Why liquid handler decks are so large – it’s a design flaw

How big does the liquid handler deck have to be? This is usually one of the first questions that an automation customer asks their liquid handler salesperson.

 

The answer that usually comes back is that larger decks offer multiple benefits, such as:

  1. More flexibility: Bigger decks mean more accessories on deck, and more pipetting/gripper arms on the gantry
  2. More walk-away time: More deck space allows for more consumables and more reagents
  3. More throughput: More deck space means more parallel processing, with multiple arms working on multiple processes and/or plates simultaneously

The conversation usually ends with the liquid handler salesperson asking in return: “So what deck size would you like? We have small, medium, large, or XL”.

For traditional liquid handler vendors, flexibility, walk-away time and throughput have always been a function of deck size. As a result, decks have over time become wider, deeper, or both. At the same time, these vendors have tried to maximise the utilisation of their decks by allowing consumables to stack, for example by using nested tips and stacked plates, and by using long eccentric gripper fingers to access storage and devices off-deck. In fact, the homogeneity of deck design in most automated liquid handlers is fairly remarkable.

These approaches come with limitations. There is a limit to how many trays of tips can be stacked on top of one another on deck not only because the obvious stability issues, but also because these tip towers, depending on where they are placed, can restrict gripper/pipetting arm access to adjacent labware. Similarly, long eccentric fingers can greatly restrict what positions can be accessed on deck, and in what orientation. 50-100 position decks simply create large amounts of room for inventory stored in the workspace, which is then inefficiently cycled, creating large horizontal decks which waste lab space.  There is no real need to have an 80-90” wide deck to deliver performance.

Many of these problems can be solved by making greater use of vertical space in the liquid handler design. Instead of attaching off-deck storage to the sides of the instrument, storage can be added directly below the deck. A gripper arm with folding joints can access this storage without having to go vertically through the deck or increasing the size of the instrument. Instead of nesting tips on deck, tips can be nested in under-deck storage stackers, where tip trays can be stacked much taller without risking collapse or impeding deck access. Most importantly, if the pipetting deck can be continuously loaded to and unloaded from while the instrument is pipetting, then the size of the deck can be shrunk dramatically without compromising throughput.

Consider the following. At any given time, the working head (aspirating and dispensing element) of an automated liquid handler works in only one position.  Some liquid handlers can have two heads working in parallel, but each head is only operating in one of the deck positions. Thus, on a very large deck, at most only two are ever active at any given time, and in the great majority of cases, it is only one at a time. Theoretically, the world’s “leanest” liquid handler would only have two positions: one in which the working head was aspirating or dispensing, and a second position that could be unloaded and loaded (“turned”) in parallel.

While a two-position deck is theoretically possible, it is practically beyond today’s process limits.  However, there is simply no reason for a large deck if lean thinking is incorporated in the design process.  For example, the Prime deck has 15 positions, 10 of which move.  This enables simultaneous loading and unloading of deck positions while the working head is active and working on the others.  It is not a two-position system, but it is a far smaller work envelope than 50-100.

The concept of a liquid handler as a collection of non-overlapping gantry arms with a large deck underneath has been around for so long that many people no longer question it. However, by asking the question, one might be surprised to find that it is very possible to have a liquid handler with a small deck without sacrificing flexibility, throughput or walk-away time.

%d bloggers like this: