Wrist Mechanism Research Articles

Characterization of Friction within a Novel 3 mm Wristed Robotic Instrument

Surgical robotic tools are being developed for a variety of surgical procedures that are executed within small workspaces. Novel designs of miniaturized cable-actuated surgical tools for cleft palate repair have previously been developed. However, the behavior and significance of friction within these tools are largely unknown. A study was conducted to investigate the friction in a pulleyless 3 mm diameter wristed instrument. The wrist utilizes cable guide channels that allow for miniaturization at the cost of increased friction. An experimental rig was developed to measure friction within the wrist link mechanism when the tool is positioned at various pitch angles. A strong relationship between the cable tension and the tool’s pitch angle was found as a result of friction. The cable tension increased as the pitch angle approached extreme values (percent increases in the cable tension of 33% and 67.3% at a pitch of 90° and −90°, respectively). However, the resultant cable tension was below the failure strength of the cable, indicating that the design is feasible. The results of this study would be useful to those considering the design of miniature robotic surgical tools that are cable-driven. Significant tool reduction can be achieved by employing static guide channels for the cables, forgoing the use of additional moving components like pulleys while maintaining cable tension well within its break strength. Future work in the design and optimization of novel miniaturized wrist mechanisms should consider frictional effects and their impact on mechanism function.

KULEX-Wrist: Design and Analysis of Linkage-Driven Exoskeleton for Wrist Assistance

Abstract This paper presents a wrist exoskeleton called the KIST Upper-Limb EXoskeleton (KULEX)-wrist for activities of daily living assistance of the elderly and the disabled. A novel linkage-based structure of the rotational mechanism with three degrees-of-freedom is proposed. The proposed wrist mechanism is composed of two prismatic-universal-spherical serial chains and one revolute-revolute-revolute spherical chain. Besides, a combination of a planar slider-crank and spherical four-bar linkages was employed as a drive mechanism for power transmission. Kinematic analysis was conducted to understand its working principle. Then, the dimensions of all the linkages were synthesized to meet the structural design suitable for the wearable exoskeleton and the transmission quality. In addition, motion twists and wrenches were geometrically derived. Finally, a prototype of the KULEX-wrist was designed, and then its performance of mechanical stiffness, motion capability, and power assistance was verified.

Hexad robot: A 6-dof parallel PnP robot to accommodate antagonistic rotational capability and structural complexity

This paper proposed a new structure of full-mobility parallel robot, which combined the advantages of high-rotational capabilities and structural simplification, for high-speed operations of material handling. The proposed robot structure integrates lightweight and simple linkages with a relatively complex (i.e., compared to the single platform with limited rotational capability) articulated mechanism or gear train as wrist mechanism to amplify the end-effector rotations, but without significantly increased structural complexity of gearbox, compared to the existing designs. Parametric modeling are carried out for position analysis, workspace evaluation, singularity identification and dynamic characterization to qualify the proposed robot. Moreover, the structure of the proximal links are designed with topology optimization to ensure design requirements of stiffness and low inertia. The performance evaluation shows that the proposed robot can be of high potential application in the industrial production line.

Development of an active wrist mechanism with passive dorsiflexion function for a myoelectric prosthetic hand

Development of an active wrist mechanism with passive dorsiflexion function for a myoelectric prosthetic hand

OpenRST: An Open Platform for Customizable 3D Printed Cable-Driven Robotic Surgical Tools

Robot-assisted minimally invasive surgery (RMIS) has been shown to be effective in improving surgeon capabilities, providing magnified 3D vision, highly dexterous surgical tools, and intuitive human-robot interfaces for high-precision tool motion control. Robotic surgical tools (RST) are a critical component that defines the performance of an RMIS system. Current RSTs still represent a high cost, with few commercially available options, which limits general access and research on RMIS. We aim to take advantage of recent progress in biocompatible 3D printing and contribute to the development of RMIS technologies, presenting an open platform for low-cost, biocompatible, and customizable RSTs. The proposed design concept consists of a 3-DOF end-effector with a decoupled wrist mechanism, a tool interface module, and a tool drive unit. We validated our end-effector design using Finite Element Analysis (FEA) to confirm that stress generated by high grip forces is maintained below the material yield stress. Validation experiments showed that the proposed RST could provide up to 10N grip forces and up to 3N pulling forces. The proposed control framework exhibited a mean absolute positioning tracking error of approximately 0.1 rad. Finally, we also demonstrated the use of the proposed RST in two surgical training tasks: pick-and-place and stitching. The designs and software control framework are open-access and freely available for customization and fast development at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/jcolan/OpenRST</uri> .

Manipulator Equipped With Differential Wrist Mechanism to Combine the Torque of Two Motors to Increase Fingertip Force and Wrist Torque

A lightweight and high-output manipulator is introduced in this letter. The manipulator comprises two parts: a robot hand part and a wrist part. The total weight of the robot hand part is approximately 450 g, and its size is almost the same as that of a human hand. Furthermore, a design concept of a differential mechanism is presented in this letter. In contrast to traditional mechanisms, in which the movement of a single motor corresponds to a single module, the proposed differential mechanism can superimpose the output forces of multiple motors and act on the movement of single or multiple modules; consequently, the output force is doubled, the low-power requirement of the motor, which drives the robot hand as the end effector to rotate around the wrist, is met, and the driving force amplification mechanism amplifies the gripping force of the fingers. The proposed differential mechanism is incorporated in the wrist part. The robot hand part is responsible for the fast grasping of objects. The wrist part is responsible for increasing the output force of the fingers to ensure a firm grasp. In addition, it enables the robot hand to rotate around the wrist. It takes 0.32 s for the fingers to transition from moving to touching the object. It takes approximately 0.9 s to grasp the object firmly, and the output force of the fingertips can reach 25.5 N. The robot hand can rotate 135 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> around the wrist, and the rotation speed is 118 deg/s.

Design of a compliant, stabilizing wrist mechanism for a pediatric hand exoskeleton.

Children affected by hand impairment due to cerebral palsy or stroke experience serious difficulties when performing activities of daily life (ADL), which reduces their quality of life and development. Wearable robots such as hand exoskeletons have been proposed to support people with hand impairment in therapy as well as daily tasks. While numerous actuated wearable robots have been developed, few designs support both fingers and wrist function, despite being mutually relevant for reach-to-grasp tasks. A recent feasibility study investigating the use of PEXO, a lightweight and fully wearable pediatric hand exoskeleton, showed that a wrist fixed in a slightly extended position may limit the user's ability to reach and grasp during ADL and restrict the user group. These insights and further interactions with clinicians inspired a novel design of PEXO that features an additional degree of freedom in the wrist. In this paper, we present a compliant wrist mechanism extending the existing leaf spring finger mechanism of the device. The novel design provides both wrist motion capability of 60° in flexion and extension and wrist stabilization at the same time while actively supporting finger motion. Preliminary results suggest that the adjustability in the wrist enables a larger variety of grasping gestures. The implemented wrist support has the potential to allow for a more versatile use of PEXO and increase the potential target user group.

ANSYS&lt;sup&gt;Ⓡ&lt;/sup&gt;-Based Gear Stress Analysis of a Lightweight 3-DOF Wrist Mechanism for a Parallel Robot with Expanded Workspace

ANSYS&lt;sup&gt;Ⓡ&lt;/sup&gt;-Based Gear Stress Analysis of a Lightweight 3-DOF Wrist Mechanism for a Parallel Robot with Expanded Workspace

How to use the Omni-Wrist III for dexterous motion: An exposition of the forward and inverse kinematic relationships

The Omni-Wrist III, invented by Ross-Hime Designs, Inc. (Rosheim, 1999, 2002), is a well known two-degree of freedom wrist mechanism that incorporates parallel links with double universal joints (N-UU). It has the advantage of singularity-free operation over the entire hemispherical work-space and maintains a constant axial distance between the two joints. These characteristics make it an appealing choice for mobile robotic appendages that require dexterous maneuvers. While the two active input joint angles are coupled, this paper presents an accessible exposition of the forward and inverse kinematics for the position and velocity of the mechanism. The novelty of this analysis lies in the parameterization of the kinematics in terms of the vector between the origins of the tool and space frames. The results of this paper provide concise equations that are readily implementable in simulation and on low power microcontrollers enabling the use of the Omni-Wrist III for highly dynamic mobile robot maneuvers.

Development of a New 2-DOF Wrist Mechanism Using Reverse Motion Transmission

In this letter, we introduced a novel 2-DOF robotic wrist with a hollow channel. The proposed wrist was developed by stacking two symmetric 5R spatial manipulators using a reverse motion transmission mechanism. As a result, the proposed wrist mechanism has not only a wide workspace, but also a huge hollow space compared to previous wrist models. The kinematic model is derived via the screw theory, and kinematic characteristics are analyzed in terms of two kinematic indices. The prototype hardware of compact size wrist was designed and implemented. Finally, the validity and feasibility of the wrist were confirmed through experiments.

Using Operator Gaze Tracking to Design Wrist Mechanism for Surgical Robots

This article assessed how surgical robot parameters influenced operator viewpoint during a simulated surgical procedure. Surgical robots are useful tools in minimally invasive surgery. However, even with robots, suturing is difficult because the needle is sometimes obscured by tissue or manipulators and is thus not always visible during the procedure. This is especially true in pediatric surgery, where the surgical environment is smaller than in adult surgery. Hence, surgeons must carefully track the instruments and tissues to understand and predict their current and expected situations. In this article, we used gaze-tracking techniques to analyze the location and timing of the gaze of participants while they manipulated a virtual robotic surgical simulation system. To differentiate between the ideal and actual viewpoint trajectories, we conducted experiments with and without obstacles (i.e., simulated tissue and the manipulator arm). In the obstacle condition, we modulated the wrist length of the manipulator to bring it into view. In the no-obstacle condition, the participants mostly watched the suture needle tip. In the with-obstacle condition, the participants spent less time watching the instruments and more time watching the target point. The amount of time spent watching the target point increased as wrist length increased. Given this tradeoff relationship, we examined the proportion of time the participants spent looking at the instruments or target points by wrist length. We calculated the Pareto solutions and clarified the relationship between wrist length and the watching parts.

Tendon-Driven Compliant Prosthetic Wrist Consisting of Three Rows Based on the Concept of Tensegrity Structure

One degree-of-freedom (DoF) virtual rolling-contact joint for the prosthetic wrist is proposed in this letter. For prosthetic wrists, the wrist mechanism should basically be lightweight and have a wide range of motion (RoM). In addition, it is desirable to have compliant characteristics to protect amputees or prosthetics from unexpected external forces. The design of the proposed wrist is based on the concept of tensegrity structure which is similar to ligamentous structure combined with bones and ligaments so that it has compliant and lightweight properties. Actually, the proposed mechanism structurally mimics three rows of the human wrist. Since these three rows move simultaneously and create a single degree-of-freedom in flexion and extension, the proposed wrist covers a wide RoM without any interference between the links, which is similar to the RoM of human wrist. The inherent compliant features of the proposed wrist are validated through experiments.

Constraint-Based Analysis of Parallel Kinematic Articulated Wrist Mechanisms

Abstract This paper presents a systematic constraint-based analysis of the performance attributes of eight parallel kinematic articulated wrist mechanisms from the existing literature. These performance attributes include the number, nature (i.e., pure rotation, or translation, or a combination), and location of a mechanism’s Degrees of Freedom (DoFs) in the nominal and displaced configurations, load transmission capability along these DoFs, and load-bearing capability along the constraint directions. This systematic analysis reveals performance tradeoffs between these performance attributes for a given mechanism as well as design tradeoffs across these mechanisms. This analysis also helps inform the suitability of a given mechanism for specific applications.

The Improved DLR Wrist: Design and Analysis of 2-Degrees-of-Freedom Rotational Mechanism Using Spatial Antiparallelogram Linkages

Abstract This article presents a kinematic analysis and modification of a wrist mechanism of the DLR robot arm, which is based on antiparallelogram linkages. This mechanism is modified to improve the range of motion (ROM), to reduce the parasitic motion, and to approximately perform the decoupled output motion. For these purposes, the elliptical rolling motion of an overconstrained antiparallelogram is first investigated in consideration of its structural modification. Also, a specific joint that has a relatively small movement is developed as a flexible hinge by further minimizing its angular displacement for design simplification. The axode analysis of the instantaneous screw axis for wrist movements is conducted to compare the rotational performance between the original and modified mechanisms. Moreover, their workspace qualities are evaluated through analyses of the workspace and the kinematic isotropy index. Finally, the improved DLR wrist of the final modification is prototyped, and its wide circumduction is demonstrated.

Design and Analysis of a Flexible, Elastic, and Rope-Driven Parallel Mechanism for Wrist Rehabilitation.

This paper proposes a bionic flexible wrist parallel mechanism to simulate human wrist joints, which is characterized by a rope-driven, compression spring-supported hybrid mechanism. Specifically, to realize the movement of the wrist mechanism, a parallel structure is adopted to support the mobile platform and is controlled by a cable, which plays the role of wrist muscles. Because the compression spring is elastic, it is difficult to directly solve inverse kinematics. To address this problem, the external force acting on the moving platform is firstly equivalent to the vector force and torque at the center of the moving platform. Then, based on inverse kinematic and static analyses, the inverse motion of the robot model can be solved according to the force and torque balance conditions and the lateral spring bending equation of the compression spring. In order to verify the proposed method, kinematics, statics, and parallel mechanism workspace are further analyzed by the software MATLAB. The obtained results demonstrate the effectiveness and feasibility of the designed parallel mechanism. This work offers new insights into the parallel mechanism with flexible joints in replicating the movements of the human wrist, thus promoting the development of rehabilitation robots and rope-driven technology to some extent.

A hybrid dynamic model for the AMBIDEX tendon-driven manipulator

Tendon-driven actuation allows for light and compact manipulator designs with enhanced safety features. One of the key challenges in model-based control of tendon-driven robots is the increased complexity of the dynamic model, due in large part to difficult-to-model behavior like nonlinear dynamic deformation and friction at the tendons. While purely data-driven modeling approaches, e.g., neural networks, free one from dealing with complex and often error-prone mechanics models, they usually do not generalize well to diverse tasks, and also do not offer the needed intuitive understanding or predictive power of traditional mechanics-based models. In this paper, we present a hybrid modeling approach for complex tendon-driven robots, which effectively complement the limitations of pure physics-based and data-driven learning-based approaches. Rigid multibody equations of motion are augmented with (i) a configuration-dependent viscous-Coulomb friction model and (ii) a recurrent neural network that captures the tendon dynamics, and estimates link joint angles from the motor positions, velocities, and torques. Experiments involving a two-dof tendon-driven parallel wrist mechanism and the 7-dof AMBIDEX tendon-driven manipulator validate the performance advantages of our hybrid model-based control framework.

Development of 3-DOF wrist mechanism for electro-hydrostatically driven robot arm

Electro-hydrostatic actuator (EHA) has backdrivability and is suitable for a robot system that cooperates with human. However, its design methodology to miniaturize and to generate high pressure has not been established. We develop a robotic arm, all joints of which are actuated by EHAs. This paper reports the development of the vane motor type EHA and a wrist mechanism using the EHA. We employ a single vane motor for a wide motion range. In order to suppress internal leakage, we carefully set the clearance of the EHA and made the rigid casing by using ceramics disks. It is confirmed that the internal leakage of the new EHA is significantly reduced compared to that of the previous model. The wrist mechanism has three degrees of freedom, consisting of three vane motors in series. The flow path between a hydraulic pump and a vane motor is designed using metal pipings, swivel joints and manifolds are presented for a compact wrist mechanism. We validated the fundamental performance of the developed wrist mechanism through experiments.

Design and Modeling of Parallel Two-degree-of-freedom Variable Stiffness Actuator

In this paper, a new 2-DOF variable stiffness actuator based on a 2-DOF spherical wrist parallel mechanism is proposed. A 2-DOF VSA based on a parallel ball wrist mechanism and a parallel arrangement of leaf spring sets is used. Control its stiffness adjustment, analysis its variable stiffness principle and actuator mechanical structure. The parallel arrangement of the leaf spring groups reduces the mass and volume of the joints, enabling simultaneous adjustment of the stiffness. The analytical formula of the rotational stiffness of the actuator is established according to the geometric nonlinearity of the large deflection of the leaf spring.

A New Gantry-Tau-Based Mechanism Using Spherical Wrist and Model Predictive Control-Based Motion Cueing Algorithm

SUMMARYThe 3 degree-of-freedom Gantry-Tau manipulator with the addition of the spherical wrist mechanism which is called Gantry-Tau-3R is designed as a high-G simulation-based motion platform (SBMP) with the capability of generating the large linear and angular displacement. The combination of both parallel and serial manipulator in newly designed Gantry-Tau-3R mechanism improves the ability of the mechanism to regenerate larger motion signals with higher linear acceleration and angular velocity. The high-frequency signals are reproduced using the parallel part of the mechanism, and sustainable low-frequency accelerations are regenerated via the serial part due to the larger rotational motion capability, which will be used through motion cueing algorithm tilt coordination channel. The proportional integral derivative (PID) and fuzzy incremental controller (FIC) are developed for the proposed mechanism to show the high path tracking performance as a motion platform. FIC reduces the motion tracking error of the newly designed Gantry-Tau-3R and increases the motion fidelity for the users of the proposed SBMP. The proposed method is implemented using Matlab/Simulink software. Finally, the results demonstrate the accurate motion signal generation using linear model predictive motion cues with a fuzzy controller, which is not possible using the common parallel and serial manipulators.

A Needlescopic Wrist Mechanism With Articulated Motion and Kinematic Tractability for Micro Laparoscopic Surgery

Invasiveness of laparoscopic surgery can be further reduced by using needlescopic instruments which diameter approaches that of a hypodermic needle. However, such needlescopic instruments are limited by the lack of wrist mechanisms with precise and sharp articulating motion. In this article, we present a two-degree-of-freedom wrist mechanism with articulating motion and enhanced kinematic tractability for micro laparoscopic surgery. The mechanism consists of two highly curved nitinol tubes serially connected by rotary joints whose axes intersect at a remote center of motion (RCM). Its elasticity is only utilized for introducing through a trocar. Once introduced, the rigid body motions of each tube by the rotary joints generate pivoting motion of the attached end-effector about the RCM point. This allows large reorientation of the end-effector's direction with minimal displacement. The serial link structure of the mechanism leads to analytic solutions for tractable kinematics. The design, manufacturing, and the validation of the kinematics of the mechanism are presented, and the feasibility of the mechanism is demonstrated through the peg transfer test using a teleoperated robot system.