| Laser micro-processing has been widely used due to its easy realization of processing conditions, high power dencity, broad processing objects and high automation. Laser is energy provider and processing objects are energy embracer in the laser micro processing system. The process is the relative movement between the laser spot and the surface of the object, so lots of processing modes can be realized. The method that laser beam is fixed and processing objects is movable is accepted in the system. The systemic design in the thesis is to the part of movement control system. The design, installation and realization are completed based on the design project.1. Components of the control system. The control system is composed of setting unit, digital controller, input channel and output channel. PC, the setting unit, downloads the setting value (processing track) to digital controller. Digital controller, the hardcore of the control system, is composed of hardware and software. It can realize the control arithmetic. Digital controller completed the closed loop movement control by getting grating scale signal, processing data and sending pulse to steeping motor.2. Selection of operater and feedback unit. Movement control realized by stepping motor drive X-Y table movement. Compared with other linear measure sensor, grating scale has the character of high precision and response speed, output signal be interfaced to digital circuit directly and installed on the X-Y table conveniently. These merits are very fit for the system. No static error control can be realized in theory because of integral character of stepping motor. But there is steady-state error in the practicable control system determined by operator and feedback unit's distinguishability. Static error of system determined by X-Y table's steeping distinguishability and feedback unit'sdistinguishability. In the system, X-Y table's stepping distinguishability is 1.25//m and grating scale's distinguishability (four folds subdivision) is 1 ?m, so the static error can belimited within 2.3. Drive of stepping motor and processing of grating scale signal. Diphase vector quantity stepping motor drive is designed based on TA8435H stepping motor drive 1C. Thecurcuit is brevity and credibility. In the system, the sigle chip EPF10K10 (FPGA)is used to complete the design of grating scale signal processing unit. The unit consists of some function units such as four folds subdivision direction judegment circuit of X and Y directions, 18 bits counter circuit, latch interface circuit, address decode circuit and bus interface. The sigle chip EPF10K10 instead tens of universual logic 1C in the system. The grating scale signal processing unit has high response speed and parallel input and output.And its access time is short to some ps. The time delay can be ignored in system. Transfer function of grating scale signal processing unit is H(z) = 1. It agrees the dynaimical property in system. The pitch of grating scale is 4 ?m. Intellect processing unitdistinguishability is 1 after four folds subdivision and direction judgement. Thisfeedback distinguishability is enough to system.4. Documentation of the processing tracks. There are three kinds of method for PC to obtain the processing movement track document. First, the coordinates of the object's pixel in CRT and X-Y table are correspondingly correlated. Base on the correspondence relation, the processing track document can be made through the keyboard or mouse. Second, lattice binary picture transformed from Word, Txt and Bmp document edit in the PC. Third, lattice binary picture transformed from image document obtained by any other image device.5. Realization of movement control. In orientating control, stepping motor is accelerated and decelerated under the closed loop condition. The error can be limitedwithin 2?m through the arithmetic. In track control, based on the grating scale closed loop,the error can be limited within 2 when the stepping motor's speed is under 2.5mm/s(pulse frequency 2KHz) .6.
|
PDF Full Text Request