Robot having arm with unequal link lengths

1. A transport apparatus comprising:

a drive with a drive axis;

a first arm connected to the drive, where the first arm comprises a first link, a second link and an end effector connected in series with the drive, where the first link and the second link have different effective lengths; and

a system for limiting rotation of the end effector relative to the second link to provide substantially only straight movement of the end effector relative to the drive when the first arm is extending or retracting,

where the end effector comprises a substrate support section and a leg connecting the substrate support section to a wrist joint of the end effector with the second link, where the leg has a first section connected to the wrist joint and a second section connected to the substrate support section, and where connection of the leg to the wrist joint is offset relative to a centerline of the substrate support section,

where the straight movement is along an axis which intersects the drive axis.

2. A transport apparatus as in claim 1 where the effective length of the first link is shorter than the effective length of the second link.

3. A transport apparatus as in claim 1 where the effective length of the first link is longer than the effective length of the second link.

4. A transport apparatus as in claim 1 where the end effector comprises a lateral offset between a wrist joint with the second link and the centerline of a substrate support section which is about equal to a difference in the effective lengths of the first and second links.

5. A transport apparatus as in claim 4 where the system for limiting rotation is configured to translate the end effector when the first arm is extended or retracted with the wrist joint being maintained at the lateral offset relative to a center axis of rotation of the drive.

6. A transport apparatus as in claim 1 where the system for limiting rotation of the end effector provides substantially only radial movement of the end effector relative to the drive when the first arm is extended or retracted.

7. A transport apparatus as in claim 1 where the system for limiting rotation of the end effector is configured to constrain orientation of the end effector such that the end effector points radially relative to the drive regardless of positions of the first and second links.

8. A transport apparatus as in claim 1 where the end effector is configured to support at least two spaced substrates thereon, and where a lateral offset is provided between a wrist joint of the end effector with the second link and a center of a path of straight linear movement of the end effector, when the first arm is extended or retracted, for substantially translation only movement of the end effector when the first arm is extended or retracted with the wrist joint being maintained at the lateral offset relative to a center axis of rotation of the drive.

9. A transport apparatus as in claim 1 where the system for limiting rotation comprises a band drive comprising pulleys and a band.

10. A transport apparatus as in claim 9 where the pulleys comprise at least one non-circular pulley.

11. A transport apparatus as in claim 9 where the pulleys comprise at least one pulley stationarily connected to the second link or the end effector.

12. A transport apparatus as in claim 1 where the first and second sections are connected to each other at an angle of between about 90 degrees and about 120 degrees.

13. A transport apparatus as in claim 1 where the end effector comprises two substrate support sections and a leg frame connecting the substrate support section to a wrist joint of the end effector with the second link, where the leg frame is substantially U-shaped with a base and two legs, where each leg is connected to a separate one of the substrate support sections, and where the wrist joint connects the end effector to the second link at a location offset from a center of the base.