Trash Can Mechanism
Introduction
The purpose of this project was to design a mechanism for trash cans which can pick trash up from the top and throw it into the bin thorough an inlet at the back. This design improves hygiene as the user never has to touch the trash can and also improves aesthetics as the opening is located at the rear so the users never see the trash inside the trash can.
Preliminary design
The first step in the process was to make a skeletal design of the mechanism. For this purpose, math illustrations software was used. The initial and final position of a part of the tray (on which the user puts their trash) were drawn. An intermediate position of that part was also drawn. This gave 3 points though which each of the edges need to travel to achieve the desired motion. From geometry, it is known that there is a point which is equidistant from each of the 3 points. This point was found by finding the point of intersection of perpendicular bisectors joining two pairs of points chosen from the 3 points. This point of intersection is joined to the corresponding point at the starting position with a line segment. The same process was done for the other edge too. Now the basic structure of the mechanism was ready. To make sure that the mechanism can rotate properly, it was made sure that the points of intersection of perpendicular bisectors were at appropriate distance from each other. This distance was based on the fact that at some stage of the motion cycle, the four links of the mechanism (including the bin, which is a grounded link) will be colinear. The mechanism was dragged with a mouse to make sure it moved as desired.
CAD design
The two connecting bars and the tray, the dimensions of which were obtained from math illustrations, were made in Solidworks as parts. The distance between end points of the connecting bars and the part of the tray in math illustrations were used as the distance between the holes in Solidworks parts.  A trash can was also made. Then these parts were assembled using Solidworks assembly. Basic and mechanical mates were used to get the different parts to their place and align properly. The mechanism was then moved manually to make sure there was no interference in motion. Then a motion study was done. A motor was added at one of the hinges and two trace paths were plotted to trace the motion of the tray. A video was then made showing the motion.
