A muscle-like recruitment actuator with modular redundant actuation units for soft robotics

Abstract

Human muscles contrast sharply with traditional robot actuators in that they consist of several motor units, connected in series and parallel, which can be progressively recruited. Some roboticists have explored this idea in robotic actuators, striving for improvements such as the ability to withstand partial damage, inexpensive repeatability by discrete open loop control and the potential of modular actuators. These systems, however, become rather complex or rely on less widely used actuation techniques such as piezo-actuators or SMAs to produce a compact implementation. This paper presents a novel design of a modular redundant actuation unit which can be combined in various combinations to form compliant actuators with varying characteristics. The actuation unit consists of discretely activated solenoids with an integrated compliant coupling. This paper presents the working principle and the physical implementation in detail. Failure of a single motor unit will merely lead to a loss in performance rather than failure of the actuator. Since each motor unit is discrete, neither power electronics nor control requires analog signals. Isometric experiments display the actuation characteristics and demonstrate the repeatability. The platform can be used in future work to further explore the virtues of exploiting discretization and redundancy in muscle-like control

An Overview of Novel Actuators for Soft Robotics

“…If the elastomeric dielectric polymers were used, the Young's modulus could be around 1 MPa while the material could sustain 380% strain in high electric fields [11]. In a non-traditional approach, a novel actuator for soft-robotics using discrete actuation units to form a muscle-like structure uses the compliance as the enabler for discretization of the muscle units [12]. Another polymer group that are used in SMP structures also have attractive properties in terms of high deformation capacity [13].…”

Characterization of Control-Dependent Variable Stiffness Behavior in Discrete Muscle-Like Actuators

“…An actuation unit is the next step up from a motor unit, and is the reconfigurable unit for the actuator as a whole. A motor unit is defined as the "smallest individually activated force producing device", while the actuation unit is defined as the "smallest building block of the actuator that can be inserted or removed" [2]. Putting these actuation units together into series and parallel bundles results in different arrays and arrangements providing the necessary configuration for the performance requirements of the task (Figure 1).…”

“…Compliance from unit-to-unit must also be a design component in order not to violate physical laws, as shown by Mathijssen et al [2]. By introducing this compliance two things happen, the first is that it makes modeling the actuator very complex as each discrete unit now has an elastic element associated with it, but it also allows for the opportunity to vary the compliance in such a way as to introduce damping-like behavior where there was not before, which will be explained in more detail later on.…”

“…In the design of discrete actuators that are aligned in parallel formations there must be compliance coupling them together in order to adhere to physical laws. See Figure 2 for reference to this concept and read [2,3] for more detail. The SEA was one of the earlier developments made in compliant actuators and provided a platform used as a basis for many of the later designs.…”

Design and Development of Robot Gripper: Shape Memory Alloy Approach

“…Now a days research is done on biometric robotic hand in which we can use shape memoryalloy as actuating muscles. [10,11] …”