Lecture 4 Flashcards
What are the three tasks of the derailleur mechanism?
Controles chain/gear alignment
Limits the range of lateral motion
Maintains a relatively constant tension on the chain
What is an eccentric bearing?
Bolt hole is offset from the centre
By adjustment at the centre is is possible to move the relative position of pulley wheel relative to the eccentric centre of the pulley wheel
What is the timing belt tension spring?
Belt is fed through the mechanism
What is the belt tension mechanism?
Similar to spring in the chambers of the derailleur
Tension on the roller causes the mechanism to move in the direction against the spring
Maintains that level of tension
What is the constant velocity joint?
The velocity of the output shaft is the same as the velocity of the input shaft
What is the double cardan joint?
Although this joint facilitates misalignment, this joint is only a CV join if the two shafts are parallel to each other
Performs similar task to the constant velocity joint
What is the door hinge?
Minor adjustments on doors adjacent to the cupboard
Spring loaded hinge
Whole structure can be moved up and down caused by the slots fixed to the ‘carcass’
Adjustment screws raises door away from the carcass
Change angle relative to another door by second screw
What are concentric bearings?
The shaft is at the centre of the bearing
What are eccentric bearings?
The shaft has a shaft offset value of ‘e’ which is the eccentricity value
What happends when a linear slide mechanism has four concentric bearings?
Horizontal motion error
Vertical instability
Complex stress profile - uneven wear
Inaccurate travel
Decreased precision
What happends when a linear slide mechanism has two concentric bearings and two eccentric bearings?
Horizonatal stability
Vertical stability
Relatively even stress profile
Decreased wear
Accurate travel
Increased precision
What do eccentric bearings within a mechanism facilitates?
Adjustment in tensioning and to remove guide/bearing gaps therefore achieving higher motion accuracy
Alignment adjustment higher motion accuracy
Adjustment for wear
Adjustment to counteract manufacture extrusion variance
What is used of axis angle change is 90 degrees?
Requires the use of a gear box mechanism using helical or worm gears
What is a universal joint?
Allows you to change the drive axis angle
Is not a constant velocity joint - i.e. the velocity of the output shaft is not the same as the velocity of the input shaft unless the two parts are absolutely aligned
What is a rzeppa joint?
CV joints used in mechanical misalignment mechanisms
This joint can facilitate an angular displacement of greater than 45 degrees
How does belt tension effect timing belts?
High belt tension - contribute to premature bearing wear
Low belt tension - lead to redues accuract, slippage, or belt dislocation
What is deflection in tension mechanisms?
When a force is applied to the belt a deflection takes place
The amount of allowable deflection depends on the belt profile, the specification of the system and any manufacturing tolerances
