Dynamic and Wrench-Feasible Workspace Analysis of a Cable-Driven Parallel Robot Considering a Nonlinear Cable Tension Model

Cable-driven parallel robots (CDPRs) have several advantages and have been widely used in many industrial fields, especially industrial applications that require high dynamics, high payload capacity, and a large workspace. In this study, a design model for a CDPR system was proposed, and kinematic and dynamic modeling of the system was performed. Experiments were carried out to identify the dynamic modulus of elastic cables based on the dynamic mechanical analysis (DMA) method. A modified kinematic equation considering cable nonlinear tension was developed to determine the optimal cable tension at each position of the end-effector, and the wrench-feasible workspace was analyzed at various motion accelerations. The simulation results show that the proposed CDPR system obtains a large workspace, and the overall workspace is satisfactory and unrestricted for moving ranges in directions limited by the X-axis and the Y-axis from −0.3 to 0.3 m and by the Z-axis from 0.1 to 0.7 m. The overall workspace was found to depend on the condition of acceleration as well as the moving ranges limited by the end-effector. With an increase in external acceleration, the cable tension distribution increased and reached a maximum in the case of 100 m/s2.

Rapid and safe wire tension distribution scheme for redundant cable-driven parallel manipulators

A non-iterative analytical approach is investigated to plan the safe wire tension distribution along with the cables in the redundant cable-driven parallel robots. The proposed algorithm considers not only tracking the desired trajectory but also protecting the system against possible failures. This method is used to optimize the non-negative wire tensions through the cables which are constrained based on the workspace conditions. It also maintains both actuators’ torque and cables’ tensile strength boundary limits. The pseudo-inverse problem solution leads to an n-dimensional convex problem, which is related to the robot degrees of redundancy. In this paper, a comprehensive solution is presented for a 1–3 degree(s) of redundancy in wire-actuated robots. To evaluate the effectiveness of this method, it is verified through an experimental study on the RoboCab cable robot in the infinity trajectory tracking task. As a matter of comparison, some standard methods like Active-set and sequential quadratic programming are also presented and the average elapsed time for each method is compared to the proposed algorithm.

Smart surgical sutures using soft artificial muscles

Wound closure with surgical sutures is a critical challenge for flexible endoscopic surgeries. Substantial efforts have been introduced to develop functional and smart surgical sutures to either monitor wound conditions or ease the complexity of knot tying. Although research interests in smart sutures by soft robotic technologies have emerged for years, it is challenging to develop a soft robotic structure that possesses a similar physical structure as conventional sutures while offering a self-tightening knot or anchor to close the wound. This paper introduces a new concept of smart sutures that can be programmed to achieve desired and uniform tension distribution while offering self-tightening knots or automatically deploying secured anchors. The core technology is a soft hydraulic artificial muscle that can be elongated and contracted under applied fluid pressure. Each suture is equipped with a pressure locking mechanism to hold its temporary elongated state and to induce self-shrinking ability. The puncturing and holding force for the smart sutures with anchors are examined. Ex-vivo experiments on fresh porcine stomach and colon demonstrate the usefulness of the new smart sutures. The new approaches are expected to pave the way for the further development of smart sutures that will benefit research, training, and commercialization in the surgical field.

Optimized Design for Large Geotextile Mats over Soft Soil

In this paper, the failure mechanisms of large geotextile mats over soft soil are carried out through finite element analyses. A finite element model is generated and validated against centrifuge testing data and previously published data of numerical simulation. Parametric study is then carried out to investigate the geotextile tension distribution and the arrangement of crashed stone. Based on the parametric study, an optimized design considering the arrangement of rock berm and a special arrangement of large geotextiles was proposed to enhance the performance of the geotextile mats. The findings of this study can provide an engineering guidance for this new technique.

DIMENSIONAL SYNTHESIS OF A GAIT REHABILITATION CABLE-SUSPENDED ROBOT ON MINIMUM 2-NORM TENSIONS

A new design of gait rehabilitation robot with cable-suspended configuration is proposed. Due to the under-constrained nature, it enables reducing the constraint feeling of patients. Cables are attached to cuffs mounted on the leg. A detailed mechanical design is presented and a kinematics model is developed. Dimensional synthesis is performed in two steps. First, the cable disposition should be determined within a range to maintain cable-suspended configuration using the minimum 2-norm solution of tensions. Second, the optimal cable disposition is achieved with the Root Mean Square of tension solutions. Gait rehabilitation robots with three or four cables are discussed and compared to determine dimensional parameters in terms of the locations of pulleys. A simulation model with ADAMS software is presented and the cable module is utilized to imitate the cable-driven system in real. Tension distribution is obtained from the simulation model, which is employed in comparison with the calculated values. The simulation results demonstrate the effectiveness of the presented method.

Avalanches During Epithelial Tissue Growth; Uniform Growth and a Drosophila Eye Disc Model

In the physicists’ perspective, epithelial tissues constitute an exotic type of active matter with non-linear properties reminiscent of amorphous materials. In the context of a circular proliferating epithelium, modeled by the quasistatic vertex model, we identify novel discrete tissue scale rearrangements, i.e. cellular flow avalanches, which are a form of collective cell movement. During the avalanches, the cellular trajectories are radial in the periphery and form a vortex in the core. After the onset of these avalanches, the epithelial area grows discontinuously. The avalanches are found to be stochastic, and their strength is determined by the density of cells in the tissue. Overall, avalanches regularize the spatial tension distribution along tissue. Furthermore, the avalanche distribution is found to obey a power law, with an exponent consistent with sheer induced avalanches in amorphous materials. To decipher the role of avalanches in organ development, we simulate epithelial growth of theDrosophilaeye disc during the third instar using a computational model, which includes both signaling and mechanistic signalling. During the third instar, the morphogenetic furrow (MF), a ∼10 cell wide wave of apical area constriction propagates through the epithelium, making it a system with interesting mechanical properties. These simulations are used to understand the details of the growth process, the effect of the MF on the growth dynamics on the tissue scale, and to make predictions. The avalanches are found to depend on the strength of the apical constriction of cells in the MF, with stronger apical constriction leading to less frequent and more pronounced avalanches. The results herein highlight the dependence of simulated tissue growth dynamics on relaxation timescales, and serve as a guide forin vitroexperiments.

Recurrent Canine Paraphimosis: Modified Surgical Approach

Background: Paraphimosis is characterized by persistent penile exposure, due to the inability to retract the penis into the prepuce.This persistent exposure of a non-erect penis might result from traumas, infections, neoplasia, anatomic or neurological alterations, or even occur in its idiopathic form. Surgical treatment is indicated when it is not possible to keep the penis covered by the foreskin by trying it manually. The surgical techniques described are efficient in small exposures, however, when these are over 1.5 cm, surgical success might become a challenge. The objective of this study is to report a modified surgical approach to solve a 5 cm recurrent paraphimosis in a dog.Case: A 1-year-old male unneuteredmixed-breed dog, weighing 26 kg, waspresented for examination with a historypersistent paraphimosis background for around 2 months without apparent cause. The animal’s tutor reported that it had been submitted to 2 unsuccessful surgical procedures. When the reproductive system was examined, the animal showed a flaccid penis with 5 cm exposure outside the foreskin. A conservative treatment was used, which was also unsuccessful. The next step was a surgical procedure that used the combination of techniques, namely, phallopexy, preputial advancement and reconstruction preputial opening with suture along with orchiectomy. After 10 days, dehiscence of the ostium stitches occurred, which required debridement and new suture. However, it was not efficient and recurrence of the paraphimosis was observed. After 1 month, a new surgery was performed by adapting the phallopexy technique, which was carried out bilaterally and associated to the reconstruction preputial opening with captonated suture, which presented a successful outcome. After 8 months as of the last procedure, the patient is healthy and has no signs of paraphimosis recurrence.Discussion: No consensus has been achieved regarding the paraphimosis treatment, and the resolution of such disorder remains a challenge. For this reason, some parameters should be considered to minimize failure when choosing the surgical technique and, consequently, the recurrence of such condition. Tissue viability, morphological alterations, time of exposure, previous surgeries, and the length of the penis exposure are some of the criteria that must be taken into consideration when choosing the surgical technique. In this case, the first choice was the association of techniques that included preputial advancement, phallopexy and suture preputial opening due to the fact that the exposure was over 1.5 cm and for the existence of a preputial ostium defect, which justified its suture. Despite these associations, paraphimosis recurrence was observed and some of the probable causes include the inadequate position of the penis inside the foreskin flap during the phallopexy and lack of preputial integrity in its ventral aspect. The preputial advancement performed was not sufficient to prevent the exposure or reduce it in the recurrence of the condition, showing that the shortening of preputial muscles and the skin tension might loosen up with time. The second surgery employed bilateral phallopexy without penis exposure to guarantee its correct position, more caudal within the foreskin at the moment of the fixation. The ostium captonated suture also had a relevant role in the tension distribution up to the full tissue healing. New surgical approaches might be needed to achieve success in the paraphimosis treatment. In this report, the length of the penis exposure and the ostium defect were complicating factors. However, the association of the modified surgical techniques resulted in a successful resolution of the condition. Keywords: phallopexy, prepuce, penis, preputial advancement.Descritores: falopexia, prepúcio, pênis, avanço prepucial.Título: Parafimose canina recidivante: abordagem cirúrgica modificada.