JP2005089013A - Forklift - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To heighten throughput of a loading operation with a forklift. <P>SOLUTION: This forklift 1 is constituted to move a fork 11 to a temporary loading height after it stops at a predetermined position at a front of a pallet P, and to detect a top end and a bottom end of a pallet opening PH by a sensor 13 installed at a tip of the fork 11 at such a position. A control part is designed to find positions of the top end and the bottom end of the pallet opening PH based on detection signals, and find clearances of a top face and a bottom face of the fork 11 from both of the positions, perform loading at that position when both of the clearances are over a predetermined value. The control part is designed to find a new position in such a manner that both of the clearances become over a predetermined value when both of the clearances are not more than a predetermined value, move the fork 11 to a new position, and detect the top end and the bottom end of the pallet opening PH by the sensor 13 again. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a forklift that detects the opening of a pallet with a sensor provided at the tip of the fork and loads the fork by inserting it into the opening of the pallet.

  In factories, warehouses, etc., unmanned forklifts are guided by electromagnetic induction means or the like on a predetermined traveling path and travel to a cargo pick-up position. Unload the placed pallet (call the pallet). In this case, the height at which the cargo is unloaded is determined in advance, but the position of the fork is determined by accumulation of unevenness and inclination of the floor surface, wear of the tires of the forklift, manufacturing errors and deflection of the pallet, and lift lift errors. There is a deviation from the position of the pallet. For this reason, if the fork is advanced toward the pallet opening at a predetermined height, the fork and the pallet may interfere with each other.

In order to solve this problem, the following Patent Document 1 discloses that the fork is moved up and down within an appropriate range centered on the height of loading, and the upper and lower end positions of the opening are detected by sensors provided at the tip of the fork. As a conventional example, a position where the fork and the pallet do not interfere with each other is obtained based on the detection result, and the fork is moved forward at that position to perform loading (first conventional example).
Patent Document 1 discloses the following as solving means. First, the fork is moved to a position higher than the position of the opening of the pallet on which the load is placed. Then, the object is detected by a sensor provided at the tip of the fork while the fork is lowered, and the position where the object is no longer detected is determined as the position of the pallet opening (actual loading height). The cargo is moved forward and taken up (second conventional example). However, since the specific structure of the sensor and the detection range in the vertical direction of the sensor are not shown in Patent Document 1, it is not certain, but the position where the sensor does not detect the object does not detect the upper plate of the pallet. It is understood as the position. It is understood that the cargo is picked up at a position where the fork is slightly lowered from the position.

JP-A-8-169698 (paragraphs 0002 to 0003, paragraphs 0018 to 0025)

However, in the first conventional example, in order to detect the upper end and the lower end of the pallet opening, the fork must be returned to the loading height after raising and lowering, which reduces the throughput of the loading operation. There's a problem.
In the second conventional example, for example, even when the pallet is bent and the opening of the pallet is narrowed, the cargo is picked up with a predetermined clearance between the upper and lower surfaces of the fork and the pallet. In this case, as in the first conventional example, the fork must be further lowered to detect the position of the lower end of the pallet opening and then raised again to the loading position. In addition, when the initial position of the fork is lower than the loading height, the fork must be further lowered after the fork is once raised to a position higher than the opening of the pallet. For this reason, similarly to the first conventional example, there is a problem that the throughput of the loading operation is lowered.

  The present invention solves the above-described problems, and an object of the present invention is to provide a forklift capable of carrying out a loading operation with high throughput (in a short time).

  In the present invention, in the forklift provided at the tip of the fork and including a sensor for detecting the opening of the pallet and a control unit for controlling the raising and lowering of the fork, the sensor is stationary from a substantially central position of the opening in the vertical direction. The upper and lower ends of the opening are detected, and respective detection signals are output. And a control part calculates | requires the position of the upper end and lower end of opening based on a detection signal.

  By doing in this way, the positions of the upper and lower ends of the pallet opening can be obtained in a stationary state from the approximate center position of the pallet opening in the vertical direction, which is the position where the cargo is actually likely to be picked up. There is no need to raise or lower the fork to determine whether or not it will interfere with the pallet when it is advanced. This increases the throughput of forklift loading. In addition, since the upper and lower ends of the pallet opening are detected in a stationary state, the loading throughput does not decrease even if a plurality of detections are performed. Then, by performing statistical processing such as averaging on a plurality of detection signals, it becomes possible to remove detection signal noise (for example, ambient light, electrical noise, etc.), and the upper end of the pallet opening and The position of the lower end can be obtained with high reliability.

  In the present invention, the control unit obtains the distance between the upper surface of the fork and the upper end of the opening and the distance between the lower surface of the fork and the lower end of the opening based on the obtained positions of the upper end and the lower end of the opening. When the value is greater than or equal to the value, the cargo is picked up at a substantially central position of the opening. By doing in this way, it is possible to pick up the cargo while securing the clearance between the upper surface and the lower surface of the fork at this position without raising and lowering the fork from the substantially central position of the opening of the pallet. This increases the throughput of forklift loading and reliably prevents interference between the fork and the pallet.

  In the present invention, the control unit obtains the distance between the upper surface of the fork and the upper end of the opening and the distance between the lower surface of the fork and the lower end of the opening based on the obtained positions of the upper and lower ends of the opening. When only one distance is less than or equal to the predetermined value, the fork is moved to a new position where both distances are greater than or equal to the predetermined value, and the cargo is picked up at that position. By doing so, even when the cargo cannot be picked up at the approximate center position of the opening of the pallet, the picking up can be performed at a new position, and the interference between the fork and the pallet is surely prevented.

  Further, in the present invention, when the control unit causes the cargo to be picked up at a new position, the control unit detects the upper end and the upper end of the opening based on the detection signals of the upper and lower ends of the opening detected by the sensor at the position. And the distance between the lower surface of the fork and the lower end of the opening, and when both distances are equal to or greater than a predetermined value, the cargo is picked up. In this way, since the upper and lower ends of the pallet opening are detected by the sensor even at a new position, even if the accuracy of the fork elevating drive unit and / or elevating amount measuring unit is low, the pallet The positions of the upper and lower ends of the opening can be obtained with high accuracy, and interference between the fork and the pallet is reliably prevented.

  Further, in the present invention, the obtained positions of the upper end and the lower end of the opening are relative positions based on the center in the vertical direction of the sensor. By doing in this way, the position of the upper end and lower end of the opening of a pallet is calculated | required with high precision, without being dependent on the precision of the raising / lowering drive part of a fork and / or the raising / lowering measuring part. Further, since the sensor is fixed to the fork, the center of the sensor and the fork are always in a fixed positional relationship, and the clearance between the upper surface and the lower surface of the fork is also required with higher accuracy. As a result, a situation in which the position of the opening of the pallet must be re-detected is not reached, and as a result, the throughput of forklift loading is increased, and interference between the fork and the pallet is reliably prevented.

  Furthermore, in the present invention, the approximate center position of the opening is the provisional load pickup height. By doing in this way, it becomes possible to obtain | require the clearance of the upper surface of a fork, and a lower surface with temporary picking height. At this height, there is a high possibility that the clearance is generally greater than or equal to a predetermined value, that is, there is a high possibility that the fork can be picked up without raising or lowering the fork.

  Further, in the present invention, the sensor is a reflection type optical sensor, and its light receiving part is composed of a plurality of light receiving elements arranged in the vertical direction, and the upper end and the lower end of the opening are detected from the arrangement of each light receiving element and the output signal. Is done. By doing so, it is possible to cancel the spot-like disturbance light by performing statistical processing on the output signals of the plurality of light receiving elements, and prevent erroneous detection due to the disturbance light. Further, if the number of light receiving elements is increased, the detection accuracy can be increased, the upper and lower ends of the pallet opening can be detected with high accuracy, and the clearance between the upper surface and the lower surface of the fork can be determined with high accuracy.

  ADVANTAGE OF THE INVENTION According to this invention, the loading operation | work of the pallet in which the load was loaded can be performed with high throughput.

  The best mode for carrying out the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a forklift 1 and a loading operation according to the present invention. FIG. 2 is a block diagram showing a control structure of the forklift 1. Although the present invention can be applied to a manned forklift, the following description will be made assuming that the forklift 1 is an unmanned forklift. First, FIG. 1 will be described. F is a floor, T is a loading platform, P is a pallet placed on the loading platform T, and W is a loading placed on the pallet P. PU is a pallet upper plate, PL is a pallet lower plate, and PH is a pallet opening.

  As shown in FIG. 1A, the forklift 1 travels on a predetermined traveling path and stops at a predetermined position on the front surface of the pallet P on which a load W for picking up cargo is placed. The mast 10 erected on the forklift 1 is provided with first and second forks 11 and 12 that can be raised and lowered. The first and second forks 11 and 12 are paired, and only the first fork 11 on the near side of the figure is shown. Except for the case where one of the first and second forks 11 and 12 is specified, it will be simply referred to as the fork 11 hereinafter. First and second sensors 13 and 14 are provided at the tips of the first and second forks 11 and 12, respectively. In the figure, only the first sensor 13 on the near side is shown. Except for the case where any one of the first and second sensors 13 and 14 is specified, the sensor 13 will be simply referred to below. The sensor 13 detects an object in front of the sensor 13 and sends a detection signal to the control unit 17.

  Next, the fork 11 moves from the state shown in FIG. 1A, and stops at a temporary load height as shown in FIG. In this figure, the fork 11 is lowered, but when the initial position of the fork 11 is lower than the provisional load height, the fork 11 is raised. The value of the temporary unloading height is received from the host (not shown) by the communication unit 19 and is stored in the control unit 17. If it is possible to carry out unloading at the temporary loading height, loading is performed at this height. In this case, the tentative load height is the actual load height.

  Next, the sensor 13 detects the upper end and the lower end of the pallet opening PH in a state where the fork 11 is stationary at the provisional loading height, and sends a detection signal (detection data) to the control unit 17. The control unit 17 obtains the positions of the upper end and the lower end of the pallet opening PH from this detection signal, and further, the distance between the upper surface of the fork 11 and the upper end of the pallet opening PH (the clearance of the upper surface of the fork 11) and the lower surface of the fork 11 and the pallet. The distance from the lower end of the opening PH (the clearance of the lower surface of the fork 11) is obtained. If both the clearances of the upper surface and the lower surface of the fork 11 are equal to or larger than a predetermined value, as shown in FIG. 1 (c), the fork lift 1 is advanced at the temporary loading height to insert the fork 11 into the pallet opening PH. Further, the pallet P is loaded onto the fork 11 by slightly raising the fork 11. Then, the forklift 1 is moved backward, and the load W on the pallet P is transported to the transport destination designated by the host.

  Further, if only one of the clearances of the upper surface and the lower surface of the fork 11 is less than or equal to a predetermined value at the temporary loading height, the fork is moved to a new position where the clearances of the upper and lower surfaces of the fork 11 are both greater than or equal to the predetermined value. After moving 11, the cargo is taken out. On the other hand, if the clearance between the upper surface and the lower surface of the fork 11 is not more than a predetermined value at the temporary loading height, error processing is performed. The details of the detection of the upper and lower ends of the pallet opening PH and the loading operation will be described later.

  Next, FIG. 2 will be described. The control unit 17 includes a CPU, a ROM, a RAM, and the like. A program and constant data are stored in the ROM, and each part such as the fork elevating drive unit 15 is controlled by the CPU executing the program. The RAM is used as a storage area for various data and a calculation work area for the CPU. The above-described provisional cargo pickup height is also stored in the RAM. The control unit 17 is connected to the first sensor 13, the second sensor 14, the fork lifting drive unit 15, the encoder 16, the travel drive unit 18, the communication unit 19, and the operation unit 20. In addition, power is supplied from the battery 21 mounted on the forklift 1 to the control unit 17, the fork lift drive unit 15, and the like.

The first and second sensors 13 and 14 are provided at the tips of the first and second forks 11 and 12, respectively, and detect the upper and lower ends of the pallet opening PH. Signals detected by the first and second sensors 13 and 14 are sent to the control unit 17, and the positions of the upper and lower ends of the pallet opening PH are obtained. The structures and functions of the first and second sensors 13 and 14 are the same.
The fork lifting / lowering drive unit 15 includes, for example, a hydraulic motor, a solenoid valve, and a hydraulic cylinder, and moves the fork 11 up and down based on a fork lifting / lowering signal received from the control unit 17. The encoder 16 is provided adjacent to the fork lifting / lowering drive unit 15 and measures the movement amount (lifting amount) of the fork 11. The measurement data is sent to the control unit 17 and stored in the RAM of the control unit 17. When the fork 11 is raised, the amount of movement is added, and when it is lowered, the amount of movement is subtracted to obtain the current height of the fork 11. This value is also stored in the RAM of the control unit 17.

  The traveling drive unit 18 causes the forklift 1 to travel on a predetermined traveling path based on a signal received from the control unit 17 and stops at a predetermined position. The communication unit 19 receives commands and data (for example, transportation instruction data) from a host (not shown) and sends them to the control unit 17. Examples of the transportation instruction data include provisional cargo pickup height and transportation destination position data. Also, the forklift 1 status data received from the control unit 17 (for example, error information described later) is transmitted to the host. The operation unit 20 is provided with various levers, switches, and the like. In the manual mode, when these levers, switches, and the like are operated, a signal corresponding to the operation is sent to the control unit 17.

  FIG. 3 is a diagram showing a positional relationship among the fork 11, the sensor 13, and the pallet P. As shown in FIG. In this figure, illustration of the load W and the loading platform T is omitted. 3A is a plan view, and FIG. 3B is a longitudinal sectional view with respect to the center line FC of the fork 11. Here, the sensor 13 is a reflection-type optical sensor disposed in the cavity at the tip of the fork 11, and receives light reflected from the pallet P and a light projecting unit 13 T that projects light toward the pallet P. Part 13J. Further, the center line FC of the fork 11 and the center line JC of the light receiving unit 13J (or the sensor 13) coincide with each other.

  On the left and right sides of the light receiving unit 13J (up and down direction in FIG. 3A), the light projecting units 13T are arranged in two stages. The light from the light projecting unit 13T is projected toward the portion PA of the pallet P immediately in front of the light receiving unit 13J in the left-right direction. Further, in the vertical direction, even if the position of the sensor 13 slightly varies in the vertical direction with respect to the pallet P, at least the upper end of the pallet opening PH (the lower end of the pallet upper plate PU) and the lower end of the pallet opening PH. The reflected light from (the upper end of the pallet lower plate PL) is projected with a predetermined spread angle so that the light receiving unit 13J receives the reflected light. As the light projecting unit 13T, a device capable of projecting light at a predetermined spread angle, for example, a light emitting diode is used. This is to detect the upper and lower ends of the pallet opening PH by utilizing the fact that the reflected light from the pallet upper plate PU or the pallet lower plate PL is received by the light receiving unit 13J and that the light is not reflected by the pallet opening PH. It is because it is. Further, a lens portion 35 (see FIG. 5) is provided on the front surface of the light receiving portion 13J so that the pallet upper plate PU and the pallet lower plate PL are imaged by the light receiving portion 13J.

  In FIG. 3B, FT is the thickness of the fork 11, FC is the center line of the fork 11, JC is the center line of the light receiving portion 13J (or sensor 13), and PHC is the center line in the height direction of the pallet opening PH. It is. 1 is substantially the same height as the center line PHC of the pallet opening PH. DP is the distance between the front surface of the pallet P and the front end of the fork 11, DJ is the distance between the light receiving portion 13J and the front end of the fork 11, and DJP is the distance between the light receiving portion 13J and the front surface of the pallet P. The distance DP is received from the host as transport instruction data and stored in the RAM of the control unit 17. Then, the forklift 1 stops in front of the pallet P so that the distance DP is in accordance with the instruction from the host (see FIG. 1A). The distance DJ is a distance inherent to the forklift 1, and this value is stored in the ROM of the control unit 17. The distance DJP is a value obtained by adding the distance DP and the distance DJ.

  CU is the distance between the upper surface of the fork 11 and the upper end of the pallet opening PH, that is, the clearance of the upper surface of the fork 11. CL is the distance between the lower surface of the fork 11 and the lower end of the pallet opening PH, that is, the clearance of the lower surface of the fork 11. As will be described later, when the clearance between the upper surface and the lower surface of the fork 11 is greater than or equal to a predetermined value, the fork 11 is inserted into the pallet opening PH for loading. Here, the dimension of each part is illustrated for reference. The thickness of the pallet upper plate PU and the pallet lower plate PL is 20 mm, the vertical width of the pallet opening PH is 100 mm, the thickness of the fork 11 is 40 mm, the distance DJ between the light receiving portion 13J and the tip of the fork 11 is 10 mm, and the light receiving portion 13J The distance DJP between the pallet P and the front surface of the pallet P is 150 mm. Then, if the clearance between the upper surface and the lower surface of the fork 11 at this time is, for example, 20 mm or more, unloading is performed.

  FIG. 4 is a diagram illustrating the light receiving unit 13 </ b> J of the sensor 13. The light receiving portion 13J is a 64 row × 1 column CCD type light receiving device, and as shown in FIG. 4A, 32 light receiving devices 13JJ are arranged in the vertical direction above and below the center line JC. . The light receiving state (ON / OFF) of each light receiving element 13JJ is read serially by the CPU via a shift register (not shown) in the light receiving unit 13J and temporarily stored in the RAM work area of the control unit 17. The

  FIG. 4B is a diagram showing a light receiving state when the center line JC of the light receiving unit 13J and the center line PHC of the pallet opening PH coincide with each other in the height direction. FIG. 4C is a diagram showing a light receiving state when the center line JC of the light receiving unit 13J is shifted upward from the center line PHC of the pallet opening PH. 4B and 4C, the upper hatched portion 13JA indicates the light receiving element 13JJ that receives the reflected light from the pallet lower plate PL, and the lower hatched portion 13JB receives the reflected light from the pallet upper plate PU. The light receiving element 13JJ is shown. The distance from the center line JC of the hatched portion 13JA and the hatched portion 13JB is the same in FIG. 4B, but not the same in FIG. 4C.

  As described above, the light receiving state (ON / OFF) of each light receiving element 13JJ is stored in the RAM of the control unit 17. Using this data, the control unit 17 detects what number of light receiving elements 13JJ above the center line JC of the light receiving unit 13J detects reflected light from the pallet lower plate PL, and what number of light receiving elements 13JJ on the lower side is detected. It is checked whether the reflected light from the pallet upper plate PU is detected. The position of the light receiving element 13JA1 closest to the center line JC for detecting the reflected light from the pallet lower plate PL corresponds to the lower end of the pallet opening PH, and is closest to the center line JC for detecting the reflected light from the pallet upper plate PU. Since the position of the near light receiving element 13JB1 corresponds to the upper end of the pallet opening PH, the positions of the upper end and the lower end of the pallet opening PH on the light receiving portion 13J can be obtained. In addition to obtaining the positions of the upper and lower ends of the pallet opening PH, it is also checked that the pallet upper plate PU and the pallet lower plate PL have a thickness greater than a predetermined value, thereby improving the detection reliability. Also good.

  The RAM of the control unit 17 stores data such as the distance DJP between the light receiving unit 13J and the front surface of the pallet P, the vertical width of each light receiving element 13JJ constituting the light receiving unit 13J, and the characteristics of the lens unit 35. . Based on these data and the obtained positions of the upper and lower ends of the pallet opening PH on the light receiving unit 13J, the upper and lower positions of the pallet opening PH are calculated by the control unit 17. The positions of the upper end and the lower end of the pallet opening PH are relative positions with respect to the center line of the light receiving unit 13J, and more specifically, the height direction between the center line JC of the light receiving unit 13J and the upper end of the pallet opening PH. And the distance in the height direction between the center line JC and the lower end of the pallet opening PH.

  Next, the clearance between the upper surface and the lower surface of the fork 11 will be described. As shown in FIG. 3, since the center line FC of the fork 11 and the center line JC of the light receiving unit 13J coincide with each other, the clearance CU on the upper surface of the fork 11 is the calculated center line of the light receiving unit 13J. This is a value obtained by subtracting half the thickness FT of the fork 11 from the distance between JC and the upper end of the pallet opening PH. The clearance CL of the lower surface of the fork 11 is a value obtained by subtracting half of the thickness FT of the fork 11 from the calculated distance between the center line JC of the light receiving portion 13J and the lower end of the pallet opening PH. When the center line FC of the fork 11 and the center line JC of the light receiving portion 13J do not coincide with each other, the clearance CU on the upper surface of the fork 11 and the lower surface of the fork 11 are determined according to the displacement amount of the center lines FC and JC. Clearance CL is corrected.

  FIG. 5 is a diagram showing an example of a specific structure of the sensor 13, and shows a structure corresponding to the aspect of FIG. FIG. 5A is a plan view of a state in which the upper plate of the housing 31 is removed. FIG. 5B is a right side view with the transparent plate 32 removed. FIG. 5C is a partial longitudinal sectional view showing a side surface of the lens portion 35. FIG. 5D is a partial longitudinal sectional view showing a side surface of the light emitting diode 33. The sensor 13 includes a housing 31, a dust-proof transparent plate 32 provided on the front surface of the housing 31, a large number of light emitting diodes 33, a CCD light receiving element 34, and a lens portion provided on the front surface of the CCD light receiving element 34. 35, a printed circuit board 36 including a drive circuit for the light emitting diode 33, a peripheral circuit for the CCD type light receiving element 34, and the like, and a connector 37 for connecting the printed circuit board 36 and the control unit 17. A hood (not shown) for preventing direct light from the light emitting diode 33 from entering the CCD light receiving element 34 is provided around the CCD light receiving element 34. In addition, illustration of the wiring which connects the light emitting diode 33, CCD type light receiving element 34, the printed circuit board 36, and the connector 37 is abbreviate | omitted.

  6 and 7 are flow charts showing the loading operation of the forklift 1 according to the present invention. When the forklift 1 stops in front of the pallet P and enters the state shown in FIG. 1A, the program shown in this flowchart is started. First, n (for example, 3) is set as the number of repetitions in the RAM of the control unit 17 (S1). Next, the fork 11 is moved to a provisional cargo pickup height (S2). Next, the upper and lower ends of the pallet opening PH are detected by the first and second sensors 13 and 14 (S3). Next, the positions of the upper and lower ends of the pallet opening PH are obtained based on the detected data, and the clearances of the upper and lower surfaces of the first and second forks 11 and 12 are obtained from the obtained positions (S4).

  Next, it is determined whether or not the clearances of the upper and lower surfaces of the first fork 11 are both greater than or equal to a predetermined value (S5). It is determined whether or not the clearances are both equal to or greater than a predetermined value (S6). If both are greater than or equal to the predetermined value, the cargo is picked up (S7) and then the caller is returned.

  If it is determined in S5 that the clearances of the upper and lower surfaces of the first fork 11 are not greater than or equal to a predetermined value, it is determined whether or not the clearances of the upper and lower surfaces of the first fork 11 are both equal to or less than a predetermined value. (S8). If both the clearances are less than or equal to a predetermined value, the clearance between the upper and lower surfaces of the first fork 11 cannot be greater than or equal to the predetermined value even if the fork 11 is moved up and down, and error processing is performed (S9). As the error processing, for example, processing such as stopping the operation of the forklift 1, transmitting error information to the host via the communication unit 19, turning on an error lamp, and sounding an alarm are performed. Then, after executing the error processing, the process returns to the caller. Normally, the clearance between the upper surface and the lower surface of the first fork 11 is not less than a predetermined value. For example, when the transport instruction data from the host is wrong, the forklift 1 is at a predetermined position on the front surface of the pallet P. Such a situation occurs when it does not stop, when a part of the pallet P is damaged, or when the first sensor 13 is out of order.

  If it is determined in S6 that the clearances of the upper and lower surfaces of the second fork 12 are not greater than or equal to the predetermined value, it is determined whether or not the clearances of the upper and lower surfaces of the second fork 12 are both equal to or less than the predetermined value. (S10). If both the clearances are equal to or smaller than the predetermined value, the clearances of the upper and lower surfaces of the second fork 12 cannot be equal to or higher than the predetermined value even when the fork 11 is moved up and down. Therefore, after error processing is performed (S9) Return to the caller.

  When it is determined in S8 or S9 that the clearances of the upper and lower surfaces of the first or second forks 11, 12 are not less than a predetermined value (the clearance of either the upper surface or the lower surface is not less than a predetermined value) Shifting to S11 in FIG. 7, the number of repetitions is decremented by one. Next, it is determined whether or not the number of repetitions is 0 (S12). If it is 0, error processing is performed (S9), and the process returns to the caller.

  If the number of repetitions is not 0, a new position of the fork 11 at which the clearances of the upper and lower surfaces of the first and second forks 11, 12 are both equal to or greater than a predetermined value is obtained (S13). For example, when the predetermined value is 20 mm, the current clearances on the upper and lower surfaces of the first fork 11 are 18 mm and 22 mm, respectively, and the current clearances on the upper and lower surfaces of the second fork 12 are 22 mm and 22 mm, respectively. The position where the fork 11 is lowered by 2 mm is a new position. On the other hand, if the current clearances on the upper and lower surfaces of the first fork 11 are 18 mm and 22 mm, respectively, and the current clearances on the upper and lower surfaces of the second fork 12 are 22 mm and 21 mm, respectively, a new position is obtained. I can't. Next, it is determined whether or not a new position of the fork 11 has been obtained (S14). If it has not been obtained, error processing is performed (S9) and then the process returns to the caller.

  When a new position of the fork 11 is obtained, the fork 11 is moved to the position (S15), and the process returns to S3. In S3, the first and second sensors 13, 14 again detect the positions of the upper and lower ends of the pallet opening PH. If the clearances of the upper and lower surfaces of the first and second forks 11 and 12 are both equal to or greater than a predetermined value at a new position, the cargo is picked up at that position. Thus, since the positions of the upper and lower ends of the pallet opening PH are detected by the first and second sensors 13 and 14 at the new position, the fork 11 and the pallet P Interference is prevented in advance.

  As described above, the fork 11 is moved to a temporary unloading height (approximately the center position of the pallet opening PH in the height direction), and the upper and lower ends of the pallet opening PH are detected by the sensor 13 in a stationary state. Based on the detection signal, the positions of the upper and lower ends of the pallet opening PH are obtained, and the clearances of the upper and lower surfaces of the fork 11 are obtained from the obtained values. If both clearances are equal to or greater than a predetermined value, the provisional load height becomes the actual load height, and the load is picked up there, so that the throughput is improved.

  Further, since the clearances of both the first and second forks 11 and 12 are examined, the pallet upper plate PU or the pallet lower plate PL is partially bent, or the floor F on which the tire of the forklift 1 contacts is inclined. Even in this case, the interference between the fork 11 and the pallet P is reliably prevented.

  In the embodiment described above, the case where the clearances of the first and second forks 11 and 12 are obtained using the first and second sensors 13 and 14 has been described. However, the number of sensors 13 and forks 11 is limited to these. Is not to be done.

  Moreover, although the said embodiment demonstrated the case where light was projected toward the whole up-down direction of the pallet P from the light projection part 13T of the sensor 13, a highly directional light beam is carried out from the upper part of the pallet P to the lower part. The upper end and the lower end of the pallet opening PH may be detected by scanning toward and detecting the reflected light. Furthermore, although the reflection type optical sensor has been described in the above embodiment, the present invention can also be applied to other types of sensors.

It is a figure which shows the operation | movement of the forklift concerning this invention and a cargo pick-up. It is a block diagram which shows the control structure of a forklift. It is a figure which shows the positional relationship of a fork, a sensor, and a pallet. It is a figure which shows the light-receiving part of a sensor. It is a figure which shows an example of the specific structure of a sensor. It is a flowchart which shows operation | movement of unloading. It is a flowchart which shows operation | movement of unloading.

Explanation of symbols

1 Forklift 11 First fork (fork)
12 Second fork 13 First sensor (sensor)
13J Light-receiving unit 13JJ Light-receiving element 13T Light-emitting unit 14 Second sensor 15 Fork lift drive unit 17 Control unit CU Clearance on top of fork CL Clearance on bottom of fork DJP Distance between front of pallet and light-receiving unit FC Fork center line FT Fork thickness JC Light receiving center line P Pallet PH Pallet upper plate PL Pallet lower plate PH Pallet opening PHC Pallet center line

Claims (7)

In a forklift that is provided at the tip of the fork and includes a sensor that detects the opening of the pallet and a control unit that controls the lifting and lowering of the fork.
The sensor detects an upper end and a lower end of the opening in a stationary state from a substantially central position of the opening in the vertical direction, and outputs respective detection signals.
The said control part calculates | requires the position of the upper end and lower end of the said opening based on the said detection signal, The forklift characterized by the above-mentioned. The forklift according to claim 1,
The control unit obtains the distance between the upper surface of the fork and the upper end of the opening and the distance between the lower surface of the fork and the lower end of the opening based on the obtained positions of the upper and lower ends of the opening, and both distances are predetermined values. In this case, the forklift is configured to pick up cargo at a substantially central position of the opening. The forklift according to claim 1,
The control unit obtains the distance between the upper surface of the fork and the upper end of the opening and the distance between the lower surface of the fork and the lower end of the opening based on the obtained positions of the upper end and the lower end of the opening. A forklift that moves the fork to a new position where both distances are equal to or greater than a predetermined value when only the distance is equal to or less than the predetermined value, and performs loading at that position. The forklift according to claim 3,
In the case where the control unit causes the cargo to be picked up at the new position, on the basis of the detection signals of the upper and lower ends of the opening detected by the sensor at the position, the control unit detects the upper surface of the fork and the upper end of the opening. A forklift characterized in that a distance and a distance between a lower surface of a fork and a lower end of the opening are obtained, and when both the distances are equal to or greater than a predetermined value, cargo is picked up. The forklift according to any one of claims 1 to 4,
The forklift characterized in that the determined positions of the upper end and the lower end of the opening are relative positions with respect to the center in the vertical direction of the sensor. The forklift according to any one of claims 1 to 5,
A forklift characterized in that a substantially central position of the opening is a provisional load pickup height. The forklift according to any one of claims 1 to 6,
The sensor is a reflection type optical sensor, and its light receiving part is composed of a plurality of light receiving elements arranged in the vertical direction, and the upper end and the lower end of the opening are detected from the arrangement of each light receiving element and the output signal. And forklift.

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