三坐标测量机简介

Fundamentals of CMMs
• Coordinate Metrology & Advantage of CMMs
• Basic Principle of Structure Design
• Basic CMM Configurations
• Structural Materials
• Guideways and Air Bearings
Basic CMM Configurations
Advantages of Fixed Bridge CMMs
Good accessibility Mass of the workpiece does not influence CMM’s dynamic behavior Lower center of gravity than moving bridge CMMs -> Less creeping, suitable for big CMMs
Considerations
Chap. 6 Non-Cartesian CMMs
Fundamentals of CMMs
• Coordinate Metrology & Advantage of CMMs
• Basic Principle of Structure Design
• Basic CMM Configurations
Fundamentals of CMMs
• Coordinate Metrology & Advantage of CMMs
• Basic Principle of Structure Design
• Basic CMM Configurations
• Structural Materials
• Guideways and Air Bearings
Basic CMM Configurations
Advantages of Moving Bridge CMMs
Easy to manufacture; Good accessibility, big working space; Mass of workpiece does not influence CMM’s dynamic behaviour.
• Drive Systems
• Displacement Transducers
• Counter Balance Mechanism
Basic Principle of Structure Design
Abbe Principle
If the scale is not exactly along the measurement axis the angle errors produce measurement errors called Abbe errors. For many instruments the Abbe offset is not near zero and significant errors can be made.
The Nature of Coordinate Metrology
• Calculating the relevant substitute geometric elements in terms of parameters specifying size, form, location and orientation. • Evaluating the required workpiece features.
Basic CMM Configurations
Variant Designs of Moving Bridge CMMs
Basic CMM Configurations
Moving Ring Bridge CMM
Advantages
• High rigidity • Less Abbe offset • Central drive
• Counter Balance Mechanism
The Nature of Coordinate Metrology
• Using 3D Cartesian coordinate system invented by the famous French philosopher and mathematician René Descartes in the early 1600's to describe the movements of a measuring machine. • Generating the measured point sets on the actual workpiece with a CMM. Each point is unique to the machine coordinate system.
Advantage of CMMs
• Enable the determination of size, form, position and orientation in one setup on one measuring machine, using one reference system. • As a result, individual error sources from multiple measuring devices in conventional metrology do not occur. • There is scarcely any workpiece whose dimensions cannot be measured with CMMs.
• Basic Principle of Structure Design
• Basic CMM Configurations
• Structural Materials
• Guideways and Air Bearings
• Drive Systems
• Displacement Transducers
Basic CMM Configurations
L-shaped Bridge CMM
Structure Characteristics:
1. Worktable (optional) 2. L-shaped bridge (movable in Xaxis) 3. Carriage (movable in Y-axis) 4. Probe shaft (movable in Z-axis)
• Moving Bridge CMMs • Cantilever CMMs • L-shaped Bridge CMMs
• Fixed Bridge CMMs
• Gantry CMMs • Horizontal Arm CMMs
Basic CMM Configurations
Moving Bridge CMMs
• Drive Systems
• Displacement Transducers
• Counter Balance Mechanism
Structural Elements of CMMs
CMM Configurations
• CMM configurations play an important role in meeting measurement requirement like accuracy, flexibility, time and cost. • Typical configurations:
Basic Principle of Structure Design
Drive Offset
The distance from the center of gravity of the moving part to the line of driving force should be as small as possible to eliminate the twist.
Basic CMM Configurations
Cantilever CMMs Structure Characteristics:
1. Worktable (fixed, workpieces are loaded on it) 2. Cantilever beam (movable in X-axis) 3. Carriage (movable in Yaxis) 4. Probe shaft (movable in Z-axis)
• Structural Materials
• Guideways and Air Bearings
• Drive Systems
• Displacement Transducers
• Counter Balance Mechanism
Fundamentals of CMMs
• Coordinate Metrology & Advantage of CMMs
Structure Characteristics:
1. Worktable (movable in Xaxis, along the guide in bed) 2. Bridge-frame (mounted on the bed, unmovable) 3. Carriage moves in Y-axis 4. Probe shaft moves in Zaxis
Biblioteka Baidu
Disdvantages of Fixed Bridge CMMs
One side scale -> Big Abbe offset
Basic CMM Configurations
Fixed Bridge CMMs
Suitable for ultra-high accuracy CMMs
Low rigidity, low system natural frequency; One side scale in X-axis -> Big Abbe offset; One side drive in X-axis -> Creeping; unsuitable for big CMMs (long, thin design is OK).
Disadvantages of Moving Bridge CMMs
One side scale in X-axis -> big Abbe-error; One side driving system of X-axis -> creeping & yaw around Z-axis; Unsuitable for large CMMs.
Basic CMM Configurations
Advantages of Cantilever CMMs
Good accessibility; Mass of the workpiece does not influence CMM’s dynamic behavior.
Disadvantages of Cantilever CMMs
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
The most widely used …
Structure Characteristics:
1. Worktable (fixed, workpieces are loaded on it) 2. Bridge-frame (movable in X-axis) 3. Carriage (movable in Yaxis) 4. Probe shaft (movable in Zaxis)