Modular robots (MRs) consist of unique robots which interconnect and work as a collective to perform objectives. Coordinating these robots rely on robust communication, as modules moving independently can lead to damaging behaviour. We present a robust structure for modular robot communication, implemented and tested on a new MR. The structure has different communication protocols depending on the importance and bandwidth of the exchanged information, has fast error responses, and considerations which allow for two modules to actuate the same joint. We evaluate the wireless protocols, novel error response, and coordinated actuation empirically, validating the system on a new modular robot, the Mori3. We find two wireless protocols can be used to balance speed and reliability; transmitting errors through both wireless and serial is more consistent and faster; and sharing motor targets, control variables, and measurements allow for motors to operate a shared joint with equal efforts.

This article presents the novel modular version of the robotic platform Cellulo, a versatile handheld robot initially designed as an educational robot. The use of Cellulo in different contexts and applications over the years has highlighted the need for modularity. Modularity adds versatility by increasing the spectrum of functionalities of the robot, as well as more robustness. Modulo Cellulo consists of three modules: a main module, a battery module, and an interaction module. We describe the new Modulo Cellulo platform, the different modules design, the mechanical and electrical inter-connectivity between them, the new adaptive controller, and the application development framework. As a show case, we present the addition of the reconfigurable robot Mori as a module for Cellulo, in an activity envisioning the collaboration between reconfigurable swarm robots.

Origami robots composed of rigid parts with flexible joints have inherent compliance that enables deployment and reconfiguration for various shape adaptations. The major drawback of such mechanical compliance is its intrinsic softness and lack of controllability of this stiffness. In this work, we propose a design of variable stiffness origami joints to be integrated into large scale origami systems with an inner controllable joint stiffness. This novel way of controlling compliance in origami structures demonstrates that the embedded variable stiffness joint in the prototype can provide rich haptic feedback to the user through its compact, collapsible interactive platform.

This paper presents a novel approach to fault tolerant reconfiguration of modular self-folding robots. Among various types of faults that probably occur in the modular system, we focus on the tolerance of complete actuation failure of active modules that might cause imprecise robotic motion and even reconfiguration failure. Our approach is to utilize the reconfigurability of modular self-folding robots and investigate intra-module connection to determine initial patterns that are inherently fault tolerant. We exploit the redundancy of actuation and distribute active modules in both layout-based and target-based scenarios, such that reconfiguration schemes with user-specified fault tolerant capability can be generated for an arbitrary input initial pattern or 3D configuration. Our methods are demonstrated in computer-aided simulation on the robotic platform of Mori, a modular origami robot. The simulation results validate that the proposed algorithms yield fault tolerant initial patterns and distribution schemes of active modules for several 2D and 3D configurations with Mori, while retaining generalizability for a large number of modular self-folding robots.

Robotic origami design allows creating meso-scale robotic systems and mechanisms not limited by degrees of freedom, miniaturization and assembly downsides of conventional transmission mechanisms. However, unlike the traditional rigid approaches, robotic origami application has been limited by the complex deformation and kinematics of the compliant joints and actuation based on active materials or conventional electric motors. To generalize their application at meso-scale requires a combination of the predictability of traditional rigid kinematics and the manufacturing flexibility of robotic origami. Here we present a study of conventional transmission mechanisms, including a slider-crank and cam-follower, made in quasi-2D form by selective machining and stacking of multiple layers of composite material with minimal assembly. Owing to a compliant design powered by low-profile piezoelectric motors, our 5.3 mm thick and lightweight mechanisms transmit rotational motion to translational movements in and out-of-plane. We develop analytic models that we validate in terms of force and motion output on our prototypes.

Modular self-folding robots are versatile systems that can change their own shape from two-dimensional patterns at instant commands. This reconfigurability is commonly restrained by power limitation in autonomous environments, The robotic systems with insufficient torque may lead to inaccurate movements and even transformation failures. This paper presents methodology for optimized reconfiguration planning with torque limitation in modular self-folding robots. We determine reconfiguration schemes with optimal initial pattern and robotic base that result in minimal peak torque by minimizing robotic inertia of the modular architecture. We present minimal bounding box and capacitated spanning tree heuristic algorithms to generate optimal initial patterns and propose 3 heuristic rules for robotic base selection. Our approach is demonstrated in simulation by applying the algorithms to the robotic concept of Mori, a modular origami robot. The simulation results show that the proposed algorithms yield reconfiguration schemes with low peak torque, thereby appropriate for real-time applications in modular robotic systems.

Robotic origami allows rapid prototyping of intelligent robots and machines constructed from thin sheets of functional materials. Multimaterial-based design freedom of origami robots creates functional versatility; however, the design parameters pose challenges in their mechanical layout and fabrication. While the conventional robot design follows a coherent and well-established design process, the construction of origami robots requires close study of their three-dimensional (3-D) and two-dimensional (2-D) geometries, compliant mechanisms, functional material specific components, and 2-D fabrication methods. In this paper, we report a systematic design methodology for building origami-inspired machines and robots based on these four essential design features. We provide their comprehensive formulation, comparing them to conventional robots and highlighting design challenges as well as potentials. We demonstrate the applicability of our procedure to the majority of origami robots in the literature and also validate it by designing a centimeter-scale jumping and crawling origami robot, Tribot, as a showcase. The 6-g Tribot crawls with fixed steps in a closed loop, adjusts its vertical jumping height by power modulation, and overcomes obstacles of 45-mm height by side jumps. This paper advances the design and fabrication methodology of origami robots, with customizable functionality from the ground-up.

Continuing research efforts in robot-assisted rehabilitation demand more adaptable and inherently soft wearable devices. A wearable rehabilitative device is required to follow the motion of the body and to provide assistive or corrective motions to restore natural movements. Providing the required level of fluidity in wearable devices becomes a challenge for rehabilitation of more sensitive and fragile body parts, such as the face. To address this challenge, we propose a soft actuation method based on a tendon-driven robotic origami (robogami) and a soft sensing method based on a strain gauge with customized stretchable mesh design. The proposed actuation and sensing methods are compatible with the requirements in a facial rehabilitative device. The conformity of robogamis originates from their multiple and redundant degrees of freedom and the controllability of the joint stiffness, which is provided by adjusting the elasticity modulus of an embedded shape memory polymer (SMP) layer. The reconfiguration of the robogami and the trajectory and directional compliance of its end-effector are controlled by modulating the temperatures, hence the stiffness, of the SMP layers. Here we demonstrate this correlation using simulation and experimental results. In this paper, we introduce a thin and highly compliant sensing method for measuring facial movements with a minimal effect on the natural motions. The measurements of the sensors on the healthy side can be used to calculate the required tendon displacement for replicating the natural motion on the paralyzed side of the face in patients suffering from facial palsy.

Vacuum-powered Soft Pneumatic Actuator (V-SPA) Modules have been described to afford advantages for rapid development of reconfigurable, multi-DoF soft pneumatic robots powered by vacuum by reducing their logistical complexity, however they also present new challenges in the control of resulting systems. This framework features modules joined together over a simple embedded pneumatic and serial communication network and requires a unique approach to both low-level control implementation and high-level control strategy. We describe the structure and activation characteristics of a V-SPA Module and present practical methods for its control. These methods utilize software generated PWM activation through a unique serial protocol designed for LED networks and a heuristic mapping strategy for simplifying the spherical control of 3-DoF actuator modules.

We present a fully edible pneumatic actuator based on gelatin-glycerol material. The actuator is monolithic, fabricated via a molding process, and measures 90 mm in length, 20 mm in width, and 17 mm in thickness. Thanks to the material mechanical characteristics similar to those of silicone elastomers, the actuator exhibits a bending angle of 170.3 ° and a blocked force of 0.34 N at the applied pressure of 25 kPa. These values are comparable to elastomer based pneumatic actuators. As a validation example, two actuators are integrated to form a gripper capable of handling various objects, highlighting the high performance and applicability of the edible actuator. These edible actuators, combined with other recent edible materials and electronics, could lay the foundation for a new type of edible robots.

There are several challenges in down-sizing robots for transportation deployment, diversification of locomotion capabilities tuned for various terrains, and rapid and on-demand manufacturing. In this paper we propose an origami-inspired method of addressing these key issues by designing and manufacturing a foldable, deployable, and self-righting version of the origami robot Tribot. Our latest Tribot prototype can jump as high as 215 mm, five times its height, and roll consecutively on any of its edges with an average step size of 55 mm. The 4 g robot self-deploys nine times of its size when released. A compliant roll cage ensures that the robot self-rights onto two legs after jumping or being deployed and also protects the robot from impacts. A description of our prototype and its design, locomotion modes, and fabrication is followed by demonstrations of its key features.

Underactuated systems offer compact design with easy actuation and control but at the cost of limited stable configurations and reduced dexterity compared to the directly driven and fully actuated systems. Here, we propose a compact origami-based design in which we can modulate the material stiffness of the joints and thereby control the stable configurations and the overall stiffness in an underactuated robot. The robotic origami, robogami, design uses multiple functional layers in nominally two-dimensional robots to achieve the desired functionality. To control the stiffness of the structure, we adjust the elastic modulus of a shape memory polymer using an embedded customized stretchable heater. We study the actuation of a robogami finger with three joints and determine its stable configurations and contact forces at different stiffness settings. We monitor the configuration of the finger using feedback from customized curvature sensors embedded in each joint. A scaled down version of the design is used in a two-fingered gripper and different grasp modes are achieved by activating different sets of joints.

Various robotic applications including surgical instruments, wearable robots and autonomous mobile robots are often constrained with strict design requirements on high degrees of freedom (DoF) and minimal volume and weight. An intuitive design to meet these contradictory requirements is to embed locking mechanism in under actuated robotic manipulators to direct the actuation from a single and remote source to drive different joints on demand. Mechanical clutches do serve such purposes but often are bulky and require auxiliary mechanism making it difficult to justify the high cost adding the additional DoF, especially in cm scale. Here, we introduce an under-actuated robotic arm with shape memory polymer (SMP) joints. Through controlling the temperature, the stiffness of the joints can be adjusted and selected joints will be activated while the rest are fixed in their position. The presented prototype can control the joints independently with a coupled actuation from two stepper motors. Since we have redundant DoFs in the arm, there can be more than one configuration to reach a given position. We use a probabilistic technique to determine the optimum configuration with the minimum number of active joints that can yield the desired posture. In this paper, we report on the performance of the proposed design for the hardware and the configuration planner.

The soft pneumatic actuators (SPAs) are a solution toward the highly customizable and light actuators with the versatility of actuation modes, and an inherent compliance. Such flexibility allows SPAs to be considered as alternative actuators for wearable rehabilitative devices and search and rescue robots. The actuator material and air-chamber design dictate the actuator's mechanical performance. Therefore, each actuator design with a single pressure source produces a highly customized motion but only a single degree of freedom (DoF). We present a novel design and fabrication method for a SPA with different modes of actuation using integrated adjustable stiffness layers (ASLs). Unlike the most SPA designs where one independent chamber is needed for each mode of actuation, here we have a single chamber that drives three different modes of actuation by activating different combinations of ASLs. Adapting customized micro heaters and thermistors for modulating the temperature and stiffness of ASLs, we considerably broaden the work space of the SPA actuator. Here, a thorough characterization of the materials and the modeling of the actuator are presented. We propose a design methodology for developing application specific actuators with multi-DoFs that are light and compact.

Origami robots (Robogamis) use architecture to strategically activate different sets and sequence of actuators to achieve large variety of reconfigurable forms. Tribot is a unique mobile origami robot that can simultaneously choose between two modes of locomotion: jumping and crawling. When assembled, Tribot measures 64 × 34 × 20 mm3, weighs 4 g, crawls at 17% of its body length per gait cycle and jumps seven times its height repeatedly without needing to be reset. To optimize the practicality of the nominally 2D design, we made two different approaches to build the prototypes. For one of them, we used the “traditional”, monolithic, layer-by-layer robogami fabrication method and the second, we printed out most parts using a multi-material 3D printer. By showing the performance of two prototypes side-by-side, we show that with the 3D printer, we can minimize the number of functional layers and reduce the fabrication time. The embedded sensors allow Tribot's crawling gait pattern and jumping height to be modulated with a closed loop control. We compare the expected gait step size and displacement to that of the presented prototype while describing the design and control parameters to achieve the experimental results. We also illustrated the preliminary graphical design tool platform developed to optimize the next design iteration of Tribot.

Materials with variable stiffness have the potential to provide a range of new functionalities, including system reconfiguration by tuning the location of rigid links and joints. In particular, wearable applications would benefit from variable stiffness materials in the context of active braces that may stiffen when necessary and soften when mobility is required. In this work, we present fibers capable of adjusting to provide variable stiffness in wearable fabrics. The variable stiffness fibers are made from shape memory materials, where shape memory alloy (SMA) is coated with a thin film of shape memory polymer (SMP). The fibers, which are fabricated via a continuous feed-through process, reduce in bending stiffness by an order of magnitude when the SMP goes through the glass transition. The transition between rubbery and glassy state is accomplished by direct joule heating of the embedded SMA wire. We employ a COMSOL model to relate the current input to the time required for the fibers to transition between stiffness states. Finally, we demonstrate how this device can be worn and act as a joint stability brace on human fingers.

Soft Pneumatic Actuator skin (SPA-skin) is a novel concept of ultra-thin (<; 1 mm) sensor embedded actuators with distributed actuation points that could cover soft bodies. This highly customizable and flexible SPA-skin is ideal for providing proprioceptive sensing by covering pre-existing structures and robots bodies. Having few limitation of the surface quality, dynamics, or shape, these mechanical attributes allow potential applications in autonomous flexible braille, active surface pattern reconfiguration, distributed actuation and sensing for tactile interface improvements. In this paper, the authors present a proof-of-concept SPA-skin. The mechanical parameters, design criteria, sensor selection, and actuator construction process are illustrated. Two control schemes, actuation mode and force sensing mode, are also demonstrated with the latest prototype.

The robotic origami (Robogami) is a low-profile, sheet-like robot with multi degrees-of-freedom (DoF) that embeds different functional layers. Due to its planar form, it can take advantage of precise 2D fabrication methods usually reserved for micro and nano systems. Not only can these methods reduce fabrication time and expenses, by offering a high precision, they enable us to integrate actuators, sensors and electronic components into a thin sheet. In this research, we study sensors, actuators and fabrication methods for Robogami which can reconfigure into various forms. Our main objective is to develop technologies that can be easily applied to Robogamis consisting of many active folds and DoFs. In this paper, after studying the performance of the proposed sensors and actuators in one fold, we use a design for a crawler robot consisting of four folds to assess the performance of these technologies.

Soft actuators made of highly elastic polymers allow novel robotic system designs, yet application-specific soft robotic systems are rarely reported. Taking notice of the characteristics of soft pneumatic actuators (SPAs) such as high customizability and low inherent stiffness, we report in this work the use of soft pneumatic actuators for a biomedical use - the development of a soft robot for rodents, aimed to provide a physical assistance during gait rehabilitation of a spinalized animal. The design requirements to perform this unconventional task are introduced. Customized soft actuators, soft joints and soft couplings for the robot are presented. Live animal experiment was performed to evaluate and show the potential of SPAs for their use in the current and future biomedical applications.

Conventional pneumatic actuators have been a popular choice due to their decent force/torque output. Nowadays, new generation of pneumatic actuator made out of highly compliant elastomers, which we call soft pneumatic actuators (SPA), are drawing increasing attention due to their ease of fabrication, high customizability and innately softness. However, there is no effective method presented to characterize and understand these actuators, such as to measure the force and torque output, range of motion and the speed of actuation. In this work, we present two types of SPAs: bending and rotary actuators. In addition, we have developed two measurement setups to characterize actuators of different geometries. The measured force/torque outputs of different actuators are presented and analyzed. Step responses to certain pressure input are presented and discussed. A simple model is presented to provide physical insight to the observed behavior of the soft actuators. This work provides the basis for designing customized SPAs with application-specific requirements.

Programmable materials based on robotic origami have been demonstrated with the capability to fold into 3D shapes starting from a nominally 2D sheet. This concept requires high torque density actuators, flexible electronics and an integrated substrate. We report on two types of stretchable circuitry that are directly applicable to robotic origami: meshed copper traces and liquid-metal-filled channels in an elastomer substrate. Both methods maintain conductivity even at large strains (during stretching) and curvatures (during folding). Both circuit designs are integrated with a tiled origami module actuated by a shape memory alloy actuator. We also integrate a soft curvature sensor into the robotic origami module that measures the full range of motion of the module in real-time.

A major issue in the field of human-robot interaction for assistance to manipulation is transparency. This basic feature qualifies the capacity for a robot to follow human movements without any human-perceptible resistive forces. In this paper we address the issue of human motion prediction in order to increase the transparency of a robotic manipulator. Our aim is not to predict the motion itself, but to study how this prediction can be used to improve the robot transparency. For this purpose, we have designed a setup for performing basic planar manipulation tasks involving movements that are demanded to the subject and thus easily predictable. Moreover, we have developed a general controller which takes a predicted trajectory (recorded from offline free motion experiments) as an input and feeds the robot motors with a weighted sum of three controllers: torque feedforward, variable stiffness control and force feedback control. Subjects were then asked to perform the same task but with or without the robot assistance (which was not visible to the subject), and with several sets of gains for the controller tuning. First results seems to indicate that when a predictive controller with open loop torque feedforward is used, in conjunction with force- feedback control, the interaction forces are minimized. Therefore, the transparency is increased.

We present a new device aimed at being used for upper limb rehabilitation. Our main focus was to design a robot capable of working in both the passive mode (i.e. the robot shall be strong enough to generate human-like movements while guiding the weak arm of a patient) and the active mode (i.e. the robot shall be able of following the arm without disturbing human natural motion). This greatly challenges the design, since the system shall be reversible and lightweight while providing human compatible strength, workspace and speed. The solution takes the form of an orthotic structure, which allows control of human arm redundancy contrarily to clinically available upper limb rehabilitation robots. It is equipped with an innovative transmission technology, which provides both high gear ratio and fine reversibility. In order to evaluate the device and its therapeutic efficacy, we compared several series of pointing movements in healthy subjects wearing and not wearing the orthotic device. In this way, we could assess any disturbing effect on normal movements. Results show that the main movement characteristics (direction, duration, bell shape profile) are preserved.