12. Mechanical design¶
Link to this week’s Group Assignment
<!— Most mechanical machines work on one direction. Mechanical systems need to have rotation. Boeing 777 wing test Boeing 787 Dreamliner: ultimate-load wing flex test
A material, after a certain amount of movements, it reaches material fatigue.
Concept of degrees of freedom:
We use mechanical systems to allow rotation. A simple element are bearings contained in a shape that only allows to be used in one direction.
Not much force is needed, made out of metal with a low friction frequency. Loads of little balls encapsulated inside a cylinder where they rotate and change place
- Dry bearings: no mechanical parts and is wet.
- Dry sliders: instead of having oils they have technical plastics (www.igus.eu)
A cylinder connected to a wheel that by having an explosion in linear movement creates a circular rotation, moving a wheel or a piston.
Gears¶
Simple way to function:
Torc is elevated or reduced depending on the way the gears are placed. Electric cars have great amounts of electronically controlled torc. Therefor they need to be small. Different types of gears exist: Motors with steppers give a higher torc output.
Straight gears:¶
A big flat surface touching another surface.
Helix gear:¶
More contact zone produces friction, producing energy loss. Complex and more silent.
Straight Bevel gear:¶
all of the above
Helix Bevel gear:¶
straight but tilted in a 45 degree on the lineal side
Pinion and rack:¶
- From lineal to rotation
Planetary gears:¶
- When distances are longer, we don’t use gears due to their size, we use either belts or chains.
- Planetary gear reduction. Sometimes more than one planetary gear chain together.
Chain:¶
- they can produce more torc
- power loss aroun 2-3%
- on bicycle it last 100000 km ######Belt: -less longlasting that a chain on high power systems
- power loss of around 7-9%
- the life expectancy of a bicycle’s belt is unlimited. the amount of power placed to it is underused, making it indefinite
- CVT (Continuos Variable Transmition) infinite gears by alternating the two cones. Gradiants instead of jumps between gear changes.
- Embrague cetrífugo [xa: busca y agrega un diagrama de ello]
Cams:¶
- Simple systems with several repetitions.
- Used in pump systems
Bearings:¶
- They come in several shapes and can have different frictions
- Ball
- Closed Bearings: they have different degrees of protection. The unit of measure is avec (dust, water and other kinds of protection)
- Flat/needle:
- Conical: a big amount of pressure can be applied to the axis.
######Cams:¶
- Ratchet:
- Geneva Wheel:
- Universal joints:
“Most machines use steppers, which come with names. “Nema” 14, 17, 23, 34 - the numbers are related to their internal coil. Could be long or short, depending on their use” Can come with reduction gear All in one exists with stepper and driver.
Some “nema” motor can have different shaft sizes. - How things are attached to a motor changes their shape and characteristics. Continuo belts can be used. A flexible cupper transmits rotation but doesn’t transmit axial forces. - High torc systems need a special type of “cupper” built with hard but flexible rubber and a spring between its teeths. - Servo motors are costly but widely used for commercial purposes. Habilitated with rotation marks, DC motors have several. - Open loop and closed loop will define what kind of stepper will be needed. Open works without feedback. Closed ones double check for feedback through an encoder. Safety is produced through high accuracy. A peak in torc detects an end stop, hitting a button and close the circuit. 3D printers are low accuracy, open loop. CNC is a machine that tends to be closed loop. SRMs have closed loops for presision since it is a weak machine (17 nema) needing accuracy. Laser cut, the troter is open loop. the cost of manufacturing with accuracy is costly 5-10 microns, increase cost
V slot bearings open loop system transports the system through a belt and the motor is on one side of the machine
there are two types of screws for machine building
backlash prevention is produced with two tuercas with a spring in between. backlash es la tensión que se produce contra el tornillo y desgasta las piezas. hay que evitar que se produzca.
marlin firmware: firmware de código abierto para RepRap y otras impresoras 3D de modelado por deposición fundida basadas en la plataforma Aurduino. System built for options and multitasking bits. High number of developers, everyone is pushing, less checked.
GRBL firmware: more professional firmware for CNC. simple, packed nice and precise. Implemented to simple platforms. Runs in Arduino shield (safety, emergency motor) Reliability vs. Options. Low team of developers, higher control. Steadier and more robust software.
Firmware is a set of instructions designed to control hardware. Low level activity. The major task on code and hardware is calculating maximum speed, how much can accelerate and de accelerate. Diagonal movements (not 45 degrees) “kinematics”. A set of instructions, g code reading in kinematic equations, calculating how to move the motors … [xa:por favor termina de completar esta parte con el audio]
Resources¶
- Boeck, P., 1880. Die Marmorirkunft. Ein Lehr-, Hand- und Mutterbuch für Buchbinderien, Buntpapierfabriken und verwandte Geschäfte. U. Bartleben’s Verlag.
- Brett, K., 2021. Making Traditional Marbled Papers. The Crowood Press.
- Eisenbart, R., 2021. The Art of Paint Marbling. Walter Forster.
- Helfer, J., 1891. Die Fortschritte der Marmorierkunst. Wilhelm Leo.