ASME B89.4.21.1-2020 pdf download.Environmental Effects on Coordinate Measuring Machine Measurements.
6 ASSESSING VIBRATION EFFECTS 6.1 Foundation Vibration Testing (Based on ASME B89.4.22 (ref. [17]) Coordinatemeasuringmachines availabletodayarecapableofobtainingextremelyaccurate measurements. However, external sources such as vibrations from machine tools, climate control systems, and materials handling systems can significantlydegradeboththeiraccuracyandrepeatability.Thus,anunderstandingofthemagnitudeofexternalvibration excitation is an important part ofthe installation site qualification. The biggest contributor to this degradation is vibra- tionstransmittedthroughthefloor,havingaparticularlynegativeimpactontherepeatability. Vibrationlimitsareusually defined in the manufacturer’s specification. It is good practice to locate the CMM in an area where vibrations are minimal or less than the CMM manufacturer’s specification. If this is not possible, site surveys should be performed to determine the vibration’s magnitude and frequency orientation of the foundation. The following should be considered when a site survey is made: (a) A reputable vendor should be chosen to record the data with the appropriate equipment. The sensors must be responsive to low-frequency vibrations. (b) The vendor should be informed of the frequency range that is important to the machine and what data is to be recorded. NormallyCMMs are mostaffectedbyvibrations inthe10 Hzto 30 Hzrange butdatashouldbe recordedinthe5 Hz to 60 Hz range. (c) The vendorshould be informed in whatformatthe analysis and outputshould be. Usuallythe CMM supplierwants the data in amplitude versus frequency or acceleration versus frequency.
Followingthe conclusion ofa site survey, evaluate the results againstthe manufacturer’s requirements and determine ifthe site is suitable for the CMM to operate. Ifthe site is not suitable for CMM operation, then determine either how to improve the CMM performance in a harsh environment or how to improve the environment. Ifdesired, use the manu- facturer’s expertise to better analyze these results and provide recommendations. The effectofvibrations, typicallycharacterized byamplitude versus time orfrequency, is usuallyminimized bythe use ofeither an active or a passive isolation system. Selecting the mostappropriate isolation system depends on the specific engineering requirements of the application and the desired vibration characteristics and is usually best left to a site vibration specialist. The most common method used is the passive system approach. While there are different configurations for passive systems, theyall incorporate the use ofsprings and an inertial confinementblock, typicallymade from either concrete or steel. Typical configurations are shown in Figure 6.1-1. Note that the springs may not actually be springs (in some cases isolationpadsareused),butcanbemodeledasaspringwithcertainstiffness.Typicalpadmaterialsincludeneoprene,felt, fiberglass, or other similar compressive material. Their natural frequencies are generally between 5 Hz and 30 Hz. Pad stabilitycan be an importantconsideration. Some material properties change as a function oftime, i.e., many getharder, and thus the natural frequency of the pad increases, resulting in a decrease in effectiveness. An active control system uses a series of transducers that produce a force equal in frequency and amplitude to the vibration presentbutis 180 deg out-of-phase with the input, with the neteffectthatthe two forcing sources cancel each other out.ASME B89.4.21.1 pdf download.