JPH03129587A - Article detector - Google Patents

Abstract

PURPOSE:To accurately detect an article by subtracting the lower limit level of a previously obtained background from the quantity of reflected light, regarding less than the lower limit level as a fixed level having no change in the quantity of light to detect the article based on the change in the light quantity. CONSTITUTION:Although the characteristics of OPQ is conventionally plotted as to the relation between a distance L from an article detector and the output of reflected light, the reflection level Vth of the background with a fixed distance L1 is subtracted from the quantity of reflected light and the characteristics of O'P'Q' i.e. less than the lower limit level Vth of an original signal, is regarded as the same P'Q' level. Namely reflected light more than the distance L1 including the background is ignored. Thereby a change in the quantity of reflected light due to the rapid movement of the background can be prevented from being detected as an article and the article can be accurately detected.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Figure 6) Means for solving the problem to be solved by the invention (Figure 1) Working example (a) 1 Description of Examples (Figures 2 to 5) (b)
Description of other embodiments Effects of the invention [Summary] Regarding an article detection device that emits detection light from a light emitting part into a detection space, receives reflected light from the detection space in a light receiving part, and detects an article from a change in the amount of light. , the purpose is to prevent rapid changes in the background from being mistakenly detected as objects, and includes a light emitting section that emits detection light into the detection space, a light receiving section that receives reflected light from the detection space and outputs a reflected light amount output, and a light receiving section that outputs the amount of reflected light. and an article detection section that detects an article by subtracting a desired lower limit level from the light output and determining a change in light amount after the subtraction.

[Industrial application field]

The present invention relates to an article detection device that emits detection light from a light emitting section into a detection space, receives reflected light from the detection space at a light receiving section, and detects an article from a change in the amount of light.

2. Description of the Related Art Stationary barcode readers are widely used in which barcode-attached articles are entered into a reading space and the barcodes of the articles are read.

In such a barcode reader, constantly emitting an optical scanning pattern into the reading space shortens the life of the light source and increases power consumption.

For this reason, the barcode reader is provided with an article detection section (device), and when it is detected that an article has entered the reading space, it emits an optical scanning pattern.

In such an article detection device, it is desired to accurately detect an article from changes in reflected light.

[Conventional technology]

FIG. 6 is an explanatory diagram of the prior art.

As shown in FIG. 6(A), the barcode reader BCR
is fixed to a desk or the like and has an article detection unit ASU and a barcode reading unit SCR, and when the article detection unit ASU emits detection light into a predetermined article detection space and detects the entry of an article from the reflected light, The barcode reading section SCR generates a light scanning pattern, emits it into the reading space, receives reflected light from the barcode of the article, analyzes it, and reads the barcode.

In the conventional article detection device, as shown in FIG. 6(B), the light emitting section 1 is driven by a driving section 1a in a pulse modulation manner, and pulse modulated detection light is emitted.

The light receiving section 2 receives the reflected light, passes the received light output through a bypass filter 3 to cut off the DC component, amplifies the AC with the AC amplifier 4, smoothes it with the integrating circuit (smoothing circuit) 5, and reflects the smoothed output DPS. The light intensity is inputted to a light amount change detection section (article detection section) 6, and the article is detected from the change in reflected light amount.

[Problem to be solved by the invention]

By the way, such an article detection device detects an article inserted between the device and the background, and the light amount change detection unit 6 for detecting the article detects whether the change in the background is due to the insertion of the article. Based on the premise that the rate of change in the amount of reflected light over time is sufficiently slower than that of the object, changes in the background and changes in the object are distinguished from each other to prevent changes in the background from being mistakenly detected as objects.

However, when the background changes rapidly, such as an operator, such differentiation cannot be made, and there is a problem in that a change in the background is mistakenly detected as insertion of an article.

Therefore, an object of the present invention is to provide an article detection device that does not erroneously detect a rapid change in the background as an article.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

As shown in FIG. 1, the present invention includes a light emitting section 1 that emits detection light into a detection space, a light receiving section 2 that receives reflected light from the detection space and outputs a reflected light amount output, and a reflected light amount output. It has an article detecting section 6 that detects an article by subtracting a desired lower limit level from the subtracted value and determining a change in the amount of light after the subtraction.

[Effect]

In the present invention, the amount of reflected light of the background is compared to the amount of reflected light of the article,
This is based on the idea that since the level is low, it is sufficient to ignore changes in the amount of reflected light from the background when detecting changes in the amount of reflected light for object detection.

Therefore, in the present invention, the lower limit level of the background obtained in advance is subtracted from the amount of reflected light, and objects below the lower limit level are regarded as a constant level with no change in the amount of light, and the object is detected.

As a result, as shown in FIG. 1(B), the relationship between the distance from the article detection device and the reflected light output is different from that of the conventional OPQ characteristic, as shown in FIG. The characteristics of 0'P'Q', that is, those below the lower limit level vth of the original signal are at the same level P'
It is treated as being at the level of Q', and this means that reflected light at a distance L1 or more where the background exists is ignored.

Therefore, it is possible to prevent a change in the amount of reflected light due to rapid movement of the background from being detected as an article.

〔Example〕

(a) Description of an Embodiment FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a waveform diagram of its essential parts.

In the figure, the same parts as shown in Figures 1 and 6 are:
They are indicated by the same symbols, and 2a is a photoelectric conversion section, which outputs the intensity of reflected light from the light receiving section 2 constituted by a photodiode to the bypass filter 3 as an electric signal.

7a is a maximum value sample and hold circuit, which samples and holds the maximum value of the AC output ■ of the AC amplifier 4 as a sample and hold signal CTL.
1-DLY is used to hold the sample,
7b is a minimum value sample hold circuit, and AC output ■
8 is a differential amplification section that samples and holds the maximum value of by using sample and hold signals CTL2-DLY;
The difference between the maximum value sample hold output ■ and the minimum value sample hold output ◎ is taken and amplified to generate a differential amplified output ◎.

The article detection section (hereinafter referred to as control section) 6 is composed of the following.

Reference numeral 9 denotes a sample and hold section, which samples and holds the differential output [F] of the differential amplifier 8 using the sample and hold signal CTL3, and 10a indicates a differential amplifier section, which samples and holds the differential output [F] of the differential amplifier 8 using the sample and hold signal CTL3. 10 is an A/D (analog/digital) converter that converts the output of the differential amplifier 10a into a digital value, and 11a is a first register that converts the A/D with the sample signal CTL4. 11b is a second register that samples and takes in the output of the A/D converter 10 using a sample signal CTL5; 12a is a first play part 3; , which delays a light emission drive pulse CTLI from the CPU 14 to be described later and outputs a sample hold signal CTL1-DLY. 12b is a second play section which delays an inverted signal CTL2 of the light emission drive pulse CTLI from the CPU 14. 13 is an A/D converter that converts the sample and hold output ■ of the sample and hold unit 9 into a digital value, and outputs the sample and hold signal CTL2-DLY.
14 is a CPU (central processing unit) that outputs the light emission drive pulse CTLI, its inverted signal CTL2, sample hold signal CTL3, and sample signal CTL4. , CTL5 and registers lla, ll
A device that reads the contents of b and calculates changes in the amount of reflected light through the process shown in FIG.
15 is a lower limit level adjusting circuit, which has a resistor r2 and an adjusting resistor r1, and adjusts the adjusting resistor r1 to adjust the lower limit level vt.
16 is an A/D conversion unit that adjusts h, and converts the lower limit level vth of the lower limit level adjustment circuit 15 into a digital value and inputs it to the CPU 4, and is used in the adjustment mode.

First, the light receiving operation shown in FIG. 2 will be explained with reference to FIG.

The CPU 14 outputs a light emission drive pulse CTLI, and causes the light emitting unit (LED) 1 to emit pulse modulated light from the drive unit 1a.

The modulated reflected light is received by the light receiving section 2, converted into an electrical signal by the photoelectric conversion section 2a, the DC component is cut by the bypass filter 3, and the AC amplified by the AC amplification section 4, resulting in an AC output (2).

The light emission drive pulse CTL 1 is delayed by the first play section 12a to create a sample hold signal CTL 1-DLY.

This sample and hold signal CTL 1-DLY is synchronized with the emitted light and is generated so as to occur at the time when the reflected light from the emitted light is at its maximum.

Similarly, the inversion signal CTL2 of the light emission drive pulse given from the CPU 14 is delayed by the second play section 12b,
Create sample hold signal CTL 2-DLY.

This sample hold signal CTL2-DLY is synchronized with the inverted signal CTL2, and is generated so as to occur at the time when the reflected light is at its minimum.

Therefore, the maximum value sample and hold section 7a holds the maximum value of the AC output (1) using the sample and hold signal CTL1-DLY. The minimum value sample and hold section 7b outputs a hold output ■, and the minimum value sample and hold section 7b outputs a sample and hold signal CT.
The minimum value of AC output ■ is held by L2-DLY, and hold output ■ is output.

The differential amplifier section 8 takes the differential of both hold outputs ■ and ■,
Amplify and output differential amplified output ■.

Therefore, the differential amplification output is the peak to
peak is detected, and the signal detection accuracy is reduced to S/
The N ratio can be improved without deteriorating, and reflected light intensity with high accuracy can be obtained.

The differential amplification output is sampled and held in the sample and hold section 9, outputs a sample and hold output ■, and is changed from the sample and hold output O to the lower limit level v in the differential amplification section 10a.
After th is subtracted, the signal is output to the A/D converter 10.

The A/D converter 10 converts the output of the differential amplifier 10a into a digital value and outputs it to registers lla and 11b.

Next, adjustment of the lower limit level vth will be explained.

First, when the adjustment mode is instructed to the CPU 4, the light emitting section 1 emits pulse light as described above.

In this state, the reference reflectance (for example,
A reflective surface with a reflectance of 30% is provided, and the light receiving section 2 receives the reflected light.

The CPUI 4 converts the output ■ of the sample hold section 9 into A/
The output of the A/D conversion section 13 that performs D conversion is taken in and displayed on a display section (not shown).

Seeing this display, the adjuster operates the adjustment resistor r1 of the lower limit level adjustment circuit 15 to change the lower limit level vth.

The lower limit level vth of the lower limit level adjustment circuit 15 is taken into the CPUI 4 from the A/D converter 16 and displayed on the display section.

Therefore, the adjuster must adjust the adjustment resistor r! so that the lower limit level of adjustment of the display unit matches the measurement level that is the output of the A/D converter 13 of the display unit. Adjust the volume and exit adjustment mode.

The lower limit level vth thus adjusted is the reference background reflected light level, as shown in FIG. 1(B), and is output to the differential amplification section 10a.

The operation of detecting an article using the reflected light intensity obtained in this way will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a flowchart of article detection processing according to an embodiment of the present invention;
The figure is an explanatory diagram of the operation.

It should be noted that the CPU 4 stores a predetermined threshold value Vthx for detecting article entry, threshold value Vth2 for detecting article ejection, the number of entry samples 01, and the number C2 of ejected samples in a built-in memory. shall be.

■ The CPU 14 first initializes each part.

■ Next, the CPU 14 sets the number of M2 samples 01 to rOJ
, give a sample instruction (referred to as Ml sample) M 1 (CTL 4) to register lla, and
The output of the D converter 10 is taken into the register 11a.

■ Next, the CPU 14 gives a sample instruction (referred to as M2 sample) M2 (CTL5) to register llb,
The output of the A/D converter 10 is taken into register llb.

Then, the CPU 14 reads the sample data Ml and M2 in registers lla and 11b, calculates (Ml-M2), and further calculates IMI-M which is the absolute value of (Ml-M2).
21 is calculated and compared with the entry detection threshold value Vth1.

■ In step ■, based on the comparison result, the CPU 14
If it is determined that Ml-M21 is not >Vths, CP
The UI 4 determines that the object entry is not detected, and updates the M2 sample number 01 to (C1+1).

Then, the CPU 14 updates the updated M2 sample number 01.
Check to see if has reached a predetermined value X1, and if not C1-Xl, return to step ■; if C1=X1, proceed to step ■
Return to

■ On the other hand, in step ■, based on the comparison result, the absolute value IM
If it is determined that I-M2 l>Vtht, the CPU 14 determines that an article has been detected and performs article presence processing.

For example, in the example of the barcode reader mentioned above, the barcode reading section SCR is activated.

(2) Next, the CPU 4 stores M2 samples in the register llb, and takes in the output of the A/D converter 10 into the register llb.

Then, the CPU 14 reads the sample data M1 and M2 in registers lla and 11b, calculates (Ml-'M2), and further calculates IMI-' which is the absolute value of (Ml-M2).
Ml1 is determined and compared with the discharge detection threshold Vth*.

■ In step ■, depending on the comparison result, IMI-Ml1<
Vth! Otherwise, it is determined that the object is in the reading space.

That is, the sample value M1 of register lla is
As it was a background level thing without goods,
If the sample value M2 of register llb does not fall to it, then
It is not detected that the article is absent, and if the value is equal to or higher than the threshold value vth, it is determined that the article is still in the reading space.

Then, the CPU 14 sets the M2 count number 02 to (C2+
1) and update the updated M2 count number C2 as the planned number
Compare with 2.

If the M2 count number 02 does not reach the planned number x2,
Returning to step (2), if the planned number X2 has been reached, it is assumed that there are articles but they are not moving, and step (2) is determined to be absent.

■ In step ■, the CPU 14 performs IMI-Ml1<V
If it is tht, it is assumed that the sample (direction M2) in register llb has fallen to the background level, it is determined that there is no article, the M2 count number 02 is set to zero, and the process returns to step (3).

In this way, as shown in FIG. 5, register 1ib is sampled at a shorter period than register lla, and both registers l
By taking the difference (Ml-M2) between la and llb, a change in register lla relative to the background level can be detected.

By converting the difference into an absolute value and comparing it with a threshold value, changes in the background level are not picked up as noise and false detection can be avoided.

The period of this M1 sample is constant at "Xl" in step (2) when there is no article, but when the article is detected, it is until no article is detected in step (2) or "Xl" in step (2).
Xl" is variable.

Further, in this embodiment, two threshold values vtht, Vth
2 can be used to conveniently detect the entry and exit of articles.

Furthermore, if it is determined that the article is present for a certain period of time X2, it is assumed that the article does not move and a process is performed to determine that the article is absent, so that the process is not wasted and repeated until the article is found to be absent.

Qll) Description of Other Embodiments In the above-described embodiments, the application to a barcode reader is explained as an example, but it can also be applied to other embodiments.

Further, the registers lla and llb may be part of the memory of the CPU, the subtraction of the lower limit level may be performed by the CPU's calculation, or a part of the CPU's calculation may be configured by dedicated hardware. .

Furthermore, the article detecting section is not limited to the one in the embodiment, and other light amount change detecting sections may be used, and the lower limit level may be automatically adjusted by the CPU 14.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, the lower limit level of the background obtained in advance is subtracted from the amount of reflected light, and anything below the lower limit level is regarded as a constant level with no change in light amount, and object detection is performed based on changes in light amount. This has the effect of preventing a rapid change in the background from being mistakenly detected as an article, and it is possible to accurately detect an article without erroneously detecting a rapid change in the operator or the like as an article.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a waveform diagram of essential parts of an embodiment of the present invention, and Fig. 4 is an article detection embodiment of the present invention. FIG. 5 is an explanatory diagram of the article detection operation of FIG. 4, and FIG. 6 is an explanatory diagram of the prior art. In the figure, 1...- Light emitting part, 2... Light receiving part, 6...-
Article detection section.

Claims (1)

[Claims] A light emitting unit (1) that emits detection light into a detection space, a light receiving unit (2) that receives reflected light from the detection space and outputs a reflected light amount output, and a desired amount of reflected light from the reflected light amount output. An article detection device comprising: an article detecting section (6) that detects an article by subtracting a lower limit level of and determining a change in the amount of light after the subtraction.