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The Evolution of Touch Probe Technology

The probe is one of the key components of the precision gauge. As a sensor that provides geometric information of the measured part, its development level directly affects the measurement accuracy, efficiency and flexibility of the precision template. The coordinate measuring machine is a typical precision measuring equipment, and its development history also shows that the coordinate measuring machine can be fundamentally changed only after the precision measuring head provides a new measuring principle for the coordinate measuring machine. Contact and new measurement accuracy. In other words, precision probes are the main factor limiting the accuracy and speed of precision instruments, and their ability to meet modern measurement requirements also depends on the innovation and continuous development of probe systems.


1. The development of the touch probe


The development of precision probes has a long history, which can be traced back to the appearance of induction microbeads in the 1920s, but the real rapid development was the emergence of CMM in the late 1950s. Until now, precision probes are generally classified into contact probes. And non-contact probe, the probe itself is divided into mechanical trigger probe and scanning probe; non-contact probe is divided into laser probe and optical video probe.


Mechanical probes, also known as touch probes, were the first probes used for precision measurements. The measurement is carried out by the positioning and orientation of the measuring head in direct contact with the measured part, and is mainly used for manual measurement. This type of probe is easy to operate, easy to operate, and has low precision. It is difficult to meet the requirements of the current precision numerical control flowmeter. At present, it is rarely used except for special occasions.


The most widely used precision probes in the market are trigger probes. The first trigger detector was developed in 1972 by the British company Renishaw. The measurement principle of the trigger probe is to determine the coordinates of the contact point between the probe and the measured part by sending a pulse signal. When the probe is in contact with the measured part, sampling is performed by precise measurement, and the coordinate value of the center of the sphere is locked by the positioning system of the instrument. This type of probe has the following advantages: However, this type of measuring head also has anisotropic errors such as preprocessing (triangle effect), which further limits the improvement of the measurement accuracy, which cannot reach a maximum value of a few microns. When a trigger probe is used for measurement on a precision flowmeter, it is usually measured by determining a two-point line, determining a three-point plane, or determining a four-point circle. The existence of the scanning probe makes up for the lack of the trigger probe.


2. Analysis of different touch probes


Scan probes are also known as quantitative scan probes. Their output is proportional to the probe's offset, which makes them very precise, very practical, and very adaptive. The measurement principle of this type of probe is to continuously measure the contact displacement of the tip of the head after contact with the part under test, and the output of the head transducer gives a signal proportional to the small deflection of the measuring rod. If the deformation of the 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 kind of detector is that the structure is complicated and the manufacturing cost is high, and it can only be manufactured by a few companies around the world.


Trigger probes or scanning probes can detect bypass points through the probes that are in contact with the part to be tested, and then perform data processing to obtain information on the location or shape of the room to be tested; due to the size of the machine tool probes, it is impossible to measure some internal dimensions. Small parts, such as notches; in addition, pressure from contact between the tip of the head and the part being tested can cause deformation and scratching of the part being tested, and it is difficult to measure the profile of the knife. As well as the flexible material of some blades. Non-contact probes can be avoided using optical methods.


Non-contact probes are generally measured by optical methods. Since the probe is not in contact with the part under test, there is no measurement force and fewer scratches on the part under test. However, this type of detector is affected by many external factors, such as the radiative properties of the terrain and reflections from the surface. At present, the measurement accuracy of non-contact probes is not very high, and it cannot replace non-contact probes in precision instruments.

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