Crane lifting device and its operation method

Abstract

The present invention discloses a lifting mechanism (1) for a crane, the lifting mechanism comprising: at least one rope drum (2) for lifting a rope (3); at least one lifting motor (4,5) for driving the rope drum (2); a gear device (6) connected between the rope drum (2) and the lifting motor (4,5), and having an input gear (7,8) on the side of the lifting motor (4,5) and an output gear (9) on the side of the rope drum (2); and a brake (10,11) for braking the input gear (7,8). The gear mechanism (6) has a differential (6a) with a first input gear (7) and a second input gear (8) arranged therein, wherein the first input gear (7) and the second input gear (8) are connected to each other and also to the output gear (9), wherein a first lifting motor (4) connected to the first input gear (7) and a second lifting motor (5) connected to the second input gear (8) are arranged therein, and wherein the first input gear (7) and the second input gear (8) have unequal total gear ratios relative to the output shaft. The invention also relates to a method for operating the lifting mechanism.

Description

Background Technology

[0001] The present invention relates to a lifting mechanism of a crane as described in the introduction of claim 1, and to a method for operating the lifting mechanism as described in the introduction of claim 12.

[0002] Nowadays, in industrial machinery, squirrel-cage motors and geared devices operated by alternating current are commonly used to generate machining motions, which are used in different ways in different machines as needed.

[0003] Cranes typically use a squirrel-cage motor operated by alternating current and a gear mechanism connected to the crane's wheels to move the wheels and thus move the crane. The same principle is also used to drive other machine parts.

[0004] A lifting mechanism typically includes at least one electric motor, at least one brake, at least one lifting rope, at least one rope drum for the lifting rope, and a lifting member for lifting the load. The lifting rope, pulled together with the rope drum, is guided from the rope drum to a fixed attachment point of the crane via a pulley arrangement of the lifting member. The pulley arrangement includes pulleys on the top of the lifting car and within the lifting member. The number of pulleys is determined by the strength of the rope and the load to be lifted.

[0005] The design process of this institution involves knowledge of many different areas and their coordination, and all of these areas affect the others.

[0006] The main process of designing the mechanism is briefly described below. The mechanism designer assembles the different sub-regions according to a technical document, which allows for the individual matching of components. Initially, the number, size, strength, and type of lifting ropes are selected. Next, the size, location, model, and position relative to the ropes are selected for the pulleys and hooks. At this stage, the rope system as a whole is checked to ensure that the aforementioned sub-regions are compatible with each other, forming a functional whole, enabling the rope system to withstand the necessary loads, and keeping the speed of the rope system and pulleys within permissible limits. If necessary, the configuration is changed to achieve the target values. Next, the mechanism designer designs or selects a lifting drum whose details, locations, rope grooves, etc., are designed to ensure compatibility with all other sub-regions. Once the rope drum has been selected, the mechanism for rotating the drum is selected. This mechanism includes various devices such as lifting gears, lifting brakes, lifting motors, and the clutches and mounting platforms required to match them. The mechanism designer selects and calculates all the aforementioned components to ensure that the required load and speed are kept within permissible limits. If necessary, the configuration is changed to achieve the target values. The selection of power and gears is performed in conjunction with the selection of the motor to find the most advantageous combination to achieve the desired performance values. The mechanism designer estimates the size of the gear unit based on the required total power, where the output gear corresponds to the drum's rotational speed and the input gear corresponds to the rated rotational speed of the motor selected based on the power. Calculations are then performed for different speeds and loads using the chosen configuration. Typically, the size of the gear unit and the gears, as well as the rated power and rotational speed of the motor, will have to be varied. During the design process, the assistance of the motor designer is needed when examining the motor's characteristics under different conditions, as the voltage supplied to the motor, the required temperature, etc., significantly affect the motor's characteristics. The gear designer needs to identify possible new and different gear options and characteristics. Because DC technology has been used for a long time, its characteristics have also determined the performance values ​​in cranes. Therefore, in the case of the discontinuation of commonly used DC motors and their replacement by squirrel-cage motors, different technical implementations must be carried out to achieve the same performance as DC motors in terms of speed and lifting capacity. (See attached figures.) Figure 3 The graph illustrates the differences between squirrel-cage motors and DC motors.

[0007] The characteristics of a lifting mechanism lie in the heavy load to be handled and the large lifting torque required, resulting in a large torque transmitted by the gear mechanism, and a significantly faster lifting and lowering speed when the lifting device is being lifted without load. This requirement is emphasized in large cranes with high lifting heights, particularly in terms of load lifting capacity and size. The number of pulleys, their positions, and different rope arrangements allow for variations in the rope force reaching the lifting mechanism. When handling heavy loads, more pulleys are selected for the mechanism, guiding the lifting ropes. In this case, the load on the lifting ropes is lower. Similarly, the rotational force on the rope drum of the lifting mechanism is lower. Likewise, the lifting speed achieved under load is lower. Therefore, the load to be lifted is divided among several ropes by different rope gears, thus changing the overall gear ratio of the entire lifting mechanism. A suitable overall gear ratio can be selected by choosing the gears of the gear mechanism and the lifting motor. Typically, the load and speed to be lifted are determined by the customer.

[0008] The lifting mechanism is designed for the heaviest loads, which means that the lifting motor is large and has a higher achievable maximum torque and power, but a lower maximum mechanical rotation speed.

[0009] Under the maximum load to be lifted, the hoisting motor is typically a three-phase squirrel-cage motor, and its preferred speed is its rated rotational speed. When lifting or lowering the empty hook or hoisting device, the motor's maximum mechanical speed can be used, at which the motor's torque is at least equal to the torque required to lift the load. In conventional squirrel-cage motors, the torque drops rapidly as the motor rotates within its rated rotational range (i.e., within the so-called field weakening range), decreasing approximately by the square of the rotational speed, i.e., at twice the speed, to about a quarter of its original value. In some cases, this torque drop is a limiting factor when determining the maximum speed of the hoisting device, for example, when the weight of the hoisting device or the load to be lifted will require a torque higher than the torque the motor is capable of producing.

[0010] The maximum continuous mechanical rotational speed allowed by large squirrel-cage motors is typically twice the rated rotational speed. Squirrel-cage motors often replace DC motors due to their lower maintenance requirements and overall lower cost, but their ability to generate power and torque at rotational speeds above the rated speed (within the so-called field weakening range) is weaker, and they present new challenges for the design of lifting mechanisms. As previously shown, the operating range of a squirrel-cage motor depends on the motor model, from 0 to approximately 2.5 times the speed, with larger motors ranging from 0 to approximately 2 times the rated rotational speed. However, despite the high maximum torque, the torque decreases rapidly after the rated rotational speed. The torque achieved by a DC motor at rotational speeds above the rated rotational speed decreases linearly, meaning that constant power can be achieved at different speeds within the field weakening range. In contrast, the torque achieved by a squirrel-cage motor decreases after the rated rotational speed by the square of the ratio between the used rotational speed and the rated rotational speed. In this case, the achievable lifting power decreases much faster than that of a DC motor, resulting in the crane's maximum power not being reached under light loads. (See attached figure.) Figure 3 As will be described in more detail later, this difference between curves 41 and 61 is illustrated graphically. When it is desired, for example, to raise or lower an empty lifting device at four times the speed, a speed range selector, which can be used separately from or in conjunction with the actual gear mechanism, can be employed.

[0011] This speed range selector is a geared transmission device with an input shaft driven by an electric motor and an output shaft driving a rope drum, where the gears can be selected between the input and output shafts. Typically, the geared transmission device has two different gears with a gear ratio of 2. When the gear ratio of the geared transmission device is changed, the mechanism cannot be used and the brake on the lifting drum remains engaged because, in the intermediate position, there is no mechanical connection between the input and output shafts. In conventional lifting mechanisms, the electric motor is designed to be large, or multiple motors are used. This is feasible to some extent, but the solution becomes impractical when the load or speed difference increases sufficiently. Differentials are primarily used in critical solutions seeking redundancy and reliability. For improved performance, this solution is not an option because it uses two equal electric motors to drive two input shafts with equal input gears relative to the output shaft, making a preferred alternative using a conventional gearbox and an electric motor with twice the power. Therefore, it is easy to recall the geared transmission device used for decades.

[0012] The requirements of this example are met when the empty lifting device can be raised or lowered at a maximum mechanical speed four times the speed of the fast gear of the gearbox, and heavy loads can be lifted slowly with the slow gear. The selection of the speed and load range of the gearbox is done manually; that is, the crane operator selects the load range to be used.

[0013] The aforementioned problem involves changing the gears of the gear mechanism, which cannot be done while the mechanism is running, but the lifting mechanism must always be stopped when changing the speed range. Similarly, reliable engagement is problematic because the gears do not rotate and engagement is not always successful. In this situation, the gear mechanism remains at a so-called intermediate clearance, in which case the power line is damaged, requiring repair by switching to local control and, if necessary, by manually assisting the gear engagement, leading to prolonged downtime of the device.

[0014] In the worst-case scenario, based on signals from sensors that measure the connection of the incorrect gear, the situation described above could lead to the gear's condition not being detected correctly and the mechanism being activated (and the brake being released), resulting in a drop in load.

[0015] Gear control technology requires sensors and actuators; failure of sensors and actuators can prevent the use of the mechanism and thus prevent the use of the crane.

[0016] The transmission gear unit is also a separate component, requiring connecting devices on both sides, and it is installed between the actual main gear unit and the electric motor, meaning it requires a relatively large amount of space in a small engine room. Furthermore, when the actuator is positioned at a critical operational location as described above, its maintenance requires specialized skills.

[0017] The difference in gear ratios at the midpoint of the gear transmission mechanism under consideration is dangerous because if this condition is not detected, the power line is "disconnected," and the weight caused by the lifting device or load will cause the load to drop. Additionally, when the motor is used at speeds exceeding its rated rotational speed, the maximum torque of the squirrel-cage motor decreases rapidly, limiting the moving speed of the lifting device.

[0018] CN 204224155 U discloses a solution for two different input shafts with two different gears arranged relative to an output shaft, and an electric motor arranged on both input shafts. In this solution, only one electric motor and one input shaft are driven at a time. The selection of the electric motor and input shaft is connected to the output shaft via a signal-guided friction clutch, thereby transmitting power from the input shaft in question to the output shaft. The two input shafts operate on similar principles, and only one input shaft can be connected to the output shaft via a clutch, so only the power of the electric motor connected to the input shaft in question can be used on the output shaft. Therefore, only the other electric motor can generate power to the output shaft. Similar to the toothed clutches of a crane's gear transmission mechanism, this friction clutch does not have engagement problems; however, this type of friction clutch cannot be used in crane applications because, unlike the toothed clutches of a gear transmission mechanism, it cannot reliably transmit torque.

[0019] Another way to achieve four times the speed with an empty lifting device is to select gears in the main gear mechanism such that the desired lifting speed at full load is achieved at the speed of the lifting motor, and this desired lifting speed is, for example, 50% of its rated rotational speed. In this case, the speed can be increased to four times before reaching the maximum mechanical rotational speed. The problem with this solution is that the motor needs to provide the same power at 50% speed so that the lifting device and the load can continue to move at the same speed. In this case, a motor with a larger rating must be selected or two or more motors continuously driven on the same shaft must be selected, along with control devices and cables for the correspondingly larger motors, which increases investment costs and space requirements.

[0020] A conventional differential with identical gears between the input shafts relative to the output shaft and with an electric motor of the same characteristics arranged on the input shaft does not provide an improvement to the described problem because the load-lifting capability achievable in terms of speed is similar to that of a conventional geared gear solution with two of the aforementioned electric motors connected in series and appropriate gears selected for that geared gear.

[0021] As previously shown, the operating range of a squirrel-cage motor is from 0 speed to approximately 2.5 times its rated rotational speed, but despite its large maximum torque, this torque decreases rapidly after the rated rotational speed.

[0022] If the input shafts of the differentials have the same gears and the same motors, the decrease in driving torque on the output shaft will have a similar shape because the torques obtained from the input shafts are equal, i.e., parallel / overlapping. Summary of the Invention

[0023] The object of the present invention is to solve the problems described above, and further, to introduce improved new features into the use of the lifting mechanism. This object is achieved using the lifting mechanism according to the invention and using the method according to the invention, the lifting mechanism being characterized by the content claimed in the characterizing portion of claim 1, and the method being characterized by the content claimed in the characterizing portion of claim 12.

[0024] Therefore, in this invention, the gear mechanism described above according to the prior art is replaced by a differential with two input gears having a different gear ratio than the output gear. This invention achieves several advantages. In designing the hoist motor drive, excessive size can be avoided, including avoiding excessive size of its peripheral components and excessive space utilization. The hoisting speed of the lightly loaded or empty hoisting member is greater, which is a significant improvement. When changing the hoisting speed, the usual coupling problems are avoided, and load drops are prevented because at least one hoist motor torque is always engaged during the change. The change of hoisting speed is smooth and reliable, thus saving time. The change of hoisting speed can be completed automatically.

[0025] In a differential, the rotational speed of the input gears is added to the output shaft. That is, if only the first input shaft rotates at speed *a* while the second input shaft is stationary, the rotational speed of the output shaft is *b*. When the second input shaft also rotates at speed *a* in addition to the first input shaft, if the two input gears have the same gear ratio relative to the output shaft, the rotational speed of the output shaft can be expressed as a product of 2*b or a sum of b+b.

[0026] In this application, the first input gear and the second input gear broadly refer to all such transmission combinations that can be combined between the first drive motor and the second drive motor, and the gear ratio of the output shaft of the differential includes the gears between the first input shaft and the second input shaft of the differential and the output shaft of the same differential, and may also be a first pre-gear added to the first input shaft or the second input shaft of the differential.

[0027] Furthermore, variations in different implementations of the motor driving the input shaft (e.g., for motors connected to the first and second input shafts), different electrical connection modes, different rated rotational speeds, different numbers of hubs, the number of motors, or other implementations affecting the rotational speed or torque of the input shaft of the differential can have different effects between the first and second input shafts.

[0028] Therefore, the total gear ratio of the first input gear and the second input gear relative to the output shaft can be constructed individually or in combination using the embodiments described above. It is worth mentioning that the first input gear and the second input gear can have their own and separate total gear ratios relative to the output shaft.

[0029] In the definition of total gear ratio described in this specification, when the speed of the input shaft of the differential remains the same, increasing the total gear ratio results in an increase in the torque of the output shaft and a decrease in its speed, and decreasing the total gear ratio results in a decrease in the torque of the output shaft and an increase in its speed.

[0030] When the mechanism has the required redundancy—that is, if the first hoisting motor, brake, driver operating the hoisting motor, etc., fails, the failed mechanism can be stopped, held in place by the brake, and the same load can be driven by the second mechanism—then a differential has previously been used in the crane. However, for both hoisting motors, the input gears are the same.

[0031] In the gear mechanism solution according to the invention, the two input gears (first and second) are connected to the output gear uninterruptedly in time, so there is no connection problem, but the first input gear and the second input gear are connected to the output shaft uninterruptedly via the differential gear.

[0032] In this invention, when the lifting mechanism is used under heavy load, the first motor mounted on the first input gear starts, and the second motor mounted on the second input gear starts, while the first motor continues to operate. However, the condition for starting the second motor is that the torque received from the second motor is at least equal to the torque required to lift the load. Therefore, under heavy load, only the first motor connected to the first input shaft is driven, the second input shaft is stopped, and preferably, the second motor connected to the second input shaft and the first motor connected to the first input shaft are driven simultaneously. In this case, the load to be lifted is usually very light, thereby achieving a high lifting speed.

[0033] A conventional differential with an input shaft having an equal relative gear to the output shaft and an electric motor with equal characteristics connected to the input shaft does not offer an improvement to the described problem. In this case, the achieved load-lift capacity-speed ratio is equal to that of a conventional geared gear solution, in which suitable gears are selected and two of the aforementioned electric motors are connected in series to the same shaft in the input shaft, or an electric motor with twice the power is selected.

[0034] The essence of this invention lies in utilizing different total gear ratios relative to the output shaft between the first and second input shafts of the differential. Furthermore, the motors arranged on the input shafts are preferably equal-speed motors. In this case, a higher speed is achieved with a lower load, and the motors connected to the first and second input shafts are driven together or separately at different speeds based on the increased load information (using a separate sensor or weighing the load based on the motor current).

[0035] For example, when i=2 is chosen as the number of gear teeth on the second input shaft relative to the output shaft (which is a typical gear difference between the slow and fast gear differences when using a separate transmission gear), a wide speed range is achieved without mechanical connection problems. In this case, twice the speed is achieved via the second input shaft without the problems described in the prior art.

[0036] When both motors connected to the first and second input shafts are driven in this exemplary case, three times the speed is achieved compared to driving only the first motor connected to the first input shaft alone. In this example, the first input shaft has a higher-speed gear, i.e., a lower achievable lifting speed.

[0037] When the number of teeth of the gear on the first input shaft relative to the output shaft is selected, for example, i = 20, and the number of teeth of the gear on the second input shaft relative to the output shaft is selected, for example, i = 10, the ratio of the total number of teeth of the first input shaft and the second input shaft is 2.

[0038] In this specification, the term "ratio of the total gear tooth ratio of the first input shaft and the second input shaft" is used to indicate the difference in the relative gear tooth ratio between the first input shaft and the second input shaft, without stating the total gear tooth ratio of the gear assembly or mechanism, which is formed together with the differential gear stages and other gears, rope diagrams, etc. of the gear assembly.

[0039] This relative difference 2 in the gear ratio between the input shafts corresponds to the typical gear ratio i = 2 in a gear change mechanism, and when using a separate gear change mechanism, it is the typical gear ratio difference between the slow gear ratio and the fast gear ratio.

[0040] When the same total gear ratio is selected for the differential, the same motor as in the case of the geared transmission described above is used, and the same performance as the high-speed gear (i.e., the slow speed step) of the geared transmission is achieved using the first input shaft.

[0041] Correspondingly, by utilizing the second input shaft, the same performance as the pinion (i.e., the fastspeed step) of a transmission gear mechanism is achieved. This enables a wide speed range without the problems described in the prior art.

[0042] The ratio of the total number of teeth of the two input gears is preferably 1.1 to 4, more preferably 1.5 to 3, and most preferably 1.5 to 2.5, thereby providing a continuously optimal operating range for the lifting motor relative to the speed of the output shaft and producing a more uniform torque over a wider speed range, thus achieving a wider usable speed range. In this way, the maximum power achievable by the crane can also be better realized under small loads, meaning the device is used with maximum efficiency. In the differential, the rotational speeds of the input shafts are summed. A squirrel-cage motor is preferably used as the motor to be coupled to the gear mechanism.

[0043] When handling heavy loads using the lifting mechanism according to the invention, a lifting motor is used (i.e., driven) and connected to an input shaft with a larger input gear (i.e., a slower lifting speed). In this case, the input shaft with a smaller gear, which produces a higher speed and a lower load capacity, is stopped. When the input shaft stops, it is held stationary by a brake. Therefore, the speed of the lifting device is determined by the speed of the slower input shaft.

[0044] When handling lighter loads, the lifting motors, which were started in the first stage and coupled to an input shaft with a larger input gear (meaning a slower lifting speed) and another input shaft with a smaller gear (meaning a faster lifting speed), are started in the second stage, and the brakes are engaged. As the two input shafts rotate, the speed of the lifting device is determined based on the sum of the individual speeds achieved by the output shafts, caused by the total gear ratio of the two input shafts.

[0045] Two squirrel-cage motors connected to the input shaft of the differential can be controlled in the same way using a common control (using a so-called DC power supply with relays, using a soft starter, using a frequency converter, etc.). However, optimal end results are achieved when each motor is controlled individually using a separate frequency converter. The squirrel-cage motor can be equipped with a sensor to monitor the rotation of the rotor shaft. Monitoring the rotor's rotation, for example, uses a frequency converter to adjust the precise rotational speed. This sensor can be a pulse sensor or an incremental sensor.

[0046] Using a frequency converter, the speeds of two motors can be steplessly and individually adjusted based on the power output of the respective motors and the torque, speed, and power required by the load. In this invention, the motors are used according to the load to be lifted. The load is weighed during lifting, and the maximum possible speed of the motors is calculated individually based on the load information. Based on the maximum mechanical speed under different load conditions, the motor speed can be freely and individually selected according to its torque and power. The motor speed is preferably set using a frequency converter. This fully utilizes the characteristics of both motors. This arrangement also allows the motors, and (if needed) the components used to control and supply power to them, to be of the same type, making them interchangeable. This provides advantages for mass production and spare parts procurement.

[0047] When lifting a medium-sized load (with a mass between its maximum value and zero), a lifting motor connected to an input shaft with a larger input gear and a slower lifting speed can be started and accelerated to its limit. Under light loads, this limit might be, for example, the maximum mechanical speed, or under maximum or medium-high loads, the limit might be the maximum achievable torque within the range of magnetic field weakening. If a further increase in lifting speed is required, a lifting motor connected to an input shaft with a smaller input gear and a larger lifting speed is started and accelerated to its limit relative to the rotational speed or torque within the so-called range of magnetic field weakening. In this way, the motor is used more efficiently and cautiously than through step-by-step control.

[0048] Since the first lifting motor drives an input shaft with a larger input gear (i.e., a slower lifting speed) and the second lifting motor drives an input shaft with a smaller gear (i.e., a higher lifting speed), depending on the load on the lifting member and the desired lifting / lowering speed, efforts are made to control the lifting motors so that the loads on the two lifting motors are substantially (not absolutely) equal, and the drive of the lifting motors is optimized so that the relative loads of the motors are divided according to the speed required by the corresponding load and rotational speed, thereby achieving maximum combined performance. Attached Figure Description

[0049] The invention will be described in more detail below with reference to the accompanying drawings, wherein...

[0050] Figure 1 A perspective view of the lifting mechanism according to the present invention is shown;

[0051] Figure 2 It shows that according to Figure 1 The schematic diagram of the solution, and

[0052] Figures 3 to 7 A solution based on conventional technology as the ratio of load to boost speed is shown, and

[0053] Figures 8 to 10 A solution based on the present invention as the ratio of load to lifting speed is shown. Detailed Implementation

[0054] Referring to the accompanying drawings, a lifting mechanism 1 of a crane according to the present invention is shown, comprising: a rope drum 2 for lifting a rope 3; two lifting motors 4 and 5 for driving the rope drum 2; and a gear assembly 6 connected between the rope drum 2 and the lifting motors 4 and 5, having input gears 7 and 8 on the side of the lifting motors 4 and 5 and an output gear 9 on the side of the rope drum 2. Additionally, there are brakes 10 and 11 for braking the input gears 7 and 8, and clutches 12 and 13 for connecting the lifting motors 4 and 5 to the gear assembly 6. The brakes 10 and 11 are equipped with sensors for monitoring the open / closed state of the brakes. When the brakes 10 and 11 are closed, they keep the input shafts 7a and 8a of the input gears 7 and 8 connected to them stationary. When the brakes 10 and 11 are open, they allow the input shafts connected to them to rotate.

[0055] The gear assembly 6 has a differential 6A, the input gears 7 and 8 of which include a first input gear 7 and a second input gear 8. The first input gear 7 and the second output gear 8 are connected to each other and also to an output gear 9.

[0056] A first lifting motor 4 can be connected to a first input gear 7, and a second lifting motor 5 can be connected to a second input gear 8. The first input gear 7 and the second input gear 8 are not equal in size relative to the output shaft. In this example, the first input gear 7 is larger than the second input gear 8. It is also possible to arrange the first input gear 7 to be smaller than the second input gear 8. The magnitude of the difference between the total gear ratios of the first input gears 7 and 8 relative to the output gear 9 can be approximately 1.1 to 4, 1.1 to 3, or 1.1 to 2.5, depending on the desired speed to be achieved under different loads. When the motors 4 and 5 driving the two input shafts 7a and 8a are driven simultaneously, the greater the difference, the greater the theoretical speed of the lifting device, but the lower the load-bearing capacity, because when the lifting motors 4 and 5 connected to the two input shafts 7a and 8a are driven simultaneously, the motor that produces a smaller torque on the output shaft of the differential is determined. The aforementioned difference in the total gear ratios relative to the output gear 9 is a good trade-off that provides almost all advantages. The first input gear 7 and the second input gear 8 can be on the same axis (center to center).

[0057] The lifting motors 4 and 5 are preferably squirrel-cage motors (controlled by a frequency converter).

[0058] Brakes 10 and 11 can be connected to the first input shaft 7a and the second input shaft 8a, and lifting motors 4 and 5 can be connected to these input shafts 7a and 8a via the aforementioned clutches 12 and 13. The shaft of the rope drum 2 preferably also has a brake 14. In case of failure of one or both of the aforementioned brakes 10 and 11, this ensures that the movement of the load is stopped in an emergency. The brake 14 of the rope drum should be designed to be large enough to withstand a large torque.

[0059] The following sections provide several examples of mutual control of lift motors, assuming the load in each example is to be lifted or lowered at maximum speed. For simplicity, the term "fast" lift motor refers to a motor that drives the input shaft of the same differential, which has a smaller total number of teeth relative to the output shaft of the differential, and thus achieves a greater lift speed; and a "slow" lift motor refers to a motor that drives the input shaft, which has a larger total number of teeth relative to the output shaft of the differential, and thus achieves a lower lift speed. Therefore:

[0060] Under maximum load, the "fast" lifting motor 5 is not driven and the brake 11 of the lifting motor 5 remains closed, and only the "slow" lifting motor 4 is driven.

[0061] Under medium loads, both "fast" and "slow" lifting motors 4 and 5 are used. Thus, the speed of the "slow" lifting motor 4 is usually limited by the maximum magnetic field weakening torque, and the speed of the "fast" lifting motor 5 is usually limited by the magnetic field weakening torque that is already at a lower rotational speed.

[0062] Under light loads, both "fast" and "slow" lifting motors 4 and 5 are used. Thus, the speed of the "slow" lifting motor 4 is usually limited by the maximum mechanical rotational speed of the lifting motor 4, and the speed of the "fast" lifting motor 5 is usually limited by the reduced torque of the magnetic field at a lower rotational speed, or otherwise usually limited by the maximum mechanical rotational speed of the lifting motor 5.

[0063] In addition to heavy loads, controlling the hoisting motors 4 and 5 based on load information allows for a wide, steplessly achievable speed range, ensuring optimal utilization of the capabilities of both motors. The determination of load information can be performed using individual load cells or based on measurements from the hoisting motors used in the hoisting process. Alternatively, the crane operator can select the desired load range from the crane control system and control the hoisting motors 4 and 5 at a predetermined speed according to the selected load range. The load information is used to determine whether the operation is performed within the operating range of the first hoisting motor 4 or within a combined operating range of the first hoisting motor 4 and the second hoisting motor 5. These operating ranges can be distinguished by load limit values.

[0064] The load limit value is determined based on the load information and the torque generated by the lift motors 4 and 5 connected to the input shaft of the differential. The load limit value is a value that allows the first lift motor 4 connected to the first input shaft 7a and the second lift motor 4 connected to the second input shaft 8a to be driven simultaneously when the value is lower than the load limit value.

[0065] Specifically, when the load limit is equal to or greater than the specified load limit, only the input shaft and the lifting motor connected to it, which generates a torque greater than that required to lift the load, are driven. In this case, the input shaft and the lifting motor connected to it, which generates a torque less than that required to lift the load, are kept stationary using one or more brakes. The load limit can be... Figure 8 , Figure 9 and Figure 10 The values ​​are graphically represented using curves 37, 38, and 39, which essentially represent the maximum values ​​in the respective implementations. Load limits can also be set lower by the supplier's choice.

[0066] When the load limit value is high, only the first motor 4 is used, while when the load limit value is low, both the first motor 4 and the second motor 5 are used together. Depending on the relative total gear ratio of the first input shaft 7a and the second input shaft 8a, the operating sequence can also be such that when the load limit value is high, only the other motor is used, and when the load limit value is low, both the first motor 4 and the second motor 5 are used together. Furthermore, in this specification, the total gear ratio of the first input shaft 7a used as an example is greater than the total gear ratio of the second input shaft 8a; therefore, the first input shaft has a higher load lifting capacity and a slower speed compared to the second input shaft 8a, but the reverse is also possible in practice. The maximum rotational speed of the lifting motors 4 and 5, which operate simultaneously or individually on the input shafts 7 and 8 connected to the differential of the same lifting mechanism, is determined based on load information.

[0067] In the event of a malfunction, such as damage to or malfunction of the motor or other components connected to and driving the input shaft, only one of the lifting motors 4 and 5 may be used. In this case, the brakes 10 and 11 of the unusable input shafts 7a and 8a are deactivated. A limiting factor for the lifting speed may be the total power absorbed by the lifting mechanism. In this case, the lifting speed may be limited so that the total power absorbed by the lifting motors 4 and 5 does not overload the system supplying power to the crane.

[0068] A comparison of conventional techniques and solutions according to the present invention based on the following examples. :

[0069] At a lifting speed of 5 m / min and a load of 400 t, in conventional technology, the gear mechanism is selected by its output mechanical torque, and the gears of this gear mechanism are selected to drive the squirrel-cage motor at its maximum power rotational speed (e.g., 1200 rpm). When the maximum permissible rotational speed of the squirrel-cage motor is 2400 rpm, the maximum speed that the lifting device can achieve is 10 m / min.

[0070] If the maximum speed required by the lifting device is 20 m / min, then for the selected lifting motor, the gears of the gear mechanism need to be changed so that the maximum permissible mechanical rotational speed of the lifting motor corresponding to the lifting device's speed of 20 m / min is 2400 rpm. In this case, when lifting a 400t load at a lifting speed of 5 m / min, the rotational speed of the lifting motor is 600 rpm (2400 * 5 / 20).

[0071] When the power required to lift the device is not changed by altering the gears in the gear mechanism, the squirrel-cage motor must produce the same power at 600 rpm as it does at 1200 rpm with the first gear. This means the motor must generate a correspondingly larger (twice the) torque. This doubled torque means the entire power line (inverter, power cable, motor) must double its power transmission capacity, increasing the cost of the device in multiple parts.

[0072] Based on the foregoing examples, the "gear changing" technology and the solution of the present invention in terms of improving solutions are discussed. Case comparison :

[0073] At a lifting speed of 5 m / min and a load of 400 t, the gear mechanism is selected via its output mechanical torque, and the gear of the gear mechanism is selected in the speed range 1 "slow" of the gear selector, so that the squirrel-cage motor is driven at its maximum power speed (e.g., 1200 rpm). When the maximum permissible mechanical rotational speed of the squirrel-cage motor is 2400 rpm, the maximum achievable lifting speed of the lifting device is 10 m / min.

[0074] If the required maximum achievable speed of the lifting device is 20 m / min, then using the speed 2 "fast" of the gear selector (gear ratio i = 2), the gears of the gear mechanism must be changed so that the maximum permissible mechanical rotational speed of the motor corresponding to the lifting device speed of 20 m / min is 2400 rpm. However, a drawback of this solution is that the mechanism needs to be stopped when making the change. Furthermore, changing the speed range is not always reliably successful.

[0075] The following describes Figures 3 to 10The diagrams illustrate that the motor and drive control in the example diagrams are speed-controlled. These diagrams compare the differences between conventional solutions and solutions according to the present invention in terms of the load-to-speed ratio:

[0076] Figure 3 :

[0077] Figure 3 The differences between a squirrel-cage electric motor and a DC motor with the same power are shown, each motor being coupled to its corresponding preferred gear unit. The gear unit has only one input shaft, but the gear ratios may differ to achieve a preferred assembly.

[0078] curve Figure 1 = Required load - speed ratio curve.

[0079] Curve 61 = A curve of the load-speed ratio generated by the linear speed / torque curve of a DC motor connected to the input shaft of a conventional fixed gear gear unit.

[0080] Curve 41 = A curve of the load-speed ratio generated by a squirrel-cage motor connected to the input shaft of a conventional fixed gear gear unit.

[0081] The gears of the gear mechanism are selected such that, at the rated speed of the motor connected to the gears (1200 rpm), the speed of the lifting device is 7 m / min. In this case, the required rated power of the motor is 127 kW.

[0082] As can be seen from the DC motor's graph, the required speed and lifting capacity have been achieved.

[0083] For squirrel-cage motors, under a load of approximately 50t and a speed of 10m / min, the speed and lifting capacity cannot fully meet the curve requirements. Figure 1 The requirements. Based on the curve. Figure 1 When curve 41 ends at a speed of approximately 14 m / min, the target is not reached at speeds above 15 m / min.

[0084] These graphs illustrate the differences between DC motors and squirrel-cage motors with the same rated power.

[0085] Figure 4 :

[0086] Figure 4 A squirrel-cage motor is shown connected to a fixed gear mechanism with only one input shaft.

[0087] curve Figure 1 = Required load - speed ratio curve.

[0088] For the calculations, the mechanism designer selects a squirrel-cage motor with a rated power of 182kW, and he / she receives the characteristics and information of the squirrel-cage motor from the motor designer.

[0089] Figure 4 A typical calculation cycle is shown, which covers the optimal solutions for the gears and motors of the gear mechanism. The mechanism designer obtains the characteristics and information of the gear mechanism from the gear mechanism designer.

[0090] Curve 53a = A curve of the load-speed ratio generated by a squirrel-cage motor connected to the input shaft of a conventional fixed gear mechanism.

[0091] In graph 53a, the gear of the gear mechanism is selected such that, at the rated speed of the motor connected to the gear (1200 rpm), the speed of the lifting device is 8 m / min. According to graph 53a, a maximum speed of approximately 16 m / min is achieved, which is far below the required 20 m / min.

[0092] Curve 53c = A curve of the load-speed ratio generated by a squirrel-cage motor connected to the input shaft of a conventional fixed gear mechanism.

[0093] In curve 53c, the gear of the gear assembly is selected such that the speed of the lifting device is 12 m / min at the rated speed of 1200 rpm of the motor connected to the gear. According to curve 53c, a maximum speed of approximately 25 m / min is achieved, but the required load limit of 90 t is not met at speeds less than 5 m / min.

[0094] Graph 53b = A graph of the load-speed ratio generated by a squirrel-cage motor connected to the input shaft of a conventional fixed gear mechanism.

[0095] In graph 53b, the gear of the gear mechanism is selected such that, at the rated speed of the motor connected to the gear (1200 rpm), the speed of the lifting device is 10 m / min. Utilizing the characteristics of the selected gear and motor, the desired performance values ​​are achieved and exceeded.

[0096] If no suitable gear is found for the geared device, the same calculations for the geared device will be performed on another motor with different ratings in terms of rated power or speed.

[0097] Figure 5 :

[0098] Figure 5 A graph showing the required load-speed ratio for a two-stage geared transmission is provided.

[0099] curve Figure 1= Required load - speed ratio curve.

[0100] Curve 34 = A curve showing the load-speed ratio generated by the motor connected to the input shaft of the transmission gear unit when a larger gear ratio (i.e., a lower speed range) is used.

[0101] Curve 44 = A curve showing the load-speed ratio generated by the motor connected to the input shaft of the transmission gear when a smaller gear ratio (i.e., a larger speed range) is used.

[0102] The gear with the larger gear ratio difference (i.e., smaller speed range) of the gear transmission device is selected such that the speed of the lifting device is 5 m / min at the rated speed of 1200 rpm of the first motor connected to the gear.

[0103] The gear with the smaller gear ratio (i.e., the larger speed range) of the gear transmission device is selected such that the speed of the lifting device is 10 m / min at the rated speed of 1200 rpm of the second motor connected to the gear.

[0104] This solution, which demonstrates the conventional technology of gear shifting, has only one input shaft.

[0105] Figure 6 :

[0106] Figure 6 A squirrel-cage motor designed for high performance is shown, which is coupled to a fixed gear mechanism having only one input shaft.

[0107] curve Figure 1 = Required load - speed ratio curve.

[0108] Curve 45 = A curve showing the load-speed ratio generated by a squirrel-cage motor connected to the input shaft of a conventional fixed gear gear unit.

[0109] The gear of the gear mechanism is selected such that the speed of the lifting device is 10 m / min at the rated speed of the motor connected to the gear (1200 rpm). In this case, the required rated power of the motor is 182 kW.

[0110] The curve of the squirrel-cage motor shows that the required speed and lifting capacity have been achieved.

[0111] Gear assemblies with fixed gears are the simplest option, but this results in excessively large components. As the required speed range or load increases further and the required power increases above a certain limit, different technical implementations must be undertaken, in which the gears of the gear assembly are interlaced.

[0112] Figure 7 :

[0113] Figure 7 A squirrel-cage motor with a first input shaft and a second input shaft having the same total gear ratio relative to the output shaft is shown.

[0114] curve Figure 1 = Required load - speed ratio curve.

[0115] Curve 26 is a curve showing the load-speed ratio generated by a 91kW squirrel-cage motor with a rated speed of 1200 rpm, connected to the first and second input shafts of the differential. The gears of the two differential stages are identical, enabling a lifting speed of 5 m / min at the motor's rated speed of 1200 rpm to be achieved using only the motor on the other input shaft. According to curve 36, twice the speed is achieved when both input shafts are used simultaneously.

[0116] Differentials are less commonly used gear mechanisms because their complex structure makes them more difficult and expensive to manufacture. For example... Figure 6 The curves in Figure 45 and Figure 7 As shown in Figure 36, no performance gain was achieved in terms of speed or load capacity using two 91kW motors and a differential.

[0117] A differential gear is used in cranes in special cases where a double lifting mechanism is needed to increase operational reliability. This corresponds to a situation where another motor or its drive fails, allowing the same load to be lifted further at half speed and the job completed.

[0118] Figure 8 :

[0119] Figure 8 A squirrel-cage motor is shown connected to the first and second input shafts of a differential, wherein the difference between the total gear ratios is doubled relative to the output shaft. The load is 15t.

[0120] curve Figure 1 = Required load - speed ratio curve.

[0121] Curve 27 = A curve showing the load-speed ratio generated by the first motor connected to the first input shaft of the differential.

[0122] Curve 37 = A curve showing the load-speed ratio generated by the second motor connected to the second input shaft of the differential.

[0123] The gear on the first input shaft of the differential is selected such that the speed of the lifting device is 5 m / min at the rated speed of 1200 rpm of the first motor connected to the gear.

[0124] The gear on the second input shaft of the differential is selected such that the speed of the lifting device is 10 m / min at the rated speed of 1200 rpm of the second motor connected to the gear.

[0125] The ratio of the total gear teeth between the first input shaft and the second input shaft is 2. According to curve 37, when the motor connected to the first input shaft and the second input shaft is driven at twice the rated rotational speed, the maximum lifting speed is 30 m / min, corresponding to a load of 15 t.

[0126] Figure 9 :

[0127] Figure 9 A squirrel-cage motor is shown connected to the first and second input shafts of a differential, wherein the ratio of the number of teeth of the first gear and the second gear relative to the total number of teeth of the output shaft is 2. The load is 50t.

[0128] Curve 28 = A curve showing the load-speed ratio generated by the first motor connected to the first input shaft of the differential.

[0129] Curve 38 = A curve showing the load-speed ratio generated by the second motor connected to the second input shaft of the differential. A 91kW squirrel-cage motor is used as the motor.

[0130] The gear on the first input shaft of the differential is selected such that the speed of the lifting device is 5 m / min at the rated speed of 1200 rpm of the first motor connected to the gear.

[0131] The gear on the second input shaft of the differential is selected such that the speed of the lifting device is 10 m / min at the rated speed of 1200 rpm of the second motor connected to the gear.

[0132] The ratio of the total number of gear teeth on the first input shaft and the second input shaft of the differential is 2.

[0133] When the first motor on the first input shaft of the differential is running at approximately 7 m / min and can lift a maximum load of 50 t, the second motor connected to the differential starts. When the second motor accelerates to its rated speed of 1200 rpm, a lifting speed of 17 m / min is achieved for a 50 t load. Furthermore, a lifting speed exceeding 25 m / min can be achieved with a lower load of 15 t.

[0134] Figure 10 :

[0135] Figure 10 A squirrel-cage motor is shown connected to the first and second gears of a differential, wherein the ratio of the total number of teeth of the first and second gears is 3.

[0136] curve Figure 1 = Required load - speed ratio curve.

[0137] Curve 29 = A curve showing the load-speed ratio generated by the first motor connected to the first input shaft of the differential.

[0138] Curve 39 = A curve showing the load-speed ratio generated by the second motor connected to the second input shaft of the differential. A 91kW squirrel-cage motor is used as the motor.

[0139] The gear on the first input shaft of the differential is selected such that the speed of the lifting device is 5 m / min at the rated speed of 1200 rpm of the first motor connected to the gear.

[0140] The gear on the second input shaft of the differential is selected such that the speed of the lifting device is 15 m / min at the rated speed of 1200 rpm of the second motor connected to the gear.

[0141] The ratio of the total number of gear teeth on the first input shaft and the second input shaft of the differential is 3.

[0142] When the first motor on the first input shaft of the differential is running at approximately 7 m / min and can lift a maximum load of 32 t, the second motor connected to the differential starts. When the second motor accelerates to its rated speed of 1200 rpm, a lifting speed of 23 m / min is achieved for a lifting device with a load of 32 t. Furthermore, a lifting speed of 30 m / min can be achieved with a lower load of 15 t.

[0143] exist Figure 8 , Figure 9 and Figure 10 With the help of [the invention], the advantages of this invention can be clearly demonstrated when light loads, empty hooks, or lifting components can be lifted at speeds exceeding 25 m / min, while the power of the electric motor can be designed to be significantly smaller. Through comparison... Figures 3 to 7 and Figures 8 to 10 Therefore, the curve group can be expanded "to the right". This has already been achieved without having to raise the curve group "up" from the left edge, that is, it has been possible to avoid making the size of the lifting motor and its power supply components too large.

[0144] The greater lifting or lowering speed of lightly loaded or unloaded components described in this application enables faster load handling, for example, in ports. Faster loading and unloading times for maritime cargo reduce the time ships spend on land, allowing them to spend more time at sea, thus improving transportation efficiency and economy. Lifting speed is particularly important in ports, which typically have high lifting heights. This solution can also be used in construction cranes, mobile cranes, and hoists in wind farms. These are characterized by a constant gravity acting on the lifting mechanism when it is desired to change the speed range to alter the lifting speed.

[0145] The connection to the lifting motor can be completed manually or automatically to rotate or stop based on load information. For automatic functionality, a comparison can be made between the load information and load limit information.

[0146] The above description of the present invention is intended only to illustrate the basic principles of the invention. Therefore, its details can be realized within the scope of the appended claims.

Claims

1. A lifting mechanism (1) for a crane, comprising: At least one rope drum (2), said at least one rope drum for lifting rope (3), At least one lifting motor (4, 5) is provided for driving the rope drum (2). A gear mechanism (6) is connected between the rope drum (2) and the lifting motor (4,5), and has an input gear (7,8) on the side of the lifting motor (4,5) and an output gear (9) on the side of the rope drum (2). The gear assembly (6) has a differential (6a) with a first input gear (7) and a second input gear (8) arranged thereon. The first input gear (7) and the second input gear (8) are interconnected and also connected to the output gear (9). The first lift motor (4) connected to the first input gear (7) and the second lift motor (5) connected to the second input gear (8) are connected to the first input shaft and the second input shaft of the differential (6a), and The first input gear (7) and the second input gear (8) have unequal total gear tooth ratios relative to the output shaft. Its features are, The lifting motors (4,5) are squirrel-cage motors, and the lifting mechanism (1) has means for determining load information for lifting, wherein the lifting mechanism is configured to select a lifting speed based on the speed of the squirrel-cage motor and the load information.

2. The lifting mechanism according to claim 1, characterized in that, The first input gear and the second input gear (7,8) are connected continuously in time via gear tooth contact with the output gear (9).

3. The lifting mechanism according to claim 1 or 2, characterized in that, The first input gear (7) has a larger total gear ratio than the second input gear (8).

4. The lifting mechanism according to claim 3, characterized in that, The ratio between the total gear ratio of the first input gear and the second input gear is approximately 1.1 to 2.

5.

5. The lifting mechanism according to claim 1 or 2, characterized in that, The first input gear (7) has a lower total gear ratio than the second input gear (8).

6. The lifting mechanism according to claim 1 or 2, characterized in that, The first input gear (7) and the second input gear (8) of the differential are not equal relative to the output shaft.

7. The lifting mechanism according to claim 1 or 2, characterized in that, The lifting motors (4, 5) are directly connected to the gear assembly.

8. The lifting mechanism according to claim 1, characterized in that, At least one lifting motor (4,5) is a motor controlled by a frequency converter.

9. The lifting mechanism according to claim 1, characterized in that, At least one lifting motor (4,5) is equipped with a sensor that measures the rotational speed of its rotor.

10. The lifting mechanism according to claim 1, characterized in that, At least one brake (10, 11) is equipped with a sensor that monitors the open-closed state of the brake.

11. A method for operating the lifting mechanism according to claim 1, characterized in that, By using the load information, it is determined that when the load limit value is high, only the lifting motor connected to the input shaft with the higher input gear is used, and when the load limit value is low, both the lifting motors connected to the first input shaft and the second input shaft are used.

12. The method according to claim 11, characterized in that, The maximum rotational speed of the lifting motor, which operates simultaneously or independently, is determined based on load information of the input shaft of the differential connected to the same lifting mechanism.

13. The method according to claim 11, characterized in that, Limit the lifting speed in order to limit the total power absorbed by the lifting mechanism.

14. The method according to claim 11, characterized in that, A squirrel-cage motor controlled by a frequency converter is selected as the lifting motor.

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