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(11) | EP 2 522 441 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Bending machine for making U-shaped bends in pipes |
| (57) A bending machine (1) comprising feeding means (5) of a plurality of substantially
rectilinear pipes, a cutting group (12) of the pipes coming from said feeding means
(5), at least one bending group (6) comprising at least one bending arm (7) suitable
for bending said plurality of pipes, coming from said cutting group (12), according
to a certain bending angle, thus making a plurality of tubular hairpins (8); extraction
means (9,13,13a) of the hairpins (8) in a collection area (10), said bending group
(6) comprising a rotary central support (23) of said bending arm (7) and a rotary
actuation group (26), coupled with said rotary central support (23), comprising at
least one electric motor (27) and a respective reducer (28), said rotary actuation
group (26) comprising a servo-actuation of said brushless electric motor (27) operating
in a closed loop and a programmable unit for controlling the operation to which said
servo-actuation is operatively connected. The servo-actuation comprises control means
(100) of the bending cycle suitable for optimising the acceleration ramp, the translation
speed and the deceleration ramp of said bending arm (7).
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TECHNICAL FIELD OF THE INVENTION
[0001] The present invention concerns a machine used for simultaneously bending many pipes into a "U" called a bending machine.
[0002] More specifically, the present invention concerns a bending machine for bending pipes intended, for example, for making heat exchangers.
STATE OF THE ART
[0003] The production of pipes intended, for example, for making finned heat exchangers, or intended for other types of use, is extensive and they come in greatly different dimensions.
[0004] In the particular case of heat exchangers, indeed, they go from small exchangers for the automobile industry or for heating, to large exchangers for air conditioning, refrigeration or for process heat exchange where the dimensions can even exceed ten metres in length.
[0005] As known, the exchangers in question consist of a bank of pipes, usually having a circular cross section, which is inserted into a finned pack, which represents the extended outer surface on the secondary fluid, which usually consists of air.
[0006] In order to make the circuits on the pipes side, they are connected, in their end parts, in series or in parallel to one another in order to have passage sections and lengths that are more suitable for heat exchange, within the limitations of the admissible load loss for the primary fluid.
[0007] In general, the connection in series of two or more parallel pipes that form part of the battery is carried out with bends that invert the flow by 180°. If the amount and length of the batteries permit, instead of mounting pairs of single pipes in parallel with one another, it is more advantageous to make pipes bent into a "U" with the parallel arms, called hairpins, and replace the single pipes with them, eliminating the need for bends at 180° during the step of making the circuit and consequently avoiding, on at least one of the two sides, the preparation of the joint and the braze welding of the bend, with the inevitable probability of losses due to problems connected with braze welding itself.
[0008] The operation of bending the pipes in a "U", indeed to make hairpins, is carried out with a dedicated automatic machine and, indeed, called bending machine. A bending machine of the known type is illustrated in the attached figures 1 and 2.
[0009] In particular, figure 1 is an overall side view of the machine, whereas figure 2 is a detail of the means that make the 180° bend of the pipes.
[0010] The bending machine - wholly indicated with A in figure 1 - starting from a reel of wound pipe, unwinds it in a controlled manner.
[0011] The bending machine A comprises a base block B, arranged directly downstream of the unwinding station of the reel of pipe, not represented. In particular, there can be a plurality of reels, at least as many as there are pipes that are wished to be bent in a single cycle of the machine A.
[0012] The pipes are introduced into the machine through an inlet C, for example comprising a plurality of guide ducts D, as many as there are pipes to be treated in parallel in each cycle.
[0013] The machine also comprises a straightening and advancing group E of the pipes that takes care of straightening and calibrating the latter, in accordance with the desired diameter.
[0014] The machine also comprises a cutting group F, arranged downstream of the aforementioned straightening and advancing group E, which has the task of cutting to size the pipes that have previously been straightened and calibrated.
[0015] Downstream of the cutting group F there is a bending group G, which indeed bend the pipes into a U, making hairpins H of the same length and with the arms parallel, as described above.
[0016] The machine finally comprises, downstream of the bending group G, an extraction group I that takes care of extracting the hairpins H from the bending group G and of then placing them in a collector L awaiting their subsequent use.
[0017] A particularly critical step of the operation of the bending machine A described above consists of that of bending the pipes by 180° into a "U" to make the hairpins H, which takes place as stated in the bending group G.
[0018] Indeed, the pipes that can be subjected to bending are made with materials capable of withstanding the implicit elongation of the process without breaking: for example, such a material can consist of copper or aluminium and alloys thereof, or carbon and stainless steel, in any composition, with or without surface treatments, and so on.
[0019] The bending group G of the bending machine A of the known type is illustrated in the detail of figure 2. The known bending group G comprises a bank M sliding on guides N the positioning of which, programmable by console, defines the length of the hairpins H.
[0020] A central support O is rotatably mounted on the bank M. The central support O has a bending arm P fixed to it, which supports the telescopic pipes Q, to guide the pipes coming from the cutting group F. The bending arm P is actuated by hydraulic cylinders R, mounted on the bank M on opposite sides, associated with respective transmissions comprising, for each of the hydraulic cylinders R, a rack S coupled with a respective pinion T. The pinion T is in turn fitted onto an axis U fixedly connected to the central support O of the bending arm P.
[0021] Operatively, after having straightened and calibrated the pipes, set in motion by the advancing group E, the latter are guided first by the telescopic pipes Q of the bending arm P, arranged in horizontal rest position, then by the shapes and bending clamps V and then by the bending cores and relative support shafts Z up to the stop abutment that defines their length before bending.
[0022] At this point, the pipes are blocked by clamps, cut to size by the cutting group F and, with the translating movement of the cutting group F that moves away from the bending arm P, are ready to be bent; the bending is carried out with the rotation of the bending arm P by 180°, which as stated is actuated by the hydraulic cylinders R through the pinion T - rack S transmission. A contribution to the correct curving of the hairpins is made by the clamps and bending shapes V, on which the pipe sits during rotation, and the support shafts Z that guide the sliding of the pipes on the inside and contribute to keeping them circular. After the forming of the hairpins H, the clamps and bending shapes V that block them are reopened; with the advancing of the extraction group I and thrusts of the straws, the hairpins H are extracted from the support shafts Z and, once free, conveyed into the collector L.
[0023] Over the years the increased cost of raw materials, the technological refinement of production processes, and greater adaptation of the thickness of the pipes to operating conditions, have led to a substantial reduction in said thickness of the pipes, with a consequent worsening of the problems linked to their bending. In addition to this, the reduction in diameter of the pipes and the compacting of the geometries of finned exchangers have further increased the criticality of the bending process.
[0024] In particular, it has been found that the greatest drawbacks are linked to the use of hydraulic actuations for carrying out the bending operation of the pipes by 180°. In greater detail, firstly the actuation of the bending arm 14 with hydraulic cylinders 16 is a so-called open loop system, which is thus based on values and parameters that are set in input and preliminary, without verifying and managing the output parameters. Secondly, as stated, the transmission of motion to the bending arm P through rack S and pinion T is actuated by two hydraulic cylinders R, which are controlled by a proportional valve that generates a flow rate of oil, indeed, directly proportional to the electrical control signal in input. The signal is taken from a encoder that controls the rotation angle of the bending arm P. The adjustment algorithm of the aforementioned proportional valve is preset based on incremental variations in length of the hairpin H. Variations of parameters like the moment of inertia of the bending arm P due to weight variations - which depends on the diameter and/or the thickness of the pipes - or the different number of bent pipes in each operating cycle are not taken into consideration at all.
[0025] Moreover, since the force applied varies as a function of the angular position of the bending arm P - therefore at the maximum at the start, limited on the vertical, and braking in the descending phase - the encoder-proportional valve system consequently reacts to the load variations.
[0026] Indeed, since it concerns a system with reactive behaviour, i.e. that acts based on variations, it generates micro-variations in pressure that in turn cause variations in the motion of the bending arm P. This translates into more or less big vibrations of the bending arm P itself during its motion: the longer the arm P, the bigger the vibrations will become, causing stress on the materials and anomalous wearing of the pinion T - rack S system. These vibrations, in particular, are more perceptible in the descending phase of the bending arm P.
[0027] In order to reduce this phenomenon, a so-called overcenter valve is usually used, which, by introducing a constant braking load to the oil discharge, increases the load of the hydraulic circuit, thus limiting the effects described earlier and due to the reactive behaviour of the proportional valve - encoder system: the variations in load are thus of lower intensity and effect, but they are still present and still cause a series of unwanted phenomena. On the other hand, the insertion of the overcenter valve means the presence of an passive extra load that absorbs a significant amount of energy.
[0028] A further drawback consists of the fact that the two hydraulic cylinders R for actuating the bending arm P are arranged at the two ends of the central support O of the arm P itself - each of which to control a respective pinion T - rack S group - and are slaved to a single proportional valve.
[0029] As can easily be understood, such two hydraulic cylinders R are unable to simultaneously transmit the same force to the two respective pinion T - rack S groups, with the consequence that the phenomenon of the occurrence of vibrations increases, even if partially dampened by the presence of the overcenter valve. Therefore, the work of the overcenter valves also cannot be considered optimal, since the oil that comes out from the discharge of the two hydraulic cylinders R is conveyed in a single overcenter valve, and thus the braking effect will be greater in the cylinder that at that time is loaded more.
[0030] Moreover, it is not possible to completely exclude the presence of air or other gases in the hydraulic circuit, which has formed or remained in some point of the circuit during the loading step of the system, or else in the presence of top ups or replacement of the oil in the tank or in the circuit. The presence of air or other gases, which are compressible, amplifies the load variations thus increasing the variations in motion of the system and thus the vibrations of the bending arm P during its motion.
[0031] It should also be noted that the different viscosity of the oil in the different operating temperature conditions makes the system to some extent dependent on external factors and this affects the possibility of the system itself being equally effective in all operating conditions; such variations in behaviour of the system, in particular of the control valves, inevitably penalises the bending cycle of the hairpins, i.e. the productivity of the bending machine in terms of bending cycles per minute.
[0032] It has also been observed that, by varying the length of the hairpins or the diameter of the pipe to be bent, i.e. by varying the thickness of the pipes, the mass of the bending arm P consequently varies; the system for controlling the movement of the bending arm P is not at all sensitive enough to adapt to any load condition and to modify its behaviour to ensure the maximum performance in the bending function.
PURPOSES OF THE INVENTION
[0033] The technical task of the present invention is therefore to improve the state of the art, providing a bending machine that allows the aforementioned drawbacks to be eliminated.
[0034] In such a technical task, a purpose of the present invention is to provide a bending machine in which the motion of the bending arm, and therefore its performance, is optimised and improved.
[0035] Another purpose of the present invention is to make a bending machine in which the motion of the bending arm in carrying out the bending operation has as little vibration and irregularity as possible due to load variations.
[0037] According to an aspect of the present invention, the bending machine comprises an actuation group of the bending arm equipped with a brushless electric motor. This solution ensures the possibility of controlling the motion of the bending arm with extreme precision, in any load condition and with any environmental condition, with the desired acceleration ramp, rotating motion and deceleration.
[0038] According to another aspect of the present invention, the actuation group of the bending arm comprises a cycloid reducer coupled with the brushless motor, to actuate the bending arm.
[0039] Such a solution makes it possible to limit to the minimum, or even to almost completely eliminate, the vibrations of the bending arm during motion, and it also makes it possible to limit to the minimum inertia and wear, and it ensures the maximum lifetime and maximum reliability, in any situation, of the bending group.
BRIEF DESCRIPTION OF THE DRAWINGS.
[0041] The characteristics of the invention will become clearer to any man skilled in the art from the following description and from the attached tables of drawings, given as a non-limiting example, in which:
figure 1 is a side view of a known bending machine;
figure 2 is a detailed axonometric view of the known machine of figure 1;
figure 3 is a side view of a bending machine according to the present invention;
figure 4 is a detailed axonometric view of the bending group of the machine according to the present invention;
figure 5 is a section view of a possible type of cycloid reducer able to be installed onto the bending machine according to the present invention;
figure 6 is a functional diagram of the bending machine according to the present invention
EMBODIMENTS OF THE INVENTION.
[0042] With reference to the attached figure 3, a bending machine according to the present invention is wholly indicated with 1.
[0043] The bending machine 1 according to the present invention can be used, in general terms, to carry out the bending of pipes, for example by 180° with the arms substantially parallel or even according to a certain bending angle different from 180°, for pipes, preferably metallic, intended for the most varied industrial uses, without any limitation.
[0044] For example, the machine according to the invention can be effectively used to produce pipes bent by 180°, i.e. hairpins, to make finned heat exchangers of any size. The bending machine 1 according to the invention comprises - as illustrated in the overall side view of figure 3, and as also already described for the known machine of figures 1,2 - a base 2 that supports, aligned with one another according to the operating sequence of the machine already described, an inlet 3 of the pipes for example through ducts 4, feeding means of substantially rectilinear pipes, wholly indicated with 5, a bending group 6 comprising at least one bending arm 7 to bend the rectilinear pipes according to a certain bending angle to obtain hairpins 8, and extraction means, wholly indicated with 9, of the hairpins 8 in a collection area 10.
[0045] More specifically, but not exclusively, the bending angle of the pipes is about 180°, to thus obtain hairpins 8 with the arms substantially parallel to one another.
[0046] In detail, the feeding means 5 of the pipes comprise a straightening and advancing group 11 and a cutting group 12 one after the other, as illustrated in figure 3.
[0047] It should in any case be noted that the aforementioned feeding means 5 of the pipes could, irrespectively, comprise other mechanical groups that are equivalent and therefore suitable for obtaining substantially the same result.
[0048] Moreover, the extraction means 9 comprise an extraction group 13 of the hairpins 8, arranged downstream of the bending group 7, equipped with straws 13a.
[0049] The machine 1 also comprises a discharge area 14 equipped with an inclined or mobile plane 15, which conveys the hairpins 8 to the collection area 10, where they are deposited by falling on a container 16.
[0050] It should however be noted that the extraction means 9 of the hairpins 8 from the bending group 6 could consist of other mechanical groups with equivalent operation.
[0051] The bending machine 1 according to the invention comprises a programmable unit for controlling the operation of the various operating steps of the machine, not illustrated in the figures but of the type substantially known in the field.
[0052] The bending group 6 of the machine according to the invention is illustrated in the axonometric detail of figure 4.
[0053] The bending group 6 is mounted on a framework 17, in turn fixed to a bank 18 that is mobile on guides 19 fixedly connected to the base 2.
[0054] The framework 17 is equipped with two flanks 20 that are substantially symmetrical with respect to the axis of the machine.
[0055] However, in other embodiments of the machine not represented in the figures, the framework 17 of the bending group 6 could be mounted on other parts of the machine, for example not mobile but fixed, in relation to the specific requirements.
[0057] The bending arm 7 also comprises a central support 23 rotatably mounted on the framework 17, a group of clamps and bending shapes 24 that keep the pipes in the correct position during the bending operation, thus defining, with the contribution of the bending cores and relative support shafts 25, their final shape and avoiding deformations, breakages or other negative phenomena.
[0058] According to an aspect of the present invention the bending group 6, unlike what occurs in the known machine of figures 1,2, comprises a rotary actuation group, wholly indicated with 26, of the bending arm 7, comprising at least one electric motor 27, associated with at least one respective reducer 28.
[0059] The electric motor 27 for actuating the bending arm 7 is, more specifically and advantageously, of the brushless type.
[0060] However, the motor could also be of another type, for example stepper, or similar, obtaining the same advantageous effects that will be described hereafter. Moreover, the rotary actuation group 26 comprises a servo-actuation of the brushless electric motor 27, operating in a closed loop, i.e. with moment by moment control of the operating parameters of the motor, for example angular position, speed, torque and others.
[0061] The aforementioned servo-actuation of the brushless electric motor 27 is operatively connected to the programmable unit for controlling the bending machine 1.
[0062] As can be seen in figure 4, the brushless electric motor 27 is directly connected to the reducer 28, which in turn is fixed to one of the flanks 20 of the framework 17 through screws 29 and a flange 30. According to a further aspect of the present invention, the reducer 28 associated with the brushless electric motor 27 is advantageously of the cycloid type.
[0063] However, the reducer could also be of another kind, for example epicycloidal or similar, obtaining equivalent effects.
[0064] Figure 5 illustrates a diametral section of a possible type of cycloid reducer 28 able to be associated with the brushless electric motor 27 of the bending group 6 of the bending machine 1 according to the present invention.
[0065] As known, a cycloid reducer 28 comprises, as indicated in the aforementioned figure 5 and extremely briefly, an eccentric input shaft 31 that sets in rotation one or more cycloidal discs 32, equipped with equally spaced peripheral seats, also called teeth.
[0066] The latter are equipped with cylindrical seats for the insertion of pins 33 fixedly connected to the output shaft 34.
[0068] The high speed motion of the eccentric inlet shaft 31 determines the subsequent engagement, in the opposite direction, of the peripheral seats of each of the cycloidal discs 32 at the rollers 36. The result is motion of the output shaft 34 in the opposite direction with respect to that of the eccentric input shaft 31, according to a typical reduction ratio of each reducer 28.
[0069] The cycloid reducer 28 mounted on the bending machine according to the present invention is of the type having an output shaft 34 consisting of a flange, as indeed illustrated in figure 5.
[0070] However, it should be noted that any other type of cycloid reducer 28 can be used; it should be repeated that the reducer illustrated in the detail of figure 5 is a mere non-limiting example, given only to allow better understanding of its operation.
[0071] The flange that constitutes the output shaft 34 of the cycloid reducer 28 is then coupled directly with a corresponding flange - not represented in the figures - of the central support 23, without the need to use shafts and the relative torque transmission means such as splines, locking sets, etc.
[0072] The operation of the bending machine 1 according to the invention is, in general terms, totally identical to that described for the known machine represented in figures 1,2.
[0073] As stated, however, the advantageous differences concern the operation of the bending group 6, and in particular the actuation of the bending arm 7.
[0074] The brushless electric motor 27, unlike a hydraulic actuation, can withstand very high load peaks, for example up to 3-4 times the normal operating load. Moreover, the brushless electric motor 27 can be effectively controlled in a very precise and accurate manner, through suitable algorithms, obtaining any type of acceleration ramp and deceleration. As described earlier, these effects cannot be obtained with a hydraulic actuation.
[0075] Moreover, the brushless electric motor 27 does not significantly suffer from the problems linked to environmental and operating temperature.
[0076] The provision of a suitably studied control based on the bending cycle and capable of optimising the acceleration ramp, the translation speed and finally the deceleration ramp of the bending arm 7, makes it possible to obtain much shorter times of the bending cycle with respect to the solution with hydraulic actuation, maximising the mechanical and productivity result.
[0077] Regarding this, see the functional diagram of figure 6. The servo-actuation, for this purpose, comprises control means 100 of the bending cycle suitable, indeed, for optimising the acceleration ramp, the translation speed and finally the deceleration ramp of the bending arm 7.
[0078] The control means 100 of the bending cycle have been developed to obtain a specific adjustment of the functionality of the bending group 6, which enhances the efficiency of the system in relation to the extremely variable characteristics of the bending arm 7.
[0079] In greater detail, the control means 100 of the bending cycle are of the adaptive type in relation to the moment of inertia of said bending arm.
[0080] In other words, the control means 100 operate according to an unconventional adjustment algorithm with control characteristic that is adaptive in relation to the moment of inertia of the bending arm 7, which produces an extremely fine behavioural adaptation in relation to the variability of its size and mass.
[0081] This adaptability of the control algorithm makes it possible to obtain bending cycles that exploit to the maximum the acceleration, translation and braking ramps, with a substantial reduction in the cycle time in comparison with a conventional hydraulic system. Continuous and progressive control of the accelerations or reductions in angular speed is also ensured, according to constantly accelerating or decelerating motion, which minimise the generation of vibrations of the bending arm 7, which are particularly important when the length of the arm 7 itself exceeds 2 - 2,5 metres in length.
[0082] The control means 100 of the bending cycle also comprise detection means 200 of the absorption of current of said electric motor 27.
[0083] The control means 100 also comprise actuation means 300 of the extraction means 9,13,13a of the hairpins 8.
[0084] The actuation means 300 are operatively slaved to the detection means 200 of the absorption of current of said electric motor 27, with the effects that will become clearer hereafter.
[0085] The control means 100, therefore, through the detection means 200, continuously check, throughout the bending cycle, the absorption of the motor, preventing the occurrence of overloads with possible consequent mechanical breakdowns, in particular in the acceleration step, if the mass of the bending arm 7 exceeds the foreseen safety limits.
[0086] In order to optimise the control of the bending cycle, the machine according to the present invention is also provided with at least one first mechanical abutment of the bending arm 7 at a bending angle of about 180°. Indeed, when the bending arm 7 is approximately at a bending angle of about 180°, the bending cycle ends.
[0087] In this step the angular speed of the bending arm 7 thus tends to zero, according to a suitable deceleration ramp.
[0088] The reaching of the aforementioned first mechanical abutment by the bending arm 7 determines an increase in the absorption of current of the electric motor 27.
[0089] This increase is recorded by the detection means 200, which as stated are active along the entire rotation of the bending arm 7.
[0090] This increase in absorption is interpreted as the concluding moment of the bending cycle, and thus represents an additional safety feature of the system in the case of failure or breakdown.
[0091] Moreover, this increase in absorption determines the sending of a suitable signal, by the detection means 200, to the actuation means 300 of the extraction means 9,13,13a of the hairpins 8, in particular when a certain predetermined value of absorption of current has been reached.
[0092] This ensures that the extraction operation of the hairpins 8 happens immediately, without delays, thus so as to reduce the cycle times as much as possible.
[0093] The machine also comprises a second mechanical abutment of the bending arm 7 at a bending angle of about 0°, corresponding to the start of the bending cycle. The bending arm 7 goes back into this position at the end of each cycle, to begin the next one.
[0094] Once the bending angle of 0° is reached, the angular rotation speed of the bending arm 7 becomes zero and there is an increase in absorption of current of the electric motor 27, detected by the detection means 200.
[0095] The presence of this second mechanical abutment, in an absolutely analogous way to what has been described for the first mechanical abutment, ensures, thanks to the detection means 200, an optimal management of the deceleration and acceleration ramps of the bending arm 7, and therefore immediate restarting of the bending cycle.
[0096] However, it should be specified that the high degree of interaction of the motor 27 - reducer 28 - servo-actuation system makes it possible to manage the size of the rotation angle of the bending arm 7 with maximum precision, to the point where it could be possible to eliminate the mechanical stop that stops the motion of the arm 7. The stop is, however, kept, as stated, in order to increase passive safety in the case in which, for example, there is an interruption in current during the descent of the bending arm 7, breakage or malfunctioning of the servo-actuation, and also to reduce the cycle times with particular reference to the extraction step of the hairpins 8.
[0097] The cycloid reducer 28 also boasts great operating precision and great torsional rigidity that, by minimising the inertia at the motor, transmits the motion in the absence of vibrations, which is a result that cannot be obtained with a hydraulic actuation. Moreover, the cycloid reducer 28, in its constructive conception, adapts excellently to this type of application, transmitting the motion to the central support 23 of the bending arm 7 through its output shaft 34 that, as stated, consists of a flange. This last solution allows higher torques to be transmitted with respect to how much can be obtained with a shaft. It is thus possible to use a single actuation group 26 of the bending arm 7, instead of two, thanks also to the fact that the central support 23 of the bending arm 7 is unaffected by torsions, being formed from particularly rigid mechanical structures like for example, but not limitingly, by fusion.
[0098] It is however possible, in other embodiments, to foresee the installation of two actuation groups 26 instead of just one, if the application requires it. Furthermore, the cycloid reducer 28, characterised by just rolling contacts, ensures limited inertia, excellent efficiency on start up, low wear and long lifetime.
1. Bending machine (1) comprising:
means (5) for feeding a plurality of substantially rectilinear pipes;
a cutting group (12) of the pipes coming from said feeding means (5);
at least one bending group (6) comprising at least one bending arm (7) suitable for bending said plurality of pipes, coming from said cutting group (12), according to a certain bending angle, thus making a plurality of tubular hairpins (8);
extraction means (9,13,13a) of the hairpins (8) in a collection area (10)
said bending group (6) comprising a rotary central support (23) of said bending arm (7) and a rotary actuation group (26), coupled with said rotary central support (23), comprising at least one electric motor (27) and a respective reducer (28),
said rotary actuation group (26) comprising a servo-actuation of said brushless electric motor (27) operating in a closed loop and a programmable unit for controlling the operation to which said servo-actuation is operatively connected,
characterised in that said servo-actuation comprises control means (100) of the bending cycle suitable for optimising the acceleration ramp, the translation speed and the deceleration ramp of said bending arm (7).
2. Machine according to claim 1, wherein said control means (100) of the bending cycle
are of the adaptive type in relation to the moment of inertia of said bending arm
(7).
3. Machine according to one of the previous claims, wherein said control means (100)
of the bending cycle comprise means (200) for detecting the absorption of current
of said electric motor (27).
4. Machine according to the previous claim, comprising a first mechanical abutment of
said bending arm (7) at a bending angle of about 180°, upon reaching which the angular
rotation speed of said bending arm (7) becomes zero and there is an increase in absorption
of current of said electric motor (27), detected by said detection means (200).
5. Machine according to the previous claim, wherein said control means (100) of the bending
cycle comprise means (300) for actuating said extraction means (9,13,13a) of the hairpins
(8) operatively slaved to said detection means (200) of the absorption of current
of said electric motor (27), said actuation means (300) being suitable for carrying
out the extraction of the hairpins (8) once a certain predetermined value of the absorption
of current has been reached.
6. Machine according to one of claims 4 or 5, comprising a second mechanical abutment
of said bending arm (7) at a bending angle of about 0°, corresponding to the start
of the bending cycle, upon reaching which the angular rotation speed of said bending
arm (7) becomes zero and there is an increase in absorption of current of said electric
motor (27), detected by said detection means (200).
7. Machine according to one of the previous claims, wherein said electric motor (27)
is of the brushless type.
8. Machine according to one of the previous claims, wherein said reducer (28) is of the
cycloid type.
9. Machine according to the previous claim, wherein said bending group (7) comprises
a framework (17) equipped with two flanks (20) substantially symmetrical with respect
to the axis of the machine, said cycloid reducer (28) comprising a flange (30) for
fastening to one of said flanks (20).
10. Machine according to claim 8 or 9, wherein said cycloid reducer (28) is of the type
having output shaft (34) consisting of a flange, coupled with said rotary central
support (23).
11. Machine according to one of the previous claims, wherein said feeding means (5) of
a plurality of substantially rectilinear pipes comprises a cutting group (12) arranged
after said straightening and advancing group (11).
12. Machine according to one of the previous claims, wherein said extraction means (9)
of the hairpins (8) in a collection area (10) comprise an extraction group (13) equipped
with straws (13a), or equivalent means.
13. Machine according to one of the previous claims, wherein said collection area (10)
comprises a container (16) fed by inclined or mobile planes (15) in which the hairpins
(8) are deposited by falling.