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wide operating range and provides a robust, reliable and compact alternative to large bend radius, wire-wound throttle cables.

MACHINE DESIGN The compact design of the Max Jac actuator gives designers greater freedom and flexibility in machine design. There is also no need for regular maintenance access so these units can be best applied to optimise functionality and performance without compromising on vehicle or system design. To suit application needs in terms of duty and load, the actuator is

available with worm or ball screw technology. The worm screw version is self-locking and will not back drive on power-off while the ball screw offers faster operation, will take higher loads and can operate at higher duty cycles. However, to exactly match design and application requirements, Thomson also offers a linear actuator customisation service. The Max Jac offers flexible operation and installation with stroke lengths

from 50 to 300mm achieved with the ball screw variant (50 to 200mm with the worm screw) and a retracted length of just 156mm longer than the stroke length. Dependent on load, the duty cycle can be 25% to 100% with a life of 500,000 cycles for a ball screw actuator with 100 mm stroke, average load of 500N and changing load direction. The worm screw actuator has a maximum dynamic load of 500N (static load 2,000N) and the ball screw 800N. Operating speeds of up to 60mm/s with no load (30mm/s full load) can be achieved with the Max Jac ball screw actuator.

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WITH TOOTH DECAY RESEARCH To understand the underlying processes that occur during tooth decay and repair, researchers at Queen Mary, University of London (QMUL), are using X ray microtomography to generate high resolution images that can detail the mineral concentrations in the tooth. The image generation involves scanning the tooth over an extended time period. In the research, microtomography is combined with the long X-ray exposure of extracted teeth to enhance the contrast ratio of the image. The resulting model reveals details of both the structure and density of the tooth. The grey levels of the image are calibrated to identify the density at any given point and this, with priori information about the composition, can be used to show mineral concentrations to a precision of better than 1%. By observing the tooth over an extended time period, changes in mineral concentration resulting from further decay or re-mineralisation treatment can be monitored. The longer the exposure time of a scan, the higher the contrast ratio, the better the mineral concentration that can be measured. So, with scans taking several hours, the mechanical stages used need to be reliable. To help, three PI (Physik Instrumente) M-500 series high

precision linear stages with recirculating ball guides and a PRS-110 high precision rotary stage with exceptionally low wobble are used in combination to scan the sample and X ray detector. One of the linear stages is used to scan the lead encased detector while the other two move the sample in the Z and focal planes. The rotary stage is used to index the sample after each scan. The detector moves dynamically with image collection triggered by position information from the linear stage. The velocity, stability, repeatability, straightness and flatness of the mechanics are the key to QMUL being able to generate the high resolution images that are subsequently combined into the computer generated 3D model of the tooth.

Physik Instrumente

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