in Proceedings of the Royal Society:A, 469: 20120671, Mar 6, 2013
This paper describes flow-relative and flow-aided navigation of a biomimetic underwater vehicle u... more This paper describes flow-relative and flow-aided navigation of a biomimetic underwater vehicle using an artificial lateral line for flow sensing. Most of the aquatic animals have flow sensing organs, but there are no man-made analogues to those sensors currently in use on underwater vehicles. Here, we show that artificial lateral line sensing can be used for detecting hydrodynamic regimens and for controlling the robot’s motion with respect to the flow. We implement station holding of an underwater vehicle in a steady stream and in the wake of a bluff object. We show that lateral line sensing can provide a speed estimate of an underwater robot thus functioning as a short-term odometry for robot navigation. We also demonstrate navigation with respect to the flow in periodic turbulence and show that controlling the position of the robot in the reduced flow zone in the wake of an object reduces a vehicle’s energy consumption.
Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for m... more Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for many underwater tasks. In this paper we implement rheotaxis behaviour in a fish robot, a behaviour common to many aquatic species. We use two pressure sensors on the head of the robot to identify the pressure differences on the left and right side and control the heading of the fish robot by turning a servo-motor actuated tail. The controller is inspired by the Braitenberg vehicle 2b, a simple biological model of tropotaxis, that has been used in many robotic applications. The experiments, conducted in a flow pipe with a uniform flow, show that the robot is able to orient itself, and keep the orientation, to the incoming current. Our results demonstrate that guidance of a fish robot relative to a flow can be implemented as a simple rheotaxis behaviour using two sensors and a Braitenberg 2b controller.
This paper describes a sensing-actuation coupling of a robotic trout that detects changes of the ... more This paper describes a sensing-actuation coupling of a robotic trout that detects changes of the laminar flow speed using an on-board pressure sensor and adjusts its tail-beat frequency for steady swimming. The caudal fin actuator closely mimics the morphology of a real trout, in particular the geometry, stiffness and stiffness distribution of the body and the caudal fin. We hypothesize that the linear relationship between the tail-beat frequency and speed, well-known and proven to hold for all fish studied so far, also holds for an artificial fish. We validate the hypothesis and use the results to derive a linear control law to adjust the tail- beat frequency to the swimming speed. We use an onboard pressure sensor to detect the flow speed and test the actuation in a controlled hydrodynamic environment in a flow pipe.
This paper describes an underwater robot navigation
strategy in flow. Our aim is to demonstrate ... more This paper describes an underwater robot navigation
strategy in flow. Our aim is to demonstrate that knowing
the relative flow speed is advantageous because it permits using
more energy efficient and stable control for trajectory following.
We use a biomimetic robot that moves in uniform flow using
a side-slipping maneuver. Side-slipping permits the robot to
move laterally with respect to the incoming flow by exploiting
its passive dynamics. The side-slipping maneuver is controlled
by adjusting the heading of the robot with respect to the flow.
We implement simple PID controllers for controlling the motion
of the side-slipping robot laterally and transversely. Also, we
compare the performance of the robot in the case where the
robot does not know the flow speed. In this latter case the
robot’s heading towards the waypoint is controlled and the
flow effect is considered as a disturbance compensated by the
control algorithm. Comparative experiments demonstrate that
it is advantageous for a robot to know not just its speed and
orientation with respect to the world’s frame of reference but
also its local flow-relative speed. It permits the robot to follow
trajectories more stable and using less energy. In the discussion
section we propose possible future directions
Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the ... more Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the caudal part of the body is passive and, acting as a carrier of energy, transfers the momentum to the surrounding water. Inspired by those findings we hypothesize that certain swimming patterns can be achieved without copying the distributed actuation mechanism of fish but rather using a single actuator at the anterior part to create the travelling wave. To test the hypothesis a pitching flexible fin made of silicone rubber and silicone foam was designed by copying the stiffness distribution profile and geometry of a rainbow trout. The kinematics of the fin was compared to that of a steadily swimming trout. Fin's propulsive wave length and tail-beat amplitude were determined while it was actuated by a single servo motor. Results showed that the propulsive wave length and tail-beat amplitude of a steadily swimming 50 cm rainbow trout was achieved with our biomimetic fin while stimulated using certain actuation parameters (frequency 2.31 Hz and amplitude 6.6 degrees). The study concluded that fish-like swimming can be achieved by mimicking the stiffness and geometry of a rainbow trout and disregarding the details of the actuation mechanism.
This paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propel... more This paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propelled by a compliant body. The key to the design is the use of a single motor to actuate the compliant body and to generate thrust. The robot has the same geometrical properties of a subcarangiform swimmer with the same length. The design is based on rigid head and fin linked together with a compliant body. The flexible part is modelled as a non-uniform cantilever beam actuated by a concentrated moment. The dynamics of the compliant body are studied and a relationship between the applied moment and the resulting motion is derived. A prototype that implements the proposed approach is built. Experiments on the prototype are done to identify the model parameters and to validate the theoretical modelling
Turbulent flows are often treated as a noisy environment by control algorithms of underwater robo... more Turbulent flows are often treated as a noisy environment by control algorithms of underwater robots. However, aquatic animals such as fish have learned to take advantage of certain unsteady flow. Periodic complex flow, such as that found in the wake of cylinders has been shown to offer energy saving opportunities to fish. We built a fish-like robot with an integrated pressure sensor array housed in the head. The robot can control its tail beat synchronization with respect to the periodic oscillations in the flow behind a cylinder. We show that vortices, represented here by pressure maxima, can be detected and exploited to increase the swimming efficiency of the robot fish while it remains rigidly mounted to a force plate. Force measurements show an efficiency gain of 23% when the tail beat of the robotic fish is synchronized at a particular phase lag.
With the overall goal being a better understanding of the sensing environment from the local pers... more With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Kármán vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Kármán vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Kármán vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Kármán vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Kármán vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors.
This paper presents a self-adapting approach to global level path planning in dynamic environment... more This paper presents a self-adapting approach to global level path planning in dynamic environments. The aim of this work is to minimize risk and delays in possible applications of mobile robots (e.g., in industrial processes). We introduce a hybrid system that uses case-based reasoning as well as grid-based maps for decision-making. Maps are used to suggest several alternative paths between specific start and goal point. The casebase stores these solutions and remembers their characteristics. Environment representation and casebase design are discussed. To solve the problem of exploration vs. exploitation, a decision-making strategy is proposed that is based on the irreversibility of decisions. Forgetting strategies are discussed and evaluated in the context of case-based maintenance. The adaptability of the system is evaluated in a domain based on real sensor data with simulated occupancy probabilities. Forgetting strategies and decision-making strategies are evaluated in simulated environments. Experiments show that a robot is able to adapt in dynamic environments and can learn to use paths that are less risky to follow.
Abstract. This paper presents a global navigation strategy for autonomous mobile robots in large-... more Abstract. This paper presents a global navigation strategy for autonomous mobile robots in large-scale uncertain environments. The aim of this approach is to minimize collision risk and time delays by adapting to the changes in a dynamic environment. The issue of obstacle ...
Abstract This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC... more Abstract This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC) material. The modeling technique is a finite element method (FEM). An applied electric field causes the drift of counterions (eg, Na+), which, in turn, drags water molecules. The mass and charge imbalance inside the polymer is the main cause of the bending motion of the IPMC. The studied physical effects have been considered as time dependent and modeled with FEM. The model takes into account the mechanical ...
Page 1. Nanoporous carbon-based electrodes for high strain ionomeric bending actuators This artic... more Page 1. Nanoporous carbon-based electrodes for high strain ionomeric bending actuators This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 Smart Mater. Struct. 18 095028 (http://iopscience.iop.org/0964-1726/18/9/095028) ...
in Proceedings of the Royal Society:A, 469: 20120671, Mar 6, 2013
This paper describes flow-relative and flow-aided navigation of a biomimetic underwater vehicle u... more This paper describes flow-relative and flow-aided navigation of a biomimetic underwater vehicle using an artificial lateral line for flow sensing. Most of the aquatic animals have flow sensing organs, but there are no man-made analogues to those sensors currently in use on underwater vehicles. Here, we show that artificial lateral line sensing can be used for detecting hydrodynamic regimens and for controlling the robot’s motion with respect to the flow. We implement station holding of an underwater vehicle in a steady stream and in the wake of a bluff object. We show that lateral line sensing can provide a speed estimate of an underwater robot thus functioning as a short-term odometry for robot navigation. We also demonstrate navigation with respect to the flow in periodic turbulence and show that controlling the position of the robot in the reduced flow zone in the wake of an object reduces a vehicle’s energy consumption.
Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for m... more Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for many underwater tasks. In this paper we implement rheotaxis behaviour in a fish robot, a behaviour common to many aquatic species. We use two pressure sensors on the head of the robot to identify the pressure differences on the left and right side and control the heading of the fish robot by turning a servo-motor actuated tail. The controller is inspired by the Braitenberg vehicle 2b, a simple biological model of tropotaxis, that has been used in many robotic applications. The experiments, conducted in a flow pipe with a uniform flow, show that the robot is able to orient itself, and keep the orientation, to the incoming current. Our results demonstrate that guidance of a fish robot relative to a flow can be implemented as a simple rheotaxis behaviour using two sensors and a Braitenberg 2b controller.
This paper describes a sensing-actuation coupling of a robotic trout that detects changes of the ... more This paper describes a sensing-actuation coupling of a robotic trout that detects changes of the laminar flow speed using an on-board pressure sensor and adjusts its tail-beat frequency for steady swimming. The caudal fin actuator closely mimics the morphology of a real trout, in particular the geometry, stiffness and stiffness distribution of the body and the caudal fin. We hypothesize that the linear relationship between the tail-beat frequency and speed, well-known and proven to hold for all fish studied so far, also holds for an artificial fish. We validate the hypothesis and use the results to derive a linear control law to adjust the tail- beat frequency to the swimming speed. We use an onboard pressure sensor to detect the flow speed and test the actuation in a controlled hydrodynamic environment in a flow pipe.
This paper describes an underwater robot navigation
strategy in flow. Our aim is to demonstrate ... more This paper describes an underwater robot navigation
strategy in flow. Our aim is to demonstrate that knowing
the relative flow speed is advantageous because it permits using
more energy efficient and stable control for trajectory following.
We use a biomimetic robot that moves in uniform flow using
a side-slipping maneuver. Side-slipping permits the robot to
move laterally with respect to the incoming flow by exploiting
its passive dynamics. The side-slipping maneuver is controlled
by adjusting the heading of the robot with respect to the flow.
We implement simple PID controllers for controlling the motion
of the side-slipping robot laterally and transversely. Also, we
compare the performance of the robot in the case where the
robot does not know the flow speed. In this latter case the
robot’s heading towards the waypoint is controlled and the
flow effect is considered as a disturbance compensated by the
control algorithm. Comparative experiments demonstrate that
it is advantageous for a robot to know not just its speed and
orientation with respect to the world’s frame of reference but
also its local flow-relative speed. It permits the robot to follow
trajectories more stable and using less energy. In the discussion
section we propose possible future directions
Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the ... more Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the caudal part of the body is passive and, acting as a carrier of energy, transfers the momentum to the surrounding water. Inspired by those findings we hypothesize that certain swimming patterns can be achieved without copying the distributed actuation mechanism of fish but rather using a single actuator at the anterior part to create the travelling wave. To test the hypothesis a pitching flexible fin made of silicone rubber and silicone foam was designed by copying the stiffness distribution profile and geometry of a rainbow trout. The kinematics of the fin was compared to that of a steadily swimming trout. Fin's propulsive wave length and tail-beat amplitude were determined while it was actuated by a single servo motor. Results showed that the propulsive wave length and tail-beat amplitude of a steadily swimming 50 cm rainbow trout was achieved with our biomimetic fin while stimulated using certain actuation parameters (frequency 2.31 Hz and amplitude 6.6 degrees). The study concluded that fish-like swimming can be achieved by mimicking the stiffness and geometry of a rainbow trout and disregarding the details of the actuation mechanism.
This paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propel... more This paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propelled by a compliant body. The key to the design is the use of a single motor to actuate the compliant body and to generate thrust. The robot has the same geometrical properties of a subcarangiform swimmer with the same length. The design is based on rigid head and fin linked together with a compliant body. The flexible part is modelled as a non-uniform cantilever beam actuated by a concentrated moment. The dynamics of the compliant body are studied and a relationship between the applied moment and the resulting motion is derived. A prototype that implements the proposed approach is built. Experiments on the prototype are done to identify the model parameters and to validate the theoretical modelling
Turbulent flows are often treated as a noisy environment by control algorithms of underwater robo... more Turbulent flows are often treated as a noisy environment by control algorithms of underwater robots. However, aquatic animals such as fish have learned to take advantage of certain unsteady flow. Periodic complex flow, such as that found in the wake of cylinders has been shown to offer energy saving opportunities to fish. We built a fish-like robot with an integrated pressure sensor array housed in the head. The robot can control its tail beat synchronization with respect to the periodic oscillations in the flow behind a cylinder. We show that vortices, represented here by pressure maxima, can be detected and exploited to increase the swimming efficiency of the robot fish while it remains rigidly mounted to a force plate. Force measurements show an efficiency gain of 23% when the tail beat of the robotic fish is synchronized at a particular phase lag.
With the overall goal being a better understanding of the sensing environment from the local pers... more With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Kármán vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Kármán vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Kármán vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Kármán vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Kármán vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors.
This paper presents a self-adapting approach to global level path planning in dynamic environment... more This paper presents a self-adapting approach to global level path planning in dynamic environments. The aim of this work is to minimize risk and delays in possible applications of mobile robots (e.g., in industrial processes). We introduce a hybrid system that uses case-based reasoning as well as grid-based maps for decision-making. Maps are used to suggest several alternative paths between specific start and goal point. The casebase stores these solutions and remembers their characteristics. Environment representation and casebase design are discussed. To solve the problem of exploration vs. exploitation, a decision-making strategy is proposed that is based on the irreversibility of decisions. Forgetting strategies are discussed and evaluated in the context of case-based maintenance. The adaptability of the system is evaluated in a domain based on real sensor data with simulated occupancy probabilities. Forgetting strategies and decision-making strategies are evaluated in simulated environments. Experiments show that a robot is able to adapt in dynamic environments and can learn to use paths that are less risky to follow.
Abstract. This paper presents a global navigation strategy for autonomous mobile robots in large-... more Abstract. This paper presents a global navigation strategy for autonomous mobile robots in large-scale uncertain environments. The aim of this approach is to minimize collision risk and time delays by adapting to the changes in a dynamic environment. The issue of obstacle ...
Abstract This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC... more Abstract This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC) material. The modeling technique is a finite element method (FEM). An applied electric field causes the drift of counterions (eg, Na+), which, in turn, drags water molecules. The mass and charge imbalance inside the polymer is the main cause of the bending motion of the IPMC. The studied physical effects have been considered as time dependent and modeled with FEM. The model takes into account the mechanical ...
Page 1. Nanoporous carbon-based electrodes for high strain ionomeric bending actuators This artic... more Page 1. Nanoporous carbon-based electrodes for high strain ionomeric bending actuators This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 Smart Mater. Struct. 18 095028 (http://iopscience.iop.org/0964-1726/18/9/095028) ...
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The caudal fin actuator closely mimics the morphology of a real trout, in particular the geometry, stiffness and stiffness distribution of the body and the caudal fin. We hypothesize that the linear relationship between the tail-beat frequency and speed, well-known and proven to hold for all fish studied so far, also holds for an artificial fish. We validate the hypothesis and use the results to derive a linear control law to adjust the tail- beat frequency to the swimming speed. We use an onboard pressure sensor to detect the flow speed and test the actuation in a controlled hydrodynamic environment in a flow pipe.
strategy in flow. Our aim is to demonstrate that knowing
the relative flow speed is advantageous because it permits using
more energy efficient and stable control for trajectory following.
We use a biomimetic robot that moves in uniform flow using
a side-slipping maneuver. Side-slipping permits the robot to
move laterally with respect to the incoming flow by exploiting
its passive dynamics. The side-slipping maneuver is controlled
by adjusting the heading of the robot with respect to the flow.
We implement simple PID controllers for controlling the motion
of the side-slipping robot laterally and transversely. Also, we
compare the performance of the robot in the case where the
robot does not know the flow speed. In this latter case the
robot’s heading towards the waypoint is controlled and the
flow effect is considered as a disturbance compensated by the
control algorithm. Comparative experiments demonstrate that
it is advantageous for a robot to know not just its speed and
orientation with respect to the world’s frame of reference but
also its local flow-relative speed. It permits the robot to follow
trajectories more stable and using less energy. In the discussion
section we propose possible future directions
The caudal fin actuator closely mimics the morphology of a real trout, in particular the geometry, stiffness and stiffness distribution of the body and the caudal fin. We hypothesize that the linear relationship between the tail-beat frequency and speed, well-known and proven to hold for all fish studied so far, also holds for an artificial fish. We validate the hypothesis and use the results to derive a linear control law to adjust the tail- beat frequency to the swimming speed. We use an onboard pressure sensor to detect the flow speed and test the actuation in a controlled hydrodynamic environment in a flow pipe.
strategy in flow. Our aim is to demonstrate that knowing
the relative flow speed is advantageous because it permits using
more energy efficient and stable control for trajectory following.
We use a biomimetic robot that moves in uniform flow using
a side-slipping maneuver. Side-slipping permits the robot to
move laterally with respect to the incoming flow by exploiting
its passive dynamics. The side-slipping maneuver is controlled
by adjusting the heading of the robot with respect to the flow.
We implement simple PID controllers for controlling the motion
of the side-slipping robot laterally and transversely. Also, we
compare the performance of the robot in the case where the
robot does not know the flow speed. In this latter case the
robot’s heading towards the waypoint is controlled and the
flow effect is considered as a disturbance compensated by the
control algorithm. Comparative experiments demonstrate that
it is advantageous for a robot to know not just its speed and
orientation with respect to the world’s frame of reference but
also its local flow-relative speed. It permits the robot to follow
trajectories more stable and using less energy. In the discussion
section we propose possible future directions