FAS A flexible Antagonistic spring element for a high performance over actuated hand

CLASH: Compliant Low Cost Antagonistic Servo Hands

“…All four tendons run over a so-called flexible antagonistic spring element (FAS) [6], which measures the tendon force and makes the fingers robust against external perturbations. A stiffness change always affects all four joints simultaneously.…”

“…However, hands such as the Awiwi hand (with 19-DoF, and driven by 38 motors in the forearm) which are built to answer a broad range of research questions, e.g., optimal hand kinematics as well as optimal kinematic and stiffness synergies, are far too complex and expensive to be used in a real industrial application. This paper introduces and describes the evolutionary development of two soft robotic hands in a new family of DLR hands, generically called CLASH (Compliant Low cost Antagonistic Servo Hand), based on the technology used in the Awiwi hand [6]. The hands have three fingers -one versatile thumb and two opposing underactuated fingerscombined with low cost servo actuators and rapid prototyping parts, leading to a light, cheap, and robust platform for grasping experimentation.…”

"FRCEF: The new friction reduced and coupling enhanced finger for the Awiwi hand"

“…However, during the implementation of the controllers, it appeared that the friction was larger than expected. The total friction along the tendon path in the forearm results from the guidings in the flexible adjustable spring mechanism located in the forearm [15], the wrist pulleys 3 , the palm guidings with pulleys or sliding surfaces and the finger sliding surfaces. In order to investigate futher the source of the discrepancies, a calibrated weight has been lifted in a triangular motion to measure the overall friction along the complete tendon path from the winder to the palm (Fig.…”

“…Two major aspects of the hand are identified as being limitations regarding the performance of the hand controller: The friction in the guiding and the creeping of the tendons. First, the tendon forces acting on the joints must be estimated since friction of the tendon path is not directly observed and the forces are measured via the deflection of the elastic elements directly next to the actuator as discussed in [15]. Moreover, the joint friction itself is not observed, and depends on many parameters such as the temperature, the surface quality Genuine design New design Fig.…”

“…The initial choice of the Dyneema R was motivated by the work of Friedl [15] that showed that for the small pulley diameters used in the Awiwi hand, the lifetime (in load cycles) of a Dyneema R tendon is 100 times higher than a steel tendon with an equivalent diameter. The material being non conductive is also a significant advantage over metallic cables.…”