• force and torque measurements
• human grasp
• intrinsic tactile sensing
• wearable

Measurement of contact forces between hand and grasped objects is a necessity for a wide array of studies on human grasping. This work presents ThimbleSense, an individual-digit wearable tactile sensor built by assembling a pair of shells around a six axis force/torque sensor. By exploiting the integration with an active marker-based motion capture system, this device also simultaneously collects information about absolute position and orientation of the fingertip, which in turn allows to obtain position of contacts and force components expressed in a global reference frame. Through use of the intrinsic tactile sensing algorithm that was first introduced in Bicchi (1993), it is also possible to obtain the position of contact points.

ThimbleSense can be employed to grasp a variety of objects, while still retaining the complete force/torque measurements that are generally not obtainable with other wearable approaches. This makes it a powerful and versatile measurement tool, that can be used to study various aspects of the human hand: for example investigation of force synergies, which has interesting applications in the construction of robotic hands.

Validation of the device is a mandatory step before performing novel research: in this work qualitative and quantitative validations are proposed that assess both reliability of measurements and differences with respect to bare finger grasping. It will be shown that measurements are fairly accurate, with force measurement errors of the order of 0.1 N and contact point position estimation errors of the order of the millimeter. Moreover, while the tactile feedback impairment caused by wearing rigid sheaths affects grasping, the validation experiment focusing on evaluating this effect will show significant indications that this can be overcome through training.