A hybrid contact state analysis methodology for robotic-based adjustment of cylindrical pair

The peg-in-hole insertion and adjustment operation is one of the most common tasks in the robotic and automatic assembly processes. Fine motion strategies associated with adjustment operations on a peg-in-hole are fundamental manipulations that can be utilised in dynamic assembly and reconfigurable workholding or fixturing systems. This paper presents a comprehensive study of robotic-based height adjustment of a cylindrical pair based on maintaining minimum contact forces between the links. The outer link is held by the end-effector of a six-DOF (Degrees of freedom) serial articulated robot manipulator. The environment represented by the inner link can be either static or dynamic. A force-based approach and a d value approach are established to determine the type of contact that exists between the links of a cylindrical pair, and to extract control parameters. Based on the comparison and analysis of these two approaches, a hybrid methodology is established by combining a d value approach with a force-based approach for contact state determination. Formulations capable of extracting necessary control parameters, which ensure minimum contact forces between the links, are established from both planar and spatial viewpoints under both static and dynamic environmental conditions. Experimental results demonstrate the effectiveness of the proposed methodology.

Concept design of a novel tactile probe tip for down scaled 3D CMMs

Although coordinate metrology has reached a very high state of development concerning versatility and accuracy for common engineering parts, a high precision capability with nano scale resolution and accuracy is often hard to achieve when it is required to measure very small parts and features. The limiting component is the bulky probing system of traditional CMMs (coordinate measuring machines). In order to satisfy increasing demand for highly accurate geometrical measurements on small parts and small structures, a new measuring probe of high sensitivity and small geometrical dimension with low contact forces needs to be developed. In this paper, a novel probing system, which combines a FBG (Fibre Bragg Grating) embedded optical fibre tactile probe with an optical sensing technique, has been proposed. With the sensor elements integrated into the probe tip directly, the system sensitivity can be increased significantly. A preliminary theoretical analysis of the sensitivity of the FBG fibre sensor under axial and lateral end point loading has been presented and the results show that this micro scale probe has great potential to realize a resolution of 1nanometer on geometrical measurement of small parts.

Design, development, and evaluation of a pinch-grasp haptic interface

Interaction with virtual or teleoperated environments requires contact with objects on a multipoint level. We describe the design of a pinch--grasp hand interface device for use as a grasping mechanism to complement haptic interfaces. To preserve a suitable level of transparency for human--computer interaction, this novel interface is designed for high-resolution contact forces, while centered around a lightweight structure. This functionality renders the device scalable and adaptable to a wide range of haptic interface structures and force level requirements. We present an optimal configuration for a pinch--grasp interface, which produces bidirectional forces to an operator's fingers and a rotational force to the wrist through a cable drive system. The device is characterized for use on a commercial haptic interface through demonstration of sustained peak performance and also workspace utilization. The dynamic performance of the pinch--grasp interface is experimentally determined, and the frequency response is identified to illustrate its contact force resolution.

Simulation of contact pressure in sheet metal trimming/blanking process

In the car body stamping process, trim/blank die cutting edges are subjected to very high tribological loads that result in loss of tool material from both the punch and die cutting edges. According to Archard’s wear model, normal contact force and sliding distance directly affects the wear. Therefore, knowledge of the acting forces on local contact areas has a pivotal role towards the prediction of tool wear. This paper presents a finite element modelling approach to determining the contact pressure distribution on the tool cutting edges during a trimming/blanking process. Characteristic areas on sheared edge profile, variation of punch force and high contact pressures affected areas have also been analysed.

Forces measured between latex spheres in aqueous electrolyte : Non-DLVO behavior and sensitivity to dissolved gas

An atomic force microscope was used to measure the forces acting between two polystyrene latex spheres in aqueous media. The results show an electrostatic repulsion at large separations which is overtaken by an attractive “hook” that pulls the two spheres into contact from a considerable range (20−400 nm), much larger than could be expected for a van der Waals attraction. The range of operation of this attraction varies from one experiment to another and is not correlated with electrolyte concentration. However, the range is found to decrease significantly when the level of dissolved gas in the water is reduced.

Attractive forces between surfaces : what can and cannot be learned from a jump-in study with the surface forces apparatus?

We study theoretically the dynamics of film thinning under the action of an attractive surface force near the point of a jump instability. Our approach is illustrated by modeling van der Waals and hydrophobic attractive forces. The main result is that with the hydrophobic force law reported previously it is often impossible to establish the jump separation with any certainty. The surfaces instead approach slowly from a distance which is much larger than the point where an actual jump is expected. We conclude that an attractive force measured by the static jump technique is overestimated, and we formulate principles of a new dynamic jump method. The use of this new technique would permit direct measurements of attractive forces at separations below the static jump distance down to contact of the surfaces.

The electrochemical surface forces apparatus : the effect of surface roughness, electrostatic surface potentials, and anodic oxide growth on interaction forces, and friction between dissimilar surfaces in aqueous solutions

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force–distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal–ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg–Healy–Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force–distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)3 phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials.

Wettability investigation of UV/oand acid functionalized MWCNT and MWCNT/PMMA nanocomposites by contact angle measurement

The dispersion state of individual MWCNT in the polymer matrix influences the mechanical, thermal, and electrical properties of the resulting composite. One method of obtaining a good dispersion state of MWCNT in a polymer matrix is to functionalize the surface of MWCNT using various treatments to enhance the surface energy and increase the dispersibility of MWCNT. In this study, wettability and surface energy of UV/Oand acid-treated multiwall carbon nanotubes (MWCNTs) and its polymethyl methacrylate (PMMA) polymer nanocomposites were measured using contact angle analysis in various solvent media. Contact angle analysis was based on ethylene glycol-water-glycerol probe liquid set and data was further fitted into geometric mean (Fowkes), van Oss-Chaudhury-Good (GvOC), and Chang-Qing-Chen (CQC) models to determine both nonpolar and acid base surface energy components. Analysis was conducted on MWCNT thin films subjected to different levels of UV/Oand acid treatments as well as their resulting MWCNT/PMMA nanocomposites. Contact angle analysis of thin films and nanocomposites revealed that the total surface energy of all samples was well fitted with each other. In addition, CQC model was able to determine the surface nature and polarity of MWCNT and its nanocomposites. Results indicated that the wettability changes in the thin film and its nanocomposites are due to the change in surface chemistry. Finally, electrical properties of nanocomposites were measured to investigate the effect of surface functionality (acid or basic) on the MWCNT surfaces.