Abstract:
A self-propelled crawler/tractor apparatus is disclosed for traveling through a tubular pipeline while conducting pipeline wall inspection operations and/or towing gear for cleaning, maintenance and the like. The crawler/tractor apparatus is propelled by a plurality of radially positioned motorized traction wheels. Each motorized traction wheel includes a brushless DC electric motor along with clutch, gearbox and other mechanical drive components integrated into a compact self-contained motorized wheel assembly which is sealed and filled with an electrically non-conductive lubricating/cooling oil. The seal integrity at each wheel assembly is maintained against oil leakage and debris ingress by a pressure-balancing mechanism which matches internal oil pressure to the exterior ambient pressure present in the pipeline. The electric motor drive for each traction wheel is individually controlled via an onboard computer to provide a wide range of torque and wheel speeds.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to a mechanical crawler or tractor device capable of traveling through a tubular pipeline and, more specifically, to a compact wheel drive assembly having an embedded electric motor for use in a pipeline tractor device. 
         [0002]    It is known in the art to cause inspection or cleaning pigs to be propelled through a pipe or tubing under the influence of a pressurized fluid. Conventionally, when inspecting the interior of a pipeline, the flow of the medium being transported is commonly used to drive forward the inspection system. However, if there is no fluid medium present or if there is only a low flow volume then the pipeline can not be traversed using such conventional driving means. In such cases, some sort of powered tractor device must be used to carry or pull the inspection apparatus through the pipeline. Although various types of self-powered tractor devices are known in the prior art, such conventional pipeline crawler devices suffer from one or more drawbacks that often render them unreliable or difficult or impractical to operate. For example, obstacles or irregularities encountered in a pipeline often caused prior art self-propelled pipeline tractor devices to lose traction and become stranded or stuck within the pipeline. Moreover, the drive components and motor systems of conventional pipeline tractors are highly susceptible to contamination and early failure caused by ambient pressure charges and debris often encountered within a pipeline. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    A self-propelled crawler/tractor apparatus is provided for traveling through a tubular pipeline for conducting interior pipeline inspection operations and/or for towing specific apparatus for cleaning, maintenance and the like. The crawler/tractor is propelled by a plurality of independently controlled motorized traction drive wheels each mounted at the end of separate radially extending drive wheel support extension arms that are evenly spaced around the periphery of the outer circumference of a predominantly cylindrical-shaped main chassis. Each drive wheel support extension arm relies on a spring mechanism which operates to urge the motorized drive wheel at the end of the extension arm outward and maintain it in contact with the interior pipeline walls with sufficient contacting force to suspend the tractor main chassis away from the pipeline walls and provide traction for the drive wheel at its contact with the pipeline wall. Alternatively, a hydraulic powered mechanism or other appropriate mechanism could be used to provide a resilient outward urging force at each suspension arm to maintain the tractor drive wheels in contact with the pipeline wall and keep the tractor centered within the pipeline. Electronic monitoring of the rotation and slippage of each individual drive wheel is performed to manage wheel traction and maintain sufficient wheel-to-wall clamping force at each individual motorized wheel to allow the tractor to negotiate diverse pipeline courses and obstacles. 
         [0004]    Each traction drive wheel assembly includes a compact internal brushless DC electric motor along with a freewheeling Sprague-type clutch mechanism, a harmonic drive reducer gear assembly and other conventional motor and wheel components (e.g., bearings and races, seals, etc.). All of the drive motor components are integrated into a compact self-contained wheel housing and all of the drive wheels are powered from a single on-board battery. Each drive wheel of the tractor is individually controlled via a separate motor drive controller circuit mounted on-board the tractor. The use of separate motor drive controller circuits enables each drive wheel to produce a wide range of torque while individually controlling wheel speed to prevent loss of traction. 
         [0005]    Each drive wheel assembly is oil-filled and the dc motor, harmonic drive gear and free-wheeling clutch components are continuously maintained in an oil bath environment which provides both lubrication and cooling. The oil-filled interior of the drive wheel also significantly reduces susceptibility of the internal motor and drive components to damage caused by vibrations or trauma and contributes to the overall durability and reliability of the pipeline tractor device. In addition, the oil also serves to insulate ambient pipeline gas from any potential sources of ignition within the motorized drive wheels. Each drive wheel assembly is appropriately outfitted with bearing seals to prevent leakage of the oil and prevent ingress of foreign material and debris into the oil filled interior. 
         [0006]    In addition, the drive wheels are also provided with a dynamic pressure-balancing mechanism for equalizing pressure differences between the interior oil pressure and exterior ambient pressure. This pressure balancing mechanism ensures that the integrity of the drive wheel bearing seals are preserved despite significant changes in ambient pressure. Maintaining a low pressure differential across the seals between the interior and the exterior of the drive wheel housing prevents oil leakage and prevents pipeline debris from entering into the moving/working parts of the drive wheel motor through the seals. One example implementation of the pressure-balancing mechanism is disclosed that uses a small diaphragm/membrane of flexible material (e.g., polyurethane) mounted within a through-passage or hole in a side wall of the drive wheel. The flexible diaphragm expands or contracts (i.e., deforms) slightly in response to changes in pressure between the interior and the exterior of the drive wheel housing. This expansion/contraction or deformation of the flexible membrane results in changes in the sealed motor housing internal volume that allow the motor housing internal oil pressure to instantly equalize (or at least closely match) changes in the exterior ambient pressure present in the pipeline and, thus, prevents a large pressure differential from building up across seals in the drive wheel that could cause the seals to prematurely fail. 
         [0007]    One aspect of the non-limiting illustrative example implementation disclosed herein is the provision of a compact and efficient brushless DC electric motor that is housed entirely within the relatively confined space of a pipeline crawler/tractor device wheel. 
         [0008]    Another aspect of the non-limiting illustrative example implementation of the pipeline crawler/tractor device disclosed herein is the provision of a compact and efficient brushless DC electric motor that is housed entirely within the confines of a wheel of the tractor device and which can be controlled independently of other motorized wheel drives of the tractor device to deliver a high torque even at low rotational velocities. 
         [0009]    Yet another aspect of the non-limiting illustrative example implementation of the pipeline crawler/tractor device disclosed herein is the provision of multiple drive wheels mounted at the end of a plurality of circumferentially arranged self-adjusting drive wheel support extension arms that produce wheel-to-wall traction and clamping forces at multiple radial points around and along the pipeline inner wall so as to ensure propulsion of the crawler/tractor device in the event of a loss-of-contact or a decrease in traction at any one or more of the individual drive wheels. 
         [0010]    Yet still another aspect of the non-limiting illustrative example implementation of the pipeline crawler/tractor device disclosed herein is the provision of a drive wheel control system that enhances the ability of the crawler/tractor device to overcome various obstacles and adverse operating conditions which it may encounter within a pipeline. In particular, a drive wheel control system is provided which constantly monitors the speed and traction at each drive wheel to assess wheel slippage and/or detect a non-contacting wheel condition and then automatically proportionately redistributes the available electric drive power to the drive wheels which remain under load having minimal slippage so to maximize the overall traction and drive of the crawler/tractor device. 
         [0011]    An example non-limiting implementation of the pipeline crawler/tractor device is now described in detail in conjunction with the drawings identified below in which like reference numerals refer to like elements throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side view of an example self-propelled mechanical tractor device for traveling and pulling other equipment through a tubular pipeline; 
           [0013]      FIG. 2  is a perspective view of a rear portion of an example pipeline tractor device showing a cut-away view of the control boards housing and showing the drive wheel support extension arms in a collapsed configuration; 
           [0014]      FIG. 3  is an end view of an example tractor device including both front and rear chassis sections with all drive wheel support extension arms shown in an expanded configuration; 
           [0015]      FIG. 4A  is a detailed sectional view of an example motorized drive wheel assembly mounted at the end of the drive wheel support extension arms; 
           [0016]      FIG. 4B  is a cut-away sectional view showing a dynamic pressure-balancing mechanism mounted in a side wall portion of a motorized drive wheel of the tractor device of  FIG. 1   a;    
           [0017]      FIG. 5  is a multiple motorized wheel motor drive control circuit schematic diagram illustrating an example arrangement for monitoring and individually controlling multiple drive wheel motors in an example pipeline tractor device as shown in  FIG. 1 ; 
           [0018]      FIG. 6  is a schematic circuit diagram illustrating an example I/O routing signal arrangement for communicating motor control and sensor signal inputs and outputs from a main processor/controller of the tractor device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIGS. 1 through 3  show various views of a non-limiting example implementation of a self-propelled mechanical crawler or tractor device  10  having self-contained motorized traction drive wheels  12  mounted on twelve drive wheel support extension arms that are pivotally attached and circumferentially arranged about the exterior of a basically cylindrically shaped main chassis  1 . Alternative drive configurations having fewer or a greater number of circumferentially mounted drive wheel support extension arms with self-contained motor drive wheels are also possible for tractor  10 . 
         [0020]      FIG. 1  presents a side view of tractor device  10  in which only seven of the twelve drive wheel support extension arms with motorized drive wheel assemblies are visible. In this non-limiting illustrative example, tractor device  10  is made up of a modular front and rear chassis section ( 10   a  and  10   b ) with each chassis section having six radially arranged support extension arms  11  that each support a drive wheel  12  incorporating an internal brushless dc motor and related drive components ( FIG. 4 ). As shown in  FIG. 1 , drive wheel extension arms  11  are in an extended configuration. A pressurized air piston or spring mechanism  15  is pivotally mounted between each extension arm and the main chassis cylindrical body portions  10   a  and  10   b  to urge the drive wheel support extension arm  11  outward from the tractor body so as to produce a strong but self-adjusting wheel-to-pipeline wall clamping force from the tractor chassis at each drive wheel. This arrangement allows the support arms to instantly and individually move and pivot to enable the motorized drive wheel to ride over small obstacles encountered within a pipeline. The radial extension or reach of each support extension arm  11  may also be adjusted by varying the position of a spring support bracket  14  along the chassis body. 
         [0021]    Each drive wheel  12  rotates about a central axel held in place at the end of support arm  11  by a wheel side bracket portion  13  fixedly attached or formed in an end portion of support arm  11 . Each drive wheel  12  contains an internal brushless dc motor that is individually powered and controlled via a power source (e.g., a battery) housed within tractor main chassis  1  or within a marshalling box portion  3  of the main chassis. Motor control and drive wheel monitoring electronics, as well as any pipeline environment sensor and monitor processing electronics, are housed within a marshalling box portion  3  of the main chassis. A wiring harness (not shown) is configured to provide the dc power from the power source and to convey motor control signals from a plurality of individual motor controllers to each individual wheel. It also conveys signals originating from sensors in each drive wheel to individual motor controllers for monitoring various operating conditions and parameters such as wheel rotational velocity, motor temperature, motor current/torque and the like. As discussed below with respect to  FIG. 4B , the interior of each drive wheel  12  is also filled with oil to protect the internal dc motor components and a side wall of the wheel is provided with a dynamic pressure-balancing membrane  20  that compensates for pressure differences between the oil-filled interior and exterior ambient pressures. 
         [0022]      FIG. 2  shows a perspective view of rear chassis section  10   b  of tractor  10  in which drive wheel support extension arms  11  are depicted in a collapsed configuration. In the non-limiting example implementation shown in  FIG. 2 , twelve motor drive controller boards  18  are arranged to fit inside of the tractor chassis housing in marshalling a box portion  3 . A main processor/drive controller I/O signal routing board  17  and a plurality of individual wheel motor drive controller boards  18  are shown in cut-away view as being mounted inside the clamshell shaped marshalling box portion  3  of the tractor chassis housing. Each controller board  18  includes a brushless dc motor drive controller chip/circuit such as, for example, conventional dc motor drive controller chips made by Omnirel of Leominster, Mass. Each motor drive controller enables individual precise control of the drive current provided to a single associated wheel drive motor and, consequently, precise control over the amount of torque generated at the drive wheel at any time. 
         [0023]      FIG. 2  also illustrates an alternative example implementation of an oil pressure balancing system for the oil filled drive wheels which differs from the dynamic pressure-balancing membrane arrangement shown in  FIG. 1 . In this alternative arrangement, an oil filled piston-type pressure compensator  16  is connected by a network of tubing  19  to each drive wheel. Pressure compensator  16  is sensitive to ambient pressure conditions and automatically adjusts the pressure of oil provided via tubing network  19  at each drive wheel to accommodate ambient pressure changes. 
         [0024]      FIG. 3  provides an end view of the tractor device shown in  FIG. 2  in which all drive wheel support extension arms  11  are depicted in an extended configuration. Six of the twelve drive wheel support extension arm assemblies shown in  FIG. 3  correspond to front chassis section  10   a,  and six of the drive wheel support extension arm assemblies correspond to rear chassis section  10   b.  Front ( 10   a ) and rear ( 10   b ) chassis sections are coupled at a marshalling box housing portion  3 . The front set of six drive wheel support extension arms are offset from the rear set of six drive wheel support extension arms such that the set of front drive wheels mounted on chassis section  10   a  are not in direct alignment with the rear set of drive wheels mounted on chassis section  10   b.  Consequently, the rear set of six drive wheels do not contact the same portions of the pipeline wall or traverse the same ‘footprint’ along the pipeline wall as that of the front set of six drive wheels. This arrangement enhances the tractor&#39;s ability to traverse various obstacles and decreases the likelihood of incurring simultaneous slippage at multiple drive wheels. 
         [0025]      FIG. 4A  shows a detailed sectional view of an exemplary motorized drive wheel assembly of the tractor device. Drive wheel assembly shown includes disk-shaped wheel bracket side portions  41   a  and  41   b  that form an end portion of a drive wheel support extension arm. Wheel bracket side portions  41   a  and  41   b  support a central axial motor shaft  42  via a set of motor shaft bearings  42   a  at axial ends of the motor shaft. Mounted on each wheel bracket side portion  41   a  and  41   b  is a conventional crossed-roller bearing assembly ( 43 ,  44 ,  45 ,  46 ) consisting of crossed-roller bearings  43 , an annular inner ring bearing race  44  and an annular outer ring bearing race  45 . The outer bearing race  45  portion also includes a set of inner and outer ring lip seals  46  which prevent loss of the cooling and lubricating oil contained within the drive wheel assembly. Crossed-roller bearing arrangements of this type are well known in the art and are readily available from various commercial bearing manufactures such as, for example, IKO Nippon Thompson Co., Ltd or the ALM Company of Westbury, N.Y. 
         [0026]    The crossed-roller bearing assembly ( 43 ,  44 ,  45 ,  46 ) supports a drive wheel tire and hub assembly having a hub  47  portion and an external tire portion  48  which is caused to rotate when engaged by a motor clutch mechanism  49 . The internal DC motor includes stator portions  50  that are secured to wheel bracket portions  41   b  and motor armature portions  51  that are secured to motor shaft  42  and a harmonic drive reducing gear mechanism  52 . A free-wheeling Sprague-type clutch mechanism  49  is attached to harmonic drive mechanism  52  and to drive wheel hub portion  47 . When an electrical drive current is provided to the dc motor stator portions  50 , the armature portions  51  rotate causing rotation of motor shaft  50  and harmonic drive mechanism  52 . At an appropriate motor shaft rotational speed, harmonic drive mechanism  52  will cause clutch mechanism  49  to engage drive wheel hub  47  and impart a driving torque to the tractor drive wheel in conventional fashion. 
         [0027]      FIG. 4B  shows a cut-away view of an example dynamic pressure-balancing membrane  20  mounted in a cylindrical passage in a side wall portion  41  of each of the motorized drive wheel assemblies  12 . Membrane  20  may be fabricated from any resilient, flexible, oil resistant material such as polyurethane or other suitable rubber or plastic. A retaining ring  21  or other suitable mechanism is used to hold membrane  20  in place and prevent leakage of oil from the interior of wheel  12 . As ambient pressure on an exterior exposed side  22  of membrane  20  changes with respect to the oil-filled interior  23  of the drive wheel housing, membrane  20  will flex either inward or outward causing the pressure differential between the interior and the exterior of the wheel housing to decrease. This helps to maintain the integrity of the wheel housing oil seals, such as crossed-roller bearing lip seals  46 . The resulting lower pressure differential between the interior and the exterior of the wheel housing prevents the wheel housing oil seals from leaking oil and prevents an ingress of foreign contaminants/materials into the wheel housing interior. 
         [0028]    In  FIG. 5 , a schematic diagram is shown which illustrates an example motorized wheel motor drive control circuit for individually controlling multiple drive wheel motors in the tractor device and for monitoring various operation and condition signals supplied by each wheel motor or associated individual drive wheel motor controller. The motorized wheel motor drive control circuit connects a main processor/controller on a chassis mounted controller board ( 17 ) with individual motor drive controller chip/circuits ( 18 ) associated to each motorized drive. The schematic signal diagram of  FIG. 5  also illustrates example power connections and sensor and control signal paths for the drive wheel motors and their associated individual motor controllers. In the disclosed example implementation, each motorized drive wheel controller of  FIG. 5  receives an individually tailored torque command signal from the main processor for precisely controlling the amount of electrical drive current delivered to each associated motorized drive wheel by the on board dc power source. Each motorized drive wheel controller of  FIG. 5  comprises an integrated circuit/chip such as, for example, the OMC507 or OMC510 drive controller made by Omnirel of Leominster, Mass. Alternatively, any other similarly functioning dc motor controller device may also be used. These type of integrated dc motor drive controller devices/circuits typically include electronic components for responding to specific motor command signals provided by a separate control processor or from some command signal source. Each drive wheel controller responds to specific predetermined command signals by appropriately controlling the electrical current/power delivered to its associated drive wheel motor. 
         [0029]    Each drive controller board/circuit may typically also include other components such as a current modulation controller circuit, a three-phase output power stage, an on-board current sense resistor, a motor bus capacitor and/or other motor control, feedback, and communication electronics. For example, in the example implementation shown in  FIG. 2 , each motor drive controller board  18  includes a controller board/circuit of the type described above that communicates with main processor drive controller  17  via a bus/wiring harness (not shown) mounted within each front and rear tractor chassis body housing portion. The bus/wiring harness electrically connects the wheel motors, the wheel controller boards and the main processor drive controller to provide communications and power and may also include signal lines for specific drive command signals, individual drive motor temperature sensor signals, motor speed and drive current feedback signals, as well as additional external sensor signals from one or more tractor mounted pipeline environment sensing/detection devices. 
         [0030]    In the presently disclosed example implementation, a drive motor current feedback signal is provided from sensors in the dc motor of each motorized drive wheel. This signal is monitored by a main processor/drive controller which also monitors signals from each drive wheel and their associated motor controller boards  18 . Each drive wheel dc motor is also provided with conventional hall effect type sensors that provide feedback signals to their associated motor controller boards which are indicative of the current rotational speed of the associated motorized drive wheel. In addition, each motorized drive wheel dc motor is provided with an internal temperature sensor that is monitored by the main processor/ drive controller board for controlling the drive motor current in a manner that will prevent overheating. 
         [0031]      FIG. 6  shows an example main processor/drive controller board and I/O signal routing board schematic circuit arrangement for communicating motor command/control signals and receiving analog sensor signal inputs from drive motors and other environmental sensor devices that may be mounted on the chassis of the tractor device. The main processor/drive controller board includes a conventional CPU/controller circuit or chip along with a RAM memory and a Flash ROM memory containing a predetermined control program for instructing the CPU/controller to issue motor control commands to the individual drive motor controllers and to monitor motor speed, current and temperature as well as signals from any environment/condition sensor devices mounted on the tractor device. The I/O board may also include conventional opto-coupler devices for converting digital electrical I/O signals to and from the main processor to digital optical signals for reducing the susceptibility to ambient electrical noise of, for example, the motor command/control signals provided to each drive motor controller. In this case, the wiring harness would also necessarily include fiber optics for carrying the optical signals and each motor controller board would also include an opto-coupler for conversion back to electrical signals. 
         [0032]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.