….E+L Bulletin 025, Web Guiding Systems
SENSING DEVICES
Web guiding relies upon an integrated feedback control system; that is, the sensing device
continuously senses web location and sends appropriate corrective signals to the actuating
device. The control signal strength is dependent upon the position of the web and is, therefore,
proportional.
Traditional sensing relies on pneumatics. The edge of the web passes between two "fingers"
which contain the opposing out breathing jets of air. The position of the edge modulates the
effects of the jets on one another, causing a pressure fluctuation in the air supply of one of the
jets. It is this pressure fluctuation, which provides the corrective signal that controls the power
unit output. E+L can supply a special porous sensor, which guides on a row of holes, or one,
which senses the edge of scrim material with openings as large as half of an inch.
Photoelectric sensing is desirable in many instances where the edge is relatively unimportant to
the process, but where following a printed line or pattern is the key "edge".
Erhardt + Leimer produces a photoelectric sensing system. This system is designed so that it is
integrated with traditional pneumatic-hydraulic power and actuation devices. It can, therefore,
be retrofitted to existing systems, or combined with them to provide alternate guiding
techniques.
E+L also manufactures special sensing devices to meet the requirements of specific
applications. An example of this is the Tuft Aligner, a pneumatic sensor that is widely used in
the carpet industry. This device guides on a row of tufts on the face of the carpet. Another
example is a special electronic sensor, which senses the hidden steel outer cord in a rubber
web on a tire cord calender.
CONTROL OPTIONS
E+L provides a number of control options that provide specific "behavior" characteristics on the
web guiding system on which they are imposed. Many of these control options have been
designed to meet standard requirements in given industries. Others have been developed to
give greater versatility to systems to suit them in a wide range of applications.
All E+L control options function by controlling either the output of the hydraulic power supply or
by controlling the source, magnitude and application of the sensing signal. In some systems,
the control option functions entirely manually, that is, the operator opens and closes valves to
achieve the desired result.
In most cases, however, the sophistication of the control system requires important interlock
features difficult to achieve with a mechanical system. In such cases, the control option is
imposed by means of solenoids, and activated by selector switches, timers, and push buttons.
DETAILED DESCRITPION AND OPERATING INFORMATION
Each major component (and many significant variations) is described in detail in the following
bulletins. Refer to each of these for the information that will describe your system fully.
Because a web guiding system is complex and comprises many variables, the equipment and
its function must be explained on a component-by-component basis. Where these components
interface, that interface is defined, often in two bulletins. While this leads to some redundancy,
it also makes possible a complete set of instructions.
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