Optimal measurement angles of the three-probe spindle error motion separation technique

Carbonitride thin films have been deposited on silicon substrate by the irradiation of energetic nitrogen ions emanated from dense plasma focus device. The carbon ions are ablated by the irradiation of relativistic electrons from the insert material (graphite) placed at the anode tip. The x-ray diffraction analysis demonstrates that a polycrystalline thin film consisting of various compounds such as Si3N4, SiC, and C3N4 is formed on the silicon (100) substrate. Crystallinity of different compounds decreases with the increase in angular positions (0°, 10°, and 20°). Raman spectroscopy shows the appearance of graphitic and disordered bands with silicon nitride and silicon carbide indicating the formation of carbonitride. Raman spectra also indicate that broadening of bands increases with the increase in focus deposition shots, leading to the amorphization of the thin film. The amorphization of the thin films depends on the ion energy flux as well as on the sample angular position. The scanning electron microscopy exhibits the damaging of the substrate surface at 0° angular position. The microstructure shows the tubular shape for higher ion dose (40 focus shots). At 10° angular position, a two phase phenomenon is observed with the ordered phase in the solid solution. A smooth and uniform surface morphology showing a small cluster is observed for the 20° angular position.

The effects of fatigue on the resultant joint moment, agonist and antagonist electromyographic activity at different angles during dynamic knee extension efforts

In previous studies, we have found that the accuracy in judging collinearity of lines or dots varies considerably from one subject to another as a function of the relative angle of the stimulus elements. A model of errors generally shows large excursions across several subranges of angular position. These do not appear to be motor errors, at least not ones that are well separated from perceptual mechanisms. The errors are most likely generated at primary visual cortex, or beyond. We examined and modeled accuracy in judging collinearity of dot pairs, varying the angular position of the dots through 360 degrees, the distance between the dots (stimulus span), and the distance at which the subject was required to respond (response span). Subjects manifested idiosyncratic profiles of error across angular positions, as reported previously. But across the tested range of spans, from 4 to 8 deg, the errors tended to be the same, irrespective of stimulus or response span. This suggests that the judgments are based on a radial (angular) measure of spatial position. We discuss these results in the context of proposals that the brain maps spatial position using rotation coordinates. These new data are consistent with the hypothesis that subjects use the z-axis coordinates as a mental protractor for judging angular position and collinearity.

To improve a robot’s absolute positioning accuracy, researchers have extensively studied the robot kinematic model containing position and orientation errors of rotary axis average lines, widely known as Denavit–Hartenberg (D-H) parameters. To further improve the absolute positioning accuracy of industrial robots, this article proposes a novel kinematic model and its identification scheme. The proposed kinematic model for a serial-linked industrial robot contains the bidirectional angular positioning deviations of each rotary axis, represented in a lookup table, in addition to its D-H parameters. The angular positioning deviations of the rotary axes are modeled as a function of angular command positions, along with the direction of rotation to model the influence of backlash. This article also proposes a novel approach to identify the proposed kinematic model with the bidirectional angular positioning deviations using a laser tracker with indexing each rotary axis at specified angular positions (“circle point method”). Moreover, the model-based compensation technique is being experimentally investigated to validate the prediction accuracy of the proposed model. The findings of the experiment show that the proposed model enhances the robot’s absolute positioning accuracy significantly over the entire workspace.

The orientation and the angular rates of the body of a robotic vehicle are required for the guidance and control of the vehicle. In the current robotic systems these quantities are obtained by the use of inertial sensing systems. Inertial sensing systems involve drift errors which can be significant even after the vehicle has traversed only short distances on the terrain. A different approach is suggested here which guarantees accurate, drift-free sensing of the angular position and rates of the vehicle body. A camera system consisting of two cameras in fixed relationship to one another is made to continuously track two stationary objects (stars or the sun). The camera system is mounted on the vehicle body through an actuated three-degree-of-freedom joint. The angular positions and rates of these joints can be used to evaluate the angular positions and rates of the vehicle body. An estimate of the absolute position of the vehicle on the terrain can also be obtained from this sensing system. This can serve as the primary system for estimating the position of a vehicle on a planet, or as an inexpensive alternative/backup to a more accurate Global Positioning System (GPS) for estimating the position of a vehicle on earth.

1. While making saccades between targets with the head stationary, eye positions are constrained to two of the possible three degrees of freedom. Classically this constraint has been described by Donders' and Listing's laws. The objective was to determine whether these laws also apply for the straight arm when pointing between different targets. Thus we determined whether the arm adopts only one angular position for every pointing direction (Donders' law) and whether these positions can be described by rotations from a reference position about axes that lie in a plane (Listing's law). 2. The angular positions (orientations) of the arm in three-dimensional space were studied as subjects pointed with a straight arm at different targets. Arm position was measured with the search coil technique by means of coils attached to the back of the hand. Pointing was studied over a range of +/- 45 degrees in all directions from a central target located 45 degrees to the right of the straight-ahead position. 3. The positions of the arm in space were described by quaternion vectors, i.e., a particular position was described in terms of the axis and amplitude of a rotation from a reference position to that position. Using this description, it was found that the straight arm adopted a similar orientation (standard deviations ranged from 2.8 to 4.8 degrees) when pointing at a particular target irrespective of which target from which it had moved. 4. The angular position vectors for arm positions associated with relatively small movements (e.g., less than +/- 30 degrees) lay in a flat surface with minimal torsion. At first sight, this surface appeared to be similar to Listing's plane of the eye. However, for positions associated with larger movements (e.g., +/- 45 degrees) it became apparent that, unlike the eye, the surface deviated from one obeying Listing's law, i.e., it was twisted and showed torsion like that produced by rotations around the horizontal and vertical axes of a Fick gimbal. (The characteristic of a Fick gimbal is that the vertical axis is fixed, whereas the horizontal axis moves with the gimbal.) 5. Although there were differences between subjects, all showed a twisted position vector surface. The twist was always in the same direction, and it was always less than that of a Fick gimbal. 6. This position vector surface had a similar shape whether the arm was stationary or was moving between targets, whether subjects pointed with or without vision, and whether the pointing arm had moved between targets or from a bent-elbow position on the lap.(ABSTRACT TRUNCATED AT 400 WORDS)

A linear and rotational two-degrees-of-freedom switched reluctance motor (2DOF-SRM) has been developed to independently control linear and rotational actuation on one actuator. The 2DOF-SRM drive system requires information on the linear and angular positions of the rotor for its control. The approximate angular position of the prototype 2DOF-SRM rotor was detected by the built-in photo-switches that utilize the salient pole of the rotor as the sensor target. The linear position of the rotor was detected by an external linear position sensor mechanically connected to the output shaft. To simplify this sensing system and improve sensing resolution, this paper presents a noncontact optical sensing method to simultaneously detect linear and angular positions of an actuating 2DOF-SRM rotor. The sensing principle for detecting the combined linear and rotational motion of the 2DOF-SRM and the performance of the linear and angular position sensing system are reported.

The aim was to study how three cues (patient's age and angular position and degree of impaction of the molar) were distributed among removed mandibular third molars associated with pathologic conditions and to compare these results with dentist' treatment decisions in another group of molars consisting of asymptomatic mandlbular third molars, as mediated by the same cues. The overall agreement was fairly high between the dentist' treatment decisions and the removal rate among the molars subjected to removal. Thus, molars partially covered by soft tissue in patients aged 19 to 40 years had a high removal rate, and molars totally covered by bone tissue had the lowest removal rate in accordance with the dentist' treatment decisions. There were some exceptions. For example, molars partially covered by soft tissue in horizontal and mesioangular positions were rated higher by the dentists than the removal rates indicated. Distoangular molars in patients aged 26 to 40 years had the highest removal rate but a considerably lower order according to the dentist' decisions. Scientific evidence indicates that molars in mesioangular and horizontal positions present a low risk and molars in distoangular position present the highest risk of developing pathologic conditions, compared with other angular positions.

An insight into the dynamics of a rigid rotor on two-lobe wave squeeze film damper

Regulation of wrist stiffness by the stretch reflex

A convergence analysis of the angular position and velocity tracking errors and parametric estimation errors for a 2-link robot dynamics in the absence of noise exist in the literature (Slotine and Li in Applied nonlinear control. Prentice- Hall Inc, Englewood Cliffs, NJ, 1991). In this paper, we consider the effect of noise on the robot dynamics as well as on the parameter update equation. Noise in the robot dynamics arises due to errors in reading \(q,\dot{q}\), i.e., the angular positions and velocities of the robot link that are used for calculating the errors e, \(\dot{e}\) used to generate the feedback torque via the PD controller. Noise is chosen as Gaussian because it is produced as the cumulative effect of several small independent random effects like electrons moving in the motor wire and dust friction, and we know from the central limit theorem that the sum of a large number of small independent effects has a Gaussian distribution. Noise in the parametric update equation arises due to finite register effects in the digital computer. Both of these noises are modeled as white Gaussian, and the robot and parametric update dynamics have thus been modeled as nonlinear coupled stochastic differential equations. Using linearization of this coupled SDE system around the non-random components of the trajectory estimation error and parametric estimation errors, we first derive stochastic integral expressions for the random components in these errors. We then evaluate the average rate of change of the Lyapunov energy function using Ito calculus and obtain conditions on the noise amplitude so that the limiting value of this average rate of change is negative, guaranteeing asymptotic average stability of the system and parametric estimation algorithm. One of the novelties of this work is the new algorithm for parameter estimation which enables us to improve on the algorithm convergence rate as compared to previous work (Slotine and Li 1991). Finally, our stochastic algorithm is verified by performing hardware experiments with the actual PHANToM Omni robot.

The article deals with problems associated with determining permissible accuracy of Earth remote sensing satellite control over observation intervals taking into account the interaction of optronics and charge-coupled devices with time-delay and integration (CCD TDI). The control accuracy requirements are determined for the condition that the allowable image shift value should not be exceeded. The allowable accuracy is proportional to the time of exposure of a resolution cell which depends on the number of CCD array storage rows and image motion velocity. The discrepancy between the image motion velocity supported by the optronics and the Earth surface scanning velocity depends to a large extent on the satellite control accuracy regarding its angular position and rotation about the centre of mass. Angular motion over observation intervals is formed based on the condition of constant specified longitudinal velocity and zero transverse velocity of image motion relative to the frame centre. The dependence of the frame-centre image shift value on the spacecraft angular motion control system follow-up errors is determined. Based on the obtained relation, an algorithm of determining allowable angular motion follow-up errors is proposed. The angular motion follow-up error influences the accuracy of the optronics optic axis pointing at the central route line. The article gives examples illustrating application of the proposed algorithm as well as assessment of en-route targeting accuracy.

Interference-enhanced micro-vision-based single-shot imaging of five degrees-of-freedom error motions for ultra-precision rotary axes

The majority of existing normative torque generation capability (torque capability for short) databases are reported in the form of torque as a function of joint angle. although it is well recognized that torque capability is a function of both the joint angular position and angular velocity. The main objective of this study was to develop the methodology of 3-D dynamic representation of torque capability using the ankle joint as an example. The ankle torque capability of 20 males and females was assessed at 5 levels of ankle joint angular positions and velocities in each direction of plantar and dorsi flexion. The ANOVA results indicated significant main effects of joint angular position, angular velocity, direction, and gender, in addition to the interaction effect of angular position and velocity (p < .003) on the torque capability of the ankle joint. The regression analysis indicated that an individualized quadratic surface response performed significantly belter than the models developed for each gender or the whole population using the coefficient of determination and standard error of the regression as criteria. Such 3-D representation of torque capability has a broad spectrum of applications ranging from rehabilitation and ergonomic to biomechanical applications.

Synchronized control of cross-flow-water-turbine-based twin towers