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(11) | EP 2 933 221 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | ELECTROMECHANICAL SYSTEM FOR LIFTING A LOAD |
| (57) Electromechanical lifting system (100, 200, 300, 500) of a load comprising: - At least one cylinder (1, 21, 301) comprising a screw (2, 22, 32, 502) connected to the load and configured for descent and ascent translating along its vertical axis Y; - At least one electric motor (3, 23, 33) connected to one extreme portion of the cylinder (1, 21, 301); - Means (4, 24, 34) for transferring the rotational motion imparted by the electric motor (3, 23, 33) into translatory motion of the screw (2, 22, 32, 502). The cylinder (1, 21, 301) comprises a tank (1b, 21b, 301b) filled with a compressible gas and mobile compression means (5, 25, 305) interconnected with one end (2b, 22b, 32b, 502b) of the screw (2, 22, 32, 502) and configured to transfer energy from the vertical translatory motion of the screw (2, 22, 32, 502), when directed towards the tank (1b, 21b, 301b), to the gas accumulating the energy and for transferring the energy from the gas to the vertical translatory motion of the screw (2, 22, 32, 502) when directed in the opposite direction. |
[0002] As is known, several mechanical organs are used in the systems for lifting loads in a repetitive manner, for example forks of forklifts, vertical axis slides of machine tools, elevators used for lifting persons or things, or even alternative handling activities, along a vertical direction, with high number of cycles, for example in stamping presses, broaching machines, pumps. In the mechanical organs of such machines, cylinder exploiting the pressure of fluids, for example hydraulic cylinders, supplied by a pump for the transmission of forces or pneumatic cylinders are usually used. These hydraulic or pneumatic cylinders have the advantage of being simple and economic constructed and are able to accumulate and reuse energy by means of special pressure containers, but only when their application requires low precision on the repeatability of the handling speed and poor positioning accuracy.
[0003] Instead, when the application requires high control of strength, speed and positioning, mechanical cylinders based on the use of the pressure of fluids require very expensive unit for the production, control and distribution of the pressurized fluid.
[0004] Therefore, normally in these cases it is preferred to use electronically driven systems for transmitting motion, thus ensuring high control of speed and positioning.
[0006] Purpose of the present invention is to provide an electromechanical system for lifting a load, which is simple and economic to realize and being able to accumulate and reuse energy even when high control of the force, of the speed and of the positioning is required, having characteristics such as to overcome the limitations which still affect systems previously described with reference to the known technique.
[0007] According to the present invention, n electromechanical system for lifting a load is provided, as defined in claim 1.
[0008] For a better understanding of the present invention a preferred embodiment is now described, purely as nonlimiting example, with reference to the accompanying drawings, in which:
- Figure 1 shows a schematic view of a first embodiment of an electromechanical system for lifting a load, according to the invention;
- Figure 2 shows a schematic view of a second embodiment of the electromechanical system for lifting a load, according to the invention;
- Figure 3 shows a schematic view of a third embodiment of the electromechanical system for lifting a load, according to the invention;
- Figure 4 shows a schematic view of a first application of the third embodiment of the electromechanical system for lifting a load, according to the invention;
- Figure 5 shows a schematic view of a second application of the third embodiment of the electromechanical system for lifting a load, according to the invention;
- Figure 6 shows a schematic view of a three-dimensional machine for pumping oil comprising the electromechanical system for lifting a load, according to the invention;
- Figures 7A-7B show respectively a schematic front view and the zoomed view of a part of the machine for pumping oil comprising the electromechanical system for lifting a load, according to the invention.
[0009] With reference to these figures, and in particular to Figure 1, an electromechanical system for lifting a load is shown, according to the invention. More specifically, the electromechanical system for lifting a load 100 comprises a cylinder 1 within which can vertically slide a screw 2, able to move along the vertical axis Y, upwards or downwards. The electromechanical lifting system 100 also comprises an electric motor 3 connected, for example flanged, at the upper end of the cylinder 1 and configured for imparting the translational movement to the screw 2. Therefore, the screw 2 can move, inside the cylinder 1, upwards or downwards depending on the direction of rotation of the motor 3. Furthermore, the electromechanical lifting system 100 comprises a nut 4, inserted into a first upper portion 1a of the cylinder 1, connected to the electric motor 3 and driven by the latter so as to transform its rotary motion into translational motion transferred to the screw 2.
[0010] Advantageously according to the invention, the screw 2 has a first free end 2a which is connected to the load, not shown in the figure, which prevents the rotation.
[0011] Moreover, advantageously according to the invention, the screw 2 has a second end 2b connected to a piston 5, placed inside the cylinder 1 and flowing into the cylinder 1 thus forming a second lower portion 1b of the cylinder 1 between the piston 5 and a closing flange 6 and acting as a tank.
[0012] Advantageously according to the invention, the second lower portion 1b of the cylinder 1 is filled with a gas, for example nitrogen, or a mixture of air and nitrogen.
[0013] According to an aspect of the invention, the electric motor 3 is a high efficiency hollow shaft motor with permanent magnets. In particular, the high efficiency hollow shaft motor with permanent magnets allows to limit the number of components of the kinematic chain.
[0014] Advantageously according to the invention, the nut 4 is planetary roller or recirculated ball.
[0015] In use, the electric motor 3 drives the nut 4 whose rotary motion is converted into translation vertical motion of the screw from the outside of the cylinder 1 towards the inside of the upper portion 1a of the cylinder 1. During the descent motion of the screw 2, the piston 5 compresses the pressed gas contained in the second lower portion 1b of the cylinder 1 by means of its lower surface and of its seals placed on the diameter of the piston 5, which are not shown in the figure. In this way, the energy supplied by the electric motor 3 is accumulated inside the gas and can be made available for the subsequent ascent of the piston 5 and of the screw 2, thus allowing the electric motor 3 to do less work.
[0016] A second embodiment of the electromechanical system for lifting a load 200 is shown in Figure 2. In particular, the electric motor 23 is a motor with solid shaft mounted laterally to the cylinder 21, so that the Y' axis of the motor 23 is parallel to the Y axis of the screw 22. In addition, the electromechanical lifting system 20 comprises a nut 24 able to rotate on external bearings 24a.
[0017] A third embodiment of the electromechanical system for lifting a load 300 is shown in figure 3. The system 300 comprises a first cylinder 31, having a first end 31a connected to a possible hydraulic facility via a flange 36.
[0018] According to an aspect of the invention, a liquid pressurized by a first piston 35 is put inside the cylinder 31, which can be suitably connected to a hydraulic facility.
[0019] According to another aspect of the invention, the cylinder 31 does not contain liquid and may be directly connected to a load to compress.
[0020] The end 32b of the screw 32 is rigidly connected to a second piston 305 and to a splined shaft 302 which can slide inside a bushing recirculated balls 304 configured to prevent the rotation of the splined shaft 302 allowing the only translation along the Y axis of the splined shaft 302 and of the screw 32. In fact, the bushing recirculated balls 304 is rigidly connected to the liner of the second cylinder 301 which is a gas accumulator and closed at the top by a flange 306. In particular, the gas is kept in a second portion 301b of the cylinder 301 between the piston 305 and the closing flange 306.
[0021] The embodiment 300 can be used in conditions in which it is not possible to directly connect the screw to the load, or if it's useful to replace the unit for producing, controlling and distributing the fluid of a hydraulic system.
[0022] Advantageously according to the invention, the portions 1b, 21b and 301b of the cylinders 1, 21 and 301 containing the gas are connectable to an expansion tank, not shown in the figures.
[0023] Figure 4 shows the configuration in which the electromechanical system for lifting a load 300 is connected by means of connecting means, such as rigid or flexible pipe, to a second single-acting cylinder in a closed circuit driven by the system 300. More in detail, the cylinder 31 containing liquid is connected, by means of the connecting means 40, for example rigid or flexible pipe, to a single-acting cylinder 41 containing a liquid kept under pressure by a piston 45 to which is connected the lower end 42a of a rod 42 whose upper end 42b is constrained to supporting means 50.
[0024] Figure 5 shows the configuration in which the electromechanical system for lifting a load 300 is connected by means of connecting means 40, for example rigid or flexible pipe, to a second single-acting cylinder driven by the system 300. More in detail, the cylinder 31 containing liquid is connected by means of connecting means 40 to a single-acting cylinder 51 containing a liquid put under pressure by the electromechanical system 300. The cylinder 51 contains, in turn, a stem 52 having the lower end 52b connected to the sucker rods used for pumping the oil from an oil well and the top end 52a pushed by the hydraulic pressure of the system 300 acting on a piston 55. The lower part of the cylinder 51 is rigidly connected to the wellhead, not shown in the figure.
[0025] According to another aspect of the invention, the part 51a can be connected to an external settling tank at atmospheric pressure.
[0026] This particular embodiment is used when the cylinder 51 is connected to the oil well to perform the extraction of crude oil.
[0027] Advantageously according to the invention, a machine for extracting oil from the ground may comprise the described electromechanical lifting system. One such machine is shown in Figures 6 and 7. The machine 550 comprises two tubular elements 551 extending vertically and parallel to each other and which act as containers for pressurized gas, for example nitrogen or a mixture of air and nitrogen, inserted by means of valves 551a. The tubular elements 551 are superiorly interconnected each other by a bracket 552 and, inferiorly, fixed to a support frame 554, for example in the central bar of an H shaped pedestal. Moreover, the machine 550 comprises, between the two tubular elements 551, the electromechanical lifting system 500 in one of its embodiments described above. The tubular elements 551 laterally comprise guides 553, such as guides having recirculating balls or rollers, configured for ensuring the proper sliding of the upper part of the screw of the electromechanical lifting system 500 and for avoiding the screw flex laterally, and are configured to counteract the rotation torque of the nut thus allowing the screw to translate along the vertical direction. In fact, the screw 502 of the electromechanical lifting system 500 is coupled to guides 553 for the sliding and anti-rotation of the screw by means of an axle 556 rigidly connected to the end 502b of the screw 502. Sliding means 557 are bound at the ends of the axis 556 and are able to slide on the guides 553 preventing the rotation of the screw 502 and rolling means 555 for supporting a hoist rope, not shown, which is configured to connect the machine 550 to the sucker rods for pumping oil from the well. Therefore, the tubular elements 551 also perform a support function of the structure and for fixing the sliding and anti-rotation guides 553.
[0028] Advantageously according to the invention, the possible applications of the electromechanical system for lifting a load are different.
[0029] An application relates to a forklift comprising the electromechanical system for lifting a load, according to the invention.
[0030] Another application relates to a machine tool comprising the electromechanical system for lifting a load, according to the invention.
[0031] A further application relates to a lift for lifting persons or things comprising the electromechanical system for lifting a load, according to the invention.
[0032] Another application relates to machines for performing activities of alternative handling, along a vertical direction, with a high number of cycles, for example molding presses, broaching machines, pumps, may comprise the electromechanical system for lifting a load, according to the invention.
[0033] The Applicant has conducted experiments on the electromechanical system for lifting a load according to the invention and has found significant advantages relative to the speed control and to the positioning of the system, due to the use of an electric motor equipped with an encoder that allows to count the cycles in a precise and reliable manner. Furthermore, these experiments showed a less power required to operate the system, thanks to the use of gas as a system for storage and release of the pressure energy to balance the constant part of the load to be lifted. In the case of application of the system to a machine for extracting oil from the ground, it was hypothesized that the weights of the sucker rods and of half load of the hydrostatic oil column can be balanced by the pressure of the gas, while the motor can be sized to lift the remaining half load of the hydrostatic oil column.
[0034] In the case of application of the system to an elevator, it has been assumed that the weights of the cabin and of half of the maximum flow can be balanced by the pressure of the gas, while the motor can be sized to lift the remaining half of the maximum capacity.
[0035] Therefore, the electromechanical system for lifting a load according to the invention enables the energy saving and the recovery of the energy of the pressed gas during the descent run, thanks also to the use of high efficiency permanent magnet motors, which, through appropriate converters, also allow the accumulation and subsequent reuse of the electrical energy generated by the operation as a brake of the electric motor.
[0036] Another advantage of the electromechanical system for lifting a load according to the invention consists in the possibility of saving on production costs compared to known electrical systems, as the energy recovery by means of gas allows the decrease of the installed peak power.
[0037] Also, the electromechanical system for lifting a load according to the invention allows an improvement in the safety of machines for the absence of liquids at high pressure, that in case of failure of a component of the plant can generate dangerous conditions; allows a low environmental impact compared to the known hydraulic systems in which liquids are kept at high pressure and there is the risk that they may spill into the environment in the event of failure of a component of the system; and it can be used in environments where flammable and / or pollutants hydraulic fluids are not allowed.
[0038] Another advantage of the electromechanical system for lifting a load according to the invention is the possibility of variation and control of the acceleration / deceleration steps, speed control and more accurate positioning with respect to the known hydraulic systems.
1. Electromechanical lifting system (100, 200, 300, 500) of a load comprising:
- At least one cylinder (1, 21, 301) comprising a screw (2, 22, 32, 502) connected to the load and configured for descent and ascent translating along its vertical axis Y;
- At least one electric motor (3, 23, 33) connected to one extreme portion of the cylinder (1, 21, 301);
- Means (4, 24, 34) for transferring the rotational motion imparted by the electric
motor (3, 23, 33) into translatory motion of the screw (2, 22, 32, 502);
characterized in that the cylinder (1, 21, 301) comprises a tank (1b, 21b, 301b) filled with a compressible
gas and mobile compression means (5, 25, 305) interconnected with one end (2b, 22b,
32b, 502b) of the screw (2, 22, 32, 502) and configured to transfer energy from the
vertical translatory motion of the screw (2, 22, 32, 502), when directed towards the
tank (1b, 21b, 301b), to the gas accumulating said energy and for transferring said
energy from the gas to the vertical translatory motion of the screw (2, 22, 32, 502)
when directed in the opposite direction.
2. Electromechanical lifting system (100, 200, 300, 500) of a load according to claim
1, characterized in that the mobile compression means (5, 25, 305) are a piston (5, 25, 305).
3. Electromechanical lifting system (100, 200, 300, 500) of a load according to the preceding
claims, characterized in that the tank (1b, 21b, 301b) filled with compressible gas is a portion (1b, 21b, 301b)
of the cylinder (1, 21, 301) between the piston (5, 25, 305) and a closing flange
(6, 26, 306) of the cylinder (1, 21, 301).
4. Electromechanical lifting system (100, 200, 300, 500) of a load according to claim
1, characterized in that the means (4, 24, 34) comprise a nut (4) planetary roller or recirculated ball inserted
in a portion (1a) of the cylinder (1) to which is connected the electric motor (3)
mounted above the nut (4).
5. Electromechanical lifting system (100, 200, 300, 500) of a load according to claim
1, characterized in that the means (4, 24, 34) comprise at least one nut (24) rotating on external bearings
(24a) inserted in an upper portion at the end of the cylinder (21) to which is connected
the electric motor (23) mounted laterally to the cylinder (21).
6. Electromechanical lifting system (100, 200, 300, 500) of a load according to any one
of the preceding claims, characterized in that it comprises a further cylinder (31) connected, at a first end (31a), to a hydraulic
actuator and containing a liquid that is put into pressure by the piston (35) to which
the end (32a) of the screw (32) is connected.
7. Electromechanical lifting system (100, 200, 300, 500) of a load according to claims
1-5, characterized in that it comprises a further empty cylinder (31) directly connectable to a load to be compressed.
8. Electromechanical lifting system (100, 200, 300, 500) of a load according to claims
1-6, characterized in that the end (32b) of the screw (32) is rigidly connected to the piston (305) and to a
splined shaft (302) slidable within a bushing recirculated balls (304) rigidly connected
to the liner of the cylinder (301) and configured to prevent rotation of the splined
shaft (302) allowing the only translation along the axis Y of the splined shaft (302)
and of the screw (32).
9. Electromechanical lifting system (100, 200, 300, 500) of a load according to any of
claims 6-8, characterized in being connected by connection means (40) to a second single-acting cylinder (41,
51) containing a liquid.
10. Electromechanical lifting system (100, 200, 300, 500) of a load according to claim
9, characterized in that the liquid in the single-acting cylinder (41) is kept under pressure by a piston
(45) to which the lower end (42a) of a rod (42) is connected, the upper end (42b)
of the rod (42) being bound to support means (50).
11. Electromechanical lifting system (100, 200, 300, 500) of a load according to claim
9, characterized in that the single-acting cylinder (51) comprises a rod (52) whose lower end (52b) is connectable
to sucker rods of an natural oil well and the upper end (52a) is driven by the hydraulic
pressure of the electromechanical lifting system (300) acting on a piston (55) connected
to a natural oil well.
12. Surface machine (550) for artificial lift of oil from underground wells via sucker
rods comprising an electromechanical lifting system (100, 200, 300, 500) of a load
according to the preceding claims.
13. Surface machine (550) for artificial lift of oil from underground wells via sucker
rods according to claim 12, characterized in that it comprises two tubular elements (551) extending vertically and parallel to each
other, containing pressurized gas inserted through valves (551a), said tubular elements
(551) being superiorly interconnected by a bracket (552) and, inferiorly, fixed to
a support frame (554), and comprising lateral sliding and anti-rotation guides (553)
to which the screw (502) of the electromechanical lifting system (500) is coupled
by means of an axle (556), rigidly connected to the end (502b) of the screw (502),
at the ends of the axle (556) being bound sliding means (557) slidable on the guides
(553) and rolling means (555) for supporting a cable connecting the machine (550)
to the sucker rods of the well.
14. Machine tool comprising an electromechanical lifting system (100, 200, 300, 500) of
a load according to claims 1-11.
15. Elevator for lifting people or things comprising an electromechanical lifting system
(100, 200, 300, 500) of a load according to claims 1-11.