TY - JOUR
T1 - Concept of a Series-Parallel Elastic Actuator for a Powered Transtibial Prosthesis
AU - Mathijssen, Glenn
AU - Cherelle, Pierre
AU - Lefeber, Dirk
AU - Vanderborght, Bram
PY - 2013/7/3
Y1 - 2013/7/3
N2 - The majority of the commercial transtibial prostheses are purely passive devices. They store energy in an elastic element during the beginning of a step and release it at the end. A 75 kg human, however, produces on average 26 J of energy during one stride at the ankle joint when walking at normal cadence, and stores/releases 9 J of energy contributing to energy efficient locomotion. According to Winter, a subject produces on average 250W peak power at a maximum joint torque of 125Nm. As a result, powering a prosthesis with traditional servomotors leads to excessive motors and gearboxes at the outer extremities of the legs. Therefore, research prototypes use series elastic actuation (SEA) concepts to reduce the power requirements of the motor. In the paper it will be shown that SEAs are able to reduce the power of the electric motor, but not the torque. To further decrease the motor size, a novel human-centered actuator concept is developed which is inspired by the variable recruitment of muscle fibers of a human muscle. We call this concept series-parallel elastic actuation (SPEA) and the actuator consists of multiple parallel springs, each connected to an intermittent mechanism with internal locking and a single motor. As a result, the motor torque requirements can be lowered and the efficiency drastically increased. In the paper the novel actuation concept is explained and a comparative study between a stiff motor, an SEA and an SPEA, that all aim at mimicking human ankle behavior, is performed.
AB - The majority of the commercial transtibial prostheses are purely passive devices. They store energy in an elastic element during the beginning of a step and release it at the end. A 75 kg human, however, produces on average 26 J of energy during one stride at the ankle joint when walking at normal cadence, and stores/releases 9 J of energy contributing to energy efficient locomotion. According to Winter, a subject produces on average 250W peak power at a maximum joint torque of 125Nm. As a result, powering a prosthesis with traditional servomotors leads to excessive motors and gearboxes at the outer extremities of the legs. Therefore, research prototypes use series elastic actuation (SEA) concepts to reduce the power requirements of the motor. In the paper it will be shown that SEAs are able to reduce the power of the electric motor, but not the torque. To further decrease the motor size, a novel human-centered actuator concept is developed which is inspired by the variable recruitment of muscle fibers of a human muscle. We call this concept series-parallel elastic actuation (SPEA) and the actuator consists of multiple parallel springs, each connected to an intermittent mechanism with internal locking and a single motor. As a result, the motor torque requirements can be lowered and the efficiency drastically increased. In the paper the novel actuation concept is explained and a comparative study between a stiff motor, an SEA and an SPEA, that all aim at mimicking human ankle behavior, is performed.
KW - Series-parallel elastic actuation
KW - Compliant actuation
KW - High torque requirements
KW - energy efficiency
U2 - 10.3390/act2030059
DO - 10.3390/act2030059
M3 - Article
VL - 2
SP - 59
EP - 73
JO - Actuators
JF - Actuators
SN - 2076-0825
ER -