Traditional material handling vehicles often use internal combustion engines as their power source, which results in exhaust emissions that pollute the environment. In contrast, automated material handling vehicles ha...Traditional material handling vehicles often use internal combustion engines as their power source, which results in exhaust emissions that pollute the environment. In contrast, automated material handling vehicles have the advantages of zero emissions, low noise, and low vibration, thus avoiding exhaust pollution and providing a more comfortable working environment for operators. In order to achieve the goals of “peaking carbon emissions by 2030 and achieving carbon neutrality by 2060”, the use of environmentally friendly autonomous material handling vehicles for material transportation is an inevitable trend. To maximize the amount of transported materials, consider peak-to-valley electricity pricing, battery pack procurement, and the construction of charging and swapping stations while achieving “minimum daily transportation volume” and “lowest investment and operational cost over a 3-year settlement period” with the shortest overall travel distance for all material handling vehicles, this paper examines two different scenarios and establishes goal programming models. The appropriate locations for material handling vehicle swapping stations and vehicle battery pack scheduling schemes are then developed using the NSGA-II algorithm and ant colony optimization algorithm. The results show that, while ensuring a daily transportation volume of no less than 300 vehicles, the lowest investment and operational cost over a 3-year settlement period is approximately 24.1 million Yuan. The material handling vehicles follow the shortest path of 119.2653 km passing through the designated retrieval points and have two shortest routes. Furthermore, the advantages and disadvantages of the proposed models are analyzed, followed by an evaluation, deepening, and potential extension of the models. Finally, future research directions in this field are suggested.展开更多
As a key to improve the performance of the interbay automated material handling system （AMHS） in 300 mm semiconductor wafer fabrication system, the real- time overhead hoist transport （OHT） dispatching problem has...As a key to improve the performance of the interbay automated material handling system （AMHS） in 300 mm semiconductor wafer fabrication system, the real- time overhead hoist transport （OHT） dispatching problem has received much attention. This problem is first formu- lated as a special form of assignment problem and it is proved that more than one solution will be obtained by Hungarian algorithm simultaneously. Through proposing and strictly proving two propositions related to the char- acteristics of these solutions, a modified Hungarian algo- rithm is designed to distinguish these solutions. Finally, a new real-time OHT dispatching method is carefully designed by implementing the solution obtained by the modified Hungarian algorithm. The experimental results of discrete event simulations show that, compared with con- ventional Hungarian algorithm dispatching method, the proposed dispatching method that chooses the solution with the maximum variance respectively reduces on average 4 s of the average waiting time and average lead time of wafer lots, and its performance is rather stable in multiple dif- ferent scenarios of the interbay AMHS with different quantities of shortcuts. This research provides an efficient real-time OHT dispatching mechanism for the interbay AMHS with shortcuts and bypasses.展开更多
The status of material delivery of an automobile general assembly line is analyzed, and the technique to achieve the real-time tracking of assembly status information is proposed based on RFID（ Radio Frequency Identi...The status of material delivery of an automobile general assembly line is analyzed, and the technique to achieve the real-time tracking of assembly status information is proposed based on RFID（ Radio Frequency Identification）. Thus the consumption of line-side buffer is obtained dynamically, then the type and quantity of needed material are fed back to the subsystem of material handling; the algorithm for determining the best time departure time of delivery driver based on minimizing of total time penalty function is proposed. This approach makes the material amount of a single delivery trip maximized and improves the efficiency of delivery drivers significantly in the case of does not affect the assembly line normal throughput. Additionally, although this dynamic material handling method is developed for the automobile assembly plant, it should be pointed out that this method is also applicable to other mixed model assembly plants such as electronics, semiconductor and aerospace industry.展开更多
Manual handling is less efficient and sometimes even hazardous to humans in many areas,for example,agriculture.Using robots in those areas not only avoids human contact with such dangerous agricultural materials but a...Manual handling is less efficient and sometimes even hazardous to humans in many areas,for example,agriculture.Using robots in those areas not only avoids human contact with such dangerous agricultural materials but also improves working efficiency.The motion of a robot is controlled using a technique called visual servoing that uses feedback information extracted from a vision sensor.In this study,a visual servoing method was proposed based on learning features and image moments for 3D targets to solve the problem of image moment-based visual servoing.A Gaussian process regression model was used to map the relationship between the image moment invariants and the rotational angles around the X-and Y-axes of the camera frame(denoted asγandβ).To obtain maximal decoupled structure and minimal nonlinearities of the image Jacobian matrix,it was assumed two image moment features,which are linearly proportional toγandβ.In addition to the other four standardized image moment features,a 6-DOF image moment-based visual servoing controller for the agricultural material handling robot was designed.Using this method,the problem of visual servoing task failure due to the singularity of the Jacobian matrix was solved,and it also had a better convergence effect for the part of the target image beyond the field of view and large displacement visual servoing system.The proposed algorithm was validated by carrying out experiments tracking bagged flour in a six-degree-of-freedom robotic system.The final displacement positioning accuracy reached the millimeter level and the direction angle positioning accuracy reached the level of 0.1°.The method still has a certain convergence effect when the target image is beyond the field of view.The experimental results have been presented to show the adequate behavior of the presented approach in robot handling operations.It provides reference for the application of visual servoing technology in the field of agricultural robots and has important theoretical significance and practical value.展开更多
To quickly and accurately estimate the expected work-in-process (WIP)of material intersection points in continuous automated material handling systems (AMHSs) ,a queuing-based performance analytical model was presente...To quickly and accurately estimate the expected work-in-process (WIP)of material intersection points in continuous automated material handling systems (AMHSs) ,a queuing-based performance analytical model was presented for continuous flow transporters (CFTs) . In the modeling procedure which considered layout of crossovers and the variability of service time of turntables, an M /G /1 queuing model with multi-class customers and a non-preemptive priority M /G /1 queuing model with multi-class customers were introduced to accurately present the queuing WIP of each material intersection point and perform the analytical model. Finally,300 mm wafer fabrication facilities (fabs)with 24 bays were applied to evaluating the proposed model. Compared with results of an Arena simulation, the model performs well in evaluating the number of queuing WIP of the intersection points and overall system of CFTs in AMHSs.展开更多
In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufactu...In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufacture a new roof bolting machine with six independent drilling apparatus on board capable of drilling and bolting the roof and ribs with material handling. The objective was to produce a machine capable of drilling and installing six bolts simultaneously with a limited number of operators. The goal of the mine is to decrease the time to bolt a cut to improve the safety level of the current roof bolting method, improve efficiency and to improve the bottom line cost of entry development. The customer wanted four drills at the front of the machine dedicated to installing roof bolts and then another two drills behind them dedicated to rib bolts. This dictated the requirement of latched controls, which would allow the operator to start drilling one hole and then latch the controls to be able to move on to the next.The result of the design is a machine with a single platform and six independent masts with drillheads:four masts strictly for drilling and installing roof bolts on the front of the platform and two masts on the back of the platform for rib bolts. The controls at each operator's station include a latch control for drilling. The six-head roof bolter allows fewer operators to drill and install roof and rib bolts, which in turn lowers the miners' roof exposure per cut. This design reduces the operator's exposure from the inherent pinch points and rotary hazards once he has engaged the latch drilling. Therefore, the machine will help to decrease the time to bolt a cut, improving productivity while enhancing the ability to operate the machine safely.展开更多
The aim of this research is to determine the effect of bridging liquid surface tension and specific surface area on strength factor of coal agglomerates. The production of coal agglomerates of the range 15-27.51 mm wa...The aim of this research is to determine the effect of bridging liquid surface tension and specific surface area on strength factor of coal agglomerates. The production of coal agglomerates of the range 15-27.51 mm was achieved. The crushing strength of the agglomerates was determined for good handling of fine （coal-liquid mixture） to improve fugitive dust control, decrease in transportation losses, reduce risk of coal freezing, lower risk of spontaneous combustion, etc. in iron and steel industries, railway corporations and coal corporations. Kerosene （paraffin oil） was used as a binder and the agglomerated coal oil mixture was pelletized using balling technique （disc）. Mechanical and physical tests like compressive strength test, etc. were carried out. The relationship between the bridging liquid surface tension and specific surface area on strength factor of coal agglomerates showed that there is considerable variation in these parameters in the coal powder systems.展开更多
Ageing work force is one of the leading causes behind the depletion in the growth rate of the labor force in construction industries.Construction industry is a paramount source of employment worldwide after agricul...Ageing work force is one of the leading causes behind the depletion in the growth rate of the labor force in construction industries.Construction industry is a paramount source of employment worldwide after agricultural industry explicitly in urban areas.Manual material handling in construction industries causes musculoskeletal disorders affecting both upper and lower extremities of the body.Studies on lower limb problems due to dynamic work like handling of heavy loads in construction industries are scanty.To analyze the level of exertion,ergonomics risk factors and the prevalence of work-related lower limb disorders among the young and elderly construction workforce.20 male construction workers in the age group of i)20 to 30 years(golden age group);ii)50 years and above were selected from a local construction site in Mumbai.Demographic data like age,height,weight,BMI,body fat,waist hip ratio and risk assessment by questionnaires study comprising QEC,NMQ,VAS,and LEFS were collected.Compared to the golden age group,the elderly subjects were found to feel more discomfort in their lower back,knee and calf regions of lower limb due to immoderate forces and motions tolerated by their lower limbs during their daily work.Muscle pliability and proper coordination diminishes with age and it is appearing to be the most probable reason behind the pain experienced in their lower limbs might be due to improper techniques and postures.For elderly workers,age related limitations become an additional factor to maintain their normal work-life.展开更多
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at ...Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates elements of applied physics and chemistry. With significant media attention focused on nanoscience and nanotechnology in recent years, materials science has been propelled to the forefront at many universities. Materials science encompasses various classes of materials, including electronic materials, functional ceramics, magnesium, material and processes for flat-panel displays, eco/environmental materials, sustainable energy materials, transportation materials, electronic packaging materials, etc.展开更多
Multiple-load carriers are widely introduced for material delivery in manufacturing systems.The real-time scheduling of multiple-load carriers is so complex that it deserves attention to pursue higher productivity and...Multiple-load carriers are widely introduced for material delivery in manufacturing systems.The real-time scheduling of multiple-load carriers is so complex that it deserves attention to pursue higher productivity and better system performance.In this paper,a support vector machine(SVM)-based real-time scheduling mechanism was proposed to tackle the scheduling problem of parts replenishment with multiple-load carriers in automobile assembly plants under dynamic environment.The SVM-based scheduling mechanism was trained first and then used to make the optimal real-time decisions between“wait”and“deliver”on the basis of real-time system states.An objective function considering throughput and delivery distances was established to evaluate the system performance.Moreover,a simulation model in eM-Plant software was developed to validate and compare the proposed SVM-based scheduling mechanism with the classic minimum batch size(MBS)heuristic.It simulated both the steady and dynamic environments which are characterized by the uncertainty of demands or scheduling criteria.The simulation results demonstrated that the SVM-based scheduling mechanism could dynamically make optimal real-time decisions for multiple-load carriers and outperform the MBS heuristic as well.展开更多
Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input, high precision and fast welding speed. Especially when w...Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input, high precision and fast welding speed. Especially when welding high strength steels, which are dominantly used in today＇s car body construction, the low heat input by laser welding bears significant advantages with regard to the properties of the weld seam. The exploitation of the full application potential of laser welding in mass production requires an appropriate manufacturing concept and corresponding auxiliary technologies. The present paper demonstrates the integration of laser welding into the surrounding manu- facturing concepts by a modular setup with different levels of automation. This approach offers flexible solutions for individual needs thereby optimizing investment cost, labor cost and productivity. Recently available laser sources enable exceptionally high welding speed on thin gauged sheet metals but require efficient material handling con- cepts to utilize the full speed potential. Industrial concepts are presented offering efficient material handling and high process robustness for mass production welding.展开更多
A two-dimensional discrete element model （DEM） simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-parti...A two-dimensional discrete element model （DEM） simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle. The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size （Bc） to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Bc decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner. The second part of the study showed that vibration could enhance flow, effectively reducing Bc. The model demonstrated the importance of vibrator location （height）, consistent with previous continuum model results, and vibration amplitude in enhancing flow.展开更多
A simple method is adopted to grow ZnO nanofibers laterally among the patterned seeds designed in advance on silicon substrate. The preparation of seed lattices is carried out by lithographing the metal zinc film evap...A simple method is adopted to grow ZnO nanofibers laterally among the patterned seeds designed in advance on silicon substrate. The preparation of seed lattices is carried out by lithographing the metal zinc film evaporated on the substrate. A layer of aluminum is covered on the zinc layer to prevent the ZnO nanorods vertically growing on the top surface. After oxidation, the patterned ZnO/Al2O3 spots are formed at the sites for the horizontal growth of ZnO nanofibers by the vapor phase transportation （VPT） method using the zinc powders as source material.展开更多
文摘Traditional material handling vehicles often use internal combustion engines as their power source, which results in exhaust emissions that pollute the environment. In contrast, automated material handling vehicles have the advantages of zero emissions, low noise, and low vibration, thus avoiding exhaust pollution and providing a more comfortable working environment for operators. In order to achieve the goals of “peaking carbon emissions by 2030 and achieving carbon neutrality by 2060”, the use of environmentally friendly autonomous material handling vehicles for material transportation is an inevitable trend. To maximize the amount of transported materials, consider peak-to-valley electricity pricing, battery pack procurement, and the construction of charging and swapping stations while achieving “minimum daily transportation volume” and “lowest investment and operational cost over a 3-year settlement period” with the shortest overall travel distance for all material handling vehicles, this paper examines two different scenarios and establishes goal programming models. The appropriate locations for material handling vehicle swapping stations and vehicle battery pack scheduling schemes are then developed using the NSGA-II algorithm and ant colony optimization algorithm. The results show that, while ensuring a daily transportation volume of no less than 300 vehicles, the lowest investment and operational cost over a 3-year settlement period is approximately 24.1 million Yuan. The material handling vehicles follow the shortest path of 119.2653 km passing through the designated retrieval points and have two shortest routes. Furthermore, the advantages and disadvantages of the proposed models are analyzed, followed by an evaluation, deepening, and potential extension of the models. Finally, future research directions in this field are suggested.
基金Supported by National Natural Science Foundation of China(Grant No.51275307)
文摘As a key to improve the performance of the interbay automated material handling system （AMHS） in 300 mm semiconductor wafer fabrication system, the real- time overhead hoist transport （OHT） dispatching problem has received much attention. This problem is first formu- lated as a special form of assignment problem and it is proved that more than one solution will be obtained by Hungarian algorithm simultaneously. Through proposing and strictly proving two propositions related to the char- acteristics of these solutions, a modified Hungarian algo- rithm is designed to distinguish these solutions. Finally, a new real-time OHT dispatching method is carefully designed by implementing the solution obtained by the modified Hungarian algorithm. The experimental results of discrete event simulations show that, compared with con- ventional Hungarian algorithm dispatching method, the proposed dispatching method that chooses the solution with the maximum variance respectively reduces on average 4 s of the average waiting time and average lead time of wafer lots, and its performance is rather stable in multiple dif- ferent scenarios of the interbay AMHS with different quantities of shortcuts. This research provides an efficient real-time OHT dispatching mechanism for the interbay AMHS with shortcuts and bypasses.
文摘The status of material delivery of an automobile general assembly line is analyzed, and the technique to achieve the real-time tracking of assembly status information is proposed based on RFID（ Radio Frequency Identification）. Thus the consumption of line-side buffer is obtained dynamically, then the type and quantity of needed material are fed back to the subsystem of material handling; the algorithm for determining the best time departure time of delivery driver based on minimizing of total time penalty function is proposed. This approach makes the material amount of a single delivery trip maximized and improves the efficiency of delivery drivers significantly in the case of does not affect the assembly line normal throughput. Additionally, although this dynamic material handling method is developed for the automobile assembly plant, it should be pointed out that this method is also applicable to other mixed model assembly plants such as electronics, semiconductor and aerospace industry.
基金supported by the Twelfth Five-Year National Science and Technology Support Program(Grant No.2015BAD18B03).
文摘Manual handling is less efficient and sometimes even hazardous to humans in many areas,for example,agriculture.Using robots in those areas not only avoids human contact with such dangerous agricultural materials but also improves working efficiency.The motion of a robot is controlled using a technique called visual servoing that uses feedback information extracted from a vision sensor.In this study,a visual servoing method was proposed based on learning features and image moments for 3D targets to solve the problem of image moment-based visual servoing.A Gaussian process regression model was used to map the relationship between the image moment invariants and the rotational angles around the X-and Y-axes of the camera frame(denoted asγandβ).To obtain maximal decoupled structure and minimal nonlinearities of the image Jacobian matrix,it was assumed two image moment features,which are linearly proportional toγandβ.In addition to the other four standardized image moment features,a 6-DOF image moment-based visual servoing controller for the agricultural material handling robot was designed.Using this method,the problem of visual servoing task failure due to the singularity of the Jacobian matrix was solved,and it also had a better convergence effect for the part of the target image beyond the field of view and large displacement visual servoing system.The proposed algorithm was validated by carrying out experiments tracking bagged flour in a six-degree-of-freedom robotic system.The final displacement positioning accuracy reached the millimeter level and the direction angle positioning accuracy reached the level of 0.1°.The method still has a certain convergence effect when the target image is beyond the field of view.The experimental results have been presented to show the adequate behavior of the presented approach in robot handling operations.It provides reference for the application of visual servoing technology in the field of agricultural robots and has important theoretical significance and practical value.
基金National Natural Science Foundations of China(No.61273035,No.71071115)National High-Tech R&D Program for CIMS,China(No.2009AA043000)
文摘To quickly and accurately estimate the expected work-in-process (WIP)of material intersection points in continuous automated material handling systems (AMHSs) ,a queuing-based performance analytical model was presented for continuous flow transporters (CFTs) . In the modeling procedure which considered layout of crossovers and the variability of service time of turntables, an M /G /1 queuing model with multi-class customers and a non-preemptive priority M /G /1 queuing model with multi-class customers were introduced to accurately present the queuing WIP of each material intersection point and perform the analytical model. Finally,300 mm wafer fabrication facilities (fabs)with 24 bays were applied to evaluating the proposed model. Compared with results of an Arena simulation, the model performs well in evaluating the number of queuing WIP of the intersection points and overall system of CFTs in AMHSs.
文摘In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufacture a new roof bolting machine with six independent drilling apparatus on board capable of drilling and bolting the roof and ribs with material handling. The objective was to produce a machine capable of drilling and installing six bolts simultaneously with a limited number of operators. The goal of the mine is to decrease the time to bolt a cut to improve the safety level of the current roof bolting method, improve efficiency and to improve the bottom line cost of entry development. The customer wanted four drills at the front of the machine dedicated to installing roof bolts and then another two drills behind them dedicated to rib bolts. This dictated the requirement of latched controls, which would allow the operator to start drilling one hole and then latch the controls to be able to move on to the next.The result of the design is a machine with a single platform and six independent masts with drillheads:four masts strictly for drilling and installing roof bolts on the front of the platform and two masts on the back of the platform for rib bolts. The controls at each operator's station include a latch control for drilling. The six-head roof bolter allows fewer operators to drill and install roof and rib bolts, which in turn lowers the miners' roof exposure per cut. This design reduces the operator's exposure from the inherent pinch points and rotary hazards once he has engaged the latch drilling. Therefore, the machine will help to decrease the time to bolt a cut, improving productivity while enhancing the ability to operate the machine safely.
文摘The aim of this research is to determine the effect of bridging liquid surface tension and specific surface area on strength factor of coal agglomerates. The production of coal agglomerates of the range 15-27.51 mm was achieved. The crushing strength of the agglomerates was determined for good handling of fine （coal-liquid mixture） to improve fugitive dust control, decrease in transportation losses, reduce risk of coal freezing, lower risk of spontaneous combustion, etc. in iron and steel industries, railway corporations and coal corporations. Kerosene （paraffin oil） was used as a binder and the agglomerated coal oil mixture was pelletized using balling technique （disc）. Mechanical and physical tests like compressive strength test, etc. were carried out. The relationship between the bridging liquid surface tension and specific surface area on strength factor of coal agglomerates showed that there is considerable variation in these parameters in the coal powder systems.
文摘Ageing work force is one of the leading causes behind the depletion in the growth rate of the labor force in construction industries.Construction industry is a paramount source of employment worldwide after agricultural industry explicitly in urban areas.Manual material handling in construction industries causes musculoskeletal disorders affecting both upper and lower extremities of the body.Studies on lower limb problems due to dynamic work like handling of heavy loads in construction industries are scanty.To analyze the level of exertion,ergonomics risk factors and the prevalence of work-related lower limb disorders among the young and elderly construction workforce.20 male construction workers in the age group of i)20 to 30 years(golden age group);ii)50 years and above were selected from a local construction site in Mumbai.Demographic data like age,height,weight,BMI,body fat,waist hip ratio and risk assessment by questionnaires study comprising QEC,NMQ,VAS,and LEFS were collected.Compared to the golden age group,the elderly subjects were found to feel more discomfort in their lower back,knee and calf regions of lower limb due to immoderate forces and motions tolerated by their lower limbs during their daily work.Muscle pliability and proper coordination diminishes with age and it is appearing to be the most probable reason behind the pain experienced in their lower limbs might be due to improper techniques and postures.For elderly workers,age related limitations become an additional factor to maintain their normal work-life.
文摘Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates elements of applied physics and chemistry. With significant media attention focused on nanoscience and nanotechnology in recent years, materials science has been propelled to the forefront at many universities. Materials science encompasses various classes of materials, including electronic materials, functional ceramics, magnesium, material and processes for flat-panel displays, eco/environmental materials, sustainable energy materials, transportation materials, electronic packaging materials, etc.
基金the National Natural Science Foundation of China(Grant No.71471135).
文摘Multiple-load carriers are widely introduced for material delivery in manufacturing systems.The real-time scheduling of multiple-load carriers is so complex that it deserves attention to pursue higher productivity and better system performance.In this paper,a support vector machine(SVM)-based real-time scheduling mechanism was proposed to tackle the scheduling problem of parts replenishment with multiple-load carriers in automobile assembly plants under dynamic environment.The SVM-based scheduling mechanism was trained first and then used to make the optimal real-time decisions between“wait”and“deliver”on the basis of real-time system states.An objective function considering throughput and delivery distances was established to evaluate the system performance.Moreover,a simulation model in eM-Plant software was developed to validate and compare the proposed SVM-based scheduling mechanism with the classic minimum batch size(MBS)heuristic.It simulated both the steady and dynamic environments which are characterized by the uncertainty of demands or scheduling criteria.The simulation results demonstrated that the SVM-based scheduling mechanism could dynamically make optimal real-time decisions for multiple-load carriers and outperform the MBS heuristic as well.
文摘Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input, high precision and fast welding speed. Especially when welding high strength steels, which are dominantly used in today＇s car body construction, the low heat input by laser welding bears significant advantages with regard to the properties of the weld seam. The exploitation of the full application potential of laser welding in mass production requires an appropriate manufacturing concept and corresponding auxiliary technologies. The present paper demonstrates the integration of laser welding into the surrounding manu- facturing concepts by a modular setup with different levels of automation. This approach offers flexible solutions for individual needs thereby optimizing investment cost, labor cost and productivity. Recently available laser sources enable exceptionally high welding speed on thin gauged sheet metals but require efficient material handling con- cepts to utilize the full speed potential. Industrial concepts are presented offering efficient material handling and high process robustness for mass production welding.
文摘A two-dimensional discrete element model （DEM） simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle. The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size （Bc） to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Bc decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner. The second part of the study showed that vibration could enhance flow, effectively reducing Bc. The model demonstrated the importance of vibrator location （height）, consistent with previous continuum model results, and vibration amplitude in enhancing flow.
基金supported by the National Natural Science Foundation of China (No. 60725413, 60576008,and 10674023)the National "863" Program of China(No. 2006AA03Z313)the National "973" Program of China (No. 2007CB936300)
文摘A simple method is adopted to grow ZnO nanofibers laterally among the patterned seeds designed in advance on silicon substrate. The preparation of seed lattices is carried out by lithographing the metal zinc film evaporated on the substrate. A layer of aluminum is covered on the zinc layer to prevent the ZnO nanorods vertically growing on the top surface. After oxidation, the patterned ZnO/Al2O3 spots are formed at the sites for the horizontal growth of ZnO nanofibers by the vapor phase transportation （VPT） method using the zinc powders as source material.
