GB2103255A

GB2103255A - Pull-off device

Info

Publication number: GB2103255A
Application number: GB08221596A
Authority: GB
Inventors: Eberhard Leins
Original assignee: Sulzer Morat GmbH
Current assignee: Sulzer Morat GmbH
Priority date: 1981-07-30
Filing date: 1982-07-26
Publication date: 1983-02-16
Also published as: DE3130051A1; JPS5823946A; DD202318A5

Abstract

Pull-off roller 1 on shaft 2 is driven by three phase motor 14 through slip coupling 11, reduction gear 8, pulleys 4 and 6 and belt or chain 5. The coupling 11 is an eddy- current coupling with an excitation winding supplied by a stabilized source 16 whose voltage is variable by potentiometer 17 to effect speed variation at constant torque. The roller may pull-off filaments or webs, e.g. fabric from a flat knitting machine. <IMAGE>

Description

SPECIFICATION Pull-off device for withdrawing filaments or webs at constant tension The invention relates to a pull-off device for withdrawing filaments or webs at constant tension.

Positively, frictionally and positively and frictionally driven take-up devices are known for taking up thread-shaped, rope-shaped, ribbonshaped or tubular material from a machine producing or processing this material, e.g. the knitted goods produced by a flat knitting machine or circular knitting machine. They generally serve to take up the produced or processed material at optimally constant tension and to feed it to a vat or to a winding-on device.

Automatic adaptation of fluctuating quantities of material can be achieved only by means of take-up devices which are either driven partly positively and partly frictionally by means of pawl drives with two pawls coming into service alternately (German Patent 1 156 197) or, like the take-up device of the type initially designated, operate exclusively frictionally and exhibit slip couplings, such as, for example, disc couplings with friction discs pretensioned by a force (German Offenlegungsschrift 2,432,083) or hysteresis couplings (German Offenlegungsschrift 2,330,752).Disc couplings are characterised by very high wear of their friction discs, which rotate relatively to each other at a high relative speed during the standstill of the material to be taken up and of the parts used for this purpose, whereas the torque of hysteresis couplings can be modified only by means of mechanical lever mechanisms, which is comparatively complicated and makes automatic control of the torque difficult It is therefore also already known, instead of slip couplings, to provide rotary field motors, gear rotary field magnets or d.c. motors for the drive of the take-up roller and in this case to control the torque by displacing an intermediate rotor, modulating the rotary field magnet or controlling the current supplied to the d.c. motor (German Patent 1 076311, German Offenlegungsschrift 2648 612, German Auslegeschrift 26 31 223).

However, such drive means are likewise comparatively complicated and not always satisfactory in operation.

The underlying aim of the invention is to improve the take-up device of the type initially designated so that it operates correctly under all applicable service conditions, is inexpensive and permits a drive of the take-up roller with constant torque even with fluctuating incidence of material over the entire speed range frdm zero up to the maximum required speed.

The characterising features of-Claim 1 are provided to achieve this aim.

The invention confers the advantage that in eddy current couplings the output torque is virtually independent of the output speed over a wide range, particularly at very low speeds. If the maximum applicable speed of the take-up roller lies in this range, a constant torque acts upon the take-up roller irrespectively of the incidence of material. Customary commercial eddy current couplings controllable by means of a simple potentiometer make it possible to produce an extremely inexpensive take-up device.

Further advantageous features of the invention are given in the sub-claims.

The invention is explained more fully below by an exemplary embodiment in conjunction with the accompanying drawing, wherein:- Fig. 1 shows schematically a preferred embodiment of the invention; Fig. 2 shows an embodiment of the eddy current coupling illustrated schematically in Fig.

1;and Fig. 3 shows the torque/speed curve of the eddv current coupling according to Fig. 2.

Ffg. l illustrates by way of example a take-up roller 1 of a flat knitting machine (e.g. German Offenlegungsschrift 2531 762). The take-up roller 1 has a shaft 2 which is mounted rotatably in bearings 3 and carries at its one end a belt pulley 4, a chain wheel, a gearwheel etc. The belt pulley 4 is coupled by means of a belt 5, a chain etc. to a belt pulley 6, a chain wheel, a gearwheel etc. The belt pulley 6 is mounted on the output shaft 7 of a reduction gear 8, the input shaft 9 of which is connected to the output part 10 (Fig. 2) of an eddy current coupling 11.As Fig. 2 particularly shows, the input part 12 of the eddy current coupling 11 is connected to the output shaft 1 3 of a three-phase a.c. motor 14, which is connected to the mains and driven in known manner, not shown in detail.

An exciter winding 1 5 of the eddy current coupling 11 is connected to a stabilised current/voitage source 16, the output voltage of which can be varied by a potentiometer 1 7.

Fig. 2 shows further particulars of the eddy current coupling or induction coupling 10.

Particularly, its input part 12 consists of a magnet wheel or rotor with pole pieces 1 8 projecting in the axial direction which point to an air gap, on the other side of which a stator 1 9 is arranged which carries the stationary annular exciter winding 1 5. Also arranged in the air gap is an armature 20 or a coupling disc which is mounted rotatably and connected for that purpose to the output part 10 mounted rotatably in bearings 22.

Whereas the input part 12 and the stator 19 consist of a ferromagnetic material, the armature 20 consists of material which is non-magnetic, but exhibits a high eiectrical conductivity. The stator 1 9 also carries a housing 23 consisting of iron, which exhibits on its end located on the rear side of the input part 12 inwardly directed radial projections 24, which serve to anchor the threephase a.c. motor 14 radially and axially with reference to the stator 1 9. The housing 23 serves as return path for the magnetic flux, which is indicated by a dashed line 25, and exhibits for this purpose a section 26 which limits the outer circumference of the radial air gap between the housing 23 and the circumference of the input part 12.

The mode of operation of the eddy current coupling is as follows: When the exciter winding 1 5 is excited by the application of a voltage, a magnetic flux which is closed through the stator 19, the housing 23, the input part 12 and the armature 20, is generated according to the dashed line 25. If at the same time the input part 12 is driven by the threephase a.c. motor 14, e.g. at constant speed, the magnetic flux in the armature 20 is modulated, whereby eddy currents are induced and a magnetic force is created at the armature circumference, which results in a torque and hence also an acceleration of the armature 20 in the direction of the rotary movement of the input part 12. The speed which is then adjusted is a function of the air gap flux, i.e. of the exciter current, whereas the torque generated is largely independent of the speed.A variation of the exciter current by means of the potentiometer 17 permits a speed variation at constant torque.

Standstill of the output part 10 is possible without disadvantage to the drive means. The speed of the three-phase a.c. motor 14 in the example illustrated is 2800 r.p.m., so that at a speed of the take-up roller of only a few revolutions per minute the slip is very great.

Eddy current couplings of this type are known (e.g. Swiss Patent 497 071). They are produced e.g. by Messrs. Pye Electric Ltd.. Lowestoft (England) and distributed by Messrs. "Eugen Schmidt s Co (esco) Getriebe- und Antriebselemente GmbH", 5210 Troisdorf (Germany) under the designation "tasc unit" (D series). Fig. 3 shows a graph of the dependence of the output torque upon the output speed for this company's "tasc unit 6D2/2".

According to Fig. 3, the output torque varies practically not at all e.g. at 67% of the nominal current within a speed range from zero to 1000.

This characteristic is utilised for the purposes of the invention.

At the normal knitting speed of a flat knitting machine, with normal incidence of material, for normal strength of the knitted fabric and for normal dimensions of the take-up roller, the speed of the take-up roller lies e.g. between zero and a maximum of approximately four r.p.m. When the eddy current coupling according to Fig. 3 is applied and if the three-phase a.c. motor 14 is driven at constant speed, this speed range delivers an output torque which is constant at approximately five kpcm. This output torque is normally not sufficient, because torques of e.g.

sixty kpcm are customarily demanded. In order to avoid the necessity for a much more powerful and more expensive three-phase a.c. motor and a much more powerful and more expensive eddy current coupling in this case, according to the invention the reduction gear 8 is adjusted to a step-down ratio of 1:12, whereby, despite the application of the eddy current coupling illustrated in Fig. 3, twelve times as great a torque of sixty kpcm is obtained at the take-up roller 1.

Under these conditions, in order to achieve a maximum speed of the take-up roller of four revolutions per minute, the output part 10 must of course be driven at a twelve times greater output speed of forty-eight r.p.m. However, as Fig. 3 clearly shows, this increase in speed has practically no influence upon the output torque, because the latter still lies in the constant range even at this output speed. Eddy current couplings of the type described therefore not only permit the take-up roller to be driven at constant torque over a wide speed range, but also above all the application of customary commercial components of small dimensions which are therefore inexpensive.

The potentiometer 1 7 permits an infinite adjustment of the torque between zero and a maximum value. If a programme control of the torque is desired, a plurality of potentiometers adjusted to different output voltages, and electrical devices controlled by a computer, a film etc. for changing over from one potentiometer to another, may be provided.

Claims

1. Take-up device for taking up thread-shaped, rope-shaped, ribbon-shaped or tubular material from a machine producing or processing this material with at least one take-up roller which is connected through an interposed slip coupling to a drive means, e.g. a three-phase a.c. motor, characterised in that the slip coupling consists of an eddy current coupling (11).

2. Take-up device according to Claim 1, characterised in that the output part (10) of the eddy current coupling is coupled to the input shaft (9) of a reduction gear (8), the output shaft (7) of which is coupled to the take-up roller (1).

3. Take-up device according to Claim 1 or 2, characterised in that the slip coupling consists of an eddy current coupling, the output torque of which is substantially constant within a range of the output speed including the zero output speed.