Method of measuring motion

• US 20010045128A1
• Filed: 05/24/2001
• Published: 11/29/2001
• Est. Priority Date: 05/24/2000
• Status: Active Grant

• Current Assignee: American GNC Corporation
• Original Assignee: American GNC Corporation
• Inventors: Lin, Ching-Fang, McCall, Hiram
• Granted Patent: US 6,494,093 B2
• Time in Patent Office: Days
• US Class Current: 73/511
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

A method for measuring motion of a user, which is adapted to apply to output signals proportional to rotation and translational motion of the carrier, respectively from angular rate sensors and acceleration sensors, is more suitable for emerging MEMS angular rate and acceleration sensors. Compared with a conventional IMU, said processing method utilizes a feedforward open-loop signal processing scheme to obtain highly accurate motion measurements by means of signal digitizing, temperature control, sensor error and misalignment calibrations, attitude updating, and damping control loops, and dramatically shrinks said size of mechanical and electronic hardware and power consumption, meanwhile, obtains highly accurate motion measurements.

Claims

1. A method for measuring motion of a user, comprising the steps of:

(a) producing three-axis angular rate signals by an angular rate producer and three-axis acceleration signals by an acceleration producer;

(b) converting said three-axis angular rate signals into digital angular increments and converting said input three-axis acceleration signals into digital velocity increments in an angular increment and velocity increment producer 6; and

(c) computing attitude and heading angle measurements using said three-axis digital angular increments and said three-axis velocity increments in an attitude and heading processor.

(d) maintaining a predetermined operating temperature throughout said above steps, wherein said predetermined operating temperature is a constant designated temperature selected between 150°

F. and 185°

F., by means of;

(d.1) performing parameter setting at turn on by initializing first and second temperature constants of first heater and second heater to a value of 1 deg centigrade greater than final destination temperature, respectively;

and for each new temperature data frame from said first and second temperature sensors, in an iterative fashion;

(d.2) adding said first temperature constant to said first temperature sensor value from said first temperature sensor and adding said first result of said last frame value of said first heater loop to form said current first result;

(d.3) loading said current first result into said first down counter used to form said length of said first pulse which varies from 0 to 100%, wherein said first pulse is used to drive said first heater;

(d.4) saving said current first result for use during said next iteration of said first heater loop;

(d.5) adding said second temperature constant to said second temperature sensor value from said second temperature sensor and adding said second result of said last frame value of said second heater loop to form said current second result;

(d.6) loading said current second result into said second down counter used to form said length of said second pulse which varies from 0 to 100%, wherein said second pulse is used to drive said second heater;

(d.7) saving said current second result for use during said next iteration of said second heater loop;

(d.8) setting said first temperature constant of said first heater loop to said final destination temperature and setting said second heater loop to off, when said temperature, which is said initially set at a value of 1 deg centigrade greater than said final destination temperature, is reached, as measured by both temperature sensors;

(d.9) setting said second temperature constant of heater loop to said value of second temperature sensor 2, and setting said second heater loop on, when said temperature cools to said final temperature, as measured by temperature sensor.

2. The method for measuring motion of a user, as recited in

claim 1

, wherein said angular rate producer and said acceleration producer are MEMS angular rate device

3. The method for measuring motion of a user, as recited in

claim 2

, wherein said step (a) further comprises said steps of:

(a.1) acquiring three-axis analog angular rate voltage signals from said angular producer, which are directly proportional to carrier angular rates, and

(a.2) acquiring three-axis analog acceleration voltage signals from said acceleration producer, which are directly proportional to carrier accelerations.

4. The method for measuring motion of a user, as recited in

claim 3

, wherein said step (a) further comprises amplifying steps of amplifying said analog voltage signals input from said angular rate producer and said acceleration producer and suppressing noise signals residing within said analog voltage signals input from said angular rate producer and said acceleration producer.

5. The method for measuring motion of a user, as recited in

claim 4

, wherein said amplifying step comprises said steps of:

(a.3) amplifying said three-axis analog angular rate voltage signals and said three-axis analog acceleration voltage signals by means of a first amplifier circuit and a second amplifier circuit respectively to form amplified three-axis analog angular rate signals and amplified three-axis analog acceleration signals respectively; and

(a.4) outputting said amplified three-axis analog angular rate signals and said amplified three-axis analog acceleration signals to an integrator circuit and an integrator circuit,

6. The method for measuring motion of a user, as recited in

claim 5

, wherein said step (b) further comprises said steps of:

(b.1) integrating said three-axis analog angular rate voltage signals and said three-axis analog acceleration voltage signals for a predetermined time interval to accumulate said three-axis analog angular rate voltage signals and said three-axis analog acceleration voltage signals as a raw three-axis angular increment and a raw three-axis velocity increment for said predetermined time interval to achieve accumulated angular increments and accumulated velocity increments, for removing noise signals that are non-directly proportional to said carrier angular rate and acceleration within said three-axis analog angular rate voltage signals and said three-axis analog acceleration voltage signals, improving signal-to-noise ratio, and removing said high frequency signals in said three-axis analog angular rate voltage signals and said three-axis analog acceleration voltage signals;

(b.2) forming an angular reset voltage pulse and a velocity reset voltage pulse as an angular scale and a velocity scale respectively;

(b.3) measuring said voltage values of said three-axis accumulated angular increments and said three-axis accumulated velocity increments with said angular reset voltage pulse and said velocity reset voltage pulse respectively to acquire angular increment counts and velocity increment counts as a digital form of angular and velocity measurements respectively; and

(b.4) scaling said voltage values of said three-axis accumulated angular and velocity increments into real three-axis angular and velocity increment voltage values.

7. The method for measuring motion of a user, as recited in

claim 6

, wherein in said step (b.1) said three-axis analog angular voltage signals and said three-axis analog acceleration voltage signals are each reset to accumulate from a zero value at an initial point of every predetermined time interval.

8. The method for measuring motion of a user, as recited in

claim 6

, wherein in said step (b.2), said angular reset voltage pulse and said velocity reset voltage pulse are implemented by producing a timing pulse by an oscillator.

9. The method for measuring motion of a user, as recited in

claim 6

, wherein in said step (b.3), said measurement of said voltage values of said three-axis accumulated angular and velocity increments are implemented by an analog/digital converter, for digitizing said raw three-axis angular and velocity increment voltage values into digital three-axis angular and velocity increments.

10. The method for measuring motion of a user, as recited in

claim 6

, wherein said step (b.3) further comprises said steps of:

(b.3.1) inputting said accumulated angular increments and said accumulated velocity increments into an angular analog/digital converter and a velocity analog/digital converter respectively;

(b.3.2) digitizing said accumulated angular increments by said angular analog/digital converter by measuring said accumulated angular increments with said angular reset voltage pulse to form a digital angular measurements of voltage in terms of said angular increment counts which is output to an input/output interface circuit;

(b.3.3) digitizing said accumulated velocity increments by said velocity analog/digital converter by measuring said accumulated velocity increments with said velocity reset voltage pulse to form a digital velocity measurements of voltage in terms of said velocity increment counts which is output to said an input/output interface circuit; and

(b.3.4) outputting said digital three-axis angular and velocity increment voltage values by said input/output interface circuit.

11. The method for measuring motion of a user, as recited in

claim 1

to 10, wherein in order to adapt to digital three-axis angular increment voltage value and three-axis digital velocity increment voltage values from said step (b), said step (c) further comprises said steps of:

(cb.1) inputting digital three-axis angular increment voltage values from said input/output interface circuit of said step (b) and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate for a short interval into a coning correction module;

computing coning effect errors in said coning correction module using said 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 for a long interval, which are called three-axis long-interval angular increment voltage values, into a angular rate compensation module,

(cb.2) inputting said coning effect errors and three-axis long-interval angular increment voltage values from said coning correction module and angular rate device misalignment parameters, fine angular rate bias, angular rate device scale factor, and coning correction scale factor from said angular rate producer and acceleration producer calibration procedure to said angular rate compensation module;

compensating definite errors in said input three-axis long-interval angular increment voltage values using said input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor;

transforming said compensated three-axis long-interval angular increment voltage values to real three-axis long-interval angular increments using said angular rate device scale factor; and

outputting said real three-axis angular increments to an alignment rotation vector computation module,

(cb.3) inputting said three-axis velocity increment voltage values from said input/output interface circuit of said step (b) and acceleration device misalignment, acceleration device bias, and acceleration device scale factor from said angular rate producer and acceleration producer calibration procedure to accelerometer compensation module;

transforming said input three-axis velocity increments voltage values into real three-axis velocity increments using said acceleration device scale factor;

compensating said definite errors in three-axis velocity increments using said input acceleration device misalignment, accelerometer bias;

outputting said compensated three-axis velocity increments to said level acceleration computation module,

(cb.4) updating a quaternion, which is a vector representing rotation motion of said carrier, using said compensated three-axis angular increments from said angular rate compensation module, an east damping rate increment from an east damping computation module, a north damping rate increment from a north damping computation module, and vertical damping rate increment from a vertical damping computation module; and

said updated quaternion is output to a direction cosine matrix computation module,

(cb.5) computing said direction cosine matrix, using said input updated quaternion; and

said computed direction cosine matrix is output to a level acceleration computation module and an attitude and heading angle extract module,

(cb.6) extracting attitude and heading angle using said direction cosine matrix from said direction cosine matrix computation module;

outputting said heading angle into a vertical damping rate computation module,

(cb.7) computing level velocity increments using said input compensated three-axis velocity increments from said acceleration compensation module and said direction cosine matrix from said direction cosine matrix computation module;

outputting said level velocity increments to an east damping rate computation module and north damping rate computation module,

(cb.8) computing east damping rate increments using said north velocity increment of said input level velocity increments from said level acceleration computation module;

feeding back said east damping rate increments to said alignment rotation vector computation module,

(cb.9) computing north damping rate increments using said east velocity increment of said input level velocity increments from said level acceleration computation module;

feeding back said north damping rate increments to said alignment rotation vector computation module, and

(cb.10) computing vertical damping rate increments using said computed heading angle from said attitude and heading angle extract module and a measured heading angle from an external sensor; and

feeding back said vertical damping rate increments to said alignment rotation vector computation module.

12. The method for measuring motion of a user, as recited in

claim 10

, wherein in order to adapt to real digital three-axis angular increment value and three-axis digital velocity increment values from said step (b), said step (c) further comprises said steps of:

(cb.1) inputting real digital three-axis angular increment values from said step (b) and coarse angular rate bias obtained from an angular rate producer and acceleration producer calibration procedure in high data rate for a short interval into a coning correction module;

computing coning effect errors in said coning correction module using said 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 a angular rate compensation module,

(cb.2) inputting said coning effect errors and three-axis long-interval angular increment values from said coning correction module and angular rate device misalignment parameters and fine angular rate bias from said angular rate producer and acceleration producer calibration procedure to said angular rate compensation module;

compensating definite errors in said input three-axis long-interval angular increment values using said input coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor; and

outputting said real three-axis angular increments to an alignment rotation vector computation module,

(cb.3) inputting said real three-axis velocity increment values from said step (b) and acceleration device misalignment, and acceleration device bias from said angular rate producer and acceleration producer calibration procedure to accelerometer compensation module;

compensating said definite errors in three-axis velocity increments using said input acceleration device misalignment, accelerometer bias;

outputting said compensated three-axis velocity increments to said level acceleration computation module,

(cb.4) updating a quaternion, which is a vector representing rotation motion of said carrier, using said compensated three-axis angular increments from said angular rate compensation module, an east damping rate increment from an east damping computation module, a north damping rate increment from a north damping computation module, and vertical damping rate increment from a vertical damping computation module; and

said updated quaternion is output to a direction cosine matrix computation module,

(cb.5) computing said direction cosine matrix, using said input updated quaternion; and

said computed direction cosine matrix is output to a level acceleration computation module and an attitude and heading angle extract module,

(cb.6) extracting attitude and heading angle using said direction cosine matrix from said direction cosine matrix computation module;

outputting said heading angle into a vertical damping rate computation module,

(cb.7) computing level velocity increments using said input compensated three-axis velocity increments from said acceleration compensation module and said direction cosine matrix from said direction cosine matrix computation module;

outputting said level velocity increments to an east damping rate computation module and north damping rate computation module,

(cb.8) computing east damping rate increments using said north velocity increment of said input level velocity increments from said level acceleration computation module;

feeding back said east damping rate increments to said alignment rotation vector computation module,

(cb.9) computing north damping rate increments using said east velocity increment of said input level velocity increments from said level acceleration computation module;

feeding back said north damping rate increments to said alignment rotation vector computation module, and

(cb.10) computing vertical damping rate increments using said computed heading angle from said attitude and heading angle extract module and a measured heading angle from an external sensor; and

feeding back said vertical damping rate increments to said alignment rotation vector computation module.