Common problems and solutions for sensor application

Common problems and solutions for sensor application

1, label paper printing position is inconsistent

The reasons for the inconsistent printing position during continuous printing are mainly caused by the paper jitter in the channel and the inconsistent gap of the paper itself, which leads to the instability of the waveform detected by the sensor and makes the positioning of continuous printing inaccurate.Solution: solve the paper in the channel jitter problem (especially small label) : by adding buffer mechanism, or add a sensor like zebra Z4M compression mechanism.Solve the problem of inconsistent gap of the label itself: by changing the firmware program and changing the positioning mode of the label, the effect of gap error can be minimized by using the backward positioning of the label gap;

2, label paper substrate paper level is not stable

Due to the paper in the channel change distance relative transmission and reflection between receiver design sensors range is bigger, cause a large luminous output rate, the change of light intensity of paper, is a major cause of transmission sensor level is not stable, in the design process, should fully consider the sensor detection range and medium within the channel of the jitter, make the jitter caused by the output voltage change is too big, because media cause detection error or not, such as paper activities from 1 mm up and down in the channel, transmission or reflection between receiver design sensors for at least 5 mm,In the design of electrical parameters, the transmission sensor level should be within the range of discriminant level when the light transmittance of paper varies within 10% at least (the voltage difference between paperless and substrate paper is greater than 1V).

3, heat sensitive printing mark discrimination can not be normal recognition

The heat sensitive materials on the thermal paper for infrared reflection is very strong, cause the sensor can't identify the thermal printer black label, because we use the sensor for infrared detectors, and the thermal paper for infrared reflection is very strong, the rest of the tested medium and mark parts of the reflectivity difference greatly decreases, and cause the mark to identify, therefore, the sensor should be fully considered in the process of the selection and use of different media in the reflective rate (rate of penetration) the influence of;

4. Sensor aging

Due to the high sensitivity of photoelectric sensor, the luminous power of luminous tube decreases slightly with time temperature and other factors.For the receiving tube, if it continuously receives reflected light, its parameter drift will be very large. Therefore, when applying photoelectric sensor, the aging problem should be avoided as far as possible in the design, such as:

(1) POS machine paper will do the detection, usually have paper, photoelectric sensor receiving tube is not receive reflected light, paper will do, paper tube fell into the groove of the paper bin, photoelectric sensor receiving tube detected reflected light and thus alarm;

(2) using the method of intermittent luminescence, when the sensor is tested, the light tube power is connected, when not detected, turn off the light tube power, reduce the aging of the light tube and receiving tube;

5. Sensor detection voltage threshold

Different sensors and detection of medium, the discriminant of threshold voltage difference is very big, selecting feasible judging threshold, is of great significance to correctly detect different medium, the binary detection: at this time should be the sensor working in saturated zone and the area, the voltage difference is big, the selection of threshold is easy to adjust the load resistance sensor, through simple level identification, can correct judgment, such as paper test, have intermediate state detection:Need to be detected as label paper with paper and without paper and paper backing, should make the sensor as far as possible at this time working in the linear area, in this way, different state changes, the output voltage of the most obvious change, the most beneficial to discrimination of different state, so that we can according to the sensors in different stages of photocurrent and reflective rate (transmittance) change, select the appropriate detection threshold;

6. Sensor discreteness

The same type of sensor under the condition of the same input, because its discrete output, brings to the signal detection of adverse effect, especially to work in the sensor has a serious effect of amplification area, such as SG - 23 fi, also in VCE = 5 v, IF = 10 mA, its current range of 0.5 mA ~ 3 mA, 5 times, in order to adapt to the discreteness of sensors on the impact of current in the company I used methods:

(1) add adjustable resistance, adjust the output voltage does not meet the requirements of the sensor, so that its output meet the requirements, but to increase the difficulty and cost of production;

(2) use multiple CPU ports to switch different load resistance to adapt to different media, need to take up additional CPU resources, adjustable range is not large, can only change a few states;

(3) use PWM to adjust the current intensity of light-emitting tube, so that the sensor works in different output characteristic curve, the adjustment range is large, but increased the difficulty of firmware detection.