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Bài giảng Kinematics and dynamics of machines - Chapter 1: Terminology, Structural design of mechanism, Degrees of Freedom/Mobilit - Phạm Huy Hoàng

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Terminology, Structural design of  
mechanism, Degrees of  
Freedom/Mobility  
PHAM HUY HOANG  
I. Terminology: Machine element and Link  
4-stroke internal combustion engine  
1. Machine element:  
smallest machine  
part detached from a  
machine.  
2. Link: one or several  
machine elements  
assembled and fixed  
together into a rigid body  
and having motion  
relative to other rigid  
bodies.  
(4-piston-and-)4-cylinder engine  
2-link group: Piston and connecting rod  
2-link group: Piston and connecting rod  
Crank shaft and 9 connecting rod  
Crank shaft and  
connecting rod  
Piston and crankshaft - V engine  
Piston and crankshaft - V engine  
Prototype of 4-stroke internal combustion engine  
Crankshaft – 4-cylinder engine  
3. Joint / Kinematic pair:  
a/ Mobility / Number of Degrees of freedom (DOF) of a link - defined as  
the number of independent movements it has.  
b/ Constraint - a simulation rule limits the movement of two links relative  
to each other. A constraint restricts the DOF of a link relative to another  
link.  
c/ Mating surfaces - surface of a link contacts to surface of another link  
to create constraint.  
d/ Joint / Kinematic pair - Set of 2 mating surfaces of 2 links that  
contact together and create constraints.  
Spherical joint with 3 or 4  
constraints (3 or 2 DOF)  
Translational / prismatic /sliding  
joint (5 constraints, 1 DOF)  
Pin joint / revolute joint  
(5 constraints, 1 DOF)  
e/ Joint classification:  
- Based on number of constraints: k-type joint has k constraints  
- Based on contact type:  
higher pair – point / line contact.  
lower pair – surface contact  
Screw joint  
Convention presentation of link and joint  
Simplified  
Using kinematic size – size relating to kinematics and  
dynamics, not considering on strength of material.  
4. Kinematic group of links, Mechanism and Machine:  
a/ Kinematic group of links: set of links connected together  
by joints.  
- Closed  
- Opened  
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