Patent Publication Number: US-2015069107-A1

Title: Method For Controlling Feeding Length Of Wire And Displacement Sensing System For The Same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Chinese Patent Application No. 201310349287.4 filed on Aug. 12, 2013 in the State Intellectual Property Office of China. 
     FIELD OF THE INVENTION 
     The present invention relates, in general, to a method and a system for controlling a feeding length of a wire and more particularly, relates to a method and a system for controlling a feeding length of a solder wire and a detecting system for performing the method. 
     BACKGROUND 
     In the prior art, a solder wire is generally fed forward under a frictional engaging force between the solder wire and a driving wheel connected to an electric motor. The feeding length of the wire is often controlled with an open loop control. For example, the number of revolutions of the electric motor is first calculated according to a predetermined feeding length of the wire, and then the electric motor is started to rotate the driving wheel to feed the wire. When the electric motor runs to the calculated number of revolutions, the electric motor is stopped, and the feeding operation of the wire is finished. Theoretically, since the calculated number of revolutions of the electric motor corresponds to the predetermined feeding length of the wire, the actual feeding length of the wire would be equal to the predetermined feeding length of the wire. However, in practice, unexpected conditions may occur. For example, the driving wheel might slip over the wire or the electric motor might idle. This might cause the actual feeding length of the wire to be inaccurate and not be equal to the predetermined feeding length. 
     SUMMARY 
     The present invention has been made to overcome or alleviate at least one aspect of the above mentioned disadvantages. 
     Accordingly, it is an object of the present invention to provide a method and a system for accurately controlling a feeding length of a wire. 
     Accordingly, it is another object of the present invention to provide a simple displacement sensing system capable of accurately sensing the actual feeding length of a wire. 
     According to an aspect of the present invention, a method for controlling a feeding length of a wire comprises the steps of setting a predetermined feeding length of a wire, feeding the wire along a path of movement, and sensing, at a point along the path of movement of the wire, the passage of the wire. Also included in this method are the steps of calculating, over a predetermined interval, the actual feeding length of the wire that passes the point along the path of movement of the wire, comparing the calculated actual feeding length of the wire with the predetermined feeding length of the wire, and stopping the feeding of the wire when an error between a predetermined feeding length of the wire and the calculated actual feeding length of the wire is zero or is within an allowable range. 
     According to another aspect of the present invention, a system for controlling the feeding length of a wire comprises a wire guiding mechanism including (a) an inlet through which a wire is received by the system, and (b) an outlet through which the wire leaves the system. This system also includes a driving mechanism that feeds the wire through the system and includes (a) a driving wheel positioned to frictionally engage the wire and feed the wire through the system when the driving wheel rotates, and (b) a driver for rotating the driving wheel. This system further includes a displacement sensing device that senses the actual feeding length of the wire and includes (a) a driven wheel positioned to frictionally engage the wire and rotate when the wire is fed through the system, and (b) a sensor for sensing the number of revolutions of the driven wheel. This system also includes a controller preset with a predetermined feeding length of the wire that calculates the actual feeding length of the wire based on the product of (i) the number of revolutions of the driven wheel of the displacement sensing device sensed by the sensor of the displacement sensing device, and (ii) the perimeter of the driven wheel. The controller also controls the feeding length of the wire based on an error between the predetermined feeding length of the wire and the calculated actual feeding length of the wire with closed loop feedback control until the error becomes zero or within an allowable range. 
     According to another aspect of the present invention, a displacement sensing system for controlling the feeding length of a wire comprises a displacement sensing device including (a) driven wheel that rotates in response to frictional contact between the perimeter of the driven wheel and a wire moving past the driven wheel, and (b) a sensor for sensing the number of revolutions of the driven wheel over a predetermined interval; and a controller for calculating an actual feeding length of the wire based on (a) the product of the number of revolutions of the driven wheel sensed by the sensor over the predetermined interval, and (b) the perimeter of the driven wheel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawing, in which: 
         FIG. 1  is an illustrative perspective view of a wire feeding system according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION 
     Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawing. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that the disclosure of the present invention will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     In an exemplary embodiment of the present invention, the wire feeding system mainly comprises (a) a wire guiding mechanism  110 ,  120 ,  130  for guiding a wire  111  to move forward in a straight line, (b) a driving mechanism  200 ,  210  for driving the wire to move forward, (c) a displacement sensing device  300 ,  310  for sensing an actual feeding length of the wire, (d) an installation frame  100  for fixing various members thereon, and (e) a controller  400  for controlling the operation of the entire system. 
     In the illustrated embodiment of  FIG. 1 , the wire guiding mechanism mainly comprises an inlet tube  110 , an outlet tube  120  and a groove member  130 . The inlet tube  110  and the outlet tube  120  are mounted, respectively, at a front end and a rear end of the installation frame  100 . The groove member  130  is mounted on the installation frame  100  between the inlet tube  110  and the outlet tube  120 . With the above configuration, the wire may pass through the inlet tube  110 , a groove  131  formed in the groove member  130  and the outlet tube  120  as the wire is fed. 
     In an exemplary embodiment of the present invention, as shown in  FIG. 1 , the driving mechanism mainly comprises a driver  200  and a driving wheel  210 . The driving wheel  210  frictionally engages the wire  111 . As a result, the wire can be fed forward under the frictional engaging force between the wire  111  and the driving wheel  210 . The driving wheel  210  is connected to the driver  200 . The driver  200  rotates the driving wheel  210  so as to feed the wire. 
     As shown in  FIG. 1 , in an exemplary embodiment of the present invention, the displacement sensing device mainly comprises a driven wheel  310  and a sensor  300  for sensing the number of revolutions of the driven wheel  310 . The driven wheel  310  frictionally engages the wire  111  and rotates under the frictional engaging force therebetween while the wire is being fed. The sensor  300  senses the number of revolutions of the driven wheel  310 , converts the number of revolutions of the driven wheel  310  into an electrical signal, and transmits the electrical signal to the controller  400 . Thereby, the controller can calculate, over a predetermine interval, the actual feeding length of the wire based on the product of the number of revolutions of the driven wheel  310  sensed by the sensor  300  and a perimeter of the driven wheel  310 . 
     As shown in  FIG. 1 , the driver  200  and the sensor  300  are fixedly mounted on a vertical side wall  140  of the installation frame  100 . 
     In an exemplary embodiment, as shown in  FIG. 1 , at least a part of the outer circumferential surface of the wire  111  is exposed at both ends of the groove of the groove member  130 , such that the circumferential surfaces of the driving wheel  210  and the driven wheel  310  may press against the exposed outer surface of the wire and frictionally engage the wire. 
     In an exemplary embodiment of the present invention, the driver  200  can be an electric motor, with the driving wheel  210  coaxially mounted on an output shaft of the electric motor. 
     In an exemplary embodiment of the present invention, the sensor  300  can be a rotary optical encoder or a rotary electrical encoder, with the driven wheel  310  coaxially mounted on an input shaft of the encoder. 
     In the illustrated embodiment of  FIG. 1 , the axis of the output shaft of the electric motor  200  is arranged to be parallel to the axis of the input shaft of the encoder  300 ; and the axis of the wire  111  is perpendicular to the axes of the output shaft of the electric motor  200  and the input shaft of the encoder  300 . 
     In an exemplary embodiment of the present invention, the controller  400  may comprise a Programmable Logic Controller, Industrial Computer or Personal Computer. 
     The following are descriptions of embodiments of methods for controlling the feeding length of a wire according to the present invention in which the wire  111  is frictionally engaged with and fed by a driving wheel  210  mounted on a driver  200 . 
     The first embodiment comprises steps of: 
     S 10 : providing a displacement sensing device comprising a driven wheel  310  and a sensor  300  for sensing the number of revolutions of the driven wheel  310 , the driven wheel  310  being in frictional engagement with the wire  111  and rotated under a friction engaging force therebetween as the wire is fed; 
     S 20 : starting the driver  200  to rotate the driving wheel  210 , so that the wire  111  is fed forward and the driven wheel  310  is rotated as the wire is fed; 
     S 30 : calculating an actual feeding length of the wire  111  based on the product of the number of revolutions of the driven wheel  310  sensed by the sensor  300  over a predetermined interval and the perimeter of the driven wheel  310 ; and 
     S 40 : controlling the feeding length of the wire  111  based on an error between a predetermined feeding length of the wire and the calculated actual feeding length of the wire with closed loop feedback control, namely controller  40  controlling driver  200 , until the error becomes zero or within an allowable range. 
     In an exemplary embodiment of the present invention, the allowable range may be a range of 0 to 0.1 mm, preferably, a range of 0 to 0.05 mm, more preferably, a range of 0 to 0.01 mm. 
     The second embodiment comprises steps of: 
     S 100 : providing a displacement sensing device comprising a driven wheel  310  and a sensor  300  for sensing the number of revolutions of the driven wheel  310 , the driven wheel  310  being in frictional engagement with the wire  111  and rotated under a frictional engaging force therebetween as the wire is fed; 
     S 200 : setting a predetermined driving amount (for example, a predetermined number of revolutions of the electric motor  200 ) for the driver  200  according to a predetermined feeding length of the wire; 
     S 300 : starting the driver  200  to rotate the driving wheel  210 , so that the wire  111  is fed forward and the driven wheel  310  is rotated as the wire is fed; 
     S 400 : stopping the driver  200  when the driver  200  reaches the predetermined driving amount, and calculating an actual feeding length of the wire  111  based on the product of the number of revolutions of the driven wheel  310  sensed by the sensor  300  and the perimeter of the driven wheel  310 ; and 
     S 500 : determining whether an error between the predetermined feeding length of the wire and the calculated actual feeding length of the wire is equal to zero or within an allowable range. If not, starting the driver  200  again and controlling a driving amount of the driver  200  based on the error with closed loop feedback control of controller  400  until the error becomes zero or within the allowable range. 
     In another exemplary embodiment of the present invention, there is provided a method for controlling a feeding length of a wire, comprising: sensing an actual feeding length of the wire; and controlling the feeding length of the wire based on an error between a predetermined feeding length of the wire and the sensed actual feeding length of the wire with closed loop feedback control until the error becomes zero or within a allowable range. 
     In an exemplary embodiment of the present invention, the wire may be solder wire, such as metal solder wire or alloy solder wire, for example, tin solder, tin brass solder wire or aluminum brazing wire. 
     It should be appreciated for those skilled in this art that the above embodiments are intended to be illustrative, and not restrictive. For example, many modifications may be made to the above embodiments by those skilled in this art, and various features described in different embodiments may be freely combined with each other without conflicting in configuration or principle. 
     Although several exemplary embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes or modifications may be made in these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined in the claims and their equivalents. 
     As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plurals of said element or step, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” or “including” an element or a plurality of elements having a particular property may include additional such elements not having that property.