计算机数字控制技术

本书从数控原理及所教授的留学生实际需求出发，是一本适用于机械工程专业留学生及高年级本科生的英文教材。 

本教材分为五个章节，主要讲解数控机床的发展史、数控系统工作原理、伺服系统结构及工作原理、机械结构、智能制造内容。本书可以作为机械工程专业留学生的专业教材、高年级本科生的双语教材,也可以供数控技术人员自学参考。

赵巍，女。从2005年博士毕业以来，一直从事数控技术的本科、留学研究生的教学工作，积累了丰富的教学经验，有中文版讲义、发表多篇相关教改论文，具有完整的授课体系、教具、教学课件，开发新实验。多次被评为A级教师，获得天津市师德先进个人。

CONTENTS

Chapter 1Introduction

1.1The history of numerical control machine tools

1.2Basic principles

1.2.1The principle of computer numerical control

(CNC) machine tools

1.2.2The definition of numerical control

1.3The characteristics of CNC machine tools

1.4Introduction to main CNC machine tools

1.5The development of machinery manufacturing systems

Chapter 2Computer numerical control (CNC) systems

2.1The working principle of the CNC system

2.1.1Development of the NC system

2.1.2The composition and working principle of the CNC system

2.1.3The hardware of the CNC unit

2.1.4Hardware composition of CNC devices

2.1.5Software components of the CNC system

2.1.6The functions of CNC devices

2.2Interpolation theory

2.2.1Overview of the interpolation

2.2.2Point by point comparison interpolation

2.2.3Digital differential analyzer interpolation

2.2.4Sampled data interpolation

2.2.5Acceleration and deceleration control

2.3Tool compensation principle

2.3.1Tool length compensation

2.3.2Tool radius compensation

Chapter 3Servo systems

3.1Overview of servo systems

3.1.1Servo system components

3.1.2Servo system classification

3.1.3Basic requirements of servo systems

3.2Commonly used driving elements

3.2.1Stepper motors

3.2.2DC servo motors

3.2.3AC servo motors

3.2.4Linear motors

3.3Commonly used detecting elements

3.3.1Rotary encoders

3.3.2Linear encoders

Chapter 4Mechanical structure of the CNC machine tool

4.1Requirements for the CNC machine tool for mechanical structure

4.2Current common types and layout of CNC machine tools

4.2.1CNC Lathes

4.2.2Machining centers

4.3Main drive system and spindle components

4.4CNC machine tool feed drive systems

4.4.1Requirements for CNC machine tools on the
feed drive system

4.4.2Connection between the motor and the lead screw

4.4.3Ball screw nut pairs

4.4.4Guide rail slider pairs

4.5Selfmade onedimensional feed mechanism

Chapter 5Intelligent manufacturing

5.1The development and application of intelligent manufacturing

5.1.1American industrial Internet

5.1.2Germany industry 4.0

5.1.3Made in China 2025

5.2The core of intelligent manufacturing

5.3Technical support for intelligent manufacturing

5.4A case study of intelligent manufacturing—Siemens Amberg factory

Experiment ATwodimensional motion control platform

Experiment BThe measure of positioning accuracy and repeated positioning

accuracy to onedimensional motion mechanism

Recommended book

前言
中巴、中非友谊源远流长，加大教育国际援助力度，具有针对性地开展紧缺教学资源建设，不仅可以提高多层次、宽领域的国际教育水平，而且有助于增进国际友谊，为“一带一路”合作绘制“工笔画”。
数控技术作为先进制造领域的核心技术，是教育援外机械专业本科生和研究生的必修知识。然而，现有数控技术课程双语教学资源不足，现有教材出版日期较早，缺乏先进数控技术及应用等方面的知识。为填补本领域空白，有针对性地为发展中国家培养数控技术人才，特编写本教材。
本教材分为5章，主要涵盖数控机床发展史、数控系统工作原理、伺服系统结构及工作原理、机械结构、智能制造等内容。本教材按照数控机床的主要工作流程编写，详略得当； 重运用、强实践，将抽象的原理与实际应用有机结合； 追踪先进技术的发展，涵盖智能制造技术最新成果。关键词语采用双语说明方式。可以作为中巴、中非合作办学的机械工程专业留学生专业教材、高年级本科生双语教材，也可以供数控技术人员自学参考。教材包含实验指导书，强化学生实践创新能力的拓展。
本教材第1章由天津职业技术师范大学赵巍、旁遮普天津技术大学MUHAMMAD ALI MANSOOR编写； 第2章由天津职业技术师范大学赵楠、旁遮普天津技术大学MUHAMMAD KASHIF IJAZ编写； 第3章由天津大学董靖川编写； 第4章由天津职业技术师范大学赵巍、张翔宇，旁遮普天津技术大学RAMEEZ UL HASSAN编写； 第5章由天津职业技术师范大学刘鹏鑫、赵楠，湖州职业技术学院王英杰编写。全书由付晓燕校稿，旁遮普天津技术大学Dr.Syed Asim Ali Shah、天津职业技术师范大学满佳老师、北京格瑞纳电子产品有限公司赵伟工程师以及研究生刘梦莹、王丽娜、何苗等也参与了本教材的审核、编辑等工作。
在教材的编写过程中参考了一些数控技术相关的教材和资料，特向其作者表示真诚的感谢。鉴于作者水平有限，书中不可避免地存在缺点、不足，敬请各位读者批评指正。
编者
2019年1月

Chapter 1Introduction
1.1The history of numerical control machine tools
(数shù控kònɡ机jī床chuánɡ史shǐ)

To assist in engineering calculating, a computer was developed at the University of Pennsylvania in 1946. It was called Electrical Numerical Integrator and Calculator which consisted of huge mass of tubes and wires. Although it was slow and stood no comparison with modern computers, it was the best at that time.

Figure 11One kind of ribs

The birth of Numerical Control (NC, 数shù控kònɡ) is generally credited to John T. Parsons, a machinist and salesman at his fathers machining company, Parsons Corp. In 1942, The United States Air Force signed a contract with Parsons Corporation to build the wooden stringers (or ribs, see Figure 11) in the rotor blades (转zhuàn子zǐ叶yè片piàn)(only 17 points were given to define the outline of stringers), but one of the blades failed. Parsons suggested a new method, which led him to consider the possibility of using stamped metal stringers instead of wood. A device would not be easy to produce given the complex outline. Looking for ideas, Parsons visited Wright Field to see Frank Stulen, the head of the Propeller Lab Rotary Wing Branch. Stulens brother worked at Curtis Wright Propeller, and mentioned that they were using punched card calculators for engineering calculations. When Parsons saw what Stulen was doing with the punched card machines, he asked Stulen if they could be used to generate an outline with 200 points instead of the 17 they were given, and offset each point by the radius of a mill cutting tool. If you cut at each of those points, it would produce a relatively accurate cutout of the stringer(横hénɡ梁liánɡ). This could cut the tool steel and then easily be filed down to a smooth template for stamping(冲chònɡ压yā) metal stringers.
Stulen made the program for the stringer which is comprised of large table consisting of numbers, without any problem. Later the program was communicated to machine. There are three operators： one reads the card while other two move the tool in Xaxis and Yaxis to follow the cutting profile. For each pair of numbers, the operators had to move the cutting head to the indicated spot and then lower the tool to make the cut. This was called the “bythenumbers method”(数shù字zì控kònɡ制zhì技jì术shù), or more technically, “plungecutting positioning” (切qiē入rù式shì定dìnɡ位wèi). It was a laborintensive prototype of todays 2.5axis machining.
At that point, Parsons conceived of a fully automated machine tool. With enough points on the outline, no manual working would be needed to make it.
In 1949, the Air Force arranged funding for Parsons to build his machines, but he was confronted by the problem that had prevented convergence of Jacquardtype controls with machining.
In the spring of 1949, Parsons turned to Gordon S. Browns Servomechanisms Laboratory at MIT, which was a world leader in mechanical computing and feedback systems(反fǎn馈kuì系xì统tǒnɡ).
A tripartite agreement was arranged between Parsons, MIT, and the Air Force. In March 1952, the MIT Labs held the first demonstration of the NC machine using a punched tape(穿chuān孔kǒnɡ带dài) to generate the movement of three axes. See Figure 12.

Figure 12The first successful NC machine, developed by MIT

1.2Basic principles
1.2.1The principle of computer numerical control(CNC) machine tools

1. Preparing stage
Manufacturing data is determined by the parts drawing and technical requirements, including tool trace coordinates, spindle, feed, cutting depth, tool and so on. Other auxiliary data, for example, tool changing, workpiece clamping(夹jiā紧jǐn) and release(松sōnɡ开kāi), cooling, lubrication, is defined, too.
2. Programming stage
For computer numerical control（CNC,计jì算suàn机jī数shù控kònɡ） machining, programs are written in forms of Gcode and Mcode, which are the understandable languages of CNC system. For instance, G00, G02, M03, M30 and so on.
3.Transmitting stage
The programs are transmitted into CNC system through the tape (outdated), disk, Internet and so on.
4.Machining stage
When the program runs, it translates codes into signals which drive the motors accordingly. The motors then move the workpiece and cutting tool to get desired dimensions required.
1.2.2The definition of numerical control
Numerical control(NC, 数shù值zhí控kònɡ制zhì，简称“数shù控kònɡ”) is also called digital control (数shù字zì控kònɡ制zhì). NC technology is to use digital information to realize controlling automation. NC has been widely used in trajectory control of the mechanical movement and switching control of the mechanical system, such as robots, machine tools, production lines and so on. The objects controlled by digital information are varied, but the NC machine tools are the most typical NC equipment.
What are NC machine tools? They mean the use of digital signals to control the machine movement and process.
What are CNC machine tools？They are developed with microprocessors or special computers as NC systems. The control system carries out automatic machining of the workpiece. Today, all the machine control units are based on the computer technology.
In CNC machine tools, digital codes, including numbers, letters and symbols, are taken to express the workpiece dimensions and a variety of operations, such as setting spindle speed, loosening or fastening the cutter, setting feed rate, shutting on or off the coolant automatically, running or stopping the program, etc. And then digital codes are transmitted into the NC device through the control medium (disks, serial ports, network). The NC device deals with the input information and performs calculation, then sends a corresponding control signal to the servo system or other driving components for automatic machining the workpieces. The CNC structure is shown as Figure 13.

Figure 13CNC system structure

1.3The characteristics of CNC machine tools
1. Adaptability
Adaptability also means flexibility, which refers to that the CNC machine can adapt to different jobs very well. For every new part, we only need to rewrite the program and enter the new one to complete the machining of the new part without changing the mechanical part and the control part. The production process is done automatically. This provides a great deal of convenience for single part, small batch production and trial production of complex structural parts. Strong adaptability is the most prominent advantage of CNC machine tools, which resulted in its rapid development.
2. High precision and stability
Firstly, compared with manual machining method, CNC reduces or eliminates operators influences. Secondly, during the design and manufacture of CNC machine tools, a number of measures are taken to achieve high accuracy and stiffness for the mechanical parts and structure. The pulse equivalency normally reaches 0.0001—0.01 mm, and CNC machining accuracy has varied from the past ± 0.01 mm to ± 0.001 mm or even higher due to the compensation of the chain reverse gap and screw pitch error realized by the NC device. In addition, the stiffness and thermal stability of transmission system and the machine structure are higher for the CNC machine tool. In particular, the batch production consistency is improved remarkably, so high product qualification and stability is achieved.
3. Higher automation, lower labor intensity
CNC machine tool operations can be carried out automatically by the control program. The operator only needs to set the job and tool and the rest is done by the program. The operator just observes the process and performs inspection, which has greatly reduced the labor. In addition, instead of being open for the conventional machine, CNC machine tool is generally closed during processing, which are both clean and safe. Today CNC machines are available in esthetic colors ranging from green to gray or white.
4. Higher efficiency, shorter machining and auxiliary time
Parts processing time mainly consists of machining time and auxiliary time. CNC machine tools are equipped with wide range of spindle speeds and feeds, so for each process we can choose the most appropriate setting. Due to the rigidity of the CNC machine tool structure, it is allowed to carry out the strong cutting, which improves the cutting efficiency and saves the machining time. Auxiliary time is also reduced as compared with the conventional machine, for example, fast movements and shorter workpiece clamping time result in much shorter automatic tool change time.
In addition, an automatic tool changer made it possible to carryout multiorder continuous processing without any delay.
5. Being conducive to the modernization of management
In the CNC machine tools, digital information and standard codes are used and transmitted, which lays the foundation for computeraided design/manufacturing and management integration.
1.4Introduction to main CNC machine tools
With regard to the manufacturing process, CNC machine tools include CNC lathes, CNC milling machines, machine enters, CNC drilling machines, CNC boring machines, CNC grinding machines, CNC electric discharge machines, CNC wirecut electric discharge machines, CNC laser beam machines, CNC punching machines or punching presses, CNC ultrasonic machines, CNC gear holling machines, CNC plasma cutting machines, CNC bending machines, CNC water cutting machines, parallel machine tools, coordinate measuring machines and so on.
The most common CNC machine tools are introduced as follows.
1. CNC lathes(数shù控kònɡ车chē床chuánɡ)
A CNC lathe (see Figure 14) includes spindle(主zhǔ轴zhóu), slide plate(溜liū板bǎn), toolholder(刀dāo架jià)and so on. CNC system, including LCD panel (液yè晶jīnɡ显xiǎn示shì屏pínɡ), control panel(控kònɡ制zhì面miàn板bǎn), electrical control system(电diàn气qì控kònɡ制zhì系xì统tǒnɡ).

Figure 14CNC lathe

CNC lathe generally has twoaxis interpolation function.Zaxis is parallel to the direction of the spindle axis while Xaxis can move vertically to the spindle. The latest turning and milling center with a Caxis can turn and mill the workpiece automatically with the milling cutter placed in the tool turret.

The CNC lathe is mainly used to process shaft or disc parts, such as cutting the inner and outer cylindrical surface, cone surface, thread surface, end surface, groove, chamfering, etc. For the rotary bodies, drilling, reaming and boring can also be done.
2. CNC milling machines (数shù控kònɡ铣xǐ床chuánɡ)
CNC milling machines (see Figure 15) can process threedimensional complex surface. They are widely used in the automotive, aerospace(航hánɡ空kōnɡ航hánɡ天tiān), mold (模mú具jù)and other industries. They can be divided into vertical CNC milling machines, horizontal CNC milling machines, duplicating CNC milling machines.

Figure 15CNC milling machine

3. Machining centers (加jiā工ɡōnɡ中zhōnɡ心xīn)
The machining center (see Figure 16) results from the development of CNC machine tools, generally considered machining centers for the CNC boring and milling machines with an automatic tool controller (ATC). Machining center can do milling(铣xǐ削xuē), boring, drilling, broaching, fraising, tapping and other processing. Machining centers are classified as vertical ones and horizontal ones. The former ones’ spindle axes are vertical, the latter ones’ spindle axes are horizontal. The horizontal machining center is particularly used to machine the large, boxy and heavy workpieces.

Figure 16Machining center

(a) Vertical machining center； (b) Horizontal machining center

4. CNC drilling machines (数shù控kònɡ钻zuàn床chuánɡ)
CNC drilling machines (see Figure 17) can be divided into vertical ones and horizontal ones. Both of them mainly used for drilling(钻zuàn削xuē)and tapping, but also for simple milling.

5. CNC grinding machines (数shù控kònɡ磨mó床chuánɡ)

Figure 17CNC drilling machine

CNC grinding machines are mainly used to machine hard surfaces with high precision. They can be classified as CNC surface grinders, inner cylinder grinding machines, contour grinding machines and so on. With the development of the automatic grinding wheel compensation technology, automatic grinding wheel(自zì动dònɡ砂shā轮lún) dressing technology and grinding fixed cycle technology, CNC grinding function becomes increasingly strong.

6. CNC electrical discharge machines(EDM)

(数shù控kònɡ电diàn火huǒ花huā机jī床chuánɡ)
CNC EDM is a special processing method, which makes use of discharge phenomenon with two different polarities of the electrode in the insulating liquid(绝jué缘yuán液yè体tǐ), and can remove the material and then complete the processing. It has special advantages for the complexshape molds and difficulttomachine materials as shown in Figure 18.

Figure 18CNC EDM

7. CNC wirecut electrical discharge machines (WEDM) (线xiàn切qiē割ɡē机jī床ｃｈｕáｎɡ)
The working principle of CNC WEDM is similar to CNC EDMs, the only difference is that the wire electrode replaces the electrode.

1.5The development of machinery manufacturing systems
With the continuous improvement of automation of CNC machine tools, the automated manufacturing systems based on CNC machine tools have become the key in the industrialized countries.

1. DNC system
The earliest definition of DNC referred to direct NC, which was researched in the 1960s. At that time, NC systems were expensive and punch tapes were easy to be broken, so the DNC systems were just some NC devices directly connected to a central computer, which was used to manage and transfer NC programs.
Since the 1970s, with the continuous development of CNC technology, the storage capacity and calculation speed of CNC systems had been greatly improved. The meaning of DNC was reformed from the simple direct NC to distributed NC. It not only includes all the functions of direct NC, but also has other advanced functions, such as the system information collection, system status monitoring, system control, and so on.
Since the 1980s, with the rapid development of the computer and communication technology, the meaning and functions of DNC had been widely expanding. Compared to the DNC system in the 1960s and 1970s, the new generation of DNC systems began to focus on the information integration of the workshop, aiming at the production plans, technical preparation, processing operations and other basic operations, hence realized the centralized monitoring and distributed control. The production tasks were dispatched to the processing units through the local area network, and the information was exchanged between them. The material handling and other systems could be extended condition permitting, thus it was not only suitable for the existing production environment to improve productivity, but also saved costs.
The main components of a DNC system are showed in Figure 19, including central computer and peripheral storage devices, communication interfaces, machine tools and machine controllers. The central computer is employed for data management, which transfers the machining programs from the largecapacity memory to the machine tools. The bidirectional information flow is controlled to dispatch data among multiple computers in order to achieve individual processing of each machine controllers. Finally, the central computer monitors and handles the feedback information from the machine tools. The information exchange and interconnections are the key issue for the DNC system. The main difference between DNC and FMS (flexible manufacturing system) is that there is no automated material handling system in the DNC, which makes it low cost and easy to implement.
DNC is suitable for multiple CNC machine tools, usually 4—6 or more and the manufacturing environment with NC program management problems (NC programs are too large for the CNC to storage, or the CNC requires changing programs frequently in machining, etc.).

Figure 19Workshop DNC model

2. Flexible manufacturing system (FMS)
According to the military standard of China, “the FMS is an automated manufacturing system which includes CNC machining equipment, material transportation devices and computer control system. It includes several flexible manufacturing cells (FMC) to achieve rapid reconfigure according to the change of manufacturing tasks or the production environment, which is suitable for multitype, small and mediumvolume production.” In short, FMS is an automated manufacturing system composed of a number of CNC devices, material handling devices and computer control systems, and can be rapidly adjusted according to the manufacturing tasks and changes in the production type. At present, the most commonly seen FMS configuration includes four or more automatic CNC machine tools (machining centers and turning centers, etc.) connected by the centralized information control system and material handling system, which can achieve multitype, small and medium batch processing and management without stopping.
FMC is the smallest scale FMS, which is the result of the development of FMS towards lowcost and small size. It has one or a small number of machining centers, industrial robots, CNC machine tools and material handling devices. The FMC has independent automatic processing functions, and also some automatic transport, monitoring and management functions, which can achieve some specific multitype smallbatch processing. Some FMCs have also achieved 24 hours unmanned running. It is more suitable for the small and medium companies with limited financial resources. Nowadays, many of the manufacturers have focused on the development of FMCs.