1、毕业 设计 （ 论文 ） 第 1 页 中文 2300 字 ,1.2 万英文字符 ,中文 3700 字 附录 3 外文翻译 Failure evaluation of coffee maker ABSTRACT:The coffee maker was disassembled, and the characteristics, working principle and process of each unit and component were investigated in this paper. The response of the system
2、under abnormal operation conditions was found through simulating test. And the failure modes of each unit failing in the test were analyzed based on the characteristics of mate-rial, structure and service condition. The failure evaluation of the coffee maker system was made using the reliability ana
3、lysis methods such as failure mode and effect analysis, fault tree analysis etc. The results show that the coffee maker can basically meet the demands for functionality. However, the hidden hazard caused by design exists for the pressure relief pipeline, which needs further improving. Inammation and
4、 explosion etc. can hardly occur to the coffee maker, but leakage of steam may take place, which should be avoided. The quality of some units in the coffee maker are poor, which is detrimental to safe use of long term, and improved processing are needed. 1. Introduction The main objective of this st
5、udy is to evaluate whether the designed function of one kind of coffee maker can realized and is safe enough or not in the work process when it is abnormally or improperly operated. First, the components and units of every subsystem were disassembled. Then possible failure modes of each unit were an
6、alyzed based on the characteristics of material, structure and service conditions. The possible failure modes of each component were inferred from the combina-tion of the inuence of unit failure on components and simulation test demonstration. Finally, security and reliability of the whole system we
7、re evaluated based on the results on the components. 2. Structural features and analysis of system functions 2.1. Classication of subsystems Structural features and analysis of system functions are fundamental to both failure and system safety evaluation 1,2. According to function characteristic, th
8、e coffee maker can be separated into three relatively independent subsystems. (1) Water circulation system. It is the center working system of the coffee maker which accomplished by supply, drawing, heat-ing and output process. This circulation system consists of the following components, water rese
9、rvoir, ow meter, pump, heater, trifurcate tube connector, brew basket, pod holder, relief valve, check valve and tube. (2) Electric control system. The electric control system acts as a nerve center (cerebrum) of the coffee maker, carrying out automation control by program including working process
10、control and error response management etc. According to function, the electric control system is composed of in-out circuit, processor and electric support circuit. Main parts of in-out circuit include negative temperature coefcient (NTC), thermostat, thermal cut off and beep. The processor refers t
11、o the master integrate circuit(IC). The electric support circuit includes 毕业 设计 （ 论文 ） 第 2 页 capacitance, resistance, inductance, triode, tri-voltage regulator, transformer, wire and plug-in board. (3) Shell structure system. The shell structure system, which composed of front shell, rear shel
12、l, chassis, lid and skeleton, is in charge of protecting and supporting the whole system. 2.2. Analysis of working process Working process of the water circulation system is vital to coffee maker. On the basis tests, we can tentatively infer the working process of water circulation, as shown in Fig.
13、 1. For example, when the coffer maker make coffer of 7oz, at rst, the coffee maker is powered on, the heater will preheat itself up to about 65 ?C(149 ?F), the pump then starts pumping water into the heater through the ow meter and heated water (not boiled) ows out of the spout. As soon as the ow m
14、eter reads 7oz (7oz mode), the pump stops. The water left in the heater will be boiled so that the steam spurts from the spout. However, when the steam pressure is too high, the relief valve turns on and excess steam is released in the chassis. In contrast, when the steam pressure is lower than 1 at
15、m, air outside will be pressed into the water circulation system through the check valve in order to keep it stable. This is the pressure hazard defense system. 2.3. Overheating hazard protection process Overheating may be the main cause of burning and explosion of the coffee maker. Its overhe
16、ating protection is realized by the following three grades, as shown in Fig. 2. Grade I hazard protection is made up of two parallel connected thermal resistances； grade II is a thermostat and grade III is a thermal cut off. When the temperature of the inner shell of the heater or heater spout is to
17、o high, the thermal resistance gets to work and the system is prevented from working. The thermostat is controlled by strong electricity. When the heater tube is over-heated, the thermostat works, cutting off the power supply of the heater and the pump to ensure safety. After the temperature returns
18、 to normal, the thermostat will re-connect to the power. The thermal cut off is the highest grade of safety protection. When the rst two grades fail to work and the temperature of the heater tube exceeds critical temperature, the thermal cut off will sever the power supply of the whole system. 3. Sa
19、fety evaluation 3.1. Failure mode and effect analysis (FMEA) FMEA is a qualitative method to analyze the hazards, which gradually analyzes the inuences of the failure of components and units on the personnel, operation and the whole system and its possible causes 3,4. The analysis results of some un
20、its of water circle subsystem were only given here, as shown in Table 1. 毕业 设计 （ 论文 ） 第 3 页 3.2. Fault tree analysis (FTA) Fault tree analysis adopts logical method to conduct dangerous analyzing work characterized by intuitiveness, straight-forwardness, clear thinking and logic. Both
21、quantitative and qualitative analysis can be conducted, which reects the sys-tematically, accuracy and predictability of the systematical project method to research safety problem. It is one of the main analyzing methods of safety system projects. On the basis of FMEA, the failure modes that have th
22、e most possibility to occur are leakage of high-temperature and high-pressure water and electricity leakage, the results are shown in Figs. 3 and 4. 4. Simulation test and analysis Simulation test aims to nd out the unknown design fault and validate FMEA conclusions by simulating failure of many kinds of main components. It is a testing way that is closest to the actual conditions. The report is concerned mainly on components in the water circulation system and the hazard protection system. The prefabricated failures often happen in actual service.
