e) Man-machine interaction interface: with convenient interface for operation.

3.3. Motion module

Fig. 3 illustrates the composition of the motion module including structure components, motion tracks, motion sliders, transmission com- ponents, and drive motors. The module comprises of a steel structure: base (L 2.50 m ∗ W 2.25 m); gantry (H 1.75 m ∗ W 2.25 m) with a lifting beam that is equipped with an electronic nozzle; and two transmission components. The lifting beam moves vertically while the gantry moves back and forth along the pair of tracks on the steel frame base, coordi- nately driven by four Panasonic motors. The effective working space is approximately  2.0  m  ∗ 2.0  m  ∗ 2.0  m  for  large  scale  component

Fig. 2. System composition Fig. 3. The motion module and extrusion module

88 J. Xu et al.  /  Automation  in Construction 76 (2017)  85–96

Fig. 4. Design of the extrusion module

manufacture. The motion module has the axis linkage function of XYZ triaxial constant position and zeroing motion, XYZ triaxial linear inter- polation and the circular interpolation motion of any the two axes.

3.4. Extrusion module

This module has a direct impact on material deposition and forming, which contains a pump, a conveying pipe and an electronic nozzle (Fig. 3), with its overall design presented in Fig. 4. A screw pump of 10 L capacity is adopted to provide  uniform  pressure when delivering material, which is controlled by a frequency trans- former. The nozzle relies on an electronic switch, which is a solenoid valve comprising of two electromagnetic coils and a sheet iron that

possess a circular hole. The sheet iron moves left and right to switch the nozzle  by  selectively  powering  the electromagnetic coils.

3.5. Data processing module

The numerical control programs (G code) for controlling the motion and the extrusion modules are accommodated in this module. The soft- ware function interface of this module is shown in Fig. 5. After an STL file is imported into the software, the model (middle area of the interface) goes through a process of model slicing and nozzle path planning (right area of the interface) by setting parameters (left area of the inter- face). The red and blue lines in the right area respectively represent the profile and filling scan lines; the nozzle closes only when moving along

Fig. 5. Software function interface of the data processing module.

J. Xu et al. / Automation in Construction 76 (2017)  85–96 89

the short lines connecting two adjacent filling scan lines at the end- points, which are called ‘jump lines’.

4. Program generation: Algorithms for model slicing and nozzle path planning

The cement mortar placement process of the 3D printing-based con- struction follows the principle of layered superposition, which relies on the model data process. Thus, the realization of this process requires the development of modified algorithms for model slicing and nozzle path

planning proposes.

that are not more than x,ΔZ is the layer thickness. Each sequence number of the incisal planes intersecting with triangular facets can be calculated according to the formulas above to establish a grouped table.

b) Intersecting of the triangular facets and incisal planes: In Fig. 7 a sche- matic of the intersection of an incisal plane and a model triangular facet ABC is presented. The z value of the incisal plane equals to h, with two intersections V1 and V2. The coordinates of points A, B, C are respectively (x1 , y1 , z1), (x2 , y2 , z2),(x3 , y3 , z3). Then the co- ordinate of point V1 is