A novel piezoelectric-actuated microgripper simultaneously integrated microassembly force, gripping force and jaw-displacement sensors: design, simulation and experimental investigation

For assembling easy-to-deform and easy-to-broken micropart, accurate acquisition of microassembly force and gripping force during microassembly process while ensuring parallel movement of jaws of microgripper is the key to ensure consistency, accuracy and reliability of microassembly without damage. In addition, simultaneously real-time detection of jaw-displacement of microgripper is also a necessary condition for rapid and accurate microassembly. This paper proposes and realizes a principle of a parallelogram compliant mechanism (PCM) based piezoelectric-actuated microgripper, which simultaneously integrates with microassembly force, gripping force and jaw-displacement sensors for the first time and ensures parallel movement of jaws under no-load and gripping micropart. The major structure of proposed microgripper is a monolithic compliant mechanism (MCM) composed of a primary lever compliant mechanism and three-stage PCM in series. Among them, the third-stage PCM is orthogonal to other two PCM in series. MCM transmits the displacement and force from piezoelectric actuator to jaws while transforming microassembly force, gripping force and jaw-displacement into surface strain of single-notch hinges of PCM with three-stage in series. On this basis, simultaneously sensing microassembly force, gripping force and jaw-displacement is realized by monitoring surface strain of single-notch hinges of three-stage PCM. The sensing equations of the microassembly force, gripping force, and jaw-displacement are established, respectively. A microgripper is manufactured, a microgripper system is realized and the integrated sensors are calibrated. The hysteresis characteristics, creep characteristics and time response are tested experimentally. Two examples of microassembly sub-process are simulated and carried out on the constructed microassembly experimental setup. The theoretical and experimental results show that the designed microgripper can simultaneously acquire the microassembly force, gripping force and jaw-displacement with high sensitivity, linearity and resolution in processes of gripping hohlraum and applying microassembly force to hohlraum while ensuring the parallel movement of the gripping jaws when gripping and not gripping micropart.

A 3D-Printed Fin Ray Effect Inspired Soft Robotic Gripper with Force Feedback

Soft robotic grippers are able to carry out many tasks that traditional rigid-bodied grippers cannot perform but often have many limitations in terms of control and feedback. In this study, a Fin Ray effect inspired soft robotic gripper is proposed with its whole body directly 3D printed using soft material without the need of assembly. As a result, the soft gripper has a light weight, simple structure, is enabled with high compliance and conformability, and is able to grasp objects with arbitrary geometry. A force sensor is embedded in the inner side of the gripper, which allows the contact force required to grip the object to be measured in order to guarantee successful grasping and to provide the most suitable gripping force. In addition, it enables control and data monitoring of the gripper’s operating state at all times. Characterization and grasping demonstration of the gripper are given in the Experiment section. Results show that the gripper can be used in a wide range of scenarios and applications, such as the service robot and food industry.

Evolutionary Grasp Planning for Sheet Metal Parts With Multi-Type Grippers

Grasping sheet metal objects for manufacturing operations requires custom-made robot-mounted end-effectors to grip the parts. Modern end-effectors use multi-type grasp where a combination of gripper types such as suction cups, magnets, and fingers may be used. This paper presents a genetic algorithm-based approach of grasp design automation. The algorithm first generates an option space of possible grasping locations by analyzing the geometry of the sheet metal part and then uses a genetic algorithm to optimize the grasp using up to five magnets and suction cups. The algorithm includes as fitness criteria the factor of safety of the total gripping force against part weight, the unbalanced moment created by the gripping forces and part weight, the cost of the grasp, and three combinations of these parameters. The GA features asexual reproduction, mutation, and elitism. The algorithm is implemented in the Siemens NX™ Knowledge Fusion language and on Microsoft VBA code. The paper presents detailed test results and sensitivity analyses that indicate that genetic algorithms can produce viable solutions for multi-type grasp configurations and that the algorithm behaves in response to varying its control parameters in ways that are logically anticipated.

Cable manipulation with a tactile-reactive gripper

Cables are complex, high-dimensional, and dynamic objects. Standard approaches to manipulate them often rely on conservative strategies that involve long series of very slow and incremental deformations, or various mechanical fixtures such as clamps, pins, or rings. We are interested in manipulating freely moving cables, in real time, with a pair of robotic grippers, and with no added mechanical constraints. The main contribution of this paper is a perception and control framework that moves in that direction, and uses real-time tactile feedback to accomplish the task of following a dangling cable. The approach relies on a vision-based tactile sensor, GelSight, that estimates the pose of the cable in the grip, and the friction forces during cable sliding. We achieve the behavior by combining two tactile-based controllers: (1) cable grip controller, where a PD controller combined with a leaky integrator regulates the gripping force to maintain the frictional sliding forces close to a suitable value; and (2) cable pose controller, where an linear–quadratic regulator controller based on a learned linear model of the cable sliding dynamics keeps the cable centered and aligned on the fingertips to prevent the cable from falling from the grip. This behavior is possible with the use of reactive gripper fitted with GelSight-based high-resolution tactile sensors. The robot can follow 1 m of cable in random configurations within two to three hand regrasps, adapting to cables of different materials and thicknesses. We demonstrate a robot grasping a headphone cable, sliding the fingers to the jack connector, and inserting it. To the best of the authors’ knowledge, this is the first implementation of real-time cable following without the aid of mechanical fixtures. Videos are available at http://gelsight.csail.mit.edu/cable/

Study on the Articulated Finger Based on Pneumatic Soft Joint

This article described a novel pneumatic soft joint used to make articulated soft fingers. This soft joint was designed by improving the basic structure of the fast pneumatic network. The joint was made of high modulus E630 silicon, which can increase the reverse exhaust speed through its high structural elasticity. Aramid fabric was used to restrain the non-working direction of joints to reduce ineffective expansion, thereby reducing air consumption. The kinematics and statics model of the joint was established by the piecewise constant curvature (PCC) method, and the model was proved to be effective. The silicone staging pouring process was used in the manufacture of joints and fingers, which can achieve high-quality product rates. A soft finger actuator composed of three soft joints was designed and manufactured, whose length was 1.3 times the human finger. The finger can nimbly achieve the target motion, and the gripping force of the fingertip can reach 7.1N. The articulated soft finger actuator has applications in soft dextrous hands and soft gripper.

Record Length Chrome Liner Run Using Innovative, Low-Marking, Non-Ferrous Dies on a Mechanical Casing Running Tool

Abu Dhabi National Oil Company (ADNOC) has steadily advanced toward the use of a casing running tool (CRT) vs. conventional casing running methods to improve efficiency and safety. This advancement focused mainly on 9 ⅝ in to 20 in diameter casing and utilized internal grip tools. Recently they have searched for an external-grip CRT system that would allow them to effectively run the smaller diameter liners of both ferrous and chrome (Cr) materials, especially in the extended reach drilling (ERD) wells with maximum reservoir contact (MRC). For 20 years CRT companies manufactured tools with gripping dies that could efficiently run ferrous material liners. Development of gripping mechanisms which can effectively run corrosion resistant alloy (CRA) materials has been met with varying success. Some of the challenges are to manufacture gripping dies from non-ferrous materials that will not contaminate the CRA liner and develop a gripping pattern that does not mark the CRA liner more than is accepted by API 5CRA industry standards, but maintain effective gripping force. In addition to hoisting and making up the string with no slippage it needs to perform fluid circulation at 3,000 psi. Until recently the liners were typically run in a conventional method using power-tongs. One of the tools chosen for the trial runs was a well-proven, external-grip mechanical CRT designed specifically for smaller diameter casing and liners. It has a 500-ton hoist capacity and a 5,000 psi circulation rating and was packaged with a combination float and cushion tool and a wireless torque turn sub. Dies had been designed to meet the non-contamination and acceptable marking criteria previously mentioned and would be compatible with liners possessing as much as 25% Cr. The dies had been extensively lab-tested, including heavy pull tests and torque application tests, but had not previously been used in field applications. The ERD-MRC well chosen for this trial was planned to have a record length of 6 ⅝ in, 24 ppf, 13% Cr liner with a wedge thread premium connection. In addition to not contaminating the liner, ADNOC expected an average running speed in joints per hour equivalent to the conventional casing running methods and a reduction in time during circulations. The result of the trial was 589 connections (25,035 ft liner length) successfully run with an average running speed matching their expectations. The liner displayed very minimal marks and there were no issues when hoisting or torqueing the connections. In addition, there were no rejected connections during the run. This publication will review the preparation for the run, actual run details, photos of the die marks, torque graphs and conclusions expressed by the operator with recommendations for changes moving forward.

A vacuum-driven rubber-band gripper

Robotic grippers that gently handle objects of various shapes are required for various applications these days. Conventional finger-shaped grippers are multifunctional and can grip various objects; however, grasping an item without slippage requires planning the positioning of the fingers at appropriate locations on the item. Hence, a ring-shaped soft gripper that coils itself around objects like a rubber band is suggested in this paper. The proposed gripper comprises a soft tube containing laminated sponges interleaved with plastic sheets. Evacuation of the air within the sponges shrinks them and decreases the diameter of the ring, thereby allowing the gripper to firmly hold objects. The gripper is therefore flexible enough to coil around objects of various shapes without gaps. Furthermore, the rigidity of the compressed sponges inside the gripper prevents wobbling of the gripped objects. The air within the gripper can be used to adjust the gripping force. The minimum diameter of the gripper after evacuating the air within the sponges is approximately one-fourth of the original diameter. Thus, the proposed gripper is expected to be used in various applications as it automatically conforms to the different shapes while simply gripping objects gently and securely.