三坐标测量机误差补偿
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Workpiece
Related to properties of the workpiece and measurement interaction with the workpiece. Including:
Part form deviation, accessibility restrictions, sampling distribution, clamping effects, contact mechanics, surface finish, elastic deformation
Some Concepts
Uncertainty
Measuring uncertainty is a calculated estimate of how much a measured result may vary from the true value, based on factors such as operator influence, as well as the environmental conditions in which the instrument is used.
Bias
Reference value Observed average value
Traceability
TrHale Waihona Puke Baiduceability
Traceability is defined as ―property of the result of a measurement or the value of a standard whereby it can be related to stated tolerance, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties‖
21 parametric errors, random components of the parametric errors, uncorrected systematic and apparently random probing errors, probe changing and probe articulation uncertainties, probing parameters, errors caused by the dynamics of the machine structure and probe, the environmental and machine temperatures and vibration.
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Error Compensation
If we can understand and mathematically characterize a CMM's predictable measurement error sources, the CMM controller software can automatically correct the measurements. Compensation algorithms are discrete digital systems applied to a dynamic analog reality. Both static geometric errors and all sorts of dynamic and thermally induced geometry errors can be compensated. An important prerequisite for the successful application of software error compensation is a "well behaved", repeatable CMM.
Sources of Uncertainty
21 parametric errors
Six errors for each axis Three perpendicularity or squareness errors between the axes.
Sources of Uncertainty
Considerations
Chap. 6 Non-Cartesian CMMs
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Error Compensation
Static geometric errors
Static geometric errors are those errors caused by microscopic imperfections in the shapes of the guide ways and scale systems that lead to errors in the measured location of the probe tip when the machine is not moving. (21 geometric errors) Static geometric errors are a property of the completely assembled machine only. In principle they do not change over time.
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Sampling Strategy
Inadequate sampling, the interaction of sampling strategy with form error, interactions of sampling with complex forms, uncertainty ―magnification‖ due to inadequate datums and even incomplete exactness of transfer of measurement results between calibration artifacts and real parts.
Some Concepts
Bias
Bias is the difference between the observed average of measurement and the reference value. It is the systematic error that is an indication of a measuring instrument. The reference value is determined by averaging several measurements using standard measuring equipment.
Error Compensation
Thermal errors
Thermal errors are changes in the machine's geometry caused by changes in temperature. Thermal errors are a function of both the thermal environment and the machine's thermal response. In order to calculate the effects of the thermal errors on the location of the probe tip we need a temperature model that characterizes the machine thermal behavior as well as input values that characterize the thermal environment.
FUNDAMENTALS OF COORDINATE MEASURING TECHNOLOGY
Prof. Dr. Liandong Yu Prof. Dr. Weishi Li
HEFEI UNIVERSITY OF TECHNOLOGY
Contents
Chap. 1 Evolution of Dimensional Measurement Chap. 2 Fundamentals of CMMs Chap. 3 Probe Systems Chap. 4 CMM Software Chap. 5 Error Compensation & Application
Sources of Uncertainty
Fitting & Evaluation Algorithms
Algorithm suitability and selection Algorithm interaction with sampling density Algorithm implementation
Sources of Uncertainty
Sources of Uncertainty
Hardware
Uncertainty caused by errors inherent to the design of the design of the machine, its scales and geometry, its probing system, its dynamics, and the environment in which it is placed. Including:
Repeatability
Repeatability is the variation in measurements obtained with one measurement instrument when used several times by an appraiser while measuring the identical characteristic on the same part. It is a component of uncertainty, but in many cases a fairly small component.
Extrinsic Factors
Apparently minor variation in operator/machine interaction (tightening of clamps, failure to wear gloves, etc.) Part cleaniness Presence of contaminates ...
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Related to properties of the workpiece and measurement interaction with the workpiece. Including:
Part form deviation, accessibility restrictions, sampling distribution, clamping effects, contact mechanics, surface finish, elastic deformation
Some Concepts
Uncertainty
Measuring uncertainty is a calculated estimate of how much a measured result may vary from the true value, based on factors such as operator influence, as well as the environmental conditions in which the instrument is used.
Bias
Reference value Observed average value
Traceability
TrHale Waihona Puke Baiduceability
Traceability is defined as ―property of the result of a measurement or the value of a standard whereby it can be related to stated tolerance, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties‖
21 parametric errors, random components of the parametric errors, uncorrected systematic and apparently random probing errors, probe changing and probe articulation uncertainties, probing parameters, errors caused by the dynamics of the machine structure and probe, the environmental and machine temperatures and vibration.
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Error Compensation
If we can understand and mathematically characterize a CMM's predictable measurement error sources, the CMM controller software can automatically correct the measurements. Compensation algorithms are discrete digital systems applied to a dynamic analog reality. Both static geometric errors and all sorts of dynamic and thermally induced geometry errors can be compensated. An important prerequisite for the successful application of software error compensation is a "well behaved", repeatable CMM.
Sources of Uncertainty
21 parametric errors
Six errors for each axis Three perpendicularity or squareness errors between the axes.
Sources of Uncertainty
Considerations
Chap. 6 Non-Cartesian CMMs
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Error Compensation
Static geometric errors
Static geometric errors are those errors caused by microscopic imperfections in the shapes of the guide ways and scale systems that lead to errors in the measured location of the probe tip when the machine is not moving. (21 geometric errors) Static geometric errors are a property of the completely assembled machine only. In principle they do not change over time.
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration
Sampling Strategy
Inadequate sampling, the interaction of sampling strategy with form error, interactions of sampling with complex forms, uncertainty ―magnification‖ due to inadequate datums and even incomplete exactness of transfer of measurement results between calibration artifacts and real parts.
Some Concepts
Bias
Bias is the difference between the observed average of measurement and the reference value. It is the systematic error that is an indication of a measuring instrument. The reference value is determined by averaging several measurements using standard measuring equipment.
Error Compensation
Thermal errors
Thermal errors are changes in the machine's geometry caused by changes in temperature. Thermal errors are a function of both the thermal environment and the machine's thermal response. In order to calculate the effects of the thermal errors on the location of the probe tip we need a temperature model that characterizes the machine thermal behavior as well as input values that characterize the thermal environment.
FUNDAMENTALS OF COORDINATE MEASURING TECHNOLOGY
Prof. Dr. Liandong Yu Prof. Dr. Weishi Li
HEFEI UNIVERSITY OF TECHNOLOGY
Contents
Chap. 1 Evolution of Dimensional Measurement Chap. 2 Fundamentals of CMMs Chap. 3 Probe Systems Chap. 4 CMM Software Chap. 5 Error Compensation & Application
Sources of Uncertainty
Fitting & Evaluation Algorithms
Algorithm suitability and selection Algorithm interaction with sampling density Algorithm implementation
Sources of Uncertainty
Sources of Uncertainty
Hardware
Uncertainty caused by errors inherent to the design of the design of the machine, its scales and geometry, its probing system, its dynamics, and the environment in which it is placed. Including:
Repeatability
Repeatability is the variation in measurements obtained with one measurement instrument when used several times by an appraiser while measuring the identical characteristic on the same part. It is a component of uncertainty, but in many cases a fairly small component.
Extrinsic Factors
Apparently minor variation in operator/machine interaction (tightening of clamps, failure to wear gloves, etc.) Part cleaniness Presence of contaminates ...
Error Compensation and Application Considerations
• • • • • • • Some Concepts Sources of Uncertainty Error Compensation Acceptance & Re-verification Tests Temperature Control Fixtures System Integration