A Proposal on Solar Powered Wheelchair

Proposed Solar-powered Wheelchair

Proposed Solar-Powered Wheelchair

Introduction

In Africa, most elderly undergo myriad physical challenges like impaired mobility, muscular and nerve degeneration, and reduced balance and motor function. As a result, the wheelchair is considered a vital tool to enhance living quality, mobility, and dignity for the elderly (Chien, 2014). The current wheelchairs are either under the electric-powered category, manual, or power-assisted (Gurrama et al. 2012). The old manual wheelchairs usually bring about a higher respiratory exchange ratio and massive oxygen consumption, hence advantageous when used effectively for the user’s health (Yang et al. 2007). Nonetheless, such wheelchairs’ gross mechanical efficiency is only about 2-13.8 percent (the metabolic and external power ratio) based on the technology of propulsion, injury level, the intensity of undertaken exercise, and the adjustments made to the wheelchair interface (Wang & Chiang, 2012). The low mechanical efficiency and a more physical strain induced on the user’s movement can lead to fatigue or strain-triggered injuries in some instances (Pasion, 2019). Therefore, designing and developing electric-powered Wheelchairs has been of great value and need in the recent decade.

Electric-powered wheelchairs essentially have a lot of merits over manual wheelchairs. For instance, electric-powered wheelchairs have minimal risks of strain-triggered injuries and reduced user effort (Chien, 2014). Consequently, they have become more prevalent in recent decades, prompting users to shift from the manual wheelchairs propelled manually to electric-powered wheelchairs that use motor propulsion (Pasion, 2019). Nevertheless, the current wheelchairs that are electrically enabled also still have a lot of demerits (de Groot et al., 2013). For example, they are heavyweight, expensive, substantial physical size, and have a long charging time (Bhatnagar et al.2022). In addition, due to their electrical and mechanical components, most electrically powered wheelchairs are not easy to maintain (Chien, 2014). Furthermore, they cannot be disassembled and folded easily; hence, they are hectic to transport and store. Due to this, they have a significant market share compared to the old manual wheelchairs.

Consequently, wheelchairs that use electric (push rim-activated power-assist wheelchairs) and human power have been developed recently (Wang & Chiang, 2012). The human-powered uses the action of arms on push rims, and the electric-powered uses electric motors’ torque from the battery (Gurrama et al. 2012). Any typical push rim-activated power-assist wheelchair can detect the torque on the push rim to produce effective assist torques by engines (De Groot et al. 2008). Also, push rim-activated power-assist wheelchairs can assist the user in maintaining physical condition due to reduced risk of injuries and pain in the upper limbs (Bhatnagar et al., 2022). Nonetheless, due to its strong dependence on user interaction, push-rim-activated power-assist wheelchairs can still be a challenge to some individual users.

Besides, the motors use batteries to run the electric wheelchairs. Therefore, they cannot travel long distances as they require frequent recharge (Wang & Chiang, 2012). Many research studies have tried to find out possible means of overcoming the limitations of electric wheelchair by developing a wheelchair fitted with solar power to ensure a constant power supply (De Groot et al. 2008). However, there are a limited number of solar power-assisted Electric Wheelchairs to date. Besides, in their design, the wheelchairs have a solar panel rigidly fixed at the back using a metal frame that cannot easily be disassembled (Chien, 2014). Also, such wheelchairs operate in electric mode only, thus, losing the benefit of being used as an exercise device. In addition, Messenger and Melanson also developed a proposal to merge electric-powered Wheelchairs with solar panels (de Groot et al., 2013). Unfortunately, both the designs still exhibit most of the old challenges with the electric-powered wheelchair, like the heavyweight, unable to fold, and substantial physical size (Wang & Chiang, 2012). Subsequently, Curran et al. made some improvements to the solar-powered wheelchair by introducing modifications to the mainframe to reduce weight (Bhatnagar et al., 2022). However, the wheelchair’s power module and frame could not fold; simultaneously, they could not be propelled manually.

To solve the challenges of the current wheelchairs, this study intends to design and develop an electric wheelchair that is solar-powered; and will enable the user to either use electric propulsion or manual by introducing a switch (Chien, 2014). Also is a mechanism to easily remove solar panels and batteries to allow quick disassembling and folding for easy transportation and storage.

Methods

Quality Function Deployment

The quality function deployment perspective is used to design this proposed wheelchair. The quality function deployment perspective includes taking a customer’s needs into engineering characteristics or design requirements that are then transformed into product requirements and process plans (Yang et al. 2007). The initial step is to know who the users are, their needs, and how to achieve such conditions. For this study, users are elderly persons from Africa, specifically Kenya (Chien, 2014). After identifying customer needs, this study will apply a statistical approach to the questionnaire data to assign a degree of importance to every customer requirement through a weighting factor with a value from 5 to 1, where 5- is very important, and 1- is not essential (De Groot et al. 2008). The connection between design and customer requirements can be shown in a house quality matrix.

Subsequently, the design requirements will consider the user’s preferences and needs for the solar-powered electric wheelchair from the quality function deployment perspective. It will also show various design specifications to be addressed to achieve market success and customer satisfaction (Wang & Chiang, 2012). In this study, a cross-functional team that includes industrial designers, clinicians, therapists, and wheelchair engineers will identify the designer requirements (Gurrama et al., 2012). Moreover, the design team will assign the strength weightings as per the relationship between the designer and customer requirements (Chien, 2014). Lastly, the relative and absolute weighting values will be accorded to every designer’s needs (Liu et al. 2010). The total weighting value will then be computed for every designer requirement as shown by the equation below:

AI j = åWi Rij ,1 £ m,

where Wi is the weighting value allocated to CRi, i = 1…, m; Rij is the weighing value illustrating the strength of the relationship between DRj [31] and CRi; and AIj is the conclusive weighting rating of DRj, j = 1,…,n (Gurrama et al. 2012).

Solar Power System Evaluation

The proposed wheelchair’s solar power system’s performance will be gauged based on statistical results received for a 5-kW solar power system considering that with daily sunshine exposure of 3.44 h in Tainan.

Travel Range

The prototype wheelchair’s highest travel range will be calculated through consumed energy over the experimental tract backed by depletion measurements of a fully charged battery of known capacity.

The prototype wheelchair’s performance will be established without and with a solar panel module connected to the power supply system (Gurrama et al., 2012). To guarantee the test result’s reliability, the test will be carried out by a subject that is nondisabled. Besides, the test procedure will be carried out between 9 a.m. and 1 p.m., with sunlight intensity of about 860 W/m2

Static Stability Test

The wheelchair’s static stability will be tested in line with International Organization for Standardization (ISO) 7176–1 standard. In particular, the wheelchair will be safeguarded on a platform through restraining straps put in such a manner that does not hinder the tipping movement (De Groot et al. 2008). A dummy of 120kg will be placed in the wheelchair, and the platform’s angle will then be adjusted slowly until the angle at which the chair tips is established (Chien, 2014). The occupied wheelchair’s stability is characterized by the lateral tip-over angle, the rearward tip-over angle, and the forward tip-over angle.

Conceptual Design

A schematic description of the electric/manual wheelchair prototype is developed from recent studies in the figure below (Gurrama et al., 2012). The wheelchair is located on a manually propelled chair and a commercially available frame to retract and assemble with convenience. In addition, the capability of electric propulsion is realized through a battery which is the primary source of power, plus the other two electric motors (Bhatnagar et al., 2022). A solar panel auxiliary power supply increases the wheelchair’s travel range (Pasion, 2019). As indicated in the figure below, the solar panel is fixed so that it acts as a roof over the head of the user, hence, not only helping as a secondary power source but also protecting the user against rain and sun (De Groot et al. 2008). Besides fitting the wheelchair, the mechanisms of a manually operated clutch are of value and enable the user to change to either electric propulsion mode or manual propulsion mode at will (Chien, 2014). Lastly, the solar panel assembly is also established on a modular design equipped with quick-release mechanisms to allow folding and collapse of the chair for transportation and storage purposes.

(Chien, 2014)

Figure 1.

Conceptual design of solar power-assisted electric/manual wheelchair

. (1) Solar panel (single crystal, 60 W).

(2) foldable frame for the solar panel.

(3) steering joystick and controller.

(4) manual/electric mode switch.

(5) quick release for solar panel frame.

(6) wheelchair handle.

(7) batteries.

(8) motor (50 W × 2).

(9) planetary gear.

On the other hand, figure 2 below shows this study’s proposed wheelchair’s electric circuit (Wang & Chiang, 2012). The battery and the solar panel are connected with a diode fused to prevent power reversal from the battery to the solar cells (Chien, 2014). During the electric propulsion mode, the control unit receives a power supply from the solar or the battery; then, it sends a command to drive the two wheels’ motors as per the velocity and direction provided by the operator through a joystick that is hand activated.

(Chien, 2014)

Figure 2.

Solar power-assisted electric/manual wheelchair’s electric circuit prototype. M = motor.

Prototype Wheelchair

The figure below demonstrates a photograph of the proposed Wheelchair prototype. The wheelchair weighs 16.4kg and is located on a commercially available manual wheelchair frame (Yang et al. 2007). Otherwise, the auxiliary compartments of the wheelchair, like the battery set, planetary gears, and the solar panels, accumulatively weigh up to 20.5 kg. as a result, the wheelchair has an approximate weight totaling 37kg (Chien, 2014). Also, as shown in figure 4 below, the proposed wheelchair uses a set of planetary gears as a switching tool between the electric driving mode and the manual driving mode and a mechanism for deceleration.

(Wang & Chiang, 2012)

Figure 3.

Photograph of a prototype of solar power-assisted electric/manual wheelchair.

Table 1.

Comprehensive particulars of solar power-assisted electric/manual wheelchair.

Item

Parameter

Contour Dimension

1050 × 610 × 870 mm

Minimum Turning Radius

650 mm

Addition Extra Weight

21.6 kg

Solar Panels

8 kg

Driving Hardware

13.6 kg

Manual Wheelchair Weight

17.4 kg

Net Weight

39 kg

Maximum Load

130 kg

Front Wheel Specifications (×2)

8 in.

Rear Wheel Specifications (×2)

24 in.

Motor Voltage

24 V (DC)

Motor Power (×2)

100 W

Battery (×2)

Lead-acid battery

Chargers Input

12V/12Ah, AC 110V/AC

220V

AC = alternating current, DV = direct current.

(Wang & Chiang, 2012)

Figure 4.

Schematic description of electric/manual mode switch mechanism.

(Wang & Chiang, 2012)

Power Sources

The two 12VDC (12Ah) YUASA (YTX14-BS, rechargeable lead-acid batteries connected in series are the main power supply for the wheelchair. Also, a solar panel will be fixed into the wheelchair to act as the auxiliary supply of power (Chien, 2014). Also, whenever the wheelchair operates electronically, the solar panel and the battery will provide the driving force. The power voltage will be influenced by the residual battery voltage and the intensity of the sunlight. Besides, whenever the wheelchair is stopped under the sun or operated manually, the solar power charges the battery for later use (Chien, 2014). The solar panel will be able to provide a maximum current of about 2.5A

Motors

Typically, electric powered wheelchairs carry the user within a speed limit of 6–12 kmh?1 in most African countries (Yang et al. 2007). A wheelchair should also be able to take a weight of at least 90kg on both flat grounds and uphill ramps. Several direct-current motors revolve at hundreds to thousands every minute. As a result, they are not advisable to directly run the standard 24 in. diameter wheelchair (De Groot et al. 2008). Moreover, even though most gear motors have a built-in reduction gear set, the reduction ratio is not enough to achieve the low speed required of the Wheelchair (Chien, 2014). Therefore, this study develops a prototype wheelchair fitted with a planetary gear set to accelerate the torque supplied to the wheels and reduce the chair’s speed (Gurrama et al. 2012). The two 3MEN BL5S brushless Direct Current gear motors are driven by 3MEN BL300–0 brushless Direct Current drivers.

Solar Panel Module

The battery set always is the source of power supply for the wheelchair, with an output voltage totaling 24 VDC. When choosing the auxiliary power supply, solar power with a nominal voltage of 25.5 and a potency of 61W will be preferred (Pasion, 2019). The dimensions of the solar panel should be 540 × 620 mm with a conversion efficiency of 15%. According to test results, a solar power module of 61W can produce 226.5Wh daily (Chien, 2014). This equals 14.76 Ah for a 12 V battery with 80 percent efficiency.

Subsequently, the solar panel would be mounted onto the wheelchair using the mechanisms of angular adjustments like a spring, a series of positioning holes, and a location pin to enhance solar power conversation efficiency.

Steering Joystick and Controller

The steering module is made up of a controller and a joystick that is hand-activated and fixed onto the armrest of the wheelchair. With the assistance of the Joystick, the wheelchair can be manipulated to move forward, reverse or, in a linear dimension, negotiate a corner to either right or left (Chien, 2014). This study’s proposed wheelchair will use two motors to run the wheels and a unique steering ability compared to electric-powered wheelchairs. Due to this, the wheelchair can pirouette.

Manual/Electric Mode Switch

In this study’s proposed wheelchair, the mechanisms of the mechanical clutch and power drive module will be adopted to enable both electronic driving mode and the manual driving mode. A switch rod that involves or disengages the driven gear with/from the driving gear (electric mode/manual mode) will be fitted into the wheelchair to facilitate shifts between the two driving modes (Chien, 2014). Besides, only a force of 20 N is required to shift the two driving modes.

Quick Release Mechanisms

This study’s prototype wheelchair will be made around the main commercial foldable MW frame. Various modules and Compartments of the Wheelchair will be attached to the mainframe by use of quick-release fasteners, hence, allowing easy collapse and dissemblance for quick transportation and storage (Wang & Chiang, 2012). The batter set and solar panel must be taken out of the frame before the wheelchair is collapsed and folded (Yang et al. 2007). Compared with old manual wheelchairs, disassembly is considered longer and has to be facilitated by an energetic person (Chien, 2014). Nevertheless, compared with the current electric-powered wheelchairs, the proposed wheelchairs offer more convenience and can be transported by a regular car, not a special van as in the case of current electric-powered wheelchairs. Thus, a significant improvement and benefit.

Battery Monitor and LED Taillights