End-effector Research Articles

Investigation of parasitic motion in 3-RRS parallel manipulator

This paper investigates the Parasitic Motion (PaMo) in a 3-Degree of Freedom (DoF) 3-RRS Spatial Parallel Manipulator (SPM) for its different link proportions. The position kinematic analysis of the manipulator is addressed initially. The PaMo is investigated and quantified as the percentage of Reachable Workspace (RW) for each link proportion at the tip of an End-Effector (EE), which is attached at the centroid of the moving platform. The PaMo which happens in the constrained DoF is an unwanted motion, and this entire process allows to know the total occupancy of PaMo in comparison to RW for each link proportion. The results are depicted with the aid of 3D plots of the reachable work-volume and the volume of PaMo for each link proportion. In order to evaluate the performance measure, a performance index called as the parasitic motion index ( PaMoI) is proposed. The PaMoI variation pattern is also discussed based on the obtained results. The conclusions are drawn at the end based on this investigation that also identify the provisions to minimize the PaMo.

Realization and Control of Robotic Injection Prototype With Instantaneous Remote Center of Motion Mechanism.

Although there have been studies conducted on the instantaneous remote center of motion (RCM) mechanism, the general closed-loop control method has not been studied. Thus, this article fills that gap and employs the advantages of this mechanism to develop a novel injection system. The injection prototype involves the instantaneous RCM mechanism, insertion unit and injection unit. The RCM system is investigated in the presence of time-varying axial stiffness of the screw drive and underactuated case. For safe interaction, compliance control is designed in the insertion system. The stability of all separate systems is investigated with the bounded parameter variation rate. The injection prototype and a robot end-effector were then combined to perform injection. Our RCM prototype can achieve a large workspace, and its control effectiveness was verified by multiple frameworks and comparison with previous studies. Compliance-controlled insertion can achieve accurate depth regulation and zero-impedance control for manually operating the needle. With the help of three-dimensional reconstruction and hand/eye calibration, the manipulator can guide the injection prototype to a proper pose for injection of a face model. The injection prototype was successfully designed. The effectiveness of the whole control system was verified by simulations and experiments. The particular robotic injection task can be performed by the prototype. This article provides alternative schemes for developing an instantaneous RCM system, screw drive-based surgical tool, and robotic insertion with small needles.

Robust Grasping of a Variable Stiffness Soft Gripper in High-Speed Motion Based on Reinforcement Learning.

Industrial robots are widely deployed to perform pick-and-place tasks at high speeds to minimize manufacturing time and boost productivity. When dealing with delicate or fragile goods, soft robotic grippers are better end effectors than rigid grippers due to their softness and safe interaction. However, high-speed motion causes the soft robotic gripper to vibrate, leading to damage of the objects or failed grasping. Soft grippers with variable stiffness are considered to be effective in suppressing vibrations by adding damping devices, but it is quite challenging to compromise between stiffness and compliance. In this article, a controller based on deep reinforcement learning is proposed to control the stiffness of the soft robotic gripper, which can accurately suppress the vibration with only a minor influence on its compliance and softness. The proposed controller is a real-time vibration control strategy, which estimates the output of the controller based on the current operating environment. To demonstrate the effectiveness of the proposed controller, experiments were done with a UR5 robotic arm. For different situations, experimental results show that the proposed controller responds quickly and reduces the amplitude of the oscillation substantially.

Large eddy simulation of end effects on a cylinder rotor

Due to the limited length of cylinders, their use in practical engineering inevitably involves end effects, which results in three-dimensional flows at the ends of cylinders. These flow fields are the main factor influencing the aerodynamic and flow field characteristics of cylinders. Regarding a finite-length cylinder rotor, a specific pattern of tip vortices will form under the action of rotation, resulting in notable differences in the aerodynamic characteristics between an ideal two-dimensional cylinder and a finite-length cylindrical rotor. In the present study, the large eddy simulation method is used to systematically investigate cylinder rotors with various aspect ratios. By analyzing the sectional aerodynamic and flow field characteristics, the variation laws of the aerodynamic force, wind pressure, and flow field characteristics of cylinder rotors under the influence of end effects were summarized. The results show that the influence range and intensity of the tip vortices on the rotor flow field and sectional aerodynamic characteristics are dominated by the dimensionless rotating speed, which in turn affects the range of the end effects. The development trend of the tip vortices is analyzed and discussed from multiple aspects, including sectional aerodynamics, the pressure coefficient, and the flow correlation, and an attempt is made to explain changes in the phenomenon.

Design and Analysis of a Breast Biopsy Robot Based on TRIZ Theory

Background: In recent years, more and more medical robots have formally stepped into clinical applications and are gradually being accepted by patients. Magnetic resonance image (MRI)-guided breast intervention robot is the most advanced technology for breast cancer treatment. Still, the very limited working space within the MRI scanner restricts the development of breast intervention robots. Objective: In this paper, a compact breast biopsy robot in MRI environment is proposed based on TRIZ theory. Methods: The structure of the robot is optimized by using the curvilinear principle and the asymmetry principle of TRIZ theory to obtain a modified cartesian coordinates robot for breast biopsy. The coordinate systems of the robot are established using D-H method. Next, 3D visualization simulation of the robot is performed by SimMechanics of MATLAB, and then kinematic simulation and workspace simulation analysis are carried out. Results: The simulation results show that motion space of the end effector of the robot meets the requirements of breast intervention surgery, and the robot structure is simple and effective. Conclusion: In this paper, a compact breast biopsy robot in MRI environment is proposed. Through the Simulink module of MATLAB to analyze its workspace, it is obtained that its working range is 250mm × 300mm × 200mm, which can cover any position in breast tissue. At the same time, the simulation results of the workspace also show that the structure optimization of the breast biopsy robot based on TRIZ theory is reasonable.

An Integrated Architecture for Robotic Assembly and Inspection of a Composite Fuselage Panel with an Industry 5.0 Perspective

Aeronautical robotic applications use quite large, heavy robots with huge end effectors that are frequently multifunctional. An assembly jig to hold a fuselage panel and two medium-sized six-axis robots fixed on linear axes, referred to as the internal and the external robot with respect to the curvature of the panel, make up the Lean robotized AssemBly and cOntrol of composite aeRostructures (LABOR) work cell. A distributed software architecture is proposed in which individual modules are developed to execute specific subprocesses, each implementing innovative algorithms that solve the main drawbacks of state-of-the-art solutions. Real-time referencing adopts a point-cloud-based strategy to reconstruct and process the part before drilling, avoiding hole positioning errors. Accurate concentric countersink diameters are made possible through the automatic adjustment of the drilling tool with respect to the skin panel, which guarantees its orthogonality, as well as the implementation of process parameter optimization algorithms based on historical results that compensate for the wear of the drilling bits. Automatic sealing and fastening strategies that involve the measurement of the main fastener quality parameters allow for the complete verification of the entire assembly process of each part. Additionally, an advanced multimodal perception system continuously monitors the collaborative workspace to ensure safe human–robot collaboration (HRC) tasks. Through this integrated architecture, LABOR substantially reduces expenses and facilitates maintenance and programming.

Development of a Minimally Invasive Surgical Robot Using Self-Helix Twisted Artificial Muscles

In the field of surgery, minimally invasive surgical robots (MISRs) have emerged as the persistent pursuit of physicians to minimize harm and perform precise surgery. The structure of newly proposed MISRs tends to change form rigid to flexible, which poses a challenge to precise control. In this work, a MISR actuated by self-helix twisted artificial muscles (SHTAMs) with large bending angle and high precision is developed. The configuration and operation principle of the MISR are illustrated. Then, the physical model of SHTAM and the kinematics model of the end effector are established. The contraction ratio of SHTAM reaches 27.5%, and the output force is 5424.2 mN. Besides, the maximum bending angle (about 92°) of MISR is measured to verify the kinematic analysis. Moreover, in the point positioning control experiments, the steady-state error is less than 0.11°. Subsequently, the trajectory tracking tests on sinusoidal trajectories with different frequencies and amplitudes are carried out, and the circular trajectory tracking experiment is also performed with a maximum error of 1.8° in cold gel environment. The experimental results indicate that the proposed MISR has a large bending angle and can achieve accurate trajectory control, which exhibits excellent prospect in precision minimally invasive surgery.

An Adaptive Control Method and Learning Strategy for Ultrasound-Guided Puncture Robot

The development of a new generation of minimally invasive surgery is mainly reflected in robot-assisted diagnosis and treatment methods and their clinical applications. It is a clinical concern for robot-assisted surgery to use a multi-joint robotic arm performing human ultrasound scanning or ultrasound-guided percutaneous puncture. Among them, the motion control of the robotic arm, and the guiding and contact scanning processes of the ultrasonic (US-) probe determine the diagnosis effect, as well as the accuracy and safety of puncture surgery. To address these challenges, this study developed an intelligent robot-assisted system integrating autonomous US inspection and needle positioning, which has relation to several intelligent algorithms such as adaptive flexible control of the robot arm, autonomous US-scanning, and real-time attitude adjustment of the puncture needle. To improve the cooperativity of the spatial operation of the robot end-effector, we propose an adaptive flexible control algorithm that allows the operator to control the robot arm flexibly with low damping. To achieve the stability and uniformity of contact detection and imaging, we introduced a self-scanning method of US-probe based on reinforcement learning and built a software model of variable stiffness based on MuJoco to verify the constant force and velocity required by the end mechanism. We conducted a fixed trajectory scanning experiment at a scanning speed of 0.06 m/s. The force curve generally converges towards the desired contact force of 10 N, with minor oscillations around this value. For surgical process monitoring, we adopted the puncture needle detection algorithm based on Unet++ to acquire the position and attitude information of the puncture needle in real time. In short, we proposed and verified an adaptive control method and learning strategy by using an UR robotic arm equipped with a US-probe and puncture needle, and we improved the intelligence of the US-guided puncture robot.

Integration of an Ultrasonic Sensor within a Robotic End Effector for Application within Railway Track Flaw Detection

Integration of an Ultrasonic Sensor within a Robotic End Effector for Application within Railway Track Flaw Detection

A novel fractional-order enhanced model reference adaptive controller (FOEMRAC) approach for magnetic end effectors

A novel fractional-order enhanced model reference adaptive controller (FOEMRAC) approach for magnetic end effectors

Design, optimization, debugging, and simulation of an agricultural biomimetic hexapod robot

This paper comprehensively studies the model establishment, kinematic analysis, hardware design, software development, and agricultural applications of hexapod robot, laying a solid foundation for their practical application in the agricultural field and proposing prospects for future research and development. This article mainly conducts in-depth research on the mechanical design, kinematic analysis, hardware implementation, software development, and application in the agricultural field of hexapod robots. Firstly, a brief introduction to biomimetic robots will be provided, and a comparative analysis will be conducted on existing common legged robots. Afterwards, use solidworks-2021 for 3D modeling to draw the legs and main structure of the robot. In terms of kinematic analysis, by studying the mechanism structure and motion characteristics of hexapod robot, the forward and inverse kinematic equations are derived, and the gait planning and motion control algorithms of the robot are analyzed in detail. These analyses provide a theoretical basis for the robot's program and actual motion. In terms of hardware, a lightweight and high-performance hexapod robot hardware platform has been designed using mainstream controllers such as Borboardino and ultrasonic sensors. This hardware platform has excellent responsiveness and adaptability, and can efficiently move and operate in complex agricultural environments. In terms of software, a comprehensive control system has been developed, including motion planning, action execution, and obstacle avoidance modules. By integrating triangular gait technology and related algorithms, robot can achieve navigation and obstacle avoidance, and perform tasks such as crop planting and spraying in the agricultural field. The simulation file of the hexapod robot was established using CoppeliaSim software, achieving motion based on the robot body, six legs, and end effectors. Finally, a 3D-printer is used to print and assemble all components, and complete the design through debugging and verification. The hexapod robot is capable of autonomous cruising in farmland, completing tasks such as planting and watering crops, providing efficient and intelligent agricultural production solutions for farmers.

Design and Simulation of End Effector for Young-Pear-Bagging Robot

In order to address the time-consuming and labor-intensive challenges as well as the suboptimal operational quality encountered in the conventional processes of fruit bagging within expansive orchards, an innovative end-of-bagging actuator is proposed, which can be installed on a fruit-production robot. Due to the excessive power sources required to complete the bagging operation, while also taking into account the quality and cost of the end effector, we have implemented a clutch transmission system to control individual motors, thereby achieving efficient bag-opening and collection actions. Through kinematic analysis of the bagging end effector, the optimal bag opening size is determined to be 40.3372 mm, with a deviation of 0.1428 mm from the design target and an error rate of 0.35%. This ensures the desired bag size for bagging juvenile fruits. Moreover, a dynamic simulation model comprising rigid drive components and a flexible clutch was developed. The simulation results demonstrate the system’s stable performance. However, it is evident that the gear speed falls below that of the flexible clutch, resulting in insufficient bag opening and bag gathering compared to the intended design target. The observed phenomenon is a result of the characteristics exhibited by the flexible clutch. Specifically, the demands for bagging and stretching can be accommodated by modifying the stiffness and geometric configuration of the flexible clutch, alongside the level of operational force. To conclude, the suggested end effector can successfully simulate the implementation of the manual bagging process. By taking into account the quality and cost of the end effector, a clutch drive system was utilized to regulate a single motor, resulting in efficient bag-opening and collection actions. This approach offers a more integrated and efficient solution compared to manual bagging and semi-automatic mechanically assisted bagging methods.

Online Capability Based Task Allocation of Cooperative Manipulators

The cooperative manipulator group can accomplish complex and heavy payload tasks of object manipulation and transportation compared to a single manipulator. Effective coordination is crucial for cooperative task accomplishments. Multi-manipulator task distribution is highly complex because of the varying dynamic capabilities of the manipulators. We have introduced a novel fastest technique to quantify the dynamic task capability of the cooperative manipulator by scalar quantity and allocate the task accordingly. The scalar quantity determines the capability of applying an external wrench by end effector (EE) in line with the required wrench at the center of mass of the manipulating object. This quantity helps to diminish tracking errors in object manipulations or transportation and actuator saturation avoidance. The task distribution among the members is in proportion to their computed dynamic capability to ensure equal priority to the individual manipulators. The proposed task distribution formulation ensures the minimum magnitude of wrench interaction at the grasp point and the minimum internal wrench build-up in the object. Several physical simulation results assure trajectory tracking performance with the proposed task capability metric. The same metric aids in identifying the least capable manipulator, rearranging members for better performance, and deciding the required number of manipulators in the manipulator group.

Upper Extremity Motion-Based Telemanipulation with Component-Wise Rescaling of Spatial Twist and Parameter-Invariant Skeletal Kinematics

This study introduces a framework to improve upper extremity motion-based telemanipulation by component-wise rescaling (CWR) of spatial twist. This method allows for separate adjustments of linear and angular scaling parameters, significantly improving precision and dexterity even when the operator’s heading direction changes. By finely controlling both the linear and angular velocities independently, the CWR method enables more accurate telemanipulation in tasks requiring diverse speed and accuracy based on personal preferences or task-specific demands. The study conducted experiments confirming that operators could precisely control the robot gripper with a steady, controlled motion even in confined spaces, irrespective of changes in the subject’s body-heading direction. The performance evaluation of the proposed motion-scaling-based telemanipulation leveraged Optitrack’s motion-capture system, comparing the trajectories of the operator’s hand and the manipulator’s end effector (EEF). This verification process solidified the efficacy of the developed framework in enhancing telemanipulation performance.

Application of Fuzzy Logic for Robotic Arm Joint Control of an Explosive Ordnance Disposal Unit

Precise luffing of payload in mobile cranes is a crucial part of material handling and safety in industrial operations. Explosive ordnance disposal uses a bomb disposal robot to safely disable explosive devices at a safe distance. This robot is a mobile jib crane type with a gripper as an end effector instead of the typical suspension cable with a hook. The common challenge of this crane type is the arm/jib movement sensitivity with respect to tip-over stability of the crane body. This is directly influenced by the payload and constrained by the degree of freedom. This paper presents a control strategy of the joint for luffing such that the back wheels remain in contact with the surface ground and avoid bucking at any given instance of weight change in the payload. Fuzzy logic was applied to control the motor torque and luffing angle of the arm in response to the load and gripper opening size to maintain the tip-over stability margin at the highest value possible. The response curves at different configurations of the two input signals were also analyzed based on the rules set to determine its precision with respect to the expected response curve.

A KMP-based interactive learning approach for robot trajectory adaptation with obstacle avoidance

Purpose Imitation learning is a powerful tool for planning the trajectory of robotic end-effectors in Cartesian space. Present methods can adapt the trajectory to the obstacle; however, the solutions may not always satisfy users, whereas it is hard for a nonexpert user to teach the robot to avoid obstacles in time as he/she wishes through demonstrations. This paper aims to address the above problem by proposing an approach that combines human supervision with the kernelized movement primitives (KMP) model. Design/methodology/approach This approach first extracts the reference database used to train KMP from demonstrations by using Gaussian mixture model and Gaussian mixture regression. Subsequently, KMP is used to modulate the trajectory of robotic end-effectors in real time based on feedback from its interaction with humans to avoid obstacles, which benefits from a novel reference database update strategy. The user can test different obstacle avoidance trajectories in the current task until a satisfactory solution is found. Findings Experiments performed with the KUKA cobot for obstacle avoidance show that this approach can adapt the trajectories of the robotic end-effector to the user’s wishes in real time, including trajectories that the robot has already passed and has not yet passed. Simulation comparisons also show that it exhibits better performance than KMP with the original reference database update strategy. Originality/value An interactive learning approach based on KMP is proposed and verified, which not only enables users to plan the trajectory of robotic end-effectors for obstacle avoidance more conveniently and efficiently but also provides an effective idea for accomplishing interactive learning tasks under constraints.

Impact dynamics of a free-falling reference test mass in space

Outer space may constitute a privileged environment for experiments involving impacts. In fact, disturbing phenomena like drag or weight forces are negligible and a nearly pure free-fall state may be achieved for the impacting bodies. The case analysed in this manuscript comes from the initialization of the science phase of a space mission (LISA Pathfinder, flown in 2015), in which an extended metallic body – starting from a caged configuration – was released to free-fall inside a spacecraft by a dedicated mechanism, the grabbing positioning and release mechanism (GPRM). During the release phase, the test mass (TM) experienced some impacts with the GPRM end effector, before being electrostatically controlled to its nominal position, i.e. still in the centre of the hosting electrode housing. The impact dynamics of the TM therefore resulted critical, since it helped reduce its kinetic energy with respect to the spacecraft. In this paper, the TM position and attitude telemetry signals are analysed, and the impacts coefficient of restitution is calculated, providing reference values for similar space instruments, where a free-falling reference body is used (for instance, for geodesy and/or spacecraft navigation).

A Manipulator Pose Planning Algorithm Based on Matrix Information Geometry

In an automatic ultrasonic testing system constituted by an ultrasonic probe and a six-axis manipulator, the manipulator needs to run from a static state to the target velocity. To prevent equipment damage caused by sudden acceleration or deceleration, it is necessary to plan the position and pose of the end effector of the manipulator at each detected point. In this manuscript, an algorithm for planning the position and pose of the manipulator is proposed based on the information geometry structure of special orthogonal groups. As the linear operation of the orthogonal matrix corresponding to the manipulator pose is not closed, the manipulator pose at each detected point was calculated using the straightness of the Lie algebra of the special orthogonal group. The matrix information geometry algorithm enabled not only the manipulator to accelerate and decelerate uniformly along the detection trajectory, but also the angular acceleration of the end effector to accelerate uniformly at first, then keep a uniform velocity, and finally decelerate uniformly. The platform motion experiments with the Turin TKB070S six-axis manipulator are carried out to verify the effectiveness of the matrix information geometry algorithm for planning the pose of the manipulator.

Factors Affecting Workers' Mental Stress in Handover Activities During Human-Robot Collaboration.

This study investigated the effects of different approach directions, movement speeds, and trajectories of a co-robot's end-effector on workers' mental stress during handover tasks. Human-robot collaboration (HRC) is gaining attention in industry and academia. Understanding robot-related factors causing mental stress is crucial for designing collaborative tasks that minimize workers' stress. Mental stress in HRC tasks was measured subjectively through self-reports and objectively through galvanic skin response (GSR) and electromyography (EMG). Robot-related factors including approach direction, movement speed, and trajectory were analyzed. Movement speed and approach direction had significant effects on subjective ratings, EMG, and GSR. High-speed and approaching from one side consistently resulted in higher fear, lower comfort, and predictability, as well as increased EMG and GSR signals, indicating higher mental stress. Movement trajectory affected GSR, with the sudden stop condition eliciting a stronger response compared to the constrained trajectory. Interaction effects between speed and approach direction were observed for "surprise" and "predictability" subjective ratings. At high speed, approach direction did not significantly differ, but at low speeds, approaching from the side was found to be more surprising and unpredictable compared to approaching from the front. The mental stress of workers during HRC is lower when the robot's end effector (1) approaches a worker within the worker's field of view, (2) approaches at a lower speed, or (3) follows a constrained trajectory. The outcome of this study can serve as a guide to design HRC tasks with a low level of workers' mental stress.

Workspace and dexterity analysis of the hybrid mechanism master robot in Sinaflex robotic telesurgery system: An in vivo experiment.

Sinaflex robotic telesurgery system has been introduced recently to provide ergonomic postures for the surgeon along with dexterous workspace for robotic telesurgery. The robot is described, and the forward and inverse kinematics are derived and validated by an experiment. The robot and operational workspaces and their dexterity are investigated and compared using the data collected during a dog vasectomy robotic telesurgery by Sinaflex. According to the simulation results, the workspace of the end effector is as large as 914.56×105mm3, which can completely cover the ergonomic human hand workspace. The dexterity of the robot for the total and operational workspace is 0.4557 and 0.6565, respectively. In terms of the workspace size and the amount of dexterity, Sinaflex master robot can be considered a good choice to fulfil the requirements of the surgeon side robot in robotic telesurgery systems.