Chi tiết máy là gì? Dấu hiệu để nhận biết chi tiết máy là phần tử có cấu tạo hoàn chỉnh và không thể tháo rời ra được hơn nữa. – Các chi tiết máy sau khi gia công xong cần được lắp ghép với nhau theo một cách nào đó để tạo thành sản phẩm hoàn chỉnh. – Các chi tiết máy được lắp ghép với nhau như sau: Các chi tiết máy được ghép với nhau bằng mối ghép cố định và mối ghép động. + Mối ghép cố định là những mối ghép mà các chi tiết được ghép không có chuyển động tương đối với nhau. Gồm hai loại là mối ghép tháo được như ghép bằng vít, ren, then, chốt…và mối ghép không tháo được như ghép bằng đinh tán, bằng hàn. Mối ghép bằng đinh tán thường được dùng khi vật liệu tấm ghép không hàn được hoặc khó hàn, mối ghép phải chịu được nhiệt độ cao, chịu lực lớn và chấn động mạnh. Ứng dụng: soong, nồi, giàn cần trục,… + Mối ghép động là những mối ghép mà chi tiết được ghép có thể xoay, trượt, lăn và ăn khớp với nhau, các chi tiết có chuyển động tương đối với nhau.
1 9/11/2023 DEPARTMENT OF EDUCATION AND TRAINING HOCHIMINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION Mechanisms and Machine Components Design CHAPTER 1: Mechanism 11-Sep-23 Theoretical contents I Machines and Mechanisms II Mobility or Degrees of freedom of mechanisms III Inversion of Mechanisms TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms General TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms 9/11/2023 General 1.1 Machinery parts Machinery parts (elements) are basic mechanical parts and features used as the building blocks of most machine TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms General 1.2 Mechanical linkage TS Phan Công Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms General 1.2 Link A link is defined as a rigid body having one or more pairing elements which connect it to other bodies for the purpose transmitting force or motion TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms 9/11/2023 General 1.3 Kinematic pair Degrees of freedom (DOF) of mechanical system is the number of independent parameters that define its configuration or state Kinematic constraints: Are constraints between rigid bodies that result in the decrease of the freedom of rigid body system Kinematic pair: is a connection between two physical object that imposes constraints on their relative movement Classification of kinematic pair: • Number of kinematic constraint • Contact surface: Higher pairs –point or line contact Lower pairs –surface contact TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms General 1.3 Kinematic pair TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 I Mechanisms General 1.3 Kinematic chain, mechanism and machine Kinematic chain is an assembly of rigid bodies connected by joints to provide constrained (or desired) motion TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 10 9/11/2023 I Mechanisms General 1.3 Kinematic chain, mechanism and machine Mechanism: Kinematic chain consists of permanent link (Fixed link) Input or drive link is provided motion to move (Input link) Another link move follow Input link (follower) TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 11 I Mechanisms General 1.3 Kinematic chain, mechanism and machine Application of four-bar mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 12 I Mechanisms General 1.3 Kinematic chain, mechanism and machine Machine: One or multi mechanisms are assembled to transmit or transform energy TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 13 9/11/2023 I Mechanisms Degree of freedom TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 14 I Mechanisms Degree of freedom 2.1 Space mechanism Definition: An unrestrained rigid body in space has six degrees of freedom: - Three translating motion along Y x, y and z axes - Rotary motion around x, y and z axes respectively X TS Phan Cơng Bình Z binhpc.tpm@gmail.com 11-Sep-23 binhpc@hcmute.edu.vn 15 I Mechanisms Degree of freedom 2.1 Space mechanisms Coincide constraint: • Constraint generated (when two stitches are linked by kinematic couple) coincide with the available constraints of the joining linkage Ví dụ: • Coincide constraint Translating z axis Rotating x axis Rotating y axis TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 16 9/11/2023 I Mechanisms Degree of freedom 2.1 Space mechanism Redundancy constraint: • Degree of freedom but redundancy in kinematics Example: • Linkage CD - → Note: Constrain of dimension and positions TS Phan Công Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 17 I Mechanisms Degree of freedom 2.1 Space mechanism Redundancy degree of freedom: • Degree of freedom but unnecessary in kinematics Example: • The roller rolls around its center → Note: Self motion without affecting the movement of the other TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 18 I Mechanisms Degree of freedom 2.1 Space mechanism W 6.n ( k pk rth rtr ) wth n: Number of kinematic link pk: K constraint rth: Redundancy constraint rtr: Coincide constraint wth: Redundancy of DOF TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 19 9/11/2023 I Mechanisms Degree of freedom 2.2 Planar mechanism Definition : • All of the relative motions of the rigid bodies are in one plane or in parallel planes Y X TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 20 I Mechanisms Degree of freedom 2.2 Planar mechanism W 3.n ( p4 p5 rth ) wth n: Number of kinematic link (số khâu động di chuyển) p4: Higher pairs (two degrees of freedom) (tiếp xúc cung tròn vd: cam, lăn, bánh răng…) p5: Lower pairs (one degrees of freedom) (tiếp xúc mặt: khớp lề xoay trượt tịnh tiến) rth: Redundancy constraint (hình bình hành) Wth: Redundancy degree of freedom (con lăn) TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 21 I Mechanisms Degree of freedom 2.3 Problems Q : predict DOF of the given mechanism? 𝑛 = 3, 𝑃 = 4, 𝑃 = 𝑊 = ⇒ 𝑊 = 3.3 − + 2.4 − − = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 22 P5 9/11/2023 2P5 Wth I Mechanisms Degree of freedom P4 2.3 Problems P5 Q : predict DOF of the given mechanism? P5 P5 P5 P5 P5 𝑛 = 7, 𝑃 = , 𝑃 = 1, 𝑊 = ⇒ 𝑊 = 3.7 − 2.9 + − = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 23 I Mechanisms Degree of freedom 2.3 Problems Q : predict DOF of the given mechanism? 24 52 16 𝑛 = 7, 𝑃 = 10, 𝑃 = 0, 𝑊 = 𝑊 = 3.7 − 2.10 + − =1 TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 24 I Mechanisms Degree of freedom 2.3 Problems Q : predict DOF of the given mechanism? 24 𝑛 = 5, 𝑃 = 7, 𝑃 = , 𝑊 = 0, 𝑟=0 𝑊 = 3.5 − 7.2 + − − = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 25 9/11/2023 I Mechanisms Degree of freedom 2.3 Problems Q : predict DOF of the given mechanism? 𝑛 = 8, 𝑃 = 11, 𝑃 = , 𝑊 = 0, 𝑟=0 𝑊 = 3.8 − 11.2 + − − = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 26 I Mechanisms Principle of creating a mechanism 3.1 Definition Drive link (input link) connected to the fixed link by one or many kinematic chains ( DOF = 0) 𝑊=𝑊 + 𝐾𝑖𝑛𝑒𝑚𝑎𝑡𝑖𝑐 𝐶ℎ𝑎𝑖𝑛𝑠 𝐷𝑂𝐹 = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 27 I Mechanisms Principle of creating a mechanism 3.2 Atxua chains A chain have W=0 ( DOF = 0) The simplest chain 1.3 Classification of Atxua chains Type : links - joints TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 28 9/11/2023 10 I Mechanisms Principle of creating a mechanism 3.3 Classification of Atxua chains Type : links joints Type n : n link polygon TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 29 I Mechanisms Principle of creating a mechanism 3.4 Principles for separating Replacing 𝑃 by 𝑃 before separating Separating from far to close the drive links Separating simple to complex After separating Atxua chains, the rest of links still move Mechanism chain is the highest Atxua chains TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 30 I Mechanisms Principle of creating a mechanism 3.4 Principles for separating Replacing higher pair by lower pair P4 P5 : A ` B B B B 21 A A A A TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 31 9/11/2023 11 I Mechanisms Principle of creating a mechanism Problems Q : Separating Atxua chain of the given mechanism 1P5 1P5 2’ A 1P5 𝑛 = 2, 𝑃 = 2, 𝑃 = Atxua chain type (2x2’) 𝑊 = 3𝑛 − 2𝑃 + 𝑃 = Drive link TS Phan Công Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 32 I Mechanisms Principle of creating a mechanism 3.5 Problems Q : Separating Atxua chain of the given mechanism 2’ 2' A 𝑊 = 3.7 − 2.10 + + − = Atxua chain type Input link1 Tính theo tách Atxua 𝑊 = + + + = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 33 I Mechanisms Principle of creating a mechanism 3.5 Problems Q : Separating Atxua chain of the given mechanism 𝑊 = 3.7 − 2.10 + + − = Atxua chains type 𝑊 =1+0=1 Driving link TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 34 9/11/2023 12 I Mechanisms Principle of creating a mechanism 3.5 Problems Q : Separating Atxua chain of the given mechanism 𝑛 = 6, 𝑃 = 8, 𝑃 = 1, 𝑟 = 0, 𝑊 = 𝑊 = 3.6 − 8.2 + + − = TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 35 I Mechanisms Principle of creating a mechanism 3.5 Problems Q4 O2 ω2 P5 3P5 P2 3P5 W 2' P2 P5 P1 O1 ω1 P1 Atxua chain type (3,4,5,6) Atxua chain type (2,2’) Input link TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 36 II Mechanisms with lower pair General 1.1 Definition Planar mechanism: All of the relative motions of rigid bodies are in one plane or parallel planes Four-bar Mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 37 9/11/2023 13 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism Types of four-bar mechanism following those principle : • Changing dimension of the links • Changing the fixed link B B C1 ω1 A4 A x D D eC v D∞ 1) Change dimension Four-bar mechanism a) Slider-crank off-center mechanism (Link moves translate D at infinity) TS Phan Công Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 38 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism 3D C B ω2 B 12 ω1 A C b) Slider-crank mechanism D c) Culit mechanism v A (b change into fixed link) v B ω1 C D A v AB C3 d) Sin mechanism e) Elip mechanism In b, A & D to infinity (In c A translate to infinity) TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 39 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism a) Four-bar mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 40 9/11/2023 14 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism c) Slider-crank mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 41 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism b) Slider-crank off-center mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 42 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism d) Culit mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 43 9/11/2023 15 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism e) Sin mechanism TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 44 II Mechanisms with lower pair General 1.2 Other types of four-bar mechanism TS Phan Cơng Bình f) Elip mechanism binhpc.tpm@gmail.com 11-Sep-23 binhpc@hcmute.edu.vn 45 II Mechanisms with lower pair General 1.3 Application of four-bar mechanism • Mechanism has link rotate B 2C Link and link rotate same ω1 ω3 clockwise A D • Mechanism has link rotate and link shake (Crushed stone machine) A B Đá F Link rotate, link swing E D 3C TS Phan Công Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 46 9/11/2023 16 II Mechanisms with lower pair Laws of mechanisms 2.1 Grahof’s law In four-bar mechanism, link can rotate fully if total length of the shortest link and the longest link ≤ total link of rest links There are cases: • If the link connected the shortest link is fixed, the shortest link can rotate and opposite link can swing • If the shortest link is fixed, connected fixed links can rotate • If the link opposite the shortest link is fixed link, link connecting fixed link can swing and the shortest link rotates => Purpose: Confirm movement of links connecting fixed link TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 47 II Mechanisms with lower pair Laws of mechanisms 2.1 Grahof’s law TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 48 II Mechanisms with lower pair Laws of mechanisms 2.1 Grahof’s law B • Mechanism diagram B 8,375" A 2" C 47,5" 8" A 7,187" C 9,625" 14" 76" D D 12" AB AD 11, 625 BC AD 18,562 TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 49 9/11/2023 17 II Mechanisms with lower pair Laws of mechanisms 2.2 Transmission ratio mechanism B 2C Transmission ratio mechanism u13 1 3 ω1 ω3 A D TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 50 II Mechanisms with lower pair Laws of mechanisms 2.3 Villis’s law 1 PD Mechanism ABCD, ω1, ω3 BC cut AD at point P Definition : u13 3 PA VB CosB Vc Cosc (1) C VB 1. AB 1.AB αC vc F VC 3.CD 3.CD B αB αC CosB AE vB ω3 E AB αB ω1 Cosc DF P • Point at B A D CD vB • ┴ AB (1) 1 AE 3 DF Vector vận tốc u13 1 DF PD • Follow direction ω1 3 AE PA • VB = ω1.lAB TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 51 II Mechanisms with lower pair Laws of mechanisms 2.3 Villis’s law Content of law: Link BC divides link AD into segments that inversely proportional to the angular velcoity of link connect link AD B C Comment: A D • When mechanism moves , P changes => PD BC / / AD P and PA change ( • If P out of AD => ω1 and ω3 have same u13 1 PD PA AD 3 PA PA rotate clockwise • If P in AD => ω1 and ω3 have contrary rotate TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 9/11/2023 52 TS Phan Cơng Bình binhpc@hcmute.edu.vn binhpc.tpm@gmail.com 11-Sep-23 18