GB2155162A - Terminating drying in tumbler dryers - Google Patents

Abstract

A tumbler dryer has a drum (1) for receiving articles to be dried and in the curved wall (7) of which between adjacent drum vanes (9) is mounted a sensor (12) for sensing the electrical resistance of articles being tumbled in the drum. The sensor is connected to an electric circuit for detecting changes in the electrical resistance and for stopping the dryer when that resistance reaches a predetermined value which may be preset by a user at the commencement of a drying cycle. <IMAGE>

Description

SPECIFICATION Improvements in or relating to tumbler dryers This invention relates to tumbler dryers and has particular but not exclusive reference to electrically heated tumbler dryers for domestic use.

Several methods exist of controlling the duration of the drying cycle of a tumbler dryer and one of such methods comprises the sensing of the electrical resistance of one or other of articles being tumble dried. The sensing is effected by a sensor mounted on the drum and connected to a control circuit via a slip ring positioned round the drum on the external surface thereof. The drum has several vanes that extend radially into the interior of the drum to assist in imparting a tumbling action to articles in the drum undergoing drying and the sensor is usually mounted on the side face of one of the vanes.

Such mounting is quite satisfactory for drums whose direction of rotation is constant because the sensor is mounted in the leading face of the vane thereby ensuring contact with articles in the drum.

However, in the case of tumbler dryers whose drum is rotated first in one direction and then in the other, and this is desirable to reduce the possibility of the articles "balling" during drying, the location of the sensor on a vane is not satisfactory because contact between the sensor and the articles is most unlikely to occur during the reverse rotation of the drum when the sensor is, in effect, located on the trailing face of the vane.

According to the present invention, a tumbler dryer having a drum for receiving articles to be dried and mounted for rotation about a horizontal axis has a sensor for contacting the articles located in the curved wall of the drum.

Preferably, the drum is formed or provided with internally extending vanes to assist in imparting a tumbling action to the articles and in this case, the sensor is located on the curved wall of the drum between two of the vanes.

Preferably, the sensor is positioned midway between the vanes.

In addition it is preferred to locate the sensor rather closer to the exit from the drum of air circulated through the latter than to the entrance to the drum of such air.

By way of example only, an electrically-heated tumbler dryer for domestic use will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a perspective view in exploded schematic form of certain parts only of the dryer, Figure 2 is a front elevation of one of the components shown in Fig. 1, Figure 3 is a section on the line Ill-Ill of Fig. 2, Figure 4 is a diametral section through another component shown in Fig. 1, Figure 5 is a front elevation of a further component shown in Fig. 1, Figure 6 is a section on the line VI-VI of Fig. 5, Figures 7 and 8 are, respectively, a rear elevation and side view of the component shown in Fig. 5, Figures 9 and 10 are, respectively, a front view and a side view of another component shown in Fig. 1, and, Figures 11, 12, 13 are, respectively, a front elevation, side elevation and end view of yet another of the components shown in Fig. 1.

The general construction of the tumbler dryer is conventional and may, for example, be of the form described in U.K. Patent Specification No.

1,226,951.

Figure 1 shows some only of the component parts of the dryer. A cylindrical drum 1, closed at its rear by a rear end wall 2, has a loading aperture 3 at the front end wall in a front wall 2a and round which is an outwardly extending flange 4 by which the drum is rotatably supported at its front end on a co-operating flange (not shown) extending rearwardly round a loading opening 5 in a front panel 6.

The rear of the drum is supported by a stub axle (not shown) that extends on the axis of the drum outwardly from the rear end wall 2 and is supported in bearings in a rear panel (not shown).

The curved wall 7 of the drum is formed with a plurality of inwardly-extending vanes, the embodiment shown in Fig. 1 having three such vanes spaced equidistantly round the periphery of the drum and referenced 8. The vanes are pressed out of the wall 7 each vane having sloping sides 9 and a rounded inner end 10. The ends of the external recesses created by the formation of the vanes 8 are closed by the end walls of the drum, there being holes 11 formed as shown.

Mounted in the wall 7 of the drum at a position about midway between two vanes is a sensor 12.

The sensor is also located somewhat forwardly of the centre point between the end walls of the drum 1.

The sensor 12 to be described in more detail below is joined by an electrical cable 13 to a slip ring in the form of an electrically-conducting annulus 14 mounted upon the front end wall 2a. The annulus 14 is electrically insulated from the front end wall 2a, for example by being mounted upon suitable electrically insulating spacers (not shown).

The annulus, shown in more detail in Figs. 2 and 3, may be formed from sheet metal, for example stainless steel and has internal and external flanges 15, 16 for strength.

The annulus 14 may be formed from any other suitable electrically-conductive material but it is important that the flat surface should be without joins or other discontinuities over part at least of its flat surface. Mounting holes 17 are equi-spaced round the flat surface adjacent the inner flange 16 and there is a further hole 18 for the reception of a connector joining the cable 13 to the annulus 14.

The sensor 12 shown in more detail in Fig. 4 comprises a stainless steel shallow cup 19 to whose rear face is welded an electrically-conducting stud 20 screw-threaded over its distal end as indicated at 21. The front face of the sensor is smooth and free from any surface imperfections which may cause "snagging" of articles during drying as will be described below. The edge 22 of the sensor is also gently rounded as shown.

The sensor 12 is mounted in a suitable hole in the wall 7 by means of a sensor holder 23 shown in Figs. 5-8. The holder 23 is of electrically insulating material, for example glass coupled polypropylene, and has a front face 24 sized to receive the shallow cup portion 19 of the sensor 12. Round the edge of the front face 24 is a rim 25 inside which fits closely the cylindrical wall 26a of portion 19 of the sensor 12.

The holder 23 has a central boss 26 that extends on both sides of the holder as shown. The boss has a central hole 27 through which the stud 20 passes.

That part 28 of the boss projecting from front face 24 is cylindrical while the other part 29 projecting from the rear face 30 is stepped as at 31 and has 'flats' 32 as shown in Fig. 8.

The rear face 30 of the holder 23 also has a peripheral rim 33 curved as indicated at 34 in Fig. 7 to mate closely with the contour of the curved wall 7 of the drum 1.

The sensor 12 is assembled to the holder 23 by passing the stud 20 through the hole 27 in a direction that allows the cup-shaped portion 19 to seat on the front face 24 with the rim of the portion 19 mated internally of, but closely to, the rim 25.

To mount the assembly on the drum wall 7, the projecting portion 29 and the stud 20 are passed from inside the drum through the hole in the drum wall, that hole being shaped to receive the flats 32 thereby preventing rotation of the holder. An isolating washer of electrically insulating material is passed over the stud 20 into contact with the stepped surface 31 of the part 29 of the boss 26.

The bore of the washer is also stepped to match the contour of the part 29. The washer ensures the electrical isolation of the stud 20 from the drum 1.

Subsequently, a nut (not shown) is screwed over the stud 20 to secure the assembly in place. The contoured edge 34 seats against the curved inside face of the drum wall and the stud 20 projects externally of the drum as shown in Fig. 1 and the cable 13 is electrically-secured to the stud.

In this way the sensor is electrically insulated from the drum.

A pick-up or brush 35, for co-operation with the annulus 14 over the part of its surface referred to above, is shown in Figs. 9 and 10 and comprises a bunch 36 of bristles of a resilient electrically conductive material, for example phosphor bronze, which is gripped in a holder 37. The holder 37 has an inner support (not shown) of a plastics material which helps to retain the bristles in the holder but which does not prevent good electrical contact with the bristles. The holder 37 has a hole at one end as at 38 by which the holder 37 is mounted upon a supporting bracket 39 (Figs 11, 12) mounted on the inner face of the front panel 6 for example by means of a flange 40 (Fig. 1). The bracket 39 is electrically insulated from the front panel 6.

The bracket 39 is shown in more detail in Figs.

11-13 and comprises a stainless steel plate of generally triangular form with mounting holes 41 adjacent one edge and a tapered portion 42 whose edges are turned-up as indicated at 43.

The holder 37 is mounted between the turned-up edges 43 by means of a mounting bolt passed through the holes 38 and a hole 44 in the bracket 39. The general disposition of the bracket 39 is such that the bunch 36 of bristles contacts the surface of the annulus 14 as indicated in Fig. 10. The bracket 39 is spring urged towards the annulus to ensure good electrical contact between the bunch 36 of bristles and the annulus 14.

The bunch 36 of bristles is connected to an electrical control circuit (not shown) which in conjunction with a timer is used to control the drying cycle of the tumbler dryer.

Connection from the drum is also made to the control circuit, that connection constituting the "earth" of the dryer and the control circuit.

In operation, articles tumbling in the drum whilst undergoing drying periodically contact the sensor 12 and, in effect, form an electrical resistance between the sensor and the drum. The smooth surface of the sensor ensures that articles in the drum slide freely over that surface and 'snagging' of the articles does not occur. The value of that resistance is monitored constantly by the electrical control circuit and when it reaches a predetermined value the control circuit terminates the heating of air supplied to the drum for drying purposes.

Preferably, the direction of rotation of the drum is periodically reversed.

By locating the sensor 12 between the vanes, contact with the articles is not affected by the direction of rotation as would be the case if the sensor was mounted in one of the sloping sides 9 of a vane 8 as has been previous practice. The vanes 8 serve to lift the articles during tumbling and thus whilst contactetween the articles and the sensor was likely during rotation of the drum in one direction, it was very considerably less likely in the other direction and this would result in a less effective monitoring of the electrical resistance of the articles.

In addition, by locating the sensor somewhat closer to the front walls 2a than the rear wall 2, movement of articles along the drum towards the front wall that sometimes happens when a few articles only are being tumble dried, period contact between the sensor and the articles is more likely to take place than if the sensor were centrally located between the end walls 2, 2a. Such movement tends to occur with small loads because of the direction of air flow through the drum which is normally from back to front. The air leaves the drum via the loading aperture 3 and enters a hollow enclosure surrounding that aperture and is then ducted to a passageway having an outlet in the front panel as indicated at 'OUTLET' and one at the rear of the machine. Normally only one outlet is used, the other being closed by a removable closure plate placed over the outlet.

Furthermore, by locating the annulus 14 on the front wall 2a of the drum its peripheral speed is considerably lower than would be the case if a corresponding conductive ring were mounted upon the curved wall 7 of the drum. Lowering of the peripheral speed reduces wear on the pick-up and also reduces noise. Noise is also reduced considerably because it is easily possible to make the annulus 14 without any join as would be necessary in the case of the conductive ring mentioned above.

In order to locate the latter ring in position, it has to be formed with a gap to enable it to pass over joins between the curved wall 7 and one or other of the end walls. Even when the ends of the ring are closely joined, there is a discontinuity and this gives rise to irritating noises.

A further reduction in peripheral speed of the surface of contact with the brush can be effected by forming or mounting on the stub axle referred to above a slip ring with which the pick-up makes contact. Such a slip ring would have a low peripheral speed.

There are, however, some advantages arising from the location of the annulus 14 shown in Fig.

1. The brush is close to the controls of the tumbler dryer which are normally on the front of the latter.

Moreover, access to the annulus for periodic cleaning that may be necessary is easy. Such access may be had via a removable top cover of the casing of the tumbler dryer or by some other easy route.

The flexible nature of the bunch of bristles ensures that good electrical contact is always made with the surface of the annulus 14 regardless of the direction of rotation of the latter.

It is not essential that the bristles be of phosphor bronze, beryllium copper is another suitable material.

In addition, the pick-up may be so mounted that changes of the direction of rotation of the drum do not tend to exert a flexing force on the pick-up. For example, a carbon brush mounted normally to the surface of the annulus would experience little or no flexural force.

In one form, the tumbler dryer control is associated with a timer that allows a delayed start to a drying cycle. A delay of up to eight hours or more would enable the dryer to be used at night time when lower electricity supply tariffs may be available. The control may have one position bringing into operation the sensing described above and other positions which allow the duration of a drying cycle to be preset.

It will be understood that if the control is operated to the one position so as to select the sensing described above, drying continues until the sensor indicates that a requisite degree of dryness of the articles has been reached.

Preferably, the degree of dryness is presettable by the user and a further control is provided to enable the user to preset, at the commencement of a drying cycle, a required degree of dryness. Such a control provides an input to the control circuit against which the sensed resistance or a parameter derived therefrom can be compared.

An additional feature of the control, in addition to the conventional "cold run" that occurs at the end of a drying operation, is a further period of say one hour during which the drum is rotated periodically to prevent undue creasing of the articles.

Such further period is used only when the user fails to switch off the dryer at the normal end of a drying cycle.

If such further period of tumbling comes into use, an audible warning may be emitted at spaced intervals during the period to warn a user that the dryer is in the further period and that the cycle should be stopped and the articles removed.

Claims (7)

1. A tumbler dryer having a drum for receiving articles to be dried and mounted for rotation about a horizontal axis has a sensor located in the curved wall of the drum, the sensor being adapted to contact, at least periodically, articles in the drum.

2. A tumbler dryer as claimed in claim 1 in which the drum has a series of spaced vanes extending into the interior of the drum and in which the sensor is located in the curved wall of the drum between two adjacent vanes.

3. A tumbler dryer as claimed in claim 2 in which the sensor is located midway between adjacent vanes.

4. A tumbler dryer as claimed in any one of claims 1-3 in which the location of the sensor is closer to that end of the drum through which air from the drum exits than to the other end of the drum.

5. A tumbler dryer as claimed in any one of the preceding claims in which the sensor comprises a shallow cup shaped member whose outer surface is free from surface imperfections and a holder of electrically insulating material by which the cup shaped member is mounted in the wall of the drum.

6. A tumbler dryer as claimed in claim 5 in which the holder has one face adapted to conform to the contour of the wall of the drum at the location of the sensor.

7. A tumbler dryer as claimed in claim 6 in which the holder has another face adapted to conform to the contour of the cup shaped member to receive the latter in mating engagement.