Abstract:
Conveying systems and method for measuring accelerations in a conveyor advancing through process equipment and taking remedial and prophylactic action in response. The conveyor system includes a conveyor with embedded accelerometers making measurements conveyor accelerations. A controller uses the measurements to control the speed of the conveyor to compensate for unwanted accelerations or to damp the unwanted accelerations. The controller can also use the measurements to warn of unwanted accelerations or to predict the failure of associated or nearby equipment so that maintenance can be scheduled and to detect imminent failures and shut down the process.

Description:
BACKGROUND 
       [0001]    The invention relates generally to power-driven conveyors conveying articles and more particularly to conveyor systems using accelerometers to measure the acceleration of a conveyor conveying articles. 
         [0002]    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. 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 conveyors. 
         [0003]    All mechanical devices generate periodic accelerations due to the motion of components such as linkages, gears, chains, and pistons. Even uniformly rotating components, such as shafts, flywheels, and disks, generate periodic accelerations due to imbalance and run-out. Components such as roller bearings in larger devices also generate characteristic periodic accelerations. These accelerations or vibrations in one or more dimensions can be measured by accelerometers. Analyzing accelerometer data using methods such as Fourier analysis can isolate these various sources. As mechanical components wear, their frequency spectra and magnitudes change over time. This information can be used to predict failure trends and support planned maintenance. Traditionally, accelerometers are permanently affixed to devices or temporarily affixed using magnetic mounts, clips, or similar methods. Multiple accelerometers located throughout a mechanical device provide desirable local information of the device, but are prohibitive because of cost and physical constraints, such as mounting and routing of wires. Thus, there is a need for economically measuring and analyzing the wear characteristics of mechanical systems to predict failures. 
       SUMMARY 
       [0004]    One version of a conveyor system embodying features of the invention comprises a conveyor conveying articles in a conveying direction and an accelerometer embedded in the conveyor to make measurements of accelerations of the conveyor. 
         [0005]    In another aspect of the invention, a conveyor belt comprises an endless belt loop and an accelerometer embedded in the endless belt loop to make measurements of accelerations of the belt loop. 
         [0006]    In yet another aspect of the invention, a method for measuring the acceleration of a conveyor comprises: (a) driving a conveyor having at least one embedded accelerometer in a conveying direction; and (b) making measurements of the acceleration of the conveyor with the at least one embedded accelerometer. 
     
    
     
       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 an isometric view of a conveyor system embodying features of the invention including accelerometers embedded in a moving conveyor; 
           [0009]      FIG. 2  is a block diagram of the conveyor system of  FIG. 1 ; 
           [0010]      FIG. 3  is a top plan view of a conveyor system as in  FIG. 1 , further showing a rotational damper on the conveyor drive shaft operated in a closed-loop system; 
           [0011]      FIG. 4  is a top plan view of a conveyor system as in  FIG. 1 , further showing a rotational damper on the conveyor idle shaft operated in a closed-loop system; 
           [0012]      FIG. 5  is a top plan view of a conveyor system as in  FIG. 1 , further showing a linear damper operated in a closed-loop system, and  FIG. 5A  is an enlarged view of the linear damper of  FIG. 5 ; 
           [0013]      FIG. 6  is a top plan view of a conveyor system as in  FIG. 1 , further showing a magnetic damper operated in a closed-loop system, and  FIG. 6A  is an enlarged view of the magnetic damper of  FIG. 6 ; 
           [0014]      FIG. 7  is a top plan view of a conveyor system as in  FIG. 1 , further showing an eddy-current damper operated in a closed-loop system, and  FIG. 7A  is an enlarged view of the eddy-current damper of  FIG. 7 ; 
           [0015]      FIG. 8  is a top plan view of a conveyor system as in  FIG. 1 , further showing intermediate drives used as dampers in a closed-loop system; 
           [0016]      FIG. 9  is a top plan view of a conveyor system as in  FIG. 1 , further showing a controller directly controlling the speed of the drive motor in a closed-loop system; 
           [0017]      FIG. 10  is a top plan view of a conveyor system as in  FIG. 1 , further showing intermediate rotational dampers engaging the linear movement of the belt; and 
           [0018]      FIG. 11  is a top plan view of a conveyor system as in  FIG. 1 , further showing a plurality of controllers controlling the application of damping along the length of the conveyor system. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    One version of a conveyor system embodying features of the invention is shown in  FIG. 1 . 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. 1 ). 
         [0020]    One or more accelerometers  24  embedded in the belt  10  make measurements of accelerations in the belt. 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. 1 , 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. 2 , 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. 1 . 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. 1 . 
         [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 , to control intermediate drives  62 , or to activate a 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]    As shown in  FIG. 3 , the accelerometer  24  embedded in the belt  10  is used to damp accelerations in the belt. Its measurements of acceleration  30  are routed over the communication link  36  to the controller  44 . The controller, using wireless or copper control lines  61 , applies damping to the drive shaft  68 ′ of the conveyor in response to unwanted accelerations measured by the accelerometer. Damping is applied to the drive shaft by a rotational damper  70  controlled by the controller in a closed-loop control system to compensate for speed changes caused by vibrations, resonances, stick-slip, chordal action, imbalance, run-out, or other conditions causing regular or intermittent speed variations.  FIG. 4  shows a similar closed-loop control system, except that the rotational damper  70  operates on the idle shaft  68  to apply damping, such as conventional speed-change damping, back tension, or controlled braking, at that point along the conveying path. 
         [0024]      FIGS. 5 and 5A  depict linear 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 linear dampers  72 , which act directly on the conveyor belt  10 . An actuator  74  associated with the linear 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 pad, forms a clamp with the carryway  60  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 material. The linear dampers can be applied intermittently along the carryway path segment  15 . 
         [0025]      FIGS. 6 and 6A  depict a similar linear damping system using magnetic or electromagnetic forces. 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 ′ 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 characteristic. 
         [0026]    Another form of damping acting on the conveyor belt itself is shown in  FIGS. 7 and 7A . In this version, the entire conveyor belt  10 ′, or portions of it, are made of an electrically conductive material. Magnetic field generators  76  disposed along the length of the conveyor belt  10 ′ produce a magnetic field through which the belt passes. Eddy currents are induced in the conductive portions of the belt. The eddy currents produce an induced magnetic field that, according to Lenz&#39;s law, opposes the direction of the motion causing the induced field, i.e., the motion of the belt in the conveying direction  13 . Consequently, the interaction of the inducing and induced magnetic fields results in a damping force applied to the conveyor belt  10 ′ opposite to the conveying direction  13 . Thus, the magnetic field generators are eddy-current dampers. They may be permanent magnets whose distance from the belt may be controlled by the controller  44  to adjust the magnitude of the fields and the damping force or electromagnets whose field strength can be electronically controlled by the controller. A similar form of damping is realized by making the conveyor belt  10 ′, or portions of it, out of a ferrous or magnetically attractive material. In this case, the magnetic field generators  76  disposed along the length of the conveyor belt  10 ′ act on the ferrous or magnetically attractive materials in the belt to create a force generally opposing the motion of the belt and so providing damping. 
         [0027]    In yet another version, shown in  FIG. 8 , the controller controls the operation of intermediate drives  62  engaged with the conveyor belt  10  at spaced apart positions along the carryway. The intermediate drives serve as dampers to damp unwanted belt accelerations. They can also serve as auxiliary drives to help the conveyor&#39;s main drive  78  advance the belt forward. This dual function is especially useful in long conveyors. The controller sends control signals  61  to each of the intermediate drives in response to acceleration measurements from the accelerometers  24  to damp unwanted accelerations in belt motion. 
         [0028]    Intermediate rotational dampers converting the linear motion of the belt surface to rotational motion may be similarly used as in  FIG. 10 . In this example, the linear motion  13  of the belt  10  is converted to rotational motion via engagement with a circular engaging element  79 , which may be a friction disk or a tire frictionally engaging the belt surface or a sprocket mechanically engaging mating drive structure in the belt. The circular engaging element  79  co-acts with an associated damper  70 , which may provide viscous-fluid damping, eddy-current damping, magnetic damping, frictional damping, electric-motor damping, or regenerative damping with an electric generator providing power  80  back to the conveyor system. 
         [0029]    In still another version, as shown in  FIG. 9 , the main conveyor drive  78  is controlled directly in response to the belt-acceleration feedback provided by the accelerometers  24 . Thus, rather than controlling the damping of the belt&#39;s dynamic system, the system&#39;s forcing function, i.e., the belt drive  78 , is controlled. Acceleration measurements  30  from the accelerometers  24  are transmitted to the controller  44  over the communications link  36 . The controller produces a control signal  61  that compensates for the unwanted accelerations and applies the signal to the main drive  78 , in this example, a variable-frequency motor drive. 
         [0030]    With one or more accelerometers  24  embedded in a conveyor  10  advancing through process equipment  11  and nearby conveyor components as in  FIG. 1 , measurements of local accelerations in the conveyor caused by the devices can be made essentially continuously. 
         [0031]    One moving accelerometer can be used to replace multiple stationary accelerometers and can provide finer-resolution data, which the controller  44  can use to perform failure-trend analysis of the process equipment in which the conveyor is installed and of other proximate devices, such as conveyor components, particularly at the infeed and discharge boundaries, and schedule the necessary maintenance. The controller can use the accelerometer-based data for protective control, such as shutting down the process, stopping the conveyor motor  52 , or sounding alarms  56 , as already described with reference to  FIG. 2 , if excessive vibration or other out-of-range speed fluctuations are sensed. In this way, the system provides both remedial and prophylactic protection of the conveyor system and the entire process. 
         [0032]      FIG. 11  shows a plurality of controllers  44  with receivers  46  distributed along the length of the conveyor at fixed locations in individual control zones  82 A-C. As belt-borne accelerometers  24  come within communication range of a receiver, sensing in the receiver&#39;s zone is switched to the in-range accelerometer or accelerometers now local to that receiver. The controller coupled to that receiver uses the measurements of the local accelerometer or accelerometers in the receiver&#39;s zone to control an associated damper  70  in that zone in a closed-loop damping control system. As an accelerometer advances past the zone of one local receiver and into the next zone, it is passed off to the receiver and the controller in the next zone. The accelerometer then becomes local to the controller controlling the damping in the next zone downstream. This distributed control system is especially useful in long conveyors. 
         [0033]    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. Although the distributed control system of  FIG. 11  is described as using an individual controller in each zone, a single controller receiving data from the receivers in all the zones and controlling all the dampers could be used instead.