毕业论文-智能饮水机水杯识别及自动注水电路设计说明书.doc

信息职业技术学院毕业设计说明书(论文)设计题目: 智能饮水机水杯识别 及自动注水电路设计 专 业: 应用电子技术 班 级: 学 号: 姓 名: 指导教师: 二00九年十二月十六日 四川信息职业技术学院毕业设计说明书目 录摘 要1第1章 绪 论21.1 智能饮水机的慨述21.2 设计的目的与意义21.3 设计要求及内容3第2章 系统方案论证42.1 电源电路42.2 水杯识别及信号处理电路42.3 定时电路52.4 电磁阀驱动电路62.5 整机电路框图7第3章 单元电路设计83.1 直流稳压源电路设计83.2 水杯识别及信号处理电路设计93.2.1 tcrt5000模块介绍93.2.2 水杯识别及信号处理电路设计103.3 定时电路设计113.3.1 555集成芯片介绍113.3.2 定时电路设计123.4 电磁阀驱动电路设计13第4章 电路仿真及制作154.1 电路仿真154.2 电路制作164.3 测试17总 结18致 谢19参 考 文 献20附 录整机原理图21ii摘 要该设计综合电子技术理论，从实际生活出发，完善了饮水机的功能。设计方案中，采用红外传感器tcrt5000模块作为检测单元，运用555定时器，继电器，电池阀等主要元器件完成设计。整个系统实现两功能，即水杯的自动识别及自动注水功能，包括检测、信号整形，定时电路和电磁阀的驱动等电路模块单元。与传统的饮水机相比，由于采用了自动检测和控制的电子设计技术，可较好地实现对水杯的自动识别和注水功能，这不仅节约了水资源也保证了用户的安全，给用户带来方便，具有广泛的应用前景。关键词 红外识别；自动注水；控制第23页第1章 绪 论随着电子技术的发展，各种电子产品逐步渗透到生活的各个角落。21世纪，电子产品将有更为迅猛的发展，它在国民经济发展中占有越来越重要的地位。可以想象，当今世界，脱离了电子产品将是一个黑暗与枯燥的世界。运用电子设计理论，充分结合生活实际，我们设计了该智能饮水机控制系统。1.1 智能饮水机的慨述安全，健康，便捷的话题随时都是社会关注的焦点，随着人们日常生活水平的提高，方便而又具有现代生活气息的饮水机早已走入寻常百姓家，并在两三年内迅速赢得了市场。据不完全统计，全国大中城市约有80以上的家庭拥有饮水机。饮水机已经不再是摆设品或奢侈品，而成为家庭的必需品，在忙碌的都市生活中人们对饮水追求的是用得便捷与喝得健康，因此饮水机也不断的朝着智能化，人性化得方向发展。随着智能饮水机种类的日益增多，各种饮水机因机型不同，功能和用途也不尽相同，不同层次的消费者对饮水机的看法不同，这就需要设计者们根据实际情况来设计出使用于不同场合的职能饮水机，来给消费者带来方便。面对消费者新的需求，众多设计者通过技术改良在产品的外观造型、附加功能等方面大做文章，希望以此来迎得消费者的青睐。然而，无论款式如何新颖，炒作多么超前，传统饮水机始终没有解决消费者真正关心的“安全、便捷，健康”问题，这也成了限制整个设计者们进一步突破的天花板。在此背景下，智能化的饮水机一经上市就引起了广泛的关注，并迅速受到消费者的青睐。相比传统的饮水机，智能饮水机在保证水质的新鲜，健康、用水的便捷，安全方面具有先天的优势：智能的饮水机都采用独特的芯片来控制整个饮水机系统，彻底切除了传统饮水机笨重与麻烦，改变了传统饮水机制取水的模式，既当水杯放上饮水机时水就自动流出，既快捷、方便又安全；不仅如此，按普通三口之家计算，使用智能饮水机，一天的耗电量仅为0.4度，整机的耗电量比传统饮水机的节省50%。1.2设计的目的与意义随着科技的不断发展，人们的生活水平的不断提高，对技术产品的越来越多的使用，人们对产品的智能化、自动化要求也越来越高。为了满足人们饮水时的方便，本课题设计出了一款智能饮水机。本着人性化化设计、安全，健康，便捷的原则，利用红外识别的科学技术原理，实现自动注水功能，解决了人们在忙碌生活着取水的不便。也给21世纪科技发展的浪潮带来了新的活力，也为电子产品智能饮水机的发展迈出了新的步伐。1.3 设计要求及内容1设计要求采用直流稳压，红外传感器，555定时器原理设计并制作一个自动识别水杯并注水的电路，主要技术指标要求：（1）电源电压5v；（2）555定时器定时时间18s；（3）555暂稳态时驱动继电器控制电磁阀工作。2设计内容主要设计一个水杯自动识别并注水的电路，其设计内容主要包括一下几个部分：（1）方案论证及系统框图；（2）单元电路设计； （5）电路安装、调试。第2章 系统方案论证2.1 电源电路 集成稳压 桥式全波整流负载滤波变压器交流电源1方案一图2-1 方案一框图该方案的设计流程方框图如上所示，交流电经过降压，整流，滤波可以得到比较平滑的直流电，但由于交流电网输入电压的被动和电路负载的变化使直流电压不稳定，故在本直流电源中增加集成稳压电路以确保设备的正常工作。 半桥整流交流电源 降压电容 分立稳压 滤波 负载2方案二图2-2 方案二框图ac220v电源电压，经降压电容，半桥整流，及滤波电容滤波和稳压二极管稳压后，取得+5的直流电来供负载使用。两种方案比较，在功能方面都能实现对负载的供电，方案一主要通过变压器的降压及整流滤波来实现直流电的输出，该方案的稳定性高，实用性大。方案二通过二极管的降压及整流滤波来实现虽然元器件少但不易实现，故直流电源部分采用方案一。2.2 水杯识别及信号处理电路1 方案一此水杯识别电路非常简单，采用tcrt5000作为信号识别元件，当水杯放到传感器上时为传感器提供反射条件，使红外线传感器输出高电平，高电平信号送到微分电 555单稳态延时 下降沿脉冲信号图2-3 方案一框图路经过微分和反相作用为555定时器提供一下降沿脉冲。该方案结构简单所用元器件较少，并且稳定性高。 红外移动传感器 微分 非门2方案二图2-4 方案二框图该电路采用灵敏度极高的红外移动传感器来对水杯进行识别，当水杯接近传感器时，微分电路得到+5v的电压信号，经过微分电路的微分和非门的作用，为555定时器提供一个下降沿脉冲，此电路所用元件价格昂贵，成本高。两种方案都能实现对水杯的自动识别和信号处理，方案一采用红外遮挡式传感器，元件独立，安装方便并且稳定性较高，方案二采用红外移动传感器，灵敏度很高但价格昂贵，经比较水杯识别及信号处理电路采用方案一。2.3 定时电路 红外遮挡传感器 三极管反相 微分1方案一图2-5 方案一框图当下降沿脉冲到来时，给555单稳态电路提供一输入信号，从而启动555定时器工作，使电路工作在暂稳态，此时555输出为高电平；当电路进入稳态时，555输出为低电平，在定时器为暂稳态阶段就本设计所需的定时时间。2方案二 触发信号 非门 电容电阻式延时电路 晶闸管控制图2-6 方案二框图当触发信号到来，经过非门的反相作用为电容电阻式延时电路提供电源电压，利用晶体管的控制对电容实现充放电，从而起定时作用。此方案定时不精确并且分立元件多，安装不方便占用pcb板位置多。两种方案都能起到定时作用，方案一采用555集成芯片来定时，定时精确并且方便制作，方案二采用大电容来定时虽然能实现定时，但定时不精确并且分立元件多，安装不方便占用pcb板位置多，经比较定时电路采用方案一来实现定时。2.4 电磁阀驱动电路 高电平电磁继电器 电磁阀1方案一图2-7 方案一框图当555定时器输出为高电平时，驱动继电器开始工作使常开状态的继电器跳变到常闭状态，从而使电磁阀导通为饮水机注水。2方案二 高电平 电磁阀 固态继电器图2-8 方案二框图该方案采用固态继电器对二通电磁阀进行控制，当高电平到来时固态继电器为电磁阀供电，从而实现注水功能。两种方案都能实现对饮水机的注水，第一种方案采用电磁继电器对电磁阀进行控制，结构简单容易实现；第二种方案采用固态继电器，虽然能实现功能但固态继电器的散热大还需在电路中加散热装置 ，故采用方案一。2.5 整机电路框图经过上述方案的论证，综合比较得出2-9整机框图： 稳压 桥式全波整流 滤波 变压器 交流电源 电磁继电器 555定时 红外遮挡式传感器 电磁阀 三极管的反相 微分图2-9 整机方案框图220v交流电压经过降压，整流，滤波可以得到平滑的直流电，再经过稳压管稳压给红外遮挡式传感器，三极管及555定时器提供工作电压。当水杯放在红外遮挡式传感器上时传感器输出高电平信号，经过微分和三极管的反相为555定时器提供一个下降沿脉冲，555定时器的输出为高电平为电磁继电器提供驱动电压，电磁继电器由常开状态跳变到常闭状态，从而使电磁阀导通为饮水机注水。定时结束时555输出为低电平，继电器由常闭跳变到常开，饮水机停止注水。第3章 单元电路设计3.1 直流稳压源电路设计该直流稳压源电路实现是+5v的电压输出，原理图如下所示：图3-1 直流稳压源电路图在连接电路中，需要在变压器的副边接入保险丝fu，以防电路短路损坏变压器或其它器件。整个电源电路结构形式为220v交流电压经过9v的变压器输入到桥式整流电路中，使得我们的交流电变成了脉动直流电，后经电源滤波电容滤波成纹波系数较小恒定直流电，在接入到三端稳压器lm7805脚输入端，稳压器内部含有过流、过热保护电路。并且lm7805脚输出固定的+5v直流电压供后面的负载使用。其原理流程框图如图3-2所示：变压整流滤波稳压图3-2 直流稳压电源流程图 相关元器件选择及数量如表3-1所示：表3-1 直流稳压电源元件清单编号名称规格数量lm7805稳压器1d1、d2、d3、d4二极管1a（iomax）4c1、c2电解电容220uf/16v2c3、c4独石电容0.1uf2fu保险丝1a（iomax）1t1变压器9v/ac13.2 水杯识别及信号处理电路设计3.2.1 tcrt5000模块介绍tcrt5000光电传感器模块是基于tcrt5000红外光电传感器设计的一款红外反射式光电开关。传感器采用高发射功率红外光电二极管和高敏度光电晶体管组成，输出信号经施密特电路整形，稳定可靠。其模块电路原理如图3-3所示：图3-3 tcrt5000传感器模块电路原理图传感器的红外发射二极管不断发射红外线，当发射出来的红外线没有被反射回来或被反射回来但强度不够大时，光敏三极管一直处于关断状态，此时模块的输出端为低电平，指示二极管一直处于熄灭状态；被检测物体出现在被检测范围内时，红外线被反射回来且强度足够大，光敏三极管饱和，此时模块的输出端为高电平，指示二级管被点亮。3.2.2 水杯识别及信号处理电路设计当水杯放到红外传感器后会传感器的输出端为高电平，但555组成的单稳态电路需要一下降沿脉冲来触发，故在555的输入端接入微分和反向电路，其原理如图3-4所示：u0图3-4 水杯识别及处理电路由于555定时器的触发只需一下降沿脉冲信号，故在输入端加入微分电路其原理如图3-5所示，电路的输入信号是图3-5（a）所示的矩形波，那么，在t 1时刻电容c因电压不能突变而使uc=0，所以，此时刻r上的输出电压u 0等于5v。此后uc按指数规律上升到5v，相应地，u 0由5v下降至零。在t 2时刻，外加信号为零uc仍为5v，致使输出电压跳变到- 5，随着电容放电，uc逐渐上升到零。待下一个矩形脉冲来到后，再重复以上过程。uc、u 0的波形分别如图3-5（b）（c）所示：微分电路提供的是瞬间的高电平，故加入反相电路来给555定时器的输入提供下降沿脉冲信号。当高电平信号到来时，三极管vt1饱和，输出为低电平（约0.3v）；输入信号为低电平时，三极管vt1截止，输出为高电平（约为+vcc）,电路就可以实现反相器的逻辑功能。从而为555定时器提供一下降沿脉冲。相关主要元器件选择及数量如表3-2所示：uit1t2t （a）uct （b）u0t （c）图3-5 微分原理图表3-2 水杯识别电路元件清单编号名称规格数量r1电阻7.5k1r2电阻3.5k1r3电阻4301c5独石电容100nf/16v1vt1三极管npn13.3 定时电路设计3.3.1 555集成芯片介绍此模块为本设计的核心电路，采用单稳态触发器来定时，控制后边的继电器工作时间，555集成芯片工作内部原理如图3-6所示：定时器的主要功能取决于比较器，比较器的输出控制rs触发器和放电管t的状态。图中rd为复位输入端，当rd为低电平时，不管其他输入端的状态如何，输出vo为低电平。因此在正常工作时，应将其接高电平。由图可知，当5脚悬空时，比较器c1和c2比较电压分别为2/3vcc和1/3vcc。1当，时，比较器c1输出低电平，比较器c2输出高电平，基本rs触发器被置0,放电三极管t导通，输出端v0为低电平。2当，时，比较器c1输出高电平，比较器c2输出低电平，基本rs触发器被置1,放电三极管t截止，输出端vo为高电平。3当，时，基本rs触发器、,触发器状态不变，电路亦保持原状态不变。综合上述分析，可得555定时器功能表如表所示。如图3-6 555定时器内部原理在电压控制端脚施加一个外加电压（其值在0-vcc之间），比较器的参考电压将发生变化，电路相应的阈值、触发电平也将随之变化，进而影响电路的工作状态。3.3.2 定时电路设计图3-7 555单稳态电路图电路中只有一种稳定状态的触发器叫做单稳态触发器。其特点：在无外加触发信号时，电路处于稳定状态，称为稳态；当输入端有外加触发脉冲信号下降沿时，输出状态立即发生跳变。电路进入暂时稳态状态，称为暂稳态，过一段时间电路自动跳变到原先的稳态。其工作波形如图3-8所示：uiu0tt（2/3）vcctuc图3-8 555单稳态工作原理图本次设计运用555的定时作用来控制继电器的工作时间，定时时间，当水杯放上红外传感器tcrt5000时，555定时器的输入端得到一下降沿脉冲，从而触发555定时器开始工作，开始定时，在得到下降沿脉冲的瞬间定时器进入暂稳态，输出电压为高电平（+5v），为继电器提供输入电压，继电器进入常闭状态，电磁阀开始为水杯注水（注水时间等于555定时器的定时时间），当水杯移走，经过微分电路会给反相器的输入提供一负电压，使三极管截止，既而整个电路都不工作。相关元器件选择及数量如表3.3所示：表3.3 定时电路元件清单编号名称规格数量555555定时器1r6电阻35k1c6电解电容47uf1c7独石电容100uf13.4 电磁阀驱动电路设计当555定时器的输出端为高电平时，电磁继电器开始工作，从而控制二通电磁阀的导通，其原理如图3-9所示：图3-9 继电器工作电路本次设计用+5v的电磁继电器，有常闭和常开两种状态，当定时器输出为高电平时，继电器的输入端加上了驱动电压，使继电器跳变为常闭状态，使二通电磁阀加上220v的交流电压，二通电磁阀开始为水杯注水。当定时器的输出为低电平时继电器的输入没有驱动电压，使继电器跳变到常开状态，此时二通电磁阀不工作。相关主要元器件选择及数量如表3-4所示：表3-4 电磁阀驱动电路元件清单编码名称规格数量k1继电器+5v1d5二极管in40011r5电阻1001电磁阀二通1vcc电源220v1 第4章 电路仿真及制作4.1 电路仿真本设计采用multisim 10对电路进行仿真，由于软件本身原因，在水杯自动识别部分用开关代替，二通电磁阀用12w的灯泡代替。当开关断开时，相当于水杯没有遮挡发光二极管的光线，红外线传感器的输出端为低电平，继电器处于常开状态，灯泡熄灭。如图4-1所示：图4-1 水杯未遮挡红外线时仿真图当开关闭合时，相当于水杯遮挡住发光二极管的光线，红外线传感器的输出端为高电平，经微分和反向作用为555定时器输入一下降沿脉冲，555定时器进入暂稳态此时输出端为高电平使继电器由常开状态跳变到常闭状态，接通灯泡电路，灯泡正常发光，如图4-2所示。当555定时器跳变到稳态时输出端为低电平时，灯泡熄灭，如图4-3所示：图4-2 水杯遮挡红外线时仿真图图4-3 水杯离开传感器时仿真图4.2 电路制作这里我采用万用印制电路板对电路进行安装制作，首先在万用板上进行电路排版，然后元器件按从上到下，从左到右，先特殊再一般，先装低矮、耐热的安装，最后装集成电路。并按如下步骤进行安装与焊接：1清查元器件的数量及质量，及时更换不合格的元件。2由孔距确定元件的安装方式，电阻器采用卧式安装，涤沦电容器、电解电容器采用立式安装，并都要求紧贴电路板。3tcrt5000模块没有引脚，故直接捆绑在电路板上面，插装555定时器芯片时务必小心，引脚全部插进后再焊接。各焊点加热时间及用锡量要适当，防止虚焊、假焊及短路，焊后剪去多余引脚，并检查所有焊点，确认无误后方可通电测试。同时还要注意电源变压器初、次级与开关及电路板的接线，不得有误。4.3 测试全部元器件及插件焊接完后，经过认真仔细检查后方可通电测试，用万用表直流电压档测量直流稳压电源的输出电压+5v左右，接上tcrt5000模块后，在手放在红外感应模块上面的瞬间，模块指示灯点亮，继电器驱动的发光二极管开始发光，过一段时间发光二极管熄灭，定时成功，说明电路正常。如过在手放上感应模块的瞬间模块的指示灯亮，但发光二极管没有被点亮说明电路没有正常工作，需进一步检查信号处理电路，555定时电路及周边元器件安装焊接是否正常。总 结通过本次毕业设计，使我获益良多，刚开始着手于毕业设计时什么都不是很明白，也不知何从下手，但经过两个月的学习使我学到了不少新的知识，也复习了很多忘记了的旧知识，本次设计基本实现了设计的目的：当水杯放在红外传感器上时对水杯进行自动识别，并注水，注水的时间由555定时器的rc来确定，当定时器输出为高电平时，使继电器进入常闭状态既而驱动电磁阀开始对水杯注水。本次设计中也有不少的问题存在，例如电路分析设计不够简洁，电路板的制作不规范，这都是我在设计中应该注意的。本次的毕业设计，在老师的耐心指导，同学的热心帮助下，顺利完成。在这次的毕业设计中，让我学到的知识得到应用与实践，培养了我独立思考的能力，学会了分析电路、设计电路的步骤以及计算机辅助作图等，在设计的实践中获得了新知。致 谢首先要感谢的是各位评委老师，感谢你们百忙中抽出时间来给我这个答辩的机会，在这里我真心的说一声：“谢谢”。经过一段时间的设计与制作，在老师的大力支持和细心指导下，本次毕业设计终于完成，在此我要对带我毕业设计的王志强老师真诚的说声谢谢，在设计期间，是你细心的给我讲解，让我从不懂到懂，而且在设计时给我提供了很多免费的器材，最重要的是在你百忙之中每次都不怕麻烦的抽时间给我耐心的讲解，在此我要说：“王老师，谢谢你，你辛苦了”。 我还要感谢平时给我讲解的其他老师，是你们给予了我必要的指导和支持，同时我还要谢谢我的同学们，是你们平时给我指出很多错误，使我在错误中取得了经验,谢谢你们。参 考 文 献1邱寄帆，唐程山数字电子技术北京人民邮电出版社，20052张树江，王成安模拟电子线路大连理工出版社，20053张玉莲传感器与自动检测技术机械工业出版社，20074余宏生，吴建设电子cad技能实训人民邮电出版社，20075杨欣，王玉风电子设计从零开始清华大学出版社，2004附 录整机原理图四川信息职业技术学院学生姓名李图东学号0710205130班级应电07-2专业应用电子技术设计题目智能饮水机水杯识别及自动注水电路设计指导教师王志强李元宏指导老师考核意见 等 级： 指导教师：答辩评语 等 级： 答辩老师： 总评成绩等级： 考核小组组长：备注以上两项成绩综合后，指导老师考核成绩占总分的60%，答辩成绩占总分的40%，按五级记分（优、良、中、及格、不及格）。毕业设计评语请删除以下内容，o(_)o谢谢！the origin of taxation in the united states can be traced to the time when the colonists were heavily taxed by great britain on everything from tea to legal and business documents that were required by the stamp tax. the colonists disdain for this taxation without representation (so-called because the colonies had no voice in the establishment of the taxes) gave rise to revolts such as the boston tea party. however, even after the revolutionary war and the adoption of the u.s. constitution, the main source of revenue for the newly created states was money received from customs and excise taxes on items such as carriages, sugar, whiskey, and snuff. income tax first appeared in the united states in 1862, during the civil war. at that time only about one percent of the population was required to pay the tax. a flat-rate income tax was imposed in 1867. the income tax was repealed in its entirety in 1872. income tax was a rallying point for the populist party in 1892, and had enough support two years later that congress passed the income tax act of 1894. the tax at that time was two percent on individual incomes in excess of $4,000, which meant that it reached only the wealthiest members of the population. the supreme court struck down the tax, holding that it violated the constitutional requirement that direct taxes be apportioned among the states by population (pollock v. farmers loan & trust, 158 u.s. 601, 15 s. ct. 912, 39 l. ed. 1108 1895). after many years of debate and compromise, the sixteenth amendment to the constitution was ratified in 1913, providing congress with the power to lay and collect taxes on income without apportionment among the states. the objectives of the income tax were the equitable distribution of the tax burden and the raising of revenue. since 1913 the u.s. income tax system has become very complex. in 1913 the income tax laws were contained in eighteen pages of legislation; the explanation of the tax reform act of 1986 was more than thirteen hundred pages long (pub. l. 99-514, oct. 22, 1986, 100 stat. 2085). commerce clearing house, a publisher of tax information, released a version of the internal revenue code in the early 1990s that was four times thicker than its version in 1953. changes to the tax laws often reflect the times. the flat tax of 1913 was later replaced with a graduated tax. after the united states entered world war i, the war revenue act of 1917 imposed a maximum tax rate for individuals of 67 percent, compared with a rate of 13 percent in 1916. in 1924 secretary of the treasury andrew w. mellon, speaking to congress about the high level of taxation, stated, the present system is a failure. it was an emergency measure, adopted under the pressure of war necessity and not to be counted upon as a permanent part of our revenue structure. the high rates put pressure on taxpayers to reduce their taxable income, tend to destroy individual initiative and enterprise, and seriously impede the development of productive business. ways will always be found to avoid taxes so destructive in their nature, and the only way to save the situation is to put the taxes on a reasonable basis that will permit business to go on and industry to develop. consequently, the revenue act of 1924 reduced the maximum individual tax rate to 43 percent (revenue acts, june 2, 1924, ch. 234, 43 stat. 253). in 1926 the rate was further reduced to 25 percent. the revenue act of 1932 was the first tax law passed during the great depression (revenue acts, june 6, 1932, ch. 209, 47 stat. 169). it increased the individual maximum rate from 25 to 63 percent, and reduced personal exemptions from $1,500 to $1,000 for single persons, and from $3,500 to $2,500 for married couples. the national industrial recovery act of 1933 (nira), part of president franklin d. roosevelts new deal, imposed a five percent excise tax on dividend receipts, imposed a capital stock tax and an excess profits tax, and suspended all deductions for losses (june 16, 1933, ch. 90, 48 stat. 195). the repeal in 1933 of the eighteenth amendment, which had prohibited the manufacture and sale of alcohol, brought in an estimated $90 million in new liquor taxes in 1934. the social security act of 1935 provided for a wage tax, half to be paid by the employee and half by the employer, to establish a federal retirement fund (old age pension act, aug. 14, 1935, ch. 531, 49 stat. 620). the wealth tax act, also known as the revenue act of 1935, increased the maximum tax rate to 79 percent, the revenue acts of 1940 and 1941 increased it to 81 percent, the revenue act of 1942 raised it to 88 percent, and the individual income tax act of 1944 raised the individual maximum rate to 94 percent. the post-world war ii revenue act of 1945 reduced the individual maximum tax from 94 percent to 91 percent. the revenue act of 1950, during the korean war, reduced it to 84.4 percent, but it was raised the next year to 92 percent (revenue act of 1950, sept. 23, 1950, ch. 994, stat. 906). it remained at this level until 1964, when it was reduced to 70 percent. the revenue act of 1954 revised the internal revenue code of 1939, making major changes that were beneficial to the taxpayer, including providing for child care deductions (later changed to credits), an increase in the charitable contribution limit, a tax credit against taxable retirement income, employee deductions for business expenses, and liberalized depreciation deductions. from 1954 to 1962, the internal revenue code was amended by 183 separate acts. in 1974 the employee retirement income security act (erisa) created protections for employees whose employers promised specified pensions or other retirement contributions (pub. l. no. 93-406, sept. 2, 1974, 88 stat. 829). erisa required that to be tax deductible, the employers plan contribution must meet certain minimum standards as to employee participation and vesting and employer funding. erisa also approved the use of individual retirement accounts (iras) to encourage tax-deferred retirement savings by individuals. the economic recovery tax act of 1981 (erta) provided the largest tax cut up to that time, reducing the maximum individual rate from 70 percent to 50 percent (pub. l. no. 97-34, aug. 13, 1981, 95 stat. 172). the most sweeping tax changes since world war ii were enacted in the tax reform act of 1986. this bill was signed into law by president ronald reagan and was designed to equalize the tax treatment of various assets, eliminate tax shelters, and lower marginal rates. conservatives wanted the act to provide a single, low tax rate that could be applied to everyone. although this single, flat rate was not included in the final bill, tax rates were reduced to 15 percent on the first $17,850 of income for singles and $29,750 for married couples, and set at 28 to 33 percent on remaining income. many deductions were repealed, such as a deduction available to two-income married couples that had been used to avoid the marriage penalty (a greater tax liability incurred when two persons filed their income tax return as a married couple rather than as individuals). although the personal exemption exclusion was increased, an exemption for elderly and blind persons who itemize deductions was repealed. in addition, a special capital gains rate was repealed, as was an investment tax credit that had been introduced in 1962 by president john f. kennedy. the omnibus budget reconciliation act of 1993, the first budget and tax act enacted during the clinton administration, was vigorously debated, and passed with only the minimum number of necessary votes. this law provided for income tax rates of 15, 28, 31, 36, and 39.6 percent on varying levels of income and for the taxation of social security income if the taxpayer receives other income over a certain level. in 2001 congress enacted a major income tax cut at the urging of president george w. bush. over the course of 11 years the law reduces marginal income tax rates across all levels of income. the 36 percent rate will be lowered to 33 percent, the 31 percent rate to 28 percent, the 28 percent rate to 25 percent. in addition, a new bottom 10 percent rate was created. since the early 1980s, a flat-rate tax system rather than the graduated bracketed method has been proposed. (the graduated bracketed method is the one that has been used since graduated taxes were introduced: the percentage of tax differs based on the amount of taxable income.) the flat-rate system would impose one rate, such as 20 percent, on all income and would eliminate special deductions, credits, and exclusions. despite firm sup