Heres everything you need to know about needle testing

Why would you want to verify a CMM needle?

As the sensor of measuring machine, measuring head is a very important part of coordinate measuring system. The working efficiency and accuracy of CMM are closely related to the measuring head. Without advanced measuring head, the excellent function of CMM cannot be brought into play. According to the measurement method, the measuring head can be divided into contact (trigger type) and non-contact type. This paper mainly introduces the trigger measuring head. The correct selection and use of measuring needle is an important factor affecting the measuring accuracy of CMM. The measuring needle is mounted on the measuring head and is a part of the measuring system that directly contacts the parts. It has a communication connection with the measuring head that triggers the signal. How to choose the appropriate measuring needle type and specification depends on the characteristics of the part under test. But in any case, measuring the stiffness and standard sphericity of the needle is essential. Measuring needle rod generally adopts non-magnetic stainless steel needle rod or carbon tungsten fiber needle rod to ensure the stiffness of measuring needle. The effective working length of the measuring needle enables the accurate position of the measuring point to be obtained when the measuring needle touches the part. Measuring needle diameter ball head size and measuring needle have calibrated working length selection depends on the part being measured. If possible, choose the measuring needle diameter as large as possible, the measuring rod as short as possible to ensure the maximum measuring needle/measuring rod distance, effective working length and measuring needle stiffness. The measuring rod can be lengthened if necessary to increase the depth of the probe, but it should be noted that using the measuring needle to lengthen the rod will reduce the stiffness, thus reducing the measurement accuracy.

There are two main reasons for verifying the CMM needle: the compensated diameter of the ruby ball and the relationship between the different Angle measurement needle positions and the first Angle measurement needle positions. In the measuring task of CMM, the ruby ball of CMM needle is used to contact the measuring part, and the CMM measuring head (sensor) sends out a touch signal, which enters the grating counting system, locks and sends to the control cabinet of the measuring machine. The control cabinet of the working measuring machine will receive the position points represented by the coordinate X, Y and Z. It can be understood as the coordinate of the center of the 3-coordinate needle measuring ruby ball, but it is different from the radius of the contact point between the needle measuring ruby ball center and the workpiece that we really need. In order to accurately calculate our desired contact coordinates, we must verify the half/diameter of the needle ruby ball with a coordinate probe.

In the actual measurement parts, parts can not be moved and turned at will. In order to facilitate the measurement, it is necessary to choose the measurement length, size and shape of different shapes according to the actual situation. In order for these measurement elements of different angles and lengths, sizes and shapes to be calculated directly, the relationship between them needs to be measured and transformed during the calculation, so measurements are required.