GEM Beamscraper Jaws

The GEM “Beamscraper” jaw set is unique to GEM. The four blades move independently and are all driven by a LinMot. Some calibration is required between the demanded position and the steps sent to the controller. For North/South this calibration is linear, for East/West it is quadratic.

Control under IBEX

The calibration curves under IBEX have been simplified to:

Jaw	Offset	Read Calibration Curve	Write Calibration Curve
North	2710	1.025*x	x / 1.025
South	1530	1.025*x	x / 1.025
East	2200	-0.13376 + 0.07169 * x  + 0.03331 * x**2	(-0.07169 + sqrt(0.07169**2 + 4 * 0.03331 *(0.13376 + x))) / (2*0.03331)
West	2200	-0.13376 + 0.07169 * x  + 0.03331 * x**2	(-0.07169 + sqrt(0.07169**2 + 4 * 0.03331 *(0.13376 + x))) / (2*0.03331)

Note that the linear calibration curve is actually incorrect in the VI as 1 / 1.025 != 0.975. Therefore in IBEX 1.025 and 1 / 1.025 are used for reading and writing respectively.

To do these calibrations an additional soft motor record has been placed between the conventional jaws db and the real motor, such as described here.

The offset / motor resolution in IBEX uses (MRES * x) + OFF when reading, therefore the new offset motor resolution in IBEX are:

Jaw	New Offset	New Motor Resolution
South	-SECI_OFF * SECI_MRES	SECI_MRES
N/E/W	SECI_OFF * SECI_MRES	-SECI_MRES

Tolerance and limits have been included in IBEX, the homing has not.