T-Series/Use of negative values with T-MM

Calculating Angle of Mirror Mount

Zaber positioning products generally accept only positive position data ranging from 0 up to the maximum range of the device. The T-MM2, however, can accept negative position data. This simplifies the calculations required to convert from linear to angular dimensions. Acceptable positions for the T-MM2 axis actuators are in the range from –62000 microsteps (the home or fully retracted position) to +62000 microsteps (the maximum extended position). A linear position of zero microsteps corresponds to an angular position of zero urad. In this position, the plane of the movable plate on which the optics are mounted should be approximately parallel to the front face of the mirror mount housing. The distance from the actuator contact points to the pivot point is 66.66 mm.

Using the approximation

dTheta = dD/L

Where dD is linear displacement of the actuator and dTheta is angular displacement of the mounting plate yields an angular resolution of 15 micro-radians per um of linear travel. This approximation is good for positions near zero but introduces an error up to 300 urad at the minimum and maximum travel.

If better accuracy is desired over the full range of motion then use the equation:

Tan(dTheta/1000) = 0.09921875*(P/L)

Where P is the actuator position in microsteps, L is 66,660 um, and Theta is the desired angular position in mrad.

T-MM2 Position Table – Dimensional Cross-Reference for firmware version 5.05 and up

Microstep Position	Microns	mrad (using 15 urad/um approximation)	mrad (using tangent equation)
-62,000 (min / home)	-6,151.56	-92.273	-92.022
0	0	0	0
+62,000 (max)	+6,151.56	92.273	92.022

T-MM2 Position Table – Dimensional Cross-Reference before firmware version 5.05

Microstep Position	Microns	mrad (using 15 urad/um approximation)	mrad (using tangent equation)
-65,536 (min / home)	-6,502.4	-97.536	-97.238
0	0	0	0
+60,671 (max)	+6,019.7	90.296	90.06