Smart Servohydraulic Robot Actuation

An electro-hydraulic servo system utilises a servo-valve under electronic control to regulate the flow of fluid to an actuator. Precise motion/force control is achieved by including sensors and a closed loop controller. This setup is common in many industries and is particularly useful for robotics due to high dynamic performance and power to weight ratio.

Moog have developed an Integrated Smart Actuator (ISA), combining the servo-valve, linear actuator, sensors and control electronics all into an additively manufactured titanium body. This setup is ideal for mobile robotics, due to its low mass and the robustness created by its component integration. It also presents an opportunity to develop a load agnostic controller.

The design and tuning of a controller requires knowledge of the dynamics of the hydraulic system, as well as the load that the actuator is to drive. For a given setup, changing the nature of either of components significantly, will alter the behaviour of the controller, potentially leading to poor performance or instability. Steps are also taken to deal with the non-linearities that are inherently present in a hydraulic system.

With the ISA, the hydraulic and sensor dynamics are 'fixed' and known in advance leaving only the load characteristics as unknown. The aim of the project is to utilise the ISA hardware to develop a force/motion control algorithm that can deal with load uncertainty with minimal tuning required, creating the first 'plug and play' servo-hydraulic actuator.

The initial stage of the project will focus on the modelling of the actuator, research into control algorithms and an initial set-up and testing of the hardware. Modelling will be done in Simulink and then compared and validated to the real system over a range of operating conditions.

The research will focus on different control algorithms that have been used on electro-hydraulic servo systems, methods of dealing with non-linearities and particularly methods for dealing with unknown loading.

The experimental setup will enable the actuator to drive a load with variable mass, spring and damping rate as well as the possibility of using hardware in the loop by driving against another high-performance actuator. The majority of this test rig is in place, including a powerpack to drive the actuator. Some components will need designing to integrate the ISA into the rig.

Later stages will involve the implementation and testing of control algorithms and selection of a real-world comparison to validate the controller against. The sensor data available also yields the possibility of system 'health monitoring', to check the status and performance of the hydraulic system. Another potential avenue is to investigate the safety requirements for robotic human interaction, vital for mobile robotics, and how these can be directly integrated within the actuator controller.