In minimally invasive surgery, indirect contact is established and haptic feedback is impaired. Stiffness has been generally related to hardness perception. However, hardness perception in terms of viscoelasticity has not up to this point, draw sufficient attention. In this study, considering the viscoelasticity of human tissues and organs, we assessed the effect of damping on hardness perception along with spring constant.

Dampers which exhibit both elastic and viscous properties were designed and manufactured with 3D printing technology. Elasticity was provided by the internal spring while viscosity by the liquid inside the cylinder. A series of damper with distinct spring constant and damping coefficient were produced.

In the experiment, the capacity of distinguishing ha...[ Read more ]

In minimally invasive surgery, indirect contact is established and haptic feedback is impaired. Stiffness has been generally related to hardness perception. However, hardness perception in terms of viscoelasticity has not up to this point, draw sufficient attention. In this study, considering the viscoelasticity of human tissues and organs, we assessed the effect of damping on hardness perception along with spring constant.

Dampers which exhibit both elastic and viscous properties were designed and manufactured with 3D printing technology. Elasticity was provided by the internal spring while viscosity by the liquid inside the cylinder. A series of damper with distinct spring constant and damping coefficient were produced.

In the experiment, the capacity of distinguishing hardness was evaluated by a magnitude estimation method. Eleven dampers described above were adopted in the experiment including one reference damper. Given a reference magnitude of hardness, rating values of all dampers were collected. Two different ways of holding the tool were adopted to investigate sensitivity of human perception in specific tasks.

The results show that force application correlated very highly with hardness perception (Pearson correlation: grip: 0.725, thumb: 0.77), followed by spring constant (Pearson correlation: grip: 0.721, thumb: 0.662) and damping coefficient (Pearson correlation: grip: 0.545, thumb: 0.609). In addition to spring constant, damping contributes to hardness perception for a viscoelastic material from 22% to 41%. Damping also contributes a further 4% to 6% to perceived hardness with thumb on top. The major factor in hardness perception in this context is force application. The same strategy was utilized to evaluate hardness, whereas different amounts of force may be applied with a grip using two-finger and another with a thumb on top of the tool. This study emphasized the role of force application in hardness perception. Relative contribution of spring and damping component to perceived hardness was investigated.