Características Geológicas

This situation will be a common phenomenon after tight turns where negative flows were generated. In this case it is useless to distinguish too large or too small flows: the corresponding elementary gain factor ‡ should always be larger thanó . Also, the

case¿

B

´

¿ ‡ should not result in a gain factor ofó . Therefore, the following definition

for ‡ seems suitable: ‡ E ¿ B ´ ½¿ ‡ ¿ B ´ if¿ B ´ I 0õ÷¿ ‡ I 0 ó otherwise 535!

4. A negative receptor output is expected, but a positive flow is measured.

Being the opposite from case 3, this situation will arise just after a tight turn is initiated. The corresponding elementary gain factor#

´ is determined in a way analogous to the

determination of ‡ : # ´ E ¿ B ‡ )¿ ´ ¿ B ‡ if¿ B ‡ I 0õö¿ ´ I 0 ó otherwise 536! 5.3.3 a An SC network An SC network that determines the elementary gain factors is shown in figure 5.5. The responses from the flow receptor (M) and the expected responses based on the swim com- mands from the . are correllated as described above. The condition of simultaneous

activity in formulae 5.33 through 5.34 given above is detected by a correlation (multiplica- tion) of the two channels under consideration; the result is used to gate the synapses of the channels on the divisor neurone (%

X

). Gating is indicated in this case by an excitatory ( %

) synapse on the gated synapse.

The network contains a neurone (1

X

) that gives of a unity (1) firing frequency: this serves to implement the default gain factor (ó ) when the two input channels are not both active at

the same time. The four projections of this spontaneously active neurone onto all output neurones are gated by an inhibitory (Z

E

) gating projection from the corresponding divisor neurone.

Thus whenever simultaneous activity occurs in a combination of the input channels, the corresponding elementary gain factor is determined, and the corresponding output neurone passes on the result, while the other output neurones pass on the output of the 1

X

cell. 5.3.3 b Elementary gain factor frequencies The elementary gain factors described in the previous section each apply to one of four dis- tinct combinations of expected and measured flow receptor responses. These combinations are mutually exclusive (for non-zero¿

B

and¿ ): at any moment only one combination applies

138 CHAPTER5. THE SPEED CONTROL SYSTEM

hence of the applicability of the corresponding elementary gain factors) is defined as the number of occurrances of each N¿

B

+

¿ ! combination divided by the total number of samples.

These frequencies (not to be confused with atemporalfrequency of e.g. paddling) are referred to as theelementary gain factor frequencies: the frequencies in which the four elementary gain factor occur. They are expressed as percentages: their sum adds up to 100%.

A feedback control system that sets the gain of the control system can in theory only approach the setpoint (the desired output) in the limit — i.e. it is never reached. This means that some deviation from the desired output will always be measured. One therefore expects the two elementary gain factors 1´ and

#

‡ to occur (i.e. have a non-ó value) in the highest

frequency, since the two approximated possible receptor responses fall in these categories. The other two elementary gain factors, ‡ and

#

´ , represent transitional states that occur

just after the beginning or ending of a tight turn is initiated. A good speed control system should be able to rectify these situations quite rapidly. It is therefore expected that

‡ and

#

´ will occur in a much lower frequency.

If one considers the fact that "normal" paddlers swim in forward directions only (as explained under point 2 above), one expects the ´ elementary gain factor to occur at

the highest frequency. The situation where a negative flow is expected and a positive flow measured (#

´ ) is handled most efficiently by temporarily reversing the thrust (active

braking). Considering the fact that the locomotor system of the paddler can only brake passively (no reverse thrust can be generated), while acceleration is handled actively, this situation will typically persist longer than the reverse situation (

‡ ), and therefore occur in

higher frequencies.

Summarising, one expects the following ranking of frequencies of non-ó elementary gain

factors (high to low): A´ ;

#

‡ or

#

´ ; ‡ .

5.3.4 Determination of the speed gain factor

The elementary gain factors determined by the SCnetwork are used to determine both the gain of the paddle controller and the tilt command passed to the pectfin. The paddle controller gain is "constructed" from the elementary gain factors by multiplying a subset of those factors. Not all cases can be handled as efficiently by the paddles (they are useless for braking for instance), and there might arise conflicting requirements on the two sides. Also there should not arise a situation when braking and acceleration are attempted at the same time. An example of a GS network that determines the speed gain ‡ for the left paddle

controller is shown in figure 5.6. It determines ‡ from a combination of elementary gain

factors that takes into account the considerations outlined above.

The speed gain is determined in this case from all ipsilateral elementary gain factors, and from the contralateral #

´ and ‡ ( #÷ø ´ and ø ‡ ). The factors A´ , ‡ and #ùø ´ are multiplied.

The resulting "positive term" is larger than 1 when a higher thrust is necessary: either because the ipsilateral flow receptor measured too low or too a negative flow, or because the contralateral flow receptor measured a positive instead of negative a flow. The latter situation can be countered by increasing the thrust on the ipsilateral side.

The positive term is divided by a "negative term". This term consists of the product

#

´

#

‡ g

ø

‡ . All these three elementary gain factors indicate that a more negative flow is

required if they are larger than 1. The same holds for their product. A more negative flow can result from diminishing the ipsilateral thrust and increasing the contralateral thrust. The latter is effected by the contralateral projection of #

5.3. AMODEL FOR A SPEED CONTROL SYSTEM IN PADDLERS 139

In document Evaluación geomecánica del macizo rocoso con fines de estabilización de talud en la Cantera Mucra, Juliaca (página 73-79)