Fingertip Design Research Articles

Automated Grasp Planning and Finger Design Space Search Using Multiple Grasp Quality Measures

As the industry shifts to automated manufacturing and the assembly of parts in smaller batches, there is a clear need for an efficient design of grippers. This paper presents a method for automated grasp planning and finger design for multiple parts using four grasp quality measures that capture the following important requirements for grasping: (i) uniform contact force distribution; (ii) better gravity wrench resistance; (iii) robustness against gripper positioning error; and (iv) ability to resist larger external wrench on the object. We introduce the fingertip score to quantify the grasp performance of a fingertip design over all the objects. The method takes the CAD model of the objects as the input and outputs the optimal grasp location and the best finger design. We use the method for a three-point grasp with a parallel jaw gripper. We validate our method on two sets of objects. Results show how each grasp quality measure behaves on different objects and the variation in the fingertip score with finger design. Finally, we test the effectiveness of the optimal finger design experimentally. The three-point grasp is suitable for grasping objects larger than is possible with shape-matching fingertips.

Soft Magnetic Fingertip With Particle-Jamming Structure for Tactile Perception and Grasping

Typically, the fingertips of a dexterous robotic hand are designed to be rigid and equipped with a variety of sensors to provide tactile perception. However, this design scheme renders the grasping of small objects difficult because rigid fingertips usually have a small contact area with the objects. In this paper, we propose a novel fingertip design that combines soft tactile skin and a particle jamming structure. Benefiting from the particle jamming structure, the soft skin and fluid-state jamming particle material ensure that the fingertip encloses the object as much as possible when in contact with it. Then, the application of a vacuum turns the particle material into a high stiffness solid state, allowing it to hold objects. Soft tactile skin integrated with permanent magnetic particles estimates contact information between the fingertip and objects. Thus, utilizing the soft tactile skin and particle jamming structure the fingertip can perceive and grasp objects simultaneously. The proposed soft fingertip module is fabricated by molding, which reduces the processing cycle time and cost. Additionally, a series of experiments were conducted to demonstrate the performance of this novel fingertip design. The results validate that the proposed robotic fingertip can grasp tiny objects while perceiving contact position and force information.

Automatic Gripper-Finger Design, Production, and Application: Toward Fast and Cost-Effective Small-Batch Production

Tactile robot-based assembly line adaptation of new products is still limited by the manual redesign, manufacturing, and exchange of the end-effector setup since the gripper fingers must often be adapted to the geometry of the product components to ensure a successful assembly process. In this article we present an automatic finger design, production, and evaluation pipeline, developed to improve this adaptation process. Two different form-closure–based design principles have been implemented to automatically generate the fingertip geometry: a projected surface representation-based approach as well as a Bézier surface fitting strategy. The resulting fingertips are printed via an automatic production unit and experimentally evaluated based on pick and insertion tasks for three different manipulation objects. To illustrate the potential usage of the introduced design methods for machine learning-based fingertip design approaches, we set up the training and testing process for a neural network-based design method. The proposed automatic fingertip design, production, and application framework represent a step further toward small-batch–size production, since the assembly adaptation effort, flexibility, and scalability are significantly improved.

Towards Task-Specific Modular Gripper Fingers: Automatic Production of Fingertip Mechanics

The adaption of robotic assembly lines to new products is generally slow and costly, binding the economical usage of a single line to a few products manufactured in masses. An important time factor is the adaption of the assembly robot's gripper fingers to the new product components - since finger design, production, and mounting is done manually. In this letter, we introduce an approach for automatic task-specific fingertip production and application. Our system is potentially able to reduce the assembly line customization time mentioned above by automatically printing customized fingertips onto a pre-produced finger-base and storing them in a dedicated finger library before the product assembly process begins. The assembly robot can then autonomously load and use these produced and stored fingers for the designated manipulation task by utilizing a specially developed quick finger exchange system. The setup is experimentally validated by conducting automatic production of three different fingertips and executing grasp-stability tests as well as multiple pick- and insertion tasks, with and without position offsets - using these fingertips. The proposed approach, indeed, goes beyond fingertip production and serves as a foundation for a fully automatic fingertip design, production, and application pipeline.

PhotoElasticFinger: Robot Tactile Fingertip Based on Photoelastic Effect.

The sense of touch is fundamental for a one-to-one mapping between the environment and a robot that physically interacts with the environment. Herein, we describe a tactile fingertip design that can robustly detect interaction forces given data collected from a camera. This design is based on the photoelastic effect observed in silicone matter. Under the force applied to the silicone rubber, owing to the stress-induced birefringence, the light propagating within the silicone rubber is subjected to the angular phase shift, where the latter is proportional to the increase in the image brightness in the camera frames. We present the calibration and test results of the photoelastic sensor design on a bench using a robot arm and with a certified industrial force torque sensor. We also discuss the applications of this sensor design and its potential relationship with human mechano-transduction receptors. We achieved a force sensing range of up to 8 N with a force resolution of around 0.5 N. The photoelastic tactile fingertip is suitable for robot grasping and might lead to further progress in robust tactile sensing.

Jamming-Free Immobilizing Grasps Using Dual-Friction Robotic Fingertips

Successful grasping of objects with robotic hands is still considered a difficult task. One aspect of the grasping problem is the physical contact interaction between the robotic fingertips and the object. Friction at the fingertip contacts can improve grasp robustness, but frictional fingertips may be difficult to precisely place on the object's perimeter. This paper describes a novel fingertip design that can switch from frictionless to frictional modes. The transformation from frictionless to frictional contact is achieved passively by the finger force exerted on the object at the target grasp. A novel swivel mechanism ensures that the force magnitude required to switch friction states is independent on the grasped object's contact normal direction, thus ensuring robustness. Analysis of the displacement and eventual sliding of the fingertip contacts in response to external torque is presented, taking into account the amount of friction and the compliant behavior of the fingertip mechanism. Experiments validate the analytic model and demonstrate the fingertip's ability to change friction modes by the applied force magnitude irrespective of the contact normal direction. In line with the analytic model predictions, the experiments show that when converted to frictional contacts, the fingertips provide a more robust and hence secure grasp in the presence of external disturbances. The robustness of the fingertips is further validated by real-world demonstrations shown in an external video referenced in the paper.

Soft Fingertips With Tactile Sensing and Active Deformation for Robust Grasping of Delicate Objects

Soft fingertips have shown significant adaptability for grasping a wide range of object shapes, thanks to elasticity. This ability can be enhanced to grasp soft, delicate objects by adding touch sensing. However, in these cases, the complete restraint and robustness of the grasps have proved to be challenging, as the exertion of additional forces on the fragile object can result in damage. This letter presents a novel soft fingertip design for delicate objects based on the concept of embedded air cavities, which allow the dual ability of tactile sensing and active shape-changing. The pressurized air cavities act as soft tactile sensors to control gripper position from internal pressure variation; and active fingertip deformation is achieved by applying positive pressure to these cavities, which then enable a delicate object to be kept securely in position, despite externally applied forces, by form closure. We demonstrate this improved grasping capability by comparing the displacement of grasped delicate objects exposed to high-speed motions. Results show that passive soft fingertips fail to restrain fragile objects at accelerations as low as 0.1 m/s $^{2}$ , in contrast, with the proposed fingertips delicate objects are completely secure even at accelerations of more than 5 m/s $^{2}$ .

The Form and System of the Roof-end tile in the founding of Daetongsa Temple in Baekje Ungjin Dynasty

대통사는 527년 백제 웅진기 공주지역에 창건되었다. 일제강점기 가루베 지온에 의해 ‘대통’명 인각와가 수습된 이후 대통사(지)는 현재 백제사의 중요한 논쟁 대상이 되고 있다. 하지만 최근까지 대통사를 입증할만한 유구는 확인되지 않았다. 2018년 공주시 반죽동 197-4번지 유적에서는 ‘대통’명으로 볼 수 있는 인각와를 비롯해 수막새와 암막새, 소조상, 치미, 토기 등 다양한 백제시기의 유물이 출토되었다. 특히 내림마루나 추녀마루에 사용된 것으로 보이는 완형의 마루수막새도 한 점 수습되었다. 수막새는 화판의 판단부에 따라 크게 7가지 형식으로 분류되었다. 이 중 창건와로는 판단원형돌기식을 비롯한 판단융기식, 판단돌기식, 판단첨형식, 돌대식 등이 추정되었다. 창건 수막새의 문양은 연화문이 주류를 이루었고, 일부 판단융기식, 판단첨형식, 돌대식 등은 그 동안 한성기~사비기 등의 백제유적에서 검출된 바 없는 초출 자료로 파악되고 있다. 수막새의 문양 계통은 대부분 남조에 있었음을 알 수 있고, 이는 사찰 창건과 관련하여 남조 장인의 백제 파견과 밀접한 관련이 있을 것으로 생각된다. 이러한 장인 파견은 비조사 창건과 관련하여 백제의 장인이 일본에 파견된 사실과 크게 다르지 않을 것으로 판단된다. 대통사지의 탐색 작업은 지금도 계속적으로 진행되고 있다. 다량의 유물이 출토되었음에도 불구하고 아직까지 대통사지의 흔적은 확인되지 않았다. 하지만 이의 형적이 드러날 날도 머지않았을 것으로 생각된다.Daetongsa Temple was founded in 527 in the Gongju area of the period of the Woongjin of Baekje. Since the recognition of ‘Daetong’ and ‘roof tile with stamped letter’ were settled by the Garobe Zion during the Japanese colonial period, Daetongsa(temple site) is now an important subject of debate of Baekje history. Until recently, however, no remains have been identified to prove the Daetongsa. In 2108, the remains from various Baekje periods, such as the roof tile with stamped letter, which can be considered as ‘Daetong’, the Roof-end tile, concave roof-end tile with finger-tip design, clay statues, ridge-end tile, and earthenware, etc. were excavated at the site of 197-4, Banjuk-dong, Gongju City. In particular, a ridge-end tile, which seems to have been used for a gable ridge or hip, was also recovered. The roof-end tile was classified into 7 types according to the appearance of the petal end. Among them, the roof tiles at the time of foundation were estimated to include the Pandanwonhyungdolgi type(petal-tip round form), Pandanyunggi type(the form in which the petal end rises), Pandandolgi type(a form with a protrusion at the end of a petal), Pandancheomhyung type(petal pointed form) and Doldae type(the form with a line in the middle of the petal). The pattern of the Roof-end tile in the founding was mainly composed of lotus pattern, and Some Pandanyunggi type, Pandancheomhyung type, and Doldae type, etc can be understood as the first data that has not been excavated from Baekje remains such as Hansung period and Sabi period. The pattern system of the roof-end tile was mostly in Namjo, China, and it is thought that this is closely related to the dispatch of the Namjo craftsman to Baekje in relation to the establishment of the temple. It is judged that the dispatch of these craftsmen is not much different from the fact that Baekje craftsmen were dispatched to Japan in relation to the establishment of Askadera in Japan. The search for Daetongsa Temple site is still ongoing. Despite the large quantity of relics being excavated, no traces of Daetonsa Temple site have been identified. However, it is thought that it will not be long before its trace is revealed.

Geometry Optimisation of a Hall-Effect-Based Soft Fingertip for Estimating Orientation of Thin Rectangular Objects.

Soft tactile sensors have been applied to robotic grippers for assembly. It is a challenging task to obtain contact information and object orientation using tactile sensors during grasping. Currently, the design of Hall-effect-based tactile sensors to perform such tasks is based on trial and error. We present a method of investigating the optimal geometrical design of a cylindrical soft sensor to increase its sensitivity. The finite element model of a soft fingertip was constructed in Abaqus with two design variables, i.e., hollow radius and magnet position. Then, the model was imported into Isight, with the maximisation of magnet displacement as the objective function. We found that the optimal design was at the boundary of the parameter design space. Four fingertips were fabricated with one intuitive, one optimal, and two optional sets of parameters. Experiments were performed, and object orientation was estimated by utilising linear approximation and a machine learning approach. Good agreements were achieved between optimisation and experiments. The results revealed that the estimated average error in object orientation was decreased by the optimised fingertip design. Furthermore, the 3-axis forces could successfully be estimated based on sensor outputs.

Assessment of soft materials for anthropomorphic soft robotic fingertips

Abstract In recent decades, research on soft robot manipulations and their materials attracted a huge momentum among various researchers. Selection of appropriate soft material is a vital role in robotic fingertip design, which enables the object to be held in proper orientation without slip and damage. Development of such an anthropomorphic type of soft hand requires knowledge about material selection, types of finger contact and the mechanism behind grasping. This research work presents a comprehensive comparison of six chosen soft materials with human skin for improved robotic manipulation. Extensive research is required to develop such soft hands for better manipulation becausein the final analysis, the human hand is the best soft manipulator as it conforms to objects easily through good contact with an object. In the past decades, many researchers have tried to replace metal hand of robots with appropriate soft materials to enable better manipulation. In this work, the magnitude of contact area, contact pressure and vertical depression of six soft materials was compared with human skin with respect to precision grasping. The simulation results clearly show that neoprene rubber exhibits a close relationship with the characteristics of human skin.

Lightweight, High-Force Gripper Inspired by Chuck Clamping Devices

In this letter, we present a novel gripper, whose design was inspired by chuck clamping devices, for transferring heavy objects and assembling parts precisely in industrial applications. The developed gripper is lightweight (0.9 kg), can manipulate heavy payloads (over 23 kgf), and can automatically align its position and posture via a grasping motion. A fingertip design criterion is presented for the position alignment, while a control strategy is presented for the posture alignment. With one actuator, this gripper realized the above features. This letter describes the mathematical analyses and experiments used to validate these key metrics.

Fingertip Surface Optimization for Robust Grasping on Contact Primitives

We address the problem of fingertip design by leveraging on the fact that most grasp contacts share a few classes of local geometries. In order to maximize the contact areas for achieving more robust grasps, we first define the concept of Contact Primitive, which represents a set of contacts of similar local geometries. Thereafter, we propose a uniform cost algorithm, which is formulated as a decision making process in a tree structure, to cluster a set of example grasp contacts into a finite set of Contact Primitives. We design fingertips by optimization to match the local geometry of each contact primitive, and then three-dimensionally print them using soft materials to compensate for optimization residuals. For novel objects, we provide an efficient algorithm to generate grasp contacts that match the fingertip geometries while together forming stable grasps. Comparing to a baseline of flat fingertip design, the experiment results show that our design significantly improves grasp stability, and it is more robust against various uncertainties.

A Riemannian-Geometric Approach for Intelligent Control and Fingertip Design of Multi-fingered Hands

Based upon the analysis of modeling and control of two-dimensional (2-D) grasping and manipulation of arbitrary rigid objects under rolling contact constraints, geometrical conditions for the design of desired fingertip shapes of robot fingers are discussed from the Riemannian-geometric standpoint. A required condition is given as an inequality expressed in terms of quantities of the second fundamental form of fingertip contour curves, although the quantities do not enter into the Euler–Lagrange equation of motion of the overall fingers/object system. Satisfaction of the inequality is necessary for stabilization of grasping by using fingers–thumb opposable control signals without use of external sensings or knowledge of an object to be grasped. At the same time, asymptotic convergence of a solution to the closed-loop dynamics of 2-D precision prehension by a pair of multi-joint robot fingers is proved under rolling contact constraints and the existence of redundancy in the system's degrees of freedom. This is regarded as an extension of the Dirichlet–Lagrange stability theorem to a dynamical system with redundancy and geometric constraints.

Towards Humanlike Social Touch for Sociable Robotics and Prosthetics: Comparisons on the Compliance, Conformance and Hysteresis of Synthetic and Human Fingertip Skins

The artificial hands for sociable robotics and prosthetics are expected to be touched by other people. Because the skin is the main interface during the contact, a need arises to duplicate humanlike characteristics for artificial skins for safety and social acceptance. Towards the goal of replicating humanlike social touch, this paper compares the skin compliance, conformance and hysteresis of typical robotic and prosthetic skin materials, such as silicone and polyurethane, with the published biomechanical behavior of the human fingertip. The objective was achieved through materials characterization, finite element (FE) modeling and validation experiments. Our initial attempt showed that the selected types of silicone and polyurethane materials did not exhibit the same qualities as the human fingertip skin. However, the methodologies described herein can be used to evaluate other materials, their possible combinations or other fingertip design configurations.

Modeling of Viscoelastic Contacts and Evolution of Limit Surface for Robotic Contact Interface

Viscoelastic contact is a type of contact which includes, in addition to linear or nonlinear elastic response, time-dependent response due to relaxation or creep phenomena that govern the contact behavior. The characteristics of the time-dependent relaxation of such a viscoelastic contact are typically exponentially decaying functions, and exponentially growing functions for creep, respectively. Such contacts can be found in anthropomorphic robotic fingers, soft materials, viscoelastic skin with rigid core, and human fingers and feet. In this paper, the nature of viscoelastic contacts is investigated, and the evolution of their friction limit surfaces and of the pressure distributions at the contact interface are studied. Two cases commonly found in robotic grasping and manipulation are discussed. Based on the modeling formulation, it is found that the two important parameters of analysis and modeling for such contacts, i.e., the radius of contact area and the profile of pressure distribution, can be chosen using proposed coupling equations as the viscoelastic contact interface evolves with time. The new contribution of this paper includes a proposal of coupling equations between the two important parameters to describe the viscoelastic contact interface, and a study of the evolution of limit surfaces for viscoelastic contact interface due to temporal dependency, and the implication on grasp stability. It is found from the evolution of limit surfaces that when normal force is applied with typical viscoelastic contacts, grasp becomes more stable as time elapses. The modeling can be applied to the design of fingertips and the analysis of robotic grasping and manipulation involving viscoelastic fingers