Detection of Movable Ground Areas of a Robot's Environment Using a Transducer Array

Abstract

An example method for detecting a movable element on a surface involves receiving, from a depth sensor coupled to a mobile robot, a first depth measurement between the depth sensor and a ground surface. The method also involves causing at least one transducer coupled to the mobile robot to emit a directional pressure wave toward the ground surface. The method further involves receiving, from the depth sensor coupled to the mobile robot, a second depth measurement between the depth sensor and the ground surface after emitting the directional pressure wave. Additionally, the method involves identifying one or more differences between the first depth measurement and the second depth measurement indicating that the ground surface includes a movable element. Further, the method involves providing navigation instructions to the mobile robot based on the identified one or more differences between the first depth measurement and the second depth measurement.

What is claimed is: 
     
         1 . A method comprising:
 causing at least one transducer coupled to a mobile robot to emit a directional pressure wave toward a ground surface in an environment of the mobile robot;   determining that the ground surface includes a movable element that was perturbed by the directional pressure wave emitted by the at least one transducer; and   providing one or more navigation instructions to the mobile robot based on determining that ground surface includes the movable element.   
     
     
         2 . The method of  claim 1 , wherein causing the at least one transducer to emit the directional pressure wave comprises:
 determining a timing sequence with which to operate the at least one transducer based on a position of the ground surface relative to the at least one transducer, wherein the timing sequence specifies a time delay and a duration with which to operate the at least one transducer, and wherein operating the at least one transducer according to the timing sequence produces one or more pressure waves that collectively form the directional pressure wave; and   causing the at least one transducer to operate in accordance with the timing sequence.   
     
     
         3 . The method of  claim 1 , wherein causing the at least one transducer to emit the directional pressure wave comprises:
 determining a phase configuration with which to operate the at least one transducer based on a position of the ground surface relative to the at least one transducer, wherein the phase configuration specifies a phasing with which to operate the at least one transducer, and wherein operating the at least one transducer according to the phase configuration produces one or more pressure waves that collectively form the directional pressure wave; and   causing the at least one transducer to operate in accordance with the phase configuration.   
     
     
         4 . The method of  claim 1 , wherein the navigation instructions cause the mobile robot to avoid stepping onto the ground surface. 
     
     
         5 . The method of  claim 1 , wherein the navigations instructions cause the mobile robot to reduce a speed with which the mobile robot places an appendage onto the ground surface. 
     
     
         6 . The method of  claim 1 , wherein the navigation instructions cause the mobile robot to (i) move an appendage above the ground surface and (ii) lower the appendage with a predetermined speed onto the ground surface until the appendage makes contact with a stable portion of the ground surface. 
     
     
         7 . The method of  claim 1 , wherein the directional pressure wave has a frequency within an ultrasonic range. 
     
     
         8 . The method of  claim 1 , further comprising:
 obtaining a planned trajectory of the mobile robot indicative of an area of the ground surface on which the mobile robot is instructed to step; and   causing the at least one transducer to emit the directional pressure wave toward the area of the ground surface defined by the planned trajectory.   
     
     
         9 . The method of  claim 1 , wherein determining that the ground surface includes the movable element that was perturbed by the directional pressure wave emitted by the at least one transducer is based on sensor data from a sensor that is separate from the at least one transducer on the mobile robot, 
     
     
         10 . The method of  claim 9 , wherein the sensor comprises a stereoscopic camera. 
     
     
         11 . The method of  claim 9 , wherein the sensor comprises a LIDAR device. 
     
     
         12 . The method of  claim 1 . wherein the at least one transducer is a monolithic ultrasonic transducer. 
     
     
         13 . The method of  claim 1 , wherein the at least one transducer is an array of ultrasonic transducers. 
     
     
         14 . A robot comprising:
 at least one transducer; and   a computing device configured to:
 cause the at least one transducer to emit a directional pressure wave toward a ground surface in an environment of the robot; 
 determine that the ground surface includes a movable element that was perturbed by the directional pressure wave emitted by the at least one transducer; and 
 provide one or more navigation instructions for the robot based on determining that e ground surface includes the movable element. 
   
     
     
         15 . The robot of  claim 14 , wherein the navigation instructions cause the robot to avoid stepping onto the ground surface. 
     
     
         16 . The robot of  claim 14 , wherein the navigations instructions cause the robot to reduce a speed with which the robot places an appendage onto the ground surface. 
     
     
         17 . The robot of  claim 14 , wherein the navigation instructions cause the robot to (i) move an appendage above the ground surface and (ii) lower the appendage with a predetermined speed onto the ground surface until the appendage makes contact with a stable portion of the ground surface. 
     
     
         18 . The robot of  claim 14 , wherein the at least one transducer is an array of ultrasonic transducers. 
     
     
         19 . The robot of  claim 14 , wherein the at least one transducer is configured to emit pressure waves which have a frequency within an ultrasonic range. 
     
     
         20 . A non-transitory computer-readable medium having instructions stored thereon that, upon execution by at least one processor, causes the at least one processor to perform operations comprising:
 causing at least one transducer coupled to a mobile robot to emit a directional pressure wave toward a ground surface in an environment of the mobile robot;   determining that the ground surface includes a movable element that was perturbed by the directional pressure wave emitted by the at least one transducer; and   providing one or more navigation instructions to the mobile robot based on determining that the ground surface includes the movable element.