Continuum robot surfaces are inherently well suited for the creation and adaptation of seat and saddle shapes. They are inherently compact and self-contained, being created by embedding artificial muscles within their bodies, in carefully designed arrangements according to the anticipated functionality of the resulting surface. The core surface body element can be selected from materials varying over a wide range of stiffness, which can be biased in different directions to match the design con- straints (Merino et al.2012). The embedded internal muscles shape the surface by contracting and elongating, inducing both stretching and bending in the body core.
This approach could be implemented via a surface with one dimensional shape variability, using a single embedded muscle. In this design the single actuator is routed through the middle of a surface (the muscle would be along the line attaining the greatest height). Lines parallel to the muscle would represent“virtual muscles”, and would represent intermediate effects of the coupling between the muscle length and surface body stiffness. Depending on the level of forces and complexity of overall shapes required, some of these virtual muscles could be implemented as physical muscle actuators.
Modeling of these surfaces is relatively straightforward (Merino et al. 2012).
Since the overall surface shape is the direct result of the influence of the (known) Fig. 5 Use of the horn on Western saddle to increase rider stability
Continuum Robot Surfaces: Smart Saddles and Seats 103
shape of the actuators embedded in it, direct interpolation of the actuator shape information can be used to accurately model the surface shape.
For example, for the muscle arrangement in the surface described above, the x and y values of the shape can be modeled by:
x(s)ẳ Z
ymins
sin Zr
k vð ịdv 0
@
1 Adr
y(s)ẳ ymin Z
ymins
cos Zr
k vð ịdv 0
@
1 Adr 0
@
1 A
ð1ị
where the lower limits of all integrals are 0,sis the arc length along the surface muscle,x(s) is orthogonal to the muscle direction (diagonally left to right down- wards), andy(s) (vertical infigure) is the“height”of the surface. The variablekis the curvature of the muscle, and the constant ymin is the minimum height. The values of the intermediate values, between the muscle and the surface exterior, can be found by suitable interpolation functions fork(Merino et al.2012).
The resulting overall (continuous) shape of the example above would be gen- erally in the shape of a saddle. The “horn”could be actively reshaped by simple expansion and contraction of the embedded actuator. It can be made more or less pronounced by pre-biasing the stiffness and shape of the core surface material. This simple single actuator design thus can be made to smoothly adjust between the
“Western”and “English”saddle shapes.
In practical robot saddle hardware, the longitudinal muscle(s) underlying the above examples can be augmented with interleaved lateral muscles, to allow the saddle to actively adjust its curvature across the back of the horse, to produce a betterfit for a given horse, and the ability for the saddle tofit different horses.
We are currently experimenting with physical prototypes exploring this design space. We are exploring the use of small pneumatic (McKibben) artificial muscles embedded within the saddle surface structure, in a pattern inspired by the veins of leaves. The muscles can be supplied via a small pressurized cylinder embedded in the base of the saddle. Control of these muscles can be achieved via simple voltage control of commercial pressure regulators. The results of our ongoing research will be reported in future papers.
4 Conclusions
Robot surfaces which conform to the human body and adapt their shape according to the needs of human activities could revolutionize aspects of leisure and health- care. The recent emergence of continuum robotics offers a new form of inherently safe and continuously deformable robot surface, offering a new form of intimate
104 I.D. Walker
human/robot interaction. In this paper, we have presented a new concept for robotic saddles and seats based on continuum robot surfaces. Possible future applications include active wound dressings and robotic physical therapy aids.
Acknowledgments The work in this paper was supported in part by the U.S. National Science Foundation under grant IIS-1527165. The author would like to thank the members of Scott Hills Equestrian Center, and in particular Uma and Wasabi, for their advice and expertise, which was very helpful in the preparation of this paper.
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Threatt, A. L., Merino, J., Green, K. E., & Walker, I. D. (2014). An assistive robotic table for older and post-stroke adults: Results from participatory design and evaluation activities with clinical staff. InProceedings of CHI 2014: The ACM Conference on Human Factors in Computing Systems(pp. 673–682), Toronto, Ontario, Canada.
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Continuum Robot Surfaces: Smart Saddles and Seats 105
Structural Parameter Identi fi cation of a Small Robotic Underwater Vehicle
Martin Langmajer and LukášBláha
Abstract This paper deals with estimating structural parameters of robotic underwater vehicle (submarine) that cannot be easily measured and determined analytically. The robotic submarine was designed for visual inspection and ultra- sonic testing of submerged technologies such as tanks with slowlyflowing liquid.
The identification procedure contains two strategies which are able to find the structural, especially hydrodynamic parameters of a given model. These parameters are then used for stability and motion control design. The validation of gained model parameters was verified in software Simulink/SimMechanics, where the outputs of the model were compared with vehicle prototype responses.
Keywords Parameter identification ROV/AUV Hydrodynamic coefficients
Motion controlModel based design
1 Introduction
Research of submerged vehicles has a long history. Especially in recent years the underwater unmanned vehicles have received new attention that comes from advanced technologies and growing industry (Christ and Wernli 2007; Inzartsev 2009). Underwater unmanned vehicles (UUV) can be divided into autonomous underwater vehicles (AUV) and remotely operated vehicles (ROV). These vehicles are mostly small submersible technologies, designed for specific applications.
Structural configuration and possibility of utilization are mostly very different from traditional submarines.
An accurate dynamic model is a crucial part of designing a stable, controllable and autonomous robotic system. However, the modeling of submerged system dynamics is full of nonlinearities and uncertainties. Moreover the hydrodynamic
M. Langmajer (&)L. Bláha
Department of Cybernetics, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic e-mail: mlangos3@gmail.com
©Springer International Publishing Switzerland 2017
D. Zhang and B. Wei (eds.),Mechatronics and Robotics Engineering for Advanced and Intelligent Manufacturing, Lecture Notes
in Mechanical Engineering, DOI 10.1007/978-3-319-33581-0_9
107
effects are often coupled between individual degrees of freedom, see Fossen (1994).
Therefore it seems very natural to design a submerged robotic vehicle as symmetric as possible and use an overactuated control strategy. This ensures that matrices of parameters of model can be considered as diagonal matrices and that the system is completely controllable and robust to parametric uncertainties.
This paper deals with estimating structural parameters of a robotic underwater vehicle that cannot be easily measured and determined analytically (Ovalle et al.
2011). The vehicle is designed as a neutrally buoyant rigid body with wheeled platform containing the phased array probe for weld testing, see Fig.1. The rest of the paper will focus on mathematical modeling and parameter identification of vehicle itself. The key part of modeling is to get a qualitatively good model, respecting all the major aspects of kinematics and dynamics, important to design of stable motion control.
In general, the identification techniques can be split into experimental techniques and into methods based on strip theory or computationalfluid dynamics. This paper uses the strategy of experimental techniques.
2 Mathematical Model
The underwater vehicle is highly nonlinear complex system. Nevertheless for a streamlined vehicle, slowly floating in non-flowing liquid, we can make some standard simplifications, as mentioned by Chen (2007) or Wang (2007).
The vehicle is assumed to have almost rounded cubic shape, symmetrical about all principal axes. The velocity of the vehicle is low enough making the vortex shedding not dominant and viscous effects can be modeled as a drag in form of linear or quadratic damping. The added mass and added inertia matrices are hard to identify in whole complexity, but it could be relatively easy to make some experimental measurement to get diagonal terms of these simplified parameters.
Moreover, the stabilizing control law will then be less dependent on such poorly Fig. 1 Schematic representation of an underwater vehicle and corresponding real prototype
108 M. Langmajer and L. Bláha
known parameters. All inaccuracies are modeled as external forces, which are subject of identification.