Abstract:
Viscoelastic dampers and belt conveyor systems using viscoelastic dampers to attenuate belt vibration and methods for damping belt speed variations. One version of the viscoelastic dampers includes a low-friction carryway element mounted to a viscoelastic pad that is firmly attached to stationary conveyor framework at various locations along the length and width of the conveyor system. Speed fluctuations of the conveyor belt supported on and advancing along the low-friction carryway elements are damped by the viscoelastic dampers. In some versions, magnetic forces are used to clamp the conveyor belt to the dampers to increase the effective damping.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 13/882,686, filed Apr. 30, 2013, which is a 371 of PCT/US2011/056511, filed Oct. 17, 2011, which claim benefit of U.S. Provisional Patent Application No. 61/409,155, filed Nov. 2, 2010. The disclosures of those patent applications are incorporated into this application by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates generally to power-driven conveyors conveying articles and more particularly to conveyor systems using viscoelastic dampers and methods for smoothing conveyor belt motion. 
         [0003]    One purpose of a conveyor, such as a conveyor belt, is to transport products or persons smoothly, either through a larger device or from one point to another in a manufacturing, logistic, or transport operation. Smooth, linear motion of the conveyor is important in many applications, such as, for example, transporting passengers, manufacturing extrusions, and conveying unstable products subject to tipping upright. But many variables cause the motion of conveyor belts not to be smooth. These variables include, but are not limited to, fluctuations in the belt&#39;s drive train, resonances in the conveyor belt, resonances in other coupled systems, and fluctuating loading caused by people walking over the surface of the belt. The fluctuations and resonances affect the conveyor belt&#39;s forward motion by causing speed changes, i.e., accelerations, which can jostle passengers, topple cans or bottles, or degrade a continuous manufacturing process. This problem is particularly evident in long conveyor systems because the accumulated elasticity of the long belt makes it difficult to control the belt&#39;s dynamic motion, which is mainly in the direction of belt travel for a moving belt. In people movers, for example, as a passenger walks or moves about on top of the belt, his shifting foot weight sets up a periodic load that acts as a forcing function. The spring constant of the long belt allows the belt to expand and compress to a degree that is noticeable and objectionable to the passenger on the belt. The dynamic motion of the belt becomes problematic. While shifting foot weight is the cause of the forcing function in this example, long belts are more elastic and more subject to resonance. Thus, there is a need for smoothly moving belt conveyors. 
       SUMMARY 
       [0004]    One version of a conveyor system embodying features of the invention comprises a conveyor belt supported in a frame. The belt advances at a belt speed in a direction of belt travel along on an upper run. A viscoelastic damper contacts the conveyor belt at a position along the upper run. The viscoelastic damper includes a bearing surface contacting the conveyor belt. A viscoelastic damping material attached to the bearing surface and to the frame is placed in shear as the conveyor belt advances on the bearing surface so that variations in the belt speed are attenuated by the viscoelastic damper. 
         [0005]    In another aspect, a viscoelastic damper embodying features of the invention comprises a bearing element having a bearing surface for contacting an advancing conveyor belt and an opposite surface. A damping pad made of a viscoelastic damping material attached to the bearing element is placed in shear as a conveyor belt contacting the bearing surface advances along the bearing element. 
         [0006]    In another aspect, a method for damping a conveyor belt comprises: (a) advancing a conveyor belt along an upper run; and (b) contacting the conveyor belt with a bearing surface backed by a viscoelastic material along the upper run of the conveyor belt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These aspects and features of the invention are better understood by referring to the following description, appended claims, and accompanying drawings, in which: 
           [0008]      FIG. 1  is a cross section of the upper run of a conveyor system embodying features of the invention including viscous dampers; 
           [0009]      FIG. 2  is a cross section of a conveyor system as in  FIG. 1  including clamped viscous dampers; 
           [0010]      FIGS. 3A and 3B  are front elevation views of two versions of inertial-viscous damper usable with a conveyor system as in  FIG. 1 ; 
           [0011]      FIG. 4  is an isometric view of another version of conveyor system embodying features of the invention including accelerometers embedded in a moving conveyor belt; 
           [0012]      FIG. 5  is a block diagram of a controller for the conveyor system of  FIG. 4 ; 
           [0013]      FIG. 6  is a top plan view of a conveyor system as in  FIG. 4 , further showing a linear damper operated in a closed-loop system, and  FIG. 6A  is an enlarged view of the linear damper of  FIG. 6 ; and 
           [0014]      FIG. 7  is a top plan view of a conveyor system as in  FIG. 4 , further showing a magnetic clamping damper operated in a closed-loop system, and  FIG. 7A  is an enlarged view of the magnetic clamping damper of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A portion of the upper run of a belt conveyor system embodying features of the invention is shown in  FIG. 1 . The underside of the conveyor belt  10  is supported on a bearing element  100  serving as a carryway element. A viscoelastic pad  102  is sandwiched between the carryway  100  and a stationary conveyor frame  104 . The carryway  100  has a flat upper bearing surface  101  and is made of a low- to moderate-friction material, such as UHMW or nylon, for example. If appropriate for the application, a high-friction material may be used. The carryway  100  can be constructed as a slider bed continuous across the width and length of the upper run, a set of laterally spaced parallel wearstrips having upper slide bearing surfaces  101  extending the length of the upper run, or a set of bearing-element segments between static wearstrip segments  106  not attached to viscoelastic pads, but rigidly attached to the frame  104 . If a slider bed, parallel wearstrips extending the length of the upper run, chevron wearstrips, or other wearstrips capable of supporting the belt and conveyed articles are used, the bearing surface would be made of a low-friction material. If the carryway is segmented along its length into wearstrip segments with and without viscoelastic damping pads, the bearing surfaces of the damping segments can be made of a high-friction material or have a serrated, high-friction surface. The carryways  104  are attached to the tops of the viscoelastic pads  102  by adhesive bonding, co-molding, co-extrusion, or mechanical affixation, for example. The bottoms of the viscoelastic pads  102  are fastened to the stationary conveyor frame  104 . Alternatively, the upper bearing surface could be formed on the tops of the viscoelastic pads themselves. 
         [0016]    As the conveyor belt  10  advances along the upper run in a direction of belt travel  108  (out of the page in  FIG. 1 ) and slides along the carryway element  100 , the viscoelastic pad  102  is placed in shear, as well as in some compression due to the weight of the belt and conveyed articles. Vibrations and pulsations in the belt&#39;s speed are transferred to the viscoelastic material through the carryway  100  to which it is rigidly attached. The vibrational energy is dissipated as heat. The wearstrip  100  and the viscoelastic pad  102  together form a damper  110  rigidly attached to the frame  104 . 
         [0017]    Another version of viscoelastic damping is illustrated in the conveyor system of  FIG. 2 . In this version ferrous material, such as slugs  112 , are molded into, embedded in, or attached to the conveyor belt  10  at spaced apart locations along its length and width. Permanent magnets or electromagnets  114  located below or to the sides ( 114 ′) of the dampers  110  attract the ferrous slugs  112  and clamp the belt against the dampers  110  as indicated by arrows  115  to form clamp means. The magnets could be located continuously or intermittently along the length of the upper run. Clamping the conveyor belt  10  to the dampers  110  increases the efficiency of the transfer of linear high-frequency accelerations from the advancing belt to the viscoelastic pad  102 . So damping with clamping can be more effective than the passive damping described with respect to  FIG. 1 . As an alternative clamp means, permanent magnets could be installed in the belt instead of the ferrous slugs, and the magnets in the conveyor framework could be replaced by ferrous material attracted to the belt magnets. 
         [0018]    Other versions of dampers are shown in  FIGS. 3A and 3B .  FIG. 3A  depicts a damper  116  that provides both viscous and inertial damping. A dense material  118 , such as steal or lead, is sandwiched between the viscoelastic pad  102  and the carryway  100 . In  FIG. 3B  the dense material  120  is embedded in the viscoelastic pad  102 ′ itself. The added mass of the dense material adds inertial damping to the viscous damping provided by the viscoelastic material. When used with a magnetic clamp, the dense material  118 ,  120  would be a non-ferrous material. 
         [0019]    Another version of a conveyor system embodying features of the invention is shown in  FIG. 4 . A conveyor, shown in this example as a conveyor belt  10  supported on a carryway  60 , carries articles  12  through a process  11  in a conveying direction  13  on an outer conveying surface  22  along a carryway segment  15  of the belt&#39;s endless conveying path. At the end of the carryway, the articles are conveyed off the conveyor belt. After rounding drive sprockets  18 , the conveyor belt  10  follows a return segment  17  on its way back around idle sprockets  20  to the carryway segment  15 . Both the drive and idle sprockets are mounted on shafts  68  (only idle shaft shown in  FIG. 4 ). 
         [0020]    One or more accelerometers  24  embedded in the belt  10  make measurements of dynamic belt motion, such as speed or acceleration changes. The term “embedded” is used in a broad sense to encompass any installation of an accelerometer in a conveyor. Examples of embedded accelerometers include accelerometers mounted on or in, molded into, inserted into, laminated in, welded to, bonded to, or otherwise rigidly connected to the advancing conveyor. The accelerometers  24  may be single-axis accelerometers sensing the component of local belt acceleration along an x-axis, for example, parallel to the conveying direction  13 ; a two-axis accelerometer sensing the components of acceleration along the x-axis and a y-axis perpendicular to the x-axis, for example, across the width of the conveyor belt; or a three-axis accelerometer sensing three orthogonal components of local acceleration, for example, along the x- and y-axes and along a z-axis extending through the thickness of the conveyor belt. In most applications, belt accelerations along the x-axis would be of most interest and more susceptible to control, but accelerations along the other axes may be of interest as well. For example, an accelerometer sensing accelerations along the z-axis, or even along the x-axis, could be used to detect the impact of an article dropped onto the conveyor belt. Examples of accelerometer technologies include piezoelectric, piezoresistive, and capacitive. For compactness, a micro-electro-mechanical—system (MEMS)-based accelerometer is useful. In  FIG. 4 , which shows a modular plastic conveyor belt loop constructed of rows of hinged modules, the accelerometers  24  are spaced apart regularly at locations along the length of the belt and across its width. 
         [0021]    As shown in  FIG. 5 , each accelerometer  24  is connected to a logic circuit  28  in the conveyor belt  10 . Each logic circuit may be realized by a programmed microcontroller or by hardwired logic elements. Conventional signal-conditioning circuit components, such as buffers, amplifiers, analog-to-digital converters, and multiplexers, may be interposed between the accelerometer and the logic circuit. The logic circuit may also include a unique address or other identifying indicia to correlate the response of each accelerometer with a specific position on the conveyor belt. The identifying indicia and the accelerometer&#39;s measurements may be stored in one or more memory elements  29 . The accelerometer measurements—one, two, or three components of acceleration—are converted into a measurement signal  30  that is transmitted remotely by a transmitter  32 . The transmitter may be a wireless RF transmitter transmitting wirelessly via an antenna  34  over a wireless communication link  36  or over an ohmic connection  38  between a conductive contact  40  on the outside of the belt  10  and a brush  42  in conveyor structure along the side of the belt, as in  FIG. 4 . A receiver  33  may also be connected to the logic circuit to receive command and control signals from a remote controller  44 , i.e., a controller not located on or in the conveyor belt. Other transmitter-receiver technologies, such as optical or infrared, for example, may be used. All the components embedded in the belt may be powered by a power source  45 , such as one or more battery cells, housed together in a cavity in the belt. Alternatively, the power source  45  may be an energy harvester harvesting energy from vibratory motion or articulation of the conveyor, thermal gradients, or other energy-producing effects inherent in the process or conveyance. The embedded power source  45  may alternatively be powered by induction or by RF charging as it recirculates past an external charging device  49 , as in  FIG. 4 . 
         [0022]    A remote receiver  46  receives the measurement signal  30  via an antenna  48  over the wireless communication link  36  or over the ohmic connection  38  from the receiver  33  embedded in the conveyor belt. The receiver  46  sends the measurement signal to the remote controller  44 . A transmitter  47  connected between the controller  44  and the antenna  48  or the ohmic connection  38  may be used to send command and control signals to the belt-borne accelerometer circuits. An operator input device  50  connected to the controller  44  may be used to select accelerometer or alarm settings or data to be displayed. The controller  44  may also be used to stop or control the speed of a motor  52  driving the main drive sprockets  18  or to activate a clamping damper  64  acting on the conveyor belt itself. A video display  54  may be used to monitor system operating conditions and settings or to display alarm conditions. A more clearly visible or audible alarm  56  may also be used by the controller to warn of irregularities in the process. The controller may be a programmable logic controller, a laptop, a desktop, or any appropriate computer device. 
         [0023]    Instead of or in addition to belt-mounted accelerometers, other sensors  62  can be used. Examples of sensors with sufficient resolution to sense the dynamic motion of the moving conveyor belt include rotary tachometers, belt-mounted strain gauges, and laser doppler velocimeters. 
         [0024]      FIGS. 6 and 6A  depict closed-loop viscoelastic damping applied to the conveyor belt  10  at positions along the carryway path  15 . Acceleration measurements made by the accelerometers  24  are transmitted over the communications link  36  to the controller  44 . Responding to the acceleration measurements, the controller activates viscoelastic dampers  72 , which act directly on the conveyor belt  10 . An actuator  74  associated with the damper  72  receives the control signal  61  from the controller to increase and decrease or otherwise modulate the pressure applied by the damper against the outer surface  22  of the conveyor belt  10 . The linear damper  72 , in the form of a movable clamping pad, such as the pad  110  in  FIG. 1 , forms clamp means with the upper slide surface  59  of the carryway  60  and the actuator to apply a clamping force against the belt  10  and damp undesired accelerations. Like a modular plastic conveyor belt and a carryway, the clamping pad may be made of a viscoelastic polymer material. The dampers can be applied intermittently along the carryway path segment  15 . In this example, the viscoelastic material is above the belt in the linear damper&#39;s clamping pad  72 . If the carryway  60  is made of or attached to a viscoelastic material, the clamping pad  72  could be made without viscoelastic damping material. Or viscoelastic material could be in both the carryway  60  and the clamp  72 . 
         [0025]      FIGS. 7 and 7A  depict a viscoelastic damping system like that of  FIG. 2  using magnetic or electromagnetic forces to clamp the belt to the damper. In this version, the belt  10 ′, the carryway  60 ′, or both are made of a viscoelastic material. The clamping force is accomplished using magnets  73 , permanent or electromagnetic. Permanent magnets or electromagnets  73  outside the belt act on ferrous or other magnetically attractive materials or magnets inside the belt  10 ′ at one or more positions across the width of the belt to generate a clamping force between the belt and the carryway. Alternatively, ferrous or other magnetically attractive materials outside the belt act on permanent magnets or electromagnets inside the belt to generate a clamping force. The controller  44  modulates the electromagnetic force or the position of the fixed attractive material to obtain the desired damping pressure. 
         [0026]    Although the invention has been described in detail with reference to exemplary versions, other versions are possible. For example, the damper control may be operated in an on/off or otherwise modulated fashion. And the damping can vary linearly or nonlinearly with belt speed.