Shape memory polymers (SMP) are the smart materials that have received the most attention and are the most commonly employed. SMP can be 4D printed to create prefabricated components with transform ...shapes, properties, or functions under different external excitations. Although smart equipment assembled from these prefabricated components is extensively used in various fields, a systematic overview summary of their design ideas still needs to be provided. This paper briefly analyzes current trends in the design ideas and application of SMP-based prefabricated components. By summarizing two different design ideas: structural combination and material modification, it demonstrates the application of smart equipment assembled from SMP-based prefabricated components in medical, industrial, and aerospace fields. Furthermore, current challenges with both design ideas are discussed.
The current research of reconfigurable parallel mechanism mainly focuses on the construction of reconfigurable joints. Compared with the method of changing the mobility by physical locking joints, ...the geometric constraint has good controllability, and the constructed parallel mechanism has more configurations and wider application range. This paper presents a reconfigurable axis (rA) joint inspired and evolved from Rubik's Cubes, which have a unique feature of geometric and physical constraint of axes of joint. The effectiveness of the rA joint in the construction of the limb is analyzed, resulting in a change in mobility and topology of the parallel mechanism. The rA joint makes the angle among the three axes inside the groove changed arbitrarily. This change in mobility is completed by the case illustrated by a 3(rA)P(rA) reconfigurable parallel mechanism having variable mobility from 1 to 6 and having various special configurations including pure translations, pure rotations. The underlying principle of the metamorphosis of this rA joint is shown by investigating the dependence of the corresponding screw system comprising of line vectors, leading to evolution of the rA joint from two types of spherical joints to three types of variable Hooke joints and one revolute joint. The reconfigurable parallel mechanism alters its topology by rotating or locking the axis of rA joint to turn all limbs into different phases. The prototype of reconfigurable parallel mechanism is manufactured and all configurations are enumerated to verify the validity of the theoretical method by physical experiments.
Exploring the transformation of spatial mechanisms from their unfolded to controlled folding states to meet the requirements of various application scenarios has long been a hot topic in mechanical ...structure research. Although conventional spatial mechanisms can be designed to meet almost any application scenario, the design’s complex and excessive combinations of structural components, kinematic pairs, and drive units are unavoidable. It introduces many problems, such as poor reliability, drive complexity, and control difficulties. Based on 4D printing technology, the design of self-folding spatial mechanisms that use pre-stressed response properties under predetermined thermal excitation to achieve different shrinkage ratios integrates the control and drive system and the structural components and kinematic pairs. It brings novel features of self-folding while effectively avoiding many problems associated with conventional mechanical design. Further, the pre-stressed response model introduces the self-folding spatial mechanisms’ excitation, morphing, and driving investigation. Self-folding spatial mechanisms with different shrinkage ratios were prepared via fused deposition modeling, which verified the theoretical analysis and pre-stress response model and the design’s correctness and feasibility by experiments. The existing 4D printing technology lacks a paradigmatic design method in the application field. Contrarily, this work organically combined the conventional mechanical structure design with materials and fabrication via fused deposition modeling. A systematic study of self-folding spatial mechanisms from structural design to morphing control was carried out. This design is expected to introduce a novel paradigm of 4D printing technology in conventional mechanical design and has considerable application prospects in spherical radar calibration mechanisms.
The use of non-smart materials in structural components and kinematic pairs allows for flexible assembly in practical applications and is promising for aerospace applications. However, this approach ...can result in a complex structure and excessive kinematic pairs, which limits its potential applications due to the difficulty in controlling and actuating the mechanism. While smart materials have been integrated into certain mechanisms, such integration is generally considered a unique design for specific cases and lacks universality. Therefore, organically combining universal mechanism design with smart materials and 4D printing technology, innovating mechanism types, and systematically exploring the interplay between structural design and morphing control remains an open research area. In this work, a novel form-controlled planar folding mechanism is proposed, which seamlessly integrates the control and actuation system with the structural components and kinematic pairs based on the combination of universal mechanism design with smart materials and 4D printing technology, while achieving self-controlled dimensional ratio adjustment under a predetermined thermal excitation. The design characteristics of the mechanism are analyzed, and the required structural design parameters for the preprogrammed design are derived using a kinematic model. Using smart materials and 4D printing technology, folding programs based on material properties and control programs based on manufacturing parameters are encoded into the form-controlled rod to achieve the preprogrammed design of the mechanism. Finally, two sets of prototype mechanisms are printed to validate the feasibility of the design, the effectiveness of the morphing control programs, and the accuracy of the theoretical analysis. This mechanism not only promotes innovation in mechanism design methods but also shows exceptional promise in satellite calibration devices and spacecraft walking systems.
To solve the problem of optimal wavelet basis function selection in feature extraction of motor imagery electroencephalogram (MI-EEG) by wavelet packet transformation (WPT), based on the analysis of ...wavelet packet transformation and wavelet basis parameters, combine with the characteristics of MI-EEG, the characteristics of wavelet basis function suitable for feature extraction of MI-EEG are summarized. On the basis of processing and analyzing of two BCI competition data sets, signal to noise ratio (SNR), root mean squared error (RMSE), classification accuracy, and kappa value are introduced as evaluation criteria for feature extraction effect, it is concluded that the rbio2.2 wavelet basis function is the optimal wavelet basis function for feature extraction of MI-EEG. Finally, the MI-EEG collected in the laboratory is processed and analyzed, further proving that the rbio2.2 wavelet basis function is the optimal wavelet basis function for feature extraction of MI-EEG.
The motor imagery electroencephalography (MI-EEG) reflects the subjective motor intention, which has received increasing attention in rehabilitation. How to extract the features of MI-EEG accurately ...and quickly is the key to its successful application. Based on the analysis and comparison of the existing feature extraction algorithms, a feature extraction method based on principal component analysis (PCA) and deep belief networks (DBN) is proposed, namely PCA-DBN. Firstly, the second-order moment is used to analyze the time-domain of MI-EEG, select the effective time interval. Secondly, PCA is used to analyze the selected time-domain interval and obtain the principal component feature points. Then, feature points are imported into DBN to realize the final feature extraction. Finally, use the softmax classifier to complete task classification. Perform algorithm validation on the BCI Competition II Data set III and BCI Competition IV Data sets 2b, classification accuracies are 96.25% and 91.71%, kappa values are 0.925 and 0.8342. The paired-sample t-test with FDR correction is carried out on the verification results, and the comparison with some better classification algorithms shows that the algorithm has better performance. In the end, this method is used to extract the features of laboratory data, the optimal classification accuracy is 97.69% and kappa value is 0.9538, the validity of the method is further verified.
With the increasingly more extensive application of the medical surgical robot in the clinic, higher requirements have been put forward for medical robots. The bone-attached robot, a popular ...orthopedic robot in recent years, has a tendency of miniaturization and refinement. Thus, a bone-attached parallel manipulator (PM) based on 6-UCU (universal-cylindrical-universal) configuration is proposed, which is characterized by small volume, compact structure, high precision and six-dimensional force feedback. To optimize the structure and make it more compact, the workspace of the 6-UCU PM is analyzed based on the analysis of three kinds of constraint, and workspace model is established through spherical coordinate search method. This study also analyzes the influence of structural parameters on workspace, which may contribute to improving the efficiency of design and ensuring small-sized robots possess relatively large workspace. Moreover, to improve the motion accuracy, an error modeling method is developed based on the structure of 6-UCU PMs. According to this established error model, the output pose error curves are drawn using MATLAB software when the structure parameters change, and the influence of the structure and pose parameters change on the output pose error of PMs is analyzed. The proposed research provides the instruction to design and analysis of small PMs such as bone-attached robots.
The emergence of additive manufacturing technology opens up avenues for developing manufacturing industries, and a clear future direction for additive manufacturing is 4D printing. As a young field, ...it is full of new elements to be researched. In a summary and overview of the current state of research and trends, existing studies are generally manually reviewed and organized. It is susceptible to subjective thinking and knowledge blindness, making it difficult to reflect the current state of research in 4D printing in a comprehensive manner. This paper constructs a visualizing technology identification framework for the global 4D printing research field for manufacturing regarding basic information, technology evolution paths, knowledge structures, and emerging trends through bibliometric techniques and Gephi and CiteSpace software. The purpose of this paper was to provide a systematic, comprehensive, dynamic, quantitative, and objective analysis of the 4D printing research field in order to deepen and refine research in the field, as well as to reveal the overall existing knowledge structure and potential emerging trends. Researchers can use it to understand current research gaps and best practice pathways.
A metamorphic linkage has the property that the effective number of links and joints can change during the movement of the device. This means the kinematic structural representation of a metamorphic ...linkage has different forms in which vertices and edges combine depending on the configuration of the device. In this paper, we use the constraint graph of computational geometry rather than the traditional topological graph to characterize a metamorphic linkage in order to simplify the representation of its configuration changes. A constraint graph has geometric elements as vertices and their relationships as edges. We find that the adjacency sub matrix of the constraint graph provides a convenient description of changes in the topology of links and joints in the operation of the metamorphic linkage. Operations on the adjacency submatrix capture topological changes in a metamorphic linkage. We illustrate our results with several examples.
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