Abstract:
A bending machine designed to bend and shape sheet metal comprises a blade-holder unit ( 10 ) with a “C” shaped cross-section, mobile along two mutually orthogonal directions with respect to a fixed bed, and on which one or more bending blades are fixed. This machine comprises a kinematic system for driving the operating units, in which servomotors ( 15, 21, 22 ) and epicyclical reduction gears are used for the movement of the blade-holder unit ( 10 ). Moreover, the blade-holder unit ( 10 ) of the bending machine uses an articulated mechanism consisting of two mechanical units ( 13, 14 ) which form a closed kinematic chain with five members connected by five kinematic turning pairs.

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns a kinematic movement system for operating units of avant-garde bending machines, that is of automatic machines for bending and shaping sheet metal. 
         [0002]    This kinematic system features electrical actuation and a particular kinematic drive of the main movements, that is those responsible for bending in the strict sense of the word, differing thereby from the machines currently produced, which have hydraulic actuation. 
         [0003]    The system according to the invention can be applied to a compact bending machine which can, in terms of weight and size, fit in a container, without the noisy and cumbersome hydraulic control unit, ecological as it does not require topping up with great quantities of mineral oil, faster and more reliable than the current machines and with more limited production costs. 
         [0004]    This invention can be applied in the production of bending machines and industrial bending machines for sheet metal. 
       BACKGROUND ART 
       [0005]    It is known that the industry relative to the production of sheet metal items uses bending machines that allow a series of bends to be made in a single piece of sheet metal, in a completely automatic and controlled way, in order to obtain a finished product such as, for example, a cooker hood or a shelf. 
         [0006]    It is also known that bending machines for sheet metal normally consist of:
       a fixed bed to support the material, for example sheet metal, to be bent;   a support frame for a clamping press;   a punch, being part of the press, and a corresponding counter-punch acting as means for clamping the material during the bending phase;   one or more bending blades that can be moved towards the material being processed;   appropriate kinematic motions designed to move the bending blade or blades along the bed for shaping the piece clamped between the punch and the counter-punch;   means for moving the sheet metal or the profile towards the blades in working conditions;   transducers or sensors of various types, to control the process, connected to an electronic unit which controls the production process.       
 
         [0014]    A bending machine of the known type described above, marketed by the applicant hereto, comprises a blade-holder structure with a “C” shaped cross-section, mobile in two reciprocally orthogonal directions with respect to the fixed bed, on which the bending blade(s) is(are) fixed. 
         [0015]    The profile of the bend that can be obtained with a known automatic bending machine is not just the classic fixed angle profile that can be obtained with a manual bending machine. The simultaneous control of the positioning of the sheet metal and of the pressure exerted on it makes it possible to obtain radial profiles. 
         [0016]    The use of traditional blades, particular tools and dies, included in the bending cycle, also makes it possible to form special profiles, without the need for the intervention of an operator when the length or the special tool changes. 
         [0017]    As with the traditional construction conception, the blades are supported by a load-bearing C-shaped structure mounted on the main frame and the unit comprises two blades: the upper one for negative bends (downwards) and the lower one for positive bends (upwards). 
         [0018]    The system controls the dimensions of the angles and the thickness of the sheet metal, adjusting the position of the blades by means of proportional valves. All the movements are carried out by proportional control hydraulic cylinders. A special mechanism guarantees the parallelism of the movements of the bending unit. 
         [0019]    The presser tool is mounted on an electrowelded structure with four arms, hinged at the rear of the main frame. 
         [0020]    The movements of the C-shaped structure and of the tools are controlled by hydraulic cylinders. The cylinders can be programmed by means of the control unit in order to achieve the highest degree of precision during all the bending phases. 
         [0021]    Traditional hydraulic bending machines, like other bending machines present on the market, are fitted with a kinematic structure which determines and controls the movement of the blade-holder unit. 
         [0022]    This structure can in some cases be the pentalateral type, that is consisting of a closed kinematic chain with five members connected by five kinematic pairs. 
         [0023]    The traditional pentalateral type kinematic chain is however used in order to provide the machine with torsional rigidity and not therefore with specific mechanical functions; in addition, the pentalateral type is not actuated by frame cranks. 
         [0024]      FIG. 1  shows the kinematic diagram of a traditional system for the movement of the blade-holder, unit P. 
         [0025]    With reference to this figure, the letters A, D, L and G indicate the frame fixed torque points around which the members rotate, while the letters B, C, E, F and H indicate the turning couplings that allow a degree of rotation freedom in the relative movement of the members. 
         [0026]    In such machines, the pentalateral is not actuated by means of frame cranks but by hydraulic cylinders and does not present any singularity combination. 
         [0027]    This is therefore, to all extents and purposes, a mechanism which presents certain structural and functional limitations, such as:
       the machine is very noisy since the entire kinematic system is driven by hydraulic type circuits and components;   it uses considerable amounts of oil to activate a very complex hydraulic circuit;   it uses considerable amounts of electricity for the functioning of the entire complex hydraulic system;   the environmental impact of the machine is therefore extremely negative as regards noise and the consumption of oil and electricity.       
 
         [0032]    Specific analyses carried out on traditional bending machines have also shown that the usual mechanism for bending the sheet metal cannot be controlled electrically since the sensitivity coefficients of the tool with respect to the frame cranks are too high. 
         [0033]    These high sensitivity coefficients of traditional bending machines are not therefore able to provide the necessary amplification to the torque provided by the reduction motors (brushless motor+epicyclical reduction gear) available on the market, and the only type of drive for known kinematic systems is therefore hydraulic. 
         [0034]    Other types of motors cannot be used due to the movement laws to be carried out; other reduction units (ordinary gear trains) are not compatible with the weights and dimensions of the machines. 
         [0035]    Another problem is the non-absolute precision of the machine, due to the fact that the two synchronized movements that make it possible to define the trajectory of the tool are, in known machines, achieved by means of two groups of hydraulic cylinders which by virtue of their position are responsible not completely independently for the horizontal and vertical movement of the tool. 
         [0036]    In other words the hydraulic cylinders responsible for the horizontal movement of the blade-holder unit also produce an unwanted vertical movement and in the same way the vertical cylinders also produce a horizontal movement. 
         [0037]    This is due to the positioning of the cylinders which are not at right angles to each other, nor do they form fixed angles with respect to the frame. 
       DESCRIPTION OF THE INVENTION 
       [0038]    This invention proposes to provide a kinematic system to drive operating units of bending machines, able to eliminate or at least reduce the disadvantages described above. 
         [0039]    The invention proposes first of all to provide a kinematic system to drive operating units of a new concept of bending machines, which foresee that servomotors and epicyclical reduction gears are used for the movement of the blade-holder unit instead of the traditional hydraulic actuators. 
         [0040]    The servomotors and reduction units do in fact make it possible to achieve definitely higher performance levels than those of a hydraulic system and also ensure a constant delivered torque that cannot be obtained with a hydraulic system that uses accumulators and thus necessarily has a pressure that slowly decreases during bending. 
         [0041]    Electric servomotors, by virtue of the intrinsic linearity of their model of behaviour, allow the use of advanced control patterns to carry out freely defined trajectories and interpolations, with practically no errors in position and speed; such levels of performance cannot be achieved with a hydraulic system controlled by means of proportional valves because of the non-linearity caused by the fluid and of the more reduced pass-band of this drive. 
         [0042]    These advantages are achieved by means of a kinematic system for driving the operating units of a bending machine, the features of which are described in the main claim. 
         [0043]    The dependent claims of the solution in question describe advantageous embodiments of the invention. 
         [0044]    The main advantages of this solution concern first of all the fact that the blade-holder unit of the bending machine uses an articulated mechanism which is, by definition, a variable speed mechanism. 
         [0045]    This means that, with the same drive speed, very low speeds can be used in the few seconds immediately prior to closing/opening and decidedly higher speeds during the rest of the presser stroke. 
         [0046]    This also allows a further reduction in cycle time and a consequent increase in machine performance. 
         [0047]    The machine is actuated electrically, by means of an appropriate electronic control unit, and employs an original mechanism for the movement of the bending blades that can produce an amplification of the torque sufficient to generate the force on the tools necessary to bend the thicknesses and lengths as per the machine specifications. 
         [0048]    The articulated system that constitutes the mechanism is considered in kinematic terms a plane mechanism, this being a mechanism in which the members move with plane motion, with the axes of the turning pairs parallel to each other and at right angles to the plane of motion. 
         [0049]    From the topological point of view (number of members and type of couplings) this a closed kinematic chain with five members connected by five kinematic turning pairs. 
         [0050]    One of these members is the frame of the machine. This kinematic chain has two actual degrees of freedom, that is to say it allows two independent motors. The two frame cranks were chosen as motor elements. 
         [0051]    From the geometric point of view, the mechanism:
       has the necessary working space for the correct movement of the bending blades in the fields foreseen by the application;   presents particular geometric configurations (corresponding to conditions of kinematic singularity in the case of kinematic inversion of motion) in a neighbourhood of the configurations in which the mechanism bends the sheet metal, sufficient to generate the necessary amplification of the torques; there are two of these configurations, corresponding to the so-called positive bend and negative bend.       
 
         [0054]    It can be observed that the mechanism according to this invention is such as to be in a condition of dual kinematic singularity (referring to inverse motion) in a neighbourhood of both the above-mentioned configurations. 
         [0055]    This dual singularity is achieved by simultaneously aligning the first motor crank with the first connecting rod and the second motor crank with the second connecting rod. 
         [0056]    This concept is independent of the geometric dimensions of the members or of the position of the frame kinematic pairs, even if it seems evident that the amplification effect depends to some extent on these dimensions, and on the working space of the machine. 
         [0057]    As the blades of the machine according to the invention are moved by means of an articulated system with two degrees of freedom that presents evident kinematic non-linearity, the movement of the bending blades, characterised by well-defined bending trajectories, is made possible and programmable by a special original inverse kinematic algorithm of the non-iterative type which, inserted in the numerical control or used as a pre-processor, makes it possible to carry out well-defined trajectories with interpolated axes such as, for example, the classic circular interpolation, already used in other achievements. 
         [0058]    In particular, a method and an algorithm typical of the field of robotics were applied to a machine tool, in an appropriately adapted way, so as to allow movement control by means of variables other than the tool coordinates, not orthogonal but independent of each other. 
         [0059]    This algorithm defines the law of motion, exactly and without approximation, which corresponds to a desired tool trajectory, unlike what occurs in hydraulic bending machines in which the trajectory is traditionally set in the actuator space, which differs from the Cartesian space, and is therefore approximated regardless of the controller quality. 
         [0060]    This algorithm resolves the position kinematics in a non-iterative way and thus with zero error. 
         [0061]    According to the invention, the inverse kinematic algorithm comprises the subsequent solution of two closed links, each of which corresponds to two non-linear closing equations in two unknown quantities. 
         [0062]    The non-iterative solution takes place by means of geometric type considerations. 
         [0063]    This inverse kinematic algorithm, combined with the high precision of the controller that works on electric axes, makes it possible to carry out particular trajectories, other than the circular one, with particular features and uses. 
         [0064]    In particular the machine according to the invention foresees the use of a new and original bending trajectory which, unlike the known solutions, allows the bending blade to turn on the sheet metal without sliding. 
         [0065]    This trajectory is particularly useful in processing materials with a protective film as it prevents the film from being torn and the consequent damage to the sheet metal. 
         [0066]    In this case, the blade and the sheet metal behave like two conjugate profiles and the resulting trajectory is a sort of circle involute. It can be observed that by mathematically imposing the non-slipping constraint between the blade and the sheet metal, a bond is achieved between the two free (or generalised) coordinates which in fact define the trajectory. 
         [0067]    The quality of the semifinished part processed by the machine according to the invention is excellent and is achieved by means of a considerably quieter machine compared to previous machines and uses reduced quantities of oil for a much simpler hydraulic circuit. 
         [0068]    The environmental impact of the new machine is therefore completely different with respect to the solutions known to the background art, since it is less noisy and uses considerably less oil. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0069]    Other features and advantages of the invention will become evident on reading the following description of one embodiment of the invention, given as a non-binding example, with the help of the drawings shown in the attached pages, in which: 
           [0070]      FIG. 1  represents a schematic side view of a traditional type bending machine; 
           [0071]      FIG. 2  represents the three-dimensional schematic view of a general model of the kinematic system according to the invention which drives the blade-holder unit of a bending machine; 
           [0072]      FIG. 3  is a schematic view of the same kinematic model represented on the flat, showing the trajectory lines of the links; 
           [0073]      FIGS. 4 to 6  show views of kinematic models of the blade-holder drive unit; 
           [0074]      FIG. 7  is a block diagram of the bending trajectory generation system in the machine according to the invention; 
           [0075]      FIGS. 8 and 9  show schematic views of the trajectory of the blade on the, sheet metal to be bent, in a first and second operating phase. 
           [0076]      FIGS. 10 and 11  respectively show, in the form of a schematic illustration and a block diagram, the calculation procedure of the inverse kinematic system in analytical form for the bending machine according to the invention. 
       
    
    
     DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION 
       [0077]    Referring first of all to  FIG. 1 , it is possible to note the described drive method of the blade-holder unit P, which is moved by a hydraulic drive system using actuators, of which points A, D, L and G refer to the fixed frame torque points, around which the members turn, while B, C, E, F, and H indicate the turning couplings that allow a rotational degree of freedom to the relative motion of the members. This system presents all the problems mentioned above, which the invention proposes to resolve. 
         [0078]    With reference to  FIG. 2 , the bending machine according to the invention is instead equipped with a blade-holder unit  10 , which uses servomotors and epicyclical reduction gears instead of traditional hydraulic actuators to control its movements. 
         [0079]    From the structural point of view, the rear part of the blade-holder unit is integral with a plurality of supports  11 , while plinths  12  are fixed on its lower part. The supports  11  and the plinths  12  are involved in the action of a particular kinematic system whose chain has two actual degrees of freedom, depending on two mechanical units indicated, respectively, by  13  and  14 . 
         [0080]    The articulated system which makes up the mechanism is kinematically considered a plane mechanism, this being a mechanism in which the members move with plane motion, with the axes of the turning pairs parallel to each other and at right angles to the plane of motion. 
         [0081]    From the topological point of view, that is the number of members and the type of couplings, this a closed kinematic chain with five members connected by five kinematic turning pairs. 
         [0082]    One of these members is the frame of the machine. This kinematic chain has two actual degrees of freedom, that is to say it allows two independent motors, each installed on the respective mechanical unit. 
         [0083]    The first independent servomotor  15  is part of the first mechanical unit  13 , to which a crank  16  is fitted, attached in turn to a connecting rod  17 , with its other end hinged to a lever  18 . 
         [0084]    This lever  18  is equipped with a pivot on the shaft  19 , while its other end, the one opposite to the coupling point with the connecting rod  17 , branches into a series of elements  18   a  and  18   b,  which are coupled to the same number of pins  20   a  and  20   b  positioned on the ends of the supports  11  integral with the blade-holder unit  10 . 
         [0085]    The second mechanical unit  14  consists of two servomotors  21  and  22  which drive respective cranks  23  and  24  hinged in turn to respective connecting rods  25  and  26 , the other ends of which are attached to the plinth  12  of the blade-holder unit  10 . 
         [0086]    It should be noted that all the cranks can be constructively represented by eccentric elements having the same function and that the two frame cranks were chosen as motor elements. 
         [0087]    From the geometric point of view, the mechanism:
       has the necessary working space for the correct movement of the bending blades in the fields foreseen by the application;   presents particular geometric configurations (corresponding to conditions, of kinematic singularity in the case of kinematic inversion of motion) in a neighbourhood of the configurations in which the mechanism bends the sheet metal, sufficient to generate the necessary amplification of the torques. There are two of these configurations, corresponding to the so-called “positive bend” and “negative bend”.       
 
         [0090]    It can be observed that this mechanism is such as to be in a condition of dual kinematic singularity (referring to inverse motion) in a neighbourhood of both the above-mentioned configurations. 
         [0091]    This dual singularity is achieved by simultaneously aligning the first motor crank  23 ,  24  with the first connecting rod  25 ,  26  and the second motor crank  16  with the second connecting rod  17 . 
         [0092]      FIG. 3  shows the trajectories of the links and in particular, the Z references indicate the following kinematic connections:
   Z 1 —crank  23 ,  24  of the first link between the motor  21 ,  22  and the connecting rod  25 ,  26 ;   Z 2 —trajectory of the connecting rod  25 ,  26  of the first link;   Z 3 —trajectory of the first link between the hinge of the connecting rod  25 ,  26  and the blade-holder unit  10 , and the hinge  20  of the lever  18 ;   Z 4 —trajectory of the first link between the hinge  20  of the lever  18  and the pivot  19  of this lever;   ZB 1 —trajectory of the second link between the pivot  19  of the lever  18  and the hinge between the crank  18  and the connecting rod  17 ;   ZB 2 —trajectory of the second link between the hinge of the crank  18  and connecting rod  17  and the hinge of the connecting rod  17  and the crank  16 ;   ZB 3 —trajectory of the second link between the hinge of the connecting rod  17  and the crank  16 , and the shaft axis of the motor  15 .     
         [0100]    The schematic  FIGS. 4 and 5  show the positions of the members, which are represented by vectors, which give rise to the dual singularity of the mechanism in the neighbourhood of the bending configurations. 
         [0101]    In particular,  FIG. 4  shows a first singular configuration with the start of a positive bend, while  FIG. 5  shows a first singular configuration with the start of a negative bend. 
         [0102]      FIG. 6  shows the second singular configuration of the crank  16  and the connecting rod  17 : fine dashed line start of the positive or negative bend and long dashed line end of the bend. 
         [0103]    It should also be pointed out that this concept is independent of the geometric dimensions of the members or of the position of the frame kinematic pairs, even if it seems evident that the amplification effect depends to some extent on these dimensions, and on the working space of the machine. 
         [0104]    As the blades of the machine according to the invention are moved by means of an articulated system with two degrees of freedom that presents evident kinematic non-linearity, the movement of the bending blades, characterised by well-defined bending. trajectories, is made possible and programmable by a special original inverse kinematic algorithm of the non-iterative type which, inserted in the numerical control or used as a pre-processor, makes it possible to carry out well-defined trajectories with interpolated axes such as, for example, the classic circular interpolation. 
         [0105]    As can be seen in  FIGS. 8 and 9 , the particular new bending trajectory is shown which allows the bending blade to turn on the sheet metal without sliding. This trajectory is particularly useful in processing materials with a protective film as it prevents the film from being torn and the consequent damage to the sheet metal. 
         [0106]    The reference X 1  in  FIG. 8  indicates the initial gap between the ends of the sheet metal to be bent and the support, while X 2  indicates the radius of the blade. 
         [0107]    In  FIG. 9 , X 3  indicates the gap and X 4  the bending angle. 
         [0108]    The blade and the sheet metal behave like two conjugate profiles and the resulting trajectory is a sort of circle involute. It can be observed that by mathematically imposing the non-slipping constraint between the blade and the sheet metal, a bond is achieved between the two free coordinates which in fact define the trajectory. 
         [0109]    The kinematic motion described leads to numerous advantages, the most evident referring to the fact that the servomotors and the reduction units make it possible to achieve definitely higher levels of performance than those of a hydraulic system and also ensure constant delivered torque which cannot be achieved with a hydraulic system that uses accumulators and thus necessarily has a pressure that slowly decreases during bending. 
         [0110]    In addition, the quality of the semifinished part processed by the machine according to the invention is excellent and is achieved by means of a considerably quieter machine compared to previous machines and uses reduced quantities of oil for a much simpler hydraulic circuit. 
         [0111]    The environmental impact of the new machine is therefore completely different with respect to the solutions known to the background art, since it is less noisy and uses considerably less oil. 
         [0112]      FIG. 7  is a block diagram relative to the control programme of the bending machine. In particular, this block diagram makes it possible to define the mathematical calculus approach used to set a condition of turning and not of sliding of the blade on the sheet metal to be bent. 
         [0113]    The invention is described above with reference to a preferred embodiment. It is nevertheless clear that the invention is susceptible to numerous variations within the framework of technical equivalents.