1.3
LVP Motors #1
When
you click on LVP Motors #1 you’ll get to
the records which are used to control all motors the LVP: LVP Lift Table record
(simple and compound), LVP Detector, LVP
Front Slits, CCD Camera Stage, and Monochromator. We’ll go through each one below.
1.3.1 Entrance Slits
1.3.2 LVP Lift Table Records (Simple and Compound)
The
LVP Lift Table is a essentially the “goniometer” that carries the LVP to position the sample
into the diffracting volume defined by the X-ray optics. Let’s be reminded that the APS coordinate system
(right handed) is such that the incident X-ray direction is defined as positive
Z, the vertical (up) direction is positive Y, and the horizontal direction
(pointing outwards, away from the center of the ring) is positive X. Describe X and Z motion here. In addition, three vertical Duff-Norton jacks
are used to drive the press up and down.
All of the three jacks are motorized and they need to be synchronized
for Y position control. In principle,
rotations about the X and Z axes can also be done by driving the three vertical
jacks independently; but we haven’t seen the needs for that yet. Details of the table
geometry is given under geometry set up below.
So the
“simple” LVP_Lift_Table record shows all the physical
motors and their positions. You'll
see several columns listed. "Motor Description" tells
you which motor you're moving, "Limits Readback"
tells you at what position that particular motor is currently sitting at. In
the "Move Absolute" field you can enter a value that you want the
motor to move to. In any MEDM screen you'll find that the mouse cursor MUST be in that entry field in order
for you to enter a value!! Once you hit
the <ENTER> key the motor will immediately move to this position. The "Tweak Jog" field
allows you to enter an increment by which you'd like to move a motor. The More Controls button for each motor allows you
to set the motor parameters such as speed, acceleration, deceleration,
backlash, etc. To drive a motor to its
new position, simply type the position (in mm) in the field under “Move
absolute”. You can also define a step
size by entering the step size (in mm) in the “Tweak Jog” field: then clicking
the right pointing arrow (“>”) will drive the motor “up” (towards positive)
by the step size specified; clicking the left pointing arrow (“<”) will
drive the motor towards negative by that step.
In this example if you enter 1.000 (again, mouse cursor
must be in the window and you have to hit <ENTER> to accept) for the
Upstream X, the motor will move by 1.000 mm every time you hit the arrow keys
on each side of the window. The left arrow key will move you -1.000 mm, the
right arrow key will move you +1.000 mm.
Don't worry about the JogR and JogF buttons, they don't really
work correctly right now. You'll also see two buttons under "Mode"
labeled "Use" and "Set." In "Use" mode numbers
you entered are taken to be positions or increments you wish to move to. By
selecting the "Set" mode you can redefine a position. For example if you click on "Set"
and then enter 10.000 in the "Move Absolute" field for the Z drive,
the motor WILL NOT move to 10.000 mm,
instead you've redefined the REAL position
13.571 to be a USER VALUE of 10.000 mm. Do not set user values for LVP Lift Table
motor positions. It's too easy to get
confused and all of a sudden be unsure about what position the motors are
really at. You'll also find some buttons in red that will issue a
"Go", "Pause", or "Stop" command...which are all
useful. There is also a button labeled
"More Controls" which allows full control of all motor
parameters...for example redefining motor positions, limits, etc. Again, unless
you're 100% sure you know what you're doing do not use these controls. And if
you do use them accidentally make sure you inform us of it. Better to be a little embarrassed than not
know where things are. All the motors have this same basic GUI layout.
In fact
for LVP lift table, you probably never need to use the simple lift table
record, because it is too hard to drive the press based on physical
motors. You’d have to drive more than
one motor at a time and have to make lots of calculations on the fly to figure
out where you are going, especially when you attempt to rotate the press, or
sometime (when running the T-Cup) scan the press along an inclined line. All of these controls are much more easily
done using the Compound Lift Table Record. As a general rule,
ALWAYS USE THE COMPOUND VERSION FOR EXPERIMENTAL
CONTROL!
The
compound Lift Table record looks like the picture on the right.
In this record, X, Y, and Z refer to the beamline coordinate (Z: beam direction, positive toward down stream; Y: vertical and perpendicular to the beam, positive is up; X: horizontal, positive toward the user. Right handed system). Teacup X and Teacup Y are inclined at 35.2644° (the T-Cup angle). Z axis is parallel to the beamline Z. These are all compound motors, which means that the “motors” shown here are actually multiple motors who motions are linked through transformation matrix, according to the lift table geometry. So if you drive the X motor, you actually drive the two X motors in the simple lift table record simultaneously. Similarly, if you drive the Y motor, you are actually driving all three Y motors synchronously. When you drive the Teacup Y motor, you are driving five physical motors: three physical Y motors and two physical X motors, so that the press is running along a trajectory that is inclined by 35.2644° from the vertical line. You can see that user operation is dramatically simplified using the compound motors.
Again, you can set up the tweak value and drive the compound motors by
prescribed steps; you can set each compound motor position to a different user
defined value (Set), and you can set the current position values to zero
(Zero). But you should not do that for
LVP Lift Table, as this will become very confusing. All motor positions should be real positions
to allow users to check their current positions based on their previous
runs. They also help us understand
whether there is any mechanical problems in the
system.
1.3.3 T-Cup Setup
The last item under compound lift table record “More” button is "Setup teacup geometry". This record sets up coordinate transformation fro the APS system to the “Teacup” system, where X” and Z” are rotated about the common Y (=Y”) axis by 35.2644° (i.e., counterclockwise rotation if viewed with X-ray coming towards you). You must make sure this angle is correctly set before running any scans in the Teacup mode. If the Teacup angle is set at 0.0° (as shown in the example on the right), the Teacup X” and Y” axes will be parallel to the X and Y.
You may press the “Define T-cup origin” button to set the Teacup X and Y
value positions for your sample to zero.
This will help you return to sample positions after any scan. This reset does not affect real positions in
global coordinates. A good practice is after you have centered the sample using
the LVP lift table (compound), set that point as T-Cup origin, so you can scan in the
T-Cup X and Y directions.
1.3.4 LVP_Detector
The
detector support has five degrees of freedom: three motorized translations
along X, Y, and Z, and two rotations - simple 2-theta (about the X axis), and
detector Phi (about the Y axis). The
stacking sequence is the following (from bottom up): (1) X translation, (2) Z
translation, (3) Phi, (4) Y translation, and (5) simple 2-theta. In addition, there is a manual rotation axis
(about Y) below the entire five axis assembly.
This manual rotation is used to align the system so that it Z
translation is as close to the global Z direction as possible. After alignment, the rotation stage is locked
by two micrometer screws.
Note: Never disturb the detector support! All your 2-theta calibration will be lost if you do so.
This LVP-Detector record controls motor positions of the detector. The top five motors are simple (or real) motors, and the Compound 2-theta is a compound motor that is achieved by rotating both Two-Theta (simple 2-theta) and Detector Phi. In the DIA mode, Detector Phi must be zero (which has been set at zero at the beginning of the alignment process). For the T-Cup mode, the true 2-theta angle is decomposed into two angles, Two Theta (which is simple 2-theta) and Detector Phi. Only Compound 2-theta will give you the true 2-theta value in the T-Cup mode.
Detector Radius is not a motor; rather it is a setup parameter, which
represents the distance between the sample and the center of the detector.
Click on the far right button for Detector Radius, select Setup Geometry, to open the following window: This is used to set up the LVP Detector Geometry. Definition of the parameters shown there are given in the record. All are in mm. Note that in setting up the T-Cup, the angle Chi should be negative, -35.264°, not positive as indicated in the record. Once the geometry parameters are correctly set, you’ll be able to drive the compound 2-theta to the desired value for your sample.
Note: A good practice for alignment is to align the incident X-ray beam with the detector first (with all the slits and collimator lined up correctly), and reset all motor positions in the LVP_Detector to zero (except for Detector Radius). Then set up the Chi angle (0 or -35.264) in the LVP Detector Geometry record. Parameters B and C should not be changed. Z0 generally also should not be changed. After all this, you can type an angle in the Compound 2-theta field, if you are running the T-Cup, to get the real 2-theta you want.
Keep in mind that the software currently has a bug, in that when you drive
the compound 2-theta at the given radius from the sample, the detector Z axis
goes positive (away from the sample).
This is why all parameters should be set at zero before driving the
compound 2-theta. To correct the Z motion error, simply type a minus sign in
front of the Z motor position in the Move Absolute field: this will reverse the
Z motor travel and put the detector on the great circle (with the given
detector radius) around the sample.
For each motor, "More Controls" gives you more information in three options
All
Gives all the information about driving this motor.
Scan Parameters button helps load scan parameters for this motor to the scan record.
Typically, use "Relative" and select "Prior Pos" so the motor will move in relative amounts and return to its position before the scan. Choose range by giving start and end points, and step size by giving number of points. Click "Load" to load the parameters to the scan record.
1.3.6 LVP Detector Base
1.3.7 LVP Detector Mount Setup
1.3.8 LVP Detector Slits
