A rigid-flexible coupling robot force-position hybrid control method and related robot

Abstract

The application discloses a kind of rigid-flexible coupling manipulator force-position hybrid control method and related manipulator.The scheme disclosed by the present application constructs real-imaginary double elastic damping model, and the opening and closing amount of fingertip is adaptively controlled according to the error of contact force and planning value, to realize the contact force control of manipulator fingertip and the object held.The application is especially suitable for the operation field of stress-sensitive materials such as explosives, and the manipulator controlled by the method can realize the safe and stable clamping of the manipulator on the material.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of highly sensitive explosives industry and robotics, specifically involving a rigid-flexible coupled manipulator force-position hybrid control method and related manipulators, which are particularly suitable for non-destructive and intrinsically safe operation of stress-sensitive, flammable and explosive solid materials. Background Technology

[0002] Currently, the unpacking and transfer processes in the raw material preparation stage of explosives production are highly dependent on manual operation. Workers are directly exposed to highly sensitive, flammable, and explosive materials, posing serious safety hazards. To achieve complete human-machine isolation and ensure inherent operational safety, robotic arms are needed to replace manual labor for delicate operations. However, explosives materials have special requirements such as electrostatic sensitivity, high mechanical sensitivity (low impact / friction / pressure thresholds), and viscoelastic mechanical properties, posing stringent challenges to the anti-static design, power failure protection, and dynamic contact force control accuracy of the robot's end effector.

[0003] See Figure 1 As shown, a rigid-flexible coupling manipulator structure generally includes a servo drive unit, two fingers 2 and two fingertips 3. The output end of the servo drive unit is connected to the two fingers. The ends of the two fingers away from the servo drive unit are hinged, and the hinge parts between the fingers 2 and the fingertips 3 are provided with springs 4 and dampers 5.

[0004] When not holding an object, the fingertips are not under force, the spring damping remains relaxed, and the fingertips do not change angle relative to the fingers. When holding object 1, driven by the servo drive unit, the two fingers move towards each other with their fingertips. The object exerts an outward contact force on the fingertips. Since the connection between the fingertips and fingers is not rigid but through a hinge, the outward contact force is reflected in the rotational deformation of the hinge, causing the fingertips to bend relative to the fingers. Because the hinge is connected in parallel with a spring damping, the rotational deformation generates a reaction force from the spring damping, preventing the fingertips from spreading too wide and keeping them in contact with the object. The reaction force and the contact force are balanced. Therefore, the contact force can be deduced from the reaction force of the spring damping.

[0005] In the prior art, CN114851182A discloses a control method for a two-finger robotic gripper based on flexible rope drive. This scheme's force control is based on the passive deformation of a torsion spring (first-order hysteresis), only achieving passive compliance with contact force. It cannot achieve rapid, overshoot-free force tracking through active acceleration adjustment, and is prone to causing instantaneous over-impact damage to materials. CN116038749A proposes a flexible gripper for agricultural harvesting scenarios using servo motor drive and photoelectric ranging sensors. This scheme lacks closed-loop control of contact force, cannot dynamically adjust the gripping action based on real-time contact force feedback, and the passive buffering effect of the fingertip silicone is insufficient to eliminate localized high pressure, making it unsuitable for delicate handling of highly sensitive materials. CN118418169A discloses a gripper for grasping and installing rollers, employing a rigid ring structure with servo cylinders and gear transmission. This scheme lacks a flexible buffer element; the upper and lower grippers are rigidly clamped, lacking compliant adaptive capability, and cannot meet the safety and dexterity requirements for unpacking explosives.

[0006] In summary, existing technologies share the following common defects: First, the control model is rudimentary, often employing simplified control based on position error or passive springs, which can only achieve a first-order hysteresis response (passive compliance) of contact force and cannot achieve force tracking of second-order dynamic characteristics through active acceleration control, resulting in response lag and easy overshoot; Second, rigid-flexible coupling is insufficient, either purely rigid (prone to impact damage) or purely flexible (poor positioning accuracy), lacking a decoupling design between rigid positioning and flexible contact, and unable to achieve adaptive adjustment of contact force while maintaining high positioning accuracy. Summary of the Invention

[0007] In view of the defects or deficiencies of the existing technology, the present invention provides a force-position hybrid control method for rigid-flexible coupled manipulators.

[0008] Therefore, the rigid-flexible coupling manipulator force-position hybrid control method provided by the present invention includes:

[0009] Step 1: Collect the bending angle of the fingertip relative to the finger within the current cycle. The contact force in the current cycle is calculated using equation (1). ; (1) Represents the execution data within the current period. Take a natural number greater than or equal to 1; This represents the lever arm length vector from the workpiece to the root of the fingertip within the current cycle. , , , These are the components of the lever arm length from the workpiece to the root of the fingertip on the x, y, and z axes, respectively, within the current cycle; Let r be the cross product matrix. ; The spring constant of the manipulator; The damping coefficient of the damper in the robotic arm; for The first derivative with respect to time is the angular velocity of the fingertip relative to the finger. Step 2, based on the fingertip opening and closing control amount within the current cycle. and The actual fingertip opening in the current cycle is obtained using formula (2). ; (2) This represents the target opening amount corresponding to the current cycle; the robot arm is initially in a closed state. hour, =0, ; for The modulus; Step 3, using the feedback control of equation (3) to calculate... After that, Performing a second-order integral with respect to time yields the fingertip opening / closing control quantity for the next cycle. ; (3) = - ; ; The target contact force corresponding to the current cycle; for First derivative with respect to time; for Second derivative with respect to time; ; ; The matrix is ​​determined by the closed-loop response characteristics; The matrix is ​​determined by the closed-loop response characteristics; I =

[0010] ; ; ; It is an ideal elastic system; For an ideal damping system; This refers to the control time step of the controller; Step 4, the servo driver according to Control the opening and closing of your fingertips.

[0011] The present invention also provides a related rigid-flexible coupling manipulator, including a servo drive unit, two fingers and two fingertips, wherein the output end of the servo drive unit is connected to the two fingers, and the ends of the two fingers away from the servo drive unit are connected by hinges, and the hinge parts between the fingers and fingertips are provided with springs and damping. The invention also includes a controller, which controls the operation of the manipulator using the above method.

[0012] This invention utilizes a virtual-real dual elastic damping system to construct a dynamic model for manipulator gripping, enabling the manipulator to respond quickly to the contact force of the workpiece and to perform second-order dynamic tracking of the contact force of the fingers on the target and the target opening amount. The method of this invention is applicable to robotic arms that combine rigidity and flexibility, taking into account both the high rigidity and precise position control of the robotic fingers and the passive and flexible contact of the fingertips, thereby achieving force-position synchronization control.

[0013] This invention also relates to related storage media and software products. The storage medium stores a computer program / instructions, characterized in that, when executed by a processor, the computer program / instructions implement the steps of the above-described method. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure and dynamics of a rigid-flexible coupling manipulator; in the diagram: 1-the object being gripped, 2-fingers, 3-fingertips, 4-springs, 5-damping, 6-hinge structure; F : Actual contact force at the fingertip, Δθ: Bending angle of the fingertip relative to the finger, Δ f c Actual fingertip opening size l The lever arm length from the workpiece to the base of the fingertip. f c : The amount of fingertip opening and closing control.

[0015] Figure 2 This is the control flowchart of the present invention.

[0016] Figure 3This illustrates the contact force following effect in the embodiment. Detailed Implementation

[0017] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art.

[0018] It should be explained that the target opening amount in the solution of this invention... Contact force with the target Based on practical application scenarios, especially the shape and size of the object being gripped, actual following experiments were conducted to ensure the stable, safe, and reliable operation of the robotic arm during the gripping process. The two closed-loop response characteristic determination matrices involved in the scheme were determined based on LQR optimal control theory to achieve the objectives of this invention. The ideal elastic system and ideal damping system were determined based on the contact force threshold requirement of the gripped workpiece and the desired dynamic response characteristics; an exemplary reasonable range is... 5×10³~5×10 4 N / m, : 5×10²~5×10³ N·s / m.

[0019] In this invention, the x-axis is the straight line containing the length of the closed part of the two fingers in the closed state of the robotic arm, and the two fingers perform opening and closing actions in the xy plane.

[0020] The principle of this invention is explained as follows: See Figure 1 As shown, when fingertip 3 pinches object 1, the actual force F is controlled by the opening and closing of the fingertip. f c Under control commands, the drive device drives the fingers to move along the X-axis, with the fingertips bending at 6 points around the hinge structure and the two fingertips spreading apart by 2Δ. f c Simultaneously subjected to the reaction torques of torsion spring 4 and damper 5, it remains in balance with the contact force. Therefore, the force balance equation of the manipulator is: (I) , The bending angle and angular velocity of the fingertip relative to the finger can be read by an encoder installed in the hinge structure. Let be the spring constant. The damping coefficient of the damper. The lever arm length from the workpiece to the base of the fingertip l A vector composed of components in the x, y, and z directions.

[0021] Formula (I) reflects , Regarding the relationship with the contact force at the fingertips, the force in purely rigid contact is discrete, while the force in a robotic arm will... Transforming it into a differentiable continuous state, the first derivative of equation (I) yields the acceleration law of the real system's fingertip: (II) The modal modeling of the contact between the fingertip surface and the workpiece is performed using an elastic damping system as follows: (III) After first derivative: (IV) in, (V) Indicates actual contact force Contact force with the target The error between them This indicates the actual fingertip opening relative to the target opening. (The inward clamping distance, Equation (III) indicates that the greater the inward clamping distance, the greater the contact force, and vice versa.)

[0022] With the acceleration of the fingertips pinching inward As input, equation (IV) satisfies the following linear state equation: (VI) Indicates the control time step of the controller, (VI) can be abbreviated as In the form of, ,enter The control objective is to make the cost function Minimum, (VII) Therefore, the optimal LQR control form for fingertip gripping amount is: (VIII) in Satisfying the Riccati equation:

[0023] Substituting (VIII) into (IV), we get (IX) Substituting (II) into (IX), we obtain the fingertip opening and closing control amount. The second-order differential: (X) As can be seen in (X), by state , , , and the planned target contact force Target opening quantity It can make a second-order response to contact force error, dynamically eliminate opening amount and contact force tracking error, and achieve adaptive compliant contact with the surface of the clamped object such as explosives.

[0024] according to Figure 2 The control process described above involves acquiring the bending angle of the fingertip relative to the finger within the current cycle (encoder reading of the hinge) through an encoder installed at the hinge structure 6. And angular velocity, the contact force is obtained through equation (I). Based on the amount of fingertip opening and closing control within the current cycle and The actual fingertip opening in the current cycle is obtained using formula (II). Subtract the target opening and closing amount get Then, by taking the difference from the previous time step, we obtain... Substituting (X) into the feedback control, we can calculate... Later, we can obtain the result through second-order integrals. Then execute via the servo driver. This allows for the tracking of the amount of pressure the fingertip can apply to the target and the contact force with the target.

[0025] Taking the workpiece gripping stage in the raw material preparation phase of explosives production as an example, the fingertips close, gripping the workpiece. The friction of the fingertips secures the workpiece to the robotic arm. As the arm moves, finger 2 tightens, subjecting the fingertips to a greater contact force. Torsion spring 4 and damper 5 buffer this force, causing the fingertips to bend and reduce the actual contact force on the workpiece surface. When the contact force exceeds the target value, the clamping amount needs to be adjusted accordingly. The acceleration is adjusted to reduce contact force; when the contact force is insufficient and the clamping is unstable, the control... The clamping action increases the contact force, ultimately enabling the controller to adapt to the contact force.

[0026] Example: The robotic arm in this embodiment uses an ELMO industrial driver and a Maxon brushless DC motor as servo drive units, and employs the method of this invention to realize the single-degree-of-freedom opening and closing motion of the gripper.

[0027] This embodiment controls execution to be of equal periodic duration, with a time step of dt = 4ms; Lever arm length from the workpiece to the base of the fingertip l The value is 0.1m; initially, the fingertips are closed. The range is [-0.1, 0, 0]. T ; In this embodiment, it is set The curve starts from 0 and ends at a constant value of 0.04m. During the test, after the grippers open to 4cm, an object with a width of 4cm is manually inserted, and the gripping force is followed by a test. =1e-4.k, k≤400; =0.04, k≥400; The robotic arm is initially in a closed position. The initial value of =0 is 0, and the initial value of the opening and closing quantity at the start of the operation is 0. This embodiment selects =diag(500, 5, 50), =1, will and Substituting the value of into the Riccati equation yields P.

[0028] Selecting a spring elastic system Damping coefficient Based on the desired rigid-flexible coupling contact effect, select , .

[0029] In the test of this embodiment, the robotic arm grasped an object with a width of 4cm, and a step-like target force was applied. ,like Figure 3 As shown, it can be seen that after a brief oscillation during the switching process, the actual clamping force converges to the target clamping force under the action of the controller, and stably follows the changes in the target clamping force.

Claims

1. A method for force-position hybrid control of a rigid-flexible coupled manipulator, characterized in that, The methods include: Step 1: Collect the bending angle of the fingertip relative to the finger within the current cycle. The contact force in the current cycle is calculated using equation (1). ; （1） Represents the execution data within the current period. Take a natural number greater than or equal to 1; This represents the lever arm length vector from the workpiece to the root of the fingertip within the current cycle. , , , These are the components of the lever arm length from the workpiece to the root of the fingertip on the x, y, and z axes, respectively, within the current cycle; Let r be the cross product matrix. ； Let be the spring constant of the manipulator; The damping coefficient of the damper in the robotic arm; for The first derivative with respect to time is the angular velocity of the fingertip relative to the finger. Step 2, based on the fingertip opening and closing control amount within the current cycle. and The actual fingertip opening in the current cycle is obtained using formula (2). ; （2） This represents the target opening amount corresponding to the current cycle; the robot arm is initially in a closed state. hour, =0, ; for The modulus; Step 3, using the feedback control of equation (3) to calculate... After that, Performing a second-order integral with respect to time yields the fingertip opening / closing control quantity for the next cycle. ; （3） = - ； ； The target contact force corresponding to the current cycle; for First derivative with respect to time; for Second derivative with respect to time; ； ； The matrix is ​​determined by the closed-loop response characteristics; The matrix is ​​determined by the closed-loop response characteristics; I = ； ； ； It is an ideal elastic system; For an ideal damping system; This refers to the control time step of the controller; Step 4, the servo driver according to Control the opening and closing of your fingertips.

2. A rigid-flexible coupling manipulator, comprising a servo drive unit, two fingers, and two fingertips, wherein, The output end of the servo drive unit is connected to two fingers. The ends of the two fingers away from the servo drive unit are connected by hinges, and the hinge part between the fingers and the fingertips is provided with springs and damping. The feature is that it also includes a controller, which controls the operation of the robot arm using the method described in claim 1.

3. A storage medium, characterized in that, It stores a computer program / instruction thereon, characterized in that the computer program / instruction, when executed by a processor, implements the steps of the method described in claim 1.

4. A software product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

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