Principles of Mechanism and Motion Transfer

Mechanism Classification

Mechanisms can be classified based on their function:

• Transmission of Motion:
  • Linear transmission (lever, pulley)
  • Rotatory transmission (gears and belt drive)
• Transformation of Motion:
  • Rotatory-linear (wheel, crank)
  • Reciprocating rotatory-linear (cam, crank and rod)
• Motion Control:
  • Direction control (ratchet and freewheel)
  • Speed reduction (brake)
• Energy Accumulation:
  • Absorption/dissipation (spring)
• Connection:
  • Linkage (clutch)
  • Support (plain bearing)

Energy and Work in Mechanisms

Mechanisms seem to increase force, but they cannot create energy on their own. All mechanisms produce the same amount of work that is done to them, including energy that is lost to friction and heat. If a mechanism increases force, it must decrease motion. Similarly, if a mechanism increases motion, it must decrease force.

Linear Motion Transmission

Linear transmission mechanisms, such as pulleys, use linear motion. We typically use these mechanisms to transmit force.

Understanding Levers

A lever is a rigid bar that turns around a point called a fulcrum. Each force produces a specific torque, which is the force multiplied by its distance from the fulcrum.

Classes of Levers Explained

We can divide levers based on the relative positions of the fulcrum, force, and resistance.

Class 1 Levers

The fulcrum is between the force and the resistance. These levers can either increase or decrease the effect of the applied force.

Class 2 Levers

The resistance is between the fulcrum and the force. These levers always increase the force that we apply.

Class 3 Levers

The force is between the fulcrum and the resistance. These levers always increase the distance that the end of the lever moves, decreasing the effect of the applied force.

Pulleys and Compound Systems

In a system of pulleys, the equilibrium between the forces depends on the path that the rope follows. A pulley is a wheel that rotates around an axis and has a groove.

A compound pulley system is a combination of fixed and movable pulleys. It is also called a block and tackle system.

Rotatory Motion Transmission

Rotatory transmission systems put two rotating elements into contact. These mechanisms have two purposes: transferring rotatory force from an input location to another location and changing the rotatory speed by using rotating elements of different sizes. Friction wheels and pulleys are often used in toys and other devices with moving parts such as conveyor belt systems. Gears are used in clocks and sprockets and chains in home appliances.

If there were more pairs of wheels in this system, we would continue by multiplying the ratio of each pair with the ratio of the next pair.

How Brakes Work

Brakes use friction to reduce speed. They are activated by some type of lever. The lever transmits force to an output receptor, which puts pressure on the wheel. This produces friction, which slows down the wheel.