wheel chair cum strecher

SASTECH 78 Volume 10, Issue 2, Sep 2011

DESIGN AND DEVELOPMENT OF CONCEPTUAL WHEELCHAIR CUM STRETCHER

Sreerag C S1, Gopinath C2, Manas Ranjan Mishra3

1-M.Sc. [Engg] Student, 2-Professor, 3-Asst. Professor, Department of Design M. S. Ramaiah School of Advanced Studies, Bangalore 560 058

Abstract

In India the number of disabled individuals is increasing every year. Mobility aids are useful for patients for transportation and a replacement for walking especially in indoor and outdoor environment. Wheelchairs and stretchers are the most commonly used medical equipment for the transportation of patients. Transferring the patients from wheelchair to stretcher or to the medical bed is always an issue for the attendant or nurse. Understanding the various issues regarding the mobility equipment and introducing a better design will be an asset for the medical field and a helping hand for disabled individuals. There is a need for a wheelchair cum stretcher to facilitate the disabled patient’s mobility and to provide a novel medical equipment for use in the Indian hospitals.

Adopting various kinds of research methods helped to obtain more information about hospital mobility aids and for data collection. It has been observed that every year the numbers of disabled individuals are increasing by different kinds of accidents. Presently wheelchairs and stretcher are the commonly used mobility aid for indoor and outdoor purpose. From the user study it was found out that the need of a wheelchair cum stretcher can be an asset for the Indian hospitals. Transferring the patients from wheelchair to the stretcher or to the bed is a difficult task in hospitals. The presently used wheelchair and stretcher design is not meeting the user’s need. From the identified need, QFD was generated and the main priorities should be given to ergonomic design, mechanism, safety and functionality. From the Quality Function Deployment (QFD), Product Design Specification (PDS) was made. Considering the issues like safety, hygienic, cleaning and functionality the concepts were generated.

New features like document holder, provision for oxygen cylinder, and rotatable handle have been introduced. Final concept was selected using Pugh selection method by evaluating all the concepts with bench marked product. A 1:2 mock up model had been made to validate the concept and feedback was collected from users. Our study shows that it is possible to save 50% space by the wheelchair- cum- stretcher design. The product will thus likely be an efficient mobility aid in hospitals.

Keywords: Mobility Aid, Dual Purpose, Wheelchair cum Stretcher, Convertible Type, Safety

Nomenclature Kg Kilogram weight mm millimeter length

Abbreviations

CAD - computer aided design PDS - Product Design Specifications QFD - Quality Function Deployment 1. INTRODUCTION

Chair and wheel were the earliest inventions of man. A wheelchair is a wheeled mobility device designed especially for disabled individuals. The device is propelled either manually (by turning the wheels by the hand) or via various automated systems. Wheelchairs are used by people for whom walking is difficult or impossible due to illness (physiological or physical), injury, or disability. Early wheelchairs were intended only to help a disabled individual to move from one place to another but today the wheelchairs are considered as not only for the transportation purpose but also a way to express users individuality. In India the number of disabled population had a tremendous augment in the past few years. Huge amount of people have congenital disabilities, another few percentages are the victim of accidents and various kind of mobility devices are inevitable part of their life [1].

1.1 Wheelchair invention

The first record of combining wheel to furniture was in Greece in 530 BC. Oldest evidence of wheeled chairs was found in China, and was spoke wheels on chariots in 1300 BC. The first dedicated wheelchair was made for King Phillip II for Spain in 1595. It was not a self -propelled one, a servant's assistance is to be needed for the movement. Self propelled wheels invention was created enormous demand in the market and it was better helping aid for the disabled individuals [2].

Fig. 1 Wheelchair

2. DESIGN METHODOLOGY

Design methodology helps to find out the best solution for each design situations. A systematic approach and


procedure is to be followed to achieve the suitable solution. It involves the following steps. • Journals and patent research • Market study and user(GEMBA)survey • Bench marking • QFD matrix • PDS • Concept generation and selection • Final concept refinement • physical modeling and validation

3. LITURATURE REVIEW Journal papers and patents explored here are

related directly or indirectly to the proposed area of work that is design and development of a Wheelchair cum Stretcher. These papers are to support and enlighten the whole process of design in the specific area.

3.1 Wheelchair and Stretcher

A wheelchair is chair with wheels, designed to help the disabled individuals. Stretchers are mobility devices used to transport the patients from one place to other. These both medical mobility aids are used in hospitals and clinics for helping the patients. Stretchers are simple in construction and the patient needs the support of an assistant to transport from one place to other. Whereas wheelchair is designed in such a way that either patient can control the device manually or with the help of someone’s assistance. The device consists of proper handle with cushion in hand rest and seating area. The direction movement is a critical part when it comes to emergency situation. Proper selection of caster wheels facilitates to overcome the situations.

3.2 Selection of Wheelchair

According to Mr. Peter Axelson, Mr. Jean Minkel, and Mr.Denise Chesney, [3] selection of an appropriate wheelchair will lead a comfortable living to the user. Performance, safety and dimensions are the three categories which have to be considered while selecting a manual or powered wheelchair. An excellent approach to the wheelchair selection is to set priorities based on user’s mobility and seating needs. It is highly recommended that a novice can consult with the rehabilitation specialists in order to select the appropriate wheelchair.

3.3 Caster Wheel Shimmy

James J. Kauzlarich, [4] says self excited vibration is one of the most interesting topics in the field of vibrations and is the science prevailing caster wheel shimmy. Self excited vibration is characterized by vibration that is produced by the motion of the system like wheelchair speed. It can be observed that in most of the cheapest wheelchairs, the design of the casters makes use of a sliding frictional damper in the spindle support to improve the shimmy characteristics. Understanding the theory of damping for the casters show how shimmy prevention works in ultra-light and powered wheelchairs.

3.4 Smart Power Assisted Wheelchair

Mr. Richard Simpson, [5] says almost 10% of all individual who are legally blind also have a mobility

impairment and majority of these individuals are dependent on others mobility. A smart power assistance module (SPAM) for manual wheelchair is being developed to provide independent mobility for this population. The power assist wheelchair that provides for obstacle detection and avoidance for those with visual impairments. The control of the wheelchair will be carried out by the microprocessor and also allow the SPAM to provide a smoother and nuanced control.

3.5 Wheelchair Configuration

According to Mr. Rory A. Cooper, [6] rehabilitation is a humanistic profession. Measurement of the user and wheelchair are critical to achieving maximum functional mobility. He says Biomechanics and ergonomics provide the information necessary to understand many aspects of wheelchair use. These factors affect seating comfort and posture, propulsion, efficiency and pain. Proper seating is an important aspect of wheelchair selection, and wheelchair cushions provide pressure relief and some postural support. Electric powered mobility may be the best choice for driving long distance and may be beneficial for people with upper and lower extremity impairments.

3.6 Patients Transfer System

Dr. Daniel E. Jolly, [7] says proper preparation should be taken before transferring the patient from wheelchair to bed or vice versa. Use of sliding boards will be helpful for paraplegic patients. The best sliding board is made of hard wood, smooth, tapered on ends. Support of two assistance, support straps, belts etc will facilitate easy transfer. The patient should not be slide into chair, lift from the wheelchair and transfer is the optional and safety method for patient transfer.

3.7 Mechanical Principles for Wheelchair Design

Mr. Amos Winter, [8] says following the mechanical principles will be helpful for a better design. Understanding the centre of gravity location is important in wheelchair design. Weight should be the other important factor for wheelchair design. Reducing weight will results the comfortable use for the user and also lowers material cost. The best strategy is to maximize the strength and minimize the weight of the frame tubing. Calculating the moment of inertia and weight results the best strength and can be used to make the strongest frame at the least weight.

3.8 Anthropometric Consideration

Mr. Debkumar Chakrabarti [9] says primary consideration should be given for comfort, so that people can sit for long time without feeling any physical discomfort. Considering the suitable materials for seat surface, frame and can make a comfortable seating for the design. Without considering the ergonomics and application can make a diverse effect to the user. Seat cushions are so important in the design of wheelchair. A wheelchair or stretcher design without cushion is not recommended for the hospital purposes. A stretcher or wheelchair design without cushion may create spinal cord injuries to the patients.

3.9 Structure of Common Wheelchair

Wheelchair is a wheeled chair consists of various parts and each part with different functions. This is an


ergonomically designed medical equipment consists of a foldable frame type mechanism for easy carry. Seating and hand resting position are well designed for a comfortable sitting. Adjustable foot rest with a heel loop on the harper bracket is provided so that user won’t get problems while transportation. Handles are placed in the back rest of wheelchair with suitable grip on that. Push rims are the other features of the wheelchair when into comes to the indoor purpose for the user. The user can be independent by the help of push rim, which may help the user to move from one place to other. Brakes are provided for stopping the wheelchair on both the push rim wheels. Caster wheels are another major part which directs the way and for easy transportation.

Fig. 2 Structure of wheelchair [10]

3.10 Structure of a common stretcher

Stretchers are the common transportation devices in hospitals, in order to carry a patient who can’t walk or stand with the help of others assistance. Mostly the accident cases and the people who are in critical stages are carried in stretcher. It is a simple design with tubular frame fixed with swivel caster wheels and metal platform form on the top side for lay the patient.

Fig. 3 Structure of stretcher [10]

3.11 Wheelchair Classification

Wheelchair classification is done based on the type and area of use. Mainly wheelchairs are classified to manual, sports and electric wheelchairs.

Fig. 4 Wheelchair classification

3.12 Types of Manual Wheelchairs

Manual wheelchair classification is done based on the use and type of material used. Travel, airport, pediatric and stainless steel wheelchairs are the commonly used wheelchairs in hospitals.

Fig. 5 Types of manual wheelchairs [10]

3.13 Types of Electric Wheelchairs

Fig. 6 Electric wheelchairs [10] Electric wheelchairs are the commonly used indoor mobility devices. The specialty of these kinds of devices is for their design especially because of the custom design. The design can be done according to the user’s convenience.


3.14 Types of sports wheelchairs

Entertainments like sports and games are the part of human life. Human who are physically challenged will have the entertainment through these kinds of wheelchairs. Various kinds of sports wheelchairs are basket ball, tennis, rugby and athletic wheelchairs.

Fig. 7 Types of sports wheelchairs [10]

3.15 Wheelchair Mechanisms

Kinds of mechanism are incorporated with wheelchairs and stretchers. This helps to get more accessibility and usability to the product. Some of the commonly used mechanisms in the wheelchairs are explained below.

Cross Brace Bar Mechanism

Cross bracing is a construction technique in which braces are crossed to form an “X” shape to support a frame. The main feature of this mechanism is the folding facility, which helps to the product into a foldable one. This folding technique helps the wheelchair a portable type and can be carried easily with less weight and less space consideration.

Fig. 8 Cross brace bar mechanism [10] Caster wheel mechanism

Caster angle is the angular displacement from the vertical axis of the suspension of a steered wheel in a vehicle measured in the longitudinal direction. It is the angle between the pivot line (in a car - an imaginary line that runs through the centre of the upper ball joint to the centre of the lower ball joint) and vertical. Car racers sometimes adjust caster angle to optimize their car's handling characteristics in particular driving situations. It is applied to ensure stability of direction by means of a special arrangement. θ is the caster angle, red line is the pivot line, grey area is the tire. A positive caster angle is shown with the front of the vehicle being to the left.

Fig. 9 Caster wheel mechanism [10]

Braking Mechanisms

Toggle clamp mechanism is fixed on rear wheel for braking in manual wheelchairs. Lever type mechanism is used in hand brake system. Hand braking system is used in most of the manual wheelchair and will be helpful for the user’s convenience.

Fig. 10 Braking mechanisms [10]

3.16 Types of Wheels in Wheelchair

Wheelchair wheels are classified into two categories, caster wheels and push rim wheels.

3.17 Wheelchair Cushions

Cushions are the integral part of wheelchair where the patients are laid. A stretcher or wheelchairs without cushions are never recommended for the hospital purpose. So study has conducted in order to get a better understanding with the types of cushions used in these products. The use of quality material raises the entire cost of the product and a comparison study has done in order to understand the various types of cushions used in wheelchair and stretcher.

Table 23. Types of cushions [10]

3.18 Bench Marking

These types are the commonly used wheelchair cum stretcher type of medical equipments in the hospitals. Some of the features are like foldable frame, foldable arm rest, foldable and detachable foot rest, dual brake system and detachable and adjustable type of head


rest. The product is manufactured with high quality of materials like stainless steel, carbon fiber etc

Fig. 11 Bench marked product [10]

4. RESEARCH AND ANALYSIS

4.1 Gemba Study and User Survey

User study needs to be conducted in order to experience the user and its environment. This may help the designer to design an appropriate product which suits the environment. User study has been conducted around 8 hospitals in order to find the user experience and various issues regarding wheelchair and stretcher. Initially all the stake holders are considered and study has conducted in order to get more information.

Ethnography study helps to identify the need of the product, product environment and users experience. This technique helps to gain more knowledge about the wheelchair/stretcher usage and various situations which affect their working environment. Wheelchairs and stretchers are the mobility equipments used to transport the patients from one place to other and various problems are identified by conducting the user study. Medical equipments, hospital environment and the stake holders related to the product are considered for conducting the gemba study.

Fig. 12 User study

Observations from the Gemba study are, • Availability of numbers of stretchers are less

compared to wheelchairs, so patients have to wait in the wheelchair if they need to transfer to the stretcher.

• Transferring of patients from vehicle to the stretcher can be done only with the help of 2-3 people.

• Transferring of patient from stretcher to the bed also a problem for the patient.

• Patients will be arriving to the hospitals with their own vehicles so at first attender will be choosing the wheelchair to transfer the patients.

• Patients with fracture in bone will be preferred to transfer in stretcher.

• Patients with low blood pressure are better to use stretcher.

• Cardiac failure patients will have problem while using stretcher, so seating will be better preferred position.

• The most preferred position for getting rest for heart will be seating posture.

4.2 Study of Technical Voices – Findings from QFD

Technical voices from QFD are listed below. These were studied and incorporated while concept ideation stage.

Ergonomics: When the wheelchair converted to stretcher, ergonomic height is considered.

Mechanism: Easy to operate and simple mechanism is considered.

Safety: Should not be harmful to the patients. Product design specification (PDS) is arrived from the QFD.

4.3 Ergonomic details All dimensions are considered according to Indian anthropometric data.

Human dimensions are considered for both male and female and 95th percentile of hip breadth, elbow to elbow and buttock to popliteal is taken for the sitting posture.

Fig. 113 Anthropometric data [9]

Elbow rest and popliteal dimensions are taken as 50th percentile and combined dimension of 210mm and 419mm respectively for the design. Stature dimension is taken as 95th percentile and the dimensions as 1771mm.

Fig. 14 Anthropometric data [9]

5. CONCEPT GENERATION Based on Product Design Specification concepts are generated using mind mapping tool.

5.1 Mind Mapping


Mind mapping technique is used to visualize various ideas. So this classification considered all the aspects for the concept design.

5.2 Concept 1

The main criteria considered for this concept is the convertible wheelchair and stretcher. So in order to convert the wheelchair into stretcher, some sort of mechanism needs to be added. In this concept a sliding tubular frame is attached to the back rest of the wheelchair. A handle is provided in the back rest so that the user can be pulled it easily and can be converted to stretcher easily. So a proper balance should be maintained in the back side because the centre of gravity of human body will be lying in between the seat and back rest portion. A caster wheel support is given so that proper balance will be achieved. A pair of bigger wheels is provided in the middle of the wheelchair, so that more strength will be attained and front caster guides the wheelchair according to the direction. The provision for oxygen cylinder is another demand which has observed during the user study and the drip holder location is provided by the sides of the wheelchair. The hand rest is designed in such a way that, it can be rotated and a removable type so that it will act as a support side for transferring the patients.

Fig. 15 Concept 1

5.3 Concept 2

This concept is slightly different from the concept one. The back rest is providing with an adjustable handle with a comfortable holding position. The length can be adjusted and the length can be maintained by adjusting the knob. The frame design is made in such a way that proper strength is provided to the wheelchair.

Fig. 16 Concept 2

5.4 Concept 3

This is concept is operated with hydraulic mechanism, so that the height can be adjusted according to the user’s convenience. The handle is designed in such a way that, the user won’t get any difficulty while handling the product. A simple design of oxygen cylinder holder is provided below the seat so that it can help to withstand stretcher with a supporting element for adjusting the weight.

Fig. 17 Concept 3 A hydraulic scissor lifter mechanism lifts the entire wheelchair into stretcher. The telescopic arrangement supports the back rest so that weight of the body will be evenly distributed in the stretcher.

Fig. 18 Concept 3 wheelchair

5.5 Concept 4

A double caster wheel mechanism gives more strength to the design, so that weight of the body can be evenly distributed. Front portion is lifted with the help of hydraulic mechanism so that the patient won’t get trouble while lifting.

Fig. 19 Concept 4


5.6 Concept 5

This concept is based on the gear mechanism. According to the rotation of the middle wheel, the front and back seats are rotated in opposite direction and stretcher arrangement is achieved.

Fig. 20 Concept 5

5.7 Concept selection and evaluation

The generated concepts were compared and studied using Pugh method with the bench marked product. Concept 3 was selected as the final concept and it was verified with user opinion. The selected concept is modeled using Alias studio tools and rendered in Hyper shot for visualization

Fig. 21 Final concept

5.8 Final concept detailing

The function of the hydraulic mechanism is mainly for adjusting the height. It should be easy for an operator to lift the entire chair into stretcher height by the use of a button.

Fig. 22 Hydraulic mechanism Easy movement is the best performance required

for the mobility devices. Caster wheels help the wheelchair or stretcher to relocate the product according to the direction of motion.

Fig. 23 Caster wheels

It can be observed in hospitals that most of the drip holder will be in separate location. This is a serious ergonomic problem for the nurses and in this concept the problem can be devastated by adding a telescopic type of drip locator in one side. Document holder helps to keep the documents safely. A rail mechanism with telescopic arrangement helps to maintain the centre of gravity of the stretcher.

Fig. 24 Features

The most important area of a wheelchair or stretcher is the cushioning part. Here the design is done with foam material and various sectioning is given so that it can be easily folded.

Fig. 25 Wheelchair cushion

Base is the area where the cushion sits. It is designed in such a way that easy folding should be possible when a wheelchair is converted to stretcher.

Fig. 26 The base

Oxygen cylinder holder is required for each of the stretcher. Most of the existing designs are very complex in design. Here a very simple oxygen cylinder holder is designed. By construction vice, it is so simple with bending. The base of the wheelchair design is constructed with the help of tubular frame. This material helps to reduce the weight of the entire product. The use of stainless

Drip locator with adjustable arm


steel material to the frame gives more strength and product will be long lasting.

Fig. 27 The frame

5.9 Mock Up Model for Selected Concept

A 1:2 Mock-up model is developed by using MS frames, MDF wood and spray painted to validate the concept. Fig 1.29 shows the dimensional drawing and mock-up model of the final concept.

Fig. 28 Mock-up model

6. VALIDATION AND DISCUSSION OF

RESULTS In order to understand the ergonomic issues of the wheelchair cum stretcher, a mannequin of human is made and the validation has been done. Though it is not a working model, functioning of hydraulic mechanism cannot be shown or validated through the mannequin. The hydraulic mechanism which is proposed for lifting the wheelchair seating to the stretcher position will be the most appropriate method for lifting. The design of the handle and the arm rest are ergonomically designed so that the user won’t get any problems while operating.

Fig. 29 Concept validation

The nurses and attendant are satisfied with the proposed design mainly because of the usability and functionality of design. The hydraulic mechanism which is operated by button control will be more user friendly to the operators. The additional features like drip holding locator, oxygen cylinder holder and the folder location for keeping the medical documents are the required features of the product. It has been concluded that the final product fulfils the requirement of the user.

7. SUMMARY The present study was intended to develop a concept for a wheelchair- cum- stretcher, with the motivation of saving space and precluding exertion by the patient. By adopting various research methods helped to identify the various issues of the topic, importance of safety and hygiene and significance of materials and manufacturing process involved in the whole product. From the identified needs ergonomic design, mechanism and safety were prioritized by Quality Function Deployment. Product Design Specification was generated based on QFD and five different concepts were created through mind mapping technique. Digital modeling was done using Alias studio tools and hyper shot software was used for better visualization. Final concept selection was done using Pugh selection matrix by comparing the bench marked product. A 1:2 mock up model of selected concept was made for validating the final concept. Our study shows that it is possible to save 50% space by the wheelchair- cum- stretcher design. The product will thus likely be an efficient mobility aid in hospitals.

8. REFERENCES [1] Anonymous, “Wheelchair history and

development”, www.newdisability.com, retrieved on 27th Sept. 2010.

[2] Anonymous, “History of the wheelchair”, www.inventors.about.com, retrieved on 27th Sept. 2010.

[3] Peter Axelson., “A guide to wheelchair selection”, paralyzed veterans of America, Library of Congress Cataloguing-in-publication data, Washington 1994.

[4] James J. Kauzlarich., “Wheelchair caster shimmy II: Damping”, Journal of Rehabilitation Research and Development, Volume. 37, No. 3, pp 305-313, May/June 2000.

[5] Cooper R, Corfman T, Fitzgerald S, Boninger M, Spaeth D, Ammer W, Arva J., “Performance Assessment of a Pushrim Activated Power


Assisted Wheelchair”, IEEE Trans Control Sys Tech, Volume 10, ISSN: 1063-6536, Jan 2002.

[6] Dr. Rory A. Cooper., “Wheelchair selection and configuration”, ISBN 1-888799 – 18 – 8, March 1998.

[7] Mr. Daniel E. Jolly., “Wheelchair transfer”, The Ohio state university college, Columbus, ohio, retrieved on 24th Sept. 2010

[8] Mr. Amos Winter, “Mechanical principle of wheelchair design”, Graduate Student,

Department of Mechanical Engineering, Massachusetts Institute of Technology, US, retrieved on 24th Sept. 2010.

[9] Debkumar Chakrabarti, “Indian Anthropometric Dimensions for Ergonomic Design Practice”, National Institute of Design, Ahmedabad, 1999.

[10] Unknown, “wheelchair, stretcher, hydraulic lifting”, www.googleimages.com, retrieved on 8th . 2010

wheel chair cum strecher

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