Six-point Method Research Articles

Oscillating Saw Calibration for Mandibular Osteotomy Robots

Accurate oscillating saw tool calibration is an important task for mandibular osteotomy robots to perform precise cutting operations. However, in contrast to traditional tool calibration which just calibrates the tool center position (TCP) or the tool feed axis, both the position and the plane orientation of the saw should be carefully calibrated. Therefore, aiming at this problem, in this paper, we propose a method to carry out oscillating saw calibration by employing an optical stereo vision tracking system. At first, hand–eye calibration is conducted to ascertain the spatial pose of the vision frame within the manipulator’s base frame. Subsequently, employing a probe, the positions of the sawtooth points on the oscillating saw plane are captured within the vision frame. These positions are then translated to the manipulator’s end-effector frame using the positional elimination algorithm proposed in this paper. Finally, the pose of the oscillating saw plane within the manipulator’s end-effector frame is extrapolated from the positions of the three sawtooth points. The result shows that the position errors of the points on the oscillating saw plane are within 0.25 mm and the variance of the plane normal direction is 1.93∘ in the five experiments. This approach enables accurate calibration of the oscillating saw plane’s position and orientation within the manipulator’s end-effector frame. Furthermore, it mitigates the necessity of continual adjustments to the joint angles of the manipulator as required by the “six-point method”. However, this approach is hinged upon the availability of precision-oriented 3D positioning equipment.

A new method for measurement and calculation of unit width suspended sediment transport rate

Abstract The unit width suspended sediment transport rate is the basis for calculating river sediment flux, which provides an important measure of river hydrology and morpho-dynamics. By integrating the vertical distribution of the suspended sediment concentration and logarithmic flow velocity, the formula for unit width suspended sediment transport rate is presented. Based on this formula, the calculation of the near-bed relative transport rate missing in field measurement is given. Moreover, a new stratified water sampling device is invented for suspended sediment transport rate measurement by the six-point method at Mengsheng hydrological station in the Lancang River basin. Results of 24 sets of measurements show that the near-bed relative sediment transport rate ranges from 3.4 to 10.7% and is significantly positively correlated with the suspension index. The unit width suspended sediment transport rate measured by the traditional depth integrating method is on average 15.0% smaller than that calculated by the theoretical formula, which can be a reference for correcting the sediment transport rate based on the traditional method. This work provides a new device and a new method for the measurement and calculation of the unit width transport rate of suspended sediment, which has theoretical and practical significance.

A Fast Prediction Method for the Target Reachable Zone of Boosting Gliding Vehicle Based on Database

This paper presents an effective method for the fast prediction of the target reachable zone of a boosting gliding vehicle in the gliding phase. Firstly, a six-point method is proposed for the rapid determination of the reachable zone and the feasible discrimination of the target. The method chooses six boundary points with notable features to characterize the reachable zone and considerably reduces the computational consumption. Furthermore, taking into account the need for a rapid launch and safety against unexpected events during the gliding phase, a database method for the prediction of the reachable zone is presented, which builds the database with time nodes and six boundary points and employs interpolation methods to calculate the reachable zone. The results suggest that online planning by the database method has significant potential for predicting the target reachable zone. The accuracy error is less than 1%, and the computational efficiency is increased by 90% when compared to the six-point approach.

Contrast Analysis of Flow-Discharge Measurement Methods in a Wide–Shallow River during Ice Periods

The discharge of natural rivers is one of the important hydrological factors that are considered when responding to ice-flood disasters during ice periods. Traditionally, holes need to be dug along the cross-section on the ice cover to gauge velocity distributions along the flow depth at each hole, and to calculate the cross-sectional flow discharge by integrating velocity profiles over the entire area. This method is time consuming, costly, and inefficient. The discharge measurement can be improved using the sectional flow-depth distribution and stream-tube methods. However, the selection of both the depth-averaged–velocity-estimation method and the typical survey-point position in the cross-section affects the estimation accuracy. This study first compared the estimation methods of the depth-averaged velocity, such as the one-, two-, three-, and six-point methods, and their estimation accuracy. Furthermore, the variations in relative-unit discharge distributions in common channels with cross-sectional topographies were analyzed, and the effects of the cross-section characteristic coefficient and typical survey-point position on the flow-discharge estimation accuracy were compared. The results show that the average errors of the depth-averaged velocity estimated by the one-point method at 0.5H, new three-point method, and six-point method were 1.96%, 1.22%, and 0.45%, respectively. The new three-point method is recommended if measurement workload and accuracy are key considerations. The cross-section characteristic coefficient is considered to be 0.5 and 0.25 for the natural river and artificial channel, respectively, and the maximum-flow-depth position in the mainstream area of the cross-section is selected as the typical survey-point position. Thus, the flow-discharge estimation accuracy can be improved. In conclusion, this study provides an improved stream-tube method for the measurement of flow discharge and velocity distribution in ice periods, which can be used as a reference during practical applications.

A mobile stereo vision system with variable baseline distance for three-dimensional coordinate measurement in large FOV

A novel mobile stereo vision system (MSVS) with variable baseline distance for three-dimensional (3D) coordinate measurement in large field of view (FOV) is established herein. Each independent mobile camera can rotate in the horizontal and vertical directions, and the position of the cameras are obtained by differential GPS in real time. In order to achieve rapid camera calibration in large FOV, a simplified model of MSVS based on differential GPS is constructed in this paper. A six-point method is proposed to quickly estimate the camera’s initial parameters (i.e. focal length, initial roll, pitch, and yaw angles) in the situation that the approximate value of the initial yaw angle is unknown. Moreover, the camera’s roll angle is equivalent to its approximate value measured by a high-precision inclinometer during the movement, and the unknown extrinsic parameters of each camera are reduced to the pitch and yaw angles after the camera moves. The refined pitch and yaw angles are eventually estimated by only using a single control point, which makes it possible that the 3D coordinate can be measured online after the camera moves. The computer simulation verifies the effectiveness of the extrinsic parameters calibration method using a single control point. The quantitative results demonstrate that the standard deviation of the focal length of the camera does not exceed 0.028 mm, and the mobile camera’s pitch angle and yaw angle estimated by a single control point is extremely close to the reference values. In addition, the average error of the 3D coordinate on each axis after the camera moves is smaller than 0.08 m in the measuring distance of 100 m, and that on X-axis and Z-axis is comparable and does not exceed 0.35 m. The proposed methods are suitable for the occasions that high accuracy is not required in the field of 3D coordinate measurement in large FOV.

Precise Measurement of Inhomogeneity of 2-D System by Six-Point Method

Nondestructive, quantitative determination of inhomogeneity degree of 2-D system by the measurement of electrical properties is presented. Six point contacts have to be located at arbitrary positions on the sample edge. The sheet resistivity and the inhomogeneity parameter are determined simultaneously by the measurement of nine so-called four-probe resistances. The method is global, i.e., the local inhomogeneity will be always detected irrespectively of their location.

Effectiveness of a Specially Designed Dental Model for Training, Evaluation, and Standardization of Pocket Probing

The aim of this study was to evaluate the effectiveness of a dental model in training, evaluation, and standardization of examiners in pocket probing and to determine the appropriate thresholds of accuracy and measuring time when using this model for evaluation of probing skills without measuring patients' pockets repeatedly. In 2011-12, a total of 66 dental professionals and 20 dental students in Japan measured the probing depths of 24 artificial teeth using the six-point method on a dental model. All examiners measured the probing depths of six tooth groups and then checked the correct depths in each group. Each examiner measured four groups in a group-by-group manner. For each group, the measuring time and examiner's accuracy were recorded. Receiver operating characteristic (ROC) curves for various thresholds of measuring time were drawn for thresholds of accuracies to determine the passing mark as a skilled examiner. The accuracy significantly increased from the first to the fourth measurements, and the measuring time was significantly reduced for both the professionals and students. The total measuring time was significantly longer for the students than the professionals. The students' accuracy was significantly lower than that of the professionals in the first measurement group. The increasing rate of accuracy was significantly higher for the students than the professionals. These results and ROC curves suggested that the dental model is effective for periodontal pocket probing training and for the evaluation and standardization of examiners' probing skill at a preclinical level. An examiner having accuracy ≥80% within four minutes for six tooth measurements in this model could be considered a skilled examiner.

Real-time position and orientation measurement with occlusion handling for distributed optical large-scale metrology systems

Occlusion is a major problem for real-time position and orientation measurement with distributed optical large-scale metrology systems. This paper presents two novel methods with occlusion handling to address this issue, which should be used in combination for practical applications. These two approaches are based on the constraints established by three control points and six control points, respectively, and then the position and orientation can be calculated through iterative optimization algorithms. In this paper, all the work is carried out by using the workspace measuring and positioning system as a verification platform. The experimental results show that the orientation accuracies of the three-point method and the six-point method are kept within 0.1 and 0.04 deg, respectively, and the position accuracy exceeds 0.15 and 0.08 mm.

Cluster analysis for acupoint specificity of acupuncture effect based on cerebral infarction rat model

To study the acupoint specificity through the comprehensive evaluation of the acupuncture effect on rat model with the middle cerebral artery occlusion (MCAO). Duplicated MCAO model by Zea-longa's thread ligation was assessed by Zausinger's six-point method, and rats with 1-3 scores were chosen to be grouped. According to the randomized and controlled principle, rats were divided into 6 basic control groups (including normal group, sham group, model control group, model group without intervention, Nimodipine group, lateral-to-Renzhong group) and 6 acupuncture groups [including Neiguan (PC6) group, Weizhong (BL40) group, Chize (LU5) group, Sanyinjiao (SP6) group, Renzhong (DU6) group and non-acupoint group]; in each acupoint or non-acupoint 9 different parameter combinations were respectively set by orthogonal intersection method. There were in total 60 groups, and each group had 12 rats. The rats were treated by acupuncture with the lifting-thrusting manipulation every 12 h, in total 6 times. Indices of neurobehavioral scores, cerebral blood flow, infarction rate, microcirculation, and light microscope, etc. were measured. In order to comprehensively evaluate the acupuncture effect to research the specificity of acupoint, a cluster analysis was made with SPSS17.0 for the comprehensive effect scores of the samples computed according to the comprehensive evaluation models, and then sorting and classification were made for the comprehensive effect scores. In the acupuncture groups every acupoint had different therapeutic effect due to different acupuncture parameter combinations; among the acupuncture groups the orders of curative effect were as followings: Neiguan group was of exceptional result, Weizhong group and Sanyinjiao group were of valid results in upper level, Chize group and Renzhong group were of valid results in lower level, and non-acupoint group was of invalid result; the therapeutic result of acupoint group was superior to non-acupoint group; and the curative effect of acupuncture group was also superior to basic control group. The acupoint has the specificity of acupuncture effect, and the acupoint specificity is relative.

Influence of acupuncture on neural movement function in rats with middle cerebral artery occlusion-A randomized controlled trial

ObjectivesTo observe recovery in movement function in rats with middle cerebral artery occlusion (MCAO) after acupuncture treatment. MethodsAccording to the randomized and controlled principle 1384 rats were divided into the basic control group (including the normal, sham, model control, model without intervention, Nimodipine, and para-Renzhong groups) and the acupuncture group (including the Neiguan (PC 6), Weizhong (BL 40), Sanyinjiao (SP 6), Chize (LU 5), Renzhong (GV 6) and non-acupoint groups). MCAO was modeled by Zea-longa's thread ligation and rats with scores of 1–3, as assessed by Zausinger's six-point method, were used in this study. Moreover, in the acupuncture group each acupoint was set with 12 different parameters by the orthogonal intersection method, resulting in 78 groups with 18 rats per group. The rats were treated by acupuncture once every 12 h for a total of six sessions and neurobehavioral scores were measured after each session. The neurobehavioral scores were compared by one-way ANOVA using the statistical software SPSS 17.0. ResultsAfter acupuncture therapy the mean neurobehavioral scores in MCAO rats increased gradually at each time point with a significant difference among the six scores, but with no significant differences between the fourth (48 h) and the fifth score (60 h), and between the fifth (60 h) and the sixth (72 h) score (P> 0.05). ConclusionsMCAO rats gradually recovered movement function over multiple acupuncture sessions. After the fouth acupuncture session (48 h), the neurobehavioral scores of rats with cerebral infarction remained stable. Acupuncture treatment had a reliable curative effect on movement function in cerebral infarction rats.

Surface optimization technique for MammoSite breast brachytherapy applicator

We present a technique to optimize the dwell times and positions of a high-dose-rate (192)Ir source using the MammoSite breast brachytherapy applicator. The surface optimization method used multiple dwell positions and optimization points to conform the 100% isodose line to the surface of the planning target volume (PTV). The study population consisted of 20 patients treated using the MammoSite device between October 2002 and February 2004. Treatment was delivered in 10 fractions of 3.4 Gy/fraction, twice daily, with a minimum of 6 h between fractions. The treatment of each patient was planned using three optimization techniques. The dosimetric characteristics of the single-point, six-point, and surface optimization techniques were compared. The surface optimization technique increased the PTV coverage compared with the single- and six-point methods (mean percentage of PTV receiving 100% of the prescription dose was 94%, 85%, and 91%, respectively). The surface method, single-point, and six-point method had a mean dose homogeneity index of 0.62, 0.68, and 0.63 and a mean full width at half maximum value of 189, 190, and 192 cGy/fraction, respectively. The surface technique provided greater coverage of the PTV than did the single- and six-point methods. Using the FWHM method, the surface, single-, and six-point techniques resulted in equivalent dose homogeneity.

Treatment volume and dose optimization of MammoSite breast brachytherapy applicator

Purpose Limited information has been reported on the dosimetry achieved with the MammoSite breast brachytherapy applicator. We present our results regarding the volume of treatment and a comparison of a single prescription point, single dwell position optimization technique with a six prescription point, multiple dwell position method. Methods and materials Between October 14, 2002 and February 28, 2003, 21 patients with early-stage breast cancer were treated using the MammoSite device. The treatment was delivered in 10 fractions of 3.4 Gy/fraction, b.i.d., with a minimum of 6 hours between the daily fractions. CT of the lumpectomy cavity was obtained both with and without the inflated balloon. A planning target volume was constructed using a three-dimensional planning system. A three-dimensional expansion of the balloon surface was performed using the chest wall and skin as limiting structures. The volume of the inflated balloon was removed from this volume, and the volume of tissue treated in each patient was determined. A sequential expansion in 1-mm increments around the empty lumpectomy cavity was performed until the closest equivalent volume to the planning target volume was obtained. The treatment for the patients in this study was planned using both a single prescription point, single dwell position optimization technique and a six-prescription point, multiple dwell position technique. The single prescription point method has been described in a previous publication. The six-prescription point method used six points placed 1 cm from the balloon surface. Four points are in a plane transverse to the balloon axis perpendicular to the axis of the catheter, and two points are placed along the axis of the catheter. The prescription points along the catheter axis are used to compensate for the decreased dose coverage owing to anisotropy dose distribution of the source. The Nucletron HDR Plato Brachytherapy planning system was used to optimize the source positions and dwell times. Results The volume of breast tissue treated by the MammoSite device was equal to the volume encompassed by a mean 1.6-cm (SD, 0.1) margin around the empty lumpectomy cavity. Compared with the single prescription point optimization method, the six prescription point method provided better dose coverage, with a mean percentage of volume receiving 90% of the prescription dose of 97.2% (SD = 2.1) vs. 89.5% (SD = 4.6) for the single-point method. The mean percentage of volume receiving 100% of the prescription dose was 88.9% (SD = 3.3) for the six-point method vs. 77.6% (SD = 6.1) for the single-point method. However, compared with the single-point method, the six-point optimization method resulted in treatment that was less uniform, with a mean dose homogeneity index of 0.62 (SD = .07) vs. 0.66 (SD = .08) for the single-point method. Conclusion The volume of normal breast tissue treated by the MammoSite device is comparable to other methods of interstitial brachytherapy that treat a 1–2-cm margin of tissue around the excision cavity. The six-prescription point, multiple dwell position method improved dose coverage with a slight decrease in dose homogeneity. The six-point method offers greater reliability of dose coverage compared with the single-point method by providing an increased number of reference points.

Encoding strategies for three‐direction phase‐contrast MR imaging of flow

Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase-contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six-point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four-point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six-point method. An alternate, balanced four-point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four-point method is more efficient and is preferred over the six-point approach.

Correlation analysis of the fading of radio waves reflected vertically from the ionosphere

The correlation analysis of Briggs et al. (1950) and phillips and Spencer (1955) has been applied to the fading of radio waves reflected from the E and F-regions of the ionosphere, observed at three closely spaced receivers. Histograms are presented showing the size of the characteristic ellipse of the radio diffraction pattern formed on the ground, and also the axial ratio and the direction of the major axis of this ellipse. Results are presented which show the importance of random changes in the pattern relative to pure drift in producing fading. Corresponding results from other parts of the world are reviewed briefly. Drift velocities found by correlation analysis are compared with those found by the simple time-delay method, and it is shown that the errors in the time-delay method are considerable. A comparison is made between the method of calculation used by Briggs et al. and the six-point method of Yerg (1955); the former is to be preferred.