Week 13

For the lesson in week 13, we learned about operating principles and mechanism designs in everyday products.

The things in our daily lives are all designed based on working principles that are either mechanical, electrical, chemical or magnetic in nature. For example, in order for a distillation column to work, the operating principle is the difference in the relative volatilities of the two liquids. In solvent extraction (LLE), the operating principle is the distribution ratio of the two liquids in the solvent.

For our chemical product, an insulated vaccine carrier box with modular parts to hold different vaccines, the main operating principle is heat transfer. Our chemical product ensures that the vaccines are stored at the required temperature during transport to prevent the vaccines from becoming ineffective. The box is most effective when there is little to no heat loss to the surroundings, thus it should be insulated well to minimise heat transfer. The box should also be made of a material that has a high specific heat capacity and low thermal conductivity. A higher specific heat capacity is desired as it will mean that more heat will be needed to raise the box's temperature by 1°C. A lower thermal conductivity will ensure that the rate of heat loss to the surroundings will be as low as possible. Another operating principle used is modularity. In order for the vaccine carrier box to hold vaccines of different dosages from different companies, we should be able to mix and match different vaccine vials which have different shapes and volumes and ensure that they can be stored in the same box to match the amount of doses needed in remote areas to prevent wastage.

In order for the operating principle to be able to work, mechanism movements are required to ensure that the operating principle is able to work efficiently. Mechanism refers to the combination of rigid or resistant bodies, formed and connected so that they move with definite relative motions with respect to one another. It is something that transforms forces and movement into a desired set of output forces and movement.

In order for the functional prototypes to work, at least one of six essential mechanisms need to be in place in order for the product to work. The six mechanisms are Actuators, Cams, Gears, Levers, Ratchets and Springs.

Actuators
Actuators convert stored energy into motion. The stored energy can be stored in the form of compressed air (pneumatic), electrical potential(electric) or liquid pressure (hydraulic). Actuators can be found in automatic door opening by using compressed air to pneumatically control the door.

Cams
Cams convert the rotation of a shaft into simple or complex reciprocating linear motion and can be sliding or rotational pieces in a mechanical linkage. Cams are often used as camshafts in piston engines.

Gears
There are many types of gears ranging from gears like spur gears to worm gears. Gears are used to transfer motion and torque between machine components in mechanical devices. Depending on the application, the gears might even be able to change the direction of movement or increase the output of speed or torque. One application of gears in our daily lives is the car’s transmission/gearbox or on bicycles.

Levers
Levers are used to transmit and amplify force by fixing the input and output about a pivot point. One example is the use of crowbars to open doors.

Ratchets
Ratchets lock in one direction, allowing them to tighten without the fear of “going backward”. It serves to limit or restrict rotary or linear motion to only one direction.

Springs
Springs have the ability to absorb, store and release energy through a change in shape. There are many different types of spring that have different purposes and applications. There are expansion springs and compression springs which have different usages/applications in the real world. Springs can be found in the car’s suspension to dampen vibration on the road and to smoothen out the ride. In other cases, car suspensions in racing help control the weight transfer of the car which helps improve the car’s handling performance through corners.


For the class activity, we were tasked to design a ping-pong ball launcher that could hold at least five balls and propel the ball forward with stored energy, using at least one of the aforementioned mechanisms.

Figure 1: Sketch of ping pong ball launcher design

The rubber ring allows pressure to be built up, and also prevents the ball from falling out when it is not being fired. The hole in the ring is slightly smaller than the ball, but it is big enough for the ball to pass through when the force acting on the ball is large enough.

The slider joints allow the chamber to slide along the gun barrel. As the chamber slides along the barrel to the back, air is trapped and there is a build-up of pressure. When the chamber slides to the front, the compressed air is released, releasing its pressure, and a force is exerted on the ball, which is propelled forward and out of the gun.

The magazine can be detached and reattached to allow the balls to be reloaded. There is a spring at the bottom of the magazine, which allows the gun to be reloaded with another ball every time a ball is fired. There are tabs at the top of the magazine that can bend inwards to allow the balls to enter the magazine, and bend outwards to allow the balls to be reloaded into the chamber. In the neutral position, they prevent the balls from popping out.