A humanoid joint needs more than an angle sensor
Illustrative image: Unsplash contributor on Pexels
A motor encoder may report exactly the expected position while a humanoid limb sits slightly out of place, because backlash, compliance and structural flex lie between the motor and the load. TDK’s Hon Hai Tech Day demonstration addresses that gap by presenting angle sensors alongside inertial sensing, temperature monitoring and the passive components needed to keep their signals usable.
The portfolio covers TMR angle sensors, absolute encoders, IMUs, NTC sensors, common-mode chokes, inductors, capacitors, haptics and ESD protection. It is a broad supplier offering, but the interesting question is how those parts work around one actuator, where position accuracy can be undermined by heat, vibration or switching noise elsewhere in the assembly.
Position and motion answer different questions
Sensor placement determines which error can be measured. A TMR sensor or encoder on the motor can track the rotor accurately while missing movement lost in the gearbox, whereas an output-side sensor observes more of the mechanism at the cost of another mounting and wiring problem. An absolute encoder also provides a defined position reference after a power cycle, while an incremental system normally needs a reference to establish its position.
An IMU adds a measurement of the segment’s acceleration and angular rate, so the controller can compare actual motion with the encoder-based estimate. TDK lists devices supporting up to 4000 degrees per second and ±32 g, with BalancedGyro intended to suppress vibration effects. Those ranges do not remove bias or integration drift and vibration performance still needs to be judged under the actuator’s own mechanical conditions.
The company also demonstrated PositionSense, which combines a six-axis IMU with a three-axis TMR magnetometer and on-chip sensor fusion. Magnetic heading can help constrain inertial drift, but motors, steel structures and current-carrying conductors distort the local field. Placement and calibration remain part of the mechanical design.
Temperature closes the torque loop
As the actuator heats, its usable torque changes with winding resistance and the temperature limits of magnets, power electronics and other materials. NTC sensors on windings, drive boards and cells give the controller a direct thermal measurement, reducing its reliance on a current-based estimate alone.
The measurement point matters because a sensor on a housing responds more slowly than the winding hotspot it is meant to protect. Thermal models can estimate the difference, provided the controller has a reliable history of current, speed, ambient temperature and cooling. A robot that repeatedly lifts, holds and lowers a load creates a very different thermal cycle from one that walks continuously.
The signal has to survive the actuator
Fast power switching, long harnesses and compact motor windings create common-mode currents and sharp voltage edges beside low-level sensor signals. TDK includes common-mode chokes, power inductors and multilayer ceramic capacitors in the stack because a correct sensor cannot help if its supply or communication link is corrupted.
Filtering has to preserve the bandwidth needed by the control loop. Too little attenuation leaves the receiver vulnerable to switching noise; too much capacitance or common-mode impedance can distort an edge, delay a safety message or create a resonance with the cable. The final choice depends on the interface, cable, grounding and inverter switching behaviour rather than the component catalogue alone.
Haptics and ESD protection sit at the human-facing edge of the same system. Touch surfaces and controls need a deliberate response while surviving discharge from a user or the environment. Their ground return and shielding can influence the sensor network inside the robot, so they cannot be added after the actuator electronics have been closed.
TDK’s portfolio spans many of the right component categories, though a demonstration cannot establish how well a finished joint will behave. That requires measurements under load, with the motor switching and the mechanism hot, when encoder error, thermal lag and communication noise can interact. A clean sensor specification on the bench only covers part of that operating condition.
Sources
Photo: Pavel Danilyuk / Pexels. Illustrative image. https://www.pexels.com/photo/close-up-photo-of-a-robot-arm-8294559/ | https://www.pexels.com/license/
