Disc dispenser: Product design and documentation
Skills:
Product design, CAD
Year:
2018
//About the project
The purpose of this project was to design a motorized machine for automating the process of dispensing discs for bacteria sample analysis, in order to relieve lab workers from repetitive labour.
A motorized device was designed to work with common existing disc dispenser loader units, taking into account manufacturing costs, functional requirements, ease of use, safety and durability.
.01Requirements
The following requirements and considerations were defined in the assignment:
The dispenser should be powered by an electric motor from Bosch, and should be able to press down on the loader unit with a force exceeding 40N, though should never exceed 80N due to risk of damage.
The operator should be able to manually place petri dishes underneath the loader unit and swap out the loader unit itself.
Expected demand was estimated to be around 5,000 units per year, and the market was characterized by competitive pricing.
Further requirements were defined for the project.
02. Quantitative structures
The disc dispenser machine has 4 primary functions; a motor, a safety mechanism, a rotational to linear motion mechanism, and a dispenser mount or placement option.
Two simple principal functional structures were drawn, and for each function, a number of alternative possible solutions were considered.
.03Conceptualization
After considering the different options based on the specified requirements and criteria, two functional concepts were created, with different selections of structures for each function.
Concept 1 consists of a magnet-based torque limiter as the safety mechanism, a threaded mechanism for transferring power, fastening the loader unit with screws/bolts and a base frame consisting of both a petri dish plate and a stand. The dispenser machine pushes the loader unit down to the stand and then dispenses discs into the petri dish placed in the plate.
Concept 2 consists of a typical crank mechanism, the simple compression force limiter solution with a pre-tensioned spring, and a base stand including the petri dish plate for several sizes of petri dishes. There is no assembly of the loader unit, as it is placed on top of the stand, and the dispenser simply presses down on the top of the loader unit by means of a piston, which is connected to the cylinder through the spring.
Concept 2 was selected for further development. Ease of use, mechanical simplicity and durability were prioritized over size of the product. The loader units as well as petri dishes can be quickly replaced and are easy to position, and the spring mechanism provides a certain flexibility in how precise the loader unit must be placed height-wise.
04.Final design
Concept 2 was further developed and detailed:
A flexible base was designed for easy adjustment of the vertical position of the loader unit, and plastic top plates and fine adjustment rings with different sized holes can be inserted to allow the machine to function with a variety of loader units.
The rear cylinder is hollowed to allow for cabling to the motor, which is placed on the rear side of the front facing part of the steel sheet housing. The moving parts are located on the front side of the steel sheet housing, along with a stabilizing arm containing a bearing for the axle connected to the drive shaft.
Plastic covers shield the motor housing and the moving mechanical parts, and can be removed for serviceability.
.05Production and assembly
Considering the relatively low expected yearly production number, standard parts and simple manufacturing processes were deemed preferable, and focusing on minimizing the use of materials was deemed less important than durability.
Standard bolts and nuts, angle brackets, as well as threaded ends on cylinders were chosen for assembly. The housing was constructed using a bent piece of sheet steel painted for erosion resistance, and thermoforming was selected for the manufacture of most of the plastic parts, as they do not need to sustain heavy loads.
