Needle measuring compensation

Three coordinates touch the part by the measuring head (hard measuring head or electronically triggered measuring head) to obtain and collect measurement data. Since the measuring needle uses the circumference of the measuring needle ball to touch the workpiece, the center point of the measuring needle ball and the radius of the measuring needle must be calculated in advance. The calibration action of the measuring needle is to first touch the standard ball with the measuring needle. After the measuring needle is calibrated (the measuring software has known the spherical center position and radius size of the measuring needle), the coordinate value accepted by the CMM control cabinet should be the coordinates of the center point of the ruby ball head when the measuring needle touches the parts. Obviously, the measuring software will automatically add a ruby ball radius along the direction the measuring needle returns from the point of contact as the measurement value. However, the measured value is a dynamic value related to the mechanical inertia of the measuring head. In fact, as a dynamic process, the measured value should take into account the machine space travel distance from the measuring needle to the coordinate value actually transmitted to the measuring cabinet. In the actual measurement, the system can automatically distinguish the compensation direction of the ruby ball radius, and the software in the control cabinet to calculate the correct compensation radius will compensate the ruby ball radius according to the direction of the measuring needle contact part. When you use the measuring needle to measure the part, the software in the measuring control cabinet will automatically increase or decrease the radius of the measuring needle to calculate the correct value.

Test the effective contact method of the needle

The correct and effective use of measuring needle contact parts can avoid many unnecessary errors. For example, when touching a part with a measuring needle, it should be as perpendicular to the measuring surface of the part as possible (as shown below). For CMM, the most ideal way to use the trigger head is to use the measuring needle to touch the part vertically. Of course, it is impossible to keep the vertical parts completely, but when touching the measuring point, at least keep the vertical Angle with the parts within ±30º, in order to prevent the needle from slipping and resulting in poor measurement accuracy.

To avoid the above problems effectively, the solution is to increase the ball diameter of the measuring head or extend the effective lengthening rod length of the measuring needle. However, both methods have drawbacks. If the ball diameter is too large, it will not be possible to measure parts with smaller apertures. If the effective measuring needle lengthens the length of the rod, the measuring error will be larger. Therefore, how to choose the appropriate extension rod length and measuring needle ball diameter to measure parts is also very important.

With the continuous improvement of enterprise production efficiency, the requirements of online measurement products also develop rapidly with the improvement of production efficiency. Because the three standard measuring machine has a powerful online measuring function, it plays an irreplaceable role, but for us, the measuring function of the three standard measuring machine can not be fully mastered, improve the measuring requirements of the three standard measuring machine is an urgent measuring task. The CMM should carry out needle calibration before the measurement work, which is a very important work step that must be carried out before the measurement, because the error in needle calibration will be randomly added to the measurement value of the parts in the future.