Illusory Sense of Human Touch From a Warm and Soft Artificial Hand

Abstract

To touch and be touched are vital to human development, well-being, and relationships. However, to those who have lost their arms and hands due to accident or war, touching becomes a serious concern that often leads to psychosocial issues and social stigma. In this paper, we demonstrate that the touch from a warm and soft rubber hand can be perceived by another person as if the touch were coming from a human hand. We describe a three-step process toward this goal. First, we made participants select artificial skin samples according to their preferred warmth and softness characteristics. At room temperature, the preferred warmth was found to be 28.4 °C at the skin surface of a soft silicone rubber material that has a Shore durometer value of 30 at the OO scale. Second, we developed a process to create a rubber hand replica of a human hand. To compare the skin softness of a human hand and artificial hands, a robotic indenter was employed to produce a softness map by recording the displacement data when constant indentation force of 1 N was applied to 780 data points on the palmar side of the hand. Results showed that an artificial hand with skeletal structure is as soft as a human hand. Lastly, the participants' arms were touched with human and artificial hands, but they were prevented from seeing the hand that touched them. Receiver operating characteristic curve analysis suggests that a warm and soft artificial hand can create an illusion that the touch is from a human hand. These findings open the possibilities for prosthetic and robotic hands that are life-like and are more socially acceptable.

Pursuing prosthetic electronic skin

“…Prosthesis consumers value skin-like coverings for their prosthetic devices that have a similar look and feel as real skin as well as good durability 8 . It has been shown that, by tuning the modulus, viscoelasticity and temperature of a skin-like coating, the touch from a prosthetic hand can be indistinguishable from a real hand 26 . Restoring both sensory feedback and the mechanical properties of natural skin may allow patients to comfortably use their devices during intimate interactions (for example, when interacting with children) 7 .…”

“…However, to fully mimic the feel and sensory properties of skin, it is important to implement materials with low elastic moduli and good stretchability 26 . On average, biological skin is stretchable to 75% strain 34 , and this allows free movement of the joints, which experience surface strains up to 55% for the knees 35 .…”

“…On average, biological skin is stretchable to 75% strain 34 , and this allows free movement of the joints, which experience surface strains up to 55% for the knees 35 . Furthermore, coverings for prosthetics that mimic skin mechanics to make the device appear and feel more natural are popular among prosthetics users 26 . Making electronics stretchable requires new materials or fabrication approaches that provide additional degrees of movement.…”

Evaluation of the Handshake Turing Test for anthropomorphic Robots

“…We use an anthropomorphic android robot designed after a human both in terms of appearance and functionality, to such an extent that the hands have heating pads inside the palms so as to give a feeling of human touch [2]. For this experiment, both the robot hand and a human test subject's hand were covered with a white butler glove as shown in Fig.…”

Modeling thermal contact resistance at the finger-object interface

“…Based on our everyday tactile observations described above, we can expect that R c depends on surface roughness, applied force, as well as mechanical and thermal properties of the skin and the contacting material. Since quantifying the contact resistance is important for design of electronics [2][3][4][5][6], thermal displays [7], artificial hands [8], haptic devices [9], and wearable thermoelectric devices [10,11], it is important to know how to combine these physical parameters to model the value of R c .…”