Standard definition and selection method for CMM needle length measurement

The CMM measuring needle is a part of the measuring head system of CMM, which is mainly used to touch the workpiece surface, generate signal trigger and collect measurement data through the displacement of the measuring head mechanical device. Ruby measuring needles are now widely used. Today, we will discuss the standard definition and selection of CMM needle length.

The standard definition of the total length of a CMM measuring needle is the length from the mounting face of the measuring needle to the center of the measuring ball

Effective Working Length (EWL)

The effective working length is the distance from the center of the measuring ball to the interference point between the measuring rod and the measured target.

Rules of needle selection

Some simple needle selection rules can be used to achieve high accuracy in most probe measurement applications.

Try to choose a short measuring needle

The smaller the diameter of the measuring needle, the larger the bending or deformation, and the lower the accuracy. The shortest possible measuring needle is yours. zuijia selection.

Minimize joints

Each additional connection between the measuring needle and the extension rod increases a potential point of bending and deformation. Minimize the number of needle measuring assemblies.

The measuring ball diameter should be as large as possible for the following reasons:

This can increase the distance between the ball/rod, thereby reducing the false trigger caused by the collision of the rod and increasing the effective working length; The larger the measuring ball is, the larger the measuring rod diameter is, and the stiffness of the measuring needle is increased. The larger the diameter of the ruby ball, the less the influence on the surface finish of the workpiece.

How to choose the measuring needle of CMM?

CMM is not unfamiliar, because the CMM for CMM precision is very high, so the choice of CMM measuring needle is a very key factor. The focus of CMM is whether it can touch the feature and ensure a certain accuracy when touching. CMM needle is very common in the market, can be said to be ichthyosaur hybrid. Although there are many types of CMM needles, prices vary due to their shapes and production materials. So, how do we choose the right CMM needle?

1. Needle selection experience of CMM

1: CMM needle length should be as short as possible. The greater the bend or tilt of the measuring needle, the lower the accuracy. Therefore, try to use a short needle when measuring.

2. The connection points of CMM are minimum. When the measuring needle is connected to the extension rod, new potential bending and deformation points can be introduced, so the number of connections should be minimized in use.

3: CMM measuring ball as large as possible

Two: three coordinate measuring instrument measuring needle shape

The shape of measuring needle of CMM includes direct measuring needle, star measuring needle, disc measuring needle, cylindrical measuring needle and so on. Direct measurement needle simple structure probe system includes industrial ruby ball and rod material with good sphericity.

Three: CMM needle measuring materials

1. Ruby, silicon nitride, zirconia and so on are the materials for measuring the tip of CMM. The most common is ruby needle measuring. Ruby is one of the hardest materials known, with excellent surface finish, excellent compressive strength and resistance to collisions. Rebar materials include steel, tungsten carbide, ceramics, carbon fiber and so on.

2. The needle measuring material of CMM is ruby, because ruby is a very hard material and the probe wear is minimal. The density is also very low, so the tip mass is small, can avoid the machine movement or vibration of the probe triggered by mistake.