Understanding Machines and Mechanisms
Machines and Mechanisms
Introduction
A machine is a device that reduces the effort required to perform a job. Mechanisms are groups of mechanical elements within a machine, each performing a specific task.
Simple and Compound Machines
Simple machines have a single point of support. Compound machines are composed of two or more simple machines.
Fundamental Law of Simple Machines
In a simple machine, the work done by the driving force equals the work done by the resisting force.
Lever
A lever is a simple machine consisting of a rigid bar that rotates around a fulcrum.
- Power (Effort): The force applied to the lever.
- Resistance (Load): The weight or force being moved.
- Power Arm: The distance between the fulcrum and the point where power is applied.
- Resistance Arm: The distance between the fulcrum and the point where the resistance is located.
Law of the Lever: The product of the power and the power arm equals the product of the resistance and the resistance arm.
Types of Levers
- First Class: The fulcrum is between the power and the resistance (e.g., seesaw).
- Second Class: The resistance is between the fulcrum and the power (e.g., wheelbarrow).
- Third Class: The power is between the resistance and the fulcrum (e.g., tweezers).
Multiple levers are formed by combining several levers of the same or different classes.
Inclined Plane or Wedge
An inclined plane is a simple machine consisting of a flat surface at an angle to the horizontal. The product of the power and the length of the incline equals the product of the resistance and the height of the plane.
Screw
A screw is a simple machine consisting of an inclined plane wrapped around a cylinder. If the screw rotates within a cylindrical hole, it’s called a nut. The ridge of the screw is called the thread. The distance between two consecutive threads is the pitch.
Type of Thread
Thread profiles can be triangular, square, trapezoidal, sawtooth, or round. The screw can rotate left or right. A screw can have one or more threads, allowing for faster movement.
Pulley
A pulley is a simple machine consisting of a wheel rotating on an axle, driven by a cord or strap. Pulleys can be fixed or movable.
A movable pulley system consists of two pulleys: one fixed and one attached to the load. The power is the force applied, and the resistance is the weight of the load.
Transmission Systems
Transmission systems transfer motion and power from a motor to other machine components.
Friction Wheels
Motion is transmitted by the friction between two wheels in contact.
Belt Drive
Two pulleys connected by a belt transmit motion. When one pulley rotates, it drives the other.
Phased Pulley Mechanism
A system of pulleys of varying diameters on parallel shafts, used to change speeds.
Chain Drive
Two sprockets connected by a chain transmit motion. Chains can be roller or articulated.
Gearings
Two or more gears with interlocking teeth transmit motion. The larger gear is called the wheel, and the smaller is called the pinion. Gears can be internal or external.
Simple Transmission
Motion is transmitted directly between two axes.
Compound Transmission
Motion involves more than two shafts.
Powertrain
A set of components that transmit power and motion from the engine to where it’s needed.
Mechanisms
A set of elements that produce or transmit movements to perform a specific function.