Patent Description:
Motion control systems utilizing movers and linear drives can be used in a wide variety of processes (e.g. packaging, manufacturing, and machining) and can provide an advantage over conventional conveyor belt systems with enhanced flexibility, extremely high-speed movement, and mechanical simplicity. The motion control system includes a set of independently controlled "movers," each supported on a track for motion along the track. The track is made up of a number of track segments that, in turn, hold individually controllable electric coils. Successive activation of the coils establishes a moving electromagnetic field that interacts with the movers and causes the mover to travel along the track.

Each of the movers may be independently moved and positioned along the track in response to the moving electromagnetic field generated by the coils. In a typical system, the track forms a closed path over which each mover repeatedly travels. At certain positions along the track other actuators may interact with each mover. For example, the mover may be stopped at a loading station at which a first actuator places a product on the mover. The mover may then be moved along a process segment of the track where various other actuators may fill, machine, position, or otherwise interact with the product on the mover. The mover may be programmed to stop at various locations or to move at a controlled speed past each of the other actuators. After the various processes are performed, the mover may pass or stop at an unloading station at which the product is removed from the mover. The mover then completes a cycle along the closed path by returning to the loading station to receive another unit of the product.

As is known to those skilled in the art, a mover may experience disturbance forces as it travels along the track. One such disturbance force is a cogging force generated within the linear drive system used to propel the mover along the track. The cogging force is a result of magnetic reluctance of the iron core stator and the interaction with the permanent magnets mounted to each mover. The cogging force is dependent on the size of the permanent magnet arrays present on a mover, on the air gap between the permanent magnet arrays on the mover and the stator extending along the track, and on the physical construction of the stator. The cogging force may also vary between "identical" movers due to component and/or manufacturing tolerances between two different movers. Other disturbance forces may be generated by sources external to the linear drive system such as friction or variations in the bearing on the mover or in the guides along the track. These external disturbance forces may vary as a function of the position of the mover along the track.

The controller driving the mover will attempt to regulate speed of the mover despite the disturbance forces experienced by a mover as it travels along the track. An exemplary command issued to a mover is to move between two locations along the track. The mover may be commanded to accelerate to a desired speed, travel at the desired speed, and then decelerate to a stop at the next location. Although the controller may generate a constant velocity reference for the mover while it is traveling at the desired speed, the disturbance forces may either oppose or add to the driving force generated in the stator. The disturbance force will cause the mover to either slow down or speed up, deviating from the desired speed. The controller, in response to detecting the speed deviation, will regulate the current supplied to the stator in an attempt to maintain the desired, constant speed. As a result, the current will increase or decrease, thereby increasing or decreasing the torque applied to the mover, where the torque controls the speed at which the mover travels. The disturbance force varies rapidly, for example, as a permanent magnet on the mover passes each coil mounted on the stator or as a mover travels over a location on the track with excessive wear or misalignment of a guide rail, resulting in excess friction at that location. The controller rapidly varies the current supplied to the stator in response to the disturbance force as it attempts to maintain the desired speed. However, the disturbance forces and resulting current regulation by the controller result in an undesired torque ripple due to the rapidly changing currents applied to the coils and a resultant velocity ripple seen on the mover as a result of torque ripple generated on the drive coils in the linear drive system.

Thus, it would be desirable to provide a system and method for monitoring the disturbance forces experienced by a mover in an independent cart system.

It would further be desirable to provide a system and method for compensating for the disturbance forces experienced by the mover in the independent cart system.

<CIT> describes a linear motor control apparatus, wherein a vector control type current controlling means is equipped therein. Also equipped is an induced voltage compensating means for adding a voltage compensation value, obtained from a detected velocity value of a mover and an induced voltage constant, to a q-axis voltage command value outputted by a thrust current control unit. Also equipped is a position-change inductance compensating means for calculating a q-axis voltage compensation value and a d-axis voltage compensation value, using a detected position value, the detected velocity value, a detected q-axis current value, and a detected d-axis current value, and compensating the q-axis voltage command value and a d-axis voltage command value (abstract).

<CIT> describes an enhanced compensation accuracy of a disturbance in a suspension system. A disturbance observer calculates the first correction quantity based on the target thrust and the stroke state of the suspension when executing the drive-control of an electromagnetic shock absorber, and further, a disturbance estimation unit estimates the disturbance from the stroke state of the suspension, and a second calculation unit calculates the second correction quantity based on the estimated disturbance. A high-pass filter and a third calculation unit correct the first correction quantity based on the frequency of the disturbance to calculate the third correction quantity. An adder adds the compensation by these two correction quantities, and corrects the target thrust to be subsequently operated, and executes the disturbance compensation (abstract).

It is the object of the present invention to provide a method and apparatus to more accurately control current in a linear drive system.

This object is solved by the independent claims.

According to one embodiment of the invention, a method for monitoring disturbance force in a linear drive system is disclosed. A commanded current to be provided to a series of coils spaced along a length of a track in the linear drive system is generated with a controller, and the controller regulates a desired current provided to each of the series of coils. The desired current corresponds to die commanded current and establishes an electromagnetic field that interacts with at least one mover in the linear drive system to propel the mover along the track. A feedback signal is received at the controller, where the feedback signal is a measured position, a measured velocity, or both a measured position and a measured velocity of the at least one mover as it is propelled along the track by the desired current. The feedback signal and the commanded current at a corresponding sample time of the feedback signal are stored in memory of the controller. A disturbance force experienced by the at least one mover is determined at a plurality of positions along the track, where the disturbance force is determined by the controller and is a function of the commanded current and the stored feedback signal.

According to another embodiment of the invention, an apparatus for monitoring disturbance force in an independent cart system includes a track having a length, a plurality of coils spaced along the length of the track, at least one mover configured to travel along the track, a position feedback assembly configured to generate a feedback signal corresponding to operation of the at least one mover, and a controller. The feedback signal is a measured position, a measured velocity, or both a measured position and a measured velocity. The controller is configured to generate a commanded current to be provided to the plurality of coils and regulate a desired current output to the plurality of coils, where the desired current corresponds to the commanded current and establishes an electromagnetic field that interacts with the at least one mover to propel the mover along the track. The controller is further configured to periodically store the commanded current and the feedback signal in memory of the controller, and determine a disturbance force experienced by the at least one mover at a plurality of positions along the track, where the disturbance force is a function of the commanded current and the stored feedback signal.

According to another embodiment of the invention, a method for monitoring disturbance force in a linear drive system is disclosed. The linear drive system includes a plurality of movers configured to travel along a track, and the following steps are performed for each of the plurality of movers. A commanded current to be provided to a series of coils spaced along a length of the track is generated in the linear drive system with a controller, and a desired current, provided to each of the series of coils, is regulated with the controller, where the desired current corresponds to the commanded current and establishes an electromagnetic field that interacts with one of the plurality of movers in the linear drive system to propel the mover along the track. A feedback signal is received at the controller, where the feedback signal is a measured position of the mover as it is propelled along the track by the desired current A disturbance force experienced by the mover at a plurality of positions along the track is determined and, the feedback signal and the disturbance force experienced by the mover are stored in memory of the controller. The disturbance force is determined by the controller and is a function of the commanded current.

These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation.

The subject matter disclosed herein is directed towards a system and method for monitoring the disturbance forces experienced by a mover in an independent cart system. As a mover travels along a track, a controller generates a current reference, where the current reference corresponds to a current required to be supplied to a series of coils spaced along a length of the track to achieve desired operation of the mover. The controller regulates the current supplied to each coil in response to the current reference and receives a feedback signal corresponding to the operation of the mover. The feedback signal may be a measured velocity or measured position of the mover as it is propelled along the track by the current supplied to the coils on the track. The controller stores a value of the current reference and of the feedback signal sampled in tandem, such that the two values correspond to the same sampling interval. The controller is able to determine a disturbance force experienced by the mover as it travels along the track as a function of the stored values of the current reference and of the feedback signal.

In addition to monitoring the disturbance forces experienced by the mover, the system and method disclosed herein compensates for the disturbance forces experienced by the mover in the independent cart system. After determining the disturbance force experienced by the mover, the controller stores the disturbance force experienced by the mover as a function of the location of the mover along the track. Because disturbance forces are commonly generated in response to variations in the physical construction, alignment, or spatial relationship of the permanent magnets and coils as well as variations in friction as a mover travels along the track, a mover is likely to experience similar disturbance forces at the same location each time it travels along the same segment of track. By storing the value of the disturbance force experienced by a mover as it travels along the track, the controller may add a compensation value to the current reference for each subsequent time the mover travels along the same length of track.

In addition, the controller may be configured to learn performance over time without requiring a commissioning process. The controller monitors the disturbance forces experienced by a mover each time the mover travels along the same segment of track. The controller may adjust the stored values of the disturbance force on subsequent trips of a mover across the same track segment For each subsequent trip, the controller may determine whether the adjustments increased or decreased the disturbance forces experienced by the mover. The controller may restore prior values of the stored disturbance force if an adjustment results in an increase in disturbance force experienced by the mover and may keep a new value of the stored disturbance force if an adjustment results in a decrease in disturbance force experienced by the mover. The controller may also be configured to maintain a table of disturbance forces for different movers such that each mover may be uniquely compensated according to the disturbance forces experienced by that mover along a particular track segment.

Turning initially to <FIG>, an exemplary transport system <NUM> (or simply "system <NUM>") for moving articles or products includes a track <NUM> made up of multiple segments <NUM>. According to the illustrated system <NUM>, two segments <NUM> are joined end-to-end to define the overall track configuration. The illustrated segments <NUM> are both straight segments having generally the same length. It is understood that track segments of various sizes, lengths, and shapes may be connected together to form the track <NUM> without deviating from the scope of the invention. Track segments <NUM> may be joined to form a generally closed loop supporting a set of movers <NUM> movable along the track <NUM>. The track <NUM> is illustrated in a horizontal plane. For convenience, the horizontal orientation of the track <NUM> shown in <FIG> will be discussed herein. Terms such as upper, lower, inner, and outer will be used with respect to the illustrated track orientation. These terms are relational with respect to the illustrated track and are not intended to be limiting. It is understood that the track may be installed in different orientations, such as sloped or vertical, and include different shaped segments including, but not limited to, straight segments, inward bends, outward bends, up slopes, down slopes and various combinations thereof. The width of the track <NUM> may be greater in either the horizontal or vertical direction according to application requirements. The movers <NUM> will travel along the track and take various orientations according to the configuration of the track <NUM> and the relationships discussed herein may vary accordingly.

According to the illustrated system <NUM>, each track segment <NUM> includes an upper portion <NUM> and a lower portion <NUM>. The upper portion <NUM> is configured to carry the movers <NUM> and the lower portion <NUM> is configured to house the control elements. As illustrated, the upper portion <NUM> includes a generally u-shaped channel <NUM> extending longitudinally along the upper portion <NUM> of each segment The channel <NUM> includes a bottom surface <NUM> and a pair of side walls <NUM>, where each side wall <NUM> includes a rail <NUM> extending along an upper edge of the side wall <NUM>. The bottom surface <NUM>, side walls <NUM>, and rails <NUM> extend longitudinally along the track segment <NUM> and define a guideway along which the movers <NUM> travel. According to one embodiment, the surfaces of the channel <NUM> (i.e., the bottom surface <NUM>, side walls <NUM> and rails <NUM>) are planar surfaces made of a low friction material along which movers <NUM> may slide. The contacting surfaces of the movers <NUM> may also be planar and made of a low friction material. It is contemplated that the surface may be, for example, nylon, Teflon®, aluminum, stainless steel and the like. Optionally, the hardness of the surfaces on the track segment <NUM> are greater than the contacting surface of the movers <NUM> such that the contacting surfaces of the movers <NUM> wear faster than the surface of the track segment <NUM>. It is further contemplated that the contacting surfaces of the movers <NUM> may be removably mounted to the housing <NUM> of the mover <NUM> such that they may be replaced if the wear exceeds a predefined amount. According to still other embodiments, the movers <NUM> may include low-friction rollers to engage the surfaces of the track segment <NUM>. Optionally, the surfaces of the channel <NUM> may include different cross-sectional forms with the mover <NUM> including complementary sectional forms. Various other combinations of shapes and construction of the track segment <NUM> and mover <NUM> may be utilized without deviating from the scope of the invention.

According to the illustrated system <NUM>, each mover <NUM> is configured to slide along the channel <NUM> as it is propelled by a linear drive system. The mover <NUM> includes a body <NUM> configured to fit within the channel <NUM>. The body <NUM> includes a lower surface <NUM>, configured to engage the bottom surface <NUM> of the channel <NUM>, and side surfaces <NUM> configured to engage the side walls <NUM> of the channel <NUM>. The mover <NUM> further includes a shoulder <NUM> extending inward from each of the side surfaces <NUM>. The shoulder <NUM> has a width equal to or greater than the width of the rail <NUM> protruding into the channel <NUM>. A neck of the mover then extends upward to a top surface <NUM> of the body <NUM>. The neck extends for the thickness of the rails such that the top surface <NUM> of the body <NUM> is generally parallel with the upper surface of each rail <NUM>. The mover <NUM> further includes a platform <NUM> secured to the top surface <NUM> of the body <NUM>. According to the illustrated embodiment, the platform <NUM> is generally square and the width of the platform <NUM> is greater than the width between the rails <NUM>. The lower surface of the platform <NUM>, an outer surface of the neck, and an upper surface of the shoulder <NUM> define a channel <NUM> in which the rail <NUM> runs. The channel <NUM> serves as a guide to direct the mover <NUM> along the track. It is contemplated that platforms or attachments of various shapes may be secured to the top surface <NUM> of the body <NUM>. Further, various workpieces, clips, fixtures, and the like may be mounted on the top of each platform <NUM> for engagement with a product to be carried along the track by the mover <NUM>. The platform <NUM> and any workpiece, clip, fixture, or other attachment present on the platform may define, at least in part, a load present on the mover <NUM>.

The mover <NUM> is carried along the track <NUM> by a linear drive system <NUM> (<FIG>). The linear drive system is incorporated in part on each mover <NUM> and in part within each track segment <NUM>. According to the illustrated embodiment, drive coils <NUM> are positioned along the length of each track segment, and one or more drive members <NUM> are mounted to each mover <NUM>. It is contemplated that the drive members may be drive magnets, steel back iron and teeth, conductors, or any other suitable member that will interact with the electromagnetic fields generated by the coils <NUM> to propel each mover <NUM> along the track <NUM>. For convenience, each drive member <NUM> will be discussed herein as a drive magnet. Alternately, it is contemplated that drive members <NUM> may be mounted along the length of each track segment and one or more drive coils <NUM> may be mounted to each mover <NUM> with the associated controllers to regulate current flow in each drive coil also mounted to each mover.

With reference to <FIG>, the drive magnets <NUM> are arranged in a block on the lower surface of each mover. The drive magnets <NUM> include positive magnet segments <NUM>, having a north pole, N, facing outward from the mover and negative magnet segments <NUM>, having a south pole, S, facing outward from the mover. According to the illustrated system <NUM>, two positive magnet segments <NUM> are located on the outer sides of the set of magnets and two negative magnet segments <NUM> are located between the two positive magnet segments <NUM>. Optionally, the positive and negative motor segments may be placed in an alternating configuration. In still other constructions, a single negative magnet segment <NUM> may be located between the positive magnet segments <NUM>. According to still another embodiment, the drive magnets <NUM> may utilize a Halbach array of magnets. The Halbach array inserts magnets rotated ninety degrees such that the north and south polarity of the rotated magnets appears as "east" or "west" to the other magnets. The effect of the rotation is to enhance the strength of the magnetic field along one side of the magnet array (i.e., the side facing the drive coils) and to reduce the strength of the magnetic field along the other side of the magnet array (i.e., the side facing away from the drive coils). Various other configurations of the drive magnets <NUM> may be utilized without deviating from the scope of the invention.

The linear drive system <NUM> further includes a series of coils <NUM> spaced along the length of the track segment <NUM>. With reference also to <FIG>, the coils <NUM> may be positioned within the housing <NUM> for the track segment <NUM> and below the bottom surface <NUM> of the channel <NUM>. The coils <NUM> are energized sequentially according to the configuration of the drive magnets <NUM> present on the movers <NUM>. The sequential energization of the coils <NUM> generates a moving electromagnetic field that interacts with the magnetic field of the drive magnets <NUM> to propel each mover <NUM> along the track segment <NUM>.

A segment controller <NUM> is provided with each track segment <NUM> to control the linear drive system and to achieve the desired motion of each mover <NUM> along the track segment <NUM>. Although illustrated in <FIG> as blocks external to the track segments <NUM>, the arrangement is to facilitate illustration of interconnects between controllers. As shown in <FIG>, it is contemplated that each segment controller <NUM> may be mounted in the lower portion <NUM> of the track segment <NUM>. Each segment controller <NUM> is in communication with a central controller <NUM> which is, in turn, in communication with an industrial controller <NUM>. The industrial controller <NUM> may be, for example, a programmable logic controller (PLC) configured to control elements of a process line stationed along the track <NUM>. The process line may be configured, for example, to fill and label boxes, bottles, or other containers loaded onto or held by the movers <NUM> as they travel along the line. In other implementations, robotic assembly stations may perform various assembly and/or machining tasks on workpieces carried along by the movers <NUM>. The exemplary industrial controller <NUM> includes: a power supply <NUM> with a power cable <NUM> connected, for example, to a utility power supply; a communication module <NUM> connected by a network medium <NUM> to the central controller <NUM>; a processor module <NUM>; an input module <NUM> receiving input signals <NUM> from sensors or other devices along the process line; and an output module <NUM> transmitting control signals <NUM> to controlled devices, actuators, and the like along the process line. The processor module <NUM> may identify when a mover <NUM> is required at a particular location and may monitor sensors, such as proximity sensors, position switches, or the like to verify that the mover <NUM> is at a desired location. The processor module <NUM> transmits the desired locations of each mover <NUM> to a central controller <NUM> where the central controller <NUM> operates to generate commands for each segment controller <NUM>.

With reference also to <FIG>, the central controller <NUM> includes a processor <NUM> and a memory <NUM>. It is contemplated that the processor <NUM> and memory <NUM> may each be a single electronic device or formed from multiple devices. The processor <NUM> may be a microprocessor. Optionally, the processor <NUM> and/or the memory <NUM> may be integrated on a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The memory <NUM> may include volatile memory, non-volatile memory, or a combination thereof. An optional user interface <NUM> may be provided for an operator to configure the central controller <NUM> and to load or configure desired motion profiles for the movers <NUM> on the central controller <NUM>. Optionally, the configuration may be performed via a remote device connected via a network and a communication interface <NUM> to the central controller <NUM>. It is contemplated that the central controller <NUM> and user interface <NUM> may be a single device, such as a laptop, notebook, tablet or other mobile computing device. Optionally, the user interface <NUM> may include one or more separate devices such as a keyboard, mouse, display, touchscreen, interface port, removable storage medium or medium reader and the like for receiving information from and displaying information to a user. Optionally, the central controller <NUM> and user interface may be an industrial computer mounted within a control cabinet and configured to withstand harsh operating environments. It is contemplated that still other combinations of computing devices and peripherals as would be understood in the art may be utilized or incorporated into the central controller <NUM> and user interface <NUM> without deviating from the scope of the invention.

The central controller <NUM> includes one or more programs stored in the memory <NUM> for execution by the processor <NUM>. The central controller <NUM> receives a desired position from the industrial controller <NUM> and determines one or more motion profiles for the movers <NUM> to follow along the track <NUM>. A program executing on the processor <NUM> is in communication with each segment controller <NUM> on each track segment via the network medium <NUM>. The central controller <NUM> may transfer a desired motion profile to each segment controller <NUM>. Optionally, the central controller <NUM> may be configured to transfer the information from the industrial controller <NUM> identifying one or more desired movers <NUM> to be positioned at or moved along the track segment <NUM>, and the segment controller <NUM> may determine the appropriate motion profile for each mover <NUM>.

A position feedback system provides knowledge of the location of each mover <NUM> along the length of the track segment <NUM> to the segment controller <NUM>. According to the system <NUM> illustrated in <FIG>, the position feedback system includes one or more position magnets <NUM> mounted to the mover <NUM> and an array of sensors <NUM> spaced along the side wall <NUM> of the track segment <NUM>. The sensors <NUM> are positioned such that each of the position magnets <NUM> is proximate to the sensor as the mover <NUM> passes each sensor <NUM>. The sensors <NUM> are a suitable magnetic field detector including, for example, a Hall-Effect sensor, a magneto-diode, an anisotropic magnetoresistive (AMR) device, a giant magnetoresistive (GMR) device, a tunnel magnetoresistance (TMR) device, fluxgate sensor, or other microelectromechanical (MEMS) device configured to generate an electrical signal corresponding to the presence of a magnetic field. The magnetic field sensor <NUM> outputs a feedback signal provided to the segment controller <NUM> for the corresponding track segment <NUM> on which the sensor <NUM> is mounted. The feedback signal may be an analog signal provided to a feedback circuit <NUM> which, in turn, provides a signal to the processor <NUM> corresponding to the magnet <NUM> passing the sensor <NUM>.

According to another arrangement, illustrated in <FIG>, the position feedback system utilizes the drive magnets <NUM> as position magnets. Position sensors <NUM> are positioned along the track segment <NUM> at a location suitable to detect the magnetic field generated by the drive magnets <NUM>. According to the illustrated embodiment, the position sensors <NUM> are located below the coils <NUM>. Optionally, the position sensors <NUM> may be interspersed with the coils <NUM> and located, for example, in the center of a coil or between adjacent coils. According to still another embodiment, the position sensors <NUM> may be positioned within the upper portion <NUM> of the track segment <NUM> and near the bottom surface <NUM> of the channel <NUM> to be aligned with the drive magnets <NUM> as each mover <NUM> travels along the tracks segment <NUM>.

Referring again to <FIG>, the segment controller <NUM> also includes a communication interface <NUM> that receives communications from the central controller <NUM> and/or from adjacent segment controllers <NUM>. The communication interface <NUM> extracts data from the message packets on the industrial network and passes the data to a processor <NUM> executing in the segment controller <NUM>. The processor may be a microprocessor. Optionally, the processor <NUM> and/or a memory <NUM> within the segment controller <NUM> may be integrated on a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). It is contemplated that the processor <NUM> and memory <NUM> may each be a single electronic device or formed from multiple devices. The memory <NUM> may include volatile memory, non-volatile memory, or a combination thereof. The segment controller <NUM> receives the motion profile or desired motion of the movers <NUM> and utilizes the motion commands to control movers <NUM> along the track segment <NUM> controlled by that segment controller <NUM>.

Each segment controller <NUM> generates switching signals to generate a desired current and/or voltage at each coil <NUM> in the track segment <NUM> to achieve the desired motion of the movers <NUM>. The switching signals <NUM> control operation of switching devices <NUM> for the segment controller <NUM>. According to the illustrated system <NUM>, the segment controller <NUM> includes a dedicated gate driver module <NUM> which receives command signals from the processor <NUM>, such as a desired voltage and/or current to be generated in each coil <NUM>, and generates the switching signals <NUM>. Optionally, the processor <NUM> may incorporate the functions of the gate driver module <NUM> and directly generate the switching signals <NUM>. The switching devices <NUM> may be a solid-state device that is activated by the switching signal, including, but not limited to, transistors, thyristors, or silicon-controlled rectifiers.

According to the illustrated system <NUM>, the track <NUM> receives power from a distributed DC voltage. A DC bus <NUM> receives a DC voltage, VDC, from a DC supply and conducts the DC voltage to each track segment <NUM>. The illustrated DC bus <NUM> includes two voltage rails <NUM>, <NUM> across which the DC voltage is present. The DC supply may include, for example, a rectifier front end configured to receive a single or multi-phase AC voltage at an input and to convert the AC voltage to the DC voltage. It is contemplated that the rectifier section may be passive, including a diode bridge or, active, including, for example, transistors, thyristors, silicon-controlled rectifiers, or other controlled solid-state devices. Although illustrated external to the track segment <NUM>, it is contemplated that the DC bus <NUM> would extend within the lower portion <NUM> of the track segment. Each track segment <NUM> includes connectors to which either the DC supply or another track segment may be connected such that the DC bus <NUM> may extend for the length of the track <NUM>. Optionally, each track segment <NUM> may be configured to include a rectifier section (not shown) and receive an AC voltage input. The rectifier section in each track segment <NUM> may convert the AC voltage to a DC voltage utilized by the corresponding track segment.

The DC voltage from the DC bus <NUM> is provided at the input terminals <NUM>, <NUM> to a power section for the segment controller. A first voltage potential is present at the first input terminal <NUM> and a second voltage potential is present at the second input terminal <NUM>. The DC bus <NUM> extends into the power section defining a positive rail <NUM> and a negative rail <NUM> within the segment controller <NUM>. The terms positive and negative are used for reference herein and are not meant to be limiting. It is contemplated that the polarity of the DC voltage present between the input terminals <NUM>, <NUM> may be negative, such that the potential on the negative rail <NUM> is greater than the potential on the positive rail <NUM>. Each of the voltage rails <NUM>, <NUM> are configured to conduct a DC voltage having a desired potential, according to application requirements. According to one arrangement, the positive rail <NUM> may have a DC voltage at a positive potential and the negative rail <NUM> may have a DC voltage at ground potential. Optionally, the positive rail <NUM> may have a DC voltage at ground potential and the negative rail <NUM> may have a DC voltage at a negative potential. According to still another arrangement, the positive rail <NUM> may have a first DC voltage at a positive potential with respect to the ground potential and the negative rail <NUM> may have a second DC voltage at a negative potential with respect to the ground potential. The resulting DC voltage potential between the two rails <NUM>, <NUM> is the difference between the potential present on the positive rail <NUM> and the negative rail <NUM>.

It is further contemplated that the DC supply may include a third voltage rail having a third voltage potential. According to one implementation, the positive rail <NUM> has a positive voltage potential with respect to ground, the negative rail <NUM> has a negative voltage potential with respect to ground, and the third voltage rail is maintained at a ground potential. Optionally, the negative voltage rail <NUM> may be at a ground potential, the positive voltage rail <NUM> may be at a first positive voltage potential with respect to ground, and the third voltage rail may be at a second positive voltage potential with respect to ground, where the second positive voltage potential is approximately one half the magnitude of the first positive voltage potential. With such a split voltage DC bus, two of the switching devices <NUM> may be used in pairs to control operation of one coil <NUM> by alternately provide positive or negative voltages to one the coils <NUM>.

The power section in each segment controller <NUM> may include multiple legs, where each leg is connected in parallel between the positive rail <NUM> and the negative rail <NUM>. According to the illustrated system <NUM>, three legs are shown arranged in a half-bridge configuration. However, the number of legs may vary and will correspond to the number of coils <NUM> extending along the track segment <NUM>. Each leg includes a first switching device 245a and a second switching device 245b connected in series between the positive rail <NUM> and the negative rail <NUM> with a common connection <NUM> between the first and second switching devices 245a, 245b. The first switching device 245a in each leg <NUM> may also be referred to herein as an upper switch, and the second switching device 245b in each leg <NUM> may also be referred to herein as a lower switch. The terms upper and lower are relational only with respect to the schematic representation and are not intended to denote any particular physical relationship between the first and second switching devices 245a, 245b. The switching devices <NUM> include, for example, power semiconductor devices such as transistors, thyristors, and silicon-controlled rectifiers, which receive the switching signals <NUM> to turn on and/or off. Each of switching devices may further include a diode connected in a reverse parallel manner between the common connection <NUM> and either the positive or negative rail <NUM>, <NUM>.

According to the embodiment illustrated in <FIG>, three legs are shown arranged in a full-bridge configuration. Again, the number of legs may vary and will correspond to the number of coils <NUM> extending along the track segment <NUM>. Each leg includes a first switching device 245a and a second switching device 245b connected in series on one side of the coil <NUM>. The first and second switching devices 245a, 245b are connected between the positive rail <NUM> and the negative rail <NUM> with a first common connection between the first and second switching devices 245a, 245b. The first common connection is connected to the first side of the coil <NUM>. Each leg further includes a third switching device 246a and a fourth switching device 246b connected in series on the other side of the coil <NUM>. The third and fourth switching devices 246a, 246b are connected between the positive rail <NUM> and the negative rail <NUM> with a second common connection between the third and fourth switching devices 246a, 246b. The second common connection is connected to the second side of the coil <NUM>. The first and third switching devices 245a, 246a in each leg may also be referred to herein as upper switches, and the second and fourth switching devices 245b, 246b in each leg may also be referred to herein as lower switches. The terms upper and lower are relational only with respect to the schematic representation and are not intended to denote any particular physical relationship between the switching devices. The switching devices <NUM>, <NUM> include, for example, power semiconductor devices such as transistors, thyristors, and silicon-controlled rectifiers, which receive the switching signals <NUM> to turn on and/or off. Each of switching devices <NUM>, <NUM> may further include a diode connected in a reverse parallel manner between the first or second common connection and either the positive or negative rail <NUM>, <NUM>.

With reference again to <FIG>, the processor <NUM> also receives feedback signals from sensors providing an indication of the operating conditions within the power segment or of the operating conditions of a coil <NUM> connected to the power segment. According to the illustrated system <NUM>, the power segment includes a voltage sensor <NUM> and a current sensor <NUM> at the input of the power segment. The voltage sensor <NUM> generates a voltage feedback signal and the current sensor <NUM> generates a current feedback signal, where each feedback signal corresponds to the operating conditions on the positive rail <NUM>. The segment controller <NUM> also receives feedback signals corresponding to the operation of coils <NUM> connected to the power segment. A voltage sensor <NUM> and a current sensor <NUM> are connected in series with the coils <NUM> at each output of the power section. The voltage sensor <NUM> generates a voltage feedback signal and the current sensor <NUM> generates a current feedback signal, where each feedback signal corresponds to the operating condition of the corresponding coil <NUM>. The processor <NUM> executes a program stored on the memory device <NUM> to regulate the current and/or voltage supplied to each coil and the processor <NUM> and/or gate driver module <NUM> generates switching signals <NUM> which selectively enable/disable each of the switching devices <NUM> to achieve the desired current and/or voltage in each coil <NUM>. With reference also to <FIG>, it is contemplated that the feedback signals from the current sensor <NUM> and/or the voltage sensor <NUM> corresponding to the operation of the coils <NUM> may be provided to a dedicated current regulator device. As shown in <FIG>, the feedback signals are provided directly to the gate driver <NUM> which would, in turn, regulate the current output to each coil and generate the switching signals <NUM> accordingly. The energized coils <NUM> create an electromagnetic field that interacts with the drive magnets <NUM> on each mover <NUM> to control motion of the movers <NUM> along the track segment <NUM>.

In one operation, each track segment <NUM> is configured to control operation of each mover <NUM> present on the track segment <NUM>. The segment controller <NUM> receives a command signal corresponding to the desired operation of each mover <NUM> and controls the current output to each coil <NUM> to achieve the desired operation. With reference to <FIG>, one implementation of a control module <NUM> executable by the segment controller <NUM> is illustrated. The control module <NUM> receives a position command signal (x*) <NUM> as an input. The position command signal (x*) is compared to a position feedback signal (x) <NUM> at a first summing junction <NUM>. A position error signal <NUM> is output from the first summing junction <NUM> and input to a position loop controller <NUM>. According to <FIG>, the position loop controller <NUM> includes a proportional and an integral (PI) controller. Optionally, the position loop controller <NUM> may be just a proportional (P) controller or further include a derivative (D) controller. Each of the proportional (P), integral (I), and/or derivative (D) controllers of the position loop controller <NUM> includes a controller gain value. The controller gain values are commonly referred to as a proportional gain (Kpp), integral gain (Kpi), and a derivative gain (Kpd). The output of the position loop controller <NUM> is a velocity reference signal (v*) <NUM>.

The velocity reference signal (v*) <NUM> is compared to a velocity feedback signal (v) <NUM> at a second summing junction <NUM>. The velocity feedback signal (v) <NUM> is generated by a derivative block <NUM> acting on the position feedback signal <NUM>. A velocity error <NUM> signal is output from the second summing junction <NUM> and input to a velocity loop controller <NUM>. According to <FIG>, the velocity loop controller <NUM> includes a proportional and an integral (PI) controller. Optionally, the velocity loop controller <NUM> may be just a proportional (P) controller or further include a derivative (D) controller. Each of the proportional (P), integral (I), and/or derivative (D) controllers of the velocity loop controller <NUM> includes a controller gain value. The controller gain values are commonly referred to as a proportional gain (Kvp), integral gain (Kvi), and a derivative gain (Kvd). The output of the velocity loop controller <NUM> is an acceleration reference signal (a*) <NUM>.

The acceleration reference signal <NUM> is passed through an additional gain and filter block <NUM>. The gain and filter block <NUM> may include one or more filters to remove unwanted components from the control system. For example, a low pass filter may be provided to attenuate undesirable high frequency components and a notch filter to attenuate specific frequency components having an undesirable effect on the controlled mechanical load. The gain and filter block <NUM> may also include an inertial gain factor or a torque constant gain factor. An inertial gain factor converts the acceleration reference to a torque reference and the torque constant gain factor converts a torque reference to a current reference, I*, <NUM>. Optionally, gain factors may be incorporated into a single gain or incorporated with filter or controller gains. Combining the inertial and/or torque constant gain factors together or with another controller gain or with the filter gain reduces the real time computational burden imposed on the segment controller <NUM>.

The current reference, I*, <NUM> is, in turn, passed to a current regulator <NUM>, which controls the current supplied to each coil <NUM> on the track segment. The current regulator <NUM> receives current feedback signals <NUM> from the current sensors <NUM> and position feedback information <NUM> identifying the measured position of each mover <NUM> or a compensated position of each mover, as will be discussed in more detail below. Because a mover <NUM> may span multiple coils <NUM>, the current regulator <NUM> determines an appropriate current for each coil <NUM> to produce the force desired to control the mover as indicated by the current reference, I*, <NUM> and determines a resultant current desired for each coil <NUM>. The current regulator <NUM> uses the current and position feedback information, <NUM> and <NUM>, to regulate the current to each coil <NUM>, accordingly.

The output of the current regulator <NUM> is provided as an input to the gate driver module <NUM>. With reference again to <FIG>, the gate driver module <NUM> converts the input to a desired output voltage having a variable amplitude and frequency. Having determined the desired output voltage required to produce the commanded input, the gate driver module <NUM> generates the gating signals <NUM> used by pulse width modulation (PWM) or by other modulation techniques to control the switching elements 245A, 245B to produce the desired currents in each coil <NUM>, resulting in the desired motion for each mover <NUM>. As illustrated in <FIG> and as discussed above, the control module <NUM> utilizes position feedback information to regulate the current output to each coil <NUM>.

In operation, a controller for the independent cart system <NUM> is configured to monitor disturbance forces present on a mover <NUM> as it travels along a track <NUM> in the independent cart system. Turning next to <FIG>, a flow diagram <NUM> for one embodiment of the method for monitoring disturbance forces present on the mover <NUM> is illustrated. For purposes of discussion, it is contemplated that the method is executing on the independent cart system <NUM> illustrated in <FIG>. Each segment controller <NUM> is configured to monitor disturbance forces of each mover <NUM> present on the corresponding track segment <NUM>. As will be discussed in more detail below, compensation of the disturbance forces will be discussed with respect to execution by the segment controllers <NUM>. Optionally a central controller <NUM> may be configured to monitor and/or compensate for disturbance forces present along multiple track segments or along the entire track <NUM>. It is contemplated that various steps of the illustrated process may be executed on the segment controller <NUM> or on the central controller <NUM> without deviating from the scope of the invention.

With reference also to <FIG>, a current regulator <NUM> executing in the segment controller <NUM> periodically samples position feedback signals <NUM> and current feedback signals <NUM>. As previously discussed, the current reference, I*, <NUM> corresponds to a current required in the linear drive system to propel a mover. This current may, however, need to be supplied by different coils <NUM> along the track as a function of the position of the mover <NUM> along each track segment <NUM>. Similarly, the total current feedback may need to be combined using current feedback signals <NUM> from multiple coils <NUM> as a function of the position of the mover <NUM> along each track segment before comparing the measured current <NUM> to the current reference <NUM>. A transform function <NUM> may be provided in the current regulator <NUM> to convert the measured current from each current feedback signal <NUM> to a total measured current <NUM> as a function of the position feedback signal <NUM> which is also provided to the transform function <NUM>. It is further contemplated that current regulation may be achieved in a reference frame other than a physical reference frame, such as a d-q reference frame. The d-q reference frame defines current as a flux producing component (i.e., the d-axis current) and a torque producing component (i.e., the q-axis current). Traditional control techniques may be applied to each of the flux producing and the torque producing components to achieve a desired flux and a desired torque in the linear drive system. Conversion between reference frames is also dependent on measured current feedback signals <NUM> and the physical location of the mover <NUM> as determined by position feedback signals <NUM>. The transform function <NUM> my further include any necessary reference frame transformations required by the current regulator <NUM>.

Turning again to <FIG>, data used to determine the disturbance force is sampled as shown in step <NUM>. The disturbance force is determined as a function of the current reference <NUM> and of either a sampled position of the mover <NUM>, sampled velocity of the mover, or a combination thereof. It is desirable that the current reference value <NUM> correspond to the sampling instant for the sample position or velocity. At the sampling instant, the sample position and/or sampled velocity and the current reference signal <NUM> may be stored in memory <NUM> of the segment controller <NUM> for subsequent use in determining the disturbance force.

At step <NUM>, the segment controller <NUM> may check whether any prior data regarding a disturbance force for the present location of a mover <NUM> travelling on the track segment <NUM>. If a prior disturbance force has been stored, the segment may generate a current compensation signal <NUM>, as will be discussed in more detail below. If a prior disturbance force has not been stored for the mover <NUM> at the present location, this is an initial calculation of a disturbance force expected at the location for the mover <NUM>. As shown in steps <NUM> and <NUM>, the segment controller <NUM> determines a disturbance force for the mover <NUM> at the present location and stores the disturbance force in memory <NUM>. Determination of the disturbance force may be performed using Equations (<NUM>)-(<NUM>) as shown below. <MAT> where:.

As indicated above, d<NUM>, d<NUM>, and d are each calculations of an acceleration present in the system as a result of the mover <NUM> experiencing a disturbance force. As is well understood by Newton's second law of motion, a force is determined by multiplying acceleration by mass. If it is desired to put the above equations in terms of a disturbance force, each of the terms may be multiplied by the mass, M, present for each mover or for the mover and payload present on the mover. However, for implementation in a motor controller, it may be desirable to utilize the equations in terms of the acceleration. As utilized herein, Equations <NUM>-<NUM> will be referenced as determining a disturbance force. However, it is understood that the equations determine an acceleration and that the relationship between the disturbance acceleration and the force is a multiple of the mass present for each mover.

The first equation uses sampled position feedback information <NUM> in order to determine a first value of a disturbance force, d<NUM>, experienced by the mover <NUM>. As noted in Equation <NUM>, samples of the position feedback information for three consecutive sampling positions are required prior to determining a value of the disturbance force, d<NUM>, for the middle of the three sampled positions. At each sampling instant, the current reference <NUM> at that sampling instant is stored with the sampled position. The current reference <NUM> may subsequently be used to determine the first value of the disturbance force, d<NUM>, after the next sampling instant has captured the next position information. The first value of the disturbance force, d<NUM>, is stored along with the corresponding position and a second value of the disturbance force, d<NUM>, experienced by the mover <NUM> may be calculated. As noted in Equation <NUM>, samples of the velocity position feedback information for two consecutive sampling positions are required prior to determining the second value of the disturbance force, d<NUM>, for the first of the pair of sampled velocities. The velocity feedback signal may be determined as a function of the sampled position using, for example, the velocity feedback signal <NUM> generated by the derivative block <NUM> acting on the position feedback signal <NUM> in the control module <NUM>. Optionally, the feedback circuit <NUM> may be configured to generate a velocity feedback signal as a function of the signals received from the sensors <NUM> positioned along track segment <NUM>. According to yet another option, the sensors <NUM> may be configured to generate a velocity feedback signal as a function of the rate of change of the magnetic field detected as the position magnet <NUM> passes each sensor. Similar to sampling the position feedback signal, the current reference <NUM> is sampled at each instant in time with the sampled velocity feedback signal in order to determine the second value of the disturbance force. According to one embodiment of the invention, the position feedback information and the velocity feedback information are sampled in tandem and a single value of the current reference signal <NUM> is stored with both sampled values for use in determining both the first and the second values of the disturbance force.

The final value of the disturbance force, d, experienced by each mover <NUM> at a location along the track is determined as a function of both the first value of the disturbance force, d<NUM>, and of the second value of the disturbance force, d<NUM>. As seen in Equation <NUM>, the final value of the disturbance force, d, is determined as a weighted average of the first value of the disturbance force, d<NUM>, and of the second value of the disturbance force, d<NUM>. A weighting factor, w, is set to a value between zero (<NUM>) and one (<NUM>). For an equal weighting between first value of the disturbance force, d<NUM>, and the second value of the disturbance force, d<NUM>, the weighting value is set to one-half (<NUM>). In some applications, either the first disturbance force calculation, d<NUM>, taken as a function of position, or the second disturbance force calculation, d<NUM>, taken as a function of velocity may be more accurate or one of the feedback signals may be subject to a greater level of noise or uncertainty. Initially, the weighting value, w, may be set to one-half. However, the weighting value, w, may be a configurable parameter stored in memory <NUM> of the segment controller <NUM>. It may be desirable to adjust the weighting value, w, to a value greater than one-half in applications where the position feedback signal is more reliable and to a value less than one-half in applications where the velocity feedback signal is more reliable. After determining a final value of the disturbance force, d, the segment controller <NUM> may store the value of the disturbance force, a corresponding location and mover identification, along with the sampled feedback signals and the current reference in memory <NUM>. The stored data may then be used during subsequent runs of the mover <NUM> over the same position.

If it was determined at step <NUM> that data has been previously stored for the mover <NUM>, the segment controller <NUM> may next determine whether compensation for the previously measured disturbance force, d, is desired, as shown in step <NUM>. Initially, it may be desirable to allow for multiple runs of the mover <NUM> across a track segment <NUM> before compensating for disturbance forces. As will be discussed in more detail below, subsequent runs of a mover <NUM> may be used to adapt the observed value of the disturbance force, d, to a more accurate value. It is contemplated that a counter may be utilized such that the mover <NUM> may travel a predefined number of times (e.g., <NUM>-<NUM> or more) across a track segment <NUM> before beginning to compensate for a measured disturbance force. In other applications, it may be acceptable to begin compensation after a single run across a track segment <NUM>. In still other applications, it may be undesirable to ever compensate for the disturbance force. Rather, the level of the disturbance force may be monitored over time for change and may be utilized to provide an indication of wear and/or required maintenance for the mover <NUM> and/or track segment <NUM>.

If compensation of the determined disturbance force is desired, the segment controller <NUM> may execute steps <NUM>, <NUM>, and <NUM> shown in <FIG>. At step <NUM>, the segment controller <NUM> reads the value of the disturbance force, d, which was previously determined for the mover <NUM> at the present location of the mover. It is contemplated that a segment controller <NUM> may maintain a look-up table containing values of a disturbance force, d, observed by each mover <NUM> in the system for each location along the length of the track segment <NUM>. With reference also to <FIG>, a graph <NUM> of an exemplary disturbance force experienced by one mover over a portion of the length of a track segment <NUM> is illustrated. The plot <NUM> shows a variation in the disturbance force experienced by the mover <NUM> as a function of the mover position along the track segment <NUM>. Based on prior measured values of disturbance force, d, the segment controller <NUM> determines a current compensation value, Icomp, <NUM> that may be added to the current regulator <NUM>. As seen in <FIG>, the current compensation value, Icomp, <NUM> may be added to the current reference <NUM> and current feedback <NUM> signals at a summing junction <NUM> prior to entering the current loop controller <NUM>. According to <FIG>, the current loop controller <NUM> includes a proportional and an integral (PI) controller. Optionally, the current loop controller <NUM> may be just a proportional (P) controller or further include a derivative (D) controller. Each of the proportional (P), integral (<NUM>), and/or derivative (D) controllers of the current loop controller <NUM> includes a controller gain value. The controller gain values are commonly referred to as a proportional gain (Kip), integral gain (Kii), and a derivative gain (Kid). The output of the current loop controller <NUM> is a desired current, Idesired, <NUM> which is, in turn, used to determine a desired current for each coil <NUM> along the track.

With the addition of the current compensation value <NUM>, the overall disturbance force is compensated, resulting in a reduction of variation in the velocity of the mover <NUM> as shown in <FIG> includes a graph <NUM> with a velocity plot <NUM> showing the velocity of a mover <NUM> as it travels along three track segments <NUM>. The first portion <NUM> and the third portion <NUM> of the velocity plot <NUM> are taken along track segments <NUM> where the corresponding segment controller <NUM> is not compensating for disturbance forces. The second portion <NUM> of the velocity plot <NUM> is taken along a track segment <NUM> which is compensating for disturbance forces. A first transition point <NUM> and a second transition point <NUM> are also illustrated, which indicate a higher level of velocity ripple occurring during a transition between track segments <NUM>. It may be observed from <FIG>, that compensating for the measured disturbance force, d, reduces the overall velocity ripple experienced by a mover <NUM> as it travels along a track segment <NUM>.

Returning again to <FIG>, the segment controller <NUM> next determines a new value of the disturbance force, d, as shown in step <NUM>. The disturbance force, d, is determined as discussed above with respect to step <NUM> and as shown in Equations <NUM>-<NUM>.

At step <NUM>, the segment controller checks whether it is configured to adapt the stored value of the disturbance force, d, as shown in step <NUM>. In many applications, it will be desirable to adapt the stored value of the disturbance force for a given mover <NUM> as the mover makes subsequent runs over the same location. As shown in steps <NUM> and <NUM>, the previously stored value may be adjusted and a new value for the disturbance force, d, stored in memory <NUM> of the segment controller <NUM>. The previous value of the disturbance force, d, may be adjusted, for example, by averaging multiple values of the disturbance force, d, measured for a mover <NUM> at the same location along the track segment <NUM>. Optionally, a comparison method may be implemented where the current compensation value <NUM> supplied to the current regulator <NUM> is increased or decreased on subsequent runs of the mover <NUM> and the resultant torque or velocity ripple is evaluated to determine whether the magnitude of the ripple increased or decreased. Still other methods of dynamically adapting the stored value of the disturbance force, d, over multiple runs may be utilized without deviating from the scope of the invention. Having the segment controller <NUM> dynamically adapt the stored value of the disturbance force, d, over multiple runs improves the accuracy of the stored value and may allow the segment controller <NUM> to monitor for changes in the disturbance force over time.

In some applications, however, it may be desirable to perform an initial commissioning run and not change the stored value of the disturbance force, d, over time. Certain applications may prefer consistent operation rather than dynamic adaptation. In those applications, the learning option checked at step <NUM> may be set to disabled and steps <NUM> and <NUM> may be bypassed. If dynamic adjustment of the disturbance force, d, is not selected, it will be desirable to obtain as accurate a value of the disturbance force, d, as possible during an initial commissioning run of the system. In other applications, it may be desirable to perform a commissioning run to determine an initial value of the disturbance force and, in combination with this initial value, still adapt the stored value based on subsequent runs of the movers <NUM> along the track <NUM>.

In either application, the commissioning run may be configured to command movers <NUM> to run at a very slow speed along the length of the track <NUM>. The segment controller <NUM> for each track segment <NUM> may create a look-up table for each mover with stored values of the disturbance force observed along the length of the corresponding track segment <NUM>. To obtain a more accurate characterization of the disturbance force experienced by each mover <NUM> as it travels along a track segment, the mover <NUM> may be commanded to travel at a slow speed. The speed may be selected, for example, in the range of one millimeter per second to five millimeters per second. Referring again to Equations <NUM> and <NUM> again, it is noted that at a very slow rate of travel, the first term in each equation will be approximately zero because the change in position or the change in velocity over the sampling interval will be very small, and both equations reduce to Equation <NUM> shown below. Further, because Equations <NUM> and <NUM> are identical, Equation <NUM>, as a weighted value of Equations <NUM> and <NUM>, also reduces to Equation <NUM> below. During a slow-speed commissioning run, therefore, the disturbance force, d, is determined as a factor of the commanded current and of two known values for the mover.

At step <NUM>, the segment controller <NUM> checks whether it is configured to monitor for a change in the disturbance force, d, over time. If the segment controller <NUM> is not configured to monitor for the change in disturbance force, the disturbance force routine may jump to the end <NUM> and will execute at the periodic sampling interval. If the segment controller <NUM> is configured to monitor for the change in disturbance force, d, execution continues at step <NUM> by comparing the value of the disturbance force determined for a mover <NUM> against an initial value of the disturbance force. The initial value may have been determined using the commissioning run discussed above or may have been established by one or more runs of the mover <NUM> along the track segment <NUM>. Once an initial set of values for the disturbance force have been determined for a mover <NUM>, they may be stored in memory <NUM>. During subsequent runs of the mover <NUM>, it is contemplated that the disturbance force determined in the subsequent runs may be compared to the initial set of values. At step <NUM>, the difference between the disturbance force determined for the present run and the initial value is compared to a predefined threshold. If the difference exceeds the threshold, a message is generated, as shown in step <NUM>. The message may be transmitted to a user interface to alert a technician that maintenance or repair of the track segment <NUM> may be required. It is contemplated, that the disturbance force determined on the present run of the mover <NUM> may be compared to the stored value of the initial run on a point-by-point basis for specific locations. Optionally, an average value of the amplitude or of a peak-to-peak amplitude for the velocity or torque ripple may be compared. A change in the disturbance force, d, over time may indicate wear on a bearing of the mover <NUM> or on a rail of the track segment, damage to the mover or track, or a change in the environmental conditions in which the mover <NUM> is operating.

It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.

Claim 1:
A method for monitoring a disturbance force in a linear drive system (<NUM>), wherein a disturbance force is a force generated within or external to a linear drive system that causes a mover (<NUM>) to slow down or speed up, deviating from a desired speed, the method comprising the steps of:
generating a commanded current to be provided to a series of coils (<NUM>) spaced along a length of a track (<NUM>) in the linear drive system with a controller (<NUM>, <NUM>);
regulating a desired current (<NUM>) provided to each of the series of coils with the controller, wherein the desired current corresponds to the commanded current and establishes an electromagnetic field that interacts with at least one mover in the linear drive system to propel the mover along the track;
receiving a feedback signal at the controller, wherein the feedback signal is a measured position, a measured velocity, or both a measured position and a measured velocity of the at least one mover as it is propelled along the track by the desired current;
storing the feedback signal and the commanded current at a corresponding sample time of the feedback signal in memory of the controller; and
determining a disturbance force experienced by the at least one mover at a plurality of positions along the track, wherein the disturbance force is determined by the controller and is a function of the commanded current and the stored feedback signal, wherein:
the controller generates the commanded current to obtain a desired interaction between the at least one mover and the electromagnetic field; and
the disturbance force is determined for the at least one mover while the controller is controlling the at least one mover to interact with the electromagnetic field.