PACKAGE STRAPPING MACHINES

MACHINES FICELEUSE D'EMBALLAGES

English Abstract

ABSTRACT
A strapping machine for binding packages with metal
or plastics strapping has a tensioning device which is
driven by an electric motor more instead of the more
usual air motor. The electric motor is coupled to the
tensioning device by a hydro-dynamic coupling which
delivers maximum torque with its output stalled but
while its input is still rotating and such that the
motor is not overloaded even though the tension is
maintained for an appreciable time. The maximum output
of the hydro-dynamic coupling can be adjusted by alter-
ing the quantity of hydraulic fluid it contains either
initially or by a fluid control circuit which causes
fluid to flow into or out of the working chamber of the
coupling to alter the amount of fluid it contains.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In package strapping apparatus a tensioning device,
an electric motor and a rotary fluid coupling drivably
connecting the electric motor to the tensioning device, the
rotary fluid coupling being such as to afford a maximum
output torque with its output stalled but while its input
continues to rotate and the input torque demanded is less
than that which would overload the electric motor.
2. A package strapping apparatus according to claim 1
wherein the output torque is that required to produce the
pre-determined tension of the strapping.
3. A package strapping apparatus according to claim 1
wherein the fluid coupling is of the hydro-dynamic type.
4. A package strapping apparatus according to claim 3
wherein the maximum output torque is adjustable by altering
the amount of hydraulic fluid contained in a working chamber
of the fluid coupling.

Description

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IMPROVEMENTS RELATING TO PACKAGE
STRAPPING MACHlNES
This invention relates to strapping tools and
machines for binding packages, parcels or the like of
the kind in which metal or plastics strapping is looped
around a package by power means or by hand, and is
tensioned and the ends of the loop s~cured one to the
other by the tool or machine.
~ ompressed air motors are often used to drive the
device which tensions the loop and these have the part-
icular advantage that the ultimate tension in the loop
can be pre-determined by arranging the air motor to
stall when the pre-determined tension is reached. The
stalled motor continues to hold the strapping under
tension while the joint between the ends of the loop is
made and, indeed, will take up any slack which may occur
due to consolidation of the package after the pre-
determined tension was first reached and without
exceeding the pre-determined tension. An air motor can
remain in the stalled condition for long periods without
overheating. However, compressed air motors are very
noisy and use large quantitie`s of compressed air which
is costly to produce so that strapping machines powered
by compressed air are fairly costly to run. There are
also often situations in which strapping tools and
machines are required but no compressed air supply is
available.
Electrically driven tensioning devices in strapping
machines are known. Electricity supply is generally
available, or can easily be provided, and electrically
powered machines and tools are cheaper to run than those
driven by compressed air, and are very much guieter in
operation. Known electrically-driven tensioning devices

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are less satisfactory than those dri~ven by air motors in
;~ respect to their ability to maintain the loop of strapping
under pre-determined tension. If allowed to stall, electric
motors overheat in a very short time. If they are disconnected
from the supply, other means have to be provided for maintaining
tension and where there is a need to take up subsequent slack
due to consoiidation of the package, complicated controls are
required which can be slow to respond.
It is an ob~ect of the present invention to provide
an electrically-driven tensioning device which is able to
afford at least some of the previously mentioned advantages
inherent in compressed-air drives.
The present invention consists in a package strapping
tool or machine having an electrically-driven tensioning device
wherein an electric motor is drivably connected to the tension
device through a rotary fluid coupling. The fluid coupling
affords a maximum output torque with its output stalled but
while its input continues to rotate. The input torque demanded
is less than that which would overload the electric motor.
~0 The maximum output torque may be that required to
produce the pre-determined tension of the strapping.
The fluid coupling may be of the hydro-dynamic type.
The maximum~output torque it will transmit may be adjusted by
altering the amount of hydraulic fluid it contains either
initially or by a fluid control circuit which causes fluid to
flow into or out of the working chamber of the coupling to
alter the amount of fluid it contains.
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An embodiment of the invention will be described,
by way of example, with reference to the accompanying
drawing which is a diagrammatic perspective view of part
of a package strapping machine having an elec~rically-
driven tensioning device according to the invention.
An electric motor 1 is connected by a belt drive 2
to a belt pulley 3 coupled to the impeller 3~not shown(
of a hydro-dynamic coupling 4, the turbine ~4not shown(
of which drives an output shaft 5, concentric with the
pulley 3. The shaft 5 drives a rotary dog 6 mounted on
the end of the shaft 5 and, through gearing 3~not shown(,
a feed wheel 7. Polypropylene or other suitable plas-
tics strapping 8 is passed from a supply 3~not shown(
between the rotary dog 6 and feed wheel 7 to a jointing
head 9.
.
The strapping 8 is gripped in the pinch between the
rotary dog 6 and feed wheel 7. Rotation of the dog 6
and feed wheel 7 in one sense draws strapping rom the
upply to enable a loop to be formed around the package.
Reversal of the dog 6 and feed wheel 7 then contracts
the loop onto the package and tensions it until the
pre-determined tension is reached at which the hydro-
dynamic coupling 4 slips. Tension is maintained on the
strapping by the dog 6 and feed wheel 7 while the two
ends of the loop are joined. If the package consoli-
dates after the dog 6 and feed wheel 7 have first
stopped rotating, they will turn again to ~ake up the
slack and maintain the pre-determined tension in the
strapping. During this time the motor 1 continues to
rotate the impeller of the hydro-dynamic coupling 4 but
the load imposed by the coupling is insufficient to
cause over loading of the motor 1. The ~uantity of
hydraulic fluid put into the hydro-dynamic coupling 4
determines the torque output at which the output shaft 5
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ceases to turn and which is chosen to suit the tension
: required in ~he strapping, but must not be so high that
the motor would be overloaded even though the tension is
maintained for an appr~ciable time.
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