Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
  • G01C21/10—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration
  • G01C21/12—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning
  • G01C21/16—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation
  • G01C21/183—Compensation of inertial measurements, e.g. for temperature effects
  • G01C21/188—Compensation of inertial measurements, e.g. for temperature effects for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems

Definitions

• the present invention relates to motion measurement, and more particularly to a process of motion measurement and a motion inertial measurement unit in micro size, which can produce highly accurate, digital angular increments, velocity increments, position, velocity, attitude, and heading measurements of a carrier under dynamic environments.
• IMU inertial measurement unit
• an inertial measurement unit relies on three orthogonally mounted inertial angular rate producers and three orthogonally mounted acceleration producers to obtain three-axis angular rate and acceleration measurement signals.
• the three orthogonally mounted inertial angular rate producers and three orthogonally mounted acceleration producers with additional supporting mechanical structure and electronic devices are conventionally called an Inertial Measurement Unit (IMU).
• the conventional IMUs may be cataloged into Platform IMU and Strapdown IMU.
• angular rate producers and acceleration producers are installed on a stabilized platform. Attitude measurements can be directly picked off from the platform structure. But attitude rate measurements can not be directly obtained from the platform.
• angular rate producers and acceleration producers are directly strapped down with the carrier and move with the carrier.
• the output signals of the strapdown rate producers and acceleration producers are expressed in the carrier body frame.
• the attitude and attitude rate measurements can be obtained by means of a series of computations.
• a conventional IMU uses a variety of inertial angular rate producers and acceleration producers.
• Conventional inertial angular rate producers include iron spinning wheel gyros and optical gyros, such as Floated Integrating Gyros (FIG), Dynamically Tuned Gyros (DTG), Ring Laser Gyros (RLG), Fiber-Optic Gyros (FOG), Electrostatic Gyros (ESG), Josephson Junction Gyros (JJG), Hemisperical Resonating Gyros (HRG), etc.
• Conventional acceleration producers include Pulsed Integrating Pendulous Accelerometer (PIPA), Pendulous Integrating Gyro Accelerometer (PIGA), etc.
• the processing method, mechanical supporting structures, and electronic circuitry of conventional IMUs vary with the type of gyros and accelerometers employed in the IMUs. Because conventional gyros and accelerometers have a large size, high power consumption, and moving mass, complex feedback control loops are required to obtain stable motion measurements. For example, dynamic-tuned gyros and accelerometers need force-rebalance loops to create a moving mass idle position. There are often pulse modulation force-rebalance circuits associated with dynamic-tuned gyros and accelerometer based IMUs. Therefore, conventional IMUs commonly have the following features:
• MEMS MicroElectronicMechanicalSystem
• inertial sensors offer tremendous cost, size, and reliability improvements for guidance, navigation, and control systems, compared with conventional inertial sensors.
• MEMS or, as stated more simply, micromachines, are considered as the next logical step in the silicon revolution. It is believed that this coming step will be different, and more important than simply packing more transistors onto silicon. The hallmark of the next thirty years ofthe silicon revolution will be the incorporation of new types of functionality onto the chip structures, which will enable the chip to, not only think, but to sense, act, and communicate as well.
• Single input axis MEMS angular rate sensors are based on either translational resonance, such as tuning forks, or structural mode resonance, such as vibrating rings.
• dual input axis MEMS angular rate sensors may be based on angular resonance of a rotating rigid rotor suspended by torsional springs.
• Current MEMS angular rate sensors are primarily based on an electronically-driven tuning fork method.
• More accurate MEMS accelerometers are the force rebalance type that use closed- loop capacitive sensing and electrostatic forcing.
• Draper's micromechnical accelerometer is a typical example, where the accelerometer is a monolithic silicon structure consisting of a torsional pendulum with capacitive readout and electrostatic torquer.
• Analog Device's MEMS accelerometer has an integrated polysilicon capacitive structure fabricated with on-chip BiMOS process to include a precision voltage reference, local oscillators, amplifiers, demodulators, force rebalance loop and self-test functions.
• MEMS angular rate sensors and MEMS accelerometers are available commercially and have achieved micro chip-size and low power consumption, however, there is not yet available high performance, small size, and low power consumption IMUs.
• a main objective ofthe present invention is to provide a micro inertial measurement unit, which can produce digital highly accurate angular increment and velocity increment measurements of a carrier from voltage signals output from the specific angular rate and acceleration producers thereof, so as to obtain highly accurate, position, velocity, attitude, and heading measurements ofthe carrier under dynamic environments.
• Another objective of the present invention is to provide a processing method of motion measurement which successfully incorporates the MEMS technology with the IMU industry.
• Another objective of the present invention is to provide a processing method of motion measurement which is adapted to be applied to output signals of rate sensors and acceleration sensors, which are proportional to rotation and translational motion ofthe carrier, respectively, and more suitable for emerging MEMS (MicroElectronicMechanicalSystem) rate and acceleration sensors.
• the present invention utilizes a feedforward open-loop signal processing scheme to obtain highly accurate motion measurements by means of signal digitizing, temperature control and compensation, sensor error and misalignment calibrations, attitude updating, and damping controlling loops, and dramatically shrinks the size of mechanical and electronic hardware and power consumption, meanwhile, obtains highly accurate motion measurements.
• Another objective of the present invention is to provide a micro inertial measurement unit and process of motion measurement, wherein output signals of angular rate producer and acceleration producer are exploited, and are preferably emerging MEMS (MicroElectronicMechanicalSystem) angular rate sensor arrays and acceleration sensor arrays. These outputs are proportional to rotation and translational motion ofthe carrier, respectively.
• the present invention utilizes a feedforward open-loop signal processing scheme to obtain highly accurate motion measurements by means of signal integration, digitizing, temperature control and compensation, sensor error and misalignment calibrations, and dramatically shrinks the size of mechanical and electronic hardware and power consumption, meanwhile, obtains highly accurate motion measurements.
• the present invention can use existing angular rate devices and acceleration devices, the present invention specifically selects MEMS angular rate devices and acceleration devices to assemble a micro IMU, wherein the micro IMU has the following unique features: Attitude Heading Reference System (AHRS) Capable Core Sensor Module.
• AHRS Attitude Heading Reference System
• Another objective ofthe present invention is to provide a micro IMU rendering into an integrated micro land navigator that has the following unique features: Miniature, light weight, low power, and low cost.
• micro IMU to function as aircraft inertial avionics, which has the following unique features:
• Another objective of the present invention is to provide a micro IMU to function as a Spaceborne MEMS IMU Attitude Determination System and a Spaceborne Fully-Coupled GPS MEMS IMU Integrated system for orbit determination, attitude control, payload pointing, and formation flight, that have the following unique features: Shock resistant and vibration tolerant
• Another objective of the present invention is to provide a micro IMU to form a marine INS with embedded GPS, which has the following unique features:
• Another objective ofthe present invention is to provide a micro IMU to be used in a micro pointing and stabilization mechanism that has the following unique features:
• Micro MEMS IMU AHRS utilized for platform stabilization.
• MEMS IMU integrated with the electrical and mechanical design of the pointing and stabilization mechanism.
• Variable pointing angle for tracker implementations include miniature antenna pointing and tracking control, laser beam pointing for optical communications, telescopic pointing for imaging, airborne laser pointing control for targeting, vehicle control and guidance
• Figure 1 is a block diagram illustrating the processing module for carrier motion measurement and a micro inertial measurement unit according to a preferred embodiment of the present invention.
• Figure 2 is a block diagram illustrating the processing modules with thermal control processing for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment ofthe present invention.
• Figure 3 is a block diagram illustrating the processing modules with thermal compensation processing for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment ofthe present invention.
• Figure 4 is a block diagram illustrating an angular increment and velocity increment producer for outputting voltage signals of the angular rate producer and acceleration producer for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment ofthe present invention.
• Figure 5 is a block diagram illustrating another angular increment and velocity increment producer for outputting voltage signals of angular rate producer and acceleration producer for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment ofthe present invention.
• Figure 6 is a block diagram illustrating another angular increment and velocity increment producer for outputting voltage signals of an angular rate producer and acceleration producer for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment of he present invention.
• Figure 7 is a block diagram illustrating another angular increment and velocity increment producer for outputting voltage signals of an angular rate producer and acceleration producer for the carrier motion measurement and micro inertial measurement unit accordmg to the above preferred embodiment ofthe present invention.
• Figure 8 is a block diagram illustrating a thermal processor for outputting analog voltage signals of the thermal sensing producer according to the above preferred embodiment of the present invention.
• Figure 9 is a block diagram illustrating another thermal processor for outputting analog voltage signals ofthe thermal sensing producer according to the above preferred embodiment ofthe present invention.
• Figure 10 is a block diagram illustrating another thermal processor for outputting analog voltage signals ofthe thermal sensing producer according to the above preferred embodiment ofthe present invention.
• Figure 11 is a block diagram illustrating a processing module for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment ofthe present invention.
• Figure 12 is a block diagram illustrating a temperature digitizer for outputting analog voltage signals of the thermal sensing producer according to the above preferred embodiment of the present invention.
• Figure 13 is a block diagram illustrating a temperature digitizer for outputting analog voltage signals of the thermal sensing producer according to the above preferred embodiment of the present invention.
• Figure 14 is a block diagram illustrating a processing module with thermal compensation processing for carrier motion measurement and the micro inertial measurement unit according to the above preferred embodiment of the present invention.
• FIG. 15 is a block diagram illustrating the attitude and heading processing module according to the above preferred embodiment ofthe present invention.
• Figure 16 is a functional block diagram illustrating the position velocity attitude and heading module according to the above preferred embodiment ofthe present invention.
• Figure 17 is a perspective view illustrating the inside mechanical structure and circuit board deployment in the micro IMU according to the above preferred embodiment of the present invention.
• Figure 18 is a sectional side view of the micro IMU according to the above preferred embodiment ofthe present invention.
• Figure 19 is a block diagram illustrating the connection among the four circuit boards inside the micro IMU according to the above preferred embodiment ofthe present invention.
• Figure 20 is a block diagram of the front-end circuit in each of the first, second, and fourth circuit boards ofthe micro IMU according to the above preferred embodiment ofthe present invention.
• Figure 21 is a block diagram of the ASIC chip in the third circuit board of the micro IMU according to the above preferred embodiment ofthe present invention.
• FIG 22 is a block diagram of processing modules running in the DSP chipset in the third circuit board of the micro IMU according to the above preferred embodiment of the present invention.
• Figure 23 is a block diagram of the angle signal loop circuitry of the ASIC chip in the third circuit board of the micro IMU according to the above preferred embodiment of the present invention.
• Figure 24 is block diagram of the dither motion control circuitry ofthe ASIC chip in the third circuit board of the micro IMU according to the above preferred embodiment of the present invention.
• Figure 25 is a block diagram ofthe thermal control circuit ofthe ASIC chip in the third circuit board of the micro IMU according to the above preferred embodiment of the present invention.
• Figure 26 is a block diagram of the dither motion processing module running in the DSP chipset of the third circuit board of the micro IMU according to the above preferred embodiment ofthe present invention.
• MEMS exploits the existing microelectronics infrastructure to create complex machines with micron feature sizes. These machines can have many functions, including sensing, communication, and actuation. Extensive applications for these devices exist in a wide variety of commercial systems.
• Micro-size angular rate sensors and accelerometers need to be obtained.
• MEMS angular rate sensors and MEMS accelerometers.
• Associated electronic circuitry needs to be designed. Associated thermal requirements design need to be met to compensate MEMS sensor's thermal effects. The size and power ofthe associated electronic circuitry need to be shrunk.
• the micro inertial measurement unit of the present invention is preferred to employ with the angular rate producer, such as MEMS angular rate device array or gyro array, that provides three-axis angular rate measurement signals of a carrier, and the acceleration producer, such as MEMS acceleration device array or accelerometer array, that provides three-axis acceleration measurement signals of the carrier, wherein the motion measurements of the carrier, such as attitude and heading angles, are achieved by means of processing procedures of the three-axis angular rate measurement signals from the angular rate producer and the three-axis acceleration measurement signals from the acceleration producer.
• the angular rate producer such as MEMS angular rate device array or gyro array
• the acceleration producer such as MEMS acceleration device array or accelerometer array
• the micro inertial measurement unit of the present invention comprises an angular rate producer 5 for producing three-axis (X axis, Y axis and Z axis) angular rate signals; an acceleration producer 10 for producing three-axis (X-axis, Y axis and Z axis) acceleration signals; and an angular increment and velocity increment producer 6 for converting the three-axis angular rate signals into digital angular increments and for converting the input three-axis acceleration signals into digital velocity increments.
• a position and attitude processor 80 is adapted to further connect with the micro IMU of the present invention to compute position, attitude and heading angle measurements using the three-axis digital angular increments and three-axis velocity increments to provide a user with a rich motion measurement to meet diverse needs.
• the position, attitude and heading processor 80 further comprises two optional running modules:
• Attitude and Heading Module 81 producing attitude and heading angle only
• Position, Velocity, Attitude, and Heading Module 82 producing position, velocity, and attitude angles.
• the angular rate producer 5 and the acceleration producer 10 are very sensitive to a variety of temperature environments.
• the present invention further comprises a thermal controlling means for maintaining a predetermined operating temperature of the angular rate producer 5, the acceleration producer 10 and the angular increment and velocity increment producer 6. It is worth to mention that if the angular rate producer 5, the acceleration producer 10 and the angular increment and velocity increment producer 6 are operated in an environment under prefect and constant thermal control, the thermal controlling means can be omitted.
• the thermal controlling means comprises a thermal sensing producer device 15, a heater device 20 and a thermal processor 30.
• the thermal sensing producer device 15 which produces temperature signals, is processed in parallel with the angular rate producer 5 and the acceleration producer 10 for maintaining a predetermined operating temperature of the angular rate producer 5 and the acceleration producer 10 and angular increment and velocity increment producer 6 of the micro IMU, wherein the predetermined operating temperature is a constant designated temperature selected between 150°F and 285°F, preferabie 176°F ( ⁇ Q.I ⁇ ).
• the temperature signals produced from the thermal sensing producer device 15 are inputted to the thermal processor 30 for computing temperature control commands using the temperature signals, a temperature scale factor, and a predetermined operating temperature of the angular rate producer 5 and the acceleration producer 10, and produce driving signals to the heater device 20 using the temperature control commands for controlling the heater device 20 to provide adequate heat for maintaining the predetermined operating temperature in the micro IMU.
• Temperature characteristic parameters of the angular rate producer 5 and the acceleration producer 10 can be determined during a series of the angular rate producer and acceleration producer temperature characteristic calibrations.
• the micro IMU ofthe present invention can alternatively comprise a temperature digitizer 18 for receiving the temperature signals produced from the thermal sensing producer device 15 and outputting a digital temperature value to the position, attitude, and heading processor 80.
• the temperature digitizer 18 can be embodied to comprise an analog/digital converter 182.
• the position, attitude, and heading processor 80 is adapted for accessing temperature characteristic parameters of the angular rate producer and the acceleration producer using a current temperature of the angular rate producer and the acceleration producer from the temperature digitizer 18, and compensating the errors induced by thermal effects in the input digital angular and velocity increments and computing attitude and heading angle measurements using the three-axis digital angular increments and three-axis velocity increments in the attitude and heading processor 80.
• the output of the angular rate producer 5 and the acceleration producer 10 are analog voltage signals.
• the three-axis analog angular rate voltage signals produced from the angular producer 5 are directly proportional to carrier angular rates, and the three-axis analog acceleration voltage signals produced from the acceleration producer 10 are directly proportional to carrier accelerations.
• the angular increment and velocity increment producer 6 may employ amplifying means 660 and 665 for amplifying the analog voltage signals input from the angular rate producer 5 and the acceleration producer 10 and suppress noise signals residing within the analog voltage signals input from the angular rate producer 5 and the acceleration producer 10, as shown in Figs. 5 and 6.
• the angular increment and velocity increment producer 6 comprises an angular integrating means 620, an acceleration integrating means 630, a resetting means 640, and an angular increment and velocity increment measurement means 650.
• the angular integrating means 620 and the acceleration integrating means 630 are adapted for respectively integrating the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals for a predetermined time interval to accumulate the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals as an uncompensated three-axis angular increment and an uncompensated three-axis velocity increment for the predetermined time interval to achieve accumulated angular increments and accumulated velocity increments.
• the integration is performed to remove noise signals that are non-directly proportional to the carrier angular rate and acceleration within the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals, to improve signal-to-noise ratio, and to remove the high frequency signals in the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals.
• the signals are directly proportional to the carrier angular rate and acceleration within the three-axis analog angular rate voltage signals and the three- axis analog acceleration voltage signals.
• the resetting means forms an angular reset voltage pulse and a velocity reset voltage pulse as an angular scale and a velocity scale which are input into the angular integrating means 620 and the acceleration integrating means 630 respectively,
• the angular increment and velocity increment measurement means 650 is adapted for measuring the voltage values of the three-axis accumulated angular increments and the three-axis accumulated velocity increments with the angular reset voltage pulse and the velocity reset voltage pulse respectively to acquire angular increment counts and velocity increment counts as a digital form of the angular increment and velocity increment measurements respectively.
• the angular increment and velocity increment measurement means 650 In order to output real three-angular increment and velocity increment values as an optional output format to substitute the voltage values ofthe three-axis accumulated angular increments and velocity increments, the angular increment and velocity increment measurement means 650 also scales the voltage values ofthe three-axis accumulated angular and velocity increments into real three-axis angular and velocity increment voltage values.
• the three-axis analog angular voltage signals and the three-axis analog acceleration voltage signals are each reset to accumulate from a zero value at an initial point of every predetermined time interval.
• the resetting means 640 can be an oscillator 66, so that the angular reset voltage pulse and the velocity reset voltage pulse are implemented by producing a timing pulse by the oscillator 66.
• the oscillator 66 can be built with circuits, such as Application Specific Integrated Circuits (ASIC) chip and a printed circuit board.
• ASIC Application Specific Integrated Circuits
• the angular increment and velocity increment measurement means 650 which is adapted for measuring the voltage values of the three-axis accumulated angular and velocity increments, is embodied as an analog/digital converter 650.
• the analog/digital converter 650 substantially digitizes the raw three-axis angular increment and velocity increment voltage values into digital three-axis angular increment and velocity increments.
• the amplifying means 660 and 665 of the angular increment and velocity increment producer 6 are embodied by an angular amplifier circuit 61 and an acceleration amplifier circuit 67 respectively to amplify the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals to form amplified three-axis analog angular rate signals and amplified three-axis analog acceleration signals respectively.
• the angular integrating means 620 and the acceleration integrating means 630 ofthe angular increment and velocity increment producer 6 are respectively embodied as an angular integrator circuit 62 and an acceleration integrator circuit 68 for receiving the amplified three- axis analog angular rate signals and the amplified three-axis analog acceleration signals from the angular and acceleration amplifier circuits 61, 67 which are integrated to form the accumulated angular increments and the accumulated velocity increments respectively.
• the analog/digital converter 650 of the angular increment and velocity increment producer 6 further includes an angular analog/digital converter 63, a velocity analog digital converter 69 and an input/output interface circuit 65.
• the accumulated angular increments output from the angular integrator circuit 62 and the accumulated velocity increments output from the acceleration integrator circuit are input into the angular analog/digital converter 63 and the velocity analog/digital converter 69 respectively.
• the accumulated angular increments are digitized by the angular analog/digital converter 63 by measuring the accumulated angular increments with the angular reset voltage pulse to form digital angular measurements of voltage in terms of the angular increment counts which are output to the input/output interface circuit 65 to generate digital, three-axis angular increment voltage values.
• the accumulated velocity increments are digitized by the velocity analog/digital converter 69 by measuring the accumulated velocity increments with the velocity reset voltage pulse to form digital velocity measurements of voltage in terms of the velocity increment counts which are output to the input/output interface circuit 65 to generate digital three-axis velocity increment voltage values.
• the thermal processor 30 can be implemented in a digital feedback controlling loop as shown in Figure 8.
• the thermal processor 30, as shown in Fig. 8, comprises an analog/digital converter 304 connected to the thermal sensing producer device 15, a digital/analog converter 303 connected to the heater device 20, and a temperature controller 306 connected with both the analog/digital converter 304 and the digital/analog converter 303.
• the analog/digital converter 304 inputs the temperature voltage signals produced by the thermal sensing producer device 15, wherein the temperature voltage signals are sampled in the analog/digital converter 304 to sampled temperature voltage signals which are further digitized to digital signals and output to the temperature controller 306.
• the temperature controller 306 computes digital temperature commands using the input digital signals from the analog/digital converter 304, a temperature sensor scale factor, and a pre-determined operating temperature of the angular rate producer and acceleration producer, wherein the digital temperature commands are fed back to the digital/analog converter 303.
• the digital/analog converter 303 converts the digital temperature commands input from the temperature controller 306 into analog signals which are output to the heater device 20 to provide adequate heat for maintaining the predetermined operating temperature of the micro IMU ofthe present invention.
• the thermal processor 30 further comprises a first amplifier circuit 301 between the thermal sensing producer device 15 and the digital/analog converter 303, wherein the voltage signals from the thermal sensing producer device 15 is first input into the first amplifier circuit 301 for amplifying the signals and suppressing the noise residing in the voltage signals and improving the signal-to-noise ratio, wherein the amplified voltage signals are then output to the analog/digital converter 304.
• the heater device 20 requires a specific driving current signal.
• the thermal processor 30 can further comprise a second amplifier circuit 302 between the digital/analog converter 303 and heater device 20 for amplifying the input analog signals from the digital/analog converter 303 for driving the heater device 20.
• the digital temperature commands input from the temperature controller 306 are converted in the digital/analog converter 303 into analog signals which are then output to the amplifier circuit 302.
• an input/output interface circuit 305 is required to connect the analog/digital converter 304 and digital/analog converter 303 with the temperature controller 306.
• the voltage signals are sampled in the analog/digital converter 304 to form sampled voltage signals that are digitized into digital signals.
• the digital signals are output to the input/output interface circuit 305.
• the temperature controller 306 is adapted to compute the digital temperature commands using the input digital temperature voltage signals from the input/output interface circuit 305, the temperature sensor scale factor, and the pre-determined operating temperature of the angular rate producer and acceleration producer, wherein the digital temperature commands are fed back to the input/output interface circuit 305.
• the digital/analog converter 303 further converts the digital temperature commands input from the input/output interface circuit 305 into analog signals which are output to the heater device 20 to provide adequate heat for maintaining the predetermined operating temperature ofthe micro IMU.
• the thermal processor 30 and the heater device 20 as disclosed in Figs. 2, 8, 9, 10, and 11 can alternatively be replaced by the analog/digital converter 182 connected to the thermal sensing producer device 15 to receive the analog voltage output from the thermal sensing producer device 15.
• an additional amplifier circuit 181 can be connected between the thermal sensing producer device 15 and the digital/analog converter 182 for amplifying the analog voltage signals and suppressing the noise residing in the voltage signals and improving the voltage signal-to-noise ratio, wherein the amplified voltage signals are output to the analog/digital converter 182 and sampled to form sampled voltage signals that are further digitized in the analog/digital converters 182 to form digital signals connected to the attitude and heading processor 80.
• an input/output interface circuit 183 can be connected between the analog/digital converter 182 and the attitude and heading processor 80.
• the input amplified voltage signals are sampled to form sampled voltage signals that are further digitized in the analog/digital converters to form digital signals connected to the input/output interface circuit 183 before inputting into the attitude and heading processor 80.
• the digital three-axis angular increment voltage values or real values and three-axis digital velocity increment voltage values or real values are produced and outputted from the angular increment and velocity increment producer 6.
• the attitude and heading module 81 comprises a coning correction module 811, wherein digital three-axis angular increment voltage values from the input/output interface circuit 65 of the angular increment and velocity increment producer 6 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure at a high data rate (short interval) are input into the coning correction module 801, which computes coning effect errors by using the input digital three-axis angular increment voltage values and coarse angular rate bias, and outputs three-axis coning effect terms and three-axis angular increment voltage values at a reduced data rate (long interval), which are called three-axis long-interval angular increment voltage values.
• the attitude and heading module 81 further comprises an angular rate compensation module 812 and an alignment rotation vector computation module 815.
• the coning effect errors and three-axis long-interval angular increment voltage values from the coning correction module 811 and angular rate device misalignment parameters, fine angular rate bias, angular rate device scale factor, and coning correction scale factor from the angular rate producer and acceleration producer calibration procedure are connected to the angular rate compensation module 812 for compensating definite errors in the three-axis long-interval angular increment voltage values using the coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor, and transforming the compensated three-axis long-interval angular increment voltage values to real three-axis long-interval angular increments using the angular rate device scale factor.
• the attitude and heading module 81 further comprises an accelerometer compensation module 813 and a level acceleration computation module 814, wherein the three-axis velocity increment voltage values from the angular increment and velocity increment producer 6 and acceleration device misalignment, acceleration device bias, and acceleration device scale factor from the angular rate producer and acceleration producer calibration procedure are connected to the accelerometer compensation module 813 for transforming the three-axis velocity increment voltage values into real three-axis velocity increments using the acceleration device scale factor, and compensating the definite errors in three-axis velocity increments using the acceleration device misalignment, accelerometer bias, wherein the compensated three-axis velocity increments are connected to the level acceleration computation module 814.
• a quaternion which is a vector representing rotation angle of the carrier, is updated, and the updated quaternion is connected to a direction cosine matrix computation module 816 for computing the direction cosine matrix, by using the updated quaternion.
• the computed direction cosine matrix is connected to the level acceleration computation module 814 and an attitude and heading angle extract module 817 for extracting attitude and heading angle using the direction cosine matrix from the direction cosine matrix computation module 816.
• the compensated three-axis velocity increments are connected to the level acceleration computation module 814 for computing level velocity increments using the compensated three-axis velocity increments from the acceleration compensation module 814 and the direction cosine matrix from the direction cosine matrix computation module 816.
• the level velocity increments are connected to the east damping rate computation module 8110 for computing east damping rate increments using the north velocity increment ofthe input level velocity increments from the level acceleration computation module 814.
• the level velocity increments are connected to the north damping rate computation module 819 for computing north damping rate increments using the east velocity increment of the level velocity increments from the level acceleration computation module 814.
• the heading angle from the attitude and heading angle extract module 817 and a measured heading angle from the external heading sensor 90 are connected to the vertical damping rate computation module 818 for computing vertical damping rate increments.
• the east damping rate increments, north damping rate increments, and vertical damping rate are fed back to the alignment rotation vector computation module 815 to damp the drift of errors ofthe attitude and heading angles.
• the real digital three-axis angular increment values from the angular increment and velocity increment producer 6 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure at a high data rate (short interval) are connected to the coning correction module 811 for computing coning effect errors in the coning correction module 811 using the digital three- axis angular increment values and coarse angular rate bias and outputting three-axis coning effect terms and three-axis angular increment values at reduced data rate (long interval), which are called three-axis long-interval angular increment values, into the angular rate compensation module 802.
• the coning effect errors and three-axis long-interval angular increment values from the coning correction module 811 and angular rate device misalignment parameters and fine angular rate bias from the angular rate producer and acceleration producer calibration procedure are connected to the angular rate compensation module 812 for compensating definite errors in the three-axis long-interval angular increment values using the coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor, and outputting the real three-axis angular increments to the alignment rotation vector computation module 815.
• the three-axis velocity increment values from the angular increment and velocity increment producer 6 and acceleration device misalignment, and acceleration device bias from the angular rate producer and acceleration producer calibration procedure are connected into the accelerometer compensation module 813 for compensating the definite errors in three-axis velocity increments using the acceleration device misalignment, and accelerometer bias; outputting the compensated three-axis velocity increments to the level acceleration computation module 814.
• the following modules use the compensated three-axis angular increments from the angular rate compensation module 812 and compensated three-axis velocity increments from the acceleration compensation module 813 to produce attitude and heading angle.
• the digital three-axis angular increment voltage values from the angular increment and velocity increment producer 6 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure at a high data rate (short interval) are connected to the coning correction module 811 for computing coning effect errors in the coning correction module 811 using the digital three-axis angular increment voltage values and coarse angular rate bias, and outputting three- axis coning effect terms and three-axis angular increment voltage values at a reduced data rate (long interval), which are called three-
• the coning effect errors and three-axis long-interval angular increment voltage values from the coning correction module 811 and angular rate device misalignment parameters, fine angular rate bias, angular rate device scale factor, coning correction scale factor from the angular rate producer and acceleration producer calibration procedure, the digital temperature signals from input/output interface circuit 183, and temperature sensor scale factor are connected to the angular rate compensation module 812 for computing current temperature ofthe angular rate producer, accessing angular rate producer temperature characteristic parameters using the current temperature of the angular rate producer, compensating definite errors in the three-axis long-interval angular increment voltage values using the coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor, transforming the compensated three-axis long- interval angular increment voltage values to real three-axis long-interval angular increments, compensating temperature-induced errors in the real three-axis long-interval angular increments using the angular rate producer
• the three-axis velocity increment voltage values from the angular increment and velocity increment producer 6 and acceleration device misalignment, acceleration bias, acceleration device scale factor from the angular rate producer and acceleration producer calibration procedure, the digital temperature signals from the input/output interface circuit 183 of the temperature digitizer 18, and temperature sensor scale factor are connected to the acceleration compensation module 813 for computing current temperature ofthe acceleration producer, accessing acceleration producer temperature characteristic parameters using the current temperature of the acceleration producer, transforming the three-axis velocity increment voltage values into real three-axis velocity increments using the acceleration device scale factor, compensating the definite errors in the three-axis velocity increments using the acceleration device misalignment and acceleration bias, compensating temperature-induced errors in the real three-axis velocity increments using the acceleration producer temperature characteristic parameters, and outputting the compensated three-axis velocity increments to the level acceleration computation module 814.
• the following modules use the compensated three-axis angular increments from the angular rate compensation module 812 and compensated three-axis velocity increments from the acceleration compensation module 813 to produce the attitude and heading angles.
• the attitude and heading module 81 can be further modified to accept the digital three-axis angular increment values from the angular increment and velocity increment producer 6 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure at a high data rate (short interval) into the coning correction module 811 for computing coning effect errors in the coning correction module 811 using the input digital three-axis angular increment values and coarse angular rate bias, and outputting three-axis coning effect data and three-axis angular increment data at a reduced data rate (long interval), which are called three-axis long-interval angular increment values, into the angular rate compensation module 812.
• the coning effect errors and three-axis long-interval angular increment values from the coning correction module 811 and angular rate device misalignment parameters and fine angular rate bias from the angular rate producer and acceleration producer calibration procedure, the digital temperature signals from the input/output interface circuit 183 and temperature sensor scale factor are connected to the angular rate compensation module 812 for computing current temperature of the angular rate producer, accessing angular rate producer temperature characteristic parameters using the current temperature of the angular rate producer, compensating definite errors in the three-axis long-interval angular increment values using the coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor, compensating temperature-induced errors in the real three-axis long-interval angular increments using the angular rate producer temperature characteristic parameters, and outputting the real three-axis angular increments to an alignment rotation vector computation module 815.
• the three-axis velocity increment values from the input/output interface circuit 65 and acceleration device misalignment and acceleration bias from the angular rate producer and acceleration producer calibration procedure, the digital temperature signals from the input/output interface circuit 183 and temperature sensor scale factor are input into the acceleration compensation module 803 for computing current temperature ofthe acceleration producer, accessing the acceleration producer temperature characteristic parameters using the current temperature ofthe acceleration producer, compensating the definite errors in the three- axis velocity increments using the input acceleration device misalignment, acceleration bias, compensating temperature-induced errors in the real three-axis velocity increments using the acceleration producer temperature characteristic parameters, and outputting the compensated three-axis velocity increments to the level acceleration computation module 804.
• the following modules use the compensated three-axis angular increments from the angular rate compensation module 812 and compensated three-axis velocity increments from the acceleration compensation module 813 to produce the attitude and heading angles.
• the Position, velocity, and attitude Module 82 comprises: a coning correction module 8201, which is same as the coning correction module 811 ofthe attitude and heading module 81; an angular rate compensation module 8202, which is same as the angular rate compensation module 812 ofthe attitude and heading module 81; an alignment rotation vector computation module 8205, which is same as the alignment rotation vector computation module 815 ofthe attitude and heading module 81; a direction cosine matrix computation module 8206, which is same as the Direction cosine matrix computation module 816 ofthe attitude and heading module 81; an acceleration compensation module 8203, which is same as the acceleration compensation module 813 of the attitude and heading module 81; a level acceleration computation module 8204, which is same as the acceleration compensation module 814 ofthe attitude and heading module 81; and an attitude and heading angle extract module 8209, which is same as the attitude and heading angle extract module 817 of the attitude and heading module 81.
• a coning correction module 8201 which is same as the coning correction module 811 ofthe attitude and heading module
• a position and velocity update module 8208 accepts the level velocity increments from the level acceleration computation module 8204 and computes position and velocity solution.
• An earth and carrier rate computation module 8207 accepts the position and velocity solution from the position and velocity update module 8208 and computes the rotation rate vector of the local navigation frame (n frame) of the carrier relative to the inertial frame (i frame), which is connected to the alignment rotation vector computation module 8205.
• the digital three-axis angular increment voltage values, the digital three-axis velocity increment, and digital temperature signals in the input/output interface circuit 65 and the input/output interface circuit 305 can be ordered with a specific format required by an external user system, such as RS-232 serial communication standard, RS-422 serial communication standard, the popular PCI/ISA bus standard, and 1553 bus standard, etc.
• the digital three-axis angular increment values, the digital three-axis velocity increment, and attitude and heading data in the input/output interface circuit 85 are ordered with a specific format required by an external user system, such as RS-232 serial communication standard, RS-422 serial communication standard, PCI ISA bus standard, and 1553 bus standard, etc.
• micro-size angular rate producer with MEMS technologies and associated mechanical supporting structure and circuitry board deployment ofthe micro IMU ofthe present invention are disclosed in the following description.
• Another of the key technologies of the present invention to achieve the micro IMU with low power consumption is to design a micro size circuitry with small power consumption, wherein the conventional AISC (Application Specific Integrated Circuit) technologies can be utilized to shrink a complex circuitry into a silicon chip.
• AISC Application Specific Integrated Circuit
• the force (or acceleration), Coriolis force (or Coriolis acceleration) or Coriolis effect is originally named from a French physicist and mathematician, Gaspard de Coriolis
• the Coriolis acceleration acts on a body that is moving around a point with a fixed angular velocity and moving radially as well.
• F Conolts is the detected Coriolis force
• m is the mass ofthe inertial element
• ⁇ Corl0 . .s is the generated Coriolis acceleration
• ⁇ is the applied (input) angular rotation rate
• V 0s ⁇ ll ⁇ uon is the oscillation velocity in a rotating frame.
• the Coriolis force produced is proportional to the product ofthe mass ofthe inertial element, the input rotation rate, and the oscillation velocity of the inertial element that is perpendicular to the input rotation rate.
• micromachined vibrating type angular rate producer are active devices. Therefore, associated high performance electronics and control should be invented to effectively use hands-on micromachined vibrating type angular rate producers to achieve high performance angular rate measurements in order to meet the requirement of the micro IMU. Therefore, in order to obtain angular rate sensing signals from a vibrating type angular rate detecting unit, a dither drive signal or energy must be fed first into the vibrating type angular rate detecting unit to drive and maintain the oscillation of the inertial elements with a constant momentum. The performance of the dither drive signals is critical for the whole performance of a MEMS angular rate producer.
• the micro IMU comprises a first circuit board 2, a second circuit board 4, a third circuit board 7, and a control circuit board 9 arranged inside a metal cubic case 1.
• the first circuit board 2 is connected with the third circuit board 7 for producing X axis angular sensing signal and Y axis acceleration sensing signal to the control circuit board 9.
• the second circuit hoard 4 is connected with the third circuit board 7 for producing
• the third circuit board 7 is connected with the control circuit board 9 for producing Z axis angular sensing signal and Z axis acceleration sensing signals to the control circuit board 9.
• the control circuit board 9 is connected with the first circuit board 2 and then the second circuit board 4 through the third circuit board 7 for processing the X axis, Y axis and Z axis angular sensing signals and the X axis, Y axis and Z axis acceleration sensing signals from the first, second and control circuit board to produce digital angular increments and velocity increments, position, velocity, and attitude solution.
• the angular producer 5 of the preferred embodiment of the present invention comprises: a X axis vibrating type angular rate detecting unit 21 and a first front-end circuit 23 connected on the first circuit board 2; a Y axis vibrating type angular rate detecting unit 41 and a second front-end circuit
• DSP Digital Signal Processor
• the first, second and third front-end circuits 23, 43, 73 are used to condition the output signal of the X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 respectively and each further comprises: a trans impedance amplifier circuit 231, 431, 731, which is connected to the respective X axis, Y axis or Z axis vibrating type angular rate detecting unit 21, 41, 71 for changing the output impedance of the dither motion signals from a very high level, greater than 100 million ohms, to a low level, less than 100 ohms to achieve two dither displacement signals, which are A/C voltage signals representing the displacement between the inertial elements and the anchor combs.
• the two dither displacement signals are output to the dither motion control circuitry 922; and a high-pass filter circuit 232, 432, 732, which is connected with the respective X axis, Y axis or Z axis vibrating type angular rate detecting units 21, 41, 71 for removing residual dither drive signals and noise from the dither displacement differential signal to form a filtered dither displacement differential signal to the angular signal loop circuitry 921.
• Each of the X axis, Y axis and Z axis angular rate detecting units 21, 41, and 71 is structurally identical except that sensing axis of each angular rate detecting unit is placed in an orthogonal direction.
• the X axis angular rate detecting unit 21 is adapted to detect the angular rate of the vehicle along X axis.
• the Y axis angular rate detecting unit 21 is adapted to detect the angular rate ofthe vehicle along Y axis.
• the Z axis angular rate detecting unit 21 is adapted to detect the angular rate ofthe vehicle along Z axis.
• Each ofthe X axis, Y axis and Z axis angular rate detecting units 21, 41 and 71 is a vibratory device, which comprises at least one set of vibrating inertial elements, including tuning forks, and associated supporting structures and means, including capacitive readout means, and uses Coriolis effects to detect vehicle angular rate.
• Each ofthe X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 receives signals as follows: 1) dither drive signals from the respective dither motion control circuitry 922, keeping the inertial elements oscillating; and
• carrier reference oscillation signals from the oscillator 925 including capacitive pickoff excitation signals.
• Each of the X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 detects the angular motion in X axis, Y axis and Z axis respectively of a vehicle in accordance with the dynamic theory (Coriolis force), and outputs signals as follows:
• angular motion-induced signals including rate displacement signals which may be modulated carrier reference oscillation signals to a trans Impedance amplifier circuit 231, 431, 731 ofthe first, second, and third front-end circuit 23; and 2) its inertial element dither motion signals, including dither displacement signals, to the high-pass filter 232, 432,732 ofthe first, second, and third front-end circuit 23.
• the three dither motion control circuitries 922 receive the inertial element dither motion signals f om the X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 respectively, reference pickoff signals from the oscillator 925, and produce digital inertial element displacement signals with known phase.
• each of the dither motion control circuitries 922 comprises: an amplifier and summer circuit 9221 connected to the trans impedance amplifier circuit 231, 431, 731 of the respective first, second or third front-end circuit 23, 43, 73 for amplifying the two dither displacement signals for more than ten times and enhancing the sensitivity for combining the two dither displacement signals to achieve a dither displacement differential signal by subtracting a center anchor comb signal with a side anchor comb signal; a high-pass filter circuit 9222 connected to the amplifier and summer circuit 9221 for removing residual dither drive signals and noise from the dither displacement differential signal to form a filtered dither displacement differential signal; a demodulator circuit 9223 connected to the high-pass filter circuit 2225 for receiving the capacitive pickoff excitation signals as phase reference signals from the oscillator 925 and the filtered dither displacement differential signal from the high-pass filter
• a low-pass filter 9225 connected to the demodulator circuit 9223 for removing high frequency noise from the inertial element displacement signal input thereto to form a low frequency inertial element displacement signal; an analog/digital converter 9224 connected to the low-pass filter 9225 for converting the low frequency inertial element displacement analog signal to produce a digitized low frequency inertial element displacement signal to the dither motion processing module 912 (disclosed in the following text) running the DSP chipset 91 ; a digital/analog converter 9226 processing the selected amplitude from the dither motion processing module 912 to form a dither drive signal with the correct amplitude; and an amplifier 9227 which generates and amplifies the dither drive signal to the respective X axis, Y axis or Z axis vibrating type angular rate detecting unit 21, 41, 71 based on
• the oscillation ofthe inertial elements residing inside each ofthe X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 is generally driven by a high frequency sinusoidal signal with precise amplitude. It is critical to provide the X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41, 71 with high performance dither drive signals to achieve keen sensitivity and stability of X-axis, Y-axis and Z axis angular rate measurements.
• the dither motion processing module 912 receives digital inertial element displacement signals with known phase from the analog/digital converter 9224 of the dither motion control circuitry 922 for:
• the three dither motion processing modules 912 is to search and lock the vibrating frequency and amplitude of the inertial elements of the respective X axis, Y axis or Z axis vibrating type angular rate detecting unit 21, 41, 71. Therefore, the digitized low frequency inertial element displacement signal is first represented in terms of its spectral content by using discrete Fast Fourier Transform (FFT).
• FFT Fast Fourier Transform
• Discrete Fast Fourier Transform is an efficient algorithm for computing discrete Fourier transform (DFT), which dramatically reduces the computation load imposed by the DFT.
• the DFT is used to approximate the Fourier transform of a discrete signal.
• the Fourier transform, or spectrum, of a continuous signal is defined as:
• the basic property of FFT is its ability to distinguish waves of different frequencies that have been additively combined.
• the digitized low frequency inertial element displacement signals are represented in terms of their spectral content by using discrete Fast Fourier Transform (FFT), Q (Quality Factor) Analysis is applied to their spectral content to determine the frequency with global maximal Q value.
• FFT discrete Fast Fourier Transform
• Q Quality Factor
• the vibration of the inertial elements of the respective X axis, Y axis or Z axis vibrating type angular rate detecting unit 21, 41, 71 at the frequency with global maximal Q value can result in minimal power consumption and cancel many of the terms that affect the excited mode.
• the Q value is a function of basic geometry, material properties, and ambient operating conditions.
• a phase-locked loop and digital/analog converter is further used to control and stabilize the selected frequency and amplitude.
• the dither motion processing module 912 further includes a discrete Fast Fourier Transform (FFT) module 9121, a memory array of frequency and amplitude data module 9122, a maxima detection logic module 9123, and a Q analysis and selection logic module 124 to find the frequencies which have the highest Quality Factor (Q)
• FFT discrete Fast Fourier Transform
• Q Quality Factor
• the discrete Fast Fourier Transform (FFT) module 9121 is arranged for transforming the digitized low frequency inertial element displacement signal from the analog/digital converter 9224 ofthe dither motion control circuitry 922 to form amplitude data with the frequency spectrum ofthe input inertial element displacement signal.
• FFT Fast Fourier Transform
• the memory array of frequency and amplitude data module 9122 receives the amplitude data with frequency spectrum to form an array of amplitude data with frequency spectrum.
• the maxima detection logic module 9123 is adapted for partitioning the frequency spectrum from the array of the amplitude data with frequency into plural spectrum segments, and choosing those frequencies with the largest amplitudes in the local segments of the frequency spectrum.
• the Q analysis and selection logic module 9124 is adapted for performing Q analysis on the chosen frequencies to select frequency and amplitude by computing the ratio of amplitude/bandwidth, wherein the range for computing bandwidth is between +-1/2 of the peek for each maximum frequency point.
• the dither motion processing module 912 further includes a phase-lock loop 9125 to reject noise of the selected frequency to form a dither drive signal with the selected frequency, which serves as a very narrow bandpass filter, locking the frequency.
• the three angle signal loop circuitries 921 receive the angular motion-induced signals from the X axis, Y axis and Z axis vibrating type angular rate detecting units 21, 41,
• each ofthe angle signal loop circuitries 921 for the respective first, second or third circuit board 2, 4, 7 comprises: a voltage amplifier circuit 9211, which amplifies the filtered angular motion- induced signals from the high-pass filter circuit 232 of the respective first, second or third front-end circuit 23, 43, 73 to an extent of at least 100 milivolts to form amplified angular motion-induced signals; an amplifier and summer circuit 9212, which subtracts the difference between the angle rates ofthe amplified angular motion-induced signals to produce a differential angle rate signal; a demodulator 9213, which is connected to the amplifier and summer circuit 9212, extracting the amplitude of the in-phase differential angle rate signal from the differential angle rate signal and the capacitive pickoff excitation signals from the oscillator 925; a low-pass filter 9214, which is connected to the demodulator 92
• the acceleration producer 10 of the preferred embodiment ofthe present invention comprises: a X axis accelerometer 42, which is provided on the second circuit board 4 and connected with the angular increment and velocity increment producer 6 provided in the AISC chip 92 ofthe control circuit board 9; a Y axis accelerometer 22, which is provided on the first circuit board 2 and connected with angular increment and velocity increment producer 6 provided in the AISC chip 92 ofthe control circuit board 9; and a Z axis accelerometer 72, which is provided on the third circuit board 7 and connected with angular increment and velocity increment producer 6 provided in the AISC chip 92 ofthe control circuit board 9.
• a X axis accelerometer 42 which is provided on the second circuit board 4 and connected with the angular increment and velocity increment producer 6 provided in the AISC chip 92 ofthe control circuit board 9
• a Y axis accelerometer 22 which is provided on the first circuit board 2 and connected with angular increment and velocity increment producer 6 provided in the AISC chip 92 ofthe control circuit board 9
• thermal sensing producer device 15 of the preferred embodiment ofthe present invention further comprises: a first thermal sensing producing unit 24 for sensing the temperature of the X axis angular rate detecting unit 21 and the Y axis accelerometer 22; a second thermal sensing producer 44 for sensing the temperature of the Y axis angular rate detecting unit 41 and the X axis accelerometer 42; and a third thermal sensing producer 74 for sensing the temperature ofthe Z axis angular rate detecting unit 71 and the Z axis accelerometer 72.
• the heater device 20 ofthe preferred embodiment of the present invention further comprises: a first heater 25, which is connected to the X axis angular rate detecting unit 21, the Y axis accelerometer 22, and the first front-end circuit 23, for maintaining the predetermined operational temperature ofthe X axis angular rate detecting unit 21, the Y axis accelerometer 22, and the first front-end circuit 23; a second heater 45, which is connected to the Y axis angular rate detecting unit 41, the X axis accelerometer 42, and the second front-end circuit 43, for maintaining the predetermined operational temperature ofthe X axis angular rate detecting unit 41, the X axis accelerometer 42, and the second front-end circuit 43; and a third heater 75, which is connected to the Z axis angular rate detecting unit 71, the Z axis accelerometer 72, and the third front-end circuit 73, for maintaining the predetermined operational temperature of the Z axis angular rate detecting unit
• the thermal processor 30 of the preferred embodiment of the present invention further comprises three identical thermal control circuitries 923 and the thermal control computation modules 911 running the DSP chipset 91.
• each of the thermal control circuitries 923 further comprises: a first amplifier circuit 9231, which is connected with the respective X axis, Y axis or Z axis thermal sensing producer 24, 44, 74, for amplifying the signals and suppressing the noise residing in the temperature voltage signals from the respective X axis, Y axis or Z axis thermal sensing producer 24, 44, 74 and improving the signal-to-noise ratio; an analogdigital converter 9232, which is connected with the amplifier circuit 9231, for sampling the temperature voltage signals and digitizing the sampled temperature voltage signals to digital signals, which are output to the thermal control computation module 911; a digital/analog converter 9233 which converts the digital temperature commands input from the thermal control computation module 911 into analog signals; and a second amplifier circuit 9234, which receives the analog signals from the digital/analog converter 9233, amplifying the input analog signals from the digital/analog converter 9233 for driving the respective first, second or third heater 25, 45
• the thermal control computation module 911 computes digital temperature commands using the digital temperature voltage signals from the analog/digital converter
• the third circuit board 7 is bonded to a supporting structure by means of a conductive epoxy, and the first circuit board 2, the second circuit board 4, and the control circuit board 9 are arranged parallelly to bond to the third circuit board 7 perpendicularly by a non conductive epoxy.
• the first circuit board 2, the second circuit board 4, and the control circuit board 9 are soldered to the third circuit board 7 in such a way as to use the third circuit board 7 as an interconnect board, thereby avoiding the necessity to provide interconnect wiring, so as to minimize the small size.
• the first, second, third, and control circuit boards 2, 4, 7, and 9 are constructed using ground planes which are brought out to the perimeter of each circuit board 2, 4, 7, 9, so that the conductive epoxy can form a continuous ground plane with the supporting structure. In this way the electrical noise levels are minimized and the thermal gradients are reduced.
• the bonding process also reduces the change in misalignments due to structural bending caused by acceleration ofthe IMU.
• the micro IMU as disclosed above processes a motion measurement according to the present invention, which comprises the following steps.
• the angular rate producer 5 and the acceleration producer 10 are very sensitive to a variety of temperature environments.
• the present invention further comprises an additional thermal controlling loop step 4, processed in parallel with the above steps 1 to 3, of maintaining a predetermined operating temperature throughout the above steps, wherein the predetermined operating temperature is a constant designated temperature selected between 150°F and 185°F, preferable 176°F ( ⁇ 0.1 °F).
• the above thermal controlling loop step 4, as shown in Figure 2, further comprises the steps of:
• 4A-2 inputting the temperature signals to the thermal processor 30 for computing temperature control commands using the temperature signals, a temperature scale factor, and a predetermined operating temperature of the angular rate producer 5 and the acceleration producer 10; 4A-3. producing driving signals to the heater device 20 using the temperature control commands; and
• Temperature characteristic parameters of the angular rate producer 5 and the acceleration producer 10 can be determined during a series of the angular rate producer and acceleration producer temperature characteristic calibrations.
• the present invention further comprises the steps of:
• 3A-2 accessing temperature characteristic parameters of the angular rate producer and the acceleration producer using a current temperature ofthe angular rate producer and the acceleration producer from the temperature digitizer 18;
• step 1 further comprises the step of: 1.1 acquiring three-axis analog angular rate voltage signals from the angular producer 5, which are directly proportional to carrier angular rates, and
• the above producing step 1 prefers to further comprise amplifying steps 1.3 and 1.4 as follows after the step 1.2 for amplifying the analog voltage signals input from the angular rate producer 5 and the acceleration producer 10 and suppressing noise signals residing within the analog voltage signals input from the angular rate producer 5 and the acceleration producer 10, as shown in Figure 5 and 11 ,
• the above converting step 2 further comprises the following steps: 2.1. Integrate the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals for a predetermined time interval to accumulate the three- axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals as a raw three-axis angular increment and a raw three-axis velocity increment for the predetermined time interval to achieve accumulated angular increments and accumulated velocity increments.
• the integration is performed to remove noise signals that are non-directly proportional to the carrier angular rate and acceleration within the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals, to improve signal- to-noise ratio, and to remove the high frequency signals in the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals.
• the signals that are directly proportional to the carrier angular rate and acceleration within the three-axis analog angular rate voltage signals and the three-axis analog acceleration voltage signals can be used in subsequent processing steps.
• 2.2 Form an angular reset voltage pulse and a velocity reset voltage pulse as an angular scale and a velocity scale respectively.
• 2.3 Measure the voltage values of the three-axis accumulated angular increments and the three-axis accumulated velocity increments with the angular reset voltage pulse and the velocity reset voltage pulse respectively to acquire angular increment counts and velocity increment counts as a digital form of angular and velocity measurements respectively.
• the converting step 2 further comprises an additional step of:
• the three-axis analog angular voltage signals and the three-axis analog acceleration voltage signals are each reset to accumulate from a zero value at an initial point of every predetermined time interval.
• the angular reset voltage pulse and the velocity reset voltage pulse in the step 2.2 may be implemented by producing a timing pulse by an oscillator 66, as shown in Figure 6.
• step 2.3 the measurement ofthe voltage values ofthe three-axis accumulated angular and velocity increments can be implemented by the analog/digital converter 650, as shown in Figure 7.
• step 2.3 is substantially a digitization step for digitizing the raw three-axis angular and velocity increment voltage values into digital three-axis angular and velocity increments.
• the above amplifying, integrating, analog/digital converter 650 and oscillator 66 can be built with circuits, such as Application Specific Integrated Circuits(ASIC) chip and a printed circuit board.
• ASIC Application Specific Integrated Circuits
• the step 2.3 further comprises the steps of: 2.3.1 inputting the accumulated angular increments and the accumulated velocity increments into the angular analog/digital converter 63 and the velocity analog/digital converter 69 respectively;
• thermal processor 30 can be implemented in a digital feedback controlling loop as shown in
• thermal controlling loop step 4 alternatively comprises the steps of:
• 4B-3 computing digital temperature commands in the temperature controller 306 using the input digital signals from the analog/digital converter 304, a temperature sensor scale factor, and a pre-determined operating temperature of the angular rate producer and acceleration producer, wherein the digital temperature commands are fed back to the digital/analog converter 303, and
• the amplifying step 4-0 Acquire voltage signals from the thermal sensing producer 15 to the first amplifier circuit 301 for amplifying the signals and suppressing the noise residing in the voltage signals and improving the signal-to-noise ratio, wherein the amplified voltage signals are output to the analog/digital converter 304.
• the heater device 20 requires a specific driving current signals.
• an amplifying step 4.5 preferred to be processed between the digital/analog converter 303 and heater device 20:
• Step 4B-5 amplifying the input analog signals from the digital/analog converter 303 for driving the heater device 20 in the second amplifier circuit 302; and closing the temperature controlling loop.
• step 4B-4 further comprises the step of:
• the input/output interface circuit 305 is required to connect the analog/digital converter 304 and digital/analog converter 303 and with the temperature controller 306.
• the step 4B-2 comprises the step of:
• step 4B-3 comprises the step of:
• the step 4B-4 further comprises the step of: 4B-4B converting the digital temperature commands input from the input/output interface circuit 305 in the digital/analog converter 303 into analog signals which are output to the heater device 20 to provide adequate heat for maintaining the predetermined operating temperature throughout the above steps 1 to 3.
• step 3A-1 can be implemented by the analog/digital converter 182 for the thermal sensing producer 15 with analog voltage output. If the voltage signals produced by the thermal sensing producer 15 are too weak for the analog /digital converter 182 to read, referring to Figure 13, there is an additional amplifying step processed between the thermal sensing producer 15 and the digital/analog converter 182.
• the step 3A-1 further comprises the steps of: 3 A- 1.1 acquiring voltage signals from the thermal sensing producer 15 to the amplifier circuit 181 for amplifying the signals and suppressing the noise residing in the voltage signals and improving the voltage signal-to-noise ratio, wherein the amplified voltage signals are output to the analog/digital converter 182, and
• the step 3A-1.2 comprises the step of: 3A-1.2A sampling the input amplified voltage signals in the analog/digital converters 182 and digitizing the sampled voltage signals to form digital signals outputting to the input/output interface circuit 183.
• step 3 further comprises the steps of:
• 3B.1 inputting digital three-axis angular increment voltage values from the input/output interface circuit 65 of the step 2 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate (short interval) into the coning correction module 801; computing coning effect errors in the coning correction module 801 using the input digital three-axis angular increment voltage values and coarse angular rate bias; and outputting three-axis coning effect terms and three-axis angular increment voltage values at reduced data rate (long interval), which are called three-axis long- interval angular increment voltage values, into the angular rate compensation module 802,
• 3B.2 inputting the coning effect errors and three-axis long-interval angular increment voltage values from the coning correction module 801 and angular rate device misalignment parameters, fine angular rate bias, angular rate device scale factor, and coning correction scale factor from the angular rate producer and acceleration producer calibration procedure to the angular rate compensation module 802; compensating definite errors in the input three-axis long-interval angular increment voltage values using the input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor; transforming the compensated three-axis long-interval angular increment voltage values to real three-axis long-interval angular increments using the angular rate device scale factor; and outputting the real three-axis angular increments to the alignment rotation vector computation module 805,
• 3B.3 inputting the three-axis velocity increment voltage values from the input/output interface circuit 65 of the step 2 and acceleration device misalignment, acceleration device bias, and acceleration device scale factor from the angular rate producer and acceleration producer calibration procedure to the accelerometer compensation module 803; transforming the input three-axis velocity increments voltage values into real three-axis velocity increments using the acceleration device scale factor; compensating the definite errors in three-axis velocity increments using the input acceleration device misalignment, accelerometer bias; outputting the compensated three-axis velocity increments to the level acceleration computation module 804, 3B.4 updating the quaternion, which is a vector representing rotation motion ofthe carrier, using the compensated three-axis angular increments from the angular rate compensation module 802, an east damping rate increment from the east damping computation module 808, a north damping rate increment from the north damping computation module 809, and vertical damping rate increment from the vertical damping computation module 810; and the updated quaternion is output to the direction cosine
• 3B.6 extracting attitude and heading angle using the direction cosine matrix from the direction cosine matrix computation module 806; outputting the heading angle into the vertical damping rate computation module 808,
• 3B.7 computing level velocity increments using the input compensated three-axis velocity increments from the acceleration compensation module 804 and the direction cosine matrix from the direction cosine matrix computation module 806; outputting the level velocity increments to the east damping rate computation module 810 and the north damping rate computation module 809,
• step 3B.10 computing vertical damping rate increments using the computed heading angle from the attitude and heading angle extract module 807 and a measured heading angle from the external sensor 90; and feeding back the vertical damping rate increments to the alignment rotation vector computation module 805.
• step 3B.1 ⁇ 3B.3 are modified into:
• 3B.1A inputting real digital three-axis angular increment values from the step 2 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate (short interval) into a coning correction module 801; computing coning effect errors in the coning correction module 801 using the input digital three-axis angular increment values and coarse angular rate bias; and outputting three-axis coning effect terms and three-axis angular increment values at reduced data rate (long interval), which are called three-axis long-interval angular increment values, into the angular rate compensation module 802,
• 3B.2A inputting the coning effect errors and three-axis long-interval angular increment values from the coning correction module 801 and angular rate device misalignment parameters and fine angular rate bias from the angular rate producer and acceleration producer calibration procedure to the angular rate compensation module 802; compensating definite errors in the input three-axis long-interval angular increment values using the input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor; and outputting the real three-axis angular increments to the alignment rotation vector computation module 805, and 3B.3A inputting the three-axis velocity increment values from Step 2 and acceleration device misalignment, and acceleration device bias from the angular rate producer and acceleration producer calibration procedure to the accelerometer compensation module 803; compensating the definite errors in three-axis velocity increments using the input acceleration device misalignment, accelerometer bias; outputting the compensated three-axis velocity increments to the level acceleration computation module 804.
• step 3A-2 further comprises the steps of: 3A-2.1 inputting digital three-axis angular increment voltage values from the input/output interface circuit 65 of the step 2 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate (short interval) into a coning correction module 801; computing coning effect errors in the coning correction module 801 using the input digital three-axis angular increment voltage values and coarse angular rate bias; and outputting three-axis coning effect terms and three-axis angular increment voltage values in reduced data rate (long interval), which are called three-axis long- interval angular increment voltage values, into the angular rate compensation module 802,
• 3A-2.2 inputting the coning, effect errors and three-axis long-interval angular increment voltage values from the coning correction module 801 and angular rate device misalignment parameters, fine angular rate bias, angular rate device scale factor, and coning correction scale factor from the angular rate producer and acceleration producer calibration procedure to the angular rate compensation module 802; inputting the digital temperature signals from input output interface circuit 183 ofthe step 3 A.1.2 and temperature sensor scale factor; computing current temperature of angular rate producer; accessing angular rate producer temperature characteristic parameters using the current temperature of angular rate producer; compensating definite errors in the input three-axis long-interval angular increment voltage values using the input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor; transforming the compensated three-axis long-interval angular increment voltage values to real three-axis long- interval angular increments; compensating temperature-induced errors in the real three-axis long-interval
• 3A-2.3 inputting the three-axis velocity increment voltage values from the input/output interface circuit 65 of the step 2 and acceleration device misalignment, acceleration bias, acceleration device scale factor from the angular rate producer and acceleration producer calibration procedure to the acceleration compensation module 803; inputting the digital temperature signals from the input/output interface circuit 183 ofthe step 3A-1 and temperature sensor scale factor; computing current temperature of acceleration producer; accessing acceleration producer temperature characteristic parameters using the current temperature of acceleration producer; transforming the input three-axis velocity increments voltage values into real three-axis velocity increments using the acceleration device scale factor; compensating the definite errors in three-axis velocity increments using the input acceleration device misalignment, acceleration bias; compensating temperature- induced errors in the real three-axis velocity increments using the acceleration producer temperature characteristic parameters; and outputting the compensated three-axis velocity increments to the level acceleration computation module 804, 3A-2.4 updating a quaternion, which is a vector representing rotation motion of the carrier, using the compensated three-axis angular increments from
• 3A-2.5 computing the direction cosine matrix, using the input updated quaternion; and the computed direction cosine matrix is output to the level acceleration computation module 804 and the attitude and heading angle extract module 807, 3A-2.6 extracting attitude and heading angle using the direction cosine matrix from the direction cosine matrix computation module 806; outputting the heading angle into the vertical damping rate computation module 808,
• 3A-2.7 computing level velocity increments using the input compensated three-axis velocity increments from the acceleration compensation module 804 and the direction cosine matrix from the direction cosine matrix computation module 806; outputting the level velocity increments to the east damping rate computation module 810 and north damping rate computation module 809,
• 3A-2.8 computing east damping rate increments using the north velocity increment of the input level velocity increments from the level acceleration computation module 804; feeding back the east damping rate increments to the alignment rotation vector computation module 805,
• step 3A-2.9 computing north damping rate increments using the east velocity increment of the input level velocity increments from the level acceleration computation module 804; feeding back the north damping rate increments to the alignment rotation vector computation module 805, and 3A-2.10 computing vertical damping rate increments using the computed heading angle from the attitude and heading angel extract module 807 and a measured heading angle from the external sensor 90; and feeding back the vertical damping rate increments to the alignment rotation vector computation module 805.
• Figure 3, 14, and 15 which use temperature compensation method, in order to adapt to real digital three-axis angular increment values and real three-axis digital velocity increment values from the step 2, the above mentioned step 3A-2.1 are modified into:
• 3A-2.1A inputting digital three-axis angular increment values from the input/output interface circuit 65 of Step 2 and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate (short interval) into a coning correction module 801; computing coning effect errors in the coning correction module 801 using the input digital three-axis angular increment values and coarse angular rate bias; and outputting three-axis coning effect terms and three-axis angular increment values in reduced data rate (long interval), which are called three-axis long-interval angular increment values, into the angular rate compensation module 802,
• 3A-2.2A inputting the coning effect errors and three-axis long-interval angular increment values from the coning correction module 801 and angular rate device misalignment parameters and fine angular rate bias from the angular rate producer and acceleration producer calibration procedure to the angular rate compensation module 802; inputting the digital temperature signals from input/output interface circuit 183 ofthe step 3A- 1.2 and temperature sensor scale factor; computing current temperature of angular rate producer; accessing angular rate producer temperature characteristic parameters using the current temperature of angular, rate producer; compensating definite errors in the input three- axis long-interval angular increment values using the input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor; compensating temperature-induced errors in the real three-axis long-interval angular increments using the angular rate producer temperature characteristic parameters; and outputting the real three-axis angular increments to an alignment rotation vector computation module 805, and 3A-2.3A in
• an additional processing step which is performed after the above embodied step 2.3.1-2.3.3, comprises:
• an additional processing step referring to Figures 1, 11 and 14, which is performed after the above embodied step 3, comprises:

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