Field

This relates to an engagement knob for opening and closing a switch. In particular, this relates to an engagement knob comprising a moveable component having an integral compliant portion configured to bias the moveable component. In some examples, the integral compliant portion can be a cantilevered compliant portion

Background Electrical switches often comprise an engagement knob configured to receive a lock-off mechanism, such as a padlock, so that the switch can be safely locked in an “off’ position during inspection and maintenance. Such engagement knobs are herein termed padlock knobs or lock-off knobs. Padlock knobs typically comprise a sliding mechanism which can be pressed by an operator to reveal a window or aperture through which the padlock or lock can be inserted. The presence of the padlock through the aperture prevents the sliding mechanism from moving, locking off the knob and preventing actuation of the switch. Such sliding mechanisms typically comprise a metal helical spring that is compressed when the operator presses the sliding mechanism. When the padlock is removed, the helical spring returns to an uncompressed state.

It is desirable to provide alternatives to conventional helical springs in such lock-off knobs.

Summary

In a first aspect, a device is provided as defined in the appended independent apparatus claim, with optional features defined in the dependent claims appended thereto. In a second aspect, a method of operating the device of the first aspect is provided as defined in the appended independent method claim. Any features of the first aspect maybe implemented as part of the method of the second aspect.

Described herein is an engagement knob for opening and closing a switch. The engagement knob comprises a housing and a moveable component moveable between a first position and second position within the housing. The moveable component comprises an integral compliant portion configured to bias the moveable component towards the first position. Use of an integral compliant portion provides a simple and cost-effective alternative to a conventional helical spring. The integral compliant portion can provide the desired resilience without requiring assembly of multiple components.

The moveable component can be configured to move towards the second position in response to an application of force in a first direction, wherein the integral compliant portion is configured to bias the moveable component in a direction opposite the first direction. In some examples, depending on the configuration of the integral compliant portion, the biasing may be at least in part in a direction other than opposite the first direction.

In some examples, the moveable component further comprises an engagement portion extending from the housing. The moveable component is configured to move towards the second position in response to the application of force to the engagement portion.

The engagement portion can be configured for engagement by a user/ operator, or may be automatically engaged by an actuator, for example.

In some specific examples described herein, the integral compliant portion is a cantilever having a fixed end and a free end, the cantilever extending at an acute angle.

In one arrangement, the free end is configured to contact an internal portion of the housing, wherein bending of the cantilever against the internal portion acts to bias the moveable component towards the first position. Other forms of deformation other than bending are also possible.

In some examples, the cantilever comprises a notch proximal to the fixed end.

A thickness of the cantilever at the free end may be greater than a thickness of the cantilever at the fixed end. In some examples, the change in thickness forms or provides the notch.

The cantilever may comprise one or more curved portions. In some examples, the cantilever comprises a curved portion proximate to the fixed end, and wherein a remainder of a length of the cantilever is straight (or substantially straight) when the moveable component is in the first position. In other examples, the cantilever may comprise curved portions along its length. In some specific arrangements, the moveable component is configured to move between the first position and the second position along a first axis, the movement relative to the housing. The first direction can be parallel (or substantially parallel) to the first axis.

The engagement knob can further comprise a base portion, wherein the housing and moveable component are moveable relative to the base portion when the moveable component is in the first position. In some examples, the moveable component further comprising a protruding portion, wherein, the protruding portion extends into a recess in the base portion when the moveable component is in the second position to prevent movement of the housing and the moveable component relative to the base portion.

In some examples, the housing and moveable component being moveable relative to the base portion comprises the housing and moveable component being rotatable relative to the base portion. Optionally, the rotation is around a rotation axis parallel (or substantially parallel) to the first axis. In other examples, the housing and moveable component being moveable relative to the base portion comprises the housing and moveable component being moveable in a lateral direction relative to the base portion. Optionally, the lateral direction is perpendicular (or substantially perpendicular) to the first axis.

The housing may comprise one or more apertures. The apertures can be arranged such that, when the moveable component is in the second position, the engagement knob comprises a through-hole, wherein when a locking member is inserted through the through-hole, the moveable component is retained in the second position. The apertures can be arranged such that, when the moveable component is in the first position, the moveable component overlaps with the one or more apertures and the engagement knob does not comprise the through-hole. A stiffness of the integral compliant portion can be predetermined based on a form and/or material and/or size of the integral compliant portion. A stiffness of the integral compliant portion can be selected or predetermined in accordance with a desired use case or application for the engagement knob. The stiffness can be greater when the moveable component is in the second position than when in the moveable component is in the first position. The integral compliant portion can be resiliently deformable by way of its form or structure. Optionally, the integral compliant portion comprises a flexure. Additionally or alternatively, the integral compliant portion can be resiliently deformable by way of its material. In some examples, the integral compliant portion comprises an elastic material. Optionally the integral compliant portion comprises a polymer. Optionally, the integral compliant portion comprises a plastic. It can be desirable, in regard to the electrical environment in which engagement knob too is for use, that at least the engagement portion of the moveable component is formed from an insulating material. Also disclosed herein is a system comprising the engagement knob of any example of the first aspect and a switch. The engagement knob is coupled (either directly or indirectly) to the switch for opening and closing the switch.

Also described herein is a method of using an engagement knob for opening and closing a switch. The engagement knob comprises a housing and a moveable component moveable between a first position and second position within the housing. The moveable component comprises an integral compliant portion configured to bias the moveable component towards the first position. The method comprises applying a force to the moveable component to move the moveable component from the first position to the second position. The method further comprises biasing, by the integral compliant component, the moveable component towards the first position in response to applying the force.

In some examples, the housing comprises one or more apertures arranged such that when the moveable component is in the second position, the engagement knob comprises a through-hole. The method further comprises inserting a locking member through the through-hole to retain the moveable component in the second position.

It will be understood that any of the features described above with reference to the device of the first aspect may be provided in any suitable combination. Moreover, any such features may be combined with any features of the method of the second aspect, or vice-verse, as appropriate.

List of Figures The following description is with reference to the following Figures. Figure 1A illustrates an example engagement knob with a moveable component in a first position, and Figure 1B illustrates the engagement knob of Figure 1A with the moveable component in a second, compressed, position;

Figure 2 shows an exemplary cross section of a moveable component (integral compliant portion not shown) illustrating a protrusion for preventing movement of the engagement knob;

Figures 3A, 3B, 3C provide schematic illustrations of example engagement knobs;

Figure 4 shows an example cantilevered integral compliant portion;

Figures 5A, 5B, 5C, 5D provide schematic illustrations of example cantilevered integral compliant portions;

Figure 6 shows an example notched cantilevered integral compliant portion;

Figure 7A shows an example cantilevered integral compliant portion in accordance with Figure 4 in a compressed state, and Figure 7B shows an example notched cantilevered integral compliant portion in accordance with Figure 6 in a compressed state; Figure 8 shows a modelled deformation of example cantilevered integral compliant portions obtained using finite element analysis;

Figures 9A to 9D provide schematic illustrations of example integral compliant portions; and Figure 10 is a flowchart showing example operations for operating an engagement knob as described herein.

Detailed description

With reference to Figure 1 (Figures 1A and 1B), a device too for opening and closing a switch is described. Device too is termed herein an engagement knob, e.g. a knob (or handle) for engagement of the switch by a user. In the following description, the term switch is used, but the knob too may be implemented in combination with any other type of electrical switching action (such as a contactor or electrical isolation device).

Knob too comprises a housing 102 and a moveable component 104. The moveable component may also be known as a “slider”. The moveable component is moveable between a first position (Figure 1A) and a second position (Figure 1B). The moveable component 104 is configured to move towards the second position of Figure 1B in response to an application of force, F, in a first direction 106.

With reference to Figure 1A, the moveable component 104 comprises an engagement portion 108 extending from the housing 102. In this example, the housing 102 is configured so that it does not extend across the entire moveable component 104, i.e. the moveable component is only partially enclosed by the housing 102. The engagement portion corresponds to the portion of the moveable component not enclosed by the housing. For example, the engagement portion 108 can extend through one or more apertures in the housing 102. In other examples, the engagement portion can be any portion of the moveable component which is external to the housing 102 and which can be engaged by a user or operator.

The moveable component is configured to move from the first position of Figure 1A towards the second position of Figure 1B in response to the application of force F to the engagement portion. In the following description, the engagement portion 108 is configured for engagement by a user. In other words, engagement or actuation of the moveable component is in response to application of force F by an operator, or user. However, in other examples the actuation may be controlled by one or more actuators or actuating mechanisms.

The moveable component 104 is configured to move between the first position and the second position along a first axis 110, represented here by the dashed line. The movement along axis 110 is movement relative to the housing 102. In other words, the housing 102 does not move when force F is applied to the moveable component 104. The first direction 106, in which the force is applied, is substantially parallel to the first axis in the specific example of Figure 1. In this example, the moveable component 104 moves relative to the housing 102 only along axis too. In other words, there is no rotational movement of the moveable component relative to the housing, and no lateral movement perpendicular to the first axis 110. Rather, there is a fixed range of motion along the first axis 110.

With further reference to Figure 1, the engagement knob too can further comprise a base portion 112. The base portion 112 can be configured to be mounted on an enclosure or casing of a switch. In other examples, the base portion 112 can be formed from the enclosure or casing of a switch; in other words, engagement knob too can be mounted directly on the switch.

When the moveable component is in the first position of Figure 1A, the housing 102 and moveable component 104 are moveable relative to the base portion. However, the moveable component can be configured such that, when the moveable component is in the second position of Figure 1B, movement of the housing 102 and the moveable component 104 relative to the base portion 112 is prevented. In other words, when a sufficient force F is applied to the moveable component, the engagement knob is prevented from moving, thereby preventing opening (or closing) of the switch. When the moveable component is in this second position, the engagement knob can be locked-off to prevent opening (or closing) of the switch during inspection or maintenance.

To facilitate this locking off, the engagement knob too comprises one or more apertures 116. The aperture(s) 116 are arranged such that when the moveable component is in the second position, the engagement knob comprises a through-hole

118 (shown in Figure 1B). A locking member (not shown) can then be inserted through the through-hole 118, to retain the moveable component 114 in the second position. However, when the moveable component is in the first position, the moveable component 114 overlaps with the one or more apertures 116 and the engagement knob toodoes not comprise the through-hole.

The moveable component defines at least a portion of the through-hole 118. In this example the locking mechanism can be inserted above the moveable component; the moveable component defines one edge of the through-hole 118, with the aperture 116 in the housing defining the other edges of the through-hole 118. In some other examples (not shown), depending on the configuration of the moveable component, the through- hole 118 can be defined through the moveable component as well as through the housing 112. The through-hole can be configured such that the locking mechanism can be inserted in any suitable position relative to the moveable component to prevent movement of the engagement knob too relative to the base portion 112.

With reference to Figure 2, a cross section of the engagement knob too of Figure 1 is shown to illustrate an example mechanism for preventing opening or closing of the switch is described. In this example, the moveable component further comprises a protruding portion 214. When the moveable component is in the second position (not shown), the protruding portion 214 extends into a recess in the base portion to prevent movement of the housing and the moveable component relative to the base portion. In some examples, the base portion is configured such that the protruding portion 214 only prevents movement of the housing and the moveable component relative to the base portion when the engagement knob too is in an “off’ position. In other words, the switch can be locked-off (and thus not switched on). In some examples, the engagement knob may be configured such that the switch may additionally or alternatively be locked “on”. When maintenance is completed and the switching equipment needs to be operational, the padlock or locking mechanism is removed from the through-hole 118 and the slider or moveable component is biased back to the uncompressed state, ensuring that the protrusion 214 comes out of the recess. Movement (rotational or lateral) of the engagement knob is then possible.

In the particular example of Figure 1, the housing and moveable component being moveable relative to the base portion 112 comprises the housing 102 and moveable component 104 being rotatable relative to the base portion 112. The rotation is rotation around a rotation axis. Optionally, the rotation axis is substantially parallel to the first axis 110. Optionally, the rotation axis passes through a centre of the housing 102. In other examples (not shown in Figure 1), the housing and moveable component being moveable relative to the base portion 112 comprises the housing 102 and moveable component 104 being moveable in a lateral direction relative to the base portion. Optionally, the lateral direction is substantially perpendicular to the first axis 110.

In the example shown in Figure 1, the moveable component 104 is configured to move in first direction 106 into the housing 102. However, it will be understood that the moveable component can move in any suitable direction. Schematic illustrations of some alternative arrangements are shown in Figure 3. Figure 3A mirrors the arrangement of Figure 1B, wherein the first direction 106 is substantially parallel with the first axis 110 of the knob too as defined in Figure 1. Figure 3B illustrates an alternative, wherein the first direction 106 is at an actuate angle with respect to the first axis 110 of Figure 1. Figure 3C illustrates another alternative, wherein the first direction 106 is substantially perpendicular to the first axis 110 of Figure 1.

In previous approaches, a separate helical spring was used to move the moveable component 104 from the second position of Figure 1B to the first position of Figure 1A upon removal of the application of force F (optionally, upon removal of the locking mechanism). However, it is desirable to reduce a number of component parts, and provide a simpler engagement knob which is quicker and cheaper to manufacture.

With reference to Figure 4, it has been recognised that the separate helical spring can be replaced by providing a moveable component 104 comprising an integral compliant portion 420. The integral compliant portion is integrated with the moveable component as a single component. In other words, the moveable component with integral compliant portion is formed as a single piece, without the need for pieces to be joined together during assembly. The component may be physically manufactured by injection molding, but any other suitable manufacturing techniques maybe used. The integral compliant portion 420 is configured to bias the moveable component 104 towards the first position of Figure 1A. In some examples, integral compliant portion 420 is configured to bias the moveable component 104 in a direction substantially opposite the first direction 106 in which the force F is applied by an operator or user. By providing an integral compliant portion, the moveable component can be formed as a single part, reducing the cost and complexity of manufacture and assembly of the engagement knob too. Moreover, a stiffness of the compliant portion can be fine-tuned to a particular application by altering the geometry of the compliant portion 420 without requiring changes to the housing 102. The compliant portion 420 is a flexible mechanism that is resiliency deformable through elastic body deformation. It gains some or all of its deformation from the relative flexibility of its members. The compliant portion 420 can be resiliently deformable by its form and/ or by its material. In some examples, the compliant portion is formed from an elastic material (i.e. a material that wants to go back in the original form when it is pushed or bent).

In the specific example of Figure 4, which shows the moveable component in the first position and a close up of the compliant portion 420 (denoted by dashed lines), the integral compliant portion 420 is provided as a cantilever having a fixed end 422 and a free end 424. The cantilever 420 extends between the fixed end 422 and the free end 424. In this example, the cantilever extends at an acute angle relative to the first axis

110 along which the moveable component moves. The following description is made with reference to a cantilevered compliant portion 420, but it will be understood that any suitable compliant portion 420 may be used to provide the desired biasing of the moveable component.

The free end 424 of the compliant portion 420 is configured to contact an internal portion 102-a of the housing 102. The internal portion 102-a of the housing 102 is fixed relative to the moveable component 104. As force is applied in direction 106 along the first axis too, the cantilever 420 is compressed between the rest of the moveable component 104 (i.e. the portion of the moveable component that comprises the engagement portion) and the internal portion 102-a. This compression causes bending of the compliant portion 420 (not shown). The bending of the cantilever against the internal portion 102-a acts to bias the moveable component 104 towards the first position of Figure 4. In other words, the bending (or deformation) of the compliant portion 420 due to the compression against the fixed internal portion 102-a creates a restoring force that acts in the opposite direction to direction 106 in which the force is applied.

The cantilevered integral compliant portion 420 of Figure 4 comprises one or more curved portions. In this example, the curved portion is proximate to the fixed end 420. Curved portion(s) can facilitate bending or deformation of the compliant portion. In this example, a remainder of a length of the cantilever 420 is substantially straight. In other words, the cantilever comprises a curved portion proximate to the fixed end, and a remainder of the length of the cantilever is substantially straight when the moveable component is in the first position. However, other cantilevered examples are possible, as discussed with respect to Figure 5.

With reference to Figure, a length of the cantilever 420 can be substantially straight, as in Figure 5C. Contrary to the example of Figure 4, this example of Figure 5C does not comprise a curved portion proximate to the fixed end. Rather, the cantilever is substantially straight along its length.

Alternatively, a length of the cantilever can comprise one or more curved portions. For example, the length of the cantilever can be substantially circular, as in Figure 5D, or the cantilever can comprise one or more curved portions along its length, as in Figures 5A and 5B. In the example of Figure 5D, it will be understood that the free end of the cantilevered portion 420 will not contact the internal portion 102-a of the housing; rather, a middle portion of the cantilever 420 will contact the housing to produce the desired deformation. Any of these examples may be configured to integrate directly with the rest of the moveable component 104 at the fixed end 422, as shown in Figure 5 (i.e., there may not be a curved portion proximate the fixed end). Alternatively, any of these examples may comprise a curved portion proximate to the fixed end 422 similar to that illustrated in Figure 4. For example, the cantilever may comprise a curved portion proximate to the fixed end, and a remainder of a length of the cantilever may comprise one or more curved portions. A geometry of the compliant portion 420 can be adjusted or altered to tune a stiffness of the compliant portion, for example by manipulation of a curvature of the cantilever or other compliant portion 420. The material of the compliant portion may (additionally or alternatively) be chosen to adjust the stiffness. In other examples, a thickness of the compliant portion can (additionally or alternatively) be used to alter or tune the stiffness, as discussed with reference to Figure 6.

In one example, illustrated in the cross-section of engagement knob too shown in Figure 6, the compliant portion 420 comprises a notch 626 (shown within the circle). The notch 626 is formed proximal to the fixed end of the cantilevered compliant portion 420. The notch 626 can be used to alter a stiffness of the compliant portion.

In particular, it has been recognised that a moveable component with an integral compliant portion is generally manufactured using a moulding process, which process requires a minimum thickness of the component to avoid any defects in the finished component. However, there is a limitation on the length of the compliant portion, since the moveable component sits within a housing 102. Due to this limitation on thickness from a manufacturing perspective, and this limitation on length from a design perspective, a complaint portion 420 with a uniform thickness (as shown in Figure 4) cannot have a stiffness less than a certain value. By providing a notch 626, a stiffness of the compliant portion can be decreased, which can facilitate easier operation of the engagement knob too by a user.

In some examples (not shown), the compliant portion has a uniform thickness along its length, with the exception of the notch 626. In other words, a notch is formed in a compliant portion of uniform thickness. The notch can be formed as a scoop, or cut out. The thickness of the compliant portion in the notch region is less than the uniform thickness of the rest of the compliant portion. In other examples, a thickness of the cantilever at the free end is greater than a thickness of the cantilever at the fixed end. In the particular example shown in Figure 6, the portion proximate the fixed end has a first thickness, t, and the remainder of the compliant portion has a second thickness, T, where T > t. In other words, thickness is increased towards the free end 424. This change in thickness along the length of the compliant portion 420 forms the notch 626. In other words, the notch is formed due to the compliant portion increasing in thickness along its length after a predetermined point (here after the curved portion proximate the fixed end, but the thickness can increase at any suitable point). The increase in thickness along the length of the compliant portion 420 reduces bending throughout the compliant portion. The majority of the bending occurs at the curved portion proximate the fixed end 422.

In Figure 6 the change in thickness is abrupt. In other examples, the change in thickness may be gradual along the length of the compliant portion. A thicker compliant portion is more durable, increasing the lifetime of the moveable component. However, a thicker compliant portion is typically stiffer. The inclusion of notch 626 acts to decrease the stiffness of the compliant portion 420 at the same time as compared to the example of Figure 4, at the same time as the thickness is increased. A more durable component can therefore be provided, which facilitates easy operation of the engagement knob too by a user. The thickness of the compliant portion and/or shape of the notch 626 can be selected for a given application to provide a desired stiffness.

Figure 6 shows the moveable component in the first position, i.e. in an uncompressed state of the compliant portion 420. Figure 7A shows the moveable component in the second position, i.e. in a compressed state, for a cantilevered compliant portion of uniform thickness. Figure 7B shows the moveable component in the second position, i.e. in a compressed state, for a cantilevered compliant portion of variable thickness having a notch.

As the moveable component moves from the first position to the second position, the point of contact between the moveable component 104 and the housing 102 changes from the free end of the cantilever to the compliant portion itself. In both cases, the free end 424 remains free in the compressed state and does not contact the housing 102. It can be seen that the compliant portion appears to lie substantially flat against the internal portion 102-a of the housing in the compressed state. However, due to the geometry of the compliant portion, there is a slight curvature in the compressed compliant portion 420, leading to a discrete point of contact 728 between the compliant portion and the internal portion 102-a. The point of contact 728 is shown at a distance x from the fixed end in Figure 7A, and at distance x’ from the fixed end in Figure 7B. The reaction force at the point of contact 728 acts to bias the moveable component towards the first position. For a cantilever beam type compliant portion 420 with total length L, let A be the required deformation of the compliant portion 420 for a given application (i.e. the deflection of the beam end). If a force F is applied at the end of the “beam”, then:

FL ³

A= -

3EI and the stiffness of the beam, K, is therefore:

F 3E1

K = - = — A I ³ where E is the modulus of elasticity and I is the moment of inertia. For the same beam, if a force, f, is applied at a distance I from the fixed end, / > 3EI where 5 is the deflection of the beam, where k is the stiffness.

Using similar triangles,

In other words, a shorter beam is stiffer. Following similar principles, the cantilevered compliant portion 420 can be designed to shift the point of contact 728 between the compressed compliant portion and the fixed internal portion 120-a of the housing away from the fixed end 422 of the compliant portion 420, thereby increasing the distance I (or x) at which the force is applied to the “beam” and so decreasing the stiffness.

This principle is illustrated in the exemplary data of Figure 8, which shows the modelled deformation of a compliant portion 420 with applied force F for a uniform thickness compliant portion and a compliant portion having a notch (modelled using finite element analysis, FEA). The uniform thickness compliant portion has a thickness of 1.34 mm. The compliant portion having a notch has a thickness in the notch region of t = 1.4 mm, and a thickness T = 2 mm for the remaining compliant portion. The integral compliant portion in both cases had an overall length of 27 mm. However, these parameters are exemplary only, and it will be understood that any suitable geometry/form/size maybe used instead. It can be seen that, initially, the stiffness of the compliant portion with a notch is higher than a uniform thickness spring. However, as the deformation increases the notch acts to reduce stiffness as compared to the uniform thickness compliant portion. In this particular example, a maximum stiffness for the compliant portion (as obtained from FEA) is:

• Uniform thickness compliant portion stiffness = 1.03 N/mm

• Compliant portion with notch stiffness = 0.65 N/mm

This modelled change in maximum stiffness is due in part from a shift in the point of contact from x = 10.5 mm from the fixed end for the uniform thickness compliant portion (as in Figure 7A) to x’ = 16.6 mm from the fixed end for the compliant portion with a notch (as in Figure 7B). These particular positions for the discrete contact point 728 are obtained by FEA. Such a shift in the point of contact can be further understood by considering bending of the cantilevered portion. For the uniform thickness compliant portion, bending occurs throughout the length of the compliant portion as the moveable component is displaced towards the second position. As the spring is compressed, the point of contact with the internal portion 102-a of the housing is towards the fixed end 422, due to bending of spring throughout the length of the compliant portion. For a thicker compliant portion, bending is reduced through the length and concentrated near the fixed end 422. Since the majority of the bending occurs near the fixed end (and not in the length), the point of contact is correspondingly located towards the free end. In other words, the point of contact is moved away from the fixed end by the notch. Overall stiffness is therefore reduced as compared to the uniform thickness compliant portion discussed herein.

A lower stiffness is desirable from an ergonomic perspective, to facilitate ease of use by a user. The use of a notched cantilevered compliant portion as described herein can facilitate provision of a low stiffness helical spring replacement which fits within an existing, compact, housing footprint. Moreover, the use of a varying thickness and/or a notched portion allows a desired stiffness curve to be determined for a given application.

Further exemplary FEA modelling considered the lifecycle of the notched compliant portion, having the parameters discussed above. When the moveable component is compressed, 61 MPa stress is induced in the compliant portion, located at the joint between the compliant portion and the rest of the moveable component. Based on this stress, and the fatigue properties of the component, it was determined that the compliant portion could withstand 7500 operational cycles of compressing and releasing the moveable component (lifecycles) without failure. A typical moveable component is only required to be operational for 2000 lifecycles. Fatigue life time of this particular exemplary integral compliant component is thus higher than the required life time of the component. It can thus be seen that the integrated compliant portion discussed herein is a feasible replacement for conventional helical springs, as well as allowing for adjustment of a desired stiffness. Use of such a compliant portion also reduces manufacturing and assembly costs as it replaces multiple parts by a single, integrated, component.

The exemplary notched compliant portion discussed above (and as illustrated in Figure

6) was compared to an engagement knob with a conventional helical spring (comparative example). An actuation force of 4.54 N was determined by FEA for the notched compliant portion, as compared to 4.6 N for a knob with a conventional helical spring (as measured using a force gauge). This actuation force of 4.54 N is within the optimum range for an operator, taking into account ergonomics and ease of use.

In these particular examples of the compliant portion, a stiffness of the integral compliant portion 420 is greater when the moveable component 104 is in the second position than when in the moveable component is in the first position. In other words, as can be seen in Figure 8, the stiffness increases as the compliant portion is compressed (i.e. as the moveable component is depressed by a user and moved towards the second position). It will be understood that such an increased stiffness is not limited to these examples, but can be achieved through a variety of integral compliant portion geometries/forms and material choices. This increased stiffness in the second position causes a higher reaction force to be exerted to bias the moveable component towards the first position. This higher biasing force can make it more difficult to remove the locking mechanism, reducing the risk of accidental un-locking of the engagement knob. Safety may therefore be improved. However, any suitable stiffness curve may be formulated for a given application.

Having regard to the use of the engagement knob for electrical switching, the moveable component is preferably (though not necessarily) formed of an insulating material. The moveable component with integrated compliant portion can be formed of a polymer.

In some examples, the moveable component is formed of a plastic. With further reference to Figure 9, other example integral compliant portions are illustrated. These may be implemented in place of the cantilevered compliant portion described above. In one example (Figure 9A), the integral compliant portion 420 may have one free end and extend in a direction parallel, or substantially parallel to, the first direction 106 in which force is applied to the moveable component 104 by a user/operator. In another example (Figure 9B), the integral compliant portion 420 may not have a free end; instead, the reliance maybe provided by deformation around point 925 (for example due to contact between point 925 and an internal portion of the housing). In another example (Figure 9C), the integral compliant portion 420 may have two free ends and extend in two directions, both of which are at an acute angle to the first direction 106 in which force is applied to the moveable component 104 by a user/operator. In another example (Figure 9D), the integral compliant portion 420 may not have a free end; instead, the reliance maybe provided by flattening around point 925 (for example due to contact between point 925 and an internal portion of the housing). Any other suitable integral compliant mechanism may be used.

With reference to Figure 10, operations for using an engagement knob too for opening and closing a switch are described. The engagement knob too is as described herein, comprising a housing and a moveable component moveable between a first position and second position within the housing. The moveable component comprises an integral compliant portion configured to bias the moveable component towards the first position.

Operation 1001 comprises applying a force to the moveable component to move the moveable component from the first position to the second position. Applying said force causes deformation of the resiliently deformable compliant portion.

Such deformation acts to exert a reaction force opposing movement of the moveable component towards the second position. Operation 1003 comprises biasing, by the integral compliant component, the moveable component towards the first position in response to applying the force. In other words, the moveable component is biased away from the second position by the deformation of the integral compliant component.

Optionally, the housing comprises one or more apertures arranged such that when the moveable component is in the second position, the engagement knob comprises a through-hole. In such examples, optional operation 1005 comprises inserting a locking member through the through-hole to retain the moveable component in the second position.

A system may also be provided comprising an engagement knob as described herein. In some examples, a system comprises the engagement knob too and a switch (or switching device) can be provided herein. The engagement knob is coupled to the switch for opening and closing the switch. For example, the engagement knob can be mounted on a casing or housing of the switch and coupled to a switching mechanism for operating the switch.

It is noted herein that while the above describes various examples of the engagement knob of the first aspect, this description should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.