Retrofitting Mikron WF41C: Distance coded homing success

distance = raw_position - position-fb // position-fb contains the distance travelled since second reset if (home_latch_v > 0) { if (distance > nominal spacing) // hit mark then delta position = nominal spacing * (distance - floor(distance)) / delta + delta + position-fb } else { position = nominal spacing * (ceil(distance) - distance) / delta + position-fb } } else { if (distance < nominal spacing) // hit mark then delta position = nominal spacing * (distance - floor(distance)) / delta + delta + position-fb } else { position = nominal spacing * (ceil(distance) - distance) / delta + position-fb } }

# activating distance coded homing (@andypugh I there is more than one parameter assiciated with distance coded homing I kept the explicit activation) HOME_DISTANCE_CODED = 1 # Nominal steps between two index marks on the equally spaced index sequence HOME_DISTANCE_CODED_N = 1000 # amount of pulses consumed by the control during one analog signal period (typically interpolation factor times 4 for quadrature) HOME_DISTANCE_CODED_OS = 20 # width of index-pulse as provided to LinuxCNC (see comments below) HOME_DISTANCE_CODED_PW = 2

case HOME_SET_INDEX_POSITION: if((H[joint_num].home_flags & HOME_DISTANCE_CODED) && (nr_ref_marks < 1)) { /* Searches for the first reference mark and store its raw encoder position in 'raw_trigger_1'. Then it resets the homing state to HOMEO_INDEX_SEARCH_START to look for the the second homing mark */ raw_trigger_1 = joint->motor_pos_raw_fb - round(joint->pos_fb * H[joint_num].encoder_scale); ++nr_ref_marks; H[joint_num].home_state = HOME_INDEX_SEARCH_START; //sent it back to index mark search }else if((H[joint_num].home_flags & HOME_DISTANCE_CODED) && (nr_ref_marks < 2)){ raw_trigger_2 = joint->motor_pos_raw_fb - round(joint->pos_fb * H[joint_num].encoder_scale); ++nr_ref_marks; // calculate and set the 'home_offset' based on raw_trigger_pos_1, raw_trigger_pos_2 int position = distance_coded_position( raw_trigger_1, raw_trigger_2, H[joint_num].home_distance_coded_n, H[joint_num].home_distance_coded_os, H[joint_num].home_distance_coded_pw ); H[joint_num].home_offset = (double)position / H[joint_num].encoder_scale; }else{ /* This state is called when the encoder has been reset at the index pulse position. It sets the current joint position to 'home_offset', which is the location of the index pulse in joint coordinates. */ /* set the current position to 'home_offset' */ joint->motor_offset = - H[joint_num].home_offset; joint->pos_fb = joint->motor_pos_fb - (joint->backlash_filt + joint->motor_offset); joint->pos_cmd = joint->pos_fb; joint->free_tp.curr_pos = joint->pos_fb; if (H[joint_num].home_flags & HOME_INDEX_NO_ENCODER_RESET) { /* Special case: encoder does not reset on index pulse. This moves the internal position but does not affect the motor position */ offset = H[joint_num].home_offset - joint->pos_fb; joint->pos_cmd += offset; joint->pos_fb += offset; joint->free_tp.curr_pos += offset; joint->motor_offset -= offset; } /* next state */ H[joint_num].home_state = HOME_FINAL_MOVE_START; immediate_state = 1; nr_ref_marks = 0; break; }

int distance_coded_position(double raw_trigger_1, double raw_trigger_2, int nominal_steps, int over_sampling, int index_pulswidth) { /* This function calculates the absolut position of the second trigger signal on a distance coded glasscale (e.g. Heidenhain LS***C) as a integer number of signal pulses after interpolation and quadrature if enabled. 'raw_trigger_1' is the raw encoder position of the first index-mark found during homing and 'raw_trigger_2' that of the second one. 'nominal_steps' is the nominal number of analog signals (before interpolation and quadrature) between constant space series of index mark on the glasscale (approximately twice the distance between two neighbouring index marks). 'over_sampling' defines how many signals LinuxCNC receives while travling over one analog signal period i.e. the interpolation factor times four if quadrature is enabled. 'index_pulswidth' is the width of the index-signal after interpolation and quadrature in units of regular distance pulses (typically the value is two). */ int Mrr = (round(raw_trigger_1) - round(raw_trigger_2)) / over_sampling; int R = 2 * ABS(Mrr) - nominal_steps; int P1 = ((ABS(R) - SGN(R) - 1) * nominal_steps / 2 + (SGN(R) - SGN(Mrr)) * ABS(Mrr) / 2) * over_sampling + SGN(Mrr) * index_pulswidth / 2; return P1; }