blog/Automatic_LinuxCNC_servo_PID_tuning_.html

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   6     <title>Petter Reinholdtsen: Automatic LinuxCNC servo PID tuning?</title>
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  14  <h1>
  15      <a href="https://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  16
  17  </h1>
  18
  19 </div>
  20
  21
  22     <div class="entry">
  23       <div class="title">Automatic LinuxCNC servo PID tuning?</div>
  24       <div class="date">16th July 2022</div>
  25       <div class="body"><p>While working on a CNC with servo motors controlled by the
  26 <a href="https://en.wikipedia.org/wiki/LinuxCNC">LinuxCNC</a>
  27 <a href="https://en.wikipedia.org/wiki/PID_controller">PID
  28 controller</a>, I recently had to learn how to tune the collection of values
  29 that control such mathematical machinery that a PID controller is.  It
  30 proved to be a lot harder than I hoped, and I still have not succeeded
  31 in getting the Z PID controller to successfully defy gravity, nor X
  32 and Y to move accurately and reliably.  But while climbing up this
  33 rather steep learning curve, I discovered that some motor control
  34 systems are able to tune their PID controllers.  I got the impression
  35 from the documentation that LinuxCNC were not.  This proved to be not
  36 true.</p>
  37
  38 <p>The LinuxCNC
  39 <a href="http://linuxcnc.org/docs/html/man/man9/pid.9.html">pid
  40 component</a> is the recommended PID controller to use.  It uses eight
  41 constants <tt>Pgain</tt>, <tt>Igain</tt>, <tt>Dgain</tt>,
  42 <tt>bias</tt>, <tt>FF0</tt>, <tt>FF1</tt>, <tt>FF2</tt> and
  43 <tt>FF3</tt> to calculate the output value based on current and wanted
  44 state, and all of these need to have a sensible value for the
  45 controller to behave properly.  Note, there are even more values
  46 involved, theser are just the most important ones.  In my case I need
  47 the X, Y and Z axes to follow the requested path with little error.
  48 This has proved quite a challenge for someone who have never tuned a
  49 PID controller before, but there is at least some help to be found.
  50
  51 <p>I discovered that included in LinuxCNC was this old PID component
  52 at_pid claiming to have auto tuning capabilities.  Sadly it had been
  53 neglected since 2011, and could not be used as a plug in replacement
  54 for the default pid component.  One would have to rewriting the
  55 LinuxCNC HAL setup to test at_pid.  This was rather sad, when I wanted
  56 to quickly test auto tuning to see if it did a better job than me at
  57 figuring out good P, I and D values to use.</p>
  58
  59 <p>I decided to have a look if the situation could be improved.  This
  60 involved trying to understand the code and history of the pid and
  61 at_pid components.  Apparently they had a common ancestor, as code
  62 structure, comments and variable names were quite close to each other.
  63 Sadly this was not reflected in the git history, making it hard to
  64 figure out what really happened.  My guess is that the author of
  65 <a href="https://github.com/LinuxCNC/linuxcnc/blob/master/src/hal/components/at_pid.c">at_pid.c</a>
  66 took a version of
  67 <a href="https://github.com/LinuxCNC/linuxcnc/blob/master/src/hal/components/pid.c">pid.c</a>,
  68 rewrote it to follow the structure he wished pid.c to have, then added
  69 support for auto tuning and finally got it included into the LinuxCNC
  70 repository.  The restructuring and lack of early history made it
  71 harder to figure out which part of the code were relevant to the auto
  72 tuning, and which part of the code needed to be updated to work the
  73 same way as the current pid.c implementation.  I started by trying to
  74 isolate relevant changes in pid.c, and applying them to at_pid.c.  My
  75 aim was to make sure the at_pid component could replace the pid
  76 component with a simple change in the HAL setup loadrt line, without
  77 having to "rewire" the rest of the HAL configuration.  After a few
  78 hours following this approach, I had learned quite a lot about the
  79 code structure of both components, while concluding I was heading down
  80 the wrong rabbit hole, and should get back to the surface and find a
  81 different path.</p>
  82
  83 <p>For the second attempt, I decided to throw away all the PID control
  84 related part of the original at_pid.c, and instead isolate and lift
  85 the auto tuning part of the code and inject it into a copy of pid.c.
  86 This ensured compatibility with the current pid component, while
  87 adding auto tuning as a run time option.  To make it easier to identify
  88 the relevant parts in the future, I wrapped all the auto tuning code
  89 with '#ifdef AUTO_TUNER'.  The end result behave just like the current
  90 pid component by default, as that part of the code is identical.  The
  91 <a href="https://github.com/LinuxCNC/linuxcnc/pull/1820">end result
  92 entered the LinuxCNC master branch</a> a few days ago.</p>
  93
  94 <p>To enable auto tuning, one need to set a few HAL pins in the PID
  95 component.  The most important ones are <tt>tune-effort</tt>,
  96 <tt>tune-mode</tt> and <tt>tune-start</tt>.  But lets take a step
  97 back, and see what the auto tuning code will do.  I do not know the
  98 mathematical foundation of the at_pid algorithm, but from observation
  99 I can tell that the algorithm will, when enabled, produce a square
 100 wave pattern centered around the <tt>bias</tt> value on the output pin
 101 of the PID controller.  This can be seen using the HAL Scope provided
 102 by LinuxCNC.  In my case, this is translated into voltage (+-10V) sent
 103 to the motor controller, which in turn is translated into motor speed.
 104 So at_pid will ask the motor to move the axis back and forth.  The
 105 number of cycles in the pattern is controlled by the
 106 <tt>tune-cycles</tt> pin, and the extremes of the wave pattern is
 107 controlled by the <tt>tune-effort</tt> pin.  Of course, trying to
 108 change the direction of a physical object instantly (as in going
 109 directly from a positive voltage to the equivalent negative voltage)
 110 do not change velocity instantly, and it take some time for the object
 111 to slow down and move in the opposite direction.  This result in a
 112 more smooth movement wave form, as the axis in question were vibrating
 113 back and forth.  When the axis reached the target speed in the
 114 opposing direction, the auto tuner change direction again.  After
 115 several of these changes, the average time delay between the 'peaks'
 116 and 'valleys' of this movement graph is then used to calculate
 117 proposed values for Pgain, Igain and Dgain, and insert them into the
 118 HAL model to use by the pid controller.  The auto tuned settings are
 119 not great, but htye work a lot better than the values I had been able
 120 to cook up on my own, at least for the horizontal X and Y axis.  But I
 121 had to use very small <tt>tune-effort<tt> values, as my motor
 122 controllers error out if the voltage change too quickly.  I've been
 123 less lucky with the Z axis, which is moving a heavy object up and
 124 down, and seem to confuse the algorithm.  The Z axis movement became a
 125 lot better when I introduced a <tt>bias</tt> value to counter the
 126 gravitational drag, but I will have to work a lot more on the Z axis
 127 PID values.</p>
 128
 129 <p>Armed with this knowledge, it is time to look at how to do the
 130 tuning.  Lets say the HAL configuration in question load the PID
 131 component for X, Y and Z like this:</p>
 132
 133 <blockquote><pre>
 134 loadrt pid names=pid.x,pid.y,pid.z
 135 </pre></blockquote>
 136
 137 <p>Armed with the new and improved at_pid component, the new line will
 138 look like this:</p>
 139
 140 <blockquote><pre>
 141 loadrt at_pid names=pid.x,pid.y,pid.z
 142 </pre></blockquote>
 143
 144 <p>The rest of the HAL setup can stay the same.  This work because the
 145 components are referenced by name.  If the component had used count=3
 146 instead, all use of pid.# had to be changed to at_pid.#.</p>
 147
 148 <p>To start tuning the X axis, move the axis to the middle of its
 149 range, to make sure it do not hit anything when it start moving back
 150 and forth.  Next, set the <tt>tune-effort</tt> to a low number in the
 151 output range.  I used 0.1 as my initial value.  Next, assign 1 to the
 152 <tt>tune-mode</tt> value. Note, this will disable the pid controlling
 153 part and feed 0 to the output pin, which in my case initially caused a
 154 lot of drift.  In my case it proved to be a good idea with X and Y to
 155 tune the motor driver to make sure 0 voltage stopped the motor
 156 rotation.  On the other hand, for the Z axis this proved to be a bad
 157 idea, so it will depend on your setup.  It might help to set the
 158 <tt>bias</tt> value to a output value that reduce or eliminate the
 159 axis drift.  Finally, after setting <tt>tune-mode</tt>, set
 160 <tt>tune-start</tt> to 1 to activate the auto tuning.  If all go well,
 161 your axis will vibrate for a few seconds and when it is done, new
 162 values for Pgain, Igain and Dgain will be active.  To test them,
 163 change <tt>tune-mode</tt> back to 0.  Note that this might cause the
 164 machine to suddenly jerk as it bring the axis back to its commanded
 165 position, which it might have drifted away from during tuning.  To
 166 summarize with some halcmd lines:</p>
 167
 168 <blockquote><pre>
 169 setp pid.x.tune-effort 0.1
 170 setp pid.x.tune-mode 1
 171 setp pid.x.tune-start 1
 172 # wait for the tuning to complete
 173 setp pid.x.tune-mode 0
 174 </pre></blockquote>
 175
 176 <p>After doing this task quite a few times while trying to figure out
 177 how to properly tune the PID controllers on the machine in, I decided
 178 to figure out if this process could be automated, and wrote a script
 179 to do the entire tuning process from power on.  The end result will
 180 ensure the machine is powered on and ready to run, home all axis if it
 181 is not already done, check that the extra tuning pins are available,
 182 move the axis to its mid point, run the auto tuning and re-enable the
 183 pid controller when it is done.  It can be run several times.  Check
 184 out the
 185 <a href="https://github.com/SebKuzminsky/MazakVQC1540/blob/bon-dev/scripts/run-auto-pid-tuner">run-auto-pid-tuner</a>
 186 script on github if you want to learn how it is done.</p>
 187
 188 <p>My hope is that this little adventure can inspire someone who know
 189 more about motor PID controller tuning can implement even better
 190 algorithms for automatic PID tuning in LinuxCNC, making life easier
 191 for both me and all the others that want to use LinuxCNC but lack the
 192 in depth knowledge needed to tune PID controllers well.</p>
 193
 194 <p>As usual, if you use Bitcoin and want to show your support of my
 195 activities, please send Bitcoin donations to my address
 196 <b><a href="bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b">15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b</a></b>.</p>
 197 </div>
 198
 199       <div class="tags">Tags: <a href="https://people.skolelinux.org/pere/blog/tags/3d-printer">3d-printer</a>, <a href="https://people.skolelinux.org/pere/blog/tags/debian">debian</a>, <a href="https://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="https://people.skolelinux.org/pere/blog/tags/linuxcnc">linuxcnc</a>, <a href="https://people.skolelinux.org/pere/blog/tags/robot">robot</a>.</div>
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 340 <li><a href="https://people.skolelinux.org/pere/blog/archive/2019/12/">December (4)</a></li>
 341
 342 </ul></li>
 343
 344 <li>2018
 345 <ul>
 346
 347 <li><a href="https://people.skolelinux.org/pere/blog/archive/2018/01/">January (1)</a></li>
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 349 <li><a href="https://people.skolelinux.org/pere/blog/archive/2018/02/">February (5)</a></li>
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 356
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 366
 367 <li><a href="https://people.skolelinux.org/pere/blog/archive/2018/12/">December (4)</a></li>
 368
 369 </ul></li>
 370
 371 <li>2017
 372 <ul>
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 374 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/01/">January (4)</a></li>
 375
 376 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/02/">February (3)</a></li>
 377
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 379
 380 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/04/">April (2)</a></li>
 381
 382 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/06/">June (5)</a></li>
 383
 384 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/07/">July (1)</a></li>
 385
 386 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/08/">August (1)</a></li>
 387
 388 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/09/">September (3)</a></li>
 389
 390 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/10/">October (5)</a></li>
 391
 392 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/11/">November (3)</a></li>
 393
 394 <li><a href="https://people.skolelinux.org/pere/blog/archive/2017/12/">December (4)</a></li>
 395
 396 </ul></li>
 397
 398 <li>2016
 399 <ul>
 400
 401 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/01/">January (3)</a></li>
 402
 403 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/02/">February (2)</a></li>
 404
 405 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/03/">March (3)</a></li>
 406
 407 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/04/">April (8)</a></li>
 408
 409 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/05/">May (8)</a></li>
 410
 411 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/06/">June (2)</a></li>
 412
 413 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/07/">July (2)</a></li>
 414
 415 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/08/">August (5)</a></li>
 416
 417 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/09/">September (2)</a></li>
 418
 419 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/10/">October (3)</a></li>
 420
 421 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/11/">November (8)</a></li>
 422
 423 <li><a href="https://people.skolelinux.org/pere/blog/archive/2016/12/">December (5)</a></li>
 424
 425 </ul></li>
 426
 427 <li>2015
 428 <ul>
 429
 430 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/01/">January (7)</a></li>
 431
 432 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/02/">February (6)</a></li>
 433
 434 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/03/">March (1)</a></li>
 435
 436 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/04/">April (4)</a></li>
 437
 438 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/05/">May (3)</a></li>
 439
 440 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/06/">June (4)</a></li>
 441
 442 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/07/">July (6)</a></li>
 443
 444 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/08/">August (2)</a></li>
 445
 446 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/09/">September (2)</a></li>
 447
 448 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/10/">October (9)</a></li>
 449
 450 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/11/">November (6)</a></li>
 451
 452 <li><a href="https://people.skolelinux.org/pere/blog/archive/2015/12/">December (3)</a></li>
 453
 454 </ul></li>
 455
 456 <li>2014
 457 <ul>
 458
 459 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/01/">January (2)</a></li>
 460
 461 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/02/">February (3)</a></li>
 462
 463 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/03/">March (8)</a></li>
 464
 465 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/04/">April (7)</a></li>
 466
 467 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/05/">May (1)</a></li>
 468
 469 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/06/">June (2)</a></li>
 470
 471 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/07/">July (2)</a></li>
 472
 473 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/08/">August (2)</a></li>
 474
 475 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/09/">September (5)</a></li>
 476
 477 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/10/">October (6)</a></li>
 478
 479 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/11/">November (3)</a></li>
 480
 481 <li><a href="https://people.skolelinux.org/pere/blog/archive/2014/12/">December (5)</a></li>
 482
 483 </ul></li>
 484
 485 <li>2013
 486 <ul>
 487
 488 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/01/">January (11)</a></li>
 489
 490 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/02/">February (9)</a></li>
 491
 492 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/03/">March (9)</a></li>
 493
 494 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/04/">April (6)</a></li>
 495
 496 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/05/">May (9)</a></li>
 497
 498 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/06/">June (10)</a></li>
 499
 500 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/07/">July (7)</a></li>
 501
 502 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/08/">August (3)</a></li>
 503
 504 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/09/">September (5)</a></li>
 505
 506 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/10/">October (7)</a></li>
 507
 508 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/11/">November (9)</a></li>
 509
 510 <li><a href="https://people.skolelinux.org/pere/blog/archive/2013/12/">December (3)</a></li>
 511
 512 </ul></li>
 513
 514 <li>2012
 515 <ul>
 516
 517 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/01/">January (7)</a></li>
 518
 519 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/02/">February (10)</a></li>
 520
 521 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/03/">March (17)</a></li>
 522
 523 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/04/">April (12)</a></li>
 524
 525 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/05/">May (12)</a></li>
 526
 527 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/06/">June (20)</a></li>
 528
 529 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/07/">July (17)</a></li>
 530
 531 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/08/">August (6)</a></li>
 532
 533 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/09/">September (9)</a></li>
 534
 535 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/10/">October (17)</a></li>
 536
 537 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/11/">November (10)</a></li>
 538
 539 <li><a href="https://people.skolelinux.org/pere/blog/archive/2012/12/">December (7)</a></li>
 540
 541 </ul></li>
 542
 543 <li>2011
 544 <ul>
 545
 546 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/01/">January (16)</a></li>
 547
 548 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/02/">February (6)</a></li>
 549
 550 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/03/">March (6)</a></li>
 551
 552 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/04/">April (7)</a></li>
 553
 554 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/05/">May (3)</a></li>
 555
 556 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/06/">June (2)</a></li>
 557
 558 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/07/">July (7)</a></li>
 559
 560 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/08/">August (6)</a></li>
 561
 562 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/09/">September (4)</a></li>
 563
 564 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/10/">October (2)</a></li>
 565
 566 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/11/">November (3)</a></li>
 567
 568 <li><a href="https://people.skolelinux.org/pere/blog/archive/2011/12/">December (1)</a></li>
 569
 570 </ul></li>
 571
 572 <li>2010
 573 <ul>
 574
 575 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/01/">January (2)</a></li>
 576
 577 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/02/">February (1)</a></li>
 578
 579 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/03/">March (3)</a></li>
 580
 581 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/04/">April (3)</a></li>
 582
 583 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/05/">May (9)</a></li>
 584
 585 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/06/">June (14)</a></li>
 586
 587 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/07/">July (12)</a></li>
 588
 589 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/08/">August (13)</a></li>
 590
 591 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/09/">September (7)</a></li>
 592
 593 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/10/">October (9)</a></li>
 594
 595 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/11/">November (13)</a></li>
 596
 597 <li><a href="https://people.skolelinux.org/pere/blog/archive/2010/12/">December (12)</a></li>
 598
 599 </ul></li>
 600
 601 <li>2009
 602 <ul>
 603
 604 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/01/">January (8)</a></li>
 605
 606 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/02/">February (8)</a></li>
 607
 608 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/03/">March (12)</a></li>
 609
 610 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/04/">April (10)</a></li>
 611
 612 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/05/">May (9)</a></li>
 613
 614 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/06/">June (3)</a></li>
 615
 616 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/07/">July (4)</a></li>
 617
 618 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/08/">August (3)</a></li>
 619
 620 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/09/">September (1)</a></li>
 621
 622 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/10/">October (2)</a></li>
 623
 624 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/11/">November (3)</a></li>
 625
 626 <li><a href="https://people.skolelinux.org/pere/blog/archive/2009/12/">December (3)</a></li>
 627
 628 </ul></li>
 629
 630 <li>2008
 631 <ul>
 632
 633 <li><a href="https://people.skolelinux.org/pere/blog/archive/2008/11/">November (5)</a></li>
 634
 635 <li><a href="https://people.skolelinux.org/pere/blog/archive/2008/12/">December (7)</a></li>
 636
 637 </ul></li>
 638
 639 </ul>
 640
 641
 642
 643 <h2>Tags</h2>
 644 <ul>
 645
 646  <li><a href="https://people.skolelinux.org/pere/blog/tags/3d-printer">3d-printer (19)</a></li>
 647
 648  <li><a href="https://people.skolelinux.org/pere/blog/tags/amiga">amiga (1)</a></li>
 649
 650  <li><a href="https://people.skolelinux.org/pere/blog/tags/aros">aros (1)</a></li>
 651
 652  <li><a href="https://people.skolelinux.org/pere/blog/tags/bankid">bankid (4)</a></li>
 653
 654  <li><a href="https://people.skolelinux.org/pere/blog/tags/betalkontant">betalkontant (9)</a></li>
 655
 656  <li><a href="https://people.skolelinux.org/pere/blog/tags/bitcoin">bitcoin (13)</a></li>
 657
 658  <li><a href="https://people.skolelinux.org/pere/blog/tags/bootsystem">bootsystem (17)</a></li>
 659
 660  <li><a href="https://people.skolelinux.org/pere/blog/tags/bsa">bsa (2)</a></li>
 661
 662  <li><a href="https://people.skolelinux.org/pere/blog/tags/chrpath">chrpath (3)</a></li>
 663
 664  <li><a href="https://people.skolelinux.org/pere/blog/tags/debian">debian (198)</a></li>
 665
 666  <li><a href="https://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (159)</a></li>
 667
 668  <li><a href="https://people.skolelinux.org/pere/blog/tags/debian-handbook">debian-handbook (9)</a></li>
 669
 670  <li><a href="https://people.skolelinux.org/pere/blog/tags/digistan">digistan (11)</a></li>
 671
 672  <li><a href="https://people.skolelinux.org/pere/blog/tags/dld">dld (18)</a></li>
 673
 674  <li><a href="https://people.skolelinux.org/pere/blog/tags/docbook">docbook (32)</a></li>
 675
 676  <li><a href="https://people.skolelinux.org/pere/blog/tags/drivstoffpriser">drivstoffpriser (4)</a></li>
 677
 678  <li><a href="https://people.skolelinux.org/pere/blog/tags/english">english (460)</a></li>
 679
 680  <li><a href="https://people.skolelinux.org/pere/blog/tags/fiksgatami">fiksgatami (23)</a></li>
 681
 682  <li><a href="https://people.skolelinux.org/pere/blog/tags/fildeling">fildeling (14)</a></li>
 683
 684  <li><a href="https://people.skolelinux.org/pere/blog/tags/freeculture">freeculture (34)</a></li>
 685
 686  <li><a href="https://people.skolelinux.org/pere/blog/tags/freedombox">freedombox (9)</a></li>
 687
 688  <li><a href="https://people.skolelinux.org/pere/blog/tags/frikanalen">frikanalen (20)</a></li>
 689
 690  <li><a href="https://people.skolelinux.org/pere/blog/tags/h264">h264 (20)</a></li>
 691
 692  <li><a href="https://people.skolelinux.org/pere/blog/tags/intervju">intervju (43)</a></li>
 693
 694  <li><a href="https://people.skolelinux.org/pere/blog/tags/isenkram">isenkram (18)</a></li>
 695
 696  <li><a href="https://people.skolelinux.org/pere/blog/tags/kart">kart (23)</a></li>
 697
 698  <li><a href="https://people.skolelinux.org/pere/blog/tags/kodi">kodi (6)</a></li>
 699
 700  <li><a href="https://people.skolelinux.org/pere/blog/tags/ldap">ldap (9)</a></li>
 701
 702  <li><a href="https://people.skolelinux.org/pere/blog/tags/lego">lego (5)</a></li>
 703
 704  <li><a href="https://people.skolelinux.org/pere/blog/tags/lenker">lenker (8)</a></li>
 705
 706  <li><a href="https://people.skolelinux.org/pere/blog/tags/linuxcnc">linuxcnc (5)</a></li>
 707
 708  <li><a href="https://people.skolelinux.org/pere/blog/tags/lsdvd">lsdvd (2)</a></li>
 709
 710  <li><a href="https://people.skolelinux.org/pere/blog/tags/ltsp">ltsp (1)</a></li>
 711
 712  <li><a href="https://people.skolelinux.org/pere/blog/tags/madewithcc">madewithcc (3)</a></li>
 713
 714  <li><a href="https://people.skolelinux.org/pere/blog/tags/mesh network">mesh network (8)</a></li>
 715
 716  <li><a href="https://people.skolelinux.org/pere/blog/tags/multimedia">multimedia (46)</a></li>
 717
 718  <li><a href="https://people.skolelinux.org/pere/blog/tags/nice free software">nice free software (15)</a></li>
 719
 720  <li><a href="https://people.skolelinux.org/pere/blog/tags/noark5">noark5 (25)</a></li>
 721
 722  <li><a href="https://people.skolelinux.org/pere/blog/tags/norsk">norsk (324)</a></li>
 723
 724  <li><a href="https://people.skolelinux.org/pere/blog/tags/nuug">nuug (199)</a></li>
 725
 726  <li><a href="https://people.skolelinux.org/pere/blog/tags/offentlig innsyn">offentlig innsyn (41)</a></li>
 727
 728  <li><a href="https://people.skolelinux.org/pere/blog/tags/open311">open311 (2)</a></li>
 729
 730  <li><a href="https://people.skolelinux.org/pere/blog/tags/opensnitch">opensnitch (4)</a></li>
 731
 732  <li><a href="https://people.skolelinux.org/pere/blog/tags/opphavsrett">opphavsrett (76)</a></li>
 733
 734  <li><a href="https://people.skolelinux.org/pere/blog/tags/personvern">personvern (114)</a></li>
 735
 736  <li><a href="https://people.skolelinux.org/pere/blog/tags/raid">raid (4)</a></li>
 737
 738  <li><a href="https://people.skolelinux.org/pere/blog/tags/reactos">reactos (1)</a></li>
 739
 740  <li><a href="https://people.skolelinux.org/pere/blog/tags/reprap">reprap (11)</a></li>
 741
 742  <li><a href="https://people.skolelinux.org/pere/blog/tags/rfid">rfid (3)</a></li>
 743
 744  <li><a href="https://people.skolelinux.org/pere/blog/tags/robot">robot (17)</a></li>
 745
 746  <li><a href="https://people.skolelinux.org/pere/blog/tags/rss">rss (1)</a></li>
 747
 748  <li><a href="https://people.skolelinux.org/pere/blog/tags/ruter">ruter (7)</a></li>
 749
 750  <li><a href="https://people.skolelinux.org/pere/blog/tags/scraperwiki">scraperwiki (2)</a></li>
 751
 752  <li><a href="https://people.skolelinux.org/pere/blog/tags/sikkerhet">sikkerhet (60)</a></li>
 753
 754  <li><a href="https://people.skolelinux.org/pere/blog/tags/sitesummary">sitesummary (4)</a></li>
 755
 756  <li><a href="https://people.skolelinux.org/pere/blog/tags/skepsis">skepsis (5)</a></li>
 757
 758  <li><a href="https://people.skolelinux.org/pere/blog/tags/standard">standard (76)</a></li>
 759
 760  <li><a href="https://people.skolelinux.org/pere/blog/tags/stavekontroll">stavekontroll (7)</a></li>
 761
 762  <li><a href="https://people.skolelinux.org/pere/blog/tags/stortinget">stortinget (14)</a></li>
 763
 764  <li><a href="https://people.skolelinux.org/pere/blog/tags/surveillance">surveillance (65)</a></li>
 765
 766  <li><a href="https://people.skolelinux.org/pere/blog/tags/sysadmin">sysadmin (5)</a></li>
 767
 768  <li><a href="https://people.skolelinux.org/pere/blog/tags/usenix">usenix (2)</a></li>
 769
 770  <li><a href="https://people.skolelinux.org/pere/blog/tags/valg">valg (9)</a></li>
 771
 772  <li><a href="https://people.skolelinux.org/pere/blog/tags/verkidetfri">verkidetfri (22)</a></li>
 773
 774  <li><a href="https://people.skolelinux.org/pere/blog/tags/video">video (80)</a></li>
 775
 776  <li><a href="https://people.skolelinux.org/pere/blog/tags/vitenskap">vitenskap (4)</a></li>
 777
 778  <li><a href="https://people.skolelinux.org/pere/blog/tags/web">web (42)</a></li>
 779
 780 </ul>
 781
 782
 783     </div>
 784     <p style="text-align: right">
 785  Created by <a href="http://steve.org.uk/Software/chronicle">Chronicle v4.6</a>
 786 </p>
 787
 788   </body>
 789 </html>