integrator_intro.lyx

CNC 的开放码,EMC2 V2.2.8版

	lyxscale 75
	width 80page%
	keepAspectRatio

\end_inset 


\layout Caption


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

\end_inset 

The AXIS Graphical Interface
\end_inset 


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename keystick.png

\end_inset 


\layout Caption


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

\end_inset 

The Keystick interface
\end_inset 


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename mini.png
	lyxscale 50
	width 80page%
	keepAspectRatio

\end_inset 


\layout Caption


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

\end_inset 

The Mini Graphical Interface
\end_inset 


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename tkemc.png
	lyxscale 50
	width 80page%
	keepAspectRatio

\end_inset 


\layout Caption


\begin_inset LatexCommand \label{fig:TkEmc_Graphical_Interface}

\end_inset 

The TkEmc Graphical Interface
\end_inset 


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\added_space_top smallskip \added_space_bottom smallskip \align center 

\begin_inset Graphics
	filename xemc.png
	display color
	width 80page%
	keepAspectRatio

\end_inset 


\layout Caption


\begin_inset LatexCommand \label{fig:XEMC_Graphical_Interface}

\end_inset 

The XEMC Graphical Interface
\end_inset 

 
\layout Standard

Tkemc and Mini will run on Linux, Mac, and Microsoft Windows if the Tcl/Tk
 programming language has been installed.
 The Mac and Microsoft Windows version can connect to a real-time EMC2 running
 on a Linux machine via a network connection, allowing the monitoring of
 the machine from a remote location.
 Instructions for installing and configuring the connection between a Mac
 or Microsoft Machine and a PC running the EMC2 can be found in the Integrators
 Handbook.
\layout Subsection

Motion Controller EMCMOT 
\begin_inset LatexCommand \label{sub:Motion-Controller-EMCMOT}

\end_inset 


\layout Standard

Motion control includes sampling the position of the axes to be controlled,
 computing the next point on the trajectory, interpolating between these
 trajectory points, and computing an output to the motors.
 For servo systems, the output is based on a PID compensation algorithm.
 For stepper systems, the calculations run open-loop, and pulses are sent
 to the steppers based on whether their accumulated position is more than
 a pulse away from their commanded position.
 The motion controller includes programmable software limits, and interfaces
 to hardware limit and home switches.
\layout Standard

The motion controller is written to be fairly generic.
 Initialization files (with the same syntax as Microsoft Windows INI
\begin_inset LatexCommand \index{INI}

\end_inset 

 files) are used to configure parameters such as number and type of axes
 (e.g., linear or rotary), scale factors between feedback devices (e.g., encoder
 counts) and axis units
\begin_inset LatexCommand \index{units}

\end_inset 

 (e.g., millimeters), servo gains, servo and trajectory planning cycle times,
 and other system parameters.
 Complex kinematics for robots can be coded in C according to a prescribed
 interface to replace the default 3-axis Cartesian machine kinematics routines.
 
\layout Subsection

Discrete I/O Controller EMCIO
\begin_inset LatexCommand \index{EMCIO}

\end_inset 

 
\begin_inset LatexCommand \label{sub:Discrete-I/O-Controller}

\end_inset 


\layout Standard

Discrete I/O controllers are highly machine-specific, and are not customizable
 in general using the INI file technique used to configure the more generic
 motion controller.
 However, since EMC2 uses the HAL, reconfiguration of the I/O subsystem
 has become very powerful and flexible.
 EMC2 contains a Programmable Logic Controller module (behaves just like
 a hardware PLC
\begin_inset LatexCommand \index{PLC}

\end_inset 

) that can be used for very complex scenarios (tool changers, etc.).
 
\layout Standard

In EMC2 there is only one big I/O controller, which provides support for
 all kinds of actions and hardware control.
 All its outputs and inputs are HAL pins (more on this later on), so you
 can use only the subset that fits your hardware and is necessary for your
 application.
\layout Subsection

Task Executor EMCTASK
\begin_inset LatexCommand \index{EMCTASK}

\end_inset 

 
\begin_inset LatexCommand \label{sub:Task-Executor-EMCTASK}

\end_inset 


\layout Standard


\begin_inset Float figure
wide false
collapsed false

\layout Caption


\begin_inset LatexCommand \label{fig:Process_diagram}

\end_inset 

EMC2 Process Diagram
\layout Standard
\align center 

\begin_inset Graphics
	filename whatpc.png
	keepAspectRatio

\end_inset 


\end_inset 


\layout Standard

The Task Executor is responsible for interpreting G and M code programs
 whose behavior does not vary appreciably between machines.
 G-code programming is designed to work like a machinist might work.
 The motion or turns of a hand wheel are coded into blocks.
 If a machinist wanted his mill to move an inch in the +X direction at some
 feed rate, he might slowly turn the hand wheel five turns clockwise in
 20 seconds.
 The same machinist programming that same move for CNC might write the following
 block of code.
\layout LyX-Code

G1 F3 X1.000
\layout Standard

G1 means that the machine is supposed to run at a programmed feed rate rather
 than at the fastest speed that it can (G0 is the way to command a rapid
 move like you would make above the work when not cutting).
 The F3 means that it should travel at 3 inches a minute or 3 millimeters
 a minute if it is working in metric mode.
 The X1.000 (assuming that the X axis started at zero) means the machine
 should move one inch in the positive X direction.
 You will read quite a bit more about G-code in the programming chapters
 .
\layout Standard

Figure 
\begin_inset LatexCommand \ref{fig:Process_diagram}

\end_inset 

 is a block diagram of how a personal computer running the EMC2 is used
 to control a machine with G-code
\begin_inset LatexCommand \index{G-code}

\end_inset 

.
 The actual G-code can be sent using the MDI
\begin_inset LatexCommand \index{MDI}

\end_inset 

 (Machine Device Interface) mode or it can be sent as a file when the machine
 is in Auto
\begin_inset LatexCommand \index{Auto}

\end_inset 

 mode.
 These choices are made by the operator and entered using one of the Graphical
 User Interfaces available with the software.
 
\layout Standard

G-code is sent to the interpreter which compares the new block with what
 has already been sent to it.
 The interpreter then figures out what needs to be done for the motion and
 input or output systems and sends blocks of canonical commands to the task
 and motion planning programs.
\layout Subsection

Modes of Operation
\begin_inset LatexCommand \label{sub:Modes-of-Operation}

\end_inset 


\layout Standard

When an EMC2 is running, there are three different major modes used for
 inputting commands.
 These are Manual
\begin_inset LatexCommand \index{Manual}

\end_inset 

, Auto
\begin_inset LatexCommand \index{Auto}

\end_inset 

, and MDI
\begin_inset LatexCommand \index{MDI}

\end_inset 

.
 Changing from one mode to another makes a big difference in the way that
 the EMC2 behaves.
 There are specific things that can be done in one mode that can not be
 done in another.
 An operator can home an axis in manual mode but not in auto or MDI modes.
 An operator can cause the machine to execute a whole file full of G-codes
 in the auto mode but not in manual or MDI.
 
\layout Standard

In manual mode, each command is entered separately.
 In human terms a manual command might be 
\begin_inset Quotes eld
\end_inset 

turn on coolant
\begin_inset Quotes erd
\end_inset 

 or 
\begin_inset Quotes eld
\end_inset 

jog X at 25 inches per minute.
\begin_inset Quotes erd
\end_inset 

 These are roughly equivalent to flipping a switch or turning the hand wheel
 for an axis.
 These commands are normally handled on one of the graphical interfaces
 by pressing a button with the mouse or holding down a key on the keyboard.
 In auto mode, a similar button or key press might be used to load or start
 the running of a whole program of G-code that is stored in a file.
 In the MDI mode the operator might type in a block of code and tell the
 machine to execute it by pressing the <return> or <enter> key on the keyboard.
\layout Standard

Some motion control commands are available and will cause the same changes
 in motion in all modes.
 These include 
\shape smallcaps 
\noun on 
abort
\shape default 
\noun default 

\begin_inset LatexCommand \index{ABORT}

\end_inset 

, 
\shape smallcaps 
\noun on 
estop
\shape default 
\noun default 

\begin_inset LatexCommand \index{ESTOP}

\end_inset 

, and 
\shape smallcaps 
\noun on 
feed rate override
\shape default 
\noun default 

\begin_inset LatexCommand \index{feed override}

\end_inset 

.
 Commands like these should be self explanatory.
\layout Standard

The AXIS user interface removes some of the distinctions between Auto and
 the other modes by making Auto-commands available at most times.
 It also blurs the distinction between Manual and MDI because some Manual
 commands like Touch Off are actually implemented by sending MDI commands.
\layout Subsection

Information Display 
\begin_inset LatexCommand \label{sub:Information-Display}

\end_inset 


\layout Standard

While an EMC2 is running, each of the modules keeps up a conversation with
 the others and with the graphical display.
 It is up to the display to select from that stream of information what
 the operator needs to see, and to arrange it on the screen in a way that
 makes it easy for the operator to understand.
 Perhaps the most important display is the mode the EMC2 is running in.
 You will want to keep your eye on the mode display.
\layout Standard

Right up there with knowing what mode is active is consistent display of
 the position of each axis.
 Most of the interfaces will allow the operator to read position based upon
 actual or commanded position as well as machine or relative position.
 
\layout Description
\noindent 
Machine
\begin_inset LatexCommand \index{Position: Machine}

\end_inset 

 This is the position of an axis relative to the place where it started
 or was homed.
 
\layout Description
\noindent 
Relative
\begin_inset LatexCommand \index{Position: Relative}

\end_inset 

 This is the position of an axis after work or tool or other offsets have
 been applied.
 
\layout Description
\noindent 
Actual
\begin_inset LatexCommand \index{Position: Actual}

\end_inset 

 This is the real position of the axis within the machine or relative system.
 
\layout Description
\noindent 
Commanded
\begin_inset LatexCommand \index{Position: Commanded}

\end_inset 

 This is where the axis is commanded to be.
\layout Standard

These may all be exactly the same if no offsets have been applied and there
 is no deadband set in the INI file.
 Deadband is a small distance which is assumed to be close enough -- perhaps
 one stepper pulse or one encoder count.
 
\layout Standard

It is also important to see any messages or error codes sent by the EMC2.
 These are used to request the operator change a tool, to describe problems
 in G-code programs, or to tell why the machine stopped running.
\layout Standard

As you work your way through this text, you will be learning, bit by bit,
 how to set up and run a machine with your copy of the EMC2 software.
 While you are learning about setting up and running a mini mill here, you
 will be thinking of other applications and other capabilities.
 These are the topics of the other linuxcnc.org handbooks.
\layout Section

Thinking Like An Integrator
\begin_inset LatexCommand \label{sec:Thinking-Integrator}

\end_inset 


\layout Standard

The biggest task of a machine integrator is figuring out how to connect
 a PC running the EMC2 to a machine and configuring the software so that
 it runs the machine correctly.
 
\layout Subsection

Units
\begin_inset LatexCommand \index{units}

\end_inset 


\begin_inset LatexCommand \label{sub:Units}

\end_inset 


\layout Standard

Units can be confusing.
 You might ask, 
\begin_inset Quotes eld
\end_inset 

Does it work in inches, feet, centimeters, millimeters, or what?
\begin_inset Quotes erd
\end_inset 

 There are several possible answers to this question but the best one is
 that it works in the units that you set it to work in.
 
\layout Standard

At a machine level, we set each axis's units to some value using an INI
 variable that looks like this.
\layout LyX-Code

UNITS = inch
\layout Standard

or
\layout LyX-Code

UNITS = mm
\layout Standard

After we have decided upon a value for the units for an axis, we tell the
 EMC2 how may step pulses or encoder pulses it should send or read for each
 unit of distance to be traveled.
 Once we have done this, the EMC2 knows how to count units of distance.
 However it is very important to understand that this counting of distance
 is different from the commanding of distance.
 You can command distance in millimeters or inches without even thinking
 about the units that you defined.
 There are G-codes that allow you to switch easily between metric and imperial.
\the_end