Applications of Industrial Sensors
Industrial sensors are used to measure the outer diameter of steel materials and the thickness of sheet film. Because they can scan continuously at minute intervals of 0.1 second or less, they are suitable for use in manufacturing plants where the object to be measured is long and continuous and is continuously measured without being cut off in the middle.
Also, the industrial sensor can be used orthogonally to measure dimensions in the XY direction, or two or more industrial sensors can be used to measure one end face of an object that has a large cross-sectional shape.
Principle of Industrial Sensors
The principle of an industrial sensor measures the length of an object by irradiating a laser beam onto the object to be measured and using the sensor to detect the width at the point where the laser beam is blocked. It is important that the laser beam is emitted parallel to the measurement axis.
The part where the laser beam is blocked is considered an edge, and the sensor detects the width at both of these edges to enable dimensional measurement. Therefore, the configuration must be divided into a light-emitting part that emits the laser, a light-receiving part that reads the emitted laser, and a display part that displays the measured values.
The laser can be a strip or a rectangle with a width of 1.5 mm or more. The light-receiving part that reads the laser needs to continuously read the laser and the part that does not receive the laser in one section, so CCD line sensors are used in most industrial sensors.
The scanning interval for reading edges and measuring dimensions depends on the processing speed of the display unit. However, a typical product can scan at 0.1-second intervals, enabling accurate measurement even if the object to be measured swings slightly.
Other Information on Industrial Sensors
1. The Difference Between the CCD Method and the Light Intensity Change Method for the Light Receiving Part of Industrial Sensors
Industrial sensors are generally available in two types of light receiving parts: CCD type and light intensity change type. The configurations for each type are quite different.
CCD Method
The CCD method uses a CCD imaging sensor to detect parallel bands of light projected onto the photodetector; the CCD is placed in a band on the photodetector side to receive parallel light, and only where an object blocks the light, a shadow is reflected on the CCD, making it possible to measure the length of the object from that portion.
Light Intensity Change Method
In this method, a lens is placed on the receiver side, and the light focused by the lens is detected by a light-receiving element such as a photodiode. Since the amount of light concentrated on an object decreases as the object blocks the light, the length of the object is detected based on the ratio of the amount of light concentrated on the object.
2. Error Factors of Industrial Sensors and Examples of Countermeasures
While industrial sensors have the advantage of non-contact measurement, they are subject to external disturbances. In particular, in places where vibration occurs, such as production sites, it can cause errors beyond the original measurement accuracy of the device.
In the case of CCD photodetectors, some models have a shading correction function that enables calibration correction of the linearity of the internal photodetector. In such cases, it is important to perform the calibration correction before the actual measurement.