US-12617105-B2 - Robotic end effector system and method with lockable compliance

US12617105B2US 12617105 B2US12617105 B2US 12617105B2US-12617105-B2

Abstract

Robotic systems and methods are provided with an end effector having lockable compliance. A robotic system for manipulating a workpiece includes an arm having a pair of sections connected by a joint assembly, with a lock disposed in the joint assembly. A gripper is connected on the arm and is configured to alternately grip and release the workpiece. A controller operates the lock to alternately lock and unlock the joint assembly. The gripper holds the workpiece during a deformation of the workpiece, while the controller may unlock the lock to allow movement of the joint assembly to relieve forces on the arm arising during a deformation of the workpiece.

Inventors

Joshua Lee Solomon
Hui-Ping Wang
Lu HUANG
DALONG GAO
Dohyun Leem

Assignees

GM Global Technology Operations LLC
NORTHWESTERN UNIVERSITY

Dates

Publication Date: 20260505
Application Date: 20220705

Claims (20)

1 . A robotic system for manipulating a workpiece, the robotic system comprising: an arm having a first section and a second section connected with the first section by a joint assembly, with a lock disposed in the joint assembly; a first gripper connected on the arm at the first section and configured to alternately grip and release the workpiece; a second gripper disposed on the second section, the first gripper and the second gripper configured to simultaneously grip the workpiece; and a controller configured to operate the lock to alternately lock and unlock the joint assembly, wherein the first and second grippers are configured to hold the workpiece during a deformation of the workpiece, with the controller being configured to unlock the lock to allow movement of the joint assembly to relieve forces on the arm arising during a deformation of the workpiece.
2 . The robotic system of claim 1 , wherein the joint assembly includes a force sensor configured to provide a force signal to the controller, wherein the controller is configured to unlock the joint assembly when the force signal exceeds a threshold force.
3 . The robotic system of claim 1 , wherein the controller is configured to unlock the lock while the first and second grippers hold the workpiece.
4 . The robotic system of claim 1 , comprising a vision system configured to provide a signal to the controller indicative of deformation of the workpiece, wherein the controller is configured to unlock the joint assembly when the signal indicates exceeding a threshold deformation.
5 . The robotic system of claim 1 , wherein the first section comprises an elongated body with a first end, a second end, and a side extending from the first end to the second end, wherein the first end is connected with the joint assembly, wherein the second end is connected with the second section, wherein the first gripper is connected at the side of the elongated body.
6 . The robotic system of claim 1 , wherein: the arm is a first arm and comprising a second arm that includes a second lock configured to alternately lock and unlock the second arm, and includes a plurality of grippers configured to alternately grip and release the workpiece, wherein the controller is configured to alternately lock and unlock the second lock.
7 . The robotic system of claim 1 , wherein the joint assembly includes a force sensor configured to provide a force signal to the controller, wherein the controller is configured to: record a baseline force on the arm, the baseline force recorded based on the force signal received prior to the deformation of the workpiece; receive a measured force from the force sensor after initiation of the deformation; compare the measured force to a threshold force; and unlock the joint assembly when the measured force exceeds the threshold force.
8 . The robotic system of claim 1 , wherein the first gripper comprises a suction cup and comprising a pneumatic system coupled with the suction cup and with the controller, the controller configured to control the pneumatic system to maintain connection between the suction cup and the workpiece during the deformation.
9 . The robotic system of claim 1 , wherein the joint assembly includes a ball and socket joint, wherein the lock includes a band encircling the ball and configured, in response to the controller, to squeeze the ball to lock the joint.
10 . The robotic system of claim 1 , wherein the first and second sections are part of a series of sections connected by a series of joints so that the arm is reconfigurable into a variety of bent shapes, in each of which the arm is lockable.
11 . A method for manipulating a workpiece, the method comprising: constructing an arm to have a first section and a second section connected with the first section by a joint assembly, with a lock disposed in the joint assembly; connecting a first gripper with the first section of the arm; connecting a second gripper on the second section; gripping the workpiece simultaneously by the first gripper and the second gripper; releasing the workpiece from the first and second grippers; operating, by a controller, the lock to alternately lock and unlock the joint assembly, holding, by the first and second grippers, the workpiece during a deformation of the workpiece, with unlocking, by the controller, the lock to allow movement of the joint assembly; and relieving, by the unlocking, forces on the arm arising during a deformation of the workpiece.
12 . The method of claim 11 , comprising: positioning a force sensor at the joint assembly; providing, by the force sensor, a force signal to the controller; and unlocking, by the controller, the joint assembly when the force signal exceeds a threshold force.
13 . The method of claim 11 , comprising, unlocking, by the controller, the lock while the first and second grippers hold the workpiece.
14 . The method of claim 11 , comprising: providing, by a vision system configured to provide a signal to the controller indicative of deformation of the workpiece; and unlocking, by the controller, the joint assembly when the signal exceeds a threshold deformation.
15 . The method of claim 11 , comprising: forming the first section with an elongated body having a first end, a second end, and a side extending from the first end to the second end; connecting the first end with the joint assembly; connecting the second end with the second section; and connecting the first gripper at the side of the elongated body.
16 . The method of claim 11 , comprising: adding a second arm that includes a second lock configured to alternately lock and unlock the second arm, and a plurality of grippers configured to alternately grip and release the workpiece; and alternately locking and unlocking, by the controller, the second lock.
17 . The method of claim 11 , comprising: positioning a force sensor at the joint assembly; providing, by the force sensor, a force signal to the controller; recording, by the controller and prior to the deformation of the workpiece, a baseline force on the arm as received from the force sensor; receiving, by the controller and from the force sensor, a measured force after initiation of the deformation; comparing, by the controller, the measured force to a threshold force; unlocking, by the controller, the joint assembly when the measured force exceeds the threshold force.
18 . The method of claim 11 , comprising: constructing the first gripper as a suction cup; coupling a pneumatic system with the suction cup and with the controller; and controlling, by the controller the pneumatic system to maintain connection between the suction cup and the workpiece during the deformation.
19 . The method of claim 11 , comprising: constructing the first and second sections as a part of a series of sections connecting the series of sections by a series of joints; reconfiguring, by the series of sections and the series of joints, the arm into a variety of bent shapes; and locking the arm in each of the bent shapes.
20 . A robotic system for manipulating a workpiece, the robotic system comprising: an end effector having a fixture; a first arm connected with the fixture, the first arm having a first section and a second section connected with the first section by a first joint assembly, with a first lock disposed in the first joint assembly; a second arm connected with the fixture, the second arm having a third section and a fourth section connected with the third section by a second joint assembly, with a second lock disposed in the second joint assembly; a first gripper on the first section and a second gripper on the second section of the first arm, the first and second grippers configured to alternately grip and release the workpiece, simultaneously; a third gripper on the third section and a fourth gripper on the fourth section of the second arm, the third and fourth grippers configured to alternately grip and release the workpiece; and a controller configured to: control the first lock to alternately lock and unlock the first joint assembly; control the second lock to alternately lock and unlock the second joint assembly; control the first gripper and the second gripper to hold the workpiece during a deformation of the workpiece; and unlock at least one of the first lock and the second lock to allow movement of at least one of the first joint assembly and the second joint assembly to relieve forces on the at least one of the first arm and the second arm arising during a deformation of the workpiece.

Description

INTRODUCTION The present disclosure generally relates to automated forming and assembly, and more particularly relates to robotic systems and methods with an end effector that includes lockable arms with selectable compliance to allow deformation of the gripped item. Carrying out certain forming and assembly operations efficiently is challenging. For components such as sheet metal panels, forming may be carried out by costly geometric-specific tools such as dies mounted in presses with complex transfer tooling for moving parts between operations. Where high-volume production runs of panels are required, stamping presses and dies that have relatively high costs and long development lead-time may be used. When low production volumes are involved, such operations may be cost-prohibitive. Robots have come into widespread use, including applications in assembly operations that are difficult to accomplish manually. Vehicle assembly plants have used robots for spot welding and painting. These applications use relatively simple end effectors such as paint sprayers and spot welders. Each manufacturing application may use its own type of end effector. Using robotic systems and end effectors for forming operations is challenging because the item being formed is gripped and then released by the robot as its dimensions are changed during forming. This requires repeatedly engaging the item with some form of gripper. Accordingly, it is desirable to provide robotic systems and methods that efficiently, accurately and repeatably carry out forming and/or assembly operations that involve dimensional changes in the item being handled. In addition, the flexibility to apply the systems to a wide variety of operations is desirable. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. SUMMARY Robotic systems and methods are provided with an end effector having lockable compliance. A robotic system for manipulating a workpiece includes an arm having a pair of sections connected by a joint assembly, with a lock disposed in the joint assembly. A gripper is connected on the arm and is configured to alternately grip and release the workpiece. A controller operates the lock to alternately lock and unlock the joint assembly. The gripper holds the workpiece during a deformation of the workpiece, while the controller may unlock the lock to allow movement of the joint assembly to relieve forces on the arm arising during a deformation of the workpiece. In additional embodiments, the joint assembly includes a force sensor configured to provide a force signal to the controller, wherein the controller is configured to unlock the joint when the force signal exceeds a threshold force. In additional embodiments, the controller is configured to unlock the lock while the gripper holds the workpiece. In additional embodiments, a vision system is configured to provide a signal to the controller indicative of deformation of the workpiece, wherein the controller is configured to unlock the joint when the signal indicates exceeding a threshold deformation. In additional embodiments, the first section comprises an elongated body with a first end, a second end, and a side extending from the first end to the second end. The first end is connected with the joint assembly, wherein the gripper is connected at the side of the body. In additional embodiments, the arm is a first arm and comprising a second arm that includes a second lock configured to alternately lock and unlock the second arm. The second arm includes a second gripper configured to alternately grip and release the workpiece. The controller is configured to alternately lock and unlock the second lock. In additional embodiments, the joint assembly includes a force sensor configured to provide a force signal to the controller. The controller: records a baseline force on the arm based on the force signal received prior to the deformation of the workpiece; receives a measured force from the force sensor after initiation of the deformation; compares the measured force to a threshold force; and unlocks the joint when the measured force exceeds the threshold force. In additional embodiments, the gripper comprises a suction cup. A pneumatic system is coupled with the suction cup and with the controller. The controller is configured to control the pneumatic system to maintain connection between the suction cup and the workpiece during the deformation. In additional embodiments, the joint assembly includes a ball and socket joint, wherein the lock includes a band encircling the ball and configured, in response to the controller, to squeeze the ball to lock the joint. In additional embodiments, the gripper is a first gripper disposed on the first section. A second gripper is disposed on the se