Development of a Wearable Walking and Standing Aid for Elderly People

Abstract

Wearable walking and standing aids have emerged as promising assistive technology devices to support elderly people in promoting mobility for sustainable healthy ageing. However, there is lack of research in this area, which necessitates the present work. In this study, a wearable walking and standing aid was developed for elderly people using the Design for Manufacture and Assembly (DFMA) method, and the device was tested for its effectiveness based on lifting capability. Through a series of engineering design processes, including conceptual design, detailed design, simulation, analysis, fabrication, and assembly, a prototype was developed and tested. The results reveal that the prototype, which supports thighs and calves, is capable of helping the user to stand and sit. The experimental results indicated a lifting capability surpassing the expected theoretical model by almost 43%. Nevertheless, several recommendations are suggested to further improve the prototype in an effort to develop a more effective and reliable wearable walking and standing aid for elderly people.

1. Introduction

The World Health Organization (WHO) forecasted that between 2015 and 2050, the proportion of the world’s population over 60 years will nearly double from 12% to 22% [1]. This shift in the distribution of a country’s population towards older ages highlights the importance of ensuring that older people maintain good health throughout the ageing process, which can contribute to reducing the burden on limited health and social care resources [2].

Walking is accessible and generally low cost or free [3]. Among elderly people, walking is prevalent in increasing physical activity levels [4]. It has been reported that regular physical activity helps improve physical functions as well as reverse some effects of chronic diseases to keep older people mobile and independent [5]. Consequently, they also experience healthier ageing trajectories [6]. Less physically active elderly people experience worse quality of life, and this may affect their ability to lead their later life free of disabilities. In an intervention aimed at increasing walking activity for hypertensive older people, a six-month community-based walking program was effective in increasing their exercise self-efficacy and reducing systolic blood pressure [7]. In fact, some studies have demonstrated that a simple daily walking habit may improve physical balance among elderly people [8,9]. Similarly, a study demonstrated that simple brisk walking is effective in improving the fitness levels of the elderly [10]. Despite this, approximately 35% of those aged 70 and over and the majority of those over 85 years are reported to face mobility limitations in their ability to move independently around their environment [11,12]. Therefore, an alternative mechanism is required to provide opportunity for elderly people with reduced bodily function to walk.

Wearable assistive technologies have become one of the most promising means of assisting elderly people [13,14,15,16,17]. The development of such devices is significant for promoting sustainable strategies for healthy ageing. Several wearable assistive technology devices have been reported. Nie et al. (2022) [18] developed a new type of wearable assistive device called Robotic Support Limbs (RSL) to provide balance and load support during standing or walking. It has a kinematically independent structure that allows it to dynamically change the support position in coordination with human legs, making the human–robot support polygon configurable. The support polygon refers to the area on the ground formed by two human feet and the robot’s two limbs. The device is worn at the waist and has two limbs, each with three active degrees of freedom (DOFs) that can be divided into three modules: robot base module, robot limb module, and robot tip module. The application of RSL is proposed to improve the quality of life for the elderly, especially for people with muscle weakness as well as other potential users such as those with an injured leg or neuromuscular disorders.

Lee et al. (2023) [19] developed a robotic hip exoskeleton called the EX1 to provide gait assistance. The device consists of seven main parts: a control pack, actuator module, thigh support frame, waist belt, thigh support strap, battery, and power switch. The study used parallel experimental (exercise with EX1) and control groups (exercise without EX1), comprising 60 elderly participants. The study’s results reveal that the spatiotemporal gait parameters, kinematics, kinetics, and muscle strength of the trunk and lower extremities improved more after exercise with the device compared to those without. Their previous studies [13,20,21] had already demonstrated that the device decreased metabolic energy and improved gait efficiency in older adults during underground walking and stair climbing. Lee’s work is evidence of the long-term effort devoted to the development of wearable assistive technology device for elderly people.

Reported work on the development of this device is scarce, highlighting the need for more studies in this area. Thus, the objectives of this study are the following:

Objective 1: To develop a wearable walking aid that assists elderly people in standing and walking using the Design for Manufacture and Assembly (DFMA) method.

Objective 2: To test the wearable walking aid in terms of its effectiveness in assisting the mobility of elderly people.

2. Methodology

2.1. Conceptual Design

2.1.1. Concept A

Concept A consists of four main parts: the waist mechanism, thigh-lifting mechanism, calf-lifting mechanism, and foot mechanism. The waist mechanism shown in Figure 1a is worn at the user’s waist, and it is connected to the thigh joint shown in Figure 1b, followed by the calf-lifting joint in Figure 2a and foot mechanism in Figure 2b, forming the whole leg mechanism. The legs are held in placed with a securing belt, and the rods were designed to be adjustable to the user’s preferred height.

2.1.2. Concept B

Concept B displayed in Figure 3 resembles Concept A, except the thigh-lifting mechanism, which uses a motor, is replaced with a pulley. The pulley rotates and in turn pulls the steel rope attached to it, thereby realizing leg lifting. The joint at the thigh section uses a bearing to ease leg rotation.

2.1.3. Concept Scoring Table

The concept scoring process for selecting the appropriate components is detailed in

Table 1. Concept scoring.

Selection Criteria	Weight	Concept
		A		B
		Rating	Weighted Score	Rating	Weighted Score
Cost	20
Material Procurement	10	3	30	4	40
Number of Components	10	3	30	2	20
Fabrication	20
Ease of Manufacture	5	4	20	3	15
Cost of Fabrication	10	3	30	3	30
Fabrication Time	5	4	20	3	15
Flexibility	20
Movability During Power Off	10	3	30	5	50
Various Walking Speed	3	5	15	4	12
Limitation of Lifting Height	7	4	28	3	21
Innovation	10
Uniqueness	10	3	30	5	50
Comfortability	20
Comfort Level to Thigh	10	4	40	3	30
Comfort Level to Waist	10	3	30	2	20
Simplicity	10
Ease of Assembly	5	4	20	3	15
Ease of Disassembly	3	3	9	3	9
Complexity of Lifting Mechanism	2	3	6	2	4
Total Score	100	49	338	45	331
Rank		1		2

. The less significant criteria are given lower weights, and the rating is based on their fulfillment, where 1 is for poor; 2, bad; 3, moderate; 4, good; and 5, excellent. Under the cost criterion, the higher total materials procurement cost needed to fabricate the design is rated lower, and the greater number of components is rated lower as well. Under the fabrication criterion, an easier manufacturing process is rated higher, a lower cost of fabrication is rated higher, and a longer fabrication time is rated lower. Additionally, there is also a flexibility criterion that consists of movability while turned off, various walking speeds, and lifting height limitations. The user may sometimes want to walk independently while the device is turned off, without being restricted by the motor gears; thus, lower restriction is rated higher. A design that can offer various walking speeds is also rated higher. A design that allows for higher leg lifting offers more flexibility and is therefore rated higher. Under the innovation criterion, the design must be innovative and unique, such that it is not on the market. Projects with radical innovation, opposed to incremental innovation, have been reported to have a higher correlation with manufacturing performance [22]. Therefore, if the design is not on the market, it is given a higher rating. The comfortability criterion is divided into two, the comfort level to thigh and comfort level to waist—the more comfortable the user, the higher the rating given. Lastly, the simplicity criterion is scored based on the ease of assembly and disassembly, as well as the complexity of the lifting mechanism. The easier the device is to assemble and disassemble the parts, the higher the rating given; a more complex lifting mechanism is rated lower.

2.1.4. Combined Conceptual Design

After scoring the concepts, the weighted scores of Concept A and Concept B were similar. Thus, both designs were combined as shown in Figure 4a,b. The thigh-lifting pulley mechanism from Concept B was selected so that the user can still move easily while the power is off without being restricted by the motor gears, while the motorized calf-lifting mechanism from Concept A was chosen.

2.2. Detailed Design

2.2.1. Part Descriptions

The combined conceptual design was then detailed and included the following parts: thigh holder, calf holder, cover for thigh holder and calf holder, adjustable tube for adjusting height, waist holder, waist cover, waist connector to connect pulley assembly and thigh assembly to the waist holder, pulley assembly bracket, pulley, joint connector, calf bearing holder, thigh bearing holder, blocker to secure bearing in place, gas strut bracket to hold the gas strut, foot joint bracket, foot holder, connector rod to connect thigh assembly with calf assembly, and pinion connector to connect the pinion to the motor arm.

Finally, the product was assembled as shown in Figure 5, which is symmetrical on both sides. The hip, knee, and ankle joints can be rotated in this design. Some other standard parts such as gas strut, bolts, and nuts are to be installed in the final product assembly. The pulley was installed with steel rope connected to the rod end joint at the thigh holder. The legs are lifted by the pulley pulling the steel rope.

2.2.2. Engineering Calculation

Engineering calculation for motor torque was conducted for three conditions as shown in Figure 6, to obtain the highest motor torque required.

Condition 1 (Motor Lifting Calf)

The free body diagram for Condition 1’s calculation is displayed in Figure 7. Two assumptions were made: the maximum mass of the user is 100 kg and the highest position the calf can lift is 90° perpendicular to the thigh. Calculation is based on one side, where the maximum mass will be 50 kg. The angle of force P, α, is calculated using a measurement from the Inventor and trigonometry function. The terms used in the calculation are as follows:

W is the weight of the calf;

P is the force caused by the gas strut;

F is the force caused by the gear torque.

$$\mathrm{W}=100 \mathrm{k}\mathrm{g}\times 9.81 {\mathrm{m}\mathrm{s}}^{-2}\times 6.18\%\times {\displaystyle \frac{1}{2}}=30.3 \mathrm{N}$$

where 6.18% corresponds to the weight percentage of the leg and foot, and is taken from published work [23].

$$\mathrm{P}=200 \mathrm{N},\mathsf{\alpha }=68.87°$$

$$+\mathsf{\circlearrowleft }\sum {\mathrm{M}}_{\mathrm{o}}=0$$

$$30.3\left(1.55\right)+200\mathrm{s}\mathrm{i}\mathrm{n}68.87°\left(155\right)+200\mathrm{c}\mathrm{o}\mathrm{s} 68.87°\left(35\right)-\mathrm{F}\mathrm{c}\mathrm{o}\mathrm{s} 20°\left(19\right)=0$$

$$\mathrm{F}=2023.9 \mathrm{N}$$

The Pinion radius is 8.5 mm; therefore, the motor torque required is

$${\mathrm{T}}_1=2023.9\mathrm{c}\mathrm{o}\mathrm{s}20°\left(0.0085\right)=16.17 \mathrm{N}\mathrm{m}$$

Condition 2 (Motor Lifting Whole Leg)

The free body diagram for Condition 2’s calculation is displayed in Figure 8. One assumption was made, which is that the highest position the thigh can be lifted is 90° perpendicular to the body. The angle of the pulley string, β, is calculated using a measurement from the Inventor and trigonometry function. The terms used in the calculation are as follows:

W is the total weight of the leg (including the thigh, calf, and foot).

T is the steel rope tension from the pulley.

$$\mathrm{W}=50 \mathrm{k}\mathrm{g}\times 9.81 {\mathrm{m}\mathrm{s}}^{-2}\times 16.7\%=81.91 \mathrm{N}$$

where 16.7% corresponds to the weight percentage of the total leg and was also taken from published work [23].

$$\mathsf{\beta }=20.83°$$

$$+\mathsf{\circlearrowleft }\sum {\mathrm{M}}_{\mathrm{o}}=0$$

$$\mathrm{T}\mathrm{s}\mathrm{i}\mathrm{n}20.83°\left(270\right)-81.91\left(159\right)=0$$

$$\mathrm{T}=135.65 N$$

The pulley’s radius is 30 mm; therefore, the motor torque required is

$$\begin{array}{ll}{\mathrm{T}}_2& =135.65\left(0.03\right)\\ & =4.0695 \mathrm{N}\mathrm{m}\end{array}$$

Condition 3 (Motor Lifting from Squatting)

The assumed lowest position the device can squat is illustrated in Figure 9. The free body diagram for Condition 3’s calculation is displayed in Figure 10. The angle of force P, γ, is calculated using a measurement from the Inventor and trigonometry function. The terms used in the calculation are as follows:

W is the weight of the upper limb offset from the center of gravity;

P is the two-force member of the gas strut;

T is the torque needed to lift the upper limb.

$$\mathrm{k}={\displaystyle \frac{265}{\mathrm{c}\mathrm{o}\mathrm{s}30°}}=306 \mathrm{m}\mathrm{m}$$

$$\mathrm{W}=50 \mathrm{k}\mathrm{g}\times 9.81 {\mathrm{m}\mathrm{s}}^{-2}\times 93.82\%=460.19 \mathrm{N}$$

where 93.82% is obtained through the subtraction of 100% by 6.18%.

$$\mathrm{P}=200 \mathrm{N},\gamma =22.05°$$

$$+\mathsf{\circlearrowleft }\sum {\mathrm{M}}_{\mathrm{o}}=0$$

$$460.19\mathrm{s}\mathrm{i}\mathrm{n}60°\left(306\right)-200\mathrm{s}\mathrm{i}\mathrm{n} 22.05°\left(350\right)-200\mathrm{c}\mathrm{o}\mathrm{s} 22.5°\left(35\right)-\mathrm{T}=0$$

$$\mathrm{T}=89.19 \mathrm{N}\mathrm{m}$$

A gear and pinion have 64 and 29 teeth, respectively; therefore, the motor torque required is

$${\displaystyle \frac{{\mathrm{T}}_3}{89.19}}={\displaystyle \frac{29}{64}}$$

$${\mathrm{T}}_3=40.41 \mathrm{N}\mathrm{m}$$

Condition 1: T₁ = 16.17 Nm

Condition 2: T₂ = 4.0695 Nm

Condition 3: T₃ = 40.41 Nm

All calculations above are based on the user fully relying on the device. In this project, the goal is to assist in lifting the legs where the user is only partially assisted by the device. After researching the motors available on the market, a DSSERVO 150 kg was found to be the most suitable and affordable motor for use in this design. It is a servo motor with 150 kg cm torque and a maximum of 173 kg cm with higher voltage.

$$173 \mathrm{k}\mathrm{g}\mathrm{c}\mathrm{m}=16.97 \mathrm{N}\mathrm{m}$$

$${\displaystyle \frac{16.97}{40.41}}\times 100\%=42\%$$

Although the motor torque is lower than T₃, the motor is still able to assist the user to save almost 42% of their energy.

Force Calculation for Simulation

An adjustable tube is used in the thigh assembly and calf assembly. The calculation is based on the tube at the calf assembly, as shown in Figure 11, Figure 12 and Figure 13, since it is at the lower section of the device, which will need to sustain more weight. The highest forces the calf assembly will experience occur during the squatting position.

From Condition 3,

$$\mathrm{W}=460.19 N$$

P is unknown in this condition, since we assumed the motor is stopped during squatting.

$$+\mathsf{\circlearrowleft }\sum {\mathrm{M}}_{\mathrm{o}}=0$$

$$460.19\left(265\right)-\mathrm{P}\mathrm{s}\mathrm{i}\mathrm{n} 52.05°\left(350\right)-\mathrm{P}\mathrm{c}\mathrm{o}\mathrm{s} 52.05°\left(35\right)=0$$

where 52.05° is obtained from the addition of 22.05° and 30°.

$$\mathrm{P}=409.9 \mathrm{N}$$

$$+\uparrow \sum {\mathrm{F}}_{\mathrm{y}}=0$$

$$409.9\mathrm{s}\mathrm{i}\mathrm{n}52.05°-460.19+{\mathrm{R}}_{\mathrm{y}}=0$$

$${\mathrm{R}}_{\mathrm{y}}=136.97 \mathrm{N}$$

$$\overrightarrow{+}\sum {\mathrm{F}}_{\mathrm{x}}=0$$

$${\mathrm{R}}_{\mathrm{x}}-409.9\mathrm{c}\mathrm{o}\mathrm{s}52.05°=0$$

$${\mathrm{R}}_{\mathrm{x}}=252 \mathrm{N}$$

$$\overrightarrow{+}\sum {\mathrm{F}}_{\mathrm{x}}=0$$

$$-{\mathrm{B}}_{\mathrm{x}}+409.9\mathrm{s}\mathrm{i}\mathrm{n}37.95°-252=0$$

$${\mathrm{B}}_{\mathrm{x}}=0$$

$$+\uparrow \sum {\mathrm{F}}_{\mathrm{y}}=0$$

$${\mathrm{B}}_{\mathrm{y}}-409.9\mathrm{c}\mathrm{o}\mathrm{s}37.95°-30.3-136.97=0$$

$${\mathrm{B}}_{\mathrm{y}}=490.5 N$$

$$+\mathsf{\circlearrowleft }\sum {\mathrm{M}}_{\mathrm{U}}=0$$

$${\mathrm{U}}_2\mathrm{c}\mathrm{o}\mathrm{s} 50°\left(15\right)-490.5\mathrm{c}\mathrm{o}\mathrm{s} 50°\left(25\right)=0$$

$${\mathrm{U}}_2=817.5 N$$

$$+\uparrow \sum {\mathrm{F}}_{\mathrm{y}}=0$$

$$490.5+817.5-{\mathrm{U}}_1=0$$

$${\mathrm{U}}_1=1308 N$$

By comparing the results in Conditions 1 and 2, it was observed that the torque required in Condition 2 is less than that in Condition 1. This is due to the gear drive in the pulley mechanism applied for thigh lifting and calf lifting. This also proves that a pulley lifting design is more energy efficient compared to a direct motor drive.

2.2.3. Material Selection

There are four commonly available materials that can be used for the adjustable tube: wood, Carbon Fiber-Reinforced Polymer (CFRP), aluminum, and steel (

Table 2. Materials that can be used for adjustable tube.

Materials	Advantages	Disadvantages
Wood	Light, cheap, easy to cut	Low stiffness, low strength
CFRP	Light, high strength, high stiffness	Expensive
Aluminum	High strength, high stiffness, easier to cut than steel	Corrodes without coating
Steel	High strength, high stiffness	Heavy, difficult to cut, gets rusty when exposed to air

). Wood and CFRP are lightweight and easy to machine. However, wood has low stiffness and strength, while CFRP is expensive. Aluminum and steel are metals and are great for high-strength applications. Between them, aluminum is more suitable for this study’s application as it is lighter and easier to machine.

2.2.4. Design for Manufacture and Assembly (DFMA) Analysis

Table 3. Design for Manufacture and Assembly (DFMA) principles used for analysis.

Principles	Description	Components
Component Name: Thigh holder
Minimize part count Design parts to be self-aligning Use standardized products Ease of components insertion and handling Design the first part large and wide	This part was improved to have smaller dimensions and a lower part count. The part was designed to use a bearing and belt of standard size to reduce operation variety. This part was also designed to be large enough for another smaller part to be attached to it.	Before
		After
Component Name: Adjustable tube
Design to eliminate fasteners Eliminate secondary operation	This part was optimized to use a ball lock pin instead of fasteners for installation. This eliminates secondary operation since it can be easily installed with the insertion of one pin. This significantly reduces the required torque [24] and improves musculoskeletal comfort for the user [25].	Before
		After
Component Name: Joint connector
Make parts multi-functional Eliminate secondary operation Poka Yoke	This design has alignment features allowing the servo arm and pinion easily fit in place.	Before
		After
Component Name: Pinion connector
Provide alignment features Easily indicate orientation for insertion	This design has alignment features allowing the servo arm and pinion to easily fit in place.	Before
		After
Component Name: Thigh bearing holder
Minimize part count Make parts multi-functional Poka Yoke Provide alignment features	This part was improved to directly connect to a potentiometer. The part also has a Poka Yoke design, and the chamfer on the edge is for alignment purposes.	Before
		After
Component Name: Pulley assembly bracket
Make parts multi-functional Use standardized products	This part was improved to support pulley assembly and a guide steel rope. It was also designed to use a standard servo motor product.	Before
		After
Component Name: Waist holder
Minimize part count Make parts multi-functional Use standardized products Ease of component insertion and assembly	This part was improved to have fewer parts and be multi-functional. It can be directly installed with a power switch, battery voltage indicator, and waist belt. All of these standard parts can be easily inserted after the design improvement.	Before
		After

displays the DFMA principles and describes how the principles are applied to the components.

2.3. Simulation and Analysis

2.3.1. Calf Holder

There are two constraint types applied to the calf holder: fixed and pin. Fixed constraints are applied at the inner wall where the adjustable tube was installed, while pin constraints are applied at the hole where ball lock pin was installed. The loads applied to the part were the joint force, servo motor, mounting force, gas strut bracket force, and the leg weight. The simulation results are recorded in

Table 4. Calf holder simulation result.

Material	Minimum Safety Factor	Maximum Displacement (mm)	Maximum Von Mises Stress (MPa)
PLA 25%	0.12	2.536	236
PLA 50%	0.13	2.5
PLA 75%	0.14	2.134
PLA 100%	0.25	2
Aluminum 6061	1.43	0.1088
Titanium	1.48	0.07317

.

The maximum Von Mises stress at the inner wall is 236 MPa, with maximum deflection of 2.536 mm using PLA infill of 25%. As the PLA infill is increased to 100%, the safety factor increases; however, it is not sufficient to support this function. The use of Aluminum 6061 and titanium led to a more promising result, with the safety factor rated above that of lower deflection. However, to save manufacturing time and cost, PLA was selected to create a prototype of this part.

2.3.2. Pinion Connector

The pinion connector was constrained with fixed constraints at the mounting holes, which are expected to be rigidly secured. The load applied is the force caused by the reaction torque on the mounted pinion. The simulation results are recorded in

Table 5. Pinion connector simulation result.

Material	Minimum Safety Factor	Maximum Displacement, (mm)	Maximum Von Mises Stress, (MPa)
PLA 25%	0.14	0.2846	200.7
PLA50%	0.15	0.2806
PLA 75%	0.17	0.2395
PLA 100%	0.31	0.2245
Steel, carbon	1.74	0.004486

. They show that PLA is also not suitable for this part. The maximum Von Mises stress is 200.7 MPa at the pinion mounting hole, with the maximum deflection occurring at 25% infill. The maximum safety factor PLA can achieve is at 100% infill with 0.31, which is still insufficient. Steel infill with carbon was shown to be capable of supporting the load applied with a safety factor of 1.74 and negligible deflection. However, due to the complexity of the part geometry, 3D printing will still be used for the part’s rapid prototyping.

2.3.3. Joint Connector

The joint connector was constrained with pin constraints at the holes to be mounted to the connector rod with bolts. The loads applied are the joint force and the forces from the calf bearing holder, which is rotated by the spur gear. The simulation results are shown in

Table 6. Joint connector simulation results.

Material	Minimum Safety Factor	Maximum Displacement (mm)	Maximum Von Mises Stress (MPa)
PLA 25%	0.76	0.2846	37.1
PLA50%	0.8	0.2806
PLA 75%	0.9	0.2395
PLA 100%	1.62	0.2245

. It is observed that PLA with 100% infill can support the loads applied. It provides a 1.62 safety factor with deflection of 0.2245 mm. The maximum Von Mises stress is only 37.1 MPa, which occurred at the elbow due to stress concentration. During prototyping, a printing infill of 80% is used as it is already sufficient for producing safety factor of at least one.

2.3.4. Adjustable Tube

The adjustable tube was constrained at the upper surface and at the holes to be installed with a ball lock pin. The end holes were selected for simulation because bending moment will always be highest at the end. The load applied includes the reaction forces caused by the bolt mounting with the foot joint bracket. The simulation results are shown in

Table 7. Adjustable tube simulation results.

Material	Minimum Safety Factor	Maximum Displacement (mm)	Maximum Von Mises Stress (MPa)
Aluminum 6061	1.29	0.7152	213 MPa

. The material selected for the simulation was Aluminum 6061. The results show that the maximum Von Mises stress is 213 MPa and deflection is 0.7152 mm. It has a safety factor of 1.29, which is higher than 1.

3. Results and Discussion

3.1. Fabrication and Assembly

For fabrication, an Anet ET4 X-R 3D Printer was used with PLA material. Figure 14 displays some of the printed parts and their assembly with other materials, such as an aluminum plate, a belt, and foam. Figure 15 displays the circuit block diagram of the device, including the Lithium Polymer (LiPo) battery and Arduino UNO R3. The prototype was finally assembled after installing all the parts, as shown in Figure 16.

3.2. Testing and Troubleshooting

During the assembly process, several problems were encountered, immediately identified, and troubleshooted. For example, the initial pulley mechanism bracket, as seen in

Table 8. Before and after images of some parts troubleshooted during assembling.

Parts	Before	After
Pulley assembly bracket
Bracket
Foot joint bracket
Blocker

, was found to easily break even with the application of a low amount of force. This is due to the many-holes design employed to reduce the weight. Thus, a revised design was printed, and after a lifting test, it was observed that the part was able to support the system. The initial gas strut bracket was unexpectedly too narrow for the rod end joint to be installed. Thus, in order for the bracket to be able to hold the gas strut without changing the designs of other parts, an L-shaped bracket was selected. During assembly, it was found that the initial foot joint bracket was too narrow, preventing the rod end joint from fitting into the part. Thus, the revised version features a small cut at the end of the bracket to free up space for the rod end joint to be installed. Lastly, the walls of the initial blocker design were found to be too thin. Thus, the part may break easily and lead to looseness at the end joint. The revised blocker was designed with a tail extended from the body to act as a blocking part to stop the waist mechanism from overturning.

3.3. Final Test

The prototype was worn at the thigh, calf, and waist using the securing belts as shown in Figure 17. When the switch was turned on, the potentiometer started to monitor the user’s movement. As the user started to move, the potentiometer was rotated and the signal was transmitted to the Arduino board to provide a feedback signal to the servo motor to rotate. The pulley mechanism pulls up the entire leg, and the calf motor slightly rotates to assist in bending the knee as well. The prototype is also capable of supporting the user to stand using the gas strut at the back of the device. This gas strut acts as a high-stiffness rod that can prevent the user’s knee from unintentionally bending. The user’s body weight can also fully rely on the device when sitting on it. This can assist the user to stand longer than normal.

A listing test was conducted on the pulley mechanism to test the effectiveness of its lifting capability. The experiment was set up by tying dumbbells to the securing belt on the thigh mechanism. Then, via manual pushing, the thigh mechanism was made to trigger the potentiometer to lift the leg. The lifting loads and the observed results are recorded in

Table 9. Lifting test.

Load, kg	Pass/Fail
0	Pass
4	Pass
8	Pass
12	Pass
16	Fail

.

The results reveal that the prototype can lift at least 12 kg of load. The theoretical model was designed to be able to lift at least 8.35 kg on one side of the leg. Comparing the experimental and theoretical results showed that the prototype is almost 43% more effective in lifting than the theoretical one, revealing that the prototype is capable of lifting more weight than expected.

$$\left(\left({\displaystyle \frac{12}{8.35}}\right)\times 100\right)-100=43\%$$

According to a review on robotic exoskeletons [26], common studies have a lifting torque ranging between 0.03 Nm/kg and 0.21 Nm/kg during lifting. With a user weight of 100 kg, the torque range will be at 3 Nm to 21 Nm. The experiment load can be converted to an equivalent torque by multiplying the load with the distance it was tied to.

$$(12\times 9.81\times 0.155=18.24 \mathrm{N}\mathrm{m})$$

It is observed that the prototype model has an equivalent torque within the range of the torque of existing exoskeletons.

4. Conclusions

An optimized wearable walking and standing aid was successfully developed using the Design for Manufacture and Assembly (DFMA) method. The experimental data demonstrate a lifting capability surpassing the theoretical value. This validates the effectiveness of the wearable aid in providing assistance during sitting and standing. While this study details the results of a significant initial development phase, future work should be guided by the insights gained from this prototype. This includes validating the device’s performance through user testing with a focused group, analyzing the device’s balance assistance, addressing the expected shelter life of the optimal selected material, and analyzing the battery consumption per various demands. This guidance will be useful in validating that the prototype is effective and reliable.