First In First Out
Application to Food & Beverage packaging an idea
developed to handle the highest Production
FIFO (First-In-First-Out) concept started to be applied some decades ago to industrial productions, specifically to manage the highest speed production lines. Returning 40 years back in time, we’d encounter ourselves when the lines producing electronics components (e.g., transistors, connectors, capacitors or resistors) or cigarettes yet were extremely fast with respect to beverage bottling lines. It is in those industrial scenarios, that the product's tracking by mean of the study of its kinematics, say the Shifting-Register method:
FIFO’s essential idea
an initial condition, e.g., a bottle neck interrupting a photocell-mirror light barrier;
- a pulse generator, mechanically fixed to the same conveyor moving containers, providing an indirect container speed reference;
- application of a three centuries old Galileo’s law, to know where should be the container in the future;
- actions, inspections or rejections, triggered on base of the precedent point 3;
started to show its limits. FIFOs were first time applied to let these productions particularly fast be feasible.
A 14-CHANNELS FIFO (click the image to enlarge) sensible to pulses as short as 500 ps, pico second (
stackoverflow.com/2013)
At high-speed, the kinematic of the parts being tracked by mean of the Shifting-Register kinematical method becomes so complex to require an exponential number of triggers, corresponding to excessive costs. As an example, two decades ago some Vendors of electronic inspectors arrived to conceive (cans’) tracking adopting 24 consecutive sensors, 100 mm far from each other. In January 1999 the Writer of these notes was personally in a United Kingdom-based Brewery front of the mission nearly impossible to let such systems function correctly in the outfeed of a 72000 cans-per-hour Seamer Machine. Cans were constantly lost by any of the 24 consecutive sensors, introducing apparent holes and successive apparent additional containers in the sequence.
Containers’ tracking by FIFO encounters ideal application all times containers’ linear speed is high and/or their weight is so small that they are intrinsically prone to slide frequently over one-half of their diameter, for non sensitive Beverages (
Unilever/2015
A mess terminated when the Vendor finally, understood that was an arid evolutionary branch of the electronic inspection field, and discontinued that optional system. Then, it started to be applied also in the Beverage Machinery field, the same FIFO concept yet applied since decades by the Industry of the Electronic Components. FIFO is not really a tracking system, rather a counting system, due to the fact that tracking really and only implies spaces and times say kinematics. FIFO, on the opposite, has no containers' passage clocking (no encoder) and its single trigger photosensor simply counts containers.
FIFO’S INNER LOGIC (click the image to enlarge) is much more complex than commonly expected. The example above shows the logic underlying a fixed capacity FIFO buffer for integer numbers (image credit Princeton University, Dept. of Astrophysical Sciences, 2014)
FIFO, between machine and inspector
Today, pure shifting-registers are replaced by a mixed solution:
FIFO + shifting-register
when:
short-radius curves and/or conveyors’ cross-overs exists, in between the machine and the trigger;
A basic idea common to different Vendors about the configuration of an in-the-machine Electronic Inspector with FIFO trigger. Configured for locating functions (Filler valves, Closer or Seamer heads) and for Advanced Sampling. The drawing of principle here visible is referred to a Canning Line
- containers’ speed > 2.8 m/s;
- inspector has non-critical inspections in-the-machine;
- containers’ dynamics is complex, typical case of extremely light containers at high-speed;
say, all times containers’ sliding is expected > ½ their diameter for a significant portion of their population, as measured by the 1st Trigger out of the machine outfeed starwheel. Digits specifying how much is significant, are related to Contractual Technical Guarantees about False Triggers. False Triggers’ limits which have to be specified by the Vendors’ technological guarantees on the inspection equipments. Shifting-registers are optionally replaced by the mixed solution FIFO + shifting-register, when:
- short-radius curves and/or conveyors’ cross-overs exists, in between the machine and the trigger;
- containers’ speed > 1.5 m/s;
- inspector has non-critical inspections in-the-machine;
- containers dynamics’ is complex, typical case of light containers.
The range of containers’ speed:
(1.5 - 2.8) m/s
is an area where it is still possible to adopt standard shifting-register solutions, increasing the number of additional triggers.
Refer to the figure below, showing just an example of FIFO area for such a kind of electronic inspector. The orange colour lines evidentiate the conveyor area and a cross-over where huge containers’ sliding are expected. FIFO is capable to compensate the sliding of one definite container until the amount of 255 container diameters. Also for this extremal sliding, information passed to the inspector by its sensors in-the-machine, shall remain coherent with the those deriving by the observation of the sequence of containers inferred by the cited inspector’s initial Trigger. There is a relevant limit: if a container disappears (i.e.: removed by an Operator), localizations shall be, starting fom this occurrence, systematically attributed to the wrong:
(valve; head; station) minus 1
The figure below shows a countermeasure capable to limit the negative effect of what above:
In-the-machine Electronic Inspector based on a FIFO with one trigger. It’s the only possible choice for the fastest lines (containers’ speed > 2.8 m/s) where the Inspector has physical references or inspections in a prior machine (capper, filler, labeler. The example above is not showing the rejector. When inspectors include FIFOs, they are invariably mixed systems: FIFO + shifting-register, with the rejector lying in the end of the shifting-register area
Here, the number:
“350000 env.”
(where “env.” means “bottle”) is an constant input defining a maximum number of containers processed, after which an automatic re-phasing procedure has to be forcedly started. This number can be set in a wide range but, however, a machine stop shall then be controlled by the inspector: it’s the only way to rephase a FIFO. The machine has to be stopped, later emptied of the containers both machine and the entire FIFO-controlled conveyor, until FIFO trigger. This last typically lying a few centimetres before the main inspector cabinet.
Containers counted in the FIFO area are represented in the figure as blue squares. The system counted 21 containers in the conveyors cross-over area where should be 15 containers, this way typically indicating a fast non-synced deceleration of the conveyors with respect to the Machine out feed or, otherwise, hinting a parametric fine-adjustment. Also, FIFO Trigger photosensor counting them one-by-one as they get out of the Machine (Filler or Closer or Seamer or Labeller) is represented as a black coloured segment 970 mm after the transfer point.
FIFO: when to refrain from using it
FIFO is an excellent solution with or without inspections in-the-machine but, if the inspections in-the-machine check for defects implying impossibility of sale for the product or, worse, risk for the final Customers, it can’t be adopted. In this case, a solution can only be reached after expensive layout optimizations, eliminating short-radius curves, rotating the machine outfeed to eliminate curves, applying all due encoders and additional triggers, etc.
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