JP7658043B2 - Light load high speed operation crane - Google Patents

Description

The present invention relates to a technology that uses the excess power generated in the hoisting motor when the load hoisted by the crane is light to rotate the motor beyond the rated speed, thereby increasing the hoisting speed of the crane.

A crane's hoisting device is able to hoist heavy loads into the air with a relatively small force by slowing down the hoisting speed using a reducer with a high reduction ratio and by using a number of wire ropes hung on the sheaves.By rolling the iron wheels on the traversing or running iron rails, it is an efficient loading and transporting machine that can move horizontally with little force.
However, because the speed of the hoisting device is slow, when no cargo is being lifted or when the cargo is light in weight, no hoisting force is required, but the hoisting speed is slow, taking a long time to operate, and there is a problem that it is not time-efficient.
Technologies have been proposed for increasing the hoisting speed above the rated speed by utilizing the surplus motor power generated when the cargo is not being lifted or the load is light, thereby shortening the cargo-handling and transporting time and improving time efficiency (see, for example, Patent Documents 1 to 3).

Japanese Unexamined Patent Publication No. 60-219999 Japanese Unexamined Patent Publication No. 4-66498 JP Patent Publication No. 7-187565

Incidentally, when no cargo is being lifted or the load is extremely light, the hoisting speed can be three or four times the rated speed if one considers only the motor's reserve power and load, but in reality, when the motor is rotated at a speed far exceeding the rated speed, a large centrifugal force acts on the rotating parts of the motor, such as the rotor. Also, the hoisting brake, which is used to hold the load, will also experience problems such as a decrease in frictional force, vibration, and noise due to the excessive speed of the sliding surface, so high-speed operation under light loads is currently limited to about twice the rated speed, and it is not possible to achieve a speed higher than that.

In addition, the braking distance during high-speed operation under a light load is the square of the braking distance at the rated speed, so if the speed during high-speed operation under a light load is increased to twice the rated speed, the braking distance will be four times the braking distance at the rated speed, and if the speed is increased by more than twice the rated speed, or even triple the rated speed, the braking distance will be nine times, which can cause problems in operability and pose a danger. Therefore, Patent Document 3 describes a technology for shortening the braking distance by increasing the deceleration above the rated speed.
However, since the output torque of the motor decreases above the rated speed, in order to realize the technology described in Patent Document 3, it is necessary to use a large-capacity motor and inverter, which poses a cost issue.

In consideration of the problems with the conventional cranes described above, the present invention aims to provide a crane that operates at high speeds using the motor's spare power during light loads during acceleration, shortening the braking distance from high speed operation and improving the safety of high speed operation under light loads, while expanding the range in which speed control is possible to increase the speed from the rated speed to a high speed, thereby further shortening the time required for loading and unloading.

In order to achieve the above-mentioned object, the high-speed operation crane under light load of the present invention is a crane equipped with a high-speed operation function for hoisting speed under light load, which rotates the crane at high speed up to a rotation speed range exceeding the rated rotation speed where the torque of the hoisting motor decreases when the load hoisted by the crane is light compared to the rated load of the crane, and is characterized in that, when decelerating from this high-speed operation state under light load, the deceleration rate is changed to a large value in response to the torque of the hoisting motor recovering and increasing as the rotation speed of the hoisting motor decreases.
In other words, when the motor's rated speed is exceeded due to high-speed operation under light load and the motor is rotating in a speed range where the torque generated by the motor is decreasing, if the motor is decelerated from that state, the torque generated by the motor will recover and increase as the speed decreases.By changing the deceleration rate to a larger value in response to the decrease in speed and the motor's torque that recovers and increases, the braking distance can be shortened without increasing the capacity of the motor or inverter, making it possible to solve the problem of a long braking distance during high-speed operation under light load.

In this case, when decelerating at a large deceleration rate, by adding a function to change the deceleration rate to a small value just before the deceleration ends and the crane stops, the deflection of the crane girder caused by the force of the sudden deceleration is slowly returned to its original position just before the crane stops, reducing the vibration of the girder after stopping and thereby suppressing the vertical vibration of the suspended load after stopping.

In addition, when accelerating the hoisting motor under light load, the acceleration rate is set to a large value using the motor's spare power, and as the torque that the hoisting motor can output decreases when the rotation speed of the motor exceeds the rated rotation speed, the acceleration rate that was set to a large value is changed to a small value as the rotation speed increases from the point where the rated rotation speed is exceeded, thereby adding a function of accelerating in a short time.

In addition, by first accelerating at a small acceleration rate immediately after starting, and then changing the acceleration rate to a larger value , the deflection of the crane girder that occurs during acceleration occurs slowly, thereby reducing the vibration of the girder after starting and suppressing up and down vibration during operation.

In addition, the acceleration time can be lengthened when accelerating the winding up, shortened when accelerating the winding down, shortened the deceleration time when decelerating the winding up, and lengthened the deceleration time when decelerating the winding down.

In addition, by setting a torque limit value so as not to exceed the maximum output torque value of the hoisting motor and setting the acceleration or deceleration time to the shortest time, it is possible to accelerate in a short time using the surplus power of the hoisting motor when accelerating under light load, and to decelerate in a short time according to the motor torque so that the rotation speed of the hoisting motor decreases as a result of deceleration and then increases.

In addition, by using a motor with a low rated rotation speed for the hoisting motor, specifically a multi-pole motor with a low rated rotation speed or a low-rotation AC motor with a low frequency as a rated power source for the hoisting motor, the speed output range for high-speed operation under light load can be widened.
In other words, by using a low-speed, high-torque motor for the hoisting motor, it is possible to eliminate the high-speed rotating parts from the rotating parts of the hoisting device and solve the effect of centrifugal force on the strength of the high-speed rotating parts, making it possible to increase the speed under light load to higher speeds than before.

The high-speed operation crane under light load of the present invention solves the problems of increased centrifugal force in the rotating parts and longer braking distances that occurred during high-speed operation under light loads when the crane is operating without a load or when the suspended load is extremely light and the motor load is small during the loading and transporting process of the crane, making it possible to increase the speed faster than before, thereby providing a highly efficient crane that significantly shortens the time required for loading and transporting work.

FIG. 1 is an explanatory diagram of a typical crane transport process. FIG. 4 is an explanatory diagram of the output torque characteristics of a motor. FIG. 1 is an explanatory diagram of a hoisting device with an expanded speed range for high-speed operation under light load. FIG. 1 is an explanatory diagram of the maximum speed that can be outputted relative to the load factor of a crane. FIG. 2 is an explanatory diagram of a deceleration curve in a high-speed operation crane under a light load according to the present invention. FIG. 2 is an explanatory diagram of an acceleration curve in a high-speed operation crane under a light load according to the present invention.

The following describes the high-speed operation crane under light load of the present invention based on an embodiment using the drawings.

FIG. 1 shows a diagram of a typical crane transport process.
When a crane CR transports a cargo CA, there is a calling process CL in which the crane CR moves to the cargo CA while empty.Then, the cargo CA is sling-loaded, lifted by the crane CR, and the crane CR transports the cargo CA to its destination while loaded through a transport process TP, where the cargo CA is transported to its destination.
After the crane CR is released from the sling at the destination, it is again moved empty to the location of another cargo CA, or moved to a waiting location for a storage process RT.
As described above, in addition to the transport process TP in which the cargo CA is suspended, the crane transport process always includes a high proportion of empty processes such as the retrieval process CL and the storage process RT. Therefore, shortening the time for the empty process by operating at high speed under light load is effective in improving the efficiency of the transport work.

When a load value M is hoisted by a crane CR at a speed V, the hoisting load torque Th applied to the hoisting device at a rotation speed N at the speed V is as shown in equation (1).
Th=(M×V)÷(2×π×N) ...Formula (1)
Here, π is the constant of the circumference of a circle.
As shown in formula (1), when the load value M is small, the hoisting load torque Th applied to the hoisting motor is proportionally small. In other words, in the retrieving process CL and the stowing process RT where the cargo CA is not suspended, the hoisting load torque Th applied to the hoisting motor is close to zero.
Also, in the transportation process TP, only a few process cranes built into the line always hoist their rated loads. Most cranes are used to hoist light loads, and high-speed operation when carrying light loads is often used effectively.
Incidentally, in a specific hoisting device in which the ratio of the speed V to the number of rotations N in equation (1) is constant (the reduction gear ratio of the machine is constant), even if the number of rotations N and the speed V are changed by controlling the speed of the hoisting motor, the hoisting load torque Th for the load value M is constant.

FIG. 2 shows motor characteristics of motor output torque Tm versus motor speed N when the speed of an AC motor is controlled using a frequency conversion device such as an inverter.
The continuous torque CT characteristic, which allows the motor to continuously output 100% rated torque, is such that the motor output torque Tm decreases once the rated rotation speed exceeds 100%.
At this time, it is necessary to prevent the hoisting load torque Th from exceeding the continuous torque CT. For this reason, when the load value M is the rated load, which is the maximum load that the crane can hoist, Th is set so as not to exceed the continuous torque CT when the speed is 100% or less, and as the load value M becomes smaller, the speed can be increased accordingly to a speed that does not exceed the continuous torque CT.

Incidentally, in the case of a six-pole AC motor, when it is rotated by a 50 Hz AC power source, the synchronous rotation speed at 100% is 1000 rotations per minute, and when the power frequency is raised to 100 Hz, the rotation speed at 200% is 2000 rotations per minute. At this time, centrifugal force acts on the rotating parts of the motor shaft, such as the motor rotor and the coupling that connects to the load, in proportion to the square of the rotation speed. This centrifugal force causes strength problems in the high-speed rotating parts, with the limit being about 2000 rotations per minute. A special structure that gives the rotating parts the strength to rotate beyond this is economically inefficient and physically difficult to achieve with a typical device configuration.
In addition to the strength issues caused by centrifugal force, a rotation speed of 2000 revolutions per minute, which is 200%, can also reduce the friction of the brake attached to the motor shaft, reducing the holding power of the load, as well as causing problems with vibration and noise from the reducer.

In order to solve this problem and to achieve a speed exceeding 200% when the load is light, the hoisting device of the high speed operation crane under light load of the present invention uses a multi-pole motor DM used in a so-called direct drive system as the hoisting motor as shown in FIG. 3, thereby eliminating the high speed rotating portion and enabling a speed of 200% or more to be output when the load is light.
For example, if the multi-pole motor DM used in a direct drive system has 30 poles, it will rotate at 200 revolutions per minute when run on a 50 Hz power supply, and even if the rotation speed is increased to 300%, it will only be 600 revolutions per minute, and even at 400%, it will only be 800 revolutions per minute. This prevents the coupling CP and brake BR attached to the motor rotor and motor shaft from becoming weak due to centrifugal force, eliminates problems such as vibration and noise from the reducer GR, and allows the high speed rotation under light load to be increased to an even higher speed.

Incidentally, when a crane is hoisted, even if a 30-pole direct drive multi-pole motor DM is used, if a so-called direct drive is used without a reducer, the hoisting speed of the crane becomes too fast, and the power to hoist a heavy load is insufficient. Therefore, as shown in Figure 3, a one-stage reducer GR is used to transmit the rotational force to the wire drum WD, thereby ensuring the power to hoist a heavy load.
In this way, while conventional hoisting reducers for cranes usually have three stages of reduction, this has been reduced to one stage, and a multi-pole motor DM for direct drive is used to keep all axes of the hoisting device at low speeds, so that problems caused by high speed rotation such as centrifugal force do not occur even if the motor is rotated at a speed significantly exceeding the rated speed when the load is light and the motor load is small.

Multi-pole motors for direct drive with low rated speeds are generally AC synchronous motors with permanent magnet rotors, but it is also possible to manufacture multi-pole AC induction motors with low rated speeds, which can similarly achieve the effect of light-load, high-speed operation up to high speeds.
Also, by manufacturing the motor so that its AC power supply is rated at a low frequency, it is possible to manufacture a motor with a similarly low rated speed, and in this case too, the effect of being able to operate at high speeds with a light load can be obtained.

Figure 4 is an explanatory diagram of the maximum speed at which the hoisting device can output for the load value M hoisted by the crane. As shown in Figure 4, when the load value M hoisted by the crane is 100% of the rated load, the combination of machines is set so that the hoisting load torque Th is equal to the motor's continuous torque CT, and the speed V is controlled so that 100% of the rated speed is output. As the load value M being hoisted becomes lighter, the speed that the motor can output becomes faster. Conventionally, the motor was controlled to increase its rotation speed to 200% of the rated speed when the load value was 25% of the rated load, and a speed limit was imposed so that the speed would not exceed 200% of the rated speed even with a load lighter than 25%. In the high-speed crane under light load of the present invention, all axes of the hoisting device are kept at low speed, and when the load being hoisted is extremely light or no load is being hoisted, the motor speed N is increased to 300% or 400% of the rated speed, making it possible to output a high speed hoisting speed of 300% or 400% under light load.

Here, the torque required when accelerating from a stop to the rotation speed Na or when decelerating from the rotation speed Na to a stop in the acceleration/deceleration time ta is the acceleration/deceleration torque Ta shown in equation (2).
Ta = (GD ² × Na) ÷ (375 × ta) ... Formula (2)
Here, ^GD2 denotes the moment of inertia.
Normally, in inverter control, the short-time torque ST is often set to 150% of the continuous torque CT, as shown in Figure 2. In this case, the continuous torque CT value of 100% is used to supply the hoisting load torque Th, and the remaining 50% of the short-time torque ST is used as the acceleration/deceleration torque Ta.
At this time, the value of the acceleration/deceleration time ta is set so that the value of the acceleration/deceleration torque Ta becomes 50%.

Since the speed V of the hoisting device of a crane is slow, the moment of inertia due to the linear movement of the load caused by the up and down movement of the load is small. Therefore, the moment of inertia of the high-speed rotating parts such as the hoisting motor, brake, and coupling account for the majority of the moment of inertia ^GD2 of the hoisting device. While the moment of inertia ^GD2 due to the linear movement of the load varies in proportion to the weight of the load, the moment of inertia ^GD2 of the rotating parts such as the hoisting motor is a fixed value specific to the hoisting device and is not affected by the load value M of the load. In other words, for a hoisting device of a crane in which the moment of inertia ^GD2 of the rotating parts accounts for the majority of the moment of inertia ^GD2 , the moment of inertia ^GD2 is hardly affected by the load value of the load and is a fixed value specific to the hoisting device.

When the crane accelerates in the hoisting direction, both the hoisting load torque Th and the acceleration/deceleration torque Ta act as loads on the motor output torque Tm, but when the crane decelerates in the hoisting direction, the hoisting load torque Th and the acceleration/deceleration torque Ta act in opposite directions, so that surplus power is generated in the hoisting motor and the deceleration time can be shortened.
During acceleration in the lowering direction, the hoisting load torque Th and the acceleration/deceleration torque act in opposite directions, so the acceleration time can be set short, but during deceleration in the lowering direction, the hoisting load torque Th and the acceleration/deceleration torque act in the same direction as a load on the motor output torque Tm, so the deceleration time becomes long.
The time required for acceleration and deceleration can be improved by lengthening the acceleration time when accelerating in the winding-up direction, shortening the acceleration time when accelerating in the winding-down direction, shortening the deceleration time when decelerating in the winding-up direction, and lengthening the deceleration time when decelerating in the winding-down direction.
In this case, however, the braking distance required when decelerating the lowering becomes long, which can lead to the risk of misjudging the start point of deceleration and causing the load to drop forcefully to the floor before it has fully decelerated, so it is necessary to make this as short as possible.

Now, when decelerating at the same deceleration rate from high speed operation under light load, the braking distance from 200% speed is four times longer than the braking distance when operating at rated speed, the braking distance from 300% speed is nine times longer, and the braking distance from 400% speed is 16 times longer. Even with the conventional high speed operation under light load limited to 200% speed, a braking distance four times longer was difficult to drive, but exceeding this and reaching a braking distance of nine times longer from 300% speed makes it dangerous.

Therefore, in the light-load high-speed operation of the present invention, if the load value M being lifted is, for example, 10%, the hoisting load torque Th is also 10% of the rated load, so the rotation speed is increased to 300% with the motor's reserve power. Then, when decelerating from that rotation speed N, at the start of deceleration, only the small value remaining after subtracting 10% of the hoisting load torque Th from the value of the motor's short-time torque ST at 300% rotation can be allocated to the acceleration/deceleration torque Ta, so the motor can only output torque for deceleration at the normal deceleration rate.
However, thereafter, as the rotational speed N decreases with deceleration, the short-time torque ST of the motor recovers and increases. At this time, the hoisting load torque Th remains at 10% regardless of the rotational speed, so the remaining value obtained by subtracting 10% of the hoisting load torque Th from the value of the short-time torque ST that has recovered and increased can be used as the acceleration/deceleration torque Ta, and the deceleration rate can be changed to a large value to shorten the braking distance. Then, when the rotational speed N is decelerated to 100% rotational speed and the short-time torque ST of the motor at this time is 150%, the remaining 140% obtained by subtracting 10% of the hoisting load torque Th can be used as the acceleration/deceleration torque Ta, and the braking distance can be shortened to 1/2.8 of the acceleration/deceleration torque Ta of 50% that was previously set.

This deceleration curve is shown in the form of a shortened braking curve DL in FIG.
By decelerating along this shortened braking curve DL, the braking distance can be reduced to about half (about 4.5 times) the braking distance for D3 from 300% speed, which was nine times that required when decelerating along the braking curve D1 from 100% speed, and is close to the braking distance for the braking curve D2 from 200%. This expands the control range of high-speed driving under light load to a speed of 300% with a braking distance equivalent to that of high-speed driving under light load with a speed limit added at 200%, while suppressing a significant increase in braking distance and preventing an increase in danger due to higher speeds.

However, when trying to maximize the motor's capacity and decelerate in a short time, the reaction force of the deceleration force at that time is generated as a deflection of the crane girder, and if the crane is decelerated to a stop at the same momentum, the deflection of the crane girder disappears instantly, causing the crane girder to oscillate up and down after the crane has stopped. As a result, the suspended load vibrates up and down, which hinders precise positioning and stopping.
Therefore, in order to suppress the up and down amplitude movement of the crane girder, the deceleration rate is changed to a small value just before stopping at the end of deceleration of the shortened braking curve DL, and the crane girder is stopped while slowly returning to its original deflection during deceleration, thereby suppressing the up and down amplitude of the crane girder after stopping, making it easier to precisely position and stop the crane, and providing a crane with good operability.

On the other hand, during acceleration, since accelerating slowly along the acceleration curve A1 shown in FIG. 6 is safer, there is little need for sudden acceleration, but in applications where it is required to shorten the transport time, the transport time can be shortened by giving the elevator the acceleration characteristics of the shortened acceleration curve AL when the suspended load is light, and reaching high-speed operation at a light load in a short period of time.
The shortened acceleration curve AL is characterized in that when the load is light, the hoisting load torque Th becomes smaller, so that the torque obtained by subtracting the hoisting load torque Th from the short-time torque ST of the hoisting motor becomes larger, and since the acceleration/deceleration torque Ta can be made large, acceleration can be achieved in a short time.As the motor output torque Tm becomes smaller once the motor rotation speed exceeds the rated rotation speed, the acceleration rate gradually changes to a smaller value .
In addition, by starting the acceleration start with a small acceleration rate and then changing the acceleration rate to a large value , the deflection of the crane girder at the start can be mitigated and the vertical vibration of the crane girder can be suppressed. This acceleration characteristic at the start can suppress the vertical vibration of the crane girder, especially when starting and stopping repeatedly in a short time by inching operation, and can improve operability.

By the way, in order to create the shortened braking curve DL and the shortened acceleration curve AL, a method of changing the acceleration/deceleration rate according to the change in the rotation speed N under the load state based on the load value of the suspended load or the load rate of the motor, etc., has been described, but a curve similar to the shortened braking curve DL and the shortened acceleration curve AL can also be created by setting a torque limit value to the curve of the short-time torque ST in Figure 2 and setting the acceleration/deceleration time to a short value. In this case, too, the deceleration rate or acceleration rate can be set to a small value at the end of deceleration or the start of acceleration to suppress the vibration of the crane girder, thereby improving operability.
However, this method of creating the shortest acceleration/deceleration curve with a torque limit value and short acceleration/deceleration time setting increases the possibility of an overcurrent trip when control is deviated unless a control device with good current control characteristics is used. However, motors used for direct drives often use AC servo motors with permanent magnet rotors that have excellent current control characteristics, and high-performance current control can be used to exert torque up to the limit of the short-term torque ST curve with torque limit and short acceleration/deceleration times without causing an overcurrent trip, allowing acceleration/deceleration at the maximum acceleration/deceleration rate according to the lifting load and rotation speed, and acceleration/deceleration with the shortest acceleration and braking distances.

FIG. 5 shows a shortened braking curve DL that enables deceleration in approximately half the braking distance required when simply decelerating from a speed of 300%. The same is true for deceleration when accelerating to a speed of 400%; whereas simply decelerating would result in a braking distance 16 times that of the braking distance required for braking curve D1 from a speed of 100%, the shortened braking curve DL can reduce the braking distance to approximately 8 times that distance.
However, a braking distance of 8 times is difficult to use with a general crane, and is required for cranes with extremely slow rated speeds, cranes with extremely long hoisting distances, inclines for transporting inclined shafts, etc. In such cases, it is necessary to take safety measures such as providing a deceleration limit switch to limit the speed by 400% so that danger does not occur due to the long braking distance.

Incidentally, permanent magnet rotor AC servo motors, which are widely used as direct drive motors, generally have a large short-term torque ST of 200% or 300% compared to the continuous torque CT, and by utilizing this large short-term torque ST, it is possible to accelerate and decelerate in a short period of time.
Furthermore, by combining this large short-time torque with acceleration and deceleration on the shortened braking curve DL and the shortened acceleration curve AL, acceleration and deceleration in an even shorter time can be achieved.

Here we have described technology that makes the most of the capabilities of the hoisting motor to accelerate and decelerate in a short period of time, but at the same time this accumulates repeated stress on the motor structure, the reducer, the mechanical surroundings such as the keys, and the power semiconductors in the control device, so it is necessary to design the relevant parts with a margin of error that takes into account their lifespan.

The above describes the high-speed operation crane under light load of the present invention based on its embodiment, but the present invention is not limited to the configuration described in the above embodiment, and the configuration can be changed as appropriate within the scope of the spirit of the present invention.

The high-speed operation crane under light load of the present invention solves the problem of the strength of the rotating parts against the centrifugal force caused by high-speed rotation during high-speed operation under light load, and also solves the problem of extended braking distance even when operating at high speed under light load, making the crane safer and easier to handle, and it can be operated up to higher speeds without increasing the motor capacity under light load, shortening the time required for loading and transporting work, making it highly useful in industry.

CR Crane CA Load CL Crane calling process TP Transport process RT Crane storage process Tm Motor output torque Th Hoisting load torque Ta Acceleration/deceleration torque N Revolutions per minute CT Continuous torque ST Short-time torque DM Multi-pole motor CP Coupling BR Brake GR Speed reducer WD Wire drum SH Sheave TS Traversing device M Load value V Speed t Time td Deceleration time D1 Braking curve (100% speed)
D2 Braking curve (200% speed)
D3 Braking curve (300% speed)
DL Shortened braking curve ta Acceleration time A1 Acceleration curve AL Shortened acceleration curve

Claims (7)

This crane has a high-speed operation function for hoisting and lowering at light loads, which rotates the hoisting motor at high speed up to a rotation speed range exceeding the rated rotation speed where the torque of the hoisting motor decreases when the load it hoists is light compared to the rated load of the crane, and is characterized in that, when decelerating from the high-speed operation state at light loads, the deceleration rate is changed to a large value in response to the torque of the hoisting motor recovering and increasing as the rotation speed of the hoisting motor decreases. 2. The high-speed operation crane under light load according to claim 1, further comprising a function for changing the deceleration rate to a small value immediately before the end of deceleration and the crane is stopped when the deceleration rate is large . 3. The high-speed operation crane under light load according to claim 1 or 2, characterized in that, when accelerating the hoisting motor under light load, the acceleration rate is set to a large value using the motor's spare power for acceleration, and as the torque that the hoisting motor can output decreases when the rotation speed of the motor exceeds the rated rotation speed, the acceleration rate that was set to a large value is changed to a small value as the rotation speed increases from the point where the rated rotation speed is exceeded, thereby adding a function of accelerating in a short time. 4. A high speed operation crane under light load according to claim 1, 2 or 3, wherein the acceleration rate is initially small when accelerating immediately after start-up, and then the acceleration rate is changed to a large value. A high-speed operation crane under light load according to claim 1, 2, 3 or 4, characterized in that the acceleration time is lengthened when accelerating hoisting, the acceleration time is shortened when accelerating lowering, the deceleration time is shortened when decelerating hoisting, and the deceleration time is lengthened when decelerating lowering. A high-speed operation crane under light load according to claim 1, 2, 3, 4 or 5, characterized in that a torque limit value is set so as not to exceed the maximum output torque value of the hoisting motor, and the acceleration or deceleration time is set to the shortest time, so that when accelerating under light load, the hoisting motor's remaining power is used to accelerate in a short time, and when decelerating from a high-speed operation state under light load, deceleration is performed in a short time according to the motor torque so that the rotation speed of the hoisting motor decreases due to deceleration, and increases. A high-speed operation crane under light load according to claim 1, 2, 3, 4, 5 or 6, characterized in that a motor with a low rated speed is used for the hoisting motor, thereby widening the speed output range for high-speed operation under light load.

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