Soft pneumatic actuator-driven origami-inspired modular robotic ‘‘pneumagami’’

This article presents a new modular robotic platform for enabling reconfigurable, actively controlled, high-degree-of-freedom (high-DoF) systems with compact form factor. The robotic modules exploit the advantages of origami-inspired construction methods and materials, and soft pneumatic actuators (SPAs) to achieve an actuator embedded, parallel kinematic mechanism with three independently controlled ‘‘waterbomb’’ base legs. The multi-material, layer-fabricated body of the modules features selectively compliant flexure hinge elements between rigid panels that define the module as a kinematic 6R spherical joint. The precision layer-fabrication technique is also used to form embedded distribution channels within the module base to connect actuators to onboard control hardware. A decentralized control architecture is applied by integrating each module with small-scale solenoid valves, communication electronics, and sensors. This design approach enables a single pneumatic supply line to be shared between modules, while still allowing independent control of each leg joint, driven by soft, inflatable pouch actuators. A passive pneumatic relay is also designed and incorporated in each module to leverage the coupled, inverted inflation, and exhaust states between antagonistic actuator pairs allowing both to be controlled by a single solenoid valve. A prototype module is presented as the first demonstration of integrated modular origami and SPA design, or pneumagami, which allows predefined kinematic structural mechanisms to locally prescribe specific motions by active effect, not just through passive compliance, to dictate task space and motion. The design strategy facilitates the composition of lightweight, high-strength robotic structures with many DoFs that will benefit various fields such as wearable robotics

Active origami platforms for human-robot interactions

Frédéric Henri Vaskin Giraud

Robots are employed to assist humans in lengthy, challenging, and repetitive tasks. However, the fields of rehabilitation, haptics, and assistive robotics have shown a significant need to support and interact with people in their everyday life. To facilitate these further needs, robots must overcome constraints in compactness, degrees of freedom (DoF), and mechanical performance. However, developing a robot with these characteristics is challenging for conventional mechanics. First, creating a meso-scale device requires the assembly of small components, which is laborious and increases manufacturing cost, time, and complexity. In addition, devices with several DoF and functionalities also require more parts to create numerous links and joints, actuators, and thus space, affecting the compactness of systems. Finally, aiming for mechanical performance in terms of force, speed, and motion range requires transmissions or bulky actuators, which also influence the size of the system. This thesis attempts to overcome the limitations of conventional mechanics by using origami robots, an alternative design approach for creating meso-scale structures with numerous folding joints. It consists in stacking layers of functional material to achieve low-profile and scalable structures that fold into 3D. Using this method, we developed three hybrid robots combining the decades of experience of conventional mechanics with the advantages of origami robotics. First, to enhance the performances of robots at the meso-scale, the creation of compact low-profile compliant transmissions benefiting from origami's minimal assembly of functional layers was explored. The transmissions obtained can reproduce conventional kinematics or generate unconventional motions using materials properties. Second, the development of multi-DoF compact robots was studied using the aforementioned low-profile compliant transmissions to create a multi-functional structure. The resulting robot is a fingertip haptic device called Haptigami that can render vibrotactile and three-DoF force feedback without compromising bulkiness. Then, this study aimed at creating a meso-scale, multi-DoF, and mechanically efficient robot. We combined the previous device contributions and developed Flexure Variable Stiffness Actuators (F-VSA), a novel compliant actuator that uses the origami flexure hinges' inherent stiffness to avoid hindering mechanical simplicity. Finally, we developed a software architecture that enables high-level control of the human-robot hardware and is compatible with multiple simulation engines. We used this architecture to control our robots and provide feedback to the user, based on interactions in a virtual environment. These novel robots rely on non-conventional structures, actuators, and kinematics that require exploring and testing suitable control strategies. Hence, kinematic and stiffness models were developed and used to tune the position, force, and stiffness of the end-effector. Several characterization platforms and experimental protocols suitable for testing our unique robotic systems were also developed to assess their precision and efficiency. Consequently, the results of this study pave the way for the development of robots that adapt to multiple environments, interactions, and application scenarios, compatible with the human bandwidth without hindering the user's motion and comfort in everyday life.

EPFL2022

Delta Thales, a novel architecture for an orientating device with fixed RCM (remote center of movement) and linear movement in direction of the RCM

Reymond Clavel, Patric Pham

A new 3 degrees of freedom (dof) structure is presented. It features rotation on two axes with a fixed remote center of motion (RCM) i.e. it always aims at the same point. The third axis is a linear movement in direction of the fixed point. This type of kinematics is useful for many applications where a parasitic translational movement during the rotation is undesirable. The kinematics is based on the well known Delta robot. It is in fact composed of two Deltas mounted on the same command arms, which are linked to the rotary actuators. Therefore the two Delta robots move in the same manner except that the one fixed at the end of the bars moves of a bigger amount than one fixed closer to the actuators. The two nacelles are then connected through a sliding universal joint and a ball-and-socket joint to the output. This connection represents the output of the robot. To guarantee a perfect RCM there needs to be a certain ratio between some geometric parameters of the machine. This ratio is based on the Thales theorem and will be explained in details in this article. The paper will also present the detailed kinematics and its optimization, some construction details of the prototype and geometric model. At the end we will propose some applications as well as the needed modifications to guarantee application specific performance.

2006

Optimisation de la conception du robot parallèle Delta cube de très haute précision

Tiavina Niaritsiry

In the high-precision industry, most operations require the use of robots able to accomplish highly accurate and repeatable motions. In order to meet the desired level of absolute accuracy, one has to limit or even suppress the effects of different sources of inaccuracy by means of an appropriate calibration. However, calibration techniques cannot be applied to compensate inaccuracies occuring along passive (non-actuated) degrees of freedom (e.g orientation errors on the end-effector of a 3 degrees-of-freedom (DOF) in translation robot). The main goal of this thesis is to evaluate and benchmark the effects of these different sources of inaccuracy. Moreover, a set of design rules are proposed in order to optimize flexure parallel robots regarding their absolute accuracy. The robots studied in this work are of "Delta Cube" type, having their kinematic chains composed of translational stages and space parallelograms (acting as universal joints). These robots have the following features: their 3 DOF are the (x, y, z) translations on the Euclidean space, the stroke of each DOF goes from ±1 mm to ± 4 mm, their repeatabilities are at the nanometre range (thanks to the absence of dry friction and mechanical play), their resolutions are within a few nanometers (only limited by the captors used), their small sizes go from 1,5 dm3 to 13 dm3. The analysis of the effects of the different sources of inaccuracy has been focused on the following points: the basic elements composing the robot structure (translational stage, space parallelogram). Studying the influence on the absolute accuracy caused by a variation of a given geometric dimension provides knowledge on how to optimize the overall robot dimensions regarding absolute accuracy; the assembly of the different basic elements on the kinematic chain (in particular their relative orientation) is also critical for the absolute accuracy of the robot since it may cause parasitic effects such as orientation errors in the end-effector; the type and location of the different captors, motors and the frame can also influence accuracy. The analysis of the influence of each source of inaccuracy (manufacturing tolerances, temperature variations, assembly defaults, effect of external loads) and their coupling has been mainly performed numerically by means of Finite-Element Models. Theoretical results have been verified by experimental data. Considering the simulation results for each basic structure as well as the comparison of different assembly variants, general design rules have been proposed in order to optimize a given flexure parallel robot regarding absolute accuracy and considering also the application the robot is made for. This work is a contribution to the design of high-precision flexure parallel robots regarding absolute accuracy. It is also an important tool for the engineer in order to make the calibration work easier.