A Design Concept and Kinematic Model for a Soft Aquatic Robot with Complex Bio-mimicking Motion

Abstract

Fish mortality assessments for turbine passages are currently performed by live-animal testing with up to a hundred thousand fish per year in Germany. A propelled sensor device could act as a fish surrogate. In this context, the study presented here investigates the state of the art via a thorough literature review on propulsion systems for aquatic robots. An evaluation of propulsion performance, weight, size and complexity of the motion achievable allows for the selection of an optimal concept for such a fish mimicking device carrying the sensors. In the second step, the design of a bioinspired soft robotic fish driven by an unconventional drive system is described. It is based on piezoceramic actuators, which allow for motion with five degrees of freedom (DOF) and the creation of complex bio-mimicking body motions. A kinematic model for the motion’s characteristics is developed, to achieve accurate position feedback with the use of strain gauges. Optical measurements validate the complex deformation of the body and deliver the basis for the calibration of the kinematic model. Finally, it can be shown, that the calibrated model presented allows the tracking of the deformation of the entire body with an accuracy of 0.1 mm.

On the influence of head motion on the swimming kinematics of robotic fish

“…A maximum deflection of 100 mm were achieved with the robot in air as the surrounding fluid. The deformation was determined with optical measurements using a high speed recordings and deformation tracking based on image segmentation, as shown in Abbaszadeh et al [25]. However, the maximum tail deflection is expected to be significantly lower in water as a result of the higher hydrodynamic loads from its 800 fold higher fluid density.…”

“…In total, this leads to a five freely adjustable parameters for the propulsion control. A more detailed description of the actuation system and its control system, as well as for the kinematic model, can be found in [25].…”

“…For the design of small, neutrally buoyant fish robots with good swimming capacities, conventional design approaches based on electromagnetic actuators were found to be inadequate because of their relative weight by Abbaszadeh et al [25]. Different unconventional approaches such as piezoelectric based actuators, also called micro fiber composites (MFCs), introduced by [26][27][28][29], as well as dielectric elastomer actuators presented by [30,31] promise to allow for higher actuation power densities under those constraints.…”

Biomimetic Soft Underwater Robot Inspired by the Red Muscle and Tendon Structure of Fish

“…Soft material robots include robots with a motor and a soft body [ 7 ], robots with a motor/wire mechanism and a soft body [ 8 , 9 , 10 ], and robots with a tensegrity mechanism that allows the rigidity of the body to be set to an arbitrary value at each body length position [ 11 , 12 ]. Meanwhile, robots have been developed using soft actuators such as pneumatic and hydrodynamic actuators that deform by fluid pressure [ 13 , 14 ]; shape memory alloys (SMA) that shorten by heating [ 15 , 16 , 17 , 18 ]; and piezoelectric composite fiber [ 19 ], dielectric elastomer actuators (DEA) [ 20 , 21 ], and hydraulically amplified self-healing electrostatic (HASEL) actuators [ 22 ] that deform by applying a voltage.…”

Variable Curvature Modeling Method of Soft Continuum Robots with Constraints

“…However, continuum robots have a theoretically infinite number of degrees of freedom (DOF), and this high flexibility allows complex deformations of the robot in response to external forces and po-sitional constraints. Therefore, the accurate and efficient modelling of continuum robots with external force remains challenging [17][18][19].…”