【正文】 rove control performance of the desktop size 3axis milling machine. The H∞ controller intentionally designed with double integrators showed better performance than PID control in terms of tracking error and stiffness for the zaxis, which is equipped with a linear motor and air bearing. But H∞ control and PID control are similar when they are applied for voice coil motor driven x and yaxes. The input shaping control is useful when high acceleration is required, but it should be used with caution for multiple axes because it may destroy the synchronization of coordinated reference trajectories for each axis. The disturbance observer showed its usefulness in counteracting disturbances. The closedloop servo system recovered from sudden impulselike disturbances parably fast when it has a disturbance observer on top of a feedback controller. The disturbance observer may help preserving machining accuracy when large cutting forces apply to the tool stage. Crosscoupled control appears to be very effective to improve not only contour error but also tracking error when a significant friction exists. In our testbed machine, a crosscoupled controller added to H∞ control servoloop showed remarkable reduction in contour errors and it gave better tracking error than a feedforward controller. 三軸工作臺(tái)銑床及運(yùn)用先進(jìn)現(xiàn)代控制算法 的數(shù)控系統(tǒng)的研發(fā) 1. 簡介 隨著新的領(lǐng)域如 IT(信息技術(shù) )、 BT(生物技術(shù) ) 和 NT(納米技術(shù) ) 的出現(xiàn)及其對(duì)工業(yè)發(fā)展的帶動(dòng)，人們對(duì)微型工廠系統(tǒng)的興趣與日俱增。 Reset). When a user click the Open Gcode button, a whole Gcode file is read in and saved in a memory area, and then the Gcodes appear at the bottom left list box. When the Start Gcode button is clicked, the user interface program takes out a line from the memory and checks its syntax and identifies all the meaningful tokens. During preprocessing a Gcode line, the user interface program is supposed to pute, a motion plane, a driving axis, maximum allowable velocity and acceleration, the starting position of the deceleration, directional cosines. If the Gcode line is about circular motion, the center point of the arc, the normal direction of the arc, and start and end angles are also puted by the user interface program. All the preprocessed information is entered in the DPRAM and handed to the DSP program. A circular buffer in the DPRAM has rooms for only 4 lines of Gcodes, so the user interface program needs to keep monitoring the circular buffer usage. When the user interface program finds that the DSP program finishes carrying out a Gcode line and empties its space, it fills in the empty space in the circular buffer with a new preprocessed Gcode line in the order in which they occur. DSP Program The DSP program interpolates the preprocessed Gcodes in realtime and generates position mands for multiple axes to follow. It also closes servo control loops. Generally a sampling rate is set to be ten times larger than the bandwidth of a plant to be controlled. The developed CNC system adopted a sampling rate of 2,000 Hz for the servo loops. The DSP program takes out a Gcode line from the circularbuffer and putes the angle between two successive Gcode lines. If the angle is less than a certain (predefined) degree and the contouring is on, it sets a flag so that the tool path does not reduce its velocity when it enters into the next segment. When a ti mer interrupt occurs, the DSP program putes the desired velocity and position of each axis and generates mands for the servo control loop. The puted velocity should be less than the maximum allowable velocity puted by the user interface program and start decreasing when the position reaches the position of deceleration to make a plete stop at the end point if contouring function is not used. If the current motion is linear, all the putations are for the driving axis and mands for the other axes are calculated from straightline equations related to the driving axis. If the current motion is circular, angular velocity and angular acceleration are similarly used as in the linear motion and the final mands are made from the polar coordinate to the Cartesian coordinate transformation. After generating realtime mands for each axis the DSP program drives the servo control loops of the 3axis. The errors which are differences between the mands and the actual feedback positions are fed into a control algorithm such as PID and the control signals for the motor drives are puted. 4. Control System Design To improve the performance of servo control for the 3axis milling machine, several control algorithms have been tested on the 3axis milling machine. They include PID, H∞ control, input shaping control, disturbance observer, and crosscoupled control. These control schemes were digitally implemented on a Daytona DSP board from Spectrumsignal Co. The DSP board has two TI320C6701 chips on it and a sampling rate of 2,000 Hz has been used. The design procedure and experimental results from each control are described as follows. H∞ Optimal Control Design Using a conventional PID controller for the zaxis which has a linear motor and airbearing, it seemed that high gain PID easily started oscillations. As an alternative, an H∞ controller was designed and applied to the zaxis and performance of hand tuned PID and H∞ control is pared. An openloop plant model for control design was obtained from experimental frequency response data. The frequency responses were measured with a dynamic signal analyzer using a swept sine method that generates fixedamplitude sine waves of varying frequencies. From the frequency responses for different input amplitudes, an averaged frequency response wasputed and a nominal continuoustime plant model was fitted. Fig. 6 shows the averaged frequency response and a nominal o