JPS6339520B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a forklift truck, and more particularly to a forklift automatic lifting/lowering speed control device for a forklift truck.

In the cargo handling equipment of forklift trucks,
In order to effectively carry out cargo handling operations, it is necessary to smoothly control the lifting and lowering speed of the forks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fork lift speed control device for a forklift truck to which the present invention is applied will be described below with reference to the accompanying drawings.

FIGS. 1 and 2 show a forklift truck to which the present invention is applied, and numeral 1 designates a pair of left and right mast parts pivotably mounted to the front of the vehicle body. The mast part 1 includes an outer mast 1a and this outer mast 1.
It is composed of an inner mast 1b that is slidably provided on the inner mast 1b, and a fork 2 is attached to the inner mast 1b via a lifting part 7 fitted so as to be able to be lifted and lowered along the inner mast 1b. There is. A lift cylinder 3a is disposed on the outer mast 1a, and a chain wheel support 4 is fixed to the upper end of a piston rod 3b extending from the cylinder 3a. 5 is provided. A lift chain 6 has one end connected to the fork 2 or the lifting section 7, and the other end connected to a fixed member such as the cylinder 3a.

Therefore, when the unloading lever 8 or the servo mechanism is operated, the lift cylinder 3a is controlled via the control valve 17, and the piston rod 3b is
The fork 2 is raised and lowered by the vertical movement of the fork. In this case, since the chain 6 is fixed on one side, the chain wheel 5 rotates. As a result, the engagement portion of the chain 6 with the wheel 5 changes, and the chain 6 appears to be transported.

As shown in FIG. 3, a pulse signal is emitted each time the rollers of the chain 6 pass near an electromagnetic pulse pickup (or an optical one) 10. As shown in FIG.

FIG. 4 shows a conventional cargo handling control system for a forklift truck. In the figure, 12 is a microcomputer which is an arithmetic processing unit, and 13 is a servo motor that operates in response to a valve opening command signal _S1 from the computer 12. 14, a control circuit 15 and a clutch 16.
has. 17 is a correction signal from the drive circuit 13
This is a control valve that controls the valve opening according to S ₂ and S ₃ . 18 is an oil tank, 19 is a hydraulic pump, 2
0 is a pump drive unit for driving the hydraulic pump 19, which is an engine or a motor.

According to the device configured as described above, the opening degree of the hydraulic control valve 17 is adjusted via the servo motor 14 and the clutch 16 in order to control the speed of the upper (lower) load to a certain value (mainly medium or low speed). conduct. The set speed is stored in the microcomputer 12,
Compare with the actual speed signal from the lift height sensor 10,
A correction signal (valve opening correction signal) is generated based on the error.
It outputs S ₂ and S ₃ and corrects the opening degree of the control valve to control the lifting height and speed. However, for example, after the speed increase correction signal is output, it takes several tens to hundreds of milliseconds for the servo motor 14 to rotate, open the valve, and increase the actual lifting speed, and the lifting speed changes with respect to the valve opening. is steep, so if the lift height sensor continues to issue a speed increase command until the actual speed increases to the set speed, and when the error disappears and a command to stop the servo motor is issued, the servo motor 14 will lose its inertia. The valve will stop when held, but since the valve opening is large, the speed will become too high, and the same reverse action will occur in the direction of closing the valve, resulting in a lack of smoothness and unstable speed. It was hot.

The present invention eliminates the above-mentioned drawbacks, and its purpose is to use a computer to set the speed in multiple stages, and to compare and calculate the actual speed with these settings and adjust the speed one step at a time. The object of the present invention is to provide a high performance and highly reliable cargo handling control device for a forklift truck.

A cargo handling control device for a forklift truck according to an embodiment of the present invention will be described below.

FIG. 5 shows the cargo handling control device according to this embodiment, where 30 is an arithmetic processing unit used in the present invention, such as a microcomputer, and 31 is a digital command signal S ₆ from the microcomputer 30 for setting the valve opening as an analog signal. This is a digital-to-analog converter (DA converter) that converts the signal _S7 . 32 is a matching circuit that receives the valve opening setting signal S ₇ from the DA converter 31 as one input; 33 is an amplifier that amplifies the deviation output signal S ₈ of the matching circuit 32; ₉ , the servo motor drive circuit 13 operates. Drive circuit 1
3 has a bridge circuit made up of transistors 34 to 37, and this bridge circuit is connected to a DC power source 51. Reference numeral 38 denotes a return potentiometer that operates in conjunction with the servo motor 14, and a feedback signal S10 is input from this return potentiometer ₃₈ to the matching circuit 32. 39 is a gear that operates in conjunction with the clutch 16; 40 is a lever fixed to the shaft of the gear 39; this lever 40 is attached to one end of springs 41a, 41b, and the other end of these springs 41a, 41b; is fixed. The valve 17 is provided with a spool that controls the opening and closing of the valves communicating with the pipes 42c and 42d, and this spool is connected to the lever 40.

In the cargo handling control device having the above configuration, the digital command signal _S6 from the computer 30 is converted into an analog signal by the DA converter 31, and the analog signal is input to the matching circuit 32 as the valve opening setting signal _S7 . Then, the servo motor drive circuit operates in accordance with the signal S ₉ obtained by amplifying the deviation signal S ₈ between the signal S ₇ and the feedback signal S ₁₀ from the return potentiometer 38, and the servo motor drive circuit operates to rotate the servo motor 14 at a predetermined speed. Angle is determined. That is, the signal
When transistors 34 and 35 are turned on in response to _S9 , the servo motor 14 rotates in the right direction, and when transistors 36 and 37 are turned on, it rotates in the opposite direction. The lever 40 rotates in accordance with this rotation angle, thereby determining the valve opening degree and the moving speed of the cylinder 3b of the lifting/lowering drive unit 3. A pulse signal _S5 from the lift height sensor, that is, the pulse generator 10, is input to the computer 30 in accordance with the moving speed of the cylinder 3b.

A predetermined set speed is set in the computer 30, and the actual speed of the fork section, that is, the cylinder 3b is compared with the set speed, and a command signal _S6 is output. The DA conversion circuit 31 generates a voltage in response to the command signal S ₆ and inputs it to the matching circuit 32 . However, the speed of the fork section 2 is as shown by curves l ₁ and l ₂ in FIG. 7. l ₁ is the characteristic curve at no load, and l ₂ is the characteristic curve at load. When the valve opening degree θ _{is 0} , it will not increase even with no load. At θ ₁ , it is at full speed when there is no load, but it does not move at all when it is loaded. At θmax, which is the maximum opening, full speed is reached even under load. Therefore, the range between θ ₀ and θmax is divided into multiple steps, for example, 50 steps, and a command signal corresponding to each opening degree is output from the microcomputer.

FIG. 6 shows the execution operation of the computer 30, in which block 43 is a time judgment section and block 44 is a time judgment section.
is used to compare the current speed and the reference speed.
Block 45 commands speed increase when the current speed is less than the reference speed, block 46 commands deceleration when the current speed is greater than the reference speed, and block 47 commands when the current speed matches the reference speed. It is an order to maintain the status quo when there is a crisis. Block 48 is a timer reset section, block 49
is the timer start part. That is, the computer 30 performs the following execution operations.

When the speed detection signal _S5 is fed back to the computer 30 from the lift height sensor 10, block 4
3, it is determined whether the timer setting time has elapsed, and if it has not elapsed, the signal is blocked again (43).
It will be returned. If several tens of milliseconds have elapsed, an execution operation is performed in block 44, and if the current speed is less than the reference speed, block 45 is executed and a command to increase the speed by +1 step is sent to block 48 for resetting the timer. do. If the current speed is greater than the reference speed, block 46 is executed and issues a command to decelerate by -1 step, and if the current speed is equal to the reference speed, block 47 issues a command to maintain the current state. Block 48 performs a timer reset, after which block 49 executes a timer start and feeds back to block 43.

In the speed control device shown in FIG. 5, a computer 30 issues a command signal _S6 having a binary code of 0 to 50 in response to a speed signal from a pulse generator 10 that corresponds to the moving speed of the piston 3b. As shown in FIG. 8, the DA converter 31 converts the command signal _S6 into an analog signal according to the code signal and generates a voltage signal, and this voltage signal becomes the valve opening setting signal _S7 . A valve opening setting signal S ₇ and a feedback signal S ₁₀ from a return potentiometer 38 are input to the matching circuit 32 . The amplifier 33 amplifies the deviation signal S ₄ of these signals S ₇ and S ₁₀ and inputs the output signal S ₉ to the servo motor drive circuit 13. In the servo motor drive circuit 13, a transistor 37, which is a switching element, is turned on and off by a signal _S9 , and the rotation of the servo motor 14 is controlled. The opening degree of the control valve 17 is determined according to the rotation of the servo motor 14, thereby controlling the amount of oil flowing into and out of the cylinder 3a from the hydraulic pump 19 through the pipes 42a to 42d, and controlling the moving speed SP of the piston 3b.

Furthermore, according to the above-mentioned cargo handling control device, the next correction signal increases or decreases by only one step depending on the difference between the actual speed and the set speed after a time delay of several tens of milliseconds after the previous correction signal is output. Not done. If the set speed and actual speed almost match and there is no need for correction, the valve opening at that time is maintained.

As explained above, in the forklift cargo handling control device of the present invention, after the correction signal is output, the next correction is made after waiting for a change in speed to occur due to the output of the correction signal, thereby preventing excessive correction.
In addition, since the adjustment step of the valve opening is sufficiently small, the servo motor rotates only a small amount, so that there is almost no overshoot due to inertia. Furthermore, since the valve opening change step is sufficiently small, the resulting speed change is slight, and sudden speed changes can be prevented.

In addition, the servo motor drive circuit is controlled based on the deviation between the valve opening correction signal created by feedback of the detection signal of the speed detection section and the one created by feedback of the detection signal of the rotational position detector, and the feedback system is Since the structure is heavy, speed control can be performed without delay in operation due to hydraulic control.

Therefore, it is possible to obtain a cargo handling control device for a forklift truck that can stably control the loading and unloading speeds and has high performance and high reliability, and the effects of the present invention are great.

[Brief explanation of drawings]

Fig. 1 is a front view of a forklift truck to which the present invention is applied, Fig. 2 is a side view thereof, Fig. 3 is a detailed view of the speed detection section, Fig. 4 is a block diagram of a conventional cargo handling control device, and Fig. 4 is a block diagram of a conventional cargo handling control device. Fig. 5 is a block diagram of the cargo handling control device according to the embodiment of the present invention, Fig. 6 is a flowchart of the microcomputer, Fig. 7 is a speed characteristic diagram of the fork section, and Fig. 8 is a valve opening diagram in response to a command signal from the microcomputer. FIG. 3 is a characteristic diagram showing the relationship between temperature setting signals. 3... Lifting drive unit, 3a... Cylinder, 3b... Piston rod, 10... Speed detector, e.g. pulse generator, 13... Servo motor drive circuit, 14... Servo motor, 17... Control valve, 19... Hydraulic pump, 30... Calculation Microcomputer as a processing unit, 31...D-A converter, 32... Matching circuit, 3
8...Reply potentiometer.

Claims (1)

[Scope of Claims] 1. A mast section vertically installed on a forklift vehicle body, a fork movably provided on the mast section, a drive section that drives the fork up and down, and a lifting operation of the drive section. a speed detection unit that detects the moving speed of the fork and issues a speed detection signal; a timer in which a predetermined operating time is set; and a drive control unit that controls the speed detection unit after the operating time of the timer has elapsed. a comparison section that compares the detection signal and a preset speed setting signal; hand,
and a command section that outputs a command signal in which the control range from zero to the maximum is divided into a predetermined number of steps, and each step is added to, subtracted from, or maintained as the previous output. , the drive control unit includes a servo motor and a servo motor drive circuit that rotationally controls the servo motor;
A hydraulic control valve whose opening degree is controlled according to the rotation of the servo motor, a rotational position detector interlocked with the servo motor, and a deviation between a detection signal of the detector and a command signal issued from the command section. A cargo handling control device for a forklift truck, comprising means for controlling the servo motor drive circuit based on a signal, and for resetting and starting the timer upon completion of the control operation.