Showing papers by "Zexiang Li published in 2012"

Dynamics based time-optimal smooth motion planning for the delta robot

Abstract: A novel method for time-optimal pick and place motion planning based on robot dynamics is introduced. By using the elliptical trajectory with modified sine motion profile, the motion is smooth and suitable for high speed applications to avoid vibration. Since the modified sine motion profile is characterized by only two parameters, time-optimal pick and place motion planning problem is transformed into a three-variable optimization problem. For the reduction of the optimization variables, this method can rapidly obtain a solution that guarantees the smoothness of torques.

An adaptive off-line NURBS interpolator for CNC machining

Abstract: As a key technique in CNC machining, nonuniform rational B-spline (NURBS) interpolator has been proposed to overcome the drawbacks caused by linear and circular interpolator, such as large data size, velocity discontinuity, shocks or variations in mechanical systems, and low machining efficiency. To improve machining quality and efficiency, an adaptive off-line interpolator was developed for NURBS curves in this paper. Both the chord accuracy and the acceleration/deceleration capability of machine tool are considered in the algorithm. There are four modules in the algorithm, adaptive feed rate adjustment, acceleration/deceleration disposal, feed rate modification, and S-type velocity generation. The acceleration/deceleration around the sharp corners is carefully calculated by those modules. A case study was provided to evaluate the feasibility of the interpolator.

A practical real-time non-uniform rational B-spline curve interpolator for computer numerical control machining

Abstract: Non-uniform rational B-spline (NURBS) interpolator, a key technique in computer numerical control (CNC) machining, has many advantages over linear and circular interpolator. A practical real-time NURBS interpolator based on an off-line algorithm, which is developed to handle the limitation of velocity and acceleration, is presented in this article. Two processing modules are employed to realize the real-time interpolator. In one module, a NURBS curve is split into shorter NURBS curves or approximated as continuous line segments according to the minimum splitting length first, and then the velocity planning of a short curve is applied. Inthe other module, the interpolation according to the velocity planning results is implemented. The proposed algorithm realizes the real-time velocity planning and interpolation of a NURBS curve regardless of the curve length or the continuity. It is also applicable to three-dimensional surface designed by computer-aided design system, which is composed of multiple NURBS cu...

Design of a High Performance Linear Stage with Floating Stator

Abstract: This paper presents a novel design for high performance positioning stage, an representative application of such positioning stage is in semi conductor packing process, whose requirements are high precision and high acceleration However, with the increase of motion acceleration(＞10g), the traditional linear stage with fixed stator structure can't suppress the base vibration caused by reactive force, then the stage accuracy decreases seriously In this design, a floating stator structure for linear stage is proposed The main goal is to reduce the effect of the reaction force on the stage from accelerating the mover For the optimal structure variables, the model of single axis stage with floating stator is first developed Then three application requirements are converted to performance indices, by taking the mechanical structure variables as optimal variable, optimization problem is formulated and solved by using Differential Evolution method The performance of proposed structure is verified by simulations Then a prototype of 2-DOF linear stage with floating stator is constructed, the concerned performance of high acceleration, high accuracy and low vibration is validated by numerous experiments

An open control system architecture with an on-line velocity filter for industrial robots

Abstract: As the industrial robot manipulators are widely used in various industrial fields, the limitation of traditional closed architectures for robot control systems becomes increasingly evident. It is almost impossible to modify the planning algorithms, the robot model, or the type of servo amplifier block. In this paper, an open architecture of robot control system is presented. It allows users to change the hardware architecture of the control system, e.g. change the geometric parameters of robots, the number/type of axes, and the servo amplifier block. It allows users to modify both the motion and interfacing software, e.g., modify/replace motion planning/control algorithms or change the human-machine interface to make it friendlier. In most traditional robot control systems, it is not provided to plan velocity profile on-line, which becomes essential in some applications. An on-line velocity filter with the function of look-ahead is thus proposed and implemented. It is integrated in the open-architecture robot control system, which provides users great flexibility to plan the motion on-line. Furthermore, the velocity look-ahead function guarantees the motion accuracy by imposing limits on velocity. Experiments validated the proposed velocity filter and the control system.

Sequential scan matching with sensor order

Abstract: ICP (Iterative Closest Point) algorithm plays an important role in sequential scan matching SLAM. In the algorithm, closest point searching is the well-recognized speed bottleneck. We realize that a searching-friendly structure already exists in the raw data sequence from range acquisition device, and the acquisition order, which we called sensor order, is naturally derived from sensor working mechanism. We show that considering these geometric relations, the searching space could be greatly reduced and can lead to an efficient 3D sequential scan matching algorithm.

A New Hybrid Control Architecture to Attenuate Large Horizontal Wind Disturbance for a Small-Scale Unmanned Helicopter

Abstract: This paper presents a novel method to attenuate large horizontal wind disturbance for a small-scale un- manned autonomous helicopter combining wind tun- nel-based experimental data and a backstepping algo- rithm. Large horizontal wind disturbance is harmful to autonomous helicopters, especially to small ones because of their low inertia and the high cross-coupling effects among the multiple inputs. In order to achieve more accurate and faster attenuation of large wind disturbance, a new hybrid control architecture is proposed to take advantage of the direct force/moment compensation based on the wind tunnel experimental data. In this architecture, large horizontal wind disturbance is treated as an additional input to the control system instead of a small perturbation around the equilibrium state. A backstepping algorithm is then designed to guarantee the stable convergence of the helicopter to the desired posi- tion. The proposed technique is finally evaluated in simulation on the platform, HIROBO Eagle, compared with a traditional wind velocity compensation method.