Paper towel dispenser innovation
From DDL Wiki
Mechanical Analysis
In our new paper towel dispenser, we incorporated a ratchet mechanism to prevent spindle from turning more than needed due to its inertia and causing paper towel to be rolled back in. For engineering analysis, we calculated and investigated to compare the effect of the additional inertia of the ratchet as well as the new resistance moment it will provide. First, we varied rotation angle of spindle and performed static analysis to measure force required for users to pull a paper towel with the original paper towel dispenser and with our new design. Then we assumed the average time it takes for a person to pull a paper towel to be 1 sec, and performed dynamic analysis of systems to find out required pulling force with (Frequired, with ratchet) and without ratchet mechanism (Frequired, w/o ratchet).
Fig.1: left view of spindle (left) and right view of spindle(right) with ratchet mechanism indicated by red box
Free Body Diagram
Where: D = diameter of spindle = 0.1m Θ = angle displacement of spindle from initial state W = weight of the spindle and ratchet gear Fbase,y = force applied by axle of the base to the spindle in y-axis Fapplied = force applied by user by pulling paper towel Mresistant = Mspring + Mratchet Mspring = moment from lever arm springs on the left side of spindle(varies with θ, angle of rotation of spindle, see Table 1) Mratchet = moment from ratchet mechanism (moment due to friction force between ratchet gear and pawl, normal force being ratchet spring force and reaction force from axle of the base)
