CN102768006B - Method for automatically measuring and adjusting large-curvature curve part in normal direction - Google Patents

Abstract

The invention discloses a method for automatic measurement and adjustment of the normal direction of large curvature curved surface parts, which establishes the coordinate system of the tooling where the large curvature curved surface parts are located and the measurement coordinate system of the industrial robot; measures the displacement value between the industrial robot and the large curved surface parts , calculate the angle between the plane γ formed by the measurement points and the robot measurement coordinate system; adjust the posture of the robot so that the OXY plane of the measurement coordinate system is parallel to the plane γ, until the accuracy meets the requirements. The invention can improve the quality and efficiency of automatic processing and assembly of large curvature curved surface parts.

Description

A method for automatic measurement and adjustment of the normal direction of large curvature surface parts

technical field

The invention belongs to the field of automatic manufacturing, and relates to a method for normal measurement and automatic adjustment of large-curvature surface parts.

Background technique

During the automatic processing and assembly of curved surface parts, the processing head needs to perform operations such as drilling or riveting in the normal direction of the curved surface. Therefore, the normal direction of the curved surface needs to be adjusted before the automatic processing of the curved surface parts, so that the processing feed direction coincides with the normal direction of the processing point. The accuracy of the normal adjustment has a great influence on the processing quality and the service life of the product. Therefore, the efficient and stable normal measurement adjustment method and equipment can improve the quality and efficiency of automatic processing of curved surface parts.

At present, the measurement and adjustment of the normal direction of curved surface parts mainly use artificial vision method and tooling adjustment method. Artificial visual monitoring and manual adjustment method, the adjustment efficiency of this method is not high, and the adjustment quality is not stable enough; in the tooling adjustment method, the large weight and volume of the tooling make the adjustment not flexible enough, and have a certain impact on the accuracy and efficiency of the normal adjustment . For example, patent CN101957175A discloses a method based on three-point microplane normal direction detection, and applies laser displacement sensor technology and data acquisition technology, and can measure the normal vector of the point to be measured on the curved surface through a certain algorithm. The detection method in this patent has high calculation accuracy, but does not involve the method and equipment for normal direction adjustment, which has certain limitations in industrial application. The literature "Research on Vector Measurement Method for Automatic Drilling and Riveting of Aircraft Panels" proposes a method for real-time measurement of the normal vector at the drilling and riveting point during the automatic drilling and riveting process of aircraft paneling: using a laser ranging sensor to obtain feature points around the drilling and riveting point coordinates, and calculate the normal vector at the drilling riveting point through the quadratic surface fitting algorithm. Patent CN100485560C relates to a control method for normal riveted curved parts, using a three-point suspension part bracket to replace the artificial visual normal control. The above-mentioned method of normal direction measurement and adjustment for automatic drilling and riveting of wall panels realizes normal adjustment by changing the attitude of placing the bracket of the wall panel. The openness of this kind of method is not good enough during processing, and the quality and weight of the bracket are relatively heavy. Larger volumes adversely affect the accuracy and flexibility of adjustment.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a method of using a six-degree-of-freedom industrial robot to realize the normal measurement and automatic adjustment of the points to be processed before automatic processing or assembly of large curvature curved surface parts. An eddy current displacement sensor is used to measure the displacement values of four points on the surface of a large curvature surface part (such as an aircraft wall panel) and the sensor, and the adjustment parameters of the industrial robot are generated through calculation. The control system changes the posture of the industrial robot according to the adjustment parameters, and realizes the automatic adjustment of the normal direction of the curved surface. The method can improve the quality and efficiency of automatic processing and assembly of parts with large curvature surfaces.

The flow chart of the technical solution adopted by the present invention to solve its technical problems is as shown in Figure 1, and comprises the following steps:

1) Establish a coordinate system: define the coordinate system of the tooling where the large curvature surface part is located as the world coordinate system, and use the positioning blocks on the tooling to establish the workpiece coordinate system of the six-degree-of-freedom industrial robot. The measuring device is installed at the end of the industrial robot, and the positional relationship with the industrial robot has been calibrated. The measuring device is composed of four eddy current displacement sensors, and the displacement sensors are distributed in a rectangular shape. Taking the rectangular symmetry center as the origin, the length direction as the X-axis direction, the width direction as the Y-axis direction, and the displacement sensor measuring head direction as the Z-axis direction, establish a right-handed Cartesian coordinate system, which is the measurement coordinate system of the industrial robot.

2) Collect data: move the industrial robot until the Z-axis of the measurement coordinate system points to the measurement point. Turn on the displacement sensors, measure the displacement value between them and the large curved surface parts, and transmit the voltage signal collected by the displacement sensors to the control system through the PLC. The control system converts the voltage value into a displacement value.

3) Calculate the normal deviation: the surface to be measured is generally a large curvature surface, that is, the width of the measurement range and the radius of curvature at the point to be measured differ by more than one order of magnitude. At this time, the normal direction of the plane γ formed by the measurement points of the displacement sensor can be regarded as the normal direction of the measurement points on the curved surface. Use the measured displacement values to calculate the angles α and β between the X and Y axes of the robot’s measurement coordinate system and the plane γ.

4) Adjusting the normal direction: the control system calls the algorithm of the robot control system to calculate the adjustment parameters of the robot based on the normal deviation α, β, and the conversion relationship between the established coordinate systems, and adjusts the posture of the robot so that the OXY plane of the measurement coordinate system is parallel in the plane γ. At this time, the negative direction of the Z axis of the measurement coordinate system is the normal direction of the surface measurement point.

5) Detection error: the control system collects the voltage value of the displacement sensor, and calculates again the error between the normal direction of the measurement point and the normal direction of the OXY plane of the measurement coordinate system. If the error is within the limited range, the control system sends a normal adjustment completion signal; otherwise, go to step 3).

The beneficial effect of this method is:

1) The use of industrial robots as the motion mechanism for normal adjustment increases the openness of the operating space and improves the flexibility of normal adjustment.

2) Using an eddy current displacement sensor to measure the displacement between a large curvature surface part (such as an aircraft wall panel) and the sensor can eliminate the influence of non-metallic obstacles on the measured surface.

3) The displacement sensor is integrated with the industrial robot control system through PLC, which makes the method have good software and hardware scalability. Adding equipment to the measuring device at the end of the industrial robot and connecting it to the PLC can easily expand the functionality of the equipment.

Description of drawings

Fig. 1 Flow chart of automatic measurement and adjustment of the normal direction of parts with large curvature surfaces;

Figure 2 Schematic diagram of the distribution of displacement sensors on the measuring head and the definition of the coordinate system;

Figure 3 is an explanatory diagram of the measurement and adjustment principle of the normal direction of a large curvature surface (three-dimensional diagram);

Fig. 4 Explanatory diagram of the principle of measurement and adjustment of the normal direction of a large curvature surface (side view);

Fig. 5 Explanatory diagram (top view) of the principle of measurement and adjustment of the normal direction of a large curvature surface.

Detailed ways

The invention is used in the automatic processing or assembly process of parts with large curvature surfaces, and realizes the measurement and automatic adjustment of the normal direction of large curvature surface parts through the cooperation of eddy current displacement sensors, six-degree-of-freedom industrial robots and control systems.

The present invention will be further described in detail below in conjunction with the accompanying drawings, implementation methods, and implementation examples.

For example: this method is used for the automatic measurement and adjustment of the normal direction of the panel before the automatic drilling and riveting of the aircraft panel assembly process. The displacement sensors on the measuring device are distributed in a rectangular shape, with a length of a = 160mm and a width of b = 110mm; the robot's measurement coordinate system is OXYZ, as shown in Figure 2.

The specific implementation steps are as follows:

1) Establish a coordinate system: define the coordinate system of the aircraft panel tooling as the world coordinate system. The position of the positioning block in the world coordinate system is known, and the position relationship between the robot workpiece coordinate system and the world coordinate system is determined according to its value, so as to establish the robot workpiece coordinate system. The measurement coordinate system OXYZ of the robot is defined on the measurement device, and the positional relationship between the measurement coordinate system and the displacement sensor is shown in Figure 2. The relationship between the above coordinate systems is determined and can be converted to each other.

2) Collecting data: the control system drives the industrial robot to drive the measuring device to move until the Z-axis of the measuring coordinate system points to the measuring point O ₁ , as shown in FIG. 3 . Start displacement sensors A, B, C, and D to obtain four voltage values U _A , _UB , _UC , and _UD . The voltage signal collected by the displacement sensor is transmitted to the control system through the PLC in the control cabinet. The control system multiplies the voltage value by the coefficient to obtain the displacement values AA ₁ , BB ₁ , CC ₁ , and DD ₁ .

3) Calculate the normal deviation: the surface of the aircraft panel is generally a quadric surface with a large curvature radius. The projection A ₁ B ₁ C ₁ D ₁ of the rectangle ABCD composed of four sensors on the aircraft wall is very small relative to the wall, as shown in Figure 3. Therefore, the normal direction of the plane A ₁ B ₁ C ₁ D ₁ can be as the normal to the measurement point _O1 on the wall. Use the displacement values AA ₁ , BB ₁ , CC ₁ , DD ₁ and the dimensions of the rectangle ABCD to calculate the angle α between the X axis of the tool coordinate system and the plane γ, and the angle β between the Y axis of the tool coordinate system and the plane γ, as shown in the figure 4. As shown in Figure 5. The formula for calculating the included angle α and β is as follows:

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; DD</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; BB</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; CC</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}$

$\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; CC</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; DD</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; BB</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; b</span>}}$

4) Adjust the normal direction: the control system establishes the conversion relationship between the coordinate systems according to the normal deviation α and β, and calls the algorithm of the robot control system to calculate the adjustment parameters of the robot, adjust the posture of the industrial robot, and make the OXY of the measurement coordinate system The plane is parallel to the plane γ. At this time, the negative direction of the Z axis of the measurement coordinate system is the normal direction of the measurement point of the surface

5) Detection error: After the attitude adjustment of the industrial robot is completed, the control system collects the voltage value of the displacement sensor again, and calculates the error between the normal direction of the measurement point _O1 and the normal direction of the measurement coordinate system OXY plane. If the error is within the limit range, then send a normal direction adjustment completion signal; otherwise, go to step 3).

Claims (1)

1., for the method that curved surface of high curvature part normal direction is automatically measured and adjusted, it is characterized in that comprising the steps:

1) coordinate system of curved surface of high curvature part place frock is defined as world coordinate system, utilizes the locating piece in frock to set up the workpiece coordinate system of Six-DOF industrial robot; Measurement mechanism is arranged on industrial machine robot end, demarcates with the position relationship in the industrial machine human world; Measurement mechanism is made up of four eddy current displacement sensors, the rectangular distribution of eddy current displacement sensor; Using rectangular symmetrical center as initial point, length direction is X-direction, and Width is Y direction, and eddy current displacement sensor measuring head direction is Z-direction, sets up right-handed Cartesian coordinate system, i.e. the surving coordinate system of industrial robot;

2) mobile industrial robot, until the Z axis of surving coordinate system points to measurement point; Open eddy current displacement sensor, measure the shift value between they and large curved surface part, by PLC, the voltage signal of eddy current displacement sensor collection is transferred to control system; Magnitude of voltage is converted to shift value by control system;

3) using eddy current displacement sensor measurement point form the normal direction of normal direction as measurement point on curved surface of plane γ; Utilize angle α, β of shift value calculating robot surving coordinate system X, Y-axis and the plane γ recorded;

4) control system is according to the transformational relation between angle α, β and the coordinate system set up, and adjustment robot pose, makes the OXY plane of surving coordinate system be parallel to plane γ; Now, the Z axis negative direction of surving coordinate system is the normal direction of measurement of curved surface point;

5) control system gathers the magnitude of voltage of eddy current displacement sensor, again computation and measurement point normal direction and surving coordinate system OXY planar process to error; If error is in limited range, control system sends normal direction adjustment settling signal; Otherwise forward step 3 to).