Linear Drive Mechanisms and Adjustment, alignment and tension Flashcards
What are the specs for pully mechanisms?
> Belt profile
> Tooth pitch
> Number of teeth
> Belt width
> Bore diameter
What are the two types of belts and what makes them different?
Closed timing belts
> Custom length and design for a specific system
> Must have sufficient tension adjustment so that it can be removed and replaced easily
> Continuous travel
Open timing belts
> Cut to the required length
> Requires tensioning mechanism
> Suitable for anchor methods
> Facilitates multiple methods of carriage drive motion
How is the distance traveled by a linear drive mechanism calculated?
Distance = Pitch × Number of teeth
What calculations are required for a rack and pinion?
The calculations for the distance travelled are the same for belts and pulleys.
What are the advantages of using a rack and pinion?
> Rigidity
> Precision
> Multiple pinions on the same rack
> Easy expandability
What is a concentric bearing?
A bearing with the shaft in the centre in the middle of the bearing [Picture9]
What are the problems with concentric bearings?
> Horizontal motion error due to the small gap between the guide and bearings
> Vertical instability due to the small gap between the guide and the bearings
> Complex stress profile
> Increased wear
> Inaccurate travel
> Decreased precision
What are eccentric bearings?
A bearing with the shaft off-centre from the middle of the bearing [Picture10]
What is eccentricity? How does this relate to the offset of the bearing edge?
> This is a measure of the maximum distance from the centre of the shaft to the centre of the bearing
> The offset of the edge is double the eccentricity
What are the benefits of an eccentric bearing?
> No Horizontal motion error
> Vertically stable
> Relatively even stress profile
> Decreased wear
> Accurate travel
> Increased precision
What is the point in eccentric bearings?
> To ensure that slides and parts are aligned
> Eccentric bearings can be used to make sure that surfaces are flush.
> The bearing can be rotated so that it can move the slide closer to the guide
What are the 3 methods of adjusting belt tension?
> Linear tension mechanisms
> Rotational tension mechanisms
[Picture11] [Picture12]
What are tension springs?
[Picture13]
