Translation of motion Flashcards
What is a constant velocity joint?
This is a way of translating the direction of motion without changing the speed of the motion
What are two methods of 90° constant velocity joints?
Helical or worm gears
What is a non-constant velocity joint?
This is a way of translating the direction of motion but causes inconsistant motion speed
What are some examples of non-constant velocity joints?
Universal joints
> This allows you to slightly change the drive axis angle.
> The velocity in is not equal to the velocity out unless the input and output shafts are absolutely aligned
Double cardan joint
> This also allows you to change the drive axis angle
> The velocity in is not equal to the velocity out unless the input and output shafts are parallel
What are some examples of linear to rotary motion?
> Internal combustion engine
> Steam train
What are some examples of rotational to linear motion?
> Oil wells
> Tattoo gun
> Industrial presses
How is the displacement of the linear part calculated? [Picture15]
θ = sin-1( h / C )
ϕ = sin-1( h / R )
ϕ = sin-1( Csin(θ) / R )
DC = Ccos(θ)
DR = Rcos(ϕ)
DC + DR = Ccos(θ) + Rcos(ϕ)
What is the equation for the maximum displacement for: [Picture15]
D = 2 × C
What is the relationship for ϕ and the ratio of R:C? [Picture15]
ϕ becomes smaller as the ratio of R:C increases
What is the efficiency calculation in terms of ϕ for the mechanism [Picture16]
% Efficient = FUseful / (FUseful + FWasted) × 100
% Efficient = FCos(ϕ) / (FCos(ϕ) + FSin(ϕ)) × 100
% Efficient = Cos(ϕ) / (Cos(ϕ) + Sin(ϕ)) × 100
% Efficient = 1 / (1 + Sinϕ / Cosϕ) × 100
% Efficient = 1 / (1 + tan(ϕ)) × 100
For the mechanism, when is the efficiency the worst?
When the rod is perpendicular to the crank.
How does vibration occur?
> When the centre of mass does not coincide with the axis of rotation.
> When there is eccentricity between the centre of mass and axis of rotation.
What is the equation for central fugal force?
FCF = meω2
> m = mass
> e = eccentricity
> ω = Angular velocity
What are the negative effects of vibration?
> Increased bearing wear
> Noise
> Heat
> Material fatigue
> Decreased resolution in precision systems
> Potential physical discomfort
> Passive transmission to other systems
What are the positive effects of vibration?
> Informative physical feedback
> Controlled agitation
- Pile drivers
- Physiotherapy
How can we have eccentric rotation without vibration?
We can have eccentric motion without vibration. As long as the centre of mass remains around the centre of rotation.
What can change the balance in mass?
> Erosion
> Build-up of contaminants
> Poor castings with air pockets
> Bearing wear
> Loss of balancing components
