The system is a brewing unit of a coffee machine for single dose capsules.
The brewing unit is a hydraulic and mechanical system that collects a capsule on its open position, seals the capsule inside a brewing chamber, allows water to flow through the capsule and goes back to the initial position to expel the capsule.
It has two main components; Main frame-cylinder and piston. The frame is still and attached to the machine chassis and the piston moves relative to the frame along its longitudinal axis from “open” position to “closed” position.
The piston is connected to a shaft by using a lever arm and link. The rotation of the shaft along its axis will produce the arms extension and contraction necessary to open and close the brewing unit. This rotation is around 90˚± 5˚ and it is mechanically limited at both initial and end positions.
This rotation movement is normally driven by a lever that is manually cranked by the user of the machine but it can also be an automatic movement driven.
The Seeker is a company that belongs to the coffee industry, is a market leader where it operates, and exports to dozens of countries.
The challenge is to find a way to drive the main shaft with an automatic device that:
Does not use any kind of electric motor or;
It uses an electric motor and it complies with the challenge requirements
The solution uses a 24V Direct Current (DC) motor with brushes together with a worm gear type transmission box attached to the brewing unit shaft (Actually brewing unit shaft and gear box shaft are the same).
The gearbox has a ratio of 1:505 and this type of gear box blocks the movement of the shaft when the motor is off.
According to the motor datasheet the rated speed at the gearbox shaft is around 9 rpm and maximum motor power at stall is 60W producing a torque of around 13 N.m on the gear box shaft but only 25 mN.m on the motor shaft, which is below the requirement XV-b (50 mN.m).
The motor is driven using a H-bridge with reference VNH7070ASTR. Both open and closed positions are detected by two micro-switch that are activated by the lever arm attached to the brewing unit shaft when it reaches any of both positions.
Choosing a motor with higher maximum power and torque will slightly increase the speed on the brewing unit shaft and keeping the same gear box ratio will also increase its maximum torque which damages system components and gear box. On the other hand, choosing a gear box with higher ratio will increase the shaft speed even more.
Present a solution that can be industrialized in the short term (Jan 2020).
To view the complete challenge details and submit your entry, click ACCEPT CHALLENGE above.
