EP-4739470-A1 - SYSTEM AND METHOD FOR CONTROLLING OPERATION OF ROBOTIC MANIPULATOR WITH SOFT ROBOTIC TOUCH

Abstract

Feedback control for controlling a robotic manipulator includes receiving measurement signals from one or more tactile sensors and filtering the measurement signals to align them with the directions of motion of the end effector to produce an impedance-shaping signal. The feedback control determines one or more control signals to the actuators to track a reference state of the end effector based on measurements of the state of the end effector and combines the control signal with the impedance shaping signal to produce control commands. Also, the feedback control may include submitting the determined control commands to the actuators causing a change in the state of the end effector, where the state of the end effector includes one or a combination of an end effector position, an end effector velocity, and an end effector force.

Inventors

• BORTOFF, SCOTT
• KASHYAP, Mruganka
• BHATIA, ANKIT

Assignees

• MITSUBISHI ELECTRIC CORPORATION

Dates

Publication Date

20260513

Application Date

20240621

Claims (20)

1. [Claim 1] A feedback controller for controlling a robotic manipulator including one or more actuators mechanically connected to joints of the robotic manipulator for moving an end effector based on measurements of one or more tactile sensors attached to the end effector, the feedback controller includes a circuitry forming modules of the feedback controller, the modules comprising: a tactile sensor compensator configured to (1) receive measurement signals from one or more tactile sensors, wherein the measurement signals include measurements of one or more magnitudes of one or more forces along one or more directions relative to the tactile sensor and (2) filter the measurement signals to align some or all of the measurement signals to one or more directions of motion of the end effector to produce an impedance shaping signal; and a motion controller configured to (1) determine one or more control signals to the actuators to track a reference state of the end effector based on measurements of the state of the end effector; (2) combine the control signal with the impedance shaping signal to produce control commands and (2) output the determined control commands to the actuators causing a change in the state of the end effector, wherein the state of the end effector includes one or a combination of an end effector position, an end effector velocity, and an end effector force.
2. [Claim 2] The feedback controller of claim 1 , wherein a filter of the tactile sensor compensator modifies magnitude of an impedance as measured at the one or more tactile sensors.
3. [Claim 3] The feedback controller of claim 1 , wherein, to produce the impedance shaping signal, the tactile sensor compensator is configured to combine values of the measurement signals into a measurement vector; and multiply the measurement vector with a sensor alignment matrix.
4. [Claim 4] The feedback controller of claim 3, wherein the tactile sensor compensator filters a product of the measurement vector with the sensor alignment matrix using a filter with a non-zero gain.
5. [Claim 5] The feedback controller of claim 4, wherein the gain is negative.
6. [Claim 6] The feedback controller of claim 3, wherein the sensor alignment matrix is computed from one or more Jacobians of the robotic manipulator forward kinematics from joint coordinates of locations of the one or more tactile sensors.
7. [Claim 7] The feedback controller of claim 3, wherein the sensor alignment matrix includes multiple rows and multiple columns defining a dimension of the sensor alignment matrix as a function of degrees-of-freedom of the end effector.
8. [Claim 8] The feedback controller of claim 1 , wherein the motion controller modules include an inner loop compensator and an outer loop compensator, wherein the inner loop compensator takes as input the sum or difference between the output of the outer loop compensator and the impedance shaping signal.
9. [Claim 9] The feedback controller of claim 8, wherein the inner loop compensator is the identity.
10. [Claim 10] The feedback controller of claim 8, wherein the inner loop compensator is configured to compensate the control commands for effects of gravity, configuration-dependent inertia, centripetal forces or torques, Coriolis forces or torques.
11. [Claim 11] The feedback controller of claim 8, wherein the outer loop compensator includes a proportional-integral-derivative (PID) controller or a proportional- derivative (PD) controller.
12. [Claim 12] The feedback controller of claim 2, wherein the filter is a matrix of one or more linear gains, low-pass filters, band-pass filters, or a combination thereof.
13. [Claim 13] The feedback controller of claim 4, wherein the filter is a matrix of one or more linear gains, low-pass filters, band-pass filters, or a combination thereof.
14. [Claim 14] The robotic manipulator controlled by the feedback controller of claim 1.
15. [Claim 15] A robotic manipulator system including a union of robotic manipulators including the robotic manipulator of claim 14.
16. [Claim 16] A method for feedback control of a robotic manipulator including one or more actuators mechanically connected to joints of the robotic manipulator for moving an end effector based on measurements of one or more tactile sensors attached to the end effector, wherein the method uses a processor coupled with stored instructions implementing the method, wherein the instructions, when executed by the processor carry out steps of the method, comprising: receiving measurement signals from one or more tactile sensors, wherein the measurement signals include measurements of one or more magnitudes of one or more forces along one or more directions relative to the tactile sensor; filtering the measurement signals to align some or all of the measurement signals to one or more directions of motion of the end effector to produce an impedance shaping signal; determining one or more control signals to the actuators to track a reference state of the end effector based on measurements of the state of the end effector; combining the control signal with the impedance shaping signal to produce control commands; submitting the determined control commands to the actuators causing a change in the state of the end effector, wherein the state of the end effector includes one or a combination of an end effector position, an end effector velocity, and an end effector force.
17. [Claim 17] The method of claim 16, further comprising: modifying a magnitude of an impedance measured at the one or more tactile sensors using a filter.
18. [Claim 18] The method of claim 16, further comprising: combining values of the measurement signals into a measurement vector; multiplying the measurement vector with a sensor alignment matrix; and filtering a product of the measurement vector with the sensor alignment matrix using a filter with a non-zero gain.
19. [Claim 19] The method of claim 18, wherein the gain is negative.
20. [Claim 20] The method of claim 18, wherein the sensor alignment matrix is computed from one or more Jacobians of the robotic manipulator forward kinematics from joint coordinates of locations of the one or more tactile sensors, and wherein the sensor aligmnent matrix includes multiple rows and multiple columns defining a dimension of the sensor alignment matrix as a function of degrees of freedom of the end effector.

Description

[DESCRIPTION] [Title of Invention] SYSTEM AND METHOD FOR CONTROLLING OPERATION OF ROBOTIC MANIPULATOR WITH SOFT ROBOTIC TOUCH [Technical Field] [0001] The present disclosure relates generally to robotic manipulation, and more particularly to controlling an operation of a robotic manipulator with a soft robotic touch suitable for applications that include object contact and collision, such as assembly of objects. [Background Art] [0002] Robotic manipulators are commonly used in applications that involve contacts or collisions among objects, such as in assembly of objects. In these applications, when a robotic manipulator comes in contact, or loses contact, with one or more objects to be manipulated, or the relative motion of a robotic manipulator causes contact or loss of contact among objects in its environment, one or more collision events occur. A collision event is the point in time when contact is made or broken among a robotic manipulator and one or more objects to be manipulated. For example, when a robotic manipulator grasps an object at rest, a collision event occurs between the robotic manipulator and the object. As another example, a robotic manipulator may be in contact with one object, and that object may collide with another object due to their relative motion. [0003] When a collision event occurs among a robot manipulator and one or more objects in its environment, an exchange of energy or momentum occurs among the robotic manipulator and the object(s). A collision event will therefore result in a change of energy or momentum of the robotic manipulator and object(s) during or after a collision event. In many robotic manipulator applications, it is beneficial to minimize the magnitude of a transfer of energy or momentum, in order to avoid damage to the object(s) or robotic manipulator, for example, or in order to successfully achieve a particular robotic manipulation task, for example. [0004] Commonly practiced strategies to reduce the magnitude of a transfer of energy or momentum among a robotic manipulator and one or more object in its environment include reducing the magnitude of a robotic manipulator approach velocity, introducing mechanical compliance to the robotic manipulator, or reducing the mass of the robotic manipulator. However, each of these strategies may be impractical or may compromise some performance metrics of the robotic manipulator. Reducing the magnitude of approach velocity of a robotic manipulator may reduce productivity, simply because it moves more slowly. Introducing compliance into the robotic manipulator can increase the trajectory tracking error, reducing the accuracy of the robotic manipulator. Reducing the mass of the robotic manipulator may require modification or redesign of the robotic manipulator, and it may not be practical or possible to achieve without compromising other performance metrics of the robotic manipulator. [0005] Another common strategy to reduce the magnitude of a transfer of energy or momentum among a robotic manipulator and one or more objects in its environment during or after a collision event is to modify the robotic manipulator motion controller in a manner that reduces the mechanical impedance of the robotic manipulator system. Herein, the term robotic manipulator system refers to the union of a robotic manipulator, its actuators and its robotic manipulator motion controller. Mechanical impedance is one of several metrics that are commonly used to characterize the performance of a robotic manipulator system, and is commonly defined as the ratio of force to velocity, where the force is between a robotic manipulator and an object, and the velocity is the result of that force. [0006] For linear systems, impedance is commonly represented in the frequency domain in a manner analogous to electrical impedance, which is the ratio of voltage to current. In this case, mechanical impedance may be a frequency-dependent transfer function that has a magnitude and phase. A mechanical impedance of a relatively large magnitude means that a given magnitude of force applied to a robotic manipulator system will result in a relatively small magnitude of velocity. In this case, the robotic manipulator system is considered colloquially “stiff.” In comparison, a mechanical impedance of a relatively small magnitude means that the same given magnitude of force applied to a robotic manipulator system will result in a comparatively larger magnitude of velocity. In this ccaassee,, the robotic manipulator system is considered colloquially “soft.” [0007] It is known to those skilled in the art that reducing the magnitude of a mechanical impedance of a robotic manipulator system reduces the transfer of energy or momentum among a robotic manipulator and one or more objects in its environment during or after a collision event. Reducing the magnitude of the mechanical impedance of a robotic manipulator system is commonly accomplished by reducing feedback control gain