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

• US 5,617,320 A
• Filed: 04/10/1996
• Issued: 04/01/1997
• 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:
  US08/628,557
• Time in Patent Office: 356 Days
• Field of Search: 364/453, 364/424.02, 318/587, 340/825.06, 180/167, 180/168, 395/500
• 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. An inertial table for an automated guided vehicle, said inertial table comprising:

an angular rate sensor, said angular rate sensor being mounted to said automated guided vehicle, said angular rate sensor having an angular rate sensor output, said angular rate sensor output having an angular rate sensor output signal which is a function of an angular rate of said automated guided vehicle; and

an oscillator, said oscillator having

an oscillator input, said oscillator input being electrically coupled to said angular rate sensor output, and

an oscillator output having an oscillator output signal, said oscillator output signal having a frequency which is a function of said angular rate sensor output signal.

2. An inertial table according to claim 1, wherein said angular rate sensor output signal has a voltage magnitude which is proportional to said angular rate of said automated guided vehicle, wherein said oscillator is a voltage controlled oscillator, and wherein said oscillator output signal frequency is proportional to said voltage magnitude of said angular rate sensor output signal.

3. An inertial table according to claim 1, further comprising a signal generator, said signal generator being electrically coupled to said oscillator output, said signal generator having first and second output signals, said first output signal being a first square wave, and said second output signal being a second square wave which is out of phase with said first square wave.

4. An inertial table according to claim 3, wherein said signal generator is an encoder emulator.

5. An inertial table according to claim 1, wherein said angular rate sensor output signal is also a function of direction of turning, said direction of turning being indicated by a polarity of said angular rate sensor output signal, and said inertial table further comprising:

a rectifier, said rectifier having a rectifier input which is electrically coupled to said angular rate sensor output and a rectifier output which is electrically coupled to said oscillator input such that said oscillator input is electrically coupled to said angular rate sensor output via said rectifier output and said rectifier input; and

a sign circuit, said sign circuit having a sign circuit input which is electrically coupled to said angular rate sensor output, and said sign circuit having a binary output signal indicative of said direction of turning.

6. An inertial table according to claim 5, further comprising a low pass filter, said low pass filter having a low pass filter input which is electrically coupled to said angular rate sensor output and a low pass filter output which is electrically coupled to said rectifier input and to said sign circuit input such that said rectifier input and said sign circuit input are electrically coupled to said angular rate sensor output via said low pass filter output and said low pass filter input.

7. An inertial table according to claim 1,

wherein said angular rate sensor output signal has a voltage magnitude which is proportional to said angular rate of said automated guided vehicle, wherein said angular rate sensor output signal is also a function of direction of turning, and wherein said direction of turning is indicated by a polarity of said angular rate sensor output signal;

and

wherein said oscillator is a voltage controlled oscillator, and wherein said oscillator output signal frequency is proportional to a voltage magnitude of said angular rate sensor output signal;

and wherein said inertial table further comprises;

a low pass filter, said low pass filter having a low pass filter input and a low pass filter output, said low pass filter input being electrically coupled to said angular rate sensor output;

a rectifier, said rectifier having a rectifier input and a rectifier output, said rectifier input being electrically coupled to said low pass filter output, and said rectifier output being electrically coupled to said voltage controlled oscillator input such that said voltage controlled oscillator input is electrically coupled to said angular rate sensor output via said rectifier output, said rectifier input, said low pass filter output, and said low pass filter input;

a sign circuit, said sign circuit being electrically coupled to said low pass filter output, said sign circuit having a sign circuit output, said sign circuit output having binary output signal indicative of said direction of turning; and

a signal generator, said signal generator having a first signal generator input which is electrically coupled to said voltage controlled oscillator output and a second signal generator input which is electrically coupled to said sign circuit output, said signal generator having first and second output signals, said first output signal being a first square wave, and said second output signal being a second square wave which is out of phase with said first square wave.

8. An inertial table according to claim 7, further comprising

a fan;

a heating element;

an enclosure, said enclosure surrounding said angular rate sensor, said low pass filter, said rectifier, said sign circuit, and said voltage controlled oscillator;

a temperature sensor, said temperature sensor being disposed within said enclosure; and

a heating control circuit, said heating control circuit having an input electrically coupled to said temperature sensor, said heating control circuit having an output electrically coupled to said fan and said heating element;

and wherein said fan, said heating element, said temperature sensor, and said heating control circuit cooperate so as to maintain a temperature inside said enclosure within a predetermined range.

9. A method of providing angular rate information to an automated guided vehicle, the method comprising the steps of:

providing an automated guided vehicle having a computer and an inertial platform including an angular rate sensor, an oscillator and a signal generator;

sensing an angular rate of said automated guided vehicle with said angular rate sensor;

producing an angular rate sensor output signal which is a function of said angular rate of the automated guided vehicle;

transmitting said angular rate sensor output signal from said angular rate sensor to said oscillator;

producing an oscillating signal with said oscillator and said signal generator, said oscillating signal having a frequency which is a function of said angular rate sensor output signal;

counting transitions of said oscillating signal; and

providing counting information regarding said counting of said transitions to said computer of said automated guided vehicle.

10. A method according to claim 9, wherein said angular rate sensor output signal has a voltage magnitude which is proportional to said angular rate of said automated guided vehicle, wherein said oscillator is a voltage controlled oscillator, and wherein said oscillator output signal frequency is proportional to said voltage magnitude of said angular rate sensor output signal.

11. A method according to claim 9, wherein said transmitting step further comprises the steps of

low pass filtering said angular rate sensor output signal;

and

rectifying said angular rate sensor output signal.

12. A method according to claim 9, further comprising the steps of

mounting said angular rate sensor in an inverted fashion;

and

reversing polarity of said angular rate sensor output signal to compensate for said inverted mounting of said angular rate sensor.

13. A method according to claim 9, further comprising the step of controlling a temperature of a region surrounding said angular rate sensor, said oscillator, a rectifier, a low pass filter, and a sign circuit.

14. A method according to claim 9, wherein said oscillating signal emulates an output of an encoder.

15. A method of calibrating an inertial table for an automated guided vehicle, the method comprising the steps of:

providing said inertial table, said inertial table having an angular rate sensor, a voltage controlled oscillator and a quadrature counter;

turning said automated guided vehicle through a first angle of a first known magnitude in a first direction;

comparing data generated by said quadrature counter during said first angle turning step to said first known magnitude of said first angle and calculating a first scale factor based on said first angle comparing step;

turning said automated guided vehicle through a second angle of a second known magnitude in a second direction;

comparing data generated by said quadrature counter during said second angle turning step to said second known magnitude of said second angle and calculating a second scale factor based on said second angle comparing step; and

storing said first and second scale factors in a memory of a computer.

16. The method according to claim 15, wherein said known magnitude of said first angle is at least 360°

.

17. An automated guided vehicle comprising

an angular rate sensor, said angular rate sensor being mounted to said automated guided vehicle, said angular rate sensor having an angular rate sensor output, said angular rate sensor output having an angular rate sensor output signal which is a function of angular rate of said automated guided vehicle;

a voltage controlled oscillator, said voltage controlled oscillator having

a voltage controlled oscillator input, said voltage controlled oscillator input being electrically coupled to said angular rate sensor output, and

a voltage controlled oscillator output having an oscillator output signal, said voltage controlled oscillator output signal having a frequency which is proportional to a voltage magnitude of said angular rate sensor output signal;

a signal generator, said signal generator having first and second signal generator inputs, said first signal generator input being electrically coupled to said voltage controlled oscillator output, said signal generator having first and second output signals, said first output signal being a first square wave, and said second output signal being a second square wave which is out of phase with said first square wave;

a quadrature counter, said quadrature counter having a first input electrically coupled to said signal generator first output, said quadrature counter having a second input electrically coupled to said signal generator second output, said quadrature counter having an output which outputs count information regarding said first and second squarewaves; and

a main processor, said main processor being electrically coupled to said quadrature counter and receiving said count information.

18. An inertial table according to claim 17, wherein said angular rate sensor output signal has a voltage magnitude which is proportional to said angular rate of said automated guided vehicle.

19. An automated guided vehicle according to claim 18, wherein said angular rate sensor output is also a function of direction of turning, said direction of turning being indicated by a polarity of said angular rate sensor output, and said automated guided vehicle further comprising:

a low pass filter, said low pass filter having a low pass filter input and a low pass filter output, said low pass filter input being electrically coupled to said angular rate sensor output;

a rectifier, said rectifier having a rectifier input and a rectifier output, said rectifier input being electrically coupled to said low pass filter output, and said rectifier output being electrically coupled to said voltage controlled oscillator input such that said voltage controlled oscillator input is electrically coupled to said angular rate sensor output via said rectifier output, said rectifier input, said low pass filter output, and said low pass filter input;

a sign circuit, said sign circuit being electrically coupled to said low pass filter output, said sign circuit having a sign circuit output which is electrically coupled to said second signal generator input, said sign circuit output having a binary output signal indicative of said direction of turning.

20. An automated guided vehicle according to claim 19, further comprising

a fan;

a heating element;

an enclosure, said enclosure surrounding said angular rate sensor, said low pass filter, said rectifier, said sign circuit and said voltage controlled oscillator;

a temperature sensor, said temperature sensor being disposed within said enclosure; and

a heating control circuit, said heating control circuit having an input electrically coupled to said temperature sensor, said heating control circuit having an output electrically coupled to said fan and said heating element;

and wherein said fan, said heating element, said temperature sensor, and said heating control circuit cooperate so as to maintain a temperature inside said enclosure within a predetermined range.