IEEE Robotics & Automation Magazine - December 2015 - 55

Figure 1. The SynGrasp GUI.

kinematic chain. A table containing the DH parameters of
each finger has to be provided to describe a hand. A cell
named DHpars, which has as many elements as the number
of fingers, collects in each element a matrix with four columns and as many rows as the number of joints of each finger. Each row represents the DH parameters, allowing us to
define the joint with respect to the preceding one or with
respect to the base reference frame. The function
SGmakeHand() defines a hand structure whose arguments
are defined by the function SGmakeFinger().
The hand configuration is defined by the joint variables
q = 6q 1 gqn q@T ! R nq . The user can modify the hand configuration through the function SGmoveHand().
The toolbox can be used to investigate the properties of
hands in which the joint displacements are coupled mechanically or by means of a suitable control algorithm. In the case
of human hand synergies, this coupling has been described
as a synergy matrix associated to the hand model [8]. For the
20-DoF model of the human hand available in the toolbox,
the synergy matrix refers to the data collected in [5] and is
provided through the function SGsantelloSynergies.
The function SGdefineSynergies() associates to a specific hand model the relative coupling matrix. The function
SGactivateSynergies()activates a synergy or a combination of synergies on the hand. The function SGplotSyn()draws the movement corresponding to the activation
of one synergy. It draws on the same plot the hand in the initial reference configuration and in the configuration obtained by activating one or more synergies.
Grasp Definition
The definition of an object and the contact point locations
are fundamental for grasp analysis. The object configura-

tion is described by a frame B fixed to the object with
respect to an inertial frame N fixed in the workspace. Let
u ! R 6 denote the vector representing the position and
orientation of B relative to N. Let n c be the number of
contact points. To define the constraints and the contact
forces imposed by the contact between the hand and the
object, a suitable contact model has to be introduced [19].
For each contact point i, the contact model selects the
contact force components m i ! R li, where the l i value
depends on the type of contact (e.g., l i = 3 for the hard
finger model [19]).
Together with the contact type, a grasp is defined by the
following:
1) the location and orientation of the object frame " B , with
respect to the wrist frame " N ,
2) the contact points coordinates
3) the directions normal to the contact surfaces on the contact
points.
With SynGrasp, these
parameters can be defined
In the last decade,
in two ways. The user can
directly specify the locarobotic hand design
tion of the contact points
anywhere on the hand
has particularly focused
with the function
SGaddContact(), while
on joint coupling and
SGaddFtipContact()

can be used if the contact
compliant devices.
point has to be located on
the fingertip. Given the
contact points on the hand, it is possible to create a structure
representing the grasped object through the function
SGmakeObject(). The structure for the grasped object
DECEMBER 2015

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Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2015
