Flexible under-actuated gripper and semi-closed-loop adaptive impedance control method thereof

Abstract

The invention discloses a flexible under-actuated gripper and a semi-closed-loop self-adaptive impedance control method thereof. The gripper comprises a flexible clamping unit, a driving part, a driving part mover position sensor and an input force sensor. The control method comprises the steps that the compliant under-actuated gripper is initialized; obtaining an equivalent parameter vector of the object to be grabbed; determining a tracking mode weight coefficient, and correcting the tracking mode weight coefficient in the two-point clamping mode; acquiring an expected jaw position; and according to the equivalent parameter vector of the object to be grabbed, the tracking modal weight coefficient and the expected jaw position are input to an adaptive impedance controller to carry out iterative optimization on the compliant under-actuated gripper. By means of the method, the feedback dependence of the system can be reduced, and then the grabbing precision of objects of different shapes and rigidities is improved. The compliant under-actuated gripper and the semi-closed-loop adaptive impedance control method thereof can be widely applied to the technical field of robot control.

Description

Technical Field

[0001] The present invention relates to the field of robot control technology, and in particular to a compliant under-actuated gripper and a semi-closed loop adaptive impedance control method thereof. Background Art

[0002] In robot operation, the gripper is a typical end effector used to complete operations such as grasping, carrying, placing, and releasing. The compliant underactuated gripper combines passive compliant elements such as compliant mechanisms, flexible materials, and underactuated principles to achieve general grasping operations. To improve the stability and safety of general gripping operations, active gripping control is required. Impedance control can control the dynamic relationship between contact force and motion and has been widely used in robot grasping mechanisms. Impedance control can be divided into traditional impedance control, learning-based impedance control, and adaptive impedance control. Among them, traditional impedance control usually uses fixed impedance parameters. When interacting with dynamic or uncertain environments, it is difficult to cope with environmental changes, resulting in poor robustness and adaptability in completing tasks. Learning-based impedance control requires large training samples to obtain a robust estimator, which is difficult to adapt to robot operations in uncertain environments. Adaptive impedance control relies on the optimization process to automatically adjust the impedance parameters without relying on large training samples. Some researchers have applied adaptive impedance control to rigid underactuated grippers. However, in this study, only trajectory tracking exists, and force tracking indicators are not given. At the same time, this study is only applicable to the two-point clamping mode of the rigid underactuated gripper, while in the compliant underactuated gripper, both the two-point clamping and the envelope clamping modes exist, and their statics and kinematics relationships are more complex than those of the rigid underactuated gripper. In addition, in this study, the robot gripper uses full closed-loop impedance control, which requires the force sensor to be placed at the gripper's actuator end, which is not conducive to robot operation in high-risk environments. Summary of the invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a compliant under-actuated gripper and a semi-closed-loop adaptive impedance control method thereof, which can reduce the feedback dependence of the system and thereby improve the grasping accuracy of objects of different shapes and stiffnesses.

[0004] The first technical solution adopted by the present invention is: a compliant underactuated clamp, comprising a compliant clamping unit, a driving component, a driving component mover position sensor and an input force sensor, wherein the driving component mover position sensor and the input force sensor are both arranged inside the driving component, and the compliant clamping unit is connected to the driving component by a hinge, wherein:

[0005] The compliant clamping unit is used to perform two-point clamping operations and enveloping clamping operations;

[0006] The driving component is used to drive the compliant clamping unit to perform corresponding operations;

[0007] The driving component mover position sensor is used to detect the position of the driving component mover;

[0008] The input force sensor is used to detect the input force of the gripper of the compliant gripping unit.

[0009] Furthermore, the flexible clamping unit is an axisymmetric structure, and the left structure of the flexible clamping unit is composed of a left outer base flexible hinge, a left driving rod, a left lower contact auxiliary flexible hinge, a left transmission rod, a left upper contact auxiliary flexible hinge, a left main actuator rod, a left inner transmission flexible hinge, a left auxiliary actuator rod, a left inner base flexible hinge and a left base, which are connected in series in a closed loop, wherein the contact unit of the lower left contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower left contact auxiliary flexible hinge, the contact unit of the lower left contact auxiliary flexible hinge is on the right side of the hinge unit of the lower left contact auxiliary flexible hinge, the contact unit of the upper left contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower left contact auxiliary flexible hinge, and the contact unit of the upper left contact auxiliary flexible hinge is on the left upper contact auxiliary flexible hinge. On the left side of the hinge unit of the chain, the right structure of the flexible clamping unit is composed of a right outer base flexible hinge, a right driving rod, a right lower contact auxiliary flexible hinge, a right transmission rod, a right upper contact auxiliary flexible hinge, a right main actuator rod, a right inner transmission flexible hinge, a right auxiliary actuator rod, a right inner base flexible hinge and a right base, which are connected in series in a closed loop, wherein the contact unit of the right lower contact auxiliary flexible hinge is integrally connected with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right lower contact auxiliary flexible hinge is on the left side of the hinge unit of the right lower contact auxiliary flexible hinge, the contact unit of the right upper contact auxiliary flexible hinge is integrally connected with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right upper contact auxiliary flexible hinge is on the right side of the hinge unit of the right upper contact auxiliary flexible hinge.

[0010] Furthermore, it also includes:

[0011] When the compliant clamping unit is in a two-point clamping operation mode, the compliant clamping unit clamps the object through the left main actuator rod and the right main actuator rod;

[0012] When the compliant clamping unit is in the envelope clamping operation mode, the compliant clamping unit clamps the object through the left main actuating rod, the left auxiliary actuating rod, the right main actuating rod and the right auxiliary actuating rod.

[0013] Furthermore, the driving component includes a force measuring beam, a guide rail, a motor bracket, a slider, a coupling, a driving beam, a lead screw, a nut slider, a support beam, a brushless motor, a left side connecting beam, a right side connecting beam and a protective cover, wherein the brushless motor is arranged in the middle of the motor bracket and fixedly connected to the motor bracket, the motor bracket is placed inside the protective cover and fixedly connected to the protective cover, the brushless motor is connected to the lead screw through a coupling, the lead screw is arranged along the symmetry axis of the flexible clamping unit, the lead screw and the nut slider form a lead screw nut kinematic pair, and the force measuring beam is fixed to the nut slider The slider, the force measuring beam and the driving beam are fixedly connected to form a linear pair with the guide rail, the lower surface of the input force sensor is bonded to the upper surface of the force measuring beam, the force measuring surface of the input force sensor is parallel to the lower surface of the driving beam, the support beam is fixedly connected to the guide rail, the left end of the driving beam is hinged to the lower end of the left side connecting beam, the right end of the driving beam is hinged to the lower end of the right side connecting beam, the left end structure of the left driving rod is hinged to the upper end of the left side connecting beam, the right end structure of the right driving rod is hinged to the upper end of the right side connecting beam, the left base is integrally connected to the right base, and both are fixedly connected to the support beam.

[0014] The second technical solution adopted by the present invention is: a semi-closed loop adaptive impedance control method for a compliant under-driven clamp, comprising the following steps:

[0015] Initialize the compliant underactuated gripper, obtain the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component, and construct a mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper;

[0016] Based on the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component and the mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper, an equivalent parameter vector of the object to be grasped is estimated by recursive least squares method to obtain the equivalent parameter vector, which includes the equivalent stiffness, damping and mass of the object to be grasped;

[0017] The tracking modal weight coefficient is determined according to the equivalent parameter vector of the object to be grasped, and the tracking modal weight coefficient in the two-point clamping mode is corrected by the Lyapunov stability criterion.

[0018] Design the adaptive impedance controller of the compliant underactuated gripper and the control module hardware of the compliant underactuated gripper to obtain the desired jaw position;

[0019] According to the equivalent parameter vector of the object to be grasped, the tracking modal weight coefficient and the expected jaw position are input into the adaptive impedance controller to iteratively optimize the compliant under-actuated gripper until the preset convergence conditions are met, thereby realizing semi-closed-loop adaptive impedance control of the compliant under-actuated gripper.

[0020] Furthermore, the step of obtaining an equivalent parameter vector of the object to be grasped by estimating by recursive least squares method based on the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component and the mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper specifically includes:

[0021] The input force of the compliant underactuated gripper is obtained by an input force sensor and substituted into a mathematical relationship model between the gripping reaction force and the input force to obtain the gripping reaction force of the compliant underactuated gripper;

[0022] The actual position of the actuator of the driving component is obtained by the actuator position sensor of the driving component, and the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode are determined;

[0023] The clamping reaction force of the compliant underactuated gripper and the position of the actuator rod of the compliant gripper unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant gripper unit in the envelope clamping mode are estimated by the recursive least squares method to obtain the equivalent parameter vector of the object to be grasped.

[0024] Further, the step of obtaining the actual position of the driving component mover through the driving component mover position sensor and determining the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode specifically includes:

[0025] Obtain the actual position of the drive component mover;

[0026] For the two-point clamping mode, if the compliant clamping unit is in a fully driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component are constructed through geometric relationships; if the compliant clamping unit is in an under-driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component are constructed through the minimum potential energy principle;

[0027] The position of the actuator rod of the compliant clamping unit in the two-point clamping mode is calculated by combining the forward kinematics model of the two-point clamping mode of the compliant clamping unit with the forward kinematics model of the driving component and the actual position of the mover of the driving component;

[0028] Construct the forward kinematics model of the enveloping clamping mode of the compliant clamping unit;

[0029] The actual position of the mover of the driving component is input into the forward kinematics model of the envelope clamping mode of the compliant clamping unit for characterization, and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode is obtained.

[0030] Furthermore, the step of determining the tracking modal weight coefficient according to the equivalent parameter vector of the object to be grasped, and correcting the tracking modal weight coefficient in the two-point clamping mode by using the Lyapunov stability criterion specifically includes:

[0031] Set the equivalent parameter vector threshold;

[0032] If the equivalent parameter vector of the object to be grasped is less than the equivalent parameter vector threshold, the tracking mode weight coefficient is set to a first preset value, and the position tracking mode is executed;

[0033] If the equivalent parameter vector of the object to be grasped is greater than the equivalent parameter vector threshold, the tracking mode weight coefficient is set to a second preset value, and the force tracking mode is executed;

[0034] The Lyapunov stability equation of the compliant underactuated gripper in the two-point clamping mode is obtained and the tracking modal weight coefficient is corrected to obtain the corrected tracking modal weight coefficient of the compliant underactuated gripper in the two-point clamping mode.

[0035] Furthermore, the adaptive impedance controller of the designed compliant under-actuated clamp and the control module hardware of the compliant under-actuated clamp include a single-chip microcomputer and a host computer. The driving component mover position sensor transmits the position of the driving component mover to the single-chip microcomputer via a first communication method, and the input force measured by the input force sensor is transmitted to the single-chip microcomputer via a second communication method. Serial communication is adopted between the single-chip microcomputer and the host computer. The host computer executes a control algorithm, obtains the desired jaw position and sends it to the single-chip microcomputer for processing and outputs the corresponding desired mover position to the driving component, so that the driving component moves to the desired mover position and obtains the desired jaw position.

[0036] Further, according to the equivalent parameter vector of the object to be grasped, the tracking modal weight coefficient and the expected jaw position are input into the adaptive impedance controller to iteratively optimize the compliant underactuated gripper until the preset convergence condition is met, thereby realizing the step of semi-closed loop adaptive impedance control of the compliant underactuated gripper, which specifically includes:

[0037] Acquire the actual position of the actuator of the driving component when the compliant gripping unit initially contacts the object to be grasped;

[0038] Determine the position of the actuator rod of the compliant clamping unit according to the actual position of the actuator of the driving component, wherein, for the two-point clamping mode, the actual position of the actuator of the driving component is substituted into the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component, and for the envelope clamping mode, the actual position of the actuator of the driving component is substituted into the envelope clamping mode forward kinematics model of the compliant clamping unit;

[0039] Obtaining the inverse function of the numerical fitting results of the forward kinematics model of the two-point clamping mode of the compliant clamping unit and the forward kinematics model of the driving component, and constructing an inverse kinematics model under the two-point clamping mode;

[0040] For the two-point clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant underactuated clamper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant clamping unit and the inverse kinematics model in the two-point clamping mode are combined to control the brushless motor to rotate to grasp the object to be grasped;

[0041] For the envelope clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant under-actuated gripper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant gripping unit and the envelope clamping mode forward kinematics model of the compliant gripping unit are combined to control the rotation of the brushless motor to grasp the object to be grasped.

[0042] The beneficial effects of the method and device of the present invention are as follows: by adopting adaptive impedance control, semi-closed-loop control and clamping mode recognition, the clamper can adjust the control parameters in real time according to the stiffness, shape and contact condition of the grasped object to ensure the precise adjustment of the clamping force and displacement. Compared with the traditional full-closed-loop control, the semi-closed-loop control reduces the feedback dependence of the system, reduces the implementation cost and complexity, and maintains a high control accuracy and system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a structural schematic diagram of a compliant underactuated clamper of the present invention;

[0044] Figure 2 It is a schematic diagram of the steps of a semi-closed loop adaptive impedance control method for a compliant under-actuated clamper of the present invention;

[0045] Figure 3 is a partial enlarged schematic diagram of a compliant underactuated clamp provided by a specific embodiment of the present invention with the support beam removed;

[0046] Figure 4 is a schematic structural diagram of a compliant clamping unit provided in a specific embodiment of the present invention;

[0047] Figure 5It is a schematic diagram of the steps of a variable tracking mode semi-closed loop adaptive impedance control method provided by a specific embodiment of the present invention;

[0048] Figure 6 It is a schematic diagram of a pseudo-rigid body model of a compliant underactuated gripper in a two-point clamping mode and an equivalent model of a two-point clamped object provided by a specific embodiment of the present invention;

[0049] Figure 7 is a schematic diagram of a pseudo-rigid body model of a compliant underactuated gripper in an enveloping gripping mode and an enveloping gripping object provided by a specific embodiment of the present invention;

[0050] Figure 8 It is a schematic diagram of control simulation results for an object with a stiffness K of 200 N / m in a two-point clamping mode provided by a specific embodiment of the present invention;

[0051] Fig. 9 It is a schematic diagram of control simulation results for an object with a stiffness K of 1900 N / m in a two-point clamping mode provided by a specific embodiment of the present invention;

[0052] Fig.10 It is a schematic diagram of control simulation results of a variable tracking modal semi-closed loop adaptive impedance control method for a compliant underdriven clamper provided in a specific embodiment of the present invention under an envelope clamping mode.

[0053] Figure numerals: 1. flexible clamping unit; 2. right side connecting beam; 3. local enlarged structure after removing the supporting beam; 4. driving beam; 5. force measuring beam; 6. lead screw; 7. supporting beam; 8. coupling; 9. motor bracket; 10. brushless motor; 11. flange connecting sleeve; 12. input force sensor; 13. lead screw nut; 14. guide rail; 15. right main actuator rod; 16. right inner transmission flexible hinge chain; 17. right upper contact auxiliary flexible hinge chain; 18. right auxiliary actuator rod; 19. right transmission rod; 20. right lower contact auxiliary hinge chain; 21. right inner base flexible hinge chain; 22. right driving rod; 23. right outer base flexible hinge chain. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0055] Reference Figure 1The present invention provides a compliant underactuated clamp, comprising a compliant clamping unit 1, a driving component, a driving component mover position sensor and an input force sensor 12, wherein the driving component mover position sensor and the input force sensor are both arranged inside the driving component, and the compliant clamping unit and the driving component are connected by a hinge, wherein:

[0056] The compliant clamping unit is used to perform two-point clamping operations and enveloping clamping operations;

[0057] Specifically, the flexible clamping unit is an axisymmetric structure, and the left structure of the flexible clamping unit is composed of a left outer base flexible hinge, a left driving rod, a left lower contact auxiliary flexible hinge, a left transmission rod, a left upper contact auxiliary flexible hinge, a left main actuator rod, a left inner transmission flexible hinge, a left auxiliary actuator rod, a left inner base flexible hinge and a left base, which are connected in series in a closed loop, wherein the contact unit of the left lower contact auxiliary flexible hinge is integrally connected with the hinge unit of the left lower contact auxiliary flexible hinge, and the contact unit of the left lower contact auxiliary flexible hinge is on the right side of the hinge unit of the left lower contact auxiliary flexible hinge, the contact unit of the left upper contact auxiliary flexible hinge is integrally connected with the hinge unit of the left lower contact auxiliary flexible hinge, and the contact unit of the left upper contact auxiliary flexible hinge is on the left side of the hinge unit of the left upper contact auxiliary flexible hinge, The right structure of the flexible clamping unit is composed of a right outer base flexible hinge 23, a right driving rod 22, a right lower contact auxiliary flexible hinge 20, a right transmission rod 19, a right upper contact auxiliary flexible hinge 17, a right main actuator rod 15, a right inner transmission flexible hinge 16, a right auxiliary actuator rod 18, a right inner base flexible hinge 21 and a right base, which are connected in series in a closed loop, wherein the contact unit of the lower right contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower right contact auxiliary flexible hinge, and the contact unit of the lower right contact auxiliary flexible hinge is on the left side of the hinge unit of the lower right contact auxiliary flexible hinge, the contact unit of the upper right contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower right contact auxiliary flexible hinge, and the contact unit of the upper right contact auxiliary flexible hinge is on the right side of the hinge unit of the upper right contact auxiliary flexible hinge.

[0058] In this embodiment, if Figure 4As shown, the compliant clamping unit is axisymmetric, and the left half of the compliant clamping unit is composed of a left outer base compliant hinge, a left driving rod, a left lower contact auxiliary compliant hinge, a left transmission rod, a left upper contact auxiliary compliant hinge, a left main actuator rod, a left inner transmission compliant hinge, a left auxiliary actuator rod, a left inner base compliant hinge and a left base, which are connected in series in a closed loop in sequence; the contact unit of the left lower contact auxiliary compliant hinge is integrally connected with the hinge unit of the left lower contact auxiliary compliant hinge, and the contact unit of the left lower contact auxiliary compliant hinge is on the left The lower contact auxiliary flexible hinge is on the right side of the hinge unit of the lower contact auxiliary flexible hinge. At the same time, in the initial state, the distance between the contact unit of the lower left contact auxiliary flexible hinge and the left driving rod is as small as possible; the contact unit of the upper left contact auxiliary flexible hinge is integrated with the hinge unit of the lower left contact auxiliary flexible hinge, and the contact unit of the upper left contact auxiliary flexible hinge is on the left side of the hinge unit of the upper left contact auxiliary flexible hinge. At the same time, in the initial state, the distance between the contact unit of the upper left contact auxiliary flexible hinge and the left driving rod is as small as possible. The right half of the flexible clamping unit is composed of a right outer base flexible hinge, a right driving rod, a right lower contact auxiliary flexible hinge, a right transmission rod, a right upper contact auxiliary flexible hinge, a right main actuator rod, a right inner transmission flexible hinge, a right auxiliary actuator rod, a right inner base flexible hinge and a right base, which are connected in a closed loop and integrated in series in sequence; the contact unit of the right lower contact auxiliary flexible hinge is integrated with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right lower contact auxiliary flexible hinge is on the left side of the hinge unit of the right lower contact auxiliary flexible hinge. At the same time, in the initial state, the distance between the contact unit of the right lower contact auxiliary flexible hinge and the right driving rod is as small as possible; the contact unit of the right upper contact auxiliary flexible hinge is integrated with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right upper contact auxiliary flexible hinge is on the right side of the hinge unit of the right upper contact auxiliary flexible hinge. At the same time, in the initial state, the distance between the contact unit of the right upper contact auxiliary flexible hinge and the right transmission rod is as small as possible.

[0059] Among them, when the flexible clamping unit is in the two-point clamping operation mode, the flexible clamping unit clamps the object through the left main actuator rod and the right main actuator rod. When the flexible clamping unit is in the envelope clamping operation mode, the flexible clamping unit clamps the object through the left main actuator rod, the left auxiliary actuator rod, the right main actuator rod and the right auxiliary actuator rod.

[0060] The driving component is used to drive the compliant clamping unit to perform corresponding operations;

[0061] Specifically, Figure 3The figure shows a local enlarged structure 3 after the support beam is removed, and the driving components include a force measuring beam 5, a guide rail 14, a motor bracket 9, a slider, a coupling 8, a driving beam 4, a lead screw 6, a nut slider, a support beam 7, a brushless motor 10, a left side connecting beam, a right measuring surface connecting beam 2 and a flange connecting sleeve 11, wherein the brushless motor is arranged in the middle of the motor bracket and fixedly connected to the motor bracket, the motor bracket is placed inside the protective cover and fixedly connected to the protective cover, i.e., the flange connecting sleeve, the brushless motor is connected to the lead screw through a coupling, the lead screw is arranged along the symmetry axis of the flexible clamping unit, and the lead screw and the nut slider form a lead screw thread. Mother 13 kinematic pair, the force measuring beam is fixedly connected to the nut slider, the slider, the force measuring beam and the driving beam are fixedly connected to form a linear pair with the guide rail, the lower surface of the input force sensor is bonded to the upper surface of the force measuring beam, the force measuring surface of the input force sensor is parallel to the lower surface of the driving beam, the support beam is fixedly connected to the guide rail, the left end of the driving beam is hinged to the lower end of the left side connecting beam, the right end of the driving beam is hinged to the lower end of the right side connecting beam, the left end structure of the left driving rod is hinged to the upper end of the left side connecting beam, the right end structure of the right driving rod is hinged to the upper end of the right side connecting beam, the left base is integrally connected to the right base, and both are fixedly connected to the support beam.

[0062] In this embodiment, the driving component is composed of a force measuring beam, a guide rail, a motor bracket, a slider, a coupling, a driving beam, a lead screw, a nut slider, a support beam, a brushless motor, a left side connecting beam, a right measuring side connecting beam and a protective cover. The brushless motor is arranged in the middle of the motor bracket and is tightly connected to the motor bracket, and the motor bracket is placed inside the protective cover and is tightly connected to the protective cover; the brushless motor is connected to the lead screw through a coupling, and the lead screw is arranged along the symmetry axis of the flexible clamping unit; the lead screw and the nut slider form a lead screw nut motion pair, and the force beam and the nut slider are tightly connected; the slider, the force beam and the driving beam are tightly connected, and form a linear pair with the guide rail; the lower surface of the input force sensor is bonded to the upper surface of the force beam; the force measuring surface of the input force sensor is parallel to the lower surface of the driving beam, and there is a gap between the two in the initial working state; the support beam is tightly connected to the guide rail; the left end of the driving beam is hinged to the lower end of the left side connecting beam, and the right end of the driving beam is hinged to the lower end of the right side connecting beam; the structure near the left end of the left driving rod is hinged to the upper end of the left side connecting beam; the mechanism near the right end of the right driving rod is hinged to the upper end of the right side connecting beam; the left base is integrally connected to the right base, and both are tightly connected to the support beam. Brushless motor: located in the center of the motor bracket, generating an angle output. The motor bracket is located inside the protective cover and is used to fix the brushless motor; the coupling connects the brushless motor and the lead screw and is used to transmit the angular output of the brushless motor to the lead screw; the lead screw is arranged along the symmetric axis of the flexible clamping unit and forms a lead screw nut pair with the nut slider to convert the rotation of the motor into linear motion; the nut slider is driven by the lead screw to move linearly along the guide rail and convert the rotation input of the lead screw into linear displacement; the guide rail is fixed to the support beam, and the linear pair formed by the guide rail and the slider is used to guide the linear motion of the force measuring beam and the driving beam; the force measuring beam is tightly connected to the nut slider to fix the force sensor and position the nut slider The displacement of the force measuring beam is transmitted to the driving beam; the input force sensor is located on the upper surface of the force measuring beam and is used to detect the force applied to the force measuring beam; the driving beam is located in the center of the system and transmits the displacement of the force measuring beam to the compliant clamping unit through the left and right side connecting beams; the left side connecting beam and the right side connecting beam are respectively located on both sides of the driving beam and are hinged at both ends of the driving beam to transmit the displacement of the driving beam; the left driving rod and the right driving rod are respectively hinged at the upper ends of the left side connecting beam and the right side connecting beam to connect and support the structure of the compliant clamping unit; the support beam is tightly connected to the guide rail and the left and right bases to provide a supporting structure for the system.

[0063] The driving component mover position sensor is used to detect the position of the driving component mover;

[0064] The input force sensor is used to detect the input force of the gripper of the compliant gripping unit.

[0065] Reference Figure 2 , a semi-closed loop adaptive impedance control method for a compliant underactuated gripper, comprising the following steps:

[0066] S100, initializing a compliant under-actuated gripper, obtaining a relationship between an end position of the compliant under-actuated gripper and a position of a mover of a driving component, and constructing a mathematical relationship model between a clamping reaction force and an input force of the compliant under-actuated gripper;

[0067] In this embodiment, a compliant under-actuated clamp with an integrated input force sensor is provided. The clamp consists of a compliant clamping unit, a driving component, a driving component mover position sensor and an input force sensor. The driving component mover position sensor and the input force sensor are arranged in the driving component, and are respectively used to detect the position of the driving component mover and the input force of the clamp in real time.

[0068] S200, based on the relationship between the end position of the compliant under-actuated gripper and the position of the mover of the driving component and the mathematical relationship model between the clamping reaction force and the input force of the compliant under-actuated gripper, an equivalent parameter vector of the object to be grasped is estimated by recursive least squares method, and the equivalent parameter vector includes equivalent stiffness, damping and mass of the object to be grasped;

[0069] Specifically, the input force of the compliant under-actuated gripper is obtained by an input force sensor and substituted into a mathematical relationship model between the clamping reaction force and the input force for solution, thereby obtaining the clamping reaction force of the compliant under-actuated gripper; the actual position of the driving component mover is obtained by a driving component mover position sensor, and the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode are determined; the clamping reaction force of the compliant under-actuated gripper and the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode are estimated by the recursive least squares method, thereby obtaining an equivalent parameter vector of the object to be grasped.

[0070] It should be noted that based on the clamp input force and the position of the driving component mover, the equivalent stiffness of the clamped object is estimated by using the recursive least squares method and the relationship between the clamping reaction force and the clamp input force, as well as the relationship between the position of the clamp end and the position of the driving component mover, and the tracking modal weight coefficient is preliminarily selected based on the equivalent stiffness value.

[0071] In this embodiment, first, the equivalent parameter vector envir = [m, CK] of the grasped object is T , state parameter vector Assign initial values ​​to the covariance matrix P;

[0072] The mathematical relationship between the clamping reaction force of the clamp and the clamp input force is further established. In the two-point clamping mode, the expression of the clamping reaction force of the clamp is:

[0073]

[0074] In the above formula, A, B, C and I OH The expressions are:

[0075] A=1 1 l 2 (M 3C -M 4D )sin(θ 2 -θ 1 )

[0076] B=l 2 l 3 (MM 1A -M 2B )sin(θ 2 -θ 3 )

[0077] C=l 1 l 3 (M 2B -M 3C )sin(θ 3 -θ 1 )

[0078]

[0079] In the above formula, l 1 is the distance between the center of the right inner base compliant hinge and the center of the right lower contact auxiliary compliant hinge, l 2 is the distance between the center of the lower right contact auxiliary compliant hinge and the center of the upper right contact auxiliary compliant hinge, l 3 is the distance between the center of the right inner transmission hinge and the center of the right upper contact auxiliary hinge, θ i (i=1, 2, 3, 4) are the angles between the line connecting the center of the right inner base compliant hinge and the center of the right lower contact auxiliary compliant hinge, the line connecting the center of the right lower contact auxiliary compliant hinge and the center of the right upper contact auxiliary compliant hinge, the line connecting the center of the right inner transmission hinge and the center of the right upper contact auxiliary hinge, and the line connecting the center of the right inner transmission hinge and the center of the right inner base compliant hinge and the horizontal direction, respectively. m, n and M ij [(i=1, 2, 3, 4, 5), (j=A, B, C, D, E)] are:

[0080] m=D+vtanθ 4

[0081]

[0082] M ij =k f δξ j

[0083] In the above formula, k f represents the rotational stiffness of the right inner base compliant hinge.

[0084] ξ j and δξ j The expressions are:

[0085] ξ 1 =θ 1 ,ξ 2 =π-θ 2 +θ 1 ,ξ 3 =θ 2 -θ 3

[0086] ξ 4 =π-θ 4 +θ 3 ,ξ 5 =θ 4

[0087] δξ j =ξ j -ξ j0

[0088] The parameter M represents the driving torque of the compliant clamping unit and its expression is:

[0089]

[0090] Among them, μ is the transmission efficiency of the screw-nut pair, f is the torque transmitted by the screw-nut pair, s is the lead of the screw in the screw-nut pair, l 1 is the length of the right driving rod, θ is the angle between the right driving rod and the horizontal direction;

[0091] Furthermore, the clamp input force F r The expression for the force acting on the driving beam by the force measuring beam is:

[0092]

[0093] In summary, the clamping unit f and the input force F can be obtained r The mathematical relationship between .

[0094] In the enveloping clamping mode, the right main actuator l 5 Clamping reaction force F 1 With F r The mathematical relationship between f and F in the two-point clamping mode r In the enveloping clamping mode, according to the static equilibrium equation in the vertical direction of the grasped object, the clamping reaction force F on the right auxiliary actuator is 2 It can be expressed as F 1 The function is expressed as:

[0095]

[0096] In the above formula, α 1 F 1 Angle with vertical.

[0097] The input force sensor is then used to measure the clamp input force, and the measured clamp input force is substituted into the mathematical relationship between the clamp reaction force of the clamp and the clamp input force, so as to indirectly measure the clamp reaction force of the clamp in the two-point clamping or envelope clamping mode.

[0098] The actual position n of the brushless motor rotor is further measured by using the drive component mover position sensor, and then the position of the actuator rod of the compliant clamping unit in the two-point clamping mode or the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode is indirectly measured;

[0099] In the two-point clamping mode, when the left and right main actuators are not in contact with the grasped object, there are two conditions: 1 ≤θ 10 , where θ 10 is the angle between the right drive rod and the horizontal direction; in the second case, θ 1 >θ 10 .

[0100] For the first condition, the gap between the contact unit of the lower right contact auxiliary flexible hinge and the right driving rod is closed. At this time, the flexible clamping unit is in a fully driven state, and its positive kinematic model is established based on the geometric relationship; for the second condition, the gap between the contact unit of the lower right contact auxiliary flexible hinge and the right driving rod is not closed. At this time, the flexible clamping unit is in an under-driven state, and its positive kinematic model is established based on the principle of minimum potential energy.

[0101] In the first case, the forward kinematic model of the compliant gripper is:

[0102] x=v+l 4 cos(β 2 +θ 1 )

[0103] In the above formula, v is the straight-line distance between the right inner base compliant hinge and the symmetry axis of the compliant clamping mechanism, (where l 1 With l 2 are the lengths of the right drive rod and the right transmission rod respectively);

[0104] In the second condition, the output displacement x of the right main actuator is b The angle θ between the right drive rod, the right transmission rod, the right main actuator rod support part, the right auxiliary actuator rod and the horizontal direction iThe geometric relationship between (i=1,2,3,4) is:

[0105]

[0106] In the above formula, l 5 is the length of the actuator end of the right main actuator rod, θ 10 ,θ 20 ,θ 30 They are θ 1 ,θ 2 ,θ 3 The initial angle of

[0107] Furthermore, x and x b The relationship between them is:

[0108] x=x 0 -x b

[0109] Among them, x 0 =v+l 4 θ 40 .

[0110] If the left main actuator rod and the right main actuator rod are not in contact with the grasped object, at a specific θ 1 Under these conditions, θ 2 ,θ 3 It can be obtained by the following minimum potential energy principle constrained optimization model. The expression of the minimum potential energy principle constrained optimization model is:

[0111] min:Π=k f ((δθ 4 ) 2 +(δθ 1 ) 2 +(δθ 3 -δθ 4 ) 2 +(δθ 2 -δθ 3 ) 2 +(δθ 1 -δθ 2 ) 2 )

[0112] st:

[0113] (l d3 +l d2 sinθ d2h )-y=l d2 sinθ 2 +l d3 cosθ 1 --l 1 sinθ 1

[0114] l 0 cosγ 1 -l 4 cosθ 4 = l 1 cosθ 1 +l 2 cosθ 2 -l 3 cosθ 3

[0115] l 0 sinγ 1 +l 4 sinθ 4 = l 1 sinθ 1 +l 2 sinθ 2 -l 3 sinθ 3

[0116] In the above formula, k f is the rotational stiffness of the arc-shaped flexible hinge, and the angle increment δθ i (i=1,2,3,4)=θ i -θ i0 ,θ i0 is the initial angle.

[0117] If both the left main actuator rod and the right main actuator rod are in contact with the grasped object, at a specific θ 1 Under these conditions, θ 2 ,θ 3 It can be obtained by the following minimum potential energy principle constrained optimization model:

[0118] The left main actuator rod and the right main actuator rod are both in contact with the grasped object. 1 Under these conditions, θ 2 ,θ 3 It can be obtained by the following minimum potential energy principle constrained optimization model:

[0119] min:

[0120] st:v+l 4 cosθ 4 -l op5 cos(π-(θ 3 -β 1 ))-Rsin(π-(θ 3 +β 1 ))=0

[0121] l 4 sinθ4 +l OH sin(π-(θ 3 +β 1 ))-Rcos(π-(θ 3 +β 1 ))-D=0

[0122] l 0 cosγ 1 -l 4 cosθ 4 = l 1 cosθ 1 +l 2 cosθ 2 -l 3 cosθ 3

[0123] l 0 sinγ 1 +l 4 sinθ 4 = l 1 sinθ 1 +l 2 sinθ 2 -l 3 sinθ 3

[0124] In the above formula, S is the movement distance of the contact point between the right main actuator rod and the grasped object, β1 is the angle between the actuator section and the support section of the right main actuator rod, and α is the angle between f and the displacement of the contact point between the right main actuator rod and the grasped object.

[0125] Using the optimization results of the above constrained optimization model, we can numerically fit the θ 2 ,θ 3 Each with θ 1 The mathematical relationship of x and x is combined with the geometric relationship of the second case mentioned above. b The relationship between θ and 1 Calculate the forward kinematic model of x;

[0126] In the envelope clamping mode, the equivalent position of the actuator rod of the compliant clamping unit is determined by the corresponding value x of the compliant clamping unit in the two-point clamping mode in the envelope clamping mode. t2 Combining n with the forward kinematics model of the compliant clamping unit in the enveloping clamping mode and the forward kinematics model of the driving component, x is calculated. t2 .

[0127] Parameters x and θ 2 ,θ 3 The relationship can be obtained from the geometric relationship:

[0128]

[0129] In the above formula, l 5 Indicates the length of the right main actuator end, and at a specific θ 1 Under these conditions, θ 2 ,θ 3 It can be obtained by the following minimum potential energy principle constrained optimization model.

[0130] Based on the above, in this enveloping clamping mode, the two contact forces F 2 and F 1 They act on the auxiliary actuator rod and the main actuator rod respectively. Therefore, the minimum potential energy principle formula at this time is:

[0131] min:

[0132]

[0133] st:Dcosθ 4 +vsinθ 4 -R=0

[0134] l 0 cosγ 1 -l 4 cosθ 4 = l 1 cosθ 1 +l 2 cosθ 2 -l 3 cosθ 3

[0135] l 0 sinγ 1 +l 4 sinθ 4 = l 1 sinθ 1 +l 2 sinθ 2 -l 3 sinθ 3

[0136] v+l 4 cosθ 4 -l op5 cos(π-(θ 3 +β 1 ))-Rsin(π-(θ 3 +β 1 ))=0

[0137] l 4 sinθ 4 +lOH sin(π-(θ 3 +β 1 ))-Rcos(π-(θ 3 +β 1 ))-D=0

[0138] Using the optimization results of the above constrained optimization model, we can numerically fit the θ 2 ,θ 3 Each with θ 1 The mathematical relationship between x and θ can be derived by combining the geometric relationship under the aforementioned enveloping clamping mode. 1 The explicit relationship between . Let x in the envelope clamping mode be x te , and x t2 With x te The mathematical relationship is:

[0139] x t2 =x te +(x t2i -x tei )

[0140] In the above formula, x t2i Indicates the x value when the left main actuator rod and the right main actuator rod initially contact the grasped object in the two-point clamping mode; x tei Indicates the x value when the left main actuator rod, the right main actuator rod, the left auxiliary actuator rod, and the right auxiliary actuator rod initially contact the grasped object in the enveloping clamping mode;

[0141] Combine x te With θ 1 The explicit relationship between t2 With x te The mathematical relationship between θ and 1 Calculate x t2 The forward kinematic model of .

[0142] The recursive least squares method is used to estimate the equivalent parameters of the grasped object: In the two-point clamping mode, for each iteration step z, the expression of the equivalent parameters of the grasped object estimated by the recursive least squares method is:

[0143] envir(z)=envir(z-1)+L(z)[f(z)-r(z)envir(z-1)]

[0144] Where L(z) and r(z) are:

[0145] L(z)=P(z-1)r T [1+r(z)P(z-1)r T (z)] -1

[0146] P(z)=[I 3 -L(z)r(z)P(z-1)]

[0147]

[0148] In the above formula, I 3 represents the identity matrix of size 3×3, P(0)=p 0 I 3 , p 0 =10 6 .

[0149] In the envelope clamping mode, it is necessary to replace f(z) with the magnitude of the clamping reaction force on the right main clamping rod in iteration step z, and replace x with x. t2 .

[0150] When envir(z) and envir(z-1) meet the following conditions, envir(z) is output and parameter estimation is completed. The expression of the condition is:

[0151]

[0152] In the above formula, diff e (z)=|envir(z-1)-envir(z)|.

[0153] S300, determining a tracking modal weight coefficient according to an equivalent parameter vector of the object to be grasped, and correcting the tracking modal weight coefficient in the two-point clamping mode by using a Lyapunov stability criterion;

[0154] Specifically, the actual position of the actuator of the driving component is obtained; for the two-point clamping mode, if the compliant clamping unit is in a fully driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the positive kinematics model of the driving component are constructed through geometric relationships; if the compliant clamping unit is in an under-driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the positive kinematics model of the driving component are constructed through the principle of minimum potential energy; the position of the actuator rod of the compliant clamping unit in the two-point clamping mode is calculated by combining the two-point clamping mode forward kinematics model of the compliant clamping unit with the positive kinematics model of the driving component and the actual position of the actuator of the driving component; the envelope clamping mode forward kinematics model of the compliant clamping unit is constructed; the actual position of the actuator of the driving component is input into the envelope clamping mode forward kinematics model of the compliant clamping unit for characterization, and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode is obtained.

[0155] First of all, it should be noted that the initial selection of the tracking modal weight coefficient is carried out as follows: when the equivalent stiffness of the grasped object is less than 600N / m, the position tracking weight coefficient Q 1 The initial value is 50000. At this time, the position tracking weight is large enough compared to the force tracking weight, and the position tracking mode is executed. When the equivalent stiffness of the grasped object is greater than or equal to 600N / m, Q 1 The initial selection is 50. At this time, the position tracking weight is not large enough compared to the force tracking weight, and the force tracking mode is executed.

[0156] In addition, in this embodiment, in the two-point clamping mode, the state equation of the grasped object is rewritten as:

[0157]

[0158] In the formula, x e =xx d , (where x d , represents the desired distance between the end of the right main actuator and the symmetry axis of the compliant clamping unit, the desired velocity of the end of the right main actuator, and the desired acceleration of the end of the right main actuator), respectively, k 0 , k 1 The state feedback matrix K = [k 0 , k 1 ] T elements.

[0159] At this time, the Lyapunov equation of the system is:

[0160]

[0161] In the formula,

[0162]

[0163] make and The Lyapunov equation is transformed into:

[0164]

[0165] According to this equation, the determinant of P can be further obtained as:

[0166]

[0167] In order to make the system stable, P needs to be positive definite, then P needs to satisfy the following conditions:

[0168] p1 1 >0.detP>0

[0169] The position tracking weight coefficient is fine-tuned until the obtained state feedback matrix K satisfies the above two inequalities.

[0170] S400, designing an adaptive impedance controller of the compliant under-actuated gripper and a control module hardware of the compliant under-actuated gripper to obtain a desired jaw position;

[0171] Specifically, the adaptive impedance controller of the compliant under-actuated clamp and the control module hardware of the compliant under-actuated clamp are designed to include a single-chip microcomputer and a host computer. The driving component mover position sensor transmits the position of the driving component mover to the single-chip microcomputer through a first communication method, and the input force measured by the input force sensor is transmitted to the single-chip microcomputer through a second communication method. A serial port communication method is adopted between the single-chip microcomputer and the host computer. The host computer executes a control algorithm, obtains the desired jaw position and sends it to the single-chip microcomputer for processing and outputs the corresponding desired mover position to the driving component, so that the driving component moves to the desired mover position and obtains the desired jaw position.

[0172] More specifically, in this embodiment, an adaptive impedance controller of the clamp is designed respectively, and then the control module hardware of the compliant under-actuated clamp is set, including a single-chip microcomputer and a host computer. The actuator position sensor of the driving component transmits the position of the actuator of the driving component to the single-chip microcomputer via CAN communication, and the input force measured by the input force sensor is transmitted to the single-chip microcomputer via RS485 communication. The single-chip microcomputer and the host computer use serial communication. The host computer is used to execute the control algorithm, and the desired jaw position is sent to the single-chip microcomputer for processing and the corresponding desired actuator position is output to the driving component, so that the driving component moves to the desired actuator position.

[0173] S500. According to the equivalent parameter vector of the object to be grasped, the tracking modal weight coefficient and the expected jaw position are input into the adaptive impedance controller to iteratively optimize the compliant under-actuated gripper until the preset convergence condition is met, thereby realizing semi-closed-loop adaptive impedance control of the compliant under-actuated gripper.

[0174] Specifically, the actual position of the mover of the driving component when the compliant clamping unit initially contacts the object to be grasped is obtained;

[0175] The position of the actuator rod of the compliant clamping unit is determined according to the actual position of the mover of the driving component, wherein, for the two-point clamping mode, the actual position of the mover of the driving component is substituted into the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component, and for the envelope clamping mode, the actual position of the mover of the driving component is substituted into the envelope clamping mode forward kinematics model of the compliant clamping unit; the inverse function of the numerical fitting results of the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component is obtained, and an inverse kinematics model under the two-point clamping mode is constructed;

[0176] For the two-point clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant under-actuated gripper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant clamping unit is combined with the inverse kinematics model in the two-point clamping mode to control the rotation of the brushless motor to grasp the object to be grasped.

[0177] For the envelope clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant under-actuated gripper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant gripping unit and the envelope clamping mode forward kinematics model of the compliant gripping unit are combined to control the rotation of the brushless motor to grasp the object to be grasped.

[0178] In this embodiment, based on the magnitude of the clamp input force detected by the input force sensor, the actual position of the drive component mover detected by the drive component mover position sensor, the expected jaw position, the expected clamping reaction force, the tracking modal weight coefficient and the clamping mode, combined with the relationship between the clamping reaction force and the input force of the clamp in the corresponding clamping mode and the forward and inverse kinematics relationship, the clamp is controlled using an adaptive impedance control model in the corresponding clamping mode, and the deviation between the actual jaw position and the expected jaw position and the expected jaw position for the next step are calculated.

[0179] Record the reading of the input force sensor of the compliant underactuated gripper during the uniform speed and no-load gripping process; when the reading of the input force sensor increases relative to its reading during the uniform speed and no-load gripping process, the left main actuator rod and the right main actuator rod make initial contact with the grasped object, or the left main actuator rod, the right main actuator rod, the left auxiliary actuator rod, and the right auxiliary actuator rod make initial contact with the grasped object together, and the specific initial contact type can be detected by machine vision; the driving component mover position sensor records the actual position of the driving component mover at the time of initial contact;

[0180] In the two-point clamping mode, the actual position of the actuator of the driving component at the initial contact is substituted into the forward kinematics model in the two-point clamping mode and the forward kinematics model of the driving component to calculate x t2i ;

[0181] In the enveloping clamping mode, the actual position of the driving component mover at the initial contact is substituted into the forward kinematics model in the enveloping clamping mode to calculate x tei .

[0182] Calculate the inverse function of the numerical fitting result of the forward kinematics model in the two-point clamping mode to form the inverse kinematics model in the two-point clamping mode;

[0183] In the two-point clamping mode, the fine-tuned position tracking weight coefficient Q 1 Substitute the force tracking weight coefficient r = 1 into the cost function In the formula (where Δf is the difference between the clamping reaction force f of the gripper and the expected value of the clamping reaction force of the gripper), the above cost function is minimized in combination with the state space equation coefficient matrix of the grasped object to obtain the state feedback matrix K; the input force of the gripper detected by the input force sensor is substituted into the relationship between the clamping reaction force and the input force of the gripper in the two-point clamping mode to indirectly measure the clamping reaction force of the gripper; the obtained K, the clamping reaction force of the gripper and the expected value of the clamping reaction force of the gripper in the two-point clamping mode are substituted into the linear quadratic regulator u=Δf, solve the linear quadratic regulator to get x, combine the inverse kinematics model in the two-point clamping mode and the inverse kinematics model of the driving component to get n and control the rotation of the brushless motor; x e With x d The result of the addition is used as the x of the next iteration step. d ;

[0184] In envelope clamp mode, first apply the following two corrections, and then use the control in two-point clamp mode for impedance control:

[0185] First correction, f and f d Converted into clamping reaction force F acting on the right main actuator rod 1 and its expected value F 1d In the envelope clamping mode, force tracking is performed on the envelope clamping force. esum With F 1 The analytical relationship of the enveloping clamping force and the expected value F esumd With F 1 The expected value F 1d The analytical relationships are:

[0186]

[0187] The second correction is to use x t2 With x te The mathematical relationship converts the x value in the envelope clamping mode to the corresponding x value in the two-point clamping mode until the control convergence condition is met, where the control convergence condition is:

[0188]

[0189] In summary, Figure 5is a control block diagram of a semi-closed loop impedance control method for a compliant under-actuated clamper according to an embodiment of the present invention, wherein f d is the desired jaw output force, x d is the desired jaw output displacement, x t is the expected next jaw displacement, n d is the desired motor rotor position, F r is the measured current input force, n is the current motor rotor position, F c is the calculated jaw output reaction force, x, are the current displacement, velocity and acceleration of the jaws, respectively; m, c, and K are the equivalent mass, damping, and stiffness of the object being grasped, respectively.

[0190] The impedance model is obtained by analyzing the pseudo-rigid body model simulated by the compliant underactuated gripper and the discrete spring, as shown in Figure 6 The pseudo-rigid body model of the compliant underactuated gripper in two-point gripping mode and its equivalent model of the gripper are shown. At this time, it is assumed that the gripped object is symmetrical with respect to the center axis of the gripper. The mass-spring-damper model system shown is subjected to a separate force analysis, where f is the force applied to the actuator by the mass-spring-damper system in the opposite direction, which is equal to and opposite to the actual gripping force of the jaws. After analysis, the dynamic model of the gripped object is:

[0191]

[0192] By introducing trajectory tracking and clamping force tracking into the above model, the control law of the impedance controller is obtained:

[0193]

[0194] x e =xx d

[0195]

[0196] where x d , They represent the expected displacement, expected velocity and expected acceleration of the contact position, respectively, Δf = ff d Refers to the actual jaw clamping reaction force f and the expected contact force f d The deviation between .

[0197] In the enveloping clamping mode, the pseudo-rigid body model of the compliant underactuated gripper and its equivalent model of the clamped object are as follows: Figure 7 As shown in the figure, the object to be grasped is assumed to be a cylinder. The model converts the contact position when the clamping radius is R into the contact position when the two-point clamping length is 2R. When the compliant gripper is used for enveloping gripping, fesum The force tracking mode is used to measure the gripping force of the gripper on the object to ensure gripping stability.

[0198] The simulation software MATLAB-Simulink is used to verify the performance of the semi-closed loop adaptive impedance control method of the present invention.

[0199] In the two-point clamping mode, the simulation results are as follows Figure 8 and Fig. 9 As shown, the stiffness K of the grasped object is defined as 200 N / m, the system adopts the position tracking mode, reaches the desired position after 2.1 s, and the steady-state error is 1.1%; the stiffness K of the grasped object is defined as 1900 N / m, the system adopts the force control mode, the adjustment time is 1.8 s, and the error is kept below 4%.

[0200] In the envelope clamping mode, the simulation results are as follows Fig.10 As shown, the radius of the grasped object is defined as 30 mm, the stiffness K is 2000 N / m, the system adopts force control mode, the adjustment time is 2.3 s, and the error is kept below 3%.

[0201] The contents of the above method embodiments are all applicable to the present system embodiments. The functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0202] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A compliant underactuated gripper, characterized in that: The invention comprises a compliant clamping unit, a driving component, a driving component mover position sensor and an input force sensor, wherein the driving component mover position sensor and the input force sensor are both arranged inside the driving component, and the compliant clamping unit and the driving component are connected by a hinge, wherein: The compliant clamping unit is used to perform two-point clamping operations and enveloping clamping operations; The driving component is used to drive the compliant clamping unit to perform corresponding operations; The driving component mover position sensor is used to detect the position of the driving component mover; The input force sensor is used to detect the input force of the gripper of the compliant gripping unit.

2. A compliant underactuated gripper according to claim 1, characterized in that: The flexible clamping unit is an axisymmetric structure, and the left structure of the flexible clamping unit is composed of a left outer base flexible hinge, a left driving rod, a left lower contact auxiliary flexible hinge, a left transmission rod, a left upper contact auxiliary flexible hinge, a left main actuator rod, a left inner transmission flexible hinge, a left auxiliary actuator rod, a left inner base flexible hinge and a left base, which are connected in series in a closed loop, wherein the contact unit of the lower left contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower left contact auxiliary flexible hinge, the contact unit of the lower left contact auxiliary flexible hinge is on the right side of the hinge unit of the lower left contact auxiliary flexible hinge, the contact unit of the upper left contact auxiliary flexible hinge is integrally connected with the hinge unit of the lower left contact auxiliary flexible hinge, and the contact unit of the upper left contact auxiliary flexible hinge is on the right side of the hinge unit of the lower left contact auxiliary flexible hinge. On the left side of the hinge unit, the right structure of the flexible clamping unit is composed of a right outer base flexible hinge, a right driving rod, a right lower contact auxiliary flexible hinge, a right transmission rod, a right upper contact auxiliary flexible hinge, a right main actuator rod, a right inner transmission flexible hinge, a right auxiliary actuator rod, a right inner base flexible hinge and a right base, which are connected in series in a closed loop, wherein the contact unit of the right lower contact auxiliary flexible hinge is integrally connected with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right lower contact auxiliary flexible hinge is on the left side of the hinge unit of the right lower contact auxiliary flexible hinge, the contact unit of the right upper contact auxiliary flexible hinge is integrally connected with the hinge unit of the right lower contact auxiliary flexible hinge, and the contact unit of the right upper contact auxiliary flexible hinge is on the right side of the hinge unit of the right upper contact auxiliary flexible hinge.

3. A compliant underactuated gripper according to claim 2, characterized in that: Also includes: When the compliant clamping unit is in a two-point clamping operation mode, the compliant clamping unit clamps the object through the left main actuator rod and the right main actuator rod; When the compliant clamping unit is in the envelope clamping operation mode, the compliant clamping unit clamps the object through the left main actuating rod, the left auxiliary actuating rod, the right main actuating rod and the right auxiliary actuating rod.

4. A compliant underactuated gripper according to claim 3, characterized in that: The driving component includes a force measuring beam, a guide rail, a motor bracket, a slider, a coupling, a driving beam, a lead screw, a nut slider, a support beam, a brushless motor, a left side connecting beam, a right side connecting beam and a protective cover, wherein the brushless motor is arranged in the middle of the motor bracket and fixedly connected to the motor bracket, the motor bracket is placed inside the protective cover and fixedly connected to the protective cover, the brushless motor is connected to the lead screw through a coupling, the lead screw is arranged along the symmetry axis of the flexible clamping unit, the lead screw and the nut slider form a lead screw nut kinematic pair, and the force measuring beam is fixedly connected to the nut slider After the slider, the force measuring beam and the driving beam are fixedly connected, they form a linear pair with the guide rail. The lower surface of the input force sensor is bonded to the upper surface of the force measuring beam. The force measuring surface of the input force sensor is parallel to the lower surface of the driving beam. The support beam is fixedly connected to the guide rail. The left end of the driving beam is hinged to the lower end of the left side connecting beam, and the right end of the driving beam is hinged to the lower end of the right side connecting beam. The left end structure of the left driving rod is hinged to the upper end of the left side connecting beam, and the right end structure of the right driving rod is hinged to the upper end of the right side connecting beam. The left base is integrally connected to the right base, and both are fixedly connected to the support beam.

5. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper, characterized in that: The following steps are involved: Initialize the compliant underactuated gripper, obtain the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component, and construct a mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper; Based on the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component and the mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper, an equivalent parameter vector of the object to be grasped is estimated by recursive least squares method to obtain the equivalent parameter vector, which includes the equivalent stiffness, damping and mass of the object to be grasped; The tracking modal weight coefficient is determined according to the equivalent parameter vector of the object to be grasped, and the tracking modal weight coefficient in the two-point clamping mode is corrected by the Lyapunov stability criterion. Design the adaptive impedance controller of the compliant underactuated gripper and the control module hardware of the compliant underactuated gripper to obtain the desired jaw position; According to the equivalent parameter vector of the object to be grasped, the tracking modal weight coefficient and the expected jaw position are input into the adaptive impedance controller to iteratively optimize the compliant under-actuated gripper until the preset convergence conditions are met, thereby realizing semi-closed-loop adaptive impedance control of the compliant under-actuated gripper.

6. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper according to claim 5, characterized in that: The step of obtaining the equivalent parameter vector of the object to be grasped by estimating by recursive least squares method based on the relationship between the end position of the compliant underactuated gripper and the position of the actuator of the driving component and the mathematical relationship model between the clamping reaction force and the input force of the compliant underactuated gripper specifically includes: The input force of the compliant underactuated gripper is obtained by an input force sensor and substituted into a mathematical relationship model between the gripping reaction force and the input force to obtain the gripping reaction force of the compliant underactuated gripper; The actual position of the actuator of the driving component is obtained by the actuator position sensor of the driving component, and the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode are determined; The clamping reaction force of the compliant underactuated gripper and the position of the actuator rod of the compliant gripper unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant gripper unit in the envelope clamping mode are estimated by the recursive least squares method to obtain the equivalent parameter vector of the object to be grasped.

7. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper according to claim 6, characterized in that: The step of obtaining the actual position of the driving component mover through the driving component mover position sensor and determining the position of the actuator rod of the compliant clamping unit in the two-point clamping mode and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode specifically includes: Obtain the actual position of the drive component mover; For the two-point clamping mode, if the compliant clamping unit is in a fully driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component are constructed through geometric relationships; if the compliant clamping unit is in an under-driven state, the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component are constructed through the minimum potential energy principle; The position of the actuator rod of the compliant clamping unit in the two-point clamping mode is calculated by combining the forward kinematics model of the two-point clamping mode of the compliant clamping unit with the forward kinematics model of the driving component and the actual position of the mover of the driving component; Construct the forward kinematics model of the enveloping clamping mode of the compliant clamping unit; The actual position of the mover of the driving component is input into the forward kinematics model of the envelope clamping mode of the compliant clamping unit for characterization, and the equivalent position of the actuator rod of the compliant clamping unit in the envelope clamping mode is obtained.

8. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper according to claim 7, characterized in that: The step of determining the tracking modal weight coefficient according to the equivalent parameter vector of the object to be grasped, and correcting the tracking modal weight coefficient in the two-point clamping mode by using the Lyapunov stability criterion specifically includes: Set the equivalent parameter vector threshold; If the equivalent parameter vector of the object to be grasped is less than the equivalent parameter vector threshold, the tracking mode weight coefficient is set to a first preset value, and the position tracking mode is executed; If the equivalent parameter vector of the object to be grasped is greater than the equivalent parameter vector threshold, the tracking mode weight coefficient is set to a second preset value, and the force tracking mode is executed; The Lyapunov stability equation of the compliant underactuated gripper in the two-point clamping mode is obtained and the tracking modal weight coefficient is corrected to obtain the corrected tracking modal weight coefficient of the compliant underactuated gripper in the two-point clamping mode.

9. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper according to claim 8, characterized in that: The adaptive impedance controller of the designed compliant under-actuated clamp and the control module hardware of the compliant under-actuated clamp include a single-chip microcomputer and a host computer. The driving component mover position sensor transmits the position of the driving component mover to the single-chip microcomputer via a first communication method, and the input force measured by the input force sensor is transmitted to the single-chip microcomputer via a second communication method. Serial communication is adopted between the single-chip microcomputer and the host computer. The host computer executes a control algorithm, obtains the desired jaw position and sends it to the single-chip microcomputer for processing, and outputs the corresponding desired mover position to the driving component, so that the driving component moves to the desired mover position and obtains the desired jaw position.

10. A semi-closed loop adaptive impedance control method for a compliant underactuated gripper according to claim 9, characterized in that: The step of inputting the tracking modal weight coefficient and the expected jaw position into the adaptive impedance controller according to the equivalent parameter vector of the object to be grasped to iteratively optimize the compliant underactuated gripper until the preset convergence condition is met to realize the semi-closed loop adaptive impedance control of the compliant underactuated gripper specifically includes: Acquire the actual position of the actuator of the driving component when the compliant gripping unit initially contacts the object to be grasped; Determine the position of the actuator rod of the compliant clamping unit according to the actual position of the actuator of the driving component, wherein, for the two-point clamping mode, the actual position of the actuator of the driving component is substituted into the two-point clamping mode forward kinematics model of the compliant clamping unit and the forward kinematics model of the driving component, and for the envelope clamping mode, the actual position of the actuator of the driving component is substituted into the envelope clamping mode forward kinematics model of the compliant clamping unit; Obtaining the inverse function of the numerical fitting results of the forward kinematics model of the two-point clamping mode of the compliant clamping unit and the forward kinematics model of the driving component, and constructing an inverse kinematics model under the two-point clamping mode; For the two-point clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant underactuated clamper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant clamping unit and the inverse kinematics model in the two-point clamping mode are combined to control the brushless motor to rotate to grasp the object to be grasped; For the envelope clamping mode, the corrected tracking modal weight coefficient is substituted into the cost function, and combined with the state space equation coefficient matrix of the object to be grasped, the cost function is minimized to obtain the state feedback matrix, and the clamping reaction force, state feedback matrix and expected jaw position of the compliant under-actuated gripper are input into the linear quadratic regulator for solution. Based on the solution result, the position of the actuator rod of the compliant gripping unit and the envelope clamping mode forward kinematics model of the compliant gripping unit are combined to control the rotation of the brushless motor to grasp the object to be grasped.

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