A two-fingered robot gripper with variable stiffness flexure hinges based on shape morphing

This paper presents a novel approach for developing robotic grippers with variable stiffness hinges for dexterous grasps. This approach for the first time uses pneumatically actuated pouch actuators to fold and unfold morphable flaps of flexure hinges thus change stiffness of the hinge. By varying the air pressure in pouch actuators, the flexure hinge morphs into a beam with various open sections while the flaps bend, enabling stiffness variation of the flexure hinge. This design allows 3D printing of the flexure hinge using printable soft filaments. Utilizing the variable stiffness flexure hinges as the joints of robotic fingers, a light-weight and low-cost two-fingered tendon driven robotic gripper is developed. The stiffness variation caused due to the shape morphing of flexure hinges is studied by conducting static tests on fabricated hinges with different flap angles and on a flexure hinge with flaps that are bent by pouch actuators subjected to various pressures. Multiple grasp modes of the two-fingered gripper are demonstrated by grasping objects with various geometric shapes. The gripper is then integrated with a robot manipulator in a teleoperation setup for conducting a pick-and-place operation in a confined environment

Design, fabrication and control of soft robots

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics.National Science Foundation (U.S.) (Grant IIS-1226883

A simple design rule for 1st order form-closure of underactuated hands

The property of form-closure of a grasp, as generally defined in the literature, is based on the assumption that contact points between the hand and the object are fixed in space. However, this assumption is false when considering a grasp exerted by an underactuated hand, since in this case, it is not possible to control the position of each phalanx independently. In spite of researchers' interest in studying form-closure, none of the available published work on this subject takes into consideration the particular kinematics of underactuated hands. Actually, there are few available tools to qualify or quantify the stability of a grasp exerted by an underactuated hand, thus the design of underactuated hands mostly results from an intuitive approach. This paper aims to reduce this gap. <br><br> A classification of underactuated hands is proposed, based on the expression of contact forces. This highlights the influence of non-backdrivable mechanisms introduced in the transmission of the closing motion of the hand on the stability of the grasp. The way to extend the original definition of form-closure to underactuated grasps is illustrated. A more general definition is formulated, which checks the stability of the set "object + hand". Using this new definition, a simple rule is proposed for designing a hand capable of achieving 1st order form-closed grasps. <br><br> <i>This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.</i&gt

A Vacuum-driven Origami “Magic-ball” Soft Gripper

Soft robotics has yielded numerous examples of soft grippers that utilize compliance to achieve impressive grasping performances with great simplicity, adaptability, and robustness. Designing soft grippers with substantial grasping strength while remaining compliant and gentle is one of the most important challenges in this field. In this paper, we present a light-weight, vacuum-driven soft robotic gripper made of an origami “magic-ball” and a flexible thin membrane. We also describe the design and fabrication method to rapidly manufacture the gripper with different combinations of lowcost materials for diverse applications. Grasping experiments demonstrate that our gripper can lift a large variety of objects, including delicate foods, heavy bottles, and other miscellaneous items. The grasp force on 3D-printed objects is also characterized through mechanical load tests. The results reveal that our soft gripper can produce significant grasp force on various shapes using negative pneumatic pressure (vacuum). This new gripper holds the potential for many practical applications that require safe, strong, and simple graspingUnited States. Defense Advanced Research Projects Agency (award number FA8650-15-C-7548)National Science Foundation (U.S.) (award number 1830901)Wyss Institute for Biologically Inspired EngineeringJD.co

An Underactuated Flexible Instrument for Single Incision Laparoscopic Surgery

More and more patients and surgeons have switched from open surgery to minimally invasive surgery over these years. This exciting advancement has brought massive benefits to patients. Researchers and institutions have proposed robot assisted surgery which combines the advantage of developed robot system and human experience. This thesis reviews state of the art in this area and analyze some advanced surgical instrument for single incision laparoscopic instrument, then propose a design of robotic instrument for single incision laparoscopic surgery which can be integrated with collaborative robot manipulator to construct a surgical robot system.Single-incision laparoscopic surgery (SILS) has its own features and advantages compare to other minimally invasive surgery techniques which also lead to special design requirements for SILS instruments, among which increased flexibility compare to multi-incision surgery instruments is an important part. So we want to design a robotic surgical instrument that has increased flexibility compare to traditional instruments for other MIS techniques. As a laparoscopic robotic instrument compactness and light weight are also our considerations.Single incision laparoscopic surgery (SILS) inserts multiple instruments and laparoscopes through a single trocar which reduces trauma. But this improvement for patients caused difficulty in operation because of instruments triangulation, laparoscope field-of-view, etc. That brings up our challenges in designing a robotic instruments. Designing a highly flexible robotic instrument that provides sufficient workspace and good triangulation in order to relieve the difficulties introduced by narrow instrument trocars.We want to implement a highly recognized surgical instrument with a designed robotic instrument actuation pack. These two parts compose a robotic surgical instrument for single incision laparoscopic surgery. And we want to analyze the performance and viability of our design approach for SILS application

Learning Haptic-based Object Pose Estimation for In-hand Manipulation Control with Underactuated Robotic Hands

Unlike traditional robotic hands, underactuated compliant hands are challenging to model due to inherent uncertainties. Consequently, pose estimation of a grasped object is usually performed based on visual perception. However, visual perception of the hand and object can be limited in occluded or partly-occluded environments. In this paper, we aim to explore the use of haptics, i.e., kinesthetic and tactile sensing, for pose estimation and in-hand manipulation with underactuated hands. Such haptic approach would mitigate occluded environments where line-of-sight is not always available. We put an emphasis on identifying the feature state representation of the system that does not include vision and can be obtained with simple and low-cost hardware. For tactile sensing, therefore, we propose a low-cost and flexible sensor that is mostly 3D printed along with the finger-tip and can provide implicit contact information. Taking a two-finger underactuated hand as a test-case, we analyze the contribution of kinesthetic and tactile features along with various regression models to the accuracy of the predictions. Furthermore, we propose a Model Predictive Control (MPC) approach which utilizes the pose estimation to manipulate objects to desired states solely based on haptics. We have conducted a series of experiments that validate the ability to estimate poses of various objects with different geometry, stiffness and texture, and show manipulation to goals in the workspace with relatively high accuracy

Design of a Variable Stiffness Passive Layer Jamming Structure for Anthropomorphic Robotic Finger Applications

Soft robots can effectively mimic human hand interface characteristics and facilitate collaborative operations with humans in a safe manner. This dissertation research concerns the design and fabrication of a low cost variable stiffness structure for applications in compliant robotic fingers. A conceptual design of a compact multi-layer structure is proposed for realizing variable stiffness, when applied to underactuated fingers of an anthropomorphic robotic hand. The proposed design comprises thin material layers with clearance that permits a progressive hardening feature while grasping and added design flexibility and tuning of the fingers’ compliance. The design permits stiffness variations in a passive manner in the soft contact regions. The design is realized to ensure ease of scalability and cost-effective fabrication by the ’Additive Manufacturing (AM)’/3D-printing technology. Both the multi-layer structures and the fingers could be fabricated as a single entity, and from a single base material with relatively low elastic modulus. The proposed design also exhibits finite degrees-of-freedom representative of the human finger - The feasibility of the design and its manufacturability are verified through prototype fabrication using a readily available 3D-printing material, namely; 'Thermoplastic PolyUrethane (TPU)' with Young’s Modulus of 25MPa. The chosen material permitted low stiffness of the multi-layer structure in the contact interface under relatively small deformations, while ensuring sufficient rigidity on the non-contact regions of the finger. A finite element (FE) model is formulated considering 3D tetrahedral elements and a nodal-normal contact detection method together with the augmented Lagrange formulation. The model is analyzed to determine the force-displacement characteristics of the structure subject to linearly increasing compressive load, under the assumption of low interface friction. A simplified analytical model of the multi-layer structure is also formulated considering essential boundary and support conditions for each individual layer. The model revealed progressive hardening characteristics of the multilayer structure during compression due to sequential jamming of individual layers. The force-displacement characteristics of the design could thus be varied by varying the multi-layer structure parameters, such as number of layers, thickness of individual layers, material properties, and clearance between the successive layers. It is shown that the simplified analytical model could provide reasonably good estimate of the force-deflection properties of the structure in a computationally efficient manner. The analytical model is subsequently used to investigate the influences of variations in the multilayer structure parameters in a computationally efficient manner. It is shown that the proposed design offers superior tuning flexibility to realize desired force-displacement characteristics of the structure for developing scalable anthropomorphic robotic fingers of a compliant robotic hand, in addition to the cost-effective manufacturability

The kinematic preshaping of triggered self-adaptive linkage-driven robotic fingers

In this paper, the issue of the kinematic - as opposed to dynamic - preshaping of self-adaptive robotic fingers driven by linkages is discussed. A method to obtain designs of these fingers capable of various behaviours during their closing motions is presented. The method is based on using triggered passive elements in carefully selected joints of the finger and the selection or optimization of geometric parameters to obtain particular kinematic relationships between the motions of the phalanges. This method is very general and can be applied to any self-adaptive robotic finger in order to obtain many different types of closing motions. Examples given in this paper are focusing on two different preshaping motions, the first one aims at allowing pinch grasps while the second mimics a human finger. The fundamental aim of this paper is to show that various preshapings of self-adaptive fingers are possible, not just one, and to give two step-by-step examples