Mechanical Mechanisms: Types, Classifications, and Transformations
Mechanical Mechanisms
A mechanism is a set of rigid or semi-rigid elements that are connected to transmit and transform motion, force, or energy. These mechanisms can change one type of motion into another, one force into another, or one form of energy into another. Elements can be simple (with two connections) or complex (with more than two connections).
One element is usually fixed, forming the frame, while others move. A mechanical system is a combination of mechanisms that transform velocities, paths, forces, or energy through intermediate transformations.
Types and Classifications of Mechanisms
- Based on the number of inputs:
- Forced Position: Mechanisms where one element’s position determines the position of all others. They have a single input.
- Multiple Input: Mechanisms with more than one input.
- Blocked: Mechanisms where no movement is possible.
- Based on the form:
- Closed Chain: Elements form a closed loop.
- Open Chain: Elements do not form a closed loop, like robot arms.
- Based on the type of movement:
- Transforming linear motion into linear motion.
- Transforming rotational motion into rotational motion.
- Transforming linear motion into rotational motion.
- Transforming rotational motion into linear motion.
Mechanisms that Transform Linear Motion into Linear Motion
These mechanisms minimize the force needed to perform an action.
Key Elements:
- Levers: A rigid bar that pivots around a fixed point (fulcrum).
Types of Levers:
- First Class: Fulcrum is between the force and the load.
- Second Class: Load is between the fulcrum and the force.
- Third Class: Force is between the fulcrum and the load.
The law of the lever states that the force multiplied by its distance from the fulcrum equals the load multiplied by its distance from the fulcrum.
- Pulleys: A wheel with a groove around its circumference for a rope or cable. Pulleys can be fixed or mobile.
Combinations of Pulleys:
- Potential Hoist: A series of pulleys.
- Exponential Hoist: Each mobile pulley has a separate rope.
Mechanisms that Transform Rotational Motion into Rotational Motion
These mechanisms can increase or decrease speed.
Types of Mechanisms:
- Friction Wheels: Two disks or wheels in contact. The driving wheel transmits rotation to the driven wheel through friction.
- Friction Cones: Used when the axes of the two wheels are not parallel.
- Belt and Pulley System: Used when the distance between the axes is large.
- Chain and Sprocket System: Two wheels with teeth that fit into the links of a chain. This system avoids slippage.
- Cylindrical and Conical Gears: Wheels with teeth that mesh together to transmit rotation.
Gear Teeth:
- Spur Gears: Teeth are parallel to the axis.
- Helical Gears: Teeth are angled to the axis.
Spur Gear Parameters: Primitive circumference, exterior circumference, interior circumference, circular pitch, tooth head height, tooth foot height, tooth height, tooth thickness, tooth space, tooth clearance.
Helical Gear Parameters: Circumferential plane, normal plane, axial plane.
- Bevel Gears: Used to transmit rotation between non-parallel axes.
- Maltese Cross: Converts continuous rotation into intermittent rotation.
- Cam and Follower: A cam transmits motion to a follower through direct contact. It has four sections: rise, dwell, return, and starting position.
Mechanisms that Transform Rotational Motion into Linear Motion
- Linear Cam and Follower: The follower moves in a linear path. The maximum displacement is when the follower is in contact with the cam.
- Rack and Pinion: A gear (pinion) meshes with a linear toothed bar (rack).
- Drum and Cable: A cylinder around which a cable is wound.
- Screw and Nut: Converts rotational motion into linear motion. The nut is threaded and can have different thread profiles (rectangular, triangular, trapezoidal).
Mechanisms that Transform Linear Motion into Rotational Motion
These mechanisms convert linear motion into rotational motion.
- Crank and Connecting Rod: Used in combustion engines. The points where the piston reverses direction are called dead points.