ASME B89.4.21.1:2020 pdf download.ENVIRONMENTAL EFFECTS ON COORDINATE MEASURING MACHINE MEASUREMENTS.
This Technical Report discusses important influences of the environment on dimensional and geometric measurements performed using coordinate measuring machines (CM Nis), 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. Ill) defines rated operating conditions (4.9) and limiting operating conditions (4.10). Machine spedfications, typically stated as maximum permissible errors (M PEs), are intended to L)e applicable to a CM M 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 MPIs). These conditions include, but are not limited to, environmental conditions. Limiting operating conditions are the extreme at which a machine can be operated without sustaining damage and without degradation of specifications when subsequently operated within its rated operati rig conditions.
2.2 Definition of Environment
For the purpose of this Technical Report, the CM NI environment includes those elements in the machine surroundings that affect CM M system performance; effects of operators are not addressed in this Report. The environmental effects included are temperature an(l humidity, illumination, vibration, electrical effects, and contamination. These effects are cause(l 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 au acceptable aCULIFaCy level. A SI1OFJ eflVir()llflleIlt IS controlle(l 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 of environmental variables on the measurement results obtained using the CMM are classified as environmental effects. The variables are identified in para. 2.2, and their influence can vary greatly among different facilities, or even within one facility. Whereas temperature and humidity may vary depending on the time of day or season oithe 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) Attempt to Remove the Source of the Influence. This may be clone by shutting down or moving equipment causing vibration or removing heat sources from the immediate vicinity of the measuring equipment.
(b) Attenuate the Effects of the influence. Vibration isolators may be used l)etween the factory or laboratory floor and the CMM, or baffles may be installed to block radiation from a heat source that cannot be moved.
(C) Compensate for the Influence. By using knowledge about how a particular influence effects the measurement and sensors to quantify the environmental state, the measurement results can be adjusted to compensate for the environment.
After mitigation, simply evaluate the influence; the uncertainty of measurement can he increased to accommodate the effect of environmental influences where these methods are not employed.ASME B89.4.21.1 pdf download.