This project was undertaken in a team of two as part of Mecheng 334: Design and Manufacture 3, and received an individual grade of A+.
The goal of this design project is to design a mechanism within the specified
design volume that can move an approximately 9.5 mm diameter steel ball from
the input hole to the exit hole [of the provided 100mm acrylic box].The mechanism may subsequently be manufactured, assembled and validated to demonstrate the feasibility of the design.
Project A Brief: Design Specification
Design
The design centers around a series of cam follower segments, which are actuated by a cam disk at the base
of the box. A spiralled path is cut into the segments, large enough for the ball to travel down only when the
segments are correctly aligned.
The motion of the cam disk is set by a compound spur-bevel gear train connected to the input shaft, which facilitates the correct reduction ratio and 90° motion coupling.
The assembly was designed in Autodesk Inventor, with the segments using the iParts function to generate each of the 48 unique variations from a table, and a linked spreadsheet to set global parameters for the assembly.
Dynamic Simulation
In addition to manual calculations, the Inventor Dynamic Simulation enrivonment was used prior to physical prototyping in order to simulate and validate the operation of the full mechanism. The simulation used a total of 48 prismatic sliding joints to constrain the motion of the followers, and 98 3D-contact constraints between the marble, cam followers, and cam disk. This demonstrated that the mechanism would work as desired, with an excellent degree of repeatability.
Manufacture and Cost Analysis
A cost and time estimation was done for the required fabrication and assembly, taking into account labour, machine time, material, and electricity costs.
The total cost was estimated at $68.84, with machine time and post-processing labour were found to be the main contributors, making up 56% and 29%, respectively.
The assembly was fabricated using a combination of laser cutting and FDM 3d printing. During this phase several design revisions were required to ensure proper tolerances and fits, due to variable print shrinkage and laser kerf-width.
Conclusions
While the protype mechanism was plagued by several unforeseen design problems, relating to smoothness of operation an ease of assembly, the concept was demonstrated to be sound in simulation.
With changes to aid assembly and modifying the path to permit smoother passage of the ball, the design has potential to work as an effective and unique marble mechanism.
