JPH0640677A - Load drop prevention circuit for load lifting device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] The purpose is to prevent the risk of dropping the load because it cannot hold the load due to a decrease in the braking means of the load lifting device, which reduces the braking torque. [Structure] When the electric motor 4 that drives the load lifting device 5 is stopped and the braking means is operated to hold the load 7, if the braking torque of the braking means decreases for some reason, the load 7 falls. The electric motor 4 is rotated as the load 7 falls, and the speed detecting means detects the rotational speed of the electric motor 4. Since the speed command value is zero when the stop command signal is issued,
If the speed mismatch detecting means detects that the difference between the speed command value and the speed detection value exceeds a predetermined value, it is judged that the braking means is abnormal, and the electric motor 4 is given a command to operate at zero speed. To be As a result, the electric motor 4 generates a torque for holding the load 7, and the load 7 can be prevented from dropping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can prevent a load from falling even if the braking means of a load lifting device driven by an electric motor operating at a desired rotation speed fails. Regarding the circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the structure of a load lifting device driven by an electric motor which operates at a variable speed. This Figure 3
In the conventional example shown in FIG. 1, the electric power from the power supply 2 is converted into AC power of a desired voltage and frequency by the inverter 3 as power conversion means, and the induction motor 4 is operated at a variable speed with this AC power. Since the hoisting device 5 as a load lifting means is coupled to the induction motor 4, the load 7 can be lifted and lowered at a desired speed. The operating procedure of the hoisting device 5 is as follows. That is, first, the operation instruction contact 12 is operated to give an operation instruction signal to the inverter 3 via the control device 10 to start the inverter 3. Next, when the speed setter 11 is set to a desired value, the AC power having the voltage and frequency corresponding to the speed command value set by the speed setter 11 is applied from the inverter 3 to the induction motor 4, so that the hoisting device 5 operates as described above. The load 7 is raised or lowered at a speed corresponding to the speed command value of. In the case of suspending this cargo handling work, after the speed command value output by the speed setter 11 is returned to zero, the stop command contact 13 is operated to give a stop command signal to the inverter 3 via the control device 10. As a result, the AC output of the inverter 3 is cut off, and at the same time, the brake 6 operates to hold the load 7 at a predetermined position.

[0003]

As described above, the brake 6 is used.
If the braking torque decreases due to foreign matter adhering to the braking friction surface to reduce the friction coefficient or the brake 6 breaks down while the load is operating and the load 7 is held, the hoisting device No. 5 cannot hold the load 7 and falls, which is extremely dangerous.

SUMMARY OF THE INVENTION An object of the present invention is to prevent the risk of dropping the load because it cannot hold the load due to a decrease in the braking torque due to an abnormality in the braking means of the load lifting device.

[0005]

In order to achieve the above object, a load drop prevention circuit of a load lifting device according to the present invention comprises an electric motor and a power conversion means for supplying electric power for operating the electric motor at a desired rotation speed. And a start / stop command means for outputting a signal for instructing the start or stop of the electric motor, a speed setting means for setting a signal for instructing the rotation speed of the electric motor, and a load driven by the electric motor. In a load lifting device including load lifting means for lifting and lowering the motor and braking means for preventing the load from falling when the electric motor is stopped, speed detection means for detecting the rotation speed of the electric motor is provided, and the start / stop command is provided. If the speed detecting means detects a rotation speed other than zero while the means outputs the stop command signal, the logic circuit may be provided to instruct the motor to operate at the zero rotation speed. However, in this logic circuit, the speed detection means for detecting the rotation speed of the electric motor and the difference between the speed detection value output by the speed detection means and the speed command value output by the speed setting means exceed a predetermined value. A speed disagreement detecting means, a logical product means for calculating a logical product of the speed disagreement signal and the stop command signal, and a time delay means for detecting that the output signal of the logical product means continues for a predetermined time. A configuration including a logical sum means for calculating a logical sum of the output signal of the time limit means and the operation command signal, and the speed setting means sets the speed command value to zero in response to the output signal of the logical sum means. The zero speed command value is set and the electric motor is operated.

[0006]

According to the present invention, when the motor for driving the load lifting device is stopped and the braking means is operated to hold the load, if the braking torque of the braking means decreases for some reason, the load falls. The electric motor is rotated by the drop of the load, and the speed detecting means detects the rotational speed of the electric motor. Since the speed command value is zero when the stop command signal is issued,
If the difference between the speed command value and the speed detection value is greater than or equal to a predetermined value, it is determined that the braking means is abnormal, and a command is given to the electric motor to operate at zero speed. As a result, the electric motor can generate a torque for holding the load and prevent the load from dropping.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a load lifting device showing a first embodiment of the present invention. A power source 2, an inverter 3 as a power converting means, an induction motor 4, a load lifting device shown in FIG. Hoisting device 5 as a means, brake 6, load 7,
The names, applications, and functions of the control device 10, the speed setting device 11, and the operation command contact 12 and the stop command contact 13 as the start / stop command means are the same as those in the conventional example described above in FIG.
These explanations are omitted.

In the present invention, a speed detector 19 for detecting the rotation speed of the induction motor 4 is connected to the induction motor 4. However, the induction motor 4 has a speed control loop,
In this case, when the speed control is performed, the speed detecting means is connected to the electric motor, so that it may be diverted. The speed detection signal from the speed detector 19 and the operation command contact 12
And the stop command signal output from the stop command contact 13 are input to the logic circuit 20. This logic circuit 20 is provided with a speed mismatch detecting means for detecting whether or not the difference between the speed command value set by the speed setter 11 and the speed detection value detected by the speed detector 19 is a predetermined value or more, If the speed disagreement is equal to or more than a predetermined value, the logical product of this and the stop command signal is calculated, and the logical product calculation result is output from the logic circuit 20. This is the zero speed operation command signal 3
0, and the zero speed operation command signal 30 is transmitted to the control device 1
Enter 0. As a result, the induction motor 4 generates a torque commensurate with the weight of the load 7, so that the load 7 does not drop even if the brake 6 fails and the braking torque decreases.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, which shows the configuration of the logic circuit 20 used in the first embodiment described above with reference to FIG. It is as follows. The speed command value set by the speed setter 11 and the speed detection value detected by the speed detector 19 are input to a comparator 21 as speed mismatch detecting means, and the comparator 21 outputs the first value when the difference between both inputs exceeds a predetermined value. 1 relay 22
Output an operation signal to. On the other hand, the second relay contact 23B is closed when the stop command contact 13A is activated to release the self-holding of the second relay 23. At this time, the first relay 22 operates by receiving the signal from the comparator 21 described above. For example, the contact 22A of the first relay 22 is closed. The second relay contact 23B and the first relay contact 22A are connected in series to form a logical product circuit. If the output of the serial connection circuit, that is, the logical product circuit excites the timer 24 as the time delay means. After a certain period of time, the contact 24A of the timer 24 closes and the third relay 25 operates.

The second relay 23 outputs a command signal to start or stop according to its operating state. The contact point 23C of the second relay 23 and the contact point 25 of the third relay 25.
B is connected in parallel to form an OR circuit. Therefore, even if the second relay contact 23C is in the open state (that is, the command to stop the induction motor 4 is issued), if the load 7 drops and a difference is generated between the speed command value and the speed detection value as described above. The third relay contact 25B is closed, and the zero speed operation command signal 30 is given from the logic circuit 20 to the control device 10. At the same time, the third relay contact 25C is also closed to notify that the brake 6 has an abnormality.

[0011]

According to the present invention, when the load elevating device is driven by the electric motor operating at a variable speed, the braking means is operated to hold the load when the operation of the electric motor is interrupted. If the speed mismatch detecting means detects that the difference between the speed command value and the speed detection value exceeds a predetermined value, even if a stop command is given to the electric motor, a command to operate this electric motor at zero speed is given. A logic circuit is provided.
If the braking means that holds the load fails and the braking torque decreases, the load falls, but when the motor starts to rotate due to the drop of the load, the above-mentioned logic circuit issues a command to operate this motor at zero speed. As a result, the electric motor generates a torque commensurate with the weight of the load, so that a large accident in which the load falls due to a failure of the braking means can be prevented. When the speed of the electric motor operating at a variable speed is controlled by the speed control loop, the electric motor rotation speed detecting means is already installed and can be used. Therefore, when the present invention is applied, the cost of the speed detecting means becomes unnecessary, and the installation cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a load lifting device showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a load lifting device driven by an electric motor that operates at a variable speed.

[Explanation of symbols]

 3 Inverter as power conversion means 4 Induction motor 5 Hoisting device as load lifting means 6 Brake 7 Load 10 Control device 11 Speed setting device 12 Operation command contact as start / stop command means 13 Stop command contact as start / stop command means 19 Speed detector 20 Logic circuit 21 Comparator as speed mismatch detection means 22 First relay 23 Second relay 24 Timer as time delay means 25 Third relay 30 Zero speed operation command signal

Claims (2)

[Claims] 1. An electric motor, power conversion means for supplying electric power for operating the electric motor at a desired rotation speed, and start / stop command means for outputting a signal for instructing the start or stop of the operation of the electric motor. A speed setting means for setting a signal for instructing a rotation speed of the electric motor, a load elevating means for elevating and lowering a load driven by the electric motor, and a braking means for preventing the load from falling when the electric motor is stopped. In the load lifting device, which is provided with speed detection means for detecting the rotation speed of the electric motor,
If the speed detection means detects a rotation speed other than zero when the start / stop command means outputs a stop command signal, a logic circuit for instructing the motor to operate at zero rotation speed is provided. Load drop prevention circuit for the load lifting device. 2. An electric motor, power conversion means for supplying electric power for operating the electric motor at a desired rotation speed, and start / stop command means for outputting a signal for instructing the start or stop of the operation of the electric motor. A speed setting means for setting a signal for instructing a rotation speed of the electric motor, a load elevating means for elevating and lowering a load driven by the electric motor, and a braking means for preventing the load from falling when the electric motor is stopped. In the load lifting device, the speed detection means for detecting the rotation speed of the electric motor and the difference between the speed detection value output by the speed detection means and the speed command value output by the speed setting means exceed a predetermined value. That the output signal of the logical product means continues for a predetermined time, and a logical product means for calculating the logical product of the speed mismatch signal and the stop command signal. And a logical sum means for calculating the logical sum of the output signal of the time limit means and the operation command signal, and the speed setting means corresponds to the output signal of the logical sum means. A load drop prevention circuit for a load lifting device, wherein a command value is set to zero and the electric motor is operated at the zero speed command value.