GB2238368A - Variable torque clutch control - Google Patents

Abstract

A method of remotely controlling torque transfer from a rotatable shaft (S) to a surrounding core via a variable torque clutch, makes use of a variable clutch mounted on the shaft between the shaft and the core, a primary power supply to cause torque transfer by the clutch and carried to the clutch via the shaft (S) and a secondary supply including a coded signal also carried by the shaft to the clutch to allow remotely controlled variation of the magnitude of torque transferred. By using a coded signal, which may be superimposed on the power supply it is possible to control independently a plurality of clutches on a single shaft whilst using the shaft to carry a common primary power supply. In one embodiment an electro- rheological fluid is located between electrodes (H) and (F), the inner body of the clutch engages the shaft (S) by a key (J), and the outer body (A) drives the core via a gripper mechanism such as a friction plate, the torque transfer being controlled by electronic means (G). Alternatively the clutch may be controlled by an electro-pneumatic transducer, the primary power supply being provided by a high pressure air line. <IMAGE>

Description

Variable Torquf Clutch The present invention relates to a variable torque clutch which can be remotely controlled. Its primary use is in the transfer of torque from a rotatable shaft to an object mounted on the shaft which is to be rotated. One particular use of such a clutch is in the restricted annular space associated with the core chuck on the rotatable centre shaft of a slitting and rewinding machine, but it can be used to advantage in any application where remotely controlled torque transfer is required.

A slitting and rewinding machine is primarily intended to slit printed packaging material in the form of a roll of foil, paper or plastic film. A conventional machine takes a roll of material of, for example, 1200mm diameter and 1600mm width which has been printed with up to about 20 or 30 patterns across the width. The machine is designed to slit material taken from the roll and then rewind the material onto individual reels of single pattern widths. The reel lengths are adjusted to suit the final packaging machine and are generally up to about 600mm diameter.

As the material is slit at various points across its width it is current practice to carry out rewinding on two rotatable rewinding shafts, with alternate ribbons of slit material being rewound on alternate shafts displaced one from another.

This prevents adjacent portions of the material interfering with each other at the slit edges. The material is wound onto formers known as rewound reel cores or, simply, "cores".

Rewind shaft mounted clutches are required to provide torque transfer from the rewind shaft to the individually slit and rewound reels. Conventionally, a rewind shaft has a diameter of about 45'irn and a core has an internal diameter of about 76mm. The clutches reside inside the rewound reel core and have an internal diameter large enough to slide over the rewind shaft. The clutches have an external diameter smaller than the core inner diameter to allow the cores to be slid over them for loading/u oading. Rewind shaft mounted clutches are sometimes referred to in the art as "core adaptors".

During winding the material may have a surface speed of around 300 metres a minute. It is important that the tension in the material is carefully controlled and this is normally achieved by transferring torque from the shaft to the core using a differential slip in the clutch. Normally, the amount of slip is adjusted so as to maintain a tension of, for example, about 25g per millimeter in the material during winding. The amount of tension in the material, and consequently the magnitude of the torque transferred will vary with the nature of the material, with the slit width, and also with the variation in diameter of the rewound reel as the material is wound on.

Thus, it is important to be able to control the torque transfer.

It is known to obtain torque transfer by use of a mechanical friction clutch and these have been widely utilised in the art of slitting and rewinding machines because they are simple in operation and can achieve a high power density between the core and rewind shaft. The standard type of friction clutch uses a bronze bush rotatable the shaft and which is forced against the core with a variable force by longitudinal compression of the clutch body. Other mechanical clutches use the compression of friction plates bearing against the core to achieve torque transfer. Both of these techniques are referred to in the art as "end loading techniques" because the load applied and hence the amount of torque transfer, is adjusted by mechanical means (e.g. a threaded bolt) operated from a free end of the shaft.These methods cannot be adjusted whilst the shaft is rotating. When several mechanical clutches are mounted on a single shaft in order to transfer torque to a plurality of cores, the conventional end loading technique can only apply a common force along the shaft which may not have an identical effect on each of the shaft mounted clutches. In order to get individual control of several clutches in the prior art it would be necessary to have a separate shaft for each rewound core, and this is not practicable where the machine is intended to be flexible and have general utility.

Other torque transfer means have been described in the prior art. Generally these are either too bulky to be used in the confined space between a rewind shaft and a core, or they have a high power consumption which causes problems in the necessity for the dissipation of generated heat. Examples of means which have previously been suggested for providing controlled torque transfer are particle clutches, eddy current couplings or individual motors. These have been precluded in all but a few specialist applications. In one suggestion it has been proposed that a pneumatic clutch could be employed on a rewind shaft and that multiple clutches could be controlled independently by providing multiple airways along the rewind shaft.This would give a degree of individual controllability, but at the expense of set up flexibility because the shaft would be dedicated to operation only with one particular arrangement of clutches.

The present invention provides a method for remotely controlled torque transfer from a rotatable shaft to a surrounding core via a variable torque clutch, the clutch being mounted on the shaft between the shaft and the core, wherein the primary power supply to cause torque transfer by the clutch is carried to the clutch via the shaft and there is additionally a secondary supply including a coded signal also carried by the shaft to the clutch to allow remotely controlled variation of the magnitude of torque transferred.

The invention also provides a clutch for use in such a method.

By using a coded signal, which may be superimposed on the power supply it is possible to independently control several clutches on a single shaft whilst using the shaft to carry a common primary power supply.

Twn non-limiting examples of the invention will now be described with reference to the accompanying drawings.

Example 1. In this example the clutch utilises an electro-rheological fluid as the torque transfer medium. An electro-rheological l fluid will change its viscosity when an electric field is applied. By applying the appropriate field it is possible to change the viscosity of such a liquid from a state of high fluidity to a state of solidity.

Electro-rheological (ER) fluids are available which comprise a suspension of finely divided solid particles in a hydrophobic liquid. The particles may, for example, be about 5-25 microns in diameter and are desirably of approximately equivalent density to the carrier liquid in order to prevent the particles separating out. The fluid may be exposed to a strong electric field generated by a potential difference of several thousand volts operating over a narrow gap of a few millimeters width. The material contained within the field can be caused to vary its viscosity by variation of the field strength.

Figure 1 shows the general arrangement of a core adaptor in the form of a ER clutch. The clutch is mounted on a shaft (S) and has a core gripper to grip the surrounding core of a rewound reel. The clutch has an associated control unit for controlling the torque transfer as the shaft is rotated.

Figure 2 shows details of the clutch oomponents. An outer body (A) drives the core via a gripper mechanism such as a friction plate or the like. Mounted on the outer body is an electrode (H) insulated from the outer body by insulator (B).

The electrode is supplied at a controlled high voltage from the electronic controls (G), via connecting wire (C). The inner body (F) of the clutch forms the second electrode, so that an electric field may be generated between electrodes (H) and (F). The inner body of the clutch engages the shaft (S) by means of a key (J). The gap between the electrodes is filled with an ER fluid. Seal (D) retains the fluid within the gap.

Power to operate the clutch is supplied by applying a voltage across the shaft and this is picked up and relayed to the electronic controls by means of brush (K). The brush (K) may pick up the power supply from an insulated track running on the rewind shaft. Control signals for varying the magnitude of torque transfer are also supplied to the electronic controls along the shaft and picked up by the brush (K).

In operation, the shaft (S) is rotated at a desired speed and this causes rotation of the inner body of the clutch. The primary power supply taken from the shaft is used to create the necessary voltage across the electrodes in order to produce the desired level of viscosity in the ER fluid and hence the desired level of torque transfer to the outer body of the clutch. The greater amount of slippage allowed by clutch the less will be the torque transferred, and it is clear that when the ER fluid is caused to be effectively solid there will be substantially no slippage and consequentially complete transfer of torque. The performance of the clutch may be controlled as the shaft is rotating by sending coded signals to vary the torque transfer.

It is currenly expected that the clutch would require an electrical power supply at up to 3000 volts and 2mA in operation. This represents a power input of only 6 watts which is not expected to cause serious problems in heat dissipation. However, from the stand point of operator safety it is undesirable to have such high voltages on the shaft.

Thus, as a further aspect of the present invention, it is proposed to incorporate the high voltage generation circuitry within the electronic control unit of the clutch assembly.

This can be achieved by utilising a low voltage supply on the shaft and transforming the voltage to the necessary high voltage only within the clutch unit.

As mentioned before several clutches according to the invention may be mounted at adjacent positions along a single shaft and may be supplied by a common low voltage supply.

Superimposed on this would be a coded signal which would instruct each individual clutch to control the torque as desired.

Example 2. In a second embodiment of the invention individual control of a clutch may be achieved by mounting an electro-pneumatic transducer on each clutch connected to a gripper mechanism in the form of a friction plate or the like.

The transducer is powered from a low voltage supply carried by the shaft and the primary power supply is a high pressure air line routed along the rewind shaft.

It is possible to operate several clutches on the same shaft: each clutch has an electro-pneumatic transducer powered from a common low voltage supply on the shaft and responding to individually coded signals superimposed on the low voltage supply. A common air supply would provide primary power to all of the clutches and the coded signals would instruct individual transducers to output the desired air pressure to each clutch to control the torque transfer characteristics.

As can be seen from the examples above the present invention can provide clutches of comparable compactness with the conventional friction clutches. These clutches are operated by remote control and the torque transfer characteristics may be varied as the shaft is rotating. The power input of these clutches may be kept relatively low in order to avoid problems of dissipation of generated heat. It is a particular advantage of the invention that two or more such clutches may be mounted in tandem on a single shaft and may be supplied with a common primary power supply whilst yet being independently controllable by coded signals.

It is recognised that there may be errors in the relation between the coded control signal and the actual torque produced and this could be in certain circumstances a limiting factor in the use of such devices within open loop tension and torque control systems. This possible problem can be overcome by including an external measuring device to the system and providing a close loop control. However external measuring devices are not considered to be generally easily incorporated within machines such as slitting and rewinding machines. It is of great importance in providing a useful slitting and rewinding machine that it should be capable of great flexibility, and should be easily set up to operate with from one or two clutches to possibly over 30 clutches in some cases. An external measuring device, if needed for each clutch this could be impractical. As a further aspect of the present invention it is therefore proposed that a torque transducer may be mounted within the clutch. The secondary supply coded signal which is externally applied for the purposes of remote control could be used to form a reference signal for a closed loop torque control system contained within the electronic control unit of the clutch. Clearly, whilst is it proposed that the closed loop system would be electronic for an ER clutch, it is conceivable that the system may be pneumatic or a combination of pneumatic and electronic where the clutch is pneumatically powered.

Claims (10)

Claims

1. A method for remotely controlled torque transfer from a rotatable shaft to a surrounding core via a variable torque clutch, the clutch being mounted on the shaft between the shaft and the core, wherein a primary power supply to cause torque transfer by the clutch is carried to the clutch via the shaft, and wherein there is additionally a secondary coded supply signal also carried by the shaft to the clutch to allow remotely controlled variation of the magnitude of torque transferred.

2. A method according to claim 1, wherein the primary power supply is electrical, and the secondary power supply is also electrical.

3. A method according to claim 1, wherein the primary power supply is pneumatic, and the secondary power supply is electrical.

4. A method according to claim 1 for remotely controlled torque transfer from a rotatable shaft, wherein two or more variable torque clutches each with a surrounding core are mounted on the shaft, and wherein the common primary power supply is carried by the shaft to the clutches, and wherein individually coded secondary supply signals for each clutch are carried by the shaft to provide individual remote control of the magnitude of torque transferred by each clutch.

5. A clutch for use in the method of any preceding claim, comprising a clutch body adapted to be mounted on a rotatable shaft and adapted to fit within a core to be rotated, the clutch having means for engaging the shaft so as to rotate therewith and means operable by a primary power supply for gripping the inside of the core so as to transfer torque from the shaft to the core, and means within the clutch body for decoding a coded supply signal received via the shaft so as to variably control the magnitude of torque transferred.

6. An electro-rheological fluid friction clutch according to claim 5.

7. An electro-pneumatic friction clutch according to claim 5.

8. A method, substantially as hereinbefore described with reference to example 1 or 2.

9. A clutch, substantially as hereinbefore described with reference to example 1 or 2.

10. A clutch, substantially as hereinbefore described with reference to figure 1 and 2 of the accompanying drawings.