A Veriﬁcation Method for TestingAbrasion in the Use of Restraint Type
Personal Care Robots
Yoji Yamada, Mao Xuewei, Kengo Yoshida, Yasuhiro Akiyama
and Shogo Okamoto

Abstract Physical stress hazards are identiﬁed as a part of the safety requirementsfor personal care robots as described in ISO 13482. We conducted a safety veriﬁcation study to clarify an inherently safe condition region in the shear stress—timerelationship: The higher the shear stress is, the smaller number of times is needed
for blister generation. For validating the veriﬁed safety data, we also built a testbed
where a manipulator is used to optimally control the position and force of a cuff incontact with a piece of porcine skin for the purpose of reproducing the contact
conditions as close as possible to those obtained when a human wears a robot.

1 Introduction
Based upon strong demands from industry, various safety test methods have beendeveloped in Japan in the framework of a nation-wide R&D project for putting
personal care robots (PCRs, hereafter) into practical use. The abstract paper reports
a part of the project activities the outcome of which includes a compilation andproposal of a V&V (Veriﬁcation and Validation) document to be standardized incompliance with the safety standard ISO 13482 for PCRs. We investigated toidentify 62 items in ISO 13482 that require new tests for one or more of the three
types of PCRs. Based upon the investigation, 34 test methods are developed anddescribed in a standard form of V&V test methods. In the test methods, the author’s
research group develops the test of physical hazard characteristics for restraint typephysical assistant robots (PARs, hereafter).
Physical stress hazards are identiﬁed from the statement in 5.9.2 of ISO 13482
stating that a PCR shall be designed to minimize or reduce physical stress or strain
Y. Yamada (&)  M. Xuewei  Y. Akiyama  S. Okamoto
Safety Intelligence Group, Department of Mechanical Science and Engineering,
Nagoya University, Nagoya, Japane-mail: yamada-yoji@mech.nagoya-u.ac.jp
K. Yoshida
Kansai Electric Power Co. Inc., Osaka, Japan© Springer International Publishing AG 2017
J. González-Vargas et al. (eds.), Wearable Robotics: Challenges and Trends,Biosystems & Biorobotics 16, DOI 10.1007/978-3-319-46532-6_34

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to its user due to continuous use. We concluded through discussions with a Japanesecompany manufacturing PARs that the risk of generating skin wounds becomes also
not negligible in such a use of restraint type PAR as to wear their cuff parts each ofwhich directly contacts human skin without any clothing in between a cuff surface
and the skin of the wearer. Later, it was also reported that friction blisters wereobserved to be generated considerably easily in the use of the PAR by a wearer
suffering liver cirrhosis. The following sections describe the test method in detail.

2 Veriﬁcation Test Method for Abrasion Risk
We develop a blister generation method for establishing a safety veriﬁcation system
focusing on skin friction trauma [1]. Porcine skin as experimental subject wasexcised from the anterior part of a pig’s shank shortly after its death, and delivered
to our lab within sixteen hours under 4 degree centigrade. Before the experiments,
each of the skin surface was shaved by a scissor, cleaned by alcohol, and theexcessive fat underneath was also cut off. In our study, the representative direction(shear direction) of force component is selected for emulating the skin surface
rubbing phenomena.
For conducting a horizontal reciprocating rubbing action, a rheometer (DHR: TAInstrument Co.) is used to exert oscillating rotational rubbing on the porcine skinwith high calibration accuracy. A piece of the porcine skin was extended and ﬁrmly
clamped between the plate with a sheet of sandpaper (40#) attached and a ﬁxation
frame. After a certain period of rubbing under oscillating shear force, the structureof the porcine skin was examined by serial sectioning at intervals of 10 lm and themicro-section is analyzed by haematoxylin and eosin (H&E), and the stained sections were observed with a microscope sequentially. The sections of both original
porcine skin without any rubbing and the microscopic appearance of porcine skinafter the ﬁrst rubbing experiment are shown in Fig. 1a, b.
It can be seen from the ﬁgures that the main epidermal structure of porcine skin,including the stratum corneum, stratum granulosum, stratum spinosum, and epidermal basal layer, keeps intact before rubbing test.
To conﬁrm the availability of the veriﬁcation data by use of porcine skin, thecharacteristics of blister generation should match those obtained in the previous
blister generation test using human skins as subjects, which was conducted by
P. F. D. Naylor in mid 1950s [2]. After some discussion on the similarity ofmechanical properties for both the human and the porcine skin, we combined theveriﬁcation data obtained through the use of both kinds of skins. In our experimental model, we set shear stress as a unit of the interactive force between theporcine skin and the rubbing head. We calculated to draw a regression curve fromthe inherently safe time points after statistical analysis including outlier one,regarded it as a pattern of inherently safe threshold, and combined it with the humansubject’s blister generation conditions as shown in Fig. 2.

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207(a). Appearance of the structure of an original porcine skin surface(intact stratum spinosum indicated by arrow)(b). Intra-epidermal clefts (indicated by arrow) after 1200s of
rubbing under shear stress value 3.2×104 Pa

Fig. 1 a Appearance of the structure of an original porcine skin surface (intact stratum spinosum
indicated by arrow). b Intra-epidermal clefts (indicated by arrow) after 1200s of rubbing undershear stress value 3.2  104 Pa
Fig. 2 Combination of
porcine skin’s and humansubjects’ blister generation
conditions

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3 Validation of the Veriﬁed Data
We conducted an experiment validating a cuff attachment in the use of a PAR after
conﬁrming the feasibility of using porcine skin for a safety veriﬁcation test. We
focused on a human subject’s “stand-up and sit-down” motion which is considered
to exhibit the largest level of relative displacement between the cuff and the skinsurface of the subject. The interaction force between the robot’s cuff and the user’s
thigh skin can be exerted repeatedly by the experimental apparatus consisting primarily of a manipulator and dummy skin built for the validation experiments.
Figure 3 shows the overview of the experimental apparatus where we adopted anadaptive controller called IFT (Iterative Feedback Tuning) to reproduce on thedummy skin the cuff motion represented by both relative displacement generated andinteractive force exerted respectively at a contact point between human skin and thecuff of a PAR [3]. Figure 4 illustrates the block diagram of the manipulator controller and Fig. 5 depicts the force reproduction in the cuff sliding direction. Threepieces of porcine skin were tested during the series of experiments, where every test
lasted for 1800s. The smallest contact area between urethane and porcine skin was
about 12  10−4 m2 and the largest shear stress applied on the porcine skin wascalculated approximately as 2.3  104 Pa to verify the safe operation condition.

Fig. 3 Overview of the experimental apparatus

Fig. 4 Control system of the manipulator

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Fig. 5 Controlled force
exerted at a contact point on
the cuff in the sliding
direction

4 Conclusion
In the paper, the authors mainly deal with his recent research and development of asafety veriﬁcation test method: We have conducted a novel study to discuss a safe
condition of not generating blisters at mechanical contact between human skin anda cuff of a restrain type personal care robot. Such wounds as blisters are estimated tohave a high risk because the probability of occurrence is high while the severity islow. An increase in the number of porcine skin samples for applying them to thedummy skin—cuff system is a part of ongoing work for biomedical veriﬁcation
with higher accuracy.
Acknowledgments This work was supported by NEDO (New Energy and Industry Organization),
Japan.

References
1. Mao, X.W., et al.: Development of a novel test method for skin safety veriﬁcation of physicalassistant robots. In: Proceedings of the IEEE International Conference on Rehabilitation
Robotics (ICORR’15), pp. 319–324, Singapore, Aug 2015
2. Naylor, P.F.D.: The skin surface and friction. Br. J. Dermatol. 67(7), 239–8 (1955)
3. Yoshida, K. et al.: Development of a safety validation test equipment for severity estimation ofwounds caused by physical assistant robot. In: Proceedings of the RSJ/SICE/JSME 20thRobotics Symposia, Karuizawa, Nagano, Japan, pp. 483–488, March 2015 (in Japanese)