06289374

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

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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.


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


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)


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


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


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,


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


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


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


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


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


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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[29] A. Rafiq, F. Tamariz, C. Boanca, V. Lavrentyev, and R. C. Merrell, Objec-tive assessment of training surgical skills using simulated tissue interfacewith real-time feedback, J. Surg. Edu., vol. 65, no. 4, pp. 270274, 2008.

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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