Forklift Alarm System

Abstract

To provide a warning device for a forklift that has a simple configuration and prevents the forklift from traveling with a movable part raised. [Solution] The alarm device 1 has a position determination unit 2 that determines whether the movable part is at a position higher than a predetermined height by detecting the magnetism of a magnet attached to a movable part that can move up and down to raise and lower cargo equipped on the forklift, a traveling determination unit 3 that determines whether the forklift is traveling by detecting the traveling current used for traveling of the forklift, and a control unit 4 that controls an alarm unit 52 to sound an alarm when the position determination unit 2 determines that the movable part is at a position higher than the predetermined height and that the forklift is traveling.

Description

Technical Field

[0001] The present invention relates to an alarm device for a forklift.

Background Art

[0002] A forklift can lift and transport goods such as luggage and pallets. If the forklift travels with the load holding part raised, there is a risk of reduced stability. Therefore, techniques for preventing travel with the load holding part raised have been studied (Patent Document 1).

[0003] According to the technique disclosed in Patent Document 1, when the movable part moves for a predetermined time or more in the raised state, the control unit outputs a warning. Thereby, it is possible to prevent traveling with the movable part raised.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the technique disclosed in Patent Document 1, the amount of movement in the height direction of the movable part is acquired using a laser displacement sensor, and a travel signal voltage is acquired from the traveling part of the vehicle unit. Then, when it is determined that the movable part is at a position higher than a predetermined height based on the amount of movement of the movable part and it is determined that the forklift is traveling based on the travel signal voltage, a warning such as a voice is issued.

[0006] A laser displacement sensor measures the distance to a reflector attached to a movable part, has a relatively complex structure, consumes a large amount of current, and requires changes to the wiring of the traveling part to obtain a traveling signal voltage. Therefore, it is preferable to introduce the technology disclosed in Patent Document 1 into a forklift by customizing it during manufacturing at a factory. However, in the case of a leased property or the like, not only the attachment of the laser displacement sensor and the acquisition of the traveling signal voltage, but also changes to the wiring such that the power supply of the warning device is obtained from the forklift may not be possible.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a warning device for a forklift that prevents traveling in a state where the movable part is raised with a simple configuration.

Means for Solving the Problems

[0008] The warning device of the present invention includes a position determination unit that determines whether or not the movable part is at a position higher than a predetermined height by detecting the magnetism of a magnet provided on a movable part that can move up and down for lifting and lowering a load provided in a forklift, a traveling determination unit that determines whether or not the forklift is traveling by detecting a traveling current used for traveling of the forklift, and a control unit that controls to issue a warning to a connected notification unit when the position determination unit determines that the movable part is at a position higher than a predetermined height and the forklift is determined to be traveling.

Effects of the Invention

[0009] According to the warning device for a forklift of the present invention, traveling in a state where the movable part is raised can be prevented with a simple configuration.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to the same components, and redundant descriptions are omitted.

[0012] FIG. 1 is a schematic configuration diagram of a forklift equipped with the alarm device of the present embodiment. The forklift 10 includes a mast 11 provided on the front side and a sliding portion 12 slidably provided on the mast 11. A claw-shaped holding portion 13 protruding forward and capable of holding a load is provided integrally with the sliding portion 12. Hereinafter, the sliding portion 12 and the holding portion 13 will be collectively referred to as a movable portion 14.

[0013] The forklift 10 is provided with the alarm device 1 of the present embodiment. The alarm device 1 includes a position determination unit 2, a travel determination unit 3, and a control unit 4. The position determination unit 2, the travel determination unit 3, and the control unit 4 are interconnected by wiring (not shown).

[0014] At a position at a predetermined height of the mast 11, a position determination unit 2 is provided, and a magnet 51 is provided on the movable part 14 (sliding part 12). As the movable part 14 moves in the vertical direction, the magnet 51 passes near the position determination unit 2. The position determination unit 2 detects the magnetism of the magnet 51 and determines whether the movable part 14 is at a position higher than the predetermined height. Therefore, the position determination unit 2 and the magnet 51 are arranged so that the position determination unit 2 can detect the magnetic force of the magnet 51 in a state where notification is required.

[0015] The traveling determination unit 3 has a current sensor provided near the power supply path to the traveling motor of the forklift 10, and determines whether the forklift 10 is traveling according to the detection result of the current.

[0016] The control unit 4 controls the notification unit 52 according to the determination result of whether the movable part 14 is at a position higher than the predetermined height by the position determination unit 2 and the determination result of whether the forklift 10 is traveling by the traveling determination unit 3. Specifically, when the state where the movable part 14 is at a position higher than the predetermined height and the forklift 10 is traveling continues for a predetermined time, the control unit 4 causes the notification unit 52 to give a notification. Note that this predetermined time can be changed according to the operation of the user. The notification unit 52 can be in any form such as a light that prompts attention by emitting light or a speaker that issues a warning by voice.

[0017] FIG. 2 is a schematic configuration diagram of the warning device 1. The warning device 1 is driven by receiving power supply from the power supply 53 and is configured to be able to control the notification unit 52. The power supply 53 may be a power supply inside the forklift 10 or an external power supply such as a mobile battery. Inside the warning device 1, the position determination unit 2 and the traveling determination unit 3 are connected to the control unit 4.

[0018] FIG. 3 is a schematic explanatory diagram of a configuration related to the position determination unit 2. The position determination unit 2 is provided with a determination unit 21, two magnetic sensors 22 and 23 aligned in the vertical direction, and an upper determination light emitting unit 24. The two magnetic sensors 22 and 23 are an upper magnetic sensor 22 located at the upper part and a lower magnetic sensor 23 located at the lower part, and are separated by a predetermined distance.

[0019] The determination unit 21 and the control unit 4 are connected via two electrodes of positive and negative polarities. The determination unit 21 receives a power supply of 12V from the control unit 4 and supplies 3.3V of power to the upper magnetic sensor 22 and the lower magnetic sensor 23. As will be described later, the determination unit 21 determines whether or not the movable part 14 is at a position higher than a predetermined height, and controls the current level between the determination unit 21 and the control unit 4 according to the determination result. The control unit 4 acquires the determination result based on the current level between the control unit 4 and the determination unit 21.

[0020] An upper determination light-emitting unit 24 is connected to the determination unit 21. When it is determined that the movable part 14 is at a position higher than a predetermined height, power is supplied to the upper determination light-emitting unit 24 to cause it to emit light. Since the current between the determination unit 21 and the control unit 4 increases while the upper determination light-emitting unit 24 is emitting light, the current level between the determination unit 21 and the control unit 4 can be controlled according to the presence or absence of light emission of the upper determination light-emitting unit 24.

[0021] The determination unit 21 records the determination result in a state recording unit 211 which is a non-volatile memory. Since the state recording unit 211 is a non-volatile memory, the determination result can be recorded even without power supply from the control unit 4. Immediately after the power supply, the determination unit 21 controls the light emission of the upper determination light-emitting unit 24 based on the determination result read from the state recording unit 211. Then, according to the light emission control of the upper determination light-emitting unit 24, the current level between the determination unit 21 and the control unit 4 changes.

[0022] The determination unit 21 has a storage capacitor 212. By having the storage capacitor 212, the determination unit 21 can operate for a certain period even after the power supply from the control unit 4 stops, and records the determination result in the state recording unit 211 within this period. Specifically, although 12V of power is supplied from the control unit 4, after the power supply stops, the determination unit 21 operates for a certain period with the power supplied from the storage capacitor 212. The determination unit 21 records the determination result in the state recording unit 211 at the timing when the driving voltage supplied from the storage capacitor 212 falls below 3.6V. By doing so, the number of recordings can be reduced, so that the long life of the state recording unit 211 can be achieved.

[0023] The determination unit 21 is connected to the upper magnetic sensor 22 and the lower magnetic sensor 23. The determination unit 21 supplies power of 3.3 V to the upper magnetic sensor 22 and the lower magnetic sensor 23. The determination unit 21 acquires a signal indicating the presence or absence of magnetic detection from the upper magnetic sensor 22 via the upper signal line, and acquires a signal indicating the presence or absence of magnetic detection from the lower magnetic sensor 23 via the lower signal line. Note that the upper magnetic sensor 22 and the lower magnetic sensor 23 preferably use Hall elements, but may be of any form.

[0024] To the right of the figure of the position determination unit 2, a magnet 51 provided on the movable part 14 is shown. The movable part 14 (sliding part 12) slidably attached to the mast 11 moves in the vertical direction. The position determination unit 2 and the magnet 51 are arranged so that when the movable part 14 is at a predetermined height where reporting is required, the magnetic force of the magnet 51 can be detected by the position determination unit 2 (upper magnetic sensor 22 and lower magnetic sensor 23).

[0025] Four states (A) to (D) are shown as the positions of the magnet 51 when the movable part 14 moves in the vertical direction. (A) is below the lower magnetic sensor 23, (B) is near the lower magnetic sensor 23, (C) is near the upper magnetic sensor 22, and (D) is above the upper magnetic sensor 22. The operation of the position determination unit 2 when the magnet 51 moves up and down and its position changes as in (A) to (D) will be described with reference to FIG. 4.

[0026] FIG. 4 is a diagram showing the operation of the determination unit 21 according to the position of the magnet 51 in the height direction. In this figure, the positions of the magnet 51 in the height direction from (A) to (D) are shown in the vertical direction. Four states are shown in the vertical direction. In order from the top, they are the state of the upper signal line connected to the upper magnetic sensor 22, the state of the lower connection line connected to the lower magnetic sensor 23, the light emission state of the upper determination light emitting unit 24, and the magnitude of the variable current between the determination unit 21 and the control unit 4.

[0027] When the upper magnetic sensor 22 and the lower magnetic sensor 23 detect magnetism respectively, they change the upper signal line and the lower signal line from high (H) level to low (L) level. When the determination unit 21 determines that the movable part 14 is at a position higher than a predetermined height, it turns on the upper determination light-emitting unit 24 and turns it off in other states. The variable current flowing between the control unit 4 and the determination unit 21 is 3 mA while the upper determination light-emitting unit 24 is on, and 0.5 mA while the upper determination light-emitting unit 24 is off. When no power is supplied to the position determination unit 2, the variable current becomes 0 mA. Therefore, the control unit 4 determines whether the movable part 14 is at a position higher than a predetermined height by judging whether the current flowing between the control unit 4 and the determination unit 21 is greater than the threshold value with the threshold value set at 2 mA. Note that the above-described current values are examples, but in order to reduce the power consumption of the entire alarm device 1, it is preferable that the current values are small enough to be distinguishable.

[0028] In the state of (B), that is, when the magnet 51 is near the lower magnetic sensor 23, since the upper magnetic sensor 22 does not detect magnetism, the upper signal line is at a high level, and since the lower magnetic sensor 23 detects magnetism, the lower signal line is at a low level. In such a state, the determination unit 21 determines that the movable part 14 is not at a position higher than a predetermined height and turns off the upper determination light-emitting unit 24. As a result, the variable current between the control unit 4 becomes 0.5 mA.

[0029] In the state of (C), that is, when the magnet 51 is near the upper magnetic sensor 22, since the upper magnetic sensor 22 detects magnetism, the upper signal line is at a low level, and since the lower magnetic sensor 23 does not detect magnetism, the lower signal line is at a high level. In such a state, the determination unit 21 determines that the movable part 14 is at a position higher than a predetermined height and turns on the upper determination light-emitting unit 24. As a result, the variable current between the control unit 4 becomes 3 mA.

[0030] In the state of (A), that is, when the magnet 51 is below the lower magnetic sensor 23, since neither the upper magnetic sensor 22 nor the lower magnetic sensor 23 detects magnetism, both the upper signal line and the lower signal line are at a high level. Similarly, in the state of (D), that is, when the magnet 51 is above the upper magnetic sensor 22, since neither the upper magnetic sensor 22 nor the lower magnetic sensor 23 detects magnetism, both the upper signal line and the lower signal line are at a high level.

[0031] In such states of (A) and (D), according to the state immediately before, the determination unit 21 determines whether the height of the movable part 14 is higher than a predetermined position. That is, in the state of (A), the determination result that the movable part 14 is not at a position higher than the predetermined height in the immediately preceding state of (B) is maintained, the upper determination light-emitting part 24 is kept OFF, and the variable current between the control unit 4 is controlled to be 0.5 mA. In the state of (D), the determination result that the movable part 14 is at a position higher than the predetermined height in the immediately preceding state of (C) is maintained, the upper determination light-emitting part 24 is kept ON, and the variable current between the control unit 4 is controlled to be 3 mA. Note that even when both the upper magnetic sensor 22 and the lower magnetic sensor 23 detect magnetism, in the states of (A) and (D), according to the state immediately before, the determination unit 21 determines whether the height of the movable part 14 is higher than a predetermined position.

[0032] In this way, the determination unit 21 determines whether the movable part 14 is at a position higher than the predetermined height, and changes the variable current according to the determination result. Note that when the magnet 51 is between the upper magnetic sensor 22 and the lower magnetic sensor 23, both the upper magnetic sensor 22 and the lower magnetic sensor 23 detect magnetism, and both the upper signal line and the lower signal line are at a low level, the determination unit 21 maintains the determination result of the immediately preceding state, similar to (A) and (D).

[0033] FIG. 5A is a schematic explanatory diagram of a configuration related to the traveling determination unit 3. The traveling determination unit 3 includes a clamp type current sensor 31. FIG. 5B is a diagram showing the structure of the clamp type current sensor 31, and shows two states when the clamp type current sensor 31 is in use and when it is attached. The clamp type current sensor 31 includes a main body portion 32 and a lid portion 33 each having a concave groove on the opposing surface. When attaching the clamp type current sensor 31 to the wiring to be detected for current, after arranging the wiring to be detected for current in the concave grooves of the main body portion 32 and the lid portion 33, the lid portion 33 is attached to the main body portion 32. In this way, the clamp type current sensor 31 can be attached so as to surround the wiring to be detected for current.

[0034] Referring again to FIG. 5A, the traveling motor 55 is driven by three-phase (UVW) power supplied from the motor drive power source 54. The clamp type current sensor 31 is provided so as to surround a power line of one phase (for example, U phase) between the motor drive power source 54 and the traveling motor 55. The motor drive power source 54 is supplied with the power line power of each phase during driving, and a magnetic field is generated in the power line which is the power supply path. Since the clamp type current sensor 31 generates a current according to the generated magnetic field, the traveling determination unit 3 can determine the driving state of the traveling motor 55 according to whether or not the generated current of the clamp type current sensor 31 is detected.

[0035] FIG. 6 is a table used for the control of the notification unit 52 by the control unit 4. As shown in this figure, based on the determination result by the position determination unit 2 as to whether or not the movable part 14 is at a position higher than a predetermined height, and the determination result by the traveling determination unit 3 as to whether or not the forklift 10 is traveling, the issuance or stop of the notification of the notification unit 52 is controlled.

[0036] According to the illustrated table, when the control unit 4 determines, based on the position determination unit 2, that the movable part 14 is at a position higher than a predetermined height, and when the state where the forklift 10 is determined to be in motion by the travel determination unit 3 continues for a predetermined time, the control unit 4 drives the notification unit 52. The control unit 4 does not drive the notification unit 52 in other cases. Note that the predetermined time is set to be variable and can be gradually changed, for example, between 0.5 and 10 seconds, according to the user's operation.

[0037] With such control of the control unit 4, since the notification unit 52 operates when the movable part 14 is in the upper position and the forklift 10 is in motion, it is possible to prevent traveling with the movable part 14 raised with a simple configuration.

[0038] According to the warning device 1 of the forklift 10 of this embodiment, the following effects can be obtained.

[0039] The warning device 1 of this embodiment includes a position determination unit 2 that determines whether the movable part 14 is at a position higher than a predetermined height by detecting the magnetism of a magnet 51 provided on the movable part 14, a travel determination unit 3 that determines whether the forklift 10 is in motion by detecting a travel current used for the travel of the forklift 10, and a control unit 4 that controls to issue a warning to the notification unit 52 when the position determination unit 2 determines that the movable part 14 is at a position higher than a predetermined height and the travel determination unit 3 determines that the forklift 10 is in motion.

[0040] According to such a configuration, the determination by the position determination unit 2 can be achieved by the magnet 51 provided on the movable part 14 and the magnetic sensors 22 and 23 provided at a position with a predetermined height, and the determination by the travel determination unit 3 can be achieved by the clamp-type current sensor 31 provided near the power supply line of the travel motor 55 of the forklift 10. The magnetic sensors 22 and 23 and the clamp-type current sensor 31 can be attached without changing the internal wiring of the forklift 10. Furthermore, since the power consumption of the magnetic sensors 22 and 23 and the clamp-type current sensor 31 is relatively small, the alarm device 1 can be driven by a low-capacity battery such as a mobile battery, and there is no need to modify the power supply wiring of the forklift 10. Therefore, it is possible to prevent the forklift 10 from traveling with the movable part 14 raised in a simple configuration.

[0041] The position determination unit 2 of the present embodiment includes an upper magnetic sensor 22 and a lower magnetic sensor 23 arranged side by side in the vertical direction, and a determination unit 21 that determines whether or not the movable part 14 is at a position higher than a predetermined height based on the detection results of the upper magnetic sensor 22 and the lower magnetic sensor 23, and transmits the determination result to the control unit 4.

[0042] When the upper magnetic sensor 22 detects magnetism, it is determined that the movable part 14 is at a position higher than the predetermined height, and when the lower magnetic sensor 23 detects magnetism, it is determined that the movable part 14 is not at a position higher than the predetermined height. When both the upper magnetic sensor 22 and the lower magnetic sensor 23 detect magnetism, and when neither of them detects magnetism, the determination result in the case where one of the upper magnetic sensor 22 and the lower magnetic sensor 23 detected magnetism immediately before is maintained.

[0043] When only one magnetic sensor is used, the passage of the movable part 14 can be determined, but the direction cannot be determined. By using two magnetic sensors 22 and 23 as in the present embodiment, it is possible to determine whether or not the movable part 14 is at a position higher than a predetermined height with a simple configuration.

[0044] The determination unit 21 of this embodiment records the determination result in the state recording unit 211 that can hold the recorded content even without power supply. After the start of power supply, when neither the upper magnetic sensor 22 nor the lower magnetic sensor 23 detects magnetism, the position determination unit 2 uses the determination result corresponding to the recorded content of the state recording unit 211. With such a configuration, even when the movable part 14 is at a position higher than the predetermined height at the start of the operation of the forklift 10, the detection of that state becomes possible.

[0045] The determination unit 21 of this embodiment includes a storage capacitor 212. When the power supply from the control unit 4 stops when the warning device 1 stops, it then switches to the power supply from the storage capacitor 212. The determination unit 21 records the determination result in the state recording unit 211 when the supplied voltage drops below a predetermined value. Even when there is no power supply from the control unit 4, the determination unit 21 can be driven for a certain period of time by the power supply from the storage capacitor 212, and thus records the determination result in the state recording unit 211 during this certain period. With such a configuration, compared with the case where the determination result is recorded every time the determination result changes, the number of times the determination result is recorded can be reduced, so the durability period of the state recording unit 211 can be improved. Also, the driving power of the warning device 1 can be reduced by reducing the number of recordings.

[0046] When the position determination unit 2 of this embodiment determines that the movable part 14 is at a position higher than the predetermined height, the magnitude of the current between it and the control unit 4 is set to the first level, and when it determines that the movable part 14 is not at a position higher than the predetermined height, the magnitude of the current between it and the control unit 4 is set to the second level. The control unit 4 determines whether the movable part 14 is at a position higher than the predetermined height according to the level of the magnitude of the current between it and the position determination unit 2.

[0047] In this way, by using a current transmission method that transmits a determination result according to the current level, it is possible to simplify the configuration and reduce the power consumption compared to providing a signal line for transmitting the determination result. In addition, the current transmission method for determining according to the current level is more resistant to noise than the voltage transmission for determining according to the voltage level. Therefore, although it is difficult to take noise countermeasures such as shielding in the alarm device 1 with a simple configuration, by using the current transmission method, the position of the movable part 14 can be appropriately determined.

[0048] The position determination unit 2 of the present embodiment further includes an upper determination light emitting unit 24. When the determination unit 21 determines that the movable part 14 is at a position higher than a predetermined height, the upper determination light emitting unit 24 is energized to emit light. Since the power consumption increases when the upper determination light emitting unit 24 emits light, when it is determined that the movable part 14 is at a position higher than the predetermined height, the magnitude of the current between the control unit 4 can be set to a larger first level, and when it is determined that the movable part 14 is not at a position higher than the predetermined height, the current between the control unit 4 can be set to a smaller second level. By providing the upper determination light emitting unit 24 in this way, not only can the determination result be displayed, but also the determination result can be transmitted to the control unit 4 by changing the current level according to the control of the light emission of the upper determination light emitting unit 24.

[0049] The alarm device 1 of the present embodiment is driven by receiving power supply from a power supply 53 which is an external battery. In the case of a forklift 10, especially when it is a leased property or a foreign-made one with little design information, it is difficult to modify the wiring, and the power supply to the alarm device 1 cannot be performed from the power source of the forklift 10. Even in such a case, by using the power supply 53 of the external battery, the alarm device 1 can be operated.

[0050] The travel determination unit 3 of this embodiment is provided on one of the three-phase power supply lines to the travel motor 55 of the forklift 10 and has a clamp-type current sensor 31 that detects the travel current. By providing the clamp-type current sensor 31 on the power supply line to the travel motor 55, the warning device 1 can be attached with a simple configuration without changing the internal wiring of the forklift 10.

[0051] When the movable part 14 is at a position higher than a predetermined height and the state where the forklift 10 is traveling continues for a predetermined time, the control unit 4 of this embodiment controls to give an alarm to the notification unit 52. In this way, by causing the notification unit 52 to give an alarm when it continues for a predetermined time, unnecessary alarms can be suppressed because alarms are not given during short-distance and short-time movements during the operation of the forklift 10.

[0052] (Modification example) As described above, the warning device 1 is not limited to the forklift 10 and may be used for detecting other movable parts. In the modification example, it can be used for detecting the movable part of an electric shutter.

[0053] FIG. 7 is a schematic configuration diagram of an electric shutter 60 to which the warning device is attached. The electric shutter 60 includes a shutter 61 that can be opened and closed in the vertical direction. A magnet 51 is provided below the movable part 14, and the position determination unit 2 and the magnet 51 are arranged so that the magnetic force of the magnet 51 can be detected by the position determination unit 2 when the lower part of the shutter 61 is at a predetermined height where an alarm is required. By using such a configuration, the warning device 1 can drive the notification unit 52 when the shutter 61 is open from a predetermined height and the electric shutter 60 is operating.

[0054] The present invention can be implemented in various embodiments and variations without departing from the broad spirit and scope of the present invention. Further, the above-described embodiments are for explaining the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is indicated by the claims rather than the embodiments. And various modifications made within the scope of the claims and within the scope of the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

Description of Reference Numerals

[0055] 1: Alarm device, 2: Position determination unit, 3: Travel determination unit, 4: Control unit, 10: Forklift, 14: Movable part, 21: Determination unit, 211: State recording unit, 212: Storage capacitor, 22: Upper magnetic sensor, 23: Lower magnetic sensor, 24: Upper determination light emitting unit, 31: Current sensor, 51: Magnet, 52: Notification unit, 53: Power supply, 54: Motor drive power supply, 55: Travel motor, 60: Electric shutter, 61: Shutter

Claims

1. a position determination unit that detects magnetism of a magnet provided on a movable part of the forklift that can move up and down to lift and lower cargo and determines whether the movable part is located at a position higher than a predetermined height; a travel determination unit that determines whether the forklift is traveling by detecting a travel current used for traveling of the forklift; A warning device for a forklift comprising: a control unit that controls a connected alarm unit to sound an alarm when the position determination unit determines that the movable part is at a position higher than the specified height and the traveling determination unit determines that the forklift is traveling.

2. the position determination unit has two magnetic sensors arranged side by side in a vertical direction, and a determination unit that determines whether or not the movable part is at a position higher than the predetermined height based on detection results of the two magnetic sensors and transmits the determination result to the control unit; The determination unit is When an upper magnetic sensor located above detects magnetism, it is determined that the movable part is at a position higher than the predetermined height, When the lower magnetic sensor located below detects magnetism, it is determined that the movable part is not at a position higher than the predetermined height, 2. The forklift warning device according to claim 1, wherein when both the upper magnetic sensor and the lower magnetic sensor are detecting a magnetism, or when neither is detecting a magnetism, a determination result corresponding to a magnetic detection state by one of the upper magnetic sensor and the lower magnetic sensor immediately before that is maintained.

3. the position determination unit operates by receiving power supply from the control unit, The determination unit is a state recording unit capable of retaining the recorded contents even when no power is supplied from the control unit, 3. The forklift warning device according to claim 2, wherein when neither the upper magnetic sensor nor the lower magnetic sensor detects magnetism after the start of power supply from the control unit, a determination result is determined according to the contents recorded in the status recording unit.

4. The determination unit further includes a storage capacitor.

4. The warning device for a forklift according to claim 3, wherein the determination unit records a determination result in the state recording unit when the voltage supplied from the storage capacitor falls below a predetermined value after the power supply from the control unit is stopped.

5. when the position determination unit determines that the movable part is at a position higher than the predetermined height, the magnitude of the current between the position determination unit and the control unit is set to a first level, and when the position determination unit determines that the movable part is not at a position higher than the predetermined height, the magnitude of the current between the position determination unit and the control unit is set to a second level; 3. The warning device for a forklift according to claim 2, wherein the control unit determines whether or not the movable part is at a position higher than the predetermined height depending on a level of a current between the control unit and the position determination unit.

6. The position determination unit further includes a light emitting unit, the first level is greater than the second level; 6. The forklift warning device according to claim 5, wherein when the position determination unit determines that the movable part is at a position higher than the predetermined height, the position determination unit energizes the light-emitting unit to emit light, thereby setting the magnitude of the current between the light-emitting unit and the control unit to the first level.

7. 7. The forklift warning device according to claim 1, wherein the device is powered by an external battery.

8. 2. The warning device for a forklift according to claim 1, wherein the traveling determination unit has a clamp-type current sensor provided on one of three-phase power supply lines to a traveling motor of the forklift, the clamp-type current sensor detecting the traveling current.

9. 2. The forklift warning device according to claim 1, wherein the control unit controls the alarm unit to issue an alarm when the position determination unit determines that the movable part is at a position higher than the predetermined height and the state in which the forklift is determined to be traveling continues for a variable predetermined time period.

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