Abstract:
Apparatus and method for monitoring chain pull of a conveyor drive that includes a conveyor drive having a fixed frame, a moveable frame, a spring assembly and a sensor assembly. The moveable frame supports a motor and is biased against the fixed frame by the spring assembly to oppose a force generated by the conveyor drive chain pull. The sensor assembly can be installed or removed without disassembly of the spring assembly and preferably without substantial interruption to the operation of the conveyor drive.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to apparatus and method for monitoring chain pull. In particular, the present invention is related to apparatus and method for monitoring chain pull, which do not required the disassembly of the conveyor drive.  
         BACKGROUND ART  
         [0002]    Many conveyor systems use chains as the driving mechanism and use conveyor drives to give the chains motion and control the speed of the conveyor chains. One example of this type of conveyor systems is a power and free conveyor system. A power and free conveyor system is generally made up of a power track, a free track, and trolleys capable of travelling along the free track. Generally, two trolleys, a leading trolley and a trailing trolley, support a carrier, which then supports a load or article being conveyed. Each leading trolley includes a driving dog which extends towards the power track and which is engageable with a pusher dog carried by a moving conveyor chain on the power track. When the pusher dog and the driving dog are engaged, the leading trolley (and the carrier) is pushed along the free track by the moving chain. When the driving dog is retracted, or otherwise disengaged from the pusher dog, the trolley stops moving, thus halting the carrier.  
           [0003]    To move the chain, one or more conveyor drives are utilized. A commonly used conveyor drive uses a caterpillar chain to transmit its driving force to the conveyor chain. The caterpillar chain is made of precision steel rollers with driving dogs that mesh with a portion of the conveyor chain.  
           [0004]    A conveyor drive may be either a fixed drive or a moveable drive. A moveable drive can be either a linear type or a rotary type. The linear type is generally built with a moveable frame that is guided and supported by ball bearing wheels attached to an outer fixed frame. In contrast, a rotary drive is mounted on a moveable frame that pivots relative to the fixed frame. One or more coil springs, placed between the fixed and moveable frames, may be used to counterbalance the chain pull and to control the movement of the moveable frame.  
           [0005]    A prior art conveyor drive may include a fixed frame and a moveable frame pivotable relative to the fixed frame. A spring is disposed between the fixed frame and the moveable frame. The force of the spring biases the movable frame against the fixed frame and opposes the force caused by chain pull.  
           [0006]    The moveable frame supports a speed reducer that has an input shaft and an output shaft. The input shaft is connected to a motor via a pulley, and the output shaft is connected to a drive sprocket.  
           [0007]    The caterpillar chain exerts a chain pull force on the sprocket (and thus the moveable frame). This force is balanced by the spring and can be monitored by a strain gauge sensor which is used to measure the chain pull force. The strain gauge sensor is installed on a rod. One end of the rod is attached to the fixed frame, and the other end of the rod is secured to the spring. As installed in the conveyor drive, the strain gauge sensor directly measures the spring force. However, because the spring force is related to the chain pull force, the strain gauge sensor can indirectly measure the chain pull force.  
           [0008]    One of the disadvantages of the prior art conveyor drive is that the strain gauge sensor is expensive and time-consuming to install or remove. It is especially so when a strain gauge sensor is only used periodically to monitor chain pull, thus requiring frequent installations and removals of the strain gauge sensor, resulting in substantial downtime for the conveyor system. For each installation or removal of the strain gauge sensor, the conveyor drive must be stopped and the spring assembly must be disassembled and reassembled. Alternatively, a permanent strain gauge sensor may be installed in each conveyor drive, thus eliminating the need for frequent installations and removals. However, this approach is costly because it requires that each conveyor drive be provided with a strain gauge sensor and data acquisition equipment.  
           [0009]    Consequently, a need has developed to provide cost-effective, less interruptive, and less time-consuming methods and apparatus for monitoring the chain pull in conveyor systems.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention meets this need by providing a simple but effective sensor assembly which can be installed or removed without the need to disassemble the spring assembly and preferably without substantial interruption to the operation of the conveyor system. The invention also provides a method to install or remove a sensor assembly with the same advantages.  
           [0011]    In accordance with one aspect of the invention, a conveyor drive includes a fixed frame, a moveable frame operatively associated with the fixed frame, a spring assembly connectable to both frames, and a sensor assembly. The moveable frame supports a motor. The spring assembly biases the moveable frame against the fixed frame and opposes a force generated by chain pull. The sensor assembly is connectable between one of the frames, and one of the spring assembly and the other frame. When the sensor assembly is connected between one of the frames and one of the spring assembly and the other frame, the force is transmitted substantially through the sensor assembly and is not transmitted substantially through the spring assembly.  
           [0012]    In accordance with another aspect of the invention, a conveyor drive includes a fixed frame, a moveable frame operatively associated with the fixed frame, a spring assembly connectable to both frames, and a sensor assembly. The moveable frame supports a motor. The spring assembly biases the moveable frame against the fixed frame and opposes a force generated by chain pull. The spring assembly is connectable between one of the frames, and one of the spring assembly and the other frame. The sensor assembly includes an adjusting mechanism, which allows the force to be transmitted substantially through the sensor assembly and not to be transmitted substantially through the spring assembly.  
           [0013]    In accordance with yet another aspect of the invention, a conveyor drive includes a fixed frame, a moveable frame operatively associated with the fixed frame, a spring assembly connectable to both frames, and a sensor assembly. The moveable frame supports a motor. The spring assembly biases the moveable frame against the fixed frame and opposes a force generated by chain pull. The spring assembly includes a cylindrical housing connected to one of the frames, and a spring. The spring is disposed in the cylindrical housing and connected to the cylindrical housing, and is connectable to the other frame. The sensor assembly includes a first member connectable to the spring assembly, a second member connectable to the other frame, a sensor connectable to the first and second members, and an adjusting mechanism connectable to the first and second members. The adjusting mechanism is capable of adjusting the relative position of the first and second members so that the force is transmitted substantially through the sensor.  
           [0014]    In accordance with a further aspect of the invention, a sensor assembly for monitoring chain pull of a conveyor drive includes first and second members, a sensor and an adjusting mechanism. The conveyor drive having a fixed frame, a moveable frame operatively associated with the fixed frame, and a spring assembly connectable to both frames and opposing a force generated by chain pull. The spring assembly includes a cylindrical housing connected to one of the frames, and a spring that is disposed in the cylindrical housing, connected to the cylindrical housing and connectable to the other frame. The first member is connectable to one of the cylindrical housing and the spring, and the second member is connectable to the other frame. The sensor is connectable to the first and second members, and the adjusting mechanism is connectable to the first and second members. The adjusting mechanism is capable of adjusting the relative position of the first and second members so that the force is transmitted substantially through the sensor.  
           [0015]    A yet further aspect of the invention is directed to a method for installing a sensor assembly for monitoring chain pull of a conveyor drive that has a fixed frame, a moveable frame operatively associated with the fixed frame, and a spring assembly that is connectable to both frames and opposes a force generated by chain pull. The spring assembly includes a cylindrical housing connected to one of the frames, and a spring that is disposed in the cylindrical housing, connected to the cylindrical housing, and connectable to the other frame. The method includes the steps of connecting a first member of the sensor assembly to one of the cylindrical housing and the spring, connecting a second member to the other frame, connecting a sensor to the first and second members, and adjusting the relative position between the first and second members so that the force is transmitted substantially through the sensor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Reference is now made to the drawings of the invention wherein:  
         [0017]    [0017]FIG. 1 shows a conveyor drive.  
         [0018]    [0018]FIG. 2 shows a sensor assembly of the present invention that is installed in a conveyor drive for monitoring chain pull. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The following description of the presently preferred embodiments of the invention refers to the accompanying drawings. The description is directed to and the drawings show exemplary embodiments of the invention, other embodiments are possible, and changes may be made to the embodiments described below without departing from the spirit and scope of the invention. The scope of the invention is defined by the appended claims. The description and drawings are merely illustrative, not limiting.  
         [0020]    [0020]FIGS. 1 and 2 show a conveyor drive  10  embodying one aspect of the invention. The conveyor drive  10  includes a fixed frame  20 , a moveable frame  30  pivotable about the fixed frame  20 , a spring assembly  50  disposed between the fixed frame  20  and the moveable frame  30 , and a sensor assembly  70  (only shown in FIG. 2). One of the differences between this conveyor drive  10  and a prior art conveyor drive is that the sensor assembly  70  of the conveyor drive  10  can be installed or removed without the need to disassemble the spring assembly  50  and preferably without substantial interruption to the operation of the conveyor system.  
         [0021]    In the illustrated embodiment, the moveable frame  30  is pivotably connected to the fixed frame  20 . The moveable frame  30  may support a speed reducer  32  that has an input shaft  34  and an output shaft  36 . The input shaft  34  is connected to a motor  38  via a pulley  40 , and the output shaft  36  is connected to a drive sprocket  42  that drives the caterpillar chain  44  of the conveyor drive  10 . The speed reducer  32  allows the drive sprocket  42  to rotate at a slower speed than the motor  38  does. The speed reducer may employ any suitable mechanism to reduce the speed. For example, the speed reducer  32  may employ a gear arrangement. Alternatively, the speed reducer  32  may employ a pulley/belt arrangement. If it is desired to have the drive sprocket  42  rotate at a higher speed than the motor  38  does, the speed reducer  32  may be replaced with a device that increases the speed. Further, if the drive sprocket  42  can operate at the same speed as the motor  38 , then a speed reducer may not be needed. Although the conveyor drive  10  shown in FIGS. 1 and 2 is of the rotary type, i.e., the moveable frame  30  can pivot relative to the fixed frame  20 , it can also be of the linear type, i.e., the moveable frame can move linearly relative to the fixed frame.  
         [0022]    In operation, the caterpillar chain  44  is under certain tension, which applies a chain pull force on the drive sprocket  42  (and the moveable frame  20 ). This chain pull force tends to cause the moveable frame  20  to pivot in one direction. The spring assembly may be any suitable device which can be used to balance the force exerted on the moveable frame  30  by the chain pull. The spring assembly  50  shown in FIGS. 1 and 2 may use any suitable type of spring. In the illustrated conveyor drive  10 , for example, the spring assembly  50  uses a coil spring  52  (see FIG. 2). Alternatively, the spring assembly  50  may use any other type of spring, such as a leaf spring. In addition to the spring  52 , the spring assembly  50  may also include a cylindrical housing  54  connected to the fixed frame  20  and a rod  56  connected to the moveable frame  30 . Preferably, the coil spring  52  is disposed in the housing  54 , and it is placed between a stop  58  fixed to the inner surface of the cylindrical housing  54  and a plate  60  connected to the rod  56 . The rod  56  extends through an orifice on the plate  60 , and two nuts  62  mounted on the rod  56  abut the plate  60 . When a chain pull force is applied to the moveable frame  30 , the moveable frame  30  may compress the coil spring  52  through the rod  56  and the plate  60 , creating a balance force against the chain pull force.  
         [0023]    The spring assembly of the present invention may have a number of alternatives. For example, the cylindrical housing  54  may be connected to the moveable frame  30 , while the rod  56  may be connected to the fixed frame  20 . In addition, the spring  52  may be connected directly to the frames  20 ,  30  without the use of the housing  54  and rod  56 . Further, the spring assembly may be a spring-loaded torque arm assembly, which is a part of the drive overload protection system. In the case of a torque arm assembly, the spring is pre-compressed, and during operation it is not further compressed until the conveyor drive is near its capacity to protect the conveyor drive from overloading. If desired, the spring assembly may also include a damper to provide a certain of damping to the spring assembly.  
         [0024]    In general, the sensor assembly preferably includes a sensor having first and second ends, which may be connected to the frames  20 ,  30  and/or the spring assembly  50  without the need to disassemble the spring assembly  50 . When the sensor is so connected, the force countering the chain pull force preferably is substantially transmitted through the sensor, allowing the sensor to monitor the chain pull force. The sensor assembly may also include an adjusting mechanism, which may be used disengaged the spring assembly so that the force countering the chain pull force preferably is substantially transmitted through the sensor.  
         [0025]    In the illustrated embodiment, the sensor assembly  70  shown in FIG. 2 includes a sensor  72  having an elongated configuration with first and second ends  74 ,  76 , first and second members  78 ,  80 , and an adjusting mechanism  82 . The first member  78  may be a tubular housing having first and second ends  84 ,  86 . The tubular housing  78  includes an inner stop  88  near its first end  84 , and the inner stop  88  abuts an end of the cylindrical housing  54  of the spring assembly  50 . The end of the cylindrical housing  54  preferably extends into the tubular housing  78  to ensure that the cylindrical housing  54  is aligned with the tubular housing  78 .  
         [0026]    The second member  80  shown in FIG. 2 preferably is an attachment in the form of a coupling bracket. The second member  80  may be coupled to a clevis  90  which connects the rod  56  of the spring assembly  50  to the moveable frame  30 . The second member  80  preferably includes hooks  92  that allow the second member  80  to capture the clevis  90 . Alternatively, the second member may include any suitable attachment, such as a clamp or fastener, for attachment to the clevis  90  or the moveable frame  30 . Preferably, the second member  80  is disposed inside the first member  78  and is coaxially arranged with the first member  78 .  
         [0027]    The sensor may be of any suitable type. For example, the sensor may be a strain gauge sensor or a piezoelectric sensor. In the illustrated embodiment, the sensor  72  preferably is connected to the first and second members  78 ,  80 . The first end  74  of the sensor  72  may extend through an opening  94  on the second end  86  of the tubular housing  78  to the outside of the tubular housing  78 , and the second end  76  of the sensor  72  is connected to the second member  80 . Preferably, the sensor  72  is disposed inside the first member  78  and is coaxially arranged with the first and second members  78 ,  80 .  
         [0028]    In the illustrated embodiment, the adjusting mechanism  82  includes threads  94  on the first end  74  of the sensor  72  and a nut  96  mounted on the threaded first end  74  of the sensor  72 . By turning the nut  96 , the relative position between the first and second members  78 ,  80  can be adjusted, pulling the rod  56  away from the spring  52  to disengage the rod  56  from the spring  52 , so that the force is substantially transmitted through the sensor  72 , allowing the sensor  72  to measure the chain pull force. An alternative to the adjusting mechanism shown in FIG. 2 may include the nuts  62  threaded on the rod  56 , and the spring assembly  50  can be disengaged by turning the nuts  62  on the rod  56  until the rod  56  is disengaged from the spring  52 , allowing the force to be transmitted substantially through the sensor  72 . In general, the adjusting mechanism may be any mechanism that can disengage the spring assembly and allows the chain pull force to be transmitted substantially through the sensor assembly  70  and preferably is not transmitted substantially through the spring assembly  50 .  
         [0029]    The invention as claimed herein may have many alternatives to the embodiment described above. For example, while the sensor assembly  70  shown in FIG. 2 is connected to the cylindrical housing  54  of the spring assembly  50 , a sensor assembly may be connected to the spring  52  or the plate  60 . Then an adjusting mechanism may be used to compress the spring  52  or the plate  60  to disengage the spring  52  from the rod  56 , so the chain pull force is transmitted substantially through the sensor assembly  50 . In another embodiment, a sensor assembly may be connected directly to the frames  20 ,  30  or to any components connected to the frames  20 ,  30 . Then the distance between the connecting points may be expanded to disengage the spring assembly  50 .  
         [0030]    The installation or removal of the sensor assembly of the present invention can be performed without the need for disassembly of the spring assembly and preferably without substantial interruption to the operation of the conveyor drive. As defined herein, “substantial interruption” means any stoppage of conveyor drive operation that is more than five minutes, more preferably less than two minutes, most preferably less than one minute. In some cases, the operation of the conveyor drive need not be stopped at all. As one of the first steps in installing the sensor assembly  70 , using the embodiment shown in FIGS. 1 and 2 as an example, the second member  80  of the sensor assembly  70  may be mounted on the clevis  90 , with the sensor  72  connected to the second member  80  or with the sensor  72  installed afterwards. Then the first member  78  may be installed with the inner stop  88  abutting an end of the cylindrical housing  54  of the spring assembly  50  and with the sensor  72  and the second member  80  placed within the first member  78 . At the same time, the first end  74  of the sensor  72  should extend through the opening  94  on the second end  86  of the first member  78  to the outside of the first member  78 . Next a nut  96  may be mounted on the threaded first end  74  of the sensor  72  and turned until the rod  56  is substantially disengaged from the spring  52  so that the force is transmitted substantially through the sensor  72 . The removal of the sensor assembly  70  is substantially the reverse of the steps described above.  
         [0031]    Some of the steps described above may be performed with the conveyor drive in operation, while others may be performed with conveyor drive shutdown. For example, while the installation of the first and second members  78 ,  80  may be installed with the conveyor drive  10  in operation, the adjustment of the nut  96  may be performed with the conveyor drive  10  shutdown.