The Cocktail Machine - How About a Drink?
The cocktail machine which is described in this article gives an insight and an impression of the other side of process automation. Just as with a conventional vending machine, with the cocktail machine everything starts with the push of a button. However, the result which follows is completely different. Normally, the workgroup of Prof. Hans-Ulrich Moritz at the Institute for Technical and Macromolecular Chemistry (University of Hamburg) carry out research into chemical reactions, so-called polymerizations, which are industrially relevant processes and a part of chemical reaction engineering. The combination of these process technologies into an illustrative exhibit for young and old was the motivation for the creation of the cocktail machine.
From Process Technology to Cocktails
We can start right at the top, at the highest point of the machine (Fig. 1). This is where the storage bladders are located. The three storage tanks contain three different kinds of juice, which pass through various stages until they reach the actual cocktail reactor. For example, a juice is passed through a reflux cooler, where it is rapidly cooled from room temperature to only a few degrees Celsius. Such reflux coolers are used in chemical laboratories for complex synthesis processes, where they prevent the solution from evaporating and escaping from the apparatus.
A different juice is treated with a flotation process before it reaches the reactor. Among other things, flotation is used to recycle waste paper by removing printing ink and increasing the whiteness of the waste paper.
The fourth juice - which completes the final "cocktail" finds its way through a dripping system, a technical chemistry spray-process which among other things is used to dry sugars or to produce granules.
Two types of juice are combined with a so-called Y-section and pass through a glass coil, where they are thoroughly mixed. Via these Y-sections the juices arrive at the actual flow-through reactor. Such reactors, with volumes of 0.5-2 l are often used in technical chemistry in order to perform so-called batch experiments.
In principle, the cocktail reactor is a continuous agitation vessel.
If the fluid level becomes dangerously low, two hose pumps, which are filled from the storage bladders described above come into operation. Via a glass capillary inside of the bladders, the juices can drain off, pass though the stages which have been described and fill the reactor up to a maximum preset level. The reactor not only thoroughly mixes the drink. It also cools the cocktail to a refreshing 5-8 °C with the aid of its temperature-controlled double jacket.
Volume Control via Software
At the beginning we mentioned the "push of a button". This is what empties exactly the content of a single cup from the reactor. But where and how does the drink get into the cup? The cocktail in the reactor is filled into the cup via a hose and a separate pump from a connector in the lower section of the reactor. In addition, with the aid of a lowering guard, the Lego programming set "Mindstorm" ensures that no juice splashes over the side of the cup while it is being filled.
If the alcoholic version of the cocktail is required, a small quantity of an alcoholic speciality is added after the juice has been filled into the cup. The software is also used for this process. Metering is carried out by means of an injector pump with a known volume of liquid. If the liquid content is becoming exhausted, a three-way valve switches to the storage vessel. The correct position of the valve is detected by the Lego software using pressure sensors. Once the injectors have been completely refilled, the valve is returned to the metering position. This principle prevents the injectors from running dry.
Smooth operation of the automatic cocktail machine also depends on suitable software to control the system. To provide the greatest possible versatility for the control and automation of the equipment, the software package LabView is used. The control program for the cocktail machine operates as a so-called "Steady-State-Machine" (or automatic state machine).
The Versatility of Automatic State Machines
A feature of an automatic state machine is that every state which the cocktail machine can adopt is precisely defined. In different states, the cocktail machine performs different actions, e.g. dispensing the cocktail or filling the reactor with juices. For example, if the user presses a button to order an alcohol-free cocktail, various different states are run through in sequence, whereby each state triggers an individual action by the cocktail machine. Although the individual states are precisely specified, the path between these states can be freely selected by the program. This is the great advantage of an automatic state machine. If the user had ordered an alcoholic cocktail in the example above, the stages which were passed though up to the addition of the alcohol would have been exactly the same. The program would then have simply inserted a state "add alcohol" and then continued operation as for an alcohol-free cocktail.
Of course, there are also states or processes of the automatic state machine of which the user is not directly aware. One of the most important processes is balancing. Once the cocktail machine has been filled and brought to the starting position, it operates completely automatically. It is impossible for the reactor to overflow, because by weighing of the storage containers and the cup, it is always known how much cocktail is present in the reactor. According to the principle „what goes out has to come in", the control unit fills the reactor as soon as a certain quantity of cocktail has been dispensed. This also demonstrates an advantage of an automatic state machine. As the cup is usually smaller than the reactor, dispensing is performed more often than filling the reactor. The program automatically decides when it needs to insert the state „fill the reactor" and therefore operates in a highly versatile manner.