”
Traditional manufacturing of magnetic code discs often follows a segmented process – moulding first, then magnetising, then assembling – and each additional step accumulates errors. SDM adopts integrated injection moulding technology, which combines the magnetic material and the disc substrate in a single injection moulding step. This not only drastically reduces accumulated tolerances from assembly but also significantly improves the structural strength and lightweighting of the disc – particularly suited for robot joints where size and weight are critical.

Magnetic-printing point magnetisation: every pole “carved with precision”
High-precision magnetic encoders demand that each N/S pole on the disc be positioned with extreme accuracy and uniform magnetic field intensity. SDM employs magnetic-printing point magnetisation – independently and precisely magnetising each pole one by one. This “carved” approach ensures uniform pole distribution and stable magnetic field intensity, fundamentally guaranteeing the sinusoidal output signal of the encoder and laying a solid magnetic foundation for high-resolution angle measurement.

Full magnetic-field waveform inspection: no “defective” disc leaves the factory
The final line of defence in magnetic code disc manufacturing is inspection. SDM performs full magnetic-field waveform inspection on every single disc before shipment. Using high-sensitivity magnetic sensors, the complete magnetic field signal during rotation is captured, and waveform diagrams are generated to analyse key parameters such as peak-to-peak errors and waveform distortion. Only discs with perfect waveforms receive a qualification tag – meaning every SDM magnetic code disc delivered to robot manufacturers has undergone 100% waveform verification, ensuring long-term stable operation in robotic joints.

IV. From “domestic substitution” to “domestic leadership”

From integrated injection moulding, to magnetic-printing point magnetisation, to full magnetic-field waveform inspection – SDM has built a complete, autonomous, and controllable manufacturing chain for magnetic encoder sensor discs with these three seemingly simple yet powerful processes.

This is not just an upgrade in manufacturing technology; it is a microcosm of China’s magnetic materials industry transitioning from “follower” to “competitor” and even “leader”. When domestic magnetic code discs are installed in the joints of Chinese robots, when “bottleneck” becomes “in our hands,” the backbone of China’s robotics industry truly stands tall.

SDM Magnetics – driving every precise rotation of Chinese robots with the power of magnetism.