Bionic design and analysis of a multi-posture wheelchair

Posture transformation is an essential function for multi-posture wheelchairs. To improve the natural motion in posture transformation that is a popular problem in the design of multi-posture wheelchairs because the current wheelchair's posture transformation mechanism cannot remain consistent between the rotation center of the wheelchair and the rotation center of the human body joints. This paper proposes a sitting–standing–lying three-posture bionic transformation mechanism for a smart wheelchair. A human–wheelchair coupling model is described and analyzed according to the biomechanical characteristics of the posture transformation of human beings and their functional requirements. The configuration of the transformation mechanism is chosen by comparing the trails of the wheelchair rotation centers and the corresponding human joint rotation centers. The kinematics of the optimized configuration are discussed in detail to obtain the most bionic motion performance using the multivariable nonlinear constraint optimization algorithm. Finally, the mechanism is designed, and its posture transformation performance is simulated and verified using Adams (Automatic Dynamic Analysis of Mechanical Systems) software.

Design and Control of an Adaptive Knee Joint Exoskeleton Mechanism with Buffering Function

A knee exoskeleton with an adaptive instantaneous rotation center and impact absorption is used for rehabilitation. Due to the human knee joint’s special physiological structure and motion characteristics, the exoskeleton mechanism needs to be designed for both static and dynamic aspects. Therefore, a novel knee exoskeleton mechanism was designed. To adapt to the rotation center of the knee joint, a mechanism with cross-configuration was designed according to the equivalent degree of freedom and the stiffness of the springs was calculated by its combination with gait motion, so that the average force of the human body was minimized. A dynamic model of the exoskeleton was established. To overcome the uncertainty in the parameters of the human and robotic limbs, an adaptive controller was designed and a Lyapunov stability analysis was conducted to verify the system. A simulation was conducted and experimental results show that the tracking error of the knee joint angle between the actual and desired trajectory was within the range of −1 to 1 degree and indicate the effectiveness of the controller.

Fast Correction of “Finite Aperture Effect” in Photoacoustic Tomography Based on Spatial Impulse Response

Photoacoustic computed tomography (PACT) is a fast-developing imaging technique, which can provide structural and functional information in biological tissues with high-resolution beyond the depth of the optical diffusion limit. However, the most current PACT reconstruction method generally employs a point detector assumption, whereas in most PAT systems with circular or spherical scanning modes, the transducer is mostly flat and with a finite size. This model mismatch leads to a notable deterioration in the lateral direction in regions far from the rotation center, which is known as the “finite aperture effect”. In this work, we propose to compensate a novel Back-projection (BP) method based on the transducer’s spatial impulse response (SIR) for fast correction of the “finite aperture effect”. The SIR accounts for the waveform change of the transducer for an arbitrary point source due to the geometry of the detection surface. Simulation results showed that the proposed SIR-BP method can effectively improve the lateral resolution and signal to noise ratio (SNR) in the off-center regions. For a target 4.5 mm far from the rotation center, this new method improved the lateral resolution about five times along with a 7 dB increase in the SNR. Experimental results also showed that this SIR-BP method can well restore the image angular blur to recover small structures, as demonstrated by the imaging of leaf veins. This new method offers a valuable alternative to the conventional BP method, and can guide the design of PAT systems based on circular/spherical scan.

Mathematical Description for a Particular Case of Ellipse Focus Quasi-Rotation Around an Elliptical Axis

In this paper is provided mathematical analysis related to a particular case for a point quasi-rotation around a curve of an elliptical axis. The research complements the previous works in this direction. Has been considered a special case, in which the quasi-rotation correspondence is applied to a point located at the elliptical axis’s focus. This case is special, since the quasi-rotation center search is not invariant and does not lead to determination of four quasi-rotation centers, as in the general case. A constructive approach to the rotation center search shows that any point lying on the elliptical axis can be the quasi-rotation center. This feature leads to the fact that instead of four circles, the quasi-rotation of a point lying in the elliptical axis’s focus leads to the formation of an infinite number of circle families, which together form a channel surface. The resulting surface is a Dupin cyclide, whose throat circle has a zero radius and coincides with the original generating point. While analyzing are considered all cases of the rotation center location. Geometric constructions have been performed based on previously described methods of rotation around flat geometric objects’ curvilinear axes. For the study, the mathematical relationship between the coordinates of the initial set point, the axis curve equation and the motion trajectory equation of this point around the axis curve, described in earlier papers on this topic, is used. In the proposed paper has been provided the derivation of the motion trajectory equation for a point around the elliptic axis’s curve.

Mathematical Description for a Particular Case of Ellipse Focus Quasi-Rotation Around an Elliptical Axis

In this paper is provided mathematical analysis related to a particular case for a point quasi-rotation around a curve of an elliptical axis. The research complements the previous works in this direction. Has been considered a special case, in which the quasi-rotation correspondence is applied to a point located at the elliptical axis’s focus. This case is special, since the quasi-rotation center search is not invariant and does not lead to determination of four quasi-rotation centers, as in the general case. A constructive approach to the rotation center search shows that any point lying on the elliptical axis can be the quasi-rotation center. This feature leads to the fact that instead of four circles, the quasi-rotation of a point lying in the elliptical axis’s focus leads to the formation of an infinite number of circle families, which together form a channel surface. The resulting surface is a Dupin cyclide, whose throat circle has a zero radius and coincides with the original generating point. While analyzing are considered all cases of the rotation center location. Geometric constructions have been performed based on previously described methods of rotation around flat geometric objects’ curvilinear axes. For the study, the mathematical relationship between the coordinates of the initial set point, the axis curve equation and the motion trajectory equation of this point around the axis curve, described in earlier papers on this topic, is used. In the proposed paper has been provided the derivation of the motion trajectory equation for a point around the elliptic axis’s curve.

Effects of the depth of the acetabular component during simulated acetabulum reaming in total hip arthroplasty

We aimed to evaluate whether there are differences in the rotation center, cup coverage, and biomechanical effects between conventional and anatomical technique. Computed tomography scans of 26 normal hips were used to simulate implantation of acetabular component. The hip rotation center and acetabular component coverage rate were calculated. Moreover, a finite element model of the hip joint was generated to simulate and evaluate the acetabular cup insertion. Micromotion and the peak stress distribution were used to quantify the biomechanical properties. The medial and superior shifts of the rotation center were 5.2 ± 1.8 mm and 1.6 ± 0.7 mm for the conventional reaming technique and 1.1 ± 1.5 mm and 0.8 ± 0.5 mm for anatomical technique, respectively. The acetabular component coverage rates for conventional reaming technique and anatomical technique were 86.8 ± 4% and 70.0 ± 7%, respectively. The micromotion of the cup with conventional reaming technique was greater than that with anatomical technique. The peak stress concentration was highest in the superior portion with conventional reaming technique, whereas with anatomical technique, there was no stress concentration. Paradoxically although the acetabular component coverage rate is larger with conventional reaming technique, anatomical technique provides less micromotion and stress concentration for initial cup stability. Thus, anatomical technique may be more suitable for acetabulum reaming during primary total hip arthroplasty.