Autonomous traction measurement of a surface

• US 10,209,682 B1
• Filed: 03/09/2018
• Issued: 02/19/2019
• Est. Priority Date: 03/09/2018
• Status: Active Grant

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Inventors: Hebert, Gabriel, Purwin, Oliver Christoph
• Primary Examiner(s): Cumbess, Yolanda R
• Application Number:
  US15/917,241
• Time in Patent Office: 347 Days
• Field of Search: None
• CPC Class Codes: B66F 9/063 Automatically guided
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01C 21/3826 Terrain data
• CPC Class Codes: G01C 21/3844 Data obtained from position sensors only, e.g. from inertial navigation
• CPC Class Codes: G05B 13/00 Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion G05B19/00 takes precedence
• CPC Class Codes: G05D 1/0234 using optical markers or beacons optical beacons per se G01S1/70
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00

Abstract

Embodiments are directed to an inventory system having one or more drive units that are used, in part, to measure traction of a surface. Traction of the surface may be one of many features that can help with the operation of drive units and may also help avoid collisions between drive units when little room is available between the drive units for navigational errors.

Claims

1. An inventory management system, comprising:

an unmanned mobile drive unit, the unmanned mobile drive unit configured to move a container holder across a surface in a storage facility; and

a management module configured to;

transmit an instruction to the unmanned mobile drive unit to perform a rotation relative to the surface, the instruction comprising accelerating or decelerating the rotation of the unmanned mobile drive unit relative to the surface;

receive wheel encoder data from the unmanned mobile drive unit, the wheel encoder data generated based at least in part on the rotation;

receive rotation gyroscope data from a gyroscope sensor of the unmanned mobile drive unit;

compare the wheel encoder data from the rotation with the rotation gyroscope data;

determine a difference between the wheel encoder data and the rotation gyroscope data, the difference between the wheel encoder data and the rotation gyroscope data corresponding with a slip value;

derive an acceleration threshold that limits the slip value to being below a slip threshold; and

instruct the unmanned mobile drive unit to modify the acceleration or deceleration of the unmanned mobile drive unit based at least in part on the acceleration threshold of the surface.

2. The inventory management system of claim 1, wherein the instruction to perform the rotation relative to the surface follows a calibration routine that syncs wheel encoder outputs with rotation gyroscope outputs to within a predetermined tolerance.

3. The inventory management system of claim 1, wherein wheels of the unmanned mobile drive unit rotate to move the unmanned mobile drive unit at least 360 degrees.

4. The inventory management system of claim 1, where the rotation comprises a plurality of incrementally increasing accelerations and a plurality of incrementally increasing decelerations.

5. A computer-implemented method for measuring traction of a surface using a mobile drive unit, the method comprising:

instructing the mobile drive unit to perform a rotation relative to the surface, the instruction comprising accelerating or decelerating the rotation relative to the surface;

receiving wheel encoder data from the mobile drive unit, the wheel encoder data generated based at least in part on the rotation;

receiving sensor data from the mobile drive unit;

comparing the wheel encoder data from the rotation with sensor data of the mobile drive unit;

determining a difference between the wheel encoder data and the sensor data, the difference between the wheel encoder data and the sensor data corresponding with a slip value; and

deriving an acceleration threshold that limits the slip value being below a slip threshold.

6. The computer-implemented method of claim 5, further comprising:

modifying acceleration or deceleration of the rotation of the mobile drive unit based at least in part on the acceleration threshold; and

transmitting a second instruction with the modified acceleration or deceleration to the mobile drive unit.

7. The computer-implemented method of claim 5, further comprising:

generating a heat map based at least in part on the acceleration threshold.

8. The computer-implemented method of claim 7, wherein the heat map identifies temporary contaminants on the surface.

9. The computer-implemented method of claim 7, wherein the heat map identifies permanent wear and tear of the surface.

10. The computer-implemented method of claim 7, further comprising:

receiving additional data from the mobile drive unit; and

updating the heat map based at least in part on the additional data.

11. The computer-implemented method of claim 7, wherein movement of the mobile drive unit is restricted away from a location identified by the heat map.

12. The computer-implemented method of claim 5, further determining an association between the difference between the wheel encoder data and the sensor data that is associated with a value of acceleration or deceleration of the mobile drive unit.

13. The computer-implemented method of claim 5, further comprising:

instructing the mobile drive unit to enter a diagnostic mode, wherein the rotation is performed in the diagnostic mode; and

instructing the mobile drive unit to enter a normal mode, wherein the normal mode allows the mobile drive unit to perform a movement over the surface, and wherein the movement over the surface is based at least in part on the acceleration threshold.

14. The computer-implemented method of claim 5, wherein the mobile drive unit is a first mobile drive unit and the method further comprises:

receiving a second acceleration threshold from a second mobile drive unit;

determining an acceleration threshold difference between the first mobile drive unit and the second mobile drive unit; and

instructing the second mobile drive unit to access a maintenance location of the surface based at least in part on the acceleration threshold difference.

15. The computer-implemented method of claim 14, wherein the acceleration threshold difference is based at least in part on a castor problem of the second mobile drive unit and the maintenance location is configured to remediate the castor problem.

16. A management module for controlling a mobile drive unit, the management module comprising:

a memory configured to store computer-executable instructions; and

a processor configured to access the memory and execute the computer-executable instructions to cause the management module to at least;

receive wheel encoder data from the mobile drive unit, the wheel encoder data generated based at least in part on the mobile drive unit rotating relative to a surface, and accelerating or decelerating rotation relative to the surface;

receive sensor data from the mobile drive unit;

compare the wheel encoder data from the rotation with sensor data of the mobile drive unit to determine a slip value; and

derive an acceleration threshold that limits the slip value being below a slip threshold.

17. The management module of claim 16, wherein the computer-executable instructions further cause the management module to receive the wheel encoder data and the sensor data from the mobile drive unit and derive the acceleration threshold from the wheel encoder data and the sensor data.

18. The management module of claim 16, wherein the computer-executable instructions further cause the management module to instruct the mobile drive unit to calibrate the wheel encoder data and the sensor data by spinning at a constant rate.

19. The management module of claim 16, wherein the mobile drive unit is further configured to move an inventory holder, wherein the acceleration threshold changes based at least in part on a weight of the inventory holder.

20. The management module of claim 16, wherein the slip threshold is a predetermined slip threshold and acceleration of the mobile drive unit is limited based at least in part on the slip threshold.