上海交通大学：《Design and Manufacturing》课程教学资源（讲义）Lecture8 Transmission Power_screws

圈上海人峰 LECTURE 8 Mechanical Design and Manufacturing II Power/Energy Transmission: Power Screws(传动螺旋) Covered: 11-1 and 11-2 in Mechanical Engineering Design 圈上我大峰 Lectures Power/Energy Conversion Power/Energy (Electrical Motors) Transmission Gears,Cam,Linkage Belt Drives, Power Screw) Joints Transmission (Fasteners, Support Connectors) (Bearings) Structural Support (Frames) Tools Statics,Dynamics, Stress Analysis,etc. 2

1 Power/Energy Transmission: Power Screws（传动螺旋） Mechanical Design and Manufacturing II LECTURE 8 Covered: 11-1 and 11-2 in Mechanical Engineering Design 2 Lectures Power/Energy Conversion (Electrical Motors) Transmission Support (Bearings) Joints (Fasteners, Connectors) Structural Support (Frames) Tools Statics, Dynamics, Stress Analysis, etc. Power/Energy Transmission (Gears, Cam, Linkage, Belt Drives, Power Screws)

国上活我人隆 Power Screw Principles! >The screw thread is one of the most important inventions ever made >Power screw using the principle of a screw thread and its mating nut >Used to convert rotation to linear motion >in actuators,production machines(Lead screws)and jacks,etc. >Transmit power,exert the necessary force to move a machine element along a desired path. >Capable of very large mechanical advantages, can lift or move large loads,the speed is often slow 国 上活大学 Power Screw Applicationsl ·Power screws >Either screw can move,as in a jack or >Nut can move,as in a positioning device. servomotor Head Lever 十 coupling Sq.threaded rod lead screw nut-

3 The screw thread is one of the most important inventions ever made Power screw using the principle of a screw thread and its mating nut Used to convert rotation to linear motion in actuators, production machines (Lead screws) and jacks, etc. Transmit power, exert the necessary force to move a machine element along a desired path. Capable of very large mechanical advantages, can lift or move large loads, the speed is often slow. Power Screw Principles1 4 Power Screw Applications1 •Power screws Either screw can move, as in a jack or Nut can move, as in a positioning device

圈上海人峰 NOSEN 餐学 5 圈上大逢 Tong' 二 6

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圈 上濟发大学 Lead Screw and Ball Screw Lead screw(传导螺用 Lead screws are essentially accurate screws used to move a nut attached to a load,and they have been used for centuries to convert rotary motion into linear motion -Lead screws are commonly used on manual economy machine tools Efficiency in a lead screw system may be 30-50% 圈上我大峰 Ball Screws (滚珠螺旋) >Ball screw is similar in function lead screw >Sliding contact between the screw and nut is replaced by rolling contact using recirculating spherical balls,reduce the thread friction,do not suffer from the stick-slip characteristics of sliding joints >Leads to higher efficiency,may have 95%efficiency >However,not self-locking. >Have a more limited fatigue life >But have very high load capacity 8

7 Lead Screw and Ball Screw Lead screw(传导螺杆) • Lead screws are essentially accurate screws used to move a nut attached to a load, and they have been used for centuries to convert rotary motion into linear motion – Lead screws are commonly used on manual economy machine tools – Efficiency in a lead screw system may be 30-50% 8 Ball screw is similar in function to lead screw Sliding contact between the screw and nut is replaced by rolling contact using recirculating spherical balls, reduce the thread friction, do not suffer from the stick-slip characteristics of sliding joints Leads to higher efficiency, may have 95% efficiency However, not self-locking. Have a more limited fatigue life But have very high load capacity Ball Screws（滚珠螺旋）

圈 :上济充大学 Ball Screws (滚珠螺旋) >Modern machine tools,automation equipment,and actuators on aircraft use ball screws for high precision, high efficiency,fast response,and smooth operation. Rotary Encoder ☒☒ ☒ AC Brushless Motor Flexible Coupling Rearing Housing Ballscrew Ballnut Support Bearings 9 chenn.cn

9 Ball Screws（滚珠螺旋） Modern machine tools, automation equipment, and actuators on aircraft use ball screws for high precision, high efficiency, fast response, and smooth operation. 10

圈上大峰 Roller Screws(滚柱螺旋) Nut Housing- rinm Thrust Bearing Wiper Seal- 圈上大峰 Other Applicationsl 12

11 Roller Screws（滚柱螺旋） 12 Other Applications1

上濟大学 Objective of This Lecture Learn to analyze power screws and to specify suitable sizes for a given application Describe the operation of a power screw and the general form of square threads,Acme threads,and buttress threads锯齿螺纹)as they are applied to power screws. Compute the torque that must be applied to a power screw to raise or lower a load Compute the efficiency of power screws Compute the power required to drive a power screw Analyze the failure modes 13 圈上我大峰 -Mawe diamete Basic Terminology3 ·Pitch,p(螺距) >Distance between adjacent thread forms measured parallel to the thread axis. ·Major Diameter,d(大径) >Largest diameter of a screw thread. ·Minor Diameter,d,(小径) >Smallest diameter of a screw thread ·Pitch Diameter,,dp(中径) >The effective diameter of the screw >Sometimes called the mean diameter,dm 14

13 Objective of This Lecture Describe the operation of a power screw and the general form of square threads, Acme threads, and buttress threads（锯齿螺纹） as they are applied to power screws. Compute the torque that must be applied to a power screw to raise or lower a load Compute the efficiency of power screws Compute the power required to drive a power screw Analyze the failure modes Learn to analyze power screws and to specify suitable sizes for a given application 14 Basic Terminology3 • Pitch, p（螺距） Distance between adjacent thread forms measured parallel to the thread axis. • Major Diameter, d（大径） Largest diameter of a screw thread. • Minor Diameter, dr （小径） Smallest diameter of a screw thread • Pitch Diameter, dp（中径） The effective diameter of the screw Sometimes called the mean diameter, dm

圈上清式廷大生 Basic Terminology3 Angle of thread Flank Slope→ -0.5p Axis -e!p yoild Crest- Pitch Root- Depth of thread- External thread Internal thread 外螺纹 内螺纹 15 圈上我大峰 Basic Terminology3 ·Lead,l(导程) >Distance the nut moves parallel to the screw axis when the nut is given one turn ·Lead Angle,(导程角、升角) >Angle between the perpendicular of the screw axis and the rise of the thread ·Helix Angle,Ψ（螺旋角） >Angle between the screw axis and the rise of the thread ·Thread Angle,.2a(牙型角2a、牙侧角a) >a:Angle between the perpendicular to the screw axis and the crest of the thread. 16

15 Basic Terminology3 External thread 外螺纹 Internal thread 内螺纹 16 Basic Terminology3 • Lead, l（导程） Distance the nut moves parallel to the screw axis when the nut is given one turn • Lead Angle, （导程角、升角） Angle between the perpendicular of the screw axis and the rise of the thread • Helix Angle,  （螺旋角） Angle between the screw axis and the rise of the thread • Thread Angle, 2 （牙型角2  、牙侧角 ）  ：Angle between the perpendicular to the screw axis and the crest of the thread

圈上大峰 Basic Terminology3 ·External Threads(外螺纹) >the threads on a screw ·Internal Threads(内螺纹) >the threads on a nut ·Engagement Length,L。(旋合长度) >length over which the nut and the screw are engaged. 圈上大峰 Multiple Screw Threads2(多线螺纹) .Screws can be multiple-threaded by having two or more threads cut beside each other Double-threaded screw(双线螺纹) >lead is equal to twice the pitch,/=2p ,Triple-threaded screw(三线螺纹) >lead is equal to 3 times the pitch,/=3p .Advantage of multiple threads:They have >Smaller thread height >Increased lead for fast advancement of nut. .Standardized products all have single thread 18

17 Basic Terminology3 • External Threads（外螺纹） the threads on a screw • Internal Threads（内螺纹） the threads on a nut • Engagement Length, Le （旋合长度） length over which the nut and the screw are engaged. 18 Multiple Screw Threads2（多线螺纹） •Screws can be multiple-threaded by having two or more threads cut beside each other •Double-threaded screw（双线螺纹） lead is equal to twice the pitch，l=2p •Triple-threaded screw （三线螺纹） lead is equal to 3 times the pitch, l=3p •Advantage of multiple threads: They have Smaller thread height Increased lead for fast advancement of nut. •Standardized products all have single thread

圈 上文大学 Multiple Screw Threads2 I=n *p,nnumber of threads 1 tan入=- 圈上我大峰 Direction of helical groove Screw in Right hand Left hand 20

19 Multiple Screw Threads2 l=n p, n—number of threads dm l  tan   20 Direction of helical groove