modular design
interface
sensor
behaviour
command
control
speech
simulation

modular design

a modular design was chosen in order to isolate code functionality into logical building blocks
the design used a tree structure with top level executable programs displaying the user interface and lower level modules providing functionality as required

error trapping was used at all levels to log any errors to a log file

interface module

this module is the executable that is run to start the program

it is the only control system module that has a user interface
it displays the results of simulation and allows servo limits, servo speed information and any other parameters required by the other control system modules to be set and recorded
experience of unattended installations of inkha have shown that any user interface parameter than can be changed will be changed so childproofing was added to the interface to disable all parameter setting unless a password is entered

a timer driven loop within the interface module calls the sensor module to read the camera, PIR and microphone statuses
a second timer driven loop interrogates the sensor module periodically in order to retrieve a vector indicating the direction in which the head assembly should move and a colour which it should report
should the cameras have moved recently then they are not re-sampled until the motors have stopped moving to allow the  image to settle: the asc16 servo controller notifies the control software when motor movement is complete whereas the ssc servo controller must use a time delay set from the user interface
there is no need for the cameras to settle before time based actions such as relaxation occur as these actions are not vision dependent

the algorithm required, defined in pseudo code, is as follows:

If Time – LastPIRMicrophoneTime > ColourTime
    Vector = PIR or microphone vector
    LastPIRMicrophoneTime = Time
If camera is not moving
    Vector = read vector from sensor module
If Time – LastColourReadTime > ColourTime
    Colour = read colour from sensor module
    LastColourReadTime = Time
ProcessVector (Vector)
DoTimedActions

for some commissions a touch screen is used and the interface module calls into the speech module to give directions, what's on information etc. when these buttons are pressed

sensor module

this module integrates the cameras, pirs and microphone and displays the user interface for them
it allows parameters and thresholds for motion detection and colour recognition to be set and displayed
a mirror image of the image received by the camera is displayed as are images showing detected motion and areas of attention, pir indicators and a microphone level

the sensor module is called periodically by the interface module
it passes back a direction vector to indicate the direction in which the control system needs to move the head and a colour which is interpreted by the behaviour module resulting in a statement issued using the speech module

information about how the sensor module detects movement and colour can be found in the vision section

behaviour module
this module modifes sensory input according to user settings (selected behaviour)
it alters inkha's responses to sensory input
behaviours are:
activity: nonchalant, skittishness (interprets interest and fright responses)
verbal: charming, tetchy, obnoxious (select speech-set from database in response to activity)
mindset: astrological, fashion, factual (selects speech-set for the hue in response to colour)
colour: density, average (alters colour recognition algorithm)

modifying vectors:
a direction vector passed from the sensor module is modified before it is sent on to the command module
for example if behaviour is nonchalant then a "high level of interest at centre" vector passed from the interface module is converted to a "low level of interest at centre" vector before it is passed to the command module

modifying colour interpretation:
a hue is determined by the sensor module
for example if behaviour is mystic then any given hue will produce a verbal comment related to astrology

command module

this module produces instructions for moving the head assembly in a lifelike way according to the passed-in command vectors and its co-operation rules
it also caters for time based movements such as relaxation (centring of the eyes), blinking and boredom, the period of which can all be controlled from the user interface

after experience of unattended installations logic was added to allow control of a relay that inkha's motors can be turned off whenever sleep mode is entered
this allows the motors to rest during unattended installation whenever there are no visitors
furthermore a working hours facility was added so that motors can be rested for given hours of the day

for each non-central vector received the target eye position is incremented by one tenth of its total movement in the direction of the vector
the percentage was determined by experimentation
co-operation logic is used to move other axes and to limit the eye movement as required

next, any relaxation is applied to the target positions before they are sent to the control module

once the desired position of the head assembly has been determined by the command module flow passes to:

• the control module so that the head can be moved
• the simulation module so that the desired position of the head assembly can be simulated.
• the speech module if speech is required

this module uses a normalised co-ordinate system with a value of zero representing any movement at its lowest or most anticlockwise position and a value of one representing any movement at its highest or most clockwise position

colour recognition, boredom and blinking occur periodically

for some commissions the command module also checks databases and the internet periodically for other information

the following rules were designed for blinking:

• within each blinking period there will be a chance one in two that a blink will happen
• if a blink does happen there will be a chance one in four that there will be a second blink immediately

control module

this module takes the target normalised position of each head assembly servo and converts it to the raw servo values that need to be sent using the limit parameters that are passed in from the interface module

it was implemented in such a way as to allow multiple servos to move simultaneously
it is also possible to control the maximum speed of any servo
more information can be found in the control section

speech module

this module uses comment types passed in from any module and parameters provided by the behaviour module to produce speech
for example the command module may instruct the speech module to produce speech for the fourth time that it is bored and the behaviour module will add to this that the speech should be obnoxious

this module also supplies a list of available voices in a format suitable for display in a list box and allows the active voice to be selected

information about how speech is produced can be found in the speech section

simulation module

this module receives positions of the various head assembly axes in normalised co-ordinates and produces a three-dimensional scaled graphical simulation of it
the simulation can be displayed by the interface module and used to plot trajectories

accurate measurements of the size and position of the key elements of the head assembly were taken and stored in constants in the simulation module so that they can be changed easily in future if the mechanism changes
measurements were also taken of the limits of rotation of each axis

from these measurements a number of simulation primitives were constructed using a series of straight lines between sampled or geometrically created points

the origins of each centre of rotation of the elements were calculated relative to the zero origin at the base of the neck
the sequence of transformations of each element around each origin was analysed and the transformations were effected for each element using a series of homogeneous co-ordinate transformations

after the last transformation the x and y co-ordinates of the resulting transformed straight lines had a scale and offset factor applied to map them to screen co-ordinates and the lines were then plotted on screen using visual basic line drawing routines