GB2107006A - A unidirectional coupling for the drive of a sequential display unit - Google Patents

Abstract

A unidirectional coupling for transmitting rotational movement in one direction from a driving member (53) to a driven member (55) rotatable about the same axis is described in which the driving member (53), a belt drive pulley, is mounted so as to be rotatable and axially displaceable relative to the driven member (55). The driving member when rotated in one direction adopts one axial position as shown in which it is freely rotatable relative to the driven member, and displacement means comprising a helical groove (64) and a dog (63) are provided for axially displacing the driving member (53) upon rotation thereof to another axial position in which cooperating engagement means in the form of pins (66 and 67) on the driving and driven member communicate the rotation of the driving member to the driven member. Two such couplings are used in a sequential display unit to allow reversal of the drive whilst maintaining the necessary tension in a display strip. <IMAGE>

Description

SPECIFICATION A unidirectional coupling This invention relates to a unidirectional coupling for transmitting rotational movement in one direction from a driving member to a driven member rotatable about the same axis.

It is an object of the invention to provide a compact and inexpensive, yet effective and reliable unidirectional coupling for the transmission of rotational movement.

Accordingly, in its broadest aspect, the invention provides a unidirectional coupling for transmitting rotational movement in one direction from a driving member to a driven member rotatable about the same axis, in which coupling the driving member is mounted so as to be rotatable and axially displaceable relative to the driven member, the driving member when rotated in one direction adopts one axial position in which it is freely rotatable relative to the driven member, and displacement means are provided for axially displacing the driving member upon rotation thereof in the other direction from its one axial position to another axial position in which cooperating engagement means on the driving and driven member communicate the rotation of the driving member to the driven member.

Preferably, the displacement means comprises a helical groove formed in a sleeve on which the driving member is rotatably mounted and a radially projecting dog carried by the driving member and engaging in the groove, the grooved sleeve being mounted for rotation about the common axis of rotation and braking means being provided to permit relative rotation of the sleeve and driven member upon a change in the direction of rotation of the driving member, whereby the dog travels along the groove and the driving member is axially displaced relative to the driven member.

Conveniently, the braking means comprise a pressure pad acting on the grooved sleeve.

In one form of the invention, the co-operating engagement means comprise an axially projecting part on the driving member and a radially projecting part on the driven member.

The invention finds particular application in a drive for driving a strip of frames in a sequential display unit in which individual frames are displayed in turn in a common display area.

Our prior Patent No. 1319771 describes a sequential display unit which comprises a rectangular casing having a display window past which is driven a strip of frames which are to be individually displayed while spanning across the window. The unit has a sensor which responds to registration of each frame with the window by stopping the drive of the strip of frames, starting a timer and switching on a source of illumination within the casing behind the strip of frames so as to illuminate the frame stopped in the window.

After the elapse of a predetermined display period, the timer extinguishes the source of illumination and restarts the drive to bring the next frame into the window. The strip of frames is wound past the display window between a pair of spools and the unit is provided with means for sensing when the final frame has been displayed in either direction of movement and for controlling the drive to reverse the direction of movement imparted to the following display of the final frame.

In the known display unit, the spools are rotated, in order to move the strip of frames past the display window, by an electric motor adapted to run in either direction. The motor drives a differential unit having two output pulleys each of which is coupled by a respective belt to a pulley rigidly attached to a drive spindle of a respective one of the spools. The spool is provided with a one-way retarder in the form of a friction brake attached to a one-way clutch which selects the direction of rotation in which the brake acts. The retarder provides resistance to rotation of its associated spool in the direction of rotation applying when the strip of frames is being unwound from that spool and thereby tensions the strip.The differential unit of the drive serves to compensate for the variation in surface speed of the strip over the spools as the strip is wound from one spool to the other.

Whilst the drive of the known display unit operates satisfactorily, it is relatively complicated and expensive to produce. Moreover, the drive occupies considerable space in the casing which, although not unduly inconvenient in the case of a large display unit, presents problems in the construction of small display units.

It is a particular object of the present invention to provide a compact and inexpensive drive for a display unit which is of relatively simple construction, yet provides for the necessary tensioning of the strip during winding and is relatively insensitive to external vibrations.

Accordingly, in this aspect of the present invention, there is provided a drive for a sequential display unit in which a strip of frames is supported on a pair of spools for movement of the strip in the direction of its length past a window of the display unit, the drive including a driving wheel for rotating an associated one of the spools in one direction of rotation of the driving wheel and means for rotating the driving wheel, in which drive the driving wheel is mounted so as to be rotatable about the same axis as, and axially displaceable relative to, a driven member of the spool, the driving wheel when rotated in one direction adopting one axial position in which it is freely rotatable relative to the spool, and displacement means are provided for axially displacing the driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which co-operating engagement means on the driving wheel and the driven member of the spool communicate the rotation of the driving wheel to the spool.

According to another aspect of the present invention, there is provided a sequential display unit including a casing formed with a display window, a pair of spools inside the casing for supporting a strip of frames for movement of the strip in the direction of its length past the window and a drive for rotating the spools to move the strip frame by frame past the window, the drive including a driving wheel for rotating an associated one of the spools in one direction of the driving wheel and means for rotating the driving wheel, in which drive the driving wheel is mounted so as to be rotatable about the same axis as, and axially displaceable relative to, a driven member of the spool, the driving wheel when rotated in one direction adopting one axial position in which it is freely rotatable relative to the spool, and displacement means are provided for axially displacing the driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which cooperating engagement means on the driving wheel and the driven member of the spool communicate the rotation of the driving wheel to the spool.

Preferably, the displacement means comprises a helical groove formed in a sleeve on which the driving wheel is rotatably mounted and a radially projecting dog carried by the driving wheel and engaging in the groove, the grooved sleeve being mounted for rotation about the said axis of rotation and braking means being provided to permit relative rotation of the sleeve and driving wheel upon a change in the direction of rotation of the driving wheel, whereby the dog travels along the groove and the driving member is axially displaced relative to the driven member.

Conveniently, the braking means comprise a pressure pad.

In one embodiment, the co-operating engagement means comprise an axially projecting part on the driving wheel and a radially projecting part on the spool.

The means for rotating the driving wheel may conveniently comprise a belt and pulley transmission and an electric motor.

Preferably, the strip of frames passes round a pair of guide rollers mounted adjacent opposite edges of the display window and a resiliently biased pressure pad is provided to press the strip against each guide roller so as to tension the portion of the strip visible in the window and conveniently, a resiliently biased spool pressure pad is associated with each spool to define a gap of a predetermined size between the portion of the strip wound on the spool and the pad.Each of the spool pressure pads may be provided on a respective arm fixedly mounted on a rotatable support member on which is also fixedly carried a further arm, the two further arms being connected together by spring means such that when the strip is wound from one spool on to the other causing the pressure pad associated with the one spool to move outwardly therefrom, the pressure pad associated with the other spool is moved inwardly toward said other spool to reduce the predetermined gap.

In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a sequential display unit; FIGURE 2 is a diagrammatic vertical sectional view of the display unit of Figure 1; FIGURE 3 is a fragmentary plan view of a support structure of a strip of frames in the display unit; FIGURE 4 is a side view of the support structure of Figure 3; FIGURES 5 and 6 illustrate diagrammatically a drive embodying the invention incorporated in the sequential display unit of Figure 1; and FIGURE 7 illustrates resilient biasing means for ensuring that the strip is uniformly wound onto and off the spool.

Referring to Figures 1 and 2, a sequential display unit comprises an upstanding shallow rectangular casing 1 formed with a rectangular window opening 2 in one of its larger vertical faces, hereinafter called the display face 3. The window opening 2 is fitted with a pane 4 of transparent plastics material, such as the polymethyl methacrylate sheet material known commercially under the Trade Mark "Perspex".

Mounted inside the casing 1 are two spools 5 and 6 arranged for rotation about vertically aligned horizontal axes, the first spool 5 being disposed at the top of the casing 1 and the second spool 6 being disposed at the bottom of the casing.

The spools 5 and 6 are rotatable in order to move a strip 7 of frames received on the spools past the window opening 2 in either direction. The construction of the strip 7 is shown in detail in Figures 3 and 4, where it can be seen that the strip comprises a transparent web 21 provided on one surface along a central longitudinal region thereof with a series of transparent pockets 22 for receiving a series of individual posters to be displayed in sequence in the window opening 2.

Each poster is of substantially the same size as the window opening 2 so that it can be registered therewith.

A marginal portion 33 (Figure 3) of one edge of the web 21 is provided adjacent each end of the web with a single opaque area (not shown) denoting the end of the strip 7. First and second photo-electric sensors 12 and 13 (Figure 2) are respectively associated with the first and second spools 5 and 6, each such sensor being arranged to detect a respective one of the opaque areas denoting the ends of the strip 7. Each of the sensors 12, 1 3 is disposed in front of the strip 7 opposite a respective low power light source 14, 1 5 arranged behind the strip so that it normally illuminates a light sensitive face of the sensor through the transparent marginal portion 23 of the web 21.

A marginal portion 24 of the other edge of the web 21 is provided with a series of opaque areas 25 associated with the individual pockets 22 of the strip 7. One opaque area 25 is provided for each pocket and it is precisely positioned so that it comes opposite the light-sensitive face of a third photo-electric sensor 1 6 when the associated pocket registers with the display window. The third sensor 1 6 is disposed in front of the strip 7 and a low power light source 17 is arranged behind the strip so that it normally illuminates the sensor 1 6 through the marginal portion 24 of the web 21.

A poster in a pocket 22 registering with the display window is illuminated from behind by a source of illumination 18, shown schematically in Figure 2 and comprising, for example, one or more fluorescent tubes shining through a diffuser plate 1 9. A reflector plate may be disposed behind the fluorescent tubes to ensure that the bulk of the light is evenly distributed over the area of the poster in the display window.

Electrical control circuitry 20 is housed in the casing 1 and comprises a first control section concerned with stopping the movement of the strip 7 when each pocket of the strip registers with the window, and a second control section for controlling the direction of movement of the strip 7. The first control section is connected to sensor 1 6 and operates, in response to darkening of sensor 1 6, to stop the movement of the strip, starting a timer, and switch on the illumination source 1 8 to illuminate the poster stopped in the display window. The second control section is connected to the sensors 1 2 and 13 and operates, on darkening of either sensor, to reverse the direction of movement of the strip 7.

Figures 3 and 4 illustrate a support structure of the strip 7 in more detail and show each pocket 22 as being formed by a transparent rectangular sheet 26 attached to the web 21 by hinge strips 27 extending transversely of the web 21.

Referring particularly to Figure 4, each hinge strip 27 has a longitudinal central portion 28 bonded to the web 21 in a gap between two successive pockets 22 and respective longitudinal edge portions 29 bonded to the outer surfaces of the respective sheets 22 at transversely extending edges 30 of the sheets 26 to attach the sheets to the web 21. The transversely extending edges 30 of the sheets 26 are folded over to form flaps 31 to locate the corresponding edges of a poster introduced into a pocket 22 between a free longitudinally extending edge 32 of the sheet 26 and the web 21. The edges 32 of the sheets 26 are provided with small dihedral tags 33 which extend into the pocket and retain the corresponding edges of the poster.

The web 21 and the pocket-forming sheets 26 are made of transparent polyester film of different grades and the hinge strips 27 are in the form of lengths of transparent double-sided adhesive tape.

In one embodiment the web 21 is provided with ten pockets 22 each for receiving paper posters or other printed sheets of A4 size.

In use of the described strip 7 in the display unit, the manner in which the pocket-forming sheets 26 are attached to the web 21 permits limited movement of the sheets 26 relative to the web 21 in the length direction of the web during winding of the strip onto the spools 5 and 6, thereby avoiding damage to the posters and absorbing variations in the surface speed of the strip 7 over the spools.

The use of a web 21 provided with pockets 22 means that relatively cheap individual paper posters and like printed sheets may be used in the display unit, so reducing the initial cost of the strip 7 and enabling the selection and sequence of the matter to be displayed to be readily and inexpensively varied.

Referring now to Figures 5 to 7, the upper spool 5 of the display unit is housed in an upper spool compartment 40 defined at the top of the casing 1 by a horizontal partition 41 extending from a rear wall 42 of the casing and terminating short of a front wall 43 of the casing. The spool has flanges 44 at its ends and a central smaller diameter portion 45 on which the strip 7 is received between the flanges. Within the compartment 40 there is also disposed a guide roller 46 around which the strip 7 passes just prior to its appearance in, or just after its disappearance from, the window 2.

The lower spool 6 is of identical form to the spool 5 and similarly housed in a lower spool compartment 47, defined at the bottom of the casing 1 by a horizontal partition 47'. A second guide roller 46' is provided in the lower spool compartment 47.

The sequential display unit described above incorporates a drive embodying the invention.

As shown in Figures 5 and 6, the drive comprises a belt and pulley transmission in which spindle 48 of an electric motor (not shown) is drivably connected via a belt 49 to an idling wheel 50.

Driving wheels 52 and 53 are mounted so as to be rotatable and axially displaceable relative to spools 5 and 6 respectively and are coupled together via a non-slip belt 54 which is trained round pulleys 51 and 56. The smaller pulley 51 is fixedly mounted on the idling wheel 50.

Figure 6 shows in detail the mounting of one driving wheel 53.

The spool 6 is fixedly mounted on a spindle 55 extending axially through the spool and through side walls 56 of the lower spool compartment 47.

The spindle 6 is rotatably supported in the side walls 56 by bearings 57.

A reduced diameter extension 58 of the spindle 55 carries a sleeve 60 which is rotatably mounted on the extension 58, such that a radially extending flange 61 of the sleeve 60 is adjacent the end of the extension 58. The sleeve 60 is retained on the extension 58 by means of a circlip 62 and a washer 62' abutting the flange 61. The driving wheel 53 is rotatably mounted on the sleeve 60 and a radially inwardly projecting dog 63 screwed into a threaded radial bore 63' of the driving wheel 53 engages in a helical groove 64 formed in the outer surface of the sleeve 60. In the illustrated embodiment, the groove 64 is formed by a 70 helix and extends for one turn of the helix.

The pitch of the helix can however be selected, as required in a particular case, in dependence upon the diameter of sleeve 60 and the desired axial displacement of the driving wheel 53. A pressure pad 65 abuts the flange 61 of the sleeve 60 to form a braking means. An axially projecting pin 66 provided on the driving wheel 53 extending toward the spindle 55 and a radially projecting pin 67 eccentrically fixedly mounted in the spindle 55 form co-operating engagement means which, as will be described hereinafter, allow the rotation of the driving wheel to be transmitted to the spindle 55. The other driving wheel 52 is similarly mounted but the grooved sleeve associated therewith (not shown) is formed with an oppositely handed helix.

As shown diagrammatically in Figure 7, resiliently biased felts pads 68 are mounted within the spool compartment spaced from the central portion 45 of the spools on the side remote from the portions 41 and 48 to define a restricted but resiliently variable gap 69 through which the strip 7 passes as it is wound onto or off a spool.

As can be seen from Figure 7, each felt pad 68 is mounted on an arm 70 rigidly fixed to a support member 71 rotatably mounted in the spool compartment. A further arm 72 is also rigidly mounted on each support member 71 so as to define a predetermined angle between the two arms. The two further arms 71 are connected together by a spring 73 which provides the resilient biasing ensuring that as one felt pad 68 is moved outwardly from the associated spool as the strip is wound onto that spool the other felt pad 68 is moved toward the spool from which the strip is being wound to reduce the associated gap 69.

As mentioned above, the second control section of the electrical control circuitry 20 controls the direction of motion of the strip 7.

Thus, when the strip 7 is to be wound from the upper spool 5 to the lower spool 6, the motor spindle 48 is rotated in a clockwise direction as seen in Figure 5, which rotation is transmitted via the belt 49 and the idling wheel 50 to the smaller pulley 51 causing the driving wheels 52 and 53 to rotate in the clockwise direction.

Rotation of the driving wheel 53 in the clockwise direction causes the projecting dog 63 carried by the driving wheel 53 to move along the helical groove 64 toward the spindle 55 displacing the driving wheel 53 from an axial position in which it is freely rotatable relative to the spindle 45 to an axial position in which the axially projecting part 66 comes into engagement with the radially projecting part 67 communicating the rotation of the driving wheel to the spindle 45.At the same time rotation of the driving wheel 52 in the clockwise direction causes the projecting dog carried by the driving wheel 52 to move along the helical groove of the associated sleeve away from the spindle of the spool 5 bringing the driving wheel into an axial position in which it is displaced from the spindle and in which position the braking means in the form of the pressure pad 65 permit relative rotation of associated sleeve and the spindle of the upper spool 5 such that the spindle of the upper spool 5 is freely rotatable allowing the strip to be wound onto the spindle 45 of the lower spool 6 driven by the driving wheel 53.

When the strip is to be wound from the lower spool 6 onto the upper spool 5, the motor spindle 48 is rotated in an anti-clockwise direction causing projecting dog of the driving wheel 52 to move along the helical groove if the associated sleeve toward the spindle of the upper spool 5 bringing the associated radially projecting part and axially projecting part into engagement causing rotation of the driving wheel 52 to be communicated to the spindle of the upper spool while the projecting dog 63 of the driving wheel 52 moves along the helical groove 64 away from the spindle 45 causing the driving wheel 53 to be axially displaced from the spindle 45 and allowing, by means of the pressure pad 65, relative rotation of the sleeve 60 and the spindle 45 such that the spindle is freely rotatable to allow the strip to be wound from the lower spool 6 onto the spindle of the upper spools driven by the driving wheel 52.

The positioning of the guide rollers 46 and 47 and pressure pads (not shown) pressing the strip against the guide rollers ensures that the portion of the strip 7 in the window is tensioned and remains flat when movement of the spool is stopped to display a frame of the strip in the window.

Although the strip 7 described above is of compound construction and involves the use of separate posters mounted in pockets of a support structure, it is envisaged that the described driving apparatus may be employed with other lands of strip, such as directly printed plastics film.

Furthermore, while the driving apparatus embodying the invention has been described as being incorporated in a display unit employing photoelectric sensors, it will be appreciated that the apparatus can equally be employed in display units employing any other land of strip position sensors, for example magnetic sensing and sensing by electrical contact pins.

Whilst the spindle of each spool in the described embodiment of the invention constitutes the driven member of the spool which is rotatable about the same axis as the driving wheel, it is envisaged that the spindle could be mounted non-coaxially but parallel to the axis of the driving wheel and the spindle driven indirectly through gearing by a further driven member arranged coaxially of the driving wheel.

Claims (1)

1. A unidirectional coupling for transmitting rotational movement in one direction from a driving member to a driven member rotatable about the same axis, in which coupling the driving member is mounted so as to be rotatable and axially displaceable relative to the driven member, the driving member when rotated in one direction adopts one axial position in which it is freely rotatable relative to the driven member, and displacement means are provided for axially displacing the driving member upon rotation thereof in the other direction from its one axial position to another axial position in which cooperating engagement means on the driving and driven member communicate the rotation of the driving member to the driven member.

2. A unidirectional coupling according to claim 1, wherein the displacement means comprises a helical groove formed in a sleeve on which the driving member is rotatably mounted and a radially projecting dog carried by the driving member and engaging in the groove, the grooved sleeve being mounted for rotation about the common axis of rotation and braking means being provided to permit relative rotation of the sleeve and driven member upon a change in the direction of rotation of the driving member, whereby the dog travels along the groove and the driving member is axially displaced relative to the driven member.

3. A unidirectional coupling according to claim 2, wherein the braking means comprise a pressure pad acting on the grooved sleeve.

4. A unidirectional coupling according to claim 1,2 or 3, wherein the co-operating engagement means comprise an axially projecting part on the driving member and a radially projecting part on the driven member.

5. A drive for a sequential display unit in which a strip of frames is supported on a pair of spools for movement of the strip in the direction of its length past a window of the display unit, the drive including a driving wheel for rotating an associated one of the spools in one direction of rotation of the driving wheel and means for rotating the driving wheel, in which drive the driving wheel is mounted so as to be rotatable about the same axis as, and axially displaceable relative to, a driven member of the spool, the driving wheel when rotated in one direction adopting one axial position in which it is freely rotatable relative to the spool, and displacement means are provided for axially displacing the driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which co-operating engagement means on the driving wheel and the driven member of the spool communicate the rotation of the driving wheel to the spool.

6. A drive according to claim 5, wherein the displacement means comprise a helical groove formed in a sleeve onswhich the driving wheel is rotatably mounted and a radially projecting dog carried by the driving wheel and engaging in the groove, the grooved sleeve being mounted for rotation about the said axis of rotation and braking means being provided to permit relative rotation of the sleeve and driving wheel upon a change in the direction of rotation of the driving wheel, whereby the dog travels along the groove and the driving member is axially displaced relative to the driven member.

7. A drive according to claim 6, wherein the braking means comprise a pressure pad acting on the grooved sleeve.

8. A drive according to claim 5, 6 or 7, wherein the co-operating means comprise an axially projecting part on the driving wheel and a radially projecting part on the spool.

9. A drive according to claim 5, 6, 7 or 8, wherein the means for rotating the driving wheel comprise a belt and pulley transmission and an electric motor.

10. A sequential display unit including a casing formed with a display window, a pair of spools inside the casing for supporting a strip of frames for movement of the strip in the direction of its length past the window and a drive for rotating the spools to move the strip frame by frame past the window, the drive including a driving wheel for rotating an associated one of the spools in one direction of the driving wheel means for rotating the driving wheel, in which drive the driving wheel is mounted so as to be rotatable about the same axis as, and axially displaceable relative to, a driven member of the spool, the driving wheel when rotated in one direction adopting one axial position in which it is freely rotatable relative to the spool, and displacement means are provided for axially displacing the driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which cooperating engagement means on the driving wheel and the driven member of the spool communicate the rotation of the driving wheel to the spool.

11. A sequential display unit according to claim 10, wherein the drive comprises a further driving wheel drivable by the means for rotating the driving wheel associated with the spool for rotating the other of the spools in a given direction of rotation of the further driving wheel opposite to the direction of the driving wheel associated with the one spool, the further driving wheel being mounted so as to be rotatable about the same axis as, and axially displaceable relative to the other spool, the further driving wheel when rotated in one direction opposite to the one direction of rotation of the driving wheel associated with the one spool adopting one axial position in which it is freely rotatable relative to the spool, and further displacement means are provided for axially displacing the further driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which cooperating engagement means on the further driving wheel and the other spool communicate the rotation of the further driving wheel to the other spool.

12. A sequential display unit according to claim 10 or 11, wherein the or each displacement means comprise a helical groove formed in a sleeve on which the driving wheel is rotatably mounted and a radially projecting dog carried by the driving wheel and engaging in the groove, the grooved sleeve being mounted for rotation about the said axis of rotation and braking means being provided to permit relative rotation of the sleeve and driving wheel upon a change in the direction of rotation of the driving wheel, whereby the dog travels along the groove and the driving member is axially displaced relative to the driven member.

13. A sequential display unit according to claim 12 wherein the or each braking means comprise a pressure pad acting on the grooved sleeve.

14. A sequential display unit according to claim 10, 11, 12 or 13, wherein the or each cooperating means comprise an axially projecting part on the driving wheel and a radially projecting part on the spool.

15. A sequential display unit according to any one of claims 10 to 14 wherein the rotating means comprises a belt and pulley transmission and an electric motor.

1 6. A sequential display unit according to any one of claims 10 to 1 5 wherein the strip of frames passes round a pair of guide rollers mounted adjacent opposite edges of the display window and a resiliently biased pressure pad is provided to press the strip against each guide roller so as to tension the portion of the strip visible in the window.

1 7. A sequential display unit according to any one of claims 10 to 1 6 wherein a resiliently biased spool pressure pad is associated with each spool to define a gap of a predetermined size between the portion of the strip wound on the spool and the pad.

18. A sequential display unit according to claim 1 7, wherein the or each of the two spool pressure pads is provided on a respective arm fixedly mounted on a rotatable support member on which is also fixedly carried a further arm, the two further arms being connected together by spring means such that when the strip is wound from one spool on to the other causing the pressure pad associated with the one spool to move outwardly therefrom, the pressure pad associated with the other spool is moved inwardly toward said other spool to reduce the predetermined gap.

19. A unidirectional coupling for transmitting rotational movement in a given direction from a driving member to a driven member rotatable about the same axis substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

20. A drive for a sequential display unit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

21. A sequential display unit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

22. Any novel feature or combination of features described herein.

New claims or amendments to claims filed on 13th July 1 982.

Superseded claims 1 and 10.

New or amended claims:

1. A unidirectional coupling for transmitting rotational movement in one direction from a driving member to a driven member rotatable about the same axis, in which coupling: the driving member is mounted so as to be rotatable and axially displaceable relative to the driven member, the driving member when rotated indefinitely in one direction adopts an axial position in which it is freely rotatable relative to the driven member, and displacement means are provided for axially displacing the driving member upon rotation thereof in the other direction from the said axial position to another axial position in which cooperating engagement means on the driving and driven member communicate the rotation of the driving member to the driven member.

1 0. A sequential display unit including a casing formed with a display window, a pair of spools inside the casing for supporting a strip of frames for movement of the strip in the direction of its length past the window and a drive for rotating the spools to move the strip frame by frame past the window, the drive including a driving wheel for rotating an associated one of the spools in one direction of the driving wheel and, means for rotating the driving wheel, in which drive the driving wheel is mounted so as to be rotatable about the same axis as, and axially displaceable relative to, a driven member of the spool, the driving wheel when rotated in one direction adopting one axial position in which it is freely rotatable relative to the spool, and displacement means are provided for axially displacing the driving wheel upon rotation thereof in the other direction from its one axial position to another axial position in which co-operating engagement means on the driving wheel and the driven member of the spool communicate the rotation of the driving wheel to the spool.