Parallel Link Mechanism Research Articles

A Novel Tailsitter UAV with Configurable Wings

In this study, we propose a novel tailsitter unmanned aerial vehicle with configurable wings using a parallel link mechanism. It has two flight modes: a hover mode and a forward flight mode by pitching, similar to conventional tailsitters. In addition, it can deform its airframe in each flight mode. In the hover mode, it can tilt the frame in the pitch direction while hovering. In the forward flight mode, it can change the configuration of the wings during forward flight. In experiments, we show that it can transition from the hover mode to the forward flight mode with three wing configurations: non-staggered wings (biplane) and positively and negatively staggered wings (tandem wing plane), using an attitude controller for conventional quadrotors.

Dynamic modeling of wheeled biped robot and controller design for reducing chassis tilt angle

Abstract The wheeled-legged robot combines the advantages of wheeled and legged robots, making it easier to assist people in completing repetitive and time-consuming tasks in their daily lives. This paper presents a study on the kinematic and dynamic modeling, as well as the controller design, of a wheeled biped robot with a parallel five-bar linkage mechanism as its leg module. During the motion of the robot, the robot relies on the tilt angle of the inverted pendulum, and this angle often results in the tilting of the chassis of the robot, presenting challenges for the installation of upper-body payloads and sensor systems. The controller proposed in this paper, which is developed by decoupling the primary motions of the robot and designing a multi-objective, multilevel controller, addresses this issue. This controller employs the pendulum pitch angle of the equivalent inverted pendulum model as the control variable and compensates for the chassis tilt angle (CTA). This control method can effectively reduce the CTA of such robots and eliminate the need for additional counterweights. It also provides a more spacious structural design for accommodating upper-body devices. The effectiveness of this control framework is verified through variable height control, walking on flat ground, and carrying loads over rough terrain and slopes.

2 DOF transformable wheel design based on geared 8 bar parallel linkage mechanism

This paper introduces a novel design and static optimization for a two-degrees-of-freedom transformable wheel based on a geared linkage mechanism. Overcoming obstacles, including stairs, with small wheels is a major challenge in the field of mobile robotics research. Among various robots, the transformable wheel, which can change the shape of the wheel to overcome steps and optimize the path, was presented and has undergone many improvements. Nevertheless, problems such as asymmetry and structural strength remain. Therefore, the design of this paper aims to address the structural inefficiencies identified in the previous research model, which were attributed to the asymmetric placement of the linear motion guide. Through the implementation of this mechanism, the linear motion of the lobe can be segregated, enabling each input motor to share the workload effectively. The optimization process focus on determining the optimal linkage length under static conditions, resulting in improved structural characteristics and force distribution of linkage within the designated workspace. As a result, asymmetry of motion is eliminated, required intervention angle of the driving motor and stress of linkage was reduced by 36.24% and 8.35%, respectively.

An open-source parallel gripper with an embedded soft skin fingertip sensor

The demand for implementing robots into our daily lives has surged in recent years, necessitating safe grasping for effective interaction with the environment. However, a majority of researchers rely on commercial grippers for their experimental studies, which are typically expensive and not accessible to everyone. Despite the existence of open-source designs, the assembly process is often challenging and requires modifications to enhance secure grasping. This paper presents a simple, compact, and low-cost gripper to offer an accessible and readily deployable solution for research and education. The gripper utilizes a parallel four-bar linkage mechanism, minimizing the number of components and incorporating off-the-shelf parts for straightforward assembly. Furthermore, to enhance its capabilities, the proposed gripper implements a soft skin tactile sensor on its fingertips. These sensors offer three-directional measurements using Hall effect sensing and embedded silicone. By controlling fingertip force based on information from the tactile sensors, the gripper achieves safe grasping. The gripper is evaluated to grasp daily life objects with different properties such as shapes, sizes, and levels of deformability. Evaluation results showcase the gripper's versatility, enabling it to securely grasp various objects, including fragile items. This outcome underscores the gripper's effectiveness, versatility, and safety in practical use.

Eagle-inspired manipulator with adaptive grasping and collapsible mechanism and modular DOF for UAV operations

This paper presents an eagle-inspired manipulator designed to enhance the efficiency of medium and large multi-rotor UAVs during contact operations such as picking, obstacle cleaning, and grasping. Drawing inspiration from the skeleton structure and motion law of an eagle’s leg, we propose a prototype design of a large load, wide range of movement, multiple DOF, and collapsible manipulator. The main structure of the manipulator consists of a planetary reducer and a coupled parallel linkage mechanism, which enables it to have greater payload capacity while also increasing its range of motion. The grasping mechanism is based on the motion law of an eagle’s claw, which effectively increases the contact area with targets. To further enhance the DOF of the grasping mechanism, we have designed an ankle mechanism that utilizes a pair of double helical telescopic mechanisms to constrain the DOF of the universal joint, connecting the grasping mechanism to the main structure of the manipulator. Regarding the comparison with existing techniques, our eagle-inspired manipulator has several advantages over previous designs. On one hand, the grasp planning strategy, which is inspired by the motion law of an eagle’s claw, can achieve more reliable and accurate grasping than existing techniques. On the other hand, the manipulator’s collapsible design facilitates easier transportation and storage while maintaining its wide range of motion. What’s more, the modular DOF design allows for greater flexibility in adapting to different payloads and operating environments when compared to existing technologies. We outline the development process of this manipulator, including kinematic modeling and control. The ability of the manipulator system is tested, and flight test experiments are conducted on a UAV carrying the manipulator to demonstrate its practicality and effectiveness.

Design and dynamic analysis of jumping wheel-legged robot in complex terrain environment.

Wheel-legged robots have fast and stable motion characteristics on flat roads, but there are the problems of poor balance ability and low movement level in special terrains such as rough roads. In this paper, a new type of wheel-legged robot with parallel four-bar mechanism is proposed, and the linear quadratic regulator (LQR) controller and fuzzy proportion differentiation (PD) jumping controller are designed and developed to achieve stable motion so that the robot has the ability to jump over obstacles and adapt to rough terrain. The amount of energy released by the parallel four-bar linkage mechanism changes with the change of the link angle, and the height of the jump trajectory changes accordingly, which improves the robot's ability to overcome obstacles facing vertical obstacles. Simulations and real scene tests are performed in different terrain environments to verify obstacle crossing capabilities. The simulation results show that, in the pothole terrain, the maximum height error of the two hip joint motors is 2 mm for the obstacle surmounting method of the adaptive retractable wheel-legs; in the process of single leg obstacle surmounting, the maximum height error of the hip joint motors is only 6.6 mm. The comparison of simulation data and real scene experimental results shows that the robot has better robustness in moving under complex terrains.

A STUDY ON STATIC MECHANICAL PROPERTIES OF VERTICAL SEISMIC ISOLATION SYSTEM WITH PARALLEL LINK MECHANISM

This paper discusses the basic mechanical properties of a newly proposed parallel link mechanism as a three-dimensional seismic isolation system capable of supporting large loads. Specifically, the static restoring force characteristics of the entire mechanism, the moment caused by the spring force, and the inclination of the top surface due to 3-dimensional displacement were analyzed. The results show that stable static restoring force can be obtained by setting the initial angle within a certain range and using multiple units with a separation distance of 4 m or more between mechanisms.

Experimental Study of the Mechanical Properties of a Spherical Parallel Link Mechanism With Arc Prismatic Pairs

A two-degrees-of-freedom spherical parallel link mechanism (2-DOF SPM) was designed to ensure that it only has rotational degrees of freedom in two directions around a fixed center. In general, 2-DOF SPM includes passive rotating pairs, and at least two actuators are needed to change the end-effector posture. The arrangement of the links and pairs determines the characteristics and performance of SPM, so 2-DOF SPMs were designed considering various requirements, such as output torque, accuracy, and space constraints for applications. To satisfy these requirements, arc prismatic pairs can be used in SPMs. In order to use in SPMs, as for arc prismatic pairs, the concrete configuration and design methods for arc prismatic pairs have been studied. Furthermore, in order to compensate for the influence of friction on the positioning error, the control model considering the friction has been proposed by constructing a feedback loop containing experimentally found parameters. However, the conventional model is not a mechanical model of friction. Therefore, it is not suitable for calculating the friction force and understanding how the limit of the workspace changes due to the influence of friction. In this study, we construct a mechanical friction model considering the intersection angle change between the input and the rail slide direction. In addition, using the friction model, we clarify the influences of friction on the workspace and driving the SPM to realize high-performance 2-DOF SPM. First, we theoretically clarified the influence of friction on the workspace by considering the case of a slider-type differential-drive 2-DOF SPM. Second, the driving torque was experimentally measured, and the influence of friction on driving was examined.

Posture Evaluation Based on Forward Kinematics and Inverse Kinematics of Parallel Link Type Machine Tool

Parallel mechanisms with multiple links have been expected to be used in machining because they are higher in rigidity, accuracy, and output power than series mechanisms, such as industrial robots. However, unlike conventional machine tools, which consist of linear and rotary axes, parallel mechanisms have a large number of error factors. In the parallel link mechanism, there is no guide surface that physically guarantees linearity, and all accuracy is determined by the operating performance of the composite axes. This makes it difficult to identify any error factors. Therefore, a kinematics model is devised, and the behavior of the tool tip is checked by inputting the encoder information during the actual operation of a specific axis. Based on the results, we evaluate the machining characteristics of the target machine tool. The target machine tool in this study is a 5-axis machine tool that combines a 3-DOF parallel mechanism consisting of three linear motion axes and a 2-DOF serial mechanism consisting of two rotary axes. In our previous research, we tried to build a forward kinematics model. Although its prediction accuracy was insufficient, it was possible to actually identify the cause of the defect in the quality of the machined surface using the servo position information of the kinematics machine. However, we have not been able to construct an inverse kinematics model that is suitable for calculating the correction position command value to improve the quality of the machined surface. In this study, based on the shape creation theory, we devise and evaluate the kinematics model of a robotic machine tool that has a parallel mechanism. As a result of comparing the kinematics model with the 3D-CAD model in order to evaluate the accuracy of the former, it was confirmed that the proposed method has high simulation accuracy. Then, machining tests were carried out to evaluate the machining accuracy by measuring, based on proposed kinematics model, the machined surfaces in order to identify the mechanism that affects the texture of the machined surface. In addition, we performed a circle interpolation to confirm the effects of reversing the motion of each drive axis on the behavior of the tool tip. As a result, it is considered that the linear motion axis has a large effect on the behavior of the tool tip on the quadrant glitch of each drive axis. It was also found that the effects of the 1st- and 3rd-axes on the behavior of the tool tip are different from those of the 2nd-axis.

4自由度球面パラレルリンク機構を有する脚部の機構解析

We have designed and built a leg named “MELEW-2LR” with a 4-DoF spherical parallel link mechanism, in order to develop a highly maneuverable 4-legged wheeled robot with active wheels mounted on the tip of the leg-type robot. This paper describes the mechanical analysis of the 4-DoF parallel link mechanism of the MELEW-2LR. In this paper, the leg mechanism of MELEW-2LR is examined and the features and DoF analysis of the designed parallel link mechanism are reported. The derivation of analytical solutions for the forward and inverse kinematics of MELEW-2LR and the range of motion of MELEW-2LR are also presented. Finally, the validity of inverse kinematics of MELEW-2LR is confirmed by conducting motion experiments in which the translational motion of the tip of its leg in the forward-backward, left-right, and vertical directions and the rotational motion of its yaw angle are controlled by inverse kinematics.

Analysis of leg mechanism with parallel link mechanism by vertically mounted linear actuators

Analysis of leg mechanism with parallel link mechanism by vertically mounted linear actuators

High Performance Pneumatic Robot Hand with Variable Stiffness Finger Module

A robot hand is required to generate a large grasping force. Furthermore, it is required that one finger should possess multiple degrees of freedom and the fingertips should be positioned freely to grasp and manipulate objects of various sizes and shapes. A function to adjust the stiffness is also required to control the force and realize stable grasping. The development of a hand with these functions at a high level is a technical problem. We propose a multi-degree-of-freedom finger module that uses pneumatic cylinders and a parallel link mechanism. The proposed hand has adjustable stiffness while maintaining high grasping force-to-weight ratio. In addition, the proposed hand was able to estimate the external force acting on the fingertip from the differential pressure and a kinematics model. By using the estimated external force for control, adjustable stiffness was realized without using a force sensor. This paper also describes the design method of the finger module. We experimentally confirmed that the proposed hand was able to satisfy various target specifications. In addition, it was able to realize multiple functions of a hand using a compact mechanism.

Parallel Link Mechanism with Redundant Passive Joints for 6DoF Finger-mounted Kinesthetic Display

Parallel Link Mechanism with Redundant Passive Joints for 6DoF Finger-mounted Kinesthetic Display

Improvement of the joint range for 5-DOF robot arm with parallel link mechanism

Improvement of the joint range for 5-DOF robot arm with parallel link mechanism

Development of On-Campus Delivery Support Vehicle Using Parallel Link Mechanism

Development of On-Campus Delivery Support Vehicle Using Parallel Link Mechanism

Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

High-performance finger module for robot hands with pneumatic cylinder and parallel link mechanism

A robot hand is required to generate a large grasping force. Furthermore, it is required that one finger should possess multiple degrees of freedom and the fingertips should be positioned freely to grasp and manipulate objects of various sizes and shapes. A function to adjust the stiffness is also required to control the force and realize stable grasping. The development of a hand equipped with these functions at a high level is a technical problem. We propose a multi-degree-of-freedom finger module that uses pneumatic cylinders and a parallel link mechanism. The proposed finger module has positioning controllability, force controllability, and adjustable stiffness while maintaining high grasping force-to-weight ratio. In addition, the proposed finger module was able to estimate the external force acting on the fingertip from the differential pressure and a kinematics model. By using the estimated external force for control, adjustable stiffness was realized without using a force sensor. We experimentally confirmed that the proposed finger module was able to satisfy various target specifications. In addition, it was able to realize multiple functions of a hand using a compact mechanism.

A Versatile Aerial Manipulator Design and Realization of UAV Take-Off from a Rocking Unstable Surface

UAVs are one of the fastest types of robots that can be deployed in a remote environment. Unfortunately, they have a limited flight time and therefore may need to stop occasionally in an unknown, uncontrolled area. However, conventional UAVs require flat and stationary surfaces for a safe landing and take-off. Some studies on adaptive landing approach for UAVs can be found in the past, but adaptive take-off from non-flat surfaces has not been discussed for the most part, yet. In this work, we discuss the problems associated with a conventional UAV take-off from non-flat surfaces and provide a novel approach for UAV take-off from a sloped or rocking surface. We also discuss the design of a novel multitasking three-arm aerial manipulator system with parallel link mechanism and achieve the above-mentioned task. With experiments, we show that the system can provide stability for a UAV landing on a rocking surface that allows for a safe take-off.

Self-Contained 2-DOF Ankle-Foot Prosthesis With Low-Inertia Extremity for Agile Walking on Uneven Terrain

Accepting the heterogeneity of amputees and enabling them to walk comfortably using little effort with light weights is the main goal of prostheses. Moreover, providing the capability of walking on various ground conditions including uneven surfaces and obstacles is a challenging but important requirement. This letter presents a 2-DOF ankle-foot prosthesis having a compact size and low inertia. It has two active degrees of freedom in the sagittal and coronal plane using a parallel linkage mechanism. A unique spring mechanism strengthens the propulsion of walking without increasing the mass of the foot. In addition, heavy elements such as actuators, springs, batteries, and controller circuits are placed at the proximal part to reduce the inertia felt by patients and to minimize the metabolic cost. Capacitive type force sensors placed at the shank frame enable the precise measurement of force from the ground without increasing foot mass. The mass including the battery is 2.25 kg which is lightweight among 2-DOF ankle-foot prostheses and the low height of 204 mm allows a broad range of amputees with various physical conditions to use it. This letter describes a gait algorithm for uneven ground by using impedance control. The force sensor test and the preliminary walking test on uneven ground verify the effectiveness of the proposed prosthesis.

Development of an Agile Omnidirectional Mobile Robot With GRF Compensated Wheel-leg Mechanisms for Human Environments

Wheeled mobile robots have been receiving continuous attention in various fields because of their stability, efficiency, and simple mechanisms. However, most of them require significantly larger occupied space than humans and have limited maneuverability in the environment for humans, such as crowded corridors, floor thresholds, ramps, and elevators. This letter presents a new wheel-leg mobile robot that combines the legs for changeable support polygon and mecanum wheels for holonomic motion. The robot has a human-like slim shape with 4 wheel-leg mechanisms, each of which has one 2-DOF leg frame and one mecanum wheel. To allow 2-DOF leg motion while maintaining the orientation of the mecanum wheels, a unique parallel link mechanism was devised. In order to achieve agile motion and impact and vibration absorption capability, a back-drivable high payload compound planetary gear was developed. The ground reaction force (GRF) compensation mechanism in each leg reduces the required payload of the actuators. The letter describes the detailed mechanical design of the robot and the actuators. The effectiveness of the proposed robot was verified in various experiments, fast omnidirectional motion test, a climbing test of a single step, and a motion test in the elevator with people.