Robotic system for moving a payload with minimal payload sway and improved positioning accuracy

Abstract

The invention relates to a robotic system for moving a payload with minimal payload sway and improved positioning accuracy. The robotic system for use with a payload includes a robot, a passive compliant mechanism, a position sensor, and an electronic control unit (ECU). Actuated joints of the robot provide actuated degrees of freedom (DOF) to the robotic system. The compliant mechanism is connected to the robot and the payload and has non-actuated joints that provide non-actuated DOF to the robotic system. The sensor measures joint positions of the joints. The ECU has a trajectory generator block that generates a payload trajectory signal in response to dynamic control inputs and an impedance control unit (ICU) that applies damping and stiffness parameters to the payload trajectory signal to generate an initial velocity command. A static friction compensation block allows the robotic system to generate a velocity offset and apply the velocity offset to the initial velocity command to produce a final velocity command for the robot.

Description

Background Technology

[0001] Manufacturing operations typically require human operators to interact with parts, tools, or other payloads within a defined workspace. For example, during vehicle assembly tasks, relatively heavy workpieces such as gearboxes, engines, or electric generator units may sometimes need to be moved within the workspace. The workload associated with positioning such payloads has traditionally been borne by the operator and lifting aids employed within the workspace, such as chains, jacks, or cranes. In modern workplaces, the associated workloads have been significantly reduced, and manufacturing efficiency and throughput have increased, thanks to numerous automation solutions. Underactuated robotic systems are one such automation solution.

[0002] In a typical underactuated robotic system, the robot is connected to a compliance mechanism as defined herein. The robot's actuated joints collectively provide the robotic system with multiple rotational and / or translational degrees of freedom (DOF). Various rotational, omnidirectional, sliding, or pivoting joints are driven by one or more corresponding joint actuators and are therefore considered "active" joints. The compliance mechanism, in itself, can be implemented as, for example, an articulated compliance mechanism or a suspended cable system. The constituent joints of the compliance mechanism are unactuated and therefore not driven by corresponding joint actuators. Thus, the compliance mechanism provides the robotic system with passive / unactuated DOF and remains free to move in response to the robot's dynamic actions and possible direct interactions with the operator. As a result, when external forces are applied to the payload or the compliance mechanism, an increased compliance, in the form of decreasing stiffness, is provided along the kinetic chain extending between the robot and the compliance mechanism. Summary of the Invention

[0003] This document discloses a robotic system for use, for example, in a manufacturing facility or assembly plant, for moving or positioning a payload. The construction of the robotic system, as detailed herein, and particularly the programming and hardware construction of the associated electronic control unit (ECU), are designed to eliminate payload swaying and improve payload positioning accuracy. Therefore, the various hardware solutions, control methods, and associated computer-readable storage-based implementations of this teaching aim to improve upon existing techniques for controlling underactuated robotic systems in the face of static friction (“stiction”) forces.

[0004] As used herein, the terms “compliant,” “compliant,” “compliantly,” and similar terms refer to the use of rotational, translational, omnidirectional, or other joints suitable for the application as flexible / non-rigid joints, or possibly other joint configurations such as spherical or parallelogram / quadrilateral joints, which together enable the transmission of force and motion. Furthermore, this control solution is based in part on the principle of underactuation. As used herein and in the general art, the term “underactuated” refers to the use of a tandem arrangement in which the actuated robot is coupled in series with a non-actuated compliant mechanism such that the actuation DOF is less than the sum of the control degrees of freedom (DOF) of the robot system.

[0005] In one possible embodiment, the robot system includes a robot, a compliant mechanism connected to the robot, a payload coupled to the compliant mechanism, and an ECU. The ECU communicates with the robot and with a set of position sensors. The robot, as envisioned herein, can be implemented differently as a multi-axis serial robot, such as, but not limited to, a 6-axis industrial robot, or an elevated powered track system or similar trolley / platform. Thus, the robot includes multiple actively controlled / actuated joints that provide multiple actuation DOFs for the robot system.

[0006] In itself, the compliant mechanism comprises multiple non-actuated joints that collectively provide multiple non-actuated points of view (DOFs) for the robotic system. Position sensors are configured to measure the joint positions of both actuated and non-actuated joints and output the measured joint positions as electronic joint position signals. At least one position sensor may be used for each non-actuated DOF of the compliant mechanism. The payload, which can be connected to the compliant mechanism via its end effector, may be implemented as, for example, a part or section, a tool, a fixture, or another object to be moved and / or positioned within a defined workspace by the robotic system.

[0007] The ECU communicates with various position sensors via wired and / or wireless means. In response to measured joint positions, and the number, type, and / or configuration of various non-actuated joints relative to the actuated joints, the ECU selectively controls the position of the robot's actuated joints. The ECU achieves this control objective through programmed control logic, represented herein as a corresponding logic / hardware block designed to eliminate payload sway, minimize position errors, and compensate for undesirable static friction forces in the aforementioned kinematic chain.

[0008] According to a non-limiting exemplary embodiment, a robotic system for use with a payload includes a robot, a compliant mechanism, position sensors, and an ECU. The robot has actuated joints that collectively provide multiple actuated points of view (DOF) for the robotic system. The compliant mechanism, coupled in series with the robot and connectable to the payload, includes non-actuated joints that collectively provide multiple non-actuated DOFs for the robotic system. The position sensors are collectively configured to measure the corresponding joint positions of the actuated and non-actuated joints.

[0009] In this embodiment, the ECU communicates with the robot and position sensors and is programmed to have a trajectory generator block operable to generate a payload trajectory signal in response to at least one dynamic control input. The ECU is also programmed to have: an impedance control unit (ICU) configured to apply predetermined damping and stiffness parameters to the payload trajectory signal to generate an initial velocity control signal; and a static friction compensation block configured to allow the robot system to generate a velocity offset and apply this velocity offset to the initial velocity control signal to generate a final velocity control signal. The ECU is operable to transmit the final velocity control signal to the robot, thereby causing the robot to move the payload.

[0010] Dynamic control inputs may include the maximum permissible speed and / or acceleration of the payload and the robot. In this case, the ECU is configured to generate a payload trajectory signal such that the actual speed and / or acceleration of the payload and the robot does not exceed the maximum permissible acceleration.

[0011] A static friction compensation block can be used to process the maximum displacement of a compliant mechanism via a saturation block, wherein the saturation block is configured to apply maximum and minimum limits to the maximum displacement to generate a constrained displacement value. The static friction compensation block may also include a low-pass filter operable to receive the constrained displacement value and a cutoff frequency setting, and to use the constrained displacement value and cutoff frequency setting to generate a velocity offset.

[0012] The ICU can be optionally configured to provide an overdamped response and prevent speed overshoot of the robot and payload.

[0013] This document also discloses a method for controlling a robotic system used with a payload. An embodiment of the method includes connecting a compliant mechanism in series with a robot and connecting a payload to the compliant mechanism. As described above, the compliant mechanism has non-actuated joints that collectively provide multiple non-actuated DOFs for the robotic system, while the robot includes actuated joints that collectively provide multiple actuated DOFs for the robotic system. The method includes measuring the corresponding joint positions of the actuated and non-actuated joints using a set of position sensors. The method further includes generating a payload trajectory signal via an ECU using a trajectory generator block in response to at least one dynamic control input, and applying predetermined damping and stiffness parameters to the payload trajectory signal via an ECU to generate an initial speed control signal. This exemplary embodiment of the method also includes generating a speed offset using a static friction compensation block of the ECU, applying the speed offset to the initial speed control signal to generate a final speed control signal, and transmitting the final speed control signal to the robot to thereby move the payload.

[0014] Another aspect disclosed in this subject matter includes a computer-readable storage medium having instructions recorded thereon that can be executed by a processor of an electronic control system of a robot system having compliant mechanisms connected to the robot and a payload, as described above. Execution of these instructions causes the processor to perform the methods outlined above.

[0015] The present invention also includes the following technical solutions.

[0016] Option 1. A robotic system for use with a payload, comprising: A robot with actuated joints, which together provide multiple actuation degrees of freedom (DOF) for the robot system. A compliant mechanism coupled in series with the robot and capable of being connected to the payload, the compliant mechanism having non-actuated joints that collectively provide multiple non-actuated dots of flight (DOF) for the robot system; A set of position sensors, collectively configured to measure the corresponding joint positions of the actuated and non-actuated joints; and An electronic control unit (ECU) that communicates with the robot and the set of position sensors, wherein the ECU is programmed to have: A trajectory generator block that is operable to generate a payload trajectory signal in response to at least one dynamic control input; An impedance control unit (ICU) is configured to apply predetermined damping and stiffness parameters to the payload trajectory signal to generate an initial velocity control signal; and A static friction compensation block is configured to allow the robot system to generate a speed offset and apply the speed offset to the initial speed control signal to produce a final speed control signal, wherein the ECU is operable to transmit the final speed control signal to the robot to thereby cause the robot to move the payload.

[0017] Option 2. The robot system according to Option 1, wherein the at least one dynamic control input includes the payload and the maximum permissible speed of the robot, and wherein the ECU is configured to generate the payload trajectory signal such that the actual speed of the payload and the robot does not exceed the maximum permissible speed.

[0018] Option 3. The robot system according to Option 1, wherein the at least one dynamic control input includes the payload and the maximum permissible acceleration of the robot, and wherein the ECU is configured to generate the payload trajectory signal such that the actual acceleration of the payload and the robot does not exceed the maximum permissible acceleration.

[0019] Option 4. The robot system according to Option 1, wherein the static friction compensation block is configured to calculate the velocity offset based on the maximum displacement of the compliance mechanism.

[0020] Option 5. The robot system according to Option 4, wherein the static friction compensation block is configured to handle the maximum displacement of the compliance mechanism by means of a saturation block, the saturation block being configured to apply maximum and minimum limits to the maximum displacement to generate a constrained displacement value.

[0021] Option 6. The robot system according to Option 5, wherein the static friction compensation block includes a low-pass filter, the low-pass filter being operable to receive the restricted displacement value and the cutoff frequency setting, and using the restricted displacement value and the cutoff frequency setting to generate the velocity offset.

[0022] Option 7. The robot system according to Option 1, wherein the robot includes a multi-axis industrial robot.

[0023] Option 8. The robot system according to Option 1, wherein the robot includes an elevated track system or a trolley.

[0024] Option 9. The robot system according to Option 1, wherein the compliance mechanism comprises a plurality of interconnected links such that the compliance mechanism comprises an articulated compliance mechanism.

[0025] Option 10. The robot system according to Option 1, wherein the ICU is configured to provide an overdamped response and avoid speed overshoot of the robot and the payload.

[0026] Option 11. A method for controlling a robotic system used with a payload, comprising: Connect the compliant mechanism in series with the robot; The payload is connected to the compliant mechanism, wherein the compliant mechanism has non-actuated joints that collectively provide multiple non-actuated degrees of freedom (DOF) for the robot system, and wherein the robot includes actuated joints that collectively provide multiple actuated DOFs for the robot system; The corresponding joint positions of the actuated joint and the non-actuated joint are measured using a set of position sensors; and Electronic control unit (ECU) communicating with the robot and the set of position sensors: The trajectory generator block of the ECU generates a payload trajectory signal in response to at least one dynamic control input; The ECU applies predetermined damping and stiffness parameters to the payload trajectory signal to generate an initial speed control signal. The static friction compensation block of the ECU is used to generate a speed offset; The speed offset is applied to the initial speed control signal to generate the final speed control signal; and The final speed control signal is transmitted to the robot, thereby causing the robot to move the payload.

[0027] Option 12. The method according to Option 11 further includes: The trajectory generator block receives the maximum permissible speed as the at least one dynamic control input; and Generate the payload trajectory signal such that the actual speeds of the payload and the robot do not exceed the maximum permissible speed.

[0028] Option 13. The method according to Option 11 further includes: Receive the maximum permissible acceleration as the at least one dynamic control input; and Generate the payload trajectory signal such that the actual acceleration of the payload and the robot does not exceed the maximum allowable acceleration.

[0029] Option 14. The method according to Option 11 further includes calculating the velocity offset by means of the static friction compensation block based on the maximum displacement of the compliance mechanism.

[0030] Option 15. The method according to Option 14 further includes processing the maximum displacement of the compliance mechanism by means of a saturation block of the ECU, including applying maximum and minimum limits to the maximum displacement to generate a constrained displacement.

[0031] Option 16. The method according to Option 15 further includes: The restricted displacement and cutoff frequency setting are received through the low-pass filter of the static friction compensation block; and The velocity offset is generated by using the restricted displacement and the cutoff frequency setting via the static friction compensation block.

[0032] Option 17. The method according to Option 11, wherein connecting the compliant mechanism to the robot includes connecting the compliant mechanism to an elevated track system or a trolley, or to a multi-axis serial robot.

[0033] Option 18. The method according to Option 11, wherein the compliant mechanism comprises a hinged compliant mechanism having a plurality of links interconnected by the non-actuated joint, and wherein connecting the compliant mechanism to the robot comprises connecting the hinged compliant mechanism to the robot.

[0034] Option 19. A computer-readable storage medium having instructions recorded thereon that are executable by a processor of an electronic control system of a robot system having compliant mechanisms connected to a robot and a payload, wherein execution of the instructions causes the processor to: The robot system receives the corresponding joint positions of its actuated and non-actuated joints from a set of position sensors. A trajectory generator block using an electronic control unit (ECU) generates a payload trajectory signal in response to at least one dynamic control input, the at least one dynamic control input including the payload and the robot's maximum speed and maximum acceleration; The damping and stiffness parameters are applied to the payload trajectory signal via the impedance control unit (ICU) of the ECU to generate an initial velocity control signal; The static friction compensation block of the ECU generates a velocity offset based on the maximum displacement of the compliance mechanism; The speed offset is applied to the initial speed control signal to generate the final speed control signal; and The final speed control signal is transmitted to the robot, thereby causing the robot to move the payload.

[0035] Option 20. The computer-readable storage medium according to Option 19, wherein the processor, through execution of the instructions by the processor, causes the processor to: The maximum displacement is processed by a saturation block, which includes applying maximum and minimum limits to the maximum displacement to generate a constrained displacement. The restricted displacement and cutoff frequency setting are received through the low-pass filter of the static friction compensation block; and The velocity offset is generated using the restricted displacement and the cutoff frequency setting.

[0036] The above-described features and advantages of this disclosure, as well as other features and advantages, will become apparent from the following detailed description of embodiments and the best mode for carrying out this disclosure, when taken in conjunction with the accompanying drawings and appended claims. Attached Figure Description

[0037] Figure 1 This is an illustration of a representative robotic system used to move a payload within a workspace, wherein the robotic system has an electronic control unit (ECU) configured to reduce swaying and static friction while improving positioning accuracy.

[0038] Figure 2 yes Figure 1 The diagram shows a schematic control diagram of a representative embodiment of the ECU.

[0039] Figure 3 This is a schematic diagram of a linear model illustrating one aspect of this teaching.

[0040] The accompanying drawings are not necessarily drawn to scale and may present slightly simplified representations of the various preferred features of this disclosure as disclosed herein, including, for example, specific dimensions, orientations, positions, and shapes. Details associated with such features will be determined in part by the specific intended application and environment of use. Detailed Implementation

[0041] Several embodiments of this disclosure are illustrated in the accompanying drawings. The same or similar reference numerals are used in the drawings and supporting description to refer to the same or similar structures. The drawings are provided in a simplified form and are not drawn to scale unless otherwise stated. For convenience and clarity, directional terms such as top, bottom, left, right, upper, above, above, below, under, back, and front may be used relative to the drawings. These and similar directional terms should not be construed as limiting the scope of this disclosure.

[0042] This disclosure relates to improved control strategies and hardware implementations for use with underactuated robotic systems. Representative examples of suitable compliant mechanisms with nonactuated joints and associated nonactuated degrees of freedom (DOF) include, but are not limited to, those disclosed in U.S. Patent Application Serial No. 16 / 773,388, entitled “Redundant Underactuated Robot with Multi-Mode Control Framework”, now published as US2020 / 0156245A1; U.S. Patent No. 10,759,634, entitled “Electromechanical System for Interaction with an Operator”, issued September 1, 2020; and U.S. Patent No. 10,626,963, entitled “Articulated Mechanism for Linear Compliance”, issued April 21, 2020, the contents of which are incorporated herein by reference in their entirety. Other suitable embodiments are contemplated within the scope of this disclosure.

[0043] Now for reference Figure 1 Robot system 10 is shown performing operations by operator 12 on payload 14. Payload 14 is connected to / suspended by a compliant mechanism 16, for example, via a set of links 15, such as rigid arms, bars, or rods, or flexible or semi-rigid variations thereof, wherein the compliant mechanism 16 is in turn connected to robot 18A or 18B. Robot 18A can be implemented as an overhead crane or powered rail system of a type well known in the art. Alternatively, robot 18B can be used as a multi-axis serial robot, such as a 6-axis industrial robot. In these or other configurations, compliant mechanism 16 is connected to the distal link (not shown) of robot 18A or 18B, which, for simplicity, will be collectively referred to below as robot 18. Thus, compliant mechanism 16 is suspended from robot 18 within a defined workspace 11, which may sometimes be shared by operator 12.

[0044] As outlined above, when a non-actuated compliant device (exemplified herein) is used... Figure 1 When the compliant mechanism 16 is connected to the actuated robot 18, an underactuated robot arrangement is formed. That is, each joint 20 of the robot 18 is driven via a corresponding joint actuator 120, such as a linear or rotary motor or other suitable actuator. This is in response to a final speed control signal 253 (arrow CC) from the associated electronic control unit (ECU) 50. V * And so it happened, the details of which are in Figure 2It is depicted in the text and described below.

[0045] For this purpose, ECU 50 receives a set of input signals 51, also marked as arrow CC for clarity. I This indicates the corresponding measured joint positions of the actuated joints 20 of robot 18 and the corresponding joint positions of the non-actuated joints 200 of the compliance mechanism 16. However, unlike the actuated joints 20 of robot 18, the non-actuated joints 200 of the compliance mechanism 16 do not have corresponding joint actuators 120 connected to them. ECU 50 is operable to generate and transmit a final speed control signal 253 to command one or more actuated joints 20 of robot 18 to move, and thus cause robot 18 to move payload 14. As described elsewhere above, this control action may occur in part based on the number, type, and configuration of the non-actuated joints 200 relative to the actuated joints 20.

[0046] As envisioned herein, ECU 50 includes one or more digital computer devices that collectively include at least one processor (P) 52 and sufficient memory (M) 54. The term "controller" and related terms such as microcontroller, control module, module, control unit, processor, and similar terms refer to one or various combinations of application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), electronic circuits, central processing units such as microprocessors, etc. Related non-transitory memory components in the form of memory 54 may include a sufficient amount of tangible non-transitory memory, such as read-only memory, flash memory, optical and / or magnetic memory, electrically programmable read-only memory, etc. Memory 54 also includes sufficient transient memory, such as random access memory and electronic buffers. The hardware components of ECU 50 may, in particular, include high-speed clocks, analog-to-digital and digital-to-analog circuits, input / output circuits and devices, and appropriate signal conditioning and buffering circuitry.

[0047] exist Figure 1 In a non-limiting representative embodiment, the compliant mechanism 16 includes end plates 24A and 24B, which are interconnected via a rod 22 using a non-actuated joint 200. The shape and size of the end plates 24A and 24B can vary depending on the application, wherein... Figure 1 The triangular shape depicted is just one possible construction. Other arrangements, such as parallelograms, can be used to achieve similar levels of compliance, or multiple compliance mechanisms 16 can be connected in series to achieve additional non-actuated degrees of freedom.

[0048] refer to Figure 2The ECU 50 includes a trajectory generator block (T-GEN) 42, where "block" as used herein refers to coded computer-executable instructions that provide the necessary functionality, and the associated hardware for executing this logic. As its core function, the trajectory generator block 42 generates a payload trajectory signal 142 describing the desired speed and travel path of the payload 14. The trajectory generator block 42 can be implemented as computer-executable code, for example using MATLAB. ® To output the payload trajectory signal 142. In one possible implementation, the trajectory generator block 42 receives different inputs: desired position command ( x * ), maximum permissible speed ( v max ) and / or maximum permissible acceleration ( Assume ECU 50 is aware of payload 14, compliance mechanism 16, and... Figure 1 The current position of robot 18 in free space. Figure 2 The trajectory generator block 42 shown can calculate the payload trajectory signal 142 as an electronic output signal.

[0049] ECU 50 also includes an impedance control unit (ICU) 44 downstream of trajectory generator block 42, wherein ICU 44 receives the payload trajectory signal 142 as an electronic input signal. ICU 44 is configured to apply a suitable impedance control law appropriate for the application to regulate the motion of payload 14. As an example, ICU 44 may model the motion of payload 14 as a mass-spring-damper system, as understood in the art, thereby producing the desired second-order behavior. While various methods may be used to implement ICU 44, one possible method is disclosed in U.S. Patent No. 10,583,557, entitled “Redundant Underactuated Robot with Multi-Mode Control Framework,” issued March 10, 2020, and is incorporated herein by reference in its entirety. This method allows ECU 50 to specify overdamped response behavior, which, as one of the incidental benefits of this teaching, allows payload 14 to move without swaying.

[0050] In order to optimize Figure 2 The performance of the ICU 44 shown can implement an impedance adjustment block 43 to enable user-based or automatic selection of impedance parameters, including damping factor (b), stiffness factor (k), and proportional gain (k). pTherefore, ICU 44 acts on the payload trajectory signal 142 within the established impedance control framework provided by the value supplied via impedance adjustment block 43 to output an initial speed control signal 153, also marked as arrow CC for clarity. V .

[0051] Furthermore, the ECU 50 can utilize a static friction compensation block 46 having a saturation block (SAT) 47 and a low-pass filter (LPF) 48, as described below. The saturation block 47 and the low-pass filter 48 ultimately work together to generate a speed offset 148, which is added to and combined with the aforementioned initial speed control signal 153 to generate a final speed control signal 253, which also... Figure 1 Depicted in the text. Now, we will continue to refer to... Figure 2 The operation of the various components of ECU 50 is described in further detail.

[0052] Impedance Adjustment: Select or adjust the impedance parameters mentioned above in this article. b , k and k p In order to act on Figure 1 The disclosed motion control objectives are met when the payload 14 is on the load. Although the ICU 44 receives the velocity trajectory signal 142 from the trajectory generator block 42, the use of the ICU 44 may still cause the robot 18 and / or the payload 14 to exceed the specified maximum permissible speed. This teaching is used to eliminate the swaying of the payload 14 to prevent the payload 14 from exceeding the defined maximum permissible speed. Adjust the stiffness coefficient ( k The maximum speed of robot 18 is controlled, thereby affecting the speed of payload 14.

[0053] Contemplated adjustments within the scope of this disclosure may include increasing the damping coefficient ( b To increase damping, that is, by adjusting the damping coefficient ( b This continues until overdamped behavior of robot 18 is achieved. This, in turn, eliminates the swaying of payload 14, and also eliminates velocity overshoot. Adjustments may also include reducing the stiffness coefficient ( k This continues until robot 18 no longer exceeds the specified maximum permissible speed of the payload trajectory signal 142 from trajectory generator block 42. However, this control action has the aforementioned drawback of increasing the position error of robot 18, which is addressed here using the anticipated static friction compensation.

[0054] Static friction compensation: The steady-state position error of the effective load 14 may sometimes be caused by... Figure 1The static friction (“stiction”) force in the compliant mechanism 16 causes this error. This error can be reduced by increasing the stiffness via ICU 44, i.e., by adjusting the aforementioned stiffness parameter (k). However, the stiffness is reduced to limit the specified speed of the observed payload trajectory signal 142. Therefore, this control strategy introduces additional control components to help compensate for the position error caused by undesirable static friction when using… Figure 1 When the robot system 10 moves the representative payload 14, this significantly reduces the overall position error.

[0055] Laws of Motion and Control: A Brief Reference Figure 3 The compliant mechanism 16 can act like a pendulum, thus using gravity as the restoring force. A simplified linear model 30 using this pendulum represents... Figure 1 The combined payload 14 and the mass block 34 of the conforming mechanism 16 are securely connected to the movable trolley 32, wherein in this case, the movable trolley 32 corresponds to Figure 1 Robot 18. The connection is represented by spring 36, which has a component also... Figure 2 The stiffness coefficient shown in the figure ( k The stiffness is indicated by (). When the mass block 34 is released, the spring 36 acts as a physical spring to center the compliant mechanism 16. Alternatively, if Figure 1 If the robot system 10 uses gravity as a restoring force, then the following is described: k s This will be a linear approximation of the stiffness. Spring 36 is then connected to the center point Cp of the fixed member 38 and the trolley 32, where spring 36 also has a damping coefficient ( b ).

[0056] like Figure 3 As shown, x1 is the position of the trolley 32 relative to the stationary member 38. x2 is the position of the payload 14 and the compliance mechanism 16, also relative to the stationary member 38. The desired impedance relationship of the end effector of the compliance mechanism 16 can be modeled as follows: (1) in m It is mass block 34. b It is the damping coefficient. k It is the stiffness coefficient, and This is the commanded location for payload 14. Furthermore, F represents, for example, by... Figure 1 The operator 12 applies an external force to the mass block 34. Ignoring friction, the force analysis of the compliant mechanism 16 yields the following equations of motion: (2) assumed Figure 1The robot 18 uses a first-order position controller, which has k p Proportional gain: (3) Solving equations (1) and (2) above, the control law for the desired macroscopic position is as follows: (4).

[0057] Static friction compensation: Figure 1 Static friction in the compliant mechanism 16 can lead to positioning errors. The following exemplary methods can be used to increase the positioning accuracy of the compliant mechanism 16 within a given impedance control framework. First, the positional error introduced by static friction can be analyzed. Given a first-order controller from equations (3) and (4), the commanded velocities of robot 18 are as follows: (5) in ,and Steady-state results can be analyzed, where robot 18 and articulated compliant mechanism 16 stop, but static friction causes the aforementioned position to be reached. x 1 and x 2 The error between them. That is, static friction causes displacement between the conformal mechanism 16 and the robot 18. ,Right now ,in f It is static friction. Therefore: (6) (7).

[0058] The above formula leads to the following steady-state error: (8) Error term By increasing the stiffness coefficient k However, in practical applications, the benefits are limited. Therefore, to compensate for static friction, a speed offset of 148 is introduced by ECU 50, expressed as... : (9) Since static friction is not directly measurable, the displacement of the conforming mechanism 16 is used as a measure of static friction in this paper. Because the displacement of the conforming mechanism 16 ( x 2 - x 1 (or simply) ΔxThis represents the static friction under minimum and static conditions, thus introducing velocity offset. It can be defined as: (10) in H(s) Represents the setting of a specific cutoff frequency. Fq )of Figure 2 The low-pass filter is 48, and This represents the saturation transfer function of saturation block 47. Therefore, the output from saturation block 47 (arrow 147) is processed by low-pass filter 48 to produce a velocity offset. The speed deviation Again corresponding Figure 2 148 in the middle.

[0059] Therefore, by Figure 1 and Figure 2 The impedance control law executed by the ECU 50 can be programmed to use the maximum permissible speed ( v max )of Figure 2 The trajectory generator block 42, via ICU 44, increases damping to achieve overdamped behavior, and via block 46, applies static friction compensation to increase overall position accuracy. The disclosed solution improves upon the performance under various loads, such as... Figure 1 The impedance-based control of the underactuated robot system when operating on the representative payload 14 shown is a general prior art.

[0060] In such Figure 3 In the simplified cart pendulum system illustrated, this solution provides an automated method for moving the payload 14 without swaying, with improved positional accuracy. This is achieved by observing the maximum permissible speed of the robot 18 and the suspended payload 14 (…). v max ) and acceleration ( When this desired control action occurs, the payload 14 is prone to oscillations and various related problems without this teaching.

[0061] To illustrate a potential problem, in an exemplary use case where the payload 14 has a desired maximum speed of 400 mm / s, the payload 14 could reach a speed of 500 mm / s simply due to the aforementioned swaying motion. However, using this teaching, the payload swaying is eliminated, and therefore the speeds of the payload 14 and the robot 18 do not exceed the specified desired maximum value. This result improves prior art on payload control in shared working environments where human operators may be present. Similarly, without applying the disclosed static friction compensation scheme, a positional error of 10-15 mm could lead to the same situation. In the same exemplary embodiment, the positional error can be reduced to less than 1 mm, or reduced by at least 90%. Therefore, the foregoing teaching also improves the general prior art on impedance control of underactuated macro-micro robotic systems by providing these and other possible benefits and performance advantages.

[0062] The detailed description and figures or drawings are intended to support and describe this disclosure, but the scope of this disclosure is defined only by the claims. While some best modes and other embodiments for implementing the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure as defined in the appended claims.

Claims

1. A robotic system for use with a payload, comprising: A robot with actuated joints, which together provide multiple actuation degrees of freedom for the robot system; A compliant mechanism coupled in series with the robot and capable of being connected to the payload, the compliant mechanism having non-actuated joints that collectively provide multiple non-actuated degrees of freedom for the robot system; A set of position sensors, collectively configured to measure the corresponding joint positions of the actuated joint and the non-actuated joint; as well as An electronic control unit that communicates with the robot and the set of position sensors, wherein the electronic control unit is programmed to have: A trajectory generator block operable to generate a payload trajectory signal in response to at least one dynamic control input, wherein the at least one dynamic control input includes the payload and the robot's maximum permissible speed and maximum permissible acceleration; An impedance control unit configured to apply adjusted damping and stiffness parameters to the payload trajectory signal to generate an initial speed control signal, wherein the adjustment includes increasing the damping coefficient until overdamped behavior of the robot is achieved, which eliminates swaying and speed overshoot of the payload, and decreasing the stiffness coefficient until the robot no longer exceeds the maximum permissible speed; and A static friction compensation block is configured to allow the robot system to generate a velocity offset and apply the velocity offset to the initial velocity control signal to generate a final velocity control signal, wherein the velocity offset is configured to compensate for positional errors of the robot and the payload due to static friction and to compensate for an increase in the robot's positional error due to a reduction in the stiffness coefficient, and wherein the electronic control unit is operable to transmit the final velocity control signal to the robot, thereby enabling the robot to move the payload without swaying.

2. The robot system according to claim 1, wherein, The electronic control unit is configured to generate the payload trajectory signal such that the actual speed of the payload and the robot does not exceed the maximum permissible speed.

3. The robot system according to claim 1, wherein, The electronic control unit is configured to generate the payload trajectory signal such that the actual acceleration of the payload and the robot does not exceed the maximum permissible acceleration.

4. The robot system according to claim 1, wherein, The static friction compensation block is configured to calculate the velocity offset based on the maximum displacement of the compliance mechanism.

5. The robot system according to claim 4, wherein, The static friction compensation block is configured to handle the maximum displacement of the compliance mechanism by means of a saturation block, which is configured to impose maximum and minimum limits on the maximum displacement to generate a constrained displacement value.

6. The robot system according to claim 5, wherein, The static friction compensation block includes a low-pass filter that is operable to receive the restricted displacement value and the cutoff frequency setting, and to use the restricted displacement value and the cutoff frequency setting to generate the velocity offset.

7. The robot system according to claim 1, wherein, The robots include multi-axis industrial robots.

8. The robot system according to claim 1, wherein, The robot includes an elevated track system or a trolley.

9. The robot system according to claim 1, wherein, The compliant mechanism includes a plurality of interconnected links, such that the compliant mechanism includes a hinged compliant mechanism.

10. The robot system according to claim 1, wherein, The impedance control unit is configured to provide an overdamped response and prevent speed overshoot of the robot and the payload.

11. A method for controlling a robotic system used with a payload, comprising: Connect the compliant mechanism in series with the robot; The payload is connected to the compliant mechanism, wherein the compliant mechanism has non-actuated joints that collectively provide multiple non-actuated degrees of freedom for the robot system, and wherein the robot includes actuated joints that collectively provide multiple actuated degrees of freedom for the robot system; The corresponding joint positions of the actuated joint and the non-actuated joint are measured using a set of position sensors; and An electronic control unit that communicates with the robot and the set of position sensors: The trajectory generator block of the electronic control unit generates a payload trajectory signal in response to at least one dynamic control input, wherein the at least one dynamic control input includes the payload and the robot's maximum permissible speed and maximum permissible acceleration; The adjusted damping and stiffness parameters are applied to the payload trajectory signal by the impedance control unit of the electronic control unit to generate an initial speed control signal, wherein the adjustment includes increasing the damping coefficient until the robot achieves overdamped behavior, which eliminates the swaying and speed overshoot of the payload, and decreasing the stiffness coefficient until the robot no longer exceeds the maximum permissible speed. The static friction compensation block of the electronic control unit generates a velocity offset, wherein the velocity offset is configured to compensate for the positional errors of the robot and the payload caused by static friction and to compensate for the increase in the positional error of the robot due to the reduction of the stiffness coefficient. The speed offset is applied to the initial speed control signal to generate the final speed control signal; and The final speed control signal is transmitted to the robot, thereby enabling the robot to move the payload without swaying.

12. The method of claim 11, further comprising: Generate the payload trajectory signal such that the actual speeds of the payload and the robot do not exceed the maximum permissible speed.

13. The method of claim 11, further comprising: Generate the payload trajectory signal such that the actual acceleration of the payload and the robot does not exceed the maximum allowable acceleration.

14. The method of claim 11, further comprising calculating the velocity offset by means of the static friction compensation block based on the maximum displacement of the compliance mechanism.

15. The method of claim 14, further comprising processing the maximum displacement of the compliance mechanism by means of a saturation block of the electronic control unit, including applying maximum and minimum limits to the maximum displacement to generate a constrained displacement.

16. The method of claim 15, further comprising: The restricted displacement and cutoff frequency setting are received through the low-pass filter of the static friction compensation block; as well as The velocity offset is generated by using the restricted displacement and the cutoff frequency setting via the static friction compensation block.

17. The method according to claim 11, wherein, Connecting the compliant mechanism to the robot includes connecting the compliant mechanism to an elevated track system or trolley, or to a multi-axis serial robot.

18. The method according to claim 11, wherein, The compliant mechanism includes a hinged compliant mechanism having a plurality of links interconnected by the non-actuated joints, and wherein connecting the compliant mechanism to the robot includes connecting the hinged compliant mechanism to the robot.

19. A computer-readable storage medium having instructions recorded thereon that are executable by a processor of an electronic control system of a robot system, the robot system having compliant mechanisms connected to the robot and a payload, wherein, The execution of the instruction causes the processor to: The robot system receives the corresponding joint positions of its actuated and non-actuated joints from a set of position sensors. The trajectory generator block of the electronic control unit generates a payload trajectory signal in response to at least one dynamic control input, the at least one dynamic control input including the payload and the robot’s maximum permissible speed and maximum permissible acceleration; The adjusted damping and stiffness parameters are applied to the payload trajectory signal by the impedance control unit of the electronic control unit to generate an initial speed control signal, wherein the adjustment includes increasing the damping coefficient until the robot achieves overdamped behavior, which eliminates the swaying and speed overshoot of the payload, and decreasing the stiffness coefficient until the robot no longer exceeds the maximum permissible speed. The static friction compensation block of the electronic control unit generates a velocity offset based on the maximum displacement of the compliant mechanism, wherein the velocity offset is configured to compensate for the positional errors of the robot and the payload caused by static friction and to compensate for the increase in the positional error of the robot due to the reduction of the stiffness coefficient. The speed offset is applied to the initial speed control signal to generate the final speed control signal; and The final speed control signal is transmitted to the robot, thereby enabling the robot to move the payload without swaying.

20. The computer-readable storage medium according to claim 19, wherein, The processor, through the execution of the instructions, causes the processor to: The maximum displacement is processed by a saturation block, which includes applying maximum and minimum limits to the maximum displacement to generate a constrained displacement. The restricted displacement and cutoff frequency setting are received through the low-pass filter of the static friction compensation block; as well as The velocity offset is generated using the restricted displacement and the cutoff frequency setting.

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