Patent Description:
Haptic gloves may be used to provide haptic or tactile feedback to a user's hand, for example when used in combination with virtual reality (VR) or augmented reality (AR) technology. Haptic gloves may provide a variety of sensations to a user's hand, ranging from giving the impression of gripping a virtual object (e.g. in a video game) to imitating texture and other surface structure on such a virtual object. Existing haptic gloves, however, are still limited in their capability of providing accurate haptic feedback and tracking a user's hand movement. Additionally, the mechanisms driving existing haptic gloves are large and heavy, limiting the adoption of haptic gloves in VR applications.

<CIT> discloses a haptic glove including a glove body including a glove digit corresponding to a phalange of a user hand. The glove digit has a pair of flexible tendons, including a first and a second tendon, which are parallel to a bend centerline that bisects a surface of the glove digit. The first and second tendons are positioned respectively on opposite sides of the bend centerline. The haptic glove further comprises an actuator coupled to the glove body and the first and second tendons, the actuator configured to actuate the tendons to control movement of the glove digit.

According to the present invention, there is provided a haptic glove for providing haptic feedback to a user's hand, the haptic glove comprising: a base portion and one or more finger portions extending from the base portion, wherein each finger portion is pivotally movable relative to the base portion, and one or more cables, each comprising a distal end connected to a respective finger portion and a proximal end extending towards the base portion; and one or more cable control assemblies, at least one (optionally each) cable control assembly comprising: a constrain mechanism configured, when engaged, to constrain movement of the proximal end of a respective cable relative to the base portion, thereby constraining movement of a respective finger portion relative to the base portion, and an SMA wire arranged, on contraction, to engage or disengage the constrain mechanism.

Due to its high energy density, SMA wire may be used as an actuator in particularly compact applications, reducing the size of the cable control assembly. The SMA wire, on contraction, selectively engages or disengages the constrain mechanism to or from the cable. The SMA wire may be powered or energized to contract, for example by passing an electrical power through the SMA wire. On elongation, e.g. due to an opposing biasing force of a biasing element (such as a resilient element, e.g. a spring or a magnet) or of an opposing SMA wire, the SMA wire respectively disengages or engages the constrain mechanism from or to the cable. This selectively constrains movement of the cable and thus the finger portion, providing haptic feedback to a user.

The constrain mechanism be coupled or connected (e.g. via one or more movable and/or intermediary parts) to the cable on contraction of the SMA wire, such that the constrain mechanism affects (i.e. constrains) movement of the cable. The constrain mechanism may be decoupled or disconnected from the cable when the SMA wire is not contracted, such that the constrain mechanism does not affect (i.e. does not constrain) movement of the cable. Alternatively, constrain mechanism be decoupled or disconnected from the cable on contraction of the SMA wire, such that the constrain mechanism does not affect (i.e. does not constrain) movement of the cable. The constrain mechanism may be coupled or connected to the cable (e.g. via one or more movable and/or intermediary parts) when the SMA wire is not contracted, such that the constrain mechanism affects (i.e. constrains) movement of the cable.

In some embodiments, the at least one (optionally each) cable control assembly comprises a constrain mechanism in the form of a locking mechanism configured, when engaged, to prevent movement of the proximal end of the respective cable relative to the base portion. The cable may thus be prevented from moving on curling of a user's finger, e.g. due to a locking part locking the cable in place (e.g. via any movable parts connected to the cable).

In some embodiments, the at least one (optionally each) cable control assembly comprises a constrain mechanism in the form of a braking mechanism configured, when engaged, to apply a frictional force to the proximal end of the respective cable. The frictional force may be so as to prevent the cable from moving. Alternatively, the frictional force may be lower so as to allow some movement of the cable when a large external force is applied to the cable, e.g. by a user. In any case, the frictional force resists movement of the cable and so may provide haptic feedback. Optionally, the cable control assembly may vary the amount of engagement with the braking mechanism so as to vary the frictional force, for example within a continuous range or between multiple discrete levels. For example, the SMA wire may, on initial contraction, engage the brake mechanism such that a first frictional force resists movement of the cable, and on further contraction, engage the brake mechanism such that a second frictional force resists movement of the cable, where the second frictional force is different to (e.g. larger than) the first frictional force.

In some embodiments, the at least one (optionally each) cable control assembly comprises a constrain mechanism in the form of a spring mechanism configured, when engaged, to apply a bias force along the respective cable. The spring mechanism, when engaged, may apply tension to the respective cable. This may give the impression to a user of the haptic glove of pulling a trigger or squeezing an elastic ball, for example. The spring mechanism may thus provide a further, different haptic sensation to the locking or brake mechanisms, thus further improving haptic feedback achievable by the haptic glove.

In some embodiments, the at least one (optionally each) cable control assembly comprises constrain mechanisms in the form of i) the spring mechanism and ii) at least one of the locking and braking mechanism. This enables improved haptic feedback compared to situations in which just one of these constrain mechanisms is provided. In some further embodiments, the at least one (optionally each) cable control assembly comprises constrain mechanisms in the form of i) the spring mechanism and ii) the locking mechanism and iii) the braking mechanism.

In some embodiments, the at least one cable control assembly (optionally each) comprises at least two SMA wires, wherein one SMA wire is arranged selectively to engage or disengage the locking or braking mechanism and another SMA wire is arranged selectively to engage or disengage the spring mechanism. So, the spring mechanism and the locking or braking mechanisms are independently controllable. In some alternative embodiments, the at least one cable control assembly comprises an SMA wire arranged, on initial contraction, to i) engage the spring mechanism or ii) disengage the locking or braking mechanism and, on further contraction, to respectively i) engage the locking or braking mechanism or ii) disengage the spring mechanism.

This SMA wire may form part of a multi-stage latch, for example, such that.

This allows a single SMA wire to selectively engage or disengage at least two constrain mechanisms. In embodiments in which three or more separate constrain mechanisms are provided, a single SMA wire (optionally in a multi-stage latch) may be used to selectively engage or disengage the three or more separate constrain mechanisms in equivalent manner.

In some embodiments, the at least one cable control assembly comprises a retraction mechanism configured to permanently apply a retracting bias force along the cable. The retraction mechanism may be embodied by a resilient element, such as a spring (e.g. torsion spring), for example. The retraction mechanism may remain connected to the cable at all times, so as to put tension on the cable at all times. The spring mechanism, when engaged, provides additional tension to the cable and so provides haptic feedback even when the retraction mechanism is engaged. Preferably, the spring mechanism provides a bias force that is at least equal to the bias force of the retraction mechanism.

In some embodiments, the at least one cable control assembly comprises a movable part that is coupled to the proximal portion of the cable. The movable part may be connected or coupled to the cable at all times. The movable part may be rotatably movable, e.g. about an axis or pivot, or may be translationally movable. The movable part may move with the cable.

In some embodiments, the movable part comprises a reel and the cable is wound on the reel. A reel provides a particularly compact arrangement for large movement of the proximal portion of the cable.

In some embodiments, the reel is a multi-diameter reel comprising portions with different diameters, and different cables are wound on the portions of the reel with different diameters.

In some embodiments, each finger portion comprises a plurality of finger segments, and different cables are connected at their distal ends to different finger segments of a respective finger portion, wherein the different cables are wound on parts of the reel with different diameters. Movement of the cables connected to the finger segments of a single finger portion may thus be geared. This allows the multiple cables to be controlled using a single cable control mechanism, simplifying control.

In some embodiments, the at least one cable control assembly comprises an intermediary part, and wherein the SMA wire is arranged to move the intermediary part so as to engage or disengage the constrain mechanism. Movement of the intermediary part may selectively connect or couple, or disconnect or decouple, the cable (e.g. via the movable part) from the constrain mechanism.

In some embodiments, the intermediary part is arranged to pivot so as to engage or disengage the constrain mechanism. This makes control of the position of the intermediary part particularly reliable, providing improved engagement and disengagement of the constrain mechanism.

In some embodiments, the SMA wire is coupled to the intermediary part via a resilient element. This may reduce the risk of damage to the SMA wire due to large external loads on the cable, which may be absorbed by the resilient element instead of the SMA wire. Furthermore, it may improve engagement or disengagement of the constrain mechanism, for example when the intermediary part comprises teeth for engaging complimentary teeth on the movable part or other part for connecting or coupling the cable to the constrain mechanism.

In some embodiments, the SMA wire is arranged to move the intermediary part into or out of engagement with the movable part so as to engage or disengage the constrain mechanism. Alternatively, the intermediary part may be in constant connection with the movable part, and the SMA wire may move the intermediary part into or out of engagement with a portion of the constrain mechanism (e.g. with the base portion or a part connected to a spring).

In some embodiments, the intermediary part and the movable part comprise engagement surfaces for engaging each other, wherein the engagement surfaces are configured, on engagement, to constrain sliding between the intermediary part and the movable part. Each engagement surface may comprise a plurality of complementary teeth, thus improving reliable coupling and suppressing sliding.

In some embodiments, the cable control assembly comprises a latch, the latch comprising a latching part movable between a latched position and an unlatched position, and wherein the SMA wire is arranged, on contraction, to move the latching part into the latched position, thereby engaging or disengaging the constrain mechanism. In some embodiments, a release SMA wire is arranged, on contraction, to move the latching part into the unlatched position, thereby respectively disengaging or engaging the constrain mechanism. The release SMA wire may move a release part so as to move the latching part into the unlatched position, for example. The latch is configured to remain in the latched or unlatched position when the SMA wire ceases to be energized. As such, energy consumption of the cable control assembly is reduced compared to a situation in which the SMA wire needs to be continuously powered to keep the constrain mechanism engaged or disengaged.

In some embodiments, the latch comprises a support structure comprising first and a second surface separated by a step, a latching part slidable along the first and/or second surfaces between the unlatched position engaging the first surface and the latched position engaging the step and second surface, and a biasing element arranged to bias the latching part against the step and the first and/or second surfaces, wherein the SMA wire is arranged, on contraction, to move the latching part along the first surface into the latched position under bias of the biasing element so as to engage or disengage the constrain mechanism. A release SMA wire may be arranged, on contraction, to move the latching part over the step into the unlatched position under bias of the biasing element. The release SMA wire may move a release part so as to move the latching part into the unlatched position, for example.

In some embodiments, the support structure comprises a second set of first and second surfaces separated by a second step, and wherein the latch further comprises: a second latching part slidably arranged along the second set of first and/or second surfaces between an unlatched position engaging the respective first surface and a latched position engaging the respective step and second surface, and a second SMA wire arranged, on contraction, to move the second latching part along the respective first surface into the latched position under bias of the second biasing element; wherein the latching part in its latched position is arranged to engage or disengage a first constrain mechanism, and the second latching part in its latched position is arranged to engage or disengage a second constrain mechanism, and wherein the release SMA wire is arranged, on contraction, to move both the latching part and the second latching part over the respective step into the respective unlatched position under bias of the respective biasing element.

As such, the latch is capable or selectively engaging or disengaging different constrain mechanism, for example the spring mechanism and one or the locking or braking mechanisms. A single SMA wire may be used to selectively disengage both constrain mechanisms.

In some embodiments, the support structure comprises a third surface separated from the second surface by a second step, wherein the latching part is slidably arranged along the first, second and/or third surfaces between the unlatched position engaging the first surface, a first latched position engaging the step and second surface and a second latched position engaging the second step and the third surface. As such, the latch may be a multi-stage latch. The multi-stage latch may adjust the frictional force of the braking mechanism, for example. The multi-stage latch may alternatively allow engaging of different constrain mechanism, for example.

In some embodiments, the release SMA wire is arranged to move the latching part from either of the first or second latched positions into the unlatched position under bias of the biasing element. As such, only a single SMA wire is required to release the latch.

In some embodiments, the release SMA wire is arranged, on initial contraction, to move the latching part from the second latched position over the second step into the first latched position under bias of the biasing element, and, on further contraction, to move the latching part from the first latched position over the first step into the unlatched position under bias of the biasing element.

According to the present invention, there is also provided a latch comprising a support structure comprising first and a second surface separated by a step, a latching part slidable along the first and/or second surfaces between an unlatched position engaging the first surface and a latched position engaging the step and second surface, and a biasing element arranged to bias the latching part against the step and the first and/or second surfaces, and an SMA wire arranged, on contraction, to move the latching part along the first surface into the latched position under bias of the biasing element. So, the latch described herein may form part of the present invention in isolation of the features of the haptic glove.

In some embodiments, the latch comprises a release SMA wire arranged, on contraction, to move the latching part over the step into the unlatched position under bias of the biasing element.

In some embodiments, the support structure comprises a second set of first and second surfaces separated by a second step, and wherein the latch further comprises: a second latching part slidably arranged along the second set of first and/or second surfaces between an unlatched position engaging the respective first surface and a latched position engaging the respective step and second surface, and a second SMA wire arranged, on contraction, to move the second latching part along the respective first surface into the latched position under bias of the second biasing element.

In some embodiments, the release SMA wire is arranged, on contraction, to move both the latching part and the second latching part over the respective step into the respective unlatched position under bias of the respective biasing element.

In some embodiments, the support structure comprises a third surface separated from the second surface by a further step, wherein the latching part is slidable along the first, second and/or third surfaces between the unlatched position engaging the first surface, a first latched position engaging the step and second surface and a second latched position engaging the further step and the third surface.

In some embodiments, the release SMA wire is arranged to move the latching part from either of the first or second latched positions into the unlatched position under bias of the biasing element.

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:.

<FIG> schematically depicts a haptic glove <NUM> in accordance with the present invention. The haptic glove <NUM> is configured to be worn on a user's hand. The haptic glove <NUM> comprises a base portion <NUM> and one or more finger portions <NUM>. The finger portions <NUM> are pivotally movable relative to the base portion <NUM>. Each finger portion <NUM> may comprise a plurality of finger segments <NUM> that are pivotally movable relative to each other and relative to the base portion <NUM>. The base portion <NUM> and the one or more finger portions <NUM> make up the structure or exoskeleton of the haptic glove <NUM>. The base portion <NUM> is herein used as a reference frame relative to which movement of other components of the haptic glove <NUM> is described (unless otherwise indicated), but it will be appreciated that the base portion <NUM> in general may be movable itself and may comprise or be made up of parts that are movable relative to each other. Details and embodiments of the base portion <NUM> and the one or more finger portions <NUM> are described below.

The haptic glove <NUM> further comprises one or more cables <NUM> that is or are coupled at one end (herein referred to as the "distal end") to a respective finger portion <NUM>. Multiple cables <NUM> may be provided per finger portion <NUM>, as described in more detail below. The cable <NUM> may be any elongate element capable of carrying a tensile force. The cable <NUM> may be deformed by forces acting laterally to the tensile force carried by the cable <NUM>.

The cable <NUM>, in particular movement of the cable <NUM>, is controlled by a cable control assembly <NUM>. The cable control assembly <NUM> may control the cable <NUM> passively, i.e. the cable control assembly <NUM> may selectively constrain (i.e. resist by a frictional force or bias force, or even prevent) movement of the cable <NUM>. The cable control assembly <NUM> need not actively move the cable <NUM>. In some embodiments, however, the cable control assembly <NUM> may actively pull on the cable <NUM> so as to move the finger portion <NUM> relative to the base portion <NUM>.

The cable control assembly <NUM> may be provided on the base portion <NUM>, as schematically shown. However, in general, the cable control assembly <NUM> may also be provided on the finger portions <NUM>, or be distributed between the base portion <NUM> and the finger portions <NUM>. The end of the cable <NUM> that is not coupled to the finger portion <NUM> (herein referred to as the "proximal end" or "proximal portion") may be coupled to the cable control assembly <NUM>. The cable control assembly <NUM> may provide haptic feedback to a user by constraining, i.e. resisting or even preventing, movement of the cable <NUM>. Details and embodiments of the cable control assembly <NUM> are described below.

The cable control assembly <NUM> may comprise at least one constrain mechanism <NUM>, for example in the form of a locking mechanism 120a, a braking mechanism 120b and/or a spring mechanism 120c. The cable control assembly <NUM> may selectively engage the constrain mechanism <NUM>. So, the constrain mechanism <NUM> may selectively constrain movement of the cable <NUM> relative to the base portion <NUM>. This selectively locks, brakes or otherwise resists (e.g. applies a force that opposes) movement of the finger portion <NUM> relative to the base portion <NUM>, thereby providing haptic feedback to the user.

Optionally, the cable control assembly <NUM> comprises at least one retraction mechanism <NUM>. The retraction mechanism <NUM> may retract the cable <NUM>, for example upon un-bending of the finger portions <NUM>. The retraction mechanism <NUM> may provide a continuous or permanent biasing force for retracting the cable <NUM>. The retraction mechanism <NUM> may be embodied by a resilient element, such as a spring (e.g. compression or tension spring, or a torsion spring) that provides the biasing force. In some embodiments, a dedicated retraction mechanism <NUM> is not provided.

Optionally, the cable control assembly <NUM> may comprise a multi-cable coupling <NUM>, thereby enabling multi-cable control. So, some provision may be made for the cable control assembly <NUM> to control multiple cables <NUM> simultaneously. Each or at least one of the retraction mechanism <NUM> and/or the constrain mechanism <NUM> may thus act on multiple cables <NUM> simultaneously, such that a single retraction mechanism <NUM> and/or constrain mechanism <NUM> may act on multiple cables <NUM>. This may make the cable control assembly <NUM> more compact and simpler. Alternatively, the cable control assembly <NUM> may control each cable <NUM> independently. Each retraction mechanism <NUM> and/or the constrain mechanism <NUM> may thus act on a single cable <NUM> only, such that a dedicated retraction mechanism <NUM> and/or constrain mechanism <NUM> is provided for each cable <NUM>. This may provide more accurate cable control, and thus improved haptic feedback.

Optionally, the cable control assembly <NUM> comprises a position sensing arrangement <NUM>. The position sensing arrangement <NUM> may determine a position of a finger portion <NUM> relative to the base portion <NUM>. The position sensing arrangement <NUM> may, for example, determine the position of the cable <NUM> relative to the base portion <NUM>. A processor (not shown) or other control circuit may receive the position data and make a determination as to whether or not to provide haptic feedback at least in part based on the position data.

Optionally, the haptic glove <NUM> comprises one or more haptic actuators <NUM> for providing localized haptic feedback to a user. The one or more haptic actuators <NUM> may be provided on the finger portion <NUM> (for example near the fingertip of a user), to selectively provide a localized haptic sensation to a specific portion of the user's hand (for example to the fingertip of the user).

Details of the haptic glove <NUM> are described below. It will be appreciated that any of the embodiments of the structure of the base portion <NUM> and/or finger portion <NUM> may be combined with any of the embodiments of the cable control assembly <NUM> described below. Furthermore, even though the parts of the cable control assembly <NUM> are described below in relation to the haptic glove <NUM>, it will be appreciated that these parts may find application in devices other than the haptic glove and may form embodiments of the present invention in their own right. Specifically, aspects of the constrain mechanism <NUM>, including the locking mechanism 120a, the braking mechanism 120b and the spring mechanism 120c, as well as the latch mechanisms described below, need not be coupled to a cable <NUM> and/or a haptic glove <NUM> and may thus form inventions separate from the haptic glove <NUM> described herein.

<FIG> schematically illustrate examples of the structure of the haptic glove <NUM>, comprising the base portion <NUM> and a finger portion20. Only a single finger portion <NUM> is shown for illustrative simplicity, but it will be appreciated that more than one finger portion <NUM> (e.g. five finger portions) may be provided. The depicted finger portions <NUM> comprise multiple finger segments <NUM>, although in general a single finger segment <NUM> may be provided. <FIG> also shows the cable control assembly <NUM> arranged on the base portion <NUM>.

The base portion <NUM> is arranged, in use, to at least partially be arranged adjacent to a user's hand. Although not shown, the base portion <NUM> may extend over the wrist of a user's hand, thus providing additional space for other components of the haptic glove <NUM>. In its simplest form, the base portion <NUM> may comprise a plate provided on the rear of a user's hand. The base portion <NUM> may be fixed relative to a user's hand, for example using suitable straps. The base portion <NUM> may also be worn on the user's hand, so as to partially or entirely surround a user's palm.

One or more (e.g. four or five) finger portions <NUM> may depend from the base portion <NUM>. The finger portion <NUM> comprises a proximal end arranged next to the base portion <NUM> and a distal end arranged away from the base portion <NUM>. Each finger portion <NUM> is to be arranged on or adjacent to a user's finger (where the thumb is considered to be one of the fingers). Each finger portion <NUM> may be pivotally arranged relative to the base portion <NUM>, i.e. the distal end of each finger portion <NUM> may pivot relative to the base portion <NUM>. The finger portion <NUM> may pivot or bend relative to the base portion <NUM> at least in a direction substantially orthogonal to a user's palm, so as to allow bending of the user's finger. The finger portion <NUM> may additionally be laterally movable relative to the base portion <NUM>, i.e. in a plane substantially parallel to a user's palm, so as to allow for lateral movement of a user's finger. This avoids constraining natural movement of a user's finger, making the haptic glove <NUM> more comfortable to wear and providing a more natural feel to a user.

The haptic glove <NUM> may comprise five finger portions <NUM>, one for each finger of a user's hand. In some embodiments, the haptic glove <NUM> may comprise fewer than five finger portions <NUM>, for example four finger portions <NUM> (for surrounding a user's fingers other than the thumb) or fewer finger portions <NUM>. In some embodiments, a finger portion <NUM> may be provided to be worn on multiple fingers. For example, a single finger portion <NUM> may be worn on the pinkie finger and ring finger of a user's hand together, such that the pinkie finger and ring finger move together.

In preferred embodiments, each finger portion <NUM> comprises one or more segments <NUM>, e.g. a plurality of segments <NUM> mechanically connected in series so as to form a chain of linkages. The segments <NUM> may be pivotally movable with respect to each other and with respect to the base portion <NUM>, so as to allow bending and/or curling of a user's finger while remaining adjacent to the user's finger. One or more bearings <NUM> may be provided between adjacent finger segments <NUM> and between the base portion <NUM> and the finger portion <NUM>, so as to allow relative movement of the finger segments <NUM> relative to each other and relative to the base portion <NUM>.

The haptic glove <NUM> comprises one or more cables <NUM>. The haptic glove <NUM> may, for example, comprise one cable <NUM> per finger portion <NUM>. This allows each finger portion <NUM> to be controlled independently.

In some embodiments, the haptic glove <NUM> comprises more than one cable <NUM> per finger portion <NUM>, for example one cable <NUM> per phalanx of a user's finger. So, the haptic glove <NUM> may comprise two cables <NUM> per finger portion <NUM> corresponding to a thumb of a user, and three cables <NUM> per finger portion <NUM> corresponding to another finger of a user. <FIG>, for example, depicts three cables <NUM> attached to finger segments <NUM> corresponding to different phalanxes of a user's hand. This may enable more accurate control of the shape of a user's finger allowed by the haptic glove <NUM> to provide haptic feedback. The haptic glove <NUM> may in general comprise any number of cables <NUM> per finger portion <NUM>.

<FIG> shows a finger portion <NUM> with three finger segments <NUM>, one per phalanx of a user's finger. <FIG> shows an alternative finger portion <NUM> with additional finger segments <NUM>, allowing the finger portion to conform to different finger sizes of a user. In general, any number of finger segments <NUM> may form part of the finger portion <NUM>. The finger portion <NUM> may be formed from a plurality (e.g. more than <NUM>) finger segments <NUM> provided in a backbone-like arrangement, for example. The finger segments <NUM> need not all surround a user's finger, but some finger segments <NUM> may be provided at the back of a user's finger only. The number of cables <NUM> per finger portion <NUM> may be three, two or one regardless of the number of finger segments <NUM>.

As described above, controlling (in particular constraining) movement of the cable <NUM> (in particular of the proximal portion of the cable <NUM>) may be used to provide haptic feedback to a user's hand. The figures described below schematically depict various aspects of the cable control assembly <NUM>. The cable control assembly <NUM> may comprise or embody one or more of a retraction mechanism <NUM> for retracting the cable <NUM>, a locking mechanism 120a for locking the proximal portion of the cable <NUM> in place, a brake mechanism 120b for braking movement of the proximal portion of the cable 30a, and a spring mechanism 120c for selectively applying a spring force to the proximal portion of the cable <NUM>, in particular along the cable <NUM>. A respective part of the cable control assembly <NUM> may be provided individually for each cable <NUM>, or multiple cables <NUM> (e.g. all cables coupled to a finger portion <NUM>) may be controlled by a single part of the cable control assembly <NUM>, for example by coupling multiple cables using the multi-cable coupling <NUM>. Described below are examples of parts of the cable control assembly <NUM> that achieve one or more of these functions.

According to the present invention, the cable control assembly <NUM> comprises a constrain mechanism <NUM>. The constrain mechanism <NUM> is configured, when engaged, to constrain movement of the proximal end of a respective cable relative to the base portion, thereby constraining movement of a respective finger portion relative to the base portion. When the constrain mechanism <NUM> is disengaged movement of the proximal end of a respective cable relative to the base portion is not constrained by the constrain mechanism <NUM>. The constrain mechanism <NUM> may be embodied by the locking mechanism 120a, the brake mechanism 120b and/or the spring mechanism 120c.

An SMA wire is arranged, on contraction, to engage or disengage the constrain mechanism <NUM>.

<FIG> schematically shows a haptic glove <NUM> comprising a base portion <NUM>, finger portion <NUM> and a cable <NUM>. The structure of the haptic glove <NUM> may, for example, be as described in relation to <FIG>.

The haptic glove <NUM> further comprises a cable control assembly <NUM>. The cable control assembly <NUM> comprises a movable part <NUM> coupled to the proximal portion of the cable. The movable part <NUM> is arranged at the proximal end of the cable <NUM>. <FIG> depicts the movable part <NUM> as a part that is separate and connected to the cable <NUM>, although in general the movable part <NUM> may form part of the cable <NUM>. The movable part <NUM> may, for example, correspond to the proximal end of the cable <NUM>. The movable part <NUM> is movable relative to the base portion <NUM> along a movement axis A that is substantially aligned with the proximal portion of the cable <NUM>. In the depicted embodiment, the movable part <NUM> is movable in an up-down direction.

A constrain mechanism <NUM> is provided for selectively constraining movement of the proximal end of the cable <NUM>. In the depicted embodiment, the constrain mechanism <NUM> is embodied by a locking or braking mechanism 120a,b in combination with a spring mechanism 120c. The constrain mechanism <NUM> is selectively engageable so as to provide haptic feedback.

Cable control assembly <NUM> comprises an intermediary part 124a,b and an SMA wire 128a,b. The intermediary part 124a,b is constrained from moving along the movement axis A. The SMA wire 128a,b, on contraction, moves the intermediary part 124a,b into engagement with the movable part <NUM>, thereby constraining movement of the movable part <NUM> relative to the base portion <NUM>. Using an SMA wire 128a,b may enable a particularly lightweight and compact mechanism. Although in the depicted embodiment the SMA wire, upon actuation (contraction) moves the intermediary part 124a,b into engagement, in alternative embodiments the SMA wire may move the intermediary part 124a,b out of engagement with the movable part <NUM>.

Although not shown, the locking or braking mechanism <NUM> may further comprise a biasing element that biases the intermediary part <NUM> out of or into engagement with the movable part <NUM> or base portion <NUM>. The SMA wire 128a,b is arranged, on actuation, to oppose the biasing force of the biasing element.

In further alternative embodiments, the intermediary part 124a,b may be constrained from moving along the movement axis relative to the movable part <NUM> (and so may move along the movement axis relative to the base portion <NUM>). The intermediary part 124a,b may be brought into or out of engagement with the base portion <NUM> by the SMA wire 128a,b, thereby constraining movement of the movable part <NUM> relative to the base portion <NUM>.

In the depicted embodiment, the SMA wire 128a,b is arranged to move the intermediary part 124a,b in a direction that is perpendicular to the movement axis A. In general, the SMA wire 128a,b may move the intermediary part 124a,b in any direction that is angled relative to the movement axis A.

In the depicted embodiment, the intermediary part 124a,b and the movable part <NUM> comprise engagement surfaces that are configured to engage each other. The engagement surfaces, on engagement, constrain sliding between the engagement surfaces. As depicted, each engagement surface may comprises a plurality of teeth, i.e. each engagement surface may be serrated. In such an embodiment, the constrain mechanism may act as a locking mechanism 120a, in that the movable part <NUM> may be locked in place when engaged by the intermediary part 124a. In general, however, the engagement surface may have any surface structure suitable for constraining relative sliding on engagement. The engagement surfaces may, for example, be relatively rough surfaces. In such an embodiment, the constrain mechanism may act as a braking mechanism 120b, in that the intermediary part 124b may brake movement of the movable part <NUM> when in engagement.

In the depicted embodiment, the two ends of the SMA wire <NUM> are fixed relative to the base portion <NUM>. The SMA wire bends around a contact portion that is in contact with the intermediary part 124a,b, thereby forming two SMA portions on either side of the contact portion. The two SMA portions are angled relative to each other. Contraction of the SMA wire 128a,b (e.g. by driving the SMA wire 128a,b using a suitable drive current) urges the intermediary part 124a,b towards and into engagement with the movable part <NUM>.

In alternative embodiments, the SMA wire 128a,b may be arranged differently to move the intermediary part 124a,b. For example, the SMA wire 128a,b may be connected between the intermediary part 124a,b and the base portion <NUM>. Contraction of the SMA wire 128a,b thus directly moves the intermediary part 124a,b relative to the base portion <NUM>. The intermediary part 124a,b may comprise a sliding surface that slidingly engages the base portion <NUM>. The sliding surface may be angled relative to the movement axis A. The SMA wire may be arranged, on contraction, to move the intermediary part 124a,b along the sliding surface. Because the sliding surface is angled relative to the movement axis A, sliding along the movement axis A may bring the intermediary part 124a,b into or out of engagement with the movable part <NUM>.

As shown in <FIG>, the constrain mechanism <NUM> may further comprise a second movable part 122c that is movable relative to the base portion <NUM>, a second intermediary part 124c, and a second SMA wire 128c arranged, on actuation, to move the second intermediary part 124c into engagement with the second movable part 122c. Engagement of the second intermediary part 124c with the second movable part 124c constrains movement of the second movable part 124c relative to the base portion <NUM>. The constrain mechanism further comprises a resilient element 123c, such as a spring, connected between the movable part <NUM> and the second movable part 122c.

When movement of the second movable part 122c relative to the base portion is constrained or even prevented, the first movable part <NUM> (and cable <NUM> connected thereto) may move against the spring force of the resilient element 123c. So, a spring force acts against movement of the first movable part <NUM> in the up-direction in <FIG>, and so curling of the respective finger portion <NUM> required a user to overcome the spring force. This may simulate squishing a virtual elastic object or pulling a trigger to a user.

<FIG> schematically depicts an alternative embodiment for engaging a constrain mechanism <NUM> to constrain movement of the proximal end of the cable <NUM>. The movable part <NUM> is arranged at the proximal portion of the cable <NUM>. The movable part <NUM> is movable relative to the base portion <NUM> along the movement axis A, which in the depicted embodiment extends in the left-right direction. Further provided are the second movable part 122c, and the resilient element 123c connected between the movable part <NUM> and second movable part 122c.

The cable control assembly <NUM> further comprises the intermediary part 124a,b and the second intermediary part 124c. When the intermediary part 124a,b is in engagement with the movable part <NUM>, the proximal end of the cable <NUM> is constrained or even prevented from moving, giving the impression of holding a rigid object to the user, as explained above. When the second intermediary part 124c is in engagement with the second movable part 122c (and the intermediary part 124a,b is not in engagement with the movable part <NUM>), moving the movable part <NUM> requires acting against the spring force of the resilient element 123c. This gives the impression of squishing an elastic object or pulling a trigger, as explained above.

Unlike in the embodiment depicted in <FIG>, only a single SMA wire <NUM> is provided to engage both the spring mechanism and the locking or brake mechanism. The single SMA wire <NUM> may move a further actuating part <NUM>. The actuating part <NUM> comprises a first sliding surface for sliding relative to the base portion <NUM>. The actuating part <NUM> further comprises a second sliding surface that allows relative sliding between the actuating part <NUM> and the intermediary part 124a,b. The intermediary part 124a,b is connected to the second intermediary part <NUM> via a spring or other resilient element. Actuation by the SMA wire <NUM> moves the actuation part <NUM> along the first sliding surface relative to the base portion <NUM>. As a result, by sliding relative to the actuation part <NUM>, the intermediary part 124a,b and second intermediary part 124c are urged towards the movable parts <NUM>, 122c. The second intermediary part 124c is arranged to engage the second movable part 122c before the intermediary part 124a,b engages the movable part <NUM>. So, in an intermediate actuation position of the SMA wire <NUM>, the intermediary part 124c engages the second movable part 122c (and the intermediary part 124a,b does not engage the movable part 122c). Upon further actuation by the SMA wire <NUM>, the intermediary part 124a,b is urged into engagement with the movable part <NUM>.

The embodiment of <FIG> thus allows use of a single SMA wire <NUM>, in a two-step actuation process, to selectively constrain movement of only the second movable part 122c or of both the movable part <NUM> and the second movable part 122c.

As explained above, the haptic glove <NUM> may in some embodiments comprise more than one cable <NUM> per finger portion <NUM>, for example one cable <NUM> per phalanx of a user's hand. The shape of the finger portion <NUM> can thus be more accurately controlled compared to providing a single cable <NUM> per finger portion <NUM>, enabling improved haptic feedback.

In general, each cable <NUM> of the multiple cables <NUM> per finger portion <NUM> may be controlled independently, either within the same cable control assembly <NUM> or by different cable control assemblies <NUM>.

The multiple cables <NUM> coupled to a finger portion <NUM> may move by proportional amounts. For example, with reference to <FIG>, a first cable <NUM> coupled a first finger segment <NUM> of the finger portion <NUM> may move by a first amount, and a second cable <NUM> coupled to a second finger segment <NUM> of the finger portion <NUM> may move by a second amount that is proportional to the first amount. When three cables are provided, a third cable <NUM> coupled to a third finger segment <NUM> of the finger portion <NUM> may move by a third amount that is proportional to the first amount. A cable <NUM> coupled to a relatively distal finger segment <NUM> may be allowed to move by a larger amount than a cable <NUM> coupled to a relatively proximal finger segment <NUM> (relative to the base portion <NUM>). This allows natural curling of a user's finger.

The multiple cables <NUM> may be coupled to one another to enable such proportional movement. This allows the multiple cables <NUM> per finger portion <NUM> to be controlled simultaneously. Control is thus simplified, because a single cable control assembly <NUM> may be used to control multiple cables <NUM>.

Figures 3A and 3B schematically show a plan view and a side view of one embodiment of a multi-cable coupling <NUM> for coupling multiple cables <NUM> together. In Figures 3A and 3B, the multi-cable coupling is in the form of a reel <NUM>, in particular a multi-diameter reel <NUM>. The multi-diameter reel <NUM> is, e.g., a rotatable drum or cylinder comprising portions 175A-C of multiple diameters. The cables <NUM> are wound on the reel <NUM>.

The multi-diameter reel <NUM> comprises portions 175A-C with different diameters. Each portion 175A-C may be a cylinder or be considered a reel by itself. Different cables <NUM> are wound on portions of the reel with different diameters. The different cables <NUM> may be cables coupled to different finger segments <NUM> of the same finger portion <NUM>, and so may be proportionally moved relative to each other. For example, a cable <NUM> coupled to a relatively distal finger segment <NUM> of the finger portion <NUM> (relative to the multi-diameter reel) may be wound on a relatively larger diameter portion 175C of the reel. A cable <NUM> coupled to a relatively proximal finger segment <NUM> of the finger portion <NUM> (relative to the multi-diameter reel) may be wound on a relatively smaller diameter portion 175A of the reel. This allows the cables <NUM> coupled to different finger segments <NUM> of the finger portion <NUM> to move proportionally, enabling the finger portion to allow a natural curling motion of a user's finger while simplifying control compared to a situation in which each cable <NUM> is controlled independently.

So, the portions of the reel <NUM> have different diameters, and allow for different movement of the different cables <NUM> relative to the base portion <NUM>. Upon bending of a finger portion, for example, the proximal phalanx may bend less than the middle phalanx, which is turn bends less than the distal phalanx. As such, the cable <NUM> connected to the distal phalanx may move more relative to the base portion <NUM> than the cable connected to the middle phalanx and the cable connected to the proximal phalanx. The multi-cable coupling may apply gearing to the movement of the cables <NUM> relative to the base portion <NUM>.

Another advantage of providing a reel on which the cable <NUM> is wound that relatively large cable movement is enabled within a relatively compact space. The excess cable length is neatly wound on the reel. In general, a single diameter reel may be provided to achieve these advantages without implementing multi-cable control <NUM>.

The constrain mechanism <NUM> comprises a movable part <NUM> that is coupled to the proximal portion of the cable <NUM>. The SMA wire <NUM> may, upon contraction, constrain movement of the movable part <NUM>, thereby constraining movement of the cable <NUM>.

The movable part <NUM> may be embodied by any part that is permanently coupled to the proximal portion of the cable <NUM>. The movable part <NUM> may be any part that moves with the cable <NUM>. In some embodiments, the movable part <NUM> is integrally formed with the cable <NUM> or is embodied by the proximal portion of the cable <NUM> itself.

Figures 3A and 3B show further examples of the movable part <NUM>, or portions of the movable part <NUM>. As shown in Figure 3A, the reel <NUM> may form the movable part <NUM>. The constrain mechanism <NUM> may thus selectively engage the reel so as to constrain movement of the cable <NUM>. Optionally, other parts may be coupled to the reel to form the movable part <NUM>. For example, a further cable <NUM>' may be coupled to the reel <NUM>, e.g. a further portion of the reel <NUM> with different diameter. The constrain mechanism <NUM> may thus selectively constrain the further cable <NUM>' or another part coupled to the further cable <NUM>. Alternatively, a rack <NUM>" may be coupled to the reel <NUM>, for example by engaging teeth of a gear forming part of the reel <NUM>. The constrain mechanism <NUM> may thus selectively constrain movement of the rack <NUM>".

In general, the movable part <NUM> may be any part that is movable with the cable <NUM>. The movable part <NUM> may be rotationally movable (like the reel <NUM>) or may be translationally movable (like the rack <NUM>"). In general, the reel <NUM> of <FIG> need not be provided.

The cable control mechanism <NUM> may comprise a retraction mechanism <NUM> for retracting the cable upon unbending of the finger portions. The retraction mechanism <NUM> may be embodied by any resilient element permanently coupled to the movable part <NUM> and capable of retracting the cable <NUM>. Preferably, the resilient element is capable of retracting the cable <NUM> over the entire movement range of the cable <NUM>.

The retraction mechanism may be embodied by a torsion spring, for example for applying a torque to the reel <NUM> for retracting the cable <NUM>. The retraction mechanism <NUM> may alternatively be embodied by a tension or compression spring, for example coupled to a movable part in the form of a rack <NUM>" or the coupling cable <NUM>'. The retraction mechanism <NUM> may also act directly on the cable, for example by a spring connected directly to the proximal end of the cable <NUM>.

In the embodiments described in relation to <FIG> and <FIG>, the SMA wire <NUM> may acts directly to selectively to engage and/or disengage the constrain mechanism <NUM>. The SMA wire <NUM> may be required to continuously be powered to keep the constrain mechanism <NUM> engaged or disengaged.

In some advantageous embodiments, a latch <NUM> is used to selectively engage and/or disengage the constrain mechanism <NUM>. The latch assembly may require powering only during switching the constrain mechanism <NUM> into or out of engagement. The latch arrangement may not require power for keeping the constrain mechanism <NUM> engaged and disengaged.

<FIG> schematically shows an example of a latch <NUM>. The latch <NUM> is a bi-stable latch assembly. So, the latch comprises a latching part movable between an unlatched position and a latched position.

The latch <NUM> comprises a support structure <NUM>. The support structure <NUM> is used herein as a reference point, relative to which movement of other components of the latch <NUM> is described (unless otherwise indicated). When integrated into the haptic glove <NUM>, the support structure <NUM> may be fixed relative to the base portion <NUM>, for example by being fixedly attached to the base portion <NUM> or integrally formed with the base portion <NUM>.

The latch <NUM> further comprises a latching part <NUM> and a biasing element <NUM>. The latching part <NUM> is movably arranged relative to the support structure <NUM>. The biasing element <NUM> biases the latch part <NUM> against the support structure <NUM>.

The support structure <NUM> comprises a catching portion <NUM>, in the form of a step <NUM> in <FIG>. The catching portion <NUM> may catch a corresponding portion of the latch part <NUM> under action of the biasing element <NUM>, such that the latching part <NUM> is caught in place by the catching portion <NUM>. Movement of the latch part <NUM> relative to the support structure <NUM> is thus constrained.

The latch assembly <NUM> further comprises an SMA wire 228a. The SMA wire <NUM> is arranged, on contraction, to move the latch part <NUM> from an unlatched position into a latched position in which the latch part <NUM> catches the catching portion <NUM> under action of the biasing element <NUM> such that movement of the latch part <NUM> is constrained.

In addition, the latch assembly <NUM> comprises a release mechanism for releasing the latch part <NUM> from the latched position into the unlatched position. The release mechanism releases the latch part <NUM> from the catching portion <NUM> of the support structure <NUM>, such that the latch part <NUM> returns, under action of the biasing element <NUM>, to the unlatched position.

With reference to <FIG>, operation of the latch assembly <NUM> is described. <FIG> depicts the latch <NUM> in an unlatched position. The biasing element <NUM> biases the latching part <NUM> against the support structure <NUM>. The support structure <NUM> comprises a catching portion <NUM> in the form of a step, separating an upper surface from a lower surface. The latch part <NUM> is biased against the upper surface of the support structure <NUM> by the biasing element <NUM>.

<FIG> depicts the latch <NUM> in a latched position. The transition from <FIG> is achieved by contraction of the SMA wire 228a. Upon contraction, the latch part <NUM> slides along the upper surface of the support structure <NUM> until it drops off the step (catching portion <NUM>) onto the lower surface. The latch part <NUM> is then held in place on the step by the biasing element <NUM>.

<FIG> depicts the latch assembly <NUM> in an unlatched position. The transition from <FIG> is achieved by contraction of the SMA wire 228b. Contraction of the SMA wire 228b slides a release part <NUM> relative to the support structure <NUM>. The release part <NUM> comprises an angled surface for lifting the latch part <NUM> off the step <NUM>. The latch part <NUM> slides back into the unlatched position under action of the biasing element <NUM>.

In general, the release mechanism may comprise any other mechanism for releasing the latch part <NUM> from the catching portion <NUM> of the support structure <NUM>, such as any mechanism capable of lifting the latch part <NUM> over the step <NUM> or other catching portion <NUM> of the support structure <NUM>.

<FIG> discloses another embodiment of a latch assembly <NUM>. The latch assembly <NUM> comprises two latch parts <NUM>, <NUM>' that may be individually brought into latched positions by respective SMA wires 228a, 228a'. The latch assembly <NUM> comprises a single release part <NUM> that, under the action of a single SMA wire 228b, may release both of the latch parts <NUM>, <NUM>' from the latched positions into the unlatched positions. This allows for a more compact assembly compared to using two latch assemblies of <FIG>.

<FIG> discloses another embodiment of the latch assembly <NUM>. The latch assembly <NUM> allows for the latch part <NUM> to selectively move between three positions. The latch assembly <NUM> may thus be considered a tri-stable latch assembly.

In particular, contracting the SMA wire 228a by a first amount leads to the latch part <NUM> falling off the first step <NUM> of the support structure <NUM>. Contracting the SMA wire 228a further, by a second amount, leads to the latch part <NUM> falling off the second step <NUM>' of the support structure <NUM>. The support structure <NUM> thus comprises two catching portions <NUM>, <NUM>' that sequentially catch the latch part <NUM> in two different positions. The release part may be configured to either release the latch part <NUM> from both latched positions simultaneously (such that the latch part <NUM> is released directly to the unlatched position form either first and second latched position), or to release the latch part <NUM> sequentially from the second and first latched positions (such that contraction of the SMA wire 228a' by a first amount releases the latch part <NUM> from the second latched position to the first latched position, and further contraction by a second amount released the latch part <NUM> from the first latched position to the unlatched position).

Although the latch assembly <NUM> of <FIG> comprises two catching portions <NUM>, <NUM>', and so the latch part <NUM> may be moved between three positions (an unlatched position and two latched positions), it will be appreciated that the latch assembly <NUM> may comprise any number of catching portions <NUM>, <NUM>' such that the latch part <NUM> may be moved between any number of positions.

The multi-stage latch <NUM> of <FIG> may be used to vary the frictional force of a brake mechanism 120b, for example. Alternatively, the multi-stage latch <NUM> may be used to selectively engage or disengage multiple different constrain mechanisms, for example when combined with the arrangement of <FIG>.

<FIG> schematically depict embodiments of a cable control assembly <NUM>. The cable control assembly <NUM> may be selectively engageable using the latch mechanism <NUM> described above, for example.

<FIG> shows a constrain mechanism <NUM> in the form of a locking mechanism <NUM>. The latch part <NUM> may be movable between a latched and an unlatched position. The latch part <NUM> is coupled to the intermediary part 124a via a resilient element <NUM>, such as a spring. Presence of the resilient element <NUM> allows for some resilience so as to prevent damaging the teeth of the movable part <NUM> and intermediary part 124a, for example. When the latch part <NUM> is in the latched position (not shown), the teeth of the intermediary part 124a engage with the teeth of the movable part <NUM> to thereby constrain rotation of the movable part <NUM>. When the latch part <NUM> is in the unlatched position (as shown), the movable part <NUM> may be free to rotate.

<FIG> shows another portion of the cable control assembly <NUM>. As shown, the control cable 102b may be connected to another movable part <NUM>'. The combination of movable part <NUM>, control cable 102b and movable part <NUM>' may be considered to correspond to one movable part <NUM>, in that movement of one of these parts may constrain movement of the combination as a whole. A retraction mechanism <NUM> in the form of a spring is connected to the movable part <NUM>', thereby applying a retraction force for retracting the cable <NUM>.

Furthermore, a spring mechanism 120c is selectively engageable with the movable part <NUM>'. When the latch part <NUM> is disengaged (as shown), the second movable part <NUM> may move with the movable part <NUM>' such that no spring force is applied by the spring mechanism 120c. When the latch part <NUM> is engaged (not shown), then the second movable part <NUM> is constrained from moving relative to the base portion <NUM>. A spring force is applied by resilient element <NUM> to the movable part <NUM>', thereby applying an additional spring force to the cables <NUM>. The resilient element <NUM> may have a comparable or higher stiffness than the retraction mechanism <NUM>.

<FIG> schematically depicts another embodiment of a spring mechanism 120c. In this embodiment, the second movable part 122c is a movable gear that may be moved into and out of engagement with at least one of the movable part <NUM> and the intermediary part 124c. When in engagement, a spring force of the resilient element 123c is applied to the movable part.

<FIG> schematically depicts another embodiment of a spring mechanism 120c. In this embodiment, the latch part <NUM> may directly engage the movable part <NUM> so as to apply the spring force of the resilient element 123c.

It will be appreciated that the spring mechanism 120c of <FIG> may be replaced with a locking mechanism 120a or a braking mechanism 120b by effectively replacing the resilient element 123c with a rigid part.

The term 'shape memory alloy (SMA) wire' may refer to any element comprising SMA. The SMA wire may have any shape that is suitable for the purposes described herein. The SMA wire may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA wire. It is also possible that the length of the SMA wire (however defined) may be similar to one or more of its other dimensions. The SMA wire may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two elements, the SMA wire can apply only a tensile force which urges the two elements together. In other examples, the SMA wire may be bent around an element and can apply a force to the element as the SMA wire tends to straighten under tension. The SMA wire may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA wire may or may not include material(s) and/or component(s) that are not SMA. For example, the SMA wire may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA wire' may refer to any configuration of SMA wire acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA wire may comprise two or more portions of SMA wire that are arranged mechanically in parallel and/or in series. In some arrangements, the SMA wire may be part of a larger piece of SMA wire. Such a larger piece of SMA wire might comprise two or more parts that are individually controllable, thereby forming two or more SMA wires.

Claim 1:
Haptic glove (<NUM>) for providing haptic feedback to a user's hand, the haptic glove (<NUM>) comprising:
a base portion (<NUM>) and one or more finger portions (<NUM>) extending from the base portion (<NUM>), wherein each finger portion (<NUM>) is pivotally movable relative to the base portion (<NUM>), and
one or more cables (<NUM>), each comprising a distal end connected to a respective finger portion (<NUM>) and a proximal end extending towards the base portion (<NUM>); and
one or more cable control assemblies (<NUM>), at least one cable control assembly (<NUM>) comprising:
a constrain mechanism (<NUM>) configured, when engaged, to constrain movement of the proximal end of a respective cable relative to the base portion (<NUM>), thereby constraining movement of a respective finger portion (<NUM>) relative to the base portion (<NUM>), and
characterised in that
the at least one cable control assembly (<NUM>) further comprising:
an SMA wire (<NUM>) arranged, on contraction, to engage or disengage the constrain mechanism (<NUM>).