Method and apparatus for an AGV inertial table having an angular rate sensor and a voltage controlled oscillator

• US 5,539,646 A
• Filed: 10/26/1993
• Issued: 07/23/1996
• Est. Priority Date: 10/26/1993
• Status: Expired due to Fees

• Current Assignee: HK Systems Incorporated (KION GROUP AG)
• Original Assignee: HK Systems Incorporated (KION GROUP AG)
• Inventors: Carter, Paul, Whatcott, Gary L., Petersen, John A. M.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): FREJD, RUSSELL WARREN
• Application Number:
  US08/143,334
• Time in Patent Office: 1,001 Days
• Field of Search: 364/453, 364/424.02, 318/587, 340/825.06, 180/167, 180/168
• US Class Current: 701/220
• CPC Class Codes: G01C 21/18 Stabilised platforms, e.g. by gyroscope

Abstract

A low-cost solid state replacement circuit for an inertial platform with the resulting consequence of increased resolution, significantly reduced cost, and improved reliability and accuracy. The invention comprises no moving parts and permits the use of a strap-down angular rate sensor system which has a fixed orientation relative to an AGV on which the circuit is used. The invention creatively emulates encoder signals previously emanating from the inertial table through the use of a voltage controlled oscillator, a direction of turn determining circuit and an encoder emulator. Cabling which exists in current inertial tables does not need to be changed and information format previously used remains unchanged.

Claims

1. A strap-down inertial table system having no moving parts, other than sensing parts of an angular rate sensor, which is a direct and compatible substitute for an inertial table being used in an unmanned automatically guided vehicle and having moving parts, said strap-down table system comprising:

an angular rate sensor which provides an output voltage which is a function of angular rate and direction of turning;

low pass means for filtering said output voltage to produce a filtered output voltage;

means for dividing the filtered output voltage from said filtering means into at least two electrical signal pathways;

means for rectifying a signal from one of such pathways to remove direction of turning;

a voltage-controlled-oscillator which receives a voltage signal from said rectifying means and produces a frequency signal proportional to the voltage of the received signal;

means for translating polarity of a signal from another of such signal pathways and producing a binary signal indicative of direction of turning;

means for receiving and processing said frequency signal and said binary signal to produce an output which emulates an encoder output;

means for connecting said emulated encoder output to a quadrature counter to thereby deliver encoded emulations of output of the moving part inertial table to a controlling navigation and guidance processor.

2. The strap-down inertial table system according to claim 1 further comprising a means for maintaining temperature of said angular rate sensor, said filtering means, said rectifying means, said polarity translating means and said voltage-controlled-oscillator within a 50°

C.±

0.1°

C. range.

3. The strap-down inertial table system according to claim 2 wherein said temperature maintaining means comprise means for sensing a temperature which exceeds a safe operating temperature, said temperature sensing means comprising means for removing power from heater elements of said temperature maintaining means.

4. The strap-down inertial table system according to claim 1 wherein said temperature maintaining means comprise means for enclosing said angular rate sensor, said filtering means, said rectifying means, said binary signal producing means and said voltage-controlled oscillator and means for forcing flow of air through said enclosing means.

5. The strap-down inertial table system according to claim 4 wherein said air flow forcing means comprise an axial fan.

6. The strap-down inertial table system according to claim 1 wherein said angular rate sensor, said filtering means, said rectifying means, said binary signal producing means and said voltage-controlled oscillator are all mounted on a printed circuit board which is horizontally disposed and rigidly attached to a vehicle.

7. The strap-down inertial table system according to claim 1 wherein said receiving and processing means in combination with said polarity translating means comprise means for compensating for inverted mounting of said printed circuit board.

8. A no-moving part, strap-down inertial table system for sensing rate of turning of an AGV, said table comprising:

an angular rate sensor which provides a voltage output which is a function of angular rate and direction of turning;

means for low-pass filtering said voltage;

means for dividing a filtered voltage output from said filtering means into at least two electrical signal pathways;

means for rectifying a signal from one of such pathways to remove direction of turning;

a voltage-controlled-oscillator which receives a voltage signal from said rectifying means and produces a frequency signal proportional to the voltage of the received signal;

means for translating polarity of a signal from another of such pathways and producing a binary signal indicative of direction of turning;

means for receiving and processing said frequency signal and said binary signal to produce an output which emulates an encoder output;

means for accumulating output of said encoder emulation for use by a navigation and control processor.

9. The strap-down inertial table system according to claim 8 further comprising a means for maintaining temperature of said angular rate sensor, said filtering means, said rectifying means, said polarity translating means and said voltage-controlled-oscillator within a 50°

C. ±

0.1°

C. range.

10. The strap-down inertial table system according to claim 9 wherein said temperature maintaining means comprise means for sensing a temperature which exceeds a safe operating temperature, said temperature sensing means comprising means for removing power from heater elements of said temperature maintaining means.

11. The strap-down inertial table system according to claim 8 wherein said temperature maintaining means comprise means for enclosing said angular rate sensor, said filtering means, said rectifying means, said binary signal producing means and said voltage-controlled oscillator and means for forcing flow of air through said enclosing means.

12. The strap-down inertial table system according to claim 11 wherein said air flow forcing means comprise an axial fan.

13. The strap-down inertial table system according to claim 8 wherein said angular rate sensor, said filtering means, said rectifying means, said binary signal producing means and said voltage-controlled oscillator are all mounted on a printed circuit board which is horizontally disposed and rigidly attached to a vehicle.

14. The strap-down inertial table system according to claim 8 wherein said receiving and processing means in combination with said polarity translating means comprise means for compensating for inverted mounting of said printed circuit board.

15. An unmanned automated guided vehicle comprising:

a navigation and guidance computer processor;

a no-moving part, strap-down inertial table comprising;

an angular rate sensor which provides a voltage output which is a function of angular rate and direction of turning;

means for low-pass filtering said voltage;

means for dividing a filtered voltage output from said filtering means into at least two electrical signal pathways;

means for rectifying a signal from one of such pathways to remove direction of turning;

a voltage-controlled-oscillator which receives a voltage signal from said rectifying means and produces a frequency signal proportional to the voltage of the received signal;

means for translating polarity of a signal from another of such pathways and producing a binary signal indicative of direction of turning;

means for receiving and processing said frequency signal and said binary signal to produce an output which emulates an encoder output;

means for accumulating output of said encoder emulation for use by a navigation and control processor.

16. A method for replacing an AGV inertial table comprising moving parts with a strap-down inertial table system having no moving parts, other than sensing parts of an angular rate sensor, comprising the following steps:

removing the inertial table comprising moving parts;

providing the strap-down inertial table system comprising;

an angular rate sensor which provides a voltage output which is a function of angular rate and direction of turning;

means for low-pass filtering said voltage;

means for dividing a filtered voltage output from said filtering mean into at least two electrical signal pathways;

means for rectifying a signal from one of such pathways to remove direction of turning;

a voltage-controlled-oscillator which receives a voltage signal from said rectifying means and produces a frequency signal proportional to the voltage of the received signal;

means for translating polarity of a signal from another of such pathways and producing a binary signal indicative of direction of turning;

means for maintaining temperature of said angular rate sensor, said filtering means, said rectifying means, said voltage-controlled-oscillator and said polarity translating and binary signal producing means at a predetermined temperature within predetermined tolerances such that necessary AGV turning accuracy measurements are realized;

means for receiving and processing said frequency signal and said binary signal to produce an output which emulates an encoder output;

means for connecting said emulated encoder output to a quadrature counter used previously as output from the removed inertial table to deliver encoded emulations of output of the moving part inertial table to a controlling navigation and guidance processor.

17. A method of calibrating a strap-down inertial table having no moving parts such that low-cost parts comprising resistors and capacitors, having tolerance specifications not more restrictive than 1% and 5%, respectively, can be used without selection in such table comprising the steps of:

providing the no-moving part, strap-down inertial table comprising an angular rate sensor which emits a voltage relative to change in angular rate, means for low-pass filtering said voltage, means for determining direction of change in angular rate from said voltage, means for removing direction from said voltage, means for emulating an output of an angular rate encoder utilizing output from the determining and removing means and means for connecting to a quadrature counter from the emulating means;

providing a means of storing and processing calibration data which is attached to said quadrature counter;

mounting said inertial table aboard a controllable vehicle which is free to move and to turn;

turning said vehicle through a first angle of known magnitude in a first direction and storing output of said quadrature counter in said processor;

turning said vehicle through a second known angle of known magnitude in a second direction which is opposite the first direction and storing output of said quadrature counter in said processor;

calculating calibrating variances between direction of turn for use when measuring rate of turn by said inertial table.

18. The method according to claim 17 wherein in at least one of said turning steps the turning angle is 360°

.

19. A solid state, no moving part inertial platform for an AGV comprising:

solid state means for receiving and processing an output voltage from an angular rate sensor comprising;

means for translating said output voltage to a frequency proportional to absolute rate of turning of the AGV;

means for determining direction of turning of the AGV;

means for maintaining temperature of said solid state

means within a predetermined temperature range;

means for receiving output from said solid state means and emulating an encoder for delivery to a quadrature counter.