System and method for providing distance-based pulses relative to motion of a surface scanned by a vision system

• US 8,687,060 B1
• Filed: 12/28/2009
• Issued: 04/01/2014
• Est. Priority Date: 12/28/2009
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Wolff, Robert A.
• Primary Examiner(s): LIN, WEN TAI
• Application Number:
  US12/648,060
• Time in Patent Office: 1,555 Days
• Field of Search: None
• US Class Current: 348/140
• CPC Class Codes: G06F 3/0304 Detection arrangements using opto-electronic means constructional details of pointing devices not related to the detection arrangement using opto-electronic means G06F3/033; optical digitisers G06F3/042
• CPC Class Codes: G06F 3/03543 Mice or pucks G06F3/03541 takes precedence

Abstract

This invention provides a system and method for estimating the time of a set of pulses based upon a plurality of position measurements of a moving object provided by a non-contacting sensor, such as a one-dimensional optical sensor that tracks movements of object features and reports position measurements with respect to time. Position measurements determine the estimated velocity. The velocity and position measurement allow the timing of a next pulse to be updated, based upon the time of the previous pulse. The pulse is output at the time of the last updated time before the first new position measurement received after the estimated pulse output time. The system allows pulses to be precisely delivered at predetermined motion distances. Where the distance is too short for the measurement rate, the system compares estimated pulse times to clock-generated pulse times and updates the clock-generated pulse times based upon the difference.

Claims

1. A system for generating emulated pulses that indicate incremental distance travelled comprising:

a clock that provides a timestamp to each of a plurality of position measurements of a moving object received from a non-contacting motion sensor;

a pulse scheduler that estimates a velocity of the object based upon the plurality of the position measurements with respect to the timestamp of each of the plurality of measurements, and that updates estimates of a time to output a next pulse based upon the estimated velocity and a reported position of each of the position measurements;

a numerically controlled oscillator operatively connected to the pulse scheduler, wherein the oscillator includes (a) a pulse generator responsive to the clock that generates 1 pulse per N clock ticks, wherein the pulses of the pulse generator are output as the emulated pulses, (b) a pulse estimation process, responsive to the pulse scheduler that generates an estimated number of pulses, and (c) a difference engine that measures a difference between pulses generated by the pulse generator and pulses generated by the estimation process and thereby provides a rate control value to vary N; and

an output process responsive to the clock that outputs the pulse at an estimated time to output the pulse.

2. The system as set forth in claim 1 wherein the numerically controlled oscillator generates pulses at times between a time in which each of the plurality of position measurements are received by the pulse scheduler.

3. The system as set forth in claim 2 wherein the oscillator is operated to generate pulses when the estimated velocity exceeds a predetermined threshold and an error in generating pulses from the oscillator is below a predetermined error value.

4. The system as set forth in claim 1 wherein the difference is passed through a filter that smoothes the rate control value over a plurality of difference values from the difference engine.

5. The system as set forth in claim 2 wherein each of the output process and the numerically controlled oscillator include outputs interconnected with a multiplexer that outputs the emulated pulse to a remote device.

6. The system as set forth in claim 5 wherein the output process includes a hardware timer operatively connected to the clock.

7. The system as set forth in claim 5 wherein the pulse defines a direction/step encoder signal.

8. The system, as set forth in claim 7 wherein the direction/step encoder signal exclusively reports forward motion of the object in a single direction.

9. The system as set forth in claim 8 wherein the device is a line scan camera and the direction/step encoder signal is used by the line scan camera as a trigger signal.

10. The system as set forth in claim 2 wherein each of the output process and the numerically controlled oscillator include outputs that are operatively connected to an interface that provides a motion reporting signal with respect to a device.

11. The system as set forth in claim 2 wherein each of the output process and the numerically controlled oscillator include outputs that are operatively connected to a device to perform a motion-dependent device operation.

12. The system as set forth in claim 11 wherein the motion dependent device operation comprises triggering of a line scan camera.

13. The system as set forth in claim 11 wherein the outputs provide an encoder signal adapted to serve an input of the device.

14. The system as set forth in claim 13 wherein the encoder signal comprises at least one of a quadrature encoder signal, a direction/step encoder signal and a direction/step encoder signal reporting exclusively in one direction of motion.

15. The system as set forth in claim 2 wherein the non-contacting motion sensor provides the plurality of position measurements based upon scanning of features of the object with a 1D sensor oriented with respect to a direction of object motion.

16. The system as set forth in claim 1 wherein the output process outputs the pulse at a most updated estimated time to output the pulse.

17. A method for generating emulated pulses that indicate incremental distance travelled comprising the steps of:

providing a clock, and generating therewith, a timestamp to each of a plurality of position measurements of a moving object received from a non-contacting motion sensor;

estimating a velocity of the object based upon the plurality of the position measurements with respect to the timestamp of each of the plurality of measurements, and using a filter to determine the updating estimates of a time to output a next pulse based upon the estimated velocity and a reported position of each of the position measurements;

generating, using a pulse generating, 1 pulse per N clock ticks, wherein the pulses are output as the emulated pulses;

generating an estimated number of pulses;

measuring a difference between pulses generated by the pulse generator and the estimated number of pulses and thereby providing a rate control value to vary N; and

in response to the clock, outputting each pulse at an estimated time to output the pulse.

18. The method as set forth in claim 17 further comprising generating, with a numerically controlled oscillator, pulses at times between a time in which each of the plurality of position measurements are received by a pulse scheduler when a relationship between an object motion distance K at which pulses are required is less than a predetermined value with respect to distances between each of the plurality of position measurements.

19. The method as set forth in claim 17 wherein the step of estimating includes applying a Kalman filter to determine the estimated time to output the next pulse.

20. A system for generating emulated pulses that indicate incremental distance travelled comprising:

a clock that provides a timestamp to each of a plurality of position measurements of a moving object received from a motion sensor, the motion sensor comprising a non-contact motion sensor that comprises a vision-based sensor that determines movement of the object based upon a texture of the object;

a pulse scheduler that estimates a velocity of the object based upon the plurality of the position measurements with respect to the timestamp of each of the plurality of measurements, and that updates estimates of a time to output a next pulse based upon the estimated velocity and a reported position of each of the position measurements;

a numerically controlled oscillator operatively connected to the pulse scheduler, wherein the oscillator includes (a) a pulse generator responsive to the clock that generates 1 pulse per N clock ticks, wherein the pulses of the pulse generator are output as the emulated pulses, (b) a pulse estimation process, responsive to the pulse scheduler that generates an estimated number of pulses, and (c) a difference engine that measures a difference between pulses generated by the pulse generator and pulses generated by the estimation process and thereby provides a rate control value to vary N; and

an output process responsive to the clock that outputs the pulse at an estimated time to output the pulse.

21. The system as set forth in claim 20 wherein the motion sensor comprises a contacting motion sensor and a non-contacting motion sensor.

22. The system as set forth in claim 20 wherein the vision based sensor is integrated within an optic of a line scan camera.

23. The system as set forth in claim 20 wherein the numerically controlled oscillator generates pulses at times between a time in which each of the plurality of position measurements are received by a pulse scheduler.

24. A method for generating emulated pulses that indicate incremental distance travelled comprising the steps of:

providing a clock, and generating therewith, a timestamp to each of a plurality of position measurements of a moving object received from a motion sensor, the motion sensor comprising a non-contact motion sensor that comprises a vision-based sensor that determines movement of the object based upon a texture of the object;

estimating a velocity of the object based upon the plurality of the position measurements with respect to the timestamp of each of the plurality of measurements, and updating estimates of a time to output a next pulse based upon the estimated velocity and a reported position of each of the position measurements;

generating, using a pulse generating, 1 pulse per N clock ticks, wherein the pulses are output as the emulated pulses;

generating an estimated number of pulses;

measuring a difference between pulses generated by the pulse generator and the estimated number of pulses and thereby providing a rate control value to vary N; and

in response to the clock, outputting each pulse at an estimated time to output the pulse.

25. The system as set forth in claim 24 wherein the motion sensor comprises a contacting motion sensor and a non-contacting motion sensor.

26. The method as set forth in claim 24 further comprising generating, with a numerically controlled oscillator, pulses at times between a time in which each of the plurality of position measurements are received by a pulse scheduler when a relationship between an object motion distance K at which pulses are required is less than a predetermined value with respect to distances between each of the plurality of position measurements.