How does the coordinate measuring machine choose the probe to measure?

The probe is a three-coordinate measuring machine that touches the signal of the tested part. It is a key component of the coordinate measuring machine. The accuracy of the measuring head determines the measurement repeatability of the measuring machine. In addition, different parts need to select different functions of the probe for measurement.

The probes can be divided into contact and non-contact (laser type). At present, the contact probe is mainly used, and the contact probe can be divided into two types: switch type (trigger type or dynamic type) and scan type (proportional or static type).

The scanning probe is substantially equivalent to the differential inductance micrometer in the X, Y and Z directions, and the movement in the three directions of X, Y and Z is supported by the parallel leaf springs in three directions, which is a gapless rotation. The offset of the probe is measured by a linear inductor. Scanning probes are primarily used to measure complex curved surfaces.

The essence of the switch probe is the zero-position switch. Take TP6 (RENISHAW) as an example. It is equivalent to three pairs of contacts connected in series in the circuit. When the probe produces displacement in either direction, it makes any contact leave. , the circuit is disconnected to send a count. The switch type is simple in structure, long in life (106~107), has good measurement repeatability (0.35~0.28μm), and has low cost and rapid measurement, so it is widely used.

Non-contact probes are mainly divided into laser scanning probes and video probes.

Laser scanning probes are primarily used for non-contact measurement of softer materials or some feature surfaces. The probe is measured at a distance from the workpiece (for example, 50mm) and within 5mm of its focus point. The picking rate is above 200 points/second. Higher accuracy is achieved by averaging processing of large amounts of acquired data.

Video probes further enhance the use of measuring machines, enabling many tasks that were previously impossible with non-contact measurements. Some such as printed wiring boards, flip-flops, pads or holes with a diameter of less than 0.1 mm can be measured with a video probe. The operator can magnify the surface of the test workpiece by more than 50 times and measure the small workpiece with a standard or convertible lens.

Here are some suggestions on how to trigger and scan the probe:

When do you use a scanning probe?

1. Measurements for parts and contours with shape requirements: The main advantage of scanning mode measurement is the ability to acquire data at high speed. This data can be used not only to determine the size and position of the part, but more importantly, to use a large number of points. Accurate description of shape and contour, which is especially suitable for parts with strict requirements on shape and contour. The shape of the part directly affects the performance of the part (such as blades, elliptical pistons, etc.);

It also applies to the fact that you can't be sure that the processing equipment you are using can produce parts of good shape.

When do you use a trigger probe?

1. The part is concerned with the size (such as small thread bottom hole), spacing or position, and does not emphasize its shape error (such as positioning pin hole);

2. Or you are sure that the processing equipment you are using has the ability to machine parts of sufficient shape, and the focus is on size and positional accuracy. Contact trigger measurements are appropriate, especially due to the measurement of discrete points;

3. The trigger type probe is faster than the scanning probe, and the trigger probe volume is small. When the measurement space is narrow, the probe is easy to access the part;

4. In general, the use of trigger probes and maintenance costs are lower;

There are a large number of geometric measurements in the machinery industry, the only concern is the size and position of the parts, so most of the measuring machines on the market today, especially medium-precision CMMs, still use contact-trigger probes.

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