With the rapid development of artificial intelligence technology, the global robotics industry is experiencing unprecedented changes and opportunities. On September 16, Analog Devices, a global leader in semiconductor technology, held a media sharing event titled “Activating Edge Intelligence, Co-creating an Embodied Future” for humanoid robots. During the event, ADI showcased two representative demos related to humanoid robots, namely the innovative multi-turn sensor ADMT4000 and the highly integrated single-chip servo drive control chip TMC9660.
Product Introduction of the Innovative Multi-Turn Sensor ADMT4000:
The ADMT4000 is the first single-chip multi-turn position sensor released by ADI, designed to fundamentally overcome the shortcomings of traditional solutions. It has an absolute measurement range of 46 turns, achieving an accuracy of ±0.25 degrees across the entire measurement range. With this new multi-turn technology, it eliminates the need for backup batteries or mechanical gears that are typically used with single-turn sensors, and it can also dispense with linear sensors in linear actuators. Furthermore, for systems that do not use traditional bulky mechanical multi-turn encoders, this sensor does not require re-homing or recalibration upon power-up, allowing it to accurately record multi-turn rotational movements in a completely passive (no power supply) state.
The technical implementation of the ADMT4000 is based on the controllable propagation of magnetic domain walls in magnetic nanowires. In magnetic materials, a magnetic domain is a region where atomic magnetic moments are aligned, while a magnetic domain wall is the transition layer between adjacent domains. This sensor utilizes the magnetic field generated by an external permanent magnet (fixed to the rotating part of the robot joint) to drive the displacement of magnetic domain walls within the internal magnetic wires. Thus, the rotational movement of the joint is directly and non-destructively converted into the displacement of the magnetic domain wall along a one-dimensional linear path.
To read the position of the magnetic domain wall, the ADMT4000 integrates four Giant Magnetoresistance (GMR) detection points along the magnetic wire. The GMR effect is a quantum mechanical phenomenon where the resistance value changes significantly with variations in the local magnetic field direction. As the magnetic domain wall sweeps past these GMR detection points, it causes changes in their respective resistance values. By accurately measuring the resistance values of these four detection points, a unique impedance characteristic corresponding to the position of the magnetic domain wall can be obtained. The system controller can then read this set of resistance values to accurately calculate the current position of the magnetic domain wall, thereby inferring the absolute rotational angle and cumulative turns of the joint.
The key point is that the position of the magnetic domain wall is a stable physical state that requires no external energy supply to maintain. This means that even if the joint moves during a power outage, this positional information is physically retained within the chip. When the system is powered back on, a single resistance reading is sufficient to immediately ascertain the current precise absolute position.
This sensor must operate within a magnetic field window of 16 to 31 mT. If there is insufficient magnetic energy or if the magnetic field strength falls below 16 mT, there is a risk of insufficient magnetic energy, preventing the magnetic domains from being displaced out of the domain wall generator and through the helix. If the magnetic field strength exceeds 31 mT, especially significantly above 31 mT, there is a risk of additional magnetic domains being added to the helix, leading to erroneous counting information, or a very strong magnetic field could cause the helix to completely reset.
Additionally, as a magnetic sensor, the ADMT4000 must consider its resistance to external stray magnetic fields in applications. In complex electromagnetic environments such as humanoid robots, it is recommended to implement magnetic shielding measures. ADI provides corresponding shielding solution reference designs, which can effectively suppress external magnetic field interference by designing shielding layers around the chip or on the PCB, ensuring the accuracy of sensor measurements.
