Final Report Summary - SPEAR (Series-Parallel Elastic Actuators for Robotics)
Actuators are key components for moving and controlling a mechanism or system. However, the torque and energy efficiency of the actuators are insufficient, much lower than biological muscles. There are several applications (prostheses, exoskeletons, manipulators) where the unavailability of suitable actuators hinders the development of well-performing machines with capabilities comparable to a human. The SPEAR project developed radically new solutions to develop a new generation of actuators that go beyond the current stiff servomotors and the Variable Stiffness Actuators. The proposed solution is based on the novel Series-Parallel Elastic Actuator (SPEA) concept, which is inspired by the series-parallel organisation of the muscle fibres in a human muscle. In a stiff actuator or a VSA all the torque that is generated at the joint, goes through the motor and consequently consumes electrical current (since torque is proportional to current). Moreover, electric motors are rarely used at optimal efficiency in robotic applications since the motor is used in its complete operating range. A stiff motor consists of an electric motor and a gearbox, a VSA consists of an electric motor, a gearbox and a mechanical spring with a mechanism and motor to adapt the stiffness. A SPEA consists of one or several electric motors, several springs arranged in series and/or parallel and locking mechanisms to adapt the topology of the actuator. As such the majority of the loads does not pass the motor and power can be optimally distributed to minimize energy consumption apart from realizing the required output loads. Several studies investigated the energy efficiency from a fundamental point of view. SPEAR developed and validated several novel topologies of such redundant actuators and developed control algorithms to do control allocation so the energy efficiency of the overall system is drastically improved. The efficiency was proven for use in prostheses, hopping robots and manipulator arms.
Moreover, robotic systems are typically dimensioned to be able to withstand occasional extreme loads, instead of being designed based on their performance tasks. This over-dimensioning results in heavy and oversized robotic systems. In SPEAR we worked on the ambitious breakthrough to develop a material-oriented solution by implementing self-healing (SH) materials for actuators. Self-healing grippers, hands, pneumatic muscles and mechanical fuses, consisting of (multiple) materials with different mechanical properties were developed using several manufacturing techniques as shaping through folding and self-healing, compression moulding and 3D printing. The original structure and properties could be regained after applying damages.
Moreover, robotic systems are typically dimensioned to be able to withstand occasional extreme loads, instead of being designed based on their performance tasks. This over-dimensioning results in heavy and oversized robotic systems. In SPEAR we worked on the ambitious breakthrough to develop a material-oriented solution by implementing self-healing (SH) materials for actuators. Self-healing grippers, hands, pneumatic muscles and mechanical fuses, consisting of (multiple) materials with different mechanical properties were developed using several manufacturing techniques as shaping through folding and self-healing, compression moulding and 3D printing. The original structure and properties could be regained after applying damages.