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A pneumatic dispensing valve can further the rotor, and is not affected by material viscosity,
improve precision, with the capability to actively input pressure or ambient temperature.
turn the flow off and on like a tap. There are a broad One example of a technology that works on this
range of valve types available, including needle principle is the preeflow eco-PEN, which enables
valves, spool valves and diaphragm valves — the the user to dispense volumes as small as 0.001 µl
appropriate valve depends on material chemistry, within 1 per cent, 99 per cent of the time, offering
cure mechanism and geometry of output. a high level of repeatability and accuracy.
Dispensing valves can mitigate some of the
variability of the flow from a time/pressure syringe Positioning with precision
dispenser, but output can still fluctuate with Dispensing valves and pumps improve control over
material viscosity change — something that may the dispensed amount, but manufacturers looking
occur with ambient temperature change, for for a very high level of precision will also want to
example. have repeatability in the placement of the material.
Dispensing equipment based on some form Manufacturers can repeat the application of
positive displacement technology bring the highest materials with positional accuracy by incorporating
levels of both accuracy and precision. The output a robot or other form of automation into their
from these is a specific volume, and they can dispensing process. Once the dispensing technology
preclude the effects of environmental and material has been specified, it can be mechanised. Options
variations on dispensed quantity. Jetting valves, for include rotary tables or simple 3-axis benchtop
example, may be a good option for manufacturers robots, usually at modest cost, right up to multi-axis
looking for speed and/or the ability to dispense very robots with vision-based control and feedback.
small dots, or to dispense onto complex 3D We all understand that robots offer productivity
surfaces, as well as high accuracy and repeatability. benefits over humans because they are faster or
more consistent, and work without breaks. But they
The highest level of precision can achieve results not possible manually, such as
At the higher end of precision, positive the application of an even bead of liquid gasketing
displacement dispensing equipment based on the around a complex profile. Return on investment
progressive cavity pump principle can achieve high calculations based on the usual automation benefits
levels of repeatability and accuracy. A progressive combined with precision- and accuracy-based
cavity pump typically consists of a single-helix productivity gains often show a quick payback.
metal rotor and a double-helix hole in an Meeting material application
elastomeric stator. This forms a sequence of small tolerances using a robot
discrete cavities which progress through the pump
as the rotor is turned, transferring the liquid. The
output represents true volumetric
dispensing, because the amount of
material is directly proportional
to the number of
rotations of

November 2020 • INDUSTRIAL TECHNOLOGY EXTRA • p6