From toomey@ifa.hawaii.edu Fri May 28 15:37:45 1999 Date: Fri, 14 May 1999 17:45:06 -1000 From: Doug Toomey To: rayner@jeans.ifa.hawaii.edu Cc: denault@duke.ifa.hawaii.edu, onaka@jeans.ifa.hawaii.edu, watanabe@jeans.ifa.hawaii.edu Subject: Spex Mechanisms Hi, Here is a start at the mechanism software/sensing documentation. I doubt that I have everything right so please let me know if you see errors. Peter can you send me the abbreviations you are using for cable labling. Doug ___________________________________________________ Here is a summary of the drive concept for the Spex mechanisms. There are four types of mechanisms, detent, continuous rotary continuous linear and two position linear. There is also the calibration lamps which are not strictly mechanisms but are controlled and are listed here. Name type hardware Notes: --------- ------------ -------------- -------------------- 1. calmir Linear PC58/Stepper 2 limits 2. callamps on/off DIO 4 DO line 3. Dit 4 pos detent PC58/Stepper Home & 1 DI. 4. OSF 16 pos detent PC58/Stepper Home & 1 DI 5. ROT continuous anamatics Home & 1 AD channel 6. SLIT 11 pos detent PC58/Stepper Home & 1 DI 7. GRAT continuous anamatics Home & 1 AD channel 8. GFLT 16 pos detent PC58/Stepper Home & 1 DI 9. AFOC Linear,cont PC58/Stepper 2 limits, home & 1 AD channel. where limits = PC58 Axis Limit input. Home = PC58 Axis Home input or SmartMotor UAI input bit. DI/DO = AD16 Digitial Input or Output lines. AD = AD16 A/D input. The formal names for the mechanisms are: Hardware Tony's name Abbreviations Calibration Box Mirror calmir Calibration Lamp1 lamp1 Calibration Lamp2 lamp2 Calibration Lamp3 lamp3 Dichroic Turret Dit Order Sorter OSF K-mirror ROT Slit Wheel SLIT Grating Turret GRAT Slit Viewer Filter Wheel GFLT Spec Array Focus AFOC Two position Linear - Calibration Box Mirror ______________________________________________ The Calibration Box Mirror is a pick off mirror on a linear slide with limits at both ends. The out position limit is the home position. The in position is the in limit position. These limits switches will be fed into the PC58 limit inputs. Calibration Lamps 1,2 and 3 ______________________________________________ There will be one discharge Lamp and two continuum lamps for calibration. They will be turned on or off by toggling the digital output bits on the AD16 board. The user software will automatically move the Calibration Box Mirror in when a Lamp is turned on. Detent Mechanisms Dichroic Turret, Order Sorter, Slit Wheel, and the Slit Viewer Filter Wheel _______________________________________________ Each of these mechanisms is effectively a wheel with descrete positions. A hall effect sensor detects the presence of a magnet when the wheel is in a detent. A comparitor circuit triggers when the hall effect output exceeds a preset level. Additionally there is one extra home magnet per wheel which is of the opposite polarity of the detent magnets. A second comparitor circuit will trigger on the home magnet only. The home magnet is position about halfway between two detent positions. The output of the home comparitor will be connected to the home input on the PC38 board. The output of the detent comparitor will be connected to the limit input or may connect to a digital input on the AD16. INIT command: For homing, the PC determines home by searching for the home signal. Always approaching it from the same direction. Then the wheel moves to a default detent position. If the home position is not accurate due to erratic motion of the wheel then software will have to be added to search for the center of slop once we have moved to the first detented position. Positions commands: The PC relies on relative positioning from the home position to place the wheel in a detented position. A lookup table for steps & detent positions are used to determine destination. The computer will check the state of the PC-58 DI line after the wheel move out of the detent and when it is positioned in a detent to insure movement is occurring. If after a position change the detent is not detected a warning message will be displayed. Continuos Rotary wheels - K-mirror, Grating Turret _________________________________________________________________________ The continuous wheels have a single magnet and hall effect device. The output of the Hall Effect device is passed as an analog signal to the a/d input of the AD16 board and also is fed through a comparitor circuit which is fed into the Smartmotor's User input (UA1) INIT command: For homing, the smartmotor searches for the comparitor home indication. When home is located, a number of (step,voltage) points are sampled around the home limit and a 2nd degree polynomial equation is fitted to the data. The peak value of the curve is used to determine an accurate home position. Position commands: Item are positioned by step counts. Continuous linear - Spec Array Focus _________________________________________________________________________ The stage has an dual magnet/HESensor setup which can encode the position of the stage using a 3rd degree polynomial equation. The sensor output is connected to a PC38 A/D, and to a comparitor which toggles ON when the stage is at/near 0 volts. This comparitor output is connect to the PC58 home input. 2 mechanical limit switches are positioned to prevent motor over travel. 2 'overtravel' comparitors are set to trigger just before mechanical limits. The overtravel mechanical & overtravel comparitors for each limit are ORed then fed to the PC-58 limit input. For homing, the computer uses the A/D value and stored equation to determine its position. Then it will sample a few points just below&above 0 volts and determine true '0' based on a linear fit. If the position is not near the zero point it will first be moved near zero before the data is sampled for the linear fit. While the curve is not linear it is close enough if you are near the zero crossing. A calibration routine will be required to measure the Hall effect output versus step position to provide data for the 3rd order fit. For positioning, the PC will move to various focus settings based on step position. The PC-58 step position & step value calculated from the A/D output will be compared and a warning will be displayed if there is a discrepancy larger than a preset threshold. We are attempting an absolute accuracy of 25 microns in position over a total travel of +-2.16mm. We have measured a backlash of 50 microns(?) and while small a backlash correction algorithm should be used. We expect a home accuracy of better than 20 microns. We have a step size of .25 microns/step. We do not plan to use the home comparitor presently.