Material or article handling – Horizontally swinging load support – Swinging about pivot
Reexamination Certificate
2001-01-26
2002-12-17
Underwood, Donald W. (Department: 3652)
Material or article handling
Horizontally swinging load support
Swinging about pivot
Reexamination Certificate
active
06494666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to robot arms, and in particular to Selective Compliance Articulated Robot for Assembly (“SCARA”) arms.
2. Description of the Prior Art
A truly general-purpose industrial robot arms usually provides six independently moving axes, or joints. Each joint is driven using a linear or rotary actuator, like a servomotor. This type of robot is said to have six degrees of freedom (“DOF”), i.e., each independently driven axis provides one DOF. Three DOF are used to position a workpiece in the Cartesian x-y-z space, and the other three DOF are used to orient the workpiece at specific pitch, roll and yaw angles with respect to the x, y, and z axis, respectively. Many industrial applications employ general-purpose robot arms because of their maximum flexibility in manipulating workpieces.
In comparison, conventional robot arms used for handling semiconductor wafers usually include at least two jointed links that move horizontally. A shoulder joint of one link, sometimes referred to as an upper arm, is supported by an elevator. A second link, sometimes referred to as the forearm, connects at an elbow joint to the distal end of the upper arm. A third link that holds semiconductor wafers, usually called and end-effector, attaches at a wrist joint to a distal end of the forearm.
One example of this second type of robot arm appears in U.S. Pat. No. 4,947,702 entitled “Industrial Robot” that issued Aug. 14, 1990, (“the '702 patent”). The SCARA arm disclosed in the '702 patent includes a base which supports an end-effector via an upper arm and a forearm. This SCARA arm includes an elevator that raises and lowers the shoulder joint of the upper arm. The upper arm and forearm are rotatably coupled to each other at an elbow joint. This SCARA arm also includes driving motors, that are located in the base body, to independently energize all motion of the upper arm, forearm, and end-effector. Mechanical transmissions, located in the base body, and in the two arms, couple the respective driving motors to each of the arms, and the end-effector.
During operation of this SCARA arm, one of the driving motors first raises or lowers the upper arm until it is at a desired height. Then, another driving motor rotates the upper arm in a horizontal plane about a shoulder joint to a desired orientation. Via a belt transmission located in the upper arm, yet another driving motor then rotates the forearm, also in a horizontal plane, about an elbow joint to a desired orientation. Finally, the end-effector of this SCARA arm rotates about a wrist joint, again in a horizontal plane, to a desired position. Including the elevator mechanism, the SCARA arm disclosed in the '702 patent provides a total of four (4) DOF.
The '702 patent states that locating the driving motors in the base body avoids having drive units located at the arm joints and wrist joint. Furthermore, the '702 patent also states that locating the driving motors in the base body increases SCARA arm reliability since electrical cables connecting to its driving motor are less liable to vibrate and/or break.
U.S. Pat. No. 5,064,340 entitled “Precision Arm Mechanism” that issued Nov. 12, 1991, (“the '340 patent”) discloses a SCARA arm similar to that of the '702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The '340 patent further discloses individual belt drives, located respectively in the upper arm and forearm, which produce linear motion of a wrist joint that joins the end-effector to the forearm. The '340 patent states that this belt drive positions the end-effector more accurately than other types of transmissions, and avoids transmitting any chattering or cogging of the driving motor to the end-effector.
U.S. Pat. No. 5,178,512 entitled “Precision Robot Apparatus” that issued Jan. 12, 1993, (“the '512 patent”) discloses a SCARA arm similar to that of the '702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. Similar to the '340 patent, the '512 patent employs belt drive transmissions to move the wrist joint that couples between an end of the forearm and an end-effector. The '512 patent emphasizes the importance of placing the diving motors near the bottom of the SCARA arm.
U.S. Pat. No. 5,741,113 entitled “Continuously Rotatable Multiple Link Robot Arm Mechanism” that issued Apr. 21, 1998, (“the '113 patent”) discloses a SCARA arm similar to that of the '702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The '113 patent further discloses the use to two motors capable of synchronized operation that permits moving the end-effector along an arbitrary path without lockout spaces to virtually any location in an available work space. The SCARA arm disclosed in the '113 patent also avoids any robot arm rewind requirement while permitting continuous rotation in one direction without kinking, twisting or breaking a conduit that delivers vacuum to the end-effector for gripping a semiconductor wafer workpiece.
U.S. Pat. No. 5,746,565 entitled “Robotic Wafer Handler” that issued May 5, 1998, (“the '565 patent”) discloses a SCARA arm similar to that of the '702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The '565 patent further discloses a SCARA arm whose upper arm and forearm are independently rotatable through multiple revolutions greater than 360°. The rotation plane of the upper arm and forearm may be raised or lowered, and may also be tilted. A track disclosed in the '565 patent permits moving horizontally back and forth the shoulder joint about which the upper arm rotates.
U.S. Pat. No. 5,789,890 entitled “Robot Having Multiple Degrees of Freedom” that issued Aug. 4, 1998, (“the '890 patent”) discloses a SCARA arm similar to that of the '702 patent with all driving motors for the upper arm and forearm being located in a base of the robot arm below the rotating upper arm and forearm. The wrist joint of the SCARA arm disclosed in the '890 patent carries motors for energizing roll, pitch and yaw motions of the arm's end-effector. The '702 patent states that the roll, pitch and yaw motions-in combination with the motions provided by the upper arm and forearm permit any desired three-dimensional motion of the end-effector, i.e. provide a total of six (6) DOF.
One characteristic shared by most of the SCARA arms described thus far is that rotation about one of the arm's joint's induces rotation about another of the arm's joints. The SCARA arms disclosed in the '340 and '890 patents exhibit this characteristic fully. That is, rotation about any of the joints of the SCARA arms disclosed in the '340 and '890 patents induces rotation about the arm's other joints. The SCARA arms disclosed in the '113, '702 and '512 patents also partially exhibit this characteristic. That is, for the SCARA arms disclosed in the '113, '702 and '512 patents rotation about an earlier joint, e.g. the shoulder joint, induces rotation about later joints, e.g. the forearm and end-effector joints. However, these SCARA arms do not exhibit the converse of this characteristic. That is, for the SCARA arms disclosed in the '113, '702 and '512 patents rotation about a later joint, e.g. the end-effector joint, does not induce rotation about an earlier joint, e.g. the forearm or shoulder joints. Clearly, controlling the position of a SCARA arm's end-effector when rotation of an earlier joint induces rotations which displace the end effector is more complicated than controlling the end-effector's position if all joint rotations are independent of one other.
For semiconductor manufacturing, the task of delivering wafers to manufacturing tools requir
Rush John M.
Ulander Torben
Wu Kung Chris
Fortrend Engineering Corporation
Schreiber D. E.
Underwood Donald W.
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