A soft gripper with variable stiffness inspired by pangolin scales,toothed pneumatic actuator and autonomous controller

Aiming at combining compliant covering and rigid lifting to the object grasping, this paper presents the design principle of a variable stiffness soft gripper and carries out its structural design, gripper fabrication and controller development. The proposed soft finger is composed of a variable stiffness layer and a pneumatic driven layer. The variable stiffness layer is inspired by the pangolins whose scales are flexible in daily activities and become tough when being threatened by predators. A toothed pneumatic actuator is designed to supply power with increased stiffness. The three-finger soft gripper is fabricated by 3D printing and molding of super elastic material. The tests for verifying grasping capability and variable stiffness are implemented. Experimental results show that the gripper can grasp a large variety of objects and achieve enhanced stiffness. The stiffness of the gripper is more than twice higher than the pneumatic gripper without variable stiffness structure. Finally, the control system for autonomous grasping is developed. The control block is divided into the actuation layer, information processing layer and user interface layer. According to the grasping process, the feedback signals in the information processing layer are collected by sensors. A safe grasping assessment is added to the control scheme for changing the gripper stiffness autonomously, which differs from the traditional soft gripper controller. The proposed soft gripper has variable stiffness, enhanced pneumatic input, autonomous control system. Therefore, it has great potential to be applied in the unstructured environment for effective, adaptable and safe object grasping.     

Adaptive neuro-fuzzy prediction of grasping object weight for passively compliant gripper

The development of universal grippers able to pick up unfamiliar objects of widely varying shapes and surfaces is a very challenging task. Passively compliant underactuated mechanisms are one way to obtain the gripper which could accommodate to any irregular and sensitive grasping objects. The purpose of the underactuation is to use the power of one actuator to drive the open and close motion of the gripper. The fully compliant mechanism has multiple degrees of freedom and can be considered as an underactuated mechanism. This paper presents a new design of the adaptive underactuated compliant gripper with distributed compliance. The optimal topology of the gripper structure was obtained by iterative finite element method (FEM) optimization procedure. The main points of this paper are in explanation of a new sensing capability of the gripper for grasping and lifting up the gripping objects. Since the sensor stress depends on weight of the grasping object it is appropriate to establish a prediction model for estimation of the grasping object weight in relation to sensor stress. A soft computing based prediction model was developed. In this study an adaptive neuro-fuzzy inference system (ANFIS) was used as soft computing methodology to conduct prediction of the grasping objects weight. The training and checking data for the ANFIS network were obtained by FEM simulations.     

Intelligent robotic gripper with adaptive grasping force

The on-off control robot gripper is widely employed in pick-and-place operations in Cartesian space for handling hard objects between two positions. Without contact force monitoring, it can not be applied in fragile or soft objects handling. Although, an appropriate grasping force or gripper opening for each target could be searched by trial-and-error process, it needs expensive force/torque sensor or an accurate gripper position controller. It has too expensive and complex control strategy disadvantages for most of industrial applications. In addition, it can not overcome the target slip problem due to mass uncertainty and dynamic factor. Here, an intelligent gripper is designed with embedded distributed control structure for overcoming the uncertainty of object’s mass and soft/hard features. A communication signal is specified to integrate both robot arm and gripper control kernels for executing the robotic position control and gripper force control functions in sequence. An efficient model-free intelligent fuzzy sliding mode control strategy is employed to design the position and force controllers of gripper, respectively. Experimental results of pick-and-place soft and hard objects with grasping force auto-tuning and anti-slip control strategy are shown by pictures to verify the dynamic performance of this distributed control system. The position and force tracking errors are less than 1 mm and 0.1 N, respectively.

     

抓取任务中的融差控制方法

依据“融差性思维”,提出了无需精确感知依旧可以在一定范围内有效工作的融差控制方法。具体分析了融差抓取方法如何运用相同控制量实现不同抓取任务的工作原理,这一原理使得融差抓取方法在面对一大类抓取任务时,不需要知道物体的具体参数,只需要知道这一大类物体的边界条件。进一步分析了融差抓取方法在欠驱动手爪上的适用性,并发现了欠驱动手爪的局限性。实验表明,在控制量设定不变的情况下,依据融差抓取方法,柔性手爪可以抓住且不抓坏宽度范围为5～45 mm的嫩豆腐,且能够成功抓取宽度范围为5～60 mm的硬质长方体;弹簧关节欠驱动手爪可以抓住且不抓坏宽度范围为20～40 mm的嫩豆腐,且能够成功抓取宽度范围为5～60 mm的硬质长方体。这体现了融差抓取方法的通用性和欠驱动手爪在抓取柔性物体时的局限性。最后,展示了柔性手爪使用融差抓取方法在桌面抓取应用中以简单的控制策略成功抓取不同形状、不同材质的物体。这充分说明了融差抓取方法不依赖于精确的对象感知及物体模型,能够简化控制策略。     

Miniature Pneumatic Curling Rubber Actuator Generating Bidirectional Motion with One Air-Supply Tube

Soft actuators driven by pneumatic pressure are promising actuators for mechanical systems in medical, biological, agriculture, welfare fields and so on, because they can ensure high safety for fragile objects from their low mechanical impedance. In this study, a new rubber pneumatic actuator made from silicone rubber was developed. Composed of one chamber and one air-supply tube, it can generate curling motion in two directions by using positive and negative pneumatic pressure. The rubber actuator, for generating bidirectional motion, was designed to achieve an efficient shape by nonlinear finite element method analysis, and was fabricated by a molding and rubber bonding process using excimer light. The fabricated actuator was able to generate curling motion in two directions successfully. The displacement and force characteristics of the actuator were measured by using a motion capture system and a load cell. As an example application of the actuator, a robotic soft hand with three actuators was constructed and its effectiveness was confirmed by experiments.     

Design and kinetostatic modeling of a compliant gripper for grasp and autonomous release of objects

A gripper with an embedded compliant bistable mechanism (BM) for gripping and autonomous release of objects is developed. Due to adhesion forces, objects might stick to the end effector of a gripper upon release, where a shaking operation may be employed to release the objects. Vibration of the end effector induced by an impact pestle adjacent to the shuttle mass of the BM may achieve autonomous release of objects adhered to the end effector. Gripping and autonomous release of objects are accomplished when the BM moves between its two stable equilibrium positions. An analytical model is developed to predict the kinetostatic behavior of the BM and to assist in the design of the gripper.     

基于软体手的机器人遥操作人机交互系统研制

为了提升抓取软体物体、易碎物体的完整性,设计制作了一种基于软体手的机器人遥操作人机交互系统。研制了一种嵌入了弯曲传感器的软体主手,获取人手的弯曲电信号,以此判断人手的弯曲程度,实现对软体从手系统的遥操作。并在远端软体从手中嵌入压力传感器,获取软体从手抓取目标时的表面压力电信号,以此来判断软体手抓取目标时的力度,实现力反馈。软体手人机交互系统能够减小传统刚体机械手抓取目标的限制,可有效抓取软体或易碎目标,实验表明了其有效性。     

Proposal of a shape adaptive gripper for robotic assembly tasks

This paper proposes a novel robotic gripper used for assembly tasks that can adaptively grasp objects with different shapes. The proposed hand has a combined structure between two kinds of shape adaptive mechanisms where one is the granular jamming and the other is a multi-finger mechanism driven by a single wire. Due to the effect of the two shape adaptive mechanisms, the pose of a grasped object does not change during an assembly operation. The proposed hand has four fingers where two are the active ones and the other two are the passive ones. The pose of the grasped object can be uniquely determined since the passive fingers are used to orient an object placed on a table before the active fingers are closed to grasp it. Assembly experiments of some kinds of parts are shown to validate the effectiveness of our proposed gripper.     

Development of universal vacuum gripper for wall-climbing robot

Task performed at a height, such as wall inspections are one of the dangerous tasks for humans. Thus, robotic technology for safety inspection is required. This research focuses on developing robots to climb vertical walls with flat and uneven surfaces, e.g. concrete, tile and riveted structure. To have wall-climbing capability, climbing robots use vacuum pads, claws, magnets, intermolecular force, and adhesive. However, each of these approaches has disadvantages. To achieve wall climbing on an uneven surface without scratching and staining, we have developed a novel vacuum pad named the Universal Vacuum Gripper (UVG), which is based on the Universal Gripper (UG). The UG is a robot hand using jamming transition of coffee powder inside a balloon to grip uneven material. The UVG is a vacuum pad with a deformable skirt based on the UG. If the skirt shape is deformed in accordance with the contact surface, air leaks can be avoided. Moreover, the deformed skirt can be stiffened, thereby working as a gripper. Here, we evaluate the proposed gripper, having both grasping and adhesion force. We also develop a wall-climbing robot with UVGs, and evaluate its performance on uneven surfaces under real-world conditions.     

gripper

Grasping of objects has been a challenging task for robots. The complex grasping task can be defined as object contact control and manipulation subtasks. In this paper, object contact control subtask is defined as the ability to follow a trajectory accurately by the fingers of a gripper. The object manipulation subtask is defined in terms of maintaining a predefined applied force by the fingers on the object. A sophisticated controller is necessary since the process of grasping an object without a priori knowledge of the object's size, texture, softness, gripper, and contact dynamics is rather difficult. Moreover, the object has to be secured accurately and considerably fast without damaging it. Since the gripper, contact dynamics, and the object properties are not typically known beforehand, an adaptive critic neural network (NN)-based hybrid position/force control scheme is introduced. The feedforward action generating NN in the adaptive critic NN controller compensates the nonlinear gripper and contact dynamics. The learning of the action generating NN is performed on-line based on a critic NN output signal. The controller ensures that a three-finger gripper tracks a desired trajectory while applying desired forces on the object for manipulation. Novel NN weight tuning updates are derived for the action generating and critic NNs so that Lyapunov-based stability analysis can be shown. Simulation results demonstrate that the proposed scheme successfully allows fingers of a gripper to secure objects without the knowledge of the underlying gripper and contact dynamics of the object compared to conventional schemes.     

A novel electrostatic based microgripper (cellgripper) integrated with contact sensor and equipped with vibrating system to release particles actively

This paper presents design and simulation of a novel electrostatic microelectromechanical systems gripper with an integrated capacitive contact sensor. Moreover, this microgripper is able to employ vibration to release micro objects (cells) actively. Lateral comb drive system is used to close the gap between the gripper arms and hold the objects while the transverse comb differential capacitances act as a contact sensor to prevent damaging the fragile micron-sized particles specifically biological cells. In addition, the capability of the microgripper in generating vibration at the end-effectors electrostatically is an advantage to facilitate releasing process by overbalancing the adhesion forces between the particle and the gripper arm. Finite element analysis based simulations are carried out to estimate the behavior of the microgripper while the standard SOI-MUMPs micromachining process is proposed for fabrication of the microgripper.     

Support vector regression methodology for prediction of input displacement of adaptive compliant robotic gripper

The prerequisite for new versatile grippers is the capability to locate and perceive protests in their surroundings. It is realized that automated controllers are profoundly nonlinear frameworks, and a faultless numerical model is hard to get, in this way making it troublesome to control utilizing tried and true procedure. Here, a design of an adaptive compliant gripper is presented. This design of the gripper has embedded sensors as part of its structure. The use of embedded sensors in a robot gripper gives the control system the ability to control input displacement of the gripper and to recognize specific shapes of the grasping objects. Since the conventional control strategy is a very challenging task, soft computing based controllers are considered as potential candidates for such an application. In this study, the polynomial and radial basis function (RBF) are applied as the kernel function of Support Vector Regression (SVR) to estimate and predict optimal inputs displacement of the gripper according to experimental tests and shapes of grasping objects. Instead of minimizing the observed training error, SVR _poly and SVR _rbf attempt to minimize the generalization error bound so as to achieve generalized performance. The experimental results show that an improvement in predictive accuracy and capability of generalization can be achieved by the SVR approach compared to other soft computing methodology.     

基于混合包围盒的碰撞检测算法

提出了一种基于k-dops包围盒与包围球相结合的碰撞检测算法。预处理阶段为几何对象构造包围盒二叉树,其中节点的内层构造k-dops包围盒,节点的外层构造包围球。碰撞检测阶段,首先利用包围球快速排除不可能发生相交的物体,然后利用k-dops包围盒进一步精确地判断物体对是否发生相交。通过与QuickCD算法的性能进行比较,证明了这种混合包围盒能够有效地提高复杂结构几何体之间碰撞检测的效率。     

Control of flexible mobile manipulators: positioning and vibration reduction using an eye-in-hand range camera

In this paper, the positioning of a long flexible manipulator on a moving platform is investigated. The problem is to position the gripper at a requested relative distance in front of an object with unknown location. For this purpose, the gripper is equipped with a range camera giving the distance to surrounding objects within, ∼1% and with a sampling rate above 1 kHz. The range measurements are used in combination with internal angle measurements from joint encoders to estimate both the flexibility in the mechanical construction and the relative distance from gripper to object. This is solved satisfactorily by an extended Kalman filter (EKF). For the motion control of the manipulator, a time-scaled feedback controller is suggested. A fast inner loop is used to damp out oscillations and reject disturbances, both from the platform and the manipulator. An outer control loop, with a lower closed-loop bandwidth, then steers the gripper, based on the range measurements, to the requested final position in front of the object. This loop assumes a stationary and rigid platform and a rigid manipulator. At this moment, only simulations of a flexible manipulator on a rigid platform have been studied. However, the results show that the flexibility can be estimated from indirect measurements of the range to the object and the joint angles. Also, good damping and disturbance rejection are achieved, as long as the bandwidth of the actuators is sufficiently high compared to the oscillation. The use of range measurements of the surrounding objects makes the positioning task very robust against an uncertain platform position.     

Novel Haptic Device Using Jamming Principle for Providing Kinaesthetic Feedback in Glove-Based Control Interface

This paper presents a new type of wearable haptic device which can augment a sensor glove in various tasks of telemanipulation. We present the details of its two alternative designs jamming tubes or jamming pads, and their control system. These devices use the jamming phenomena to change the stiffness of their elements and block the hand movement when a vacuum is applied. We present results of our experiments to measure static and dynamic changes in stiffness, which can be used to change the perception of grabbing hard or soft objects. The device, at its current state is capable of resisting forces of up to 7 N with 5 mm displacement and can simulate hardness up to the hardness of a rubber. However, time necessary for a complete change of stiffness is high (time constant 0.5 s); therefore, additional cutaneous interface was added in a form of small vibration motors. Finally, we show an application of the haptic interface in our teleoperation system to provide the operator with haptic feedback in a light weight and simple form.     

Development of a new noncontact gripper using swirl vanes

In this paper, we proposed a new noncontact gripper called as swirl gripper. It generates swirling air flow to create an upward lifting force. This force can be used to pick up a work piece placed underneath the swirl gripper without any contact. In comparison with conventional pneumatic noncontact grippers, the uniqueness of the new gripper lies in that it is electrically (rather than pneumatically) activated. We carry out this study for clarifying the mechanism of the swirl gripper. First, we show the design of the swirl gripper and briefly illustrate the mechanism by which it forms a negative pressure to create a lifting force. Then, we experimentally investigate the characteristics of the pressure distribution, based on which a theoretical analysis on the swirling flow is conducted. Furthermore, we measure the relationship between the lifting force and gap clearance and reveal that there exists a levitation zone where a work piece can maintain a stable levitation. Finally, we verify the practicability by successfully noncontact handling a Φ300 mm silicon wafer with four swirl grippers.     

Thin-film electrode based on TCNQ complex and immobilized enzyme for a glucose sensor

A thin film of TCNQ (tetracyanoquinodimethane) complex and immobilized glucose oxidase (GOD) has been prepared as a new type of enzyme electrode, and evaluated for an amperometric glucose-sensor application. This enzyme electrode is coated with two layers. The inner layer is TCNQ charge-transfer complex, which is prepared by the spontaneous electrolysis of Ag substrate in TCNQ solution. The outer layer consist of GOD and an electron mediator (dimethylferrocene) dispersed uniformly in the polymer matrix. Electron transfer from the outer layer to the inner layer take place with the aid of the mediator and the conducting charge-transfer complex. This enzyme electrode shows a rapid current response and is not affected by fluctuations of the dissolved oxygen concentration. Furthermore, a glucose-sensing system has been constructed by placing the counter electrode near the enzyme electrode. This system shows a rapid current response to a drop of glucose solution and a linear relationship between the response current and the glucose concentration on applying low potential. Therefore the system has been applied to human serum containing up to 25 mM glucose without preliminary treatment (diluting or mixing the sample).     

Automated Gripper Jaw Design and Grasp Planning for Sets of 3D Objects

An algorithm for automatically generating a common jaw design and planning grasps for a given set of polyhedral objects is presented. The algorithm is suitable for a parallel‐jaw gripper equipped with three cylindrical fingers. The common jaw design eliminates the need for custom made grippers and tool changing. The proposed jaw configuration and planning approach reduces the search associated with locating the finger contacts from six degrees‐of‐freedom to one degree‐of‐freedom. Closed‐form algorithms for checking force closure and for predicting jamming are developed. Three quality metrics are introduced to improve the quality of the planned grasps. The first is a measure of the sensitivity of the grasp to errors between the actual and planned finger locations. The second is a measure of the efficiency of the grasp in terms of the contact forces. The third is a measure of the dependence of force closure on friction. These quality metrics are not restricted to cylindrical fingers and can be applied to n finger grasps. Running on a standard PC, the algorithm generated a solution in less than five minutes for a set of five objects with a total of 456 triangular facets. © 2003 Wiley Periodicals, Inc.