Endoscopy is a growing branch of minimally invasive surgery whereby an endoscope is inserted in a patient’s natural orifice and travels down to a target site along one of the patent’s lumens (e.g. colon, intestine, oesophagus, bronchioles, etc.). A range of procedures might be performed in succession at the target site or as separate procedures including staging, diagnosis and operation.

An endoscope is the instrument used for endoscopy and commonly comprises a long tube with working channels, cables and optics running along its length. Traditionally, they have a proximal body, from which the operator controls the scope, a long, flexible main body (i.e. an insertion tube), and a distal bending section at the distal tip with which a camera sits and tools may extend from.

Endoscopes are generally flexible in bending along their length but stiff in torsion. Angulation is achieved by having a highly flexible distal bending section which can bend in two planes allowing the distal tip of the endoscope to be orientated as desired. Ordinarily, the bending of the endoscope is control by angulation cables that connect to the distal tip at points spaced 90° apart, e.g. at 3, 6, 9 and 12 o’clock, so that pairs of cables can actuate bending in two planes (up-down and left-right). These pairs of angulation cables are in fact a single angulation cable (or two connected cables that may be considered a single cable) that extends back to the proximal end of the endoscope, wrapping around a gear in the body such that rotating the gear applies an axial force to the distal tip of the endoscope and causes the bending section to flex in a specific plane.

Endoscope bending sections have been developed alongside this four cable I dual pulley system and are well suited to bending along two perpendicular axes (e.g. the 3 - 9 o’clock axis and the 12 - 6 o’clock axis), typically including several vertebrae that rotate about either one of these axes. However, as endoscope control mechanisms continue to develop, existing bending sections are becoming less suitable for the new mechanisms and are susceptible to damage from unwanted friction between endoscope components and torque at the vertebrae connections if, for example, the number or position of angulation cables in the endoscope is altered. Therefore, it is desirable to provide an endoscope that addresses these issues while providing a high level of control.

SUMMARY

According to the present invention there is provided an endoscope comprising: a plurality of sequentially arranged segments; wherein each segment of the plurality of segments is rotatably connected to an adjacent first segment about a first axis, and rotatably connected to an adjacent second segment about a second axis; wherein the first axis is angularly offset from the second axis by a segment offset angle that is less than 90°.

The segments being rotatably connected meaning that adjacent segments rotate relative to each other about the connection point between the adjacent segments.

Having the same segment offset angle between each adjacent segment defines a segment unit length, where the segment unit length is the number of adjacent segments before a segment axis of rotation (such as the first and second axis) has rotated 180°. For example, when the segment offset angle is 60° the segment unit length is three, and when the segment offset angle is 45° the segment unit length is four.

In this way, unwanted torque from angulation cables or control mechanisms configured to manipulate the plurality of segments may be reduced. This reduces hysteresis in the endoscope, increasing its ease of control and lengthening service life.

Typically, the plurality of segments are arranged within a bending section of an endoscope insertion tube, though they may also be arranged anywhere along the insertion tube.

The adjacent segments may be rotatably connected by interlocking pivots, wherein the pivots are tapered to prevent adjacent segments disconnecting. Providing tapered interlocking pivots prevents adjacent segments disconnecting while minimising the profile of the segments, enabling the size of the endoscope to be reduced. Furthermore, the tapered pivots prevent disconnecting segments without having to introduce additional components (e.g. a nut and bolt fastener).

Each segment of the plurality of segments may be rotatably connected to the adjacent first segment by first and second pivots, and rotatably connected to the adjacent segment by third and fourth pivots; wherein the first and second pivots define the first axis; and wherein the third and fourth pivots define the second axis.

Each segment of the plurality of segments may comprise a channel; wherein an endoscope component may be passed through the plurality of segments via the channels.

The endoscope component may be, for example, an angulation cable or an endoscopy tool such as optics or a vacuum tube. Having the segments include a channel means that the endoscope component can be passed through the interior of the plurality of segments, protecting the endoscope component and minimising the profile of the endoscope.

At least one segment of the plurality of segments may comprise a cable guide configured to guide an angulation cable through the segment.

The cable guide ensures the angulation cable remains within a specific region of the segment during use of the endoscope, preventing the cable or nearby components becoming stuck or tangled. In some examples of the invention the cable guide may be the segment channel itself, while in others the cable guide is a distinct component such as a slot, cleat, or eyelet.

In some examples of the invention, every segment of the plurality of segments comprises a cable guide, while in other examples this is not the case - e.g. every other or every third segment in the sequence comprises a cable guide for a given angulation cable. Furthermore, a segment may comprise a plurality of cable guides for a single angulation cable.

The cable guide may be arranged on the interior of the channel. This further reduces the size of the plurality of segments. The segment offset angle may be 60°.

The plurality of segments may be uniformly shaped. In this way, a uniform level of rotation between adjacent segments is provided through the plurality of segments.

The plurality of segments may be formed connected to each other. For example, the plurality of segments may be laser-cut or machined from a single hypodermic tube. This provides strongly connected plurality of segments with a small profile.

In some other examples of the invention, the plurality of segments may be formed separately and connected to each other before use. For example, the segments are machined individually and subsequently welded to either side of a pivot to connect adjacent segments. This may allow the plurality of segments to be easily repaired or modified.

A central axis may be defined as extending between a proximal end and a distal end of the endoscope, wherein the central axis is orthogonal to the first and second axes when the plurality of segments are in an unbent configuration; and the endoscope further comprises a plurality of angulation cables; wherein a first plane defined by a first angulation cable and the central axis is orthogonal to the first axis; and wherein a second plane defined by a second angulation cable and the central axis is orthogonal to the second axis. In this way, the endoscope is configured to avoid undesirably torqueing the plurality of segments, thereby increasing the service life of the segments.

The endoscope may further comprise: a plurality of control mechanisms, wherein each control mechanism comprises: a translation unit arranged at a proximal end of the endoscope; and an angulation cable comprising a proximal end and a distal end; wherein the proximal end of the angulation cable is connected to the translation unit, and the distal end of the angulation cable extends along the plurality of segments towards a distal end of the endoscope; wherein the plurality of control mechanisms are arranged such that, in use, an operator can direct angular movement of the endoscope at the distal end by movement of the angulation cables via their respective translation units.

In this way, each angulation cable connecting to the distal end of the endoscope is also connected to a unique translation unit, and so each cable may be actuated independently of the others. This means each of the plurality of control mechanisms is able to keep the angulation cable taut while the distal end is manoeuvred - avoiding backlash in the control mechanism and reducing hysteresis in the endoscope. Furthermore, the control mechanism eliminates the need for pre-tensioning of the angulation cable, as moving a particular cable does not have a direct effect on any other angulation cables (as it would in current endoscopes).

The angulations cables may extend through the plurality of segments towards the distal end of the endoscope.

The endoscope may comprise a central axis extending between the proximal end to the distal end of the endoscope, wherein the central axis is orthogonal to the first and second axes when the plurality of segments are in an unbent configuration; and wherein the plurality of control mechanisms are arranged around the central axis, such that adjacent control mechanisms are angularly offset from each other.

That is, a first plane defined by a first angulation cable (of a first control mechanism) and the central axis is angularly offset from a second plane defined by a second angulation cable (of a second control mechanism) and the central axis. This allows the control mechanisms to act in concert with each other to direct the angulation of the distal end of the endoscope across different planes. For example a first control mechanism may direct the distal end through a first (e.g. horizontal) plane, while a second control mechanism is angularly offset from the first control mechanism and so can direct the distal end through a second plane (with a component perpendicular to the first). The adjacent control mechanisms may be angularly offset from each other by a same mechanism offset angle. As the control mechanisms are evenly spaced around the central axis, tension in the cables is more evenly distributed when directing the distal end, thereby increasing service life of the control mechanisms and endoscope.

The endoscope may comprise three control mechanisms, such that the mechanism offset angle is 120°. This allows the control mechanisms to direct the distal end of the endoscope back and forth through orthogonal (e.g. horizontal and vertical) planes, while occupying less space within the endoscope and allowing a smaller endoscope design to be provided.

The endoscope may further comprise a control system; wherein the control system is configured to receive a movement input from an operator, and send a control signal to a translation unit of at least one of the control mechanisms; wherein the movement input is associated with the desired angular movement of the distal end of the endoscope; and wherein the translation unit is configured to move the corresponding angulation cable in response to the received control signal.

In this way, the control system is able to process a movement input from an operator and precisely actuate the control mechanisms, providing easier operation and/or a higher degree of control than an operator would otherwise be able to achieve by manually actuating the control mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows an example configuration of an endoscope;

Figure 2 shows an example configuration of a control mechanism of the endoscope; Figures 3A-3C show an example of a bending section of the endoscope; and

Figures 4A and 4B show a cross section of an example of the bending section of the endoscope.

DETAILED DESCRIPTION

An example of an endoscope 1 is generally illustrated in an assembled configuration in Figure 1 . The endoscope 1 comprises a body 5 arranged towards a proximal end 2 of the endoscope 1 , and an insertion tube 6 extending from the body 5 towards a distal end 3 of the endoscope 1 . Though the full length of the insertion tube 6 is not shown in Figure 1 , the insertion tube 6 is significantly longer than the body 5 and is flexible along its length. The insertion tube 6 comprises a bending section 7 towards the distal end 3 of the endoscope. A central axis 4 of the endoscope 1 extends between the proximal end 2 and the distal end 3 of the endoscope 1 , running through the centre of the endoscope 1 when the insertion tube 6 is in an unflexed (i.e. straight or unbent) configuration as shown in Figure 1.

Figure 2 shows an alternative view of the endoscope 1 to highlight the control mechanisms 10 housed within; two control mechanisms 10 are visible in Figure 2. These control mechanisms 10 can be actuated to direct the angular movement of the distal end 3 of the endoscope 1. Each control mechanism 10 comprises a translation unit 11 arranged toward the proximal end 2 of the endoscope 1 (outside of the insertion tube 6) and an angulation cable 12. A proximal end 13 of the angulation cable 12 is connected to the translation unit 11 and a distal end 14 of the cable 12 extends, from the translation unit 11 , towards a distal end 3 of the endoscope 1 where it connects to the bending section 4. In this example, the distal end 14 of the cable 12 extends through the insertion tube 6 and connects to the bending section 7.

Due to the connection at the proximal end 13 of the cable 12, the translation unit 11 of each mechanism 10 is configured to actuate the angulation cable 12 - tensioning and moving it along the length of the endoscope 1 relative to the unit 11 so as to control the position and loading of the cable 12. As the angulation cable 12 is also connected to the bending section 7, this movement may be used to control the angular movement of the distal end 3 of the endoscope 1 (i.e. the bending section 7).

The translation unit 11 may be any component that can actuate the angulation cable 12 and control the distal end 3 of the endoscope 1. Typically, this is through linear translation or rotation of the cable 12 and the unit 11 may be, for example, a mechanical actuator, pneumatic actuator, hydraulic actuator, SMA actuator, electrical actuator, thermal actuator, a mechanical handle-puller system etc.

As shown in Figure 2, the angulation cable 12 of each control mechanism 10 passes through (at least one) Bowden cable 16 that runs along the insertion tube 6 up until the bending section 7, at which point the Bowden cable 16 terminates and the angulation cable 12 continues to extend towards the distal end 3. In some examples of the endoscope 1 the Bowden cables may extend from the translation unit 11. These Bowden cables 16 may be placed anywhere within the cross section of the insertion tube 6 and may be free to float along the tube 6 (and body 5). Bowden cables 16 have been described in this example but torque/torsion coils may also be used interchangeably.

Each translation unit 11 is connected to a corresponding individual angulation cable 12 such that the endoscope 1 comprises the same number of translation units 11 as it does angulation cables 12 - with the position and tension of each cable 12 controlled by its corresponding unit 11. This decouples the motion of each angulation cable 12 from any others, allowing the cables 12 to be controlled independently and ensuring no slack is present or backlash occurs. The ability to control the length of each angulation cable 12 independently also means that the cables 12 can be controlled to accommodate the curved path of the insertion tube 6 of the endoscope 1 , eliminating the pre-tensioning effect found in existing endoscopes.

The arrangement of the control mechanisms 10 within the endoscope 1 (in particular the position of the translation unit 11 and the connection(s) between the angulation cable 12 and the bending section 7) determine how the distal end 3 of the endoscope 1 is controlled by said mechanisms 10. The angulation cables 12 can run along/through the bending section 7 in any placement or configuration to achieve the desired range of motion, though the preferred configuration for bending in two orthogonal directions is to have the angulation cables 12 (and, optionally, the translation units 11) spaced equally around the central axis 4. This configuration may be described as angularly offsetting adjacent control mechanisms 10 from each other around the central axis 4, where the mechanism offset angle 15 is equal to 360/N degrees and N is the number of control mechanisms 10. In this way, the motion of each angulation cable 12 is decoupled from the others and a maximum level of control is provided to each control mechanism 10.

Figure 4A shows an example cross section of a segment 30 of a bending section 7 of an endoscope 1 with three control mechanisms 10. The angulation cables 12 can be seen to pass through the of the segment 30, in particular through a single channel 35, and are equally angularly offset from one another with a mechanism offset angle 15 of 120°. Having three control mechanisms 10 provides the minimum number of angulation cables 12 required to achieve angulation of the distal end 3 of the endoscope 1 in two planes. This minimises the volume occupied by the control mechanisms 10, allowing a smaller endoscope 1 to be provided. This is hugely beneficial given that a primary function of an endoscope 1 is to be directed through a patient’s lumen.

In some examples of the endoscope 1 , it may be advantageous to include a greater number of control mechanisms 10. For example, including more control mechanisms 10 may allow tension in the angulation cables 12 to be more evenly distributed across the different cables 12 - reducing tension on a particular control mechanism 10 and increasing the service life of the endoscope 1. Furthermore, increasing the number of control mechanisms 10 in an endoscope 1 can facilitate finer tuning of the angular movement of the distal end 3 of the endoscope 1.

Preferably, an electronic control system 20 (not shown) is used to coordinate actuation of the plurality of control mechanisms 10 within the endoscope 1 , so as to direct angular movement of the distal end 3 without introducing unnecessary tension or slack in the angulation cables 12. The control system 20 maps a movement input from an operator to control signals sent to the translation unit(s) 11 in order to tension the angulation cables 12 accordingly, providing a higher degree of control than an operator would otherwise be able to achieve manually. The control system 20 may be located either on or near the endoscope 1 or in a separate location so as to connect the movement inputs of the operator to the endoscope 1 (after processing).

The control system 20 takes a movement input (i.e. an input vector) from an operator (e.g. via a user interface device located on or near the body 5). Once received, the data signal of the input vector may be processed to, for example, remove noise and disturbances by filtering the signal. The magnitude of the input vector relates to the amount of bending (i.e. the degree of rotation) desired at the distal end 3 of the endoscope 1 , and the direction of the input vector defines the direction of bending/orientation desired at the distal end 3. The input vector is then mapped to control signals applied to the translation unit 11 controlling each angulation cable 12 that needs to be adjusted.

An example method for mapping a movement input to control signals uses a polar transform function. The polar transform takes the 2-dimensional input vector where the two components (x and y) define the desired bending in the horizontal and vertical plane respectively and normalizes it to have a magnitude between 0 and 1 , where 0 equals no bending and 1 equates to maximum bending. The locations of the angulation cables 12 along the bending section 7 are represented in the same vector space with the central axis 4 equating to the origin and the horizontal to the x-axis.

The dot product between the input vector and the cable 12 locations relates to the control signal for each translation unit 11. For example, if the dot product is negative this indicates the cable 12 needs to extend and a control signal will be sent to the respective translation unit 11 to achieve such whilst maintaining a minimum tension and therefore ensuring the angulation cable 12 does not go slack. The signals outputted from the polar transform function can undergo further manipulation before being sent to the translation units 11 , such manipulation may incorporate feedback to modulate the magnitude of the control signal.

Figures 3A-3C show an example of a bending section 7 of an endoscope 1. The bending section 7 comprises a plurality of sequentially arranged segments 30, where each segment 30 is rotatably connected to two adjacent segments 30 (i.e. one on the proximal side and one on the distal side). In order to allow the bending section 7 to bend in any direction, a first pair of adjacent segments will be connected so as to rotate about a first axis 31 that is angularly offset from a second axis 32 which a second pair (e.g. comprising one of the segments 30 of the first pair and the next adjacent segment 30) rotate about. The first axis 31 and second axis 32 are offset by a segment offset angle 33 that is less than 90°.

Figure 3B shows a specific example where a given segment 30 is rotatably connected to an adjacent first segment 30a on its proximal side by first and second pivots 34a, 34b (not shown) and an adjacent second segment 30b on its distal side by third and fourth pivots 34c, 34d. The first and second pivots 34a, 34b define the first axis 31 that the segment 30 and adjacent first segment 30a rotate about, while the third and fourth pivots 34c, 34d define the second axis 32 that the segment and adjacent second segment 30b rotate about.

It is preferable that segment offset angle 33 is the same between any given adjacent segments 30 of the plurality of segments 30. In the example of Figures 3A-C the segment offset angle 33 is 60°, also shown in Figure 4B, which means it takes a sequence of three adjacent segments 30 before the axis of rotation connecting the adjacent segments rotates 180° to be parallel with the original axis of rotation.

It can be seen from Figures 3A-C that adjacent segments 30 are rotatably connected by pivots 34. Preferably, the interlocking parts on adjacent segments forming these pivots 34 are tapered (e.g. towards or away from the central axis 4) to prevent adjacent segments 30 disconnecting from each other. In alternative examples, the connections may be provided by other joints such as living hinges. The segments 30 of Figures 3 and 4 are ring shaped with an annular cross section perpendicular to the central axis 4. This allows for angulation cables 12 or other endoscopy tools (e.g. optics or a vacuum) to be passed along through a channel 35 formed by the segment 30. In some other examples the segments 30 may not be ring shaped but instead are solid cylinders with a plurality of channels 35 running through each segment, for example individual channels 35 for each angulation cable 12 and a further channel 35 for endoscopy tools. Typically, the plurality of segments 30 are uniformly shaped in order to provide a uniform level of bending over the length of the bending section 7 and to reduce the costs of manufacture. However this is not always necessary and some bending sections 7 may comprise segments 30 of different shapes and sizes. For example, a greater degree of bending across a given length may be desired in the plurality of segments 30 near the distal end 3 of the endoscope, and so shorter segments 30 can be provided with less distance between adjacent segments 30 (and therefore the segment axes of rotation) to facilitate this.

The segments 30 may also include cable guides 36 to guide an angulation cable 12 through the segment 30. The cable guides 36 ensure the angulation cables 12 remain within a specific region of the segment 30 as they pass along the plurality of segments 30 and are actuated during use of the endoscope 1 . This provides a more consistent and predictable level of tension in an angulation cable 12, helps to prevent the cables 12 get stuck or tangled, and improves the control of the angular movement of the distal end 3 of the endoscope 1 .

The cable guides 36 may be provided in any suitable form. For example Figure 3B uses slots formed into the sides of the segments 30 as cable guides 36 - the slots are configured to act as cleats with the angulation cables 12. In another example, the cable guides 36 comprise eyelets fixed onto the side of the segment 30. It is not necessary for each segment 30 to include a cable guide 36 in order to achieve the associated benefits, however it is preferable that they are evenly distributed along the length of the plurality of segments 30. Furthermore, though the examples of the endoscope 1 described so far show the angulation cables 12 passing through the interior channel 35 of the plurality of segments 30, in other examples the angulation cables 12 run along the outside of the segments 30 - so the cable guides 36 are also arranged on the outside of the segments 30.

The plurality of segments 30 shown in Figures 3A-C and 4A-B are formed with a uniform shape and a segment offset angle 33 between adjacent segments of 60°. This configuration is well suited to an endoscope 1 with three angulation cables 12, as shown in Figure 4B, as each angulation cable 12 corresponds to a different axis of rotation in the plurality of segments 30 and so a high degree of control is provided over the distal end 3 of the endoscope 1. However, this same configuration is also compatible with other endoscopes 1 comprising a different number (e.g. four) of angulation cables 12, as the plurality of segments 30 still provides full angulation of the distal end 3 in two planes. In some endoscopes 1 , when a greater number of angulation cables 12 is included, the segment offset angle 33 is decreased accordingly in order to avoid undesirably torqueing the plurality of segments 30 and causing damage.

The plurality of segments 30 may be manufactured by machining a single hypodermic tube - e.g. by laser-cutting the pivots 34 and segments 30 into the tube so that it is formed as a single piece with the segments 30 attached to each other. Alternatively, the plurality of segments 30 may be manufactured separately (e.g. individually) and are attached to one another at a later time - for example, by welding a segment 30 to either side of a pivot 34.

In another example of the endoscope 1 (not shown), rather than comprising a plurality of ring shaped segments 30, the bending section 7 may comprise a central rod separated into segments with pivots (e.g. hinges or ball and socket joints) linking adjacent segments. Alternatively again, the bending section 7 may comprise a central continuum rod that deforms or bends when actuated by the angulation cables 12. In both of these examples, the angulation cables 12 run along the outside of the bending section 7 and are supported in position by cable guides 36.

Further examples of the present disclosure are set out in the following numbered clauses: Numbered clause 1 : An endoscope comprising: a plurality of control mechanisms, wherein each control mechanism comprises: a translation unit arranged at a proximal end of the endoscope; and an angulation cable comprising a proximal end and a distal end; wherein the proximal end of the angulation cable is connected to the translation unit, and the distal end of the angulation cable extends towards a distal end of the endoscope; wherein the plurality of control mechanisms are arranged such that, in use, an operator can direct angular movement of the endoscope at the distal end by movement of the angulation cables via their respective translation units.

Numbered clause 2: The endoscope of clause 1 , wherein the endoscope comprises a central axis extending from the proximal end to the distal end of the endoscope; and wherein the plurality of control mechanisms are arranged around the central axis, such that adjacent control mechanisms are angularly offset from each other.

Numbered clause 3: The endoscope of clause 2, wherein adjacent control mechanisms are angularly offset from each other by a same mechanism offset angle.

Numbered clause 4: The endoscope of clause 3, wherein the endoscope comprises three control mechanisms, such that the mechanism offset angle is 120°.

Numbered clause 5: The endoscope of any preceding clause, further comprising a control system in communication with the plurality of control mechanisms; wherein the control system is configured to receive a movement input from an operator, and send a control signal to a translation unit of at least one of the control mechanisms; wherein the movement input is associated with the desired angular movement of the distal end of the endoscope; and wherein the translation unit is configured to move the corresponding angulation cable in response to the received control signal. Numbered clause 6: The endoscope of any preceding clause, further comprising: a plurality of sequentially arranged segments; wherein each segment of the plurality of segments is rotatably connected to an adjacent first segment about a first axis, and rotatably connected to an adjacent second segment about a second axis; wherein the first axis is angularly offset from the second axis by a segment offset angle that is less than 90°; and wherein the plurality of segments are arranged such that the angulation cables extend along the plurality of segments towards the distal end of the endoscope.

Numbered clause 7: The endoscope of clause 6, wherein the plurality of segments are arranged such that a first plane defined by a first control mechanism and the central axis is orthogonal to the first axis; and wherein a second plane defined by a second control mechanism and the central axis is orthogonal to the second axis.

Numbered clause 8: The endoscope of either clause 6 or 7, wherein the angulation cables extend through the plurality of segments towards the distal end of the endoscope.

Numbered clause 9: The endoscope of any of clauses 6 to 8, wherein adjacent segments are rotatably connected by interlocking pivots, wherein the pivots are tapered to prevent adjacent segments disconnecting.

Numbered clause 10: The endoscope of any of clauses 6 to 9, wherein each segment of the plurality of segments is rotatably connected to the adjacent first segment by first and second pivots, and rotatably connected to the adjacent segment by third and fourth pivots; wherein the first and second pivots define the first axis; and wherein the third and fourth pivots define the second axis.

Numbered clause 11 : The endoscope of any of clauses 6 to 10, wherein each segment of the plurality of segments comprises a channel; wherein an endoscope component may be passed through the plurality of segments via the channels.

Numbered clause 12: The endoscope of any of clauses 6 to 11 , wherein at least one segment of the plurality of segments comprises a cable guide configured to guide an angulation cable through the segment. Numbered clause 13: The endoscope of clauses 11 and 12, wherein the cable guide is arranged on the interior of the channel.

Numbered clause 14: The endoscope of any of clauses 6-13, wherein the segment offset angle is 60° Numbered clause 15: The endoscope of any of clauses 6-14, wherein the plurality of segments are uniformly shaped.

Numbered clause 16: The endoscope of any of clauses 6-15, wherein the plurality of segments are formed connected to each other.

Numbered clause 17: The endoscope of any of clauses 6-16, wherein the plurality of segments are formed separately and connected to each other before use.