This project involved the development of a highly compact, fully cased and potted 36V motor control solution designed to drive a precision hydraulic actuator for use in a medical environment. The application placed exceptionally high demands on safety, reliability, environmental robustness, and electromagnetic compatibility, while also requiring a small mechanical footprint and long operational life. The resulting solution represents a carefully engineered balance between electrical performance, mechanical integration, regulatory compliance, and manufacturability.
At the core of the system is a brushed DC motor control platform operating from a nominal 36V supply. The motor drives a hydraulic pump, which in turn actuates a medical mechanism requiring smooth, repeatable motion and predictable force output. As the actuator forms part of medical electrical equipment, the motor controller is classified as a safety-critical subsystem and was therefore designed in compliance with a wide range of international standards governing medical safety, EMC performance, and environmental resilience.
System Architecture and Electrical Design
One of the defining challenges of the project was the need to integrate significant electrical functionality into a very small, sealed enclosure. To achieve this, the electronics were split across two separate printed circuit boards, arranged in a sandwiched configuration and interconnected using high-reliability board-to-board connectors.
The lower PCB is dedicated primarily to power electronics. This board incorporates the high-current motor drive stage, including MOSFETs, current sensing, gate drive circuitry, bulk capacitance, and transient protection. Particular attention was paid to thermal performance, as the fully potted construction removes the possibility of convective cooling. Power dissipation was carefully managed through low-loss component selection, optimized switching strategies, and direct thermal coupling to the casing via thermally conductive potting compound.
The upper PCB contains the control, sensing, and communication electronics. This includes the microcontroller, signal conditioning, safety monitoring circuits, and interfaces to external sensors and system controls. By separating high-power and low-power circuitry across two boards, the design minimizes noise coupling, improves EMC performance, and allows each PCB to be optimized for its specific function.
The inter-board connectors were selected to provide high mechanical robustness, low contact resistance, and excellent vibration tolerance. Their layout and pin assignment were carefully engineered to maintain signal integrity, provide adequate creepage and clearance distances, and support safe separation between power and control domains in line with medical safety requirements.
Mechanical Integration and Potting Strategy
The electronics assembly is housed within a custom-designed casing that provides both mechanical protection and environmental sealing. The casing geometry was developed in parallel with the PCB layout to ensure efficient use of space while maintaining compliance with relevant standards for ingress protection and mechanical strength.
Once assembled, the entire electronics stack is fully potted using a specially selected compound that provides electrical insulation, vibration damping, moisture protection, and thermal conductivity. Potting introduces its own challenges, particularly in relation to heat dissipation, component stress, and long-term reliability. These risks were addressed through extensive material selection, simulation, and testing.
The potting compound was chosen to remain stable over a wide temperature range, resist chemical degradation, and withstand prolonged exposure to moisture and saline environments. The result is a sealed electronics module that is effectively immune to dust, water ingress, and corrosion, making it suitable for use in demanding clinical and industrial settings.
Functional Safety and Medical Compliance
As a component of medical electrical equipment, the motor controller was designed to comply with IEC 60601-1, which defines the general requirements for basic safety and essential performance. This standard strongly influenced the overall system architecture, including isolation strategies, fault detection, and fail-safe behavior.
The controller continuously monitors key parameters such as supply voltage, motor current, temperature, and internal fault states. In the event of an abnormal condition, the system transitions to a defined safe state, preventing uncontrolled motion or overheating of the hydraulic actuator. The firmware and hardware were developed together to ensure predictable behavior under both normal operation and fault conditions.
Electromagnetic compatibility was addressed in accordance with IEC 60601-1-2. Given the combination of high-current motor switching and sensitive medical equipment operating nearby, EMC performance was a critical concern. Extensive filtering, shielding, grounding strategies, and PCB layout techniques were employed to limit both conducted and radiated emissions, while ensuring robust immunity to external electromagnetic disturbances.
Environmental and Mechanical Robustness
In addition to medical safety and EMC compliance, the controller was required to operate reliably in harsh environmental conditions. Compliance with IEC 60529 was achieved, with the sealed and potted construction providing a high degree of ingress protection against dust and water.
The design was validated against ISO 9227 salt spray testing, demonstrating resistance to corrosion in saline environments. This is particularly important for medical equipment that may be exposed to aggressive cleaning agents or coastal deployment conditions.
Mechanical durability was proven through a comprehensive suite of environmental tests in accordance with the IEC 60068 family of standards. This included vibration testing to DIN IEC 60068-2-34, ensuring that the controller can withstand sustained mechanical excitation without electrical or mechanical degradation. Shock testing to IEC 60068-2-27 and free-fall testing to IEC 60068-2-32 verified that the assembly remains functional after sudden impacts or drops during handling and installation.
Thermal resilience was demonstrated through temperature change testing in accordance with IEC 60068-2-14. The system was shown to operate correctly across rapid and repeated temperature transitions, with no loss of performance, cracking of potting material, or degradation of electrical connections.
Outcome and Engineering Significance
The completed motor control solution delivers precise, reliable control of a hydraulic actuator in a compact, sealed, and medically compliant form factor. The two-PCB sandwiched architecture, combined with a custom casing and full potting, enabled a level of integration that would not have been possible using a conventional single-board approach.
From an engineering perspective, the project highlights the importance of concurrent electrical, mechanical, and regulatory design. Every aspect of the solution—from PCB layout and component selection to potting material and casing geometry—was shaped by the requirements of medical safety, environmental durability, and long-term reliability.
The result is a robust, production-ready motor controller that meets stringent international standards and demonstrates how complex motor control electronics can be successfully deployed in demanding medical applications without compromising on size, performance, or compliance.