123


were well below these specified maximums. Therefore, the velocity controller for joint 0

fulfilled the specified requirements.

 Velocity setpoints used for joint 1 during the search operation varied from -50 to +50

deg/sec. The action of the search routine for joint 1 was almost identical to that of joint 0 with

velocities switching between the positive and negative values of the velocity setpoint. Thus,

the performance tests simulated this action by switching the velocity setpoints between the

positive and negative values of the desired velocities. Plots which represent the closed-loop

responses of joint 1 to step inputs of different magnitudes are shown in Figures 9.4, 9.5, and 9.6. In

Figure 9.4, velocity setpoints of 32.6 deg/sec were used for achieving the joint's response to

alternating steps while joint 2 was retracted. Average positive and negative steady-state

velocities of 29.3 deg/sec and -29.4 deg/sec were observed indicating steady-state errors of 11

percent with no overshoot. Also using alternating input steps of 32.6 deg/sec, the response of

the system was examined while joint 2 was extended from the center of its support (Figure 9.5).

In this case, overshoot values as large as 5.9 deg/sec (18 percent) were observed. Steady-state

velocities of 29.0 deg/sec (12 percent) and -29.8 deg/sec (10 percent) were attained. For



 40Joint 1 Velocity Velocity Setpoint



 20


 0
 0

 S -20


 -40 -
 0 60 120 180 240 300 360 420
 Time (1/60 sec)

Figure 9.4. Typical closed-loop response of joint 1 to an alternating step input of 32.6 deg/sec,
 joint 2 retracted.