stepconf.lyx

CNC 的开放码,EMC2 V2.2.8版

\series bold 
0
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

PWM 1:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
0
\end_inset 
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

Speed 2:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
1000
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

PWM 1:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
1
\end_inset 
</cell>
</row>
</lyxtabular>

\end_inset 


\layout Standard

Finish the remaining steps of the configuration process, then launch EMC
 with your configuration.
 Turn the machine on and select the MDI tab.
 Start the spindle turning by entering: 
\family typewriter 
M3 S100
\family default 
.
 Change the spindle speed by entering a different S-number: 
\family typewriter 
S800
\family default 
.
 Valid numbers range from 1 to 1000.
\layout Standard

For two different S-numbers, measure the actual spindle speed in RPM.
 Record the S-numbers and actual spindle speeds.
 Run Stepconf again.
 For 
\begin_inset Quotes eld
\end_inset 

Speed
\begin_inset Quotes erd
\end_inset 

 enter the measured speed, and for 
\begin_inset Quotes eld
\end_inset 

PWM
\begin_inset Quotes erd
\end_inset 

 enter the S-number divided by 1000.
\layout Standard

Because most spindle drivers are somewhat nonlinear in their response curves,
 it is best to:
\layout Itemize

Make sure the two calibration speeds are not too close together in RPM
\layout Itemize

Make sure the two calibration speeds are in the range of speeds you will
 typically use while milling
\layout Standard

For instance, if your spindle will go from 0RPM to 8000RPM, but you generally
 use speeds from 400RPM to 4000RPM, then find the PWM values that give 1600RPM
 and 2800RPM.
\layout Section

Axis Travel, Home Location, and Home Switch Location
\begin_inset LatexCommand \index{Axis Travel}

\end_inset 


\begin_inset LatexCommand \index{Home Location}

\end_inset 


\begin_inset LatexCommand \index{Home Switch Location}

\end_inset 


\begin_inset LatexCommand \label{sec:Axis-Travel-Home}

\end_inset 


\layout Standard

For each axis, there is a limited range of travel.
 The physical end of travel is called the 
\series bold 
hard stop
\series default 
.
\layout Standard

Before the 
\series bold 
hard stop
\series default 
 there is a 
\series bold 
limit switch
\series default 
.
 If the limit switch is encountered during normal operation, EMC shuts down
 the motor amplifier.
 The distance between the 
\series bold 
hard stop
\series default 
 and 
\series bold 
limit switch
\series default 
 must be long enough to allow an unpowered motor to coast to a stop.
 
\layout Standard

Before the 
\series bold 
limit switch
\series default 
 there is a 
\series bold 
soft limit
\series default 
.
 This is a limit enforced in software after homing.
 If a MDI command, or gcode program would pass the soft limit, it is not
 executed.
 If a jog would pass the soft limit, it is terminated at the soft limit.
\layout Standard

The 
\series bold 
home switch
\series default 
 can be placed anywhere within the travel (between hard stops).
 As long as external hardware does not deactivate the motor amplifiers with
 the limit switch is reached, one of the limit switches can be used as a
 home switch.
\layout Standard

The 
\series bold 
zero position
\series default 
 is the location on the axis that is 0 in the machine coordinate system.
 Usually the 
\series bold 
zero position
\series default 
 will be within the 
\series bold 
soft limits
\series default 
.
 On lathes, constant surface speed mode requires that machine 
\series bold 
X=0
\series default 
 correspond to the center of spindle rotation when no tool offset is in
 effect.
\layout Standard

The 
\series bold 
home position
\series default 
 is the location within travel that the axis will be moved to at the end
 of the homing sequence.
 This value must be within the 
\series bold 
soft limits
\series default 
.
 In particular, the 
\series bold 
home position
\series default 
 should never be exactly equal to a 
\series bold 
soft limit
\series default 
.
\layout Standard


\begin_inset Note
collapsed false

\layout Standard

a diagram of all these limits would be nice
\end_inset 


\layout Subsection

Operating without Limit Switches
\begin_inset LatexCommand \index{Operating without Limit Switches}

\end_inset 


\begin_inset LatexCommand \label{sub:Operating-without-Limit}

\end_inset 


\layout Standard

A machine can be operated without limit switches.
 In this case, only the 
\series bold 
soft limits
\series default 
 stop the machine from reaching the 
\series bold 
hard stop
\series default 
.
 
\series bold 
Soft limits
\series default 
 only operate after the machine has been homed.
 Since there is no switch, the machine must be moved by eye to the home
 position before pressing the 
\begin_inset Quotes eld
\end_inset 

Home
\begin_inset Quotes erd
\end_inset 

 or 
\begin_inset Quotes eld
\end_inset 

Home All
\begin_inset Quotes erd
\end_inset 

 button.
\layout Subsection

Operating without Home Switches
\begin_inset LatexCommand \index{Operating without Home Switches}

\end_inset 


\begin_inset LatexCommand \label{sub:Operating-without-Home}

\end_inset 


\layout Standard

A machine can be operated without home switches.
 If the machine has limit switches, but no home switches, it is best to
 use a limit switch as the home switch (e.g., choose 
\series bold 
Minimum Limit + Home X
\series default 
 in the pinout).
 If the machine has no limit switches, or the limit switches cannot be used
 as home switches for another reason, then the machine must be homed 
\begin_inset Quotes eld
\end_inset 

by eye
\begin_inset Quotes erd
\end_inset 

.
 Homing by eye is not as repeatable as homing to switches, but it still
 allows the 
\series bold 
soft limits
\series default 
 to be useful.
\layout Section

Latency Test
\begin_inset LatexCommand \index{Latency Test}

\end_inset 


\begin_inset LatexCommand \label{sec:Latency-Test}

\end_inset 


\layout Standard

Generating step pulses in software has one very big advantage - it's free.
 Just about every PC has a parallel port that is capable of outputting step
 pulses that are generated by the software.
 However, software step pulses also have some disadvantages:
\layout Itemize

limited maximum step rate 
\layout Itemize

jitter in the generated pulses
\layout Itemize

loads the CPU
\layout Standard

Latency is how long it takes the PC to stop what it is doing and respond
 to an external request.
 In our case, the request is the periodic "heartbeat" that serves as a timing
 reference for the step pulses.
 The lower the latency, the faster you can run the heartbeat, and the faster
 and smoother the step pulses will be.
\layout Standard

Latency is far more important than CPU speed.
 A lowly Pentium II that responds to interrupts within 10 microseconds each
 and every time can give better results than the latest and fastest P4 Hyperthre
ading beast.
\layout Standard

The CPU isn't the only factor in determining latency.
 Motherboards, video cards, USB ports, and a number of other things can
 hurt the latency.
 The best way to find out what you are dealing with is to run the HAL latency
 test.
\layout Standard

To run the test, from Applications/Accessories/Terminal (Ubuntu) open a
 shell and run the following command: 
\layout LyX-Code

latency-test 
\layout Standard

You should see something like this:
\layout Standard
\align center 

\begin_inset Graphics
	filename latency.png

\end_inset 


\layout Standard

While the test is running, you should "abuse" the computer.
 Move windows around on the screen.
 Surf the web.
 Copy some large files around on the disk.
 Play some music.
 Run an OpenGL program such as glxgears.
 The idea is to put the PC through its paces while the latency test checks
 to see what the worst case numbers are.
 
\layout Standard


\series bold 
Do not run EMC2 or Stepconf while the latency test is running.
\layout Standard

The important numbers are the 
\begin_inset Quotes eld
\end_inset 

max jitter
\begin_inset Quotes erd
\end_inset 

.
 In the example above, that is 17894 nanoseconds, or 17.9 microseconds.
 Record this number, and enter it in Stepconf when it is requested.
\layout Standard

In the example above, latency-test only ran for a few seconds.
 You should run the test for at least several minutes; sometimes the worst
 case latency doesn't happen very often, or only happens when you do some
 particular action.
 For instance, one Intel motherboard worked pretty well most of the time,
 but every 64 seconds it had a very bad 300uS latency.
 Fortunately that was fixable.
 
\layout Standard

For the latest information on fixing SMI issues goto:
\layout Standard


\begin_inset LatexCommand \htmlurl["Fixing SMI Issues"]{http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?FixingSMIIssues}

\end_inset 


\layout Standard

So, what do the results mean? If your Max Jitter number is less than about
 15-20 microseconds (15000-20000 nanoseconds), the computer should give
 very nice results with software stepping.
 If the max latency is more like 30-50 microseconds, you can still get good
 results, but your maximum step rate might be a little disappointing, especially
 if you use microstepping or have very fine pitch leadscrews.
 If the numbers are 100uS or more (100,000 nanoseconds), then the PC is
 not a good candidate for software stepping.
 Numbers over 1 millisecond (1,000,000 nanoseconds) mean the PC is not a
 good candidate for EMC, regardless of whether you use software stepping
 or not.
\layout Standard

Note that if you get high numbers, there may be ways to improve them.
 Another PC had very bad latency (several milliseconds) when using the onboard
 video.
 But a $5 used Matrox video card solved the problem - EMC does not require
 bleeding edge hardware.
\layout Section

Home and Limit Switch wiring options
\begin_inset LatexCommand \index{Home and Limit Switch wiring options}

\end_inset 


\begin_inset LatexCommand \label{sec:Home-and-Limit}

\end_inset 


\layout Standard

The ideal wiring for external switches would be one input per switch.
 However, the PC parallel port only offers a total of 5 inputs, while there
 are as many as 9 switches on a 3-axis machine.
 Instead, multiple switches are wired together in various ways so that a
 smaller number of inputs are required.
\layout Standard

The figures below show the general idea of wiring multiple switches to a
 single input pin.
 In each case, when one switch is actuated, the value seen on INPUT goes
 from logic HIGH to LOW.
 However, EMC expects a TRUE value when a switch is closed, so the corresponding
 
\begin_inset Quotes eld
\end_inset 

Invert
\begin_inset Quotes erd
\end_inset 

 box must be checked on the pinout configuration page.
\layout Standard


\begin_inset Float figure
placement H
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename switch-nc-series.eps
	width 50page%
	keepAspectRatio

\end_inset 


\layout Caption


\begin_inset LatexCommand \label{cap:Wiring-Normally-Closed}

\end_inset 

Wiring Normally Closed switches in series (simplified diagram)
\end_inset 


\layout Standard


\begin_inset Float figure
placement H
wide false
collapsed false

\layout Standard
\align center 

\begin_inset Graphics
	filename switch-no-parallel.eps
	width 50page%
	keepAspectRatio

\end_inset 


\layout Caption


\begin_inset LatexCommand \label{cap:Wiring-Normally-Open}

\end_inset 

Wiring Normally Open switches in parallel (simplified diagram)
\end_inset 


\layout Standard

The following combinations of switches are permitted in Stepconf:
\layout Itemize

Combine home switches for all axes
\layout Itemize

Combine limit switches for all axes
\layout Itemize

Combine both limit switches for one axis
\layout Itemize

Combine both limit switches and the home switch for one axis
\layout Itemize

Combine one limit switch and the home switch for one axis
\layout Standard

The last two combinations are also appropriate when a 
\begin_inset Quotes eld
\end_inset 

home to limit
\begin_inset Quotes erd
\end_inset 

 is used.
\the_end