src/modules/tools/zprobe/ZProbe.cpp

   1 /*
   2       This file is part of Smoothie (http://smoothieware.org/). The motion control part is heavily based on Grbl (https://github.com/simen/grbl).
   3       Smoothie is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
   4       Smoothie is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
   5       You should have received a copy of the GNU General Public License along with Smoothie. If not, see <http://www.gnu.org/licenses/>.
   6 */
   7
   8 #include "ZProbe.h"
   9
  10 #include "Kernel.h"
  11 #include "BaseSolution.h"
  12 #include "Config.h"
  13 #include "Robot.h"
  14 #include "StepperMotor.h"
  15 #include "StreamOutputPool.h"
  16 #include "Gcode.h"
  17 #include "Conveyor.h"
  18 #include "Stepper.h"
  19 #include "checksumm.h"
  20 #include "ConfigValue.h"
  21 #include "SlowTicker.h"
  22 #include "Planner.h"
  23 #include "SerialMessage.h"
  24 #include "PublicDataRequest.h"
  25 #include "EndstopsPublicAccess.h"
  26 #include "PublicData.h"
  27 #include "LevelingStrategy.h"
  28 #include "StepTicker.h"
  29 #include "utils.h"
  30
  31 // strategies we know about
  32 #include "DeltaCalibrationStrategy.h"
  33 #include "ThreePointStrategy.h"
  34 #include "ZGridStrategy.h"
  35
  36 #define enable_checksum          CHECKSUM("enable")
  37 #define probe_pin_checksum       CHECKSUM("probe_pin")
  38 #define debounce_count_checksum  CHECKSUM("debounce_count")
  39 #define slow_feedrate_checksum   CHECKSUM("slow_feedrate")
  40 #define fast_feedrate_checksum   CHECKSUM("fast_feedrate")
  41 #define return_feedrate_checksum CHECKSUM("return_feedrate")
  42 #define probe_height_checksum    CHECKSUM("probe_height")
  43 #define gamma_max_checksum       CHECKSUM("gamma_max")
  44
  45 // from endstop section
  46 #define delta_homing_checksum    CHECKSUM("delta_homing")
  47 #define rdelta_homing_checksum    CHECKSUM("rdelta_homing")
  48
  49 #define X_AXIS 0
  50 #define Y_AXIS 1
  51 #define Z_AXIS 2
  52
  53 #define STEPPER THEKERNEL->robot->actuators
  54 #define STEPS_PER_MM(a) (STEPPER[a]->get_steps_per_mm())
  55 #define Z_STEPS_PER_MM STEPS_PER_MM(Z_AXIS)
  56
  57 #define abs(a) ((a<0) ? -a : a)
  58
  59 void ZProbe::on_module_loaded()
  60 {
  61     // if the module is disabled -> do nothing
  62     if(!THEKERNEL->config->value( zprobe_checksum, enable_checksum )->by_default(false)->as_bool()) {
  63         // as this module is not needed free up the resource
  64         delete this;
  65         return;
  66     }
  67
  68     // load settings
  69     this->on_config_reload(this);
  70     // register event-handlers
  71     register_for_event(ON_GCODE_RECEIVED);
  72
  73     THEKERNEL->step_ticker->register_acceleration_tick_handler([this](){acceleration_tick(); });
  74
  75     // we read the probe in this timer, currently only for G38 probes.
  76     probing= false;
  77     THEKERNEL->slow_ticker->attach(1000, this, &ZProbe::read_probe);
  78 }
  79
  80 void ZProbe::on_config_reload(void *argument)
  81 {
  82     this->pin.from_string( THEKERNEL->config->value(zprobe_checksum, probe_pin_checksum)->by_default("nc" )->as_string())->as_input();
  83     this->debounce_count = THEKERNEL->config->value(zprobe_checksum, debounce_count_checksum)->by_default(0  )->as_number();
  84
  85     // get strategies to load
  86     vector<uint16_t> modules;
  87     THEKERNEL->config->get_module_list( &modules, leveling_strategy_checksum);
  88     for( auto cs : modules ){
  89         if( THEKERNEL->config->value(leveling_strategy_checksum, cs, enable_checksum )->as_bool() ){
  90             bool found= false;
  91             // check with each known strategy and load it if it matches
  92             switch(cs) {
  93                 case delta_calibration_strategy_checksum:
  94                     this->strategies.push_back(new DeltaCalibrationStrategy(this));
  95                     found= true;
  96                     break;
  97
  98                 case three_point_leveling_strategy_checksum:
  99                     // NOTE this strategy is mutually exclusive with the delta calibration strategy
 100                     this->strategies.push_back(new ThreePointStrategy(this));
 101                     found= true;
 102                     break;
 103
 104                 case ZGrid_leveling_checksum:
 105                      this->strategies.push_back(new ZGridStrategy(this));
 106                      found= true;
 107                      break;
 108
 109                 // add other strategies here
 110                 //case zheight_map_strategy:
 111                 //     this->strategies.push_back(new ZHeightMapStrategy(this));
 112                 //     found= true;
 113                 //     break;
 114             }
 115             if(found) this->strategies.back()->handleConfig();
 116         }
 117     }
 118
 119     // need to know if we need to use delta kinematics for homing
 120     this->is_delta = THEKERNEL->config->value(delta_homing_checksum)->by_default(false)->as_bool();
 121     this->is_rdelta = THEKERNEL->config->value(rdelta_homing_checksum)->by_default(false)->as_bool();
 122
 123     // default for backwards compatibility add DeltaCalibrationStrategy if a delta
 124     // will be deprecated
 125     if(this->strategies.empty()) {
 126         if(this->is_delta) {
 127             this->strategies.push_back(new DeltaCalibrationStrategy(this));
 128             this->strategies.back()->handleConfig();
 129         }
 130     }
 131
 132     this->probe_height  = THEKERNEL->config->value(zprobe_checksum, probe_height_checksum)->by_default(5.0F)->as_number();
 133     this->slow_feedrate = THEKERNEL->config->value(zprobe_checksum, slow_feedrate_checksum)->by_default(5)->as_number(); // feedrate in mm/sec
 134     this->fast_feedrate = THEKERNEL->config->value(zprobe_checksum, fast_feedrate_checksum)->by_default(100)->as_number(); // feedrate in mm/sec
 135     this->return_feedrate = THEKERNEL->config->value(zprobe_checksum, return_feedrate_checksum)->by_default(0)->as_number(); // feedrate in mm/sec
 136     this->max_z         = THEKERNEL->config->value(gamma_max_checksum)->by_default(500)->as_number(); // maximum zprobe distance
 137 }
 138
 139 bool ZProbe::wait_for_probe(int& steps)
 140 {
 141     unsigned int debounce = 0;
 142     while(true) {
 143         THEKERNEL->call_event(ON_IDLE);
 144         if(THEKERNEL->is_halted()){
 145             // aborted by kill
 146             return false;
 147         }
 148
 149         bool delta= is_delta || is_rdelta;
 150
 151         // if no stepper is moving, moves are finished and there was no touch
 152         if( !STEPPER[Z_AXIS]->is_moving() && (!delta || (!STEPPER[Y_AXIS]->is_moving() && !STEPPER[Z_AXIS]->is_moving())) ) {
 153             return false;
 154         }
 155
 156         // if the probe is active...
 157         if( this->pin.get() ) {
 158             //...increase debounce counter...
 159             if( debounce < debounce_count) {
 160                 // ...but only if the counter hasn't reached the max. value
 161                 debounce++;
 162             } else {
 163                 // ...otherwise stop the steppers, return its remaining steps
 164                 if(STEPPER[Z_AXIS]->is_moving()){
 165                     steps= STEPPER[Z_AXIS]->get_stepped();
 166                     STEPPER[Z_AXIS]->move(0, 0);
 167                 }
 168                 if(delta) {
 169                     for( int i = X_AXIS; i <= Y_AXIS; i++ ) {
 170                         if ( STEPPER[i]->is_moving() ) {
 171                             STEPPER[i]->move(0, 0);
 172                         }
 173                     }
 174                 }
 175                 return true;
 176             }
 177         } else {
 178             // The probe was not hit yet, reset debounce counter
 179             debounce = 0;
 180         }
 181     }
 182 }
 183
 184 // single probe with custom feedrate
 185 // returns boolean value indicating if probe was triggered
 186 bool ZProbe::run_probe_feed(int& steps, float feedrate, float max_dist)
 187 {
 188     // not a block move so disable the last tick setting
 189     for ( int c = X_AXIS; c <= Z_AXIS; c++ ) {
 190         STEPPER[c]->set_moved_last_block(false);
 191     }
 192
 193     // Enable the motors
 194     THEKERNEL->stepper->turn_enable_pins_on();
 195     this->current_feedrate = feedrate * Z_STEPS_PER_MM; // steps/sec
 196     float maxz= max_dist < 0 ? this->max_z*2 : max_dist;
 197
 198     // move Z down
 199     STEPPER[Z_AXIS]->move(true, maxz * Z_STEPS_PER_MM, 0); // always probes down, no more than 2*maxz
 200     if(this->is_delta || this->is_rdelta) {
 201         // for delta need to move all three actuators
 202         STEPPER[X_AXIS]->move(true, maxz * STEPS_PER_MM(X_AXIS), 0);
 203         STEPPER[Y_AXIS]->move(true, maxz * STEPS_PER_MM(Y_AXIS), 0);
 204     }
 205
 206     // start acceleration processing
 207     this->running = true;
 208
 209     bool r = wait_for_probe(steps);
 210     this->running = false;
 211     STEPPER[X_AXIS]->move(0, 0);
 212     STEPPER[Y_AXIS]->move(0, 0);
 213     STEPPER[Z_AXIS]->move(0, 0);
 214     return r;
 215 }
 216
 217 // single probe with either fast or slow feedrate
 218 // returns boolean value indicating if probe was triggered
 219 bool ZProbe::run_probe(int& steps, bool fast)
 220 {
 221     float feedrate = (fast ? this->fast_feedrate : this->slow_feedrate);
 222     return run_probe_feed(steps, feedrate);
 223 }
 224
 225 bool ZProbe::return_probe(int steps)
 226 {
 227     // move probe back to where it was
 228
 229     float fr;
 230     if(this->return_feedrate != 0) { // use return_feedrate if set
 231         fr = this->return_feedrate;
 232     } else {
 233         fr = this->slow_feedrate*2; // nominally twice slow feedrate
 234         if(fr > this->fast_feedrate) fr = this->fast_feedrate; // unless that is greater than fast feedrate
 235     }
 236
 237     this->current_feedrate = fr * Z_STEPS_PER_MM; // feedrate in steps/sec
 238     bool dir= steps < 0;
 239     steps= abs(steps);
 240
 241     bool delta= (this->is_delta || this->is_rdelta);
 242     STEPPER[Z_AXIS]->move(dir, steps, 0);
 243     if(delta) {
 244         STEPPER[X_AXIS]->move(dir, steps, 0);
 245         STEPPER[Y_AXIS]->move(dir, steps, 0);
 246     }
 247
 248     this->running = true;
 249     while(STEPPER[Z_AXIS]->is_moving() || (delta && (STEPPER[X_AXIS]->is_moving() || STEPPER[Y_AXIS]->is_moving())) ) {
 250         // wait for it to complete
 251         THEKERNEL->call_event(ON_IDLE);
 252          if(THEKERNEL->is_halted()){
 253             // aborted by kill
 254             break;
 255         }
 256     }
 257
 258     this->running = false;
 259     STEPPER[X_AXIS]->move(0, 0);
 260     STEPPER[Y_AXIS]->move(0, 0);
 261     STEPPER[Z_AXIS]->move(0, 0);
 262
 263     return true;
 264 }
 265
 266 bool ZProbe::doProbeAt(int &steps, float x, float y)
 267 {
 268     int s;
 269     // move to xy
 270     coordinated_move(x, y, NAN, getFastFeedrate());
 271     if(!run_probe(s)) return false;
 272
 273     // return to original Z
 274     return_probe(s);
 275     steps = s;
 276
 277     return true;
 278 }
 279
 280 float ZProbe::probeDistance(float x, float y)
 281 {
 282     int s;
 283     if(!doProbeAt(s, x, y)) return NAN;
 284     return zsteps_to_mm(s);
 285 }
 286
 287 void ZProbe::on_gcode_received(void *argument)
 288 {
 289     Gcode *gcode = static_cast<Gcode *>(argument);
 290
 291     if( gcode->has_g && gcode->g >= 29 && gcode->g <= 32) {
 292
 293         // make sure the probe is defined and not already triggered before moving motors
 294         if(!this->pin.connected()) {
 295             gcode->stream->printf("ZProbe not connected.\n");
 296             return;
 297         }
 298         if(this->pin.get()) {
 299             gcode->stream->printf("ZProbe triggered before move, aborting command.\n");
 300             return;
 301         }
 302
 303         if( gcode->g == 30 ) { // simple Z probe
 304             // first wait for an empty queue i.e. no moves left
 305             THEKERNEL->conveyor->wait_for_empty_queue();
 306
 307             int steps;
 308             bool probe_result;
 309             if(gcode->has_letter('F')) {
 310                 probe_result = run_probe_feed(steps, gcode->get_value('F') / 60);
 311             } else {
 312                 probe_result = run_probe(steps);
 313             }
 314
 315             if(probe_result) {
 316                 gcode->stream->printf("Z:%1.4f C:%d\n", zsteps_to_mm(steps), steps);
 317                 // move back to where it started, unless a Z is specified
 318                 if(gcode->has_letter('Z')) {
 319                     // set Z to the specified value, and leave probe where it is
 320                     THEKERNEL->robot->reset_axis_position(gcode->get_value('Z'), Z_AXIS);
 321                 } else {
 322                     return_probe(steps);
 323                 }
 324             } else {
 325                 gcode->stream->printf("ZProbe not triggered\n");
 326             }
 327
 328         } else {
 329             if(!gcode->has_letter('P')) {
 330                 // find the first strategy to handle the gcode
 331                 for(auto s : strategies){
 332                     if(s->handleGcode(gcode)) {
 333                         return;
 334                     }
 335                 }
 336                 gcode->stream->printf("No strategy found to handle G%d\n", gcode->g);
 337
 338             }else{
 339                 // P paramater selects which strategy to send the code to
 340                 // they are loaded in the order they are defined in config, 0 being the first, 1 being the second and so on.
 341                 uint16_t i= gcode->get_value('P');
 342                 if(i < strategies.size()) {
 343                     if(!strategies[i]->handleGcode(gcode)){
 344                         gcode->stream->printf("strategy #%d did not handle G%d\n", i, gcode->g);
 345                     }
 346                     return;
 347
 348                 }else{
 349                     gcode->stream->printf("strategy #%d is not loaded\n", i);
 350                 }
 351             }
 352         }
 353
 354     } else if(gcode->has_g && gcode->g == 38 ) { // G38.2 Straight Probe with error, G38.3 straight probe without error
 355         // linuxcnc/grbl style probe http://www.linuxcnc.org/docs/2.5/html/gcode/gcode.html#sec:G38-probe
 356         if(gcode->subcode != 2 && gcode->subcode != 3) {
 357             gcode->stream->printf("error:Only G38.2 and G38.3 are supported\n");
 358             return;
 359         }
 360
 361         // make sure the probe is defined and not already triggered before moving motors
 362         if(!this->pin.connected()) {
 363             gcode->stream->printf("error:ZProbe not connected.\n");
 364             return;
 365         }
 366
 367         if(this->pin.get()) {
 368             gcode->stream->printf("error:ZProbe triggered before move, aborting command.\n");
 369             return;
 370         }
 371
 372         // first wait for an empty queue i.e. no moves left
 373         THEKERNEL->conveyor->wait_for_empty_queue();
 374
 375         // turn off any compensation transform
 376         auto savect= THEKERNEL->robot->compensationTransform;
 377         THEKERNEL->robot->compensationTransform= nullptr;
 378
 379         if(gcode->has_letter('X')) {
 380             // probe in the X axis
 381             probe_XYZ(gcode, X_AXIS);
 382
 383         }else if(gcode->has_letter('Y')) {
 384             // probe in the Y axis
 385             probe_XYZ(gcode, Y_AXIS);
 386
 387         }else if(gcode->has_letter('Z')) {
 388             // probe in the Z axis
 389             probe_XYZ(gcode, Z_AXIS);
 390
 391         }else{
 392             gcode->stream->printf("error:at least one of X Y or Z must be specified\n");
 393         }
 394
 395         // restore compensationTransform
 396         THEKERNEL->robot->compensationTransform= savect;
 397
 398         return;
 399
 400     } else if(gcode->has_m) {
 401         // M code processing here
 402         int c;
 403         switch (gcode->m) {
 404             case 119:
 405                 c = this->pin.get();
 406                 gcode->stream->printf(" Probe: %d", c);
 407                 gcode->add_nl = true;
 408                 break;
 409
 410             case 670:
 411                 if (gcode->has_letter('S')) this->slow_feedrate = gcode->get_value('S');
 412                 if (gcode->has_letter('K')) this->fast_feedrate = gcode->get_value('K');
 413                 if (gcode->has_letter('R')) this->return_feedrate = gcode->get_value('R');
 414                 if (gcode->has_letter('Z')) this->max_z = gcode->get_value('Z');
 415                 if (gcode->has_letter('H')) this->probe_height = gcode->get_value('H');
 416                 break;
 417
 418             case 500: // save settings
 419             case 503: // print settings
 420                 gcode->stream->printf(";Probe feedrates Slow/fast(K)/Return (mm/sec) max_z (mm) height (mm):\nM670 S%1.2f K%1.2f R%1.2f Z%1.2f H%1.2f\n",
 421                     this->slow_feedrate, this->fast_feedrate, this->return_feedrate, this->max_z, this->probe_height);
 422
 423                 // fall through is intended so leveling strategies can handle m-codes too
 424
 425             default:
 426                 for(auto s : strategies){
 427                     if(s->handleGcode(gcode)) {
 428                         return;
 429                     }
 430                 }
 431         }
 432     }
 433 }
 434
 435 uint32_t ZProbe::read_probe(uint32_t dummy)
 436 {
 437     if(!probing || probe_detected) return 0;
 438
 439     // TODO add debounce/noise filter
 440     if(this->pin.get()) {
 441         probe_detected= true;
 442         // now tell all the stepper_motors to stop
 443         for(auto &a : THEKERNEL->robot->actuators) a->force_finish_move();
 444     }
 445     return 0;
 446 }
 447
 448 // special way to probe in the X or Y or Z direction using planned moves, should work with any kinematics
 449 void ZProbe::probe_XYZ(Gcode *gcode, int axis)
 450 {
 451     // enable the probe checking in the timer
 452     probing= true;
 453     probe_detected= false;
 454     THEKERNEL->robot->disable_segmentation= true; // we must disable segmentation as this won't work with it enabled (beware on deltas probing in X or Y)
 455
 456     // get probe feedrate if specified
 457     float rate = (gcode->has_letter('F')) ? gcode->get_value('F')*60 : this->slow_feedrate;
 458
 459     // do a regular move which will stop as soon as the probe is triggered, or the distance is reached
 460     switch(axis) {
 461         case X_AXIS: coordinated_move(gcode->get_value('X'), 0, 0, rate, true); break;
 462         case Y_AXIS: coordinated_move(0, gcode->get_value('Y'), 0, rate, true); break;
 463         case Z_AXIS: coordinated_move(0, 0, gcode->get_value('Z'), rate, true); break;
 464     }
 465
 466     // coordinated_move returns when the move is finished
 467
 468     // disable probe checking
 469     probing= false;
 470     THEKERNEL->robot->disable_segmentation= false;
 471
 472     float pos[3];
 473     {
 474         // get the current position
 475         ActuatorCoordinates current_position{
 476             THEKERNEL->robot->actuators[X_AXIS]->get_current_position(),
 477             THEKERNEL->robot->actuators[Y_AXIS]->get_current_position(),
 478             THEKERNEL->robot->actuators[Z_AXIS]->get_current_position()
 479         };
 480
 481         // get machine position from the actuator position using FK
 482         THEKERNEL->robot->arm_solution->actuator_to_cartesian(current_position, pos);
 483     }
 484
 485     uint8_t probeok= this->probe_detected ? 1 : 0;
 486
 487     // print results using the GRBL format
 488     gcode->stream->printf("[PRB:%1.3f,%1.3f,%1.3f:%d]\n", pos[X_AXIS], pos[Y_AXIS], pos[Z_AXIS], probeok);
 489     THEKERNEL->robot->set_last_probe_position(std::make_tuple(pos[X_AXIS], pos[Y_AXIS], pos[Z_AXIS], probeok));
 490
 491     if(!probeok) {
 492         if(gcode->subcode == 2) {
 493             // issue error if probe was not triggered and subcode == 2
 494             gcode->stream->printf("ALARM:Probe fail\n");
 495             THEKERNEL->call_event(ON_HALT, nullptr);
 496
 497         }else{
 498             // if the probe stopped the move we need to correct the last_milestone as it did not reach where it thought
 499             THEKERNEL->robot->reset_position_from_current_actuator_position();
 500         }
 501     }
 502 }
 503
 504 // Called periodically to change the speed to match acceleration
 505 void ZProbe::acceleration_tick(void)
 506 {
 507     if(!this->running) return; // nothing to do
 508     if(STEPPER[Z_AXIS]->is_moving()) accelerate(Z_AXIS);
 509
 510     if(is_delta || is_rdelta) {
 511          // deltas needs to move all actuators
 512         for ( int c = X_AXIS; c <= Y_AXIS; c++ ) {
 513             if( !STEPPER[c]->is_moving() ) continue;
 514             accelerate(c);
 515         }
 516     }
 517
 518     return;
 519 }
 520
 521 void ZProbe::accelerate(int c)
 522 {   uint32_t current_rate = STEPPER[c]->get_steps_per_second();
 523     uint32_t target_rate = floorf(this->current_feedrate);
 524
 525     // Z may have a different acceleration to X and Y
 526     float acc= (c==Z_AXIS) ? THEKERNEL->planner->get_z_acceleration() : THEKERNEL->planner->get_acceleration();
 527     if( current_rate < target_rate ) {
 528         uint32_t rate_increase = floorf((acc / THEKERNEL->acceleration_ticks_per_second) * STEPS_PER_MM(c));
 529         current_rate = min( target_rate, current_rate + rate_increase );
 530     }
 531     if( current_rate > target_rate ) {
 532         current_rate = target_rate;
 533     }
 534
 535     // steps per second
 536     STEPPER[c]->set_speed(current_rate);
 537 }
 538
 539 // issue a coordinated move directly to robot, and return when done
 540 // Only move the coordinates that are passed in as not nan
 541 // NOTE must use G53 to force move in machine coordiantes and ignore any WCS offsetts
 542 void ZProbe::coordinated_move(float x, float y, float z, float feedrate, bool relative)
 543 {
 544     char buf[32];
 545     char cmd[64];
 546
 547     if(relative) strcpy(cmd, "G91 G0 ");
 548     else strcpy(cmd, "G53 G0 "); // G53 forces movement in machine coordinate system
 549
 550     if(!isnan(x)) {
 551         int n = snprintf(buf, sizeof(buf), " X%1.3f", x);
 552         strncat(cmd, buf, n);
 553     }
 554     if(!isnan(y)) {
 555         int n = snprintf(buf, sizeof(buf), " Y%1.3f", y);
 556         strncat(cmd, buf, n);
 557     }
 558     if(!isnan(z)) {
 559         int n = snprintf(buf, sizeof(buf), " Z%1.3f", z);
 560         strncat(cmd, buf, n);
 561     }
 562
 563     // use specified feedrate (mm/sec)
 564     int n = snprintf(buf, sizeof(buf), " F%1.1f", feedrate * 60); // feed rate is converted to mm/min
 565     strncat(cmd, buf, n);
 566     if(relative) strcat(cmd, " G90");
 567
 568     //THEKERNEL->streams->printf("DEBUG: move: %s\n", cmd);
 569
 570     // send as a command line as may have multiple G codes in it
 571     struct SerialMessage message;
 572     message.message = cmd;
 573     message.stream = &(StreamOutput::NullStream);
 574     THEKERNEL->call_event(ON_CONSOLE_LINE_RECEIVED, &message );
 575     THEKERNEL->conveyor->wait_for_empty_queue();
 576 }
 577
 578 // issue home command
 579 void ZProbe::home()
 580 {
 581     Gcode gc("G28", &(StreamOutput::NullStream));
 582     THEKERNEL->call_event(ON_GCODE_RECEIVED, &gc);
 583 }
 584
 585 float ZProbe::zsteps_to_mm(float steps)
 586 {
 587     return steps / Z_STEPS_PER_MM;
 588 }