Seat assembly for a wheelchair

Abstract

A seat assembly (1) for a wheelchair, comprising: a seat base (3), a backrest holding frame (5) including: a first bracket (7a) connected to the seat base (3), a second bracket (7b) connected to the seat base (3), and an intermediate member (9) extending between and being pivotably connected to the first bracket (7a) and the second bracket (7b); a first linear actuator (11) pivotably connected to the first bracket (7a) and connected to the intermediate member (9), a second linear actuator (13) pivotably connected to the second bracket (7b) and connected to the intermediate member (9), an electric motor assembly (17) mounted to the intermediate member (9), a first flex shaft (19a) connected to the electric motor assembly (17) and to the first linear actuator (11), the first flex shaft (19a) being configured to be rotated by operation of the electric motor assembly (17) to thereby transfer rotational motion from the electric motor assembly (17) to actuate the first linear actuator (11), and a backrest (21) attached to the intermediate member (9), wherein the second linear actuator (13) is operatively connected to the electric motor assembly (17) to actuate the second linear actuator (13), wherein actuation of the first linear actuator (11) and the second linear actuator (13) causes a change in an angle of the intermediate member (9) relative to the first bracket (7a) and relative to the second bracket (7b).

Description

SEAT ASSEMBLY FOR A WHEELCHAIRTECHNICAL FIELDThe present disclosure generally relates to seat assemblies for wheelchairs.BACKGROUNDWheelchairs may have a backrest attached to a seat plate. Wheelchairs may be provided with the functionality to adjust and set the angle of the backrest relative to the seat plate. This has traditionally often been done by using a single actuator that pivots a frame on which the backrest is attached. The single actuator is usually arranged at a lateral side of the seat plate, meaning that the frame that holds the backrest is required to be very torsionally stiff to ensure that the frame is strong enough to hold during operation of the actuator. This is particularly relevant since the user is typically in the wheelchair when the backrest angle is adjusted.US2019 / 0365584 At and EP 3831353 Al disclose backrest assemblies for wheelchairs, which comprise a handle for one-handed unlocking and folding or unfolding of the backrest.SUMMARYA general object of the present disclosure is to provide a seat assembly for a wheelchair, adapted for adjusting or setting the backrest angle of the wheelchair, which solves or at least mitigates the problems of the prior art.There is hence according to a first aspect of the present disclosure provided a seat assembly for a wheelchair, comprising: a seat base, a backrest holding frame including: a first bracket connected to the seat base, a second bracket connected to the seat base, and an intermediate member extending between and being pivotably connected to the first bracket and the second bracket; a first linear actuator pivotably connected to the first bracket and connected to the intermediate member, a second linear actuator pivotably connected to thesecond bracket and connected to the intermediate member, an electric motor assembly, a first flex shaft connected to the electric motor assembly and to the first linear actuator, the first flex shaft being configured to be rotated by operation of the electric motor assembly to thereby transfer rotational motion from the electric motor assembly to actuate the first linear actuator, and a backrest attached to the intermediate member, wherein the second linear actuator is operatively connected to the electric motor assembly to actuate the second linear actuator, wherein actuation of the first linear actuator and the second linear actuator causes a change in an angle of the intermediate member relative to the first bracket and relative to the second bracket.US2019 / 0365584 Ai and EP 3831353 Al, as noted above, disclose unlocking of, and folding and unfolding of the backrest. These documents at least fail to disclose controlling two linear actuators by means of a motor to change an angle of an intermediate member relative to a first bracket and relative to a second bracket. Paragraph

[0058] of US2019 / 0365584 Ai, for example, discloses various examples of actuators but there is no teaching of using a motor to drive even a single linear actuator, and there is no teaching that a linear actuator would be driven by a flex shaft.The present electric motor assembly, which may comprise a single electric motor, thus drives the two linear actuators, i.e., the first linear actuator and the second linear actuator, each pivotably connected to a respective one of the first bracket and the second bracket. The angle of the intermediate member relative to the first bracket and the second bracket may therefore be adjusted in such a way that the force is symmetrically distributed to the linear actuators from the single electric motor assembly. An angle of the backrest which is attached or mounted to the intermediate member is thus also adjusted or set. In particular, the position of the backrest may be set in one of a plurality of positions or fixed positions between an upright end position and a reclined end position. Therefore, the backrest holding frame does not have to be designed to withstand high torsional forces. The first flex shaft facilitates transfer of rotational motion to the first linear actuator, while the second linear actuator may be actuated via a direct connection to the electricmotor assembly or via a second flex shaft. Further, due to the flexible nature of the first flex shaft, the electric motor assembly and the first linear actuator are allowed to move relative to each other, e.g., due to pivoting of the backrest holding frame in relation to the first bracket and the second bracket.Additionally, the minimal height of the wheelchair may be lowered because the actuator(s) for operating the backrest is / are not placed underneath the seat base like in some prior art solutions.According to the present disclosure the adjustment or setting of the angle and the position of the backrest is typically done with the user, e.g. a heavy user, seated in the seat assembly when it forms part of a wheelchair.Further, a very high torque, in the order of 500 Nm may be obtained. This is typically not obtainable with traditional solutions.The electric motor assembly comprises a rotating electric motor. The rotating electric motor may comprise a stator and a rotor rotatably arranged in the stator.A “flex shaft” as described herein is a flexible shaft. The flex shaft may for example comprise a plurality of stranded wires, forming a wire rope, or a coil which is flexible. The wires may for example be made of metal, such as steel, or they may comprise a polymer material, e.g., jacketed bundles of aramid fibres. The flex shaft is a component that is rotated by rotation of the rotor, thus transferring rotational motion from the rotor to the first linear actuator, which is thereby moved linearly. Rotational motion of the electric motor assembly is thus transferred to the first linear actuator via the first flex shaft, wherein the rotational motion is transformed to linear motion by the first linear actuator.The first flex shaft may comprise a core, for example a plurality of stranded wires forming e.g., a wire rope, or coil, and a cover, such as a jacket, that covers the core. The cover may for example comprise a polymer material.The backrest may be attached or mounted to a front side of the intermediate member. Alternatively, the backrest may be attached or mounted to the electric motor assembly, if for example the electric motor assembly is centred in relation to the intermediate member.In general, the backrest may be attached or mounted directly or indirectly to the intermediate member.According to one embodiment the first flex shaft extends directly, in a single length between the electric motor assembly and the first linear actuator. The first flex shaft may thus be directly connected to the electric motor assembly and directly connected to the first linear actuator.One embodiment comprises a second flex shaft connected to the electric motor assembly and to the second linear actuator, the second flex shaft being configured to be rotated by operation of the electric motor assembly to thereby transfer rotational motion from the electric motor assembly to actuate the second linear actuator.The second flex shaft may comprise a core, for example a plurality of wires forming e.g., a wire rope, or coil, and a cover, such as a jacket, that covers the core. The cover may for example comprise a polymer material.According to one embodiment the second flex shaft extends directly, in a single length between the electric motor assembly and the second linear actuator. The second flex shaft may thus be directly connected to the electric motor assembly and directly connected to the second linear actuator.According to one embodiment the first flex shaft comprises a plurality of stranded wires arranged in several layers, wherein the wires of the outermost layer are laid with a first lay direction. The first flex shaft thus obtains a higher torsional stiffness in the first lay direction. This is advantageous when the first flex shaft is rotated by the electric motor assembly. The first lay direction may be laid such that the higher torsional stiffness is achieved forthe direction of rotation of the first flex shaft when the backrest holding frame is moved from a reclined position towards an upright position.According to one embodiment the second flex shaft comprises a plurality of stranded wires arranged in several layers, wherein the wires of the outermost layer are laid with a second lay direction opposite to the first lay direction. The second flex shaft thus obtains a higher torsional stiffness in the second lay direction. Since the first flex shaft and the second flex shaft are rotated in opposite direction when operating the first linear actuator and the second linear actuator, respectively, the opposite lay directions ensure higher torsional stiffness for both flex shafts.According to one embodiment the first linear actuator is a lead screw linear actuator comprising a first lead screw with a thread having a first handedness, wherein the first flex shaft is rotationally fixedly attached to the first lead screw. When rotated by the electric motor assembly, the first flex shaft causes rotation of the first lead screw. This leads to extension or length retraction of the first linear actuator, thus changing the angle between the intermediate member and the first bracket.According to one embodiment the second linear actuator is a lead screw linear actuator comprising a second lead screw with a thread having a second handedness opposite to the first handedness, wherein the second flex shaft is rotationally fixedly attached to the second lead screw. When rotated by the electric motor assembly, the second flex shaft causes rotation of the second lead screw. This leads to extension or length retraction of the second linear actuator, thus changing the angle between the intermediate member and the second bracket.According to one embodiment the first lay direction and the first handedness are in the same direction.According to one embodiment the electric motor assembly is configured to control the change in the angle to set the backrest in one of a plurality of fixed positions between an upright end position and a reclined end position.A fixed position of the backrest means that the backrest is fixed in, or maintains, or is at least temporarily locked in the attained position.According to one embodiment the electric motor assembly is configured to control the change in the angle in a continuous or stepless manner between the upright end position and the reclined end position, the backrest thereby being able to attain any fixed position between the upright end position and the reclined end position.The electric motor assembly may be mounted to the intermediate member, to the backrest, or to e.g., the second linear actuator in case the seat assembly comprises only one flex shaft, i.e., the first flex shaft.According to one embodiment the electric motor assembly is arranged in a sagittal plane of the seat assembly. In particular, the longitudinal axis of the rotor shaft of the rotor may be arranged parallel with the sagittal plane of the seat assembly.According to one embodiment, the electric motor assembly comprises an output shaft structure rotatably connected to the electric motor assembly, wherein the output shaft structure has a first opening which in cross-section has a non-circular inner surface, wherein the first flex shaft has a first end portion arranged in the first opening, wherein the first end portion has a noncircular cross-section dimensioned to engage with the in cross-section noncircular inner surface of the first opening. In particular, the first end portion of the core of the first flex shaft may have the non-circular cross-sectional shape. Due to the non-circular cross-sections, the output shaft structure is able to transfer rotational motion to the first flex shaft. Further, while relation rotation between the first end portion and the output shaft structure is not possible due to the matching non-circular cross-sectional shapes, the first end portion of the first flex shaft can be moved axially along the firstopening by e.g., a technician. This facilitates in adjustment of the width of the intermediate member to accommodate different width requirements of users.The first end portion may alternatively be provided with a sleeve e.g., clamped, welded, or otherwise attached onto the core of the first end portion, thus providing the non-circular cross section dimensioned to engage with the, in cross-section, non-circular inner surface of the first opening.The, in cross-section, non-circular inner surface may for example be rectangular, have a spline structure, or any other non-circular cross-sectional shape suitable for transferring rotation.According to one embodiment the output shaft structure has a second opening which in cross-section has a non-circular inner surface, wherein the second flex shaft has a second end portion arranged in the second opening, wherein the second end portion has a non-circular cross-section dimensioned to engage with the in cross-section non-circular inner surface of the second opening. In particular, the first end portion of the core of the second flex shaft may have the non-circular cross-sectional shape. This facilitates in adjustment of the width of the intermediate member to accommodate different width requirements of users.The second end portion may alternatively be provided with a sleeve clamped, welded, or otherwise attached onto the core of the second end portion, thus providing the non-circular cross section dimensioned to engage with the, in cross-section, non-circular inner surface of the second opening.According to one example, the electric motor assembly comprises an angle gear engaging with the rotor. The first flex shaft is connected to the angle gear. The angle gear transfers rotation of the rotor to the first flex shaft.According to one example, the second flex shaft is connected to the angle gear. The angle gear transfers rotation of the rotor to the second flex shaft.One embodiment comprises a seat base, wherein the first bracket and the second bracket are attached to the seat base.There is according to a second aspect of the present disclosure provided a wheelchair comprising a seat assembly of the first aspect.One embodiment comprises a control system, wherein the control system is configured to control the electric motor assembly to thereby change the angle and an angle of the backrest.One embodiment comprises a user interface configured to provide user input to the control system for controlling the electric motor assembly.According to one embodiment the wheelchair is a power wheelchair.Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means”, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.BRIEF DESCRIPTION OF THE DRAWINGSThe specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:Fig. 1 is a perspective view of an example of a seat assembly;Fig. 2 is a rearview of the seat assembly in Fig. 1;Fig. 3 is a rearview of the seat assembly in Fig. 1 when the seat assembly is widened;Fig. 4 is a close-up view of a region of the electric motor assembly; andFig. 5 is a perspective view of an example of a wheelchair comprising the seat assembly in Fig. 1.DETAILED DESCRIPTIONThe inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.Fig. 1 shows a perspective view of an example of a seat assembly 1 for a wheelchair, such as a power wheelchair.The seat assembly 1 comprises a seat base 3. The seat base 3 may be or comprise a seat plate.The seat assembly 1 may comprise a seat cushion 4. The seat cushion 4 is mounted to the seat base 3.The seat assembly 1 comprises a backrest holding frame 5.The backrest holding frame 5 comprises a first bracket 7a and a second bracket 7b.The first bracket 7a is connected to the seat base 3. The first bracket 7a may be mounted to the seat base 3. The first bracket 7a may be mounted to a first lateral side of the seat base 3.The second bracket 7b is connected to the seat base 3. The second bracket 7b may be mounted to the seat base 3. The second bracket 7b may be mounted to a second lateral side of the seat base 3. The first lateral side and the second lateral side may be opposite sides of the seat base 3.The backrest holding frame 5 further comprises an intermediate member 9.The intermediate member 9 maybe formed of a single piece or multiple parts assembled with each other.The intermediate member 9 extends between the first bracket 7a and the second bracket 7b. A first end of the intermediate member 9 is pivotably connected to the first bracket 7a. A second end of the intermediate member 9 is pivotably connected to the second bracket 7b. The intermediate member 9 may have an essentially upside-down oriented U-shape.The intermediate member 9 may have a first portion 9a connected to the first bracket 7a and extending upwards from the first bracket 7a, a second portion 9b connected to the second bracket 7b and extending upwards from the second bracket 7a, and a crossbeam portion 9c which extends between the first portion 9a and the second portion 9b.The first portion 9a may be inclined towards the median plane of the seat assembly 1. The second portion 9b may be inclined towards the median plane of the seat assembly 1. The first portion 9a and the second portion 9b may extend towards each other in a direction from the seat base 3 towards the crossbeam portion 9c. The intermediate member 9 may thus be narrower in width at the crossbeam portion 9c than at its attachment points with the first bracket 7a and the second bracket 7b. This makes the footprint of the seat assembly 1 smaller.The seat assembly 1 comprises a first linear actuator 11, and a second linear actuator 13.The first linear actuator 11 is pivotably connected to the first bracket 7a. A first end of the first linear actuator 11 may be pivotably connected to the first bracket 7a.The first bracket 7a may comprise a first spacer element 15a extending in a rearward direction relative to a front end of the seat base 3 from a main body of the first bracket 7a. The first linear actuator 11 may be pivotably connected to the first spacer element 15a. The first spacer element 15a may be immovably attached to the main body of the first bracket 7a.The first linear actuator n is also connected to the intermediate member 9. The first linear actuator 11 may be mounted to the intermediate member 9. The first linear actuator 11 may be immovably mounted to the intermediate member 9. Thus, the first linear actuator 11 is not pivotable relative to the intermediate member 9. The first linear actuator 11 may be mounted to the first portion 9a.The first linear actuator 11 may be a lead screw linear actuator.The second linear actuator 13 is pivotably connected to the second bracket 7b. A first end of the second linear actuator 13 may be pivotably connected to the second bracket 7a.The second bracket 7b may comprise a second spacer element 15b extending in a rearward direction relative to the front end of the seat base 3 from a main body of the second bracket 7b. The second linear actuator 13 maybe pivotably connected to the second spacer element 15b. The second spacer element 15b may be immovably attached to the main body of the second bracket 7b.The first spacer element 15a and the second spacer element 15b may advantageously be present in examples in which the first portion 9a and the second portion 9b are tilted or inclined towards each other, as discussed above. This enables adjusting or setting the angle of the intermediate member 9 relative to the first bracket 7a and the second bracket 7b, and thus relative to the seat base 3. Angle adjustment would otherwise not be possible in examples in which the first linear actuator 11 and the second linear actuator 13 are mounted to a respective one of the first portion 9a and the second portion 9b.The second linear actuator 11 is also connected to the intermediate member 9. The second linear actuator 13 may be mounted to the intermediate member 9. The second linear actuator 13 may be immovably mounted to the intermediate member 9. Thus, the second linear actuator 13 is not pivotablerelative to the intermediate member 9. The second linear actuator 13 may be mounted to the second portion 9b.The second linear actuator 13 may be a lead screw linear actuator.The seat assembly 1 may comprise a backrest 21. The backrest 21 may be mounted to the intermediate member 9. The backrest 21 may for example be mounted to the crossbeam portion 9c of the intermediate member 9.The seat assembly 1 comprises an electric motor assembly 17. The electric motor assembly 17 may be mounted to the intermediate member 9, to the backrest 21, or to e.g., the first linear actuator 11. The electric motor assembly 17 may be mounted to the crossbeam portion 9c, like in the example show in Fig. 1.The electric motor assembly 17 may be arranged in a sagittal plane of the seat assembly 1, for example in the median plane of the seat assembly 1.The electric motor assembly 17 comprises a rotating electric motor. The rotating electric motor comprises a stator and a rotor provided with a rotor shaft rotatably arranged in the stator. The electric motor assembly 17 may comprise a single rotating electric motor.The seat assembly 1 comprises a first flex shaft 19a. The first flex shaft 19a is connected to the electric motor assembly 17 and to the first linear actuator 11. The electric motor assembly 17 drives the first flex shaft 19a, which thereby drives or actuates the first linear actuator 11. In particular, the first flex shaft 19a is configured to be rotated by operation of the electric motor assembly 17 to thereby transfer rotational motion to the first linear actuator 11 for driving or operating the first linear actuator 11.The first flex shaft 19a may extend directly, in a single length between the electric motor assembly 17 and the first linear actuator 11.The first flex shaft 19a may comprise a core. The core may comprise a plurality of layers of stranded wires arranged in several layers. The wires mayfor example be metal wires, such as steel, copper, or aluminium wires, or they may be polymeric wires or composite wires. The wires of the outermost layer may be laid with a first lay direction. The wires of the different layers may be arranged with alternate lay directions, such that for example the layer directly inside the outermost layer may have wires arranged in the opposite direction in relation to the first lay direction.The first flex shaft 19a may comprise a cover, such as a jacket, that surrounds the core. The cover may for example comprise a polymer material. The first flex shaft 19a may comprise bearings to disengage the cover from the core. The cover is thus not rotated when the core is rotated by the electric motor assembly 17.In examples in which the first linear actuator 11 is a lead screw linear actuator, the first linear actuator 11 comprises a first lead screw with a thread having a first handedness, and a first nut configured to run along the first lead screw. The first lead screw is rotationally fixedly attached to the first flex shaft 19a. Thus, rotation of the first flex shaft 19a causes rotation of first lead screw. As a result, the first nut moves along the first lead screw. The first nut may be fixed to a lower end of the first linear actuator 11, which is pivotably attached to the first bracket 7a.The first handedness and the first lay direction may be the same direction.The second linear actuator 13 is connected to the electric motor assembly 17 to actuate the second linear actuator 13. The second linear actuator 13 is operatively connected to the electric motor assembly 17.According to the example shown in Fig. 1, the seat assembly 1 comprises a second flex shaft 19b. The second flex shaft 19b is connected to the electric motor assembly 17 and to the second linear actuator 13. The electric motor assembly 17 drives the second flex shaft 19b, which thereby drives or actuates the second linear actuator 13. In particular, the second flex shaft 19b is configured to be rotated by operation of the electric motor assembly 17 tothereby transfer rotational motion to the second linear actuator 13 for driving or operating the second linear actuator 13.The second flex shaft 19b may extend directly, in a single length between the electric motor assembly 17 and the second linear actuator 13.The second flex shaft 19b may comprise a core. The core may comprise a plurality of layers of stranded wires arranged in several layers. The wires may for example be metal wires, such as steel, copper, or aluminium wires, or they may be polymeric wires or composite wires. The wires of the outermost layer may be laid with a second lay direction, which is opposite to the first lay direction. The wires of the different layers may be arranged with alternate lay directions, such that for example the layer directly inside the outermost layer may have wires arranged in the opposite direction in relation to the first lay direction.The second flex shaft 19b may comprise a cover, such as a jacket, that surrounds the core. The cover may for example comprise a polymer material. The second flex shaft 19b may comprise bearings to disengage the cover from the core. The cover is thus not rotated when the core is rotated by the electric motor assembly 17.In examples in which the second linear actuator 13 is a lead screw linear actuator, the second linear actuator 13 comprises a second lead screw with a thread having a second handedness opposite to the first handedness. Further, the second linear actuator 13 comprises a second nut configured to run along the second lead screw. The second lead screw is rotationally fixedly attached to the second flex shaft 19b. Thus, rotation of the second flex shaft 19b causes rotation of the second lead screw. As a result, the second nut moves along the second lead screw. The second nut may be fixed to a lower end of the second linear actuator 13, which is pivotably attached to the second bracket 7b.The second handedness and the second lay direction may be the same direction.According to another example, the second linear actuator 13 may be directly connected to the electric motor assembly 17, i.e., without any second flex shaft provided between the second linear actuator 13 and the electric motor assembly 17. In this case, the electric motor assembly 17 may for example be mounted to the second linear actuator 13.In all examples, operation of the electric motor assembly 17 concurrently drives the first linear actuator 11 and the second linear actuator 13 an equal amount. The pitch of the thread of the first lead screw and the thread of second lead screw is thus the same.By actuation of the first linear actuator 11 and the second linear actuator 13 a change in an angle of the intermediate member 9 relative to the first bracket 7a and relative to the second bracket 7b, and thus relative to the seat base 3, is obtained. Thus, by actuating the first linear actuator 11 and the second linear actuator 13 the angle of the intermediate member 9 relative to the first bracket 7a and relative to the second bracket 7b, and thus relative to the seat base 3 may be set. By actuating the first linear actuator 11 and the second linear actuator 13 the position of the backrest 21 maybe set to an upright end position or a reclined end position, or any of a plurality of positions or fixed positions in between the upright end position and the reclined end position. The position of the backrest 21 may thereby be adjusted or set without needing to reinforce the intermediate member 9 to withstand as high torsional stiffness as for solutions using a single linear actuator. Moreover, a single electric motor is required for the operation of both the first linear actuator 11 and the second linear actuator 13.According to one example, the backrest holding frame 5 may comprise a profile, or a cover, 9d which covers at least a portion of the intermediate member 9. The profile or cover 9d may cover the crossbeam portion 9c.Fig. 2 shows a rearview of the seat assembly 1, without the seat base 3, the backrest 21, and the seat cushion 4.According to the example in Fig. 2, in which the profile or cover 9d has been removed to facilitate illustration, the electric motor assembly 17 comprises an output shaft structure 23. The output shaft structure 23 is connected to the rotor of the electric motor in a rotatably fixed manner. The output shaft 23 is thus driven by the electric motor. For example, the output shaft structure 23 may engage with the angle gear connected to the rotor shaft of the rotor.The output shaft structure 23 engages with a first end portion, which may be composed of an end fitting, of the first flex shaft 19a. The output shaft structure 23 thus drives the first flex shaft 19a.The output shaft structure 23 may according to one example engage with a second end portion, which may be composed of an end fitting, of the second flex shaft 19b. The output shaft structure 23 thus drives the second flex shaft 19b.As shown in Fig. 3, the crossbar portion 9c of the intermediate member 9 may be configured to be separable into two parts. The intermediate member 9 may be disconnected from the electric motor assembly 17 from two opposite sides of the electric motor assembly 17. In one example, by varying the distance between the right and left parts of the crossbar portion 9c, the width of the seat assembly 1 may be set or adjusted, for example based on the needs of a specific user. In other examples, each of the profile or cover 9d and the crossbar portion 9c may be manufactured in a plurality of different lengths, and suitably sized profile or cover 9d and / or crossbar portion 9c may be selected to set the width of the seat assembly 1 based on the needs of a specific user.With reference to Fig. 4, a close-up view of the region R shown in Fig. 3 is depicted. The width adjustment may also require adjusting the connection of the first flex shaft 19a, and the second flex shaft 19b, if present, to the output shaft structure 23 to which it / they are connected. To this end, the output shaft structure 23 may have a first opening 23a, which in cross-section, transverse to a longitudinal axis of the first opening 23a, has a non-circularinner surface and the first end portion 20 of the first flex shaft 19a may be configured to be inserted into the first opening 23a and engage with the inner surface. The first end portion 20 may therefore have a corresponding noncircular cross-section dimensioned to engage with the in cross-section noncircular inner surface of the first opening 23a. For example, the shape of the cross-section of both the inner surface and the first end portion 20 may be elliptical but non-circular, or polygonal such as rectangular. The first end portion 20 may thus be moved along the longitudinal axis of the first opening 23a when the width of the intermediate member 9 is to be adjusted.In examples comprising also the second flex shaft 19b, the output shaft structure 23 may have a second opening which in cross-section, transverse to a longitudinal axis of the first opening 23a, has a non-circular inner surface. The second flex shaft 19b may be configured to be inserted into the second opening and engage with the inner surface of the second opening. The second end portion may therefore have a corresponding non-circular cross-section dimensioned to engage with the in cross-section non-circular inner surface of the second opening and the second end portion maybe elliptical but non- circular, or polygonal such as rectangular. The second end portion may be moved along the longitudinal axis of the second opening when the width of the intermediate member 9 is to be adjusted.Fig. 5 depicts an example of a power wheelchair 25. The power wheelchair 25 may be of front wheel drive, midwheel drive, or rear wheel drive type.The power wheelchair 25 may comprise a chassis 27 and swing arms 31 provided with respective caster wheels, pivotably connected to the chassis 27. Further, the power wheelchair 25 comprises drive wheels 29.The power wheelchair 25 comprises the seat assembly 1. The seat assembly 1 may be mounted to the chassis 27. The seat assembly 1 may be of a height adjustable type and / or of tiltable type.The power wheelchair 25 may have a user interface, e.g., a joystick or similar, with which the angle of the intermediate member 9 can be adjusted relativeto the seat base 3. The user interface thus allows for reclining and bringing the backrest 21 upright as desired by the user by controlling the electric motor assembly 17 and thus the first linear actuator 11 and the second linear actuator 13.The seat assembly 1 may alternatively form part of a manual wheelchair. The manual wheelchair may comprise a user interface for controlling the electric motor assembly 17 of the seat assembly 1.The power wheelchair 25, or the manual wheelchair, may comprise a control system configured to control the electric motor assembly 17 of the seat assembly 1. By controlling the electric motor assembly 17, the control system controls the angle of the intermediate member 9 relative to the first bracket 7a and the second bracket 7b to thereby set the intermediate member 9 and thus the backrest 21 in any of a plurality of fixed positions between and including the upright end position and the reclined end position. The position of the backrest 21 may thereby be set by the user as desired for user comfort. For example, the backrest 21 may be set in the reclined end position, in the upright end position, or in one or more fixed positions between these two end positions by means of the control system which controls the electric motor assembly 17. In one example, the backrest 21 may be set in any fixed position between the reclined end position and the upright end position by means of the control system, which in this example is configured to control the electric motor assembly 17 to attain any fixed position between the two end positions in a continuous or stepless manner.User input via the input interface concerning control of the position of the backrest 21 causes the control system to control the electric motor assembly 17 accordingly to set the position of the backrest 21 as desired.The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.

Claims

CLAIMS1. Seat assembly (1) for a wheelchair, comprising: a seat base (3), a backrest holding frame (5) including: a first bracket (7a) connected to the seat base (3), a second bracket (7b) connected to the seat base (3), and an intermediate member (9) extending between and being pivotably connected to the first bracket (7a) and the second bracket (7b); a first linear actuator (11) pivotably connected to the first bracket (7a) and connected to the intermediate member (9), a second linear actuator (13) pivotably connected to the second bracket (7b) and connected to the intermediate member (9), an electric motor assembly (17), a first flex shaft (19a) connected to the electric motor assembly (17) and to the first linear actuator (11), the first flex shaft (19a) being configured to be rotated by operation of the electric motor assembly (17) to thereby transfer rotational motion from the electric motor assembly (17) to actuate the first linear actuator (11), and a backrest (21) attached to the intermediate member (9), wherein the second linear actuator (13) is operatively connected to the electric motor assembly (17) to actuate the second linear actuator (13), wherein actuation of the first linear actuator (11) and the second linear actuator (13) causes a change in an angle of the intermediate member (9) relative to the first bracket (7a) and relative to the second bracket (7b).

2. Seat assembly (1) as claimed in claim 1, wherein the first flex shaft (19a) extends directly, in a single length between the electric motor assembly (17) and the first linear actuator (11).

3. Seat assembly (1) as claimed in claim 1 or 2, comprising a second flex shaft (19b) connected to the electric motor assembly (17) and to the second linear actuator (13), the second flex shaft (19b) being configured to be rotated by operation of the electric motor assembly (17) to thereby transfer rotational motion from the electric motor assembly (17) to actuate the second linear actuator (13).

4. Seat assembly (1) as claimed in claim 3, wherein the second flex shaft (19b) extends directly, in a single length between the electric motor assembly (17) and the second linear actuator (13).

5. Seat assembly (1) as claimed claim 3 or 4, wherein the first flex shaft (19a) comprises a plurality of stranded wires arranged in several layers, wherein the wires of the outermost layer are laid with a first lay direction.

6. Seat assembly (1) as claimed in claim 5, wherein the second flex shaft (19b) comprises a plurality of stranded wires arranged in several layers, wherein the wires of the outermost layer are laid with a second lay direction opposite to the first lay direction.

7. Seat assembly (1) as claimed in any of the preceding claims, wherein the first linear actuator (11) is a lead screw linear actuator comprising a first lead screw with a thread having a first handedness, wherein the first flex shaft (19a) is rotationally fixedly attached to the first lead screw.

8. Seat assembly (1) as claimed in claim 7, wherein the second linear actuator (13) is a lead screw linear actuator comprising a second lead screw with a thread having a second handedness opposite to the first handedness, wherein the second flex shaft (19b) is rotationally fixedly attached to the second lead screw.

9. Seat assembly (1) as claimed in claim 7 or 8, dependent of claim 6, wherein the first lay direction and the first handedness are in the same direction.

10. Seat assembly (1) as claimed in any of the preceding claims, wherein the electric motor assembly (17) is configured to control the change in the angle to set the backrest (21) in one of a plurality of fixed positions between an upright end position and a reclined end position.

11. Seat assembly (1) as claimed in claim 10, wherein the electric motor assembly (17) is configured to control the change in the angle in a continuous or stepless manner between the upright end position and the reclined end position, the backrest thereby being able to attain any fixed position between the upright end position and the reclined end position.

12. Seat assembly (1) as claimed in any of the preceding claims, wherein the electric motor assembly (17) is arranged in a sagittal plane of the seat assembly (1).

13. Seat assembly (1) as claimed in any of the preceding claims, wherein the electric motor assembly (17) comprises an output shaft structure (23) rotatably connected to the electric motor assembly (17), wherein the output shaft structure (23) has a first opening (23a) which in cross-section has a non-circular inner surface, wherein the first flex shaft (19a) has a first end portion (20) arranged in the first opening (23a), wherein the first end portion (20) has a non-circular cross-section dimensioned to engage with the in cross-section non-circular inner surface of the first opening (20).

14. Seat assembly (1) as claimed in claim 13 dependent of claim 3, or claim 13 dependent of any of claims 4-11 depending of claim 3, wherein the output shaft structure (23) has a second opening which in cross-section has a non- circular inner surface, wherein the second flex shaft (19b) has a second end portion arranged in the second opening, wherein the second end portion has a non-circular cross-section dimensioned to engage with the in cross-section non-circular inner surface of the second opening.2215- Seat assembly (1) as claimed in any of the preceding claims, comprising a seat base (3), wherein the first bracket (7a) and the second bracket (7b) are attached to the seat base (3).

16. Wheelchair comprising a seat assembly (1) as claimed in any of the preceding claims.

17. Wheelchair as claimed in claim 16, comprising a control system, wherein the control system is configured to control the electric motor assembly (17) to thereby change the angle and an angle of the backrest.

18. Wheelchair as claimed in claim 17, comprising a user interface configured to provide user input to the control system for controlling the electric motor assembly (17).

19. Wheelchair as claimed in any of the claims 16-18, wherein the wheelchair is a power wheelchair (25).

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