Kinematics and mechanisms Flashcards
What are the five principles of kinematic constraint
1.any unconstrained rigid body has 6 degrees of freedom;
- contact between bodies occurs at frictionless points;
- a contact with another body removes a degree of freedom;
- the number of contacts with a second rigid body is the number of constraints on the first body;
- the contacts must be carefully chosen to be independent –some configurations of contacts are degenerate.
Describe the design for a kelvin clamp
three v-shaped grooves that are 120 degrees seperated
- two branches stacked on top of each other connected by bolts passed through annular contact pads
-in each connecting bolt are then two kinematic constraints
as a general rule, how are the number of teeth on a gear determined?
gear pitch diameter / number of teeth = 0.08
gear pitch diameter is the diameter from the middle of a tooth x2 added to the gear diameter
What are the maximum forces that should be applied to a metallic gear and a plastic gear?
1 N per mm tooth width for metal and 10 N per mm tooth for plastic
What materials do metallic gears use?
- carbon
-stainless steel
-aluminium
-titanium
-bronze
what materials do plastic gears use and how should they be set up?
- Polyamide and polyacetal
- they should always run against metal gears
what are the three components of the harmonic drive and the basic operation?
- wave generator
- flexspline
- circular spline
a step motor drives the wave generator which couples with the flexspline via ball bearings. The rotation of the flexspline is many times slower than the rotation of the wave generator
What are the three main advantages of harmonic gears over normal gears?
- lightweight
- compact
- high gear ratio
How does the thermal conductivity of wet lubricants compare to that of dry lubricants?
It can be up to 10x higher
