This paper presents closed-loop position control of a pneumatically actuated modular robotic platform "pneumagami" that can be stacked to enlarge work and design space for wearable applications. The module is a 3 degrees of freedom (DoF) parallel robot with two rotational and one translational motion, which is actuated by three antagonistic pneumatic pouch motor pairs attached to three leg joints. To control the pouch motors, we utilize miniature proportional valves. As for the sensing, we introduce a novel embedded resistive sensor mechanism utilizing rotary-to-translational transmission. The sensor's transmission is modeled and verified by experiments. Furthermore, we study analytic forward and inverse kinematic models of the pneumagami module. Utilizing the models, we design a closed-loop feedback controller to track two different trajectories. The experimental results show that the module follows the desired trajectories successfully. Thus, we report that the proposed pneumagami modules can be utilized for achieving a controllable robotic third arm with higher DoFs and range of motion (RoM) when connected in series.

Self-folding enables compact, deployable and reconfigurable structures for close and far remote applications. As the degree-of-freedom in achieving folded shapes is dictated by the number of actuators, distributed on a quasi-2-D lattice, their design remains challenging in terms of size, weight, efficiency, repeatability and fabrication. While the traditional electric motors are difficult to downscale and assemble, the active materialbased actuators consume high power and are limited by slow and irreversible motions. Here we present a new selective fluiddriven actuation and embedment method for constructing multicreased, self-folding and reversible robotic origami structures. Our design enables an underactuated, yet a distributed control of origami hinges with single and multi-step folding sequence by programming the fluidic networks. The proposed tunable fluidic actuator-channel networks are compactly embedded in a rapid multi-layer lamination process with minimal assembly. We provide an analytic model for the folding actuator unit, validate it with several prototypes and demonstrate its integration into complex networks for folding multi-hinged tessellations, including Miura-ori and sequentially folding box patterns.

Series elastic actuators (SEAs) and variable elastic actuators (VSAs) provide shock resistance, energy storage, and stable force control. However, they usually require extra springs, mechanical parts, and transmissions, increasing size, weight, number of moving parts, and reducing the mechanical efficiency. In particular, this mechanical complexity is one of the significant challenges in the design of wearable and scalable force feedback devices. In this article, flexure variable stiffness actuators (F‐VSAs), which combine kinematic transmission, elasticity, and stiffness modulation via a network of folding patterns using flexure hinges, are presented. Thus, F‐VSAs allow the creation of robots benefiting from the advantages of SEAs and VSAs without hindering form factor or mechanical efficiency. To illustrate the design strategy of F‐VSAs, a 4‐design‐of‐freedom (DoF) robot that provides stiffness and force output is presented. An analytical model that estimates the inherent stiffness and the end‐effector force output for any given configuration of the folding pattern is proposed. Finally, stiffness modulation and force control of the robot are implemented and good agreement with the predictions from the model is observed. Thus, this novel design strategy allows the creation of compact and scalable robots with stiffness and force output for wearable, rehabilitation, and haptic applications.

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Achieving safe human-robot interaction becomes crucial with the developments of many robotics fields such as rehabilitation, assistance, service, wearables, and haptics. To this end, researchers have explored alternatives to conventional fully rigid actuation methods such as soft actuators and electromechanical motors combined with elastic elements. Soft actuators using pneumatics, [1] hydraulics, [2,3] elastomers, [4] and smart materials [5] have proven to enhance the user's safety. [6,7] This category also includes variable stiffness soft actuators relying on jamming [8,9] or smart materials. [5,10] However, soft actuators suffer from complex modeling, difficult control, low actuation speed, and bulky power supplies. [11,12] This study focuses on the alternative compliant actuation method that uses conventional actuators coupled with elastic elements such as series elastic actuators (SEAs) and variable stiffness actuators (VSAs), which show better performance regarding the aforementioned soft actuators limitations.SEAs [13][14][15][16][17][18][19] consist of actuators connected to elastic elements and loads in series. [20] The elastic elements serve three main purposes: 1) storing and releasing energy, thus improving energy efficiency, [21] 2) converting the force control problem to a position control problem due to the well-defined relationship between elastic deformation and output force, [20] and 3) reducing peak forces on the motor and user during impact, thereby improving safety. [22] However, SEAs usually hinder the actuator's bandwidth, thus limiting the performance. Moreover, they cannot adapt their stiffness with respect to the different loads and conditions, which can cause undesired oscillations. [23] Unlike SEAs, VSAs [24][25][26] tune the stiffness of their elastic elements to adapt their compliance and bandwidth to changing environments and conditions. For example, higher-stiffness configurations enable faster response and better fidelity performance, while lower-stiffness configurations reduce the impact of collision and achieve safer and more stable force and torque output. VSAs are categorized into three general groups based on how they vary their stiffness: spring pretension, changing transmission, and changing physical properties of springs. [20,27] While each of these categories has specific assets and liabilities, they suffer from a common limitation: the need for extra components and mechanisms [20,28,29] which leads to an increase in complexity, weight, size, and time of assembly. [30] These challenges set back the ability of VSAs to target applications requiring miniaturized devices with multi-degree-of-freedom (DoF) force outputs [16] such as wearable devices and haptics.To address mechanical complexity issues of VSAs, researchers have investigated the use of flexure hinges for compliant mechanisms. Flexure-based mechanisms enable the design of miniaturized, compact, and lightweight multi-DoF mechanisms and robots with a reduced number of components. [31][32][33][34][35][36] In VSA, exi...