Interfacial instabilities in multimaterial co-injection mouldings Part 1 – Background and initial experiments

Abstract

Interfacial adhesion between the skin and core is vital for successful co-injection moulding. This is the first paper in a series, which introduces and describes an in mould method of mixing that is applicable regardless of the compatibility of the materials. It works by inducing turbulent mixing at the interface between the skin and core materials. It makes use of the change that occurs from laminar to turbulent flow at high injection speeds in co-injection moulding. This novel approach takes advantage of the moulding parameters already available within the co-injection system to offer an expanded range of material combinations for multimaterial moulding. Comparisons are made between multimaterial mouldings made with miscible polymers, immiscible polymers with no compatibiliser, and immiscible polymers bonded by compatibilisers.     

Variation of the Electrostatic Adhesion Force on a Rough Surface due to the Deformation of Roughness Asperities During Micromanipulation of a Spherical Rigid Body

The micromanipulation of objects of size between 10 μm and 1 mm is often disturbed by the adhesion between the contacting surfaces. The electrostatic force in the contact alone can significantly perturb the micromanipulation by its important adhesion effect. The electrostatic adhesion force is influenced by many factors, i.e., the materials of the contacting bodies and the topography of the contact surface. Micromanipulation by contact involves applying a squeezing force to hold the object firmly which causes the contact surface to deform, flattening the surface asperities. The prime purpose of this work is to study the influence of the plastic deformation of the surface asperities on the electrostatic adhesion force considering the contact between two conductors. A single-level model of the surface roughness was considered in this study, approximating the shape of a surface asperity by a sine function. A simulation tool based on the finite element method was used to compute the elastic–plastic deformation of the model surface asperities during micromanipulation. Another numerical model was used to compute the electrostatic adhesion force acting on the surface asperities in the initial and in the deformed configurations. A magnification factor of up to 20 was obtained for the electrostatic force in the contact evaluated numerically, related to the flattening of the surface asperities, which can potentially lead to perturbations when releasing the object. The observed effect is merely a lower bound of the real one, considering the simplifying assumptions of the numerical models.     

Dynamic Compaction of Pure Copper Powder Using Pulsed Magnetic Force

The compaction of pure Cu powder was carried out through a series of experiments using dynamic magnetic pulse compaction, and the effects of process parameters, such as discharge energy and compacting direction, on the homogeneity and the compaction density of compacted specimens were presented and discussed. The results indicated that the compaction density of specimens increased with the augment of discharge voltage and time. During unidirectional compaction, there was a density gradient along the loading direction in the compacted specimen, and the minimum compaction density was localized to the center of the bottom of the specimen. The larger the aspect ratio of a powder body, the higher the compaction density of the compacted specimen. And high conductivity drivers were beneficial to the increase of the compaction density. The iterative and the double direction compaction were efficient means to manufacture the homogeneous and high-density powder parts.     

Active compliant motion: a survey

Whether they are asked to polish or assemble parts, clean the house or open doors, the future generation of robots will have to cope with contact tasks under uncertainty in a stable and safe manner. Obtaining a controlled contact motion under uncertainty is still a major challenge for the robotics community. At present most research groups focus on one of the subcomponents (i.e., modeling, planning, estimation or control) of the system, and no overall system is developed yet. This paper presents a literature survey of the state-of-the-art of the subcomponents and points to the need for effective integration of those components.     

Influence of static magnetic fields on the protective ability of phosphate coatings on aluminium alloys

Abstract

Phosphate coatings on aluminium are used to improve the corrosion resistance of aluminium before the latter is painted. Phosphate coatings deposited in phosphate solution treated with a magnetic field prior to deposition can take on new properties. A magnetic field can either improve or deteriorate the properties of the phosphate coating formed, depending on the composition of aluminium.     

10—THE MECHANICS OF FRICTION-TWISTING

An analysis is given from which equations can be derived that relate the variations of twist factor, tension, and yam path through a false-twist friction spindle. The solution of these (differential) equations leads to predictions about the dependence of over-all twist factor and tension ratio on, among other parameters, the ratio of yam speed to spindle speed, the angle of wrap, and the input tension. These are compared with the early experimental results of Arthur and Weller and with more recent results.

The equations also yield the variation of twist factor and tension over the spindle surface and could be used to estimate wear.

The early part of the analysis would have general application in any situation in which a yarn is moving over a surface.     

Dynamics Analysis of Some Limited-Degree-of-Freedom Parallel Manipulators with n UPS Active Legs and a Passive Constraining Leg

This paper presents a methodology for the unified analysis of the dynamics of some parallel manipulators (PMs) with n UPS-type active legs and a passive constraining leg. First, some formulae are derived for solving linear/angular velocity of active and constraining legs at their mass center, linear/angular accelerations of active and constraining legs at their mass center, and Jacobian matrices of active and constraining legs. Second, based on the principle of virtual work and Jacobian matrices of active and constraining legs, the inertia wrench and gravity of active/constraining legs and the friction of the joints in a PM are mapped into a part of the dynamic workload. Third, the general formulae are derived for solving the dynamic workload and the dynamic active forces/constrained wrench. Finally, the procedure is illustrated by means of a PM with 4 UPS active legs and one passive constraining leg.     

Virtual Force/Tactile Sensors for Interactive Machines Using the User's Biological Signals

This study proposes a new approach to virtual realization of force/tactile sensors in machines equipped with no real sensors. The key of our approach is that a machine exploits the user's biological signals. Therefore, this approach is not dependent on controlled objects and is expected to be widely applicable for a variety of machines including robots. This article describes an example robotic system comprised of an industrial robot manipulator, a motion capture system and a surface electromyogram (EMG) measurement apparatus. By monitoring/recording the user's surface EMG and postural information in real-time, we show that a robot equipped with no force/tactile sensors behaved similarly to one possessing sensors over its body. Another advantage of our approach is demonstrated by a task in which a robot and a user cooperatively hold and move a heavy load.     

Compliant motion using a mobile manipulator: an operational space formulation approach to aircraft canopy polishing

The operational space formulation provides a framework for the analysis and control of robotic systems with respect to interactions with their environments. In this paper, we discuss its implementation on a mobile manipulator programmed to polish an aircraft canopy with a curved surface of unknown geometry. The polishing task requires the robot to apply a specified normal force on the canopy surface while simultaneously performing a compliant motion keeping the surface of the grinding tool tangentially in contact with the workpiece. A human operator controls the mobile base via a joystick to guide the polishing tool to desired areas on the canopy surface, effectively increasing the mobile manipulator's reachable workspace. The results demonstrate the efficacy of compliant motion and force regulation based on the operational space formulation for robots performing tasks in unknown environments with robustness towards base motion disturbances. The mobile manipulator consists of a PUMA 560 arm mounted on top of a Nomad XR4000 mobile base. Implementation issues are discussed and experimental results are shown.