Post Processor for robot 3D printing

This section shows how to modify a robot post processor to calculate the extruder speed before executing a movement instruction for 3D printing. Alternatively, these operations can be made on the robot controller with the Extruder program call (default command to drive the extruder).

By customizing a robot post processor, it is possible to make the integration of an extruder for 3D printing easier before sending the program to the robot. To accomplish such task, we need to do some calculations and output customized code when the program is generated in the robot post processor.

The first step is to intercept the Extruder calls and read the new Extruder values (E values) inside the RunCode section in the post processor. The following section processes all program calls generated for a program:

    def RunCode(self, code, is_function_call = False):

        if is_function_call:

            if code.startswith("Extruder("):

                # Intercept the extruder command.

                # if the program call is Extruder(123.56)

                # we extract the number as a string

                # and convert it to a number

                self.PRINT_E_NEW = float(code[9:-1])

                # Skip the program call generation

                return

            else:

                self.addline(code + "()")

        else:

            # Output program code

            self.addline(code)

The Extruder value (length/E) is saved as the PRINT_E_NEW variable in the robot post processor.

We need to trigger a function call named new_move with each new linear movement instruction. We can add this call at the beginning of the MoveL command:

    def MoveL(self, pose, joints, conf_RLF=None):

        """Add a linear movement"""

        # Handle 3D printing Extruder integration

        self.new_move(pose)    

       ...

We must also add the following variables in the header of the post processor to calculate the extruder increments:

 

    # 3D Printing Extruder Setup Parameters:

    PRINT_E_AO = 5 # Analog Output ID to command the extruder flow

    PRINT_SPEED_2_SIGNAL = 0.10 # Ratio to convert the speed/flow to an analog output signal

    PRINT_FLOW_MAX_SIGNAL = 24 # Maximum signal to provide to the Extruder

    PRINT_ACCEL_MMSS = -1 # Acceleration, -1 assumes constant speed if we use rounding/blending

  

    # Internal 3D Printing Parameters

    PRINT_POSE_LAST = None # Last pose printed

    PRINT_E_LAST = 0 # Last Extruder length

    PRINT_E_NEW = None # New Extruder Length

    PRINT_LAST_SIGNAL = None # Last extruder signal

Finally, we need to define a new procedure that will generate appropriate extruder feed commands according to the distance between movements, the robot speed and the robot acceleration. This assumes the extruder feed is driven by a specific analog output or a customized program call.

We need to add the following code before the def MoveL program definition.

 

    def calculate_time(self, distance, Vmax, Amax=-1):

        """Calculate the time to move a distance with Amax acceleration and Vmax speed"""

        if Amax < 0:

            # Assume constant speed (appropriate smoothing/rounding parameter must be set)

            Ttot = distance/Vmax

        else:

            # Assume we accelerate and decelerate

            tacc = Vmax/Amax;

            Xacc = 0.5*Amax*tacc*tacc;

            if distance <= 2*Xacc:

                # Vmax is not reached

                tacc = sqrt(distance/Amax)

                Ttot = tacc*2

            else:

                # Vmax is reached

                Xvmax = distance - 2*Xacc

                Tvmax = Xvmax/Vmax

                Ttot = 2*tacc + Tvmax

        return Ttot

           

    def new_move(self, new_pose):                       

        """Implement the action on the extruder for 3D printing, if applicable"""

        if self.PRINT_E_NEW isNone or new_pose is None:

            return

           

        # Skip the first move and remember the pose

        if self.PRINT_POSE_LAST isNone:

            self.PRINT_POSE_LAST = new_pose

            return         

 

        # Calculate the increase of material for the next movement

        add_material = self.PRINT_E_NEW - self.PRINT_E_LAST

        self.PRINT_E_LAST = self.PRINT_E_NEW

       

        # Calculate the robot speed and Extruder signal

        extruder_signal = 0

        if add_material > 0:

            distance_mm = norm(subs3(self.PRINT_POSE_LAST.Pos(), new_pose.Pos()))

            # Calculate movement time in seconds

            time_s = self.calculate_time(distance_mm, self.SPEED_MMS, self.PRINT_ACCEL_MMSS)

           

            # Avoid division by 0

            if time_s > 0:

                # This may look redundant but it allows you to account for accelerations and we can apply small speed adjustments

                speed_mms = distance_mm / time_s

               

                # Calculate the extruder speed in RPM*Ratio (PRINT_SPEED_2_SIGNAL)

                extruder_signal = speed_mms * self.PRINT_SPEED_2_SIGNAL

       

        # Make sure the signal is within the accepted values

        extruder_signal = max(0,min(self.PRINT_FLOW_MAX_SIGNAL, extruder_signal))

       

        # Update the extruder speed when required

        if self.PRINT_LAST_SIGNAL isNone or abs(extruder_signal - self.PRINT_LAST_SIGNAL) > 1e-6:

            self.PRINT_LAST_SIGNAL = extruder_signal

            # Use the built-in setDO function to set an analog output

            self.setDO(self.PRINT_E_AO, "%.3f"% extruder_signal)

            # Alternatively, provoke a program call and handle the integration with the robot controller

            #self.addline('ExtruderSpeed(%.3f)' % extruder_signal)

       

        # Remember the last pose

        self.PRINT_POSE_LAST = new_pose