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68 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
2013
Development of Tool-Type Devices for aMultifingered Haptic
Interface Robot
Takahiro Endo, Member, IEEE, Satoshi Tanimura, and Haruhisa
Kawasaki, Senior Member, IEEE
AbstractThis paper presents the design of tool-type devices fora
multifingered Haptic Interface Robot (HIRO), and summarizesthe
experimental results. HIRO consists of a robot arm with
afive-fingered hand to which a variety of tools can be attached.
Thesystem is able to present the force sensation of many
tool-typedevices. In the medical field, manufacturing industry, and
otherfields, there are tools of a variety of shapes with a range of
uses,and a haptic interface that can present the force sensation
formany tools will be important for virtual training systems.
HIROhas five fingers, and thus, we must clarify how many fingers
needto be connected to the tool-type device and which fingers
shouldbe used for the connection. Solving these problems is
importantwith regard to presenting an operator the force feeling
through thetool-type device. To solve these problems, we propose an
optimalconnection method from the mobility and singularity points
of view,and we have developed the tool-type devices for HIRO based
onthe proposed method. We describe here several experiments
thatwere carried out to investigate the performance of the
developeddevices.
Index TermsClosed-loop robots, haptic interfaces, virtualreality
(VR).
I. INTRODUCTION
I T is possible to communicate with a virtual environmentvia a
haptic interface. An operator using the haptic inter-face can feel
force sensations from the virtual environment andcan in turn
provide force and position information to the vir-tual environment.
Unlike the traditional interface using visualand audio cues, the
haptic interface is unique, as it provides abidirectional
interaction between a human being and the vir-tual environment
[1][3]. Therefore, the haptic interface is akey input/output device
for communication with highly realis-tic sensations and has the
potential for use in many applicationareas.
One of the application areas for the haptic interface is
virtualtraining systems in the medical field, manufacturing
industry,and other fields. For example, during surgical training,
medicaldoctors use various surgical tools, such as scissors,
tweezers, andsurgical knives, and they must train with these tools
to masterspecific procedures or techniques. However, it is neither
easy
Manuscript received December 28, 2011; revised June 8, 2012;
acceptedAugust 3, 2012. Date of publication August 28, 2012; date
of current versionFebruary 1, 2013. This paper was recommended for
publication by AssociateEditor T. Asfour and Editor W. K. Chung
upon evaluation of the reviewerscomments. This work was supported
by the Strategic Information and Commu-nications R&D Promotion
Programme of the Ministry of Internal Affairs andCommunications and
by the Japan Society for the Promotion of Science underGrant-in-Aid
for Young Scientists (B) (23700143).
The authors are with the Gifu University, Gifu 501-1193, Japan
(e-mail:[email protected]; [email protected];
[email protected]).
Color versions of one or more of the figures in this paper are
available onlineat http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TRO.2012.2212831
nor safe for this training with surgical tools to occur in a
realenvironment, and thus, a training system that uses virtual
reality(VR) and a haptic interface technology has been
researchedaggressively. With the construction of a virtual training
system,training can be safely carried out and a trainee can
practicein various situations that might be difficult to experience
in thereal world. Furthermore, the results of some studies indicate
thatsuch a system could increase the skill with which real
surgerycan be performed [4] and contribute to the learning of real
motorskills [5], [6].
Based on the need for such systems, many researchers havebeen
developing tool-type haptic interfaces [7][13]. For exam-ple,
Okamura et al. [7] developed a scissors-type haptic inter-face. It
has two degree of freedom (DOF) of motion and forcefeedback: one
for cutting, namely, the single blade rotation, andone for
translational motion of the device. Their group also pre-sented an
analytical model to compute force applied to scissorsduring cutting
of a slab of material [8] and evaluated the cuttingmodel using the
aforementioned scissors-type haptic interface.Sato et al. [9]
developed a brain retractor-type haptic interfaceto train surgeons
in brain surgery and investigated the soft tis-sue pushing
operation using the haptic device for simulationof brain tumor
resection. In another study [10], a microscissor-type haptic device
was developed, which presented the cuttingresistance forces to the
operator. Goksel et al. [11] developed aneedle-type haptic device
and a probe-type haptic device, anda haptic simulator for prostate
brachytherapy with simulatedneedle and probe interaction. The use
of haptic technology inmedical simulators has attracted attention
for many years, andvarious commercialized products are already
available, such asLapSim [12], LAP mentor [13], and others. By
using a tool-typehaptic interface in a virtual environment, an
operator can carryout virtual training, while feeling force
sensations; however,these tool-type haptic interfaces present the
force sensation ofonly the corresponding single type of tool. To
present the forcesensations of a variety of tools, many tool-type
haptic interfacesare required, which requires multiple installation
locations andcosts a great deal.
For this reason, we previously developed a haptic systemthat
presents the force sensations of a variety of tools [14].This
system consists of a multifingered haptic interface robotnamed
Haptic Interface Robot (HIRO) and numerous tool-typedevices,
including a surgical knife, scissors, and syringe. HIROhas five
haptic fingers, and a variety of tool-type devices caneasily be
attached to and removed from HIROs haptic fingers,enabling the
system to present the force sensations of manytool-type devices.
However, we must consider how many hapticfingers need to be
connected to the tool-type device and which
1552-3098/$31.00 2012 IEEE
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ENDO et al.: DEVELOPMENT OF TOOL-TYPE DEVICES FOR A
MULTIFINGERED HAPTIC INTERFACE ROBOT 69
Fig. 1. Multifingered haptic interface robot. (a) HIRO III and
(b) a fingerholder.
haptic fingers should be used for the connection. In our
previousresearch, we determined the connection by trial and error,
andwe did not clarify the optimal connection between HIRO and
thetool-type device. Technically clarifying the optimal
connectionis important with regard to presenting the operator the
forcefeeling through the tool-type device.
To solve these problems, we propose an optimal connectionmethod
from mobility and singularity points of view, and basedon the
proposed method, we have developed new tool-type de-vices. There
are many types of tools in our real world, and theycan be divided
into two main classes: tools with no joints andtools with joints.
For example, the knife has no joints, and thus,its DOF is 6. On the
other hand, the tweezers and the scissorshave one joint, allowing 1
DOF, and thus, the DOF is 7. Wedeveloped a knife-type device as the
tool with no joints and atweezers-type device as the tool with
joints. Furthermore, we de-scribe our experimental investigation of
the tools performance.
The preliminary versions of this paper have been published[15],
[16]. This extended version contains a development ofnew knife-type
device, new experimental results, and the newdiscussion about the
applicability of the proposed connectionmethod to other tool-type
devices.
This paper is organized as follows: In the next section,
amultifingered haptic interface robot, HIRO, and our
previoustool-type devices for HIRO are introduced. Section III
presentsthe optimal connection method between HIRO and the
tool-type device, and a newly developed knife-type device and
atweezers-type device are presented in Section IV and V,
respec-tively. The experimental results that are described in
Section VIdemonstrate the great potential of our system. Finally,
SectionVII presents our conclusions.
II. FIVE-FINGERED HAPTIC INTERFACE ROBOTAND PREVIOUS TOOL-TYPE
DEVICES
A. Five-Fingered Haptic Interface RobotWe have developed a
multifingered haptic interface robot,
named HIRO III [17], which is shown in Fig. 1. HIRO III
canpresent three-directional forces at an operators five
fingertips.The specifications of HIRO III are shown in Table I.
HIRO IIIcan be briefly summarized as follows.
TABLE ISPECIFICATIONS OF HIRO III
TABLE IISPECIFICATIONS OF HIRO IIIS FORCE SENSOR
HIRO III consists of an arm and a haptic hand. The armconsists
of an upper arm, a lower arm, and a wrist. The arm has3 DOF at the
arm joint and 3 DOF at the wrist joint. The arm,therefore, has six
joints, allowing 6 DOF. The haptic hand isconstructed of five
haptic fingers. Each haptic finger has threejoints, allowing 3 DOF.
The first joint relative to the hand baseallows
abduction/adduction, while the second and the third jointallow
flexion/extension. The total DOF of HIRO III is 21, andits working
space covers VR manipulation on the space of adesktop. A three-axis
force sensor is installed at the top of eachhaptic finger. The
force sensor was custom made for HIROIII [17]. Its specifications
are shown in Table II.
Note that the maximum displayable stiffness given in Table
Iexpresses the maximum spring coefficient of a virtual wall thatone
haptic finger of HIRO III can present stably, with the virtualwall
made using a springdamper model. This value was mea-sured by a
contact experiment involving a virtual wall [18]. Inthis
experiment, the haptic finger was in a configuration that canbe
really used in haptic display mode. Furthermore, the maxi-mum
output force of the haptic finger in Table I depends on
theconfiguration of the haptic finger. The maximum output forceof
the haptic finger is 3.6 N in the worst configuration case. Formore
details, see [17].
To manipulate HIRO III, an operator wears a finger holder,a
sample of which is shown in Fig. 1(b), on each of
his/herfingertips. The finger holder has a steel sphere, and the
hapticfinger has a permanent magnet at its fingertips. By means of
themagnet force, the finger holder can be connected to HIRO III,as
shown in Fig. 1(a). Here, note that the sphere, when attachedto the
permanent magnet at the force sensor tip, forms a passivespherical
joint. Its role is to adjust for differences between thehuman and
haptic finger orientations. Hereafter, this version ofthe
multifingered haptic interface robot is described as HIRO.
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70 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
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Fig. 2. HIRO with surgical knife. (a) HIRO with surgical knife.
(b) Tooldevices steel sphere. (c) Surgical knife and operators
hand.
B. Previous Tool-Type Devices for HIROOur previously developed
haptic interface presents the force
sensation of plural tools using HIRO. As tool-type devices,
asurgical knife, scissors, and syringe devices were developed.
Asdescribed previously, HIRO has a permanent magnet at each ofits
fingertips. Thus, if we install the steel spheres in the
tooldevice, the device is easily attached to HIRO by the
magneticpower, and it is easy to exchange the plural tool-type
devices.As an example, Fig. 2 shows the surgical knife device,
andthe steel spheres are installed as shown in Fig. 2(b), and
thissetup presents the force sensation of the knife device to
anoperator. Here, note that HIRO has the force sensors, motors,and
encoders required to create the force sensation, and thus,the
tool-type devices only require a structure similar to that ofthe
associated real tool.
III. CONNECTION BETWEEN HIROAND TOOL-TYPE DEVICES
HIRO has five haptic fingers. It is a big challenge to
de-termine how many haptic fingers need to be connected to agiven
tool-type device, and which fingers should be used forthe
connections. These problems are bound up with presentingthe
operator the force feeling through the tool-type device. Tosolve
these problems, we propose an optimal connection methodfrom
mobility and singularity points of view. Here, note that thearm is
not included in the analysis because the force display ofHIRO is
accomplished by haptic finger parts. For more detailsconcerning the
control of HIRO, see Section VI.
A. Connection Analysis by MobilityWhen HIRO is connected to the
tool-type device via several
haptic fingers, the system acts as a parallel mechanism. (Weshow
an example of the connection between three haptic fingersand a
knife-type device in Fig. 3.) Having the features of aparallel
mechanism, the system is highly accurate, with highoutput force, a
high level of stiffness, and other advantageousfeatures that are
important elements for a haptic interface. Wenote that, in the
parallel mechanism, the number of joints does
Fig. 3. Haptic fingers and knife device.
not correspond to the DOF of the overall system. In this case,
themobility index M [19] implies the DOF of the overall system,as
follows:
M = 6(N m 1) +m
i=1
li (1)
where N is the number of links, m is the number of joints,and li
is the DOF of the ith joint. Thus, using the mobility, wedetermine
the number of fingers necessary for HIRO to haveconnected to the
tool-type device. Here, we assume that thesystem has no passive or
idle DOF, which does not affect themotion of the other links [19],
[20]. Under this assumption, weconsider the number of the required
fingers.
In particular, by using the mobility, we consider the
followingtwo points: 1) the realization of DOF of the tool-type
deviceand 2) the control of all DOF of the overall system. For item
1),to realize the tool-type devices DOF Ftool , the mobility
mustsatisfy
M Ftool. (2)For item 2), to control all DOF of the overall
system, the
number of active joints D must satisfyD M. (3)
From these two points, we determine the required number ofhaptic
fingers that satisfies conditions (2) and (3). For a concen-trated
method of determination, see Sections IV and V.
B. Connection Analysis by SingularityIn the previous section, we
determined the number of haptic
fingers for the connection, but we did not clarify which
fin-gers should be used. Remembering that the parallel mechanismhas
the drawback of singularity [21], we remember also thatsingularity
is the particular configuration where the system be-comes
uncontrollable [22] and that we must, therefore, avoidsingularity.
By considering the avoidance of singularity, we candetermine which
fingers should be used.
When the inputoutput relationship of the parallel mechanismcan
be written as
Aq = Bv
where q Rn is the actuated joint velocity vector, v Rmis the
platform Cartesian coordinate velocity vector, and A Rnn and B Rnm
(n m) are appropriate matrixes, the
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MULTIFINGERED HAPTIC INTERFACE ROBOT 71
singularity of the parallel mechanism consists of three kinds
ofsingularities [23]. The first kind of singularity is defined
whenA is singular, the second kind of singularity is defined when
Bis singular, and the third kind of singularity is defined when
Aand B are singular at the same time. To avoid the three kinds
ofsingularity, we introduce the following performance index:
PI = WAWB + Wq (4)
WA = |detA| , WB =
det(BT B) (5)
Wq = p
i=1
i [e(qiai ) + e(qibi ) ] (6)
where , , and i are the weighting coefficients ofWAWB ,Wq , and
the ith actuated joint, respectively, p is thenumber of the
actuated joint, qi is the angle of the ith actuatedjoint, is the
parameter to adjust an exponential function, andai and bi are the
lower and upper limits of the angle of the ithactuated joint,
respectively.
In (4), WA is well-known manipulability, and the manipula-bility
becomes high and the configuration of the system is awayfrom the
first kind of singularity when the value of WA be-comes large. WB
evaluates the second kind of singularity, andif the value of WB
becomes large, the system is away from thesecond kind of
singularity. We set the multiplication WAWBin (4). Thus, if WAWB
becomes large, then the configurationof the system is away from the
first and the second kinds ofsingularity, and this corresponds to
the third kind of singularity.Here, note that the joint of the
robot usually has a limit to itsmovable range. If we consider the
value of WAWB only, it ispossible that the configuration of the
system is away from thesingularities but the joints go to the
outside of the limit of themovable range. We therefore add the
penalty function Wq to theperformance index, which corresponds to
the limits of the jointangles. From these points of view, which
haptic fingers shouldbe used is decided upon by maximizing PI. For
a concentratedmethod of determination, see Sections IV and V.
IV. DEVELOPMENT OF A KNIFE-TYPE DEVICE
This section describes our development of a knife-type
devicebased on the proposed connection method.
A. Connection Analysis by MobilityFirst, we analyze the number
of haptic fingers necessary to
have connected to the knife-type device. Haptic fingers and
aknife-type device are connected through the passive sphericaljoint
described in Section II. Three or more haptic fingers arenecessary
to support the device. Here, note that when we use twohaptic
fingers at the connection, the system has an idle DOF, i.e.,the
system allows spin movement around an axis through thecenter of two
spherical joints at the connection points betweenHIRO and the
tool-type device. Thus, to support the knife-typedevice with the
haptic fingers, three or more haptic fingers arenecessary.
When the device is connected to HIRO with three haptic fin-gers,
the mobility index (1) is M = 6 because of N = 11, m
= 12, andm
i=1 li = 18 (nine revolute joints and three spher-ical joints).
The DOF of the knife-type device Ftool is 6, andcondition (2) is
satisfied. The number of active joints D is nine,because three
haptic fingers are used to hold the device, andthus, condition (3)
is satisfied. Although conditions (2) and (3)are satisfied when the
number of haptic fingers is four or more,we used three haptic
fingers in our device, which is the minimalacceptable number, at
the connection.
B. Kinematics of the Knife-Type DeviceTo evaluate the connection
using a performance index (4), we
first consider the kinematics of the overall system, as
illustratedin Fig. 3. The system consists of three haptic fingers
and a knife-type device, in which the ith haptic finger contacts
the device atpoint Ci . The coordinate systems are defined as
follows: b isthe base coordinate system, tool is the object
coordinate systemfixed on the device, and F i is the ith fingertip
coordinatesystem fixed on the ith haptic fingertip. In addition,
the followingnotations are used: bpF i R3 is the position vector of
F i withrespect to b , bRF i R33 is the orientation matrix of F
iwith respect to b , bptool R3 is the position vector of toolwith
respect to b , and bRtool R33 is the orientation matrixof tool with
respect to b .
Since the contact at Ci is fixed, the following constraint
be-tween the haptic fingertip position and the knife-type
deviceposition is obtained:
bptool + bRtool toolpC i = bpF i + bRF iF ipC i (7)where toolpC
i R3 is the position vector of Ci with respect totool , and F ipC i
R3 is the position vector of Ci with respectto F i .
Differentiating (7) yields
b ptool [(bRtool toolpC i)]btool= b pF i [(bRF iF ipC i)]bF i
(8)
where btool R3 and bF i R3 are the angular velocities ofthe
knife-type device and the ith haptic fingertips, respectively,(p)
R33 is a skew-symmetric matrix expressing the cross-product form of
a vector p R3 , and the fact that toolpC i andF ipC i are constants
was used in the derivation of (8).
Now, we define the following matrices:
Dtooli = [I33 ,(bRtool toolpC i)] R36 (9)DF i = [I33 ,(bRF iF
ipC i)] R36 (10)
where I33 R33 is an identity matrix. Furthermore, the ithhaptic
fingertip velocity and the joint angle velocity are relatedby
[ b pF ibF i
]= JF i qi (11)
where JF i R63 is a Jacobian, and qi R3 is the joint anglevector
of the ith haptic finger.
From (8)(11), we can obtain the following kinematics:Dtoolvtool
= JCF q (12)
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72 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
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TABLE IIIPARAMETERS IN CONNECTION ANALYSIS OF THE KNIFE-TYPE
DEVICE
where Dtool = col[Dtool1 ,Dtool2 ,Dtool3 ] R96 , vtool =col[b
ptool, btool] R6 is the velocity vector of the knife-typedevice,
JCF = diag[DF 1JF 1 ,DF 2JF 2 ,DF 3JF 3] R99 ,and q = col[q1 , q2 ,
q3] R9 .
On the other hand, from the principle of virtual work,
thefollowing relation is obtained:
F tool = DTtoolfC (13)where F tool = col[f tool , ntool] R6 is
the total force/momentvector applied to the knife device by the
haptic fingers, f c =col[fC 1 , fC 2 , fC 3] R6 , and each haptic
finger applies aforce fC i at the contact point Ci .
C. Connection Analysis by SingularityBased on the kinematics and
the performance index, we can
determine which haptic fingers should be used for the
connec-tion. From Section IV-A, we know that three haptic fingers
willbe used. For the combination of all three haptic fingers, the
jointangles that maximize the value of (4) are derived, and we
setthe knife-type device to be connected to the haptic fingers
thatmaximize the performance index. In this case, the
performanceindex (4) can be rewritten as
PI = WAWB + Wq (14)
WA = |det JCF | , WB =
det(DTtoolDtool) (15)
Wq = 3
i=1
3
j=1
j [e(qi j ai j ) + e(qi j bi j ) ] (16)
where j is the weighting coefficient of the jth joint angle of
thehaptic finger, qij is the jth joint angle of the ith haptic
finger,and aij and bij are the lower and upper limits of the jth
jointangle of the ith haptic finger, respectively.
In the derivation of the haptic fingers that maximize PI,
theconjugate gradient method and the parameters in Table III
wereused. In addition, it is easy to see that the position and
theorientation of the object coordinate system tool are not
relatedto the value of PI. For example, the variables of the
functionWA and Wq are qij , and these functions are not related
totool . Furthermore, Dtool , in this case, becomes a grasp
matrixbecause of (9), and it is well known that WB is not related
totool [24]. Thus, in the derivation, tool was fixed on the
bladeedge of the knife device, and tool was set on a centroid of
atriangle formed by three haptic fingertips.
The value of (14) reaches a maximum when the combinationof the
thumb, index finger, and pinky finger is used. In this case,
TABLE IVJOINT ANGLES FOR THE KNIFE-TYPE DEVICE
Fig. 4. Developed knife device. (a) Knife-type device. (b)
Knife-type devicethat connects to HIRO.
WA = 2.49 1011 ,WB = 2.01 102 , Wq = 1.47 1013 ,and PI = 3.52
1013 . The joint angles in this case are shownin Table IV.
For the development of the knife-type device, we consideredthe
following guidelines: The device is connected to the
hapticfingertip positions that maximize the value of (14), namely,
theknife device is connected to HIRO at the angles shown in Ta-ble
IV, HIRO and the device are connected by passive sphericaljoints,
the device is set to the direction that most helps an oper-ators
grasp, and an actual surgical knife is used to maintain
theappearance of a real surgical knife. Based on these
guidelines,the knife device was developed. Fig. 4 shows the
developedknife device. The actual surgical knife is connected to
HIROthrough the white connections known as the offset arm. The
off-set arm was made of acrylonitrile-butadiene-styrene resin
andwas screwed to the actual surgical knife. In addition, three
steelspheres were screwed to the offset arm, and thus, the
knife-typedevice and three haptic fingers were connected by
magneticpower.
We investigated the effect of variation of the weights (, , ,i)
on the optimal solution, and the results are shown in Fig. 5.Fig.
5(a) shows the value of PI in the case that changes,Fig. 5(b) shows
the value of PI in the case that changes,Fig. 5(c) shows the value
of PI in the case that changes, andFig. 5(d) shows the value of PI
in the case that i changes. (Here,we set 1 , 2 , and 3 to the same
value.) The horizontal axis isthe value of the corresponding
weight, and the vertical axis is thevalue of PI. The parameters
that we used are shown in the caption
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MULTIFINGERED HAPTIC INTERFACE ROBOT 73
Fig. 5. Effect of variation of the weights (, , , i ) on the
knife-type device.(a) Effect of variation of . The following were
used as parameters other than: = 1.0 1013 , 1 = 1.2, 2 = 1.0, 3 =
1.1, and = 10. (b) Effect ofvariation of . The following were used
as parameters other than : = 1.0,1 = 1.2, 2 = 1.0, 3 = 1.1, and =
10. (c) Effect of variation of . Thefollowing were used as
parameters other than : = 1.0, = 1.0 1013 , 1= 1.2, 2 = 1.0, and 3
= 1.1. (d) Effect of variation of i . The following wereused as
parameters other than i : = 1.0, = 1.0 1013 , and = 10.
of the figure. As shown in Fig. 5(a), when becomes large, PIalso
becomes large. However, in this case, the joint angles of thehaptic
fingers approach their movable limit, and the joint anglesthat
maximize PI go outside of the movable range when >3.1. In
contrast, if becomes small, the manipulability of thehaptic fingers
is reduced, because the influence of Wq becomeslarge, and thus, the
systems performance of the force display ispoor.
The effect of variation of , as shown in Fig. 5(b), was
con-trary to the case of , and PI becomes large when becomessmall.
However, in this case, the joint angles of the haptic
fingersapproach their movable limit, and the joint angles that
maximizePI go outside of the movable range when < 4.0 1014 .
Incontrast, if becomes large, the manipulability of the
hapticfingers is reduced, because the influence of Wq becomes
large.As shown in Fig. 5(c), if approaches a small value, the
jointangles of the haptic fingers become small, and the joint
anglesthat maximize PI go outside of the movable range when <
3.0.
Finally, in Fig. 5(d), i has the same effect as . That is, if
ibecomes small, then PI becomes large, but in this case, the
jointangles of the haptic fingers approach their movable limit, and
thejoint angles that maximize PI go outside of the movable
rangewhen i < 0.4. If i becomes large, the manipulability of
thehaptic fingers is reduced, because the influence of Wq
becomeslarge, and the systems performance of the force display is
poor.
V. DEVELOPMENT OF A TWEEZERS-TYPE DEVICE
In Section IV, we developed the knife-type device for HIRO.The
knife device has no joints, and thus, its DOF is 6. However,some
commonly used tools have joints. In this section, we focuson
tweezers as an example of a tool with joints. We describe
ourdevelopment of a tweezers-type device.
Fig. 6. Haptic fingers and tweezers-type device.
Fig. 7. Tweezers-type device and the object coordinate
system.
A. Connection Analysis by MobilityUsing the same method as
described in Section IV-A, we can
determine the number of haptic fingers necessary to have
con-nected to the tweezers-type device. Here, note that, unlike
thecase of the knife-type device, a pair of tweezers has 7 DOF.
Hap-tic fingers and a tweezers-type device are connected through
thepassive spherical joint. Therefore, to support the tweezers
withthe haptic fingers and not to generate an idle DOF, three or
morehaptic fingers are necessary. When the device is connected
toHIRO with three haptic fingers, the mobility index is M = 7
be-cause of N = 12, m = 13, and
mi=1 li = 19 (ten revolute joints
and three spherical joints). At this time, the number of
activejoints D is nine, and thus, condition (3) is satisfied.
Furthermore,the DOF of the tweezers is 7, and condition (2) is
satisfied. Al-though conditions (2) and (3) are satisfied when
there are threeor more haptic fingers, we used three haptic
fingers, which is aminimal acceptable number, at the
connection.
B. Kinematics of the Tweezers-Type DeviceNext, we consider the
kinematics of the tweezers-type device,
as illustrated in Fig. 6. The system consists of three
hapticfingers and tweezers, in which the ith haptic finger contacts
thetweezers at point Ci . The coordinate systems are the same as
inSection IV-B.
We connected two haptic fingers to one side of the blade(blade
A), as shown in Fig. 7, and we connected one haptic fingerto other
side of the blade (blade B). Based on this setup plan, we
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74 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
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set the object coordinate system. The object coordinate
systemtool is fixed on blade A. The origin of tool is the
fulcrumpoint of the tweezers, and its z-axis coincides with the
opening-and-closing axis. The y-axis is set in a tip-to-fulcrum
directionalong blade A. The x-axis is set so that tool becomes
theright-handed coordinate system. On the other hand, we definethe
object coordinate system tool2 on blade B. tool2 is thecoordinate
system that rotates tool rad at the z-axis. Here, is the
opening-and-closing angle of the tweezers.
Since the contact at Ci (i = 2, 3) is fixed, we can obtainthe
following velocity relation, as in the case of the
knife-typedevice:
b ptool [(bRtool toolpC i)]btool= b pF i [(bRF iF ipC i)]bF i,
for i = 2, 3 (17)
Here, note that we cannot obtain the same relation for C1
be-cause of . For the contact at C1 , we can obtain the
followingconstraint:
bptool + bRtool toolRtool2 tool2pC 1 = bpF 1 + bRF 1F 1pC
1(18)
where tool2pC 1 R3 is the position vector of C1 with respectto
tool2 . Differentiating (18) yields
b ptool [(bRtool2 tool2pC 1)]btool bRtool [(toolRtool2 tool2pC
1)]tooltool2= b pF 1 [(bRF 1F 1pC 1)]bF 1 (19)
where tooltool2 R3 is the angular velocity of tool2 . Here,note
that tooltool2 = [0, 0, ]T because tool2 rotates aroundthe z-axis
with respect to tool . From this property, (19) can berewritten as
follows:
b ptool [(bRtool2 tool2pC 1)]btool+ bRtool [([0, 0, 1]T
)]toolRtool2 tool2pC 1 = b pF 1 [(bRF 1F 1pC 1)]bF 1 (20)
Now, we define the following matrices:
Dtool1 = [I33 ,[(bRtool2 tool2pC 1)],bRtool [([0, 0, 1]T
)]toolRtool2 tool2pC 1 ] R37 (21)
Dtooli = [I33 ,[(bRtool2 tool2pC i)], O31 ] R37
for i = 2, 3 (22)where O31 R3 is a zero matrix. As in the case
of the knife-type device, we can obtain the relation (11) between
the ithhaptic fingertip velocity and the joint angle velocity.
Thus, from(17), (20)(22), (10), and (11), we can obtain the
followingkinematics:
Dtoolvtool = JCF q (23)where Dtool = col[Dtool1 ,Dtool2 ,Dtool3
] R97 , vtool =col[b ptool, btool, ] R7 is the velocity vector of
the tweezers-type device, and JCF and q are the same as in the case
of theknife-type device.
TABLE VPARAMETERS IN CONNECTION ANALYSIS OF THE TWEEZERS-TYPE
DEVICE
On the other hand, from the principle of virtual work,
thefollowing relation is obtained:
F tool = DTtoolfC (24)
where F tool = col[f tool , ntool, n ] R7 , f tool and ntool
arethe total force and moment vector applied to the
tweezers-typedevice by the haptic fingers, respectively, and n is
the torqueat the opening-and-closing axis.
C. Connection Analysis by SingularityBased on the performance
index (14) and using an actual pair
of tweezers, we developed a tweezers-type device. From Sec-tion
V-A, we know that three haptic fingers are used. By usingthe
conjugate gradient method for all three haptic fingers, wederived
the joint angles of haptic fingers, the position bptool ,and the
orientation bRtool that maximize (14). Here, note that,unlike the
knife-type device, Dtool does not result in the graspmatrix because
the opening-and-closing angle exists. There-fore, bptool and bRtool
of the object coordinate system tool arerelated to the value of PI.
Furthermore, note that, if we set nocondition for bptool , the
derived bptool diverges. Thus, we mustset a condition for bptool .
It is preferable that bptool be small,because the required haptic
fingertip force to hold the tweezers-type device f c increases if
bptool becomes large. However, ifbptool becomes small, there is a
danger that the tweezers and thehaptic hand of HIRO will collide.
As stated previously, we usedactual tweezers, and we found that the
distance between the tipand the opening-and-closing axis was 106.9
mm; therefore, weestablished that bptool was located 106.9 mm from
a centroidof a triangle formed by three haptic fingertips in the
directionof outward normal, and we set bptool so that we could
avoid acollision between the tweezers and the haptic hand.
According to the instruction manual for tweezers, we operatethe
tweezers by moving the handheld handle. It is important toavoid a
collision between the operators hand and HIROs handduring the use
of the tweezers, and thus, we made a conditionfor bRtool so that
the z-axis of tool is parallel to the triangleformed by three
haptic fingers. Furthermore, the parameters inTable V were
used.
As a result, the value of (14) reaches a maximum when thethumb
and index fingers are connected to blade A and the pinkyfinger is
connected to blade B. Furthermore, WA = 2.47 1011 ,WB = 1.69 103 ,
Wq = 1.28 1014 , and PI =2.90 1014 . The joint angles in this case
are shown in Table VI,
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TABLE VIJOINT ANGLES FOR THE TWEEZERS-TYPE DEVICE
Fig. 8. Developed tweezers-type device. (a) Tweezers-type
device.(b) Tweezers-type device that connects to HIRO.
and bRtool has the following values:
bRtool =
0.086 0.888 0.4530.286 0.457 0.8420.954 0.057 0.293
For the development of the tweezers-type device, we
consideredthe following guidelines: The device is connected to the
fingertippositions that maximize the value of (14), namely, the
tweezers-type device is connected to HIRO at the angles of the
hapticfingers shown in Table VI, HIRO and the device are
connectedby the passive spherical joints, bRtool satisfies the
aforemen-tioned conditions, and the device uses actual tweezers.
Basedon these guidelines, the tweezers-type device was
developed.Fig. 8 shows the developed tweezers-type device. We can
seethat the actual pair of tweezers is connected to HIRO throughthe
offset arm as in the case of the knife-type device.
We investigated the effect of variation of the weights (, , ,i)
on the optimal solution, like the case of the knife-type device.The
results are shown in Fig. 9. Fig. 9(a) shows the value of PIin the
case that changes, Fig. 9(b) shows the value of PI inthe case that
changes, Fig. 9(c) shows the value of PI in thecase that changes,
and Fig. 9(d) shows the value of PI in thecase that i changes
(Here, we set 1 , 2 , and 3 to the samevalue.). The parameters that
we used are shown in the caption ofthe figure. The tendency of the
effect of variation of the weights(, , , and i) is the same as that
in the case of the knife-typedevice. As shown in Fig. 9(a), when
becomes large, PI alsobecomes large, and in this case, the joint
angles of the hapticfingers approach their movable limit, and the
joint angles that
Fig. 9. Effect of variation of the weights (, , , i ) on the
tweezers-typedevice. (a) Effect of variation of . The following
were used as parameters otherthan : = 1.0 1014 , 1 = 1.2, 2 = 1.0,
3 = 1.1, and = 10. (b) Effectof variation of . The following were
used as parameters other than : = 1.0,1 = 1.2, 2 = 1.0, 3 = 1.1,
and = 10. (c) Effect of variation of . Thefollowing were used as
parameters other than : = 1.0, = 1.0 1014 , 1= 1.2, 2 = 1.0, and 3
= 1.1. (d) Effect of variation of i . The following wereused as
parameters other than i : = 1.0, = 1.0 1014 , and = 10.
maximize PI go outside of the movable range when > 3.9.
Incontrast, if becomes small, the manipulability of the
hapticfingers is reduced, because the influence of Wq becomes
large,and thus, the systems performance of the force display is
poor.
The case of , as shown in Fig. 9(b), was contrary to thecase of
, and PI also becomes large when becomes small.In this case, the
joint angles of the haptic fingers approach theirmovable limit, and
the joint angles that maximize PI go outsideof the movable range
when < 2.5 1015 . On the contrary,if becomes large, the
manipulability of the haptic fingers isreduced, because the
influence of Wq becomes large. As shownin Fig. 9(c), if approaches
a small value, the joint angles of thehaptic fingers become small,
and the joint angles that maximizePI go outside of the movable
range when < 2.5.
Finally, as shown in Fig. 9(d), i has the same effect as .That
is, if i becomes small, then the value of PI becomes large,but in
this case, the joint angles of the haptic fingers approachtheir
movable limit, and the joint angles that maximize PI gooutside of
the movable range when i < 0.3. In contrast, ifi becomes large,
the manipulability of the haptic fingers isreduced, because the
influence of Wq becomes large, and thus,the systems performance of
the force display is poor.
D. Applicability of the Proposed Connection Methodto Other
Tool-Type Devices
As described previously, we developed the tweezers-type de-vice
based on the proposed connection method. The proposedmethod can
also be applied to the scissors-type device, whichlike the tweezers
is a tool with a joint. Since the proposed methodcan also be
applied to tools without joints, we considered theapplicability of
the proposed connection method to other tools.Here, we consider the
applicability from the mobility point ofview.
First, we assumed a tool consisting of k revolute joints and k+
1 links. We show an example of such a tool in Fig. 10. The link
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76 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
2013
Fig. 10. Haptic fingers and a tool consisting of three revolute
joints.
is connected to the joint, and all joints are revolute joints,
andits rotational axes are all in the same direction. Let ltoolj be
theDOF of the jth joint of the tool. Then, we obtain kj=1 ltoolj =
k.Now, we set n haptic fingers to be connected to the tool. In
thiscase, the number of links of the haptic fingers is given as Nn
=3n, and the number of joints of the haptic fingers is given asmn =
3n. In addition, let lnij be the DOF of the jth joint of theith
haptic finger, and we obtain
ni=1
3j=1 l
nij = 3n.
The haptic fingers and the tool are connected through the
pas-sive spherical joint described in Section II, and the number
ofjoints at n contact points is given as mcont = n. Thus, the DOFof
the joint at the ith contact point lconti is
ni=1 l
conti = 3n.
By substituting these values into (1), we obtain M = k + 6
be-cause of N = (k + 1) + Nn + 1, m = k + mn + mcont , andm
i=1 li =k
j=1 ltoolj +
ni=1
3j=1 l
nij +
ni=1 l
conti . From
this, we found that condition (2) is always satisfied. By
con-sidering the relationship between D active joints and k
tooljoints, which satisfies condition (3) (namely, D k + 6),
weobtain the following results: 1) When three haptic fingers
areused in the connection, D = 9, and thus, we can connect a
toolwith up to three joints to HIRO; 2) when four haptic fingers
areused in the connection, D = 12, and thus, we can connect a
toolwith up to six joints to HIRO; and 3) when five haptic
fingersare used in the connection, D = 15, and thus, we can
connecta tool with up to nine joints to HIRO. In addition, if we
obtainthe concrete form of the tool and if we derive the
kinematicsof the overall system, we can clarify which fingers
should beemployed with the given tool by using the performance
index(14).
In the newly developed knife-type and tweezers-type devices,the
use of three haptic fingers is sufficient for the connectionbetween
HIRO and the tool-type device. Thus, the remainingtwo haptic
fingers that have not connected to the tool-type deiceare fixed in
the straight state (for example, see Fig. 4 as the caseof the
knife-type device). However, for devices other than theknife-type
or the tweezers-type device, there is a possibility thatfour or
more haptic fingers are needed for connection betweenHIRO and the
tool-type device. Since HIRO has five fingers, itcan respond to
such a situation, and we believe there is a bigmerit and the
potential to use a five-fingered hand to manipulatetool-type
devices.
VI. EXPERIMENTS
To evaluate the developed devices, we carried out two
ex-periments. One was to manipulate the knife-type device, andthe
other was to manipulate the tweezers-type device. In
eachexperiment, the manipulability-optimized control was used asthe
control law of HIRO [25]. This is a mixed control methodconsisting
of a haptic finger-force control and an arm positioncontrol
intended to maximize the control performance index(27). The force
control of the haptic finger is given by
F (t) = K1JTF F e(t) + K2JTF
t
0F e(s)ds
+ JTF F d K3 qf (t) (25)where F = [ T1 , T2 , T3 ]T R9 is a
joint torque vector of thehaptic finger in use, JF is a Jacobian, F
= [F T1 ,F T2 ,F T3 ]T R9 is a force vector whose subvector is the
force vectorat the fingertip, F d = [F Td1 ,F Td2 ,F Td3]T R9 is
the desiredforce, F e = F d F , and qf = [qT1 , qT2 , qT3 ]T R9 is
ajoint angle vector of the haptic finger. Furthermore, Ki is
thepositive feedback gain matrix. The control of the arm is givenby
the following PD (proportional and derivative) control
withgravitational and external force compensators:
A (t) = KA1(qAd qA ) + KA2(qAd qA ) + gA (qA )
+ JTA
3
i=1
F di
3
i=1
(pi phb) F di
(26)
where qA R6 is the arm joint angle vector, qAd R6 isthe desired
arm joint angle vector, which is to be determined,A R6 is the arm
joint torque, KAi is the positive feedbackgain matrix, gA (qA ) is
the gravitational compensator term, JAis a Jacobian, pi R3 is the
ith fingertip position vector, andphb R3 is the tip of the arm.
Here, note that qAd is definedto maximize the following control
index (27) under a constraintcondition in which the five haptic
fingertip positions are fixedto the operator fingertip
positions:
CPI = WA + Wq + QA (27)
QA = 12(qAd qA )T (qAd qA )
where and are weighting coefficients, WA is a manipulabil-ity
measure of the haptic finger (15), Wq is a penalty functionto keep
the finger joint angles within the movement range (16),QA is the
penalty function to prevent a large change of the armangle, and
> 0 is a weighting matrix. Here, a finger/arm thatreaches the
limit of the movable range is switched to a positioncontrol to keep
the joint angle within the movable range, and therest joints of the
fingers/arm are controlled by (25) and (26). Af-ter returning to
within the movable range, the control is switchedback again to (25)
and (26). Thus, the force display of HIROis accomplished by the
haptic finger. Details of the control lawhave been shown in [25].
For the experiment, the control PC
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Fig. 11. VR environment of the knife-type device.
Fig. 12. Reaction forces of the virtual knife.
used a real-time OS (ART-Linux) to guarantee a 1-ms
samplingtime.
A. Manipulation of the Knife-Type DeviceTo evaluate the
developed knife-type device, we considered
manipulation of the device in a constraint space.In the
experiment, a virtual plane was made in the VR en-
vironment, as shown in Fig. 11. When the virtual knife, whichis
in the VR environment, touches the virtual plane, the forceis
presented to the operator through the knife-type device. Thedesired
presented force is calculated by the penetration depthof the blade
edge of the virtual knife. For this, we first set theseveral
contact points V Ci at the blade edge of the virtual knife,as shown
in Fig. 12. For each V Ci , the force f i is calculatedas f i = f
ci + f
fi , where f ci andf
fi are the constraint and the
friction force, respectively. In the experiment, we set f ci and
ffi
as the following: f ci = Kani + Dvnif fi ={
i fni ti + divti (in the case of the static friction force)i fni
ti + ivti (in the case of the dynamic friction force)
where the penetration depth vector of the V Ci into the vir-tual
plane is decomposed to a normal directional vector aniand a
frictional directional vector ati ,vni and vti are the nor-mal and
the frictional directional relative speeds between theV Cis
velocity and virtual plane velocity, respectively, K is
thestiffness of the plane, and D is the damping coefficient of
theplane. Furthermore, i is the coefficient of static friction
givenby i = ati / ani , di is the damping coefficient, i is
thecoefficient of the dynamic frictional force, i is the
dampingcoefficient at the dynamic friction state, and ti is the
unit vectorof the frictional force direction. (For technical
details, see [26].)Then, the force of the virtual knife, F tool =
col[f tool , ntool], iscalculated, where f tool = fi , ntool = (bpV
C ibptool)f i ,and bpV C i is the position vector of V Ci with
respect to b . Fi-nally, using F tool and (13), we calculate the
desired hapticfingertip forces, and the haptic fingers are
controlled by (25) toaccomplish the desired haptic fingertip
forces. Here, note that
Fig. 13. Time responses of fto ol in the knife-type devices. (a)
Previouslydeveloped knife-type device. (b) Newly developed
knife-type device.
the aim of this experiment was to investigate the force
displayof the device, and thus, we did not consider the cutting of
thevirtual plane by the knife.
We compared the results gained with the newly
developedknife-type device, which is shown in Fig. 4, with the
resultsgained with the previously developed knife-type device,
whichis shown in Fig. 2. In both experiments, an operator
graspedthe knife-type device and moved the knife-type device toward
avirtual plane. When the virtual knife touched the virtual
plane,the operator felt the reaction force through the knife-type
device.The touching operation was repeated several times during
eachexperiment. Fig. 13 shows the experimental results. Fig.
13(a)and (b) shows the responses of the z-axis force f tool of
thepreviously and newly developed knife-type device,
respectively.In the figures, a dashed line is the desired value and
the solid lineis the measured value. We only show the z-axis force
becausethe value of the z-axis force is larger than those of the x-
andy-axis forces. First, the operator moved the device toward
thevirtual plane, and then, the operator touched the virtual
planethrough the device. The average values of the absolute
forceerror of the previously and newly developed surgical
kniveswere 0.28 and 0.21 N, respectively. The difference was
only0.07 N, and the force response of the newly developed deviceis
only slightly better than the force response of the
previouslydeveloped device.
We also compared the values of PI of both devices, and
weconfirmed that the PI of the previously developed
knife-typedevice was smaller than the PI of the newly developed one
in allintervals. We believe this was caused by the difference
betweenthe values of WB in the two devices. Although there is no
largedifference in the values of WA and Wq in the devices
(becauseHIRO is controlled so that the value of CPI in (27)
becomeslarge), the values of WB of the two devices are very
different.The values of WB in the two devices during the
aforementionedexperiments are shown in Fig. 14. In this figure, the
solid lineshows WB of the newly developed knife-type device, and
thedashed line shows WB of the previously developed knife-type
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78 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
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Fig. 14. Time responses of WB in the knife-type devices.
Fig. 15. Norms of fingertip force in the knife-type devices. (a)
Previouslydeveloped knife-type device. (b) Newly developed
knife-type device.
device. To facilitate visualization, we used the logarithmic
scalein the vertical axis. We see that WB of the previously
developedknife-type device is about 100 times smaller than the WB
ofthe newly developed knife-type device. WB is related to thesecond
kind of singularity, and if the value of WB becomes large,the
system is away from the second kind of singularity. Here,note that
WB is also related to the well-known manipulating-force ellipsoid,
which denotes the force transmission from thecontact force f c to
the total force/moment vector F tool appliedon the knife-type
device because of (13). The value of WBindicates how F tool can be
more or less easily produced bythe haptic fingers, and thus, if the
system is close to the secondkind of singularity, the resulted
haptic fingertip force becomeslarge. The norms of the haptic
fingertip forces are shown inFig. 15. Fig. 15(a) and (b) show the
norms of the three-axisfingertip forces at the thumb, index, and
pinky haptic fingersin the experiments with the previously and
newly developedknife-type device, respectively. In fact, the
fingertip forces inthe newly developed device are small values in
all intervals andthe fingertip forces in the previously developed
device werelarge. This shows that the newly developed knife-type
devicehas good force transmission ability from f c to F tool .
Note that the maximum value of the force in Fig. 13(b) is only1
N, but the developed knife device can present greater force tothe
operator. The maximum value of the presented force of thedeveloped
knife device is over about 11 N. As an example, weshow the large
force response of the developed knife device inFig. 16. As shown in
the figure, the developed knife device canpresent a high level of
force. The presentation of about 4.5 Nof force is enough to cut an
elastic object [27], [28], and it isobvious that the developed
device can fully display this level offorce.
Fig. 16. Time responses of large fto ol in the knife-type
device.
Fig. 17. Displayable regions of the KD plane in the knife-type
device.
Next, to investigate the displayable stiffness of the
developedknife-type device, we carried out a contact experiment
involv-ing a virtual wall [18]. In this experiment, a user grasps
thedeveloped knife-type device. We made a virtual wall by usinga
springdamper model, and the desired force at contact pointV Ci at
the blade edge of the virtual knife was calculated byf i = f ci =
Ka
ni + Dv
ni . Four people in their twenties partic-
ipated in the experiment. The experimental procedure was
asfollows: 1) A damping coefficient D was set; 2) the
participantgrasped the knife-type device; 3) the participant
enlarged thestiffness coefficient K from 0 N/m at intervals of 100
N/m; and4) the participant touched the virtual wall through the
knife-type device and moved the device on the surface of the
virtualwall in every case. If the participant felt vibration, the
stiffnesscoefficient K before one-step was the maximum
displayablestiffness coefficient at the damping coefficient, which
was setin step 1). Then, the participant returned to step 1) and
set thedamping coefficient D to the next value. Here, the step size
ofD was 10 Ns/m. The displayable stiffness levels for four
par-ticipants are shown in Fig. 17. In the figure, the region
formedby the D-axis, the K-axis, and each participants curve is the
re-gion where the corresponding participant could feel the
smoothsurface of the virtual wall with no vibrations. We observed
nolarge differences among the different subjects curves, and
themaximum displayable stiffness was about 20 kN/m.
B. Manipulation of the Tweezers-Type DeviceTo evaluate the
developed tweezers-type device, we consid-
ered the manipulation of the device in a constraint space.
Here,note that we previously did not develop a tweezers-type
device,and thus, we did not consider the difference between a newly
de-veloped tweezers-type device and a previously developed one,as
in the case of the experiment with the knife-type device. Inthe
experiment, a virtual object was made in a VR environment,as shown
in Fig. 18. In the figure, the blue object is the virtualobject.
When the virtual tweezers touched a virtual object, theforce was
presented to an operator through the tweezers-type
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MULTIFINGERED HAPTIC INTERFACE ROBOT 79
Fig. 18. VR environment of the tweezers-type device.
Fig. 19. Experimental results for the tweezers-type device. (a)
Torque n .(b) Angle . (c) Times responses of PI. (d) Norms of
fingertip forces.
device. Furthermore, when the operator grasped the object
withthe tweezers-type device, the torque at the
opening-and-closingaxis was presented to the operator through the
tweezers-typedevice. The presented force and torque were calculated
usingthe penetration depth of the tips of the tweezers-type
deviceinto the object in the same manner as the case of the
knife-typedevice. The obtained reaction force F tool was translated
to f cusing (24), and then, f c was applied by controlling HIRO.
Inthe experiment, the operator held the handle of the tweezers-type
device, and grasped the object. Then, the operator liftedthe object
and released it.
Fig. 19 shows the experimental results. Fig. 19(a) and (b)
Fig. 20. Time responses of large torque n in the tweezers-type
devices.
shows the responses of the torque n and the angle at
theopening-and-closing axis, respectively. In Fig. 19(a), a solid
lineshows the response of n , and a dashed line shows the
responseof the desired torque. The average value of the absolute
torqueerror during the experiment was 0.024 Nm. From the figures,we
see that the absolute value of the torque was large wheneverthe
operator grasped the object with tweezers, and the operatorfelt the
grasping sensation of the object through the tweezers-type device.
Here, note that the initial value of angle , namely,the angle in
the case that the tweezers has no external forces asshown in Fig.
8(a), is = 12. On the other hand, Fig. 19(c)shows the time response
of the performance index, PI. Fromthe figure, although there were
some variations, we see that thedeveloped tweezers-type device
maintained a high PI value, andwe were able to confirm the good
operability of the device in theexperiment. Fig. 19(d) shows the
norms of the haptic fingertipforces. From this figure, we can
confirm that the haptic fingerswere able to display the required
forces.
The maximum value of the torque in Fig. 19(a) is only0.2 Nm, but
the developed tweezers-type device can presentlarger torque to the
operator. The maximum value of the pre-sented torque of the
developed tweezers-type device is overabout 0.39 Nm. As an example,
we show the torque responseof the developed device in Fig. 20. From
Fig. 20, we can see thatthe developed tweezers-type device can
present larger torque.For example, for a suturing task, which
closes an incision ina wound closure pad (i.e., a simulated skin
pad), the tweezersare used to grasp the tissue lips in passing the
suture across theincision. In this case, the presentation of about
3-N force at thehandle of the tweezers is sufficient to accomplish
the task [29].If this value is converted into the torque n , it is
0.32 Nm, andwe can see that the developed tweezers-type device can
fullydisplay the required torque.
Finally, we measured the displayable stiffness of the devel-oped
tweezers-type device, like the case of the knife-type de-vice. We
made a virtual object by using a springdamper model.When the
operator grasps the virtual object with the tweezers-type device,
the desired force at contact point V Ci at the virtualtweezers was
calculated by f i = f ci = Kani + Dvni . Four peo-ple in their
twenties participated in the experiment. The exper-imental
procedure was as follows: 1) A damping coefficient Dwas set; 2) the
participant handled the tweezers-type device; 3)the participant
enlarged the stiffness coefficient K from 0 N/mat intervals of 50
N/m; and 4) the participant grasped the virtualobject using the
tweezers-type device and moved the device onthe surface of the
virtual object in every case. Here, note that thevirtual object was
fixed in the environment, and the object did
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80 IEEE TRANSACTIONS ON ROBOTICS, VOL. 29, NO. 1, FEBRUARY
2013
Fig. 21. Displayable regions of the KD plane in the
tweezers-type device.
not move. If the participant felt the vibration, the stiffness
coeffi-cient K before one-step was the maximum displayable
stiffnesscoefficient at the damping coefficient, which was set in
step 1).Then, the participant returned to step 1) and set the
dampingcoefficient D to the next value. Here, the step size of D
was5 Ns/m. The displayable stiffness levels for four
participantsare shown in Fig. 21. We observed no large differences
amongthe different subjects curves, and the maximum
displayablestiffness was about 6 kN/m.
VII. CONCLUSIONWe have described a knife-type device and a
tweezers-type
device that we developed for the multifingered haptic
interfacerobot HIRO. The knife-type device represents a tool
devicewith no joints, and the tweezers-type device represents a
toolwith joints. To determine the optimal connection between
HIROand the tool-type devices, we have proposed the optimal
con-nection method from mobility and singularity points of
view.After we analyzed the kinematics of the knife-type device
andthe tweezers-type device, we have developed the devices forHIRO
that satisfied the optimal connections and tested them
ex-perimentally. In the experiment with the knife-type device,
wehave compared the newly developed knife-type device with
apreviously developed one and found that the newly
developedknife-type device has good force transmission ability. In
the ex-periment with the tweezers-type device, we have confirmed
thatthe operator feels the grasping sensation of the object
throughthe tweezers-type device, and device has good operability.
Theseresults show the great potential of our tool-type haptic
interfacesystem that is able to present the force sensation of many
tool-type devices, as well as the validity of the proposed
connectionmethod.
In this paper, we have developed a knife-type and a
tweezers-type device. However, human beings work with many tools.
Forexample, in the medical field, there are many tools of
differ-ent shapes and uses, such as surgical knives, scissors,
syringes,and many others; therefore, a haptic interface that can
createthe force sensation of many different tools is important for
vir-tual training systems. We plan to develop many other
tool-typedevices for use in a virtual training system in
future.
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ENDO et al.: DEVELOPMENT OF TOOL-TYPE DEVICES FOR A
MULTIFINGERED HAPTIC INTERFACE ROBOT 81
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Takahiro Endo (M06) received the Dr. Eng. de-gree from the Tokyo
Institute of Technology, Tokyo,Japan, in 2006.
Since April 2006, he has been with the facultyof Engineering,
Gifu University, Gifu, Japan, wherehe is currently an Assistant
Professor. His researchinterests include haptic interfaces,
robotics, and thecontrol of infinite dimensional systems.
Satoshi Tanimura received the B.S. degree in hu-man and
information systems engineering from GifuUniversity, Gifu, Japan,
where he is currently work-ing toward the M.S. degree in human and
informationsystems engineering.
His research interests focus on haptic interfaces invirtual
reality and robot control.
Haruhisa Kawasaki (M91SM10) received theM.S. and Dr. degrees
from Nagoya University,Nagoya, Japan, in 1974 and 1986,
respectively.
He is currently a Professor with the Faculty of En-gineering,
Gifu University, Gifu, Japan. From 1974 to1990, he was a Research
Engineer with NTT Labora-tories. From 1990 to 1994, he was a
Professor with theKanazawa Institute of Technology, Kanazawa,
Japan.From July 1998 to January 1999, he was a VisitingProfessor
with the University of Surrey, Surrey, U.K.His research interests
are in the areas of robot control,
humanoid robot hands, haptic interfaces in virtual reality, and
computer algebraof robotics.
Dr. Kawasaki has contributed to the community as a member of
many or-ganizations, such as the Japan Society of Mechanical
Engineers (JSME), theRobotics Society of Japan (RSJ), the Society
of Instrument and Control Engi-neers, and the Virtual Reality
Society of Japan. He is a Fellow of JSME and RSJ.He has received
several awards, such as the Best Paper Award from the
WorldAutomation Congress in 2004 and the Prizes for Science and
Technology fromthe Commendation for Science and Technology by the
Minister of Education,Culture, Sports, Science and Technology of
Japan in 2006, as well as JSMEFunai Award in 2009. He was the
National Organizing Committee Chair ofthe Ninth International
Federation of Automatic Control Symposium on RobotControl in
2009.
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