coordinates.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/
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\layout Chapter

Coordinate System and G92 Offsets
\layout Section

Introduction
\layout Standard

You have seen how handy a tool length offset can be.
 Having this allows the programmer to ignore the actual tool length when
 writing a part program.
 In the same way, it is really nice to be able to find a prominent part
 of a casting or block of material and work a program from that point rather
 than having to take account of the location at which the casting or block
 will be held during the machining.
\layout Standard

This chapter introduces you to offsets as they are used by the EMC.
 These include;
\layout Itemize

machine coordinates (G53
\begin_inset LatexCommand \index{G53}

\end_inset 

) 
\layout Itemize

nine offsets (G54-G59.3
\begin_inset LatexCommand \index{G54}

\end_inset 


\begin_inset LatexCommand \index{G55}

\end_inset 


\begin_inset LatexCommand \index{G56}

\end_inset 


\begin_inset LatexCommand \index{G57}

\end_inset 


\begin_inset LatexCommand \index{G58}

\end_inset 


\begin_inset LatexCommand \index{G59}

\end_inset 


\begin_inset LatexCommand \index{G59.1}

\end_inset 


\begin_inset LatexCommand \index{G59.2}

\end_inset 


\begin_inset LatexCommand \index{G59.3}

\end_inset 

 ) 
\layout Itemize

a set of global offsets (G92
\begin_inset LatexCommand \index{G92}

\end_inset 

).
\layout Section

The Machine Position Command (G53)
\layout Standard

Regardless of any offsets that may be in effect, putting a G53
\begin_inset LatexCommand \index{G53}

\end_inset 

 in a block of code tells the interpreter to go to the real or absolute
 axis positions commanded in the block.
 For example
\layout Standard

g53 g0 x0 y0 z0 
\layout Standard

will get you to the actual position where these three axes are zero.
 You might use a command like this if you have a favorite position for tool
 changes or if your machine has an auto tool changer.
 You might also use this command to get the tool out of the way so that
 you can rotate or change a part in a vice.
 
\layout Standard

G53 is not a modal command.
 It must be used on each line where motion based upon absolute machine position
 is desired.
 
\layout Section

Fixture Offsets (G54-G59.3
\begin_inset LatexCommand \index{G54}

\end_inset 


\begin_inset LatexCommand \index{G55}

\end_inset 


\begin_inset LatexCommand \index{G56}

\end_inset 


\begin_inset LatexCommand \index{G57}

\end_inset 


\begin_inset LatexCommand \index{G58}

\end_inset 


\begin_inset LatexCommand \index{G59}

\end_inset 


\begin_inset LatexCommand \index{G59.1}

\end_inset 


\begin_inset LatexCommand \index{G59.2}

\end_inset 

 
\begin_inset LatexCommand \index{G59.3}

\end_inset 

)
\layout Standard


\begin_inset Float figure
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename offsets.png
	display color
	width 80text%

\end_inset 


\layout Caption


\begin_inset LatexCommand \label{fig:offsets}

\end_inset 

Work Offsets
\end_inset 


\layout Standard

Work or fixture offset are used to make a part home that is different from
 the absolute, machine coordinate system.
 This allows the part programmer to set up home positions for multiple parts.
 A typical operation that uses fixture offsets would be to mill multiple
 copies of parts on "islands" in a piece, similar to figure 
\begin_inset LatexCommand \ref{fig:offsets}

\end_inset 


\layout Standard

The values for offsets are stored in the VAR file that is requested by the
 INI file during the startup of an EMC.
 In our example below we'll use 
\begin_inset LatexCommand \index{G55}

\end_inset 

G55.
 The values for each axis for G55 are stored as variable numbers.
 
\layout Quote

5241\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5242\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5243\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5244\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5245\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5246\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Standard

In the VAR file scheme, the first variable number stores the X offset, the
 second the Y offset and so on for all six axes.
 There are numbered sets like this for each of the fixture offsets.
 
\layout Standard

Each of the graphical interfaces has a way to set values for these offsets.
 You can also set these values by editing the VAR file itself and then issuing
 a [reset] so that the EMC reads the new values.
 For our example let's directly edit the file so that G55 takes on the following
 values.
\layout Quote

5241\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 2.000000
\layout Quote

5242\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 1.000000
\layout Quote

5243\SpecialChar ~
\SpecialChar ~
 -2.000000
\layout Quote

5244\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5245\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Quote

5246\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 0.000000
\layout Standard

You should read this as moving the zero positions of G55 to X = 2 units,
 Y= 1 unit, and Z = -2 units away from the absolute zero position.
\layout Standard

Once there are values assigned, a call to G55 in a program block would shift
 the zero reference by the values stored.
 The following line would then move each axis to the new zero position.
 Unlike G53, G54 through G59.3 are modal commands.
 They will act on all blocks of code after one of them has been set.
 The program that might be run using figure 
\begin_inset LatexCommand \ref{fig:offsets}

\end_inset 

 would require only a single coordinate reference for each of the locations
 and all of the work to be done there.
 The following code is offered as an example of making a square using the
 G55 offsets that we set above.
\layout Quote

G55 G0 x0 y0 z0
\layout Quote

g1 f2 z-0.2000
\layout Quote

x1
\layout Quote

y1
\layout Quote

x0
\layout Quote

y0
\layout Quote

g0 z0
\layout Quote

g54 x0 y0 z0
\layout Quote

m2
\layout Standard


\begin_inset Quotes eld
\end_inset 

But,
\begin_inset Quotes erd
\end_inset 

 you say, 
\begin_inset Quotes eld
\end_inset 

why is there a G54 in there near the end.
\begin_inset Quotes erd
\end_inset 

 Many programmers leave the G54 coordinate system with all zero values so
 that there is a modal code for the absolute machine based axis positions.
 This program assumes that we have done that and use the ending command
 as a command to machine zero.
 It would have been possible to use g53 and arrive at the same place but
 that command would not have been modal and any commands issued after it
 would have returned to using the G55 offsets because that coordinate system
 would still be in effect.
\layout Quote


\begin_inset LatexCommand \index{G54}

\end_inset 

G54\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
use preset work coordinate system 1
\layout Quote


\begin_inset LatexCommand \index{G55}

\end_inset 

G55\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
use preset work coordinate system 2
\layout Quote


\begin_inset LatexCommand \index{G56}

\end_inset 

G56\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
use preset work coordinate system 3
\layout Quote


\begin_inset LatexCommand \index{G57}

\end_inset 

G57\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
use preset work coordinate system 4
\layout Quote


\begin_inset LatexCommand \index{G58}

\end_inset 

G58\SpecialChar ~
\SpecialChar ~