CA1121259A

CA1121259A - Package strapping machines

Info

Publication number: CA1121259A
Application number: CA000340780A
Authority: CA
Inventors: Frank E. Woolley
Original assignee: Gerrard Industries Ltd
Current assignee: Gerrard Industries Ltd
Priority date: 1978-11-28
Filing date: 1979-11-28
Publication date: 1982-04-06
Also published as: FR2442768B3; FR2442768A1; DE2947717A1

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.

Description

~ ~2~V59 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 iZ59 .
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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9LZ~9 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.
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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 ' ~L~2~l%~9 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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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.