Strategija upravljanja pozicijom ultrazvučnog motora s putujućim valom

Since a conventional controller is continuous one, control period is normally set for a long time. When applying that controller for a travelling-wave ultrasonic motor whose parameters and performance are time-varying as a result of increasing temperature and operating condition, it is consequently resulted in degradation of the control performance. In this paper, a digital control algorithm is proposed for position control of the motors to shorten the long control period to maintain the stability of the motor performance. The proposed controller is digitally implemented by a SH7125 microcomputer utilizing a high-performance embedded workshop. The state quantities such as acceleration, speed and position, which are necessary for digital implementation, are provided by a rotary encoder. However, the optical encoder causes quantization errors in the speed information. To overcome the problem, a digital Variable Structure System (VSS) observer is also included to estimate the state quantities. The control input will be calculated after comparing the measured values and the estimated values given by the VSS observer. In short, a small, low cost and fast responsive digital controller is designed, based on a digital VSS observer, by using the SH7125 microcomputer. Effectiveness and reliability of the proposed digital controller are experimentally verified.Strategija upravljanja pozicijom ultrazvučnog motora s putujućim valom Sažetak: S obzirom da je standardni regulator najčešće kontinuirani, period upravljanja obično je postavljen na duži period. Koristeći takav regulator pri upravljanju ultrazvučnim motorom s putujućim valom, čiji su parametri i svojstva vremenski promjenjivi zbog povećanja temperature i promjena uvjeta rada, rezultat su smanjena upravljačka svojstva. U ovome radu predložen je digitalni upravljački algoritam za upravljanje pozicijom motora u svrhu smanjenja dugačkog perioda upravljanja za održavanje stabilnosti svojstava motora. Regulator je implementiran koristeći SH7125 mikroračunalo uz HEW (engl. high-performance embedded workshop) okruženje. Iznosi veličina kao što su akceleracija, brzina i pozicija, nužnih za digitalnu implementaciju, dobiveni su iz rotirajućeg enkodera. Međutim, optički enkoder dovodi do greške kvantizacije kod proračuna brzine. U svrhu smanjenja tog problema, u proces proračuna iznosa varijabli uključen je VSS (engl. Variable Structure System) estimator. Upravljački ulaz računa se nakon usporedbe mjerenih i estimiranih vrijednosti dobivenih korištenjem VSS-a. Dizajniran je digitalni regulator malih dimenzija, jeftine cijene i brzog odziva, temeljen na digitalnom VSS estimatoru koristeći SH7125 mikroračunalo. Eksperimentalno je provjerena efikasnost i pouzdanost digitalnog regulatora

Cross-sectional study of sexual behaviour and knowledge about HIV among urban, rural, and minority residents in Viet Nam

OBJECTIVE: A cross-sectional survey was conducted in three districts of Quang Ninh province, Viet Nam, to find out what proportion of the people who lived there engaged in behaviour that put them at risk of becoming infected with HIV, and to measure their knowledge about HIV infection and AIDS. METHODS: The survey was conducted in a rural district, Yen Hung; a mountainous district inhabited primarily by ethnic minority groups, Binh Lieu; and an urban district, Ha Long. Participants aged 15-45 years were randomly selected from the general population to be interviewed. FINDINGS: A total of 630 people from 707 households were interviewed; 8% were not home despite repeated visits and 3% refused to participate. The prevalence of premarital intercourse ranged from 9% to 16% among married men and 4% to 7% among married women. Among single men the proportion who had ever had intercourse ranged from 6% to 16%. Fewer than 3% reported having ever had sex with a sex worker. The median number of extramarital sex partners was 1. Knowledge about HIV/AIDS was high in the urban and rural areas but low in the mountainous area. Being male and being 20-29 years old were associated with having multiple sex partners. CONCLUSION: The low prevalence of individuals reporting that they had had intercourse with sex workers and partners other than their spouse may explain the low rates of HIV infection among the heterosexual population; these rates are in contrast to the high rates of HIV infection found among injecting drug users. The association between having extramarital partners and being a younger man suggests that the tendency to have more sexual partners may increase in the future. If this happens, the potential for HIV to be spread through heterosexual sex will increase