Flashcards in January Exam Deck (56)

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1

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Two categories of bearing for the two types of mechanical motion

Three types of mechanical contact bearings

Three types of mechanical non-contact bearings

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Linear, rotary

Sliding, flexing, rolling

Fluid film (hydrostatic)

Fulid film (hydrodynamic)

2

## Two types of friction, equations for both

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Static friction, kinetic/dynamic friction

Fs = μ*F(N)

μ = coefficient of static friction

Fk = μ*F(N)

μ = coefficient of kinetic friction

F(N) = force downwards (m*g)

Fs/Fk = force required to move object

3

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Slide bearings: used for linear or rotary?

Where are they placed between?

Pros, cons

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Both

Between shafts and housings

Pros: low noise, cheap, small

Cons: high friction, can be damaged from lubricants, stringent lubricant requirements

4

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Special slide bearings: jewel bearings

Properties

Where are they used?

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Low friction

Thermally stable

High hardness

Bearing is stronger than shaft

Watches, compasses, precision instruments

5

## Sliding bearings in a linear application: pros, 5 of them

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Self lubricating

Low friction, noise

Dust and shit doesn't stick to bearing

Resists corrosion

Light weight

6

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Sliding bearing: dovetail linear slide

Pros, cons

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Pros: adjustable tension

Precision defined by adjustment

Cons: regular maintenance

Undefined static friction

7

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Application loading: what is is

Two types, which direction on a shaft they come from

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Direction of forces on the bearings

Axial/thrust load: goes through shaft

Radial load: perpendicular to shaft

8

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Rolling bearings: two types

What two grouping types for each of these are there

Spherical roller thrust bearings, tapered roller bearings: pros and cons

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Ball or roller

Can be classified as either radial or thrust/axial

SRTB: Pros-help with misalignment

Cons-expensive to produce

TRB: Pros-cheaper to produce

Cons-Doesn't help with misalignment

9

## Needle radial bearings: applications and pros

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Planetary gears

Universal joints

Constant mesh gears

Pros: low profile, lightweight, higher load capacity, cheap

10

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Linear roller bearing-where sliding and rolling meet

Pros, cons

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Pros: reduces risk of 'Stick-slip' (increased static friction due to angular forces)

Cons: expensive, bigger, more shaft damage

11

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Slides: whats the ratio of length to width

Where should the F(pull/push) be on the slide?

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1.6:1

As close to the centre line of mass as possible

12

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Stepper motor equations: Whats pitch (definition)?

How to read a thread metric e.g. Tr, 12 x 3

Equation for number of motor steps?

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P: distance between threads on a screw

Diameter of 12mm, pitch of 3mm

No. of steps = 306/( Step Angle) * Distance/Pitch

13

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Stepper motor equations:

Relationship between travel time and step frequency

Equation for resolution

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Travel Time = 1/Step Frequency

R = (Step angle*pitch)/360

14

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Use for lead screw linear drives-think about stuff from lectures

For one revolution of a pulley, calculate distance travelled

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Syringe driver, scissor action lift

Distance = Pitch * Number of teeth

15

## Rack and Pinion: what is it, pros over belt

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A rigid belt with a cog on an axel rotating along it

Pros: rigid, precise, easy to expand

16

## Micro-stepping the stepper motor vs adding a gear box to the drive: pros and cons

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MS: Pros-better resolution (256x)

Cons-torque, speed would decrease

GB: Pros-more torque, resolution would increase by gear box ratio

Cons-speed would decrease

17

## Derailleur on a bike: what three tasks does it perform (the thing that sits on gears)

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Controls chain/gear alignment

Limits range of lateral motion

Maintains a relatively constant tension on chain

18

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Concentric and eccentric bearings: where is the shaft in both?

How to work out total offset using 'e' through 360°

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CB: shaft at centre of the bearing

EB: shaft offset by value 'e', the eccentricity value

2*e

19

## Eccentric bearings pros, cons

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Pros: Can adjust for tension and remove gaps

Can adjust for wear and to counteract variance

Achieve higher motion accuracy

Cons: more expensive, set up required

20

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Universal joint, cardan joint:

Use for both

What do they look like

What about velocity do you have to remember?

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Change the axis angle of a rotational system-not for 90°

Pipe with a hinge in it

Pipe with two hinges in it

Velocity of output shaft isn't same as input shaft unless they are aligned

21

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Whats a Rzeppa joint used for

What effect does high and low belt tension have?

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When an angle greater than 45° is needed

HBT: premature bearing wear

LBT: reduced accuracy and/or dislocation

22

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Two ways to adjust a belt/pulley system

Adjustment distance for both

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Linear and rotational tension adjustment

L: slot distance

R: 2*R(p)*sin(θ/2)

R(p) = radius from pivot point

θ = angle to move

23

## Tension measurement methods: two of them

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Force/displacement measurement

Sonic measurement

24

## Rotary to linear equations-remember mechanics

### Revise-lecture 5

25

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When does vibration occur?

Relate it back to bearings

Equation for centrafugal force F(CF)

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When centre of mass does not coincide with the axis of rotation

I.e. when there is eccentricity 'e' betwwen CoM and AoR

F(CF) = m*e*ω^2

m = mass

e = eccentricity

ω = speed of rotation

26

## Effects of vibration-mostly negative but two positive

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Cons: increased bearing wear, noise, heat

Material fatigue, decreased resolution

Pros: physical feedback, controlled agitation (like pile drivers)

27

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Absolute vs relative position on a computer system

Also works for angles

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AP: measure each point from an absolute origin

RP: Make a point on the shape a temporary origin and measure from there

28

## Origin of drawing space in G code

### Left and lower most location

29

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Mechanical switch overview:

Poles

Throws

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Poles (P): how many switches are activated by the same mechanism

Single (S), Double (D), 3, 4 etc

Throws (T): How many contacts can it be switched to

SIngle(S)(1): One possible, one normally open contact (NO) OR one normally closed contact (NC)

Double(D)(2): two possible, one NO AND one NC

3, 4 etc throws: one NC, rest NO

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