Off-line studies of the laser ionization of yttrium at the IGISOL facility

A laser ion source is under development at the IGISOL facility, Jyvaskyla, in order to address deficiencies in the ion guide technique. The key elements of interest are those of a refractory nature, whose isotopes and isomers are widely studied using both laser spectroscopic and high precision mass measurement techniques. Yttrium has been the first element of choice for the new laser ion source. In this work we present a new coupled dye-Ti:Sapphire laser scheme and give a detailed discussion of the results obtained from laser ionization of yttrium atoms produced in an ion guide via joule heating of a filament. The importance of not only gas purity, but indeed the baseline vacuum pressure in the environment outside the ion guide is discussed in light of the fast gas phase chemistry seen in the yttrium system. A single laser shot model is introduced and is compared to the experimental data in order to extract the level of impurities within the gas cell.Comment: 18 pages submitted to NIM

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyvaskyla, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4 to 8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SPIG has been experimentally determined to be 10^12 ions/s before space charge effects start to take effect. A direct comparison with the simulation has been made using data obtained via light-ion fusion evaporation. Both experiment and simulation show an encouraging agreement as a function of current extracted from the ion guide.Comment: Latex formatted, submitted to NIM B, 17 pages with 22 .eps figure

Current measurement in control and monitoring of piezoelectric actuators

This thesis discusses the usability of current measurement in controlling and monitoring piezoelectric actuators. Current measurement contains information about the actuator and its environment. This work presents methods for utilizing the information in several control applications used in microrobotics, such as displacement control and external force estimation. The importance of current measurement is also discussed in context with piezoactuator -related problems, such as self-heating. After an introduction to the topic, an electromechanical model of a piezoelectric actuator is presented. The model summarizes the different effects and inputs that affect the output of piezoelectric actuators. The model is later utilized as basis for the development of more specialized models for several control applications. This thesis presents several control schemes which utilize current measurement in displacement control. The control methods utilize inverse actuator models to estimate the current required for the actuator to move as desired. The experiment results are very good: hysteresis is less than 2% and drift about 1% of the motion range. Force estimation without the use of force sensors is accomplished with an actuator model that approximates the present external force by combining information about the current, voltage and displacement. The measured displacement can be simultaneously utilized in feedback control, thus enabling precise microrobotic operations. The accuracy of the estimated force is within 10% of the force range, with an average inaccuracy of about 3%. Current measurement can be used to estimate the self-heating of periodically actuated piezoactuators. Peak-to-peak current increases concurrently with increasing temperature. Experiments show that the current increase is 0.5% per one degree increase in actuator temperature. In addition, a compensation method is presented for the displacement changes induced by self-heating. The displacement error of the heated actuator is reduced to an average of one third when the proposed compensation is used. This thesis discusses current measurement as a part of a self-diagnostic system. Current measurement has potential in diagnosing faults and monitoring the condition of piezoelectric actuators. The experimental results achieved with several control applications indicate that the proposed electromechanical actuator model is feasible. Moreover, the results reveal that current measurement provides valuable information that can be utilized in displacement control, and force and self-heating estimation, among others. Consequently, the information obtained by current measurement can often be used to replace a sensor, thus decreasing the complexity of the system

Current measurement in control and monitoring of piezoelectric actuators

This thesis discusses the usability of current measurement in controlling and monitoring piezoelectric actuators. Current measurement contains information about the actuator and its environment. This work presents methods for utilizing the information in several control applications used in microrobotics, such as displacement control and external force estimation. The importance of current measurement is also discussed in context with piezoactuator -related problems, such as self-heating. After an introduction to the topic, an electromechanical model of a piezoelectric actuator is presented. The model summarizes the different effects and inputs that affect the output of piezoelectric actuators. The model is later utilized as basis for the development of more specialized models for several control applications. This thesis presents several control schemes which utilize current measurement in displacement control. The control methods utilize inverse actuator models to estimate the current required for the actuator to move as desired. The experiment results are very good: hysteresis is less than 2% and drift about 1% of the motion range. Force estimation without the use of force sensors is accomplished with an actuator model that approximates the present external force by combining information about the current, voltage and displacement. The measured displacement can be simultaneously utilized in feedback control, thus enabling precise microrobotic operations. The accuracy of the estimated force is within 10% of the force range, with an average inaccuracy of about 3%. Current measurement can be used to estimate the self-heating of periodically actuated piezoactuators. Peak-to-peak current increases concurrently with increasing temperature. Experiments show that the current increase is 0.5% per one degree increase in actuator temperature. In addition, a compensation method is presented for the displacement changes induced by self-heating. The displacement error of the heated actuator is reduced to an average of one third when the proposed compensation is used. This thesis discusses current measurement as a part of a self-diagnostic system. Current measurement has potential in diagnosing faults and monitoring the condition of piezoelectric actuators. The experimental results achieved with several control applications indicate that the proposed electromechanical actuator model is feasible. Moreover, the results reveal that current measurement provides valuable information that can be utilized in displacement control, and force and self-heating estimation, among others. Consequently, the information obtained by current measurement can often be used to replace a sensor, thus decreasing the complexity of the system

Simultaneous actuation and force estimation using piezoelectric actuators

This paper introduces a force estimation method that enables simultaneous actuation and force estimation using piezoelectric actuators. The method combines an actuator input voltage and a current together with a displacement measurement to a force estimator. The force estimator contains a non linear actuator model to approximate the present external force without the use of force sensors. The measured displacement can simultaneously be utilized in feedback control to enable precise microrobotic operations. The results show that the method enables estimation of both static and varying forces under simultaneous position feedback control. Experimented displacement trajectories contain both stationary and mobile phases. The achieved accuracy in force estimation according to experiments is better than 10% of the full force scale. Therefore force sensing without the use of separate force sensors is feasible, which opens new applications for force sensing in microrobotics.Peer reviewe

Current control of piezoelectric actuators with power loss compensation

This paper introduces a feedforward charge control method, which controls the displacement by the amount of current fed to the actuator. The method includes estimation and compensation of the power losses occurring in the actuator. Power losses are estimated with an experimentally created dynamic model, that does not include the load and self heating effects. Even though the method is based on feedforward control, the amount of current is controlled in closed loop, using a precise current measurement and a PID controller. Experiments with a piezo bender show promising results; the hysteresis was nearly reduced to one part in twenty and drift to one part in ten, in comparison to open-loop voltage control. The proposed method can predict the power losses quite accurately and can therefore be utilized not only for the control but also for power estimation in applications where power consumption is critical.Peer reviewe

Self heating of piezoelectric actuators. measurement and compensation

This paper introduces the effect of self heating on the displacement of piezoelectric actuators and a novel method to quantify self heating. Issues influencing self heating include; the frequency and the amplitude of the driving voltage, and the size, or more specifically the volume-area ratio of the actuator and they are also discussed. The effect of a load on the heat generation is studied. According to the experiments, the peakto- peak value of the consumed current is a good indication of the temperature rise of the actuator. This can be used for the protection of the actuator from overheating, or as the authors will propose in the paper, it can be used to compensate for the changes in the displacement induced by the self heating. The displacement error of the heated actuator reduces in average down to one part in three when the proposed compensation is used.Peer reviewe

Microcutting of living tissue slices and stem cell colonies by using mechanical tool

There is a growing need for methods to cut living tissues in vitro and cell cultures in microscale in biological and medical research. This paper presents two different microrobotic methods for cutting: mechanical microdissection using a sharp needle and liquid jet cutting utilizing a pressured liquid jet. Test devices for both the methods were built and the experiments were conducted with thin tissue slices and stem cell colonies. The devices built as well as the structure of the experiments and the results gained are discussed in this paper and the methods are compared with each other.Peer reviewe

Quantifying groundwater dependence of a sub-polar lake cluster in Finland using an isotope mass balance approach

A stable isotope study of 67 kettle lakes and ponds situated on an esker aquifer (90 km²) in northern Finland was carried out to determine the role and extent of groundwater inflow in groundwater-dependent lakes. Distinct seasonal fluctuations in the δ¹⁸O and δ²H values of lakes are the result of seasonal ice cover prohibiting evaporation during the winter. An iterative isotope mass balance approach was used to calculate the inflow-to-evaporation ratios (<i>I</i>_TOT/<i>E</i>) of all 67 lakes during the summer of 2013 when the isotopic compositions of the lakes were approaching a steady-state. The balance calculations were carried out independently for ²H and ¹⁸O data. Since evaporation rates were derived independently of any mass balance considerations, it was possible to determine the total inflow (<i>I</i>_TOT) and mean turnover time (MTT) of the lakes. Furthermore, the groundwater seepage rates to all studied lakes were calculated. A quantitative measure was introduced for the dependence of a lake on groundwater (<i>G</i> index) that is defined as the percentage contribution of groundwater inflow to the total inflow of water to the given lake. The <i>G</i> index values of the lakes studied ranged from ca. 39 to 98%, revealing generally large groundwater dependency among the studied lakes. This study shows the effectiveness of applying an isotope mass balance approach to quantify the groundwater reliance of lakes situated in a relatively small area with similar climatic conditions