Design journey of an affordable manual standing wheelchair

Abstract Purpose Only 1 in 10 people with disabilities can access assistive devices, underlining the critical need for low-cost assistive products. This paper describes the design evolution of a manual user-operated standing wheelchair (SWC), translating from prototype to product. Methods The SWC design has been refined over 5 years through multiple iterations based on comments from user trials. The SWC product, Arise, provides standing functionality, facile outdoor mobility, affordability, customisability, and is aesthetically pleasing. A one-time fitting and training ensure optimal effort for operation, correct posture, and comfortable user experience. The SWC accommodates users of different sizes and body weights (up to 110 kg) and minimises user effort with the use of a gas spring. Incorporating discrete adjustments enables customisation while retaining the advantages of mass manufacturing, which is necessary for ensuring affordability. Results The SWC has been field-tested and well received by over 100 wheelchair users, and Arise was launched recently by the industry partner. Conclusions It should be noted that RESNA cautions on the use of any standing device without medical consultation. Nevertheless, with appropriate dissemination and awareness, it is anticipated that the affordable SWC product, Arise, will immensely benefit the eligible users and make a difference in their quality of life. Implications for Rehabilitation Provides standing functionality, outdoor mobility, affordability and customisability Accommodates users of different sizes and body weights in a mass-manufacturable design Ergonomic design reduces net user effort during sit-to-stand, stand-to-sit activity Design iterated and refined based on feedback from over 100 user trials


Introduction
Disability should not be a loss of independence, with assistive technologies providing either total or partial personal autonomy. Unfortunately, the reality is that more than one billion people in the world need assistive technology (with 75 million people needing wheelchairs) [1]. A major reason for this unmet need is the lack of affordability in low-income countries. Only 1 in 10 people with disabilities (PwD) have access to the assistive products they need [1] besides limited access to therapists, signifying the critical need for low-cost assistive products for broader outreach.
People with disabilities such as spinal cord injury (SCI), spina bifida, multiple sclerosis, etc. may have little or no control over their lower limbs. While they may use wheelchairs and other aids to move, their ability to stand independently is often compromised. Standing posture is essential, not only to perform certain activities of daily living (ADLs) but also to retain wide-ranging health benefits. Some studies have also found that standing improves respiratory function, skin integrity and bone mineral density [2]. Standing as therapy is essential for some wheelchair users to prevent secondary health problems associated with prolonged sitting [3]. However, some users of conventional wheelchairs have limited or no control over their lower limb musculature and require considerable effort, assistance and/or aids to stand. Furthermore, for users who are economically disadvantaged or living in remote places, access to therapy or a regular standing program is next to impossible.
According to the Rehabilitation Engineering and Assistive Technology Society of North America (RESNA), standing wheelchairs (SWCs) are often medically necessary as they facilitate some individuals to improve their overall quality of life (QoL) [3]. The QoL changes include improved functional reach and access to enable participation in ADLs, improved mobility in individuals with preserved muscle strength in lower limbs, improved circulation, and improved range of motion and reduced risk of contractures. The SWCs also promote bone health and vital organ capacity, including pulmonary, bowel, and bladder functions. Besides, the SWCs reduce abnormal muscle tone and spasticity, and the occurrence of pressure ulcers and skeletal deformities.
A variety of SWCs is currently available in the market for the PwD to choose [4][5][6][7][8]. Nevertheless, most of the SWCs available in the market are custom-designed for a specific user, motorised, and expensive. The expense makes the SWCs out-of-reach of the 2.2 million wheelchair users in India [9] and millions of other wheelchair users worldwide. Therefore, the motivation for this work was to develop an affordable SWC that could significantly improve the QoL for PwD.
A proof-of-concept of SWC was the outcome of a graduate student project at the TTK Centre for Rehabilitation Research and Device Development (R2D2) in IIT Madras (IITM), Chennai, India [10]. Preliminary studies suggested that the concept could significantly improve people's QoL both therapeutically and functionally. The GRID (Grants, Research, Industry, and Dissemination) model was applied to translate the concept into the market through five design iterations [11]. This paper presents the 5-year journey of the affordable manual user-operated SWC from prototype to product, which involved design iterations, exhaustive testing, trials and user and clinician feedback.

Nothing about Us without Us
R2D2 recognises "Nothing about us without us" [12]. Starting from version-1 of the SWC, co-design [13][14][15] and user-centred [16] design approaches were taken through the active involvement of the end-users (rural and urban) along with the designers and rehabilitation professionals -physiatrists, physical and occupational therapists. During the development of version-2 of the SWC, the immersive empathy approach of design thinking [17][18][19] was used for the empowerment of the wheelchair users. Members from The Spinal Foundation, an India based SCI self-help group, actively participated in the design process [20].

Assistive device lifecycle
The needs and opportunities within the assistive product lifecycle, as well as issues concerning different stages of assistive product deployment worldwide, were reported based on work from a summit coordinated by the WHO Global Cooperation on Assistive Technology (GATE) [13]. This position paper discusses the dangers of focussing on products outside the context and rolling out products without a plan. Furthermore, typical models of R&D may not be effective for assistive products owing to the R&D costs involved in a market with limited purchasing power [11]. The model implemented for the SWC has evolved from the functioning of R2D2 at IIT Madras, Chennai, India. The model, termed GRID, is based on the four pillars of Grants, Research, Industry, and Dissemination [11].
In the case of the SWC, the Grant came from Wellcome (a UK foundation) under the "Affordable Healthcare in India" program [21]. The funding also covered the industry partner's development expenses, allowing the industry to offer an affordable product to the end-user. The research was conducted at R2D2 in IITM, where additional resources in the form of students, faculty expertise and the infrastructure act as a grant-multiplier. The Industry partner was Phoenix Medical Systems (P) Ltd., India [22], a manufacturer and supplier of healthcare and assistive products. Dissemination was through The Association of People with Disability (APD), India [23], The Spinal Foundation [20], and CMC Vellore [24].

Development goals
Typically, custom-made assistive devices (using niche manufacturing) are more expensive than mass-manufactured products. For affordability, the goal was to ensure that the SWC is mass-manufactured and yet customisable for users of different sizes and weights. We envisioned that a manual wheelchair with an integrated hand-powered standing mechanism would be easily repairable and affordable to wheelchair users, enabling them to be more functional and undertake economic activities.
The SWC would have low maintenance requirements using only pin joints and off-the-shelf wheelchair parts. The standing mechanism would have a non-powered assist to reduce user effort. The linkage-based standing mechanism of the SWC would be locked in both the sitting and standing positions. Additionally, the standing mechanism's links and joints would be non-obtrusive and lie within the wheelchair space, preferably under the seat, for ease in navigation.
As many SWC users would not have control over their lower limbs, a vertical standing posture is not recommended. Therefore, the SWC would provide a maximum seat inclination of 75 � with respect to the ground during standing, an angle typically used in tilt tables for therapy. The orientation of the backrest remains constant throughout the sit-to-stand activity, for user safety and comfort.

Translation from prototype to product
The SWC was developed over five design iterations. The standing mechanism remained the same across the SWC prototypes. However, design iterations were necessary to address user needs, safety aspects, strength considerations, and manufacturability. At the design development stage, ANSYS TM (Ansys Inc., Canonsburg, PA) was used to analyse stresses in the solid model of the SWC design. Maximum forces were experienced with an empty SWC in the upright position, as the internal forces applied by the gas spring generate large forces at the joints. This finding was taken into account to generate the reaction forces at all the joints, and the individual parts were analysed to ensure the design safety. Industrial designers were included during the design process to provide input on human-centric design and styling.
All SWC versions from Version-2 onwards underwent mechanical testing (curb drop test and double drum test) as per ISO 7176 standards. Testing fixtures, designed and developed in-house, were used to conduct mechanical tests to meet international safety standards. After exhaustive mechanical testing, the SWC prototypes were used in user trials. The user trials were approved by the institutional ethics committee (IITM-IEC protocol number IEC/2016/01/SS/09).
The inclusion criteria for subject selection were as follows: � Age: 18þ years � Height: 122-183 cm � Weight: 40-100 kg � Currently use wheelchairs and preferably use standing devices The exclusion criteria for subject selection were as follows: � Existing contracture � Osteoporosis � Skeletal deformities � Lack of standing tolerance The methodology used for the user trials was as follows: � Demonstration of the SWC functioning � Explanation of benefits and risks of using SWC � Explanation of test activities and test durations � Examination of the user by a consulting clinician (physiatrist, physiotherapist or occupational therapist) � Obtaining the consent to trial participation from the user/guardian � Training of the selected users for using SWC � Conduct of the test activities using SWC (see Table 1) � Observations by the design and clinical team � Collecting user comments about the SWC Before any training or test activities, the SWC was adjusted for each user to achieve proper fit. The seat depth and footrest height adjustments were made based on the user's thigh length and shank lengths, respectively. Gas spring adjustment was made based on the user weight. Training was given to the users by conducting the thirteen activities (see Table 1) in an assisted-manner. The typical duration of the testing sessions was 30 min. Figure 1 captures the 5-year design journey of the SWC. The colour bands indicate the features achieved with each SWC version. In contrast, the intensities of the colour bands indicate the extent of feature implementation within each SWC version. The summary includes the functionalities achieved and issues identified with each SWC version. Details of each of the five versions of the SWC are discussed in the following sections.

SWC versions 0 and 1
The conceptualization of the standing mechanism was an outcome of a student class project in 2011-2012. The initial version (V0) of the SWC was an outcome of a graduate student project [25,26]. The SWC V0 (see Figure 2), built using aluminium and wood, used a compression spring for weight balancing. The initial prototype of a manually operated SWC successfully demonstrated the proof-of-concept of the standing mechanism.
The next version V1 of the SWC (see Figure 3) was built entirely with aluminium. The shape of the handle that allows controlled actuation of the mechanism was changed to an arc-shape. In SWC V1 and following versions of the SWC, a gas spring replaced the compression spring for weight balancing. The link lengths and gas spring specifications were calculated for an average user's weight and height.
As opposed to a compression or extension spring, the gas spring was an ideal choice as it gives almost constant force characteristics. In addition, the gas spring dampens sudden movement when the user is required to change their gripping position, i.e. release the handle and grip it at a different point at the end of each stroke. The gas spring plays a critical role in assisting the user during the sit-to-stand and stand-to-sit by reducing the maximum required forces. By balancing the weight, the gas spring allows the user to safely change the holding position of the handle during transitions.
In both SWC V0 and V1, the standing functionality worked satisfactorily for non-disabled users. The next design objective was to get the SWC tested by wheelchair users. However, this required the SWC to include safety features such as appropriate knee and trunk restraints, and incorporation of adjustability to accommodate users of different heights and weights.

SWC version 2
For the next version of the SWC, the design objective was to validate the working of the standing mechanism with wheelchair users. Version-2 (V2) of the SWC (refer to Figure 4) was designed and fabricated in the second quarter of 2015. The industry partner  Phoenix Medical Systems (P) Ltd., Chennai, TN, India, undertook the fabrication of SWC V2 and all subsequent versions of the SWC. The SWC V2 was a fully functional wheelchair with a standing mechanism.
Most SWC users require restraints at the knees and possibly, at the chest, depending on the level of muscle control they have to enable them to stand. The position of the restraints, the weight to be lifted, and other adjustments required to attain a biomechanically correct standing posture vary between users. Therefore, customisability is critical in a SWC. A constrained standing posture and forces applied, if not appropriate, could cause extreme pain and discomfort to a SWC user.
The safety features of SWC V2 included chest support, knee block, heel restraint and brakes. Additional features such as the ability to adjust the footrest height, seat depth and gas spring were included in SWC V2 to ensure that users maintained a biomechanically correct posture in the standing position. The attachment point of the gas spring could be varied without altering the geometry of the standing mechanism. The ideal position of the gas spring was determined for each SWC user. The shape of the handle was modified to improve ergonomics, reachability, and convenience for the user to grip and push forward (using multiple strokes) with minimal effort for the entire range of sit-tostand motion.  Starting from SWC V2, co-design [13][14][15] and user-centred [16] design approaches were followed. The details of the trial locations for SWC V2 are shown in Figure 5, and the user demographics are shown in Table 2. The trial users included a population from both the genders and a wide-ranging age group. Fifty wheelchair users tested the SWC V2. All the 50 users (100% users) were able to perform the thirteen activities, which validated the functionality. Most users could operate the standing functionality in SWC V2 with ease once the wheelchair dimensions and gas spring settings were adjusted to their height and weight. Paraplegic users were able to stand with ease. Furthermore, quadriplegic users (max C5) were able to stand with the help of quad-handles (see Figure 6).
Although SWC V2 tests successfully validated the standing functionality with wheelchair users, the trials revealed new design challenges. Owing to the additional weight of the standing mechanism, the SWC V2 was difficult to propel as compared to a regular wheelchair. Moving on rough terrain would be an even more significant challenge. Seven users from rural settings gave feedback that going outdoors is very important, and travelling outdoors for 1-2 km was important for economic independence. Their current wheelchair, Motivation Rough Terrain, offered better propulsion on rough rural terrain. These seven users (14% users) were better representatives of the socio-economic status that the product would be targeted towards. Furthermore, validation of the user feedback was done by comparing pushes required by a user to cover the same outdoor distance. With the three-wheel   chassis equivalent product, 30% fewer pushes were required compared to the four-wheel SWC V2. Providing outdoor mobility would enable SWC users to undertake economic activities and be more independent. Since the Wellcome grant objective was to have an impact, especially in rural settings, providing outdoor mobility for at least 1-2 km became a necessary design criterion. The key learning from the user trials of SWC V2 was the need to improve propulsion, provide outdoor mobility, and reduce mechanical complexity.

SWC version 3
For the next version of the SWC, the design objective was to overcome the design challenges identified with SWC V2. Version-3 (V3) of the SWC (see Figure 7) implemented concepts from industrial design. While exploring the SWC design concepts, a minimalistic concept was chosen over the fluidic and bold design concepts (terminologies used by the industrial designers involved in the SWC development to describe the visual design). The fluidic design looked easy on the eyes but involved form design in a way that would have increased manufacturing processes and tool investment, and hence cost. The bold design would bring the wheelchair into attention compared to the other two options and was not considered desirable. The minimalist design allowed manufacturing and tooling investment costs to remain low and made the user more visible than the wheelchair. Using an immersive empathy approach of design thinking [17][18][19], the design team realised that outdoor mobility is vital for the economic empowerment of wheelchair users. The challenges foreseen for developing countries such as India included prevalence of rough terrain, ease in maintenance at widely available cycle repair shops, and portability for ease of transportation.
The design team tested commercial SWCs at rehabilitation trade fairs held in Japan and Germany. Also, the specification sheets, user manuals, and product videos of different SWCs were reviewed. After a benchmark study of wheelchairs that are considered to offer good propulsion (Invacare Action 2NG, Vermeiren Jazz S50, Whirlwind Roughrider, Motivation Rough Terrain), a major change was implemented in SWC V3 and subsequent versions of SWC. The major difference was using a 3-wheel chassis instead of the 4-wheel chassis used in previous SWC versions. For quick iteration, SWC V3 was built by modifying the chassis of a Motivation Rough Terrain wheelchair [27].
The SWC V3 and subsequent versions of SWC have a longer three-wheel chassis, making the wheelchair more stable for uneven outdoor terrain. The extended base reduced the mechanical complexity by obviating the need for an additional linkage, used in the four-wheel SWC designs, to contact the footrest with the ground and increase the base of support in the standing position. The three-wheel configuration enabled safe and easier outdoor mobility for the SWC. Additional industrial design features incorporated in SWC V3 included rigid backrest design for better support and propulsion, folding backrest for portability, fixed footrest design to reduce complexity. The footrest was height adjustable but fixed to the frame instead of the linkage-based moving footrest of SWC V2. Overall, SWC V3 demonstrated better outdoor mobility as well as reduced mechanical complexity.   The details of the field visit and trial locations for SWC V3 are shown in Figure 8, and the user demographics are shown in Table 3. Field visits were conducted to understand the lifestyle of wheelchair users and their environment. Fifteen wheelchair users from rural areas tested the SWC V3. It was observed that the users could use the standing functionality with ease and comfortably propel the wheelchair on rough rural terrain. The three-wheel configuration offered better outdoor propulsion over SWC V2. Standing was stable on the three-wheel configuration of the SWC V3. However, the standing posture was incorrect, and redness was observed on the knees in 11 users (73.3% users).

SWC version 4
The design objective of Version-4 (V4) of the SWC was to overcome the issue of standing posture identified during the trials of SWC V3. The footrest angle was modified to correct the standing posture in SWC V4. Compared to previous SWC versions, the footrest was moved forward and widened (refer to Figure 9). Other industrial design elements incorporated in SWC V4 (refer to Figure 10) included minimal backrest design allowing functionality, adjustable lumbar cushion for better support, concentric handle with wheel, ergonomic knee-block, and dip to allow easy entry and exit. Twenty wheelchair users tested the SWC V4. The user demographics for the SWC V4 are shown in Table 4. With SWC V4, no redness was observed on the user's knees. The critical issues identified during the trial were the weight and aesthetics of the SWC V4.

SWC version 5
Owing to R2D2's recognition of "Nothing about us without us," version-5 (V5) of the SWC overcame all the drawbacks in previous versions. Industrial design inputs to improve ergonomics, usability, aesthetics and design principles for manufacturability and assembly were incorporated in this production-ready design. The usability enhancements (see Figure 11) incorporated in the SWC V5 included removable knee block, hybrid handle, foldable armrest and split footrest.
Twenty-four users tested the SWC V5. The user demographics for the SWC V5 are shown in Table 5. The SWC V5 provides    -cervical  3  SCI-thoracic T1-T5  6  SCI-thoracic T6-T12  11 standing functionality, outdoor mobility, affordability, customisability, and is aesthetically pleasing. A one-time fitting and training ensure optimal operation and comfortable user experience.
The following sections present details of these features.
Standing and safety locks. The SWC V5 has a standing angle of 75 � . The standing handle has knobs in the front end, and the handle is continuous towards the back. The knee support is of swivel type and operable with a single hand. The flexible chest strap is provided with a buckle lock. The heel restraint is a cushioned rigid support. The arm supports are foldable for easy transfer to and from the SWC. The wheel brakes are of knurled type. The SWC includes three safety locks to avoid accidental standing. A toggle lock auto-locks upon sitting. An additional sitting lock allows standing only when intended to actuate. A knee support interlock prevents a person from standing if the knee support is not in position.
Outdoor mobility. The SWC V5 provides a three-point ground contact for stability on uneven terrain. The long-wheelbase ensures stability in the standing position and on uneven terrain and slopes. The big front castor wheel ensures that the SWC easily moves over stones or potholes. The cambered (3 � ) back wheels enhance the stability of the SWC on side slopes. The pneumatic tires reduce the propulsion effort and provide suspension. The seat dump angle (6 � ) is intended to prevent the chance of being thrown out of the SWC on uneven terrain. The ground clearance of the SWC is 115 mm. The solid back support ensures good posture while travelling outdoors over longer distances. Overall, the robust nature of this SWC makes it suitable for outdoor use. But a limitation is that the long-wheelbase, which improves propulsion and stability outdoors, restricts manoeuvrability in cramped indoor environments.
Customisability. The seat width of the SWC V5 can be chosen from four different sizes based on the user's hip-width. The seat depth, footrest height, and knee block width and height are adjustable based on the user's height. The gas spring position, adjustable to the user's weight, enables a smooth transition between the sitting and standing positions. The rear wheel position is adjustable based on the desired propulsion. The backrest height, backrest angle, and the lumbar supports are changeable based on user comfort. To accommodate users of different limb lengths, the seat depth is adjustable in the range of 350-450 mm. Moreover, the centre of gravity is adjustable by changing the rear wheel axle's position back and forth across a range of 75 mm. This adjustability allows the wheelchair to be set appropriately for individuals with good trunk balance and control in situations where wheel rolling resistance is lower, and effort to do a wheelie to negotiate small bumps is lower. Similarly, it allows the wheelchair to be set appropriately for individuals with poor trunk balance and control to reduce the chances of toppling backward in some situations. The SWC allows a user weight up to 110 kg and is available in four sizes. Overall, integrating discrete adjustability allows the SWC to be used by a wide range of users. Customisability is key to ensuring affordability as discrete adjustments are incorporated into mass-manufactured parts.
Portability. The SWC V5 is collapsible for ease in transportation. The procedure to collapse the SWC starts with the removal of the standing handle, followed by folding of the armrest and backrest,   Table 6. After a 30-min interactive training session, the participants were asked to try certain general activities to get used to the SWC as well as some functional activities. Based on the use of the SWC, the participants responded to a Likert-scale questionnaire. Details of the safety study are presented elsewhere. Figure 13 contains tiled images showing the sequence of a participant demonstrating the sit-to-stand (a-e) and the stand-to-sit (f-j) operations using Arise. After the completion of the safety study, Arise was launched in November 2019 by the industry partner. R2D2's journey did not end with the commercialisation of the SWC. As part of the GRID model's fourth pillar-Dissemination [11], an Arise SWC awareness video and the forms required by medical professionals to determine the suitability, prescribe and check out the fit for Arise SWC have been prepared (see Supplementary Information).

Conclusion
The 5-year design journey of a manual user-operated SWC that accommodates users of different widths (360-480 mm), heights (152-183 cm) and body weights (40-110 kg) and minimises user effort is presented. The SWC design has been refined over time through multiple iterations using inputs from users and clinicians, conducting surveys, and studying its mechanics to improve the ergonomics and reduce net user effort during the activity. Overall, the SWC is robust, simple, easy to operate and customisable. Most importantly, the SWC is affordable for a developing country-its exfactory price in India is INR 15,000 (about USD 210, at current exchange rates). The affordability is not only a result of the GRID model, which covered a majority of the R&D costs, but also an outcome of incorporating customisability in a mass-manufacturable design. A lesson relearned during the SWC design journey was to engage with the end-users throughout the requirement understanding, design, and test phases. The voice of the end-user should be the guiding force for the product design. Understanding their needs and the environmental constraints they operate in necessitated innovations in the design that have resulted in a US patent [28], and other patents pending.
Over 100 wheelchair users provided feedback on the SWC after a hands-on experience with it. While the design has been tested by users with different medical conditions such as SCI, post-polio paralysis, cerebral palsy, muscular dystrophy, etc., the trials showed that users with SCI are the most likely to benefit from this device. The SWC product, Arise, was recently launched by the industry partner. The commercialization of the SWC by the industry partner demonstrates a success story of the GRID model in translating assistive product concepts in an affordable manner  into the market. An awareness video and assessment, prescription, and fit checkout forms have been made available for potential users on the R2D2 website [29] to inform them of the product capabilities and processes involved in its prescription and use. This knowledge is critical since customising and ensuring fit is essential for providing maximum benefit to the user. Future work includes studying the QoL outcomes from longterm SWC usage, the influence of the standing and propulsion biomechanics on the elbow and shoulder joints, and the muscle performance during these activities. Also in the pipeline is the development of a SWC version with improved manoeuvrability for indoor use. The COVID-19 (coronavirus) pandemic continues to cause significant challenges in everyone's lives. Due to this unprecedented global crisis, remote user assessment is currently being explored as an alternative to the conventional face-to-face user assessment.

Note of caution
It is noteworthy that RESNA cautions that standing may not be appropriate for all individuals, and a user must receive a proper assessment. RESNA also warns that clinicians should consider cardiovascular, orthopaedic, and positioning implications before recommending any kind of standing device to a client [3]. Nonetheless, with appropriate dissemination and awareness [29], it is anticipated that the affordable manual SWC presented here will immensely benefit eligible users and make a difference in their QoL.