全自动咖啡机的设计-自动奶茶机含12张CAD图
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第15页外文翻译Failure evaluation of coffee makerABSTRACT: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 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 analysis 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 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. IntroductionThe main objective of this study 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 analyzed 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 were evaluated based on the results on the components.2. Structural features and analysis of system functions2.1. Classication of subsystemsStructural features and analysis of system functions are fundamental to both failure and system safety evaluation 1,2. According to function characteristic, the 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 reservoir, 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 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 to the master integrate circuit(IC). The electric support circuit includes 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 shell, chassis, lid and skeleton, is in charge of protecting and supporting the whole system.2.2. Analysis of working processWorking 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. 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 meter 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 atm, 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 processOverheating may be the main cause of burning and explosion of the coffee maker. Its overheating 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 too 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 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. Safety evaluation3.1. 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 units of water circle subsystem were only given here, as shown in Table 1.3.2. 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 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 the 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 analysisSimulation 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. 4.1. Outlet clogging of creamy pod holderThis clogging often occurs in practical service. If coffee powder is carelessly put into the creamy pod holder, the water will ow to the cup through the pressure relief pipe, indicating that the pressure hazard protection system run normally. However, the pod holder is full of hot water. Under pressure the lid cannot be opened immediately so that users would open it forcibly to be scalded. This clogging experiment also holds for the outlet clogging.4.2. Clogging of waterspout of relief valveFailure of the simulation test would occur if the relief piston was clogged as the scale deposits lie in the relief discharging outlet in the underpin or the spring is ruptured because of erosion. During the test, the system ran normally and the adhesive plaster clogging the discharging outlet was sunken. Therefore, only under great pressure would the relief pipeline be opened. Despite no signicant inuence of the failure on the system, the failure still makes the pressure hazard protection system in the water-circulating system malfunction, which is hard to be observed. Once the heater pipeline is clogged, it may be ruptured to cause rapid leakage of the hot water and even electric shock or scalding of people because of the dramatically rising pressure.4.3. Leakage of check valveThe failure of the check valve leakage was simulated in this test, which also holds for any leakage of the outlet pipeline of the heater. As aforementioned, the failure caused by the aging, thermal melting, and hot water leakage possibly occurs for silicone tube, rmware, connector in the outlet pipelines in the high-temperature and high-pressure vapor. Once the failure takes place, the leakage of the outlet pipeline may cause the short circuit and scalding of people. Therefore, such leakage is a dangerous mode of failure which occurs commonly. The check valve is an important element for the pressure hazard protection, which can relieve negative pressure of the system. Different from the leakage in the coffee maker, as the inlet of the check valve directly leads to fascia cover in front of the crust, water (steam) with high-temperature and high-pressure will directly ow out of the coffee maker if the ow direction is reversed. It could cause serious harm to people.4.4. Replacement of NTC 1#and NTC 2#This test has conducted a survey of the working situation of the protection system of temperature danger after the NTC 1# and NTC 2#and electromagnetic pump fails to function simultaneously. After the NTC 1#and 2#are invalidated simultaneously, the thermostat should exercise the function of overheating protection at the second level. After the heater reaches the critical temperature during the dry burning process, the thermostat will cut off the chief power. During the simulation test process, although the thermostat at last exercises the function of cutting off the power, the NTC holder has already invalidated in the initial stage, which leads to the leakage of high-temperature vapor in the water-circulating system, as shown in Fig. 5. Such NTC holder suffers from failure for serious distortion of melting and perforation at temperature about 100 C(212 F), as shown in Fig. 6.The NTC holder is made of PP plastic. PP plastic has good hardness, toughness, high thermal resistance temperature, goodfatigue property, good chemical stability and oxidation resistance. It can endure the high-temperature from 110 C(230 F) to120 C(248 F), even 150 C(302 F) without force operation. NTC holder has strength much lower than that of trifur connector though they are made of the same PP. NTC holder is of semi-transparent and yellowish color while trifurcate tube connector is of opaque and white color. The obvious difference in color and roughness can be ascribed to different processing qualities. These results show that NTC holder failure is due to the processing of manufacture. In addition, lid lower of the coffee maker was found that material drop by delamination occurred around the screw of the lid, as indicated by the arrow in Fig. 7. The lid is made of PPS (Polyphenylene Sulde) which has good thermal, inaming, mechanical, chemical, wearing resistance, and also better dimension stability. It can serve in between 220 and 240 C for long time. Both short-term thermal resistance and long-term thermal stability are superior to any other engineering plastics. Thus, this kind of material is suitable for inner units of the coffee maker. Lid, slider and chassis are all made of PPS. It should be pointed out that delaminating drop may be due to the improper fabrication and installation process of the environment-friendly PPS. The reliability of security of the coffee maker would be guaranteed by adopting the correct fabrication technology of PPS. 5. Analysis and discussionThe coffee maker can basically meet the demands for functionality according to test and analysis above. However, the hidden hazard also exists in design and few parts, which will detailed as follow, and needs further improving.5.1. Design factorDesign fault is quite serious and unacceptable and thus must be improved in that probability of failure caused by unreasonable design is highest. Test results showed that the main problems existed in design include:(a) Unreasonable design of the heat tube. For example, the structure of the NTC holder is rather complex and the innerdiameter of tube is small and the wall is too thin such that thermal melting, poring and rupturing are easy to occur.(b) Hidden hazards in design of the pressure relief pipeline. The exit of the pressure relief pipeline lies inside the chassis. It doesnt work in normal service. But high-temperature vapor will leak rapidly through this pipeline under anomalous conditions such as overheat and overhigh pressure etc, which would scald people. Therefore, the design of this pipe-line should be further considered. We propose that the pipeline should directly lead to the water reservoir.(c) The PPS in the cover lower of the brew vessel is subjected to high stress and is the only connector to the shower cap. The aging or delamination of the PPS here will lead the inner bolt and the shower cap to drop off. Therefore, the hot water or steam will leak. This is the un-negligible hidden hazard.5.2. Manufacture factorThe quality of processing is the important guarantee for the reliability of the coffee maker. The processing quality of NTC holder is poor. Early failure of NTC holder would lead to leakage of water circle subsystem, which may result in scald. 5.3. Unpredictable accidentAccident in service cannot be controlled by designers and manufacturers. By designing a perfect protection system harm would be possibly minimized. These accidents mainly include bulk exotic articles introduced into the water-circulating system, incorrect operation and so on. Test clearly showed that the outlet would be completely clogged if coffee powder is put into the creamy pod holder. Improvement in design is indispensable for this component.6. Conclusions(1) Design in system, structure and safety protection of the coffee maker is reasonable. This product satises the requirements by safety design and will not fail severely in normal operation for a short term.(2) The safety protection system of the coffee maker works well to be able to deal with accidents properly and thus ensure that no severe safety events happen in service.(3) Inammation and explosion etc. can hardly occur to the coffee maker. However, leakage of steam etc. may take place, which should be avoided.(4) The processing quality of some particular elements is poor and will impose the hidden hazard on the whole system.References1 Chunhu Tao, Nan Du, Weifang Zhang. Tactic thought about progress of failure analysis. Fail Anal Prevent 2006;1(1):15.2 Seyed-Hosseini SM, Safaei N, Asgharpour MJ. Reprioritization of failures in a system failure mode and effects analysis by decision making trial andevaluation laboratory technique. Reliab Eng Syst Safe 2006;91(8):87281. 19543 Foster, Tandon, Zoghi. Evaluation of failure behavior of transversely loaded unidirectional model composites. Exp Mech 2006;46(2):21743.4 Mosleh A, Parry GW, Zikria AF. An approach to the analysis of common cause failure data for plant-specic application. Nucl Eng Des 1999;(150):2547.中文翻译：咖啡机的失效评估摘要：本文对某型咖啡机做了拆卸，对各个元器件的工作原理、工作过程和特点进行了研究。通过模拟实验，对在异常运行情况下的系统响应做出监测。根据材料的特点、结构、和工作条件分析测试中每一个失效的单元模式。在咖啡机失效系统的评估中利用可靠性分析方法，如故障模式和影响分析，故障树分析等。结果表明，咖啡机可满足基本功能。然而，在设计中管道压力隐患问题仍然需要改善。虽然一些爆炸和腐蚀不会发生在咖啡机上，但蒸汽泄露时有发生，应该尽力避免。咖啡机的一些元器件的质量差，不利于长期安全的使用，需要对其进行一些改进和提升。1、引言本研究的目的主要是评估某型咖啡机在异常或者不正常操作的时候是否能正常实现其设计功能和工作过程中是否安全两个方面。首先，将整个咖啡机系统分解为几个子系统。然后根据材料特点、结构和工作环境条件分析每个单元可能的故障模式。在此基础上，推断出由元件组成的器件会出现何种失效模式以及失效后的影响，并通过模拟实验加以验证。最后，根据器件分析结果评估整个咖啡机系统的安全性和可靠性。2、结构特点和系统功能分析 2.1子系统分类 系统功能的分析和结构上的特点是失效和系统安全评估的基础。根据功能特点，咖啡机可以分为三个相对独立的子系统。（1）水循环系统。这个工作系统是通过供应、汲取、加热与输出的开放性循环系统过程构成。这个循环系统通过一下部分构成：水库、流量计、泵、加热器、三叉管接头、咖啡泡制杯、热熔器、安全阀、止回阀及水管等。（2）电气控制系统。电气控制系统是咖啡机的神经中枢，它以程控的方式对咖啡机进行自动化控制，包括工作流程控制和误差应急处理等。该部分包括热电阻（NTC）、恒温控制器（Themostat）、熔断器(ThermalCutOff)和蜂鸣器（Beef）等。该处理器涉及到掌握集成电路。电动辅助电路包括电容，电阻，电感，三极管，三电压调节器，变压器，导线和插件版。（3）外壳结构体系。壳体结构系统由前壳、后壳、底盘、盖和骨架组成，发挥支撑和防护的功能。 2.2工作过程分析水循环系统的工作过程对咖啡机至关重要。在一些测试资料的基础上，我们可以初步推断水循环的工作过程，如图1所示。当泡制7盎司的咖啡时，首先开机后，加热器开始预热，温度升高到65摄氏度左右，电磁摆动泵开始工作，水通过流量计抽到加热器中进行加热。加热后的水从出水口处流出。当流量计计算出到达指定7盎司的水量时，泵停止抽水，加热器中的存水被继续加热至沸腾，水煮沸成蒸汽从出水口喷出。如果出现管路蒸汽压力过大，安全阀开启，多余蒸汽排在底盘内。如果由于冷却作用等原因，蒸汽压力低于一个大气压时，止回阀开启，将外界空气抽回至水循环系统内，以此来保持水循环系统蒸汽压力的稳定。这种设计构成了咖啡机的压力危险防护体系。图1 水循环系统总图 2.3过热危险防护方法过热可能是咖啡机燃烧和爆炸的主要原因。该咖啡壶过热防护主要分为三个等级（图2）I级危险的保护是由两个热电阻并联而成。级和级温控器是一种热切断。当加热器的内腔或加热器的出口温度过高时，热电阻发生作用，系统中断工作。恒温控制器由强电控制。当加热管过热时，温控器工作，切断加热器电源，保证水泵安全。当加热器温度恢复正常后，温控器将重新连接电源。热切断是最高的安全等级保护，在前两级未能起到作用的情况下，当加热器超过临街温度时，熔断器将切断全系统的供电。图2 咖啡机过热防护体系3、安全性评估 3.1 失效模式与影响分析FMEA是一种定性的危险分析方法，是从元器件的失效开始，逐次分析其失效对人员、操作及整个系统的影响和可能产生失效的原因。咖啡机水循环系统及部分元器件的失效模式见表1。 3.2 故障树分析故障树分析的特点是直观、明了，思路清晰、逻辑性强，可以做定性分析，也可以做定量分析。体现了以系统公曾方法研究安全问题的系统性、准确性和预测性，它是安全系统工程的主要分析方法之一。在对FMEA失效模拟的基础上，确定咖啡机最有可能的失效为高温高压水蒸汽的泄漏和漏电，绘出故障树图3和图4。图3 高温高压水蒸气泄漏图4 咖啡机漏电4、模拟实验及分析失效模拟实验室通过对各类主要器件的失效模拟，验证FMEA的结论，找出设计中的未知缺陷。它是一种最接近实际情况的测试方式。本报告主要针对水循环系统和电气信息输入系统中的主要器件进行失效模拟，这些失效都是在实际使用中容易出现的情况。 4.1 奶油热熔器出口堵塞这种堵塞经常发生在实际使用中。如果不小心把咖啡粉放入奶油热熔器中，这时热熔器出水口会被堵塞，压力危险防护体系启用，水通过减压管路，最终流出到杯中。然而由于此时热熔器中盛满热水，导致顶盖在压力作用下不能立即开启，使用者有可能强行开启造成烫伤。试验表明，这种堵塞也会发生在出水管路。 4.2 排水阀堵塞如果有水垢沉淀堵塞位于底盘中的安全排水口，或因弹簧腐蚀断裂等原因将安全活塞卡死，都会出现模拟试验的失效情况。试验过程中系统运行正常，排水口堵塞的胶布凹陷，由此可见安全管路只有在压力较大时才会开启。虽然这种失效对系统正常工作影响不大，但会导致水循环系统压力危险防护丧失功能，且不易被人发现，有可能导致管路因压力急剧升高而破裂，从而引发高温水蒸汽的快速泄漏，对人造成烫伤或触电等伤害。因此该安全阀堵塞问题值得关注。 4.3 止回阀泄漏试验模拟了止回阀泄漏失效，对于加热器出水管路任一点泄漏均适用。元器件在高温高压的蒸汽环境下有可能发生老化和热熔而导致此类泄漏。一旦发生失效故障，出水管路中的泄漏点流出有可能早恒电气系统短路和烫伤。因此这一类泄漏是比较危险而又比较容易发生的失效。止回阀压力保护的一个重要功用是减轻系统的压力负担。与咖啡机内泄漏不同的是，由于止回阀进气端直通外壳前挡板，如果其反向导通，高温高压水蒸气会直接导出咖啡壶，有可能造成人员的严重伤害，因此止回阀的质量非常值得关注。 4.4 1、2热电阻同时置换模拟实验本试验检测了1和2热电阻同时失效后，温度危险防护系统的工作亲狂。在1和2热电阻同时失效后，恒温器应承担起二级过热防护的功能，加热器在干烧过程中达到临界温度后，恒温器切断总电源。在模拟试验过程中虽然最终恒温器发挥了作用切断了电源，但热电阻保持架在低于正常工作温度下就发生了严重的热熔变
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