Mechanical arrangement and components for reducing error in deduced reckoning

• US 20050222710A1
• Filed: 04/06/2004
• Published: 10/06/2005
• Est. Priority Date: 04/06/2004
• Status: Abandoned Application

• Current Assignee: iRobot Corporation
• Original Assignee: iRobot Corporation
• Inventors: Schell, Steven E., Brown, Joseph Michael
• Application Number:
  US10/818,756
• Publication Number:
  US 20050222710A1
• Time in Patent Office: Days
• US Class Current: 700/245
• CPC Class Codes: G01C 21/12 executed aboard the object being navigated; Dead reckoning

Abstract

The present application discloses a mechanical arrangement and components for reducing errors in position estimation in mobile robotic vehicles that use deduced reckoning. The arrangement provides a method for determining the weight to be carried by the driven wheels to provide increased or maximum contact force between the driven wheels and a support surface, which in turn reduces or minimizes wheel slippage and reduces or minimizes vehicle tilting. The arrangement further provides uniquely shaped rolling elements that generate reduced sideways directed forces on the vehicle, thus reducing or minimizing wheel slippage.

Claims

1. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a maximum acceleration equal to a₁, having a maximum deceleration equal to a₂, and having a total vehicle weight;

at least a first driven wheel and a second driven wheel, the driven wheels being rotatable about a drive axis, a vertical axis through the center of gravity of the vehicle intersecting or nearly intersecting the drive axis at or near a midpoint between the driven wheels, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests;

at least a first rolling element located to a first side of the drive axis, the first rolling element being rotatable about a first rolling axis that is parallel to the drive axis and separated from the drive axis by a first horizontal distance r₁; and

at least a second rolling element located to a second side of the drive axis, the second rolling element being rotatable about a second rolling axis that is parallel to the drive axis and separated from the drive axis by a second horizontal distance r₂, wherein

a percentage of the total vehicle weight carried by the drive wheels is less than or equal to the following quantity

$\min <br><br>\left(1-\frac{a_1<br><br>h}{{\mathrm{gr}}_1},1-\frac{a_2<br><br>h}{{\mathrm{gr}}_2}\right);<br><br>$

where

g is equal to gravitational acceleration in a vicinity of the vehicle.

2. The mechanical arrangement of claim 1, wherein the driven wheels are translatable with respect to the vehicle.

3. The mechanical arrangement of claim 1, wherein the rolling elements are fixed against translation with respect to the vehicle.

4. The mechanical arrangement of claim 1, wherein the rolling elements are fixed with respect to the vehicle against rotation about a vertical axis that is parallel to the vertical axis through the vehicle center of gravity.

5. The mechanical arrangement of claim 1, wherein the rolling elements are shaped as generally as prolate spheroids.

6. The mechanical arrangement of claim 5, wherein only a narrow central band of each rolling element contacts the support surface as the vehicle moves.

7. The mechanical arrangement of claim 1, wherein the rolling elements are constructed of a durable, long-wearing material having a low coefficient of friction on the support surface.

8. The mechanical arrangement of claim 7, wherein the rolling element is constructed of acetal plastic.

9. The mechanical arrangement of claim 1, wherein the portions of the driven wheels that contact the support surface are constructed of a durable, long-wearing material having a high coefficient of friction on the support surface.

10. The mechanical arrangement of claim 9, wherein the portions of the driven wheels that contact the support surface are constructed of urethane.

11. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a maximum acceleration equal to a₁, and having a total vehicle weight;

at least a first driven wheel and a second driven wheel, the driven wheels being rotatable about a drive axis, a vertical axis through the center of gravity of the vehicle intersecting or nearly intersecting the drive axis at or near a midpoint between the driven wheels, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests; and

at least a first rolling element located to a first side of the drive axis, the first rolling element being rotatable about a first rolling axis that is parallel to the drive axis and separated from the drive axis by a first horizontal distance r₁;

wherein

a percentage of the total vehicle weight carried by the drive wheels is less than or equal to the following quantity

$1-\frac{a_1<br><br>h}{{\mathrm{gr}}_1};<br><br>$

where

g is equal to gravitational acceleration in a vicinity of the vehicle.

12. The mechanical arrangement of claim 11, further comprising at least a second rolling element located to a second side of the drive axis, the second rolling element being rotatable about a second rolling axis that is parallel to the drive axis.

13. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a maximum deceleration equal to a₂, and having a total vehicle weight;

at least a first driven wheel and a second driven wheel, the driven wheels being rotatable about a drive axis, a vertical axis through the center of gravity of the vehicle intersecting or nearly intersecting the drive axis at or near a midpoint between the driven wheels, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests; and

at least a first rolling element located to a first side of the drive axis, the first rolling element being rotatable about a first rolling axis that is parallel to the drive axis and separated from the drive axis by a first horizontal distance r₂;

wherein

a percentage of the total vehicle weight carried by the drive wheels is less than or equal to the following quantity

$1-\frac{a_2<br><br>h}{g<br><br>\text{\hspace{1em}<br><br>}<br><br>r_2};<br><br>$

where

g is equal to gravitational acceleration in a vicinity of the vehicle.

14. The mechanical arrangement of claim 13, further comprising at least a second rolling element located to a second side of the drive axis, the second rolling element being rotatable about a second rolling axis that is parallel to the drive axis.

15. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a maximum acceleration equal to a₁, having a maximum deceleration equal to a₂, and having a total vehicle weight;

at least a first driven wheel, the driven wheel being rotatable about a drive axis, a vertical axis through the center of gravity of the vehicle intersecting or nearly intersecting the driven wheel, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests;

at least a first rolling element located to a first side of the drive axis, the first rolling element being rotatable about a first rolling axis that is parallel to the drive axis and separated from the drive axis by a first horizontal distance r₁; and

at least a second rolling element located to a second side of the drive axis, the second rolling element being rotatable about a second rolling axis that is parallel to the drive axis and separated from the drive axis by a second horizontal distance r₂;

wherein

a percentage of the total vehicle weight carried by the driven wheel is less than or equal to the following quantity

$\min <br><br>\left(1-\frac{a_1<br><br>h}{g<br><br>\text{\hspace{1em}<br><br>}<br><br>r_1},1-\frac{a_2<br><br>h}{g<br><br>\text{\hspace{1em}<br><br>}<br><br>r_2}\right);<br><br>$

where

g is equal to gravitational acceleration in a vicinity of the vehicle.

16. A rolling element for supporting a mobile robotic vehicle, the rolling element comprising a rolling surface having a generally prolate spheroid shape.

17. The rolling element of claim 16, wherein the rolling element has a minimum radius and a maximum radius, and a ratio of the minimum radius to the maximum radius is less than ¾

.

18. The rolling element of claim 17, wherein the ratio of the minimum radius to the maximum radius is less than ½

.

19. The rolling element of claim 17, wherein the ratio of the minimum radius to the maximum radius is less than ¼

.

20. The rolling element of claim 16, wherein when the rolling element is viewed in front elevational aspect, the rolling element resembles an ellipse having flattened ends.

21. The rolling element of claim 16, wherein as the rolling element rolls in a straight line across a support surface, only a narrow central band of the rolling element contacts the support surface.

22. The rolling element of claim 16, wherein the rolling element is constructed of a durable, long-wearing material having a low coefficient of friction on a support surface.

23. The rolling element of claim 22, wherein the rolling element is constructed of acetal plastic.

24. A rolling element for supporting a mobile robotic vehicle, the rolling element comprising a central portion that is substantially cylindrical, and end portions that each taper monotonically from a larger diameter to a smaller diameter in a direction away from the central portion.

25. The rolling element of claim 24, wherein when the rolling element is viewed in front elevational aspect, surfaces of the end portions define smooth curves.

26. The rolling element of claim 24, wherein when the rolling element is viewed in front elevational aspect, surfaces of the end portions define straight lines.

27. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a first driven wheel and a second driven wheel, the driven wheels being rotatable about a drive axis;

at least a first rolling element located aft of the drive axis and a second rolling element located fore of the drive axis;

wherein

the rolling elements are each fixed with respect to the vehicle against rotation about a vertical axis and translation along the vertical axis; and

each rolling element comprises a rolling surface having a prolate spheroid shape.

28. The mechanical arrangement of claim 27, wherein the driven wheels are translatable with respect to the vehicle along the vertical axis.

29. The mechanical arrangement of claim 27, wherein a vertical axis through the center of gravity of the vehicle intersects or nearly intersects the drive axis at or near a midpoint between the driven wheels.

30. A mechanical arrangement for deduced reckoning that reduces or minimizes deduced reckoning error accumulation in a mobile robotic vehicle, the arrangement comprising:

a mobile robotic vehicle having a maximum acceleration equal to a₁, having a maximum deceleration equal to a₂, and having a total vehicle weight;

a first driven wheel and a second driven wheel, the driven wheels being rotatable, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests;

a first rolling element located to a first side of the driven wheels, the first rolling element being rotatable and being separated from the driven wheels by a first horizontal distance r₁; and

a second rolling element located to a second side of the driven wheels, the second rolling element being rotatable and being separated from the driven wheels by a second horizontal distance r₂;

wherein

a percentage of the total vehicle weight carried by the drive wheels depends at least in part upon the following quantities;

a₁, a₂, h, r₁, and r₂.

31. A mobile robotic vehicle, comprising:

a vehicle body, at least one motor providing locomotion to the vehicle, at least one power source and at least one control system, the vehicle having a maximum acceleration equal to a₁, having a maximum deceleration equal to a₂, and having a total vehicle weight;

at least a first driven wheel and a second driven wheel, the driven wheels being rotatable about a drive axis, a vertical axis through the center of gravity of the vehicle intersecting or nearly intersecting the drive axis at or near a midpoint between the driven wheels, the center of gravity of the vehicle being located at a height h above a support surface upon which the vehicle rests;

at least a first rolling element located to a first side of the drive axis, the first rolling element being rotatable about a first rolling axis that is parallel to the drive axis and separated from the drive axis by a first horizontal distance r₁; and

at least a second rolling element located to a second side of the drive axis, the second rolling element being rotatable about a second rolling axis that is parallel to the drive axis and separated from the drive axis by a second horizontal distance r₂;

wherein

a percentage of the total vehicle weight carried by the drive wheels is less than or equal to the following quantity

$\min <br><br>\left(1-\frac{a_1<br><br>h}{g<br><br>\text{\hspace{1em}<br><br>}<br><br>r_1},1-\frac{a_2<br><br>h}{g<br><br>\text{\hspace{1em}<br><br>}<br><br>r_2}\right);<br><br>$

where

g is equal to gravitational acceleration in a vicinity of the vehicle.