ASME B89.4.21.1 pdf download

ASME B89.4.21.1 pdf download Environmental Effects on Coordinate Measuring Machine Measurements
1 SCOPE
This Technical Report discusses important influences of the environment on dimensional and geometric measure- ments performed using coordinate measuring machines (CMMs), including influences on both the machine and the workpieces to be measured. This Report discusses the thermal effects related to the use of tactile CMMs, but many of these effects are also applicable to optical and other noncontact coordinate measurement systems.
2 INTRODUCTION AND BACKGROUND
2.1 Operating Conditions
JCGM 200 (ref. [1]) defines rated operating conditions (4.9) and limiting operating conditions (4.10). Machine speci- fications, typically stated as maximum permissible errors (MPEs), are intended to be applicable to a CMM that is used within its rated operating conditions. These rated operating conditions are the conditions that must be fulfilled for the machine to perform as designed (i.e., meet the MPEs). These conditions include, but are not limited to, environmental conditions.Limitingoperatingconditionsaretheextremeatwhichamachinecanbeoperatedwithoutsustainingdamage and without degradation of specifications when subsequently operated within its rated operating conditions.
2.2 Definition of Environment
For the purpose ofthis Technical Report, the CMM environmentincludes those elements in the machine surroundings that affect CMM system performance; effects of operators are not addressed in this Report. The environmental effects included are temperature and humidity, illumination, vibration, electrical effects, and contamination. These effects are caused or transmitted by surrounding air, building structure, other equipment, supply air, and the electrical system. For the purpose of this Technical Report, environments are classified as “laboratory” or “shop.” A laboratory envi- ronment is controlled in order to perform measurements at an acceptable accuracy level. A shop environment is controlled only to the level required to produce acceptable workpieces. A shop environment may not be acceptable for performing measurement tasks.
2.3 Environmental Effects
The influence ofenvironmental variables on the measurementresults obtained using the CMM are classified as envir- onmentaleffects.Thevariablesareidentifiedinpara.2.2,andtheirinfluencecanvarygreatlyamongdifferentfacilities,or evenwithinone facility. Whereas temperature andhumiditymayvarydependingonthe timeofdayorseasonofthe year, influences such as illumination, electrical noise, and vibration may be fairly constant for a given CMM installation. Contamination, either airborne or on the CMM and workpieces, may be either a steady-state or varying condition. The ability to manage contamination will depend on the nature of the installation and the perceived impact of the contamination on measurement results.
Three main methods are employed to mitigate the influence of the environmental effects, as follows:
(a) Attemptto Remove the Source ofthe Influence. This may be done by shutting down or moving equipment causing vibration or removing heat sources from the immediate vicinity of the measuring equipment.
(b) Attenuate the Effects ofthe Influence. Vibration isolators may be used between the factory or laboratory floor and the CMM, or baffles may be installed to block radiation from a heat source that cannot be moved.