Diagnostics of cycloidal gear speed reducers in vertical multirotor system

V. Barzdaitis*, V.V. Barzdaitis**, K. Kazlauskienė***, A. Tadžijevas**** *Kaunas University of Technology, Studentu str. 56-332, 51424, Kaunas, Lithuania, E-mail: vytautas.barzdaitis@ktu.lt **Vytautas Magnus University, Vileikos str. 8, 44404, Kaunas, Lithuania, E-mail: v.barzdaitis@if.vdu.lt ***Kaunas University of Technology, Studentu str. 56-345, 51424, Kaunas, Lithuania, E-mail: kristina.kazlauskiene@ktu.lt ****Klaipėda University, Bijūnų str.17, 91225, Klaipėda, Lithuania, E-mail: tadzijevas@gmail.com


Introduction
High productivity vertical axis rotating diffusion machine driven by multiple drives is complicated system for technical condition monitoring, diagnostics and failure prognosis.The failure diagnostic problems of vertical axis rotating machine driven by ten cycloidal gear reducers is complicated from practical diagnostics point of view using vibration monitoring parameters [1].Unlike many others gear power transmissions the cycloidal gear driver is not typically back drivable and in case of only one drive failures it may cause failure of driving involute pinion tooth or in worst casefailure of expensive driven gear.The operation of cycloidal gear drive is based on the eccentric motion nature of the cycloidal disc.Generally each cycloidal gear drive includes two subsystemshigh and low rotational speed stages.Each stage comprises two cycloidal discs.The two stages cycloidal gear drive has many antifriction bearings with additional 2 bearings of output rotor with involute pinion tooth.Such design scheme drive is perfectly balanced and eliminates rotor unbalance caused vibration [2][3][4].The cycloidal gear drives severe vibration mainly caused by antifriction bearings failures.In industry the electric motor and drive defects diagnostics are concentrated on machine mechanical vibration periodic monitoring in situ.This is one of several stages of technical condition assessment of whole rotating system in general and each element in particular.The traditional rotating machinery diagnostic methods described in International Standards (ISO 13373-1:2002, ISO 13373-2:2005, ISO 13379:2003, ISO 2954:2012, ISO 7919 and ISO 10916, etc.).All of those methods are used in practice.But it is a general view in fault diagnostics technique, but not acceptable for different design machines and specific operation conditions.In this work we put attention of fault diagnostics of vertical rotating system simultaneously running with ten cycloidal gear drives with doubled crankshafts and antifriction bearings.The experimental research was based on each drive absolute vibration measurements data in situ at full load of diffusion machine operation.

Research object
The general scheme of diffusion machine with ten cycloidal gear drives is shown in Fig. 1.Cycloidal drive represent first CR1 and second CR2 stages and has the same design scheme but difference in geometrical size reference to large output rotor 3v torque.

Vibration measurement data and results
Bearings housings absolute vibration was measured with pjezoaccelerometers 2PH, 3PA, 5PA, 5PH and 8PH (sensitivity 100 mV/g, resonance frequency 22 kHz) in two directions: radial (H) and axial (A) reference to vertical axis of rotation.Measurement data was analysed with Vibration signal analysers (Ahash A4300, A4101, CZ).The pjezoaccelerometers were attached at 5 local points on CR1 and CR2 bearing housings as shown in Fig. 2. Too many measurement points used to pick up main points that measurement data effectively helps to identified main vibration parameters and increased accuracy of evaluation of technical condition of CR1 and CR2 in general and crankshafts eccentric bearings in particular.The many years diagnostics practice indicated that some cycloidal speed reducer elements (cycloidal discs, ring gear pins/rollers, the crankshafts with main two bearings) are sufficiently reliable in comparison with the technical condition of crankshafts eccentric bearings.The main accent of this research was put on technical condition monitoring of whole drive, especially of crankshaft's two eccentric bearings.Because in case of these bearings failure cycloidal speed reducer can damaged pinion or gear involute tooth zm, zd as practical diagnostic data indicated.The damaged (1st drive) and undamaged (6th drive) drives 2nd bearings vibration velocities spectra measured in radial direction with 2PH transducer is shown in Fig. 4, a

Conclusions
1. Vertical axis cycloidal gear speed reducers with antifriction bearings failure diagnostics can be successful when systematic condition monitoring procedure is provided with seismic transducers attached to CR first stage CR1 bearing housings in radial and axial directions.
2. The CR first stage CR1 rotor doublet crankshaft excited vibration velocity amplitude is dominated in all ten drives 26.2 Hz = 2X in comparison with CR1 stage rotor synchronized rotation 1X frequency.
3. The high frequency (up to 5000 Hz) vibration acceleration root mean square value arms is more informative parameter in comparison with vibration velocity parameter measured up to 1000 Hz frequency, according to ISO 10816 norms.

Fig. 5
Fig. 5 Radial vibration acceleration spectra of damaged 1st and undamaged 6th drives, 2PH transducer: a -damaged 1st drive; b -undamaged 6th drive The damaged and undamaged CR drives 2nd bearings vibration acceleration spectra measured in radial direction with 2PH transducer is shown in Fig. 5, a, b.The high frequency vibration acceleration amplitudes are more informative for identification of damaged CR drive.The