METHOD OF PROCESSING ENCODER SIGNALS

• US 20110187355A1
• Filed: 08/17/2007
• Published: 08/04/2011
• Est. Priority Date: 08/18/2006
• Status: Active Grant

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Li, Jiang, Reeve, John Martin, Williams, Connel Brett, Dixon, Christopher David
• Granted Patent: US 8,466,672 B2
• Time in Patent Office: Days
• US Class Current: 324/207.25
• CPC Class Codes: G01D 18/001 Calibrating encoders
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence
• CPC Class Codes: G01P 3/481 of pulse signals
• CPC Class Codes: G01P 3/487 delivered by rotating magnets

Abstract

A method of processing signals in a rotary encoder of the kind which comprises at least one annular track of encoding regions arranged as an alternating pattern of first encoding regions and second encoding regions, comprises providing a first detector at a first fixed position which is arranged to produce a first alternating output signal as the track of encoding regions rotates about its axis past the detector, the alternating signal comprising a series of transitions between a first state corresponding to the detector being aligned with a first encoding region and a second state corresponding to the detector being aligned with second encoding region;

• providing a second detector at a second fixed position which is arranged to produce a first alternating output signal as the track of encoding regions rotates about its axis past the detector, the alternating signal comprising a series of transitions between a first state corresponding to the detector being aligned with a first encoding region and a second state corresponding to the detector being aligned with second encoding region;
• identifying a usable pair of transitions in the first and second signals comprising a transition of the first signal from the first state to the second state followed by a transition in the second signal from the first state to the second state without in the intervening period having changed from the second state to the first state; measuring the elapsed time between the transitions of the identified usable pair, and determining the angular velocity by combining the elapsed time with the spacing between the first and second detectors.

Claims

1. A method of processing signals in an encoder comprising the following steps:

(a) providing a rotary encoder that includes at least one annular track having an axis and encoding regions arranged as an alternating pattern of first encoding regions and second encoding regions, said rotary encoder also including a first detector at a first fixed position which is arranged to produce a first alternating output signal as said annular track of encoding regions rotates about its axis past said first detector, said first alternating output signal comprising a series of transitions between a first state corresponding to said first detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said first detector being aligned with a second encoding region being one of said second encoding regions, said rotary encoder further including a second detector at a second fixed position which is arranged to produce a second alternating output signal as said annular track of encoding regions rotates about its axis past said second detector, said second alternating signal comprising a series of transitions between a first state corresponding to said second detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said second detector being aligned with a second encoding region being one of said second encoding regions;

(b) identifying a usable pair of transitions in said first and second alternating output signals comprising a transition of said first alternating output signal from said first state to said second state followed by a transition in said second alternating output signal from said first state to said second state without in an intervening period having changed from said second state to said first state;

(c) measuring an elapsed time between said transitions of said identified usable pair, and

(d) determining an angular velocity by combining said elapsed time with a spacing between said first and second detectors.

2. A method of claim 1 wherein said first and second encoding regions comprise North and South pole magnets.

3. A method of claim 2 wherein said first encoding region is a north pole and said second encoding region is a south pole.

4. A method of claim 1 which further comprises identifying all adjacent transitions of said first alternating output signal followed by said second alternating output signal, rejecting those which do not comprise said usable pairs, and using at least one of said remaining usable pairs to determine velocity.

5. A method of claim 1 which further comprises identifying said usable pair of transitions in said first and second alternating output signals comprising a transition of said first alternating output signal from said second state to said first state followed by a transition in said second alternating output signal from said second state to said first state without in an intervening period having changed from said first state to said second state.

6. A method of claim 1 which comprises the steps of identifying at least four pairs of transitions received in sequence comprising two usable pairs and two “

unusable”

pairs, adding together times between all four pairs and dividing by four.

7. A method of claim 1 which further comprises a step of determining a position of said encoder.

8. A method of claim 7 which further comprises the steps of:

identifying a sequence of four pairs of temporally adjacent transitions in said first and second alternating output signals, said four pairs including two usable pairs and two rejectable pairs;

determining a time lapse between transitions of at least one of said rejectable pairs; and

comparing a time lapse for said usable pair with each time lapse for said rejectable pairs so as to determine an elapsed time error value for each rejectable pair.

9. The method of claim 8 wherein said error time is converted to an angular error for each rejected pair by combining said error time with an estimate of velocity.

10. The method of claim 1 which further includes the steps of identifying said usable pair of transitions in said first and second alternating output signals which corresponds to a transition between pairs of magnets that occurs at a known position, and

referencing all other position measurements to this known position.

11. An encoder comprising:

at least one annular track having an axis and encoding regions arranged as an alternating pattern of first encoding regions and second encoding regions;

a first detector at a first fixed position which is arranged to produce a first alternating output signal as said annular track of encoding regions rotates about its axis past said first detector, said first alternating output signal comprising a series of transitions between a first state corresponding to said first detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said first detector being aligned with a second encoding region being one of said second encoding regions;

a second detector at a second fixed position which is arranged to produce a second alternating output signal as said annular track of encoding regions rotates about its axis past said second detector, said second alternating signal comprising a series of transitions between a first state corresponding to said second detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said detector being aligned with a second encoding region being one of said second encoding regions; and

a processor arranged to;

identify a usable pair of transitions in said first and second alternating output signals comprising a transition of said first alternating output signal from said first state to said second state followed by a transition in said second alternating output signal from said first state to said second state without in an intervening period having changed from said second state to said first state;

measure an elapsed time between said transitions of identified said usable pair; and

determine an angular velocity by combining said elapsed time with a spacing between said first and second detectors.

12. An encoder according to claim 11 which comprises two tracks of magnets arranged side by side.

13. An encoder according to claim 11 wherein the encoder regions comprise magnets.

15. An encoder according to claim 12 which comprises two tracks of magnets, each magnet defining an encoding region, a magnetic field from one or more magnets in one track interfering with a field of one or more magnets of a second track to introduce an elapsed time measurement error in a measured time between transitions from a first state to a second state of an alternating output signal.

14. (canceled)

16. (canceled)