Bot having high speed stability
An autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle includes at least two drive wheels and a controller, where each drive wheel is independently driven and a drive wheel encoder is disposed adjacent each drive wheel. The controller, in communication with the drive wheel encoders, is configured to determine a kinematic state of the autonomous transport vehicle within the storage and retrieval system based on incremental data from the drive wheel encoders only and independent of drive wheel slippage.
1. An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising:
at least two drive wheels, each drive wheel being independently driven;
a drive wheel encoder disposed adjacent each drive wheel; and
a controller in communication with the encoders configured to identify a kinematic state of the autonomous transport vehicle within the storage and retrieval system based only on incremental data from the drive wheel encoders, received from each encoder, and independent of drive wheel slippage.
2. The autonomous transport vehicle of claim 1 , wherein the controller is configured to determine command logic for operating the autonomous transport vehicle based on the kinematic state.
3. The autonomous transport vehicle of claim 1 , wherein the autonomous transport vehicle includes one or more of a wheel encoder for each drive wheel, an inertial sensor, at least one storage slat sensor and at least one line following sensor, wherein the controller is configured to receive data from the one or more of the wheel encoder for each drive wheel, the inertial sensor, the at least one storage slat sensor and the at least one line following sensor for identifying the kinematic state.
4. The autonomous transport vehicle of claim 1 , wherein the controller is further configured to determine a position of the autonomous transport vehicle within the storage and retrieval system independent of drive wheel slippage.
5. The autonomous transport vehicle of claim 4 , wherein the controller is configured to determine the position of the autonomous transport vehicle based on a drive wheel having a lowest velocity of the at least two drive wheels when a positive torque is applied by the at least two drive wheels.
6. The autonomous transport vehicle of claim 4 , wherein the controller is configured to determine the position of the autonomous transport vehicle based on a drive wheel having a highest velocity of the at least two drive wheels when a negative torque is applied by the at least two drive wheels.
7. The autonomous transport vehicle of claim 4 , wherein the controller is configured with an extended Kalman filter for filtering spurious data from each of the encoders.
8. The autonomous transport vehicle of claim 4 , wherein the autonomous transport vehicle includes at least one line following sensor configured to sense guide lines on a surface of the storage and retrieval system, the controller being further configured to weight data from each of the encoders based on a guide line deviation signals provided by the at least one line following sensor.
9. The autonomous transport vehicle of claim 4 , wherein the controller is configured to verify a position of the autonomous transport vehicle by detecting one or more datum lines on a surface of the storage and retrieval system.
10. The autonomous transport vehicle of claim 1 , wherein the autonomous transport vehicle includes at least one releasably lockable caster wheel.
11. A storage and retrieval system comprising:
at least one autonomous transport vehicle including
at least two drive wheels, each drive wheel being independently driven;
a drive wheel encoder disposed adjacent each drive wheel;
a controller in communication with the drive wheel encoders of the at least one autonomous transport vehicle and being configured to identify a kinematic state of the at least one autonomous transport vehicle within the storage and retrieval system based only on incremental data from the drive wheel encoders, received from each encoder, and independent of drive wheel slippage;
wherein the controller periodically verifies the kinematic state along a travel path of the at least one autonomous transport vehicle wherein the period of verification is based on detection of a position datum having a predetermined position relative to a surface being traversed by the at least one autonomous transport vehicle.
12. The storage and retrieval system of claim 11 , wherein the controller is configured to determine command logic for operating the at least one autonomous transport vehicle based on the kinematic state.
13. The storage and retrieval system of claim 11 , wherein the at least one autonomous transport vehicle includes one or more of a wheel encoder for each drive wheel, an inertial sensor, at least one storage slat sensor and at least one line following sensor, wherein the controller is configured to receive data from the one or more of the wheel encoder for each drive wheel, the inertial sensor, the at least one storage slat sensor and the at least one line following sensor for verifying the kinematic state.
14. The storage and retrieval system of claim 11 , wherein the controller is further configured to determine a position of the at least one autonomous transport vehicle within the storage and retrieval system independent of drive wheel slippage.
15. The storage and retrieval system of claim 14 , wherein the controller is configured to determine the position of the at least one autonomous transport vehicle based on a drive wheel having a lowest velocity of the at least two drive wheels when a positive torque is applied by the at least two drive wheels.
16. The storage and retrieval system of claim 14 , wherein the controller is configured to determine the position of the at least one autonomous transport vehicle based on a drive wheel having a highest velocity of the at least two drive wheels when a negative torque is applied by the at least two drive wheels.
17. The storage and retrieval system of claim 14 , wherein the controller is configured with an extended Kalman filter for filtering spurious data from each of the encoders.
18. The storage and retrieval system of claim 14 , wherein the at least one autonomous transport vehicle includes at least one line following sensor configured to sense guide lines on a surface of the storage and retrieval system, the controller being further configured to weight data from each of the encoders based on a guide line deviation signals provided by the at least one line following sensor.
19. The storage and retrieval system of claim 14 , wherein the controller is configured to verify a position of the at least one autonomous transport vehicle by detecting one or more datum lines on a surface of the storage and retrieval system.
20. The storage and retrieval system of claim 14 , wherein the at least one autonomous transport vehicle includes at least one releasably lockable caster wheel.
21. A method for controlling an autonomous transport vehicle within a storage and retrieval system comprising: receiving incremental data from at least two drive wheel encoders, each drive wheel encoder being disposed adjacent a corresponding one of at least two drive wheels of the autonomous transport vehicle; identifying a kinematic state of the autonomous transport vehicle within the storage and retrieval system based only on incremental data from the at least two drive wheel encoders independent of drive wheel slippage; and periodically verifying the kinematic state along a travel path of the autonomous transport vehicle wherein the period of verification is based on detection of a position datum having a predetermined position relative to a surface being traversed by the autonomous transport vehicle; and determining a command logic for operating the autonomous transport vehicle based on the kinematic state; and issuing the command.
22. The method of claim 21 , wherein verifying the kinematic state of the autonomous transport vehicle is further based on data from each of the at least two wheel encoders for each drive wheel, an inertial sensor, at least one storage slat sensor and at least one line following sensor.
23. The method of claim 21 , further comprising determining a position of the autonomous transport vehicle within the storage and retrieval system independent of drive wheel slippage.
24. The method of claim 23 , further comprising determining the position of the autonomous transport vehicle based on a drive wheel having a lowest velocity of the at least two drive wheels when a positive torque is applied by the at least two drive wheels.
25. The method of claim 23 , further comprising determining the position of the autonomous transport vehicle based on a drive wheel having a highest velocity of the at least two drive wheels when a negative torque is applied by the at least two drive wheels.
26. The method of claim 23 , further comprising filtering spurious data from each of the at least two wheel encoders with an extended Kalman filter.
27. The method of claim 23 , further comprising sensing a guide line on a surface of the storage and retrieval system with the at least one line following sensor and weighting data from each of the at least two wheel encoders based on guide line deviation signals provided by the at least one line following sensor.
28. The method of claim 27 , further comprising verifying the position of the autonomous transport vehicle by detecting one or more datum lines on the surface of the storage and retrieval system.