Robot lawn mower bumper system

• US 20180184583A1
• Filed: 12/30/2016
• Published: 07/05/2018
• Est. Priority Date: 12/30/2016
• Status: Active Grant

• Current Assignee: iRobot Corporation
• Original Assignee: iRobot Corporation
• Granted Patent: US 10,375,880 B2
• Time in Patent Office: Days
• CPC Class Codes: A01D 34/008 for automated or remotely controlled operation
• CPC Class Codes: B25J 5/007 mounted on wheels

Abstract

In one aspect, a mobile robot includes a chassis, a shell moveably mounted on the chassis by a shell suspension system, and a sensor assembly configured to sense a distance and a direction of shell movement relative to the chassis. The sensor assembly includes a magnet disposed on an underside of the shell. The sensor assembly further includes three or more Hall effect sensors disposed on the chassis in a triangular pattern at fixed distances such that the three or more Hall effect sensors are positioned beneath the magnet when no force is applied to the shell, wherein relative motion between the magnet and the Hall effect sensors causes the sensors to produce differing output signals. The mobile robot also includes a controller configured to receive output signals from the Hall effect sensors and to determine a distance and a direction of movement of the shell relative to the chassis.

Claims

1. A mobile robot comprising:

a chassis;

a shell moveably mounted on the chassis by a shell suspension system;

a sensor assembly configured to sense a distance and a direction of shell movement relative to the chassis, the sensor assembly comprising;

a magnet disposed on an underside of the shell and;

three or more Hall effect sensors disposed on the chassis in a triangular pattern at fixed distances such that the three or more Hall effect sensors are positioned beneath the magnet when no force is applied to the shell, wherein relative motion between the magnet and the Hall effect sensors causes the sensors to produce differing output signals; and

a controller, configured to receive output signals from the Hall effect sensors and to determine a distance and a direction of movement of the shell relative to the chassis.

2. The mobile robot of claim 1, wherein the magnet is sized based on an amount of shell movement relative to the chassis allowed by the suspension system.

3. The mobile robot of claim 2, wherein the magnet is rectangular and a center of the magnet aligns axially with a center of the triangular pattern.

4. The mobile robot of claim 1, wherein a center of the magnet and a center of the triangular pattern are located along the center line of the robot.

5. The mobile robot of claim 1, wherein the shell suspension system comprises:

a plurality of suspension posts, each suspension post comprising;

a spring; and

a locking mechanism configured to couple the chassis to the shell.

6. The mobile robot of claim 5, wherein the spring has a spring constant in a range of 2 to 10 N/mm.

7. The mobile robot of claim 5, wherein each suspension post is located near a corner of the shell.

8. The mobile robot of claim 1, wherein the sensor assembly is configured to sense at least eight differing states of contact with the shell.

9. The mobile robot of claim 1, wherein, based on the outputs from the sensors, the controller is configured to determine an angle at which the shell contacted an obstacle and determines a sequence of movements to move the mobile robot around the obstacle.

10. The mobile robot of claim 1, wherein the center of the triangular pattern is positioned no further than 11 centimeters from the center of the chassis.

11. The mobile robot of claim 1, wherein each of the Hall effect sensors is surrounded by a coil.

12. The mobile robot of claim 1, wherein the sensor assembly senses no contact with an obstacle when each of the Hall effect sensors is covered by the magnet.

13. The mobile robot of claim 1, wherein the three or more Hall effect sensors are co-located on a circuit board with a footprint area between 15 and 30 square centimeters.

14. The mobile robot of claim 1, wherein the three or more Hall effect sensors are co-located on a circuit board and a ratio of an area of the circuit board to an area of the shell is between 150:

1 and 300;

1.

15. The mobile robot of claim 1, further comprising a charge pump and a capacitor, wherein the charge pump and the capacitor are electrically connected to at least one motor of the mobile robot.

16. The mobile robot of claim 15, wherein the at least one motor of the mobile robot can only operate when the capacitor is charged.

17. The mobile robot of claim 16, wherein the capacitor cannot be charged unless at least one of the three or more Hall effect sensors is covered by the magnet.

18. A method of detecting contact between a mobile robot and an obstacle comprising:

sensing, with a sensor assembly comprising a magnet disposed on a shell of the mobile robot and three or more Hall effect sensors disposed on a chassis of the mobile robot, an analog response of three or more Hall effect sensors based on an orientation of the magnet in relation to the Hall effect sensors;

receiving, at a controller, signals provided by the three or more Hall effect sensors of the sensor assembly;

determining, by the controller, a distance and a direction of movement of the shell relative to the chassis; and

modifying at least one behavior of the mobile robot based on the distance and direction of movement of the shell relative to the chassis.

19. The method of claim 18 wherein determining a distance and a direction of movement of the shell relative to the chassis comprises determining from which of at least eight differing states of contact with the shell the contact occurred.

20. The method of claim 18, wherein determining a distance and a direction of movement of the shell relative to the chassis comprises determining an angle at which the mobile robot contacted an obstacle.

21. The method of claim 18, wherein determining a distance and a direction of movement of the shell relative to the chassis comprises using a look-up table.

22. The method of claim 18, further comprising cutting power to a motor of the mobile robot if none of the Hall effect sensors sense the magnet.

23. The method of claim 18, further comprising sending an electrical current through a coil surrounding a Hall effect sensor of the sensor assembly and determining, at a controller, whether the sensor assembly is functioning properly.

24. The method of claim 18, wherein modifying the behavior of the mobile robot comprises:

identifying and providing an instruction to a drive system of the mobile robot based on the distance and direction of shell movement relative to the chassis.

25. The method of claim 24, wherein the instruction comprises a command to execute an obstacle avoidance maneuver.

26. The method of claim 25, wherein the avoidance maneuver comprises a command for the mobile robot to back up a computed distance from the obstacle.

27. The method of claim 24, wherein identifying and providing an instruction for a drive system of the mobile robot comprises using machine learning.