Contact sensor – explained from the principle and characteristics

As the name suggests, this sensor measures position by touching the contact directly to the detection object. As shown in the figure on the right, when the height of the main shaft changes, the displacement amount can be obtained internally. As the main use, it is suitable for detecting the height, thickness and warpage of workpieces.

Contact displacement sensor with “touch” detection

summary

As the name suggests, this sensor measures position by touching the contact directly to the detection object. As shown in the figure on the right, when the height of the main shaft changes, the displacement amount can be obtained internally. As the main use, it is suitable for detecting the height, thickness and warpage of workpieces.

[Cylinder type for measuring by extending the spindle]

Measurement can be performed directly with the sensor head fixed, so there is no need to move the sensor head itself. Installation can be performed in a space-saving manner, and man-hours at the time of introduction can be greatly reduced.

Contact sensor – explained from the principle and characteristics

Features

【Comparison by detection method】

Principles and main types

The detection principle of the contact displacement sensor is roughly classified into the following two types.

• “Differential transformer” method[usingthecoilmethod[采用线圈的方式

• “Scale” method[internaluseofascale(ruler)[在内部采用刻度尺(尺子)的方式

Differential Transformer Method

The principle of the differential transformer method is that a magnetic field is generated when the current passes through the inner coil.

If a core is inserted in it, the impedance of the coil changes depending on the amount of insertion, and the signal level also changes.

The change in the signal level is detected and converted into the movement amount.

Advantage: The “absolute position” can be grasped because the signal level changes according to the position of the spindle. (No zero point adjustment, no tracking error)

Disadvantages: ○Accuracy drops near the end of the spindle. Since the principle of the coil is used, the magnetic field is uniform near the center, but there is a tendency to lose balance near the ends.

○ Linearity or temperature characteristics need to be considered.

scale method

Advantages: ○High precision. (Accuracy is basically determined by the scale accuracy of the scale)

○ The scale width of the scale does not change regardless of whether it is near the center or the end of the scale, so there is no need to consider linearity.

○ Even if there is a temperature change, the scale of the scale does not change greatly, so the temperature characteristics are better.

Disadvantages: ○ When the spindle moves violently due to vibration, etc., the photoelectric sensor has no time to respond, and a tracking error will occur.

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