S. M. Hadi Sadati

Stiffness Control of Soft Robotic Manipulator for Minimally Invasive Surgery MIS Using Scale Jamming

Continuum and soft robotics showed many applications in medicine from surgery to health care where their compliant nature is advantageous in minimal invasive interaction with organs. Stiffness control is necessary for challenges with soft robots such as minimalistic actuation, less invasive interaction, and precise control and sensing. This paper presents an idea of scale jamming inspired by fish and snake scales to control the stiffness of continuum manipulators by controlling the Coulomb friction force between rigid scales. A low stiffness spring is used as the backbone for a set of round curved scales to maintain an initial helix formation while two thin fishing steel wires are used to control the friction force by tensioning. The effectiveness of the design is showed for simple elongation and bending through mathematical modelling, experiments and in comparison to similar research. The model is tested to control the bending stiffness of a STIFF-FLOP continuum manipulator module designed for surgery.

A geometry deformation model for compound continuum manipulators with external loading

The complexity of soft continuum manipulators with hybrid and tuneable structures poses a challenging task to achieve an inverse kinematics model which is both precise and computationally efficient for control and optimization purposes. In this paper, a new method based on the principle of virtual work and a geometry deformation approach is presented for the inverse kinematics model of the STIFF-FLOP arm which is a pneumatically actuated continuum manipulator. We propose a novel simplified and computationally efficient yet accurate analytical solution to analyse the static behaviour of a compound soft manipulator in the presence of external and body forces which is verified against experimental data, showing promising agreement with 10% mean error for planar movements. In the process, we present a new modelling approach for braided soft extensor actuators with no braid-surface relative slip constraint. For the first time, our model predicts a simple analytical solution for the cross section deformation which is essential to control soft manipulators with regional tunable stiffness structure.

A Geometry Deformation Model for Braided Continuum Manipulators

Continuum manipulators have gained significant attention in the robotic community due to their high dexterity, deformability and reachability. Modeling of such manipulators has been shown to be very complex and challenging. Despite many research attempts, a general and comprehensive modeling method is yet to be established. In this paper, for the first time, we introduce the bending effect in the model of a braided extensile pneumatic actuator with both stiff and bendable threads. Then, the effect of the manipulator cross section deformation on the constant curvature and variable curvature models is investigated using simple analytical results from a novel geometry deformation method and is compared to experimental results. We achieve 24% simulation accuracy using our constant curvature model for a braided continuum manipulator in presence of body load and 10% error using our variable curvature model in presence of extensive external loads. With proper model assumptions and taking to account the cross section deformation, an 8-20% increase in the simulation accuracy is achieved compared to a fixed cross section model. The presented models can be used for the exact modeling and design optimization of compound continuum manipulators by providing an analytical tool for the sensitivity analysis of the manipulator performance. Our main aim is the application in minimal invasive manipulation with limited workspaces and manipulators with regional tuneable stiffness in their cross section.

Mechanics of continuum manipulators, a comparative study of five methods with experiments

Investigations on control and optimization of continuum manipulators have resulted in a number of kinematic and dynamic modeling approaches each having their own advantages and limitations in various applications. In this paper, a comparative study of five main methods in the literature for kinematic, static and dynamic modeling of continuum manipulators is presented in a unified mathematical framework. The five widely used methods of Lumped system dynamic model, Constant curvature, two-step modified constant curvature, variable curvature Cosserat rod and beam theory approach, and series solution identification are re-viewed here with derivation details in order to clarify their methodological differences. A comparison between computer simulations and experimental results using a STIFF-FLOP continuum manipulator is presented to study the advantages of each modeling method.

Control Space Reduction and Real-Time Accurate Modeling of Continuum Manipulators Using Ritz and Ritz–Galerkin Methods

To address the challenges with real-time accurate modeling of multisegment continuum manipulators in the presence of significant external and body loads, we introduce a novel series solution for variable-curvature Cosserat rod static and Lagrangian dynamic methods. By combining a modified Lagrange polynomial series solution, based on experimental observations, with Ritz and Ritz–Galerkin methods, the infinite modeling state space of a continuum manipulator is minimized to geometrical position of a handful of physical points (in our case two). As a result, a unified easy to implement vector formalism is proposed for the nonlinear impedance and configuration control. We showed that by considering the mechanical effects of highly elastic axial deformation, the model accuracy is increased up to 6%. The proposed model predicts experimental results with 6%–8% (4–6 mm) mean error for the Ritz–Galerkin method in static cases and 16%–20% (12–14 mm) mean error for the Ritz method in dynamic cases, in planar and general three-dimensional motions. Comparing to five different models in the literature, our approximate solution is shown to be more accurate with the smallest possible number of modeling states and suitable for real-time modeling, observation, and control applications.

Toward Computing with Spider Webs: Computational Setup Realization

Spiders are able to extract crucial information, such as the location prey, predators, mates, and even broken threads from propagating web vibrations. The complex structure of the web suggests that the morphology itself might provide computational support in form of a mechanical signal processing system - often referred to as morphological computation. We present preliminary results on identifying these computational aspects in naturally spun webs. A recently presented definition for physical computational systems, consisting of three main elements: (i) a mathematical part, (ii) a computational setup with a theoretical and real part, and (iii) an interpretation, is employed for the first time, to characterize these morphological computation properties. Signal transmission properties of a real spider orb web, as the real part of a morphological computation setup, is investigated in response to step transverse inputs. The parameters of a lumped system model, as the theoretical part of a morphological computation setup, are identified empirically and with the help of an earlier FEM model for the same web. As the possible elements of a computational framework, the web transverse signal filtering, attenuation, delay, memory effect, and deformation modes are briefly discussed based on experimental data and numerical simulations.

Singularity-free planning for a robot cat free-fall with control delay: Role of limbs and tail

Cat free fall righting maneuverer has inspired many aerial, space and legged robotic research. Conservation of angular momentum principle is used to derive the inverse differential kinematic and TMT vector form dynamics of the motion for three robotic models: a two-link model, a three-link model with tail, and a comprehensive eight-link model with the addition of legs. The path planning problem in the presence of geometric and kinematic constraints is addressed using a novel singularity free single shooting optimization method. While a 2 DOF torso is sufficient to perform a full maneuver, the addition of the tail reduces the time and increases the maneuverability despite the leg motions that has adverse effects. The method performance is investigated numerically and a simulation in MSC.ADAMS software is used to verify the results. The structural parameters are optimized showing the significant advantageous of a light and symmetric body shape. A prototype will be fabricated based on these results in near future.

A bio-inspired electro-active Velcro mechanism using Shape Memory Alloy for wearable and stiffness controllable layers

Smart attachment mechanisms are believed to contribute significantly in stiffness control of soft robots. This paper presents a working prototype of an active Velcro based stiffness controllable fastening mechanism inspired from micro active hooks found in some species of plants and animals. In contrast to conventional passive Velcro, this active Velcro mechanism can vary the stiffness level of its hooks to adapt to external forces and to maintain the structure of its supported layer. The active hooks are fabricated using Shape Memory Alloy (SMA) wires which can be actuated using Lenz-Joule heating technique via thermo-electric manipulation. In this paper, we show experimental results for the effects of active SMA Velcro temperature, density and number on the attachment resisting force profile in dynamic displacement. We aim to provide new insights into the novel design approach of using active hook systems to support future implementation of active velcro mechanisms for fabrication of wearable stiffness controllable thin layers.