Bài giảng Chapter 1: Structure of Mechanism môn Hoá đại cương | Trường Đại học Bách khoa - Đại học Quốc gia Thành phố Hồ Chí Minh

Ho Chi Minh City University of Technology (HCMUT), VNU-HCM CHAPTER 1 STRUCTURE OF MECHANISM
Assoc.Prof.Dr. Le Thanh Long ltlong@hcmut.edu.vn 1
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM OUTLINE 1. Basic Definitions.
2. Degree of Freedom of Mechanisms. 3. Assur Group.
4. All low pair planar mechanism, four bar linkage mechanism. 5. Special structures. 2
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions 1.1 Machine Element and Link.
1.2 Kinematic Pair and Pair element.
1.3 Classifications of Kinematic Pairs.
1.4 Kinematic Diagram of a Mechanism.
1.5 Kinematic chain and classification of kinematic chain. 3
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions 1.1 Machine Element and Link
Machine element: all the machines are made up of elements or parts and units, each
element can be separated but still own its functions is called machine element
Link: during working, all of parts has relative motion with respect to others is called a link 4
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.2 Kinematic Pair and Pair element. Degree of Freedom of a link
• One independent movability of a link with respect to a reference frame is called one degree of freedom 5
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.2 Kinematic Pair and Pair element. Degree of Freedom of a link
• Between 2 links in a plane  3 dof : Tx, Ty, Qz
• Between 2 links in a space  6 dof : Tx, Ty, Tz, Qx, Qy, Qz 6
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.2 Kinematic Pair and Pair element.
Kinematic pair : connection between two links to limit their relative movement.
All points of contact between two links is called a Pair element.
pair element of the right hinges
pair element of the left hinges 7
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the number of constrains: type k joint has k constrains Type 1 8
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the number of constrains: type k joint has k constrains Type 2 9
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the number of constrains: type k joint has k constrains Type 3 10
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the number of constrains: type k joint has k constrains Type 4 11
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the number of constrains: type k joint has k constrains Type 5 12
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs a. By the contact:
• Higher pair: pair elements are points or lines
• Lower pair: pair elements are surfaces 13
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.3 Classifications of Kinematic Pairs
a. By the contact : type k joint has k constrains
• Lower pair: pair elements are surfaces 14
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.4 Kinematic Diagram of a Mechanism.
a. Kinematic Diagram of a joint
For the convenience of research, joints are represented by kinematic diagrams 15
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.4 Kinematic Diagram of a Mechanism. b. Kinematic diagram of link.
Links are represented by kinematic diagram.
In the kinematic diagram of links: - All pairs must be presented. -
All dimensions effect to the motion of the mechanism must be presented 16
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.5 Kinematic chain and classification of kinematic chain
Kinematic chain: the combination of links and pairs
Classification of kinematic chains: - Closed kinematic chain. - Open kinematic chain. - Planar kinematic chain. - Spatial kinematic chain. 17
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.5 Kinematic chain and classification of kinematic chain
- Closed kinematic chain : Links are connected together into one or more closed
perimeters (each link must participate in at least 2 dynamic joints) 18
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.5 Kinematic chain and classification of kinematic chain
- Open kinematic chain : Links aren’t connected together into one or more closed
perimeters (some links only participate in one dynamic joint) 19
Department of Machine Design - Faculty of Mechanical Engineering
Ho Chi Minh City University of Technology (HCMUT), VNU-HCM 1. Basic Definitions
1.5 Kinematic chain and classification of kinematic chain
- Planar kinematic chain : Links move in the same plane or parallel planes. 20
Department of Machine Design - Faculty of Mechanical Engineering