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17
The chair
3.3
Safety mechanisms
Obstruction safeguard
The pivot under the chair is kept in a specified position during movement by springs (also with a fixed chair). This
position is monitored by an opto coupler. If the chair is in the right position, the control is released.
The maximum allowed swivel angles are not protected by limit switches or mechanical stops. It is expected that
when the chair rotates too much the footrest will hit an obstruction and then will be triggered by the anti-squeeze
mechanism which also uses an opto coupler (Figure 3-8).
At the moment that the chair runs into an obstruction, the chair is pushed out of position against the spring
pressure. The opto coupler detects that the chair has turned and signals this to the control.
The control will the execute an emergency stop sequence by placing the motor in active brake mode followed by an
action to activate the friction brake.
The drive is stopped immediately. The user can no longer move any further forwards, but can move backwards for
max 10cm
The user can continue moving forwards after removing the obstacle.
Figure 3-9: Swivel motor control principle
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