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:
This application is a national stage filing under 35 U.S.C. 371 of International Application PCT/IT2004/000581, filed on Oct. 22, 2004. The entire teachings of the referenced Application is incorporated herein by reference. International Application PCT/IT2004/000581 was published under PCT Article 21(2) in English. 
     BACKGROUND 
     1. Field 
     The present disclosure concerns a kinematic movement system for operating units of avant-garde bending machines. These are automatic machines for bending and shaping sheet metal. 
     This kinematic system features the electrical actuation and a particular kinematic drive of the main movements responsible for bending. The disclosure differs from machines currently produced which have hydraulic actuation. 
     The system according to the disclosure can be applied to a compact bending machine. In terms of weight and size such a machine can fit in a container, without the noisy and cumbersome hydraulic control unit. An ecological advantage is that it does not require topping up with great quantities of mineral oil. The machine is faster and more reliable than current machines and has more limited production costs. 
     This disclosure can be applied in the production of bending machines, and also to industrial bending machines for sheet metal. 
     2. General Background 
     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. 
     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.       

     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, movable in two reciprocally orthogonal directions with respect to the fixed bed, on which the bending blade(s) is (are) fixed. 
     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. 
     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. 
     SUMMARY 
     The blades are supported by a load-bearing C-shaped structure mounted on the main frame. The unit comprises two blades: the upper one for negative bends (downwards) and the lower one for positive bends (upwards). 
     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. 
     The presser tool is mounted on an electrowelded structure with four arms, hinged at the rear of the main frame. 
     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. 
     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. 
     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. 
     The traditional pentalateral type kinematic chain is 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. 
    
    
     
       DRAWINGS 
       The above-mentioned features and objects of the present disclosure will become more apparent with reference to the following description taken in conjunction with the accompanying drawings wherein like reference numerals denote like elements and in which: 
         FIG. 1  represents a schematic side view of a traditional type bending machine; 
         FIG. 2  represents the three-dimensional schematic view of a general model of the kinematic system according to the disclosure which drives the blade-holder unit of a bending machine; 
         FIG. 3  is a schematic view of the same kinematic model represented on the flat, showing the trajectory lines of the links; 
         FIGS. 4 to 6  show views of kinematic models of the blade-holder drive unit; 
         FIG. 7  is a block diagram of the bending trajectory generation system in the machine according to the disclosure; 
         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. 
         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 disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the kinematic diagram of a traditional system for the movement of the blade-holder unit P. 
     With reference to  FIG. 1 , 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. 
     In such machines, the pentalateral is not actuated by means of frame cranks but by hydraulic cylinders. This does not present any singularity combination. 
     This is 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.       

     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. 
     These high sensitivity coefficients of traditional bending machines are unable to provide the necessary amplification to the torque provided by the reduction motors (brushless motor+epicyclical reduction gear) available on the market. The only type of drive for known kinematic systems is therefore hydraulic. 
     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. 
     Another problem is the non-absolute precision of the machine. This is due to the two synchronized movements that make it possible to define the trajectory of the tool are achieved by two groups of hydraulic cylinders which by virtue of their position are not completely independently for the horizontal and vertical movement of the tool. 
     The hydraulic cylinders responsible for the horizontal movement of the blade-holder unit also produce an unwanted vertical movement. In the same way the vertical cylinders also produce a horizontal movement. 
     This is due to the positioning of the cylinders which are not at right angles to each other, and also do not form fixed angles with respect to the frame. 
     This disclosure provides a kinematic system to drive operating units of bending machines. The system is able to eliminate or at least reduce the disadvantages described above. 
     The disclosure provides a kinematic system to drive operating units of a new concept of bending machines. Servomotors and epicyclical reduction gears are used for the movement of the blade-holder unit instead of the traditional hydraulic actuators. 
     The servomotors and reduction units make it possible to achieve higher performance levels than those of a hydraulic system. This also ensures 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. 
     Electric servomotors, by virtue of the intrinsic linearity of their model of behavior, 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. 
     These advantages are achieved by a kinematic system for driving the operating units of a bending machine. These features are described in the main claim. 
     The dependent claims describe advantageous embodiments of the disclosure. 
     A main advantage of this solution is that the blade-holder unit of the bending machine uses an articulated mechanism. By definition, this is a variable speed mechanism. 
     This means that, with the same drive speed, very low speeds can be used in the few seconds immediately prior to closing/opening. Decidedly higher speeds can be used during the rest of the presser stroke. 
     This also allows a further reduction in cycle time and a consequent increase in machine performance. 
     The machine is actuated electrically, by an appropriate electronic control unit. This employs an original mechanism for the movement of the bending blades. This 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. 
     The articulated system that constitutes the mechanism is a kinematic plane mechanism. This is 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. 
     From the topological point of view (number of members and type of couplings) this is a closed kinematic chain with five members connected by five kinematic turning pairs. 
     One of these members is the frame of the machine. This kinematic chain has two actual degrees of freedom. This allows two independent motors. The two frame cranks were chosen as motor elements. 
     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.       

     The mechanism according to this disclosure 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. 
     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. 
     This concept is independent of the geometric dimensions of the members or of the position of the frame kinematic pairs. The amplification effect depends to some extent on these dimensions, and on the working space of the machine. 
     The blades of the machine according to the disclosure are moved by an articulated system with two degrees of freedom that presents evident kinematic non-linearity, the movement of the bending blades. This is characterized by well-defined bending trajectories, and is made possible and programmable by a special original inverse kinematic algorithm of the non-iterative type. This is inserted in the numerical control or used as a pre-processor. This makes it possible to carry out well-defined trajectories with interpolated axes such as, for example, the classic circular interpolation. 
     In particular, a method and an algorithm typical of the field of robotics were applied to a machine tool, in an appropriately adapted way. This allows movement control by variables other than the tool coordinates, not orthogonal but independent of each other. 
     This algorithm defines the law of motion, exactly and without approximation. This 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. 
     This algorithm resolves the position kinematics in a non-iterative way and thus with zero error. 
     According to the disclosure, 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. 
     The non-iterative solution takes place by geometric type considerations. 
     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. 
     In particular the machine according to the disclosure foresees the use of a new and original bending trajectory. This is unlike the known solutions, 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. 
     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 define the trajectory. 
     The quality of the semifinished part processed by the machine according to the disclosure is excellent. This is achieved by a considerably quieter machine compared to previous machines and uses reduced quantities of oil for a much simpler hydraulic circuit. 
     The environmental impact of the new machine is completely different with respect to the solutions known, since it is less noisy and uses considerably less oil. 
       FIG. 1  shows the described drive method of the blade-holder unit P moved by a hydraulic drive system using actuators. Points A, D, L and G refer to the fixed frame torque points, around which the members turn. 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 disclosure resolves. 
     In  FIG. 2 , the bending machine according to the disclosure is equipped with a blade-holder unit  10 , which uses servomotors and epicyclical reduction gears instead of traditional hydraulic actuators to control its movements. 
     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. The chain has two degrees of freedom, depending on two mechanical units indicated, respectively, by  13  and  14 . 
     The articulated system which makes up the mechanism is kinematically considered a plane mechanism. This is a mechanism in which the members move with plane motion. The axes of the turning pairs are parallel to each other and at right angles to the plane of motion. 
     From the topological point of view, the number of members and the type of couplings, is a closed kinematic chain with five members connected by five kinematic turning pairs. 
     One of these members is the frame of the machine. This kinematic chain has two degrees of freedom. This allows two independent motors, each installed on the respective mechanical unit. 
     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 . 
     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 . These branch 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 . 
     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 are attached to the plinth  12  of the blade-holder unit  10 . 
     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. 
     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 neighborhood 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”.       

     This mechanism is in a condition of dual kinematic singularity (referring to inverse motion) in a neighborhood of both the above-mentioned configurations. 
     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 . 
       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 . 
       FIGS. 4 and 5  show the positions of the members, which are represented by vectors. These give rise to the dual singularity of the mechanism in the neighborhood of the bending configurations. 
       FIG. 4  shows a first singular configuration with the start of a positive bend. 
       FIG. 5  shows a first singular configuration with the start of a negative bend. 
       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. 
     It should also be pointed out that the disclosed concept is independent of the geometric dimensions of the members or of the position of the frame kinematic pairs. It is evident that the amplification effect depends to some extent on these dimensions, and on the working space of the machine. 
     The blades of the machine according to the disclosure are moved by an articulated system with two degrees of freedom that presents evident kinematic non-linearity. The movement of the bending blades is characterized by well-defined bending trajectories. This 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. This makes it possible to carry out well-defined trajectories with interpolated axes such as, for example, the classic circular interpolation. 
     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. 
     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. 
     In  FIG. 9 , X 3  indicates the gap and X 4  the bending angle. 
     The blade and the sheet metal behave like two conjugate profiles and the resulting trajectory is a sort of circle involute. 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. 
     The kinematic motion described leads to numerous advantages. 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. This cannot be achieved with a hydraulic system that uses accumulators and thus necessarily has a pressure that slowly decreases during bending. 
     In addition, the quality of the semifinished part processed by the machine according to the disclosure 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. 
     The environmental impact of the new machine is completely different with respect to the known solutions, since it is less noisy and uses considerably less oil. 
       FIG. 7  is a block diagram relative to the control program of the bending machine. 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. 
     The disclosure is described above with reference to a preferred embodiment. It is nevertheless clear that the disclosure is susceptible to numerous variations within the framework of technical equivalents.