This paper investigates the effectiveness of three types of haptic feedback: normal stress, tangential force, and vibrotactile stimulation. Modern prosthetic limbs currently available on the market do not provide a wide range of sensory information to amputees, forcing amputees to mainly rely on visual attention when manipulating objects. We aim to develop a haptic system that can convey information to the central nervous system (CNS) through haptic feedback. To this end, we aim to find out which type of feedback performs best under static conditions, so that it can be used to restore a sense of grasping force to amputees. We tested the three main stimulation methods by inputting a series of five force magnitudes to each haptic device, so that the device applied the corresponding feedback to the participants' finger pads. The participants then pressed on a force sensor, with the goal of applying the same level of force to a force sensor as they believed the haptic device had initially conveyed to them via their finger pads. While the subjects pressed on the force sensor, the haptic device applied a level of feedback to their forearms that corresponded to the pressure they were applying to the sensor. These tests provided fifteen numerical data per subject and a total of 180 trials for all twelve subjects. The end results indicate that even though all the stimulation methods provided a sufficient level of feedback, normal stress seems more effective than either tangential force or vibrotactile stimulation, at conveying the sense of pressure to the finger pad.

<div class=""abs_img""> <img src=""[disp_template_path]/JRM/abst-image/00270004/12.jpg"" width=""300"" /> A wearable haptic device</div> This paper presents a novel wearable haptic device that provides the user with knowledge of a vertical force, measured at the fingertips, by applying pressure at three different locations on the user’s body. Human prehension and manipulation abilities rely on the ability to convert tactile information into controlled actions, such as the regulation of gripping force. Current upper-limb prosthetics are able to partially replicate the mechanical functions of the human hand, but most do not provide any sensory information to the user. This greatly affects amputees, as they must rely solely on their vision to perform grasping actions. Our device uses a twisted wire actuator to convert rotational motion into linear displacement, which allows the device to remain compact and light-weight. In the past, the main shortcoming of this type of actuator was its limited linear range of motion; but with a slight modification of the principle, we have extended our actuator’s linear range of motion by 40%. In this paper, we present the design of our haptic device, the kinematic and dynamic modelling of the actuator, and the results of the experiments that were used to validate the system’s functionality. </span>