Technological System Flashcards
What is a technological system?
A set of parts, mechanisms, devices, or machines that are assembled to accomplish a specific function
In order to understand technological system, so we must understand: (3)
-effects of forces on materials
-Basic mechanical functions
-Complex mechanical functions
Mechanical constraints describe
The effect produced within a material when it is subjected to external forces
What are the main forces (5)
- Flexion (bending)
- Tension
- Compression
- Shearing
- Torsion
What is flexion?
Force that bends an object or materials
What’s tension?
Force that tends to stretch an object or materials or distance two parts
What’s compression?
Force that compresses or crushes an object or materials or brings two objects closer together
Shearing
Forces that cuts or tears an object or materials
Torsion
Force that twists an object or materials
The effects on materials (2)
Materials can only resist mechanical contraints (force) a certain amount before being deformed.
IF a force does to cause sone form of deformation, it may cause movement instead
What is elastic deformation?
Temporary deformation, material returns to its original shape after the force is removed
What is plastic deformation?
Deformation remains after force removed
What is fracture deformation?
Break or rupture in material
Mechanical properties (2)
A mechanical property determines how much a material will react when subjected to one or more mechanical constraints
Choose materials based on their ability to react to different forces by resisting deformation (elastic or plastically)
Resisting deformation (2 & define)
Hardness: Resists being scratched penetrated or deformed
Ex: ceramic floors are hard
Compressive strength/stiffness: resists being compressed
Ex: Concrete resists deformation
Reacting by Elastic deformation
Tensile strength/rigidity: resists tension without becoming permanently deformed
Elasticity: Regains its initial shape after being subject to a force
Ex: polychloroprene (neoprene) is a stretchy material that shapes to the person that wears it
Resilience (usually compression): resists physical impacts (resists being permanently deformed) by absorbing shocks and forces
Ex: car bumpers are resilient, they allow cars to withstand impacts
Reacting by plastic deformation
Ductility: stretches without breaking
Ex: Copper is very ductile - it can be stretched to make wires
Malleability: flattens if bends to hold a new shape without breaking
Ex: aluminium is malleable enough to be flattened into sheets
Types of deformation
- Elastic
- Plastic
- Fracture
Types of motion:
- Unidirectional translation
- Bidirectional translation
- Unidirectional rotation
- Bidirectional rotation
- Unidirectional helical motion
- Bidirectional helical motion
Translational motion
Motion describing a rectilinear trajectory in a same direction
Rotational motion
Motion describing a circular trajectory
Helical motion
Motion describing a spiral trajectory
What is a mechanical function?
The role played by a mechanism inside a more or less complex technical object
What is a link?
A basic mechanical function which two or more parts are connected together
What is guiding control?
A basic mechanical function which one or more parts allow an object to move in a certain way (rotational, translational or both)
Types of links
Must be 4:
Direct or indirect
Removable or non-removable
Rigid or elastic
Complete or partial
Direct vs indirect
Direct: A connection without an intermediate or link mechanism. The parts have complementary pieces
Indirect: A link which requires one or more intermediate mechanisms for example nails, a screw or glue
Removable vs non-removable
Removable: this link can be used to separate the parts without damaging the link surface or parts
Non-removable: this link does not allow the connected parts to be separated without damaging them or the link mechanism
Rigid vs elastic
Rigid: this link does not allow the position of the assembled parts to be changed
Elastic: this link allows the parts to be deformed. Usually use springs or rubber blocks
Complete vs partial
Complete: this link does not allow the parts to move independently of each other. If one part moves the other will make the same motion
Partial: this link allows the connected parts to move independently of each other
Rotational guide (2)
Only allows the rotation of moving parts
Cylindrical parts are best suited for this type of motion
Ex: hinges on a door
Translational guide (2)
Only allows the translational movement of moving parts
Straight grooved parts are best suited for this motion
Helical guide (2)
Enables parts to nove in a translational manner when these parts are rotated
Threaded parts are best suited for this type of motion
Complex mechanical function
When a system’s role is t transfer a motion inside a technical object: consists of motion transformation or transmission
Components of a system
Driver: root of system’s motion, receives the power and gives the motion
Driven component: the part that receives the motion and transmit it
Intermediate: the part in between driver and driven, connector
What’s a motion transmission?
A transfer of motion through parts WITHOUT changing the type of motion
The different types of system for motion transmission
- friction gears
- gear train
- belt and pulley
- chain and sprocket
- worm and worm gears
Friction gear system (3)
- Rotational motion being transmitted by friction between two or more gears
- Must be touching = no intermediate
- No teeth and move in opposite direction
Belt and pulley system (4)
-Rotational motion between two or more pulleys
-Transmitted by a belt (intermediate)
- inside belt, travel same direction (vice versa)
- needs sufficient adhesion which can be improved with notches or grooves
Speed changes in gears and pulleys systems
bigger to smaller = increase and vice versa
Gear trains (2)
-Rotational motion transmitted between two or more gears due to their teeth
-Gears in contact rotate in opposite directions
Chain and sprocket (3)
- Rotational motion transmitted between two or more sprockets
- Linked by a chain (intermediate)
- Same direction inside the chain (vice versa)
Worm and worm gears
- Use when a large reduction in rotational speed required
- threaded worm (driver) contact toothed gear (driven)
- 1 rotation = 1 tooth
Reversibility (2)
A reversible system is when the driver component becomes the driving component
Motion transmission = change in speed (all except worm and worm gears)
Motion transformation
A transfer of motion while CHANGING the type of motion
Slider and crank
- Reversible
- Transforms rotational to translational or vice versa
Ex: engine, pump
Components:
- Crank = rotationally
- Piston (slider) = translationally
- Rod = intermediate
Cam and follower
- non-reversible
- Transforms rotational to translational
Components:
- Irregular shaped disc (cam/driver) rotates
- Rod (follower/driven) press
Rack and pinion
- Reversible
- Transforms rotational motion into translational motion (vice versa)
Ex: steering system, stage adjustment knobs
Components:
- straight rod or rack with the teeth which moves translationally
- gear with teeth (rotationally)
Screw gear system
- Transforms rotational motion to translational motion
- Non-reversible
Components:
- nut and screw
Design Plan
- Simplified representation of a technical object
- different colour for different materials
Includes:
- the names of the parts
- the motions performed by the parts, expressed in symbols
- the forces in actions, expressed in symbols
