System and method for controlling a manipulator in response to backdrive forces

• US 9,795,445 B2
• Filed: 12/01/2015
• Issued: 10/24/2017
• Est. Priority Date: 08/03/2012
• Status: Active Grant

• Current Assignee: Stryker Corporation
• Original Assignee: Stryker Corporation
• Inventors: Bowling, David Gene
• Primary Examiner(s): Kiswanto, Nicholas
• Assistant Examiner(s): WEBER, TAMARA L
• Application Number:
  US14/955,927
• Publication Number:
  US 20160089211A1
• Time in Patent Office: 693 Days
• Field of Search: None
• CPC Class Codes: A61B 17/16 Bone cutting, breaking or removal means other than saws, e.g. Osteoclasts; Drills or chisels for bones; Trepans arthroscopic bone cutters A61B17/320016; dental implant drills potentially for other surgical use A61C8/0089; bone grinders A61F2/4644, A22C17/06; A61B17/1662 takes precedence over all other subgroups except A61B17/17
• CPC Class Codes: A61B 17/1626 Control means; Display units
• CPC Class Codes: A61B 18/148 having a short, rigid shaft for accessing the inner body transcutaneously, e.g. for neurosurgery or arthroscopy
• CPC Class Codes: A61B 2018/00565 Bone
• CPC Class Codes: A61B 2018/00601 Cutting
• CPC Class Codes: A61B 2034/107 Visualisation of planned trajectories or target regions
• CPC Class Codes: A61B 2034/2046 Tracking techniques
• CPC Class Codes: A61B 2090/066 for measuring torque
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 34/30 Surgical robots
• CPC Class Codes: A61B 34/32 operating autonomously
• CPC Class Codes: A61B 34/37 Master-slave robots A61B34/35 takes precedence
• CPC Class Codes: A61B 34/70 Manipulators specially adapted for use in surgery
• CPC Class Codes: A61B 34/76 Manipulators having means for providing feel, e.g. force or tactile feedback
• CPC Class Codes: B25J 13/00 Controls for manipulators programme controls B25J9/16; control in general G05
• CPC Class Codes: B25J 13/085 Force or torque sensors B25J13/082, B25J13/084 take precedence
• CPC Class Codes: B25J 9/009 being mechanically linked with one another at their distal ends
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: G05B 2219/40191 Autonomous manipulation, computer assists operator during manipulation
• CPC Class Codes: G05B 2219/45117 Medical, radio surgery manipulator
• CPC Class Codes: G16H 40/63 : for local operation

Abstract

A system and method for controlling a manipulator are provided. A manipulator controller measures an actual torque and calculates an expected torque for at least one joint motor of the manipulator. The manipulator controller computes a backdrive force for the at least one joint motor based on the actual torque and expected torque. A surgical tool of the manipulator is modeled as a virtual rigid body. The manipulator controller computes a total force or torque to apply to the virtual rigid body based on the backdrive force. The manipulator controller determines a target position of the surgical instrument based on the total force or torque and commands positioning of the joint motors to advance the surgical instrument to the target position.

Claims

1. A system comprising:

a surgical instrument and an energy applicator;

a manipulator configured to position said surgical instrument and said energy applicator, said manipulator comprising a plurality of joints and a plurality of joint motors; and

a manipulator controller configured to (1) determine a backdrive force for at least one joint motor based on an actual torque for said at least one joint motor and an expected torque for said at least one joint motor, (2) model said surgical instrument and said energy applicator as a virtual rigid body, (3) compute a total force or torque to apply to said virtual rigid body based on said backdrive force, (4) determine a target position of said surgical instrument based on said total force or torque, and (5) command positioning of said joint motors to advance said surgical instrument to said target position.

2. The system of claim 1 further comprising a sensor configured to sense forces or torques applied to said surgical instrument.

3. The system of claim 2 wherein said sensor is defined as a six degree-of-freedom force-torque sensor.

4. The system of claim 2 wherein said manipulator controller is further configured to compute said total force or torque based on forces or torques applied to said surgical instrument.

5. The system of claim 2 wherein said backdrive force is outputted by said at least one joint motor in response to external forces applied to said manipulator beyond said forces or torques applied to said surgical instrument.

6. The system of claim 1 wherein said actual torque is torque that said at least one joint motor applies to advance said surgical instrument to said target position.

7. The system of claim 1 wherein said actual torque is determined by measuring current drawn by said at least one joint motor.

8. The system of claim 1 wherein said expected torque is torque that said at least one joint motor should output if external forces and torques are not present.

9. The system of claim 1 wherein said expected torque is determined based on an angular position of at least one joint and a commanded joint angle for said at least one joint.

10. The system of claim 1 wherein said manipulator controller is further configured to determine said backdrive force by computing a difference between said expected torque and said actual torque.

11. A method for operating a manipulator controller of a system, the system comprising a surgical instrument and an energy applicator, a manipulator configured to position the surgical instrument and the energy applicator, with the manipulator comprising a plurality of joints and a plurality of joint motors, and the manipulator controller in communication with the manipulator, the method comprising:

measuring an actual torque for at least one joint motor;

calculating an expected torque for the at least one joint motor;

computing a backdrive force for the at least one joint motor based on the actual torque and the expected torque;

modeling the surgical instrument and the energy applicator as a virtual rigid body;

computing a total force or torque to apply to the virtual rigid body based on the backdrive force;

determining a target position of the surgical instrument based on the total force or torque; and

commanding positioning of the joint motors to advance the surgical instrument to the target position.

12. The method of claim 11 further comprising the step of receiving signals outputted by a sensor sensing forces or torques applied to the surgical instrument.

13. The method of claim 12 wherein the step of computing the total force or torque is further defined as computing the total force or torque based forces or torques applied to the surgical instrument.

14. The method of claim 12 wherein the backdrive force occurs in response to external forces applied to the manipulator beyond the forces or torques applied to the surgical instrument.

15. The method of claim 11 wherein the step of measuring the actual torque is further defined as measuring torque that the at least one joint motor applies to advance the surgical instrument to the target position.

16. The method of claim 11 wherein the step of measuring the actual is further defined as measuring current drawn by the at least one joint motor.

17. The method of claim 11 wherein the step of calculating the expected torque is further defined as calculating torque that the at least one joint motor should output if external forces and torques are not present.

18. The method of claim 11 wherein the step of calculating the expected torque is further defined as comparing an angular position of at least one joint and a commanded joint angle for at least one joint.

19. The method of claim 11 wherein the step of determining the backdrive force is further defined as computing a difference between the expected torque and the actual torque.