Makoto Shimojo

A tactile sensor sheet using pressure conductive rubber with electrical-wires stitched method

A new type of tactile sensor using pressure-conductive rubber with stitched electrical wires is presented. The sensor is thin and flexible and can cover three-dimensional objects. Since the sensor adopts a single-layer composite structure, the sensor is durable with respect to external force. In order to verify the effectiveness of this tactile sensor, we performed an experiment in which a four-fingered robot hand equipped with tactile sensors grasped sphere and column. The sensor structure, electrical circuit, and characteristics are described. The sensor control system and experimental results are also described.

Human shape recognition performance for 3D tactile display

The paper describes the relationship between the pin-matrix density of a tactile display and the recognition performance of displayed 3D shapes. Three types of pin-matrix tactile display, that generate 3D shapes, were used for the experiment. The pitch of pins was 2 mm, 3 mm, 5 mm each. We assumed that surfaces, edges, and vertices were primitive 3D shape information, so tested shapes were classified into these three categories. We assumed two types of finger touching mode: 1) fingertip-only, allowed full use of spatial shape information given to the fingertip; and 2) allowed tracing of the object. Recognition time and the classified error rate were measured. We obtained results on the relationship between pin pitch and recognition performance data. Regression curves for pin pitch and recognition time were plotted. A significance test of recognition time versus pin pitch was done. The error rate of identification versus pin pitch was described. Our results provide basic knowledge for developing tactile presentation devices.

Mechanical filtering effect of elastic cover for tactile sensor

Tactile sensors are ordinarily covered with an elastic cover to protect the sensor from being damaged by shock or chemical contamination. The cover, however, greatly decreases the sensors spatial resolution. This effect becomes serious in the fabrication of a high-spatial-resolution sensor, even if the cover is only 0.2 mm thick, when the sensor requires a spatial resolution of less than 1 mm. This paper analyzes the low-pass spatial filtering effect of the cover, calculates the filtering gain for different types of elastic cover materials using the finite-element method, and gives preliminary experimental results.

Grasping force control of multi-fingered robot hand based on slip detection using tactile sensor

To achieve a human like grasping with a multi- fingered robot hand, the grasping force should be controlled without using information from the grasped object such as its weight and friction coefficient. In this study, we propose a method for detecting the slip of a grasped object using the force output of Center of Pressure (CoP) tactile sensors. CoP sensors can measure the center position of a distributed load and the total load applied on the surface of the sensor, within 1 ms. These sensors are arranged on the fingers of the robot hand, and their effectiveness as slip detecting sensors is confirmed in tests of slip detection during grasping. Finally, we propose a method for controlling grasping force to resist tangential force applied to the grasped object using a feedback control system with the CoP sensor force output.

A flexible high resolution tactile imager with video signal output

A high-resolution and sheetlike form imaging tactile sensor with video signal output has been developed. The sensor has a 64*64 array of sensing elements on a flexible PC board with 1-mm spatial resolution. Since the sensor outputs pressure distribution as a video signal, a real-time tactile image can be observed using a TV monitor. As the sensor is made up of a sheet of pressure-sensitive conductive rubber and stripe electrodes, there are undesirable currents passing between sensing elements. Thus these undesirable current passes must be cut within a short scanning period (500 ns for each element). The authors used a ground potential method and proved it useful under such a high-speed scanning condition. The properties of pressure-sensitive conductive rubber, including hysteresis and creep effects, are presented. A spatial filtering effect of an elastic cover for a tactile sensor is analyzed.<<ETX>>

A High-Speed Mesh of Tactile Sensors Fitting Arbitrary Surfaces

A tactile sensor is developed with the aim of covering a robots entire structure, while reducing wiring requirement and ensuring high-speed response. The sensor detects the center point of load distribution on 2-D surfaces as well as the overall load. There are only four signal wires from the sensor. The sensor response time is nearly constant (within 1 ms) regardless of the number of detection elements, their placements or sensor areas. In this paper, the principles behind the operation of this sensor and the results of experiments using the sensor are described.

An active touch sensing method using a spatial filtering tactile sensor

A sensor system that measures the surface pattern of objects by using a spatial filtering tactile sensor is described. The sensor has a bandpass spatial filtering function and changes its center of spatial frequency with the tactile motion. The idea of this method is based on the nervous system in a human finger. This sensor system is characterized by robot measurement for nonuniform contact states, adaptability for a wide spatial frequency range in the surface pattern of objects, and high spatial resolution. The characteristics of the sensor are analyzed, an adaptive operation algorithm for identifying the surface pattern of objects is described, and simulation and experimental results are given.<<ETX>>

One-handed knotting of a flexible rope with a high-speed multifingered hand having tactile sensors

This paper proposes a new strategy for making knots with a high-speed multifingered robot hand having tactile sensors. The strategy is divided into three skills: loop production, rope permutation, and rope pulling. Through these three skills, a knot can be made with a single multifingered robot hand. The dynamics of the rope permutation are analyzed in order to improve the success rate, and an effective tactile feedback control method is proposed based on the analysis. Finally, experimental results are shown.

Object localization with multiple sensors

We present a method to obtain the position and orientation of an object through measurement from multiple sensors. Raw sensor measurements are subject to limitations of sensor precision and accuracy. Although for most measurements the estimate of position parameters is a linear function of the measurements, the estimate of orientation parameters is a nonlinear function of the measurements. Thus, error in orien tation estimate depends on the distance over which the raw measurements are made. For example, the estimate of the orientation of a line is better, the farther apart two points on the line are. The problem of finding the orientation parame ters is formulated in two steps. The first step computes vec tors from sensor measurements of points. A concept of best features is developed to select an optimal set of all possible vectors. The second step relates the orientation parameters to the vectors from the first step as a linear system. The best estimate is obtained by solving a weighted linear system of the optimal set of vectors in a least squares sense. The opti mal selection of best features improves the estimate substan tially. This method has been implemented for localizing an object in a manipulator end-effector instrumented with cen troid and matrix tactile sensors.

Dynamic Pen Spinning Using a High-speed Multifingered Hand with High-speed Tactile Sensor

We propose a tactile feedback system in real time using a high-speed multifingered robot hand and high-speed tactile sensor. The system is respectively capable of high-speed finger motion up to 180deg per 0.1s and high-speed tactile feedback with a sampling rate higher than 1kHz. In this paper, we describe dynamic pen spinning as an example of a skillful manipulation task using a high-speed multifingered hand equipped with tactile sensors. The paper describes the tactile feedback control strategies and experimental results