CN109975819B

CN109975819B - Low-cost optimization method for laser measurement data

Info

Publication number: CN109975819B
Application number: CN201711454810.4A
Authority: CN
Inventors: 姜铁程; 褚明杰; 孟庆铸; 李健; 聂宏勋
Original assignee: Shenyang Siasun Robot and Automation Co Ltd
Current assignee: Shenyang Siasun Robot and Automation Co Ltd
Priority date: 2017-12-28
Filing date: 2017-12-28
Publication date: 2023-03-24
Anticipated expiration: 2037-12-28
Also published as: CN109975819A

Abstract

The invention relates to a low-cost optimization method for laser measurement data, which combines the acquisition frequency of a laser sensor with the rotating speed of a laser motor to acquire laser data and comprises the following steps: selecting sampling interval points to ensure that the sampling interval points cannot be divided by 360 degrees; and adjusting the rotating speed of the motor, and controlling the output duty ratio of the PWM so that the actual average value of the sampling intervals reaches a selected value. The invention makes the sampling points of adjacent circles staggered, and after n circles, the sampling points return to the initial point. In this case, the angular resolution is increased by n times, the rotation speed is not reduced much, and the dynamic sensitivity is not affected. In the application of 2D-SLAM mapping, a higher and more accurate environment can be provided without a mobile robot, so that the attributes can be directly updated in the grids within the effective scanning distance range.

Description

Low-cost optimization method for laser measurement data

Technical Field

The invention relates to a low-cost optimization method for laser measurement data, and belongs to the field of laser navigation of mobile robots.

Background

With the rapid development of automation technology, the trend of using automated machinery on a factory production line to replace manpower is more and more obvious. In the field of mobile robots, the robots require various sensors to sense the outside. How a robot autonomously moves and walks in a certain environment has been a subject of research for a long time.

In the prior art, 2D-slam is mature, distance information is obtained on a plane through a sensor, a whole map is built by means of an algorithm, and a path can be planned from any point a to a point B in the map. In this, the sensor plays its important role, which is the eye of the robot, which is the basis for the overall slam behavior. The sensors are of various types, most commonly lasers, but also ultrasound, depth cameras, etc. The laser is high in data accuracy, and the scanning angle is large, so that the laser becomes a preferred sensor of the 2D-slam.

Laser sensor manufacturers for navigation are known as SICK, north ocean and other manufacturers, the laser sensors are often used in industrial occasions, and consumer products can only be forbidden due to cost reasons. But in recent years low cost lidar has begun to emerge in the market, e.g. Rplidar etc., at prices of the order of thousands of dollars. Although the technical parameter level is also lower, the method is still applicable to occasions with low requirements, and has extremely high cost performance.

The low-cost laser sensor has low performance on laser measurement precision and measurement frequency, and adverse effects can be brought when a map is established. Taking a certain Rplidar as an example, the measurement resolution can reach 1 degree, and the measurement range is 8m. When a grid map with 5cm accuracy is built, as shown in fig. 1, at a maximum distance of 8m, the corresponding angle of the 5cm grid is about 5 × 360/800/3.1415926/2=0.358 °, and the minimum resolution of the laser sensor cannot meet the requirement. As shown in fig. 2, in a typical regular environment, the initial scanning of the laser will result in an unscanned area of 8m, forming a grid of blocks with unknown scatter-like properties. These areas may be swept up after the laser sensor moves along with the robot, and the grids may be updated on the map. However, the robot movement needs to know the displacement, which needs the support of the matching algorithm of the laser data. It is really helpful to the accuracy and completeness of the mapping if the problem can be improved from the laser data level.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a method for acquiring laser data in a controllable periodic sampling mode, wherein adjacent sampling points in each circle are different, and the low-cost laser angular resolution is improved in a phase-changing mode.

The technical scheme adopted by the invention for solving the technical problems is as follows: a low-cost optimization method for laser measurement data combines the acquisition frequency of a laser sensor and the rotating speed of a laser motor to acquire laser data, and comprises the following steps:

selecting sampling interval points to ensure that the sampling interval points cannot be divided by 360 degrees;

and adjusting the rotating speed of the motor, and controlling the output duty ratio of the PWM so that the actual average value of the sampling intervals reaches the value of the selected sampling interval point.

The selecting of the sampling interval point comprises the following steps:

making 360 × H/(sampling point interval × H) not divisible, (sampling point interval × H) as an integer containing a prime number that is not divisible by 360 × H; after n circles of prime number determination, the sampling point returns to the initial point. H represents the multiple of the expansion required to make the sampling interval an integer.

And H is 10.

The sampling points of adjacent circles do not coincide.

When the sampling interval is chosen, the (sampling interval H) contains 7, while other prime numbers that cannot be divided exactly by 360H cannot be included.

The sampling points are spaced 1.4 deg. apart.

The invention has the following beneficial effects and advantages:

the invention provides a method for deliberately selecting sampling intervals on the basis of the existing conditions in consideration of the performance limitations of the existing low-cost laser sensor in various aspects, so that the sampling points of adjacent circles are staggered, and the sampling points return to the initial point after n circles. In this case, the angular resolution is increased by n times, the rotation speed is not reduced much, and the dynamic sensitivity is not affected. In the application of 2D-SLAM mapping, a higher and more accurate environment can be provided without a mobile robot, so that the attributes can be directly updated in the grids within the effective scanning distance range.

Drawings

FIG. 1 is a schematic diagram of the relationship between low cost laser light and 5cm grid angle over a distance of 8 m;

FIG. 2 is a diagram illustrating the problem of the non-renewable grid of the conventional low-cost laser in the effective range;

FIG. 3 is a schematic diagram of a laser sensor triangulation distance measurement principle;

FIG. 4 is a schematic diagram showing an example of a plurality of sampling points staggered by an angle interval of 1.4 degrees;

the system comprises a laser 1, a 25 cm grid, an environment contour 3, a grid area 4 which cannot be updated, a transmitting tube 5, a receiver 6 and a reflecting surface 7 with different distances.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The method mainly uses a method of selecting a proper sampling interval near an expected refresh rate, so that the laser sensor has angle difference at intervals in the process of uniform rotation, and completes the whole cycle within considerable turns and returns to the initial angle, so that points with the same angle or random points cannot be always repeatedly acquired, the angular resolution is improved in a variable mode, and the frequency of repeated sampling of the same points cannot be obviously reduced.

Low cost lasers are typically triangulated, as shown in fig. 3, with a transmitting tube 5 that emits the laser light and reflects it after it encounters an object 7. The distance is different, and the incident point of the laser light reflected on the vision sensor 6 is also different. After simple geometric operation, the distance of the object 7 can be calculated.

Because of the performance limitation of selected devices, the visual sensor of the low-cost laser sensor collects and processes reflected photoelectric data to calculate distance data, and the process can generally reach 2000 to 4000Hz. If the laser rotation period is 10Hz, 200 to 400 samples are taken every 360 °. The rotation speed of the laser is controlled by PWM, and after the laser vision sensor collects and processes the data, the code wheel information of the laser motor at the time is combined together to calculate a laser data point. In general, the laser acquisition frequency and the laser motor rotation speed are independent of each other, the rotation speed of the laser motor is controllable by a user, and if the rotation speed is reduced by half, the acquired data points in each circle are doubled, so that the angular resolution can be increased, and the disadvantage is that the refresh frequency is reduced.

According to the method for acquiring the laser data in the controllable periodic sampling mode by combining the laser acquisition frequency with the rotating speed of the laser motor, the appropriate sampling interval point is selected, so that the sampling interval point cannot be completely divided by 360 degrees, and thus the sampling points of adjacent circles are staggered and return to the initial point after n circles.

The code disc of low-cost laser is also low-cost, and the general precision can only reach 0.1 degree. Then the sampling point spacing can only be chosen to the nearest 0.1. To make the sample interval point not divisible by 360 °, i.e., 3600/(sample interval 10), the integer (sample interval 10) should contain a prime component that is not divisible by 3600. The prime number component determines how many times the sample point returns to the initial point.

The minimum prime number which cannot be divided by 3600 is 7, so when selecting a sampling interval, (sampling point interval 10) contains 7, and cannot contain other prime number components which cannot be divided by 3600, so that the sampling points of adjacent circles are staggered, and after 7 circles (motor revolutions), the sampling points return to the initial points. This is equivalent to an increase of angular resolution by 7 times, while the rotational speed is not reduced by 7 times, and the dynamic sensitivity is not affected.

After selecting the proper sampling interval, the PID mode is used to regulate the motor speed and control the PWM output duty ratio (the PID input is the selected sampling interval, the feedback is the actual sampling interval mean value, the calculated output PWM duty ratio) to make the actual sampling interval mean value reach the selected value.

The particular choice of sampling interval is made as desired. The requirements are from two perspectives: if the demand is determined by the frame refresh frequency (i.e. the rotation speed), we can find a suitable sampling interval in the vicinity of the demanded rotation speed, and the resolution is obviously improved under the condition of small rotation speed change. If the demand is determined by the resolution, the refresh rate of the frame can be obviously improved while the resolution is maintained, and the response to the dynamic barrier change is improved.

Taking a laser with a sampling frequency of 2000Hz as an example, the sampling point interval is selected to be 1.4 °, (1.4 × 10) =14=2 × 7, where 2 can be evenly divided by 3600 and 7 cannot, which conforms to the principle that we select the sampling interval. The motor speed should be 2000 × 1.4/360=7.7778hz at this time. As shown in fig. 4, assuming that the sampling first point angle is 0 °, the angle is 361.2 °, i.e., 1.2 ° at the 259 th sampling point, which is the first point of the 2 nd turn. The first point angle of the 3 rd turn may be pushed 1.0 °, the fourth 0.8 °, the fifth 0.6 °, the sixth 0.4 °, the seventh 0.2 °, and the eighth back to 0 °. Therefore, 7 circles are a whole cycle, on the basis of realizing the effect of 0.2 degrees of angular resolution, compared with the situation that the rotating speed of a motor directly selecting 0.2 degrees as sampling point intervals is only 1.111Hz, the method has a faster refresh rate, and can react faster to the dynamic change of the surrounding environment.

Claims

1. A low-cost optimization method for laser measurement data is characterized in that the acquisition frequency of a laser sensor is combined with the rotating speed of a laser motor to acquire laser data, and the method comprises the following steps:

selecting sampling point intervals to ensure that the sampling point intervals cannot be divided by 360 degrees;

adjusting the rotating speed of the motor, and controlling the output duty ratio of PWM to enable the actual sampling interval mean value to reach the value of the selected sampling point interval;

the rotation speed of the laser is controlled by PWM, and after the laser vision sensor collects and processes the data, the code wheel information of the laser motor at the time is combined together to calculate a laser data point.

2. A method for optimizing low-cost laser measurement data according to claim 1, wherein the selecting the sampling point interval comprises the following steps:

making 360 × H/(sampling point interval × H) not divisible, (sampling point interval × H) as an integer containing a prime number that is not divisible by 360 × H; after the prime number is determined to pass n circles, the sampling point returns to the initial point; h represents the multiple of the expansion required to make the sampling interval an integer.

3. The method of claim 2, wherein the method comprises the following steps: and H is 10.

4. The method of claim 1, wherein the method comprises the following steps: the sampling points of adjacent circles do not coincide.

5. The method of claim 1, wherein the method comprises the following steps: when the sampling interval is chosen, the (sampling interval H) contains 7, while other prime numbers that cannot be divided exactly by 360H cannot be included.

6. A method of optimizing low cost laser survey data as claimed in claim 1 wherein the sample points are spaced 1.4 °.