WO2025156038A1

WO2025156038A1 - Control system for electrically assisted wheelchair

Info

Publication number: WO2025156038A1
Application number: PCT/CA2025/050078
Authority: WO
Inventors: Gabriel Feron; Alexandre STEPHANI; Camille GUILBAULT; Mikael PROUS; Benjamin Palmer; Michel Labrecque; Yannick Vallee; Alain Chevigny; Pier Alexandre ETHIER; Jean-Sébastien BREAULT; Cédric MELANCON; Alexandre FRANCOEUR; Patrick GOUDREAU
Original assignee: Motion Composites Inc
Current assignee: Motion Composites Inc
Priority date: 2024-01-22
Filing date: 2025-01-21
Publication date: 2025-07-31
Anticipated expiration: 2026-07-22

Abstract

A system for controlling power assistance to a user-propelled wheelchair having wheels and at least one motor drivingly engaged to one or more driving wheel of the wheels, the system having: a controller having a processing unit and a non-transitory computer-readable medium operatively connected to the processing unit and having stored thereon instructions executable by the processing unit for: determining, based on signals received by the controller, a commanded state of operation of the wheelchair desired by the user of the wheelchair; quantifying an assistive power to be transmitted to the one or more driving wheel based on the commanded state of operation; and adding the assistive power to the one or more driving wheel with the at least one motor.

Description

CONTROL SYSTEM FOR ELECTRICALLY ASSISTED WHEELCHAIR

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present disclosure claims benefit from United States provisional patent application No. 63/623,457 filed on January 22, 2024, the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD

[0002] The present application relates to wheelchairs and, more particularly, to motorization of wheelchairs and to a control thereof.

BACKGROUND

[0003] Some wheelchairs are motorized. Such motorized wheelchairs tend to differ from standard self-powered wheelchairs, in that the motorization system with battery, transmission, motor, is located under the seat. The user has access to a controller, such as a joystick, to then control the wheelchair.

[0004] There is however an interest in providing motorization to standard self-powered wheelchairs, in the form of propulsion assistance, contributing to the human effort in driving the wheelchair forward. Such a system would add wattage to a user’s propulsion forces on the wheels of the wheelchair. However, as the human occupant participates in the propulsion of the wheelchair, there may be some challenges in adding wattage to the user’s propulsion forces. For example, the human force applied on right and left wheel may differ, for different reasons. This may lead to an undesired movement drifting away from a straight line. Moreover, the intermittent propulsion pushes from a human occupant may result in an uneven velocity.

SUMMARY

[0005] It is an aim of the present disclosure to provide a control system for electrically- assisted wheelchairs that addresses issues associated with the prior art.

[0006] In one aspect, there is provided a system for controlling power assistance to a user-propelled wheelchair having wheels and at least one motor drivingly engaged to one or more driving wheel of the wheels, the system comprising: a controller having a processing unit and a non-transitory computer-readable medium operatively connected to the processing unit and having stored thereon instructions executable by the processing unit for: determining, based on signals received by the controller, a commanded state of operation of the wheelchair desired by the user of the wheelchair; quantifying an assistive power to be transmitted to the one or more driving wheel based on the commanded state of operation; and adding the assistive power to the one or more driving wheel with the at least one motor.

[0007] The system described above may include any of the following features, in any combinations.

[0008] In some embodiments, the determining of the commanded state of operation includes: quantifying a movement of the wheelchair and an input provided by the user to the one or more driving wheel; determining that the movement and the input are protagonists; and quantifying the assistive power required for the wheelchair to maintain the movement of the wheelchair.

[0009] In some embodiments, the determining of the commanded state of operation includes: quantifying a movement of the wheelchair and an input provided by the user to the one or more driving wheel; determining that the movement and the input are antagonists; and quantifying the assistive power required for the wheelchair to oppose the movement of the wheelchair.

[0010] In some embodiments, the quantifying of the movement includes determining, based on a signal received from the inertial sensor unit, one or more of: a roll angle of a ground against which the wheelchair is rolling relative to an axis of rotation of the wheels; a pitch angle of the ground; a rate of change of a speed of the wheelchair.

[0011] In some embodiments, the inertial sensor unit includes one or more of an accelerometer, a gyroscope, a GPS, and an inclinometer.

[0012] In some embodiments, the quantifying of the input provided by the user includes: determining a force applied by the user on the one or more driving wheel.

[0013] In some embodiments, a motor sensor unit is operatively connected to the at least one motor, the determining of the force includes: determining, based on a signal received from the motor sensor unit, a difference between an actual rotational speed of the one or more driving wheel and a driven rotational speed of the one or more driving wheel, the driven rotational speed corresponding to a rotational speed of the one or more driving wheel caused by the at least one motor.

[0014] In some embodiments, the motor sensor unit includes one or more of a rotary encoder, a Hall effect sensors, and a torque sensor.

[0015] In some embodiments, the determining of the commanded state of operation includes: determining a mode of operation selected by the user, the mode being one or more of a turn assistance mode; a straight trajectory assistance mode; a cruise control mode; a power assistance mode; an automatic assistance mode; a regenerative mode; and a camber surface assistance mode; determining one or more of a desired speed and a desired direction of the wheelchair; and monitoring one or more of an actual speed and an actual direction of the wheelchair and modulating the assistive power provided by the at least one motor to reach the one or more of the desired speed and the desired direction of the wheelchair.

[0016] In some embodiments, the monitoring of the one or more of the actual speed and the actual direction further includes: monitoring an input provided by the user to the one or more driving wheel; determining a change in an effort from the user on the one or more driving wheel indicative that the user desires a change of speed and/or direction; and driving the at least one motor for the wheelchair to change the actual speed to an increased desired speed.

[0017] In some embodiments, the determining of the mode of operation includes determining that the mode of operation is a cruise control mode, an input provided by the user to the one or more driving wheel being in a form of periodic torque applied to the one or more driving wheel, the adding the assistive power includes: adding the assistive power intermittently to compensate for a drop in a torque applied to the one or more driving wheel by the user.

[0018] In some embodiments, the computer-readable medium further has instructions executable by the processing unit for: detecting, based on the signals, a change in operating conditions of the wheelchair; and adjusting the assistive power to the one or more driving wheel based on the change in the operating conditions. [0019] In some embodiments, the computer-readable medium further has instructions executable by the processing unit for: identifying, based on the signals, that a perceived change in the input provided by the user to the one or more driving wheel is caused by an environment of the wheelchair instead of by the user; and ignoring the change in the input while continuing to add the assistive power.

[0020] In some embodiments, the identifying that the change in the input is caused by the environment includes: determining that a rate of change in the input is above a rate threshold indicative that the change in an input is caused by the environment.

[0021] In another aspect, there is provided a wheelchair comprising the system described above.

[0022] In another aspect, there is provided a system for controlling a power assistance to a user-propelled wheelchair comprising: one or more processors; a non-transitory computer-readable memory communicatively coupled to one or more processors and having computer-readable program instructions executable by the one or more processors for: receiving signals indicative of a movement and/or a condition of a wheelchair as being propelled by a user of the wheelchair, quantifying the movement and/or the condition from the signals; and driving at least one motor coupled to at least one wheel of the wheelchair to add power to the at least one wheel of the wheelchair as a function of the quantifying.

[0023] The system described above may include any of the following features, in any combinations.

[0024] In some embodiments, quantifying the movement and/or the condition from the signals includes measuring a current velocity of the wheelchair.

[0025] In some embodiments, driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant.

[0026] In some embodiments, quantifying the movement and/or the condition from the signals includes detecting an increased effort from the user of the wheelchair. [0027] In some embodiments, driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant at an increased velocity.

[0028] In yet another aspect, there is provided a motorization apparatus for a wheelchair comprising: at least a pair of motorization devices, each of the motorization devices including: a motor block including at least a motor and an output roller operatively coupled to the motor, the output roller configured to contact a wheel of the wheelchair to impart torque to the wheel, the motor block having an engaged configuration in which the motor block is configured to contact a wheel of the wheelchair, and a disengaged configuration in which the motor block is separated from the wheel of the wheelchair; and a bridge assembly the bridge assembly having a body interconnecting the motorization devices, a frame interface adapted to be connected to a frame of the wheelchair, and a latch mechanism for releasable connection of the body to the frame interface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Fig. 1 is a perspective view of a wheelchair featuring motorization devices in accordance with an aspect of the present disclosure;

[0030] Fig. 2 is a front view of the wheelchair of Fig. 1 , showing one of the motorization devices in an engaged configuration, and another of the motorization devices is an disengaged configuration;

[0031] Fig. 3 is a perspective view of a wheelchair featuring a motorization apparatus in accordance with another aspect of the present disclosure;

[0032] Fig. 4 is a perspective view of a variant of the motorization apparatus of Fig. 3;

[0033] Fig. 5 is a perspective view of the variant of Fig. 4, illustrating a sliding engagement;

[0034] Fig. 6 is a perspective view, fragmented, of the variant of the motorization apparatus of Fig. 4, illustrating a latch and keeper;

[0035] Fig. 7 is a block diagram of a controller unit for electrically-assisted wheelchairs as in Figs. 1 to 3; [0036] Fig. 8 is a graph showing an assistance mode for electrically-assisted wheelchairs as in Figs. 1 to 3, as applied by the controller unit of Fig. 7;

[0037] Fig. 9 is a graph showing an assistance mode for electrically-assisted wheelchairs as in Figs. 1 to 3, as applied by the controller unit of Fig. 7;

[0038] Fig. 10 is a flowchart illustrating steps of a method performed by the controller unit of Fig. 7;

[0039] Figs. 11-12 are schematic representations of a trained model of the controller unit of Fig. 7; and

[0040] Fig. 13 is a schematic representation of a controller in accordance with one embodiment.

DETAILED DESCRIPTION

[0041] Referring to the drawings and, more particularly, to Figs. 1 and 2, a wheelchair with motorization devices is generally shown at 10. The wheelchair 10 may therefore be referred to as an electrically-assisted wheelchair. The wheelchair 10 has rear drive wheels 11 and a frame 12 having for example a plurality of tubular frame members, the frame 12 forming the structure supporting a plurality of components, such as rear wheel mounting brackets, a brake system, foot rests, etc. While not described in full detail, the frame 12 interfaces the wheels 11 to a seat 13, a backrest 14, armrests 15, caster assemblies 16, and/or a rigidizer bar(s) 17 (that may be part of the frame 12) among other components. The rigidizer bar 17 is a cross-beam that extends from one side of the frame 12 to the other, and that serves as a structure for the wheelchair 10 to maintain its shape. While one rigidizer bar 17 is shown under the seat 13 (Fig. 2), another one of such bars 17 may be under the seat, or behind the backrest 14 or may be at any other location. For clarity, the rolling direction of the wheel 11 in a forward movement of the chair is illustrated by A. While the frame 12 has tubular frame members of circular cross-section, it may formed of other types of structural members as an alternative or as a complement to tubular members. For example, plates may be used.

[0042] A pair of motorization devices 20 are mounted to the frame 12. The motorization devices 20 may each include an electric motor, such as a battery operated motor. In the illustrated embodiment, one of the motorization devices 20 is mounted to the left-hand side of the wheelchair 10, while the other one of the motorization devices 20 is mounted to the right-hand side of the wheelchair 10. It is considered to have a single motorization device 20, whether on the left-hand side or the right-and side. The motorization devices 20 are essentially mirror-images of one another (though this is optional), depending on the side of the wheelchair 10 to which they will be mounted, if the wheelchair 10 has a pair of the motorization devices 20. In another aspect, the two motorization devices 20 of Fig. 1 are interconnected as part of a motorization apparatus 40, as shown in Fig. 3. The motorization apparatus 40 may have two of the motorization devices 20, or motorization devices similar to shown at 20, with a bridge assembly interconnecting them. Accordingly, the description provided below for Figs. 1 to 2 may extend to the aspect of Fig. 3. The motorization devices 20 and the motorization apparatus 40 may for example be as described in PCT patent application publication no. WO 2022/150923, filed on January 14, 2022, the content of which is incorporated herein in its entirety by reference.

[0043] The motorization devices 20 may optionally be configured to be displaced between an engaged configuration with the wheel 11 , as shown for the right-hand side motorization device 20, and a disengaged configuration with the wheel 11 , as shown for the left-hand side motorization device 20. In the engaged configuration, the motorization device 20 drives the wheel 11 , while in the disengaged configuration, the motorization device 20 does not contact the wheel 11 . The motorization devices 20 are also configured to impart a driving torque to the wheel 11 by being in contact with a tire or tyre of the wheel 11. The motorization devices 20 could alternatively come into engagement contact with a rim of the wheel 11 , for example. The motorization device(s) 20 may impart a driving torque concurrently with a driving torque being applied by a user of the wheelchair 10. Other transmission types could also be present, such as pulleys and belt, gears, chain and sprockets, etc.

[0044] Referring to Fig. 3, another aspect of the present disclosure shows a motorization apparatus 40. The motorization apparatus 40 is shown relative to a wheelchair 10, the wheelchair 10 being similar in configuration to the wheelchair 10 of Figs. 1 and 2, whereby like reference numerals will be used to identify like components. The wheelchair fitted with the motorization apparatus 40 of Fig. 3, may be referred to as an electrically-assisted wheelchair. In fact, the motorization apparatus 40 has numerous components in common with the motorization devices 20, such as a pair of electric motors, i.e,, one for each wheel 11.

[0045] The motorization apparatus 40 has a bridge assembly 41 at the ends of which are connected motorization devices 20 (two shown, more may be present, e.g., two motorization devices 20 per wheel 11). The motorization apparatus 40 and each motorization device 20 form an articulated motor support by which the motorization devices 20 may achieve the engaged configuration and the disengaged configuration with the respective wheels 11. In similar fashion to the motorization devices 20 of Figs. 1 and 2, the motorization devices 20 of Fig. 3 may be configured to be displaced between an engaged configuration with the wheel 11 , and a disengaged configuration with the wheel 11 , though this is optional. In the engaged configuration, both the motorization devices 20 drive the wheels 11 , while in the disengaged configuration, the motorization devices 20 do not contact the wheel 11. In every embodiment, the motorization devices 20 may only have the option of being in the engaged configuration when on the wheelchair 10. The motorization devices 20 may be in opposite configurations concurrently, i.e., one engaged and one disengaged. The motorization devices 20 are configured to impart a driving torque to the wheel 11 by being in contact with a tire or tyre of the wheel 11. The motorization devices 20 could alternatively come into engagement contact with a rim of the wheel 11 , for example. Other transmission types could also be present, such as pulleys and belt, gears, chain and sprockets, etc. The motorization device(s) 20 may impart a driving torque concurrently with a driving push being applied by a user of the wheelchair 10, which push may be referred to as power input, propulsion, etc. The power input by the user is typically applied by the user’s hands grabbing on to hand rims on the drive wheels 11 of the wheelchair 10.

[0046] In an embodiment, the motorization apparatus 40 can be removed from the wheelchair 10. For example, as shown in Figs. 4-6, in a variant, the bridge assembly 41 has a main body 42 that is releasably connected to a frame interface 43. The frame interface 43 may have one or more frame connectors 43A remaining optionally connected to the wheelchair 10 to facilitate the reinstallation of the motorization apparatus 40 to the wheelchair 10. As observed from Figs. 4-6, the removed portion of the motorization apparatus is removed as a block, i.e., as a single assembly. This is optional. In the example shown, the frame connectors 43A may be tightenable clamps that can be fixed to one of the rigidizer bars 17, or to opposite sides of the frame 12. The frame connectors 43A interface the motorization devices 20 to the frame 12, via the rigidizer bar 17 for example. The frame connectors 43A may each form a cylindrical joint with the frame 12, with rotation possible about axis R1. Other types of joints are possible, such as a sliding joint (i.e., translation only), or the frame connectors 43 may be secured to the frame without a possibility of adjustment, in a variant. In a variant, axis R1 may be coincident with a central axis of the tubular member of the frame 12, to which the frame connectors 43 are connected. The frame connectors 43 may translate in a direction parallel to axis R1. The frame connector(s) 43 may have a shape complementary to that of the frame portion to which it(they) will connect, such as circular, square, obround, etc.

[0047] The frame interface 43 may further include a plate body 43B having a pair of channels 43C, for the sliding engagement of rails 42C of the main body 42 therein. Different shapes may be used for the body 43B, i.e., not necessarily a plate. However, the plate body 43B is well suited for the sliding engagement of the main body 42 with the frame interface 43. Moreover, the elongated shape of both the main body 42 and the frame interface 43 (via the plate body 43B) may contribute to the stability, rigidity and limited play when the main body 42 is engaged to the frame interface 43. A detent and latch assembly featuring a latch 42E and detent 42F on the main body 42, and a complementary keeper 43E (or hole, catch) in the frame interface 43, may be present to releasably lock the main body 42 to the frame interface 43. In a variant, the latch 42E automatically engages the keeper 43E during sliding engagement of the main body 42 into the frame interface 43. The detent 42F is then depressed to enable a user to pull the main body 42 out of engagement with the frame interface 43. This is one configuration among others, as the motorization apparatus 40 may be permanently fixed to the wheelchair 10.

[0048] Optionally, a brake support clamp may be provided, with a tightenable clamp and pivot adjustment, to receive a wheel brake lever 45. The brake lever 45 may be seen in 3, but may also be present in the variant of Figs. 1 and 2. The brake lever 45 is one of other possible braking interfaces, and is merely shown as a non-limitative example. The bridge assembly 41 may be a structural component in that it interconnects the motorization devices 20. [0049] The motorization apparatus 40 may also include a control system for controlling the motorization apparatus 40. The control system may include a controller unit 100 to drive and control the motorization devices 20, as well as a power source that may or may not be part of the controller unit 100. In a variant, the controller unit 100 is mostly or entirely in the main body 42, though it may be at other locations. Moreover, while Figs. 1 and 2 are shown as being discrete units, a common controller unit 100 may be present, or individual controller units 100 may be in each of the motorization devices 20, with wireless or wired communication enabling the motorization devices 20 to be operated jointly, in the manner described below. By being in the main body 42, the controller unit 100 may be removed along with a remainder of the motorization apparatus 40 from the wheelchair 10, excluding the frame interface 43 that may remain on the wheelchair 10. Wires may also optionally be external, though internal routing is also possible, for connecting the controller unit 100 to the motorization devices 20.

[0050] Referring to Fig. 7, the controller unit 100 may include one or more processors 100A, all necessary electronic components for operation of the motorization apparatus 100 (e.g., PCB, chips, wires, etc), and non-transitory computer-readable memory 100B communicatively coupled to the processing unit 100A and having computer-readable program instructions executable by the processing unit 100A for operating the motorization apparatus 100 in providing propulsion assistance to the wheelchair 10. For example, the actions may include synchronizing the propulsion assistance, and are detailed hereinbelow. A user interface may be present for the user to program the controller unit 100, to select modes of assistance and/or operation of the motorization devices 20, etc. In variant, the controller unit 100 has a wireless communication capability (e.g., Wifi, Bluetooth®, ANT+) such that the user interface may be a smart phone, a tablet, etc, via an application, software, etc. Hence, the controller unit 100 may have access to the cloud for data export. The controller unit 100 may also have the capacity to go into sleep mode rapidly, and to the opposite start up also rapidly, to limit energy consumption.

[0051] The controller unit 100 may include a battery 100C, though it may also be said that the battery 100C is separate from the controller unit 100. The battery 100C may be releasably connected to the main body 42, so as to be removed when required. For example, the battery 100C may be removed for a replacement battery to be installed. The battery 100C may also be removed from the main body 42 to be recharged. In a variant, it is contemplated to enable wired recharge, by providing a port on the battery 100C for wired connection to a power source (e.g., grid). In a variant, charge level indicator(s) may be on the battery 100C. The charge level indicator(s) may for example by LED(s), a screen, etc. The charge level indicator(s) may also be on the main body 42, or on other parts of the motorization apparatus 40, or charge level may be accessed through a smart device (e.g., smart phone, tablet) with an application related to the motorization apparatus 40.

[0052] The controller unit 100 may have various types of sensors to monitor the movements and conditions of the wheelchair 10, to then provide propulsion assistance according to different programs. For example, the controller unit 100 may include or may be used with an inertial sensor unit 101 . The inertial sensor unit 101 may include various sourceless sensors, such as one or more accelerometers, one or more gyroscopes, one or more inclinometers. The inertial sensor unit 101 may be fixed to the wheelchair 10, such as by being in the main body 42 of the motorization apparatus 40. By being fixed to wheelchair 10, the readings from the inertial sensor unit 101 may be indicative of the movements and conditions of the wheelchair 10. For example, by way of the inertial sensor unit 101 , the controller unit 100 may determine the acceleration and deceleration of the wheelchair 10, the velocity of the wheelchair 10, the slope of the terrain on which the wheelchair 10 is moving. The slope of the terrain may have an incline (i.e., relative to a pitch axis of the wheelchair 10), or camber surfaces (relative to the roll axis of the wheelchair 10). Still by way of the inertial sensor unit 101 , the controller unit 100 may determine a change of terrain, for example by detecting vibrations and/or dampening. The inertial sensor unit 101 may not be limited to the inertial sensors or to the types of inertial sensors described above. Hence, the inertial sensor unit 101 may also be referred to as a sensor unit 101 , a sensor system 101 , including multiple sensors. For example, additional sensor(s) that may be part of the sensor unit 101 is a global positioning system (GPS), a compass, etc. The GPS may provide a velocity and a direction of movement to the controller unit 100, to allow the controller unit 100 to act based on the velocity and/or direction of the wheelchair 10, as described below.

[0053] The controller unit 100 may have other types of sensors, such as sensor units 102 associated with the wheels 11 , still to monitor the movements and conditions of the wheelchair 10, to then provide propulsion assistance according to different programs. For example, the sensor units 102 may include Hall-effect sensors for each motor 20, to monitor the operation of the motors 20, and detect signals that are related to the operation of the movement of the wheelchair 10. The sensor units 102 may include rotary encoders or like sensors to measure a rotational speed of the wheels 11 , so as to derive from the rotational speed a velocity of the wheel 11 , force or torque sensors to quantify forces applied to the wheels 11.

[0054] As part of the computer-readable instructions, the controller unit 100 may be provided with data filters that may use approaches such as Kalmann + Chadwick, or any other detection algorithm. Accordingly, in addition to the monitoring of movement and conditions from readings of the sensor units 101 and/or 102, the controller unit 100 may be configured to distinguish human propulsion (e.g., acceleration) from external environment changes/triggers, such as a surface change, a slope detection.

[0055] Thus, with the data obtained from the sensor units 101 and/or 102, the controller unit 100 may monitor the movement and conditions of the wheelchair 10. The controller unit 100 may then use this data to drive the motorization device(s) 20, for example in accordance with selected modes of operation, default mode of operation, etc. The controller unit 100 may be equipped with low noise motor controls using high frequency field-oriented controls to command the motors 20. The data may be send to a machinelearning system to teach an artificial intelligence system the operation of a wheelchair assistance, for subsequent use.

[0056] In accordance with an assistance configuration, the controller unit 100 operates an automatic assistance during turns, i.e., about the yaw axis. For example, as part of the turn assistance, the controller unit 100 reduces the speed on the motor 20 in the internal side of the turn. As a result, the differential speed may result in a lower energy consumption, and/or faster rotation about the yaw axis. In a variant, this turn assistance is a default setting, and may include monitoring the forces applied onto the wheels 11 to determine the user’s turning intentions.

[0057] In accordance with another assistance configuration, the controller unit 100 may detect that the wheelchair 10 does not receive an equal user push on both of wheels 11. This may be due to the fact the user has a stronger arm. If the intention of the user is to move in a straight trajectory, for example as entered as a mode, the controller unit 100 may provide additional torque on the weaker side, for both wheels 11 to rotate at the same speed, and thus for the wheelchair to maintain a straight trajectory.

[0058] In accordance with another assistance configuration, the controller unit 100 may detect that the wheelchair 10 is on camber surfaces. In such a condition, the wheelchair 10 may have a tendance to rotate about the yaw axis to move right or left due to the effect of gravity. The controller unit 100 may compensate by driving the motors 20 to maintain a speed differential between wheels 11 , for the wheelchair 10 to move in a straight trajectory, and/or for the motorization apparatus 40 to auto-align the wheelchair 10.

[0059] Referring to Fig. 8, in accordance with another assistance configuration, the controller unit 100 may provide a cruise control mode. The controller unit 100 may monitor the velocity of the wheelchair 10, and modulate the assistance from the motorization devices 20 for the wheelchair 10 to maintain a steady speed S1. For example, the controller unit 100 provides power assistance P2 to add to the intermittent power input P1 from the user (i.e., force applied to the wheels 11), so as to maintain the steady speed S1. The graph of Fig. 8 shows total power input P1 and power assistance P2, i.e., for the combination of the two motorization devices 20, for simplicity. However, each motorization device 20 may have its own graph, considering that a user’s power input may be stronger on one side over the other. The controller unit 100 may ensure that any weak side deficiency is compensated by supplemental power assistance on the weak side, to maintain for example a straight line of movement for the wheelchair 10. This is optional. All graphs herein may be for the combination of the two motorization devices 20, for simplicity.

[0060] This cruise control assistance configuration may have one or more preset velocities that can be adjusted by a user. In a variant, the speed S1 may be increased in value, upon monitoring an increase in the user’s power input. The increase in the user’s power input may be observed by a greater force applied and/or by an increase in the frequency in the user’s power input, i.e., the user increasing the pace. Thus, the assistance configuration may include moving from one preset speed to another, or increasing/decreasing speed, by the monitoring of manual propulsion from the users.

[0061] Referring to Fig. 9, in accordance with another assistance configuration, the controller unit 100 may provide a power assistance driving mode detecting the projected speed of the wheelchair 10, and by driving the motorization devices 20 to provide an assistance P2 by decreasing the deceleration rate to provide additional distance from a single manual propulsion P1. To illustrate this, plot A1 shows the acceleration profile of the wheelchair 10, without power assistance P2 from the motorization devices 20. Plot A2 shows the acceleration profile of the wheelchair 10, with the combination of the manual propulsion P1 (i.e., the power input from the user) and of the power assistance P2. It can be observed that the deceleration rate is lower on plot A2, resulting in a greater distance travelled for a same power input P1 .

[0062] In another assistance configuration, the controller unit 100 may detect a downhill condition with the sensor unit 101. Optionally, the controller unit 100 may detect a deceleration force applied to wheel(s) 11 via the sensor unit 102. The controller 100 may therefore go in a regeneration mode to generate power and concurrently provide braking torque with the hysteresis of the motors 20. In a similar assistance mode, a human touch applied to the wheel(s) 11 may automatically trigger the braking mode of the motors 20.

[0063] At least some of the assistance configurations described above may be used concurrently and automatically. For example, the controller unit 100 may provide the turn assistance and the auto-alignment on camber surfaces.

[0064] Therefore, the control system for the wheelchair 10 may be described as being a system for controlling a power assistance to a user-propelled wheelchair. The control system may have one or more processors; a non-transitory computer-readable memory communicatively coupled to one or more processors and having computer-readable program instructions executable by the one or more processors for: receiving signals indicative of a movement and/or a condition of a wheelchair as being propelled by a user of the wheelchair, quantifying the movement and/or the condition from the signals; and driving at least one motor coupled to at least one wheel of the wheelchair to add power to the at least one wheel of the wheelchair as a function of the quantifying. In a variant, quantifying the movement and/or the condition from the signals includes measuring a current velocity of the wheelchair. In a variant, driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant. In a variant, quantifying the movement and/or the condition from the signals includes detecting an increased effort from the user of the wheelchair. In a variant, driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant at an increased velocity.

[0065] Referring now to Fig. 9, a method performed by the controller unit 100 or any other controller for an assisted wheelchair 10 is shown at 1000. The method 1000 includes: determining, based on the signals received by the controller unit 101 , a commanded state of operation of the wheelchair 10 desired by the user of the wheelchair 10 at 1002; quantifying an assistive power to be transmitted to the wheels 11 of the wheelchair 10 based on the commanded state of operation at 1004; and adding the assistive power to the wheels 11 with the motors 20. The commanded state of operation of the wheelchair 10 may be, for instance, a turning state, a change of speed state (e.g., deceleration or acceleration), and a cruising state (e.g., constant speed travel).

[0066] To determine the commanded state of operation, the controller unit 101 may quantify the movement of the wheelchair 10 and the input provided by the user, and determine that the movement and the input are protagonists. For instance, the wheelchair 10 may accelerate while the user provides a forward torque on the wheels of the wheelchair 10, or the wheelchair 10 decelerates while the user provides a rearward torque on the wheel. Again, the wheelchair 10 may be turning left or right while the user is applying an asymmetrical torque on the wheels. The controller unit 101 may thus quantify the assistive power required for the wheelchair 10 to maintain the movement of the wheelchair 10 as commanded by the user.

[0067] Also, the determining of the commanded state of operation may include quantifying the movement of the wheelchair 10 and the input provided by the user and determining that the movement and the input are antagonists. For instance, the wheelchair 10 may accelerate while the user provides a rearward or braking torque on the wheels of the wheelchair 10, or the wheelchair 10 decelerates while the user provides a forward torque on the wheel. Again, the wheelchair 10 may be turning left or right as the user is applying an asymmetrical torque on the wheels to keep the wheelchair 10 in a straight direction. The controller unit 101 may thus quantify the assistive power required for the wheelchair 10 to maintain the movement of the wheelchair 10 as commanded by the user. [0068] As previously discussed, the sensors include the inertial sensor unit 101 that may include one or more of an accelerometer, a gyroscope, a GPS, an inclinometer, and so on. The controller unit 100 may quantify the movement of the wheelchair 10 by determining one or more of a roll angle of a ground against which the wheelchair 10 is rolling relative to an axis of rotation of the wheels, a pitch angle of the ground, and a rate of change of the speed of the wheelchair 10. A variation in the roll angle would indicate that the wheelchair 10 is on a cambered surface for instance, whereas a variation in the pitch angle would indicate that the wheelchair 10 is going uphill or downhill.

[0069] The controller unit 100 may also quantify the input provided by the user to the wheels of the wheelchair 10. This may be achieved by determining a force applied by the user on the wheel. This force may be determined from the signals received from the sensor unit 101 , which may include one or more of rotary encoder, a Hall effect sensor, a torque sensor, and so on. The input may be determined by calculating a difference between an actual rotational speed of wheels and a driven rotational speed of the wheels. The driven rotational speed corresponding to a rotational speed of the one or more driving wheel caused by the motors 20. Put differently, if the user wishes to accelerate, he or she will provide a torque on the wheels to cause an increase in their rotational speeds. At some point, these wheels, which are driven also by the motors 20, will see their rotational speeds increase beyond the speed they should be rotating at if they were only driven by the motors 20. One of the sensors, such as the rotary encoder, will detect this increase in rotational speed and the controller will be able to determine that the commanded state of operation of the wheelchair 10 is an acceleration. The driven rotational speed of the wheels may be known based on a current (e.g., voltage) supplied to the motors 20. Based on this current, it is possible to determine the rotational speed of a shaft of the motors 20 and of the wheels. For example, if the wheelchair 10 is at rest and no power is provided by the motors 20 to the wheels, the driven rotational speed is zero. If the user exerts a torque on the wheel, the rotary encoder will detect that rotation of the wheel and the controller unit 100 will determine that the user wishes to accelerate the wheelchair 10.

[0070] The determining of the commanded state of operation at 1002 may include determining a mode of operation selected by the user using the user interface as described above. The possible modes of operation may include, for instance, a turn assistance mode; a straight trajectory assistance mode; a cruise control mode; a power assistance mode; an automatic assistance mode; a regenerative mode; and a camber surface assistance mode. Once the mode is set, the controller unit 100 may determine one or more of a desired speed and a desired direction of the wheelchair and monitor an actual speed/direction of the wheelchair 10 and modulate the assistive power to reach the desired speed/direction.

[0071] Monitoring the actual speed and actual direction may include monitoring the input provided by the user to the wheels; determining an increased effort form the user on the wheels indicative that the user desires an increased desired speed; and driving the motor 20 for the wheelchair 10 to increase the actual speed to the increased desired speed.

[0072] As shown in Figs. 8-9 for the cruise control mode during which the user provides the input in a form of periodic torque (e.g., the user repeatedly pushes on the wheels to cause their rotation), the controller unit 100 may cause adding the assistive power intermittently to compensate for a drop in the torque applied to the wheel by the user. In other words, the torque may be added by the motors while the user is devoid of contact with the wheels and while repositioning his or her hands for a subsequent push.

[0073] The controller unit 100 may adjust the assistive power based on a change in operating conditions of the wheelchair. The operating conditions may include, for instance, a condition of the ground on which the wheelchair 10 is rolling, wind exerted on the user and the wheelchair 10, and so on. The condition of the ground may include a type of surface of the ground (e.g., gravel, wood, tiles, asphalt, concrete, etc). The condition may also include whether snow, water, or other medium is present on the ground. For example, if the wheelchair 10 continues travelling at the same speed, but the input provided by the user on the wheels increases, the controller until 100 may determine that the wheelchair 10 is rolling on snow and/or that a headwind is present, and may provide assistive power as a function of the determination.

[0074] The controller unit 100 may also prevent obstacles in the ground from being perceived as a change in the commanded state of operation. In other words, the controller unit 100 may determine that a perceived change in the input provided by the user is caused by an environment of the wheelchair instead of by the user. The controller unit 100 may thus determine that this perceived change in the input should be ignored. For instance, if the wheelchair 10 is rolling over a bump, the controller unit 100 may falsely perceive this sudden deceleration as the user desiring to decelerate the wheelchair 10. However, if the rate of change of the speed is above a rate threshold, it may be determined that it is not actually caused by the user and ignore this perceived input. The perceived input may thus be labelled as a “false” input and ignored. The controller unit 100 may also use sensor data to confirm that a bump has indeed been passed.

[0075] Referring to Fig. 10, in some embodiments, the controller unit 100 may include a trained model 110 being trained using machine learning and training data 111. The training data 111 may include, for instance, change in input provided by the user associated with characteristics of the road and operating conditions. The characteristics of the road may include a degree of cambering of the road, a degree of upward or downward slope, type of surface (e.g., wood, concrete, etc), the presence of obstacles. The operating conditions may include, for instance, wind, presence of a medium on the road, and so on. GPS coordinates may be used to memorize locations of change in the conditions of the road and the presence of obstacles. The trained model 110 may be used to determine the assistive power to supply to the wheels with the motors based on inputs received from the sensors and/or the motors.

[0076] The trained model 110 may be trained using the training data 311 , also referred to as historical data. A suitable type of (e.g., classification) trained model may be constructed according to example embodiments of the present disclosure. For instance, a random forest (RF) model and/or a neural network (NN) model may be constructed. In some embodiments, non-linear regression with or without regularization may be used. In some embodiments, one or more of gradient boost machine, artificial neural network, selforganizing maps, and/or deep learning may be used. In some embodiments, a RF regression model of corrosion and erosion data may be constructed.

[0077] In the present embodiment, the trained model 110 may be trained using one or more supervised learning algorithms. Such supervised learning algorithm(s) may build a mathematical model of a set of data that contains both the inputs and the desired outputs. The data is known as training data, and consists of a set of training examples (e.g., data sets). Each training example has one or more inputs and the desired output, also known as a supervisory signal. In the mathematical model, each training example may be represented by an array or vector, sometimes called a feature vector, and the training data is represented by a matrix. Through iterative optimization of an objective function, the supervised learning algorithm(s) may learn a function that can be used to predict the output associated with new inputs. An optimal function may allow the algorithm to correctly determine the output for inputs that were not a part of the training data. An algorithm that improves the accuracy of its outputs or predictions over time is said to have learned to perform that task.

[0078] Types of supervised-learning algorithms include active learning, classification and regression. Classification algorithms are used when the outputs are restricted to a limited set of values, and regression algorithms are used when the outputs may have any numerical value within a range. In the present case, a suitable classification algorithm may be used to output a suitable class label (e.g., one of four possible class labels) for the training data 111.

[0079] Referring to Fig. 11 , a supervised machine learning module 112 of the trained model 110 uses supervised learning algorithms by which it builds a mathematical model from a set of data (e.g., training data 111) that contains both the inputs (e.g., image data) and the desired outputs (e.g., identification number data). Through iterative optimization of an objective function, the supervised machine learning module learns a function that can be used to predict the output associated with new inputs. An optimal function will allow the trained model 110 to correctly determine the output for inputs that were not a part of the historical data 111.

[0080] With reference to Fig. 12, an example of a computing device 1300 is illustrated. For simplicity only one computing device 1300 is shown but the system may include more computing devices 1300 operable to exchange data. The computing devices 1300 may be the same or different types of devices. The controller 100 may be implemented with one or more computing devices 1300.

[0081] The computing device 1300 comprises a processing unit 1302 and a memory 1304 which has stored therein computer-executable instructions 1306. The processing unit 1302 may comprise any suitable devices configured to implement the method 1000 such that instructions 1306, when executed by the computing device 1300 or other programmable apparatus, may cause the functions/acts/steps performed as part of the method 1000 as described herein to be executed. The processing unit 1302 may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

[0082] The memory 1304 may comprise any suitable known or other machine-readable storage medium. The memory 1304 may comprise non-transitory computer readable storage medium, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory 1304 may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), compact disc readonly memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. Memory 1304 may comprise any storage means (e.g., devices) suitable for retrievably storing machine- readable instructions 1306 executable by processing unit 1302.

[0083] The methods and systems described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device 1300. Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems described herein may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems described herein may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit 1302 of the computing device 1300, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method 1000. [0084] Computer-executable instructions may be in many forms, including program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0085] The embodiments described herein are implemented by physical computer hardware, including computing devices, servers, receivers, transmitters, processors, memory, displays, and networks. The embodiments described herein provide useful physical machines and particularly configured computer hardware arrangements. The embodiments described herein are directed to electronic machines and methods implemented by electronic machines adapted for processing and transforming electromagnetic signals which represent various types of information. The embodiments described herein pervasively and integrally relate to machines, and their uses; and the embodiments described herein have no meaning or practical applicability outside their use with computer hardware, machines, and various hardware components. Substituting the physical hardware particularly configured to implement various acts for non-physical hardware, using mental steps for example, may substantially affect the way the embodiments work. Such computer hardware limitations are clearly essential elements of the embodiments described herein, and they cannot be omitted or substituted for mental means without having a material effect on the operation and structure of the embodiments described herein. The computer hardware is essential to implement the various embodiments described herein and is not merely used to perform steps expeditiously and in an efficient manner.

[0086] The term “connected” or "coupled to" may include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0087] The technical solution of embodiments may be in the form of a software product. The software product may be stored in a non-volatile or non-transitory storage medium, which can be a compact disk read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (personal computer, server, or network device) to execute the methods provided by the embodiments.

[0088] It is noted that various connections are set forth between elements in the preceding description and in the drawings. It is noted that these connections are general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. A coupling between two or more entities may refer to a direct connection or an indirect connection. An indirect connection may incorporate one or more intervening entities. The term “connected” or "coupled to" may therefore include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0089] It is further noted that various method or process steps for embodiments of the present disclosure are described in the preceding description and drawings. The description may present the method and/or process steps as a particular sequence. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the description should not be construed as a limitation.

[0090] Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0091] While various aspects of the present disclosure have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the present disclosure. For example, the present disclosure as described herein includes several aspects and embodiments that include particular features. Although these particular features may be described individually, it is within the scope of the present disclosure that some or all of these features may be combined with any one of the aspects and remain within the scope of the present disclosure. References to “various embodiments,” “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. The use of the indefinite article “a” as used herein with reference to a particular element is intended to encompass “one or more” such elements, and similarly the use of the definite article “the” in reference to a particular element is not intended to exclude the possibility that multiple of such elements may be present.

[0092] The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.

Claims

CLAIMS:

1. A system for controlling power assistance to a user-propelled wheelchair having wheels and at least one motor drivingly engaged to one or more driving wheel of the wheels, the system comprising: a controller having a processing unit and a non-transitory computer-readable medium operatively connected to the processing unit and having stored thereon instructions executable by the processing unit for: determining, based on signals received by the controller, a commanded state of operation of the wheelchair desired by the user of the wheelchair; quantifying an assistive power to be transmitted to the one or more driving wheel based on the commanded state of operation; and adding the assistive power to the one or more driving wheel with the at least one motor.

2. The system of claim 1 , wherein the determining of the commanded state of operation includes: quantifying a movement of the wheelchair and an input provided by the user to the one or more driving wheel; determining that the movement and the input are protagonists; and quantifying the assistive power required for the wheelchair to maintain the movement of the wheelchair.

3. The system of claim 1 , wherein the determining of the commanded state of operation includes: quantifying a movement of the wheelchair and an input provided by the user to the one or more driving wheel; determining that the movement and the input are antagonists; and quantifying the assistive power required for the wheelchair to oppose the movement of the wheelchair.

4. The system of claim 2 or 3, comprising an inertial sensor unit, the quantifying of the movement includes determining, based on a signal received from the inertial sensor unit, one or more of: a roll angle of a ground against which the wheelchair is rolling relative to an axis of rotation of the wheels; a pitch angle of the ground; a rate of change of a speed of the wheelchair;

5. The system of claim 4, wherein the inertial sensor unit includes one or more of an accelerometer, a gyroscope, a GPS, and an inclinometer.

6. The system of any one of claims 2 to 5, wherein the quantifying of the input provided by the user includes: determining a force applied by the user on the one or more driving wheel.

7. The system of claim 6, comprising a motor sensor unit operatively connected to the at least one motor, the determining of the force includes: determining, based on a signal received from the motor sensor unit, a difference between an actual rotational speed of the one or more driving wheel and a driven rotational speed of the one or more driving wheel, the driven rotational speed corresponding to a rotational speed of the one or more driving wheel caused by the at least one motor.

8. The system of claim 7, wherein the motor sensor unit includes one or more of a rotary encoder, a Hall effect sensors, and a torque sensor.

9. The system of claim 1 , wherein the determining of the commanded state of operation includes: determining a mode of operation selected by the user, the mode being one or more of a turn assistance mode; a straight trajectory assistance mode; a cruise control mode; a power assistance mode; an automatic assistance mode; a regenerative mode; and a camber surface assistance mode; determining one or more of a desired speed and a desired direction of the wheelchair; and monitoring one or more of an actual speed and an actual direction of the wheelchair and modulating the assistive power provided by the at least one motor to reach the one or more of the desired speed and the desired direction of the wheelchair.

10. The system of claim 9, wherein the monitoring of the one or more of the actual speed and the actual direction further includes: monitoring an input provided by the user to the one or more driving wheel; determining a change in an effort from the user on the one or more driving wheel indicative that the user desires a change of speed and/or direction; and driving the at least one motor for the wheelchair to change the actual speed to an increased desired speed.

11. The system of claim 9, wherein the determining of the mode of operation includes determining that the mode of operation is a cruise control mode, an input provided by the user to the one or more driving wheel being in a form of periodic torque applied to the one or more driving wheel, the adding the assistive power includes: adding the assistive power intermittently to compensate for a drop in a torque applied to the one or more driving wheel by the user.

12. The system of any one of claims 1 to 11 , wherein the computer-readable medium further has instructions executable by the processing unit for: detecting, based on the signals, a change in operating conditions of the wheelchair; and adjusting the assistive power to the one or more driving wheel based on the change in the operating conditions.

13. The system of any one of claims 1 to 12, wherein the computer-readable medium further has instructions executable by the processing unit for: identifying, based on the signals, that a perceived change in the input provided by the user to the one or more driving wheel is caused by an environment of the wheelchair instead of by the user; and ignoring the change in the input while continuing to add the assistive power.

14. The system of claim 13, wherein the identifying that the change in the input is caused by the environment includes: determining that a rate of change in the input is above a rate threshold indicative that the change in an input is caused by the environment.

15. A wheelchair comprising the system of any one of claims 1 to 14.

16. A system for controlling a power assistance to a user-propelled wheelchair comprising: one or more processors; a non-transitory computer-readable memory communicatively coupled to one or more processors and having computer-readable program instructions executable by the one or more processors for: receiving signals indicative of a movement and/or a condition of a wheelchair as being propelled by a user of the wheelchair, quantifying the movement and/or the condition from the signals; and driving at least one motor coupled to at least one wheel of the wheelchair to add power to the at least one wheel of the wheelchair as a function of the quantifying.

17. The system according to claim 15, wherein quantifying the movement and/or the condition from the signals includes measuring a current velocity of the wheelchair.

18. The system according to claim 16, wherein driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant.

19. The system according to claim 17, wherein quantifying the movement and/or the condition from the signals includes detecting an increased effort from the user of the wheelchair.

20. The system device according to claim 18, wherein driving at least one motor coupled to at least one wheel of the wheelchair includes driving the at least one motor for the wheelchair to maintain the current velocity constant at an increased velocity.

21 . A motorization apparatus for a wheelchair comprising: at least a pair of motorization devices, each of the motorization devices including: a motor block including at least a motor and an output roller operatively coupled to the motor, the output roller configured to contact a wheel of the wheelchair to impart torque to the wheel, the motor block having an engaged configuration in which the motor block is configured to contact a wheel of the wheelchair, and a disengaged configuration in which the motor block is separated from the wheel of the wheelchair; and a bridge assembly the bridge assembly having a body interconnecting the motorization devices, a frame interface adapted to be connected to a frame of the wheelchair, and a latch mechanism for releasable connection of the body to the frame interface.