Table Axis Research Articles

Symmetry centering of artifacts on limited-range rotary carriages or joints

This note describes a symmetry-based technique to center a part or artifact having a complete, partial or intermittent fiducial surface having an axis-of- revolution onto the axis-of-rotation of a rotating joint, stage, or flexure which has limited rotational travel. It is shown that using limited rotations and by sensing in the X-direction, the Y misalignment can be independently determined and/or by sensing in the Y-direction the X misalignment can be independently determined. Further if measurements are balanced using an ±ε < 40° rotations then the sensed magnitude variation is approximately ε/30° times the offset in the orthogonal direction when the joint is balanced halfway between the ±ε excursions. This may also be of use when positioning hemispheres or artifacts on rotary tables with their axis of rotation perpendicular rather than parallel to the rotary table axis. This technique also allows for adjustments during the initial alignment when the error may be greater than the working range of a probe and thus preventing a full 180° reversal for centering determination. Although it is possible to get both eccentricity components using single direction measurement it is not recommended due to much higher sensor-noise-related uncertainty.

Correction to: Biomechanical Influence of Treatment Table Axis Location on Axial Rotation of Lumbar Spine

Correction to: Biomechanical Influence of Treatment Table Axis Location on Axial Rotation of Lumbar Spine

Biomechanical Influence of Treatment Table Axis Location on Axial Rotation of Lumbar Spine

Various treatment devices or tables have been developed for generating axial rotation of the lumbar spine during spinal mobilization. However, the effects of the design of such treatment devices on the axial rotation of the lumbar spine have not been thoroughly investigated. In this study, the influences of the location of the treatment table rotational axis on the biomechanical behaviors of the lumbar spine were investigated for spinal mobilization using finite element analysis. The axial rotation of spinal mobilization with a supine posture on a treatment table was simulated. The sacrum was rotated by 10° along the axial rotation axis. The initial axis location was around the posterior edge of the nucleus pulposus of the L5–S intervertebral disc. The axis location was varied in the posterior direction from 0 to 200 mm in increments of 50 mm. Changes in the spine biomechanics, such as the intersegmental rotation, intradiscal pressure, and stresses on the ligaments and fibers of the annulus fibrosus, were investigated. Upon movement of the rotation axis towards the posterior direction, (1) the rotation angle along the lateral bending direction increased, (2) the intradiscal pressure increased, (3) the stresses on fibers of the annulus fibrosus and ligaments increased, and (4) the facet joint forces increased. Based on these findings, we conclude that careful consideration of the rotation axis location is important and necessary in the development of treatment beds for spinal manipulation.

The impact of isocentric shifts on delivery accuracy during the irradiation of small cerebral targets-Quantification and possible corrections.

PurposeTo assess the impact of isocenter shifts due to linac gantry and table rotation during cranial stereotactic radiosurgery on D98, target volume coverage (TVC), conformity (CI), and gradient index (GI).MethodsWinston‐Lutz (WL) checks were performed on two Elekta Synergy linacs. A stereotactic quality assurance (QA) plan was applied to the ArcCHECK phantom to assess the impact of isocenter shift corrections on Gamma pass rates. These corrections included gantry sag, distance of collimator and couch axes to the gantry axis, and distance between cone‐beam computed tomography (CBCT) isocenter and treatment beam (MV) isocenter. We applied the shifts via script to the treatment plan in Pinnacle 16.2. In a planning study, isocenter and mechanical rotation axis shifts of 0.25 to 2 mm were applied to stereotactic plans of spherical planning target volumes (PTVs) of various volumes. The shifts determined via WL measurements were applied to 16 patient plans with PTV sizes between 0.22 and 10.4 cm3.ResultsArcCHECK measurements of a stereotactic treatment showed significant increases in Gamma pass rate for all three measurements (up to 3.8 percentage points) after correction of measured isocenter deviations. For spherical targets of 1 cm3, CI was most severely affected by increasing the distance of the CBCT isocenter (1.22 to 1.62). Gradient index increased with an isocenter‐collimator axis distance of 1.5 mm (3.84 vs 4.62). D98 (normalized to reference) dropped to 0.85 (CBCT), 0.92 (table axis), 0.95 (collimator axis), and 0.98 (gantry sag), with similar but smaller changes for larger targets. Applying measured shifts to patient plans lead to relevant drops in D98 and TVC (7%) for targets below 2 cm3 treated on linac 1.ConclusionMechanical deviations during gantry, collimator, and table rotation may adversely affect the treatment of small stereotactic lesions. Adjustments of beam isocenters in the treatment planning system (TPS) can be used to both quantify their impact and for prospective correction of treatment plans.

Uji Kinerja Surface Scanner 3D Menggunakan Sensor VL53L0X dan Mikrokontroler ATMEGA8535

Digital data recording of the geometry of 3-dimensional objects require a 3D scanner tool which are mostly using an imagery sensor. However there is hardly used information of scanned result, named color. Imagery sensor requires high spesification processing unit as capable as a personal computer for data acquisition processing. This research aims to build a 3D surface scanner using a time of flight laser ranging sensor and to develop its simple function to become more valuable device. Using point to point displacement method, the sensor measures the distance between the outermost point of the object and the sensor surface perpendicularly, once when one measurement is done then the object to be rotated along with the rotary table. The prototype was built using the VL53L0X sensor and ATMEGA8535 microcontroller as a motor controller for rotary table and vertical axis. Scanned data is sent from the microcontroller to the computer to be visualized in real time. The results show that the VL53L0X sensor is suitable for scanning convex objects but it is not capable to handle objects with multiple cavities.

Investigation of physical and mechanical properties of coatings based on intermetallics of the Ti-Al system obtained in acetylene environment from vacuum-arc discharge plasma

At the present time, protective coatings have found wide application in various branches of industry: mechanical engineering, aircraft engine building and also in the tool manufacture. In this work presented the results of the researches of the physico-mechanical properties of coatings based on the intermetallics of the Ti-Al system, obtained in the acetylene environment from vacuum-arc discharge plasma. The thickness, microhardness, and phase composition of the coatings were investigated when samples were placed at various distances from the table axis and rotation speeds.

Development of Automatic Servo Tuning Function in Rotary Axis with DDM for Machine Tools and its Performance for Stable Machining

To advance technology of 5-axis control machining centers and future machine tools, it is essential to improve not only the performance of linear axes but also that of rotary axes. Therefore, direct drive motors (DDMs) employed for rotary axes of machine tools was developed by using the quality engineering and the FEM analysis of the electro-magnetic field. In this paper, the improvement impact on the performance of rotary axes from DDMs is described, and the influence of a workpiece position on the machine tool table on the kinematic performance is evaluated. Moreover, a novel method for tuning servo parameters automatically is proposed in order to improve the kinematic performance of a table axis with a workpiece which employs the DDM.

SU-G-TeP2-04: Comprehensive Machine Isocenter Evaluation with Separation of Gantry, Collimator, and Table Variables

Purpose: To develop and demonstrate application of a method that characterizes deviation of linac x-ray beams from the centroid of the volumetric radiation isocenter as a function of gantry, collimator, and table variables. Methods: A set of Winston-Lutz ball-bearing images was used to determine the gantry radiation isocenter as the midrange of deviation values resulting from gantry and collimator rotation. Also determined were displacement of table axis from gantry isocenter and recommended table axis adjustment. The method, previously reported, has been extended to include the effect of collimator walkout by obtaining measurements with 0 and 180 degree collimator rotation for each gantry angle. Twelve images were used to characterize the volumetric isocenter for the full range of available gantry, collimator, and table rotations. Results: Three Varian True Beam, two Elekta Infinity and four Versa HD linacs at five institutions were tested using identical methodology. Varian linacs exhibited substantially less deviation due to head sag than Elekta linacs (0.4 mm vs. 1.2 mm on average). One linac from each manufacturer had additional isocenter deviation of 0.3 to 0.4 mm due to jaw instability with gantry and collimator rotation. For all linacs, the achievable isocenter tolerance was dependent on adjustment of collimator position offset, transverse position steering, and alignment of the table axis with gantry isocenter, facilitated by these test results. The pattern and magnitude of table axis wobble vs. table angle was reproducible and unique to each machine. Conclusion: This new method provides a comprehensive set of isocenter deviation values including all variables. It effectively facilitates minimization of deviation between beam center and target (ball-bearing) position. This method was used to quantify the effect of jaw instability on isocenter deviation and to identify the offending jaw. The test is suitable for incorporation into a routine machine QA program. Software development was performed by Radiological Imaging Technology, Inc.

SU‐E‐T‐54: A New Method for Optimizing Radiation Isocenter for Linac‐Based SRS

Purpose:To develop a new method to minimize deviation of linac x‐ray beams from the centroid of the volumetric radiation isocenter for all combinations of gantry and table angle.Methods:A set of ball‐bearing (Winston‐Lutz) images was used to determine the gantry radiation isocenter as the midrange of deviation values. Deviations in the cross‐plane direction were minimized by calibration of MLC leaf position offset, and by adjusting beam position steering for each energy. Special attention was also paid to matching the absolute position of isocenter across all energies by adjusting position steering in the gun‐target axis. Displacement of table axis from the gantry isocenter, and recommended table axis adjustment for contemporary Elekta linacs, was also determined. Eight images were used to characterize the volumetric isocenter for the full range of gantry and table rotations available. Tabulation of deviation for each beam was used to test compliance with isocenter tolerance.Results:Four contemporary Elekta linacs were evaluated and the radius in the gun‐target axis of the radiation isocenter was 0.5 to 0.7 mm. After beam steering adjustment, the radius in the cross‐plane direction was typically 0.2 to 0.4 mm. Position matching between energies can be reduced to 0.28 mm. Maximum total deviation was 0.68 to 1.07 mm, depending primarily on the effect of systematic table axis wobble with rotation.Conclusion:This new method effectively facilitates minimization of deviation between beam center and target position. The test, which requires a few minutes to perform, can be easily incorporated into a routine machine QA program. A tighter radiation isocenter for contemporary Elekta linacs would require reducing the effect of gantry arm flex and/or table axis wobble that are the two main components of deviation from the designated isocenter point.

SU-E-T-149: Couch and Gantry Rotation Isocenter QA Using Portal Imager

Purpose: Propose a method for extending digital image starshot analysis to gantry and couch rotation isocenters using and EPID. Methods: The portal imager can easily be used for creating spoke shots for the collimator rotation, but for the couch and gantry rotation typically films (traditional or GafChromics) are used. (a) For couch rotation a metal rod or a narrow slit in a metal sheet (e.g. an electron block cutout) is placed on the top of the couch. Exposures with several couch angles are obtained with the portal imager to create the spoke shot. (b) For gantry angle measurement a long rod is placed obliquely on the table top from the table axis and exposures are obtained with several gantry angles resulting in a spoke shot. The image summations and spoke shot evaluations were performed with DoseLab quality assurance/image analysis software (developed by Mobius Medical Systems). Results: The resulting spoke shots were all suitable for analysis (see supporting data). For couch rotation isocenter, the slit in an electron block worked better than a solid rod. For the gantry rotation isocenter the best Results was obtained with about ∼60 degree angle between the rod and the long axis of the table, and using 0, 70, 90, 110 and 180 degree gantry angles. The source‐portal imager distance was extended to 180cm, in order to decrease the differences in intensity between the proximal and distal parts of the rod. Conclusion: The method is easy to use and is faster than using films for isocenter analysis. This process also eliminates the need to scan films after exposure. All tests can be performed in one session with three entries into the treatment room. The DoseLab software performed the rotation isocenter tests for all three easily and efficiently.

Accuracy of robotic patient positioners used in ion beam therapy

BackgroundIn this study we investigate the accuracy of industrial six axes robots employed for patient positioning at the Heidelberg Ion Beam Therapy Center.MethodsIn total 1018 patient setups were monitored with a laser tracker and subsequently analyzed. The measurements were performed in the two rooms with a fixed horizontal beam line. Both, the 3d translational errors and the rotational errors around the three table axes were determined.ResultsFor the first room the 3d error was smaller than 0.72 mm in 95 percent of all setups. The standard deviation of the rotational errors was at most 0.026° for all axes. For the second room Siemens implemented an improved approach strategy to the final couch positions. The 95 percent quantile of the 3d error could in this room be reduced to 0.53 mm; the standard deviation of the rotational errors was also at most 0.026°.ConclusionsRobots are very flexible tools for patient positioning in six degrees of freedom. This study proved that the robots are able to achieve clinically acceptable accuracy in real patient setups, too.

Factors Influencing on the Dimensions Accuracy in Laser Cutting

This research aims to establish the influence of different factors on the dimensions accuracy in laser cutting. Samples with different thickness were made of DC01 EN 10130 steel. On each sample 32 round or square holes were cut in 4 rows by different laser beam movement schemes linear, zig-zag and random. The tests were made by pulse CO2 laser with regimes, recommended for each sheet thickness, by the machine operating manual. The diameters of the round holes and the dimensions of the square holes along the laser head and the table axes were measured by a projector. The varying intervals of the dimensions and the shape deviations were calculated. It was established that three groups of factors influence on the dimensions accuracy in laser cutting: factors, related to the machine, laser parameters power, laser cutting speed and focus distance, determining the technological process parameters, and the material characteristics thermal physical properties and sample sizes. Factors, related to the machine, exert effect mainly on the intervals of dimensions varying, while the laser parameters and the material properties influence on the dimensions value independently of the cutting scheme. In the all laser cutting schemes the increasing of the sample thickness leads to the larger interval of the dimensions varying and increasing of the shape deviation. Nomenclature

Factors Influencing on the Dimensions Accuracy in Laser Cutting

This research aims to establish the influence of different factors on the dimensions accuracy in laser cutting. Samples with different thickness were made of DC01 EN 10130 steel. On each sample 32 round or square holes were cut in 4 rows by different laser beam movement schemes linear, zig-zag and random. The tests were made by pulse CO2 laser with regimes, recommended for each sheet thickness, by the machine operating manual. The diameters of the round holes and the dimensions of the square holes along the laser head and the table axes were measured by a projector. The varying intervals of the dimensions and the shape deviations were calculated. It was established that three groups of factors influence on the dimensions accuracy in laser cutting: factors, related to the machine, laser parameters power, laser cutting speed and focus distance, determining the technological process parameters, and the material characteristics thermal physical properties and sample sizes. Factors, related to the machine, exert effect mainly on the intervals of dimensions varying, while the laser parameters and the material properties influence on the dimensions value independently of the cutting scheme. In the all laser cutting schemes the increasing of the sample thickness leads to the larger interval of the dimensions varying and increasing of the shape deviation. Nomenclature

A Comparison of Different Optimization Techniques for Variation Propagation Control in Mechanical Assembly

Variation propagation control is one of the procedures used to determine product quality in the manufacturing assembly process. The quality of a product assembly is also greatly dependent on the product type and the optimization criteria employed in the assembly. This paper presents three procedures for optimizing the assembly of component stacks by controlling variation propagation. The procedures considered are: (i) straight-build assembly by minimizing the distances from the centres of components to table axis; (ii) parallelism-build assembly by minimizing the angular errors between actual and nominal planes; (iii) target-axis-build assembly by minimizing the distances from the centres of components to a target axis. Simulation results are presented for the assembly of four cylindrical components. The results show that the variation can be reduced significantly by optimization; for example, Procedure 1 can reduce the variation by 48%, Procedure 2 by 63% and Procedure 3 by 35%, compared to assembly without the minimization. The results also show that the 3 proposed assembly methods have reasonable consistency, the maximum of the standard deviation is 0.0726 mm in Procedure 1, 3.5×10−4 rad in Procedure 2, and 0.029 mm in Procedure 3. These demonstrate that the three assembly techniques are fully functional on their own. Thus, the relevant assembly techniques need to be selected carefully in accordance with the particular industrial application.

Variation propagation control in mechanical assembly of cylindrical components

Variation propagation control is one of the procedures used to improve product quality in the manufacturing assembly process. The quality of a product assembly depends on the product type and the optimization criteria employed in the assembly. This paper presents two assembly procedures of component stacks by controlling variation propagation. The procedures considered are: (i) straight-build assembly by minimizing the distances from the centres of components to table axis; (ii) parallelism-build assembly by minimizing the angular errors between actual and nominal planes. Simulation results are presented for the assembly of four cylindrical components. The results indicate that the variation can be reduced significantly by using these procedures, compared to that without minimization. The results also indicate that the variation not only greatly relies on the assembly procedures, but also on the number of available orientations at the assembly stage. The radial variation increases with the stage for the straight-build assembly, while the angular error decreases with the stage for the parallelism-build assembly. The assembly quality for the two assembly procedures can be improved by increasing the number of orientations. The variation decreases exponentially and monotonically with the number of orientations. The information obtained is useful for manufacturing processes and the assembly modeling.

Straight-Build Assembly Optimization: A Method to Minimize Stage-by-Stage Eccentricity Error in the Assembly of Axisymmetric Rigid Components (Two-Dimensional Case Study)

For assembly of rotating machines, such as machining tools, industrial turbomachinery, or aircraft gas turbine engines, parts need to be assembled in order to avoid internal bending of the geometric axis of the rotor to meet functional and vibration requirements. Straight-build assembly optimization is a way of joining parts together in order to have a straight line between the centers of the components. Straight-build assembly is achieved by minimizing eccentricity error stage-by-stage in the assembly. To achieve minimal eccentricity, this paper proposes three assembly procedures: (i) table-axis-build assembly by minimizing the distances from the centers of components to table axis; (ii) minimization of the position error between actual and nominal centers of the component; and (iii) central-axis-build assembly by minimizing the distances from the centers of components to a central axis. To test the assembly procedures, two typical assembly examples are considered using four identical rectangular components and four nonidentical rectangular components, respectively. Monte Carlo simulations are used to analyze the tolerance build-up, based on normally distributed random variables. The results show that assembly variations can be reduced significantly by selecting best relative orientation between mating parts. The results also show that procedures (i) and (ii) have the most potential to minimize the error build-up in the straight build of an assembly. For these procedures, the variation is reduced by 45% and 40% for identical and nonidentical components, respectively, compared to direct-build assembly. Procedure (iii) provides better performance than direct-build assembly for identical components assembly, while it gives smaller variation at the first two stages and larger variation at the third stage for nonidentical components assembly. This procedure could be used in an assembly with limited stages.

SU‐GG‐I‐61: Is It Safe? A Look at Exposures in the Shadow of MDCT Scanner Gantries

Purpose: Computed tomography (CT) is used quite frequently as an imaging tool during interventional radiology (IR) procedures. Interventional radiologists at our institution often stand adjacent to the gantry of the CT scanner while scanning in “biopsy” mode, as it is commonly thought that the shadow of the gantry is the safest place to be if one remains in the room during CT scanning. An investigation was performed to more closely investigate the radiation dose to persons standing in the shadow of the gantry. Method and Materials: OSL area monitors were used to gather long‐term dose data at various points outside the CT gantry. Measurements were performed on 16 and 64 slice scanners used in the IR department. Results: Dose rates varied substantially within the shadow of the CT scanner gantry for both the 16 slice and 64 slice scanners. Compared to the value in the center of the gantry shadow, doses measured halfway between the center and edge of the gantry towards the “foot” side were 34.8 and 17.0 times higher for the 16 slice and 64 slice scanners, respectively. Similarly measured doses towards the “head” side were 4.2 and 3.4 times higher than dose levels in the center of the shadow for the 16 slice and 64 slice scanners, respectively. The ratio of foot side to head side doses was 8.2 and 5.0 for the 16 slice and 64 slice scanners, respectively. Conclusion: Asymmetric distribution of hardware within the gantry can lead to steep dose gradients along the table axis in the shadow of modern CT gantries. It was found that the dose to someone standing in the shadow of a CT gantry can vary by as much as a factor of 35 based on position within the shadow.

Motion coordination for industrial robotic systems with redundant degrees of freedom

This work investigates how to distribute in an optimum fashion the desired movement of the end-effector of an industrial robot with respect to the workpiece, when there are redundant degrees of freedom, such as a positioning table. The desired motion is given as a series of acceleration functions in respective time intervals. The constraints of the optimisation are the available acceleration limit of axes, such as the table axes, the upper bounds to velocity and displacement of each axis and the avoidance of singular point areas of the robot, as defined by its manufacturer. The optimisation criterion is minimum total work for the motion. A genetic algorithm was used to solve the problem. The fitness function of the genetic algorithm calls a kinematics and dynamics simulation model of the robotic installation constructed in Matlab™, in order to compute the work consumed and to check possible violation of constraints. Examples of straight line and circular movement are given to prove the concept. Results are encouraging, yet demand on computing power is high.

CT and MR Imaging of Nitinol Stents with Radiopaque Distal Markers

To evaluate imaging characteristics and artifacts of a nitinol stent with distal tantalum markers with computed tomography (CT) angiography and magnetic resonance (MR) angiography. A vascular phantom was built to simulate in-stent restenosis. A nitinol stent with tantalum markers (Luminexx stent) was evaluated with CT angiography in different orientations relative to the z-axis and with MR angiography in different positions relative to both B0 and the readout gradient. Stenosis measurements were compared with conventional digital subtraction angiography for both modalities. In-stent signal intensity obtained with different flip angles was assessed in two nitinol stents with distal markers (Luminexx stent and SMART stent) and one without markers (Memotherm-FLEXX stent). Stenosis detection was not possible with CT angiography when the stent was perpendicular to the z-axis because of streak-like artifacts induced by tantalum markers. Stenosis evaluation with multiplanar reformation was accurate when the stent was in parallel and oblique orientations relative to the table axis. With MR angiography, metallic artifacts were mostly related to the stent orientation with B0, whereas orientation of the readout gradient had little influence. The mean error (overestimation) for stenosis measurements varied between 0.1% and 7.4% for CT imaging in parallel and oblique positions and 3.6% and 9.5% for MR imaging. Higher flip angles did not improve signal intensity inside the three stents tested. CT and MR angiography can be used for evaluating the patency of stents with distal markers that are parallel or oblique relative to the table axis (iliac, carotid, or femoral stents). MR angiography is preferred if the stent is perpendicular to the table axis (renal stent).

A method for determining the alignment accuracy of the treatment tableaxis at an isocentric irradiation facility

At an isocentric irradiation facility, the rotation axis of the treatmenttable has to be accurately aligned in vertical orientation to the isocentre,which is usually marked by three perpendicular laser planes. In particular,high precision radiotherapy techniques, such as radiosurgery or intensitymodulated radiotherapy, require a higher alignment accuracy of the table axisthan routinely specified by the manufacturers. A simple and efficient methodis presented to measure the direction and the size of the displacement of thetable axis from the isocentre as marked by the lasers. In addition, theinclination of the table axis against the vertical direction can bedetermined. The measured displacement and inclination provide the requireddata to correct for possible misalignments of the treatment table axis and tomaintain its alignment. Measurements were performed over a period of two yearsfor a treatment table located at the German heavy ion therapy facility. Themean radial distance between the table axis and the isocentre was found to be0.25±0.25 mm. The mean inclination of the table axis in the XZ- andYZ-planes was measured to be -0.03±0.02° and -0.04±0.01°,respectively. The measurements demonstrate the good alignment of the treatmenttable over the analysed time period. The described method can be applied toany isocentric irradiation facility, especially including isocentric linearaccelerators used for radiosurgery or other high precision irradiation techniques.