Patent Publication Number: US-2005127600-A1

Title: Conveyor mechanism using an electro-pneumatic roll lift mechanism

Description:
CROSS REFERENCE TO OTHER APPLICATIONS  
      This application claims priority to U.S. Provisional Patent application No. 60/511,052 filed Oct. 10, 2004, the disclosure of which is hereby explicitly incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a press feed or conveyor mechanism for feeding sheet and/or strip stock material into a machine, such as a press, and more specifically to a mechanism employing an electro-pneumatic roll lift mechanism.  
      2. Description of the Related Art  
      A common way of feeding material to a press is by clamping the stock material between two rolls and rotating those two rolls in a manner that advances the material into the press. To provide this clamping action, one roll is normally fixed for rotation and the second roll is free to move toward and away from the first roll. The fixed roll is often called a feed roll, and the moveable roll is commonly named a pinch roll.  
      In some press applications, after the required amount of material is fed into the press, it is necessary to unclamp the material so that it can be properly aligned with the guide before the workpiece is formed. This unclamping or separation of the pinch roll from the feed roll is termed roll lift. Roll lift, if not accurate and/or in time, can prohibit alignment of the material, causing damage to the workpiece and/or the die. Furthermore, the pinch roll needs to resume its clamping position in a controlled manner. Slamming of the pinch roll into the material can cause the roll to bounce and/or deform the material.  
      What is needed in the art is a conveyor system employing a feed roll and a pinch roll that will promote accurate and timely lifting of the feed roll, as well as the controlled return of the pinch roll into its clamping position.  
     SUMMARY OF THE INVENTION  
      The present invention relates to a press feed conveyor mechanism used to feed stock material into a press, the conveyor mechanism incorporating an electro-pneumatic means of performing roll lift. The electro-pneumatic roll lift mechanism includes a pneumatic piston/cylinder arrangement with an integrated solenoid valve and is operatively linked to a pinch roll of the conveyor mechanism. The pressure to the piston/cylinder arrangement is controlled by a proportional air pressure controller, which receives feedback from a linear encoder through a programmable logic controller. The linear encoder monitors the position of the pinch roll, and the pressure to the piston/cylinder mechanism is accordingly adjusted based upon the actual position desired.  
      The present invention, in one form thereof, is a conveyor mechanism for feeding stock material into a material working station. The conveyor mechanism includes a frame, a feed roll, a pinch roll, a pinch roll lift mechanism, and a height monitoring device. The feed roll has a feed roll axis, the feed roll axis being rotatably fixed relative to the frame. The pinch roll opposes the feed roll and is selectively moveable relative thereto. The pinch roll has a roll lift position relative to the feed roll. The pinch roll lift mechanism is configured for selectively controlling the roll lift position of the pinch roll. The height monitoring device is configured for monitoring and measuring an actual roll lift height of the pinch roll. The height monitoring device is operatively coupled with the pinch roll lift mechanism in order to permit the actual roll lift height to be used by the pinch roll lift mechanism in selectively controlling the roll lift position.  
      An advantage of the present invention is that the roll lift mechanism permits continuous monitoring and adjusting of the roll lift position and/or height, thereby allowing for optimal roll lift performance.  
      Another advantage of the present invention is that the roll lift mechanism allows for higher cycle rates by facilitating the minimization of unnecessary roll lift height.  
      Yet another advantage resulting from the minimization of the needed roll lift height is a reduction of slamming of the roll and/or roll bounce.  
      A further advantage of the present invention is that the system may be operated in an automated manner upon entry of the desired clamp force and roll lift height. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
       FIG. 1  is a perspective, partial schematic view of the conveyor system of the present invention, employing an electro-pneumatic roll lift mechanism;  
       FIG. 2  is a schematic view of a sheet material processing system incorporating the conveyor system of  FIG. 1 ; and  
       FIG. 3  is a side, schematic view of the feed and pinch rolls and the interposed sheet material of  FIG. 1 , with the pinch roll shown in a open or raised position. 
    
    
      Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.  
     DETAILED DESCRIPTION OF THE INVENTION  
      The conveyor mechanism  10  of the present invention, as shown in  FIG. 1 , is configured for conveying a sheet material  12  in a feed direction F toward a workstation  14  (shown in block format in  FIG. 2 ). Workstation  14 , in a preferred embodiment of the present invention, is a machine press, but may, for example, be any station at which the sheet material  12  is one of mechanically worked; thermally treated; chemically cleaned, treated, or etched; and/or otherwise processed. Returning to  FIG. 1 , conveyor system  10  generally includes a conveyor frame  16 , a feed roll  18 , a pinch roll  20 , and an electro-pneumatic roll lift mechanism  21 . Roll lift mechanism  21  further includes a pivotable pinch roll mount system  22 , pneumatic piston/cylinder system  24 , solenoid valve  42 , a first proportional pressure controller (PPC)  26 , a second PPC  28 , and a controller, such as programmable logic controller (PLC)  30 . Conveyor system  10  further includes a roll lift position monitor  32 .  
      The rotation of feed roll  18  in rotational direction R F  and the simultaneous rotation of pinch roll  20  in direction R P  together causes sheet material  12  to move in feed direction F. Feed roll  18  is pivotably fixed in machine frame  16  (the frame  16  being shown in phantom, proximate feed roll  18 ). Meanwhile, pinch roll  20  is controllably movable up and down via electro-pneumatic roll lift mechanism  21  and, specifically, by pivotable pinch roll mount system  22 .  
      Pinch roll mount system  22  includes a roll mount linkage  34  and a linkage pivot shaft  36 . Pinch roll  20  is pivotably mounted within one end of roll mount linkage  34 , while pneumatic piston/cylinder system  24  is operatively coupled to the other end of such linkage  34 . Roll mount linkage  34 , in turn, is mounted about linkage pivot shaft  36 . Linkage pivot shaft  36  is fixably rotatable within frame  16  (shown in phantom adjacent to shaft  36 ). Due to the combined operations of roll lift mechanism  21  and linkage pivot shaft  36 , roll mount linkage  34  is able to selectively raise and lower pinch roll  20  about pivot shaft  36  in a pivotal direction P.  
      Piston/cylinder system  24  is able to create linear movement along cylinder direction C. An extension of piston/cylinder system  24  (specifically an extension of a cylinder rod (not illustrated) of system  24 ) along direction C causes linkage  34  to pivot in a manner so as to move pinch roll  20  away from feed roll  18  into an open position. Retraction of piston/cylinder system  24  results in the pinch roll  20  being pivoted or closed toward feed roll  18  via movement of linkage  34 . If pivoted close enough together, such action will clamp sheet material  12  between the two rolls  18 ,  20  for controlled movement based on the controlled rotation of rolls  18 ,  20  (i.e., stopped or rotating to produce a desired feed speed). As such, piston/cylinder system  24  can be used to accommodate various thicknesses of sheet material  12  between rolls  18 ,  20  and, more generally can be used to control whether or not pinch roll  20  engages sheet material  12 . Additionally, the amount of force applied on sheet material  12  by pinch roll  20  can selectively be adjusted to promote stoppage of material  12  or to optimize roll grip (minimized slip) and feed efficiency combinations.  
      Piston/cylinder system  24  includes a front (rod) side  38  directed toward roll mount linkage  34  and further includes a rear side  40 . Mounted on rear side  40  of piston/cylinder system  24  is a solenoid valve  42 . Fluid pressure such as pressurized air is provided to front side  38  of piston/cylinder system  24  which biases the piston/cylinder system to retract and apply a clamp force between rolls  18  and  20 . This pressure, as per the present embodiment, is always constant and is controlled by first proportional pressure controller (PPC)  26 . The necessary clamping force (the force needed to stop or controllably move sheet  12  using rolls  18 ,  20 ) can be set at the control panel (not shown) for conveyor mechanism  10 . This inputted clamping force is received by programable logic controller (PLC)  30 , which then interprets and sends the appropriate signals to PPC  26 . PPC  26  changes the pressure based on the electrical signal it receives. It is to be understood that the function of PLC  30  can be fulfilled by a personal computer (PC) or by another type of machine controller. Such alternatives for PLC  30  are considered to be within the scope of the present invention.  
      When it is time to open roll  20  away from roll  18 , solenoid valve  42  allows air to flow into the rear of piston/cylinder system  24  to cause extension of piston/cylinder system  24  (in particular the cylinder thereof (not shown)) toward roll mount linkage  34  and thereby open rolls  18 ,  20 . The air (or other fluid) pressure provided to rear side  40  of piston/cylinder system  24  must be sufficient enough to overcome the pressure in the front side  38  in order for the cylinder rod of piston/cylinder system  24  to be able to extend. The air pressure to solenoid valve  42  is controlled by second PPC  28 . During the roll lift operation described, the operating voltage of the solenoid valve  42  is momentarily increased above its normal operating specification (i.e., a rating of 24 volts). This temporary increase in operating voltage enhances the valve responsiveness and thereby increases the achievable roll lift rates. As a result, the press feed can achieve higher cycle rates and be able to match press speeds.  
      In an alternative embodiment (not shown), front side  38  of piston/cylinder system  24  could also be provided with a solenoid valve; this provision would permit a variably controlled degree of air pressure to be introduced into the front side of piston/cylinder system  24 . Variable control of the pressure would be available at both the front and back side  38 ,  40  of piston/cylinder system  24 , thereby increasing the flexibility for controlling system  24 .  
      Roll lift position monitor  32  is in the form of a linear encoder in the present embodiment, yet it is to be understood that other position monitoring means could instead be employed within the scope of the present invention. Height position monitor/linear encoder  32  detects and measures roll lift height H ( FIG. 3 ), which is measure relative to surfaces positions S of material  12 . During each press forming cycle, the set or zero position of pinch roll  20 , when the roll is closed and clamping material  12 , is equal to surface position S and is encoded by linear encoder  32 . Linear encoder  32  relays this set position value to PLC  30 .  
      Pinch roll  20  is then moved so as to be a distance roll lift height H above surface position S. Linear encoder  32  then registers the position which corresponds to that roll lift position (i.e., H+S) and provides the appropriate position signal to PLC  30 . (Note that H+S actually also equals the separation distance between roll  18 ,  20  in the roll lift positions.) PLC  30  interpolates the signal (H ACTUAL =(H+S)−S), compares it to a set roll lifts height value H entered at the control panel of the machine or other data entry means, and sends the appropriate logic control signal to PPC  28 . The signal will indicate the degree of adjustment in pressure to be made in PPC  28  to achieve the desired roll lift height H and thereby control the amount of opening between rolls  18 ,  20 , as needed. If an adjustment is needed, PPC  28  will then produce or control a new pressure output based on this signal. This adjustment procedure assures the same amount of roll lift height H each time, regardless of any variances in material thickness. That is, by knowing the linear position at which pinch roll  20  is in contact with material  12 , pinch roll  20  need only be moved further upwards by a distance of the desired roll lift height H to be at its desired lift position, no matter the potentially changing thickness of material  12 .  
      PLC  30  and linear encoder  32  form a feedback control system allowing roll lift mechanism  21  to operate as a closed-loop servo feedback configuration. This closed-loop servo feedback configuration permits continuous monitoring and adjusting of the desired roll lift position, either for the clamped or open (roll lift height H) position. Such continuity promotes optimal roll lift performance. By optimizing roll lift performance, various shortcomings can be avoided. Excessive roll lift height (H) increases the amount of time to open or close roll  20  relative to roll  18 , resulting in lower cycle rates. Thus, by minimizing unnecessary roll lift heights, higher cycle rates can be obtained. Yet further, minimizing of roll lift height H (to provide the minimum clearance needed for realignment of material  12 ) also reduces slamming of rolls  18 ,  20  and/or roll bounce therebetween.  
      The closed-loop servo feedback configuration of the present invention allows the system to operate in a fully automated manner. Both the clamp force and roll lift height H can be entered at the control panel of the machine. From there, PLC  30  is able to automatically control the operation of conveyor mechanism  10 .  
      While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.