Initial Orientation Errors Research Articles

Modeling and Reduction of the Initial Orientation Error of a Coil Vector Magnetometer

The initial orientation error of a coil vector magnetometer directly determines the measurement accuracy of the magnetic field direction. The traditional initial orientation method requires auxiliary manually operated instruments. To solve this problem, we propose an electrical orientation method based on applying bias fields. To analyze quantitatively the orientation error of the proposed method, a physical model for the coil orientation indicator and measurement errors of the magnetic direction was developed that exploits measurements of the deflected field obtained after applying two oppositely directed bias fields. The simulation results show that, when the difference indicator is 0.7 nT, the measurement error of the magnetic direction is less than 9°. Moreover, when the bias field strength is greater than 30% of the geomagnetic field strength during the orientation operation, the influence of the change in strength of the bias field on the measurement error of the magnetic direction diminishes significantly. The indirect effect of the measurement error of the total-field sensor on the measurement accuracy of the magnetic direction was also analyzed. To verify this method, we designed an experimental setup and conducted a comparative experiment. The results show that as the difference indicator increases, the measurement error of the magnetic direction increases accordingly. When this indicator is adjusted to about0.7 nT, the measurement error of the magnetic direction is less than 11.16'', which is in agreement with theoretical results.

The Task of Walking Straight as an Interactive Serious Game for Blind Children

This paper describes Following the Cuckoo Sound'', a responsive floor system designed to train blind children in walking straight. Its characteristics and potentialities are evaluated in the framework of the guidelines of instruction and assistance to blind children defined by two government agencies. Veering data analysis confirm the validity of the game in correcting both the initial orientation error and the errors in the step direction and provide further insights about veering and its relationship with walking speed and participants' clinical or experiential conditions. Moreover the system provides an engaging sensorial experience which fits not only the orientation and mobility programs but also other areas of the curriculum for blind children such as sensory efficiency, recreation and leisure, and education in the use of technology.

Propagation mechanism analysis of navigation errors caused by initial state errors for long-range vehicles

The inertial navigation system is aligned and leveled before the launch of a long-range vehicle. However, the non-uniformity of the Earth can lead to initial state errors including initial positioning errors and initial orientation errors, causing navigation errors in flight dynamics and eventually impact-point deviations up to approximately 1 km. In order to analyze the propagation mechanisms of initial state errors and rapidly estimate their influence magnitudes, navigation perturbation equation subject to apparent acceleration coupling is established based on state space perturbation theory in the launch inertial coordinate system. Afterwards, a series of analytical form of deviations are derived including gravitational acceleration deviation, apparent acceleration projection deviation, apparent acceleration coupling deviation, initial velocity errors and initial position errors. Then, the analytical propagation model of engine-cutoff state deviations and impact-point deviations are acquired by solving the navigation perturbation equation. In the simulations, computer codes are programmed to calculate the propagation matrices of engine-cutoff state deviations and impact-point deviations in the case of fixed launch azimuth, followed by the propagation mechanism analyses of initial state errors. Next, two more scenarios of different launch azimuths and different launch points are simulated to further verify the reliability of the proposed analytical propagation model. The results show that analytical solutions of the propagation model proposed in this paper can well coincide with numerical solutions, with relative errors being all less than 1%, which is also suitable for multiple distinct simulation scenarios compared with previous methods.

Literal grid map models for animal navigation: Assumptions and predictions

Many animals can navigate from unfamiliar locations to a familiar target location with no outward route information or direct sensory contact with the target or any familiar landmarks. Several models have been proposed to explain this phenomenon, one possibility being a literal interpretation of a grid map. In this paper we systematically compare four such models, which we label: Correct Bicoordinate navigation, both Target and Release site based, Approximate Bicoordinate navigation, and Directional navigation. Predictions of spatial patterns of initial orientation errors and efficiencies depend on a combination of assumptions about the navigation mechanism and the geometry of the environmental coordinate fields used as model inputs. When coordinates axes are orthogonal at the target the predictions from the Correct Bicoordinate (Target based) model and Approximate Bicoordinate model are identical. However, if the coordinate axes are non-orthogonal different regional patterns of initial orientation errors and efficiencies can be expected from these two models. Field anomalies produce high magnitudes of orientation errors close to the target, while region-wide nonlinearity leads to orientation errors increasing with distance from the target. In general, initial orientation error patterns are more useful for distinguishing between different assumption combinations than efficiencies. We discuss how consideration of model predictions may be helpful in the design of experiments.

A model for navigational errors in complex environmental fields

Many animals are believed to navigate using environmental signals such as light, sound, odours and magnetic fields. However, animals rarely navigate directly to their target location, but instead make a series of navigational errors which are corrected during transit. In previous work, we introduced a model showing that differences between an animal׳s ‘cognitive map’ of the environmental signals used for navigation and the true nature of these signals caused a systematic pattern in orientation errors when navigation begins. The model successfully predicted the pattern of errors seen in previously collected data from homing pigeons, but underestimated the amplitude of the errors. In this paper, we extend our previous model to include more complicated distortions of the contour lines of the environmental signals. Specifically, we consider the occurrence of critical points in the fields describing the signals. We consider three scenarios and compute orientation errors as parameters are varied in each case. We show that the occurrence of critical points can be associated with large variations in initial orientation errors over a small geographic area. We discuss the implications that these results have on predicting how animals will behave when encountering complex distortions in any environmental signals they use to navigate.

Gyro Drift Calibration Method Based on Free Double-Position Ground Self-Alignment for SIMS

The gyro drift is a crucial factor for initial orientation error and measurement error of SIMS (Strapdown Inertial Measurement System). Accurate ground calibration of gyro drift is an important way to reduce errors of alignment and inertial measurement. Based on the initial alignment principle of SIMS on stationary base and inertial navigation algorithm, the gyro drift models are established. A new method that a gyro drift calibration method based on free double-position ground self-alignment is proposed. The simulation and experiment results show that the method can calibrate and compensate the gyro drift, improve the measurement precision of SIMS, and verify the efficiency of the proposed method.

A geometric model for initial orientation errors in pigeon navigation

All mobile animals respond to gradients in signals in their environment, such as light, sound, odours and magnetic and electric fields, but it remains controversial how they might use these signals to navigate over long distances. The Earth's surface is essentially two-dimensional, so two stimuli are needed to act as coordinates for navigation. However, no environmental fields are known to be simple enough to act as perpendicular coordinates on a two-dimensional grid. Here, we propose a model for navigation in which we assume that an animal has a simplified ‘cognitive map’ in which environmental stimuli act as perpendicular coordinates. We then investigate how systematic deviation of the contour lines of the environmental signals from a simple orthogonal arrangement can cause errors in position determination and lead to systematic patterns of directional errors in initial homing directions taken by pigeons. The model reproduces patterns of initial orientation errors seen in previously collected data from homing pigeons, predicts that errors should increase with distance from the loft, and provides a basis for efforts to identify further sources of orientation errors made by homing pigeons.

Evidence for Automatic On-Line Adjustments of Hand Orientation During Natural Reaching Movements to Stationary Targets

Control of the spatial orientation of the hand is an important component of reaching and grasping movements. We studied the contribution of vision and proprioception to the perception and control of hand orientation in orientation-matching and letter-posting tasks. In the orientation-matching task, subjects aligned a "match" handle to a "target" handle that was fixed in different orientations. In letter-posting task 1, subjects simultaneously reached and rotated the right hand to insert a match handle into a target slot fixed in the same orientations. Similar sensory conditions produced different error patterns in the two tasks. Furthermore, without vision of the hand, final hand-orientation errors were smaller overall in letter-posting task 1 than in the orientation-matching task. In letter-posting task 2, subjects first aligned their hand to the angle of the target and then reached to it with the instruction not to change their initial hand orientation. Nevertheless, hand orientation changed during reaching in a way that reduced the initial orientation errors. This did not occur when there was no explicitly defined target toward which the subjects reached (letter-posting task 3). The reduction in hand-orientation errors during reach, even when told not to change it, suggests the engagement of an automatic error correction mechanism for hand orientation during reaching movements toward stationary targets. The correction mechanism was engaged when the task involved transitive actions directed at the target object. The on-line adjustments can occur without vision of the hand and even when target orientation is defined only by proprioceptive inputs.

Multi-Wavelength Mueller Matrix Polarimeter

The retardation of two quarter-wave plates designed for a particular wavelength decreases or increases in accordance with the wavelength of input light beam. Compensating the shifted retardation at each measurement wavelength allows us to get Mueller matrices of samples at different wavelengths without exchanging the plates. Initial orientation errors of two plates and an analyzer, which remain constant through all wavelengths, are also taken into consideration. The availability and accuracy of this polarimeter is assessed by measurement of a quarter-wave plate designed for 632.8 nm wavelength. The results show that this system is very attractive to measure optical properties and dispersion in samples.

Magnetic attitude control of a spinning satellite.

Design of a self-contained magnetic attitude control system for a spinning satellite is described, and particular control techniques for sensing and actuation are developed. A specific control problem associated with the alignment of spin axis normal to the orbit plane in the presence of external perturbations is examined in detail, and a simple control system mechanization consisting of a coil and a magnetometer is described. Some of the problems associated with acquisition (control effectiveness when the initial orientation errors are large) are discussed. Finally, a control system design procedure is described with pertinent design parameters for application to a specific satellite system.