Machine element or mechanism – Control lever and linkage systems – Multiple controlling elements for single controlled element
Reexamination Certificate
2000-03-01
2001-12-04
Bucci, David A. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Multiple controlling elements for single controlled element
C901S021000
Reexamination Certificate
active
06324934
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a robot arm having an end effector located at the remote end of the robot arm maintaining the same orientation regardless of rotational movements of the arm. The robot arm also has at least one idler pulley located within one of the links that allow the diameter of the joints to be enlarged so that wires or other elongated components may pass through the interior of the joints.
BACKGROUND OF THE INVENTION
In the semiconductor industry, robot arms have typically been employed to move semiconductor wafers from one location to another. It is desired in the design of a robot arm in the semiconductor industry to have the end effector maintain the same orientation when the arm moves radially inward and outward. As discussed, for example, in U.S. Pat. Nos. 4,299,533 and 5,064,340, robot arms have been provided with two links and an end effector mounted at a distal end of the second link. The proximal end of the first link is mounted coaxially with a pulley, referred to herein as the “fixed” pulley. The proximal end of the second link is pivotally connected to the distal end of the first link. A first belt connects the fixed pulley to a second link pulley at the proximal end of the second-link, whereas a second belt connects a housing fixed to the distal end of the first link to a pulley on the end effector. If the lengths of the links are equal, and if the pulleys are selected so that the ratio of rotation of the end effective to rotation of the second link is −½ and the ratio of rotation of the second link to rotation of the first link is −2, the end effector will remaining fixed orientation but will move radially when the first link rotates relative to the fixed pulley.
While this approach is effective, it imposes some serious design constraints. To provide the desired ratios, a relatively large end effector pulley is needed. For the end effector to rotate one-half the rotation of the second link, the pulley at the end effector must be twice as large as the housing on the distal end of the first link. When the pulley at the end effector is large, it adds significant mass to the end of the robot arm, increasing inertia and making it much more difficult to control precisely the movements of the arm.
Also, to provide the desired ratios, the second link pulley and the housing at the distal end of the second link must be of relatively small diameter, i.e., half the diameter of the fixed pulley. This makes it difficult to connect to wires, pneumatic tubes, or other elongated components extending from the first to the second neighboring link through a hollow bore at the exit of the second link pulley and housing. Such wires, tubes and other elongated components are usually part of the control system for controlling the end effector. Thus, it would be desired to create a robot arm with enough space at the joint between the links so that these wires and tubes can pass through the center of the joint.
The robot arm of the present invention addresses the problems set forth above and is described more fully below.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a robot arm comprises a first and a second link, the first link having a proximal end and a distal end and the second link having a proximal and a distal end. The proximal end of the first link is pivotally connected to a base for rotation relative to a first pivot axis. The proximal end of the second link is pivotally mounted to the distal end of the first link and is capable of rotation about a second pivot axis that is parallel to the first pivot axis. An end effector is pivotally connected to the distal end of the second link and is capable of rotation about a third pivot axis which is parallel to the first and second pivot axes. A fixed pulley, with a circumferential surface concentric with the first pivot axis is mounted at the proximal end of the first link. A second-link pulley is fixed to the second link for rotation with the second link about the second pivot axis. The second link pulley has a circumferential surface concentric with the second pivot axis. A housing is provided and is fixed to the first link at its distal end. The housing has a circumferential surface concentric with the second pivot axis. An end effector pulley is fixed to the end effector for rotation about the third pivot axis and the end effector pulley has circumferential surfaces concentric with the third pivot axis. A first belt drive is also provided and includes one or more belts connected between the circumferential surface of the fixed pulley and the circumferential surface of the second-link pulley so that rotation of the first link relative to the fixed pulley about the first pivot axis causes rotation of the second link about the second pivot axis relative to the first link. The first belt drive is arranged to provide a first ratio between the rotation of the first link relative to the fixed pulley and rotation of the second link relative to the fixed pulley. A second belt drive includes one or more belts connected between the circumferential surface of the housing and the circumferential surface of the end effector pulley so that rotation of the second link relative to the first link, about the second pivot axis, causes rotation of the end effector about the third pivot axis relative to the second link. The second belt drive is arranged to provide a second ratio between the rotation of the second link relative to the first link and rotation of the end effector relative to the second link. One or more idler pulleys are provided and are rotatably mounted to one or both of the links. Each of the idler pulleys define a first and second circumferential surface. At least one of the belt drives includes a first belt engaged with the first circumferential surface of an idler pulley and a second belt engaged with the second circumferential surface of the same idler pulley.
Preferably, the first ratio has a value of −2 where rotation of the first link through an angle &thgr; causes the second link pulley and the second link to turn through an angle of −2&thgr; with respect to the first link. Thus, if the first link travels through a 45° angle counterclockwise, this will result in the second link pulley and the second link turning through an angle of 90° in the clockwise direction relative to the first link.
It is also preferred that the second ratio has a value of −½ where rotation of the second link through an angle &thgr; causes the end effector pulley and the end effector to turn through an angle of −½&thgr; with respect to the second link. For example, if the second link turns through an angle of 90 degrees in the clockwise direction, this will result in the end effector pulley and the end effector turning through an angle of 45° in the counterclockwise direction relative to the second link.
Because one or more of the belt drives includes an idler pulley and two belts, the pulley and housing diameters need not be selected as described above in connection with the prior art belt drives. For example, where the robot arm includes a first idler pulley mounted to the first link, the first belt of the first belt drive engages the first circumferential surface of the idler pulley and the circumferential surface of the fixed pulley. The second belt of the first belt drive engages the second circumferential surface of the first idler pulley and the circumferential surface of the second-link pulley.
Also preferably, the robot arm has a second idler pulley mounted to the second link. The second belt drive desirably comprises a first belt extending from the circumferential s surface of the housing to the first circumferential surface of the second idler pulley. The second belt drive desirably further comprises a second belt extending from the second circumferential surface of the second idler pulley to the end effector pulley. Preferably, the ratio of the diameter of the first circumferential surface of the second i
Bucci David A.
Creative Design Corporation
Hansen Colby
Lerner David Littenberg Krumholz & Mentlik LLP
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