Mechanics of Localized Slippage in Tactile Sensing

And Application to Soft Sensing Systems

verfasst von: Anh-Van Ho, Shinichi Hirai

Verlag: Springer International Publishing

Buchreihe : Springer Tracts in Advanced Robotics

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Über dieses Buch

Localized slippage occurs during any relative sliding of soft contacts, ranging from human fingertips to robotic fingertips. Although this phenomenon is dominant for a very short time prior to gross slippage, localized slippage is a crucial factor for any to-be-developed soft sensing system to respond to slippage before it occurs. The content of this book addresses all aspects of localized slippage, including modeling and simulating it, as well as applying it to the construction of novel sensors with slip tactile perception.

Inhaltsverzeichnis

Frontmatter

Introduction

Abstract

TOUCH is a common but important action in everyday life. It permits us to accurately determine the surface properties and other properties of an object, including its weight and shape, which facilitates grasping tasks, as well as to determine many functions of the motor system. Until the 1970s, however, research on touching was limited to psychophysical studies. Given that the neural mechanisms underlying tactile sensation have been found to be critical to the success of adept manipulations [1], recent robotics research on dexterous manipulation has sought to imitate the natural touch mechanism, as well as the anatomy of human fingers, to optimize the ideal anthropomorphic artificial hand. Among the factors constituting an artificial hand, tactile perception is considered to be very important [2]. Without tactile feedback, failures in adept manipulation can occur, both to humans and robots. A sensory system must provide information about contact force, friction, and roughness, all of which are helpful for identifying objects. Moreover, during stable grasping, a sensory system must be able to recognize incipient and overt slips between the touching system and the object.

Anh-Van Ho, Shinichi Hirai

Mechanical Modeling of Localized Slippage

Frontmatter

Two Dimensional Beam Bundle Model of a Frictional Sliding Soft Fingertip

Abstract

We propose a dynamic model of a soft fingertip to investigate its sliding motion on a plane with friction. The fingertip is comprised virtually of a finite number of elastic compressible and bendable beams whose free ends act as contact points. Moreover, we utilize virtual linkage spring-damper elements between the contact points to represent interactions between neighboring beams on the contact surface. By introducing Coulomb’s law into each contact point, we are able to capture the frictional characteristic during sliding motions of the fingertip, especially stick-slip motions. During analysis, we have found a phenomenon called Localized Displacement which takes an important role in assessing slip perception of soft object. This phenomenon is then verified by our fine experiential setup.

Anh-Van Ho, Shinichi Hirai

Three-Dimensional Beam Bundle Model of a Sliding Soft Fingertip

Abstract

Slip, especially incipient slip, is a complicated process for soft fingertips and detection of this slip is an important factor in assuring stable manipulation for both human and robotic fingertips. By using experimental tools, previous studies have attempted to perceive this phenomenon, but none of them can explain fully the dynamic changes that occur during this process.

In the previous chapter, we proposed a 2-D dynamic model to investigate the sliding motion of semicylindrical soft fingertips on a plane with friction. However, this model cannot be exploited to describe the slip motion of soft fingertips that have complicated 3-D shapes, such as humanlike fingertips. Therefore, in this chapter, we propose a simplified yet adequate model that can act as a platform for the wide range modeling of fingertips. In the model, the fingertip is virtually comprised of a finite number of elastic compressible and bendable beams whose free ends act as infinitesimal contact points. The contact surface is meshed afterward using an FE method based on the coordinates of the contact points. We call this model the 3D-Beam Bundle Model (BBM). By introducing Coulomb’s law and contact compliance into each contact point, we are able to assess the frictional characteristic during sliding motions of the fingertip. We also successfully described dynamically LDP on the contact surface during stick-slip transition, which is typical of the sliding motion of a soft fingertip. This model can be applied to different typical shapes of robotic fingertip.

Anh-Van Ho, Shinichi Hirai

Modeling of a Sliding Human Fingertip

Abstract

In this thesis, we employed our proposed Beam Bundle Model (BBM) (see previous chapters) in the attempted modeling of a human fingertip. In order to implement this, we utilized magnetic resonance imaging (MRI) of a subject’s fingertip to construct a mathematical model of the structure of a fingertip. We first characterize pre-sliding regime on a real human finger in order to find out which factors is the most important in term of haptic display. We succeeded in creating a representation of localized displacements (also referred to as local skin stretch) during the pre-slide phase of the fingertip, which is considered crucial to assessing stick/slip events on the contact surface during contact with the outside world. The results of this research can be utilized in further studies in haptic sensation, and to develop sensors for the detection of slippage.

Anh-Van Ho, Shinichi Hirai

Tactile Sensing of Localized Slippage

Frontmatter

Tactile Sensing via Micro Force/Moment Sensor

Abstract

In previous chapters, we introduced a model of a sliding soft fingertip, and proposed the idea of LDP, which dominates the stick-to-slip phase of sliding motion, and is considered important in assessing slip detection in soft tactile systems. We can use this model to analyze the slip action of a soft tactile system, predict responses from sensors during sliding, and propose an efficient method of detecting slippage. In this chapter, we show our attempt to fabricate a tactile soft fingertip with an embedded MFMS. We employ a 2-D BBM to elaborate the slip action and corresponding responses from sensors, then utilize the LDP idea to propose a slip detection method. As mentioned in Chapter 1, tactile systems with slip perception have been developed over the past 20 years with various proposals regarding design and perception. There is a trade-off between the precision of physical quantity measurement and the speed of slip detection. A precise sensing system that can bring an exact exerted force/moment to act on a fingertip cannot detect slippage in a timely way since measurement is implemented mostly in the static state. Conversely, a dynamically responding tactile system that is suitable for the detection of slippage can only respond to physical phenomena, yet exact values. In this research, we aim to combine both above issues in one design with the assistance of the LDP.

Anh-Van Ho, Shinichi Hirai

Slip Perception via Soft Robotic Skin Made of Electroconductive Yarn

Abstract

We have developed a fabric sensor knitted of tension-sensitive electroconductive yarns. This sensor differs from other fabric-based sensors, in that the sensor itself is a piece of cloth with high density of knitted yarns. Each yarn has an elastic core, around which is wound two other separate, tensionsensitive electro-conductive threads, making this sensor inherently flexible and stretchable and allowing it to conform to any complicated surface on a robot, acting as a robotic skin. The pile-shaped surface of the sensor enhances its ability to detect tangential traction, while also enabling it to sense a normal load. Our aim is to utilize this sensor in applications involving relative sliding between its surface and a touched object, such as contact recognition, slip detection, and surface identification through a sliding motion. We carefully analyzed the static and dynamic characteristics of this sensor while varying the load and stretching force, to fully understand its response and determine its degree of flexibility and stretchability. We found that a Discrete Wavelet Transformation (DWT) may be used to indicate stick/slip states while the sensor is sliding over surfaces. This method was then utilized to detect slippage events acting on the sensor’s surface, and to decode textures in a classification test using an Artificial Neural Network (ANN). Due to its flexibility and sensitivity, this sensor can be used widely as a robotic skin in humanoid robots.

Anh-Van Ho, Shinichi Hirai

Slip Perception Using a Tactile Array Sensor

Abstract

In this chapter, we present the concept of using image processing for tactile sensors as appropriate tools in localizing/recognizing objects in robotic in-hand manipulation tasks, a concept originally derived from our localized displacement phenomenon (LDP) idea. Our approach operates on a moderately high-resolution intensive array of data obtained from a tactile sensor when a robotic gripper grasps an object that is small relative to the size of the fingers. Instead of using tactile data as an array of discrete numbers, we treat the data as grayscale images. By working with successive images from the tactile sensor by exploiting image-processing tools, we are able to extract rich information about the contact situation between an object and the gripper. Experimental results show that from the processed data, one can realize the grasped object’s position/orientation, contact shape, especially the stickslip condition on the contact surface, which is derived for the first time by this sensor.We also modeled an object-grasping gripper with tactile feedback for various postures of the object, utilizing Beam Bundle Model, and a corresponding experiment setup to validate computed results. The success of this research once again shows the potential of LDP in soft tactile systems, even for the commercialized sensor used in this chapter.

Anh-Van Ho, Shinichi Hirai

Concluding Remarks

Conclusion

Our objective in this book was to propose a dynamic model of a sliding soft fingertip to understand in detail how and when slip occurs on a contact surface, from which we can assess the slip perception of soft tactile systems. Our model is simplified to be implemented with less computation cost, dynamically, and be re-creatable by other researchers. This model is implemented under the scenario of a unilateral sliding motion on a flat rigid contact surface of a homogeneous soft fingertip.

Anh-Van Ho, Shinichi Hirai

Backmatter

Titel: Mechanics of Localized Slippage in Tactile Sensing
verfasst von: Anh-Van Ho
Shinichi Hirai
Verlag: Springer International Publishing
Electronic ISBN: 978-3-319-04123-0
Print ISBN: 978-3-319-04122-3
DOI: https://doi.org/10.1007/978-3-319-04123-0