Research

IndexFigure2

Monolithic systems lab creates synthesis, analysis and manufacturing tools for soft mechanical systems, compliant mechanisms and in general any device that deforms. Traditional machines with rigid links, joints and heavy actuators are designed using centuries-old knowledge often marked by a systems approach where kinematics, actuation and passive elements are decoupled. In contrast, bio-inspired soft mechanical systems have inherently coupled behavior, and extracting design methods pose a unique challenge.

We rely on design insight rather than purely computational techniques to tackle these challenges. Our hypothesis is that the design of physical systems such as soft and compliant mechanical systems can be insightful by the right representation of their physics. Our research makes fundamental advances in mechanics-based representation of soft and compliant mechanisms so that they are useful to design. We apply the design insight to several novel and practical applications in manipulation, wearable devices, locomotion and mechanical Metamaterials. Since our interest in design tools is domain specific, we are involved in the complete design cycle: conceptual design, embodiment design, prototyping, control, and testing. Our research can be broadly divided into (a) Mechanics-based modeling tools and (b) Application of these tools in products and other real world applications.

Please read on to understand past and current projects.


Mechanics-Based Modeling and Design Tools for Soft Robots


Current Projects:

Generative design methodology for soft robots

Bio-inspired shape adaptive structures combining compliant actuators and passive members in a spatial or planar mesh have demonstrated success in shape morphing applications, design of soft robotic backbones, exoskeletons, etc. The design of such networks has been traditionally posed as multi-material topology optimization, which leaves little scope for a thorough exploration of the design space. There has been growing interest in implementing generative methods for mechanism synthesis and mechanical design to explore the design space better and generate multiple feasible solutions to address one or more design objectives. Generative design methods ranging from graph enumeration to modern advancements including GANs have shown promise in mechanical design. We are leveraging some of these core ideas and bio-inspiration based on bipennate musculature to develop an enumeration-based generative framework for designing shape-adaptive structures for application in compliant mechanisms and meshed soft robots.

Personnel: Sabyasachi Dash

 


Modeling and Control of Soft Continuum Actuators

Controlling soft actuators, such as the BR2, presents many challenges.  With infinite degrees of freedom and only two actuations, it is common to create simplified models of the soft actuator.  

This work uses a constant curvature and torsion model to approximate the shape of the BR2.  By working in the configuration space, the developed control method are invariant to the specific properties of the BR2.  An additional degree of freedom was added in the form of a rotating base.  This allows the arm to reach the same point in space in different orientations. Control of the arm begins with a feed-forward step that attempts to determine the configuration that most closely matches the goal pose.  Due to inaccuracies in the configuration to the actuation map, a corrective loop is used to achieve the desired configuration.  Once the desired configuration is achieved, there may still be an error due to model approximations.  This error is reduced using a task space feedback loop until the desired error tolerance is achieved.

Personnel: Ben Walt, Arushi Tiwari


Modeling and Control of Dual Continuum Arms

The inherent compliance of soft arms introduces the concept of “cooperative robotics,” which involves using one or more soft arms to assist others in completing a task. A similar approach in traditional rigid robotic arms is both catastrophic and redundant due to the lack of compliance, leading to potential damage to the arm. Assistive robotic arms seek to improve common drawbacks of soft arms: weak manipulation forces, limited workspace, and a lack of possible configurations for a desired endpoint. Incorporating traditional rigid actuators can further improve these drawbacks by providing the necessary assistance outside the operating area of the continuum arms. Simplifying the modeling methodology can provide fast dynamic configurations of the cooperative arms in a simulated environment; allowing for analysis and control of a large design space.

Personnel: John Golden, James Nam, Everett Wang

 


Design of Continuum Compliant Manipulators

The design, modeling, and control of tendon-driven continuum robots have been well studied, with a plethora of methods devised for understanding their behavior. We are primarily focused on exploring design methods for improving the task space and effective manipulation of the robots in clustered environments. Some of the focus areas include optimal routing of the cables, selective stiffening of segments of the robot, and exploiting axial twisting of the backbone in parallel routing manipulators. In addition, other higher-fidelity modeling methods with minimal assumptions are being explored.

Personnel: Sabyasachi Dash, John Golden


Grasp State Classification in Agricultural Manipulation

The agricultural setting poses additional challenges for robotic manipulation, as fruit is firmly attached to plants and the environment is cluttered and occluded. Therefore, accurate feedback about the grasp state is essential for effective harvesting. This study examines the different states involved in fruit picking by a robot, such as successful grasp, slip, and failed grasp, and develops a learning-based classifier using low-cost, computationally light sensors (IMU and IR reflectance). The Random Forest multi-class classifier accurately determines the current state and along with the sensors can operate in the occluded environment of a plant. The classifier was successfully trained and tested in the lab and showed 100% success at identifying slip and grasp failure and 80% success identifying successful picks on a real cherry tomato plant. By using this classifier, corrective actions can be planned based on the current state, thus leading to more efficient fruit harvesting.

Personnel: Ben Walt

 


Past Projects:

Analysis and Synthesis of Fiber-Reinforced Elastomeric Enclosures

We investigate the fundamental building blocks for soft mechanical systems known as the Fiber Reinforced Elastomeric Enclosure (FREEs). Fiber Reinforced Elastomeric Enclosures (FREEs) and are based in design and construction to the popular Pneumatic Artificial Muscles (PAM) or McKibben actuators. They constitute a hollow elastomeric core on which two families of helical fibers are reinforced. While in PAMs and their composite variants the two families of fibers are antisymmetric (see Figure below), FREEs permit arbitrary variation of fiber orientations. This not only broadens the design space, but also enables several spatial motion patterns that are otherwise unattainable with conventional actuators. To create knowledge on using FREEs for different applications, we require systematic modeling and analysis tools.

In this project, we are inspired by inflatables such as balloons and bellows that tend to maximize their enclosed volume subject to constraints imposed by seams. In FREEs these constraints can be due to the inextensibility of fibers.

Personnel: Gaurav Singh, Sreeshankar Satheeshbabu

Sponsors: NSF ERC for Compact and Efficient Fluid Power and NSF CMMI-1454276

Publications:

J15. G. Singh and G. Krishnan, “A constrained maximization formulation to analyze deformation of fiber reinforced elastomeric actuators,” Smart Mater. Struct., vol. 26, no. 6, p. 065024, Jun. 2017.

J10. G. Krishnan, J. Bishop-Moser, C. Kim, and S. Kota, “Kinematics of a Generalized Class of Pneumatic Artificial Muscles,” J. Mech. Robot., vol. 7, no. 4, p. 041014, Nov. 2015.

C19. G. Singh and G. Krishnan, “An Isoperimetric Formulation to predict Deformation Behavior of Pneumatic Fiber Reinforced Elastomeric Actuators,” in IEEE International Conference on Intelligent Robots and Systems, 2015, pp. 1738–1743.

C24. S. Satheeshbabu and G. Krishnan, “Towards a Constraint-Based Design of Soft Mechanisms,” in Volume 5A: 40th Mechanisms and Robotics Conference, 2016, p. V05AT07A019.

C18. G. Krishnan, “Kinematics of a new class of smart actuators for soft robots based on generalized pneumatic artificial muscles,” in IEEE International Conference on Intelligent Robots and Systems, 2014, pp. 587–592.

C14. Bishop-Moser, G. Krishnan*, S. Kota, ‘Force and Hydraulic Displacement Amplification of Fiber Reinforced Soft Actuators’, to appear in 2013 ASME-IDETC conference proceedings.

C13. Bishop-Moser, G. Krishnan*, C. Kim, S. Kota, ‘Design of Soft Robotic Actuators using Fluid-filled Fiber Reinforced Elastomeric Enclosures in Parallel Combination’, in-proceedings of the IEEE International Conference for Intelligent Robot and Systems (IROS), Vilamoura, Algarve (Portugal), October 7-12, 2012.

C12. Bishop-Moser, G. Krishnan*, C. Kim, S. Kota, ‘Kinematic Synthesis of Fiber Reinforced Soft Actuators in Parallel Combination’, presented at the 2012 ASME-IDETC/CIE, Chicago, IL, August 15-17, 2012.

C11. Krishnan*, J. Bishop-Moser, C. Kim, S. Kota. ‘Evaluating the Mobility Behavior of Fluid Filled Fiber Reinforced Elastomeric Enclosures’, presented at the 2012 ASME-IDETC/CIE, Chicago, IL, August 15-17, 2012.


Designing Systems of Fiber Reinforced Elastomeric Enclosures

Fiber Reinforced Elastomeric Enclosures (FREEs) are soft pneumatic representative elements that can form the basis for building soft self actuating structures/mechanisms. When placed in different configurations they exhibit unique stroke amplification characteristics that can be leveraged to create interesting deformation patterns. Such deformations occur as a combination of axial and bending deflection due to internal pressurization and external forces. This work presents a lumped reduced order model and a Homogenized Strain Induced Model that enables quick and accurate analysis of such mechanisms made from FREEs grouped as a system. The models serve as quick and accurate analysis tools for conceptual design of soft robots that occur as a combination of FREEs.

Personnel: Nicholas Thompson, Sreeshankar Satheeshbabu

Sponsors: NSF ERC for Compact and Efficient Fluid Power

Publications:

J19. S. Satheeshbabu and G. Krishnan, “ Modeling the Bending Behavior of Fiber Reinforced Pneumatic Actuators Using a Pseudo Rigid Body Model,” to appear in ASME Journal of Mechanisms and Robotics, 2019 (in press)

J14. X. Zhang and G. Krishnan, “A nested pneumatic muscle arrangement for amplified stroke and force behavior,” J. Intell. Mater. Syst. Struct., p. 1045389X1773092, Sep. 2017.

C27. S. Satheeshbabu and G. Krishnan, “Designing systems of fiber reinforced pneumatic actuators using a pseudo-rigid body model,” in 2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2017, pp. 1201–1206.


Inverse Design of FREEs for large spatial deformation

There is a direct correlation between deformation of FREEs and their fiber orientations. This can be exploited to conduct an inverse design to optimize the FREE fibers so as to attain a required spatial deformation profile. We have studied this thoroughly for designing FREEs to match a planar curve and also investigated FREEs that undergo snake like spiral winding. Our results are presented as design maps or charts and can be used without the need for computationally intensive solvers. In the video below the FREEs are designed to take the shape of ‘SoRo’ the acronym for the soft robotics journal.

Personnel: Gaurav Singh, Naveen Uppalapati

Sponsors: NSF CMMI-1454276

Publications:

J20. Singh, G. and Krishnan, G., “Designing Fiber Reinforced Soft Actuators for Planar Curvilinear Shape Matching” submitted to the journal of Soft Robotics.

J18. N. K. Uppalapati and G. Krishnan, “Towards Pneumatic Spiral Grippers: Modeling and Design Considerations,” Soft Robot., vol. 00, no. 00, p. soro.2017.0144, Jul. 2018. Doi: 10.1089/soro.2017.0144


Insightful Synthesis Tools for Spatial Compliant Mechanisms

Conceptual design of spatial compliant mechanisms with distinct input and output ports may be hard because of its complex interconnected topology, and is currently accomplished by computationally intensive automated techniques. Our work focuses on a user insightful method for generating conceptual compliant topology solutions. The method builds on recent advances where the compliant mechanism deformation is represented as load flow in its constituent members. The nature of load flow enables functional decomposition of compliant mechanisms into maximally decoupled building blocks namely a Transmitter member and a Constraint member. The proposed design methodology seeks to synthesize spatial compliant designs by systematically combining transmitter-constraint members by first, identifying kinematically feasible transmitter load paths between input(s) and output(s), and then selecting appropriate constraints that enforce the load path. We have built a Virtual Reality tool for users to follow simple guidelines and generate simple topologies.

Personnel: Sreekalyan Patiballa

Sponsors: NSF CMMI-1454276

J17.S. K. Patiballa and G. Krishnan, “Qualitative Analysis and Conceptual Design of Planar Metamaterials With Negative Poisson’s Ratio,” J. Mech. Robot., vol. 10, no. 2, p. 021006, Feb. 2018.

C29. S. Patiballa, K. Uchikata, R. K. Ranganath, and G. Krishnan, “A Conceptual Design Tool for Synthesis of Spatial Compliant and Shape Morphing Mechanisms,” in Volume 5B: 42nd Mechanisms and Robotics Conference, 2018, p. V05BT07A009.


Products and Other Applications


Current Projects:

Design of a Soft Robotic Shower Head

Many older adults encounter significant barriers in performing essential daily tasks such as bathing and grooming, which can lead to increased fall risks, greater dependency, and reduced quality of life. To address these challenges, this project aims to develop an intelligent, soft robotic showerhead, integrating three modes of operation: voice control, gesture control, and fully autonomous control. Leveraging the inherent dexterity and adaptability of soft robotics, the Soft Arm Showerhead offers enhanced motion range and precision in interaction with the user. The voice control mode allows for intuitive command-based operation, particularly suited for individuals with limited mobility. Gesture control provides a personalized and adaptive interface through motion recognition, while the fully autonomous mode enables a seamless and user-independent bathing experience. This solution seeks to promote independence and improve the quality of life for older adults by providing a safer, more accessible, and user-friendly approach to personal hygiene.

Personnel: Nikhil, Zhiyu Ren


Design of Lightweight structures for Automobile Applications

Stiff, strong, and low-cost lightweight structures are essential for various applications in the automobile and aerospace industries. However, contemporary engineering approaches to manufacturing lightweight structures force a trade-off between cost and weight reductions. A manufacturing-friendly approach is proposed by reinforcing hollow thin-walled sections with bio-inspired internal structures. The design combination increases overall strength, stiffness, and energy absorption capability from simulating structures in Nature such as balsa wood and crustacean exoskeletons. The guidelines for designing reinforced thin-walled structures are provided and can be extended for generalized loading conditions. An AI-assisted algorithm is also developed to accelerate the analysis of base structures and the auto-generation of optimal reinforcement strategies.

Personnel: Ruoyu Sun


Design of a compact robot manipulator and rover for High tunnels

Personnel: Poojan, James, Pavan, Kendall


Soft Robot perception, planning, and control for obstacles

Personnel: Kendall, Shivani, Samhita


Past Projects:

Design of Soft Pneumatic Crutch Orthoses (in collaboration with Prof. Elizabeth Hsiao-Wecksler, MechSE).

This project has two main goals: to develop novel high-force, energy storing, miniature soft pneumatic actuators, and to directly integrate them as the structure for soft robotic upper extremity orthoses for pediatric patients that use crutches for ambulation. While walking with crutches, peak loads observed in the wrist typically approach 50% of body weight and wrist postures experience extreme extension angles ~35°. These repetitive, high loads and poor wrist postures have been shown to lead to joint pain and injury, carpal tunnel syndrome, arthritis, or joint deformity. Currently, the natural progression finds pediatric crutch users often transitioning to using wheelchairs, as their arms cannot support their body weight as they grow and the effects of these secondary injuries become unsustainable. This transition reduces mobility, fitness, and quality of life. Creating an effective orthosis would be beneficial for these pediatric patients or any assistive mobility device users, whom are susceptible to overuse injury and pain (those with acute limb injury or surgery, elderly, adult pathology populations).

We seek to develop a light-weight (< 1 kg), pliable (tunable modulus of rigidity), powered (by <100 psi) wrist orthosis and integrated compact actuators to reduce these transient loads and associated wrist stresses by 50% and improve wrist posture to a more neutral position; therefore lowering the risk for joint injury such as carpal tunnel syndrome, while allowing for normal wrist and arm range of motion when not used for load bearing. We will expand the range and functionality of current contracting McKibben muscles, which are based on simple equal and opposite fibers, by developing a robust analysis framework to generalize the construction and operating principles for FREE actuators to yield different deformation patterns.

Personnel: Gaurav Singh, Chenzhang Xiao

Sponsor: NSF ERC for Compact and Efficient Fluid Power

Sleeve

Publications:

J16. G. Singh, C. Xiao, E. T. Hsiao-Wecksler, and G. Krishnan, “Design and analysis of coiled fiber reinforced soft pneumatic actuator,” Bioinspir. Biomim., Feb. 2018.

C22. G. Singh, C. Xiao, G. Krishnan, and E. Hsiao-Wecksler, “Design and Analysis of Soft Pneumatic Sleeve for Arm Orthosis,” in ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2016, p. V05AT07A034-V05AT07A034.

J11. C. Xiao, Y. L. Oo, D. Farooq, G. Singh, G. Krishnan, and E. T. Hsiao-Wecksler, “Pneumatic Sleeve Orthosis for Lofstrand Crutches: Application of Soft Pneumatic FREE Actuator 1,” J. Med. Device., vol. 10, no. 2, p. 020959, May 2016.

P2. E. T. Hsiao-Wecksler, D. Farooq, C. Xiao, G. Krishnan, G. Singh, and Y. L. Oo, “Forearm and Wrist Support for Crutch Users,” US9662263 B2, 2017.


Compact modular wearable upper-extremity exoskeleton

This project seeks to explore design architectures for wearable exoskeletons using miniaturized FREEs. It is well known that the forces in the pneumatic actuators decrease greatly when scaled down. However, to make exoskeletons wearable and discreet miniaturization is required. The only way to overcome this trade-off is by using multiple miniaturized FREEs in unique architectures. The architectures have different functionalities. A helical winding architecture just aids in stiffening the joint to assist in load bearing, while linear nested architectures produce large stroke to actuate. All the actuator architectures fit within the contours of the body.

Publications:

C31. N. Thompson, X. Zhang, F. Ayala, E. T. Hsiao-Wecksler, and G. Krishnan, “Augmented Joint Stiffness and Actuation Using Architectures of Soft Pneumatic Actuators,” in 2018 IEEE International Conference on Robotics and Automation (ICRA), 2018, pp. 1533–1538

J14. X. Zhang and G. Krishnan, “A nested pneumatic muscle arrangement for amplified stroke and force behavior,” J. Intell. Mater. Syst. Struct., p. 1045389X1773092, Sep. 2017.

C21. X. Zhang, G. Singh, and G. Krishnan, “A soft wearable sleeve for joint stiffness modulation,” in Advanced Intelligent Mechatronics (AIM), 2016 IEEE International Conference on, 2016, pp. 264–269.


BR2: A single section spatial manipulator  

Soft pneumatic continuum manipulators are increasingly popular because of their ability to interact safely with humans, maneuver around obstacles and enable cost-effective operation. However, to increase their workspace, state-of-the-art soft manipulators are composed of independently controllable modular or serial segments that are complex to manufacture and integrate. Furthermore, they suffer from increased inertial effects and reduced load-bearing ability. We present the design and forward analysis of a first-of-its-kind purely parallel manipulator BR2, (one bending mode and two rotation modes) which is capable of spatial motion. This manipulator uses a repertoire of deformation patterns that are obtainable from novel pneumatic actuators known as Fiber Reinforced Elastomeric Enclosures (FREEs). Experimental characterization of the manipulator reveals the importance of a “coupling effect”, where the deformation mode of one actuator is restricted by the other. The inclusion of this effect along with gravity and other external forces is used predict the workspace of manipulator with reasonable accuracy.

Personnel: Naveen Kumar Uppalapati, Sreeshankar Satheeshbabu

Publications:

C30. N. K. Uppalapati, G. Singh, and G. Krishnan, “Parameter estimation and modeling of a pneumatic continuum manipulator with asymmetric building blocks,” in 2018 IEEE International Conference on Soft Robotics (RoboSoft), 2018, pp. 528–533.

Uppalapati, N. K., & Krishnan, G. (2018). Design of soft continuum manipulators using parallel asymmetric combination of fiber reinforced elastomers. to be submitted to IEEE TRO.


 A pipe crawling robot:  We present a pipe crawling robot gait using a three-FREE segment.

 


Design of Distributed Compliant Mechanisms using System-Level and Continuum-Level Design Maps

The objective of the project is to create a unifying framework for the synthesis of distributed compliant mechanisms by systematically channeling flow of information between the system-level and continuum-level phases in the design process. This flow of information is envisioned through two global design space maps that uniquely represent any compliant mechanism, namely (a) System Design Space (SDS) that characterizes the lumped system-level attributes, and a (b) Continuum Design Space (CDS) that characterizes topological, material and manufacturing attributes. The flow of information between the SDS and CDS will (i) enable objective comparison of several potential conceptual solutions based on inherent attributes that define the design space map, (ii) ascertain feasibility and existence of a solution by juxtaposing the problem specifications with these inherent attributes, (iii) enable synthesis of new designs at the system and continuum level by combining several sub-systems, (iv) set guidelines for systematic redesign of an existing solution to improve feasibility.

The theoretical underpinnings of the SDS and CDS will be enabled by three system and continuum level models namely, (a) Spring-Mass Lever model (SML) that characterizes the lumped behavior of any arbitrary compliant mechanism (b) a kinetostatic representation based on Load Flow Visualization that maps topological constituents of a compliant mechanism to its functionality and (c) a Distributed Compliance Metric that characterizes the state of stress distribution of the compliant mechanism.

Personnel: Sreekalyan Patiballa and John Shanley


Mobility analysis of Flexure systems and Soft Mechanical Systems using Load Flow Visualization

Mobility analysis is an important step in the conceptual design of flexure systems. It involves identifying directions with unrestricted motion (freedoms) and those that are constrained. This paper proposes a unique framework for mobility analysis of wire flexures by characterizing a kinetostatic vector field known as “load flow” through its geometry. The relationship between load flow and the flexure axis is used to determine if a flexure behaves as a constraint or a freedom. This knowledge is utilized to formulate a matrix-based reduction technique to determine flexure mobility in an automated fashion. Several examples with varying complexity are illustrated to validate the efficacy of this technique. This technique is particularly useful in analyzing complex hybrid flexure topologies, which may be non-intuitive or involved with traditional methods. This is illustrated through the automated mobility analysis of a bio-inspired fiber reinforced elastomer pressurized with fluids. The proposed framework combines both visual insight and analytical rigor, and will complement existing analysis and synthesis techniques.

Personnel: Sreeshankar Satheeshbabu

Fig4-Section3


Nonlinear Spring Synthesis for Orthotic Brace (with Adicep Inc)

Recent research indicates that utilization of nonlinear mechanical energy storage devices (i.e. springs) can fundamentally change rehabilitative/assistive device architectures in ways that result in benefits not previously possible. Currently, no unified theory or design methodology exists that can help researchers in assistive devices create nonlinear springs. Moreover, commercially available nonlinear springs limit rather than enable their research. This proposal seeks to develop a design framework for creating distributed-compliance energy storage devices by researchers in assistive devices that addresses this problem. The proposed innovation is to incorporate the constant-stress hypothesis in synthesizing springs made of compliant members that undergo large deformation compared to their overall size. These synthesized springs must meet specified force/displacement functions satisfying fatigue and manufacturing requirements (e.g. weight, size, maximum stress).

Four tasks involving basic and applied research are planned. The basic tasks are (1) quantify and evaluate distributed compliance from the fundamentals of continuum mechanics and (2) create a design framework for synthesizing energy storage devices given user specifications; the applied tasks include (3) create a real-world nonlinear torsion spring for use in an orthosis and (4) develop a practical scheme for field adjusting the weight handling capability of the spring element in a lower-limb orthosis

Personnel: Sreekalyan Patiballa and John Shanley

SpringSpec