Hydrostatic Asymmetric Journal Gas Bearings for Largely Unbalanced Rotors of Seismic ACROSS Transmitters

Imanishi

Asami

et al. 2014

Self Cite

Experimental verification of externally pressurized gas journal bearings with asymmetric gas supply (Supply gas pressure control operation using a small size test rig) 2Ise, Imanishi, Asami, Tokumiya, Takada, Kimura and Yamaguchi, Journal of Advanced Mechanical Design, Systems, and Manufact, Vol.8, No.3 (2014) © 2014 The Japan Society of Mechanical Engineers [DOI: 10.1299/jamdsm.2014jamdsm0029] Fig. 1 Configuration of an X-ray CT gantry being more useful in terms of support of the load compared with the previously developed bearings (Okano, et al., 2006), (Ise, et al., 2007a), (Ise, et al., 2010), (Ise, et al., 2007b).We propose that this type of bearing is applicable for use in an X-ray computed tomography (hereafter called as X-ray CT) scanner gantry (Tokumiya, et al., 2013). The rotary drum of the gantry has electrical units to computed tomography scanning, as shown in Fig.1. The drum is supported by rolling contact bearing. The dynamic unbalance is roughly canceled by the arrangement of these devices. The rotary drum inner diameter is 800 or 1,000 mm and the rotating speed is 100 or 220 rpm. In present devices, rolling contact bearings are used to support the rotor. The maximum circumferential speed exceeds 11.5 m/s in present conditions. Rotation produces a somewhat unbalanced centrifugal force since the rotary drum has a small eccentricity although the unbalance is cancelled; therefore, the force due to residual unbalance with the drum mass gives to the bearings as the load. For these reasons, a large torque is required in the operation. A greater rotational speed is presently demanded of the gantry because realization of high speed rotation will result in higher precision scanning. However, a higher rotational speed results in a shorter bearing lifetime and an increase of noise, which tends to create higher patient anxiety. Radiation exposure of the patient also can be reduced by this mechanism because examination time decreases by high speed rotation. The use of the proposed gas bearings can potentially solve these problems.The final purpose is application of this bearing for the X-ray CT gantry. For this purpose, verification of the proposed bearing mechanism under the supply gas pressure control condition is first necessary. This report presents rotational tests of the proposed hydrostatic gas journal bearings with asymmetric gas supply using a small sized preliminary test rig to verify the effectiveness of the proposed mechanism. Ise, Imanishi, Asami, Tokumiya, Takada, Kimura and Yamaguchi, Journal of Advanced Mechanical Design, Systems, and Manufact, Vol.8, No.3 (2014) Working mechanism of the proposed bearingExperimental verification of the capacity of externally pressurized gas journal bearings with asymmetric gas supply (called AGS bearings hereafter) to support large load rotors was conducted. The working mechanism and the characteristics of the AGS bearing were examined by comparison with the conventional type of externally pressurized gas journal bearing. A schematic of the proposed AG...

Section: Introductionmentioning

confidence: 99%

“…1 Configuration of an X-ray CT gantry being more useful in terms of support of the load compared with the previously developed bearings (Okano, et al, 2006), (Ise, et al, 2007a), (Ise, et al, 2010), (Ise, et al, 2007b).…”

mentioning

confidence: 99%

Experimental verification of externally pressurized gas journal bearings with asymmetric gas supply (Supply gas pressure control operation using a small size test rig)

Imanishi

Asami

et al. 2014

Self Cite

“…In previous study, hydrostatic journal gas bearing with asymmetric bearing area was proposed and investigated to support largely unbalanced rotors such as seismic ACROSS transmitters (9), (10) . The test results shown that the bearing has large load capacity compared with the conventional symmetric bearing.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Supply Type Hydrostatic Journal Gas Bearings to Support Large Load Rotors

Miyatake

Asami

2012

Self Cite

Rotating machinerys have problems at bearings to support a rotor such as seismic ACROSS transmitters. The ACROSS ( Accurately Controlled Routinely Operated Signal System ) is a new technical method to detect subtle changes in the physical state of Earth's structure using precise and continuous signal transmitter-receiver systems. The signal is a type of sinusoidal elastic waves, which is generated by a large unbalanced rotor. The rotor is supported by rolling contact bearings. The bearings in the transmitters, large heat generation occur caused by the high frictional loss. In order to solve this problem, use of hydrostatic gas bearings was studied. Effectiveness of the gas bearings was clarified by the test for decrease of frictional loss. However, large gas flow rate was required to support large load. In this paper, asymmetric supply type hydrostatic journal gas bearing is developed to support large load with decreasing of gas flow rate. Numerical calculation of the bearing characteristics is conducted and the results are compared with previously studied and conventional bearing. The test bearing and a rig were made and the test was conducted. Availability of the bearing is verified by the test.

“…However, the load capacity of hydrostatic gas bearings is much smaller than rolling contact bearings, the bearing dimensions become large and as the result, large gas flow rate is required. To improve this demerit, a new type of hydrostatic gas bearing with asymmetric bearing surface is investigated (6) . With such type of bearings, rotor amplitude becomes zero at a certain rotational frequency, which changes depending on the bearing supply gas pressure.…”

Section: Introductionmentioning

confidence: 99%

Hydrostatic Asymmetric Journal Gas Barings for Seismic ACROSS Transmitters -Improvement of Safety Operation by Supply Gas Pressure Control under the Rotational Frequency Modulation-

Torii

Morita

et al. 2007

Self Cite

The ACROSS ( Accurately Controlled Routinely Operated Signal System ) is used to detect subtle changes in the physical state of Earth's structure. The signal is sinusoidal elastic waves generated by the rotation of a rotor with eccentric mass set in ACROSS transmitters. In currently working transmitters, since the rotor is supported by rolling contact bearings, bearing losses are so large that the cooling, lubrication management and bearing life become serious problems. To solve these problems, hydrostatic asymmetric journal gas bearings have been proposed to support the eccentric mass rotors. This paper describes the experimental investigation of rotational characteristics of proposed hydrostatic asymmetric journal gas bearings. It is verified that the rotor amplitude in the journal bearings can be zero at a certain rotational frequency by using trial test rig. In order to decrease the gas consumption and increase more safely operation, test of rotational frequency modulation using electro-pneumatic pressure regulator was carried out. In fixed supply pressure condition, rotor amplitude largely changes in accordance with change of rotational frequency. In controlled supply pressure condition, the rotor amplitude decrease under the operation and the gas consumption also largely decreased.