Search

Mobile robots with manipulators have been more and more commonly applied in extreme and hostile environments to assist or even replace human operators for complex tasks. In addition to autonomous abilities, mobile robots need to facilitate the human–robot interaction control mode that enables human users to easily control or collaborate with robots. This paper proposes a system which uses human gestures to control an autonomous mobile robot integrating a manipulator and a video surveillance platform. A human user can control the mobile robot just as one drives an actual vehicle in the vehicle’s driving cab. The proposed system obtains human’s skeleton joints information using a motion sensing input device, which is then recognized and interpreted into a set of control commands. This is implemented, based on the availability of training data set and requirement of in-time performance, by an adaptive cerebellar model articulation controller neural network, a finite state machine, a fuzzy controller and purposely designed gesture recognition and control command generation systems. These algorithms work together implement the steering and velocity control of the mobile robot in real-time. The experimental results demonstrate that the proposed approach is able to conveniently control a mobile robot using virtual driving method, with smooth manoeuvring trajectories in various speeds. [ABSTRACT FROM AUTHOR]

The structural build-up of cement-based materials is often characterized by the determination of the evolution of static yield stress with time. This property is crucial to many applications of concrete. However, the measurement of static yield stress may disturb the structure of cement-based material. As a consequence, the true structural build-up of the materials may not be detected. In this paper, the evolution of static yield stress and storage modulus (G′) determined by small amplitude oscillatory test was determined to characterize the evolution of the structural build-up of cement pastes. Results showed that G′ and static yield stress developed similarly with time. When the tests were carried out on the same sample, the measurement of static yield stress disturbed the structure of cement paste and had a significant effect on the following measurement of G′, but a slight effect on the following measurement of static yield stress. [ABSTRACT FROM AUTHOR]

• The hydration, structural build-up and strength development of cement pates with different accelerators were investigated. • Accelerators increase the structural build-up rate by different mechanisms. • Mechanical efficiency of C-S-H may give wrong ranking on the efficiency of C-S-H. Fast structural build-up and strength development of fresh/hardened cement-based materials are always desired in many scenarios, where accelerators are often used. In this paper, the hydration, structural build-up and strength development of cement pates with different accelerators were investigated. The growth of static yield stress was used to characterize the structural build-up of fresh cement paste with 1% nano silica. Calorimetric curves, zeta potential and conductivity of pastes and strength development of mortars were also measured. Results showed that accelerators promote the reaction of C 3 S or C 3 A at different stages and in different mechanisms. Mechanical efficiency of C-S-H determined by growth of elastic modulus or yield stress over cumulated hydration heat may give wrong ranking on the efficiency of C-S-H. Apart from formation of C-S-H gel, structural build-up may originate from other sources. [ABSTRACT FROM AUTHOR]

• Buildability of 3D printing mortar was evaluated by the deformation of stacking layers. • A deformation monitoring device was designed to monitor the deformation of printing layer. • An equation between the optimal interval time and structural build-up rate was proposed. The buildability of fresh concrete is of great importance to 3D printing technology. In this paper, the buildability of 3D printing mortar was evaluated from the perspective of deformation of fresh mortar during the process of printing. A deformation monitoring device was designed to monitor the change of deformation of printing layer with stacking. The physical and chemical effects on the evolution of structural build-up were evaluated by the growth rate of static yield stress and penetration resistance. Results showed that the chemical effect was more effective than the physical effect, and the combination of physical and chemical effects was the most effective one. The growth of penetration resistance had a linear relationship with the growth of static yield stress, and both of them can be used to characterize the structural build-up of fresh mortar. The deformation value and optimal printing interval time could be obtained by simulating the printing process using the deformation monitoring device. An equation between the optimal interval time and the growth rate of static yield stress was established. [ABSTRACT FROM AUTHOR]

Highlights • The effect of temperature on the structural buildup of cement pastes with various mineral admixtures was studied. • The hydration kinetics of cement paste was studied by boundary nucleation and growth model. • The relation between hydration kinetics and structural buildup was analyzed. Abstract The temperature dependence of structural build-up is of great importance to some new concrete technologies, such as 3D printing and slip-form casting concrete. In this paper, the structural build-up of cement paste with various mineral admixtures, characterized by the growth of static yield stress, were measured at 10, 20 and 40 °C. They were related with the calorimetric curves of cement paste at various temperatures. Nucleation kinetic (K N) and growth kinetic (K G) were introduced to analyze the hydration dynamics. The results showed that the addition of fly ash and slag were unfavorable for the structural build-up of cement paste at 10 and 20 °C, however, a favorable phenomenon was observed at 40 °C. The additions of nano-CaCO 3 or nano-SiO 2 had positive effect on structural build-up at all temperatures. The incorporation of silica fume had negative effect on structural build-up at 10 °C, while positive effect at 20 and 40 °C. Both the K N and K G played important roles on the structural build-up rate of cement paste. K G contributed more to the temperature dependence of structural build-up than K N. [ABSTRACT FROM AUTHOR]