Table 8.4. Vision control variables as used in Figures 8.17 and 8.18.

 Joint Variables
 Toint 0 Toint 1 Both Description
 vi0erl vileri previous vision error value
 vi0er viler current vision error value
 vi0sp vilsp vision set point
 ycent xcent location of fruit centroid in the image plane
 dummyst temporary state storage variable
 state state which called vision control
 scale valve control scale factor
 p2 current joint 2 position value
 vi0k scale calculation factor
 vilk minimum scale value
 vi_touch vision touch state
 occluded occluded state
 v0cwd vlcwd view valve control signal
 vi0b1 vilbl coefficient from equation 8-8
 vi0al vilal coefficient from equation 8-9
 vi0a2 vila2 coefficient from equation 8-10
 v0cw vicw integer value of valve control signal



 Controller Tuning

 After implementation of each of the control schemes, values of the lag-lead controller

parameters for each joint were needed. These values were determined from the knowledge of

the systems being controlled. As previously mentioned, one distinguishing characteristic of a

stable system was that the resonant peak which was located at the hydraulic natural

frequency would remain less than unity. Also noted was the point that the steady-state error

could be decreased by an increased gain value for the lower frequencies. Likewise, faster system

response and reduced overshoot were desired and achievable by higher values of the

bandwidth or crossover frequency. A knowledge of these principles was used during the tuning

phase of the control system implementation. In the design of the compensators according to the

frequency-response method, Bode diagrams were useful for placing the lag and lead values (ri

and Td, respectively). The time constants of the controller, zi and cd, were adjusted to change the

frequencies at which the controller effected the system frequency response (see Figures 8.20 and

8.21). Note that the break points of the frequency-response curve occurred at the reciprocal

value of the respective time constant. For instance, a ri value of 2.0 sec would decrease the