Analysis of CMM: From Basic Principles to Breakthroughs in Measuring Oblique Holes

The three-coordinate Measuring Machine, through mathematical modeling and algorithm processing of a vast number of points, reconstructs the three-dimensional digital model of the workpiece, thereby achieving precise measurement from simple geometric elements (points, lines, surfaces) to complex surfaces and free-form surfaces. It is applicable in various industries, such as:

1. In the automotive manufacturing process, the three-coordinate measuring machineis involved in the detection of key parameters such as the coaxiality of the crankshaft hole in the engine cylinder block and the positional accuracy of the valve guide holes in the cylinder head.
2. In the aerospace field where measurement accuracy is more demanding, the three-coordinate measuring machineuses high-precision scanning probes and intelligent coordinated scanning of tens of thousands of points to construct a three-dimensional model of the blade, and then uses the dedicated analysis Software PowerBlade to comprehensively evaluate key parameter indicators such as the leading and trailing edges, blade profile, chord length, chord angle, position accuracy, maximum thickness, edge thickness, waviness, and twist angle, achieving continuous, high-speed, and non-stop scanning of complex curves, fully capturing the full-size features of the blade backside/back basin profile, leading and trailing edges, dovetail and slot, etc., ensuring that the contour accuracy of each blade is controlled within ±0.005mm.
3. In the semiconductor industry, whether it is simple shaft sleeves or complex irregular parts, the three-coordinate measuring machinefully covers the detection requirements of various core components of semiconductor equipment.

The difficulty in three-coordinate measurement technology: measurement of inclined holes Structures such as inclined oil holes and valve guide tube holes in automotive engines usually form an angle of 30° to 60° with the reference surface. Traditional methods are unable to accurately measure them. The difficulty in inclined hole measurement technology lies in:

1. Constraint on the direction of the normal vector: During measurement, the probe must be touched along the axis direction of the inclined hole (the normal vector direction); otherwise, projection errors will occur;
2. Coordinate system conversion: When the workpiece is placed randomly, there is a spatial angle deviation between the inclined hole coordinate system and the machine tool coordinate system;
3. Movement restriction of the probe: Fixed probes cannot freely rotate and are difficult to align with the inclined surface.

Industry Solutions

1. Probe Rotation Technology

High-end measuring instruments are equipped with a 360° rotating probe base. Through automatic adjustment of the A angle/B angle direction, the probe always touches the workpiece along the normal direction of the inclined hole;

2. Intelligent Coordinate System Alignment

For measuring heads that cannot be rotated, the 3-2-1 alignment principle is adopted. Iteration and optimal fitting create the coordinate system:

(1) Measurement reference plane (3 points establish the Z-axis)

(2) Measurement reference line (2 points establish the X-axis)

(3) Measurement reference origin (1 point establish the coordinate system)

(4) Through two-dimensional rotation calculation, the machine tool coordinate system is converted to the workpiece coordinate system.

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