Case Studies: Vibration Analysis

Case Study 1:
Vibration Stabilization System for Bulk Unloading Conveyor

Case Study 2:
Vibration Analysis of Integrated Circuit Fabrication Equipment

Case Study 3:
Remote Vibration Monitoring System

Case Study 4:
Magnetic Vibratory Bulk Loader

Vibratory Controlled Conveyor

Problem: Client requires low cost design for resonant vibratory controlled conveyor capable of controlling multiple systems using a single variable frequency drive for batch unloading process.

Investigation: Stroke deflection from loaded to unloaded condition was calculated and found to exceed limits of sensitive conveyor components when operating at or near resonance.

Measurements: Deflection measured using a linear voltage differential transformer on each trough.

Solution: Custom software is used to regulate a control signal to the variable frequency drive to limit over stroke conditions. Design uses a micro controller vs. PLC as a cost saving measure.

Results: Simple low cost system controls and protects conveyor.

Vibration Analysis of Integrated Circuit Fabrication Equipment

Problem: A client who is a world leader in computer printer ink jet cartridge manufacturing planned to add production capacity in Europe to supply its global market. Ink jet cartridge manufacturing makes extensive use of precision equipment in a clean room environment. Vibration of lasers and photo reduction equipment has been shown to result in scrap and is therefore undesirable. The client had been producing high quality cartridges in the USA and wanted to measure or characterize the vibration here; then furnish that data to the new facility to help ensure that vibration, if limited to a similar level, would not adversely affect quality.

Vibration isolators are used on some equipment and quality problems had been associated with installation problems already experienced.

The European facility was to be located near a busy road and traffic induced vibration was anticipated to cause vibration induced quality problems during production.

Investigation: One machine vendor had established a maximum vibration level specification; however, most did not.

Measurement: Acceleration measurements were made throughout the production facility and on multiple locations of each sensitive machine. Both overall and filtered vibration data was collected, analyzed and reported on simply graphic renderings of each area or machine.

Results: The Client was able to use the vibration levels in the USA as a reference for new equipment in Europe to ensure that vibration was appropriately limited. Start-up problems were reduced when vibration isolation treatments were determined to be functioning properly.

Remote Vibration Monitoring System

Problem : Sensitive components of a large structure could be damaged by aggressive demolition activities nearby.

Investigation: The structure had one side that faced the demolition efforts and was susceptible to varying degrees of potentially damaging vibration at different locations along its length. Demolition was to be completed over a period of many months; 24 hours a day, 7 days a week. Workers would need to be alerted to curtail their activities if vibration exceeded specific damage control criteria.

Measurements: Multiple channels of seismic accelerometers were located on and near the structure.

Solution: A computerized system automatically monitored vibration, recorded events, calculated statistics, logged time stamped data. The system was installed along with a phone line, modem and software that permitted the exchange of data and remote control. Alarms were activated and recorded whenever vibration exceeded preset levels.

Results: Workers were able to perform demolition as quickly and as aggressively as possible with confidence that they were not damaging another structure in the process. Data was reviewed and analyzed remotely in a cost effective manner.

Magnetic Vibratory Bulk Loader

Problem: A client was filling an annular ring with a granular high density material using a torsionally excited vibratory bulk loader but was experiencing quality problems and thus, high scrap losses. Multiple bulk loaders were used to support fabrication of components for high volume assembly. The loaded item was sealed, then stored, for future assembly with other components. Loading quality was not detectable until an operational test, after final assembly; just prior to packaging. A 15 second cycle time often resulted in so many rejected assemblies that the client’s ability to make corrections was at times, overwhelmed; leading to warranty claims after delivery.

Investigation: A review of the process showed considerable variation in operational qualities of the bulk loaders. Ancillary issues affecting quality were also observed. Addressing of these ancillary issues led to serendipitous benefits that were realized later. A diode and resistor based magnetic vibratory device control system was used but offered very limited control and was prone to constant adjustment by operators. The mechanics of the magnetic vibratory drive units required extensive tuning of springs and air gaps.

Measurements: Acceleration in both horizontal directions taken 90 degrees apart and displayed on an oscilloscope showed the degree of torsion motion.

Solution: Magnet spring orientations and air gaps were adjusted to obtain a more pure torsional motion. Periodic checks of torsional vibration directed magnet air gap adjustments and was the basis of a quality control preventative maintenance program. Controllable SCR’s were installed and provided improved control.

Results: Quality of loading produced by the bulk loaders was improved. Reliable service of the bulk loaders was maintained by periodic measurement and adjustment.