BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is related to construction, civil engineering, structural engineering, advanced manufacturing, additive manufacturing, robotics, concrete technology, and pottery.

In particular, the present invention features an integrated system and method for quality monitoring and control during additive manufacturing (AM; i.e., 3D printing). Specifically, the present invention features an electrical impedance-based approach for a non-destructive, automated and in situ method for quality monitoring and control during 3D printing, a layer-by-layer extrusion process, of structures and components made of concrete/cementitious materials, ceramic, or clay. The quality of printing is monitored in situ by continuously measuring the impedance change of the printing material and product with time during the printing process, through four-point probing with movable electrodes carried by the printer head, robot arms or gantry system. This generates a real-time fingerprint of the printing process, shown as the electrical response signature comprising measured impedance and capacitance curves as a function of printing time, printing path and printing location. Characteristics of the fingerprint curves provide key information on the 3D printing process and quality. In addition to real-time quality monitoring, real-time quality control can also be achieved by establishing a closed-loop control, feeding the measured electrical signal back to the controller of the printer, robotic arms or gantry system. This provides real-time and in situ adjustment of the pumping force, printing speed, material ingredients supply, or the reversal of the printing path to remove imperfections, in order to control and assure quality of the 3D printing concrete structural product.

Background Art

Concrete additive manufacturing (AM), otherwise known as concrete 3D printing, is an exponentially emerging technology in the construction industry. Different from the conventional concrete casting method with prefabricated formworks, concrete AM uses robotic arms or computer-controlled gantry cranes to deposit concrete in a layer-by-layer method to achieve versatile structural geometries. Concrete AM allows for tremendous opportunities in the construction industry, architectural design, land-based and offshore wind industry, wave energy devices, military defense, rapid deployment, and NASA space exploration. It enables rapid and automated construction of concrete structures or components with reduced costs of labors and materials, removal of cumbersome formworks, increased reliability, versatile geometries, and allows construction in harsh and less accessible environments.

There has been a lack of approach to monitor the quality of 3D printing concrete and structural components during this AM process. The 3D printing process will inevitably introduce imperfections, such as material deposition discontinuities, non-homogeneities, flaws, pores, and printing interlayers into the structural components. These imperfections will greatly affect the quality of 3D printed concrete components and their bonding with steel reinforcements, and eventually greatly affect the structural performance, safety and durability. In current practices, the best available approach is visual inspection. This method, however, is subjective, limited to surface features, and does not provide any quantitative measurements that can be used for assessing and controlling the quality of the printed products.

Currently, there is no real-time quality control and monitoring method available for the additive manufacturing of concrete-, cement-, ceramics-, or clay-based materials. Compared with visual inspection, this present invention is more accurate, quantitative rather than subjective, real-time, in situ, and offers spatial resolution of concrete quality, imperfections, and strength development at every location along the printing path. In addition, this automated process is much less labor-intensive and cheaper than visual inspection. It is also low-cost because this method does not require installation of expensive sensors; rather, it engages the material and product that are being 3D printed to behave as a sensing media and only uses highly cheap electrodes (not sensors) for injecting AC current and collecting impedance data. Therefore, this method provides both spatial-continuous and time-continuous information on the 3D printing process and quality. Furthermore, the invention allows closed-loop control: the real-time monitored electrical data can be fed into the controller system of the printing equipment (e.g., robotic arm or gantry printer) to adjust the printing speed and path, material ingredients supply and flow during in situ manufacturing for improving and controlling the quality of the 3D printed products. This unprecedented quality control and assurance method will lead to higher quality, more reliable concrete products with safer, stronger, and more durable performance and less initial costs as well as lifecycle costs.

The field of concrete 3D printing/additive manufacturing is rapidly emerging in Research & Development and industrial applications. Yet this invention is novel because currently there is no quality monitoring and control methods available for concrete 3D printing/additive manufacturing, except visual inspection that is subjective and only limited to surface features. The present invention will address the bottleneck of quality control for achieving reliable 3D printed concrete structural products with increasing confidence to meet society's safety, economical, and efficiency demands.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the present invention to provide systems, methods, and electrical signatures (fingerprints) and their characteristics that allow for real-time and automated monitoring, measurement and control of 3D printed concrete quality during the AM process, as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

The present invention features: 1) a system of four electrodes (a four-point probing system), two of which are automatically carried by the printing head at the same time as concrete printing proceeds and two of which are located at the baseline layer of the printing path for a closed-loop four-point probing system; 2) a system of 3D printing and monitoring using the four-point probing system and in some embodiments of the present invention, a two-point probing system can be used; 3) a method of in situ electrical impedance, resistance or capacitance measurement as a function of time with movable electrodes during 3D printing using the systems described herein; 4) a method of using the systems described herein for monitoring the quality of 3D printing; 5) a method of using the systems described herein to control and adjust the quality of 3D printing; and 6) using the systems described herein, obtaining a fingerprint or electrical response signature or characteristic curve of 3D printing comprising printing quality, path and time characteristics. This unique design of closed-loop probing and real-time generation of fingerprints allow for a method of continuous monitoring that is based on continuously measuring electrical impedance change (or resistance, capacitance, phase angle) of the fresh material product additively manufactured (e.g., concrete, cement, ceramic, day) during the printing process. The real-time measured impedance, resistance and capacitance curves as a function of printing time, printing path and printing location represent an electrical response signature or the fingerprint of the 3D printed concrete product. This fingerprint contains critical and necessary information on the changes of printing quality with time and along the printing path, allowing the real-time detection of location and severity of imperfections. The fingerprint also enables monitoring and quantifying concrete strength development during printing. Furthermore, the system allows closed-loop control to assure the printing quality through real-time adjustment and corrections of the printing parameters such as pumping speed and force, material flow, and printing path.

One of the unique and inventive technical features of the present invention is the set of four electrodes uniquely located to allow a closed-loop four-point probing system integrated with the AM or 3D printing process. Two electrodes are attached to the movable printer head, and two electrodes are attached to the baseline layer of the printing path. The two electrodes attached to the printer head are automatically carried by the printing head at the same time as concrete printing proceeds. Without wishing to limit the invention to any theory or mechanism, it is believed that the closed-loop four-point probing system of the present invention advantageously provides for an electrical impedance-based method for generating electrical response signatures or fingerprints for real-time monitoring of 3D printing concrete quality, imperfections, and strength development during the AM process.

A second unique and inventive technical feature of the present invention is the integration of impedance data collection with the printing process, as two of the electrodes move along with the printing head to be at the same locations at the same time along the printing path.

A third unique and inventive technical feature of the present invention is to engage the printing material (e.g., concrete or cementitious material) to behave as a sensor or a sensing media for monitoring the quality of the material or product itself, without installing or embedding actual sensors. This approach turns the printing material (e.g., concrete or cementitious material) into a self-sensing material, and the impedance data collected from the printing material provides spatially continuous information (or resolution) as well as time-continuous information on printing quality and product strength, wherever the material is located.

A fourth unique and inventive technical feature of the present invention is to use the fingerprints generated in real-time by the systems described herein, to extract key information on the printing process and quality change as a function of printing time and path, and to timely identify occurrences and locations of printing imperfections and flaws.

A fifth unique and inventive technical feature of the present invention is the closed-loop control by feeding the measured electrical signal back to the controller of the 3D printer to provide real-time and in situ adjustment of the pumping force, printing speed, material ingredients supply, or the reverse of the printing path to remove imperfections, in order to control and assure quality of the 3D printing concrete structural product. As prior quality control systems are based on visual inspection that is subjective and only limited to surface features and/or installation of expensive sensors, none of the presently known prior references or work has the unique design of the present invention comprising a closed-loop four-point probing system using inexpensive electrodes (not sensors) integrated with an automated printing process to generate real-time, electrical signatures or fingerprints of the printed material product; none of the presently known prior references or work has the unique method of obtaining as well as interpreting the electrical signatures or fingerprints of the printed material product to provide information on printing quality and location of imperfections.

Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.

