JP2002354883A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator which can protect a motor by preventing an excessive current flow into the motor and also prevent breakdown of the actuator itself and devices in the side to be driven. SOLUTION: This electric actuator comprises a motor 20 coupled with a load, a current sensor 28 for detecting a current flowing into the motor, a comparator 31 for comparing the current value detected with the current sensor 28 with the predetermined current comparison setting value, a current control circuit (FET chopper switch 29, PWM controller) for limiting the motor current depending on an output of the comparator 31, and a current limiting time detecting circuit (current sensor 28, comparator 31 and current limiting time setting circuit 32) for detecting the time where the motor current is limited with the current controller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric actuator used in a lifting device driven by an electric motor.

[0002]

2. Description of the Related Art Instead of a hydraulically driven forklift, an electric forklift using an electric motor has been developed for miniaturization, compact structure, and low cost. In this electric forklift, a drive shaft is connected to an output shaft of an electric motor via a reduction gear mechanism.
Combine the feed screw mechanism consisting of drive screw and moving nut,
The moving nut is connected to a fork (elevator) that receives a load via a connecting link. The electric motor is rotatable in the forward and reverse directions, and moves the luggage on a fork while lifting and lowering the luggage and transporting the luggage.

[0003]

However, in such an electric forklift, when an excessive load is applied and an overload operation is performed, an excessive current exceeding a rated value flows to the electric motor, and the electric forklift is operated. It burns out or deteriorates, shortening its life. Further, when the motor is started, an excessive thrust due to an excessive current exceeding the rating may be generated, which may cause an impact on the actuator itself or a device on the driven side, and may cause damage or deterioration.

The present invention has been made in consideration of the above-mentioned prior art, and protects the motor by preventing an excessive current from flowing through the motor, and at the same time, protects the actuator itself and the equipment on the driven side from being damaged. The purpose is to provide an actuator.

[0005]

In order to achieve the above object, according to the present invention, there is provided a motor on which a load acts, a current sensor for detecting a current flowing through the motor, and a current value detected by the current sensor. A current comparison setting value, a current control circuit for limiting the motor current according to an output of the comparison unit, and a current limit time detection for detecting a time when the motor current is limited by the current control circuit. An electric actuator characterized by comprising a circuit.

According to this configuration, the value of the current flowing through the motor is detected, and when this current value is larger than a predetermined value, the current to the motor is limited to prevent the generation of excessive thrust, and the actuator itself and the driven Prevent equipment damage. Further, by detecting the current limiting time to the motor, when the time during which the current is limited is equal to or longer than a predetermined value, it can be determined that an abnormal load is acting.

In a preferred configuration example, a protection switch circuit is provided which cuts off the current to the motor when the current limit time detected by the current limit time detection circuit is larger than a predetermined set value.

According to this configuration, when the current limitation to the motor continues for a predetermined time or more, it is determined that the motor is abnormal, and the current to the motor is automatically cut off to protect the motor.

Another preferred configuration is characterized in that it comprises an alarm means for issuing an alarm when the current limit time detected by the current limit time detection circuit is larger than a predetermined set value.

According to this configuration, when the current limit to the motor has continued for a predetermined time or more, an abnormal state is determined and an alarm signal is output, whereby the operator recognizes the abnormal state and quickly responds to the abnormality. it can.

In a further preferred configuration, the current control circuit comprises a PWM control circuit.

According to this configuration, the power loss can be reduced by the pulse width modulation method, the power consumption of the battery can be suppressed, and the device can be downsized with a compact configuration.

In a further preferred embodiment, the motor is a forward / reverse rotatable DC motor for an elevating device, and includes a limiting current value setting circuit for automatically switching the current comparison set value between forward rotation and reverse rotation. It is characterized by that.

According to this configuration, the set value of the limiting current is changed between when the load state of the motor is different and when the load is different, so that the actuator is protected by the optimum limited current corresponding to the load at the time of the rising and the lowering. Is achieved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an application example of the present invention, and is a schematic view of a forklift using an electric actuator according to the present invention.

As shown, the lifting device 1 according to the present invention
The drive by the electric motor 2 rotates the feed screw mechanism 5 via the speed reduction mechanism 3 and the coupler 4. The feed screw mechanism 5 includes a driving screw 6 and a moving nut 7 which moves up and down in the direction of arrow A by the rotation of the driving screw 6, and the moving nut 7 is connected via a link lever 10 to a lifting platform (fork) for loading a load. ) 8 is connected to the connecting portion 9. The elevating table 8 moves up and down by the moving nut 7 moving up and down in the direction of arrow A, for example, by pivoting the connecting portion 9 in the direction of arrow B with the middle part of the link lever 10 as a fulcrum.
At this time, when the connecting portion 9 moves upward, the front wheel 11 housed in the lift 8 protrudes in the direction of arrow C by the link rod 12. The elevating table 8 is also connected to the upper part of the vehicle body 13 that covers the elevating device 1 by a link 14, and swings up and down in the direction of arrow D in conjunction with the movement of the connecting portion 9. The vehicle body 13 is an operation handle 1 for operating a forklift.
5 at the top.

FIG. 2 shows another application example of the present invention, and is a schematic view of a load lifting lift using the electric actuator according to the present invention. As shown, the lift comprises two arms 18 having a fixed end point (pivot axis) 16 and a moving end point 17 which are pivotally connected to each other in an X-shape at a central portion, and by changing the angle of the arms, the loading platform is changed. 19 is moved up and down. The lifting nut 1 moves the moving nut 7 in the direction of the arrow E. The moving nut 7 has one end 18 of an X-shaped arm having a fixed end point 16 and a moving end point 17.
And the other arm is connected to the coupler 4. The moving end point 17 moves in the direction of arrow F in conjunction with the movement of the moving nut 7 in the direction of arrow E. As a result, the upper moving end point 17 rotates in the direction of arrow G, and the loading platform 19 on which the load is loaded moves up and down in the direction of arrow H.

FIG. 3 is a block diagram of the electric actuator according to the present invention. The motor 20 is a battery 21
And drive-controlled by the controller 22.
The controller 22 has its output terminal 22a connected to motor control relays 23 and 24 for raising and lowering, and operating switches 25 and 26 for raising, respectively, to operate the motor 2.
Rotate 0 in forward or reverse direction. Output terminal 22a
Is an alarm circuit 2 such as an alarm buzzer or an alarm lamp.
7 and issues an alarm when an abnormal condition is detected.

As a circuit constituting the controller 22,
Current sensor 2 for detecting current flowing through motor 20
8, a FET chopper switch 29 for flowing a controlled constant current, a PWM control unit 30 for performing current control of the motor 20 by a pulse width modulation method, and a current sensor 28.
A comparison unit 31 for limiting the motor current by comparing the detection signal from the control unit with a predetermined set value, and a time during which the motor current is limited according to a comparison result of the comparison unit 31 exceeds a predetermined set delay time. In this case, a current limit time setting circuit 32 for interrupting a current is provided, and an output switch circuit 33 is provided.

The controller 22 further includes a stabilized power supply 34 for supplying operating power to each of the above circuits, and a current value setting circuit for changing the comparison set value of the output from the current sensor 28 between rising and falling. 35, and an ascending and descending operation switch delay time setting circuit 36.

FIGS. 4 and 5 are explanatory diagrams of the motor current limiting operation by the controller 22 of FIG.

FIG. 4 shows a case where a load within the rated range of the lifting device is applied. In the figure, a graph a shows ON / OFF of the control power supply, a graph b shows ON / OFF of the lift operation switch (in this case, an up switch), and a graph c shows the motor current when the motor current control is not performed (as is conventional). Graph d shows the motor current when the motor current control is performed according to the present invention. When the up switch is turned on (Graph b) while the control power supply is ON (Graph a), a large inrush current flows when the motor current rises (Graph c). The inrush current rises once and then falls to a current value equal to or less than the rated current Is corresponding to a predetermined rated load.

In the present invention, the motor current is compared with a predetermined set current value Is, and as shown in a graph d, when the motor current rises and exceeds the set current value Is, the constant current value The motor current is limited, for example, via the FET chopper switch 29 (FIG. 3) so as to be maintained at Is.
When the motor current is equal to or smaller than the set current value Is, this current limitation is not performed.

Further, according to the present invention, when the time t during which the motor current is limited exceeds a predetermined time Ts, the motor current is cut off and an alarm is issued. FIG.
In the example, since the motor current is equal to or less than the set current value Is within the set time Ts, it is determined that the motor current is normal, and the motor current is passed as it is to continue the ascending operation.

FIG. 5 shows a case where an excessive load exceeding the rated value is applied to the lifting device. In FIG. 5, graph a shows ON / OFF of the control power supply, graph b shows ON / OFF of the lift operation switch (in this case, the up switch), and graph c.
Represents the motor current when the motor current control is not performed (as it is conventionally), graph d represents the motor current when the motor current control is performed according to the present invention, and graph e represents the overload alarm output.

As in the case of FIG. 4, the control power supply is turned on.
When the up switch is turned on in the state (graph a) (graph b), the motor current rises and a large rush current flows (graph c). This inrush current rises once and then falls. In the example of FIG. 5, when the inrush current decreases, the state exceeds a predetermined set value Is. This indicates that the motor is overloaded beyond the rated value.
If the motor current continues to flow in this overloaded state as shown in graph c, the motor will burn or deteriorate.

In the present invention, as in the case of FIG.
The motor current is compared with a predetermined set current value Is, and FIG.
As shown in the graph d, when the motor current rises and exceeds the set current value Is, the motor current is limited so as to be maintained at the constant current value Is.

Further, in the present invention, when the time t during which the motor current is limited exceeds Ts as compared with the predetermined time Ts, the motor current is cut off and an alarm is issued. FIG.
In the example, since the motor current limit time t has reached the set time Ts, it is determined that the motor is in an abnormal state, and the relay is activated to cut off the current to the motor. Thereby, the graph e
As shown in the figure, an alarm is output. Alarm is O of control power supply.
Reset by FF.

FIG. 6 is a flowchart showing the operation of the electric actuator of the present invention. The operation of each step is as follows. Step S1: The lifting switch is manually operated to raise or lower the luggage stand of the lifting device. Step S2: Determine whether the up / down switch is on the up side or down side.

Step S3: When the up / down switch is on the up side, the limiting current value Is (see FIGS. 4 and 5) is set to the up current value. Step S4: When the up / down switch is on the down side, the limiting current value Is is set to the down current value. Note that the set value for descending is smaller than the set value for ascending.

Step S5: A motor current value is detected by a current sensor. Step S6: The detected motor current is converted to the above-mentioned step S6.
Compare with the limit current value Is set in 3 or S4.

Step S7: Motor current is limited current value I
If s is exceeded, the motor current is maintained at a constant current of the limited current value Is by pulse width modulation control. Step S8: The time during which the motor current is limited in step S7 is compared with a preset time Ts (see FIGS. 4 and 5).

Step S9: When the current limit time exceeds Ts, an alarm is output and a shutdown signal is output to stop the current to the motor and stop driving the motor. This is performed by turning off the elevating switch via a relay (graph b in FIGS. 4 and 5).

Step S10: The control power is turned off to stop the system operation. Step S11: If the current is less than or equal to the current limit Is in step S6 and if the current limit time is less than or equal to Ts in step S8, the ascent / descent operation is continued.

[0035]

As described above, according to the present invention, the value of the current flowing through the motor is detected, and when this current value is larger than a predetermined value, the current to the motor is limited to prevent the generation of excessive thrust. To prevent the actuator itself and driven equipment from being damaged. Further, by detecting the current limiting time to the motor, when the time during which the current is limited is equal to or longer than a predetermined value, it is possible to determine that an abnormal load is acting, and thereby the abnormal When the state is detected, the current to the motor is automatically cut off to protect the motor.

[Brief description of the drawings]

FIG. 1 is a schematic view of a forklift using an electric actuator according to the present invention, showing an application example of the present invention.

FIG. 2 is a schematic view of a lift using an electric actuator according to the present invention, showing another application example of the present invention.

FIG. 3 is a block diagram of an electric actuator according to the present invention.

FIG. 4 is an explanatory diagram of a constant current control operation within a rated load range.

FIG. 5 is an explanatory diagram of a constant current control operation when the load exceeds a rated load.

FIG. 6 is a flowchart showing the operation of the electric actuator of the present invention.

[Explanation of symbols]

1: lifting device, 2: electric motor, 3: reduction mechanism, 4: coupler, 5: feed screw mechanism, 6: driving screw, 7: moving nut, 8: lifting table, 9: connecting portion, 10: link lever, 1
1: front wheel, 12: link rod, 13: body, 14: link, 15: operation handle, 16: fixed end point, 17: moving end point, 18: arm, 19: bed, 20: motor, 2
1: battery, 22: controller, 23: relay,
24: relay, 25: up switch, 26: down switch, 27: alarm circuit, 28: current sensor, 29: FET
Chopper switch, 30: PWM control unit, 31: comparison unit, 32: current limit time setting circuit, 33: output switch circuit, 34: stabilized power supply, 35: current value setting circuit, 3
6: Delay time setting circuit 36.

Claims (5)

[Claims] 1. A motor on which a load acts, a current sensor for detecting a current flowing through the motor, a comparison unit for comparing a current value detected by the current sensor with a predetermined current comparison set value, and the comparison unit An electric actuator, comprising: a current control circuit that limits the motor current according to the output of the current control circuit; and a current limit time detection circuit that detects a time during which the motor current is limited by the current control circuit. 2. The protection switch circuit according to claim 1, further comprising a protection switch circuit for cutting off a current to the motor when the current limit time detected by the current limit time detection circuit is larger than a predetermined set value. The electric actuator according to any one of the preceding claims. 3. The electric motor according to claim 1, further comprising an alarm unit for issuing an alarm when the current limit time detected by the current limit time detection circuit is larger than a predetermined set value. Actuator. 4. The electric actuator according to claim 1, wherein said current control circuit comprises a PWM control circuit. 5. The motor according to claim 1, wherein said motor is a DC motor capable of forward / reverse rotation for a lifting / lowering device, and further comprises a limiting current value setting circuit for automatically switching said current comparison set value between forward rotation and reverse rotation. The electric actuator according to any one of claims 1 to 4, wherein