Generic vibration criteria for vibration-sensitive equipment
The vibration criterion (VC) curves, commonly used in the design of facilities which house vibration-sensitive instruments and tools, were developed by the author and his colleagues, in the early 80's, published by SPIE in 1991 and by IEST in 1993. Each of the criterion curves A through E is associated with a 'line width' or 'detail size' which was an attempt by the authors to describe the capabilities of the tools with which each curve might be associated. In the years since the curves were developed there have been substantial developments in tool design and isolation. In this paper the curves are reviewed in the context of present-day tools and processes. Changes are proposed where these might be justified.
System and Control Design of a Voice Coil Actuated Mechanically Decoupling Two-Body Vibration Isolation System
Structural modes such as decoupling of a mechanical subsystem are in general unwanted effects in high precision positioning systems. This paper introduces intentional decoupling as a design choice by using a connecting flexure-damper configuration that allows high bandwidth control of a stiff first subsystem and lower bandwidth control of a bulky second subsystem at the same time. An experimental setup of a single degree of freedom system with one body intentionally decoupling above 190 Hz is developed and analyzed, showing good agreement with the analytical modeling. A model-based H<inline-formula><tex-math notation="LaTeX">$_\infty$</tex-math></inline-formula>-controller to actively control the position of the first body is designed and the damping in the system is revealed as an important design parameter to reduce the control effort around the decoupling frequency. It is demonstrated that with the derived controller, the first and the second body of the resulting prototype can simultaneously be controlled with bandwidths of 1.4 kHz and 180 Hz, respectively. When exposed to a disturbance profile with 12.4 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m root mean square (rms) value in the laboratory environment, the remaining rms positioning errors for the actively and passively controlled subsystems are as small as 0.12 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m and 0.81 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m, respectively.
Affordable housing in London
Introduction. The Housing Situation in London. Housing, Land Use Planning, and the Government of London, a Brief History. Land Use Regulations. Positive Local Authority Powers in London. Sources of Affordable Housing: the Rented Sectors. Grants to Assist Access to Affordable Housing. Conclusions. Bibliography.