CHAPTER 1

• Kinematics is the study of object motion independent of the forces.
• The very building block of mechanisms is the link.
• Classification of Links

  Binary

  Ternary

  Quarternary
• When two or more links are joined together at their nodes, their group is now called a linkage.
• Several links may be joined together in such a way that prevents rigid body motion. These unmoving linkages are called structures.
• If a linkage can exhibit controlled output motion, then it is called a kinematic chain.
• If at least one link of a kinematic chain is fixed ,grounded, or secured to a reference frame, this kinematic chain is now called a mechanism.
• A closed-chain mechanism is one whose links connect to one another in an unbroken loop.
• An open-chain mechanism is the exact opposite, and in this category we will find robot arms of various sizes and functions.
• Now, should a mechanism be delivering power or useful mechanical work, it is now called a machine.
• degrees of freedom - how many types of basic movement an object can undergo.
• Joints, or kinematic pairs, are formed when two links connect while allowing some motion.
• Types of kinematic pairs

  • by mobility/type of motion allowed

  • contact type

  • enclosure

  • constraint
• Lower pairs - Also called full joints, these are kinematic pairs with area contact between links.
• Revolute (R) Joint

  Also called the pin joint, the R-joint restricts all motion save for rotation on one axis (θ).
• Prismatic (P) Joint

  Also called the sliding joint, the P-Joint restricts motion to translation on a single axis (x).

  Thus, it only has 1 DOF. Examples include the piston-cylinder coupling in engines.
• Helical (H) Joint

  Also the screw joint, examples of this kinematic pair include the lead screws in 3D Printers, power threads in engine lathes, and the nut and bolt fastener. While it may exhibit two types of motion (translation (x) along and rotation (θ) on one axis), the H-joint only has 1 DOF.
• Cylindrical (C) Joint Unlike the H-joint, this kinematic pair allows independent translation (x) and rotation (θ) in one axis. Thus, it has 2 DOF.
• Spherical (S) Joint

  This kinematic pair is known alternatively as the ball-and-socket joint. It allows freedom to rotate in all three axes (θ, φ, γ); hence, 3DOF.
• Planar (PL) Joint

  Planar joints permit general plane motion on a level surface (x, y, θ). Thus, 3 DOF.