stepper_diagnostics.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

Steppers
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If what you get is not what you expect if you pay attention you get some
 experience.
 
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Diagnosing problems is best done by divide and conquer.
 By this I mean if you can remove 1/2 of the variables from the equation
 each time you will find the problem the fastest.
 In the real world this is not always the case but a good place to start
 usually.
 
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Common Problems
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Stepper Moves One Step
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The most common reason in a new installation for the stepper not to move
 is the step and direction signals are backwards.
 If you press the jog foward and backward key and the stepper moves one
 step each time in the same direction there is your sign.
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No Steppers Move
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Many drives have an enable pin or need a charge pump to enable the output.
 
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Distance Not Correct
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If you command the axis to move a specific distance and it does not move
 that distance then your scale is wrong.
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Error Messages
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Following Error
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The concept of a following error is funny when talking about stepper motors.
 Since they are an open loop system, there is no position feedback to let
 you know if you actually are out of range.
 EMC calculates if it can keep up with the motion called for and if not
 then it gives a following error.
 Following errors usually are the result of one of the following on stepper
 systems.
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FERROR to small
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MIN_FERROR to small
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MAX_VELOCITY to fast
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MAX_ACCELERATION to fast
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BASE_PERIOD set to long
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Any of the above can cause the RT pulsing to not be able to keep up with
 the speed needed or the requested step rate is not possible at the BASE_PERIOD
 setting.
 This happens when you change one of the above in your ini file, so go back
 and change it back to what it was and try again.
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RTAPI Error
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When you get this error:
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RTAPI: ERROR: Unexpected realtime delay on task n
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It is usually an indication that the BASE_PERIOD in the [EMCMOT] section
 of the ini file is set too low.
 You should run the Latency Test for an extended period of time to see if
 you have any delays that would cause this problem.
 
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EMC2 tracks the number of CPU cycles between invocations of the real-time
 thread.
 If some element of your hardware is causing delays or your realtime threads
 are set too fast you will get this error.
 
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NOTE: This error is only displayed once per session.
 If you had your BASE_PERIOD too low you could get hundreds of thousands
 of error messages per second if more than one was displayed.
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\begin_inset Note
collapsed false

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add link to latency test when that page is done.
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\layout Section

Testing
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Step Timing
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If you are seeing an axis ending up in the wrong location over multiple
 moves, it is likely that you do not have the correct direction hold times
 or step timing for your stepper drivers.
 Each direction change may be losing a step or more.
 If the motors are stalling, it is also possible you have either the MAX_ACCELER
ATION or MAX_VELOCITY set too high for that axis.
 
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The following program will test the Z axis configuration for proper setup.
 Copy the program to your emc2/nc_files directory and name it TestZ.ngc or
 similar.
 Zero your machine with Z = 0.000 at the table top.
 Load and run the program.
 It will make 200 moves back and forth from 0.5 to 1".
 If you have a configuration issue, you will find that the final position
 will not end up 0.500" that the axis window is showing.
 To test another axis just replace the Z with your axis in the G0 lines.
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( test program to see if Z axis loses position )
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( msg, test 1 of Z axis configuration ) 
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G20 #1000=100 ( loop 100 times )  
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( this loop has delays after moves )
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( tests acc and velocity settings )
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o100 while [#1000] 
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   G0 Z1.000
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   G4 P0.250 
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G0 Z0.500 
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   G4 P0.250 
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   #1000 = [#1000 - 1] 
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o100 endwhile 
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( msg, test 2 of Z axis configuration S to continue) 
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M1 (stop here)
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#1000=100 ( loop 100 times ) 
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( the next loop has no delays after moves )
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( tests direction hold times on driver config and also max accel setting
 ) 
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o101 while [#1000] 
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   G0 Z1.000 .
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   G0 Z0.500 
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   #1000 = [#1000 - 1] 
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o101 endwhile 
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( msg, Done...Z should be exactly .5" above table ) 
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M2
\the_end