Robust control of a compact disc mechanism

A compact disc (CD) player is an optical decoding device that reproduces high-quality audio from a digitally coded signal recorded as a spiral-shaped track on a reflective disc. Apart from the audio application, other optical data systems (CD-ROM, optical data drive) and combined audio/video applications (CD-interactive, CD-video) have emerged. An important research area for these applications is the possibility of increasing the rotational frequency of the disc to obtain faster data readout and shorter access time. For higher rotational speeds, however, a higher servo bandwidth is required that approaches the res onance frequencies of bending and torsional modes of the CD mechanism. Moreover, the system behavior varies from player to player because of manufacturing tolerances of CD players in mass production, which explains the need for robustness of the controller. Further, an increasing percentage of all CD-based applications is for portable use. Thus, additionally, power consumption and shock sensitivity play a decisive role in the performance assessment of controller design for CD systems. In this chapter we concentrate on the possible improvements of both the track-following and focusing behavior of a CD player, using robust control design techniques

Effect of change in blood volume in skin plus active muscle on heart rate drift during submaximal exercise

The purpose of the present study was to examine the effect of change in blood volume in skin plus active muscle on heart rate drift during moderate exercise and heavy exercise for 30 min. Total hemoglobin concentration (Total Hb) in the vastus lateralis muscle plus its skin was determined by near-infrared spectroscopy. Total Hb significantly increased and remained stable from 20 min in moderate exercise and from 10 min in heavy exercise. Heart rate (HR) rapidly increased until 3 min and showed a steady state in moderate exercise. HR at 30 min was significantly higher than that at 3 min in moderate exercise. HR rapidly increased until 3 min and then gradually but significantly increased in heavy exercise. Increase in total Hb was not significantly related with HR after 3 min of exercise when HR was around 120 beats per min in moderate exercise. Increase in total Hb was significantly related with HR from 3 min to 10 min in the heavy exercise (correlation coefficients ranged from 0.959 to 0.702). It is concluded that an increase in the blood volume in skin plus active muscle is not simply associated with HR drift

Arbetsmiljöarbete och effekter en kunskapsöversikt

Work environment improvements and effects a literature review This report addresses the question 'Do work-environment improvements have any effects?' The aim was to produce a summary of knowledge that includes the methodological problems of measuring and evaluating effects, as well as literature reviews of effects from work environment improvement efforts on musculoskeletal health, health promotion, and economy. Results show that published literature reviews do not give unambiguous support for health benefits of interventions against musculoskeletal problems, when only studies using natural science criteria with experimental or quasi-experimental design are included. There are, on the other hand, many case studies in the so called 'grey' literature that report positive effects. Further, results show that health promotion interventions, and especially physical activity, have a positive effect on low back pain. Workplace interventions to increase physical activity are effective and lead to increased physical activity amongst employees. More studies are needed, however, at the organisational level. There is some support for the profitability of work-environment investments at the organisational level; even though there are few studies and methodological problems. The review also indicates that the financial benefits come mostly from quality and productivity improvements and, to a lesser extent from reductions in costs related to sickness absenteeism. While more recent literature reviews of the effects of health promotion interventions seem to show a stronger effect than older studies, comparisons of older versus more recent studies of interventions against musculoskeletal problems give a more ambiguous picture. Often, the focus of these reviews is on study design with less priority on the quality of the interventions themselves. Multifactorial interventions are particularly difficult to evaluate. At the same time, many studies and research reviews emphasise the need for multifactorial approaches as necessary for successful intervention. Inclusion criteria in literature reviews that only consider experimental designs in organisational interventions exclude studies with good interventions that can't be evaluated with traditional experimental methods. Difficulties in proving the effectiveness of interventions depends on views of what constitutes good scientific quality in the studies. This shows a need for a critical examination of the assumptions used for knowledge generation in this area. Conclusions are that work-environment improvement efforts have effects that are clear in some cases but are difficult to show in others. Effect evaluation poses large methodological challenges. These difficulties are considered to be an important cause of the lack of clear evidence, especially in the area of interventions against musculoskeletal problems. There is a need for new non-experimental research strategies that are suited to today's complex systems and an increased focus on practical, well conducted multifactorial interventions. Key words: Intervention, health promotion, ergonomics, economy, methodology, researchDetta arbete har inriktats mot frågeställningen om arbetsmiljöarbete har några effekter. Syftet har varit att göra en kunskapssammanställning som omfattar en beskrivning och problematisering av metodiken att mäta eller utvärdera effekter, samt litteraturöversikter om vad arbetsmiljöarbete har för belastningsergonomiska, hälsofrämjande och ekonomiska effekter. Resultaten visar att publicerade litteraturöversikter inte ger säkra belägg för att belastningsergonomiska interventioner har effekter på besvärsförekomst, i de fall enbart studier inkluderats utifrån naturvetenskapliga kriterier med krav på experimentell eller kvasi-experimentell metodik. Däremot finns ett flertal fallstudier och så kallad grå litteratur som i högre grad rapporterar positiva effekter. Vidare framgår det att hälsofrämjande interventioner, och speciellt fysisk aktivitet har en positiv effekt på ländryggsbesvär. Interventioner på arbetsplatser för att öka den fysiska aktiviteten är effektiva och ger en ökad fysisk aktivitet hos arbetstagarna. Fler studier behövs emellertid på organisationsnivå. Det finns visst belägg för att arbetsmiljösatsningar ofta är lönsamma på organisationsnivå, även om studierna är få och uppvisar metodbrister. Det finns flera indikationer på att lönsamheten i huvudsak härrör från produktivitets- och kvalitetsförbättringar, och i mindre grad från minskade frånvarokostnader. Nya litteraturöversikter om hälsofrämjande interventioner tycks uppvisa starkare effekter än gamla, medan jämförelser mellan äldre och nyare studier om belastningsergonomiska interventioner ger en mer mångtydig bild. Ofta ligger fokus på utvärderingsdesign, samtidigt som kvaliteten hos interventionens genomförande och utformning i sig inte ges samma prioritet. Interventioner med multifaktoriella insatser blir synnerligen svåra och komplexa att utvärdera, samtidigt som det i många studier och forskningsöversikter betonas att en förutsättning för framgång i förändringsarbetet är att man arbetar med en mångfald av insatser. Inklusionskriterier i litteraturöversikter som förutsätter experimentella upplägg i organisationsinterventioner selekterar bort studier med goda interventioner som inte kan utvärderas med traditionella metoder. Svårigheten att identifiera effekter av interventioner bedöms bero på synen om vad som utmärker god vetenskaplig kvalitet hos studier. Detta visar på behovet att närmare kritiskt granska förutsättningarna för kunskapsbildning inom området. Slutsatsen är att arbetsmiljöarbete i vissa fall har effekter men att det i andra fall är svårt att påvisa effekter. Effektutvärdering innebär stora metodologiska svårigheter. Dessa svårigheter bedöms vara en viktig orsak till bristen på underlag, speciellt inom det belastningsergonomiska området. Det finns ett stort behov av nya icke experimentella undersökningsstrategier som är anpassade till dagens komplexa system, såväl som ett behov av starkare fokus på praktiskt väl genomförda multifaktoriella interventioner