problems with the control of the manipulator. By allowing the dynamic response to overshoot

the desired value, greater speeds were achievable and thus faster pick cycle times.


 Vision Control Requirements

 Of all the control systems, the most critical operations took place while the robot was

operating under the vision control. After the vision system identified a fruit while in the

search mode, the intelligence base switched control of joints 0 and 1 from velocity control to

vision control. Using vision control, joints 0 and 1 were aligned with the targeted fruit and joint

2 extended to position the end-effector near the fruit. The operations which used vision control

required that the motion of the fruit be tracked by the end-effector and ultimately that the

end-effector be positioned so that the fruit would lie within the picking envelope.

 As previously pointed out, the two worst observed cases of fruit motion were: Case I:

 swinging motions up to 50 cm in magnitude with 2 sec (0.5 HZ) cycle times and Case II: swinging

 motions 12.5 cm in magnitude with cycle times of 0.9 sec (1.1 HZ). Also, the established picking

 envelope indicated that the fruit position could be allowed to fluctuate by 2 cm (47 pixels) in

 the x direction (joint 1) and 3 cm (65 pixels) in the y direction (joint 0) from the center of the

 picking envelope. Controllers for the vision system of the robot were thus needed to cause the

 end-effector to be able to track these fruit motions with errors not to exceed 3 cm for joint 0 and 2

 cm for joint 1.

 Because the units of the vision system were pixels, the amplitudes of the fruit and the

 end-effector were converted to pixel units (Figure 7.6). As presented in the figure, the image

 plane was assumed to be infinitely large and the fruit was assumed to be its maximum pickable

 distance (16.2 cm) from the camera optical center, Oc. The trigonometric relations indicated

 that the image of a fruit whose magnitude was 500 mm would have a magnitude of 1077 pixels

 on the infinite image plane. Likewise, a fruit magnitude of 125 mm corresponded to an image

 magnitude of 269 pixels.