Patent Description:
Further, <CIT> discloses a friction type rotating shaft comprising a shell, a fixed shaft, a friction member and a rotating structural member. The friction member is fixed on the shell, arranged on the periphery of the fixed shaft in a sleeving manner and contained in an inner cavity of the shell. The friction type rotating shaft can realize positioning at any angle.

Further, <CIT> discloses a friction hinge apparatus using a clip-type torsion spring comprising a housing equipped with a slot in which a downward protrusion of multiple clip type flat springs is inserted. The slit is formed into a shape with a gradually increasing or decreasing thickness in the axial direction.

Further, <CIT> discloses a friction hinge capable of stably generating prescribed torque over long-term use, and capable of improving durability. The friction hinge has a shaft, a plurality of elastic friction rings, and a bearing member. The respective friction rings are formed as a structure for generating frictional force between contact surfaces with an outer peripheral surface by sandwiching the outer peripheral surface of the shaft by mutually opposing receiving part and pressing part and applying a pressing force to the pressing part by a first elastic part and a second elastic part.

Finally, <CIT> discloses a low torque friction hinge that comprises a first connecting plate and a second connecting plate respectively provided with a rotary connection side having a protruding member and a recess engaging with each other. A friction structure is provided between the protruding member and a recess wall of the recess, so as to provide resistance when the first connecting plate and the second connecting plate rotate relative to each other. A circular friction component is provided in the friction structure.

The accompanying drawings illustrate implementations of the concepts conveyed in the present document. Features of the illustrated implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings. Like reference numbers in the various drawings are used wherever feasible to indicate like elements. Further, the left-most numeral of each reference number conveys the FIG. and associated discussion where the reference number is first introduced. Where space permits, elements and their associated reference numbers are both shown on the drawing page for the reader's convenience. Otherwise, only the reference numbers are shown.

The present concepts relate to devices, such as computing devices employing variable resistance hinge assemblies that can rotationally secure first and second device portions relative to a hinge axis. The variable resistance hinge assemblies can define a range of orientations that the first and second portions can rotate through. For example, the range of orientations can be bounded by a closed orientation of zero degrees and an open orientation, such as <NUM> degrees. The variable resistance hinge assembly can provide increasing resistance as rotation continues in a given direction, such as from closed to open. When rotation switches direction, the variable resistance hinge can provide a lesser resistance that once again increases as rotation continues. In this way, the hinge may have high resistance when the device is fully opened (e.g., to keep the device from inadvertently closing) and when the device is fully closed (e.g., to keep the device from inadvertently opening) with low resistance when the device is partially open (e.g., to increase user accessibility by requiring less force to move the device between the open and closed orientations). These and other aspects are described below.

Introductory <FIG> collectively show an example device <NUM> that has first and second portions <NUM> and <NUM> that are rotatably secured together by variable resistance hinge assemblies <NUM>. In the illustrated implementation, two variable resistance hinge assemblies <NUM>(<NUM>) and <NUM>(<NUM>) are employed (e.g., one near each end (outer edges) of the device), but other implementations could employ a single variable resistance hinge assembly or more than two variable resistance hinge assemblies. In the illustrated configuration, the variable resistance hinge assemblies <NUM> define a center of the device from which the first and second portions extend.

The first portion <NUM> can extend from a hinge end <NUM> to a distal end <NUM>. The second portion <NUM> also can extend from a hinge end <NUM> to a distal end <NUM>. The first portion <NUM> can include first and second surfaces <NUM> and <NUM> and the second portion <NUM> can include first and second surfaces <NUM> and <NUM>.

The variable resistance hinge assemblies <NUM> can define the hinge axis (HA) around which the first and second portions <NUM> and <NUM> rotate. The variable resistance hinge assemblies <NUM> can also provide resistance to rotation around the hinge axis. The resistance to rotation can contribute to the first and second portions maintaining a specific orientation unless acted upon by a force, such as supplied by the user wanting to rotate the device portions to another orientation.

<FIG> shows the device <NUM> in a closed orientation with the first surfaces <NUM> and <NUM> of the first and second portions <NUM> and <NUM> positioned against one another. The variable resistance hinge assemblies <NUM> can provide a relatively low amount of resistance to rotation in an opening direction. <FIG> also shows a user <NUM> applying a small force (e.g., arrow F) to open the first and second portions <NUM> and <NUM>. <FIG> shows the first and second portions rotated to about a <NUM>-degree orientation where the variable resistance hinge assemblies can provide slightly more resistance to further rotation in the opening direction. To overcome the additional resistance, the force F imparted by the user is larger to keep opening the device. <FIG> shows the first and second portions further rotated to about a <NUM>-degree orientation, which in this implementation is approaching a fully open orientation. At this point, the variable resistance hinge assemblies <NUM> can provide greater resistance to further opening rotation so that the device maintains this orientation (e.g., does not continue to rotate in the opening direction) unless the user applies additional force. However, the variable resistance hinge assemblies can offer less resistance to rotation in the opposite direction (e.g., in the closing direction).

<FIG> shows the first and second portions <NUM> and <NUM> rotated in the opposite (e.g., closing) direction from the orientation of <FIG>. At this point, the variable resistance hinge assemblies <NUM> provide greater resistance to further rotation in the closing direction than they did in the open orientation of <FIG>. <FIG> shows the first and second portions rotated all the way back to the closed orientation. At this point, the variable resistance hinge assemblies provide relatively large resistance to further rotation in the closing direction while providing relatively low resistance to rotation in the opening direction as discussed relative to <FIG>.

Stated another way, the resistance to rotation provided by the variable resistance hinge assemblies <NUM> is increasing as the closing rotation progresses from the open orientation of <FIG> toward the closed orientation of <FIG>. Thus, torque T<NUM> that the user must input to overcome this resistance to rotation is increasing. Conversely, the resistance to rotation in the opposite direction (e.g., in the opening direction) is decreasing and thus the torque Ti the user must input to overcome the resistance to rotation to open is decreasing. Thus, the user will have a pleasant experience of being able to easily reopen the device, such as with one hand. Yet, as the device orientation progresses toward the fully open orientation, the increasing resistance can ensure that the device maintains the orientation that the user desires.

<FIG> show another example device 100A that can include variable resistance hinge assembly(s) <NUM>. In this case the first and second portions <NUM> and <NUM> are orientated close to a fully open orientation of the device. For example, the first and second portions can be oriented at approximately <NUM> degrees and the fully open orientation can be <NUM> degrees. At this point, the variable resistance hinge assembly <NUM> can provide relatively high resistance at <NUM> to further opening rotation around the hinge axis. This relatively high resistance to rotation can ensure that the device maintains this orientation and does not 'fall' further open. In contrast, if the user is done working on the device and want to close it, the variable resistance hinge assembly offers relatively low resistance at <NUM> to rotation in the closing direction.

<FIG> and <FIG> provide two form factors that can implement the present concepts. Other form factors are contemplated, such as various other computing devices, wearable devices, vehicles, etc. The discussion below introduces example component configurations for achieving the functionality described above, among other functionalities.

<FIG> collectively illustrate an example variable resistance hinge assembly 106B. <FIG> shows a perspective view of the variable resistance hinge assembly 106B. <FIG> shows a similar view, but with some components shown in ghost so that underlying components can be visualized. <FIG> are exploded perspective views. <FIG> is an elevational view of some components.

In this case, variable resistance hinge assembly 106B includes first portion arm <NUM>, second portion arm <NUM>, hinge shaft <NUM>, collar <NUM>, aperture <NUM>, aperture <NUM>, friction clips <NUM>, spacers <NUM>, aperture <NUM>, contact surface <NUM>, and contact surface <NUM>. In this example, ten friction clips <NUM> are utilized, but the use of any plural number of friction clips is contemplated. Also, in this implementation all of the friction clips have the same width W, but other configurations are contemplated. One such implementation is described below relative to <FIG>.

The first portion arm <NUM> can facilitate securing the variable resistance hinge assembly 106B to the first portion (<NUM>, <FIG>). Similarly, the second portion arm <NUM> can facilitate securing the variable resistance hinge assembly 106B to the second portion (<NUM>, <FIG>). The hinge shaft <NUM> can extend along the hinge axis. The collar <NUM> can be positioned on the hinge shaft <NUM> and can secure the hinge shaft to the first and second portion arms <NUM> and <NUM>, such as with fasteners (not shown) through aligned holes in the collar <NUM> and the first and second portions (shown, but not specifically designated). In this configuration, the hinge shaft <NUM> can be secured in a fixed (e.g., non-rotational relationship) to the first portion arm <NUM> and rotationally secured to the second portion arm <NUM>.

The friction clips <NUM> can be positioned sequentially on the hinge shaft <NUM> in alternating fashion with the spacers <NUM>. Other implementation may omit the spacers. In this case, the friction clips <NUM> are friction fit onto the hinge shaft <NUM>. The friction fit can be achieved by the aperture <NUM> of the friction clips <NUM> being slightly smaller than an outside diameter of the hinge shaft <NUM>, among other techniques.

A free range of rotation (RoR) of the friction clips <NUM> can be defined at least in part by a width of the friction clip and/or the distance (in degrees of rotation) between the first contact surface <NUM> and the second contact surface <NUM>. (See <FIG>). Note that the free range of rotation can be different (e.g., unique) for different friction clips <NUM>. For instance, the free range of rotation (RoRi) of friction clip <NUM>(<NUM>) is defined by the distance between contact surface <NUM> and contact surface <NUM>(<NUM>). The free range of rotation (RoR<NUM>) of friction clip <NUM>(<NUM>) is defined by the distance between contact surface <NUM> and contact surface <NUM>(<NUM>). Thus, in this configuration, friction clip <NUM>(<NUM>) has the greatest free range of rotation and the free range of rotations get progressively smaller with friction clip <NUM>(<NUM>) having the smallest free range of rotation.

Given the friction fit of the friction clips <NUM> on the hinge shaft <NUM>, the friction clips will rotate with the hinge shaft within their free range of rotation. When the friction clip reaches either end of the free range of rotation, e.g. contacts either contact surface <NUM> or contact surface <NUM>, further rotation of the hinge shaft <NUM> will cause slippage between the friction clip <NUM> and the hinge shaft <NUM> (e.g., the hinge shafts rotates within the aperture of the friction clip). The friction associated with this slippage produces at least a portion of the resistance to rotation introduced above. Recall that there are multiple independent friction clips that encounter different free ranges or rotation. The collection of friction clips can provide the variable resistance to rotation introduced above. These aspects are discussed in more detail below relative to <FIG>.

<FIG> collectively illustrate how the hinge shaft <NUM>, friction clips <NUM>, and contact surfaces <NUM> and <NUM> can cooperatively provide the variable resistance to rotation of the first and second portions relative to the hinge shaft. These components are illustrated on another example variable resistance hinge assembly 106C that is similar to variable resistance hinge assembly 106B. For ease of explanation, only four friction clips <NUM> are illustrated.

<FIG> shows the variable resistance hinge assembly 106C in a closed or zero-degree orientation. At this point, the friction clips <NUM> are all positioned against contact surface <NUM>. Individual friction clips also have a corresponding individual (portion) of contact surface <NUM>. For instance, the free angle of rotation (RoRi) for friction clip <NUM>(<NUM>) is defined between contact surface <NUM> and contact surface <NUM>(<NUM>). For purposes of explanation, assume that the user wants to open the device (indicated as clockwise rotation of the first portion arm <NUM> relative to the second portion arm <NUM>). At this point, all of the friction clips <NUM> are free to rotate in the clockwise direction (e.g., not blocked by contact surface <NUM>) so the friction clips do not provide any resistance to rotation in the clockwise direction.

<FIG> shows the variable resistance hinge assembly 106C after about <NUM> degrees of rotation in the clockwise direction relative to <FIG>. At this point, none of the friction clips <NUM> have encountered contact surfaces <NUM>. As such, the friction clips are free to rotate with the hinge shaft <NUM>. (Note that in <FIG> and in some of the subsequent FIGS. , first portion arm <NUM> is represented by a single dashed line to reduce clutter on the drawing page).

<FIG> shows the variable resistance hinge assembly 106C after about <NUM> more degrees of rotation in the clockwise direction relative to <FIG>. At this point, friction clip <NUM>(<NUM>) has just encountered contact surfaces <NUM>(<NUM>). As such, the friction clip <NUM>(<NUM>) is blocked from further rotation. In order for the hinge shaft <NUM> to continue to rotate, the hinge shaft will have to spin within friction clip <NUM>(<NUM>). The friction associated with such spinning creates resistance to rotation. At this point, friction clips <NUM>(<NUM>)-<NUM>(<NUM>) remain free to continue to rotate.

<FIG> shows the variable resistance hinge assembly 106C after about another <NUM> degrees of rotation in the clockwise direction relative to <FIG>. At this point, friction clip <NUM>(<NUM>) has just encountered contact surfaces <NUM>(<NUM>). As such, the friction clip <NUM>(<NUM>), as well as friction clip <NUM>(<NUM>), is now blocked from further rotation. In order for the hinge shaft <NUM> to continue to rotate, the hinge shaft <NUM> will have to spin within friction clips <NUM>(<NUM>) and <NUM>(<NUM>). The friction associated with such spinning creates resistance to rotation. At this point, friction clips <NUM>(<NUM>) and <NUM>(<NUM>) remain free to continue to rotate.

<FIG> shows the variable resistance hinge assembly 106C after about another <NUM> degrees of rotation in the clockwise direction relative to <FIG>. At this point, friction clip <NUM>(<NUM>) has just encountered contact surface <NUM>(<NUM>). As such, the friction clip <NUM>(<NUM>) as well as friction clips <NUM>(<NUM>)-<NUM>(<NUM>) are now blocked from further rotation. In order for the hinge shaft <NUM> to continue to rotate, the hinge shaft will have to spin within friction clips <NUM>(<NUM>)-<NUM>(<NUM>). The friction associated with such spinning (both static friction and kinetic friction) creates resistance to rotation.

In reviewing <FIG>, the sequence begins at <FIG> with all friction clips <NUM> free to rotate with the hinge shaft <NUM> in the clockwise direction so the friction clips do not provide resistance to rotation. <FIG> shows one friction clip blocked from further rotation, so resistance to further rotation is created. <FIG> shows two friction clips blocked from further rotation so the resistance to further hinge shaft rotation increases. <FIG> shows all four friction clips blocked from further rotation so the resistance to further clockwise rotation is maximized (four of four friction clips contributing). As mentioned above relative to <FIG> this feature can, for instance, help the variable resistance hinge assembly maintain the device orientation. For instance, <FIG> can represent a fully open device orientation, such as <NUM>-<NUM> degrees for a notebook computer. The variable resistance hinge assembly can provide the resistance to rotation so the device holds this open orientation. Note however, that the resistance can be uni-directional (e.g., the friction clips are blocked from further clockwise rotation, but not from counter-clockwise (CCW) rotation. Assume for purposes of explanation that the user now wants to close the device, which will rotate the hinge shaft in the opposite or counter-clockwise direction.

<FIG> shows the hinge shaft <NUM> and the friction clips <NUM> rotated about <NUM> degrees counter-clockwise relative to <FIG>. Note that at this point none of the friction clips <NUM> are blocked from rotation in the counter-clockwise direction and thus do not contribute to resistance of rotation of the hinge shaft <NUM>.

<FIG> shows the hinge shaft <NUM> and the friction clips <NUM> rotated about another <NUM> degrees counter-clockwise relative to <FIG>. At this point friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are blocked from further rotation in the counter-clockwise direction by contact surfaces <NUM> and thus are providing resistance to further counter-clockwise rotation. Friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are in their mid-ranges of their free range of rotation (e.g., are not in contact with either contact surface) and thus do not contribute to resistance to rotation of the hinge shaft <NUM>. Thus, at this point the resistance to rotation in the counter-clockwise direction is at about <NUM>% of its highest value (e.g., friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are providing resistance to rotation but friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are not). Another approximately <NUM> degrees of rotation will cause friction clip <NUM>(<NUM>) to encounter contact surface <NUM> and thus increase the resistance to rotation to about <NUM>%. Finally, a further <NUM> degrees of rotation will cause friction clip <NUM>(<NUM>) to be stopped by contact surface <NUM>. At that point, the orientation resembles the closed orientation of <FIG> where the variable resistance hinge assembly is providing its highest resistance to further rotation in the counter-clockwise direction, but no resistance to rotation in the clockwise direction.

Note that in the illustrated configuration of <FIG>, the contact surfaces <NUM> are evenly distributed away from the opposite contact surface <NUM>. For instance, in a configuration with a desired open configuration of about <NUM>-<NUM> degrees between the first and second portions, contact surface <NUM>(<NUM>) can be at <NUM> degrees from contact surface <NUM>, contact surface <NUM>(<NUM>) can be at <NUM> degrees from contact surface <NUM>, <NUM>(<NUM>) can be at <NUM> degrees from contact surface <NUM>, contact surface <NUM>(<NUM>) can be at <NUM> degrees from contact surface <NUM>. Thus, resistance to rotation goes up by about <NUM>% for each <NUM>% of rotation. However, an alternative configuration could have the contact surfaces <NUM> concentrated at one portion of the overall range of rotation of the first and second portions. For instance, relative to the <NUM> degree fully open implementation, the contact surfaces <NUM> could be positioned at <NUM> degrees, <NUM> degrees, <NUM> degrees, and <NUM> degrees, for example. This configuration would provide little or no resistance to rotation through the first <NUM> degrees of rotation and then the resistance to rotation would quickly go up through the last <NUM> degrees of rotation. Further, while even distribution is used in these examples. Other implementations could use dissimilar values to achieve a desired resistance to rotation (e.g., torque) profile. For instance, the contact surfaces <NUM> could be positioned at <NUM> degrees, <NUM> degrees, <NUM> degrees, and <NUM> degrees, for example.

<FIG> collectively show another example variable resistance hinge assembly 106D that is similar to the variable resistance hinge assembly 106C of <FIG> and as such not all elements are reintroduced for sake of brevity. Of note, variable resistance hinge assembly 106D includes an additional friction clip <NUM>(<NUM>) and contact surface <NUM>(<NUM>). In this case, contact surface <NUM> and contact surface <NUM>(<NUM>) define a free range of rotation RoRs for the friction clip <NUM>(<NUM>) that equals a width of the friction clip. Stated another way, friction clip <NUM>(<NUM>) is captured between contact surface <NUM> and contact surface <NUM>(<NUM>) and has an effective free range of rotation of zero. Thus, friction clip <NUM>(<NUM>) always provides resistance to rotation in either direction (e.g., clockwise or counter-clockwise). As such, friction clip <NUM>(<NUM>) can provide continuous resistance to rotation for device applications where a minimum amount of resistance to rotation is desired. The remaining friction clips <NUM>(<NUM>)-<NUM>(<NUM>) function similar to those described above and increase resistance to rotation depending on the orientation of the first portion arm <NUM> and the second portion arm <NUM> and the direction of rotation.

Starting at <FIG>, and beginning to rotate in the clockwise direction, only friction clip <NUM>(<NUM>) provides resistance to rotation. <FIG> shows the variable resistance hinge assembly 106D after about <NUM> degrees of clockwise rotation. At this point, friction clips <NUM>(<NUM>), <NUM>(<NUM>), and <NUM>(<NUM>) are providing resistance to rotation while friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are rotating freely.

<FIG> shows the variable resistance hinge assembly 106D after about another <NUM> degrees of clockwise rotation. At this point, all of the friction clips <NUM>(<NUM>)-<NUM>(<NUM>) are providing resistance to further rotation in the clockwise direction. <FIG> shows the variable resistance hinge assembly 106D after about <NUM> degrees of counter-clockwise rotation. At this point, friction clips <NUM>(<NUM>), <NUM>(<NUM>), and <NUM>(<NUM>) are providing resistance to further rotation while friction clips <NUM>(<NUM>) and <NUM>(<NUM>) are rotating freely with the hinge shaft <NUM>.

In the implementations described above, the contact surfaces <NUM> are manifest as a set of vertical surfaces with interposed horizontal surfaces. These implementations can be viewed as representing a spiral staircase or stepped surfaces defining a portion of a helix. Other configurations are contemplated. One such configuration is described below relative to <FIG>.

<FIG> collectively show another example variable resistance hinge assembly 106E. In this case, contact surface <NUM> is manifest as a single curved helical contact surface. A free range of rotation of an individual friction clip <NUM> is defined by contact surface <NUM> and a point on contact surface <NUM> at an elevation of the friction clip when the friction clip rotates with the hinge shaft <NUM>. Note that for sake of brevity, only a single friction clip is illustrated, but any number of friction clips can be employed.

In some implementations, the friction clip <NUM> may gradually create resistance to rotation. For instance, <FIG> shows the friction clip rotating clockwise with the hinge shaft <NUM> and just beginning to contact the contact surface <NUM>. The friction clip may flex slightly and ride up the contact surface a short distance before rotation stops as shown in <FIG>. The gradual stop can gradually increase the resistance to rotation imparted by the friction clip <NUM> on the hinge shaft <NUM>.

<FIG> collectively show another example variable resistance hinge assembly 106F. In this case, contact surfaces <NUM> and <NUM> are manifest as parallel vertical surfaces (e.g., they are parallel to one another and to the hinge axis). In this configuration, as can be seen in <FIG>, the width W of individual friction clips <NUM> can vary relative to other friction clips <NUM>. In this case, friction clip <NUM>(<NUM>) has the narrowest width W<NUM>, friction clip <NUM>(<NUM>) has the next larger width W<NUM>, friction clip <NUM>(<NUM>) has the next larger width W<NUM>, and friction clip <NUM>(<NUM>) has the widest width W<NUM>. While linear width is used here, the dimensions could alternatively be expressed relative to angles subtended by individual friction clips <NUM>.

<FIG> shows the friction clips <NUM> all rotated against contact surface <NUM> in the `fully open' orientation. At this point, each of the friction clips <NUM> is providing resistance to further rotation of the hinge shaft <NUM> in the clockwise direction.

<FIG> show the hinge shaft <NUM> and friction clips <NUM> rotated in the counter-clockwise direction by about <NUM> degrees relative to <FIG>. During this rotation, the friction clips <NUM> were free to rotate and did not contribute to resistance to rotation for the hinge shaft <NUM>. At this point, friction clip <NUM>(<NUM>) is just contacting contact surface <NUM> and will now provide resistance to further rotation of the hinge shaft <NUM> in the counter-clockwise direction. Friction clips <NUM>(<NUM>)-<NUM>(<NUM>) remain free to rotate and are not contributing significant resistance to rotation.

<FIG> shows the variable resistance hinge assembly 106F after about another <NUM> degrees of counter-clockwise rotation relative to <FIG>. At this point, all of the friction clips <NUM> are contacting contact surfaces <NUM> and will contribute resistance to rotation to any further rotation of the hinge shaft <NUM> in the counter-clockwise direction. Thus, in these implementations, the differing widths of the friction clips <NUM> causes them to encounter the contact surfaces <NUM> and <NUM> at differing points in the overall range of rotation of the first and second portions. The resistance to rotation is determined at least in part, by the point in the rotation and which fiction clips are blocked from further rotation and which are rotating freely.

Multiple example implementations of variable resistance hinge assemblies <NUM> are described above where a combination of friction clips <NUM> and contact surfaces <NUM> and <NUM> collectively create variable resistance to rotation over a range of rotation in one direction and another variable resistance to rotation over the range of rotation in the opposite direction. Other manifestations of various components are contemplated for achieving these concepts.

Individual elements of the variable resistance hinge assemblies can be made from various materials, such as metals, plastics, and/or composites. These materials can be prepared in various ways, such as in the form of sheet metals, die cast metals, machined metals, 3D printed materials, molded or 3D printed plastics, and/or molded or 3D printed composites, among others, and/or any combination of these materials and/or preparations can be employed.

The present hinge assembly concepts can be utilized with any type of device, such as but not limited to notebook computers, smart phones, wearable smart devices, tablets, vehicles, and/or other types of existing, developing, and/or yet to be developed devices.

Claim 1:
A computing device (<NUM>), comprising:
first and second portions (<NUM>, <NUM>);
a hinge shaft (<NUM>) that is fixedly secured to the first portion (<NUM>) and rotationally secured to the second portion (<NUM>);
the second portion (<NUM>) defining a first contact surface (<NUM>) spaced apart from a second contact surface (<NUM>); and,
multiple friction clips friction fit around the hinge shaft (<NUM>)
characterized in that
the multiple friction clips rotate with the hinge shaft (<NUM>) between the first contact surface (<NUM>) and the second contact surface (<NUM>), individual friction clips (<NUM>) having different free ranges of rotation as defined by the first contact surface (<NUM>) and the second contact surface (<NUM>); and
rotation of the hinge shaft (<NUM>) beyond the free range of rotation of an individual friction clip (<NUM>) causes slippage between the hinge shaft (<NUM>) and the individual friction clip (<NUM>).