Feature: Processors and MCUs
Figure 2: Example system architecture for BLDC motor control in elbow joint servo drive below 500W
A-PMD2 and ADC can work together to apply Toshiba’s PWM-shiſt technology, providing additional time for the ADC to complete the measurement. Rotor position information can be acquired through the A-ENC2 advanced encoder interface for precise angle feedback, or estimated using a sensorless method, to complete the control cycle. T e timing critical stages of the control
cycle are completed through dedicated hardware before the next control cycle begins. T e Cortex-M4 remains available for communications, diagnostics and the application soſt ware that coordinates the servo drive with the rest of the robotic system. Humanoid robotic joints can benefi t from
higher PWM frequencies than the 16-20kHz commonly used in conventional motor control applications. Frequencies of 40kHz, 50kHz or, even, 100kHz can help move switching noise beyond the audible range, reduce current ripple and improve motor effi ciency, thereby limiting heat generation within the joint. However, increasing the PWM frequency also shortens the time available for motor control calculations. To maintain dynamic response and
positioning accuracy, the FOC calculations should therefore be completed within a single PWM cycle, or at most two cycles. Achieving this using soſt ware alone becomes increasingly demanding as carrier frequencies rise. By executing the time-critical vector control calculations in dedicated hardware, the Vector Engine meets this requirement while leaving the
CPU available for functions such as torque management and positioning. T is can also avoid the need to select or clock the CPU solely around the worst-case FOC workload, with corresponding benefi ts of lower energy consumption and heat dissipation.
Building a robotic servo drive T e output of the motor control subsystem is only the beginning of the servo drive. T e PWM signals must still pass through the power stage before electrical commands become controlled motor torque. T e gate driver converts the PWM
outputs from the controller into the drive signals needed to switch the power devices. Where the control electronics and power stage operate in diff erent voltage domains, digital isolation provides the required separation between them. T e inverter, implemented with MOSFETs, then converts the DC supply into the controlled three- phase currents that drive the servo motor. T e choice of components depends on the application’s motor voltage, phase current and switching frequency requirements. In a robotic joint these elements must
increasingly be integrated into the joint itself rather than housed in separate electronics; see Figure 2. Available PCB area may be constrained further by the mechanical joint and by the need to accommodate motor, power and communications connections. T e resulting design challenge is therefore not simply to control the motor, but to provide the required intelligence, power, feedback, communications and protection within a tightly-constrained electrical
and thermal envelope, whilst also limiting component count and BOM. In Figure 2, the MCU is part of a wider
motor control solution for the robotic joint. T is includes an eFuse for overcurrent protection (1), a load switch providing reverse-polarity and current protection (2), and an LDO supplying the voltages required by the motor control subsystem (3). T e MCU (4) controls the motor through a programmable gate driver with additionally integrated current amplifi er (5), while the MOSFETs (6) are selected according to the joint’s voltage and power requirements. Soſt ware completes the system. Device
confi guration, motor commissioning, fault handling and communications all remain the responsibility of the application soſt ware.
Supporting diff erent robotic joints Despite the application-specifi c diff erences between joints within a humanoid robot, the underlying control architecture changes much less. Every servo drive still depends on accurate current measurement, reliable position feedback and predictable control timing to regulate motor torque, speed and position. T e controller must also retain capacity for wider system functions. Architectures that partition time-critical
motor control functions from higher-level soſt ware provide one way of meeting these competing requirements. As robotic systems continue to evolve, the eff ectiveness of a servo drive will increasingly depend not only on processor performance, but also on how the control architecture distributes real-time tasks throughout the system.
www.electronicsworld.co.uk October 2026 29
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