JP6863049B2 - Autonomous mobile robot - Google Patents

Description

The present invention relates to an autonomous mobile robot.

A technique is known in which a mobile robot that moves autonomously creates and updates an environmental map while calculating its own position together with its reliability (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-203145

The mobile robot can receive an environment map created by another mobile robot and perform self-position estimation while comparing it with the current sensor output of its own sensor. Alternatively, when the mobile robot that created the environment map executes another task, it can perform self-position estimation while comparing the environment map that has already been created with the current sensor output. However, if a part of the environmental map includes a region with low reliability, there is a problem that highly accurate self-position estimation cannot be performed from the sensor output that senses the space corresponding to the region.

The present invention has been made to solve such a problem, and provides a technique for a mobile robot to accurately estimate its own position while referring to an environmental map.

The autonomous mobile robot according to the first aspect of the present invention is an autonomous mobile robot that autonomously moves in a target space, and is divided into a distance sensor that measures a distance to an object existing in the vicinity and a target space into a plurality of cell spaces. Then, the acquisition unit that acquires the environment map that expresses each cell space with the evaluation value indicating the certainty of the existence of the object, and the self-position that is the position of the autonomous mobile robot itself on the environment map based on the distance measurement by the distance sensor. The position estimation unit is provided with a position estimation unit for estimating the distance, and when estimating the self-position, the position estimation unit performs distance measurement by pointing the distance sensor at the cell space having an evaluation value having a higher probability of existence of the object, and the distance is measured. The self-position is estimated by comparing the measurement result with the environmental map.

According to the present invention, the mobile robot can accurately estimate its own position while referring to the environment map.

It is external perspective view of the mobile robot which concerns on this embodiment. It is a control block diagram of a mobile robot. It is a figure explaining the state of the distance measurement using a distance sensor. It is a figure which shows the example of the object space which moves autonomously. It is a figure explaining the acquired environment map. It is a figure explaining the plan of a route and a posture. It is a flow figure explaining the processing flow of a mobile robot.

Hereinafter, the present invention will be described through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Moreover, not all of the configurations described in the embodiments are indispensable as means for solving the problem.

FIG. 1 is an external perspective view of the mobile robot 100 according to the present embodiment. The mobile robot 100 is roughly divided into a carriage portion 110 and an arm portion 120.

The bogie 110 is mainly composed of a base 111, two drive wheels 112 attached to the base 111, and one caster 113. The two drive wheels 112 are arranged so that the rotation axis coincides with each of the opposite sides of the base 111. Each drive wheel 112 is independently rotationally driven by a motor (not shown). The caster 113 is a driven wheel, and a swivel shaft extending in the vertical direction from the base 111 is provided so as to support the wheel apart from the rotation shaft of the wheel, and follows the moving direction of the bogie portion 110. .. For example, the mobile robot 100 goes straight if the two drive wheels 112 are rotated in the same direction at the same rotation speed, and turns around a vertical axis passing through the center of gravity if the two drive wheels 112 are rotated at the same rotation speed in the opposite direction.

The dolly unit 110 is provided with various sensors for detecting obstacles and recognizing the surrounding environment. The camera 114 is one of the sensors, and two cameras 114 are arranged in front of the base 111. The camera 114 includes, for example, a CMOS image sensor, and transmits a captured image signal to a control unit described later. A distance sensor 115 is further arranged in front of the base 111. The distance sensor 115 is a sensor that measures the distance to an object existing in the vicinity. The distance sensor 115 in the present embodiment is a rider that measures the distance to the projection point by projecting the laser beam while scanning it in the horizontal cross-sectional direction and detecting the reflected light. Specifically, it will be described later.

A control unit 190 is provided on the carriage portion 110. The control unit 190 includes a control unit and a memory, which will be described later.

The arm portion 120 is mainly composed of a plurality of arms 121, 122, 123 and a hand 124. One end of the arm 121 is pivotally supported by the base 111 so as to be rotatable around a vertical axis. One end of the arm 122 is pivotally supported by the other end of the arm 121 so as to be rotatable around a horizontal axis. The arm 123 is rotatable in the radial direction at the other end of the arm 122, and one end thereof is pivotally supported by the other end of the arm 122. The hand 124 is pivotally supported at the other end of the arm 123 so as to be rotatable around a central axis parallel to the extension direction of the arm 123.

The hand 124 is a gripping mechanism for gripping a transported object or the like. The mobile robot 100 is not limited to transporting the transported object, and can be applied to various purposes. The arm unit 120 grips various work objects according to the task given to the mobile robot 100.

FIG. 2 is a control block diagram of the mobile robot 100. The control unit 200 is, for example, a CPU, and is a mobile robot 100 by transmitting and receiving information such as commands and sampling data to and from the drive wheel unit 210, the arm unit 220, the sensor unit 230, the memory 240, the reception unit 250, and the like. Performs various operations related to the control of.

The drive wheel unit 210 is provided in the bogie unit 110, and includes a drive circuit for driving the drive wheels 112, a motor, an encoder for detecting the amount of rotation of the motor, and the like. The drive wheel unit 210 functions as a moving mechanism for autonomous movement. The control unit 200 executes rotation control of the motor by sending a drive signal to the drive wheel unit 210. In addition, by receiving the detection signal of the encoder, the moving speed, moving distance, turning angle, etc. of the moving robot 100 are calculated.

The arm unit 220 is provided in the arm unit 120, and includes a drive circuit and an actuator for driving the arms 121, 122, 123 and the hand 124, an encoder for detecting the amount of movement of the actuator, and the like. The control unit 200 operates the actuator by sending a drive signal to the arm unit 220, and executes attitude control and grip control of the arm unit 120. Further, by receiving the detection signal of the encoder, the operating speed, operating distance, posture, etc. of the arm unit 120 are calculated.

The sensor unit 230 includes various sensors in addition to the camera 114 and the distance sensor 115, and these are dispersedly arranged in the carriage portion 110 and the arm portion 120. The control unit 200 acquires the output by sending a control signal to each sensor. For example, the camera 114 executes a shooting operation according to a control signal from the control unit 200, and transmits the shot frame image data to the control unit 200. Further, the distance sensor 115 transmits the projection direction of the laser beam and the distance from the reference position to the object to the control unit according to the request signal from the control unit 200.

The memory 240 is a non-volatile storage medium, and for example, a solid state drive is used. The memory 240 stores a control program for controlling the mobile robot 100, various parameter values used for control, a function, a look-up table, and the like. In particular, it includes a storage area of the map DB 241 which is a database in which various map information for autonomous movement is described.

The receiving unit 250 receives various information and control signals sent from an external device or another mobile robot under the control of the control unit 200. The receiving unit 250 is, for example, a wireless LAN unit, and of course may have a function as a transmitting unit. In the present embodiment, the receiving unit 250 functions as an acquiring unit that receives and acquires the created environment map from another mobile robot.

The control unit 200 also plays a role as a function execution unit that executes various calculations and controls related to control. The position estimation unit 201 compares the environment map stored in the map DB 241 with the output of the distance sensor 115, and provides a control program that performs self-position estimation to determine where the mobile robot 100 exists in the target space. Execute. Specifically, it will be described in detail later.

FIG. 3 is a diagram illustrating a state of distance measurement using the distance sensor 115. The distance sensor 115, which is a rider, projects laser light in the horizontal cross-sectional direction at a height h from the floor surface. Specifically, for example, a micromirror is driven to scan the laser beam in a range of about 90 degrees in front of the base 111. Then, the distance to the reflection point is calculated by detecting the reflected light with respect to the scanned projected light.

_{If an object exists within a distance L 0} from the laser projection unit, which is a reference point, the distance sensor 115 can detect the distance to the object. That is, the detection region is a range of about 90 degrees ahead and a radius L _{0 centered on the reference point.} When the object 601 exists in the detection region as shown in the figure, the detection points at which the distance can be measured appear continuously and linearly on the surface of the object 601 (thick line portion in the figure). At this time, the distance sensor 115 outputs the projection direction of the laser and the distance from the reference point for each detection point. The projection direction of the laser is, for example, the angle formed with respect to the front direction. In the illustrated detection point example, the distance is L _x and the projection direction is θ _x . If the distance sensor 115 cannot detect an object within the range of the _{distance L 0, the distance sensor 115 outputs the result that there is no detected object.}

FIG. 4 is a diagram showing an example of a target space in which the mobile robot 100 autonomously moves. As described above, the target space is recognized as a horizontal cross section at a height h from the floor surface measured by the distance sensor 115, but FIG. 4 is shown as a schematic view of the target space 600 in which the mobile robot 100 moves around. There is.

The target space 600 is entirely surrounded by a wall 611, and a part facing the passage is an entrance 612 that can come and go to and from the passage. A part of the wall 611 is composed of a transparent glass door 613. In addition, there are a plurality of pillars 614 in the target space 600. In addition, a plurality of shelves 615 are installed. In the target space 600, 690 people are occasionally working.

Prior to executing a task in such a target space, the mobile robot 100 acquires an environment map of the target space created by another mobile robot, a map creation robot, via the receiving unit 250. Like the mobile robot 100, the map-creating robot includes a distance sensor that projects a laser beam in the horizontal cross-sectional direction at a height h from the floor surface, and creates an environmental map from the output result. That is, the environment map acquired by the mobile robot 100 is a map in a horizontal cross section at a height h of the target space.

Here, an example will be described of how the environmental map is created. In the target space for creating a map, the map creation robot finds a route that it can pass through using camera image information, etc., and moves as far as possible in the target space while grasping its own position by dead reckoning. .. The mapping robot operates a distance sensor to detect whether or not an object exists in the sensing range with respect to the traveling direction. Specifically, the map-creating robot acquires the position of the reference point at the time of sensing, the projection direction of the laser beam, the distance to the detected object, and the verification value thereof.

The verification value is a value indicating the certainty of the detection result detected by the distance sensor. As the verification value, for example, when the intensity of the reflected light is high, a high value is given on the assumption that the distance can be detected with high accuracy. On the contrary, when the intensity of the reflected light is small, a low value is given because the detection result is uncertain. Specifically, for example, when a laser is projected onto transparent glass, the reflectance on the surface thereof is low, so that the intensity of the detected reflected light is weakened. Further, even if the surface of the object is vibrating or the material absorbs the laser beam, the detection result may vary or the intensity of the reflected light may be weakened. That is, the detected result is uncertain depending on the state of the surface of the object irradiated with the laser beam and the material, and in such a case, a low verification value is given.

The environment map divides the target space into a plurality of cell spaces, and gives each cell space an evaluation value indicating the certainty as to whether or not there is an object that occupies at least a part of each cell space. It was done. The evaluation value given to each cell space is calculated based on the verification value of the distance sensor obtained by the map-creating robot while moving around the target space.

FIG. 5 is a diagram for explaining the acquired environmental map. The target space 600 is defined as a set of cell spaces divided into m × n in one layer including a horizontal cross section at a height h from the floor surface.

The mapping robot determines that the object did not exist in the cell space through which the laser beam projected by the distance sensor passed, and determines that the object existed in the cell space where the laser beam was reflected. Further, it is assumed that the existence or nonexistence of the object cannot be confirmed in the cell space farther than the cell space where the laser beam is reflected. The mapping robot determines the cell space through which the laser beam has passed and the cell space reflected by the laser beam based on the position of the reference point at the time of sensing, the projection direction of the laser beam, and the distance to the detected object. When the distance sensor does not detect an object, the cell space included in the detectable range from the reference point is determined to be the cell space in which the object did not exist.

Further, as described above, since the sensing result includes the verification value, the map creation robot calculates the evaluation value of each cell space based on the verification value. The evaluation value is a value indicating the certainty as to whether or not there is an object that occupies at least a part of each cell space as described above.

For example, when the evaluation value is set to any value of 0 or more and 1 or less, "0" is defined as "there is no object" and "1" is defined as "there is an object". A value of "0.5" means "the existence or nonexistence of an object is unknown". Therefore, the closer the value is to "0", the more certain it is that "the object does not exist", and the closer the value is to "1", the more certain it is that "the object exists". On the contrary, the closer the value is to the median value "0.5", the more it can be said that "it is unknown whether or not the object exists".

The verification value indicating the certainty of the detection result is a small value when, for example, transparent glass is detected as described above. That is, the verification value can be regarded as representing the certainty that the object exists at the detection point. Therefore, if the verification value is large, an evaluation value close to "1" can be given to the cell space including the detection point, and an evaluation value close to "0" can be given to the cell space in between. On the contrary, if the verification value is small, an evaluation value close to "0.5" may be given to both the cell space including the detection points and the cell space in between. That is, the map-creating robot can convert the verification value output by sensing into each evaluation value given to each cell space by a predetermined conversion formula.

Further, due to the movement of the mapping robot, the distance sensor may project the laser beam into the same cell space many times. In that case, it is advisable to update the evaluation value of the related cell space according to the detection result. The map-creating robot can, for example, set the average value of the previously calculated evaluation value and the newly calculated evaluation value as the latest evaluation value.

Each cell space shown in FIG. 5 has an evaluation value calculated in this way. A cell space having an evaluation value close to "0" (evaluation value less than 0.35 in this case) is shown in white, and a cell space having an evaluation value close to "1" (evaluation value of 0.65 or more in this case) is shown in white. It is represented by a diagonal line. Further, the cell space having an evaluation value close to "0.5" (here, the evaluation value of 0.35 or more and less than 0.65) is represented by dots, and the cell space in which the existence or nonexistence of the object could not be confirmed is represented by black. There is. Then, the lower left part is enlarged to show what kind of numerical value is specifically given to each cell space.

As shown in FIG. 4, since the glass door 613 exists in the lower left, the evaluation value of the cell space corresponding to the glass door 613 is close to “0.5”. On the other hand, the evaluation value of the cell space corresponding to the pillar 614 is a value close to "1", and it can be seen that the object exists more reliably at that position. In addition, since there was a person 690 as a moving object near the center right side of the target space 600, a group of cell spaces having an evaluation value close to "0.5" on the environmental map corresponding to this existed on the center right side. It can be seen that it exists in the vicinity.

The mobile robot 100 divides the target space into a plurality of cell spaces in this way, and displays an environment map in which each cell space is expressed by an evaluation value indicating the certainty of the existence or nonexistence of an object from the map creation robot via the receiving unit 250. get. Then, with reference to the acquired environment map, the movement route according to the task and the posture during the route movement are planned. FIG. 6 is a diagram illustrating a plan for a movement route and a posture during route movement.

Task mobile robot 100 to be executed is moved from the start point to the point P _1, P _2, removed conveyed from the shelf 615 running the arm unit 150 is assumed to return to the starting point. At this time, it is assumed that the mobile robot 100 selects the route indicated by the solid line and the arrow as the optimum route.

The mobile robot 100 moves along the selected path, but during the movement, in addition to the dead reckoning that estimates the self-position from the driving amount of the drive wheels, or instead of the dead reckoning, the environment map and the distance sensor 115 The self-position is estimated by comparing with the detection result of. Specifically, the location where the presence / absence status of surrounding objects recognized from the detection result of the distance sensor 115 matches the presence / absence information of the object shown on the environmental map is searched for, and the distance and direction to the matching location are used to determine the current status of the object. Calculate the position.

By the way, _{the cell space surrounded by thick lines V 1} and V ₂ in the environment map is a cell space having an evaluation value with a small probability of existence of an object. When the mobile robot 100 tries to estimate its own position using the detection result of sensing performed on such a cell space, it cannot properly collate with the environment map, and the estimation accuracy drops. .. Therefore, in the present embodiment, the mobile robot 100 refers to the acquired environment map and directs the distance sensor 115 to the cell space having an evaluation value having a greater certainty of the existence or nonexistence of the object so that the distance measurement can be performed. Control your posture while moving.

Specifically, the mobile robot 100, when traveling in the vicinity of the cell space surrounded by a thick line V _1, V _2, as the distance sensor 115 in the direction indicated by the outline arrows are directed, to control the posture of the mobile robot 100 .. The mobile robot 100 can make the moving direction and the direction of the distance sensor 115 different by giving a difference in the amount of rotation of the left and right drive wheels 112. In the route not shown by the white arrow, the distance sensor 115 is moved toward the front.

For example _{, in the path toward the point P 1 , when the cell space of V 1} starts to be included in the detection area of the distance sensor 115, the mobile robot 100 makes the direction of the distance sensor 115 the detection area a _{1 indicated by the dotted line.} , Tilt a little to the left with respect to the direction of travel. Then, further the proceeds, so as to face opposite to the cell space of V ₁ was in turn, as the orientation of the distance sensor 115 is a detection region a _2, slightly inclined to the right side to the traveling direction.

Similarly, in the path back from the point P ₂ to the start point, if the distance to the detection area of the sensor 115 starts to include the cell space of V _2, as the direction of the distance sensor 115 is a detection region a ₃ indicated by a dotted line , Tilt a little to the left with respect to the direction of travel. In this way, _{if the orientation of the distance sensor 115 is adjusted when traveling in the vicinity of the cell space of V 1} and V ₂ , the environment map and the detection result of the distance sensor 115 will be based on the cell space in which the presence or absence of an object is more certain. Can be collated, so that the mobile robot 100 can estimate its own position with high accuracy. In addition, since the self-position can be estimated with high accuracy, it is possible to return to the movement route of our place more correctly when it is recognized that the movement route is deviated from the planned movement route.

In the example described above, prior to the execution of the task, the movement route and the posture during the route movement were planned with reference to the acquired environment map. However, only the movement path is planned at the start of task execution, and when moving along the movement path, a cell space in which the existence or nonexistence of an object is uncertain enters or enters the detection area of the distance sensor 115. You may control your own posture after recognizing that. FIG. 7 is a flow chart illustrating a processing flow of the mobile robot 100 in such an example. The given task shall be executed at any time in the flow.

First, the control unit 200 acquires an environment map of the target space 600 for which the task is to be executed (step S101). Then, with reference to the acquired environment map, a route to be moved in order to execute the task is planned (step S102).

The control unit 200 transmits a control signal to the drive wheel unit 210 to execute the movement along the planned route (step S103). The control unit 200 continues the movement, monitors the movement amount, and refers to the map to determine whether or not a specific cell space in which the existence or nonexistence of the object is uncertain enters the detection area of the distance sensor 115 ( Step S104). When it is determined that the robot is approaching, the posture of the mobile robot 100 is controlled to change the direction of the distance sensor 115 so that the detection area of the distance sensor 115 does not include the specific cell space as much as possible, and the process proceeds to step S106. If it is determined that the vehicle does not enter, step S105 is skipped and the process proceeds to step S106.

The position estimation unit 201 of the control unit 200 acquires a detection result from the distance sensor 115 (step S106), and estimates its own position by collating the detection result with the environment map (step S107). Then, the control unit 200 determines whether or not the estimated self-position deviates from the planned route (step S108), and if it deviates, corrects the position to return to the planned route (step S109). When the position correction is completed, or when it is determined in step S108 that the route is not deviated, the process proceeds to step S110.

In step S110, the control unit 200 determines whether or not the task has been completed and the user has returned to the starting point. If it is determined that the device has not returned, the process returns to step S103. When it is determined that the product has returned, the series of processes is terminated.

In the embodiment described above, the environment map represents one layer obtained by horizontally cutting the target space, but an environment map defined by three-dimensionally divided cell spaces may be used. If a three-dimensional environmental map is used, a distance sensor that can scan in the height direction may be adopted, or a plurality of distance sensors may be arranged in the height direction.

Further, in the embodiment described above, the rider is adopted as the distance sensor 115, but the distance sensor 115 does not have to be a rider. An ultrasonic sensor, a distance image sensor, or the like may be used as long as it is a distance sensor capable of measuring the distance to an object. Further, instead of a single distance sensor including a scanning mechanism, for example, a distance sensor array in which each is directed in a different direction may be used. Further, if the distance sensor is installed on a swivel base, the base may be swiveled to change only the direction of the distance sensor without changing the posture of the mobile robot 100. ..

Further, the mobile robot 100 is not limited to a robot that travels on the floor with wheels, and may be a walking type robot or, for example, a drone type robot that moves in the air. When there is a cell space in which the existence or nonexistence of an object is uncertain in the acquired environment map, the type of movement mechanism is not limited as long as the robot avoids such cell space and measures the distance to estimate its own position.

100 mobile robot, 110 carriage, 111 base, 112 drive wheels, 113 casters, 114 camera, 115 distance sensor, 120 arm, 121, 122, 123 arm, 124 hand, 190 control unit, 200 control, 201 position estimation Unit, 210 drive wheel unit, 220 arm unit, 230 sensor unit, 240 memory, 241 map DB, 250 receiver, 600 target space, 601 object, 611 wall, 612 entrance, 613 glass door, 614 pillar, 615 shelf, 690 Man

Claims (1)

An autonomous mobile robot that autonomously moves in the target space
A distance sensor that measures the distance to objects in the vicinity,
An acquisition unit that divides the target space into a plurality of cell spaces and acquires an environment map in which each cell space is represented by an evaluation value indicating the certainty of the existence or nonexistence of an object.
It is provided with a position estimation unit that estimates its own position, which is the position of the autonomous mobile robot itself on the environment map, based on the distance measurement by the distance sensor.
When estimating the self-position, the position estimation unit controls the posture of the autonomous mobile robot so that the distance sensor faces the cell space having the evaluation value having a greater probability of existence of an object, and the control is performed. An autonomous mobile robot that performs distance measurement in a vertical posture and estimates its own position by collating the result of the distance measurement with the environment map.

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