Parallel platform tracking control apparatus using visual device as sensor and control method thereof

Patent metadata

Field	Value
Publication number	US-9971357-B2
Application number	US-201515562898-A
Country	US
Kind code	B2
Filing date	Dec 23, 2015
Priority date	Apr 16, 2015
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

A parallel platform tracking control apparatus and method using a visual device as a sensor are disclosed. The apparatus comprises a parallel platform body, a CCD camera ( 11 ), a lens ( 6 ), a camera light source ( 9 ), a computer ( 11 ), a Dspace semi-physical simulation controller, an ultrasonic motor driver and the like. The parallel platform comprises an ultrasonic linear motor ( 1 ), a linear grating encoder ( 5 ), a driven rod ( 2 ), a moving platform ( 3 ), a stationary platform ( 4 ) and the like. The CCD camera photographs the moving platform in a perpendicular and opposite manner, and the photographed images are subjected to an image processing algorithm to measure the position of the corresponding marker on the moving platform, which is not only applicable to measurement, but also implements real-time feedback of the termination position of the moving platform, such that a full closed-loop system is constituted. In this way, the parallel platform is precisely positioned.

First claim

What is claimed:

1. A parallel platform tracking control apparatus using a visual device as a sensor, comprising a parallel platform mechanism, a CCD camera-based visual measurement system, and a position tracking feedback control apparatus;
wherein the parallel platform mechanism comprises: a stationary platform, a moving platform arranged above the stationary platform, three ultrasonic linear motors, an ultrasonic linear motor driver; the moving platform has three rotary shafts distributed uniformly in equilateral triangle at an outer edge of the moving platform; the three ultrasonic linear motors are distributed and mounted in equilateral triangle at an edge of the stationary platform; shaft ends of rotation shafts installed on the ultrasonic linear motors are connected to one of the rotary shafts of the moving platform via a driven rod; and the ultrasonic linear motors are each provided with a linear grating encoder;
one ultrasonic linear motor, one driven rod and one rotary shaft of the moving platform constitute a parallel branch;
the three ultrasonic linear motors collaboratively drive the driven rods, such that the moving platform moves to a target position;
the ultrasonic linear motors, during movement, drives the linear grating encoder to move, to detect actual positions of the ultrasonic linear motors;
a first point light source marker and a second point light source marker that are linearly distributed and configured to focus blue laser are mounted on the moving platform as visual detection features;
the CCD camera-based visual measurement system comprises: a CCD camera arranged above the moving platform, a lens mounted on an end portion of the CCD camera, a camera light source arranged on a side of the lens, a USB interface and a computer; wherein the CCD camera is connected to the computer via the USB interface;
the lens is perpendicular and opposite to the moving platform, such that a central point of the lens coincides with an origin point of the moving platform;
the position tacking feedback control apparatus comprises a Dspace semi-physical simulation controller having an incremental encoder interface module and a D/AC interface; the D/AC interface is connected to the ultrasonic linear motor driver, each of the linear grating encoders is connected to the incremental encoder interface module, the incremental encoder interface module is connected to the computer, and the computer is connected to the D/AC interface.

2. The parallel platform tracking control apparatus using a visual device as a sensor according to claim 1 , wherein the CCD camera further comprises a support mechanism, wherein the support mechanism comprises a bracket having a movable joint and a magnetic base configured to fix the bracket, and the CCD camera is fixed to an end portion of the bracket.

3. A control method of a parallel platform tracking control apparatus using a visual device as a sensor as defined in claim 2 , comprising the following steps:
(I) a CCD camera-based visual measurement step, comprising:
acquiring an image signal of a moving platform via photographing by the CCD camera, and transmitting the image signal to the computer via the USB interface;
upon acquiring the image signal, performing image processing by the computer, extracting features of the first point light source marker and the second point light source marker on the moving platform, and obtaining coordinates via calculation;
calculating parallel displacements Δx and Δy and a rotation angle Δθ of the moving platform according to the coordinates of the first point light source marker and the second point light source marker;
wherein the two parallel displacements Δx and Δy and the rotation angle Δθ of the moving platform are calculated using the following formulae:
assuming that a coordinate of the first point light source marker before movement is (x 1 ,y 1 ) and a coordinate of the first point light source marker after movement is (x 1 ′,y 1 ′), and a coordinate of the second point light source marker before movement is (x 2 ,y 2 ) and a coordinate of the second point light source marker after movement is (x 2 ′,y 2 ′), and assuming that the first point light source marker and the second point light source marker before movement constitute a vector S=((x 2 −x 1 ),(y 2 −y 1 )), and the vector changes to S′=((x 2 ′−x 1 ′),(y 2 ′−y 1 ′) after movement;
the displacements of the moving platform are

Δ
⁢

⁢
x

=

(

x
2

-

x
1

)

-

(

x
2
′

-

x
1
′

)

2

,

⁢

Δ
⁢

⁢
y

=

(

y
2

-

y
1

)

-

(

y
2
′

-

y
1
′

)

2

;

wherein if Δx is greater than 0, the moving platform moves towards a positive direction of x-axis, and if Δx is less than 0, the moving platform moves towards a negative direction of x-axis; and if Δy is greater than 0, the moving platform moves towards a positive direction of y-axis, and if Δy is less than 0, the moving platform moves towards a negative direction of y-axis;
the rotation angle of the moving platform is

Δ
⁢

⁢
θ

=

Assignees

• Univ South China Tech

Inventors

• Zhang Xianmin
• Mo Jiasi
• Qiu Zhicheng
• Wei Junyang
• Li Hai

Classifications

• G05D3/12 Primary

  using feedback · CPC title

• G05B19/404

  characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia (G05B19/19, G05B19/41 take precedence) · CPC title

• G05B2219/50162

  Stewart platform, hexapod construction · CPC title

• H02K41/02

  Linear motors; Sectional motors · CPC title

• G06T2207/30204

  Marker · CPC title