1、附 录 英文原文 Feed rate control of the wire-EDM process 1、 Introduction The CNC wire-EDM machines first appears in the market in the 1970s， Although the wire-EDM process has been playing an important role in the tooling and manufacturing industry， especially for the production of punches and dies， The me
2、tal removal process of wire-EDM is very complex with stochastic and time-varying characteristics 。 Moreover ， many machining conditions such as workpiece properties(material， thickness)， machining settings(wire feed， table feed， flushing pressure， etc。 )and power settings(pulse on-time， pulse interv
3、al， etc。 )have an effect to the machining process。 In order to improve the machining efficiency， stability and quality， many efforts have been made by the researchers and manufacturers to develop pulse discrimination and control system。 Liao et al。 developed a pulse discrimination system to study th
4、e characteristics of pulse trains in the wire-EDM process。 They also proposed an approximate method for estimating the variation of the average gap width。 Wire breakage and unstable machining drastically reduce the machining efficiency and accuracy in wire-EDM。 Some adaptive control systems using th
5、e fuzzy control strategy employed the sensing parameters detected by the developed pulse discriminating and control system to monitor and control wire rupture suppression as well as maintain stable machining。 Although these adaptive control systems can be applied to a wide rangeof machining conditio
6、ns， they cannot respond to the gap conditions properly when there is an unexpected disturbance such as the condition of machining a stair-shape workpiece。 In order to carry out the processing of a workpiece with variable height， Rajurkar et al。 presented an adaptive control system to on-line optimiz
7、e the sparking frequency by estimating the workpiece height with a multi-input model。 This paper presents a new computer-aided pulse discriminating and control system for process motoring and control in wire-EDM。 By means of the pulse discriminating and control system， the relationships between mach
8、ine settings and sensing parameters are analyzed quantitatively。 According to the identified gap states， a control strategy is proposed by adjusting the feed rate in real-time to achieve stable machining。 2、 Feed rate control and the process parameters The quality of feed rate control determines the
9、 stability of the gap width the machining process。 The following four process variables can be used for feed control： A、 Gap voltage This process characteristic is average value of the gap voltage。This mean value depending on the different burning voltage levels of spark and arc as well as on the ig
10、nition delay time。 The determination of the middle gap voltage and its technical implementation for gap width control isrelatively easy in comparison with other methods。 The gap voltage was directly proportional to the working gap width。 B、 Ignition delay timeThe ignition delay time characterizes th
11、e conditions for the voltage breakdown of the gap。 The theoretical consideration， that a small gap offers better conditions for a breakdown than a large gap leads therefore to shorter ignition delay times。 In this way， the ignition delays time can be used as a controlled variable for the feed rate c
12、ontrol。 The gap conditions at spark erosion are ideal if the voltage breakdown occurs after a short ignition delay。 Longer ignition delays， the danger for occurring arc discharges arises。 The measurement of the ignition delay of the dielectric breakdown has the advantage compared to other procedures
13、 that critical states the gap before the actual power pulse can be found， In addition， the disturbance afflicted current and voltage measurements are replaces by time measurement。 The start of measurement is given by the generator control。 The time interval ends with reaching a reference voltage or
14、a reference current。 C、 Voltage breakdown The voltage breakdown is characteristic of subsequent discharge because the slope of this breakdown is determined by the dominating mechanism of conducting。 D、 High-frequency parts of the burning voltage The practical investigations show that the spark volta
15、ge has a high-frequency part while the arc burning voltage does not have this one。 Using this， process analyses and feed rate controls achieving a sufficiently good machining result were developed。 Today the feed rate control is carried out via the analysis of the above-mentioned process parameters。
16、 There are hardly problems if a sufficiently good process analysis determines the “critical” process states and eliminates them via a process control， the new feed rate controls must be adapted to theses variable conditions at shortest times。 3、 Pulse discriminating and control system A new pulse di
17、scriminating and control system has been developed for wire-EDM process as shown in Fig.1。 Fig.1 The developed pulse discriminating and control system of wire-EDM In the system， it consists of two parts。 Those are gap states examination module and motion control module。 In the Gap states examination
18、 module， a high voltage in the gap can be changed into a low voltage by a voltage divider for digital circuits。There are three voltage levels 70， 50 and 10V labeled as Vh， Vm and Vl， respectively。A comparator is used produce three different states by comparing the gap voltage signal 。 A complex programmable logic device(CPLD) ， which allows easy modification of the design， clocked by a 4MHz crystal oscillator is not only employed to generate the pulse control signals(i.e.P1 and P2)， it is also used to discriminate the
