An investigation of critical success factors for robotic masonry

Automating masonry wall construction faces several challenging mechanical control issues reaching from the dehacking and delivery of bricks, the application of mortar, to actual placement of bricks to create straight and even elements. The first objective of this research work was to study the complex operations done by hand in order to understand what is necessary to meet standards, what affects the brick-mortar interfaces, and what leads to required bond strengths. The Critical Success Factor method was used to identify the most relevant problem areas that needed to be addressed and solved. Using this approach, the following six factors were defined: (1) design automation, (2) dehacking, (3) brick quality control, (4) brick placement quality, (5) mortar application quality, and (6) brick-mortar bond strength. Consequently, each factor was studied followed by the design and execution of necessary experiments. The research showed that isolating these factors was useful in identifying a focused list of topics that affect them. The issue of brick-mortar interaction and its importance in achieving bond strength was especially important in that the skill of a mason had to be replicated with a mechanical approach. Experimental tests showed that the bond strength was affected by the profile of the mortar joint applied and the depth of mortar penetration in the brick holes. The final step of this study included a comparison between robotically and manually placed bricks. Utilizing a standardized Bond Wrench Test apparatus, it was found that the consistency of bond strength values of ten prisms placed robotically matched that of ten prisms laid manually. Mortar application proved to be the most difficult problem. Consistently smooth pulsation-less mortar joints were not achieved even after many redesigns of the progressive cavity pump setup. Conceptual pressure models demonstrated that the resultant pressure at the end of the pumping apparatus, after friction losses and pressure drops, was critical in producing acceptable mortar joints. A modified pump model was recommended for future research. The experiments highlighted the factors affecting mortar pumping using this kind of pumping mechanism, such factors included: (1) the speed of the pump motor drive, (2) the size of the rotor-stator opening, and (3) the length of the rotor-stator assembly. Measuring the pressure inside the pump lay outside the scope of this research but should be the focal point in future work. Overall, the work showed difficulty in achieving established quality standards in masonry construction using robotics. On the other hand, the project solved some unique problems by integrating electronics, computing, and mechanical concepts in innovating ways. For example, the problem of dehacking work led to the design of the pneumatic adaptive brick gripper. For the design of the brick quality control work cell, data collected from a photoelectric sensor was manipulated in order to substitute the human sensory skill of detecting different colors. For applying mortar bed joints, a nozzle plate was redesigned, with the same cross-section as that of a manually placed mortar joint, in order to pump mortar where it is most effective.