IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 6, DECEMBER 2010 871
Design of a Novel Bimanual Robotic System
for Single-Port Laparoscopy
Marco Piccigallo, Umberto Scarfogliero, Member, IEEE, Claudio Quaglia, Gianluigi Petroni,
Pietro Valdastri, Member, IEEE, Arianna Menciassi, Member, IEEE, and Paolo Dario, Fellow, IEEE
Abstract—This paper presents the design and fabrication of
Single-Port lapaRoscopy bImaNual roboT (SPRINT), a novel tele-
operated robotic system for minimally invasive surgery. SPRINT,
specifically designed for single-port laparoscopy, is a high-dexterity
miniature robot, able to reproduce the movement of the hands of
the surgeon, who controls the system through a master interface.
It comprises two arms with six degrees of freedom (DOFs) that
can be individually inserted and removed in a 30-mm-diameter
umbilical access port. The system is designed to leave a central
lumen free during operations, thus allowing the insertion of other
laparoscopic tools. The four distal DOFs of each arm are actuated
by on-board brushless dc motors, while the two proximal DOFs of
the shoulder are actuated by external motors. The constraints gen-
erated by maximum size and power requirements led to the design
of compact mechanisms for the actuation of the joints. The wrist
is actuated by three motors hosted in the forearm, with a peculiar
differential mechanism that allows us to have intersecting roll–
pitch–roll axes. Preliminary tests and validations were performed
ex vivo by surgeons on a first prototype of the system.
Index Terms—Bimanual robot, miniature robotic arm, mini-
mally invasive surgery, robotic surgery, single-port laparoscopy
(SPL).
I. INTRODUCTION
LAPAROSCOPIC surgery is a standard in today’s medicine.Surgical techniques of this kind consist of the use of stiff
and long instruments that are inserted in the abdomen through
small incisions, after having inflated the abdominal cavity, while
an endoscope transmits the bidimensional images of the organs
on a video screen. Although the patient benefits from the reduced
invasiveness, the surgeon’s sensory, and motor capabilities are
limited [1]. The insertion points limit the freedom of movements
of a rigid laparoscopic instrument to only four degrees of free-
dom (DOFs): this means that each reachable point inside the
abdomen can only be approached with a fixed orientation of the
instrument, and that some anatomical regions are not accessi-
ble. The insertion point acts as fulcrum constraint on the long,
stiff instruments, thus causing nonintuitive effects on the tip
movements, such as movement inversion and velocity scaling.
Manuscript received February 24, 2010; revised June 18, 2010; accepted
September 7, 2010. Date of publication October 14, 2010; date of current
version December 15, 2010. Recommended by Guest Editor K. Masamune.
This work was supported by the European Commission in the framework of
ARAKNES FP7 under European Project 224565.
The authors are with the CRIM Lab, Scuola Superiore Sant’Anna, Pisa 56025,
Italy (e-mail: m.piccigallo@sssup.it; u.scarfogliero@sssup.it; c.quaglia@
sssup.it; g.petroni@sssup.it; p.valdastri@sssup.it; a.menciassi@sssup.it;
p.dario@sssup.it).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMECH.2010.2078512
In the past few years, novel surgical techniques have been
progressing from research to clinical practice with the aim of
further reducing invasiveness and access trauma. Natural ori-
fices transluminal endoscopic surgery (NOTES) [2] is a totally
scarless technique by which it is possible to reach the peritoneal
cavity through a transluminal incision performed with flexible
instruments inserted either from the mouth, the anus, or the
vagina. Despite a clear esthetic benefit, the intentional perfora-
tion of a healthy organ and the current lack of a well-established
method for closing such a perforation make NOTES effective
mainly in the case of vaginal access [3], [4]. Additionally, at
the moment NOTES is performed with traditional endoscopic
instrumentation that is not specifically designed for this kind of
surgery [5].
A novel technique that is halfway between traditional laparo-
scopic surgery and NOTES is single-port laparoscopy (SPL),
which consists of a single incision at the umbilicus through
which multiple instruments can be placed [6]. This seems to
have more possibilities to be accepted as a standard practice in
a short period since it allows a direct access to the abdominal
cavity by exploiting a pre-existing scar, thus avoiding additional
incisions on the patient’s body. However, SPL has more limita-
tions than the laparoscopic approach, because it does not allow
triangulation from two different points, thus severely limiting
the dexterity of the surgeon, although several ad hoc instruments
have been developed and are already on the market [6], [7].
Furthermore, retraction of the organs is hampered, and this is
another issue that led to research and development of novel
devices and techniques [8].
The introduction of robotics in surgery generated a tremen-
dous impact, with over 1000 surgical robots in regular clini-
cal use worldwide, and research and development at over 100
universities [9]. In particular, the da Vinci Surgical System
(Intuitive Surgical, Inc., Sunnyvale, CA) solved the dexterity
problems of traditional laparoscopic surgery with a teleoper-
ated master–slave manipulator that comprises a “master” con-
sole from which the surgeon controls the movements, while
the “slave” part acts directly on the patient [10]. Thanks to an
advanced cable-drive mechanism (EndoWrist, Intuitive Surgi-
cal, Inc., Sunnyvale, CA), the natural movement of the human
wrist is almost completely restored on the teleoperated surgical
instrument [11]. Additionally, stereoscopic vision enables the
surgeon to perceive depth. These innovative features reduce by
far the complexity of laparoscopic execution of certain proce-
dures, such as suturing, still preserving the minimally invasive
approach, with typically four incisions. Recently, the da Vinci
Surgical System has been applied also to NOTES [12] and to
1083-4435/$26.00 © 2010 IEEE
872 IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 6, DECEMBER 2010
Fig. 1. 3-D simulation showing the concept of the bimanual robot for SPL.
SPL [13], [14] demonstrating that both these procedures are fea-
sible using the current robotic system, though, with considerable
limitations [15].
Robotic systems designed specifically for NOTES and SPL
approaches have the potential of making scar-less surgery ef-
fective and reliable, thus finally realizing its full potential and
paving the way to the next generation of surgical robots. Sev-
eral robotic solutions have already been specifically designed
for NOTES [16]–[18]. However, the lack of a stable anchoring
and the size constraint imposed by the endoluminal access pre-
vent them to reach the same performance in terms of force and
speed as the da Vinci Surgical System. Other robotic devices
are being studied, designed specifically for SPL [19], [20]. A
robotic system designed for SPL may benefit from both a di-
rect and rigid link with an external support and a considerably
large diameter of the access port. This approach has been pur-
sued by the authors in designing a novel bimanual and modular
robotic system to be used in single-port surgery. This paper
presents the design and prototyping of Single-Port lapaRoscopy
bImaNual roboT (SPRINT). In particular, the design of mech-
anisms and solutions that allow the actuation of two 6-DOF
robotic arms through an umbilical access port is reported. Sec-
tion II illustrates the concept of the system, while in Section III a
detailed description of the robot is presented. In Section IV, the
performances of the first prototype of single arm are discussed
together with some test results. Section V draws the conclusion
and underlines future developments.
II. THE SPRINT ROBOTIC SYSTEM
SPRINT is a multiarm robot aimed at enabling bimanual
interventions with a single access port (Fig. 1).
The robotic arms are introduced in the abdomen through a
cylindrical access port. The navel is surgically considered as a
natural scar and it can be used to gain access to the abdomen in a
practically scar-less way. According to medical constraints, the
maximum diameter achievable of the orifice is 30–35 mm [6].
The umbilical access port has been specifically designed to
allow the insertion of each arm separately, and each arm could
be removed in order to clean or replace the tool (Fig. 2).
The surgeon controls the robotic arms in a master–slave con-
figuration through a dedicated console, and the robotic arms
Fig. 2. Phases of insertion of the robotic arms, showing how two arms can fit
through the umbilical access port (a) and (b) and be kept in working position by
a central holder (c) and (d).
reproduce the movements of the surgeon’s hands. The advan-
tages of this robotic platform is that surgeon has more control
on the operating room respect to the da Vinci system, while
the resulting apparatus is much less bulky and could lead in the
future to a rapid set-up of the operating room.
Up to four arms can be inserted: in addition to the two main
arms, a stereoscopic-camera holder and, for example, a retractor
could be introduced. A central lumen of 12 mm is left open
after the insertion of the arms, and assistive tools could be
inserted for additional tasks (e.g., hemostatic sponge, suturing
needle, and wire). Each robotic arm has six active DOFs plus the
gripper, arranged in a serial configuration, and it is designed for
achieving a large workspace, necessary for completing surgical
tasks while attached to the umbilical access port. As regards
the desirable robotic arm diameter, keeping it in the range of
18 mm would allow us to extend the impact of the presented
design from SPL to NOTES, following a similar approach to the
one proposed in [17], where a 17-mm-diameter bimanual robot
is introduced endoscopically through the esophagus to perform a
NOTES cholecystectomy. For the same reason the total length of
each robotic arm has been targeted to 120 mm. The limited size
of the robot implies strong mechanical constraints in the design,
taking into account the force and speed needed for executing
a variety of surgical tasks. The arm would be inserted in the
umbilical access port parallel to the axis of the insertion cylinder.
A guiding rail could be used during the insertion to facilitate or
automatize the insertion motion. As the arms reach the bottom
of the umbilical port, they have to be rotated by 90◦, reaching
the operative configuration as shown in Fig. 2(c). This operation
is allowed by a cable-driven joint placed at the base of the arm,
operated by external motors. As described later, this joint is not
present in the first robot prototype, mainly used for testing the
design and dexterity of the arm itself. Guiding rails on which
the robotic arms slide ensure the proper rigidity to the system.
The procedure for the insertion of the arms would consist of
the following steps:
1) incision of the abdomen at the navel;
2) insertion of the umbilical access port with panoramic
camera;
3) insertion of the stereoscopic camera supporting arm (not
shown in Fig. 2);
PICCIGALLO et al.: DESIGN OF A NOVEL BIMANUAL ROBOTIC SYSTEM FOR SINGLE-PORT LAPAROSCOPY 873
Fig. 3. Schematic drawing of one arm showing the kinematic configuration.
4) insertion of the first operative arm [Fig. 2(a)];
5) insertion of the second operative arm [Fig. 2(c)];
6) insertion of additional tools if needed.
In the design of the access port, it is fundamental to guarantee
a safe removal of the robotic arms also in case of misfunctioning,
and the possibility of folding the robot back into the introduction
cylinder must not be precluded. Thus, the arms are back-drivable
enough to be retrieved in case of failure inside the insertion port
pulling them from outside.
The use of guiding rails on the insertion cylinder, and the
design of the transmission system, allows the insertion of addi-
tional smaller arms on the upper and lower side. As previously
indicated, one slot would be used for a small arm with a stereo-
scopic camera, while the other could be useful for retraction, for
positioning lightening fibers or a camera, and for introducing
sensors or additional tools. The whole system can be held by a
positioner that keeps the introduction cylinder in fixed position
during the operation.
The following sections present the design chosen for actuat-
ing six DOFs in a 18-mm-diameter arm, and the implemented
mechanical solutions are described in detail.
III. SYSTEM DESCRIPTION
As already described in Section II, the main part of the sys-
tem comprises two arms for bimanual operations inside the
abdomen. The robot is inserted through a single access port
in the navel, with an incision of about 30–35 mm. Each arm
is a 6-DOF manipulator in an anthropomorphic serial config-
uration. The arrangement of DOFs in the kinematic chain was
chosen to match the workspace and dexterity required by sur-
geons that collaborated in defining these specifications. The dis-
tal DOFs used for positioning are roll–pitch–pitch, followed by
a roll–pitch–roll compact spherical wrist with intersecting axes
(Fig. 3); therefore, each point of the workspace can be reached
with any orientation (Fig. 4). Being the abdomen inflated, the
maximum distance (with the arm in the straight position) be-
tween the base of the arm and the point of intervention could be
up to 275 mm, and we designed the arm accordingly [21].
The requirements for selecting actuators and designing the
mechanisms have been evaluated considering the measurements
reported in the literature. The typical forces that a laparo-
scopic device should withstand are reported in [22] and [23].
Fig. 4. 2-D graphical representation of the workspace of one robotic arm.
Performance, in terms of force and speed, of other teleoperated
systems for surgery have also been taken into account and eval-
uated [10], [24]. Forces exerted on the tip do not usually exceed
5 N, while the mean gripping force needed is measured to be
about 10 N. A speed of the joints of at least 360◦/s is necessary
for the slave robot in order to follow the surgeon’s movement at
the master interface [25].
The design has been carried out taking into account these re-
quirements. Although some robots for SPL use a flexible trans-
mission with external actuators, like those described in [19]
and [20], a configuration featuring most of the motors embed-
ded has been preferred for the SPRINT robot. Having a rigid
transmission allows higher stiffness and the possibility of exert-
ing higher torques. On the other hand, miniature cable/pulleys
mechanisms are mostly suited for 3-DOF wrists, while for SPL,
where both the arms are inserted through the same port, up to
seven DOFs are required for each internal arm in order to per-
form traditional operations. Such a dexterity requires roll joints,
which may be prohibitive to actuate by cable-driven mecha-
nisms, resulting in a bulky and complex system. Moreover, the
selected motors are already commonly used in dental applica-
tions, and are sterilizable on request.
The torque applied on the joints depends on the present po-
sition of the tip, but in the worst case the shoulder joint should
be capable to generate a torque equal to the force applied on the
end-effector times the sum of all the link lengths. This implies
a value of power up to 4 W for the proximal joints and about
1 W for the wrist, considering feasible values for the link lengths
(about 60 mm). However, small electric motors cannot exert the
power needed to actuate the shoulder joint. Considering the
strict size requirements, mainly on the diameter of the links
(18 mm), it is not feasible to put all the six actuators inside
the arm; hence, the motors operating the two proximal joints
have been placed outside. Restrictions on the size and power of
the external actuators are much less critical; however, mechan-
ical power must be transmitted from the motors to the proximal
joints by a rigid or flexible mechanical transmission. In the final
design, as described in Section II, both the main arms should
be introduced from a cylindrical tube and then the first link
should be rotated by 90◦, so that the link axis and tube axis are
perpendicular (Fig. 2). A cable-driven transmission between ex-
ternal motors and joints J1 and J2 (with the notation of Fig. 3)
is, therefore, the most suitable solution, according to the main
874 IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 6, DECEMBER 2010
Fig. 5. Computer-aided design drawing of the shoulder mechanism.
concept of the system described in the previous section and
depicted in Figs. 1 and 2. However, for the first prototype de-
scribed in this paper, a rigid shaft transmission has been chosen
in order to simplify the fabrication and to prove the concept of
the proposed design.
A. Shoulder Mechanism
The mechanism that activates the two proximal joints (i.e.,
the shoulder) consists of a system of bevel gears arranged in a
differential configuration (Fig. 5). Bevel gear a1 transmits the
movement to the roll joint (J1), while bevel gear a2 transmits
the movement to the pitch joint (J2). Being the two shafts of
bevel gears a3 and a4 coaxial, the mechanism allows us to
transmit the mechanical power to the pitch joint J2 overcoming
the first roll joint J1, implying at the same time that the two
movements are kinematically coupled.
Defining the gear ratio Ni,j between two consecutive gears
as
Ni,j =
zi
zj
(1)
where z is the number of teeth, i and j are the leading and
follower gears, the equations relating joint movements θJ 1 and
θJ 2 to the rotation θin,1 , θin,2 , respectively, of the gears a1, a2
can be expressed as follows:{
θJ 1 = θin,1Na1,a3
θJ 2 = θin,2Na2,a4Na5,a6 − θin,1Na1,a3Na5,a6. (2)
The two input bevel gears a1 and a2 are actuated by two
externally positioned dc motors (Faulhaber 2342). These are 18-
W motors coupled with 43:1 gearheads, so that the two proximal
joints can exert a torque of 700 N·mm at 540◦/s.
As shown in Fig. 5, two long shafts, placed inside the inser-
tion tube, are used to transmit mechanical power to the bevel
gears a1 and a2. As discussed at the end of the previous sec-
tion, this rigid transmission has been chosen only for the first
prototype in order to simplify manufacturing and validate the
shoulder mechanism. In the next prototype, currently under de-
sign, the same mechanism depicted in Fig. 5 will be used, but
a different kind of transmission will be implemented to actuate
gears a3 and a4: each gear will be connected to a cable-driven
pulley by a purposely studied design. This will allow us to add
a rotational joint while preserving the transmission of motion to
Fig. 6. Schematic of a planar 2-DOF robot that shows the relation between
the rotational speed of the two links during a linear retraction motion.
the subsequent J1 and J2 joints from the external motors. The
additional rotational joint will be required to rotate the arm in
the operative position after the insertion (Fig. 2(b)).
B. Elbow Mechanism With On-Board Actuation
The elbow, corresponding to J3 in Fig. 3, is actuated by a
brushless dc motor placed in the rigid link connecting J2 to J3.
The motion is transmitted from the arm axis to the perpendicular
joint axis by means of two bevel gears coupling the motion of
forearm to the motor. The actuator is a Faulhaber 1226, able to
provide 9 W of power within 12 mm diameter. The reduction
gear ratio is 161:1; therefore, the motor is able to exert a torque
of 360 N·mm at a speed of 1188◦/s. The power and the reduc-
tion gear of the motor have been chosen in order to achieve a
rotational speed double respect to the shoulder, while allowing
the desired maximum force at the tip (5 N). The dimensioning
criterion of double speed in the elbow allows us to keep a maxi-
mum linear speed of the tool along a straight line, which can be
useful during the retraction motion. Fig. 6 shows a schematic
2-DOF manipulator, where for clarity rotational speeds ϕ˙ and
ϑ˙, respectively, of link 1 and link 2 are positive when bringing
positive retraction motion y˙. As in our case the two links (arm
and forearm) measure about the same length, the motion is ver-
tical when ϕ˙ = θ˙. The relative elbow rotational speed of link 2
with respect to link 1 is ϕ˙r = ϕ˙ + θ˙, and it becomes ϕ˙r = 2θ˙
during linear motion. Thus, the optimal performances can be
achieved when the motor of the elbow is chosen for a reference
speed that is twice the speed of the shoulder.
Regarding the range of motion of the elbow joint, it is essential
that the maximum bending exceeds significantly 90◦, in order
to preserve the wide workspace, especially needed for bimanual
operations. To allow a wide inward rotation, the elbow joint has
been designed with the axis of rotation J3 not intersecting the
motor axis (Fig. 7), but translated of a few millimeters. This also
allows us to relief the motor shaft from the axial and radial forces
created by the bevel gear, while shortening the link length. As
can be noticed in Fig. 7, the motor shaft s1 rotates the spur gear
b1 that leads the gear b2 and thus transmits the rotation to the
forearm through the couple of bevel gears b3 and b4. In this way
the elbow can reach an inward motion of +130◦, while allowing
an extension of −55◦. Considering Nb1,b4 as the gear ratio of
the whole mechanism shown in Fig. 7, the angular displacement
PICCIGALLO et al.: DESIGN OF A NOVEL BIMANUAL ROBOTIC SYSTEM FOR SINGLE-PORT LAPAROSCOPY 875
Fig. 7. Structure of the elbow allows wide range of motion and reduce the
articulation length.
Fig. 8. Disposition of the three motors in the forearm for the wrist actuation.
θJ 3 of the joint can be written as follows:
θJ 3 = Nb1,b4θin,3 (3)
where θin,3 is the angular position of input gear b1.
C. The Wrist Mechanism With On-Board Actuation
As introduced previously, the elbow and wrist of the robotic
arm have on-board actuation. The forearm hosts three Maxon
EC6 brushless motors of 6 mm in diameter, and a mean power
of 1.2 W each, actuating the distal 3 DOFs (roll–pitch–roll) of
the wrist. Each motor is equipped with an encoder and a 221:1
reduction gear head, providing a nominal torque of 50 N·mm,
and a speed of 600◦/s. The three axes are intersecting thanks to a
particular design of the transmission mechanism. In the 18 mm
diameter, the three motors are aligned along the forearm axis
(Fig. 8).
While one motor actuates directly the roll J4, the other two
are coupled in a differential mechanism that actuates the pitch
J5 and the roll J6. Due to the size constraints, the motors are
mounted with the axes parallel to the forearm. The joint angle
θJ 4 can be simply computed as follows:
θJ 4 = N4θin,4 (4)
where N4 is the reduction ratio of joint J4. As shown in Fig. 9,
the differential mechanism is composed of a triplet of three bevel
gears for each motor. The two triplets are coupled by spur gears
c7, c8, c9 that build up the differential. The gears c2 and c5 are
idle on the shaft s5, while gears c3 and c6 are rigidly attached
respectively to spur gears c7 and c8. The spur gear c9 rotates the
Fig. 9. Differential mechanism used for the two distal DOFs of the robotic
arm.
shaft s6 resulting in the roll motion J6. When the two motors
rotate in the same direction with the same speed, only the pitch
J5 is actuated along the shaft s5, while the roll J6 is actuated
when the two motors rotate in opposite direction and the same
speed.
As previously described for the shoulder mechanism, the
equations relating pitch and roll rotations to motor’s motion
can be derived as function of the motor’s rotations θin,5 and
θin,6 . An equal gear ratio has been selected for the two triplets
of bevel gears composing the differential, and for the two spur-
gear couples
{
Nb = Nc4,c5 = Nc1,c2 = Nc6,c5 = Nc3,c2
Ng = Nc7,c9 = Nc8,c9.
(5)
Thus, θJ 5 and θJ 6 can be derived as follows:⎧⎨
⎩
θJ 5 =
θin,5 − θin, 6
2 Nb
θJ 6 =
θin,5 + θin, 6
2 Ng.
(6)
D. Overview of the Control Architecture
For the first prototype of the robot, the PHANTOM Omni
(SensAble Technologies, Woburn, MA) has been chosen as the
master interface because it can sense the position in 6 DOFs.
Four externally positioned EPOS 24/1 position controllers by
Maxon are used to drive the four internal motors, while two
Faulhaber MCDC 3006C controllers are used to drive the ex-
ternal motors. Encoders embedded in the motors provide the
current relative angular position of each motor shaft (θmi), thus
enabling a position control. All the drivers communicate via
CAN-Bus with a Linux-based personal computer (PC). A C++
software that runs on the PC reads the position and orientation of
the master from the IEEE 1394 interface and sends the desired
positions of the motors to the controllers through a CAN-PCI
card (PEAK-System Technik, Germany). Each motor controller
implements a local closed-loop by means of a proportional-
integral-derivative position control. The workspace of the mas-
ter is thus mapped on the workspace of the slave.
At each instance of the control loop the absolute position
and orientation of the master are acquired and then computed
relatively to the starting position, chosen by the user at the
876 IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 6, DECEMBER 2010
beginning of the procedure, as follows:
RM rel = RTM start · RM (7)
where RM is the absolute rotation matrix of the master, RM start
is the rotation matrix of the starting position, and RM rel is
the rotation relative to the starting position. The desired 3×3
rotation matrix of the end-effector with respect to the base frame
is thus computed as follows:
R06 = R
0
6 start · RM rel (8)
where R06 start is the rotation matrix of the starting position of the
end-effector. Similarly, the desired position of the end-effector
is computed as follows:
P = P M rel + P start (9)
where P M rel is the position of the master, relative to the
its starting position P M start , and P start is the starting po-
sition of the slave’s end-effector. The vector of joint angles
θJ = {θJ 1 · · · θJ 6} is then computed by inverting the kinemat-
ics of the robot. As the 6 DOFs arm has a spherical wrist, the
calculation of the first three joint angles can be decoupled from
that of the last three. The position of the wrist center, P w , can
be determined as follows:
P w = P − z6 · d (10)
where d is the distance between the wrist center and the tool
and z6 is the unit vector that represents the z-axis of the tool
reference frame. P w can be written as a function of the joint
angles θJ 1 , θJ 2 , and θJ 3 , while the three joint angles can be
computed by inverting the kinematics. Then, the last three joint
angles are computed by solving the following equation:
R36 = R
0
3
T · R06 start · RM rel. (11)
The vector of the angular positions of the output shafts of the
motors θin = {θin,1 . . . θin,6} is then computed by inverting the
systems of (2)–(4), and (6). The vector θm = {θm1 . . . θm6} of
the target angular positions of each motor is transmitted to the
motor drivers and it is computed as follows:⎧⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨
⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩
θm1 =
θJ 1
Nm1Na1,a3
θm2 =
θJ 2 + θJ 1Na5,a6
Nm2Na2,a4Na5,a6
θm3 =
θJ 3
Nm3N3
θm4 =
θJ 4
Nm4N4
θm5 =
NbθJ 6 + NgθJ 5
NbNgNm5
θm6 = −−NbθJ 6 + NgθJ 5
NgNm6Nb
(12)
where Nmi is the gearhead ratio of motor i.
IV. PRELIMINARY TESTS AND PERFORMANCE
Characteristics and performance values of the robotic arm
are summarized in Table I. A single arm has been fabricated
TABLE I
PERFORMANCE
Fig. 10. Picture of the testbed for the pick-and-place exercise.
to validate the concept of the proposed design and to assess
the validity of the system’s dimensioning. The total length of
this first prototype, from the first joint to the base of the tool,
is 142 mm: 64 mm for the arm, 70 mm for the forearm, and
8 mm for the distal link. The maximum diameter of the arm is
23 mm, despite the link between the shoulder and the elbow is
16 mm in diameter. The diameter can be reduced by using higher
precision computer-numerical-control (CNC) machining in the
fabrication of some parts. Joint limits are [−90◦, 90◦] for J1,
[−45◦, 90◦] for J2, [−55◦, 130◦] for J3, [0, 360◦] for J4 and
[−60◦, 60◦] for J5 and [0, 360◦] for J6. Each joint of the first
prototype has a backlash of about 2◦ that causes an error of about
8 mm of the end-effector (measured with a magnetic localization
system). We expect to reduce this value to 2 mm maximum in
the next prototype by using more precise couplings and a higher
teeth number in the gears. Considering each joint at its nominal
speed, the tool linear speed is around 1 m/s, depending on the
robot configuration, while the maximum force exerted has been
measured to be 5 N. This is a preliminary confirmation that
the proposed design meets the requirements we adopted at the
beginning of the design phase.
Pick-and-place tests have been carried out in which the proto-
type has been used by six people (five engineers and an experi-
enced surgeon). A setup has been prepared with some rings and
PICCIGALLO et al.: DESIGN OF A NOVEL BIMANUAL ROBOTIC SYSTEM FOR SINGLE-PORT LAPAROSCOPY 877
Fig. 11. Close-up picture of the SPRINT arm prototype.
holders in order to verify the dexterity of the arm in a master–
slave teleoperated configuration. The aim of the exercise was to
pick up a ring with the robotic arm from one ring holder and
place it on another one. The distance between the two ring hold-
ers is 90 mm in the horizontal direction and 60 mm in the vertical
one. Each tester was asked to perform the exercise watching the
testbed scene on a video display as captured by an endoscopic
camera (Fig. 10), positioned in the same configuration as in a
real surgical intervention. A hook-shaped tool has been used as
end-effector for these preliminary trials (Fig. 11), as the exer-
cises were limited to the validation of the robotic-arm design
and actuation. For the next prototype, a closing gripper will be
developed. Testers of the system performed 10 pick-and-place
tasks and they needed an average time of 25 s to move one
ring from one stick to another, without any specific previous
training on the SPRINT arm. Based on these encouraging re-
sults, we can envisage a quite fast learning curve for operating
the system. However, additional extensive tests are required in
order to further support this conclusion. The average latency
between the movement acquired at the master side and the re-
sponse of the robotic platform is about 16 ms. This value was
computed by comparing the desired trajectory, imposed by the
user on the master interface, with the readings of the motor en-
coders. In particular, such a total delay time includes the reading
of master position, the computation of inverse kinematics, trans-
mission of the target positions to each motor drivers over the
CAN-Bus, and the low-level closed loops on motor positions.
Regarding the electromechanical bandwidth of the robotic arm,
a value of 5 Hz has been estimated by a model of the system.
V. CONCLUSION AND FUTURE WORKS
In this paper, a novel robotic platform named SPRINT for SPL
in a master–slave configuration has been presented. To the best
of the authors’ knowledge, this is the first bimanual teleoperated
robot purposely designed for an umbilical SPL access that has
been reported so far. The system allows high dexterity, thanks
to 6 DOFs for each arm, and can exert 5 N force on the tip while
moving at a speed comparable to the surgeon’s hand. Each arm
can be introduced and removed separately, thus allowing us to
change the surgical instrument on the fly. Two additional smaller
arms can be inserted in the same access port. A first single-arm
prototype of the design described in the paper has been fabri-
cated, assembled and tested in a pick-and-place exercise. Future
works will address a reduction in robot size and diameter. It is
already possible to reduce the diameter of some links from cur-
rent 23 mm to 18 mm by using high-precision CNC machining.
The next step will also involve the design of cable-transmission
mechanisms in the shoulder, in order to facilitate the insertion
and positioning of the arms in the operative configuration. Tool
exchange during operations and the durability of the platform
will also be investigated in future developments and extensive
tests. A six-axis load cell, such as the 17 mm diameter Nano
17 (ATI, Apex, NC), will be placed in between the tool and
the wrist in order to enable both force feedback and position-
force teleoperation [26], [27]. Furthermore, custom embedded
electronics will be designed and integrated inside the arm and
forearm in order to improve the performance of the control loop
and to minimize the number of external cables. An improvement
in the latency can be achieved by moving the control system to
a real-time dedicated operative system and by adopting a com-
munication faster than the CAN-Bus. In conclusion, despite a
lot of work is still ahead of us before the final deployment of the
complete platform, the design of a robotic system for umbilical
SPL access may pave the way to the next generation of surgical
robots, pursuing a scar-less approach for the sake of a faster
recovery and an improved cosmetic effect for the patient.
ACKNOWLEDGMENT
The authors would like to thank N. Funaro, A. Melani,
G. Favati, and C. Filippeschi for prototype manufacturing and
also they are grateful to medical doctors A. Cuschieri, M.O.
Schurr, and A. Peri for their medical advice.
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Marco Piccigallo received the M.Sc. degree in me-
chanical engineering from the University of Pisa,
Pisa, Italy, in 2003, and the Ph.D. degree in
biorobotics science and engineering jointly from the
IMT Institute for Advanced Studies, Lucca, Italy, and
the Scuola Superiore Sant’Anna, Pisa, in 2008.
Since 2004, he has been with the CRIM Lab,
Scuola Superiore Sant’Anna. His current research
interests include biomedical robotics and computer-
assisted surgery.
Umberto Scarfogliero (M’06) received the Master’s
degree in mechanical engineering from the Politec-
nico di Milano, Milan, Italy, in 2004, and the Ph.D.
degree in biorobotics science and engineering jointly
from the Scuola Superiore Sant’Anna, Pisa, Italy, and
the IMT Institute for Advanced Studies, Lucca, Italy
in 2008.
Since 2005, he has been with the CRIM Lab,
Scuola Superiore Sant’Anna di Pisa, where he is in-
volved in the design of miniature legged robots. His
research interests include mechanism design and op-
timization of surgical robotics.
Claudio Quaglia received the Master’s degree in me-
chanical engineering from the University of Pisa,
Pisa, Italy, in 2005. His degree thesis focused on
the employment of a triaxial accelerometer for tool
condition monitoring in automatic machining. Since
2006, he has been working toward the Ph.D. degree
in bioengineering at the Scuola Superiore Sant’Anna,
Pisa.
His current research interests include medical
robotics and micromechanical systems.
Gianluigi Petroni was born in 1984 in Lucca, Italy.
He received the M.Sc. degree in biomedical engineer-
ing from the University of Pisa, Pisa, Italy, in 2009.
He is currently working toward the Ph.D. degree in
microbiorobotics at the Scuola Superiore Sant’Anna,
Pisa.
His current research interests include biorobotics
and teleoperated control systems.
Pietro Valdastri (M’05) received the Master’s de-
gree in electronic engineering (Hons.) from the Uni-
versity of Pisa, Pisa, Italy, in 2002, and the Ph.D.
degree in bioengineering from the Scuola Superiore
Sant’Anna, Pisa, in 2006.
He is currently an Assistant Professor of Biomed-
ical Robotics at the Scuola Superiore Sant’Anna,
where he is engaged in research on implantable
robotic systems and active capsule endoscopy. He
is involved in several European projects regarding
the development of minimally invasive and wireless
biomedical devices.
Arianna Menciassi (M’00) received the Master’s de-
gree in physics from the University of Pisa, Pisa, Italy,
in 1995, and the Ph.D. degree from the Scuola Supe-
riore Sant’Anna, Pisa, in 1999.
She is currently an Associate Professor of Biomed-
ical Robotics at the Scuola Superiore Sant’Anna. Her
current research interests include biomedical micro-
and nanorobotics for the development of innovative
devices for surgery, therapy, and diagnostics. She is
the coauthor of more than 130 international papers,
about 70 in ISI journals, and of five book chapters on
medical devices and microtechnologies.
Paolo Dario (F’ 02) received the Master’s degree in
mechanical engineering from the University of Pisa,
Pisa, Italy, in 1977.
He is a Professor of Biomedical Robotics at the
Scuola Superiore Sant’Anna, Pisa, where he super-
vises a team of about 150 young researchers. His cur-
rent research interests include biorobotics, including
mechatronic and robotic systems for rehabilitation,
prosthetics, surgery, and microendoscopy. He is the
author of more than 160 ISI journal papers, many
international patents, and several book chapters on
medical robotics.
Dr. Dario is a recipient of the Joseph Engelberger Award as a Pioneer of
Biomedical Robotics.