Abstract:
A cylindrical drum is driven for rotation about its axis by a drive mechanism. A braking mechanism selectively applies braking forces to the drum to impede or brake its rotational movement. A first movement sensor senses movement of the drive mechanism while a second movement sensor senses movement of the drum. An electronic comparator circuit compares these sensed movements and generates a control signal when the drive mechanism movement and drum movement are not in synchronism. In response to such loss of synchronism, a control mechanism causes the braking mechanism to apply braking forces.

Description:
FIELD 
       [0001]    The present disclosure relates generally to sand molding equipment used in the foundry industry. More particularly, the disclosure relates to improvements in a rollover machine used to invert a sand mold pattern box. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Rollover machines are used in the foundry industry to invert heavy sand mold pattern boxes containing sand that defines a mold. Once inverted, the mold is filled with molten metal to form the casting. Rollover machines are typically used in applications where the pattern box and sand are too heavy to be lifted by hand. Rollover machines are thus typically designed to carry very heavy loads and are thus themselves quite massive. For example, a typical rollover machine may weigh 25,000 pounds or more. Machines this massive generate an enormous amount of momentum when moving to invert the pattern box containing sand. 
       SUMMARY 
       [0004]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0005]    In accordance with one aspect, the disclosed rollover machine employs a generally cylindrical drum driven for rotation about its axis by a drive mechanism. A braking mechanism selectively applies braking forces to the drum to thereby impede rotational movement of the drum. A first movement sensor senses movement of the drive mechanism and produces a first output indicative of drive mechanism movement. A second movement sensor senses movement of the drum and produces a second output indicative of drum movement. 
         [0006]    An electronic comparator circuit compares the first and second outputs and generates a control signal when the drive mechanism movement and drum movement are not in synchronism. A control mechanism coupled to the comparator circuit and interfaced with the braking mechanism causes the braking mechanism to apply braking forces to the drum when the control signal indicates the drive mechanism movement and drum movement are not in synchronism. 
         [0007]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0008]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0009]      FIGS. 1A-1G  comprise a sequence of side view diagrams showing the basic operation of a rollover machine; 
           [0010]      FIG. 2  is a perspective view of the rollover machine; 
           [0011]      FIG. 3  is a top view of the rollover machine; 
           [0012]      FIG. 4  is an end view of the rollover machine illustrating how the drum is supported on rollers and showing the general position of the chain; 
           [0013]      FIG. 5  is a side view of the rollover machine, illustrating how control signals are coupled between the control panel and the machine; 
           [0014]      FIG. 6  is a cross-sectional view taken substantially along the line  6 - 6  in  FIG. 5  and showing the spring mechanism and hydraulic release used to actuate the braking system; 
           [0015]      FIG. 7  is an opposite end view of the rollover machine, showing the pattern box in cross-section; 
           [0016]      FIG. 8  is a detailed partial view of the base of the rollover machine, showing how the chain drive mechanism is configured; 
           [0017]      FIG. 9  is a partial view of the rollover machine, showing how the drum is disposed relative to the rollers and mounting frame; 
           [0018]      FIG. 10  is a detailed view showing the shaft of the drive mechanism; 
           [0019]      FIG. 11  is an enlarged perspective view of the chain and sprocket drive mechanism; 
           [0020]      FIG. 12  is another enlarged perspective view of the chain and sprocket drive mechanism; 
           [0021]      FIG. 13  is a cross-sectional view taken substantially along the line  13 - 13  of  FIG. 6 , showing the braking band and lining in greater detail; 
           [0022]      FIG. 14  is an electronic circuit diagram illustrating how freewheeling detection may be accomplished; 
           [0023]      FIG. 15  is a perspective view of another embodiment of the rollover machine; 
           [0024]      FIG. 16  is a perspective view showing the brake band assembly in greater detail; 
           [0025]      FIG. 17  is a perspective view showing the brake band in greater detail; 
           [0026]      FIG. 18  is a side view of the brake band of  FIG. 17 ; 
           [0027]      FIG. 19  is a perspective view of the brake actuator; 
           [0028]      FIG. 20  is a detailed view of the brake actuator; 
           [0029]      FIG. 21  is a cross-sectional view of the brake actuator sub assembly; 
           [0030]      FIG. 22  is a side view of the encoder wheel sub assembly; and 
           [0031]      FIG. 23  is a cross-sectional view of the encoder wheel sub assembly taken along the line  23 - 23  in  FIG. 22 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0033]    The automatic braking technology disclosed herein represents an important improvement over conventional rollup machinery used in the foundry industry. In order to understand the invention, a basic understanding of the rollover machine operation will be presented. 
         [0034]    Referring to  FIG. 1A , the pattern box  10  filled with no-bake sand  12  is laterally conveyed onto the lower conveyer assembly  14  located within the interior of the rollover draw machine drum  16 . In this orientation, the upper conveyor assembly  18  is positioned well above the pattern box  10 . 
         [0035]    Next, as seen in  FIG. 1B , the upper conveyor assembly  18  is lowered into contact with the open end of the pattern box, as illustrated. Next, as shown in  FIG. 1C , the drum  16  is rotated 180° about its central axis  20 , resulting in the pattern box and sand being inverted, as shown. Then, as shown in  FIG. 1D , the upper conveyor assembly  18  (now supporting the sand  12 ) is lowered while the pattern box  10  remains held by a clamping mechanism associated with the lower conveyor assembly  14 . Because the inner surfaces of the sidewalls of the pattern box are slightly tapered, the sand  12  slides easily apart from the pattern box. Note the sand has a slightly tapered shape or frustum shape that mirrors the tapered inner walls of the pattern box. 
         [0036]    With the sand  12  now resting on the upper conveyor  18 , it can be removed from the drum as shown in  FIG. 1E . Thus, the sand is conveyed laterally onto an adjacent conveyor which conveys the sand downstream to the next processing station (not shown). In order to eject the pattern box from the drum, the drum is again rotated 180° about its access  20 , as shown in  FIG. 1F . In this orientation, the lower conveyor assembly  14  is once again disposed in its original starting position, as shown in  FIG. 1A . The pattern box  10  may then be removed, as shown in  FIG. 1G , by conveying it on the same conveyor that took the sand mold downstream. Thus, it will be seen that the rollover draw machine essentially draws the sand from its associated pattern box and then places the inverted sand mold and pattern box sequentially onto a conveyor that transports both to a downstream foundry process. 
         [0037]    In a typical application, these rollover draw machines are made in sizes as high as 25,000 pounds and potentially much higher. The operating sequence illustrated in  FIGS. 1A-1G  is such that when rolling over, the pattern box and sand can potentially be quite a bit off-center. In other words, the rollover draw machine must be of substantial size and strength to accommodate off-center forces as the drum is rotated about its central axis. As will be seen and described in subsequent figures, the typical rollover draw machine is driven by a jackshaft-type drive mechanism that has a pair of chains that are attached to both sides of the drum. In the alternative, cables or gears can be used in place of the chains, to produce axial rotation of the drum about at least a 180-degree range of rotation. When the shaft is driven, the drum rotates in its base frame. Normally, the drive is hydraulic but there are cases where electric drives may be used. 
         [0038]    During normal operation, the jackshaft drive system and associated chains are engineered to withstand the substantial forces that exist during operation. With that said, the drum does not rotate at steady state when in use, but rather the drum must rotate 180°—then stop—then rotate 180° again. Thus, angular accelerations are applied to the drive mechanism and chains each time the drum starts and stops rotating. Thus, it has been conventional practice to greatly “over engineer” the loading capacities of the drive mechanism and chain to ensure that the rollover drum cannot jump out of its frame or “freewheel” from the desired loading-unloading position to a point of balance. 
         [0039]    The presently disclosed improvement provides further assurance that the drum will not jump out of its frame or freewheel to an undesired position. The solution employs a set of externally-compressing band brakes that compress on the outer diameter of the drum in two instances: (1) any time the system control calls for a stop, and (2) in the event a freewheel condition occurs. To detect the freewheel condition, a presently preferred embodiment uses a pair of rotary encoders, one placed on the drive mechanism and the other placed on the drum (or on a rotating member attached to or communicating with the drum). The control system constantly monitors these encoder outputs and if they do not match exactly, the system causes the compressing band to clamp tightly around the drum, locking it into place. Although different control mechanisms are possible, one embodiment measures the respective rotating speeds of the drive and drum and causes the brakes to be applied when the speeds do not match within predefined tolerances. In addition, the system can send an alarm, allowing a technician to inspect the system prior to starting the cycle again. The encoders may be physically attached, as by clamping to a shaft associated with the drive mechanism (to sense the drive mechanism rotation), and attached to a shaft or roller that moves with the drum (to sense the drum rotation). An encoder that monitors the linear movement of the chain is also possible. 
         [0040]    While a pair of encoders has been illustrated here, other sensing techniques and mechanisms can be used instead. Essentially, the braking system uses a control system that has a first sensing point coupled to sense movement of the drum and a second sensing point coupled to sense movement of the drive mechanism, or its associated linkage. The mechanisms used as these two sensing points can be of the same character (e.g., two optical encoders) or they can be of a different character (e.g., an RPM sensor or speed sensor on the drive mechanism and an optical encoder or other type of movement encoder on the drum. The control system works by detecting when detected movement of the drum is not in synchronism with the drive mechanism, such as would happen were the drive chains to break. 
         [0041]    Referring now to  FIG. 2 , the rollover machine is seen in perspective, showing the pattern box  10  resting on the lower conveyor assembly  14 , and with upper conveyor assembly  18  disposed in its uppermost position of rest. The control panel  24  is conveniently disposed on a mounting rack  26 . Control leads (not shown) connect the control panel  24  to the drive mechanism, actuators and sensors disposed on the rollover machine. The drum  16  is supported on four rollers  28  and rotated about its central axis by a drive motor  30  that couples to lengths of chain  32  disposed about part of the circumference of the drum. Note, the chains  32  require sufficient length to permit the drum to be rotated 180 degrees and then back. Details of the drive motor  30  and associated chain driving mechanism is seen more clearly in  FIG. 8 . 
         [0042]    As illustrated in  FIG. 8 , the drive motor turns a shaft having a pair of sprockets  36  adjacent the rollers  28 . These sprockets engage the chain  32 . The chain is attached to the outer rim of the hub, as seen in  FIG. 2 , and the sprockets thus impart pushing and pulling movements to the chain, causing the drum to rotate in the desired clockwise or counterclockwise direction. 
         [0043]    The braking mechanism is shown in  FIG. 6 . A steel band  40  lined with brake pad material  41  spans slightly more than 180 degrees of the outer periphery of the drum. Details of the brake pad lining and steel band are also seen in  FIG. 13 . 
         [0044]    The band is held in tension by a hydraulically controlled spring mechanism  42 . The spring mechanism is controlled by the hydraulic cylinder release mechanism  44  which, when energized, pushes the spring mechanism  42  into compression, loosening the pulling tension on the band, allowing the drum to rotate about its axis. When the hydraulic cylinder is de-energized, the compressed spring returns to its relaxed state, thereby pulling the steel band  40  in tension, so that the brake pad lining makes friction contact with the drum. In so doing, the braking bands cause the drum to stop rotation. The continued braking force of the bands against the drum hold the drum in a stationary position, resisting against any freewheeling forces that may exist due to loading and weight distribution of the rollover machine components and the pattern box and sand. 
         [0045]    The hydraulic cylinder release mechanism  44  is electronically controlled. In an exemplary embodiment shown in  FIG. 14 , a pair of shaft encoders  50 , such as optical encoders as illustrated, are attached to the rollover machine in suitable locations where they can rotate with rotation of the drum  16  (e.g., as with rollers  28 ) and drive mechanism (e.g., as with shaft  34 ). Preferably, these shaft encoders are configured or calibrated so that each produces a pulse train and such that the respective pulse trains are in synchronism during normal (non-freewheeling) operation. For example, the shaft encoders can be appropriately geared so that they turn at the same rate; or the encoders can be provided with electronic frequency dividing/multiplying electronics (e.g., using Flip-Flops or microprocessor circuitry, for example) so that they produce pulse trains in synchronism during normal operation. 
         [0046]    Two possible embodiments for decoding the shaft encoders are illustrated in  FIG. 14 . At  60  a pair of counters  62  and  64  count pulses from the respective shaft encoders A and B. A comparator  66  periodically samples the counter outputs (and then resets the counts). If the counts match, then normal conditions are signaled. If the counts do not match, then a freewheeling condition or error condition is signaled. 
         [0047]    In the second embodiment, shown at  68 , a collection of logic gates: NOR gate  70 , AND gate  72 , and OR gate  74  produce a truth table that decodes when the pulses do not occur in synchronism. When a lack of synchronism is detected, the freewheeling or error condition is signaled. 
         [0048]    Of course, the described decoding functions can also be performed using a suitably programmed microprocessor or microcontroller. 
         [0049]    Referring to  FIG. 15 , another embodiment of the rollover machine is illustrated. As with the first embodiment, the rollover machine receives the pattern box  10  into drum  16  via the lower conveyor  14 . The upper conveyor  18  is shown above the pattern box  10 . As with the first embodiment, the drum is rotated by the drive motor  30 . The electronic control panel  24  may be mounted on a suitable rack  26 , as illustrated. An operator control console  27  is also included. Interconnecting cables between the control panel  24 , control console  27  and the rollover machine have not been illustrated in  FIG. 15 . 
         [0050]    In  FIG. 15 , two brake band assemblies  80  can be seen encircling the drum at the outer peripheries, as illustrated. The brake band actuator assemblies  82  are preferably supported at ground level and operate to apply braking pressure to the drum when signaled to do so by the control system based on signals received from the encoders, or actuation of an emergency stop button, as will be more fully explained. 
         [0051]    Referring to  FIGS. 16, 17 and 18 , the brake band assemblies are shown in greater detail. Preferably, each band is welded together as a one-piece construction for equal load distribution. Each brake band is outfitted with a set of five band catches  84 , also seen in  FIG. 15 , that restrain the brake band in place around the drum even in the unlikely event of a band breakage. Attached to each brake band are a series of brake pads  86  composed of brake material selected with a high coefficient of friction to increase stopping power. The pads are deployed as a series of sections for serviceability. The brake pads are preferably outfitted with a pair of deep slots (e.g., 0.12 inches wide by 0.25 inches deep) to catch brake pad wear debris. The brake material is selected to conform easily to the band radius. Preferably, the brake pads  86  may be bolted to the brake band to allow the pads to be replaced when worn. Welded to the ends of each band, a knuckle  88 , comprising hardened steel bushings, is designed to mate with hardened steel pins for long wear life. 
         [0052]    As shown in  FIG. 18 , each band assembly is outfitted with five follower cam side roller guides  90  to ensure that the band tracks correctly on the drum wheel. 
         [0053]    Shown in greater detail in  FIGS. 19, 20 and 21 , the brake actuator assemblies  82  each feature an actuator clevis  92  that is supported on a threaded rod  94  (see  FIG. 21 ) to easily adjust the clevis to the pin connecting point on the band knuckle  88  ( FIG. 17 ). As best seen in  FIG. 21 , spring adjusters  96  are used to pre-load die springs  98  to achieve the desired actuator brake load. The actuator shaft  100  is mounted in bronze bushings  102  for long life and bind-free movement. An internal hard stop  104  allows the brakes to be released consistently every time cycled. The actuator shaft uses a seal to keep foreign objects out of the shaft bearing. A sand guard  106  helps keep sand away from the shaft seal. 
         [0054]    The actuator  82  uses die springs  98  to mechanically apply the brakes upon a system failure. A single acting hydraulic cylinder  108  ( FIG. 20 ) applies a force in opposition to the die springs to release the brakes during normal rotation of the drum. Specifically, the hydraulic cylinder extends a deactivator pusher  109  that contacts the actuator shaft  100 . Preferably, the hydraulic cylinder  108  is designed with dual ports on the cap end for high-speed free flow of oil when the brakes are mechanically applied. Proximity switches  110  shown in  FIG. 20  detect when the brake pads are worn beyond a predetermined limit, indicating that the pads need to be replaced. The proximity switches also detect when an actuator adjustment is needed. 
         [0055]    Shown in  FIGS. 22 and 23 , rotational motion of the drum is monitored by the drum encoder  112 , which employs an external rotary encoder  114  driven by a wheel  116  that rides directly on the drum. The drum encoder automatically adjusts for wheel wear by being spring-loaded against the drum. This is accomplished, as perhaps best seen in  FIG. 23 , by a mounting plate  118  that is pivotally mounted at  120  and biased by extension spring  122 . 
         [0056]    The control system monitors the drive motor speed (measured by an encoder mounted on the drive motor) and compares it with the drum speed (measured by the external drum-mounted encoder). For a “freewheeling” condition, set points are established, and then set up and stored in the control system operating program. The brake will automatically apply if the speed increases or decreases outside these set points. 
         [0057]    The band brake is monitored by the control system to ensure it releases correctly before the system will be allowed to rotate. The system is monitored for when the brake band is out of adjustment or brake pads are worn and this establishes a fault condition causing the brakes to be immediately applied. If a stop or decal switch fails during the roll cycle of the machine, a signal is immediately sent to apply the brakes. 
         [0058]    Preferably, the control system is a programmed processor, programmed to cause the brakes to be automatically applied for the following conditions: 
         [0059]    1. An emergency stop button is pressed; 
         [0060]    2. Electric power is lost; 
         [0061]    3. Hydraulic power unit fails; 
         [0062]    4. Hydraulic hose failure on a brake release cylinder; 
         [0063]    5. Main drive motor failure; 
         [0064]    6. Main drive brake failure; 
         [0065]    7. Breakage of both drum chains; 
         [0066]    8. Stop or deceleration switch failure; and 
         [0067]    9. System fault. 
         [0068]    Note that the system has built-in redundancy, which allows for one-half the braking power should one of the two braking systems fail. Thus even if one of the two braking systems fails, the other braking system has sufficient stopping power to bring the rotating drum to a halt. 
         [0069]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.