The design of a new six-degree-of-freedom (6-DOF) parallel-kinematics machine (PKM) has been proposed. Different from the conventional Stewart-Gough platform which has six extensible legs, the new PKM employs three identical RPRS legs to support the moving platform. Since all joint axes, excluding the three spherical joints at the leg ends, are parallel to each other and perpendicular to the base plane, this 6-DOF PKM presents a promising platform structure with decoupled-motion architecture (DMA) such that translation in a horizontal plane and rotation about a vertical axis are driven by the three active revolute joints, while translation in the vertical direction and rotation about horizontal axes are driven by the three active prismatic joints. As a result, this 6-DOF 3RPRS PKM with DMA has simple kinematics, large cylindrical reachable workspace, and high stiffness in the vertical direction. These features make it appropriate for light machining and heavy parts assembly tasks. Because of the DMA, a projection technique is employed for its kinematics analysis. By projecting the manipulator onto horizontal directions and vertical planes, the kinematics issues such as the displacement, singularity, and workspace analysis are significantly simplified.

Kinematic design of a six-DOF parallel-kinematics Machine with decoupled-motion architecture.

The position or movement control of an automated guided vehicle (AGV) is crucial for its operation. However, choosing the AGV position sensor is not a trivial task. This paper investigates the sensors and sensing techniques in machine vision applied in AGV position control in the past 5 years of published academic research. Using a systematic literature review method, we seek to answer the main research question: which sensors and sensing techniques are used in indoor AGV positioning control problems according to the past 5 years of published research and their technological impact. In doing so, we address three sub-question: (i) is the sensor/sensing technique related to the AGV application area; (ii) is the sensor/sensing technique applied to the problem related to the control strategy and/or the AGV guide; (iii) is the sensor/sensing technique related to the required AGV accuracy/sensitivity level. The paper contributions are the application of a systematic method of literature review in AGV position sensors, the research area overview from the selected 31 articles of the past 5 years, and a research agenda proposal.

Sensors applied to automated guided vehicle position control: a systematic literature review

In order to avoid motor saturation in turning maneuvers, an iterative Lame-trajectory planning scheme is proposed to generate a smooth curvature-bounded transition trajectory for a differential-driving wheeled mobile robot (DWMR) switching from one straight path to another. The scheme consists of Lamecurve blending, inverse-kinematics computation, peak-torque positioning and torque-saturation avoidance. Firstly, a Lame-curve blending procedure based on affine transformations, is formulated to generate a smooth G2-continuous transition trajectory for connecting two straight paths. Secondly, the platform twist is calculated according to the curvature of the Lame-curve trajectory, then transformed into the actuated-joint rates by means of the inverse-kinematics model. Thirdly, a peak-torque positioning technique is developed to estimate the peak torques of the driving wheels when the DWMR tracks the trajectory, by combining the computed-torque method and the inverse-dynamics model. Finally, an iterative r-step saturation-avoidance prediction planning strategy is devised to suppress the peak motor torques, by means of two torque limitation schemes via adjusting trajectory curvature and robot speed. The simulation results show that, compared with the conventional planning techniques for circular arcs, our trajectory planning scheme can generate a smooth saturation-free transition trajectory with feasible curvature and traveling speed. The scheme is significantly beneficial for trajectory tracking under finite actuation torque in turning maneuvers, thereby preventing any possible path deviation caused by insufficient torque.

/pdf/trajectory-planning-with-lame-curve-blending-for-motor-53p5lsxh8i.pdf

Trajectory Planning With Lamé-Curve Blending for Motor-Saturation Avoidance Upon Mobile-Robot Turning

The essence of biomimetics in human-computer interaction (HCI) is the inspiration derived from natural systems to drive innovations in modern-day technologies. With this in mind, this paper introduces a biomimetic adaptive pure pursuit (A-PP) algorithm tailored for the four-wheel differential drive robot (FWDDR). Drawing inspiration from the intricate natural motions subjected to constraints, the FWDDR's kinematic model mirrors non-holonomic constraints found in biological entities. Recognizing the limitations of traditional pure pursuit (PP) algorithms, which often mimic a static behavioral approach, our proposed A-PP algorithm infuses adaptive techniques observed in nature. Integrated with a quadratic polynomial, this algorithm introduces adaptability in both lateral and longitudinal dimensions. Experimental validations demonstrate that our biomimetically inspired A-PP approach achieves superior path-following accuracy, mirroring the efficiency and fluidity seen in natural organisms.

Biomimetic Adaptive Pure Pursuit Control for Robot Path Tracking Inspired by Natural Motion Constraints.

When developing a prototype for any physical system, modeling can be used to study and analyze the performance of a system. This study explored the validation of the kinematics and dynamics models of a robotic manipulator using the MATLAB robotics toolbox. A literature survey on the robotics kinematics and dynamics was done to get a deeper understanding of the topic. The kinematic diagram was used to determine the Denavit-Hartenberg (DH) parameters of the robotic manipulator. Joint velocities of the robotic manipulator were determined using the Jacobian matrixes while the mass of each link was determined using SolidWorks mass properties tool. The Gruebler equation was used to determine the degrees of freedom of the manipulator. MATLAB robotic toolbox was then used to evaluate the kinematics and dynamics of the manipulator. Findings reveal that the maximum joint velocity of the robotic arm is 8.11 rad/s and the maximum joint torque is 87.1 N m at the first joint. Also, the manipulator has a total of seven links, including the end effector and six degrees of freedom (D.O.F). The overall mass of the robotic manipulator was found to be 4.2 kg using Kevlar 53% material and MG996R and SG90 Micro servo motors were selected as joint actuators. Also, a safety factor of 2 was used to cater for the omitted components during calculations and the power rating obtained was 1400 W. For future work, researchers recommend an easier interconnection between the Computer-Aided Drawing (CAD) and MATLAB software to be developed as they encountered some difficulties in doing so during this study. 

Validation of the kinematics and dynamics models of a robotic manipulator using the MATLAB robotics toolbox

Applying computer vision to mobile robot navigation has been studied for over two decades. One of the most challenging problems for a vision-based mobile robot involves accurately and stably tracking a guide path in the robot limited field of view under high-speed manoeuvres. Pure pursuit controllers are a prevalent class of path tracking algorithms for mobile robots, while their performance is rather limited to relatively low speeds. In order to cope with the demands of high-speed manoeuvres, a multi-loop receding-horizon control framework, including path tracking, robot control, and drive control, is proposed in this paper. This is done within the vision guidance of differential-driving wheeled mobile robots (DWMRs). Lame curves are used to synthesize a trajectory with G 2 -continuity in the field of view of the mobile robot for path tracking, from its current posture towards the guide path. The platform twist—point velocity and angular velocity—is calculated according to the curvature of the Lame-curve trajectory, then transformed into actuated joint rates by means of the inverse-kinematics model; finally, the motor torques needed by the driving wheels are obtained based on the inverse-dynamics model. The whole multi-loop control process, initiated from Lame-curve blending to computational torque control, is conducted iteratively by means of receding-horizon guidance to robustly drive the mobile robot manoeuvring close to the guide path. The results of numerical simulation show the effectiveness of our approach.

Receding-Horizon Vision Guidance with Smooth Trajectory Blending in the Field of View of Mobile Robots

The subject of this paper is the elastostatics of a novel three-limb, full-mobility parallel-kinematics machine (PKM) with flexible links, dubbed the SDelta robot. Due to the inherent flexibility of the light-weight limb rods under fast operations, they are modeled as identical linearly elastic beams. The moving platform of the PKM is assumed to be elastically attached to the base platform via a six-dof generalized spring. Because of the symmetric design of the SDelta robot, the constant generalized stiffness matrix becomes isotropic. Moreover, the posture-dependent Cartesian stiffness matrix is derived. Based on the preliminary design of a prototype at the desktop scale, its stiffness matrix is numerically evaluated.

Elastostatics of a Full-Mobility PKM with Flexible Links

A systematic and effective approach to the formulation of the dynamics of a planar parallel robot is proposed in this paper, based on the concept of the natural orthogonal complement (NOC). This approach is demonstrated on a robot designed for high-frequency, small-amplitude operations . Its kinematic relations are formulated based on planar screw theory. Then, the constraint wrenches in the Newton-Euler equation s are eliminated with the aid of the NOC, namely, the twist-shaping matrix, which maps the active joint-rate array into the robot twist array. The dynamics model of minimum dimension is formulated. Then, upon comparison with the ADAMS simulation results, our model is proven to be not only accurate, but also effective fo r the dynamics modeling, which shows that the approach is suitabl e for the dynamics simulation and real-time control of the robot of interest.

Dynamics Modeling and Validation of a 3-PRR Planar Parallel Robot

The subject of this paper is the elastodynamics of a novel three-limb, full-mobility parallel-kinematics machine (PKM) with flexible links, intended for high-frequency, small-amplitude operations. By modeling the light-weight limb-rods as identical linearly elastic beams, the flexibility of the in-house developed SDelta robot is taken into account. The PKM is modeled as a six-dof Cartesian mass-spring undamped system. The Cartesian stiffness and mass matrices are derived based on the virtual-joint model. The elastodynamics performance of the SDelta prototype at the desktop scale is numerically evaluated. The calculation results shows that the prototype has the ability to operate at a frequency below 30 Hz with a 5-kg payload.

Cartesian Elastodynamics Model of a Full-Mobility PKM with Flexible Links

The Cartesian elastodynamics linear model of mechanical systems with flexible links

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