Table Axis Research Articles

A modified contour error controller for a high speed XY table

This article deals with a contour error controller (CEC) applied in a high speed biaxial table. It works simultaneously with the table axes controllers, helping them. In the early stages of the investigation, it was observed that its main problem is imprecision when tracking non-linear contours at high speeds. The objectives of this work are to show that this problem is caused by the lack of exactness of the contour error mathematical model and to propose modifications in it. An additional term is included, resulting in a more accurate value of the contour error, enabling the use of this type of motion controller at higher feedrate. The response results from simulated and experimental tests are compared with those of common PID and non-corrected CEC in order to analyse the effectiveness of this controller over the system. The main conclusions are that the proposed contour error mathematical model is simple, accurate, almost insensible to the feedrate and that a 20:1 reduction of the integral absolute contour error is possible.

The measurement of linear accelerator isocenter motion using a three-micrometer device and an adjustable pointer

Purpose : The small motions of the major axes of a linear accelerator observed during gantry and treatment table rotation were measured to improve beam-target alignment during stereotactic radiosurgery (SRS). Methods and Materials : Measurements of gantry isocenter motion and table rotational axis wobble were performed with an adjustable front pointer and a three-micrometer device. Nominal gantry and table isocenters were specified. The gantry motion path and table isocenter coordinates were then applied to offset simulated treatment target coordinates so as to compensate for gantry sag. Target simulation films were examined to document improvement of beam-target alignment. Results : The overall precision of the measurement of gantry and table isocenter coordinates was 0.2 mm. Over gantry rotation of 0 to 360°, the gantry isocenter was found to follow a pinched loop with a maximum point to point distance of 1 mm. Table axis motion was found to be negligible relative to the reproducibility of gantry isocenter motion. Thus, a table isocenter was defined that was invariant to table rotation. Conclusion : Results indicate that the three-micrometer device and adjustable front pointer are useful tools for three-dimensional (3D) mapping of gantry, collimator and table isocenters and their motions. It is suggested that such measurements may be useful in the quality assurance of linear accelerators, particularly to improve beam-target alignment during SRS and other high dose external beam therapy.

Angle Interferometer Cross-Axis Errors

Angle interferometers are commonly used to measure surface plate flatness. An error can exist when the centerline of the double corner cube mirror assembly is not square to the surface plate and the guide bar for the mirror sled is curved. Typical errors can be one to two microns per meter. A similar error can exist in the calibration of rotary tables when the centerline of the double corner cube mirror assembly is not square to the axes of rotation of the angle calibrator and the calibrator axis is not parallel to the rotary table axis. Commercial double corner cube assemblies typically have non-parallelism errors of ten milli-radians between their centerlines and their sides and similar values for non-squareness between their centerlines and end surfaces. The authors have developed a simple method for measuring these errors and correcting them by remachining the reference surfaces.

Study on the improvement of cutting accuracy of NC hobbing machines. Improvement of tooth lead error.

In this paper, with the purpose of achieving high precision machining by means of NC hobbing machines, the problem points of the NC indexing system software, the angle detection accuracy of the hob and table axes, and the achievement of high precision of synchronism of the two axes is investigated. With regard to the indexing system software, numerical simulation of the tooth lead error was carried out, and it was clearly shown that the size of the unit used in carrying out the calculation had a strong influence on the machining precision. In addition, it was recognized that the quantization of the hob spindle encoder and the table spindle angle detection device exerted a great influence on the machining precision. Together with these results, gear cutting machining was carried out by means of the actual machine, making it possible to achieve an improvement in the tooth lead error.

シリコンウエハ研削面の真直度に関する研究 ウエハ自転研削法に関する研究 ＩＩ

In this paper, the straightness of silicon wafer ground by wafer rotation grinding method is discussed, which is caused by the parallel error between grinding wheel axis and rotary table axis. The parallel error is defined by two angles, that is inclination angle θ and direction angle α. And the effect of the parallel error on the straightness is examined theoretically and experimentally. The main results obtained are as follows: (1) The profile and the straightness of the ground surface are largely effected by the direction angle α. (2) The direction angle al exists which makes the straightness minimum. (3) Practically, the straightness is maintained in the lowest level when the direction in which the thermal deformation of surface grinder is maximum is coincide with the direction angle α=0° or α=180°. (4) The straightness is proportional to the inclination angle θ. (5) In this experiment, the variation of the straightness was maintained less than ±1 μm at α_??_180° when the grinding operation was continued in several days using an ordinary surface grinder.

A novel application of parallel strip hinges

An instrument has been designed using radial diffraction gratings to measure the transmission errors in gear hobbing machine table drives. Potential errors of measurement, due to eccentricity of the grating unit with respect to the table axis, and axis wander effects are avoided by the use of the linkage described.