An indirect feedback control method for excavator bucket joint

Abstract

The application provides an indirect feedback control method for a shovel joint of a excavator, aiming at the problems that the irreversible mapping between the joint angle and the cylinder elongation leads to the difficulty in closing loop of the joint space feedback, the poor reliability when the sensor is directly installed on the shovel body or the cylinder, or the high modification cost, the method pastes an inertial measurement unit on the middle connecting rod of the four connecting rod mechanism of the shovel to obtain the included angle between the connecting rod and the horizontal plane in real time, combines the joint angle of the boom and the stick to obtain the azimuth angle of the vector GE through vector geometry operation, takes the difference between the included angle and the azimuth angle as the folding angle, and calculates the actual elongation of the cylinder through the cosine law; and after the path planning in the joint space is completed, the joint angle sequence of the shovel is converted into the cylinder elongation sequence as the target in advance, and the actual elongation is taken as the feedback for the closed loop control in the driving space. The sensor arrangement of the method is simple and reliable, bypasses the irreversible mapping, and can be used for the semi-autonomous feedback control of the shovel joint of the excavator.

Description

Technical Field

[0001] This invention relates to the field of intelligent control technology for construction machinery, and in particular to an indirect feedback control method for the bucket joint of an excavator. Background Technology

[0002] The bucket tilting of an excavator is typically achieved by a drive cylinder via a four-bar linkage. The extension and retraction of the cylinder are transmitted to the bucket body through intermediate and connecting rods, thereby causing the bucket to rotate around its hinge point with the stick. In semi-autonomous or even autonomous operation, real-time and accurate acquisition of the bucket joint's motion state and its closed-loop control are crucial for determining operational accuracy and stability.

[0003] However, due to the geometric nonlinearity of the four-bar linkage, there is an irreversible mapping relationship between the bucket joint angle and the extension of the drive cylinder: the bucket joint angle can be uniquely calculated from the cylinder extension, but conversely, the cylinder extension cannot be uniquely determined from the bucket joint angle through inverse calculation. Therefore, schemes that directly use the bucket joint angle as the controlled variable for feedback in the joint space often struggle to achieve stable and effective closed-loop operation.

[0004] To obtain the status of the bucket joint, one intuitive approach is to directly place sensors on the bucket body. However, under conditions of digging and crushing, the bucket is subjected to severe impacts and vibrations, making the sensors prone to loosening or damage, and compromising system reliability. Another approach is to install built-in displacement sensors on the drive cylinder, which necessitates mechanical modifications or structural integration of the cylinder, resulting in significant workload and high costs. Furthermore, most existing research has stopped at the derivation of the forward and inverse kinematics of the bucket mechanism. A complete and directly engineeringable derivation is still lacking on how to utilize actual measurements from a small number of sensors and calculate the actual driving force of the bucket joint through coordinate transformation to support the closed loop, making it difficult to directly apply to actual equipment.

[0005] Therefore, a bucket joint feedback control method is needed that can avoid the irreversible mapping between the bucket joint angle and the cylinder extension, facilitate reliable sensor placement, and have a complete feedback calculation link. Summary of the Invention

[0006] This invention proposes an indirect feedback control method for excavator bucket joints to address the following issues in bucket joint feedback control: the irreversible mapping between the bucket joint angle and the cylinder extension makes it difficult to effectively close the loop of joint space feedback; when sensors are directly placed on the bucket body or cylinder, reliability is poor and modification costs are high; and there is a lack of complete calculation and derivation techniques for the actual driving amount of the bucket joint measured by the sensors.

[0007] To solve the above-mentioned technical problems, the present invention provides an indirect feedback control method for the bucket joint of an excavator. The bucket of the excavator is driven by a hydraulic cylinder via a four-bar linkage mechanism. The four-bar linkage mechanism consists of the excavator's stick, an intermediate link GF, a connecting rod FH, and the bucket body. One end of the intermediate link GF is hinged to hinge point G, which is fixed on the stick, and the other end is hinged to hinge point F. The two ends of the connecting rod FH are respectively hinged to hinge point F and hinge point H, which is fixed on the bucket body. The bucket body is driven by a hydraulic cylinder via a four-bar linkage mechanism. The cylinder is hinged to the stick, with one end hinged to hinge point E fixed on the stick and the other end hinged to hinge point F, driving the four-bar linkage to move. Hinge point F is the common movable hinge point of the cylinder, the intermediate connecting rod GF, and the connecting rod FH, and moves with the extension and retraction of the cylinder; the method includes: An inertial measurement unit is attached to the intermediate connecting rod GF, and the inertial measurement unit outputs the angle between the intermediate connecting rod GF and the horizontal plane in real time. Based on the boom joint angle and stick joint angle of the excavator, a vector pointing from hinge point G to hinge point E is obtained through vector geometry calculations. The azimuth angle; The difference between the azimuth angle and the included angle is taken as the angle value of the fold formed by hinge point E, hinge point G and hinge point F; The actual elongation of the hydraulic cylinder is determined based on the angle value of the bending angle, the distance from hinge point E to hinge point G obtained in advance, and the length of the intermediate connecting rod GF. Using the actual elongation as a feedback quantity, the actual elongation is compared with the target elongation obtained from path planning, and the hydraulic cylinder is subjected to closed-loop control to achieve feedback control of the bucket joint.

[0008] Preferably, the vector azimuth Determine using the following formula: ; in and The vectors are respectively The components along the horizontal and vertical directions in the working plane coordinate system of the excavator, wherein the working plane coordinate system takes the hinge point between the boom and the body of the excavator as the origin, the horizontal direction as the X-axis, and the vertical direction as the Y-axis.

[0009] Preferably, the component and It is determined by the difference between the position vectors of hinge point E and hinge point G; Hinge points E and G relative to the origin of the working plane coordinate system position vector and The calculation expression is: ; ; ; ; ; ; in, The angle of the boom joint. The angle of the boom joint. and Points The distance to hinge points E and G, and The angle is the inherent angle determined by the fixed structural parameters of the four-bar linkage according to the law of cosines. and They are vectors and The azimuth angle relative to the horizontal direction of the working plane coordinate system; , and The hinge points are, in sequence, the hinge points between the boom and the vehicle body, the hinge points between the boom and the stick, and the hinge points between the stick and the bucket. is the origin of the coordinate system of the working plane.

[0010] Preferably, the inherent angle and The calculation expression is: ; ; in For point Time distance, and Points Distances to hinge points E and G.

[0011] Preferably, the actual elongation of the hydraulic cylinder Determine using the following formula: ; in Let E be the distance from hinge point E to hinge point G. The length of the intermediate connecting rod GF is... The angle value of the fold.

[0012] Preferably, the measuring axis of the inertial measurement unit is aligned with the axial direction of the intermediate connecting rod GF.

[0013] Preferably, the method for obtaining the target elongation includes: performing path planning on the joint angles of the bucket to obtain a bucket joint angle sequence; pre-converting the bucket joint angle sequence into a corresponding hydraulic cylinder elongation sequence, and using the hydraulic cylinder elongation sequence as the target elongation sequence for the closed-loop control; the closed-loop control uses the difference between the actual elongation and the target elongation corresponding to the target elongation sequence as the error to control the hydraulic cylinder.

[0014] Preferably, the closed-loop control is PID control, where the difference between the actual elongation and the target elongation is used as the error input of the PID controller, the PID controller outputs a control quantity, and the control quantity is transmitted to the hydraulic control unit via the controller, which then drives the cylinder to extend and retract.

[0015] Preferably, the boom joint angle and the stick joint angle are obtained in real time by tilt sensors attached to the sides of the boom and stick of the excavator, respectively.

[0016] Preferably, the method is executed cyclically according to a set control cycle. In each control cycle, the included angle is acquired in real time, the actual elongation of the cylinder is updated, and the control quantity of the cylinder is updated according to the deviation between the actual elongation and the target elongation.

[0017] The beneficial effects of the present invention include at least the following: 1) The inertial measurement unit of the present invention is attached to the middle link inside the four-bar linkage, which avoids the strong impact load borne by the bucket body and does not require any mechanical modification to the cylinder or pin. Therefore, the sensor arrangement is simple and the reliability is significantly improved. 2) This invention utilizes the connecting rod angle measured by the inertial measurement unit, combined with the joint angle between the boom and the stick, and calculates the actual extension of the hydraulic cylinder completely through vector geometry calculation and the law of cosines. This establishes a complete feedback calculation link from the sensor's actual measurement to the bucket joint drive amount, filling the gap in related derivations. 3) Since both feedback and control are performed in the drive space with the cylinder extension as the controlled variable, the present invention bypasses the irreversible mapping between the bucket joint angle and the cylinder extension, enabling the closed-loop feedback control of the bucket joint to be realized stably and effectively. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the four-bar linkage mechanism for driving the bucket joint of an excavator in an embodiment of the present invention; Figure 2This is a schematic diagram showing the installation position of the inertial measurement unit on the excavator in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0020] This embodiment uses a certain type of excavator as an example for description, but the present invention is not limited to this model. The control system of this embodiment includes an upper controller and a lower hydraulic control unit in its architecture. The upper controller completes the path planning, coordinate calculation and closed-loop control calculation of the bucket joint, and the lower hydraulic control unit receives the control input and drives the hydraulic valve. The two communicate with each other via a CAN bus.

[0021] like Figure 1 As shown, the four-bar linkage of the bucket joint consists of the stick, intermediate link GF, connecting rod FH, and the bucket body, and is driven by the hydraulic cylinder EF. One end of the intermediate link GF is hinged to hinge point G, which is fixed to the stick, and the other end is hinged to movable hinge point F; one end of the connecting rod FH is hinged to movable hinge point F, and the other end is hinged to hinge point H, which is fixed to the bucket body; the bucket body passes through the hinge point... Hinged to the stick. One end of the drive cylinder is hinged to hinge point E, which is fixed to the stick, and the other end is hinged to movable hinge point F. During operation, the extension and retraction of the EF cylinder changes the distance between hinge points E and F, pushing F, which serves as the common movable hinge point, to move: on the one hand, it drives the intermediate connecting rod GF to rotate around the fixed hinge point G; on the other hand, it pushes and pulls the bucket body through the connecting rod FH, causing the bucket body to rotate around the hinge point. The relative rotation of the stick converts the linear extension and retraction motion of the hydraulic cylinder into the tilting motion of the bucket. In this mechanism, the stick is relatively fixed as a frame, and the tilting configuration of the bucket can therefore be uniquely characterized by the extension of the hydraulic cylinder.

[0022] Before implementation, the fixed structural parameters of the four-bar linkage are measured and recorded. These parameters include the distances between each hinge point, specifically the distance from hinge point E to hinge point G. Length of intermediate connecting rod GF Length of connecting rod FH Hinge point Distance to hinge point H and hinge points , Distance between hinge points E and G , , , , It also includes several inherent angles determined by the cosine theorem from the aforementioned distances.

[0023] In this embodiment, a typical set of values ​​for the above distance parameters is: 2140mm 590mm For 600mm, 450mm For 800mm, 2580mm 3048mm For 2600mm, The value is 470mm. The above parameters can be directly read from the assembly drawing of the whole machine, or measured and calibrated on the actual machine with measuring tools; since they only depend on the fixed geometry of the mechanism, once calibrated, they can be used for a long time.

[0024] In this embodiment of the invention, the working plane coordinate system of the excavator is established: based on the hinge point between the boom and the body. With the origin of the coordinate system as the reference point, and the horizontal direction as the reference point... The positive direction of the axis is vertically upward. Positive direction of the axis; This is the hinge point between the boom and the stick. This is the hinge point between the boom and the bucket. All angles are based on... The positive direction of the axis is the reference, and the counterclockwise direction is positive.

[0025] Based on this, the boom joint angle For boom relatively Azimuth angle of the shaft, angle of the boom joint For the pole relative boom The angle of rotation in the extended direction, i.e. In this embodiment, and The tilt angle is obtained from tilt sensors mounted on the sides of the boom and stick respectively: the absolute tilt angle output by the tilt sensor on the boom side is the boom joint angle. The absolute tilt angle of the stick is output by the stick side tilt angle sensor, and then the absolute tilt angle of the boom is subtracted to obtain the joint angle of the stick relative to the boom. Hinge points E and G are relative. azimuth , Then by , It is obtained by superimposing it segment by segment with the inherent perspective of the institution.

[0026] like Figure 2As shown, the inertial measurement unit (IMU) is mounted on the middle link GF of the four-bar linkage, with its measurement axis aligned with the axis of the middle link GF. This allows the IMU to output the angle between the middle link GF and the horizontal plane in real time. During installation, positioning fixtures can be used to ensure that the measuring axis is parallel to the GF axis. After assembly, static calibration is performed, that is, the mechanism is placed in a known configuration, and the output of the inertial measurement unit is compensated to the theoretical azimuth angle of GF under that configuration to eliminate installation deviations. To ensure measurement stability, the inertial measurement unit is fixed to the metal surface of the connecting rod GF using a high-strength metal clamp or welded mounting base, so that there is no relative sliding between the two. Its housing should have an IP67 or higher protection rating to resist dust and hydraulic oil contamination in the working environment. To address vibration interference during operation, a low-pass filter can be applied to the output of the inertial measurement unit to suppress high-frequency noise.

[0027] In this embodiment of the invention, the intermediate connecting rod GF is chosen as the installation position because GF is located inside the four-bar linkage, and its impact load is significantly reduced compared to the bucket body, which is directly exposed to digging and crushing impacts, resulting in higher reliability. Furthermore, compared to installing a built-in displacement sensor on the hydraulic cylinder, no mechanical modification to the cylinder is required, making installation simpler and less costly. (Boom joint angle) Angle with the stick joint As before, the tilt angles are measured in real time by tilt sensors attached to the sides of the boom and stick, respectively.

[0028] Based on the actual measurements from the aforementioned sensors, the actual extension of the hydraulic cylinder can be calculated and used as feedback for the drive space. Therefore, the boom joint angle is first determined... Angle with the stick joint Determine the positions of hinge points E and G in the work plane coordinate system. Hinge point E is relative to... The azimuth is , among which the inherent angle From triangle The lengths of the three fixed sides are determined by the law of cosines, that is... Based on this, hinge point E is relative to The direction vector is Hinge point G relative to azimuth From its inherent perspective Similarly, the direction vector is obtained as follows: .

[0029] Translate the above vector to the position shown. Using a coordinate system with the origin as the origin, we get and Subtracting the two gives the vector. ,Right now ; where the boom vector In the subtraction, it is eliminated as a common term, hence the vector Only depends on and That is, it depends only on the relative geometry of the stick and its hinge points, and is independent of the boom configuration. Let the vector be... The components along the horizontal and vertical directions are respectively and Then its azimuth is .

[0030] The included angle is output in real time by the inertial measurement unit on the intermediate link GF. After the aforementioned static calibration, this becomes the azimuth angle of the connecting rod GF, and thus the angle formed by hinge points E, G, and F. equal to vector The difference between the azimuth angle and the included angle, i.e. .because Already by , The calculation fully incorporates the configurations of the boom and stick. The determination of the angle is independent of the movement of the boom and stick, thus decoupling the bucket joint from the other joints, allowing the angle to be determined by a single inertial measurement unit on the connecting rod GF.

[0031] Furthermore, in triangle EGF formed by hinge points E, G, and F, the length of side EG... Length of edge GF All are known fixed values, including the included angle. Since the value has been obtained from the above formula, the length of the opposite side EF, which is the actual elongation of the cylinder, can be calculated using the Law of Cosines. This is the actual extension of the cylinder at the current moment, which serves as a feedback quantity in the drive space and participates in the closed loop.

[0032] It should be noted that the bucket joint angle With cylinder elongation There exists an irreversible mapping, that is, given the cylinder elongation... The configuration of the four-bar linkage is thus uniquely determined, and the bucket joint angle is determined accordingly. It can be uniquely computed; conversely, given Therefore, because the four-bar linkage has multiple possible assembly configurations, it cannot be determined by... Uniquely determined through inverse operation .

[0033] If the traditional method is used to solve this problem, in the joint space... Directly closing the loop to the target would be difficult to achieve. Therefore, in this embodiment, after completing the path planning for the bucket joint angles in the joint space and obtaining the bucket joint angle sequence, the positive mapping from the cylinder extension to the bucket joint angle is used in the actual assembly configuration. In the offline stage, through numerical inversion or a pre-established extension-angle lookup table, the bucket joint angle sequence is uniquely converted into the corresponding cylinder extension sequence, and this cylinder extension sequence is used as the target extension sequence for closed-loop control. During control, the actual extension calculated in real time is used. The control error is obtained by subtracting the target elongation corresponding to the current moment in the target elongation sequence. In this way, although path planning is completed in joint space, closed-loop control is carried out entirely in the drive space with the cylinder elongation as the controlled variable. There is no need to perform online inverse calculations on the above irreversible mapping during the control process, thus avoiding the difficulties caused by the irreversibility of the mapping.

[0034] Based on this, the aforementioned control error is used as the input to the PID controller. The PID controller outputs a control quantity through proportional, integral, and derivative calculations. This control quantity is sent to the lower-level hydraulic control unit via the CAN bus. The hydraulic control unit adjusts the opening of the hydraulic valve accordingly, controlling the flow and direction of the hydraulic oil entering the bucket cylinder, thereby driving the cylinder to extend and retract. This allows the actual extension of the cylinder to gradually approach and track the target extension, achieving precise position control of the bucket joint. The above calculation and control are executed cyclically according to a set control cycle: within each control cycle, the outputs of the boom and stick tilt sensors and the connecting rod GF inertial measurement unit are collected in real time to update the included angles. The actual elongation of the hydraulic cylinder is recalculated, and the control quantity is updated based on the deviation between the actual elongation and the target elongation until the bucket joint reaches the planned target configuration.

[0035] Using the above method, the actual extension of the bucket cylinder can be obtained in real time and closed-loop control of the drive space can be achieved solely by two tilt sensors on the boom and stick and one inertial measurement unit on the connecting rod GF, without the need to install sensors on the bucket body or cylinder. Verified on actual equipment, this method enables the position control of the bucket joint to meet the accuracy required for engineering operations, and the system operates stably with reliable sensor placement.

[0036] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0037] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. An indirect feedback control method for the bucket joint of an excavator, characterized in that, The excavator's bucket is driven by a hydraulic cylinder via a four-bar linkage. This four-bar linkage consists of the excavator's boom, intermediate link GF, connecting rod FH, and the bucket body. One end of the intermediate link GF is hinged to hinge point G, which is fixed to the boom, and the other end is hinged to hinge point F. The two ends of the connecting rod FH are respectively hinged to hinge point F and hinge point H, which is fixed to the bucket body. The bucket body is driven by the hydraulic cylinder via the four-bar linkage. The cylinder is hinged to the stick, with one end hinged to hinge point E fixed on the stick and the other end hinged to hinge point F, driving the four-bar linkage to move. Hinge point F is the common movable hinge point of the cylinder, the intermediate connecting rod GF, and the connecting rod FH, and moves with the extension and retraction of the cylinder; the method includes: An inertial measurement unit is attached to the intermediate connecting rod GF, and the inertial measurement unit outputs the angle between the intermediate connecting rod GF and the horizontal plane in real time. Based on the boom joint angle and stick joint angle of the excavator, a vector pointing from hinge point G to hinge point E is obtained through vector geometry calculations. The azimuth angle; The difference between the azimuth angle and the included angle is taken as the angle value of the fold formed by hinge point E, hinge point G and hinge point F; The actual elongation of the hydraulic cylinder is determined based on the angle value of the bending angle, the distance from hinge point E to hinge point G obtained in advance, and the length of the intermediate connecting rod GF. Using the actual elongation as a feedback quantity, the actual elongation is compared with the target elongation obtained from path planning, and the hydraulic cylinder is subjected to closed-loop control to achieve feedback control of the bucket joint.

2. The method according to claim 1, characterized in that, The vector azimuth Determine using the following formula: ； in and The vectors are respectively The components along the horizontal and vertical directions in the working plane coordinate system of the excavator, wherein the working plane coordinate system takes the hinge point between the boom and the body of the excavator as the origin, the horizontal direction as the X-axis, and the vertical direction as the Y-axis.

3. The method according to claim 2, characterized in that, The component and It is determined by the difference between the position vectors of hinge point E and hinge point G; Hinge points E and G relative to the origin of the working plane coordinate system position vector and The calculation expression is: ； ； ； ； ； ； in, The angle of the boom joint. The angle of the boom joint. and Points The distance to hinge points E and G, and The angle is the inherent angle determined by the fixed structural parameters of the four-bar linkage according to the law of cosines. and They are vectors and The azimuth angle relative to the horizontal direction of the working plane coordinate system; , and The hinge points are, in sequence, the hinge points between the boom and the vehicle body, the hinge points between the boom and the stick, and the hinge points between the stick and the bucket. is the origin of the coordinate system of the working plane.

4. The method according to claim 3, characterized in that, The inherent angle and The calculation expression is: ； ； in For point Time distance, and Points Distances to hinge points E and G.

5. The method according to claim 1, characterized in that, The actual elongation of the hydraulic cylinder Determine using the following formula: ； in Let E be the distance from hinge point E to hinge point G. The length of the intermediate connecting rod GF is... The angle value of the fold.

6. The method according to claim 1, characterized in that, The measurement axis of the inertial measurement unit is aligned with the axial direction of the intermediate connecting rod GF.

7. The method according to claim 1, characterized in that, The method for obtaining the target elongation includes: performing path planning on the joint angles of the bucket to obtain a bucket joint angle sequence; pre-converting the bucket joint angle sequence into a corresponding hydraulic cylinder elongation sequence, and using the hydraulic cylinder elongation sequence as the target elongation sequence for the closed-loop control; the closed-loop control uses the difference between the actual elongation and the target elongation corresponding to the target elongation sequence as the error to control the hydraulic cylinder.

8. The method according to claim 1, characterized in that, The closed-loop control is PID control. The difference between the actual elongation and the target elongation is used as the error input of the PID controller. The PID controller outputs a control quantity, which is transmitted to the hydraulic control unit via the controller. The hydraulic control unit then drives the cylinder to extend and retract.

9. The method according to claim 1, characterized in that, The boom joint angle and the stick joint angle are respectively measured in real time by tilt sensors attached to the sides of the boom and stick of the excavator.

10. The method according to claim 1, characterized in that, The method is executed cyclically according to a set control cycle. In each control cycle, the included angle is acquired in real time, the actual elongation of the cylinder is updated, and the control quantity of the cylinder is updated according to the deviation between the actual elongation and the target elongation.

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