Defeatable interlock mechanism

Abstract

A defeatable interlock system 100 for use with a switch of an electrical system (800, figure 8A-B). The electrical system has an operating shaft (202, figure 2) for opening and closing the switch, the

Description

Field

[0001] The present invention relates to the provision and operation of interlock mechanisms. A defeatable interlock mechanism is described having an integral compliant portion. Background

[0002] An interlock system is used to gain access to the enclosure of an electrical system. For safety reasons, the interlock system is designed to allow access to the enclosure of the electrical system only when the electrical system is de-energised, i.e., when the main circuit within the enclosure is open and an electric current through the main circuit is broken (an “off’ position).

[0003] This is achieved by coupling the handle of the interlock system to a switch of the electrical system, so that when the handle is moved into a position that unlocks the door to the enclosure and allows it to be opened, the switch moves to the “off’ position. Conversely, in order to move the switch into the “on” position, thereby closing the main circuit and energising the electrical system, the handle must be moved into a position that locks the door to the enclosure, thereby preventing access.

[0004] However, certain maintenance activities require defeat of the interlock system so that access may be afforded to the enclosure of the electrical system while the electrical system is energised. A system so configured is called a “defeatable” interlock system.

[0005] Conventionally, a defeatable interlock system comprises an interlock plate with an opening, the interlock plate arranged within a housing having another opening. The openings allow for the coupling of the defeatable interlock system to an operating shaft that has a protrusion (usually called a “locking pin”). In use, the locking pin can pass through the opening in the housing but not the opening in the interlock plate. The locking pin is retained within the housing by the interlock plate. By pressing a pin in contact with the interlock plate, the operator can displace the interlock plate so that the opening of the interlock plate and the opening of the housing align, or overlap, in such a way that the locking pin can pass through both openings. The defeatable interlock system can then be removed from the operating shaft, allowing the door to the enclosure to be opened without moving the switch to the “off’ position. For example, the handle can be decoupled and / or removed from an operating shaft of the switch. A metal helical spring provides the force required to keep the interlock plate in its normal position (in which the door cannot be opened without de-energising the electrical system) in the absence of an input force on the pin from the user / operator.

[0006] It is desirable to provide alternative defeatable interlock mechanisms. Summary

[0007] A defeatable interlock system, and a method for operating the system, is provided for use with a switch of an electrical system, wherein the electrical system comprises an operating shaft for opening and closing the switch, the operating shaft having a locking pin.

[0008] In a first aspect of the present disclosure, a system is provided in the appended independent apparatus claim, with optional features defined in the dependent claims appended thereto. In a second aspect, a method is provided of operating the device of the first aspect as defined in the appended independent method claim. Any features of the first aspect may be implemented as part of the method of the second aspect.

[0009] The system provided in the first aspect is a defeatable interlock system for use with a switch of an electrical system, wherein the electrical system comprises an operating shaft for opening and closing the switch, the operating shaft having a locking pin. The defeatable interlock system comprises a housing with a first opening, an interlock plate comprising a main body portion and an integral compliant portion, wherein a second opening is formed in the main body portion, and a pin extending from the housing. The interlock plate is configured to be compressed from a first state to a second state within the housing and the integral compliant portion of the interlock plate is configured to bias the main body portion of the interlock plate towards the first state. In particular, the interlock plate is configured such that, in the first state, the locking pin can pass through the first opening but not the second opening, while, in the second state, the first opening and the second opening align or overlap such that the locking pin can pass through both the openings and the defeatable interlock system can be removed from the operating shaft of the switch. The pin is configured to exert a force on the interlock plate to compress the interlock plate from the first state to the second state when depressed.

[0010] In this way, a defeatable interlock system which is reliable and cheap to construct can be provided. The integral compliant portion biases the main body portion towards the first state, thereby helping to ensure that in the absence of a force exerted on the interlock plate by the pin (to compress it from the first state to the second state), the defeatable interlock system cannot be removed from the operating shaft of the switch because the locking pin is retained within the housing by the interlock plate. This can be a simple, cost-effective, and versatile alternative to a conventional helical spring. The number of components required to construct the defeatable interlock mechanism disclosed herein can also be lower than a conventional design, helping to ensure reliability and resilience, and dispensing with the time and effort required to assemble a conventional mechanism or design.

[0011] The defeatable interlock mechanism disclosed herein is one in which the interlock plate itself deforms. This contrasts with conventional defeatable interlock mechanisms, in which the interlock plate is configured to be displaced rather than deformed. The compliant portion may be compliant by the way of its form and / or material.

[0012] The pin may be configured to be depressed in response to a force applied in a first direction, and the integral compliant portion of the interlock plate is configured to bias the main body portion of the interlock plate in a direction opposite to the first direction. This can help provide a quick and efficient defeatable interlock mechanism. However, in some examples, depending on the configuration of the interlock plate, the biasing of the main body portion by the integral compliant portion maybe at least in part in a direction other than opposite the first direction.

[0013] The pin may be configured to be depressed by a user or operator. In other examples, the pin may be configured to be depressed automatically by an actuator.

[0014] The first state of the interlock plate may correspond to a partially compressed state. This can increase the stiffness of the compliant portion, increasing the force required to defeat the interlock and reducing accidental activation of the interlock plate. In other examples, the first state corresponds to an uncompressed state or a substantially uncompressed state of the interlock plate. The fact that the interlock plate remains in an uncompressed state or a substantially uncompressed state unless or until the pin is made to exert a force on it can help improve the longevity and reliability of the interlock plate and, thereby, the whole defeatable interlock system.

[0015] The interlock plate may be formed from a polymer. Polymers are cost-effective, abundant, durable, lightweight and safe materials to work with. They have design flexibility and economies of scale. Alternatively, the interlock plate may be constructed from metal or any other material which can be formed to provide a compliant portion, depending on design requirements.

[0016] The interlock plate may be manufactured using an injection moulding process. The advantages of injection moulding include its compatibility with a wide range of materials, its efficiency, repeatability, reliability and importantly the fact that it allows for complex geometries with high tolerances. In other examples, the interlock plate maybe manufactured using an additive manufacture process (such as 3D printing), compression moulding, vacuum casting, carving or any other suitable method. The method of manufacture maybe chosen based on a desired shape and thickness of the integral compliant component.

[0017] In some examples, the integral compliant portion of the interlock plate is formed as a cantilever beam having a fixed end and a free end. Cantilevers constitute an efficient means of providing support to counteract loads or forces. Moreover, they are flexible and may be designed to achieve different support and load bearing requirements.

[0018] The cantilever beam that forms the integral compliant portion in some examples may comprise one curved portion or two or more curved portions. When comprised of two curved portions, one curved portion may be convex and one curved portion maybe concave in shape (i.e., have different orientations). Alternatively, the two or more curved portions may have different radii of curvature but the same orientation (also referred to herein as “double arc”). Such configurations afford design flexibility, such that by simply changing a few parameters such as the length / width / curvature of each curved portion, the force curve as a function of the displacement (e.g., the stiffness) of the cantilever beam may be adjusted to meet design requirements or preferences. In addition, one may also vary the width of the cantilever beam along the length of each curved portion to change the stiffness; this can be particularly advantageous given the compact design space for the interlock mechanism.

[0019] In yet further examples where the integral compliant portion of the interlock plate is formed as a cantilever beam having a fixed end and a free end, the bending of the cantilever acts to bias the interlock plate towards the first state. Moreover, since the fixed end of the cantilever is integrally formed with the main body portion of the interlock plate, the location where the cantilever integrates with the main body portion of the interlock plate is another parameter that may be adjusted to meet stiffness / design requirements.

[0020] Alternatively, the integral compliant portion of the interlock plate may comprise two cantilever portions orientated in opposite directions. Having two cantilever portions divides the force acting on each cantilever portion, which may in some examples further increase the durability and reliability of the integral compliant portion.

[0021] In some examples, the main body portion of the interlock plate is substantially U shaped. A U shape allows the second opening in the interior of the main body portion to define shape, and is furthermore robust.

[0022] In other examples, the second opening comprises a through hole in the main body portion of the interlock plate. Such configurations are alternative ways of designing a robust interlock plate.

[0023] In some examples, the second opening is arranged between the pin and the integral compliant portion of the interlock plate. Such an arrangement facilitates a simple and reliable defeatable interlock mechanism that is quick to operate and compact.

[0024] In the first state the system may be fixedly coupled to the operating shaft. This ensures that, in the first state, access cannot be gained to the enclosure of the electrical system without de-energising the electrical system by disconnecting the main circuit. The operating shaft may comprise one or more protrusions which engage with the interlock plate to fixedly couple the system to the operating shaft.

[0025] Also disclosed herein is a system comprising the defeatable interlock system of the first aspect, a switch, and an operating shaft for opening and closing the switch, wherein the operating shaft is configured to couple the defeatable interlock system to the switch.

[0026] Also disclosed herein is a method of using the defeatable interlock system. The method comprises: applying a force to the pin to depress the pin; in response to depressing the pin, compressing the interlock plate from the first state to the second state; and biasing, by the integral compliant portion of the interlock plate, the interlock plate towards the second state in response to compressing the interlock plate.

[0027] The skilled person will recognise that the features of the device of the first aspect described above may be combined as appropriate, and that optional elements of the first aspect may also be applied to other aspects. Brief description of the figures

[0028] Figure 1A illustrates an example defeatable interlock system in a first state. Figure 1B illustrates an example defeatable interlock system in a second state.

[0029] Figure 2 illustrates an example defeatable interlock system arranged on an operating shaft, where the defeatable interlock system is in the second state of Figure 1B.

[0030] Figures 3A-D provide schematic illustrations of example integral compliant portions of an interlock plate, where each example integral compliant portion is formed as a cantilever.

[0031] Figures 4A-C provide further schematic illustrations of example integral compliant portions of an interlock plate.

[0032] Figure 5 illustrates an example defeatable interlock system with a cantilevered integral compliant portion having curved portions of different radii of curvature.

[0033] Figure 6 illustrates an example cantilever beam.

[0034] Figures 7A, 7B illustrate example defeatable interlock systems with cantilevered integral compliant portions of different lengths. Figure 7C shows the modelled force exerted by the cantilevered portions as a function of displacement for example integral compliant portions (obtained using finite element analysis).

[0035] Figures 8A, 8B illustrate exploded-view diagrams of a portion of example electrical systems comprising a defeatable interlock system and an operating shaft for opening and closing a switch.

[0036] Figure 9 is a flowchart showing example operations for operating a defeatable interlock system as described herein. Detailed description

[0037] The present disclosure provides a defeatable interlock system that allows an operator or user, in certain circumstances (for example, in order to perform certain maintenance activities), to defeat the interlock mechanism and gain access to the enclosure of an electrical system while the electrical system is energised (i.e., the main circuit of the electrical system is “on”).

[0038] Figure 1 (Figures 1A and 1B) illustrates an example defeatable interlock system too for use with a switch of an electrical system. The defeatable interlock system 100 comprises a housing 102 with a first opening, an interlock plate 110, and a pin 108 extending from the housing. The interlock plate 110 comprises a main body portion 104 with a second opening, and an integral compliant portion 106. In this example, the second opening formed within the main body portion 104 (or simply “the opening of the main body portion 104” or “second opening”) is arranged between the pin 108 and the integral compliant portion 106 of the interlock plate 110. The term “integral” used herein in the phrase “integral compliant portion” refers to the fact that the main portion and compliant portion is formed as a single piece. This helps to ensure a cheaper and more efficient production assembly, since sub-assembly is not needed.

[0039] The electrical system to which the defeatable interlock system may be coupled comprises an operating shaft that extends along an axis 112. The operating shaft opens and closes the switch. Moreover, the operating shaft has a locking pin. A locking pin may be any type of protrusion on the operating shaft, or any other feature which is configured to couple the operating shaft to the defeatable interlock system. The term switch is to be understood as any type of device with an electrical switching action, such as a contactor or electrical isolation device.

[0040] The interlock plate 110 is configured to be compressed from a first state (Figure 1A) to a second state (Figure 1B) within the housing 102. However, the integral compliant portion 106 of the interlock plate 110 is configured to bias the main body portion 104 of the interlock plate 110 (or simply and equivalently bias the interlock plate 110) towards the first state (Figure 1A). The first state may also be called the “normal” state. This biasing helps prevent accidental or unintended movement of the integral plate towards the second state. In the first state, the operating shaft is fixedly coupled to the interlock plate. In particular, in the first state, the locking pin can pass through the first opening but not the second opening when in use. In other words, the locking pin is retained within the housing by the interlock plate.

[0041] In the second state (Figure 1B), which may also be called the “defeated” state, the interlock plate (110) is configured such that the first opening within the housing 102 and the second opening formed within the main body portion 104 of the interlock plate 110 align. In particular, in this second state, the first opening and the second opening overlap, or align, such that the locking pin can pass through both the openings when in use. This overlap or alignment of the two openings allows the defeatable interlock system too to be removed from the operating shaft of the switch. Note that sufficient clearance must be provided between the operating shaft and the aligned openings in the second state to accommodate the curved motion of the defeatable interlock system 100 as the door to the enclosure turns around its hinges relative to the operating shaft.

[0042] In order to facilitate the transition of the system 100 from the first state (Figure 1A) to the second state (Figure 1B), the pin 108 is configured to exert a force on the interlock plate 110 to compress the interlock plate 110 from the first state to the second state when the pin is depressed.

[0043] Figure 1A illustrates an example first state of the system 100, in which the pin 108 extends from the housing 102. The first state may correspond to an uncompressed state or a substantially uncompressed state of the interlock plate no. In other examples, the interlock plate may be partially compressed in the first state.

[0044] Figure 1B illustrates an example second state of the system too. In this state, the pin is depressed, and this depression exerts a force on the interlock plate no, transitioning it to a compressed state. In this example, the pin 108 is depressed in response to a force F applied in a direction 114 that is opposite to the direction in which the integral compliant portion 106 of the interlock plate no is configured to bias the main body portion 104 of the interlock plate no.

[0045] The pin may be depressed by a user or operator, or may be configured to be depressed by an actuator.

[0046] Figure 2 illustrates how the defeatable interlock system 100 may be coupled with the operating shaft 202 of an electrical switch. In this example, the operating shaft 202 extends through the first opening of the housing 102 and the second opening formed within the main body portion 104 of the interlock plate no along the axis 112.

[0047] In this example, the locking pin 204 or other protrusion at one end of the operating shaft 202 ensures that the operating shaft 202 is fixedly coupled to the system 100. Therefore, under normal circumstances, the interlock system 100 is in a first (“normal”) state in which it is prevented (by the protrusion or locking pin 204 retained within the housing by the interlock plate) from being removed from the operating shaft 202 without opening the switch and de-energising the electrical system. The opening and closing of the switch may be achieved by coupling the operating shaft to a rotatory handle. By turning the switch to the “off” position, the operating shaft is rotated by some angle around axis 112. In this configuration, the locking pin 204 is not impeded by the interlock plate 110 and the interlock system 100 may be removed from the operating shaft 202 of the switch. In other words, the second opening aligns with the locking pin 204 to allow the interlock system too to be decoupled from the shaft 202 when the switch is open.

[0048] The “defeatable” nature of the interlock system 100 is used in non-normal circumstances where the interlock system too needs to be removed from the operating shaft 202 of the switch, thereby gaining access to the enclosure of the electrical system, without opening the switch. As illustrated in Figure 2, this may be achieved by applying a force to the pin 108, which in turn exerts a force on the interlock plate 110, causing it to compress into a second (“defeated”) state within the housing 102 in which the openings of the housing 102 and the main body portion 104 align in such a way that the locking pin 204 no longer impedes the interlock system 100 from being removed from the operating shaft 202. In other words, the locking pin 204 and the second opening align in the second state to accommodate or allow movement of the locking pin 204. In some examples, the second opening can include one or more recesses formed to accommodate or allow movement of the locking pin 204 or protrusions through the second opening when the interlock plate is in the second state.

[0049] The component of the interlock system 100 that allows such a “defeatable” feature, as described above with reference to the example illustrated in Figure 2, is the integral compliant portion 106 of the interlock plate 110. The main body portion is understood to be generally non-compliant to facilitate appropriate coupling with the shaft 202.

[0050] Figure 3 illustrates, schematically, various examples in which the integral compliant portion 106 of the interlock plate 110 is formed as a cantilever having a fixed end and a free end. As illustrated, the fixed end of the cantilever is integrally formed with the main body portion 104 of the interlock plate 110. In these examples, it is the bending of the cantilever that acts to bias the interlock plate 110 towards the first state. Therefore, compliance is provided by the form of the integral compliant portion 106. The main body portion 104 maybe any suitable shape to provide the second opening.

[0051] Figure 3A illustrates an example in which the integral compliant portion 106a is a substantially straight cantilever beam.

[0052] Figure 3B illustrates an alternative example in which the integral compliant portion 106b comprises a curved portion.

[0053] Figures 3C and 3D illustrate further examples in which the cantilever beam comprises two curved portions. When the two curved portions comprise substantially two arcs, such a configuration may be described as a “double arc”. In the example illustrated in Figure 3C, the two curved portions comprise two arcs with the same orientation, but different curvatures (or different radii of curvature). The example of Figure 3D illustrates another possibility wherein one curved portion is convex in shape and one curved portion is concave in shape (i.e., have different orientations).

[0054] Figure 4 illustrates, schematically, yet further example configurations incorporating an integral compliant portion 106. In these examples, the main body portion maybe U-shaped. Alternatively, the second opening formed within the main body portion 104 may comprise a through hole in the main body portion 104, or may be any suitable shape to provide the second opening.

[0055] Figure 4A illustrates an example in which the integral compliant portion 406a has two fixed ends that are integrally formed, at different points, with the main body portion 104.

[0056] Figure 4B illustrates another example in which the integral compliant portion comprises a plurality of components 4o6b-d that are respectively integrally formed, at different points, with the main body portion 104. Specifically, in the example illustrated in this figure, the integral compliant portion of the interlock plate comprises two cantilever portions 4o6b-c orientated in opposite directions and additional compliant portion 4o6d. In an alternative embodiment, 4o6d may constitute a component of the main body portion 104 of the interlock plate 110, rather than the integral compliant portion 106. In other words, the portion 4o6d may be non-compliant.

[0057] Figure 4C illustrates a further example in which the integral compliant portion comprises a plurality of components 4o6e-i distributed around the main body portion 104 of the interlock plate 110. As with the example illustrated in Figure 4B, in an alternative embodiment, the component 406c may be non-compliant, and, therefore, constitute a component of the main body portion 104.

[0058] The skilled person will recognise that the shapes illustrated in Figures 3 and 4 are schematic and, rather than limiting the possible shapes that the integral compliant portion 106 may take, they emphasize the plethora of possible shapes and designs available to the skilled person in order to achieve the intended result of biasing the interlock plate 110 towards the first state.

[0059] Figure 5 illustrates an example system too, in which the integral compliant portion 106 of the interlock plate 110 is formed as a cantilever beam.

[0060] The free end 510 of the compliant portion 106 may be configured to contact an internal portion of the housing 102 that is fixed relative to the interlock plate 110. As force is applied to compress the interlock plate 110 from the first state to the second state, this compression causes bending of the compliant portion 106. The bending of the cantilever acts to bias the interlock plate 110 towards the first state. In other words, the bending (or deformation) of the integral compliant portion 106 due to the compression against the fixed internal portion of the housing 102 creates a restoring force that acts in a direction opposite to the direction 114 in which the force is applied to the pin 108.

[0061] The example illustrated in Figure 5 demonstrates the freedom available to the skilled person to modify various parameters of the design of the integral compliant portion 106 in order to achieve a desired stiffness profile for the integral compliant portion 106.

[0062] The integral compliant portion 106 formed as a cantilever may comprise two arcs (“double arc”). In other words, the compliant portion may comprise two curved portions (arcs), each arc with a different radii of curvature but having the same orientation. The relative size of the two arcs may be modified or changed. The use of a “double arc” provides flexibility in terms of the shape of the compliant portion, enabling provision of a compact spring arm feature. In particular, due to limitations on compliant portion thickness from a manufacturing perspective and limitations on length from a design perspective, a single arc spring with uniform thickness can have a stiffness which is above a desired threshold (in terms of ease of use, ergonomics, etc.). However, by providing two arcs with variable radii, length and merge locations, a compact spring arm feature of suitable thickness may be provided.

[0063] As illustrated in Figure 5 (see also Figure 6), in some examples the relative size of the two arcs may be different, such that the cantilever beam comprises a main arc proximate the main body portion and a second (smaller) arc located distal from the main body portion (proximate the free end of the cantilever beam). In such an example, given the relative sizes (length, radius, thickness) of the main arc and the second arc, one may broadly model the cantilever beam as consisting of a single arc.

[0064] With reference to Figures 5 and 6, the “arm” of the cantilever beam corresponds to the portion of the cantilever beam (modelled as a single arc) from a first axis defined by direction 114 and the free end of the cantilever beam. The length of the arm is denoted a in Figures 5 and 6.

[0065] The various tuneable / modifiable parameters available to the skilled person in the example illustrated in Figure 5 (see also Figure 6) include: • the radius of curvature R of the arc; • the length a of the arm; • the width or thickness w of the compliant portion, or more generally the cross-sectional area of the compliant portion. This maybe variable across the length of the arc; • the merge location of the integral compliant portion 106 with the main body portion 104, i.e., the position of the fixed end 508 of the arc; and / or • the merge location 512 of the main arc and the second (smaller) arc.

[0066] Note that the total length of the arc L may be simply calculated from the length a of the arm, the radius of curvature R of the arc and the position of the fixed end 508 of the arc. With reference to Figure 6, the (total) length of the arc is stated as: L = a + b.

[0067] Additionally, the shape of the main body portion 104 may be varied. For example , the main body portion 104 of the interlock plate 110 may be substantially U shaped (as shown in Figures i and 5) or, alternatively, the second opening of the main body portion 104 may comprise a through hole in the main body portion 104 of the interlock plate 110, so that the main body portion 104 is generally or substantially O shaped.

[0068] Furthermore, the material from which the integral compliant portion 106 (and the rest of the interlock plate no) is manufactured may be chosen according to design requirements in order to achieve the desired stiffness profile for the integral compliant portion 106. In some examples, the interlock plate no is formed from a polymer which is a versatile, cheap and durable material. In such examples, the interlock plate no may be manufactured using an injection moulding process.

[0069] Depending on the material used the operating temperature range of the defeatable interlock system too maybe from -25°C to 5O°C.

[0070] Figure 6 illustrates a close-up view of an example integral compliant portion 106 formed as a cantilever comprising two curved portions, but which maybe modelled as a single arc given the relative size of the two curved portions. As described above with reference to Figure 5, the stiffness of the integral compliant portion 106 may be tuned by changing one or more of: the length a of the arm, the width or thickness w (or more generally the cross-sectional area) of the compliant portion, also known as the “section modulus”, the radius of curvature R of the arc, the position of the fixed end 508 of the arc, and the material of the interlock plate.

[0071] The deflection or displacement, denoted 5, of the free endpoint 510 of the cantilever depends on the above-cited parameters through the following formula: „ „3 r® .sin (20) F R - H--i—-

[0072]  8 =---—,

[0073] where F is the force acting on the endpoint of the beam in direction 614, R is the radius of the arc, 9 is the angular distance of the arc (see Figure 6), I is the moment of inertia of the cross-sectional area, and E is the Young’s modulus. The stiffness K of the beam can thus be calculated.

[0074] For example, for a cantilever beam with a rectangular cross section with base b and height t, the moment of inertia is:

[0075] I = b t3 / 12.

[0076] The Young’s modulus E parameterises properties of the material; in particular, the ability of the material to withstand changes in length when under lengthwise tension or compression and is given by the ratio of the uniaxial stress a to the strain e:

[0077] E = a / E.

[0078] Rewriting the formula for the displacement in terms of the force required to generate a specific displacement gives a stiffness K:

[0079] F ~ SEI / L3 ~ K8,

[0080] where L is the length of the arc. With reference to Figure 6, L = a + b.

[0081] From the above formula for the force, a greater displacement requires a greater force. Moreover, the stiffness is inversely proportional to the length of the arc L to the power 3. Thus, small changes in the arc length can be used to manufacture a wide range of compliant portion stiffnesses.

[0082] Figure 7 illustrates a simple example of how changing the length of the arc produces different force profiles for the integral compliant portion 106.

[0083] Figure 7A is a schematic illustration of a defeatable interlock system 100 with a short cantilever beam acting as the integral compliant portion 106, while Figure 7B is a schematic illustration of a defeatable interlock system 100 with a long cantilever beam acting as the integral compliant portion 106.

[0084] Figure 7C illustrates how varying the length of the arc can be used to change the force profile of the integral compliant portion 106. In this example, the integral compliant portion 106 is of uniform thickness, which means that the slope or gradient of each curve is substantially constant. The slope of the force-displacement curve defines the modelled stiffness K of the integral compliant portion 106 (acting as a “spring” arm).

[0085] The data in Figure 7C has been obtained from modelling the force exerted as a function of displacement using finite element analysis. Note that Figure 7C shows the force exerted on the endpoint 510 of the cantilevered integral compliant portion 106.

[0086] As explained above, many parameters may be used to change the stiffness of the integral compliant portion 106 to the required value for a given application, including e.g., designing an integral compliant portion 106 with a variable stiffness across its length by, for example, having a non-uniform cross-sectional area (not shown). This ensures that the design is adaptable to any design space and constraint.

[0087] Figure 8A is an exploded-view drawing of an example electrical system 800 comprising a defeatable interlock system too, with a housing 102, interlock plate 110, and a pin 108. Note that in this example, the integral compliant portion 106 of the interlock plate 110 comprises two cantilever portions orientated in opposite directions, and the opening within the interlock plate 110 comprises a through hole in the main body portion 104 of the interlock plate 110, so that the main body portion 104 is substantially O shaped.

[0088] The example electrical system 800 further comprises a switch (not shown) operated by an internal rotatory handle 804, and an operating shaft 202 for opening and closing the switch. The operating shaft 202 is configured to couple the defeatable interlock system 100 to the rotatory handle 804. The locking pin 204 is configured such that the operating shaft 202 is fixedly coupled to the system 100 in the first state.

[0089] The electrical system may further comprise a switch plate 802 that indicates to the user whether the switch is open or closed, a nut 806 that fixes the rotatory handle 804 in place, a front plate 808 that also indicates the status of the switch, an external rotatory handle 810 for rotating the operating shaft 202 and thereby changing the position of the internal rotatory handle 804, and a padlock slider 812 for restricting access to the enclosure of the electrical system to, for example, only authorised personnel (e.g., by allowing to lock the external rotary handle 810).

[0090] Similarly, Figure 8B is an exploded-view drawing of another example electrical system 800 comprising a defeatable interlock system 100, with a housing 102, an interlock plate 110 having a single cantilevered portion, and a pin 108.

[0091] Figure 9 is a flowchart showing example operations for operating a defeatable interlock system 100 as described herein.

[0092] Operation 901 comprises applying a force F in direction 114 to the pin 108 to depress the pin 108. The force F acts to compress the interlock plate and needs to be of sufficient force to counter the biasing of the main body portion 104 of the interlock plate 110, by the integral compliant portion 106, towards the first state. When force F in direction 114 is greater than the biasing force from the integral compliant portion 106, the interlock mechanism is defeated and can be decoupled from shaft 202.

[0093] Operation 903 comprises, in response to depressing the pin 108, compressing the interlock plate 110 from the first state to the second state.

[0094] Operation 905 comprises biasing, by the integral compliant portion 106, the interlock plate no towards the second state in response to compressing the interlock plate no.

[0095] It should be realised that the foregoing embodiments are not to be construed as limiting and that other variations, modifications and equivalents will be evident to those skilled in the art and are intended to be encompassed by the claims unless expressly excluded by the claim language.

[0096] Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or in any generalisation thereof. Claims may be formulated to cover any such features and / or combination of such features derived therefrom. 13 11 24

Claims

1. A defeatable interlock system for use with a switch of an electrical system, the electrical system comprising an operating shaft for opening and closing the switch, the operating shaft having a locking pin, the defeatable interlock system comprising:a housing comprising a first opening;an interlock plate comprising a main body portion and an integral compliant portion, wherein a second opening is formed in the main body portion, the interlock plate configured to be compressed from a first state to a second state within the housing, the integral compliant portion of the interlock plate configured to bias the main body portion of the interlock plate towards the first state, wherein the interlock plate is configured such that:in the first state, the locking pin can pass through the first opening but not the second opening, andin the second state, the first opening and the second opening overlap such that the locking pin can pass through both the openings and the defeatable interlock system can be removed from the operating shaft of the switch; anda pin extending from the housing, the pin configured to exert a force on the interlock plate to compress the interlock plate from the first state to the second state when depressed.

2. The defeatable interlock system of claim i, wherein the pin is configured to be depressed in response to a force applied in a first direction, and wherein the integral compliant portion of the interlock plate is configured to bias the main body portion of the interlock plate in a direction opposite to the first direction.

3. The defeatable interlock system of any one of the preceding claims, wherein the pin is configured to be depressed by a user.

4. The defeatable interlock system of any one of the preceding claims, wherein the first state corresponds to an uncompressed state of the interlock plate.

5. The defeatable interlock system of any one of the preceding claims, wherein the interlock plate is formed from a polymer.13 11 246. The defeatable interlock system of claim 5, wherein the interlock plate is manufactured using an injection moulding process.

7. The defeatable interlock system of any one of the preceding claims, wherein the integral compliant portion of the interlock plate is formed as a cantilever beam having a fixed end and a free end.

8. The defeatable interlock system of claim 7, wherein the cantilever beam comprises a curved portion.

9. The defeatable interlock system of claim 8, wherein the cantilever beam comprises two curved portions.

10. The defeatable interlock system of claim 9, wherein one curved portion is convex in shape and one curved portion is concave in shape.

11. The defeatable interlock system of any one of claims 7-10, wherein the bending of the cantilever acts to bias the interlock plate towards the first state.

12. The defeatable interlock system of any one of claims 1-6, wherein the integral compliant portion of the interlock plate comprises two cantilever portions orientated in opposite directions.

13. The defeatable interlock system of any one of the preceding claims, wherein the main body portion of the interlock plate is substantially U shaped.

14. The defeatable interlock system of any one of claims 1-12, wherein the second opening comprises a through hole in the main body portion of the interlock plate.

15. The defeatable interlock system of any one of the preceding claims, wherein the second opening is arranged between the pin and the integral compliant portion of the interlock plate.

16. The defeatable interlock system of any one of the preceding claims, wherein in the first state the defeatable interlock system is fixedly coupled to the operating shaft.17- An electrical system, comprisingthe defeatable interlock system of any one of the preceding claims;a switch; andan operating shaft for opening and closing the switch, wherein the operating shaft is configured to couple the defeatable interlock system to the switch.

18. A method of using the defeatable interlock system of any one of claims 1-17, the method comprising:applying a force to the pin to depress the pin;in response to depressing the pin, compressing the interlock plate from the first state to the second state; andbiasing, by the integral compliant portion of the interlock plate, the interlock plate towards the second state in response to compressing the interlock plate.CM

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