Showing papers by "Zexiang Li published in 2013"

Type Synthesis, Kinematic Analysis, and Optimal Design of a Novel Class of Schönflies-Motion Parallel Manipulators

Abstract: A novel class of spatial four degree-of-freedom Schonflies-motion parallel manipulators with four identical subchains is presented. Their features are that each serial subchain undergoes the pure Schonflies motion without redundant joints. The parallel mechanisms possess the simplest topology and are suitable for pick-and-place operations. Kinematic analysis of the 4-PRPaR parallel manipulator, including its inverse and forward kinematics, singularity, and workspace, is discussed in detail. The analysis shows that the moving platform and the base must be in dissimilar dimension for good manipulability performance. The optimal design of the parallel manipulator is formulated as a multiobjective optimization problem. A novel performance index characterizing the approximation of the generated workspace to the prescribed regular workspace, the regular workspace share, is proposed to serve as one of the design objectives. The other objective is the global condition index, which measures the manipulability. The multiobjective optimization problem provides multiple optimal solutions for choice. Simulation verifies that the designed parallel manipulator can approximate the prescribed regular workspace with good condition index.

Exponential submanifolds: A new kinematic model for mechanism analysis and synthesis

Abstract: This paper aims to develop a new kinematic model, the exponential submanifolds (EXPSs) eΩ with Ω a subspace of se(3) (the Lie algebra of the special Euclidean group SE(3)), for mechanism analysis and synthesis. The EXPSs provide perfect models for many global motion types appearing in the past mechanisms, robotics and kinesiology literatures which cannot be modeled as the well known Lie subgroups or their product. We derive in this paper both the sufficient and necessary conditions on Ω such that eΩ is an EXPS, and geometric properties of the EXPS for mechanism analysis and synthesis.

Kinematics and optimal design of a novel 3-DoF parallel manipulator for pick-and-place applications

Abstract: In this paper, a novel 3-degree-of-freedom planar parallel manipulator, the V3 robot, is introduced. The manipulator consists of three revolute joint) subchains, which are respectively arranged in three-parallel planes. The three-actuated joints are designed to have a common rotation axis, which contributes the large workspace and unlimited rotational capability of the robot. The kinematics, including the loop-closure equations, the inverse kinematics, singularity, and workspace are briefly analysed. By directly considering the velocity and the accuracy indices for pick and place operations, the optimal design problem is formulated to maximise the good performance workspace, where lower bounds on the average extreme velocity and upper bounds on the average extreme error are applied as constraints. The optimal design shows greatly improved performance in workspace, velocity, and accuracy.

A low-cost and robust optical flow CMOS camera for velocity estimation

Abstract: This paper presents a robust velocity estimation algorithm applicable to low-cost monocular platform with a tri-axial gyroscope. The algorithm is developed based on PX4FLOW platform which is an open software and open hardware solution for monocular speed estimation. The paper provides three main contributions. The first is the improved robustness achieved by various methods including feature block selection, feed-forward rotation, motion compensation, failure case detection and filtering. The second contribution is the improved performance in terms of resolution and search range achieved by adaptive frame interval and advanced search algorithm. The final contribution is a systematical strategy for parameter selection to fully utilize the hardware resources and optimize the performance in different contexts. The performance was benchmarked against the PX4FLOW and GPS. Results indicated that the proposed algorithm achieved levels of robustness exceeding that of PX4FLOW in measuring velocity. Also, the integrated trajectory agreed with the position calculated by an on-board GPS system.

Cartesian stiffness evaluation of a novel 2 DoF parallel wrist under redundant and antagonistic actuation

Abstract: In this paper, we present an experimental evaluation of the Cartesian stiffness of a novel parallel wrist under redundant and antagonistic actuation. The mechanism in consideration is Omni-Wrist V (OW5), a two degrees-of-freedom (DoF) parallel mechanism redundantly actuated by three subchains. We first give a brief review of its kineto-statics and derive its reduced Cartesian stiffness model. To illustrate the stiffness enhancement of OW5 under redundant and antagonistic actuation, its Cartesian stiffness is measured and evaluated under four control schemes: the non-redundant control, the minimum 2-norm torque control without or with redundant encoder, and the antagonistic actuation control. Measurement data are represented using stiffness matrices and stiffness ellipses. Our study offers a quick quantitative evaluation of stiffness enhancement of OW5 under redundant and antagonistic actuation.

Application of Speed Observer for XY-Stage of Wire Bonder

Abstract: Wire bonder is important equipment in semiconductor post-packaging. In this paper, a speed observer is applied in the motion control system for XY-stage of wire bonder. A simplified friction model is introduced in the observer to take place of traditional friction compensator. With the introduced manual tuning steps, the model can be easily and exactly identified. The compensator of observer is designed by pole placement. As experiments results showing, high motion speed and acceleration of XY-stage is achieved by applying the introduced control structure. The efficiency of wire bonding process is significantly improved.

Application of a Force Sensor in Wire Bonding Process

Abstract: Wire bonder is important equipment in semiconductor end-package. The benefits of using force sensor are precisely force control and earlier contact detection. In this paper, we introduced an application of a force sensor in the wire bonding process. We proposed the control strategy of the whole bonding process with the force sensor. In the bonding process, it's very important to make sure the safety before switching between the force control and position control. A contact detection method in force mode was introduced to get a smooth switch from position control to force control. Before switching from the force control to position control, a two- steps method was proposed to prevent vibrations. The experiments results show that a good bonding performance was achieved by applying with the force sensor. Copyright © 2013 IFSA.

High speed motion control system based on predictive observer

Abstract: Phase lags limit loop gains and ultimately reduce the responsiveness of the high speed motion control system. We propose a predictive position and velocity observer. The predictive observer can provide a significant phase lead therefore the controller can be designed as if the control system does not have these phase lag elements. The implementation and tuning steps of the observer is also introduced. The simulations verify that the proposed observer can significantly improve the performance of the motion control system.

Velocity estimator via fusing inertial measurements and multiple feature correspondences from a single camera

Abstract: In this paper, we present a novel real-time velocity estimation algorithm A sensor assembly consisting of a monocular camera and an inertial measurement unit with three-axis accelerotmeter and gyroscope is considered To improve the robustness of the velocity estimator with respective to image noise, we apply a coarse-to-fine structure based on multiple feature correspondences over three consecutive frames The presented algorithm starts with an initial guess by solving a set of linear equations from modified epipolar constraints, which has increased accuracy and computational efficiency in comparison to previous work Then, a highly accurate velocity estimation is achieved by non-linear minimization of the reprojection errors using the Levenberg-Marquardt algorithm We implement our approach and present the results both in simulation and on real data