ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

3. MATERIAL AND METHODS
3.1 Experiments and Data acquisition
Sixteen grasping experiments were performed over 4 bottles of different sizes, weights
and materials (Fig 1a). Six right-handed subjects with different anthropometric
characteristics were selected for the experiments, which consisted in 2 grasping tasks
with each bottle and 2 different filling levels (L1 and L2), all of them carried out
randomly within the same session (4 bottles x 2 tasks x 2 filling levels). The tasks were:
to move the bottle to a different position (T1) and to pour the bottle content into a
recipient (T2). Each experiment implied 5 repetitions of the same task, bottle and filling
level, carried out after a rehearsal session (5 identical tests). The subjects were asked to
perform the tasks in a natural way. A right-hand Cyberglove was used to collect hand
postures during the grasping experiments, after a proper calibration [16] in every
session. The glove provides the main joint angles of the hand with an acquisition rate of
15Hz. The Cyberglove system has been proved to be valid for the measurement of
hand postures during grasping tasks, ranging its sensors’ repeatability errors from 1.2º
to 5º. In a previous grasping characterization study [17] it was stated that the hand
posture was repeatable for the same subject, bottle, filling level and task. Fig 1b
displays an image of the glove with the abbreviations used for the joint angles studied in
this work: thumb and index finger metacarpophalangeal joints (MCP1,2), proximal
interphalangeal joint of the index finger (PIP2), interphalangeal joint of the thumb (IP1)
and rotation and ab/adduction of the thumb carpometacarpal joint (ROLL, ABD1).
Table 1 shows the bottles’ features: identification, material, height (h), diameter at
contact area (d), empty weight (W0), and weights at filling levels 1 (W1) and 2 (W2).
Table 2 shows the subjects’ data, including hand breadth (HB) and hand length (HL).
These hand parameters, also displayed in Fig. 2a, are representative of the hand size and
are used for scalability purposes in the grasp model developed in [3]. Fig.2b shows an
image of one of the 16 experiments. Table 3 shows the 16 experiments. Each one
implied 5 new input-target sequences, yielding a set of 480 data sequences. A statistical
analysis over the output data standard deviations (SD) was done. For each joint angle
and experiment (8 different experiments as the filling level is not significant), the SD
was computed. The mean, standard deviation and maximum values were computed for
the 48 SD values in order to compare the ANN errors with the deviations of real data.
Table 1. Features of the bottles employed in the experiments.
Bottle ID Material h(m) d(m) W0(kg) W1(kg) W2(kg)
B1 glass 0.300 0.08 0.5235 0.550 1.00
B2 plastic 0.350 0.08 0.0490 0.150 0.55
B3 plastic 0.245 0.075 0.0445 0.150 0.55
B4 Plastic 0.222 0.065 0.0285 0.150 0.55
Table 2. Features of the subjects participating in the experiments.
Subject ID Gender Age Height(m) Weight(kg) HL(m) HB(m)
S1 Male 47 0.174 82 0.186 0.088
S2 Male 38 0.185 78 0.202 0.081
S3 Female 28 0.164 69 0.165 0.077
S4 Male 40 0.173 84 0.190 0.086
S5 Male 25 0.177 76 0.195 0.085
S6 Female 35 0.171 60 0.180 0.080