Payload maximization for mobile flexible manipulators in environment with an obstacle

A mobile flexible manipulator is developed in order to achieve high performance requirements such as high-speed operation, increased high payload to mass ratio, less weight, and safer operation due to reduced inertia. Hence, this paper presents a method for finding the Maximum Allowable Dynamic Load (MADL) of geometrically nonlinear flexible link mobile manipulators. The full dynamic model of a wheeled mobile base and the mounted flexible manipulator is considered with respect to dynamics of non-holonomic constraint in environment including an obstacle. In dynamical analysis, an efficient model is employed to describe the treatment of a flexible structure in which both the geometric elastic nonlinearity and the foreshortening effects are considered. Then, a path planning algorithm is developed to find the maximum payload that the optimal strategy is based on the indirect solution to the open-loop optimal control problem. In order to verify the effectiveness of the presented algorithm, several simulation studies are carried out for finding the optimal path between two points in the presence of obstacles. The results clearly show the effect of flexibility and the proposed approach on mobile flexible manipulators

Mechanical Behavior of Lumbar Spine Functional Units in Response to Cement Augmentation of Vertebra Body

Introduction: Cement augmentation in vertebrae is used to promote mechanical strength after spinal fracture and recently vertebroplasty gaining popularity as a treatment for patients. The numerical simulation could be helpful to enhance the quality of treatments such as vertebroplasty via exact modeling of the lumbar spine. Materials and Methods: In this study, a three-dimensional finite element model created from CT images of L1-L3. According to clinical observation and recent studies, we consider that L2 augmented with two different volumes in 10 different distributions. Loadings were assumed to be pure momentum which applied in three anatomical directions (axial rotation, flexion, and lateral bending). Results: Our results were validated with experimental data which shows segments range of motion, ligaments forces, and intradiscal pressure had good agreement with our results. Cement augmentation increases max Von Misses stress in L2 cancellous bone and Increment in Cement volume has the same result. Cement augmentation increases L1-L2 intradiscal pressure. Cement augmentation decreases segments range of motion. Finally, Cement augmentation increases total stiffness of model. Conclusion: Taken together, vertebroplasty as a well-known method to treat the fractured vertebra, could be optimized to enhance patients' range of motion and decrease the complication of treatment

Simulation of incremental forming processes of a pyramidal ring made of two materials

Incremental forming is one of the most well-known forming processes for complex and asymmetric parts. This method uses a CNC machine, simple forming tool, and a die. This study focused on effects of some parameters such as the material, feed rate, pitch, rotational speed and movement strategy of tool on the dimensional precision, forming force, thickness distribution and fracture in the welding area. The results showed that single point incremental forming (SPIF) led to a better thickness distribution with lower tool force, whereas two-point incremental forming led to better dimensional accuracy. Rotational speed does not have any significant impact on the forming process while decreasing the feed rate partially reduced the forming force. According to the results, although dimensional precision in double point incremental forming is better than SPIF, when it comes to the thickness distribution, forming force, and economic issues, SPIF is in favor. The results also showed that by connecting two materials, different parameters for the two materials could be investigated simultaneously in one simulation process

Effects of TIG dressing, PWHT and temper bead techniques on microstructure and fatigue strength of fillet welded steel patch repairs: an experimental investigation

In-service patch welding is frequently used to repair corroded or damaged steel structures. However, the repair welding may adversely affect the long-term mechanical integrity of the structure. Fatigue treatment techniques could reduce such drawbacks. However, the effectiveness of treatment techniques in the case of in-service fillet welded steel patch repairs has not received due attention. This paper deals with the fatigue behavior of fillet welded patch repairs made on normalized A516 GR.70 carbon steel plates. The test specimens received different thermal treatments, including post-weld heat treatment (PWHT), TIG-dressing (TD), and temper bead (TB) welding. The pros and cons of these treatments were evaluated through quasi-static tensile tests, high-cycle constant amplitude fatigue testing, microstructural assessments, and hardness measurements. The TD treatment provided the most significant fatigue improvement, owing to beneficial changes it made to the geometry, microstructure and hardness of the weld toe area. The fatigue life and the fatigue-prone locations in the PWHT and TB specimens did not significantly vary from those in the untreated welded specimens. However, there was a reduction of the ultimate tensile strength in the PWHT specimens. The microstructure of the heat-affected zone plus the hardness of the weld toe areas significantly contributed to the fatigue performance. The fatigue lives of the fillet welded patch repairs were also interrelated to the geometrical changes caused in the weld toe by the treatment method

Case Report: Combination Therapy with Mesenchymal Stem Cells and Granulocyte-Colony Stimulating Factor in a Case of Spinal Cord Injury

Introduction: Various neuroregenerative procedures have been recently employed along with neurorehabilitation programs to promote neurological function after Spinal Cord Injury (SCI), and recently most of them have focused on the acute stage of spinal cord injury. In this report, we present a case of acute SCI treated with neuroprotective treatments in conjunction with conventional rehabilitation program. Methods: A case of acute penetrative SCI (gunshot wound), 40 years old, was treated with intrathecal bone marrow derived stem cells and parenteral Granulocyte-Colony Stimulating Factor (G-CSF) along with rehabilitation program. The neurological outcomes as well as safety issues have been reported. Results: Assessment with American Spinal Injury Association (ASIA), showed neurological improvement, meanwhile he reported neuropathic pain, which was amenable to oral medication. Discussion: In the acute setting, combination therapy of G-CSF and intrathecal Mesenchymal Stem Cells (MSCs) was safe in our case as an adjunct to conventional rehabilitation programs. Further controlled studies are needed to find possible side effects, and establish net efficacy