Multi-DM™ User Manual Section 10 - Reference Information
BMC Document Number: DOC-0009 Rev. 5.2 Page 65
10.10 Deflection and Inter-Actuator Coupling
For segmented DMs, the actual displacement is determined only by
the magnitude of the command sent to the actuator.
By their nature, segmented DMs have no inter-actuator coupling.
For continuous DMs, the actual displacement is determined by:
• The magnitude of the command sent to the actuator.
• An offset caused by inter-actuator coupling.
The magnitude of this offset is related to the stroke, the actuator spacing, and the relative
displacement of adjacent actuators.
As the mirror surface that is directly controlled by an individual actuator is attached to the
mirror surfaces over adjacent actuators, the position of those adjacent surfaces negates
the full effect of the actuator.
The closer the surrounding surfaces are to the actuator's driven position the greater the
coupling.
While quantifying inter-actuator coupling becomes complicated when
the adjacent mirror surfaces are at differing positions, it is relatively straightforward
when the adjacent surfaces are un-powered.
The DM- and Driver-specific System Data Sheet supplied with the system contains
Deflection vs. Command curves for the following scenarios:
• A single actuator with the adjacent surfaces un-deflected.
This is a common occurrence at the edges of the active actuator array that is
bordered by 2 actuator-sized rows of mirror surface that do not have actuators.
Inter-actuator coupling is at its maximum in this scenario, to the point that in larger
stroke models full deflection is not possible.
• A contiguous 4 x 4 actuator array with the adjacent surfaces un-deflected.
This is a more common occurrence within the active actuator array. Due to the fact
that in this case 16 actuators are pulling on the adjacent un-powered actuators,
inter-actuator coupling at the center of this array is significantly reduced from the
single actuator scenario described above.
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