Cross Transfer Functions Research Articles

Investigation of the effects of Stewart platform-type industrial robot on stability of robotic milling

Mobile machining with industrial robots is proposed as a cost-effective and portable manufacturing alternative to large scale CNC machine tools in large-scale part manufacturing. Robotic milling, one of the widely used mobile machining approaches, involves several technical challenges and distinct characteristics in terms of machining dynamics and stability due to completely different structural build up. In this paper, distinctive effects of Stewart platform-type of hexapod robot on stability of robotic milling is investigated based on characterisation of its structural dynamics, simulation of stability limits and experimental validation. Three aspects are demonstrated: (1) the position-dependent stability diagrams due to the position-dependent dynamics of the hexapod platform, (2) the effects of cross transfer function due to the complex kinematic chain on milling stability and (3) the role of feed rate direction in stability of robotic milling. The conditions for minimised position-dependent stability through appropriate tooling are also illustrated through simulations and experimental verification. The cases where process stability may be governed by either the hexapod robot or the cutting tool modes are discussed and identified through stability analysis. It is shown that the feed rate direction becomes a significant parameter for stability limits in robotic milling. The conditions at which the cross transfer function becomes significant on milling stability are discussed through simulations and experimental results. It is shown that cross transfer functions may significantly affect milling stability especially when the radial depth of cut is less than 50 % of the tool diameter. As one of the important outcomes of this research, it is found that appropriate tooling may decrease the reliance of milling stability on robot position.

Development of Novel Anisotropic Boring Tool for Chatter Suppression

A novel chatter suppression method in boring operation is proposed in the present study. The anisotropic boring tool with a step portion and notches on the cylinder periphery is designed, which has anisotropic dynamic characteristics. Since the direct and the cross transfer function components of the proposed tool are designed to cancel out each vibration, the nominal compliance of the boring tool in cutting process can be reduced significantly. Hammering tests of the developed tool clarified that appropriate anisotropic frequency response function is roughly attained by the proposed design. The developed tool was subsequently applied to turning experiments, and it was clarified that the stability limit in the radial depth of cut significantly increases by using the proposed boring tool as compared to the ordinary boring tool.

Effect of Cross Transfer Function on Chatter Stability in Plunge Cutting

An accurate analytical model for regenerative chatter vibration in plunge cutting is proposed. Effects of the cross transfer function and the cutting force ratio on chatter stability are considered in the proposed model. Equivalent transfer function is defined, which is useful to understand those effects on chatter stability. Basic plunge cutting experiments were conducted to verify the proposed model. Although the critical widths of cut in the CW and CCW rotation processes were significantly different from each other in the experiment, even when the other conditions were the same, chatter stability limits were predicted accurately by the proposed model as compared with the conventional model.

D20 Effect of Cross Transfer Function on Chatter Stability in Plunge Cutting(Analytical advancement of machining process)

An accurate analytical model for the regenerative chatter vibration in the plunge cutting is proposed in the present research. Effects of the cross transfer function and the cutting force ratio on the chatter stability are considered in the proposed model. Equivalent transfer function is defined, which is useful to understand those effects on the chatter stability. It is verified experimentaly that the chatter stability limits can be predicted accurately by the proposed model as compared with the conventional model.

-cascade crossfunction digital filter with arbitrary zeros

Gray–Markel digital filters for lossless realisations and the lossless bounded real (LBR) structures have transmission zeros constrained to 0, infmity or the unit circle. This results in cross-transfer function synthesis with low stopband sensitivity. In the Letter, a cross-function synthesis with arbitrary zeros is proposed. A design example is provided.

Computational analysis of a holographic optical head configuration

The best configuration for holographic optical heads for compact disk players is discussed from the viewpoint of considering the misalignment allowance for head components. Focus-error and trackingerror signals of the proposed head configurations are simulated with a ray-tracing method and by using optical cross transfer function theory. The misalignment allowance for the head components, such as the objective lens, the holographic optical element, and the photodetector, are calculated for several configurations. The misalignment allowance is found to increase greatly when the holographic optical element is placed in close proximity to the objective lens and then when this assembly is moved as a unit.

Localization of Structural Flaws using Cross Transfer Function Zeros

Abstract Frequency based localization is a technique which locates structural flaws by monitoring changes in transfer function pole and zero frequencies. This technique has been successfully applied to isolate simulated structural flaws in a modal database representation of a spacecraft using transfer function poles and driving point zeros. However, the number of usable frequencies and, therefore, the achievable spatial resolution, was limited by high modal density and narrow excitation bandwidth. In this paper, the feasibility of improving spatial resolution by incorporating the zeros of cross transfer functions is demonstrated. The frequency based procedure was developed specifically to support structural health monitoring in an environment that is less than ideal for modal testing. For spacecraft on-orbit, testing to detect structural flaws is constrained by the limited availability of sensors and excitation sources, and by the requirement for minimal impact on mission operations. Frequency based localization is well suited for this application, since measurements of input forces and modal frequencies only arc required. This greatly reduces the requirements for sensors and data acquisition compared to localization techniques that rely on measurements of mode shapes.

Noninteracting Control of Dynamically Tuned Dry Gyro and Its Application to Measurement of Two-Axis Angular Accelerations

This paper presents a method of reducing the interaction effect between the input and output peculiar to the Dynamically Tuned Dry Gyro (TDG), and the possibility of measuring angular accelerations about two axes, through improvements of the Rebalance Control Circuit (RCC) installed on the TDG. First, the use of the TDG as a two-axis rate sensor is shown along with direct and cross transfer functions relating two outputs and two inputs; and it is shown that the TDG makes it possible to simultaneously measure two-axis angular velocities and two-axis angular accelerations if the RCC is improved to facilitate noninteracting control. Next, the design procedure and the results of the trial manufacture on the hardware of each element of the RCC necessary to meet its capability are shown. Third, from the results of the experiments using this manufactured RCC it is clarified that the frequency characteristics of direct transfer functions which prescribe the system performance are hardly influenced by the manufacturing accuracy of the RCC, but the gain chracteristics of cross transfer functions, which correspond to the degree of reduction of the interaction effect, are significantly influenced by the manufacturing accuracy.

Sine wave response of an annular aperture under partially coherent illumination

The imagery of extended objects by a system having aberration free annular aperture and employing partially coherent illumination has been investigated. The generalized cross transfer functions for the system have been evaluated and applied to investigate the images of sine wave objects. The dependence of the spatial frequency response upon the coherence parameter and the obscuration ratio of the aperture has been discussed.

Images of Periodic Objects under Partially Coherent Illumination

The imagery of periodic objects under partially coherent illumination by an optical system employing an annular condenser for illumination has been considered. The problem has been studied in terms of the generalized cross transfer functions and the results have been discussed in terms of the contrasts in the images of periodic objects commonly employed, namely the sine wave, rectangular wave and triangular wave objects. It has been shown that the effect of using a central obscuration on the condenser of the illuminating system is to improve the response of the system at higher spatial frequencies with a corresponding reduction in the response at lower spatial frequencies. The irradiance distribution in the images of these objects have also been discussed and some interesting features have been brought out.