Motor Drivers

KAIST Exoskeleton Lab

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Motor Drivers (MD)

MD is a high-performance BLDC motor driver equipped with advanced control technology. Featuring position, velocity, and current control capabilities, it delivers high power output relative to its compact form factor. With a high sampling rate for precise motor control, MD provides strong responsiveness and accuracy, making it suitable for demanding applications.

As a platform-integrated device, MD provides multiple communication interfaces and operates on a WaSP-compliant firmware structure, enabling seamless interaction with high-level controllers. When high-level control inputs are delivered in the designated platform format, MD performs the corresponding joint-level actuation, ensuring consistent, modular, and scalable control across the entire system.

MD is fully supported by Web- and MATLAB-based GUIs that streamline the configuration workflow, from basic actuator setup to advanced identification tasks such as system identification and friction model identification. These tools allow users to derive accurate models and, based on these models, configure a wide range of control functionalities, including robust position control and highly transparent interaction control, within the unified platform environment.







Protocol
Standardized Communication Protocol

To ensure reliable and scalable communication among modules in the proposed platform, a customized application-level communication protocol is implemented on top of the FD-CAN layer. The system employs two independent FD-CAN channels, each configured in standard identifier mode (11-bit) and operated at a data rate of 5 Mbps using Bit Rate Switching (BRS) to improve throughput. Automatic retransmission and transmit pause features are enabled to enhance communication reliability under time-critical control conditions.

To support modular and extensible communication, the 11-bit standard identifier is structured into three subfields: message type, source node ID, and target node ID. The message type, occupying the upper three bits of the identifier, defines the functional category of the transmitted data. This message type is categorized into four classes: emergency (EMCY), synchronization (SYNC), Service Data Object (SDO), and Process Data Object (PDO).

This proposed communication protocol provides platform-level scalability, as new devices can be integrated by assigning node IDs without modifying the protocol structure. Message priority is inherently managed through the identifier field, allowing critical messages to be transmitted with higher arbitration precedence. This modular design supports seamless expansion and reliable coordination across distributed modules.


Function 1
Nonlinear Friction Compensator

For precise position control and transparent force control, it is essential to compensate for inherent nonlinear friction in the drive system. MD provides a GUI-based framework that enables direct measurement of friction forces across a wide range of operating velocities, from low-speed bidirectional motion to high-speed regimes. Using these measurements, users can identify an appropriate nonlinear friction model tailored to the actuator’s characteristics. The resulting model can be incorporated as a feedforward compensator when the velocity reference is known, or applied as a feedback-based compensation strategy when it is not. Through the GUI, users can tune key parameters such as compensator smoothness, the remaining level of linear damping, and compensator gain, enabling efficient design, adjustment, and validation of a customized friction-compensation controller.


Function 2
Corridor-based Impedance Controller

For robots that physically interact with the external environment, particularly with humans, it is often necessary not only to maintain robustness but also to shape interaction dynamics in a controlled and intuitive manner. MD supports this capability through a corridor-based impedance controller, which allows system impedance to vary smoothly as the actuator state moves within a user-defined corridor. By configuring the corridor’s shape and parameters, users can tailor how stiffness, damping, or interaction forces evolve across different regions. Moreover, time-varying corridors can be implemented to enable adaptive interaction behaviors, allowing the robot to provide natural, responsive, and context-appropriate assistance during human–robot interaction.




Function 3
Disturbance Observer (DoB)

In practical robotic applications, actuators inevitably experience external disturbances that degrade tracking performance and hinder precise control. To address this, MD incorporates a disturbance observer (DoB) that estimates and compensates for these disturbances in real time based on an identified model. Using experimentally obtained system identification data, a nominal actuator model is constructed, and the DoB injects an additional compensation input so that the actual plant behaves as closely as possible to this nominal model, even in the presence of disturbances. Through MD’s GUI, users can perform system identification, configure the disturbance observer, and select an appropriate Q-filter cut-off frequency, enabling the design of a robust, disturbance-rejection-capable control architecture.