Linear Serial Elastic Hydraulic Actuator: Digital Prototyping and Force Control

In aggressive environments for humans, such as those present in the offshore industry, the main alternative is to replace human labor by remotely controlled robots, and some cases completely autonomous robots. The environment affects directly on robots tasks. When a robot works in a structured environment, its automation is easier since the environment can be modeled by dynamics equations. However if the environment is non-structured this modeling is quite difficult and presents a high computational effort. To overcome this difficult, over the years series elastic actuator (SEA) has been applied in non-structured environments. Actuators of the mechanical systems are always rigidly connected to the load to be moved. This can be observed in the hydraulic systems of agricultural, highway construction and mining equipment and in elevation and cargo transportation, among others. Unlike rigid actuators, a SEA contains an elastic element in series with the mechanical energy source. Such an elastic element gives SEA's several unique properties compared to rigid actuators, including tolerance to impact loads, low mechanical output impedance, passive mechanical energy storage, and increased peak power output. However it is not trivial to select the correct spring for the system. The spring has to be able to support the loads, but the spring cannot be too stiff, otherwise system impedance will be high. Iterative methods are needed to select the spring, which fits in impedance and bandwidth parameters. The resonance frequency is another issue for SEAs. This paper describes an entire digital prototyping of a linear serial elastic hydraulic actuator. It is done a digital prototyping of a tubular actuator design, which encapsulates the mechanical and electrical components and sensors. The digital prototype dimensions, mass and inertia properties are used to build the dynamic model for simulations and implementation of a controller. Moreover the methodology adopted results in a good response actuator with a compact and high force design