Two-axis Tracking Research Articles

Solar geometry for fixed and tracking surfaces

A general expression for the solar radiation incidence angle in terms of the slope and surface azimuth is derived for both fixed and tracking surfaces. Using this expression, relationships for the slope and azimuth of optimally tracked one- and two-axis tracking surfaces are developed. This information is necessary in determining incident solar radiation based upon horizontal measurements.

Comparison of Advanced Engines for Parabolic Dish Solar Thermal Power Plants

A paraboloidal dish solar thermal power plant produces electrical energy by a two-step conversion process. The collector subsystem is composed of a two-axis tracking paraboloidal concentrator and a cavity receiver. The concentrator focuses intercepted sunlight (direct, normal insolation) into a cavity receiver whose aperture encircles the focal point of the concentrator. At the internal wall of the receiver the electromagnetic radiation is converted to thermal energy. A heat engine/generator assembly, which is mounted directly behind th receiver, then converts the thermal energy captured by the receiver to electricity. Developmental activity has been concentrated on relatively small power modules which employ 11- to 12-m-diam dishes to generate nominal power levels of approximately 20 kW. A comparison of advanced heat engines for use on the dish power module is presented in terms of the performance potential of each engine as weighed against its requirements for advanced technology development. Three advanced engine possibilities are considered. These are the Brayton (gas turbine), Brayton/Rankine combined cycle, and Stirling engines. All three engine candidates are attractive in terms of overall system performance potential.

A simple method for calculating the annual insolation on solar collectors

The annual average insolation incident upon a variety of principal solar collector types-including shading effects-is calculated by approximating the annual variation of daily radiation by its value on one average day, equinox. The rationale for the selection of equinox is discussed, and results are presented for concentrating collectors with two-axis, one-axis polar, one-axis east-west and one-axis north-south tracking, and for flat plate collectors. We compare our results with the Rabl correlations[1], which are based on actual weather data from a variety of locations throughout the U.S.A. Values predicted from the coarse approximation of treating the entire year as one specific average day (equinox) turn out to be surprisingly accurate. For the specific cases considered, the predictions deviate from the Rabl correlations by 5 per cent at most.

Thermal Buffering of Receivers for Parabolic Dish Solar Thermal Power Plants

A parabolic dish solar thermal power plant comprises a field of parabolic dish power modules where each module is composed of a two-axis tracking parabolic dish concentrator which reflects sunlight (insolation) into the aperture of a cavity receiver at the focal point of the dish. The heat generated by the solar flux entering the receiver is removed by a heat transfer fluid. In the dish power module, this heat is used to drive a small heat engine/generator assembly which is directly connected to the cavity receiver at the focal point. A computer analysis is performed to assess the thermal buffering characteristics of receivers containing sensible and latent heat thermal energy storage. Parametric variations of the thermal inertia of the integrated receiver-buffer storage systems coupled with different fluid flow rate control strategies are carried out to delineate the effect of buffer storage, the transient response of the receiver-storage systems and corresponding fluid outlet temperature. It is concluded that addition of phase change buffer storage will substantially improve system operational characteristics during periods of rapidly fluctuating insolation due to cloud passage.

Effect of vertical active vibration isolation on tracking performance and on ride qualities: F. P. DiMasi, R. E. Allen and P. C. Calcaterra 1972 NASA CR-2146. (79 pages, 33 figures, 8 tables, 6 references)

An investigation to determine the effect on pilot performance and comfort of an active vibration isolation system for a commercial transport pilot seat is reported. The test setup consisted of: a hydraulic shaker which produced random vertical vibration inputs; the active vibration isolation system; the pilot seat; the pilot control wheel and column; the side-arm controller; and a two-axis compensatory tracking task. The effects of various degrees of pilot isolation on short-term (two-minute) tracking performance and comfort were determined.

Two-axis manual positioning and tracking controls

In this article, the author examines the characteristics of joysticks and trackballs, two of the more common controls used for positioning tasks, such as occur with radar or some computer displays, and for continuous tracking tasks such as vehicle steering or weapon aiming. Results are given of a number of tests with digital positioning controls, and the author discusses the prediction of operator performance on tracking tasks, also the use of ‘aiding’ circuits to increase control response.

Two-axis manual tracking control systems with complex display and operation

This paper describes the results of two-axis manual tracking control systems which are compounded with two single-axis systems, by using a complex display and operation.Each of the reference values is independent Gaussian noise angular frequency of break point is 0.5-6.0rad/sec. The display is a two-channel synchroscope. The controller is a two-axis stick manufactured by authors and also additionally knobs, and its values operated are transfered to D.C. voltage by potentiometers. And each of the controlled systems is propotional dynamics without cross coupling.The results are shown as follows. 1) Horizontal and vertical manual tracking control well agreed with each other. 2) Pursuit and compensatory manual tracking task well agreed with each other. 3) Each of control performances is approximated by A× (the angular frequency of break point of reference value) B, where A=0.207-0.218, B=0.843-0.866, and correlation coefficients are 0.995-0.998. 4) Cross coupling in the human information processing system from eyes to arm is little. 5) Two-axis stick is superior in the case of two-axis manual tracking control and also knob in the case of single-axis.Furtter investigations which is examining the influence of cross coupling between horizontal and vertical controlled systems and its dynamics, are carring out.

Investigation of Motion Requirements in Compensatory Control Tasks

Tests consisting of one- and two-axis closed-loop tracking tasks, with and without motion, have been made to define some areas where motion cues are beneficial. Tests were made with reduced scaling on the motion input to investigate the minimum requirements of motion cues in those tests where motion was found to be of assistance. For the set of conditions tested, little or no difference in the measurement criteria was observed in the single-axis motion/no motion runs. Similar results were obtained when comparing two single-axis tests with different pitch orientation. The two-axis tests, which consisted of pitch and yaw and pitch and roll, did, however, produce a difference in the error measurements in the motion/no motion comparison. A decrease in normalized tracking error and an increase in closed-loop system frequency were observed when motion was added. Tests were also run, in pitch and yaw only, in which the scale of the motion input was reduced. These tests were performed by the subject in sequence starting with no motion all the way to full motion and back down to no motion. Each motion scale condition (none, 1/16, ⅛, ¼, ½, and full) constituted a test. The normalized tracking error remained constant for full, ½, and ¼ motion scaling, but increased with a further reduction in motion scaling.

The Human as an Optimal Controller and Information Processor

A mathematical model of the instrument-monitoring behavior of the human operator is developed. The model is based on the assumption that the operator behaves as an optimal controller and information processor, subject to his inherent physical limitations. The resulting model depends explicitly on the control task and the control actions. Provision is made for the ability to obtain information from the peripheral visual field. There are no restrictions on signal coupling. The specific characteristics of the operator's visual sampling behavior are predicted by solving a nonlinear, deterministic optimization problem. A two-axis compensatory tracking example is investigated, and the results exhibit the general characteristics expected of a human operator performing a similar task.

Human Information Processing Rates during Certain Multiaxis Tracking Tasks with a Concurrent Auditory Task

A series of experiments was conducted to determine the information processing rates of several subjects performing one- and two-axis compensatory tracking tasks with a secondary auditory task. The experimental variables were the order of controlled element dynamics, the forcing function, and the addition of a secondary task. Human information processing rates decreased slightly on each tracking channel with the addition of the second tracking channel or the secondary auditory task. Other than this effect, the information processing rates were additive until a limit in the total information processing rate was reached. This limit was related to the order of the controlled element.

Human Performance in Single and Two-Axis Tracking Systems

A compensatory tracking experiment was performed on single and uncoupled two-axis tracking systems to determine the effects of training on model parameters of the human operator as well as one-two-axis differences in tracking performance. The plant dynamics were identical in both the single-axis system and the symmetrical two-axis system. Second-order dynamics consisting of a pure integration and first-order lag were used. Task difficulty was varied by changing the magnitude of the lag time constant and the frequency bandwidth of the input disturbance. Linear second- order describing functions, obtained by a model matching technique, were used to model the operator's performance.