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