61


 80

 60-

 40-

 I 20



 -20-

 40 l i i i --- i i .
 0 15 30 45 60 75 90 105 120
 Time (1/60 sec)

 1500

 10


 so-


 0 15 30 45 60 75 90 105 120
 Time (1/60 sec)

Figure 6.4. Typical response of joint 0 of the orange-picking robot to a step input of 1200 D/A
 bits with joint 2 centered in the Hooke joint.


this system was calculated using equation 6-4 as approximately 0.038 (deg/sec)/(D/A word).

These values represent an overshoot of 19 deg/sec (580 A/D bits) which corresponds to 41

percent. Using this measured overshoot in equation 6-5, a damping ratio of 0.27 was calculated.

The time to peak was determined by finding the number of counter ticks required for the

velocity of the joint to reach its maximum and dividing by the scale factor, 60 ticks per sec. In

this case, the joint reached its maximum velocity in 10 counter ticks or 0.17 sec. This value along

with the already determined damping ratio was used in equation 6-6 to find the hydraulic

natural frequency of the joint of 20 rad/sec or 3.1 HZ.

 Open-loop step tests were conducted on joint 0 for different directions of motion and

different positions of joint 2. The tests were conducted with the tube extended, in the center of

its working range, and retracted. Repetitions of the tests included step inputs that caused the

end-effector to be moved down from a raised position and up from a lowered position, or in