Development of a Wheelchair with a Lifting Function

Yoshikazu Mori

, Norikatsu Sakai

and Kaoru Katsumura

Department of Intelligent Systems Engineering, Ibaraki University, Nakanarusawa 4-12-1, Hitachi, 316-8511, Japan

SMC Corp., Akihabara UDX15F, 4-14-1, Sotokanda, Chiyoda-ku, 101-0021, Japan

Tamron Co., Ltd., 1385 Hasunuma, Minuma-ku, Saitama-city, Saitama 337-8556, Japan

Keywords: Medical and Welfare Assistance, Mechatronics, Design, Disabled Person, Care Lift, Transferring.

Abstract: A wheelchair with a lifting function is designed to assist a caregiver when transferring a wheelchair user not

only indoors but also outdoors. The target user is typically a severely disabled person with disabled upper

and lower limbs, and therefore needs the physical support when using a toilet or transferring from a bed to a

wheelchair and so forth. Both the wheelchair and the lift are driven by their respective motors. The user can

approach above the toilet stool or the bed from the rear because the large driving wheels are located in front

of the body and the seat can be folded. This wheelchair is allowed to travel on public roads because of the

mechanism of folding the frame for lifting. This paper presents the concept design and the experimental

results of a full-sized prototype wheelchair with the lifting function, which confirms the design

effectiveness.

1 INTRODUCTION

Persons with disabilities attributable to the lower

limbs are becoming increasingly numerous

worldwide. In Japan, they number about 3,480,000

(severely disabled persons were about 760,000) in

2006. Most of them use wheelchairs in daily life.

Representative nursing care in daily life entails

basing, evacuating, and feeding. Transfer when

basing, evacuating, and other processes causes back

pain to caregivers. Matsumoto et al. reported that

77% of caregivers and 64% of nurses have back pain

(Matsumoto and Kusunose, 1999). Consequently,

various devices and robots have been developed.

Molift Inc. developed the “Quick Raiser 2”, which

lifts a user with a linear actuator and supports the

standing-up and seating motions (Molift, 2012).

Sankai proposed some exoskeleton-type power-

assisted systems using electric motors and air

actuators (Satoh et al., 2009). Bostelman et al.

developed a robot system that a user himself wears

and enables him to use a toilet, a bed, and so forth

(Bostelman and Albus, 2007). A caregiver robot “RI-

MAN” developed at RIKEN is aimed at realizing

autonomous motion transfer (Onishi et al., 2007).

Some of those tools and robots are, however,

expensive and are limited for use in indoor

environments.

We take notice of a transfer tool that can be used

even when going away. Similar to some commercial

transfer products, “Komawari-san” is a simple tool

based on lever principles (HEARTS-EIKO, 2012).

These tools, however, are too large and heavy to

carry over long distances. “RODEM” is a new type

of electric wheelchair on which the user can ride

from the backside and which can run outdoors, but

the target is limited to mild patients (VEDA, 2012).

This paper presents a wheelchair with a lifting

function that is intended mainly for use by an

electric wheelchair user with disabled upper and

lower limbs. This equipment has good

maneuverability. Moreover, it can move over a step

because of the front driving wheels. It realizes easy

and safe transfer from/to a bed and a toilet stool by

virtue of the opposite wheel allocation of a usual

wheelchair. Furthermore, the mechanism of folding

the frame for lifting allows this wheelchair to travel

on public roads. We demonstrate its design

effectiveness through several indoor and outdoor

experiments.

2 CONCEPTUAL DESIGN

We assume a single caregiver for the use of this

wheelchair. It helps alleviate the burden of the

caregiver when a disabled person moves between the

wheelchair and toilet/bed easily and safely.

489

Mori Y., Sakai N. and Katsumura K..

Development of a Wheelchair with a Lifting Function.

DOI: 10.5220/0004114904890492

In Proceedings of the 9th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2012), pages 489-492

ISBN: 978-989-8565-22-8

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: Analysis of the strength when lifting.

(1) The wheelchair has a lifting function. The lifting

mechanism comprises a lifting frame, a sling

seat, and a winch such as a conventional. The

winch is driven by an electric motor that a

caregiver operates using an up/down switch.

This winch is not back-drivable because a worm

gear and a worm wheel are used in it. Therefore,

this design is safe: the previous state remains

even if the power source is cut off. A toileting

sling is used for this equipment. Therefore the

user can wear it in a seated position and take off

underclothes in the lifting position easily.

(2) Large driving wheels are located in front of the

body, and the seat can be folded. Therefore, the

user can approach above a toilet stool and a bed

from the rear. As a result, this equipment can lift

a user easily and safely. Furthermore, this

location: front driving wheels are rigid and rear

wheels are casters, has good maneuverability

resembling that of a forklift truck.

The user can travel outdoors, even on public

roads, because a driving unit for an electric

wheelchair is used for this equipment and it has a

mechanism of folding the frame for lifting.

3 ANALYSES OF STRENGTH

AND STABILITY

The strength of the equipment is analyzed using

finite element method with COSMOSWorks, which

is add-in software of 3D-CAD software SolidWorks.

The conditions of the analysis are the following: The

user weight is 150 kg. Vertical loads are taken to the

lifting frame or the seat frame. Aluminum alloy

(A6063, yield stress = 145 N/mm

) is referred. The

following results were obtained through these

analyses:

(1) The maximum stress is 54.8 N/mm

at the lifting

frame when lifting. This value is under the yield

stress of the aluminum alloy (145 N/mm

(2) The maximum displacement is 4.00 mm at the

lifting frame when lifting.

(3) The safety ratio is 2.15 FOS when lifting. The

results are portrayed in Figure 1. Here, the

minimum value is shown in a circle.

Next, the equipment stability during transfer is

discussed. We discuss two cases because the user is

lifted vertically in a stationary state; then the user

moves to a target point in horizontal direction. We

analyze the former and latter cases respectively using

the stability margin and Zero moment point (ZMP).

Figure 2: Model for analysis of falling.

Figure 2 shows the model during expansion. Here,

and

respectively signify the distances between

the projected point of the center of gravity (COG)

and the positions of the rear casters and the front

wheels.

signifies the distance between COG and

the line that connects the front wheel and the rear

caster. Also,

denotes the height of COG from the

floor.

The calculated position of COG of the equipment

when carrying a subject (166 cm height, 65 kg

weight), considering the weights of the equipment

and the subject, is nearly at the top of his thigh (

651.8 mm), and

and

are 352.6 mm, 357.4

mm and 292.1 mm, respectively. Those values

respectively equal the backward, forward and

sideward stability margins. Here, the direction of the

rear casters is assumed to be in the front of each

rotation axis because the equipment goes backward

to a toilet stool and a bed (see Figure 2).

ICINCO 2012 - 9th International Conference on Informatics in Control, Automation and Robotics

490

Joystick

Hook

Pulleys

(a) when expanding (b) when folding

Figure 3: A full-sized prototype of a wheelchair with a

lifting function.

Next, we discuss stability during travel. The

safety acceleration against falling

(

=1, 2, 3) is

calculated as

zMaxMg



(

=1, 2) and

(1)

131

zMayMg 

(2)

where

represents the total mass of the user and

the equipment, and

signifies acceleration of

gravity. The position of the rear caster to the rotation

axis changes according to the traveling direction,

=472.6 mm,

=357.4 mm and

=295.9 mm

when traveling forward, whereas

=352.6 mm,

=357.4 mm, and

=292.1 mm when traveling

backward. Therefore, the safety accelerations against

falling are calculated:

=7.11 m/s

and

=4.46

m/s

when traveling forward, whereas

=5.31 m/s

and

=4.41 m/s

when traveling backward.

4 EXPERIMENTS

We address two basic operations: traveling and

transfer experiments. The subject was a man (166 cm,

65 kg) with no leg motion impairment.

Figure 3 shows the appearance of the hardware.

The size in expanding is 100(L)



68(W)



162(H)

cm, and that in folding is 100(L)



68(W)



105(H)

cm, excluding the height of the cushion, and the

weight is 47 kg. Road Traffic Law in Japan does not

allow a wheelchair which size is over

120(L)



70(W)



109(H) cm to travel on public

roads, however, the size in folding is within the

limited size.

Figure 4: Snapshots of the traveling experiments when

going up a step.

The winch gearbox of the lifting mechanism that

comprises a DC motor (250 W, RE75; Maxon Corp.),

a winding rod, spur gears, a worm gear and a worm

wheel. The worm gear and the worm wheel make this

winch back-drivable, so the user is safe even if the

power source is cut off. The lifting cord connected to

the winding rod is split into two parts and passes on

the pulleys that are attached to the lifting frame. A

hook is attached to each end of the lifting cord, and

two hooks connect the lifting cord to the sling seat.

Output torque of 44.2 Nm is necessary to lift a 100

kg load. The maximum torque of the winch (its

reduction ratio = 1/257) is 95.6 Nm (transmission

efficiencies of the spur gears and worm gears =

0.98% and 0.5%, respectively). The maximum lifting

rate is designed to be 10 mm/s. We used a V55 CPU

board (16 MHz; Japan System Design Corp.) and

two batteries (WP2.6-12; Kung Long Batteries

Industrial Co., Ltd.) for the lifting mechanism, which

was controlled based on PD control theory. The

sampling time was 20 ms.

This equipment has large driving wheels in the

front that are the parts of a commercial electric

driving unit for a wheelchair (Joy Unit, 8.2 km/1-

charge, forward: 2.5 km/h and 4.5 km/h, backward:

2.0 km/h, approximately 17 kg including a battery,

YAMAHA Corp.).

4.1 Traveling Experiments

First, we confirmed the motions of traveling forward

and backward and for turning in indoor environments.

The user operated the equipment using a joystick in

the same way as that used for a commercial electric

wheelchair. Consequently, we noted that the user was

not required to lean the joystick when turning

because the driving wheels were arranged in front of

the body.

Development of a Wheelchair with a Lifting Function

491

0 10 20 30 40

Time [s]

Lifting height [cm]

Target

Actual

Figure 5: Time response of the lifting height when lifting.

Figure 6: Snapshots when transferring to a toilet.

Figure 4 shows results of the outdoor examination

when ascending a 5 cm step. It was possible to go

up/down the step because of the front driving wheels,

although it is difficult for a conventional electric

wheelchair to go up about 3 cm step. We also

confirmed that the equipment had sufficient ability to

travel on a field.

4.2 Transfer Experiment

We examined the lifting motions. The results are

presented in Figure 5. The lifting velocity was

calculated from the difference of the lifting height

measured by an encoder installed in the winch. The

motion is operated manually using an up/down

switch. The lifting mechanism was controlled with

trapezoidal speed profile, with target acceleration of

2.5 cm/s

and target maximum velocity of 1 cm/s.

The directing maximum lifting velocity was about

one-third of that of commercial lifts considering the

clearance about 20 cm from the lifting frame to the

head of the user. Accuracy of better than

approximately 0.3 cm for the lifting height and

approximately 0.04 cm/s for the lifting velocity at 25

s was obtained. The error of the lifting height was

approximately 0.01 cm after 30 s. Those results

show that this winch can follow the target trajectory.

The trapezoidal speed controller realized smooth

up/down motions, and the subject was lifted stably.

Figure 6 depicts the experimentally obtained

result obtained for transfer to a toilet stool in a toilet

for physically handicapped persons. The toilet stool

height was 45.6 cm. The toilet stool width was about

20 cm, although the minimum width between the

rear frames of the equipment is 37 cm. We

confirmed that the subject was able to approach

above the toilet stool from the rear.

5 CONCLUSIONS

We proposed a novel wheelchair with a lifting

function for an electric wheelchair user with disabled

upper and lower limbs. This equipment facilitates

easy and safe transfer from/to a bed and a toilet stool

by virtue of the opposite allocation of wheels from

that for a usual wheelchair. Furthermore, the

mechanism of frame folding for lifting allows this

wheelchair to be used on public roads. Results show

that this equipment had good maneuverability like a

forklift truck. We also demonstrated that the

equipment had sufficient ability of moving up/down

a 5 cm step and of traveling on a field. It can be used

in an actual toilet. In future works, we plan to

improve this system for better practical use,

mechanical strength, and design.

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Matsumoto, T. and Kusunose, K., 1999. The status quo

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