Signal Jitter of Robot Magnetic Encoder Sensors – From Symptom Treatment To Systematic Root Cause Resolution

1. Signal Jitter: The Core Pain Point in Robot Joint Control

In applications that demand stringent position control – such as robot joints, pan-tilt units, and high-precision servo systems – magnetic encoders are rapidly replacing traditional optical encoders thanks to their non-contact operation, high reliability, and long service life. Yet many engineers encounter a frustrating issue during actual debugging: unstable angle readings, exhibiting periodic jumps or random noise.

The manifestations of signal jitter are varied: at low speeds, high-frequency small-amplitude angle jumps cause speed-loop fluctuations, positioning tremors, and increased torque ripple; the pulse widths of A/B quadrature outputs become uneven, with the phase difference jittering around 90°; in severe cases, communication frame losses and data glitches occur, directly degrading control accuracy, causing motor abnormal noise, or even triggering system shutdowns.

As one engineer noted in an online forum: “The pulse widths of the A/B outputs from the magnetic encoder jitter – even at constant speed, the widths are uneven, whereas the optical encoder does not have this problem.” This comparison highlights the essence of the problem: signal jitter in magnetic encoders is not an inherent chip defect, but rather the combined result of multiple factors – hardware layout, magnetic circuit design, signal integrity, and software processing.

2. Three Root Causes of Signal Jitter

2.1 Mechanical Installation Errors – The Most Common Culprit

Magnetic encoders are extremely sensitive to air gap, coaxiality, tilt, and magnet eccentricity. Excessive eccentricity shifts the magnetic field centre, distorts the sinusoidal signals, and introduces periodic angle errors; an air gap that is too large or too small alters the induced signal amplitude, degrades the signal-to-noise ratio, and increases jitter; axial tilt causes asymmetric field distribution and waveform distortion. Even an eccentricity of 0.5 mm can introduce significant second-harmonic errors at high rotational speeds.

2.2 Magnetic Field and Environmental Interference

Stray leakage flux from motor ends, inverter radiation, and coupled magnetic fields from high-power cables can superimpose directly on the encoder’s sensing plane, causing signal jumps. Eddy currents induced in metal brackets and motor housings also attenuate or distort the useful magnetic field. Moreover, magnetic encoders are highly sensitive to field strength and are susceptible to strong vibrations in harsh industrial environments.

2.3 Electrical and Communication Issues

Excessive power-supply ripple, floating grounds, and improper single-ended shielding grounding introduce common-mode interference. I⊃2;C communication, especially at high speeds or over long distances, is vulnerable to interference, leading to data glitches and jitter. SPI communication can also suffer from timing mismatches and high bit-error rates, resulting in data anomalies.

3. From “Chip-Level” to “System-Level” Solutions

Addressing signal jitter calls for a comprehensive, system-wide approach.

Hardware aspects: Magnet installation must follow the “three-axis” alignment principle – axial alignment, precise vertical gap control (recommended 0.5 mm – 2.0 mm), and parallelism assurance. The air gap should be kept within tolerance, and coaxiality deviation should be controlled below 0.03 mm. On the PCB, copper pour and routing are forbidden under the encoder chip; the distance between SPI pins and the MCU pins should be kept within 10 cm. Power-supply ripple must be held below 10 mV, with multi-stage decoupling applied.

Communication aspects: Prefer the SPI interface over I⊃2;C – hardware SPI offers far better noise immunity than bit-banged I⊃2;C. SPI lines should use shielded twisted-pair cables, with differential signals wrapped by ground wires to reduce EMI. Communication speed and timing parameters must be precisely matched to keep the bit-error rate within acceptable limits.

Algorithmic aspects: Apply error compensation algorithms to correct mechanical installation deviations in software; use digital filtering to improve the signal-to-noise ratio; and optimise logic for multi-turn counter overflow handling. Dynamic feed-forward compensation and adaptive PID tuning can also effectively suppress lag effects caused by transmission backlash.

4. Magnet Material Quality – The “Foundation” of Signal Stability

When discussing solutions for signal jitter, one fundamental aspect is often overlooked: the quality of the magnet itself. The accuracy of a magnetic encoder is first determined by the uniformity and stability of the magnetic field distribution. Cheap magnets may suffer from asymmetric poles or uneven field strength, causing periodic distortion in the output curve. Key parameters such as remanence (Br) and surface field uniformity are equally critical.

5. Hangzhou SDM: A Deep-Rooted Player in Magnetic Materials

In the foundational domain of magnetic materials, Hangzhou SDM Magnetics Co., Ltd. is a company worth noting. Founded in 2009 and headquartered in Hangzhou, it is a national high-tech enterprise dedicated to magnets and magnetic solutions.

Against the backdrop of the rapidly growing robotics industry, SDM leverages its deep expertise in rare-earth permanent magnets to actively expand into robotics-related applications.

For Robot Magnetic Encoder Sensors, high-performance permanent magnets are the “first line of defence” in ensuring signal stability and suppressing jitter. SDM’s technical strengths in magnet formulation, magnetic circuit design, and magnetic assembly systems position it well to play a significant role in the upstream material chain – delivering customised magnet solutions with more uniform field distribution and better temperature stability for encoders, thereby reducing jitter caused by inferior magnet quality right at the source.

As the demand for high-precision position feedback in robotics continues to grow, the issue of signal jitter in magnetic encoders will receive increasing attention. The fundamental cure lies in end-to-end optimisation – from magnet materials to system integration. SDM’s role in this chain deserves sustained attention from the industry.