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1、 密 级分类号编 号成 绩本科生毕业设计 (论文)外 文 翻 译原 文 标 题CNC DRILLING MACHINE CONTROL SYSTEM DESIGN译 文 标 题数控钻床控制系统设计作者所在系别电子工程系作者所在专业自动化作者所在班级作 者 姓 名作 者 学 号指导教师姓名指导教师职称完 成 时 间2011年12月07日北华航天工业学院教务处制译文标题伺服系统的设计3-Axis数控钻床基于xPC目标原文标题Design of Servo System for 3-Axis CNC Drilling Machine Based on xPC Target作 者Butler Jero
2、me译 名杰罗姆巴特勒等国 籍美国原文出处Atomation Professional English CauseAbstract As special equipments, the CNC drilling machines require servo systems specially designed. So there is a substantial waste of time and energy. In order to solve this problem, a design proposal for the servo system of 3-axis CNC drilli
3、ng machine based on xPC Target is presented in this paper. Taking a CNC drilling machine model as the experiment platform, the block diagram of the servo system was designed using SIMULNK tools, and compiled into a real time system by VC complier, which could run on X86 computer. Rapid developing of
4、 a servo system for 3-axis CNC drilling machine is easily implemented by this proposal. The experimental results demonstrate that the feed system of the drilling machine model could carry out a quick precisionpositioning. Key words-servo systems; drilling machines; xPC Target;I. INTRODUCTIONThe CNC
5、drilling machine is mainly for drilling holes with numerical control. The most products are special Figure 1. The control system structure of 3-axis CNC drilling machineequipments, which are widely used in hole processing technology for the PCB and large porous tube sheet parts.1 And, these products
6、 most are special equipments, can be classified as CNC vertical drill, drilling center, CNC PCB drill, CNC deep-hole drill and other large CNC drilling machine.2 It is applicable to machining the parts with lots of precise holes in procedures of drilling, spreading, weaning and threading. Especially
7、, its important to improve the machining accuracy and efficiency that choose a special CNC drilling machine to work the PCB and large porous tube sheet. While, the design of servo system is the most complex in the process of designing a special CNC drilling, and require plenty of time to program and
8、 debug. So, it not only consumes the valuable intellectual resources, but constrains to market the product timely. XPC Target is a tool set based on Matlab/SIMULINK that is provided by MathsWorks. It has a wealth of I/O device modules which support the majority of integrated circuit boards.3 And, xP
9、C Target introduced a host-target technical means, one PC as host computer, and another industrial computer as target computer, two computers connected with network cards and communicate through TCP/IP protocol. The systems by xPC Target can run onX86 computer real-time. It achieves simulation on bo
10、ard and rapid prototyping of control systems. The CNC technology lab for scientific research in Guangdong province developed a 3-axis CNC drilling machine model which is based on the product manufactured by Shenzhen Open Technology Corporation. Using the drilling machine model as test platform, desi
11、gned the special servo system based on XPC Target. II. SERVO CONTROL SYSTEM STRUCTURE OF THE 3-AXIS CNC DRILLING MACHINE The control system of the 3-axis CNC drilling machineis a two-level computer control structure: the host computeris a personal computer, and carries out drawings,commands, communi
12、cations etc. the lower computer is anembedded computer of PC/104, as the core unit of servocontrol system in the drilling machine.The host computer communicates the data of commands and motion states with the embedded computer of PC/104 by RS232, As shown in Fig.1. And, apply the Modbus communicatio
13、n protocol to keep the data mutually transmitted exactly. In this system, ADT652 expansion card according with PC/104 bus is used as the I/O interface of the system. Using the software of SIMULINK, designed servo control system of 3-axis CNC drilling machine based on XPC Target. And, the software of
14、 the system was downloaded to the PC/104 and real-time operated ascompiled and debugged successfully. After complicated computing, the PC/104 modulates the results into a corresponding PWM signal that is exported to the motor drive circuit through ADT652 board. Then, the motor driving the correspond
15、ing axis rotates at a definite speed under control. At the other side, a incremental rotational photoelectric encoder was fixed on the servo motor of the relevant feeding mechanism to obtain its position，which is fed back to the PC/104 by the I/O port of ADT652. While, the motional speed of the spin
16、dle servo motor is obtained by speed senor, and is fed back to the PC/104 by the ADC channel of ADT652.III. ESTABLISH THE SERVO CONTROL SYSTEMIn general, the servo control of CNC drilling machines feeding mechanism is point-to-point control. And, thefeeding rate of X, Y-axis could obviously affects
17、promoting the production efficiency, but the Z-axis feeding rate would not archive the effect for the factors of the drill and the processing materials. On this platform, a DC motor is used as the power set of the feeding mechanism. Compared with AC motor control, DC motors drive circuit is more sim
18、ple and reliable. Moreover, the speed adjusting accuracy and dynamic response characteristics of the DC motor are more ideal with a greater speed range and higher speed adjusting accuracy.4 So, it can be satisfied with the experiment requirement better. As the value of inductance (L) in the armature
19、 circuit of DC motor is very low, it can be ignored in the mathematical model of the servo systems. Then, taking the armature voltage (Ua(s) as the input value and the motor speed (s) as the output value, the mathematical model of armature-control DC motor is established, and the model can be regard
20、ed as a 1st-order system. The transfer functionof the model is: Taking the angle of the motor (s) as the input valueand the linear displacement of the workbench (Xo(s) as the output value, the mathematical model of the working platform can be also simplified as a 2nd-order system. Its transfer funct
21、ion is:With comprehensive consideration on the mathematical model of the DC motor and the working platform, the servo system can be simplified as a 2nd-order system model. Its transfer function is:The servo control system of the X-axis feeding system for the CNC Drilling Machine is presented in this
22、 paper.And the other feeding systems are not described in detail for being similar with the X-axis.A. Mathematics modelingOn the 3-axis CNC drilling machine model, a Maxon motor F2260 is fixed as the power set of the X-axis feedingmechanism. And the rotation of motor can be converted into the linear
23、 motion of the workbench through the mechanism of lead screw. We can create the transfer function with the characters about the motor and workbench which is shown in the table I. The transfer function of X-axis servo system is obtained by the above parameters of Motor and workbench: B. PID controlle
24、r designIn this paper, a PID compensator is designed to adjust the motion of the servo system according to themathematical model above. And its parameters are set withthe experiential formula of Ziegler-Nichols5 by MATLAB software. The formula is: In the formula, the Km is the value of proportional
25、gain as the time systems begin to shock, and the m is theoscillation frequency at this point. Firstly, the mathematical model of the controlled object is converted into a discrete model using zero-order holder. Then, use the commands of rlocus and rlocfind to obtain the oscillation gain Km and the o
26、scillation frequencym at the critical point . Finally, the parameters of the PIDcompensator can be obtained by the formula (5):The step responding curves about the pre-tuning and after-tuning are shown in Fig.2. We can find that theoscillation and overshoot of the systems step responding was elimina
27、ted for the adjustment of the PID compensator, and the system can get to a steady-state in 1.5 seconds. In addition, an integral weakening technique is introduced in the PID compensator to enhance the stability of the servo systems. the technique is that when thedeviation value (ei) between the feed
28、back value and the aim parameter of servo system is greater than a stipulated threshold, the section of integral doesnt work. So the integral value will not be too large. Only when the deviation value is small, It works to eliminate the static error of system. Its PID algorithm is presented as posit
29、ion type: The outcome of simulation indicates vividly that the PID compensator fulfills the requirements very much of quick precision positioning in the point-to-point control of CNC drilling machine.C. Design servo system base on xPC targetThere are a set of xPC target tools in the SIMULINK softwar
30、e, such as RS232 communication tool, timing tool,I/O interface tool etc. these can be used in to establish control block diagram of the servo system.6According to the servo system models which be described as the formula (4), using MATLAB/SIMULINKwe can easily establish the simulation models for the
31、 3-axis CNC drilling machine. The control block diagram of the X-axis servo system is shown in fig.3. This is only a non-real-time, off-line simulation studies.7 But, when the system is running on the actual hardware in which integration of in-the-loop testing and debugging can beachieved.On the har
32、dware, an ADT652 based on the PC/104 bus is used as the data acquisition card. And, the PORTA ofADT652 reads pulses of the incremental rotational photoelectric encoder in real-time, and sends it to PC/104which would converts it into a angle value as feedback of the system.8 Here, the PORTAs address
33、is 0x308, andthe base address of ADT652 is set as 0x300 through jumper. Then, the deviation value (ei) between the feedback value and the aim parameter of servo system is involved in the operation of the PID compensator designed well. The skill of limiting integration is use in the PID compensator.
34、At last, a regulating variable comes to output. the regulating variable is converted to a PWM signal which is sent to the motor drive circuit through the PORTB of ADT652, which address is 0x309. So, the speed control loop for the servo motor of X-axis is created. With MATLAB/ SIMULINK running on the
35、 host computer, and the development environment9 of Real-TimeWorkshop, xPC Target and VC6.0 compiler set well, the block diagram of the servo system designed well could be converted into an application which would be download to the target computer (PC/104) through TCP/IP protocol. Then, the CNC sys
36、tem is created and could run on the 3-axis CNC drilling machine model in real-time.The servo control block diagrams of the other feeding systems for the three-axis CNC drilling machine modelare similar with the X axis, so they are no longer detaileddescribed hereThe three-axis CNC drilling machine m
37、odel was used as the experimental platform which dimension is 200mm150mm50mm corresponding to its XYZ axis. And the servo system is established and regulated according to the Fig.1. Then, the servo control system block diagram was complied into an application by the VC compiler in a MatlabRTW enviro
38、nment properly set up. At last, an experiment was carried out to detect the performance of the system designed here on the drilling machine model, taking a personal computer as the host computer and the PC/104 as the target computer in which the application generated is running in real-time.the coor
39、dinate point of the target is situated at 100000 m,70000m,30000m. And the host computer sent the coordinates and control commands to the lower computer. The workbench ran to the target point with the control of the CNC system. The actual position of the workbench was measured exactly by the grating
40、rules which were installed on the lathe guide rails. The measurement accuracy of the grating rule is 1(m).10 In each experiment, the workbench ran from the zero position to the same target described above. And, the experimental data on position by grating rules is shown in the table below. The overa
41、ll precision parameters of the drilling machine system can be drawn after analysis of the data in the table II: the positioning accuracy : 0.02(mm) the reorientation accuracy: 0.01(mm).Theoretically, the control accuracy could be achieved to 3(m), because an optical encoder with 500 lines isused on
42、the servo motor.But the actual error is greater than that. There are some reasons.1) The elastic deformation of workbench impacts.2) There is a measurement error on the grating rule.3) The error of screw assembly impacts4) The error of zero point impacts.V. CONCLUSIONThis paper presents a design pro
43、posal for the servo control system of three-axis CNC drilling machine based onXPC Target. The development of the whole control system could be completed in a short time by this method. And, the experimental results demonstrate that the feeding system can run to the target position quickly and precis
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