Underactuated Mechanism Research Articles

Discrete modular serpentine robotic tail: design, analysis and experimentation

SUMMARYThis paper presents the design, analysis and experimentation of a Discrete Modular Serpentine Tail (DMST). The mechanism is envisioned for use as a robotic tail integrated onto mobile legged robots to provide a means, separate from the legs, to aid stabilization and maneuvering for both static and dynamic applications. The DMST is a modular two-degree-of-freedom (DOF) articulated, under-actuated mechanism, inspired by continuum and serpentine robotic structures. It is constructed from rigid links with cylindrical contoured grooves that act as pulleys to route and maintain equal displacements in antagonistic cable pairs that are connected to a multi-diameter pulley. Spatial tail curvatures are produced by adding a roll-DOF to rotate the bending plane of the planar tail curvatures. Kinematic and dynamic models of the cable-driven mechanism are developed to analyze the impact of trajectory and design parameters on the loading profiles transferred through the tail base. Experiments using a prototype are performed to validate the forward kinematic and dynamic models, determine the mechanism's accuracy and repeatability, and measure the mechanism's ability to generate inertial loading.

Practical considerations on proprioceptive tactile sensing for underactuated fingers

Underactuated mechanisms are becoming more prevalent in new robotic graspers, partly because of the desire to reduce the complexity and associated costs of conventional fully actuated systems. With the same objective of reducing the costs of the components needed to provide a sensory feedback, several authors have worked on finding alternatives to external tactile sensors. This paper is about one of these methods, namely proprioceptive tactile sensing, especially designed for underactuated fingers. It focuses on certain practical considerations, such as the impact of the curvature of the grasped object and the reconfiguration of the finger after the contact, and proposes the analysis of their influence on the precision of the algorithm. To this aim, simulations and experimental data are provided for different grasping scenarios. It is shown that the effect of local curvature remains limited compared with other causes of imprecision such as friction in the system. It is also demonstrated that the reconfiguration, if within reasonable limits, does not cause significant variations on the estimation of the contact location.

Rapid prototyping prosthetic hand acting by a low-cost shape-memory-alloy actuator

The purpose of this article is to develop a new concept of modular and operative prosthetic hand based on rapid prototyping and a novel shape-memory-alloy (SMA) actuator, thus minimizing the manufacturing costs. An underactuated mechanism was needed for the design of the prosthesis to use only one input source. Taking into account the state of the art, an underactuated mechanism prosthetic hand was chosen so as to implement the modifications required for including the external SMA actuator. A modular design of a new prosthesis was developed which incorporated a novel SMA actuator for the index finger movement. The primary objective of the prosthesis is achieved, obtaining a modular and functional low-cost prosthesis based on additive manufacturing executed by a novel SMA actuator. The external SMA actuator provides a modular system which allows implementing it in different systems. This paper combines rapid prototyping and a novel SMA actuator to develop a new concept of modular and operative low-cost prosthetic hand.

A Hand Prosthesis with an Under-Actuated and Self-Adaptive Finger Mechanism

One of the major problems faced by hand amputees is the unavailability of a lightweight and powered multi-functional hand prosthesis. Under-actuated finger designs play a key role to make the hand prosthesis lightweight. In this paper, a hand prosthesis with an under-actuated and self-adaptive finger mechanism is proposed. The proposed finger is capable to generate passively different flexion/extension angles for a proximal interphalangeal (PIP) joint and a distal interphalangeal (DIP) joint for each flexion angle of metacarpophalangeal (MCP) joint. In addition, DIP joint is capable to generate different angles for the same angle of PIP joint. Hand prosthesis is built on the proposed finger mechanism. The hand prosthesis enables user to grasp objects with various geometries by performing five grasping patterns. Thumb of the hand prosthesis includes opposition/apposition in addition to flexion/extension of MCP and interphalangeal (IP) joint. Kinematic analysis of the proposed finger has been carried out to verify the movable range of the joints. Simulations and experiments are carried out to verify the effectiveness of the proposed finger mechanism and the hand prosthesis.

HyPro: A Multi-DoF Hybrid-Powered Transradial Robotic Prosthesis

This paper proposes a multi-DoF hybrid-powered transradial robotic prosthesis, named HyPro. The HyPro consists of two prosthetic units: hand and wrist that can achieve five grasping patterns such as power grasp, tip grasp, lateral grasp, hook grasp, and index point. It is an underactuated device with 15 degrees of freedom. A hybrid powering concept is proposed and implemented on hand unit of HyPro where the key focus is on restoration of grasp functions of biological hand. A novel underactuated mechanism is introduced to achieve the required hand preshaping for a given grasping pattern using electric power in the pregrasp stage and body power is used in grasp stage to execute the final grasping action with the selected fingers. Unlike existing hybrid prostheses where each of the joints is separately controlled by either electric or body power, the proposed prosthesis is capable of delivering grasping power in combination. The wrist unit of HyPro is designed and developed to achieve flexion-extension and supination-pronation using electric power. Experiments were carried out to evaluate the functionality and performance of the proposed hybrid-powered robotic prosthesis. The results verified the potential of HyPro to perform intended grasping patterns effectively and efficiently.

Robust H∞ control of a tendon–driven elastic continuum mechanism via a systematic description of nonlinearities

Abstract This work treats the pose control of an underactuated elastic continuum mechanism via a linear H∞ approach. To incorporate the nonlinearities into the linear design method, a systematic framework is proposed that describes the nonlinear part of the system as uncertainty in a parameter-affine state-space description. With the established description of the nonlinear system, a robust H∞ controller is synthesized applying the structured singular value framework. The designed controller is evaluated in simulation and hardware experiments on the Elastic Continuum Mechanism (ECM) used as a robotic neck of DLR’s humanoid robot David. The robust controller designed under consideration of the systematic treatment of nonlinearities is able to stabilize the system for a reference step with negligible inaccuracy which is superior to a comparable conventional mixed synthesis H∞ controller or a simple PD design.

Humanoid design of mechanical fingers using a motion coupling and shape-adaptive linkage mechanism

This paper proposes a novel underactuated finger mechanism based on a motion coupling and shape-adaptive linkage design that combines anthropomorphic free motion and adaptive grasping. The proposed three-joint finger mechanism with one active Degree of Freedom (DOF) consists of a five-linkage mechanism in the proximal phalanx and a mechanism comprising two parallel planar four-bar linkages in the middle phalanx. The respective mechanism allows the simultaneously rotation of their corresponding phalanges in the plane before making contact with an object, and can fully envelop an object, even if certain phalanges are blocked. The duel parallel four-bar linkage mechanism is adopted to improve the grasping capacity of the distal phalanx. An optimal design of the finger is presented according to anthropomorphic phalanx trajectories and maximized grasping forces obtained with consideration for the angular velocity relationships of the three phalanges and their force transmission performances. The functionality of the proposed finger mechanism is verified through multiple simulations and grasping experiments using a prototype finger.

Research of motion reduction device with under-actuated parallel-link mechanism

Research of motion reduction device with under-actuated parallel-link mechanism

Optimal Sliding Mode Controller Design Based on Dynamic Differential Evolutionary Algorithm for Under-Actuated Crane Systems

In this paper, aiming at the payload residual vibration problem, a dynamic differential evolutionary algorithm-based sliding-mode controller (DDE-SMC) is designed for the under-actuated crane systems. According to the under-actuated crane systems mechanism of action, a fusion sliding function combined with position and angle sliding function is first given, and the corresponding control law by incorporating switching and equivalent control law is designed during the control process. Moreover, in order to configure the control parameter efficiently, the DDE algorithm is proposed and utilized for improving the anti-swing control performance. Through computer simulation and comparisons under different operation conditions, the proposed DDE-SMC demonstrates the effectiveness in damping the payload oscillations of the under-actuated crane system.

1-Actuator 3-DOF Manipulation Using an Underactuated Mechanism with Multiple Viscoelastic Joints

This paper discusses a dynamic nonprehensile manipulation by using a vibrating plate. The manipulation method, where 3-DoF (degrees of freedom) position and orientation of the object on the plate surface is controlled by a single actuator, is proposed. First, we introduce an underactuated mechanism with one active joint and multiple viscoelastic passive joints. This mechanism is characterized in that all joints are set to be nonparallel. Via a numerical example, it is revealed that not only the shape of the plate vibrational orbit but also the rotational direction can be changed by the input frequency of the active joint. Finally, we show experimental results using a prototype for confirming the feasibility of the proposed method.

Numerical Iterative Algorithm for Solving Kinematics and Dynamics of Under-actuated Mechanisms with Flexible Joints

Numerical Iterative Algorithm for Solving Kinematics and Dynamics of Under-actuated Mechanisms with Flexible Joints

Underactuated Finger Mechanism Using Contractible Slider-Cranks and Stackable Four-Bar Linkages

This paper presents an underactuated finger mechanism that is able to conduct both self-adaptive grasping and natural motions, such as flexion and extension. The robotic finger is realized with a three degrees-of-freedom mechanism composed of stackable four-bar linkages and contractible slider-cranks having a linear spring in each mechanism layer. Kinematics and static force analysis are performed to reveal the operation principle of the proposed finger mechanism. The procedure for synthesizing the linkages is also suggested using Freudenstein's equation. Finally, both simulations and experiments are conducted to confirm the design feasibility.

Mechanical adaptability analysis of underactuated mechanisms

Abstract Underactuated mechanisms have been implemented in a good number of automation mechanical systems due to their adaptability. There are few measures to quantitatively analyze the mechanical adaptability, although it has been mentioned repeatedly as one of the highlights of underactuated mechanisms in literatures. This paper presents a quantitative analysis methodology for the mechanical adaptability of underactuated mechanisms. Different from compliance, namely the reciprocal of stiffness, the adaptability is presented as an ability of mechanical motion under environment constraint. To quantitatively analyze the adaptive behavior of underactuated mechanisms, a measure based on the relation of force and motion is proposed. The measure is used for the prediction of underactuated grasping process and the evaluation of mechanical adaptability. Meanwhile, we apply this measure to compare the inherent adaptability of three typical compliant underactuated mechanisms, and to analyze the adaptive behavior of other underactuated mechanisms in different structure types.

Kinematic Analysis of a Novel Couple-Adaptive Underactuated Finger Mechanism

This paper presents the design of finger mechanism with one active DOF that combines underactuation mechanism and spring elements. The three phalanges of human finger can not only rotate simultaneously with a certain ratio before touching the grasped object, but can also envelop the object successively even if some of them are blocked, called the Couple-Adaptive feature. To realize this function in the finger mechanism, a novel underactuated four-bar mechanism is proposed in this paper. The kinematics model has been derived based on a vector analysis. The simulations of kinematic analysis show that this underactuated finger mechanism has anthropomorphic motion and grasping feature. And its workspace indicates that this prosthetic finger could complete most of grasping tasks.

劣駆動ハンド uGRIPP の握力把持力解析

This study analyzed the power grip force for the underactuated gripper for power and precision grasp (uGRIPP). uGRIPP is a robot hand equipped with three underactuated fingers. It can grasp objects in power and precision grips utilizing its underactuated mechanism. In the previous study, we proposed an analytical method to derive the relationship between the precision grip force and the actuation force on the basis of the principle of virtual power. The present study propose a method for analysis of the power grip force based on the finger linkage model. Furthermore, we measured the actual power grip force experimentally, and the results prove the validity of the method.

劣駆動パラレルリンク機構による動揺低減装置の開発

Due to the wave, it is dangerous for the crew to transfer from ship to port and offshore platform. Accordingly, some large vessel are equipped a movement reduction device using parallellink mechanism. However, they are too big and expensive to put on the smaller ship such as pleasure cruiser. In this paper, we derive the model of the under-actuated parallel link mechanism for the motion reduction device. For simplicity, planner closed-link with 4 rotational joints and 2 linear actuators is considered. Then a controller is designed for each case with and without gravity.

Fully Rotational Joint Underactuated Finger Mechanism and Its Kinematics Analysis

Fully Rotational Joint Underactuated Finger Mechanism and Its Kinematics Analysis

Adaptive approximate input–output linearizing control with applications to ball and beam mechanism

This paper presents the design and implementation of adaptive control with approximate input–output linearization for underactuated open-loop unstable non-linear mechanical systems. Control of a ball and beam (BB) mechanism is selected as a benchmark problem for testing the designed control. The method of input–output linearization is reviewed and an adaptive input–output linearizing control design procedure is given. An approximate BB model is developed using Euler–Lagrange equations, and input–output linearization-based adaptive tracking control is designed for the system. The model is parameterized with respect to ball mass for adaptive tracking, and the proposed control structure is tested via computer simulations and experiments. The results present the tracking performance of designed control for various ball masses, and reveal the proposed method’s capability to cover ball mass variations over non-adaptive control. The proposed control exhibits improved error performance in the presence of parametric variations in the plant. Results of the BB control case reveal successful control of underactuated non-linear mechanisms when a system parameter is unknown or time varying.

Design of a Transmission With Gear Trains for Underactuated Mechanisms

This paper proposes a design method of transmissions for underactuated mechanisms. This transmission consists of active and passive gear trains that align a series of gears over several joints. The transmission has no kinematic singular point that restricts the workspace. Thus, arbitrary joint-connected motions of the underactuated mechanisms can be designed by combining the gear trains. We investigate the kinematics and statics of underactuated mechanisms to find a transmission matrix that realizes the desired connected motions and adaptive grasps. We also develop a method to design gear trains that corresponds to the transmission matrix. We extend this design method with stepped gears and belt–gear mechanisms to increase the design flexibility. The proposed method was experimentally validated using the two- and three-jointed mechanisms.

Analyzing of flexible gripper by computational intelligence approach

Adaptive grippers should be able to detect and recognize grasping objects. To be able to do it control algorithm need to be established to control gripper tasks. Compliant underactuated mechanisms with passive behavior can be used for modelling of adaptive robotic fingers. Undearactuation is a feature which allows fully adaptability of robotic fingers for different objects. In this study gripper with two fingers was established. Finite element method (FEM) procedure was used to optimize the gripper structural topology. Kinetostatic model of the underactuated finger mechanism was analyzed. 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. The sensors could be used for grasping shape detection. Given that the contact forces of the finger depend on contact position of the finger and object, it is suitable to make a prediction model for the contact forces in function of contact positions of the finger and grasping objects. The prediction of the contact forces was established by using a soft computing (computational intelligence) approach. To perform the contact forces estimation adaptive neuro-fuzzy (ANFIS) methodology was used. FEM simulations were performed in order to acquire experimental data for ANFIS training. The main goal was to apply ANFIS network in order to find correlation between sensors’ stresses and finger contact forces. Afterwards ANFIS results were compared with benchmark models (extreme learning machine (ELM), extreme learning machine with discrete wavelet algorithm (ELM-WAVELET), support vector machines (SVM), support vector machines with discrete wavelet algorithm (SVM-WAVELET), genetic programming (GP) and artificial neural network (ANN)). The reliability of these computational models was analyzed based on simulation results.