Support dual x-carriage printers

Dual x-carriage designs offer some substantial improvements for dual
extruder printing.

Marlin/Configuration_adv.h

   #define EXTRUDERS 1
 #endif
 
+// Enable this for dual x-carriage printers. 
+// A dual x-carriage design has the advantage that the inactive extruder can be parked which
+// prevents hot-end ooze contaminating the print. It also reduces the weight of each x-carriage
+// allowing faster printing speeds.
+#define DUAL_X_CARRIAGE
+#ifdef DUAL_X_CARRIAGE
+// Configuration for second X-carriage
+// Note: the first x-carriage is defined as the x-carriage which homes to the minimum endstop;
+// the second x-carriage always homes to the maximum endstop.
+#define X2_MIN_POS 88     // set minimum to ensure second x-carriage doesn't hit the parked first X-carriage
+#define X2_MAX_POS 350.45 // set maximum to the distance between toolheads when both heads are homed 
+#define X2_HOME_DIR 1     // the second X-carriage always homes to the maximum endstop position
+#define X2_HOME_POS X2_MAX_POS // default home position is the maximum carriage position 
+    // However: In this mode the EXTRUDER_OFFSET_X value for the second extruder provides a software 
+    // override for X2_HOME_POS. This also allow recalibration of the distance between the two endstops
+    // without modifying the firmware (through the "M218 T1 X???" command).
+    // Remember: you should set the second extruder x-offset to 0 in your slicer.
+
+// Pins for second x-carriage stepper driver (defined here to avoid further complicating pins.h)
+#define X2_ENABLE_PIN 29
+#define X2_STEP_PIN 25
+#define X2_DIR_PIN 23
+
+// The following settings control the behaviour of the automatic parking and unparking of inactive extruder
+#define TOOLCHANGE_PARK_ZLIFT 0.1        // the distance to raise Z axis when parking an extruder
+#define TOOLCHANGE_UNPARK_ZLIFT 1        // the distance to raise Z axis when unparking an extruder
+#define TOOLCHANGE_UNPARK_SKIP_TRAVEL_MOVES // disable if slicer natively suports dual x-carriage mode. 
+    // When enabled this avoids unnecessary & inadvertant moves from the last position of old extruder. 
+#endif // DUAL_X_CARRIAGE
+    
 //homing hits the endstop, then retracts by this distance, before it tries to slowly bump again:
 #define X_HOME_RETRACT_MM 5 
 #define Y_HOME_RETRACT_MM 5 

Marlin/Marlin.h

 
 void manage_inactivity();
 
-#if defined(X_ENABLE_PIN) && X_ENABLE_PIN > -1
+#if defined(DUAL_X_CARRIAGE) && defined(X_ENABLE_PIN) && X_ENABLE_PIN > -1 \
+    && defined(X2_ENABLE_PIN) && X2_ENABLE_PIN > -1
+  #define  enable_x() do { WRITE(X_ENABLE_PIN, X_ENABLE_ON); WRITE(X2_ENABLE_PIN, X_ENABLE_ON); } while (0)
+  #define disable_x() do { WRITE(X_ENABLE_PIN,!X_ENABLE_ON); WRITE(X2_ENABLE_PIN,!X_ENABLE_ON); } while (0)
+#elif defined(X_ENABLE_PIN) && X_ENABLE_PIN > -1
   #define  enable_x() WRITE(X_ENABLE_PIN, X_ENABLE_ON)
   #define disable_x() WRITE(X_ENABLE_PIN,!X_ENABLE_ON)
 #else

Marlin/Marlin_main.cpp

 XYZ_CONSTS_FROM_CONFIG(float, home_retract_mm, HOME_RETRACT_MM);
 XYZ_CONSTS_FROM_CONFIG(signed char, home_dir,  HOME_DIR);
 
+#ifdef DUAL_X_CARRIAGE
+  #if EXTRUDERS == 1 || defined(COREXY) \
+      || !defined(X2_ENABLE_PIN) || !defined(X2_STEP_PIN) || !defined(X2_DIR_PIN) \
+      || !defined(X2_HOME_POS) || !defined(X2_MIN_POS) || !defined(X2_MAX_POS) \
+      || !defined(X_MAX_PIN) || X_MAX_PIN < 0
+    #error "Missing or invalid definitions for DUAL_X_CARRIAGE mode."
+  #endif
+  #if X_HOME_DIR != -1 || X2_HOME_DIR != 1
+    #error "Please use canonical x-carriage assignment" // the x-carriages are defined by their homing directions
+  #endif  
+    
+static float x_home_pos(int extruder) {
+  if (extruder == 0)
+    return base_home_pos(X_AXIS) + add_homeing[X_AXIS];
+  else
+    // In dual carriage mode the extruder offset provides an override of the
+    // second X-carriage offset when homed - otherwise X2_HOME_POS is used.
+    // This allow soft recalibration of the second extruder offset position without firmware reflash 
+    // (through the M218 command).
+    return (extruder_offset[X_AXIS][1] != 0) ? extruder_offset[X_AXIS][1] : X2_HOME_POS;
+}
+
+static int x_home_dir(int extruder) {
+  return (extruder == 0) ? X_HOME_DIR : X2_HOME_DIR;
+}
+
+static bool active_extruder_parked = false;
+static float raised_parked_position[NUM_AXIS];
+static unsigned long delayed_move_time = 0;
+#endif     
+
 static void axis_is_at_home(int axis) {
+#ifdef DUAL_X_CARRIAGE
+  if (axis == X_AXIS && active_extruder != 0) {
+    current_position[X_AXIS] = x_home_pos(active_extruder);
+    min_pos[X_AXIS] =          X2_MIN_POS;
+    max_pos[X_AXIS] =          X2_MAX_POS;
+    return;
+  }
+#endif  
   current_position[axis] = base_home_pos(axis) + add_homeing[axis];
   min_pos[axis] =          base_min_pos(axis) + add_homeing[axis];
   max_pos[axis] =          base_max_pos(axis) + add_homeing[axis];
 static void homeaxis(int axis) {
 #define HOMEAXIS_DO(LETTER) \
   ((LETTER##_MIN_PIN > -1 && LETTER##_HOME_DIR==-1) || (LETTER##_MAX_PIN > -1 && LETTER##_HOME_DIR==1))
+
   if (axis==X_AXIS ? HOMEAXIS_DO(X) :
       axis==Y_AXIS ? HOMEAXIS_DO(Y) :
       axis==Z_AXIS ? HOMEAXIS_DO(Z) :
       0) {
+    int axis_home_dir = home_dir(axis);
+#ifdef DUAL_X_CARRIAGE
+    if (axis == X_AXIS)
+      axis_home_dir = x_home_dir(active_extruder);
+#endif
 
     // Engage Servo endstop if enabled
     #ifdef SERVO_ENDSTOPS
       {
         current_position[X_AXIS] = 0;current_position[Y_AXIS] = 0;
 
+       #ifdef DUAL_X_CARRIAGE
+        int x_axis_home_dir = home_dir(X_AXIS);
+       #else
+        int x_axis_home_dir = x_home_dir(active_extruder);
+       #endif
+        
         plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
-        destination[X_AXIS] = 1.5 * X_MAX_LENGTH * X_HOME_DIR;destination[Y_AXIS] = 1.5 * Y_MAX_LENGTH * Y_HOME_DIR;
+        destination[X_AXIS] = 1.5 * max_length(X_AXIS) * x_axis_home_dir;destination[Y_AXIS] = 1.5 * max_length(Y_AXIS) * home_dir(Y_AXIS);
         feedrate = homing_feedrate[X_AXIS];
         if(homing_feedrate[Y_AXIS]<feedrate)
           feedrate =homing_feedrate[Y_AXIS];
 
       if((home_all_axis) || (code_seen(axis_codes[X_AXIS])))
       {
+      #ifdef DUAL_X_CARRIAGE
+        int tmp_extruder = active_extruder;
+        active_extruder = !active_extruder;
+        HOMEAXIS(X);
+        active_extruder = tmp_extruder;
+        active_extruder_parked = false; 
+        delayed_move_time = 0;
+      #endif         
         HOMEAXIS(X);
       }
 
         }
       }
       plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
-#endif // DELTA
+#endif // else DELTA
           
       #ifdef ENDSTOPS_ONLY_FOR_HOMING
         enable_endstops(false);
       if(tmp_extruder != active_extruder) {
         // Save current position to return to after applying extruder offset
         memcpy(destination, current_position, sizeof(destination));
+      #ifdef DUAL_X_CARRIAGE
+        if (Stopped == false && delayed_move_time == 0 && current_position[X_AXIS] != x_home_pos(active_extruder))
+        {
+          // Park old head: 1) raise 2) move to park position 3) lower
+          plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS] + TOOLCHANGE_PARK_ZLIFT, 
+                current_position[E_AXIS], max_feedrate[Z_AXIS], active_extruder);
+          plan_buffer_line(x_home_pos(active_extruder), current_position[Y_AXIS], current_position[Z_AXIS] + TOOLCHANGE_PARK_ZLIFT, 
+                current_position[E_AXIS], max_feedrate[X_AXIS], active_extruder);
+          plan_buffer_line(x_home_pos(active_extruder), current_position[Y_AXIS], current_position[Z_AXIS], 
+                current_position[E_AXIS], max_feedrate[Z_AXIS], active_extruder);
+          st_synchronize();
+        }
+        
+        // only apply Y extruder offset in dual x carriage mode (x offset is already used in determining home pos)
+        current_position[Y_AXIS] = current_position[Y_AXIS] -
+                     extruder_offset[Y_AXIS][active_extruder] +
+                     extruder_offset[Y_AXIS][tmp_extruder];
+                     
+        active_extruder = tmp_extruder;
+
+        // Inactive head always starts at its parked position.
+        axis_is_at_home(X_AXIS);
+
+        // record raised toolhead position for use by unpark
+        memcpy(raised_parked_position, current_position, sizeof(raised_parked_position));
+        raised_parked_position[Z_AXIS] += TOOLCHANGE_UNPARK_ZLIFT;
+        
+        active_extruder_parked = true;
+        delayed_move_time = 0;
+      #else    
         // Offset extruder (only by XY)
         int i;
         for(i = 0; i < 2; i++) {
         }
         // Set the new active extruder and position
         active_extruder = tmp_extruder;
+      #endif //else DUAL_X_CARRIAGE
         plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
         // Move to the old position if 'F' was in the parameters
         if(make_move && Stopped == false) {
                      active_extruder);
   }
 #else
+
+#if defined(DUAL_X_CARRIAGE)
+  if (active_extruder_parked)
+  {
+    if (current_position[E_AXIS] == destination[E_AXIS])
+    {
+      // this is a travel move
+#ifdef TOOLCHANGE_UNPARK_SKIP_TRAVEL_MOVES
+      if (delayed_move_time != 0xFFFFFFFFUL)
+      {
+        // skip this move but still update current_position in main so that it can 
+        // be used as starting position before extrusion (but not in planner)
+        memcpy(current_position, destination, sizeof(current_position)); 
+        if (destination[Z_AXIS] > raised_parked_position[Z_AXIS])
+          raised_parked_position[Z_AXIS] = destination[Z_AXIS];
+        delayed_move_time = millis();
+        return;
+      }
+      delayed_move_time = 0;
+#else
+      // this will cause the unpark code below to execute the specified lift in moving to the initial (travel move) position.
+      memcpy(current_position, destination, sizeof(current_position)); 
+#endif      
+    }
+    // unpark extruder: 1) raise, 2) move into starting XY position, 3) lower
+    plan_buffer_line(raised_parked_position[X_AXIS], raised_parked_position[Y_AXIS], raised_parked_position[Z_AXIS],    current_position[E_AXIS], max_feedrate[Z_AXIS], active_extruder);
+    plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], raised_parked_position[Z_AXIS], 
+        current_position[E_AXIS], min(max_feedrate[X_AXIS],max_feedrate[Y_AXIS]), active_extruder);
+    plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], 
+        current_position[E_AXIS], max_feedrate[Z_AXIS], active_extruder);
+    active_extruder_parked = false;
+  }
+#endif //DUAL_X_CARRIAGE
+
   // Do not use feedmultiply for E or Z only moves
   if( (current_position[X_AXIS] == destination [X_AXIS]) && (current_position[Y_AXIS] == destination [Y_AXIS])) {
       plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate/60, active_extruder);
        || !READ(E2_ENABLE_PIN)
     #endif
     #if EXTRUDER > 1
+      #if defined(X2_ENABLE_PIN) && X2_ENABLE_PIN > -1
+       || !READ(X2_ENABLE_PIN)
+      #endif
        || !READ(E1_ENABLE_PIN)
     #endif
        || !READ(E0_ENABLE_PIN)) //If any of the drivers are enabled...
      WRITE(E0_ENABLE_PIN,oldstatus);
     }
   #endif
+  #if defined(DUAL_X_CARRIAGE) && defined(TOOLCHANGE_UNPARK_SKIP_TRAVEL_MOVES)
+    // handle delayed move timeout
+    if (delayed_move_time != 0 && (millis() - delayed_move_time) > 1000)
+    {
+      // travel moves have been received so enact them
+      delayed_move_time = 0xFFFFFFFFUL; // force moves to be done
+      memcpy(destination,current_position,sizeof(destination));
+      prepare_move(); 
+    }
+  #endif  
   check_axes_activity();
 }
 

Marlin/stepper.cpp

 
     // Set the direction bits (X_AXIS=A_AXIS and Y_AXIS=B_AXIS for COREXY)
     if((out_bits & (1<<X_AXIS))!=0){
-      WRITE(X_DIR_PIN, INVERT_X_DIR);
+      #ifdef DUAL_X_CARRIAGE
+      if (active_extruder != 0)
+        WRITE(X2_DIR_PIN,INVERT_X_DIR);
+      else
+      #endif        
+        WRITE(X_DIR_PIN, INVERT_X_DIR);
       count_direction[X_AXIS]=-1;
     }
     else{
-      WRITE(X_DIR_PIN, !INVERT_X_DIR);
+      #ifdef DUAL_X_CARRIAGE
+      if (active_extruder != 0)
+        WRITE(X2_DIR_PIN,!INVERT_X_DIR);
+      else
+      #endif        
+        WRITE(X_DIR_PIN, !INVERT_X_DIR);
       count_direction[X_AXIS]=1;
     }
     if((out_bits & (1<<Y_AXIS))!=0){
     #endif
       CHECK_ENDSTOPS
       {
-        #if defined(X_MIN_PIN) && X_MIN_PIN > -1
-          bool x_min_endstop=(READ(X_MIN_PIN) != X_ENDSTOPS_INVERTING);
-          if(x_min_endstop && old_x_min_endstop && (current_block->steps_x > 0)) {
-            endstops_trigsteps[X_AXIS] = count_position[X_AXIS];
-            endstop_x_hit=true;
-            step_events_completed = current_block->step_event_count;
-          }
-          old_x_min_endstop = x_min_endstop;
-        #endif
+        #ifdef DUAL_X_CARRIAGE
+        // with 2 x-carriages, endstops are only checked in the homing direction for the active extruder
+        if ((active_extruder == 0 && X_HOME_DIR == -1) || (active_extruder != 0 && X2_HOME_DIR == -1))
+        #endif          
+        {
+          #if defined(X_MIN_PIN) && X_MIN_PIN > -1
+            bool x_min_endstop=(READ(X_MIN_PIN) != X_ENDSTOPS_INVERTING);
+            if(x_min_endstop && old_x_min_endstop && (current_block->steps_x > 0)) {
+              endstops_trigsteps[X_AXIS] = count_position[X_AXIS];
+              endstop_x_hit=true;
+              step_events_completed = current_block->step_event_count;
+            }
+            old_x_min_endstop = x_min_endstop;
+          #endif
+        }
       }
     }
     else { // +direction
       CHECK_ENDSTOPS 
       {
-        #if defined(X_MAX_PIN) && X_MAX_PIN > -1
-          bool x_max_endstop=(READ(X_MAX_PIN) != X_ENDSTOPS_INVERTING);
-          if(x_max_endstop && old_x_max_endstop && (current_block->steps_x > 0)){
-            endstops_trigsteps[X_AXIS] = count_position[X_AXIS];
-            endstop_x_hit=true;
-            step_events_completed = current_block->step_event_count;
-          }
-          old_x_max_endstop = x_max_endstop;
-        #endif
+        #ifdef DUAL_X_CARRIAGE
+        // with 2 x-carriages, endstops are only checked in the homing direction for the active extruder
+        if ((active_extruder == 0 && X_HOME_DIR == 1) || (active_extruder != 0 && X2_HOME_DIR == 1))
+        #endif          
+        {
+          #if defined(X_MAX_PIN) && X_MAX_PIN > -1
+            bool x_max_endstop=(READ(X_MAX_PIN) != X_ENDSTOPS_INVERTING);
+            if(x_max_endstop && old_x_max_endstop && (current_block->steps_x > 0)){
+              endstops_trigsteps[X_AXIS] = count_position[X_AXIS];
+              endstop_x_hit=true;
+              step_events_completed = current_block->step_event_count;
+            }
+            old_x_max_endstop = x_max_endstop;
+          #endif
+        }  
       }
     }
 
 
         counter_x += current_block->steps_x;
         if (counter_x > 0) {
-          WRITE(X_STEP_PIN, !INVERT_X_STEP_PIN);
+          #ifdef DUAL_X_CARRIAGE
+          if (active_extruder != 0)
+            WRITE(X2_STEP_PIN,!INVERT_X_STEP_PIN);
+          else
+          #endif        
+            WRITE(X_STEP_PIN, !INVERT_X_STEP_PIN);
           counter_x -= current_block->step_event_count;
           count_position[X_AXIS]+=count_direction[X_AXIS];   
-          WRITE(X_STEP_PIN, INVERT_X_STEP_PIN);
+          #ifdef DUAL_X_CARRIAGE
+          if (active_extruder != 0)
+            WRITE(X2_STEP_PIN,INVERT_X_STEP_PIN);
+          else
+          #endif        
+            WRITE(X_STEP_PIN, INVERT_X_STEP_PIN);
         }
   
         counter_y += current_block->steps_y;
   #if defined(X_DIR_PIN) && X_DIR_PIN > -1
     SET_OUTPUT(X_DIR_PIN);
   #endif
+  #if defined(X2_DIR_PIN) && X2_DIR_PIN > -1
+    SET_OUTPUT(X2_DIR_PIN);
+  #endif
   #if defined(Y_DIR_PIN) && Y_DIR_PIN > -1 
     SET_OUTPUT(Y_DIR_PIN);
   #endif
     SET_OUTPUT(X_ENABLE_PIN);
     if(!X_ENABLE_ON) WRITE(X_ENABLE_PIN,HIGH);
   #endif
+  #if defined(X2_ENABLE_PIN) && X2_ENABLE_PIN > -1
+    SET_OUTPUT(X2_ENABLE_PIN);
+    if(!X_ENABLE_ON) WRITE(X2_ENABLE_PIN,HIGH);
+  #endif
   #if defined(Y_ENABLE_PIN) && Y_ENABLE_PIN > -1
     SET_OUTPUT(Y_ENABLE_PIN);
     if(!Y_ENABLE_ON) WRITE(Y_ENABLE_PIN,HIGH);
     WRITE(X_STEP_PIN,INVERT_X_STEP_PIN);
     disable_x();
   #endif  
+  #if defined(X2_STEP_PIN) && (X2_STEP_PIN > -1) 
+    SET_OUTPUT(X2_STEP_PIN);
+    WRITE(X2_STEP_PIN,INVERT_X_STEP_PIN);
+    disable_x();
+  #endif  
   #if defined(Y_STEP_PIN) && (Y_STEP_PIN > -1) 
     SET_OUTPUT(Y_STEP_PIN);
     WRITE(Y_STEP_PIN,INVERT_Y_STEP_PIN);

README.md

 *   Heater power reporting. Useful for PID monitoring.
 *   PID tuning
 *   CoreXY kinematics (www.corexy.com/theory.html)
+*   Delta kinematics
+*   Dual X-carriage support for multiple extruder systems
 *   Configurable serial port to support connection of wireless adaptors.
 *   Automatic operation of extruder/cold-end cooling fans based on nozzle temperature
 *   RC Servo Support, specify angle or duration for continuous rotation servos.