CN206235453U - The measurement apparatus of the flexible doublejointed mechanical arm vibration based on machine vision - Google Patents

Abstract

The utility model discloses a vibration measuring device of a flexible double-joint mechanical arm based on machine vision. The device includes a double-joint flexible mechanical arm, a CCD camera, a camera fixing device, an absolute encoder, a plurality of LED light-emitting tubes and a PC. The absolute value encoder is installed on the rotating motor, the LED light-emitting tube is placed at the end of the two arms, the CCD camera is placed at the middle joint, and the output ports of the CCD camera and the encoder are connected to the PC. The camera fixing device makes the direction of the camera lens in the direction of the angle bisector of the angle formed by the two arms, and each frame of image detected by the CCD camera and the real-time positioning data of the encoder are sent to the PC; after processing by the PC, the movement position Comparing the position of the spot at rest, the vibration displacement of the light source is obtained, and then the vibration characteristics of the manipulator are analyzed. The utility model can measure the vibration characteristics of the two arms without contacting or changing the vibration characteristics of the measured object, which is convenient for comparison and research and can be widely used.

Description

Measuring device for vibration of flexible double-joint manipulator based on machine vision

Technical field:

The utility model relates to a vibration measuring device of a flexible double-joint mechanical arm, in particular to a measuring device for the vibration of a flexible double-joint mechanical arm based on machine vision.

Background technique:

Multi-joint robotic arms, also known as joint robots, are one of the most common forms of industrial robots in the industrial field today. It is suitable for mechanical automation operations in many industrial fields, such as automatic assembly, painting, handling, welding and other work. The modal damping of this type of flexible structure is small, and once it is subjected to a certain exciting force, its large-amplitude vibration will last for a long time. This will not only affect the work of the structure, but also cause premature fatigue failure of the structure, affect the service life of the structure, or cause damage to the instruments in the structure. There is therefore a need to measure and dampen the vibrations of such flexible structures.

In the prior art, the vibration measurement of the flexible joint manipulator mainly adopts methods such as piezoelectric sheet, accelerometer sensor, angular rate gyroscope sensor, photoelectric position sensor (Position Sensitive Detector) and fiber grating sensor (Fiber Grating Sensor): Signal delay and phase lag will be caused by signal amplification, filtering and other links during electric film measurement, the measurement speed is slow and the range is limited; the accelerometer sensor and angular rate gyroscope sensor are sensitive to noise, and there are problems such as hysteresis and temperature drift that affect them. Accuracy; the measurement range of photoelectric position sensors is small, the structure is complex, the operation is difficult, the calculation process is cumbersome and the cost is expensive; the main problem of fiber grating sensors is the demodulation of sensing signals. It is very easy to damage, so it needs to be packaged before it can be used, and the packaging process and protection measures are complicated.

Invention content:

The purpose of this utility model is to provide a simple structure, stable performance, and convenient measurement device for measuring the vibration of a flexible double-joint manipulator based on machine vision, so as to realize non-contact, real-time and accurate one-time measurement and obtain the vibration characteristics of two manipulators at the same time .

The technical solution to realize the purpose of this utility model is a measuring device for the vibration of a flexible double-joint manipulator based on machine vision, which includes a double-joint flexible manipulator, a CCD camera, a camera fixing device, an absolute encoder, a plurality of LED light-emitting tubes and PCs, absolute encoders are installed on the rotating motors of the arm levers of the two joints, and the output ends of the encoders are connected to the PCs, the LED light-emitting tubes are placed at the ends of the two arm levers, and the CCD cameras are placed on the two mechanical arms On the joint between the arms, and the CCD camera is equipped with a lens, and the output port of the CCD camera is connected with the PC. The camera fixing device ensures that the direction of the camera lens is always at the angle bisector of the angle formed by the two arms, and the CCD camera can simultaneously measure each frame of the vibration of the LED light-emitting tube at the end of the two arms, and transmit it to the PC; The real-time data of the encoder is transmitted to the PC for calculation and positioning of the moving position of the manipulator; the PC processes the image and compares it with the position of the spot when the moving position is still to obtain the vibration displacement at the LED light-emitting tube and reflect the low-frequency vibration of the flexible double-joint manipulator structure parameters.

Compared with the prior art, the utility model has the following significant advantages: (1) The detection method based on machine vision is not only more intuitive and easier to obtain the low-frequency vibration information of the flexible mechanical arm, but also the whole device can be operated through the detection of the LED light-emitting tube. It is simple, convenient to implement, and has low measurement noise. (2) The absolute value encoder is used to locate the position of the mechanical arm, which has strong anti-interference characteristics and high data reliability. (3) For the special structure of the robotic arm, a CCD camera that can change direction with the movement is placed at the joint, which can simultaneously detect the two LED light-emitting tube light sources at the ends of the arms of the two robotic arms, which greatly simplifies the device structure and saves costs. (4) Without changing the vibration characteristics of the measured object, the machine vision is used to track the light source and detect the dynamic displacement of the flexible structure, which has the advantages of non-contact, wide measurement range, and no change of the measured object’s vibration characteristics.

Description of drawings:

Fig. 1 is the structural representation of the measuring device of the vibration of the flexible double-joint manipulator based on machine vision of the utility model;

Fig. 2 is a schematic diagram of a camera fixing device;

Fig. 3 is a schematic diagram of image analysis;

detailed description:

The utility model will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The utility model adopts the method of machine vision to realize the low-frequency mode analysis device by collecting the vibration displacement of the light source at the tail end of the mechanical arm at different moving positions.

As shown in Figure 1, the vibration measurement device of a flexible double-joint manipulator based on machine vision includes a double-joint flexible manipulator 1, a CCD camera 2, a camera fixing device 3, an absolute encoder 4, multiple LED light-emitting tubes 5 and a PC machine 6; the flexible double-joint mechanical arm 1, an absolute value encoder 4 is installed on the arm lever rotation motor of the two joints, and the output end of the encoder is connected to the PC machine 6, and the LED light-emitting tube 5 is placed on the double-joint flexible mechanical arm At the tail ends of the two arms of the arm 1, the CCD camera 2 is arranged on the joint between the arms of the two mechanical arms, and the CCD camera is equipped with a lens, and the output port of the CCD camera 2 is connected with the PC 6 . As shown in Figure 2, the camera fixing device forms a diamond-shaped structure with the two arms of the double-joint flexible mechanical arm, and the diagonal line adopts a stretchable material as a CCD camera bracket, and the bracket can change direction according to the movement position of the mechanical arm. On the diagonal bracket of the rhombus structure, it is ensured that the direction of the CCD camera lens is always in the direction of the angle bisector of the angle formed by the two arms.

The measurement method of the vibration of the flexible double-joint manipulator based on machine vision, the steps are as follows:

Step 1: According to the position of the LED luminous tube 5 in the image of each frame collected by the CCD camera 2, the whole image is divided into sub-regions corresponding to the LED luminous tube 5 at the tail end of the two arms, and the upper correspondence of each region is determined The light source collection position;

Step 2: Determine the centroid position of each light source spot in the image coordinate system according to the camera image data imported into the PC 6;

Step 3: collect data according to the absolute encoder 4, locate the motion angle of the mechanical arm, and record the motion angle data corresponding to the position of the center of mass collected in the second step in the PC 6;

As shown in Figure 3, when the motor rotates to drive the mechanical arm to work, the absolute encoder 4 in the motor records the rotation angle, and the rotation angle of the arm 1 is obtained as α, and the rotation angle of the arm 2 is 180°-β (the directions are both initial horizontal direction and counterclockwise rotation), the rotation range of α and β is 0°<α>90°, 0°<β>90°, for the projection of the two-armed pole in the image coordinate system at (α, β) The location is:

In the formula, Y _{1(α, β)} and Y _{2(α, β)} are respectively the y-axis coordinate positions of arm 1 and arm 2 in the (α, β) position image coordinate system, and l ₁ , l ₂ are The distance from the LED light-emitting tube 5 to the lens of the CCD camera 2 is set at the tail end of the two arms of the double-joint flexible mechanical arm 1 .

There is no displacement in the x-axis direction at rest, so when there is no vibration at rest and the manipulator is in the (α, β) position, the coordinates of the light source on the arm 1 and arm 2 in the image coordinate system of the CCD camera 2 are:

Step 4: According to the centroid position of the light spot collected under different vibration measurement conditions, process with the centroid position of the static light spot under the moving position of the double-joint flexible robotic arm 1 at this time, and obtain the horizontal displacement Δx of two corresponding LED light-emitting tubes 5 and vertical displacement Δy, the specific steps are as follows:

According to the detection steps in the first and second steps and shown in Figure 3, at the position (α, β), the frame of image recorded by the CCD camera is calculated to obtain the position of the center of mass of the light source on the arm 1 and arm 2 in the image coordinate system :

(X ₁ ,Y ₁ )′ _(α,β) = (x ₁ ,y ₁ ), (X ₂ ,Y ₂ )′ _(α,β) =(x ₂ ,y ₂ ) (3)

Then the displacement of the light source on the two arms in the image coordinate system is obtained:

In the formula, Δx ₁ , Δy ₁ , Δx ₂ , Δy ₂ are the horizontal displacement and vertical displacement in the image coordinate system of the two arms, respectively.

Step 5: According to the parameters of the CCD camera 2, the vertical displacement conversion factor K _x and the horizontal conversion factor K _y of the two LED light-emitting tubes 5 from the image coordinate system to the world coordinate system are calibrated, and the specific steps are as follows:

Establish a coordinate system: take the upper arm of the flexible double-joint manipulator 1 as an example, take the placement position O _W of the LED light-emitting tube 5 at the end of the arm as the origin, and the direction of the arm pointing to the camera 2 when it is stationary is the Z axis, and establish World coordinate system O _W -W _W X _W Y _W Z _W ; take the optical center O _C of the CCD camera 2 as the origin. The direction of the camera lens, that is, the direction of the angle bisector of the angle formed by the two arms of the double-joint flexible robotic arm 1 is the Z-axis to establish an image coordinate system O _C -W _C X _C Y _C Z _C ;

The transformation relationship between the horizontal displacement and vertical displacement in the image coordinate system O _C -W _C X _C Y _C Z _C to the world coordinate system O _W -W _W X _W Y _W Z _W is:

x=K _x Δx,y=K _y Δy (6)

Among them, Δx, Δy are the horizontal displacement and vertical displacement in the image coordinate system, x, y are the actual horizontal displacement and vertical displacement in the world coordinate system, K _x K _y is the horizontal displacement conversion factor from the image coordinate system to the world coordinate system and Vertical displacement transformation factor.

Step 6: According to the horizontal displacement Δx, vertical displacement Δy of each LED light-emitting tube 5 in the image and the horizontal conversion factor K _x and vertical conversion factor K _y calibrated in step 5, the actual horizontal displacement x of each LED light-emitting tube is obtained , the actual vertical displacement y, the specific steps are as follows:

Combining formula (4), formula (5) and formula (7) to get:

The actual horizontal displacement and actual vertical displacement of the light source on the boom 1 are:

x ₁ =K _x Δx ₁ =x ₁ (8)

The actual horizontal displacement and actual vertical displacement of the light source on the boom 2 are:

x ₂ =K _x Δx ₂ =x ₂ (10)

Step 7: Draw the position curve of each LED luminous tube 5 according to the actual displacement obtained in the 6th step, perform fast Fourier transform on the displacement of each LED luminous tube 5, and obtain the vibration value of the flexible double-joint manipulator 1 First-order modal frequency and second-order modal frequency. Specific steps are as follows:

Measure the displacement of the light source at the tail end of the arm at different positions (α ₁ , β ₁ ), (α ₂ , β ₂ )... and other positions multiple times, and perform fast Fourier transform on it to obtain a flexible double-joint manipulator 1 The first-order modal frequency and second-order modal frequency of the two arms.

To sum up, the machine vision vibration measurement device constructed by the method proposed in the utility model can be used for the special structure of the double-joint manipulator, and the absolute value encoder is used for positioning, and one CCD camera can measure two vibrations. This method has many advantages such as non-contact, no change of the vibration characteristics of the measured object, simple device and high accuracy.

Claims (2)

1. A measuring device for the vibration of a flexible double-joint mechanical arm based on machine vision, comprising a double-joint flexible mechanical arm (1), characterized in that: the device also includes a CCD camera (2), a camera fixture (3), an absolute A value encoder (4), a plurality of LED light-emitting tubes (5) and a PC (6), the flexible double-joint mechanical arm (1), LED light-emitting tubes (5) are arranged at the tail ends of the two arms, and cameras are placed at the joints The fixing device (3), the CCD camera (2) is fixed on the device and equipped with a lens, the two joints are provided with an absolute encoder (4), the output ports of the CCD camera (2) and the absolute encoder (4) are connected to the PC (6) Connection. 2. The measuring device of the vibration of the flexible double-joint manipulator based on machine vision according to claim 1, characterized in that: the camera fixing device (3) forms a joint with the two arms of the double-joint flexible manipulator (1). The rhombus structure, the diagonal adopts stretchable materials as the bracket of the CCD camera (2), the bracket can change the direction according to the movement position of the mechanical arm, the CCD camera (2) is on the bracket of the diagonal of the rhombus structure, ensuring that the CCD camera (2) The direction of the lens is always in the direction of the angle bisector of the angle formed by the two arms.