fruit. The desired motions were achieved by setting velocity set points necessary for scanning

and calling the velocity control routines for joints 0 and 1. This scanning technique was

terminated when a fruit was identified by the vision system. Therefore, performance criteria

for velocity control of joints 0 and 1 did not prove to be critical. By adjusting the set points

which determined position of the joint at which the control was switched from one mode to

another, the overshoot specifications for joint 0 and 1 velocity controllers could be relaxed or

tightened. Steady-state error requirements could also be relaxed by increasing the velocity set

points. Experience with the robot operation indicated that actual velocity of joints 0 and 1

could overshoot the set point velocity by as much as 45 percent without greatly affecting the

performance of the search procedure. Also, deviations of 40 percent from the desired velocity

did not adversely affect the picking performance of the manipulator.

 Although the velocity requirements of joints 0 and 1 were used only during the fruit

search, the velocity control algorithm for joint 2 was used during the picking operation to

extend the end-effector toward a targeted fruit during the approach states. Therefore, its

performance proved to be more critical than that for joints 0 and 1. Most critical was the ability

of joint 2 to extend in a smooth, rapid manner and respond quickly to velocity set point changes.

Also, the detection of robot/limb collisions during extension and the detection of unremovable

fruit during retraction relied upon the ability to accurately control the joint 2 velocity. The

intelligence base detected these events by monitoring the joint 2 velocity control word which

was generated from the velocity error by the velocity controller. Large velocity control words

over a specified period of time were used to indicate that joint motion was restricted either by

an obstacle in the arm's path or by the inability of the arm to remove a fruit from its stem.

During the picking operation, overshoot values up to 25 percent of the desired joint 2 velocity

were regarded as acceptable and velocity steady-state errors of up to 10 percent were

determined tolerable based on experience with the robot.