JPS6058160B2 - Optical detection device for pallet detection in unmanned forklifts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light detection device used to detect the height position of a pallet (a platform on which cargo is placed) during automatic loading and unloading operations using an unmanned forklift.

In recent years, there has been a trend toward labor-saving in cargo handling operations, and loading, unloading, and transportation of cargo have been increasingly automated.

For example, automatic loading and unloading using an unmanned forklift is performed as follows. In other words, as shown in FIG. 1a, the cargo 4 stacked on a pallet 5
When transferring items one by one to another location, first, the unmanned forklift 1 is advanced until the tip of the fork 2 is located just in front of the item 4.

When unmanned forklift 1 stops, move fork 2 to load 4
Raise it to a height of . Then, it is slowly lowered in the opposite direction, and when the height of the fork 2 becomes the same as the height of the pallet 5, the lowering is stopped. After stopping, the unmanned forklift 1 is moved forward again and the fork 2 is inserted into the pallet 5. When you have finished inserting it, stop moving forward,
Raise the fork 2 a little to lift the load 4 and move it to another location. By the way, in the above-mentioned automatic loading and unloading work, the photodetector 3 is used as a means for detecting the position of the pallet 5 and positioning the fork 2 at the same height as the pallet 5.

This photodetecting device 3 is attached to the lower end of the fork 2 as shown in FIG. 1a. Its configuration is, for example, as shown in FIG.
a and a light receiving element 3b provided between the lamps 3a, 3a. Pallet 5 is detected using lamps 3a, 3a.
This is done using reflected light. That is, when the fork 2 is lowered just before the cargo 4, if the fork 2 does not reach the position of the pallet 5, the light projected from the lamps 3a, 3a will be reflected by the cargo 4 and return to the light receiving element 3.
b, the amount of light received increases. When the height is the same as that of the pallet 5, most of the light projected by the lamps 3a, 3a passes into the pallet 5, so the amount of light received by the light receiving element 3b decreases. Therefore, the magnitude of the detection value of the light receiving element 3b is checked, and the lowering of the fork 2 is stopped when the value becomes equal to or less than a predetermined value. By the way, in the detection method using light as described above, even if the fork 2 is at the same height as the pallet 5, the detected value of the light receiving element 3b may not be large due to the influence of external light (sunlight, fluorescent light, etc.). The fork 2 may not stop lowering.

Therefore, in order to avoid being affected by disturbance light, the light from the lamps 3a, 3a is normally modulated and projected, so that only the reflected light from the lamps 3a, 3a can be extracted from the received light. I have to. However, even if only the reflected light from the lamps 3a, 3a is extracted using modulated light as described above, if the amount of ambient light is large, the light-receiving element 3b will be saturated, making it impossible to distinguish it from the ambient light. I end up.

Therefore, in the past, an infrared transmission filter was used to prevent the light receiving element 3b from becoming saturated with the ambient light. However, this method also has the drawback that it cannot be used when the illuminance of the ambient light exceeds a certain level, for example, 3000 lux or higher. This invention was made in view of the above points, and is an unmanned forklift pallet that actively utilizes ambient light for detection and is able to detect even when the ambient light illuminance is high. The present invention aims to provide a detection device.

According to this invention, when the illuminance of ambient light is not very high, a modulated light component is extracted from the detection signal of the light receiving element, and the pallet is detected based on the magnitude of this modulated light component, and the light receiving element is saturated. If the illuminance of the disturbance light is so great that it causes a disturbance, the modulated light component cannot be extracted, so the detection signal is used as is and the pallet is detected based on the magnitude of this signal.

The present invention will be described in detail below based on an embodiment of the accompanying drawings.

In FIG. 2, the light projected from the lamp 3a is modulated by a modulation signal output from the oscillator 6.

The light projected from the lamp 3a is reflected by the luggage 4 and enters the light receiving element 3b. At the same time, disturbance light is also reflected by the baggage 4 and enters the light receiving element 3b. The light receiving element 3b outputs a detection signal in which the modulated light and the disturbance light are mixed, and guides it to the AC amplifier 7 and the waveform smoothing circuit 12. The detection signal guided to the amplifier 7 is passed through a band pass filter 8, a full wave rectifier 9 and a waveform smoothing circuit 1.
0, and only the modulated light component contained in the signal is converted into direct current and extracted. That is, the detection signal guided to the AC amplifier 7 has its AC component amplified here, and is then input to the bandpass filter 8, where only the modulated light component contained therein is extracted. The extracted modulated light component signal is rectified by a full-wave rectifier 9, and is also rectified by a waveform smoothing circuit 1.
The signal is smoothed by zero and becomes a DC signal corresponding to the magnitude of the modulated light component received by the light receiving element 3b. A DC signal output from the waveform smoothing circuit 10 is input to a comparator 11. The comparator 11 outputs a detection signal ゜"0" when the input DC signal is greater than a predetermined value, and outputs a detection signal ゜"1" when it is less than that, that is, when the pallet 5 is detected. This pallet detection signal of the comparator 11 is used when the illuminance of the disturbance light is low.
The signal guided from the light-receiving element 3b to the waveform smoothing circuit 12 is waveform-smoothed (converted to direct current) and then applied to the comparator 13. The comparator 13 outputs a detection signal ゜゛ when the input DC signal is greater than a predetermined value, and outputs a detection signal ゜゜1゛ when it is less than a predetermined value, that is, when the pallet 5 is detected. The detection signal is used when the illuminance of the ambient light is large enough to saturate the light receiving element 3b.By the way, in this embodiment, the pallet detection signal is switched and used depending on the magnitude of the ambient light as described above. Therefore, the outputs of comparators 11 and 13 are connected to the common output line I via switches SWl and SW2, respectively.
By switching the switches SWl and SW2, the output of one comparator is always connected to the signal line 1.
It is becoming connected to. The output of the comparator 13 is used to switch the switches SWl and SW2. This is because the output of the comparator 13 also changes depending on the magnitude of the disturbance light. Therefore, the reference value set in the comparator 13 is determined according to the saturation voltage of the light receiving element 3b. That is, the light receiving element 3b
The output of the comparator 13 is set to 0 when the output is large enough to saturate the light receiving element 3b, and 1 to 1 when it is not so large as to saturate the light receiving element 3b.
The output of the comparator 13 is connected to a delay circuit 14, and the output of the delay circuit 14 is connected to the switching terminal of the switch SW1 and the inverter 15 to the switch SW2.
is connected to the switching terminal. Therefore, the output of the comparator 13 is ゜゜0'' (the luminous intensity of the disturbance light is large).
At this time, the switch SWl is off, the switch SW2 is on, and the comparator 13 is connected to the common output line 1. Further, when the output of the comparator 13 is "1" (illuminance of ambient light is low), the switch SWl is turned on, the switch SW2 is turned off, and the comparator 11 is connected to the common output line 1.By the way, the comparator 11 is connected to the common output line 1. The output of 13 is used not only for switching the switches SWl and SW2, but also as a pallet detection signal when the illuminance of the ambient light is high as described above.
The delay circuit 14 is for reliably guiding the pallet detection signal of the comparator 13 to the common output line l.
In other words, if this delay circuit 14 is not provided, the switch SW2 will be turned off the moment the output of the comparator 13 reaches 46r', so the output of the switch SW2 will always be "0" regardless of the output of the comparator 13. The pallet detection signal output from switch SW1 or SW2 is led via a common output line I to a central control unit (not shown).

The central control device issues an operation command to the fork 2 based on the detection output of the pallet 5 (for example, when this detection signal is ゜゜0゛, a descending command is given, and when it reaches ``1゛, a stop command is given]).
give. Here, the operation of the apparatus shown in FIG. 2 will be described with reference to FIG. 3 when the illuminance of the disturbance light is so great as to saturate the light receiving element 3b.

In FIG. 3, the left side of the dotted line shows the states of each signal and switch when the pallet 5 is not detected, and the right side shows the states of the respective signals and switches when the pallet 5 is detected. When the pallet 5 has not yet been detected, the disturbance light reflected by the cargo 4 enters the light receiving element 3b, so that the light receiving element 3b becomes saturated. Therefore, the output of the light receiving element 3b (the output of the light receiving element 3b is negative when the amount of light received is large and positive when the amount of light received is small) hardly includes an alternating current component (modulated light component) as shown in FIG. 3a. Therefore, the DC signal input to the comparator 11 is 0 or extremely small. Therefore, the output of the comparator 11 becomes "゜1" as shown in FIG.
'60'' as shown in , and this causes the switch S
W2 is on as shown in d of the same figure, and switch SWl is off as shown in e of the same figure. Therefore, the signal led to the output line I is the signal output from the comparator 13, and is ゜゜0゛ as shown in Fig. 5f. Therefore, a command to lower the fork 2 is issued from the central control device (not shown). When the fork 2 descends and reaches the height of the pallet 5, the amount of disturbance light input to the light receiving element 3b decreases, so the output of the comparator 13 becomes "゜1゛."
Figure 3c). At this time, the light receiving element 3b is released from the saturated state, but the modulated light component from the lamp 3a passes through the pallet 5, so the modulated light component decreases.
The output of the comparator 11 continues to be at ゜゜1゛ (Fig. 3b). The output ゜゜1゛ of the comparator 13 turns off the switch SW2 (FIG. 3d) and turns on the switch SWl (FIG. 3e) after a predetermined time delay. Therefore, line 1
When the output of the comparator 13 reaches "1" (when the pallet 5 is detected), the signal led to the output terminal switches to "1" (FIG. 3f). In this way, the pallet 5 can be detected even if the illuminance of the disturbance light is high. Incidentally, the central control device gives a command to the fork 2 to stop lowering based on the signal led to the line 1. Next, a case where the illuminance of the disturbance light is not so high will be described using FIG. 4.

4, the left side of the dotted line shows the state when the pallet 5 is not detected, and the right side shows the state when it is detected, as in FIG. 3. When the pallet 5 has not yet been detected, the amount of reflected light from the lamp 3a to be received is large, and the light receiving element 3b is not in a saturated state, so the output of the light receiving element 3b is as shown in FIG. 4a. AC minute (
(modulated wave component) is included.

Therefore, the DC signal input to the comparator 11 becomes large, and its output becomes 0 as shown in FIG. 4b. In addition, since the illuminance of the disturbance light is small, the output of the comparator 13 is always "゜1゛" as shown in Fig. 4c.Therefore, the switch SWl is always on as shown in Fig. 4d. Therefore, the output of comparator 11 “
゜0゛ is led to the common output line 1, by means of which the central control unit gives a lowering command to the fork 2. fork 2
When it descends and reaches the height of the pallet 5, the modulated light component received by the light receiving element 3b decreases. Therefore, the output of the comparator 11 becomes "゛1".As mentioned above, when the illuminance of the ambient light is small, the switch SWl is always on, so the output of the comparator 11 "6r" becomes "゛1". (Fig. 4 e). As a result, the central controller issues a descending stop command to the fork 2. In this way, even when the illuminance of the ambient light is low, the pallet 5 can be detected. According to this invention, since the output for detecting the pallet is switched and used according to the illuminance of the ambient light, it is possible to accurately detect the pallet even if the illuminance of the ambient light is high. effective.

[Brief explanation of drawings]

Fig. 1a is a schematic side view showing the loading and unloading of cargo using an unmanned forklift, Fig. 1b is a perspective view showing the mounting state of the lamp and light receiving element on the fork used for pallet detection, The figure is a block diagram showing an embodiment of the present invention, FIG. 3 is an operation explanatory diagram explaining the operation of the embodiment shown in FIG. 2 when the illuminance of the disturbance light is large, and FIG. FIG. 3 is an operation explanatory diagram illustrating the operation of the embodiment shown in FIG. 2 above when the illuminance is low. 1... Unmanned forklift, 2... Fork, 3... Light detection device, 3a...
Lamp, 3b... Light receiving element, 4... Baggage, 5... Pallet.

Claims (1)

[Claims] 1. A light emitting means installed near the tip of the fork and emitting modulated light toward the front of the fork, and a light emitting means arranged near the light emitting means so as to receive reflected light from the light emitted from the light emitting means from the front of the fork. a filter for extracting a modulated light component emitted from the light emitting means from the output signal of the light receiving element; a first comparator that outputs a detection signal when the output becomes smaller than a value, and a second comparator that outputs a detection signal when the output of the filter becomes smaller than a predetermined value corresponding to the light emission level of the light emitting means. and selecting the output of the first comparator when no detection signal is output from the first comparator;
selection means for selecting the output of the second comparator when a detection signal is output from the first comparator, and selecting the output of the first or second comparator selected by the selection means. The output is used as a pallet detection signal,
Optical detection device for pallet detection on unmanned forklifts.