Patent Description:
There are many motor-based systems known in the art. One such system comprises an antenna system mounted on an aircraft, a mobile ground platform, a shipboard platform, a fixed platform (e.g., a ground station) or other object. The antenna system has a reflector coupled to a motorized pedestal. The motorized pedestal is generally configured to rotate and position the parabolic reflector during use for various purposes such as direction finding for locating, identify and tracking a moving emitter (e.g., an orbiting satellite). The rotation/positioning of the reflector is achieved using servo motors and a servo control system. The document <CIT> discloses an electric motor controller system for modulating requested motor torque via oscillating the instantaneous torque, including a bi-stable torque controller; a proportional-integral velocity controller a proportional-integral-differential position controller; and sinusoidal zero-velocity table mapping. Further, the document <CIT> discloses a multi-loop control system for a gimballed antenna that employs devices for measuring both absolute line-of-sight and relative angular position. The control system uses both signals simultaneously, thereby increasing the performance and pointing accuracy capability. Two control loops operate simultaneously to provide for optimum performance. The first loop is an inner high-bandwidth control loop that uses the relative gimbal angle measurement to control pointing of the antenna along a precommanded profile. The inner loop may run alone to provide for coarse pointing. When available, the line-of sight measurement is used in a low-bandwidth outer loop to provide corrections to the command profile of the inner loop. Control logic is provided that allows switching between several control modes. Additionally, <NPL>, discloses a method for controlling two-axis gimbal systems.

This document concerns systems and methods for operating a motorized system (e.g., an antenna system). The method of the invention is defined by independent claim <NUM>.

In some scenarios, the motorized system comprises an antenna system. The antenna system can comprise: a gimbal; a resolver coupled to the gimbal; first and second motors configured to cause movement of the gimbal in azimuth and elevation; first and second motor encoders respectively coupled to shafts of the first and second motors; a position reference generator configured to generate a position signal specifying a stable position of the gimbal; and a controller configured to use the stable position of the gimbal to control operations of the first and second motors. The resolver can include, but is not limited to, a gimbal resolver.

The position signal is generated using the method of independent claim <NUM>.

This disclosure is facilitated by reference to the following drawing figures, in which like numerals represent like items throughout the figures.

It will be readily understood that the solution described herein and illustrated in the appended figures could involve a wide variety of different configurations. Thus, the following more detailed description, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of certain implementations in various different scenarios. While the various aspects are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized should be or are in any single embodiment. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment.

Motorized pedestal antenna systems have an undesirable level of stiffness (e.g., low) for certain applications. Motor system stiffness has been conventionally addressed by reducing the dynamics of the system, incorporating feedback linearization within the system and/or using notch filters. Such conventional approaches are not suitable for applications in which certain specifications need to be met. Thus, an alternative approach for addressing motor system stiffness is presented herein.

The present solution generally uses two forms of feedback in combination. The two forms of feedback include (i) a dynamic response of a first feedback device that is coupled to a load and (ii) dynamic response(s) of stiffer second feedback device(s) that are coupled to the back of the motors. The first feedback device can include a gimbal resolver, while the second feedback device(s) can include motor encoder(s). The load can include a gimbal with an antenna reflector coupled thereto. Gimbal resolvers, motor encoders, gimbals and antenna reflectors are well known. In this case, the dynamic response of the gimbal resolver comprises a first reference gimbal axis position. The dynamic response of a motor encoder comprises a motor shaft position. The motor shaft position is converted into a motor shaft velocity, which is scaled and integrated to generate a second reference gimbal axis position. The first and second gimbal axis positions are then combined to generate a single position estimate. The second reference gimbal axis position may have an offset relative to the first reference gimbal axis position. This offset may be addressed prior to when the first and second reference gimbal axis positions are combined. The signal position estimate is then used by a controller to control the speed and/or position of the motors via a single control signal. This single-input-single-output (SISO) motor control technique allows higher dynamics without allowing the resonance associated with a spring constant to cause an issued in the motorized pedestal.

In some scenarios, two motors are being used as dual opposing motors on each axis (e.g., two motors in elevation and two motors in azimuth). A first motor can move the gimbal in the azimuth direction, while the second motor provides an opposing force to remove the slop in the gear train. The average velocity of the two motors is computed, filtered, scaled through a gear train, and/or integrated to generate a second position reference for use in controlling the axis.

Referring now to <FIG>, there is provided an illustration of a system <NUM> implementing the present solution. System <NUM> comprises an antenna system that is configured to send and receive Radio Frequency (RF) signals in accordance with known wireless signal communication techniques. The antenna system is mounted on an object <NUM>. The object can include, but is not limited to, an aircraft, a mobile ground platform, a shipboard platform, a fixed platform (e.g., a ground station) or other object. The antenna system has a reflector <NUM> coupled to a motorized pedestal <NUM>. The motorized pedestal <NUM> is generally configured to rotate and position the reflector <NUM> during use for various purposes such as direction finding for locating, identifying and tracking a moving emitter (e.g., an orbiting satellite). The rotation/positioning of the reflector <NUM> is achieved using motors and a motor control system as discussed below.

A block diagram of the system <NUM> is provided in <FIG>. As shown in <FIG>, the motorized pedestal <NUM> comprises a controller <NUM>, positioning motor(s) <NUM>, motor encoder(s) <NUM>, a gimbal resolver <NUM>, an AC signal source <NUM>, a position reference generator <NUM>, and a gimbal <NUM>. Each of the listed components <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is well known. The positioning motor(s) <NUM> can include azimuth motor(s) <NUM> and/or elevation motor(s) <NUM>. The motor(s) <NUM>, <NUM> can include, but are not limited to, servo motors. Servo motors are well known. A motor encoder <NUM> is disposed on a shaft of each motor <NUM>, <NUM>. The gimbal resolver <NUM> is coupled to the back gimbal <NUM> on which the reflector <NUM> is disposed.

The controller <NUM> is communicatively coupled to the motor(s) <NUM>, <NUM>, and provides the same with control signal(s) <NUM> for controllably changing a position and/or orientation of the antenna reflector <NUM>. The control signal(s) <NUM> is(are) generated using a stable load position <NUM> estimated by the position reference generator <NUM>. The stable load position <NUM> is generated in a manner that addresses motor stiffness of system <NUM>. The term motor stiffness as used herein refers to the stiffness or spring constant between a motor output and a load.

The stable load position <NUM> is generated in a novel manner by combining (fusing) together signals <NUM>, <NUM> output from the motor encoder(s) <NUM> and the gimbal resolver <NUM>. The signal <NUM> output from each motor encoder <NUM> can comprise a pulsed signal indicating a motor shaft position (e.g., via a position count <NUM>, <NUM>, <NUM>, etc.). The signal <NUM> output from the gimbal resolver <NUM> comprises a digital or analog signal indicating an axis position for the gimbal <NUM>. The signals <NUM>, <NUM> are fused together by position reference generator <NUM> in accordance with the present solution. Operations of position reference generator <NUM> will now be discussed in detail in relation to <FIG>.

As shown in <FIG>, the position reference generator <NUM> comprises a resolver branch <NUM> and an encoder branch <NUM>. One or more gimbal resolvers can be provided with system <NUM>. In the case that a single gimbal resolver is provided with system <NUM>, the gimbal axis position 214a output from the gimbal resolver is passed to a fusing operator <NUM>.

In contrast, when two or more gimbal resolvers are provided with system <NUM>, the gimbal axis position signals 214a, 214b output from the resolvers are combined in block <NUM> to generate a load position signal Resolverm. The manner in which the gimbal axis position signals 214a, 214b are combined can be the same as or similar to that described in <CIT> to Cathy, which is incorporated herein by reference in its entirety. The load position signal Resolverm is passed to the fusing operator <NUM>. A graph is provided in <FIG> which shows an illustrative resolver-based load position signal <NUM> that corresponds to the load position signal Resolverm.

In the encoder branch <NUM>, another load position signal Encoderm is generated from the motor shaft position signals 210a, 210b output from the motor encoders <NUM>. The load position signal Encoderm is generated by: performing a combiner differential equation in block <NUM> using the motor shaft position signals 210a, 210b as inputs to convert the motor shaft positions to a scaled load velocity specified by signal Velocitym; optionally performing low pass filter operations in block <NUM> to produce a filtered scaled load velocity signal Velocitym'; and performing integrator operations in block <NUM> to convert the scaled load velocity signal Velocitym or Velocitym' to the load position signal Encoderm. The load position signal Encoderm is provided as an input to the fusing operator <NUM>. Combiner differential equations, low pass filter operations and integrator operations are well known.

In some scenarios, operations of the combiner differentiator <NUM> can be defined by the following mathematical equations (<NUM>). <MAT> where Δs210a represents a change in motor shaft position derived from signal 210a, Δs210b represents a change in motor shaft position derived from signal 210b, and Δt represents a change in time. The operations of integrator <NUM> can be defined by the following mathematic equation (2A) in a digital application and mathematical equation (2B) in an analog application. <MAT> <MAT> where x(t) represents the distance the load traveled from time <NUM> to time t, V represents the scaled velocity of the load (i.e., Velocitym or Velocitym'), and dt represents a change in time. The position of the load is then determined from a last known position and x(t). The present solution is not limited to the particulars of these scenarios. Other combiner differentiation and/or integration algorithms can be employed.

At the fusing operator <NUM>, the load position signal Resolverm is fused or otherwise combined with the load position signal Encoderm to generate the stable load position <NUM>. A graph is provided in <FIG> which shows an illustrative encoder-based load position signal <NUM> that corresponds to the load position signal Encoderm. The pulses of the encoder-based load position signal <NUM> are offset from the corresponding pulses of the resolver-based load position signal <NUM>. An FIR filter can be employed by the fusing operator <NUM> to remove this offset as shown in <FIG>. FIR filters are well known.

In the case that an FIR filter is employed, the fusing operator <NUM> implements the following mathematical equations (<NUM>)-(<NUM>). <MAT> or <MAT> <MAT> <MAT> where Taps represents the number of taps for the FIR filter, an represents the FIR filter coefficients divided by the constant from the previous filter of K, am represents the coefficients for the FIR filter, K is a constant that controls the rate of convergence, Avei represents a running average of output from an Infinite Impulse Response (IIR) filter, and the CombinedOutputm+<NUM> represents the stable load position <NUM> which is input into controller <NUM>. A detailed block diagram for an illustrative architecture implementing mathematical equations (<NUM>)-(<NUM>) is provided in <FIG>.

In the case that a FIR filter is not employed, the fusing operator implements the following mathematical equations (<NUM>)-(<NUM>). <MAT> <MAT> <MAT>.

It should be noted that additional operations can be performed to ensure that the difference between the load positions specified in signals Resolverm and Encoderm is correct. For example, let's assume that the load position of Resolverm is -<NUM> (+/- <NUM>°) or <NUM> (<NUM>°), and the load position of Encoderm is <NUM> (+/- <NUM>°) or <NUM> (<NUM>°). In this case, the difference between the load positions of Resolverm and Encoderm should be <NUM>. Operations are performed to ensure that the difference is <NUM> rather than -<NUM>. The present solution is not limited to the particulars of this example.

As shown in <FIG>, the fusing operator <NUM> may comprise subtractors <NUM>, <NUM>, a multiplier <NUM>, an IIR filter <NUM>, an optional FIR filter <NUM>, and an adder <NUM>. The subtractor <NUM> is configured to subtract Encoderm from Resolverm to generate a first difference signal Diff<NUM>. Diff<NUM> is defined by the following mathematical equation (<NUM>).

Subtractor <NUM> is configured to subtract the difference signal Diff<NUM> from Avei to produce a second difference signal Diff<NUM>. Diff<NUM> is defined by the following mathematical equation (<NUM>).

The second difference signal Diff<NUM> is then multiplied by an in block <NUM> to produce a signal P, which is defined by the following mathematical equation (11A) or (11B). <MAT> <MAT> Signal P may then be passed to the FIR filter which is implemented by block(s) <NUM>, <NUM>. The output of block <NUM> is signal Err<NUM>-Taps, and the output of block <NUM> is Err'<NUM>-Taps.

Next in block <NUM>, Err<NUM>-raps or Err'<NUM>-Taps is subtracted from Avei to produce signal Avei+<NUM>. Signal Avei+<NUM> can be defined by the following mathematical equation (<NUM>). <MAT> Signal Avei+<NUM> is combined with a next encoder reference position signal Encoderm+<NUM> in block <NUM> to generate the stable load position <NUM>. The stable load position <NUM> can be defined by the following mathematical equation (<NUM>).

Blocks <NUM>-<NUM> can be implemented by a processor and a non-transitory computer-readable storage medium comprising programming instructions that are configured to cause the processor to implement the above-described subtraction, multiplication and addition operations. Alternatively or additionally, the implementing system may include logic circuits (e.g., subtractors, adders, multipliers, etc.), passive circuit components (e.g., resistors, capacitors, switches, delays, etc.) and/or other active circuit components (e.g., transistors, combiners, etc.).

Referring now to <FIG>, there is provided a method <NUM> for operating a motorized system (e.g., system <NUM> of <FIG>). Method <NUM> implements the process described above in relation to <FIG>. Method <NUM> begins with <NUM> and continues with <NUM> where a circuit (e.g., position reference generator <NUM> of <FIG> and/or computing system <NUM> of <FIG>) receives a first position signal (e.g., signal <NUM> of <FIG>, 214a of <FIG> or Resolverm of <FIG>) generated by a gimbal resolver (e.g., gimbal resolver <NUM> of <FIG>) coupled to a load (e.g., gimbal <NUM> of <FIG>). The circuit also receives a second position signal (e.g., signal 210a of <FIG>) generated by a first motor encoder (e.g., motor encoder <NUM> of <FIG>) coupled to a shaft of a first motor (e.g., azimuth motor <NUM>), as shown by <NUM>. It should be noted that the gimbal resolver and the motor encoders can run at the same or different rates. In the latter case, the integration happens at a relatively high speed and the equations happen every Nth (e.g., tenth) sample from the motor encoders. The circuit further receives a third position signal (e.g., signal 210b of <FIG>) generated by a second motor encoder (e.g., motor encoder <NUM> of <FIG>) coupled to a shaft of a second motor (e.g., elevation motor <NUM>), as shown by <NUM>. The first position signal may specify a gimbal axis position, the second position signal may specify a position for the shaft of the first motor, and the third position signal may specify a position for the shaft of the second motor.

In <NUM>, the circuit performs operations to convert the second and third position signals (e.g., signals 210a and 210b of <FIG>) into a velocity signal (e.g., signal Velocitym) specifying a scaled velocity of the load. This conversion may be achieved using a combiner differentiation algorithm. The velocity signal is converted <NUM> into a fourth position signal (e.g., signal Encoderm of <FIG>) specifying a position of the load.

The first position signal (e.g., signal <NUM> of <FIG>, 214a of <FIG> or Resolverm of <FIG>) and the fourth position signal (e.g., signal Encoderm of <FIG>) are combined to generate a fifth position signal (e.g., signal <NUM> of <FIG>) representing a stable position of the load, as shown by <NUM>. This combining may be achieved in accordance with mathematical equation (<NUM>)-(<NUM>) or (<NUM>)-(<NUM>) provided above. In <NUM>, the fifth position signal is used to control operations of the first and second motors. Subsequently, <NUM> is performed where method <NUM> ends or other operations are performed.

Referring now to <FIG>, there is shown a hardware block diagram comprising an example computer system <NUM> that can be used for implementing all or part of the motorized pedestal <NUM> of <FIG>. The machine can include a set of instructions which are used to cause the circuit/computer system to perform any one or more of the methodologies discussed herein. While only a single machine is illustrated in <FIG>, it should be understood that in other scenarios the system can be taken to involve any collection of machines that individually or jointly execute one or more sets of instructions as described herein.

The computer system <NUM> is comprised of a processor <NUM> (e.g., a Central Processing Unit (CPU)), a main memory <NUM>, a static memory <NUM>, a drive unit <NUM> for mass data storage and comprised of machine readable media <NUM>, input/output devices <NUM>, an optional display unit <NUM> (e.g., a Liquid Crystal Display (LCD) or a solid state display, and one or more interface devices <NUM>. Communications among these various components can be facilitated by means of a data bus <NUM>. One or more sets of instructions <NUM> can be stored completely or partially in one or more of the main memory <NUM>, static memory <NUM>, and drive unit <NUM>. The instructions can also reside within the processor <NUM> during execution thereof by the computer system. The input/output devices <NUM> can include a keyboard, a multi-touch surface (e.g. a touchscreen) and so on. The interface device(s) <NUM> can be comprised of hardware components and software or firmware to facilitate an interface to external circuitry. For example, in some scenarios, the interface devices <NUM> can include one or more Analog-to-Digital (A/D) converters, Digital-to-Analog (D/A) converters, input voltage buffers, output voltage buffers, voltage drivers and/or comparators. These components are wired to allow the computer system to interpret signal inputs received from external circuitry, and generate the necessary control signals for certain operations described herein.

The drive unit <NUM> can comprise a machine readable medium <NUM> on which is stored one or more sets of instructions <NUM> (e.g. software) which are used to facilitate one or more of the methodologies and functions described herein. The term "machine-readable medium" shall be understood to include any tangible medium that is capable of storing instructions or data structures which facilitate any one or more of the methodologies of the present disclosure. Exemplary machine-readable media can include solid-state memories, Electrically Erasable Programmable Read-Only Memory (EEPROM) and flash memory devices. A tangible medium as described herein is one that is non-transitory insofar as it does not involve a propagating signal.

Computer system <NUM> should be understood to be one possible example of a computer system which can be used in connection with the various implementations disclosed herein. However, the systems and methods disclosed herein are not limited in this regard and any other suitable computer system architecture can also be used without limitation. Dedicated hardware implementations including, but not limited to, application-specific integrated circuits, programmable logic arrays, and other hardware devices can likewise be constructed to implement the methods described herein. Applications that can include the apparatus and systems broadly include a variety of electronic and computer systems. Thus, the exemplary system is applicable to software, firmware, and hardware implementations.

Further, it should be understood that embodiments can take the form of a computer program product on a tangible computer-usable storage medium (for example, a hard disk or a CD-ROM). The computer-usable storage medium can have computer-usable program code embodied in the medium. The term computer program product, as used herein, refers to a device comprised of all the features enabling the implementation of the methods described herein. Computer program, software application, computer software routine, and/or other variants of these terms, in the present context, mean any expression, in any language, code, or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code, or notation; or b) reproduction in a different material form.

Claim 1:
A method (<NUM>) for operating a motorized system, comprising:
receiving, by a circuit, a first position signal (<NUM>) generated by a resolver coupled to a load, a second position signal (<NUM>) generated by a first motor encoder coupled to a shaft of a first motor, and a third position signal (<NUM>) generated by a second motor encoder coupled to a shaft of a second motor;
converting (<NUM>), by the circuit, the second and third position signals into a velocity signal specifying a scaled velocity of the load;
converting (<NUM>), by the circuit, the velocity signal into a fourth position signal specifying a position of the load;
generating (<NUM>), by the circuit, a fifth position signal, which represents a stable position of the load, wherein, when a Finite Impulse Response, FIR, filter is employed, the generating comprises operations implementing the following mathematical equations:
(<NUM>) <MAT>
(<NUM>) <MAT>
(<NUM>) <MAT>
and wherein, when a FIR filter is not employed, the generating comprises operations implementing the following mathematical equations:
(<NUM>) <MAT>
(<NUM>) <MAT>
(<NUM>) <MAT>
wherein Taps represents the number of taps for the FIR filter, am represents the coefficients for the FIR filter, Velocitym, represents the velocity signal, Resolverm represents the first position signal, Encoderm represents the fourth position signal, Avei represents an average signal output from an infinite impulse response filter, Encoderm+<NUM> represents a sixth signal specifying a next position of the load, CombinedOutputm+<NUM> represents the signal specifying the stable position of the load, and K is a constant that controls a rate of convergence of the filter; and
using (<NUM>), by the circuit, the fifth position signal to control operations of the first and second motors.