control system principles

the following principles were developed for the control system in order to achieve lifelike movement whilst keeping the software simple:

• the system will not be aware of world co-ordinates
  it will exhibit proprioception i.e. it will know where it is in relation to itself but its only knowledge of the world will be through the image that is viewed by the camera
• tracking of an object will move the eyes alone
  a second layer of control will trap movement of the eyes past their extremes and convert it to neck movement. this principle clearly mimics human behaviour and is termed "co-operation"
• time-based code will attempt to centre the eyes and compensate with neck movements once the object being tracked is centred or when there is nothing of interest to view
  this is termed "relaxation" and mimics vestibular occular reflex as described in the vision section
• periodic behaviour such as blinking, boredom and colour recognition will be time- based and will work independently of the tracking system
• lifelike behaviour such as fright and interest will be aperiodic and will be dependent upon sensory stimulation

an inner loop in the control module implements simultaneous movement of servos and speed restrictions on servos using the following logic which is written here as pseudo-code:

Find Distance to be moved by each servo
Find Maximum Distance to be moved by any servo
For each servo
    Timedelay = Timedelay for this servo * Distance / Maximum Distance
Timedelay to use is the maximum of these Timedelays
For Step = 1 to Maximum Distance step Granularity
    Move each servo to current position plus Step * Distance / Maximum Distance
    Wait for Timedelay
Move each servo to final position

a single time-delay parameter for each servo was found to be insufficient as different speeds are required for different movements
for example a fright movement needs to move the neck quickly whilst a relaxation movement needs to move it slowly
as a solution to this two sets of delays were implemented, one for fast movement and one for slow movement  the command module chooses between the two speeds depending upon the vector being processed and passes the speed to the control module as a parameter