JPH04272097A - Control device for forklift - Google Patents

Abstract

PURPOSE:To provide a control device for a forklift by which even a fragile load can be safely handled with no damage by landing a fork without an impact. CONSTITUTION:A fall position of work machine lever is detected while detecting lift height of a fork by a position sensor, and only when both the lift height and fall position are detected ON, the fork is controlled by a flow control amount lower than the standard flow control amount and landed with no shock. Consequently, a load can be prevented from being damaged while reducing a burden for a worker. Further, control is inhibited by detecting a wire break of the position sensor, so that safety is more improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a forklift that can perform cargo handling using an electromagnetic hydraulic system, and has been improved so that particularly fragile cargo can be safely landed.

0002

2. Description of the Related Art Conventionally, as a control device for a forklift that can be operated in an electrohydraulic manner, for example, the one shown in FIG. As shown in the figure, hydraulic pressure from a hydraulic pump 101 is divided into an electromagnetic proportional control valve 102 and a power steering control valve (not shown). Electromagnetic proportional control valve 102
An oil chamber 102a for pilot operation is formed in the oil chamber 102a, and a pilot piston 102b is slidably fitted into the oil chamber 102a. This pilot piston 102
b is connected to a spool 102c that switches the oil path. Pilot piston 102b and spool 102c
are connected to springs 103a and 103b, respectively, and are held at a neutral position without hydraulic pressure. Pilot inflow pipes 10 are provided on both sides of the pilot piston 102b.
2d and 102e are provided, respectively. The pilot inflow pipes 102d and 102e are equipped with electromagnetic on-off valves 102f,
It is connected to the power steering hydraulic system via 102g. Therefore, by opening and closing the electromagnetic on-off valves 102f and 102g, the pilot piston 102b and the spool 102c move from side to side in the figure. Spool 102
When c moves, pressure oil is supplied to and discharged from the work machine cylinder 104 via this spool 102c, and the work machine cylinder 10
4 expands and contracts. Depending on the movement position of the spool 102c, the flow rate of pressure oil supplied to and discharged from the working machine cylinder 104 is adjusted, and the speed of elevation thereof is adjusted. As the working machine cylinder 104, various types can be used, such as one that raises and lowers a fork (not shown), one that tilts it, and the like.

On the other hand, the opening and closing of the electromagnetic on-off valves 102f and 102g are controlled by a flow rate control signal from a controller 105. The controller 105 is a work machine lever 106
A flow rate control signal is output based on the lever operation signal from. The work machine lever 106 includes a potentiometer and outputs a lever operation signal according to the tilt angle and the tilt direction. The work implement lever 106 does not output any output in the neutral position. Therefore, by operating the work machine lever 106,
Pressure oil is supplied and discharged from the electromagnetic proportional control valve 102 to the working machine cylinder 104 by opening and closing the electromagnetic on-off valves 102f and 102g,
When the work machine cylinder 104 expands and contracts to lift, lower, tilt, etc. the fork, and adjust the inclination angle of the work machine lever 106, the flow rate of pressure oil to the work machine cylinder 104 is adjusted, freely controlling the lifting speed, etc. be able to.

0004

[Problems to be Solved by the Invention] During cargo handling operations using a forklift, if a load lifted by a fork is simply lowered and landed on the ground, a shock is applied to the load upon landing. For this reason, when handling fragile items such as bottles and roof tiles, there is a risk of damage due to impact upon landing. For this reason, just before the fork touches down, the operator returns the work equipment lever to the neutral position to stop the fork from descending, and then reduces the inclination angle of the work equipment lever to slowly bring the fork into contact with the ground through an inching motion. , so as not to cause any shock. However, it is a troublesome task for the operator to temporarily stop the fork in the middle of its descent and then perform an inching operation, and requires skill. Furthermore, the heavier the load, the lower the load must be to lower the load in order to avoid impact, which is a time-consuming task even for experienced operators. The present invention has been made in view of the above-mentioned prior art, and it is an object of the present invention to provide a forklift control device that improves work efficiency and allows cargo handling operations to be carried out safely without damaging fragile objects.

[0005]

[Means for Solving the Problems] The configuration of the present invention that achieves the above object includes a controller that outputs a flow rate control signal to an electromagnetic proportional control valve in response to a lever operation signal from a work equipment lever, and a flow rate control signal from the controller. In a forklift control device comprising: an electromagnetic proportional control valve that supplies and discharges pressure oil to and from a work equipment cylinder according to a control signal; and a work equipment cylinder that expands and contracts with the pressure oil from the electromagnetic proportional control valve to raise and lower a fork. , a low-speed operation table that corresponds to a lever operation signal with a flow control signal lower than a standard flow control signal, a position sensor that detects when the lift height of the fork falls below a certain level, and the work equipment lever. A lever lowering detection sensor detects the lowering position of the fork, and the position sensor detects that the lift height of the fork has become below a certain level,
and control amount output means for outputting a flow rate control signal read from the low-speed operation table when the lowered position of the work equipment lever is detected by the lever lowering detection sensor; The present invention is characterized by being provided with a disconnection detection means for detecting a disconnection in the system and stopping the various controls described above.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings. An embodiment of the present invention is shown in FIGS. 1 to 4. FIG. 3 is a perspective view showing an example of a forklift truck applied to this embodiment. As shown in the figure, the lift cylinder 1 is fixed to a pair of left and right outer masts 2, and as the piston rod 1a expands and contracts, the pair of left and right inner masts 3 is raised and lowered using the outer masts 2 as a guide. At this time, the outer mast 2 is fixed to the vehicle body 7 in front of the vehicle body 7. As a result, inner mast 3
As the truck moves up and down, the lifting section consisting of a bracket 5 suspended on a chain and a fork 4 for directly loading cargo moves up and down. The tilt cylinder 8 is used to tilt the elevating section together with the outer mast 2 and the inner mast 3 forward (toward the vehicle body 7 side) and rearward (toward the vehicle body 7 side). That is, it tilts forward when unloading, and tilts backward when lifting or transporting cargo, thereby maintaining good workability and ensuring safety.

The work equipment levers 9a and 9b are operated by an operator to control the operation of the lift cylinder 1 and the tilt cylinder 8 via the controller 10 and the electromagnetic proportional control valve 11, and are used to perform an emergency stop. It is housed in a joystick box 13 along with a safety switch 12 for carrying out the operation. Work machine levers 9c, 9d, 9
e is various attachments, such as roll clamps,
This is for when a bail clamp or the like is installed. The seat switch 14 is a switch that operates when an operator sits on the driver's seat 15, and its output signal is output to the controller 10. FIG. 4 is a block diagram showing an example of the forklift control device. As shown in the figure,
The work equipment levers 9a and 9b are formed by potentiometers, and a lever operation signal S1 whose current value is proportional to the operation amount
is sent to the controller 10. controller 10
is the electromagnetic proportional control valve 11 based on the lever operation signal S1.
A flow rate control signal S2 is sent out to adjust the opening degree of the spool. The electromagnetic proportional control valve 11 moves the spool in proportion to the magnitude of the flow rate control signal S2, controls the flow rate of the pressure oil flowing through the hydraulic line 16, and adjusts the operating speed of the lift cylinder 1 and tilt cylinder 8 to the working machine. Control is performed to correspond to the amount of operation of the levers 9a and 9b.

The oil pressure sensor 17 is disposed in the oil pressure line 16 and sends out an oil pressure signal S3 representing the oil pressure in the oil pressure line 16. The controller 10 processes the hydraulic signal S3 to calculate the load acting on the lift cylinder 1 and the tilt cylinder 8. Further, the controller 10 operates by being supplied with power from the battery 21 when a starter switch 20, which is housed in a console box 19 together with a warning light 18, is turned on, and when the safety switch 12 is operated and the seat switch 14 is not operated. When the person is away from the seat, the current value of the flow rate control signal S2 is set to zero, and the opening degree of the electromagnetic proportional control valve 11 is controlled to be zero. In the figure, 22 is a hydraulic pump, and 23 is a hydraulic oil source. Further, the number of hydraulic components such as the electromagnetic proportional control valve 11, the hydraulic pipe line 16, and the hydraulic pressure sensor 17 is provided in a number corresponding to the number of work machine levers 9a to 9e. In this embodiment, two work machine levers 9 for lifting and tilting are used to perform lifting and tilting operations.
a and 9b, two hydraulic systems may be provided.

FIG. 1 shows the main parts of a forklift control device according to an embodiment of the present invention. As shown in the figure, the controller 10 of this embodiment includes a control amount extraction means 25
, manipulated variable/controlled variable correspondence table 26, controlled variable output means 2
7. A disconnection detection means 34 is provided. The operation amount/control amount correspondence table 26 includes a standard operation table 26a and a low speed operation table 26b. Standard operation table 2
Reference numeral 6a stores a lever operation signal S1 for the work equipment lever 9a and a standard flow rate control signal S2a in correspondence with each other, and a table 26b for low speed operation stores the lever operation signal S1 for the work equipment lever 9a in correspondence with the standard flow rate control signal S2a.
The lever operation signal S1 of step a and the flow rate control signal S2b lower than the standard are stored in correspondence. The flow rate control signals S2a and S2b stored in the standard operation table 26a and the low speed operation table 26b are both flow rate control signals S according to the inclination direction and inclination angle of the work equipment lever 9a.
2, but as shown in FIG. 6, the flow rate control signal S2a
is always larger than the flow rate control signal S2b. These standard operation table 26a and low speed operation table 26b
The flow rate control signals S2a and S2b selectively extracted from the control amount extracting means 25 are outputted to the electromagnetic proportional control valve 11 by the controlled amount outputting means 27. Hereinafter, selecting and controlling the low-speed operation table 26b will be referred to as soft touch control. The control amount extraction means 26 includes the determination means 29
Accordingly, the table 26a for standard operation and the table 26b for low speed operation are selected. The determining means 29 is connected to a position sensor 24 provided on the lift cylinder and a lever lowering detection sensor 30 provided on the working machine lever 9a. The position sensor 24 detects that the lift height is below a certain level just before the fork lands, and outputs an ON signal.
Further, the lever lowering detection sensor 30 is connected to the work equipment lever 9a.
It turns on when it detects that the lever is in the lowered position. The constant lift height refers to, for example, about 30 cm above the ground. The determining means 29 is an AND circuit of the position sensor 24 and the lever lowering detection sensor 30, and when an ON signal is output from both, the low speed operation table 26
It outputs to the control amount extraction means 26 that selection b should be made, and in other cases, it outputs to the control amount extraction means 26 that selection of the standard operation table 26a should be made.

Therefore, in the case of ascending control, the standard operation table 26a is always selected, and in the case of descending control, the standard operation table 26a is selected until the position sensor 24 detects a certain lift height immediately before the fork lands. table 26a will be selected. Further, in the lowering control, if the position sensor 24 detects that the lift height of the fork is below a certain level, the low-speed operation table 26b is selected. For this reason, soft touch control is performed, and the fork descends at a low speed, resulting in a slow landing. The descending speed of the fork at this time varies depending on the ratio of the flow rate control signal S2b and the flow rate control signal S2a, but it is generally preferable to set it to a speed that allows the load to land without impact. Note that even if the position sensor 24 detects that the lift height of the fork is below a certain level, in the case of lift control, the standard operation table 2
6a is selected, the fork can be raised at high speed, and work can be done efficiently. That is, after the position sensor 24 detects that the lift height of the fork is below a certain level, when the work implement lever 9a is returned to the neutral position, the lowering control is stopped, and the lowering control is switched to the higher lifting control, the high-speed Not only can you work efficiently by raising the fork, but even if the work equipment lever 9a is returned to the neutral position and the lowering control is interrupted, the lowering control is restarted safely with no impact due to soft touch control. It is possible to land on .

Furthermore, the controller 10 includes a limit control amount extraction means 31 and a load/limit control amount correspondence table 3.
2 and comparison means 33 are provided. The load/limit control amount correspondence table 32 sets a limit value for the flow rate control signal according to the load of the load loaded on the fork, and restricts the flow rate control signal so that it does not exceed that value. As shown in FIG. 7, two types of tables are set. This means that the heavier the load,
This is because the influence of gravity, which tries to lower the lift cylinder due to its own weight, is large, and if the flow rate control signal is the same for both heavy and light loads, there is a risk that the heavier the load, the faster the lowering speed. Therefore, the heavier the load of the load, the lower the limit value of the flow rate control signal, so that even if the load of the load is different, the load can be lowered at a constant speed. The limit control amount extraction means 31 is
It is connected to the oil pressure sensor 9, and reads the limit value from the load/limit control amount correspondence table 32 in accordance with the oil pressure detected by the oil pressure sensor 17 (that is, equivalent to the load of the load loaded on the fork). The limit value is output to the comparing means 33. Comparison means 33
Now, compare this limit value with the flow rate control signals S2a, S2b, and if the flow rate control signals S2a, S2b are lower than the limit value, the flow rate control signals S2a, S2 are used as they are.
b is used, and conversely, if the flow rate control signals S2a, S2b are larger than the limit value, the flow rate control signals S2a,
Instead of S2b, the limit value is output to the control amount output means 27. Therefore, the control amount output means 27 does not output a signal exceeding the limit value to the electromagnetic proportional control valve 11, so whether the load loaded on the fork is light or heavy, it is always lowered at a constant speed. be able to.

Furthermore, the disconnection detection means 34 includes a position sensor 2
This detects the disconnection of the signal line No. 4, and its specific configuration is shown in FIG. That is, in FIG. 8, the controller 10 is shown in terms of hardware, and the controller 10 includes a CPU 120, a clock generator 121, a memory 122, and an A/D converter 123.
, an interface 124, a solenoid valve drive circuit 125, a power supply circuit 126, a battery 50, and the like. The lever operation signal S1 output from the work equipment lever 9a and the detection signal output from the position sensor 24 are converted into digital signals by the A/D converter 123, and then
It is sent to the CPU 120. The input signals for the automatic lowering switch and the manual switch are sent to the CPU 120 via the interface 124. The CPU 120 implements functions written in various software stored in the memory 122 and performs various calculations, and the calculation processing is synchronized with the clock of the clock generator 121. CPU1
The electromagnetic valve drive circuit 125 is driven based on the calculation result of step 20, and the flow rate control signal S2 is output to the electromagnetic proportional control valve 11.

Here, like the other means, the disconnection detection means 34 also transfers software from the memory 122 to the CPU 120.
This is realized by reading the resistor R1 provided in the position sensor 24 and having a resistance value r1, and the resistor R2 provided in the controller 10 and having a resistance value r2. Resistance R1
and resistor R2 are connected by a position sensor signal line 24a, and a signal voltage V is applied to this signal line 24a. If the position sensor signal line 24a is normal and not disconnected, and the position sensor 24 is OFF, A
The voltage V1 input via the /D converter 123 is
It is shown by the following formula. V1=V・r2/(r1+r2) Also, when the position sensor signal line 24a is disconnected,
The voltage V1 inputted via the A/D converter 123 is at ground potential, that is, 0, unlike the above. Therefore, as shown in FIG. 9, the controller 10 first determines whether the voltage V1 inputted through the A/D converter 123 is 0 or not, and when V1=0, it is determined that there is a disconnection. Incidentally, when it is determined that the wire is broken, it is convenient to display that fact on the wire breakage display section 51. When it is determined that the wire is disconnected in this way, the CPU 120 outputs a flow rate control signal S2 for stopping control of the fork 4 to the electromagnetic proportional control valve 11, so that the current state of the fork 4 is maintained. On the other hand, when the voltage V1 input via the A/D converter 123 is not 0, it is a normal state with no disconnection. At this time, as shown in FIG. 9, V1=V・r2/(
r1+r2), the position sensor 24 is OFF.
If so, the soft touch control is stopped, and if not, the position sensor 24 is assumed to be ON and the soft touch control is started. Therefore, when the soft touch control described above cannot be performed due to a break in the position sensor signal line 24a, even if an attempt is made to start the control to lower the fork 4, the CPU 120 of the controller 120 will stop the lowering of the fork 4. This makes it extremely safe as there is no shock to the luggage when it lands. Further, since the disconnection display section 51 displays the fact that there is a disconnection, it becomes easy to find the abnormal location, and the position sensor signal line 24a can be quickly restored to resume work.

Specifically, in this embodiment having the above configuration, a forklift is controlled according to the flowchart shown in FIG. First, after initialization, it is determined whether the work implement lever is in the neutral position, lowered position, or raised position. When the work equipment lever is in the neutral position, neutral control is performed to maintain the fork at a constant height, and the lever lowering detection sensor 3
When the raised position or lowered position of the working machine lever is detected by 0, lift raising control to raise the fork or lift lowering control to lower the fork is performed. however,
In the lift lowering control, it is determined whether or not the position sensor 24 is turned on, and when it is detected that the position sensor 24 is turned on and the lift height is below a certain level, soft touch control is performed. That is, when both the lift lowering detection sensor 30 and the position sensor 24 are ON,
The control amount extracting means 25 selects the low-speed operation table 26b according to the instruction from the determining means 29, and extracts the flow rate control signal S2 from the low-speed operation table 26b.
b is output to the control amount output means 27. Position sensor 24
When is OFF, the determination means 2 performs normal control.
9, the control amount extraction means 25 selects the standard operation table 26a and outputs the flow control signal S2a to the control amount extraction means 27. Thereafter, the limit control amount extracting means 31 extracts the load/load amount according to the load loaded on the fork.
The limit value is read from the limit control amount correspondence table 31 and output to the comparison means 33. The comparison circuit 33 compares the limit value with the flow rate control signals S2a, S2b, and if the flow rate control signals S2a, S2b are lower than the limit value, the flow rate control signals S2a, S2b are used as they are, and conversely, the flow rate control signals S2a, S2b are used. When the signals S2a and S2b are larger than the limit value, the limit value is output to the control amount output means 27 in place of the flow rate control signals S2a and S2b.

As described above, in the above embodiment, the position sensor 2
4, when it is detected that the lift height of the fork is below a certain level, the low speed operation table 26b is selected and soft touch control is performed, so the lowering speed is automatically reduced to a low speed.
It can be landed without impact. Therefore, even fragile items can be handled safely. Furthermore,
After the position sensor 24 detects that the lift height of the fork has become below a certain level, the work equipment lever 9a is returned to the neutral position and the lowering control is interrupted and then resumed. Since the lowered position of 9a has been detected, it will be controlled by soft touch control, and it will be possible to land safely without impact. In particular, in the case of fragile cargo, it is necessary to suppress not only the shock upon landing but also the vibration during descent, in which case it is necessary to temporarily interrupt the descent and then resume the descent slowly. This provides safer control. On the other hand, after the position sensor 24 detects that the lift height of the fork has become below a certain level, the work equipment lever 9a is returned to the neutral position, the lowering control is stopped, and when switching to ascending work, the normal control is used to increase the speed. You can control the lift and work efficiently. In the above embodiment, the limit value is calculated by the limit control amount extraction means 31 so that the descending speed is constant regardless of the load of the load, but this is not particularly necessary for a forklift that handles light loads. do not have.

[0016]

[Effects of the Invention] As explained above in detail based on the embodiments, the present invention provides a state in which the fork is lowered,
In addition, when the lift height of the fork is below a certain level, soft touch control is performed to automatically lower the fork at a low speed, so even fragile cargo can be safely landed on the ground without impact. Furthermore, even if the lift height of the fork is below a certain level, when the fork is in a rising state, it will rise at a normal speed, so that work can be done efficiently. Furthermore, when the position sensor cannot be used due to a disconnection, the disconnection detection circuit stops the control of the fork, so it is safe even when soft touch control is not possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing essential parts of an embodiment of the present invention.

FIG. 2 is a flowchart showing the steps of an embodiment of the present invention.

FIG. 3 is an external perspective view of a forklift to which the present invention is applied.

FIG. 4 is a block diagram showing the overall configuration of a forklift control device according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional forklift control device.

FIG. 6 is a graph showing the relationship between a lever operation signal and a flow rate control signal.

FIG. 7 is a graph showing the relationship between load and load limit value.

FIG. 8 is an explanatory diagram showing a specific configuration of a wire breakage detection means.

FIG. 9 is a flowchart showing the process of wire breakage detection by wire breakage detection means.

[Explanation of symbols]

1 Lift cylinder 1a Piston rod 2 Outer mast 3 Inner mast 4 Fork 5 Bracket 10 Controller 11 Electromagnetic proportional control valve 14 Seat switch 16 Hydraulic line 17 Oil pressure sensor 24 Position sensor 24a Position sensor signal line 25 Controlled amount extraction means 26 Manipulated amount /Controlled amount correspondence table 26a Standard operation table 26b Low speed operation table 27 Controlled amount output means 29 Judgment means 30 Lever lowering detection sensor 31 Limit control amount extraction means 32 Load/Limit control amount correspondence table 33 Comparison means 34 Disconnection detection means 50 Battery 51 Disconnection indicator 120 CPU 121 Clock generator 122 Memory 123 A/D converter 124 Interface 125 Solenoid valve drive unit 126 Power supply circuit S1 Lever operation signal S2 Flow rate control signal S2a Flow rate control signal S2b Flow rate control signal

Claims (1)

[Claims] [Claim 1] A controller that outputs a flow rate control signal to an electromagnetic proportional control valve in accordance with a lever operation signal from a work equipment lever, and supplies and discharges pressure oil to and from a work equipment cylinder in accordance with the flow rate control signal from the controller. In a forklift control device equipped with an electromagnetic proportional control valve and a work equipment cylinder that expands and contracts with pressure oil from the electromagnetic proportional control valve to raise and lower the fork, the flow rate is lower than the standard flow rate control signal in response to a lever operation signal. a low-speed operation table that corresponds to a control signal; a position sensor that detects when the lift height of the fork falls below a certain level; a lever lowering detection sensor that detects the lowering position of the work equipment lever; and the position sensor. When it is detected that the lift height of the fork has become below a certain level, and when the lowering position of the work equipment lever is detected by the lever lowering detection sensor, the flow rate read from the low-speed operation table A control device for a forklift, comprising: a control amount output means for outputting a control signal; and a wire breakage detection means for detecting a wire break in the signal system of the position sensor and stopping the various controls.