The 2010 IEEE/RSJ International Conference onIntelligent Robots and Systems
October 18-22, 2010, Taipei, Taiwan

Development of a Nursing-Care Assistant Robot RIBA
That Can Lift a Human in Its Arms
Toshiharu Mukai, Shinya Hirano, Hiromichi Nakashima, Yo Kato,
Yuki Sakaida, Shijie Guo and Shigeyuki Hosoe

Abstract— In aging societies, there is a strong demand for
robotics to tackle problems caused by the aging population.
Patient transfer, such as lifting and moving a bedridden
patient from a bed to a wheelchair and back, is one of themost physically challenging tasks in nursing care, the burdenof which should be reduced by the introduction of robot
technologies. We have developed a new prototype robot named
RIBA with human-type arms that is designed to perform heavy
physical tasks requiring human contact, and we succeeded intransferring a human from a bed to a wheelchair and back.
To use RIBA in changeable and realistic environments, cooperation between the caregiver and the robot is required. The
caregiver takes responsibility for monitoring the environmentand determining suitable actions, while the robot undertakes
hard physical tasks. The instructions can be intuitively givenby the caregiver to RIBA through tactile sensors using a newly
proposed method named tactile guidance. In the present paper,
we describe RIBA’s design concept, its basic specifications, andthe tactile guidance method. Experiments including the transferof humans are also reported.

I. I NTRODUCTION
With the advent of an aging society, the demand forhuman-interactive robots that can help on-site caregivers
by playing a part in nursing humans, particularly the elderly, is increasing. For this purpose, many robots havebeen proposed, for example, robots for feeding people whoare paralyzed [1], mental commitment robots dedicated formental healing [2], and smart wheelchairs [3]. There arealso wearing-type robots [4] that can support a caregiver’s
or patient’s motion.
Tasks involving the transfer of patients, such as liftingand moving a bedridden patient from a bed to a wheelchairand back, are among the most physically challenging tasks
in nursing care. Although patient-lifting devices have beendeveloped and commercialized, they are not widely usedin nursing-care facilities in Japan. According to [5], theproportion of caregivers in Japanese nursing-care facilities
always or sometimes using portable patient lifts is limited to
14.8%. The reasons for this include the long time required
for their use, the difficulty of attaching slings, the risk ofdropping a patient, and the mental and physical discomfortof the patient. In addition, it was reported in [6] that thephysical burden of the caregiver is not reduced in many cases
by using patient lifts.
T. Mukai, S. Hirano, H. Nakashima, Y. Sakaida, and S. Hosoe are withRIKEN RTC, 2271-130, Anagahora, Shimoshidami, Moriyama-ku, Nagoya
463-0003, Japan {tosh,hirano,nakas,sakaida,hosoe}@nagoya.riken.jp
Y. Kato and S. Guo are with SR Laboratory, Tokai Rubber Industries, 1, Higashi 3-chome, Komaki, Aichi 485-8550, Japan{yoh.katoh,shiketsu.kaku}@tri.tokai.co.jp

978-1-4244-6676-4/10/$25.00 ©2010 IEEE

Under this situation, robotics is required to help withpatient-transferring tasks. Daihen Corporation has developed
a patient-transfer apparatus named C-Pam [7] that can transfer a patient between a bed and a stretcher. It consists of aflat board covered with motorized endless belts, and gently
crawls under the patient who is lying on the bed. Panasonicdeveloped Transfer Assist Robot [8] that has flat board-type
arms with motorized endless belts, and can transfer a patientfrom a bed to an almost flat wheelchair with a reclining
function. However, these robots cannot transfer a patientfrom a bed to a wheelchair without a reclining function. Thelong time taken to use these devices is another difficulty.
Another approach to assisting with transfer tasks by robotics
is the use of wearing-type robots [4]. A robot of this type isworn by the caregiver, and assists with his or her motion. In
nursing-care facilities, however, caregivers have to performmany other tasks in addition to patient transfer, and wearing
such a robot may interfere with these tasks.
We consider that robots for performing patient-transfer
tasks between a bed and a wheelchair are needed in nursingcare facilities and hospitals, and we are developing prototype
robots for this purpose. In 2006, we presented a robot named
RI-MAN [9], [10], which succeeded in lifting a dummy
human. However RI-MAN had several strong limitations forthe use in realistic situations. First, its mechanical structure
was not satisfactory regarding payload, motion accuracy,
and ranges of joint movement. The weight of the lifteddummy was no more than 18.5 kg, and because of thelimited ranges of joint movement, it could not put the dummy
down. Second, it could not deal with various and changeable
situations, and its working environment had to be carefully
controlled. For example, the dummy had to be set in thepredetermined position and posture before lifting. Third, it
did not have sufficient safety for handling a human.
To cope with these difficulties, we have developed a newrobot named RIBA (Robot for Interactive Body Assistance).
It has adopted a new human-robot interface, tactile guidance,
based on tactile sensors. It has satisfactory power, manipulability, and safety to handle a human. RIBA succeeded intransferring a human between a bed and a wheelchair, using
human-type arms. These arms give RIBA the ability to adapt
its lifting motion to different situations, which include lifting
to and from a wheelchair without a reclining function.
In the remainder of this paper, we first describe the designconcept of RIBA, then outline its basic specifications. Next,
we explain the concept of tactile guidance. Next, experiments
including the lifting and putting down of humans are described, and finally we conclude this paper.

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C. Whole Body Manipulation

II. D ESIGN C ONCEPTA. Patient Transfer Using Human-Type Arms
To deal with a bedridden person using robots, several
methods have been proposed.
1) The use of human-type arms for transferring a person(our method).
2) The use of board-type arms with endless conveyer belts
that enable frictionless insertion under a bedridden
person before transferring the person [8].
3) Part of the patient’s bed is detached and jointed to therobot arms, and the patient is lifted with the detachedpart [11].
4) The use of a simple and small bed fixed on the robot
arms. A bedridden person must first be transferredfrom the normal bed to the small bed [12].
5) Part of the bed is transformed to a smart wheelchair[13].
There are some advantages of our method of using humantype arms. First, the robot can be applied to various types oflifting and other tasks such as assisting with rehabilitation
training. RIBA succeeded in transferring a patient between
a bed and a normal wheelchair without a reclining function,
which cannot be achieved by the other methods. Second, if
a robot lifts a patient but does not put him or her down in ashort time, it is occupied by the patient for a long time andcannot be used with other patients, which is the standard
usage of 4) and 5). In our method, the robot can be shared
among many patients. The third merit is that the humantype arms can be inserted into small spaces under a patientlying on a bed, which results in insertion taking less timethan that using endless belts in 2). If the caregiver makes
a small space under a patient lying on a bed, for example,
by bending the patient’s knees, the robot can insert its arm
under the knees. Similarly, the robot can insert its other arm
under the patient’s back after the caregiver has slightly raised
the upper body of the patient.
For the above reasons, we have adopted a method ofpatient transfer using human-type arms. Its disadvantages
include the increased cost and probability of malfunction
caused by the complexity of the arm structure, and the dangerof dropping the lifted patient, which should be overcome byfarther research.
B. Trade-Off among Size, Speed, and Payload
To use robots for patient transfer in nursing-care facilities
and hospitals, they must be able to go through doors andmove into narrow spaces between beds. On the other hand,
they must be able to support the weight of a human, andthe lifting motion must be acceptably quick for caregivers
and patients. These conditions have a trade-off relation, but
all conditions must be satisfied to an acceptable level. In thedesign of RIBA, we set the following priorities in decreasingorder of importance: i) a payload that enables the robot tolift a human (over 60 kg), ii) a size that allows RIBA tomove into small spaces (width less than 80 cm), iii) a joint
speed as high as possible while satisfying conditions i) andii).

We have adopted whole body manipulation [14], in which
not the end effectors but the entire body can be considered as
the contact area between the robot and the manipulated object. When the object is a human, whole body manipulationmeans that many areas of the robot body may come in contact
with the human, and thus the state of the robot surface
is important for the safety and comfort of the human. We
decided to embed all cables in the body, and we designed asoft and smooth outer shell without projections. In particular,
the joints are covered and isolated to prevent fingers or hairfrom being trapped in their gears.
D. Cooperation between the Caregiver and the Robot
Even using state-of-the-art technology, it is almost impossible to build fully autonomous robots that can performpatient-transfer tasks in environments such as nursing-carefacilities and hospitals. It is very difficult for robots to detecthuman positions and postures in various environments, toplan a suitable lifting motion from the detected information,and to understand the patient’s physical and mental condition
from the patient’s facial expression and body posture to
determine whether the patient is ready to be lifted. It is alsodifficult to detect dangerous and unexpected situations fromsensor data. Furthermore, it is necessary to clarify where
the responsibility lies regarding the determination of robot
motion.
To realize patient-transfer robots under these conditions,
we have adopted a system based on the cooperation of the
caregiver and the robot, where the caregiver becomes theoperator and takes charge of recognizing the environmentand deciding the lifting procedure, while the robot undertakes
physically hard tasks. The robot operates autonomously
when safety is guaranteed, whereas at times when more
complex decision making is required, such as when a large
force is to be exerted on a human for lifting, it leaves the
final decision to the accompanying caregiver.
It is desirable that the interface for transmitting instructions from the caregiver to the robot should be simple andusable without additional devices. In addition, its use should
allow easy and intuitive control of the many degrees of
freedom (d.o.f.) of the robot. To this end, we developed a
new method named ‘tactile guidance’ for controlling robots
by touching and leading the robot motion. Details will
be described in Section IV. Using tactile guidance, thecaregiver can control the robot by touching it with one hand,
while performing delicate jobs unsuitable for high-powerrobots, such as lifting up the patient’s head, using the otherhand. The caregiver can remain close to the patient while
controlling the robot, which we believe is more relaxing forthe patient.
In nursing-care facilities, a bedridden patient is usuallytransferred by two or more caregivers. If the role of the
caregiver with the greater physical load can be replaced bya robot, it will save manpower and allow him or her toconcentrate on more mental jobs.

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1

0

2
3

17

6

8
9

4
5

7

16

15
14

10
11

(a) Without cover

12

Fig. 2.

(b) With cover

Tactile sensors on the upper arm

13

Fig. 1.
RIBA (Robot for Interactive Body Assistance) and its joint
configuration
TABLE I
BASIC SPECIFICATIONS OF RIBA
Dimensions

Width
Depth
HeightWeight inc. batteries
D.O.F.
Head
Arm
Waist
Cart
Base movement
Actuator type
PayloadOperation timePower
Sensors
VisionAudio
Tactile750 mm (when arms are folded)
840 mm
1,400 mm
180 kg3 (only 1 in current use)
7 each2
3 (with 4 motored wheels)
Omnidirectional with omnidirectional wheels
DC motor
63 kg (tested value)
1 hour in standard use
NiMH batteries
2 cameras
2 microphones
Upper arm (128 pts. each)
Forearm (94 pts. each)
Hand (4 pts. each)Shoulder pad (8 pts. each)III. BASIC S PECIFICATIONS
The developed robot RIBA and its joint configuration are
shown in Fig. 1, and its basic specifications are given in
Table I. The link length, joint configuration, and movable
ranges of the joints were determined by performing a computer simulation of lifting a human and from our experiencebased on our previous robot RI-MAN. We adopted a coupleddrive [15] mechanism that uses a pair of motors for providing
2 d.o.f. in the joint pairs (0,1), (2,3), (4,5), (7,8), (9,10), and(11,12). This mechanism allows the output of the two motors
to be concentrated at one joint if the other joint in the pairis not required to move. This enables the robot to realize ahigh payload with thin and light arms.
The width of 750 mm in Table I is that when the arms
are fully folded. When the arms are straight, as in Fig. 1,
the robot width is 1200 mm. Omni-directional wheels are
adopted so that the cart can freely move around in narrow
spaces such as the space between beds.
RIBA has speech recognition ability so that it can understand voice commands. It also has face recognition and soundsource localization functions to find the operating caregiver.
As tactile sensors, we developed a flexible tactile sheet with
8 × 8 semiconductor pressure sensors and a readout circuit
embedded in an elastic material [16]. This type of tactile

sensor is mounted on the upper arms (Fig. 2) and forearms.
The numbers of sensing points on the upper arm and theforearm are 128 and 94, respectively. RIBA also has tactile
sensors in its hands and shoulder pads that are made ofpressure-sensitive rubber. These tactile sensors are used formotion adjustment, tactile feedback, communication, andensuring safety.
Basic trajectories for motions are given to RIBA in advance. One of motions is selected by the operator using
voice commands such as ‘Lift up from the bed’. The selectedtrajectory is modified using tactile guidance when necessary.
RIBA can operate as a stand-alone robot with all theprocessors and batteries inside it. The main PC (CPU: Intel
CoreDuo, 2GHz) and more than 20 local processing boards(CPU: Microchip dsPIC33F) for the sensors and motor
controllers constitute the distributed information-processing
network in RIBA. This distributed network contributes toreducing the computational load of the main PC, decreasing
the number of cables in RIBA, and reducing the sensor noiseby shortening the analog transmission length. RIBA can beaccessed via wireless LAN when necessary.
To ensure safety in the case of unexpected contact, andthe stability and comfort of the lifted patient by increasing
the contact area, the entire body of RIBA including its
joints is covered with soft materials such as polyurethane
foam and a silicone elastomer. We adopted a clean andfriendly appearance for RIBA, similar to that of a giant white
teddy bear, because a mechanical appearance would not havesuited nursing-care situations and a humanoid appearance
may cause psychological discomfort to the patient.
RIBA has succeeded in lifting a human from a bed, placing
a human on a bed, lifting a human from a wheelchair, putting
a human down on a wheelchair, and moving with a human in
its arms. The current maximum weight of the lifted person
is 63 kg. Fig. 3 shows RIBA lifting a human in its arms.
IV. TACTILE G UIDANCE
Many methods have been proposed for instructing robots,for example, through the use of a remote controller, voicecommands, motion capture, and force/torque sensors. However, these methods are unsatisfactory for controlling RIBA.
In human-robot cooperative patient transfer, we consider
that the caregiver should be able to operate the robot using
one hand, in order to use the other hand for adjusting thepatient’s posture and skin contact. The above methods do
not satisfy our requirements, because some of the methods
require additional devices, some have insufficient recognition
accuracy, some are unsuitable for instructing a robot toassume a posture determined by multiple degrees of freedom,5998

Region B

Region C
Region A

Region F

Region E

Fig. 4.

Joint angle q

Fig. 3.

RIBA lifting a human in its arms

and some require the operator to remain in a specific region
to grasp the control devices.
For use during human-robot cooperative patient transfer,
we have developed a direct and intuitive ‘tactile guidance’
method, where the caregiver indicates the position, direction,
and/or speed of the desired motion by directly touching therobot on the part that is concerned with the motion. Thismethod was inspired by the way a teacher instructs the
motion of a student through touch and directly guides thestudent’s motion when teaching sport or dance.
RIBA has tactile sensors covering the entire area on
the arms except the joints. By touching these sensors, thecaregiver gives instructions to the robot. The wide area ofthe control interface results in little constraint on the positionof the caregiver, and the caregiver can operate the robot
using one hand. The coincidence of the force-applied point
and the force detecting point is another advantage, whichenables detecting small force that is difficult for force/torquesensors mounted on the base of a link to detect. The
tactile sensors provide two-dimensional pattern information,
to which pattern processing techniques can be applied. For
example, it is possible to detect sliding motion on the tactile
sensor, to cancel the output from the load of the lifted person
while detecting an instruction at another contact, and to countthe number of active elements to omit output from only one
element, with the aim of achieving robustness.
In the current RIBA, we have incorporated three tactile
guidance modes, a cart control mode, a posture-forming
mode, and a motion-adjusting mode. The switching between
these modes is initiated by a voice command. The pushingforce or sliding distance is used as the operation input.
Operation is activated only when the sensor is being touched
and stops when the touching finishes.
For cart control, we use three Regions A, B, and C
assigned on the outer side (the opposite side from liftedpatient) of the upper arms, as shown in Fig. 4. By touching
Region A and sliding the touching position forward or
backward, the cart moves forward or backward, respectively.
The sliding distance determines the speed of motion. We
assigned Region B for side translation and Region C for
gyration. The direction of side translation or gyration isdetermined by whether the left or right side of the arm ispushed and the speed is determined by the pushing force.

Region D

Regions on an arm for tactile guidanceTrajectory for a tall person
q = f (t,1)
q = f (t, p)
q = f (t,0)
Trajectory for a short person

The trajectory appropriate to the lifted
person is selected by changing ptime tFig. 5.

Concept of motion adjustment by tactile guidance

Both arms can be used for these operations.
In the posture-forming mode, all the 16 joints in botharms and the waist are controlled by touching the arms.
This mode may be used for forming the motion of RIBA bydirectly touching the robot. For example, elbow extension
or flexion is realized by pushing the inner or outer sideof the forearm, respectively, and elbow rotation is realized
by sliding the contact point along a circular direction. The
motion of other joints is also assigned to different positions
or touching conditions (pushing or sliding), so as to be
intuitively understandable to the operator.
The motion-adjusting mode is used during lifting thepatient up and down. The concept of adjusting the motion
is shown in Fig. 5. The trajectories for lifting a tall or ashort person with different distances between both arms are
given by the designer in advance, and the trajectory suitable
to the present patient is made by interpolating these two
trajectories. The interpolation is adjusted by the parameterp (0 ≤ p ≤ 1), and the progress of the motion is controlled
by the time parameter t. Tactile guidance is used to change
the parameters p and t. The adjustment of t is assigned tothe outer side (the opposite side from the lifted patient) of
the forearms. Pushing Region E or D in Fig. 4 changes thetime t forward or backward, respectively, and the pushingforce determines the changing rate of t. In preliminary
experiments, it was found that the lifted person sometimes
caused a load on the side of the forearms (Region F); hence,
we decided to omit the side regions and use only the central
regions of the outer side of the forearms for instructions. The
adjustment of the parameter p is assigned to the grasping of
the left or right half of RIBA’s hand.

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45
Desired0 [kg]
30 [kg]+42 [deg]

35
30
25

35

30

-4 [deg]+
43 [deg]Desired0 [kg]
30 [kg]40
Angle [deg]a

Weight of 30 [kg]for each arm

Angle [deg]a

40

-

20

25
0

+

-

5000
Time [ms]

10000

0

(a) Elbow

5000
Time [ms]10000(b) Shoulder

2Payload test posture

Desired0 [kg]
60 [kg]0

V. E XPERIMENTS
A. Handling Heavy Objects
The principal objective of RIBA is to transfer a humanweighing 60 kg or more from a bed to a wheelchair, and viceversa. To confirm RIBA’s ability to handle heavy objects, wetested the power of the elbow-bending joint (J11), shoulderrotating joint (J8), and the joint allowing the waist to bend
back and forth (J14) when the forearm was almost level asshown in Fig. 6. This posture is similar to that when starting
to lift a human. We placed a weight of 30 kg on the joint
between the forearm and the hand of each arm so that RIBA
bore a total weight of 60 kg.
As the desired trajectory, a 0.2 Hz sinusoidal wave wasapplied from the above posture to the elbow, shoulder, andwaist joints. The amplitude of the sinusoidal wave was determined so as not to exceed the maximum angular velocityof each joint, and was 10 deg for the elbow, 7.5 deg forthe shoulder, and 5 deg for the waist. The actual trajectories
with and without the weight were recorded. The results areshown in Fig. 7.
In all cases, the actual trajectory was in satisfactory agreement with the desired trajectory. During lifting in patienttransfer, the patient is usually mounted on the middle of theforearms, which gives a payload margin. The main structureof the arms was designed to support 120 kg in principle,
but for safety reasons, we have so far limited the weight to
63 kg.
B. Motion Control by Touching
To test the controllability of tactile guidance, we conducted experiments in which the elbow-bending joint (J11)or elbow-rotating joint (J12) was moved 30 deg using theposture-forming mode of tactile guidance when RIBA wasin the posture shown in Fig. 6. The operator was instructedto move the joint of the left arm so as to follow thecorresponding joint of the right arm that was used to show
the desired angles. In addition to the visual cue, sound was
also used for indicating that the actual joint angle was within±1 deg, over 1 deg above, or over 1 deg below the desired
angle.
The results are shown in Fig. 8. In addition to the desired
and actual joint angles, the pushing force or sliding distancethat was used as the operation input for tactile guidance isindicated. In the elbow-bending experiment, the operation
input was the pushing force calculated as the sum of theoutputs of all pressure-sensing elements on the tactile sensor.

Angle [deg]aFig. 6.

-2
-4
-6
-8
-10
0

5000

10000

Time [ms](c) Waist
Fig. 7.

Experimental results of payload test

The unit was approximately 0.1 N. In the case of elbow
rotation, the operation input was the sliding distance of thecontact point, where the unit was the pitch of the pressuresensing elements (21.5 mm). When the operation input was
the pushing force, fine adjustments were performed. For
example, motion was slowed down when the joint angle wasnear the desired value. On the other hand, when the operation
input was the sliding distance, adjustment was not frequentand the actual angle was sometimes moved past the desired
angle. From these experiments, we can conclude that force
is more suitable than sliding distance as the operation input
for motion that requires fine adjustment.
C. Patient Transfer
We evaluated the patient-transfer ability of RIBA using
10 adults (1 male and 9 females). The sequence of liftingfrom the bed is shown in Fig. 9 and that of lifting from thewheelchair is shown in Fig. 10. Putting a human down on
the bed or the wheelchair is also possible by applying thereverse motion.
In both cases, the caregiver made fine adjustments of
RIBA’s position and motion according to the patient’s position and posture by touching RIBA’s arms. The caregiverused one hand to raise the head of the patient (Fig. 9(c))
when lifting him or her from the bed and to raise the legs
(Figs. 10(d) and (e)) when the patient was lifted from thewheelchair, while using the other hand to operate RIBA.
Each lifting took approximately 40 s. Lifting was stable andno danger of dropping the patient was observed.
VI. C ONCLUSION
We have developed a prototype robot, RIBA, to assist withpatient transfer. RIBA succeeded in transferring a humanfrom a bed to a wheelchair and back using its human-type
arms. To the best of our knowledge, RIBA is the first robotthat can transfer a human between a bed and a wheelchairwithout a reclining function using human-type arms. RIBA

6000

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800
DesiredActualOperation input

600
400

Angle [deg]

40

200

30

0
-200

20

-400
10

Operation input (Pushing force)

50

(b)

(c)

(d)

(e)

(f)

(h)

(i)

-600

0

-800
0

5

10
Time [s]1520(a) Elbow bending
2
DesiredActualOperation input

10

1.5
1

0
0.5
-10
0
-20
-0.5
-30

-1

-40

Operation input (Sliding distance)

20

Angle [deg]

(a)

(g)

Fig. 10.

Lifting from wheelchair

-1.5
0

5

10
Time [s]1520(b) Elbow rotation
Fig. 8.

Results of tactile guidance experiments

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 9.

Lifting from bed

weighs 180 kg and can lift a patient with a weight of up to
63 kg; the payload to weight ratio is as high as 0.35.
We developed a tactile guidance method in which the caregiver adjusts robot motion through tactile sensors, enabling
it to cope with changeable situations. This also allows the
caregiver to remain close to the patient, which we believe
is less stressful for the patient. The aims of our future work
include increasing the payload, ensuring the comfort of thelifted person, and reinforcing safety.
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