The development of precision probes has a long history, which can be traced back to the appearance of inductive micrometers in the 1920s; but the real rapid development benefited from the appearance of three-coordinate measuring machines in the late 1950s. So far, precision probes are usually divided into two types: contact probes and non-contact probes, of which contact probes are divided into mechanical probes, trigger probes and scanning probes; non-contact probes are divided into For laser probe and optical video probe.
The mechanical probe, also known as the contact hard probe, is an earlier type of probe used in precision measuring instruments. The measurement is completed by direct contact between the probe end and the workpiece to be measured for positioning and aiming, and is mainly used for manual measurement.
This type of touch probe has a simple structure and is easy to operate, but its accuracy is not high, and it is difficult to meet the requirements of current CNC precision measuring instruments. Except for a few occasions, this type of probe is rarely used at present.
The most widely used precision probes on the market are trigger probes. The first trigger probe was developed by the British Renishaw company in 1972.
The measuring principle of the trigger probe is that when the measuring end of the measuring probe is in contact with the workpiece to be measured, the precision measuring instrument sends out a sampling pulse signal, and the coordinate value of the ball center of the measuring end is latched by the positioning system of the instrument at this time, so as to determine the measuring point. The coordinates of the contact point between the end and the workpiece to be measured.
This type of probe has the advantages of simple structure, convenient use, low manufacturing cost and high trigger accuracy, and is the most widely used probe among 3d probe CNC.
However, this type of probe also has errors such as anisotropy (triangular effect) and pre-travel, which limit the further improvement of its measurement accuracy, and the highest accuracy can only reach a few tenths of a micron.
When measuring with a trigger probe on a precision measuring instrument, it is usually two-point alignment, three-point surface alignment, three-point or four-point circle alignment, etc. The essence is to use the coordinates of several points to determine the ideal geometric elements. However, the touch trigger probe shows obvious defects in the measurement of shape and position errors; the appearance of scanning probes makes up for the shortcomings of trigger probes.
Scanning probes are also called quantitative probes, and the output of the probe is proportional to the offset of the probe. As a probe with high precision, strong function and wide adaptability, it also has the functions of position detection of spatial coordinate points and scanning measurement of curves and surfaces.
The measurement principle of this type of probe is that after the probe end touches the workpiece to be measured, the contact displacement is continuously measured, and the conversion device of the probe outputs a signal proportional to the small deviation of the measuring rod. The precise coordinates of the point on the measured workpiece can be obtained by superimposing the signal and the corresponding coordinate value of the precision measuring instrument.
If the deformation of the measuring rod is not considered, the scanning probe is isotropic, so its accuracy is much higher than that of the trigger probe. The disadvantage of this type of measuring head is that the structure is complex and the manufacturing cost is high. At present, only a few companies in the world can produce it.