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