Clamping Position Research Articles

A New Fast Method for Obtaining Flux-Linkage Characteristics of SRM

This paper proposes a new fast method to determine the entire flux-linkage characteristics of a switched reluctance machine (SRM), which are critical for performance estimation and advanced control of the machine. The proposed method mainly consists of two steps, namely, measuring and calculating. In the measuring step, the flux-linkage characteristics of the SRM are measured at four specific rotor positions by a new indirect method without rotor clamping devices and position sensors. The magnetic coupling among phases is considered to improve the accuracy of measurement. In the calculating step, based on the measured results, the analytical expression of the flux-linkage characteristics is proposed, which only needs a few coefficients. With the expression, the flux-linkage characteristics at any rotor position can be calculated. The entire flux-linkage characteristics of a 1-kW three-phase 12/8-pole SRM obtained by the proposed method and traditional rotor clamping method are compared, and a good agreement can be found, which verifies the feasibility and accuracy of the proposed method. Furthermore, with the entire flux-linkage characteristics calculated by the proposed analytical method, the dynamic performances of the SRM prototype under both motoring and generating modes are simulated and compared with those from other methods and experiments, which further verify the accuracy of the proposed method.

Optimization of machining fixture layout using integrated response surface methodology and evolutionary techniques

Fixtures are the work-holding devices, widely used in manufacturing, to completely immobilize the workpiece during machining. The position of fixture elements around the workpiece strongly influences the workpiece deformation which in-turn affects the machining accuracy. The workpiece deformation can be minimized by finding the appropriate position for the locators and clamps. Thus, it is necessary to model the complex behavioral relationship that exists in the fixture–workpiece system. In this research paper, response surface methodology is used to model the relationship between position of locators and clamps and maximum deformation of the workpiece during end-milling, and then the developed model has been optimized by genetic algorithm and particle swarm optimization. As the predictive model is being developed by response surface methodology, a huge reduction in computational complexity and time is achieved during the optimization of machining fixture layout. Also, it is evident that the approach which integrates response surface methodology and particle swam optimization produces better results.

Reverse Trendelenburg position is a safer technique for lowering central venous pressure without decreasing blood pressure than clamping of the inferior vena cava below the liver.

Bleeding remains an important intraoperative complication in patients who undergo hepatectomy. It is generally believed that a reduction in central venous pressure will decrease bleeding from the hepatic venous system. To our knowledge, however, no study has compared the effectiveness of these techniques for controlling bleeding. So we compared the effectiveness of central venous pressure control techniques, such as infrahepatic inferior vena cava clamping, changes in surgical position of the patient, and hypoventilation anesthesia, for lowering central venous pressure. The study group comprised 50 patients who underwent hepatectomy in our department from 2012 through 2013. A central venous catheter was inserted into the right internal jugular vein, and the tip was placed in the superior vena cava. A transducer was placed along the mid-axillary line of the left side of the chest. After opening the abdomen, changes in central venous pressure were measured during inferior vena cava clamping, the reverse Trendelenburg position, the Trendelenburg position, and hypoventilation anesthesia. The inclination relative to the transducer, as measured with an inclinometer, was -10 degrees for the Trendelenburg position and +10 degrees for the reverse Trendelenburg position. The tidal volume was set at 10 mL/kg during conventional anesthesia and 5 mL/kg during hypoventilation anesthesia. The mean central venous pressure was 8.0 cm H(2)O in the supine position during conventional anesthesia, 5.0 cm H(2)O during inferior vena cava clamping, 5.6 cm H(2)O during reverse Trendelenburg position, 10.6 cm H(2)O during Trendelenburg position, and 7.6 cm H(2)O during hypoventilation anesthesia. The mean central venous pressure during inferior vena cava clamping and reverse Trendelenburg position was significantly lower than that during supine position (P = 0.0017 and P = 0.0231, respectively). The mean central venous pressure during hypoventilation anesthesia was not significantly lower than that during supine position (P = 0.9934). Mean systolic blood pressure was significantly decreased during inferior vena cava clamping (P = 0.0024), but not during reverse Trendelenburg position (P = 0.6344). Reverse Trendelenburg position decreased central venous pressure without significantly decreasing the systolic blood pressure, suggesting that it is possible to perform hepatectomy with reverse Trendelenburg position more safely than with inferior vena cava clamping.

Parametric Variational Analysis of Compliant Sheet Metal Assemblies with Shell Elements

One of most demanding tasks in the manufacturing field is controlling the variability of parts as it may affect strongly the deliverability of key characteristics defined at the final (product) assembly level. Current CAT systems offer a good solution to the tolerance analysis/synthesis task, but to handle flexible objects with shape errors more effort is needed to include methods able to capture the elastic behaviour of parts that adds more variability on the final assembly. Usually, sheet metal assemblies require dedicated fixtures and clamps layout to control the gap between parts in the specific location where a join must be placed. Due to the variability of parts the position of clamps can also be varied. The paper describes a FEM-based method able take into account part flexibility and shape error to parametrically analyse sheet metal assemblies by acting on some key parameters to look for the optimal clamp layout that guarantee the gap between parts to be under control after joining parts together. This method offers, with respect to commercial solutions, the ability to model fixtures, clamps and different joint types with no matter on the mesh nodes’ position. Locations of such elements are based on the shape functions defined at element (shell) mesh level and modelled as local constraints. So the user can generate a mesh without a previous knowledge of the exact positions of clamps, for example. This allows to conduit a faster parametric analysis without remeshing the surfaces and with no need to physically model the clamps. An aeronautic case study is described with a four-part assembly riveted on a quite complex fixture by using several clamps.

Error compensation of thin plate-shape part with prebending method in face milling

Low weight and good toughness thin plate parts are widely used in modern industry, but its flexibility seriously impacts the machinability. Plenty of studies focus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surface errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling forces calculated by the micro-unit cutting force model are loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed method not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.

Research on Transfer Clamp of Rear Fender Extension Plate Multi-Station Stamping

Multi-station stamping production with high production efficiency and low overall cost is an important technology for mass production of automotive components. This paper aims at the shape characteristics and overall process of the rear fender extension plate, determines the clamping position, works out the clamp plan during the parts transmission from OP20 to OP30, and builds the horizontal and vertical deflection mechanical models. After calculation and comparison, a suitable mode is selected for the production of clamping. The selection and check of clamping position provides a method and practical example for real production.

Development of Stamping Process CAD System on Automatic Production Line for Robotic Manipulation

. When transporting the large and medium-sized stamping parts on automatic stamping production line, robotic end picking-up device (tooling) needs reasonable clamping positions to ensure smooth precision transmission and safe production. Based on UG platform, this paper has used the secondary development technique to develop a stamping process CAD system on automatic production line for robot manipulation with UG/Open API functions in Visual c++ 6.0 environment, the system can quickly analyze the stamping process and the clamping positions for robots and generate a three-dimensional entity mould, which effectively shorten the production line product development cycle, improve the quality and production efficiency of stamping parts.

Influence of Clamping Systems During Drilling Carbon Fiber Reinforced Plastics

During postprocessing of carbon fiber reinforced plastics, drilling is one of the mostly used machining processes. With increasing complexity of components the requirements on the clamping systems are rising. This paper shows the investigation of drilling tests fordifferent types of clamping positions which are examined regarding their influence on the resulting workpiece quality. The clamping of the planar specimens was realized by 3 and 4 points and by a ring clamping system with variable distances from the drill axis to the fixed points. During the experiments the process forces were measured and the resulting delamination and fiber pullouts at the workpiece surface were determined. The results demonstrate that the distance from the drill axis to the fixed points has a significant influence on the process forces and the achievable workpiece quality.

Virtual Prototyping Simulation of Flexible Multi-Point Auxiliary Support Fixture for Blade Machining

Spatial curved blades have been widely used in major aerospace manufacturers due to their light weight, high structural efficiency, high reliability, etc. However, their processing deformation, processing difficulty, and so on limit their use. In order to deal with the situation, flexible multi-point auxiliary supporting fixture for the processing of spatial curved thin-walled parts has become a major topic of current researches. The layout of positioning and clamping points of the flexible multi-point fixture direct affects the stiffness of clamping positions on the thin-walled parts to be processed. When cutting force is definite at a certain point in machining, the greater the stiffness at the processing positions on the part, the smaller the processing deformation due to the cutting force. Therefore, in order to reduce the machining deformation due to the poor stiffness, a suitable positioning and clamping layout is needed to improve the surface stiffness at the machining positions. Thus, the machining quality of thin-walled parts can be improved.

Fast Flux Linkage Measurement for Switched Reluctance Motors Excluding Rotor Clamping Devices and Position Sensors

It is essential to experimentally determine the profile of flux linkage, current, and position of a switched reluctance motor (SRM) in both design verifications and high-performance control implementations. In this paper, a fast measurement method of the flux linkage profile is proposed. In the proposed method, the rotor is first rotated to the aligned position, and then, the voltage pulses are applied to all phases simultaneously. The dc voltage and phase current waveforms are recorded to estimate the flux linkage curves at three different positions. These curves are used to calculate the coefficients of a second-order Fourier series flux linkage model, which represents the entire flux linkage profile of an SRM. The feasibility and accuracy of the proposed method are verified by experimental study with an 8/6 SRM. The impacts of rotor misalignment and phase couplings are investigated. A comparative study with the well-recognized rotor clamping method is given to demonstrate the advantages of the proposed method. The proposed method eliminates the requirements on rotor clamping devices or position sensors; therefore, it is suitable for product test in massive production and fast field measurement.

Corrosion Properties of Rebar Welded Joints

The main reason that causes the premature failure of concrete structure is rebar corrosion damage. Furthermore, the chloride ion penetration is the main reason of rebar corrosion damage. Stress corrosion in welding joint of rebar is studied. Separate rebar into 5 groups, each group have 3 pieces. Grouping experimental method is used to make welded joints soaked, compare the variation law of mechanical properties of flush welded joint under the influence of corrosive environment. Combining with Finite Element Analysis shows that a higher stress concentration during welding process is the important reason to the performance degradation of rebar in corrosive environments. Comparative tests have shown that stress corrosion cracking more likely occur in the welding zone and welding clamping position. The results show that the rebar production process must be strictly controlled, and effectively prevent the erosion of the corrosive medium to ensure the long-term safety of the building.

Finite-element modelling of a novel flanging process on a cylinder with a large diameter–thickness ratio

To solve existing problems of current processing methods for flanged cylinders with a large diameter–thickness ratio, a double-roller clamping spinning (DRCS) process is proposed as a novel flanging process on a cylinder. Finite-element (FE) numerical simulation is used to research the DRCS process. First, on the basis of non-linear FE analysis software Abaqus/Explicit, an FE model for the DRCS process is established. Second, some key problems in FE modelling of DRCS are solved, for example, the definition of contact, the treatment of meshing, the load curves applied on the rollers, the optimal clamping position, and the bending point on the defined initial workpiece. Then, the reliability of the FE model is verified using the energy-conservation principle and experimental results. Finally, the DRCS process of the flange is simulated using the verified FE model, and the equivalent stress field, equivalent strain field, and wall-thickness distribution on the flange during the whole forming process are obtained. The FE model established in this study can be used to explore and develop the DRCS process.

A tip for controlling the main pulmonary artery during video-assisted thoracic major pulmonary resection: the outside-field vascular clamping technique

Cross-clamping the main pulmonary artery (PA) is a risky, stressful procedure for the general thoracic surgeon performing video-assisted thoracic major pulmonary resection (VATS). However, converting VATS to thoracotomy each time PA clamping is planned is a poor tactic. We present a simpler technique for VATS than the traditional method involving a thoracotomy. In VATS, DeBakey vascular clamps with double angle jaws are inserted through 1-cm access incisions. We clamped the main PA so as to maintain the limited visual field through the working port. Thus, we modified the position of these vascular clamps, which we call 'the outside-field vascular clamping technique'. Our technique should be used for VATS lobectomy to prevent conversion to open thoracotomy when one requires scheduled control of the PA during VATS.

Commentary on Laboratory evaluation of laparoscopic vascular clamps using a load-cell device—are all clamps the same?

The use of effective vascular clamps is key to successful laparoscopic partial nephrectomy. Based on our clinical experience, the occlusive capabilities of vascular clamps appeared to be quite variable. We compared the occlusive force of currently available laparoscopic vascular clamps. The jaw force of 3 laparoscopic vascular clamps (Aesculap(R) Klein Surgical Systems, San Antonio, TX and Karl Storztrade mark) were measured by clamping a 2.2 mm compression load cell (Interface Advanced Force Measurement, Scottsdale, Arizona) in pound-force. The variables tested were handheld Satinsky, DeBakey, and Storz clamps vs. bulldog clamps, proximal, middle, and distal application position, new vs. used bulldog clamps and new vs. used Satinsky handheld clamps. In addition, handheld clamps were tested according to the force generated by the notches in the locking mechanism. Force retention was also determined for all instruments after clamping a 20Fr latex rubber catheter for an hour. Finally, leak pressure studies were performed using a harvested porcine artery to determine the relationship between jaw force and leak pressure in mm Hg of bulldog and Satinsky handheld clamps using a pressure gauge [Cole-Parmer(R)]. Handheld vascular clamps provided greater force than bulldog clamps. The proximal position closest to the hinge provided the greatest force across all instruments. Compared with new clamps, the 2-year-old Klein Surgical Systems bulldog clamps showed a greater than 40% decrease in jaw force at all positions, whereas the 3-year-old Aesculap bulldog clamps decreased in jaw force by less than 9% at all positions. The 2-year-old Satinsky handheld clamps showed a decrease of 20%, 9%, and 0% at the distal, middle, and proximal jaw positions, respectively. Also, there was a positive correlation between force and the number of notches applied in handheld clamps. In addition, all instruments maintained jaw force after 1 hour of continuous clamping. Finally, leak pressure studies performed with used clamps showed that Klein Surgical Systems bulldog, Aesculap bulldog, and Satinsky handheld clamps leaked at a pressure of 153 to 223, 465 to 795, and 1,500 to 2,600 mm Hg, respectively. Vascular clamps have varying occlusive forces according to clamp type, manufacturer, jaw and teeth characteristics, jaw clamping position, and duration of use. However, across all clamps the jaw force was greatest at the proximal position. This is most important when applying laparoscopic bulldog clamps. In contrast, all handheld vascular clamps generated higher force than intracorporeal bulldog clamps. At 1 notch, the handheld vascular clamps provided supra-physiologic occlusion force regardless of position or manufacturer.

Laboratory Evaluation of Laparoscopic Vascular Clamps Using a Load-Cell Device—Are All Clamps the Same?

The use of effective vascular clamps is key to successful laparoscopic partial nephrectomy. Based on our clinical experience the occlusive capabilities of vascular clamps appeared to be quite variable. We compared the occlusive force of currently available laparoscopic vascular clamps. The jaw force of 3 laparoscopic vascular clamps (Aesculap(R), Klein Surgical Systems, San Antonio, Texas and Karl Storztrade mark) were measured by clamping a 2.2 mm compression load cell (Interface Advanced Force Measurement, Scottsdale, Arizona) in pound-force. The variables tested were handheld Satinsky, DeBakey and Storz clamps vs bulldog clamps, proximal, middle and distal application position, new vs used bulldog clamps and new vs used Satinsky handheld clamps. In addition, handheld clamps were tested according to the force generated by the notches in the locking mechanism. Force retention was also determined for all instruments after clamping a 20Fr latex rubber catheter for an hour. Finally, leak pressure studies were performed using a harvested porcine artery to determine the relationship between jaw force and leak pressure in mm Hg of bulldog and Satinsky handheld clamps using a pressure gauge (Cole-Parmer(R)). Handheld vascular clamps provided greater force than bulldog clamps. The proximal position closest to the hinge provided the greatest force across all instruments. Compared to new clamps the 2-year-old Klein Surgical Systems bulldog clamps showed a greater than 40% decrease in jaw force at all positions, whereas the 3-year-old Aesculap bulldog clamps decreased in jaw force by less than 9% at all positions. The 2-year-old Satinsky handheld clamps showed a decrease of 20%, 9% and 0% at the distal, middle and proximal jaw positions, respectively. Also, there was a positive correlation between force and the number of notches applied in handheld clamps. In addition, all instruments maintained jaw force after 1 hour of continuous clamping. Finally, leak pressure studies performed with used clamps showed that Klein Surgical Systems bulldog, Aesculap bulldog and Satinsky handheld clamps leaked at a pressure of 153 to 223, 465 to 795 and 1,500 to 2,600 mm Hg, respectively. Vascular clamps have varying occlusive forces according to clamp type, manufacturer, jaw and teeth characteristics, jaw clamping position and duration of use. However, across all clamps the jaw force was greatest at the proximal position. This is most important when applying laparoscopic bulldog clamps. In contrast, all handheld vascular clamps generated higher force than intracorporeal bulldog clamps. At 1 notch the handheld vascular clamps provided supraphysiological occlusion force regardless of position or manufacturer.

Employing shimming for clamping compliant sheet-metal parts

The purpose of clamping is to hold the part against locators and to resist the effects of manufacturing process forces. As initial matching gaps exist between the part and the locators, these gaps are forced to close during the clamping action by deforming the part to the nominal position. This is especially true for compliant sheet-metal parts. One way to reduce clamping deformation is to apply shim spacers between the part and its corresponding clamp, which slightly changes the normal clamping position of the part. However, it is generally very time-consuming to determine the optimal shim size for each clamp. An algorithm for clamp shimming optimisation is proposed in this paper. Application results of an industrial part demonstrated that the proposed algorithm effectively achieves the objective.

Investigation on the bar clamping position of a new type of precision cropping system with variable frequency vibration

The purpose of this paper is to obtain the correct clamping position of the bar during the cropping process based on a new type of precision cropping system with variable-frequency vibration. The mathematical model is built by finite-element method and the simulation experiments were designed by means of an orthogonal method. The analytical results show that the diameter D of the bar exerts an influence on the ratio of the maximum tension stress to the maximum shear stress near the notch bottom remarkably. The influence of the length L2 of second-segment bar extending out the clamping die on it can be minimal. The reasonable geometrical parameters of the clamping bar for a segment of bar with definite length to diameter ratio are determined: the proportion of L1 to the diameter D of the bar is 0.3, and the proportion of L2 to D is 0.25. According to the special feature of the obtained cutting surface, a new measurement method is proposed and applied to assess the quality of the cross-section. The theoretical analysis and experiments prove that, by reasonably setting clamping position of the bar, high-quality cross-section can be obtained.

Clamp Shimming Optimization for Minimizing Sheet-Metal Assembly Deformation

Clamps are the major fixturing devices that constrain workpieces to perform manufacturing operations. As gaps exist between the clamp and workpiece, these gaps are forced to close during the clamping action and accordingly undesirable structural deformation results. This is especially true for sheet-metal assembly processes. One way to reduce clamping deformation in an assembly process is to apply clamp shimming, which slightly changes the normal clamping position of a part. However, it is generally very time-consuming to determine the optimal shim size for each clamp. An algorithm for clamp shimming optimization is proposed in this paper. Application results of two industrial parts demonstrated that the proposed algorithm effectively achieve the objective.

Optimisation of machining fixture layout under multi-constraints

Fixture layout including locator layout and clamp layout plays a vital role in fixture performance. Current researches have been focused on fixtures for components with regular geometry, the results of which are not always applicable for components with complex geometry. This paper presents a methodology of fixture layout optimisation carried out in consideration of the repeatability, immobility and stability of fixturing. The locator layout is optimised based on the criteria of workpiece repeatability and location accuracy. The clamp layout optimisation offers a method to minimize the magnitude of the clamping force. The procedure of clamp optimisation is (1) to find the feasible clamping position in terms of the immobility requirement; (2) to get the best clamp among the feasible clamping positions under constraint of the stability. The optimal fixture layout is considered in a global range and is especially suitable for the workpiece with complex surfaces. A fixture layout design for the aerofoil of a turbine blade is analysed as an example, and the optimal fixture layout is demonstrated.

Automatic Modular Fixture Generation in Computer-Aided Process Planning Systems

Fixturing is the most commonly used manufacturing constraint in setup planning. The computer-aided fixture design technique is being rapidly developed to reduce the lead-time involved in manufacturing planning. An automated fixture configuration design system has been developed to select modular fixture components automatically and place them in position with satisfactory assembly relationships. In this paper, an automated fixture generation system for prismatic components is presented. Sequential steps for automatic fixture layout planning for machining setups, focusing on determining the most suitable locating and clamping positions in accordance with the 3-2-1 configuration, considering geometrical and dimensional constraints are presented. A software has been developed which takes two-dimensional-manufacturing drawings of the prismatic components as input and generates fixture design automatically. The modularity concept is incorporated in the developed software application and enables locating positions to be as wide apart as possible. The clamping positions are obtained directly opposite to the respective locators as far as possible. The software is tested successfully with numerous examples of prismatic parts involving similar design characteristics.