Kinematic Links: Basic Terminology

Definition

A Kinematic Link (or element) is the individual, resistant body or a group of bodies that constitute a part of a machine, moving relative to another part. To be considered a link, the part must be resistant—meaning it should be capable of transmitting force with negligible deformation—and it must be connected to other links to form a kinematic chain.

Main Content

1. Rigid Links

A link is considered "rigid" if it does not undergo any detectable deformation while transmitting motion.
Example: The connecting rod or crank in an internal combustion engine is designed to be rigid to ensure accurate power transmission.

2. Flexible Links

A link is "flexible" if it undergoes partial deformation while transmitting motion, yet still performs its intended function effectively.
Example: Belts, ropes, and chains used in power transmission systems are flexible links. They transmit force through tension without being rigid.

3. Fluid Links

A link is considered "fluid" when the motion is transmitted through a fluid medium, such as oil or air, usually under pressure.
Example: Hydraulic brakes in a car, where the fluid acts as the connecting medium between the pedal and the brake pads.

[Representation of a Link]
      +-----------+
      |  Rigid    |  <-- Link 1 (Fixed)
      +-----------+
            | (Joint)
      +-----------+
      |  Moving   |  <-- Link 2 (Moving)
      +-----------+

Working / Process

1. Identification of Resistant Bodies

Engineers analyze the mechanism to determine which components act as the skeleton (the links).
It involves ensuring the material stiffness is sufficient for the load being applied.

2. Establishing Connectivity

Once links are identified, they are connected via joints (kinematic pairs).
Connectivity determines the degree of freedom allowed for the mechanism.

3. Transmission of Motion

The mechanism is set in motion. The "Input Link" receives energy, transmits it through the "Coupler" or intermediate links, and moves the "Output Link" to perform useful work.

Advantages / Applications

Mechanical Advantage: Kinematic links allow for the amplification of force, enabling heavy loads to be moved with minimal input effort (e.g., a lever).
Motion Conversion: They are essential for converting one type of motion to another, such as converting rotary motion from a motor into reciprocating motion in a piston.
Precision Control: By using specific link lengths and joint types, machines can achieve highly predictable and repeatable movements required in robotics and manufacturing.

Summary

A kinematic link is any resistant component within a mechanism that moves relative to others to transmit force or motion. Whether rigid, flexible, or fluid, these links form the foundation of all machinery.

Key Concept: Links must be resistant to deformation under normal operating conditions.
Mechanism: A sequence of connected links forms a kinematic chain.
Important Terms: Rigid Link, Flexible Link, Fluid Link, Kinematic Pair, and Resistant Body.