Archived project

Integrable Stiffening Interfaces for Soft Robots

Goal: 1. Bio-inspired helical scale jamming interface as a friction based interlocking design for stiffness regulation and impedance control of soft structures
2. 3D printable thermoactive helical interface as an interlocking stiffening design
3. Thermoactive SMA Velcro design for wearable layer jamming

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Project log

S.M.Hadi Sadati
added a research item
As it was discussed in previous chapters of Part I, soft continuum trunk and tentacle manipulators have high inherent dexterity and reconfigurability and have become an attractive candidate for safe manipulation and explorations in surgical and space robotic applications, recently. However, achieving accuracy in precise tasks is a challenge with these highly flexible structures , for which stiffness variable designs based on jamming, smart material, antagonistic actuation, and morphing structures have been introduced in the recent years. In this chapter, variable stiffness properties of an electro-active poly (sodium acrylate) (pNaAc) hydrogel are tested. An anisotropic stiffness ion pattern is printed on the hydrogel straps giving them shape memory properties. The hydrogel swells up to two times its original size and soften (4.2-0 KN/m) in an ethanol aquatic solution depending on the ethanol saturation while preserving its programmed shape. Changing the solution ethanol saturation can be used to control the hydrogel stiffness based of which a conceptual design for a stiffness controllable STIFF-FLOP module is presented and will be fabricated in the future. 79
S.M.Hadi Sadati
added a research item
The book was inadvertently published with an incorrect version of an author’s name in Chapter 13 as “Althoefer Kaspar” whereas it has been updated as “Kaspar Althoefer”.
S.M.Hadi Sadati
added a research item
Inspired by teleost fish scale, this paper investigates the possibility of implementing stiffness control as a new source of robots dexterity and flexibility control. Guessing about the possibility of biological scale jamming in real fish, we try to understand the possible underlying actuation mechanism of such behavior by conducting experiments on a Cyprinus carpio fish skin sample. Bulking tests are carried out on an encapsulated skin sample, in thin latex rubber, for unjammed and vacuum jammed cases. For the first time, we observed biological scale jamming with very small hysteresis due to the unique scale morphology and jammed stacking formation. We call this unique feature "Geometrical Jamming" where the resisting force is due to the stacking formation rather than the interlocking friction force. Inspiring by this unique morphology and helical arrangement of the scale, in this research, we investigate different possible design and actuation mechanisms for an integrable scale jamming interface for stiffness control of continuum manipulators. A set of curved scales are 3D printed which maintain a helix formation when are kept in place and jammed with two thin fishing steel wires. The non-self locking jagged contact surfaces replicate inclined stacking formation of the jammed fish scale resulting in the same reversible low hysteresis characteristics, in contrast to the available interlocking designs. The effectiveness of the designs are shown for uniaxial elongation experiments and the results are compared with similar research. The contact surfaces, in our design, can be lubricated for further hysteresis reduction to achieve smooth, repeatable and accurate stiffness control in dynamic tasks.
S.M.Hadi Sadati
added a research item
We present a 3D-printable thermoactive scale jamming interface as a new way to control a continuum manipulator dexterity by taking inspiration from the helical arrangement of fish scales. A highly articulated helical interface is 3D-printed with thermoactive functionally graded joints using a conventional 3D printing device that utilizes UV curable acrylic plastic and hydroxylated wax as the primary and supporting material. The joint compliance is controlled by regulating wax temperature in phase transition. Empirical feed-forward control relations are identified through comprehensive study of the wax melting profile and actuation scenarios for different shaft designs to achieve desirable repeatability and response time. A decentralized control approach is employed by relating the mathematical terms of the Cosserat beam method to their morphological counterparts in which the manipulator local anisotropic stiffness is controlled based on the local stress and strain information. As a result, a minimalistic central controller is designed in which the joints' thermo-mechanical states are observed using a morphological observer, an external fully monitored replica of the observed system with the same inputs. Preliminary results for passive shape adaptation, geometrical disturbance rejection and task space anisotropic stiffness control are reported by integrating the interface on a continuum manipulator.
S.M.Hadi Sadati
added a research item
We present a 3D-printable thermoactive scale jamming interface as a new way to control a continuum manipulator dexterity by taking inspiration from the helical arrangement of fish scales. A highly articulated helical interface is 3D-printed with thermoactive functionally graded joints using a conventional 3D printing device that utilizes UV curable acrylic plastic and hydroxylated wax as the primary and supporting material. The joint compliance is controlled by regulating wax temperature in phase transition. Empirical feed-forward control relations are identified through comprehensive study of the wax melting profile and actuation scenarios for different shaft designs to achieve desirable repeatability and response time. A decentralized control approach is employed by relating the mathematical terms of the Cosserat beam method to their morphological counterparts in which the manipulator local anisotropic stiffness is controlled based on the local stress and strain information. As a result, a minimalistic central controller is designed in which the joints' thermo-mechanical states are observed using a morphological observer, an external fully monitored replica of the observed system with the same inputs. Preliminary results for passive shape adaptation, geometrical disturbance rejection and task space anisotropic stiffness control are reported by integrating the interface on a continuum manipulator.
S.M.Hadi Sadati
added a project reference
S.M.Hadi Sadati
added a project goal
1. Bio-inspired helical scale jamming interface as a friction based interlocking design for stiffness regulation and impedance control of soft structures
2. 3D printable thermoactive helical interface as an interlocking stiffening design
3. Thermoactive SMA Velcro design for wearable layer jamming
 
S.M.Hadi Sadati
added 3 research items
We investigate how unmanned aerial vehicles (UAVs) with flexible wings can be designed to exploit the aeroelasticity of wing deformation that is present in bat wings, with a view to improve the efficiency of flight. We constructed a robotic bat wing with fully passive elastic wing-folding properties. The robotic wing is powered by a gearbox running two synchronised motors, effectively providing one degree of motion: the upstroke and down-stroke of the wing. Through numerical simulations and setup experiments, we observed that by integrating a span-wise elastic network into the bat wing, we were able to achieve passive wing-folding that mimics the 8-shape wing-folding seen in bats' high speed flight. This way, we were able to reduce the complexity and additional actuation associated with wing-folding in a robotic wing.
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.
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.