Experimental investigation of a gimbal in the frequency domain

Haller, Michen Christian (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: When it comes to renewable energies, the reduction of initial investment costs help make these generation methods a more viable option for governments, or private companies. For Concentrated Solar Power (CSP) plants, a particular example of this would be the initial investment costs associated with the heliostats. Heliostat foundation preparation and heliostat structure quality need to be of a high standard for a heliostat to remain within its calibration parameters for long periods of time. If calibrations, inspections and cleaning of these heliostats can be done more regularly, the time for which the heliostat needs to maintain its calibration parameters is reduced, thereby reducing foundation preparation costs and heliostat manufacturing costs. At the University of Stellenbosch, the Solar Thermal Energy Research Group (STERG) is investigating the use of automated drones to perform inspections, calibrations and cleaning of heliostats. In order to attach sensors to the drone, a gimbal is used. This isolates the sensor from the drone’s rotations. Gimbal dynamic performance data, which is relevant to design engineers, is not readily available. In this thesis, the pitch responses of a two-axis gimbal to pitch and roll disturbances are measured for varying disturbance frequencies and amplitudes, without vibration isolation pads. In addition to producing the gimbal performance data, it is found that the largest gains observed occurred in region where no structural natural frequencies were found. It is suspected that the knocking of the gimbal Inertial Measurement Unit (IMU) cable, which is connected to the device-mount IMU, is the source of these peak responses. The responses to pitch and roll actuations differed significantly, with the largest reponse attenuation observed for pitch actuations between 31 Hz and 46 Hz. It is also found that the gimbal is sensitive to frame vibrations, especially at frame natural frequencies, which highlights the need for vibration isolation pads during use. It is recommended that further research be conducted in the frequency domain for roll and yaw responses. In addition, it is recommended that the efficacy of gimbal vibration isolation pads, for blade pass frequencies, be investigated. Lastly, it is recommended that a more detailed analysis of the gain attenuation observed for the responses to pitch actuations, be conducted.

AFRIKAANSE OPSOMMING: In die hernubare energie bedryf, help die vermindering van aanvanklike beleggingskoste om hernubare kragvoorsieningsmetodes ’n lewensvatbare opsie te maak vir regerings en privaatmaatskappye. Wat betref gekonsentreerdesonkragaanlegte, is ’n spesifieke voorbeeld hiervan die aanvanklike beleggingskoste van heliostate. Die voorbereiding van die fondamente van heliostate en heliostaatstrukture moet van ’n hoë standaard wees, ten einde te verseker dat die heliostaat vir lang tye binne die gekalibreerde parameters sal bly. Indien die kalibrering, die inspeksie en die skoonmaak van hierdie heliostate meer gereeld gedoen kan word, sal dit die tydsduur verminder waar die heliostaat binne sy gekalibreerdeparameters moet bly, asook die koste verbonde aan die voorbereiding van fondamente en vervaardiging van heliostate. By die Universiteit van Stellenbosch ondersoek die Sontermieseenergienavorsingsgroep (STERG) die gebruik van selfaangedrewe hommeltuie om die inspeksies, kalibrerings en skoonmaak van die heliostate uit te voer. Ten einde sensors aan die hommeltuig te kan vasheg, word ’n kompasbeuel (gimbal) gebruik. Die kompasbeuel isoleer die hommeltuig se bewegings van die sensor. Volledige inligting oor die werksverrigting van die kompasbeuel, wat relevant is vir ontwerpingenieurs, is nie geredelik beskikbaar nie. In hierdie tesis word ’n tweeas- kompasbeuel, sonder vibrasie-isoleringskussinkies, se responsie met betrekking tot helling- en rolversteurings gemeet vir verskillende versteuringsfrekwensies en –amplitudes. Bykomend tot die verskaffing van die gimbal-prestasiedata, is daar gevind dat die grootste aanwinste wat waargeneem kon word, plaasgevind het waar geen strukturele natuurlike frekwensies was nie. Daar word vermoed dat die beweging van die gimbal se traagheidsmeterkabel (Inertial Measurement Unit - IMU), wat gekoppel is aan die toestelraam (device-mount IMU), die bron van hierdie piek gedrag was. Die responsies op helling- en rolversteurings het aansienlik verskil, met die grootste attenuasie in die responsie op hellingsteuring tussen 31 Hz en 46 Hz. Daar is ook bevind dat die kompasbeuel sensitief is vir vibrasies in die raamwerk, veral by natuurlike frekwensies van die raamwerk. Dit toon duidelik die behoefte aan vibrasie-isoleringskussingkies. Daar word aanbeveel dat verdere frekwensiedomeinmetings gedoen behoort te word op rol- en gierresponsies. Daar word verder aanbeveel dat die doeltreffenheid van die kompasbeuelvibrasieisoleringskussinkies in die besonder ook vir frekwensies, veroorsaak deur lemrotering, ondersoek moet word. Laastens word aanbeveel dat ‘n meer gedetailleerde analise van die aanwinsattenuasie, waargeneem by die responsies op hellingsteurings, uitgevoer behoort te word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105972
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