Mohammad M. Aref

Geometrical workspace analysis of a cable-driven redundant parallel manipulator: KNTU CDRPM

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible high speed and large workspace applications. This newly developed mechanisms have several advantages compared to the conventional parallel mechanisms. Its rotational motion range is relatively large, its redundancy improves safety for failure in cables, and its design is suitable for long-time high acceleration motions. In this paper, collision-free workspace of the manipulator is derived by applying fast geometrical intersection detection method, which can be used for any fully parallel manipulator. Implementation of the algorithm on the Neuron design of the KNTU CDRPM leads to significant results, which introduce a new style of design of a spatial cable-driven parallel manipulators. The results are elaborated in three presentations; constant-orientation workspace, total orientation workspace and orientation workspace.

On the control of the KNTU CDRPM: A cable driven redundant parallel manipulator

This paper is devoted to the control of a cable driven redundant parallel manipulator, which is a challenging problem due the optimal resolution of its inherent redundancy. Additionally to complicated forward kinematics, having a wide workspace makes it difficult to directly measure the pose of the end-effector. The goal of the controller is trajectory tracking in a large and singular free workspace, and to guarantee that the cables are always under tension. A control topology is proposed in this paper which is capable to fulfill the stringent positioning requirements for these type of manipulators. Closed-loop performance of various control topologies are compared by simulation of the closed-loop dynamics of the KNTU CDRPM, while the equations of parallel manipulator dynamics are implicit in structure and only special integration routines can be used for their integration. It is shown that the proposed joint space controller is capable to satisfy the required tracking performance, despite the inherent limitation of task space pose measurement.

Dynamics analysis of a redundant parallel manipulator driven by elastic cables

In this paper the dynamic analysis of a cable-driven parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of large adaptive reflector (LAR), the Canadian design of next generation giant radio telescopes. This structure consists of a parallel redundant manipulator actuated by long cables. The dynamic equations of this structure are nonlinear and implicit. Long cables, large amounts of impelling forces and high accelerations raise more concern about the elasticity of cables during dynamic analysis, which has been neglected in the preceding works. In this paper, the kinematic analysis of such manipulator is illustrated first. Then the nonlinear dynamic of such mechanism is derived using Newton-Euler formulation. Next a simple model for cable dynamics containing elastic and damping behavior is proposed. The proposed model neither ignores longitude elasticity properties of cable nor makes dynamic formulations heavily complicated like previous researches. Finally, manipulator dynamic with cable dynamic is derived, and the cable elasticity effects are compared in a simulation study. The results show significant role of elasticity in a cable-driven parallel manipulator such as the one used in LAR mechanism.

Integrated controller for an over-constrained cable driven parallel manipulator: KNTU CDRPM

This paper presents an approach to the control of the KNTU CDRPM using an integrated control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. By the proposed controller, the inherent nonlinear behavior of the cable and the target tracking errors are simultaneously compensated. In this paper asymptotic stability analysis of the close loop system is studied in detail. Moreover, it is shown that the integrated control strategy reduces the tracking error by 80% compared to that of a single loop controller in the considered manipulator. The closed-loop performance of the control topology is analyzed by a simulation study that is performed on the manipulator. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

Bounded-velocity motion control of four wheel steered mobile robots

In this paper, we address the problem of motion control for a mobile robot with four independently steer and drive wheels. Our solution fully takes advantage of steerability of all wheels and provide capability of independent control of translation and rotation of the robot. Using non-linear control techniques, we provide a motion control law that makes the base follow a given desired smooth path and heading profile. Derivation of motion control is three folded. Assuming velocity vector orientation and angular velocity of the base as control signals, control laws are derived to solve the path and heading profile following problem. Then these control signals are mapped to eight actuator signals (driving and steering). In a later stage, robot base speed magnitude is controlled in such a way to keep the control signals under predefined limits. Simulations as well as experiment on a real robot show the efficacy of the proposed method.

Explicit dynamics formulation of Stewart-Gough platform: A Newton-Euler approach

Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.

Unified framework for rapid prototyping of Linux based real-time controllers with Matlab and Simulink

We propose a systematic solution for real-time software development for safety critical mechatronic systems. The solution is based on Matlab/Simulink toolboxes and off-the-shelf drivers provided by hardware manufacturers, to address software development challenges in the area of PC based automation. In many cases, developers especially control systems designers found themselves immersed in technical difficulties of real-time programming and hardware interfacing. The remote development environment described here is used to develop real-time software based on Linux operating systems. Unlike other solutions that supports only limited interfaces, it demonstrates systematic methodology to develop reusable Simulink blocks for communicating with wide variety of device drivers and services. Some examples are given based on Xenomai realtime Linux. As a case study, the software development for a mobile robot based on this methodology is presented. The models and blocks developed for this study are available to interested developers for download and test.

Position-based visual servoing for pallet picking by an articulated-frame-steering hydraulic mobile machine

This paper addresses a visual servoing problem for a mobile manipulator. Specifically, it investigates pallet picking by using visual feedback using afork lift truck. A manipulator with limited degrees of freedom and differential constraint mobility together with large dimensions of the machine require reliable visual feedback (pallet pose) from relatively large distances. To address this challenge, we propose a control architecture composed of three main sub-systems: (1) pose estimation: body and fork pose estimation in the pallet frame; (2) path planning: from the current pose to the origin (pallet frame); and (3) feedback motion control. In this architecture, the pallet becomes the local earth fixed frame in which poses are resolved and plans are formulated. Choosing the pallet as the origin provides a natural framework for fusing the wheel odometry/inertial sensor data with vision, and planning is required only once the pallet is detected for the first time (because the target is always the origin). Visual pallet detection is non-real-time and unreliable, especially owing to large distances, unfavorable vibrations, and fast steering. To address these issues, we introduce a simple and efficient method that integrates the vision output with odometry and realizes smooth and non-stop transition from global navigation to visual servoing. Real-world implementation on a small-sized forklift truck demonstrates the efficacy of the proposed visual servoing architecture.

A macro-micro controller for pallet picking by an articulated-frame-steering hydraulic mobile machine

This paper addresses the macro-micro configuration of a mobile manipulation problem for a forklift; specifically, it investigates pallet picking with visual feedback. A manipulator with limited degrees of freedom and differential constraint mobility, together with the large dimensions of the machine, requires reliable visual feedback (pallet pose) and navigation from relatively large distances. It has been shown that the problem can be divided into two parts in order to solve the related issues based on path following theories and visual servoing. Moreover, visual pallet detection is non-real-time and unreliable, especially due to large distances, unfavorable vibrations, and fast steering. To address these issues, we introduce a simple and efficient method that integrates the vision output with odometry and realizes a smooth and nonstop transition from global navigation to visual servoing. Real-world implementation on a small-sized forklift demonstrates the efficacy of the proposed macro-micro architecture.

Mechatronic Design of a Four Wheel Steering Mobile Robot with Fault-Tolerant Odometry Feedback

Abstract In this paper, the mechatronics design of a four wheel steered mobile robot is discussed in detail. Mechanical structure and electrical interfaces are presented. Low-level software architecture based on embedded pc-based control is designed that enables the robot to operate its eight independent actuators synchronously. Kinematics models are elaborated, and it is shown that how mechanical structure of the robot affects kinematics and the feedback. Based on kinematics models, a fault tolerant wheel odometry is proposed to make the feedback robust to practical wheel odometry faults during the solution of forward kinematics. Real-time implementation of presented to support the the efficacy of proposed methods.