Dynamic control of a robot with its center of mass decoupled from an end effector by a redundant linkage

• US 5,214,749 A
• Filed: 06/12/1991
• Issued: 05/25/1993
• Est. Priority Date: 06/12/1991
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Brown, Kevin L.
• Primary Examiner(s): MacDonald, Allen R.
• Application Number:
  US07/714,422
• Time in Patent Office: 713 Days
• Field of Search: 395/95, 395/96, 395/94, 901/48, 364/424.02
• US Class Current: 700/260
• CPC Class Codes: B25J 9/1643 redundant control
• CPC Class Codes: G05B 2219/40376 Moving center of mass and end effector for dynamic task of lifting heavy weight
• CPC Class Codes: G05B 2219/40377 Impact force on stationary end effector, move center of mass, no reaction to base
• CPC Class Codes: G05B 2219/40378 Keep center of mass fixed, no counterweight, no reaction on base

Abstract

A robot is provided with a dynamically controlled center of mass which is decoupled from the end effector. The robot is comprised of a moving arm including a redundant linkage of connecting links and joints coupled to an end effector. The movement of the links and joints of the robot are coordinated by a dynamic servo controller. The robot has at least twice as many degrees of freedom as the number of operating dimensions. Also, for each dimension of operation, there is one group of masses that moves in the same direction as the end effector and another group of masses capable of independently moving in the same or opposite direction. This separation of the motion of the center of mass from the motion of the end effector can be used to decrease reaction forces and to generate significant forces at the end effector.

Claims

1. A robot with a dynamically controlled center of mass comprising:

(a) a robot arm including;

(i) an end effector linkage including an end effector which can move in n dimensions of operation, wherein for each dimension of operation, a first mass is provided which moves in the same direction of movement as the end effector,

(ii) a redundant linkage, including a plurality of links and joints, coupled to said end effector, wherein the redundant linkage includes a second mass which can be independently moved in the same or opposite direction of movement of the first mass, and

(b) a dynamic controller for moving the robot arm so that for each dimension of movement of the end effector there are at least two degrees of freedom of the robot arm to decouple the center of mass from the end effector.

2. A zero-reaction force robot comprising:

(a) a base;

(b) a robot arm with a center of mass including;

(i) an end effector linkage including an end effector which can move in n dimensions, where n is an integer, and for each dimension of operation, the end effector includes a first mass which moves in the same direction of movement as the end effector,

(ii) a redundant linkage, including a plurality of links and joints, which connects the end effector to the base such that the robot arm has 2n degrees of freedom wherein the redundant linkage includes a second mass which can be independently moved in the same or opposite direction of movement of the first mass of the end effector, and

(c) a dynamic controller for moving the robot arm such that the redundant linkage is repositioned in response to end effector movement to fix the position of the center of mass and prevent the coupling of reaction forces to the base.

3. A zero-reaction force robot, as recited in claim 2, wherein the redundant linkage further comprises:

a first link;

a second link coupled to said first link and said base by a first moving joint;

a third link coupled to said first link by a second moving joint;

a fourth link coupled to said second link by a third moving joint; and

a fourth moving joint coupling said third and fourth links together so that the redundant linkage forms a planar parallelogram.

4. A zero-reaction force robot, as recited in claim 3, wherein the end effector linkage further comprises:

a fifth link with a first end and a second end;

a fifth moving joint coupled to said first end of said fifth link and to said fourth moving joint;

a sixth moving joint connected to said second end of said fifth link; and

a sixth link, with a tip which serves as the end effector, coupled to said fifth link by said sixth moving joint so that the sixth link tip moves in a plane.

5. A zero-reaction force robot, as recited in claim 4, wherein the dynamic controller moves the redundant linkage and the end effector in accordance with the following constraint:

##STR5## where x, y is the position of the end effector tip,

x, y is velocity of the end effector,

X, Y is the position of the robot center of mass,

X, Y is the velocity of the robot center of mass,

φ

₁ is the angular displacement of a diagonal connecting the first and fourth joints from the base,

φ

₂ is the angular displacement of the end effector from the base,

θ

₁ is the angular displacement of the diagonal from the first link,

θ

₂ is the angular displacement of the fifth link and the sixth link from the plane of the redundant linkage,

A₁ is the length of the redundant linkage completely extended,

A₂ is the length of the end effector completely extended,

A₃ is the center of mass location of the redundant linkage, and

A₄ is the center of mass location of the end effector linkage.

6. A zero-reaction force robot, as recited in claim 5, wherein the robot configuration is controlled in accordance with a joint position feedback signal and a joint velocity feedback signal.

7. A zero-reaction force robot comprising:

a linkage including a plurality of vertexes;

an end effector connected to a first vertex of said linkage;

a base connected to a second vertex of said linkage which is opposite the vertex connected to the end effector; and

a motor which varies the shape and position of the linkage in accordance with the movement of the end effector such that the center of mass of the robot remains fixed.

8. A method of eliminating reaction forces in a robot, said robot including a robot arm, a base, and a linkage coupling the robot arm to the base, said method comprising the steps of:

(a) determining the desired position of the robot arm;

(b) calculating the shape and position of the linkage which will balance the reaction forces produced by the moving robot arm so that the center of mass of the robot remains fixed;

(c) moving the robot arm to the desired position; and

(d) controlling the movement of the linkage according to the calculated values during the movement of the robot arm so that the center of mass of the robot remains fixed.

9. A humanoid zero-reaction force robot with a dynamically controlled center of mass comprising:

a base link,

a first moving joint,

a redundant linkage including;

a leg link,

said first moving joint coupling the leg link to the base link,

a body link,

a second moving joint coupling the body link to said leg link,

an end effector linkage including;

a first arm link coupled to said body link by a third moving joint,

a second arm link, including a holding tip which serves as an end effector, coupled to said first arm link by a fourth moving joint,

wherein for each dimension of operation, the end effector linkage includes a first mass which moves in the same direction of movement as the end effector and the redundant linkage includes a second mass which can be moved in the opposite direction of movement of the first mass of the end effector,

a head unit, connected to the body unit, including;

a video camera, and

a dynamic controller for moving the robot arm so that for each dimension of operation of the end effector there are at least two degrees of freedom of the robot arm to decouple the center of mass from the end effector and prevent the coupling of reaction forces to the base link.

10. A robot with a dynamically controlled center of mass comprising:

(a) a base,

(b) a robot arm including;

(i) an end effector linkage having a clamping tip which can move in n dimensions, said clamping tip is attached to a final point at which force is to be applied, for each dimension of operation, the end effector linkage includes a first mass which moves in the same direction of movement as the end effector linkage,

(ii) a redundant linkage, including a plurality of links and joints, which connects the end effector linkage to the base such that the robot arm has 2n degrees of freedom wherein the redundant linkage includes a second mass which can be independently moved in the same or opposite direction of movement of the first mass of the end effector linkage, and

(c) a dynamic controller for moving the robot arm such that the robot center of mass is accelerated and decelerated to apply an impulsive force at the clamping tip.

11. A robot, as recited in claim 10, wherein the robot center of mass moves along a line which passes through the fixed point attached to the clamping tip such that reactive forces are decoupled from the base.

12. A humanoid robot with a dynamically controlled center of mass comprising:

a base link,

a first moving joint,

a redundant linkage including;

a leg link,

said first moving joint coupling the leg link to the base link,

a body link,

a second moving joint coupling the body link to said leg link,

an end effector linkage including;

a first arm link coupled to said body link by a third moving joint,

a second arm link, including a clamping tip which serves as an end effector attached to a fixed point, coupled to said first arm link by a fourth moving joint,

wherein for each dimension of operation, the end effector linkage includes a first mass which moves in the same direction of movement as the end effector and the redundant linkage includes a second mass which can be independently moved in the same or opposite direction of movement of the first mass of the end effector,

a head unit, connected to the body unit, including;

a video camera, and

a dynamic controller for moving the robot arm so that for each dimension of operation of the end effector there are at least two degrees of freedom of the robot arm to decouple the center of mass from the end effector to accelerate the center of mass to impart an impulsive force at the fixed point.

13. A method of applying an impulsive force using a robot, said robot including a base, a robot arm including an end effector having a clamping tip and a redundant linkage, and a dynamic controller for moving the robot arm, said method comprising:

(a) attaching the clamping tip to a fixed point at which force is to be applied,

(b) determining the desired force to be applied at the fixed point,

(c) calculating the required movement of the robot arm to accelerate the center of mass to impart the desired force of the fixed point, and

(d) dynamically controlling the movement of the robot arm in accordance with the calculated required movement to accelerate the center of mass to impart an impulsive force at the fixed point.

14. A method, as recited in claim 13, wherein the robot center of mass moves along a line which passes through the fixed point attached to the clamping tip such that reactive forces are decoupled from the base.

15. A robot with a dynamically controlled center of mass comprising:

(a) a base, resting on a surface,

(b) a robot arm including;

(i) an end effector which can move in n dimensions,

(ii) a redundant linkage, including a plurality of links and joints, which connects the end effector to the base such that the robot arm has 2n degrees of freedom, and

(c) a dynamic controller for moving the robot arm such that the robot center of mass is accelerated away the surface to cause the entire robot and base to jump off the surface.

16. A robot with a dynamically controlled center of mass comprising:

(a) a base, resting on a first surface,

(b) a robot arm including;

(i) an end effector, with a clamping tip for holding an object resting on a second surface, which can move in n dimensions,

(ii) a redundant linkage, including a plurality of links and joints, which connects the end effector to the base such that the robot arm has 2n degrees of freedom; and

(c) a dynamic controller for moving the robot arm such that the robot center of mass is accelerated so that the object is lifted off the second surface.