Optimized parallel joint springs in dynamic motion: Comparison of simulation and experiment

Abstract

Inspired by human tendon function, parallel springs in the joints of bipedal walking robots allow for a significant reduction of the cost of locomotion in simulation. An experimental setup is presented here which enables to verify the simulation results. The beneficial effects of parallel springs are investigated for a four-link robot arm equipped with a parallel spring at the last link. The desired motion results from simultaneous optimization of spring properties and motion which was shown to achieve the best reduction of actuation effort. Spring utilization is considered for two types of motion, free space motion and motion including contact with the environment at the end-effector. It is shown that the absolute reduction of effort through the utilization of an optimal spring is independent of friction. Hence, influence of the spring on effort is more relevant at higher speeds where the motion itself requires more actuation effort. Furthermore, for motion with environmental contact, a spring can reduce actuation effort more than in free space motion, especially for stiffer environments.

A clutched parallel elastic actuator concept: Towards energy efficient powered legs in prosthetics and robotics

“…A spring in parallel to a motor does reduce the energy consumption and torque requirements for motions with torque patterns that fit the parallel spring [7], [1], [3]. In other motions or gait phases however, it can hinder the movement.…”

“…For example, [2] report for the design of an exoskeleton a theoretical reduction in peak torque requirements of 48% for ankle actuation and up to 66% for hip actuation when using parallel springs around these joints in addition to motors. Other examples that exploit parallel elasticity to reduce actuation requirements include the Virtual Scenario Haptic Rendering Device of TU Munich [3], the gravity compensating mechanism in the knee joint of the robot Saika-4 [4], and the powered ankle-foot prosthesis of MIT [5], [6].…”

Maneuver based design of a passive-assist device for augmenting linear motion drives

“…One way more energy can be saved is if the maneuver and PAD are designed together. Significant research has gone into the simultaneous optimization of springs and gait designs in walking robots [18], [24]. These works demonstrate the potential advantages of simultaneous maneuver and spring optimization including the performance of simultaneous optimization vs sequential optimization [24].…”

An energy efficiency index for elastic actuators during resonant motion

“…These results are task specific, since they depend on the locomotion speed. Several other examples of system-specific and task-specific analyses can be found, for example, on walking robots [25,[39][40][41], hopping robots [42][43][44], manipulators [45][46][47][48] and even wheeled robots [49]. In search of generalized rules for elastic actuator design, some authors have studied the motion of a pendulum at different frequencies.…”

“…As the inherent mechanical damping is low, we used a soft spring in order to obtain noticeably differences between indices η and η WC as discussed in the previous section. For each load, Table III reports the parameters ξ and σ defined in (56) and (45). The motor Coulomb friction is compensated using a sign(ẋ m ) function and neglected because its nonlinear nature is not considered in our analysis.…”