LIFTING APPARATUS OF CRANE AND METHOD OF OPERATION THEREOF

Abstract

A hoisting mechanism of a crane comprising at least one rope drum for a hoist rope, at least one hoist motor for driving the rope drum, a gearing coupled between the rope drum and the hoist motor, and having an input gear on the hoist motor side and an output gear on the rope drum side, and a brake for braking the input gear. The gearing has a differential to which a first input gear and a second input gear are arranged, wherein the first input gear and the second input gear are coupled to each other and further coupled to the output gear, wherein a first hoist motor connected to the first input gear, and a second hoist motor connected to the second input gear are arranged, and wherein the first input gear and the second input gear have unequal total gear ratios relative to an output shaft. The invention also relates to a method for operating this hoisting mechanism.

Claims

1. A hoisting mechanism of a crane comprising at least one rope drum for a hoist rope, at least one hoist motor for driving the rope drum, a gearing coupled between the rope drum and the hoist motor, and having an input gear on the hoist motor side and an output gear on the rope drum side, wherein the gearing has a differential to which a first input gear and a second input gear are arranged, wherein the first input gear and the second input gear are coupled to each other and further coupled to the output gear, a first hoist motor connected to the first input gear, and a second hoist motor connected to the second input gear are arranged, and wherein the first input gear and the second input gear have un equal total gear ratios relative to an output shaft.

2. The hoisting mechanism according to claim 1, wherein the first and the second input gears are timewise uninterruptedly coupled via gear tooth contact to the output gear.

3. The hoisting mechanism according to claim 1, wherein the first input gear has a greater total gear ratio than the second input gear.

4. The hoisting mechanism according to claim 1, wherein the ratio between the total gear ratios of the first and second input gears is in the magnitude of approximately 1.1-2.5.

5. The hoisting mechanism according to claim 1, wherein the first input gear has a lower total gear ratio than the second input gear.

6. The hoisting mechanism according to claim 1, wherein the first input gear and the second input gear of the differential are unequal relative to the output shaft.

7. The hoisting mechanism according to claim 1, wherein the hoist motors are directly coupled to the gearing.

8. The hoisting mechanism according to claim 1, wherein the hoist motor is a squirrel cage motor.

9. The hoisting mechanism according to claim 8, wherein at least one hoist motor is a frequency converter-controlled electric motor.

10. The hoisting mechanism according to claim 8, wherein at least one hoist motor is equipped with a sensor measuring the speed of rotation of its rotor.

11. The hoisting mechanism according to claim 8, wherein at least one brake is equipped with a sensor monitoring the open-closed state of the brake.

12. A method for operating the hoisting mechanism according to claim 1, wherein at higher values of the load limit value, only a hoist motor coupled to the input shaft having a higher input gear is used, and at lower values of the load limit value, hoist motors coupled to the first input shaft and the second input shaft are simultaneously used.

13. The method according to claim 12, wherein the maximum speed of rotation for the hoist motors running simultaneously or separately, connected to the input shafts of the differential of the same hoisting mechanism, is determined on the basis of load information.

14. The method according to claim 12, wherein hoisting speeds are limited in order to limit the total power absorbed by the hoisting mechanisms.

15. The method according to claim 12, wherein frequency converter-controlled squirrel cage motors are selected as the hoist motors.

Description

LIST OF FIGURES

[0049] In the following the invention will be described in greater detail with reference to the attached drawings, in which

[0050] FIG. 1 illustrates a perspective view of a hoisting mechanism according to the invention;

[0051] FIG. 2 illustrates a principle picture of a solution according to FIG. 1, and

[0052] FIGS. 3-7 illustrate a solution according to the traditional technology as a ratio of load and hoisting speed, and

[0053] FIGS. 8-10 illustrate a solution according to the invention as a ratio of load and hoisting speed.

DETAILED DESCRIPTION OF THE INVENTION

[0054] With reference to the drawings, there is shown a hoisting mechanism 1 of a crane according to the invention comprising a rope drum 2 for a hoist rope 3; two hoist motors 4,5 for driving the rope drum 2; a gearing 6 coupled between the rope drum 2 and the hoist motor 4,5, and having an input gear 7, 8 on the hoist motor 4, 5 side and an output gear 9 on the rope drum 2 side. In addition, there are brakes 10, 11 for braking the input gear 7, 8, and clutches 12, 13 for coupling the hoist motors 4, 5 to the gearing 6. The brakes 10, 11 are equipped with a sensor monitoring the open-closed state of the brake. When the brake 10, 11 is closed, it holds the input shaft 7a, 8a of the input gear 7, 8 coupled to it still. When the brake 10, 11 is open, it allows the input shaft coupled to it to rotate.

[0055] The gearing 6 has a differential 6A, the input gear 7, 8 of which comprises a first input gear 7 and a second input gear 8. The first input gear 7 and the second output gear 8 are coupled to each other and further coupled to the output gear 9.

[0056] The first hoist motor 4 can be coupled to the first input gear 7 and the second hoist motor 5 can be coupled to the second input gear 8. The first input gear 7 and the second input gear 8 are unequal relative to the output shaft. In this example, the first input gear 7 is greater than the second input gear 8. It can also be arranged so that the first input gear 7 is smaller than the second input gear 8. The difference between the total gear ratios of the first input gears 7, 8 relative to the output gear 9 can be in the magnitude of approximately 1.1-4, 1.1-3, or 1.1-2.5, depending on the desired speeds to be achieved with different loads. The greater the difference between the, the greater the theoretical speed of the hoisting means, when motors 4,5 driving both input shafts 7a, 8a are driven simultaneously, but the load bearing capacity is lower, because when driving the hoist motors 4,5 coupled to both input shafts 7a, 8a simultaneously, of these, the motor which generates smaller moment on the output shaft of the differential, is determining. The above-mentioned difference in the total gear ratio relative to the output gear 9 is a good compromise that provides virtually all advantages. The first and second input gears 7, 8 may be on the same axis line (center—to center).

[0057] The hoist motors 4,5 are preferably (frequency converter controlled) squirrel cage electric motors.

[0058] The brakes 10, 11 can be coupled with the first input shaft 7a and the second input shaft 8a and the hoist motors 4,5 can be coupled with these input shafts 7a, 8a via the above-mentioned clutches 12, 13. The shaft of the rope drum 2 preferably also has a brake 14. This, in case of an emergency if one or both of the above-mentioned brakes 10, 11 fail, ensures that the motion of the load is stopped. The brake 14 of the rope drum should be designed large enough because it is subjected to a large moment.

[0059] In the following, a few examples are presented of the mutual control of hoist motors, it is assumed that the load of the example is intended to be hoisted or lowered at maximum speed. For shortening the descriptions, the term “fast” hoist motor means a motor that drives the input shaft of the differential having a smaller total gear relative to the output shaft of the same differential, and thus a greater hoisting speed is achieved, and “slow” hoist motor means a motor that drives the input shaft having a greater total gear relative to the output shaft of the same differential, and thus a lower hoisting speed is achieved. So:

[0060] With maximum loads, the “fast” hoist motor 5 is not driven and the brake 11 of the hoist motor 5 is held closed, and only the “slow” hoist motor 4 is driven.

[0061] With medium-sized loads, both “fast” and “slow” hoist motors 4, 5 are used, whereby the speed of the “slow” hoist motor 4 is limited usually by the maximum field weakening moment, and the speed of the “fast” hoist motor 5 is limited usually by the field weakening moment already at lower speeds of rotation.

[0062] With light loads, both “fast” and “slow” hoist motors 4, 5 are used, whereby the speed of the “slow” hoist motor 4 is limited usually by the maximum mechanical speed of rotation of the hoist motor 4, and the speed of the “fast” hoist motor 5 is limited usually by the field weakening moment already at lower speeds of rotation, or then usually the maximum mechanical speed of rotation of the hoist motor 5.

[0063] Controlling the hoist motors 4,5 on the basis of the load information allows, in addition to heavy load, a wide achievable speed range steplessly, so that the capacity of both hoist motors 4, 5 is best used. The determination of the load information can be carried out with separate weighing sensors or on the basis of the measured values of the hoist motors used in the hoisting. Alternatively, the crane operator can select the load range to be utilized from the crane control system and the hoist motors 4,5 are controlled according to the predetermined speeds of the selected load range of the control system. The load information is used to determine whether the operation is performed in the operating range of the first hoist motor 4 or in the combined operating range of the first and second hoist motors 4, 5. These operating ranges can be distinguished by a load limit value.

[0064] The load limit value is determined on the basis of the load information and the moment generated by the hoist motors 4,5 coupled to the input shafts of the differential. The load limit value is the value, that at lower values than the load limit value, the first hoist motor 4 coupled to the first input shaft 7a and the second hoist motor 4 coupled to the second input shaft 8a can be simultaneously driven.

[0065] Respectively, with values equal to or greater than the load limit value, only the input shaft and the hoist motor coupled to it, generating a moment greater than the moment required for hoisting the load, are driven. In this case, the input shaft and the hoist motor coupled to it, generating a moment smaller than the moment required for hoisting the load, are held still with a brake or brakes. The load limit values may be presented graphically in FIGS. 8, 9, and 10 by means of curves 37, 38, and 39, which may present substantially the maximum value in the respective implementation. The load limit value may also be set lower in a manner selected by the supplier.

[0066] At higher values of the load limit value only the first motor 4 is used and at lower values of the load limit value the first and second motors 4, 5 are used together. Depending on the relative total gear ratios of the first and the second input shafts 7a, 8a the order of operation may also be such that only the other motor is used at the higher values of the load limit value and at the lower values of the load limit value the first and the second motor 4,5 are used together. The total gear ratio of the first input shaft 7a, used as an example in the descriptions, is greater than the total gear ratio of the second input shaft 8a and thus has a higher load hoisting capacity and a slower speed than the second input shaft 8a, but the opposite implementation is also possible. On the basis of the load information, the maximum speed of rotation of the simultaneously or separately running hoist motors 4, 5 connected to the input shafts 7, 8 of the differential of the same hoisting mechanism is determined.

[0067] In the event of a fault in which the motor or other component, coupled to the input shaft and driving it, is damaged or prevented from being used, only one of the hoist motors 4,5 may be used, in which case the brake 10, 11 of the input shaft 7a, 8a removed from use is closed. The factor limiting the hoisting speed may be the total power absorbed by the hoisting mechanisms. In this case, the hoisting speeds may be limited, so that the total power absorbed by the hoist motors 4,5 does not cause an overload to the system supplying power to the crane.

[0068] Comparison of the traditional technology and a solution according to the invention in light of the following example:

[0069] At a hoisting speed of 5 m/min and a load of 400 t, in the traditional technology the gearing is selected through its outgoing mechanical moment and the gears of the gearing are selected so that the squirrel cage motor is driven at its maximum power speed of rotation, for example 1200 rpm. When the maximum allowed speed of rotation of the squirrel cage motor is 2400 rpm, then the maximum speed of the hoisting means that can be achieved is 10 m/min.

[0070] If the required maximum speed of the hoisting means to be achieved is 20 m/min, with this selected hoist motor the gears of the gearing need to be changed so that the maximum allowed mechanical speed of rotation of the hoist motor corresponding to the speed of the hoisting means of 20 m/min is 2400 rpm. In this case, when hoisting a load of 400 t at a hoisting speed of 5 m/min, the speed of rotation of the hoist motor is 600 rpm (2400*5/20).

[0071] When the power required to hoist the hoisting means does not change by changing the gear of the gearing, the squirrel cage motor must generate the same power at 600 rpm, as at the speed of rotation of 1200 rpm of the first gear. This means that the motor must generate a correspondingly greater (double) moment. This double moment means that the entire power line (frequency converter, supply cables, motor) must be doubled in terms of power transmission capacity, which increases the costs of the device through multiple sections.

[0072] Comparison of the “gear changing” technology and a solution according to the invention in a hoisting situation according to the previous example:

[0073] At a hoisting speed of 5 m/min and a load of 400 t, the gearing is selected via its output mechanical moment and the gears of the gearing 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, for example 1200 rpm. When the mechanical maximum allowed speed of rotation of the squirrel cage motor is 2400 rpm, the maximum achievable hoisting speed of the hoisting means is 10 m/min.

[0074] If the required maximum achievable speed of the hoisting means is 20 m/min, the speed 2 “fast” (gear ratio i=2) of the gear selector is used, with this selected motor, the gear of the gearing must be changed so that the maximum allowed mechanical speed of rotation of the motor corresponding with the speed of the hoisting means 20 m/min is 2400 rpm. However, the disadvantage of this solution is the need to stop the mechanism while performing the change. In addition, the change of speed ranges is not always successful reliably.

[0075] In the following the illustrations of FIGS. 3-10 are described. The motors and drive controls of the examples according to the figures are speed controlled. These figures compare the differences between a traditional solution and a solution according to the invention in terms of the ratio of load and hoisting speed:

FIG. 3:

[0076] FIG. 3 illustrates the differences between a squirrel cage motor and a DC motor having the same power, each coupled to their respective preferable gearing. The gearings have only one input shaft, but the gear ratios may differ in order to achieve a preferable assembly.

[0077] Graph 1=a graph of the required load-to-speed ratio.

[0078] Graph 61=a graph of the load-to-speed ratio generated by a linear speed/moment curve of a DC motor coupled to the input shaft of a traditional fixed gear gearing.

[0079] Graph 41=a graph of the load-to-speed ratio generated by a squirrel cage motor coupled to the input shaft of a traditional fixed gear gearing.

[0080] The gear of the gearing is selected so that at a rated speed of 1200 rpm of the motors coupled to it, the speed of the hoisting means is 7 m/min. In this case, the required rated power of the motor is 127 kW.

[0081] From the graph of the DC motor it can be seen that the required speed and hoisting capacity are achieved.

[0082] With a squirrel cage motor, the speed and the hoisting capacity do not fully meet the requirement of graph 1 with a load of approximately 50 t and a speed of 10 m/min. According to graph 1, the goal is not also reached at speeds above 15 m/min, when graph 41 ends at a speed of approximately 14 m/min.

[0083] The graphs show differences in DC motors and squirrel cage motors of the same power rating.

FIG. 4:

[0084] FIG. 4 illustrates a squirrel cage motor coupled to a fixed gearing having only one input shaft.

[0085] Graph 1=a graph of the required load-to-speed ratio.

[0086] For the calculation, the mechanism designer selects a squirrel cage motor with a rated power of 182 kW, the characteristics and information of which he/she receives from the motor designer.

[0087] FIG. 4 illustrates a typical calculation cycle in which the most optimal solution for the gear of the gearing and the motor is bracketed. The mechanism designer obtains the characteristics and information of the gearing from the gearing designer.

[0088] Graph 53a=a graph of the load-to-speed ratio generated by a squirrel cage motor coupled to the input shaft of a traditional fixed gearing.

[0089] In the graph 53a, the gear of the gearing is selected so that at a rated speed of 1200 rpm of the motor coupled to it, the speed of the hoisting means is 8 m/min.

[0090] According to graph 53a, a maximum speed of approximately 16 m/min is reached, which is well below the required 20 m/min.

[0091] Graph 53c=a graph of the load-to-speed ratio generated by a squirrel cage motor coupled to the input shaft of a traditional fixed gearing.

[0092] In the graph 53c, the gear of the gearing is selected so that at a rated speed of 1200 rpm of the motor coupled to it, the speed of the hoisting means is 12 m/min.

[0093] According to graph 53c, a maximum speed of approximately 25 m/min is reached, but at a speed of less than 5 m/min the requirement of the required load limit of 90 t is not reached.

[0094] Graph 53b=a graph of the load-to-speed ratio generated by a squirrel cage motor coupled to the input shaft of a traditional fixed gearing.

[0095] In the graph 53b, the gear of the gearing is selected so that at a rated speed of 1200 rpm of the motor coupled to it, the speed of the hoisting means is 10 m/min. With this selected gear and the selected motor characteristics, the required performance values are achieved and exceeded.

[0096] If a suitable gear for the gearing had not been found, the same calculations for the gear of the gearing would have been performed on another motor, having different ratings in terms of rated power or speed.

FIG. 5:

[0097] FIG. 5 illustrates the graphs of the required load-to-speed ratio of a two-step speed changing gearing.

[0098] Graph 1=a graph of the required load-to-speed ratio.

[0099] Graph 34=a graph of the load-to-speed ratio generated by the motor coupled to the input shaft of the speed changing gearing when the greater gear ratio, i.e. lower speed range, is coupled.

[0100] Graph 44=a graph of the load-to-speed ratio generated by the motor connected to the input shaft of the speed changing gearing when the lower gear ratio, i.e. greater speed range, is coupled.

[0101] The gear of the greater gear step, i.e. lower speed range, of the speed changing gearing, is selected so that at a rated speed of 1200 rpm of the first motor coupled to it, the speed of the hoisting means is 5 m/min.

[0102] The gear of the lower gear ratio, i.e. greater speed range, of the speed changing gearing, is selected so that at a rated speed of 1200 rpm of the second motor coupled to it, the speed of the hoisting means is 10 m/min.

[0103] This solution, which illustrates the traditional technology of the speed changing gear, has only one input shaft.

FIG. 6:

[0104] FIG. 6 illustrates a squirrel cage motor, designed to be high-performance, coupled to a fixed gearing having only one input shaft.

[0105] Graph 1=a graph of the required load-to-speed ratio.

[0106] Graph 45=a graph of the load-to-speed ratio generated by a squirrel cage motor coupled to the input shaft of a traditional fixed gear gearing.

[0107] The gear of the gearing is selected so that at a rated speed of 1200 rpm of the motor coupled to it, the speed of the hoisting means is 10 m/min. In this case, the required rated power of the motor is 182 kW.

[0108] From the graph of the squirrel cage motor it is seen that the required speed and hoisting capacity are achieved.

[0109] A gearing with a fixed gear is the simplest option, but this oversizes components and as the required speed range or load further increases and the required power increases above a certain limit, a different technical implementation has to be made, where the gears of the gearing are staggered.

FIG. 7:

[0110] FIG. 7 illustrates a squirrel cage motor coupled to the first and the second input shafts of the differential having the same total gear ratio relative to the output shaft.

[0111] Graph 1=a graph of the required load-to-speed ratio.

[0112] Graph 26=a graph of the load-to-speed ratio generated by 91 kW squirrel cage motors, having rated speeds of 1200 rpm, coupled to the first and the second input shafts of the differential. The gear of both differential stages is the same, so that by only using the motor of the other input shaft, a 5 m/min speed of the hoisting means is achieved at a rated speed of 1200 rpm of the motor. When both input shafts are used simultaneously, twice the speed is reached according to graph 36.

[0113] The differential is a less commonly used gearing, being more difficult to manufacture due to its complex structure and having higher costs. With two 91 kW motors and a differential, no performance gains in terms of speed or load capacity are achieved, as illustrated in the graph 45 in FIG. 6 and the graph 36 in FIG. 7.

[0114] The differential is used in special cases in cranes where a double hoisting mechanism is required to increase operational reliability. This corresponds to a situation where the other motor or its drive fails, allowing the same load to be further hoisted at half speed and the job to be completed.

FIG. 8:

[0115] FIG. 8 illustrates a squirrel cage motor coupled to the first and the second input shafts of the differential, in which the difference between the total gear ratios is double relative to the output shaft. The load is 15 t.

[0116] Graph 1=a graph of the required load-to-speed ratio.

[0117] Graph 27=a graph of the load-to-speed ratio generated by the first motor coupled to the first input shaft of the differential.

[0118] Graph 37=a graph of the load-to-speed ratio generated by the second motor coupled to the second input shaft of the differential.

[0119] The gear of the first input shaft of the differential is selected so that at a rated speed of 1200 rpm of the first motor coupled to it, the speed of the hoisting means is 5 m/min.

[0120] The gear of the second input shaft of the differential is selected so that at a rated speed of 1200 rpm of the second motor coupled to it, the speed of the hoisting means is 10 m/min.

[0121] The ratio between the total gear ratios of the first input shaft and the second input shaft is two. According to graph 37, the maximum hoisting speed is 30 m/min, corresponding to a load of 15 t, when the motors coupled to the first and the second input shafts are driven at twice the rated speed of rotation.

FIG. 9:

[0122] FIG. 9 illustrates a squirrel cage motor coupled to the first and the second input shaft of the differential, in which the ratio of the total gear ratios of the first and the second gears relative to the output shaft is 2. The load is 50 t.

[0123] Graph 28=a graph of the load-to-speed ratio generated by the first motor coupled to the first input shaft of the differential.

[0124] Graph 38=a graph of the load-to-speed ratio generated by the second motor coupled to the second input shaft of the differential. A 91 kW squirrel cage motor is used as the motors.

[0125] The gear of the first input shaft of the differential is selected so that at a rated speed of 1200 rpm of the first motor coupled to it, the speed of the hoisting means is 5 m/min.

[0126] The gear of the second input shaft of the differential is selected so that at a rated speed of 1200 rpm of the second motor coupled to it, the speed of the hoisting means is 10 m/min.

[0127] The ratio of the total gear ratios of the first and the second input shafts of the differential is 2.

[0128] The second motor coupled to the differential starts when the speed of the first motor of the first input shaft of the differential is approximately 7 m/min and the maximum load that can be hoisted is 50 t. When the second motor is accelerated to a rated speed of 1200 rpm, a speed of 17 m/min is achieved for the hoisting means with a load of 50 t. And further, with a lower load of 15 t, a hoisting speed of over 25 m/min can be achieved.

FIG. 10:

[0129] FIG. 10 illustrates a squirrel cage motor coupled to the first and the second gear of the differential, in which the ratio of the total gear ratios of the first and the second gears is 3.

[0130] Graph 1=a graph of the required load-to-speed ratio.

[0131] Graph 29=a graph of the load-to-speed ratio generated by the first motor coupled to the first input shaft of the differential.

[0132] Graph 39=a graph of the load-to-speed ratio generated by the second motor coupled to the second input shaft of the differential. A 91 kW squirrel cage motor is used as the motors.

[0133] The gear of the first input shaft of the differential is selected so that at a rated speed of 1200 rpm of the first motor coupled to it, the speed of the hoisting means is 5 m/min.

[0134] The gear of the second input shaft of the differential is selected so that at a rated speed of 1200 rpm of the second motor coupled to it, the speed of the hoisting means is 15 m/min.

[0135] The ratio of the total gear ratios of the first and the second input shafts of the differential is 3.

[0136] The second motor coupled to the differential starts when the speed of the first motor of the first input shaft of the differential is approximately 7 m/min and the maximum load that can be hoisted is 32 t. When the second motor is accelerated to rated speed 1200 rpm, a speed of 23 m/min is achieved for the hoisting means with a load of 32 t. And further, with a lower load of 15 t, a hoisting speed of 30 m/min can be achieved.

[0137] With the aid of FIGS. 8, 9, and 10, the advantage of the invention can be clearly demonstrated when a light load, an empty hook or a hoist member can be hoisted at speeds of over 25 m/min, while the powers of the motors can be designed clearly smaller. By comparing FIGS. 3-7 and 8-10, it is thus possible to spread the set of curves “to the right”. This has been accomplished without the need to raise the set of curves “up” from the left edge, i.e. it has been possible to avoid oversizing the hoist motors and their power supply components.

[0138] The greater hoisting or lowering speed of a light load or an empty load member described in this application enables faster load handling in for example ports. Faster loading and unloading times of sea freight enable shorter times that the ships are on land, causing the ships to have the possibility to be more at seas, thus improving the efficiency and economics of the transport. The hoisting speeds matter particularly in ports having typically high hoist heights. The solution can be utilized also in construction cranes, mobile cranes and in hoists of windmill power plants. These are characterized by a constant force of gravity acting on the hoisting mechanism when it is desired to change the speed range in order to change the hoisting speed.

[0139] Coupling of the hoist motors to rotate or stop based on the load information can be done manually or automatically. To enable the automatic functioning, a comparison can be done between the load information and the load limit information.

[0140] The above description of the invention is only meant for illustrating the basic idea according to the invention. Therefore, the details of it may be implemented within the scope of the attached claims.