Tilt-compensated laser rangefinder

• US 6,873,406 B1
• Filed: 01/13/2003
• Issued: 03/29/2005
• Est. Priority Date: 01/11/2002
• Status: Expired

• Current Assignee: Opti-Logic Corporation
• Original Assignee: Opti-Logic Corporation
• Inventors: Johnson, Matthew A., Goodman, William L, Hines, Robin H., Murphy, Patrick J.
• Primary Examiner(s): Gregory, Bernarr E.
• Assistant Examiner(s): Andrea, Brian
• Application Number:
  US10/341,122
• Time in Patent Office: 806 Days
• Field of Search: 356 401- 515, 356/141.1
• US Class Current: 356/141.1
• CPC Class Codes: F41G 1/467 for bows
• CPC Class Codes: F41G 3/06 with rangefinder rangefinders per se G01C
• CPC Class Codes: F41G 3/08 with means for compensating for speed, direction, temperature, pressure, or humidity of the atmosphere measuring G01
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 7/4808 Evaluating distance, position or velocity data
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

The present invention is a laser ranging device that incorporates an internal tilt sensor, an internal temperature sensor, and an internal pressure sensor. The tilt sensor is used to measure the target'"'"'s vertical angle relative to the horizontal reference plane. Digital signal processing circuitry controls the firing of the laser pulse, calculation of time-of-flight range, measurement of the vertical angle of the tilt sensor, measurement of ambient temperature and storage of tilt sensor and temperature sensor calibration data. The digital signal processing circuitry then provides the user temperature corrected ballistic ranging information, including horizontal range. Additionally, an automatic gain control system minimizes the effects of target to target variance in reflectivity and its associated errors. It is also an object of this invention to electronically minimize errors in the measurement of a vertical angle caused by housing vibration and by temperature variance errors.

Claims

1. A tilt compensated laser ranging device comprising:

a housing disposed in a reference horizontal plane;

a laser transmitter disposed within the housing and adapted to fire a series of laser pulses of short duration at a selected target, said series of laser pulses having a pulse repetition rate frequency, said selected target having a target surface, said target surface reflecting at least a portion of said series laser pulses as at least one return pulse, each said return pulse having an amplitude;

a laser pulse return detection system disposed within the housing and comprising;

a laser pulse return detector adapted to emit an electronic signal upon detection of each said return pulse, each said electronic signal having an amplitude corresponding to the amplitude of the detected return pulse;

a signal-to-noise discriminator adapted to receive each said electronic signal from said laser pulse return detector;

an automatic gain control system for adjusting the gain of the laser pulse return detector such that the variance in the amplitudes of said electronic signals from said laser pulse return detector is less than the variance in amplitudes of said detected return pulses;

a vertical tilt sensor system disposed in the housing for determining a vertical angle between the target and the housing'"'"'s reference horizontal plane, said vertical tilt sensor system comprising;

a vertical tilt sensor; and

vertical angle signal circuitry adapted to produce a vertical angle data signal corresponding to said vertical angle;

a digital signal processing circuit disposed in the housing, said digital signal processing circuit comprising circuitry configured to;

store vertical tilt sensor system calibration data, said vertical tilt sensor system calibration data comprising vertical tilt sensor system calibration look-up tables;

calculate a time-of-flight range;

calculate a vertical angle from data comprising vertical angle data and vertical tilt sensor system calibration data; and

calculate a horizontal range from the time-of-flight range and the vertical angle;

wherein vertical tilt sensor system calibration data is determined by stepping the vertical tilt sensor system through a series of discrete predetermined vertical angles, measuring the vertical angle data signals corresponding to said vertical angles and storing the measurement values of said vertical angle data signals corresponding to each predetermined vertical angle; and

an output signal system disposed within the housing and adapted to selectable produce a horizontal range output data signal corresponding to the horizontal range to the target.

2. The device of claim 1 further comprising a temperature sensor system disposed in the housing and adapted to produce a temperature data signal corresponding to ambient environmental temperature.

3. The device of claim 2 wherein the digital signal processing circuit further comprises circuitry configured to:

store temperature sensor system calibration data, said calibration data comprising temperature sensor system calibration data look-up tables; and

calculate the vertical angle from data further comprising temperature data and temperature sensor system calibration data.

4. The device of claim 1 further comprising a triggering system adapted such that upon manipulation by a user, the triggering system electronically signals the tilt compensated laser ranging device to operate through one operating cycle, said operating cycle comprising sequentially firing at least one laser pulse and attempting to detect each reflected laser pulse, and further comprising sequentially making multiple measurements of the data signal corresponding to the vertical angle.

5. The device of claim 1 wherein the automatic gain control system adjusts the gain of the laser pulse return detector based on the amplitude of the previously received laser pulse return detector signal, such that a majority of said laser pulse return detector signals passed to the signal-to-noise discrimination system have amplitudes within a predetermined range for optimal laser pulse return detector signal amplitude.

6. The device of claim 1 wherein the housing is suitable for hand held operation.

7. The device of claim 1 wherein the housing is suitable for mounting to a user portable base.

8. The device of claim 1 wherein the housing is suitable for mounting to a user portable launcher.

9. The device of claim 8 wherein the user portable launcher comprises a launcher selected from the group a rifle, a shotgun, a pistol, a crossbow, a bow, a mortar, grenade launcher or a paintball gun.

10. The device of claim 1 further comprising an aiming system.

11. The device of claim 1 wherein the aiming system comprises a low light reflex sighting system.

12. The device of claim 1 wherein the aiming system comprises a targeting laser.

13. The device of claim 1 wherein the aiming system comprises an optical sight, said optical sight means selected from the group comprising:

an optical reticle, a cross hairs etched on an optical element, a light emitting diode reticle, a liquid crystal display reticle, a pair of cross hairs, or aiming pin.

14. The device of claim 1 wherein the aiming system comprises an image magnification system.

15. The device of claim 1 further comprising a pressure sensor system disposed in the housing and constructed to produce a data signal corresponding to ambient atmospheric pressure.

16. The device of claim 1 wherein the vertical tilt sensor comprises an accelerometer.

17. The device of claim 16 wherein the accelerometer comprises a micro-electronic machine silicone accelerometer.

18. The device of claim 1 wherein the vertical tilt sensor comprises a sensor selected from the group comprising:

an electrolytic liquid level tilt sensor, a optical bubble tilt sensor, a capacitive bubble tilt sensor, pendulum mechanism, rotary optical encoder, rotary electro-resistive encoder, hall effect device or a ceramic capacitive tilt sensor.

19. The device of claim 1 wherein the digital signal processing circuit further comprises at least one microprocessor having a memory means for storing instructions and data.

20. The device of claim 1 wherein the digital signal processing circuit comprises circuitry adapted to calculate the height of a target from a time-of-flight range and at least two vertical angles, wherein the at least two vertical angles comprise a vertical angle to the top of the target and a vertical angle to the bottom of the target.

21. The device of claim 1 wherein the digital signal processing circuit further comprises circuitry adapted to calculate time-of-flight range from multiple measurements of the elapsed time data signal.

22. The device of claim 1 wherein the digital signal processing circuit comprises circuitry adapted to calculate vertical angle from multiple measurements of the vertical angle data signal.

23. The device of claim 1 wherein the laser transmitter further comprises a laser transmitter adapted to fire said series of laser pulses for a period of time having duration of between 1 nano-seconds and 60 seconds, said laser pulses having a pulse repetition rate frequency of between 1 hertz and 20,000 hertz.

24. The device of claim 1 wherein the output signal system further comprises an output signal system adapted to selectablely produce a data signal corresponding to the vertical angle to the target.

25. The device of claim 1 wherein the output signal system further comprises an output signal system constructed to selectablely produce a data signal corresponding to an output parameter selected from the group comprising:

time-of-flight range, height of target, ambient temperature, or ambient pressure.

26. The device of claim 1 wherein the output signal system comprises an output display system constructed to selectablely display the horizontal range to the target.

27. The device of claim 1 wherein the output signal system comprises an output display system constructed to selectablely display the vertical angle.

28. The device of claim 1 wherein the output signal system comprises an output display system constructed to selectablely display output data selected from the group comprising:

time-of-flight range, target height, temperature or pressure.

29. The device of claim 1 wherein the triggering system comprises:

a user manipulated, release-to-return triggering switch having at least two positions, said two positions comprising a standby position and a release position, wherein selection of the standby position requires continuous user manipulation while the standby position is selected and wherein removal of user manipulation automatically reselects the release position; and

a release to fire circuitry adapted such that user selection of the standby position of the triggering switch prevents a firing signal from being sent to the laser transmitter while causing a standby voltage to be applied to the device components, such that selection of the release position of the triggering switch causes a firing signal from being sent to the laser transmitter while causing a firing voltage to be applied to the device components, and such that selection of the release position of the triggering switch for a duration of period of time causes a low power voltage to be applied to the device components, said period of time selectable between 1 second and 60 seconds.

30. A tilt compensated laser ranging device for firing a series of laser pulses at a selected target and measuring target reflections of said laser pulses, said device comprising:

a laser pulse return detector for detecting reflected laser pulses and providing an electronic signal output corresponding to each detected reflected laser pulse, said laser pulse return detector further having an automatic gain control system that adjusts the gain of the laser pulse return detector, said adjustment based on the amplitude of the previously received laser pulse return detector signal, such that a majority of said laser pulse return detector signals have amplitudes within a predetermined range;

a vertical tilt sensor for determining the vertical angle to the target and having a vertical angle signal circuitry adapted to produce a vertical angle data signal corresponding to said vertical angle;

a temperature sensor adapted to produce a temperature data signal corresponding to ambient environmental temperature; and

a microprocessor configured to;

store vertical tilt sensor system calibration look-up tables;

store temperature sensor system calibration data look-up tables;

calculate a time-of-flight range;

calculate a vertical angle from data comprising vertical angle data, vertical tilt sensor system calibration look-up tables, temperature data and temperature sensor system calibration data; and

calculate a horizontal range from the time-of-flight range and the vertical angle;

wherein measurement of vertical angle data signals are taken at each of a series of discrete predetermined vertical angles and each measurement value of said vertical angle data signals and each corresponding predetermined vertical angle are stored in lookup tables; and

wherein determination of the vertical angle to the target sequentially making multiple measurements of the data signal corresponding to the vertical angle.

31. A tilt compensated laser ranging device comprising:

a vertical tilt sensor system for determining a vertical angle between a reflected laser pulse and a reference horizontal plane, said vertical tilt sensor system comprising;

a vertical tilt sensor; and

vertical angle signal circuitry adapted to produce a vertical angle data signal corresponding to said vertical angle;

a digital signal processing circuit comprising circuitry configured to;

calculate a time-of-flight range;

calculate a vertical angle; and

calculate a horizontal range from the time-of-flight range and the vertical angle; and

an output signal system adapted to produce a horizontal range output data signal corresponding to the horizontal range to the target.