Abstract:
A metal spinning machine includes a mandrel kept in rotation, a roller tool with which a plate blank workpiece is pressed against the mandrel to form the workpiece, linear motors that generate thrust force in proportion to driving electrical current and drive the roller tool, an operating lever that gives an operator command to the linear motor and a control unit that includes a memory. Manual operation of the roller tool with the operating lever by an operator receiving a teaching of the operator command forms the workpiece in a prescribed shape. The memory of the control unit stores the operator command that is then given to the linear motor to enable a same shape to be subsequently formed relative to plate blank workpieces repeatedly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a metal spinning machine and more particularly to a metal spinning machine of the teaching playback system. 
         [0003]    2. Description of the Prior Art 
         [0004]    Metal spinning is a plastic forming process that executes forming by attaching a plate or pipe blank workpiece to a mandrel, spinning the workpiece in conjunction with the mandrel and pressing the workpiece with a roller tool against the mandrel. This forming process is widely used, as a method for forming products having a metal used as a raw material, for the production of parts and products, such as domestic containers, decorative craftworks, lighting fixtures, boilers, tanks, nozzles, engine parts, parabolic antennas and tire wheels. 
         [0005]    A metal spinning machine comprises a main shaft for spinning the mandrel and the workpiece and a plurality of mutually intersecting linear actuators for pressing the workpiece against the mandrel by driving the roller tool. In the conventional spinning machines, hydraulic cylinders or ball screw mechanisms that are rotationally driven by servomotors have been used as linear actuators for driving the roller tool. 
         [0006]    On the other hand, in the control of the roller tool, the teaching playback method that, besides resorting to the ordinary numerical control operated by having position coordinates input in numerical values, requires the operator to perform actual forming by manually operating the roller tool with an operating lever, playback an operator command memorized in the meantime and cause the subsequent forming to be actuated by the operator command has been widely used. While the multi-pass metal spinning that gradually deforms a workpiece attaches importance to the trajectory of the roller tool based on the experience and the skill of a skilled operator, the teaching playback method enables this important trajectory to be easily reflected in automatic production. Further, while the metal spinning requires accurate control of the clearance between the mandrel and the roller tool in conformity with the wall thickness of a product obtained after the forming, the teaching playback method enables easy realization of an adequate clearance because the gauging is implemented at the time of teaching. 
         [0007]    Incidentally, when the ball screw mechanisms are used as linear actuators, since the servomotor is generally subjected to position control or speed control and consequently suffered to assume a state of increased rigidity, the interference taking place between the roller tool and the mandrel during the course of teaching possibly results in generating overload and inflicting damage as on the power transmission mechanism. Thus, more often than not the metal spinning machine of the teaching playback system uses the hydraulic cylinder as an actuator. Japanese Patents No. 1640675 and No. 1704269 propose to use in the metal spinning machine of the teaching playback system a method for restraining the hydraulic pressure as by means of a relief valve and consequently preventing the excess forming force. 
         [0008]    The conventional metal spinning machine that drives the roller tool with a hydraulic mechanism entails labor hour in coping with the fluid resistance in the piping system for hydraulic fluid, righting the responsibility of the valve and further maintaining the management of the hydraulic fluid and tends toward suffering the characteristic properties to succumb to the influences of the temperature change. It also has been at a disadvantage in threatening environmental pollution by leakage of hydraulic fluid and inviting restriction on the location of installation. On the other hand, when the ball screw mechanism is used, the force control with sufficient responsibility has not been easily realized because of the frictional resistance and the backlash of the screw mechanism, the elasticity of the joint between the driving motor and the ball screw and the like. 
         [0009]    This invention has been accomplished in view of the true state of affairs mentioned above and is aimed at providing a metal spinning machine of the teaching playback system that, in spite of the use of an electric actuator capable of easy handling, enables the teaching operations to be performed without inducing the possibility of causing breakage due to overload even when the roller tool and the mandrel interfere with each other. 
       SUMMARY OF THE INVENTION 
       [0010]    With a view to accomplishing the above object, the present invention provides as the first aspect thereof a metal spinning machine comprising a mandrel kept in rotation, a roller tool with which a plate blank workpiece is pressed against the mandrel form the workpiece, linear motors that generate thrust force in proportion to driving electrical current and drive the roller tool, an operating lever that gives an operator command to the linear motors and a control unit that includes a memory, wherein manual operation of the roller tool with the operating lever by an operator receiving a teaching of the operator command forms the workpiece in a prescribed shape, and the memory of the control unit stores the operator command that is then given to the linear motor to enable a same shape to be subsequently formed relative to plate blank workpieces repeatedly. 
         [0011]    The second aspect of the invention includes the metal spinning machine of the first aspect, wherein the operator command indicates a target position of the roller tool obtained by integrating a speed input to the linear motor in proportion to an angle of the operating lever, and the driving electrical current of the linear motor is decided based on feedback of a variation between a current position and the target position of the roller tool. 
         [0012]    The third aspect of the invention includes the metal spinning machine of the second aspect, wherein for each movement of the target position of the roller tool over more than a fixed distance during the teaching of the operator command, the target position and a time of that instant are stored in the memory and a correspondence between the target position and a time of passage is variable at a time of playback. 
         [0013]    This invention is configured as described above and enabled to manifest the effect that will be described below. 
         [0014]    In the metal spinning machine of this invention, the linear motors used therein are capable of generating thrust force in proportion to driving electrical current and causing the generated thrust force to be exerted directly on the object being driven without the intervention of a transmission mechanism, such as ball screws. Since the machine possesses no sliding part, the frictional resistance is suffered to emanate solely from the linear bearing in the linear guide mechanism and, therefore, the loss of thrust force caused by friction is small. Thus, it is rendered possible to configure a forming machine of the teaching playback system that has no possibility of suffering the overload to inflict breakage on the transmission mechanism. 
         [0015]    According to this invention, therefore, the metal spinning machine adapted to perform forming a plate blank workpiece by pressing the workpiece with a roller tool against a mandrel kept in rotation is provided with linear motors that generate thrust force in proportion to driving electrical current and drive the roller tool, an operating lever that gives an operator command to the linear motors and a control unit that includes a memory. Therefore, the operator is allowed, on receiving a teaching of the operator command, to form a workpiece in a prescribed shape by manually operating the roller tool with the operating lever, cause an operator command to be stored in the meantime in the memory of the control unit and enable the same shape to be subsequently formed relative to plate blank workpieces repeatedly by giving the operator command stored in the memory to the linear motor. This machine enables easier handling as in maintenance than when hydraulic cylinders are used and obviates the necessity of providing a means to prevent excessive forming force. Even when the roller tool interferes with the mandrel, the teaching operation for the spinning can be executed without possibly inducing breakage due to overload as experienced in the ball screw mechanism. 
         [0016]    Further, this invention enables the motion of the roller tool to be played back nearly as faithfully as in the case of teaching even in the presence of disturbance, such as friction because the operator command pertains to the target position of the roller tool obtained by integrating the speed input to the linear motors in proportion to the angle of the operating lever, and the driving electrical current of the linear motor is decided based on the feedback of the difference between the current position of the roller tool and the target position. 
         [0017]    This invention enables storage of teaching data in a small memory capacity even when the teaching takes time and allows reduction of the forming time during the course of playback because in the metal spinning machine, for each movement of the target position of the roller tool over more than a fixed distance during the teaching of the operator command, the target position and the time of that instant are stored in the memory and the correspondence between the target position and the time of passage is variable at the time of playback. 
         [0018]    The above and other objects, characteristic features and advantages of the present invention will become apparent to those skilled in the art from the description to be given herein below with reference to the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic view illustrating one example of the metal spinning machine contemplated by this invention. 
           [0020]      FIG. 2(   a ) is an explanatory view illustrating the outline of the control in the teaching mode of the metal spinning machine of  FIG. 1 . 
           [0021]      FIG. 2(   b ) is an explanatory view illustrating the outline of the control in the playback mode of the metal spinning machine of  FIG. 1 . 
           [0022]      FIG. 3  is an explanatory view illustrating the concept of the target position in the teaching data of the metal spinning machine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    The object of executing a teaching operation without either using hydraulic mechanisms or possibly inducing breakage due to overload even in the presence of interference between the roller tool and the mandrel is realized by a forming device that is provided with linear motors generating thrust force in proportion to driving electrical current, an operating lever serving to give an operator command to the linear motors and a control unit including a memory and consequently, on receiving a teaching, is enabled to store the operator command in the memory and thereafter causes the operator command stored in the memory to be played back with the linear motors. 
         [0024]    Now, one example of the metal spinning machine of this invention will be described below by reference to the accompanying drawings. 
         [0025]      FIG. 1  is a schematic view of the metal spinning machine of this invention. A workpiece  1  is centered on a mandrel  3  with a tail stock  2  and made by a main shaft motor  4  to rotate together with the mandrel  3 . A roller tool  5  is made to progress or regress in the radial direction (y-direction) of the mandrel  3  by a linear table  7  driven by a linear motor  6  composed of a stator  6   a  and a moving element  6   b . The linear table  7  is made to progress or regress in the direction of the rotation axis (x-direction) of the mandrel  3  by a linear table  9  driven by a linear motor  8  composed of a stator  8   a  and a moving element  8   b . The workpiece  1  is pressed with the roller tool  5  against the mandrel  3  and transformed from a flat plate  1   a  in the initial shape finally to a shape  1   b  conforming to the mandrel  3 . 
         [0026]    An operating lever  10  is provided with a built-in potentiometer and enabled to enter voltage signals of speed inputs proportionate respectively to the inclinations of the lever in the x-direction and the y-direction into the A/D converters  12   x  and  12   y  of a computer (control unit)  11 . The electrical current commands directed toward linear motors are output into servo amplifiers  14   x  and  14   y  via D/A converters  13   x  and  13   y  and made to generate driving electrical currents to the linear motors  6  and  8 . The linear motors  6  and  8  are provided with position sensors, such as encoders, capable of detecting the positions of the moving elements  6   b  and  8   b  and the resultant position signals are entered in a counter  15 . A CPU  16  of the computer (control unit)  11  brings in the relevant signals via the A/D converter  12   x  and  12   y  and the counter  15 , carries out a computer processing for the sake of control, induces production of control signals from the D/A converters  13   x  and  13   y  to the servo amplifiers  14   x  and  14   y  and stores an operator command in a memory  17 . 
         [0027]    A conceptual diagram of the control contemplated by this invention is illustrated in  FIG. 2 . In the teaching mode of  FIG. 2(   a ), when an operator manipulates the operating lever  10 , a speed input (Vx, Vy) proportionate to the angle of the lever are generated. The electrical current commands to the servo amplifier  14  are determined by calculating the difference (Δx, Δy) between the target position (xd, yd) of the roller tool obtained by integrating the speed input (Vx, Vy) with an integrator and the current positions x and y of the roller tool input from the counter  15  and applying a position control rule, such as the proportional-plus-derivation control, thereto. In consequence of the preceding operation, it is rendered possible to move the roller tool and form the workpiece in accordance with the operator&#39;s lever manipulation. By setting the feedback gain in the proportional-plus-derivation control at a magnitude on the small side or by setting the largest electrical current control in the electrical current command to the servo amplifier, it is made possible to prevent the occurrence of overload even in the presence of interference between the roller tool and the mandrel. Further, at the same time, the target position (xd, yd) of the roller tool busy at service are stored in the form of an array of operator commands in the memory  17 . 
         [0028]    On the other hand, in the playback mode of  FIG. 2(   b ), the target positions (xd, xy) of the roller tool stored in the memory  17  are sequentially extracted as operator commands and input in the position control side similarly to the teaching mode of  FIG. 2(   a ). As a result, the roller tool is capable of playing back the same motion as the motion taught by the operator and forming the workpiece in the same shape. In this case, when the operator commands happen to be stored as electrical current commands to the servo amplifier or the speed commands of the roller tool in the memory  17 , the accumulation of control errors as due to friction possibly prevents the same motion from being necessarily played back as in the case of teaching. When the target positions of the roller tool are stored in advance as operator commands in accordance with this invention, however, the motion of the roller tool nearly equal to the motion brought by teaching can be faithfully played back even in the presence of disturbance due to friction because the disturbance is compensated by the position control rule and the roller tool is made to stop near the target position. 
         [0029]    In the teaching mode, when the operator is particularly unskilled or the workpiece is in an inexperienced material shape, it possibly happens that the operator is required, in the course of being taught, to stop the roller tool and observe the state of forming or continue the forming while slowing the motion of the roller tool greatly. The storage of operator commands is generally implemented at intervals of a fixed length. When such a teaching operation as mentioned above takes place, a large volume of memory is consumed by the futile data acquired while the roller tool is kept in a practically stopped state and superfluous time is spent also in the forming of playback. 
         [0030]    For each movement of the target position of the roller tool over more than a fixed distance, therefore, the target position and the time of that instant are stored ( FIG. 3 ). At the instant at which the expression, (x−x n−1 ) 2 +(y−y n−1 ) 2 ≧d 2 , wherein (x n−1 , y n−1 ) denotes the target position stored last and (x, y) denotes the current target position of the roller tool, (x, y) is stored as the next target position (x n , y n ). Also, the time of that instant is stored as Tn. The distance between the adjacent target positions so stored is approximately “d.” 
         [0031]    In the case of playback, when Tn is assumed to denote the time elapsing from the reference time and when the roller tool is caused to follow the target position (x n , y n ), the mode of motion of the roller tool becomes completely equal to that acquired by the playback. The correspondence between the target position (x n , y n ) and the time of elapse may be varied. When the target position (x n , y n ) is followed at the intervals of a fixed length, nΔT, in the place of Tn, for example, the target positions are fated to move at a fixed speed d/Δ. By doing so, it is rendered possible to eliminate the time during which the roller tool remains stopped and reduce the forming time during the course of playback. 
         [0032]    The metal spinning machine contemplated by this invention has been described by reference to the illustrated example. Needless to say, this invention does not need to be limited to this example but may be embodied in various modes within the scope of the technical matters set forth in the appended claims.