Method and system for load estimation and gravity compensation on a robotic arm

• US 10,702,988 B2
• Filed: 05/07/2018
• Issued: 07/07/2020
• Est. Priority Date: 09/21/2017
• Status: Active Grant

• Current Assignee: HIWIN Technologies Corp.
• Original Assignee: HIWIN Technologies Corp.
• Inventors: Jian, Jia-Huei, Chen, Cheng-Chin, Hou, Jung-Fu
• Primary Examiner(s): Marc, Mcdieunel
• Application Number:
  US15/972,459
• Publication Number:
  US 20190084154A1
• Time in Patent Office: 792 Days
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G01L 25/003 for measuring torque
• CPC Class Codes: G01L 5/226 to manipulators, e.g. the force due to gripping
• CPC Class Codes: G05B 2219/39194 Compensation gravity

Abstract

A method for load estimation and gravity compensation on a robotic arm including a joint is provided, and includes: receiving a first torque signal and a first joint angle when the arm is at a first position and subjected to a current load; generating a first torque value, correction parameters, and no-load and maximum-load torque values; changing the load applied to the arm to an unknown load; receiving a second torque signal and generating a second torque value; estimating an estimated load value of the unknown load; moving the arm to a second position; receiving a second joint angle; and generating a compensating torque value and outputting the compensating torque value to a driver module of the arm.

Claims

1. A method for load estimation and gravity compensation on a robotic arm, the method to be implemented by a load estimation and gravity compensation system, the robotic arm including at least one joint and a driver module that is installed on the at least one joint, the load estimation and gravity compensation system including a signal processor that is coupled to the driver module, a load estimation module that corresponds with the at least one joint and that is coupled to the signal processor, and a gravity compensation module that is coupled to the load estimation module, the load estimation module including a gravity module correction unit, a virtual robotic arm unit and a computing component, the method comprising steps of:

operating the driver module in a manipulating mode to move the robotic arm to a first position, and switching the driver module to a location control mode, the robotic arm being subjected to a current load at the first position;

receiving a first torque signal and a first joint angle outputted by the driver module in the location control mode, the first torque signal being associated with the current load, the first joint angle being associated with the joint at the first position;

upon receipt of the first torque signal, converting, by the signal processor, the first torque signal into a first torque value;

upon receipt of the first torque value, generating, by the gravity module correction unit, a set of correction parameters;

upon receipt of the set of correction parameters and the first joint angle, generating, by the virtual robotic arm unit, a no-load torque value and a maximum-load torque value;

changing the load subjected to the robotic arm to an unknown load;

receiving a second torque signal outputted by the driver module, the second torque signal being associated with the unknown load;

upon receipt of the second torque signal, converting, by the signal processor, the second torque signal into a second torque value;

estimating, by the computing component, an estimated load value of the unknown load based on the first torque value, the no-load torque value, the maximum-load torque value and the second torque value;

switching the driver module to a torque control mode, and moving the robotic arm to a second position;

receiving a second joint angle outputted by the driver module, the second joint angle being associated with the second position; and

generating, by the gravity compensation module, a compensating torque value based on the estimated load value and the second joint angle, and outputting the compensating torque value to the driver module.

2. The method of claim 1, wherein the step of estimating an estimated load value includes obtaining a load difference between the unknown load and the current load, and estimating the estimated load value by adding up the current load and the load difference.

3. The method of claim 2, the computing component including a torque-load conversion unit and a load calculating unit, wherein the step of estimating an estimated load value includes sub-steps of:

calculating, by the torque-load conversion unit, the load difference based on the first torque value, the no-load torque value, the maximum-load torque value and the second torque value; and

calculating, by the load calculating unit, the estimated load value by adding the current load and the load difference.

4. The method of claim 3, wherein the sub-step of calculating the load difference includes:

establishing a parametric equation based on a maximum load that can be applied to the robotic arm, the no-load torque value and the maximum-load torque value; and

applying each of the first torque value and the second torque value to the parametric equation, so as to obtain the load difference.

5. The method of claim 1, the robotic arm including at least two connecting rods connected to each other through the at least one joint,

wherein the step of generating a compensating torque value includes calculating the compensating torque value further based on an axial direction of an output shaft of the at least one joint, a weight of each of the connecting rods, and a position of a center of mass of each of the connecting rods.

6. The method of claim 5, wherein a direction of a force from each of the current load and the unknown load does not intersect and is not parallel to the axial direction of the output shaft of the at least one joint.

7. The method of claim 5, the robotic arm including a plurality of joints, and a plurality of connecting rods connected to one another through the joints,

wherein the step of generating a compensating torque value includes calculating the compensating torque value further based on a number of the joints, an axial direction of an output shaft of each of the joints, and the second joint angle of each of the joints.

8. The method of claim 1, the driver module including an actuator, a mechanical component connected to the actuator, and an encoder connected to the mechanical component, wherein:

in the manipulating mode, the actuator outputs a control signal to the mechanical component so as to move the robotic arm to the first position;

in the step of receiving a first torque signal and a first joint angle, the first torque signal is outputted by the actuator, and the first joint angle is outputted by the encoder;

in the step of receiving a second torque signal, the second torque signal is outputted by the actuator; and

in the step of receiving a second joint angle, the second joint angle is outputted by the encoder.

9. The method of claim 8, wherein:

each of the first torque signal and the second torque signal outputted by the actuator is a current signal including an electrical current value;

the step of converting the first torque signal into a first torque value includes calculating, by the signal processor, the first torque value based on the electrical current value of the first torque signal and a torque parameter associated with the actuator; and

the step of converting the second torque signal into a second torque value includes calculating, by the signal processor, the second torque value based on the electrical current value of the second torque signal and the torque parameter.

10. A load estimation and gravity compensation system for use with a robotic arm, the robotic arm including at least one joint and a driver module that is installed on the at least one joint, the load estimation and gravity compensation system comprising:

a signal processor to be coupled to the driver module for receiving a first torque signal and a first joint angle therefrom when the robotic arm is subjected to a current load, and for converting the first torque signal to a first torque value, wherein said signal processor further receives a second torque signal and a second joint angle from the driver module when the robotic arm is subjected to an unknown load, and converts the second torque signal to a second torque value;

a load estimation module that corresponds with the at least one joint, that is coupled to said signal processor for receiving the first and second torque values therefrom, and that is programmed to

generate a set of correction parameters based on the first torque value,

generate a no-load torque value and a maximum-load torque value based on the set of correction parameters and the first joint angle, and

estimate an estimated load value of the unknown load based on the first torque value, the no-load torque value, the maximum-load torque value and the second torque value; and

a gravity compensation module coupled to said load estimation module for generating a compensating torque value based on the estimated load value and the second joint angle, and outputting the compensating torque value to the driver module.

11. The load estimation and gravity compensation system of claim 10, wherein said load estimation module is programmed to obtain a load difference between the unknown load and the current load, and estimating the estimated load value by adding the current load and the load difference.

12. The load estimation and gravity compensation system of claim 11, wherein said load estimation module includes:

a torque-load conversion unit programmed to calculate the load difference based on the first torque value, the no-load torque value, the maximum-load torque value and the second torque value; and

a load calculating unit programmed to calculate the estimated load value by adding the current load and the load difference.

13. The load estimation and gravity compensation system of claim 12, wherein calculating the load difference includes said torque-load conversion unit:

establishing a parametric equation based on a maximum load that can be applied to the robotic arm, the no-load torque value and the maximum-load torque value; and

applying each of the first torque value and the second torque value to the parametric equation, so as to obtain the load difference.