integrator_intro.lyx

CNC 的开放码,EMC2 V2.2.8版

#LyX 1.3 created this file. For more info see http://www.lyx.org/
\lyxformat 221
\textclass book
\begin_preamble
\usepackage[plainpages=false,pdfpagelabels,colorlinks=true,linkcolor=blue]{hyperref}
\end_preamble
\language english
\inputencoding default
\fontscheme bookman
\graphics default
\float_placement !!h
\paperfontsize 10
\spacing single 
\papersize Custom
\paperpackage a4
\use_geometry 1
\use_amsmath 0
\use_natbib 0
\use_numerical_citations 0
\paperorientation portrait
\paperwidth 8.5in
\paperheight 11in
\leftmargin 1.2in
\topmargin 1in
\rightmargin 0.6in
\bottommargin 0.6in
\secnumdepth 5
\tocdepth 5
\paragraph_separation skip
\defskip smallskip
\quotes_language english
\quotes_times 2
\papercolumns 1
\papersides 2
\paperpagestyle default

\layout Chapter


\begin_inset LatexCommand \label{first-section}

\end_inset 

The Enhanced Machine Control
\layout Standard


\begin_inset Note
collapsed false

\layout Standard

add the latency test somewhere
\end_inset 


\layout Section

Introduction
\begin_inset LatexCommand \label{sec:Introduction}

\end_inset 


\layout Standard

For normal stepper based installations see the Getting Started Guide.
 Once EMC is installed and configured see the User Manual for information
 on using EMC.
\layout Standard

The Integrator Manual scope is on more complex machines, configurations
 and installations.
 As the system integrator your task is bringing together all the component
 subsystems into a whole and ensuring that those subsystems function together.
 EMC being one of the subsystems.
 
\layout Section

The Big CNC Picture
\begin_inset LatexCommand \label{sec:The-Big-CNC}

\end_inset 


\layout Standard

The term CNC has taken on a lot of different meanings over the years.
 In the early days CNC replaced the hands of a skilled machinist with motors
 that followed commands in much the same way that the machinist turned the
 hand wheels.
 From these early machines, a language of machine tool control has grown.
 This language is called RS274 and several standard variants of it have
 been put forward.
 It has also been expanded by machine tool and control builders in order
 to meet the needs of specific machines.
 If a machine changed tools during a program it needed to have tool change
 commands.
 If it changed pallets in order to load new castings, it had to have commands
 that allowed for these kinds of devices as well.
 Like any language, RS274 has evolved over time.
 Currently there are several dialects.
 In general each machine tool maker has been consistent within their product
 line but different dialects can have commands that cause quite different
 behavior from one machine to another.
\layout Standard

More recently the language of CNC has been hidden behind or side-stepped
 by several programming schemes that are referred to as 
\begin_inset Quotes eld
\end_inset 

Conversational
\begin_inset Foot
collapsed false

\layout Standard

One machine tool manufacturer, Hurco, claims to have a right to the use
 of these programming schemes and to the use of the term conversational
 when used in this context.
 
\end_inset 

 programming languages.
\begin_inset Quotes erd
\end_inset 

 One common feature of these kinds of programming schemes is the selection
 of a shape or geometry and the addition of values for the corners, limits,
 or features of that geometry.
\layout Standard

The use of Computer Aided Drafting has also had an effect on the CNC programming
 languages.
 Because CAD drawings are saved as a list or database of geometries and
 variables associated with each, they are available to be interpreted into
 G-Code.
 These interpreters are called CAM (Computer Aided Machining) programs.
\layout Standard

Like the CAD converters, the rise of drawing programs, like Corel
\begin_inset Formula $^{\textrm{TM}}$
\end_inset 

 and the whole bunch of paint programs, converters have been written that
 will take a bitmap or raster or vector image and turn it into G-Code that
 can be run with a CNC.
\layout Standard

You're asking yourself, 
\begin_inset Quotes eld
\end_inset 

Why did I want to know this?
\begin_inset Quotes erd
\end_inset 

 The answer is that the EMC2 as it currently exists does not directly take
 in CAD or any image and run a machine using it.
 The EMC2 uses a variant of the earlier CNC language named RS274NGC.
 (Next Generation Controller).
 All of the commands given to the EMC2 must be in a form that is recognized
 and have meaning to the RS274NGC interpreter.
 This means that if you want to carve parts that were drawn in some graphical
 or drafting program you will also have to find a converter that will transform
 the image or geometry list into commands that are acceptable to the EMC2
 interpreter.
 Several commercial CAD/CAM programs are available to do this conversion.
 At least one converter (Ace) has been written that carries a copyright
 that makes it available to the public.
\layout Standard

There has been recent talk about writing a 
\begin_inset Quotes eld
\end_inset 

conversational
\begin_inset Quotes erd
\end_inset 

 or geometric interface that would allow an operator to enter programs is
 much the same way that several modern proprietary controls enter programs
 but it isn't in there yet.
 
\layout Section

Computer Operating Systems
\begin_inset LatexCommand \label{sec:Computer-Operating-Systems}

\end_inset 


\layout Standard

The EMC2 code can be compiled on almost any GNU-Linux Distribution (assuming
 it has been patched with a real time extension).
 In addition to the raw code, some binary distributions are available.
 The latest packages have been created around the Ubuntu
\begin_inset LatexCommand \index{Ubuntu}

\end_inset 

 GNU-Linux
\begin_inset LatexCommand \index{GNU-Linux}

\end_inset 

 Distribution.
 Ubuntu is one of the distributions that is aimed at novice Linux users,
 and has been found to be very easy to use.
 Along with that, there are lots of places around the world that offer support
 for it.
 Installing EMC2 on it is trivial, see section 
\begin_inset LatexCommand \ref{sec:EMC2-Ubuntu-Live-CD}

\end_inset 


\layout Standard

The EMC2 will not run under a Microsoft (TM) operating system.
 The reason for this is that the EMC2 requires a real-time environment for
 the proper operation of its motion planning and stepper pulse outputs.
 Along with that, it also benefits from the much-needed stability and performanc
e of the Linux OS.
\layout Section

History of the Software
\begin_inset LatexCommand \label{sec:History-of-the}

\end_inset 


\layout Standard

The EMC code was started by the Intelligent Systems Division at the National
 Institute of Standards and Technology in the United States.
 The quotation below, taken from the NIST
\begin_inset LatexCommand \index{NIST}

\end_inset 

 web presence some time back, should lend some understanding of the essential
 reasons for the existence of this software and of the NIST involvement
 in it.
\layout Quotation

As part of our (NIST) collaboration with the OMAC
\begin_inset LatexCommand \index{OMAC}

\end_inset 

 User's Group, we have written software which implements real-time control
 of equipment such as machine tools, robots, and coordinate measuring machines.
 The goal of this software development is twofold: first, to provide complete
 software implementations of all OMAC modules for the purpose of validating
 application programming interfaces; and second, to provide a vehicle for
 the transfer of control technology to small- and medium-sized manufacturers
 via the NIST Manufacturing Extension Partnership.
 The EMC software is based on the NIST Real-time Control System (RCS
\begin_inset LatexCommand \index{RCS}

\end_inset 

) Methodology, and is programmed using the NIST RCS Library.
 The RCS Library eases the porting of controller code to a variety of Unix
 and Microsoft platforms, providing a neutral application programming interface
 (API) to operating system resources such as shared memory, semaphores,
 and timers.
 The RCS Library also implements a communication model, the Neutral Manufacturin
g Language, which allows control processes to read and write C++ data structures
 throughout a single homogeneous environment or a heterogeneous networked
 environment.
 The EMC software is written in C and C++, and has been ported to the PC
 Linux, Windows NT, and Sun Solaris operating systems.
 When running actual equipment, a real-time version of Linux is used to
 achieve the deterministic computation rates required (200 microseconds
 is typical).
 The software can also be run entirely in simulation, down to simulations
 of the machine motors.
 This enables entire factories of EMC machines to be set up and run in a
 computer integrated manufacturing environment.
 
\layout Standard

EMC has been installed on many machines, both with servo motors and stepper
 motors.
 Here is a sampling of the earliest applications.
 
\layout Itemize

3-axis Bridgeport
\begin_inset LatexCommand \index{Bridgeport}

\end_inset 

 knee mill at Shaver Engineering.
 The machine uses DC brush servo motors and encoders for motion control,
 and OPTO-22 compatible I/O interfaced to the PC parallel port for digital
 I/O to the spindle, coolant, lube, and e-stop systems.
 
\layout Itemize

3-axis desktop milling machine used for prototype development.
 The machine uses DC brush servo motors and encoders.
 Spindle control is accomplished using the 4th motion control axis.
 The machine cuts wax parts.
 
\layout Itemize

4-axis Kearney & Trecker horizontal machining center at General Motors Powertrai
n in Pontiac, MI.
 This machine ran a precursor to the full-software EMC which used a hardware
 motion control board.
 
\layout Standard

After these early tests, Jon Elson found the Shaver Engineering notes and
 replaced a refrigerator sized Allen Bradley 7300 control on his Bridgeport
 with the EMC running on a Red Hat 5.2 distribution of Linux.
 He was so pleased with the result that he advertised the software on several
 newsgroups.
 He continues to use that installation and has produced several boards that
 are supported by the software.
 
\layout Standard

From these early applications news of the software spread around the world.
 It is now used to control many different kinds of machines.
 More recently the Sherline
\begin_inset LatexCommand \index{Sherline}

\end_inset 

 company 
\begin_inset LatexCommand \url{http://www.sherline.com}

\end_inset 

 has released their first CNC mill.
 It uses a standard release of the EMC.
 
\layout Standard

The source code files that make up the controller are kept in a repository
\begin_inset LatexCommand \index{CVS}

\end_inset 

 on 
\begin_inset LatexCommand \url{http://cvs.linuxcnc.org}

\end_inset 

.
 They are available for anyone to inspect or download.
 The EMC2 source code (with a few exceptions
\begin_inset Foot
collapsed false

\layout Standard

some parts of EMC2 are released under the 
\begin_inset Quotes eld
\end_inset 

Lesser
\begin_inset Quotes erd
\end_inset 

 GPL (LPGL), which allows them to be used with proprietary software as long
 as certain restrictions are observed.
\end_inset 

) is released under the GNU General Public License (GPL).
 The GPL
\begin_inset LatexCommand \index{GPL}

\end_inset 

 controls the terms under which EMC2 can be changed and distributed.
 This is done in order to protect the rights of people like you to use,
 study, adapt, improve, and redistribute it freely, now and in the future.
 To read about your rights as a user of EMC2, and the terms under which
 you are allowed to distribute any modifications you may make, see the full
 GPL at 
\begin_inset LatexCommand \url{http://www.gnu.org/copyleft/gpl.html}

\end_inset 

.
\layout Section

How EMC2 Works
\begin_inset LatexCommand \label{sec:How-EMC2-Works}

\end_inset 


\layout Standard

The Enhanced Machine Controller (EMC2) is a lot more than just another CNC
\begin_inset LatexCommand \index{CNC}

\end_inset 

 mill program.
 It can control machine tools, robots, or other automated devices.
 It can control servo motors, stepper motors, relays, and other devices
 related to machine tools.
 In this handbook we focus on only a small part of that awesome capability,
 the mini mill.
\layout Standard


\begin_inset Float figure
wide false
collapsed false

\layout Caption


\begin_inset LatexCommand \label{fig:Typical_machine}

\end_inset 

Simple EMC2 Controlled Machine
\layout Standard
\align center 

\begin_inset Graphics
	filename whatstep1.png

\end_inset 


\end_inset 


\layout Standard

Figure 
\begin_inset LatexCommand \ref{fig:Typical_machine}

\end_inset 

 shows a simple block diagram showing what a typical 3-axis EMC2 system
 might look like.
 This diagram shows a stepper motor system.
 The PC, running Linux
\begin_inset LatexCommand \index{Linux}

\end_inset 

 as its operating system, is actually controlling the stepper motor drives
 by sending signals through the printer port.
 These signals (pulses) make the stepper drives move the stepper motors.
 The EMC2 can also run servo motors via servo interface cards or by using
 an extended parallel port to connect with external control boards.
 As we examine each of the components that make up an EMC2 system we will
 remind the reader of this typical machine.
\layout Standard

There are four main components to the EMC2 software: a motion controller
 (EMCMOT), a discrete I/O controller (EMCIO), a task executor which coordinates
 them (EMCTASK), and a collection of text-based or graphical user interfaces.
 An EMC2 capable of running a mini mill must start some version of all four
 of these components in order to completely control it.
 Each component is briefly described below.
 In addition there is a layer called HAL
\begin_inset LatexCommand \index{HAL}

\end_inset 

 (Hardware Abstraction Layer) which allows simple reconfiguration of EMC2
 without the need of recompiling.
\layout Subsection

Graphical User Interfaces
\begin_inset LatexCommand \label{sub:Graphical-User-Interfaces}

\end_inset 


\layout Standard

A graphical interface is the part of the EMC2 that the machine tool operator
 interacts with.
 The EMC2 comes with several types of user interfaces: 
\layout Itemize

a character-based screen graphics program named keystick
\begin_inset LatexCommand \index{keystick}

\end_inset 

 
\begin_inset LatexCommand \ref{fig:The Keystick Interface}

\end_inset 


\layout Itemize

an X Windows programs named xemc
\begin_inset LatexCommand \index{xemc}

\end_inset 

 
\begin_inset LatexCommand \ref{fig:XEMC_Graphical_Interface}

\end_inset 

 
\layout Itemize

two Tcl/Tk-based GUIs named tkemc
\begin_inset LatexCommand \index{tkemc}

\end_inset 

 
\begin_inset LatexCommand \ref{fig:TkEmc_Graphical_Interface}

\end_inset 

 and mini
\begin_inset LatexCommand \index{mini}

\end_inset 

 
\begin_inset LatexCommand \ref{fig:The Mini Graphical Interface}

\end_inset 

.
 
\layout Itemize

an OpenGL-based GUI, with an interactive G-Code previewer, called AXIS
\begin_inset LatexCommand \index{AXIS}

\end_inset 

 
\begin_inset LatexCommand \ref{fig:The AXIS Graphical Interface}

\end_inset 


\layout Standard


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename axis.png