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18. Actuator Angle Monitoring

In V3.410+ of the motion software the facility to monitor actuator angles has been added. When monitoring is enabled the actuator angles are monitored continuously. When the angle between an actuator and the platform base, or between an actuator and the moving plane of the platform becomes too acute the motion software will limit the cues.

The cue output is resumed once new cue conditions arise that no longer cause the acute angle limits to be breached.

Angle monitoring can be used to prevent some conditions in which a platform/actuator mechanical design allows contact between the actuators and each other or the platform structure when the actuators are moved within their normal working ranges. The feature should be used cautiously - the best way to ensure a safe operating envelope for a motion platform is to ensure the actuator placement and strokes are such that their mechanical stops effectively limit movement to within safe ranges.

Settings:

Angle monitoring is enabled in the .bff configuration file. The following parameters should be added to the .bff file before the End of File indicator:

;==================

;Actuator angle monitoring - enable

;Monitor_Acts is an 8 bit binary number to switch angle monitoring on or off for individual actuators
;Bits are in order b7 b6 b5 b4 b3 b2 b1 b0
;b0 = switch monitoring for ALL actuators on=1 or off=0
;b1 = actuator 1 on=1 or off=0, b2 = actuator 2 on/off etc

Monitor_Acts=00000001
 

;examples-

;00000001 = switch angle monitoring for all actuators ON

;00001100 = switch angle monitoring for actuators 2 & 3 ON

;Actuator minimum permitted angle relative to base of platform - degrees
Ang_bottom_1=10.0
Ang_bottom_2=10.0
Ang_bottom_3=10.0
Ang_bottom_4=10.0
Ang_bottom_5=10.0
Ang_bottom_6=10.0

;Actuator minimum permitted angle relative to the plane of the moving platform - degrees
Ang_top_1=5.0
Ang_top_2=5.0
Ang_top_3=5.0
Ang_top_4=5.0
Ang_top_5=5.0
Ang_top_6=5.0

;===================

In the above example angle monitoring is switched ON for ALL actuators. In this illustration the angle between an actuator and the base of the platform (bottom) should not be less than 10 deg, nor less than 5 deg between an actuator and moving plane of the platform (top).

If monitoring is required only for some actuators then individual bits in parameter Monitor_Acts can be set. Limiting angles can be set for individual actuators

Operation:

Once enabled the actuator angle monitoring is automatic and is calculated for each cue output set.

The actuator angle data can be displayed using the Angles button. The display window will also indicate when an actuator has breached its angle limits.

Once an angle limit breach recovers and the actuator cues concerned move back into permitted working range the software will attempt to smoothly restore normal cue movement by limiting the speed of movement for a period of 2 seconds following breach recovery.

The motion cues can change rapidly in a simulation and the particular combination of cues that caused an angle limit breach may not be the same as the combination that exists when the angle breach recovers. This can lead to a slight kick in the cue output as the software attempts to reintroduce the live cues following an angle breach. 

Determining Angle Settings:

Appropriate angle limit settings can be determined using the Angles display window and the Manual_Override sliders. For this to work the By DOF checkbox MUST be ticked - the angle monitoring does not work when the actuator positions are overridden using the By Act setting.

Using the Manual_Override sliders in By DOF mode the platform can be moved in each DOF, or with combinations of DOF's to carefully force the actuators towards clash conditions. The actuator top and bottom angles can be observed and appropriate limits can then be set in the .bff file to limit movement.

NOTE: the actuator angles are calculated on the underlying motion cues BEFORE Hold/Drive positions are enforced - so you will not see the angles change as the platform moves into or out of Hold position. You may also see the angles change whilst limiting is active and is being applied to the output cues.

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