US-20260124758-A1 - AUTOMATED METHOD TO SET PAYLOAD OF COLLABORATIVE ROBOT

US20260124758A1US 20260124758 A1US20260124758 A1US 20260124758A1US-20260124758-A1

Abstract

A method and system for automatically setting a payload weight value for a collaborative robot, where one or more objects are picked up by a robot gripper, the weight of the objects is automatically determined by a force sensor and the weight is used for the payload, and the payload value is automatically adjusted when any of the objects is dropped off. Only one weight measurement is needed when all objects are known to be of the same weight, and objects of different weights can be handled with a weight measurement for each object. The system handles payload adjustment automatically without the need for manual adjustment or custom programming. The robot uses the payload weight value when detecting any externally applied force indicating contact with an operator or other object, and also for ensuring that payload accelerations do not exceed gripping force capacity or robot joint load limits.

Inventors

Haochen Yu
Jake Weinmann
Ganesh Kalbavi

Assignees

FANUC AMERICA CORPORATION

Dates

Publication Date: 20260507
Application Date: 20251016

Claims (20)

1 . A method for setting a payload weight value of an industrial robot, said method comprising: providing a plurality of objects available for grasping; grasping a quantity of the objects by a gripper fitted to the robot; measuring a total weight of the quantity of objects, using a load sensor fitted to the robot or the gripper; setting the payload weight value using the total weight of the quantity of objects and including a known empty gripper weight value; when the grasped objects all have a same weight, determining a weight of each object as the total weight divided by the quantity, moving the gripper to a destination position, dropping off a subset of the quantity of objects, and reducing the payload weight value by an amount equal to a number of the objects dropped off multiplied by the weight of each object; and when the grasped objects do not all have the same weight, moving the gripper to a destination position, dropping off a subset of the quantity of objects, measuring a new weight of a reduced quantity of objects using the load sensor, and setting the payload weight value using the new weight.
2 . The method according to claim 1 further comprising dropping off a next subset of the quantity of objects and re-setting the payload weight value until the gripper is empty, whereupon the payload weight value is set to the empty gripper weight value.
3 . The method according to claim 1 wherein, when the quantity of objects is one and all of the objects available for grasping have the same weight, grasping the one object, measuring the weight of only a first one of the objects, setting the payload weight value using the weight of the first one of the objects including the known empty gripper weight value, dropping off the one object, and repeating grasping and dropping off additional ones of the objects without measuring the weight of each of the additional ones.
4 . The method according to claim 1 wherein, when the quantity of objects is one, and all of the objects available for grasping do not have the same weight, grasping the one object, measuring the weight of the one object, setting the payload weight value using the weight of the one object including the known empty gripper weight value, dropping off the one object, and repeating grasping and dropping off additional ones of the objects including measuring the weight of each of the additional ones.
5 . The method according to claim 1 wherein the payload weight value is used in calculating a trajectory for movement of the objects by the robot, where the trajectory includes a spatial path of the gripper and velocity and acceleration profiles along the spatial path.
6 . The method according to claim 5 wherein calculating a trajectory includes calculating robot joint loads and gripper-object forces based on the trajectory and the payload weight value and, when the robot joint loads or the gripper-object forces exceed corresponding predefined limits, recalculating the trajectory until the robot joint loads and the gripper-object forces do not exceed the limits.
7 . The method according to claim 5 wherein the robot is a collaborative robot configured for operation with a human operator in proximity to the robot, and where the payload weight value is also used to establish a threshold value of an external force on the robot which triggers robot motion stoppage.
8 . The method according to claim 1 wherein the robot is performing a palletizing or depalletizing operation by grasping and moving the objects.
9 . The method according to claim 1 wherein the gripper is a vacuum gripper including a plurality of suction elements which are individually and selectively activatable, where each of the objects is grasped by activating one or more of the suction elements and released by deactivating the one or more of the suction elements.
10 . The method according to claim 1 wherein a configuration parameter, indicating whether the objects available for grasping all have the same weight, is defined in advance of the grasping of the quantity of objects.
11 . A method for setting a payload weight value of an industrial robot, said method comprising: providing a plurality of objects available for grasping, where a configuration parameter is defined which indicates whether the objects available for grasping all have the same weight; grasping a quantity of the objects by a gripper fitted to the robot, where the gripper is a vacuum gripper including a plurality of suction elements which are individually and selectively activatable, where each of the objects is grasped by activating one or more of the suction elements; measuring a total weight of the quantity of objects, using a load sensor fitted to the robot or the gripper; setting the payload weight value using the total weight of the quantity of objects and including a known empty gripper weight value; when the grasped objects all have a same weight, determining a weight of each object as the total weight divided by the quantity, moving the gripper to a destination position, dropping off a subset of the quantity of objects, and reducing the payload weight value by an amount equal to a number of the objects dropped off multiplied by the weight of each object; when the grasped objects do not all have the same weight, moving the gripper to a destination position, dropping off a subset of the quantity of objects, measuring a new weight of a reduced quantity of objects using the load sensor, and setting the payload weight value using the new weight; and dropping off a next subset of the quantity of objects and re-setting the payload weight value until the gripper is empty, whereupon the payload weight value is set to the empty gripper weight value, where the payload weight value is used in calculating a trajectory used to move the gripper to the destination position, where the trajectory includes a spatial path of the gripper and velocity and acceleration profiles along the spatial path.
12 . The method according to claim 11 wherein, when the quantity of objects is one, grasping the one object, measuring the weight of the one object, setting the payload weight value using the weight of the one object including the known empty gripper weight value, dropping off the one object, and repeating grasping and dropping off additional ones of the objects, only measuring the weight of each of the additional ones of the objects when the objects available for grasping do not all have the same weight.
13 . The method according to claim 11 wherein calculating a trajectory includes calculating robot joint loads and gripper-object forces based on the trajectory and the payload weight value and, when the robot joint loads or the gripper-object forces exceed corresponding predefined limits, recalculating the trajectory until the robot joint loads and the gripper-object forces do not exceed the limits.
14 . The method according to claim 13 wherein the robot is a collaborative robot configured for operation with a human operator in proximity to the robot, and where the payload weight value is also used to establish a threshold value of an external force on the robot which triggers robot motion stoppage.
15 . A robotic pick and place system with automatic payload compensation, said system comprising: an industrial robot fitted with a gripper, and a load sensor coupled to the robot and/or the gripper; and a robot controller in communication with the robot, the gripper and the load sensor, said controller configured to perform steps including; grasping, from a plurality of objects available for grasping, a quantity of objects by the gripper; measuring a total weight of the quantity of objects, using the load sensor; setting the payload weight value using the total weight of the quantity of objects and including a known empty gripper weight value; when the grasped objects all have a same weight, determining a weight of each object as the total weight divided by the quantity, moving the gripper to a destination position, dropping off a subset of the quantity of objects, and reducing the payload weight value by an amount equal to a number of the objects dropped off multiplied by the weight of each object; and when the grasped objects do not all have the same weight, moving the gripper to a destination position, dropping off a subset of the quantity of objects, measuring a new weight of a reduced quantity of objects using the load sensor, and setting the payload weight value using the new weight.
16 . The system according to claim 15 the controller is further configured for dropping off a next subset of the quantity of objects and re-setting the payload weight value until the gripper is empty, whereupon the payload weight value is set to the empty gripper weight value.
17 . The system according to claim 15 wherein the controller is further configured for, when the quantity of objects is one and all of the objects available for grasping have the same weight, grasping the one object, measuring the weight of only a first one of the objects, setting the payload weight value using the weight of the first one of the objects including the known empty gripper weight value, dropping off the one object, and repeating grasping and dropping off additional ones of the objects without measuring the weight of each of the additional ones.
18 . The system according to claim 15 wherein the controller is further configured for, when the quantity of objects is one, and all of the objects available for grasping do not have the same weight, grasping the one object, measuring the weight of the one object, setting the payload weight value using the weight of the one object including the known empty gripper weight value, dropping off the one object, and repeating grasping and dropping off additional ones of the objects including measuring the weight of each of the additional ones.
19 . The system according to claim 15 wherein the payload weight value is used by the controller in calculating a trajectory for movement of the objects by the robot, where the trajectory includes a spatial path of the gripper and velocity and acceleration profiles along the spatial path.
20 . The system according to claim 19 wherein calculating a trajectory includes calculating robot joint loads and gripper-object forces based on the trajectory and the payload weight value and, when the robot joint loads or the gripper-object forces exceed corresponding predefined limits, recalculating the trajectory until the robot joint loads and the gripper-object forces do not exceed the limits.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of the priority date of U.S. Provisional Patent Application Ser. No. 63/715,043, titled AUTOMATED METHOD TO SET PAYLOAD OF COLLABORATIVE ROBOT, filed Nov. 1, 2024. BACKGROUND Field The present disclosure relates generally to the field of industrial robot control and, more particularly, to a method for automatically setting a payload weight value for a collaborative robot, where one or more objects are picked up by a robot gripper, the weight of the objects is automatically determined by a force sensor and the weight is used for the payload, and the payload value is automatically adjusted when any of the objects is dropped off. Discussion of the Related Art The use of industrial robots to perform a wide range of manufacturing, assembly and material movement operations is well known. Many of these operations and tasks are performed by articulated robots, such as five-or six-axis robots with a servo motor at each rotational joint. Control of such robots is provided in real time, where a motion program is divided into small increments of motion, and a robot controller performs real-time feedback control calculations to compute joint motor input commands which move the robot end-of-arm tool center point along a prescribed trajectory. One common type of robotic task is material movement, which involves moving packages or workpieces from an origin location to a destination location. A particular application of this type is where the robot is fitted with a vacuum gripper tool and the robot picks up packages (e.g., boxes) and moves them to a prescribed location. This type of robotic operation is commonly used for depalletizing or palletizing (i.e., moving boxes from a pallet to a conveyor, or vice versa). In operations of the type described above, it is necessary to know the weight of the “payload”, or the objects which are being moved by the robot arm. The payload is typically considered to include the gripper (often a vacuum gripper of substantial weight) along with the box or boxes which are being carried by the gripper at any given time. The payload weight value is used for computing a robot end-of-arm trajectory and corresponding velocities and accelerations which maintain robot joint loads within prescribed limits, and which also prevent detachment of the box(es) from the vacuum gripper. Certain applications dictate the use of collaborative robots, which are robots designed for use alongside a human operator in a workspace. Collaborative robots include control features for preventing forceful contact between the robot or its payload and the human operator. In collaborative robot applications, the payload weight value is used for establishing the control parameters which detect contact with any obstacle in the workspace, in addition to the trajectory calculation purposes described above. Various methods have been used for setting a payload weight value for robots. In the simplest case, a robot only moves one box at a time, every box has the same weight, and the weight is known. In this case, the payload weight value is simply the weight of the gripper if the gripper is not carrying a box, or the weight of the gripper plus the known box weight if the gripper is carrying a box. Most real applications are more complex, however, including boxes of various sizes and weights on a single pallet, and the need for the robot to pick up multiple boxes at the same time, drop off some of the boxes at one location and other boxes at other locations, and so forth. In applications such as this, determination of the payload weight value can be complicated and time-consuming. One known technique for establishing a payload weight value is simply to measure the weight of all boxes being carried after each grasping or ungrasping operation. The weight measurement may be performed by a force sensor mounted on the robot arm proximal the vacuum gripper. The disadvantage of this technique is that the robot must stop after each grasp or ungrasp operation and the weight measurement then takes a certain amount of time. These measurement delays seriously reduce the productivity of the robot which is performing the package movement. Even if box weights are known (all boxes having the same weight, or boxes of various known weights), most palletizing/depalletizing operations require the flexibility to grasp and ungrasp boxes in different numbers and combinations, depending on the makeup of particular pallets. For example, in one task the robot may need to grasp three boxes of different weights and drop them one at a time at different locations, and in the next task the robot may need to grasp four boxes of the same weight and drop them off in quantities of two, one and one. Each of these different task combinations requires a specific payload schedule, where each payload schedule identifies the payload weight value at each of the multiple steps of the task. This quickl