Apparatus for routing a flexible circuit

Abstract: A portable electronic apparatus is disclosed. The apparatus has first and second portions arranged to be movable relative to each other. Electrical connection between the portions is effected through use of a flexible electrical connector. The route of the connector between the two portions is impeded by an obstacle so that in a first configuration, the connector is constrained to follow a first route, and in a second configuration, the connector is constrained to follow a second, different, route.

Description: This invention relates to an apparatus for electrically connecting a number of relatively movable parts using a flexible printed circuit. It finds particular utility in folding electronic apparatus such as personal organisers, laptop computers or mobile telephones. It is desirable to be able to manufacture a number of portable electrical devices such that they can be folded into a relatively flat, minimal volume configuration when not in use, and unfolded, possibly to reveal further functional parts, when in use. As an example, it is convenient for a user of a portable telephone to be able to carry it unobtrusively about his person. However, small telephones can suffer from problems with smaller displays, smaller keypads, and reduced distance between loudspeaker and microphone which can adversely affect audio quality in each direction of communication. However, if a folding configuration is adopted for the telephone, a larger surface area can be made available for a given volume, when compared to a non-folding configuration. This mitigates the problems referred to above. For instance, a keypad and display can be concealed inside the folded telephone, to be revealed when the telephone is unfolded. However, a problem with foldable electronic devices is how to electrically connect the two or more sections to each other. Known solutions have used wires and cables, either individually or in the form of ribbon cable, to connect the sections. However, such wires can be too bulky and inflexible to be used in today's miniature devices. The preferred method of connection now utilises a flexible connector, such as a flexible printed circuit board (PCB) to provide electrical connection. Flexible PCBs consist of one or more insulating substrates onto which one or more layers of conductive tracks are printed, with the layers of conductive tracks being insulated from each other by respective layers of the substrate material. A problem with such an arrangement, however, arises over the lifetime of the apparatus in which it is incorporated. A laptop computer, or a foldable telephone is generally designed to have a life-span of several years. As part of the life calculations for such a device, a certain number of folding and unfolding operations are required. It is not unusual for the number of such operations to be in the range of hundreds of thousands to greater than a million (100,000 → >1,000,000). Such a large number of iterations places a great deal of stress on the moving parts of the folding apparatus and can result in malfunction before the specified number of operations has been reached. Figures 1a and 1b shows the simplest possible method of using a flexible PCB to connect two halves of a foldable device, such as a telephone. In this case, rigid PCB 110 in a first half of the telephone 100 is connected to rigid PCB 120 in a second half of the telephone 100 by flexible PCB 130. The flexible PCB 130 passes through the hinge mechanism 140 holding the two halves of the telephone together. As the telephone is opened, as shown in Figure 1b, the flexible PCB moves through a large angle (generally in the range 0 - 180°). As the telephone is opened and closed repeatedly over many such cycles, the cumulative stress on the flexible PCB can cause damage to the conductive tracks. Also, this technique requires a large ungathered surplus of flexible PCB to be contained within the hinge mechanism in the closed position. This increases the chances of the flexible PCB 'kinking', and so damaging the connections it carries. It also requires the internal dimensions of the hinge mechanism to be larger than would otherwise be required in order to accommodate the excess flexible PCB. The apparatus shown at Figure 1 is a rather simplistic view of how such interconnection may be achieved in practice. The hinge mechanism is generally more complicated, and may incorporate such additional elements as self-opening mechanisms, locking mechanisms or damping mechanisms. All these other elements make the passage of the flexible PCB through the hinge significantly more complicated. One way of overcoming such difficulties is disclosed in European patent application EP0961370. This patent application describes a flexible connection between two halves of a telephone which requires the flexible PCB to perform a helical twist along its length. There is a possibility, in implementing such a system, that the flexible PCB is able to chafe against itself inside the hinge mechanism. Such chafing is then liable to adversely affect the electrical connection between the two halves of the telephone. US5027394 discloses a folding type of telephone apparatus comprising a first housing and a second housing connected by a hinge. The electronic components and printed circuit boards of the housings are connected by an electrical connecting member which is wound at least two times around a shaft of the hinge. US5681176 discloses a hinge connector including a pair of tubular members formed with hollow portions. The tubular members are coupled with each other so as to be turnable relative to each other. A flexible connector is turned and arranged in the hollow portions of the tubular members. US5390075 discloses an electronic apparatus which includes two portions that are electrically connected by a flexible cable. The flexible cable passes through a movable member intermediate the two portions, and engages the member during movement of one/both of the two portions to assist in the member's rotation. According to a first aspect of the present invention, there is provided a portable electronic apparatus comprising first and second portions, which are arranged such that the two portions are relatively rotatable between a first configuration and a second configuration, and are electrically connected by a flexible electrical connector, wherein the route of the connector between the two portions is defined by an obstacle, such that in the first configuration, the connector is constrained to follow a first route, and in the second configuration, the connector is constrained to follow a second, different, route; wherein the obstacle is provided by a plurality of projections arranged parallel to the axis of rotation and one of the plurality of projections ceases to play a part in the route of the connector at a given relative position of the first and second portions. An advantage of this invention is the provision of a means of reliable electrical interconnection between two parts of an apparatus which are movable in relation to each other. Another advantage of this invention is that the stress and strain to which the flexible connector is subjected throughout the opening and closing operations of the portable apparatus are kept at acceptable, determinable levels. This is achieved by routing the connector through the hinge in such a way that the connector follows a defined route, which alters as the configuration of the apparatus alters, and maintains a substantially constant length for all relative positions of the apparatus. The constant length route is achieved through careful selection of a series of obstacles which act to guide the connector on a defined routed through the hinge. The positions and sizes of the obstacles are carefully chosen so that the route taken by the connector does not alter its length significantly in moving from a fully open to a fully closed configuration. An embodiment of the invention guides the connector around a series of projections attached to a plate arranged so that the plate rotates in accordance with the position of the hinge. In this way, the exact route taken by the flexible connector varies in relation to the relative position of the parts of the foldable apparatus. The plate may be made to move in relation to the hinge position by attaching it to one portion of the apparatus. An embodiment of the invention employs three cylindrical projections disposed across the diameter of a circular plate, and arranged to extend longitudinally in a direction parallel to the axis of rotation of the two portions. The connector is routed through the projections such that in one extreme configuration, the connector contacts opposing sides of adjacent projections. Conveniently, the projections are arranged to be disposed within a spool which may be fitted into the hinge mechanism of the apparatus. At one extreme of movement of the two parts, all projections play a part in forming the route followed by the flexible connector. At the other extreme of movement, one of the projections plays no part in forming the route. Consequently, at some given point in the range of possible relative positions of the two portions, one of the projections ceases to be involved in forming the route. An advantage of embodiments of the invention is that the route taken by the connector is repeatable and predictable. That is, for a given position of the first portion relative to the second portion, the route of the connector can be determined. It is found that flexible connectors have a minimum bend radius, which if violated increases the likelihood of damage to the conductive tracks, which in turn compromises the electrical connection between the sections of the apparatus. An aspect of this invention is the routing of the flexible connector via an obstacle in such a way that the minimum bend radius is not reached, thus mitigating possible damage to the connector. Advantageously, the flexible connector may be in the form of a flexible printed circuit board, which may be manufactured by one of a number of known processes. A preferred embodiment of the apparatus is a portable telephone, particularly a foldable portable telephone. Another embodiment has the first portion accommodating a display, and the second portion accommodating a keyboard. For a better understanding of the present invention, and to understand how the same may be brought into effect, the invention will now be described, by way of example only, with reference to the appended drawings in which: Figure 1 shows a prior art solution to the problem of electrically connecting hinged components of a portable electronic device; Figure 2 shows an exploded profile view of a hinge component according to an embodiment of the present invention; Figure 3 shows a profile view of a hinge component according to an embodiment of the present invention; Figures 4a-c show profile views of the hinge component of Figures 2 and 3 in various positions between open and closed positions of the portable electronic apparatus; and Figures 5a-c show plan views of the hinge component of in equivalent positions to those shown in Figures 4a-c. Figure 2 shows an exploded view of a spool 200 which forms part of the hinge mechanism of a foldable portable electronic device, such as a mobile telephone. The spool 200 comprises two interlocking portions. Both portions are flat discs having one or more spindles and apertures. Both discs are manufactured from a suitable plastics material. The first portion 210 has a spindle 220 extending from the disc surface. The spindle is circular in cross section and is concentric with the disc. The first portion 210 also has two apertures 245, 255 disposed one each side of the central spindle, towards the outer perimeter of the disc. The apertures and the central spindle 220 thus lie on a diameter of the disc. The second portion 230 may be considered to be constructed as an inverse of the first portion in that it has an aperture 225 positioned concentric with the disc. It also has two spindles 240, 250 disposed one each side of the central aperture 225, towards the outer perimeter of the disc. The aperture and the spindles thus lie on a diameter of the disc. The correspondence between apertures on one disc and spindles on the other provides for a mating connection between the two discs. Each spindle 220, 240, 250 is shaped so as to provide a firm frictional fit with its respective corresponding aperture 225, 245, 255 in the other portion of the spool 200. In the particular embodiment shown, all spindles are equally dimensioned, and adjacent spindles are equidistant from each other. However, other configurations are possible which would operate similarly. Figure 3 shows the spool 200 when the first and second portions 210, 230 are mated together. The axis of rotation of the hinge of the foldable apparatus is co-axial with the spindle 220 of the first portion of the spool. That is to say that the spool rotates about its central axis. The spool is positioned in the hinge of the apparatus so that the spool is fixed relative to one movable part of the foldable apparatus, and rotates with the hinge axis relative to another movable part of the apparatus. Figure 2 shows the passage through the spool 200 of the flexible connector 300. In this instance, the flexible connector is a flexible printed circuit board (PCB) comprising one or more conductive signal tracks, on one or more layers, printed onto one or more insulating substrates. The flexible PCB may be a unitary element which accommodates components in each part of the foldable apparatus, or alternatively, each part of the apparatus may have its own separate PCB, which may be flexible or rigid, which is connected to the other by a length of flexible PCB. PCB 300 is first guided past fixed spindle 260. Spindle 260 is fixed in position in one movable part of the apparatus, and so the spool moves relative to spindle 260. The spindle 260 acts to ensure that the PCB enters the spool at a defined orientation, regardless of the rotational position of the spool. Figure 2 shows the position of the spool when the two parts of the foldable apparatus are positioned at approximately 45° to each other. The PCB is guided around the three spindles of the spool such that it makes a pass around spindle 240 in an anti-clockwise direction; it then makes a pass around the central spindle 220 in a clockwise direction; and then makes a pass around the final spindle 250 in an anti-clockwise direction before emerging from the spool. As the connector passes through the spool, it is merely guided around each projection before either being guided around another, or exiting from the spool altogether. Figures 4a-c show perspective views of the spool as it is when the apparatus is in (a) the closed position, (b) an intermediate position and (c) the fully open position. In each view, only the lower portion 230 of the spool is shown; the top portion 210 has been removed for clarity, so that the route of the flexible PCB 300 can be followed through the spool. In Figure 4a, it can be seen that the PCB 300, passes at least part of the way around each of the three spindles 240, 250 and 220 (not shown), before exiting the spool. As the apparatus comprising the spool is opened, to the intermediate position shown in Figure 4b, spindle 240 plays no further part in guiding the PCB through the spool, and its route is determined solely by spindles 220 and 250. As the apparatus is opened further to the fully open position shown in Figure 4c, the PCB makes almost a complete circuit of the central spindle 220, before passing around spindle 250 to exit the spool. Figures 4a-c show the route taken by the PCB at three distinct points in the complete range of movement of the apparatus, but it is simple to envisage the points intermediate to those shown. The configuration chosen for the spool 200 is inspired by the realisation that in order to minimise stress, strain, fatigue and kinking of the flexible PCB during its passage through the hinge of a foldable electronic apparatus it is desirable, amongst other factors, to: seek to exercise some degree of control over its route through the hinge; configure the route taken such that the connector does not experience any bends smaller than the minimum bend radius; attempt to ensure that stretching of the PCB is maintained within predefined limits; and attempt to reduce friction (both against other parts and itself). The embodiment so far described addresses these issues by: arranging the connector's route such that it generally follows a consistent defined path for relative positions of the foldable apparatus; guiding the connector through the spool around spindles which have a radius which is larger than the minimum bend radius; and configuring the spool such that the path followed by the PCB is substantially the same length for any given position of the foldable apparatus. Figures 5a-c correspond to the position of the apparatus shown in Figures 4a-c, but are shown in plan view for ease of understanding. Figure 5a shows the position of the spool with the apparatus in the closed configuration. The points marked X and Y are the entry and exit points respectively of the spool. The length of PCB between these points is the length which requires some form of management so that the possibility of it incurring damage, in any of the ways so far mentioned, is kept to a minimum. As the spool moves through its entire range of angles between the positions shown in Figures 5a and 5c, it is found in practice that the length of the route between points X and Y only varies by a small amount. Such a small variation helps to minimise the frictional forces experienced by the PCB throughout its lifetime, and also yields the result that on the one hand, there is not a large amount of slack PCB occupying the space in the hinge where it could be damaged, and on the other hand, that the PCB is not subjected to any great strain during movement of the apparatus between open and closed positions. In the light of the foregoing description, it will be clear to the skilled man that various modifications may be made within the scope of the invention. In particular, an embodiment has been described which shows a folding telephone. The skilled man will realise that the invention can be equally applied to any apparatus which requires electrical connection between two or more components having a rotational connection. For instance, the invention could be used to facilitate connection between the display portion of a laptop computer and the keyboard section, or the viewfinder of a digital camera and the lens section. The spool for routing the connector may be made to any dimension whilst maintaining the general configuration described previously. In this way, the spool can be adapted to route a connector having a large number of individual conductive tracks, in which case the projections about which the connector is guided may be made longer. The spool may be scaled up or down in dimension to suit a particular apparatus and/or connector material.

Claims: A portable electronic apparatus comprising first and second portions, which are arranged such that the two portions are relatively rotatable between a first configuration and a second configuration, and are electrically connected by a flexible electrical connector (300), wherein the route of the connector (300) between the two portions is defined by an obstacle (200), such that in the first configuration, the connector (300) is constrained to follow a first route, and in the second configuration, the connector (300) is constrained to follow a second, different, route; wherein the obstacle (200) is provided by a plurality of projections (220, 240, 250) arranged substantially parallel to the axis of rotation and one of the plurality of projections (220, 240, 250) ceases to play a part in the route of the connector (300) at a given relative position of the first and second portions. A portable electronic apparatus as claimed in claim 1 wherein the first and second configurations represent extremes of movement of the two portions of the apparatus. A portable electronic apparatus as claimed in claim 1 or 2 wherein the first and second portions are mechanically connected along an axis of rotation. A portable electronic apparatus as claimed in claim 3 wherein the axis of rotation is provided by a hinge. A portable electronic apparatus as claimed in any one of the preceding claims wherein the flexible electrical connector (300) is a flexible printed circuit board (PCB). A portable electronic apparatus as claimed in any one of the preceding claims wherein the obstacle (200) is arranged to move with one of the portions. A portable electronic apparatus as claimed in any one of the preceding claims wherein the obstacle (200) is incorporated into a spool (200) mounted coaxially with the axis of rotation. A portable electronic apparatus as claimed in any one of the preceding claims wherein the projections (220, 240, 250) are cylindrical in shape. A portable electronic apparatus as claimed in claim 8 wherein the projections (220, 240, 250) are substantially dimensionally similar. A portable electronic apparatus as claimed in any one of the preceding claims wherein the projections (220, 240, 250) are arranged to have a radius larger than the minimum bend radius of the flexible connector (300). A portable electronic apparatus as claimed in any one of the preceding claims wherein the portable electronic apparatus is a portable telephone. A portable electronic telephone as claimed in daim 11 wherein the telephone is a foldable telephone and the first and second configurations correspond to relatively open and closed configurations of the telephone. A portable electronic apparatus as claimed in any of the preceding claims wherein the first portion comprises a keyboard and the second portion comprises a display. A portable electronic apparatus as claimed in any one of the preceding claims wherein the plurality of projections (220, 240, 250) are arranged collinearly. A portable electronic apparatus as claimed in any one of the preceding claims wherein the number of projections (220, 240, 250) is three.

Inventors: KOCH-OSBORNE ANDREW, KOCH-OSBORNE, ANDREW
Applicants: NOKIA CORP, NOKIA CORPORATION
Application year: 2001
Main classification: H01R35
IPC codes: H01R35, H05K1, H05K7, G06F1