Robotic machining with a flexible manipulator

• US 9,110,456 B2
• Filed: 09/06/2005
• Issued: 08/18/2015
• Est. Priority Date: 09/08/2004
• Status: Active Grant

• Current Assignee: ABB Research Ltd. (ABB Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Zhang, Hui, Gan, ZhongXue, Wang, Jianjun, Zhang, George
• Primary Examiner(s): Shaawat, Mussa A
• Assistant Examiner(s): KIM, KYUNG J
• Application Number:
  US11/220,174
• Publication Number:
  US 20060048364A1
• Time in Patent Office: 3,633 Days
• Field of Search: 700/245, 700/260, 318/568.16, 901/6, 901/7, 901/8, 901/26, 901/41, 901/9, 901/10, 134/62, 134/66, 134/76, 134/140, 29/26.A, 29/40, 292/42, 293/435.4, 293/48, 294/070.8, 297/09, 414/676, 414/735, 414/736, 269/20, 269/309, 821/25, 821/60, 483/14, 483/901
• US Class Current: 1/1
• CPC Class Codes: B23Q 17/0966 by measuring a force on parts of the machine other than a motor
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: B25J 9/1641 compensation for backlash, friction, compliance, elasticity in the joints
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 2219/37319 Derive acceleration, force, torque from current
• CPC Class Codes: G05B 2219/37355 Cutting, milling, machining force
• CPC Class Codes: G05B 2219/42033 Kind of servo controller
• CPC Class Codes: G05B 2219/45068 Cutting robot
• CPC Class Codes: G05B 2219/49079 Control cutting torque, force
• CPC Class Codes: G05B 2219/49082 Maintain constant material removal rate
• CPC Class Codes: G05B 2219/49099 Cutting force, torque
• CPC Class Codes: Y10T 29/49776 Pressure, force, or weight determining
• CPC Class Codes: Y10T 29/53039 with control means energized in response to activator stimulated by condition sensor

Abstract

A robot machining with a flexible manipulator has an end effector which may either hold the tool to perform the machining or the work piece to be machined. A signal representative of a force applied by said tool to said work piece is used to control either the relative motion between the tool and the work piece to give a controlled material removal rate (CMRR) or the relative position between the tool or the work piece to provide deformation compensation or both CMRR and deformation compensation. A force sensor provides the signal for deformation compensation. For CMRR the signal may be obtained from either a force sensor or the current flowing in the motor of the robot'"'"'s spindle. The force sensor can be mounted either on the robot or together with either the tool or work piece adjacent to the robot.

Claims

1. In a system having a robot and a tool for machining a work piece, the robot including a plurality of robot joints, a method for compensating for deformation of the robot joints during said machining comprising:

obtaining a stiffness model using joint angles only, said stiffness model relating the force applied at a tip of said tool to the deformation of said tool tip;

obtaining after said stiffness model is obtained a signal from a force sensor of a force applied by said tool to said work piece;

using said signal and said stiffness model to determine the deformation of said robot joints due to said force applied by said tool to said work piece; and

using said determined deformation of said robot joints to modify the relative position between said tool and said work piece to compensate for said deformation of said robot during said machining.

2. The method of claim 1 further comprising mounting said force sensor either on said robot or together with said tool or work piece adjacent to said robot.

3. The method of claim 1 further comprising mounting said force sensor either on said robot or together with said tool or work piece adjacent to said robot to thereby provide said signal.

4. The method of claim 1 wherein said robot is a six degree of freedom robot having six axes of rotation.

5. The method of claim 4 wherein said stiffness model is determined prior to said machining by:

applying a load to said tool at one or more different robot orientations and measuring the displacement of said tool under load.

6. The method of claim 1 wherein said stiffness model comprises rotational stiffness coefficients for said plurality of robot joints.

7. The method of claim 1 wherein K_q is solved using least squares method according to:

F=J(Q)<sup>−

T</sup>K_qJ(Q)<sup>−

1</sup>Δ

X.

8. The method of claim 1 wherein said stiffness model relates the force applied in one direction at a tip of said tool to the deformation of said tool tip in all directions.

9. In a system having a robot and a tool held by said robot for machining a work piece a method for compensating for variability of height of the surface of said work piece during said machining comprising:

determining a stiffness model prior to said machining by applying a load to said tool at one or more different robot orientations and measuring the displacement of said tool under load;

using only said tool held by said robot to remove material from said surface of said work piece;

setting a constant material removal rate for said tool to remove material from said surface of said work piece;

generating from a force sensor mounted on said tool a signal representative of the force applied in real time to said work piece by said tool during said machining of said work piece by said tool; and

using said force sensor signal and said stiffness model to modify the relative position between said tool and said work piece to maintain a constant material removal rate during said machining of said work piece by said tool.

10. A controller for controlling a robot having a plurality of joints and carrying a tool for machining a work piece, said controller having software executable to:

obtain a stiffness model using joint angles only, said stiffness model relating the force applied at a tip of said tool to the deformation of said tool tip;

obtain after said stiffness model is obtained a signal from a force sensor of a force applied by said tool to said work piece;

use said signal and said stiffness model to determine the deformation of said robot due to said force applied by said tool to said work piece; and

use said determined deformation of said robot to modify the relative position between said tool and said work piece to compensate for said deformation of said robot during said machining.

11. The controller of claim 10 wherein said stiffness model comprises rotational stiffness coefficients for said plurality of robot joints.

12. The method of claim 11 wherein K_q is solved using least squares method according to:

F=J(Q)<sup>−

T</sup>K_qJ(Q)<sup>−

1</sup>Δ

X.

13. The controller of claim 11 wherein said stiffness model relates the force applied in one direction at a tip of said tool to the deformation of said tool tip in all directions.