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Flashcards in January Exam Deck (56)
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1

Two categories of bearing for the two types of mechanical motion
Three types of mechanical contact bearings
Three types of mechanical non-contact bearings

Linear, rotary
Sliding, flexing, rolling
Fluid film (hydrostatic)
Fulid film (hydrodynamic)

2

Two types of friction, equations for both

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

Slide bearings: used for linear or rotary?
Where are they placed between?
Pros, cons

Both
Between shafts and housings
Pros: low noise, cheap, small
Cons: high friction, can be damaged from lubricants, stringent lubricant requirements

4

Special slide bearings: jewel bearings
Properties
Where are they used?

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

Self lubricating
Low friction, noise
Dust and shit doesn't stick to bearing
Resists corrosion
Light weight

6

Sliding bearing: dovetail linear slide
Pros, cons

Pros: adjustable tension
Precision defined by adjustment
Cons: regular maintenance
Undefined static friction

7

Application loading: what is is
Two types, which direction on a shaft they come from

Direction of forces on the bearings
Axial/thrust load: goes through shaft
Radial load: perpendicular to shaft

8

Rolling bearings: two types
What two grouping types for each of these are there
Spherical roller thrust bearings, tapered roller bearings: pros and cons

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

Planetary gears
Universal joints
Constant mesh gears
Pros: low profile, lightweight, higher load capacity, cheap

10

Linear roller bearing-where sliding and rolling meet
Pros, cons

Pros: reduces risk of 'Stick-slip' (increased static friction due to angular forces)
Cons: expensive, bigger, more shaft damage

11

Slides: whats the ratio of length to width
Where should the F(pull/push) be on the slide?

1.6:1
As close to the centre line of mass as possible

12

Stepper motor equations: Whats pitch (definition)?
How to read a thread metric e.g. Tr, 12 x 3
Equation for number of motor steps?

P: distance between threads on a screw
Diameter of 12mm, pitch of 3mm
No. of steps = 306/( Step Angle) * Distance/Pitch

13

Stepper motor equations:
Relationship between travel time and step frequency
Equation for resolution

Travel Time = 1/Step Frequency
R = (Step angle*pitch)/360

14

Use for lead screw linear drives-think about stuff from lectures
For one revolution of a pulley, calculate distance travelled

Syringe driver, scissor action lift
Distance = Pitch * Number of teeth

15

Rack and Pinion: what is it, pros over belt

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

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)

Controls chain/gear alignment
Limits range of lateral motion
Maintains a relatively constant tension on chain

18

Concentric and eccentric bearings: where is the shaft in both?
How to work out total offset using 'e' through 360°

CB: shaft at centre of the bearing
EB: shaft offset by value 'e', the eccentricity value
2*e

19

Eccentric bearings pros, cons

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

Universal joint, cardan joint:
Use for both
What do they look like
What about velocity do you have to remember?

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

Whats a Rzeppa joint used for
What effect does high and low belt tension have?

When an angle greater than 45° is needed
HBT: premature bearing wear
LBT: reduced accuracy and/or dislocation

22

Two ways to adjust a belt/pulley system
Adjustment distance for both

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

Force/displacement measurement
Sonic measurement

24

Rotary to linear equations-remember mechanics

Revise-lecture 5

25

When does vibration occur?
Relate it back to bearings
Equation for centrafugal force F(CF)

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

Cons: increased bearing wear, noise, heat
Material fatigue, decreased resolution
Pros: physical feedback, controlled agitation (like pile drivers)

27

Absolute vs relative position on a computer system
Also works for angles

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

Mechanical switch overview:
Poles
Throws

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

30

Mechanical switch overview: maintained, momentary
What do their circuit diagrams look like

Mech: throw position is maintained when switched (light switch)
Normal switch
Moment: throw position reverts to a static position when released (button)
Switch with a line pressing down into it with bar above