Dan Wu

Design and Analysis of Precision Active Disturbance Rejection Control for Noncircular Turning Process

In this paper, a new fast tool servocontrol method for noncircular turning process (NCTP) is presented. Based on the tracking and disturbance rejection requirements for NCTP, the controller is designed through a combined active disturbance rejection control and feedforward arrangement by exploiting the unique disturbance estimation and compensation concept and the known reference acceleration signals. In such a design framework, an extended state observer is applied to estimate and compensate for the variant dynamics of the system, nonlinearly variable cutting load, and other uncertainties. Then, a simple proportional integral controller and the acceleration feedforward design produce the control law. To quantify the controller performances, the transfer function description of the controller is derived, and the dynamic stiffness and tracking have been analyzed. By defining the vector margin variation rate, the effects of the plant parameter variations on closed-loop stability are also addressed. Experimental results of machining the first- and second-order oval profiles demonstrate that the tracking error is less than 3 mum for different cutting parameters.

Frequency-Domain Analysis of Nonlinear Active Disturbance Rejection Control via the Describing Function Method

Active disturbance rejection control (ADRC) is a new design concept that shows promising power in dealing with the uncertainties of control systems. However, most of the previous work has been numerical time-domain development and frequency-domain analysis for the linear framework. This paper focuses on the frequency-domain analysis of the nonlinear ADRC behavior using the describing function method and characterizes the effect of the

Design of a Normal Stress Electromagnetic Fast Linear Actuator

{\rm fal}

Limit cycle analysis of active disturbance rejection control system with two nonlinearities

nonlinearity parameter on the performance of the closed-loop system. Both the describing function of the nonlinearity and the transfer function description of the systems linear portion are derived. The stability, dynamic stiffness, and tracking performance are analyzed for a second-order single-input single-output plant. The analysis results show that the nonlinearity parameter plays a crucial role in the system performance. The nonlinear ADRC has higher control efficiency than the linear ADRC but reduces the stability margin of the system. Using the fast tool servo case, simulations and hardware experiments are conducted, and the results further support the analysis.

Application of active disturbance rejection to tracking control of a fast tool servo system

This paper describes the design of a normal stress electromagnetic linear actuator for fast tool servos during nonrotationally symmetric diamond turning. By using the permanent magnet as the biasing flux generator and the total armature pole surface for force generation, the actuator is designed to achieve both linear operation characteristics and high acceleration. A design methodology is presented, which is based on analytical and finite element method magnetic circuit analysis. For design optimization, a new criterion, high actuating force density, is introduced. Based on the optimized structural parameters and the strategy of design for manufacturing, a novel axisymmetric fast linear actuator is developed that has a stroke of 100 ¿m and 500 G acceleration. The linearity of the actuating force versus both the excitation current and the armature displacement is experimentally demonstrated. It is shown that the experimental and calculated results agree well with each other.

Influence of metal chips on drilling quality of carbon fiber reinforced plastic and titanium stacks

Introduction of nonlinearities to active disturbance rejection control algorithm might have high control efficiency in some situations, but makes the systems with complex nonlinearity. Limit cycle is a typical phenomenon that can be observed in the nonlinear systems, usually causing failure or danger of the systems. This paper approaches the problem of the existence of limit cycles of a second-order fast tool servo system using active disturbance rejection control algorithm with two fal nonlinearities. A frequency domain approach is presented by using describing function technique and transfer function representation to characterize the nonlinear system. The derivations of the describing functions for fal nonlinearities and treatment of two nonlinearities connected in series are given to facilitate the limit cycles analysis. The effects of the parameters of both the nonlinearity and the controller on the limit cycles are presented, indicating that the limit cycles caused by the nonlinearities can be easily suppressed if the parameters are chosen carefully. Simulations in the time domain are performed to assess the prediction accuracy based on the describing function.

Quantitative Analysis and Improvement of Countersink Depth in Stack Drilling

This paper addresses the design and implementation of a digital tracking controller for a fast tool servo to drive the cutting tool to machine workpieces with noncircular cross section in a lathe. The main idea of the controller lies in its actively rejecting disturbance while maintaining the simplicity and intuitiveness of existing PID approach. The proposed active disturbance rejection controller (ADRC) mainly consists of an extended state observer (ESO) and a nonlinear proportional derivative controller. The ESO is uniquely designed to estimate the unknown system dynamics and external disturbance, and compensate in each sampling period. Both simulation and experimental results demonstrate the ADRC concept and its validity

Optimization Design for Normal Direction Measurement in Robotic Drilling

The mechanism in drilling of carbon fiber reinforced plastic (CFRP) is different from that of CFRP and titanium stacks. The evacuation of the titanium chips through the hole causes damage to the CFRP. To investigate the quality characteristics of CFRP-layer in drilling of CFRP/Ti stacks, an automated drilling prototype is developed and the drilling experiments of single CFRP and CFRP/Ti stacks are designed respectively for purpose of analyzing the influence of the titanium chips formation with various cutting parameters on the drilling performance of CFRP-layer. The chips morphology are firstly observed, then the mechanism of entrance spalling, high surface roughness (Ra), and hole diameter out of tolerance is studied. The results show that, low feed rate and high cutting speed generates long and folded chips wrapped around the drill, which damage the CFRP strongly. The damage can be controlled by optimization of the cutting parameters. Low feed rate helps to eliminate the entrance spalling, but enlarger the hole diameters in both the CFRP and the titanium layers. To prevent the chips from wrapping on the drill, the cutting speed should be selected in a moderate range. Therefore, the cutting parameters on the titanium layer can be recommended as the feed rate between 0.09 mm/r to 0.13 mm/r, and the cutting speed in a range of 12 m/min to 24 m/min.

Mechanical behavior of cells in microinjection: a minimum potential energy study.

While bolt fastening is the most commonly used method for fastening components, hole quality is an important technology standard in modern manufacturing, especially in the aircraft industry. With low stiffness, the machining deformation of aerospace structures has been a striking problem, which makes it difficult to achieve tight tolerance of countersink depth in one-shot drilling of stacked materials. As a result of the manufacturing errors between the workpieces and the digital models, the position of the workpiece surface can hardly be known before drilling. Moreover, the cutting force adds to the deformation of the thin-walled workpiece in the direction of the feed axis. In view of problems mentioned above, a method of position compensation based on the clamp foot displacement is proposed in the paper, which ensures the countersink depth accuracy by compensating for the deformations of clamping and countersinking respectively in different stages of drilling. Some drilling experiments were conducted, in which the forces in the feed direction were real-time monitored and recorded for FEM simulation. The influencing factors of countersink depth error are firstly discussed in this study, which mainly consists of the size of clamping force and the stiffness differences of variable drilling positions. Numerical simulations were carried out to study the deformation characteristics of workpiece under the combining effect of clamping force and cutting force achieved above. Comparing the simulation results and the experiment results, some other influencing factors of countersink depth are discussed.Copyright

The simplest creeping gait for a quadruped robot

In large assemblies, the perpendicularity of a bolting hole has remarkable effects on the fatigue life and fluid dynamic configuration. While the Computer Aided Design (CAD) model of complexly curved workpieces is hardly satisfied because of manufacturing errors, it is very necessary to measure the normal direction in robotic drilling. One advisable approach is to arrange four laser displacement sensors at the vertices of a rhombus whose center aims at the drilling position. The influencing factors of the measurement precision are firstly discussed in this study, and a novel method to optimize the arrangement size of the displacement sensors for higher precision is introduced. The measurement error for the normal direction consists of the principle error and instrumental error, caused by inconstant curvature of the surfaces and distance measuring errors of instruments, respectively. When the displacement sensors are arranged closer to each other, the principle error will be decreased, whereas the instrumental error will be increased. After the curvature feature of the surface is obtained with the introduced method, the graph of the measurement precision and the arrangement size is plotted. Then, the graph can contribute to developing an optimized design of arrangement size for higher precision. Finally, an example of the curvature obtainment and the arrangement optimization is given. The experimental results show that the optimized design has achieved a higher precision of ± 0.17° for αY and ± 0.26° for αX, whereas the precision of another design is about ± 0.21° for αY and ± 0.29° for αX. The proposed optimization method will bring greater benefit for complexly curved surfaces in practical products and it offers a chance to optimize the arrangement during design phase with little costs.Copyright