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 highspeed 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.

For some implementations, a motion control system includes a distributed control system. In such a system, each mover is individually controlled by the track segment on which the vehicle travels. As the mover moves from one track segment to another track segment, the motion control and tracking of the mover are handed off from one segment to the other. At the track segment junctions, the physical gap among segment coils posts particular challenges to motion control.

First, the absence of an active driving coil at the segment junction results in the reduction in thrust available for mover control. Second, with iron-core movers, the air gap at the segment junction also represents the disruption of cogging force patterns due to the order of magnitude differences in magnetic permeability between the iron core and air. Third, the discrepancies between adjacent movers in a mover position feedback signal and controller timing results in uncertainties in system dynamics.

As a result, track portions around the segment junctions are declared "no-station zones," which refer to portions of the track that actuators should not interact with a mover (e.g., to load or unload the mover). The inclusion of no-station zones limits flexibility with customer system design and increases system cost and floor space. Track designers desire a better system to reduce or remove "no-station zones," thereby decreasing system cost and improving floor space. Thus, it would be desirable to provide an improved method and system for controlling operation of the mover as it transitions between track segments to reduce pulsations occurring during the transition.

<CIT> discloses conveying system including: a linear induction motor including a stator provided with a plurality of primary coils arranged along a conveying path and a mover provided movably along the conveying path; one or more first inverters that are provided corresponding to at least one of the primary coils in one or more areas requiring positioning on the conveying path to perform vector control with a photo sensor (abstract).

<CIT> discloses a transport unit of a long stator linear motor transiting from a first control zone to a following second control zone in a movement direction, wherein a first segment control unit is responsible for controlling the movement of the transport unit and the first control zone is extended, in the movement direction, by a number of virtual drive coils. The first segment control unit assigned to the first control zone, calculates manipulated variables for the virtual drive coils, and transmits the manipulated variables for the virtual drive coils to the second segment control unit, which is assigned to the second control zone.

<CIT> discloses a method for controlling moving elements including: communicating data related to control of the moving element conveyor between a zone controller and at least one first motor gateway and at least one second motor gateway, wherein the data is communicated in a structured manner to compensate for network or processing timing.

<CIT> discloses a moving-magnet type linear motor comprising a plurality of moving elements travelling along a track; and a stator armature provided along the entire travelling track of moving elements, wherein each moving element travels separately and independently and comprises a number of permanent magnets disposed face to face with the stator armature.

It is the object of the present invention to provide an improved solution for mover transport systems.

Embodiments of the invention disclose a motion control system that automatically transitions between a first control with first gain values for positions in track segments and a second control with second gain values for position around segment junctions. Optimal motion performances are achieved through the entire track without the intervention of the user.

In some implementations, each track segment is divided into at least two zones. The segment includes a first zone or zones near one or more track segment junction and the remainder of the track segment is defined as a second zone. In a specific implementation, two groups of a proportional-integral-derivative (PID) controllers, PIDA and PIDB, are configured for optimized motion performances in the first zone(s) and the second zone, respectively. In a further implementation, a transition zone can be used to address hysteresis behavior when switching between the two PID controllers.

According to one embodiment of the invention, a transport system comprising a mover having an axis, and a track. The track includes a first track segment including a first coil, a second track segment adjacent to the first track segment and including a second coil, and a controller operative to drive the first coil to control movement of the mover along the first track segment towards the second track segment. The controller is further operative to define a first zone for the first track segment having a first set of controller gain values, define a second zone for the first track segment having a second set of controller gain values, drive the first coil to control movement of the mover with the first set of controller gain values when the location of the axis is in the first zone, and drive the first coil to control movement of the mover with the second set of controller gain values when the location of the axis is in the second zone.

According to another embodiment of the invention, a method to extend range of operations in an independent mover transport system. The transport system can include a mover having an axis, a track comprising a first track segment including a first coil, the track comprising a second track segment adjacent to the first track segment and including a second coil, and a controller operative to drive the first coil to control movement of the mover along the first track segment towards the second track segment. The method includes moving the mover along the track, defining a first zone for the first track segment having a first set of controller gain values, defining a second zone for the first track segment having a second set of controller gain values, driving the first coil to control movement of the mover with the first set of controller gain values when the location of the axis is in the first zone, and driving the first coil to control movement of the mover with the second set of controller gain values when the location of the axis is in the second zone.

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. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

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 <NUM>, which may also be referred to in some implementations as a linear motor, is incorporated in part on each mover <NUM> and in part within each track segment <NUM>. One or more drive magnets <NUM> are mounted to each mover <NUM>. 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>. 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 within 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. 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 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 and either the positive or negative rail <NUM>, <NUM>.

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>. 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 from the current sensors <NUM> and position feedback information 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 <NUM> and <NUM> information 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>.

Turning next to <FIG> and <FIG> and according to one construction of the system <NUM>, each track segment <NUM> is one meter (<NUM>) in length. As a mover <NUM> travels along the track, each track segment <NUM> is defined within the central controller as having a position that corresponds to the one meter length. For example, a first track segment <NUM> is assigned the position from zero to one meter. A second track segment <NUM> is assigned the position from one meter to two meters. A third track segment <NUM> is assigned the position from two meters to three meters and so on. Ideally, a second end of the leading track segment 15C is positioned tightly against a first end of the following track segment 15B to provide a smooth transition between track segments. However, as a result of tolerances, the gaps <NUM> exist among the track segments <NUM>. The gaps <NUM> may be, for example, only one millimeter or may vary from several millimeters up to tens of millimeters. Similarly, the gaps <NUM>, for example, may purposely vary to much larger distances to save on system <NUM> cost. These gaps <NUM> introduce motion noise within the transport system <NUM>. Motion noise refers to a disturbance in the movement of a mover <NUM> along the track <NUM> of the transport system <NUM>.

As just described, motion noise may be caused by a mechanical imperfection. Another motion noise may be caused by an electro-magnetic imperfection. For example, another potential source of motion noise is a linear drive system gap <NUM> between the coils 115B and 115C of the two track segments 15B and 15C. Ideally, the ends of the coils <NUM> of the linear drive systems <NUM> are positioned tightly to the ends of the track segments <NUM>. However, similar to mechanical gap tolerances, the ends of the coils <NUM> may not be positioned tightly to the ends of the track segments <NUM>. The linear drive system gap <NUM> results in electro-magnetic imperfection, thereby providing additional motion noise. Additionally, the linear drive system gap <NUM> results in a loss of thrust applied to the mover <NUM> as it transitions between adjacent track segments <NUM> since there are fewer coils <NUM> present under the movers magnet array <NUM> than when the mover <NUM> is positioned fully over the drive coils <NUM> and a subsequently reduced electromagnetic force present in the gap to interact with the magnet array <NUM>.

Motion of a mover <NUM> as it crosses junction <NUM> will be discussed with respect to an exemplary mover <NUM> and track segments 15B and 15C illustrated in <FIG> and <FIG>. It will be assumed that the first track segment 15B is assigned a location along the track <NUM> of one meter to two meters (<NUM>-<NUM>) and the second track segment 15C assigned a location along the track <NUM> of two meters to three meters (<NUM>-<NUM>). A position gap <NUM> exists at the junction <NUM> between the two track segments 15B and 15C. An electro-magnetic gap <NUM> exists between the two sets of coils 115B and 115C.

A center axis <NUM> of the mover <NUM> and a center line <NUM> of the junction <NUM> are each illustrated in <FIG> and <FIG>. As the mover <NUM> travels from the first segment 15B to the second segment 15C, the center axis <NUM> of the mover <NUM> is initially located over the first segment 15B while a forward edge of the mover <NUM> crosses the junction <NUM> and is located on the second segment 15B, as shown in <FIG>. At the midpoint in the crossing, as shown in <FIG>, the center axis <NUM> of the mover <NUM> is aligned with the center line <NUM> of the junction <NUM> between the two segments 15B, 15C, and an equal portion of the mover <NUM> is located on each segment. As the mover <NUM> continues across the junction <NUM>, the center axis <NUM> and a greater portion of the mover <NUM> is present on the second segment 15B and the trailing edge of the mover <NUM> remains of the first segment 15B. Eventually, the mover <NUM> continues moving until the entire mover <NUM> is located over the second segment 15B.

As a mover <NUM> approaches the gap <NUM>, the segment controller <NUM> for the first track segment 15B initially controls current output to coils 115B of the first track segment 15B for controlling motion of the mover <NUM>. The first segment 15B remains responsible for control of the mover <NUM> until the mover reaches the middle point shown in <FIG>. As the center axis <NUM> of the mover <NUM> crosses the center line <NUM> of the junction <NUM>, control of the mover <NUM> is passed from the segment controller <NUM> of the first segment 15B to the segment controller <NUM> of the second segment 15C.

In order for control of the mover <NUM> to transition between segments, both segments 15B and 15C must have knowledge of the position of the mover <NUM>. As illustrated in <FIG>, the mover <NUM> includes an array of position magnets <NUM> spaced along the length of the mover <NUM>. The center axis <NUM> of the mover <NUM> is positioned over the first segment 15B, and therefore, the segment controller in the first segment 15B is responsible for control of the mover <NUM>. A first portion of the position magnets <NUM> in the magnet array are located over the first segment 15B and a second portion of the position magnets <NUM> in the magnet array are located over the second segment 15C. The position sensors <NUM> (<FIG>), spaced along the length of both segments are able to detect the position magnets <NUM> located over the respective segment. The segment controller <NUM> in both segments receives position feedback signals from those position sensors <NUM> that are able to detect one of the position magnets <NUM> and generates a value for the position of the mover <NUM> responsive to those position feedback signals.

Referring back to <FIG>, each segment controller <NUM> may use a PID controller for controlling the mover <NUM> while the mover <NUM> is within the region <NUM> or on the segment <NUM>. The controller gain values for the PID controller are commonly referred to as a proportional gain (Kpp), integral gain (Kpi), and derivative gain (Kpd). Other control techniques and other controller gain values can be used in alternative to or in combination with the PID gain values.

Now with reference to <FIG>, the graph shows a mover <NUM> moving through a three track system from zero to three meters. The track <NUM> has four stops. The first stop is at <NUM> meters, the second stop is at <NUM> meters, the third stop is at <NUM> meters, and the fourth stop is at <NUM> meters. Using a first set of gain values optimized for in-section movement and settling, the resulting settling error is shown in <FIG>. As shown in <FIG>, track portions around the junctions <NUM> (which fall within the linear drive system gap <NUM>) are typically defined as "no-station zones" due to changes in thrust and reluctance force pattern. This results in limiting flexibility in track system design and increasing system cost and floor space.

In alternative to using the first set of gain values for <FIG>, a second set of gain values can be optimized for over junction <NUM> settling. Performing the same movements as <FIG>, the settling error for a mover <NUM> for the second set of gain values being optimized for over the junction settling. The result is a significant improvement for settling in track portions around the junction <NUM>, but also an introduction of significant settling issues in the middle of each track section <NUM>. Accordingly, the solution is worse than the problem in <FIG> since the linear drive system gaps <NUM> are typically a small portion of the track segments <NUM> compared to the portions of the track segments that include coils <NUM>.

In embodiments of the invention, a transport system <NUM> automatically transitions between controller gain values (e.g., PID gain values) for positions in segments <NUM> and around junctions <NUM>. Optimal motion performances are achieved through the entire track <NUM> without the intervention of the user. A center axis <NUM> of the mover <NUM> and a center line <NUM> of the junction <NUM> are each illustrated in 14A-14F. As the mover <NUM> travels from the first segment 15B to the second segment 15C, a plurality of zones are defined for each segment 15B and 15C. When the center axis <NUM> of the mover <NUM> is located in the first zone <NUM> (<FIG>), the segment controller <NUM> of segment 15B uses a first set of controller gain values for the first zone <NUM>. When the center axis <NUM> of the mover <NUM> is located in the third zone <NUM> (<FIG>), the segment controller <NUM> of segment 15C also uses the first set of controller gain values the first zone <NUM>. However, before proceeding further, it should be noted that the set of controller gain values in the third zone <NUM> may alternatively be different from the set of controller gain values in the first zone <NUM>. Using unique controller gain values for each zone <NUM> and <NUM> leads to a more complex solution, while using the same controller gain values in zones <NUM> and <NUM> leads to a more simplistic solution. For the remainder of this disclosure, it will be assumed that the controller gain values for zone <NUM> will be the same as the controller gain values for zone <NUM>.

When the center axis <NUM> of the mover <NUM> is located in the second zone <NUM> (<FIG>), the segment controllers <NUM> of segments 15B and 15C use the second set of gain values for zone <NUM>. The second zone <NUM> may be a different size from the linear drive system gap <NUM>, but may also be the same size as the linear drive system gap <NUM>. Whether a coil <NUM> of segment 15B and/or 15C is energized can depend on the implementation discussed with reference to <FIG>. Regardless, embodiments of the present invention use at least two different controller gain values for each segment <NUM>. The first set of controller gain values for zone <NUM> (and zone <NUM>) correspond to in section movement and settling, as discussed with <FIG>. The second set of controller gain values for zone <NUM> correspond to over junction <NUM> movement and settling, as discussed with <FIG>.

<FIG> provides the results of a test for a mover <NUM> performing the same movements in <FIG>, however the track <NUM> includes multiple zoned controllers. More specifically, each segment controller <NUM> includes a first zone operation optimized for in-segment operation and a second zone operation optimized for an in-junction operation (i.e., operation similar to what was discussed for <FIG>). By the automatic application of multiple controllers (e.g., PID controllers with different PID gain values) optimized for specified zones in the track, consistent motion performances can be achieved over stations both in-segment and in-gap. <FIG> show the settling error for a mover <NUM> of an improved system incorporating the invention.

In the further implementation shown in <FIG>, another zone, referred to herein as a transition zone <NUM>, is included between zones <NUM> and <NUM>. Instantaneous transitions, as described in connection with <FIG>, provide a significant improvement over the prior art, as shown in <FIG>. However, instantaneous transitions can lead to bad behavior at positions where the transition occurs. This can be seen in <FIG> where some motion noise still occurs when the mover is first settling, particularly when the station is near the gap <NUM>. For <FIG>, a second transition zone <NUM> is included between zones <NUM> and <NUM>. When the mover <NUM> is in the transition zone <NUM>, the segment controller <NUM> for segment 15B transitions between the controller gain values of zone <NUM> and the gain values of zone <NUM>. When the mover is in the transition zone <NUM>, the segment controller <NUM> for segment 15C transitions between the controller gain values of zone <NUM> and the gain values of zone <NUM>. The transition may be linear or nonlinear.

<FIG> represent controller gain values <NUM> for a PID gain linearly transitioning from a first gain value to a second gain value. The segment controller <NUM> only needs to know the first gain value and the second gain value and can linearly interpolate between the two values based on position. The effective gain <NUM> and the coverage (and thrust constant) <NUM> resulting from the controller gain values <NUM>, in one implantation, is also shown in <FIG>. The coverage, and resultant thrust constant, decrease as the mover travels over the linear drive system gaps <NUM>. However, by increasing the controller gain values <NUM>, the effective gain in the controller remains approximately constant. In some cases, it is desirable to slowly (or quickly) increase bandwidth. As a result, some transitions for controller gain values may be non-linear (e.g., squared).

In another implementation, the transition zone may alternatively be a hysteresis zone <NUM>. <FIG> represents controller gain values <NUM> for two PID gains as a mover moves between two zones <NUM> and <NUM>. Using a hysteresis zone <NUM> helps to prevent gain values flipping back and forth at the transition location since the mover <NUM> must travel back or forth a distance before flipping to the other value. In a specific implementation, the hysteresis zone <NUM> is less than one-half the length of the smaller of zones <NUM> and <NUM>. When the axis <NUM> of the mover <NUM> is within zone <NUM>, but not zone <NUM>, then the controller gain values of zone <NUM> are used. When the axis <NUM> of the mover <NUM> is within zone <NUM>, but not zone <NUM>, then the controller gain values of zone <NUM> are used. If the mover <NUM> is moving under the controller gain values of zone <NUM>, then the controller gain values only switch to the controller gain values of zone <NUM> when the axis <NUM> of mover <NUM> moves though zone <NUM> into the neighboring zone <NUM>. If the mover <NUM> is moving under the controller gain values of zone <NUM>, then the controller gain values only switch to the controller gain values of zone <NUM> when the axis <NUM> of mover <NUM> moves though zone <NUM> into the neighboring zone <NUM>.

Claim 1:
A transport system (<NUM>) comprising:
a mover (<NUM>) having an axis (<NUM>); and
a track (<NUM>) comprising:
a first track segment (15B) including a first coil (<NUM>);
a second track segment (15C) adjacent to the first track segment and including a second coil (<NUM>); and
a controller (<NUM>) operative to drive the first coil to control movement of the mover along the first track segment towards the second track segment, wherein the controller includes a proportional-integral-derivative ,PID, controller, the controller being characterized by being further operative to
define a first zone (<NUM>) for the first track segment having a first set of controller gain values, wherein the first set of controller gain values includes a first proportional gain value, a first integral gain value, and a first derivative gain value, wherein the first set of controller gain values for the first zone (<NUM>) correspond to in section movement and settling,
define a second zone (<NUM>) for the first track segment having a second set of controller gain values, wherein the second set of controller gain values includes a second proportional gain value, a second integral gain value, and a second derivative gain value, wherein the second set of controller gain values for the second zone (<NUM>) correspond to over junction (<NUM>) movement and settling,
drive the first coil to control movement of the mover with the first set of controller gain values when the location of the axis is in the first zone, and drive the first coil to control movement of the mover with the second set of controller gain values when the location of the axis is in the second zone.