Byungjune Choi

Development of tactile sensor for detecting contact force and slip

In this paper, a fingertip tactile sensor is presented which can detect contact normal force as well as incipient slip. The sensor, based on polyvinylidene fluoride (PVDF), and pressure variable resistor ink, is physically flexible enough to be deformed into any three-dimensional geometry. In order to detect incipient slip, a PVDF strip is arranged along the direction normal to the surface of the finger of the robot hand. Also, a thin flexible sensor to sense the static force as well as the contact location, is fabricated into an arrayed type using pressure variable resistor ink. In addition, a tactile sensing system is developed with miniaturized electronic hardware such as charge amplifier, signal processing unit etc., and it feasibility is validated experimentally.

Haptic display in the virtual collaborative workspace shared by multiple users

This paper describes a method of haptic display in the virtual world shared by multiple remote users connected via network. Up to now, most investigations of haptic display are devoted to those related to single user or if multiple users exist even share the resources including computers which has no difference from the case of single user. In this paper, we are interested in the display of force feel in collaborative virtual workspace where multiple users participate via communication network. Excluding the possibility of large time delay among the users, the way of configuring individual haptic display systems is presented including the computation of interaction forces, joint driving forces of haptic devices and simulation of the virtual objects. A haptic display system is developed consisting of two haptic display devices operated by two remote users, and experimental results showing the validity of the proposed method are also presented.

A semi-direct drive hand exoskeleton using ultrasonic motor

We address an exoskeletal type haptic device which helps the human actively feel the sense of touch in palmar and dorsal directions. The device consisting of two finger-like parts taken by thumb and index finger, is designed in modular type to expand easily for five fingers. The proposed device is semi-directly driven by ultrasonic motors which have high power-to-weight ratio, and it provides haptic feedback to each joint of fingers. Methods for measuring the angular displacements and torques of the fingers are proposed and basic experiments are performed to verify the effectiveness of the system.

Pen-type sensor for surface roughness perception

Surface roughness is one of the most intractable physical properties and its sensing heavily depends on the application and the capability of the sensor. In this paper, a pen-type sensor is proposed for sensing surface roughness. The sensor with a rigid contact probe is able to measure 3D contact forces and the dynamic contact responses along the axial direction of the probe, which facilitate the roughness representation using parameters of roughness profile rather than complex, high level interpretation methods. Strain gauges and a force sensor are used for measuring contact forces and a PVDF sensor is used for the dynamic sensing. The sensor is a self-contained one, and it can transmit sensed data via Bluetooth to the host computer. As preliminary tests, experiments are performed on the measurement of the coefficient of friction and the response to dynamic stimuli of different surface patterns.

Development of Tactile Sensor for Detecting Contact Force and Slip

In this paper, we present a finger tip tactile sensor which can detect contact normal force as well as slip. The sensor is made up of two different materials, such as polyvinylidene fluoride (PVDF) known as piezoelectric polymer, and pressure variable resistor ink. In order to detect slip on the surface of the object, two PVDF strips are arranged along the normal direction in the robot finger tip and the thumb tip. The surface electrode of the PVDF strip is fabricated using silk-screening technique with silver paste. Also a thin flexible force sensor is fabricated in the form of a matrix using pressure variable resistor ink in order to sense the static force. The developed tactile sensor is physically flexible and it can be deformed three-dimensionally to any shape so that it can be placed on anywhere on the curved surface. In addition, a tactile sensing system is developed, which includes miniaturized charge amplifier to amplify the small signal from the sensor, and the fast signal processing unit. The sensor system is evaluated experimentally and its effectiveness is validated.

Design of a Dexterous Anthropomorphic Robot Hand

According to the study of grasping of the human hand, it is noted that the metacarpal link of the thumb plays the key role in power grasping. Also the face of fingertip can be discriminated into five parts depending on the grasping modalities such as pinch grasp, fingertip grasp and power grasp. In this paper, the design of the anthropomorphic robot hand which has a thumb and three fingers is proposed. A difference of SKKU hand II from the previous gripperlike robot hand is that the metacarpal bone is connected between the thumb and the palm. This thumb mechanism is specially designed to get the degree of freedom which can realize flexible motions relative to objects. Based on the analysis, the hand mechanism is developed. Since the driving circuits for the hand are embedded in the hand, only the communication lines supporting CAN protocol with DC power cable are necessary as the input. A new robot is manufactured and feasibility of the hand is validated through preliminary experiments.

Pen-type Sensor for Surface Texture Perception

In this paper a hand-held sensor for surface texture perception is presented. The sensor with a metal contact probe is able to measure the roughness and frictional property of a surface, which are among the most important parameters for contact texture perception. Two strain gauges and a force sensor are employed to measure 3D-contact forces at the tip of the contact probe. The friction coefficient can be calculated by using the normal force and tangential one. A PVDF film is used for the dynamic sensing of contact stress in the axial direction of the contact probe. Measurement results are transmitted to a host computer via Bluetooth wireless communication link for further data processing. Design issues are discussed in details, and the preliminary experimental evaluations are performed.