SU1689975A1 - Dashed marks scanistor - Google Patents

Abstract

The invention relates to automation and computing, in particular to the reading of line marks from the storage medium. The purpose of the invention is to improve accuracy. The device is a scanner consisting of an emitter and two photodiodes, whose radiation patterns are directed towards the target label. The difference signal from the photodiodes is fed simultaneously to the second input of the adder and to the low-pass filter, from the output of which the signal with opposite polarity goes to the first input of the adder. As the scanner moves near the mark, the photodiodes receive a reflected flux of radiation from the scale and the voltages on the photodiodes change. At the moment when the radiation patterns are located symmetrically on both sides of the tag, the difference signal from the photodiodes is zero, which is a signal that the scanner symmetry plane coincides with the longitudinal axis of symmetry of the tag. 6 Il. THX

Description

The invention relates to automation and computing, in particular to the reading of line marks from the storage medium.

The purpose of the invention is to improve accuracy.

Figure 1 shows the block diagram of the device; figure 2 - the relative position of the emitter and two photodetectors relative to the controlled label; FIG. 3 is a schematic of the formation of a dash mark signal; Fig. 4 shows diagrams of voltage variations from photodiodes and their sum for the ideal case; figure 5 - the relative position of the label and the axis of the radiation pattern; Fig. 6 shows diagrams of voltage changes when the characteristic is shifted upwards.

The device contains two photodetectors 1 and 2, made, for example, in the form of photodiodes, which are housed in collimated optically isolated channels 3 and 4, made in the body of the scanner 5.

A radiation source 6 is located between the collimated channels in the longitudinal plane of symmetry of the NN scanner 5. Longitudinal ori diagrams 7 and 8 of directivity from collimated channels 3 and 4 are directed to the edges of dash mark 9, which has a different reflective ability. relative to the surrounding background.

The photodiodes 1 and 2 are connected in parallel and connected to the input of the generator 10 of the bar-mark signal, consisting of an analog adder 11 and a low-pass filter 12. The adder 11

Os 00 Yu ChE h |

cl

is an operational amplifier 13, to the non-inverting input of which resistor 15 is connected, resistors 14 and 16 and 17 are connected to the inverting input. The second end of resistor 14 is connected to the output of amplifier 13. A low-pass filter 12 consists of an operational amplifier 18, to an inverting input which are connected to the resistors 19 and the capacitor 20, the second ends of which are connected to the output of the amplifier 18. To the inverting input of this amplifier is connected adjustable resistor 21, the second end of which with the second end of the resistor 17 an input of the resistor 10. The second end 16 connected to the output amplifier 18,

The device works as follows.

The scanner 5, together with the emitter 6 and the photodiodes 1 and 2, moves (suppose to the right) parallel to the plane of the mark 9 (Fig. 2). When there are no marks in the field of view of both photodiodes, i.e. when the radiation patterns 7 and 8 do not touch the mark 9, then from the surrounding background, in the particular case from the white surface of the information carrier, enters channels 3 and 4 the same radiated flux, which is reflected from the information carrier irradiated by the radiator 6. With the same parameters The photodiodes and the same channels 3 and 4 of the voltage from the photodiodes are equal to Ut Ite and, when they are switched on counter, the total voltage Ui2 Ui - IJ2 (Fig. 3) is zero. Since at the inputs of the adder 11 and the filter 12, the input signal Uia is zero, then at the output of the amplifier 13, the output signal of the OUT is equal to zero - this is an ideal case,

Figure 4 shows time diagrams of voltage changes Ui (from the left photodiode), U2 (from the right photodiode) and their sum Ui2 Ui - Ite for the ideal case, where X is the movement of the longitudinal NN symmetry of the indicator 5 relative to the longitudinal axis of symmetry of the label. These diagrams are constructed for the frequently used in practice case d B 2Ak (Fig. 5), where B is the width of radiation patterns in the plane of their intersection with the mark, d is the width of the mark, 2AK is the distance between the longitudinal axes of the radiation patterns in the plane. tags,

The ratio d B 2dc is selected according to the following conditions. At such ratios, the sensitivity is theoretically obtained, i.e. the greatest steepness of the signal U12 is near the point O (in FIG. 4) of the zero crossing.

When the scanner 5 moves, the mark 9 enters the field of view of the photodiodes, i.e. Since radiation patterns 7 and 8 cross mark 9, then, due to the low reflectivity of the mark, different amounts of radiation flow enter the photodiode channels. The variable component of voltage Ui2 is formed (figure 4), the filter 12 is configured so that the variable component of the signal Ui2 does not pass through it, therefore, the adder 11 receives only the signal Ui2.

The cutoff frequency of the filter is f0 -,, „

f. 31 t (

where R is the resistance value of the resistor 19 and C is the capacitance value of the capacitor 20. The period of passage of the signal Ui2, as follows from FIG. 4, is Tc 3d / V, where V is the linear scanning speed. To do this, in order for a signal with a frequency f 1 / Tc not to pass through the filter, the condition f0 «f must be satisfied.

The moment of transition of the signal Ui2 (Fig. 4) through the zero level (from positive to negative at the O point) and, consequently, the signal from the device (Fig. 3) through the zero level corresponds to the alignment moment of the NN plane of symmetry of the scanner 5 with the longitudinal the axis of symmetry of the label, since at this moment the label covers the same areas of the 7 and 8 directivity patterns. This case is depicted in Fig. 5, where a cross-section of the radiation patterns in the plane of their intersection with the mark 9 is shown (the areas covered by the area mark of the radiation patterns are shaded),

With a rectangular cross section of channels 3 and 4, the non-overlapped areas of the radiation patterns vary linearly depending on the displacement X. Therefore, assuming linearity of the transfer characteristics (dependence of the voltage on the photodiode on the radiation flux) of the photodiodes, the voltage on the photodiodes Ui and LJ2 vary also linearly

Ui - Ki (X-Ci): U2 -K2 (X + C2), (1)

where KI and 2 are the steepness of the characteristics of the left and right photodiodes depending on the movement of the scanner;

Ci and C2 - offset of the center of the radiation patterns of the left and right photodiodes from the plane of symmetry NN of the scanner.

As follows from the design of the scanner

(fmg.2) |.

The dependences Ui (X) and U2 (X) are graphically reflected by direct AP and EB (Fig. 4).

The graph of the change in the total voltage U12 reflects the direct AV

Ui2 - (Ki + K2) x + (Ki-K2) | (2)

As follows from this equation, when Ki K2 is equal and when X «0, the signal Ui2 0 (FIG. 4) is an ideal case.

Almost during manufacture of the scanner, as well as during operation due to various destabilizing factors, for example, changes in the characteristics of photodiodes, contamination of channels 3 and 4, the presence of interference occurs, the unbalance Ki “2, for example, Ki“ 2 and the new dependence UG (X) reflects the direct DF. Now the graph of the total voltage will reflect another direct DB.

As follows from equation (2), when X o, the voltage Uia is not zero

U12 U0 (Kl-K2) f

Since the condition for fixing the axis of symmetry of the label is to register the stresses at the moment of its passage through zero, now the error is equal to the interval 00.

To eliminate this error, at X 0 it is necessary to fix point C. To do this, the adder 11 is supplied with the bias voltage Uc -U0 to shift the straight DB down by the value of the OC. Then, at X o, the signal after the adder is equal to Oout 0. 0. The bias voltage Uc is formed by a low-pass filter. Based on the condition dB - 2AK for x - 0, the compensation of the signals Ui and U2 should occur with half-covered fields of view of the photodiodes (figure 5), which determines the value of the filter transmission coefficient at low frequencies, equal to Кф-1/2.

When scanning the background, the total signal from the photodiodes is

U4, uT (-f) + U2 (-fd)

Using expressions (1) and taking into account

% n

the equality U2 (-yd) () 2 is defined by g5

I am signal from the background (the difference of the lengths of the segments ED - FB) 11f - (Ki - K2) d. Considering that the signal U12 is fed to the inverting input of amplifier 18, then the two inputs of the adder 11 will be signals from the opposite

five

ten

15 20

25

30 35 40 45

50

g5

polarity, and at the input of amplifier 13, the resulting signal represents the difference of these signals Ui2 - KfUf, which at x 0 will always be equal to zero Uo - Kf1) φ 0, i.e. Regardless of the difference between the coefficients Ki and “2, when x 0, the signal at the output of the adder is also always zero and zero, 0.

If X changes within 3d, the bias voltage Uc from the filter output will not have time to change due to the properties of the low-pass filter (the voltage on the capacitor 20 does not have time to change in this short period of time), and the signal Ui2 changes during this time. Thus, the voltage at the output of the accumulator willow at time x 0 is zero.

In the manufacture of the scanner, as well as during operation, it will be found that Ci Ca

 And - where the coefficient I is different from one. In this case, it can be shown that to compensate for the voltage Ui2 Uo (Ki - K2) And the transmission coefficient of the filter on

low frequencies should be equal to I / 2. To set the gain ratio, use a divider with a variable division factor from resistors 19 and 21 (Fig. 3).

Consider another destabilizing factor - the shift characteristics, for example Ui (X) up as shown in Fig.6. In this case, the graph of the total voltage Ui2 will reflect a direct DB that does not intersect the X axis, therefore, in the absence of a filter, the device would not work.

As follows from Fig. 6, in order for the device to work and to exclude the registration error of the axis of symmetry of the label, the filter transmission coefficient should be equal to one, i.e. Uc -Uo. Practically, in order to obtain the greatest accuracy of the device, based on the operating conditions of the device, the parameters of the photodiodes and the size of the scanner, the filter transmission coefficient must be chosen experimentally.

As a radiator, an infrared LED can be used. These photodiodes can also be used as photodiodes, but in photogeneration mode.

The resistor 14, together with the resistors 16 and 17, serves to obtain the necessary gain factor of the adder 11.

Resistor 15 is needed to eliminate the influence of the input currents of amplifier 13.

The proposed device has its structural and circuit simplicity, great performance in the presence of destabilizing factors and accuracy.

Claims (1)

Apparatus of the Invention A device for reading bar-marks containing emitters and photo-receivers located in the scananag housing, made, for example, in the form of photodiodes, outputs of photo-detectors are connected to the input of a bar-shaped signal former, characterized in that photo-receivers are located in collimated to increase accuracy optically isolated channels made in the scanner housing symmetrically with respect to the optical axis of the emitter at a distance equal to the width of the dashed mark, and the dash mark former consists of a low-pass filter and an analog adder, the photodiodes are connected opposite in parallel and connected to the low-pass filter input and to the first analog input an adder whose second input is connected to the output of the low-pass filter and the output is the output of the device. Fm8 / 19 20 F "/ e." 3 Y Fig .: N 16 17 N F “e. FTs8.