《电磁铁》教学构想

一、教学目的要求(一)通过本课的教学,要求学生知道电磁铁在通电条件下有磁性,电磁铁也有两极,它的两极是可以改变的。(二)要求学生知道电磁铁的磁力大小与串联电池的数量、线圈匝数有关系(即电池多、线圈匝数多、磁力比较大)。

Kinematic Characteristics Analysis of 3-PRS Parallel Manipulator

The 3-PRS parallel mechanisms,whose kinematic chain is connected by prismatic joint P,revolute joint R and spherical joint S,have two rotational and one translational DOF.But the DOF of 3-PRS parallel mechanism cannot be explained by the Grubler-Kutzbach method or Herve method.To illuminate the special kinematic characteristics of 3-PRS parallel mechanism,a novel analytical approach is proposed in this paper.All the feasible instantaneous motions of 3-PRS mechanism are studied by using this method.The analysis of kinematic characteristics of 3-PRS mechanism help to understand the mechanism and estimate the motion capacity of mechanism.Finally,it is also helpful to optimize the topology of the mechanism and the trajectory for desired performance.

Design methods of headed studs for composite decks of through steel bridges in high-speed railway

Aimed at two typical composite floor systems of through steel bridges in high speed railway,design methods of headed studs were put forward for different composite members through comparing and analyzing the structure,mechanical characteristics and transmission routes of deck loads.The simplified calculation models were brought out for the stud design of the longitudinal girders and transverse girders in the composite floor system of Nanjing Dashengguan Yangtze River Bridge (NDB).Studs were designed and arranged by taking the middle panel of 336 m main span for example.The results show that under deck loads,the longitudinal girders in the composite floor system of through steel bridges are in tension-bending state,longitudinal shear force on the interface is caused by both longitudinal force of "The first mechanical system" and vertical bending of "The second mechanical system",and studs can be arranged with equal space in terms of the shear force in range of 0.2d (where d is the panel length) on the top ends.Transverse girders in steel longitudinal and transverse girders-concrete slab composite deck are in compound-bending state,and out-of-plane bending has to be taken into account in the stud design.In orthotropic integral steel deck-concrete slab composite deck,out-of-plane bending of transverse girders is very small so that it can be neglected,and studs on the orthotropic integral steel deck can be arranged according to the structural requirements.The above design methods and simplified calculation models have been applied in the stud design of NDB.

Error Analysis of Robotic Assembly System Based on Screw Theory

Assembly errors have great influence on assembly quality in robotic assembly systems. Error analysis is directed to the propagations and accumula-tions of various errors and their effect on assembly success.Using the screw coordinates, assembly errors are represented as 'error twist', the extremely compact expression. According to the law of screw composition, relative position and orientation errors of mating parts are computed and the necessary condition of assembly success is concluded. A new simple method for measuring assembly errors is also proposed based on the transformation law of a screw.Because of the compact representation of error, the model presented for error analysis can be applied to various part- mating types and especially useful for error analysis of complexity assembly.

A linear rotary magnetorheological damper for vehicles

A new type of linear rotary magnetorheological damper (MRD) is proposed, which consists of a cylinder-type MRD and a screw mechanism to transform a linear motion into revolving motion. It is found that the structure parameters of MRD have complex relationship with the force of the damper, especially the lead angle, width and radius of the inner rotor. The analyses and simulation calculation of the static magnetic field give some usable data, and experiments of the damping component indicate that the proposed methods is feasible for developing linear rotary MRD.

Pedicle screw placement in the thoracic spine： a randomized comparison study of computer-assisted navigation and conventional techniques

Objective： To evaluate the accuracy of computer-assisted pedicle screw installation and its clinical benefit as compared with conventional pedicle screw installation techniques. Methods： Total 176 thoracic pedicle screws placed in 42 thoracic fracture patients were involved in the study randomly, 20 patients under conventional fluoroscopic control （84 screws） and 22 patients had screw insertion under three dimensional （3D） computer-assisted navigation （92 screws）. The 2 groups were compared for accuracy of screw placement, time for screw insertion by postoperative thincut CT scans and statistical analysis by χ^2 test. The cortical perforations were then graded by 2-mm increments： Grade Ⅰ （good, no cortical perforation）, Grade Ⅱ （screw outside the pedicle 〈2 mm）, Grade Ⅲ （screw outside the pedicle 〉2 mm）. Results： In computer assisted group, 88 （95.65%） were Grade Ⅰ （good）, 4 （4.35%） were Grade Ⅱ （〈2mm）, no Grade Ⅲ （〉2 mm） violations. In conventional group, there were 14 cortical violations （16.67%）, 70 （83.33%） were Grade Ⅰ （good）, Ⅱ （13.1%） were Grade Ⅱ （〈2 mm）, and 3 （3,57%） were Grade Ⅲ （〉2 mm） violations （P〈0.001）. The number （19.57%） of upper thoracic pedicle screws （ T1-T4 ） inserted under 3D computer-assisted navigation was significantly higher than that （3.57%） by conventional fluoroscopic control （P〈0.001）. Average screw insertion time in conventional group was （4.56 ±1.03） min and （2.54 ± 0.63） min in computer assisted group （P〈0.001）. In the conventional group, one patient had pleura injury and one had a minor dura violation. Conclusions： This study provides further evidence that 3D computer-assisted navigation placement ofpedicle screws can increase accuracy, reduce surgical time, and be performed safely and effectively at all levels of the thoracic spine, particularly upper thoracic spine.

Minimally invasive percutaneous compression plating versus dynamic hip screw for intertrochanteric fractures： a randomized control trial

Objective：Intertrochanteric femur fracture is a common injury in elderly patients.The dynamic hip screw （DHS） has served as the standard choice for fixation; however it has several drawbacks.Studies of the percutaneous compression plate （PCCP） are still inconclusive in regards to its efficacy and safety.By comparing the two methods,we assessed their clinical therapeutic outcome.Methods：Atotal of 121 elderly patients with intertrochanteric femur fractures （type AO/OTA 31.A 1-A2,Evans type 1） were divided randomly into two groups undergoing either a minimally invasive PCCP procedure or a conventional DHS fixation.Results：The mean operation duration was significantly shorter in the PCCP group （55.2 min versus 88.5 min,P＜0.01）.The blood loss was 156.5 ml±18.3 ml in the PCCP group and 513.2 ml±66.2 ml in the DHS group （P＜0.01）.Among the patients treated with PCCP,3.1％ needed blood transfusions,compared with 44.6％ of those that had DHS surgery （P＜0.01）.The PCCP group displayed less postoperative complications （P＜0.05）.The mean American Society of Anesthesiologists score and Harris hip score in the PCCP group were better than those in the DHS group.There were no significant differences in the mean hospital stay,mortality rates,or fracture healing.Conclusion：Due to several advantages,PCCP has the potential to become the ideal choice for treating intertrochanteric fractures （type AO/OTA 31.A1-A2,Evans type 1）,particularly in the elderly.