A Real-Time Height Measurement and Feedback System for 3D Concrete Printing

Recent years have seen a rapid growth of additive manufacturing methods for concrete construction. Generally, these methods are based on a linear sequence of design -> print path definition -> actual printer actions in a print environment. However, printing experiments show that a large number of parameters influence the printing process. Not all of these can be predicted accurate on forehand. Therefore, a method is introduced that allows real-time adjustment of the print process. As a proof-of-concept, a measurement system for the nozzle height has been developed and tested. Because this variable relates to machine properties, environmental conditions as well as material behaviour, it is a crucial parameter to control. In two case study prints, the effectiveness of the device was shown. In one study, the printer could follow a range of irregular curves in the print bed, whereas only a simple flat rectangular print path had been programmed. In the other, it was shown the print path could be adjusted to vertical deformation of the previous layers of printed filament in a tubular object of several dozen layers. Thus, premature failure through irregular loading of the object during printing was avoided. Further expansion of the use of real-time measurement devices may be anticipated in the future. Besides more advanced geometrical measuring, chemical and physical conditions such as concrete temperature (both before and after deposition), surface wetness, and environment humidity, can be recorded. Combined with the machine action log, this should result in a detailed set of as-built data of the printed object, allowing e.g. for a geometrical clash control with the design as well as other quality controls.