General Description

 

Customer's Perspective:

Sharpener accommodates a standard size pencil

By turning handle, pencil tip forms a point, exposing lead

Assembly and maintenance should be simple and minimal

The sharpener is cleaned by simply removing the casing and emptying the shavings

The sharpener should be strongly constructed

Must be inexpensive

Casing catches all shavings, with no mess created

Sharpener should be as aesthetically pleasing as possible

Engineer's Perspective:

Diameter of hole must be just larger than that of standard pencil

Customer should detect only two separable pieces

Functional Requirements:

Anticipated Subsystems:

1. Metal handle and shaft transfer manual work to rotate the inner gears and blade cylinder; handle also has a freely spinning plastic attachment

2. Blade cylinder with attached gear and corresponding gear that allows the blades to spin while the whole subsystem revolves around the pencil tip

3. Plastic casing and mounting base; houses shaft and gear assembly

 

 

Black Box Diagram

Engineering Specifications Table 

 

Functional Requirements / Constraints

Test
   
FUNCTIONAL REQUIREMENTS  
Evenly sharpen pencil to conical point  
Simple operation by turning handle clockwise  
Small size for desktop use  
Mounting capabilities for wall/table use  
Inexpensive, but durable  
   
CONSTRAINTS  
Forces  
Force on handle creates moment about axis of shaft; transferred through gears Calculate by M=[e*(r cross F)]e; should be less than x N-m for manual operation
Force pushing pencil into sharpener Must be large enough to push pencil just past rotating blade cylinder, at least y N
Couple applied to pencil as it is pushed into sharpener to prevent rotation Couple must be equal in magnitude and opposite in direction to above moment; Cmax<(1/2)PI *r^3*(taumax)for wood in torsion, i.e. C < x N-m
   
Kinematics  
Durability of gears Test different materials (steel for strength, aluminum for weight)
   
Safety  
Hole must be large enough for pencil and too small for fingers Test different pencil diameters; find standard size of approx. z mm
Sharp blade cylinder enclosed by casing Verify casing in engineering drawings
   
Ergonomics  
Handle fits comfortably between fingers Compare to human geometry handbook
Aesthetic, unimposing appearance See engineering drawings for rounded edges, translucent plastic casing
   
Cost  
Less than $5 Check all materials, manufacturing, and marketing; add costs.

Gantt Chart: Reverse Engineering Project