Trajectory Of Robot End-effector Research Articles

Underactuated Humanoid Peeling Approach for Pickled Mustard Tuber Based on Metamorphic Constraints.

Pickled mustard tuber (PMT), also known as Brassica juncea var. tumida, is a conical tuberous vegetable with a scaly upper part and a coarse fiber skin covering the lower part. Due to its highly distorted and complex heterogeneous fiber network structure, traditional manual labor is still used for peeling and removing fibers from pickled mustard tuber, as there is currently no effective, fully automated method or equipment available. In this study, we designed an underactuated humanoid pickled mustard tuber peeling robot based on variable configuration constraints that emulate the human "insert-clamp-tear" process via probabilistic statistical design. Based on actual pickled mustard tuber morphological cluster analysis and statistical features, we constructed three different types of pickled mustard tuber peeling tool spectral profiles and analyzed the modular mechanical properties of three different tool configurations to optimize the variable configuration constraint effect and improve the robot's end effector trajectory. Finally, an ADAMS virtual prototype model of the pickled mustard tuber peeling robot was established, and simulation analysis of the "insert-clamp-tear" process was performed based on the three pickled mustard tuber statistical classification selection. The results showed that the pickled mustard tuber peeling robot had a meat loss rate of no more than 15% for each corresponding category of pickled mustard tuber, a theoretical peeling rate of up to 15 pieces per minute, and an average residual rate of only about 2% for old fibers. Based on reasonable meat loss, the efficiency of peeling was greatly improved, which laid the theoretical foundation for fully automated pickled mustard tuber peeling.

Robot Time-Optimal Trajectory Planning Based on Quintic Polynomial Interpolation and Improved Harris Hawks Algorithm

Time-optimal trajectory planning is one of the most important ways to improve work efficiency and reduce cost and plays an important role in practical application scenarios of robots. Therefore, it is necessary to optimize the running time of the trajectory. In this paper, a robot time-optimal trajectory planning method based on quintic polynomial interpolation and an improved Harris hawks algorithm is proposed. Interpolation with a quintic polynomial has a smooth angular velocity and no acceleration jumps. It has widespread application in the realm of robot trajectory planning. However, the interpolation time is usually obtained by testing experience, and there is no unified criterion to determine it, so it is difficult to obtain the optimal trajectory running time. Because the Harris hawks algorithm adopts a multi-population search strategy, compared with other swarm intelligent optimization algorithms such as the particle swarm optimization algorithm and the fruit fly optimization algorithm, it can avoid problems such as single population diversity, low mutation probability, and easily falling into the local optimum. Therefore, the Harris hawks algorithm is introduced to overcome this problem. However, because some key parameters in HHO are simply set to constant or linear attenuation, efficient optimization cannot be achieved. Therefore, the nonlinear energy decrement strategy is introduced in the basic Harris hawks algorithm to improve the convergence speed and accuracy. The results show that the optimal time of the proposed algorithm is reduced by 1.1062 s, 0.5705 s, and 0.3133 s, respectively, and improved by 33.39%, 19.66%, and 12.24% compared with those based on particle swarm optimization, fruit fly algorithm, and Harris hawks algorithms, respectively. In multiple groups of repeated experiments, compared with particle swarm optimization, the fruit fly algorithm, and the Harris hawks algorithm, the computational efficiency was reduced by 4.7019 s, 1.2016 s, and 0.2875 s, respectively, and increased by 52.40%, 21.96%, and 6.30%. Under the optimal time, the maximum angular displacement, angular velocity, and angular acceleration of each joint trajectory meet the constraint conditions, and their average values are only 75.51%, 38.41%, and 28.73% of the maximum constraint. Finally, the robot end-effector trajectory passes through the pose points steadily and continuously under the cartesian space optimal time.

遠隔操作における操作入力および見まね学習による経路生成との融合による把持支援手法

This paper proposes an imitation learning-based approach to assistive teleoperation for a reaching task with multiple objects. First, according to the approaching velocity of the user's input, we estimate the user's intention of the target object. Then, by integrating user input and the output of the demonstrated trajectroy via Dynamic Movement Primitives, we generate the robot endeffector trajectory that will converge to the position of the target object. We present experimental results of an object reaching task to demonstrate the effectiveness of the proposed method in a simulated robot teleoperation system.

Robot programming by demonstration with a monocular RGB camera

PurposeThis paper aims to present a new approach for robot programming by demonstration, which generates robot programs by tracking 6 dimensional (6D) pose of the demonstrator’s hand using a single red green blue (RGB) camera without requiring any additional sensors.Design/methodology/approachThe proposed method learns robot grasps and trajectories directly from a single human demonstration by tracking the movements of both human hands and objects. To recover the 6D pose of an object from a single RGB image, a deep learning–based method is used to detect the keypoints of the object first and then solve a perspective-n-point problem. This method is first extended to estimate the 6D pose of the nonrigid hand by separating fingers into multiple rigid bones linked with hand joints. The accurate robot grasp can be generated according to the relative positions between hands and objects in the 2 dimensional space. Robot end-effector trajectories are generated from hand movements and then refined by objects’ start and end positions.FindingsExperiments are conducted on a FANUC LR Mate 200iD robot to verify the proposed approach. The results show the feasibility of generating robot programs by observing human demonstration once using a single RGB camera.Originality/valueThe proposed approach provides an efficient and low-cost robot programming method with a single RGB camera. A new 6D hand pose estimation approach, which is used to generate robot grasps and trajectories, is developed.

Offset Trajectory Planning of Robot End Effector and its Jerk with Curvature Theory

Some situations that change the parameters of the kinematic structure may cause the robot end effector to deviate [Merlet [2005] Parallel Robots, Vol. 128 (Springer Science & Business Media, Germany)] from the desired trajectory. This effect is called the robustness of the robot by Merlet. One of the ways to correct the robustness is by updating the robot trajectory. The jerk vector of the robot end effector is the third-order positional variation of the TCP and defined as thus the time derivative of the acceleration vector. If there is a high curvature on the transition curve trajectory of robot, then there is a tangential jerk along the trajectory. In this study, the geometrically offset trajectory of the robot end effector from the current trajectory was obtained by using the curvature theory. The angular velocity and angular acceleration of the offset trajectory were calculated. An example of the main trajectory of robot end effector and its offset is given. Also, the jerk of the robot end effector of the offset trajectory was calculated according to the curvature of the trajectory surface in case of a jerk problem caused by a high curvature in the transition curve along the offset trajectory curve.

Shape-Preserving and Reactive Adaptation of Robot End-Effector Trajectories

Variation in task requirements and operation in uncertain environments require robots that can continuously adapt their motions during execution. To do this successfully, the original motion characteristics must be preserved. This paper presents an approach for on-line adaptation of end-effector trajectories for robot manipulators. The trajectory generator aims to preserve the shape of a given model trajectory through its coordinate-invariant shape description. In addition, this trajectory generator is coupled to a task specification and control framework that enables reactive behavior of the robot. Simulation results on the UR10 robot indicate the capability of the developed approach to generalize end-effector trajectories towards new targets while preserving the original trajectory shape. The controller's reactivity is shown towards moving targets and obstacles in the environment. The combination of shape preservation and reactive control may endow robots with better on-line motion generalization capabilities.

Industrial Internet for Manufacturing

This paper describes a novel method for robotic gear chamfering called dual-edge chamfering which can facilitate simultaneous chamfering of the two edges of adjacent gear teeth and overcome typical registration errors arising due to the placement of the workpiece in the robot workspace. Deviations of the robot end-effector trajectory when compared to the nominal trajectory due to registration errors are discussed first; such trajectory deviations caused by typical registration errors due to gear center translation and rotation are quantified. Dual-edge chamfering process is described and an efficient trajectory design strategy is developed by considering the kinematic constraints imposed by the profiles of the gear edge and the abrasive tool. The dual-edge chamfering robot trajectory is facilitated by a simple procedure for identifying the gear and gear root centers by employing the robot. To execute the dual-edge chamfering trajectory, an efficient motion/force control strategy that includes active compliance from the tool mounted on the robot is proposed. A number of real-time experiments are conducted to evaluate the proposed method by employing a commercial six degree-of-freedom robot. Two types of large cylindrical metal gears are utilized for testing, an external gear with teeth on the outside and an internal gear with teeth on the inside. In addition to these, two different robotic compliant tools with axial and radial compliance are tested. A representative sample of the experimental results are presented and discussed.

Dual-edge robotic gear chamfering with registration error compensation

• In this paper, key challenges for robotic chamfering are identified and numerical examples and analysis of the effects of workpiece registration error on robotic chamfering via contour following are provided. • A novel method called dual-edge chamfering is developed to overcome the difficulties associated with robotic chamfering due to the registration error. • Trajectory generation and associated identification procedures are presented for dual-edge chamfering method. • A motion/force control strategy for gear root identification and dual-edge chamfering is described and extensive experiments were conducted using an industrial robot and large gears to validate the proposed method. This paper describes a novel method for robotic gear chamfering called dual-edge chamfering which can facilitate simultaneous chamfering of the two edges of adjacent gear teeth and overcome typical registration errors arising due to the placement of the workpiece in the robot workspace . Deviations of the robot end-effector trajectory when compared to the nominal trajectory due to registration errors are discussed first; such trajectory deviations caused by typical registration errors due to gear center translation and rotation are quantified. Dual-edge chamfering process is described and an efficient trajectory design strategy is developed by considering the kinematic constraints imposed by the profiles of the gear edge and the abrasive tool. The dual-edge chamfering robot trajectory is facilitated by a simple procedure for identifying the gear and gear root centers by employing the robot. To execute the dual-edge chamfering trajectory, an efficient motion/force control strategy that includes active compliance from the tool mounted on the robot is proposed. A number of real-time experiments are conducted to evaluate the proposed method by employing a commercial six degree-of-freedom robot. Two types of large cylindrical metal gears are utilized for testing, an external gear with teeth on the outside and an internal gear with teeth on the inside. In addition to these, two different robotic compliant tools with axial and radial compliance are tested. A representative sample of the experimental results are presented and discussed.

The adjoint trajectory of robot end effector using the curvature theory of ruled surface

The ruled surface is formed by the movement of a director based on a curve. The point P not on the director vector at fixed frame o-ijk draws a curve. However, each position of this point on the curve always corresponds to position of director on the ruled surface, or this point is adjoint to director vector. Thus, the curve is adjoint to the ruled surface. In this study, we expressed the adjoint trajectory of robot end effector. We can change the trajectory of the robot movement by defining the adjoint trajectory when it may not be physically achievable and not re-computation of the robot trajectory. We investigated the angular acceleration and angular velocity of adjoint trajectory of the robot end effector. Also, we obtained the condition that moving point is a fixed point.

A novel force and motion control strategy for robotic chamfering of gears

Accurate positioning of the workpiece in the robotic work cell is currently required to perform machining operations such as chamfering in order to obtain high quality products. However, registration and workpiece fixturing errors are inevitable and lead to uncertainty in the desired robot end-effector trajectory which will lead to poor quality of the finished product. This paper proposes a method for robotic gear chamfering that can compensate for the registration error of the workpiece while avoiding use of expensive and time-consuming metrology devices for accurately registering the gear in the robot workspace. We highlight the problems in chamfering with workpiece uncertainty when traditional contour following methods are employed. A novel chamfering trajectory based on a part identification procedure is proposed that can account for the gear registration uncertainty. A force control strategy is employed in identifying the gear center and gear root positions. Based on this identification, we employ a novel force/motion strategy that can simultaneously chamfer two edges of the adjacent gear teeth. We have conducted a number of real-time experiments with a six degree-of-freedom robot to evaluate the proposed strategy, and representative chamfering experimental results are presented and discussed.

Virtual Reality-Based Time-Delayed Haptic Teleoperation Using Point Cloud Data

This paper presents a methodology for bilateral teleoperation of robots based on the use of point cloud data obtained with an RGB-D camera for providing haptic feedback, as well as a virtual robot workspace that allows the user to interact with the teleoperated robot and the environment, regardless of the time-delay between the master device and the slave robot. The robot movements are executed first in the Virtual Workspace and then in the real one. The Virtual Workspace is created using point cloud data, and the haptic feedback is calculated directly using this data. The proposed methodology was validated in 2D and 3D trajectory-following experiments with 20 volunteers each teleoperating a KUKA industrial robot. In addition, we studied two inverse kinematic teleoperation modes: “Proportional Workspace” and “Delta end-effector movements”, with the objective of determining which one is more suitable for the haptic teleoperation methodology proposed. The results obtained confirm that the proposed haptic teleoperation methodology enhances the precision of the operator by reducing the average error between the robot end-effector trajectory and the goal trajectory. Furthermore, the likelihood that the end-effector will collide with objects in the environment is reduced. The methodology also diminishes the time that it takes to complete the trajectory-following task in an unknown workspace. The inverse kinematic teleoperation mode with the better results is the “Proportional Workspace”, which is more intuitive for operators (users).

Programming by Demonstration Using Two-Step Optimization for Industrial Robot.

The paper presents programming by demonstration approach for industrial robots that uses two steps trajectory optimization. On the first stage, optimization is done by statistical methods, on the second stage, the robot end-effector trajectory is obtained based on minimization of energy consumption and task execution time criteria. We verified our approach using 7 degree-of-freedom redundant robot KUKA iiwa and Microsoft Kinect 2.0 motion capture system.

Research on Method of Serial Robot Relative Position Correction

For the problem of serial robot structure error, method of relative position correction was researched. An adaptive filtering correction method based on robot joint position feedback was proposed. The method built a robot joint adaptive filtering corrector (AFC) to correct robot joint feedback. The real spatial position of robot end-effector can be got through the forward kinematics computation with the corrected joint feedback. Thus, the robot structure error is corrected. Weights matrices of AFC were trained with relative positions between calibration points on the standard calibration module. The proposed method of relative positions correction provides a new way for serial robot structure error correction, which does not directly modify the robot kinematics design parameters, dose not need measuring equipment, and can be applied in field. The simulation results got with LabVIEW robot module show that the corrected trajectory of robot end-effector is more approaching to its true trajectory than before, which means the robot structure error is effectively corrected.Keywords: Correction; Relative position; Serial robot; Kinematics