本毕业设计课题任务的内容：电动助力式小型播种机以人力和电动机（48V直流）动力相结合，主要用于农户田间播种和设施种植播种（以小麦、玉米为主），增加部分装置也可用于施肥、耙磨、除草等田间作业。技术要求：播种深度20~60mm连续可调，播种行距200~500mm连续可调，播种穴距0~500mm可调，种子破碎率和播种均匀度符合国家标准，工作要求：最大生产率为10亩/日。该机结构主要由机架、动力装置、操纵机构、开沟器、镇压轮、播种量调节器和料斗等组成。本设计要求达到结构合理、生产成本低、能耗小，效率高，满足工作性能，而且操作方便的目的。设计成果要求设计图纸和设计计算书各1套，并进行计算机仿真样机和优化设计。

3、对本毕业设计（论文）课题成果的要求（包括图表、实物等硬件要求）：

设计说明书不少于2万字；工程绘图量不少于折合成图幅为A0号的图纸3张；用计算机进行设计、计算与绘图一般不少于2/3；并进行计算机仿真样机和优化设计。查阅文献15篇以上，翻译与课题有关的外文资料，译文字数不少于3000字。

4、主要参考文献

[1] 董刚李建功潘凤章主编.机械设计（第三版）北京：机械工业出版社1998

[2]成大先主编.械设计图册北京：化学工业出版社 1997

[3]蔡春源主编.机电液设计手册北京：机械工业出版社 1997

[4]徐灏主编.新编机械设计师手册北京：机械工业出版社 1995

[5]朱喜林张代治主编.机电一体化设计基础北京：科学出版社 2004

[6]求是科技编著.PLC应用开发技术与工程实践北京：人民邮电出版社 2005

[7]雷天觉主编.液压工程手册北京：机械工业出版社 1990

[8]孙桓陈作模主编.机械原理（第六版）北京：高等教育出版社 2001

[9]王爱玲主编.现代数控机床北京：国防工业出版社 2003

[10]赵如福主编.金属机械加工人员手册（第三版）上海科学技术出版社 1990

[11]齐麟张亚雄黎上威董学朱胡松春编著蜗杆传动设计（上、下册）北京：机械工业出版社 1987

[12]齿轮手册编委会编著齿轮手册（上、下册）北京：机械工业出版社 1990

[13]《现代机械传动手册》编委会编著现代机械传动手册北京：机械工业出版社 1995

[14]郭爱莲主编.新编机械工程技术手册经济日报出版社 1991

[15]杨公源主编.机电控制技术及应用北京：电子工业出版社 2005

[16]袁任光编著.可编程序控制器选用手册北京：机械工业出版社 2002

[17]饶振纲王勇卫编著.滚珠丝杠副及自锁装置北京:国防工业出版社 1990

[18]陆玉何在洲佟延伟主编.机械设计课程设计（第三版）北京：机械工业出版社 1999

[19]数字化手册系列（软件版）编写委员会编著.机械设计手册（软件版）R2.0北京：机械工业出版社 1999

5、本毕业设计（论文）课题工作进度计划：

起迄日期工作内容

3.19～3.25

3.26～4.08

4.09～5.20

5.21～6.17

6.18～6.24

完成毕业实习报告，开题报告。

设计任务分析与总体方案的确定。

实施设计、计算、绘图、试验。

进行计算机仿真样机和优化设计，并编写设计说明书。

毕业设计（论文）答辩及成绩评定。

摘要

随着近来温室大棚的发展以及环保发展意识的日益增强，小型机的需求就显得更为重要，尤其以电力为动力装置的机械。然而目前广泛应用的播种机是以内燃机及人力为动力装置。本设计电动小型播种机与传统的播种机相比.新颖之处在于播种机完全采用电力为动力装置，从而改善了人们在田间作业时的工作环境，况且更符合环保发展的观点。

本设计主要用于农户田间播种和设施种植播种.增加部分装置也可用于施肥、耙磨、除草等田间作业。详细介绍了播种机的结构组成以及各部件的形式、要求以及功用。详细介绍了电动小型播种机动力装置及各部件要求，包括播种机的动力选择、机械传动的选择及尺寸、排种轮设计、排肥轮的设计、开沟器的设计、轴的设计、链轮的设计、其他的各部件设计以及播种机的工作要求、播种前的准备及播种机的使用等。在设计中考虑播种深度连续可调、播种行距连续可调、播种穴距可调、种子破碎率和播种均匀度符合国家标准。设计中在考虑实用的同时，兼顾经济节约，从而达到结构合理、生产成本低、能耗小、效率高，而且操作方便的目的。

关键词：电动小型播种机

Abstract

With the development of the greenhouse and the consiousness of protecting our ervironment ,boosting up ,the apply of the powy machine becomes more important ,especially the machine with electric power .but at the present time the seeding-machine which is adopted abroadly is drived ba gad engine or man power .this kind of minitype seeding-machine knows from the conventional seeding-machine .Its novel aspect is its drive set which are drived by electric power completly ,so they will improve the work condition ,and accord with euthenics .

This design is applied mostly with the farms of the farmers ,they can also used to fertilize、abrade、get rid of grass and so on ,when we incress some equipment .My design introduce the structure of the seeding-machine and the types of many parts 、some request an fuction .My design introduce the drive equipment of the machine and the types of many parts 、request and fuction .My design also introduce the drive equipment of the machine and the request of the parts which consist of the selecting of the power 、the size 、the design of the axial 、chain wheel 、some other parts and so on .We must consider suiting well of the depth 、the row spacing 、the distance of scoop and the rate of seeds breaking up when seeding .In my design ,while thinking over applied ,I give attention to saving econmy ,consequently achieve structure in reason 、the cost of produce lowness 、the cost of power lowness 、the effidiency highness and convenient when operating .

KEY WORDS :electromotion minitype seeding-machine

第1章前言1

1.1播种机的常识和技术现状1

1.2播种方式及常见播种类型3

1.2.1条播3

1.2.2穴播4

1.2.3撒播4

1.2.4精密播种4

1.2.5联合作业机和免耕播种5

1.3播种工作过程和机械构造5

1.3.1工作过程5

1.3.2机械构造6

1.4播种机械的发展趋势7

第2章总体设计9

2.1 概述9

2.2 设计任务10

2.3 设计目的10

2.4 动力方案选择10

2.5 设计题目分析及设计思想12

2.6 设计主参数及机构类型确定12

2.6.1工作速度12

2.6.2播量的确定13

2.6.3种、肥箱的容积13

2.6.4机架设计14

2.6.5工作幅度14

2.6.6 排种、排肥机构设计14

2.6.7开沟器设计18

2.6.8覆土器设计22

2.6.9镇压轮设计23

2.6.10 地轮设计23

第3章传动设计及播种技术措施25

3.1传动原理简图和动力传递路线图25

3.1.1传动原理简图25

3.1.2动力传动路线图25

3.2传动原理25

3.3技术措施26

3.3.1播种均匀性和各行排量一致性措施26

3.3.2降低破种率措施27

3.3.3种肥同播时，肥料的利用率27

第4章零部件设计28

4.1种箱及肥箱设计28

4.2开沟器设计及校核29

4.3排种器31

4.4地轮参数确定32

4.4.1轮子直径和轮辋宽度的确定32

4.4.2轮子滚动阻力计算32

4.5电机和电瓶选择及链轮设计33

4.5.1电机总功率确定33

4.5.2电动机及电瓶的选择34

4.5.3传动比的确定35

4.5.4链轮选择及设计计算36

4.6地轮轴设计40

4.7键的校核47

4.8销的校核48

4.9轴承的校核48

第5章电气控制系统设计49

5.1电气系统设计原则49

5.2电气元件的选择49

第6章播种机使用52

6.1播种量调整52

6.2实际操作说明53

6.2.1播种作业前准备53

6.2.2播种机的试播及作业55

6.2.3播种机的保养与保管56

6.2.4播种质量检查56

第7章毕业设计小结59

参考文献61

第1章前言

1.1 播种机的常识和技术现状

以作物种子为播种对象的机械称为种植机械，即播种机械。农业是关系国计民生的基础产业，而播种作业是农业生产过程中六大环节之一，播种机械化是农业机械化过程中最为复杂，也是最为重要的工作。播种机械所面对的播种方式、作物种类、品种变化繁多，这就需要播种机械有较强的适应性并且能满足不同种植要求的工作性能。

播种机一般由机架、牵引或悬挂装置、种子箱、排种器、传动装置、输种管、开沟器、划行器、行走轮和覆土镇压装置等组成。其中影响播种质量的主要是排种装置和开沟器。

1.机械播种的农业技术要求：

1)播量符合要求且准确，排种（排肥）均匀稳定，穴距及每穴粒数均匀。

2)播深符合要求且均匀一致，种子应播在湿土上，用湿土覆盖，无露籽现象，覆土均匀，干早地区播后应同时镇压，以利保墒。

3)播行直，行距一致，地头整齐，不重不漏。

4)尽量采用联合作业。

2.播种机的性能指标：排量稳定性、各行排量一致性、排种均匀性和播种均匀性、穴粒数合格率、粒距合格率、播深稳定性、种子破损率。

3.播种机的分类：

播种机的种类很多，一般可按下列方法进行分类。

1)按播种方式分为撒播机、条播机、穴播机和精密播种机。

2)按适应作物分为谷物播种机、中耕作物播种机及其他作物播种机。

3)按联合作业分为施肥播种机、播种中耕通用机、旋耕播种机、旋耕铺膜播种机。

4)按动力联接方式分为牵引式、悬挂式和半悬挂式。

5)按排种原理分为机械式、气力式和离心式播种机。

公元前1世纪,中国已推广使用耧，这是世界上最早的条播机具，至今仍在北方旱作区广泛应用（如图1—1）。

图1—1三耧车

欧洲第一台播种机于1636年在希腊制成。1830年，俄国人在畜力多铧犁上加装播种装置制成犁播机。英、美等国在1860年以后开始大量生产畜力谷物条播机。20世纪以后相继出现了牵引和悬挂式谷物条播机，以及运用气力排种的播种机。1958年挪威出现第一台离心式播种机，50年代以后逐步发展各种精密播种机（如图1—2）。

图1—2气吸式播种机

中国在20世纪50年代从国外引进谷物条播机、棉花播种机等，60年代先后研制成功悬挂式谷物播种机（如图1-3）、离心式播种机、通用机架播种机和气吸式播种机等多种机型,并研制成功了磨纹式排种器。到70年代,已形成播种中耕通用机和谷物联合播种机两个系列并投入生产。供谷物、中耕作物、牧草、蔬菜用的各种条播机和穴播机都已得到推广使用。与此同时，还研制成功了多种精密播种机。

图1—3 国内常见的谷物播种机

1.2 播种方式及常见播种类型

播种方式应根据作物品种和当地农业技术要求而定，并随农业生产的发展而发展。基本播种方式有：条播、穴播（点播）、撤播、精密播种、及联合作业播种机五种。

与播种方式对应，播种机主要有谷物条播机、玉米穴播机、棉花穴播机、牧草撒播机等。这几种机型的辅助部件基本相同，只是其核心工作部件——排种器有较大差异。

1.2.1条播：

按要求的行距、播深和播量将种子播成条行，称为条播。条播一般不计较种子粒距，只注意一定长度区段内的粒数。条播的作物便于进行中耕除草、追肥、喷药等田间管理工作，故应用广泛。条播根据作物生长习性不同，有窄行条播、宽带条播、宽窄行条播等不同形式。其条播机主要用于谷物、蔬菜、牧草等小粒种子的播种作业。

1.2.2穴播（点播）：

按规定的行距、穴距、播深将种子定点播入土中，称为点播。在地上定点掘穴，将几粒种子成簇的播入种穴，称为穴播。这种播种方法可保证苗株在田间分布合理、间距均匀。较条播节省种子。成簇播种可以提高出苗能力。每穴可播 1粒或多粒种子，分别称单粒精播和多粒穴播。其穴播机主要用于玉米、棉花、甜菜、向日葵、豆类等需要中耕的作物,通常又称中耕作物播种机。

1.2.3撒播：

将种子按要求的播量撒布于地表，称为撒播。撒播时种子分布不太均匀，且不能完全被土覆盖，因出苗率低。常用的撒播机为离心式撒播机，附装在农用运输车的后部，由种子箱及其下方的一个高速旋转的撒布轮构成。撒布轮由运输车的地轮通过链条传动。种子由种子箱落到撒布轮上，在离心力作用下沿切线方向撒出,播幅可达8～12米，但作业粗放,种子不易播匀,且露于地表，易遭鸟兽啄食。撒播机也可用以施撒粉状或粒状肥料、石灰及其他物料。附装撒播装置也可安装在农用飞机上使用。

1.2.4精密播种：

以精确的播种量、株行距和深度，将种子播入土中，称为精密播种。具有节省种子、免除出苗后的间苗作业、使每株作物的营养面积均匀等优点。多为单粒穴播和精确控制每穴粒数的多粒穴播。一般在穴播机各类排种器的基础上改进而成。如改进窝眼轮排种器上孔型的形状和尺寸，使其只接受一粒种子并防止空穴；将排种器与开沟器直接连接或置于开沟器内以降低投种高度，控制种子下落速度，避免种子弹跳；在水平圆盘排种器上加装垂直圆盘式投种器，以改变投种方向和降低投种高度，避免种子位移;在双圆盘式开沟器上附装同位限深轮,以确保播种深度稳定。多粒精密穴播机是在排种器与开沟器之间加设成穴机构，使排种器排出的单粒种子在成穴机构内汇集成精确数量的种子群，然后播入种沟。此外，还研制了一些新的结构，如使用事先将单粒种子按一定间距固定的纸带播种，或使种子从一条垂直回转运动的环形橡胶或塑料制种带孔排入种沟等。

1.2.5联合作业和免耕播种：

如在谷物条播机上加设肥箱、排肥器和输肥管，即可在播种的同时施肥，称为联合作业和免耕播种。与土壤耕作、喷撒杀虫剂和除莠剂、铺塑料薄膜（地膜覆盖机械）等项作业联合组成的联合作业机，有的能一次完成土壤播前耕作、施种肥、土壤消毒、开排水沟、播种、施杀虫剂和除莠剂等项作业。免耕播种机是在前茬作物收获后的茬地上直接开出种沟播种，也称直接播种机或硬茬播种机，可防止土壤流失，节约能源，降低作业成本，多用于谷物、牧草和青饲玉米等作物的播种作业。

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内容简介：: 河北建筑工程学院毕业设计（论文）任务书课题名称小型电动助力播种机设计系：机械工程系专业：机械设计制造及其自动化班级：机081班姓名：张亚东学号： 26号起迄日期： 2012年3月19日 2012年 6月24日设计（论文）地点: 机械系小院指导教师：孙有亮辅导教师：发任务书日期： 2012年3月 19 日 1、本毕业设计（论文）课题应达到的目的： 1）培养学生综合应用所学理论知识和技能，分析和解决机械工程实际问题的能力，熟悉生产技术工作的一般程序和方法。 2）培养学生懂得工程技术工作所必须的全局观念、生产观念和经济观念，树立正确的设计思想和严肃认真的工作作风。 3）培养学生调查研究，查阅技术言文献、资料、手册，进行工程计算、图样绘制及编写技术文件的能力。2、本毕业设计（论文）课题任务的内容和要求（包括原始数据、技术要求、工作要求等）：本毕业设计课题任务的内容：电动助力式小型播种机以人力和电动机（48V直流）动力相结合，主要用于农户田间播种和设施种植播种（以小麦、玉米为主），增加部分装置也可用于施肥、耙磨、除草等田间作业。技术要求：播种深度2060mm连续可调，播种行距200500mm连续可调，播种穴距0500mm可调，种子破碎率和播种均匀度符合国家标准，工作要求：最大生产率为10亩/日。该机结构主要由机架、动力装置、操纵机构、开沟器、镇压轮、播种量调节器和料斗等组成。本设计要求达到结构合理、生产成本低、能耗小，效率高，满足工作性能，而且操作方便的目的。设计成果要求设计图纸和设计计算书各1套，并进行计算机仿真样机和优化设计。3、对本毕业设计（论文）课题成果的要求（包括图表、实物等硬件要求）：设计说明书不少于2万字；工程绘图量不少于折合成图幅为A0号的图纸3张；用计算机进行设计、计算与绘图一般不少于2/3；并进行计算机仿真样机和优化设计。查阅文献15篇以上，翻译与课题有关的外文资料，译文字数不少于3000字。4、主要参考文献1 董刚李建功潘凤章主编.机械设计（第三版）北京：机械工业出版社19982成大先主编.械设计图册北京：化学工业出版社 19973蔡春源主编.机电液设计手册北京：机械工业出版社 19974徐灏主编.新编机械设计师手册北京：机械工业出版社 19955朱喜林张代治主编.机电一体化设计基础北京：科学出版社 20046求是科技编著.PLC应用开发技术与工程实践北京：人民邮电出版社 20057雷天觉主编.液压工程手册北京：机械工业出版社 19908孙桓陈作模主编.机械原理（第六版）北京：高等教育出版社 20019王爱玲主编.现代数控机床北京：国防工业出版社 200310赵如福主编.金属机械加工人员手册（第三版）上海科学技术出版社 199011齐麟张亚雄黎上威董学朱胡松春编著蜗杆传动设计（上、下册）北京：机械工业出版社 198712齿轮手册编委会编著齿轮手册（上、下册）北京：机械工业出版社 199013现代机械传动手册编委会编著现代机械传动手册北京：机械工业出版社 199514郭爱莲主编.新编机械工程技术手册经济日报出版社 199115杨公源主编.机电控制技术及应用北京：电子工业出版社 200516袁任光编著.可编程序控制器选用手册北京：机械工业出版社 200217饶振纲王勇卫编著.滚珠丝杠副及自锁装置北京:国防工业出版社 199018陆玉何在洲佟延伟主编.机械设计课程设计（第三版）北京：机械工业出版社 199919数字化手册系列（软件版）编写委员会编著.机械设计手册（软件版）R2.0北京：机械工业出版社 19995、本毕业设计（论文）课题工作进度计划：起迄日期工作内容3.193.253.264.084.095.205.216.176.186.24完成毕业实习报告，开题报告。设计任务分析与总体方案的确定。实施设计、计算、绘图、试验。进行计算机仿真样机和优化设计，并编写设计说明书。毕业设计（论文）答辩及成绩评定。教研室审查意见：教研室主任签字：年月日系审查意见：系主任签字：年月日The numerical modelling of excavator bucket filling using DEMC.J. Coetzee*, D.N.J. ElsDepartment of Mechanical and Mechatronic Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South AfricaReceived 15 February 2007; received in revised form 25 February 2009; accepted 28 May 2009Available online 25 June 2009AbstractThe filling of an excavator bucket is a complex granular flow problem. In order to optimize the filling process, it is important to under-stand the different mechanisms involved. The discrete element method (DEM) is a promising approach to model soil-implement inter-actions and it was used in this study to model the filling process of an excavator bucket. Model validation was based on the accuracy withwhich the model predicted the bucket drag force and the development of the different flow regions. Compared to experimental measure-ments, DEM predicted lower bucket drag forces, but the general trend was accurately modelled. At the end of the filling process the errorin predicted drag force was 20%. Qualitatively, there was a good agreement between the observed and the modelled flow regions in termsof position and transition from one stage to the other. During all stages of filling, DEM was able to predict the volume of material insidethe bucket accurately to within 6%.? 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.1. IntroductionEarthmoving equipment plays an important role in theagricultural, earthmoving and mining industries. Theequipment is highly diverse in shape and function, but mostof the soil cutting machines can be categorised into one ofthree principal classes, namely blades, rippers and buckets(shovels). This paper focuses on the numerical modelling ofexcavator bucket filling using the discrete element method(DEM).Buckets are found on a number of earthmoving machin-ery. Draglines are used to remove blasted overburden fromopen cut mines. Its removal exposes the coal depositsbeneath for mining. A dragline is a crane-like structurewith a huge bucket of up to 100 m3in volume suspendedby steel ropes. Draglines are an expensive and essential partof mine operations and play an important role in the com-petitiveness of South African mines. In the coal miningindustry it is generally accepted that a 1% improvementin the efficiency of a dragline will result in an R1 millionincrease in annual production per dragline 1. Bucketsare also found on hydraulic excavators, loaders and shovelexcavators.The filling of a bucket is a complex granular flow prob-lem. Instrumentation of field equipment for measuringbucket filling is difficult and expensive. It is possible touse small-scale (usually 1/10th scale) experimental rigs toevaluate bucket designs 1,2 but they are expensive andthere are questions regarding the validity of scaling 3,4.To scale-up results from model experiments is problematicsince there are no general scaling laws for granular flows asthere are for fluid dynamics 5.According to Cleary 5 the filling of buckets, in theabsence of very large rocks, is observed to be relativelytwo-dimensional with little motion in the transverse direc-tion. The flow pattern along a cross-section of the bucket inthe drag direction is the most important aspect of fillingand can be analysed satisfactorily using two-dimensionalmodels. Rowlands 2 made similar observations based ondragline bucket filling experiments.According to Maciejewski et al. 6, in practical caseswhen the motion of a bucket or bulldozer blade is dis-cussed, plane strain conditions apply only in some defor-mation regions. The plane strain solution for such toolscan be assumed only with limited accuracy. Maciejewski0022-4898/$36.00 ? 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.jterra.2009.05.003*Corresponding author. Tel.: +27 21 808 4239; fax: +27 21 808 4958.E-mail address: ccoetzeesun.ac.za (C.J. Coetzee)./locate/jterraAvailable online at Journal of Terramechanics 46 (2009) 217227JournalofTerramechanicset al. 6 also investigated the assumption of plane strainconditions in soil bins where the soil and tool motion isconstrained between two transparent walls. For measure-ments in such a bin, the force acting on the tool due tothe friction between the soil and the sidewalls has to be esti-mated or neglected. They have shown that for a high num-ber of teeth on the bucket, the teeth do not act as separatethree-dimensional objects but as one wide tool built upfrom several modules. The deformation pattern in frontof such an assembly of teeth was found to be plane straindeformation. The authors, however, concluded that thiswas true for the particular cohesive soil (sandy clay) andmay not apply to other (especially rocky and brittle) mate-rials. In this study the bucket had a full-width lip with noteeth and based on the findings by Maciejewski et al. 6,the assumption of plane strain was made and two-dimen-sional DEM models were used.Analytical methods 711 used to model soiltool inter-action are limited to infinitesimal motion of the tool andthe given geometry of the problem. These methods werenot expected to be valid for the analysis of the subsequentstages of advanced earth digging problems 12. The analyt-ical methods are based on Terzaghis passive earth pressuretheory and assumptions of a preliminary soil failure pattern13. Complicated tool geometry (such as buckets) and largedeformations cannot be modelled using these methods 14.The discrete element method is a promising approach tomodel soil-implement interaction and can be used to over-come some of the difficulties encountered by analyticalmethods 15. In DEM, the failure patterns and materialdeformation are not needed in advance. The tools are mod-elled using a number of flat walls and the complexity of thetool geometry does not complicate the DEM model. Largedeformation in the granular material and the developmentof the granular material free surface are automatically han-dled by the method.Cleary 5 modelled dragline bucket filling using DEM.Trends were shown and qualitative comparisons made, butno experimental results were presented. The process ofhydraulic excavator bucket filling was investigated experi-mentally by Maciejewski and Jarzebowski 12. The aim oftheir research was optimization of the digging process andbucket trajectories. It is shown that the most energy efficientbucket is the one where the pushing effect of the back wall isminimized.Owenetal.21modelled3Ddraglinebucketfill-ing. In there approach, the bucket was modelled with thefinite element method and the soil with DEM. Ellipsoidsand clumped spheres were used to approximate the particleangularity. The bucket followed a prescribed path.Esterhuyse 1 and Rowlands 2 investigated the fillingbehaviour of scaled dragline buckets experimentally withthe focus on rigging configuration, bucket shape and teethspacing. They have shown that the aspect ratio of thebucket (width to depth) plays and important role in thedrag distance needed to fill a bucket. The bucket with theshortest fill distance was found to produce the highest peakdrag force.The main objective of this study was to demonstrate theability of DEM to predict the drag force on the bucket andthe material flow patterns that develop as the bucket fillsup. The DEM results were compared to experiments per-formed in a soil bin.2. The discrete element methodDiscrete element methods are based on the simulation ofthe motion of granular material as separate particles. DEMwas first applied to rock mechanics by Cundall and Strack16. In this study, all the simulations were two-dimensionalandperformedusingcommercialDEMsoftwarePFC2D17.A linear contact model was used with a spring stiffness knin the normal direction and a spring stiffness ksin the sheardirection (Fig. 1). Frictional slip is allowed in the tangentialdirectionwithafrictioncoefficientl.Thedampingforceactson a particle in the opposite direction to the particle velocityand is proportional to the resultant force acting on the par-ticle with a proportionality constant (damping coefficient)C 17. For a detailed description of DEM, the reader isreferred to Cleary and Sawley 18, Cundall and Strack16, Hogue 19 and Zhang and Whiten 20.3. ExperimentalTwo parallel glass panels were fixed 200 mm apart toform the soil bin. The bucket profile was fixed to a trolleywhich was driven by a ball screw and stepper motor. TheFrictionknksFig. 1. DEM contact model.218C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227complete rig could be set at an angle h to the horizontal asshown in Fig. 2a. The first arm was then rotated and fixedsuch that both arms remained vertical. The second armremained free to move in the vertical direction. First, coun-terweights were added at position A (Fig. 2a) to balancethe combined weight of the bucket profile and the secondarm assembly. This resulted in a weightless” bucket.Counterweights were then added at position B to set theeffective” bucket weight. Since arm 2 was always verticaleven for rig angles other then zero, the effective bucketweight always acted vertically downwards (Fig. 2c). Bucketweights of 49.1 N, 93.2 N, 138.3 N and 202.1 N were used.When the bucket was dragged in the direction as indi-cated, it was also free to move in the vertical direction asa result of the effective bucket weight and the force of thegrains acting on it. The bottom edge of the bucket wasalways set to be parallel to the drag direction and the mate-rial free surface. This type of motion resembles that of adragline bucket which is dragged in the drag direction bya set of ropes, but with freedom of motion in all otherdirections 2.Spring loaded Teflon wipers were used to seal the smallopening between the bucket profile and the glass panels. Aforce transducer was designed and built to measure the dragforce on the bucket. A set of strain gauges was bonded to asteel beam of which the position is shown in Fig. 2a. Theset of four strain gauges was used to measure the force inthe drag direction. Other force components were notmeasured. The force transducer was calibrated and thecalibration checked regularly to avoid drift in the measure-ments. For rig angles other than zero, the force transducerwas zeroed before the drag commenced. This compensatedforthecomponentofthebucketweightthatactedinthedragdirection. The vertical displacement of the bucket was mea-sured with a linear variable differential transformer (LVDT)andusedasinputtotheDEMsimulation. Inboththeexper-imentsandtheDEMsimulationsthebucketwasgivenadragvelocity of 10 mm s?1. The dimensions of the bucket profileare shown in Fig. 2b.In this study corn grains were used. Although the corngrains are not real soil, Rowlands 2 observed that seedgrains are suitable for experimental testing and closelyresemble natural soil flow into dragline buckets.4. DEM parameters and numerical modelFig. 3 shows the range of measured grain dimensionsand the equivalent DEM grain. A normal distributionwithin the range of dimensions given was used to createthe clumped particles. Clumps can be formed by addingtwo or more particles (discs in 2D and spheres in 3D)together to form one rigid particle, i.e. particles includedin the clump remain at a fixed distance from each other17. Particles within a clump can overlap to any extentand contact forces are not generated between these parti-cles. Clumps cannot break up during simulations regardlessof the forces acting upon them. In the model 20,00030,000clumped particles were used.A calibration process, presented in another paper, wasdeveloped for cohesionless material. The particle size, shapeand density were determined from physical measurements.The laboratory shear tests and compressions tests were usedto determine the material internalfriction angleandstiffnessrespectively. These tests were repeated numerically usingDEM models with different sets of particle friction coeffi-cientsandparticle stiffness values.Thecombinationofsheartestandcompressiontestresultscouldbeusedtodetermineaunique set of particle friction and particle stiffness values,Table 1.ADirection of drag Direction of vertical motion 2nd Arm1st ArmBForce transducer 100 mm200 mm150 mm Max volume 35 mm45WbcosWbCounter weights abcFig. 2. Experimental setup.5 - 98 - 125 - 64 - 53 - 6R 2.5 - 4.5 R 1.5 - 3.0 3.0 - 5.0 abFig. 3. (a) Physical grain dimensions and (b) DEM grain model.Dimensions in (mm).C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227219In the software used, PFC2D, so-called walls are used tobuild structures. The test rig and the bucket, with the samedimensions as in the experiment, were built from walls. Thewalls are rigid and move according to prescribed transla-tional and rotational velocities. The forces and momentsacting on the walls do not influence the motion of the wall.During the experiments a constant drag velocity of10 mm s?1was applied while the vertical displacementwas measured. The vertical displacement was influencedby both the rig angle and the effective bucket weight. A typ-ical result is shown in Fig. 4. Except for the initial transi-tion, the vertical velocity was nearly constant, for a givensetup, and increased with an increase in bucket weight. Inthe DEM model, the drag velocity was set to 10 mm s?1and the measured vertical displacement was read from adata file and applied to the bucket.Standard functions build into PFC2Dwere used toobtain the forces and moments acting on individual wallsand on the bucket as a whole. For rig angles other thanzero, the rig was kept horizontal but the gravity compo-nents were set accordingly.5. Results and discussionIt is difficult to make quantitative comparisons regard-ing flow patterns. When comparing the material freesurface, some comparisons could however be made. Figs.5 and 6 show how the material flowed into the bucket forrig angles of h = 0? and h = 20?, respectively. When com-paring the shape of the material free surface, the simula-tions were able to predict the general shape during theinitial stages of filling. The simulations however failed toaccurately predict the material free surface during the finalstages of filling.Curves were fitted to the experimental free surface andoverlaid on the numerical results in Figs. 5 and 6. The max-imum difference between the two free surfaces (heapheight) was measured along the direction perpendicularto the drag direction. Two measurements were made, onewhere DEM predicted a higher heap height, and onemeasurement where DEM predicted a lower heap height.The values and the positions where they were measuredare indicated in the figures. Taking the nominal particlesize as 10 mm, DEM predicted the heap height accuratelywithin 1.54.5 particle diameters.Fig. 7 shows typical drag forces obtained from experi-ments and simulations. The large jump in the drag forceat the beginning of the experiment was observed in mostof the runs and could not be explained and needs furtherinvestigation. From this result, it is clear that the DEMmodel captured the general trend in drag force, but it pre-dicted lower values compared to the measured values. Overthe complete drag of 800 mm, the model predicted a forcewhich was 1550 N lower than the measured force. At theend of the drag the error was 20%. The frictional forcebetween the Teflon wipers and the glass panels was mea-sured in a run without grains. This frictional force was sub-tracted from the measured drag force. Frictional forcesbetween the grains and the side panels would also havean influence on the measured results. These frictional forcescould not be measured or included in the 2D DEM modeland might be the reason why the model predicts lower dragforces 6.The drag energy was defined as the area under the dragforcedisplacement curve. Making use of different rigangles h and effective bucket weights Wb, the drag energyE700up to a displacement of 700 mm is compared in Fig. 8.The first observation that could me made was that withan increase in effective bucket weight, for a given rig angleh, there was a linear increase in required drag energy. Acloser investigation showed that with an increase in bucketweight, the bucket was forced deeper into the materialwhich caused a higher drag force when compared to abucket with less weight.The second observation that can be made is that with anincrease in the rig angle, there is a decrease in drag energy.The effective bucket weight Wbalways acted verticallyTable 1Summary of corn properties and DEM parameters used.Macro propertyMeasuredDEMInternal friction angle23?24?Angle of repose25 2?24 1?Bulk density778 kg m?3778 kg m?3Confined bulk modulus1.60 MPa1.52 MPaMaterial-steel friction14?14?Calibrated DEM propertiesParticle stiffness, kn= ks450 kN/mParticle density, qp855 kg/m3Particle friction coefficient, l0.12Other propertiesDamping, C0.2Model width0.2 m0100200300400500Drag displacement mm60070020406080100Vertical displacement mm120Wb= 202.1 N138.3 N93.2 N 49.1 N Fig. 4. Measured vertical displacement of the bucket with h = 10? andfour values of effective bucket weight Wb.220C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227downward (Fig. 2c) so that the normal force pushing thebucket into the material is given by Wb? cos (h). Thus, withan increase in rig angle, there is a decrease in the normalforce pushing the bucket into the material. This caused areduction in the drag force, and hence a reduction in thedrag energy, when compared to results using a lower rigangle. The DEM simulations were able to capture the gen-eral trends, but it predicted drag energies lower than themeasured. The reason for this is that the predicted dragforces were too low due to the exclusion of the frictionforces between the grains and the glass panels. It would,however, still be possible to use the simulation results forqualitative optimization of bucket filling.Using the simulation results it was possible to identifyhow much of the total force was exerted on each of thebucket sections. In Fig. 9 the bucket was divided into sixsections. The graphs show, as a ratio of the total dragforce, the force on each of the sections. From the startup to a displacement of 200 mm (25% of total displace-ment) the total force acted mainly on the lip and the bot-tom section. As material started to flow into the bucket,the other sections came into play, first the inner curveand finally the front section. Less than 5% of the forceacted on the top section. This was far less than the bottomsection (30%). The reason for this is that the material insidethe bucket showed little movement relative to the bucketFig. 5. Bucket filling results with rig angle h = 0?.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227221and the pressure on the top section was only due to theweight of the material inside the bucket. On the bottomsection, the pressure was due to the combined weight ofthe material inside the bucket and the weight of the bucketitself. During the complete filling process, 2030% of thedrag force acted on the lip. This shows that the design ofthe lip and teeth is important. It is well known that thelength of the lip/teeth and the angle of attack are importantfactors influencing bucket filling 2 .Rowlands 2 made use of mixtures of millet, peas andcorn in his 2D test rig. The observation of the filling behav-iour led to the development of a theory that describes theflow characteristics and patterns of material entering thebucket. Rowlands 2 named this concept the Shear ZoneTheory. He observed that definite planes of shear (rupture)formed between distinct moving material regimes. Theseshear planes changed orientation and location dependingon initial setup and during different stages of the filling pro-cess itself. The generalised theory is shown in Fig. 10. Thedifferent flow regions, as named by Rowlands 2, are indi-cated on the figure. The movements of the material relativeto the bucket are indicated by the arrows.The virgin material remains largely undisturbed until thefinal third of the drag during which bulldozing” occurs.The initial laminar layer flows into the bucket during thefirst third of the drag (Fig. 10a). After entering to a certaindistance, this layer fails at the bucket lip and subsequentlybecomes stationary with respect to the bucket for theFig. 6. Bucket filling results with rig angle h = 20?.222C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227remainder of the drag (Fig. 10b and c). At steeper dragangles, the material flows more rapidly towards the rearbecause of the added gravitational assistance. This effectcan be seen by comparing Figs. 5 and 6.With the laminar layer becoming stationary, a new zone,the active flow zone, develops (Fig. 10). In this zone, thematerial displacement is predominantly in the verticaldirection. The active dig zone is located above the teethand bucket lip. This area develops as material starts toenter the bucket and increases in size after failure of the ini-tial laminar layer. In this zone, the virgin material fails andeither flows into the bucket as part of the laminar layerduring the first part of filling or moves into the active flowzone during the latter part of filling.The dead load that has resulted from live” material inthe active flow zone ramps up and over the initial laminarlayer. Some of the material in the initial laminar layer failsand starts to form part of the dead load (Fig. 10c). Duringexperiments and while the material was flowing, a definiterupture or shear line could be observed here. With anincrease in drag angle, the active dig zone and active flowzone tended to join into one continuous band.1002003004005006007008000ExperimentSimulation250200Drag force N 15010050Displacement in drag direction mm Fig. 7. Typical bucket drag forces with rig angle h = 10? and a bucketweight Wb= 138.3 N. = 0 = 10 = 20 Experiment Simulation 40 40220200 180160140120WbN 10080 60 506070 80100 120 110 90E700 J Fig. 8. Bucket drag energy E700as a function of the bucket weight Wbfordifferent rig angles h.010020030040050060070080000.10.20.30.40.5Displacement mm Drag force ratio FrontInner curveTopLip Bottom Outer curve LipTopBottomFrontInner curveOuter curveFig. 9. Bucket drag force distribution with h = 10?.Active dig zone Initial laminar layer Active dig zone Initial laminar layerActive flow zone Virgin material Active dig zone Dead loadActive flow zone Initial laminar layer Shear lineShear line Shear line Dead load shear line Virgin material Virgin material bcaFig. 10. The Shear Zone Theory according to Rowlands 2.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227223It should be noted that Fig. 10 only shows three stagesof the filling process, but in reality there is a gradual tran-sition from one stage to the next. It should also be notedthat this is a generalised theory and there will be variationsin the results when different materials and bucket geome-tries are used. During experiments two definite shear linescould be observed. The one extended from the tip of thelip up to the free surface. This is named the cutting shearline. The second line is the one between the initial laminarlayer and the dead load, called the dead load shear line.Making use of DEM and investigating the flow regionsfurther, the following procedure was devised. The bucketwas moved through the material and paused” after each100 mm. The displacement vector of each particle was thenset to be zero after which the bucket was given a furtherdisplacement of 1015 mm (13 particle lengths). The par-ticle displacement ratio PDR was defined as the ratio of themagnitude of the particle absolute displacement vector tothe magnitude of the bucket absolute displacement vector.The particles were then coloured according to their individ-ual PDR values. A PDR equal to unity means that the par-ticle is moving with the bucket. The result is shown inFig. 11. This is in effect the average velocity ratio over ashort period.The flow regimes as predicted by the Shear Zone Theoryare indicated on the figure. The three pictures correspondFig. 11. Flow regions using the particlebucket displacement ratio.224C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227to the three pictures given in Fig. 10. After a displacementof 100 mm, the active dig zone is clearly visible with0.40 6 PDR 0.65. The initial laminar layer moves intothe bucket with 0.10 6 PDR 0.25. This corresponds wellto the flow zones shown in Fig. 10a.After 500 mm, the characteristic V” shape of the activeflow zone can be seen with 0.10 6 PDR 0.25. Althoughthe PDR is relatively low, the displacement is predomi-nantly in the vertical direction. The active dig zone is stillpresent and in the back of the bucket, the initial laminarlayer starts to become stationary relative to the bucket.This is visible by the PDR values that increase towardsthe back of the bucket. This corresponds well to the flowzones shown in Fig. 10b.After 800 mm the existence of the dead load shear line isclearly visible. When compared to Fig. 10c, the active flowzone and active dig zone cannot be distinguished from thedead load. The reason for this is that at a bucket displace-ment of 800 mm, the bulldozing effect is large and over-shadows the other flow zones.Dragline bucket optimization is very important in termsof force and energy requirements and cycle time. In someapplications it would be advantageous to fill the bucketusing the minimum amount of energy. In other applica-tions, it would be advantageous to fill the bucket as quicklyas possible to decrease cycle time 1. To investigate fillrates, images from the experiment were taken at differentstages of filling, the outline of the material digitized, andthe volume of material inside the bucket calculated andexpressed as a percentage of the maximum bucket volume.The maximum bucket volume of 0.0146 m3is defined inFig. 2b. Using the DEM results, the same procedure wasfollowed and the results compared.Fig. 12 shows the experimental results using three differ-ent rig angles. The bucket fill percentage is plotted againstbucket displacement in terms of bucket-lengths. In thedragline industry, the target is to get the bucket completelyfilled in 23 bucket-lengths. With an increase of the rigangle from 0? to 10?, there is a slight increase in fill percent-age towards the latter stages of filling. This is due to thefact that when material is disturbed, it flows more easilyinto the bucket. When the rig angle is further increasedto 20? there is, however, a decrease in fill percentage. A fur-ther investigation showed that with an increase in rig angle,the bucket displacement into the material is less. It hasbeen shown that the force perpendicular to the materialsurface is given by Wb? cos (h). Hence, with an increasein the rig angle, the force component forcing the bucketto dig in, decreases. When this force component decreases,the penetration depth of the bucket into the material isreduced and the bucket scoops up less material. Whenthe bucket scoops up less material, there is a decrease in fillpercentage.The comparison between experimental and DEM fillpercentages is summarised in Fig. 13. Using three rigangles h = 0?, 10? and 30? and two effective bucketweights Wb= 49.1 N and 138.3 N, the fill percentagewas calculated at displacements of 100, 200, 300, 400,500, 600 and 700 mm. The 42 data points were plottedand the two lines indicate that in all cases, except fortwo, the DEM results were within 6% of the experi-mental results.In practice, the bucket is rotated to prevent the majorityof the material to fall out when the bucket is disengaged.This principle is depicted in Fig. 14 where, at the end ofits displacement, the bucket was lifted out of the materialand kept at the rig angle. The effect of bucket orientationis clear on the amount of material that the bucket couldhold. Again, the experimental free surface outline is shownon the DEM results with good agreement for h = 0?. Forh = 20?, the DEM model predicts additional material inthe back of the bucket which can be explained by the differ-ence in the final fill state as seen in Fig. 6 at a displacementof 800 mm.0.511.522.50102030405060708090100Displacement bucket lengthBucket fill % = 0 = 10 = 20 Fig. 12. Bucket fill percentage as a function of bucket displacement fordifferent rig angles. = 0, Wb = 49.1 N = 10, Wb = 49.1 N = 20, Wb = 49.1 N = 0, Wb = 138.3 N = 10, Wb = 138.3 N = 20, Wb = 138.3 N102030Experimental %405060010203040Simulation %5060- 6% + 6% Fig. 13. Comparison between experimental and DEM fill percentages.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 2172272256. ConclusionsThe main objective of this paper was to demonstratehow accurately the discrete element method can predictthe process of excavator bucket filling. The flow patternsof material entering the bucket, drag force acting on bucketdue to material interaction, energy requirements and thebucket fill rates were compared to experimental observa-tions and measurements. The study was limited to cohe-sionless granular material and two-dimensional models.The conclusions of the paper are:1. Comparing the material free surface, DEM can accu-rately model the flow of material into the bucket duringthe initial stages of filling. During the latter stages of fill-ing DEM, however, fails to accurately predict the mate-rial free surface.2. DEM can accurately predict the general trend in bucketdrag force. Over the complete drag of 800 mm DEMpredicts a drag force 1550 N lower than the measuredvalues. The maximum measured drag force is 250 Nwhile DEM predicts a maximum drag force of 200 N.3. DEM fails to accurately predict the drag energy. Thegeneral trends are however correct and it is shown thatthe drag energy increases linearly with an increase inbucket weight.4. Based on the DEM re

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