SCREWDRIVER DECONSTRUCTION PROJECT
A Black and Decker Lithium Pivotdriver (Li2000) was disassembled, the multistage epicyclic gear train ratio was modeled in Creo Parametric 3.0, the gear ratio was calculated, examples of Design for Manufacturing and Assembly (DFMA) were demonstrated, the power/manual option was explained, and a graphical product structure was created.
GEAR TRAIN CALCULATION WITH EXPLANATIONS
Number of Teeth for Sun (NS), Ring (NR), and Planetary Carrier (NPC):
NS=6
NR=48
NPC=NS+NR
NPC=6+48
NPC=54
Gear Ratio for Identical Epicyclic Gear Sets, with fixed rings, (GR1 and GR2):
GR1=NPC /NS
GR1=54/6
GR1=9
GR2=NPC/NS
GR2=54/6
GR2=9
Total Gear Ratio (GR):
GR=GR1*GR2
GR=9*9
GR=81
Pitch Diameter for Planet Gears:
C=center-to-center distance between two identical planet gears
PDP=C
PDP=.518
Pitch Diameter of Sun Gears:
CS,P=center-to-center distance between a sun gear and planet gear
PDS=(CS,P)-(.5 * PDP)
PDS=(.776)-(.5 * .518)
PDS=.170
Black and Decker most likely decided to use an multistage epicyclic gear train because of the ability to get a very high gear ratio by multiplying each individual gear ratio. Using a very small sun and large ring allows the company to maximize the gear ratio of each individual gear set.
Power/Manual Mode Explanation
GRAPHICAL PRODUCT STRUCTURE
The graphical product structure breaks down the screwdriver into five assemblies and one sub-assembly, the epicyclic gear train.
