This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
The final version of record is available at
http://dx.doi.org/10.1109/LRA.2018.2795649

IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED DECEMBER, 2017

Lightweight, high-force gripper inspired bychuck clamping devices
Toshihiro Nishimura1, Student Member, IEEE, Masanari Tennomi1, Student Member, IEEE, Yosuke
Suzuki2, Member, IEEE, Tokuo Tsuji2, Member, IEEE, and Tetsuyou Watanabe2, Member, IEEE
Abstract—In this paper, we present a novel gripper, whose
design was inspired by chuck clamping devices, for transferring
heavy objects and assembling parts precisely in industrial
applications. The developed gripper is lightweight (0.9 kg), canmanipulate heavy payloads (over 23 kgf), and can automaticallyalign its position and posture via a grasping motion. A fingertip
design criterion is presented for the position alignment, while acontrol strategy is presented for the posture alignment. With one
actuator, this gripper realized the above features. This paper
describes the mathematical analyses and experiments used tovalidate these key metrics.
Index Terms— Grippers and Other End-Effectors, Grasping,
Mechanism Design, Underactuated Robots, Assembly

M

I. INTRODUCTION
ANY robotic grippers [1][2] have been developed for the

purpose of factory automation. The grippers’ primaryfunctions are transferring and assembling parts or products. In
these operations, the preferable functional requirements for thegripper are as follows: 1) it must be able to generate high force
to grasp objects stably and transfer heavy objects; 2) it must be
lightweight relative to the payload of manipulator; and 3) its
position and posture must automatically align appropriately for
precise assembly via a grasping motion. This paper presents a
novel gripper that satisfies these three requirements.
In industrial applications, robotic grippers must
accommodate large payloads (i.e., weight of the grasped object)and grasping forces. In general, large actuators or transmissions
are needed to construct high force gripper, resulting in heavy
gripper designs; there is a direct relationship between payload
magnitude and weight. Nonetheless, a lightweight, high-force
gripper design is preferable. In assembly processes, the precisealignment of the gripper’s position and posture is necessary toensure high processing speed and smooth operation.
Many common parts, such as gears and shafts, are cylindricalin shape. Thus, the gripper described in this paper wasdeveloped to manipulate cylindrical objects. Drilling andturning machines utilize chuck devices to grasp cylindrical
tools. Inspired by these chuck devices, we developed alightweight, high-force gripper as shown in Fig. 1. The feedscrew mechanism transduces motor torque into a large driving

Manuscript received: September, 10, 2017; Revised December, 2, 2017;
Accepted December, 24, 2017.
This paper was recommended for publication by Editor Han Ding uponevaluation of the Associate Editor and Reviewers’ comments. This work was
supported by NEDO Project P17004.

force, which generates a large grasping force. Even wheninterrupting the electric supply to the motor, the grasping force
is maintained by the self-locking property of the screw. The
developed prototype gripper has a weight of 0.9 kg and its
payload is over 23 kgf. As shown in Fig. 1, the gripper has two
grasping modes. One drawback of the chuck-based gripper
design is its narrow space for grasping, which makes it difficult
to grasp wide objects. Therefore, the expanded mode shown in
Fig. 1(b) was implemented to grasp objects that were too wide
to be grasped in the normal mode shown in Fig. 1(a). In the
expanded mode, the fingers protrude outside of the cover toprovide a wide space for grasping. In both modes, the fingers
close towards the center of the gripper in synchrony, and theposition and posture of the grasped object can be automaticallyaligned.

(a) Normal mode(b) Expanded mode

Figure 1. Developed gripper

A. Related work
Many types of robotic hand devices have been produced [3],including for the purpose of producing high forces[4]–[18],similar to the goal of this study. Table I lists the related
specifications for these high-force robotic hands. The SLUM
gripper [14], flexible gripper [15], and Multi-DOF hand [16]designs can maintain large grasping forces without an electric
supply, by utilizing rocking mechanisms. We defined apayload-to-weight ratio calculated by dividing the payload by
the weight of the device, to evaluate the largest obtainable
payload at the lowest possible weight. When handling an object
with a gripper attached to a manipulator, the summation of theweights of the object and gripper must be under the given
payload for the manipulator. A large payload-to-weight ratio
maximizes the payload for a given manipulator. In this context,
the gripper developed in our present study attained the best
performance, as shown in Table I.
1
T. Nishimura and M. Tennomi are with the Graduated school of Naturalscience and Technology, Kanazawa University, Kakuma-machi, Kanazawa,
9201192 Japan (e-mail: to.nishimura@stu.kanazawa-u.ac.jp).
2
Y. Suzuki, T. Tsuji, and T. Watanabe are with the Faculty of MechanicalEngineering, Institute of Science and Engineering, Kanazawa University,
Kakuma-machi, Kanazawa, 9201192 Japan (e-mail: te-watanabe@ieee.org).
Digital Object Identifier (DOI): see top of this page.

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
The final version of record is available at
http://dx.doi.org/10.1109/LRA.2018.2795649

IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED DECEMBER, 2017
In assembly processes, the precise alignment of parts isnecessary, and several approaches have been used to achieve
automatic alignment during assembly. Zhang et al. proposed analgorithm for aligning the posture of a part with parallel-jaw
grippers [19][20]. Harada et al. proposed a strategy in which theposition and posture of an object on a table were aligned byutilizing two passively and two actively moving fingers [21].
Dobashi et al. proposed a strategy for assembling parts whose
position and posture were uncertain, with four cylindricalfingers [22]. Hirata et al. proposed a design in which the gripper
mechanisms were capable of automatic part alignment [23][24].
This study also challenges to embed the automatic partalignment function in the gripper. A fingertip design method ispresented for the position alignment, while a control strategy ispresented for the posture alignment.
TABLE I.

SPECIFICATIONS AND PERFORMANCE; THE DEVELOPED GRIPPER
AND RELATED ROBOTIC HANDS
Fingertip
Payload-toWeight
Payloadforce
weight
[kg]
[kgf]
[N]
ratio[-]*DLR Hand II [4][5]
1.8
30
4.9**
2.7
Robotiq
2.3
60
10
4.3
3-Finger gripper [6]Barrett Hand [7][8]
0.98
6.0
6.1
Tokyo-TECH 100N0.94
10012.2**
13.0
Hand [10]FRH-4 hand[13]0.22***
11.2-****
SLUM gripper [14]
3.5
10
2.9
Flexible gripper [15]
2.61
4.0
1.5
Multi-DOF hand [16]
2.4
113
50
20.8
Underactuated soft
0.7
3.0
4.3
gripper [17]Jamming gripper
0.64***
4.5-****(3.5” Head) [18]0.9Over 23Developed gripper
350
25.6

The bold value indicates the best performance in each metric.
* Payload-to-weight ratio: Payload/Weight** The payload was not presented, and the value was calculated by the multiplication of the fingertip
force, number of fingers, and friction coefficient (0.4)*** The weight did not include air supply devices**** We did not calculate these values because the weight did not include air supply devices

Figure 2. Schematic view of the main mechanism based on chuck device

II. GRIPPER DESIGN.
A. Functional requirements
To ensure the gripper would be suitable for use in industrial
tasks, such as product assembly, the functional requirements ofthe gripper were set as follows:
1. The payload of the gripper must be greater than 196 N (20kgf).
2. The weight of the gripper must be less than 1.0 kg.
3. The gripper must be able to grasp objects with a width
greater than 100 mm.
4. Position and posture alignments must be automatically
performed via a grasping motion.
5. The gripper must be able to grasp cylindrical parts, withradial symmetry.

We designed the gripper to satisfy the requirements in thenormal or expanded mode.
B. Main mechanism
Based on the mechanism of chuck device, we adopted themechanism shown in Fig. 2, where the three fingers close withbeing pushed out owing to the feed screw mechanism andconstraint by the cover. The feed screw mechanism transduces
the motor torque into a high driving force to ensure a large
grasping force. Similarly to chuck device, the gripper canmaintain a large grasping force without electric supply by the
self-locking property of the screw. As shown in Fig. 2, thefingers are radially arranged at regular intervals on a circle, andtheir closing motion facilitates automatic alignment of theposition and posture of the part.
C. Structure
Fig. 3 shows the CAD models for the developed gripper. The
gripper mainly consists of the three fingers (red parts in Fig. 3),
the finger base (light blue part in Fig. 3), the cover, theservomotor (Dynamixel, XM430-W210), the 6 guide rails, andthe feed screw mechanism. The fingers are mounted on thefinger base and constrained by the guide rails so that the fingers
can slide in the direction of opening and closing of the gripper.
Fig. 3(b) shows the finger structure. The finger pad is beveled
for the automatic alignment and grasping of small objects. The
phalange and base are connected through torsion spring, and thephalange is abducted if the constraint of the cover is removed.
The finger surface is knurled for increasing friction so that an
object can be easily grasped especially at the expanded mode.
The guide rails are mounted on the inside of the cover, as shownin Fig. 3(c). The slide pin at the finger base (yellow parts at Fig.
3(b)) slides along the guide rails for converting the straightmotion of the feed screw into the opening and closing motionsof the gripper or fingers (See Fig. 3(c)). Fig. 4(a) shows theschematic view of the motions of the shafts, finger base, andfingers at the normal mode. The outer shaft with internal screw
thread is attached to the servomotor, while the finger base isattached on the tip of the inner shaft with external screw thread.
The rotational motion of the outer shaft by the servomotor
drives the straight motion of the inner shaft and finger base. As
shown in Fig. 4, the fingers are pushed out (pulled in) by thestraight motion of the finger base, and opened (closed). With
this structure, even when opening and closing the gripper, theposition of the servomotor does not change, which is preferable
for the durability of motor and wiring. The three fingers close,moving the same distance to approach the center of the gripper,
and the position of the part is aligned at the center while its
posture is aligned so that the longitudinal direction of the partcoincides with that of the fingers. The maximum width ofgraspable object at the normal mode is 42 mm. To grasp an
object whose width is over the maximum width, the expanded
mode is adopted. If the pushing of the finger base is continued
after finishing the closing of fingers at the normal mode, theconstraint by the cover is released and the fingers are protruded
owing to the torsion springs, as shown in Fig. 4(b). If the finger
base is pulled from this state, the protruded fingers close owing

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
The final version of record is available at
http://dx.doi.org/10.1109/LRA.2018.2795649

NISHIMURA et al: LIGHTWEIGHT, HIGH-FORCE GRIPPER INSPIRED BY CHUCK CLAMPING DEVICES(a) CAD models of the developed gripper(b) CAD models of the finger(c) Structure of the guide rail for one finger (Two guide rails for one finger)
Figure 3. CAD models of the developed gripper and the structure of thefinger3

important role in the position alignment. This section describes
the derivation of . For simplicity, the shape of the object was
assumed to be cylindrical, and the object was located on aslippery table. Planar analysis was conducted. If an object is notcentered, the following steps are traced with the closing of thefingers (Fig. 5). Step 1: the object contacts one finger first. Step
2: the object comes in contact with two fingers. Step3: theobject contacts all the three fingers and becomes centered. Notethat it is possible that step1 is skipped. When contacting only
one finger, the object slides on the table. On the other hand,when contacting two fingers, it is possible that the sliding of theobject stops and the position alignment fails. Therefore, we
consider the case when a cylindrical object contacts two fingers,
as shown in Fig. 6. It is noted that we do not consider thesituation where the gripper loses its hold on the object during
the closing, because the grasp planning is beyond the scope ofand∈ 1,2 denote the normal andthis study.
tangential components of the force applied to the object byfinger , respectively.
denotes the static maximum (kinetic
when sliding) frictional force applied to the object from thetable, and its direction is opposite to that of the resultant force∑. The coordinate frame
was set so thataxis could be parallel to the direction of ∑andits positive direction would be toward the center of the gripper.
Let
be the angle between axis and the contact tangential
direction. We will analyze the system by taking into account thesymmetry with respect to the axis.
The condition for realizing the position alignment is that theobject continues moving/sliding until it reaches the center of thegripper. The condition is then written as

Figure 5. Schematic view of the position alignment(a) Normal mode(a) Forces applied to the object(b) Expanded mode(b) Zoomed-up view for the othersetting

Figure 6. Model for the analysis of the position alignment

Figure 4. Schematic view of the motions at each modeto the constraint resulting from the contact between the coverand the rear side of the fingers. With this mechanism, wide
objects can be grasped at the expanded mode.
III.

POSITION AND POSTURE ALIGNMENT MECHANISM

A. Position alignment
As shown in Fig. 5, the closing motion provides the positionalignment. The angle of the bevel
shown in Fig. 6 has an

‖

‖

0

(1)
(2)

denotes the unit vector along the positive
axis.
where
When closing the fingers, they are pushed out in the positive
direction by the feed screw. Accordingly, the tangential contact
force is large while the normal contact force is small at thecontact point between the object and each finger. Therefore, thecontact can be regarded as a kinetic friction state. If the contact

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
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IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED DECEMBER, 2017
is not the kinetic friction state, the closing motion of the gripper
stops and the object cannot be grasped. Taking
as the kinetic
frictional coefficient at the contact point between the object andthe fingers, the magnitude of the tangential component of thecontact force applied from finger is given by ‖ ‖‖ ‖. Then, considering the symmetry of the system andthen ‖ ‖ ‖ ‖, (1) and (2) can be rewritten by
2‖

sin

cos

cos

‖

‖

‖

Figure 7. System setup for investigating the function of position alignment

(3)

(4)
sin
cos cos0‖‖
where cosis the magnitude of the mappedonplane ( is the angle between
plane and ).
the
Since a slippery table is assumed, ‖ ‖ is small. Additionally,‖ ‖ would increase until (3) can be satisfied if (4) is held,
and the closing motion then continues. Therefore, we only haveto satisfy (4) for the position alignment. From the relation
between the inner angles of the quadrangle P P P P shown in⁄2 60°. Moreover, 1 cos
Fig. 6(b), we get
0.Then, the sufficient condition for satisfying (4) is(5)tan
120° 2 tan
This is the condition forfor realizing the positionalignment. Assuming that the materials for the object andfingers are plastic (PLA), the kinetic frictional coefficient canbe set as
0.2. Then, we set
145° considering the
manufacturing error.
We investigated the function of position alignment by using
the fingers with
145°. The experimental setup is shownin Fig. 7. The objects were cylinders with a diameter of 10, 20,
and 25 mm and cuboid with the 20mm square bottom face. The
nominal closing speed was 0.8 mm/s and we also investigatedthe case when the speed was 0.4 mm/s for comparison (Notethat the available speed was 0~0.8 mm/s).
,
be the geometrical center of the baseLetof the object captured by the camera,,be thecenter of the gripper, derived by considering it to correspond to
the geometrical center of the triangle constructed by connecting
the three apexes of the fingertips captured by the camera at theinitial state. Here, we define the following position error of theobject.
(6)
Fig. 8 shows the experimental results of the cylinder with adimeter of 20 mm giving the overview of the position alignment
and time series data of ‖ ‖. We conducted over 30
experiments for each object by changing the initial object
positionrandomly. If ‖ ‖ converged to less than 1 mm, we
judged the position alignment to be successful. In Fig. 9, thered and blue makers show the initial positions for success andfailure cases, respectively. Fig. 9(a) illustrates that the positionalignment function works well if the initial position error
is less than 10.3, 12.8 and 15.7 mm forthe cylinders with the diameter of 10, 20, and 25 mm,
respectively. In Fig. 9(b), the distribution of the red maker(success case) was not uniform. As suggested/implied by (5),the alignment function does not work if the angle between thesides of the object and fingertips ( ) is small. The angle varies(a) Composited image of the initial(b) Time series data of the position
and final positions
error ‖ ‖Figure 8. Representative data of position alignment test(a) Cylinders with different diameters(b) Cuboid
Figure 9. Experimental results of the position alignment

with the initial position of cuboid. This is the reason for the nonuniform results. The results also indicates the effect of initialorientation of the object. No effect of different speeds wasobserved.
B. Posture alignment
As shown in Fig. 10, the posture is aligned when grasping thecylindrical object even when the initial posture is different fromthe aligned posture, where the longitudinal direction of theobject coincides with that of the fingers. The posture alignment
fails only when the rotational motion of the object stops before
the alignment completes. The problematic rotation is theaxis shown in Figs. 10 and 11,
rotation around the
because the allowable rotational direction is only positive, andthen the rotation could stop, due to the constraint by the table.
Therefore, we focus on the rotation around the contact point 1(C ) on finger 1 at theplane and try to positively rotate
the object at C around theaxis without stopping before
completion, which leads to the posture alignment. It is notedthat the sliding at C does not contribute directly to the posturealignment. The velocities of fingers 1 and 2 at the closing
motion are given by(7)
cos 60°cos 60°
cos
,
sin
,
tan ,
is thewhereis the rotational frequency andtaper angle of the finger,
0 when the motor positively rotates, is the pitch of thefeed screw (See Fig. 11).

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
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NISHIMURA et al: LIGHTWEIGHT, HIGH-FORCE GRIPPER INSPIRED BY CHUCK CLAMPING DEVICES

respectively, at C ( ∈ 1,2,3 ). Then, the condition for
accelerating the positive rotation can be written as
0
(9)
where
cos
4
sin
cos
cos
tan
cos

Here,

0,

0

on theplane,,

is the mappedis the gravity term, andandis the posture of the object,
are the ratio of the magnitude of frictional force to thenormal force at the contact points between the object andfingers, and the object and table, respectively. Taking
andas the maximum frictional coefficients at the contact points,
we getand. If the diameter of the object isFigure 12. System setup for testing the function of the posture alignment

°

40〜45

30〜35

Initial posture error

35〜40

20〜25

25〜30

10〜15

0

15〜20

°

40〜45

30〜35

Initial posture error

35〜40

20〜25

25〜30

10〜15

15〜20

0〜5

0

50

0〜5

50

100

5〜10

Success rate [%]

100

5〜10

2
,
). The motion of C provides a positive rotation
around C , which indicates that C moves toward the direction
where C is detached from the table. Then, the posturealignment can work. It is noted that it is possible that therotation around C by the velocity (motion) of C ( ) could
be negative when thecoordinate of C is larger than that of
C because the object angle () is large. In this case,⁄3
T /2sin (tan)
is the distance between C and C . The definitions forwhere
the other variables are shown in Fig. 15. Then, the condition for
⁄
0 is
tan
. If assumingthat the object is thin,≫and then
0 isalways held. We move the gripper (xyz-stage) with a speed ofwhile closing it so that C can be fixed with respect to thetable. It is remarked that the setting ofassumed that there
was no sliding at C . Practically, the sliding could occur and we
could compensate the sliding motion by adding thecompensation term at. However, another sensor such as acamera is required for the compensation and then it will not becost-effective. Additionally, even if the sliding occurs, we canapply the strategy by regarding C as the one that should be
fixed when the sliding stops. There are several concave areas
on the surface of the fingers, and the sliding stops with highpossibility when C reaches the area. Therefore, we took thiseasy control strategy.
Here, we investigated the available range for the posturealignment. Fig. 12 shows the experimental setup. A cup was
utilized to set the initial posture of the object. Taking
andas the initial postures of the object and gripper,

respectively, we defined the initial posture error of the object:(8)
To prevent the collision between the object and table after thesuch that. We
posture alignment, we set
into the incremental ranges, each spanning
split the range of
5°, and repeated the investigation by randomly selecting
until the number of trial times for each range was more than
three. Fig. 13 shows the success rate, and Fig. 14 shows thesnapshots for the successful case. Fig. 13(b) shows the caseutilizing the strategy. A success rate of 100% was obtained in
all the ranges, which shows the validity of the proposed control
strategy. Fig. 13(a) shows the case when the strategy is not
utilized. The posture alignment failed when
, namely,
was large. Here, we discuss the reason. Fig.
for constant
15 shows the model for the analysis, where each unilateralarrow shows the positive direction for each corresponding
variable. Let
be the moment around theaxis, and,be the normal and tangential contact forces,

Success rate [%]Figure 10. Schematic view of the posture alignment

The aim of the strategy is to control finger 1 so that C canbe fixed with respect to the table (or base frame), when closing
the finger/gripper. The fixing of C indicates that the allowablemotion of the object is the rotation around C , while C moves
toward the positive
and negative
directions via theclosing motion of the fingers (3/5(a) Without control(b) With control
Figure 13. Experimental results: initial posture error versus the success rateof the posture alignment(a) When closing (0)(b) When opening (0)

Figure 11. Direction of the velocity of the fingertip in the posture alignment
strategy:is the rotational frequiency and is the pitch of the feed screw.
,tan ,tan cos 60°

Figure 14. Snapshot of the posture alignment test

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
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IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED DECEMBER, 2017(a) Geometrical representations(b) Statics

where each unilateral arrow at Fig. 16(a) shows the positive
direction for each corresponding variable. Note thatis the maximum
corresponds to the grasping force, andstatic frictional coefficient (Table II), anddenotes the
tip/taper angle of the finger. By considering the instant whensliding occurs at the contact point between the object and thefinger, the optimal problem for deriving maximum
is givenbymax
Subject to
0 0
0 0
⁄3
0,

Figure 15. Model for analyzing the posture alignment

small ( ≫) andis small, we get
0. Here,0 is assumed. Then, if
is small (tan 2 ⁄
tan 1⁄
67° for
7.5 mm,
0.3 , α0 and then0 (9) can be
130 mm,( ∈ 2,3 ). Note thatsatisfied irrespective of the values of
68° corresponds to
23° 68°45° . If
is not small, it is possible that
0 and the motion forthe posture alignment stops before completion. This is thereason for the failure results shown in Fig. 13(a). From (9),0 . It is noted that0should be small forindicates the case when losing the contact with the table, andthen
0 is always satisfied under the condition ofis the0cos
0 . In other words,
condition for
0 when losing contact with the table.
IV. FEASIBILITY STUDYThis section shows the maximum payload (weight ofgraspable object) by the developed gripper.
A. Analysis
As shown in Fig. 16, the target is a cylindrical object and wewill derive the maximum weight of the graspable object at the
expanded mode. Because of cylindrical symmetry, we consider
the half section of the system as shown in Fig. 16. The
maximum payload at the normal mode can be regarded as theone in the case where the angle between the object and finger,(Fig. 16(b)), is zero. Because the problem is indeterminate,
we will formulate it as an optimal problem for power grasp[25][26] and then solve it.
Let
,
,
,
,
, and
be the normal
and tangential forces at each contact point, as shown in Fig. 16,

Figure 16. Model for deriving maximum holding force and payload; (a) staticand (b) geometrical representations.
Kinetic
frictionalcoefficient between
the object and fingers

where

1 0
0 1
0 0

1 0
1 0

⁄

(10)
0,

0

0

0,0,
,

,

,

,

sin ,
cos ,
sin
,
and
cos
.
If we utilize 3
as the criterion function,is
we can get the maximum payload. Because
constant, there is no essential difference in formulation. The fist
represents the equilibrium of the force andconstraint
moment at the connecting point, andrepresents therestored torque at the torsion spring. The direction of
was derived by considering the sliding direction at the instantwhen sliding occurs [27]. Please see Fig. 16 for the definitionsof the other variables. The second constraint represents thefrictional condition at the contact point between the finger andthe inside of the cover, andis the frictional coefficient at
the contact point. The third constraint represents theunilaterality of the normal force at each contact point and the⁄3. From
maximum load applicable to the feed screw
the Motosh equation [28], the relation between the fastening
torqueand the load applied to the fastener at the feedscrew is given by
(11)
2 cos
where = 0.2 is the frictional coefficient in threads,
9.026 mm is the effective diameter of thread contact,
30°
is the half angle of thread form, and
1.5 mm is the thread
pitch. It is noted that there is no head at feed screw mechanism
and the term for the head is then removed at (11). Because
2000 Nmm,
1560 N.
We calculated
for
0°– 60°. Fig. 17 shows the
0.4,
40 mm, andresult when
25 mm,
5 mm. Note that
becauseis the static coefficient.

TABLE II.
DEFINITION OF THE FRICTIONAL COEFFICIENTS
Ratio of the static frictional force toRatio of the static frictional force to thethe normal force between the object
normal force between the object andand fingers. Maximum value istable. Maximum value isMaximum static frictional coefficient at
the contact point between the finger andthe inside of the cover

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
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NISHIMURA et al: LIGHTWEIGHT, HIGH-FORCE GRIPPER INSPIRED BY CHUCK CLAMPING DEVICES
If we consider the case when0°, which corresponds tothe normal mode,
347 N and the maximum payload
is 3
416 N (42 kgf). If assuming thatthe knurl, which provides a high friction, is utilized in the
expanded mode,
113 N with setting
2.0 and60° , and the maximum payload is 3
45 N (4.6 kgf).
400
300
200
100
0

0

10

20

Figure 17. Opening angle

30

40

50

60

Figure 18. System setup for measurement of resistible load
TABLE III

EXPERIMENTAL RESULTS FOR RESISTIBLE LOAD
Style
Normal mode
Expanded mode
1
2
3
4
5
C*
S**
C
S
LC***
LC
LC
225
225
152
174
52.1
47.5
40.8
(23)
(23)
(16)
(18)
(5.3)
(4.9)
(4.2)
0

0

of the can with water. In the style 2, the maximum payload wasover 15 kgf. If focusing on the expanded mode, the maximum
payload was 52.1 N (5.3 kgf) on average in style 3, while 4.9
and 4.2 kgf in styles 4 and 5.
V. GRASPING AND OPERATION TESTS
A. Grasping test
This section presents the results of the grasping test where
we tried to grasp several industrial products. The items were
initially placed on a table or inside a basin or cup, and thengrasped manually. Figs. 1 and 19 show the representative
results of the grasping test, which demonstrate the efficacy ofthe developed gripper (see also attachment video clip).

versus maximum holding force

B. Experimental validation
Here, we experimentally investigated the maximum payload
when grasping an object with the styles shown in Fig. 18. For
comparison, we investigated the payload in different loading
directions:direction for the styles 1 and 3 while
direction in the styles 2, 4 and 5. The styles 1 and 3 correspondto the one analyzed in the previous section. We fixed the gripper,
grasped the object with a motor torque of 2000 Nmm, andstopped the power supply to the motor. After attaching thegrasped object to the plastic container can, water was poured
into the can until the object fell down. We measured the weightof the can, including the amount of water when the object fell.
The maximum weight of the can with water was 225 N (23 kgf).
The target objects for the normal mode were a cylinder(diameter: 20 mm, length: 70 mm) and square rod (20 20
70 mm), while that for the expanded mode was a cylinder(diameter: 90 mm, length: 30 mm). The examination was
conducted five times for each object except for the style 4 (threetimes). The lowest fingertip always broke off at the style 4 andthen we stopped the experiment after the third times of theexperiment for safety reason. Table III shows the results. If
focusing on the normal mode, in the style 1, the maximum
payload was over 225 N (23 kgf), which is the maximum weight

Average[N (kgf)]
Standard
deviation

7

13.6

24.5

12.3

2.45

* C: Cylinder (D: 20, L: 70mm), ** S: Square rod (203.75
70 mm),*** LC: Large Cylinder (D: 90, L: 70 mm)(a) Normal mode(b) Expanded mode
Figure 19. Representative results of the grasping test

B. Operation test
In order to determine whether the developed gripper can beutilized in practical operations, the following four operations
were conducted utilizing the gripper: 1) cutting a wooden board
by a saw, 2) hammering a nail, 3) tightening an M6 screw witha torque of 5 Nm by a torque wrench and 4) picking up a 2-L
PET bottle of water from a corrugated carton. Note that the
manipulation was manually conducted. Fig. 20 shows anexample of the results demonstrating the efficacy of the gripper(see also attachment video clip).

Figure 20. Examples of the operation tests; Hammering a nail

VI. DISCUSSION
The five functional requirements of the gripper design were
defined in Section II. We determined that requirements 4(automatic position and posture alignments) and 5 (cylindricalparts are graspable) were satisfied as discussed in sections III
and IV. The maximum payload was over 23 kgf in the normalmode, while the weight of the developed gripper was 0.9 kg;
thus, requirements 1 and 2 were also satisfied. An expanded
mode was created to facilitate the grasping of wide objects. The
CD cake box, shown in Fig. 19(b), was grasped by the gripper
in the expanded mode and had a width of 130 mm. This result
demonstrates that requirement 3 was satisfied.
The experimental results shown in section III validated thedesign of the angle of the bevel based on (5) for the positionalignment, as well as the control strategy based on (7) for the
posture alignment. The maximum load values obtained by the
analysis in section IV.A were close to the values obtained by
the experiments for styles 1 and 3 in section IV.B. It indicatesthe validity of the presented approach. From the experimental
results for style 2, 4, and 5, it can be seen that the maximum
payload in the lateral direction decreased to over 15 and 4 kgf

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This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.
The final version of record is available at
http://dx.doi.org/10.1109/LRA.2018.2795649

IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED DECEMBER, 2017
in the normal and expanded modes, respectively. The
decreasing amount in the expanded mode was small comparing
to the normal mode. The knurl can locally envelop an object
and then the friction force can generate in a wide range ofdirections. Additionally, the object could get stuck at the knurl.
This might be the reason for the small difference. The payload
for the expanded mode was small but enough large if
considering the payload of manipulator. We conducted theassembly task with the expanded mode (see attachment videoclip). The task simulates the assembly task of Robotic Graspingand Manipulation Competition @ IROS 2017. The successful
smooth gear (680g) insertion validated the efficacy of the
expanded mode.
This paper didn’t focus on the operation speed, but the speedup is often required in industrial fields. The high force isgenerated by the fastening torque of the feed screw and 2 Nm
is required to operate the feed screw. Therefore, any motor thatcan generate over 2 Nm can be adopted. The maximum closing
speed of the developed gripper was 0.8 mm/sec and theminimum closing time was 25.5 s. The operation speed canincrease with a higher power motor, although the total weight
could increase. An operation, where a required closing distanceat a grasping motion is small, is preferable for the gripper.
Motion planning including manipulator can make the required
closing distance small. Furthermore, an assembly operation andoperation utilizing tools are preferable because at these
operations, position and posture alignment ability and highgrasping force are more important than grasping speed. The sizeof the gripper is large and a large motion is required for amanipulator to conduct operations. The size reduction ispossible but the maximum payload would decrease. The size
should be selected based on a given task.
VII. CONCLUSION
This paper presents a novel gripper for industrial applications,such as part transferring and assembly. The main features of thegripper are its lightweight and high force. The developed
gripper was inspired by a chuck clamping device, and thefingers are pushed out by a feed screw mechanism and an outer
cover restraint. The developed three-jaw gripper has anotherfeature; the automatic alignment function of its position andposture via a grasping motion. We presented a design criterion
for the angle of the bevel for realizing the position alignment aswell as a control strategy of gripper velocity for realizing theposture alignment irrespective of an aligned posture. These
three features were evaluated analytically and experimentally.
Future work will involve the development of autonomous
operation methodologies utilizing the developed gripper.
REFERENCE
[1]
[2]
[3]

Mitsubishi electric, “Multifunctional Electric Hand,” [Online].
Available: http://www.mitsubishielectric.com/fa/products/rbt/robot/
pmerit/option/hand/index.html#pageUnit01. .
Schunk, “PZN-plus,” [Online]. Available:
http://www.swt.co.kr/file/schunk/PZN-plus_gesamt_EN.pdf. .
M. Controzzi, C. Cipriani, and M. C. Carrozza, “Design of Artificial
Hands: A Review,” 2014, pp. 219–246.

[4]

G. Hirzinger, J. Butterfass, M. Fischer, M. Grebenstein, M. Hahnle, H.
Liu, I. Schaefer, and N. Sporer, “A mechatronics approach to the designof light-weight arms and multifingered hands,” Proc. Millenn. IEEE Int.
Conf. Robot. Autom. Symp. Proc. vol. 1, pp. 46–54, 2000.
[5] J. Butterfass, M. Fischer, M. Grebenstein, S. Haidacher, and G.
Hirzinger, “Design and experiences with DLR hand II,” World Autom.
Congr. Proc. Tenth Int. Symp. Robot. with Appl., pp. 105–109, 2004.
[6] Robotiq, “3-Finger Adaptive Robot Gripper,” [Online]. Available:
http://robotiq.com/en/products/industrial-robot-hand/. .
[7] W. Townsend, “The BarrettHand grasper – programmably flexible part
handling and assembly,” Ind. Robot An Int. J., vol. 27, no. 3, pp. 181–
188, Jun. 2000.
[8] Barret Technology Inc., “Barret Hand BH8-282,” [Online]. Available:
http://www.barrett.com/robot/index.htm. .
[9] Shadow Robot Company, “Shadow Dexterous Hand,” 2015. [Online].
Available: http://www.shadowrobot.com/products/dexterous-hand/.
[10] T. Takayama, Y. Chiba, and T. Omata, “Tokyo-TECH 100 N Hand :Three-fingered eight-DOF hand with a force-magnification mechanism,”in 2009 IEEE Int. Conf. on Robot. Autom., pp. 593–598.
[11] SAKE ROBOTICS, “EZGripper Robotic Grippers,” [Online].
Available: http://sakerobotics.com/products2/. [Online]. Available:
http://sakerobotics.com/products2/.
[12] L. U. Odhner, L. P. Jentoft, M. R. Claffee, N. Corson, Y. Tenzer, R. R.
Ma, M. Buehler, R. Kohout, R. D. Howe, and a. M. Dollar, “A
compliant, underactuated hand for robust manipulation,” Int. J. Rob.
Res., vol. 33, no. 5, pp. 736–752, 2014.
[13] I. Gaiser, S. Schulz, A. Kargov, H. Klosek, A. Bierbaum, C. Pylatiuk, R.
Oberle, T. Werner, T. Asfour, G. Bretthauer, and R. Dillmann, “A newanthropomorphic robotic hand,” - 8th IEEE-RAS International
Conference on Humanoid Robots, 2008, pp. 418–422.
[14] J. Hsu, E. Yoshida, K. Harada, and A. Kheddar, “Self-locking
Underactuated Mechanism for Robotic Gripper,” in 2016 IEEE Int.
Conf. on Advanced Intelligent Mechatronics, 2017, pp. 620–627.
[15] M. Tavakoli, L. Marques, and A. T. De Almeida, “Flexirigid, a novel
two phase flexible gripper,” IEEE Int. Conf. Intell. Robot. Syst., pp.
5046–5051, 2013.
[16] NAMIKI PRECISION JEWEL CO., “Multiple DOF hand with grasp
force higher than 50kgf (in Japanese),” [Online]. Available:
http://www.jst.go.jp/pr/announce/20160307/. .
[17] T. Nishimura, K. Mizushima, Y. Suzuki, T. Tsuji, and T. Watanabe,“Variable-grasping-mode underactuated soft gripper with environmental
contact-based operation,” IEEE Robot. Autom. Lett., vol. 2, no. 2, pp.
1164–1171, 2017.
[18] EMPIRE ROBOTICS, “VERSABALL GRIPPER,” [Online]. Available:
http://empirerobotics.com/products. .
[19] M. T. Zhang and K. Goldberg, “Gripper point contacts for partalignment,” IEEE Trans. Robot. Autom., vol. 18, no. 6, pp. 902–910,
Dec. 2002.
[20] M. T. Zhang and K. Goldberg, “Designing robot grippers: optimal edge
contacts for part alignment,” Robotica, vol. 25, no. 3, pp. 341–349,2007.
[21] K. Harada, K. Nagata, J. Rojas, I. G. Ramirez-Alpizar, W. Wan, H.
Onda, and T. Tsuji, “Proposal of a shape adaptive gripper for robotic
assembly tasks,” Adv. Robot., vol. 30, no. 17–18, pp. 1186–1198, 2016.
[22] H. Dobashi, J. Hiraoka, T. Fukao, Y. Yokokohji, A. Noda, H. Nagano,
T. Nagatani, H. Okuda, and K. Tanaka, “Robust grasping strategy forassembling parts in various shapes.,” Adv. Robot., vol. 28, no. 15, pp.
1005–1019, 2014.
[23] Y. Hirata, A. Kaisumi, K. Yamaguchi, and K. Kosuge, “Design ofhandling device for caging and aligning circular objects,” in 2011 IEEE
Int. Conf. on Robotics and Automation, 2011, pp. 4370–4377.
[24] K. Yamaguchi, Y. Hirata, A. Kaisumi, and K. Kosuge, “Design of parts
handling and gear assembling device,” Proc. - IEEE Int. Conf. Robot.
Autom., vol. 1, no. c, pp. 2570–2577, 2012.
[25] Yong Yu, K. Takeuchi, and T. Yoshikawa, “Optimization of robot hand
power grasps,” in Proceedings. 1998 IEEE International Conference on
Robotics and Automation, 1998, vol. 4, pp. 3341–3347.
[26] T. Yoshikawa, T. Watanabe, and M. Daito, “Optimization of powergrasps for multiple objects,” in Proceedings, IEEE International
Conference on Robotics and Automation, 2001, vol. 2, pp. 1786–1791.
[27] T. Omata and K. Nagata, “Rigid body analysis of the indeterminate
grasp force in power grasps,” IEEE Trans. Robot. Autom., vol. 16, no. 1,
pp. 46–54, 2000.
[28] John H. Bickford, An Introduction to the Design and Behavior of Bolted
Joints, Second edi. 1990.

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