In our daily study, work and life, we often come into contact with composition. Composition is a style composed of words, which expresses a theme through language organization after people's ideological consideration. Then the question comes, how to write an excellent composition? The following is the document review format template of the composition I helped you organize. Welcome to read the collection.
Text format of literature review:
First, the first-level title (bold small three)
1. Secondary title (small four in bold)
1) Three-level title (Song Ti Xiao No.4)
(Except for titles at all levels, the text adopts Song Zixiao No.4, and the line spacing is set to 1.25 times. )
(Figures, tables, formulas and other requirements are the same as graduation thesis)
How to write a literature review?
First of all, what is literature review?
1, the concept of literature review
Literature review is an academic paper made by sorting out, analyzing and refining a large number of documents of a certain discipline, specialty or subject, and it is a highly concentrated literature product. According to the different contents involved, the review can be divided into two types: comprehensive review and special review. The so-called comprehensive review is aimed at a subject or major, and the special review is aimed at a topic.
Literature review reflects the historical position, latest progress, academic viewpoints and suggestions of an important subject in a branch or field, and often reflects the new trends, trends, levels, principles and technologies of related issues. Literature review is to analyze and describe the work and progress of predecessors in a certain research field, and it is necessary to review the trends and frontier issues of related research at home and abroad in detail to provide reference. Generally speaking, the author does not express personal opinions and suggestions, nor does he make any comments, but reflects the facts objectively and generally.
2. The role of literature review
Literature review is to highly concentrate the achievements, existing problems or controversial points of dozens or even hundreds of scattered similar documents, and summarize them to make them systematic and systematic. It not only saves a lot of precious time for researchers to consult and analyze documents in the early stage of labor, but also helps researchers to learn from the achievements of others, grasp the main direction and lead scientific decision-making.
3. Let students understand the significance of writing a summary.
1) Through the process of collecting documents and materials, you can be more familiar with the methods of searching documents and accumulating materials, and expand your knowledge in the process of searching;
2) Searching for literature and writing a literature review is the first step of selecting a topic for scientific research, so learning the writing of literature review is also a process of laying the foundation for future scientific research activities;
3) By summarizing the writing process, the ability of induction, analysis and synthesis can be improved, which is conducive to the improvement of independent work ability and scientific research ability.
Secondly, the topic selection of literature review and the collection of literature materials.
(A) the principle of topic selection
1. Choose your major or basic topic according to what you have learned, otherwise it will be difficult to write a high-level summary.
2. Choose topics according to the quality and quantity of literature.
3. The topic must reflect the focus, new achievements and new trends of contradictions in new disciplines.
4. The topic should not be too big and the scope should not be too wide. There are few documents consulted in this way, and it is easy to summarize and sort out when writing. Otherwise, the topic selection is too large, the literature review time is too long, which affects the practice, and it is difficult to summarize and sort out, and the final summary is short or irrelevant.
(2) Collecting documents and information
1, collection of documents and materials
(1) Use relevant retrieval tools (including contents, abstracts, indexes, etc. ) collect documents and information.
(2) Use the international online retrieval system to collect documents.
(3) Use original documents (including professional journals, scientific reports, patent documents, dissertations, conference documents, monographs and standards, etc.). ) to collect files.
(4) Using three kinds of documents (including abstracts, summaries, encyclopedias, yearbooks and manuals, etc.). ) to collect files.
(5) Collect documents through Internet and CD-ROM database.
2. Collection methods of documents and materials
The process of storing documents in the brain or other carriers to form a "database" that can be accessed at any time is called document collection. Including reading method, newspaper clipping method, note-taking method and modern technology storage method (such as copying, computer storage, CD storage, etc.). ).
Third, the format and writing.
The format of literature review is different from that of general research papers. This is because research papers focus on research methods and results, while literature review requires readers to introduce detailed information, trends, progress, prospects and comments on the above aspects. Therefore, the format of literature review is quite diverse, but generally speaking, it includes the following specific formats: preface, theme, abstract and reference. When writing a literature review, you can write an outline according to these four parts, and then write according to the outline.
foreword
The preface mainly explains the purpose of writing, introduces related concepts and definitions, outlines the scope, and briefly explains the current situation or focus of debate of related topics, so that readers can have a preliminary outline of the problems to be described in the full text. The preface should be written clearly:
(1) first explain the purpose of writing.
(2) Definition of related concepts.
(3) Clarify the scope of review, including: "the subject scope involved in the topic", the scope of review should not be too wide or too miscellaneous, and the "time range" must indicate the starting and ending years of the cited documents.
(4) Briefly explain the current situation of relevant issues or the focus of debate, and lead to the core theme of the written abstract, which is the most concerned and interested by readers and the main line of writing the abstract.
(2) Theme part
The theme part is the main body of the summary, and the writing methods are diverse and there is no fixed format. It can be summarized in chronological order and compared from different angles according to different problems. No matter which format is adopted, the collected documents should be summarized, sorted, analyzed and compared, and the historical background, present situation and development direction of related topics and comments on these issues should be made clear. The topic part should pay special attention to generation.
Citation and summary of literature with strong expressiveness, scientificity and creativity.
(3) Summary part
The summary part is somewhat similar to the summary of the research paper. It briefly summarizes the theme of the full text, and authors who have studied the summarized theme had better put forward their own opinions.
(4) references
Although references are placed at the end of the article, they are an important part of literature review. Because it not only shows the respect for the author of the cited literature and the basis of the cited literature, but also provides clues for readers to discuss related issues in depth. So take it seriously. The arrangement of references should be clear, easy to find and accurate.
Fourth, matters needing attention
Due to the characteristics of literature review, its writing is different from "reading notes" and "reading reports", and it is also different from general scientific research papers. Therefore, we should pay attention to the following issues when writing literature review:
1, the collection of files should be as complete as possible. Mastering a large number of comprehensive documents is the premise of writing a good summary, otherwise it is impossible to write a lot of summaries by collecting a little information casually, and even the articles written will not be a summary at all.
2. Pay attention to the representativeness, reliability and scientificity of the cited documents. There may be similar views in the collected documents, and the reliability and scientificity of some documents are not the same, so we should pay attention to choosing representative, reliable and scientific documents when quoting documents.
3. We should compare and analyze the various viewpoints of the literature around the theme, and don't simply summarize and state the relevant theories and school viewpoints in the form of textbooks.
4. Literature review should be logical and reasonable, that is, the distant literature should be cited first and the closest literature should be cited last.
5, comments (especially when criticizing the shortcomings of predecessors) should quote the original author's original text (to prevent misunderstanding of the original author's argument), don't belittle others and raise themselves, let alone judge the original author's "mistakes" from second-hand materials.
6. The results of literature review should clarify the shortcomings of previous work and clarify the necessity and theoretical value of further research.
7. The viewpoints and contents adopted in the literature should indicate the source, and the sources of models, charts and data should be indicated to avoid ambiguity.
8. At the end of the literature review, there should be a brief summary, indicating the work foundation laid by the predecessors for the research in this field.
9. All the references mentioned should be directly related to the problem studied.
10, literature review, should be mainly selected from academic journals or academic conferences.
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In short, a good literature review should have complete literature, comments and analysis, and accurately reflect the theme.
Model template of literature review
Design of double-column car elevator
Design, manufacture and automation of specialized machinery
First, the purpose and significance of the topic
With the rapid development of economy and the continuous improvement of national income, cars have entered thousands of households, which has brought a broad space for the development of elevators. Hoist plays a vital role in automobile maintenance and is an essential tool for vehicle overhaul or minor repair. Maintenance enterprises of different sizes, whether it is a comprehensive repair shop that repairs a variety of models or a street shop with a single business scope, are almost equipped with elevators. Among them, the double-column hoist is the mainstream hoist widely used at present, and 70% of them are double-column hoists in the market, which is the type of hoist with the largest sales volume. But also has the advantages of quick installation, low noise and smooth lifting. Different types of support parts can be adjusted.
Second, the history and classification of elevators.
Shortly after the invention of the car, the car mechanic thought, "How can I lift the car into the air so that I can work under it?" ? 65438+In the early 1920s, maintenance worker PeterLunati was always looking for a more convenient way to repair cars. One day in the barber shop, he saw a chair that could be rotated and lifted, and his inspiration flashed. We can lift a chair, why not lift a car? Thus, in 1925, Lunati invented the first hydraulic lift for automobiles, and he became the founder of the Rotary Club. The early single-column foundation hydraulic elevator can rise and fall and rotate quickly to adapt to "customers" of different heights and sizes, which greatly improved the functions of jacks and supports before it came out. The rotation function of this early elevator can rotate the car 360 degrees after lifting. At present, some auto repair shops still use this elevator to provide customers with daily auto repair services. After taking the first step to lift the car, the types of car lifts began to increase, and various patterns were designed to provide the repair shop with lifts suitable for their needs. At present, there are Jiege (Jinhua), Han mckesson,,, Orfu (mainly carts, buses and heavy vehicles). The hoists produced are classified according to the column structure, mainly including single-column hoists, double-column hoists, four-column hoists, scissor hoists and gutter hoists. According to the shape, it can be generally divided into three categories: two columns, four columns and scissors; According to the function, it can be divided into four-wheel positioning type and plane type; According to the occupied space, it can be divided into above-ground type and underground type.
Scissor hoist is easy to use and does not occupy space. It is welcomed by many powerful special maintenance stations, and it is also the development direction of future hoists. However, the scissor lifter is more precise, and poor workmanship or design can easily lead to uneven countertops, unilateral lifting and other dangers. If the scissor lift is used as a four-wheel positioning platform, the requirements will be more stringent.
Double-column elevator This kind of elevator is quick to install and has no big restrictions on the use conditions. General maintenance companies can install it without digging. This product has the characteristics of low noise and smooth lifting, and can adjust different types of support parts. This crane is suitable for lifting small and medium-sized cars for maintenance and assembly. The main users are repair shops and 4S shops which mainly focus on assembly overhaul. Four-column elevator can be applied to most models. However, the wide support device often hinders the normal maintenance work of the staff. Compared with the two-column elevator, this type of product has the advantage of rapid take-off and landing, and the main users are small enterprises with rapid maintenance. At the same time, there is a great demand for four-column elevators in 4S shopping malls. But also has reliable performance, low energy consumption, convenient operation and simple structure; The asymmetric arm can be telescopic, which ensures the safety; The lowest position of the drag foot is low, which makes the venue of the vehicle relatively low and expands the adaptability to various vehicles; The most important thing is low price and large market share.
Third, the development status of elevators
Hoist is a typical equipment in automobile maintenance industry, and almost every automobile maintenance enterprise needs one of them. However, due to the long service life, the overall scale is not large. At present, the domestic annual demand is only about 20,000 sets, but more than half of the market is occupied by foreign products, and the domestic output is about 8,000 sets, which is a certain gap compared with imported brands.
According to the investigation of HC Network, Figure 1 shows the market share of elevator market in 2008.
Elevator market share (figure 1)
Obviously, two elevators are still the mainstream of the market. According to different financial resources, maintenance projects and workshop scale, different maintenance enterprises have different requirements for elevator types. With its consistent characteristics of low price, stable quality and convenient operation, the double-column hoist occupies an overall market share of 865,438+0% and is still the dominant market at present. Figure 2 shows the popularity of domestic enterprise brand elevators.
Analysis of brand awareness in elevator market (Figure 2)
The survey results show that Jacky, Zhong Da, Xu Da, Hamilton McPherson and other brands are in the first echelon, and the brand mention rate is above 10%. The mention rate of brands such as Gaochang and Wan 'an is also very high. Compared with the high share of imported brands, the popularity of domestic enterprises' products has improved obviously, which shows that domestic enterprises are developing from single pursuit of quality improvement to brand marketing, and brands drive the market.
Figure 3 shows the market price trend of elevators.
Elevator market price trend (Figure 3)
As can be seen from Figure 3, the price distribution of elevators is obvious. Some double-column elevator brands widely used in China, the domestic price is about 0.6 ~/kloc-0.4 million yuan, and the import price is about/kloc-0.8 million ~ 28 thousand yuan. The domestic equipment price of four-column hoist is1.0 ~ 35,000 yuan, and the imported brand is1.8 ~ 45,000 yuan. The greater the lifting tonnage, the higher the price. Scissor elevator, the general domestic equipment price is 1.0 ~ 40000 yuan, and the imported products are 1.5 ~ 45000 yuan.
Fig. 4 is the statistics of important factors when users buy elevators.
Factors that users value when buying elevators (Figure 4)
Among the multiple-choice questions of the most important factors for elevator users, quality and safety are the top two factors. Moreover, excellent quality and safety can always be directly linked. At present, hoisting machinery manufacturers put safety in a high position, and similar mechanical failures often occur, such as not moving or not in place, which is also related to improper operation by users. However, domestic machines usually have many problems, so domestic enterprises should pay attention to product safety while taking into account the quality of their own products. Some unnecessary small problems are often the decisive factors that lead users to refuse to buy.
Four. Types of cranes in emerging markets
Ordinary double-column truck crane (Figure 5) Gantry crane
Gantry double-column truck crane (Figure 6)
Four-post truck crane (Figure 7)
Scissor car lift (Figure 8)
Combined mobile truck crane (Figure 9)
Single-column truck crane (figure 10)
Main parameters of common double-column truck crane
Five, the structure design of the hoist
The structure is designed for ordinary double-column truck crane, and the overall structure is shown as follows:
General structure of common double-column truck crane (figure 1 1)
(1) lifting structure
The hoisting mechanism consists of hydraulic system and electrical system. The hydraulic unit is controlled by the electrical system, and the oil enters and exits the hydraulic cylinder, which drives the whole equipment to move up and down through the sliding table chain, as shown in the following figure:
Schematic diagram of hoist (figure 12)
When l, a, θ, α, w and Vy are all the same, the piston thrust when the hydraulic cylinder is arranged on the right side is obviously smaller than that when the hydraulic cylinder is arranged on the left side. Compared with 1), the piston speed when the hydraulic cylinder is arranged on the right side is higher than that when the hydraulic cylinder is arranged on the left side. It can be seen that the reduction of piston thrust is at the expense of the increase of piston speed.
The hydraulic cylinder is arranged on the right side of the scissor mechanism, which reduces the piston thrust of the hydraulic cylinder, so that the hydraulic cylinder with smaller diameter can be selected, which is beneficial to the arrangement of the hydraulic cylinder in the scissor mechanism; The problem is that the effective stroke of the hydraulic cylinder is long. If the lifting range of the table is not large, the increase of the hydraulic cylinder stroke is limited.
It can be seen that the arrangement of hydraulic cylinders in scissor mechanism has great influence on its motion parameters and dynamic parameters. After the scissor mechanism is folded, the α0 angle is small and the platform is small.
In the case of small surface lift, in order to reduce the diameter of the hydraulic cylinder and facilitate the arrangement, the hydraulic cylinder should be arranged on the right side of the scissor mechanism. In this design, in order to avoid the hydraulic cylinder being too long, the hydraulic cylinder should be arranged on the left side of the scissor mechanism.
(2) Upright column and supporting mechanism
The upright post of the elevator includes a left upright post and a right upright post, and a sliding table and a hydraulic system are placed in the middle. The supporting mechanism of the elevator is the supporting arm. When the car enters the elevator range, the width of the whole working range of the bracket arm is changed by changing the angle or direction of the rocker arm.
(3) Balance mechanism
Because the elevator must have a forced balancing device to ensure the horizontal position of the whole car when it rises or falls, this design adopts a symmetrical wire rope direction. By changing the tension of the wire rope, the balance between the left and right sliding tables can be maintained during the lifting process.
(4) Insurance institutions and guarantees
Automobile lift is a kind of equipment with particularly high safety requirements. There are usually a variety of safety devices and protective measures: hydraulic circuit pressure maintenance, mechanical locking safety device, mechanical self-locking device, hoist overload protection, jack-up protection, anti-skid and so on.
In this design, the electromagnet safety lock mechanism consists of two sliding platforms with safety clips. After the car rises, the clips and the support plate connected with the electromagnet form a mechanical self-locking mechanism.
Reference of intransitive verbs
1, car lifts come from all aspects of the car insurance industry, car maintenance 20 10/9.
2, analysis and comparison of two kinds of hydraulic cylinder arrangement in scissor mechanism [journal paper]-Journal of Gansu University of Technology 2000,26 (1)
3. HC Auto Maintenance Network
4. Transportation Industry Standard of the People's Republic of China -JT/T 155—2004.
5. Design of hydraulic system of truck crane [Journal of Yantai University] 2007/ 10 Vol.20 No.4.
6. Kong Hongmei, et al., Hydraulic lifting synchronization system (J), hydraulic pneumatic and sealing. 2000,( 1):20-23.
7. Zhong Yurong, Zhuang Qingxi, Zhang Geyu, Li Baoxin. Development of YFJ-50 mobile gas-liquid elevator (J), electromechanical engineering technology. 08 was released in 2004.
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