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32 pages, 6211 KiB  
Article
Mechanical Structure Design and Motion Simulation Analysis of a Lower Limb Exoskeleton Rehabilitation Robot Based on Human–Machine Integration
by Chenglong Zhao, Zhen Liu, Yuefa Ou and Liucun Zhu
Sensors 2025, 25(5), 1611; https://doi.org/10.3390/s25051611 - 6 Mar 2025
Viewed by 22
Abstract
Population aging is an inevitable trend in contemporary society, and the application of technologies such as human–machine interaction, assistive healthcare, and robotics in daily service sectors continues to increase. The lower limb exoskeleton rehabilitation robot has great potential in areas such as enhancing [...] Read more.
Population aging is an inevitable trend in contemporary society, and the application of technologies such as human–machine interaction, assistive healthcare, and robotics in daily service sectors continues to increase. The lower limb exoskeleton rehabilitation robot has great potential in areas such as enhancing human physical functions, rehabilitation training, and assisting the elderly and disabled. This paper integrates the structural characteristics of the human lower limb, motion mechanics, and gait features to design a biomimetic exoskeleton structure and proposes a human–machine integrated lower limb exoskeleton rehabilitation robot. Human gait data are collected using the Optitrack optical 3D motion capture system. SolidWorks 3D modeling software Version 2021 is used to create a virtual prototype of the exoskeleton, and kinematic analysis is performed using the standard Denavit–Hartenberg (D-H) parameter method. Kinematic simulations are carried out using the Matlab Robotic Toolbox Version R2018a with the derived D-H parameters. A physical prototype was fabricated and tested to verify the validity of the structural design and gait parameters. A controller based on BP fuzzy neural network PID control is designed to ensure the stability of human walking. By comparing two sets of simulation results, it is shown that the BP fuzzy neural network PID control outperforms the other two control methods in terms of overshoot and settling time. The specific conclusions are as follows: after multiple walking gait tests, the robot’s walking process proved to be relatively safe and stable; when using BP fuzzy neural network PID control, there is no significant oscillation, with an overshoot of 5.5% and a settling time of 0.49 s, but the speed was slow, with a walking speed of approximately 0.18 m/s, a stride length of about 32 cm, and a gait cycle duration of approximately 1.8 s. The model proposed in this paper can effectively assist patients in recovering their ability to walk. However, the lower limb exoskeleton rehabilitation robot still faces challenges, such as a slow speed, large size, and heavy weight, which need to be optimized and improved in future research. Full article
(This article belongs to the Section Sensors and Robotics)
Show Figures

Figure 1

Figure 1
<p>Schematic diagram of the human gait cycle (R: Right leg; L: Left leg; IC: Initial Contact; FO: Foot Off; MS: Mid-swing).</p>
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<p>Experiment procedure: (<b>a</b>) distribution of muscle groups in human gait; (<b>b</b>) marker placement locations; (<b>c</b>) tracking of the moving target points.</p>
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<p>Gait model.</p>
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<p>Joint angle change curves within the gait cycle: (<b>a</b>) hip joint angle change; (<b>b</b>) knee joint angle change; (<b>c</b>) ankle joint angle change.</p>
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<p>Lower limb exoskeleton rehabilitation robot joint design: (<b>a</b>) hip joint; (<b>b</b>) knee joint; (<b>c</b>) ankle joint; (<b>d</b>) overall 3D structure.</p>
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<p>Lower limb exoskeleton rehabilitation robot joint design: (<b>a</b>) hip joint; (<b>b</b>) knee joint; (<b>c</b>) ankle joint; (<b>d</b>) overall 3D structure.</p>
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<p>Schematic diagram of the kinematic coordinate system configuration for the left leg of the lower limb exoskeleton.</p>
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<p>Three-dimensional model of the left leg.</p>
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<p>Inverse kinematics verification: (<b>a</b>) forward kinematics model; (<b>b</b>) inverse kinematics model.</p>
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<p>Membership function plots: (<b>a</b>) membership function of input variable <span class="html-italic">e</span>; (<b>b</b>) membership function of input variable <span class="html-italic">ec</span>; (<b>c</b>) membership function of output variable <span class="html-italic">k<sub>p</sub></span>; (<b>d</b>) membership function of output variable <span class="html-italic">k<sub>i</sub></span>; (<b>e</b>) membership function of output variable <span class="html-italic">k<sub>d.</sub></span></p>
Full article ">Figure 9 Cont.
<p>Membership function plots: (<b>a</b>) membership function of input variable <span class="html-italic">e</span>; (<b>b</b>) membership function of input variable <span class="html-italic">ec</span>; (<b>c</b>) membership function of output variable <span class="html-italic">k<sub>p</sub></span>; (<b>d</b>) membership function of output variable <span class="html-italic">k<sub>i</sub></span>; (<b>e</b>) membership function of output variable <span class="html-italic">k<sub>d.</sub></span></p>
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<p>Structure of BP neural network.</p>
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<p>Simulink simulation results: (<b>a</b>) no disturbance; (<b>b</b>) with disturbance.</p>
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<p>Prototype donning demonstration.</p>
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<p>EMG amplitude (%MVC): (<b>a</b>) gastrocnemius; (<b>b</b>) biceps femoris; (<b>c</b>) rectus femoris; (<b>d</b>) tibialis anterior.</p>
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<p>EMG amplitude (%MVC): (<b>a</b>) gastrocnemius; (<b>b</b>) biceps femoris; (<b>c</b>) rectus femoris; (<b>d</b>) tibialis anterior.</p>
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<p>Walking gait test.</p>
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2 pages, 141 KiB  
Editorial
Selected Papers from MEDER 2024: Advances of Mechanism Design for Robotic Machines
by Marco Ceccarelli and Erwin Christian Lovasz
Machines 2025, 13(3), 208; https://doi.org/10.3390/machines13030208 - 5 Mar 2025
Viewed by 77
Abstract
This Special Issue aims to promote and circulate the recent developments and achievements of the international community in the field of Robot Design within Mechanism and Machine Science, ranging from theoretical contributions to experimental and practical applications [...] Full article
71 pages, 30249 KiB  
Article
Dimensional Synthesis of Parallel Robots Using Bilevel Optimization for Design Optimization and Resolution of Functional Redundancy
by Moritz Schappler
Robotics 2025, 14(3), 29; https://doi.org/10.3390/robotics14030029 - 4 Mar 2025
Viewed by 183
Abstract
Parallel-kinematic machines or parallel robots have only been established in a few applications where their advantage over serial kinematics due to their high payload capacity, stiffness, or dynamics with their limited workspace-to-installation-space ratio pays out. However, some applications still have not yet been [...] Read more.
Parallel-kinematic machines or parallel robots have only been established in a few applications where their advantage over serial kinematics due to their high payload capacity, stiffness, or dynamics with their limited workspace-to-installation-space ratio pays out. However, some applications still have not yet been sufficiently or satisfactorily automated in which parallel robots could be advantageous. As their performance is much more dependent on their complex dimensioning, an automated design tool—not existing yet—is required to optimize the parameterization of parallel robots for applications. Combined structural and dimensional synthesis considers all principally possible kinematic structures and performs a separate dimensioning for each to obtain the best task-specific structure. However, this makes the method computationally demanding. The proposed computationally efficient approach for dimensional synthesis extends multi-objective particle swarm optimization with hierarchical constraints. A cascaded (bilevel) optimization includes the design optimization of components and the redundancy resolution for tasks with rotational symmetry, like milling. Two case studies for different end-effector degrees of freedom demonstrate the broad applicability of the combined structural and dimensional synthesis for symmetric parallel robots with rigid links and serial-kinematic leg chains. The framework produces many possible task-optimal structures despite numerous constraints and can be applied to other problems as an open-source Matlab toolbox. Full article
(This article belongs to the Special Issue Robotics and Parallel Kinematic Machines)
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Figure 1

Figure 1
<p>Overview of the procedure for combined structural and dimensional synthesis, which structures the paper. Abbreviations: degree of freedom (DoF); optimal (opt.).</p>
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<p>Sketch of the general parallel-robot kinematics for the conventional approach (<b>a</b>) and the modified model for functional redundancy with different definitions for first and following leg chains (<b>b</b>). Constraints are denoted by <math display="inline"><semantics> <mi mathvariant="bold-italic">δ</mi> </semantics></math> for the full set or by <math display="inline"><semantics> <mi mathvariant="bold-italic">ψ</mi> </semantics></math> if a component related to the redundant coordinate was removed.</p>
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<p>Single design problems within the parallel-robot synthesis in the notation of [<a href="#B44-robotics-14-00029" class="html-bibr">44</a>].</p>
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<p>Parallel-robot synthesis as a simplified co-design problem in the notation of [<a href="#B44-robotics-14-00029" class="html-bibr">44</a>].</p>
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<p>Flowchart diagram summarizing the dimensional-synthesis optimization problem.</p>
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<p>Flowchart diagram of the particle swarm optimization and the structure of the fitness function with hierarchical constraints. Mod. from [<a href="#B99-robotics-14-00029" class="html-bibr">99</a>].</p>
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<p>Parallel robot with annotation of geometric structural entities. Mod. from [<a href="#B103-robotics-14-00029" class="html-bibr">103</a>].</p>
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<p>Geometric principles for circular alignments of the base-coupling joint with given coupling joint frame (the blue <span class="html-italic">z</span>-axis corresponds to first joint axis): (<b>a</b>) <span class="underline">v</span>ertical (mod. from [Figure 9.10g] in [<a href="#B6-robotics-14-00029" class="html-bibr">6</a>]), (<b>b</b>) <span class="underline">t</span>angential (mod. from [Figure 9.14] in [<a href="#B104-robotics-14-00029" class="html-bibr">104</a>]), (<b>c</b>) <span class="underline">r</span>adial (mod. from [<a href="#B105-robotics-14-00029" class="html-bibr">105</a>]), (<b>d</b>) <span class="underline">c</span>onical ([Figure 9.10f] in [<a href="#B6-robotics-14-00029" class="html-bibr">6</a>]).</p>
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<p>Geometric principles for pairwise circular alignments of the base-coupling joint with given coupling joint frames: (<b>a</b>) <span class="underline">V</span>ertical (mod. from [Figure 2f] in [<a href="#B103-robotics-14-00029" class="html-bibr">103</a>]), (<b>b</b>) <span class="underline">T</span>angential (mod. from [Figure 2a] in [<a href="#B103-robotics-14-00029" class="html-bibr">103</a>]), (<b>c</b>) <span class="underline">R</span>adial (top view on base), (<b>d</b>) <span class="underline">C</span>onical/pyramidal (source: Daniel Ramirez, LUH; mod).</p>
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<p>Extended dimensional-synthesis scheme with design optimization (<a href="#sec3dot3-robotics-14-00029" class="html-sec">Section 3.3</a>) and loop over assembly modes (see <a href="#sec3dot5-robotics-14-00029" class="html-sec">Section 3.5</a>), mod. from [<a href="#B97-robotics-14-00029" class="html-bibr">97</a>] (there published under <a href="http://creativecommons.org/licenses/by/4.0/" target="_blank">CC-BY License</a>).</p>
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<p>Block diagram of extending the existing optimization scheme (<b>a</b>) by the dynamics regressor form (<b>b</b>), mod. from [<a href="#B100-robotics-14-00029" class="html-bibr">100</a>]. The dynamics parameters <math display="inline"><semantics> <msub> <mi mathvariant="bold-italic">p</mi> <mi>dyn</mi> </msub> </semantics></math> may be in inertial- or base-parameter form.</p>
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<p>Dimensional synthesis scheme with functional redundancy. Mod. from [<a href="#B101-robotics-14-00029" class="html-bibr">101</a>].</p>
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<p>Photograph of the LuFI wave basin with sketched dimensions (not true to scale) of the allowed robot installation space (green) and workspace (blue) (<b>a</b>), rendering of the robot (<b>b</b>) with detail on the end effector (<b>c</b>). Geometrical relations and perspectives are depicted qualitatively. Modified from [<a href="#B113-robotics-14-00029" class="html-bibr">113</a>].</p>
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<p>Pareto fronts for design-oriented objectives for chains with three and four joints with lightweight link dimensioning without the link-design optimization loop.</p>
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<p>Visualization of valid solutions for the naval-testbed robot from <a href="#robotics-14-00029-f014" class="html-fig">Figure 14</a>. The fixed base is at the top, and the moving platform is at the bottom. Red cuboids mark active prismatic joints, and blue cylinders or spheres mark passive joints.</p>
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<p>Pareto fronts for combinations of coupling-joint alignments of selected parallel robots: (<b>a</b>) Hexapod, (<b>b</b>) Hexa, and (<b>c</b>) HexaSlide.</p>
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<p>Grouped Pareto fronts of all results of the naval-testbed robot.</p>
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<p>Details of the engineering solution; modified from [<a href="#B113-robotics-14-00029" class="html-bibr">113</a>]: (<b>a</b>) leg chain (modified from the catalog “Electromechanical cylinders EMC” from Bosch Rexroth AG, Lohr am Main, Germany), (<b>b</b>) spherical joint, (<b>c</b>) universal joint (derived from a CAD file of Elso Elbe GmbH &amp; Co. KG., Hofheim, Germany), (<b>d</b>) hexapod assembly, (<b>e</b>) moving platform, and (<b>f</b>) fixed base.</p>
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<p>Visualization of selected results for the handling task from the Pareto diagrams in <a href="#robotics-14-00029-f020" class="html-fig">Figure 20</a>.</p>
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<p>Pareto fronts for robots with (<b>a</b>) prismatic and (<b>b</b>) revolute actuation. The notation of [<a href="#B6-robotics-14-00029" class="html-bibr">6</a>] is used for distinguishing kinematic structures, where two <math display="inline"><semantics> <mrow> <mover> <mi mathvariant="normal">R</mi> <mo>̀</mo> </mover> </mrow> </semantics></math> denote two parallel revolute joints and Ŕ denotes a joint with a different axis. In addition to [<a href="#B6-robotics-14-00029" class="html-bibr">6</a>], prismatic joints with an axis parallel to a revolute <math display="inline"><semantics> <mrow> <mover> <mi mathvariant="normal">R</mi> <mo>̀</mo> </mover> </mrow> </semantics></math> joint are denoted by <math display="inline"><semantics> <mrow> <mover> <mi mathvariant="normal">P</mi> <mo>̀</mo> </mover> </mrow> </semantics></math>.</p>
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<p>Trajectory of end-effector position (<b>a</b>) and of the planar rotation (redundant coordinate) within the force performance map with markers for constraint violation (<b>b</b>) for the 4-R<span class="underline">P</span>UR.</p>
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<p>Redundant-coordinate trajectory (<b>a</b>) and Pareto fronts (<b>b</b>,<b>c</b>) for another 4-R<span class="underline">P</span>UR structure based on the same parameters with different inverse-kinematics optimization objectives. The method legend in (<b>b</b>) holds for all (<b>a</b>–<b>c</b>). Large markers in (<b>b</b>,<b>c</b>) represent parameters for the performance map in (<b>a</b>).</p>
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<p>Pareto fronts for the design-oriented objectives for chains with five and six joints and fixed-dimension lightweight links without link design optimization.</p>
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<p>Pareto fronts for the resulting link dimensioning of the results above together with the collision distance as third optimization objective. Only Pareto-dominant particles in these two criteria are shown. The legend is identical to that of <a href="#robotics-14-00029-f0A3" class="html-fig">Figure A3</a> and <a href="#robotics-14-00029-f0A4" class="html-fig">Figure A4</a>.</p>
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<p>Pareto fronts for the actuator-oriented objectives for prismatic actuation.</p>
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<p>Pareto fronts for the actuator-oriented objectives for revolute actuation.</p>
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<p>Comparison of particle swarm optimization (blue) and genetic algorithm (red) for the same settings as <a href="#robotics-14-00029-f0A3" class="html-fig">Figure A3</a> and <a href="#robotics-14-00029-f0A4" class="html-fig">Figure A4</a> for three different parallel robots (<b>a</b>–<b>c</b>). Each independent repetition has its own marker. The optimal solution after several iterations (from <a href="#robotics-14-00029-f0A3" class="html-fig">Figure A3</a> and <a href="#robotics-14-00029-f0A4" class="html-fig">Figure A4</a>) is marked in green for reference. Identical markers were thinned out to improve visibility.</p>
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<p>Computation time of the fitness function (logarithmic scale) in relation to the number of the violated constraint (from <a href="#sec3dot2dot2-robotics-14-00029" class="html-sec">Section 3.2.2</a>) that led to abortion. The class “chainlength” comes from checking if the length of a leg chain that includes a prismatic joint exceeds the maximum allowed length. Outlier markers were thinned out (193 of 97 k left over) to increase visibility of the data. Duplicate constraints result from multiple similar checks, e.g., for different Jacobian matrices in constraint 9.</p>
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<p>Visualization of the results with <span class="html-italic">prismatic actuation</span> from <a href="#robotics-14-00029-t0A1" class="html-table">Table A1</a> with corresponding marker from <a href="#robotics-14-00029-f017" class="html-fig">Figure 17</a> and <a href="#robotics-14-00029-f0A3" class="html-fig">Figure A3</a>—part 1.</p>
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<p>Visualization of the results with <span class="html-italic">prismatic actuation</span> from <a href="#robotics-14-00029-t0A1" class="html-table">Table A1</a> with corresponding marker from <a href="#robotics-14-00029-f017" class="html-fig">Figure 17</a> and <a href="#robotics-14-00029-f0A3" class="html-fig">Figure A3</a>—part 2.</p>
Full article ">Figure A9
<p>Visualization of the results with <span class="html-italic">revolute actuation</span> from <a href="#robotics-14-00029-t0A3" class="html-table">Table A3</a> with corresponding marker from <a href="#robotics-14-00029-f017" class="html-fig">Figure 17</a> and <a href="#robotics-14-00029-f0A4" class="html-fig">Figure A4</a>.</p>
Full article ">Figure A10
<p>Visualization of <span class="html-italic">3T0R</span> parallel robots for the handling task with <span class="html-italic">revolute</span> actuation. Markers are consistent with <a href="#robotics-14-00029-f020" class="html-fig">Figure 20</a>.</p>
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<p>Visualization of <span class="html-italic">3T1R</span> parallel robots for the handling task with <span class="html-italic">revolute</span> actuation.</p>
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<p>Visualization of <span class="html-italic">3T0R</span> parallel robots for the handling task with <span class="html-italic">prismatic</span> actuation. Markers are consistent with <a href="#robotics-14-00029-f020" class="html-fig">Figure 20</a>. Continued in <a href="#robotics-14-00029-f0A13" class="html-fig">Figure A13</a>.</p>
Full article ">Figure A13
<p>Visualization of <span class="html-italic">3T0R</span> parallel robots (part 2), continuation of <a href="#robotics-14-00029-f0A12" class="html-fig">Figure A12</a>.</p>
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<p>Visualization of <span class="html-italic">3T1R</span> parallel robots for the handling task with <span class="html-italic">prismatic</span> actuation.</p>
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<p>Pareto fronts for robots with prismatic actuation using only 27 reference points.</p>
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<p>Visualization of the 3T0R parallel robots with parameters from [<a href="#B123-robotics-14-00029" class="html-bibr">123</a>], listed in the bottom of <a href="#robotics-14-00029-t0A5" class="html-table">Table A5</a> and <a href="#robotics-14-00029-t0A6" class="html-table">Table A6</a>.</p>
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<p>Distribution of actuator force (<b>a</b>,<b>b</b>), position error/precision (<b>c</b>,<b>d</b>), and dexterity (<b>e</b>,<b>f</b>) as performance criterion computed with parameters from Table 4 of [<a href="#B123-robotics-14-00029" class="html-bibr">123</a>] with this paper’s implementation (left side) in comparison to the original results obtained from [<a href="#B123-robotics-14-00029" class="html-bibr">123</a>] (right side, with structures for comparison in red).</p>
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<p>Performance maps for the prismatic-actuation parallel robots of <a href="#robotics-14-00029-f0A14" class="html-fig">Figure A14</a> with maximum actuator force as IK objective and heat-map criterion. For marker legend, see below in <a href="#robotics-14-00029-f0A19" class="html-fig">Figure A19</a>.</p>
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<p>Performance maps for the revolute-actuation parallel robots of <a href="#robotics-14-00029-f0A11" class="html-fig">Figure A11</a> with maximum actuator torque as IK objective and heat-map criterion.</p>
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<p>Performance maps for the prismatic-actuation parallel robots of <a href="#robotics-14-00029-f0A14" class="html-fig">Figure A14</a> with position error (precision) as heat-map criterion and trajectory from <a href="#robotics-14-00029-f0A18" class="html-fig">Figure A18</a>. For marker legend, see below in <a href="#robotics-14-00029-f0A21" class="html-fig">Figure A21</a>.</p>
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<p>Performance maps for the revolute-actuation parallel robots of <a href="#robotics-14-00029-f0A11" class="html-fig">Figure A11</a> with position error as heat-map criterion and trajectory from <a href="#robotics-14-00029-f0A19" class="html-fig">Figure A19</a>. Color scale is different than in <a href="#robotics-14-00029-f0A20" class="html-fig">Figure A20</a> above.</p>
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<p>Performance maps for the prismatic-actuation parallel robots of <a href="#robotics-14-00029-f0A14" class="html-fig">Figure A14</a> with IK-Jacobian condition number as heat-map criterion and trajectory from <a href="#robotics-14-00029-f0A18" class="html-fig">Figure A18</a>. For marker legend, see below in <a href="#robotics-14-00029-f0A23" class="html-fig">Figure A23</a>.</p>
Full article ">Figure A23
<p>Performance maps for the revolute-actuation parallel robots of <a href="#robotics-14-00029-f0A11" class="html-fig">Figure A11</a> with IK-Jacobian condition number as heat-map criterion and trajectory from <a href="#robotics-14-00029-f0A19" class="html-fig">Figure A19</a>. Color scale is different than in <a href="#robotics-14-00029-f0A22" class="html-fig">Figure A22</a> above.</p>
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20 pages, 4186 KiB  
Article
Deep Learning-Emerged Grid Cells-Based Bio-Inspired Navigation in Robotics
by Arturs Simkuns, Rodions Saltanovs, Maksims Ivanovs and Roberts Kadikis
Sensors 2025, 25(5), 1576; https://doi.org/10.3390/s25051576 - 4 Mar 2025
Viewed by 207
Abstract
Grid cells in the brain’s entorhinal cortex are essential for spatial navigation and have inspired advancements in robotic navigation systems. This paper first provides an overview of recent research on grid cell-based navigation in robotics, focusing on deep learning models and algorithms capable [...] Read more.
Grid cells in the brain’s entorhinal cortex are essential for spatial navigation and have inspired advancements in robotic navigation systems. This paper first provides an overview of recent research on grid cell-based navigation in robotics, focusing on deep learning models and algorithms capable of handling uncertainty and dynamic environments. We then present experimental results where a grid cell network was trained using trajectories from a mobile unmanned ground vehicle (UGV) robot. After training, the network’s units exhibited spatially periodic and hexagonal activation patterns characteristic of biological grid cells, as well as responses resembling border cells and head-direction cells. These findings demonstrate that grid cell networks can effectively learn spatial representations from robot trajectories, providing a foundation for developing advanced navigation algorithms for mobile robots. We conclude by discussing current challenges and future research directions in this field. Full article
(This article belongs to the Special Issue Smart Sensor Systems for Positioning and Navigation)
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Figure 1

Figure 1
<p>An overview of the high-level system architecture for grid cell-based robotic navigation, detailing the flow from input data generation through trajectory simulation in Gazebo, data preprocessing and storage, model training with Long Short-Term Memory (LSTM) and linear layers.</p>
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<p>The diagram illustrates the relationships between various brain regions and cell types involved in spatial navigation.</p>
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<p>The diagram illustrates the flow of data from trajectory inputs of a UGV robot in a simulation environment through the Supervised Learning Grid Cell Module (SLGCM), using an RNN and LSTM layer to predict and simulate grid cell activity that supports vector-based navigation.</p>
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<p>Architecture of a grid cell network for robotic navigation, detailing the flow from the input layer (taking velocity and angular components) through the LSTM recurrent layer, a linear layer for feature transformation, and separate linear decoders for place and head-direction cells, which output activations for spatial and directional mapping.</p>
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<p>Tensorflow 2.9.1 implementation architecture of supervised learning grid cell module.</p>
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<p>Husky UGV robot in Gazebo environment.</p>
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<p>The flow of dataset generation and environment interaction for the Husky UGV in a Gazebo simulation, showing how commands are processed through the EIM module, robot movements are controlled, sensor data are collected and transformed, and the data is finally stored in TFRecord format for training purposes.</p>
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<p>Husky robot’s traveled trajectories during dataset generation, with each colored line representing a different path within a 6.4-meter-square area (±3.2 m on both the X and Y axes).</p>
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<p>Dataset trajectory generation from Clearpath Husky in Gazebo to dataset in TFRecords format.</p>
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<p>Spatial activity plots from the linear layer after 124 training epochs show similar to grid cell activations. These activations exhibit periodic and varied firing patterns, reflecting learned spatial encoding across different units.</p>
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<p>Spatial autocorrelograms of ratemaps after 124 training epochs, displaying distinct circular patterns that reflect spatial regularity.</p>
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22 pages, 491 KiB  
Review
Domain Generalization Through Data Augmentation: A Survey of Methods, Applications, and Challenges
by Junjie Mai, Chongzhi Gao and Jun Bao
Mathematics 2025, 13(5), 824; https://doi.org/10.3390/math13050824 - 28 Feb 2025
Viewed by 176
Abstract
Domain generalization (DG) has become a pivotal research area in machine learning, focusing on equipping models with the ability to generalize effectively to unseen test domains that differ from the training distribution. This capability is crucial, as real-world data frequently exhibit domain shifts [...] Read more.
Domain generalization (DG) has become a pivotal research area in machine learning, focusing on equipping models with the ability to generalize effectively to unseen test domains that differ from the training distribution. This capability is crucial, as real-world data frequently exhibit domain shifts that violate the assumption of independent and identically distributed (i.i.d.) data, resulting in significant declines in model performance. Among the various strategies to address domain generalization, data augmentation has garnered substantial attention as an effective approach for mitigating domain shifts and improving model robustness. In this survey, we examine the role of data augmentation in domain generalization, offering a comprehensive overview of its methods, applications, and challenges. We present a detailed taxonomy of data augmentation techniques, categorized along three dimensions: scope, nature, and training dependency. Additionally, we provide a comparative analysis of key methods, highlighting their strengths and limitations. Finally, we explore the domain-specific applications of data augmentation and analyze their effectiveness in enhancing generalization across various real-world tasks, including computer vision, NLP, speech, and robotics. We conclude by examining key challenges—such as computational cost and augmentation overfitting—and outline promising research directions, with a focus on advancing cross-modal augmentation techniques and developing standardized evaluation benchmarks. Full article
(This article belongs to the Special Issue Mathematical and Computing Sciences for Artificial Intelligence)
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<p>Comparison of model representations before and after image augmentation using geometric transformations in GeomTex.</p>
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12 pages, 305 KiB  
Review
Artificial Intelligence in Breast Reconstruction: A Narrative Review
by Andrei Iulian Rugină, Andreea Ungureanu, Carmen Giuglea and Silviu Adrian Marinescu
Medicina 2025, 61(3), 440; https://doi.org/10.3390/medicina61030440 - 28 Feb 2025
Viewed by 295
Abstract
Breast reconstruction following mastectomy or sectorectomy significantly impacts the quality of life and psychological well-being of breast cancer patients. Since its inception in the 1950s, artificial intelligence (AI) has gradually entered the medical field, promising to transform surgical planning, intraoperative guidance, postoperative care, [...] Read more.
Breast reconstruction following mastectomy or sectorectomy significantly impacts the quality of life and psychological well-being of breast cancer patients. Since its inception in the 1950s, artificial intelligence (AI) has gradually entered the medical field, promising to transform surgical planning, intraoperative guidance, postoperative care, and medical research. This article examines AI applications in breast reconstruction, supported by recent studies. AI shows promise in enhancing imaging for tumor detection and surgical planning, improving microsurgical precision, predicting complications such as flap failure, and optimizing postoperative monitoring. However, challenges remain, including data quality, safety, algorithm transparency, and clinical integration. Despite these shortcomings, AI has the potential to revolutionize breast reconstruction by improving preoperative planning, surgical precision, operative efficiency, and patient outcomes. This review provides a foundation for further research as AI continues to evolve and clinical trials expand its applications, offering greater benefits to patients and healthcare providers. Full article
(This article belongs to the Section Surgery)
17 pages, 2630 KiB  
Article
Multimodal Deep Learning Model for Cylindrical Grasp Prediction Using Surface Electromyography and Contextual Data During Reaching
by Raquel Lázaro, Margarita Vergara, Antonio Morales and Ramón A. Mollineda
Biomimetics 2025, 10(3), 145; https://doi.org/10.3390/biomimetics10030145 - 27 Feb 2025
Viewed by 155
Abstract
Grasping objects, from simple tasks to complex fine motor skills, is a key component of our daily activities. Our approach to facilitate the development of advanced prosthetics, robotic hands and human–machine interaction systems consists of collecting and combining surface electromyography (EMG) signals and [...] Read more.
Grasping objects, from simple tasks to complex fine motor skills, is a key component of our daily activities. Our approach to facilitate the development of advanced prosthetics, robotic hands and human–machine interaction systems consists of collecting and combining surface electromyography (EMG) signals and contextual data of individuals performing manipulation tasks. In this context, the identification of patterns and prediction of hand grasp types is crucial, with cylindrical grasp being one of the most common and functional. Traditional approaches to grasp prediction often rely on unimodal data sources, limiting their ability to capture the complexity of real-world scenarios. In this work, grasp prediction models that integrate both EMG signals and contextual (task- and product-related) information have been explored to improve the prediction of cylindrical grasps during reaching movements. Three model architectures are presented: an EMG processing model based on convolutions that analyzes forearm surface EMG data, a fully connected model for processing contextual information, and a hybrid architecture combining both inputs resulting in a multimodal model. The results show that context has great predictive power. Variables such as object size and weight (product-related) were found to have a greater impact on model performance than task height (task-related). Combining EMG and product context yielded better results than using each data mode separately, confirming the importance of product context in improving EMG-based models of grasping. Full article
(This article belongs to the Special Issue Intelligent Human–Robot Interaction: 3rd Edition)
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<p>Seven zones for surface EMG placement from [<a href="#B24-biomimetics-10-00145" class="html-bibr">24</a>].</p>
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<p>CDF with the proposed cut-off threshold (700 samples), along with the percentage of rejected samples (7.77%).</p>
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<p>Data distributions by class and contextual data: (<b>a</b>) Weight. (<b>b</b>) Task height.</p>
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<p>Comparison of SPAN distributions by class: (<b>a</b>) Span 1, main span of the product. (<b>b</b>) Span 2, secondary span of the product.</p>
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<p>(<b>a</b>) CNN for EMG signals; (<b>b</b>) FC neural network for contextual data.</p>
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<p>Hybrid model architecture (M_HYBRID).</p>
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<p>Training results of the models: (<b>a</b>) EMG, (<b>b</b>) contextual, (<b>c</b>) hybrid.</p>
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<p>Confusion matrices of the models: (<b>a</b>) EMG, (<b>b</b>) contextual, (<b>c</b>) hybrid.</p>
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<p>Comparison of accuracy and loss for hybrid models. The dashed lines indicate the best values achieved.</p>
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9 pages, 377 KiB  
Article
Rebound Effects Caused by Artificial Intelligence and Automation in Private Life and Industry
by Wolfgang Ertel and Christopher Bonenberger
Sustainability 2025, 17(5), 1988; https://doi.org/10.3390/su17051988 - 26 Feb 2025
Viewed by 158
Abstract
Many tasks in a modern household are performed by machines, e.g., a dishwasher or a vacuum cleaner, and in the near future most household tasks will be performed by smart service robots. This will relieve the residents, who in turn can enjoy their [...] Read more.
Many tasks in a modern household are performed by machines, e.g., a dishwasher or a vacuum cleaner, and in the near future most household tasks will be performed by smart service robots. This will relieve the residents, who in turn can enjoy their free time. This newly gained free time will turn out to cause the so-called spare time rebound effect due to more resource consumption. We roughly quantify this rebound effect and propose a CO2-budget model to reduce or even avoid it. In modern industry, automation and AI are taking over work from humans, leading to higher productivity of the company as a whole. This is the main reason for economic growth, which leads to environmental problems due to higher consumption of natural resources. We show that, even though the effects of automation at home and in the industry are different (free time versus higher productivity), in the end they both lead to more resource consumption and environmental pollution. We discuss possible solutions to this problem, such as carbon taxes, emissions trading systems, and a carbon budget. Full article
(This article belongs to the Special Issue AI and Sustainability: Risks and Challenges)
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<p>The service robot Marvin (<b>left</b>) assisting a physically disabled person in the kitchen (<b>right</b>) (Photo: Felix Kästle).</p>
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17 pages, 755 KiB  
Article
Industrial Robotics, Resource Efficiency, Energy Transition, and Environmental Quality: Designing a Sustainable Development Goals Framework for G7 Countries in the Presence of Geopolitical Risk
by Yuhan Xia and Mahmood Ahmad
Sustainability 2025, 17(5), 1960; https://doi.org/10.3390/su17051960 - 25 Feb 2025
Viewed by 237
Abstract
In recent years, the integration of industrial robotics has emerged as a powerful tool in reshaping industries by enhancing production efficiency, reducing waste generation, and optimizing resource utilization. However, industrial robotics, particularly in manufacturing and production, require significant energy that can potentially impact [...] Read more.
In recent years, the integration of industrial robotics has emerged as a powerful tool in reshaping industries by enhancing production efficiency, reducing waste generation, and optimizing resource utilization. However, industrial robotics, particularly in manufacturing and production, require significant energy that can potentially impact on environmental quality. Despite the growing adoption of artificial intelligence (AI)-based industrial robotics, there is a paucity of literature on the impact of industrial robotics on the ecological footprint (EF), particularly in the context of advanced economies. In this context, this study aims to investigate the impact of industrial robotics, resource efficiency, energy transition, and geopolitical risk EF in G7 countries from 1993 to 2021. The study employed advanced econometric techniques, including Kernel-based Regularized Least Squares (KRLS) and Artificial Neural Network (ANN) machine learning methods. The results unveiled that industrial robotics significantly curtail environmental degradation by impeding the EF. Resource efficiency and energy transition posed a significant and negative impact on the EF. Geopolitical risks and economic growth exacerbate the EF. Based on the results, the study proposes important policy implications for achieving sustainable development. Full article
(This article belongs to the Special Issue Energy and Environment: Policy, Economics and Modeling)
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<p>ANN scheme. Source: authors constructed it using the MATLAB (version R2023B).</p>
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<p>ANN plots. Source: authors constructed it using the MATLAB (version R2023B).</p>
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<p>Error histogram. Source: authors constructed it using the MATLAB (version R2023B).</p>
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15 pages, 3274 KiB  
Article
Gesture-Controlled Robotic Arm for Small Assembly Lines
by Georgios Angelidis and Loukas Bampis
Machines 2025, 13(3), 182; https://doi.org/10.3390/machines13030182 - 25 Feb 2025
Viewed by 207
Abstract
In this study, we present a gesture-controlled robotic arm system for small assembly lines. Robotic arms are extensively used in industrial applications; however, they typically require special treatment and qualified personnel to set up and operate them. Towards this end, hand gestures can [...] Read more.
In this study, we present a gesture-controlled robotic arm system for small assembly lines. Robotic arms are extensively used in industrial applications; however, they typically require special treatment and qualified personnel to set up and operate them. Towards this end, hand gestures can provide a natural way for human–robot interaction, providing a straightforward means for control without the need for significant training of the operators. Our goal is to develop a safe, low-cost, and user-friendly system for environments that often involve non-repetitive and custom automation processes, such as in small factory setups. Our system estimates the 3D position of the user’s joints in real time with the help of AI and real-world data provided by an RGB-D camera. Then, joint coordinates are translated into the robotic arm’s desired poses in a simulated environment (ROS), thus achieving gesture control. Through the experiments we conducted, we show that the system provides the performance required to control a robotic arm effectively and efficiently. Full article
(This article belongs to the Special Issue AI-Integrated Advanced Robotics Towards Industry 5.0)
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<p>Schematic representation of our proposed gesture-controlled robotic arm system.</p>
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<p>Proposed setup for controlling a robotic arm through human gestures. The frames considered for reference are depicted in red for the <span class="html-italic">x</span>-axis, green for the <span class="html-italic">y</span>-axis, and blue for the <span class="html-italic">z</span>-axis.</p>
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<p>The 21 estimated hand joints from the work presented in [<a href="#B42-machines-13-00182" class="html-bibr">42</a>,<a href="#B50-machines-13-00182" class="html-bibr">50</a>].</p>
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<p>Direct vectors computed between the index PIP joint and the wrist (blue), pinky MCP, and index MCP joints (red). These vectors are used as references for computing the orientation of the operator’s hand (frame <math display="inline"><semantics> <msub> <mi>h</mi> <mi>r</mi> </msub> </semantics></math>).</p>
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<p>Rotations of the user’s chest frame of reference (<span class="html-italic">c</span>) in order to align its axes with those of the camera’s coordinate frame (<span class="html-italic">s</span>).</p>
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<p>The two categories of studied hand poses for controlling the robotic arm. (<b>a</b>) Pose 1, the palm’s surface is perpendicular to the camera; (<b>b</b>) Pose 2, where palm appears parallel relatively to the camera.</p>
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<p>Snapshots of the developed system’s operation.</p>
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<p>The two boundary conditions for the gripper’s opening <span class="html-italic">w</span> values.</p>
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<p>The trajectory of the user’s hand, with respect to the frame of reference <span class="html-italic">c</span>, and the end effector, with respect to <span class="html-italic">b</span>. 33 points are depicted with blue for the human hand and orange for the Panda arm. The left graph is a side-view comparison of the movements, while the right one illustrates the same sequence from a top view.</p>
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6 pages, 431 KiB  
Proceeding Paper
Design of Maximally Permissive Controllers for Solving Deadlock Problems in Flexible Manufacturing Systems
by Yen-Liang Pan, Wen-Yi Chuang, Kuang-Hsiung Tan and Ching-Yun Tseng
Eng. Proc. 2025, 89(1), 10; https://doi.org/10.3390/engproc2025089010 - 24 Feb 2025
Viewed by 105
Abstract
Industry 5.0 aims to integrate humans and machines to achieve greater productivity, personalization, and sustainable development in the production process. Built on the foundation of Industry 4.0 which emphasizes automation, digitalization, and intelligent production processes, Industry 5.0 highlights the importance of human resources [...] Read more.
Industry 5.0 aims to integrate humans and machines to achieve greater productivity, personalization, and sustainable development in the production process. Built on the foundation of Industry 4.0 which emphasizes automation, digitalization, and intelligent production processes, Industry 5.0 highlights the importance of human resources in modern manufacturing. Robotic arms have replaced traditional manpower, particularly in flexible manufacturing systems. However, integrating advanced machinery into workflows has increased competition in terms of securing resources, resulting in frequent deadlocks. Various deadlock prevention policies have been proposed to address this issue. Despite these efforts, resolving system deadlocks while achieving the optimal number of reachable states remains challenging. Based on existing research, we have developed a novel deadlock recovery method applicable to various flexible manufacturing systems. We designed an adaptable system and a controller that can restore the system to its fully operational state. Full article
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<p>Example of S<sup>3</sup>PR net.</p>
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15 pages, 7444 KiB  
Article
Soft Robot Workspace Estimation via Finite Element Analysis and Machine Learning
by Getachew Ambaye, Enkhsaikhan Boldsaikhan and Krishna Krishnan
Actuators 2025, 14(3), 110; https://doi.org/10.3390/act14030110 - 23 Feb 2025
Viewed by 410
Abstract
Soft robots with compliant bodies offer safe human–robot interaction as well as adaptability to unstructured dynamic environments. However, the nonlinear dynamics of a soft robot with infinite motion freedom pose various challenges to operation and control engineering. This research explores the motion of [...] Read more.
Soft robots with compliant bodies offer safe human–robot interaction as well as adaptability to unstructured dynamic environments. However, the nonlinear dynamics of a soft robot with infinite motion freedom pose various challenges to operation and control engineering. This research explores the motion of a pneumatic soft robot under diverse loading conditions by conducting finite element analysis (FEA) and using machine learning. The pneumatic soft robot consists of two parallel hyper-elastic tubular chambers that convert pneumatic pressure inputs into soft robot motion to mimic an elephant trunk and its motion. The body of each pneumatic chamber consists of a series of bellows to effectively facilitate the expansion, contraction, and bending of the body. The first chamber spans the entire length of the soft robot’s body, and the second chamber spans half of it. This unique asymmetric design enables the soft robot to bend and curl in various ways. Machine learning is used to establish a forward kinematic relationship between the pressure inputs and the motion responses of the soft robot using data from FEA. Accordingly, this research employs an artificial neural network that is trained on FEA data to estimate the reachable workspace of the soft robot for given pressure inputs. The trained neural network demonstrates promising estimation accuracy with an R-squared value of 0.99 and a root mean square error of 0.783. The workspaces of asymmetric double-chamber and single-chamber soft robots were compared, revealing that the double-chamber robot offers approximately 185 times more reachable workspace than the single-chamber soft robot. Full article
(This article belongs to the Special Issue Bio-Inspired Soft Robotics)
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<p>The soft actuator inspired by the elephant trunk [<a href="#B6-actuators-14-00110" class="html-bibr">6</a>].</p>
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<p>Overall approach.</p>
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<p>Soft robot model. The measurement unit is mm.</p>
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<p>Soft robot base and tip and two pneumatic chambers.</p>
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<p>Analysis setup: (<b>a</b>) constraints for gravitational load analysis, (<b>b</b>) eccentricity, and (<b>c</b>) surface contacts.</p>
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<p>The effects of gravity on bending displacement and stress.</p>
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<p>Neural network architecture.</p>
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<p>Mean square errors vs. training epochs.</p>
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<p>Regression plots of neural network accuracy.</p>
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<p>Residual analysis of displacement responses: without noise (<b>left</b>) and with 0.1% Gaussian noise (<b>right</b>).</p>
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<p>Soft robot actuation for selected loading cases in <a href="#actuators-14-00110-t002" class="html-table">Table 2</a>.</p>
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<p>Soft robot tip paths for loading cases in <a href="#actuators-14-00110-t002" class="html-table">Table 2</a>.</p>
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<p>Soft robot tip paths estimated by trained NN for loading cases in <a href="#actuators-14-00110-t002" class="html-table">Table 2</a>.</p>
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<p>Estimated workspace of soft robot tip for pressure inputs between 600 kPa and 700 kPa: top (<b>a</b>), front (<b>b</b>), side (<b>c</b>), and isometric (<b>d</b>) views of workspace in reference frame R1.</p>
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<p>Workspace of the single-chamber soft robot tip for pressure inputs between 0 and 700 kPa: top (<b>a</b>), front (<b>b</b>), side (<b>c</b>), and isometric (<b>d</b>) views.</p>
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<p>Comparisons between asymmetric and single-chamber pneumatic soft robots.</p>
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27 pages, 3932 KiB  
Article
How Programmable Construction Can Shape the Future of Sustainable Building in Italy
by Silvia Mazzetto, Haidar H. Hosamo and Mohamed Ezzat Al-Atroush
Sustainability 2025, 17(5), 1839; https://doi.org/10.3390/su17051839 - 21 Feb 2025
Viewed by 281
Abstract
The construction industry has traditionally relied on labor-intensive methods, often resulting in inefficiencies, cost overruns, and extended project timelines. Despite advancements in automation and robotics, the potential of programmable construction to address these challenges remains underexplored, particularly in the context of small to [...] Read more.
The construction industry has traditionally relied on labor-intensive methods, often resulting in inefficiencies, cost overruns, and extended project timelines. Despite advancements in automation and robotics, the potential of programmable construction to address these challenges remains underexplored, particularly in the context of small to medium-scale projects. This study investigates the impact of programmable construction on time, cost, and sustainability, using a detailed case study of a residential project in Italy. This research adopts a comparative approach, analyzing traditional construction techniques versus automated construction systems. Production rates from previous research and real-world applications are used to develop alternative schedules that reflect the efficiencies of these advanced technologies. The findings demonstrate that programmable construction can reduce project timelines by up to 82.6% and achieve cost savings of approximately 40.6%. Automated systems also offer significant environmental advantages, including a 70.25% reduction in carbon emissions and a 70% decrease in energy consumption in several tasks such as soil treatment. This study suggested that programmable construction sites can significantly shorten project timelines and reduce costs. The precision and speed of AI and robotics minimize reliance on human labor, streamline construction processes, and enhance project performance and work quality by reducing human error while promoting sustainability through reduced resource consumption and lower environmental impact. Full article
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<p>Research methodology framework.</p>
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<p>Architectural floor plan of the small residential unit in the Veneto Region, Italy.</p>
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<p>Small residential unit: front porch during the construction works (credit: authors).</p>
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<p>Small residential unit: the figure represents the phase of roof installation during the construction works (credit: authors).</p>
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<p>Productivity rates of traditional construction methods and automated systems across various construction tasks.</p>
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<p>Cost savings and environmental benefits associated with automated systems compared to traditional construction methods.</p>
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<p>Time required to complete various construction tasks using traditional methods versus automated systems.</p>
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<p>Number of workers required for different construction tasks when using traditional methods versus automated systems.</p>
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<p>Safety improvements achieved with the use of automated systems across various construction tasks.</p>
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<p>Multi-tasking capabilities of different automated systems.</p>
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20 pages, 4945 KiB  
Article
At-Home Stroke Neurorehabilitation: Early Findings with the NeuroExo BCI System
by Juan José González-España, Lianne Sánchez-Rodríguez, Maxine Annel Pacheco-Ramírez, Jeff Feng, Kathryn Nedley, Shuo-Hsiu Chang, Gerard E. Francisco and Jose L. Contreras-Vidal
Sensors 2025, 25(5), 1322; https://doi.org/10.3390/s25051322 - 21 Feb 2025
Viewed by 288
Abstract
Background: Democratized access to safe and effective robotic neurorehabilitation for stroke survivors requires innovative, affordable solutions that can be used not only in clinics but also at home. This requires the high usability of the devices involved to minimize costs associated with support [...] Read more.
Background: Democratized access to safe and effective robotic neurorehabilitation for stroke survivors requires innovative, affordable solutions that can be used not only in clinics but also at home. This requires the high usability of the devices involved to minimize costs associated with support from physical therapists or technicians. Methods: This paper describes the early findings of the NeuroExo brain–machine interface (BMI) with an upper-limb robotic exoskeleton for stroke neurorehabilitation. This early feasibility study consisted of a six-week protocol, with an initial training and BMI calibration phase at the clinic followed by 60 sessions of neuromotor therapy at the homes of the participants. Pre- and post-assessments were used to assess users’ compliance and system performance. Results: Participants achieved a compliance rate between 21% and 100%, with an average of 69%, while maintaining adequate signal quality and a positive perceived BMI performance during home usage with an average Likert scale score of four out of five. Moreover, adequate signal quality was maintained for four out of five participants throughout the protocol. These findings provide valuable insights into essential components for comprehensive rehabilitation therapy for stroke survivors. Furthermore, linear mixed-effects statistical models showed a significant reduction in trial duration (p-value < 0.02) and concomitant changes in brain patterns (p-value < 0.02). Conclusions: the analysis of these findings suggests that a low-cost, safe, simple-to-use BMI system for at-home stroke rehabilitation is feasible. Full article
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<p>Timeline and phases of the early-feasibility testing for the NeuroExo BMI-exoskeleton system.</p>
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<p>Graphics user interface (GUI) depicting the visual feedback provided to the user during the positioning of the NeuroExo device on the head. The impedance of EEG electrodes—scalp and EOG sensors—face are color-coded from low impedance (white) to high impedance (black) values. The correct positioning of the headset leads to lower impedance values.</p>
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<p>An example of a participant fitted with the NeuroExo device and upper-limb exoskeleton while performing a trial at home. The tablet allowed the participant to set up the system and receive visual feedback (reproduced with permission from [<a href="#B12-sensors-25-01322" class="html-bibr">12</a>]).</p>
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<p>Characterizations of the performance of the NeuroExo system in terms of users’ compliance, perceived BCI performance, and electrode signal quality. (<b>a</b>). For each of the five participants with chronic stroke, the age, sex, impaired side, and home state are provided. Each graph depicts the level of electrode impedance [0, <math display="inline"><semantics> <mrow> <mn>100</mn> <mspace width="3.33333pt"/> <mi mathvariant="normal">k</mi> <mo>Ω</mo> </mrow> </semantics></math>] (five symbols are used to code for electrode location along the frontocentral scalp in the 10–20 system). Users’ compliance is denoted as the number of blocks performed by the users per week in a counterclockwise direction (shading). The percentage of adequate impedance values (&lt;=<math display="inline"><semantics> <mrow> <mn>100</mn> <mspace width="3.33333pt"/> <mi mathvariant="normal">k</mi> <mo>Ω</mo> </mrow> </semantics></math>) per week is shown in parenthesis. Note that participant S3 conducted NeuroExo therapy over 18 weeks due to therapy interruptions caused by extensive travel. Perceived BCI performance is color-coded by week on each graph. (<b>b</b>). The signal quality distribution is shown; the majority of the percentages for adequate impedances are located in upper buckets. Key: * indicates that these participants did not receive any assistance from family or friends during therapy.</p>
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<p>Trial block duration decreased with training. Boxplots display the distribution of impedance data across weeks and participants, with a linear fit overlaid to highlight trends in trial block duration (min) over time. Red + symbol indicates the outliers in the data. The fit was performed using MATLAB’s polynomial curve fitting function. Key: * indicates that these participants did not receive assistance from family members or friends during the trial.</p>
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<p>MRCP amplitude in early versus late sessions. Early MRCPs in blue represent the MRCP across a block of trials at the beginning of this longitudinal study and green MRCPs represent the last block of trials at the end of the longitudinal study. The annotation of the impedance values is provided to assess signal quality. Key: * indicates that these participants were not assisted by family members/friends.</p>
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<p>AUC amplitude in FC1, FCz, and FC2 in early versus late sessions. Each graph shows the early versus late Area Under the Curve (AUC) computed from the first and last two blocks in this longitudinal study for every participant by channel location. Red + symbol indicate the outliers in the data.</p>
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<p>Newest NeuroExo headset version. Based on user feedback, some of the joints were reinforced, the micro-USB was replaced with USB-C, and the positioning of the EEG electrodes was more stable and easy to adjust.</p>
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<p>System assessment survey. Survey taken by participants after every session. It includes five prompts to assess usability, comfort, and perceived BCI performance of system.</p>
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16 pages, 1768 KiB  
Review
The Next Frontier in Neuroprosthetics: Integration of Biomimetic Somatosensory Feedback
by Yucheng Tian, Giacomo Valle, Paul S. Cederna and Stephen W. P. Kemp
Biomimetics 2025, 10(3), 130; https://doi.org/10.3390/biomimetics10030130 - 21 Feb 2025
Viewed by 393
Abstract
The development of neuroprosthetic limbs—robotic devices designed to restore lost limb functions for individuals with limb loss or impairment—has made significant strides over the past decade, reaching the stage of successful human clinical trials. A current research focus involves providing somatosensory feedback to [...] Read more.
The development of neuroprosthetic limbs—robotic devices designed to restore lost limb functions for individuals with limb loss or impairment—has made significant strides over the past decade, reaching the stage of successful human clinical trials. A current research focus involves providing somatosensory feedback to these devices, which was shown to improve device control performance and embodiment. However, widespread commercialization and clinical adoption of somatosensory neuroprosthetic limbs remain limited. Biomimetic neuroprosthetics, which seeks to resemble the natural sensory processing of tactile information and to deliver biologically relevant inputs to the nervous system, offer a promising path forward. This method could bridge the gap between existing neurotechnology and the future realization of bionic limbs that more closely mimic biological limbs. In this review, we examine the recent key clinical trials that incorporated somatosensory feedback on neuroprosthetic limbs through biomimetic neurostimulation for individuals with missing or paralyzed limbs. Furthermore, we highlight the potential impact of cutting-edge advances in tactile sensing, encoding strategies, neuroelectronic interfaces, and innovative surgical techniques to create a clinically viable human–machine interface that facilitates natural tactile perception and advanced, closed-loop neuroprosthetic control to improve the quality of life of people with sensorimotor impairments. Full article
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<p>Human studies on biomimetic tactile feedback in upper-limb (<b>A</b>–<b>D</b>) and lower-limb (<b>E</b>) neuroprosthetics. (<b>A</b>) Biologically inspired prosthesis system. Neuromorphic (i.e., mimicking biological structure and function) tactile sensors combined with biomimetic (i.e., mimicking biological processes and signals) neuron models provided specific responses that corresponded to different objects. Adapted from [<a href="#B63-biomimetics-10-00130" class="html-bibr">63</a>]. (<b>B</b>) Biomimetic encoding strategies outperformed non-biomimetic sensory stimulation during object size and compliance discrimination tasks. * <span class="html-italic">p</span> &lt; 0.05. Adapted from [<a href="#B64-biomimetics-10-00130" class="html-bibr">64</a>]. (<b>C</b>) Implemented and compared sensory encoding strategies, including amplitude neuromodulation (ANM), frequency neuromodulation (FNM), and hybrid neuromodulation (HNM). Adapted from [<a href="#B65-biomimetics-10-00130" class="html-bibr">65</a>]. (<b>D</b>) Biomimetic ICMS resulted in improved sensitivity of the electrode with reduced just-noticeable differences (JNDs) and higher resolution force feedback compared with non-biomimetic stimulation. Adapted from [<a href="#B47-biomimetics-10-00130" class="html-bibr">47</a>]. (<b>E</b>) Biomimetic stimulation provided more natural tactile perception (rated from 0: totally unnatural to 5: totally natural) in both participants with lower-limb amputations. Adapted from [<a href="#B68-biomimetics-10-00130" class="html-bibr">68</a>]. All figures were reprinted with permissions.</p>
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<p>Next-generation neuroprosthetics that integrate biomimetic tactile feedback shown in steps. Flexible, electronic skin (e-skin) converts captured tactile data into biologically relevant outputs through biomimetic circuit designs. The tactile information is then processed using encoding strategies and neural networks to create multichannel biomimetic stimulation patterns. Subcellular-scale stimulation electrodes provide the precision needed to target individual neurons, selectively activating the sensory fiber populations responsible for conveying specific tactile information in response to the tactile stimuli. Meanwhile, high-density recording electrodes allow for improved decoding of motion intent. A surgical construct that biologically separates motor and sensory axons within the peripheral nerve provides optimal access to mechanoreceptors, facilitating accurate and naturalistic biomimetic tactile feedback.</p>
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<p>Current technologies that can potentially facilitate biomimetic tactile feedback. (<b>A</b>) E-skin. Adapted from [<a href="#B90-biomimetics-10-00130" class="html-bibr">90</a>]. (<b>B</b>) Sharpened subcellular electrode. Adapted from [<a href="#B99-biomimetics-10-00130" class="html-bibr">99</a>]. Scale bars, 500 μm. (<b>C</b>) High-density neural electrode. Adapted from [<a href="#B100-biomimetics-10-00130" class="html-bibr">100</a>]. (<b>D</b>) Composite Regenerative Peripheral Nerve Interface (C-RPNI) approach to access mechanoreceptors. Adapted from [<a href="#B101-biomimetics-10-00130" class="html-bibr">101</a>]. All figures were reprinted with permissions.</p>
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