CN107962480B - A processing force control method for blade robot abrasive belt grinding - Google Patents

Abstract

The invention discloses a blade robot abrasive belt grinding force control method, comprising the following steps: voltage signal modulation and processing; converted force compensation; force control strategy. Among them, the modulation and processing of the voltage signal includes: obtaining the voltage signal of six channels of the sensor; performing software filtering on the obtained voltage signal; converting the filtered voltage signal into a force signal. Compensating the converted force includes: zero drift compensation of the sensor itself and gravity compensation of the end load of the robot. Force control strategies include: force-position hybrid control and PI/PD control. The abrasive belt grinding force control method of the blade robot of the present invention can not only improve the efficiency of the grinding process, overcome the poor consistency of the manual grinding process, but also realize the constant force grinding process, so that the surface material removal amount is relatively low. Uniform and consistent, while improving the processing precision and surface quality, it also improves the surface consistency of the blade.

Description

A processing force control method for blade robot abrasive belt grinding

technical field

The invention relates to the application field of industrial robots, in particular to a method for controlling the processing force of blade robot abrasive belt grinding.

Background technique

At present, grinding processing mainly has great advantages in the field of simple geometric parts, such as cylindrical grinding, internal grinding and surface grinding of parts. However, for the grinding and finishing of complex curved surfaces, traditional grinding equipment and processes lack flexibility and poor adaptability, and the modification of the process takes a long time and is expensive. More importantly, most of them are currently manual grinding, such as , Aviation blades, steam turbine blades and other grinding industries. This leads to low grinding efficiency and poor product consistency, which seriously hinders the development of productivity; moreover, the on-site grinding environment is poor, which poses a greater potential threat to the health of personnel.

Patent document CN103507070 discloses a robot control device using a three-axis force sensor for force control, and performs force control by estimating forces and moments that cannot be detected by the three-axis force sensor. The device completes the force control by setting the force estimation point, then performing force estimation on the estimation point, and then correcting the force estimation point. And this device is a robot holding tool to process the workpiece.

However, the robot control device disclosed in patent document CN103507070 using a three-axis force sensor for force control has the following problems:

(1) In the above-mentioned patent documents, the robot holds the tool and works on the workpiece, so the proposed force estimation point control and correction are all based on the robot holding the tool.

(2) The force control method of the above-mentioned patent is to perform force control by estimating the force and moment that cannot be detected by the triaxial force sensor, that is, to perform force estimation on the set estimation point, so as to correct the force estimation point.

(3) The force control method of the above-mentioned patent is an estimated force control, so the force control accuracy is not high, and it cannot be applied to the processing of complex curved surface parts.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a method for controlling the processing force of blade robot abrasive belt grinding. different. Through the control of the grinding force during the processing, the grinding process can be controlled more accurately, which can not only improve the efficiency of grinding, overcome the poor consistency of manual grinding, but also achieve constant force grinding Machining makes the surface material removal amount more uniform, while improving the machining accuracy and surface quality, it also improves the surface consistency of the blade.

In order to achieve the above object, the present invention provides a method for controlling the processing force of blade robot abrasive belt grinding, comprising the following steps:

S101: Convert the voltage signal acquired by the sensor into a force signal, and process it to correspond to the force of the grinding process, and monitor the change of force in real time;

S102: Control and process the monitored force to make the grinding force constant and meet the requirements of constant force grinding;

S103: Acquire voltage signals of six channels of the sensor;

S104: Modulate the acquired voltage signal;

S105: converting the processed voltage signal into a force signal, thereby indirectly sensing force changes;

S106: Perform zero drift compensation to reduce the error introduced by the sensor itself;

S107: Gravity compensation is performed on the end load of the sensor;

S108: Transform the compensated force into the base coordinate system, and then into the tool coordinate system, so as to directly correspond to the process force during processing;

S109: Force/position hybrid control defines two complementary and mutually orthogonal spaces to realize simultaneous control of force and position;

S110: PI/PD control, eliminates large force deviation, obtains faster system response, thus obtains more ideal output force, and realizes force control of blade robot abrasive belt grinding.

As a further preference of the present invention, the control of force during the grinding process in step S102 includes the following steps:

S201: Judging the size of the actual grinding force and the theoretical reference force, if the actual force>reference force, then go to step S202;

S202: The robot feeds along the negative direction of its Z axis;

S203: If the actual force<=reference force, then go to step S204;

S204: The robot feeds and moves along the positive direction of its Z axis;

S205: Calculate the corresponding theoretical robot position information according to the actual force;

S206: Convert the rigidity of the robot grinding coefficient into the position information that the robot can recognize, and complete the corresponding position movement;

S207: Through adjustment, the constant force grinding force control is completed.

As a further preference of the present invention, the calculation method of the robot grinding coefficient stiffness is:

where F _Z is the actual force, K, B, M are the method stiffness, damping and inertia of the robot's grinding method, and ΔZ is the offset of the robot in the Z direction.

As a further preference of the present invention, if the actual force is not close to the theoretical force, the corresponding offset distance is calculated by the robot grinding coefficient stiffness calculation method, so as to be further converted into position point information that can be recognized by the robot, and then After it is transmitted to the robot control cabinet, the robot will perform feed motion along the Z positive or negative direction until the actual grinding force is equal to or close to the theoretical grinding force.

As a further preference of the present invention, when the force/position hybrid control and PI/PD control are applied in the Cartesian space coordinate system, the control model is:

Among them, F _D is the input force, X _D is the expected displacement in Cartesian space, X _f is the output displacement after force control, X _p is the output displacement after position control, F _e is the output force, X _e is the comprehensive displacement, s is the correlation coefficient, k _pp and k _pd are the correlation coefficients of PD position control, and k _fp and k _fi are the correlation coefficients of PI force control.

As a further preference of the present invention, the voltage signals of the six channels in step S103 are acquired by an ATI six-dimensional force sensor.

As a further preference of the present invention, the six-dimensional force sensor senses voltage changes through three strain gauges arranged in a "Y" shape, and the gauges are spaced apart by 120°.

As a further preference of the present invention, step S104 includes software filtering and a stable voltage interval.

As a further preference of the present invention, the two complementary and mutually orthogonal spatial force spaces and position spaces mentioned in step S109.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

(1) The control method of blade robotic abrasive belt grinding processing of the present invention has different specific parameter settings and different processing process parameters according to different processing objects. Through the control of the grinding force during the processing, the grinding process can be controlled more accurately, which can not only improve the efficiency of grinding, overcome the poor consistency of manual grinding, but also achieve constant force grinding Machining makes the surface material removal amount more uniform, while improving the machining accuracy and surface quality, it also improves the surface consistency of the blade.

(2) In the control method of blade robot abrasive belt grinding processing of the present invention, the blade is held by the robot for grinding processing, wherein the contact wheel of the grinding and polishing machine is an elastic contact wheel, and there is a certain concession during the processing process, which can realize grinding Belt flexible grinding.

(3) In the blade robot abrasive belt grinding processing control method of the present invention, the grinding force (mainly referring to F _Z ) is determined according to the specific processing object, processing environment and corresponding process parameters in the processing process; The size of the grinding force is different in different parts.

(4) The control method of blade robot abrasive belt grinding processing of the present invention, the acquisition and processing of voltage signals, remove noise points through signal conditioning methods such as filtering and stable voltage intervals, can ensure the stability of voltage signals, and will not be affected by external interference. A mutation occurs.

(5) The control method of the blade robot abrasive belt grinding process of the present invention, the subsequent zero-point drift compensation and gravity compensation of the force can further reduce the influence of the external environment on the sensor itself, so that the compensated force is close to the real force.

(6) In the method for controlling blade robot abrasive belt grinding of the present invention, after compensation, during grinding, the displayed force is the grinding force, and the effect of grinding is indirectly represented by controlling this force. Under the condition that the grinding force is set reasonably, when the constant force grinding is used, the surface processing consistency of the blade is better, and the surface roughness is within 0.4 μm, which can meet the surface quality requirements.

Description of drawings

Fig. 1 is a schematic diagram of a blade robot abrasive belt grinding force control in an embodiment of the present invention;

Fig. 2 is a schematic diagram of force control in the process of blade robot abrasive belt constant force grinding according to an embodiment of the present invention;

Fig. 3 is a diagram of the corresponding robot movement process after the application of the abrasive belt grinding force control strategy of the blade robot according to the embodiment of the present invention;

Fig. 4 is a schematic diagram of a blade robot abrasive belt grinding process according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Fig. 1 is a schematic diagram of a blade robot abrasive belt grinding process force control principle according to an embodiment of the present invention. As shown in Figure 1, a blade robot abrasive belt grinding force control method in this embodiment specifically includes:

S101. The acquisition and monitoring of grinding force is used to convert the voltage signal acquired by the sensor into a force signal, and process it to correspond to the force in the grinding process, and monitor the change of force in real time;

S102. The control strategy of grinding force is used in the process of robot abrasive belt grinding to control and process the monitored force so that the grinding force is constant and meets the requirements of constant force grinding;

S103. Obtain voltage signals of six channels through the ATI six-dimensional force sensor;

S104. Process the obtained voltage signal, including: software filtering and stabilizing the voltage interval, etc.;

S105, converting the conditioned voltage signal into a force signal through a certain formula, so as to indirectly perceive the change of force;

S106. The six-dimensional sensor senses the change of voltage through three strain gauges arranged in the word "Y". When the terminal is unloaded, it needs to be compensated for zero drift to reduce the introduction of errors;

S107. The gravity of the clamps and blades installed at the end of the sensor cannot be ignored. Therefore, in order to more directly reflect the process force of the grinding process, gravity compensation is required for the load at the end of the sensor;

S108. The force after compensation is in the sensor coordinate system, but the grinding force needs to be in the tool coordinate system, so it is necessary to transform the compensated force into the base coordinate system, and then into the tool coordinate system;

S109. Force/position hybrid control defines two complementary and mutually orthogonal spaces: force space and position space, realizing simultaneous control of force and position;

S110, PI control has the following advantages: simple form, easy to realize discretization, no steady-state error, can eliminate large force deviation, and obtain a more ideal output force; PD control can obtain faster system response speed. Therefore, the position control law adopts PD control, and the force control law adopts PI control, so as to realize constant force grinding.

Fig. 2 is a schematic diagram of force control during constant force grinding of a blade robot abrasive belt according to an embodiment of the present invention. As shown in Fig. 2, the force control principle during constant force grinding of the present invention includes:

S201: Judging the actual grinding force and the theoretical reference force, IF actual force>reference force;

S202: The robot feeds along the negative direction of its Z axis;

S203: Judging the size of the actual grinding force and the theoretical reference force, IF actual force<=reference force;

S204: The robot feeds and moves along the positive direction of its Z axis;

S205: Calculation formula for robot stiffness, F _z =K·ΔZ;

S206: According to the above stiffness calculation formula, convert the corresponding force into position information that can be recognized by the robot, so as to complete the corresponding position movement;

S207: The measured force is equal to the reference force, and the constant force grinding force control is completed;

S208: theoretical processing path of offline planning;

S209: The actual processing path after force control adjustment.

When the force/position hybrid control and PI control are applied in the Cartesian space coordinate system, the control model is as follows:

Among them, F _D is the input force, X _f is the output displacement after force control, X _p is the output displacement after position control, F _e is the output force, X _e is the comprehensive displacement, k _pp and k _pd are PD position The correlation coefficients for control, k _fp and k _fi are the correlation coefficients for PI force control.

Since the contact force is mainly the grinding force relative to the Z direction in the tool coordinate system T, the force control strategy is also mainly aimed at F _Z , because the force in this direction has the greatest impact on the quality of the grinding process, and at the same time, in this direction The force received is also the largest, so the force control strategy is mainly to control the grinding force received in the Z direction to keep it constant, so as to achieve constant force grinding and improve the surface quality and consistency of processing.

Considering the robot processing system as a rigid body, and its grinding process is the interaction with the external environment, according to the generalized Newton's law, then:

where K, B, M are the method stiffness, damping and inertia of the robot grinding method, and ΔZ is the offset of the robot in the Z direction.

Because the robot maintains a constant speed during the grinding process, and the change of its speed and acceleration can basically be considered close to zero, so the above formula is simplified as:

F _z =K·ΔZ

Through the real-time monitoring of the grinding force, it can be adjusted in real time. In Figure 2, at the current moment, if the actual force is not close to the theoretical force, the corresponding deflection can be calculated by the above robot grinding coefficient stiffness formula. The position distance can be further transformed into the position point information that the robot can recognize, and then passed to the robot control cabinet. The robot will move in the positive or negative direction of Z until the actual grinding force is equal to the theoretical grinding force or near. S208 is the theoretical machining path of off-line programming without applying force control strategy, while S209 is the machining path adjusted in real time after applying force control strategy. By discretizing and interpolating the processing path, the processing path is more stable and the processing method is more stable, which meets the needs of complex processing environments.

Fig. 3 is a diagram of the corresponding robot movement process after the application of the force control strategy provided by the present invention. S301 is a security point. Please refer to FIG. 3 , S302 is the approach point, S303 is the start point, S304 is the transition point, S305 is the end point, and S306 is the departure point. Because the robot moves from point to point, the processing path planned offline is composed of a series of points. Therefore, when the robot is close to the abrasive belt on the contact wheel of the grinding and polishing machine, the force control adjustment has been completed at the starting point. A constant force is achieved for grinding operations. In the case of powerless control, the programming path is from S301 to S303; after the application of force control, the robot's motion path is from S301 to S302 and then to S303, which is equivalent to interpolating S302 to make its motion path more gentle and stable.

Figure 3 shows a grinding process path, and the blade grinding process path is composed of a series of processing paths as shown in Figure 3, and each path is composed of a series of processing points. These points are all adjusted positions after adopting the force control strategy. When the robot processes along such a path, it can realize constant force grinding and fulfill the force control requirements.

Fig. 4 is a schematic diagram of the abrasive belt grinding process of the blade robot provided by the present invention. As shown in Figure 4, S401 is the robot, S402 is the end flange of the robot, S403 is the flange connecting the robot and the sensor, S404 is the ATI six-dimensional force sensor, S405 is the flange connecting the sensor and the fixture, and S406 is the Tooling fixture, S407 is the workpiece blade, S408 is the abrasive belt, and S409 is the contact wheel of the grinding and polishing machine. In this method, the blade is held by the robot for grinding, and the contact wheel of the grinding and polishing machine is an elastic contact wheel. During the processing, there is a certain concession, which can realize the flexible grinding process of the abrasive belt. The grinding force (mainly refers to F _Z ) in the processing process is determined according to the specific processing object, processing environment and corresponding process parameters; at the same time, the grinding force of the blade varies according to the different parts of the processing. , the machining of the air inlet and outlet edge is much smaller than the machining of the blade surface. According to the processing requirements of the method, the grinding force of the air inlet and outlet edges of the blade is controlled between 15N-35N, while the grinding force of the blade surface is controlled between 30N-80N. The theoretical grinding force cannot be set too large, otherwise the blade will be scrapped due to over-grinding.

The acquisition and processing of the voltage signal in the process of the present invention removes noise points through signal conditioning methods such as filtering and stabilizing the voltage interval, which can ensure the stability of the voltage signal and prevent sudden changes due to external interference. Subsequent zero-point drift compensation and gravity compensation for force can further reduce the influence of the external environment on the sensor itself, making the compensated force close to the real force. When there is no contact after compensation, the grinding force fluctuates within ±1N under static conditions, and when the robot feeds at a speed of 50mm/s, its grinding force fluctuates within ±3N, which is due to the sensor itself and its end load Caused by the steady-state error of , it is random. Therefore, after compensation, during grinding, the displayed force is the grinding force, and the effect of grinding can be indirectly represented by controlling this force. Under the condition that the grinding force is set reasonably, when the constant force grinding is used, the surface processing consistency of the blade is better, and the surface roughness is within 0.4 μm, which can meet the surface quality requirements.

According to the different processing objects, the force control method proposed by the present invention has different specific parameter settings, as well as different processing process parameter settings. Through the control of the grinding force during the machining process, the grinding process can be controlled more accurately, so that the removal of surface material is more uniform, and while satisfying the surface quality, the surface consistency of the blade is improved. It is of great significance to improve processing efficiency and improve the working environment.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (7)

1. A blade robot abrasive belt grinding force control method, is characterized in that, comprises the steps: S101: Convert the voltage signal acquired by the sensor into a force signal, and process it to correspond to the force of the grinding process, and monitor the change of force in real time; S102: Control and process the monitored force to make the grinding force constant and meet the requirements of constant force grinding, including the following steps: S201: Judging the size of the actual grinding force and the theoretical reference force, if the actual force>reference force, then go to step S202; S202: The robot feeds along the negative direction of its Z axis; S203: If the actual force<=reference force, then go to step S204; S204: The robot feeds and moves along the positive direction of its Z axis; S205: Calculate the corresponding theoretical robot position information according to the actual force; S206: Convert the rigidity of the robot grinding coefficient into the position information that the robot can recognize, and complete the corresponding position movement; S207: complete the constant force grinding force control through adjustment; S103: Acquire voltage signals of six channels of the sensor; S104: Modulate the acquired voltage signal; S105: converting the processed voltage signal into a force signal, thereby indirectly sensing force changes; S106: Perform zero drift compensation to reduce the error introduced by the sensor itself; S107: Gravity compensation is performed on the end load of the sensor; S108: Transform the compensated force into the base coordinate system, and then into the tool coordinate system, so as to directly correspond to the process force during processing; S109: Force/position hybrid control defines two complementary and mutually orthogonal spaces to realize simultaneous control of force and position; S110: PI/PD control, eliminates large force deviation, obtains faster system response, thus obtains more ideal output force, and realizes force control of blade robot abrasive belt grinding; When the force/position hybrid control and PI/PD control are applied in the Cartesian space coordinate system, the control model is:

Among them, F _D is the input force, X _D is the expected displacement in Cartesian space, X _f is the output displacement after force control, X _p is the output displacement after position control, X _c is the position obtained after force control, F _e is the output force, X _e is the comprehensive displacement, s is the correlation coefficient, k _pp and k _pd are the correlation coefficients of PD position control, and k _fp and k _fi are the correlation coefficients of PI force control. 2. A method for controlling blade robot abrasive belt grinding force according to claim 1, wherein the method for calculating the stiffness of the robot grinding coefficient is: where F _Z is the actual force, K, B, M are the method stiffness, damping and inertia of the robot's grinding method, and ΔZ is the offset of the robot in the Z direction. 3. A method for controlling blade robot abrasive belt grinding force according to claim 1, wherein if the actual force is not close to the theoretical force, then the corresponding force is calculated by the method for calculating the stiffness of the robot grinding coefficient. The offset distance can be further transformed into position point information that can be recognized by the robot, and then passed to the robot control cabinet. The robot will perform feed motion along the Z positive or negative direction until the actual grinding force and the theoretical grinding force equal or close to. 4 . The method for controlling the processing force of blade robot abrasive belt grinding according to claim 1 , wherein the voltage signals of the six channels in step S103 are obtained by an ATI six-dimensional force sensor. 5. A method for controlling the processing force of blade robot abrasive belt grinding according to claim 4, wherein the six-dimensional force sensor senses the voltage change through three strain gauges arranged in a "Y" shape, The slices are spatially separated by 120°. 6 . The method for controlling the processing force of blade robot abrasive belt grinding according to claim 1 , wherein step S104 includes software filtering and a stable voltage interval. 7 . 7 . The method for controlling the processing force of blade robotic abrasive belt grinding according to claim 1 , wherein the two complementary and mutually orthogonal space force spaces and position spaces are described in step S109 .

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