TW201615533A - Lifting device and stacker type crane and method of maintaining height of lifting platform - Google Patents

Abstract

The subject of the present invention is to prevent overload error of a servomotor for lifting. The lifting device comprises: a mechanism part for raising and lowering a lifting platform; and a servomotor for raising and lowering the lifting platform by means of a driving mechanism part, wherein when the lifting process of the lifting platform is stopped to maintain the height, the servomotor is controlled in a manner of using the servomotor to only lower the lifting platform by a predetermined height after the lifting platform has been stopped.

Description

Height keeping method of lifting device and stacking crane and lifting platform

The invention relates to a lifting device and a stacker crane, in particular to the maintenance of the height of the lifting platform.

Patent Document 1 (Japanese Patent No. 4962535) discloses a stacker crane that lifts a lifting platform by a servo motor. Here, if the height of the lifting platform is maintained by the servo motor itself, and the brake is not provided, the stacking crane can be made lighter.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent 4962535

The inventors have found that if the brake of the fixed lifting platform is not provided and the weight that balances the weight of the lifting platform is not provided, the torque of the servo motor will increase to near the rated torque after the lifting platform is stopped. There is a situation that causes an overload error. Therefore, an object of the present invention is that when the elevating table is stopped and the height is maintained by the torque of the servo motor, an overload error due to an increase in torque does not occur.

The present invention relates to a lifting device including: a mechanism unit that elevates and lowers a lifting platform; and a servo motor that elevates and lowers the elevating platform by a driving mechanism unit, wherein the control unit includes a control unit and a control unit When the lifting and lowering of the lifting platform is stopped and the height is maintained, the servo motor is controlled such that the lifting table is lowered by a predetermined height only by the servo motor after the lifting platform is stopped.

Moreover, the present invention is a method for maintaining the height of a lifting platform in a lifting device comprising: a mechanism portion for lifting the lifting platform; and a servo motor for lifting the lifting platform by the driving mechanism portion A method for maintaining the height of the lifting platform is characterized in that, when the lifting and lowering of the lifting platform is stopped and the height is maintained, the lifting table is lowered by a predetermined height by the servo motor after the lifting platform is stopped.

The inventors found the following.

‧When the lifting platform is raised and stopped, or when the lifting platform is lowered and stopped, the torque required to maintain the height of the lifting platform is raised or lowered before the lifting platform is stopped. Change in state.

‧When the elevator is in the ascending state before the stop, the torque of the servo motor will increase after stopping, and will remain at a higher value thereafter.

‧ Since the lifting platform is lifted and lowered by the servo motor, even if it is stopped after the rise, there is a case where it is overshooted and then lowered before the stop. Moreover, in the case of stopping after the descent, there is also a case where the overshoot is performed before the stop is stopped.

‧The holding torque will become smaller when it is in a falling state before stopping, which means that the force from the mechanism is opposed to the falling of the lifting platform, and the force is still after the stopping be kept. Further, the holding torque is increased when the vehicle is in the ascending state immediately before the stop, which means that the force applied from the mechanism portion against the rise of the lifting platform is maintained, and the force is maintained after the stop.

‧If the servo motor only drops a slight height after the stop of the lifting platform, the height of the lowering is small and the lowering speed of the lifting platform is small. Therefore, the lifting platform does not undershoot, and the lifting platform stops while descending. .

Therefore, if the elevator is to be lowered by a predetermined height by the servo motor after the stop of the elevator, the torque required to maintain the height of the elevator is reduced, and the overload of the servo motor can be prevented. Furthermore, in the present specification, the description of the lifting device is applicable to both the stacking crane and the height maintaining method of the lifting platform.

Preferably, the control unit is configured to monitor the torque of the servo motor after the suspension platform is stopped, and to lower the elevation of the servo motor only when the torque of the servo motor is equal to or greater than a predetermined threshold. The torque is monitored, for example, by the drive current of the servo motor. As a result, when the lifting platform stops moving up and down, if the torque required for the height is increased, the lifting platform is lowered to reduce the required torque. The effect on the cycle time of the lifting platform can be reduced compared to the case where the lifting platform is again lowered after stopping.

Preferably, the mechanism unit is configured not to have the weight of the lifting platform or the brake of the fixing mechanism portion, but to maintain the height of the lifting platform only by the torque of the servo motor. As a result, the lifting device is small and lightweight.

For example, the height raising method of the lifting device or the lifting platform of the present invention is applied to a stacker crane having a mast and a mast that is erected upward from the trolley, and the mechanism portion is housed in the mast, and the lifting platform is lifted along the mast . In this way, it is possible to prevent the servo motor from being overloaded after the elevator of the stacker is stopped. In particular, it is lightweight and small when it does not have a counterweight or a brake with a fixed mechanism. Type of high-rise crane.

Preferably, the mechanism unit includes a gear that is attached to the lower portion and the upper portion of the mast and a ring-shaped driving medium that is wound around the upper and lower gears, and the servo motor is configured to be connected to any of the upper and lower gears, and The gear is fixed by the torque from the servo motor. In this way, do not balance the weight with the brakes to maintain the height of the lifting platform.

2‧‧‧Head height crane

4‧‧‧Trolley

5‧‧‧Moving wheels

6‧‧‧ mast

7‧‧‧Connecting Department

8‧‧‧ Lifting platform

9‧‧‧Transfer device

10‧‧‧Chain

12‧‧‧Sprocket

14‧‧‧Servo motor

15‧‧‧ Torque sensor

16‧‧‧Encoder

17‧‧‧Control Department

18‧‧‧Differentiator

20‧‧‧ Position Command Generator

22‧‧‧ Comparator

24‧‧‧Speed command generator

26‧‧‧ Current command generator

28‧‧‧Servo amplifier

S1~S4‧‧‧ steps

W‧‧‧ goods

Figure 1 is a front elevational view of the stacker of the embodiment.

Fig. 2 is a block diagram showing a control portion of a servo motor in the embodiment.

Fig. 3 is a view showing the relationship between the behavior immediately before the lifting device is stopped and the torque for maintaining the height position of the lifting platform.

Fig. 4 is a flow chart showing the algorithm for maintaining the height position of the lifting platform in the embodiment.

The preferred embodiments for carrying out the invention are shown below. The scope of the present invention should be determined in accordance with the description of the scope of the claims, the description of the specification, and the well-known technology in the field, and the understanding of those of ordinary skill in the art.

[Examples]

In Figs. 1 to 4, the stacking crane 2 is taken as an example to show the lifting device of the embodiment. Furthermore, the present invention can also be applied to an overhead traveling vehicle, a lifting device for lifting the lifting platform along a fixed mast, and the like. In the figure, the component symbol 4 is a trolley and is provided with a traveling wheel 5. The component symbol 6 is, for example, a pair of right and left masts, and is coupled by the connecting portion 7. The number of the masts 6 is arbitrary, and may be, for example, one. Component symbol 8 The lifting platform is provided with a selective compliant assembly robot arm (SCARA; Selective Compliance Assembly Robot Arm) and a transfer device 9 such as a sliding fork. The lifting table 8 is lifted and lowered by, for example, the chain 10 support. The component symbol 12 is a sprocket of the chain 10, the component symbol 14 is a servo motor for lifting and lowering, and the servo motor 14 rotates the sprocket 12. Although the servo motor 14 drives the sprocket at the lower portion of the mast 6, it can also drive the upper sprocket. Further, a belt or the like may be used instead of the chain 10, and a gear or the like may be used instead of the sprocket 12. Further, the component symbol W is a cargo placed on the transfer device 9.

The stacker 2 does not have the weight of the lift table 8, thereby reducing the weight and the size of the mast 6. Further, the electromagnetic or mechanical brake that fixes the sprocket 12 by friction or the like is not provided, and the sprocket 12 is fixed by the servo motor 14, whereby the lift table 8 is held at a fixed height. Thereby, the stacker crane 2 is further lightened. Furthermore, even in the case of having a counterweight or having an electromagnetic brake or the like, the embodiment is effective when the output torque of the servo motor 14 is used for the position of the lifting platform 8.

The scope of application of the embodiment is not limited to the stacker crane 2. The overhead traveling vehicle is provided with a trolley and a hoist for lifting the lifting platform, and the embodiment can be applied to a servo motor for lifting and lowering the lifting platform of the crane. Further, the embodiment can also be applied to a lifting device or the like that does not have a trolley and has a lifting platform that moves up and down along a fixed mast.

2 shows the control unit 17 of the servo motor 14, and the component symbol 15 is a torque sensor. The torque sensor 15 measures the output torque of the servo motor 14 based on the drive current of the servo motor 14. The component symbol 16 is an encoder, and the differentiator 18 determines a speed signal related to the rotation of the servo motor 14 based on the difference in time unit of the signal of the encoder 16. Component symbol 20 is a position command generator that will lift The target value of the height position of the stage is generated as a position command. The target value of the height position is fixed at the time of stopping (when the height of the lifting platform is maintained). Further, the component symbol 22 is a comparator that compares the torque of the servo motor with a threshold. The speed command generator 24 generates a speed command based on the position command and the error in the height position obtained from the encoder 16. The current command generator 26 generates a current command based on the speed command and the error of the speed signal obtained by the differentiator 18. The servo amplifier 28 supplies a current to the servo motor 14 so as to eliminate the difference between the current command and the motor current obtained by the torque sensor 15 or the like.

The comparator 22 receives the drive current of the servo motor 14 from the torque sensor 15 and compares it with a predetermined threshold. Further, instead of the drive current, the drive voltage of the servo motor 14 or the like may be used as a signal indicating the output torque. The comparator 22 starts to operate when the elevator is stopped, and stops when the next target position is raised and lowered. When the output torque of the servo motor 14 becomes a predetermined value or more, the comparator 22 inputs a signal having its meaning to the position command generator 20, and for the signal, the position command generator 20 sets the height of the lift table. The target value of the position is lowered only by the predetermined height, and the elevator is lowered by the servo motor 14. Further, the predetermined height is determined such that the height of the lifting platform after the lowering is not lower than the allowable range, and is, for example, about 1 mm to 5 mm. When the elevating table is lowered by a predetermined height and the elevating table is stopped, the comparator 22 can be operated again or the comparator 22 can be prevented from being operated again.

If the height of the lift table is maintained by the servo motor 14, the output torque of the servo motor 14 may increase to near the rated torque. This causes an overload error of the servo motor 14. On the other hand, if the position of the elevating table is lowered before the output torque of the servo motor 14 increases to the vicinity of the rated torque, the torque required for holding the elevating table is reduced, and an overload error does not occur.

This case will be explained using FIG. The torque required to maintain the height of the lifting platform varies depending on whether the lifting platform is rising or falling before the stop is stopped, regardless of whether the lifting platform is stopped after being lifted, or when the lifting platform is lowered. More specifically, when the elevator is in the ascending state immediately before the stop, the torque of the servo motor is increased by the time constant of several tens of m seconds after the stop, and the degree of the lifting of the lifting platform is required. Torque or higher torque, and thereafter maintained at a higher value.

Since the elevator is lifted and lowered by the servo motor 14, even if it is stopped after the rise, there is a case where the overshoot is immediately stopped before the stop. Moreover, even in the case of a stop after the fall, there is a case where the overshoot is caused before the stop and then rises. Moreover, the torque required for the holding of the lifting platform is large in the case of being in a rising state immediately before the stop, and the holding torque is small in the case of the falling state. Secondly, although the holding torque of the lifting platform is the same regardless of whether the upper sprocket is connected to the servo motor or the lower sprocket is connected to the servo motor, if the cargo is present on the lifting platform, the holding torque becomes large.

The holding torque is reduced when it is in a state of being lowered immediately before stopping, which means that the force against the falling force is applied from the lifting platform to the chain, the sprocket, etc., and the force is maintained after the stopping. Conversely, the holding torque is increased when it is in a rising state immediately before the stop, which means that the force against the rise is applied from the lifting platform to the chain, the sprocket, etc., and the force is maintained after the stop. .

In the embodiment, the lifting platform is not controlled to be lowered before stopping, and the output torque of the servo motor is monitored after the lifting platform is stopped. If the torque exceeds a predetermined value, the lifting platform is only lowered by a predetermined height. . Figure 4 shows the control algorithm of the embodiment. In step S1, the lifting platform is stopped at the height position of the target, and then the target value of the height is kept fixed (step S2), and the output of the servo motor is monitored. Moment (step S3). When the output torque is equal to or greater than a predetermined value, the target height of the elevator is lowered by a predetermined height, and the elevator is lowered by the servo motor (step S4). Since the predetermined height is small and the descending speed of the lifting platform is small, the lifting platform does not undershoot, and the lifting platform stops while descending. Thereby, the torque required to maintain the height of the lifting platform is lowered, and the overload of the servo motor can be prevented.

In the embodiment, although the torque of the servo motor 14 is monitored, for example, it may be determined based on the output of the encoder immediately before the stop, or the recording of the speed command of the servo motor, or the recording of the direction of the drive current. Whether the elevator is in a rising state or a falling state before stopping. Therefore, after stopping the elevator, it is also possible to determine whether or not it is necessary to perform a small distance reduction based on the records. Moreover, regardless of whether it is in a rising state or a falling state immediately before stopping, the lifting platform can be lowered only to a predetermined height after stopping, but if it is uniformly lowered, the cycle time required for the lifting and lowering of the lifting platform becomes long, so Just use it according to the required cycle time.

The examples can obtain the following effects.

1) It is not necessary to have a counterweight or a brake such as an electromagnetic brake, so that the stacker crane 2 can be lightweight and small.

2) It can prevent the overload of the servo motor for lifting and lowering.

3) Although it is difficult to control the lifting platform while stopping and stopping, it is easier to monitor the output torque of the servo motor after stopping.

4) Since the lifting platform can be lowered as long as the output torque increases after stopping, the influence on the cycle time is small.

In the embodiment, the chain 10 and the upper and lower sprocket wheels 12 are used as the mechanism portion, but may be a toothed belt and upper and lower gears, a rack and pinion, a ball screw or the like. Moreover, the torque is affected by the absolute value, and the direction of the torque has no effect.

Claims (7)

A lifting device comprising: a mechanism portion for lifting and lowering a lifting platform; and a servo motor for moving up and down the lifting platform by a driving mechanism portion; wherein the control unit is provided with a control unit When the lifting and lowering of the lifting platform is stopped and the height is maintained, the servo motor is controlled such that the lifting table is lowered by a predetermined height only by the servo motor after the lifting platform is stopped. The lifting device according to claim 1, wherein the control unit is configured to monitor a torque of the servo motor after the elevating table is stopped, and to cause the elevating table to descend only to a predetermined height if the torque of the servo motor is equal to or greater than a predetermined threshold. The lifting device of claim 1 or 2, wherein the mechanism portion is configured to have neither the weight of the lifting platform nor the brake of the fixing mechanism portion, but only the torque of the servo motor to maintain the lifting platform height. A stacking crane, comprising: a trolley; a mast that rises upward from the trolley; and the lifting device of any one of claims 1 to 3; the mechanism is housed in the mast, and the lifting platform is It is configured to move up and down along the mast. The stacker according to claim 4, wherein the mechanism unit includes a gear that is attached to the lower portion and the upper portion of the mast, and a ring-shaped driving medium that is wound around the upper and lower gears, and the servo motor is configured to be It is connected to either of the upper and lower gears and is fixed by the torque from the servo motor. A method for maintaining a height of a lifting platform is a height holding method of a lifting platform provided in a lifting device that includes: a mechanism portion that lifts and lowers the lifting platform; and a servo motor that is driven by the driving mechanism portion Elevating platform lifting; such lifting platform The height holding method is characterized in that when the lifting and lowering of the elevating table is stopped and the height is maintained, the elevating table is lowered by a predetermined height by the servo motor after the elevating table is stopped. The height maintaining method of the lifting platform of claim 6, wherein the lifting crane is equipped with the height maintaining method of the lifting platform, wherein the stacking crane has the above-mentioned lifting device, the trolley, and the self-trailer upward The erected mast, the mechanism portion is housed in the mast, and the lifting platform is raised and lowered along the mast.